Tag: Ophthalmology

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Ocular Thelaziosis in dogs, France

During 2005–2008, veterinary practitioners reported ocular infection by Thelazia spp. nematodes in 115 dogs and 2 cats in southwestern France. Most cases were detected in Dordogne, particularly in 3 counties with numerous strawberry farms, which may favor development of the fruit fly vector. Animal thelaziosis may lead to emergence of human cases. Thelazia spp.(Spirurida, Thelaziidae) nematodes live in the conjunctival sac of warm-blooded vertebrates. These nematodes are responsible for epiphora, conjunctivitis, keratitis, and corneal ulcers. Thelazia spp. nematodes are transmitted by different species of flies feeding from the lacrimal secretions of the definitive hosts. Among the 10 species, T. californiensis and T. callipaeda parasitize carnivores and sometimes humans. T. californiensis is confined to the western United States and has never been reported in Europe. T. callipaeda, the “oriental eye worm,” is common in the former Soviet republics and in India, Thailand, People’s Republic of China, and Japan, where it causes infections in humans, dogs, and cats. Wild mammals, such as foxes and lagomorphs, are reservoir hosts for the nematodes. During the past decade T. callipaeda infection was proven to be widespread among dogs and cats from northern (Aosta valley) to southern (Basilicata region) Italy. In Ticino, a region of southern Switzerland, a retrospective study identified 106 T. callipaeda–positive dogs and 5 positive cats during 2005–2007. Recently, the first autochthonous case of thelaziosis in a dog was described in southern Germany. Locally transmitted cases of thelaziosis were first reported in 4 dogs and 1 cat that lived or spent time in the department of Dordogne in southwestern France.

At the end of 2008, we contacted veterinary practitioners from 938 veterinary practices in 16 departments in France by regular mail. The survey covered a large part of southwestern France, where the first thelaziosis cases in dogs and cats were reported in 2007. Veterinary practitioners were asked whether they had diagnosed ocular thelaziosis in a dog or a cat during the previous 3 years. For each clinical case, a short questionnaire asked for a description of the animal (i.e., sex, age, breed, use), description of the place where the animal lived, and treatment protocol. A total of 117 clinical cases of thelaziosis (115 dogs and 2 cats) was reported in 22 veterinary practices from 9 departments (Ariège, Dordogne, Gironde, Haute-Garonne, Lot-et-Garonne, Puy-de-Dôme, Pyrénées-Atlantiques, Tarn, and Tarn-et-Garonne). Most (104 [89%]) cases were diagnosed from 10 practices in Dordogne. In each of the other departments, only a few (1–6) cases were diagnosed. Furthermore, most of the infected animals in other departments had spent time in Dordogne a few months before clinical signs developed. In Dordogne, most cases were from the center of the department, with 3 counties overrepresented (60 cases in Vergt, 16 cases in Saint-Pierre-de-Chignac, and 9 cases in Villamblard). In these counties, strawberry production is predominant and may favor development of the fruit fly vector, Phortica variegata; in other areas of Dordogne, other types of fruit production (plum or apple) are reported. All infected dogs and the cats were 6 months–14 years of age and privately owned. Ninety-one (78%) of the 117 animals lived in a small village; 22 were farm dogs. Twenty-six animals lived in a city, but all had free access to the outdoors.

The animals were referred to veterinary practitioners for unilateral or bilateral conjunctivitis. For all animals, nematodes were observed on the eye surface. The first cases of thelaziosis were detected in 2 dogs and 1 cat in the county of Vergt at the end of 2005. During 2006, a total of 27 cases were detected in late summer and autumn; animals may have been contaminated by infected vectors during the peak of the male Phortica spp. fly population in summer 2006. During 2007 and 2008, clinical cases were detected throughout the year. The apparent absence of seasonality for detecting adult Thelazia spp. nematodes in definitive hosts is in accordance with previous observations in areas in Italy to which Thelazia spp. nematodes are endemic. Nematodes were collected from the eyes of 19 dogs and 1 cat and morphologically identified. To determine the haplotype sequence, we processed specimens using the specific amplification of a partial sequence of the mitochondrial cytochrome c oxidase subunit 1 gene (cox1, 605 bp), as previously described. The sequences obtained were identical to the sequence representing haplotype 1 of T. callipaeda (GenBank accession no. AM042549) previously reported in Italy and Switzerland but they displayed a 1.3%-nt difference from the haplotype recently detected in Germany.

Emerging Infectious Diseases
December 7, 2010

Original web page at Emerging Infectious Diseases

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Discovery of a gene linked to the spread of eye melanoma

Although more research is needed, the researchers say the discovery is an important step in understanding why some tumors spread (metastasize) and others don’t. They believe the findings could lead to more effective treatments. Reporting online in the journal Science Express, the team found mutations in a gene called BAP1 in 84 percent of the metastatic eye tumors they studied. In contrast, the mutation was rare in tumors that did not metastasize. Muscular melanoma, also called uveal melanoma, is the most common eye cancer and the second-most common form of melanoma, striking about 2,000 adults in the United States each year. It can affect people at any age but is most common in patients over 50. The tumors arise from pigment cells, called melanocytes, that reside in the layer below the retina called the uveal tract. Up to half of those with the cancer eventually develop metastatic disease, which is universally fatal. “The most common site where the cancer spreads is the liver,” Harbour says. “If it spreads, it goes to the liver about 90 percent of the time, generally leading to death within months.”

Researchers at Washington University School of Medicine in St. Louis have identified a gene linked to the spread of melanoma of the eye. Although more research is needed, the researchers say the discovery is an important step in understanding why some tumors spread and others don’t. Metastasis is the most common cause of death in cancer patients. There is growing evidence that mutations in so-called metastasis suppressor genes may promote the spread of cancer, while having little to do with earlier stages in the life of a tumor. Very few such genes have been identified, but this finding strongly implicates the gene BAP1 as a new member of that small group. To improve survival, scientists need to understand more about what causes the tumor cells to metastasize, according to Harbour, the Paul A. Cibis Distinguished Professor of Ophthalmology and Visual Sciences, professor of cell biology and of molecular oncology and director of ocular oncology at the Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine. Harbour and co-investigator Anne M. Bowcock, PhD, professor of genetics of pediatrics and of medicine, have been looking at DNA in tumor cells for clues about why some tumors spread. Tumors had already been grouped into two classes based on gene expression profiles. Class 1 tumors have a low risk of spreading, while class 2 tumors carry a high risk of metastasis. In addition, 90 percent of class 2 tumors have lost a copy of chromosome 3, unlike class 1 tumors, which tend to retain both copies of the chromosome.

In this study, the team looked for differences in genes on chromosome 3 between the cells in class 1 and class 2 tumors. They started with tissue taken from a pair of class 2 tumors. “We looked for common genetic differences, called polymorphisms, that would unlikely have much of an effect,” Bowcock says. “We eliminated those variations and then went back to look at which gene on chromosome 3 had additional alterations. There was one gene, called BAP1, that had mutations in both of the tumors we analyzed.” BAP1 is short for BRCA1-associated protein. As it happens, BRCA1 is linked to breast cancer in some women.

“It points, possibly, to a common theme in cancer genetics,” Bowcock says. “After identifying mutations in BAP1 in the first two tumors, we went back and looked at DNA from another 29 class 2 tumors, as well as 25 class 1 tumors. And we found that 84 percent of the class 2 tumors had damaging mutations in BAP1. We also found that in most cases, the class 2 tumor cells had only one copy of chromosome 3 – where the gene is located – so patients had only a single copy of the BAP1 gene, and because of damaging mutations, it could not fulfill its proper role in the cell.” It appears that what the gene is supposed to do, Harbour says, is to act as a metastasis suppressor. When it is damaged, the tumor can spread. “There are several ways this discovery could improve patient care,” Harbour says. “If we could detect BAP1 mutations at an earlier stage, for example, we might be able to monitor a patient’s blood for detectable melanoma cells as an early sign that they’re developing metastatic disease.” He also says a better understanding of the normal role of the BAP1 protein could provide powerful insights into ways to therapeutically target eye tumors that are likely to spread. He and Bowcock already are beginning those studies. “We know now that BAP1 is the big player in class 2 tumors, but there are other players, too,” Bowcock adds. “We’d also like to understand what other genes are mutated in class 1 tumors and why they don’t metastasize.”

Bowcock and Harbour identified a single class 1 tumor with a BAP1 mutation. One possible explanation for that finding may be that the tumor was evolving into a class 2 tumor. In a second series of experiments, the researchers found that if they put ocular melanoma cells in culture and depleted their supply of BAP1, the cells began to change in appearance and to resemble class 2 tumors in just five days. “Now we’re trying to knock down BAP1 levels for weeks to months and find out whether we start to see some of the chromosomal changes that are present in class 2 tumors,” Harbour says. He says it remains unclear whether class 1 and class 2 tumors are different from their very inception or whether ocular melanoma tumors begin their existence as class 1 tumors and then, eventually, develop cells with BAP1 mutations. “We have hints, both from experimental work and from patient samples, that the latter scenario is more likely, that the tumors start off as class 1 and evolve into class 2 tumors,” Harbour explains. “But that is still somewhat speculative, and we’ll need to do more experiments to test that hypothesis.” The BAP1 mutation represents only the second common genetic mutation ever reported in ocular melanoma, and it is the only mutation linked to metastasis in this type of cancer.

PhysOrg.com
November 23, 2010

Original web page at PhysOrg.com

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New retinal implant enables blind people to see shapes and objects

Research published in Proceedings of the Royal Society B reveals that a group of researchers based in Germany have developed a retinal implant that has allowed three blind people to see shapes and objects within days of the implant being installed. One blind person was even able to identify and find objects placed on a table in front of him, as well as walking around a room independently and approaching people, reading a clock face and differentiating seven shades of grey. The device, which has been developed by the company Retinal Implant AG together with the Institute for Ophthalmic Research at the University of Tuebingen, represents an unprecedented advance in electronic visual prostheses and could eventually revolutionise the lives of up 200,000 people worldwide who suffer from blindness as a result of retinitis pigmentosa, a degenerative eye disease. In this disease light receptors in the eye cease to function. Writing in Proceedings of the Royal Society B, Prof. Dr. Eberhart Zrenner (founding Director of Retinal Implant AG and Director and Chairman of the University of Tuebingen Eye Hospital) states that “The results of this pilot study provide strong evidence that the visual functions of patients blinded by a hereditary retinal dystrophy can, in principle, be restored to a degree sufficient for use in daily life.”

The device — known as a subretinal implant — sits underneath the retina, directly replacing light receptors lost in retinal degeneration. As such, it uses the eyes’ natural image processing capabilities beyond the light detection stage to produce a visual perception in the patient that is stable and follows their eye movements. Other types of retinal implants — known as epiretinal implants — sit outside the retina and because they bypass the intact light-sensitive structures in the eyes they require the user to wear an external camera and processor unit. The subretinal implant described in this paper achieves unprecedented clarity because it has a great deal more light receptors than other similar devices. As Prof. Dr. Zrenner states, “The present study…presents proof-of-concept that such devices can restore useful vision in blind human subjects, even though the ultimate goal of broad clinical application will take time to develop.”

Science Daily
November 23, 2010

Original web page at Science Daily

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Eye test for neurological diseases in livestock developed

The eyes of sheep infected with scrapie — a neurological disorder similar to mad cow disease — return an intense, almost-white glow when they’re hit with blue excitation light, according to a research project led by Iowa State University’s Jacob Petrich. The findings suggest technologies and techniques can be developed to quickly and noninvasively test for transmissible spongiform encephalopathies, progressive and fatal neurological diseases such as mad cow disease in cattle and Creutzfeldt-Jakob disease in humans. Petrich, in fact, is working to develop a testing device. The findings were published earlier this year in the journal Analytical Chemistry. The project was supported by a grant from the U.S. Department of Defense. The research is the result of an accidental discovery while Petrich and his collaborators were developing a fluorescence spectroscopy device that’s now used in slaughterhouses to test livestock carcasses for feces and possible E. coli contamination. “One day we were testing the apparatus by shining light on the carcass and we saw the spinal cord glow — it fluoresced,” said Petrich, professor and chair of Iowa State’s chemistry department. “We saw the spinal cord through the skin. The light was pretty intense. It was an amazing result.”

That sparked some new thinking: Maybe fluorescence technology could be used to test animals for transmissible spongiform encephalopathies such as bovine spongiform encephalopathy — what’s often called mad cow disease. To reduce the risk of human exposure to the diseases, the brains and spinal cords of animals are removed during slaughter and processing. But there is no quick test to identify animals with the diseases. And so Petrich and a team of researchers began studying the feasibility of a fluorescence test. The researchers collected 140 eyeballs from 73 sheep. Thirty five of those sheep were infected with scrapie; 38 were not. The researchers took fluorescence readings from various parts of the eyes of all the sheep. “The bottom line is the scrapie-positive retinas fluoresced like crazy,” Petrich said. “And the scrapie-negative ones did not.” A previous study published in the journal Veterinary Pathology reported that the function and structure of retinas are altered in cattle infected with transmissible mink encephalopathy. Members of that study team included Iowa State researchers M. Heather West Greenlee, an associate professor of biomedical sciences in the College of Veterinary Medicine; Justin Greenlee, a collaborator assistant professor of biomedical sciences; and Juergen Richt, a collaborator associate professor of veterinary microbiology and preventive medicine. Other studies have reported that lipofuscin, an intracellular fluorescent pigment, accumulates in the eyes of animals infected with the neurological diseases. Petrich and his team attribute the glow from scrapie-positive retinas to the elevated levels of lipofuscin.

Whatever the cause, Petrich said it’s clear there are distinct differences in the fluorescence and spectroscopic signatures of retinas from sheep that were naturally infected with scrapie and those that were not. And so he and his research team think there’s great promise for a diagnostic test based on that discovery. That has Petrich starting to develop a device (he likes to call it a “gizmo”) that could be used in meat plants to test the retinas of animals for signs of neurological diseases. He expects it will take several years to develop, build and test a useful device. “What I like about this is it’s really simple,” Petrich said. “It’s light in and light out.”

Science Daily
November 9, 2010

Original web page at Science Daily

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Promising results of gene therapy to treat diseases of the eye

The easy accessibility of the eye and the established link between specific genetic defects and ocular disorders offer hope for using gene therapy to provide long-term therapeutic benefit. Two reports in the current issue of Human Gene Therapy, a peer-reviewed journal published by Mary Ann Liebert, Inc., describe the effective replacement of a human gene to preserve photoreceptor function in a mouse model of severe retinal degeneration. Basil Pawlyk and colleagues from Harvard Medical School and Massachusetts Eye and Ear Infirmary (Boston, MA) delivered the human gene for RGPR-interacting protein-1 to mice affected with Leber congenital amaurosis (LCA), a condition linked to a mutated form of RPGRIP1 that causes degeneration of photoreceptors in the eye. The researchers packaged the gene in an adeno-associated virus (AAV) vector and injected the vector under the retinas of the affected mice. They demonstrated expression of the human gene in the photoreceptors, with correct localization to the cilia. Further evaluation revealed improved function and survival of the photoreceptors in the treated eyes. The authors conclude that the results of this study validate a gene therapy design that could serve as the basis for a future clinical trial in patients affected by this form of LCA.

Science Daily
August 31, 2010

Original web page at Science Daily

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Retina created from human embryonic stem cells

UC Irvine scientists have created an eight-layer, early stage retina from human embryonic stem cells, the first three-dimensional tissue structure to be made from stem cells. It also marks the first step toward the development of transplant-ready retinas to treat eye disorders such as retinitis pigmentosa and macular degeneration that affect millions. “We made a complex structure consisting of many cell types,” said study leader Hans Keirstead of the Reeve-Irvine Research Center and the Sue and Bill Gross Stem Cell Research Center at UCI. “This is a major advance in our quest to treat retinal disease.” In previous studies on spinal cord injury, the Keirstead group originated a method by which human embryonic stem cells could be directed to become specific cell types, a process called differentiation. Results of those studies are leading to the world’s first clinical trial using a stem cell-based therapy for acute spinal cord injury. In this study, the Keirstead team utilized the differentiation technique to create the multiple cell types necessary for the retina. The greatest challenge, Keirstead said, was in the engineering. To mimic early stage retinal development, the researchers needed to build microscopic gradients for solutions in which to bathe the stem cells to initiate specific differentiation paths.

“Creating this complex tissue is a first for the stem cell field,” Keirstead said. “Dr. Gabriel Nistor in our group addressed a really interesting scientific problem with an engineering solution, showing that gradients of solutions can create complex stem cell-based tissues.” The retina is the inside back layer of the eye that records the images a person sees and sends them via the optic nerve from the eye to the brain. Retinal diseases are particularly damaging to sight. More than 10 million Americans suffer from macular degeneration, the leading cause of blindness in people over 55. About 100,000 have retinitis pigmentosa, a progressive, genetic disorder that usually manifests in childhood. “What’s so exciting with our discovery,” Keirstead said, “is that creating transplantable retinas from stem cells could help millions of people, and we are well on the way.” The UCI researchers are testing the early-stage retinas in animal models to learn how much they improve vision. Positive results would lead to human clinical trials. The study appeared online in the Journal of Neuroscience Methods.

Science Daily
June 22, 2010

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Gene therapy cures canines of inherited form of day blindness

Veterinary ophthalmology researchers from the University of Pennsylvania have used gene therapy to restore retinal cone function and day vision in two canine models of congenital achromatopsia, also called rod monochromacy or total color blindness. Achromatopsia is a rare autosomal recessive disorder with an estimated prevalence in human beings of about 1 in 30,000 to 50,000. It primarily affects the function of the cone photoreceptors in the retina and serves as a representative model for other more common inherited retinal disorders affecting cones. Cone function is essential for color vision, central visual acuity and most daily visual activities, which underlines the importance of the newly developed treatment. The treatment cured younger canines regardless of the mutation that caused their achromatopsia. It was effective for the 33 months of the study and most likely is permanent; however, researchers also observed a reproducible reduction in the cone therapy success rate in dogs treated at 54 weeks of age or older. The successful therapy in dogs was documented by the restoration of the cone function using electroretinography and by objective measure of day vision behavior. The behavioral results suggest that inner retinal cells and central visual pathways were able to usefully process the input from the recovered cones.

The results represent the second successful cone-directed gene replacement therapy in achromatopsia animal models and the first outside of mouse models. The gene therapy targets mutations of the CNGB3 gene, the most common cause of achromatopsia in humans. Achromatopsia-affected dogs represent the only natural large animal model of CNGB3-achromatopsia. The results hold promise for future clinical trials of cone-directed gene therapy in achromatopsia and other cone-specific disorders. “The successful restoration of visual function with recombinant adeno-associated virus-mediated gene replacement therapy has ushered in a new era of retinal therapeutics,” said András M. Komáromy, assistant professor of ophthalmology at the Penn School of Veterinary Medicine and lead author of the study.

Many vision-impairing disorders in humans result from genetic defects, and, to date, mutations have been identified in ~150 genes out of ~200 mapped retinal disease loci. This wealth of genetic information has provided fundamental understanding of the multiple and specialized roles played by photoreceptors and the retinal pigment epithelium in the visual process and how mutations in these genes result in disease. Together with the development of gene-transfer technologies, it is now possible to realistically consider the use of gene therapy to treat these previously untreatable disorders. The article, available online in advance of its publication in the journal Human Molecular Genetics, was conducted by Komáromy, Jessica S. Rowlan and Gustavo D. Aguirre of the Department of Clinical Studies at Penn Vet; Monique M. Garcia, Asli Kaya and Jacqueline C. Tanaka of Temple University; John J. Alexander of the University of Florida and the University of Alabama; Vince A. Chiodo and William W. Hauswirth of the University of Florida; and Gregory M. Acland of Cornell University.

Science Daily
May 11, 2010

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Stem cells restore sight in mouse model of retinitis pigmentosa

An international research team led by Columbia University Medical Center successfully used mouse embryonic stem cells to replace diseased retinal cells and restore sight in a mouse model of retinitis pigmentosa. This strategy could potentially become a new treatment for retinitis pigmentosa, a leading cause of blindness that affects approximately one in 3,000 to 4,000 people, or 1.5 million people worldwide. The study appears online ahead of print in the journal Transplantation (March 27, 2010 print issue). Specialized retinal cells called the retinal pigment epithelium maintain vision. Retinitis pigmentosa results from the death of retinal cells on the periphery of the retina, leading to “tunnel vision,” where the field of vision is narrowed considerably and everything outside the “tunnel” appears blurred or wavy. “This research is promising because we successfully turned stem cells into retinal cells, and these retinal cells restored vision in a mouse model of retinitis pigmentosa,” said Stephen Tsang, M.D., Ph.D., assistant professor of ophthalmology, pathology and cell biology, Columbia University Medical Center, and lead author of the paper. “The transplanted cells not only looked like retinal cells, but they functioned like them, too.”

In Dr. Tsang’s study, sight was restored in one-fourth of the mice that received the stem cells. However, complications of benign tumors and retinal detachments were seen in some of the mice, so Dr. Tsang and colleagues will optimize techniques to decrease the incidence of these complications in human embryonic stem cells before testing in human patients can begin. “Once the complication issues are addressed, we believe this technique could become a new therapeutic approach for not only retinitis pigmentosa, but age-related macular degeneration, Stargardt disease, and other forms of retinal disease that also feature loss of retinal cells,” said Dr. Tsang. In age-related macular degeneration, retinal cells in the center of the retina degenerate and cause the center part of vision to become blurry or wavy. In 2010, macular degeneration is prevalent in nine million Americans and its incidence is expected to double by 2020. It is estimated that 30 percent of the population will have some form of macular degeneration by the time they reach the age of 75.

Replacement of damaged retinal cells in patients with macular degeneration is currently offered in some hospitals, but the therapy is limited by a shortage of donor retinal pigment epithelium cells. By using stem cells and turning them into retinal pigment epithelium cells, the supply is virtually unlimited. Similar approaches to macular degeneration have demonstrated efficacy in other rodent models, but since these models are of rare, unique pathophysiologies of retinal degeneration, they may not be generalizable to most human forms of retinal degeneration, e.g., age-related macular degeneration, retinitis pigmentosa or Stargardt disease. “It’s a good thing that more models are being tried, as this shows there may be real potential for stem cells to treat different causes of the loss of retinal pigment epithelium in humans,” said Dr. Tsang.

Science Daily
March 23, 2010

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Chickens ‘one-up’ humans in ability to see color

Researchers at Washington University School of Medicine in St. Louis have peered deep into the eye of the chicken and found a masterpiece of biological design. Scientists mapped five types of light receptors in the chicken’s eye. They discovered the receptors were laid out in interwoven mosaics that maximized the chicken’s ability to see many colors in any given part of the retina, the light-sensing structure at the back of the eye. “Based on this analysis, birds have clearly one-upped us in several ways in terms of color vision,” says Joseph C. Corbo, M.D., Ph.D., senior author and assistant professor of pathology and immunology and of genetics. “Color receptor organization in the chicken retina greatly exceeds that seen in most other retinas and certainly that in most mammalian retinas.” Corbo plans follow-up studies of how this organization is established. He says such insights could eventually help scientists seeking to use stem cells and other new techniques to treat the nearly 200 genetic disorders that can cause various forms of blindness. Scientists published their results in the journal PLoS One.

Birds likely owe their superior color vision to not having spent a period of evolutionary history in the dark, according to Corbo. Birds, reptiles and mammals are all descended from a common ancestor, but during the age of the dinosaurs, most mammals became nocturnal for millions of years. Vision comes from light-sensitive photoreceptor cells in the retina. Night-vision relies on receptors called rods, which flourished in the mammalian eye during the time of the dinosaurs. Daytime vision relies on different receptors, known as cones, that are less advantageous when an organism is most active at night. Birds, now widely believed to be descendants of dinosaurs, never spent a similar period living mostly in darkness. As a result, birds have more types of cones than mammals. “The human retina has cones sensitive to red, blue and green wavelengths,” Corbo explains. “Avian retinas also have a cone that can detect violet wavelengths, including some ultraviolet, and a specialized receptor called a double cone that we believe helps them detect motion.”

In addition, most avian cones have a specialized structure that Corbo compares to “cellular sunglasses”: a lens-like drop of oil within the cone that is pigmented to filter out all but a particular range of light. Researchers used these drops to map the location of the different types of cones on the chicken retina. They found that the different types of cones were evenly distributed throughout the retina, but two cones of the same type were never located next to each other. “This is the ideal way to uniformly sample the color space of your field of vision,” Corbo says. “It appears to be a global pattern created from a simple localized rule: you can be next to other cones, but not next to the same kind of cone.” Corbo speculates that extra sensitivity to color may help birds in finding mates, which often involves colorful plumage, or when feeding on berries or other colorful fruit. “Many of the inherited conditions that cause blindness in humans affect cones and rods, and it will be interesting to see if what we learn of the organization of the chicken’s retina will help us better understand and repair such problems in the human eye,” Corbo says.

Science Daily
March 9, 2010

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Cornea cell density predictive of graft failure at six months post-transplant

A new predictor of cornea transplant success has been identified by the Cornea Donor Study (CDS) Investigator Group. New analysis of data from the 2008 Specular Microscopy Ancillary Study (SMAS), a subset of the CDS, found that the preoperative donor cell count of endothelial cells, previously considered to be an important predictor of a successful transplant, did not correlate with graft success. Instead the study found that a patient’s endothelial cell count six months post-cornea transplant is a better indicator of subsequent failure of the graft rather than the donor’s cell count. These results offer an additional, reliable indicator of success that surgeons can use for monitoring patients at the six-month milestone after transplantation. Endothelial cells form the back layer of the cornea and keep the cornea clear and prevent it from swelling. Previously it was thought that the more endothelial cells/mm2 in the donor cornea, the better, which put pressure on the eye banks to have donors with the highest count possible to distribute to corneal surgeons. However, the SMAS findings show no correlation between it and a patient’s graft success rate five-years post transplant, as long as the industry standard minimum of 2,000 cells/mm2 was met. The results of this study are published in the January issue of the Archives of Ophthalmology.

“These new findings of the SMAS are excellent examples of evidence-based medicine impacting clinical practice,” says Jonathan H. Lass, M.D., senior author of the study and Professor and Chair of the Department of Ophthalmology and Visual Sciences at Case Western Reserve University School of Medicine and University Hospitals Case Medical Center. “This evidence offers surgeons a broader pool of donors for their patients and will allow more individuals to donate to eye banks.” The results were analyzed at the Specular Microscopy Reading Center, part of the Department of Ophthalmology and Visual Sciences at Case Western Reserve University and the University Hospitals Eye Institute. Conceived in 1998, the CDS is a prospective cohort study that has already reported: 1) The age of the donor does not impact transplant survival after five years for conditions with moderate risk for graft failure due to endothelial dysfunction (Fuchs’ dystrophy, pseudophakic/aphakic corneal edema) (Ophthalmology 2008); 2) Incompatibility of blood type between the donor and recipient also does not impact graft survival at five years (Am J Ophthalmology 2009); and 3) There was a trend toward greater endothelial cell loss (75%) in the older donor age group (over 65 years to 75 years of age) than the younger donor age group (under 65 years) (69%), but this difference did not impact graft survival at five years (Ophthalmology 2008). This NIH-funded study has been extended through 2012 in order to determine whether these findings persist for a total of ten years post-transplant.

Science Daily
January 26, 2010

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Clearer view of how eye lens proteins are sorted

New research reveals how proteins that are critical for the transparency of the eye lens are properly sorted and localized in membrane bilayers. The study, published by Cell Press in the November 3rd issue of Biophysical Journal, analyzes how interactions between lipid and protein molecules can selectively concentrate proteins in certain regions of the cell membrane. All cells are surrounded by a dynamic semi-permeable structure called the plasma membrane. Cell plasma membranes are made of a thin bilayer of lipids interspersed with a diverse complement of proteins. Research has shown that the lipids and proteins are not randomly distributed across the plasma membrane. Instead, functional microdomains or “rafts” are enriched for certain lipids and proteins. Although raft sequestration of many classes of lipids and proteins has been extensively studied, mechanisms for sorting proteins that span the membrane to form channels are not as well understood.

Dr. Thomas J. McIntosh from the Department of Cell Biology at Duke University Medical Center and his colleagues were interested in examining whether the plasma membrane distribution of the major eye lens channel proteins depends on how they are sorted between raft and non-raft microdomains. “We already knew that lens cell plasma membranes contain high concentrations of the raft lipids cholesterol and sphingomyelin, and that rafts form in lens membranes,” says Dr. McIntosh. “In addition, we knew that lens channel proteins, connexins and aquaporin, are preferentially located in different regions of lens cell plasma membranes.” Using both detergent extraction and confocal microscopy to analyze reconstituted membranes, the researchers discovered that lens connexins were primarily located in non-raft domains. In contrast, the microdomain location of aquaporin depended on its aggregation status, which was controlled by the protein: lipid ration in the membrane. Specifically, under conditions where aquaporin molecules are known to cluster together (homo-oligomerize), aquaporin was enriched in non-raft domains. “Our observation that sequestration of aquaporin into raft microdomains was markedly increased under conditions where homo-oligomerization was observed supports the theory that protein clustering might modify microdomain sorting,” offers Dr. McIntosh. “Taken together, our data suggest that protein-lipid interactions, as modified by aquaporin homo-oligomerization, can be a key factor in the sorting of proteins in lens cell membranes.”

Science Daily
December 1, 2009

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A chip for the eye? Artificial vision enhancers being put to the test

Visually impaired or blind patients with degenerative retina conditions would be very happy if they were able to regain mobility, find their way around, be able to lead an independent life and to recognize faces and read again. These wishes were documented by a survey conducted by a research team ten years ago to find out what patients’ expectations of electronic retina prostheses (retina implants) were. Today these wishes look set to become reality, as the presentations given at the international symposium “Artificial Vision” on 19 September 2009 at the Wissenschaftszentrum Bonn demonstrated. The symposium was staged by the Retina Implant Foundation and the Pro Retina Stiftung zur Verhütung von Blindheit (Pro Retina Foundation for the Prevention of Blindness), a foundation of the patients’ organization Pro Retina Deutschland e.V. Scientists have been working on developing retina prostheses for more than twenty years now. Research has been conducted particularly intensively in Germany, where scientists and patients have worked in tandem and have succeeded in obtaining government funding. “Back then we didn’t want high-tech just for space and defence programs but finally high-tech for people as well,” Professor Rolf Eckmiller, a neuro-informatics specialist at the University of Bonn and a pioneer in the field, recalls.

This investment is now bearing fruit. The German research consortiums lead the field in this area of research. Three of the four research teams presenting their findings in Bonn are from Germany. As the presentations show, all the electronic retina prostheses convey visual impressions, so-called phosphenes. Patients participating in a US study were able to distinguish light and dark and to register movement and the presence of larger objects. In addition, early reports from a project being conducted by a German research group led by Profesor Eberhart Zrenner at the University of Tübingen indicate that restoring visually impaired patients’ ability to read is not just wishful thinking. Some patients are able to read letters if these are eight centimetres high. “We’re in the final run-up,” explains Professor Peter Walter from the University Eye Clinic in Aachen. Walter is scientific director of the symposium “Artificial Vision.” “The final studies prior to market launch have begun or are set to begin,” he says in his latest progress report. These studies are designed to test the long-term tolerability of the retina implants and their benefits in everyday life. The manufacturers expect the implants to be approved in 2011.

Naturally, there is a lot of interest among patients in the new products. “Compared with the study we conducted ten years ago, patients now have a much clearer idea of what they expect from retina prostheses,” says Helma Gusseck, chairperson of the Stiftung Retina-Implantat (Retina Implant Foundation). Gusseck, who also chairs the Pro Retina Stiftung, suffers herself from Retinitis pigmentosa, a degenerative retina condition and can now only distinguish between light and dark. For her the research findings are a relief: “You can, so to speak, go blind without worrying about it, because you know that the systems will soon be ready and we therefore have an option.” Nevertheless, this is really only the beginning. “What we’re seeing is different systems racing to compete,” says Peter Walter. In one of the systems – the sub-retinal implant – the chip is implanted under a layer of nerve cells in the retina. There, like the photoreceptors in the retina, it receives light impulses, converts these into electrical signals and transmits them to the nerve cells of the retina. The retina prosthesis developed by Professor Zrenner’s team in Tübingen and that developed by a US team led by Joe Rizzo and Shawn Kelly at the Boston Implant Project in Cambridge, Massachusetts, work according to the same principle. In the case of the so-called epiretinal implant the chip is fixed to the upper-most layer of nerve cells. There it receives data from a small camera installed in glasses worn by the patient and likewise converts these into impulses for the nerve cells. This is the principle employed by the retina prostheses developed by the two other German research teams. One of the systems – IRIS – was developed by the Bonn company IMI, the other (EPIRET3) by a research consortium that includes scientists from the RWTH Aachen and the Fraunhofer Institut für Mikroelektronische Schaltungen und Systeme (Institute for Microelectronic Circuits and Systems) and doctors at the University Eye Clinic Aachen led by Peter Walter.

Alongside these various systems, which also differ from one another in a number of other details, the next generation of retina prostheses is already in the pipeline in laboratories around the world. Engineers, computer science specialists, biologists and doctors are pooling their knowledge to evolve new strategies for linking electronic devices and nervous systems. Teams of researchers in Switzerland and Japan, for example, are developing systems in which the chip is no longer implanted in the eye but outside it on the dermis that protects the eyeball in the socket. Only the electrodes that stimulate the nerve cells in the retina are inserted inside the eye through a small incision. Chinese researchers are developing retina prostheses that, instead of stimulating the nerve cells of the retina, stimulate the optic nerve directly. And an American team is trying to activate the visual cortex in the brain directly. At this point it is not clear when, if ever, any of these systems will be ready for patient trials – currently they are still at the experimentation stage. Much interest has also been shown in projects to use other communication signals between nerve cells. Australian and American scientists are working on retina prostheses that produce biochemical impulses instead of electrical ones. The idea is for the retina prostheses to release neurotransmitters according to spatially and temporally controlled patterns and thus stimulate the nerve cells.

The question remains whether retina prostheses will eventually be able to register shapes, as Rolf Eckmiller hopes they will. “To do this will require a retina prosthesis capable of learning and that is able to produce a kind of melody of impulses that can be recognized by the brain and classified as a particular shape, like a cup.” Eckmiller is convinced that the complex central vision system – which occupies a third of the cerebral cortex – can only register a shape if the right “melody” is transmitted via a sufficiently large number of cells.

Science Daily
October 6, 2009

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Retina cells created from skin-derived stem cells

A team of scientists from the University of Wisconsin-Madison School of Medicine and Public Health has successfully grown multiple types of retina cells from two types of stem cells — suggesting a future in which damaged retinas could be repaired by cells grown from the patient’s own skin. Even sooner, the discovery will lead to laboratory models for studying genetically linked eye conditions, screening new drugs to treat those conditions and understanding the development of the human eye. A Waisman Center research team led by David Gamm, an assistant professor of ophthalmology and visual sciences, and Jason Meyer, a research scientist, announced their discovery in the Aug. 24 edition of the Proceedings of the National Academy of Sciences. “This is an important step forward for us, as it not only confirms that multiple retinal cells can be derived from human iPS cells using the Wisconsin approach, but also shows how similar the process is to normal human retinal development,” Gamm says. “That is quite remarkable given that the starting cell is so different from a retinal cell and the whole process takes place in a plastic dish. We continue to be amazed at how deep we can probe into these early events and find that they mimic those found in developing retinas. Perhaps this is the way to close the gap between what we know about building a retina in mice, frogs and flies with that of humans.”

Gamm says the work built on the strong tradition of stem cell research at UW-Madison. James Thomson, a School of Medicine and Public Health faculty member and director of regenerative medicine at the Morgridge Institute for Research on the UW-Madison campus, announced that he had made human stem cells from skin, called induced pluripotent stem (iPS cells), in November 2007. Su-Chun Zhang, UW-Madison professor of anatomy and a Waisman researcher, was among the first to create neural cells from embryonic stem cells. Zhang was also part of the Gamm lab’s retinal study. Meyer says the retina project began by using embryonic stem cells, but incorporated the iPS cells as they became available. Ultimately, the group was able to grow multiple types of retina cells beginning with either type of stem cell, starting with a highly enriched population of very primitive cells with the potential to become retina. This is critical, as it reduces contamination from unwanted cells early in the process. In normal human development, embryonic stem cells begin to differentiate into more specialized cell types about five days after fertilization. The retina develops from a group of cells that arise during the earliest stages of the developing nervous system. The Wisconsin team took cells from skin, turned them back into cells resembling embryonic stem cells, then triggered the development of retinal cell types.

“This is one of the most comprehensive demonstrations of a cell-based system for studying all of the key events that lead to the generation of specialized neural cells,” Meyer says. “It could serve as a foundation for unlocking the mechanisms that produce human retinal cells.” Because the group was successful using the iPS cells, they expect this advance to lead to studying retinal development in detail and treating conditions that are genetically linked. For example, skin from a patient with retinitis pigmentosa could be reprogrammed into iPS cells, then retina cells, which would allow researchers to screen large numbers of potential drugs for treating or curing the condition. Likewise, someday ophthalmologists may be able to repair damage to the retina by growing rescue or repair cells from the patient’s skin. Earlier this year, scientists from the University of Washington showed that human ES cells had the potential to replace retinal cells lost during disease in mice. “We’re able to produce significant numbers of photoreceptor cells and other retinal cell types using our system, which are lost in many disorders,” Meyer says. Photoreceptors are light-sensitive cells that absorb light and transmit the image as an electrical signal to the brain. The team had similar success in creating the multiple specialized types of retina cells from embryonic stem cells, underscoring the similarities between ES and iPS cells. However, Gamm emphasizes that there are differences between these cell types as well. More work is needed to understand their potential and their limitations.

Science Daily
September 8, 2009

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Heat shock proteins provide protection against cataracts

The human eye lens consists of a highly concentrated mix of several proteins. Protective proteins prevent these proteins from aggregating and clumping. If this protective function fails, the lens blurs and the patient develops cataracts. Two research groups at the Department of Chemistry of the Technische Universitaet Muenchen (TUM) have succeeded in explaining the molecular architecture of this kind of protective protein. Their findings, which are published online in the current early edition of PNAS (Proceedings of the National Academy of Sciences), shed new light on the work of these proteins and may be able to help in the development of new treatments. Cells have a variety of protein complexes that manage vital tasks. The functions of these “molecular machines” depend largely on their three-dimensional structure. In the first instance, proteins are long chains of amino acids, like a long piece of woolen thread. So-called chaperones help them to fold in the desired three-dimensional form after their production. If this folding process fails, the protein thread becomes an inextricable, useless tangle.

Small heat shock proteins (sHsps) are a particularly important group of chaperones. They prevent the clumping of proteins under stress conditions. αB-crystallin and the related sHsp αA-crystallin are the main representatives of the sHsps found in humans. Whereas αA-crystallin mainly occurs in the eye lens, αB-crystallin is also very common in the brain and in the heart and muscle tissue. In the eye lens, they counteract diseases like cataracts. Malfunctions of the αB-crystallin in tissue cells can give rise to cancer and neurological defects, including Alzheimer’s disease. Many research groups have focused their work on the α-crystallins due to their medical relevance. Despite intensive efforts, up to now, none of them have managed to determine the molecular architecture of these proteins. However, TUM biochemists have now succeeded in producing αA-crystallins and αB-crystallins recombinantly in bacteria and in obtaining uniform, clearly-structured complexes. A detailed structural analysis of these proteins was carried out in cooperation with the Chemistry Department’s Center of Electron Microscopy. The research groups were able to show for the first time here that, contrary to previous suppositions, αB-crystallin forms a defined globular structure comprising 24 subunits, which are reminiscent of a perforated soccer ball. Thanks to the identification of the three-dimensional structure of αB-crystallin, which is currently being further refined, the basis has now been established for comparing healthy and disease-promoting mutants and, based on this, for clarifying the way they function. The scientists hope that this will lead to the discovery of new treatments.

Science Daily
August 25, 2009

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New evidence that popular dietary supplement may help prevent, treat, cataracts

Researchers are reporting evidence from tissue culture experiments that the popular dietary supplement carnosine may help to prevent and treat cataracts, a clouding of the lens of the eye that is a leading cause of vision loss worldwide. In the new study, Enrico Rizzarelli and colleagues note that the only effective treatment for cataracts is surgical replacement of the lens, the clear disc-like structure inside the eye that focuses light on the nerve tissue in the back of the eye. Cataracts develop when the main structural protein in the lens, alpha-crystallin, forms abnormal clumps. The clumps make the lens cloudy and impair vision. Previous studies hinted that carnosine may help block the formation of these clumps. The scientists exposed tissue cultures of healthy rat lenses to either guanidine — a substance known to form cataracts — or a combination of guanidine and carnosine. The guanidine lenses became completely cloudy, while the guanidine/carnosine lenses developed 50 to 60 percent less cloudiness. Carnosine also restored most of the clarity to clouded lenses. The results demonstrate the potential of using carnosine for preventing and treating cataracts, the scientists say.

Science Daily
August 11, 2009

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Primate eye evolution: Small evolutionary shifts make big impacts — like developing night vision

In the developing fetus, cell growth follows a very specific schedule. In the eye’s retina, for example, cones — which help distinguish color during the day — develop before the more light-sensitive rods — which are needed for night vision. But minor differences in the timing of cell proliferation can explain the large differences found in the eyes of two species — owl monkeys and capuchin monkeys — that evolved from a common ancestor. Researchers from Cornell, St. Jude’s Children’s Research Hospital in Tennessee and the Federal University of Para, Brazil, have found an evolutionary mechanism that provides insight into how important changes in brain structure of primates can evolve. That evolution appears to proceed via simple genetic changes that affect the timing of development of brain regions, they report in a paper published May 18 online and in a future print issue of Proceedings of the National Academy of Sciences.

In both monkey species, the specialized eye cells develop in the growing embryo from a single retinal progenitor cell. In their basic design, the eyes of these primates have the capability and necessary architecture to be either nocturnal or diurnal, based on a species’ ecological niche and needs, said Cornell neurobiologist and psychologist Barbara Finlay. Finlay and her colleagues compared the developing eyes in fetuses of the two species to better understand how the nocturnal owl monkeys developed retinas with many more rod cells than cones, while capuchin monkeys, which are active during the day (diurnal), developed more cone cells than rods. “These two species evolved about 15 million years ago from a common ancestor that had a diurnal eye,” said Finlay, a Cornell professor of psychology and senior author of the paper.

“So we believed that comparing how their eyes develop during embryonic growth could help us understand what evolutionary changes would be required to evolve from a diurnal to a nocturnal eye,” said Finlay. By comparing the timing of retinal cell proliferation in the two species, the researchers found evidence that an extended period of progenitor cell proliferation in the owl monkey gave rise to an increased number of rod and other associated cells that make its eyes adept at night vision; the eyes also evolved to be large, with bigger light-gathering and light-sensing structures needed for nocturnal sight.

Science Daily
June 2, 2009

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Secret to night vision found in DNA’s unconventional ‘architecture’

Researchers have discovered an important element for making night vision possible in nocturnal mammals: the DNA within the photoreceptor rod cells responsible for low light vision is packaged in a very unconventional way, according to a report in the April 17th issue of Cell. That special DNA architecture turns the rod cell nuclei themselves into tiny light-collecting lenses, with millions of them in every nocturnal eye. The conventional architecture seen in almost all nuclei is invariably present in the rod cells of diurnal mammals, including primates, pigs and squirrels,” said Boris Joffe of Ludwig-Maximilians University Munich. “On the other hand, the unique inverted architecture is universally present in nocturnal mammals,” for instance, mice, cats and deer. That architecture has important ramifications for the optical properties of those cells, added Jochen Guck of the University of Cambridge. “Diurnal nuclei are basically scattering obstacles,” he said. “In nocturnal animals, they are little lenses. In one case, light is scattered in all directions and in the other it is focused in the forward direction,” meaning that even at night, what little light there is can travel deeper into the eye where it can be perceived.

Coming to the realization that the structure of the nuclei of rod cells might have something to do with animals’ behavior at night versus during the day took a great leap and an interdisciplinary team, Joffe added. That’s because biologists typically think of DNA and its packaging into chromatin in terms of its effect on gene activity. “We tried every other possible explanation,” Joffe added. “The idea that it had something to do with vision was a daring idea. People laughed at first.” In non-dividing cells, DNA is associated with proteins to form the so-called chromatin, with more condensed “heterochromatin” at the periphery and less condensed “euchromatin” in the interior. Although cell type-specific variants of nuclear architecture can differ notably in details, the researchers explained, the pattern described above is nearly universal and is conserved in both single-celled and multicellular organisms. The reason for the evolutionary stability of nuclear architecture is most probably the important role that the spatial arrangement of chromatin plays in regulating nuclear functions, they said.

Given that notion, the team took great interest in the fact that the nuclei of mouse rod cells shows essentially the opposite, inverted pattern. The central portion of their nuclei is occupied by a large mass of heterochromatin, while transcription factors that control the activity of genes are enriched at the nuclear periphery. Mice aren’t born with those unusual rod cells, they now report. Rather, the conventional nuclear architecture in their rod cells is completely transformed over the animals’ first few weeks into the inverted pattern. The inverted nuclear architecture found in mice is also present in other nocturnal animals, they found. “Our data revealed a wholly unexpected but very clear correlation between the rod nuclear architecture and lifestyle that was further supported by data on nearly forty animals,” the researchers said. “Nocturnal mammals had the inverted pattern, while the diurnal ones showed the conventional one.” The correlation between the inverted nuclear architecture and night vision suggested that the inverted pattern might have an optical ramification, they said. After all, nocturnal mammals see at light intensities a million times lower than those available during the day, and their rod photoreceptors are known to possess a light sensitivity down to the level of a few photons. This high sensitivity demands a large number of rod cells, which increases the thickness of the retinas’ outer nuclear layer (ONL). The optimization of light transmission through the ONL could therefore provide crucial advantages for nocturnal vision.

Indeed, measurements of how individual nuclei taken from the rod cells of nocturnal animals interact with light show that they act as collecting lenses. Computer simulations indicate that columns of such nuclei like those found in nocturnal animals’ retinas would channel light efficiently toward the light-sensing rod outer segments. The importance of this special nuclear arrangement comes only when you consider the columns, Guck said. “If each nuclei scattered light, it would all be over. The inversion in nocturnal animals makes sure that light is passed from one nucleus to the next. It is handed down so that it doesn’t scatter.” The results show that despite the strong evolutionary conservation of the conventional pattern, nuclear architecture in rod cells was modified several times in the evolution of mammals, Joffe said.

Science Daily
May 4, 2009

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Stem cell therapy makes cloudy corneas clear

Stem cells collected from human corneas restore transparency and don’t trigger a rejection response when injected into eyes that are scarred and hazy, according to experiments conducted in mice by researchers at the University of Pittsburgh School of Medicine. Their study will be published in the journal Stem Cells and appears online today. The findings suggest that cell-based therapies might be an effective way to treat human corneal blindness and vision impairment due to the scarring that occurs after infection, trauma and other common eye problems, said senior investigator James L. Funderburgh, Ph.D., associate professor, Department of Ophthalmology. The Pitt corneal stem cells were able to remodel scar-like tissue back to normal. “Our experiments indicate that after stem cell treatment, mouse eyes that initially had corneal defects looked no different than mouse eyes that had never been damaged,” Dr. Funderburgh said. The ability to grow millions of the cells in the lab could make it possible to create an off-the-shelf product, which would be especially useful in countries that have limited medical and surgical resources but a great burden of eye disease due to infections and trauma.

“Corneal scars are permanent, so the best available solution is corneal transplant,” Dr. Funderburgh said. “Transplants have a high success rate, but they don’t last forever. The current popularity of LASIK corrective eye surgery is expected to substantially reduce the availability of donor tissue because the procedure alters the cornea in a way that makes it unsuitable for transplantation.” A few years ago, Dr. Funderburgh and other University of Pittsburgh researchers identified stem cells in a layer of the cornea called the stroma, and they recently showed that even after many rounds of expansion in the lab, these cells continued to produce the biochemical components, or matrix, of the cornea. One such protein is called lumican, which plays a critical role in giving the cornea the correct structure to make it transparent. Mice that lack the ability to produce lumican develop opaque areas of their corneas comparable to the scar tissue that human eyes form in response to trauma and inflammation, Dr. Funderburgh said. But three months after the lumican-deficient mouse eyes were injected with human adult corneal stem cells, transparency was restored.

The cornea and its stromal stem cells themselves appear to be “immune privileged,” meaning they don’t trigger a significant immune response even when transplanted across species, as in the Pitt experiments. “Several kinds of experiments indicated that the human cells were alive and making lumican, and that the tissue had rebuilt properly,” Dr. Funderburgh noted. In the next steps, the researchers intend to use the stem cells to treat lab animals that have corneal scars to see if they, too, can be repaired with stem cells. Under the auspices of UPMC Eye Center’s recently established Center for Vision Restoration, they plan also to develop the necessary protocols to enable clinical testing of the cells.

EurekAlert! Medicine
April 21, 2009

Original web page at EurekAlert! Medicine

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Scientists see the light: how vision sends its message to the brain

New article in The FASEB Journal reports that scientists have finally captured the elusive signaling device our retinas use to tell us what we see. Bethesda, MD—Scientists have known for more than 200 years that vision begins with a series of chemical reactions when light strikes the retina, but the specific chemical processes have largely been a mystery. A team of researchers from the United States and Switzerland, have shined new light on this process by “capturing” this chemical communication for future study. This research, published in the February 2009 issue of The FASEB Journal (http://www.fasebj.org), may lead to the development of new treatments for some forms of blindness and vision disorders. At the center of the discovery is the signaling of rhodopsin to transducin. Rhodopsin is a pigment in the eye that helps detect light. Transducin is a protein (sometimes called “GPCR”) which ultimately signals the brain that light is present. The researchers were able to “freeze frame” the chemical communication between rhodopsin and transducin to study how this takes place and what goes wrong at the molecular level in certain disorders.

According to Krzysztof Palczewski, a senior scientist involved in the research, “The results may have important implications for discovery and development of more specific medicines to treat GPCR-linked dysfunction and disease.” Examples of health problems involving GPCR dysfunction include blindness, diabetes, allergies, depression, cardiovascular defects and some forms of cancer. To make their discovery, scientists isolated rhodopsin/transducin directly from bovine retinas. These membranes were suspended in solution and exposed to light to start the chemical signaling process. After light exposure, any contaminating proteins were removed, and the remaining rhodopsin and transducin “locked” in their chemical communication were removed using a centrifuge. In addition to helping scientists understand how vision begins, this research may also impact disorders affecting heart beat, blood pressure, memory, pain sensation, and infection response because it is believed that they are regulated by similar chemical communications involving similar proteins. “Until now, scientists have been in the dark when it comes to exactly how vision begins. This exciting new work shows how light becomes a chemical signal to the brain,” said Gerald Weissmann, Editor-in-Chief of The FASEB Journal. “Now that we see the light, so to speak, entirely new types of custom-fit become possible for a wide range of diseases.”

The FASEB Journal
February 10, 2009

Original web page at The FASEB Journal

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Mice made to regrow damaged retina nerve cells

Researchers at the University of Washington (UW) have reported for the first time that mammals can be stimulated to regrow inner nerve cells in their damaged retinas. Located in the back of the eye, the retina’s role in vision is to convert light into nerve impulses to the brain. The findings on retina self-repair in mammals is published the week of November 24 in the Early Edition of the Proceedings of the National Academy of Sciences. Other scientists have shown before that certain retina nerve cells from mice can proliferate in a laboratory dish. This new report gives evidence that retina cells can be encouraged to regenerate in living mice. The UW researchers in the laboratory of Dr. Tom Reh, professor of biological structure, studied a particular retinal cell called the Müller glia. “This type of cell exists in all the retinas of all vertebrates,” Reh said, “so the cellular source for regeneration is present in the human retina.” He added that further studies of the potential of these cells to regenerate and of methods to re-generate them may lead to new treatments for vision loss from retina-damaging diseases, like macular degeneration.

The researchers pointed out the remarkable ability of cold-blooded vertebrates like fish to regenerate their retinas after damage. Birds, which are warm-blooded, have some limited ability to regenerate retinal nerve cells after exposure to nerve toxins. Fish can generate all types of retinal nerve cells, the researcher said, but chicks produce only a few types of retinal nerve cell replacements, and few, if any, receptors for detecting light. Müller glia cells generally stop dividing after a baby’s eyes pass a certain developmental stage. In both fish and birds, the researchers explained, damage to retinal cells prompts the specialized Müller glia cells to start dividing again and to increase their options by becoming a more general type of cell called a progenitor cell. These progenitor cells can then turn into any of several types of specialized nerve cells. Compared to birds, the scientist said, mammals have an even more limited Müller glia cell response to injury. In an injured mouse or rat retina, the cells may react and become larger, but few start dividing again. Because the Müller glia cells appeared to have the potential to regrow but won’t do so spontaneously after an injury, several groups of researchers have tried to stimulate them to grow in lab dishes and in lab animals by injecting cell growth factors or factors that re-activate certain genes that were silenced after embryonic development. These studies showed that the Müller glia cells could be artificially stimulated to start dividing again, and some began to show light-detecting receptors.

However, these studies, the researchers noted, weren’t able to detect any regenerated inner retina nerve cells, except when the Müller glia cells were genetically modified with genes that specifically promote the formation of amacrine cells, which act as intermediaries in transmitting nerve signals. “This was puzzling,” Reh said, “because in chicks amacrine cells are the primary retinal cells that are regenerated after injury.” To resolve the discrepancy between what was detected in chicks and not detected in rodents, the Reh laboratory conducted a systematic analysis of the response to injury in the mouse retina, and the effects of specific growth factor stimulation on the proliferation of Müller glia cells. The researchers injected a substance into the retina to eliminate ganglion cells (a type of nerve cell found near the surface of the retina) and amacrine cells. Then by injecting the eye with epidermal growth factor (EGF), fibroblast growth factor 1 (FGF1) or a combination of FGF1 and insulin, they were able to stimulate the Müller glia cells to re-start their dividing engines and begin to proliferate across the retina. The proliferating Müller glia cells first transformed into unspecialized cells. The researchers were able to detect this transformation by checking for chemical markers that indicate progenitor cells. Soon some of these general cells changed into amacrine cells. The researchers detected their presence by checking for chemicals produced only by amacrine cells. Many of the progenitor cells arising from the dividing Müller glia cells, the researchers observed, died within the first week after their production. However, those that managed to turn into amacrine cells survived for at least 30 days. “It’s not clear why this occurs,” the researchers wrote, “but some speculate that nerve cells have to make stable connections with other cells to survive.”

Science Daily
December 23, 2008

Original web page at Science Daily

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As rods go, so go the cones

Rod cells in our eyes help us see in dim light. They also ensure that the cones, the other light-sensitive cells we depend on for vision, get enough food, a new study reveals. The findings may shed light on a common cause of blindness. Approximately 100,000 people in the United States have retinitis pigmentosa, an incurable inherited retinal disease that leads to blindness. More than 40 genes can contribute to the disease, often by damaging important proteins in retinal cells. The disease’s initial symptom, night-vision loss, appears when rods start dying off. This attrition usually begins in childhood, and though it’s inconvenient, most people get by with their cones–the photoreceptive cells that work in bright light. But by the time affected people reach adulthood, the cones begin dying, too, ultimately resulting in total blindness. This has confounded scientists, because the faulty genes aren’t active in the cones, only in the rods.

To crack this mystery, biologist Constance Cepko of Harvard University and her colleague Claudio Punzo, a postdoctoral researcher, first evaluated previous theories. Some researchers thought that when the rods died, they produced a toxin that killed the cones. Others hypothesized that because rods use lots of oxygen in the retina, their death might leave behind a large amount of oxygen that overloads and damages the remaining cones. But neither of these seemed to fit the pattern, Cepko says, so he and Punzo decided to look for a new explanation. The researchers measured gene activity in four different strains of mice with defective rod cells. They discovered more than 200 genes that are switched on at about the same time the cones started dying, many of them related to cell metabolism. “That was our first clue that perhaps the cells weren’t getting enough nutrients,” Cepko says. Several of these genes were tied to a protein known as the mammalian target of rapamycin, or mTOR, which lets the cell know whether it has enough nutrients–especially glucose. But if starvation lasts long enough, mTOR directs the cell to digest itself. That’s exactly what the cones were doing.

To determine whether a glucose drop-off was killing the cones, the researchers abdominally injected some of the mice with insulin to increase their glucose levels. The shots did cause the cones to hang on a little longer, but they nonetheless died a few weeks later. Cepko and Punzo think the cones might starve because of the retina’s crumbling architecture. A thin layer of cells, known as the retinal pigment epithelium (RPE), covers the rods and cones like a circus tent and delivers their nutrients. Rods significantly outnumber cones in the retina, so when they die, most of the RPEs’ “tent poles” die with them. The tent collapses, the cones lose their nutrient connection, and they slowly starve. The study is published online this week in Nature Neuroscience. “I think it’s very exciting,” says Rafael Caruso, an ophthalmologist with the U.S. National Eye Institute in Bethesda, Maryland. “It’s a new approach to the problem.” Caruso says that the researchers “make a pretty persuasive case for their conclusions,” especially because the same mutations in the tested mice are also found in humans. Unfortunately, both Cepko and Caruso agree that the finding does little for researchers looking for treatments. But it does suggest a new framework for thinking about the problem. By exploring different ways to get nutrients into the cones, Cepko says, researchers might one day be able to help people with retinitis pigmentosa keep their daytime vision for a longer period of time.

ScienceNow
December 23, 2008

Original web page at ScienceNow

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New treatment method for canine eye diseases developed

An Iowa State University researcher is exploring a new method of getting medicine to the eyes of infected dogs that is more effective and reliable than using eye drops. Dr. Sinisa Grozdanic, an assistant professor of veterinary clinical sciences at Iowa State’s College of Veterinary Medicine, is working with a drug manufacturer to develop a method of implanting biodegradable medicine into the tissue surrounding a dog’s eyes. The medicine releases gradually and treats the infected eye for an entire year. This is the first time the procedure has been tried to improve auto-immune corneal diseases that can cause pain, redness, inflammation and other eye problems for canines. This type of drug application is designed to replace eye drops that may require an owner to put drops in a dog’s eyes several times a day, sometimes without noticeable effect. “With drops, immediately after putting them in the eye, there is a lot of medicine going where it needs to go,” said Grozdanic. “Then the amount of medicine getting into the eye goes down quickly. Also, you have a specific time for how long that drug will be therapeutically active.” With drops, there are also other issues such as missing a dose and not getting all the medicine into a fidgety dog’s eyes.

“It’s a hassle for the owner to get the drops in. It is a hassle for the dog as well,” he said. By putting this small pellet inside the tissue surrounding the eye, medicine constantly gets to the needed area for an entire year, he said. “With this new method, you don’t miss a dose. And it works for 24 hours for an entire year.” The polymer is made by the company Nicast Ltd. in Israel, which is developing the technology for both animal and human use. The technology the company uses is called electrospinning. In making the implant, the needed drug is mixed with a polymer and formed into ultra-fine fibers. “From the fibers, a fabric is created, from which numerous medical devices, including drug release devices, can be fashioned,” said Benjamin Eliason, CEO of Nicast. “Various drugs can be incorporated into or onto the polymer fibers, or encapsulated inside miniature electrospun polymer capsules, and released inside the body over time.” To insert the medicine, Grozdanic makes a small incision in the dog’s conjunctiva, the mucous membrane surrounding the eye. He then closes the opening with one, tiny stitch. The entire process takes just a few minutes and is done with local anesthetic. To date, Grozdanic has used the new drug delivery method on six dogs. None of the dogs had been improving with the use of eye drops. Grozdanic is getting results with the new treatment. “In all the dogs we saw positive results,” said Grozdanic. “In some dogs, the results were spectacular. In some, the results were decent. The results were always positive. That’s very good considering that they were non-responsive to treatment using other eye medication before receiving the implants,” he said.

Science Daily
November 25, 2008

Original web page at Science Daily

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Therapeutic effect of a potent IL-12/IL-23 inhibitor STA-5326 on experimental autoimmune uveoretinitis

The purpose of this study was to determine whether oral administration of the IL-12/IL-23 inhibitor, STA-5326, is effective in experimental autoimmune uveoretinitis (EAU). C57BL/6J mice were immunized with human interphotoreceptor retinoid binding protein peptide (IRBP1-20). STA-5326 at a dose of either 5 mg/kg or 20 mg/kg, or vehicle alone, was orally administered once a day, 6 days per week from day 0 to day 14. Fundus examination was performed on day 14 and day 18 after immunization. Mice were sacrificed on day 18 and eyes were enucleated for histopathological examination. In vivo-primed draining lymph node cells were stimulated with IRBP1-20 and culture supernatant was harvested for assay of interferon (IFN)-gamma and IL-17 by enzyme linked immunosorbent assay (ELISA). Intracellular expression of IFN-gamma and IL-17 in CD4+ T cells of cultured draining lymph node cells was assessed by flow cytometry. The level of IL-12 p40 in serum was examined in STA-5326 treated or vehicle treated mice receiving immunization.

The level of IL-12 p40 in serum was decreased in STA-5326 treated mice. Oral administration of STA-5326 (5 mg/kg or 20 mg/kg) reduced the severity of EAU on day 14 and 18. In addition, mice treated with STA-5326 (20 mg/kg) showed significantly decreased severity of EAU by histopathological analysis. Although IFN-gamma production of draining lymph node cells was increased in STA-5326 treated mice by ELISA analysis, the proportion of IFN-gamma producing cells was not significantly altered. However, IL-17 production and the proportion of IL-17 producing cells were significantly reduced in STA-5326 treated mice. Furthermore, oral administration of STA-5326 during the effector phase reduced the severity of EAU. These results indicate that oral administration of the IL-12/IL-23 inhibitor STA-5326 is effective in suppressing inflammation in the EAU model, and reduces the expansion of IL-17 producing cells. STA-5326 may represent a new therapeutic modality for human refractory uveitis.

BioMed Central
October 28, 2008

Original web page at Biomed Central

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The role of stem cells in renewing the cornea

A group of researchers in Switzerland has published a study appearing in the Oct 1 advance online edition of the Journal Nature that shows how the cornea uses stem cells to repair itself. Using mouse models they demonstrate that everyday wear and tear on the cornea is repaired from stem cells residing in the corneal epithelium, and that more serious repair jobs require the involvement of other stem cells that migrate from the limbus, a region between the cornea and the conjunctiva, the white part of the eye. The integrity of the cornea, the transparent outer layer of the eye, is critical for vision. Millions of people around the world suffer from partial or complete blindness when their corneas lose transparency. Treatment options involve corneal transplants and, more recently, stem cell therapy. The surface of the cornea is naturally in a state of constant renewal; its upper layer, or epithelium, is completely turned over once every 7-14 days. Because slow-cycling stem cells have been found in the mouse limbus, researchers have assumed that these stem cells are the ones responsible for corneal renewal.

The research led by Professor Yann Barrandon, who holds a joint appointment at EPFL and the Lausanne University Hospitals (CHUV), challenges this prevailing opinion that the limbus is the only place where corneal stem cells reside. The researchers demonstrated that the epithelium of the cornea also contains stem cells, and that these cells have the capacity to generate two different epithelial tissues: corneal (covering the transparent part of the eye) and conjunctival (covering the white part of the eye). They demonstrated experimentally that these are the cells activated in everyday corneal renewal. The stem cells residing in the limbus have a different role; they are only activated when the cornea is seriously wounded.

To explain this distribution of stem cells and the different roles played by stem cells in different zones of the eye, the researchers propose that the expanding epithelia of the cornea and the conjunctiva act like tectonic plates, squeezing the limbus between them into a kind of equilibrium zone. Due to the constant expansion, stem cells accumulate in this zone. In the event of a rupture in the equilibrium, such as a large corneal injury, these limbal stem cells migrate into the cornea and conjunctiva and differentiate into the appropriate cell type to make repairs. The limbus is already recognized as a source of cells for corneal stem cell therapy in humans, and this new research indicates that the cornea itself can also be explored as a potential source of these cells. And because cancer has been associated with the presence of adult stem cells, the model also helps explain why transitional zones like the limbus, where stem cells accumulate, are sites where cancer tends to occur more frequently.

EurekAlert! Medicine
October 14, 2008

Original web page at EurekAlert! Medicine

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Retinal transplants see fleeting success

Retina transplants could potentially save the sight of millions. It was six months after her operation that Elisabeth Bryant first started to see the effects, quite literally. Clinically blind, Bryant began to make out the swinging pendulum of her grandfather clock from across the room. Since then her vision improved to the point that she could read large print editions of Reader’s Digest, send emails and continue with past activities like sewing and knitting. Bryant is one of ten patients to have received a retinal transplant as part of a phase II trial to replace diseased photoreceptors in conditions such as retinitis pigmentosa (RP) and age-related macular degeneration (AMD). Before the transplant she could see nothing but shadows. But within a year her vision had improved from 20/800 to 20/160, a remarkable recovery. Each of the patients in the trial received a small 4 millimetre square of retinal tissue, complete with retinal progenitor cells and the retinal pigment epithelium that nourishes them. The tissues were placed in the sub-retinal space beneath the fovea, the area of the retina responsible for sharp central vision.

Seven of the subjects experienced an improvement in their visual acuity, says Norman Radtke, the ophthalmologist who carried out the surgery at the Retina Vitreous Resource Center in Louisville, Kentucky. The results are reported in the August issue of the American Journal of Ophthalmology. The results may appear to improve the chances of restoring vision in sufferers of RP and AMD — the most common causes of blindness in developed countries, affecting millions of people. But it is far from clear just how much hope this research really offers. “I think this approach will never work as a standard clinical therapy,” says Marco Zarbin director of the Institute of Ophthalmology and Visual Sciences at New Jersey Medical School, in Newark. One reason is the fact that the transplanted tissue is obtained from aborted fetuses, he says. “Even if it proves to work wonderfully, the number of patients that would need to be treated worldwide or even in the United States alone would be in the millions.” There simply wouldn’t be enough donors available, and the logistics of getting the ethical approval to use them would act as a major barrier to treatment.

Another concern is the efficacy of the procedure. Despite 20 years of research on animals by co-authors Robert Aramant at research firm Ocular Transplantation, also in Louisville, and Magdalene Seiler at the University of California, Irvine, there is still no clear evidence that the improved vision in humans is directly due to the transplanted photoreceptor cells replacing the function of host cells within the retina. The transplanted grafts are made up of the entire thickness of the donor retina, says Robert MacLaren, a vitreoretinal surgeon at Moorfields Eye Hospital, in London. This means that for synaptic connections to form between the donor photoreceptors with the host retina, they would have to grow through several layers of donor cells. And despite rigorous post-operative testing, there is no evidence of this, he says, nor of any blood vessels growing to keep the graft alive. “An alternative explanation is that the graft is releasing growth factors that are aiding the recovery of dying host photoreceptors,” says MacLaren. If true, it may be simpler to introduce these growth factors instead. In animals, there is evidence for synaptic connections forming, says Aramant, but this is difficult to establish in humans. “For now, nobody can say to what extent we have a rescue effect in humans,” he says.

And there is another major issue. The improved visual acuity seems to only last for a couple of years. Six years on after her transplant, Bryant’s visual acuity has now dropped down to 20/320. “There may be a time limit on how effective this might be,” says Radtke. “That is a legitimate concern.” The real value of this trial is the demonstration that cells can be placed in the sub-retinal space without any adverse reaction, says Zarbin. This holds promise for other possible forms of cell-based treatment currently being explored, such as introducing stem cells into the retina and getting them to differentiate into new photoreceptors.

Nature
September 30, 2008

Original web page at Nature

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Mutation found in dachshund gene may help develop therapies for humans with blindness

Cone-rod dystrophies (CRDs) are a group of eye diseases caused by progressive loss of the photoreceptor cells in the retina. Researchers have identified a novel mutation in a gene associated with CRD in dogs, raising hopes that potential therapies can be developed for people suffering from these eye disorders. CRD represents a heterogeneous set of disorders characterized by progressive loss of retinal cone function. As these photoreceptor cells allow us to see in bright light, loss of cones results in what is commonly known as dayblindness, and can advance to blindness altogether. Thus far, investigations into the genetic basis for autosomal recessively inherited cases of human CRD have turned up only a few genes associated with the disorder, therefore it is likely there are other genes associated with CRD not yet identified.

Eye disorders are one of the most frequently inherited disorders in dogs, however canine CRD is limited to only a few breeds. A gene mutation had previously been associated with CRD in the miniature long-haired dachshund, while a genetic basis for CRD in the standard wire-haired dachshund and the pit bull terrier remained unknown. In this study, scientists led by Dr. Frode Lingaas of the Norwegian School of Veterinary Science and Dr. Kerstin Lindblad-Toh of the Broad Institute of MIT and Harvard have identified a mutation in a novel gene for early-onset CRD in standard wire-haired dachshund by genome-wide association mapping of a dachshund family. The genome-wide strategy utilized by Lingaas’ group isolated a region on chromosome 5 associated with CRD in dachshund. A search for mutations of this area revealed that a portion of the nephronophthisis 4 (NPHP4) gene has been deleted and is likely responsible for recessively inherited CRD in the standard wire-haired dachshund. The finding is particularly interesting, as the human form of NPHP4 has been previously implicated in disease. “This gene has been associated with a combination of kidney and eye disease in human patients,” explained Lingaas. “Here, we found a mutation that affects only the eyes, suggesting that this gene might be a candidate for human patients with eye disease only.”

The researchers suggest that the protein coded for by the mutant form of NPHP4 may lack a domain that would normally interact with other proteins involved in eye function, yet still retain the region involved in kidney function. “The new information that the NPHP4 gene can be involved in eye diseases only can shed light on the etiology of some low-frequency eye diseases in people where similar mutations may be involved,” Lindblad-Toh said. Lingaas noted that identification of causal mutations for diseases has practical implications for dogs, as genetic tests could be implemented to avoid new cases of the disorder and reduce the frequency of the mutation in the population. Furthermore, this investigation of the genetic basis for CRD in dogs could facilitate the development of treatments for humans.

Science Daily
September 2, 2008

Original web page at Science Daily

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Blindness in old age may be triggered by hyperactive immune resistance

Age-dependent macular degeneration (AMD) is the commonest cause of blindness in the western industrialised nations. Hereditary changes in the regulation of the immune system influence the risk of contracting AMD. Opthalmologists at the University Clinic in Bonn, working in co-operation with researchers from Göttingen, Regensburg and Great Britain, have now, for the first time, demonstrated that in cases of senile blindness the patient´s immune resistance is hyperactive throughout his entire body. An Anglo-German research team embracing immunologists from Göttingen University has added a further important aspect to our current knowledge of the processes leading to senile blindness. For the first time, they have been able to show that in the case of patients with AMD their entire immune system is hyperactive. It had not previously been known whether such an immune reaction affecting the entire body played any role in this eye disease. The investigation was conducted by scientists from Bonn, Göttingen, Regensburg and Oxford under the leadership of Privatdozent Dr. Hendrik Scholl of Bonn University´s Eye Clinic.

The Anglo-German research team worked on the hypothesis that one cause of the appearance of senile blindness, AMD, might be faulty regulation of the so-called complement system. This system is an important element in our hereditary immune resistance, and is involved where inflammatory reactions occur. Previously, it had only been known that changes in genes containing the hereditary information for proteins in the complement system increase the risk of contracting AMD. Some of these proteins activate, others inhibit, the complement system. The team examined the blood of a total of 112 AMD-patients and 67 healthy control persons for signs of faults in the regulation of their complement systems. They sought out changes in protein concentration which would indicate activation of the complement system. The experiments were conducted in Göttingen University´s Department for Cellular and Molecular Immunology under the leadership of Professor Dr. Martin Oppermann. The investigations of the patients´ blood did, indeed, reveal clear changes in the concentrations of a number of complement proteins which, moreover, correlated closely to the previously identified hereditary factors.

“Our study has revealed for the first time that in the case of AMD patients the complement system is hyperactive over the entire body”, Dr. Hendrik Scholl declares. The typical substances indicating a permanent inflammatory reaction circulate in the blood. “These results infer that senile blindness may arise from a permanent state of inflammation in the body. This can obviously lie dormant for decades, then in advanced old age can lead to the appearance of symptoms of the disease. According to Dr. Scholl, the point of most acute vision, at the centre of the retina, appears to be the susceptible point. In Germany, an estimated 4.5 million people suffer from age-dependent macular degeneration (AMD). With this disease, the point of most acute vision on the retina (macula) becomes subject to progressive deterioration. The patient can no longer read, and he or she loses the ability to lead an independent existence. Opthalmologists had hitherto known comparatively little about the causes of this disease, except that hereditary factors were involved, and also other easily influenced factors, such as smoking.

Science Daily
August 5, 2008

Original web page at Science Daily

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“Mind’s eye” influences visual perception

Letting your imagination run away with you may actually influence how you see the world. New research from Vanderbilt University has found that mental imagery—what we see with the “mind’s eye”—directly impacts our visual perception. “We found that imagery leads to a short-term memory trace that can bias future perception,” says Joel Pearson, research associate in the Vanderbilt Department of Psychology. and lead author of the study. “This is the first research to definitively show that imagining something changes vision both while you are imagining it and later on.” “These findings are important because they suggest a potential mechanism by which top-down expectations or recollections of previous experiences might shape perception itself,” Pearson and his co-authors write.

It is well known that a powerful perceptual experience can change the way a person sees things later. Just think of what can happen if you discover an unwanted pest in your kitchen, such as a mouse. Suddenly you see mice in every dust ball and dark corner—or think you do. Is it possible that imagining something, just once, might also change how you perceive things? “You might think you need to imagine something 10 times or 100 times before it has an impact,” says Frank Tong, associate professor of psychology and co-author of the study. “Our results show that even a single instance of imagery can tilt how you see the world one way or another, dramatically, if the conditions are right.” To test how imagery affects perception, Pearson, Tong and co-author Colin Clifford of the University of Sydney had subjects imagine simple patterns of vertical or horizontal stripes, which are strongly represented in the primary visual areas of the brain. They then presented a green horizontal grated pattern to one eye and a red vertical grated pattern to the other to induce what is called binocular rivalry. During binocular rivalry, an individual will often alternately perceive each stimulus, with the images appearing to switch back and forth before their eyes. The subjects generally reported they had seen the image they had been imagining, proving the researcher’s hypothesis that imagery would influence the binocular rivalry battle.

Additional experiments found that the effect of imagery on perception was approximately the same as showing the research subject a faint representation of one of the patterns between trials. Stronger shifts in perception were found if subjects either viewed or imagined a particular pattern for longer periods of time. They found that both imagery and perception can lead to a build-up of a “perceptual trace” that influences subsequent perception. Pearson, Clifford and Tong also discovered that changing the orientation of the image from what had been imagined greatly reduced the impact of imagery on perception. Because orientation is processed in early visual areas, this suggests that imagery’s interaction with perception may occur at early stages of visual processing. The new findings offer an objective tool to assess the often-slippery concept of imagination. “It has been very hard to pin down in the laboratory what exactly someone is experiencing when it comes to imagery, because it is so subjective,” Tong says. “We found that the imagery effect, while found in all of our subjects, could differ a lot in strength across subjects. So this might give us a metric to measure the strength of mental imagery in individuals and how that imagery may influence perception.” The findings may also help settle a longstanding debate in the research community over whether mental imagery is visual—that one imagines something just as one sees it—or more abstract.

Science Daily
July 22, 2008

Original web page at Science Daily

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MicroRNAs appear essential for retinal health

Retinas in newborn mice appear perfectly fine without any help from tiny bits of genetic material called microRNAs except for one thing — the retinas do not work. In the first-ever study of the effects of the absence of microRNAs in the mammalian eye, an international team of researchers directed by the University of Florida and the Italian National Research Council describes a gradual structural decline in retinas that lack microRNAs — a sharp contrast to the immediate devastation that occurs in limbs, lungs and other tissues that develop without microRNAs. The discovery, reported in May 7 issue of the Journal of Neuroscience, may lead to new understanding of some blinding diseases and further penetrates the cryptic nature of microRNAs — important gene regulators that a decade ago were considered to be little more than scraps floating around the cell’s working genetic machinery.

“MicroRNAs are behaving differently in the nervous system than they are in other bodily tissues,” said Brian Harfe, Ph.D., an assistant professor of molecular genetics and microbiology at the University of Florida College of Medicine. “Judging by our previous studies in limb development, I was expecting to see lots of immediate cell death in the retina. I was not expecting a normal-looking retina in terms of its form. It would be something like finding a perfectly formed arm at birth that just did not work.” Production of microRNAs is dependent on Dicer, an enzyme widely used by living things to kick-start the process of silencing unwanted genetic messages. By breeding mice that lack one or both of the forms — or alleles — of the gene that produces Dicer in the retina, scientists were able to observe retinal development when Dicer levels were half of normal or completely eliminated.

Electrical activity in retinas devoid of Dicer was abnormally low at the time of eye opening and became progressively worse at 1-, 3- and 5-month stages. Structurally, the retinas initially appeared normal, but the cells progressively became disorganized, followed by widespread degeneration. Retinas in animals equipped with a single form of the Dicer gene never underwent the inexorable structural decline that occurs in total absence of Dicer, but they also never functioned normally, according to electroretinograms. “We have removed Dicer from about 30 different tissues,” said Harfe, a member of the UF Genetics Institute. “In all of those cases with half the amount of Dicer, you still had a normal animal. In the retina, there were functional abnormalities. This is the first indication that the dose of Dicer is important for normal retinal health.”

Inherited forms of retinal degeneration affect about 100,000 people in the United States, according to the National Eye Institute. The problems typically occur with the destruction of photoreceptor cells called rods and cones in the back of the eye. More than 140 genes have been linked to these diseases, which only account for a fraction of the cases. “We have many types of retinal degeneration and not enough mutations to explain them,” said Enrica Strettoi, a senior researcher at the Institute of Neurosciences of the Italian National Research Council in Pisa, Italy. “Finding that ablation of Dicer causes retinal degeneration might be helpful in discovering candidate disease genes. What we’ve done is target virtually all microRNAs in the retina by ablating Dicer, the core enzyme regulating their synthesis. The next step is to try to address each one separately, and find the role of specific microRNAs. Removal of Dicer from other areas of the central nervous system has also produced functional and structural abnormalities, confirming the fundamental role of this enzyme in neurons.” More than 400 microRNAs have been identified in both mice and humans, and each one has the potential to regulate hundreds of target genes. They have also been linked to human diseases such as diabetes, hepatitis C, leukemia, lymphoma, Kaposi’s sarcoma and breast cancer.

EurekAlert! Medicine
May 27, 2008

Original web page at EurekAlert! Medicine

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Blind mice see the light

Bright lights make treated ‘blind’ mice leap into action. Blind mice have been made to sense light by inserting a protein derived from algae into their eyes. A similar method could one day be used to treat certain forms of blindness in humans, the researchers hope. The light-sensitive protein, called channelrhodopsin-2 (ChR2), is used by algae to sense light for photosynthesis. Some researchers are interested in using these light-sensitive proteins to replace damaged or missing photoreceptors in animals’ eyes. This happens in several human conditions, including the late stages of a relatively common form of blindness: age-related macular degeneration. At present, there are no cures for such patients, though treatments including gene therapy and laser surgery are being tested. The algae protein has been used by neuroscientists before in the lab, in order to make ‘light switches’ that turn neurons of interest on and off in lab animals. But its use as a therapy against blindness is in very early stages. If the technique can be perfected, it could allow people rendered totally blind by the loss of photoreceptors able to see — albeit in black and white.

Botond Roska of the Friedrich Miescher Institute for Biomedical Research in Basel, Switzerland, and his team looked at mice that were entirely missing photoreceptors in their eyes. These photoreceptors usually feed signals about light to the next layer of cells, called bipolar cells, before a signal is relayed on to the brain, providing a visual image. The researchers used a harmless virus to carry the protein into the mice’s bipolar cells. The protein ended up in only about 7% of the cells this way, but that was enough for light signals to be transmitted to the next layer of the retina — the ganglion cells – and eventually the brain, the team determined through studies of brain activity. While untreated mice didn’t respond to light at all, treated mice kept in the dark jumped into action when a bright light was turned on, they report in Nature Neuroscience.

It’s difficult to gauge exactly how well the mice could see after the treatment. The team tested vision, rather than just light perception, by showing the mice a series of moving stripes and seeing if they could follow them. The treated mice were better than untreated animals, but “you can’t ask the mouse”, says Roska. Mouse vision isn’t that good in the first place, he adds, which makes it harder to tell. A previous attempt at conferring sight on blind mice by a team based at Wayne State University School of Medicine, Detroit, showed that the same technique could activate the brain’s visual cortex. But these mice did not change their behaviour when lights were turned on, as the mice in Roska’s study did. The reason for the difference, Roska suggests, may be that in the previous study, ChR2 was randomly inserted into many cell types in the retina. There are over 60 types of cell here, some of which are switched on by light, and others that are inhibited by it. Slotting the light-sensitive protein into all of these cells means the opposing effects might cancel each other out, says Roska, or muddle up the output to the brain so much that a signal can’t be interpreted. Nonetheless, says Zhuo-Hua Pan, who led the previous study in Detroit, “many of the results of this paper nicely confirmed our early findings”. Roska and his colleagues are already setting up a collaboration with clinical groups to develop the technique for people. But even then, it’s likely to be a last-chance treatment, says Roska. If even a tiny bit of vision remains, other treatments will likely be more useful for some time, says Roska. “The method should only be used if there’s absolutely no vision left,” he says.

Nature
May 13, 2008

Original web page at Nature