Tag: Cell Biology

Therapeutic stem cells can be made without introducing genetic changes that could later lead to cancer, a study in PLOS Genetics has found.

The discovery, made by researchers at the Wellcome Trust Sanger Institute, is a boost for scientists working on ways to make regenerative medicines from induced pluripotent stem (iPS) cells; a type of stem cell made by reprogramming healthy body cells.

It is the first time scientists have tracked the genetic mutations gathered by iPS cells as they are grown in the laboratory.

The idea behind the research was to follow the whole journey iPS cells will take when used in clinical therapy. The Sanger Institute team, led by Professor Allan Bradley and Dr Kosuke Yusa, started with blood cells donated by a 57-year-old man.

As a person grows from embryo, to child, to adult, and as they age, the cells in their body generate a mosaic of tiny genetic changes. Most of these mutations have no effect but some can lead to cancer. The Sanger Institute team traced the history of genetic changes in both the donated blood cell and the iPS cells created from it.

The results reveal that mutations arise 10 times less often in iPS cells than they do in lab-grown blood cells and that none of the iPS cell mutations are in genes known to cause cancer.

Lead researcher Dr Foad Rouhani said: “None of the mutations we found in induced pluripotent stem cells were cancer-driver mutations or mutations in cancer-causing genes. We didn’t find anything that would preclude the use of iPS cells in therapeutic medicine.”

In addition, the team used the iPS cells, reprogrammed from the donated blood cell, to trace the history of every mutation that one cell had developed from the time it was a fertilised egg all the way up to the moment it was taken out of the body.

This is the first time that mutation rates of both types of cells, the donor cell and iPS cell, have been calculated and compared.

Professor Allan Bradley said: “Until now the question of whether generating iPS cells and growing them in cell culture creates mutations has not been addressed in detail. If human cells are really to be reprogrammed on a large scale for use in regenerative medicine then understanding the mutations the donor cells carry will be a crucial step. We now have the tools to do this.”

The ability to track the genetic changes in cells over a lifetime could also improve scientists’ understanding of how, when and why mutations can lead to cancer.

Dr Kosuke Yusa said: “One of the exciting things is that we have found a way to use iPS cells as a tool to look at the genetic history of a single cell. It also underlines the fact that before you use these cells you really need to characterise them to a high degree to know where the mutations that have been introduced are.”

The team also found that the genetic changes that do take place in iPS cells in the lab might be caused by a mechanism known as oxidative stress. They hope this knowledge will help to find ways to improve the process of making iPS cells.

Researchers from the University of Cambridge and the European Bioinformatics Institute also contributed to the study.

https://www.sciencedaily.com/  Science Daily

https://www.sciencedaily.com/releases/2016/04/160407150325.htm  Original web page at Science Daily

Researchers at the University of Arizona have discovered what causes and regulates collective cell migration, one of the most universal but least understood biological processes in all living organisms.

The findings, published in the March 13, 2015, edition of Nature Communications, shed light on the mechanisms of cell migration, particularly in the wound-healing process. The results represent a major advancement for regenerative medicine, in which biomedical engineers and other researchers manipulate cells’ form and function to create new tissues, and even organs, to repair, restore or replace those damaged by injury or disease.

“The results significantly increase our understanding of how tissue regeneration is regulated and advance our ability to guide these processes,” said Pak Kin Wong, UA associate professor of mechanical and aerospace engineering and lead investigator of the research.

“In recent years, researchers have gained a better understanding of the molecular machinery of cell migration, but not what directs it to happen in the first place,” he said. “What, exactly, is orchestrating this system common to all living organisms?”

The answer, it turns out, involves delicate interactions between biomechanical stress, or force, which living cells exert on one another, and biochemical signaling.

The UA researchers discovered that when mechanical force disappears — for example at a wound site where cells have been destroyed, leaving empty, cell-free space — a protein molecule, known as DII4, coordinates nearby cells to migrate to a wound site and collectively cover it with new tissue. What’s more, they found, this process causes identical cells to specialize into leader and follower cells. Researchers had previously assumed leader cells formed randomly.

Wong’s team observed that when cells collectively migrate toward a wound, leader cells expressing a form of messenger RNA, or mRNA, genetic code specific to the DII4 protein emerge at the front of the pack, or migrating tip. The leader cells, in turn, send signals to follower cells, which do not express the genetic messenger. This elaborate autoregulatory system remains activated until new tissue has covered a wound.

The same migration processes for wound healing and tissue development also apply to cancer spreading, the researchers noted. The combination of mechanical force and genetic signaling stimulates cancer cells to collectively migrate and invade healthy tissue.

Biologists have known of the existence of leader cells and the DII4 protein for some years and have suspected they might be important in collective cell migration. But precisely how leader cells formed, what controlled their behavior, and their genetic makeup were all mysteries — until now.

“Knowing the genetic makeup of leader cells and understanding their formation and behavior gives us the ability to alter cell migration,” Wong said.

With this new knowledge, researchers can re-create, at the cellular and molecular levels, the chain of events that brings about the formation of human tissue. Bioengineers now have the information they need to direct normal cells to heal damaged tissue, or prevent cancer cells from invading healthy tissue.

The UA team’s findings have major implications for people with a variety of diseases and conditions. For example, the discoveries may lead to better treatments for non-healing diabetic wounds, the No. 1 cause of lower limb amputations in the United States; for plaque buildup in arteries, a major cause of heart disease; and for slowing or even stopping the spread of cancer, which is what makes it so deadly.

The research also has the potential to speed up development of bioengineered tissues and organs that can be successfully transplanted in humans.

In the UA Systematic Bioengineering Laboratory, which Wong directs, researchers used a combination of single-cell gene expression analysis, computational modeling and time-lapse microscopy to track leader cell formation and behavior in vitro in human breast cancer cells and in vivo in mice epithelial cells under a confocal microscope.

Their work included manipulating leader cells through pharmacological, laser and other means to see how they would react.

“Amazingly, when we directed a laser at individual leader cells and destroyed them, new ones quickly emerged at the migrating tip to take their place,” said Wong, who likened the mysteries of cell migration and leader cell formation to the processes in nature that cause geese to fly in V-formation or ants to build a colony.

https://www.sciencedaily.com/  Science Daily

https://www.sciencedaily.com/releases/2015/03/150313094551.htm  Original web page at Science Daily

Cells with higher fat content outlive lean cells, shows a new study. This study has implications for larger organisms, such as humans, as the results support the phenomenon known as the “obesity paradox.” This concept shows that overweight people have the lowest all-cause mortality rates while fit people, oddly enough, have mortality rates comparable to those categorized as slightly obese. Cells with higher fat content outlive lean cells, says a new study from Michigan State University.

“The obesity paradox baffles scientists across numerous disciplines,” said Min-Hao Kuo, MSU biochemist and molecular biologist who published the study in the current issue of PLoS Genetics. “But when it comes to yeast, which is an excellent model for the studies of human aging, increasing the cellular content of triacylglycerol, or fat, extends the lifespan.”

Kuo’s team was the first to show a positive correlation between Triacylglycerol, or TAG, content and lifespan. The connection provides support for the obesity paradox theory, he added.

TAG is a fat found in all eukaryotes that include animals, plants and fungi. The lipid’s ability to store excessive energy, provide insulation and accumulate in response to many stressors is well known. What’s perplexing, though, is how TAG influences lifespan.

“Our team used genetic approaches to manipulate the cellular capacity of triacylglycerol reproduction and degradation,” Kuo said. “Via sophisticated analyses, we demonstrated that it preserves life through a mechanism that is largely independent of other lifespan regulation pathways common in yeast as well as humans.”

The first thing Kuo’s team did was delete TAG lipases, enzymes that break down the lipid into smaller molecules for different uses including energy extraction. Unable to utilize TAG, these yeast accumulated fat inside the cells. In addition, Kuo and his colleagues boosted the production of the fat by increasing the enzyme for TAG synthesis.

In both cases, blocking TAG breakdown and forcing its production, yeast cells are fatter and have longer lifespan. In contrast, yeast cells depleted of the ability to synthesize TAG are lean but die early. Overexpressing a TAG lipase in an otherwise normal strain forces TAG breakdown. These cells also suffer from a shorter lifespan.

Interestingly, those fat and long-living yeast cells do not seem to suffer from obvious growth defects. They mate and produce progeny well. They also have normal resistance to different environmental stresses. On the other hand, other common methods of extending lifespan, such as caloric restriction and deletion of genes key to nutrient sensing, frequently cause cells to grow slowly or be less tolerant of environmental stresses.

While the team suspects that the pro-longevity function exists in humans, they’ve yet to prove that triacylglycerol could drive the intriguing phenomenon in humans.

“Our paper likely will stimulate a new wave of research that has broad and deep impacts, including potential advances in human medicine,” Kuo said.

https://www.sciencedaily.com/  Science Daily

https://www.sciencedaily.com/releases/2016/02/160223143302.htm  Original web page at Science Daily

In new research appearing in the journal Nature Biotechnology, an international research team led by The Hebrew University of Jerusalem describes a new technique for growing human hepatocytes in the laboratory. This groundbreaking development could help advance a variety of liver-related research and applications, from studying drug toxicity to creating bio-artificial liver support for patients awaiting transplantations.

The liver is the largest internal organ in the human body, serving as the main site of metabolism. Human hepatocytes — cells that comprise 85% of the liver — are routinely used by the pharmaceutical industry for study of hepatotoxicity, drug clearance and drug-drug interactions. They also have clinical applications in cell therapy to correct genetic defects, reverse cirrhosis, or support patients with a liver-assist device.

Regrettably, while the human liver can rapidly regenerate in vivo, recognized by the ancient Greeks in the myth of Prometheus, this capability to proliferate is rapidly lost when human cells are removed from the body. Thus far, attempts to expand human hepatocytes in the laboratory resulted in immortalized cancer cells with little metabolic function. The scarce supply of human hepatocytes and this inability to expand them without losing function is a major bottleneck for scientific, clinical and pharmaceutical development.

To address this problem, Prof. Yaakov Nahmias, director of the Alexander Grass Center for Bioengineering at the Hebrew University of Jerusalem, partnered with leading German scientists at upcyte technologies GmbH (formerly Medicyte) to develop a new approach to rapidly expand the number of human liver cells in the laboratory without losing their unique metabolic function.

Based on early work emerging from the German Cancer Research Center (DKFZ) on the Human Papilloma Virus (HPV), the research team demonstrated that weak expression of HPV E6 and E7 proteins released hepatocytes from cell-cycle arrest and allowed them to proliferate in response to Oncostatin M (OSM), a member of the interleukin 6 (IL-6) superfamily that is involved in liver regeneration. Whereas previous studies caused hepatocytes to proliferate without control, turning hepatocytes into tumor cells with little metabolic function, the researchers carefully selected colonies of human hepatocytes that only proliferate in response to OSM. Stimulation with OSM caused cell proliferation, with doubling time of 33 to 49 hours. Removal of OSM caused growth arrest and hepatic differentiation within 4 days, generating highly functional cells. The method, described as the upcyte© process (upcyte technologies GmbH), allows expanding human hepatocytes for 35 population doubling, resulting in 1015 cells (quadrillion) from each liver isolation. By comparison, only 109 cells (billion) can be isolated from a healthy organ.

“The approach is revolutionary,” said Dr. Joris Braspenning, who led the German group. “Its strength lies in our ability to generate liver cells from multiple donors, enabling the study of patient-to-patient variability and idiosyncratic toxicity.” The team generated hepatocyte lines from ethnically diverse backgrounds that could be serially passaged, while maintaining CYP450 activity, epithelial polarization, and protein expression at the same level as primary human hepatocytes. Importantly, the proliferating hepatocytes showed identical toxicology response to primary human hepatocytes across 23 different drugs.

“This is the holy grail of liver research,” said Prof. Nahmias, the study’s lead author. “Our technology will enable thousands of laboratories to study fatty liver disease, viral hepatitis, drug toxicity and liver cancer at a fraction of the current cost.” Nahmias noted that genetic modifications preclude using the cells for transplantation, “but we may have found the perfect cell source for the bio-artificial liver project. ”

The proliferating hepatocyte library was recently commercialized by upcyte technologies GmbH (Hamburg, Germany), which is expanding the scope of the technology. “upcyte© hepatocytes represent the next generation of cell technology,” said Dr. Astrid Nörenberg, the company’s managing director. “We are poised to become the leading cell supplier for pharmaceutical development and chemical toxicity testing.”

http://www.sciencedaily.com/  Science Daily

http://www.sciencedaily.com/releases/2015/11/151126104303.htm  Original web page at Science Daily