Biphasic onset of splenic apoptosis following hemorrhagic shock: critical implications for Bax, Bcl-2 and Mcl-1 proteins

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The innate immune response to trauma-hemorrhage involves inflammatory mediators, thus promoting cellular dysfunction as well as cell death in diverse tissues. These effects ultimately bear the risk of post-traumatic complications, such as organ dysfunction, multiple organ failure or adult respiratory distress syndrome. In this study, a murine model of resuscitated hemorrhagic shock (HS) was used to determine the apoptosis in spleen as a marker of cellular injury and reduced immune functions. Male C57BL-6 mice were subjected to sham operation or resuscitated HS. At t = 0 hrs, t = 24 hrs and t = 72 hrs, mice were euthanized, the spleens were removed and evaluated for apoptotic changes via DNA fragmentation, caspase activities and activation of both extrinsic and intrinsic apoptotic pathways. Spleens from untreated mice were used as control samples.

HS was associated with distinct lymphocytopenia as early as t = 0 hrs after hemorrhage without regaining baseline levels within the consecutive 72 hrs when compared with sham and control group, respectively. A rapid activation of splenic apoptosis in HS mice was observed on t = 0 hrs and t = 72 hrs after hemorrhage and predominantly confirmed by increased DNA fragmentation, elevated caspase-3/7, -8, -9 activities and enhanced expression of intrinsic mitochondrial proteins, respectively. Accordingly, mitochondrial pro-apoptotic Bax and anti-apoptotic Bcl-2 proteins were inversely expressed within the 72 hrs observation period, thereby supporting significant pro-apoptotic changes. Solely on t = 24 hrs, expression of the anti-apoptotic Mcl-1 protein shows significant increase when compared with sham operated and control animals. Furthermore, expression of extrinsic death receptors was only slightly increased. Our data suggest that HS induces apoptotic changes in spleen through a biphasic caspase dependent mechanism and implies a detrimental imbalance of pro- and anti-apoptotic mitochondrial proteins Bax, Bcl-2 and Mcl-1, thereby promoting post-traumatic immunosuppression.

BioMed Central
February 5, 2008

Original web page at BioMed Central

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