It is now established that programmed-cell death contributes to secondary neuronal death after traumatic brain injury TBI in experimental models and in humans; however, recent data suggest that multiple cell death pathways exist. Specifically, an alternate/additional pathway of cell death involving the mitochondrial protein apoptosis-inducing factor AIF about that produces large scale DNA fragmentation and cell death that it is inhibited by bcl-2 and hsp7O, but not by caspase inhibitors, appears to contribute to neuronal cell death in models of nitrosative stress in vitro, and after TBI in vivo. The objective of this research is to determine whether divergent and parallel cell death pathways contribute to neuronal demise after acute brain injury. The HYPOTHESIS is that caspase-independent neuronal death, mediated by AIF occurs in experimental models and in humans after TBI and that inhibiting nuclear translocation and/or activation of AIF reduces secondary neuropathologic damage after TBI. Abbreviated SPECIFIC AIMS are: 1) Confirm that caspase-independent, AIF-mediated programmed cell death occurs in primary cortical neurons exposed to nitrosative/oxidative stress and establish a role for AIF using both key regulators and selective inhibitors. 2) Characterize the subcellular redistribution of AIF after TBI in rats and bcl-2 over-expressing mice. Determine the temporal association of AIF translocation into nuclei and large scale DNA fragmentation, the regions of brain and cell-types where nuclear translocation of AIF occurs, and compare the relative contributions of and regional differences between AlF-mediated and caspase-3-mediated cell death and necrosis after TBI. 3) Establish a role for AIF-mediated cell death after TBI in rats and bcl-2 over-expressing mice. Test the effects of these key regulators of AIF on biochemical footprints of AIF-mediated cell death and for their effects on histological and functional outcome using a standard and stringent paradigm. 4) Determine whether AIF-mediated cell death occurs in humans after TBI. TBI is a major cause of morbidity and mortality in adults and children. Delayed cell death contributes to morbidity and mortality and currently no specific therapies have successfully transitioned from experimental studies to the bedside. Preliminary studies suggest that other non-necrotic caspase-independent cell death pathways participate in overall neuronal death after TBI. This proposal addresses the key question: Does AIF-mediated programmed cell death contribute to delayed neuronal death and cognitive deficits after TBI? If inhibition of AIF translocation reduces neuronal death and improves neurological outcome after TBI in vivo and AIF-mediated cell death is confirmed in humans, a novel, clinically-relevant strategy targeting multiple cell death pathways will be available for the treatment of acute brain injury.
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