Traumatic brain injury (TBI) is a significant cause of death in individuals under the age of 45 in the United States and survivors are faced with chronic brain damage leading to debilitating behavioral dysfunction. Brain damage and behavioral dysfunction may be, in part, due to neuronal ane glial death and typical pathologies in post-mortem head-injured brains include a combination of focal contusions and diffuse axonal injury (DAI). While neuronal death is associated with contusions, death of oligodendrocytes may contribute to or occur as a result of axonal injury. Using animal models that predominantly exhibit either gray or white matter pathology, we will test the working hypotheses in this proposal that (a) neuronal and glial apoptosis contribute the pathology of clinical brain trauma, and (b) that post-traumatic apoptotic cell death is controlled via a concomitant activation of cell death-inducing proteins and inhibition of proteins that promote cell survival. The objectives of this proposal are (1) to determine the contribution of apoptotic cell death in pathology of human head injury, (2) to determine the extent of activation of the death- inducing protease, caspase-3, and the pro-apoptotic c-Jun N-terminal kinase (JNK) signaling pathway, along with the extent of inhibition of the pro-survival extracellular signal-regulated kinase (ERK) pathway, (3) determine the role of JNK in mediating neuronal and oligodendroglial apoptosis, and, (4) examine the possibility that neuronal and glial death following TBI in animals and humans is associated with coordinate alterations in expression of multiple death-associated genes. The association between apoptosis, determined using in situ DNA fragmentation and morphology, and cellular activation of caspase-3 and the JNK signaling pathway, will be evaluated using immunohistochemistry and biochemical assays. The anti-apoptotic effect of JNK following TBI will be tested by subjecting mice that are deficient in JNK to either gray matter or white matter injury. Finally, individual neurons and oligodendrocytes from either human head-injured tissue or injured rat brain, exhibiting activated caspase-3 (indicative of the commitment to apoptosis), will be evaluated for the expression of cell death associated genes such as p53, hsp72, c-jun, Bcl-2, Bcl-x and Bax using the single cell antisense RNA amplification technique. While neurons and oligodendrocytes may share regulators of cell death, it is also likely that there might be cell-specific death processes at play. The long term goal is to use the information derived from these experiments to develop effective therapies aimed at specific cellular processes that promote cell survival or inhibit death.
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