ACTIVATION OF CPP32-LIKE CASPASES CONTRIBUTES TO NEURONAL APOPTOSIS AND NEUROLOGICAL DYSFUNCTION AFTER TRAUMATIC BRAIN INJURY

We examined the temporal profile of apoptosis after fluid percussion-i nduced traumatic brain injury (TBI) in rats and investigated the poten tial pathophysiological role of caspase-3-like proteases in this proce ss. DNA fragmentation was observed in samples from injured cortex and hippocampus, but not from contralateral tissue, beginning 4 hr after T BI and continuing for at least 3 d. Double labeling of brain with term inal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeli ng (TUNEL) and an antibody directed to neuronal nuclear protein identi fied apoptotic neurons with high frequency in both traumatized rat cor tex and hippocampus. Cytosolic extracts from injured cortex and hippoc ampus, but not from contralateral or control tissue, induced internucl eosomal DNA fragmentation in isolated nuclei with temporal profiles co nsistent with those of DNA fragmentation observed in vivo. Caspase-3 m RNA levels, estimated by semiquantitative RT-PCR, were elevated fivefo ld in ipsilateral cortex and twofold in hippocampus by 24 hr after TBI . Caspase-1 mRNA content also was increased after trauma, but to a les ser extent in cortex. Increased caspase-3-like, but not caspase-1-like , enzymatic activity was found in cytosolic extracts from injured cort ex. Intracerebroventricular administration of z-DEVD-fmk-a specific te trapeptide inhibitor of caspase-3-before and after injury markedly red uced post-traumatic apoptosis, as demonstrated by DNA electrophoresis and TUNEL staining, and significantly improved neurological recovery. Together, these results implicate caspase-3-like proteases in neuronal apoptosis induced by TBI and suggest that the blockade of such caspas es can reduce post-traumatic apoptosis and associated neurological dys function.