APOPTOSIS-SUPPRESSOR GENE BCL-2 EXPRESSION AFTER TRAUMATIC BRAIN INJURY IN RATS

Neuronal death after experimental traumatic brain injury (TBI) has fea tures of both apoptosis and necrosis. Neurons in the peritrauma cortex , hippocampus, and dentate gyrus are particularly vulnerable. The apop tosis-suppressor gene bcl-2 is induced in brain after ischemia and epi lepsy-induced injury and may serve to regulate neuronal death. We stud ied expression of bcl-2 mRNA and protein after experimental TBI in rat s. To determine whether bcl-2 protein expression occurred in cells wit h evidence of apoptosis, triple-labeling studies were performed using (1) antibody against bcl-2, (2) bis-benzimide dye to examine gross nuc lear morphology, and (3) terminal deoxynucleotidyl transferase-mediate d biotin-dUTP nick-end labeling (TUNEL) to assess for DNA fragmentatio n. At 6 and 24 hr, bcl-2 mRNA was induced in ipsilateral peritrauma co rtex, hippocampus, and dentate gyrus. By 72 hr the increase in bcl-2 m RNA was detected only in cortex. bcl-2 protein was induced at 8, 24, 7 2, and 168 hr in ipsilateral cortex and hippocampus. Cells expressing bcl-2 protein included neurons in the peritrauma cortex, hippocampus, hilus, and dentate gyrus. The gross nuclear morphology of neurons expr essing bcl-2 appeared normal. Furthermore, biochemical evidence of DNA fragmentation, in a pattern characteristic of either apoptosis or nec rosis, was seldom seen in neurons expressing bcl-2 protein (bcl-2 colo calized with TUNEL in 0-2% of TUNEL-positive cells observed). These da ta suggest that bcl-2 may play an important role in the regulation of neuronal death after TBI, and they support a role for bcl-2 as an indu cible neuroprotective gene.