Activation of p53 and its target genes p21(WAF1/Cip1) PAG608/Wig-1 in ischemic preconditioning

A brief, 3 min period of global forebrain ischemia in the rat, induced by b ilateral common carotid occlusion combined with hypotension, confers resist ance to hippocampal pyramidal neurons against a subsequent 10 min ischemia, which is normally lethal to these cells. The molecular mechanisms underlyi ng this ischemic preconditioning, or tolerance, are poorly understood. The tumor suppressor p53 is a transcription factor implicated in neuronal death following various insults, including cerebral ischemia. p53 is activated i n response to cellular stress, e.g. hypoxia and DNA damage. Using in situ h ybridization, we investigated the hippocampal mRNA expression of p53, and t wo of its target genes, p21(WAF1/Cip1) and the recently cloned PAG608/Wig-1 , in a two-vessel occlusion model of ischemic preconditioning. We also eval uated changes in the protein levels of p53 and PAG608/Wig-1 using immunohis tochemistry. The mRNA levels of all three genes increased in the ischemia s ensitive CAI region both following 3 min (non-lethal) preconditioning and 1 0 min of (lethal) nonconditioned ischemia. In contrast, after 10 min of isc hemia preconditioned by a 3 min ischemic insult 48 h earlier, no upregulati on of these genes was detected in the CA1. Following 10 min of noncondition ed ischemia, increased neuronal immunostaining of p53 and PAG608/Wig-1 was observed in the hippocampus, which was less pronounced following 3 min of p reconditioning ischemia and 10 min of preconditioned ischemia. Our results demonstrate that activation of p53 and its response genes p21(WAF2/Cip1) an d PAG608/Wig-1 occurs in the brain following lethal as well as non-lethal i schemic insults, and that ischemic preconditioning markedly diminishes this activation. (C) 1999 Elsevier Science B.V. All rights reserved.