p53-independent transient p21 super(WAF1/CIP1) mRNA induction in the rat brain following experimental traumatic injury

The expression of the cyclin-dependent kinase inhibitor p21 super(WAF1/CIP1) mRNA after traumatic brain injury in rats was investigated using an in situ hybridization technique, along with regulating gene p53 and stress response gene hsp70 mRNA levels. At 3h postinjury, p21 super(WAF1/CIP1) mRNA was markedly increased in the cortex, white matter, thalamus, CA2, a part of CA1,3 and dentate gyrus of the injured side. Hybridization signals remained elevated at 6h in injured cortex and hippocampus and returned to the baseline by 24h post-insult. On the other hand, p53 mRNA induction was not observed in any brain sections throughout the post-injury time course. Slight expression of hsp70 mRNA was detected in the injured cortex 3-6 h following injury and this was similar to the temporary pattern of p21 super(WAF1/CIP1) mRNA expression. This study showed p21 super(WAF1/CIP1) mRNA to be transiently induced after traumatic brain injury, independent of p53, this possibly being an early stress response to protect cells by arresting them in the cycle and allow DNA repair.