Targeting the p53 Pathway to Protect the Neonatal Ischemic Brain

Objective: To investigate whether inhibition of mitochondrial p53 association using pifithrin-mu (PFT-mu) represents a potential novel neuroprotective strategy to combat perinatal hypoxic-ischemic (HI) brain damage. Methods: Seven-day-old rats were subjected to unilateral carotid artery occlusion and hypoxia followed by intraperitoneal treatment with PFT-mu, an inhibitor of p53 mitochondrial association or PFT-alpha an inhibitor of p53 transcriptional activity. Cerebral damage, sensorimotor and cognitive function, apoptotic pathways (cytosolic cytochrome c, Smac/DIABLO, active caspase 3), and oxidative stress (lipid peroxidation and PARP-1 cleavage) were investigated. Results: PFT-mu treatment completely prevented the HI-induced increase in mitochondrial p53 association at 3 hours and reduced neuronal damage at 48 hours post-HI. PFT-mu had long-term (6-10 weeks post-HI) beneficial effects as sensorimotor and cognitive outcome improved and infarct size was reduced by similar to 79%. Neuroprotection by PFT-mu treatment was associated with strong inhibition of apoptotic pathways and reduced oxidative stress. Unexpectedly, PFT-mu also inhibited HI-induced upregulation of p53 target genes. However, the neuroprotective effect of inhibiting only p53 transcriptional activity by PFT-alpha was significantly smaller and did not involve reduced oxidative stress. Interpretation: We are the first to show that prevention of mitochondrial p53 association by PFT-mu strongly improves functional outcome and decreases lesion size after neonatal HI. PFT-mu not only inhibits mitochondrial release of cytochrome c, but also inhibits oxidative stress. We propose that as a consequence nuclear accumulation of p53 and transcription of proapoptotic target genes are prevented. In conclusion, targeting p53 mitochondrial association by PFT-mu may develop into a novel and powerful neuroprotective strategy. ANN NEUROL 2011;70:255-264