Targeting the p53 pathway to protect the neonatal ischemic brain

To investigate whether inhibition of mitochondrial p53 association using pifithrin-micro (PFT-micro) represents a potential novel neuroprotective strategy to combat perinatal hypoxic-ischemic (HI) brain damage.

Seven-day-old rats were subjected to unilateral carotid artery occlusion and hypoxia followed by intraperitoneal treatment with PFT-micro, an inhibitor of p53 mitochondrial association or PFT-α 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.

PFT-micro treatment completely prevented the HI-induced increase in mitochondrial p53 association at 3 hours and reduced neuronal damage at 48 hours post-HI. PFT-micro had long-term (6-10 weeks post-HI) beneficial effects as sensorimotor and cognitive outcome improved and infarct size was reduced by ~79%. Neuroprotection by PFT-micro treatment was associated with strong inhibition of apoptotic pathways and reduced oxidative stress. Unexpectedly, PFT-micro also inhibited HI-induced upregulation of p53 target genes. However, the neuroprotective effect of inhibiting only p53 transcriptional activity by PFT-α was significantly smaller and did not involve reduced oxidative stress.

We are the first to show that prevention of mitochondrial p53 association by PFT-micro strongly improves functional outcome and decreases lesion size after neonatal HI. PFT-micro 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-micro may develop into a novel and powerful neuroprotective strategy.