Perinatal nicotine exposure alters AKT/GSK-3β/mTOR/autophagy signaling leading to development of hypoxic-ischemic sensitive phenotype in rat neonatal brain.

Maternal cigarette smoking is a major perinatal insult that contributes to an increased risk cardiovascular and neurodevelopmental diseases in offspring. Our previous studies have revealed that perinatal nicotine exposure reprograms a sensitive phenotype in neonatal hypoxic-ischemic encephalopathy (HIE), yet the underlying molecular mechanisms remain largely elusive. The present study tested the hypothesis that perinatal nicotine exposure impacts autophagy signaling in the developing brain resulting in enhanced susceptibility to neonatal HIE. Nicotine was administered to pregnant rats via subcutaneous osmotic minipumps. Neonatal HIE was conducted in 9-day-old male rat pups. AKT/GSK-3β/mTOR signaling and key autophagy markers were determined by Western blotting analysis. Rapamycin and MK2206 were administered via intracerebroventricular (i.c.v.) injection. Nicotine exposure significantly inhibited autophagy activities in neonatal brain tissues, characterized by an increased ratio of p-mTOR/total mTOR protein expression but reduced levels of ATG5, Beclin 1 and LC3β I/II. Treatment with mTOR inhibitor rapamycin effectively blocked nicotine-mediated autophagy deficiency and more importantly, reversed nicotine-induced increase in HI brain infarction. In addition, nicotine exposure significantly upregulated p-AKT and p-GSK-3β. Treatment with the AKT selective inhibitor MK2206 reversed the enhanced p-AKT and p-GSK-3β, restored basal autophagic flux and abolished nicotine-mediated HI brain injury. These findings suggest that perinatal nicotine-mediated alteration of AKT/GSK-3β/mTOR signaling plays a key role in down-regulation of autophagic flux, which contributes to the development of hypoxia/ischemia-sensitive phenotype in the neonatal brain.