Fetal stress-mediated hypomethylation increases the brain susceptibility to hypoxic–ischemic injury in neonatal rats

• Fetal hypoxia induces global DNA hypomethylation in offspring brain.
• DNA hypomethylation increases HIF-1α expression in the developing brain.
• DNA hypomethylation sensitizes brain to HI injury in a HIF-1α-dependent manner.
• Hypomethylation contributes to fetal hypoxia enhanced susceptibility to HIE.

Background and purposeFetal hypoxia increases brain susceptibility to hypoxic–ischemic (HI) injury in neonatal rats. Yet mechanisms remain elusive. The present study tested the hypothesis that DNA hypomethylation plays a role in fetal stress-induced increase in neonatal HI brain injury.MethodsPregnant rats were exposed to hypoxia (10.5% O2) from days 15 to 21 of gestation and DNA methylation was determined in the developing brain. In addition, 5-aza-2′-deoxycytidine (5-Aza) was administered in day 7 pups brains and the HI treatment was conducted in day 10 pups. Brain injury was determined by in vivo MRI 48 h after the HI treatment and neurobehavioral function was evaluated 6 weeks after the HI treatment.ResultsFetal hypoxia resulted in DNA hypomethylation in the developing brain, which persisted into 30-day old animals after birth. The treatment of neonatal brains with 5-Aza induced similar hypomethylation patterns. Of importance, the 5-Aza treatment significantly increased HI-induced brain injury and worsened neurobehavioral function recovery six weeks after the HI-treatment. In addition, 5-Aza significantly increased HIF-1α mRNA and protein abundance as well as matrix metalloproteinase (MMP)-2 and MMP-9, but decreased MMP-13 protein abundance in neonatal brains. Consistent with the 5-Aza treatment, hypoxia resulted in significantly increased expression of HIF-1α in both fetal and neonatal brains. Inhibition of HIF-1α blocked 5-Aza-mediated changes in MMPs and abrogated 5-Aza-induced increase in HI-mediated brain injury.ConclusionThe results suggest that fetal stress-mediated DNA hypomethylation in the developing brain causes programming of hypoxic–ischemic sensitive phenotype in the brain and increases the susceptibility of neonatal brain to hypoxic–ischemic injury in a HIF-1α-dependent manner.