UC Irvine

Background and purpose

Fetal 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.

Methods

Pregnant 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.

Results

Fetal 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.

Conclusion

The 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.