Aims: Hypoxia causes protein kinase C epsilon (PKCε) gene repression in foetal hearts, resulting in heightened cardiac susceptibility to ischaemic injury in offspring. We tested the hypothesis that hypoxia inducible factor 1 (HIF-1) and/or reactive oxygen species (ROS) mediate hypoxia-induced PKCε gene repression.
Methods and results: Hypoxia induced in vivo to pregnant rats, ex vivo to isolated foetal rat hearts, and in vitro in the rat embryonic ventricular myocyte cell line H9c2 resulted in a comparable decrease in PKCε protein and mRNA abundance in foetal hearts and H9c2 cells, which was associated with a significant increase in CpG methylation of the SP1-binding sites at the PKCε promoter. In H9c2 cells and foetal hearts, hypoxia caused nuclear accumulation of HIF-1α, which was inhibited by 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole and 2-methoxy estradiol. The HIF-1α inhibitors had no significant effect on hypoxia-induced PKCε mRNA repression. Hypoxia produced a time-dependent increase in ROS production in H9c2 cells and foetal hearts that was blocked by ROS scavengers N-acetyl-cysteine or tempol. In accordance, N-acetyl-cysteine and tempol, but not apocynin, inhibited the hypoxic effect and restored PKCε protein and mRNA expression to the control values in foetal hearts and H9c2 cells. The ROS scavengers blocked hypoxia-induced CpG methylation of the SP1-binding sites, restored SP1 binding to the PKCε promoter, and abrogated the hypoxia-induced increase in the susceptibility of the heart to ischaemic injury in offspring.
Conclusions: The results demonstrate that hypoxia induces epigenetic repression of the PKCε gene through a NADPH oxidase-independent ROS-mediated pathway in the foetal heart, leading to heightened heart vulnerability to ischaemic injury in offspring.