Aims: foetal nicotine exposure results in decreased protein kinase C epsilon (PKCε) expression and increased cardiac vulnerability to ischaemia and reperfusion injury in adult rat offspring. The present study tested the hypothesis that maternal nicotine administration causes increased promoter methylation of the PKCε gene resulting in PKCε repression in the heart.
Methods and results: nicotine treatment of pregnant rats starting at day 4 of gestation increased the methylation of the Egr-1 binding site at the PKCε gene promoter and decreased PKCε protein and mRNA abundance in near-term foetal hearts. Methylation of the Egr-1 binding site reduced Egr-1 binding to the PKCε promoter in the heart. Site-specific deletion of the Egr-1 binding site significantly decreased PKCε promoter activity. The effects of nicotine were sustained in the heart of adult offspring. Ex vivo studies found no direct effect of nicotine on PKCε gene expression. However, maternal nicotine administration increased norepinephrine content in the foetal heart. Treatment of isolated foetal hearts with norepinephrine resulted in the same effects of increased methylation of the Egr-1 binding site and PKCε gene repression in the heart. 5-Aza-2'-deoxycytidine inhibited the norepinephrine-induced increase in methylation of the Egr-1 binding site and restored Egr-1 binding and PKCε gene expression to the control levels.
Conclusion: this study demonstrates that prolonged nicotine exposure increases the sympathetic neurotransmitter release in the foetal heart and causes programming of PKCε gene repression through promoter methylation, linking maternal smoking to pathophysiological consequences in the offspring heart.