Abstract
Introduction: Sex differences in susceptibility to ischemia/reperfusion (I/R) injury have been mostly attributed to sex hormones. Recently we examined the role of sex chromosomes in sex differences in myocardial I/R injury. We discovered that gonadectomized mice with two X chromosomes (XX or XXY) have ~50% larger infarct size after I/R injury, compared to mice with one X chromosome (XY or XO). Only few X genes escape X inactivation and are expressed higher in XX than XY individuals. Here we examined the role of “X escapee” histone demethylase Kdm6a which is important in cardiac development. Methods: Female mice with a heterozygous global knockout of Kdm6a (Kdm6a+/-) and with 2 copies of Kdm6a (Kdm6a+/+, regular WT) were used. Isolated mouse hearts were subjected to 30 min global normothermic ischemia followed by 60 min reperfusion. RNA-Seq analysis was performed by comparing gene expression in hearts of Kdm6a+/+ vs. Kdm6a+/- females at baseline before ischemia. We calculated an unbiased composite score of relevance in which the level of significance of the Kdm6a effect on expression (p value) was integrated with the size of the KDM6A effect on expression (fold change), and with the amount of H3K27me3 mark found on the genes in the heart based on online ChIP-Seq data. Two way ANOVA was used for statistical analysis. P<0.05 was considered statistically significant. Values are expressed as mean± SE. Results: Kdm6a+/+ female mice had significantly lower heart functional recovery compared to their littermate Kdm6a+/- (LVDP: 46.7±9.8% vs. 79.8±3.5%; RPP: 44.1±10.5% vs. 76.2±8.5%, n=6-8 mice/group, p<0.01). The integration of our RNA-Seq data using the hearts of female mice with 2 vs. 1 copy of Kdm6a (n=4 samples per group) with online datasets measuring the H3K27me3 mark, sex differences in expression in humans and mice, and involvement in ischemic heart failure, revealed carbonic anhydrase-3 (Car3) as the most interesting candidate (upregulated ~7 fold in the hearts of Kdm6a+/+ vs. Kdm6a+/- female mice) at baseline. Car3 encodes one isoform of carbonic anhydrase, involved in pH regulation, which is a critical part of I/R injury. Conclusion: Histone demethylase KDM6A contributes to X chromosome dependent I/R injury via epigenetic regulation
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