ABSTRACT Male and female disease states differ in their prevalence, treatment responses, and survival rates. In cardiac disease, women almost uniformly fare far worse than men. Though sex plays a critical role in cardiac disease, the mechanisms underlying sex differences in cardiac homeostasis and disease remain unexplained. Here, in adult and embryonic hearts we reveal sex-specific transcriptomes and proteomes and show that cardiac sex differences are predominately accounted for by post-transcriptional mechanisms. We found differential expression of male-female proteins in the cardiomyocytes. Using a quantitative proteomics-based approach, we characterized differential sex-specific enriched cardiac proteins, protein complexes, and biological sex processes in the context of global genetic diversity of the Collaborative Cross, an established surrogate for human diversity. We also found that sex differences in cardiac protein expression are established by both hormonal and sex chromosomal mechanisms. We have demonstrated the onset of sex-biased protein expression and discovered that sex disparities in heart tissue occur at the earliest stages of heart development at a period that preceeds mammalian gonadal development. Collectively, these findings may explain why congenital heart disease, a leading cause of death whose origin is often developmental, is sex biased. Our results reveal molecular foundations for differences in cardiac tissue that underlie sex disparities in health, disease, and treatment outcomes.

Cardiac Sex Differences are Established Prior to Gonad Formation