The core circadian clock factor, Bmal1, transduces sex-specific differences in both rhythmic and non-rhythmic gene expression in the mouse heart

It has been well established that cardiovascular diseases exhibit significant differences between sexes in both preclinical models and humans. In addition, there is growing recognition that disrupted circadian rhythms can contribute to the onset and progression of cardiovascular diseases. However, little is known about sex differences between the cardiac circadian clock and circadian transcriptomes in mice. Here, we show that the core clock genes are expressed in common in both sexes, but the cardiac circadian transcriptome is very sex specific. Hearts from female mice expressed significantly more rhythmically expressed genes (REGs) than male hearts, and the temporal distribution of REGs was distinctly different between sexes. To test the contribution of the circadian clock in sex-specific gene expression in the heart, we knocked out the core circadian clock factor Bmal1 in adult cardiomyocytes. The sex differences in the circadian transcriptomes were significantly diminished with cardiomyocyte-specific loss of Bmal1. Surprisingly, loss of cardiomyocyte Bmal1 also resulted in a roughly 8-fold reduction in the number of all differentially expressed genes (DEGs) between male and female hearts. We highlight sex-specific changes in several cardiac-specific transcription factors, including Gata4, Nkx2-5 and Tbx5. While there is still much to learn, we conclude that cardiomyocyte-specific Bmal1 is vital in conferring sex-specific gene expression in the adult mouse heart.