Cardiomyocyte-Specific Disruption of the Circadian BMAL1–REV-ERBa/ß Regulatory Network Impacts Distinct miRNA Species in the Murine Heart
Circadian clocks are cell autonomous timekeeping mechanisms that govern critical biological processes.  Regarding the heart, the cardiomyocyte circadian clock regulates a diverse array of processes, ranging from transcription and translation, to signaling, metabolism, electrophysiology, and contractility.  The importance of this mechanism is underscored by observations that genetic disruption of the cardiomyocyte circadian clock in murine models leads to adverse cardiac remodeling, heart failure, and reduced lifespan.  However, the precise molecular links between the cardiomyocyte circadian clock and cardiac physiology/pathology have not been characterized fully.  Given that recent studies have highlighted that small RNA species (such as miRNAs) influence both cardiac physiology and pathology, we sought to determine the extent to which cardiomyocyte circadian clock disruption impacts cardiac small RNA species.  Accordingly, hearts were collected from cardiomyocyte-specific Bmal1 knockout (CBK) and littermate control (CON) mice at distinct times of the day.  Small RNA-seq revealed 47 differentially expressed miRNA species in CBK hearts (in the absence of significant time-of-day-dependent effects).  Subsequent bioinformatic analyses predicted that differentially expressed miRNA species in CBK hearts potentially influence processes such as circadian rhythmicity, cellular signaling, and metabolism.  Of the induced miRNAs in CBK hearts, 7 were predicted to be targeted by the transcriptional repressors REV-ERB?/? (integral circadian clock components that are directly regulated by BMAL1).  Similar to CBK hearts, cardiomyocyte-specific Rev-erb?/? double knockout (CM-RevDKO) mouse hearts exhibited increased let-7c-1-3p, miR-23b-5p, miR-139-3p, miR-5123, and miR-7068-3p levels.  Importantly, 19 putative targets of these 5 miRNAs were commonly repressed in both CBK and CM-RevDKO heart (of which 16 are targeted by let-7c-1-3p).  These observations suggest that disruption of the BMAL1–REV-ERB?/? axis in the heart leads to induction of a subset of miRNAs, whose predicted mRNA targets have established functions in biological processes such as metabolism and cellular signaling. Overall design: Comparative gene expression profiling analysis of small RNA-seq data for biventricular heart tissue isolated from cardiomyoycte-specific BMAL1 knockout (CBK) and littermate control (CON) mice. Heart tissue samples were harvested at different times of the day denoted as zeitgeber time (ZT).