Abstract Body: Circadian rhythms critically govern pathophysiological homeostasis, and their disruption magnifies the severity of myocardial ischemia/reperfusion (MI/R) injury. Growing evidence indicates that oscillations in the clock gene help coordinate communication and stress-response pathways. Despite notable advances in understanding how circadian dysregulation in the heart contributes to cardiomyocyte pathology, the impact of adipose Bmal1 on cardiac vulnerability remains poorly characterized.
We investigated the influence of adipose-specific Bmal1 on the severity of cardiac injuries by subjecting mice to 45-min ischemia, followed by 24-h of reperfusion, at two distinct circadian time points: ZT0 (morning) and ZT12 (evening). Wild-type (WT) mice were compared with adipocyte-specific Bmal1 knockout (ABK) mice to pinpoint whether Bmal1 absence in fat tissue amplified differences in ischemic damage. Myocardial function measurements revealed that at ZT12, MI/R resulted in pronounced declines in cardiac function, with larger infarct sizes that were more severe in ABK mice. Analysis of small extracellular vesicles (sEVs) showed alterations in the composition, implicating adipose derived factors in this exacerbation of cardiac injury. Mechanistically, a key alteration in autophagy flux was observed. Specifically, while LC3II and Beclin-1 were unchanged during MIR, LAMP2 decreased, and p62 was markedly increased. This indicates that autophagic flux was disrupted in hearts at ZT12 compared to ZT0, suggesting a blockage in the clearance stages of autophagic flux but not in the formation stages. The activity of the lysosomal enzymes cathepsin L and D was suppressed whilst not cathepsin B. Notably, the loss of adipose Bmal1 worsened this decline, as ABK mice exhibited greater impairment in the autophagic clearance steps and further suppression of cathepsin L and D. These observations support the notion that the rhythmic regulation of adipose Bmal1 is critical for maintaining adequate cardioprotective autophagy during MI/R.
In summary, our findings highlight the crucial role of the adipose clock gene BMAL1 in regulating cardioprotective mechanisms through autophagy and bioactive sEVs. The oscillation of adipose Bmal1 expression significantly influences myocardial autophagic activity and the severity of MI/R injury. Targeting the adipose-driven circadian clock and enhancing autophagy may provide new strategies for improving cardiac resilience and reducing ischemic injury.