Circadian Dysfunction in Skeletal Muscle Impairs Limb Perfusion and Muscle Regeneration in Peripheral Artery Disease [Myotube-ATACseq]
Peripheral arterial disease (PAD), caused by atherosclerosis, leads to limb ischemia, muscle damage, and impaired mobility in the lower extremities. Recent studies suggest that circadian rhythm disruptions can hinder vascular repair during ischemia, but the specific tissues involved and the impact on muscle health remain unclear. This study investigates the role of the skeletal muscle circadian clock in muscle adaptation to ischemic stress using a surgical mouse model of hindlimb ischemia. We used mice with specific genetic loss of the circadian clock activator, BMAL1, in adult skeletal muscle tissues (Bmal1muscle). Bmal1muscle mice and controls underwent femoral artery ligation surgery to induce hindlimb ischemia. Laser doppler imaging was used to assess limb perfusion at various time points after the surgery. Muscle tissues were analyzed with RNA sequencing and histological examination to investigate PAD-related muscle pathologies. Additionally, we studied the role of BMAL1 in muscle fiber adaptation to hypoxia using RNA and ATAC sequencing analyses in primary myotube culture model. Disrupted expression of circadian rhythm-related genes was observed in existing RNA-seq datasets from PAD patient-derived endothelial cells and ischemic limb skeletal muscles. Genetic loss of Bmal1 specifically in adult mouse skeletal muscle tissues delayed reperfusion recovery following induction of hindlimb ischemia. Histological examination of muscle tissues showed reduced regenerated myofiber number and a decreased proportion of type IIB fast-twitch myofibers in Bmal1musc mouse muscles in the ischemic limbs, but not in their contralateral non-ischemic limbs. Transcriptomic analysis revealed abrogated metabolic, angiogenic, and myogenic pathways relevant to hypoxia-adaptation in Bmal1musc mouse muscles. These changes were corroborated in Bmal1-deficient cultured primary myotubes cultured under hypoxic conditions. Overall design: We isolated primary myoblasts from Bmal1-floxed mice and induced the cells into myotubes. The myotubes were then infected with Cre-expressing adenovirus for 48 hours to induce deletion of the circadian clock activator, BMAL1. Myotubes infected with an empty vector-expressing virus were served as control. The viral infected myotubes were then exposed to 21% O2 or 1% O2 for 6 hours to simulate post-surgery intramuscular hypoxia.