Circadian rhythms, the molecular clock, and skeletal muscle

Area of Science:

• * Chronobiology
• * Molecular biology
• * Skeletal muscle physiology

Background:

• * Circadian rhythms, approximately 24-hour biological cycles, are regulated by the molecular clock, a transcriptional-translational feedback loop involving core clock genes (e.g., Bmal1, Clock, Per, Cry).
• * While the central circadian clock in the suprachiasmatic nucleus (SCN) is well-understood, peripheral clocks, particularly in skeletal muscle, are emerging areas of research.
• * Skeletal muscle, comprising ~45% of body mass, possesses a functional molecular clock influencing over 2300 genes involved in myogenesis, transcription, and metabolism.

Purpose of the Study:

• * To investigate the significance of circadian rhythms within skeletal muscle.
• * To explore the impact of circadian rhythm disruption on skeletal muscle function and metabolic health.
• * To highlight the need for further research into skeletal muscle clock mechanisms and entrainment.

Main Methods:

• * Review of existing literature on circadian rhythms and molecular clock mechanisms.
• * Analysis of gene expression patterns in skeletal muscle.
• * Examination of the functional consequences of circadian disruption in skeletal muscle.

Main Results:

• * Over 2300 genes in skeletal muscle exhibit circadian expression patterns, impacting diverse functions.
• * Skeletal muscle circadian rhythms can be synchronized by light (via SCN) and by feeding/activity timing.
• * Disruption of skeletal muscle circadian rhythms leads to fiber-type changes, altered muscle structure, reduced mitochondrial respiration, and impaired muscle function.

Conclusions:

• * Skeletal muscle circadian rhythms are vital for both muscle integrity and systemic health.
• * Disrupted circadian rhythms in skeletal muscle negatively affect metabolic health, contributing to impaired glucose tolerance and insulin sensitivity.
• * Further research is essential to elucidate skeletal muscle clock mechanisms, entrainment pathways, and cross-tissue circadian synchrony.