Time‐of‐day dependent effects of contractile activity on the phase of the skeletal muscle clock

Abstract

Key points Disruptions in circadian rhythms across an organism are associated with negative health outcomes, such as cardiometabolic and neurodegenerative diseases. Exercise has been proposed as a time cue for the circadian clock in rodents and humans. In this study, we assessed the effect of a single bout of endurance exercise on the skeletal muscle clock in vivo and a bout of muscle contractions in vitro. Timing of exercise or contractions influences the directional response of the muscle clock phase in vivo and in vitro. Our findings demonstrate that muscle contractions, as a component of exercise, can directly modulate the expression of muscle clock components in a time‐of‐day dependent manner. Abstract Exercise has been proposed to be a zeitgeber for the muscle circadian clock mechanism. However, this is not well defined and it is unknown if exercise timing induces directional shifts of the muscle clock. Our purpose herein was to assess the effect of one bout of treadmill exercise on skeletal muscle clock phase changes. We subjected PERIOD2::LUCIFERASE mice (n = 30F) to one 60 min treadmill exercise bout at three times of day. Exercise at ZT5, 5 h after lights on, induced a phase advance (100.2 ± 25.8 min; P = 0.0002), whereas exercise at ZT11, 1 h before lights off, induced a phase delay (62.1 ± 21.1 min; P = 0.0003). Exercise at ZT17, middle of the dark phase, did not alter the muscle clock phase. Exercise induces diverse systemic changes so we developed an in vitro model system to examine the effects of contractile activity on muscle clock phase. Contractions applied at peak or trough Bmal1 expression induced significant phase delays (applied at peak: 27.2 ± 10.2 min; P = 0.0017; applied at trough: 64.6 ± 6.5 min, P < 0.0001). Contractions applied during the transition from peak to trough Bmal1 expression induced a phase advance (49.8 ± 23.1 min; P = 0.0051). Lastly, contractions at different times of day resulted in differential changes of core clock gene expression, demonstrating an exercise and clock interaction, providing insight into potential mechanisms of exercise‐induced phase shifts. These data demonstrate that muscle contractions, as part of exercise, are sufficient to shift the muscle circadian clock phase, likely through changes in core clock gene expression. Additionally, our findings that exercise induces directional muscle clock phase changes confirms that exercise is a bona fide environmental time cue for skeletal muscle.

Exercise: it's only a matter of time

“…The recently published work by Kemler et al . (2020) now provides clear evidence that exercise can also be considered a potent zeitgeber. Using both in vivo and in vitro models, they eloquently demonstrate that exercise elicits specific time‐of‐day effects on circadian rhythms and the core molecular clock machinery in skeletal muscle.…”

“…While previous studies have shown that exercise training can influence the circadian phase, Kemler et al . (2020) are the first to report that a single exercise session can shift the circadian phase in a direction that is dependent on when the exercise is conducted. Given that several populations, including a significant portion of the workforce, are routinely exposed to risk factors for circadian misalignment, this work provides important insights that will enable further exploration into the potential therapeutic effects of exercise on circadian rhythmicity.…”

“…Kemler et al . (2020) generated C2C12 myotubes that exhibited an endogenous rhythm of core clock gene expression, and contained a BMAL1::Luciferase reporter gene. At times associated with the highest, mid, and lowest levels of Bmal1 mRNA expression, the myotubes were electrically stimulated with pulse contractions designed to replicate the contractions experienced by mice during treadmill running (25 ms pulse, 10 V at 6 Hz, every 5 s).…”

“…Kemler et al . (2020) also examined the time‐of‐day effects of myotube contractions on the expression of core clock genes. When contractions were performed at mid Bmal1 mRNA expression, Per2 mRNA expression significantly decreased.…”

“…In summary, Kemler et al . (2020) have demonstrated that exercise has a time‐of‐day‐specific influence on circadian rhythms and is a zeitgeber for skeletal muscle. The methods employed in this study can be further utilised to investigate the underlying mechanisms for time‐of‐day‐specific, exercise‐induced health benefits, and improve our current understanding of the link between exercise and circadian rhythms.…”