| Summary: | Background: Atrogin1, which is one of the key genes for the promotion of muscle atrophy, exhibits day-night variation. However, its mechanism and the role of its day-night variation are largely unknown in a muscle atrophic context. Methods: The mice were induced a muscle atrophy by hindlimb-unloading (HU). To examine a role of circadian clock, Wild-type (WT) and Clock mutant mice were used. To test the effects of a neuronal effects, an unilateral ablation of sciatic nerve was performed in HU mice. To test a timing-dependent effects of weight-bearing, mice were released from HU for 4 h in a day at early or late active phase (W-EAP and W-LAP groups, respectively). Findings: We found that the day-night oscillation of Atrogin1 expression was not observed in Clock mutant mice or in the sciatic denervated muscle. In addition, the therapeutic effects of weight-bearing were dependent on its timing with a better effect in the early active phase. Interpretation: These findings suggest that the circadian clock controls the day-night oscillation of Atrogin1 expression and the therapeutic effects of weight-bearing are dependent on its timing. Fund: Council for Science, Technology, and Innovation, SIP, “Technologies for creating next-generation agriculture, forestry, and fisheries”. Keywords: Circadian rhythm, Chrono-exercise, Atrogin1, Hindlimb-unloading, Weight-bearing
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