Cryptochromes Suppress HIF1α in Muscles

Area of Science:

• Molecular Biology
• Exercise Physiology
• Chronobiology

Background:

• Muscle metabolism (glycolytic vs. oxidative) is intensity-dependent.
• Circadian rhythms influence muscle gene expression for metabolism and exercise response.
• Circadian repressors CRY1 and CRY2 inhibit PPARδ, a key regulator of oxidative metabolism and endurance.

Purpose of the Study:

• To investigate the role of cryptochromes (CRYs) in regulating muscle metabolism and exercise response.
• To elucidate the mechanism by which CRYs influence hypoxia-responsive transcription in muscles.
• To determine the contribution of CRYs to the circadian modulation of muscle metabolism.

Main Methods:

• Analysis of CRY-deficient mice and primary myotubes.
• Assessment of peroxisome proliferator-activated receptor delta (PPARδ) activation and exercise performance.
• Investigation of hypoxia-inducible factor 1-alpha (HIF1α)-BMAL1 heterodimer activity and HIF1α protein levels.
• Evaluation of metabolic alterations in CRY-deficient myotubes.

Main Results:

• CRY deficiency in mice led to enhanced PPARδ activation and increased maximum running speed, but not endurance.
• CRYs were found to limit hypoxia-responsive transcription by repressing HIF1α-BMAL1 heterodimers.
• CRY2 was more potent than CRY1 in reducing HIF1α protein levels in myotubes and muscle tissue.
• CRY-deficient myotubes displayed metabolic changes indicative of suppressed HIF1α activity.

Conclusions:

• Cryptochromes (CRYs) play a significant role in limiting hypoxia-responsive transcription in muscles via HIF1α suppression.
• CRY deficiency enhances certain aspects of muscle exercise adaptation, suggesting a role in metabolic regulation.
• These findings highlight the contribution of cryptochromes to the circadian control of muscle metabolism.