Effect of Time of Aerobic Exercise in the Light-dark Cycle on Glycemic Control, SIRT1 Protein Expression, and NAD+/NADH Ratio in Skeletal Muscle of Type 2 Diabetes Model Mice

Introduction: Mitochondrial function is regulated by the dark-light cycle under physiological and pathological conditions. Time-dependent exercise interventions may affect metabolic health in diabetic patients by regulating hyperglycemia. However, limited data are available about the correlation between the time of exercise and the regulation of muscle circadian rhythm in diabetes conditions. This study aimed to investigate the effect of time of exercise in the dark-light cycle on SIRT1 protein expression and the NAD+/NADH ratio in the gastrocnemius muscle of diabetic mice. Materials and Methods: In this experimental study, thirty healthy male NMRI mice were randomly divided into three groups: control, diabetic, and diabetic+exercise. Type 2 diabetes was induced using a combination of a high-fat diet (five weeks) and streptozotocin injection (20 mg/kg body weight). Eight weeks of aerobic exercise with moderate intensity (5 days, 80-60 minutes) were performed on a treadmill at two times of the day, the early light phase (ZT3) at 9:00 AM and the early dark phase (ZT15) at 9:00 PM. Gastrocnemius muscles were collected at two times of the day, and SIRT1 protein expression was evaluated by Western blot analysis. The cellular NAD+/NADH content and glucose concentrations were measured using the colorimetric method. A two-way analysis of variance was used to analyze the data. Results: Eight weeks of aerobic exercise significantly increased SIRT1 protein and NADH levels (P<0.001) and improved hyperglycemia (P=0.005) only in the early dark phase. Aerobic exercise increased the NAD+/NADH ratio independently of time (P=0.003). Conclusion: Proper exercise timing in the early dark, along with SIRT1 protein and NAD+ level circadian changes, may strengthen the effects of exercise and correct hyperglycemia more effectively.