Up to 70% of the population experiences (SJL), which disrupts circadian rhythms and may impact heart health.
SJL resulted in significant shifts in physical activity timing during weekends for both sedentary and exercised mice.
Exercise improved the speed of re-entrainment to the weekday schedule for mice under SJL conditions.
Both control and SJL-exercised mice exhibited exercise-induced myocardial hypertrophy.
SJL decreased expression of mitochondrial fusion proteins MFN1 and OPA1, while inhibiting exercise-induced increases in MFN2.
These findings indicate that SJL disrupts the normal adaptations of heart muscle to exercise.
Simplified
(SJL) represents the behavioral misalignment of sleep and wake times on work days and free days, and potently disrupts the circadian rhythm. SJL affects up to 70% of the population worldwide and is associated with increased risk for many cardiometabolic diseases. Animal models of acute SJL have shown disruption in locomotor activity and expression of clock genes in select tissues, its impact on the heart remains unclear. The purpose of this study was to investigate the effects of prolonged SJL (6 weeks), on activity rhythms, and the impact on exercise-induced adaptations in the heart. Male mice (n = 40, C57BL6) were assigned to a control light:dark (LD) cycle or SJL schedule (4-hour shift on weekends) for 6 weeks. Mice in each condition were further divided into voluntary exercise (EX) or sedentary (SED) groups. SJL resulted in significant shifts in the onset of physical activity in both sedentary (SJL-SED) and exercised (SJL-EX) mice on weekends, and exercise accelerated the speed of re-entrainment to the weekday schedule. Exercise induced myocardial hypertrophy in both CON-EX and SJL-EX groups. While there were no changes in mitochondrial content, SJL decreased expression of mitochondrial fusion proteins MFN1 and OPA1, and inhibited exercise-induced increases in MFN2. Taken together, these findings suggest that exercise hastens re-entrainment to the weekday schedule under SJL, but that SJL disrupts exercise-induced alterations to mitochondrial fusion/fission dynamics in the heart. Further investigation of cardiovascular function is warranted and will enable the development of strategies to prevent the effects of SJL on the heart.
Key numbers
15.28
Activity Onset Delay
Onset time for -SED mice on Weekend Day 1.
0.522
Mitochondrial Fusion Protein Expression
MFN2 expression in -EX compared to CON-EX.
0.003
Heart Mass Increase
Main effect of exercise on absolute heart mass.
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