Diurnal oscillations of endogenous H₂O₂ sustained by p66^Shc regulate circadian clocks

Redox balance, an essential feature of healthy physiological steady states, is regulated by circadian clocks, but whether or how endogenous redox signalling conversely regulates clockworks in mammals remains unknown. Here, we report circadian rhythms in the levels of endogenous H₂O₂ in mammalian cells and mouse livers. Using an unbiased method to screen for H₂O₂-sensitive transcription factors, we discovered that rhythmic redox control of CLOCK directly by endogenous H₂O₂ oscillations is required for proper intracellular clock function. Importantly, perturbations in the rhythm of H₂O₂ levels induced by the loss of p66^Shc, which oscillates rhythmically in the liver and suprachiasmatic nucleus (SCN) of mice, disturb the rhythmic redox control of CLOCK function, reprogram hepatic transcriptome oscillations, lengthen the circadian period in mice and modulate light-induced clock resetting. Our findings suggest that redox signalling rhythms are intrinsically coupled to the circadian system through reversible oxidative modification of CLOCK and constitute essential mechanistic timekeeping components in mammals.