Aging is accompanied by the progressive deterioration of circadian clock function, characterized by reduced amplitude, increased period variability, and impaired metabolic coupling. Declining intracellular nicotinamide adenine dinucleotide (NAD+) levels and SIRT1 activity have been implicated as key mediators of age-associated circadian disruption. Ergothioneine (EGT), a diet-derived antioxidant with longevity-associated effects, has recently been reported to improve healthspan and modulate redox metabolism. However, its effects on the circadian clock remain unclear. Here, we examined whether EGT mitigates age-related decline in circadian rhythmicity using PER2::LUC mouse embryonic fibroblasts (MEFs). Chronic EGT treatment enhanced the amplitude of the PER2::LUC rhythm in a dose-dependent manner without markedly altering the baseline period length. Aging-associated NAD+ decline was modeled using FK866, a NAMPT inhibitor that depletes intracellular NAD+, which reduced rhythm amplitude, lengthened the period, and increased cycle-to-cycle variability. Notably, co-treatment with EGT significantly restored rhythm amplitude, attenuated FK866-induced period lengthening, and reduced period variability. Biochemical analyses revealed that EGT increased the NAD+/NADH ratio under basal conditions and significantly elevated both NAD+ levels and the NAD+/NADH ratio under FK866-induced NAD+ depletion. This effect was not attributable solely to cytoprotection. This study demonstrates that EGT enhances circadian rhythm robustness and counteracts NAD+-depletion-induced clock dysfunction. EGT may ameliorate age-related circadian decline by improving intracellular redox balance and NAD+ metabolism. Given that EGT crosses the blood-brain barrier, it may represent a novel nutritional strategy to preserve circadian function during aging.
Circadian Biology