NAD+ Replenishment Reduces Cardiomyocyte Senescence and Improves Diastolic Function in the Aged Male Heart

Abstract

Aims: Cardiomyocyte senescence is a hallmark of cardiac aging and closely associated with diastolic dysfunction and heart failure in older adults. Strategies to effectively delay or reverse cardiomyocyte senescence in the aged heart remain limited. We investigated whether NAD replenishment regulates cardiomyocyte senescence and cardiac function in aging. Methods and Results: Ventricular NAD metabolism, senescence markers, and cardiac function were assessed in young and aged mice of both sexes. Aged male mice exhibited reduced cardiac NAD levels due to impaired biosynthesis, limited mitochondrial mobilization, and increased consumption, leading to suppressed SIRT1 and SIRT6 activity and accumulation of senescent cardiomyocytes. These changes were accompanied by diastolic dysfunction, myocardial hypertrophy, and fibrosis. In cultured cardiomyocytes, NAD depletion induced cellular senescence, which was reversed by supplementation with the NAD precursors nicotinamide riboside (NR) and dihydronicotinamide riboside (NRH). In aged male mice, two months of NR or NRH treatment suppressed senescence markers, improved diastolic function, and reduced hypertrophy and fibrosis. Mechanistically, both NR and NRH activated SIRT1 and suppressed cell cycle arrest markers. NRH induced more robust SIRT1 activation, which deacetylated SIRT6, promoting its binding to histones and enhancing DNA damage repair. In contrast, aged female mice exhibited diastolic dysfunction without significant decline in cardiac NAD levels and did not respond to NR or NRH treatment. Conclusion: NAD is a critical regulator of cardiomyocyte senescence in aging male hearts. NAD replenishment, particularly with NRH, reverses senescence-associated cardiac dysfunction through coordinated activation of SIRT1 and SIRT6. The sex-specific differences observed highlight distinct mechanisms underlying cardiac aging and emphasize the importance of considering biological sex in the development of NAD-based therapeutic strategies.