Abstract

Heart disease is the leading cause of death in the elderly population and the heart is a highly energy-consuming tissue. Aging-related heart failure is often driven by energy depletion in cardiomyocytes (CM), which rely on their abundant, cristae-dense mitochondria for ATP production. ATP synthase, localized along the cristae rims, plays a critical role in energy conversion, but the connection between its organization and function remains unclear. Here, we explored the spatiotemporal organization of ATP synthase in senescent CM at the level of individual complexes. Using single-molecule localization and tracking microscopy, we observed reduced enzyme mobility within the cristae, coinciding with decreased ATP synthase activity, despite a stable resting mitochondrial membrane potential. This reduction in activity was independent of changes in ATP synthase expression or dimerization. Electron tomography revealed an increased prevalence of curved inner membranes and fenestrated cristae in senescent CM, explaining the reduced enzyme mobility. Senescent CM displayed irregular autonomous and paced beating patterns. These abnormalities suggest that impaired cardiac function is directly driven by disrupted energy metabolism, rooted in the suboptimal organization and function of ATP synthase in altered cristae.