Age‐associated attenuation of autophagy underlies ryanodine receptor hyperactivity

Abstract

Aging is associated with reduced autophagy and altered mitochondrial function; yet, the link between these processes and altered calcium (Ca) homeostasis remains unknown. We used ventricular myocytes from young (5–9 months) and old (4–5 years) rabbit hearts to test the hypothesis that reduced autophagy leads to dysfunctional mitochondria that produces ROS, leading to oxidation of ryanodine receptors (RyRs) and changes in Ca homeostasis. Markers of autophagy were measured via western blotting and β‐galactosidase staining. Age‐associated changes in ROS production, mitochondrial membrane potential, and Ca handling were determined in myocytes using confocal microscopy. Specific markers confirmed reduced autophagy. In aged myocytes, ROS production was increased and mitochondrial membrane was depolarized; both parameters were exacerbated with beta‐adrenergic agonist isoproterenol. Also with isoproterenol, aged myocytes showed decreased Ca transient amplitude, SR Ca load, and latency of spontaneous Ca waves, which were reversed with the mitochondria‐specific antioxidant mito‐TEMPO. These data suggest that age‐related attenuation of autophagy may lead to mitochondrial dysfunction that underlies increased thiol‐oxidation of RyRs. This process could explain the reduced RyR refractoriness leading to spontaneous Ca release in senescent cardiomyocytes making aged hearts more prone to arrhythmia.