Defective sarcoplasmic reticulum-mitochondria calcium exchange in aged mouse myocardium

Abstract

Mitochondrial alterations are critically involved in increased vulnerability to disease during aging. We investigated the contribution of mitochondria-sarcoplasmic reticulum (SR) communication in cardiomyocyte functional alterations during aging. Heart function (echocardiography) and ATP/phosphocreatine (NMR spectroscopy) were preserved in hearts from old mice (420 months) with respect to young mice (5-6 months). Mitochondrial membrane potential and resting O 2 consumption were similar in mitochondria from young and old hearts. However, maximal ADP-stimulated O 2 consumption was specifically reduced in interfibrillar mitochondria from aged hearts. Second generation proteomics disclosed an increased mitochondrial protein oxidation in advanced age. Because energy production and oxidative status are regulated by mitochondrial Ca 2+, we investigated the effect of age on mitochondrial Ca 2+ uptake. Although no age-dependent differences were found in Ca 2+ uptake kinetics in isolated mitochondria, mitochondrial Ca 2+ uptake secondary to SR Ca 2+ release was significantly reduced in cardiomyocytes from old hearts, and this effect was associated with decreased NAD(P)H regeneration and increased mitochondrial ROS upon increased contractile activity. Immunofluorescence and proximity ligation assay identified the defective communication between mitochondrial voltage-dependent anion channel and SR ryanodine receptor (RyR) in cardiomyocytes from aged hearts associated with altered Ca 2+ handling. Age-dependent alterations in SR Ca 2+ transfer to mitochondria and in Ca 2+ handling could be reproduced in cardiomyoctes from young hearts after interorganelle disruption with colchicine, at concentrations that had no effect in aged cardiomyocytes or isolated mitochondria. Thus, defective SR-mitochondria communication underlies inefficient interorganelle Ca 2+ exchange that contributes to energy demand/supply mistmach and oxidative stress in the aged heart.