Defective sarcoplasmic reticulum-mitochondria calcium exchange in aged mouse myocardium.

C Fernandez-Sanz,E Nuñez,J Vázquez,M Loureiro,E Miro-Casas,A Rodriguez-Sinovas,D Garcia-Dorado,M Poncelas,I Barba,M Ruiz-Meana,J Castellano

doi:10.1038/cddis.2014.526

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 (>20 months) with respect to young mice (5–6 months). Mitochondrial membrane potential and resting O2 consumption were similar in mitochondria from young and old hearts. However, maximal ADP-stimulated O2 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 Ca2+, we investigated the effect of age on mitochondrial Ca2+ uptake. Although no age-dependent differences were found in Ca2+ uptake kinetics in isolated mitochondria, mitochondrial Ca2+ uptake secondary to SR Ca2+ 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 Ca2+ handling. Age-dependent alterations in SR Ca2+ transfer to mitochondria and in Ca2+ 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 Ca2+ exchange that contributes to energy demand/supply mistmach and oxidative stress in the aged heart.

Highlights

Age is the main independent risk factor for cardiovascular morbidity and mortality.[1]
The results of the present study indicate that sarcoplasmic reticulum (SR)–mitochondria communication is altered in aged cardiomyocytes, as manifested by reduced physical interaction among ryanodine receptors (RyR) and voltage-dependent anion channel (VDAC)
As a consequence of reduced Ca2+ exchange, mitochondrial regeneration of the electron donor NADH and the antioxidant NADPH is depressed in old cardiomyocytes when exposed to increased frequency of pacing, reflecting an uncoupled bioenergetic feedback response, and mitochondrial ROS production is concomitantly increased under these conditions

Summary

Introduction

Age is the main independent risk factor for cardiovascular morbidity and mortality.[1] It increases heart vulnerability to cardiac diseases as well as the severity of their clinical manifestations, and reduces the efficacy of cardioprotective interventions.[2] At the cellular level, some of the structural and functional age-dependent changes resemble those of failing cardiac myocytes.[3,4] disturbed Ca2+ homeostasis and excitation–contraction coupling,[5] as well as deficient mitochondrial energetics[6] and excessive ROS production,[7] have been consistently reported in senescent cardiomyocytes. We hypothesized that aging may negatively impact on mitochondria–SR communication by mechanisms involving defective Ca2+ transmission, and we identified reduced physical interaction between RyR and mitochondrial voltage-dependent anion channel (VDAC) as the main responsible of this effect

Methods

Results

Conclusion