Abstract 17508: Defective SR-mitochondria Calcium Transfer and Increased Mitochondrial Oxidative State in Aged Myocardium
Mitochondrial alterations have been proposed as critical players of impaired myocardial function during aging by mechanisms not fully elucidated. We investigate the role of altered sarcoplasmic reticulum (SR)-mitochondria Ca2+ transfer in these changes.
Methods and results: In subsarcolemmal and interfibrillar mitochondria isolated from old (>18 months) and young (<6 months) mouse hearts no differences in resting respiration through the different complexes (oxymeter) were detected, and only maximal O2 consumption stimulated by ADP was specifically reduced in interfibrillar mitochondria. ATP/phosphocreatine ratio in intact myocardium (NMR spectroscopy) and mitochondrial membrane potential in cardiomyocytes (JC-1) were preserved in old mice. Second generation proteomics (GELSILOX) detected increased mitochondrial protein oxidation in old hearts. Since reduced mitochondrial Ca2+ uptake limits regeneration of NADH/NAD(P)H, leading to energy demand/supply uncoupling and increased oxidative stress, we investigated SR Ca2+ transfer to mitochondria (rhod-2) in permeabilized cardiomyocytes submitted to a caffeine pulse, and found a significant reduction in mitochondrial Ca2+ uptake in old as compared to young cardiomyocytes (73% reduction, p=0.01). Reduced mitochondrial Ca2+ uptake was not due to dysfunctional mitochondrial Ca2+ uniporter, because Ca2+ uptake was not altered in isolated mitochondria. However, it appeared to be dependent on impaired SR function, as SR Ca2+ transient amplitude and rate during pacing were depressed, and total SR Ca2+ load was reduced. In addition, advanced age was associated with increased frequency of spontaneous SR Ca2+ sparks and altered morphology (SparkMaster, Image J). Moreover, SR-mitochondria communication appeared to be modified during aging, because disruption of the physical arrangement between both organelles with colchicine markedly deteriorated SR Ca2+ transfer to mitochondria in young cardiomyocytes but had no effect in old cardiomyocytes or in isolated mitochondria.
Conclusion: Mitochondrial dysfunction in cardiomyocytes from old hearts depends, in part, on impaired Ca2+ transfer from the SR secondary to altered SR Ca2+ handling and defective SR-mitochondria communication.
- © 2013 by American Heart Association, Inc.