Abstract 11554: Integrating Intracellular Calcium Leak and Mitochondrial Dysfunction in Heart Failure
Growing evidence indicates that mitochondrial function is impaired in heart failure (HF). However, the molecular mechanisms involved remain relatively obscure. It is widely recognized that increased sarcoplasmic reticulum (SR) Ca2+ leak via the cardiac ryanodine receptor (RyR2) plays a key role in HF. We have recently demonstrated that mitochondria and SR are tightly connected in a unique functional unit. In this study we sought to clarify the relationship between intracellular Ca2+ leak and mitochondrial dysfunction in HF. We assessed mitochondrial function in a PKA phosphomimetic knock-in mouse model (RyR2S2808D) with constitutively leaky RyR2 channels. S2808D mice displayed a significant reduction in cardiac function compared to WT and to S2808A mutants (that cannot be phosphorylated on Ser2808). To determine whether leaky RyR2 channels can cause mitochondrial damage we analyzed ultrastructural morphology of cardiac mitochondria. We found a significant morphological damage induced by RyR2 Ca2+ leakage, mirrored by alterations in mitochondrial function. Indeed, S2808D cardiomyocytes showed a reduction in ATP production and a significant increase in the dissipation of the mitochondrial potential (Δψm). Moreover, we found that cardiac RyR2 isolated from S2808D mice were oxidized and depleted of the stabilizing subunit calstabin2, contributing to SR Ca2+ leak. To determine whether mitochondria are the source of reactive oxygen species (ROS) that oxidize cardiac RyR2 in S2808D mice, we crossed these animals with mCAT mice (which overexpress human catalase in mitochondria reducing mitochondrial ROS production). After MI, S2808D/mCAT mice displayed less reduction in cardiac function compared to S2808D littermates. IP analysis of heart samples showed that genetic enhancement of mitochondrial anti-oxidant activity was able to reduce RyR2 oxidation after MI. Our results indicate for the first time that intracellular Ca2+ leak via defective RyR2 plays a critical role in the pathophysiology of mitochondrial dysfunction in HF pointing to a vicious cycle in which SR Ca2+ leak results in mitochondrial Ca2+ overload and increased ROS production, which in turn oxidize RyR2 and enhance the SR Ca2+ leak, contributing thereby to impaired contractility.
- Heart failure
- Transgenic models
- Mitochondrial energetics, heart failure, arrhythmias
- © 2013 by American Heart Association, Inc.