SR-Mitochondria Crosstalk Shapes Ca Signalling to Impact Pathophenotype in Disease Models Marked by Dysregulated Intracellular Ca Release

AIMS Diastolic Ca release (DCR) from sarcoplasmic reticulum (SR) Ca release channel ryanodine receptor (RyR2) has been linked to multiple cardiac pathologies, but its exact role in shaping divergent cardiac pathologies remains unclear. We hypothesize that the SR-mitochondria interplay contributes to disease phenotypes by shaping Ca signaling. METHODS AND RESULTS A genetic model of catecholaminergic polymorphic ventricular tachycardia (CPVT2 model of CASQ2 knockout) and a pre-diabetic cardiomyopathy model of fructose fed mice (FFD), both marked by DCR, are employed in this study. Mitochondria Ca (mCa) is modulated by pharmacologically targeting mitochondria Ca uniporter (MCU) or permeability transition pore (mPTP), mCa uptake and extrusion mechanisms, respectively. An MCU activator abolished Ca waves in CPVT2 but exacerbated waves in FFD cells. Mechanistically this is ascribed to mitochondria's function as a Ca buffer or source of reactive oxygen species (mtROS) to exacerbate RyR2 functionality, respectively. Enhancing mCa uptake reduced and elevated mtROS production in CPVT2 and FFD respectively. In CPVT2, mitochondria took up more Ca in permeabilized cells, and had higher level of mCa content in intact cells vs FFD. Conditional ablation of MCU in the CPVT2 model caused lethality and cardiac remodeling, but reduced arrhythmias in the FFD model. In parallel, CPVT2 mitochondria also employ upregulated mPTP-mediated Ca efflux to avoid mCa overload, as seen by elevated incidence of MitoWinks (an indicator of mPTP-mediated Ca efflux) vs FFD. Both pharmacological and genetic inhibition of mPTP promoted mtROS production and exacerbation of myocyte Ca handling in CPVT2. Further, genetic inhibition of mPTP exacerbated arrhythmias in CPVT2. CONCLUSION In contrast to FFD, which is more susceptible to mtROS-dependent RyR2 leak, in CPVT2 mitochondria buffer SR-derived DCR to mitigate Ca-dependent pathological remodeling and rely on mPTP-mediated Ca efflux to avoid mCa overload. SR-mitochondria interplay contributes to the divergent pathologies by disparately shaping intracellular Ca signaling. TRANSLATIONAL PERSPECTIVE It is well-established that RyR2 dysfunction is involved in a spectrum of pathological conditions including cardiac arrhythmias. In this study, two disease models marked by RyR2 dysfunction were employed to explore how the interplay between SR and mitochondria contributes to divergent cardiac pathologies. We found mitochondria act as essential Ca buffer to absorb SR-derived Ca to mitigate pathological remodeling in the genetic arrhythmic syndrome CPVT, but they are more susceptible to Ca overload or ROS-related exacerbation of RyR2 dysfunction in pre-diabetic cardiomyopathy. Thus, tailored therapies should be developed to target SR-mitochondria interplay in the aims of treating these diseases.