Depressing Mitochondria-Reticulum Interactions Protects Cardiomyocytes From Lethal Hypoxia-Reoxygenation Injury

Background Under physiological conditions, Ca2+ transfer from the endoplasmic reticulum (ER) to mitochondria might occur at least in part at contact points between the 2 organelles and involves the VDAC1/Grp75/IP3R1 complex. Accumulation of Ca2+ into the mitochondrial matrix may activate the mitochondrial chaperone cyclophilin D (CypD) and trigger permeability transition pore opening, whose role in ischemia/reperfusion injury is well recognized. We questioned here whether the transfer of Ca2+ from ER to mitochondria might play a role in cardiomyocyte death after hypoxia-reoxygenation. Methods and Results We report that CypD interacts with the VDAC1/Grp75/IP3R1 complex in cardiomyocytes. Genetic or pharmacological inhibition of CypD in both H9c2 cardiomyoblasts and adult cardiomyocytes decreased the Ca2+ transfer from ER to mitochondria through IP3R under normoxic conditions. During hypoxia-reoxygenation, the interaction between CypD and the IP3R1 Ca2+ channeling complex increased concomitantly with mitochondrial Ca2+ content. Inhibition of either CypD, IP3R1, or Grp75 decreased protein interaction within the complex, attenuated mitochondrial Ca2+ overload, and protected cells from hypoxia-reoxygenation. Genetic or pharmacological inhibition of CypD provided a similar effect in adult mice cardiomyocytes. Disruption of ER-mitochondria interaction via the downregulation of Mfn2 similarly reduced the interaction between CypD and the IP3R1 complex and protected against hypoxia-reoxygenation injury. Conclusions Our data (1) point to a new role of CypD at the ER-mitochondria interface and (2) suggest that decreasing ER-mitochondria interaction at reperfusion can protect cardiomyocytes against lethal reperfusion injury through the reduction of mitochondrial Ca2+ overload via the CypD/VDAC1/Grp75/IP3R1 complex.