Role of Translocon in calcium exchanges in cell compartments and in cell death during myocardial infarction

Cardiovascular diseases are one of the main causes of death in the world. Myocardial infarction is characterized by an occlusion of an artery, causing the emergence of an ischemic area. Even if reperfusion is necessary, it still causes myocardial injuries. At cellular level, cardiomyocytes sustain an alteration of calcium (Ca2+) homeostasis between reticulum (ER) and mitochondria, which contributes to cell death. Translocon (TLC), a major component of the translation machinery, is one of the main reticular Ca2+ leak channel and is involved in Ca2+ homeostasis. The aim of our work is to better understand the role of TLC in Ca2+ exchanges between ER and mitochondria in a physiological context and during hypoxia-re-oxygenation (HR) sequence. After location TLC, we then assessed whether its pharmacological modulation could have an impact on ER-mitochondria Ca2+ exchanges and in cell death. Rat cardiomyoblast H9C2 cell line was used in all of our experiments. Ca2+ and ATP levels in cell compartments were assessed in imaging experiments, using Ca2+ and ATP sensors. Puromycin and anisomycin were used to open and close TLC, respectively. The location of this channel was obtained with immunoblot and cell death was evaluated by flow cytometry. Our data show that TLC is a functional reticular Ca2+ leak channel: application of 40 μM puromycin leads to a Ca2+ leak from ER while anisomycin pre-treatment prevents this effect. These treatments impact Ca2+ exchanges between ER and mitochondria, especially by increasing IP3-R response to ATP stimulation in Ca2+ hotspots (in the outer mitochondrial membrane). In addition, puromycin pre-treatment increases the mitochondrial ATP content. Finally, TLC modulation during HR sequence show a decrease of cell death. Pharmacological modulations of TLC could be an effective cardioprotection strategy, by regulating Ca2+ exchanges between ER and mitochondria, to reduce cell death after a MI.