Molecular pathology of SMIM20 deficiency in the mouse heart

Mitochondria are key to cellular energetics, metabolism, and signaling. Their dysfunction is linked to devastating diseases including mitochondrial disorders, diabetes, neurodegenerative diseases, cardiac disorders, and cancer. Here, we present a novel knockout mouse model lacking the complex IV assembly factor SMIM20/MITRAC7. SMIM20-/- mice display cardiac pathology with reduced heart weight and cardiac output. Heart mitochondria present with reduced levels of complex IV associated with increased complex I activity, have altered fatty acid oxidation, and display elevated levels of ROS production. Interestingly, mutant mouse cardiomyocytes show unphysiological Ca2+ handling, which can be attributed to the increase in mitochondrial ROS production. Our study presents a new example of a tissue-specific phenotype in the context of OXPHOS dysfunction. Moreover, we identify a molecular link between complex IV dysfunction and Ca2+ handling at the endoplasmic reticulum through ROS signalling.