The mitochondrial Na+/Ca2+ exchanger is essential for Ca2+ homeostasis and viability

Mitochondrial calcium (mCa2+) has a central role in both metabolic regulation and cell death signalling, however its role in homeostatic function and disease is controversial1. Slc8b1 encodes the mitochondrial Na+/Ca2+ exchanger (NCLX), which is proposed to be the primary mechanism for mCa2+ extrusion in excitable cells2,3. Here we show that tamoxifen-induced deletion of Slc8b1 in adult mouse hearts causes sudden death, with less than 13% of affected mice surviving after 14 days. Lethality correlated with severe myocardial dysfunction and fulminant heart failure. Mechanistically, cardiac pathology was attributed to mCa2+ overload driving increased generation of superoxide and necrotic cell death, which was rescued by genetic inhibition of mitochondrial permeability transition pore activation. Corroborating these findings, overexpression of NCLX in the mouse heart by conditional transgenesis had the beneficial effect of augmenting mCa2+ clearance, preventing permeability transition and protecting against ischaemia-induced cardiomyocyte necrosis and heart failure. These results demonstrate the essential nature of mCa2+ efflux in cellular function and suggest that augmenting mCa2+ efflux may be a viable therapeutic strategy in disease. Conditional deletion of the mitochondrial Na+/Ca2+ exchanger NCLX in adult mouse hearts causes sudden death due to mitochondrial calcium overload, whereas its overexpression limits cell death elicited by ischaemia reperfusion injury and heart failure. The relevance of mitochondrial calcium exchange in vivo has been controversial. Here, John Elrod and colleagues explore the physiological significance of this process in the mouse heart. Conditional deletion of the mitochondrial sodium–calcium exchanger NCLX in adult mouse hearts caused sudden death owing to mitochondrial calcium overload and necrotic cell death. Conversely, overexpression of NCLX in mouse hearts limited cell death caused by ischaemia reperfusion injury, the tissue damage caused when blood rushes back to a site that has suffered a lack of oxygen. The authors conclude that cardiomyocyte mitochondrial calcium exchange is a prominent mitochondrial regulatory mechanism in cardiac disease.