PT - JOURNAL ARTICLE AU - N Vishnu AU - A Hamilton AU - A Bagge AU - A Wernersson AU - E Cowan AU - H Barnard AU - Y Sancak AU - K.J. Kamer AU - P Spégel AU - M Fex AU - A Tengholm AU - V.K. Mootha AU - DG Nicholls AU - H Mulder TI - Mitochondrial clearance of Ca<sup>2+</sup> controls insulin secretion AID - 10.1101/830323 DP - 2019 Jan 01 TA - bioRxiv PG - 830323 4099 - http://biorxiv.org/content/early/2019/11/05/830323.short 4100 - http://biorxiv.org/content/early/2019/11/05/830323.full AB - Transport of Ca2+ from the cytosol to the mitochondrial matrix of insulin-secreting pancreatic β-cells facilitates nutrient-mediated insulin secretion. However, the underlying mechanism is unclear. The establishment of the molecular identity of the mitochondrial Ca2+ uniporter (MCU) and associated proteins has allowed mitochondrial Ca2+ transport to be modified in intact cells. We examined the consequences of deficiency of the accessory protein, MICU2, in rat and human insulin-secreting cell lines as well as in mouse islets. Glucose-induced mitochondrial Ca2+ elevation and inner membrane hyperpolarization were reduced, together with cytosolic ATP/ADP-ratios and insulin secretion. Insulin secretion in Micu2 knock out mice was attenuated in vitro as well as in vivo. While KCl-evoked sub-plasmalemmal Ca2+ increases were more pronounced, the global cytosolic Ca2+ response was, surprisingly, diminished in MICU2-deficient cells. These findings were supported by selective inhibition of mitochondrial Ca2+ uptake by mitochondrial depolarization. It is concluded that mitochondrial Ca2+ transport plays an additional and hitherto unrecognized role in stimulated β-cells by regulating net Ca2+ entry across the plasma membrane. This is likely accounted for by clearing of sub-plasmalemmal Ca2+ levels by mitochondria located near the plasma membrane.