Mitochondrial clearance of Ca²⁺controls insulin secretion

Abstract

11 Running title: MICU2-deficiency impairs insulin secretion 12 Character Count: [Insert total character count <55,000 characters] 13 14 15 16 17 18 19 20 SUMMARY 21Transport of Ca 2+ from the cytosol to the mitochondrial matrix of insulin-secreting pancreatic 22 β-cells facilitates nutrient-mediated insulin secretion. However, the underlying mechanism is 23 unclear. The establishment of the molecular identity of the mitochondrial Ca 2+ uniporter (MCU) 24 and associated proteins has allowed mitochondrial Ca 2+ transport to be modified in intact cells. 25We examined the consequences of deficiency of the accessory protein, MICU2, in rat and human 26 insulin-secreting cell lines as well as in mouse islets. Glucose-induced mitochondrial Ca 2+ 27 elevation and inner membrane hyperpolarization were reduced, together with cytosolic 28 ATP/ADP-ratios and insulin secretion. Insulin secretion in Micu2 knock out mice was attenuated 29 in vitro as well as in vivo. While KCl-evoked sub-plasmalemmal Ca 2+ increases were more 30 pronounced, the global cytosolic Ca 2+ response was, surprisingly, diminished in MICU2-31 deficient cells. These findings were supported by selective inhibition of mitochondrial Ca 2+ 32 uptake by mitochondrial depolarization. It is concluded that mitochondrial Ca 2+ transport plays 33 an additional and hitherto unrecognized role in stimulated β-cells by regulating net Ca 2+ entry 34 across the plasma membrane. This is likely accounted for by clearing of sub-plasmalemmal Ca 2+ 35 levels by mitochondria located near the plasma membrane. 36 37 Keywords: mitochondrial calcium uniportervoltage-dependent calcium channels -38 bioenergeticsknock out micestimulus-secretion coupling 39

Proinflammatory cytokines suppress nonsense-mediated RNA decay to impair regulated transcript isoform processing in pancreatic β cells

“…150200, Nunc, Buckingham, England), 300,000 INS1(832/13) or EndoC-bH3 cells were cultured and preincubated for 2 days. GSIS was carried out using Krebs-Ringer buffer containing 2 mM or 17 mM glucose, as described (11,18).…”