title: Essential role of mitochondrial Ca2+ uniporter in the generation of mitochondrial pH gradient and metabolism-secretion coupling in insulin-releasing cells.
abstract: In pancreatic β-cells, ATP acts as a signaling molecule initiating plasma membrane electrical activity linked to Ca(2+) influx, which triggers insulin exocytosis. The mitochondrial Ca(2+) uniporter (MCU) mediates Ca(2+) uptake into the organelle, where energy metabolism is further stimulated for sustained second phase insulin secretion. Here, we have studied the contribution of the MCU to the regulation of oxidative phosphorylation and metabolism-secretion coupling in intact and permeabilized clonal β-cells as well as rat pancreatic islets. Knockdown of MCU with siRNA transfection blunted matrix Ca(2+) rises, decreased nutrient-stimulated ATP production as well as insulin secretion. Furthermore, MCU knockdown lowered the expression of respiratory chain complexes, mitochondrial metabolic activity, and oxygen consumption. The pH gradient formed across the inner mitochondrial membrane following nutrient stimulation was markedly lowered in MCU-silenced cells. In contrast, nutrient-induced hyperpolarization of the electrical gradient was not altered. In permeabilized cells, knockdown of MCU ablated matrix acidification in response to extramitochondrial Ca(2+). Suppression of the putative Ca(2+)/H(+) antiporter leucine zipper-EF hand-containing transmembrane protein 1 (LETM1) also abolished Ca(2+)-induced matrix acidification. These results demonstrate that MCU-mediated Ca(2+) uptake is essential to establish a nutrient-induced mitochondrial pH gradient which is critical for sustained ATP synthesis and metabolism-secretion coupling in insulin-releasing cells.
authors.affiliation: From the Department of Physiology, Yonsei University Wonju College of Medicine, Wonju, Gangwon-Do 220-701, Korea.
authors.forename: Xianglan
authors.initials: X
authors.lastname: Quan
authors.affiliation: From the Department of Physiology, Yonsei University Wonju College of Medicine, Wonju, Gangwon-Do 220-701, Korea.
authors.forename: Tuyet Thi
authors.initials: TT
authors.lastname: Nguyen
authors.affiliation: From the Department of Physiology, Yonsei University Wonju College of Medicine, Wonju, Gangwon-Do 220-701, Korea.
authors.forename: Seong-Kyung
authors.initials: SK
authors.lastname: Choi
authors.affiliation: From the Department of Physiology, Yonsei University Wonju College of Medicine, Wonju, Gangwon-Do 220-701, Korea.
authors.forename: Shanhua
authors.initials: S
authors.lastname: Xu
authors.affiliation: From the Department of Physiology, Yonsei University Wonju College of Medicine, Wonju, Gangwon-Do 220-701, Korea.
authors.forename: Ranjan
authors.initials: R
authors.lastname: Das
authors.affiliation: From the Department of Physiology, Yonsei University Wonju College of Medicine, Wonju, Gangwon-Do 220-701, Korea.
authors.forename: Seung-Kuy
authors.initials: SK
authors.lastname: Cha
authors.affiliation: Department of Physiology, College of Medicine, Inje University, Busan 614-735, Korea.
authors.forename: Nari
authors.initials: N
authors.lastname: Kim
authors.affiliation: Department of Physiology, College of Medicine, Inje University, Busan 614-735, Korea.
authors.forename: Jin
authors.initials: J
authors.lastname: Han
authors.affiliation: Nestlé Institute of Health Sciences, 1015 Lausanne, and.
authors.forename: Andreas
authors.initials: A
authors.lastname: Wiederkehr
authors.affiliation: Department of Cell Physiology and Metabolism, University of Geneva, 1211 Geneva 4, Switzerland.
authors.forename: Claes B
authors.initials: CB
authors.lastname: Wollheim
authors.affiliation: From the Department of Physiology, Yonsei University Wonju College of Medicine, Wonju, Gangwon-Do 220-701, Korea, qsang@yonsei.ac.kr.
authors.forename: Kyu-Sang
authors.initials: KS
authors.lastname: Park
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D049109:Cell Proliferation; D002478:Cells, Cultured; D004734:Energy Metabolism; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007124:Immunoenzyme Techniques; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D007340:Insulinoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D008297:Male; D053078:Membrane Potential, Mitochondrial; D008928:Mitochondria / Q000378:metabolism*; D010085:Oxidative Phosphorylation; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D027682:Cation Transport Proteins; D007328:Insulin; C000594751:LETM1 protein, rat; D012333:RNA, Messenger; D034741:RNA, Small Interfering; C034703:mitochondrial calcium uniporter; D000255:Adenosine Triphosphate; D005947:Glucose; D002118:Calcium
keywords: INS-1E cells; Leucine zipper-EF hand-containing transmembrane protein 1; Mitochondrial Ca2+ uniporter; Mitochondrial pH gradient; insulin secretion; mitochondrial membrane potential; mitochondrial metabolism; mitochondrial respiratory chain complex; mitochondrial transport; pancreatic islet