title: Strategic Positioning and Biased Activity of the Mitochondrial Calcium Uniporter in Cardiac Muscle.
abstract: Control of myocardial energetics by Ca2+signal propagation to the mitochondrial matrix includes local Ca2+delivery from sarcoplasmic reticulum (SR) ryanodine receptors (RyR2) to the inner mitochondrial membrane (IMM) Ca2+uniporter (mtCU). mtCU activity in cardiac mitochondria is relatively low, whereas the IMM surface is large, due to extensive cristae folding. Hence, stochastically distributed mtCU may not suffice to support local Ca2+transfer. We hypothesized that mtCU concentrated at mitochondria-SR associations would promote the effective Ca2+transfer. mtCU distribution was determined by tracking MCU and EMRE, the proteins essential for channel formation. Both proteins were enriched in the IMM-outer mitochondrial membrane (OMM) contact point submitochondrial fraction and, as super-resolution microscopy revealed, located more to the mitochondrial periphery (inner boundary membrane) than inside the cristae, indicating high accessibility to cytosol-derived Ca2+inputs. Furthermore, MCU immunofluorescence distribution was biased toward the mitochondria-SR interface (RyR2), and this bias was promoted by Ca2+signaling activity in intact cardiomyocytes. The SR fraction of heart homogenate contains mitochondria with extensive SR associations, and these mitochondria are highly enriched in EMRE. Size exclusion chromatography suggested for EMRE- and MCU-containing complexes a wide size range and also revealed MCU-containing complexes devoid of EMRE (thus disabled) in the mitochondrial but not the SR fraction. Functional measurements suggested more effective mtCU-mediated Ca2+uptake activity by the mitochondria of the SR than of the mitochondrial fraction. Thus, mtCU "hot spots" can be formed at the cardiac muscle mitochondria-SR associations via localization and assembly bias, serving local Ca2+signaling and the excitation-energetics coupling.
authors.affiliation: From the MitoCare Center for Mitochondrial Imaging Research and Diagnostics, Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
authors.forename: Sergio
authors.initials: S
authors.lastname: De La Fuente
authors.affiliation: the Center for Translational Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, and.
authors.forename: Celia
authors.initials: C
authors.lastname: Fernandez-Sanz
authors.affiliation: From the MitoCare Center for Mitochondrial Imaging Research and Diagnostics, Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
authors.forename: Caitlin
authors.initials: C
authors.lastname: Vail
authors.affiliation: From the MitoCare Center for Mitochondrial Imaging Research and Diagnostics, Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
authors.forename: Elorm J
authors.initials: EJ
authors.lastname: Agra
authors.affiliation: the Center for Molecular Medicine, Laboratory of Molecular Biology, and.
authors.forename: Kira
authors.initials: K
authors.lastname: Holmstrom
authors.affiliation: the Systems Biology Center, Laboratory of Cardiac Physiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Junhui
authors.initials: J
authors.lastname: Sun
authors.affiliation: the Center for Translational Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, and.
authors.forename: Jyotsna
authors.initials: J
authors.lastname: Mishra
authors.affiliation: the Penn EM Resource Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
authors.forename: Dewight
authors.initials: D
authors.lastname: Williams
authors.affiliation: the Center for Molecular Medicine, Laboratory of Molecular Biology, and.
authors.forename: Toren
authors.initials: T
authors.lastname: Finkel
authors.affiliation: the Systems Biology Center, Laboratory of Cardiac Physiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Murphy
authors.affiliation: From the MitoCare Center for Mitochondrial Imaging Research and Diagnostics, Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
authors.forename: Suresh K
authors.initials: SK
authors.lastname: Joseph
authors.affiliation: the Center for Translational Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, and.
authors.forename: Shey-Shing
authors.initials: SS
authors.lastname: Sheu
authors.affiliation: From the MitoCare Center for Mitochondrial Imaging Research and Diagnostics, Department of Pathology, Anatomy, and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, Gyorgy.Csordas@jefferson.edu.
authors.forename: György
authors.initials: G
authors.lastname: Csordás
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D020013:Calcium Signaling; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008929:Mitochondria, Heart / Q000378:metabolism; D051336:Mitochondrial Membranes / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012519:Sarcoplasmic Reticulum / Q000235:genetics / Q000378:metabolism
chemical_list: D015220:Calcium Channels; C000622748:Emre protein, mouse; C034703:mitochondrial calcium uniporter; D002118:Calcium
keywords: calcium channel; calcium transport; microscopic imaging; mitochondrial transport; signaling