Faculty Collaboration Database

Strategic Positioning and Biased Activity of the Mitochondrial Calcium Uniporter in Cardiac Muscle. J Biol Chem 2016 Oct 28;291(44):23343-23362

Date

10/30/2016

Pubmed ID

27637331

Pubmed Central ID

PMC5087749

DOI

10.1074/jbc.M116.755496

Scopus ID

2-s2.0-84994034038 (requires institutional sign-in at Scopus site)   47 Citations

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.

Author List

De La Fuente S, Fernandez-Sanz C, Vail C, Agra EJ, Holmstrom K, Sun J, Mishra J, Williams D, Finkel T, Murphy E, Joseph SK, Sheu SS, Csordás G

Author

Jyotsna Mishra PHD Research Scientist I in the Anesthesiology department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Animals
Calcium
Calcium Channels
Calcium Signaling
Male
Mice
Mice, Inbred C57BL
Mitochondria, Heart
Mitochondrial Membranes
Myocardium
Myocytes, Cardiac
Rats
Rats, Sprague-Dawley
Sarcoplasmic Reticulum