Strategic positioning and biased activity of the mitochondrial calcium uniporter in cardiac muscle

Sergio De la Fuente, Celia Fernandez-Sanz, Caitlin Vail, Elorm J. Agra, Kira Holmstrom, Junhui Sun, Jyotsna Mishra, Dewight Williams, Toren Finkel, Elizabeth Murphy, Suresh K. Joseph, Shey Shing Sheu, György Csordás

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Abstract

Control of myocardial energetics by Ca 2+ signal propagation to the mitochondrial matrix includes local Ca 2+ delivery from sarcoplasmic reticulum (SR) ryanodine receptors (RyR2) to the inner mitochondrial membrane (IMM) Ca 2+ 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 Ca 2+ transfer. We hypothesized that mtCU concentrated at mitochondria-SR associations would promote the effective Ca 2+ 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 Ca 2+ inputs. Furthermore, MCU immunofluorescence distribution was biased toward the mitochondria-SR interface (RyR2), and this bias was promoted by Ca 2+ 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 Ca 2+ 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.

Original languageEnglish (US)
Pages (from-to)23343-23362
Number of pages20
JournalJournal of Biological Chemistry
Volume291
Issue number44
DOIs
Publication statusPublished - Oct 28 2016
Externally publishedYes

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ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

Cite this

De la Fuente, S., Fernandez-Sanz, C., Vail, C., Agra, E. J., Holmstrom, K., Sun, J., ... Csordás, G. (2016). Strategic positioning and biased activity of the mitochondrial calcium uniporter in cardiac muscle. Journal of Biological Chemistry, 291(44), 23343-23362. https://doi.org/10.1074/jbc.M116.755496