TY - JOUR
T1 - Strategic positioning and biased activity of the mitochondrial calcium uniporter in cardiac muscle
AU - De la Fuente, Sergio
AU - Fernandez-Sanz, Celia
AU - Vail, Caitlin
AU - Agra, Elorm J.
AU - Holmstrom, Kira
AU - Sun, Junhui
AU - Mishra, Jyotsna
AU - Williams, Dewight
AU - Finkel, Toren
AU - Murphy, Elizabeth
AU - Joseph, Suresh K.
AU - Sheu, Shey Shing
AU - Csordás, György
PY - 2016/10/28
Y1 - 2016/10/28
N2 - 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.
AB - 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.
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U2 - 10.1074/jbc.M116.755496
DO - 10.1074/jbc.M116.755496
M3 - Article
C2 - 27637331
AN - SCOPUS:84994034038
SN - 0021-9258
VL - 291
SP - 23343
EP - 23362
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 44
ER -