title: Overexpression of ryanodine receptor type 1 enhances mitochondrial fragmentation and Ca2+-induced ATP production in cardiac H9c2 myoblasts.
abstract: Ca(+) influx to mitochondria is an important trigger for both mitochondrial dynamics and ATP generation in various cell types, including cardiac cells. Mitochondrial Ca(2+) influx is mainly mediated by the mitochondrial Ca(2+) uniporter (MCU). Growing evidence also indicates that mitochondrial Ca(2+) influx mechanisms are regulated not solely by MCU but also by multiple channels/transporters. We have previously reported that skeletal muscle-type ryanodine receptor (RyR) type 1 (RyR1), which expressed at the mitochondrial inner membrane, serves as an additional Ca(2+) uptake pathway in cardiomyocytes. However, it is still unclear which mitochondrial Ca(2+) influx mechanism is the dominant regulator of mitochondrial morphology/dynamics and energetics in cardiomyocytes. To investigate the role of mitochondrial RyR1 in the regulation of mitochondrial morphology/function in cardiac cells, RyR1 was transiently or stably overexpressed in cardiac H9c2 myoblasts. We found that overexpressed RyR1 was partially localized in mitochondria as observed using both immunoblots of mitochondrial fractionation and confocal microscopy, whereas RyR2, the main RyR isoform in the cardiac sarcoplasmic reticulum, did not show any expression at mitochondria. Interestingly, overexpression of RyR1 but not MCU or RyR2 resulted in mitochondrial fragmentation. These fragmented mitochondria showed bigger and sustained mitochondrial Ca(2+) transients compared with basal tubular mitochondria. In addition, RyR1-overexpressing cells had a higher mitochondrial ATP concentration under basal conditions and showed more ATP production in response to cytosolic Ca(2+) elevation compared with nontransfected cells as observed by a matrix-targeted ATP biosensor. These results indicate that RyR1 possesses a mitochondrial targeting/retention signal and modulates mitochondrial morphology and Ca(2+)-induced ATP production in cardiac H9c2 myoblasts.
authors.affiliation: Center for Translational Medicine, Department of Medicine, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania;
authors.forename: Jin
authors.initials: J
authors.lastname: O-Uchi
authors.forename: Bong Sook
authors.initials: BS
authors.lastname: Jhun
authors.forename: Stephen
authors.initials: S
authors.lastname: Hurst
authors.forename: Sara
authors.initials: S
authors.lastname: Bisetto
authors.forename: Polina
authors.initials: P
authors.lastname: Gross
authors.forename: Ming
authors.initials: M
authors.lastname: Chen
authors.forename: Sarah
authors.initials: S
authors.lastname: Kettlewell
authors.forename: Jongsun
authors.initials: J
authors.lastname: Park
authors.forename: Hideto
authors.initials: H
authors.lastname: Oyamada
authors.forename: Godfrey L
authors.initials: GL
authors.lastname: Smith
authors.forename: Takashi
authors.initials: T
authors.lastname: Murayama
authors.forename: Shey-Shing
authors.initials: SS
authors.lastname: Sheu
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D002460:Cell Line; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D032386:Myoblasts, Cardiac / Q000378:metabolism*; D051381:Rats; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000378:metabolism*
chemical_list: D019837:Ryanodine Receptor Calcium Release Channel; D000255:Adenosine Triphosphate; D002118:Calcium
keywords: fluorescence resonance energy transfer; mitochondria; mitochondrial Ca2+ uniporter; mitochondrial morphology; ryanodine receptor type 1