title: Raising Ca2+ in L6 myotubes mimics effects of exercise on mitochondrial biogenesis in muscle.
abstract: Skeletal muscle adapts to endurance exercise with an increase in mitochondria. Muscle contractions generate numerous potential signals. To determine which of these stimulates mitochondrial biogenesis, we are using L6 myotubes. Using this model we have found that raising cytosolic Ca2+ induces an increase in mitochondria. In this study, we tested the hypothesis that raising cytosolic Ca2+ in L6 myotubes induces increased expression of PGC-1, NRF-1, NRF-2, and mtTFA, factors that have been implicated in mitochondrial biogenesis and in the adaptation of muscle to exercise. Raising cytosolic Ca2+ by exposing L6 myotubes to caffeine for 5 h induced significant increases in PGC-1 and mtTFA protein expression and in NRF-1 and NRF-2 binding to DNA. These adaptations were prevented by dantrolene, which blocks Ca2+ release from the SR. Exposure of L6 myotubes to caffeine for 5 h per day for 5 days induced significant increases in mitochondrial marker enzyme proteins. Our results show that the adaptive response of L6 myotubes to an increase in cytosolic Ca2+ mimics the stimulation of mitochondrial biogenesis by exercise. They support the hypothesis that an increase in cytosolic Ca2+ is one of the signals that mediate increased mitochondrial biogenesis in muscle.
authors.affiliation: Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: Edward O
authors.initials: EO
authors.lastname: Ojuka
authors.forename: Terry E
authors.initials: TE
authors.lastname: Jones
authors.forename: Dong-Ho
authors.initials: DH
authors.lastname: Han
authors.forename: May
authors.initials: M
authors.lastname: Chen
authors.forename: John O
authors.initials: JO
authors.lastname: Holloszy
mesh_terms: D000818:Animals; D001596:Benzylamines / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D002460:Cell Line; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D003620:Dantrolene / Q000494:pharmacology; D003576:Electron Transport Complex IV / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015444:Exercise / Q000502:physiology*; D051268:GA-Binding Protein Transcription Factor; D006801:Humans; D008931:Mitochondria, Muscle / Q000187:drug effects / Q000378:metabolism*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D051265:NF-E2-Related Factor 1; D051266:Nuclear Respiratory Factor 1; D051264:Nuclear Respiratory Factors; D013449:Sulfonamides / Q000494:pharmacology; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D000096926:Benzenesulfonamides
chemical_list: D001596:Benzylamines; D002110:Caffeine; D002118:Calcium; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D004268:DNA-Binding Proteins; D003620:Dantrolene; D003576:Electron Transport Complex IV; D004791:Enzyme Inhibitors; D051268:GA-Binding Protein Transcription Factor; D051265:NF-E2-Related Factor 1; D051266:Nuclear Respiratory Factor 1; D051264:Nuclear Respiratory Factors; D013449:Sulfonamides; D015534:Trans-Activators; D014157:Transcription Factors; C495633:NRF1 protein, human; C111264:peroxisome-proliferator-activated receptor-gamma coactivator-1; C072105:KN 93; D000096926:Benzenesulfonamides