title: Myoglobin and the regulation of mitochondrial respiratory chain complex IV.
abstract: CONCLUSIONS
  Mitochondrial respiration is regulated by multiple elaborate mechanisms. It has been shown that muscle specific O2 binding protein, Myoglobin (Mb), is localized in mitochondria and interacts with respiratory chain complex IV, suggesting that Mb could be a factor that regulates mitochondrial respiration. Here, we demonstrate that muscle mitochondrial respiration is improved by Mb overexpression via up-regulation of complex IV activity in cultured myoblasts; in contrast, suppression of Mb expression induces a decrease in complex IV activity and mitochondrial respiration compared with the overexpression model. The present data are the first to show the biological significance of mitochondrial Mb as a potential modulator of mitochondrial respiratory capacity.
  Mitochondria are important organelles for metabolism, and their respiratory capacity is a primary factor in the regulation of energy expenditure. Deficiencies of cytochrome c oxidase complex IV, which reduces O2 in mitochondria, are linked to several diseases, such as mitochondrial myopathy. Moreover, mitochondrial respiration in skeletal muscle tissue tends to be susceptible to complex IV activity. Recently, we showed that the muscle-specific protein myoglobin (Mb) interacts with complex IV. The precise roles of mitochondrial Mb remain unclear. Here, we demonstrate that Mb facilitates mitochondrial respiratory capacity in skeletal muscles. Although mitochondrial DNA copy numbers were not altered in Mb-overexpressing myotubes, O2 consumption was greater in these myotubes than that in mock cells (Mock vs. Mb-Flag::GFP: state 4, 1.00 ± 0.09 vs. 1.77 ± 0.34; state 3, 1.00 ± 0.29; Mock: 1.60 ± 0.53; complex 2-3-4: 1.00 ± 0.30 vs. 1.50 ± 0.44; complex IV: 1.00 ± 0.14 vs. 1.87 ± 0.27). This improvement in respiratory capacity could be because of the activation of enzymatic activity of respiratory complexes. Moreover, mitochondrial respiration was up-regulated in myoblasts transiently overexpressing Mb; complex IV activity was solely activated in Mb-overexpressing myoblasts, and complex IV activity was decreased in the myoblasts in which Mb expression was suppressed by Mb-siRNA transfection (Mb vector transfected vs. Mb vector, control siRNA transfected vs. Mb vector, Mb siRNA transfected: 0.15 vs. 0.15 vs. 0.06). Therefore, Mb enhances the enzymatic activity of complex IV to ameliorate mitochondrial respiratory capacity, and could play a pivotal role in skeletal muscle metabolism.
authors.affiliation: Faculty of Human Sciences, Kanazawa University, Kanazawa, 920-1192, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Yamada
authors.affiliation: Faculty of Health and Sports Science, Doshisha University, Kyotanabe, 610-0394, Japan.
authors.forename: Hisashi
authors.initials: H
authors.lastname: Takakura
authors.affiliation: Department of Biochemistry and Molecular Medicine, University of California Davis, Davis, 95616-8635, CA, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Jue
authors.affiliation: Faculty of Sports Sciences, Ritsumeikan University, Kusatsu, 525-8577, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Hashimoto
authors.affiliation: Faculty of Human Sciences, Kanazawa University, Kanazawa, 920-1192, Japan.
authors.forename: Rie
authors.initials: R
authors.lastname: Ishizawa
authors.affiliation: Department of Health Promotion Science, Tokyo Metropolitan University, Hachioji, 192-0397, Japan.
authors.forename: Yasuro
authors.initials: Y
authors.lastname: Furuichi
authors.affiliation: Faculty of Pharmacy, Kanazawa University, Kanazawa, 920-1192, Japan.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Kato
authors.affiliation: Faculty of Sports Sciences, Ritsumeikan University, Kusatsu, 525-8577, Japan.
authors.forename: Nobumasa
authors.initials: N
authors.lastname: Iwanaka
authors.affiliation: Faculty of Human Sciences, Kanazawa University, Kanazawa, 920-1192, Japan.
authors.forename: Kazumi
authors.initials: K
authors.lastname: Masuda
mesh_terms: D000818:Animals; D002460:Cell Line; D003576:Electron Transport Complex IV / Q000378:metabolism*; D051379:Mice; D008931:Mitochondria, Muscle / Q000378:metabolism*; D032446:Myoblasts / Q000378:metabolism; D009211:Myoglobin / Q000235:genetics / Q000378:metabolism*
chemical_list: D009211:Myoglobin; D003576:Electron Transport Complex IV