title: Prolyl hydroxylase domain 2 deficiency promotes skeletal muscle fiber-type transition via a calcineurin/NFATc1-dependent pathway.
abstract: BACKGROUND
  Hypoxia exposure is known to induce an alteration in skeletal muscle fiber-type distribution mediated by hypoxia-inducible factor (HIF)-α. The downstream pathway of HIF-α leading to fiber-type shift, however, has not been elucidated. The calcineurin pathway is one of the pathways responsible for slow muscle fiber transition. Because calcineurin pathway is activated by vascular endothelial growth factor (VEGF), one of the factors induced by HIF-1α, we hypothesized that the stabilization of HIF-1α may lead to slow muscle fiber transition via the activation of calcineurin pathway in skeletal muscles. To induce HIF-1α stabilization, we used a loss of function strategy to abrogate Prolyl hydroxylase domain protein (PHD) 2 responsible for HIF-1α hydroxylation making HIF-1α susceptible to ubiquitin dependent degradation by proteasome. The purpose of this study was therefore to examine the effect of HIF-1α stabilization in PHD2 conditional knockout mouse on skeletal muscle fiber-type transition and to elucidate the involvement of calcineurin pathway on muscle fiber-type transition.
  
  
  RESULTS
  PHD2 deficiency resulted in an increased capillary density in skeletal muscles due to the induction of vascular endothelial growth factor. It also elicited an alteration of skeletal muscle phenotype toward the type I fibers in both of the soleus (35.8 % in the control mice vs. 46.7 % in the PHD2-deficient mice, p < 0.01) and the gastrocnemius muscle (0.94 vs. 1.89 %, p < 0.01), and the increased proportion of type I fibers appeared to correspond to the area of increased capillary density. In addition, calcineurin and nuclear factor of activated T cell (NFATc1) protein levels were increased in both the gastrocnemius and soleus muscles, suggesting that the calcineurin/NFATc1 pathway was responsible for the type I fiber transition regardless of PGC-1α, which responded minimally to PHD2 deficiency. Indeed, we found that tacrolimus (FK-506), a calcineurin inhibitor, successfully suppressed slow fiber-type formation in PHD2-deficient mice.
  
  
  CONCLUSIONS
  Taken together, stabilized HIF-1α induced by PHD2 conditional knockout resulted in the transition of muscle fibers toward a slow fiber type via a calcineurin/NFATc1 signaling pathway. PHD2 conditional knockout mice may serve as a model for chronic HIF-1α stabilization as in mice exposed to low oxygen concentration.
authors.affiliation: Department of Medicine & Science in Sport & Exercise, Tohoku University School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575 Japan.
authors.forename: Junchul
authors.initials: J
authors.lastname: Shin
authors.affiliation: Department of Medicine & Science in Sport & Exercise, Tohoku University School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575 Japan.
authors.forename: Aki
authors.initials: A
authors.lastname: Nunomiya
authors.affiliation: Department of Medicine & Science in Sport & Exercise, Tohoku University School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575 Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Kitajima
authors.affiliation: Division of Molecular Medicine and Therapy, United Centers for Advanced Research and Translational Medicine (ART), Tohoku University School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575 Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Dan
authors.affiliation: Division of Molecular Medicine and Therapy, United Centers for Advanced Research and Translational Medicine (ART), Tohoku University School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575 Japan.
authors.forename: Toshio
authors.initials: T
authors.lastname: Miyata
authors.affiliation: Department of Medicine & Science in Sport & Exercise, Tohoku University School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575 Japan.|Division of Biomedical Engineering for Health and Welfare, Tohoku University Graduate School of Biomedical Engineering, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575 Japan.|Center for Sports Medicine and Science, United Centers for Advanced Research and Translational Medicine (ART), Tohoku University School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575 Japan.
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Nagatomi
mesh_terms: D000818:Animals; D019703:Calcineurin / Q000378:metabolism*; D065095:Calcineurin Inhibitors / Q000494:pharmacology; D002196:Capillaries / Q000378:metabolism; D015687:Cell Hypoxia; D002460:Cell Line; D005838:Genotype; D006900:Hydroxylation; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases / Q000172:deficiency* / Q000235:genetics; D018345:Mice, Knockout; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects / Q000201:enzymology*; D018482:Muscle, Skeletal / Q000098:blood supply / Q000187:drug effects / Q000201:enzymology*; D050778:NFATC Transcription Factors / Q000378:metabolism*; D018919:Neovascularization, Physiologic; D010641:Phenotype; D055550:Protein Stability; D015398:Signal Transduction / Q000187:drug effects; D016559:Tacrolimus / Q000494:pharmacology; D013997:Time Factors; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
chemical_list: D065095:Calcineurin Inhibitors; C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D050778:NFATC Transcription Factors; C494005:Nfatc1 protein, mouse; D042461:Vascular Endothelial Growth Factor A; C467480:vascular endothelial growth factor A, mouse; C490189:Egln1 protein, mouse; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases; D019703:Calcineurin; D016559:Tacrolimus
keywords: Calcineurin; Hypoxia-inducible factor α; NFATc1; Prolyl hydroxylate domain protein 2; Type I muscle fiber