title: Negative regulation of HIF in skeletal muscle of elite endurance athletes: a tentative mechanism promoting oxidative metabolism.
abstract: The transcription factor hypoxia-inducible factor (HIF) has been suggested as a candidate for mediating training adaptation in skeletal muscle. However, recent evidence rather associates HIF attenuation with a trained phenotype. For example, a muscle-specific HIF deletion increases endurance performance, partly through decreased levels of pyruvate dehydrogenase kinase 1 (PDK-1). HIF activity is regulated on multiple levels: modulation of protein stability, transactivation capacity, and target gene availability. Prolyl hydroxylases (PHD1-3) induces HIF degradation, whereas factor-inhibiting HIF (FIH) and the histone deacetylase sirtuin-6 (SIRT6) repress its transcriptional activity. Together, these negative regulators introduce a mechanism for moderating HIF activity in vivo. We hypothesized that long-term training induces their expression. Negative regulators of HIF were explored by comparing skeletal muscle tissue from moderately active individuals (MA) with elite athletes (EA). In elite athletes, expression of the negative regulators PHD2 (MA 73.54 ± 9.54, EA 98.03 ± 6.58), FIH (MA 4.31 ± 0.25, EA 30.96 ± 7.99) and SIRT6 (MA 0.24 ± 0.07, EA 11.42 ± 2.22) were all significantly higher, whereas the response gene, PDK-1 was lower (MA 0.12 ± 0.03, EA 0.04 ± 0.01). Similar results were observed in a separate 6-wk training study. In vitro, activation of HIF in human primary muscle cell culture by PHD inactivation strongly induced PDK-1 (0.84 ± 0.12 vs 4.70 ± 0.63), providing evidence of a regulatory link between PHD activity and PDK-1 levels in a relevant model system. Citrate synthase activity, closely associated with aerobic exercise adaptation, increased upon PDK-1 silencing. We suggest that training-induced negative regulation of HIF mediates the attenuation of PDK-1 and contributes to skeletal muscle adaptation to exercise.
authors.affiliation: Karolinska Institutet, Department of Physiology and Pharmacology, Stockholm, Sweden;
authors.forename: M E
authors.initials: ME
authors.lastname: Lindholm
authors.affiliation: Karolinska Institutet, Department of Medical Laboratory Sciences and Technology, Huddinge, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Fischer
authors.affiliation: Karolinska Institutet, Department of Cell and Molecular Biology, Stockholm, Sweden; and.
authors.forename: L
authors.initials: L
authors.lastname: Poellinger
authors.affiliation: Karolinska Institutet, Department of Cell and Molecular Biology, Stockholm, Sweden; and.
authors.forename: R S
authors.initials: RS
authors.lastname: Johnson
authors.affiliation: Karolinska Institutet, Department of Medical Laboratory Sciences and Technology, Huddinge, Sweden.
authors.forename: T
authors.initials: T
authors.lastname: Gustafsson
authors.affiliation: Karolinska Institutet, Department of Physiology and Pharmacology, Stockholm, Sweden;
authors.forename: C J
authors.initials: CJ
authors.lastname: Sundberg
authors.affiliation: Karolinska Institutet, Department of Physiology and Pharmacology, Stockholm, Sweden; Karolinska Institutet, Department of Cell and Molecular Biology, Stockholm, Sweden; and Helene.rundqvist@ki.se.
authors.forename: H
authors.initials: H
authors.lastname: Rundqvist
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D056352:Athletes; D001706:Biopsy; D002478:Cells, Cultured; D003430:Cross-Sectional Studies; D004734:Energy Metabolism / Q000502:physiology*; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D051793:Hypoxia-Inducible Factor 1 / Q000235:genetics* / Q000378:metabolism*; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases / Q000378:metabolism; D066298:In Vitro Techniques; D008137:Longitudinal Studies; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D010084:Oxidation-Reduction; D010807:Physical Endurance / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D015398:Signal Transduction / Q000502:physiology; D037761:Sirtuins / Q000378:metabolism; D055815:Young Adult
chemical_list: D051793:Hypoxia-Inducible Factor 1; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; C490190:EGLN1 protein, human; C447780:EGLN2 protein, human; C488894:EGLN3 protein, human; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases; D017346:Protein Serine-Threonine Kinases; C516592:SIRT6 protein, human; D037761:Sirtuins
keywords: adaptation; aerobic exercise; gene regulation; human skeletal muscle; mitochondria