Journal
AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY INTEGRATIVE AND COMPARATIVE PHYSIOLOGY
Volume 307, Issue 3, Pages R248-R255Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpregu.00036.2013
Keywords
aerobic exercise; human skeletal muscle; gene regulation; mitochondria; adaptation
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Funding
- Swedish Research Council
- Swedish National Centre for Research in Sports
- Swedish Heart-Lung Association Foundation
- Fraenckel Foundation
- Magn. Bergvall Foundation
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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.
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