Effects of Hypobaric and Normobaric Hypoxia on Myogenic and Proteolytic Gene Expression in Humans

Current research suggests that physiological responses to hypobaric and normobaric hypoxia may be different. It is unknown if these differences extend to skeletal muscle and the transcriptional responses regulating muscle mass. PURPOSE: To determine the effects of hypobaric and normobaric hypoxia on myogenenic and proteolytic gene expression. METHODS: Recreationally trained subjects (n = 15; age = 24 ± 4 y; VO2max = 3.60 ± 0.83 L · min-1) completed three trials of 60-min cycling at 70% of Wmax followed by 4-h recovery at ambient conditions (975 m), hypobaric hypoxia (4,420 m), and normobaric hypoxia (4,420 m). A muscle biopsy was taken each trial from the vastus lateralis before exercise and at the end of the 4-h recovery period for gene expression analysis (RT-qPCR). RESULTS: There were no differences in the myogenic gene expression of MYOD, MYF-5, or MYOG between trials (p \u3e 0.05). MYF-6 was higher after exercise (p \u3c 0.05) regardless of trial. MSTN decreased pre- to post-exercise in all conditions (p \u3c 0.001) and was lower in hypobaric hypoxia compared to control and normobaric conditions (p \u3c 0.05). There were no differences in the expression of atrogin-1 with exercise or between trials (p \u3e 0.05). However, FOXO3 and MuRF-1 increased with exercise (p \u3c 0.05) but were not different between conditions (p \u3e 0.05). CONCLUSION: These data indicate that differences in hypobaric and normobaric hypoxia recovery from exercise does not affect myogenic and proteolytic gene expression with the exception of a modest attenuation of myostatin in hypobaric hypoxia