title: Mitochondrial content and distribution changes specific to mouse diaphragm after chronic normobaric hypoxia.
abstract: Chronic hypoxia reduces aerobic capacity (mitochondrial content) in limb skeletal muscles, and one of the causes seems to be decreased physical activity. Diaphragm and other respiratory muscles, however, may have a different pattern of adaptation as hypoxia increases the work of breathing. Thus, we hypothesized that chronic hypoxia would not reduce mitochondrial content in mouse diaphragm. Adult male C57BL/6J mice were kept in normoxia (Fi(O(2)) = 21%, control) or normobaric hypoxia (Fi(O(2)) = 10%, hypoxia) for 1, 2, and 4 wk. Mice were then killed, and the diaphragm and gastrocnemius muscles collected for analysis. In the diaphragm, cytochrome c oxidase histochemistry showed less intense staining in the hypoxia group. The total content of subunits from the electron transport chain, pyruvate dehydrogenase kinase 1 (PDK1), and voltage-dependent anion channel 1 (VDAC1) was evaluated by Western blot. These proteins decreased by 25-30% after 4 wk of hypoxia (P < 0.05 vs. control for all comparisons), matching a comparable decrease in diaphragmatic mitochondrial volume density (control 33.6 +/- 5.5% vs. hypoxia 26.8 +/- 6.7%, P = 0.013). Mitochondrial volume density or protein content did not change in gastrocnemius after hypoxia. Hypoxia decreased the content of peroxisome proliferator-activated receptor gamma (PPARgamma) and PPARgamma cofactor 1-alpha (PGC-1alpha) in diaphragm but not in gastrocnemius. PGC-1alpha mRNA levels in diaphragm were also reduced with hypoxia. BCL2/adenovirus E1B interacting protein 3 (BNIP-3) mRNA levels were upregulated after 1 and 2 wk of hypoxia in diaphragm and gastrocnemius, respectively; BNIP-3 protein content increased only in the diaphragm after 4 wk of hypoxia. Contrary to our hypothesis, these results show that chronic hypoxia decreases mitochondrial content in mouse diaphragm, despite the increase in workload. A combination of reduced mitochondrial biogenesis and increased mitophagy seems to be responsible for the decrease in mitochondrial content in the mouse diaphragm after hypoxia.
authors.affiliation: Department of Physiology, University of Kentucky, Lexington, KY 40536, USA.
authors.forename: Jorge L
authors.initials: JL
authors.lastname: Gamboa
authors.forename: Francisco H
authors.initials: FH
authors.lastname: Andrade
mesh_terms: D000818:Animals; D001274:Atmospheric Pressure; D001343:Autophagy / Q000502:physiology; D015153:Blotting, Western; D002908:Chronic Disease; D003964:Diaphragm / Q000201:enzymology / Q000502:physiology*; D003576:Electron Transport Complex IV / Q000378:metabolism; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008854:Microscopy, Electron; D008928:Mitochondria / Q000201:enzymology / Q000502:physiology* / Q000648:ultrastructure; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism; D018482:Muscle, Skeletal / Q000201:enzymology / Q000502:physiology; D010100:Oxygen / Q000494:pharmacology; D047495:PPAR gamma / Q000378:metabolism; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D012333:RNA, Messenger / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors
chemical_list: C508686:BNip3 protein, mouse; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D047495:PPAR gamma; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; C485290:Ppargc1a protein, mouse; D012333:RNA, Messenger; D015534:Trans-Activators; D014157:Transcription Factors; D003576:Electron Transport Complex IV; D010100:Oxygen