Differential impact of sex on regulation of skeletal muscle mitochondrial function and protein homeostasis by hypoxia‐inducible factor‐1α in normoxia

• Published in: The Journal of physiology 2024-06, Vol.602 (12), p.2763-2806
• Main Authors: Welch, Nicole, Mishra, Saurabh, Bellar, Annette, Kannan, Pugazhendhi, Gopan, Amrit, Goudarzi, Maryam, King, Jasmine, Luknis, Mathew, Musich, Ryan, Agrawal, Vandana, Bena, James, Koch, Cameron J., Li, Ling, Willard, Belinda, Shah, Yatrik M., Dasarathy, Srinivasan
• Format: Article
• Language: English
• Subjects: Animals; Biological analysis; Cell cycle; Cellular stress response; Electron transport chain; Female; Gas chromatography; Homeostasis; Hypoxia; hypoxia inducible factor‐1 alpha; Hypoxia-Inducible Factor 1, alpha Subunit - genetics; Hypoxia-Inducible Factor 1, alpha Subunit - metabolism; Intermediates; Male; Mass spectroscopy; Mice; Mice, Inbred C57BL; Mitochondria; Mitochondria, Muscle - metabolism; Muscle Fibers, Skeletal - metabolism; Muscle, Skeletal - metabolism; muscle‐specific deletion; Musculoskeletal system; Myotubes; normoxia; Oxygen consumption; Oxygen Consumption - physiology; physiology; Protein biosynthesis; Proteins; Proteolysis; Senescence; Sex; Sex Characteristics; sex‐differences; Signal transduction; Skeletal muscle; Titration; Tricarboxylic acid cycle
• ISSN: 0022-3751; 1469-7793; 1469-7793
• DOI: 10.1113/JP285339

Hypoxia‐inducible factor (HIF)‐1α is continuously synthesized and degraded in normoxia. During hypoxia, HIF1α stabilization restricts cellular/mitochondrial oxygen utilization. Cellular stressors can stabilize HIF1α even during normoxia. However, less is known about HIF1α function(s) and sex‐specific effects during normoxia in the basal state. Since skeletal muscle is the largest protein store in mammals and protein homeostasis has high energy demands, we determined HIF1α function at baseline during normoxia in skeletal muscle. Untargeted multiomics data analyses were followed by experimental validation in differentiated murine myotubes with loss/gain of function and skeletal muscle from mice without/with post‐natal muscle‐specific Hif1a deletion (Hif1amsd). Mitochondrial oxygen consumption studies using substrate, uncoupler, inhibitor, titration protocols; targeted metabolite quantification by gas chromatography–mass spectrometry; and post‐mitotic senescence markers using biochemical assays were performed. Multiomics analyses showed enrichment in mitochondrial and cell cycle regulatory pathways in Hif1a deleted cells/tissue. Experimentally, mitochondrial oxidative functions and ATP content were higher with less mitochondrial free radical generation with Hif1a deletion. Deletion of Hif1a also resulted in higher concentrations of TCA cycle intermediates and HIF2α proteins in myotubes. Overall responses to Hif1amsd were similar in male and female mice, but changes in complex II function, maximum respiration, Sirt3 and HIF1β protein expression and muscle fibre diameter were sex‐dependent. Adaptive responses to hypoxia are mediated by stabilization of constantly synthesized HIF1α. Despite rapid degradation, the presence of HIF1α during normoxia contributes to lower mitochondrial oxidative efficiency and greater post‐mitotic senescence in skeletal muscle. In vivo responses to HIF1α in skeletal muscle were differentially impacted by sex. Key points Hypoxia‐inducible factor ‐1α (HIF1α), a critical transcription factor, undergoes continuous synthesis and proteolysis, enabling rapid adaptive responses to hypoxia by reducing mitochondrial oxygen consumption. In mammals, skeletal muscle is the largest protein store which is determined by a balance between protein synthesis and breakdown and is sensitive to mitochondrial oxidative function. To investigate the functional consequences of transient HIF1α expression during normoxia in the basal state, myotubes and skeleta