Pdk-1/Hif-1α Ratios Define Geniohyoid Muscle Fiber Phenotypes

Author(s): Gary Lau, Daniel D. Nguyen, Ronal M. Harper, Eung-Kwpn Pae

Background: The relationships between muscle fiber-type expression and the ratio between pyruvate dehydrogenase kinase (Pdk)-1 and hypoxia inducible factor (Hif)-1α was investigated using Hif-1α heterozygous knockout (“Het”) mice. Because Pdk-1/Hif-1α ratio changes could alter skeletal muscle phenotypes following brief sustained hypoxia as demonstrated earlier, we aimed to examine if the genetically down-regulated Hif-1α level influences skeletal muscle phenotypes in an intermittent hypoxic (IH) condition. This query is important because upper airway dilating muscles in patients with obstructive sleep apnea who frequently exposed to IH conditions tend to have an increased Type II fibers with increased Hif-1α levels. Methods: Here, we examined whether Pdk-1/Hif-1 ratios play a role in Het Hif-1α KO mice when exposed to brief IH (altering ambient oxygen levels between 10.3% and 20.8% every 240s). We performed single fiber analysis and Western blots on the harvested geniohyoid (GH) muscle after IH treatment for 5h. Results: Wild-type (WT) GH muscles in mice contain muscle fibers composed of myosin heavy chain (MyHC) IIa and MyHC IIa/IIb proteins, as opposed to the GH muscle in Het mice expressing MyHC IIa, IIa/IIb as well as IIb (p<0.001). Fiber composition in WT GH showed no significant changes under IH. In Het mice, a higher proportion of MyHC IIb fibers were expressed, as the number of IIa fibers decreased (p< 0.05) in IH. Pdk-1/Hif-1α ratios in the Het-GH muscle did not alter significantly after 5h IH exposure. Conclusion: The increased numbers of glycolytic fibers with high Pdk-1/Hif-1 ratios resulted in Het-GH muscles being able to avoid excessive ‘oxidative stress’ under IH. However, Het-GH muscles might have become more fatigable after IH exposure, compared to WT mice, since Het-GH muscles after IH contain higher numbers of MyHC IIb-containing glycolytic fibers that are more fatigable in nature than WT-GH muscles.

Fatigability, Geniohyoid Muscle, Hif-1α, Hypoxia, Myosin Heavy Chains, Pdk-1

1. Pramsohler S, Schilz R, Patzak A, Rausch L, Netzer NC. Periodic breathing in healthy young adults in normobaric hypoxia equivalent to 3500 m, 4500 m, and 5500 m altitude. Sleep Breath 2019;23:703-709. doi: 10.1007/s11325-019-01829-z.
2. Pham LV, Meinzen C, Arias RS, Schwartz NG, Rattner A, Miele CH, Smith PL, Schneider H, Miranda JJ, Gilman RH, Polotsky VY, Checkley W, Schwartz AR. Cross-Sectional Comparison of Sleep-Disordered Breathing in Native Peruvian Highlanders and Lowlanders. High Alt Med Biol 2017;18: 11-19. https://doi: 10.1089/ham.2016.0102
3. Skelly JR, Rowan SC, Jones JF, O'Halloran KD. Upper airway dilator muscle weakness following intermittent and sustained hypoxia in the rat: effects of a superoxide scavenger. Physiol Res 2013;62: 187-196
4. Rolan T. Neurology and altitude illness. Neurol Clin Pract 2015;5: 102-107. https://doi: 10.1212/CPJ.0000000000000100
5. Pae EK, Wu J, Nguyen D, Monti R, Harper RM. Geniohyoid muscle properties and myosin heavy chain composition are altered after short-term intermittent hypoxic exposure. J Appl Physiol (1985) 2005;98: 889-894
6. Sériès FJ, Simoneau SA, St Pierre S, Marc I. Characteristics of the genioglossus and musculus uvulae in sleep apnea hypopnea syndrome and in snorers. Am J Respir Crit Care Med 1996;153: 1870-1874
7. Nguyen DD, Kim G, Pae EK. Modulation of Muscle Fiber Compositions in Response to Hypoxia via Pyruvate Dehydrogenase Kinase-1. Front Physiol 2016;7: 604. https://doi.org/10.3389/fphys.2016.00604
8. Mason S, Johnson RS. The role of HIF-1 in hypoxic response in the skeletal muscle. Adv Exp Med Biol 2007;618: 229-244.
9. Lindholm ME, Fischer H, Poellinger L, Johnson RS, Gustafsson T, Sundberg CJ, Rundqvist H. Negative regulation of HIF in skeletal muscle of elite endurance athletes: a tentative mechanism promoting oxidative metabolism. Am J Physiol Regul Integr Comp Physiol 2014;307: R248-255. https://doi: 10.1152/ajpregu.00036.2013
10. Hoppeler H, Vogt M. Muscle tissue adaptations to hypoxia. J Exp Biol 2001;204: 3133-3139
11. Horscraft JA, Kotwica AO, Laner V, et al. Metabolic basis to sherpa altitude adaptation. Proc Natl Acad Sci U S A. 2017;114: 6382-6387. doi: 10.1073/pnas.1700527114
12. Favier FB, Britto FA, Freyssenet DG, Bigard XA, Benoit H. HIF-1-driven skeletal muscle adaptations to chronic hypoxia: molecular insights into muscle physiology. Cell Mol Life Sci 2015 72(24):4681-96. doi: 10.1007/s00018-015-2025-9
13. Kim JW, Tchernyshyov I, Semenza GL, Dang CV. HIF-1-mediated expression of pyruvate dehydrogenase kinase: a metabolic switch required for cellular adaptation to hypoxia. Cell Metab 2006;3: 177-185.
14. Benderro GF, Gamble J, Schiefer MA, Baskin JZ, Hernandez Y, Strohl KP. Hypoglossal nerve stimulation in a pre-clinical anesthetized rabbit model relevant to OSA. Respir Physiol Neurobiol 2018;250: 31-38. https://doi: 10.1016/j.resp.2018.01.015
15. Van de Graaff WB, Gottfried SB, Mitra J, van Lunteren E, Cherniack NS, Strohl KP. Respiratory function of hyoid muscles and hyoid arch. J Appl Physiol Respir Environ Exerc Physiol. 1984;57: 197-204.
16. Iyer NV, Kotch LE, Agani F, Leung SW, Laughner E, Wenger RH, Gassmann M, Gearhart JD, Lawler AM, Yu AY, Semenza GL. Cellular and developmental control of O2 homeostasis by hypoxia-inducible factor 1 alpha. Genes Dev 1998;12: 149-162.
17. McSharry D, O'Connor C, McNicholas T, Langran S, O'Sullivan M, Lowery M, McNicholas WT. Genioglossus fatigue in obstructive sleep apnea. Respir Physiol Neurobiol 2012;183: 59-66. https://doi: 10.1016/j.resp.2012.05.024
18. Wiegand DA, Latz B, Zwillich CW, Wiegand L. Geniohyoid muscle activity in normal men during wakefulness and sleep. J Appl Physiol (1985) 1990;69: 1262-1269.
19. Mason SD, Howlett RA, Kim MJ, Olfert IM, Hogan MC, McNulty W, Hickey RP, Wagner PD, Kahn CR, Giordano FJ, Johnson RS. Loss of skeletal muscle HIF-1alpha results in altered exercise endurance. PLoS Biol 2004;2: e288.
20. Mason SD, Rundqvist H, Papandreou I, Duh R, McNulty WJ, Howlett RA, Olfert IM, Sundberg CJ, Denko NC, Poellinger L, Johnson RS. HIF-1alpha in endurance training: suppression of oxidative metabolism. Am J Physiol Regul Integr Comp Physiol 2007;293: R2059-R2069.
21. Baldwin KM, Haddad F, Pandorf CE, Roy RR, Edgerton VR. Alterations in muscle mass and contractile phenotype in response to unloading models: role of transcriptional/pretranslational mechanisms. Front Physiol. 2013;4: 284. https://doi: 10.3389/fphys.2013.00284