Hypoxia-inducible factor plays significant roles in hyoid muscle type changes

Hypoxia-inducible factor (HIF-1) is a heterodimeric transcription factor responsible for cellular adaptation to hypoxic condition. In skeletal muscle, HIF-1á was found to be constitutively expressed at higher levels in glycolytic (fast-twitch) muscles compared to oxidative (slow-twitch) muscles. Previously we demonstrated fiber-types of the geniohyoid (GH) muscle change to glycolytic varieties after intermittent hypoxic (IH) exposure for 5 hrs in rats.

Objectives: To investigate potential role of HIF-1 in skeletal muscle fiber transition, we used heterogenic knock-out (Het-KO, C57/BL6 x SV129 outbreed) mice. Four wild-type (WT) and 5 Het-KO were treated under intermittent hypoxia. Four WT and 2 Het-KO were untreated control.

Methods: We measured changes in muscle tension and fatigability of the GH in vivo and differences in fiber-types using harvested single fibers.

Results: The geniohyoid muscle harvested from WT mice consists of myosin heavy chain (MHC) 2A and 2B; however, more 2A fibers than 2A/2B or 2B alone. After IH challenge for 5 hrs, a combination of MHC 2A and 2B fibers increased significantly (P < 0.05). However, fatigability of the GH muscle remained unchanged. Muscle tensions measured from the GH muscle of WT were greater than those of Het-KO mice. The geniohyoid muscle harvested from both untreated and treated Het-KO mice consisted of MHC 2A/2B, which indicates IH challenge for 5 hrs did not effect fiber composition of the GH in Het-KO mice. Fatigability and muscle tensions over 120 seconds did not differ, either.

Conclusion: We conclude that IH challenge to Het-KO did not influence composition of fiber-types and fatigability of the GH muscle in C57/BL6 x SV129 outbred mice.