Low-Intensity Pulsed Ultrasound Prevents Hypoxia-Induced Skeletal Muscle Atrophy in Association with HIF-1α Suppression.

Abstract

Objectives: Hypoxia is a known contributor to muscle atrophy. While low-intensity pulsed ultrasound (LIPUS) has been shown to promote myogenic cell proliferation and differentiation, its effect on hypoxia-induced muscle atrophy remains unclear. This study aimed to investigate whether LIPUS can alleviate hypoxia-induced muscle atrophy and to elucidate the underlying molecular mechanisms.

Methods: In vitro, C2C12 myoblasts were exposed to chemical hypoxia (CoCl₂) and treated with LIPUS at varying intensities to determine the optimal parameter. In vivo, mice were housed in a 10% hypoxic chamber and received 30 mW/cm² LIPUS irradiation on quadriceps (anterior thigh) and the triceps surae (posterior calf muscles). Muscle mass, cross-sectional area, strength, and molecular markers (HIF-1α, MSTN, AKT/mTOR, mitochondrial dynamics) were assessed. Pharmacologic inhibition of HIF-1α was used to verify its regulatory role in MSTN expression.

Results: LIPUS at 30 mW/cm² was identified as the most effective intensity for reversing chemical hypoxia induced inhibition of myoblast proliferation. In physically hypoxic mice, LIPUS significantly attenuated the reduction in muscle fiber cross-sectional area, muscle mass, and strength. Mechanistically, LIPUS suppressed HIF-1α and MSTN expression, reduced mitochondrial fission proteins while increasing fusion proteins, and upregulated the AKT/mTOR anabolic pathway. In vitro, graded inhibition of HIF-1α led to a corresponding reduction in MSTN expression. Notably, correlation analysis revealed a significant positive association between HIF-1α and MSTN protein levels, further supporting their correlative relationship under chemically hypoxic conditions.

Conclusions: LIPUS ameliorates hypoxia-induced muscle atrophy, along with the downregulation of HIF-1α, which coordinately regulates mitochondrial dynamics-related proteins and the AKT/mTOR pathway. These findings provide experimental evidence for LIPUS as a potential noninvasive physical therapy for hypoxia-related muscle atrophy.