27-Hydroxycholesterol inhibits muscle cell viability via mitochondrial dysfunction: Protective role of ROS-induced HIF-1α.

The oxysterol 27-hydroxycholesterol (27OHC), which is widely distributed in various tissues and circulation, plays a notable role in pathological processes, such as including breast cancer, atherosclerosis, and neurodegenerative diseases. Although these processes are closely linked to muscle pathophysiology, the effects of 27OHC on metabolic changes associated with muscular atrophy and sarcopenia remain poorly understood. In this study, we demonstrated that 27OHC decreased skeletal muscle viability by activating pro-apoptotic signaling pathways. RNA sequencing revealed that 767 and 989 genes were upregulated and downregulated, respectively, in 27OHC-treated myoblasts. Upregulated genes were associated with hypoxia-inducible factor 1-alpha response, whereas downregulated genes were commonly involved in the phosphoinositide 3-kinase pathway and muscle differentiation process. Myoblast cell death induced by 27OHC was mediated by generation of reactive oxygen species followed by mitochondrial morphological impairments and disruption of mitochondrial membrane potential (ΔΨm). Moreover, 27OHC reduced mitochondrial gene expression via glycogen synthase kinase-3 beta activation, ultimately leading to increased mitochondrial ROS. Concurrently, hypoxia-inducible factor 1-alpha induction upon 27OHC exposure activated cellular defense mechanisms to mitigate oxidative damage. In addition, a significant reduction was observed in the expression of genes involved in myotube differentiation and fusion index following 27OHC treatment, and hypoxia-inducible factor 1-alpha knockdown further aggravated the impairment of tube formation. Furthermore, mice treated with 27OHC exhibited reduced exercise endurance, decreased muscle cross-sectional area, and impaired muscle recovery following barium chloride-induced injury. As plasma levels of 27OHC are increased in elderly individuals, our findings suggest that pharmacological inhibition of 27OHC generation could be a therapeutic strategy to treat age-related muscle atrophy.