The Dual Role of Interleukin-6 in the Pathophysiology of Skeletal Muscle: Mechanisms, Challenges, and Therapeutic Prospects.

Interleukin-6 (IL-6) is a cytokine with multiple biological effects. It plays a complex and seemingly paradoxical central role in both the physiological homeostasis and pathological processes of skeletal muscle. Under physiological conditions, particularly during acute exercise, IL-6 produced and secreted by the contracting skeletal muscle itself acts as an important "myokine." It operates in an autocrine, paracrine, or endocrine manner to regulate systemic energy metabolism, insulin sensitivity, muscle regeneration, and adaptive hypertrophy. This function is crucial for the health benefits conferred by exercise. However, under various pathological conditions-such as cancer cachexia, sepsis, muscular dystrophy, denervation, disuse atrophy, and chronic inflammatory diseases-persistently elevated systemic or local IL-6 levels become a key mediator driving skeletal muscle atrophy, metabolic disorders, and functional decline. This review systematically elaborates on the dual role of IL-6 in skeletal muscle. It provides an in-depth analysis of its downstream signaling pathways (e.g., JAK/STAT, gp130, MAPK, PI3K-Akt) and upstream regulatory mechanisms (e.g., the Piezo1/KLF15 axis, calcium signaling, mitochondrial function, oxidative stress). A particular focus is placed on discussing the distinct biological effects of classical IL-6 signaling versus trans-signaling. Furthermore, we address current challenges in research and practice, including the cell specificity of IL-6 signaling, the complexity of its temporal regulation, the definition of physiological versus pathological concentrations, discrepancies between animal models and human diseases, and the plasticity of its function across different pathological contexts. Finally, this review explores the potential of targeting the IL-6 signaling pathway as a therapeutic strategy for skeletal muscle atrophy and related metabolic diseases. Potential interventions include IL-6/IL-6R monoclonal antibodies, JAK/STAT inhibitors, gp130 modulators, exercise interventions, and nutritional strategies. This aims to provide a theoretical foundation and novel perspectives for future translational research and clinical interventions.