Skeletal muscles secrete various factors, such as proteins/peptides, nucleotides, and metabolites, which are referred to as myokines. Many of these factors are transported into extracellular bodily fluids in a free or protein-bound form. Furthermore, several secretory factors have been shown to be wrapped up by small vesicles, particularly exosomes, secreted into circulation, and subsequently regulate recipient cells. Thus, exosome contents can be recognized as myokines. In recipient cells, proteins, microRNAs, and metabolites in exosomes can regulate the expression and activity of target proteins associated with nutrient metabolism and immune function. The levels of circulating exosomes and their contents are altered in muscle disorders and metabolic-related states, such as metabolic dysfunction, sarcopenia, and physical fitness. Therefore, such circulating factors could mediate various interactions between skeletal muscle and other organs and may be useful as biomarkers reflecting physiological and pathological states associated with muscular function. Here, this review summarizes secretory regulation of muscle-derived exosomes. Their metabolic and immunological roles and the significance of their circulating levels are also discussed.

骨骼肌分泌各种因子，例如蛋白质/肽、核苷酸和代谢物，它们被称为肌因子。许多这些因子以游离或蛋白质结合的形式被转运到细胞外体液中。此外，一些分泌因子已被证明被小囊泡包裹，特别是外泌体，分泌到循环中，随后调节受体细胞。因此，外泌体内容物可以被识别为肌因子。在受体细胞中，外泌体中的蛋白质、微小RNA和代谢物可以调节与营养代谢和免疫功能相关的靶蛋白的表达和活性。循环外泌体的水平及其含量在肌肉疾病和代谢相关状态下发生变化，例如代谢功能障碍、肌肉减少症和身体健康。所以，这种循环因子可以介导骨骼肌和其他器官之间的各种相互作用，并可用作反映与肌肉功能相关的生理和病理状态的生物标志物。在这里，这篇综述总结了肌肉来源的外泌体的分泌调节。还讨论了它们的代谢和免疫学作用以及它们的循环水平的重要性。