Skeletal muscle, the largest organ in the human body, is primarily responsible for locomotion through the contraction and force generation required to pull bones. Sarcopenia is a disease associated with aging, characterized by the loss of muscle mass, strength and function, and has become an important global health problem. Sarcopenia is mainly manifested by muscle atrophy, which can lead to the thinning or even disappearance of muscle fibers. However, the pathological state of muscle fiber thinning has not been clearly reported, and the specific manifestations are still unclear. Muscle atrophy with sarcopenia not only damages motor function, but also increases the risk of falls and fractures, affects daily activities and increases mortality. The pathogenesis of skeletal muscle atrophy includes decreased regeneration ability of muscle satellite cells, decreased protein synthesis and accelerated degradation of myotube cells (Chen et al., 2024).

Dexamethasone, a synthetic glucocorticoid, is highly lipophilic, allowing it to readily diffuse across cell membranes. Existing research indicates that dexamethasone activates glucocorticoid receptors in the cytoplasm through a binding mechanism. The activated glucocorticoid receptors then associate with other transcription factors and translocate to the nucleus. Within the nucleus, they bind to specific DNA sequences, regulating the transcription of associated genes. This process enhances the expression of muscle atrophy factors MuRF1 and MAFbx. Furthermore, by activating autophagy and the ubiquitin-proteasome system, dexamethasone increases the rate of protein degradation, thereby further promoting the degradation of muscle proteins.

MuRF1 is a protein responsible for marking other proteins for degradation through ubiquitination, closely related to muscle atrophy and weakness in conditions such as aging and cancer cachexia. Another protein involved in muscle protein degradation, MAFbx, also leads to muscle atrophy and weakness in certain cases. The FOXO signaling pathway is regulated by FOXO proteins and plays an important role in muscle quality and function by regulating muscle protein degradation. FOXO3, as a member of the forkhead transcription factor family, is involved in various physiological processes (Hah et al., 2022). When FOXO3 is activated, it induces the expression of MuRF1 and MAFbx, triggering muscle protein degradation (Jia et al., 2022). Therefore, by regulating muscle protein degradation, MuRF1, MAFbx, and the FOXO signaling pathway are closely related to muscle quality and function, with elevated levels typically associated with muscle atrophy and weakness (Hah et al., 2023).

Exosomes are a subtype of extracellular vesicles (EVs), typically ranging from 30 to 150 nanometers in diameter, formed from endogenous endosomal processes and subsequently released into the extracellular space. They contain a variety of bioactive molecules, including proteins, lipids, and nucleic acids, and can mediate intercellular signaling through binding to target cells or by being internalized (Che et al., 2021).

Accumulating evidence has demonstrated that stem cell-derived exosomes play pivotal roles in cell migration, proliferation, differentiation, and tissue repair (Wang et al., 2019a). Specifically, stem cell-derived exosomes have shown therapeutic potential in a variety of diseases through mechanisms such as regulating inflammatory responses (Meng et al., 2024), promoting angiogenesis (Ji et al., 2022), and inhibiting apoptosis.Stem cell exosomes have received unprecedented attention and have become a research hotspot worldwide, including but not limited to mesenchymal stem cell exosomes (Zhou et al., 2021), adipose-derived stem cell exosomes (Feng et al., 2022), hematopoietic stem cell-derived exosomes (Radosinska and Bartekova, 2017), and satellite cell-derive exosomes (Liu et al., 2024), umbilical cord stem cell exosomes (Ma et al., 2024). These studies have reported that stem cell exosomes can promote tissue damage repair. Previous studies have confirmed that the application of stem cell-derived exosomes successfully alleviates muscle atrophy and reduces the degradation rate of actin (Wang et al., 2019a, Meng et al., 2024, Ji et al., 2022, Zhou et al., 2021, Feng et al., 2022, Radosinska and Bartekova, 2017, Liu et al., 2024, Ma et al., 2024, Yan et al., 2020). However, past research has primarily focused on the molecular level of proteins and RNA (Wada et al., 2002, Cheon et al., 2024), lacking visual observation of the extent of improvement (Wada et al., 2002, Cheon et al., 2024, Wang et al., 2022a, Hu et al., 2025a, Song et al., 2023). There have been no reports on the study of muscle atrophy at the muscle fiber level.

In the present study, we established a simplified and efficient protocol for isolating single muscle fibers, successfully applying it to visualize and quantify dexamethasone-induced atrophy at the single-fiber leve (Zeng et al., 2023a). This allowed us to achieve visualization of muscle atrophy at the level of single muscle fibers. Based on single muscle fiber diameter., we were able to better demonstrate the degradation of actin and intuitively reflect the level of muscle atrophy.