Duchenne muscular dystrophy is driven by defective membrane repair and annexin-A2 dysregulation in skeletal muscle

Background: Duchenne muscular dystrophy (DMD) is caused by mutations in the DMD gene, which encodes dystrophin in skeletal muscle cells. Although the role of dystrophin as a structural protein is well known, the cellular processes underlying myofiber degeneration are still not fully understood. Despite advances from studies in murine models, these models do not fully replicate the human pathology. Methods: We investigated sarcolemmal integrity, membrane repair capacity, and annexin protein expression in DMD patient muscle biopsies and human skeletal muscle cell lines using immunohistochemistry, a shear stress-based injury assay, western blotting, and live-cell imaging of GFP-tagged annexins. Results: We identified defective membrane repair in DMD skeletal muscle cells, independent of increased membrane fragility. Massive intracellular IgG uptake and impaired resealing after mechanical stress, respectively observed ex vivo and in vitro, confirmed this defect. We also observed altered expression patterns of annexins, a family of key proteins involved in membrane repair. Control skeletal muscle cells upregulate ANXA5 and ANXA6 upon mechanical stress, likely as part of an adaptive mechanism to counteract membrane damage. Conversely, DMD cells failed to induce this upregulation. Strikingly, ANXA2 was not only significantly overexpressed in DMD cells but also aberrantly localized to the extracellular space due to the defect in membrane repair. This extracellular ANXA2 is associated with adipocyte accumulation in muscle tissue, suggesting a mechanism similar to that seen in dysferlinopathies. Conclusions: Our findings propose that ANXA2 contributes to muscle degeneration in DMD and highlight it as a potential therapeutic target to prevent adipogenesis and muscle loss.