Cellular senescence in skeletal muscle regeneration.

Skeletal muscle possesses a remarkable capacity for regeneration, driven by the activation and proliferation of Pax7-positive muscle stem cells within a dynamic niche that includes immune cells, fibro-adipogenic progenitors, endothelial cells, pericytes, and neural elements. Cellular senescence, a stress-induced program featuring stable cell-cycle arrest and the senescence-associated secretory phenotype (SASP), has emerged as a critical yet paradoxical regulator of this process. Accumulating evidence indicates that transient senescence, particularly in FAPs, macrophages, and other niche cells during acute muscle injury, plays a beneficial role in supporting muscle regeneration. These senescent cells promote cellular plasticity, enhance myoblast differentiation, facilitate phagocytic clearance of debris, and modulate inflammation and repair via timely SASP factor secretion. However, conflicting findings suggest that senescent cells exert detrimental effects, impairing regeneration by establishing a sustained pro-inflammatory and pro-fibrotic niche, especially when senescence persists in aged or dystrophic muscle. This review synthesizes the complex and contradictory roles of cellular senescence in skeletal muscle regeneration, underscores the distinction between transient pro-regenerative and persistent deleterious senescence, highlights the importance of cell-type-specific contributions, and emphasizes the need for precise characterization of senescent cell dynamics and fate. Resolving these discrepancies will be critical for developing targeted senotherapeutic strategies to enhance muscle regeneration in aging and degenerative diseases.