Loss of dystrophin expression in skeletal muscle is associated with senescence of macrophages and endothelial cells.

Cellular senescence is the irreversible arrest of normally dividing cells and is driven by cell cycle inhibitory proteins such as p16, p21 and p53. When cells enter senescence, they secrete a host of proinflammatory factors known as the senescence associated secretory phenotype which has deleterious effects on surrounding cells and tissues. Little is known of the role of senescence in Duchenne Muscular Dystrophy (DMD), the fatal X-linked neuromuscular disorder typified by chronic inflammation, extracellular matrix remodeling and a progressive loss in muscle mass and function. Here, we demonstrate using C57-mdx (8-week-old) and D2-mdx mice (4-week and 8-week-old), two mouse models of DMD, that cells displaying canonical markers of senescence are found within skeletal muscle. 8-week-old D2-mdx mice, which display severe muscle pathology, had greater numbers of senescent cells associated with areas of inflammation which were mostly Cdkn1a-positive macrophages while in C57-mdx muscle, senescent populations were endothelial cells and macrophages localized to newly regenerated myofibers. Interestingly, this pattern was similar to cardiotoxin (CTX)-injured wildtype (WT) muscle which experienced a transient senescent response. Dystrophic muscle demonstrated significant upregulations in senescence pathway genes (Cdkn1a (p21), Cdkn2a (p16INK4A), Trp53 (p53)) which correlated with the quantity of SA-b-Gal-positive cells. These results highlight an underexplored role for cellular senescence in murine dystrophic muscle.