Adamts5 deletion exacerbates inflammation and fibrosis resulting in compromised skeletal muscle regeneration

The extracellular matrix (ECM) protease Adamts5 and its ECM substrates are critical regulators of inflammation and fibrosis, whether Adamts5 also regulates muscle regeneration is not known. Right tibialis anterior (TA) muscles from adult <i>Adamts5</i>^-/- or wild-type mice were injected with glycerol to induce injury. In uninjured muscles and at 7 and 14 days after injury, TA contractile function was determined in situ, followed by an assessment of pathology using histology and immunohistochemistry. Immunoblotting was performed for the versikine fragment, which is generated when Adamts5 cleaves its substrate versican. Versikine protein, which correlates with Adamts5 proteolytic activity, was lower in uninjured and injured TA muscles from <i>Adamts5</i>^-/- versus wild-type mice. In uninjured TA muscles, Adamts5 deletion of the catalytic and ancillary domains decreased the absolute (P_o) and normalized to muscle size (sP_o) force output, with no significant effect on muscle mass and myofiber size. Adamts5 deletion compromised regeneration with greater impairment evident at the later timepoint. Force output (P_o and sP_o) was lower in <i>Adamts5</i>^-/- mice at 7 and 14 days after injury. TA mass and myofiber size were only decreased at 14 days after injury, whereas embryonic myosin heavy chain expression did not significantly differ between genotypes. Degeneration, mononuclear infiltrates, and ECM deposition including fibronectin protein were greater in injured TA muscles from <i>Adamts5</i>^-/- mice. Resolution of inflammation was also delayed in <i>Adamts5</i>^-/- mice, with more infiltrating macrophages observed at 14 days after injury. In conclusion, Adamts5 regulates the balance between muscle regeneration, fibrosis, and inflammation following glycerol injury.<b>NEW & NOTEWORTHY</b> Glycerol injury to mouse hindlimb muscles results in inefficient regeneration and fibrosis. Adamts5 is a secreted protease, which degrades extracellular matrix (ECM) proteins and has an emerging role in inflammation, fibrosis, and muscle development. In Adamts5-deficient mice, muscle degeneration, inflammation, and fibrosis were increased, and contractile function was impaired for up to 14 days after glycerol injury when compared with wild-type mice. These findings demonstrate the significant role of Adamts5 in muscle regeneration.