Amelioration of contusion-induced muscle injury via regulation of the NLRP3 inflammasome

Inflammasomes, including NLRP3 (nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain-containing protein 3), participate in regulating immune activation and inflammation. Nonetheless, their specific roles in muscle contusion, one of the most common forms of sports injury, remain unknown. To address this, we investigated the role of NLRP3 in muscle contusion in <i>Nlrp3</i>-knockout (KO) mice, using a model of mass-drop injury (MDI)-induced contusion of the gastrocnemius muscle. Wild-type (WT) and <i>Nlrp3</i>-KO mice were assigned to four experimental groups: (1) WT-N: wild-type without MDI (control); (2) NLRP3-N: <i>Nlrp3</i>-KO without MDI; (3) WT-I: WT with MDI; and (4) NLRP3-I: <i>Nlrp3</i>-KO with MDI. Following MDI, tissue and serum samples were collected at 0, 48, 96, and 192 h. Muscle injury, recovery, and the extent of inflammation were evaluated by measuring body and muscle weight, serum biochemical markers, complete blood counts, and via histopathological immunohistochemical analysis. In the early phase following contusion, muscle weight was lower in the NLRP3-I group than in the WT-I group; however, in the later stages, it was significantly greater in the NLRP3-I group. Serum aspartate aminotransferase, lactate dehydrogenase, and creatine kinase were significantly lower in the NLRP3-I group than in the WT-I group, indicating reduced muscle damage following <i>Nlrp3</i> knockout. The white blood cell and neutrophil counts were markedly higher in the WT-I group than in the NLRP3-I group. Based on histopathology, the NLRP3-I group exhibited less severe muscle injury, reduced tumor necrosis factor (TNF)-α, interleukin (IL)-6, CD68, CD206 and Caspase-3 expression, and reduced fibrosis, indicating a diminished contusion-induced inflammatory response and improved regeneration relative to the WT-I group. <i>Nlrp3</i> knockout thus ameliorated contusion-induced muscle injury and inflammation. We hypothesize that NLRP3 regulates TNF-α and IL-6, with <i>Nlrp3</i> downregulation reducing contusion-related muscle damage and fibrosis. NLRP3 thus represents a promising therapeutic target for treating sports injuries and for rehabilitation.