Intra-Articular Administration of Cramp into Mouse Knee Joint Exacerbates Experimental Osteoarthritis Progression

Osteoarthritis (OA) is the most common type of arthritis and is associated with wear and tear, aging, and inflammation. Previous studies revealed that several antimicrobial peptides are up-regulated in the knee synovium of patients with OA or rheumatoid arthritis. Here, we investigated the functional effects of cathelicidin-related antimicrobial peptide (Cramp) on OA pathogenesis. We found that Cramp is highly induced by IL-1β via the NF-κB signaling pathway in mouse primary chondrocytes. Elevated Cramp was also detected in the cartilage and synovium of mice suffering from OA cartilage destruction. The treatment of chondrocytes with Cramp stimulated the expression of catabolic factors, and the knockdown of Cramp by small interfering RNA reduced chondrocyte catabolism mediated by IL-1β. Moreover, intra-articular injection of Cramp into mouse knee joints at a low dose accelerated traumatic OA progression. At high doses, Cramp affected meniscal ossification and tears, leading to cartilage degeneration. These findings demonstrate that Cramp is associated with OA pathophysiology.