CD5L aggravates rheumatoid arthritis progression via promoting synovial fibroblasts proliferation and activity.

Rheumatoid arthritis (RA) is a chronic inflammatory disease with progressive cartilage erosion and joint destruction. Synovial fibroblasts (SFs) play a crucial role in the pathogenesis of RA. This study aims to explore the function and mechanism of CD5L during RA progression. We examined the levels of CD5L in synovial tissues and SFs. The collagen-induced arthritis (CIA) rat models were used to investigate the effect of CD5L on RA progression. We also investigated the effects of exogenous CD5L on the behavior and activity of RA synovial fibroblasts (RASFs). Our results showed that CD5L expression was significantly upregulated in synovium of RA patients and CIA-rats. Histology and Micro-CT analysis showed that synovial inflammation and bone destruction were more severe in CD5L-treated CIA rats compared with control rats. Correspondingly, CD5L blockade alleviated bone damage and synovial inflammation in CIA-rats. The exogenous CD5L treatment promoted RASFs proliferation invasion and proinflammatory cytokine production. Knockdown of CD5L receptor by siRNA significantly reversed the effect of CD5L treatment on RASFs. Moreover, we observed that CD5L treatment potentiated PI3K/Akt signaling in the RASFs. The promoted effects of CD5L on IL-6 and IL-8 expression were significantly reversed by PI3K/Akt signaling inhibitor. In conclusion, CD5L promote RA disease progression via activating RASFs. CD5L blocking is a potential therapeutic approach for RA patients.