Anti-proliferative effect of recombinant human endostatin on synovial fibroblasts in rats with adjuvant arthritis

Rheumatoid arthritis (RA) is characterized by pronounced synovial hyperplasia resulting in pannus formation, cartilage erosion and ultimately joint destruction. Activated RA synovial fibroblasts (SFs) mediate the invasion and destruction of cartilage and bone. We previously demonstrated that recombinant human endostatin (rhEndostatin) is sufficient to induce SF apoptosis in adjuvant arthritis (AA) rats. However, the effect of this protein on SF proliferation is unknown. This study was designed to assess the inhibitory effect and mechanisms of rhEndostatin on the proliferation of cultured AA SFs. MTT assay and flow cytometric detection were performed to investigate SF proliferation and cell cycle progression, respectively. Also, the expression levels of p53, p21, cyclin D1, CDK4 and PCNA in AA SFs were detected by real-time PCR and western blotting assays. Our data revealed that AA SF proliferation was significantly inhibited by rhEndostatin in a concentration-dependent manner. In addition, rhEndostatin (50 μg/ml) caused the G0/G1 cell cycle arrest of AA SFs. There were significant decreases in the expression levels of p53, p21, cyclin D1 and PCNA in AA SFs treated with rhEndostatin, and a significant increase in CDK4 expression. Collectively, our data suggest that rhEndostatin inhibits AA SF proliferation, which is preceded by cell cycle arrest at the G0/G1 phase. This is partly due to the inhibitory effect of rhEndostatin on cyclin D1 and PCNA by a p53–p21–CDK4-independent mechanism. Taken together, these findings highlight the potential use of rhEndostatin for RA treatment.