Comparative Study of Normal and Rheumatoid Arthritis Fibroblast-Like Synoviocytes Proliferation under Cyclic Mechanical Stretch: Role of Prostaglandin E2

Fibroblast-like synoviocytes (FLSs) are one of the main contributors of prostaglandin E-2 (PGE(2)) in the hyperplastic synovium of rheumatoid arthritis (RA) patients. cyclooxygenase-2 (COX-2)/PGE(2) pathway is involved in the proliferation of several cell types. We have previously shown that mechanical stretch affects COX-2 and PGE(2) production in human RA FLSs; however, its role in cell proliferation remains to be elucidated. In this study, a comparison is drawn between human RA and normal FLSs to understand the role of mechanical stretch and PGE(2) on the proliferation of FLSs. The results showed that physiological level (6%, 1 Hz) of cyclic mechanical stretch significantly decreased the proliferation of RA FLSs but not normal FLSs, while the induction of apoptosis was not observed by stretch in either RA or normal FLSs. IL-1 beta (5 ng/ml)-induced COX-2/PGE(2) levels are downregulated by stretch in RA FLSs only. Further investigation showed that high concentration (100 and 500 ng/ml) of PGE(2) significantly induced cell proliferation only in RA FLSs, and this induction failed to be suppressed by stretch. In conclusion, this study demonstrated that elevated levels of PGE(2) in the synovial cavity are involved in the proliferation of RA FLSs, and cyclic mechanical stretch regulates the RA synovial hyperplasia.