Prostaglandin E2 regulates the expression of connective tissue growth factor (CTGF/CCN2) in human osteoarthritic chondrocytes via the EP4 receptor

Articular cartilage samples were obtained from patients with osteoarthritis (OA) and chondrocytes were isolated and cultured in vitro. Chondrocytes were stimulated with PGE2, PGE receptor (EP)-specific agonists, or interleukin (IL)-1. CTGF expression was analyzed using quantitative polymerase chain reaction, Western blot, and enzyme-linked immunosorbent assay. The inhibitory effects of EP receptor antagonists (for EP2 and EP4) against PGE2 stimulation were also investigated. Stimulation of chondrocytes with PGE2 or IL-1 significantly suppressed CTGF expression. The suppressive effect of PGE2 was reproduced by EP2/EP4 receptor agonists but not by EP1/EP3 receptor agonists, and was partially blocked by an EP4 receptor antagonist, suggesting that the EP4 receptor has a dominant role.PGE2 may be involved in the regulation of CTGF/CCN2 expression in human articular chondrocytes via the EP4 receptor. Elucidation of EP4-mediated signaling in chondrocytes may contribute to a better understanding of the effects of PGE2 in arthritis.Connective tissue growth factor/CCN family member 2 (CTGF/CCN2) is a member of the CCN family, which is a group of secreted multifunctional proteins that contain high levels of cysteine (reviewed in [1]). During skeletal development, CTGF is strongly expressed in the mesenchyme, including in hypertrophic chondrocytes, and plays an essential role in endochondral ossification by promoting angiogenesis, proliferation, and differentiation of chondrocytes [2]. In adult tissue, CTGF is expressed during wound healing and in fibrotic tissue [2,3]. Transforming growth factor (TGF)-β stimulates CTGF expression, and TGF-β-induced CTGF is involved in scarring and fibrogenesis [3]. In chondrocytes, CTGF contributes to the production of the extracellular matrix by stimulating chondrocyte proliferation, the expression of type II collagen, and aggrecan among other factors, and the activation of integrin signaling [4,5]. CTGF expression is detected in normal human