TLR4-dependent induction of vascular adhesion molecule-1 in rheumatoid arthritis synovial fibroblasts: Roles of cytosolic phospholipase A2α/cyclooxygenase-2

✍ Scribed by Cheng-Ying Wu; Pei-Ling Chi; Hsi-Lung Hsieh; Shue-Fen Luo; Chuen-Mao Yang

• Publisher: John Wiley and Sons
• Year: 2010
• Tongue: English
• Weight: 639 KB
• Volume: 223
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.22059

✦ Synopsis

Lipopolysaccharide (LPS)/Toll-like receptor 4 (TLR4)-mediated signaling pathways have caught the attention of strategies designed for rheumatoid arthritis (RA). In this study, we identified that cPLA 2 a acted as a modulator of LPS-induced VCAM-1 expression and THP-1 (human acute monocytic leukemia cell line) adherence. Treatment of RA synovial fibroblasts (RASFs) with LPS, a TLR4 agonist, promoted the VCAM-1 expression and THP-1 adherence which were decreased by pretreatment with a selective cytosolic phospholipase A 2 (cPLA 2 ) inhibitor (AACOCF 3 ), implying the involvement of cPLA 2 a in these responses. This notion was further confirmed by knockdown of cPLA 2 a expression by transfection with cPLA 2 a small interfering RNA (siRNA) leading to a decrease in VCAM-1 expression and THP-1 adherence induced by LPS. Subsequently, the LPS-stimulated cPLA 2 a phosphorylation was attenuated by pretreatment with a MEK1/2 inhibitor (U0126), suggesting that LPS-stimulated cPLA 2 a phosphorylation and activity are mediated through an ERK-dependent mechanism. Moreover, COX-2-derived PGE 2 production appeared to involve in LPS-induced VCAM-1 expression which was attenuated by pretreatment with selective COX-2 inhibitors (NS-398 and celecoxib), transfection with COX-2 siRNA, or PGE 2 receptor antagonists. In addition, pretreatment with ecosapentaenoic acid (EPA), a substrate competitor of arachidonic acid (AA), also blocked LPS-induced VCAM-1 mRNA and protein expression, and THP-1 adherence. Collectively, these results suggest that LPS-induced VCAM-1 expression and adhesion of THP-1 cells are mediated through the TLR4/ERK/cPLA 2 a phosphorylation and COX-2 expression/PGE 2 synthesis in RASFs.