Heme oxygenase 1 attenuates interleukin‐1β–induced cytosolic phospholipase A2 expression via a decrease in NADPH oxidase/reactive oxygen species/activator protein 1 activation in rheumatoid arthritis synovial fibroblasts

Abstract

Reactive oxygen species (ROS) produced by cytokines induce the expression of inflammatory mediators in rheumatoid arthritis (RA). Heme oxygenase 1 (HO-1) exerts an antiinflammatory effect. The aim of this study was to examine the mechanisms underlying interleukin-1β (IL-1β)-induced cytosolic phospholipase A2 (cPLA2) expression through ROS generation as modulated by HO-1 in RA synovial fibroblasts (RASFs). IL-1β-induced ROS generation was determined by flow cytometry. The involvement of MAPKs and NADPH oxidase (NOX)/ROS in IL-1β-induced cPLA2 expression was investigated using pharmacologic inhibitors and transfection with small interfering RNAs (siRNAs) and was analyzed by Western blotting and promoter assay. Overexpression of HO-1 was performed by transfection of RASFs with a recombinant adenovirus containing human HO-1 plasmid. SCID mice with inflammation caused by IL-1β were infected with adenovirus containing HO-1. Histologic characterization of joint inflammation and local expression of cPLA2 were evaluated after treatment. IL-1β-induced cPLA2 expression was mediated through NOX activation/ROS production, which was attenuated by N-acetylcysteine (NAC; a scavenger of ROS), the inhibitors of NOX (diphenyleneiodonium chloride and apocynin), MEK-1/2 (U0126), and JNK-1/2 (SP600125), transfection with the respective siRNAs, and the overexpression of HO-1 in RASFs. IL-1β-induced cPLA2 expression was mediated through recruitment of activator protein 1 (AP-1) to the cPLA2 promoter region, which was attenuated by NAC and overexpression of HO-1. Furthermore, HO-1 overexpression inhibited IL-1β-mediated cPLA2 expression in SCID mice. In RASFs, IL-1β induced cPLA2 expression via activation of p42/p44 MAPK and JNK-1/2, leading to p47phox phosphorylation, ROS production, and AP-1 activation. The induction of HO-1 exerted protective effects on the pathogenesis of RA.