Hyaluronan inhibits p38 mitogen-activated protein kinase via the receptors in rheumatoid arthritis chondrocytes stimulated with fibronectin fragment

This study was aimed to examine the inhibitory mechanism of high molecular weight hyaluronan (HA) on nitric oxide (NO) production by NH2-terminal heparin-binding fibronectin fragment (FN-f) in rheumatoid arthritis (RA) chondrocytes. When the RA cartilage explants or the isolated RA chondrocytes in monolayer were incubated with FN-f, the fragment stimulated NO production with induction of inducible nitric oxide synthase (iNOS) and activation of p38 mitogen-activated protein kinase. Pretreatment with 2,700 kDa HA resulted in significant suppression of FN-f-stimulated NO production in RA cartilage as well as in chondrocyte monolayer cultures in association with iNOS down-regulation. Inhibition studies with p38 inhibitor indicated the requirement of p38 for FN-f-induced NO production. HA suppressed p38 activation by the FN-f, leading to a decrease in NO production. Immunofluorescence cytochemistry revealed HA association with intercellular adhesion molecule-1 (ICAM-1) and CD44. While the individual antibody to ICAM-1 or CD44 partially reversed HA effect on the FN-f action, both antibodies in combination completely blocked the HA effect. The present study clearly demonstrated that the high molecular weight of HA suppressed the FN-f-activated p38 via ICAM-1 and the CD44 in RA chondrocytes. HA could down-regulate the catabolic action of FN-f in RA joints through the mechanism demonstrated in this study.