4-mer hyaluronan (HA) oligosaccharides stimulate proinflammatory effects in different cell types by interacting with both the toll-like receptor 4 (TLR-4) and -2 (TLR-2). This interaction induces the activation of the transforming growth factor activated kinase-1 (TAK-1) that activates the nuclear factor kappaB (NF-κB) either directly and/or through the p38-mitogen-activated protein kinase (p38- MAPK) intervention. This in turn induces the transcription of pro-inflammatory mediators that prime inflammation. Our aim was to investigate the involvement of TAK-1 and p38-MAPK in 4-mer HA oligosaccharide-induced inflammatory response in mouse synovial fibroblasts obtained from normal DBA/J1 mice (NSF) and from mice subjected to collagen-induced arthritis (CIA). Treatment of NSF and rheumatoid arthritis synovial fibroblasts RAFS with 4-mer HA showed a marked up-regulation of TLR-4, TLR-2, TAK-1 and p38-MAPK mRNA expression of the related proteins, as well as NK-κB activation. High levels were also detected of TNF-alpha, IL-1beta, MMP-13 and iNOS. Treatment of NSF and RASF, previously stimulated with 4-mer HA oligosaccharides, with TAK-1 and /or p38-MAPK specific inhibitors significantly reduced all the parameters, although the p38-MAPK inhibitory effect was less effective than that of TAK-1. The addition of CD44 antibody to both NSF and RASF showed that CD44 was not involved in the 4-mer HA-induced inflammation.
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