TAK1 MEDIATES HMGB1-INDUCED MACROPHAGE ACTIVATION IN OSTEOARTHRITIS

Abstract

Osteoarthritis, the most common degenerative joint disease, significantly impairs life quality and labor capability of patients. Synovial inflammation, initiated by HMGB1 (High mobility group box 1)-induced activation of macrophage, precedes other pathological changes. As an upstream regulator of NF-κB (nuclear factor-kappa B) and MAPK (mitogen-activated protein kinase) signaling pathway, TAK1 (TGF-β activated kinase 1) participates in macrophage activation, while its function in osteoarthritis remains unveiled. This study aims to investigate the role of TAK1 in the pathogenesis of osteoarthritis via both in vitro and in vivo approaches.We performed immunohistochemical staining for TAK1 in synovial tissue, both in osteoarthritis patients and healthy control. Besides, immunofluorescence staining for F4/80 as macrophage marker and TAK1 were conducted as well. TAK1 expression was examined in RAW264.7 macrophages stimulated by HMGB1 via qPCR (Quantitative polymerase chain reaction) and Western blotting, and the effect of TAK1 inhibitor (5z-7 oxozeaenol) on TNF-α production was evaluated by immunofluorescence staining. Further, we explored the influence of intra-articular shRNA (short hairpin RNA) targeting TAK1 on collagenase-induced osteoarthritis in mice.Immunohistochemical staining confirmed significant elevation of TAK1 in osteoarthritic synovium, and immunofluorescence staining suggested macrophages as predominant residence of TAK1. In HMGB1-stimulated RAW264.7 macrophages, TAK1 expression was up-regulated both in mRNA and protein level. Besides, TAK1 inhibitor significantly impairs the production of TNF-α by macrophages upon HMGB1 stimulation. Moreover, intra-articular injection of lentivirus loaded with shRNA targeting TAK1 (sh-TAK1) reduced peri-articular osteophyte formation in collagenase-induced osteoarthritis in mice.TAK1 exerts a potent role in the pathogenesis of osteoarthritis by mediating the activation of macrophages.