The expression of adamts4, a major aggrecanase in osteoarthritic synovium, is synergistically up-regulated by IL-1ALPHA, TNF-ALPHA and TGF-BETA

Abstract

Purpose: ADAMTS 1, 4, 5, 8, 9, 15, 16, 18 and 20 show the ability to degrade aggrecan, a major proteoglycan in articular cartilage. However, limited information is available for which species play a major role in osteoarthritis (OA) and how the expression of the ADAMTS species is regulated. Methods: Synovial tissue obtained from OA patients was used for expression analyses and primary synovial fibroblasts were cultured from the tissue. Screening of the expression for aggrecanase-type ADAMTS species was done by RT-PCR and real-time PCR. Effect of IL-1α, IL-1β, TNF-α, TGF-β, VEGF or HB-EGF on the ADAMTS4 expression was analyzed by real-time PCR and immunoblotting. The signaling pathways for downstream molecules of these cytokines were examined by using their inhibitors and effect of anti-arthritic drugs including high-molecular-weight hyaluronan (Suvenyl), Adalimumab (Humira) and Tocilizumab (Actemra) on the ADAMTS4 expression was also examined. Results: Among the ADAMTS species examined, ADAMTS1, 4, 5, 9 and 16 were expressed in OA synovium and synovial fibroblasts. IL-1α, TNF-α and TGF-β, but not VEGF or HB-EGF, up-regulated the ADAMTS4 expression, but the effects of these factors were minimal for ADAMTS1, 9 and 16. In contrast, ADAMTS5 expression was constitutive, and no expression of ADAMTS8, 15, 18 and 20 was observed. The ADAMTS4 expression was synergistically up-regulated by IL-1α and TNF-α, IL-1α and TGF-β, or IL-1α, TNF-α and TGF-β. Inhibition studies showed that the IL-1α-stimulated ADAMTS4 expression is predominantly through TAK1, and the TNF-α-stimulated expression is via TAK1 and partially by NF-κB. The TGF-β-stimulated expression was through the ALK5/Smad2/3 and TAK1 pathways. Adalimumab abolished the TNF-α-stimulated expression. Under the co-stimulation with IL-1α, TNF-α and TGF-β, the ADAMTS4 expression was completely inhibited by combination of Adalimumab and TAK1 inhibitor or ALK5/Smad2/3 inhibitor. Conclusions: Our data demonstrate that ADAMTS4 is a major aggrecanase in OA synovium and synergistically up-regulated by IL-1α, TNF-α and TGF-β in OA synovial fibroblasts, and suggest that combined therapy with anti-TNF-α drug and signaling pathway inhibitor(s) may be a useful remedy for OA.