IL-6 Reduces Spheroid Sizes of Osteophytic Cells Derived from Osteoarthritis Knee Joint via Induction of Apoptosis.

Osteophytes in osteoarthritis (OA) joints contribute to restriction of joint movement, joint pain, and OA progression, but little is known about osteophyte regulators. Examination of gene expression related to cartilage extracellular matrix, endochondral ossification, and growth factor signaling in articular cartilage and osteophytes obtained from OA knee joints showed that several genes such as COL1A1, VCAN, BGLAP, BMP8B, RUNX2, and SOST were overexpressed in osteophytes compared with articular cartilage. Ratios of mesenchymal stem/progenitor cells, which were characterized by co-expression of CD105 and CD166, were significantly higher in osteophytic cells than articular cells. A three-dimensional culture method for cartilage and osteophyte cells was developed by modification of cultures of self-assembled spheroid cell organoids (spheroids). These spheroids cultured in the media for mesenchymal stem cells containing transforming growth factor-ß3 showed characteristic morphologies and gene expression profiles of articular cartilage and osteophytes, respectively. The effects of IL-1ß, tumor necrosis factor-α, and IL-6 on the spheroids of articular and osteophytic cells were studied. To the best of our knowledge, they provide the first evidence that IL-6 suppresses the spheroid size of osteophytic cells by inducing apoptosis and reducing extracellular matrix molecules. These data show that IL-6 is the suppressor of osteophyte growth and suggest that IL-6 expression and/or activity are implicated in the regulation of osteophyte formation in pathologic joints.

Implication of HYBID (Hyaluronan-Binding Protein Involved in Hyaluronan Depolymerization) in Hyaluronan Degradation by Synovial Fibroblasts in Patients with Knee Osteoarthritis.

Cell migration-inducing hyaluronidase 1 (CEMIP), also known as hyaluronan (HA)-binding protein involved in HA depolymerization (HYBID), plays a role in HA degradation. CEMIP2, also known as transmembrane protein 2 (TMEM2), possessing a sequence similarity with HYBID, is reported as a hyaluronidase in mice. However, the expression of these molecules in osteoarthritic synovium and their involvement in HA degradation in synovial fluid (SF) from patients with knee osteoarthritis remain elusive. This study examined their expression in synovial tissue and the relationship with molecular weight of HA in SF in knee osteoarthritis patients. Quantification of mRNA demonstrated that HYBID expression is significantly (5.5-fold) higher in osteoarthritic synovium than in normal control synovium, whereas TMEM2 expression level is similar between the two groups. By immunohistochemistry, HYBID was localized mainly to CD68-negative and fibroblast-specific protein 1-positive synovial lining cells and sublining fibroblasts in osteoarthritic synovium. The mRNA expression levels of HYBID, but not TMEM2, in osteoarthritic synovium positively correlated with distribution of lower-molecular-weight HA with below 1000 kDa in SF. HA-degrading activity in osteoarthritic synovial fibroblasts was abrogated by siRNA-mediated knockdown of HYBID. Among the 12 factors examined, IL-6 significantly up-regulated the HYBID expression and HA-degrading activity in osteoarthritic synovial fibroblasts. These data suggest that HYBID overexpressed by IL-6-stimulated synovial fibroblasts is implicated in HA degradation in osteoarthritic synovium.

High molecular weight hyaluronan protects cartilage from degradation by inhibiting aggrecanase expression.

Hyaluronan (HA) is an extracellular matrix (ECM) component of articular cartilage and has been used to treat patients with osteoarthritis (OA). A disintegrin and metalloproteinases with thrombospondin motifs (ADAMTSs) play an important role in cartilage degradation in OA. We have previously reported that ADAMTS4 and ADAMTS9 were induced by cytokine stimulation. However, the effect of HA on the cytokine-inducible ADAMTS9 has never been investigated. Moreover, it is unclear whether HA protects cartilage by suppressing aggrecan degradation. Here, we examined the effects of HA on ADAMTS expression in vitro and on cartilage degradation in vivo. ADAMTS9 expression was higher than that of the other aggrecanases (ADAMTS4 and 5) in human chondrocytes, chondrocytic cells, and rat cartilage. ADAMTS4 and 9 mRNA levels were upregulated in cytokine-stimulated chondrocytes and chondrocytic cells. Pre-incubation with HA significantly inhibited ADAMTS9 mRNA expression in cytokine-stimulated cells. In a rat OA model, Adamts5 and 9 mRNA levels were transiently increased after surgery; intra-articular HA injections attenuated the induction of Adamts5 and 9 mRNA. HA also blocked aggrecan cleavage by aggrecanase in OA rats in a molecular size-dependent manner. These results demonstrate that HA attenuates induced aggrecanases expression in OA and thereby protects articular cartilage degradation by this enzyme. Our findings provide insight into the molecular basis for the beneficial effects of HA in OA. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 36:3247-3255, 2018.