Osteoarthritic synovial tissue inhibition of proteoglycan production in human osteoarthritic knee cartilage: Establishment and characterization of a long-term cartilage-synovium coculture

Abstract

Objective. Although both cartilage and synovium are affected in osteoarthritis (OA), no in vitro coculture models of human OA tissue have been described. The aim of this study was to develop an in vitro model that includes both the synovium and cartilage of patients with knee OA.Methods. Explants of human OA cartilage and synovium were cultured alone or in coculture for 21 days. Histologic evaluation and analyses of lactate dehydrogenase release, matrix metalloproteinase (MMP) activity, content, release, and synthesis of glycosaminoglycan (GAG), and cytokine production were used to evaluate synovial tissue functionality and its effect on cartilage metabolism. To assess the possibility of intervention in the model system, the effect of triamcinolone was studied.Results. Throughout the entire culture period, OA synovial tissue remained viable and produced cytokines.Monocultures of synovial and cartilage explants produced different cytokine subsets, with the subsets found in coculture being most similar to those previously described in OA synovial fluid. MMP activity was detectable only in the synovial explant monoculture and in coculture. Cocultures showed a reduction in final GAG content (P < 0.02), attributable to an inhibition of GAG production (P < 0.001) rather than an increase in GAG release. Addition of triamcinolone inhibited cytokine production and MMP activity in coculture and synovial tissue monoculture and counteracted the inhibition of GAG production induced by coculture. In cartilage monoculture, however, triamcinolone reduced GAG production. Conclusion. OA synovium affects cartilage metabolism by reducting GAG production. Triamcinolone can relieve this effect of synovial tissue, while being inhibitory when added to cartilage monoculture. These results clearly indicate the importance of tissue coculture as a promising tool for studying OA pathophysiology and for development of possible interventions.Osteoarthritis (OA) is a major health problem that affects more than 14% of individuals ages 25-74 years in the United States (1). With aging of the population, an increasing incidence of OA is anticipated in the near future. At this time, there is no cure for OA, only symptomatic relief or, in patients with end-stage OA, total joint arthroplasty. To this day, the exact pathogenesis and etiology of OA remain unclear and are still the subject of much debate and research. Various

A Three-Dimensional Chondrocyte-Macrophage Coculture System to Probe Inflammation in Experimental Osteoarthritis

“…These studies have demonstrated the enhanced production of key inflammatory mediators from chondrocytes exposed to OA synovial fluid or the synovium itself, which may act to further stimulate macrophage inflammation. 12,56,57,68,69 Cumulatively, our results agree well with changes seen in early OA and with similar in vitro model systems using NCs.…”

“…Similarly, the cytokine expression data are also similar to two previous reportsone in which healthy human chondrocytes were treated with the synovial fluid of OA patients, 68 and another wherein healthy cartilage explants were cocultured with synovium from OA patients. 69 Effect of coculture on AMs. In addition to NC response, we also investigated the phenotypic shift of AMs cocultured with NCs, which has generally remained unexplored in the literature.…”

Immune Modulation to Improve Tissue Engineering Outcomes for Cartilage Repair in the Osteoarthritic Joint

“…36,37 Long-term coculture models of synovial tissue and cartilage explants highlight the role of activated synoviocytes in cartilage destruction associated with OA. 38 The synovial tissue was found to secrete high levels of interleukin (IL)-6, IL-8, and osteoprotegerin, and to produce cytokines throughout the culture period. Furthermore, cartilage explant glycosaminoglycan (GAG) content was found to be significantly lower following a 21-day exposure to the synovial tissue compared with cartilage monocultures.…”

“…Furthermore, cartilage explant glycosaminoglycan (GAG) content was found to be significantly lower following a 21-day exposure to the synovial tissue compared with cartilage monocultures. 38 It is evident that pro-inflammatory mediators produced by inflamed synovium are capable of driving the progression of OA through induction of destructive processes in cartilage (Table 1), and the abundance of such catabolic factors in an osteoarthritic joint may greatly impede cartilage tissue engineering strategies.…”

“…39 These cells are capable of phagocytosis and antigen presentation, and they play a prominent role in the production of the pro-inflammatory cytokines tumor necrosis factor-a (TNF-a), IL-1b, IL-6, and oncostatin M. 38,[40][41][42] IL-1b and TNF-a induce destructive processes in chondrocytes associated with OA pathology including downregulation of collagen type II and proteoglycan, and upregulation of MMP-9 and cyclooxygenase-2 (COX-2). 43 The enzyme COX-2 functions in the production of prostaglandins, which are known to play a role in pain and inflammation, and COX-2 expression is elevated in multiple immune cell types.…”