The recombinant Link module of human TSG-6 suppresses cartilage damage in models of osteoarthritis: a potential disease-modifying OA drug

ObjectivesTo investigate the role of endogenous TSG-6 in human osteoarthritis (OA) and assess the disease-modifying potential of a TSG-6-based biological treatment in cell, explant and animal models of OA.MethodsKnee articular cartilages from OA patients were analysed for TSG-6 protein and mRNA expression using immunohistochemistry and RNAscope, respectively. The inhibitory activities of TSG-6 and its isolated Link module domain (Link_TSG6) on cytokine-induced glycosaminoglycan loss in OA cartilage explants were compared. Mesenchymal stem/stromal cell (MSC)-derived chondrocyte pellet cultures were used to determine the effects of Link_TSG6 and full-length TSG-6 on IL-1α-, IL-1β- or TNF-stimulated ADAMTS4, ADAMTS5 and MMP13 mRNA expression. Link_TSG6 was administered i.a. to the rat ACLTpMMx model and cartilage damage and tactile allodynia were assayed.ResultsTSG-6 is predominantly associated with chondrocytes in regions of cartilage damage and its expression is negatively correlated with MMP13, the major collagenase implicated in OA progression. Link_TSG6 is more potent than full-length TSG-6 at dose-dependently inhibiting cytokine-mediated matrix breakdown in human OA cartilage explants; about 50% of donor cartilages, from 59 tested, were responsive to Link_TSG6 treatment. Similarly, Link_TSG6 displayed more potent effects in 3D pellet cultures, suppressing aggrecanase and collagenase gene expression. Link_TSG6 treatment reduced touch-evoked pain and dose-dependently inhibited cartilage damage in a rodent model of surgically-induced OA.ConclusionsNative TSG-6 is associated with a low catabolic chondrocyte phenotype in OA cartilage. Link_TSG6, which has enhanced chondroprotective activity compared to the full-length TSG-6 protein, demonstrates potential as a disease modifying OA drug (DMOAD) and warrants further investigation and development.KEY MESSAGESWhat is already known about this subject?TSG-6, a protein with anti-inflammatory and protective effects in other tissues, is expressed in joints affected by osteoarthritis – a condition for which there are no disease-modifying drugs.What does this study add?A novel protective mechanism has been identified, whereby TSG-6 inhibits inflammatory cytokine-induced catabolic pathways in cartilage.The Link module of TSG-6 (Link_TSG6) has been shown to have greater potency than TSG-6 as an inhibitor of cartilage damage and is efficacious in a rat model of osteoarthritis.Data from cartilage explants indicate that OA patients can be stratified for Link_TSG6 responsiveness.How might this impact on clinical practice or future developments?Link_TSG6 has been identified as potential disease-modifying OA drug that mimics an intrinsic protective process.