IL37 ameliorates experimental murine osteoarthritis

Abstract

Purpose: Osteoarthritis (OA) is the world’s most common degenerative joint disorder and leads to pain and disability. Currently, no disease-modifying drugs are available, resulting in a large unmet clinical need. Recently, we have shown that the anti-inflammatory cytokine IL37 lowers pro-inflammatory cytokine production, MMP3 expression and sulfated glycosaminoglycan loss in ex vivo cultured chondrocytes and human OA cartilage explants. In this study, we further explored the ability of IL37 to ameliorate OA pathology by studying its effects both in vitro on synovial fibroblasts and in vivo in experimental OA in mice. Methods: Primary human synovial fibroblasts were obtained by enzymatic digestion of synovial biopsies of 10 patients undergoing total joint replacement surgery. IL37 was overexpressed in these fibroblasts using an adenovirus (Ad-IL37) and subsequently cells were challenged with IL1β or OA-synovium conditioned medium (OAS-cm). Experimental OA was induced by a single intra-articular injection of 3 units of collagenase type VII in the right knee joint of 10 weeks old female C57BL/6J mice, i.e. collagenase-induced OA (CiOA). Four days after collagenase injection, Ad-IL37 or Ad-Luc (= control) was injected in the same joint, and after two weeks this injection was repeated. Mice were sacrificed on day 7, 28 and 42 after collagenase injection. Synovial thickening, cartilage damage (OARSI score) and osteophyte formation (size) were measured histologically. IL37, MMP3 and VDIPEN expression were investigated by immunohistochemistry. Results: In primary synovial fibroblasts, IL1β- and OAS-cm-induced expression of MMP1, MMP3, IL1B and IL6 was reduced by more than 50% by IL37. Prolonged (28 days) overexpression of IL37 in naïve knee joints did not lead to synovial thickening, cartilage damage or osteophyte formation and no overt immune response was detected. Strikingly, at day 7 of CiOA, IL37 overexpression significantly reduced synovial thickness, whereas in cartilage MMP3 protein and the presence of the metalloproteinase-generated aggrecan-degradation neoepitope VDIPEN was reduced. At day 28 of CiOA, cartilage damage was significantly reduced by IL37 treatment at both the lateral and medial side of the femur by 46% and 41%, respectively. Furthermore, osteophyte size at the medial femur was reduced by 70%. At day 42 of CiOA, IL37 overexpression could no longer be detected, in contrast to day 7 and 28. Osteophyte size formation at the medial femur was still significantly reduced by 46%, but only a trend (p = 0.06) towards reduced cartilage damage was observed on both femur and tibia at this time point. Conclusions: Our results show that IL37 inhibits the production of catabolic mediators in OA synovial fibroblasts, similar to what we previously observed in cartilage and chondrocytes. Furthermore, IL37 clearly lowered synovial thickening and ameliorated cartilage damage and osteophyte formation in murine experimental OA. These results indicate that IL37 acts on multiple OA-related processes in multiple joint tissues, which supports IL37 as a potential therapeutic agent for OA.