Depletion of Protease‐Activated Receptor 2 but Not Protease‐Activated Receptor 1 May Confer Protection Against Osteoarthritis in Mice Through Extracartilaginous Mechanisms

Abstract

Objective. To explore the involvement of proteaseactivated receptor 1 (PAR-1) and PAR-2 in the pathologic processes of osteoarthritis (OA) and to identify the cells/tissues primarily affected by ablation of PAR-1 or PAR-2 in mice.Methods. OA was induced in the joints of wildtype (WT), PAR-1 ؉/؉ , PAR-1 ؊/؊ , and PAR-2 ؊/؊ mice by destabilization of the medial meniscus (DMM), and scores of histologic features (cartilage aggrecan loss and erosion, subchondral bone sclerosis, osteophytes, and synovitis) were compared at 1, 4, and 8 weeks post-DMM. The effects of PAR ablation on cartilage degradation and chondrocyte metalloproteinase expression/ activity were studied in cultures of mouse femoral head tissue with or without interleukin-1␣ (IL-1␣). At 1 week post-DMM, synovial expression of cytokines and metalloproteinase genes was measured by reverse transcription-polymerase chain reaction, and populations of inflammatory cells were quantified by flow cytometry.Results. Deletion of PAR-2, but not that of PAR-1, in mice significantly delayed the progression of cartilage damage and inhibited subchondral bone sclerosis following DMM. There was no inhibitory effect of PAR-1 or PAR-2 ablation on IL-1␣-induced cartilage degradation or chondrocyte metalloproteinase expression/activation. A low but significant level of synovitis persisted in mice subjected to DMM compared to that in control mice subjected to sham surgery, but no differences between the genotypes were seen 4 or 8 weeks post-DMM. One week after DMM, increased synovial expression of proinflammatory cytokines and metalloproteinase genes, along with increased levels of CD4؉ T cells, inflammatory monocytes, and activated macrophages, were seen in all genotypes. However, there was a significant reduction in the percentage of activated macrophages in PAR-2 ؊/؊ mice compared to PAR-1 ؊/؊ and WT mice.Conclusion. Deletion of PAR-2, but not that of PAR-1, results in a significant decrease in DMMinduced cartilage damage. The chondroprotection in PAR-2 ؊/؊ mice appears to occur indirectly through modulation of extracartilaginous events such as subchondral bone remodeling and synovial macrophage activation, rather than through alteration of chondrocyte catabolic responses.The synovial joint is an "organ" with communication and interdependence between the component tissues and cells necessary for maintenance of normal articular function (1). Osteoarthritis (OA) is the most common arthropathy, and although progressive loss of articular cartilage is pathognomonic, there are varying

Systemic inhibition of IL-6/Stat3 signalling protects against experimental osteoarthritis

“…Indeed, we previously showed that the BV/TV decreased early after DMM, at week 4 but not at weeks 6 and 9 23. To the difference of Stattic, MR16-1 significantly decreased the extent of synovitis, which occurred early in the DMM model 29 34. This suggests that MR-16 might act through other pathways than Stat3 in the synovium tissue.…”

“…Here, we show for the first time that the systemic use of anti-IL-6R monoclonal antibody has protective effects in an experimental OA model, thus providing the relevance for IL-6 therapeutic targeting in OA. We hypothesise that both synovitis and angiogenesis, common findings in the DMM model,25 29 allowed for the MR16-1 and Stattic to reach the joint cavity and to exert their effects on cartilage. This finding supports ongoing clinical investigations of the efficacy of tocilizumab, a humanised anti-IL-6R monoclonal neutralising antibody, for severe subsets of patients with OA (ClinicalTrials.gov NCT02477059), as has been done with tumour necrosis factor alpha (TNFα) blockers 30…”

Proteinase-activated receptor 2 modulates OA-related pain, cartilage and bone pathology

“…In addition, synovitis was assessed histologically using a recently developed scoring system. 6 This was modified to focus only on pannus formation, synovial membrane thickening and subsynovial hyperplasia (see online supplementary table S1). Agreement between scorers was good with intraclass correlation coefficient of 0.88 (95% CI 0.65 to 0.95), the mean difference in score being 0.1 (95% CI −0.46 to 0.67).…”

Novel Insights into Osteoarthritis Joint Pathology from Studies in Mice

“…Finally, in a study conducted by Jackson et al [80], PAR-2 deletion prevented cartilage destruction in DMM-induced OA; however, this effect was not attributable to the direct effects of PAR-2 on chondrocytes [80], but was probably mediated in part through reduced subchondral bone thickening. Combined, the data suggested that, although subchondral bone changes were associated with cartilage degeneration, they could precede cartilage loss and thus play a potential role in the initiation of murine OA.…”