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treated in OA milieu showed an increase of CXCR3, CCR3 and IL6R and a decrease of CCR1 receptors. Blocking experiments demonstrate that CXCL10/IP10 was the only chemokine of the OA milieu down-modulated after treatment with GMP-ASC. We confirmed that CXCL10/IP10 was mainly positive on synovial macrophages. Conclusions: In conclusion, our study demonstrates a novel specific effect of OA milieu on both GMP-ASC migration and cytokine receptor expression that were strictly dependent on an inflammatory environment and hypoxic condition. Therefore, only the use of a specific culture OA environment allows to specifically define the real therapeutic effect of GMP-ASC, suggesting that their specific recruitment to synovial macrophages is partially dependent on CXCL10/IP10-CXCR3 axis. This is the first study that focuses on an adequate GMP-ASC injection environment, presenting novel indications that contribute to understand the role of OA milieu on GMP-ASC .

Sivelestat (100 mg/ml), were used on cartilage explants treated by conditioned medium of macrophages pre-treated or not by IL-6 (CM-IL-6). Cartilage catabolism was determined by histology, and matrix metalloproteinase MMP-3 production was evaluated by Western Blot and immunohistochemistry (IHC). Weekly intraarticular injections of Sivelestat (1mM) were performed in the DMM to determine the role of Elane in OA. Results: DSerpina3n Col2 mice had more severe OA lesions than control littermates 6 weeks after DMM, with greater cartilage damage (mean±SD OARSI score: 5.6±0.4 vs 3.4±0.5, p¼0.01), increased synovitis scores (3.0±0.3 vs 1.9±0.3, p¼0.03) and bigger osteophytes (7.2±0.8x10 7 vs 3.8±0.8x10 7 m 3 , p¼0.048). Conversely, WT mice treated with intraarticular injections of SerpinA3N 15nM exhibited less severe cartilage loss than mice treated with PBS after DMM (OARSI score: 2.1±0.4 vs 3.9±0.5, p¼0.02). Elane mRNA expression was increased in macrophages upon IL-6 stimulation. In cartilage explants, CM-IL-6 activated cartilage catabolism and MMP-3 production, and effect that was blunted by Ser-pinA3N and Sivelestat. Finally, mice treated with intra-articular injections of Sivelestat had less severe cartilage damage than those treated with PBS after DMM (OARSI score: 3.3±0.5 vs 5.8±0.5, p¼0.0046). Conclusions: SerpinA3N protects against experimental OA via the inhibition of Elane, a pro-catabolic serine protease produced by macrophages upon IL-6 stimulation. This results describe a novel mechanism by which macrophages drive cartilage catabolism and open up new therapeutic perspectives.