P118 Transforming growth factor beta induced (TGFΒi,) a new player in the therapeutic effect of mesenchymal stem cells

Introduction Osteoarthritis (OA) is the most common form of chronic joint diseases. In recent years, stem cell-based therapies have been investigated as an alternative approach to treat OA. Mesenchymal Stem Cells (MSCs) have demonstrated therapeutic efficacy in the context of pre-clinical studies. More than the capacity of these cells to differentiate into chondrocytes, their effect is primarily associated with a paracrine function. Objectives Because the Transforming Growth Factor β (TGFβ) pathway plays a critical role in joint homeostasis, we investigated whether the therapeutic effect of MSCs could be mediated by members of the TGFβ family. Using a secretome analysis, we identified Transforming Growth Factor β Induced (TGFβI), a potential candidate for a chondroprotective role of MSCs. Methods Murine chondrocytes were isolated from 3 days old C57BL/6 mice and cultured for 5 days. OA-like chondrocytes were obtained by incubation with IL1β for 24 hour. Bone marrow-derived MSCs were used to produce a conditioned medium for 24 hour following or not a pre-activation step with TGFβ3 for 24 hour. For co-culture experiments, MSCs were seeded on transwells and pre-activated or not with TGFβ3 for 24 hour. Supernatants or MSC-containing transwells were added to OA-like chondrocytes (ratio 1 MSC:3 chondrocytes) for 24 hour before cell recovery for RT-qPCR analysis. For silencing experiments, siRNA directed against TGFβI were transfected in MSCs and chondrocytes with oligofectamine and lipofectamine, respectively. The Collagenase-Induced OsteoArthritis murine model (CIOA) was induced by collagenase injection in knee joints of C57BL/6 mice at day 0 and 2. MSCs were transfected twice with siRNA before being injected in knee joints at day 7 (250,000 cells/5 µL). At day 42, paws fixed in 4% formaldehyde and scanned by microCT and confocal laser scanning microscopy before being processed for histology. Results Addition of conditioned medium from MSCs or MSCs in transwells on OA-like murine chondrocytes allows to reinduce expression of the chondrocyte markers, aggrecan and type IIB collagen. Addition of transwells containing pre-activated MSCs on OA-like chondrocytes not only increased the expression of aggrecan and type IIB collagen but decreased the expression of catabolic markers, MMP13 and ADAMTS5. This effect was associated with an increased expression of TGFβI in both chondrocytes and MSCs. We therefore investigated the consequence of TGFβI silencing in either chondrocytes or MSCs. Interestingly, silencing of TGFβI in MSCs resulted in a significant reduction of their therapeutic effect. In the CIOA model, down-regulation of TGFβI in MSCs resulted in lower therapeutic effect on OA features as visualised by a reduced protective effect on cartilage and sub-chondral bone histomorphometric parameters. Conclusions Altogether, our results indicated that TGFβI secreted by MSCs can regulate cartilage homeostasis by regulating the expression of anabolic and catabolic mediators and that TGFβI participates to the protective effect of MSCs in OA. Disclosure of interest None declared