OP0071 REVEALING THE LINK BETWEEN OSTEOARTHRITIS DEVELOPMENT AND MESENCHYMAL STEM CELL SENESCENCE
Authors: Olivier Malaise, Yassin Tachikart, Michael Constantinides, Marcus Mumme, Daniele Noel, Jing Wang, Christian Jorgensen, Jean-Marc Brondello
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background</h3> Tissue accumulation of p16<sup>INK4A</sup>-positive senescent cells is associated with age-related disorders such as osteoarthritis (OA). These senescent cells induce a tissue loss of function through a particular secretory phenotype called SASP (senescence-associated secretory phenotype). <h3>Objectives</h3> Links between OA onset and cellular senescence remain poorly detailed. We wanted to determine the localization of articular senescent cells in <i>in vivo</i> OA mouse models and study the involvement of mesenchymal stem cells (MSC) senescence in OA pathogenesis. <h3>Methods</h3> Wild-type mice C57BL/6, SAMP8/R1 (senescence accelerated mouse-prone and resistant), transgenic <i>p16<sup>INK4A</sup></i><sup>+/Luc</sup> and <i>p16<sup>INK4A</sup></i><sup> Luc/Luc</sup> were used. Experimental OA was induced by intraarticular injections of collagenase (CIOA). Cartilage, synovial tissue and subchondral bone were analyzed by histology, RT-qPCR and micro-tomography. MSCs come from healthy human donors and primary chondrocytes from OA patients. <h3>Results</h3> (1) CIOA was induced in senescence-driven luciferase transgenic mice. Under CCD camera, a peak in luminescence was detected at day 24 post-injection revealing the presence of senescent cells in the joint. Remarkably, articular senescence is not only a marker of the pathology but contributes to OA onset: mice deficient in p16<sup>INK4a</sup>, a main senescence-driving known cell cycle inhibitor, were partially protected against CIOA. These results were confirmed in C57Bl/6 mice after CIOA by showing an increase in gene expression for senescence, catabolic and inflammatory markers in the synovial tissue preceding cartilage degradation. (2) MSCs found in synovial, cartilage, fat pad and bone marrow participate in joint homeostasis. Because MSC are proposed to be at the root of OA development, we hypothesize that cellular senescence onset in these progenitor cells would be a possible etiological factor for OA. We have established an <i>in vitro</i> p16<sup>INK4A</sup>-induced senescence model on human primary MSC: their intrinsic properties such as self-renewing are altered during senescence onset. Furthermore, in co-culture conditions with chondrocytes from OA patients, senescent MSC lost their extrinsic chondroprotective properties. (3) To <i>in vivo</i> challenge these findings, we rely on the mouse model of accelerated senescence SAMP8, which develop spontaneous OA at the age of 6 months with cartilage degradation, synovial hypertrophy, osteophytosis and subchondral bone remodeling associated to meniscal calcification. Isolated MSC from these mice express senescence but non-inflammatory markers (p16<sup>INK4a</sup>, p21waf1, MMP13, TGF-β1). Remarkably, intra-articular injection of these isolated SAMP8-derived MSC compared to SAMR1-derived control MSC, in young wid-type C57Bl/6 mice, was suffisant by its own, to induce significant articular cartilage degradation (OA score of 12.2 ± 1.5 vs 6.1 ± 3.5 for SAMP8 and SAMR1 MSC respectively. p &lt;0.05). <h3>Conclusion</h3> p16<sup>INK4A</sup>-induced cellular senescence in MSC played a causative role in cartilage loss of function and OA pathogeny. <i>In vitro</i>, senescent MSC show altered intrinsic and extrinsic supportive tissue functions. <i>In vivo</i>, intra-articular injection of senescent MSC was sufficient to induce cartilage degradation. Specific targeting of such deleterious senescent cells could be an innovating and promising treatment in OA. <h3>Acknowledgement</h3> We acknowledge FOREUM and AGEMED as supporters of our projects. <h3>Disclosure of Interests</h3> Olivier Malaise Speakers bureau: Amgen, Yassin Tachikart: None declared, Michael Constantinides: None declared, Marcus Mumme: None declared, Daniele Noel: None declared, Jing Wang: None declared, Christian Jorgensen: None declared, Jean-Marc Brondello: None declared