P119 Local administered adipose-derived mesenchymal stromal cells reduce experimental oa-pathology via interleukin-1Β-mediated immunomodulation of pro-inflammatory PMNS
Authors: S van Dalen, M van den Bosch, A Sloetjes, L Casteilla, A Blom, P Van Lent
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Introduction</h3> Adipose-derived mesenchymal stromal cells (ASCs) exhibit anti-inflammatory characteristics and reduce development of joint pathology after injection into murine experimental inflammatory osteoarthritis (CiOA) joints.<sup>1,2</sup> This protection is only achieved when ASCs are applied in early CiOA. This early, but not the late phase of CiOA, is characterised by strongly elevated levels of S100A8/A9 and interleukin-1 beta (IL-1β),<sup>3</sup> suggesting that the inflammatory environment mediates the protective effect of ASCs. <h3>Objectives</h3> To examine the mechanism behind ASC-mediated amelioration of CiOA pathology. <h3>Methods</h3> CiOA was induced by intra-articular collagenase injection. Knee joint sections were stained with haematoxylin/eosin, the PMN-specific antibody NIMP-R14, or CD271 to locate ASCs. Gene expression and protein release of chemokines by IL-1β- or S100A8/A9-stimulated ASCs were assessed with qPCR and Luminex. Migration of MACS-isolated PMNs towards ASC-conditioned medium through Transwell membranes was examined using flow cytometry. ASC-PMN co-cultures were analysed with microscopy and Luminex. Phagocytic capacity of PMNs was measured with fluorescent labelled zymosan particles. <h3>Results</h3> Intra-articular ASC injection on day 7 of CiOA (when IL-1β and S100A8/A9 levels are highest) strongly attracted particularly PMNs, which clustered around ASCs in the synovium 6 hour after injection. IL-1β-stimulation of ASCs <i>in vitro</i> strongly increased protein expression of PMN-attracting chemokines KC, CXCL5, and CXCL7, whereas S100A8/A9 did not. Migration of PMNs towards conditioned medium of IL-1β-stimulated ASCs (IL-1β-CM) was significantly enhanced (two-fold increase) when compared to CM of non-stimulated ASCs (NS-CM). After 6 hour co-culturing ASCs with PMNs, both the number of ASCs clustering with PMNs and clustered PMNs per ASC were significantly increased after IL-1β-stimulation. Interestingly, association of PMNs with ASCs significantly diminished the release of KC protein by ASCs (69% lower after 24 hour), and also strongly reduced the release of S100A8/A9 protein by the PMNs. Finally, phagocytosis of zymosan by PMNs was strongly enhanced after priming with IL-1β-CM. <h3>Conclusions</h3> Local application of ASCs in inflamed CiOA joints results in attraction and clustering of PMNs with ASCs in the synovium, which is likely mediated by IL-1β-induced up-regulation of chemokine release by ASCs. This results in lowered levels of pro-inflammatory S100A8/A9 and enhanced phagocytic capacity of PMNs, enabling the clearance of debris to cease synovitis and promote tissue repair. <h3>References</h3> . Ter Huurne M, et al. Arthritis Rheum2012November;64(11):3604–13. . Schelbergen RF, et al. Osteoarthritis Cartilage2014August;22(8):1158–66. . Schelbergen RF, et al. Ann Rheum Dis2016January;75(1):218–25. <h3>Acknowledgements</h3> This research was supported by ADIPOA2. <h3>Disclosure of interest</h3> None declared