A8.19 Locally administrated adipose derived mesenchymal stem cells reinforce their anti-inflammatory effect through IL-1β mediated attraction of neutrophils into knee joints with experimental osteoarthritis
Authors: SCM van Dalen, RFP Schelbergen, A Slöetjes, NAJ Cremers, M ter Huurne, FA Wagener, WB van den Berg, van Lent PLEM
Journal: Annals of the Rheumatic Diseases (2015)

<h3>Introduction</h3> Osteoarthritis (OA) is characterised by cartilage breakdown and ectopic bone formation in joints. Recent studies have shown that low grade synovial inflammation, reflected by inflammatory factors like interleukin-1 beta (IL-1β), contributes to joint pathology. Recently we found that adipose derived mesenchymal stem cells (ASCs) exhibit anti-inflammatory characteristics<sup>1</sup> and reduce joint pathology after local application into mouse knee joints with experimental OA.<sup>2</sup> This anti-inflammatory effect is only observed after intra-articular injection in early but not late phase OA, suggesting that the effect may be mediated by pro-inflammatory mediators.<sup>1</sup> <h3>Objective</h3> To study the effect of IL-1β on the anti-inflammatory potency of ASCs in early OA. <h3>Methods</h3> Experimental OA was induced by injection of collagenase into murine knee joints (CIOA). Total knee joints were stained with haematoxylin/eosin and the PMN specific antibody NIMPR14. ASCs were isolated from adipose tissue and stimulated with IL-1β or interferon-gamma (IFN-γ). Gene expression in synovium and stimulated cells were analysed using qPCR. Protein levels of chemokines and cytokines were measured in the supernatant and washouts using Luminex. ASCs were co-cultured with MACS isolated bone marrow (BM-) PMNs and analysed using histology, qPCR and Luminex. <h3>Results</h3> Injection of ASCs into day 7 CIOA knee joints (when synovitis is highest) caused a strong influx of immune cells into the joint cavity shortly after injection (6 h), which had largely disappeared after 24 h. Immunohistochemistry revealed that particularly PMN-like cells were attracted. Synovial gene expression of neutrophil attracting chemokines KC, CXCL5, and CXCL7 was increased. In line with this, IL-1β stimulated ASCs injected in naive knee joints also resulted in massive influx of PMN-like cells. IL-1β and IFN-γ (as a positive control) stimulation of ASCs <i>in vitro</i> strongly enhanced gene expression of KC, CXCL5, and CXCL7 and protein levels of KC. Finally, we co-cultured ASCs with BM-PMNs in the presence of IL-1β or IFNγ. After 3 h, a clear clustering of neutrophils around ASCs was observed which significantly decreased protein levels of KC (-69% after 24 h; -76% after 48 h). <h3>Conclusion</h3> ASCs attract PMN-like cells when injected locally into a day 7 CIOA knee-joint expressing low levels of IL-1β. <i>In vitro</i>, IL-1β stimulated ASCs show an increase in chemokine expression, leading to attraction and clustering with neutrophils and significantly decreased levels of pro-inflammatory factors like KC. The anti-inflammatory effect of locally applied ASCs into OA joints showing synovitis may be triggered by IL-1β and attraction of PMN-like cells. This research was supported by the Dutch Arthritis Association. <h3>References</h3> ter Huurne M, Schelbergen R, Blattes R, <i>et al</i> . <i> Arthritis Rheum </i> 2012; <b> 64 </b>:3604–13. Schelbergen RF, van Dalen S, ter Huurne M, <i>et al</i> . <i> Osteoarthritis Cartilage </i> 2014; <b> 22 </b>:1158–66.