OP0007 CCR2 inhibition abrogates IL-6–induced activation of matrix metalloproteinases in cartilage
Authors: A Latourte, J Maillet, J Goossens, H-K Ea, M Cohen-Solal, E Haÿ, P Richette
Journal: Annals of the Rheumatic Diseases (2017)

<h3>Background</h3> Interleukin 6 (IL-6) plays a crucial role in many rheumatic diseases, including osteoarthritis (OA) [1]. In cartilage, IL-6 activates chondrocyte catabolism by increasing the production of matrix-degrading enzymes, including matrix metalloproteinase 3 (MMP-3) and MMP-13, but it could have other roles. <h3>Objectives</h3> We aimed to identify new biological processes regulated by IL-6 in cartilage. <h3>Methods</h3> RNA-seq analysis (Illumina HiSeq platform) was used to determine biological pathways associated with IL-6/IL-6R (100 ng/ml) stimulation in mouse primary articular chondrocytes. Results were further validated by qPCR and western blot analysis. The effect of stimulation with CC chemokine ligand 2 (CCL2; 10 ng/ml), CCL7 and CCL8 (100 ng/ml) was investigated <i>in vitro</i> and <i>ex vivo</i> in mouse femoral head cartilage explants. The impact of targeted inhibition of CCL2 or CCL7 by siRNA or blockade of their common receptor CCR2 by a specific antagonist (RS-504393) was determined in IL-6–treated chondrocytes and/or cartilage explants. <h3>Results</h3> Transcriptomic analysis revealed overrepresentation of multiple functional clusters of genes in IL-6–stimulated chondrocytes, with strongly increased expression of signalling molecules and especially cytokines. Two of the 10 top genes upregulated by IL-6 were <i>Ccl7</i> (log2 fold change [FC] 2.33, adjusted p-value [p<sub>adj</sub>] =3.35x10<sup>-62</sup>) and <i>Ccl2</i> (log2 FC 1.85, p<sub>adj</sub> =9.10x10<sup>-26</sup>), which encode for CCR2 ligands. qPCR and western blot validations confirmed these results and revealed that IL-6 stimulation also increased the mRNA level of <i>Ccl8</i>, another CCR2 ligand not identified by RNA-seq analysis. CCL2 and CCL7 but not CCL8 activated extracellular signal-regulated kinase 1/2 and c-Jun N-terminal kinase signalling and increased MMP-3 and MMP-13 production and activation. CCR2 blockade but not the specific inhibition of CCL2 or CCL7 by siRNA, greatly abrogated the IL-6–induced catabolism <i>in vitro</i> and <i>ex vivo</i>. <h3>Conclusions</h3> We identified 2 chemokines, CCL2 and CCL7, as key targets of IL-6 in chondrocytes. Although their main role is to mediate monocyte/macrophage recruitment to the joint, their receptor, CCR2, is also strongly involved in IL-6–induced cartilage catabolism. These results suggest a novel mechanism by which CCL2/CCR2 and CCL7/CCR2 signalling could be involved in rheumatic diseases, especially OA [2]. <h3>References</h3> Latourte A, Cherifi C, Maillet J, et al. Systemic inhibition of IL-6/Stat3 signalling protects against experimental osteoarthritis. Ann Rheum Dis Published Online First: 27 Oct 2016. doi:10.1136/annrheumdis-2016–209757. Raghu H, Lepus CM, Wang Q, et al. CCL2/CCR2, but not CCL5/CCR5, mediates monocyte recruitment, inflammation and cartilage destruction in osteoarthritis. Ann Rheum Dis Published Online First: 13 Dec 2016. doi:10.1136/annrheumdis-2016–210426. <h3>Disclosure of Interest</h3> None declared