AB0124 Detection of precursors of rank- osteoclast-like cells (OLCS) in peripheral blood and olcs in bone tissue from rheumatoid arthritis patients
Authors: K. Yokota, S. Tanaka, M. Sekikawa, Y. Aizaki, K. Sato, H. Oda, T. Mimura
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Previously, we reported that novel osteoclast-like cells (OLCs) were induced, both <i>in vitro</i> and <i>in vivo</i>, from mouse bone marrow-derived macrophages (BMMs) by addition of a combination of TNFα and IL-6<sup>1</sup>. Recently, O'Brien <i>et al</i> showed that TNF/IL-6 can drive osteoclastogenesis in BMMs from <i>RANK</i>-deficient mice<sup>2</sup>. <h3>Objectives</h3> We aimed to examine the differentiation of OLCs, which were induced by a combination of TNFα and IL-6 from human peripheral blood mononuclear cells (PBMCs) and CD14 +monocytes and to identify differences in molecular expression patterns between OLCs and conventional osteoclasts. Furthermore, we identified OLCs and osteoclasts on the bone tissue of the joint in patients with rheumatoid arthritis (RA). <h3>Methods</h3> PBMCs and CD14 +monocytes from healthy volunteers and/or RA patients were stimulated with TNFα and IL-6 or RANKL. Quantitative RT-PCR was used to measure mRNA expression levels of <i>RANK, cathepsin K, calcitonin receptor, and dendritic cell-specific transmembrane protein</i>. Prepared undecalcified tibial bone from 6 RA or osteoarthritis (OA) patients undergoing joint surgery were stained by tartrate-resistant acid phosphatase (TRAP) staining and immunohistochemistry with anti-RANK antibody, expression of which were analysed. Osteoclasts and OLCs were identified as multinucleated TRAP+/RANK +cells and TRAP+/RANK- cells, respectively, adherent to the bone surface. <h3>Results</h3> The number of OLCs treated with a combination of TNFα and IL-6 from PBMCs or CD14 +monocytes in RA patients was significantly increased compared to that in healthy volunteers. Expression levels of <i>RANK</i> mRNA was clearly up-regulated in osteoclasts, and was obviously down-regulated in OLCs compared to that in osteoclast precursors. In cancellous bone, the number of TRAP+/RANK +osteoclasts was significantly increased in RA patients compared to that in OA patients. Interestingly, numerous TRAP+/RANK- OLCs were present in the cancellous bone of RA patients, while almost none were observed in the cancellous bone of OA patients. <h3>Conclusions</h3> The combination of TNFα and IL-6 strongly induced the differentiation of OLCs from PBMCs or CD14 +monocytes in RA patients. OLCs was characterised with TRAP+/RANK- multinucleated cells, which can distinguish conventional TRAP+/RANK +multinucleated osteoclasts. TRAP+/RANK- OLCs also were present in the bone tissue of RA patients. These results suggest that conventional osteoclasts and novel OLCs could be involved in the pathogenic mechanisms of inflammatory bone destruction such as RA. <h3>References</h3> [1] Yokota K, Sato K, Miyazaki T, Kitaura H, Kayama H, Miyoshi F, Araki Y, Akiyama Y, Takeda K, Mimura T. Combination of tumor necrosis factor α and interleukin-6 induces mouse osteoclast-like cells with bone resorption activity both in vitro and in vivo. Arthritis Rheumatol 2014Jan;66(1):121–9. [2] O'Brien W, Fissel BM, Maeda Y, Yan J, Ge X, Gravallese EM, Aliprantis AO, Charles JF. RANK-Independent Osteoclast Formation and Bone Erosion in Inflammatory Arthritis. Arthritis Rheumatol.2016Dec;68(12):2889–2900. <h3>Disclosure of Interest</h3> None declared