Kim et al. Arthritis Research & Therapy (2021) 23:124 https://doi.org/10.1186/s13075-021-02491-1 RESEARCH ARTICLE Open Access Regulation of osteoclastogenesis by mast cell in rheumatoid arthritis Kyoung-Woon Kim1, Bo-Mi Kim2, Ji-Yeon Won1, Hong-Ki Min3, Kyung-Ann Lee4, Sang-Heon Lee3 and Hae-Rim Kim3* Abstract Background: In the pathogenesis of rheumatoid arthritis (RA), the role of mast cells has not been revealed clearly. We aimed to define the inflammatory and tissue-destructive roles of mast cells in rheumatoid arthritis (RA). Methods: Serum and synovial fluid (SF) concentration levels of tryptase, chymase, and histamine were quantified using ELISA. After activating mast cells using IL-33, the production of TNF-α,IL-1β, IL-6, IL-17, RANKL, and MMPs was determined using real-time PCR and ELISA. Osteoclastogenesis was assessed in CD14+ monocytes from peripheral blood and SF, which were cultured with IL-33-activated mast cells, by counting TRAP-positive multinucleated cells. Results: The concentration levels of serum tryptase, chymase, and histamine and SF histamine were higher in patients with RA than in controls. FcεR1 and c-kit-positive mast cells were higher in RA synovium than in osteoarthritic (OA) synovium. Stimulation of mast cells by IL-33 increased the number of trypatse+chymase− and tryptase+chymase+ mast cells. IL-33 stimulation also increased the gene expression levels of TNF-α,IL-1β, IL-6, IL-17, RANKL, and MMP-9 in mast cells. Furthermore, IL-33 stimulated human CD14+ monocytes to differentiate into TRAP+ multinucleated osteoclasts. When CD14+ monocytes were co-cultured with mast cells, osteoclast differentiation was increased. Additionally, IL-33- activated mast cells stimulated osteoclast differentiation. The inhibition of intercellular contact between mast cells and monocytes using inserts reduced osteoclast differentiation. Conclusions: IL-33 increased inflammatory and tissue-destructive cytokines by activation of mast cells. Mast cells stimulated osteoclast differentiation in monocytes. Mast cells could stimulate osteoclastogenesis indirectly through production of tissue-destructive cytokines and directly through stimulation of osteoclast precursors. Keywords: Rheumatoid arthritis, Mast cell, Osteoclast, Cytokine Background Mast cells, which are typically found in allergic diseases, Rheumatoid arthritis (RA) is characterized by intercellular are also found in RA synovial tissues and synovial fluid interactions between macrophages, lymphocytes, synovial (SF). They are also known to be involved in RA pathogen- fibroblasts, osteoclasts, and chondrocytes, resulting in esis. In RA, the synovium shows hyperplasia of mast cells, chronic inflammation and joint destruction [1]. Although which can comprise up to 5% of all RA synovial cells. The the roles of most of these cells in RA pathogenesis are number of mast cells in RA synovium is higher than that well-studied, mast cells and basophils remain important in osteoarthritic synovium [3]. Mast cells are mainly found exceptions [2]. around blood vessels, in the sublining area, and in areas of cartilage erosion. There are 2 types of mast cells: tryptase- * Correspondence: [email protected] positive MCT cells and tryptase/chymase double-positive 3Division of Rheumatology, Department of Internal Medicine, Research Institute of Medical Science, Konkuk University School of Medicine, 120-1 MCTC cells [3]. MCTC cells can be found in the normal Neungdong-ro, Gwangjin-gu, Seoul 05030, South Korea synovium. The number of MCT cells increases during Full list of author information is available at the end of the article © The Author(s). 2021 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Kim et al. Arthritis Research & Therapy (2021) 23:124 Page 2 of 13 early RA, indicating tissue inflammation, while that of 16.8 years, rheumatoid factor (RF) 175.8 ± 49.1 IU/L, anti- MCTC cells increases during advanced RA, indicating CCP antibody 462.2 ± 163.2 IU/L, erythrocyte sedimenta- tissue remodeling [4]. tion rage (ESR) 59.6 ± 7.2 mm/h, C-reactive protein (CRP) The role of mast cells in RA is unclear. Some reports 4.5 ± 1.0 mg/dl, DAS28-CRP 4.29 ± 0.2, and disease have demonstrated pathogenic inflammatory roles of duration 2.8 ± 1.7 years. Thirteen patients were not mast cells in RA, while others have shown anti- taking medications, and others were taking oral inflammatory roles of mast cells in RA. Four broad lines disease-modifying antirheumatic drugs (DMARDs). SF of argument have been made for claiming that mast cells was collected from 20 RA patients and 20 patients have an inflammatory role in RA. First, the number of with osteoarthritis of knee joints. All SF samples were mast cells increases in RA synovium and this correlates obtained through therapeutic arthrocentesis before with disease activity parameters [3]. Patients with active steroid injection into the swollen joints. Clinical data RA have more mast cells in synovial tissues than patients of RA patients are as follows: 12 females and 8 males, with end-stage RA [5]. Second, mast cells release various age 53.9 ± 3.2 years, rheumatoid factor (RF) 143.5 ± inflammatory cytokines in RA synovial joints, including 39.3 IU/L, anti-CCP antibody 418.1 ± 155.7 IU/L, ESR interleukin (IL)-6, tumor necrosis factor (TNF)-α, and 51.5 ± 7.8 mm/h, CRP 3.7 ± 1.1 mg/dl, DAS28-CRP 3.8 ± IL-8. Third, histamine and other mast cell mediators 1.1, and disease duration 5.4 ± 1.6 years. Two patients have a potential for angiogenesis, fibroblast and macro- were not taking medications, 1 patient was taking tofaciti- phage activation, osteoclast differentiation, and leukocyte nib, and others were taking oral DMARDs. Synovial recruitment [6–10]. In our previous study, histamine, a tissues were isolated from three RA patients (mean age preformed mediator of activated mast cells, was found to 63.4 ± 4.6 years; range 38–76) and three osteoarthritis stimulate the production of receptor activator of nuclear (OA) patients (mean age 63.5 ± 4.5 years; range 59–68) factor kappa-Β ligand (RANKL) and osteoclast differenti- undergoing total knee-replacement surgery. Informed ation via the histamine H4 receptor [10]. Fourth, mast consent was obtained from all patients. All protocols were cell-deficient animal models are resistant to arthritis performed in accordance with relevant guidelines and reg- [11–13]. In contrast to these arguments, there is also ulations and were approved by the Institutional Review evidence for the anti-inflammatory role of mast cells in Board for Human Research in Konkuk University Hospital RA. First, mast cells suppress monocyte and fibroblast (KUH1010960). activation, dendritic cell migration, and Th1 differenti- ation by inducing the secretion of IL-10, IL-4, IL-13, and Reagents transforming growth factor (TGF)-β [8, 14–16]. Second, Recombinant IL-33, RANKL, and M-CSF were purchased the development of arthritis in animal models is not from R&D systems (Minneapolis, MN). affected by the deficiency of mast cells [17, 18]. Third, serum tryptase levels in RA patients are negatively corre- Human mast cell line culture and stimulation lated with the levels of C-reactive protein [19]. The human mast cell line (LUVA) was purchased from In this study, we aimed to assess the inflammatory and Kerafast (Kerafast, MA, USA) and maintained in tissue-destructive roles of mast cells in RA. We quantified StemPro-34 SFM at a concentration of 5 × 105 cells/ml. the serum and SF concentration of mast cell mediators The cells were grown at 37 °C with 5% CO2, and the such as tryptase, chymase, and histamine in RA patients medium was exchanged weekly with 50% fresh medium and characterized mast cell phenotypes of the mono- without exogenous cytokines. The mast cells were nuclear cells in the SF of RA patients. We also determined seeded in 6-well plates at a density of 5 × 104 cells/ml. the expression and production of proinflammatory After 1 day, the medium was replaced with StemPro-34 cytokines, IL-17, matrix metalloproteinases (MMPs), and SFM culture medium with or without cytokines. The RANKL after stimulating mast cells with IL-33. Finally, we mast cells were then stimulated with 100 ng/mL human examined the effects of activated mast cells on osteoclast recombinant IL-33 (R&D Systems, Inc.) for 24 and 72 h. differentiation in human monocytes. The supernatants and RNA were harvested and stored at − 80 °C until analysis. Methods Ethics statement and patients Enzyme-linked immunosorbent assay (ELISA) Written informed consent was obtained from healthy SF and serum samples obtained from healthy volunteers volunteers and patients with RA and osteoarthritis. All and patients with RA and osteoarthritis were subjected RA patients fulfilled the 2010 ACR/EULAR classification to tryptase, chymase, and histamine analyses using tryp- criteria for RA [20]. Serum was collected from 20 RA tase (Boster Biological Technology, CA), chymase (Aviva patients and 20 healthy volunteers.