From osteoarthritic synovium to synovial-derived cells characterization: synovial macrophages are key effector cells

Abstract

BackgroundThe aim of the study was to characterize synovial cells from OA synovium with low-grade and moderate-grade synovitis and to define the role of synovial macrophages in cell culture.MethodsSynovial tissue explants were analyzed for the expression of typical markers of synovial fibroblasts (SF), synovial macrophages (SM) and endothelial cells. Synovial cells at passage 1 (p.1) and 5 (p.5) were analyzed for different phenotypical markers by flow cytometric analysis, inflammatory factors by multiplex immunoassay, anabolic and degradative factors by qRT-PCR. P.1 and p.5 synovial cells as different cell models were co-cultured with adipose stem cells (ASC) to define SM effects.ResultsSynovial tissue showed a higher percentage of CD68 marker in moderate compared with low-grade synovitis. Isolated synovial cells at p.1 were positive to typical markers of SM (CD14, CD16, CD68, CD80 and CD163) and SF (CD55, CD73, CD90, CD105, CD106), whereas p.5 synovial cells were positive only to SF markers and showed a higher percentage of CD55 and CD106. At p.1 synovial cells released a significantly higher amount of all inflammatory (IL6, CXCL8, CCL2, CCL3, CCL5) and some anabolic (IL10) factors than those of p.5. Moreover, p.1 synovial cells also expressed a higher amount of some degradative factors (MMP13, S100A8, S100A9) than p.5 synovial cells. Co-culture experiments showed that the amount of SM in p.1 synovial cells differently induced or down-modulated some of the inflammatory (IL6, CXCL8, CCL2, CCL3, CCL5) and degradative factors (ADAMTS5, MMP13, S100A8, S100A9).ConclusionsWe found that p.1 (mix of SM and SF) and p.5 (only SF) synovial cells represent two cell models that effectively reproduce the low- or moderate-grade synovitis environment. The presence of SM in culture specifically induces the modulation of the different factors analyzed, confirming that SM are key effector cells.Electronic supplementary materialThe online version of this article (doi:10.1186/s13075-016-0983-4) contains supplementary material, which is available to authorized users.

Focal Defects of the Knee Articular Surface: Evidence of a Regenerative Potential Pattern in Osteochondritis Dissecans and Degenerative Lesions

“…The slides were developed as described [25]. Negative controls were performed by omitting the primary antibody, and isotype-matched controls were performed by using an isotype-matched primary antibody.…”

Inflamed synovial fluid induces a homeostatic response in bone marrow mononuclear cells in vitro: Implications for joint therapy

“…[3][4][5] Synovial macrophages are the main drivers of cytokine production and the inflammatory response in the OA-affected synovium. 6,7 While synovial fibroblasts participate in amplifying this response, they cannot primarily incite it. 6,7 Early in vivo studies have reported that depletion of synovial macrophages decreases synovial inflammation in experimentally induced arthritis, 8 clinical cases of rheumatoid arthritis, 9 and more recently ex vivo.…”

“…6,7 While synovial fibroblasts participate in amplifying this response, they cannot primarily incite it. 6,7 Early in vivo studies have reported that depletion of synovial macrophages decreases synovial inflammation in experimentally induced arthritis, 8 clinical cases of rheumatoid arthritis, 9 and more recently ex vivo. 6,7 Taken together, these studies demonstrate that controlling the response of synovial macrophages can benefit the treatment of OA and other types of arthritis.…”

“…12 When these physiological functions become overwhelmed, synovial macrophages upregulate inflammation, recruiting lymphocytes, and neutrophils in response to increased demands for repair. 7,13,14 Sustained joint damage impedes the resolution of the inflammatory response and related cytokines and catabolic enzymes lead to joint degeneration. 6,15 Therefore, the resolution of inflammation is a needed event to interrupt the catabolic processes in OA and to reestablish a homeostatic synovial environment favorable for tissue anabolism and turnover.…”

<b>Pro-inflammatory Cytokine Production in Co-culture of Human Monocytes and Synovial Fibroblasts from the Human Temporomandibular Joint </b>

“…Both types of monocytes stained positive for CD14 and CD68 using immunocytochemistry. CD68 positive staining is mainly found on synovial macrophages located in the OA synovial membrane (9). We consider that these findings suggest that the monocytes used in this study can differentiate into macrophages by monolayer culture and that these monocytes are useful as an in vitro synovitis model.…”