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.
Highlights
The 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
OA synovial tissue explant characterization Synovial tissue explants from 26 patients with OA were first scored on hematoxylin-eosin-stained slides, as reported by Krenn [24] and we found low-grade synovitis in 4 samples and moderate-grade synovitis in 22 samples
For indepth analysis of the main synovial cell populations present in the synovial tissue, we analyzed CD68 and CD55 to establish the percentage of synovial macrophages and synovial fibroblasts, in both low- and moderate-grade synovitis
Summary
The 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. Different reports have recognized the importance of synovial inflammation as a key factor associated with the pain and symptoms of OA, even in the early phase of the disease [3,4,5]. A recent report has identified a gene expression pattern of cells from inflamed and non-inflamed areas of synovial tissue in OA [7]. Synovial inflammation is a process characterized by synovial thickening (hypertrophy and hyperplasia) and cell infiltration (lymphocytes and macrophages) [8, 9]. Histological analysis of synovium in OA shows an increased number of lining cells and infiltrating cells, mainly
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