Objective: To examine the effect of different sources of Good Manufacturing Practice clinical grade adipose‐derived mesenchymal stem cells (AD‐MSCs) on inflammatory factors in osteoarthritic (OA) chondrocytes and synoviocytes.Methods: AD‐MSCs from infrapatellar Hoffa fat, subcutaneous (SC) hip fat, and SC abdominal fat were cocultured in Transwells with chondrocytes or synoviocytes. Inflammatory factors (interleukin‐1β [IL‐1β], tumor necrosis factor α, IL‐6, CXCL1/growth‐related oncogene α, CXCL8/IL‐8, CCL2/monocyte chemotactic protein 1, CCL3/macrophage inflammatory protein 1α, and CCL5/RANTES) were evaluated by quantitative reverse transcription–polymerase chain reaction or multiplex bead–based immunoassay. The role of different immunomodulators was analyzed.Results: All the inflammatory factors analyzed were down‐modulated at the messenger RNA or protein level independently by all 3 AD‐MSC sources or by allogeneic AD‐MSCs used in coculture with chondrocytes or synoviocytes. Inflammatory factor down‐modulation was observed only when AD‐MSCs were cocultured with chondrocytes or synoviocytes that produced high levels of inflammatory factors, but no effect was observed in cells that produced low levels of those factors, thus highlighting a dependence of the AD‐MSC effect on existing inflammation. The immunomodulators IL‐10, IL‐1 receptor antagonist, fibroblast growth factor 2, indoleamine 2,3‐dioxygenase 1, and galectin 1 were not involved in AD‐MSC effects, whereas the cyclooxygenase 2 (COX‐2)/prostaglandin E₂ (PGE₂) pathway exerted a role in the mechanism of antiinflammatory AD‐MSC action.Conclusion: The antiinflammatory effects of AD‐MSCs are probably not dependent on AD‐MSC adipose tissue sources and donors but rather on the inflammatory status of OA chondrocytes and synoviocytes. AD‐MSCs seem to be able to sense and respond to the local environment. Even though a combination of different molecules may be involved in AD‐MSC effects, the COX‐2/PGE₂ pathway may play a role, suggesting that AD‐MSCs may be useful for therapies in osteoarticular diseases.

To define if adipose mesenchymal stromal cell (ASC) treatment mediated switching of the pro-inflammatory profile of M1-like macrophages as a means to develop a tailored in vitro efficacy/potency test. We firstly performed immunohistochemical analysis of CD68, CD80 (M1-like) and CD206 (M2-like) macrophages in osteoarthritic (OA) synovial tissue. ASC were co-cultured in contact and in transwell with activated (GM-CSF + IFNγ)-M1 macrophages. We analyzed IL1β, TNFα, IL6, MIP1α/CCL3, S100A8, S100A9, IL10, CD163 and CD206 by qRT-PCR or immunoassays. Prostaglandin E2 (PGE2) blocking experiments were performed using PGE2 receptor antagonist. In moderate grade OA synovium we did not always find a higher percentage of CD80 with respect to CD206. M1-like-activated macrophage factors IL1β, TNFα, IL6, MIP1α/CCL3, S100A8 and S100A9 were down-modulated both in contact and in transwell by ASC. However, in both systems ASC induced the typical M2-like macrophage markers IL10, CD163 and CD206. Activated-M1-like macrophages pre-treated with PGE2 receptor antagonist failed to decrease secretion of TNFα, IL6 and to increase that of IL10, CD163 and CD206 when co-cultured with ASC confirming a PGE2 specific role. We demonstrated that ASC are responsible for the switching of activated-M1-like inflammatory macrophages to a M2-like phenotype, mainly through PGE2. This evidenced that activated-M1-like macrophages may represent a relevant cell model to test the efficacy/potency of ASC and suggests a specific role of ASC as important determinants in therapeutic dampening of synovial inflammation in OA.

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. Synovial 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. Synovial 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). We 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.

Human mesenchymal stem cells (hMSCs) are pluripotent adult stem cells capable of being differentiated into osteoblasts, adipocytes, and chondrocytes. The osteogenic differentiation of hMSCs is regulated either by systemic hormones or by local growth factors able to induce specific intracellular signal pathways that modify the expression and activity of several transcription factors. Runt-related transcription factor 2 (Runx2) and Wnt signaling-related molecules are the major factors critically involved in the osteogenic differentiation process by hMSCs, and SRY-related high-mobility-group (HMG) box transcription factor 9 (SOX9) is involved in the chondrogenic one. hMSCs have generated a great interest in the field of regenerative medicine, particularly in bone regeneration. In this paper, we focused our attention on the molecular mechanisms involved in osteogenic and chondrogenic differentiation of hMSC, and the potential clinical use of hMSCs in osteoarticular pediatric disease characterized by fracture nonunion and pseudarthrosis.