Human inflammatory synovial fibroblasts induce enhanced myeloid cell recruitment and angiogenesis through a hypoxia‐inducible transcription factor 1α/vascular endothelial growth factor–mediated pathway in immunodeficient mice

Abstract

Objective. Hyperplasia and phenotypic changes in fibroblasts are often observed in chronic inflammatory lesions, and yet the autonomous pathogenic contribution of these changes is uncertain. The purpose of this study was to analyze the intrinsic ability of fibroblasts from chronically inflamed synovial tissue to drive cell recruitment and angiogenesis.Methods. Fibroblasts from patients with rheumatoid arthritis (RA) or osteoarthritis (OA), as well as fibroblasts from healthy synovial tissue and healthy skin, were cultured and subcutaneously engrafted into immunodeficient mice. Cell infiltration and angiogenesis were analyzed in the grafts by immunohistochemical studies. The role of vascular endothelial growth factor (VEGF), CXCL12, and hypoxia-inducible transcription factor 1␣ (HIF-1␣) in these processes was investigated using specific antagonists or small interfering RNA (siRNA)-mediated down-regulation of HIF-1␣ in fibroblasts.Results. Inflammatory (OA and RA) synovial fibroblasts, compared with healthy dermal or synovial tissue fibroblasts, induced a significant enhancement in myeloid cell infiltration and angiogenesis in immunodeficient mice. These activities were associated with increased constitutive and hypoxia-induced expression of VEGF, but not CXCL12, in inflammatory fibroblasts compared with healthy fibroblasts. VEGF and CXCL12 antagonists significantly reduced myeloid cell infiltration and angiogenesis. Furthermore, targeting of HIF-1␣ expression by siRNA or of HIF-1␣ transcriptional activity by the small molecule chetomin in RA fibroblasts significantly reduced both responses.Conclusion. These results demonstrate that chronic synovial inflammation is associated with stable fibroblast changes that, under hypoxic conditions, are sufficient to induce inflammatory cell recruitment and angiogenesis, both of which are processes relevant to the perpetuation of chronic inflammation.Fibroblasts are ubiquitous mesenchymal cells with vital functions during development and adulthood. They synthesize the extracellular matrix components of connective tissues needed for homeostasis and reparative responses. During development, interactions between mesenchymal and other cell lineages are necessary for the formation of many organs, and fibroblasts are sufficient to provide the positional cues required for the induction and development of the different tissues (1,2). In the adult, multiple evidence points to specialized fibroblasts as a major force in the regulation of cell homing, migration, and differentiation of highly dynamic cell populations, such as cells of the immune system or the bone marrow (3,4). With regard to the pathologic

A novel Saa3-promoter reporter distinguishes inflammatory subtypes in experimental arthritis and human synovial fibroblasts

“…To define low and high inflammatory subtypes, we analysed gene identities in the subclusters (A to E) displaying clearly differential gene expression between subgroups (figure 5B). Consistent with prior studies, group III could be classified as a high inflammatory subtype based on significantly increased expression of genes involved in chemotaxis, angiogenesis and transforming growth factor β/activin A pathways 10 25 26…”

A novel pathogenic role of the ER chaperone GRP78/BiP in rheumatoid arthritis

“…Because RA synoviums contain high numbers of inflammatory cells (e.g., macrophages) compared with OA synoviums, higher levels of ER signature in RA synoviums could be just a result of higher numbers of macrophages expressing UPR genes. To address this issue, we freshly isolated OA macrophages from OA ( Reddy et al, 2003;Misra et al, 2005Misra et al, , 2006Pyrko et al, 2007). Evidence is also emerging that GRP78 protects many tissues and organs under ER stress (Wang et al, 2010;Pfaffenbach and Lee, 2011).…”

DNA methylation regulates the expression of CXCL12 in rheumatoid arthritis synovial fibroblasts

“…16,17,20,23,40 The role of CXCL12 in cartilage destruction was further supported by in vivo experiments, which showed that CXCL12 antagonists inhibit fibroblast-induced cell infiltration in immunodeficient mice. 41 CXCL12 can signal via CXCR4 and CXCR7. Expression of CXCR4 has been detected in synovium of healthy individuals as well as in OA and RA patients.…”