Background One of the major causes of death in systemic sclerosis (SSc) patients is heart involvement which phenotypically resembles inflammatory dilated cardiomyopathy (iDCM) . Recent investigations in animal models of iDCM have demonstrated that the main source of pathological myofibroblasts originates from the bone marrow .
Objectives We hypothesized that the monocyte/macrophage compartment is responsible for the onset and progression of myocardial fibrosis in SSc. Therefore, we studied the differentiation potential of this cellular compartment and their interaction with stromal and lymphoid cell compartments.
Methods We isolated CD14+ monocytes from the peripheral blood of SSc patients and healthy subjects and differentiated them towards a myofibroblast phenotype by stimulation with TGF-β1, IL-1β, IL-4, IL-10 and IL-13. After 7 days, cells were screened for expression of the myofibroblast marker genes α-smooth muscle actin (αSMA), fibronectin and collagen I, and Fra-2 and Wnt gene expression. Additionally, we established a coculture system allowing direct coculture of monocytes with human fibroblasts or T-cells in order to analyse the role of direct and indirect cell-to-cell-interaction on both monocyte and fibroblast differentiation.
Results CD14+ monocytes differentiated towards a myofibroblast phenoypte as demonstrated by upregulation of αSMA (9.6 fold), fibronectin (380 fold) and collagen I (32.5 fold). This process involves Fra-2 signaling (2.2 fold upregulation) and Wnt signaling (Wnt-1 and Wnt-5a only detectable in stimulated cells). Inhibitor studies demonstrated that canonical TGF-β1 signaling is crucial for differentiation, although the application of TGF-β1 alone is not sufficient to induce in vitro differentiation in monoculture. However, direct coculture of monocytes with fibroblasts induced upregulation of αSMA (9.6 fold), fibronectin (150 fold) and collagen I (900 fold) in the presence of TGF-β1. In direct coculture with stimulated T-cells, monocytes also upregulated myofibroblast marker genes even without the addition of cytokines.
Conclusions We showed that monocytes from the peripheral blood have the potential to differentiate towards a myofibroblast phenotype and therefore represent a potential cellular source for pathological myofibroblasts in SSc. In vivo, this differentiation might be driven by the interaction with stimulated T-cells and resident fibroblasts. A deeper insight into the pathways that drive this process might present a novel strategy to develop disease modifying treatment for SSc in general and in heart involvement in particular.
Venalis P et al., Cardiomyopathy in murine models of systemic sclerosis. Arthritis & Rheumatology. 2014 [epub ahead of print]
Kania G et al., Heart-infiltrating prominin-1+/CD133+ progenitor cells represent the cellular source of transforming growth factor beta-mediated cardiac fibrosis in experimental autoimmune myocarditis. Circulation research. 2009;105(5):462-70.
Disclosure of Interest V. Haunerdinger: None declared, E. Pachera: None declared, R. Dobrota Grant/research support from: Actelion, Pfizer, P. Blyszczuk: None declared, O. Distler Grant/research support from: 4D Science, Actelion, Active Biotec, Bayer-Schering, Biogen, Biovitrium, BMS, Boehringer Ingelheim Pharma, EpiPharm, Ergonex, GSK, Inventiva, Medac, Novartis, Pfizer, Pharmacyclics, Roche/Genentech, Sanofi/Genzyme, Serodapharm, Sinoxa, United BioSource Corporation, Consultant for: 4D Science, Actelion, Active Biotec, Bayer-Schering, Biogen, Biovitrium, BMS, Boehringer Ingelheim Pharma, EpiPharm, Ergonex, GSK, Inventiva, Medac, Novartis, Pfizer, Pharmacyclics, Roche/Genentech, Sanofi/Genzyme, Serodapharm, Sinoxa, United BioSource Corporation, G. Kania: None declared