Background Cardiac dysfunction is a significant cause of the high mortality in systemic sclerosis (SSc). Heart involvement in SSc patients resembles inflammatory dilated cardiomyopathy (iDCM) with inflammation and fibrosis. Myofibroblasts are the main players in cardiac fibrogenesis, but their origin remains unknown.
Objectives Here, we aim to determine the role of specific myocardial stromal cell populations in myocardial remodeling in SSc.
Methods The Fos-related antigen 2 (Fra2) tg mouse model of SSc/iDCM was studied. Immunohistochemistry (IHC) and immunofluorescence (IF) were performed on endomyocardial biopsies (EMBs) from SSc/iDCM patients (n=10) and on hearts from Fra2 tg mice (n=5). Flow cytometry analysis was used to identify subsets of myocardial stromal cells (Ter119–CD45–CD31–Sca1+CD29+). Different stromal cell subsets were sorted, cultured and stimulated with TGFβ1. The differentiation potential was assessed by qPCR, IF, stress fiber staining, SIRCOL and contraction assay on sorted cells. The antisense oligonucleotide GapmeR was used to downregulate Fra2.
Results Fra2 tg mice showed increased CD45+ leukocyte infiltrates and massive collagen deposition in the heart tissue similarly to the myocardium of SSc/iDCM patients. Moreover, the myocardium of Fra2 tg mice revealed increased expression of pro-fibrotic markers such as αSMA, vimentin, collagen I and fibronectin compared to wild type mice.
Four myocardial stromal cell populations were identified: gp38+CD90.2–, gp38+CD90.2+, gp38–CD90.2+ and gp38–CD90.2–. The frequency of gp38+CD90.2– (single positive) cells and gp38+CD90.2+ (double positive) cells was significantly higher in Fra2 myocardium compared to control mice (p=0.009; n=11).
Importantly, in the myocardium of Fra2 tg mice, the majority of gp38+ cells co-expressed αSMA, vimentin, collagen and fibronectin indicating that myocardial gp38+ stromal cells might proliferate and/or differentiate towards the myofibroblast phenotype.
Myocardial single and double positive stromal cells were cultured in vitro. After TGFβ1 stimulation, both cell populations up-regulated αSMA mRNA levels. Importantly, stromal cells from Fra2 tg mice showed the presence of αSMA fibers and stress fibers even without TGFβ1 stimulation as well as an increased contraction capability compared to control cells. These findings indicate that Fra2 overexpression might trigger the differentiation of these cells.
Consequently, Fra2 silencing resulted in a decreased differentiation capability of gp38+ stromal cells: mRNA levels of the pro-fibrotic genes αSMA and collagen I were significantly downregulated (p=0.0075 and p=0.0073; n=5). Moreover, Fra2 downregulation impaired the secretion of collagens and the formation of αSMA fibers.
Conclusions We suggest that cardiac gp38+ stromal cell populations might serve as a cellular source of pathological myofibroblasts playing a pivotal role in TGFβ/Fra2-driven myocardial remodeling in SSc.
A better understanding of the mechanisms triggering myocardial dysfunction in SSc might be helpful in developing novel and effective therapies.
Disclosure of Interest M. Stellato: None declared, M. Rudnik: None declared, F. Renoux: None declared, E. Pachera: None declared, K. Sotlar: None declared, K. Klingel: None declared, J. Henes: None declared, P. Blyszczuk: None declared, O. Distler Grant/research support from: Bayer, Sanofi, Ergonex, Boehringer Ingelheim, Actelion, Pfizer, Consultant for: from 4 D Science, Actelion, Active Biotec, Bayer, BiogenIdec, BMS, Boehringer Ingelheim, EpiPharm, Ergonex, espeRare foundation, Genentech/Roche, GSK, Inventiva, Lilly, medac, MedImmune, Pharmacyclics, Pfizer, Serodapharm, Sinoxa, G. Kania: None declared