Abstract 12459: Downregulated Fli1 in Scleroderma Myeloid Cells May Contribute to Cardiac Fibrosis via a Galectin-3/mTOR Dependent Pathway

Abstract

Introduction: Scleroderma (SSc) is an autoimmune fibrotic disease with high mortality and no effective therapies. Cardiac fibrosis in SSc is common and has a poor prognosis, but pathogenesis is unclear. Galectin-3 secretion by macrophages has been implicated in cardiac fibrosis, but its specific contribution to SSc cardiac disease has not been elucidated. We recently demonstrated that Fli1, a member of the Ets family of transcription factors, is decreased in SSc myeloid cells, and that Fli1 depleted macrophages have a profibrotic phenotype. We aim to evaluate the contribution of myeloid Fli1 to SSc cardiac fibrosis. Methods: Levels of galectin-3 were assessed by ELISA in serum, and qPCR and immunofluorescence in monocytes. Primary human cardiac fibroblasts were co-cultured with macrophages using inserts. Rapamycin (10nM) was used to treat the co-cultures. Western blot was used to assess protein levels of collagen and p70S6K. Collagen deposition in hearts from mice with conditional deletion of Fli1 in macrophages ( LysMCre/Fli1 fl/f l ) was assessed by picrosirius red. Results: SSc patients had higher expression of galectin-3 in monocytes and serum compared to healthy controls. Co-culture of human cardiac fibroblasts and Fli1 depleted macrophages resulted in induction of galectin-3 expression by macrophages, and activation of the mTOR/p70S6K pathway with enhanced collagen type I protein deposition by fibroblasts. These effects were blocked by the mTOR inhibitor Rapamycin, and by treatment of macrophages with siRNA against galectin-3. Deletion of Fli1 in macrophages via Cre-mediated recombination using LysMCre mice predisposed mice to develop cardiac fibrosis. Conclusions: These findings suggest that Fli1 deficiency in macrophages may contribute to SSc cardiac fibrosis, and that Rapamycin may be a potential therapeutic option for heart involvement in SSc.