A novel role of endothelin-1 in linking Toll-like receptor 7-mediated inflammation to fibrosis in congenital heart block

Autoimmune associated congenital heart block (CHB) may result from pathogenic cross-talk between inflammatory and profibrosing pathways. Incubation of macrophages with immune complexes (IC) composed of Ro60, a target of the pathologic maternal autoantibodies necessary for CHB, hY3 ssRNA, and affinity-purified anti-Ro60 antibody induces the Toll-like receptor 7 (TLR7)-dependent generation of supernatants that provoke a fibrosing phenotype in human fetal cardiac fibroblasts. We show herein that these cells are a major source of TGFβ and that endothelin-1 (ET-1) is one of the key components responsible for the profibrosing effects generated by stimulated macrophages. Supernatants from macrophages incubated with IC induced the fibroblast secretion of TGFβ, which was inhibited by treating the macrophages with an antagonist of TLR7. Under the same conditions, the induced fibroblast secretion of TGFβ was decreased by inhibitors of the ET-1 receptors ETa or ETb or by an anti-ET-1 antibody but not by an isotype control. Exogenous ET-1 induced a profibrosing phenotype, whereas fibroblasts transfected with either ETa or ETb siRNA were unresponsive to the profibrosing effects of the IC-generated macrophage supernatants. Immunohistochemistry of the hearts from two fetuses dying with CHB revealed the presence of ET-1-producing mononuclear cells in the septal region in areas of calcification and fibrosis. In conclusion, these data support a novel role of ET-1 in linking TLR7 inflammatory signaling to subsequent fibrosis and provide new insight in considering therapeutics for CHB.