Abstract 11611: The Wnt Inhibitor Secreted Frizzled-Related Protein 3 Protects Mitral Valve Endothelium from Mi-Induced Endothelial to Mesenchymal Transition

Abstract

Introduction: There are changes in the mitral valve (MV) leaflets seen within 2-6 months post-myocardial infarction (MI) that include endothelial to mesenchymal transition (EndMT) and fibrosis. Early modulation of EndMT and fibrosis in MV leaflets may limit ischemic mitral regurgitation and heart failure. The onset of EndMT and fibrosis in MV leaflets and the mechanism of their instigation are not known. Hypothesis: We hypothesized that circulating molecules present in plasma within days after MI incite EndMT and fibrotic processes in MV leaflets. Methods: Using flow cytometric analysis and immunofluorescence staining, we examined the onset of EndMT in 20 adult sheep: 8 sheep with IMI, 8 with sham surgery, and 4 naïve controls with immediate excision of hearts under general anesthesia. The effect of plasma on EndMT induction in primary MV endothelial cells (VECs) was assessed by qPCR, migration assays, and immunofluorescence staining. Plasma cytokine levels were assessed using a cytokine array. Immunoblotting, immunofluorescence staining, RNA sequencing and bioinformatic analysis were used to identify biochemical changes by post-MI plasma. Results: Ovine MVs harvested 8-10 days after inferior MI revealed an onset of EndMT, shown by increased CD31/α-SMA-positive cells in post-MI MV leaflets. In contract to sham plasma, post-MI plasma induced EndMT and pro-fibrotic markers and enhanced migration of primary mitral VECs. Analysis of sham versus post-MI plasma revealed a significant drop in the Wnt antagonist sFRP3 in post-MI plasma. Addition of recombinant sFRP3 to post-MI plasma reversed its EndMT-inducing effect on mitral VECs, measured by restored VE-cadherin, reduced α-SMA, and reduced TGFβ1-3 expression. RNA-seq analysis of mitral VECs exposed to post-MI showed upregulated FOXM1. Blocking FOXM1 with Siomycin A reduced EndMT and pro-fibrotic transcripts in mitral VECs treated with post-MI plasma. Finally, FOXM1 induced by post-MI plasma was downregulated by sFRP3. Conclusions: Reduced sFRP3 in post-MI plasma facilitates EndMT and fibrosis in mitral VECs by increasing the transcription factor FOXM1. Restoring sFRP3 levels and/or inhibiting FOXM1 may provide new strategies to minimize MI-induced maladaptive changes that occur in the MV.