637 Abrogation of Sox9 expression in the endothelium blocks aberrant vascular EndMT and fibrosis

Abstract

The endothelium possesses a profound regenerative capacity to adapt and reorganise in homeostasis and disease. The capacity to regenerate is increasingly attributed to a population of vessel-resident endovascular progenitor (EVP) cells that governs an endothelial hierarchy and have the ability to form entirely new de novo vascular networks. Using fate map analysis, we show that two transcription factors Sox9 and Rbpj specifically demarcate the EVP population and regulates lineage specification; either endothelial or mesenchymal. Conditional knock-out of Sox9 from the vasculature (Sox9fl/fl/Cdh5-CreER RosaYFP) drove the depletion of EVP to a mature differentiated endothelial phenotype with a complete loss of self-renewal capacity and enhanced Rbpj expression and Notch signalling. Additionally, skin wound analysis from Sox9 knock-out mice demonstrated a significant reduction in pathological endothelial to mesenchymal transition (EndMT) resulting in reduced scar area. The converse was observed with Rbpj conditionally knocked-out from the vasculature (Rbpjfl/fl/Cdh5-CreER RosaYFP), with enhanced Sox9 and EndMT-related gene expression. We now report that vascular sonic hedgehog signalling (Ptch1fl/fl/Cdh5-CreER RosaYFP) upregulates the expression Sox9 and is key in driving pathological EndMT and vascular fibrosis, resulting in over 3-fold increase in scar area in skin wound healing. Importantly, using topical administration of siRNA against Sox9 on skin wounds significantly reduced scar area by blocking pathological EndMT. The understanding of how vascular resident EVP function opens exciting new avenues for more effective therapies in blocking vascular fibrotic disease.