Endothelial to mesenchymal transition (EndMT) is a leading cause of fibrosis and disease, however its mechanism has yet to be elucidated. The endothelium possesses a profound regenerative capacity to adapt and reorganize that is attributed to a population of vessel-resident endovascular progenitors (EVP) governing an endothelial hierarchy. Here, using fate analysis, we show that two transcription factors SOX9 and RBPJ specifically affect the murine EVP numbers and regulate lineage specification. Conditional knock-out of Sox9 from the vasculature (Sox9^fl/fl/Cdh5-Cre^ER RosaYFP) depletes EVP while enhancing Rbpj expression and canonical Notch signalling. Additionally, skin wound analysis from Sox9 conditional knock-out mice demonstrates a significant reduction in pathological EndMT resulting in reduced scar area. The converse is observed with Rbpj conditionally knocked-out from the murine vasculature (Rbpj^fl/fl/Cdh5-CreER RosaYFP) or inhibition of Notch signaling in human endothelial colony forming cells, resulting in enhanced Sox9 and EndMT related gene (Snail, Slug, Twist1, Twist2, TGF-β) expression. Similarly, increased endothelial hedgehog signaling (Ptch1^fl/fl/Cdh5-CreER RosaYFP), that upregulates the expression of Sox9 in cells undergoing pathological EndMT, also results in excess fibrosis. Endothelial cells transitioning to a mesenchymal fate express increased Sox9, reduced Rbpj and enhanced EndMT. Importantly, using topical administration of siRNA against Sox9 on skin wounds can substantially reduce scar area by blocking pathological EndMT. Overall, here we report distinct fates of EVPs according to the relative expression of Rbpj or Notch signalling and Sox9, highlighting their potential plasticity and opening exciting avenues for more effective therapies in fibrotic diseases.

内皮细胞向间质转化（EndMT）是纤维化和疾病的主要原因，但是其机理尚待阐明。内皮具有适应和重组的强大再生能力，这归因于控制内皮层级的大量血管驻留性血管内祖细胞（EVP）。在这里，使用命运分析，我们显示了两个转录因子SOX9和RBPJ专门影响鼠EVP数量并调节谱系规范。有条件地从脉管系统中剔除Sox9（Sox9 ^{fl / fl} / Cdh5-Cre ^ER RosaYFP）会消耗EVP，同时增强Rbpj表达和典型的Notch信号传导。此外，Sox9的皮肤伤口分析有条件的基因敲除小鼠表现出病理性EndMT的显着降低，导致疤痕面积减少。反过来与观察RBPJ有条件敲除来自鼠脉管系统（RBPJ ^{FL / FL} / CDH5-CreER RosaYFP）或缺口在人内皮细胞集落信令形成细胞，从而增强抑制Sox9的和EndMT相关基因（蜗牛，蛞蝓， Twist1，Twist2，TGF-β）表达。同样，内皮刺猬信号（Ptch1 ^{fl / fl} / Cdh5-CreER RosaYFP）增加，这上调了Sox9的表达在接受病理性EndMT的细胞中，也会导致过量的纤维化。过渡到间充质命运的内皮细胞表达增加Sox9，减少Rbpj和增强EndMT。重要的是，在皮肤伤口上局部施用针对Sox9的siRNA可以通过阻断病理性EndMT来显着减少疤痕面积。总体而言，在这里我们根据Rbpj或Notch信号和Sox9的相对表达报告了EVP的不同命运，突出了它们的潜在可塑性，为在纤维化疾病中进行更有效的治疗开辟了令人兴奋的途径。