Active repression of Sox9 by Jag1 is required for silencing the default chondrogenic fate of the vascular smooth muscle wall [set 1]

Acquisition and maintenance of vascular smooth muscle fate is essential for the morphogenesis and function of the circulatory system. Loss of contractile properties or changes in the identity of vascular smooth muscle cells (vSMC) can result in structural alterations associated with aneurysms and vascular wall calcifications. Here we report that maturation of sclerotome-derived vSMC is dependent on a transcriptional switch between mouse embryonic days 13 and 14.5. At this time point, Jag1-mediated repression of sclerotome transcription factors Pax1, scleraxis and Sox9 is necessary to fully enable vSMC maturation. Specifically, Notch signaling in vSMC antagonizes sclerotome and cartilage transcription factors, and promotes upregulation of contractile genes. In the absence of Jag1, vSMC acquire a chondrocytic transcriptional repertoire that can lead to ossification of the vascular wall. Importantly, our findings suggest that sustained Notch signaling is essential throughout vSMC life to maintain contractile function, prevent vSMC reprogramming and promote vascular wall integrity. mRNA profile of vascular Smooth Muscle Cells, isolated from the descending aorta of Immorto mouse, treated or not with gamma-secretase inhibitor was generated by deep sequencing, in triplicate.

血管平滑肌细胞命运的获得与维持，对于循环系统的形态发生与功能发挥至关重要。血管平滑肌细胞（vascular smooth muscle cells, vSMC）收缩特性的丧失或表型改变，可引发与动脉瘤、血管壁钙化相关的结构异常。本研究发现，生骨节来源的vSMC的成熟，依赖于小鼠胚胎第13天至14.5天之间发生的转录开关事件。在此阶段，Jag1介导的对生骨节转录因子Pax1、scleraxis及Sox9的抑制作用，是完全激活vSMC成熟程序的必要条件。具体而言，vSMC内的Notch信号通路可拮抗生骨节与软骨相关转录因子，并促进收缩相关基因的表达上调。当Jag1缺失时，vSMC会获得软骨细胞样的转录谱，进而引发血管壁骨化。值得注意的是，本研究结果表明，在vSMC的整个生命周期中维持Notch信号通路的活性，对于维持其收缩功能、阻止vSMC重编程以及维护血管壁完整性均不可或缺。本研究采用深度测序（deep sequencing）技术，对经γ-分泌酶抑制剂（gamma-secretase inhibitor）处理或未处理的、从永生小鼠（Immorto mouse）降主动脉中分离得到的vSMC的mRNA表达谱进行了三次生物学重复检测。