Development of Vascular Smooth Muscle Stem Cell Niche

项目摘要 该项目的长期目标是揭示血管平滑肌干细胞群的生态位 细胞（VSMCs）在胚胎发生过程中建立。越来越清楚的是，VSMC的间皮起源 由全身的许多血管系统保存，如心脏、肠、肠系膜、肺， 肝脏在成人中，间皮在伤口愈合期间产生VSM干细胞和VSMC。尽管 尽管间皮细胞在VSMCs来源中的重要性，但对间皮细胞生态位如何 在体腔内腔和内部器官表面诱导和限定。 我们最近开发了一种全面的高分辨率实时成像系统， 是时候观察胚胎内体腔的形成了。目前还没有已知的管腔形成机制， 如细胞内空泡的融合、离子通道介导的渗透压变化和细胞凋亡。 检测到相反，我们发现：（a）侧板中胚层（LPM）和内胚层产生长 丝状突起，类似于特化的细胞丝丝状伪足（CF）;（B）LPM的CF延伸通过 层粘连蛋白1丰富的细胞外基质（ECM），到达外胚层，并直接接受BMP 7从 外胚层;（c）内胚层CF向腹侧LPM延伸;（d）在直接接触胚层间时， 在CF中，LPM中水平出现小开口。他们随后的融合建立了一个单一的 （e）ephrinA 2和ephrinB 1因子沿沿着 背腹轴（LPM夹在ephrinA 2 +/ephrinB 1-外胚层和ephrinA 2-/ephrinB 1+外胚层之间 最后（f）在几种外胚层形态发生剂中，外胚层BMP 7对所有关键步骤都至关重要 用于体腔形成以启动VSM干细胞龛发育。 基于这些令人惊讶的发现，本申请提出实验性地测试以下新颖模型 间皮生态位发育：容纳VSM干细胞和VSMC的间皮生态位由以下启动： 两种沿着背腹轴的不对称信号传递机制：（1）CF介导的胚层间传递 信号传导因子从外胚层和内胚层到中胚层的形态发生分离 LPM通过Eph/ephrin基因家族的不对称表达。 这项研究提供了一个新的机制模型，不对称的细胞和分子之间的相互作用， LPM和上覆的外胚层和下伏的内胚层，以及这是如何建立间皮的 藏着VSM干细胞的小生境。这项研究的结果也将作为一个新的框架， 用于治疗血管疾病的未来治疗方法。

Project Summary The longterm goal of this project is to uncover how the niche for a stem population of vascular smooth muscle cells (VSMCs) is established during embryogenesis. It is becoming clear that a mesothelium origin of VSMCs is conserved by many vascular systems throughout the body, such as the heart, intestine, mesentery, lung, and liver. In the adult, the mesothelium generates VSM stem cells and VSMCs during wound healing. Despite the importance that the mesothelium in sourcing of VSMCs, little is known about how the mesothelium niche is induced and defined at the body cavity lumen and internal organ surface. We have recently developed a comprehensive high resolution live imaging system that enabled us for the first time to view body cavity formation within embryos. None of currently known mechanisms for lumen formation, such as fusion of intracellular vacuoles; ion channel-mediated osmolality changes; and apoptosiswere detected. Instead, we have found that: (a) The lateral plate mesoderm (LPM) and the endoderm produced long filamentous projections, that resembled specialized cytoneme filopodia (CF); (b) LPM's CFs extended through Laminin1-rich extracellular matrix (ECM), reached to the ectoderm, and directly received BMP7 from the ectoderm; (c) Endodermal CFs extended toward the ventral LPM; (d) Upon direct inter-germ layer contacts of the CFs, small openings appeared horizontally in the LPM. Their subsequent fusions established a single continuous body cavity lumen; (e) Factors ephrinA2 and ephrinB1 were expressed asymmetrically along the dorsoventral axis (the LPM was sandwiched by ephrinA2+/ephrinB1- ectoderm and ephrinA2-/ephrinB1+ endoderm); and finally (f) Of several ectodermal morphogens, ectodermal BMP7 was crucial for all key steps listed above for body cavity formation to initiate VSM stem cell niche development. Based on these surprising findings, this application proposes to experimentally test the following novel models for mesothelial niche development: The mesothelial niche housing VSM stem cells and VSMCs is initiated by two asymmetric signaling mechanisms along the dorsoventral axis: (1) CF-mediated inter-germ layer transfer of signaling factor(s) from the ectoderm and endoderm to the mesoderm; and (2) Morphogenetic separation of the LPM by an asymmetric expression of the Eph/ephrin gene family. The proposed study offers a new mechanistic model of asymmetric cellular and molecular interactions between the LPM and the overlaying ectoderm and underlying endoderm, and how this establishes the mesothelial niche that harbors VSM stem cells. The outcomes of this study will also serve as a new framework to design future therapeutic approaches for treatment of vascular diseases.