Microenvironmental control of the Wnt pathway for the establishment of barrier heterogeneity in the CNS vasculature

血脑屏障（BBB）由神经血管单位形成，包括内皮细胞、周细胞、星形胶质细胞、神经元和小胶质细胞，并且对于神经功能至关重要。我们已经证明，Wnt/β-连环蛋白信号传导-经典途径-在脑血管生成期间在内皮细胞中是活跃的，通过调节屏障相关基因促进BBB的发展。最近，我们提供的证据表明，内皮激活经典Wnt信号正常化神经胶质瘤血管通过调节Pdgfb，导致减少瘤周水肿。近年来，研究表明，其他几条通路如音刺猬通路、视黄酸通路也参与了内皮细胞屏障功能的诱导、成熟和维持。与此同时，很明显，不同脑区的内皮屏障特征并不相同。最引人注目的例子是室周器官（CVOs），由于其神经分泌和/或神经感觉功能，缺乏内皮血脑屏障。我们已经收集了初步的数据，支持的解释，Wnt/β-连环蛋白通路的活动是特别缺乏在血管的室周器官。这表明，在CVOs的一个特定的微环境的血管分化和重塑成为建立在胚胎发育过程中，禁止Wnt途径activation.Dominant激活内皮β-catenin信号转导导致上调的屏障和下调的通透性相关基因claudin-5和MECA-32，分别。这一观察结果表明，CVO中的血管能够分化为屏障内皮细胞。虽然一些研究描述和讨论，不同地区的中枢神经系统表现出不同的血脑屏障的性质，没有什么是已知的发展和介导的差异内皮屏障表型的形成的分子线索。基于我们已发表和未发表的结果，我们假设CNS中的血管异质性是通过微环境对Wnt/β-连环蛋白信号传导的影响实现的，在CVOs中最明显。为了验证这一假设，我们的目标是：1。详细描述CVO血管的发育、屏障和通透性标志物的表达以及Wnt通路组分及其与其他通路的相互作用.利用转基因、他莫昔芬诱导的动物模型，研究体内β-连环蛋白的内皮特异性功能获得的结果3。这些方法将有助于理解屏障异质性的基本原理，以及内皮屏障特性在CNS水平衡和免疫反应调节中的功能参与。

The blood-brain barrier (BBB) is formed by the neurovascular unit, comprising endothelial cells, pericytes, astrocytes, neurons and microglia, and is crucial for neural function. We have shown that Wnt/beta-catenin signalling - canonical pathway - is active in endothelial cells during brain angiogenesis, contributing to the development of the BBB by regulating barrier-associated genes. More recently, we have provided evidence that endothelial activation of canonical Wnt signalling normalizes glioma vessels by regulating Pdgfb, leading to reduced peritumoral oedema. Since recently, several other pathways like sonic hedgehog, retinoic acid have been shown be involved in the induction, maturation and maintenance of barrier properties in endothelial cells. In parallel it became evident that endothelial barrier characteristics are not identical in different brain regions. The most striking examples are the circumventricular organs (CVOs) that, due to their neurosecretory and/or neurosensory function, lack an endothelial BBB.We have collected preliminary data that support the interpretation that Wnt/beta-catenin pathway activity is specifically absent in vessels of the circumventricular organs. This suggests that in the CVOs a specific microenvironment of vascular differentiation and remodelling becomes established during embryonic development, prohibiting Wnt pathway activation.Dominant activation of endothelial beta-catenin signalling led to up-regulation of the barrier- and down-regulation of the permeability-related genes claudin-5 and MECA-32, respectively. This observation suggests that vessels in the CVOs are capable of differentiating into barrier endothelia. Although several studies describe and discuss that different areas of the CNS exhibit different BBB properties, nothing is known about the development and about the molecular cues that mediate the formation of differential endothelial barrier phenotypes. Based on our published and unpublished results, we hypothesize that vascular heterogeneity in the CNS is achieved by micro-environmental impact on Wnt/beta-catenin signalling, most evident in the CVOs. To test this hypothesis, we aim to: 1. characterize in detail the development of the CVO vessels, the expression of barrier and permeability markers, as well as Wnt pathway components and their interaction with other pathways.2. investigate the consequences of endothelial-specific gain-of-function of beta-catenin in vivo, making use of transgenic, tamoxifen-inducible animal models3. characterize the physiological and pathological consequences of beta-catenin activation, focussing on water homeostasis and on neuroinflammatory conditions.These approaches will help to understand basic principles of barrier heterogeneity, as well as functional involvement of endothelial barrier properties in the regulation of water homeostasis and immune responses in the CNS.