Notch-dependent regulation of neural stem cells in the neurovascular niche

在成年哺乳动物的大脑中，新的神经元在其一生中被创造出来。两个主要的生发生态位之一位于侧脑室侧壁下方，称为脑室下区(SVZ)。神经干细胞(NSCs)存在于SVZ中，产生运输放大前体细胞和神经母细胞，它们离开SVZ并向嗅球(OB)移动。在那里，成年出生的中间神经元整合到局部电路中，并对嗅觉信息处理做出贡献。协调这些事件的分子机制在很大程度上依赖于Notch信号作为细胞命运决定的中央调节因子。然而，Notch对NSC分化和SVZ偏离的精确调控知之甚少。此外，Notch在OB中新神经元整合到现有神经网络中的作用几乎还没有阐明。神经干细胞生命周期的一个重要调节因素是血管周围的壁龛，它由围绕神经干细胞的血管形成。它提供了一个专门的基膜，支持干细胞的身份，并有助于动员SVZ居民。最近，我们发现了表皮生长因子样蛋白7(EGFL7)，它是一组较大的EGF样蛋白(EGFL)中的一员，是血管周围细胞外基质的一种新成分(布拉德，2013)。此前，我们已经证明由神经元和内皮细胞分泌的EGFL7通过抑制Notch而降低NSCs的自我更新能力，并促进NSCs的神经元分化(NAT Cell Biol，2009)。此外，在中风时，血管会上调EGFL7的表达(神经病理学报，2014)。在我们的项目中，我们将分析EGFL7和其他EGFL如何通过脑室注射和敲除模型在体内调节SVZ来源的NSCs。此外，我们还将探索Notch通路的哪些组成部分参与了NSCs的细胞命运决定过程。Ii)随后，我们将分析这些蛋白质如何调控OB中的神经发生，并将使用我们的新小鼠模型在行为范式中研究体内新创建的神经元的功能。最后，我们将通过可诱导的组织特异性基因敲除和基因敲入小鼠模型，比较血管周围干细胞巢中的神经和血管细胞对神经干细胞调控的贡献。我们的项目将使我们对EGFL和Notch在神经干细胞调节中的作用有一个详细的了解，我们将对神经-血管接口的作用有一个更深入的了解。了解血管和神经干细胞如何沟通来调节神经发生，使我们有机会通过简单的注射来操纵神经干细胞池，这可能为开发神经干细胞用于治疗目的提供途径，例如用于治疗中风和造福患者。

In the adult mammalian brain new neurons are created throughout its lifetime. One of the two major germinal niches is localized beneath the lateral walls of the lateral ventricles and is termed the subventricular zone (SVZ). Neural stem cells (NSCs) reside in the SVZ and give rise to transit amplifying precursors and neuroblasts, which depart from the SVZ and travel towards the olfactory bulb (OB). There, adult-born interneurons integrate into the local circuitry and contribute to olfactory information processing. The molecular mechanisms orchestrating these events rely heavily on Notch signaling as a central regulator of cell fate decision. However, little is known about the precise regulation of NSC differentiation and SVZ departure by Notch. Furthermore, the contribution of Notch to the integration of new neurons into the existing neural network in the OB has barely been elucidated. One significant regulator of the NSC lifecycle is the perivascular niche, which is formed by blood vessels surrounding NSCs. It provides a specialized basal lamina that supports stem cell identity and contributes to the mobilization of SVZ residents. Recently, we identified the epidermal growth factor-like protein 7 (EGFL7), a member of a larger group of EGF-like proteins (EGFLs), as a novel component of the extracellular matrix surrounding blood vessels (Blood, 2013). Previously, we had demonstrated that EGFL7 secreted by neurons and endothelial cells decreased the self-renewal potential of NSCs and stimulated neuronal differentiation of NSCs by the inhibition of Notch (Nat Cell Biol, 2009). Furthermore, EGFL7 was upregulated by blood vessels upon stroke (Acta Neuropathol, 2014). These findings offer EGFL7 as a novel component of the perivascular niche and a neurovascular regulator of NSCs.In our project, we will I) analyze how EGFL7 and other EGFLs regulate SVZ-derived NSCs in vivo by using intraventricular injections and knock-out models. Additionally, we will explore which components of the Notch pathway are involved in cell fate decision processes of NSCs. II) Subsequently, we will analyze how these proteins regulate neurogenesis in the OB and we will study the functionality of newly created neurons in vivo using our new mouse models in behavior paradigms. III) Lastly, we will compare the contributions of neural and vascular cells in the perivascular stem cell niche to the regulation of NSCs by the application of inducible tissue-specific knock-out and knock-in mouse models. Our project will yield a detailed understanding of the role of EGFLs and Notch in the regulation of NSCs and we will achieve a deeper understanding of the role of the neuro-vascular interface. Learning how blood vessels and NSCs communicate to regulate neurogenesis gives us the opportunity to manipulate the NSC pool by simple injection, which may provide an avenue for the exploitation of NSCs for therapeutic purposes, e.g., for the treatment of stroke and benefit for the patients.