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不断产生。两个主要生发壁龛之一位于侧脑室侧壁下方，称为室下区（SVZ）。神经干细胞（NSCs）驻留在SVZ并产生转运扩增前体和神经母细胞，它们离开SVZ并向嗅球（OB）行进。在那里，成年出生的中间神经元整合到局部电路中，参与嗅觉信息处理。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心调节器。然而，Notch对NSC分化和SVZ偏离的精确调控尚不清楚。此外，Notch对OB中新神经元整合到现有神经网络中的贡献几乎没有得到阐明。NSC生命周期的一个重要调节因子是血管周围生态位，它是由NSC周围的血管形成的。它提供了一个特殊的基底层，支持干细胞的身份，并有助于SVZ居民的动员。最近，我们发现表皮生长因子样蛋白7 （EGFL7）是血管周围细胞外基质的一种新成分，它是一个更大的表皮生长因子样蛋白（EGFLs）群体的成员（blood, 2013）。之前，我们已经证明神经元和内皮细胞分泌的EGFL7会降低NSCs的自我更新潜能，并通过抑制Notch刺激NSCs的神经元分化（Nat Cell Biol, 2009）。此外，EGFL7在中风时被血管上调（Acta Neuropathol, 2014）。这些发现提供了EGFL7作为血管周围生态位的新成分和NSCs的神经血管调节剂。在我们的项目中，我们将I)通过脑室注射和敲除模型分析EGFL7和其他egfl如何在体内调节svz来源的NSCs。此外，我们将探索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节OB中的神经发生，我们将在行为范式中使用我们的新小鼠模型研究新创建的神经元在体内的功能。III)最后，我们将通过应用诱导型组织特异性敲除和敲入小鼠模型，比较血管周围干细胞生态位中的神经和血管细胞对NSCs调控的贡献。我们的项目将详细了解egfl和Notch在NSCs调控中的作用，我们将对神经血管界面的作用有更深入的了解。了解血管和NSCs如何沟通以调节神经发生，使我们有机会通过简单的注射来操纵NSC池，这可能为利用NSCs用于治疗目的提供一条途径，例如用于治疗中风并使患者受益。

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.