Investigating Pericyte Roles in Blood-Brain Barrier Formation

摘要 血脑屏障（BBB）作为血液和大脑之间的信号和运输界面。的 BBB在胚胎发育早期开始形成，因为中胚层来源的脉管系统侵入了血脑屏障。 不成熟的中枢神经系统（CNS），并获得BBB特征，如紧密连接和缺乏 窗孔进一步成熟后，成熟的血脑屏障具有极低的通透性和丰富的分子量， 运输系统，通过与神经血管单位（NVU）的支持细胞相互作用来维持。最近 研究表明，CNS周细胞在BBB形成中的重要性，周细胞触发降低 细胞转胞吞、白细胞粘附分子表达减少和适当的紧密连接组织。 然而，在血脑屏障形成过程中引起这些重要变化的周细胞源性因子的身份， 不知道。因此，我们对BBB形成的分子机制的理解是 不完整;在这项提案中，我们的目标是进一步研究脑周细胞影响的机制， BBB形成。探索血脑屏障形成的一种强有力的创新方法是使用人类诱导的 多能干细胞（iPSC）技术来模拟BBB和NVU的相关支持细胞。我们将 证明脑周细胞不仅可以从iPSC分化，它们还可以调节关键的BBB， iPSC衍生的脑内皮细胞（BMEC）的特性。与此同时，使用基因组学方法， 鉴定了一组周细胞来源的分泌因子，其中几种可以在iPSC中诱导BBB特性， 衍生BMEC。结合这些方法，我们将研究周细胞衍生的细胞凋亡的机制。 分泌的因子可以差异性地调节iPSC衍生的BMEC中的BBB形成。初步数据显示 周细胞来源的分泌因子之一BMP 5可以影响已知的标志性BBB特性， 由脑周细胞调节也就是说，BMP 5可以减少转胞吞作用并改善细胞中的紧密连接结构。 iPSC衍生的BMEC。为了进一步研究BMP5调节血脑屏障形成的机制， 我们将使用遗传小鼠模型来探索BMP 5信号传导是否是BBB所必需的。 形成和功能。最后，我们将评估BMP5补充是否可以在小鼠中治疗。 多发性硬化症的模型了解血脑屏障形成的周细胞来源的调节因子可以产生许多 关于脑疾病的新机制的见解，有明显的周细胞参与。知识 屏障形成途径也可能为恢复BBB功能开辟新的途径， 神经系统疾病

ABSTRACT The blood-brain barrier (BBB) acts as a signaling and transport interface between the blood and brain. The BBB begins to form early in embryonic development as the mesoderm-derived vasculature invades the immature central nervous system (CNS) and acquires BBB characteristics such as tight junctions and a lack of fenestrae. After further maturation, the adult BBB, with its very low permeability and a wealth of molecular transport systems, is maintained by interactions with supporting cells of the neurovascular unit (NVU). Recent studies have indicated the importance of CNS pericytes in BBB formation, with pericytes triggering reduced transcytosis, reduced expression of leukocyte adhesion molecules and proper tight junction organization. However, the identity of pericyte-derived factors that can elicit these important changes during BBB formation are not known. Thus, our understanding of the molecular mechanisms underpinning BBB formation is incomplete; and in this proposal, we aim to further examine the mechanisms by which brain pericytes impact BBB formation. A powerful and innovative approach to explore BBB formation is the use of human induced pluripotent stem cell (iPSC) technology to model the BBB and the associated support cells of the NVU. We will demonstrate that not only can brain pericytes be differentiated from iPSCs, they can also regulate key BBB properties in iPSC-derived brain endothelial cells (BMECs). In parallel, using genomics approaches, we have identified a cohort of pericyte-derived secreted factors, several of which can induce BBB properties in iPSC- derived BMECs. Combining these approaches, we will examine the mechanisms whereby pericyte-derived secreted factors can differentially regulate BBB formation in iPSC-derived BMECs. Preliminary data indicate that one of the pericyte-derived secreted factors, BMP5, can influence hallmark BBB properties known to be regulated by brain pericytes. Namely, BMP5 can reduce transcytosis and improve tight junction structures in iPSC-derived BMECs. To further examine the mechanism by which BMP5 regulates BBB formation during development, we will use genetic mouse models to explore whether BMP5 signaling is necessary for BBB formation and function. Finally, we will assess whether BMP5 supplementation can be therapeutic in a mouse model of multiple sclerosis. Understanding the pericyte-derived regulators of BBB formation could yield many new mechanistic insights regarding brain diseases that have demonstrable pericyte involvement. Knowledge of the barrier formation pathways could also open new avenues for restoring BBB function in debilitating neurological disease.