RXRalpha and PPARdelta Signaling as Novel Regulators of the Blood-Brain Barrier

描述（由申请人提供）：血脑屏障（BBB）作为血液和脑之间的信号传导和转运界面。BBB在胚胎发育早期开始形成，因为中胚层衍生的脉管系统侵入未成熟的中枢神经系统（CNS）并开始获得BBB特征，例如紧密连接和缺乏窗孔。在进一步成熟后，具有非常低的渗透性和丰富的分子转运系统的成体BBB通过与神经血管单位的支持细胞的相互作用来维持。虽然最近的研究表明Wnt/β-连环蛋白、血管紧张素II和音刺猬信号传导对BBB发育的重要性，但当这些途径被破坏时，许多BBB属性仍不受影响。因此，我们对BBB形成的分子机制的理解是不完整的，在这个提议中，我们的目标是进一步研究调节BBB发育和维持的机制。最近，我们已经确定了核受体RXR α和PPARdelta作为两个潜在的调节BBB功能。如初步数据中所述，与外周内皮相比，这些受体在BBB处特异性表达，受体激动剂可以驱动从人多能干细胞（hPSC衍生的BMEC）分化的内皮细胞中的BBB表型，并且这些受体的内皮特异性缺失导致部分新生儿致死（RXR α）和体内BBB渗漏（PPARdelta）。因此，我们假设核受体RXR α和PPARdelta是BBB发育和维持的关键调节因子。为了验证我们的假设，我们将评估小鼠胚胎和出生后内皮特异性缺失RXR α和PPAR δ后的体内BBB表型。将使用hPSC衍生的BMEC的分化过程作为人BBB诱导和维持的窗口来评价由RXR α和PPARdelta激活控制的分子机制。最后，将在体内和体外评估由RXR α和PPARdelta共活化引起的对BBB形成的潜在协同作用。了解BBB诱导的调节因子可以产生许多关于胎儿脑疾病的新见解。此外，屏障形成和屏障维持途径的知识可以为在衰弱性神经疾病中恢复BBB功能开辟新的途径。

DESCRIPTION (provided by applicant): 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 begins to gain 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. While recent studies have indicated the importance of Wnt/beta- catenin, angiotensin II, and sonic hedgehog signaling on BBB development, many BBB attributes remain unaffected when these pathways are disrupted. Thus, our understanding of the molecular mechanisms underpinning BBB formation is incomplete, and in this proposal we aim to further examine the mechanisms that regulate BBB development and maintenance. Recently, we have identified nuclear receptors RXRalpha and PPARdelta as two potential regulators of BBB function. As described in the preliminary data, these receptors are specifically expressed at the BBB compared to peripheral endothelia, receptor agonists can drive BBB phenotypes in endothelial cells differentiated from human pluripotent stem cells (hPSC-derived BMECs), and endothelial-specific deletion of these receptors results in partial neonatal lethality (RXRalpha) and a leaky BBB (PPARdelta) in vivo. Thus, we hypothesize that the nuclear receptors RXRalpha and PPARdelta are crucial regulators of BBB development and maintenance. To test our hypothesis, we will evaluate the in vivo BBB phenotype upon embryonic and postnatal endothelial-specific deletion of RXRalpha and PPARdelta in mice. The molecular mechanisms governed by RXRalpha and PPARdelta activation will be evaluated using the differentiation process of hPSC-derived BMECs as a window to human BBB induction and maintenance. Finally, potential synergy on BBB formation arising from RXRalpha and PPARdelta co-activation will be assessed in vivo and in vitro. Understanding the regulators of BBB induction could yield many new insights regarding fetal brain disease. Furthermore, knowledge of the barrier-genesis and barrier maintenance pathways could open new avenues for restoring BBB function in debilitating neurological disease.