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

描述(申请人提供)：血脑屏障(BBB)在血液和大脑之间起信号和运输接口的作用。血脑屏障在胚胎发育早期开始形成，随着中胚层来源的血管侵入未成熟的中枢神经系统(CNS)并开始获得血脑屏障的特征，如紧密连接和缺乏窗孔。成人血脑屏障在进一步成熟后，由于其极低的通透性和丰富的分子运输系统，通过与神经血管单位的支持细胞相互作用来维持。虽然最近的研究表明Wnt/β-catenin、血管紧张素II和声波刺激物信号在血脑屏障发育中的重要性，但当这些途径被破坏时，许多血脑屏障属性仍然没有受到影响。因此，我们对BBB形成的分子机制的理解是不完整的，在这项建议中，我们的目标是进一步研究调节BBB发育和维持的机制。最近，我们发现核受体RXRpha和PPARDelta是BBB功能的两个潜在调节因子。如初步数据所述，与外周血管内皮细胞相比，这些受体特异性地表达于血脑屏障，受体激动剂可以驱动从人多能干细胞(hPSC来源的BMECs)分化的内皮细胞的血脑屏障表型，这些受体的内皮特异性缺失会导致体内部分新生儿死亡(RXRpha)和漏血血脑屏障(PPARDelta)。因此，我们假设核受体RXRpha和PPARDelta是血脑屏障发育和维持的关键调节因子。为了验证我们的假设，我们将在小鼠体内评估胚胎和出生后内皮细胞特异性缺失RXRpha和PPARDelta时的血脑屏障表型。将利用hPSC来源的BMECs的分化过程作为人血脑屏障诱导和维持的窗口来评估RXRpha和PPARDelta激活所控制的分子机制。最后，将在体内和体外评估RXRpha和PPARDelta共同激活对BBB形成的潜在协同作用。了解血脑屏障诱导的调节因素可以为胎儿脑部疾病带来许多新的见解。此外，对屏障发生和屏障维持途径的了解可以为恢复衰弱神经疾病中的血脑屏障功能开辟新的途径。

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.