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）作为血液和大脑之间的信号和运输接口。在胚胎发育早期，当中胚层来源的脉管系统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。成年血脑屏障在进一步成熟后，其渗透性极低，具有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和超音hedgehog信号在血脑屏障发育中的重要性，但当这些通路被破坏时，许多血脑屏障属性仍不受影响。因此，我们对血脑屏障形成的分子机制的理解是不完整的，在本提案中，我们的目标是进一步研究血脑屏障发育和维持的调节机制。最近，我们发现核受体rxrα和PPARdelta是血脑屏障功能的两个潜在调节因子。如初步数据所述，与外周内皮相比，这些受体在血脑屏障处特异性表达，受体激动剂可以在人多能干细胞（hpsc衍生的BMECs）分化的内皮细胞中驱动血脑屏障表型，内皮特异性缺失这些受体会导致新生儿部分死亡（RXRalpha）和血脑屏障泄漏（PPARdelta）。因此，我们假设核受体rxr α和ppar δ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，我们将评估小鼠胚胎和出生后内皮特异性缺失rxrα和PPARdelta对血脑屏障表型的影响。rxrα和PPARdelta激活的分子机制将通过hpsc衍生的bmec的分化过程来评估，作为人类血脑屏障诱导和维持的窗口。最后，将在体内和体外评估rxrα和PPARdelta共激活对血脑屏障形成的潜在协同作用。了解血脑屏障诱导的调节因子可以对胎儿脑部疾病产生许多新的见解。此外，屏障发生和屏障维持途径的知识可以为恢复衰弱性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.