Norrin Signaling in the Retina: Regulation of the Blood-Retina Barrier

我们的总体目标是了解Norrin/Frizzled4信号在血液-视网膜调节中的作用 人类疾病中的屏障(BRB)，以小鼠为模型系统。BRB的损伤会导致浮肿和IS 与糖尿病视网膜病变、老年性黄斑变性、早产儿视网膜病变、家族性 渗出性玻璃体视网膜病变(FEVR)和葡萄膜炎。BRB的引入和维护由关键的 B-连环蛋白依赖(典型)Norrin/Frizzled4信号通路。Norrin/Frizzled4信号中断原因 FEVR。Norrin/Frizzled4信号通路的损伤如何引起病理变化？ 在压力下调节，如果激活Norrin/Frizzled4信号是恢复 BRB功能障碍，都是不了解的。这些知识差距需要被填补，以利用巨大的 Norrin/Frizzled4信号用于治疗干预的基础研究进展。Aim1：我们展示了 发育小鼠内皮细胞特异性失活Norrin信号为研究提供了新的模型 BRB崩溃的病理后果。新的模型不显示复合病理 在现有的以周细胞缺陷、灌注缺陷为特征的BRB中断模型中观察到 低氧，使我们能够研究BRB缺陷本身的病理后果。内皮细胞特异性 在发育成熟的小鼠中Norrin/Frizzled4信号的中断导致免疫球蛋白外溢，补体 视网膜电流图(ERG)有激活、囊样水肿、b波减少等表现。我们将利用老鼠的遗传学来 检测经典补体途径在调节BRB长期病理后果中的作用 在其他方面完好无损的血管系统的崩溃。荧光血管造影术和ERG将在多个 1年结束时的时间点和组织病理学。成功完成这一目标将决定角色 视网膜疾病中经典补体途径在老年性黄斑病变中的已知作用 退化。AIM2：初步数据显示，内皮细胞中应激感受器蛋白水平的增加 强烈抑制典型信号，负向调节BRB功能。我们将使用条件鼠标 遗传学激活内皮细胞中的应力传感器，确定BRB功能，并测试基因 与b-连环蛋白信号水平升高或降低的相互作用。将进行基于细胞的分析以 确定这一强大监管的机制基础。成功完成这一目标将提供 对压力下BRB调节的新见解。这些机制可以被利用来调制 BRB，例如在恢复疾病中的屏障或用于药物输送的情况下。目标3：目前的努力是 靶向Norrin/Frizzled4信号治疗干预集中在抗血管生成方法上 增殖性视网膜病变。我们将确定内皮细胞中b-连环蛋白的激活是否会恢复BRB 在一过性缺氧性疾病模型中发挥作用。这一目标的成功实现预计将提供一个 模型，以测试途径激动剂恢复功能障碍的BRB的能力(AIM3)。

Our overall objective is to understand the role of norrin/frizzled4 signaling as regulator of the blood-retina barrier (BRB) in human disease, using mice as model system. Impairment of the BRB causes edema and is associated with diabetic retinopathy, age-related macular degeneration, retinopathy of prematurity, familial exudative vitreoretinopathy (FEVR), and uveitis. BRB induction and maintenance are controlled by the critical b-catenin-dependent (canonical) norrin/frizzled4 signaling pathway. Disrupted norrin/frizzled4 signaling causes FEVR. How the impairment of norrin/frizzled4 signaling causes pathological changes, how the pathway is regulated under stress, and if activation of norrin/frizzled4 signaling is a valid therapeutic approach to restore BRB dysfunction, are all not understood. These knowledge gaps need to be addressed to exploit the enormous basic research progress on norrin/frizzled4 signaling for therapeutic intervention. Aim1: We showed that endothelial cell-specific inactivation of norrin signaling in developed mice provides a new model to study pathological consequences of BRB breakdown. The new model does not display compound pathologies observed in existing models of BRB disruption characterized by pericyte defects, perfusion defects, and hypoxia, allowing us to study pathological consequences of BRB defects per se. Endothelial cell-specific disruption of norrin/frizzled4 signaling in developed mice causes immunoglobulin extravasation, complement activation, cystoid edema, and reduced b-wave in electroretinography (ERG). We will use mouse genetics to test the role of the classical complement pathway in mediating long-term pathological consequences of BRB breakdown in an otherwise intact vasculature. Fluorescein angiography and ERG will be performed at multiple time points, and histopathology at the 1-year end-point. Successful completion of this aim will determine roles of the classical complement pathway in retinal disease beyond the known roles in age-related macular degeneration. Aim2: Preliminary data show that increased levels of a stress sensor protein in endothelial cells strongly inhibit canonical signaling and negatively regulate BRB function. We will use conditional mouse genetics to activate the stress sensor in endothelial cells, determine BRB function, and test for genetic interactions with increased or reduced levels of b-catenin signaling. Cell-based assays will be performed to determine the mechanistic basis of this powerful regulation. Successful completion of this aim will provide novel insights into the regulation of the BRB under stress. These mechanisms may be exploited for modulating the BRB, e.g., in the context of restoring the barrier in disease, or for drug delivery. Aim3: Current efforts to target norrin/frizzled4 signaling for therapeutic intervention have focused on anti-angiogenesis approaches in proliferative retinopathies. We will determine if the activation of b-catenin in endothelial cells restores BRB function in a transient hypoxia disease model. Successful completion of this aim is expected to provide a model to test agonists of the pathway for their ability to restore a dysfunctional BRB (aim3).