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

我们的总体目标是了解norrin/frizzled4信号作为血视网膜调节因子的作用。 屏障（BRB）在人类疾病中的作用，使用小鼠作为模型系统。BRB受损会导致水肿， 与糖尿病视网膜病变、年龄相关性黄斑变性、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-连环蛋白依赖性（经典）norrin/frizzled4信号通路。norrin/frizzled4信号传导中断 FEVR。norrin/frizzled4信号传导的损伤如何导致病理变化，该途径如何 在压力下调节，并且如果norrin/frizzled4信号传导的激活是一种有效的治疗方法， BRB功能障碍，都不了解。这些知识差距需要加以解决，以利用巨大的 norrin/frizzled4信号通路用于治疗干预的基础研究进展目标1：我们证明， 在发育小鼠中内皮细胞特异性失活norrin信号提供了一个新的研究模型 BRB崩溃的病理后果。新模型未显示复合病理 在现有的BRB破坏模型中观察到，其特征在于周细胞缺陷，灌注缺陷， 缺氧，使我们能够研究BRB缺陷本身的病理后果。内皮细胞特异 在发育中的小鼠中norrin/frizzled4信号传导的破坏导致免疫球蛋白外渗，补体 视网膜电图（ERG）中的激活、囊样水肿和b波降低。我们将利用老鼠遗传学 测试经典补体途径在介导BRB的长期病理后果中的作用 在其他完好的脉管系统中分解。将在多个时间点进行血管造影和ERG 时间点和1年终点时的组织病理学。成功完成这一目标将决定作用 经典补体途径在视网膜疾病中的作用超出了年龄相关性黄斑病变中的已知作用， 退化目的2：初步数据显示，内皮细胞中应激传感器蛋白水平的增加 强烈抑制典型信号传导并负调节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，并测试遗传学 与增加或降低的β-连环蛋白信号传导水平的相互作用。将进行基于细胞的测定， 确定这一强有力的调节机制的基础。成功实现这一目标将为 对压力下BRB调节的新见解。这些机制可用于调节 BRB，例如，在恢复疾病屏障的背景下，或用于药物递送。目标3：目前的努力 用于治疗干预靶向Norrin/Frizzled4信号传导已经集中于抗血管生成方法， 增生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能恢复BRB 在短暂性缺氧疾病模型中发挥作用。这一目标的成功实现将为 模型来测试途径的激动剂恢复功能失调的BRB（aim3）的能力。

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).