Wnt信号通路与视网膜发育的机理研究

The retina constitutes an integral part of the visual system. Accordingly, congenital defects caused by retinal maldevelopment often lead to low vision or complete vision loss. Examples for such defects are microphthalmia, anophthalmia and coloboma (MAC), which combined contribute to profound vision impairment. Signaling pathways play important role in retinal development. As such, mutations of BMP, SHH, and components of retinoic acid signaling have been identified in human MAC disease. The role of Wnt pathway in retinal development remains elusive. Genetic ablation of Wnt signaling component of either Lrp6, or Fz5 led to ocular defects of microphthalmia and coloboma, suggesting that Wnt pathway is likely an etiology of MAC. However, the retinal Wnt pathway composition, its cellular events and signaling networks have yet to be uncovered. In this proposal, we set several specific aims toward dissection of the retinal Wnt pathway, assessing the signaling events in retinal neurogenesis and optic fissure closure/development in detail. We expect that our proposed research will generate novel knowledge to bridge the gap between the Wnt pathway and the disease mechanism of MAC.

视网膜是视觉系统的一个重要组成部分。先天性视网膜发育不全会导致从弱视到失明不同程度的视觉障碍。如小眼，无眼和眼裂 （Mirophthalmia， Anophthalmia and Coloboma, MAC）就属于视网膜形态发生异常而诱发的眼科疾病。已知信号通路组件的突变（如BMP，SHH和维甲酸通路组件等突变）是引发先天性MAC疾病重要遗传因素。然而，作为主要的信号通路之一的Wnt通路，其突变还没有在MAC病群中发现。我们和其他研究小组在小鼠的工作表明，基因敲除Wnt通路组件Lrp6或Fz5 均导致小鼠视网膜发育缺陷，发生小眼和眼裂，暗示了Wnt通路异常可能是MAC的一个病原。然而，在视网膜发育中，这一通路的组成，细胞生物学事件及其网络作用关系还都不清楚。解决这些问题必然会深化对视网膜神经发生，视裂形态发生和对MAC发病机理的认识，近而对疾病介入和治疗起临床指导作用。

先天性视网膜发育不全，如小眼，无眼和眼裂 （Microphthalmia， Anophthalmia and Coloboma, MAC）会导致从弱视到失明不同程度的视觉障碍。Wnt共受体Fz5和Lrp6突变小鼠有小眼和眼裂的表型，然而是否在病人存在类似的突变以及他们在视网膜发育的作用机制尚不清楚。Wnt通路可分为经典（beta-catenin依赖）及非经典通路（如Wnt/PCP）通路。二者的作用分子机理不同,但关系密切。本项目对Fz5，Lrp6及Wnt配基的相互关系，Wnt/Fz5 通路的分子及生化事件，Wnt通路介导的视网膜视裂闭合, 及Wnt/Fz5的基因网络关系进行了研究。 研究的主要发现有：1）Fz5与Lrp6相互作用，共同介导Wnt3a和Wnt7a的信号转导；2）导致小眼和眼裂的FZD5突变蛋白通过获得性功能阻断正常Wnt信号转导； 3) 突变的FZD5与正常的FZD5蛋白竞争WNT配基; 4）Fz5与Wnt/PCP成员Prickle 1共同维系视裂闭合, 并可能采取与眼睑闭合类似机制; 5)发现几个可能的Fz5上由调控因子及维系成体视网膜功能的下游基因网络。该项目研究成果使我们对视网膜发育和疾病的机制有了更深入的认识，并为疾病的治疗提供可供检验的分子靶点。