Investigating the Mechanism of Optic Nerve disorders associated with Down Syndrome

项目摘要 唐氏综合征(DS)患者中视神经发育不良(ONH)的患病率超过100 折叠率高于普通人群。ONH的特点是视神经不发达，纤细 通常是由继发性视网膜神经节细胞(RGC)丢失引起的，是儿童合法的主要原因 发达国家的失明问题。我们通过操纵木桶建立了一种ONH的小鼠模型 (钙/钙调蛋白依赖的丝氨酸蛋白激酶)基因。CASK突变小鼠的ONH病理研究 概括了人类ONH的许多方面，包括病理开始的时间(在RGC之后 发展，即继发性损失)和病理的非进行性。除了ONH、DS和 与木桶突变相关的病理有其他相似之处，如小头畸形。生化 实验表明，与DS相似，木桶突变会改变线粒体功能，导致异常脂肪 酸代谢。我们发现了ω-6多不饱和脂肪酸花生四烯酸(Ara)的缺陷。 在木桶突变小鼠的中枢神经系统(CNS)中。含有ARA的脂类的特定减少有 在死后的人类DS脑中也有报道。在木桶突变小鼠和DS小鼠模型中 对比敏感度降低。根据文献和我们的观察，我们假设ARA 视神经缺失(ON)导致DS的ONH。如果这一假设是正确的，饮食中的ARA 补充剂可改善DS患者的ONH。在这个方案中，我们计划使用两个独立的小鼠DS 模型(Ts65Dn和DP16小鼠)，以研究视网膜回路和视网膜原基连接使用适当的 标记和示踪剂以及成像技术。骨桥的三维超微形态计量学研究 在DS小鼠模型中，将使用连续块面扫描电子显微镜(SBFSEM)进行。 行为实验将记录视觉缺陷。视觉回路功能将在体内用一种新的方法进行评估 电生理技术，我们称之为视觉兴奋的网络反应(神经)，一种方法， 将适用于超出这一建议，以更好地了解啮齿动物的视觉处理。线粒体新陈代谢， 视网膜、视神经中的活性氧生成、氧化损伤和脂肪酸代谢缺陷 并对两个独立的DS小鼠模型进行脑部测量。我们还将量化两种ω的水平- 多不饱和脂肪酸(二十二碳六烯酸和ARA)，以及磷脂，在这两种类型的ON中 DS小鼠的数量。最后，我们将测试补充ARA是否能改善视力和对比度方面的已知缺陷 这两种DS小鼠模型的敏感度。我们的研究可能提供有关DS病理生物学的数据，并提供 明确DS并发ONH的机制。此外，我们ARA的有希望的结果 补充研究将立即转化为临床实践，以改善ONH 患有DS的个体。

PROJECT ABSTRACT The prevalence of optic nerve hypoplasia (ONH) among individuals with Down syndrome (DS) is more than ~100 folds higher than in the general population. ONH is characterized by a thin, underdeveloped optic nerve that often results from secondary loss of retinal ganglion cells (RGCs) and is the leading cause of childhood legal blindness in developed nations. We have developed a murine model of ONH by manipulating the CASK (calcium/calmodulin dependent serine protein kinase) gene. The ONH pathology of CASK mutant mice recapitulates many aspects of human ONH, including the timing of the onset of pathology (after RGC development, i.e., secondary loss) and the non-progressive nature of the pathology. In addition to ONH, DS and pathology associated with CASK mutation share other similarities such as microcephaly. Biochemical experiments suggest that similar to DS, CASK mutation alters mitochondrial function, resulting in aberrant fatty acid metabolism. We have uncovered a deficiency of the ω-6 polyunsaturated fatty acid arachidonic acid (ARA) in the central nervous system (CNS) of CASK mutant mice. A specific reduction of ARA-containing lipids has been also reported in postmortem human DS brains. In both CASK mutant mice and the DS murine model visual contrast sensitivity is reduced. Based on the literature and our observations, we hypothesize that ARA deficiency in the optic nerve (ON) leads to ONH in DS. If this hypothesis is correct, dietary ARA supplementation could ameliorate ONH in DS. In this proposal, we plan to use two independent murine DS models (Ts65Dn and DP16 mice) to investigate retinal circuit and retinogeniculate connectivity using appropriate markers and tracers along with imaging techniques. Three-dimensional ultrastructural morphometry of the ON in DS murine models will be performed using serial block-face scanning electron microscopy (SBFSEM). Behavioral experiments will document visual defects. Visual circuit function will be evaluated with a novel in vivo electrophysiological technique we have named Network Response to Visual Excitation (NeRVE), a method that will be applicable beyond this proposal to better understand rodent vision processing. Mitochondrial metabolism, reactive oxygen species generation, oxidative damage, and fatty acid metabolic defects in the retina, optic nerve and brain of two independent DS mouse models will be measured. We will also quantify the levels of two ω- polyunsaturated fatty acids (docosahexaenoic acid and ARA), as well as phospholipids, in the ON of both types of DS mice. Finally, we will test if ARA supplementation ameliorates known defects in visual acuity and contrast sensitivity in these two DS mouse models. Our study is likely to provide data on DS pathobiology and provide a clear mechanism for the co-occurrence of ONH in DS. Furthermore, promising results from our ARA supplementation study would be immediately translatable into clinical practice for the amelioration of ONH in individuals with DS.