Role of fatty acid metabolism in optic nerve hypoplasia

摘要 视神经发育不全是一种非常常见的先天性视神经疾病， 在发达国家的儿童失明。在过去的二十年中，ONH的发病率增加了约8倍。 ONH的特征是薄的、不发达的ON，其通常由视网膜神经节的继发性损失引起 细胞（RGC）。ONH最常见的产前决定因素是年轻的未经产母亲，不健康的 母亲的生活方式，包括酗酒和营养缺乏。我们已经开发并出版了鼠 通过操纵X连锁基因CASK建立ONH模型，因为人类的CASK突变与 哦。CASK突变小鼠的ONH病理学重现了人类ONH，包括病理学的时间 发病（在RGC发展之后;即，继发性损失）和病理学的非进行性性质。 生化实验表明，CASK与代谢蛋白相互作用，调节线粒体 功能CASK缺乏导致脂肪酸氧化增加和ω-6脂肪酸花生四烯酸缺乏。 在中枢神经系统（CNS）中的酸（ARA）。ARA缺乏症也在其他相关疾病中观察到 关于ONH我们假设ONH是由早期ARA缺乏引起的，因此ONH可以通过以下方式加重： 干扰脑ARA代谢（通过星形胶质细胞功能障碍）并通过饮食ARA改善 补充。在妊娠晚期，ARA仅从母亲获得;在新生儿中， ARA也可从饮食中获得，直到具有足够的酶活性（必需脂肪酸亚油酸的转化 酸进入ARA）。这种新生儿后ARA获得从饮食到合成的转变可能有助于 ONH的非进步性质。在中枢神经系统中，脂肪酸代谢（包括ARA的摄取和产生） 主要是在星形胶质细胞中。在这个提议中，我们计划在两只独立的ONH小鼠中测试我们的假设。 模型：1）CASK（+/-）杂合子敲除小鼠，和2）先前发表的胎儿酒精综合征（FAS） 小鼠模型利用这些模型，我们将研究线粒体代谢，氧化损伤和脂肪酸 视网膜、ON和大脑中的代谢缺陷。我们还将量化两种ω-脂肪酸（二十二碳六烯酸）的水平， 酸和ARA），以及两种类型的ONH小鼠的ON中的磷脂。下一步，我们将从基因上破坏 星形胶质细胞（对脑ARA代谢至关重要）在CASK亚型ONH模型中的功能 星形胶质细胞中CASK的缺失。我们将研究这种操作是否会加剧代谢缺陷， ONH在形态和功能上进行评估，使用视觉行为分析和创新的 视觉刺激网络反应（Network Response to Visual Excitation，NeRVE）。最后，我们将测试ARA是否 在上述两种模型中，补充剂改善了ONH。我们的研究可能会发现ARA 缺乏作为最后的共同途径，解释了ONH与营养缺乏，孕产妇 糖尿病、婴儿胆汁淤积症和FAS。ARA补充的阳性结果将很容易翻译。

ABSTRACT Optic nerve hypoplasia (ONH) is a very common congenital optic nerve (ON) disorder and is the leading cause of childhood blindness in developed nations. ONH incidence has increased ~8-fold over the last two decades. ONH is characterized by a thin, underdeveloped ON that often results from secondary loss of retinal ganglion cells (RGCs). The most common prenatal determinants of ONH are a young primiparous mother, an unhealthy maternal lifestyle including alcohol abuse, and nutritional deprivation. We have developed and published murine models of ONH by manipulating the X-linked gene CASK, since CASK mutations in humans are associated with ONH. The ONH pathology of CASK mutant mice recapitulates human ONH, including the timing of pathology onset (after RGC development; i.e., secondary loss) and the non-progressive nature of the pathology. Biochemical experiments show that CASK interacts with metabolic proteins and modulates mitochondrial function. CASK deficiency leads to increased fatty acid oxidation and a deficit of the ω-6 fatty acid arachidonic acid (ARA) in the central nervous system (CNS). ARA deficiency is also observed in other conditions associated with ONH. We hypothesize that ONH results from an early ARA deficit, thus ONH can be exacerbated by perturbing brain ARA metabolism (via astrocyte dysfunction) and ameliorated by dietary ARA supplementation. During the third trimester, ARA is exclusively obtained from the mother; in neonates, brain ARA is also obtained from the diet until adequate enzymatic activity (conversion of the essential fatty acid linoleic acid into ARA) is reached. This post-neonatal shift in ARA acquisition from diet to synthesis may contribute to ONH’s non-progressive nature. In the CNS, fatty acid metabolism (including ARA uptake and production) occurs predominantly in astrocytes. In this proposal we plan to test our hypothesis in two independent ONH mouse models: 1) CASK(+/-) heterozygous knockout mice, and 2) a previously published fetal alcohol syndrome (FAS) mouse model. With these models, we will examine mitochondrial metabolism, oxidative damage and fatty acid metabolic defects in the retina, ON and brain. We will also quantify levels of two ω-fatty acids (docosahexaenoic acid and ARA), as well as phospholipids in the ON of both types of ONH mice. Next, we will genetically disrupt the function of astrocytes (crucial for brain ARA metabolism) in a CASK hypomorph ONH model by complete deletion of CASK in astrocytes. We will investigate if this manipulation exacerbates the metabolic defect and ONH as assessed both morphologically and functionally, using a visual behavioral assay and an innovative electrophysiological tool called Network Response to Visual Excitation (NeRVE). Finally, we will test if ARA supplementation ameliorates ONH in the two models described above. Our study is likely to identify ARA deficiency as the final common pathway that explains ONH’s association with nutritional deprivation, maternal diabetes, infantile cholestasis and FAS. Positive results from ARA supplementation will be readily translatable.