Significance of CYP46A1 and other P450s in retinal function

 性状（由申请人提供）：胆固醇是一种普遍存在的脂质，对正常人体发育、生长和生理至关重要。胆固醇存在于视网膜中，其通过平衡胆固醇输入（局部生物合成和从体循环的组织摄取）和胆固醇输出（局部代谢为氧固醇并通过脂蛋白转运至体循环）来维持胆固醇稳态。精细的机制控制和协调视网膜胆固醇的输入和输出，以维持稳态胆固醇水平。视网膜胆固醇与年龄相关性黄斑变性（AMD）有关，AMD是工业化国家老年人视力丧失的主要原因。胆固醇-AMD的细节 然而，这种联系尚不清楚，部分原因是我们对视网膜胆固醇的认识存在重大差距。在先前的资助期间，我们使用人体组织和小鼠来研究视网膜胆固醇稳态的两个方面：1）通过细胞色素P450酶CYP 27 A1和CYP 46 A1局部代谢为氧化固醇，以及2）视网膜对饮食和药物治疗的反应。氧化固醇的代谢似乎是视网膜胆固醇输出的重要贡献者，并且是维持视网膜血管系统正常状态的过程。我们发现氧化固醇的产生受到光诱导的视网膜脂质过氧化作用的干扰，但部分受到B6维生素吡哆胺（pyridoxamine）治疗的保护。局部胆固醇生物合成和脂蛋白清除胆固醇是视网膜中对药物治疗有反应的另外两个胆固醇相关途径。辛伐他汀和TO 901317分别抑制前者，上调后者。辛伐他汀是一种降胆固醇药物，TO 901317是一种肝脏X受体家族转录因子的激动剂。出乎意料的是，我们确定了两种蛋白质，载脂蛋白D（apoD）和酰基辅酶A胆固醇酰基转移酶1（ACAT 1）作为视网膜胆固醇运输和储存，分别潜在的重要。在这次更新中，我们将重点关注视网膜胆固醇输入和输出的那些未知方面，这些方面对于我们了解如何对抗AMD具有毫无疑问的重要性。具体目标是：1）确定局部胆固醇生物合成和组织吸收血源性胆固醇对视网膜病变的贡献。 胆固醇以及这些贡献是否被高胆固醇饮食或辛伐他汀治疗改变; 2）建立apoD和ACAT 1的视网膜意义以及视网膜胆固醇转运和储存的途径; 3）评估具有视网膜胆固醇显著积累和视网膜血管异常的小鼠的药物治疗的有效性。我们将主要获得有关视网膜胆固醇获得、消除和储存的新信息，填补我们关于视网膜胆固醇维持的知识中最关键的空白，并促进与视网膜中胆固醇有害积累相关的眼部疾病的药物治疗的发展。

 DESCRIPTION (provided by applicant): Cholesterol is a ubiquitous lipid essential for normal human development, growth, and physiology. Cholesterol is present in the retina, which maintains cholesterol homeostasis by balancing cholesterol input (local biosynthesis and tissue uptake from the systemic circulation) and cholesterol output (local metabolism to oxysterols and transport to the systemic circulation by lipoproteins). Elaborate mechanisms control and coordinate retinal cholesterol input and output to maintain steady-state cholesterol levels. Retinal cholesterol has been linked to age-related macular degeneration (AMD), the leading cause of vision loss in the elderly of the industrialized world. The details of the cholesterol-AMD link are, however, unclear, due in part to significant gaps in our knowledge about retinal cholesterol. During the previous grant period, we used human tissues and mice to investigate two aspects of retinal cholesterol homeostasis: 1) local metabolism to oxysterols by cytochrome P450 enzymes CYP27A1 and CYP46A1, and 2) retinal responses to dietary and pharmacologic treatments. Metabolism to oxysterols appeared to be an important contributor to retinal cholesterol output, and a process maintaining the normal status of retinal vasculature. We found that the production of oxysterols is disturbed by light-induced retinal lipid peroxidation but protected in part by mouse treatments with pyridoxamine, a B6 vitamer. Local cholesterol biosynthesis and cholesterol elimination by lipoproteins were the other two cholesterol-related pathways in the retina responsive to pharmacologic treatments. The former was suppressed and the latter was upregulated by the treatments with simvastatin and TO901317, respectively. Simvastatin is a cholesterol lowering drug and TO901317 is an agonist of transcription factors from the family of liver X receptors. Unexpectedly, we identified two proteins, apolipoprotein D (apoD) and acyl-CoA cholesterol acyltransferase 1 (ACAT1) as potentially important for retinal cholesterol transport and storage, respectively. In this renewal we will focus on those unknown aspects of retinal cholesterol input and output that are of unquestionable importance for our understanding of how to combat AMD. The Specific Aims are: 1) to ascertain the contributions of local cholesterol biosynthesis and tissue uptake of blood-borne cholesterol to a pool of retinal cholesterol and whether these contributions are changed by high- cholesterol diet or treatment with simvastatin; 2) to establish retinal significance of apoD and ACAT1 and the pathways of retinal cholesterol transport and storage; 3) to assess the effectiveness of pharmacologic treatments of mice with significant accumulations of retinal cholesterol and abnormalities of retinal vasculature. We will obtain principally new information about retinal cholesterol acquisition, elimination and storage, fill the most critical gaps in our knowledge about retinal cholesterol maintenance, and facilitate the development of pharmacologic treatments for ocular diseases associated with deleterious accumulations of cholesterol in the retina.