Molecular Components Affecting Ocular Retinoid Homeostasis

摘要 维生素A对脊椎动物眼睛的重要作用早已为人所知，因为维生素A缺乏或过量， 这种维生素会损害眼睛的发育和功能。维生素A是至少两种重要的维生素的前体。 代谢物，11-顺式-视黄醇，视觉G蛋白偶联受体的发色团，和视黄酸，配体 细胞核受体。由于类维生素A不能由人类从头合成，因此膳食前体必须是必需的。 被肠道吸收并进行代谢转化。转化后的类维生素A 在体内储存并输送到目标组织如眼睛。这个过程显然取决于 在特定的转运蛋白和结合蛋白上。这些组件最近吸引了广泛的科学和 临床兴趣，因为它们与2型糖尿病和致命的马修- 伍德综合征。然而，由于缺乏对这些疾病的研究，我们对这些疾病的病理学知识很少。 同源哺乳动物模型。这样的研究将有助于我们理解生物化学 维生素A的运输，以及管理类维生素A稳态的调节机制。长期 本研究的目的是分析影响眼部类维生素A代谢的两个关键步骤： B，b-胡萝卜素向视黄醇的吸收和代谢转化以及B，b-胡萝卜素衍生的视黄醇的摄取 眼睛里在目标1中，我们将讨论肠特异性同源框转录因子ISX的作用， 抑制分别编码类胡萝卜素转运蛋白的Srb 1和Bcmo 1基因活性， 用于将B，b-胡萝卜素转化为类维生素A的酶。通过遗传解剖，我们将分析 B，b-胡萝卜素吸收和转化为类维生素A以及该途径的调节。为此， 我们将研究Isx、Srb 1和Bcmo 1单独和复合物中的B、b-胡萝卜素代谢和类维生素A稳态 敲除小鼠将进行启动子/报告基因研究，以阐明这一过程的分子细节。 调节包括视黄酸在这一过程中的作用。在目标2中，我们将建立敲除小鼠， STRA 6（stimulated by retinoic acid 6）蛋白研究致死性Matthew-Wood的代谢基础 综合征我们还将产生缺乏STRA 6和血清视黄醇结合的化合物敲除。 蛋白4（RBP 4），以测试RBP 4触发在STRA 6中观察到的病理学改变的假设。 缺陷此外，我们将分析视黄酸在调节血液视黄醇稳态中的作用， 不同的老鼠突变体这些研究将为类维生素A代谢和控制 类维生素A稳态，这将提高对人类疾病状态的理解， 过程，并可能提供其预防和/或治疗的概念。

ABSTRACT The essential role of vitamin A for the vertebrate eye has long been known because deficiency in or excess of this vitamin can impair eye development and function. Vitamin A is the precursor for at least two critical metabolites, 11-cis-retinal, the chromophore of visual G-protein-coupled receptors, and retinoic acid, a ligand for nuclear receptors. Since retinoids cannot be synthesized de novo by humans, dietary precursors must be absorbed by the intestine and metabolically converted. The converted retinoids must then be transported within the body for storage and delivered to target tissues such as the eyes. This process evidently depends on specific transporters and binding proteins. These components have recently attracted broad scientific and clinical interest since they are associated with diseases as diverse as type 2 diabetes and the fatal Matthew- Wood syndrome. Yet our knowledge of the pathology of these diseases is scant due to a lack of studies in homologous mammalian animal models. Such study would contribute to our understanding of the biochemistry of vitamin A transport as well as the regulatory mechanisms that govern retinoid homeostasis. The long-term objective of the proposed studies is to analyze two key steps affecting ocular retinoid metabolism: the intestinal absorption and metabolic conversion of b,b-carotene to retinol and the uptake of b,b-carotene-derived retinol into the eyes. In Aim 1, we will address the role of the intestine specific homeobox transcription factor ISX that suppresses Srb1 and Bcmo1 gene activities which respectively encode a carotenoid transporter and the key enzyme for b,b-carotene conversion into retinoids. By genetic dissection, we will analyze the molecular basis of b,b-carotene absorption and conversion into retinoids and the regulation of this pathway. For this purpose, we will study b,b-carotene metabolism and retinoid homeostasis in Isx, Srb1 and Bcmo1 single and compound knockout mice. Promoter/reporter gene studies will be performed to elucidate the molecular details of this regulation including the role of retinoic acid in this process. In Aim 2, we will establish knockout mice lacking STRA6 (stimulated by retinoic acid 6) protein to study the metabolic basis of the fatal Matthew-Wood syndrome. We also will generate compound knockouts lacking both STRA6 and the serum retinol binding protein 4 (RBP4) to test for the hypothesis that RBP4 triggers the pathological alterations seen in STRA6- deficiency. Furthermore, we will analyze the role retinoic acid in regulating blood retinol homeostasis in the different mouse mutants. These studies will provide new insights into retinoid metabolism and the control of retinoid homeostasis which will improve understanding of human disease states caused by disturbances in this process and may provide concepts for their prevention and/or therapy.