Regulation of Liver Growth and Function

描述（由申请人提供）：营养摄入超过能量消耗是肥胖和2型糖尿病在世界范围内流行的一个主要因素。传统上，营养物质被认为是大分子生物合成的前体，是产生参与能量代谢的分子的底物。然而，它们现在被理解为通过信号转导级联来调节包括蛋白质合成在内的各种细胞过程。营养感应通路不仅在多个水平上相互连接，而且与胰岛素受体信号通路紧密耦合。因此，营养感应和胰岛素受体信号通路不是孤立地起作用，而是作为一个更大的、细胞内通讯的综合系统的组成部分。本文提出的项目重点是肝脏，肝脏是人体对营养摄入反应的一个特别重要的器官，因为它的位置与胃肠道有关，使它能够立即进入门静脉的消化产物。该项目还将重点放在蛋白质合成上，因为肝脏和胃肠道对混合膳食的蛋白质合成反应占全身蛋白质合成反应的25%。最后，该项目侧重于转化控制机制，这是一个研究领域，PI实验室的专业知识得到了很好的认可，并且越来越多地认识到在基因表达调控中发挥着突出作用。该项目将使用非糖尿病和糖尿病小鼠维持四种不同的饮食，旨在增加脂肪和热量的摄入。需要验证的假设是，慢性营养过剩和糖尿病单独或共同通过翻译控制机制作用，导致肝脏蛋白表达模式的全局和特异性变化，从而导致与代谢不适应相关的病理。该假设将通过以下三个具体目标进行验证：(1)确定不同饮食方案和糖尿病（单独或联合）对非糖尿病和糖尿病小鼠肝脏中蛋白质表达模式的整体和特异性变化的影响，eIF2和eIF4F介导的翻译控制机制，以及营养感知和胰岛素受体信号通路的激活状态；(2)定量分析mTORC1抑制因子REDD1在非糖尿病和糖尿病小鼠肝脏中对营养过剩的表达，明确其表达上调的调控机制，并明确其作用机制；(3)阐明糖尿病引起的高血糖和营养过剩介导肝脏翻译抑制因子4E-BP1表达增加的信号通路和分子机制。总体而言，该项目有望产生新的知识，为设计治疗与肥胖和糖尿病相关的全身代谢失调所导致的病理的策略提供见解。

DESCRIPTION (provided by applicant): Nutrient intake in excess of energy expenditure is a major contributing factor to the world-wide epidemic of obesity and type 2 diabetes. Traditionally nutrients have been considered to be precursors for the biosynthesis of macromolecules and as substrates for the production of molecules involved in energy metabolism. However, they are now understood to act through signal transduction cascades to regulate various cellular processes including protein synthesis. The nutrient-sensing pathways are not only interconnected at multiple levels but are tightly coupled to the insulin receptor signaling pathway. Thus, nutrient-sensing and insulin receptor signaling pathways do not function in isolation, but rather as components of a larger, integrated system of intracellular communication. The project proposed herein focuses on the liver, which is an especially important organ in regards to the body's response to nutrient intake because of its position in relation to the gastrointestinal tract, affording it immediate access to the products of digestion appearing in the portal vein. The project also focuses on protein synthesis because the liver, in combination with the gastrointestinal tract, accounts for 25% of the whole body protein synthetic response to a mixed meal. Finally, the project focuses on translational control mechanisms, an area of research for which the expertise of the PI's laboratory is well recognized and one becoming increasingly recognized as playing a prominent role in the regulation of gene expression. The project will employ non-diabetic and diabetic mice maintained on four different diets designed to increase both the fat and caloric intake. The hypothesis to be tested is that chronic nutrient excess and diabetes, alone and in combination, acting through translational control mechanisms, cause both global and specific changes in hepatic protein expression patterns that contribute to pathologies associated with maladapted metabolism. The hypothesis will be tested by pursuing the three following specific aims: (1) define the effects of different dietary regimens and diabetes, alone and in combination, on global and specific changes in protein expression patterns, the translational control mechanisms mediated by eIF2 and eIF4F, and the activation state of nutrient- sensing and insulin receptor signaling pathways in the liver of nondiabetic and diabetic mice; (2) quantitate expression of the mTORC1 repressor REDD1 in the liver of nondiabetic and diabetic mice in response to nutrient excess, define regulatory mechanisms contributing to its upregulated expression, and define its mechanisms of action; and (3) elucidate the signaling pathways and molecular mechanisms through which diabetes-induced hyperglycemia and nutrient excess mediate increased hepatic expression of the translational repressor 4E-BP1. Overall, the project is expected to produce new knowledge that will provide insight into designing strategies for the treatment of pathologies resulting from the maladapted whole body metabolism associated with obesity and diabetes. PUBLIC HEALTH RELEVANCE: Chronic intake of excess nutrients leads to accumulation of lipid in tissues, resulting in the development of insulin resistance and the pathological progression to type 2 diabetes and other metabolic diseases. The project proposed herein will employ a number of novel experimental models and specialized techniques to define effects of nutrient excess and diabetes, alone and in combination, on molecular events that modulate the pattern of protein expression in the liver. Knowledge gained from the project will provide insight into designing strategies for treatment of pathologies resulting from the maladapted whole body metabolism associated with obesity and diabetes.