Role of Lipid Phosphatases in Cholesterol and Triglyceride Synthesis

描述（申请人提供）：心脑血管疾病是世界范围内导致死亡的主要原因。肥胖、循环胆固醇和甘油三酯水平升高以及循环脂蛋白组成改变是心脑血管疾病的主要危险因素。肥胖是一种能量平衡失调。当能量输入超过能量输出时，消耗的大部分多余卡路里转化为甘油三酯并储存在脂肪组织中。同样，当胆固醇的重新合成和饮食来源提供的胆固醇之间的平衡超过正常胆固醇需求和消除这种必需胆固醇的能力时，循环胆固醇的增加导致胆固醇沉积在脉管系统中。肥胖及其并发症（包括高胆固醇血症）的临床治疗目前主要集中在饮食、身体活动和行为的改变上。由于这些策略的有效性有限，肥胖的患病率继续增加。药物抑制胆固醇合成是目前临床治疗高胆固醇血症的主要和最有效的策略。虽然到目前为止，针对肥胖的药物治疗策略主要集中在抑制食欲和干扰脂质吸收方面，但取得了一定的成功，最近在小鼠模型上的研究进展表明，抑制甘油三酯合成可能是一种可行且有效的治疗策略。因此，确定甘油三酯和胆固醇合成途径的组成部分，并全面了解这些过程是如何被调节的，对于开发新的或改进的治疗肥胖和高胆固醇血症的药物至关重要。由于它们在细胞代谢中的关键地位，负责胆固醇和甘油三酯从头合成的途径已被深入研究，但我们的知识仍然存在重大差距。两类脂质磷酸酯，聚类异戊二烯二磷酸盐和磷脂酸是合成胆固醇和甘油三酯的关键中间体，但使这些中间体去磷酸化的酶直到最近才被发现。本研究的总体目标是通过研究两种新发现的脂质磷酸酶的调节和功能来解决我们知识中的这些空白，这两种酶在类异戊二烯、固醇和甘油三酯的合成中起着核心作用。我们的研究使用生物化学、细胞和分子生物学技术来研究这些酶在体外和生物医学相关的模型细胞系统中的调节和功能。在第一个目标中，我们将使用这些方法来检验一个假设，即称为多异戊二烯二磷酸磷酸酶的整体膜酶是胆固醇合成和蛋白质异戊二烯化的调节剂。在该提案的第二个目标中，我们将测试一个假说，即催化甘油三酯合成关键步骤的磷脂酸磷酸酶的活性是由一个新的膜靶向基序调节的。公共卫生相关性：肥胖和胆固醇水平升高是心脑血管疾病的主要危险因素，而心脑血管疾病是该国死亡的主要原因。肥胖是一种能量平衡失调。当能量输入超过能量输出时，消耗的大部分多余卡路里转化为甘油三酯，并作为身体脂肪储存起来。同样，当胆固醇合成和膳食来源提供的胆固醇之间的平衡超过正常的胆固醇需求和胆固醇排泄时，循环胆固醇就会增加。在这个研究项目中，我们将测试关于新发现的在脂肪和胆固醇的合成和代谢中起核心作用的酶的调节和功能的特定假设。我们的工作的完成将为这些脂质的合成是如何被调节的，这一过程在疾病中是如何改变的，以及针对这些过程为肥胖和心血管疾病提供新疗法的可行性提供新的见解。

DESCRIPTION (provided by applicant): Cardiovascular and cerebrovascular diseases are the leading causes of death worldwide. Obesity, elevations in circulating levels of cholesterol and triglycerides and alterations in the composition of circulating lipoproteins are major risk factors for cardiovascular and cerebrovascular disease. Obesity is a disorder of energy balance. When energy input exceeds energy output most of the excess calories consumed are converted to triglycerides and stored in adipose tissue. Similarly, increases in circulating cholesterol leading to cholesterol deposition in the vasculature occur when the balance between de novo synthesis of cholesterol and provision of cholesterol from dietary sources exceeds normal cholesterol requirements and capacity to eliminate this essential sterol. Clinical management of obesity and its complications including hypercholesterolemia presently focuses on modifications of diet, physical activity and behavior. Because these strategies are of limited effectiveness, the prevalence of obesity continues to increase. Pharmacological inhibition of cholesterol synthesis is the primary and presently most effective strategy for the clinical management of hypercholesterolemia. Although to date efforts to develop pharmacological strategies for treatment of obesity focusing on appetite suppression and interference with lipid absorption have met with moderate success, recent advances using mouse models suggest that inhibition of triglyceride synthesis may be a viable and effective treatment strategy. Identification of components of the pathways responsible for synthesis of triglycerides and cholesterol and development of a complete understanding of how these processes are regulated is therefore critical for the development of new or improved agents for treatment of obesity and hypercholesterolemia. Because of their pivotal position in cellular metabolism, the pathways responsible for the de novo synthesis of cholesterol and triglycerides have been intensively studied but significant gaps in our knowledge remain. Two classes of lipid phosphate esters, polyisoprenoid diphosphates and phosphatidic acid are critical intermediates in the synthesis of cholesterol and triglyceride but enzymes that dephosphorylate these intermediates have only recently been identified. The overall goal of this research is to address these gaps in our knowledge by investigating the regulation and function of two newly identified lipid phosphatases that play central roles in the synthesis of isoprenoids, sterols and triglycerides. Our research uses techniques of biochemistry, cell and molecular biology to study the regulation and function of these enzymes in vitro and in biomedically relevant model cell systems. In the first aim we will use these approaches to test the hypothesis that an integral membrane enzyme termed polyisoprenoid diphosphate phosphatase is a regulator of cholesterol synthesis and protein isoprenylation. In the second aim of the proposal we will test the hypothesis that activity of a phosphatidic acid phosphatase enzyme that catalyses a critical step in triglyceride synthesis is regulated by a novel membrane targeting motif. PUBLIC HEALTH RELEVANCE: Obesity and elevated cholesterol levels are major risk factors for Cardiovascular and Cerebrovascular disease which are the leading causes of death in this country. Obesity is a disorder of energy balance. When energy input exceeds energy output most of the excess calories consumed are converted to triglycerides and stored as body fat. Similarly, increases in circulating cholesterol occur when the balance between cholesterol synthesis and provision of cholesterol from dietary sources exceeds normal cholesterol requirements and cholesterol excretion. In this research project we will test specific hypotheses about the regulation and function of newly identified enzymes that play central roles in the synthesis and metabolism of fat and cholesterol. Completion of our work will provide new insights into how synthesis of these lipids is regulated, how this process may be altered in disease and the feasibility of targeting these processes to provide novel therapies for obesity and cardiovascular disease.