Mouse Models to Characterize the Role of Lrp6 in Metabolic Syndrome

描述（由申请人提供）：心血管疾病（CVD）是美国死亡的主要原因。遗传低密度脂蛋白受体相关蛋白6 （LRP6）突变的患者由于代谢综合征（一系列症状，包括高血清LDL和甘油三酯水平、高血压和糖尿病），在很小的年龄就发展为心血管疾病。这些知识增加了更好地了解导致代谢综合征发展的因素的机会。使用新的小鼠模型，我们试图确定哪种细胞类型受到LRP6功能降低的影响，从而导致代谢综合征。受这种突变影响的原代细胞类型的两个潜在来源是脂肪细胞和肝细胞。为了检查Lrp6在这些细胞中的功能，我们将创建并表征携带肝细胞或脂肪细胞特异性Lrp6缺失的小鼠。在Specific Aim 1中，Lrp6-flox小鼠将在白蛋白启动子（albumin -cre）的控制下与表达cre重组酶的菌株杂交。这将直接表达特异性和高外显率到肝脏。Albumin-cre;研究人员将评估Lrp6-flox/flox小鼠和对照组的低脂和高脂饮食对肝功能的影响，以及与代谢综合征相关的血清成分水平的变化（重点是血清低密度脂蛋白和甘油三酯水平）。我们假设，当喂食高脂肪饮食时，这些小鼠的血清低密度脂蛋白和甘油三酯水平会升高。我们进一步预测，这将使这些小鼠易患动脉粥样硬化。在Specific Aim 2中，将Lrp6-flox小鼠杂交到一个由脂肪酸结合蛋白4基因（FABP4-cre） 5.4 kb启动子片段控制的表达cre重组酶的菌株。FABP4-cre小鼠仅在脂肪细胞中表达cre，几乎完全外显。FABP4-cre;研究人员将评估Lrp6-flox/flox小鼠和对照组的低脂和高脂饮食中脂肪沉积的变化和与代谢综合征相关的血清成分水平的变化。我们假设这些脂肪细胞特异性缺失Lrp6的小鼠将显示脂肪细胞功能缺陷，最终导致小鼠的全身变化，包括糖尿病的发展。公共卫生相关性：遗传低密度脂蛋白受体6 （LRP6）基因突变的人明显易患代谢综合征（一系列症状，包括血清低密度脂蛋白和甘油三酯水平高、高血压和糖尿病，显著增加心血管疾病的风险）。我们将创建携带Lrp6中肝脏或脂肪细胞特异性失活突变的小鼠，以深入了解受影响的组织类型，并开发可用于测试治疗干预措施的代谢综合征小鼠模型。鉴于心血管疾病是美国的头号杀手，这项工作对于更好地了解这种疾病的潜在原因将非常重要。

DESCRIPTION (provided by applicant): Cardiovascular disease (CVD) is the leading cause of death in the United States. Patients who inherit a mutation in the low density lipoprotein receptor related protein 6 (LRP6) developed CVD at a very early age due to metabolic syndrome (a constellation of symptoms which includes high serum levels of LDL and triglycerides, hypertension, and diabetes). This knowledge increases opportunities to better understand the factors that lead to the development of metabolic syndrome. Using novel mouse models, we seek to identify which cell type(s) are affected by reduced LRP6 function to cause metabolic syndrome. Two potential sources for the primary cell type affected by this mutation are the adipocytes and hepatocytes. To examine Lrp6 function in these cells, we will create and characterize mice carrying hepatocyte- or adipocyte-specific deletions of Lrp6. In Specific Aim 1, Lrp6-flox mice will be crossed to a strain expressing cre recombinase under the control of the albumin promoter (Albumin-cre). This will direct expression specifically and with high penetrance to the liver. Albumin-cre; Lrp6-flox/flox mice and littermate controls maintained on low- and high-fat diets will be evaluated for changes in liver function, as well as alterations in serum levels of components relevant to metabolic syndrome (with an emphasis on serum levels of LDL and triglycerides). We hypothesize that these mice will develop elevated levels of serum LDL and triglycerides when fed a high fat diet. We further predict that this will predispose these mice to the development of atherosclerosis. In Specific Aim 2, Lrp6-flox mice will be crossed to a strain expressing cre recombinase under the control of the 5.4 kb promoter fragment of the Fatty acid binding protein 4 gene (FABP4-cre). FABP4-cre mice express cre exclusively in adipocytes with virtually full penetrance. FABP4-cre; Lrp6-flox/flox mice and littermate controls maintained on low- and high-fat diets will be evaluated for changes in fat deposition and alterations in serum levels of components relevant to metabolic syndrome. We hypothesize that these mice with adipocyte-specific deletion of Lrp6 will display defects in adipocyte function which will eventually induce systemic changes in the mice, including the development of diabetes. PUBLIC HEALTH RELEVANCE: People who inherit a mutation in the low-density lipoprotein receptor 6 (LRP6) genes are dramatically predisposed to metabolic syndrome (a constellation of symptoms including high serum LDL and triglyceride levels, hypertension, and diabetes that dramatically increases the risk of cardiovascular disease). We will create mice carrying liver- or adipocyte-specific inactivating mutations in Lrp6 to gain insight into the tissue type(s) affected and to develop a mouse model of metabolic syndrome that can be used to test therapeutic interventions. Given that cardiovascular disease is the leading killer in the United States, this work will be very significant in gaining a better understanding of the underlying causes of this disease.