The role of hepatocyte tPA in hepatic VLDL production.

动脉粥样硬化是由动脉内含载脂蛋白B(ApoB)的积聚引起和促进的 激活慢性炎症反应的脂蛋白。肝细胞是载脂蛋白B的主要来源。 脂蛋白颗粒通过其分泌极低密度脂蛋白(VLDL)的能力，然后被水解为 血液中的中密度脂蛋白(IDL)，然后是低密度脂蛋白(LDL)。目前的胆固醇- 通过增强低密度脂蛋白受体(LDLR)介导的低密度脂蛋白降低治疗主要针对低密度脂蛋白-胆固醇水平 通行证。然而，这些降低低密度脂蛋白的治疗(例如，他汀类药物和PCSK9抑制剂)效果不大 对残留的致动脉粥样硬化载脂蛋白B-胆固醇成分的影响，包括极低密度脂蛋白和 IDL-胆固醇。尽管通过这些降低低密度脂蛋白的治疗达到了低密度脂蛋白-胆固醇的最佳水平， 不受控制的极低密度脂蛋白和低密度脂蛋白胆固醇仍然是高残留动脉粥样硬化的重要原因 人群中的心血管疾病(CVD)风险。我们小组最近有了一个新发现，一把钥匙 肝细胞中的血栓溶解蛋白，组织型纤溶酶原激活物(TPA)，限制apoB-2的产生。 小鼠和原代培养肝细胞中的脂蛋白。这项提案的总体目标是探讨 肝细胞组织型纤溶酶原激活剂降低血浆载脂蛋白胆固醇的机制 级别。目的1：探讨肝细胞tPA抑制极低密度脂蛋白(VLDL)脂化的分子机制。分泌物 极低密度脂蛋白颗粒的形成需要适当的载脂蛋白B脂化作用，但在我们对其机制的理解上仍有很大差距 这一切都是通过它发生的。我们的初步数据有力地支持了我们的假设，即沉默肝细胞tPA 通过促进肝脏极低密度脂蛋白的脂化来增加血浆载脂蛋白-胆固醇。完成这一目标将 为理解致动脉粥样硬化的载脂蛋白B-脂蛋白的产生增加新的见解。目标2：确定 肝细胞tPA是否促进载脂蛋白B-极低密度脂蛋白分泌前细胞内降解。细胞内 载脂蛋白B-极低密度脂蛋白颗粒在分泌之前的降解对于维持最佳血浆水平是重要的。 导致动脉粥样硬化的胆固醇和正常的肝脏脂质水平，但其机制尚不清楚。我们将增加 肝细胞tPA在小鼠体内的表达以验证肝细胞tPA增强极低密度脂蛋白细胞内的假说 分泌物之前的降解。这一目标的完成将提供一种新的机制来维持肝内 脂质动态平衡。目的3：确定血脂异常时肝细胞tPA升高是否能减少动脉粥样硬化， 而不会增加患脂肪肝的风险。降低循环中的残余胆固醇(在 极低密度脂蛋白和极低密度脂蛋白)，同时保持肝内脂质水平的动态平衡是一种有希望的策略，以减少 残余的动脉粥样硬化风险。然而，在降低致动脉粥样硬化胆固醇方面，治疗上的差距仍然存在 增加肝脏脂肪堆积。我们假设，在血脂异常的小鼠中，tPA表达增加会降低 载脂蛋白-胆固醇，可缓解动脉粥样硬化，而不会在肝脏中积聚脂质。完成 这一目标将提供新的治疗靶点，以降低残余动脉粥样硬化性心血管疾病的风险。

Atherosclerosis is initiated and promoted by the arterial accumulation of apolipoprotein B (apoB)-containing lipoproteins which activate a chronic inflammatory response. The hepatocyte is the major source of apoB- lipoprotein particles via its ability to secrete very-low-density lipoprotein (VLDL), which is then hydrolyzed into intermediate-density lipoprotein (IDL) and then low-density lipoprotein (LDL) in the blood. Current cholesterol- lowering therapies primarily target LDL-cholesterol levels by enhancing LDL receptor (LDLR)-mediated LDL clearance. However, these LDL-lowering treatments (e.g., statins and PCSK9 inhibitors) have only modest effects on the remnant atherogenic apoB-containing lipoprotein-cholesterol constituents, including VLDL- and IDL-cholesterol. Despite reaching optimal levels of LDL-cholesterol with these LDL-lowering treatments, uncontrolled VLDL- and IDL-cholesterols still significantly contribute to the high residual atherosclerotic cardiovascular disease (CVD) risk in the population. Our group recently made the novel discovery that a key blood clot lysis protein, tissue-type plasminogen activator (tPA), in hepatocytes limits the production of apoB- lipoproteins in mice and cultured primary hepatocytes. The overarching objective of this proposal is to explore the underlying mechanisms by which hepatocyte tPA lowers plasma apoB-containing lipoprotein-cholesterol levels. Aim 1: Determine the molecular mechanisms by which hepatocyte tPA limits VLDL lipidation. Secretion of VLDL particles requires proper apoB lipidation, but major gaps remain in our understanding of the mechanisms by which this happens. Our preliminary data strongly support our hypothesis that silencing hepatocyte tPA increases plasma apoB lipoprotein-cholesterol by promoting hepatic VLDL lipidation. Completion of this aim will add novel insights to the understanding of the production of atherogenic apoB-lipoproteins. Aim 2: Determine whether hepatocyte tPA enhances apoB-VLDL intracellular degradation before secretion. Intracellular degradation of apoB-VLDL particles prior to their secretion is important to maintain the optimal plasma levels of atherogenic cholesterol and normal liver lipid levels, but the mechanism is poorly understood. We will increase hepatocyte tPA expression in mice to test hypothesis that hepatocyte tPA enhances VLDL intracellular degradation before secretion. Completion of this aim will provide a novel mechanism to maintain intrahepatic lipid homeostasis. Aim 3: Determine whether increasing hepatocyte tPA in dyslipidemia reduces atherosclerosis, without raising the risk of fatty liver disease. Lowering circulating remnant cholesterol (the cholesterol found in VLDL and IDL) while maintaining the homeostasis of intrahepatic lipid levels is a promising strategy to reduce the residual atherosclerotic risk. However, therapeutic gaps remain in lowering atherogenic cholesterol without increasing liver lipid accumulation. We hypothesize that increasing tPA expression in dyslipidemic mice reduces apoB lipoprotein-cholesterol, alleviates atherosclerosis, without accumulating lipids in the liver. Completion of this aim will provide novel therapeutic targets to reduce residual atherosclerotic CVD risk.