Regulation of SREBP-1 Processing Lipogenesis by LPCAT

项目摘要 固醇调节元件结合蛋白-1（SREBP-1）是脂肪生成酶的关键激活剂 参与脂肪酸的合成。SREBP-1的转录和蛋白水解切割受到以下因素的严格调控： 生理和病理条件下的营养和激素因素。胰岛素显著增加 SREBP-1 mRNA的转录主要通过增加LXR的活性，并促进翻译后 蛋白质的加工。在ob/ob糖尿病小鼠肝脏中，核SREBP-1c被高度诱导， 肝脏脂肪酸生物合成增加和脂肪变性。除了甾醇，其他脂质也被证明是 调节SREBP-1加工，包括不饱和脂肪酸（FA）和磷脂。的机制 磷脂对SREBP-1c表达的影响机制尚待研究。我们实验室最近的工作 鉴定了一种LXR-Lpcat 3途径，其动态调节膜磷脂（磷脂酰胆碱和 磷脂酰乙醇胺）组成对细胞脂质代谢变化的反应。激活LXR 优先驱动多不饱和脂肪酸掺入磷脂，通过诱导 重塑酶Lpcat 3。肝脏中Lpcat 3的缺失选择性地减少肝膜中的花生四烯酸酰PC， 并导致膜流动性降低。在我们最初的工作之后，我们发现Lpcat 3调节 LXR介导的参与脂肪酸生物合成的基因表达。我们的初步数据显示， Lpcat 3主要通过操纵SREBP的蛋白水解切割来调节脂肪生成基因的表达。 1.在这项提案中，我们的目标是1）定义Lpcat 3调节SREBP-1加工的机制， Lpcat 3肝特异性敲除原代肝细胞和小鼠。2)确定Lpcat 3和磷脂 在生理或病理条件下，SREBP-1c在肝脏中的表达与肝脏重塑有关 条件我们将评估Lpcat 3是否介导胰岛素诱导的SREBP-1在肝细胞和WT中的表达。 和LKO小鼠肝脏。我们将检测Lpcat 3抑制对SREBP-1的影响， 在ob/ob小鼠中处理。最后，我们将确定Lpcat 3和磷脂重塑在 人类非酒精性脂肪肝疾病（NAFLD）。考虑到新生血管的调节失调 脂肪生成和主要人类疾病，了解SREBP-1表达的调控， 为脂肪肝和血脂异常发展的分子控制提供了新的见解， 提示这些疾病的潜在治疗机会。

Project Summary Sterol regulatory element-binding protein-1 (SREBP-1) is a pivotal activator of lipogenic enzymes involved in fatty acid synthesis. Transcription and proteolytic cleavage of SREBP-1 is tightly regulated by nutritional and hormonal factors under physiological and pathological conditions. Insulin dramatically increases the transcription of SREBP-1 mRNA primarily by increasing the activity of LXRs, and promotes post-translational processing of the protein. In ob/ob diabetic mouse livers, nuclear SREBP-1c is highly induced and contributes to the elevated hepatic fatty acid biosynthesis and steatosis. Besides sterols, other lipids have also been shown to regulate SREBP-1 processing, including unsaturated fatty acids (FAs) and phospholipids. The mechanisms by which phospholipids affect SREBP-1c expression remain to be resolved. Recent work from our lab has identified an LXR-Lpcat3 pathway that dynamically modulates membrane phospholipid (phosphatidylcholine and Phosphatidylethanolamine) composition in response to changes in cellular lipid metabolism. Activation of LXRs preferentially drives the incorporation of polyunsaturated fatty acids into phospholipids through induction of the remodeling enzyme Lpcat3. Loss of Lpcat3 in liver selectively reduces arachidonoyl PC in liver membranes, and results in decreased membrane fluidity. Following on our initial work, we discovered that Lpcat3 regulates the LXR-mediated expression of genes involved in fatty acid biosynthesis. Our preliminary data suggest that Lpcat3 regulates the expression of lipogenic genes mainly through manipulating proteolytic cleavage of SREBP- 1. In this proposal, we aim to 1) Define the mechanisms by which Lpcat3 regulates SREBP-1 processing using Lpcat3 liver specific knockout primary hepatocytes and mice. 2) Determine whether Lpcat3 and phospholipid remodeling are involved in the regulation of SREBP-1c expression in liver under physiological or pathological conditions. We will assess if Lpcat3 mediates insulin-induced SREBP-1 expression in hepatocytes and in WT and LKO mouse livers during fasting/refeeding. We will examine the effect of Lpcat3 inhibition on SREBP-1 processing in ob/ob mice. Finally we will determine the involvement of Lpcat3 and phospholipid remodeling in human nonalcoholic fatty liver diseases (NAFLD). Given the close association between dysregulation of de novo lipogenesis and major human diseases, understanding the regulation of SREBP-1 expression is expect to provide novel insights into the molecular control of the development of fatty liver and dyslipidemia, and may suggest potential therapeutic opportunities for these diseases.