A Novel Cellular Mechanism for Reducing Hyperlipidemia

降低高脂血症的新细胞机制

• 批准号: 8774170
• 负责人: JINGWEN LIU
• 金额: --
• 依托单位: VETERANS ADMIN PALO ALTO HEALTH CARE SYS
• 依托单位国家: 美国
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8774170
• 关键词: ASCL1 gene; Acyl Coenzyme A; Adenoviruses; Agonist; Animal Model; Binding; Binding Proteins; Biological Assay; Biology; Blood Circulation; Cardiovascular Diseases; Catabolic Process; Catabolism; Cell Line; Cells; Cholesterol; Coenzyme A Ligases; Comorbidity; Complementary DNA; DNA; Development; Diabetes Mellitus; Diet; Disease; Dyslipidemias; Elements; Enzymes; Event; Exhibits; Family; Fatty Acids; Fatty Liver; Functional disorder; Funding; Gel; Gene Delivery; Gene Expression; Gene Targeting; Genes; Genetic Transcription; Goals; Hamsters; Health; Health Care Costs; HepG2; Hepatic; Hepatocyte; Human; Hyperlipidemia; Hypertension; Hypertriglyceridemia; Individual; Insulin Resistance; Isoenzymes; Laboratories; Lead; Ligands; Link; Lipids; Lipoproteins; Liver; Luciferases; Maps; Mediating; Messenger RNA; Metabolic; Metabolic Diseases; Metabolic syndrome; Modeling; Molecular; Molecular Target; Non-Insulin-Dependent Diabetes Mellitus; Nonesterified Fatty Acids; Obesity; PPAR delta; Pathway interactions; Peroxisome Proliferator-Activated Receptors; Physiological; Plasma; Play; Protein Isoforms; Proteins; Proteomics; Regulation; Reporter; Role; Therapeutic; Time; Tissues; Trans-Activators; Transcription Coactivator; Transcriptional Regulation; Triglycerides; Up-Regulation; Veterans; Virus; Work; adenoviral-mediated; base; cell growth regulation; chromatin immunoprecipitation; cytokine; fatty acid metabolism; gain of function; in vivo; in vivo Model; insight; lipid metabolism; loss of function; member; new therapeutic target; novel; novel therapeutic intervention; oncostatin M; oxidation; promoter; response; small hairpin RNA; transcription factor; uptake; very low density lipoprotein triglyceride; viral gene delivery

DESCRIPTION (provided by applicant): The liver plays a central role in whole-body lipid metabolism by regulating the uptake, synthesis, oxidation and export of lipids. Dysfunction of lipid metabolism in liver underlies the development of obesity, diabetes, and hepatic steatosis. Although the mechanisms that regulate the hepatic uptake, activation, and metabolism of fatty acids (FAs) are not fully understood, nearly all pathways of FA metabolism require conversion of FAs to acyl-CoAs by acyl-CoA synthetases. Long-chain acyl-CoAs are formed by a family of five acyl-CoA synthetases (ACSL1, ACSL3, ACSL4, ACSL5, and ACSL-6). Gain-of-function as well as loss-of-function studies suggest that each of ACSL isoform has a distinct function in directing acyl-CoAs to one or more specific downstream pathways. Thus, the level of expression of individual ACSL isozymes could directly influence the FA metabolic fates in liver tissue. Currently, the cellular mechanisms that regulate the hepatic expression of ACSLs under either physiological or pathological conditions remain largely unexplored. Previously, our laboratory demonstrated that the isozyme ACSL3 was transcriptionally upregulated by the cytokine oncostatin M (OM) in HepG2 cells accompanied by reduced cellular triglyceride content and enhanced FA 2-oxidation. During the last funding period we investigated the molecular mechanism underlying the OM-induced activation of ACSL3 gene transcription and identified the peroxisome proliferator-activated receptor 4 (PPAR4) as the critical trans-activator that mediated the OM induction of ACSL3 gene transcription. Our work, for the first time, revealed an important functional link between ACSL family and PPAR4, a key transcription factor for modulating a cascade of gene expressions in lipid metabolism. Interestingly, we have also observed an increase in mRNA levels of two other members of the ACSL family (ACSL5 and ACSL4) along with ACSL3 in HepG2 cells that were treated with the PPAR4 agonist L165041. This observation suggested that PPAR4 might regulate the transcription of multiple ACSL isozymes in liver cells. The expression level of PPAR4 directly correlates with its transactivating capacity in modulation of gene expression. Thus, it has become important to understand how PPAR4 expression is regulated in liver. However, currently, little is known about the cellular mechanisms governing hepatic PPAR4 transcription. Furthermore, the in vivo role of PPAR4 in regulating ACSL isozymes under normolipidemic and hyperlipidemic conditions has not been examined. Therefore, the overall objectives of this renewal application are to comprehensively define all the molecular determinants that control the basal and OM-induced gene transcription of PPAR4 in hepatic cells and to use hamsters as our in vivo model to thoroughly examine the roles of PPAR4 in gene expression of the ACSL family and in lipid catabolic process of the liver tissue. The specific aims of this Merit Review renewal application are to: 1) functionally characterize PPAR4 promoter to identify critical regulatory sequences for the basal transcriptional activity of PPAR4 in liver cells and to precisely map the OM-responsive element; 2) comprehensively identify the trans-activator that mediates OM stimulatory effect on PPAR4 transcription as well as those transcriptional factors that are critical for PPAR4 gene transcription in responding to hepatic metabolic demands; and 3) thoroughly investigate the in vivo regulatory role of PPAR4 in the hepatic expression of ACSL isozymes under normolipidemic and hyperlipidemic conditions in two hamster models that either increase or knockdown expression levels of PPAR? in liver tissue through applying adenoviral-mediated gene delivery approaches. Metabolic disorders such as obesity and type II diabetes exhibit altered FA metabolism, to which dysregulated expression of ACSL isozymes could contribute to the disease development. Through these proposed studies we hope to reach a better understanding of the interplay between the ACSL enzyme family and PPAR4 under normolipidemic and hyperlipidemic conditions to gain insights for identifying new therapeutic targets to treat hyperlipidemia.

描述（由申请人提供）： 肝脏通过调节脂质的摄取、合成、氧化和输出，在全身脂质代谢中发挥核心作用。肝脏脂质代谢功能障碍是肥胖、糖尿病和肝脂肪变性发生的基础。尽管调节脂肪酸 (FA) 的肝脏摄取、活化和代谢的机制尚未完全清楚，但几乎所有 FA 代谢途径都需要通过酰基辅酶 A 合成酶将 FA 转化为酰基辅酶 A。长链酰基辅酶 A 由五种酰基辅酶 A 合成酶家族（ACSL1、ACSL3、ACSL4、ACSL5 和 ACSL-6）形成。功能获得和功能丧失研究表明，每种 ACSL 亚型在将酰基辅酶 A 导向一个或多个特定下游途径方面都具有独特的功能。因此，单个 ACSL 同工酶的表达水平可以直接影响肝组织中 FA 的代谢命运。目前，在生理或病理条件下调节 ACSL 肝脏表达的细胞机制在很大程度上仍未被探索。此前，我们实验室证明HepG2细胞中细胞因子制瘤素M（OM）转录上调同工酶ACSL3，并伴随细胞甘油三酯含量降低和FA 2-氧化增强。在上一个资助期间，我们研究了 OM 诱导的 ACSL3 基因转录激活的分子机制，并确定过氧化物酶体增殖物激活受体 4 (PPAR4) 是介导 OM 诱导 ACSL3 基因转录的关键反式激活因子。我们的工作首次揭示了 ACSL 家族和 PPAR4 之间的重要功能联系，PPAR4 是调节脂质代谢中一系列基因表达的关键转录因子。有趣的是，我们还观察到在用 PPAR4 激动剂 L165041 处理的 HepG2 细胞中，ACSL 家族的其他两个成员（ACSL5 和 ACSL4）以及 ACSL3 的 mRNA 水平有所增加。这一观察结果表明 PPAR4 可能调节肝细胞中多种 ACSL 同工酶的转录。 PPAR4 的表达水平与其调节基因表达的反式激活能力直接相关。因此，了解 PPAR4 表达在肝脏中的调节机制变得非常重要。然而，目前人们对肝脏 PPAR4 转录的细胞机制知之甚少。此外，尚未检查 PPAR4 在正常血脂和高血脂条件下调节 ACSL 同工酶的体内作用。因此，本次更新申请的总体目标是全面定义控制肝细胞中 PPAR4 基础转录和 OM 诱导基因转录的所有分子决定因素，并使用仓鼠作为我们的体内模型来彻底检查 PPAR4 在基因转录中的作用。 ACSL 家族的表达和肝组织的脂质分解代谢过程。本次优秀评审更新申请的具体目标是：1）对 PPAR4 启动子进行功能表征，以确定肝细胞中 PPAR4 基础转录活性的关键调控序列，并精确定位 OM 响应元件； 2）全面鉴定介导OM对PPAR4转录的刺激作用的反式激活因子，以及对PPAR4基因转录响应肝脏代谢需求至关重要的转录因子； 3) 在正常血脂和高血脂条件下，在两种仓鼠模型中彻底研究 PPAR4 在 ACSL 同工酶肝脏表达中的体内调节作用，这两种仓鼠模型要么增加或敲低 PPAR 的表达水平？通过应用腺病毒介导的基因传递方法在肝组织中。肥胖和 II 型糖尿病等代谢性疾病表现出 FA 代谢的改变，ACSL 同工酶的表达失调可能导致疾病的发展。通过这些拟议的研究，我们希望更好地了解 ACSL 酶家族和 PPAR4 在正常血脂和高血脂条件下之间的相互作用，从而为确定治疗高血脂的新治疗靶点获得见解。