A Novel Cellular Mechanism for Reducing Hyperlipidemia

降低高脂血症的新细胞机制

• 批准号: 8241550
• 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/8241550
• 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; 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，在全身脂质代谢中起着核心作用。肝脏中脂质代谢功能障碍是肥胖，糖尿病和肝脂肪变性的发展。尽管尚不完全了解调节肝脏摄取，激活和代谢的机制，但几乎所有FA代谢的所有途径都需要通过酰基-COA合成酶将FAS转化为酰基-COAS。长链酰基-COA由五个酰基-COA合成酶（ACSL1，ACSL3，ACSL4，ACSL5和ACSL-6）组成。功能收益以及功能丧失研究表明，每个ACSL同工型都在将酰基-COA引导到一个或多个特定的下游途径方面具有独特的功能。因此，单个ACSL同工酶的表达水平可以直接影响肝组织中的FA代谢命运。当前，在生理或病理条件下调节ACSL的肝表达的细胞机制在很大程度上尚未探索。以前，我们的实验室表明，同工酶ACSL3在HEPG2细胞中的细胞因子oncostin M（OM）在转录上上调，并伴有降低的细胞甘油三酸酯含量和增强的FA 2-氧化。在上一个资金期间，我们研究了OM诱导的ACSL3基因转录激活的基础分子机制，并确定了过氧化物酶体增殖物激活的受体4（PPAR4）是介导ACSL3基因转录的OM诱导的关键反式激活剂。我们的工作首次揭示了ACSL家族与PPAR4之间的重要功能联系，这是调节脂质代谢中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（ACSL5和ACSL4）的其他两个成员的mRNA水平以及ACSL3升高。该观察结果表明，PPAR4可能调节肝细胞中多个ACSL同工酶的转录。 PPAR4的表达水平与其在基因表达的调节中的反式激活能力直接相关。因此，了解如何在肝脏中调节PPAR4表达是很重要的。但是，目前，关于控制肝PPAR4转录的细胞机制知之甚少。此外，尚未研究PPAR4在正常脂肪和高脂血症条件下调节ACSL同工酶中的体内作用。因此，这种续签应用的总体目标是全面定义所有控制肝细胞中PPAR4基础和OM诱导的基因转录的分子决定因素，并将使用仓鼠作为我们的体内模型，以彻底检查PPAR 4在ACSL家族和Lipid catibolic Citabolic Fastere的基因表达中的作用。此功绩审查更新应用的具体目的是：1）功能表征PPAR4启动子，以识别肝细胞中PPAR4基础转录活性的关键调节序列，并精确映射OM反应元件； 2）全面确定介导对PPAR4转录刺激作用的反式激活因子以及对于响应肝代谢需求时PPAR4基因转录至关重要的转录因子； 3）在两个仓鼠模型中，PPAR4在正常脂质血症和高脂症状条件下，PPAR4在ACSL同工酶在ACSL同工酶的肝表达中的体内调节作用会增加PPAR的表达水平或敲低表达水平？通过应用腺病毒介导的基因递送方法，在肝组织中。肥胖症和II型糖尿病等代谢疾病表现出改变的FA代谢，ACSL同工酶的失调表达可能有助于疾病的发展。通过这些提出的研究，我们希望在正常脂肪和高脂症状条件下更好地理解ACSL酶家族与PPAR4之间的相互作用，以获得识别新的治疗靶标以治疗高脂血症的见解。