Control of liver autophagy by phosphatidic acid signaling

通过磷脂酸信号控制肝脏自噬

• 批准号: 8533522
• 负责人: Gilbert Di Paolo
• 金额: $ 24万
• 依托单位: COLUMBIA UNIVERSITY HEALTH SCIENCES
• 依托单位国家: 美国
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-06-01 至 2015-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8533522
• 关键词: Acid Lipase; Acute; Adult; Affect; Age; Aging; Albumins; Autophagocytosis; Autophagosome; Biogenesis; Biological Assay; Catabolism; Cells; Complement; Cultured Cells; Data; Defect; Diet; Disease; Electron Microscopy; Embryo; Endosomes; Energy Supply; Energy-Generating Resources; Ensure; Enzymes; Equilibrium; Exhibits; Fatty Acids; Fatty Liver; Fatty acid glycerol esters; Fibroblasts; Fluorescence Microscopy; Future; Genes; Genotype; Hepatic; Hepatocyte; Homeostasis; Human; Knock-out; Lead; Lecithin; Life; Lipids; Lipolysis; Liver; Liver diseases; Lysosomes; Measures; Mediating; Membrane; Membrane Protein Traffic; Metabolic syndrome; Molecular; Mus; Mutant Strains Mice; Nutrient; Nutritional; Organelles; Pathway interactions; Phenotype; Phosphatidic Acid; Process; Property; Proteins; Publishing; Recycling; Role; Signal Transduction; Staining method; Stains; Starvation; Testing; Therapeutic; Tissues; Triglycerides; Vesicle; Work; base; cell type; deprivation; light microscopy; lipid metabolism; macromolecule; mouse model; mutant; non-alcoholic fatty liver; phospholipase D1; protein aggregate; public health relevance; stressor; tool; wasting

DESCRIPTION (provided by applicant): Proper storage and utilization of lipids is essential to maintain cellular energy homeostasis and perturbation of this balance can lead to a variety of human disorders, including metabolic syndrome. Cellular lipids are generally stored as triglycerides in the form of lipid droplets and are hydrolyzed into fatty acids for energy supply during nutrient deprivation. Recently, macroautophagy (simply called autophagy) has emerged as a major cellular pathway mediating the catabolism of triglycerides and the clearance of lipid droplets (i.e., "macrolipophagy") in hepatocytes and many other cell types. Autophagy ensures the recycling of macromolecules under conditions of nutritional scarcity, as well as the elimination of defective organelles, long- lived proteins, and intracellular protein aggregates. Because of its remarkable efficiency at eliminating cellular "waste" and consuming energy sources, autophagy is increasingly viewed as a pathway that can be exploited for the therapy of various human conditions. The recent discovery of macrolipophagy has raised a number of fundamental questions, including whether there are molecular pathways dedicated to this selective type of autophagy and whether the efficacy of this process is affected by diet and aging. In this proposal, we explore the possibility that the lipid enzyme phospholipase D1 (PLD1) is a positive modulator of macrolipophagy. PLD1 hydrolyzes phosphatidylcholine into the bioactive lipid phosphatidic acid, which regulates signaling and membrane trafficking processes. Our published data indicate that mice lacking PLD1, which are viable, exhibit defects in autophagy in the liver, based on the occurrence of both fewer and smaller autophagosomes in mutant hepatocytes. Remarkably, this phenotype is induced by starvation conditions and is not associated with the accumulation of protein aggregates, as typically observed in mutant mice lacking genes such as Atg5 or Atg7 which are essential for both basal and starvation-induced autophagy. At the mechanistic level, our results suggest that a key function of PLD1-derived phosphatidic acid is to promote the maturation of autophagosomes by facilitating the fusion of these organelles with endosomes/lysosomes. Together with preliminary observations showing that lipid droplets are more prominent in Pld1 knockout liver from starved mice as well as in knockout fibroblasts, our results strongly suggest that PLD1 is implicated in starvation- induced macrolipophagy. In this proposal, we plan to directly test this hypothesis using mice that lack PLD1 selectively in hepatocytes. We also assess the impact of "stressors", such as high fat diet and age, on the efficacy of macrolipophagy, with the prediction that they may further unmask genotype-specific differences in fat accumulation and lipid metabolism. We anticipate our studies will clarify the role of macrolipophagy in the control of lipid metabolism and provide the basis for future work testing whether stimulating the PLD1 pathway can be exploited to promote macrolipophagy in human conditions, such as fatty liver diseases.

描述（由申请人提供）：脂质的适当储存和利用对于维持细胞能量稳态和这种平衡的扰动至关重要，可能导致各种人类疾病，包括代谢综合征。细胞脂质通常以脂质液滴的形式存储为甘油三酸酯，并将脂肪酸水解为脂肪酸，以在养分剥夺期间进行能量供应。最近，大型噬噬菌（简单地称为自噬）已成为介导甘油三酸酯分解代谢的主要细胞途径，以及在肝细胞和许多其他细胞类型中的脂质滴（即“ Macrolipophagy”）的清除。自噬可确保在营养稀缺条件下以及消除有缺陷的细胞器，长寿命蛋白和细胞内蛋白质聚集体的情况下回收大分子。由于其在消除细胞“废物”和消耗能源的效率下，自噬越来越被视为一种可以利用用于治疗各种人类状况的途径。最近发现的大量噬菌体提出了许多基本问题，包括是否有专门用于这种选择性类型的自噬的分子途径，以及该过程的功效是否受饮食和衰老的影响。在此提案中，我们探讨了脂质酶D1（PLD1）是大寄生虫的正调节剂的可能性。 PLD1将磷脂酰胆碱水解为生物活性脂质磷脂酸，从而调节信号传导和膜运输过程。我们已发表的数据表明，缺乏可行的PLD1的小鼠基于突变肝细胞突变体肝细胞中较小和较小的自噬体的发生，在肝脏中表现出缺陷。值得注意的是，这种表型是由饥饿条件诱导的，并且与蛋白质聚集体的积累无关，因为在缺乏ATG5或ATG7的突变小鼠中通常观察到，这对于基础和饥饿诱导的自噬都是必不可少的。在机械水平上，我们的结果表明，PLD1衍生的磷脂酸的关键功能是通过促进这些细胞器与内体/溶酶体的融合来促进自噬体的成熟。加上初步观察结果表明，脂质液滴在饥饿小鼠以及基因敲除成纤维细胞中更为突出，我们的结果强烈表明PLD1与饥饿诱导的大酚噬菌有关。在此提案中，我们计划使用在肝细胞中选择性缺乏PLD1的小鼠直接检验该假设。我们还评估了“压力源”（例如高脂肪饮食和年龄）对大酚寄生虫功效的影响，并预测它们可能会进一步揭示脂肪积累和脂质代谢的基因型特异性差异。我们预计我们的研究将阐明大酚寄生在控制脂质代谢中的作用，并为未来的工作测试提供基础，以测试是否可以利用刺激PLD1途径来促进在人类状况（例如脂肪肝疾病）中促进大酚。