Trafficking of Triacylglycerol in Adipocytes

描述(申请人提供)：白色脂肪组织的一个特殊功能是在蛋白涂层液滴中储存中性脂肪。这种脂肪储存功能既提供了能量储存库，又提供了隔离多余脂肪的场所，否则会对肌肉、血管、肝脏和胰腺等组织产生毒性影响，从而增加糖尿病、心脏病和非酒精性脂肪性肝病的风险。新合成的三酰甘油是如何被包装并插入脂类储存液滴中的，目前尚不清楚。此外，人们对包裹脂滴的蛋白质的身份和功能知之甚少。这项研究计划的总体目标是发现脂类在细胞内运输到其在脂肪细胞内储存位置的机制。了解这些机制可能会阐明在脂肪过度储存(肥胖)和脂肪细胞低效分配(脂肪营养不良/脂肪萎缩)的情况下出现了什么问题。初步数据揭示了一个脂滴成熟的过程，在这个过程中，脂肪细胞蛋白S3-12包裹新形成的脂滴，促进三酰甘油的积累。我们假设，S3-12通过包裹新生的脂滴并介导它们掺入Perilipin包被的储存液滴，促进了新合成的三酰甘油有效地包装成储存液滴。根据这一模型，S3-12用于引导三酰甘油进入储存途径，而不是水解途径。目的1研究活性三酰甘油包装过程中脂肪细胞和脂滴蛋白质组的变化。目的2试图在活细胞中记录脂滴的生物发生过程，并确定S3-12如何促进三酰甘油的积累和脂滴的组织。S3-12介导其靶向新生脂滴的结构特征及其功能将通过突变分析得到图谱。最后，Aim 3研究了S3-12在小鼠体内的全球过表达是否会促进三酰甘油在脂肪细胞中的积累，并通过将三酰甘油隔离在储存液滴中来保护其他组织免受脂毒性，从而限制脂解作用并减少有毒脂类代谢物的产生。通过这些研究，应该可以揭示细胞内脂质运输的基本机制。

DESCRIPTION (provided by applicant): A specialized function of white adipose tissue is to store neutral lipids within protein-coated droplets. This lipid storage function provides both an energy reservoir and a site to sequester excess lipids that otherwise would have toxic effects on tissues such as muscle, blood vessels, liver, and pancreas, thereby increasing the risk for diabetes mellitus, heart disease, and nonalcoholic fatty liver disease. How newly synthesized triacylglycerol is packaged and inserted into lipid storage droplets is not understood. Also, little is known about the identity and function of the proteins that coat the lipid droplet. The overall goal of this research plan is to discover the mechanisms by which lipids traffic intracellularly to their site of storage within the adipocyte. Understanding such mechanisms may illuminate what goes wrong in conditions of excessive lipid storage (obesity) and inefficient partitioning of lipid into adipocytes (lipodystrophy /lipoatrophy). The preliminary data reveal a process of lipid droplet maturation in which the adipocyte protein S3-12 coats newly formed lipid droplets and promotes triacylglycerol accumulation. We hypothesize that S3- 12 promotes efficient packaging of newly synthesized triacylglycerol into storage droplets by coating nascent lipid droplets and mediating their incorporation into perilipin-coated storage droplets. According to this model, S3-12 serves to channel triacylglycerol into the storage rather than hydrolytic pathway. Aim 1 seeks to define changes in the adipocyte and lipid droplet proteomes during active triacylglycerol packaging. Aim 2 seeks to document in live cells the process of lipid droplet biogenesis and to determine how S3-12 promotes triacylglycerol accumulation and lipid droplet organization. The structural features of S3-12 that mediate its targeting to nascent lipid droplets and its function will be mapped by mutational analysis. Finally, Aim 3 investigates whether global overexpression of S3-12 in the mouse will promote triacylglycerol accumulation in adipocytes and protect against lipotoxicity in other tissues by sequestration of triacylglycerol within storage droplets, thereby limiting lipolysis and reducing the production of toxic lipid metabolites. By these studies, fundamental mechanisms of intracellular lipid trafficking should be revealed.