Trafficking of Triacylglycerol in Adipocytes

描述（由申请人提供）：白色脂肪组织的特殊功能是将中性脂储存在蛋白质包裹的液滴内。这种脂质储存功能既提供了一个能量库，也提供了一个隔离多余脂质的场所，否则这些脂质会对肌肉、血管、肝脏和胰腺等组织产生毒性作用，从而增加患糖尿病、心脏病和非酒精性脂肪性肝病的风险。新合成的三酰基甘油是如何被包装并插入到脂质储存液滴中尚不清楚。此外，人们对包裹在脂滴上的蛋白质的特性和功能知之甚少。本研究计划的总体目标是发现脂质在细胞内运输到脂肪细胞内储存部位的机制。了解这些机制可以阐明在脂肪储存过度（肥胖）和脂质分配到脂肪细胞效率低下（脂肪营养不良/脂肪萎缩）的情况下是什么出了问题。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包裹新形成的脂滴并促进三酰甘油的积累。我们假设S3- 12通过包覆新生脂滴并介导其与佩里平包覆的存储滴的结合，促进了新合成的三酰基甘油有效包装成存储滴。根据该模型，S3-12的作用是引导三酰甘油进入储存而不是水解途径。目的1旨在确定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形成过程，并确定S3-12如何促进甘油三酯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来绘制。最后，Aim 3研究了S3-12在小鼠体内的全面过表达是否会促进甘油三酯在脂肪细胞中的积累，并通过将甘油三酯隔离在储存液滴内，从而限制脂肪分解，减少有毒脂质代谢物的产生，从而防止其他组织中的脂肪毒性。通过这些研究，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.