Trafficking of Triacylglycerol in Adipocytes

描述（由申请人提供）：白色脂肪组织的专门功能是将中性脂质储存在蛋白质包被的液滴内。这种脂质储存功能提供了一个能量库和一个位点来隔离多余的脂质，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，从而增加糖尿病、心脏病和非酒精性脂肪肝的风险。新合成的三酰甘油是如何包装并插入脂质储存液滴中的尚不清楚。此外，对包被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。了解这些机制可能会阐明在过度脂质储存（肥胖）和脂质向脂肪细胞分配效率低下（脂肪营养不良/脂肪萎缩）的情况下出现的问题。初步数据揭示了脂滴成熟的过程，其中脂肪细胞蛋白S3-12包被新形成的脂滴并促进三酰甘油积累。我们假设，S3- 12通过包被新生脂滴并介导其并入周脂蛋白包被的储存液滴中来促进新合成的三酰甘油有效包装成储存液滴。根据该模型，S3-12用于将三酰甘油导入储存途径而不是水解途径。目的1旨在确定在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旨在记录活细胞中脂滴生物发生的过程，并确定S3-12如何促进三酰甘油积累和脂滴组织。将通过突变分析绘制介导其靶向新生脂滴的S3-12的结构特征及其功能。最后，目的3研究了小鼠中S3-12的整体过表达是否会促进脂肪细胞中三酰甘油的积累，并通过将三酰甘油隔离在储存液滴内来保护其他组织免受脂毒性，从而限制脂解并减少有毒脂质代谢产物的产生。通过这些研究，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.