Lipid Droplet Metabolism

描述(由申请人提供)： 在过去的几年里，细胞内脂滴(LDS)的生物学引起了人们的极大兴趣，这是因为人们认识到LDS不仅仅是用于储存脂质的静态储存库，而且是参与相互作用和与细胞的大部分机械相互作用的动态细胞内“细胞器”。我们对LD代谢的了解已经通过各种方法取得了进展，包括显微镜、蛋白质组学和全基因组筛查。低密度脂蛋白与储存三酰甘油(TAG)的脂肪细胞关系最为显著。脂肪组织对全身新陈代谢的主要贡献是以TAG的形式储存能量，并动员这种储存的能量导致游离脂肪酸的释放，这一过程被称为脂肪分解。然而，LDS并不是仅存在于脂肪细胞中，而是在许多组织和细胞中都可以发现，包括肝脏、骨骼肌、心肌、肠细胞和白细胞，在某些生理和病理生理条件下，LDS通常作为能量储存库。此外，在生理状态下，主要由胆固醇酯(CEs)组成的低密度脂蛋白主要存在于肾上腺和卵巢中，而在病理生理状态下，动脉粥样硬化病变中的巨噬细胞泡沫细胞中也有明显的低密度脂蛋白。肾上腺和卵巢中富含CE的低密度脂蛋白是类固醇激素产生的重要胆固醇底物来源。这项建议的总体目标是促进我们对LDS细胞生物学的理解，鉴于其生物学重要性，这可能对健康具有广泛的影响 此外，我们还注意到LD胆固醇被用来生产类固醇激素的可能性，以及飞沫中脂质过度积累是肥胖、2型糖尿病、肝脏脂肪变性、动脉粥样硬化和其他代谢性疾病的标志，这些疾病在全球范围内普遍存在，在退伍军人中尤其普遍。总体目标将通过检验两个主要假设来实现。首先，我们假设LDS的物理性质是由特定的液滴相关蛋白以定量的方式显著改变的，这些物理性质有助于LD的大小(生长和融合)和新陈代谢。这一假设将使用专门的设备进行测试，以测量粘弹性特性(粘度、表面张力等)。在正常脂肪细胞和特定LD相关蛋白已被基因打靶操纵的脂肪细胞中的LDS。其次，我们假设富含CE的LDS的形成在重要和可识别的方式上不同于富含标签的LDS，并且富含CE的LDS具有一组液滴相关蛋白，这特别有助于它们用于类固醇的合成。这一假说将通过探索特定的LD相关蛋白在LD动态平衡和类固醇生成的胆固醇运输中的功能来验证。这些研究的结果应该确定LD生物学中关键分子的途径和功能，其中一些有望成为治疗靶点，应有助于遏制与过度LD积累相关的发病率。

DESCRIPTION (provided by applicant): There has been an explosion of interest in the biology of intracellular lipid droplets (LDs) over the past several years that has been fueled by the realization that LDs are not simply static repositories for lipid storage, but are dynamic intracellular "organelles" that participate in interactions and interplay with much of the cell's machinery. Advances in our understanding of LD metabolism have been made through a variety of approaches, including microscopy, proteomics, and genome-wide screens. LDs are most prominently associated with adipose cells, where triacylglycerol (TAG) is stored. The major contribution of adipose tissue to whole body metabolism is the storage of energy in the form of TAG and the mobilization of this stored energy leading to the release of free fatty acids, the process known as lipolysis. However, LDs do not occur exclusively in adipose cells, but can be found in many, if not most, tissues and cells, including liver, skeletal muscle, cardiac muscle, enterocytes, and leukocytes, under certain physiological and pathophysiological conditions where the LDs generally serve as an energy repository. In addition, LDs that are primarily composed of cholesteryl esters (CEs) are prominently found in adrenals and ovaries under physiological conditions and in macrophage foam cells in atherosclerotic lesions under pathophysiological conditions. The CE-rich LDs in the adrenal and ovary serve as important sources of cholesterol substrate for steroid hormone production. The overall goal of this proposal is to advance our understanding of the cell biology of LDs, which is likely to have broad implications for health in light of the biological importance of LD cholesterol utilization for steroid hormone production and the fact that excessive accumulation of lipids in droplets is a hallmark of obesity, type 2 diabetes, hepatic steatosis, atherosclerosis, and other metabolic diseases that are prevalent worldwide and particularly prevalent among the population of veterans. The overall goal will be accomplished by testing 2 major hypotheses. First, we hypothesize that the physical properties of LDs are distinctively altered in quantifiably defined ways by specific droplet-associated proteins and these physical properties contribute to LD size (growth and fusion) and metabolism. This hypothesis will be tested using specialized equipment to measure the viscoelastic properties (viscosity, surface tension, etc.) of LDs within normal adipocytes and within adipocytes in which specific LD-associated proteins have been manipulated by gene targeting. Second, we hypothesize that the formation of CE-rich LDs differs in important and identifiable ways from TAG-rich LDs and that CE-rich LDs have a complement of droplet-associated proteins that specifically facilitates their utilization for steroidogenesis. This hypothesis will be tested through the exploration of the function of specific LD-associated proteins on LD homeostasis and cholesterol transport for steroidogenesis. The results from these studies should identify pathways and functions of key molecules in LD biology, some of which are expected to emerge as therapeutic targets that should help curb the morbidities associated with excessive LD accumulation.