Regulation of Lipid Droplet Biogenesis and Lipophagy

摘要 代谢性疾病是美国一个紧迫的公共卫生问题。随着胰岛素的迅速崛起 抵抗，肥胖和动脉粥样硬化，对脂质代谢的机制理解不能再多了 势在必行这些代谢紊乱中的许多涉及脂质不适当地储存到细胞脂质储存中 称为脂滴（LDs）的细胞器。这些独特的细胞器，其中包含一个核心的三酰基甘油和 胆固醇酯，积累时，膳食中的游离脂肪酸是丰富的，相反，得到消耗时， 对能源的需求很高。因此，LD对细胞和全身都是必不可少的。 体内平衡存在于LD表面的蛋白质在LD的动态周转中起关键作用， 控制储存在其中的脂质的摄入和释放。虽然LD的代谢作用很好， 已知，用于调节单个LD的生长和代谢的机制很差 明白我们已经确定了两种蛋白质，DFCP 1和WHAMM，它们将作为关键的功能发挥作用。 LD的代谢开关特别是，我们发现DFCP 1定位于参与细胞凋亡的区室。 LD生物成因和catalysts。此外，我们发现DFCP 1具有独特的生化特性， 这使得它能够在LD上形成低聚物涂层，这表明它可能在LD的束缚中发挥作用， 和其他LD。迫使DFCP 1从LD上拆卸导致LD催化剂失调。因此，在本发明中， 我们假设DFCP 1作为一个分子开关，从ER释放生长中的LD， 猫有趣的是，LD释放与Arp 2/3复合物的激活剂的积累相关联， WHAMM和肌动蛋白。我们发现WHAMM和肌动蛋白对LDs的积累特异性地发生在 饥饿，在那里它驱动肌动蛋白介导的动员和LD的收缩。因此， 这一建议是为了确定DFCP 1，WHAMM和肌动蛋白的分子机制， 细胞骨架来驱动LD催化剂。为了充分解决这些问题，我们将采用自下而上的方法， 确定允许DFCP 1将LD从生长转换为催化的机制和分子特性 (Aim 1）。同时，我们将研究WHAMM和Arp 2/3复合体如何与DFCP 1协调以驱动LD 动力学和催化剂（目标2）。这些研究所获得的机理见解将提供新的见解 LD代谢如何帮助维持细胞内稳态，以及如何错误调节这一过程， 有助于代谢疾病的发病机制。

ABSTRACT Metabolic diseases are a pressing public health issue in the United States. With the meteoric rise of insulin resistance, obesity, and atherosclerosis, mechanistic understanding of lipid metabolism could not be more imperative. Many of these metabolic disorders involve improper storage of lipids into cellular lipid storage organelles known as lipid droplets (LDs). These unique organelles, which contain a core of triacylglycerols and cholesterol esters, accumulate when dietary free fatty acids are abundant, and conversely get consumed when there is a high demand for energy. In this way, LDs are essential for both cellular and whole-body homeostasis. Proteins that reside on the surface of LDs play critical roles in the dynamic turnover of LDs by controlling the intake and release of the lipids stored within. Although the metabolic roles of LDs are well known, the mechanisms employed to regulate the growth and catabolism of individual LDs are poorly understood. We have identified two proteins, DFCP1 and WHAMM, which are poised to function as crucial metabolic switches for LDs. In particular, we found that DFCP1 localizes to compartments that are involved in both LD biogenesis and catabolism. Moreover, we discovered that DFCP1 has unique biochemical properties that allow it to form an oligomeric coat on LDs, which suggests that it could play a role in the tethering of LDs to the ER and other LDs. Forcing DFCP1 to disassemble from LDs leads to misregulated LD catabolism. Thus, we postulate that DFCP1 functions as a molecular switch that releases growing LDs from the ER for catabolism. Interestingly, LD release is coupled to the accumulation of the activator of the Arp2/3 complex, WHAMM, and actin. We found that accumulation of WHAMM and actin to LDs occurs specifically in response to starvation, where it drives actin-mediated mobilization and constriction of LDs. Consequently, the goals of this proposal are to define the molecular mechanisms employed by DFCP1, WHAMM, and the actin cytoskeleton to drive LD catabolism. To fully address these questions, we will use a bottom-up approach to determine the mechanism and molecular properties that allow DFCP1 to switch LDs from growth to catabolism (Aim 1). In parallel, we will examine how WHAMM and the Arp2/3 complex coordinate with DFCP1 to drive LD dynamics and catabolism (Aim 2). The mechanistic insight obtained by these studies will provide new insights into how LD metabolism helps to maintain cellular homeostasis, but also how misregulation of this process contributes to the pathogenesis of metabolic diseases.