Role of PAT proteins in ectopic fat deposition

描述（由申请人提供）：异位脂肪沉积，即脂肪组织外脂滴的积聚，被认为是肥胖和脂肪营养不良患者发生胰岛素抵抗和“代谢综合征”的一个重要预后因素。因此提出了一个关键问题，即异位脂肪是否不仅仅是一个标志，而是实际上是疾病的媒介。我们现在在肝细胞培养系统中有了初步的结果，脂滴表面蛋白的siRNA基因抑制剂诱导胰岛素抵抗，提供了一些第一个证据表明异位脂肪确实是疾病的中介。为了更好地了解异位脂肪沉积的病理生理机制，我们建议研究脂滴表面蛋白在非脂肪细胞和组织中控制脂肪分解的功能和机制，以及脂滴组成和活性的潜在变化作为肥胖这些病理生理后果的潜在原因，并可能作为治疗干预的新生化途径。在健康状态下，脂滴通过储存任何多余的NEFA作为甘油三酯（TAG）并在需要时释放它来维持细胞非酯化脂肪酸（NEFA）的稳态。这种减少过量NEFA的能力被认为可以防止“脂肪毒性”，其特征是胰岛素抵抗导致炎症，在极端情况下细胞凋亡。此外，NEFA的两种储存和释放途径都涉及到二酰基甘油酯（DAG）的中间产生，DAG也具有信号功能。这是可能的，增加的DAG生产失调的脂肪分解可能有一个作用，与异位脂肪相关的不良反应。因此，NEFA脂滴储存和释放的调节是异位脂肪导致疾病的一个强有力的候选机制。尽管对脂滴的调节仍知之甚少，但大量研究表明，PAT蛋白家族的一个或多个成员似乎总是与脂滴表面有关，其中一个名为Perilipin的蛋白已被证明有助于调节脂肪细胞的脂肪分解。PAT蛋白家族由具有高一级序列的脂滴外壳蛋白组成，与载脂蛋白相似，有些具有组织特异性。因此，本提案的总体目标是了解已知在非脂肪形成组织中表达的三种功能未表征的PAT蛋白ADRP， TIP47和PAT-1（或MLDP）的病理生理重要性。根据我们的初步结果，这些蛋白是调节非脂肪生成组织中脂滴脂解的强有力候选者，它们的功能障碍可能是异位脂肪介导的胰岛素抵抗的一个原因。这些拟议的研究将验证这一假设，如果正确，将为疾病预防或治疗干预提供一种方法。

DESCRIPTION (provided by applicant): Ectopic fat deposition, which is the accumulation of lipid droplets outside the adipose tissue, is well recognized as a strong prognostic factor for the development of insulin resistance and "metabolic syndrome" in obesity and people with lipodystrophies. Therefore a key question has been raised as to whether ectopic fat is not simply a marker but in fact a mediator of disease. We now have preliminary results in a liver cell culture system where siRNA gene inhibitors of lipid droplet surface proteins induce insulin resistance, providing some of the first evidence suggesting that ectopic fat is indeed a mediator of disease. To continue this promising line of investigation to better understand the pathophysiology associated with ectopic fat deposition, we propose to investigate the function and mechanism of lipid droplet surface protein to control lipolysis in non-adipogenic cells and tissues as well as potential changes in lipid droplet composition and activity as the underlying cause of these pathophysiological consequences of obesity, and potentially as a new biochemical pathway for therapeutic intervention. In the healthy state, lipid droplets maintain cellular non-esterifed fatty acid (NEFA) homeostasis by storing any excess NEFA as triglyceride (TAG) and releasing it when needed. This ability to minimize excess NEFA is thought to provide protection from "lipotoxicity", characterized by insulin resistance leading to inflammation, and in extreme cases cellular apoptosis. In addition, both of the pathways for storage and release of NEFA involve the intermediate production of diacylglyceride (DAG), which also has a signaling function. It is possible that an increase in DAG production by disregulated lipolysis may have a role in the adverse effects associated with ectopic fat. Therefore, regulation of lipid droplet storage AND release of NEFA is a strong candidate for a mechanism by which ectopic fat contributes to disease. Although lipid droplet regulation remains poorly understood, numerous studies have revealed that one or more members of the PAT protein family always seem to be associated with the lipid droplet surface and one, Perilipin, has been shown to help regulate adipocyte lipolysis. The PAT protein family is composed of lipid droplet coat proteins sharing high primary sequences, and similarity with apolipoproteins, and some are tissue specific. Therefore, the overall goal of this proposal is to understand the pathophysiological importance of three functionally uncharacterized PAT proteins, ADRP, TIP47 and PAT-1 (or MLDP) known to be expressed in non-adipogenic tissues. Given our preliminary results, these proteins are strong candidates for regulating lipid droplet lipolysis in non-adipogenic tissues and their disfunction is a likely cause of ectopic fat mediated insulin resistance. These proposed studies will test this hypothesis, and if correct provide an approach for prevention of disease or therapeutic intervention.