Lipid Binding Proteins in Obesity and Diabetes Syndromes

分子和生理学研究表明，脂肪组织的炎症是代谢综合征发展的关键决定因素，各种动物模型已被用来确定脂肪细胞和巨噬细胞与疾病之间的联系机制。其中，脂肪酸结合蛋白4 （FABP4，也称为aP2）失增小鼠在发展我们目前对炎症、内质网应激、线粒体功能障碍和代谢疾病的理解方面尤其有见地。脂肪酸结合蛋白是在脂肪细胞和巨噬细胞中高水平表达的细胞内FFA伴侣蛋白。令人惊讶的是，当喂食高脂肪食物时，FABP4基因敲除小鼠表现出代谢综合征的减轻特征，包括脂肪分解减少、TNFα减少和脂联素表达增加、胰岛素敏感性提高、NF-κB活化降低、哮喘保护、动脉粥样硬化能力减弱和神经炎症减轻。相反，脂肪组织中过表达FABP的小鼠表现出代谢综合征的增强特征，包括脂肪分解增加、胰岛素抵抗加剧、脂联素分泌减少和轻度心脏肥大。与动物模型相似，脂肪细胞FABP降低（通过FABP4/aP2启动子多态性产生）的人患高甘油三酯血症、2型糖尿病和心血管疾病的风险降低。在上一个资助周期中，实验室发现了一种新的FABP4-SirT1-UCP2轴，它调节巨噬细胞和脂肪细胞的脂质代谢。简而言之，FABP的分子、遗传或药理学损失导致细胞脂肪酸增加，以及与SirT1激活和UCP2上调相关的一系列事件。UCP2的表达增加可增加FFA的β-氧化，减少丙酮酸进入线粒体，降低活性氧水平和氧化应激。ROS的减少减少了线粒体蛋白氧化、线粒体未折叠蛋白反应（mtUPR）、NF-κB信号的激活和炎症小体的诱导。该应用的中心假设是FABP4-FFA平衡控制巨噬细胞中SirT1的激活和随后的UCP2表达。此外，UCP2的上调是将高脂肪喂养小鼠的免疫细胞从经典激活的促炎M1表型转变为替代激活的抗炎M2形式的必要和充分条件。为了验证这一假设，提出了以下具体目标：目标1。评价脂肪酸对SirT1的调控和FABP4对SirT1的控制。目标2。观察稳定过表达UCP2的培养巨噬细胞的细胞代谢和极化。目标3。评估巨噬细胞特异性敲除和UCP2过表达对实验小鼠的代谢影响。

Molecular and physiological studies have revealed that inflammation of adipose tissue is a key determinant in the development of the metabolic syndrome and a variety of animal models have been utilized to identify mechanisms that link adipocytes and macrophages to disease. Of these, the Fatty Acid Binding Protein 4 (FABP4, also known as aP2) loss/gain mouse has been particularly insightful in developing our current understanding of inflammation, ER stress, mitochondrial dysfunction and metabolic disease. Fatty acid binding proteins are intracellular FFA chaperones found expressed at high levels in adipocytes and macrophages. Surprisingly, when placed on high fat diets, FABP4 knockout mice exhibit attenuated characteristics of the metabolic syndrome including diminished lipolysis, reduced TNFα and increased adiponectin expression, improved insulin sensitivity, decreased NF-κB activation, protection from asthma, diminished atherogenic capacity and attenuate neuroinflammation. In contrast, mice over-expressing FABP in adipose tissue exhibit potentiated characteristics of the metabolic syndrome including increased lipolysis, exacerbated insulin resistance, decreased adiponectin secretion, and mild cardiac hypertrophy. Similar to the animal models, humans with decreased adipocyte FABP (arising via a polymorphism in the FABP4/aP2 promoter) exhibit reduced risk for hypertriglyceridemia, type 2 diabetes and cardiovascular disease. During the last funding cycle the laboratory has identified a novel FABP4-SirT1-UCP2 axis that regulates lipid metabolism in macrophages and adipocytes. Briefly, molecular, genetic or pharmacologic loss of FABP leads to increased cellular fatty acids and a cascade of events linked to SirT1 activation and the up regulation of UCP2. Increased expression of UCP2 enables increased β-oxidation of FFA, attenuates pyruvate entry into the mitochondrion, reduces the level of reactive oxygen species and oxidative stress. Diminished ROS reduces mitochondrial protein oxidation, the mitochondrial Unfolded Protein Response (mtUPR), activation of NF-κB signaling, and induction of the inflammasome. The central hypothesis for this application is that the FABP4-FFA equilibrium controls activation of SirT1 and subsequently UCP2 expression in macrophages. Moreover, up regulation of UCP2 is both necessary and sufficient to shift immune cells of high fat fed mice from a classically activated pro-inflammatory M1 phenotype to the alternatively activated anti-inflammatory M2 form. To test this hypothesis, the following specific aims are proposed: Aim 1. Evaluate the regulation of SirT1 by fatty acids and its control by FABP4. Aim 2. Examine cellular metabolism and polarization of cultured macrophages stably overexpressing UCP2. Aim 3. Evaluate the metabolic effects of macrophage-specific knockout and overexpression of UCP2 in experimental mice.