CD36 AND INTESTINAL FAT ABSORPTION

描述（由申请人提供）：清道夫受体CD36在近端肠上皮细胞的顶端以及整个器官的内皮细胞和免疫细胞上高度表达。我们之前记录了CD36在肠道摄取脂肪酸（FA）和胆固醇以及促进乳糜微粒合成中的生理作用。在资助期间，我们做了一些新的观察。我们发现CD36在两个C端赖氨酸上泛素化，泛素化是由FA和二甘油酯诱导的，并且发生在脂质吸收过程中。同样的c端赖氨酸也被发现对CD36将信号转导到src激酶和下游的细胞外调节激酶（ERK1/2）的能力至关重要。CD36-ERK通路在乳糜微粒形成的早期阶段以脂质依赖的方式被激活。此外，我们发现src-ERK通路也参与了cd36介导的花生四烯酸衍生的促炎性类二十烷的合成调节。我们的假设是，在吸收早期，CD36-ERK信号通路启动平行乳糜微粒合成和对饮食脂质的急性炎症反应。随着消化的进行，腔内脂质通过诱导其泛素化而下调CD36，这种反馈循环起到限制炎症的作用。这一假设将在目标1中进行检验。我们将研究稳定表达CD36或信号受损突变形式的cco -2细胞中ERK1/2和甘油三酯分泌的脂质调节。平行研究将使用肠道特异性CD36缺失（intCD36-/-）或修复（intCD36+/+）的新生小鼠模型的肠段和肠细胞进行。基于我们的新数据显示CD36二聚体和二聚体的乙酰化，我们将确定这些修饰在CD36信号传导和甘油三酯分泌中的作用。在目的2 （A - C）中，我们将使用intCD36-/-和intCD36+/+小鼠研究肠道CD36在影响全身代谢、肠道免疫细胞和脂质诱导炎症中的作用。我们的研究方法也将涉及翻译组件（aim2D）。我们最近表明，常见的CD36单核苷酸多态性（snp）有助于空腹脂蛋白的个体差异。几个显著snp的影响与CD36蛋白表达的改变有关（在单核细胞和血小板上测定）。我们现在提议（目的2D）测试这些表达snp （eSNPs）对餐后脂质和脂质诱导的类二十烷酸分泌和炎症的影响。最后，在目标3中，我们将探索新的初步数据背后的机制，这些数据表明CD36缺失增加了胆汁酸池，降低了胆汁疏水性，并有效地防止了胆结石的形成。这项工作所产生的发现应该增强我们对关键代谢蛋白吸收功能的理解。它们应该为肠道脂质处理的分子步骤以及脂质处理如何与炎症相互联系提供见解。我们应该了解靶向肠道CD36是否可能对肥胖、胰岛素抵抗和胆结石形成等疾病有益。

DESCRIPTION (provided by applicant): The scavenger receptor CD36 is highly expressed on the apical side of enterocytes of the proximal intestine and on endothelial and immune cells throughout the organ. We previously documented the physiological role of CD36 in intestinal uptake of fatty acids (FA) and cholesterol and in promoting chylomicron synthesis. During this funding period, we made several novel observations. We found that CD36 is ubiquitinated on two C- terminal lysines, that ubiquitination is induced by FA and diglycerides and that it occurs during lipid absorption. The same C-terminal lysines were also found crucial for CD36's ability to transduce signals to the src kinase and downstream to the extracellular regulated kinase (ERK1/2). The CD36-ERK pathway is activated in a lipid- dependent manner during early stages of chylomicron formation. Furthermore we found that the src-ERK pathway is also involved in CD36-mediated regulation of the synthesis of arachidonic acid derived pro- inflammatory eicosanoids. Our hypothesis is that during early absorption the CD36-ERK signaling pathway functions to initiate in parallel chylomicron synthesis and an acute inflammatory response to dietary lipid. As digestion proceeds, luminal lipids down-regulate CD36 by inducing its ubiquitination and this feedback loop acts to limit inflammation. This hypothesis will be tested in aim 1. We will examine lipid regulation of ERK1/2 and triglyceride secretion in Caco-2 cells stably expressing CD36 or a mutant form with impaired signaling. Parallel studies will be conducted using intestinal segments and enterocytes from newly generated mice models with intestine-specific CD36 deletion (intCD36-/-) or rescue (intCD36+/+). Based on our new data showing CD36 dimerization and acetylation of the dimer, we will determine the role of these modifications in CD36 signaling and triglyceride secretion. In aim 2 (A - C) we will examine the role of intestinal CD36 in influencing systemic metabolism, gut immune cells and lipid-induced inflammation using the intCD36-/- and intCD36+/+ mice. Our research approach will also involve a translational component (aim2D). We recently showed that common CD36 single nucleotide polymorphisms (SNPs) contribute to individual differences in fasting blood lipoproteins. The effects of several significant SNPs were related to alterations in CD36 protein expression (determined on monocyte and platelets). We now propose (aim 2D) to test impact of these expression SNPs (eSNPs) on postprandial lipids and on lipid-induced eicosanoid secretion and inflammation. Finally in aim 3 we will explore the mechanisms underlying our novel preliminary data demonstrating that CD36 deletion increases the bile acid pool, decreases bile hydrophobicity and effectively protects against gallstone formation. The findings generated from the work proposed should enhance our understanding of the absorptive function of a key metabolic protein. They should provide insight into the molecular steps involved in intestinal lipid processing and into how lipid processing interconnects with inflammation. We should learn whether targeting intestinal CD36 may be beneficial in disorders like obesity, insulin resistance and gallstone formation.