CD36 AND INTESTINAL FAT ABSORPTION

描述（由申请方提供）：清道夫受体CD 36在近端肠的肠上皮细胞顶侧以及整个器官的内皮细胞和免疫细胞上高度表达。我们以前记录的生理作用，CD 36在肠道摄取脂肪酸（FA）和胆固醇，并在促进乳糜微粒的合成。在此期间，我们提出了一些新的意见。我们发现CD 36在两个C-末端赖氨酸上被泛素化，泛素化由FA和甘油二酯诱导，并且它发生在脂质吸收期间。同样的C-末端赖氨酸也被发现对于CD 36将信号传递到src激酶和下游的细胞外调节激酶（ERK 1/2）的能力至关重要。CD 36-ERK通路在乳糜微粒形成的早期阶段以脂质依赖性方式被激活。此外，我们发现src-ERK途径也参与CD 36介导的花生四烯酸衍生的促炎类花生酸合成的调节。我们的假设是，在早期吸收的CD 36-ERK信号通路的功能，以启动在平行的乳糜微粒合成和急性炎症反应的饮食脂质。随着消化的进行，管腔脂质通过诱导其泛素化下调CD 36，并且该反馈回路起到限制炎症的作用。这一假设将在目标1中得到检验。我们将研究在稳定表达CD 36或信号受损的突变形式的Caco-2细胞中ERK 1/2和甘油三酯分泌的脂质调节。将使用来自新生成的小鼠模型的肠段和肠细胞进行平行研究，所述小鼠模型具有精氨酸特异性CD 36缺失（intCD 36-/-）或拯救（intCD 36 +/+）。基于我们显示CD 36二聚化和二聚体乙酰化的新数据，我们将确定这些修饰在CD 36信号传导和甘油三酯分泌中的作用。在目标2（A-C）中，我们将使用intCD 36-/-和intCD 36 +/+小鼠来检查肠CD 36在影响全身代谢、肠免疫细胞和脂质诱导的炎症中的作用。我们的研究方法还将涉及一个翻译组件（aim 2D）。我们最近发现，常见的CD 36单核苷酸多态性（SNPs）有助于空腹血脂蛋白的个体差异。几个显著的SNP的影响与CD 36蛋白表达的改变有关（在单核细胞和血小板上测定）。我们现在提出（aim 2D）测试这些表达SNP（eSNP）对餐后脂质和脂质诱导的类花生酸分泌和炎症的影响。最后，在目标3中，我们将探索我们新的初步数据的机制，这些数据表明，CD 36缺失增加了胆汁酸池，降低了胆汁疏水性，并有效地防止胆结石形成。这项研究的结果将增强我们对一种关键代谢蛋白的吸收功能的理解。他们应该提供深入了解参与肠道脂质加工的分子步骤，以及脂质加工如何与炎症相互联系。我们应该了解靶向肠道CD 36是否对肥胖、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.