Division of Clinical Pharmacology, Vanderbilt University, Nashville, Tennessee 37232-6602, USA.
J Biol Chem. 2011 May 20;286(20):18170-80. doi: 10.1074/jbc.M110.213470. Epub 2011 Mar 25.
Peroxidation of plasma lipoproteins has been implicated in the endothelial cell activation and monocyte adhesion that initiate atherosclerosis, but the exact mechanisms underlying this activation remain unclear. Lipid peroxidation generates lipid aldehydes, including the γ-ketoaldehydes (γKA), also termed isoketals or isolevuglandins, that readily modify the amine headgroup of phosphatidylethanolamine (PE). We hypothesized that aldehyde modification of PE could mediate some of the proinflammatory effects of lipid peroxidation. We found that PE modified by γKA (γKA-PE) induced THP-1 monocyte adhesion to human umbilical cord endothelial cells. γKA-PE also induced expression of adhesion molecules and increased MCP-1 and IL-8 mRNA in human umbilical cord endothelial cells. To determine the structural requirements for γKA-PE activity, we tested several related compounds. PE modified by 4-oxo-pentanal induced THP-1 adhesion, but N-glutaroyl-PE and C(18:0)N-acyl-PE did not, suggesting that an N-pyrrole moiety was essential for cellular activity. As the N-pyrrole headgroup might distort the membrane, we tested the effect of the pyrrole-PEs on membrane parameters. γKA-PE and 4-oxo-pentanal significantly reduced the temperature for the liquid crystalline to hexagonal phase transition in artificial bilayers, suggesting that these pyrrole-PE markedly altered membrane curvature. Additionally, fluorescently labeled γKA-PE rapidly internalized to the endoplasmic reticulum (ER); γKA-PE induced C/EBP homologous protein CHOP and BiP expression and p38 MAPK activity, and inhibitors of ER stress reduced γKA-PE-induced C/EBP homologous protein CHOP and BiP expression as well as EC activation, consistent with γKA-PE inducing ER stress responses that have been previously linked to inflammatory chemokine expression. Thus, γKA-PE is a potential mediator of the inflammation induced by lipid peroxidation.
血浆脂蛋白的过氧化作用与引发动脉粥样硬化的内皮细胞激活和单核细胞黏附有关，但这种激活的确切机制尚不清楚。脂质过氧化作用会产生脂质醛，包括 γ-酮醛（γKA），也称为异酮或异戊烯基化，这些醛很容易修饰磷脂酰乙醇胺（PE）的胺基头部基团。我们假设 PE 的醛修饰可能介导脂质过氧化作用的一些促炎效应。我们发现，γKA 修饰的 PE（γKA-PE）诱导 THP-1 单核细胞黏附于人脐静脉内皮细胞。γKA-PE 还诱导人脐静脉内皮细胞中黏附分子的表达，并增加 MCP-1 和 IL-8 mRNA 的表达。为了确定 γKA-PE 活性的结构要求，我们测试了几种相关化合物。4-氧戊醛修饰的 PE 诱导 THP-1 黏附，但 N-戊二酰-PE 和 C（18:0）N-酰基-PE 没有，这表明 N-吡咯部分对于细胞活性是必需的。由于 N-吡咯头部基团可能会扭曲膜，我们测试了吡咯-PE 对膜参数的影响。γKA-PE 和 4-氧戊醛显著降低了人工双层膜液晶到六方相转变的温度，这表明这些吡咯-PE 显著改变了膜曲率。此外，荧光标记的 γKA-PE 迅速内化到内质网（ER）中；γKA-PE 诱导 C/EBP 同源蛋白 CHOP 和 BiP 的表达以及 p38 MAPK 活性，而 ER 应激抑制剂降低了 γKA-PE 诱导的 C/EBP 同源蛋白 CHOP 和 BiP 的表达以及 EC 的激活，这与 γKA-PE 诱导的 ER 应激反应一致，先前的研究表明 ER 应激反应与促炎趋化因子的表达有关。因此，γKA-PE 可能是脂质过氧化作用诱导的炎症的潜在介质。
