Centre for Lipid Research, Key Laboratory of Metabolism on Lipid and Glucose, Chongqing Medical University, Chongqing, P.R. China ; Department of Cardiology, The First Affiliated Hospital of Chongqing Medical University, Chongqing, P.R. China ; John Moorhead Research Laboratory, Centre for Nephrology, University College London (UCL) Medical School, Royal Free Campus, London, United Kingdom.
PLoS One. 2013 Oct 16;8(10):e75650. doi: 10.1371/journal.pone.0075650. eCollection 2013.
Inflammatory stress promotes foam cell formation by disrupting LDL receptor feedback regulation in macrophages. Sterol Regulatory Element Binding Proteins (SREBPs) Cleavage-Activating Protein (SCAP) glycosylation plays crucial roles in regulating LDL receptor and 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGCoAR) feedback regulation. The present study was to investigate if inflammatory stress disrupts LDL receptor and HMGCoAR feedback regulation by affecting SCAP glycosylation in THP-1 macrophages. Intracellular cholesterol content was assessed by Oil Red O staining and quantitative assay. The expression of molecules controlling cholesterol homeostasis was examined using real-time quantitative RT-PCR and Western blotting. The translocation of SCAP from the endoplasmic reticulum (ER) to the Golgi was detected by confocal microscopy. We demonstrated that exposure to inflammatory cytokines increased lipid accumulation in THP-1 macrophages, accompanying with an increased SCAP expression even in the presence of a high concentration of LDL. These inflammatory cytokines also prolonged the half-life of SCAP by enhancing glycosylation of SCAP due to the elevated expression of the Golgi mannosidase II. This may enhance translocation and recycling of SCAP between the ER and the Golgi, escorting more SREBP2 from the ER to the Golgi for activation by proteolytic cleavages as evidenced by an increased N-terminal of SREBP2 (active form). As a consequence, the LDL receptor and HMGCoAR expression were up-regulated. Interestingly, these effects could be blocked by inhibitors of Golgi mannosidases. Our results indicated that inflammation increased native LDL uptake and endogenous cholesterol de novo synthesis, thereby causing foam cell formation via increasing transcription and protein glycosylation of SCAP in macrophages. These data imply that inhibitors of Golgi processing enzymes might have a potential vascular-protective role in prevention of atherosclerotic foam cell formation.
炎症应激通过破坏巨噬细胞中 LDL 受体的反馈调节促进泡沫细胞形成。固醇调节元件结合蛋白(SREBPs)裂解激活蛋白(SCAP)糖基化在调节 LDL 受体和 3-羟-3-甲基戊二酰辅酶 A 还原酶(HMGCoAR)反馈调节中起着至关重要的作用。本研究旨在探讨炎症应激是否通过影响 THP-1 巨噬细胞中 SCAP 糖基化来破坏 LDL 受体和 HMGCoAR 反馈调节。通过油红 O 染色和定量测定评估细胞内胆固醇含量。使用实时定量 RT-PCR 和 Western blot 检测控制胆固醇稳态的分子的表达。通过共聚焦显微镜检测 SCAP 从内质网(ER)到高尔基体的易位。我们证明,暴露于炎症细胞因子会增加 THP-1 巨噬细胞中的脂质积累,即使在存在高浓度 LDL 的情况下,SCAP 的表达也会增加。这些炎症细胞因子还通过增强高尔基体甘露糖苷酶 II 的表达来延长 SCAP 的半衰期,从而增强 SCAP 的糖基化。这可能增强 SCAP 在 ER 和高尔基体之间的易位和循环,护送更多的 SREBP2 从 ER 到高尔基体进行蛋白水解切割激活,如 SREBP2 的 N 端(活性形式)增加所证明的那样。结果,LDL 受体和 HMGCoAR 的表达上调。有趣的是,这些作用可以被高尔基体甘露糖苷酶抑制剂阻断。我们的结果表明,炎症增加了天然 LDL 的摄取和内源性胆固醇从头合成,从而通过增加巨噬细胞中 SCAP 的转录和蛋白糖基化导致泡沫细胞形成。这些数据表明,高尔基体加工酶抑制剂可能在预防动脉粥样硬化泡沫细胞形成方面具有潜在的血管保护作用。