巨噬细胞内吞脂质的分子机制

动脉粥样硬化性心脑血管疾病是危害人类健康最主要的杀手之一。一般认为，动脉粥样硬化（As）是一种巨噬细胞和淋巴细胞对侵入动脉壁的病原性脂蛋白所产生的炎症反应，最早肉眼可见的病变是脂纹的形成，其主要成分是大量摄取脂质后从巨噬细胞所衍变成的泡沫细胞。研究认为，脂质在巨噬细胞中的大量积聚主要由清道夫受体介导。在众多的清道夫受体中，A类清道夫受体是目前公认的介导氧化型低密度脂蛋白进入细胞的主要受体之一。     

清道夫受体与肺部感染疾病的研究进展

<正>概述最早有研究在巨噬细胞上发现了具有吸收及降解ac LDL能力的清道夫受体,随后其他的清道夫受体家族陆续被发现,依据它们的序列和结构特点,清道夫家族有A-J10个亚分类~([1])。已经证实清道夫受体可以识别广谱的配体,包括微生物病原体PAMPs,以及宿主自身分子,如:热休克蛋白、脂蛋白等,基于清道夫受体能与病原微生物及内源性自身     

A类清道夫受体参与动脉粥样硬化形成的机制

A类清道夫受体是单核巨噬细胞表面的一种跨膜糖蛋白的三聚体,调节巨噬细胞内脂质沉积,参与动脉粥样硬化斑块的形成。现综述且整理相关A类清道夫受体的最新进展,通过炎症调控、内质网应激、巨噬细胞由M1向M2型转化以及胰岛素抵抗等途径,阐明A类清道夫受体在动脉粥样硬化形成中的作用,同时简述了饮食及药物对A类清道夫受体水平的影响。     

天然及氧化型脂蛋白(a)与巨噬细胞表面结合

为探讨脂蛋白 (a)及氧化型脂蛋白 (a)在巨噬细胞上的结合和降解途径 ,将生物素标记的脂蛋白与小鼠腹腔巨噬细胞进行结合和竞争性结合试验。结果发现 ,脂蛋白 (a)能以一定的亲和力、可饱和性地与巨噬细胞表面结合 ;低密度脂蛋白对其结合无明显抑制作用 ,而氧化型低密度脂蛋白、氧化型脂蛋白 (a)均能不同程度地抑制这种结合。脂蛋白 (a)经氧化修饰后 ,与巨噬细胞的结合量显著增加。脂蛋白 (a)、低密度脂蛋白不能有效竞争氧化型脂蛋白 (a)的结合 ,而氧化型脂蛋白 (a)和氧化型低密度脂蛋白为有效的竞争性抑制剂。提示脂蛋白 (a)主要经清道夫受体与巨噬细胞表面结合 ;氧化型脂蛋白 (a)除经清道夫受体介导外 ,可能还通过其它特异性受体与巨噬细胞表面结合。     

阻断清道夫受体AⅠ对巨噬细胞源泡沫细胞基质金属蛋白酶及其组织抑制剂表达的影响

为探讨巨噬细胞源泡沫细胞基质金属蛋白酶及其组织抑制剂的表达及活性与清道夫受体AⅠ的关系，应用油红O染色、高效液相色谱法检测巨噬细胞的泡沫化，逆转录聚合酶链反应检测细胞清道夫受体AⅠ的表达，Westem blot明胶酶谱法观测巨噬细胞泡沫化后阻断清道夫受体AⅠ对THP—1细胞基质金属蛋白酶2、基质金属蛋白酶9、组织型基质金属蛋白酶抑制剂1及组织型基质金属蛋白酶抑制剂2表达的影呐。结果发现，THP—1细胞在佛波酯处理24h后有清道夫受体AⅠ的表达，清道夫受体AⅠ反义寡核苷酸及其抗体能显著降低基质金属蛋白酶2和基质金属蛋白酶9的蛋白表达和活性，并增加组织型基质金属蛋白酶抑制剂1和组织型基质金属蛋白酶抑制剂2的表达。结果提示，阻断清道夫受体AⅠ有助于基质金属蛋白酶与组织型基质金属蛋白酶抑制剂的平衡维持，从而抑制细胞外基质的降解。     

清道夫受体A在机体防御系统中的作用

清道夫受体A(scavenger receptor A,SR-A)是清道夫膜受体蛋白家族成员之一,主要存在于单核-巨噬细胞和内皮细胞表面。近年研究发现,SR-A除了有内吞经修饰的血浆脂蛋白、促使动脉粥样硬化斑块形成外,它在抗原识别、内毒素清除、细胞粘附和调控炎性递质分泌等机体防御反应中起重要作用,现作一综述。 1 SR-A的分类、结构和分布 SR-A是一种完整的三聚体膜糖蛋白。Kodoma et al于1990年首先鉴定和克隆出两种类型的SR-A,将其分为SR-AI,SR-AⅡ两种亚型,M,分别为220000和95000,后者又称为Macrosialin,与小鼠的CD68为同类物质。最近Laan et al又发现了一种具有胶原结构的SA-A,称之为MARCO     

巨噬细胞内胆固醇平衡机制研究进展

巨噬细胞内脂质含量增多形成泡沫细胞是动脉粥样硬化早期病变的特征变化之一.巨噬细胞可以通过CD36和清道夫受体A-Ⅰ等膜受体摄入胆固醇,同时通过清道夫受体B-Ⅰ、ABC家族等逆转运膜受体将胆固醇逆转运出细胞,从而维持细胞内胆固醇平衡,阻止其在细胞内堆积形成泡沫细胞.本文对巨噬细胞内与胆固醇平衡机制做一综述.     

SR-A 在肺部疾病的研究进展

清道夫受体 A(scavenger receptor class A,SR-A)是一种以三聚体形式跨膜的糖蛋白受体,主要表达在单核细胞和巨噬细胞细胞膜。SR-A 在细胞黏附、介导吞噬凋亡细胞、脂质代谢等方面发挥重要的生物学功能。最新研究发现 SR-A 通过启动机体初始免疫进而在肺部疾病发生过程中发挥作用。本文就 SR-A 与肺部疾病关系作一综述。     

过氧化物酶体增殖体激活受体和肝X受体对巨噬细胞作用的研究进展

巨噬细胞作为体内的高级清道夫,吞噬微生物和凋亡坏死的细胞,吸收修饰的脂蛋白微粒。生理情况下巨噬细胞的这些功能受严密的调控。病理条件下,动脉管壁巨噬细胞聚集大量胆固醇而成为泡沫细胞,从而促进动脉粥样硬化的发展。过氧化物酶体增殖体激活受体和肝X受体作为核受体超家族的转录因子,是巨噬细胞平衡的关键调控者。本综述旨在通过讨论过氧化物酶体增殖体激活受体和肝X受体对巨噬细胞作用的研究,从而加深对动脉粥样硬化发病的病理生理机制的理解,为研发新药提供新思路。     

VLDL和ox-LDL对单核巨噬细胞的作用及机制探讨

目的:探讨极低密度脂蛋白(VLDL)、氧化修饰的低密度脂蛋白(ox-LDL)对单核巨噬细胞的作用及机制。方法:分析VLDL、ox—LDL对单核巨噬细胞清道夫受体A(SRA)、VLDL受体(VLDLR)基因转录、细胞因子肿瘤坏死因子(TNF—α)、基质金属蛋白酶(MMP-9)蛋白质表达,以及细胞生长状态的影响。结果:①VLDL增加ox-LDL介导的巨噬细胞SRA mRNA及蛋白质表达,ox—LDL则能增加VLDL介导的巨噬细胞VLDLR基因转录;②VLDL与ox—LDL协同作用显著减少巨噬细胞抗脂质摄取载脂蛋白E分泌;③两种脂蛋白能诱导巨噬细胞TNF-α及MMP-9释放,并能抑制巨噬细胞凋亡,促进增殖。结论:VLDL、ox-LDL对单核巨噬细胞增生、细胞因子释放及脂蛋白受体表达均有协同作用,可能体内的情况多为两种脂蛋白的协同作用。     

Glucose-regulated protein 78 inhibits scavenger receptor A-mediated internalization of acetylated low density lipoprotein

Class A scavenger receptor (SR-A) plays an important role in foam cell formation. However, the mechanism underlying the internalization of the receptor–ligand complexes remains unclear. The aim of the present study was to investigate the molecular mechanism to regulate SR-A-mediated intracellular lipid accumulation in macrophages. A pull-down assay was performed and glucose-regulated protein 78 (GRP78) was identified to bind with the cytoplasmic domain of SR-A (CSR-A). Immunoprecipitation and artificially expressed protein binding assay demonstrated the direct specific binding of GRP78 with SR-A in cells. Indirect immunofluorescence assay and western blot analysis showed their co-localization in membrane and cytoplasm. Over-expression of GRP78 specifically inhibited SR-A-mediated uptake of fluorescent acetylated low-density lipoprotein, a specific ligand for SR-A, without altering cellular SR-A expression and binding ability, and significantly inhibited cholesterol ester accumulation in cells, which can be partly attributed to the suppression of c-Jun-NH2-terminal kinase signaling pathway. These results suggest that GRP78 may act as an inhibitor of SR-A-mediated internalization of modified low-density lipoprotein into macrophages.     

Increased stability of phosphatase and tensin homolog by intermedin leading to scavenger receptor A inhibition of macrophages reduces atherosclerosis in apolipoprotein E-deficient mice

Intermedin, a novel member of calcitonin gene-related peptide family, is an endogenous cardiovascular-protective peptide. Because intermedin exists in human atherosclerotic plaque, we studied the role of intermedin in macrophage scavenger receptor A (SR-A)-mediated foam-cell formation and atherogenesis. In an in vitro foam-cell formation model (induced by acetylated low-density lipoprotein [AcLDL]) with mouse (C57BL/6J) macrophages, intermedin reduced AcLDL uptake and binding, decreased intracellular cholesterol content, and suppressed both mRNA and protein levels of SR-A. Simultaneously, intermedin increased phosphatase and tensin homolog (PTEN) protein levels by increasing PTEN phosphorylation and inhibiting ubiquitin-mediated PTEN degradation. These effects were blocked by the intermedin receptor antagonist or cAMP-protein kinase A inhibitors. PTEN overexpression mimicked the inhibitory effects of intermedin on SR-A expression and AcLDL uptake. However, knockdown of PTEN by short-hairpin RNA completely blocked all inhibitory effects of intermedin. Furthermore, in apolipoprotein E-deficient (apoE(-/-)) mice, 6-week intermedin infusion reduced AcLDL uptake and SR-A mRNA and protein levels and increased PTEN protein level in peritoneal macrophages. PTEN level was increased and SR-A expression decreased in parallel in macrophages in atherosclerotic lesions. Thus, intermedin inhibited atherosclerosis in apoE(-/-) mice. Increased stability of PTEN by intermedin leads to SR-A inhibition in macrophages, which ameliorates foam-cell formation and atherosclerosis in apoE(-/-) mice.     

Analysis of macrophage scavenger receptor (SR-A) expression in human aortic atherosclerotic lesions

The class A scavenger receptors (SR-As) are trimeric, integral membrane glycoproteins that exhibit unusually broad ligand-binding properties. A number of studies have suggested that these receptors may play an important role in host defense and in many macrophage-associated pathological processes, including atherosclerosis and Alzheimer's disease. The study of the expression and function of these receptors in human disease has been hampered by the lack of suitable antibodies recognizing human SR-A. This has generated questions regarding the nature of receptors responsible for scavenger receptor activity detected in a variety of cell types, including monocytes, macrophages, smooth muscle cells, and endothelial cells. To address these questions, we have produced high-titer antisera recognizing human SR-A by using mice deficient for SR-A (SR-A -/-). We show that SR-A -/- mice produce a significantly higher-titer immune response than do wild-type (SR-A +/+) littermates, with antisera of the former having a broad species reactivity and recognizing SR-A from humans, mice, and rabbits. The antisera recognize both type I and II SR-A in a wide range of immunological techniques. Using these antisera we show that the expression of SR-A protein is induced during monocyte to macrophage differentiation and that SR-A mediates 80% of the uptake of acetylated low density lipoprotein by human monocyte-derived macrophages. We also establish that human SR-A is expressed by tissue macrophages in liver and lung and by macrophage-derived foam cells within aortic atherosclerotic lesions, with little detectable expression by smooth muscle cells or aortic endothelium.     

CD36, serves as a receptor for advanced glycation endproducts (AGE)

Interaction of advanced glycation endproducts (AGE) with AGE receptors induces several cellular phenomena relating potentially to diabetic complications. Five AGE receptors identified so far are receptor for AGE (RAGE), 80 K-H, OST-48, galectin-3, and macrophage scavenger receptor, types I and II (SR-A) [Eur. J. Biochem. 230 (1995) 408; Nature 386 (1997) 292.]. Since SR-A is known to belong to the class A scavenger receptor family and the scavenger receptor collectively represents a family of multiligand lipoprotein receptors, it is possible that CD36 belonging to class B scavenger receptor family (SR-B) can recognize AGE proteins as a ligand. This was tested in the present study at the cellular level by using Chinese hamster ovary (CHO) cells overexpressing human CD36 (CHO-CD36 cells). 125I-AGE-bovine serum albumin (BSA) was endocytosed in a dose-dependent fashion and underwent lysosomal degradation by CHO-CD36, but not wild-type CHO cells. Endocytic uptake of 125I-AGE-BSA by these cells was inhibited 50% by oxidized low-density lipoprotein (Ox-LDL) and 60% by FA6-152, an anti-CD36 antibody inhibiting cellular binding of Ox-LDL. Our results indicate that CD36 expressed by these cells mediates endocytic uptake and subsequent intracellular degradation of AGE proteins. Since CD36 is one of the major Ox-LDL receptors and is up-regulated in macrophage- and smooth muscle cell-derived foam cells in human atherosclerotic lesions, the present results suggest that, like Ox-LDL, AGE proteins generated in situ are recognized by CD36, which might contribute to the pathogenesis of diabetic macrovascular complications.     

Retrovirus-mediated, stable scavenger-receptor gene transfer leads to functional endocytotic receptor expression, foam cell formation, and increased susceptibility to apoptosis in rabbit aortic smooth muscle cells

The type II, class A macrophage scavenger receptor (SR-A) plays an important role in the pathogenesis of atherosclerosis and foam cell formation. However, its role in nonmacrophage cell lines remains unknown. To test the hypothesis that SR-A activity leads to proatherogenic changes in nonmacrophage cell lines, we generated Moloney murine leukemia virus- and vesicular stomatitis virus G protein-pseudotyped retroviruses containing SR-A type II cDNA, which were used for stable transfection of SR-A activity into mouse fibroblasts and rabbit aortic smooth muscle cells (SMCs). beta-Galactosidase-transfected cell lines were used as controls. Transfected cell lines expressed functional SR-A mRNA and protein. Expression of SR-A activity was stable for at least 9 months. By electron microscopy, transfected receptors were located in coated pits and in intracellular structures resembling endocytotic vesicles. Expression of SR-A on the cell surface was verified by flow cytometry and by uptake and degradation of (125)I-labeled acetylated low density lipoprotein (LDL). Increases of 5- to 25-fold and of 6- to 8-fold in the rate of acetylated LDL degradation were observed in transfected fibroblasts and SMCs, respectively, compared with beta-galactosidase-transfected control cell lines. Incubation of the transfected SMCs and fibroblasts with acetylated or oxidized LDL led to foam cell formation. Incubation with oxidized LDL also led to increased apoptosis and cell death. An altered morphology with increased cell size and granularity was observed in the most active SR-A SMC clones. It is concluded that stable overexpression of SR-A leads to foam cell formation and other proatherogenic changes in nonmacrophage cell lines. Stable SMC and fibroblast cell lines can be used as models for foam cell formation. The results also suggest that increased SR activity may play an important role in SMC-related pathology in atherosclerotic arteries.     

Oxidized low-density lipoprotein and atherosclerosis implications in antioxidant therapy

Low-density lipoprotein (LDL)-cholesterol is important for cellular function, but in high concentrations, it can lead to atheroma formation. Over the past several decades, it has become abundantly evident that the oxidized form of LDL-cholesterol (ox-LDL) is more important in the genesis and progression of atherosclerosis than native unmodified LDL-cholesterol. Ox-LDL leads to endothelial dysfunction, an initial step in the formation of an atheroma. Ox-LDL acts via binding to a number of scavenger receptors (SR), such as SR-A1, SR-A2 and lectin-like oxidized low-density lipoprotein receptor (LOX-1). Ox-LDL can upregulate expression of its own receptor LOX-1 on endothelial cells and activate these cells. In addition, ox-LDL promotes the growth and migration of smooth muscle cells, monocytes/macrophages and fibroblasts. Ox-LDL also leads to the generation of reactive oxygen species that in physiologic concentrations combat invasion of the body by noxious agents, but when in excess, can lead to a state of oxidative stress. There is evidence for the presence of oxidative stress in a host of conditions such as atherosclerosis and aging. In this review, we discuss the role of oxidative stress, ox-LDL and LOX-1 in atherogenesis and the reasons why the traditional approaches to limit oxidant stress have not been successful.     

Expression of CD36 in macrophages and atherosclerosis: the role of lipid regulation of PPARgamma signaling

Several macrophage scavenger receptors have been identified that bind and internalize modified low-density lipoprotein particles. Although the pathophysiologic roles played by these receptors in human disease are still unproven, data from murine models of atherosclerosis have demonstrated a significant role in atherosclerotic foam cell development and vascular lesion development for two receptors: the type A scavenger receptor (SR-A) and the type B scavenger receptor, CD36. This review addresses the regulation and potential role of CD36 in macrophage foam cell formation and atherosclerosis, with particular emphasis on the mechanisms by which CD36 expression is altered in response to lipid modulation of peroxisome proliferator-activated receptor gamma signaling.