CD36调控脂质代谢作用及机制

脂质代谢是机体的重要代谢过程,其紊乱会导致众多疾病的发生。人类白细胞分化抗原36(cluster of differentiation 36,CD36)是一种在单核细胞、巨噬细胞、平滑肌细胞以及脂肪细胞高度表达的清道夫受体,是识别氧化低密度脂蛋白及长链脂肪酸的主要受体和转运蛋白,在脂质代谢过程中发挥着重要作用。本文综述了CD36基因及蛋白的结构和生理功能,阐述了清道夫受体CD36在脂质代谢过程中发挥的作用,并系统地总结了其级联AMPK、mTOR和MAPK信号通路参与脂质代谢过程的分子机制,为相关生物学研究提供了理论基础。     

重组斑马鱼CD36蛋白的原核表达及纯化

目的：在大肠杆菌中重组表达斑马鱼CD36蛋白胞外区38～432氨基酸残基段并纯化。方法：PCR扩增斑马鱼CD36蛋白的基因编码区,连接到带有6~His标签的原核表达载体pET-28a中,构建重组表达质粒pET28a-CD36,并转化大肠杆菌BL21（DE3）,用IPTG诱导表达,优化表达条件后用Ni^2＋柱进行纯化。结果：构建了pET28a-CD36重组质粒;目的蛋白在大肠杆菌中获得表达,亲和纯化后,SDS-PAGE显示相对分子质量为预期的46．8×10^3。结论：获得了斑马鱼CD36融合蛋白,为其生物学功能研究奠定了基础。     

ABCA1和PPARγ与糖尿病动脉粥样硬化关系的研究

目的：研究ATP结合盒转运体A1（ABCA1）在多种糖尿病特有因素刺激下在巨噬细胞中的表达,以及PPARγ激动剂干预后其表达的变化,探讨ABCA1及PPARγ在糖尿病大血管并发症发展中的作用机制。从而为研究糖尿病大血管并发症的发生机制及防治提供一定的理论依据。方法：以巨噬细胞为研究对象,体外模拟糖尿病状态,分别以高葡萄糖、高胰岛素和糖基化终末产物刺激巨噬细胞,检测细胞中ABCA1表达的变化;以PPARγ激动剂预处理巨噬细胞后,再以上述因素刺激细胞,分别检测巨噬细胞中ABCA1的表达并比较。结果：高葡萄糖、高胰岛素和糖基化终末产物（AGE）可作为独立因素,导致细胞中ABCA1表达减少（P〈0.05）。PPARγ激动剂预处理后,ABCA1表达量增加（P〈0.05）。结论：糖尿病状态下,一些糖尿病特有的刺激因素如：高葡萄糖、高胰岛素和糖基化终末产物等作为独立因素使ABCA1表达减少,可能是糖尿病患者动脉粥样硬化发生率较非糖尿病人群增高的原因。PPARγ激动剂干预后,糖尿病状态下ABCA1的表达增加,这提示我们应用PPARγ激动剂可能延缓糖尿病患者动脉硬化进展。     

慢病毒介导CD36基因沉默细胞株的构建及其对caveolin-1蛋白表达的影响

CD36作为重要的清道夫受体密切参与了巨噬细胞对氧化低密度脂蛋白的摄取作用,为了进一步研究CD36的功能,本文利用慢病毒介导的shRNA干扰技术,构建了CD36基因沉默巨噬细胞(J774A.1)株,并以此为模型分析了CD36在caveolin-1蛋白表达过程中的作用。首先,针对CD36基因序列设计合成5条shRNA片段,并构建得到pLKO.1-CD36-shRNA慢病毒干扰载体,测序鉴定后与psiCHECK-Ⅱ-CD36载体共转染入293T细胞中,筛选出有效的CD36-shRNA。将慢病毒干扰载体与病毒包装质粒共转染入293T细胞,包装得到慢病毒颗粒,之后感染J774A.1细胞,经嘌呤霉素筛选后得到CD36基因沉默稳转细胞株。Western blotting及激光共聚焦检测结果表明CD36基因沉默效率达90%,并且伴随着CD36的基因沉默,与之结合的DiI-oxLDL也随之大幅降低,证明构建成功具有良好生物学活性的CD36基因沉默细胞株。最后,抑制剂处理及oxLDL给药刺激实验结果表明,CD36的基因沉默能够显著降低JNK及ERK的磷酸化水平,进而抑制了caveolin-1的蛋白表达,表明CD36能够经由JNK及EKR信号传导调节caveolin-1的蛋白表达。     

CD36与脂类味觉感受

CD36是一种脂类结合蛋白,在大鼠和小鼠的舌上皮细胞中均被发现,与长链脂肪酸（LCFA）具有高度亲和力,是啮齿类动物感受脂类的重要因子之一。研究表明这种蛋白质受体在口腔的脂类感受中起着至关重要的作用。CD36位于啮齿类口腔味蕾部分神经感受细胞的顶端部分,任轮廓状乳头中有特别高的表达,在叶状乳头中有少量表达,而在菌状乳头中几乎没有表达。     

CD36原核表达载体的构建及生物信息学分析

[目的]对CD36基因进行体外克隆表达,建立CD36基因cDNA在大肠杆菌中表达的实验技术以及进行CD36蛋白三级结构的预测并利用生物信息学方法进行分析。[方法]以人血液RNA为模板,RT-PCR扩增CD36的基因序列;并构建原核表达质粒pET-32a-CD36转化到大肠杆菌DE3中后,经过IPTG诱导表达后进行SDS-PAGE验证。[结果]成功克隆了人CD36基因并构建出原核表达质粒,成功转入表达菌大肠杆菌DE3中后经IPTG诱导成功表达,且在1 mmol/L的诱导剂浓度下培养6 h表达量最佳。利用Phyre2和Abcpred软件预测蛋白质结构和B细胞抗原表位,B细胞抗原表位评分大于0.85的CD36的B细胞抗原表位有8个。[结论]成功建立了人CD36基因的原核表达的实验技术,并对CD36的结构及B细胞抗原表位进行了预测,为后续研究CD36基因的功能和抗体制备提供方向和奠定基础。     

CD 36和胞外信号调节激酶通路在脂多糖诱导炎症因子中的作用研究

本研究以鼠源巨噬细胞RAW264．7为模型,研究CD36和胞外信号调节激酶（ERK ）通路对脂多糖（LPS）诱导巨噬细胞分泌炎症因子的影响。首先用100 ng／ml LPS刺激正常及小干扰RNA （siRNA ）技术沉默CD36表达的巨噬细胞16 h ,检测巨噬细胞的ERK活性及分泌炎症因子如肿瘤坏死因子α（TNF‐α）、白细胞介素6（IL‐6）和IL‐10的水平;继而以20 nmol／L ERK抑制剂处理细胞,再用LPS刺激,检测以上各项指标的变化,进一步明确ERK通路与LPS诱导巨噬细胞分泌炎症因子的相关性。结果显示,经LPS刺激,巨噬细胞的ERK活性显著增强,分泌的促炎因子 TNF‐α和 IL‐6显著增高,抑炎因子 IL‐10水平无明显变化;与CD36正常表达的巨噬细胞相比,CD36表达下降的巨噬细胞ERK活性及促炎因子TNF‐α、IL‐6水平显著下降,抑炎因子IL‐10显著增多。与未处理组相比,ERK抑制剂预处理的巨噬细胞中LPS诱导的ERK活性显著降低,促炎因子 TNF‐α和 IL‐6水平降低,抑炎因子 IL‐10水平升高。结果提示,LPS能通过其受体———CD36,激活巨噬细胞内ERK活性,进而促进巨噬细胞促炎因子的分泌。     

Inhibition of Glutathione Production Induces Macrophage CD36 Expression and Enhances Cellular-oxidized Low Density Lipoprotein (oxLDL) Uptake

The glutathione (GSH)-dependent antioxidant system has been demonstrated to inhibit atherosclerosis. Macrophage CD36 uptakes oxidized low density lipoprotein (oxLDL) thereby facilitating foam cell formation and development of atherosclerosis. It remains unknown if GSH can influence macrophage CD36 expression and cellular oxLDL uptake directly. Herein we report that treatment of macrophages with l-buthionine-S,R-sulfoximine (BSO) decreased cellular GSH production and ratios of GSH to glutathione disulfide (GSH/GSSG) while increasing production of reactive oxygen species. Associated with decreased GSH levels, macrophage CD36 expression was increased, which resulted in enhanced cellular oxLDL uptake. In contrast, N-acetyl cysteine and antioxidant enzyme (catalase or superoxide dismutase) blocked BSO-induced CD36 expression as well as oxLDL uptake. In vivo, administration of mice with BSO increased CD36 expression in peritoneal macrophages and kidneys. BSO had no effect on CD36 mRNA expression and promoter activity but still induced CD36 protein expression in macrophages lacking peroxisome proliferator-activated receptor γ expression, suggesting it induced CD36 expression at the translational level. Indeed, we determined that BSO enhanced CD36 translational efficiency. Taken together, our study demonstrates that cellular GSH levels and GSH/GSSG status can regulate macrophage CD36 expression and cellular oxLDL uptake and demonstrate an important anti-atherogenic function of the GSH-dependent antioxidant system by providing a novel molecular mechanism.     

Fisetin, morin and myricetin attenuate CD36 expression and oxLDL uptake in U937-derived macrophages

Dietary flavonoid intake has been reported to be inversely associated with the incidence of coronary artery disease. To clarify the possible role of flavonoids in the prevention of atherosclerosis, we investigated the effects of some of these compounds, including fisetin, morin and myricetin, on the susceptibility of low-density lipoprotein (LDL) to oxidative modification and on oxLDL uptake in macrophages. The results demonstrated that fisetin had stronger inhibitory activity than the other two on inhibiting Cu(2+)-mediated LDL oxidation measured by thiobarbituric acid-reactive substances assay (TBARS), conjugated diene formation and electrophoretic mobility. The class B scavenger receptor, CD36, to which oxLDL binds, is present in atherosclerotic lesions. Treatment of U937-derived macrophages with myricetin (20 microM) significantly inhibited CD36 cell surface protein and mRNA expression (p<0.01). Fisetin, morin and myricetin (20 microM) also reduced the feed-forward induction of CD36 mRNA and surface protein expression by PPARgamma. The inhibition of CD36 by flavonols was mediated by interference with PPARgamma activation thus counteracting the deleterious autoamplification loop of CD36 expression stimulated by PPARgamma ligand. All three flavonols (10 and 20 microM) markedly decreased the uptake of 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanide perchlorate (DiI)-labeled oxLDL uptake in U937-derived macrophages dose-dependently. Current evidences indicate that fisetin, morin and myricetin not only prevent LDL from oxidation but also block oxLDL uptake by macrophages at least in part through reducing CD36 gene expression on macrophages. In conclusion, flavonols may play a role in ameliorating atherosclerosis.     

CD36 and atherosclerosis

CD36 has been associated with diverse normal and pathologic processes. These include scavenger receptor functions (uptake of apoptotic cells and modified lipid), lipid metabolism and fatty acid transport, adhesion, angiogenesis, modulation of inflammation, transforming growth factor-beta activation, atherosclerosis, diabetes and cardiomyopathy. Although CD36 was identified more than 25 years ago, it is only with the advent of recent genetic technology that in-vivo evidence has emerged for its physiologic and pathologic relevance. As these in-vivo studies are expanded, we will gain further insight into the mechanism(s) by which CD36 transmits a cellular signal, and this will allow the design of specific therapeutics that impact on a particular function of CD36.     

DHHC4 and DHHC5 Facilitate Fatty Acid Uptake by Palmitoylating and Targeting CD36 to the Plasma Membrane

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CD36/SR-B2-TLR2 Dependent Pathways Enhance Porphyromonas gingivalis Mediated Atherosclerosis in the Ldlr KO Mouse Model

There is strong epidemiological association between periodontal disease and cardiovascular disease but underlying mechanisms remain ill-defined. Because the human periodontal disease pathogen, Porphyromonas gingivalis (Pg), interacts with innate immune receptors Toll-like Receptor (TLR) 2 and CD36/scavenger receptor-B2 (SR-B2), we studied how CD36/SR-B2 and TLR pathways promote Pg-mediated atherosclerosis. Western diet fed low density lipoprotein receptor knockout (Ldlr°) mice infected orally with Pg had a significant increase in lesion burden compared with uninfected controls. This increase was entirely CD36/SR-B2-dependent, as there was no significant change in lesion burden between infected and uninfected Ldlr° mice. Western diet feeding promoted enhanced CD36/SR-B2-dependent IL1β generation and foam cell formation as a result of Pg lipopolysaccharide (PgLPS) exposure. CD36/SR-B2 and TLR2 were necessary for inflammasome activation and optimal IL1ß generation, but also resulted in LPS induced lethality (pyroptosis). Modified forms of LDL inhibited Pg-mediated IL1ß generation in a CD36/SR-B2-dependent manner and prevented pyroptosis, but promoted foam cell formation. Our data show that Pg infection in the oral cavity can lead to significant TLR2-CD36/SR-B2 dependent IL1ß release. In the vessel wall, macrophages encountering systemic release of IL1ß, PgLPS and modified LDL have increased lipid uptake, foam cell formation, and release of IL1ß, but because pyroptosis is inhibited, this enables macrophage survival and promotes increased plaque development. These studies may explain increased lesion burden as a result of periodontal disease, and suggest strategies for development of therapeutics.     

Intra-Section Analysis of Human Coronary Arteries Reveals a Potential Role for Micro-Calcifications in Macrophage Recruitment in the Early Stage of Atherosclerosis

Background

Vascular calcification is associated with poor cardiovascular outcome. Histochemical analysis of calcification and the expression of proteins involved in mineralization are usually based on whole section analysis, thereby often ignoring regional differences in atherosclerotic lesions. At present, limited information is available about factors involved in the initiation and progression of atherosclerosis.

Aim of This Study

This study investigates the intra-section association of micro-calcifications with markers for atherosclerosis in randomly chosen section areas of human coronary arteries. Moreover, the possible causal relationship between calcifying vascular smooth muscle cells and inflammation was explored in vitro.

Technical Approach

To gain insights into the pathogenesis of atherosclerosis, we performed analysis of the distribution of micro-calcifications using a 3-MeV proton microbeam. Additionally, we performed systematic analyses of 30 to 40 regions of 12 coronary sections obtained from 6 patients including histology and immuno-histochemistry. Section areas were classified according to CD68 positivity. In vitro experiments using human vascular smooth muscle cells (hVSMCs) were performed to evaluate causal relationships between calcification and inflammation.

Results

From each section multiple areas were randomly chosen and subsequently analyzed. Depositions of calcium crystals at the micrometer scale were already observed in areas with early pre-atheroma type I lesions. Micro-calcifications were initiated at the elastica interna concomitantly with upregulation of the uncarboxylated form of matrix Gla-protein (ucMGP). Both the amount of calcium crystals and ucMGP staining increased from type I to IV atherosclerotic lesions. Osteochondrogenic markers BMP-2 and osteocalcin were only significantly increased in type IV atheroma lesions, and at this stage correlated with the degree of calcification. From atheroma area type III onwards a considerable number of CD68 positive cells were observed in combination with calcification, suggesting a pro-inflammatory effect of micro-calcifications. In vitro, invasion assays revealed chemoattractant properties of cell-culture medium of calcifying vascular smooth muscle cells towards THP-1 cells, which implies pro-inflammatory effect of calcium deposits. Additionally, calcifying hVSMCs revealed a pro-inflammatory profile as compared to non-calcifying hVSMCs.

Conclusion

Our data indicate that calcification of VSMCs is one of the earliest events in the genesis of atherosclerosis, which strongly correlates with ucMGP staining. Our findings suggest that loss of calcification inhibitors and/or failure of inhibitory capacity is causative for the early precipitation of calcium, with concomitant increased inflammation followed by osteochondrogenic transdifferentiation of VSMCs.     

Uptake of Oxidized Low Density Lipoprotein by CD36 Occurs by an Actin-dependent Pathway Distinct from Macropinocytosis

The class B scavenger receptor CD36 has numerous ligands that include modified forms of low density lipoprotein, fibrillar amyloid, apoptotic cells, and Plasmodium falciparum-infected red blood cells, linking this molecule to atherosclerosis, Alzheimer disease, malaria, and other diseases. We studied the signaling events that follow receptor engagement and lead to CD36 and ligand internalization. We show that oxidized low density lipoprotein or antibody-induced clustering of CD36 triggers macropinocytosis and internalization of the receptor-ligand complex. Remarkably, however, CD36 internalization is independent of macropinocytosis and occurs by a novel endocytic mechanism that depends on actin, but not dynamin. This actin-driven endocytosis requires the activation Src family kinases, JNK, and Rho family GTPases, but, unlike macropinocytosis, it is not affected by inhibitors of phosphatidylinositol 3-kinase or Na/H exchange. Manipulation of this unique mode of internalization may prove helpful in the prevention and management of the wide range of diseases in which CD36 is implicated.Uptake and storage of cholesterol by macrophages are key contributors to the formation of atherosclerotic plaque. Endothelial cells, seemingly activated by the deposition of modified forms of low-density lipoprotein (LDL),³ release chemokines that recruit macrophages into the vascular intima. Infiltrated macrophages can then readily oxidize and take up the modified LDL. Accumulation of lipids derived from oxidized LDL (oxLDL) transforms macrophages into foam cells, which release excess cytokines, triggering an inflammatory cascade. In addition, foam cells express proteases and other factors that contribute to plaque rupture and subsequent thrombosis.OxLDL particles are recognized by a variety of receptors, including the class A scavenger receptor SR-A and the class B scavenger receptor CD36. CD36 is thought to be responsible for ∼50% of oxLDL uptake by murine and human macrophages (1–3). In addition, this protein mediates cholesterol uptake from high density lipoprotein (4) and is also a receptor for internalization of oxidized high density lipoprotein (5).CD36 encodes a protein with two transmembrane domains located near the N and C termini, leaving only short cytoplasmic tails at each end. Despite having small intracellular domains, engagement of CD36 by its cognate ligands triggers signaling reactions that lead to the internalization of the resulting complex. However, the precise pathways that are activated and the specific mode of internalization remain unclear.Jones and Willingham (6) demonstrated that, in macrophages, modified LDL stimulates ruffling activity and the formation of phase-bright macropinosomes. By transmission electron microscopy they found that gold-conjugated modified LDL associated with ruffles and was present within macropinosomes. These observations underlie the widely accepted view that uptake of modified LDL occurs by macropinocytosis. However, Zeng et al. (7) showed that internalized DiI-oxLDL and CD36 were found in moderately sized cytoplasmic structures that co-localized with a glycosylphosphatidylinositol-anchored protein, suggesting uptake via lipid raft endocytosis. Moreover, Sun et al. (8) reported that uptake of oxLDL by CD36 was independent of actin but dependent on dynamin. The results of these two studies are not easily reconciled with mediation by macropinocytosis, an actin-dependent process that generates large vacuoles, and they suggest instead that CD36 is internalized by a more conventional endocytic pathway.It is not clear whether the apparent discrepancy stems from the engagement of different receptors in the different biological systems used in these studies. Jones and Willingham used macrophages, whereas Zeng et al. and Sun et al. studied, respectively, Chinese hamster ovary and COS cells heterologously transfected with CD36. The types and abundance of receptors capable of binding modified LDL in all likelihood differ greatly in these systems, and heterologous (over)expression in immortalized cells is liable to produce results of questionable biological relevance.In view of this uncertainty and considering the important and versatile roles of CD36, we set out to reexamine the mode of internalization of this receptor. We used both primary and cultured macrophages and selectively targeted CD36 using specific antibodies. The responses triggered by selective CD36 cross-linking were also compared with those elicited by oxLDL. We show that clustering CD36 initiates a signaling cascade that results in the activation of both macropinocytosis and internalization of CD36. Remarkably, however, CD36 internalization is largely independent of macropinocytosis and occurs by a novel dynamin-independent, actin-driven process that requires activation of Src family and c-Jun N-terminal kinases.     

CD147、基质金属蛋白酶与动脉粥样硬化

CD147分子是细胞外基质金属蛋白酶（MMP）的诱导剂,在多种肿瘤细胞和组织中高表达,通过诱导MMP的分泌促进肿瘤的侵袭和转移。MMP在动脉粥样硬化的发生、发展和斑块破裂等心血管并发症的发生中起重要作用。论述了粥样斑块中CD147的表达、CD147对MMP的调控,以及MMP活化对斑块的形成、破裂、引发心肌梗死等急性心血管事件的关联性。