植物血凝素样氧化低密度脂蛋白受体-1与动脉粥样硬化

动脉粥样硬化(AS)是由一系列细胞及分子参与的炎症反应性疾病,在AS发生发展的过程中氧化低密度脂蛋白(ox-LDL)发挥了极其重要的作用。其主要通过2种机制促进AS病变进展:一是通过巨噬细胞的清道夫受体进入细胞,促进细胞的泡沫化,进而泡沫细胞堆积,促进血管内壁脂纹形成;二是引起     

血凝素样氧化低密度脂蛋白受体-1

血凝素样氧化低密度脂蛋白受体-1(LOX-1)是内皮细胞摄取氧化低密度脂蛋白(ox-LDL)的特异性受体.高脂血症、氧化应激等多种因素可以促进LOX-1的表达.LOX-1表达通过诱导各种黏附分子和炎症因子的表达、激活蛋白激酶、诱导细胞凋亡等途径促进平滑肌细胞和巨噬细胞吞噬脂质,并转化为泡沫细胞,促进动脉粥样硬化斑块的形成.     

Atherosclerosis: the low-density lipoprotein receptor hypothesis.

Recent biochemical, genetic, and ultrastructural studies have disclosed that non-hepatic human cells, such as fibroblasts, lymphocytes, and aortic smooth muscle cells, utilize a specific metabolic pathway, the low-density lipoprotein (LDL) pathway, to supply themselves with cholesterol. The critical component of this pathway is a specific high-affinity receptor on the cell surface that binds LDL, the major cholesterol-carrying lipoprotein of human plasma. Cellular uptake of the receptor-bound LDL is followed by intralysosomal degradation of the lipoprotein with release of its cholesterol for use in cellular membrane synthesis. When the LDL receptor is genetically absent, as in the homozygous form of familial hypercholesterolemia, the degradation of LDL is impaired, the lipoprotein accumulates to very high levels in the plasma, and a severe form of atherosclerosis ensues. In this paper we present the hypothesis that the normal function of the high-affinity cell-surface LDL receptor is to allow non-hepatic cells to supply themselves with cholesterol at a time when the LDL concentration in plasma is maintained at low levels. We then discuss a mechanism by which this hypothesis might explain the widespread occurrence of atherosclerosis in humans with “normal” plasma LDL-cholesterol levels. The data on the LDL pathway lend biochemical support to the conclusion previously derived from epidemiologic studies—namely, that the “normal” plasma level of LDL-cholesterol in Western man is unphysiologically high.     

植物凝集素样氧化型低密度脂蛋白受体-1与动脉粥样硬化

植物凝集素样氧化型低密度脂蛋白受体-1（lectin-likeoxidizedlow-densitylipoprotein receptor-1, LOX-1）是氧化型低密度脂蛋白（oxidized low-density lipoproteins, oxLDL）的主要受体之一。近年来的研究表明,LOX-1不仅可以结合、中和以及降解oxLDL,还能与一些非氧化脂蛋白和凋亡的血细胞结合,通过激活血小板、诱导炎症反应、促进血管平滑肌细胞增殖和迁移等多种途径参与动脉粥样硬化进程。文章从LOX-1的结构、功能及其与脂质代谢、动脉粥样硬化发病机制间的关系等方面,对相关研究进展进行了综述。     

Lectin-like oxidized low-density lipoprotein receptor 1 mediates matrix metalloproteinase 3 synthesis enhanced by oxidized low-density lipoprotein in rheumatoid arthritis cartilage

OBJECTIVE: To investigate for the presence of oxidized low-density lipoprotein (ox-LDL) and lectin-like oxidized LDL receptor 1 (LOX-1) in cartilage specimens from rheumatoid arthritis (RA) joints and to determine whether the interaction of ox-LDL with LOX-1 can induce matrix metalloproteinase 3 (MMP-3) in articular cartilage explant culture. METHODS: Human articular cartilage specimens obtained from patients with RA, osteoarthritis (OA), and femoral neck fractures were examined for LOX-1 and ox-LDL by confocal fluorescence microscopy. The association between ox-LDL and LOX-1 was evaluated by immunofluorescence analysis. Articular cartilage specimens from patients with femoral neck fractures were incubated with ox-LDL, with or without preincubation with neutralizing anti-LOX-1 antibody. MMP-3 synthesis by chondrocytes in explant cartilage was evaluated by immunofluorescence, and protein secretion into conditioned medium was monitored by immunoblotting and enzyme-linked immunosorbent assay. RESULTS: The majority of the RA chondrocytes stained positively with both anti-LOX-1 and anti-ox-LDL antibodies; however, no positive cells were found in OA and normal cartilage specimens. Anti-LOX-1 antibody suppressed the binding of DiI-labeled ox-LDL to chondrocytes in explant culture, suggesting that the interaction was mediated by LOX-1. In contrast to native LDL, ox-LDL induced MMP-3 synthesis by articular chondrocytes in association with the induction of LOX-1, which resulted in enhanced secretion of MMP-3 into the culture medium. Anti-LOX-1 antibody reversed ox-LDL-stimulated MMP-3 synthesis to control levels. CONCLUSION: Ox-LDL, principally mediated by LOX-1, enhanced MMP-3 production in articular chondrocytes. Increased accumulation of ox-LDL with elevated expression of LOX-1 in RA cartilage indicates a specific role of the receptor-ligand interaction in cartilage pathology in RA.     

Lectin-like oxidized low-density lipoprotein receptor 1 mediates leukocyte infiltration and articular cartilage destruction in rat zymosan-induced arthritis

OBJECTIVE: The relationship between rheumatoid arthritis and atherosclerosis has been recognized for >20 years. This study aimed to elucidate the roles of oxidized low-density lipoprotein (ox-LDL; one of the main pathogenic factors of atherosclerosis) and its endothelial receptor, lectin-like ox-LDL receptor 1 (LOX-1), in arthritic joints using a rat zymosan-induced arthritis (ZIA) model. METHODS: LOX-1 expression and ox-LDL accumulation in arthritic joints were detected by immunohistochemistry using specific mouse anti-LOX-1 and anti-ox-LDL monoclonal antibodies, respectively. To elucidate the effects of the expressed LOX-1 on arthritis, ZIA rats were treated with anti-LOX-1 antibody or normal mouse IgG. The severity of arthritis was analyzed by joint swelling. Cell infiltration, synovial hyperplasia, and proteoglycan losses were also determined by histologic scoring. Proinflammatory cytokine and nitrite levels in serum and joint fluid were also measured. RESULTS: Immunohistochemical study of ZIA demonstrated LOX-1 expression on synovial endothelium and postcapillary venules at 6 hours after the induction of inflammation, with maximum expression detected at 24 hours. LOX-1 was also expressed weakly on both joint cartilage and synovium. Ox-LDL, a ligand of LOX-1, was also detected in articular chondrocytes. Administration of anti-LOX-1 antibody, which blocks LOX-1 activity, suppressed joint swelling (by 33.5%), leukocyte infiltration, and joint nitrite accumulation at 24 hours, as well as cartilage destruction at 7 days, compared with control rats. CONCLUSION: LOX-1 induction in arthritic joints might play a role in promoting joint inflammation and cartilage destruction by mediating leukocyte infiltration into the arthritic joints of ZIA rats.     

Lectin-like oxidized low-density lipoprotein 1 receptor in a reduced uteroplacental perfusion pressure rat model of preeclampsia

Preeclampsia is a major cause of maternal and fetal morbidity and mortality that has been associated with endothelial dysfunction attributed, in part, to dyslipidemia, an imbalance in angiogenic factors and oxidative stress. One of the many factors that have been shown to be elevated in women with preeclampsia is low-density lipoprotein (LDL) and the more oxidizable, small dense LDL, which can lead to increased vascular oxidative stress and decreased bioavailability of NO. Lectin-like oxidized LDL-1 receptor (LOX-1) is a specific receptor for oxidized LDL. We hypothesized that a reduction of placental perfusion using a rat model of reduced uteroplacental perfusion pressure would result in enhanced LOX-1 expression in the maternal vasculature causing impaired vascular endothelial function through the actions of increased superoxide production and decreased NO-mediated vasodilation. We demonstrated a significant increase in the expression of the LOX-1 receptor (4.3-fold; P=0.002), endothelial NO synthase (2.7-fold; P=0.001), and superoxide (P=0.02) in thoracic aorta of the reduced uteroplacental perfusion pressure model, whereas maximal vasodilator function was modestly decreased (P<0.05). Endothelial-dependent vasodilator function was unaffected by either oxidized LDL or an LOX-1 receptor inhibitor in controls but was modestly increased in the presence of both oxidized LDL and the LOX-1 receptor inhibitor in reduced uteroplacental perfusion pressure (P=0.03). In summary, we have shown that, in a rat model of preeclampsia, there is a dramatic increase in the expression levels of both the LOX-1 receptor and the endothelial NO synthase enzyme, along with evidence of increased superoxide production and subsequent modestly decreased endothelial function.     

Uptake of oxidized low-density lipoprotein in a THP-1 cell line lacking scavenger receptor A

We previously isolated THP-1 subtype cells (sTHP-1), a cell line that expresses scanty amounts of scavenger receptor A (ScR-A) and does not undergo foam cell formation when incubated with acetylated low-density lipoprotein (Ac-LDL). In this study, we investigated the accumulation of esterified cholesterol in sTHP-1 cells incubated with oxidized LDL (Ox-LDL), a physiologically modified lipoprotein in human. While sTHP-1 cells incubated with Ac-LDL accumulated only small amounts of esterified cholesterol, those incubated with Ox-LDL accumulated amounts similar to those accumulated by parent THP-1 (pTHP-1) cells. sTHP-1 cells expressed CD36 in amounts similar to the amounts expressed by pTHP-1 cells, and Ox-LDL was internalized through this CD36. The amount of accumulated esterified cholesterol was 73-81% of that accumulated in pTHP-1 cells expressing ScR-A. The levels of 125I-Ox-LDL binding, association, and degradation in sTHP-1 cells were 64-70% of the corresponding levels in pTHP-1 cells. In our experiments utilizing ScR-A-deficient sTHP-1 cells and a specific antibody against human CD36, most of the Ox-LDL interacted with the CD36 receptor. In addition, a substantial amount of Ox-LDL (28-42%) was bound and degraded by sTHP-1 macrophages when both of the two major scavenger receptors, ScR-A and CD36, were deficient or blocked. These results indicate that CD36 in macrophages plays an important role in foam cell formation by Ox-LDL, while additional scavenger receptor(s) may take part in significant pathways of Ox-LDL uptake in macrophages.     

Lectin-like oxidized low-density lipoprotein receptor 1 mediates phagocytosis of aged/apoptotic cells in endothelial cells

Recognition of the exposure of phosphatidylserine (PS) on the outer surface of plasma membrane has been implicated in the phagocytosis of aged/apoptotic cells. Because oxidized low-density lipoprotein (OxLDL) has been reported to block the phagocytosis, here we examined whether lectin-like OxLDL receptor 1 (LOX-1), the OxLDL receptor in endothelial cells, mediates phagocytosis of aged/apoptotic cells by endothelial cells. Cultured bovine aortic endothelial cells (BAE) and Chinese hamster ovary (CHO) cells expressing bovine LOX-1 (BLOX-1-CHO), but not wild-type CHO-K1 cells, bound aged red blood cells (RBC) and apoptotic cells, which were further phagocytosed. The binding of aged RBC and the phagocytosis of apoptotic cells were inhibited by OxLDL, acetyl LDL, and other LOX-1 ligands in both BAE and BLOX-1-CHO. mAb against LOX-1 blocked the binding of aged RBC to BAE, suggesting a role for LOX-1 in the recognition of aged cells. The recombinant soluble LOX-1 inhibited the interactions of aged/apoptotic cells with both BLOX-1-CHO and BAE and distinguished aged RBC from native RBC and apoptotic cells from native cells. PS liposome inhibited these LOX-1-mediated interactions with aged/apoptotic cells, suggesting LOX-1 recognizes PS of the apoptotic cells. PS exposed on the surface of apoptotic cells is known to be procoagulant. Accordingly, increased OxLDL may be one of the reasons for enhanced coagulation in atherosclerosis, inhibiting the removal of apoptotic cells.     

Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) in atherogenesis.

Lectin-like oxidized low density lipoprotein receptor-1 (LOX-1) is a type-II membrane protein belonging to the C-type lectin family molecules, which can act as a cell surface endocytosis receptor for atherogenic oxidized LDL (Ox-LDL). LOX-1 is synthesized as a 40 kDa precursor protein with N-linked high mannose-type carbohydrate, which is further glycosylated and processed into a 50 kDa mature form. LOX-1 expression is not constitutive but can be induced by proinflammatory, oxidative, and mechanical stimuli. In addition to endothelial cells, macrophages and activated vascular smooth muscle cells express LOX-1. In vivo, endothelial cells covering early atherosclerotic lesions and macrophages and smooth muscle cells accumulated in the intima of advanced atherosclerotic plaques express LOX-1. LOX-1 is cleaved at membrane proximal extracellular domain by some protease activities and released from the cell surface. Measurement of soluble LOX-1 in vivo may provide novel diagnostic strategy for the evaluation and prediction of atherosclerosis and vascular diseases.     

Baseline levels of low-density lipoprotein cholesterol and lipoprotein (a) and the AvaII polymorphism of the low-density lipoprotein receptor gene influence the response of low-density lipoprotein cholesterol to pravastatin treatment

To investigate some individual and genetic factors that may influence the response of low-density lipoprotein cholesterol (LDL-C) to pravastatin treatment, we recruited 440 subjects with hypercholesterolemia (mean age, 57 years; 43% men) from 21 primary health care centers-outpatient clinics into a prospective, multicentered intervention trial. Pravastatin (20 mg/d) was prescribed for 16 weeks. The main outcome was the percentage variation in LDL-C concentration relative to baseline. Blood analyses and genotyping were performed centrally. The results indicated that LDL-C decreased by 20.5% (range, +21% to -66%) after pravastatin treatment. Baseline concentration of LDL-C (the higher the concentration, the greater the decrease), lipoprotein (a) levels (the lower the concentration, the greater the response), and Ava II polymorphism of the LDL-receptor gene significantly influenced the hypolipemic effect ( P < .001, P = .014, and P = .004, respectively). These 3 factors combined explained 10.6% of the variation in LDL-C response. Age, sex, smoking habit, alcohol consumption, body mass index, and apolipoprotein E genotype had no significant effect on response. We conclude that baseline levels of LDL-C and lipoprotein (a) together with the Ava II polymorphism of the LDL-receptor gene have a significant influence on the LDL-C response to pravastatin treatment in patients monitored in a standard primary health care outpatient clinic setting.     

血凝素样氧化低密度脂蛋白受体1与动脉粥样硬化

血凝素样氧化低密度脂蛋白受体1(LOX-1)是氧化低密度脂蛋白的主要受体,属C型血凝素家族,LOX-1可通过损伤内皮细胞,促进单核细胞黏附聚集,诱导细胞凋亡等机制促进动脉粥样硬化的形成和发展。炎症因子、一氧化氮缺乏等因素可促进 LOX-1表达,一些相关药物通过抑制LOX-1的表达在动脉粥样硬化中起作用,为临床抗动脉粥样硬化治疗提供新的途径。     

Effect of simvastatin in familial hypercholesterolemia on the affinity of electronegative low-density lipoprotein subfractions to the low-density lipoprotein receptor

The effect of simvastatin therapy on the biologic characteristics of the electronegative low-density lipoprotein (LDL) subfraction of patients with familial hypercholesterolemia (FH) was studied. Total LDL, isolated from FH plasma at 0, 3 and 6 months of simvastatin treatment, was subfractionated into electropositive LDL (LDL[+]) and electronegative LDL (LDL[-]) by anion exchange chromatography. LDL isolated from healthy normolipemic (NL) subjects was used as a control. The LDL(-) proportion was twofold higher in patients with FH than in NL subjects (17.6 +/- 1.6% vs 7.8 +/- 1.5%, respectively; p <0.05) and was progressively reduced by simvastatin therapy (15.7 +/- 1.6% at 3 months; 13.8 +/- 2.5% at 6 months; p <0.05). Both LDL subfractions from patients with FH had a higher relative cholesterol content and decreased apolipoprotein B and triglycerides than NL subfractions. Simvastatin progressively induced changes in lipid content of both LDL subfractions in patients with FH, and lipid composition was closer to these subfractions in NL subjects after 6 months of therapy. Binding displacement experiments in human fibroblasts demonstrated that LDL(-) from both groups of subjects had a lower affinity of binding to the LDL receptor that LDL(+). In addition, LDL(+) in patients with FH presented an intermediate binding affinity between LDL(-) and LDL(+) in NL subjects. Simvastatin-induced changes in LDL composition were accompanied by a progressive increase in affinity of LDL(+) and LDL(-) in patients with FH. After 6 months of therapy, LDL(+) in FH had an affinity similar to that of LDL(+) in NL subjects. The LDL(-)-induced release of chemokines interleukin-8 and monocyte chemotactic protein-1 from cultured endothelial cells was twofold higher compared with that of LDL(+). No difference in chemokine release between patients with FH and NL subjects or the effect of simvastatin were observed. We conclude that simvastatin therapy was able to modify LDL subfraction composition in subjects with FH and increase their affinity to the LDL receptor. This improvement could contribute to the observed reduction in LDL(-) proportion induced by simvastatin.     

Expression of scavenger receptor-BI and low-density lipoprotein receptor and differential use of lipoproteins to support early steroidogenesis in luteinizing macaque granulosa cells

An ovulatory hCG stimulus to rhesus macaques undergoing controlled ovarian stimulation protocols results in a rapid and sustained increase in progesterone synthesis. The use of lipoproteins as a substrate for progesterone synthesis remains unclear, and the expression of lipoprotein receptors [very-low-density lipoprotein receptor (VLDLR), low-density lipoprotein receptor (LDLR), and scavenger receptor-BI (SR-BI)] soon after human chorionic gonadotropin (hCG) (<12 h) has not been characterized. This study investigated lipoprotein receptor expression and lipoprotein (VLDL, LDL, and HDL) support of steroidogenesis during luteinization of macaque granulosa cells. Granulosa cells were aspirated from rhesus monkeys undergoing controlled ovarian stimulation before or up to 24 h after an ovulatory hCG stimulus. The expression of VLDLR decreased within 3 h of hCG, whereas LDLR and SR-BI increased at 3 and 12 h, respectively. Granulosa cells isolated before hCG were cultured for 24 h in the presence of FSH or FSH plus hCG with or without VLDL, LDL, or HDL. Progesterone levels increased in the presence of hCG regardless of lipoprotein addition, although LDL, but not HDL, further augmented hCG-induced progesterone. Other cells were cultured with FSH or FSH plus hCG without an exogenous source of lipoprotein for 24 h, followed by an additional 24 h culture with or without lipoproteins. Cells treated with hCG in the absence of any lipoprotein were unable to maintain progesterone levels through 48 h, whereas LDL (but not HDL) sustained progesterone synthesis. These data suggest that an ovulatory stimulus rapidly mobilizes stored cholesterol esters for use as a progesterone substrate and that as these are depleted, new cholesterol esters are obtained through an LDLR- and/or SR-BI-mediated mechanism.