Toll-like receptor 1 inhibits Toll-like receptor 4 signaling in endothelial cells

Toll-like receptor 4 (TLR4) is the signal-transducing component of the LPS recognition complex and is essential for LPS-induced septic shock. Here we demonstrate that TLR1 has the capacity to abrogate TLR4 signaling. Human microvascular endothelial cells express TLR4 but not TLR1 and respond to LPS through TLR4. The ability of these cells to respond to LPS was lost, however, when they were transfected with TLR1. Inhibition was specific for TLR1 because TL5 failed to block TLR4 function. Moreover, TLR1 had no effect upon TNF-alpha signaling, indicating that TLR1 operated at a step upstream of the convergence between the two pathways. Inhibition of TLR4 signaling was mediated by the extracellular, but not cytoplasmic domain of TLR1. In addition, TLR1 physically associated with TLR4 in co-precipitation experiments. These findings suggest that TLR1 might restrain potentially dangerous innate response to LPS by binding to TLR4 and preventing the formation of active signaling complexes.     

Porphyromonas gingivalis lipopolysaccharide antagonizes Escherichia coli lipopolysaccharide at toll-like receptor 4 in human endothelial cells

E. coli lipopolysaccharide (LPS) induces cytokine and adhesion molecule expression via the toll-like receptor 4 (TLR4) signaling complex in human endothelial cells. In the present study, we investigated the mechanism by which Porphyromonas gingivalis LPS antagonizes E. coli LPS-dependent activation of human endothelial cells. P. gingivalis LPS at 1 micro g/ml inhibited both E. coli LPS (10 ng/ml) and Mycobacterium tuberculosis heat shock protein (HSP) 60.1 (10 micro g/ml) stimulation of E-selectin mRNA expression in human umbilical vein endothelial cells (HUVEC) without inhibiting interleukin-1 beta (IL-1beta) stimulation. P. gingivalis LPS (1 micro g/ml) also blocked both E. coli LPS-dependent and M. tuberculosis HSP60.1-dependent but not IL-1beta-dependent activation of NF-kappaB in human microvascular endothelial (HMEC-1) cells, consistent with antagonism occurring upstream from the TLR/IL-1 receptor adaptor protein, MyD88. Surprisingly, P. gingivalis LPS weakly but significantly activated NF-kappaB in HMEC-1 cells in the absence of E. coli LPS, and the P. gingivalis LPS-dependent agonism was blocked by transient expression of a dominant negative murine TLR4. Pretreatment of HUVECs with P. gingivalis LPS did not influence the ability of E. coli LPS to stimulate E-selectin mRNA expression. Taken together, these data provide the first evidence that P. gingivalis LPS-dependent antagonism of E. coli LPS in human endothelial cells likely involves the ability of P. gingivalis LPS to directly compete with E. coli LPS at the TLR4 signaling complex.     

Toll-like receptor 4 signaling promotes epithelial-mesenchymal transition in human hepatocellular carcinoma induced by lipopolysaccharide

Chronic pulmonary diseases are a major cause of morbidity and mortality and their impact is expected to increase in the future. Respiratory viruses are the most common cause of acute respiratory infections and it is increasingly recognized that respiratory viruses are a major cause of acute exacerbations of chronic pulmonary diseases such as asthma, chronic obstructive pulmonary disease and cystic fibrosis. There is now increasing evidence that the host response to virus infection is dysregulated in these diseases and a better understanding of the mechanisms of abnormal immune responses has the potential to lead to the development of new therapies for virus-induced exacerbations. The aim of this article is to review the current knowledge regarding the role of viruses and immune modulation in chronic pulmonary diseases and discuss avenues for future research and therapeutic implications.     

Negative regulation of Toll-like receptor 4 signaling by the Toll-like receptor homolog RP105

Activation of Toll-like receptor (TLR) signaling by microbial signatures is critical to the induction of immune responses. Such responses demand tight regulation. RP105 is a TLR homolog thought to be mostly B cell specific, lacking a signaling domain. We report here that RP105 expression was wide, directly mirroring that of TLR4 on antigen-presenting cells. Moreover, RP105 was a specific inhibitor of TLR4 signaling in HEK 293 cells, a function conferred by its extracellular domain. Notably, RP105 and its helper molecule, MD-1, interacted directly with the TLR4 signaling complex, inhibiting its ability to bind microbial ligand. Finally, RP105 regulated TLR4 signaling in dendritic cells as well as endotoxin responses in vivo. Thus, our results identify RP105 as a physiological negative regulator of TLR4 responses.     

LPS induces inflammatory responses in human aortic vascular smooth muscle cells via Toll-like receptor 4 expression and nitric oxide production

Inflammation is an important event in the development of vascular diseases such as hypertension, atherosclerosis, and restenosis. In addition, the stimulation of Toll-like receptor 4 (TLR4) by lipopolysaccharide (LPS) induces the release of critical proinflammatory cytokines that activate potent immune responses. In this study, LPS was found to induce TLR4 expression and increased nitric oxide (NO) production by increasing the expression of inducible nitric oxide synthase (iNOS). Furthermore, LPS was found to induce interleukin (IL)-8 and vascular endothelial growth factor (VEGF) production, as well as intracellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression. Taken together, these results indicate that LPS induces inflammatory responses in HASMC. Moreover, NOS inhibitor (L-NAME) and anti-TLR 4mAb reduced the LPS-induced NO, IL-8 and VEGF production and ICAM-1 expression. Additionally, TLR4 expression was reduced by NOS inhibitor. Taken together, these results indicate that LPS-induced inflammatory responses are regulated by TLR4 expression and NO production.     

肝素通过TLR4减少脂多糖刺激的人内皮细胞IL-8表达

目的:观察肝素对脂多糖(lipopolysaccharide, LPS)刺激的人内皮细胞白细胞介素8(interleukin-8,IL-8)水平的影响,并探讨Toll样受体4(Toll-like receptor 4,TLR 4)在其中的可能影响。方法:用LPS(10 mg/L)刺激人肺微血管内皮细胞诱导损伤,肝素治疗组提前15 min分别加入100 U/L及10³ U/L普通肝素,正常对照组加入等量磷酸盐缓冲液。分别在刺激2、6、12 h收集细胞上清,采用酶联免疫吸附法测定上清中IL-8的浓度。在刺激2、6、12 h收集细胞提取RNA,应用实时荧光定量聚合酶链反应检测各组细胞中IL-8、CD14及TLR4 mRNA水平变化。结果:与正常对照组比较,LPS刺激组IL-8 mRNA水平增高,6 h达到高峰,其蛋白水平于12 h达到高峰。LPS刺激下TLR4 mRNA水平增高,6 h达到高峰,肝素降低其水平,差异有统计学意义(P＜0.05)。未检测到CD14 mRNA的表达。结论:LPS刺激下人肺微血管内皮细胞IL-8表达增加。肝素可能通过调节TLR4降低IL-8的水平,从而发挥保护作用。     

4-1BB信号对小鼠树突状细胞表面TLR4表达的调节

目的 探讨4-1BB（CD137）激发型单克隆抗体2A对小鼠骨髓来源的树突状细胞（DC）表面TLR4表达的调节.方法 用不同剂量2A、LPS以及2A与LPS联合,或用LPS预刺激后再加入2A,以流式细胞术检测这些处理因素作用下DC表面TLR4表达情况.结果 LPS可下调DC TLR4的表达,下调作用可维持24 h,而2A可使DC TLR4的表达上调,上调作用可维持12 h,并可拮抗LPS对TLR4的下调作用.用LPS预处理DC后再加入2A,也可拮抗LPS的下调作用.结论 4-1BB信号可以上调DC表面TLR4的表达.     

Histamine induces Toll-like receptor 2 and 4 expression in endothelial cells and enhances sensitivity to Gram-positive and Gram-negative bacterial cell wall components

Histamine is a major inflammatory molecule released from the mast cell, and is known to activate endothelial cells. However, its ability to modulate endothelial responses to bacterial products has not been evaluated. In this study we determined the ability of histamine to modulate inflammatory responses of endothelial cells to Gram-negative and Gram-positive bacterial cell wall components and assessed the role of Toll-like receptors (TLR) 2 and 4 in the co-operation between histamine and bacterial pathogens. Human umbilical vein endothelial cells (HUVEC) were incubated with lipopolysaccharide (LPS), lipoteichoic acid (LTA), or peptidoglycan (PGN) in the presence or absence of histamine, and the expression and release of interleukin-6 (IL-6), and NF-kappaB translocation were determined. The effect of histamine on the expression of mRNA and proteins for TLR2 and TLR4 was also evaluated. Incubation of HUVEC with LPS, LTA and PGN resulted in marked enhancement of IL-6 mRNA expression and IL-6 secretion. Histamine alone markedly enhanced IL-6 mRNA expression in HUVEC, but it did not stimulate proportional IL-6 release. When HUVEC were incubated with LPS, LTA, or PGN in the presence of histamine marked amplification of both IL-6 production and mRNA expression was noted. HUVEC constitutively expressed TLR2 and TLR4 mRNA and proteins, and these were further enhanced by histamine. The expression of mRNAs encoding MD-2 and MyD88, the accessory molecules associated with TLR signalling, were unchanged by histamine treatment. These results demonstrate that histamine up-regulates the expression of TLR2 and TLR4 and amplifies endothelial cell inflammatory responses to Gram-negative and Gram-positive bacterial components.     

Characterization and regulation of the urokinase receptor of human endothelial cells

Endothelial cells synthesize and secrete urokinase-type plasminogen activators (u-PA) in response to various stimuli. To modulate the local expression of u-PA activity both intravascularly and pericellularly during angiogenesis, endothelial cells express both inhibitors (primarily PAI-1) and receptors (u-PAR) for u-PA. The interaction of u-PA with receptors on the surface of endothelial cells may play an important role in the regulation of fibrinolysis and cell migration. Using radioligand binding studies, we and others have demonstrated that human umbilical vein endothelial cells (HUVEC) express high affinity receptors for urokinase on the cell surface. We have demonstrated that single chain urokinase (scu-PA, prourokinase) binds only via the growth factor domain, while two chain high molecular weight urokinase (tcu-PA) can bind to the receptor or to cell- or matrix-associated PAI-1. We have isolated a ∼46kDa glycoprotein from HUVEC using affinity chromatography which retains the ability to specifically bind u-PA. At least three post -translational modifications appear to occur including removal of an N-terminal signal peptide; N-linked glycosylation, and C-terminal cleavage with addition of a phosphatidylinositol-glycan moiety which links the externally oriented protein to the cell surface. Using the polymerase chain reaction and published sequence information of the u-PAR cloned from a transformed fibroblast cDNA library, we amplified cDNAs of u-PAR from HUVEC and PMA-treated U937 cells. The specificity of the cDNAs was confirmed by restriction mapping and direct sequence analysis. Using these probes and radioligand binding studies we have demonstrated that at least two independent protein kinase pathways exist in endothelial cells for upregulating u-PA receptor expression. Down regulation of receptors may be pathophysiologic in thrombosic disorders whereas up regulation may be important in promoting wound healing, vascular repair, and protection from thrombosis. Up regulation could be harmful as well in such conditions as pathologic neovascularization (e.g., diabetic retinopathy) and in tumour metastasis as well as in tumour-related angiogenesis. Understanding the control and functional significance of u-PA binding to cells in general will hopefully enable the design of therapies to optimize the beneficial aspects and minimize any harmful effects of this interaction. Changes in the local expression of u-PA, PAM and u-PAR by endothelial cells may affect the extent of angiogenesis or the degree of local intravascular fibrinolysis, which might be critical in conditions such as unstable angina and myocardial infarction.     

Toll样受体4介导的自噬减轻糖基化高密度脂蛋白诱导的血管内皮细胞凋亡

目的:探讨自噬对糖基化高密度脂蛋白(glycosylated high-density lipoprotein,gly-HDL)所致的血管内皮细胞凋亡的影响及其分子机制。方法:体外培养人脐静脉内皮细胞(human umbilical vein endothelial cells,HUVECs),分别与100 mg/L HDL和不同浓度(25、50和100 mg/L)gly-HDL共同孵育24 h;另再培养HUVECs给予1μmol/L自噬诱导剂雷帕霉素或2 mmol/L自噬抑制剂3-甲基腺嘌呤(3-methyladenine,3-MA)预处理1 h,或5 mg/L抗Toll样受体4(Toll-like receptor 4,TLR4)单克隆中和抗体预处理30 min,再与gly-HDL(100 mg/L)共同孵育24 h。采用MTT法检测细胞活力,Annexin V-FITC/PI双染法检测细胞凋亡情况,试剂盒测定培养液中乳酸脱氢酶(lactate dehydrogenase,LDH)活性,采用Western blot技术检测自噬标志分子beclin-1和微管相关蛋白1轻链3-Ⅱ(microtubule-associated protein 1 light chain 3-Ⅱ,LC3-Ⅱ)、内质网应激凋亡途径关键分子caspase-12及TLR4的表达变化,采用激光共聚焦显微镜观测细胞内LC3的变化。结果:经gly-HDL处理的HUVECs活力下降,LDH漏出和细胞凋亡显著增加(P<0.01),且caspase-12被激活(P<0.05);雷帕霉素预处理HUVECs后,gly-HDL对细胞的损伤作用和对caspase-12的活化作用减弱(P<0.05);而3-MA预处理HUVECs后,gly-HDL对细胞的损伤作用和对caspase-12的活化作用则进一步加强(P<0.05)。gly-HDL显著上调TLR4的表达,并触发自噬反应,表现为beclin-1和LC3-Ⅱ表达上调及LC3显著颗粒化,且呈浓度依赖性(P<0.05);而抗TLR4单克隆中和抗体预处理可显著抑制gly-HDL所诱导的beclin-1上调和LC3颗粒化(P<0.01)。结论:TLR4介导gly-HDL对HUVECs自噬的诱导作用,而一定程度的自噬可通过抑制caspase-12活化减轻gly-HDL所诱导的HUVECs凋亡。     

4-羟基壬烯酸诱导人主动脉内皮细胞和心肌细胞凋亡

我们应用4-羟基壬烯酸(HNE)诱导培养的人主动脉内皮细胞和心肌细胞的氧化应激,观察不同浓度的HNE促使培养的主动脉内皮细胞和心肌细胞凋亡的程度。1材料与方法1·1人主动脉内皮细胞(HAOEC)和心肌细胞的培养:人主动脉内皮细胞(购自美国细胞应用公司CA 92121)和人心肌细胞(购自ATCC公司CRL-1446)培养于改良Eagle’s培养基中(DMEM培养基),37℃条件下进行原代和传代培养。所有的实验在2周内完成。1·2在培养的细胞中加入HNE:在加入HNE(Calb iochem公司)之前,先用含有钙、镁离子和葡萄糖的磷酸盐缓冲液洗去细胞培养液,然后分别加入1…     

LPS对晶状体上皮细胞TLR4和CD14 mRNA表达的影响

目的:探讨脂多糖(LPS)对晶状体上皮细胞(LECs)Toll样受体4(TLR4)和CD14表达的影响。方法:采用不同浓度的LPS与体外培养的牛LECs共同孵育不同时间,再用一步法反转录多聚酶链反应(PCR)检测LECs中TLR4mRNA和CD14mRNA的表达。结果:50μg/LLPS组、100μg/LLPS组、200μg/LLPS组、500μg/LLPS组、1000μg/LLPS组的LECs中TLR4mRNA的表达均分别显著高于对照组(P0.01);100μg/LLPS作用24h、48h、72h后LECs的TLR4mRNA表达均显著高于对照组(P0.01);100μg/LLPS作用24h后LECs的CD14mRNA表达亦显著高于对照组(P0.05)。结论:LPS可促进LECs中TLR4mRNA和CD14mRNA的表达,提示白内障手术后眼内细胞反应和后发性白内障的发生发展可能与TLR4和CD14表达增加有关。     

Toll-like receptor 4 signaling in dysfunction of cardiac microvascular endothelial cells under hypoxia/reoxygenation

Objective  

This study was designed to detect the role of Toll-like receptor 4 (TLR4) signaling in the dysfunction of cardiac microvascular endothelial cells (CMECs) after hypoxia/reoxygenation (H/R).     

Caspase-dependent and -independent apoptosis of mast cells induced by withdrawal of IL-3 is prevented by Toll-like receptor 4-mediated lipopolysaccharide stimulation

IL-3-dependent mucosal-like mast cells undergo apoptosis upon withdrawal of IL-3. Generally, the apoptosis is mediated by the activation of caspases and inhibited by addition of the pan-caspase inhibitors z-VAD-FMK or BOC-D-FMK. However, DNA fragmentation, a typical characteristic of apoptosis, is not inhibited by z-VAD-FMK or BOC-D-FMK in mast cell apoptosis. In this study, we demonstrate that the apoptosis of mast cells is mediated by both caspase-dependent and -independent mechanisms. The caspase-independent apoptosis is mediated by the translocation of endonuclease G from mitochondria into nuclei. Withdrawal of IL-3 caused down-regulation of Bcl-xL, resulting in a drop in mitochondrial membrane transition potential followed by the release of cytochrome c and endonuclease G from mitochondria. However, stimulation of mast cells through Toll-like receptor 4 (TLR4) by lipopolysaccharide prevented mast cell apoptosis by inducing expression of Bcl-xL. Moreover, the activation of mast cells by LPS is enhanced in the presence of IFN-gamma, which up-regulates the expression of cell surface TLR4. Taken together, these observations provide evidence that mast cells play important roles not only in allergic reactions but also in innate immunity recognizing enterobacteria through TLR4, and are regulated differently from allergic inflammation by Th1 cytokines.