Intracellular recognition of lipopolysaccharide by toll-like receptor 4 in intestinal epithelial cells

Toll-like receptor (TLR)4 has recently been shown to reside in the Golgi apparatus of intestinal crypt epithelial m-ICcl2 cells, colocalizing with internalized lipopolysaccharide (LPS). Here we demonstrate that disruption of the integrity of the Golgi apparatus significantly reduced LPS-mediated nuclear factor kappaB activation. Also, the TLR4 adaptor protein MyD88 and the serine/threonine kinase IRAK-1 were rapidly recruited to the Golgi apparatus upon stimulation. LPS-mediated activation required lipid raft formation and intact clathrin-dependent internalization. In contrast to macrophages, prevention of ligand internalization by use of LPS-coated beads significantly impaired recognition by epithelial cells. The localization of TLR4 to the Golgi apparatus was abrogated by expression of a genetically modified form of the TLR4 binding chaperone gp96. Thus, our data provide evidence that in contrast to the situation in macrophages, LPS recognition in intestinal epithelial cells may occur in the Golgi apparatus and require LPS internalization.     

Oligosaccharides of Hyaluronan activate dendritic cells via toll-like receptor 4.

Low molecular weight fragmentation products of the polysaccharide of Hyaluronic acid (sHA) produced during inflammation have been shown to be potent activators of immunocompetent cells such as dendritic cells (DCs) and macrophages. Here we report that sHA induces maturation of DCs via the Toll-like receptor (TLR)-4, a receptor complex associated with innate immunity and host defense against bacterial infection. Bone marrow-derived DCs from C3H/HeJ and C57BL/10ScCr mice carrying mutant TLR-4 alleles were nonresponsive to sHA-induced phenotypic and functional maturation. Conversely, DCs from TLR-2-deficient mice were still susceptible to sHA. In accordance, addition of an anti-TLR-4 mAb to human monocyte-derived DCs blocked sHA-induced tumor necrosis factor alpha production. Western blot analysis revealed that sHA treatment resulted in distinct phosphorylation of p38/p42/44 MAP-kinases and nuclear translocation of nuclear factor (NF)-kappa B, all components of the TLR-4 signaling pathway. Blockade of this pathway by specific inhibitors completely abrogated the sHA-induced DC maturation. Finally, intravenous injection of sHA-induced DC emigration from the skin and their phenotypic and functional maturation in the spleen, again depending on the expression of TLR-4. In conclusion, this is the first report that polysaccharide degradation products of the extracellular matrix produced during inflammation might serve as an endogenous ligand for the TLR-4 complex on DCs.     

Human immunodeficiency virus type 1 protease inhibitors block toll-like receptor 2 (TLR2)- and TLR4-Induced NF-kappaB activation

Coinfections with opportunistic and pathogenic bacteria induce human immunodeficiency virus (HIV) replication through microbial antigen activation of NF-kappaB. Here, we assessed whether HIV type 1 protease inhibitors (PI) block microbial antigen activation of NF-kappaB. Human microvessel endothelial cells were transiently transfected with either endothelial cell-leukocyte adhesion molecule NF-kappaB luciferase or interleukin 6 (IL-6) promoter luciferase constructs by using FuGENE 6, and they were treated with PI (nelfinavir, ritonavir, or saquinavir) prior to stimulation with the Toll-like receptor 4 (TLR4) and TLR2 ligands, with lipopolysaccharide (LPS), soluble Mycobacterium tuberculosis factor, or Staphylococcus epidermidis phenol-soluble modulin, respectively, or with tumor necrosis factor alpha (TNF-alpha). Luciferase activity was measured by using a Promega luciferase kit. TNF-alpha release from the supernatant was measured by enzyme-linked immunosorbent assay. Cell death was assessed by lactate dehydrogenase assay. We observed that PI pretreatment blocked the TLR2- and TLR4- as well as the TNF-alpha-mediated NF-kappaB activation, in a dose-dependent manner. PI pretreatment also blocked the LPS-induced IL-6 promoter transactivation and TNF-alpha secretion. These data suggest that PI block HIV replication not only by inhibiting the HIV protease but also by blocking the TLR- and TNF-alpha-mediated NF-kappaB activation and proinflammatory cytokine production. These findings may help explain the immunomodulatory effects of PI, and they suggest an advantage for PI-containing drug regimens in the treatment of HIV-infected patients who are coinfected with opportunistic and pathogenic bacteria.     

Effects of eritoran tetrasodium, a toll-like receptor 4 antagonist, on intestinal microcirculation in endotoxemic rats

Lipopolysaccharide (LPS) or endotoxin can induce Toll-like receptor 4 signaling and cause microcirculatory dysfunction, which can lead to multiple organ dysfunction. The goal of this study was to investigate whether Toll-like receptor 4 antagonist, eritoran tetrasodium, can attenuate microcirculatory dysfunction in endotoxemic rats. Seventy-two male Wistar rats were divided into three groups as follows: control, LPS, and eritoran + LPS. These rats received laparotomy to exteriorize a segment of terminal ileum for microcirculation examination on intestinal mucosa, muscle, and Peyer patch. The rats in the eritoran + LPS group received 10 mg kg?1 eritoran intravenously. The rats in the LPS and eritoran + LPS groups received 15 mg kg?1 LPS intravenously. Microcirculatory blood flow intensity was measured by full-field laser perfusion imager. Total and perfused small-vessel densities, microvascular flow index, and heterogeneity index were investigated by sidestream dark-field video microscope. Our results revealed that eritoran restored the mean arterial pressure. At 240 min, the microcirculatory blood flow intensity was higher in the eritoran + LPS group than in the LPS group as follows: mucosa (1,094 [SD, 398] vs. 543 [SD, 163] perfusion unit [PU]; P < 0.001), muscle (752 [SD, 124] vs. 357 [SD, 208] PU; P < 0.001), and Peyer patch (961 [SD, 162] vs. 480 [SD, 201] PU; P < 0.001). Eritoran also attenuated endotoxin-induced elevation in the serum level of D-dimer. In conclusion, we have established a promising rat protocol to investigate the intestinal microcirculation in endotoxemia. Our data indicate that eritoran can reduce microcirculatory dysfunction in endotoxemic rats.     

Toll样受体4与结直肠癌的相关性

Toll样受体4(toll-like receptor 4,TLR4)在炎症诱发的结直肠癌(colorectal cancer,CRC)中的作用日益受到关注.活化的TLR4通过髓样分化因子88 (myeloid differentiation factor 88,MyD88)激活核转录因子-κB (nuclear factor-κB,NF-κB)产生大量炎症介质并募集炎症细胞形成肿瘤微环境,从而成为炎症与肿瘤的纽带贯穿于CRC发生、发展的整个过程中.本文着重对TLR4信号通路参与CRC的起始、进展、转移、遗传变异和表观遗传调控进行了讨论.尤其,文章中强调了TLR4在CRC发展和发病机制中的角色,并提出调节TLR4信号通路可能为CRC的治疗带来新的前景.     

Anthrolysin O and other gram-positive cytolysins are toll-like receptor 4 agonists

Exposure of bone marrow-derived macrophages (BMDMs) to low concentrations of Bacillus anthracis lethal toxin (LT), whose catalytic subunit is lethal factor (LF), results in induction of a robust apoptotic response dependent on activation of Toll-like receptor (TLR)4. A similar TLR4-dependent apoptotic response is observed when BMDMs are infected with live B. anthracis (Sterne strain). However, TLR4 is considered to be a specific signaling receptor for lipopolysaccharide (LPS), a typical product of gram-negative bacteria, whereas B. anthracis is gram-positive. To understand how B. anthracis can activate TLR4, we analyzed its culture supernatants and found them to contain a potent TLR4-stimulating activity that can also induce apoptosis in macrophages in which the antiapoptotic p38 MAP kinase (whose activation is prevented by LF) was inhibited. Purification of this activity suggested it consists of anthrolysin O (ALO), a member of the cholesterol-dependent cytolysin (CDC) family. We show that recombinant ALO can activate TLR4 in a manner independent of LPS contamination and, together with LT, can induce macrophage apoptosis. We also provide genetic evidence that ALO is required for induction of macrophage apoptosis in response to infection with live B. anthracis and that other CDC family members share the ability to activate TLR4.     

跑台训练对大鼠脑缺血再灌注后脑组织toll样受体2、toll样受体4信号转导通路活性的影响

目的:探讨跑台训练对大鼠脑缺血再灌注神经功能恢复和脑组织toll样受体2(TLR2)、toll样受体4(TLR4)、核转录因子-KB(NF-kB)与髓样分化因子(MyD88)信号转导通路活性的影响.方法:用线栓法制作Wistar大鼠大脑中动脉缺血再灌注模型,35只大鼠随机分为假手术组(SH组)、跑台训练组(O+TR组)和手术对照组(Oc组).O+TR和OC组又分为跑3d、跑7d、跑14d 3个亚组,各亚组及SH组每组5只大鼠.O+TR组于术后第3天开始给予跑台训练,SH组及OC组不予跑台训练.于跑3d、跑7d、跑14d 3个时间点进行神经功能评估后处死大鼠.采用RT-PCR和Western-blot技术测定大鼠梗死组织TLR2、TLR4及下游因子MyD88、NF-κB 的转录活性及蛋白表达的水平.结果:O+TR组在跑3d、7d、14d神经功能评分明显优于OC组(P＜0.05).TLR2、TLR4、MyD88及NF-κB表达O+TR组与OC组均较SH组高,3d组表达最多,之后呈逐渐下降的趋势,但O+TR组表达均较OC低(P＜0.05).结论:跑台训练通过降低大鼠脑组织缺血再灌注后上调的TLR2、TLR4及下游因子MyD88、NF-κB的表达,抑制脑组织炎症反应,从而有利于脑缺血后神经功能的恢复.     

内皮源性toll样受体4在急性肺损伤中的作用

目的 探索内皮源性或髓源性细胞表面toll样受体4(TLR4)介入急性肺损伤(ALI)的作用. 方法 采用TLR4基因突变(C3H/HeJ品系,TLR4mut/mut)及野生型(C3H/HeN,TLB4+/+)小鼠,通过骨髓移植建立"内皮细胞TLR4+/+髓系细胞TLR4mut/mut"(WT/Mutant:受体/供体)及Mutant/WT嵌合体小鼠,尾静脉注射LPS(5 mg·kg-1)复制ALI模型,5 h后测肺组织湿干重比(W/D),肺通透指数(LPI),肺组织髓过氧化物酶(MPO)水平、炎症因子及黏附分子水平. 结果 TLR4mut/mut小鼠肺损伤较TLR4+/+小鼠较轻,WT/Mutant组小鼠肺组织损伤较Mutant/WT组重,且WT/Mutant组与WT/WT组差异无统计学意义.WT/Mutant组小鼠肺组织MPO水平、ICAM-1表达水平较Mutant/WT组高,且ICAM-1表达水平WT/Mutant组小鼠与WT/WT小鼠比较差异无统计学意义.炎症因子TNF-α、IL-1β的水平Mutant/WT组较WT/Mutant组高. 结论 内皮源性TLR4通过调控黏附分子表达而促进PMN肺组织招募,在介导LPS诱导的ALI中的发挥核心作用.     

Interleukin 1 receptor dependence of serum transferred arthritis can be circumvented by toll-like receptor 4 signaling

Inflammatory arthritis is associated with the release of a network of key cytokines. In T cell receptor transgenic K/BxN mice interleukin (IL)-1 plays a key role in joint swelling and destruction, as suggested by the ability of anti-IL-1receptor (IL-1R) antibody treatment to delay the onset and slow the progression of this disease. This mechanism is dependent on the signaling pathway intermediary myeloid differentiation factor 88 (MyD88), such that neither IL-1R nor MyD88-deficient mice developed visually detectable synovitis after transfer of arthritogenic sera. The Toll-like receptors (TLRs) share the same signaling pathway through MyD88 as the IL-1R. The administration of a TLR-4 ligand, lipopolysaccharide, concomitant with arthritogenic serum in IL-1 receptor-deficient mice resulted in acute paw swelling, but not in MyD88-deficient mice. Also, serum transferred arthritis was not sustained in TLR-4 mutant mice compared with controls. These results suggest that innate immune functions via TLR-4 might perpetuate inflammatory mechanisms and bypass the need for IL-1 in chronic joint inflammation.     

The future of toll-like receptor therapeutics

Since the discovery of human TLRs, manipulating the activity of these receptors to modulate immune responses for therapeutic purposes has initiated intense activity in the pharmaceutical industry. The focus of these activities has been largely in the areas of infectious diseases, cancer, allergic diseases and vaccine adjuvants. Although initial clinical trials for infectious diseases and cancer showed early promise, subsequent longer-term trials have been disappointing and more research is required to find dosing regimes that balance efficacy with acceptable side-effect profiles. As only a small number of doses are given, TLR agonists as vaccine adjuvants appear to hold greater potential and have less safety concerns than for other applications. Several innovative strategies for using TLR agonists in vaccine development are currently being pursued, and these are discussed in more detail in this review.     

Differential expression of toll-like receptor genes: sepsis compared with sterile inflammation 1 day before sepsis diagnosis

Toll-like receptors (TLRs) are critical components of innate immunity. This study was designed to evaluate differential expression of genes for TLR and associated signal transduction molecules in critically ill patients developing sepsis compared with those with sterile inflammation. Uninfected critically ill patients with systemic inflammatory response syndrome were prospectively followed daily for development of sepsis. They were divided into two groups and compared in a case-control manner: (a) preseptic patients (n = 45) who subsequently developed sepsis, and (b) uninfected systemic inflammatory response syndrome patients (n = 45) who remained uninfected. Whole blood RNA was collected (PAXGene tube) at study entry and 1, 2, and 3 days before clinical sepsis diagnosis (or time-matched uninfected control) and analyzed via Affymetrix Hg_U133 Plus 2.0 microarrays. Genes were considered differentially expressed if they met univariate significance controlled for multiple comparisons at P < 0.005. Differentially expressed probes were uploaded into the Database for Annotation, Visualization and Integrated Discovery. The TLR pathway (Kyoto Encyclopedia of Genes and Genomes-KEGG) significance was determined via Expression Analysis Systematic Explorer (EASE) scoring. A total of 2,974 Affymetrix probes representing 2,190 unique genes were differentially expressed 1 day before sepsis diagnosis. Thirty-six probes representing 25 genes were annotated to the TLR pathway (KEGG) via the Database for Annotation, Visualization and Integrated Discovery with an EASE score at P < 0.0004. Notable TLR genes demonstrating increased expression include TLR-4 (median, 1.43-fold change), TLR-5 (2.08-fold change), and MAPK14 (1.90-fold change). An additional 11 unique genes were manually annotated into the TLR pathway based on known relevance such as TLR-8 (1.54-fold change). The total 36 genes contained 28 showing increased expression and 8 showing decreased expression. Differential gene expression was noted for TLR receptors (eight genes), TLR intracellular signal transduction cascade molecules (27 genes), and TLR-related effector molecules (one gene). The TLR and downstream signaling genes are differentially expressed in critically ill patients developing sepsis compared with those with sterile inflammation. These expression differences occur before phenotypic-based diagnosis of clinical sepsis.     

Emerging paradigm: toll-like receptor 4-sentinel for the detection of tissue damage

The systemic inflammatory response syndrome initiated by infection shares many features in common with the trauma-induced systemic response. The toll-like receptors (TLRs) stand at the interface of innate immune activation in the settings of both infection and sterile injury by responding to a variety of microbial and endogenous ligands alike. Recently, a body of literature has evolved describing a key role for TLRs in acute injury using rodent models of hemorrhagic shock, ischemia and reperfusion, tissue trauma and wound repair, and various toxic exposures. This review will detail the observations implicating a TLR family member, TLR4, as a key component of the initial injury response.     

HMGB1 signals through toll-like receptor (TLR) 4 and TLR2

In response to bacterial endotoxin (e.g., LPS) or endogenous proinflammatory cytokines (e.g., TNF and IL-1beta), innate immune cells release HMGB1, a late cytokine mediator of lethal endotoxemia and sepsis. The delayed kinetics of HMGB1 release makes it an attractive therapeutic target with a wider window of opportunity for the treatment of lethal systemic inflammation. However, the receptor(s) responsible for HMGB1-mediated production of proinflammatory cytokines has not been well characterized. Here we demonstrate that in human whole blood, neutralizing antibodies against Toll-like receptor 4 (TLR4, but not TLR2 or receptor for advanced glycation end product) dose-dependently attenuate HMGB1-induced IL-8 release. Similarly, in primary human macrophages, HMGB1-induced TNF release is dose-dependently inhibited by anti-TLR4 antibodies. In primary macrophages from knockout mice, HMGB1 activates significantly less TNF release in cells obtained from MyD88 and TLR4 knockout mice as compared with cells from TLR2 knockout and wild-type controls. However, in human embryonic kidney 293 cells transfected with TLR2 or TLR4, HMGB1 effectively induces IL-8 release only from TLR2 overexpressing cells. Consistently, anti-TLR2 antibodies dose-dependently attenuate HMGB1-induced IL-8 release in human embryonic kidney/TLR2-expressing cells and markedly reduce HMGB1 cell surface binding on murine macrophage-like RAW 264.7 cells. Taken together, our data suggest that there is a differential usage of TLR2 and TLR4 in HMGB1 signaling in primary cells and in established cell lines, adding complexity to studies of HMGB1 signaling which was not previously expected.     

沉默Toll样受体4基因表达的RNAi慢病毒载体的构建

背景：Toll样受体4（toll-like receptor4,TLR4）是介导内毒素/脂多糖应答的主要受体,在由内毒素诱导的炎性反应的信号通路中发挥着重要作用。目的：构建人TLR4基因的RNA干扰慢病毒载体,并观察其对人脐静脉内皮细胞TLR4在蛋白水平的沉默效应。方法：利用Invitrogen在线软件设计人TLR4基因shRNA序列,合成、退火形成双链寡核苷酸后克隆到线性载体pENTRTM/H1/TO的黏性末端,并进行DNA测序。得到的阳性重组子再与慢病毒载体进行重组反应,从而获得干扰TLR4基因真核表达的慢病毒载体。在脂质体的介导下将慢病毒包装辅助复合体和TLR4基因的真核表达慢病毒载体导入293FT细胞包装病毒,测定病毒滴度,感染人脐静脉内皮细胞,检验其干扰TLR4基因表达的有效性。结果与结论：实验成功构建TLR4基因真核表达慢病毒干扰载体并获得相应的慢病毒,病毒滴度为8.7×106U/mL。免疫印迹杂交结果表明,所获得的慢病毒感染人脐静脉内皮细胞TLR4基因在蛋白水平的表达显著降低。实验成功构建了人TLR4基因慢病毒RNA干扰表达载体,并验证了其在人脐静脉内皮细胞上的有效性。     

沉默Toll样受体4基因表达的RNAi慢病毒载体的构建

背景:Toll样受体4(toll-like receptor4,TLR4)是介导内毒素/脂多糖应答的主要受体,在由内毒素诱导的炎性反应的信号通路中发挥着重要作用。目的:构建人TLR4基因的RNA干扰慢病毒载体,并观察其对人脐静脉内皮细胞TLR4在蛋白水平的沉默效应。方法:利用Invitrogen在线软件设计人TLR4基因shRNA序列,合成、退火形成双链寡核苷酸后克隆到线性载体pENTRTM/H1/TO的黏性末端,并进行DNA测序。得到的阳性重组子再与慢病毒载体进行重组反应,从而获得干扰TLR4基因真核表达的慢病毒载体。在脂质体的介导下将慢病毒包装辅助复合体和TLR4基因的真核表达慢病毒载体导入293FT细胞包装病毒,测定病毒滴度,感染人脐静脉内皮细胞,检验其干扰TLR4基因表达的有效性。结果与结论:实验成功构建TLR4基因真核表达慢病毒干扰载体并获得相应的慢病毒,病毒滴度为8.7×106U/mL。免疫印迹杂交结果表明,所获得的慢病毒感染人脐静脉内皮细胞TLR4基因在蛋白水平的表达显著降低。实验成功构建了人TLR4基因慢病毒RNA干扰表达载体,并验证了其在人脐静脉内皮细胞上的有效性。     

Ketamine inhibits LPS-mediated BV2 microglial inflammation via NMDA receptor blockage

Microglial inflammation leads to the upregulation of proinflammatory cytokine and proinflammatory enzyme expression, resulting in inflammation-induced neuronal cell apoptosis. Ketamine, an anesthetic mostly used in critical patients, has been reported to possess neuroprotective effects. However, the potential mechanism is still not well understood. In the present study, we investigated how ketamine attenuates lipopolysaccharide (LPS)-mediated BV2 cell inflammation. LPS upregulated proinflammatory cytokine and proinflammatory enzyme expression, increased NF-κB phosphorylation and nuclear translocation, and augmented calcium (Ca²⁺)/calmodulin-dependent protein kinase II (CaMK II) phosphorylation and Ca²⁺ levels in BV2 cells. Ketamine could reverse these LPS-induced effects. Furthermore, AP5, an inhibitor of NMDA receptors, inhibited LPS-induced inflammatory effects in BV2 cells, which was similar to the effects of ketamine. Moreover, these effects of ketamine against LPS-mediated inflammation in BV2 cells could be reversed by D-serine, an activator of NMDA receptors. The present study suggests that ketamine, by inhibiting NMDA receptors, attenuating Ca²⁺ levels, and inhibiting CaMK II phosphorylation, NF-κB phosphorylation and nuclear translocation, may ameliorate LPS-mediated inflammation in BV2 cells.     

肥胖患者外周血单个核细胞Toll样受体4表达及活性研究

目的研究肥胖患者外周血单个核细胞（PBMCs）Toll样受体4（11LR4）表达及活性。方法收集16例肥胖患者和16例正常对照者的PBMCs,蛋白印迹法检测PBMCsTLR4及IKBct蛋白表达,实时荧光定量PCR检测PBMCsTLR4及白细胞介素6（IL-6）mRNA表达,并测定空腹血糖、空腹胰岛素、血游离脂肪酸（FFA）、IL-6及肿瘤坏死因子仪（TNF-a）。结果与正常对照组比较,肥胖组血FFA、IL-6、TNF-a及稳态模型评估的胰岛素抵抗指数（HOMA-IR）明显增高[FFA：（879±64）、（458±48）umoL／L,t=24．613、P=0．000;IL-6：（2．20±0．35）、（1．264-0．25）ng／L,t=14．993、P=0．000;TNF—a（1．964-0．32）、（1．384-0．24）ng／L,t=9．128、P=0．000;HOMA．IR：1．84-0．2、0．44-0．1,t=32．254、P=0．000];肥胖组PBMCsTLR4mRNA及蛋白表达显著升高（TLR4mRNA：3．13±0．21与0．99±0．03,f=54．758,P〈0．05;TLR4蛋白：7．04±0．42与2．53±0．17,t：77．450,P〈0．05）;肥胖组PBMCsIKBet蛋白表达显著降低（2．52±0．16与4．00±0．30,t=23．284,P〈0．05）,IL-6mRNA表达显著升高（2．55±0．15与1．03±O．11,t=53．981,P〈0．05）。结论肥胖患者PBMCsTLR4表达及活性显著增加,可能在肥胖患者胰岛素抵抗的发生、发展中具有重要作用。