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.     

乌司他丁对脂多糖诱导的大鼠肺组织Toll样受体4信号通路表达的影响

目的 探讨乌司他丁对脓毒性大鼠肺损伤的保护机制.方法 选健康清洁级SD大鼠30只,随机(随机数字法)分为生理盐水对照组10只、脂多糖(LPS)组10只、脂多糖+乌司他丁(LPS+ UTI)组10只.注药24 h后取肺组织观察形态学改变,分别应用RT-PCR或Western blot 及ELISA方法测定肺组织Toll样受体4(TLR4)、核因子-κB (NF-κB)及肿瘤坏死因子TNF-α mRNA及蛋白表达.结果 脂多糖导致大鼠肺组织损伤,乌司他丁可下调肺组织TLR4 mRNA (t=3.563,P=0.032)、TNF-α mRNA(t=5.147,P=0.028)及TLR4蛋白(t=2.692,P=0.041)、NF-κB蛋白(t=2.459,P=0.024)、TNF-α蛋白(t=3.336,P=0.037)表达,并减轻肺损伤.结论 乌司他丁对脂多糖致肺损伤具有一定保护作用,其机制之一可能与抑制TLR4-NF-κB信号途径转导有关.     

The Molecular Mechanism of B Cell Activation by toll-like Receptor Protein RP-105

The B cell–specific transmembrane protein RP-105 belongs to the family of Drosophila toll-like proteins which are likely to trigger innate immune responses in mice and man. Here we demonstrate that the Src-family protein tyrosine kinase Lyn, protein kinase C β I/II (PKCβI/II), and Erk2-specific mitogen-activated protein (MAP) kinase kinase (MEK) are essential and probably functionally connected elements of the RP-105–mediated signaling cascade in B cells. We also find that negative regulation of RP-105–mediated activation of MAP kinases by membrane immunoglobulin may account for the phenomenon of antigen receptor–mediated arrest of RP-105–mediated B cell proliferation.     

Cbl-b negatively regulates B cell antigen receptor signaling in mature B cells through ubiquitination of the tyrosine kinase Syk

Members of the Cbl family of molecular adaptors play key roles in regulating tyrosine kinase-dependent signaling in a variety of cellular systems. Here we provide evidence that in B cells Cbl-b functions as a negative regulator of B cell antigen receptor (BCR) signaling during the normal course of a response. In B cells from Cbl-b-deficient mice cross-linking the BCRs resulted in sustained phosphorylation of Igalpha, Syk, and phospholipase C (PLC)-gamma2, leading to prolonged Ca2+ mobilization, and increases in extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal protein kinase (JNK) phosphorylation and surface expression of the activation marker, CD69. Image analysis following BCR cross-linking showed sustained polarization of the BCRs into large signaling-active caps associated with phosphorylated Syk in Cbl-b-deficient B cells in contrast to the BCRs in Cbl-b-expressing B cells that rapidly proceeded to form small, condensed, signaling inactive caps. Significantly, prolonged phosphorylation of Syk correlated with reduced ubiquitination of Syk indicating that Cbl-b negatively regulates BCR signaling by targeting Syk for ubiquitination.     

Activation mediated by RP105 but not CD40 makes normal B cells susceptible to anti-IgM-induced apoptosis: a role for Fc receptor coligation

Signals through the B cell antigen receptor lead to a variety of cellular events such as activation, anergy, and apoptosis. B cells select these outcomes to establish and maintain self-tolerance, and to mount adequate antibody responses. However, it is not fully understood how one and the same signal causes such different consequences. In the present study, we have studied the effect of activation signals on the outcome of responses to antigen receptor ligation. Two distinct growth- promoting signals were used to activate B cells. Ligation of either RP105, a newly discovered B cell surface molecule, or the CD40 molecule, drove B cells to proliferate. Resultant blastic cells were then exposed to anti-immunoglobulin M (IgM). Blast cells that had been stimulated with anti-RP105 ceased growing and underwent apoptosis after cross-linking of surface IgM. Coligation of the Fc gamma receptor IIB with surface IgM augmented, rather than aborted, this response. In contrast to RP105-activated B cells, blast cells that had been activated by CD40 ligation were unaltered by anti-IgM. On the other hand, CD40-activated B cells became extremely susceptible to Fas- mediated apoptosis, whereas RP105-activated B cells were much less sensitive. Anti-IgM-induced apoptosis in RP105 blasts was independent of Fas, because it was demonstrable with Fas-deficient MRL-lpr/lpr mice. These results demonstrate that the nature of an initial activation signal has a great influence on the fate of activated B cells after (re)engagement of the antigen receptor. RP105, as well as CD40, may be important in this life/death decision.     

A novel B lymphocyte-associated adaptor protein, Bam32, regulates antigen receptor signaling downstream of phosphatidylinositol 3-kinase

We have identified and characterized a novel src homology 2 (SH2) and pleckstrin homology (PH) domain-containing adaptor protein, designated Bam32 (for B cell adaptor molecule of 32 kD). cDNAs encoding the human and mouse Bam32 coding sequences were isolated and the human bam32 gene was mapped to chromosome 4q25-q27. Bam32 is expressed by B lymphocytes, but not T lymphocytes or nonhematopoietic cells. Human germinal center B cells show increased Bam32 expression, and resting B cells rapidly upregulate expression of Bam32 after ligation of CD40, but not immunoglobulin M. Bam32 is tyrosine-phosphorylated upon B cell antigen receptor (BCR) ligation or pervanadate stimulation and associates with phospholipase Cgamma2. After BCR ligation, Bam32 is recruited to the plasma membrane through its PH domain. Membrane recruitment requires phosphatidylinositol 3-kinase (PI3K) activity and an intact PI(3,4, 5)P(3)-binding motif, suggesting that membrane association occurs through binding to 3-phosphoinositides. Expression of Bam32 in B cells leads to a dose-dependent inhibition of BCR-induced activation of nuclear factor of activated T cells (NF-AT), which is blocked by deletion of the PH domain or mutation of the PI(3,4,5)P(3)-binding motif. Thus, Bam32 represents a novel B cell-associated adaptor that regulates BCR signaling downstream of PI3K.     

WIP regulates signaling via the high affinity receptor for immunoglobulin E in mast cells

Wiskott-Aldrich syndrome protein-interacting protein (WIP) stabilizes actin filaments and is important for immunoreceptor-mediated signal transduction leading to actin cytoskeleton rearrangement in T and B cells. Here we report a role for WIP in signaling pathways downstream of the high affinity receptor for immunoglobulin (Ig)E (FcepsilonRI) in mast cells. WIP-deficient bone marrow-derived mast cells (BMMCs) were impaired in their capacity to degranulate and secrete interleukin 6 after FcepsilonRI ligation. Calcium mobilization, phosphorylation of Syk, phospholipase C-g2, and c-Jun NH2-terminal kinase were markedly decreased in WIP-deficient BMMCs. WIP was found to associate with Syk after FcepsilonRI ligation and to inhibit Syk degradation as evidenced by markedly diminished Syk levels in WIP-deficient BMMCs. WIP-deficient BMMCs exhibited no apparent defect in their subcortical actin network and were normal in their ability to form protrusions when exposed to an IgE-coated surface. However, the kinetics of actin changes and the cell shape changes that follow FcepsilonRI signaling were altered in WIP-deficient BMMCs. These results suggest that WIP regulates FcepsilonRI-mediated mast cell activation by regulating Syk levels and actin cytoskeleton rearrangement.     

Regulation of cytokine and toll-like receptor signaling by SOCS family genes

Bacterial lipopolysaccharide (LPS) triggers innate immune responses through the Toll-like receptor (TLR) 4. Regulation of TLR signaling is a key step for inflammation, septic shock and innate/adaptive immunity. TLR signaling is shown to be regulated by cytokines, such as interferon-gamma (positive) and interleukin-10 and IL-4 (negative). However, molecular mechanisms of the regulation of LPS signaling by cytokines have not been clarified. Cytokine signaling is regulated by CIS/SOCS family proteins. Both SOCS1 and SOCS3 can inhibit JAK tyrosine kinase activity. We demonstrate that SOCS1 and SOCS3 play an important regulatory role in macrophages and dendritic cells (DCs) by modulating TLR signaling. SOCS1 negatively regulates not only the JAK/STAT pathway, but also the TLR-NF-kappaB pathway. SOCS3 protein was strongly induced by both IL-6 and IL-10 in the presence of LPS, but selectively inhibited IL-6 signaling. Therefore lack of SOCS3 gene in macrophages resulted in suppression of TLR signaling by hyperactivation of STAT3.     

Entry of B cell receptor into signaling domains is inhibited in tolerant B cells

Signal transduction through the B cell antigen receptor (BCR) is altered in B cells that express a receptor that recognizes self-antigen. To understand the molecular basis for the change in signaling in autoreactive B cells, a transgenic model was used to isolate a homogeneous population of tolerant B lymphocytes. These cells were compared with a similar population of naive B lymphocytes. We show that the BCR from naive B cells enters a detergent-insoluble domain of the cell within 6 s after antigen binding, before a detectable increase in BCR phosphorylation. This fraction appears to be important for signaling because it is enriched for lyn kinase but lacks CD45 tyrosine phosphatase and because the BCR that moves into this domain becomes more highly phosphorylated. Partitioning of the BCR into this fraction is unaffected by src family kinase inhibition. Tolerant B cells do not efficiently partition the BCR into the detergent-insoluble domain, providing an explanation for their reduced tyrosine kinase activation and calcium flux in response to antigen. These results identify an early, regulated step in antigen receptor signaling and self-tolerance.     

Regulatory T cells selectively express toll-like receptors and are activated by lipopolysaccharide

Regulatory CD4 T cells (Treg) control inflammatory reactions to commensal bacteria and opportunist pathogens. Activation of Treg functions during these processes might be mediated by host-derived proinflammatory molecules or directly by bacterial products. We tested the hypothesis that engagement of germline-encoded receptors expressed by Treg participate in the triggering of their function. We report that the subset of CD4 cells known to exert regulatory functions in vivo (CD45RB(low) CD25(+)) selectively express Toll-like receptors (TLR)-4, -5, -7, and -8. Exposure of CD4(+) CD25(+) cells to the TLR-4 ligand lipopolysaccharide (LPS) induces up-regulation of several activation markers and enhances their survival/proliferation. This proliferative response does not require antigen-presenting cells and is augmented by T cell receptor triggering and interleukin 2 stimulation. Most importantly, LPS treatment increases CD4(+) CD25(+) cell suppressor efficiency by 10-fold and reveals suppressive activity in the CD4(+) CD45RB(low) CD25(-) subset that when tested ex-vivo, scores negative. Moreover, LPS-activated Treg efficiently control naive CD4 T cell-dependent wasting disease. These findings provide the first evidence that Treg respond directly to proinflammatory bacterial products, a mechanism that likely contributes to the control of inflammatory responses.     

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.     

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.     

Elucidation of toll-like receptor and adapter protein signaling in vascular dysfunction induced by gram-positive Staphylococcus aureus or gram-negative Escherichia coli

Pathogens contain specific pathogen-associated molecular patterns, which activate pattern recognition receptors of the innate immune system such as Toll-like receptors (TLRs). Although there is a clear evidence of how macrophages sense pathogens, we know less about such processes in vessels. This is critical to understand because activation of vascular cells and the subsequent induction of inflammatory genes by bacteria are crucial events in the development of septic shock. In the current study we have used genetically modified mice to investigate the role of TLRs, adapter proteins, tumor necrosis factor alpha (TNFalpha), and nitric oxide synthase II (NOSII) in vascular dysfunction induced by Gram-positive (Staphylococcus aureus) or Gram-negative (Escherichia coli) bacteria. Our data show that Gram-positive S. aureus or Gram-negative E. coli causes vascular dysfunction via the induction of NOSII. For S. aureus, this process requires TLR2, TLR6, myeloid differentiation factor 88 (MyD88) adapter-like, MyD88, and TNF, but not TLR4 or TLR1. Vascular dysfunction induced by E. coli requires TLR4 but has no requirement for TLR2, TLR1, TLR6, or TNF, and a partial but incomplete requirement of MyD88 and TIR domain-containing adapter inducing interferon-beta. Staphylococcus aureus induced NOSII protein expression in vascular smooth muscle cells but not in macrophages, whereas E. coli induced NOSII in both cell types. Our data are the first to establish the definitive roles of specific TLRs in the sensing of Gram-positive and Gram-negative bacteria by vessels and demonstrate that macrophages and blood vessels may differ in their response to pathogens.     

Hyperbaric oxygen therapy reduces the toll-like receptor signaling pathway in multiple organ failures

Purpose  

Zymosan-induced generalized inflammation is the only experimental model that reproduces characteristics of human multiple organ dysfunction syndrome (MODS). Toll-like receptors (TLRs) are key components in innate immune responses and their signaling pathway is known to activate target genes such as nuclear factor-κB (NF-κB) and cytokines that are involved in inflammation and immune responses. We previously reported that hyperbaric oxygen (HBO) therapy is effective in the treatment of severe zymosan-induced inflammation in MODS. The aim of this study was to investigate the effect of HBO exposure on TLR2 and TLR4 signal transduction and organ dysfunction during MODS induced by zymosan in the rat.     

核因子-κB及Toll样受体4介导脂多糖诱导内皮细胞单层通透性增高

目的:探讨核因子-κB(nuclearfactor-kappaB,NF-κB)及Toll样受体4(Toll-likereceptor4,TLR4)在脂多糖(lipopolysaccharide,LPS)诱导的内皮细胞单层通透性增高中的作用。方法:采用免疫荧光法及改良Boydon小室测定LPS对人脐静脉内皮细胞株ECV-304的单层细胞通透性及其F-肌动蛋白分布的影响;以免疫组织化学染色及RT-PCR法检测LPS刺激细胞NF-κB活化后的核转位及TLR4mRNA的表达。结果:LPS作用ECV-3041h后,免疫组织化学染色证实NF-κB活化后发生核转位;LPS以一定的剂量-时间依赖方式上调TLR4mRNA的表达,ECV-304单层通透性也随之增加。结论:NF-κB及TLR4可能在LPS诱导内皮细胞单层损伤导致通透性增高过程中发挥重要作用。     

八肽缩胆囊素受体在血管内皮细胞中的表达及脂多糖的影响

目的 观察八肽缩胆囊素受体(CCK-R)mRNA在人脐静脉内皮细胞株ECV-304中的表达,并探讨内毒素脂多糖(LPS)对CCK-AR、CCK-BR mRNA表达的影响.方法 培养人脐静脉内皮细胞株ECV-304,以LPS 0.01、0.1、1、10 mg/L孵育ECV-304 2 h或用1 mg/L LPS孵育ECV-304 0.5、2、6、12 h,采用逆转录-聚合酶链反应(RT-PCR)检测CCK-AR、CCK-BR的mRNA表达,并对扩增产物的特异性进行测序分析.结果 与空白对照组比较,0.01、0.1及1 mg/L LPS孵育细胞2 h可剂量依赖性引起CCK-AR及CCK-BR的mRNA表达明显升高(P均<0.05),其中0.01 mg/L LPS诱导CCK-AR mRNA效应不明显,但可明显诱导CCK-BR mRNA表达;与1 mg/L LPS组比较,10 mg/L LPS孵育细胞2 h CCK-AR及CCK-BR的mRNA表达未继续出现明显升高(P均>0.05).与空白对照组比较,1 mg/L LPS孵育细胞0.5～2 h CCK-AR及CCK-BR的mRNA表达呈时间依赖性升高(P均<0.05);与LPS孵育2 h比较,1 mg/L LPS孵育细胞6 h CCK-AR及CCK-BR的mRNA表达明显下降,但仍高于空白对照组(P均<0.05);与LPS孵育6 h比较,1 mg/L LPS孵育细胞12 h CCK-AR及CCK-BR的mRNA表达进一步降低(P均<0.05),且与空白对照组比较已无显著差异(P均>0.05).结论 CCK-AR与CCK-BR的mRNA在ECV-304中均有表达;LPS可诱导CCK-AR及CCK-BR的mRNA表达上调.     

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.     

MicroRNA-29a在脂多糖诱导人单核细胞凋亡中的作用和机制

目的 探讨microRNA-29a (miR-29a)对人单核细胞株THP-1凋亡的作用及其机制.方法 体外培养人单核细胞株THP-1和人胚肾细胞株293T,合成人miR-29a的拟似物(mimic)和抑制剂(inhibitor).用脂质体Lipofectamine RNAiMAX转染miR-29a的mimic或inhibitor进入THP-1细胞,分组处理后收集细胞标本.第1组细胞转染mimic (100 nmol/L) 48 h;第2组细胞先转染inhibitor(100 nmol/L) 24 h,再用脂多糖(LPS)诱导24h,分别用流式细胞仪方法检测两组细胞凋亡,用real time RT-PCR方法检测抗凋亡基因Bcl-2和Mcl-1的表达变化.构建Bcl-2和Mcl-1的荧光素酶报告基因载体,用脂质体Lipofectamine 2000转染293T细胞(DNA质粒和miRNA片段共转染),双荧光素酶报告基因系统(luciferase)检测荧光素酶的表达变化.应用SPSS 13.0统计软件,采取单因素方差分析或t检验进行数据统计分析.结果 THP-1细胞转染miR-29a的mimic48 h后,细胞凋亡较对照组增加(17.38％增加至42.06％);单独用LPS诱导THP-1细胞,24 h后细胞凋亡较对照组增加;THP-1细胞先转染inhibitor 24 h后,再用LPS诱导24 h,细胞凋亡较单独用LPS诱导组减少(由51.50％降至38.09％);THP-1细胞转染miR-29a的mimic后,抗凋亡基因Bcl-2和Mcl-1的表达水平降低明显(P＜0.05).另外,Luciferase检测结果显示,在293T细胞中,双萤光报告系统显示miR-29a可特异抑制带有Bcl-2和Mcl-13'UTR上野生型识别元件的报告基因表达(P＜0.05).结论 上调miR-29a的表达水平能促进THP-1细胞发生凋亡,下调miR-29a的表达水平则能抑制LPS诱导的THP-1细胞凋亡,miR-29a调控THP-1的凋亡水平是通过靶向于两个抗凋亡基因Bcl-2和Mcl-1实现的,提示miR-29a在调控免疫细胞的凋亡过程中具有重要的作用.