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Farlow J, Seo D, Broaders KE, Taylor MJ, Gartner ZJ, Jun YW. Formation of targeted monovalent quantum dots by steric exclusion. Nat Methods 2013; 10:1203-5. [PMID: 24122039 PMCID: PMC3968776 DOI: 10.1038/nmeth.2682] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2013] [Accepted: 08/30/2013] [Indexed: 11/09/2022]
Abstract
Precise control over interfacial chemistry between nanoparticles and other materials remains a major challenge that limits broad application of nanotechnology in biology. To address this challenge, we used 'steric exclusion' to completely convert commercial quantum dots (QDs) into monovalent imaging probes by wrapping each QD with a functionalized oligonucleotide. We demonstrated the utility of these QDs as modular and nonperturbing imaging probes by tracking individual Notch receptors on live cells.
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Affiliation(s)
- Justin Farlow
- 1] Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California, USA. [2] Tetrad Graduate Program, University of California San Francisco, San Francisco, California, USA. [3] Center for Systems and Synthetic Biology, University of California San Francisco, San Francisco, California, USA
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52
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Snodgrass RG, Huang S, Choi IW, Rutledge JC, Hwang DH. Inflammasome-mediated secretion of IL-1β in human monocytes through TLR2 activation; modulation by dietary fatty acids. THE JOURNAL OF IMMUNOLOGY 2013; 191:4337-47. [PMID: 24043885 DOI: 10.4049/jimmunol.1300298] [Citation(s) in RCA: 181] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Many studies have shown that TLR4- and TLR2-deficient mice are protected from high-fat diet-induced inflammation and insulin resistance, suggesting that saturated fatty acids derived from the high-fat diet activate TLR-mediated proinflammatory signaling pathways and induce insulin resistance. However, evidence that palmitic acid, the major dietary saturated fatty acid, can directly activate TLR has not been demonstrated. In this article, we present multiple lines of evidence showing that palmitic acid directly activates TLR2, a major TLR expressed on human monocytes, by inducing heterodimerization with TLR1 in an NADPH oxidase-dependent manner. Dimerization of TLR2 with TLR1 was inhibited by the n-3 fatty acid docosahexaenoic acid. Activation of TLR2 by palmitic acid leads to expression of pro-IL-1β that is cleaved by caspase-1, which is constitutively present in monocytes, to release mature IL-1β. Our results reveal mechanistic insight about how palmitic acid activates TLR2, upregulates NALP3 expression, and induces inflammasome-mediated IL-1β production in human monocytes, which can trigger enhanced inflammation in peripheral tissues, and suggest that these processes are dynamically modulated by the types of dietary fat we consume.
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Affiliation(s)
- Ryan G Snodgrass
- U.S. Department of Agriculture, Agricultural Research Service Western Human Nutrition Research Center, Davis, CA 95616
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53
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van Bergenhenegouwen J, Plantinga TS, Joosten LAB, Netea MG, Folkerts G, Kraneveld AD, Garssen J, Vos AP. TLR2 & Co: a critical analysis of the complex interactions between TLR2 and coreceptors. J Leukoc Biol 2013; 94:885-902. [PMID: 23990624 DOI: 10.1189/jlb.0113003] [Citation(s) in RCA: 108] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
TLRs play a major role in microbe-host interactions and innate immunity. Of the 10 functional TLRs described in humans, TLR2 is unique in its requirement to form heterodimers with TLR1 or TLR6 for the initiation of signaling and cellular activation. The ligand specificity of TLR2 heterodimers has been studied extensively, using specific bacterial and synthetic lipoproteins to gain insight into the structure-function relationship, the minimal active motifs, and the critical dependence on TLR1 or TLR6 for activation. Different from that for specific well-defined TLR2 agonists, recognition of more complex ligands like intact microbes or molecules from endogenous origin requires TLR2 to interact with additional coreceptors. A breadth of data has been published on ligand-induced interactions of TLR2 with additional pattern recognition receptors such as CD14, scavenger receptors, integrins, and a range of other receptors, all of them important factors in TLR2 function. This review summarizes the roles of TLR2 in vivo and in specific immune cell types and integrates this information with a detailed review of our current understanding of the roles of specific coreceptors and ligands in regulating TLR2 functions. Understanding how these processes affect intracellular signaling and drive functional immune responses will lead to a better understanding of host-microbe interactions and will aid in the design of new agents to target TLR2 function in health and disease.
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Hawley KL, Martín-Ruiz I, Iglesias-Pedraz JM, Berwin B, Anguita J. CD14 targets complement receptor 3 to lipid rafts during phagocytosis of Borrelia burgdorferi. Int J Biol Sci 2013; 9:803-10. [PMID: 23983613 PMCID: PMC3753444 DOI: 10.7150/ijbs.7136] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2013] [Accepted: 08/03/2013] [Indexed: 12/03/2022] Open
Abstract
Phagocytosis of Borrelia burgdorferi, the causative agent of Lyme disease, is mediated partly by the interaction of the spirochete with Complement Receptor (CR) 3. CR3 requires the GPI-anchored protein, CD14, in order to efficiently internalize CR3-B. burgdorferi complexes. GPI-anchored proteins reside in cholesterol-rich membrane microdomains, and through its interaction with partner proteins, help initiate signaling cascades. Here, we investigated the role of CD14 on the internalization of B. burgdorferi mediated by CR3. We show that CR3 partly colocalizes with CD14 in lipid rafts. The use of the cholesterol-sequestering compound methyl-β-cyclodextran completely prevents the internalization of the spirochete in CHO cells that co-express CD14 and CR3, while no effect was observed in CD11b-deficient macrophages. These results show that lipid rafts are required for CR3-dependent, but not independent, phagocytosis of B. burgdorferi. Our results also suggest that CD14 interacts with the C-lectin domain of CR3, favoring the formation of multi-complexes that allow their internalization, and the use of β-glucan, a known ligand for the C-lectin domain of CR3, can compensate for the lack of CD14 in CHO cells that express CR3. These results provide evidence to understand the mechanisms that govern the interaction between CR3 and CD14 during the phagocytosis of B. burgdorferi.
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Affiliation(s)
- Kelly L Hawley
- Department of Veterinary and Animal Sciences, University of Massachusetts at Amherst, Amherst, MA 01003, USA
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55
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Lei L, Li H, Yan F, Xiao Y. Hyperlipidemia impaired innate immune response to periodontal pathogen porphyromonas gingivalis in apolipoprotein E knockout mice. PLoS One 2013; 8:e71849. [PMID: 23977160 PMCID: PMC3745424 DOI: 10.1371/journal.pone.0071849] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Accepted: 07/04/2013] [Indexed: 12/18/2022] Open
Abstract
A finely-tuned innate immune response plays a pivotal role in protecting host against bacterial invasion during periodontal disease progression. Hyperlipidemia has been suggested to exacerbate periodontal health condition. However, the underlying mechanism has not been addressed. In the present study, we investigated the effect of hyperlipidemia on innate immune responses to periodontal pathogen Porphyromonas gingivalis infection. Apolipoprotein E-deficient and wild-type mice at the age of 20 weeks were used for the study. Peritoneal macrophages were isolated and subsequently used for the study of viable P. gingivalis infection. ApoE−/− mice demonstrated inhibited iNOS production and impaired clearance of P. gingivalis in vitro and in vivo; furthermore, ApoE−/− mice displayed disrupted cytokine production pattern in response to P. gingivalis, with a decreased production of tumor necrosis factor-α, interleukin-6 (IL-6), IL-1β and monocyte chemotactic protein-1. Microarray data demonstrated that Toll-like receptor (TLR) and NOD-like receptor (NLR) pathway were altered in ApoE−/− mice macrophages; further analysis of pattern recognition receptors (PRRs) demonstrated that expression of triggering receptors on myeloid cells-1 (TREM-1), an amplifier of the TLR and NLR pathway, was decreased in ApoE−/− mice macrophages, leading to decreased recruitment of NF-κB onto the promoters of the TNF-α and IL-6. Our data suggest that in ApoE−/− mice hyperlipidemia disrupts the expression of PRRs, and cripples the host’s capability to generate sufficient innate immune response to P. gingivalis, which may facilitate immune evasion, subgingival colonization and establishment of P. gingivalis in the periodontal niche.
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MESH Headings
- Animals
- Apolipoproteins E/deficiency
- Apolipoproteins E/genetics
- Bacteroidaceae Infections/immunology
- Bacteroidaceae Infections/microbiology
- Cells, Cultured
- Cytokines/genetics
- Cytokines/metabolism
- Gene Expression Regulation/immunology
- Hyperlipidemias/complications
- Hyperlipidemias/immunology
- Immunity, Innate
- Macrophages, Peritoneal/immunology
- Macrophages, Peritoneal/metabolism
- Macrophages, Peritoneal/microbiology
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Periodontal Diseases/immunology
- Periodontal Diseases/microbiology
- Phagocytosis
- Porphyromonas gingivalis/immunology
- Promoter Regions, Genetic
- Protein Binding
- Receptors, Pattern Recognition/genetics
- Receptors, Pattern Recognition/metabolism
- Transcription Factor RelA/metabolism
- Transcriptome
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Affiliation(s)
- Lang Lei
- School and Hospital of Stomatology, Fujian Medical University, Fuzhou, China
| | - Houxuan Li
- School and Hospital of Stomatology, Fujian Medical University, Fuzhou, China
| | - Fuhua Yan
- Institute and Hospital of Stomatology, Nanjing University Medical School, Nanjing, Jiangsu, China
- * E-mail: (FY); (YX)
| | - Yin Xiao
- Bone Research Lab, Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Australia
- * E-mail: (FY); (YX)
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Ciesielski F, Griffin DC, Rittig M, Moriyón I, Bonev BB. Interactions of lipopolysaccharide with lipid membranes, raft models — A solid state NMR study. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:1731-42. [DOI: 10.1016/j.bbamem.2013.03.029] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Revised: 03/08/2013] [Accepted: 03/28/2013] [Indexed: 01/09/2023]
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57
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Herre J, Grönlund H, Brooks H, Hopkins L, Waggoner L, Murton B, Gangloff M, Opaleye O, Chilvers ER, Fitzgerald K, Gay N, Monie T, Bryant C. Allergens as immunomodulatory proteins: the cat dander protein Fel d 1 enhances TLR activation by lipid ligands. THE JOURNAL OF IMMUNOLOGY 2013; 191:1529-35. [PMID: 23878318 DOI: 10.4049/jimmunol.1300284] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Allergic responses can be triggered by structurally diverse allergens. Most allergens are proteins, yet extensive research has not revealed how they initiate the allergic response and why the myriad of other inhaled proteins do not. Among these allergens, the cat secretoglobulin protein Fel d 1 is a major allergen and is responsible for severe allergic responses. In this study, we show that similar to the mite dust allergen Der p 2, Fel d 1 substantially enhances signaling through the innate receptors TLR4 and TLR2. In contrast to Der p 2, however, Fel d 1 does not act by mimicking the TLR4 coreceptor MD2 and is not able to bind stably to the TLR4/MD2 complex in vitro. Fel d 1 does, however, bind to the TLR4 agonist LPS, suggesting that a lipid transfer mechanism may be involved in the Fel d 1 enhancement of TLR signaling. We also show that the dog allergen Can f 6, a member of a distinct class of lipocalin allergens, has very similar properties to Fel d 1. We propose that Fel d 1 and Can f 6 belong to a group of allergen immunomodulatory proteins that enhance innate immune signaling and promote airway hypersensitivity reactions in diseases such as asthma.
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Affiliation(s)
- Jurgen Herre
- Department of Medicine, University of Cambridge School of Medicine, Cambridge CB2 0QQ, United Kingdom
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58
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A quantitative comparison of single-dye tracking analysis tools using Monte Carlo simulations. PLoS One 2013; 8:e64287. [PMID: 23737978 PMCID: PMC3667770 DOI: 10.1371/journal.pone.0064287] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2013] [Accepted: 04/10/2013] [Indexed: 11/19/2022] Open
Abstract
Single-particle tracking (SPT) is widely used to study processes from membrane receptor organization to the dynamics of RNAs in living cells. While single-dye labeling strategies have the benefit of being minimally invasive, this comes at the expense of data quality; typically a data set of short trajectories is obtained and analyzed by means of the mean square displacements (MSD) or the distribution of the particles' displacements in a set time interval (jump distance, JD). To evaluate the applicability of both approaches, a quantitative comparison of both methods under typically encountered experimental conditions is necessary. Here we use Monte Carlo simulations to systematically compare the accuracy of diffusion coefficients (D-values) obtained for three cases: one population of diffusing species, two populations with different D-values, and a population switching between two D-values. For the first case we find that the MSD gives more or equally accurate results than the JD analysis (relative errors of D-values <6%). If two diffusing species are present or a particle undergoes a motion change, the JD analysis successfully distinguishes both species (relative error <5%). Finally we apply the JD analysis to investigate the motion of endogenous LPS receptors in live macrophages before and after treatment with methyl-β-cyclodextrin and latrunculin B.
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59
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Fernandez-Lizarbe S, Montesinos J, Guerri C. Ethanol induces TLR4/TLR2 association, triggering an inflammatory response in microglial cells. J Neurochem 2013; 126:261-73. [PMID: 23600947 DOI: 10.1111/jnc.12276] [Citation(s) in RCA: 121] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2013] [Revised: 04/11/2013] [Accepted: 04/17/2013] [Indexed: 02/06/2023]
Abstract
Alcohol consumption can induce brain damage, demyelination, and neuronal death, although the mechanisms are poorly understood. Toll-like receptors are sensors of the innate immune system and their activation induces inflammatory processes. We have reported that ethanol activates and recruits Toll-like receptor (TLR)4 receptors within the lipid rafts of glial cells, triggering the production of inflammatory mediators and causing neuroinflammation. Since TLR2 can also participate in the glial response and in the neuroinflammation, we investigate the effects of ethanol on TLR4/TLR2 responses. Here, we demonstrate that ethanol up-regulates TLR4 and TLR2 expression in microglial cells, inducing the production of inflammatory mediators which triggers reactive oxygen species generation and neuronal apoptosis. Ethanol also promotes TLR4/TLR2 recruitment into lipid rafts-caveolae, mimicking their activation by their ligands, lipopolysaccharide, and lipoteichoic acid (LTA). Immunoprecipitation and confocal microscopy studies reveal that ethanol induces a physical association between TLR2 and TLR4 receptors, suggesting the formation of heterodimers. Using microglia from either TLR2 or TLR4 knockout mice, we show that TLR2 potentiates the effects of ethanol on the TLR4 response reflected by the activation of MAPKs and inducible NO synthase. In summary, we provide evidence for a mechanism by which ethanol triggers TLR4/TLR2 association contributing to the neuroinflammation and neurodegeneration associated with alcohol abuse.
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Affiliation(s)
- Sara Fernandez-Lizarbe
- Department of Cellular Pathology, Príncipe Felipe Research Centre, Eduardo Primo Yúfera, Valencia, Spain
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60
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Synergic activation of toll-like receptor (TLR) 2/6 and 9 in response to Ureaplasma parvum & urealyticum in human amniotic epithelial cells. PLoS One 2013; 8:e61199. [PMID: 23593431 PMCID: PMC3625198 DOI: 10.1371/journal.pone.0061199] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Accepted: 03/07/2013] [Indexed: 12/04/2022] Open
Abstract
Ureaplasma species are the most frequently isolated microorganisms inside the amniotic cavity and have been associated with spontaneous abortion, chorioamnionitis, premature rupture of the membranes (PROM), preterm labour (PL) pneumonia in neonates and bronchopulmonary dysplasia in neonates. The mechanisms by which Ureaplasmas cause such diseases remain unclear, but it is believed that inappropriate induction of inflammatory responses is involved, triggered by the innate immune system. As part of its mechanism of activation, the innate immune system employs germ-lined encoded receptors, called pattern recognition receptors (PRRs) in order to “sense” pathogens. One such family of PRRs are the Toll like receptor family (TLR). In the current study we aimed to elucidate the role of TLRs in Ureaplasma-induced inflammation in human amniotic epithelial cells. Using silencing, as well as human embryonic kidney (HEK) transfected cell lines, we demonstrate that TLR2, TLR6 and TLR9 are involved in the inflammatory responses against Ureaplasma parvum and urealyticum serovars. Ureaplasma lipoproteins, such as Multiple Banded antigen (MBA), trigger responses via TLR2/TLR6, whereas the whole bacterium is required for TLR9 activation. No major differences were observed between the different serovars. Cell activation by Ureaplasma parvum and urealyticum seem to require lipid raft function and formation of heterotypic receptor complexes comprising of TLR2 and TLR6 on the cell surface and TLR9 intracellularly.
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61
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Chakraborty M, Jiang XC. Sphingomyelin and its role in cellular signaling. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2013; 991:1-14. [PMID: 23775687 DOI: 10.1007/978-94-007-6331-9_1] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Sphingolipid de novo biosynthesis is related with metabolic diseases. However, the mechanism is still not quite clear. Sphingolipids are ubiquitous and critical components of biological membranes. Their biosynthesis starts with soluble precursors in the endoplasmic reticulum and culminates in the Golgi complex and plasma membrane. The interaction of sphingomyelin, cholesterol, and glycosphingolipid drives the formation of plasma membrane rafts. Lipid rafts have been shown to be involved in cell -signaling, lipid and protein sorting, and membrane trafficking. It is well known that toll-like receptors, class A and B scavenger receptors, and insulin receptor are located in lipid rafts. Sphingomyelin is also a reservoir for other sphingolipids. So, sphingomyelin has important impact in cell -signaling through its structural role in lipid rafts or its catabolic inter-mediators, such as ceramide and glycoceramide. In this chapter, we will discuss both aspects.
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Affiliation(s)
- Mahua Chakraborty
- Department of Cell Biology, SUNY Downstate Medical Center, Brooklyn, NY 11203, USA
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62
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Gauss A, Buchholz I, Zahn A, Schmitz G, Stremmel W, Fuellekrug J, Ehehalt R. Flotillin-2 expression in the human gut: from a cell model to human tissue in health and inflammatory bowel diseases. Int J Med Sci 2013; 10:1259-70. [PMID: 23983584 PMCID: PMC3752715 DOI: 10.7150/ijms.6358] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/29/2013] [Accepted: 07/22/2013] [Indexed: 01/01/2023] Open
Abstract
BACKGROUND AND AIMS The etiopathogenesis of inflammatory bowel diseases (IBD) remains largely unexplained. Flotillins (flotillin-1 and flotillin-2) are ubiquitous proteins which have been linked to inflammation and regeneration. We hypothesized that alterations in the expression of flotillin-2 in enterocytes may be related to the pathogenesis of IBD as a classical example of an inflammatory disorder of mostly unknown origin. METHODS Cell and tissue localization of flotillin-2 (and -1) were investigated by immunofluorescent staining in 1. polarized and unpolarized CaCo-2w cells as a model of human enterocytes (native and after TNFα stimulation) and 2. intestinal biopsies from controls, patients with ulcerative colitis (UC) and patients with Crohn's disease (CD). For quantification of flotillin-2, we analyzed its expression in ileal and colonic biopsies from controls, UC patients and CD patients using real-time RT-PCR, Western blot and indirect immunofluorescence. RESULTS In polarized CaCo-2w cells and human enterocytes in biopsies, flotillins were localized at the basolateral membrane and on subapical vesicles, but not in the apical membrane. Flotillin-2 expression did not differ between UC patients, CD patients and controls. However, it was significantly higher in colonic biopsies compared to ileal biopsies in all groups. CONCLUSIONS By virtue of its abundant expression in enterocytes, flotillin-2 must have an essential function in intestinal physiology, especially in the colon. Yet our data could not link flotillin-2 to the pathogenesis of IBD.
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Affiliation(s)
- Annika Gauss
- University Hospital Heidelberg, Department of Gastroenterology, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
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63
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Abstract
Atherosclerosis is the major cause of mortality in the developed countries. Although presently known risk factors have some predictive value for the disease, a major part of the variability in this process remains unexplained. It is extremely important to find new approaches for better understanding of the disease and for treating it. Exploration of the sphingolipid metabolism is one of these approaches. Sphingolipids are a large class of lipids with structural and signaling functions. Recent researches indicated that these lipids play important roles in the development of atherosclerosis. In this chapter, we summarized the major findings in the field.
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Affiliation(s)
- Xian-Cheng Jiang
- Department of Cell Biology, SUNY Downstate Medical Center, Brooklyn, NY 11203, USA.
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64
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Aaron JS, Carson BD, Timlin JA. Characterization of differential Toll-like receptor responses below the optical diffraction limit. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2012; 8:3041-9. [PMID: 22807232 PMCID: PMC3613986 DOI: 10.1002/smll.201200106] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2012] [Revised: 04/25/2012] [Indexed: 05/18/2023]
Abstract
Many membrane receptors are recruited to specific cell surface domains to form nanoscale clusters upon ligand activation. This step appears to be necessary to initiate cell signaling, including pathways in innate immune system activation. However, virulent pathogens such as Yersinia pestis (the causative agent of plague) are known to evade innate immune detection, in contrast to similar microbes (such as Escherichia coli) that elicit a robust response. This disparity has been partly attributed to the structure of lipopolysaccharides (LPS) on the bacterial cell wall, which are recognized by the innate immune receptor TLR4. It is hypothesized that nanoscale differences exist between the spatial clustering of TLR4 upon binding of LPS derived from Y. pestis and E. coli. Although optical imaging can provide exquisite details of the spatial organization of biomolecules, there is a mismatch between the scale at which receptor clustering occurs (<300 nm) and the optical diffraction limit (>400 nm). The last decade has seen the emergence of super-resolution imaging methods that effectively break the optical diffraction barrier to yield truly nanoscale information in intact biological samples. This study reports the first visualizations of TLR4 distributions on intact cells at image resolutions of <30 nm using a novel, dual-color stochastic optical reconstruction microscopy (STORM) technique. This methodology permits distinction between receptors containing bound LPS from those without at the nanoscale. Importantly, it is also shown that LPS derived from immunostimulatory bacteria result in significantly higher LPS-TLR4 cluster sizes and a nearly twofold greater ligand/receptor colocalization as compared to immunoevading LPS.
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Affiliation(s)
- Jesse S. Aaron
- Sandia National Laboratories PO Box 5800, MS-0895 Albuquerque, NM 87185
| | - Bryan D. Carson
- Sandia National Laboratories PO Box 5800, MS-0895 Albuquerque, NM 87185
| | - Jerilyn A. Timlin
- Sandia National Laboratories PO Box 5800, MS-0895 Albuquerque, NM 87185
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65
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Fine-Coulson K, Reaves BJ, Karls RK, Quinn FD. The role of lipid raft aggregation in the infection of type II pneumocytes by Mycobacterium tuberculosis. PLoS One 2012; 7:e45028. [PMID: 23024786 PMCID: PMC3443240 DOI: 10.1371/journal.pone.0045028] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2012] [Accepted: 08/11/2012] [Indexed: 11/18/2022] Open
Abstract
Dynamic, cholesterol-dense regions of the plasma membrane, known as lipid rafts (LR), have been observed to develop during and may be directly involved in infection of host cells by various pathogens. This study focuses on LR aggregation induced in alveolar epithelial cells during infection with Mycobacterium tuberculosis (Mtb) bacilli. We report dose- and time-dependent increases in LR aggregation after infection with three different strains at multiplicities of infection of 1, 10 and 100 from 2-24 hr post infection (hpi). Specific strain-dependent variations were noted among H37Rv, HN878 and CDC1551 with H37Rv producing the most significant increase from 15 aggregates per cell (APC) to 27 APC at MOI 100 during the 24 hour infection period. Treatment of epithelial cells with Culture Filtrate Protein, Total Lipids and gamma-irradiated whole cells from each strain failed to induce the level of LR aggregation observed during infection with any of the live strains. However, filtered supernatants from infected epithelial cells did produce comparable LR aggregation, suggesting a secreted mycobacterial product produced during infection of host cells is responsible for LR aggregation. Disruption of lipid raft formation prior to infection indicates that Mtb bacilli utilize LR aggregates for internalization and survival in epithelial cells. Treatment of host cells with the LR-disruption agent Filipin III produced a nearly 22% reduction in viable bacteria for strains H37Rv and HN878, and a 7% reduction for strain CDC1551 after 6 hpi. This study provides evidence for significant mycobacterial-induced changes in the plasma membrane of alveolar epithelial cells and that Mtb strains vary in their ability to facilitate aggregation and utilization of LR.
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Affiliation(s)
- Kari Fine-Coulson
- Department of Infectious Diseases, University of Georgia, Athens, Georgia, United States of America
| | - Barbara J. Reaves
- Department of Infectious Diseases, University of Georgia, Athens, Georgia, United States of America
| | - Russell K. Karls
- Department of Infectious Diseases, University of Georgia, Athens, Georgia, United States of America
| | - Frederick D. Quinn
- Department of Infectious Diseases, University of Georgia, Athens, Georgia, United States of America
- * E-mail:
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66
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Nishiyama A, Isobe H, Iwao Y, Takano T, Hung WC, Taneike I, Nakagawa S, Dohmae S, Iwakura N, Yamamoto T. Accumulation of staphylococcal Panton-Valentine leukocidin in the detergent-resistant membrane microdomains on the target cells is essential for its cytotoxicity. ACTA ACUST UNITED AC 2012; 66:343-52. [PMID: 22924956 DOI: 10.1111/j.1574-695x.2012.01027.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2011] [Revised: 07/24/2012] [Accepted: 07/27/2012] [Indexed: 12/23/2022]
Abstract
The mechanisms for the cytotoxicity of staphylococcal Panton-Valentine leukocidin (PVL), a pore-forming toxin consisting of LukS-PV and LukF-PV, in human immune cells are still unclear. Because LukS-PV binds to ganglioside GM1, a constituent of detergent-resistant membrane microdomains (DRMs) of the plasma membrane, the role of DRMs in PVL cytotoxicity was examined in human polymorphonuclear neutrophils (PMNs), monocytes, HL-60 cells, and THP-1 cells. PVL binding capacities in HL-60 and THP-1 cells were higher than those in PMNs and monocytes; however, the PVL concentration to obtain more than 80% cell lysis in HL-60 cells was 10 times higher than that in PMNs and PVL even at such concentration induced < 10% cell lysis in THP-1 cells. After incubation of PMNs with LukS-PV, more than 90% of LukS-PV bound to the detergent-soluble membranes. Subsequent incubation with LukF-PV at 4 °C induced the accumulation of more than 70% of PVL components and 170- to 220-kDa complex formation in DRMs in an actin-independent manner. However, only 30% of PVL was found, and complex formation was under detectable level in DRMs in HL-60 cells. PVL did not accumulate in DRMs in THP-1 cells. Our observations strongly indicate that PVL accumulation in DRMs is essential for PVL cytotoxicity.
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Affiliation(s)
- Akihito Nishiyama
- Division of Bacteriology, Department of Infectious Disease Control and International Medicine, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
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Ciesielski F, Davis B, Rittig M, Bonev BB, O'Shea P. Receptor-independent interaction of bacterial lipopolysaccharide with lipid and lymphocyte membranes; the role of cholesterol. PLoS One 2012; 7:e38677. [PMID: 22685597 PMCID: PMC3369841 DOI: 10.1371/journal.pone.0038677] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2012] [Accepted: 05/10/2012] [Indexed: 01/18/2023] Open
Abstract
Lipopolysaccharide (LPS) is a major constituent of bacterial outer membranes where it makes up the bulk of the outer leaflet and plays a key role as determinant of bacterial interactions with the host. Membrane-free LPS is known to activate T-lymphocytes through interactions with Toll-like receptor 4 via multiprotein complexes. In the present study, we investigate the role of cholesterol and membrane heterogeneities as facilitators of receptor-independent LPS binding and insertion, which underpin bacterial interactions with the host in symbiosis, pathogenesis and cell invasion. We use fluorescence spectroscopy to investigate the interactions of membrane-free LPS from intestinal Gram-negative organisms with cholesterol-containing model membranes and with T-lymphocytes. LPS preparations from Klebsiella pneumoniae and Salmonella enterica were found to bind preferentially to mixed lipid membranes by comparison to pure PC bilayers. The same was observed for LPS from the symbiote Escherichia coli but with an order of magnitude higher dissociation constant. Insertion of LPS into model membranes confirmed the preference for sphimgomyelin/cholesterol-containing systems. LPS insertion into Jurkat T-lymphocyte membranes reveals that they have a significantly greater LPS-binding capacity by comparison to methyl-β-cyclodextrin cholesterol-depleted lymphocyte membranes, albeit at slightly lower binding rates.
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Affiliation(s)
- Filip Ciesielski
- School of Biomedical Sciences, University of Nottingham, Nottingham, United Kingdom
| | - Benjamin Davis
- School of Biology, University of Nottingham, Nottingham, United Kingdom
| | - Michael Rittig
- School of Biomedical Sciences, University of Nottingham, Nottingham, United Kingdom
| | - Boyan B. Bonev
- School of Biomedical Sciences, University of Nottingham, Nottingham, United Kingdom
- * E-mail: (BBB); (PS)
| | - Paul O'Shea
- School of Biology, University of Nottingham, Nottingham, United Kingdom
- * E-mail: (BBB); (PS)
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68
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The role of inflammatory processes in Alzheimer's disease. Inflammopharmacology 2012; 20:109-26. [PMID: 22535513 DOI: 10.1007/s10787-012-0130-z] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2011] [Accepted: 03/05/2012] [Indexed: 02/07/2023]
Abstract
It has become increasingly clear that inflammatory processes play a significant role in the pathophysiology of Alzheimer's disease (AD). Neuroinflammation is characterized by the activation of astrocytes and microglia and the release of proinflammatory cytokines and chemokines. Vascular inflammation, mediated largely by the products of endothelial activation, is accompanied by the production and the release of a host of inflammatory factors which contribute to vascular, immune, and neuronal dysfunction. The complex interaction of these processes is still only imperfectly understood, yet as the mechanisms continue to be elucidated, targets for intervention are revealed. Although many of the studies to date on therapeutic or preventative strategies for AD have been narrowly focused on single target therapies, there is accumulating evidence to suggest that the most successful treatment strategy will likely incorporate a sequential, multifactorial approach, addressing direct neuronal support, general cardiovascular health, and interruption of deleterious inflammatory pathways.
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69
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Activation of myeloid cell-specific adhesion class G protein-coupled receptor EMR2 via ligation-induced translocation and interaction of receptor subunits in lipid raft microdomains. Mol Cell Biol 2012; 32:1408-20. [PMID: 22310662 DOI: 10.1128/mcb.06557-11] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The adhesion class G protein-coupled receptors (adhesion-GPCRs) play important roles in diverse biological processes ranging from immunoregulation to tissue polarity, angiogenesis, and brain development. These receptors are uniquely modified by self-catalytic cleavage at a highly conserved GPCR proteolysis site (GPS) dissecting the receptor into an extracellular subunit (α) and a seven-pass transmembrane subunit (β) with cellular adhesion and signaling functions, respectively. Using the myeloid cell-restricted EMR2 receptor as a paradigm, we exam the mechanistic relevance of the subunit interaction and demonstrate a critical role for GPS autoproteolysis in mediating receptor signaling and cell activation. Interestingly, two distinct receptor complexes are identified as a result of GPS proteolysis: one consisting of a noncovalent α-β heterodimer and the other comprising two completely independent receptor subunits which distribute differentially in membrane raft microdomains. Finally, we show that receptor ligation induces subunit translocation and colocalization within lipid rafts, leading to receptor signaling and inflammatory cytokine production by macrophages. Our present data resolve earlier conflicting results and provide a new mechanism of receptor signaling, as well as providing a paradigm for signal transduction within the adhesion-GPCR family.
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70
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Mani V, Weber TE, Baumgard LH, Gabler NK. Growth and Development Symposium: Endotoxin, inflammation, and intestinal function in livestock. J Anim Sci 2012; 90:1452-65. [PMID: 22247110 DOI: 10.2527/jas.2011-4627] [Citation(s) in RCA: 127] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Endotoxin, also referred to as lipopolysaccharide (LPS), can stimulate localized or systemic inflammation via the activation of pattern recognition receptors. Additionally, endotoxin and inflammation can regulate intestinal epithelial function by altering integrity, nutrient transport, and utilization. The gastrointestinal tract is a large reservoir of both gram-positive and gram-negative bacteria, of which the gram-negative bacteria serve as a source of endotoxin. Luminal endotoxin can enter circulation via two routes: 1) nonspecific paracellular transport through epithelial cell tight junctions, and 2) transcellular transport through lipid raft membrane domains involving receptor-mediated endocytosis. Paracellular transport of endotoxin occurs through dissociation of tight junction protein complexes resulting in reduced intestinal barrier integrity, which can be a result of enteric disease, inflammation, or environmental and metabolic stress. Transcellular transport, via specialized membrane regions rich in glycolipids, sphingolipids, cholesterol, and saturated fatty acids, is a result of raft recruitment of endotoxin-related signaling proteins leading to endotoxin signaling and endocytosis. Both transport routes and sensitivity to endotoxin may be altered by diet and environmental and metabolic stresses. Intestinal-derived endotoxin and inflammation result in suppressed appetite, activation of the immune system, and partitioning of energy and nutrients away from growth toward supporting the immune system requirements. In livestock, this leads to the suppression of growth, particularly suppression of lean tissue accretion. In this paper, we summarize the evidence that intestinal transport of endotoxin and the subsequent inflammation leads to decrease in the production performance of agricultural animals and we present an overview of endotoxin detoxification mechanisms in livestock.
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Affiliation(s)
- V Mani
- Department of Animal Science, Iowa State University, Ames 50011, USA
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71
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Aye ILMH, Waddell BJ, Mark PJ, Keelan JA. Oxysterols exert proinflammatory effects in placental trophoblasts via TLR4-dependent, cholesterol-sensitive activation of NF-κB. Mol Hum Reprod 2012; 18:341-53. [PMID: 22238372 DOI: 10.1093/molehr/gas001] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Oxidized cholesterol metabolites (oxysterols) promote inflammation in a variety of cell types and are thought to be involved in a number of disease pathologies. Oxysterol concentrations are increased in pregnancy, together with systemic oxidative stress and inflammation. We tested the hypothesis that oxysterols 25-hydroxycholesterol (25-OHC) and 7-ketocholesterol (7-ketoC) promote placental trophoblast inflammation, and determined the mechanisms involved. Treatment of primary trophoblasts in culture with 25-OHC and 7-ketoC increased the production of proinflammatory cytokines (interleukin-6, macrophage inflammatory protein-1β and tumour necrosis factor-α) in a concentration-dependent fashion. Inhibition of TLR4 activation using selective inhibitors of TLR4 complex formation (OxPAPC) or signalling transmission (CLI095) prevented lipopolysaccharide (LPS)- and oxysterol-induced inflammatory cytokine production. Pretreatment of trophoblasts with selective inhibitors of I-kB kinase activity (parthenolide and TPCA-1) reduced oxysterol- and LPS-stimulated inflammatory responses, consistent with the involvement of the nuclear factor kappa B (NF-κB) pathway downstream of TLR4 signalling. Both oxysterols also increased the phosphorylation and nuclear localization of NF-κB subunit p65/RelA. Oxysterols are also known to activate liver X receptors (LXRs) which can inhibit inflammatory signalling, either directly or indirectly via membrane cholesterol reduction. Treatment with the LXR agonist, T0901317, exerted significant anti-inflammatory effects, reducing LPS- and oxysterol-driven cytokine production. Treatment with methyl-β-cyclodextrin to deplete membrane microdomain cholesterol and thereby disrupt TLR4 signalling, similarly abrogated their effects. Together, these findings indicate that although oxysterols likely activate both pro- and anti-inflammatory pathways in the placenta, the predominant effect is the promotion of placental inflammation via TLR4-dependent activation of NF-κB.
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Affiliation(s)
- Irving L M H Aye
- School of Women's and Infants' Health, Faculty of Medicine, Dentistry and Health Sciences, King Edward Memorial Hospital, 374 Bagot Rd, Subiaco, The University of Western Australia, Perth, WA 6008, Australia.
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Lemaire-Ewing S, Lagrost L, Néel D. Lipid rafts: a signalling platform linking lipoprotein metabolism to atherogenesis. Atherosclerosis 2011; 221:303-10. [PMID: 22071358 DOI: 10.1016/j.atherosclerosis.2011.10.016] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/08/2011] [Revised: 09/22/2011] [Accepted: 10/12/2011] [Indexed: 01/16/2023]
Abstract
Lipid rafts are microdomains of the plasma membrane which are enriched in cholesterol and sphingolipids. They serve as a platform for signal transduction, in particular during immune and inflammatory responses. As hypercholesterolemia and inflammation are two key elements of atherogenesis, it is conceivable that the cholesterol and cholesterol oxide content of lipid rafts might influence the inflammatory signalling pathways, thus modulating the development of atherosclerosis. In support of this emerging view, lipid rafts have been shown to be involved in several key steps of atherogenesis, such as the oxysterol-mediated apoptosis of vascular cells, the blunted ability of high density lipoproteins (HDL) to exert anti-inflammatory effects, and the exacerbated secretion of pro-inflammatory cytokines by immune cells. Additional studies are now required to address the relative contribution of lipid raft abnormalities to the pathophysiology of atherosclerosis and cardiovascular disease.
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74
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Falvo JV, Ranjbar S, Jasenosky LD, Goldfeld AE. Arc of a vicious circle: pathways activated by Mycobacterium tuberculosis that target the HIV-1 long terminal repeat. Am J Respir Cell Mol Biol 2011; 45:1116-24. [PMID: 21852682 DOI: 10.1165/rcmb.2011-0186tr] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
In this review, we examine how a subset of signal transduction cascades initiated by Mycobacterium tuberculosis (Mtb) infection modulates transcription mediated by the human immunodeficiency virus type 1 long terminal repeat (HIV-1 LTR). We describe two distinct phases of signaling that target transcription factors known to bind the HIV-1 LTR, and thus drive viral transcription and replication, in cells of the Mtb-infected host. First, Mtb-derived molecules, including cell wall components and DNA, interact with a number of host pattern recognition receptors. Second, cytokines and chemokines secreted in response to Mtb infection initiate signal transduction cascades through their cognate receptors. Given the variation in cell wall components among distinct clinical Mtb strains, the initial pattern recognition receptor interaction leading to direct LTR activation and differential cytokine and chemokine production is likely to be an important aspect of Mtb strain-specific regulation of HIV-1 transcription and replication. Improved understanding of these molecular mechanisms in the context of bacterial and host genetics should provide key insights into the accelerated viral replication and disease progression characteristic of HIV/TB coinfection.
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Affiliation(s)
- James V Falvo
- Immune Disease Institute and Program in Cellular and Molecular Medicine, Children’s Hospital Boston, MA, USA.
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75
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Location, location, location: is membrane partitioning everything when it comes to innate immune activation? Mediators Inflamm 2011; 2011:186093. [PMID: 21765613 PMCID: PMC3134105 DOI: 10.1155/2011/186093] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2010] [Accepted: 03/27/2011] [Indexed: 01/25/2023] Open
Abstract
In the last twenty years, the general view of the plasma membrane has changed from a homogeneous arrangement of lipids to a mosaic of microdomains. It is currently thought that islands of highly ordered saturated lipids and cholesterol, which are laterally mobile, exist in the plane of the plasma membrane. Lipid rafts are thought to provide a means to explain the spatial segregation of certain signalling pathways emanating from the cell surface. They seem to provide the necessary microenvironment in order for certain specialised signalling events to take place, such as the innate immune recognition. The innate immune system seems to employ germ-lined encoded receptors, called pattern recognition receptors (PRRs), in order to detect pathogens. One family of such receptors are the Toll-like receptors (TLRs), which are the central “sensing” apparatus of the innate immune system. In recent years, it has become apparent that TLRs are recruited into membrane microdomains in response to ligands. These nanoscale assemblies of sphingolipid, cholesterol, and TLRs stabilize and coalesce, forming signalling platforms, which transduce signals that lead to innate immune activation. In the current paper, we will investigate all past and current literature concerning recruitment of extracellular and intracellular TLRs into lipid rafts and how this membrane organization modulates innate immune responses.
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76
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Koistinaho J, Malm T, Goldsteins G. Glycogen synthase kinase-3β: a mediator of inflammation in Alzheimer's disease? Int J Alzheimers Dis 2011; 2011:129753. [PMID: 21629736 PMCID: PMC3100542 DOI: 10.4061/2011/129753] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2011] [Accepted: 03/04/2011] [Indexed: 02/03/2023] Open
Abstract
Proliferation and activation of microglial cells is a neuropathological characteristic of brain injury and neurodegeneration, including Alzheimer's disease. Microglia act as the first and main form of immune defense in the nervous system. While the primary function of microglia is to survey and maintain the cellular environment optimal for neurons in the brain parenchyma by actively scavenging the brain for damaged brain cells and foreign proteins or particles, sustained activation of microglia may result in high production of proinflammatory mediators that disturb normal brain functions and even cause neuronal injury. Glycogen synthase kinase-3β has been recently identified as a major regulator of immune system and mediates inflammatory responses in microglia. Glycogen synthase kinase-3β has been extensively investigated in connection to tau and amyloid β toxicity, whereas reports on the role of this enzyme in neuroinflammation in Alzheimer's disease are negligible. Here we review and discuss the role of glycogen synthase-3β in immune cells in the context of Alzheimer's disease pathology.
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Affiliation(s)
- Jari Koistinaho
- Department of Neurobiology, A.I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, P.O. Box 1627, 70211 Kuopio, Finland
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Jo HY, Kim SY, Lee S, Jeong S, Kim SJ, Kang TM, Lee KY. Kir3.1 channel is functionally involved in TLR4-mediated signaling. Biochem Biophys Res Commun 2011; 407:687-91. [DOI: 10.1016/j.bbrc.2011.03.076] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2011] [Accepted: 03/16/2011] [Indexed: 01/12/2023]
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Liévin-Le Moal V, Beau I, Rougeaux C, Kansau I, Fabrega S, Brice C, Korotkova N, Moseley SL, Servin AL. Apical expression of human full-length hCEACAM1-4L protein renders the Madin Darby Canine Kidney cells responsive to lipopolysaccharide leading to TLR4-dependent Erk1/2 and p38 MAPK signalling. Cell Microbiol 2011; 13:764-85. [PMID: 21352462 DOI: 10.1111/j.1462-5822.2011.01575.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
CEACAM1 expressed by granulocytes and epithelial cells is recognized as a membrane-associated receptor by some Gram-negative pathogens. Here we report a previously unsuspected role of human CEACAM1-4L (hCEACAM1-4L) in polarized epithelial cells. We find that in contrast with non-transfected cells, Madin Darby Canine Kidney strain II (MDCK) engineered for the apical expression of the long cytoplasmic chain protein hCEACAM1-4L showed a serum-independent increase in the phosphorylation of the extracellular signal-regulated kinase 1/2 (Erk1/2) and p38 mitogen-activated protein kinases (MAPKs) after treatment with lipopolysaccharide (LPS) of wild-type, diffusely adhering Afa/Dr Escherichia coli (Afa/Dr DAEC) strain IH11128. Aggregates of FITC-LPS bind the apical domain of MDCK-hCEACAM1-4L cells colocalizing with the apically expressed hCEACAM1-4L protein and do not bind MDCK-pCEP cells, and surface plasmon resonance analysis shows that LPS binds to the extracellular domain of the CEACAM1-4L protein. We showed that cell polarization and lipid rafts positively control the LPS-IH11128-induced phosphorylation of Erk1/2 in MDCK-hCEACAM1-4L cells. Structure-function analysis using mutated hCEACAM1-4L protein shows that the cytoplasmic domain of the protein is needed for LPS-induced MAPK signalling, and that phosphorylation of Tyr-residues is not increased in association with MAPK signalling. The hCEACAM1-4L-dependent Erk1/2 phosphorylation develops in the presence of lipid A and does not develop in the presence of penta-acylated LPS. Finally, small interfering RNA (siRNA) silencing of canine TLR4 abolishes the hCEACAM1-4L-dependent, LPS-induced phosphorylation of Erk1/2. Collectively, our results support the notion that the apically expressed, full-length hCEACAM1-4L protein functions as a novel LPS-conveying molecule at the mucosal surface of polarized epithelial cells for subsequent MD-2/TLR4 receptor-dependent MAPK Erk1/2 and p38 signalling.
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Affiliation(s)
- Vanessa Liévin-Le Moal
- INSERM, UMR756 «Signalisation et Physiopathologie des Cellules Epithéliales», Châtenay-Malabry, France Université Paris-Sud 11, Faculté de Pharmacie, Châtenay-Malabry, France
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79
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Ostuni R, Zanoni I, Granucci F. Deciphering the complexity of Toll-like receptor signaling. Cell Mol Life Sci 2010; 67:4109-34. [PMID: 20680392 PMCID: PMC11115668 DOI: 10.1007/s00018-010-0464-x] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2010] [Revised: 07/02/2010] [Accepted: 07/09/2010] [Indexed: 12/26/2022]
Abstract
Toll-like receptors (TLRs) are essential players in the innate immune response to invading pathogens. Although extensive research efforts have provided a considerable wealth of information on how TLRs function, substantial gaps in our knowledge still prevent the definition of a complete picture of TLR signaling. However, several recent studies describe additional layers of complexity in the regulation of TLR ligand recognition, adaptor recruitment, posttranslational modifications of signaling proteins, and the newly described, autonomous role of the TLR4 co-receptor CD14. In this review, by using it as model system for the whole TLR family, we attempt to provide a complete description of the signal transduction pathways triggered by TLR4, with a particular emphasis on the molecular and cell biological aspects regulating its function. Finally, we discuss a recently reported model of CD14-dependent signaling and highlight its biological implications.
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Affiliation(s)
- Renato Ostuni
- Department of Biotechnology and Bioscience, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milan, Italy
| | - Ivan Zanoni
- Department of Biotechnology and Bioscience, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milan, Italy
| | - Francesca Granucci
- Department of Biotechnology and Bioscience, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milan, Italy
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Leborgne-Castel N, Adam T, Bouhidel K. Endocytosis in plant-microbe interactions. PROTOPLASMA 2010; 247:177-93. [PMID: 20814704 DOI: 10.1007/s00709-010-0195-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Accepted: 08/04/2010] [Indexed: 05/10/2023]
Abstract
Plants encounter throughout their life all kinds of microorganisms, such as bacteria, fungi, or oomycetes, with either friendly or unfriendly intentions. During evolution, plants have developed a wide range of defense mechanisms against attackers. In return, adapted microbes have developed strategies to overcome the plant lines of defense, some of these microbes engaging in mutualistic or parasitic endosymbioses. By sensing microbe presence and activating signaling cascades, the plasma membrane through its dynamics plays a crucial role in the ongoing molecular dialogue between plants and microbes. This review describes the contribution of endocytosis to different aspects of plant-microbe interactions, microbe recognition and development of a basal immune response, and colonization of plant cells by endosymbionts. The putative endocytic routes for the entry of microbe molecules or microbes themselves are explored with a special emphasis on clathrin-mediated endocytosis. Finally, we evaluate recent findings that suggest a link between the compartmentalization of plant plasma membrane into microdomains and endocytosis.
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Affiliation(s)
- Nathalie Leborgne-Castel
- UMR Plante-Microbe-Environnement 1088 INRA/5184 CNRS/Université de Bourgogne, 17 Rue Sully, BP 86510, 21065 Dijon Cedex, France.
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81
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Wang Z, Che PL, Du J, Ha B, Yarema KJ. Static magnetic field exposure reproduces cellular effects of the Parkinson's disease drug candidate ZM241385. PLoS One 2010; 5:e13883. [PMID: 21079735 PMCID: PMC2975637 DOI: 10.1371/journal.pone.0013883] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2010] [Accepted: 10/18/2010] [Indexed: 12/20/2022] Open
Abstract
Background This study was inspired by coalescing evidence that magnetic therapy may be a viable treatment option for certain diseases. This premise is based on the ability of moderate strength fields (i.e., 0.1 to 1 Tesla) to alter the biophysical properties of lipid bilayers and in turn modulate cellular signaling pathways. In particular, previous results from our laboratory (Wang et al., BMC Genomics, 10, 356 (2009)) established that moderate strength static magnetic field (SMF) exposure altered cellular endpoints associated with neuronal function and differentiation. Building on this background, the current paper investigated SMF by focusing on the adenosine A2A receptor (A2AR) in the PC12 rat adrenal pheochromocytoma cell line that displays metabolic features of Parkinson's disease (PD). Methodology and Principal Findings SMF reproduced several responses elicited by ZM241385, a selective A2AR antagonist, in PC12 cells including altered calcium flux, increased ATP levels, reduced cAMP levels, reduced nitric oxide production, reduced p44/42 MAPK phosphorylation, inhibited proliferation, and reduced iron uptake. SMF also counteracted several PD-relevant endpoints exacerbated by A2AR agonist CGS21680 in a manner similar to ZM241385; these include reduction of increased expression of A2AR, reversal of altered calcium efflux, dampening of increased adenosine production, reduction of enhanced proliferation and associated p44/42 MAPK phosphorylation, and inhibition of neurite outgrowth. Conclusions and Significance When measured against multiple endpoints, SMF elicited qualitatively similar responses as ZM241385, a PD drug candidate. Provided that the in vitro results presented in this paper apply in vivo, SMF holds promise as an intriguing non-invasive approach to treat PD and potentially other neurological disorders.
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Affiliation(s)
- Zhiyun Wang
- Department of Biomedical Engineering, The Johns Hopkins University, Baltimore, Maryland, United States of America
| | - Pao-Lin Che
- Department of Biomedical Engineering, The Johns Hopkins University, Baltimore, Maryland, United States of America
| | - Jian Du
- Department of Biomedical Engineering, The Johns Hopkins University, Baltimore, Maryland, United States of America
| | - Barbara Ha
- Department of Biomedical Engineering, The Johns Hopkins University, Baltimore, Maryland, United States of America
| | - Kevin J. Yarema
- Department of Biomedical Engineering, The Johns Hopkins University, Baltimore, Maryland, United States of America
- * E-mail:
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Lipid based therapy for ulcerative colitis-modulation of intestinal mucus membrane phospholipids as a tool to influence inflammation. Int J Mol Sci 2010; 11:4149-64. [PMID: 21152327 PMCID: PMC2996791 DOI: 10.3390/ijms11104149] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2010] [Revised: 10/15/2010] [Accepted: 10/16/2010] [Indexed: 02/06/2023] Open
Abstract
Ulcerative colitis (UC) is the result of an inappropriate colonic inflammatory response triggered by environmental and genetic factors. We have recently shown that mucus from UC patients has a decreased phosphatidylcholine (PC) content, while clinical trials revealed that therapeutic addition of PC to the colonic mucus alleviated the inflammatory activity. The mechanisms behind this are still unclear. We hypothesized that PC has at least two possible functions in the intestine: First, it establishes the surface hydrophobicity of the mucus and therefore protects the underlying tissue against intraluminal aggressors; recent experiments on surgical specimens revealed reduced surface tension and hydrophobicity in UC patients. Second, mucus phospholipids might also be integrated into the plasma membranes of enterocytes and thereby influence the signaling state of the mucosa. PC has been shown to inhibit TNF-α induced pro-inflammatory responses including: (1) assembly of plasma membrane actin; (2) activation of MAP kinases ERK and p38; and (3) activation of NF-κB and synthesis of pro-inflammatory gene products. Other phospholipids like phosphatidylethanolamine or sphingomyelin had no effect. PC also inhibited latex bead phagosome actin assembly, killing of M. tuberculosis in macrophages, and sphingosine-1-phosphate induced actin assembly in macrophages. Collectively, these results provide a molecular foundation that shows PC, firstly, as an anti-inflammatory, and secondly, as a surface hydrophobicity increasing compound with promising therapeutic potential in the treatment of inflammatory bowel disease.
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83
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Zhu X, Owen JS, Wilson MD, Li H, Griffiths GL, Thomas MJ, Hiltbold EM, Fessler MB, Parks JS. Macrophage ABCA1 reduces MyD88-dependent Toll-like receptor trafficking to lipid rafts by reduction of lipid raft cholesterol. J Lipid Res 2010; 51:3196-206. [PMID: 20650929 DOI: 10.1194/jlr.m006486] [Citation(s) in RCA: 256] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
We previously showed that macrophages from macrophage-specific ATP-binding cassette transporter A1 (ABCA1) knockout (Abca1(-M/-M)) mice had an enhanced proinflammatory response to the Toll-like receptor (TLR) 4 agonist, lipopolysaccharide (LPS), compared with wild-type (WT) mice. In the present study, we demonstrate a direct association between free cholesterol (FC), lipid raft content, and hyper-responsiveness of macrophages to LPS in WT mice. Abca1(-M/-M) macrophages were also hyper-responsive to specific agonists to TLR2, TLR7, and TLR9, but not TLR3, compared with WT macrophages. We hypothesized that ABCA1 regulates macrophage responsiveness to TLR agonists by modulation of lipid raft cholesterol and TLR mobilization to lipid rafts. We demonstrated that Abca1(-M/-M) vs. WT macrophages contained 23% more FC in isolated lipid rafts. Further, mass spectrometric analysis suggested raft phospholipid composition was unchanged. Although cell surface expression of TLR4 was similar between Abca1(-M/-M) and WT macrophages, significantly more TLR4 was distributed in membrane lipid rafts in Abca1(-M/-M) macrophages. Abca1(-M/-M) macrophages also exhibited increased trafficking of the predominantly intracellular TLR9 into lipid rafts in response to TLR9-specific agonist (CpG). Collectively, our data suggest that macrophage ABCA1 dampens inflammation by reducing MyD88-dependent TLRs trafficking to lipid rafts by selective reduction of FC content in lipid rafts.
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Affiliation(s)
- Xuewei Zhu
- Departments of Pathology/Lipid Sciences, Wake Forest University School of Medicine, Winston-Salem, NC, USA
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Ehehalt R, Braun A, Karner M, Füllekrug J, Stremmel W. Phosphatidylcholine as a constituent in the colonic mucosal barrier--physiological and clinical relevance. Biochim Biophys Acta Mol Cell Biol Lipids 2010; 1801:983-93. [PMID: 20595010 DOI: 10.1016/j.bbalip.2010.05.014] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2010] [Revised: 05/21/2010] [Accepted: 05/24/2010] [Indexed: 02/09/2023]
Abstract
Phosphatidylcholine (PC) is an important constituent of the gastrointestinal tract. PC molecules are not only important in intestinal cell membranes but also receiving increasing attention as protective agents in the gastrointestinal barrier. They are largely responsible for establishing the hydrophobic surface of the colon. Decreased phospholipids in colonic mucus could be linked to the pathogenesis of ulcerative colitis, a chronic inflammatory bowel disease. Clinical studies revealed that therapeutic addition of PC to the colonic mucus of these patients alleviated the inflammatory activity. This positive role is still elusive, however, we hypothesized that luminal PC has two possible functions: first, it is essential for surface hydrophobicity, and second, it is integrated into the plasma membrane of enterocytes and it modulates the signaling state of the mucosa. The membrane structure and lipid composition of cells is a regulatory component of the inflammatory signaling pathways. In this perspective, we will shortly summarize what is known about the localization and protective properties of PC in the colonic mucosa before turning to its evident medical importance. We will discuss how PC contributes to our understanding of the pathogenesis of ulcerative colitis and how reinforcing the luminal phospholipid monolayer can be used as a therapeutic concept in humans.
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Affiliation(s)
- Robert Ehehalt
- Department of Gastroenterology, University hospital Heidelberg, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany.
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85
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Abstract
Lipid rafts are envisaged as islands of highly ordered saturated lipids and cholesterol that are laterally mobile in the plane of the plasma membrane. Lipid rafts are thought to provide a means to explain the spatial segregation of certain signalling pathways emanating from the cell surface. They seem to provide the necessary microenvironment in order for certain specialised signalling events to take place- such as the innate immune recognition. The innate immune system seems to employ germ-lined encoded receptors, called pattern recognition receptors (PRRs) in order to "sense" pathogens. One family of such receptors are the Toll like receptors (TLRs), which are the central "sensing" apparatus of the innate immune system. In recent years, it has become apparent that TLRs are recruited into membrane microdomains in response to ligands and these constitute signalling platforms, which transducer singals that lead to innate immune activation. In this chapter will review all past and current literature concerning recruitment of TLRs into lipid rafts and how this membrane compartmentalization is crucial for innate immune responses.
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86
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Wang Z, Sarje A, Che PL, Yarema KJ. Moderate strength (0.23-0.28 T) static magnetic fields (SMF) modulate signaling and differentiation in human embryonic cells. BMC Genomics 2009; 10:356. [PMID: 19653909 PMCID: PMC2907690 DOI: 10.1186/1471-2164-10-356] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2009] [Accepted: 08/04/2009] [Indexed: 12/18/2022] Open
Abstract
Background Compelling evidence exists that magnetic fields modulate living systems. To date, however, rigorous studies have focused on identifying the molecular-level biosensor (e.g., radical ion pairs or membranes) or on the behavior of whole animals leaving a gap in understanding how molecular effects are translated into tissue-wide and organism-level responses. This study begins to bridge this gulf by investigating static magnetic fields (SMF) through global mRNA profiling in human embryonic cells coupled with software analysis to identify the affected signaling pathways. Results Software analysis of gene expression in cells exposed to 0.23–0.28 T SMF showed that nine signaling networks responded to SMF; of these, detailed biochemical validation was performed for the network linked to the inflammatory cytokine IL-6. We found the short-term (<24 h) activation of IL-6 involved the coordinate up-regulation of toll-like receptor-4 (TLR4) with complementary changes to NEU3 and ST3GAL5 that reduced ganglioside GM3 in a manner that augmented the activation of TLR4 and IL-6. Loss of GM3 also provided a plausible mechanism for the attenuation of cellular responses to SMF that occurred over longer exposure periods. Finally, SMF-mediated responses were manifest at the cellular level as morphological changes and biochemical markers indicative of pre-oligodendrocyte differentiation. Conclusion This study provides a framework describing how magnetic exposure is transduced from a plausible molecular biosensor (lipid membranes) to cell-level responses that include differentiation toward neural lineages. In addition, SMF provided a stimulus that uncovered new relationships – that exist even in the absence of magnetic fields – between gangliosides, the time-dependent regulation of IL-6 signaling by these glycosphingolipids, and the fate of embryonic cells.
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Affiliation(s)
- Zhiyun Wang
- Department of Biomedical Engineering, The Johns Hopkins University, Baltimore, MD, USA.
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87
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Motshwene PG, Moncrieffe MC, Grossmann JG, Kao C, Ayaluru M, Sandercock AM, Robinson CV, Latz E, Gay NJ. An oligomeric signaling platform formed by the Toll-like receptor signal transducers MyD88 and IRAK-4. J Biol Chem 2009; 284:25404-11. [PMID: 19592493 DOI: 10.1074/jbc.m109.022392] [Citation(s) in RCA: 283] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Toll-like receptors (TLRs) mediate responses to pathogen-associated molecules as part of the vertebrate innate immune response to infection. Receptor dimerization is coupled to downstream signal transduction by the recruitment of a post-receptor complex containing the adaptor protein MyD88 and the IRAK protein kinases. In this work, we show that the death domains of human MyD88 and IRAK-4 assemble into closed complexes having unusual stoichiometries of 7:4 and 8:4, the Myddosome. Formation of the Myddosome is likely to be a key event for TLR4 signaling in vivo as we show here that pathway activation requires that the receptors cluster into lipid rafts. Taken together, these findings indicate that TLR activation causes the formation of a highly oligomeric signaling platform analogous to the death-inducing signaling complex of the Fas receptor pathway.
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Affiliation(s)
- Precious G Motshwene
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, United Kingdom
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88
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Urothelial cultures support intracellular bacterial community formation by uropathogenic Escherichia coli. Infect Immun 2009; 77:2762-72. [PMID: 19451249 DOI: 10.1128/iai.00323-09] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Uropathogenic Escherichia coli (UPEC) causes most community-acquired and nosocomial urinary tract infections (UTI). In a mouse model of UTI, UPEC invades superficial bladder cells and proliferates rapidly, forming biofilm-like structures called intracellular bacterial communities (IBCs). Using a gentamicin protection assay and fluorescence microscopy, we developed an in vitro model for studying UPEC proliferation within immortalized human urothelial cells. By pharmacologic manipulation of urothelial cells with the cholesterol-sequestering drug filipin, numbers of intracellular UPEC CFU increased 8 h and 24 h postinfection relative to untreated cultures. Enhanced UPEC intracellular proliferation required that the urothelial cells, but not the bacteria, be filipin treated prior to infection. However, neither UPEC frequency of invasion nor early intracellular trafficking events to a Lamp1-positive compartment were modulated by filipin. Upon inspection by fluorescence microscopy, cultures with enhanced UPEC intracellular proliferation exhibited large, dense bacterial aggregates within cells that resembled IBCs but were contained with Lamp1-positive vacuoles. While an isogenic fimH mutant was capable of forming these IBC-like structures, the mutant formed significantly fewer than wild-type UPEC. Similar to IBCs, expression of E. coli iron acquisition systems was upregulated by intracellular UPEC. Expression of other putative virulence factors, including hlyA, cnf1, fliC, kpsD, and the biofilm adhesin yfaL also increased, while expression of fimA decreased and that of flu did not change. These results indicate that UPEC differentially regulates virulence factors in the intracellular environment. Thus, immortalized urothelial cultures that recapitulate IBC formation in vitro represent a novel system for the molecular and biochemical characterization of the UPEC intracellular life cycle.
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89
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Thibault S, Fromentin R, Tardif MR, Tremblay MJ. TLR2 and TLR4 triggering exerts contrasting effects with regard to HIV-1 infection of human dendritic cells and subsequent virus transfer to CD4+ T cells. Retrovirology 2009; 6:42. [PMID: 19419540 PMCID: PMC2691729 DOI: 10.1186/1742-4690-6-42] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2008] [Accepted: 05/06/2009] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND Recognition of microbial products through Toll-like receptors (TLRs) initiates inflammatory responses orchestrated by innate immune cells such as dendritic cells (DCs). As these cells are patrolling mucosal surfaces, a portal of entry for various pathogens including human immunodeficiency virus type-1 (HIV-1), we investigated the impact of TLR stimulation on productive HIV-1 infection of DCs and viral spreading to CD4+ T cells. RESULTS We report here that engagement of TLR2 on DCs increases HIV-1 transmission toward CD4+ T cells by primarily affecting de novo virus production by DCs. No noticeable and consistent effect was observed following engagement of TLR5, 7 and 9. Additional studies indicated that both HIV-1 infection of DCs and DC-mediated virus transmission to CD4+ T cells were reduced upon TLR4 triggering due to secretion of type-I interferons. CONCLUSION It can thus be proposed that exposure of DCs to TLR2-binding bacterial constituents derived, for example, from pathogens causing sexually transmissible infections, might influence the process of DC-mediated viral dissemination, a phenomenon that might contribute to a more rapid disease progression.
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90
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Epelman S, Berenger B, Stack D, Neely GG, Ma LL, Mody CH. Microbial Products Activate Monocytic Cells through Detergent-Resistant Membrane Microdomains. Am J Respir Cell Mol Biol 2008; 39:657-65. [DOI: 10.1165/rcmb.2007-0390oc] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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91
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Abstract
Infections of the lung are prevented first by denial of access, mediated by humoral and cellular systems that obscure the pathogen's target, simultaneously acting to kill and clear the pathogen. Where pathogens penetrate these initial defence systems, rapid detection of their presence is achieved by their engagement with a large family of pattern recognition receptors, including Toll-like receptors, retinoic-acid-inducible gene-like helicases and Nod-like receptors. Activation of a coordinated inflammatory response is achieved by cooperative signalling between sentinel leucocytes such as alveolar macrophages and lung tissue, following which a profound pro-inflammatory response mobilizes phagocytes such as neutrophils and monocytes to the lung. Resolution of the innate immune response, largely dependent upon neutrophil apoptosis, results in restoration of normal tissue architecture. In chronic disease, dysregulated inflammation maintains these systems in a state of constant activation, potentially resulting in tissue damage and progressive disease.
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Affiliation(s)
- Nazia Chaudhuri
- Academic Unit of Respiratory Medicine, School of Medicine and Biomedical Sciences, University of Sheffield, UK.
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92
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Parker LC, Prestwich EC, Ward JR, Smythe E, Berry A, Triantafilou M, Triantafilou K, Sabroe I. A phosphatidylserine species inhibits a range of TLR- but not IL-1beta-induced inflammatory responses by disruption of membrane microdomains. THE JOURNAL OF IMMUNOLOGY 2008; 181:5606-17. [PMID: 18832719 DOI: 10.4049/jimmunol.181.8.5606] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
TLRs detect conserved molecular patterns that are unique to microbes, enabling tailored responses to invading pathogens and modulating a multitude of immunopathological conditions. We investigated the ability of a naturally occurring stearoyl-arachidonoyl form of phosphatidylserine (SAPS) to inhibit the proinflammatory effects of TLR agonists in models of inflammation investigating the interaction of leukocytes with epithelial and endothelial cells. The responses to LPS of both epithelial and endothelial cells were highly amplified in the presence of PBMCs. Coincubation with SAPS markedly inhibited activation of cocultures by LPS, principally through inhibition of the TLR4 signaling pathway in PBMCs; however, this was not through downmodulation of TLR4 or coreceptor expression, nor was IL-1beta-induced cytokine release affected. SAPS also impaired Pam(3)CSK(4) (TLR2/1), Gardiquimod (TLR7/8), and Streptococcus pneumoniae-induced cytokine release, but had only modest effects on poly(I:C) (TLR3)-induced responses. Fluorescence resonance energy transfer analysis of molecular associations revealed that SAPS disrupted the association of both TLR4 and TLR2 with their respective membrane partners that are required for signaling. Thus, our data reinforce the existence and importance of cooperative networks of TLRs, tissue cells, and leukocytes in mediating innate immunity, and identify a novel disrupter of membrane microdomains, revealing the dependence of TLR signaling on localization within these domains.
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Affiliation(s)
- Lisa C Parker
- Academic Unit of Respiratory Medicine, School of Medicine and Biomedical Sciences, University of Sheffield, Sheffield, United Kingdom
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93
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Erridge C, Kennedy S, Spickett CM, Webb DJ. Oxidized phospholipid inhibition of toll-like receptor (TLR) signaling is restricted to TLR2 and TLR4: roles for CD14, LPS-binding protein, and MD2 as targets for specificity of inhibition. J Biol Chem 2008; 283:24748-59. [PMID: 18559343 DOI: 10.1074/jbc.m800352200] [Citation(s) in RCA: 182] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The generation of reactive oxygen species is a central feature of inflammation that results in the oxidation of host phospholipids. Oxidized phospholipids, such as 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphorylcholine (OxPAPC), have been shown to inhibit signaling induced by bacterial lipopeptide or lipopolysaccharide (LPS), yet the mechanisms responsible for the inhibition of Toll-like receptor (TLR) signaling by OxPAPC remain incompletely understood. Here, we examined the mechanisms by which OxPAPC inhibits TLR signaling induced by diverse ligands in macrophages, smooth muscle cells, and epithelial cells. OxPAPC inhibited tumor necrosis factor-alpha production, IkappaBalpha degradation, p38 MAPK phosphorylation, and NF-kappaB-dependent reporter activation induced by stimulants of TLR2 and TLR4 (Pam3CSK4 and LPS) but not by stimulants of other TLRs (poly(I.C), flagellin, loxoribine, single-stranded RNA, or CpG DNA) in macrophages and HEK-293 cells transfected with respective TLRs and significantly reduced inflammatory responses in mice injected subcutaneously or intraperitoneally with Pam3CSK4. Serum proteins, including CD14 and LPS-binding protein, were identified as key targets for the specificity of TLR inhibition as supplementation with excess serum or recombinant CD14 or LBP reversed TLR2 inhibition by OxPAPC, whereas serum accessory proteins or expression of membrane CD14 potentiated signaling via TLR2 and TLR4 but not other TLRs. Binding experiments and functional assays identified MD2 as a novel additional target of OxPAPC inhibition of LPS signaling. Synthetic phospholipid oxidation products 1-palmitoyl-2-(5-oxovaleryl)-sn-glycero-3-phosphocholine and 1-palmitoyl-2-glutaryl-sn-glycero-3-phosphocholine inhibited TLR2 signaling from approximately 30 microm. Taken together, these results suggest that oxidized phospholipid-mediated inhibition of TLR signaling occurs mainly by competitive interaction with accessory proteins that interact directly with bacterial lipids to promote signaling via TLR2 or TLR4.
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Affiliation(s)
- Clett Erridge
- Strathclyde Institute of Pharmacy and Biomedical Sciences, Univesity of Strathclyde, 204 George St., Glasgow G1 1XW, United Kingdom.
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94
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Ali GS, Reddy A. PAMP-triggered immunity: Early events in the activation of FLAGELLIN SENSITIVE2. PLANT SIGNALING & BEHAVIOR 2008; 3:423-6. [PMID: 19704848 PMCID: PMC2634595 DOI: 10.4161/psb.3.6.5472] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2007] [Accepted: 12/27/2007] [Indexed: 05/05/2023]
Abstract
The Arabidopsis FLAGELLIN SENSITIVE2 (FLS2) protein is a leucine-rich repeat receptor-like kinase (LRR-RLK) that plays important roles in pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI). The binding of bacterial flagellin, one of the PAMPs, to the extracellular domain of FLS2 leads to activation of signaling cascades resulting in activation or repression of a specific set of genes involved in plant defense. The mechanisms at the cell membrane that lead to the activation of this signalling pathway are, however, not fully understood. Recently, we have shown that after ligand-treatment the mobility of FLS2 in the cell membrane is reduced and that the activation of FLS2 does not involve its constitutive or ligand-dependent homodimerization. Our data together with recently published reports suggest that FLS2 activation involves its association with other proteins, including BRI1-associated kinase 1 (BAK1), another LRR-RLK, and localization to less mobile areas, probably lipid rafts, in a ligand-dependent manner to initiate PTI.
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Affiliation(s)
- Gul Shad Ali
- Department of Biology and Program in Molecular Plant Biology; Colorado State University; Fort Collins, Colorado USA
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95
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A Toll-like receptor 2-integrin beta3 complex senses bacterial lipopeptides via vitronectin. Nat Immunol 2008; 9:761-8. [PMID: 18516040 DOI: 10.1038/ni.1618] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2008] [Accepted: 04/23/2008] [Indexed: 11/08/2022]
Abstract
Toll-like receptor 2 (TLR2) initiates inflammation in response to bacterial lipopeptide (BLP). However, the molecular mechanisms enabling the detection of BLP by TLR2 are unknown. Here we investigated the interaction of BLP with human serum proteins and identified vitronectin as a BLP-recognition molecule. Vitronectin and its receptor, integrin beta(3), were required for BLP-induced TLR2-mediated activation of human monocytes. Furthermore, monocytes from patients with Glanzmann thrombasthenia, which lack integrin beta(3), were completely unresponsive to BLP. In addition, integrin beta(3) formed a complex with TLR2 and this complex dissociated after BLP stimulation. Notably, vitronectin and integrin beta(3) coordinated responses to other TLR2 agonists such as lipoteichoic acid and zymosan. Our findings show that vitronectin and integrin beta(3) contribute to the initiation of TLR2 responses.
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96
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Jackson SK, Abate W, Parton J, Jones S, Harwood JL. Lysophospholipid metabolism facilitates Toll-like receptor 4 membrane translocation to regulate the inflammatory response. J Leukoc Biol 2008; 84:86-92. [PMID: 18403647 DOI: 10.1189/jlb.0907601] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Sepsis, an overwhelming inflammatory response to infection, is a major cause of morbidity and mortality worldwide and has no specific therapy. Phospholipid metabolites, such as lysophospholipids, have been shown to regulate inflammatory responses in sepsis, although their mechanism of action is not well understood. The phospholipid-metabolizing enzymes, lysophospholipid acyltransferases, control membrane phospholipid composition, function, and the inflammatory responses of innate immune cells. Here, we show that lysophosphatidylcholine acyltransferase (LPCAT) regulates inflammatory responses to LPS and other microbial stimuli. Specific inhibition of LPCAT down-regulated inflammatory cytokine production in monocytes and epithelial cells by preventing translocation of TLR4 into membrane lipid raft domains. Our observations demonstrate a new regulatory mechanism that facilitates the innate immune responses to microbial molecular patterns and provide a basis for the anti-inflammatory activity observed in many phospholipid metabolites. This provides the possibility of the development of new classes of anti-inflammatory and antisepsis agents.
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Affiliation(s)
- Simon K Jackson
- Centre for Research in Biomedicine, University of the West of England, Bristol, BS16 1QY, UK.
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97
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Sabroe I, Parker LC, Dower SK, Whyte MKB. The role of TLR activation in inflammation. J Pathol 2008; 214:126-35. [PMID: 18161748 DOI: 10.1002/path.2264] [Citation(s) in RCA: 150] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The Toll-like receptor family was originally identified in Drosophila, where it provides important developmental and immunological signalling. In mammals, the developmental signal appears to have been lost, but the immunological defence role of these receptors has been expanded to provide broad recognition of bacterial, fungal, viral and parasitic pathogens. There is increasing evidence that these receptors go beyond the recognition of microbial molecules to sense host tissue damage. Recognition of host molecules and commensal microbes is also involved in the restoration of normal tissue architecture after injury and in maintenance of epithelial health. Recent developments in the TLR field highlight the importance of these molecules to human health and disease and demonstrate that their targeting, to boost immunity or inhibit inflammation, is both feasible and also potentially challenging.
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Affiliation(s)
- I Sabroe
- Academic Unit of Respiratory Medicine, Section of Infection, Inflammation and Immunity, School of Medicine and Biomedical Sciences, University of Sheffield, UK.
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98
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Draing C, Sigel S, Deininger S, Traub S, Munke R, Mayer C, Hareng L, Hartung T, von Aulock S, Hermann C. Cytokine induction by Gram-positive bacteria. Immunobiology 2008; 213:285-96. [PMID: 18406374 DOI: 10.1016/j.imbio.2007.12.001] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2007] [Revised: 11/30/2007] [Accepted: 12/10/2007] [Indexed: 01/13/2023]
Abstract
Despite similar clinical relevance of Gram-positive and Gram-negative infections, immune activation by Gram-positive bacteria is by far less well understood than immune activation by Gram-negative bacteria. Our group has made available highly purified lipoteichoic acids (LTA) as a key Gram-positive immunostimulatory component. We have characterized the reasons for lower potency of LTA compared to Gram-negative lipopolysaccharide (LPS), identifying lack of IL-12/IFNgamma induction as a general characteristic of TLR2 agonists, and need for presentation of LTA on surfaces for enhanced immunostimulatory potency, as major aspects. Aspects of chemokine induction, where LTA is more potent than LPS, have been addressed. Furthermore, novel complement and plant defence activation, as well as CD36 as a new LTA receptor, were identified. The bacterial costimuli and modulators of LTA inducible responses are being investigated: LTA isolated from so far 16 bacterial species, although different in structure, behave remarkably similar while whole live and killed bacteria differ with regard to the pattern of induced responses. The purification and characterization of the respective components of the bacterial cell wall has begun.
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Affiliation(s)
- Christian Draing
- Biochemical Pharmacology, University of Konstanz, 78457 Konstanz, Germany
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99
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Prostaglandin E2 inhibits tumor necrosis factor-alpha RNA through PKA type I. Biochem Biophys Res Commun 2007; 366:104-9. [PMID: 18060853 DOI: 10.1016/j.bbrc.2007.11.091] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2007] [Accepted: 11/19/2007] [Indexed: 11/20/2022]
Abstract
Tumor necrosis factor-alpha (TNF-alpha) is a cytokine that may contribute to the pathogenesis of septic shock, rheumatoid arthritis, cancer, and diabetes. Prostaglandins endogenously produced by macrophages act in an autocrine fashion to limit TNF-alpha production. We investigated the timing and signaling pathway of prostaglandin-mediated inhibition of TNF-alpha production in Raw 264.7 and J774 macrophages. TNF-alpha mRNA levels were rapidly modulated by PGE(2) or carbaprostacylin. PGE(2) or carbaprostacyclin prevented and rapidly terminated on-going TNF-alpha gene transcription within 15 min of prostaglandin treatment. Selective activation of PKA type I, but not PKA type II or Epac, with chemical analogs of cAMP was sufficient to inhibit LPS-induced TNF-alpha mRNA levels. The mechanisms by which prostaglandins limit TNF-alpha mRNA levels may underlie endogenous regulatory mechanisms that limit inflammation, and may have important implications for understanding chronic inflammatory disease pathogenesis.
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100
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De Schepper S, De Ketelaere A, Bannerman DD, Paape MJ, Peelman L, Burvenich C. The toll-like receptor-4 (TLR-4) pathway and its possible role in the pathogenesis of Escherichia coli mastitis in dairy cattle. Vet Res 2007; 39:5. [PMID: 18073092 DOI: 10.1051/vetres:2007044] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2006] [Accepted: 08/02/2007] [Indexed: 12/30/2022] Open
Abstract
Mastitis is one of the most costly production diseases in the dairy industry that is caused by a wide array of microorganisms. In this review, we focus on the Gram-negative Escherichia coli infections that often occur at periods when the innate immune defence mechanisms are impaired (i.e., parturition through the first 60 days of lactation). There is substantial evidence demonstrating that at these periods, the expected influx of polymorphonuclear neutrophil leukocytes (PMN) into the mammary gland is delayed during inflammation after intramammary infection with E. coli. Here, we provide some hypotheses on the potential mechanisms of action on how the disease may develop under circumstances of immunosuppression, and describe the potential involvement of the toll-like receptor-4 signal transduction pathway in the pathogenesis of E. coli mastitis. In addition, some ideas are proposed to help prevent E. coli mastitis and potentially other diseases caused by Gram-negative infections in general.
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Affiliation(s)
- Stefanie De Schepper
- Laboratory of Physiology, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium
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