A Microbial TLR2 Agonist Imparts Macrophage-Activating Ability to Apolipoprotein A-1

Lipoprotein Extraction from Microbial Membrane and Lipoprotein/Lipopeptide Transfection into Mammalian Cells

Microbial lipoproteins/lipopeptides are important virulence factors for periodontal diseases. The membrane lipoproteins from Mycoplasma salivarium or Tannerella forsythia can be easily extracted by exploiting a characteristic feature of Triton X-114: its aqueous nature at low temperatures (0-4 °C), which is absent at room temperature (25-37 °C). Transfection of these lipopeptides into macrophages was performed using the protein transfection reagent, PULSin.

Cross-linking Proteomics Indicates Effects of Simvastatin on the TLR2 Interactome and Reveals ACTR1A as a Novel Regulator of the TLR2 Signal Cascade

Toll-like receptor 2 (TLR2) is a pattern recognition receptor that, upon ligation by microbial molecules, interacts with other proteins to initiate pro-inflammatory responses by the cell. Statins (hydroxymethylglutaryl coenzyme A reductase inhibitors), drugs widely prescribed to reduce hypercholesterolemia, are reported to have both pro- and anti-inflammatory effects upon cells. Some of these responses are presumed to be driven by effects on signaling proteins at the plasma membrane, but the underlying mechanisms remain obscure. We reasoned that profiling the effect of statins on the repertoire of TLR2-interacting proteins might provide novel insights into the mechanisms by which statins impact inflammation. In order to study the TLR2 interactome, we designed a coimmunoprecipitation (IP)-based cross-linking proteomics study. A hemagglutinin (HA)-tagged-TLR2 transfected HEK293 cell line was used to precipitate the TLR2 interactome upon cell exposure to the TLR2 agonist Pam3CSK4 and simvastatin, singly and in combination. To stabilize protein interactors, we used two different chemical cross-linkers with different spacer chain lengths. Proteomic analysis revealed important combinatorial effects of simvastatin and Pam3CSK4 on the TLR2 interactome. After stringent data filtering, we identified alpha-centractin (ACTR1A), an actin-related protein and subunit of the dynactin complex, as a potential interactor of TLR2. The interaction was validated using biochemical methods. RNA interference studies revealed an important role for ACTR1A in induction of pro-inflammatory cytokines. Taken together, we report that statins remodel the TLR2 interactome, and we identify ACTR1A, a part of the dynactin complex, as a novel regulator of TLR2-mediated immune signaling pathways.

TLR7 rs2897827 Polymorphism Affects TLR7 Gene mRNA Expression and Serum Apolipoprotein A1 Level of Ischemic Stroke Patients in a Chinese Han Population

Stroke is a multi-factorial disorder that has become the leading cause of death and disability worldwide. Previous studies reported that TLR7 mRNA expression is associated with poor outcome of ischemic stroke (IS). This study aimed to assess whether TLR7 mRNA expression affects IS occurrence, as well as the association of TLR7 rs2897827 with susceptibility to IS and TLR7 mRNA expression and serum apolipoprotein and lipid levels in a Chinese Han population. A total of 816 stroke patients and 816 healthy controls were included in this study. mRNA expression was determined by quantitative real-time PCR. The Sequenom MassARRAY iPLEX platform was used to genotype the TLR7 rs2897827 polymorphism. TLR7 mRNA expression of the IS cases was statistically significantly higher than that of the controls in the male or female group (male, P = 0.014; female, P = 0.025). In the male IS cases, TLR7 mRNA expression of the T allele carriers was statistically significantly higher than that of the C allele carriers (P = 0.018). However, a significant difference was not observed in the female cases (P = 0.545). In either the male or female group, the distribution of genotype or allele had no statistical significance (P > 0.050). The ApoA1 level of the T carriers was statistically significantly higher than the C carriers in males (t = -2.383, P = 0.020); however, the ApoB and lipid levels were not associated with rs2897827 (P > 0.050). In female patients, no significant difference was observed between different genotypic/allelic carriers in serum apolipoprotein and lipid levels (all P > 0.050). The expression of the TLR7 gene may affect IS occurrence. TLR7 gene rs2897827 may influence TLR7 mRNA expression and the plasma ApoA1 level in male IS patients.

Toll-like receptors mediating vascular malfunction: Lessons from receptor subtypes

Toll-like receptors (TLR) are a subfamily of pattern recognition receptors (PRR) implicated in a variety of vascular abnormalities. However, the pathophysiological role and the interplay between different TLR-mediated innate and adaptive immune responses during the development of vascular diseases remain largely unspecified. TLR are widely distributed in both immune and nonimmune cells in the blood vessel wall. The expressions and locations of TLR are dynamically regulated in response to distinct molecular patterns derived from pathogens or damaged host cells. As a result, the outcome of TLR signaling is agonist- and cell type-dependent. A better understanding of discrete TLR signaling pathways in the vasculature will provide unprecedented opportunities for the discovery of novel therapies in many inflammatory vascular diseases. The present brief review discusses the role of individual TLR in controlling cellular functions of the vascular system, by focusing on the inflammatory responses within the blood vessel wall which contribute to the development of hypertension and atherosclerosis.

A potential pathogenic factor from Mycoplasma hominis is a TLR2-dependent, macrophage-activating, P50-related adhesin

PROBLEM

Mycoplasma hominis has been implicated in many inflammatory conditions of the human urogenital tract in particular amniotic infections that lead to fetal and neonatal disease and pre-term labor. The mechanisms responsible are poorly defined.

METHOD OF STUDY

Biochemical and immunological methods were used to extract, purify, and characterize an inflammatory component present in M. hominis.

RESULTS

We isolated and purified to homogeneity a 40-kDa bioactive lipoprotein from M. hominis that was a potent TLR2-dependent, CD14-independent activator of the human THP-1 macrophage cell line. Homology searches of the N-terminal sequence revealed that 22 of the first 23 residues were identical to those seen for the phase-variable M. hominis p50 adhesin. The truncated P50t lipoprotein importantly retained its adhesive properties for human macrophages.

CONCLUSION

The unique adhesin/macrophage activator may play a key role in M. hominis infections by triggering an inflammatory cytokine cascade.

Mycoplasma superantigen initiates a TLR4-dependent Th17 cascade that enhances arthritis after blocking B7-1 in Mycoplasma arthritidis-infected mice

Mycoplasma arthritidis is a natural pathogen of rodents causing arthritis, toxic shock and necrotizing fasciitis. It secretes a potent superantigen (SAg), MAM, that differentially affects the immune system depending upon presence or absence of TLR4, thus potentially influencing disease outcomes. Here, we establish that antibody to co-stimulatory molecule B7-1(CD80) enhances arthritis in wild-type C3H/HeSnJ (TLR2+4+) mice but suppresses arthritis in TLR4-defect C3H/HeJ (TLR2+4-) mice. Also, blockade of the B7-1/CD28 co-stimulatory pathway in C3H/HeSnJ mice resulted in a marked increase in an alternative co-stimulatory pathway ICOS/ICOSL that was associated with elevation of the IL-17/Th17cascade with enhanced IL-23, IL-6, and the RORγt and STAT3 transcriptional factors on CD4+ T cells. Anti- B7-1 also increased inflammatory chemokines and the stress protein HMGB1 that promotes cellular infiltration to joints. Using a MAM-deficient strain of M. arthritidis, a monoclonal antibody to TLR4 and a TLR4-defective mouse strain, we established that both MAM and TLR4 are required for the systemic and local joint triggering of the Th17/IL-17 cascade in mice treated with anti-B7-1 antibody. Importantly, blocking of IL-17 with anti-IL-17 antibody suppressed the elevated arthritis in M. arthritidis-infected mice treated with anti-B7-1 antibody. Thus, this unique model of arthritis illustrates how microbial agonists can bridgeinnate and adaptive immune responses to redirect signalling pathways, thus promoting chronic inflammatory and autoimmune disease.

Leptospiral LruA is required for virulence and modulates an interaction with mammalian apolipoprotein AI

Leptospirosis is a worldwide zoonosis caused by spirochetes of the genus Leptospira. While understanding of pathogenesis remains limited, the development of mutagenesis in Leptospira has provided a powerful tool for identifying novel virulence factors. LruA is a lipoprotein that has been implicated in leptospiral uveitis as a target of the immune response. In this study, two lruA mutants, M754 and M765, generated by transposon mutagenesis from Leptospira interrogans serovar Manilae, were characterized. In M754, the transposon inserted in the middle of lruA, resulting in no detectable expression of LruA. In M765, the transposon inserted toward the 3' end of the gene, resulting in expression of a truncated protein. LruA was demonstrated to be on the cell surface in M765 and the wild type (WT). M754, but not M765, was attenuated in a hamster model of acute infection. A search for differential binding to human serum proteins identified a serum protein of around 30 kDa bound to the wild type and the LruA deletion mutant (M754), but not to the LruA truncation mutant (M765). Two-dimensional separation of proteins from leptospiral cells incubated with guinea pig serum identified the 28-kDa apolipoprotein A-I (ApoA-I) as a major mammalian serum protein that binds Leptospira in vitro. Interestingly, M754 (with no detectable LruA) bound more ApoA-I than did the LruA-expressing strains Manilae wild type and M765. Our data thus identify LruA as a surface-exposed leptospiral virulence factor that contributes to leptospiral pathogenesis, possibly by modulating cellular interactions with serum protein ApoA-I.

Tmprss3 loss of function impairs cochlear inner hair cell Kcnma1 channel membrane expression

Before acquiring their mature state, cochlear hair cells undergo a series of changes in expression of ion channels. How this complex mechanism is achieved is not fully understood. Tmprss3, a type II serine protease expressed in hair cells, is required for their proper functioning at the onset of hearing. To unravel the role of Tmprss3 in the acquisition of mature K(+) currents, we compared their function by patch-clamp technique in wild-type Tmprss3(WT) and Tmprss3(Y260X)-mutant mice. Interestingly, only outward K(+) currents were altered in Tmprss3(Y260X)-mutant mice. To determine by which mechanism this occurred, we compared the protein network of Tmprss3(WT) and Tmprss3(Y260X)-mutant mice using proteomic analysis. This led to the identification of a pathway related to potassium Kcnma1 channels. This pathway was validated by immunohistochemistry, focusing on the most downregulated protein that was identified as a cochlear Kcnma1-associated protein, APOA1. Finally, we show that, in contrast to Tmprss3(WT), Kcnma1 channels were absent at the neck of inner hair cells (IHCs) in Tmprss3(Y260X)-mutant mice. In conclusion, our data suggest that lack of Tmprss3 leads to a decrease in Kcnma1 potassium channels expression in (IHCs).

Toll Like Receptors Signaling Pathways as a Target for Therapeutic Interventions

This review summarizes the key role of Toll-Like Receptor (TLRs) molecules for igniting the immune system. Activated by a broad spectrum of pathogens, cytokines or other specific molecules, TLRs trigger innate immune responses. Published data demonstrate that the targeting and suppression of TLRs and TLR-related proteins with particular inhibitors may provide pivotal treatments for patients with cancer, asthma, sepsis, Crohn's disease and thrombosis. Many drugs that target cytokines act in the late phases of the activated pathways, after the final peptides, proteins or glycoproteins are formed in the cell environment. TLR activity occurs in the early activation of cellular pathways; consequently inhibiting them might be most beneficial in the treatment of human diseases.

Alternatively Expressed Genes Identified in the CD4+ T Cells of Allograft Rejection Mice

Allograft rejection is a leading cause for the failure of allotransplantation. CD4+ T cells play critical roles in this process. The identification of genes that alternatively expressed in CD4+ T cells during allograft rejection will provide critical information for studying the mechanism of allograft rejection, finding specific gene markers for monitoring, predicting allograft rejection, and opening new ways to regulate and prevent allograft rejection. Here, we established allograft and isograft transplantation models by adoptively transferring wild-type BALB/c mouse CD4+ T cells into severe combined immunodeficient (SCID) mice with a C57BL/6 or BALB/c mouse skin graft. Using the whole transcriptome sequencing-based serial analysis of gene expression (SAGE) technology, we identified 97 increasingly and 88 decreasingly expressed genes that may play important roles in allograft rejection and tolerance. Functional classification of these genes shows that apoptosis, transcription regulation, cell growth and maintenance, and signal transduction are among the frequently changed functional groups. This study provides a genome-wide view for the candidate genes of CD4+ T cells related to allotransplantation, and this report is a good resource for further microarray studies and for identifying the specific markers that are associated with clinical organ transplantations.

Serum lipoproteins attenuate macrophage activation and Toll-Like Receptor stimulation by bacterial lipoproteins

BACKGROUND

Chlamydia trachomatis was previously shown to express a lipoprotein, the macrophage infectivity potentiator (Mip), exposed at the bacterial surface, and able to stimulate human primary monocytes/macrophages through Toll Like Receptor (TLR)2/TLR1/TLR6, and CD14. In PMA-differentiated THP-1 cells the proinflammatory activity of Mip was significantly higher in the absence than in the presence of serum. The present study aims to investigate the ability of different serum factors to attenuate Mip proinflammatory activity in PMA-differentiated THP-1 cells and in primary human differentiated macrophages. The study was also extend to another lipoprotein, the Borrelia burgdorferi outer surface protein (Osp)A. The proinflammatory activity was studied through Tumor Necrosis Factor alpha (TNF-α) and Interleukin (IL)-8 release. Finally, TLR1/2 human embryonic kidney-293 (HEK-293) transfected cells were used to test the ability of the serum factors to inhibit Mip and OspA proinflammatory activity.

RESULTS

In the absence of any serum and in the presence of 10% delipidated FBS, production of Mip-induced TNF-α and IL-8 in PMA-differentiated THP-1 cells were similar whereas they were significantly decreased in the presence of 10% FBS suggesting an inhibiting role of lipids present in FBS. In the presence of 10% human serum, the concentrations of TNF-α and IL-8 were 2 to 5 times lower than in the presence of 10% FBS suggesting the presence of more potent inhibitor(s) in human serum than in FBS. Similar results were obtained in primary human differentiated macrophages. Different lipid components of human serum were then tested (total lipoproteins, HDL, LDL, VLDL, triglyceride emulsion, apolipoprotein (apo)A-I, B, E2, and E3). The most efficient inhibitors were LDL, VLDL, and apoB that reduced the mean concentration of TNF-α release in Mip-induced macrophages to 24, 20, and 2%, respectively (p < 0.0001). These lipid components were also able to prevent TLR1/2 induced activation by Mip, in HEK-293 transfected cells. Similar results were obtained with OspA.

CONCLUSIONS

These results demonstrated the ability of serum lipids to attenuate proinflammatory activity of bacterial lipoproteins and suggested that serum lipoproteins interact with acyl chains of the lipid part of bacterial lipoproteins to render it biologically inactive.

The Toll-like receptor 2 (TLR2) ligand FSL-1 is internalized via the clathrin-dependent endocytic pathway triggered by CD14 and CD36 but not by TLR2

Little is known of how Toll-like receptor (TLR) ligands are processed after recognition by TLRs. This study was therefore designed to investigate how the TLR2 ligand FSL-1 is processed in macrophages after recognition by TLR2. FSL-1 was internalized into the murine macrophage cell line, RAW264.7. Both chlorpromazine and methyl-beta-cyclodextrin, which inhibit clathrin-dependent endocytosis, reduced FSL-1 uptake by RAW264.7 cells in a dose-dependent manner but nystatin, which inhibits caveolae- and lipid raft-dependent endocytosis, did not. FSL-1 was co-localized with clathrin but not with TLR2 in the cytosol of RAW264.7 cells. These results suggest that internalization of FSL-1 is clathrin dependent. In addition, FSL-1 was internalized by peritoneal macrophages from TLR2-deficient mice. FSL-1 was internalized by human embryonic kidney 293 cells transfected with CD14 or CD36 but not by the non-transfected cells. Also, knockdown of CD14 or CD36 in the transfectants reduced FSL-1 uptake. In this study, we suggest that (i) FSL-1 is internalized into macrophages via a clathrin-dependent endocytic pathway, (ii) the FSL-1 uptake by macrophages occurs irrespective of the presence of TLR2, and (iii) CD14 and CD36 are responsible for the internalization of FSL-1.

Peripheral arterial occlusive disease: global gene expression analyses suggest a major role for immune and inflammatory responses

Background

Peripheral arterial disease (PAD), a major manifestation of atherosclerosis, is associated with significant cardiovascular morbidity, limb loss and death. However, mechanisms underlying the genesis and progression of the disease are far from clear. Genome-wide gene expression profiling of clinical samples may represent an effective approach to gain relevant information.

Results

After histological classification, a total of 30 femoral artery samples, including 11 intermediate lesions, 14 advanced lesions and 5 normal femoral arteries, were profiled using Affymetrix microarray platform. Following real-time RT-PCR validation, different algorithms of gene selection and clustering were applied to identify differentially expressed genes. Under a stringent cutoff, i.e., a false discovery rate (FDR) <0.5%, we found 366 genes were differentially regulated in intermediate lesions and 447 in advanced lesions. Of these, 116 genes were overlapped between intermediate and advanced lesions, including 68 up-regulated genes and 48 down-regulated ones. In these differentially regulated genes, immune/inflammatory genes were significantly up-regulated in different stages of PAD, (85/230 in intermediate lesions, 37/172 in advanced lesions). Through literature mining and pathway analysis using different databases such as Gene Ontology (GO), and the Kyoto Encyclopedia of Gene and Genomics (KEGG), genes involved in immune/inflammatory responses were significantly enriched in up-regulated genes at different stages of PAD(p < 0.05), revealing a significant correlation between immune/inflammatory responses and disease progression. Moreover, immune-related pathways such as Toll-like receptor signaling and natural killer cell mediated cytotoxicity were particularly enriched in intermediate and advanced lesions (P < 0.05), highlighting their pathogenic significance during disease progression.

Conclusion

Lines of evidence revealed in this study not only support previous hypotheses, primarily based on studies of animal models and other types of arterial disease, that inflammatory responses may influence the development of PAD, but also permit the recognition of a wide spectrum of immune/inflammatory genes that can serve as signatures for disease progression in PAD. Further studies of these signature molecules may eventually allow us to develop more sophisticated protocols for pharmaceutical interventions.

Complicated atheromatous plaque as integral atherogenesis

Genesis of plaque lesion as atherosclerosis is based on the involvement of endothelium and smooth muscle cells

Inflammatory lipoproteins purified from a toxigenic and arthritogenic strain of Mycoplasma arthritidis are dependent on Toll-like receptor 2 and CD14

Mycoplasma arthritidis is a naturally occurring murine pathogen, and the disease model has been used extensively to understand inflammatory mechanisms. Recently, Triton X-114 extracts of a virulent strain of M. arthritidis were found to be more potent in activating macrophages than were those from an avirulent strain, suggesting a role in disease. Here, octyl glucoside extraction of cells was used to identify four distinct bioactive moieties, with molecular masses of approximately 41, 37, 34, and 17 kDa. Their bioactivities were resistant to proteinase K but were destroyed by alkaline hydrolysis and oxidation. As for MALP-2, all were dependent upon Toll-like receptor 2, but unlike MALP-2, they were also dependent upon CD14. The M. arthritidis lipoproteins exhibited infrared absorbances at 2,900 cm(-1) and 1,662 cm(-1), similar to those seen in Pam(3)-Cys-Ser-(Lys)(4). Edman degradation failed to reveal N-terminal sequences, suggesting that they were blocked and therefore might be triacylated. However, mass spectrometry of fragments revealed that the 41-kDa moiety, which binds to serum apolipoprotein A-1, had similarity with the recently described MlpD lipoprotein of M. arthritidis.