Presence Of Toll-like Receptor 4 Research Articles

Seasonal Variation in TLR4 Expression in The Testis and Epididymis of Anatolian Ground Squirrels (Spermophilus xanthoprymnus): Insights from Non-Breeding Period of Pre-Hibernation and Hibernation

This study investigates the modulation of Toll-like receptor 4 (TLR4) expression within the testis and epididymis of Anatolian ground squirrels (Spermophilus xanthoprymnus) during the non-breeding period of pre-hibernation and hibernation. Immunohistochemical investigation showed that TLR4 was not detected in germ cells, Leydig cells, or Sertoli cells in the testicular tissue during the pre-hibernation period. Nevertheless, there was a presence of TLR4 in the vessels walls and certain interstitial cells within the intertubular regions. Epithelial cells in the caput, corpus, and cauda regions of the epididymis showed no TLR4 expression. However, it was observed in the vessel walls, smooth muscle layers, and some interstitial cells. TLR4 expression was seen in spermatogonia and primary spermatocytes during hibernation, with strong labeling observed in the vessel walls of the intertubular area. In contrast, TLR4 was detected in the epididymal epithelium, as well as in the smooth muscle layers and vessel walls throughout all segments. A notable upregulation in the expression of TLR4 in the testis was identified through quantitative image analysis during hibernation as compared to pre-hibernation. During pre-hibernation, the cauda segment of the epididymis exhibited the highest expression of TLR4, whereas during hibernation, the corpus segment demonstrated the highest expression. These findings suggest a dynamic modulation of TLR4 in response to hibernation, highlighting its potential role in reproductive function and immune adaptation.

Frequency of toll-like receptor 4 variants and association with treatment response in children with primary immune thrombocytopenia.

To investigate the frequency of toll-like receptor 4 (TLR4) variants c.896A>G (p.Asp299Gly) and c.1196C>T (p.Thr399Ile) among Egyptian children with primary immune thrombocytopenia (pITP), and their association with disease course and response to treatment. A case-control study that included 80 children with pITP and 50 age- and sex-matched healthy controls. TLR4 c.896A>G and c.1196C>T variants were genotyped using polymerase chain reaction-restriction fragment length polymorphism. Patients were classified according to their response to treatment after 3months as responders and nonresponders. Compared with controls, children with pITP had significantly higher minor allele frequencies of TLR4 p.Asp299Gly (16.25% vs. 6%, odds ratio [OR] 3.04, 95% confidence interval [CI]: 1.16-9.36, p = .014) and p.Thr399Ile (20% vs. 4%, OR 6, 95% CI: 2.02-24.01, p<.001). The presence of p.Asp299Gly variant was significantly associated with chronic ITP (OR 7.78, 95% CI: 2.04-35.69, p<.001) and non-response to therapy with steroid (OR 11.67, 95% CI: 1.32-104.08, p = .012), but not thrombopoietin-receptor agonist (OR 1.67, 95% CI: 0.35-8.19, p = .464). Likewise, having p.Thr399Ile variant was significantly associated with chronic ITP (OR 5.14, 95% CI: 1.6-17.4, p = .002) and non-response to therapy with steroid (OR 6.1, 95% CI: 1.01-49.06, p = .046) but not thrombopoietin-receptor agonist (OR 1.57, 95% CI: 0.33-7.58, p = .515). The presence of TLR4 p.Asp299Gly or p.Thr399Ile variant may be associated with ITP predisposition, chronicity, and non-response to upfront steroid therapy. These findings enhance our understanding of the complex pathophysiology of pITP with potentially important clinical implications.

THE RESEARCH OF TLR4 INVOLVEMENT IN SIGNALING PATHWAYS ACTIVATED IN MURINE OVARIAN CELLS UNDER THE INFLUENCE OF LIPOPOLYSACCHARIDE

Toll-like receptor 4 (TLR4) is a widely described transmembrane protein involved in the inflammatory process. Bacterial infection is one of the main factors influencing the change in TLR4 expression. At the same time, the level of TLR4 expression directly correlates with the severity of the process, which in some cases allows considering these receptors as an early markers of infection. Early it was shown disruption of ovarian cell functions under the condi-tions of experimental endotoxemia in mice. Pathological changes of follicular environment of oocytes resulted in impairment of oocyte meiotic maturation. However, involvement of TLR4 in activation of signaling pathways in ovar-ian cells under the influence of lipopolysaccharide (LPS), requires careful study. In the present work we have investi-gated pharmacological effect of TAK242 (inhibitor of TLR4) on oocyte meiotic maturation in vitro under the influ-ence of LPS. The study was done on cumulus oocyte complexes (COCs) and oocytes, denuded from cumulus cells, which were isolated from ovaries of Albino mice. It was shown that LPS inhibited meiotic maturation in vitro of COCs and cumulus-denuded oocytes. However, 15 min pretreatment with TLR4 inhibitor (ТАК242) with the subsequent ad-dition of LPS to the culture medium, improved meiotic maturation of both COCs and cumulus-denuded oocytes. More-over, simultaneous exposure to ТАК242 and LPS did not show any significant differences in meiotic maturation of both COCs and cumulus-denuded oocytes compared with 15 min pretreatment with ТАК242. The results obtained may indicate the presence of TLR4 on murine oocytes and cumulus cells. Also the results can serve as the basis for the re-search of feasibility of therapeutic use of TLR4 inhibitors in diseases in the course of which interaction between TLR4 and its ligands (in particular LPS) occur.

Distinct alterations of gut morphology and microbiota characterize accelerated diabetes onset in nonobese diabetic mice

Distinct alterations of gut morphology and microbiota characterize accelerated diabetes onset in nonobese diabetic mice

Alcohol-induced adipose tissue macrophage phenotypic switching is independent of myeloid Toll-like receptor 4 expression.

Alcoholic liver disease results from a combination of immune and metabolic pathogenic events. In addition to liver injury, chronic alcohol consumption also causes adipose tissue inflammation. The specific immune mechanisms that drive this process are unknown. Here, we sought to determine the role of the innate immune receptor Toll-like receptor 4 (TLR4) in alcohol-induced adipose tissue inflammation. Using a model of chronic, multiple-binge alcohol exposure, we showed that alcohol-mediated accumulation of proinflammatory adipose tissue macrophages was absent in global TLR4 knockout mice. Proinflammatory macrophage accumulation did not depend on macrophage TLR4 expression; LysMCre-driven deletion of Tlr4 from myeloid cells did not affect circulating endotoxin or the accumulation of M1 macrophages in adipose tissue following alcohol exposure. Proinflammatory cytokine/chemokine production in the adipose stromal vascular fraction also occurred independently of TLR4. Finally, the levels of other adipose immune cells, such as dendritic cells, neutrophils, B cells, and T cells, were modulated by chronic, multiple-binge alcohol and the presence of TLR4. Together, these data indicate that TLR4 expression on cells, other than myeloid cells, is important for the alcohol-induced increase in proinflammatory adipose tissue macrophages.

Association of TLR4 (D299G, T399I), TLR9 -1486T>C, TIRAP S180L and TNF-α promoter (-1031, -863, -857) polymorphisms with risk for systemic lupus erythematosus among South Indians.

The rationale of this case-control study was to explore the association of Toll-like receptor 4 (TLR4) D299G, TLR4 T399I, TLR9 -1486 T>C, TIR-domain-containing adaptor protein (TIRAP) S180 L and tumor necrosis-α (TNF-α) promoter polymorphisms with susceptibility and phenotypic heterogeneity of systemic lupus erythematosus (SLE). PCR-RFLP, real-time PCR was used for the genetic analysis and expression studies and ELISA was used for the determination of specific autoantibodies. TLR4 D299G was associated with the risk for SLE (OR: 1.57, 95% CI: 1.08-2.28), while the TNF-α (-1031, -863, -857) CCC haplotype conferred protection. TLR4 and TIRAP polymorphisms were associated with reduced expression of HLA-DR. The presence of TLR4 and TLR9 polymorphisms increases the MHC2TA expression, while TIRAP polymorphism was associated with reduced expression. TLR4 D299 G showed an inverse association with pulmonary hypertension. TLR 4 T399I and TLR9 -1486 T>C showed a positive association with seizures and photosensitivity, respectively. TIRAP S180 L showed a positive association with alopecia and malar rashes, while an inverse association with psychosis was observed. TLR4 T399I (r = 0.14, p = 0.05) and TIRAP S180 L (r = 0.15, p = 0.03) showed a positive association with anti-Ro antibodies. On the other hand, TLR9 -1486 T>C showed an inverse association with anti-La antibodies (r = -0.20, p = 0.006). To conclude, TLR4 D299G increases the risk for SLE, while TNF-α CCC haplotype reduces the risk for SLE. All these polymorphisms contribute toward phenotypic heterogeneity. TLR4 T399I, TLR9 -1486 T>C and TIRAP S180 L influence specific autoantibody production in SLE.

Lipid a from lipopolysaccharide recognition: Structure, dynamics and cooperativity by molecular dynamics simulations

Molecular dynamics simulations of Lipid A and its natural precursor Lipid IVA from E.coli have been carried out free in solution, bound to the myeliod differentiation protein 2 (MD2) and in the complex of MD2 with the toll like receptor 4 (TLR4). In addition, simulations of the ligand free MD2 and MD2-TLR4 complex were performed. A structural and energetic characterization of the bound and unbound states of Lipid A/IVA was generated. As the crystal structures depict, the main driving force for MD2-Lipid A/IVA are the hydrophobic interactions between the aliphatic tails and the MD2 cavity. The charged phosphate groups do strongly interact with positively charged residues, located at the surface of MD2. However, they are not essential for keeping the lipids in the cavity, indicating a more prominent role in binding recognition and ionic interactions with TLR4 at the MD2/TLR4 interface. Interestingly, in the absence of any ligand MD2 rapidly closes, blocking the binding cavity. The presence of TLR4, though changing the dynamics, was not able to impede the aforementioned closing event. We hypothesize that fluctuations of the H1 region are essential for this phenomenon, and it is plausible that an equilibrium between the open and closed states exists, although the lengths of our simulations are not sufficient to encompass the reversible process. The MD2/Lipid A-TLR4 complex simulations show that the presence of the ligand energetically stabilizes the complex relative to the ligand-free structures, indicating cooperativity in the binding process.

β‐Arrestin 2 regulates toll‐like receptor 4‐mediated apoptotic signalling through glycogen synthase kinase‐3β

Toll-like receptor 4 (TLR4), a key member of the TLR family, has been well characterized by its function in the induction of inflammatory products of innate immunity. However, the involvement of TLR4 in a variety of apoptotic events by an unknown mechanism has been the focus of great interest. Our investigation found that TLR4 promoted apoptotic signalling by affecting the glycogen synthase kinase-3beta (GSK-3beta) pathway in a serum-deprivation-induced apoptotic paradigm. Serum deprivation induces GSK-3beta activation in a pathway that leads to subsequent cell apoptosis. Intriguingly, this apoptotic cascade is amplified in presence of TLR4 but greatly attenuated by beta-arrestin 2, another critical molecule implicated in TLR4-mediated immune responses. Our data suggest that the association of beta-arrestin 2 with GSK-3beta contributes to the stabilization of phospho-GSK-3beta, an inactive form of GSK-3beta. It becomes a critical determinant for the attenuation of TLR4-initiated apoptosis by beta-arrestin 2. Taken together, we demonstrate that the TLR4 possesses the capability of accelerating GSK-3beta activation thereby deteriorating serum-deprivation-induced apoptosis; beta-arrestin 2 represents an inhibitory effect on the TLR4-mediated apoptotic cascade, through controlling the homeostasis of activation and inactivation of GSK-3beta.

Leishmania pifanoiProteoglycolipid Complex P8 Induces Macrophage Cytokine Production through Toll-Like Receptor 4

The P8 proteoglycolipid complex (P8 PGLC) is a glyconjugate expressed by Leishmania mexicana complex parasites. We previously have shown that vaccination with P8 PGLC provides protection against cutaneous leishmaniasis in susceptible BALB/c mice. However, the biological importance of this complex remains unknown. Here we show that P8 PGLC localizes to the surface of Leishmania pifanoi amastigotes and that upon exposure to macrophages, P8 PGLC binds and induces inflammatory cytokine and chemokine mRNAs such as tumor necrosis factor alpha and RANTES early after stimulation. Our studies indicate that cytokine and chemokine induction is dependent upon Toll-like receptor 4 (TLR4). Interestingly, key inflammatory cytokines and chemokines (such as interleukin-6 [IL-6], macrophage inflammatory protein 1beta, and beta interferon [IFN-beta]) that can be induced through TLR4 activation were not induced or only slightly upregulated by P8 PGLC. Activation by P8 PGLC does not occur in the presence of TLR4 alone and requires both CD14 and myeloid differentiation protein 2 for signaling; this requirement may be responsible for the limited TLR4 response. This is the first characterization of a TLR4 ligand for Leishmania. In vitro experiments indicate that L. pifanoi amastigotes induce lower levels of cytokines in macrophages in the absence of TLR4; however, notably higher IL-10/IFN-gamma ratios were found for TLR4-deficient mice than for BALB/c mice. Further, increased levels of parasites persist in BALB/c mice deficient in TLR4. Taken together, these results suggest that TLR4 recognition of Leishmania pifanoi amastigotes is important for the control of infection and that this is mediated, in part, through the P8 PGLC.

Monomeric IgE and lipopolysaccharide synergistically prevent mast-cell apoptosis

The apoptosis of bone marrow-derived mast-cells (BMMCs) after growth factor withdrawal was significantly prevented by a high concentration of IgE in the absence of antigen, and further enhanced by the presence of Toll-like receptor4 (TLR4) ligand, lipopolysaccharide (LPS). The effect of LPS was mediated by TLR4, since TLR4-deficient BMMCs did not show synergistic effects with IgE. The neutralizing amount of anti-IL-3 did not reverse the anti-apoptotic effects of both IgE and combination with LPS. LPS treatment with monomeric IgE synergistically prevented the loss of mitochondrial membrane potentials and was associated with an enhanced expression of anti-apoptotic protein, Bcl-xL, or with a reduced expression of proapoptotic protein, Puma, and Bim, respectively. Altogether, these results suggest that LPS, in a TLR4-dependent manner, together with IgE, synergistically prevent mast-cell apoptosis and may contribute to regulate the tissue mast-cell number.

A39 LPS induced catabolic effect on articular cartilage is dependent on the presence of toll-like receptor-4 and is antagonized by osteogenic protein-1

A39 LPS induced catabolic effect on articular cartilage is dependent on the presence of toll-like receptor-4 and is antagonized by osteogenic protein-1

For Whom the Toll Receptor Signals Death

When mammals are infected with potentially deadly bacteria, the microbes wage a signaling battle with the macrophages of the host's innate immune system. When Toll-like receptors on the macrophages detect molecules of bacterial origin, this stimulates the macrophages to dispense with the invading cells. The anthrax bacterium, B. anthracis , counters by producing lethal toxin, which prevents antiapoptotic signaling through the p38 mitogen-activated protein kinase. Furthermore, Toll-like receptors can produce both antiapoptotic and apoptotic signals, and Hsu et al. now report that the signals generated by Toll-like receptor 4 (TLR4) can turn in favor of the invaders by promoting apoptosis of stimulated macrophages. The authors found that macrophages exposed to an inhibitor of p38 (mimicking a lethal toxin) and to heat-inactivated B. anthracis underwent apoptosis in a manner dependent on the presence of TLR4. The TLR4 signal that promoted cell death was diminished in cells lacking the double-stranded RNA-responsive kinase PKR, a known mediator of TLR signaling, or in cells lacking the adaptor protein TRIF, which links TLR4 to activation of PKR. PKR in turn can inhibit protein synthesis by phosphorylating eukaryotic translation initiation factor 2α (eIF2α). Indeed, eIF2α appeared to be a key target of PKR, because cells from knockin mice expressing a mutant form of eIF2α in which the PKR phosphorylation site was disrupted were less sensitive to a combination of lipopolysaccharide (a bacterial cell wall component) and p38 inhibitor than were wild-type cells. The authors note that inhibition of PKR provides a potential therapeutic strategy to thwart bacteria like B. anthracis that can otherwise use auxiliary factors like lethal toxin to turn TLR signals to deadly effect. L.-C. Hsu, J. M. Park, K. Zhang, J.-L. Luo, S. Maeda, R. J. Kaufman, L. Eckmann, D. G. Guiney, M. Karin, The protein kinase PKR is required for macrophage apoptosis after activation of Toll-like receptor 4. Nature 428 , 341-345 (2004). [Online Journal]

Toll-like receptor 4 on stromal and hematopoietic cells mediates innate resistance to uropathogenic Escherichia coli.

Innate host defenses at mucosal surfaces are critical in the early stages of many bacterial infections. In addition to cells of the traditional innate immune system, epithelial cells can also produce inflammatory mediators during an infection. However, the role of the epithelium in innate host defense in vivo is unclear. Recent studies have shown that lipopolysaccharide (LPS) recognition is critical for bladder epithelial cells to recognize and respond to Escherichia coli. Moreover, the LPS-nonresponsive mouse strain C3HHeJ, which has a mutation in the primary LPS receptor, Toll-like receptor 4 (TLR4), is extremely susceptible to infection with uropathogenic strains of E. coli. In this study, a bone marrow transplant approach was used to investigate the specific contributions of the bladder epithelium (and other stromal cells) in the TLR4-mediated innate immune response to the invading E. coli pathogen. Mice expressing the mutant TLR4 in the epithelialstromal compartment were not able to mount a protective inflammatory response to control the early infection even when their hematopoietic cells expressed wild-type TLR4. However, the presence of TLR4(+) epithelialstromal cells was not sufficient to activate an acute inflammatory response unless the hematopoietic cells were also TLR4(+). These results demonstrated that bladder epithelial cells play a critical role in TLR4-mediated innate immunity in vivo during a mucosal bacterial infection.

Induction of innate immune responses by Escherichia coli and purified lipopolysaccharide correlate with organ- and cell-specific expression of Toll-like receptors within the human urinary tract.

Mucosal epithelial linings function as physical barriers against microbes. In addition, they participate in the first line of host defence by production of a variety of proinflammatory mediators when exposed to microbes and microbial agents. Here, we use a human urinary tract infection model to demonstrate that organ- and cell-specific innate responses induced by lipopolysaccharides (LPS) present on Gram-negative bacteria correlates with the expression of Toll-like receptor 4 (TLR4). The presence of TLR4 on human bladder epithelial cells enables them to rapidly respond to bacterial infections in vitro and in vivo. In contrast, TLR4 is not expressed on human proximal tubule cells isolated from the renal cortex, which may explain the cortical localization of bacteria in pyelonephritis. TLR4-negative renal epithelial cells, A498, are non-responsive to purified LPS, however, they respond to viable bacteria via a mannose-sensitive attachment-mediated pathway. To identify LPS components recognised by bladder epithelial cells, a bacterial lipid A mutant and LPS of different chemotypes were tested. Full interleukin 8 induction required hexa-acylated lipid A and was decreased by between 50% and 70% in the presence of O-antigen. Taken together, we propose that multiple independent pathways, which are organ- and cell-specifically expressed, mediate bacterial recognition and determine the outcome of innate responses to infection.