A mouse model of human TLR4 D299G/T399I SNPs reveals mechanisms of altered LPS and pathogen responses.
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ABSTRACT:
SUBMITTER: Richard K
PROVIDER: S-EPMC7685774 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Dysregulated Toll-Like Receptor (TLR) signalling and genetic polymorphisms in these proteins are linked to many human diseases. We investigated TLR4 functional variants D299G and T399I to assess the impact on LPS-induced responsiveness in comparison to wild-type TLR4. The mechanism by which this occurs in unclear as these SNPs do not lie within the lipid A binding domain or dimerisation sites of the LPS-TLR4/MD2 receptor complexes. Transfection of TLR4D299G, TLR4T399I or TLR4D299G. T399I into HEK cells resulted in constitutive activation of an NF-?B reporter gene and a blunting of the LPS-induced reporter activation compared to WT-TLR4. Unstimulated human monocyte/macrophages, from patients with the D299G and T399I SNPs demonstrated a downregulation of many genes, particularly Tram/Trif signalling pathway constitutents compared to the TLR4 wild-type subjects supporting the concept of basal receptor activity. Monocyte/macrophages from carriers of the TLR4 D299G and T399I polymorphisms stimulated with LPS showed >6 fold lower levels of NF-?B and ?12 fold higher IFN-? gene expression levels compared to wild-type subjects (P<0.05; MWU test) and dramatically altered resultant cytokine profiles. We conclude that these TLR4 SNPs affect constitutive receptor activity which impacts on the hosts ability to respond to LPS challenge leading to a dysregulated sub-optimal immune response to infection.
| S-EPMC4218727 | biostudies-literature
Project description:Activation of Toll-like-receptor 4 (TLR4) causes chronic inflammation that can result in obesity and metabolic syndrome (MeS). This study aimed to investigate the role of TLR4 polymorphisms of TLR4D299G/T399I, and its impact on protein expression of TLR4 in obese female subjects. A prospective cross-sectional association study was performed on Arab female subjects from Qatar University. The subjects were categorized according to BMI classifications into two groups: "obese; n = 69" and "non-obese; n = 136". Anthropometric measurements, weight (kg), height (m) and waist circumference (WC) were evaluated, and the body mass index (BMI) was calculated. Fasting blood samples were collected, and assessment of glucose, lipid profile, C-reactive protein (CRP), leptin, IL-6 and insulin was performed. Insulin resistance was computed using HOMA-IR. Genotyping of the TLR4 polymorphisms of TLR4D299G (rs4986790) and TLR4T399I (rs4986791) was performed by the 5' nuclease assay by TaqMan MGB probe. Flow cytometry was used to evaluate the monocyte cell surface expression of TLR4. The frequency distribution of the genotype revealed that homozygous AA is the most frequent among obese subjects (86.4%) for (TLR4D299G, A > G) and the homozygous CC genotype is the most frequent (92.4%) for (TLR4T399I, C > T). Haplotype analysis of TLR4 D299G/T399I showed that GT carriers had a significant association with increased probability of insulin resistance (odds ratio = 4.73; 95% CI 1.19-18.90; p-value = 0.016). The monocyte cell surface of TLR4 was significantly higher by 1.3 folds in obese compared to non-obese subjects. TLR4 D299G/T399I haplotype polymorphism is associated with an increased risk of insulin resistance with the upregulation of TLR4 protein expression in obese subjects.
| S-EPMC7397302 | biostudies-literature
Project description:BACKGROUND:TLR4 polymorphism replacing Asp-299 with Gly and Thr-399 with Ile (D299G/T399I) causes LPS hyporesponsiveness. RESULTS:TLR4(SNPs)·MD-2·LPS exhibits an agonistic 2:2:2 architecture. Local structural differences were observed around D299G, but not around T399I, SNP site. CONCLUSION:These local differences cause the modulation of surface properties of TLR4, which may affect ligand binding. SIGNIFICANCE:This study provides structural evidence of the functionality of the mutant TLR4 carrying the SNPs. Toll-like receptor 4 (TLR4) and its coreceptor MD-2 recognize bacterial lipopolysaccharide (LPS) and signal the innate immune response. Two single nucleotide polymorphisms (SNPs) of human TLR4, D299G and T399I, have been identified and suggested to be associated with LPS hyporesponsiveness. Moreover, the SNPs have been proposed to be associated with a variety of infectious and noninfectious diseases. However, how the SNPs affect the function of TLR4 remains largely unknown. Here, we report the crystal structure of the human TLR4 (D299G/T399I)·MD-2·LPS complex at 2.4 Å resolution. The ternary complex exhibited an agonistic "m"-shaped 2:2:2 architecture that was similar to that of the human wild type TLR4·MD-2·LPS complex. Local structural differences that might affect the binding of the ligands were observed around D299G, but not around T399I, SNP site.
| S-EPMC3504774 | biostudies-literature
Project description:Leptospirosis is a worldwide re-emerging zoonosis caused by pathogenic Leptospira spp. All vertebrate species can be infected; humans are sensitive hosts whereas other species, such as rodents, may become long-term renal carrier reservoirs. Upon infection, innate immune responses are initiated by recognition of Microbial Associated Molecular Patterns (MAMPs) by Pattern Recognition Receptors (PRRs). Among MAMPs, the lipopolysaccharide (LPS) is recognized by the Toll-Like-Receptor 4 (TLR4) and activates both the MyD88-dependent pathway at the plasma membrane and the TRIF-dependent pathway after TLR4 internalization. We previously showed that leptospiral LPS is not recognized by the human-TLR4, whereas it signals through mouse-TLR4 (mTLR4), which mediates mouse resistance to acute leptospirosis. However, although resistant, mice are known to be chronically infected by leptospires. Interestingly, the leptospiral LPS has low endotoxicity in mouse cells and is an agonist of TLR2, the sensor for bacterial lipoproteins. Here, we investigated the signaling properties of the leptospiral LPS in mouse macrophages. Using confocal microscopy and flow cytometry, we showed that the LPS of L. interrogans did not induce internalization of mTLR4, unlike the LPS of Escherichia coli. Consequently, the LPS failed to induce the production of the TRIF-dependent nitric oxide and RANTES, both important antimicrobial responses. Using shorter LPS and LPS devoid of TLR2 activity, we further found this mTLR4-TRIF escape to be dependent on both the co-purifying lipoproteins and the full-length O antigen. Furthermore, our data suggest that the O antigen could alter the binding of the leptospiral LPS to the co-receptor CD14 that is essential for TLR4-TRIF activation. Overall, we describe here a novel leptospiral immune escape mechanism from mouse macrophages and hypothesize that the LPS altered signaling could contribute to the stealthiness and chronicity of the leptospires in mice.
| S-EPMC7447051 | biostudies-literature
Project description:Endometriosis is a widespread multifactorial disease in which environmental, genetic, and epigenetic factors contribute to the phenotype. Single Nucleotide Polymorphisms (SNPs) in genes implicated in pivotal molecular mechanisms have been investigated as susceptible risk factors in distinct populations. Among these, Toll-like receptor 4 (TLR4) represents a good candidate due to its role in the immune/inflammatory response and endometriosis pathogenesis. The TRL4 gene T399I SNP (C/T transition, rs4986791) was investigated in 236 Italian endometriosis patients and 150 controls by using the PCR-RFLP method. One-tailed Fisher's exact test was used to compare differences between categorical variables. T399I genotype distribution was evaluated for Hardy-Weinberg equilibrium in both groups using the Chi-squared test for given probabilities. Fisher's exact test comparing C and T allele frequencies showed a difference in the frequency of T alleles between patients and controls (OR = 1.96, 95% confidence interval 0.91-4.23; p-value = 0.0552). Genotype frequencies did not show any significant difference between patients and controls. The homozygous TT genotype was observed in 2% of endometriosis women and not in controls. Our results show that the TLR4 rs4986791 T variant may be considered a genetic risk factor for endometriosis in Italian women. More extensive studies in other populations are needed to confirm this result.
| S-EPMC7277393 | biostudies-literature
Project description:BACKGROUND: Toll-like-receptor 4 (TLR) is discussed to provide a molecular link between obesity, inflammation and insulin resistance. Genetic studies with replications in non-diabetic individuals in regard to their fat distribution or insulin resistance according to their carrier status of a common toll-like receptor 4 (TLR4) variant (TLR4(D299G/T399I)) are still lacking. METHODOLOGY/PRINCIPAL FINDINGS: We performed a cross-sectional analysis in individuals phenotyped for prediabetic traits as body fat composition (including magnetic resonance imaging), blood glucose levels and insulin resistance (oral glucose tolerance testing, euglycemic hyperinsulinemic clamp), according to TLR4 genotype determined by candidate SNP analyses (rs4986790). We analyzed N?=?1482 non-diabetic individuals from the TÜF/TULIP cohort (South Germany, aged 39±13 y, BMI 28.5±7.9, mean±SD) and N?=?5327 non-diabetic participants of the METSIM study (Finland, males aged 58±6 y, BMI 26.8±3.8) for replication purposes. German TLR4(D299G/T399I) carriers had a significantly increased body fat (XG in rs4986790: +6.98%, p?=?0.03, dominant model, adjusted for age, gender) and decreased insulin sensitivity (XG: -15.3%, Matsuda model, p?=?0.04; XG: -20.6%, p?=?0.016, clamp; both dominant models adjusted for age, gender, body fat). In addition, both liver fat (AG: +49.7%; p?=?0.002) and visceral adipose tissue (AG: +8.2%; p?=?0.047, both adjusted for age, gender, body fat) were significantly increased in rs4986790 minor allele carriers, and the effect on liver fat remained significant also after additional adjustment for visceral fat (p?=?0.014). The analysis in METSIM confirmed increased body fat content in association with the rare G allele in rs4986790 (AG: +1.26%, GG: +11.0%; p?=?0.010, additive model, adjusted for age) and showed a non-significant trend towards decreased insulin sensitivity (AG: -0.99%, GG: -10.62%). CONCLUSIONS/SIGNIFICANCE: TLR4(D299G/T399I) associates with increased total body fat, visceral fat, liver fat and decreased insulin sensitivity in non-diabetic Caucasians and may contribute to diabetes risk. This finding supports the role of TLR4 as a molecular link between obesity and insulin resistance.
| S-EPMC2981584 | biostudies-literature
Project description:Subacute ruminal acidosis (SARA) is known to trigger a systemic inflammatory response that is possibly caused by the translocation of lipopolysaccharides (LPS) from the gastrointestinal tract into the bloodstream. The aim of this study is to investigate this causal relationship between the increases of circulating LPS and liver inflammation. Here we found that SARA goats exhibited significantly increased LPS concentrations in both the rumen and portal vein. The livers of these goats exhibited increased mRNA concentrations of pro-inflammatory genes that indicated inflammation. Meanwhile, the occurrence of liver inflammation was further validated by the enhanced protein expression of those cytokines in the livers of SARA goats. These increased expressions of detected pro-inflammatory genes were likely mediated by enforced TLR4 signaling because SARA increased the concentrations of TLR4 mRNA and protein in the liver and the abundance of both the NF-kB-p65 factor and its active phosphorylated variant. We also verified that the enhanced TLR4 expression was accompanied by chromatin decompaction and demethylation of the proximal TLR4 promoter. Hence, epigenetic mechanisms are involved in the enforced expression of immune genes during SARA, and these findings open innovative routes for interventions via the modulation of these epigenetic mechanisms.
| S-EPMC4770722 | biostudies-literature
Project description:Viral infection is associated with approximately one-half of acute exacerbations of chronic obstructive pulmonary disease (COPD), which in turn, accelerate disease progression. In this study, we infected mice exposed to a combination of elastase and LPS, a constituent of cigarette smoke and a risk factor for development of COPD, with rhinovirus serotype 1B, and examined animals for viral persistence, airway resistance, lung volume, and cytokine responses. Mice exposed to elastase and LPS once a week for 4 wk showed features of COPD such as airway inflammation and obstruction, goblet cell metaplasia, reduced lung elastance, increased total lung volume, and increased alveolar chord length. In general, mice exposed to elastase or LPS alone showed intermediate effects. Compared with rhinovirus (RV)-infected PBS-exposed mice, RV-infected elastase/LPS-exposed mice showed persistence of viral RNA, airway hyperresponsiveness, increased lung volume, and sustained increases in expression of TNFalpha, IL-5, IL-13, and muc5AC (up to 14 days postinfection). Furthermore, virus-induced IFNs, interferon response factor-7, and IL-10 were deficient in elastase/LPS-treated mice. Mice exposed to LPS or elastase alone cleared virus similar to PBS-treated control mice. We conclude that limited exposure of mice to elastase/LPS produces a COPD-like condition including increased persistence of RV, likely due to skewing of the immune response towards a Th2 phenotype. Similar mechanisms may be operative in COPD.
| S-EPMC2777490 | biostudies-literature
Project description:TLR4 polymorphisms such as Asp299Gly and Thr399Ile related to Gram-negative sepsis have been reported to result in significantly blunted responsiveness to LPS. Our study group previously screened other TLR4 polymorphic variants by checking the NF-κB activation in comparison to wild type (WT) TLR4 in human embryonic kidney 293T cells. In this study, we found that the Lys694Arg (K694R) polymorphism reduced the activation of NF-κB, and the production of downstream inflammatory factors IL-1, TNF-α and IL-6, representing the K694R polymorphism, led to blunted responsiveness to LPS. Then, we examined the influence of the K694R polymorphism on total and cell-surface TLR4 expression by Western blotting and flow cytometry, respectively, but observed no differences between the K694R polymorphism and WT TLR4. We also used co-immunoprecipitation to determine the interaction of the K694R polymorphism and WT TLR4 with their co-receptor myeloid differentiation factor 2 (MD2) and their downstream signal adaptor MyD88. We found that K694R reduced the recruitment of MyD88 in TLR4 signalling but had no impact on the interaction with MD2.
| S-EPMC8504268 | biostudies-literature
Project description:Mice deficient in the hemochromatosis gene, Hfe, have attenuated inflammatory responses to Salmonella infection associated with decreased macrophage TNF-alpha and IL-6 biosynthesis after exposure to LPS. In this study, we show that the abnormal cytokine production is related to impaired TLR4 signaling. Despite their abnormal response to LPS, Hfe KO macrophages produced amounts of TNF-alpha similar to those in WT cells after TLR2 stimulation. Consistent with this finding, LPS-induced activation of Mal/MyD88-dependent events was normal in the mutant macrophages. However, LPS-induced IFN-beta expression, a TRAM/TRIF-dependent response activated by TLR4, was reduced by Hfe deficiency. This reduction could be replicated in WT macrophages with the use of iron chelators. In contrast, TLR3-activated expression of IFN-beta, a TRIF-dependent response, was normal in Hfe KO macrophages and was unaffected by iron chelation. Our data suggest that low intracellular iron selectively impairs signaling via the TLR4/TRAM/TRIF pathway proximal to TRIF and results in reduced LPS-induced cytokine expression. Furthermore, by mimicking the altered iron metabolism associated with Hfe deficiency, we found that 3 different inhibitors of hepcidin attenuated Salmonella-induced and noninfectious enterocolitis. Thus, manipulation of iron homeostasis could represent a new therapeutic approach to controlling inflammation.
| S-EPMC2769199 | biostudies-literature