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Defining the molecular basis of dendritic cell mediated tolerance

ABSTRACT: Using a TCR transgenic transplantation model a series of differently modulated bmDC (IL10, TGFb and VD3 treated, +/-LPS) were established that could mediate tolerance following adaptive transfer. These modified cells, in contrast to untreated 'immature' bmDC retained their capacity to tolerise following exposure to LPS. The unmodified, non-tolerogenic, LPS-treated cells provided a comparator population to facilitate investigation into molecular expression patterns that correlate with functional phenotype. Keywords: pattern searching, immune tolerance, dendritic cell

ORGANISM(S): Mus musculus

PROVIDER: GSE10651 | GEO | 2008/02/28

SECONDARY ACCESSION(S): PRJNA107735

REPOSITORIES: GEO

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Project description:Siglec-E is a murine CD33-related siglec that functions as an inhibitory receptor and is expressed mainly on neutrophils and macrophage populations. Recent studies have suggested that siglec-E is an important negative regulator of LPS-TLR4 signalling and one report (Wu et al 2016) claimed that siglec-E is required for TLR4 endocytosis following uptake of Escherichia coli by macrophages and dendritic cells (DCs). Our attempts to reproduce these observations using cells from wildtype (WT) and siglec E deficient mice were unsuccessful. We used a variety of assays to determine if siglec-E expressed by different macrophage populations can regulate TLR-4 signalling in response to LPS, but found no consistent differences in cytokine secretion in vitro and in vivo, comparing 3 different strains of siglec-E-deficient mice with matched WT controls. No evidence was found that the siglec-E deficiency was compensated by expression of siglecs-F and –G, the other murine inhibitory CD33-related siglecs. Quantitative proteomics was used as an unbiased approach and provided additional evidence that siglec-E does not suppress inflammatory TLR4 signaling. Interestingly, proteomics revealed a siglec E dependent alteration in macrophage phenotype that could be relevant to functional responses in host defence. In support of this, siglec-E-deficient mice exhibited enhanced growth of Salmonella enterica serovar Typhimurium in the liver following intravenous infection, but macrophages lacking siglec-E did not show altered uptake or killing of bacteria in vitro. Using various cell types including bone marrow derived DCs (BMDC), splenic DCs and macrophages from WT and siglec-E-deficient mice, we showed that siglec-E is not required for TLR4 endocytosis following E.coli uptake or LPS challenge. We failed to see expression of siglec-E by BMDC even after LPS-induced maturation, but confirmed previous studies that splenic DCs express low levels of siglec-E. Taken together, our findings do not support a major role of siglec-E in regulation of TLR4 signalling functions or TLR4 endocytosis in macrophages or DCs. Instead, they reveal that induction of siglec-E by LPS can modulate the phenotype of macrophages, the functional significance of which is currently unclear.

Project description:Human monocyte-derived dendritic cells (moDCs) have been used as an in vitro model for studying tolerance and immunity. However, the underlying metabolic states of tolerogenic (dexamethasone and vitamin D3-treated), immature and immunogenic (mature, LPS-treated) moDCs have not been completely characterized. Through transcriptomic analyses, we determined that tolerogenic moDCs exhibit augmented catabolic pathways with respect to oxidative phosphorylation (OXPHOS), fatty acid oxidation (FAO) and glycolysis. Functionally, tolerogenic moDCs showed the highest mitochondrial membrane potential, production of reactive oxygen species and superoxide, and increased mitochondrial spare respiratory capacity. Tolerogenic and mature moDCs manifested differential FAO gene expression with FAO activity being significantly higher in tolerogenic and immature moDCs than in mature. In addition, tolerogenic and mature moDCs demonstrated similar levels of glycolytic rate, but not glycolytic capacity and reserve, which were more pronounced in tolerogenic and immature moDCs. Finally, tolerogenic and immature moDCs, but not mature moDCs, showed high plasticity to compensate the intracellular ATP content after inhibition of different energetic metabolic pathways. Overall, tolerogenic moDCs exhibit a metabolic signature of increased, stable OXPHOS programing and high plasticity for metabolic adaptation. These findings provide a framework for future research of metabolic properties of human DCs. Total RNA of sixteen samples from four moDC types (tolerogenic, LPS-tolerogenic, immature and mature) were extracted by Trizol (Invitrogen) followed by a clean-up procedure using RNeasy Micro Kit (Qiagen). All RNA samples had an integrity number ≥9.6 assessed by Agilent Bioanalyzer. Total RNA samples were amplified using TargetAmp™ and the biotinilated cRNA was prepared by Nano-g™ Biotin-aRNA Labeling Kit for the Illumina® System (Epicentre). After the hybridization to the Illumina Human HT-12 v4 Beadchips for 17 h at 58°C, the arrays were washed, stained (Illumina Wash Protocol) and then scanned using BeadArray Scanner 500GX. Array data were extracted at the probe level without background correction using Illumina GenomeStudio software. These raw data were quantile normalized and log2 transformed. Technical replicates were obtained from the hybridization in duplicate of three samples. Pearson correlation analysis showed high correlation between the technical replicates (r>0.99). Differentially expressed genes (DEGs) were identified using Limma16 with Benjamini-Hochberg multiple testing correction (p<0.05). DEGs were further clustered into different groups according to the patterns of expression change among the different moDC types using STEM software17. The analysis was performed in R v.2.12.2 (http://www.R-project.org) with Bioconductor 2.12 (http://www.bioconductor.org) and enabled by Pipeline Pilot (www.accelrys.com).

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Defining the molecular basis of dendritic cell mediated tolerance

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