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Identification of Hedgehog Signaling and Novel Transcription Factors Involved in Regulation of Systemic Response to LPS

ABSTRACT: Background: Our understanding of the role host genetic factors play in the initiation and severity of infections caused by Gram negative bacteria is incomplete. Methods: To identify novel regulators of the host response to lipopolysaccharide (LPS), 11 inbred murine strains were challenged with LPS systemically. RNA from lung, liver, and spleen tissue was profiled on oligonucleotide microarrays to determine if unique transcripts differentiate susceptible and resistant strains of mice. Gene expression data were analyzed to identify over-represented pathways and transcription factors (TFs). The role of several TFs in innate immune response to LPS was examined by RNA interference in a mouse macrophage cell line. Mouse lines with targeted mutations were utilized to further confirm involvement of two novel genes in innate immunity. Results: In addition to two strains lacking functional TLR4 (C3H/HeJ and C57BL/6JTLR4-/-), three murine strains with functional TLR4 (C57BL/6, 129/SvlmJ, and NZW/LacJ) were found to be resistant to systemic LPS challenge; the other six strains were classified as sensitive. Gene expression analysis supports the involvement of a number of previously identified genes, molecular pathways, and TFs in the host response to LPS but also identifies Hedgehog signaling as a novel pathway activated by LPS. B6;129Ptch1+/+ wild-type mice were shown to be more sensitive to systemic LPS than B6;129Ptch1+/- heterozygote littermates further supporting the role of Hedgehog signaling in systemic LPS response. RNA interference-mediated inhibition of 6 TFs (C/EBP, Cdx-2, E2F1, Hoxa4, Nhlh1, and Tead2), out of 15 tested, was found to diminish production of IL-6 and TNFalpha protein in murine macrophages. The role of E2F1 was confirmed by showing that B6;129E2F1-/- knockout mice are more sensitive to systemic LPS than wild-type controls. Conclusions: Our analysis of gene expression data identified novel pathways and transcription factors that regulate the host response to systemic LPS. Our results provide potential sepsis biomarkers and therapeutic targets that should be further investigated in human populations. Keywords: disease state analysis

ORGANISM(S): Mus musculus

PROVIDER: GSE14675 | GEO | 2009/07/01

SECONDARY ACCESSION(S): PRJNA112375

REPOSITORIES: GEO

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Project description:Background: Our understanding of the role host genetic factors play in the initiation and severity of infections caused by Gram negative bacteria is incomplete. Methods: To identify novel regulators of the host response to lipopolysaccharide (LPS), 11 inbred murine strains were challenged with LPS systemically. RNA from lung, liver, and spleen tissue was profiled on oligonucleotide microarrays to determine if unique transcripts differentiate susceptible and resistant strains of mice. Gene expression data were analyzed to identify over-represented pathways and transcription factors (TFs). The role of several TFs in innate immune response to LPS was examined by RNA interference in a mouse macrophage cell line. Mouse lines with targeted mutations were utilized to further confirm involvement of two novel genes in innate immunity. Results: In addition to two strains lacking functional TLR4 (C3H/HeJ and C57BL/6JTLR4-/-), three murine strains with functional TLR4 (C57BL/6, 129/SvlmJ, and NZW/LacJ) were found to be resistant to systemic LPS challenge; the other six strains were classified as sensitive. Gene expression analysis supports the involvement of a number of previously identified genes, molecular pathways, and TFs in the host response to LPS but also identifies Hedgehog signaling as a novel pathway activated by LPS. B6;129Ptch1+/+ wild-type mice were shown to be more sensitive to systemic LPS than B6;129Ptch1+/- heterozygote littermates further supporting the role of Hedgehog signaling in systemic LPS response. RNA interference-mediated inhibition of 6 TFs (C/EBP, Cdx-2, E2F1, Hoxa4, Nhlh1, and Tead2), out of 15 tested, was found to diminish production of IL-6 and TNF protein in murine macrophages. The role of E2F1 was confirmed by showing that B6;129E2F1-/- knockout mice are more sensitive to systemic LPS than wild-type controls. Conclusions: Our analysis of gene expression data identified novel pathways and transcription factors that regulate the host response to systemic LPS. Our results provide potential sepsis biomarkers and therapeutic targets that should be further investigated in human populations. Keywords: disease state analysis For each strain of mice, 6 mice were treated with LPS and 6 with saline. RNA of 3 animals was pooled to make two pools per condition (two biological replicates). Each pool was labeled with Cy3 and Cy5 and co-hybridized with Stratagene Univeral Mouse Reference (dye flip techical replicates). RNA from lung, liver, and spleen tissue was profiled on oligonucleotide microarrays

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.

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Identification of Hedgehog Signaling and Novel Transcription Factors Involved in Regulation of Systemic Response to LPS

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