Mountain View
biomedical and healthCAre Data Discovery Index Ecosystem
help Advanced Search
Title: Changes in colon gene expression assoc. with increased colon inflam. in IL-10-/- mice inoculated with Enterococcus sp.      
Transcriptome or Gene expression
Inappropriate response to normal intestinal bacteria is involved in the development of Inflammatory Bowel Diseases (IBD, e.g. Crohn’s Disease (CD), ulcerative colitis (UC)) and variations in the host genome may mediate this process. IL-10-/- mice develop CD-like colitis mainly in the colon, in part due to inappropriate responses to normal intestinal bacteria including Enterococcus strains. Comprehensive characterization of changes in gene expression associated with the observed inflammation in the IL-10-/- mouse model has yet to be reported. Our aim was to characterize changes in colonic gene expression in IL-10-/- and C57BL/6J (C57; control) mice resulting from oral bacterial inoculation with 12 Enterococcus faecalis and faecium (EF) strains isolated from calves or poultry, complex intestinal flora (CIF) collected from healthy control mice, or a mixture of the two (EF•CIF). At 12 weeks of age, total RNA extracted from intact colon was hybridized to Agilent 44k mouse arrays. Lists of differentially expressed genes were generated using linear models for microarray analysis (Bioconductor), and genes clustered using GeneSpring GX and Ingenuity Pathways Analysis software. Intestinal inflammation was increased in IL-10-/- mice as a result of inoculation, with the strongest effect being in the EF and EF.CIF groups; expression of >4,000 gene probes was altered in colon tissue compared with similarly inoculated C57 mice. Genes differentially expressed in IL-10-/- mice as a result of EF or EF.CIF inoculation were associated with the following pathways: inflammatory disease (111 genes differentially expressed), immune response (209 genes), antigen presentation (11 genes, particularly major histocompatability complex Class II), fatty acid metabolism (30 genes) and detoxification (31 genes). Our results suggest that the colonic inflammation in EF and EF.CIF-inoculated IL-10-/- mice is mediated by mechanisms similar to those of human IBD, in particular CD. Example logFC calculation This example describes the calculation of the fold-change value (logFC) for a single spot (in this case, spot 27222) for a single comparison. This calculation method was applied to generate all of the comparison data shown in the supplementary data files. The comparison in question is for: colon tissue from C57BL/6J mouse with EF.CIF treatment (represented by duplicate samples GSM307282 (Title: C57BL/6J_Colon_EF.CIF_Rep1_(Pool17)) and GSM307283 (Title: C57BL/6J_Colon_EF.CIF_Rep2_(Pool18)) vs. colon tissue from C57BL/6J mouse under conventional conditions (represented by duplicate samples GSM307270 (Title: C57BL/6J_Colon_Conventional_Rep1_(Pool5)) and GSM307271 (Title: C57BL/6J_Colon_Conventional_Rep2_(Pool6)) Important Note: Limma analysis maps the treatments on each slide to the M values which are by convention always log2(R) - log2(G). Because this experiment is a reference design, with the reference RNA always Cy5 (i.e. red, channel 2) and the treatment sample Cy3 (i.e. green, channel 1), and we are interested in the values of the treatment samples compared with the reference, the M values in the data files are displayed as log2(G) - log2(R) The average expression is what is important here, which is calculated from the normalized M values for the appropriate comparison of interest as follows: [1] Mean value for Spot 27222, for each treatment: C57BL/6J mouse, EF.CIF: = mean (0.26363587 (GSM307282), 0.05084283 (GSM307283)) = 0.15723935 C57BL/6J mouse, conventional = mean (1.42951674 (GSM307270),1.15444106 (GSM307271)) = 1.2919789 [2] Calculation of LogFC for the comparison of interest: The contrast of interest is C57BL/6J: EF.CIF vs Conventional, so by performing a subtraction of these values for the comparison of interest (i.e. (mean for EF.CIF) - (mean for Conventional), the common reference is cancelled out, thus: C57BL/6J: EF.CIF vs Conventional = 0.15723935 - 1.2919789 = -1.13473955 So, the fold-change value (logFC) for spot 27222 for the comparison in question (C57BL/6J: EF.CIF vs. Conventional) is: -1.13473955 Overall design: Animals. Twenty five male IL-10-/- (C57BL/6J background, formal designation B6.129P2-IL-10/J) mice and twenty five male C57BL/6J (C57) control mice were received from The Jackson Laboratory (Bar Harbor, Maine, USA) at approximately five weeks of age. Mice were housed either in pairs or groups of three (5 mice per treatment) in shoebox-style cages containing untreated wood shavings and a plastic tube for environmental enrichment. The animal room was maintained at a temperature of ~22°C and humidity of ~50% with a 12 hour light/dark cycle. All mice had ad libitum access to water, which was refreshed twice a week. An AIN-76A powdered diet was supplied twice a week, with sufficient provided to meet the daily intake of IL-10-/- mice, as determined in a previous feeding trial (data not shown). The diet for all groups was sterilized by gamma irradiation (Schering-Plough, Wellington, New Zealand) to a level required for SPF conditions, to minimize the possibility of bacterial introduction to the SPF group of animals. All mice were weighed three times weekly and carefully monitored for disease symptoms (weight loss, soft faeces and inactivity). Experimental design. Both IL-10-/- and C57 mice were randomly divided into five treatment groups with five animals per group. SPF. Housed in Specific Pathogen Free (SPF) conditions (isolator cages supplied with HEPA filtered air (Tecniplast SpA, Buguggiate, Italy)). C. Maintained under conventional conditions. EF. Maintained under conventional conditions and orally inoculated (200 microlitres) with a solutions containing 12 pure strains of Enterococcus (1.2 x 10^8 colony forming units (CFU)). CIF. Maintained under conventional conditions and orally inoculated with conventional intestinal flora (CIF) derived from healthy age-matched C57BL/6 mice which had been raised under conventional conditions. The CIF inoculation protocol was included to better mimic the complete microbiota associated with the mouse gastrointestinal tract. EF•CIF. Maintained under conventional conditions and orally inoculated with a combination of the EF and CIF inoculation solutions (6.0 x 10^7 CFU from the EF inoculum). All mice were euthanised via CO2 asphyxiation and cervical dislocation at 12 weeks of age. Blood was collected from euthanised mice by cardiac puncture. Plasma was separated from red blood cells by centrifugation (2000 g, 10 min, 4 ºC), frozen in liquid nitrogen and stored at - 80 ºC. The intestine was removed, cut open lengthwise and flushed with 0•9 % NaCl to remove digesta residues. The proximal half of the colon was cut in two pieces, one for histological evaluation and other for gene expression studies. Samples of the colon tissue for gene expression analysis were frozen in liquid nitrogen and stored at - 80 ºC. Samples for histological analysis were stored in formalin solution (10 % neutral buffered) at room temperature. Total RNA was extracted from the colon tissues using Trizol (Invitrogen, Carlsbad, CA, USA) as described by the manufacturer, with a subsequent purification step using RNeasy columns (Qiagen, San Diego, CA, USA). RNA was quantified using a NanoDrop ND-1000 spectrophotometer (NanoDrop Technologies, Wilmington, DE, USA) and RNA quality was examined using a RNA 6000 LabChip Kit and a 2100 Bioanalyser (Agilent Technologies, Palo Alto, CA, USA). The Low RNA Input Fluorescent Linear Amplification Kit (Agilent Technologies Inc., Palo Alto, California, USA) was used to synthesize cDNA and fluorescent cRNA. Labelled cRNA was made on the same day for all sample pools, including the reference sample. cDNA was synthesized from 500 ng of purified total RNA from each pool using T7 promotor primer and Moloney Murine Leukemia Virus Reverse Transcriptase according to the manufacturer’s protocol. Cy3 (PerkinElmer, Waltham, Massachusetts 02451, USA) was used to label sample groups, while the reference RNA was labeled with Cy5 (PerkinElmer, Waltham, Massachusetts 02451, USA). HYBRIDIZATION Microarray hybridization was performed according to a reference design without dye swap. The in situ hybridization kit-plus (Agilent Technologies Inc., Palo Alto, California, USA) was used to hybridize cRNA samples to Agilent Technologies Mouse G4121A - 44k 60mer oligonucleotide arrays. Cy3-labelled cRNA (sample, 0.75 µg) and Cy5-labelled cRNA (reference, 0.75 µg) were hybridised onto the microarray according to the manufacturer’s protocol. Following hybridisation, slides were washed in solutions I, II and III (Agilent Technologies, Santa Clara, CA, USA) and air-dried. SCAN PROTOCOL Slides were scanned using a GenePix 4200A scanner (Molecular Devices Corporation, Sunnyvale, CA, USA) at a photomultiplier tube (PMT) setting of 450 V. Spot identification and quantification were performed using GenePix 6.0 software (Molecular Devices Corporation, Sunnyvale, CA, USA). Spot identification and quantification was performed using GenePix 6.0 software (Molecular Devices). All slides were individually checked and manually flagged for abnormalities. DATA PROCESSING Statistical analysis was performed using linear models for microarray analysis (limma) within the Bioconductor framework. Before analysis, poor quality spots were manually flagged and filtered out. Quality of the microarray data was assessed on diagnostic plots (boxplots and density plots) and spatial images generated from the raw (non-processed) data. All twenty arrays passed these strict criteria and were included in the analyses. Intensity ratio values for all microarray spots were normalized using a within-slide global Locally Weighted Scatterplot Smoothing (Loess) procedure to remove the effect of systematic variation in the microarrays; no background correction was necessary due to homogeneous hybridization. The normalized data from the arrays of each treatment group were averaged. For each comparison, differentially expressed genes were identified using false discovery rate (FDR) control with a threshold of q < 0.05. Data were log transformed before analysis and the mean difference between treatments calculated on this scale, resulting in a log ratio for each probe. The normalized values in the database consist of these log ratios. MA plots of the microarray data were drawn in order to check that there was no dependence of the log ratio on the intensity for any slide. The significance of the log ratio for each probe was determined by calculating one modified t-statistic per probe using an empirical Bayes approach. The probability values were then corrected for multiple testing using the Benjamini and Hochberg correction, and a false discovery rate (FDR) calculated. Probes that had an FDR of less than 5 % (q<0*05) were considered to be differentially expressed between treatment.
Mus musculus
National Center for Biotechnology Information
NCBI BioProject