BackgroundPouchitis is common after ileal pouch-anal anastomosis (IPAA) surgery for ulcerative colitis (UC). Similar to inflammatory bowel disease (IBD), both host genetics and the microbiota are implicated in its pathogenesis. We use the IPAA model of IBD to associate mucosal host gene expression with mucosal microbiomes and clinical outcomes. We analyze host transcriptomic data and 16S rRNA gene sequencing data from paired biopsies from IPAA patients with UC and familial adenomatous polyposis. To achieve power for a genome-wide microbiome-transcriptome association study, we use principal component analysis for transcript and clade reduction, and identify significant co-variation between clades and transcripts.ResultsHost transcripts co-vary primarily with biopsy location and inflammation, while microbes co-vary primarily with antibiotic use. Transcript-microbe associations are surprisingly modest, but the most strongly microbially-associated host transcript pattern is enriched for complement cascade genes and for the interleukin-12 pathway. Activation of these host processes is inversely correlated with Sutterella, Akkermansia, Bifidobacteria, and Roseburia abundance, and positively correlated with Escherichia abundance.ConclusionsThis study quantifies the effects of inflammation, antibiotic use, and biopsy location upon the microbiome and host transcriptome during pouchitis. Understanding these effects is essential for basic biological insights as well as for well-designed and adequately-powered studies. Additionally, our study provides a method for profiling host-microbe interactions with appropriate statistical power using high-throughput sequencing, and suggests that cross-sectional changes in gut epithelial transcription are not a major component of the host-microbiome regulatory interface during pouchitis.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-015-0637-x) contains supplementary material, which is available to authorized users.

BACKGROUND & AIMS Genome-wide association studies (GWAS) have identified 200 inflammatory bowel disease (IBD) loci, but the genetic architecture of Crohn’s disease (CD) and ulcerative colitis (UC) remains incompletely defined. Here we aimed to identify novel associations between IBD and functional genetic variants using the Illumina ExomeChip. METHODS Genotyping was performed in 10,523 IBD cases and 5,726 non-IBD controls. 91,713 functional single nucleotide polymorphism (SNP) loci in coding regions were analyzed. A novel identified association was further replicated in two independent cohorts. We further examined the association of the identified SNP with microbiota from 338 mucosal lavage samples in the Mucosal Luminal Interface (MLI) cohort measured using 16S sequencing. RESULTS We identified an association between CD and a missense variant encoding alanine (Ala) or threonine (Thr) at position 391 in the zinc transporter solute carrier family 39, member 8 protein (SLC39A8 Ala391Thr, rs13107325) and replicated the association with CD in two replication cohorts (combined meta-analysis p=5.55×10−13). This variant has previously been associated with distinct phenotypes including obesity, lipid levels, blood pressure and schizophrenia. We subsequently determined that the CD-risk allele was associated with altered colonic mucosal microbiome composition in both healthy controls (p=0.009) and CD cases (p=0.0009). Moreover, microbes depleted in healthy carriers strongly overlap with those reduced in CD patients (p=9.24×10−16) and overweight individuals (p=6.73×10−16). CONCLUSIONS Our results suggest that an SLC39A8-dependent shift in the gut microbiome could explain its pleiotropic effects on multiple complex diseases including CD.

IntroductionInflammatory complications following ileal pouch-anal anastomosis (IPAA) for ulcerative colitis (UC) are common and thought to arise through mechanisms similar to de novo onset inflammatory bowel disease. The aim of this study was to determine whether specific organisms in the tissue-associated microbiota are associated with inflammatory pouch complications.MethodsPatients having previously undergone IPAA were recruited from Mount Sinai Hospital. Clinical and demographic information were collected and a pouchoscopy with biopsy of both the pouch and afferent limb was performed. Patients were classified based on post-surgical phenotype into four outcome groups: familial adenomatous polyposis controls (FAP), no pouchitis, pouchitis, and Crohn’s disease-like (CDL). Pyrosequencing of the 16S rRNA V1-V3 hypervariable region, and quantitative PCR for bacteria of interest, were used to identify organisms present in the afferent limb and pouch. Associations with outcomes were evaluated using exact and non-parametric tests of significance.ResultsAnalysis at the phylum level indicated that Bacteroidetes were detected significantly less frequently (P<0.0001) in the inflammatory outcome groups (pouchitis and CDL) compared to both FAP and no pouchitis. Conversely, Proteobacteria were detected more frequently in the inflammatory groups (P=0.01). At the genus level, organisms associated with outcome were detected less frequently among the inflammatory groups compared to those without inflammation. Several of these organisms, including Bacteroides (P<0.0001), Parabacteroides (P≤2.2x10-3), Blautia (P≤3.0x10-3) and Sutterella (P≤2.5x10-3), were associated with outcome in both the pouch and afferent limb. These associations remained significant even following adjustment for antibiotic use, smoking, country of birth and gender. Individuals with quiescent disease receiving antibiotic therapy displayed similar reductions in these organisms as those with active pouch inflammation.ConclusionsSpecific genera are associated with inflammation of the ileal pouch, with a reduction of typically ubiquitous organisms characterizing the inflammatory phenotypes.