Abstract 2400: Complex gut microbiota modulate rat colon adenoma susceptibility, metabolites, and host gene expression
Authors: Busi Susheel Bhanu , Lei Zhentian , Sumner Lloyd , Amos-Landgraf James 
Published: August 2018

Abstract
We used a multi-omics approach to identify signatures of differential susceptibility in the F344/NTac-Apc+/Pirc (Pirc) rat model of familial adenomatous polyposis. We assessed how different gut microbiomes (GMs) effect the metabolome and host transcriptome to reveal mechanisms of susceptibility. We previously found that differences in the GM are causative determinants of cancer susceptibility using complex microbiota targeted rederivation (CMTR), in which isogenic Pirc rat embryos are transferred into surrogate dams each harboring distinct specific pathogen free gut microbiota: GM-1 and GM-2. Fecal samples collected from CMTR Pirc rats at 1 month of age were analyzed using ultra-high performance liquid chromatography mass spectrometry (UHPLC/MS) to assess the impact of bacterial metabolites on disease susceptibility. At 6 months of age animals were sacrificed, tumor burden assessed, and normal colonic epithelium (NE) and tumor (T) tissues were collected for RNASeq analysis. Metabolomic analysis identified several features that were unique to either GM-1 or GM-2, and principal component analysis revealed a significant separation of the groups. Based on mass-charge ratios, 117 features were significantly different between the groups, of which 28 were putatively identifiable metabolites through the HMDB (Human Metabolite Database) and METLIN databases. Hierarchical cluster analysis of the 1 month metabolome data based on Euclidean distance measurements (Ward's algorithm) showed separation of samples based on tumor burden at sacrifice. Metabolites present prior to observable disease onset at 1 month were correlated with adenoma burden 5 months later. RNAseq between GM-1 and GM-2 tissues identified 2173 differentially expressed genes (DEGs) in the normal epithelium, and 3406 DEGs between tumor groups (FDR &lt; 0.05). Ordinate analysis confirmed both NE and T samples were significantly distinct between rats harboring the two GM profiles. Integrated pathway (IP) analysis of metabolome and RNASeq data based on detected features showed that bile acid biosynthesis was enriched in GM-1, identifying 14 target genes affecting this pathway. Metabolome data from serum samples from an independent group of 1 month old Pirc and wildtype rats with GM-1 also identified metabolites from bile acid biosynthesis elevated in Pirc serum. Six out of the 14 target genes from the IP analysis showed significant differences (FDR &lt; 0.05) between GM-1 and GM-2 in the NE and T tissues indicating a potential role of metabolites modulating both NE and T gene expression. DEG pathway analysis indicated increased fatty acid metabolism and mucin biosynthesis in the high susceptibility group, and apoptosis and calcium signaling pathways increased in the resistant group. These data show the utility of using metabolomics for early detection of adenomas and provide insights into the mechanism of how the GM modulates colon cancer.
Citation Format: Susheel Bhanu Busi, Zhentian Lei, Lloyd Sumner, James Amos-Landgraf. Complex gut microbiota modulate rat colon adenoma susceptibility, metabolites, and host gene expression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2400.