Unraveling the role of the endogenous complex gut microbiota in the Pirc rat model of human colon cancer

Abstract

The gut microbiota (GM) has recently been shown to modulate several systemic conditions in human and model systems, most importantly in intestinal disorders. It has also been demonstrated to have significant impacts on patients' susceptibility to colon cancer. The GM can be defined as the dynamic communities of bacteria, viruses, fungi and archaea that inhabit our gut, skin, and most mucosal surfaces. Considering the fact that the human body is exposed to a large number of microorganisms on a daily basis, the constant flux and dynamic interactions between host genetics and the GM can lead to the variability seen in disease manifestation and susceptibility. This leads to a larger question about the relationship of the GM to model systems, and also whether the constant interactions between the taxa affect the development and progression of disease. Colon cancer is the 3rd leading cause of cancer-related death in the USA. We used embryo rederivation to give isogenic APC-gene mutant Pirc rats, a preclinical model of colon cancer distinct complex GMs to understand its effect on disease susceptibility. In this study, we observed significant differences in intestinal tumor multiplicity based on GM profile. Using 16S rRNA sequencing, we characterized the microbial populations of two distinct GM groups and further determined functional differences by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) to identify metabolic differences between GM groups. Colonic epithelium and tumors were simultaneously profiled via RNASeq transcriptome analysis. Metabolomics analysis allowed detection of differential metabolites between GM groups and potential bacterial-modulated biomarkers of tumor susceptibility. Simultaneously, bacterial relative abundances showed taxa correlating with suppression of both tumor growth and phenotype penetrance as early as 1 month of age. To determine the role of individual bacteria Pirc rats were treated with 3 different bacteria associated with reduced or increased adenoma burden namely, Desulfovibrio vulgaris Hildenborough, Prevotella copri, and Fusobacterium nucleatum. The work outlined here addresses adenoma development in Pirc rats to identify the potential relationship between these taxa and the endogenous, complex GM through multiple approaches. The research presented in this dissertation may potentially help unravel the molecular mechanisms contributing to disease susceptibility, and could identify therapeutic targets and biomarkers for early non-invasive detection and treatment of colon cancer.