Defining the changing microbiome composition and host-microbe mechanistic effects following Apc inactivation during colorectal cancer pathogenesis

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Project Summary Globally, colorectal cancer (CRC) is the second leading cause of cancer-related deaths in men and women and is projected to increase by 70% in the next 20 years. One of the earliest initiating events of CRC is mutation of adenomatous polyposis coli (APC), a tumor suppressor gene. This mutation initiates the gradual progression from normal proliferating colon epithelial cells (CECs) to dysplastic lesions, to the eventual formation of tumors, known as adenomas. Somatic APC mutations occur in >80% of sporadic CRCs. Growing evidence demonstrates that factors within the local microenvironment can significantly influence cancer risk and onset. One key characteristic of the colon adenomatous environment is an imbalanced microbiome. Disruption in the makeup of these microbiota, known as dysbiosis, is related to many diseases, including colitis, inflammatory bowel disease, and CRC. While dysbiosis contributes to promoting adenoma progression and CRC, whether APC mutation triggers changes in the local microenvironment to facilitate tumor progression and microbiome dysbiosis remains largely unknown. Using an inducible murine model of CEC Apc truncation, our lab found that Apc inactivation and subsequent colon tumorigenesis results in microbiome dysbiosis and outgrowth of pathogenic species, further, associated with increased bacterial mucosal adherence. This proposal aims to define the timing and mechanisms by which the early microbiome changes following Apc inactivation. We hypothesize that Apc loss alters the microenvironment to cause early loss of commensal species and provides a habitat for pathogenic outgrowth and pro-carcinogenesis. We will test our hypothesis through the following aims. Aim 1: Defining the effects of Apc inactivation on the composition, spatial/temporal dynamics, and tumorigenic potential of the host microbiome. Using 16S rRNA amplicon sequencing and microbiology, I will identify early microbiome changes following Apc loss during gradual colon tumorigenesis and will determine if this differs by colon region. I will use germ-free models to evaluate if the changing microbiome is sufficient to induce colon tumorigenesis. Aim 2: Identifying the mechanism(s) by which Apc inactivation contributes to microbiome dysbiosis and the expansion of pathogenic species. I will utilize transcriptomics and metabolomics to examine changes in metabolic pathways and gene regulation in association with changes in microbiome composition and timing of Apc inactivation. This research will provide novel insights into the events occurring upon Apc mutation and the crosstalk between mutated CECs and the local microbiome.