Oral Pathobionts Promote CRC Development by Alteration of the Host Epigenome and Immunomic Microenvironment

Abstract Text: Gut microbiota play a major role in the immunological and clinical outcomes of colorectal cancer (CRC). Previously, using metagenomic studies, we and other researchers detected the enrichment of Parvimonas micra (P. micra), an oral pathobiont in human feces and colon mucosa of CRC patients. These findings lead us to test the hypothesis that P. Micra enrichment causes tumor-associated phenotype in host cells. We focused on tumor cells and the immunomic microenvironment.
CRC-prone mice; TS4CreAPClox468 were antibiotic treated and then given a healthy human microbiome transplant (FMT), either with or without P. micra. Analysis of fecal pellet 16S rRNA sequencing revealed establishment of the human microbes in both groups. Addition of P. micra changed the composition of the bacterial community, enriched the population of other CRC-associated bacteria, and increased tumor load. DNA methylation sequencing of crypt epithelial cells in CRC prone mice using the RRBS (Reduced Representation Bisulfite Sequencing) method revealed differential methylation in tumor development pathways, including regulation of Wnt signaling and epithelial-mesenchymal transition pathways. By analyzing the methylation data and the RNA sequencing results in tandem, we also found deregulation of circadian genes in the P. micra group, which is another CRC related pathway. Methylation changes were also detected in the DNA of naïve CD4 T-cells isolated from the mesenteric lymph nodes. The experiment was repeated with tamoxifen-inducible CRC mice. Ongoing analyses of the DNA methylation and gene expression data (combined with immunohistology) aim to determine biological processes that are affected by and contribute to the carcinogenesis process.