Abstract 3051: Commensal microbiota, host DNA methylation and gene expression: A pilot study in colorectal adenomas
Authors: Yang Yaohua , Long Jirong , Shrubsole Martha J. , Cai Qiuyin , Zhao Zhiguo , Ye Fei , Li Zhigang , Guo Xingyi , Li Bingshan , Bordenstein Seth R. , Lau Ken S. , Murff Harvey J. , Ness Reid M. , Coffey Robert J. , Zheng Wei 
Published: June 2022

Abstract
Increasing evidence suggests that gut microbiota plays a critical role in colorectal cancer (CRC) development; however, the underlying mechanism is largely unknown. We investigated the relationship of commensal microbiota with host DNA methylation (DNAm) and gene expression in colorectal adenoma, the major precursor of CRC.
This study included 72 participants from the Tennessee Colorectal Polyp Study. Microbiome, DNA methylome, and transcriptome data of fresh frozen conventional adenoma samples were generated using 16S rRNA gene sequencing, HumanMethylation450 BeadChip, and RNA-seq, respectively. Among 35 participants with microbiome and matched DNA methylome data, microbial features were evaluated for their associations with DNAm at CpG sites (CpGs) via linear regression. False-discovery rate (FDR) correction was conducted separately for each microbial feature and significant associations were identified at FDR&lt;0.1. DNAm at microbiome-associated CpGs were then tested for their correlations with expression of flanking genes (500Kb) among 45 subjects with DNA methylome and matched transcriptome data. For genes with expression significantly (FDR&lt;0.1) correlated with DNAm at microbiome-associated CpGs, their differential expression between colorectal adenomas and adenocarcinomas were examined using microarray data from Gene Expression Omnibus (GEO, 363 conventional adenoma samples) and CRC Subtyping Consortium (CRCSC, 2,760 adenocarcinoma samples). The R package “limma” was used to identify significantly differentially expressed genes at FDR&lt;0.1.
Four alpha diversity indexes, three beta diversity matrices, and 194 taxa were investigated for their associations with DNAm at 28,081 variable CpGs (variance&gt;0.02 across samples). Faith’s phylogenetic diversity index and abundance of 11 taxa were significantly associated with DNAm at 68 CpGs. Among them, the most significant association was observed between Lactococcus and cg03292388 (β=-0.67, P=4.39×10-9). DNAm at 11 of the 68 CpGs were significantly correlated with expression of 12 genes (551 genes tested). Six of these 12 genes were found in data from GEO and CRCSC, and three showed a significant differential expression between adenomas and adenocarcinomas. Integrating these results revealed potential bacteria-DNAm-gene-adenocarcinoma pathways in which Bacteroides ovatus, three CpGs, and three genes were involved. Specifically, increased abundance of B. ovatus was associated with decreased DNAm at cg19003815 (β=-0.28, P=7.64×10-5), which was correlated with increased expression of RARB (rho=-0.65, P=2.18×10-6). These findings are in line with the higher expression of RARB in adenocarcinomas compared to adenomas (fold-change=1.51, P=8.58×10-10).
In conventional adenomas, bacterial-related host DNAm changes may affect expression of nearby genes, which might be implicated in adenoma-carcinoma development.
Citation Format: Yaohua Yang, Jirong Long, Martha J. Shrubsole, Qiuyin Cai, Zhiguo Zhao, Fei Ye, Zhigang Li, Xingyi Guo, Bingshan Li, Seth R. Bordenstein, Ken S. Lau, Harvey J. Murff, Reid M. Ness, Robert J. Coffey, Wei Zheng. Commensal microbiota, host DNA methylation and gene expression: A pilot study in colorectal adenomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3051.