Differences in the expression of microRNAs implicated in colorectal carcinogenesis and involved in the WNT signalling pathway in the macroscopically-normal epithelium of people at higher-risk of colorectal cancer

Abstract

People with ulcerative colitis (UC) or adenomatous polyps (adenomas) are at increased risk of colorectal cancer (CRC)(1). Altered expression of microRNAs (miRNAs), small non-coding RNAs that regulate gene expression post-transcriptionally, has been observed in those with UC(2) and adenomas(3). Importantly, abnormally-expressed miRNAs contribute to the initiation and progression of CRC and are potential biomarkers for diagnosis and prognosis of this cancer(4). This study aimed to investigate differences in the expression of a panel of miRNAs in the macroscopically-normal mucosa of people at higher-risk of CRC. We quantified expression of 8 miRNAs that are (i) implicated in CRC, (ii) regulators of WNT signalling, a pathway frequently aberrantly activated in CRC(5), and/or (iii) whose expression is altered by butyrate treatment in healthy participants (n = 56) and in patients at higher CRC risk with quiescent UC (n = 26) or history of adenomatous polyps (n = 12). RNA was isolated from mucosal biopsies of macroscopically-normal tissue collected at 10 cm from the anal verge. cDNA was synthesised by reverse transcription and used to quantify the expression of miR-17, miR-19a, miR-19b, miR-20a, miR-25, miR-93, miR-106b and miR-424 by quantitative PCR. For normally distributed data, the ANOVA General Linear Model was used to compare miRNA expression between the 3 risk groups, adjusting for age, sex and endoscopy procedure as covariates. Where data were not normally distributed, the nonparametric Kruskal-Wallis test was used. [TABLE PRESENTED] We observed significantly higher miR-424 expression (p< 0•01), a miRNA reported to be increased in CRCs(6), and reduced miR-20a expression (p = 0•055) in participants with quiescent UC (Table 1). miR-20a expression also appears to be reduced in polyp patients. Alterations in miRNA expression may be detected in the healthy tissue of people at higher-risk of CRC and may represent very early molecular changes contributing to the progression from normal mucosa to carcinoma.