Comparative effects of diet and carcinogen on microRNA expression in the stem cell niche of the mouse colonic crypt

• Carcinogen modulates stem cell miRNAs.
• n − 3 PUFA and butyrate modulates stem cell miRNAs following exposure to carcinogen.
• miR-125a-5p, miR-190 and miR-191 are colonic stem cell (Lgr5 +) specific miRNAs.
• miR-125a-5p and their targets are modulated by chemoprotective diet.
• PDE4B and TCF4-directly target miR-26b and 203; miR-19b indirectly targets PTK2B.

There is mounting evidence that noncoding microRNAs (miRNA) are modulated by select chemoprotective dietary agents. For example, recently we demonstrated that the unique combination of dietary fish oil (containing n − 3 fatty acids) plus pectin (fermented to butyrate in the colon) (FPA) up-regulates a subset of putative tumor suppressor miRNAs in intestinal mucosa, and down-regulates their predicted target genes following carcinogen exposure as compared to control (corn oil plus cellulose (CCA)) diet. To further elucidate the biological effects of diet and carcinogen modulated miR's in the colon, we verified that miR-26b and miR-203 directly target PDE4B and TCF4, respectively. Since perturbations in adult stem cell dynamics are generally believed to represent an early step in colon tumorigenesis and to better understand how the colonic stem cell population responds to environmental factors such as diet and carcinogen, we additionally determined the effects of the chemoprotective FPA diet on miRNAs and mRNAs in colonic stem cells obtained from Lgr5-EGFP-IRES-creERT2 knock-in mice. Following global miRNA profiling, 26 miRNAs (P < 0.05) were differentially expressed in Lgr5high stem cells as compared to Lgr5negative differentiated cells. FPA treatment up-regulated miR-19b, miR-26b and miR-203 expression as compared to CCA specifically in Lgr5high cells. In contrast, in Lgr5negative cells, only miR-19b and its indirect target PTK2B were modulated by the FPA diet. These data indicate for the first time that select dietary cues can impact stem cell regulatory networks, in part, by modulating the steady-state levels of miRNAs. To our knowledge, this is the first study to utilize Lgr5+ reporter mice to determine the impact of diet and carcinogen on miRNA expression in colonic stem cells and their progeny.