miR-29a, b and c Regulate SLC5A8 Expression in Intestinal Epithelial Cells.

Abstract

Short chain fatty acids (SCFAs) produced by bacterial fermentation of dietary fiber exert myriad of beneficial effects including the amelioration of inflammation. SCFAs exist as anions at luminal pH, their entry into the cells depends on the expression and function of monocarboxylate transporters. In this regard, sodium-coupled monocarboxylate transporter-1 (SMCT-1) is one of the major proteins involved in the absorption of SCFA in the mammalian colon. However, very little is known about the mechanisms of regulation of SMCT-1 expression in health and disease. MicroRNAs (miRs) are known to play a key role in modulating gene expression. In silico analysis showed miR-29abc with highest context score and its binding region was conserved among mammals. The 3`-untranslated region (UTR) of human SMCT-1 gene was cloned into pmirGLO vector upstream of luciferase reporter and transiently transfected with miR-29a, b and c mimics into Caco-2 and/or T-84 cells. The presence of UTR of this gene significantly decreased luciferase activity compared to empty vector. Co-transfection with miR-29a, b or c resulted in further decrease in 3`UTR activity of SMCT-1 luciferase constructs. Mimic transfection significantly decreased SMCT-1 protein expression without altering mRNA expression. Further, the expression of miR-29a and c were significantly lower in mouse colon compared to small intestine, consistent with higher levels of SMCT-1 protein in the colon. Our studies demonstrated a novel finding in which miR-29a, b and c down-regulate SMCT-1 expression in colonic epithelial cells and may partly explain the differential expression of these transporters along the length of the GI tract.