The cellular expression of SMCT2 and its comparison with other transporters for monocarboxylates in the mouse digestive tract

SMCT1 (slc5a8) is a sodium-coupled monocarboxylate transporter expressed in the brush border of enterocytes. It regulates the uptake of short-chain fatty acids (SCFAs) produced by bacterial fermentation in the large intestine. Another subtype, SMCT2 (slc5a12), is expressed abundantly in the small intestine, but its precise expression profile remains unknown. The present study using in situ hybridization method, immunohistochemistry, and quantitative PCR analysis examined the distribution and cellular localization of SMCT2 in the digestive tract of mice and compared the expression pattern with those of other transporters for monocarboxylates. While an abundant expression of SMCT2 was found in the jejunum, this was negligible in the duodenum, terminal ileum, and large intestine. In contrast, SMCT1 had predominant expression sites in the large bowel and terminal ileum. Subcellularly, SMCT2 was localized in the brush border of enterocytes in the intestinal villi-as is the case for SMCT1, suggesting its involvement in the uptake of food-derived monocarboxylates such as lactate and acetate. MCT (slc16) is a basolateral type transporter of the gut epithelium and conveys monocarboxylates in an H+-dependent manner. Since among the main subtypes of MCT family only MCT1 was expressed significantly in the small intestine, it is able to function as a counterpart to SMCT2 in this location.