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

Abstract

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 foodderived 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.

<b>Cellular distributions of monocarboxylate transporters: a r</b><b>eview </b>

“…2b) and the expression levels of MCT2 are low in the other parts of the gut (38, 39). Our quantitative PCR analysis confirmed the restricted distribution of MCT2 in the glandular stomach (146). Immunostaining detects an intense localization of MCT2 along the basolateral membrane of parietal cells, in accordance with an in situ hybridization study at the mRNA level.…”

“…The epithelial cells in the mouse small intestine express faintly immunoreactive MCT4 along the basolateral membrane. These findings are supported by our real-time PCR analysis in the mouse (146). Cell types other than epithelial cells expressing MCTs include smooth muscle cells (MCT1) throughout the gut ( Fig.…”

“…5d) and some endocrine cells (MCT1), the latter being abundant in the glandular stomach. The liver parenchyma preferentially expresses MCT2 rather than MCT1 in the hamster (38, 39); Semi-quantitative RT-PCR in mice also reveals a predominant expression in the small intestine, with the highest expression in the proximal one third (146) (Fig. 3).…”

Intensified expressions of a monocarboxylate transporter in consistently renewing tissues of the mouse

“…The small intestine, stomach, and esophagus Our previous studies for mRNA expressions of MCT and GLUT families in the murine gastrointestinal tract demonstrated abundant expressions of MCT1, GLUT2, and GLUT5 (33,37). Although the mRNA expression of MCT1 was intense in the large intestine and less intense in the small intestine and stomach, the present immunostaining of the small intestine detected an intense expression of MCT1 in some populations of epithelial cells.…”

“…Fresh frozen sections, 14-μm-thick, were fixed with 4% formaldehyde in 0.1 M phosphate buffer for 15 min and then acetylated with 0.25% acetic anhydride in 0.1 M triethanolamine-HCl (pH 8.0) for 10 min. Hybridization was performed at 42°C for 10 h with a hybridization buffer containing 33 P-labeled oligonucleotide probes (10,000 cpm/μL). The sections were rinsed at room temperature for 30 min in 2 × SSC (1 × SSC: 150 mM sodium chloride, 15 mM sodium citrate) containing 0.1% N-lauroylsarcosine sodium, then rinsed twice at 55°C for 40 min in 0.1 × SSC containing 0.1% N-lauroylsarcosine sodium, dehydrated through a graded series of ethanol, and air-dried.…”