Histochemical demonstration of a Na+-coupled transporter for short-chain fatty acids (Slc5a8) in the intestine and kidney of the mouse

Short-chain fatty acids in the intestinal lumen affect colonic cell proliferation as well as function as an energy source for intestinal epithelial cells. A novel transporter of monocarboxylates, Slc5a8, is expressed abundantly in the colon, where it may participate in the Na+-coupled absorption of short-chain fatty acids produced by bacterial fermentation of dietary fiber. The present study examined the cellular localization of Slc5a8 in the murine gastrointestinal tract and kidney by in situ hybridization and immunohistochemistry. The hybridization signals were recognized in the terminal ileum and whole length of the large intestine, and were especially intense in the distal colon and rectum. The immunoreactivity of Slc5a8 was restricted to the striated border (the brush border) of enterocytes, and was not present in goblet cells, Paneth cells, or lamina propria cells. In the kidney, proximal tubules of both the cortex and the outer stripe of the outer medulla intensely expressed Slc5a8 mRNA, while the distal portions, including the loop of Henle, lacked the signals. The renal Slc5a8 immunoreactivity was localized only in the brush border of proximal tubules, not along the basolateral membrane. Thyroid follicular cells were immunoreactive for Slc5a8, with predominant labeling on the apical membrane. No other organs, including the esophagus, stomach, liver, pancreas, and salivary glands contained any notable signals of Slc5a8. These findings on the cellular and subcellular localization of Slc5a8 under normal conditions are helpful for understanding the physiological and pathological roles of Slc5a8.