Expression and regulation of the neutral amino acid transporter B0AT1 in rat small intestine

PLoS One. 2017 Sep 15;12(9):e0184845. doi: 10.1371/journal.pone.0184845. eCollection 2017.

Abstract

Absorption of neutral amino acids across the luminal membrane of intestinal enterocytes is mediated by the broad neutral amino acid transporter B0AT1 (SLC6A19). Its intestinal expression depends on co-expression of the membrane-anchored peptidase angiotensin converting enzyme 2 (ACE2) and is additionally enhanced by aminopeptidase N (CD13). We investigated in this study the expression of B0AT1 and its auxiliary peptidases as well as its transport function along the rat small intestine. Additionally, we tested its possible short- and long-term regulation by dietary proteins and amino acids. We showed by immunofluorescence that B0AT1, ACE2 and CD13 co-localize on the luminal membrane of small intestinal villi and by Western blotting that their protein expression increases in distal direction. Furthermore, we observed an elevated transport activity of the neutral amino acid L-isoleucine during the nocturnal active phase compared to the inactive one. Gastric emptying was delayed by intragastric application of an amino acid cocktail but we observed no acute dietary regulation of B0AT1 protein expression and L-isoleucine transport. Investigation of the chronic dietary regulation of B0AT1, ACE2 and CD13 by different diets revealed an increased B0AT1 protein expression under amino acid-supplemented diet in the proximal section but not in the distal one and for ACE2 protein expression a reverse localization of the effect. Dietary regulation for CD13 protein expression was not as distinct as for the two other proteins. Ring uptake experiments showed a tendency for increased L-isoleucine uptake under amino acid-supplemented diet and in vivo L-isoleucine absorption was more efficient under high protein and amino acid-supplemented diet. Additionally, plasma levels of branched-chain amino acids were elevated under high protein and amino acid diet. Taken together, our experiments did not reveal an acute amino acid-induced regulation of B0AT1 but revealed a chronic dietary adaptation mainly restricted to the proximal segment of the small intestine.

MeSH terms

  • Amino Acid Transport Systems, Neutral / biosynthesis*
  • Angiotensin-Converting Enzyme 2
  • Animals
  • CD13 Antigens / metabolism*
  • Dietary Supplements
  • Gene Expression Regulation / drug effects*
  • Intestine, Small / metabolism*
  • Isoleucine / pharmacology*
  • Male
  • Peptidyl-Dipeptidase A / metabolism*
  • Rats
  • Rats, Wistar

Substances

  • Amino Acid Transport Systems, Neutral
  • SLC6A19 protein, rat
  • Isoleucine
  • CD13 Antigens
  • Peptidyl-Dipeptidase A
  • ACE2 protein, human
  • Ace2 protein, rat
  • Angiotensin-Converting Enzyme 2

Grant support

This work was supported by the Swiss National Science Foundation (http://www.snf.ch) grant 310030_166430 to FV. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.