Expression and membrane localization of MCT isoforms along the length of the human intestine

Abstract

Recent studies from our laboratory and others have demonstrated the involvement of monocarboxylate transporter (MCT)1 in the luminal uptake of short-chain fatty acids (SCFAs) in the human intestine. Functional studies from our laboratory previously demonstrated kinetically distinct SCFA transporters on the apical and basolateral membranes of human colonocytes. Although apical SCFA uptake is mediated by the MCT1 isoform, the molecular identity of the basolateral membrane SCFA transporter(s) and whether this transporter is encoded by another MCT isoform is not known. The present studies were designed to assess the expression and membrane localization of different MCT isoforms in human small intestine and colon. Immunoblotting was performed with the purified apical and basolateral membranes from human intestinal mucosa obtained from organ donor intestine. Immunohistochemistry studies were done on paraffin-embedded sections of human colonic biopsy samples. Immunoblotting studies detected a protein band of approximately 39 kDa for MCT1, predominantly in the apical membranes. The relative abundance of MCT1 mRNA and protein increased along the length of the human intestine. MCT4 (54 kDa) and MCT5 (54 kDa) isoforms showed basolateral localization and were highly expressed in the distal colon. Immunohistochemical studies confirmed that human MCT1 antibody labeling was confined to the apical membranes, whereas MCT5 antibody staining was restricted to the basolateral membranes of the colonocytes. We speculate that distinct MCT isoforms may be involved in SCFA transport across the apical or basolateral membranes in polarized colonic epithelial cells.

Cellular expression of monocarboxylate transporters (MCT) in the digestive tract of the mouse, rat, and humans, with special reference to slc5a8

“…Fresh frozen original study by Garcia et al (9) demonstrated immunohistochemically the selective localization of MCT1 at the basolateral membrane of enterocytes in the cecum of hamsters, suggesting a role for MCT1 in the transport of monocarboxylates from the epithelium to the blood. However, subsequent studies using immunohistochemistry and the immunoblotting of purifi ed membrane fractions have reported the predominant localization of MCT1 in the luminal membrane of intestinal epithelial cells in humans (10,26), pigs (26), rats (29), and in a colonic cell line (3). At present, discussion on the functional signifi cance of MCT1 appears to be based on the apical localization of MCT1, as described in recent review articles (6, 13).…”

Intestinal transporters for endogenic and pharmaceutical organic anions: the challenges of deriving in-vitro kinetic parameters for the prediction of clinically relevant drug–drug interactions

“…Colon > ileum, not in jejunum [24] MCT5 SLC16A4 N.R. Jejunum > colon [14] Colon > ileum, not in jejunum [24] MRP1 ABCC1 Ab Jejunum = ileum = colon [27] Jejunum, ileum > duodenum [28] Jejunum = colon [14] Duodenum [19] Jejunum [20] Small intestine [21,29] Colon [29,30] Small intestine and colon [31] Too low expression in jejunum, ileum and colon for protein determination [29] MRP2 ABCC2 Ex Jejunum > ileum > > colon [27] Duodenum > ileum > > colon [32] Duodenum = ileum > colon [16] Jejunum, ileum > duodenum [28] Duodenum > > colon [33] Jejunum > colon [18] Duodenum [19] Jejunum [16,20] Small intestine [21] Jejunum > ileum = colon [27] MRP3 ABCC3 Ab Colon > Ileum = duodenum [16] Jejunum, ileum > duodenum [28] Colon > jejunum [18] Duodenum [19] Jejunum [16,20] Small intestine [21,32] Colon [28,32] Small intestine and colon [29] MRP4 ABCC4 N.R.…”

“…The direction of transport and the intestinal localization of the transporters are listed in Table 1. [13,17,22,[24][25][26][27][28]30,31,34,37] In the intestine, the absorptive transporters facilitate the absorptive permeability of drug substances and endogenous substances from the intestinal lumen into the mesenteric blood, whereas the exsorptive transporters will work to counteract the absorptive process and promote drug excretion into the gut lumen. Absorptive and exsorptive transporters are located at both the apical and the basolateral membrane.…”

“…The intestinal expression of the absorptive transporter OATP1A2 is less evident. Two scientific papers have suggested that OATP1A2 is expressed at mRNA levels in the small intestine, and this transporter has also been [12,13] Jejunum > colon [14] Ileum [15] Ileum > duodenum [13] BCRP ABCG2 Ex Ileum > duodenum, colon [16] Duodenum > ileum > colon [17] Jejunum > colon [14,18] Duodenum [19] Jejunum [20] Small intestine [21] Duodenum = ileum = colon [22] Small intestine and colon [23] MCT1 SLC16A1 Ab Colon > duodenum > ileum [16] Colon > duodenum [24] Colon > jejunum [18] Colon > ileum [25] Jejunum = colon [15] Small intestine [21,26] Colon > ileum > jejunum [24] Colon [25] MCT3 SLC16A8 N.R. N.R.…”

From the gut to the peripheral tissues: the multiple effects of butyrate

“…More recent studies suggest the existence of species differences and different transporter isoforms expressed in enterocytes along the intestine (67) . On the apical membrane of the epithelial cell, distinct transport mechanisms have been reported, i.e.…”