Glucose transporter expression in the human colon

Abstract

Aim: To investigate by immunostaining glucose transporter expression in human colorectal mucosa in controls and patients with inflammatory bowel disease (IBD).

Methods: Colorectal samples were obtained from patients undergoing lower endoscopic colonoscopy or recto-sigmoidoscopy. Patients diagnosed with ulcerative colitis (n = 18) or Crohn's disease (n = 10) and scheduled for diagnostic colonoscopy were enrolled. Patients who underwent colonoscopy for prevention screening of colorectal cancer or were followed-up after polypectomy or had a history of lower gastrointestinal symptoms were designated as the control group (CTRL, n = 16). Inflammatory status of the mucosa at the sampling site was evaluated histologically and/or endoscopically. A total of 147 biopsies of colorectal mucosa were collected and processed for immunohistochemistry analysis. The expression of GLUT2, SGLT1, and GLUT5 glucose transporters was investigated using immunoperoxidase labeling. To compare immunoreactivity of GLUT5 and LYVE-1, which is a marker for lymphatic vessel endothelium, double-labeled confocal microscopy was used.

Results: Immunohistochemical analysis revealed that GLUT2, SGLT1, and GLUT5 were expressed only in short epithelial portions of the large intestinal mucosa. No important differences were observed in glucose transporter expression between the samples obtained from the different portions of the colorectal tract and between the different patient groups. Unexpectedly, GLUT5 expression was also identified in vessels, mainly concentrated in specific areas where the vessels were clustered. Immunostaining with LYVE-1 and GLUT5 antibodies revealed that GLUT5-immunoreactive (-IR) clusters of vessels were concentrated in areas internal to those that were LYVE-1 positive. GLUT5 and LYVE-1 did not appear to be colocalized but rather showed a close topographical relationship on the endothelium. Based on their LYVE-1 expression, GLUT5-IR vessels were identified as lymphatic. Both inflamed and non-inflamed mucosal colorectal tissue biopsies from the IBD and CTRL patients showed GLUT5-IR clusters of lymphatic vessels.

Conclusion: Glucose transporter immunoreactivity is present in colorectal mucosa in controls and IBD patients. GLUT5 expression is also associated with lymphatic vessels. This novel finding aids in the characterization of lymphatic vasculature in IBD patients.

Keywords: Colon; Crohn’s disease; Glucose transporter; LYVE-1, Immunohistochemistry; Ulcerative colitis.

Conflict of interest statement

Conflict-of-interest statement: All authors declare no conflicts of interest.

Figures

Figure 1

Immunoperoxidase staining showing GLUT2 (A-D) and SGLT1 (E and F) immunoreactivity in epithelial cells of the cecum (A and B), descending (C and D), and sigmoid (E and F) colon of human intestine. White arrows indicate staining on the apical pole, black arrows on the basolateral membrane of epithelial intestinal cells. Scale bar: (A, C, D) 50 μm; (B, E, F) 5 μm.

Figure 2

Immunoperoxidase staining showing GLUT5 immunoreactivity in the brush border membrane of epithelial cells in lumen of cecum (A and B), ascending (C and D), transverse (E and F), descending (G and H), sigmoid (I and J) colon, and rectum (K and L). The boxed area in (A, C, E, G, I, K) is shown at higher magnification in (B, D, F, H, J, L, respectively). Scale bar: (A, E, G, I) 50 μm; (C, K) 25 μm; (D, F) 10 μm; (B, H, J, L) 5 μm.

Figure 3

Immunoperoxidase staining showing GLUT5 immunoreactivity in small, rounded vessels in cecum (A and C), ascending (B and I), transverse (D and E), and sigmoid (F-H) colon of human intestine. No specific staining is observed in adjacent sections (I and J) when GLUT5 antibody was omitted (J). The boxed area in (D and F) is shown at higher magnification in (E and G, respectively). Scale bar: (I and J) 125 μm; (A, C, D, F) 50 μm; (B, E, G, H) 10 μm.

Figure 4

Immunoperoxidase staining showing GLUT5 immunoreactivity in vessel clusters in ascending (A and B), descending (C and D) colon, and rectum (E and F). The boxed area in (A, C, E) is shown at higher magnification in (B and D, F respectively). Scale bar: (A, C, E) 125 μm; (B, D, F) 25 μm.

Figure 5

GLUT5 immunoreactivity is shown in vessel clusters localized beneath the epithelium (A and B) or around the glands (C and D), and in vacuolar structures in the epithelium (E and F). The boxed area in (A and C) is shown at higher magnification in (B, D, respectively). Scale bar: (A, C, E and F) 25 μm; (D) 10 μm; (B) 5 μm.

Figure 6

Bar graphs of the percentage of samples with GLUT5-immunoreactive clusters of lymphatic vessels in the proximal tract (Panel A) and distal tract (Panel B) of large intestine of patients with ulcerative colitis, Crohn’s disease, and controls. Inflamed and non-inflamed mucosa can be distinguished for each patient group. In the UC and CTRL groups, the percentage is similar for inflamed and non-inflamed mucosa in the proximal tract, and higher for non-inflamed than inflamed mucosa in the distal tract. In the CD group, the percentage is higher for inflamed than non-inflamed mucosa in both the proximal and the distal tract. UC: Ulcerative colitis; CD: Crohn’s disease; CTRL: Controls.

Figure 7

Scanning electron (A and C) and light (B and D) microscopy images of a sample of descending colon with non-inflamed mucosa after immunoperoxidase GLUT5 staining from a ulcerative colitis patient. Scale bar: (A and B) 250 μm; (C and D) 100 μm.

Figure 8

Light (A-C) and scanning electron (D-H) microscopy images of a sample of descending colon with non-inflamed mucosa after immunoperoxidase GLUT5 staining from a UC patient. The boxed areas in (A) and (D) are corresponding areas and are shown enlarged in (B) and (G), respectively. The yellow area in (E) represents the immunostaining area shown in (B). The boxed area in (B, E, G) is shown at higher magnification in (C, F, H, respectively). Scale bar: (D) 100 μm ; (A, E, G) 50 μm; (B) 25 μm; (C, F, H) 5 μm.

Figure 9

Immunoperoxidase staining showing GLUT5 and LYVE-1 immunoreactivity in samples of the distal tract of large intestine from UC (A-F) and CD (G-L) patients. In both samples, the mucosa was non- inflamed. The boxed area in (A and B) is enlarged in (C and D, respectively), the area in (C and D) is enlarged in (E and F, respectively), the area without an asterisk in (G and H) is enlarged in (I and J, respectively), the area with an asterisk in (G and H) is enlarged in (K and L, respectively). Scale bar: (A, B, G, H) 100 μm; (C, D, I-L) 25 μm; (E and F) 10 μm.

Figure 10

Double-immunofluorescent confocal microscopy showing expression of GLUT5 (red) with LYVE-1 (green) in samples of descending colon from UC (A-C, J-R) and CD (D-I) patients. The mucosa was inflamed in the UC sample and non-inflamed in the CD sample. The boxed area in (D-F) is shown at higher magnification in (G-I, respectively); the boxed area in (J-L) is shown at higher magnification in (M-O, respectively). Scale bar: (C, F, L, R) 20 μm; (I, O) 10 μm.