Duodenal-Jejunal Bypass Restores Sweet Taste Receptor-Mediated Glucose Sensing and Absorption in Diabetic Rats

Abstract

Aim: The aim of the study is to identify the regulatory role of intestinal sweet taste receptors (STRs) and glucose transporters (SGLT1, GLUT2) and gut peptide secretion in duodenal-jejunal bypass (DJB)-ameliorated glycemic control in Type 2 diabetes. Materials and Methods: DJB and sham surgeries were performed in streptozotocin-induced diabetic male rats. The blood GLP-1 and GLP-2 levels were evaluated under feeding and fasting conditions. The expression of STRs (T1R2, T1R3), sweet taste signaling effector (Gα-gustducin), SGLT1, and GLUT2 was detected in the intestinal alimentary limb (A limb), biliopancreatic limb (BP limb), and common limb (C limb). The effects of STR inhibition on glucose control were measured with lactisole. Results: Glucose tolerance was improved in DJB-operated rats compared with the sham group, similar to that of normal control rats, without significant differences in food intake and body weight. The plasma GLP-1 levels of DJB rats were increased under diet-fed condition, and GLP-2 levels were increased after fasting. The villus height and crypt depth were significantly increased in the A limb of DJB-operated rats. In addition, GLP-1 expression was restored in enterocytes. The expression of T1R2, Gα-gustducin, and SGLT1 was elevated in the A limb after DJB, while GLUT2 was downregulated in the A, BP, and C limbs. The localization of GLUT2 was normalized in the three intestinal limbs after DJB. However, the beneficial effects of DJB on glucose control were abolished in the presence of lactisole in vivo. Conclusion: DJB ameliorates glycemic control probably by restoring STR-mediated glucose sensing and absorption with the responses of GLP-1 and GLP-2 to carbohydrate.

Keywords: DJB; GLP-1; GLUT2; T1R2; lactisole.

Figure 1

Effects of duodenal–jejunal bypass on body weight, food intake, and glucose homeostasis in diabetic rats. Oral glucose tolerance test (OGTT) and area under curve for (a) OGTT before surgery as indicated. (b) Body weight, (c) food intake, and (d) fasting blood glucose before and after surgery. (e) Feeding plasma insulin, (f) GLP-1 (f), and (g) GLP-2 concentrations in chow diet-fed rats for 5 weeks after DJB or sham operation. (h) OGTT with area under curve, (i) the secretion of insulin, (j) GLP-1, (k) GLP-2 during OGTT, (l) HOMA-IR, and (m) ITT were examined 6 weeks postsurgery. Ctrl group (black, n = 6), T2D-Sham group (blue, n = 5–6), T2D-DJB group (red, n = 5–6). Data are presented as the mean ± SD. ^∗p < 0.05, ^∗∗p < 0.01, and ^∗∗∗p < 0.001 versus the Ctrl group; ^#p < 0.05, ^##p < 0.01, and ^###p < 0.001 versus the T2D-Sham group.

Figure 2

Changes in villus height and crypt depth in the alimentary limb, biliopancreatic limb, and common limb after DJB. (a) Schematic diagram of DJB and sham operation. (b) Cross-sections of intestinal segments of Ctrl, T2D-Sham, and T2D-DJB rats 6 weeks postsurgery (HE staining). (c) Villus height and (d) crypt depth in the A limb, BP limb, and C limb of Ctrl, T2D-Sham, and T2D-DJB rats. Scale bar, 1 mm. Data are presented as the mean ± SD. ^∗p < 0.05; ^∗∗p < 0.01.

Figure 3

Transcriptomic analysis revealed that glucose sensing and absorption-related signaling played important roles in the alimentary limb after DJB. (a) Volcano plot of differentially expressed genes (DEGs) between T2D-Sham and T2D-DJB in the alimentary limb using the following thresholding criteria: fold change > 2 and false discovery rate (FDR) p value < 0.05. (b) Gene Ontology (GO) analysis delineated the enrichment of differentially expressed genes in three major categories, named biological process (BP), molecular function (MF), and cellular components (CC). (c) GSEA showed the sensory perception of the sweet taste–associated gene set and intestinal hexose absorption-associated gene set. (d) Expression of T1R2 and T1R3 in the alimentary limb. Immunofluorescence analysis with T1R2 (red), T1R3 (green), and DAPI (blue) in sections of the rat alimentary limb. The arrows (white) denote the colocalization of T1R2 and T1R3 in the small intestine. NES = Normalized Enrichment Score. Positive and negative values of NES indicated up- and downregulated gene expression patterns, respectively. Heatmap showing the relative RNA expression of genes included in specific gene sets.

Figure 4

Expression levels of glucose sensors and transporters were altered in the A limb, BP limb, and C limb after DJB. The expression levels of (a) GLP-1, T1R2, T1R3, Gα-gust, SGLT1, and GLUT2 were detected by real-time PCR and western blot, respectively, in the (b, c) A limb, (d, e) BP limb, and (f, g) C limb of T2D-DJB (DJB) rats and corresponding limbs of Ctrl and T2D-Sham (sham) rats. Fold change was calculated based on the Ctrl limbs and normalized to GAPDH. Data are presented as the mean ± SD. ^∗p < 0.05.

Figure 5

GLUT2 localization was normalized in the small intestine after DJB. Immunostaining of GLUT2 (green) and sucrase (red) in the apical membranes of intestinal epithelial cells and DAPI in the nucleus (blue) in sections of rat intestinal alimentary limbs. White arrows indicate the localization of GLUT2 in the apical membranes of the intestinal epithelial cells in the T2D-Sham groups.

Figure 6

The effect of DJB-improved glycemic control was inhibited by lactisole. (a) The dose of lactisole was tested in control rats. OGTT results after lactisole administration with (b) high glucose and the (c) area under curve as indicated. ^∗p < 0.05.