Intestinal sodium/glucose cotransporter 3 expression is epithelial and downregulated in obesity.

AIM: We aimed to determine whether the sodium/glucose cotransporter family member SGLT3, a proposed glucose sensor, is expressed in the intestine and/or kidney, and if its expression is altered in mouse models of obesity and in humans before and after weight-loss surgery. MAIN METHODS: We used in-situ hybridization and quantitative PCR to determine whether the Sglt3 isoforms 3a and 3b were expressed in the intestine and kidney of C57, leptin-deficient ob/ob, and diabetic BTBR ob/ob mice. Western blotting and immunohistochemistry were also used to assess SGLT3 protein levels in jejunal biopsies from obese patients before and after weight-loss Roux-en-Y gastric bypass surgery (RYGB), and in lean healthy controls. KEY FINDINGS: Sglt3a/3b mRNA was detected in the small intestine (duodenum, jejunum and ileum), but not in the large intestine or kidneys of mice. Both isoforms were detected in epithelial cells (confirmed using intestinal organoids). Expression of Sglt3a/3b mRNA in duodenum and jejunum was significantly lower in ob/ob and BTBR ob/ob mice than in normal-weight littermates. Jejunal SGLT3 protein levels in aged obese patients before RYGB were lower than in lean individuals, but substantially upregulated 6 months post-RYGB. SIGNIFICANCE: Our study shows that Sglt3a/3b is expressed primarily in epithelial cells of the small intestine in mice. Furthermore, we observed an association between intestinal mRNA Sglt3a/3b expression and obesity in mice, and between jejunal SGLT3 protein levels and obesity in humans. Further studies are required to determine the possible role of SGLT3 in obesity.

Sigmoidal kinetics define porcine intestinal segregation of electrogenic monosaccharide transport systems as having multiple transporter population involvement.

Kinetic characterization of electrogenic sodium-dependent transport in Ussing chambers of d-glucose and d-galactose demonstrated sigmoidal/Hill kinetics in the porcine jejunum and ileum, with the absence of transport in the distal colon. In the jejunum, a high-affinity, super-low-capacity (Ha/sLc) kinetic system accounted for glucose transport, and a low-affinity, low-capacity (La/Lc) kinetic system accounted for galactose transport. In contrast, the ileum demonstrated a high-affinity, super-high-capacity (Ha/sHc) glucose transport and a low-affinity, high-capacity (La/Hc) galactose transport systems. Jejunal glucose transport was not inhibited by dapagliflozin, but galactose transport was inhibited. Comparatively, ileal glucose and galactose transport were both sensitive to dapagliflozin. Genomic and gene expression analyses identified 10 of the 12 known SLC5A family members in the porcine jejunum, ileum, and distal colon. Dominant SGLT1 (SLC5A1) and SGLT3 (SLC5A4) expression was associated with the sigmoidal Ha/sLc glucose and La/Lc galactose transport systems in the jejunum. Comparatively, the dominant expression of SGLT1 (SLC5A1) in the ileum was only associated with Ha glucose and La galactose kinetic systems. However, the sigmoidal kinetics and overall high capacity (Hc) of transport is unlikely accounted for by SGLT1 (SLC5A1) alone. Finally, the absence of transport and lack of pharmacological inhibition in the colon was associated with the poor expression of SLC5A genes. Altogether, the results demonstrated intestinal segregation of monosaccharide transport fit different sigmoidal kinetic systems. This reveals multiple transporter populations in each system, supported by gene expression profiles and pharmacological inhibition. Overall, this work demonstrates a complexity to transporter involvement in intestinal electrogenic monosaccharide absorption systems not previously defined.

Islet microarchitecture and glucose transporter expression of the pancreas of the marmoset monkey display similarities to the human.

The common marmoset New World monkey (Callithrix jacchus), is a primate model with great potential for scientific research, including research on diabetes. However, in opposite to Rhesus and Java monkeys (Macaca mulatta and Macaca fascicularis) little is known about the marmosets islet microarchitecture, glucose transporter and pancreatic marker gene expression. In this work we analyze differences and similarities in size, shape, cellular composition and intra-islet topography between the common marmoset and the human endocrine pancreas. Different sized, circular and a-circular shaped islets of the common marmoset and human display α-cells in the whole islet organ leading to a ribbon-like islet type. The number of islets was significantly higher in the common marmoset compared with humans. However, the area of insulin-producing cells was significantly higher in the human pancreas. Intra-islet distribution pattern of δ- and ß-cells was similar in both species. The morphology of the exocrine pancreas regarding acinar and ductal cells was quite similar as confirmed by ultrastructural analysis. Additionally the ultrastructure of secretory granules from α-, δ- and ß-cells of human and non-human primate pancreas showed the same characteristics. Molecular analysis showed the presence of endocrine pancreatic marker genes like PMCA2, NCX1, SUR1, KIR6.2, MAFA, NGN3 and PDX1 also expressed in the human. For the first time we could show presence of Glut 5 and 9 transporters in addition to the low abundance transporter Glut2 and the highly expressed Glut1 glucose transporter. We propose that Callithrix jacchus displays a new animal model for diabetes research and regenerative medicine.

Biology of human sodium glucose transporters.

There are two classes of glucose transporters involved in glucose homeostasis in the body, the facilitated transporters or uniporters (GLUTs) and the active transporters or symporters (SGLTs). The energy for active glucose transport is provided by the sodium gradient across the cell membrane, the Na(+) glucose cotransport hypothesis first proposed in 1960 by Crane. Since the cloning of SGLT1 in 1987, there have been advances in the genetics, molecular biology, biochemistry, biophysics, and structure of SGLTs. There are 12 members of the human SGLT (SLC5) gene family, including cotransporters for sugars, anions, vitamins, and short-chain fatty acids. Here we give a personal review of these advances. The SGLTs belong to a structural class of membrane proteins from unrelated gene families of antiporters and Na(+) and H(+) symporters. This class shares a common atomic architecture and a common transport mechanism. SGLTs also function as water and urea channels, glucose sensors, and coupled-water and urea transporters. We also discuss the physiology and pathophysiology of SGLTs, e.g., glucose galactose malabsorption and familial renal glycosuria, and briefly report on targeting of SGLTs for new therapies for diabetes.

Regulation of renal glucose transporters during severe inflammation.

Severe sepsis is accompanied by acute renal failure (ARF) with renal tubular dysfunction and glucosuria. In this study, we aimed to determine the regulation of renal tubular glucose transporters during severe experimental inflammation. Male C57BL/6J mice were injected with LPS or proinflammatory cytokines, and renal perfusion, glomerular filtration rate (GFR), fractional glucose excretion, and expression of tubular glucose transporters were determined. We found a decreased plasma glucose concentration with impaired renal tissue perfusion and GFR and increased fractional glucose excretion associated with decreased expression of SGLT2, SGLT3, and GLUT2 after LPS injection. Similar alterations were observed after application of TNF-alpha, IL-1beta, IL-6, or IFN-gamma. To clarify the role of proinflammatory cytokines, we performed LPS injections in knockout mice with deficiencies for TNF-alpha, IL-1 receptor type 1, IFN-gamma, or IL-6 as well as LPS injections in glucocorticoid-treated wild-type mice. LPS-induced alterations of glucose transporters also were present in single-cytokine knockout mice. In contrast, glucocorticoid treatment clearly attenuated LPS-induced changes in renal glucose transporter expression and improved GFR and fractional glucose excretion. LPS-induced decrease of renal perfusion was not improved by glucocorticoids, indicating a minor role of ischemia in the development of septic renal dysfunction. Our results demonstrate modifications of tubular glucose transporters during severe inflammation that are probably mediated by proinflammatory cytokines and account for the development of ARF with increased fractional glucose excretion. In addition, our findings provide an explanation why single anti-cytokine strategies fail in the therapy of septic patients and contribute to an understanding of the beneficial effects of glucocorticoids on septic renal dysfunction.