Regulation of GLUT5 gene expression in rat intestinal mucosa: regional distribution, circadian rhythm, perinatal development and effect of diabetes

Abstract

1. GLUT5 gene expression was studied in small intestine under a variety of conditions characterized by altered intestinal absorption of monosaccharides. 2. RNA-blotting studies showed that GLUT5 mRNA was abundantly expressed in rat and rabbit intestine and kidney, but it was not detected in heart or brown adipose tissue. GLUT5 mRNA levels were higher in the upper segments of the small intestine (duodenum and proximal jejunum) than in the lower segments (distal jejunum and ileum). 3. The intestinal expression of GLUT5 mRNA in rat proximal jejunum showed circadian rhythm. A 12-fold increase in GLUT5 mRNA levels was detected at the end of the light cycle and at the beginning of the dark cycle when compared with the early light period. In keeping with this, GLUT5 protein content in brush-border membranes was also increased at the beginning of the dark cycle compared with that in the light period. 4. In streptozotocin-induced diabetes an 80% increase in GLUT5 mRNA levels in mucosa from the proximal jejunum was detected under conditions in which enhanced intestinal absorption of monosaccharides has been reported. 5. The intestinal expression of GLUT5 mRNA showed regulation during perinatal development. Levels of GLUT5 mRNA were low during fetal life, increased progressively during the postnatal period and reached levels comparable with the adult state after weaning. Weaning on to a high-fat diet partially prevented the induction of GLUT5 gene expression. 6. Our results indicate that GLUT5 gene expression is tightly regulated in small intestine. Regulation involves maximal expression in the upper part of the small intestine, circadian rhythm, developmental regulation dependent on the fat and carbohydrate content in the diet at weaning and enhanced expression in streptozotocin-induced diabetes. Furthermore, changes observed in intestinal GLUT5 expression correlate with reported alterations in intestinal absorption of fructose. This suggests a regulatory role for GLUT5 in fructose uptake by absorptive enterocytes.

Coordinated, diurnal hexose transporter expression in rat small bowel: Implications for small bowel resection

“…[1][2][3][4][5][6][7][8]10 In agreement with these reports, we demonstrated that the diurnal rhythms in hexose transporter mRNA and protein levels in proximal bowel appear to be entrained by or are at least associated with the nocturnal feeding behavior of rats. Studies of transporter-mediated glucose uptake studies correlated with the nocturnal feeding behavior of rats showing maximal uptake during the dark cycle; this has been shown previously for SGLT1.…”

“…14 C-D-Glucose was used as a marker for transporter-mediated uptake. 3 H-L-glucose, which is not taken up via facilitated transport, was used to correct for passive diffusion and adherent fluid. After following incubation, tissues were rinsed in 30ml of chilled (4°C) mammalian Ringer's stirred at 1,200 rpm to remove adherent glucose and placed in glass scintillation vials.…”

Clock is important for food and circadian regulation of macronutrient absorption in mice

“…Several studies indicate that transporters involved in the absorption of fat, carbohydrates, and proteins show diurnal rhythms. For example, apical Na + /glucose cotransporter 1 (SGLT1) and fructose transporter 5 (GLUT5) as well as the basolateral hexose transporter GLUT2 show rhythmic expression (31)(32)(33)(34)(35)(36). In addition, the expression of protoncoupled, oligopeptide transporter 1 (PEPT1), which is also a nutrient and drug transporter, shows diurnal expression ( 32,37 ).…”

Developmental reprogramming of rat GLUT-5 requires de novo mRNA and protein synthesis

“…The brush-border fructose transporter GLUT-5 (4) is normally expressed at significant levels in rat and rabbit intestines only after completion of weaning (6,19,22,25). In rats, the expression of GLUT-5, which appears only after 28 days of age, is considerably delayed compared with that of SGLT-1 and many intestinal amino acid transporters, all of which are active well before birth (2).…”