Hexose Transporter Expression and Function in Mouse Small Intestine: Role of Diurnal Rhythm

Background Expression and function of hexose transporters vary diurnally in rat small intestine; however, this subject remains unexplored in mice. Aim The aim of the study was to investigate the diurnal expression and function of hexose transporters SGLT1, GLUT2, and GLUT5 in mouse small bowel. Methods Twenty-four c57b16 mice maintained in a 12-h light/dark room (6 AM-6 PM) were sacrificed at 9 AM, 3 PM, 9 PM, and 3 AM (n=6 each). In duodenal, jejunal, and ileal mucosa, total cellular mRNA and protein levels were quantitated by real-time PCR and semiquantitative Western blotting, respectively. The everted sleeve technique measured transporter-mediated glucose uptake at 9 AM and 9 PM. Results mRNA expression of SGLT1, GLUT2, and GLUT5 varied diurnally in all three intestinal segments (p <= 0.03). SGLT1, GLUT2, and GLUT5 protein levels varied diurnally in duodenum and jejunum (p<0.05) but not in ileum. Transporter-mediated glucose uptake was greater at 9 PM than 9 AM (p <= 0.04) in all three segments. V-max was greater in duodenum (10 vs 6 nmol/cm/s) and jejunum (8 vs 5 nmol/cm/s) at 9 PM compared to 9 AM (p=0.01); K-m remained unchanged. Summary mRNA levels of intestinal hexose transporters varied diurnally. Protein levels peaked 6-12 h later during dark cycle when > 70% of food intake occurred; glucose transport followed a similar pattern with increased uptake at 9 PM. Conclusion Hexose transporter expression and function vary diurnally with nocturnal feeding patterns of mice.