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 c57bl6 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.