Glycaemia and body weight are regulated by sodium-glucose cotransporter 1 (SGLT1) expression via O-GlcNAcylation in the intestine
K. Nishimura, Yukihiro Fujita, Shogo Ida, Tsuyoshi Yanagimachi, Natsuko Ohashi, Kiyoto Nishi, Atsushi Nishida, Yasumasa Iwasaki, Katsutaro Morino, Satoshi Ugi, Eiichiro Nishi, Akira Andoh, Hiroshi Maegawa
Abstract
OBJECTIVE: The intestine is an important organ for nutrient metabolism via absorption and endocrine systems. Nutrients regulate O-GlcNAcylation, a post-translational modification of various proteins by O-GlcNAc transferase (OGT). We have previously shown that general OGT knockout induced severe weight loss and hypoglycaemia in mice, but little is known about how O-GlcNAcylation in the intestine modulates nutrient metabolism, especially glucose metabolism, through absorption. We aimed to reveal the roles of O-GlcNAcylation in glucose absorption by the small intestine and elucidate the mechanism by which O-GlcNAcylation regulates sodium-glucose cotransporter 1 (SGLT1) expression. METHODS: First, we fasted normal mice and examined the changes in glucose transporters and O-GlcNAcylation in the intestine. Then, we generated two lines of small intestine-specific OGT-deficient mice (congenital: Ogt-VKO, tamoxifen-inducible: Ogt-iVKO) and observed the changes in body weight and in glucose and lipid metabolism. Finally, we investigated Sglt1 gene regulation by O-GlcNAcylation using enteroendocrine STC-1 cells. RESULTS: Fasting decreased O-GlcNAcylation in the intestinal epithelium of normal mice. The Ogt-VKO mice showed significantly lower non-fasted blood glucose levels and were underweight compared with litter matched controls. Glycaemic excursion in the Ogt-VKO mice was significantly lower during the oral glucose tolerance test but comparable during the intraperitoneal glucose tolerance test. Furthermore, the Ogt-VKO mice exhibited lower Sglt1 expression in the small intestine compared with the control mice. We obtained similar results using the Ogt-iVKO mice only after tamoxifen administration. The oral d-xylose administration test revealed that the intestinal sugar absorption was diminished in the Ogt-iVKO mice and that GLP-1 secretion did not sufficiently increase after glucose gavage in the Ogt-iVKO mice. When using STC-1 cells, O-GlcNAcylation increased Sglt1 mRNA via a PKA/CREB-dependent pathway. CONCLUSION: Collectively, loss of O-GlcNAcylation in the intestine reduced glucose absorption via suppression of SGLT1 expression; this may lead to new treatments for malabsorption, obesity and diabetes.