Fibroblast growth factor 21 improves glucose homeostasis partially via down-regulation of Na + -d-glucose cotransporter SGLT1 in the small intestine.

Fibroblast growth factor-21 (FGF-21), an endocrine hormone, is regarded as a therapeutic target for diabetes base on its potent effects on improving hyperglycemia. Sodium-dependent glucose cotransporter 1 (SGLT1) is mainly expressed in the small intestine (SI) for intestinal glucose absorption. It has been demonstrated that SGLT1 expression is increased in diabetes, which is thought to contribute to the rapidly rising postprandial blood glucose levels. Thus, we aim to examine whether FGF-21 regulates expression of intestinal SGLT1 in diabetes. The db/db mice were treated with insulin, low and high dose of FGF-21 for 5 weeks and then measured changes in glucose metabolism, intestinal glucose absorption and SGLT1 expression. The results showed that FGF-21 improved glucose homeostasis, inhibited intestinal glucose uptake and reduced intestinal SGLT1 expression compared with insulin in db/db mice. To further explore the mechanism of effects of FGF-21 on SGLT1 expression. The murine intestinal epithelial MODE-K cells were treated with FGF-21 for 3 h, 6 h, 12 h and 24 h and then measured glucose uptake, SGLT1 expression, another glucose transporter GLUT2 expression and associated mechanism. Our results showed that FGF-21 inhibited glucose uptake and reduced SGLT1 expression in MODE-K cells, which were due to inactivating SGK-1 pathway. Moreover, above effects of FGF-21 on MODE-K cells were abolished by PD173074, a FGFR1 inhibitor. In conclusion, FGF-21 regulates glucose level in diabetes partially due to inhibiting glucose absorption in the SI via inactivating SGK-1 pathway. These results expand our knowledge about how FGF-21 regulates glucose metabolism.