Fibroblast growth factor 21 regulates glucose metabolism in part by reducing renal glucose reabsorption

Although previous studies have shown the potential of FGF21 to regulate blood glucose in animal and humans, the precise mechanisms of the action have not been well explored. The kidney plays a crucial role for glucose homeostasis. The purpose of this study is to explore the effect of FGF21 on renal glucose reabsorption. Administration of type 2 and type 1 diabetic mice with FGF21 reduced the transport maximum of glucose in the kidney and enhanced urinary glucose excretion in a dose-dependent manner. The inhibition of glucose reabsorption results showed little change in diabetic mice treated with Insulin. In physiological state, both FGF21 and insulin had no effect on glucose reabsorption and urinary glucose excretion. Next, we examined the expression of SGLT2 in the kidney, which is an important molecule for renal glucose reabsorption. SGLT2 was highly expressed in the kidneys of diabetic mice. Administration of FGF21 reduced SGLT2 expression in the kidney of diabetic mice. In contrast, the expression of SGLT2 had little change in diabetic mice treated with Insulin. FGF21 and Insulin did not promote SGLT2 expression in physiological state. To explore the mechanism which drives these changes, we detected the expression of PPARδ in mice and HK-2 cells, which plays a major role in regulating SGLT2 expression. Treatment with FGF21 promoted PPARδ expression in diabetic mice, whereas Insulin had no effect on PPARδ expression. At dose of 2 mg/kg FGF21 treatment promoted PPARδ expression in physiological state, whereas at dose of 1 mg/kg FGF21 did not. In HK-2 cells, treatment with FGF21 enhanced PPARδ expression, whereas Insulin treatment had no effect on PPARδ expression. Importantly, the expression of SGLT2 and PPARδ showed little change in HK-2 cells when β-klotho was knocked down. In conclusion, we discovered for the first time that FGF21 ameliorates hyperglycemia in part via reducing renal glucose reabsorption through PPARδ mediated SGLT2 pathway.