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SummaryRegulation of hepatic carbohydrate homeostasis is crucial for maintaining energy balance in the face of fluctuating nutrient availability. Here, we show that the hormone fibroblast growth factor 15/19 (FGF15/19), which is released postprandially from the small intestine, inhibits hepatic gluconeogenesis, like insulin. However, unlike insulin, which peaks in serum 15 min after feeding, FGF15/19 expression peaks approximately 45 min later, when bile acid concentrations increase in the small intestine. FGF15/19 blocks the expression of genes involved in gluconeogenesis through a mechanism involving the dephosphorylation and inactivation of the transcription factor cAMP regulatory element-binding protein (CREB). This in turn blunts expression of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) and other genes involved in hepatic metabolism. Overexpression of PGC-1α blocks the inhibitory effect of FGF15/19 on gluconeogenic gene expression. These results demonstrate that FGF15/19 works subsequent to insulin as a postprandial regulator of hepatic carbohydrate homeostasis.

SummaryInsulin rapidly suppresses hepatic glucose production and slowly decreases expression of genes encoding gluconeogenic proteins. In this study, we show that an immediate effect of insulin is to redirect newly synthesized glucose-6-phosphate to glycogen without changing the rate of gluconeogenesis. This process requires hepatic Akt2, as revealed by blunted insulin-mediated suppression of glycogenolysis in the perfused mouse liver, elevated hepatic glucose production during a euglycemic-hyperinsulinemic clamp, or diminished glycogen accumulation during clamp or refeeding in mice without hepatic Akt2. Surprisingly, the absence of Akt2 disrupted glycogen metabolism independent of GSK3α and GSK3β phosphorylation, which is thought to be an essential step in the pathway by which insulin regulates glycogen synthesis through Akt. These data show that (1) the immediate action of insulin to suppress hepatic glucose production functions via an Akt2-dependent redirection of glucose-6-phosphate to glycogen, and (2) insulin increases glucose phosphorylation and conversion to glycogen independent of GSK3.