Glucose and metformin differentially regulate FGF19 signaling in human HepG2 cells

Background:

Fibroblast growth factor 19 (FGF19) is a physiological key regulator of various metabolic processes such as hepatic bile acid synthesis as well as carbohydrate and lipid metabolism. On the other hand, pathological hyper-activation of FGF19 expression and down-stream signaling via fibroblast growth factor receptor 4 (FGFR4) has been observed in various human cancers including hepatocellular carcinoma. In this ongoing project, we aim to analyze the molecular mechanisms that regulate the FGF19/FGFR4 pathway in the liver under physiological and pathological conditions.

Methods:

Human HepG2 cells were cultivated under conditions of glucose abundance or glucose deprivation (high or low glucose medium) and stimulated with recombinant FGF19. Activation of the FGF19/FGFR4 signaling pathway was quantified via Western blot and qPCR. The anti-diabetic drug metformin as well as the AMP analog AICAR were used to test a potential contribution of the AMP-activated protein kinase (AMPK) to the regulation of FGF19/FGFR4 signaling. Cell proliferation was monitored using the MTT assay.

Results:

Only cultivation of cells with high glucose medium allowed for robust activation of FGF19 signaling as indicated by increased phosphorylation of ERK1/2 and strong regulation of FGF19 target genes. In contrast, HepG2 grown in low glucose medium showed much weaker activation of pERK1/2 and less pronounced regulation of target genes after FGF19 stimulation.

Vice versa, pre-treatment with the anti-diabetic drug metformin or the AMP analog AICAR blunted FGF19 signaling in cells cultivated in high glucose medium. Moreover, metformin pre-treatment also inhibited the proliferation of HepG2 cells in the presence of FGF19. Interestingly, inhibitory effects of metformin and AICAR on FGF19 signaling were also found in a human non-cancer hepatocyte cell line (i.e. immortalized human hepatocytes, IHH).

Conclusion:

This study suggests that the availability of cellular energy substrates such as glucose has a significant impact on the FGF19/FGFR4 signaling pathway in liver cells. Moreover, our data point to a potential involvement of the AMP-activated protein kinase (AMPK) in the regulation of this process and indicate that the anti-diabetic drug metformin may be useful for pharmacological inhibition of hyper-activated FGF19 signaling under pathological conditions. Further analysis using in vivo models is therefore warranted.