Hepatocyte FRS2 is essential for the endocrine fibroblast growth factor to limit the amplitude of bile acid production induced by prandial activity.
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abstract
In addition to being positively regulated by prandial activity, bile acid production is also negatively controlled by the endocrine fibroblast growth factor 19 (FGF19) or the mouse ortholog FGF15 from the ileum that represses hepatic cholesterol 7 -hydroxylase (Cyp7a1) expression through activating FGF receptor four (FGFR4). However, how these two regulatory mechanisms interplay to control bile acid homeostasis in the body and the downstream pathways by which FGFR4 regulates Cyp7a1 expression are not fully understood. Here we report that hepatocyte FGFR substrate 2 (FRS2), a scaffold protein essential for canonical FGFRs to activate the ERK and AKT pathways, was required for the regulation of bile acid production by the FGF15/19-FGFR4 signaling axis. This occurred through limiting the extent of increases in Cyp7a1 expression induced by prandial activity. Excess FGFR4 kinase activity reduced the amplitude of the increase whereas a lack of FGFR4 augmented the increase of Cyp7a1 expression in the liver. Ablation of Frs2 alleles in hepatocytes abrogated the regulation of Cyp7a1 expression by FGFR4. Together, the results demonstrate that FRS2-mediated pathways are essential for the FGF15/FGF19-FGFR4 signaling axis to control bile acid homeostasis.
