Selective regulation of FGF19 and FGF21 expression by cellular and nutritional stress

Abstract

Fibroblast growth factor 19 (FGF19) and FGF21 are members of a subfamily of the FGFs called endocrine FGFs. FGF19 regulates the bile acid synthetic pathway. FGF19 expression is induced by farnesoid X receptor (FXR), a nuclear hormone receptor activated by bile acids in the small intestine. FGF21 plays an important role in lipolysis that occurs in white adipose tissue. FGF21 expression is stimulated by the nuclear fatty acid receptor peroxisome proliferator-activated receptor α (PPARα) in the liver. FGF19 and FGF21 were recently identified as targets of activating transcription factor 4 (ATF4), which is activated in response to endoplasmic reticulum (ER) stress. ATF4 is also activated by oxidative stress and amino acid deprivation. In this study, we investigated FGF19 and FGF21 expression in response to oxidative stress and amino acid deprivation. We found that FGF19 mRNA is induced by oxidative stress inducers in Caco-2 cells, which are derived from the human intestinal epithelium, and rat intestinal epithelial IEC6 cells. In contrast, ileal FGF15 expression, the rodent ortholog of human FGF19, is not increased by oxidative stress. No notable changes in expression of FGF15/19 took place under amino acid deprivation either in vitro or in vivo. In contrast, FGF21 expression is induced by oxidative stress and amino acid deprivation both in vitro and in vivo. These results indicate distinctive patterns of regulation of FGF19 expression by ER stress, and FGF21 expression by ER stress, oxidative stress, and amino acid deprivation through ATF4 activation.