FGF21 Alleviates Hepatic Endoplasmic Reticulum Stress under Physiological Conditions

Abstract

Summary Fibroblast growth factor 21 (FGF21), mainly synthesized and secreted from the liver, is an endocrine FGF that regulates glucose and fatty acid metabolism to maintain whole body energy homeostasis. Gene expression of FGF21 was previously reported to be induced by endoplasmic reticulum (ER) stress through activating transcription factor 4 (ATF4). It has been reported that drug-induced ER stress is reduced by overexpression of FGF21. However, the function of endogenous FGF21 under physiological conditions such as the postprandial state remains unknown. Here, we examined the effects of both endogenous and exogenous FGF21 on postprandial hepatic ER stress. In mice, postprandial and tunicamycin-induced ER stress was significantly reduced by overexpression of FGF21 using a recombinant adenovirus. FGF21-deficient mice exhibited a more considerable increase in drug-induced ER stress target gene expression than wild-type mice. Following refeeding after fasting, FGF21 deficiency caused severe ER stress in the liver. The postprandial ER stress response was significantly reduced when hepatic FGF21 gene expression was increased by feeding a diet containing the soy protein b-conglycinin which activates ATF4. Together, these results demonstrate that FGF21 reduces the increased expression of a subset of genes in the liver in response to ER stress and may correct metabolic disorders caused by ER stress. Key Words FGF21, ER stress, ATF4, b-conglycinin Fibroblast growth factor 21 (FGF21), a member of the endocrine FGF subfamily (also known as the FGF19 subfamily), is mainly produced by the liver. FGF21 is secreted into the blood circulation, after which it acts on target tissues through a cell-surface FGF receptor (FGFR) together with its coregulator, bKlotho (1). In adipose tissues, FGF21 induces lipolysis and glucose uptake by activation of hormone sensitive lipase and glucose transporter 4, respectively (2, 3). Some hepatic energy metabolic pathways, including ketogenesis and gluconeogenesis, are also regulated by FGF21 in response to fasting. Expression of FGF21 is transcriptionally regulated during fasting via peroxisome proliferator-activated receptor a (PPARa), a nuclear hormone receptor (2, 4). More importantly, several studies revealed that FGF21 improves whole-body insulin sensitivity, inhibits high-fat diet-induced body weight gain and reduces fatty liver disease. Thus, FGF21 is an attractive target molecule for the prevention of metabolic diseases.Endoplasmic reticulum (ER) stress is triggered by excess accumulation of either unfolded or misfolded proteins in the ER, which in turn activates three ER membrane proteins: activating transcription factor 6a (ATF6a), inositol-requiring enzyme 1 (IRE1), and protein kinase RNA-like ER kinase (PERK). During ER stress, activation of PERK results in the phosphorylation of eukaryotic initiation factor 2a (eIF2a) and translational activation of activating transcription factor 4 (ATF4). Subsequently, ATF4 induces a series of target genes involved in amino acid metabolism, red...

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“…When the ERS occurs, one of ERS specific pathway, containing CHOP, is activated, and consequently expression of endogenous FGF21 is upregulated49. Furthermore, intraperitoneal injection of tunicamycin, an endoplasmic reticulum stressor, to normal mice can also induce hepatic FGF21 expression directly50. The same results are also confirmed in the adipocyte45 and H9C2 cardiomyocytes51.…”

Metabolic Cytokines at Fasting and During Macronutrient Challenges: Influence of Obesity, Female Androgen Excess and Sex

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Fibroblast growth factor 21 attenuates iron overload-induced liver injury and fibrosis by inhibiting ferroptosis

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