Hepatic Fibroblast Growth Factor 21 Research Articles

Fibroblast Growth Factor 21 Mediates Glycemic Regulation by Hepatic JNK.

The cJun NH2-terminal kinase (JNK)-signaling pathway is implicated in metabolic syndrome, including dysregulated blood glucose concentration and insulin resistance. Fibroblast growth factor 21 (FGF21) is a target of the hepatic JNK-signaling pathway and may contribute to the regulation of glycemia. To test the role of FGF21, we established mice with selective ablation of the Fgf21 gene in hepatocytes. FGF21 deficiency in the liver caused marked loss of FGF21 protein circulating in the blood. Moreover, the protective effects of hepatic JNK deficiency to suppress metabolic syndrome in high-fat diet-fed mice were not observed in mice with hepatocyte-specific FGF21 deficiency, including reduced blood glucose concentration and reduced intolerance to glucose and insulin. Furthermore, we show that JNK contributes to the regulation of hepatic FGF21 expression during fasting/feeding cycles. These data demonstrate that the hepatokine FGF21 is a key mediator of JNK-regulated metabolic syndrome.

Acyl CoA synthetase 5 (ACSL5) ablation in mice increases energy expenditure and insulin sensitivity and delays fat absorption.

ObjectiveThe family of acyl-CoA synthetase enzymes (ACSL) activates fatty acids within cells to generate long chain fatty acyl CoA (FACoA). The differing metabolic fates of FACoAs such as incorporation into neutral lipids, phospholipids, and oxidation pathways are differentially regulated by the ACSL isoforms. In vitro studies have suggested a role for ACSL5 in triglyceride synthesis; however, we have limited understanding of the in vivo actions of this ACSL isoform.MethodsTo elucidate the in vivo actions of ACSL5 we generated a line of mice in which ACSL5 expression was ablated in all tissues (ACSL5−/−).ResultsAblation of ACSL5 reduced ACSL activity by ∼80% in jejunal mucosa, ∼50% in liver, and ∼37% in brown adipose tissue lysates. Body composition studies revealed that ACSL5−/−, as compared to control ACSL5loxP/loxP, mice had significantly reduced fat mass and adipose fat pad weights. Indirect calorimetry studies demonstrated that ACSL5−/− had increased metabolic rates, and in the dark phase, increased respiratory quotient. In ACSL5−/− mice, fasting glucose and serum triglyceride were reduced; and insulin sensitivity was improved during an insulin tolerance test. Both hepatic mRNA (∼16-fold) and serum levels of fibroblast growth factor 21 (FGF21) (∼13-fold) were increased in ACSL5−/− as compared to ACSL5loxP/loxP. Consistent with increased FGF21 serum levels, uncoupling protein-1 gene (Ucp1) and PPAR-gamma coactivator 1-alpha gene (Pgc1α) transcript levels were increased in gonadal adipose tissue. To further evaluate ACSL5 function in intestine, mice were gavaged with an olive oil bolus; and the rate of triglyceride appearance in serum was found to be delayed in ACSL5−/− mice as compared to control mice.ConclusionsIn summary, ACSL5−/− mice have increased hepatic and serum FGF21 levels, reduced adiposity, improved insulin sensitivity, increased energy expenditure and delayed triglyceride absorption. These studies suggest that ACSL5 is an important regulator of whole-body energy metabolism and ablation of ACSL5 may antagonize the development of obesity and insulin resistance.

Endurance Exercise Reduces Hepatic Fat Content and Serum Fibroblast Growth Factor 21 Levels in Elderly Men.

Age-related hepatic fat accumulation increases the risk of cardiometabolic diseases, and the fibroblast growth factor (FGF) 21-resistant state caused by fatty liver underlies the pathogenesis of these diseases. Previous studies suggested that a higher level of cardiorespiratory fitness was associated with both lower hepatic fat content and serum FGF21 levels; however, the effect of endurance exercise on hepatic fat content and serum FGF21 concentration has not been studied. Therefore, we aimed to elucidate whether endurance exercise reduced hepatic fat content and serum FGF21 levels. This is a randomized crossover trial. The study setting was an institutional practice. Thirty-three elderly Japanese men participated in the study. The intervention was a 5-week endurance exercise program comprising three cycle ergometer sessions per week. Hepatic fat content was assessed by proton magnetic resonance spectroscopy, and serum FGF21 level was determined by ELISA. A 5-week endurance exercise program decreased the hepatic fat content and serum FGF21 levels without weight loss, and the changes were higher in the exercise period than in the control period (P = .021 and P = .026, respectively). Correlation analysis demonstrated that only the change in hepatic fat content was significantly and positively correlated with change in serum FGF21 levels (r = 0.366, P = .006). A 5-week endurance exercise program decreased hepatic fat content and serum FGF21 levels without weight loss in elderly men, and exercise-induced hepatic fat reduction mediated the reduction in serum FGF21 levels. These findings suggest that endurance exercise modulates hepatic fat content and FGF21 resistance, regardless of obesity status.

FGF21 Mediates Endocrine Control of Simple Sugar Intake and Sweet Taste Preference by the Liver

The liver is an important integrator of nutrient metabolism, yet no liver-derived factors regulating nutrient preference or carbohydrate appetite have been identified. Here we show that the liver regulates carbohydrate intake through production of the hepatokine fibroblast growth factor 21 (FGF21), which markedly suppresses consumption of simple sugars, but not complex carbohydrates, proteins, or lipids. Genetic loss of FGF21 in mice increases sucrose consumption, whereas acute administration or overexpression of FGF21 suppresses the intake of both sugar and non-caloric sweeteners. FGF21 does not affect chorda tympani nerve responses to sweet tastants, instead reducing sweet-seeking behavior and meal sizevia neurons in the hypothalamus. This liver-to-brain hormonal axis likely represents a negative feedback loop as hepatic FGF21 production is elevated by sucrose ingestion. We conclude that the liver functions to regulate macronutrient-specificintake by producing an endocrine satiety signal that acts centrally to suppress the intake of "sweets."

Differentiated embryo chondrocyte 1 (DEC1) is a novel negative regulator of hepatic fibroblast growth factor 21 (FGF21) in aging mice

Human differentiated embryo chondrocyte expressed gene 1 (DEC1) is frequently used as a marker of senescence in vivo. Fibroblast growth factor 21 (FGF21), a novel endocrine-like member of the FGF superfamily, is highly expressed in the liver, and FGF21-transgenic mice have extended lifespans. Thus, we hypothesized that FGF21 may play a role in the DEC1-mediated aging process. In this study, DEC1 knockout (KO) mice were used to characterize the mechanism by which FGF21 protects mice from aging. Aging is strongly diminished in DEC1 KO mice, which is reflected by decreased lipid levels and oxidative stress, leading to an amelioration of liver function and structure. The expression of FGF21 decreased with aging in wild-type (WT) mice, whereas ATF4, Phospho-ERK and Phospho-p38 expression was maintained and was accompanied by a compensatory rise of FGF21 mRNA and protein expression in DEC1 KO mice. Over-expression of DEC1 markedly abolished the hepatic expression of FGF21, and siRNA-mediated inhibition of endogenous DEC1 increased the expression of FGF21. DEC1 further diminished the expression of ATF4 in HepG2 cells over-expressing DEC1. The induction of FGF21 and ATF4 at the mRNA and protein levels during the course of aging supports the view that DEC1 KO mice are able to restore the age-related imbalance of metabolism. Collectively, the data obtained in this study suggest that DEC1 is a novel negative regulator of hepatic FGF21 expression.

Pharmacologic stimulation of central GLP-1 receptors has opposite effects on the alterations of plasma FGF21 levels induced by feeding and fasting

Fibroblast growth factor 21 (FGF21) functions as an endocrine hormone to regulate energy metabolism. Circulating FGF21 is derived from the liver and is produced in response to alterations of nutritional status. Here we show the effects of liraglutide, a human glucagon-like-peptide-1 (GLP-1) receptor agonist, injected into the third cerebral ventricle on body weight and plasma FGF21 levels in free-feeding mice, food-deprived mice, and mice provided 1g after the injection. In free-feeding mice, liraglutide (5–100μg/kg) injected into the third cerebral ventricle suppressed food intake and body weight after 24h in a dose-dependent manner. Liraglutide (50 and 100μg/kg) significantly increased plasma FGF21 levels and hepatic FGF21 expression, whereas smaller doses (5 and 10μg/kg) had no effect. In food-deprived mice, body weight did not differ significantly between the saline control and liraglutide-treated groups, but liraglutide (100μg/kg) significantly decreased plasma FGF21 levels at 24h compared with the saline control. In mice provided 1g food, body weight did not differ significantly between the saline control and liraglutide-treated groups, but liraglutide (50μg/kg) significantly decreased plasma FGF21 levels at 24h compared with the saline control. These findings suggest that intracerebral injection of liraglutide decreases body weight by inhibiting food intake and increases plasma FGF21 levels in free-feeding mice, whereas it suppresses the elevations of plasma FGF21 levels induced by fasting or the restricted feeding. Thus, pharmacologic stimulation of central GLP-1 receptors has opposite effects on the alterations of plasma FGF21 levels induced by feeding and fasting.

Alterations in Hepatic FGF21, Co-Regulated Genes, and Upstream Metabolic Genes in Response to Nutrition, Ketosis and Inflammation in Peripartal Holstein Cows.

In rodents, fibroblast growth factor 21 (FGF21) has emerged as a key metabolic regulator produced by liver. To gather preliminary data on the potential importance of FGF1, co-regulated genes, and upstream metabolic genes, we examined the hepatic mRNA expression in response to nutrition and inflammation in dairy cows. In experiment 1, induction of ketosis through feed restriction on d 5 postpartum upregulated FGF21, its co-receptor KLB, and PPARA but only elicited a numerical increase in serum FGF21 concentration. In experiment 2, cows in control (CON) or receiving 50 g/d of L-carnitine (C50) from -14 through 21 d had increased FGF21, PPARA, and NFIL3 on d 10 compared with d 2 postpartum. In contrast, compared with CON and C50, 100 g/d L-carnitine (C100) resulted in lower FGF21, KLB, ANGPTL4, and ARNTL expression on d 10. In experiment 3, cows were fed during the dry period either a higher-energy (OVE; 1.62 Mcal/kg DM) or lower-energy (CON; 1.34 Mcal/kg DM) diet and received 0 (OVE:N, CON:N) or 200 μg of LPS (OVE:Y, CON:Y) into the mammary gland at d 7 postpartum. For FGF21 mRNA expression in CON, the LPS challenge (CON:Y) prevented a decrease in expression between d 7 and 14 postpartum such that cows in CON:N had a 4-fold lower expression on d 14 compared with d 7. The inflammatory stimulus induced by LPS in CON:Y resulted in upregulation of PPARA on d 14 to a similar level as cows in OVE:N. In OVE:Y, expression of PPARA was lower than CON:N on d 7 and remained unchanged on d 14. On d 7, LPS led to a 4-fold greater serum FGF21 only in OVE but not in CON cows. In fact, OVE:Y reached the same serum FGF21 concentration as CON:N, suggesting a carryover effect of dietary energy level on signaling mechanisms within liver. Overall, results indicate that nutrition, ketosis, and inflammation during the peripartal period can alter hepatic FGF21, co-regulated genes, and upstream metabolic genes to various extents. The functional outcome of these changes merits further study, and in particular the mechanisms regulating transcription in response to changes in energy balance and feed intake.

Expression of hepatic Fibroblast Growth Factor 19 is enhanced in Primary Biliary Cirrhosis and correlates with severity of the disease.

Cholestasis induces adaptive mechanisms protecting the liver against bile acids (BA) toxicity including modulation of BA synthesis. Whether fibroblast growth factor 19 (FGF19) or farnesoid X receptor (FXR) dependent signaling are involved in the regulation of BA homeostasis in primary biliary cirrhosis (PBC) remains unknown. Here we analyzed hepatic expression of FGF19 and other genes relevant to the adaptive response to cholestasis in tissues from non-cirrhotic (n = 24) and cirrhotic (n = 21) patients along with control tissues (n = 21). Moreover we searched for relationships between serum FGF19 and laboratory/clinical findings in 51 patients. Hepatic FGF19 mRNA expression was increased in non-cirrhotic and cirrhotic tissues (9-fold,p = 0.01; 69-fold,p < 0.0001, respectively). Protein levels of FGF19, FGF receptor 4, FXR and short heterodimer partner were increased in cirrhotic livers (9-fold, p < 0.001; 3.5-fold,p = 0.007; 2.4-fold,p < 0.0001; 2.8-fold,p < 0.0001 vs controls, respectively) which was accompanied by down-regulation of CYP7A1 (50% reduction, p = 0.006). Serum and liver levels of FGF19 correlated with worse liver biochemistry, BAs, quality of life and Mayo Risk Score. Serum FGF19 was elevated in UDCA non-responders. We conclude that PBC induces characteristic changes in liver expression of BAs synthesis regulatory molecules. FGF19 correlates with severity of liver disease and can potentially serve as an indicator of chronic cholestatic liver injury.

Betaine alleviates hepatic lipid accumulation via enhancing hepatic lipid export and fatty acid oxidation in rats fed with a high-fat diet.

To assess the effects of betaine on hepatic lipid accumulation and investigate the underlying mechanism, thirty-two male Sprague-Dawley rats weighing 100 (sd 2·50) g were divided into four groups, and started on one of four treatments: basal diet, basal diet with betaine administration, high-fat diet and high-fat diet with betaine administration. The results showed that no significant difference of body weight was found among experimental groups. Compared with high-fat diet-fed rats, a betaine supplementation decreased (P< 0·05) hepatic TAG accumulation induced by high-fat diet, which was also supported by hepatic histology results. Additionally, hepatic betaine-homocysteine methyltransferase concentration [corrected] as well as its mRNA abundance and lecithin level were found increased (P< 0·05) by betaine supplementation in both basal diet-fed rats and high-fat diet-fed rats. Betaine administration in high-fat diet-fed rats exhibited a higher (P< 0·05) concentration [corrected] of hepatic carnitine palmitoyltransferase 1 (CPT1) compared with high-fat diet-fed rats. High-fat diet inhibited (P< 0·05) the gene expression of hepatic PPARα and CPT1. However, betaine administration in high-fat diet-fed rats elevated (P< 0·05) the gene expression of PPARα and CPT1. Moreover, concentration, gene and protein expressions of hepatic fibroblast growth factor 21 (FGF21) were increased (P< 0·05) in response to betaine administration in high-fat diet group; meanwhile the gene expression of hepatic AMP-activated protein kinase was increased (P< 0·05) as well. The results suggest that betaine administration enhanced hepatic lipid export and fatty acid oxidation in high-fat diet-fed rats, thus effectively alleviating fat accumulation in the liver.

R‐α‐lipoic acid potentiates fasting‐induced transcription and secretion of hepatic fibroblast growth factor 21 (FGF21)

Recombinant FGF21 (rFGF21) is an experimental polypeptide therapy against type‐2 diabetes and lipid anomalies. However, the high costs of producing rFGF21 and the mode of delivery by injection are important limitations to its wide therapeutic use. The stimulation of endogenous FGF21 production through diet is being explored as an alternative approach. Our research showed that naturally occurring dietary organosulfur compound R‐α‐lipoic acid (LA) stimulated liver Fgf21 expression (+175%) and blood FGF21 levels (+330%) and replicated the adaptive metabolic response to fasting evoked by FGF21 in vivo. In the present study, we examined the mechanism(s) by which serum manipulation and LA induce FGF21 in HepG2 human hepatocellular carcinoma cells. Serum starvation markedly induced FGF21 mRNA levels (50 fold) and FGF21 secreted in the media (19 fold). LA induced FGF21 mRNA 7 fold above DMSO‐treated control cells and FGF21 secretion 3 fold. These effects were several‐fold greater than those of PPARα agonist, Wy14643, an inducer of FGF21. The use of transcription inhibitor, actinomycin D, revealed that de novo mRNA synthesis drives FGF21 secretion in response to serum starvation and LA, and FGF21 does not accumulate in HepG2 cells to a significant degree. Previously unrecognized loci of FGF21 distal promoter were nucleosome depleted and transcriptionally active revealing new putative transcription factors. We conclude that LA activates FGF21 distal promoter resulting in FGF21 secretion by liver cells. LA may prove to be a safe and affordable means to stimulate FGF21 production. Supported by UNL ARD Hatch, and Layman Seed Award.

Role of fibroblast growth factor 21 in the early stage of NASH induced by methionine- and choline-deficient diet

Fibroblast growth factor 21 (FGF21) is a modulator of energy homeostasis and is increased in human nonalcoholic liver disease (NAFLD) and after feeding of methionine- and choline-deficient diet (MCD), a conventional inducer of murine nonalcoholic steatohepatitis (NASH). However, the significance of FGF21 induction in the occurrence of MCD-induced NASH remains undetermined. C57BL/6J Fgf21-null and wild-type mice were treated with MCD for 1week. Hepatic Fgf21 mRNA was increased early after commencing MCD treatment independent of peroxisome proliferator-activated receptor (PPAR) α and farnesoid X receptor. While no significant differences in white adipose lipolysis were seen in both genotypes, hepatic triglyceride (TG) contents were increased in Fgf21-null mice, likely due to the up-regulation of genes encoding CD36 and phosphatidic acid phosphatase 2a/2c, involved in fatty acid (FA) uptake and diacylglycerol synthesis, respectively, and suppression of increased mRNAs encoding carnitine palmitoyl-CoA transferase 1α, PPARγ coactivator 1α, and adipose TG lipase, which are associated with lipid clearance in the liver. The MCD-treated Fgf21-null mice showed increased hepatic endoplasmic reticulum (ER) stress. Exposure of primary hepatocytes to palmitic acid elevated the mRNA levels encoding DNA damage-inducible transcript 3, an indicator of ER stress, and FGF21 in a PPARα-independent manner, suggesting that lipid-induced ER stress can enhance hepatic FGF21 expression. Collectively, FGF21 is elevated in the early stage of MCD-induced NASH likely to minimize hepatic lipid accumulation and ensuing ER stress. These results provide a possible mechanism on how FGF21 is increased in NAFLD/NASH.

Effects of omega-3 fatty acids and pioglitazone combination on insulin resistance through fibroblast growth factor 21 in type 2 diabetes mellitus

Fibroblast growth factor 21 (FGF21) is an effective regulator of glucose and lipid metabolism. It is mainly regulated by peroxisome proliferator activated receptors, and is widely associated with cases of insulin resistance as obesity and type 2 diabetes (T2D). Our study aimed to investigate the potential effects of omega-3 fatty acids, pioglitazone, and their combination on serum and liver FGF21 concentrations, and its hepatic gene expression in a rat model of T2D. We also studied the modulating effects of these treatments on blood glucose, lipid profile, and insulin resistance. T2D was induced in male Sprague–Dawley rats by combination of high fat diet and low dose streptozotocin (35 mg/kg). Diabetic rats were treated with omega-3 fatty acids (10%W/W diet), pioglitazone (20 mg/kg), and their combination for a period of 4 weeks. Serum FGF21 concentration was significantly increased in diabetic rats. In contrast, hepatic FGF21 concentration, and gene expression were significantly decreased. Omega-3 fatty acids, pioglitazone, and their combination significantly decreased serum FGF21. Omega-3 fatty acids and combination therapy significantly decreased liver FGF21 concentration, with non-significant changes in gene expression. On the other hand, pioglitazone significantly increased hepatic FGF21 concentration and gene expression. Omega-3 fatty acids, pioglitazone and their combination significantly improved lipid profile. Pioglitazone and combination significantly decreased blood glucose levels and improved insulin resistance. In conclusion, this study introduces the first evidence regarding the antidiabetic effects of omega-3 fatty acids and pioglitazone combination, such effects are mediated through FGF21.

Alpha lipoic acid induces hepatic fibroblast growth factor 21 expression via up-regulation of CREBH

Hepatic expression of fibroblast growth factor 21 (FGF21), one of the most promising therapeutic candidates for metabolic syndrome, is induced by multiple factors associated with fasting, including cyclic AMP response element-binding protein H (CREBH). Alpha lipoic acid (ALA), a naturally occurring thiol antioxidant, has been shown to induce metabolic changes that are similar to those induced by FGF21, including weight loss and increased energy expenditure. Here, we investigated the effect of ALA on hepatic FGF21 expression. ALA treatment enhanced CREBH and FGF21 mRNA expression and protein abundance in cultured hepatocytes. ALA increased FGF21 promoter activity by up-regulating CREBH expression and increasing CREBH binding to the FGF21 promoter, indicating that ALA up-regulates FGF21 at the transcriptional level. Moreover, inhibition of endogenous CREBH expression by siRNA attenuated ALA-induced FGF21 expression. Finally, treatment of mice with ALA enhanced fasting-induced up-regulation of CREBH and FGF21 in the liver and inhibited feeding-induced suppression of their expression. Consistently, ALA increased serum FGF21 levels in both fasted and fed mice. Collectively, these results indicate that ALA increases hepatic FGF21 expression via up-regulation of CREBH, identifying ALA as a novel positive regulator of FGF21.

Fibroblast growth factor 21 is induced upon cardiac stress and alters cardiac lipid homeostasis

Fibroblast growth factor 21 (FGF21) is a PPARα-regulated gene elucidated in the liver of PPARα-deficient mice or PPARα agonist-treated mice. Mice globally lacking adipose triglyceride lipase (ATGL) exhibit a marked defect in TG catabolism associated with impaired PPARα-activated gene expression in the heart and liver, including a drastic reduction in hepatic FGF21 mRNA expression. Here we show that FGF21 mRNA expression is markedly increased in the heart of ATGL-deficient mice accompanied by elevated expression of endoplasmic reticulum (ER) stress markers, which can be reversed by reconstitution of ATGL expression in cardiac muscle. In line with this assumption, the induction of ER stress increases FGF21 mRNA expression in H9C2 cardiomyotubes. Cardiac FGF21 expression was also induced upon fasting of healthy mice, implicating a role of FGF21 in cardiac energy metabolism. To address this question, we generated and characterized mice with cardiac-specific overexpression of FGF21 (CM-Fgf21). FGF21 was efficiently secreted from cardiomyocytes of CM-Fgf21 mice, which moderately affected cardiac TG homeostasis, indicating a role for FGF21 in cardiac energy metabolism. Together, our results show that FGF21 expression is activated upon cardiac ER stress linked to defective lipolysis and that a persistent increase in circulating FGF21 levels interferes with cardiac and whole body energy homeostasis.

MicroRNA 34a inhibits beige and brown fat formation in obesity in part by suppressing adipocyte fibroblast growth factor 21 signaling and SIRT1 function.

Brown fat generates heat through uncoupled respiration, protecting against hypothermia and obesity. Adult humans have brown fat, but the amounts and activities are substantially decreased in obesity, by unknown mechanisms. Here we show that elevated microRNA 34a (miR-34a) in obesity inhibits fat browning in part by suppressing the browning activators fibroblast growth factor 21 (FGF21) and SIRT1. Lentivirus-mediated downregulation of miR-34a in mice with diet-induced obesity reduced adiposity, improved serum profiles, increased the mitochondrial DNA copy number, and increased oxidative function in adipose tissue in both BALB/c and C57BL/6 mice. Remarkably, downregulation of miR-34a increased coexpression of the beige fat-specific marker CD137 and the browning marker UCP1 in all types of white fat, including visceral fat, and promoted additional browning in brown fat. Mechanistically, downregulation of miR-34a increased expression of the FGF21 receptor components, FGFR1 and βKL, and also that of SIRT1, resulting in FGF21/SIRT1-dependent deacetylation of PGC-1α and induction of the browning genes Ucp1, Pgc-1α, and Prdm16. Importantly, anti-miR-34a-mediated beneficial effects, including decreased adiposity, are likely from multiple tissues, since downregulation of miR-34a also improves hepatic FGF21 signaling and lipid oxidation. This study identifies miR-34a as an inhibitor of beige and brown fat formation, providing a potential target for treating obesity-related diseases.

Fructose ingestion acutely stimulates circulating FGF21 levels in humans.

ObjectiveFibroblast growth factor 21 (FGF21) is a hormone with pleiotropic metabolic activities which, in rodents, is robustly regulated by fasting and ketogenic diets. In contrast, similar dietary interventions have either no or minimal effects on circulating FGF21 in humans. Moreover, no intervention or dietary challenge has been shown to acutely stimulate circulating FGF21 in either humans or animals. Recent animal data suggest that the transcription factor Carbohydrate Responsive-Element Binding Protein (ChREBP) stimulates hepatic FGF21 expression and that fructose may activate hepatic ChREBP more robustly than glucose. Here, we examined whether fructose ingestion can acutely stimulate FGF21 in humans.MethodsWe measured serum FGF21, glucose, insulin, and triglyceride levels in ten lean, healthy adults and eleven adults with the metabolic syndrome following oral ingestion of 75 g of glucose, fructose, or a combination of the two sugars.ResultsFGF21 levels rose rapidly following fructose ingestion, achieved a mean 3.4-fold increase at two hours (P < 0.01), and returned to baseline levels within five hours. In contrast, FGF21 did not increase in the first two hours following ingestion of a glucose load, although more modest increases were observed after three to four hours. Both baseline and fructose-stimulated FGF21 levels were 2–3 fold elevated in subjects with metabolic syndrome.ConclusionsFructose ingestion acutely and robustly increases serum FGF21 levels in humans in a pattern consistent with a hormonal response. While FGF21 appears to be critical for the adaptive response to fasting or starvation in rodents, these findings suggest that in humans, FGF21 may play an important role in fructose metabolism.

FGF21 is an endocrine signal of protein restriction.

Enhanced fibroblast growth factor 21 (FGF21) production and circulation has been linked to the metabolic adaptation to starvation. Here, we demonstrated that hepatic FGF21 expression is induced by dietary protein restriction, but not energy restriction. Circulating FGF21 was increased 10-fold in mice and rats fed a low-protein (LP) diet. In these animals, liver Fgf21 expression was increased within 24 hours of reduced protein intake. In humans, circulating FGF21 levels increased dramatically following 28 days on a LP diet. LP-induced increases in FGF21 were associated with increased phosphorylation of eukaryotic initiation factor 2α (eIF2α) in the liver, and both baseline and LP-induced serum FGF21 levels were reduced in mice lacking the eIF2α kinase general control nonderepressible 2 (GCN2). Finally, while protein restriction altered food intake, energy expenditure, and body weight gain in WT mice, FGF21-deficient animals did not exhibit these changes in response to a LP diet. These and other data demonstrate that reduced protein intake underlies the increase in circulating FGF21 in response to starvation and a ketogenic diet and that FGF21 is required for behavioral and metabolic responses to protein restriction. FGF21 therefore represents an endocrine signal of protein restriction, which acts to coordinate metabolism and growth during periods of reduced protein intake.

Hepatic FGF21 production is increased in late pregnancy in the mouse.

Female mammals call on hormonally driven metabolic adaptations to meet the energy demand of late pregnancy and lactation. These maternal adaptations preserve limiting nutrients and promote their transfer to the uterus during pregnancy or mammary gland during lactation. The novel metabolic hormone fibroblast growth factor-21 (FGF21) was recently shown to increase suddenly at the onset of lactation in dairy cows, but whether FGF21 is induced during the reproductive cycle of other mammals is unknown. To start addressing this question, we studied subsets of mice when virgin (V), on day 18 of pregnancy (P18) and on lactation day 1 (L1), L5 and L14. Plasma FGF21 increased from nearly undetectable levels to over 8 ng/ml between V and P18 and returned to V levels by L1. Gene expression studies showed that liver was the major source of plasma FGF21 at P18 with little or no contribution from other known expressing tissues or from the developing placenta and mammary epithelial cells. The increased FGF21 production at P18 was dissociated from plasma nonesterified fatty acids and liver lipids, unlike that seen in fasted V mice. Changes in FGF21 signaling components in target tissues were modest except for reduced β-Klotho and FGFR1c expression in P18 adipose tissue. The placenta expressed both β-Klotho and FGFR1c, raising the possibility that it responds to FGF21. In conclusion, maternal FGF21 is increased when products of conception account for ∼ 40% of maternal weight, suggesting that FGF21 orchestrates some of the adaptations needed to meet the energy demand of late pregnancy.

Orphan nuclear receptor Nur77 mediates fasting-induced hepatic fibroblast growth factor 21 expression.

The fasting-induced hepatic hormone, fibroblast growth factor 21 (FGF21), is a potential candidate for the treatment of metabolic syndromes. Although peroxisome proliferator-activated receptor (PPAR)α is known to play a major role in the induction of hepatic FGF21 expression, other fasting-induced transcription factors that induce FGF21 expression have not yet been fully studied. In the present study, we investigated whether the fasting-induced activation of the orphan nuclear receptor Nur77 increases hepatic FGF21 expression. We found that fasting induced hepatic Nur77 and FGF21 expression. Glucagon and forskolin increased Nur77 and FGF21 expression in vivo and in vitro, respectively, and adenovirus-mediated overexpression of Nur77 (Ad-Nur77) increased FGF21 expression in vitro and in vivo. Moreover, knockdown of endogenous Nur77 expression by siRNA-Nur77 abolished the effect of forskolin on FGF21 expression. The results of ChIP assays, EMSA, and mutagenesis analysis showed that Nur77 bound to the putative NBRE of the FGF21 promoter in cultured hepatocytes and fasting induced Nur77 binding to the FGF21 promoter in vivo. Knockdown of PPARα partially inhibited forskolin-induced FGF21 expression, suggesting PPARα involvement in glucagon-stimulated FGF21 expression. In addition, double knockdown of PPARα and Nur77 further diminished FGF21 expression in cultured hepatocytes. In conclusion, this study shows that Nur77 mediates fasting-induced hepatic FGF21 expression, and suggests an alternative mechanism via which hepatic FGF21 transcription is mediated under fasting conditions.

Glucagon stimulates hepatic FGF21 secretion through a PKA- and EPAC-dependent posttranscriptional mechanism.

Previous studies have shown that whole body deletion of the glucagon receptor suppresses the ability of starvation to increase hepatic fibroblast growth factor 21 (FGF21) expression and plasma FGF21 concentration. Here, we investigate the mechanism by which glucagon receptor activation increases hepatic FGF21 production. Incubating primary rat hepatocyte cultures with glucagon, dibutyryl cAMP or forskolin stimulated a 3-4-fold increase in FGF21 secretion. The effect of these agents on FGF21 secretion was not associated with an increase in FGF21 mRNA abundance. Glucagon induction of FGF21 secretion was additive with the stimulatory effect of a PPARα activator (GW7647) on FGF21 secretion. Inhibition of protein kinase A (PKA) and downstream components of the PKA pathway [i.e. AMP-activated protein kinase and p38 MAPK] suppressed glucagon activation of FGF21 secretion. Incubating hepatocytes with an exchange protein directly activated by cAMP (EPAC)-selective cAMP analog [i.e. 8-(4-chlorophenylthio)-2'-O-methyladenosine-3', 5'-cyclic monophosphate (cpTOME)], stimulated a 3.9-fold increase FGF21 secretion, whereas inhibition of the EPAC effector, Rap1, suppressed glucagon activation of FGF21 secretion. Treatment of hepatocytes with insulin also increased FGF21 secretion. In contrast to glucagon, insulin activation of FGF21 secretion was associated with an increase in FGF21 mRNA abundance. Glucagon synergistically interacted with insulin to stimulate a further increase in FGF21 secretion and FGF21 mRNA abundance. These results demonstrate that glucagon increases hepatic FGF21 secretion via a posttranscriptional mechanism and provide evidence that both the PKA branch and EPAC branch of the cAMP pathway play a role in mediating this effect. These results also identify a novel synergistic interaction between glucagon and insulin in the regulation of FGF21 secretion and FGF21 mRNA abundance. We propose that this insulin/glucagon synergism plays a role in mediating the elevation in FGF21 production during starvation and conditions related to metabolic syndrome.