Induction Of Fibroblast Growth Factor 21 Research Articles

Short-term hypercaloric carbohydrate loading increases surgical stress resilience by inducing FGF21

Dietary restriction promotes resistance to surgical stress in multiple organisms. Counterintuitively, current medical protocols recommend short-term carbohydrate-rich drinks (carbohydrate loading) prior to surgery, part of a multimodal perioperative care pathway designed to enhance surgical recovery. Despite widespread clinical use, preclinical and mechanistic studies on carbohydrate loading in surgical contexts are lacking. Here we demonstrate in ad libitum-fed mice that liquid carbohydrate loading for one week drives reductions in solid food intake, while nearly doubling total caloric intake. Similarly, in humans, simple carbohydrate intake is inversely correlated with dietary protein intake. Carbohydrate loading-induced protein dilution increases expression of hepatic fibroblast growth factor 21 (FGF21) independent of caloric intake, resulting in protection in two models of surgical stress: renal and hepatic ischemia-reperfusion injury. The protection is consistent across male, female, and aged mice. In vivo, amino acid add-back or genetic FGF21 deletion blocks carbohydrate loading-mediated protection from ischemia-reperfusion injury. Finally, carbohydrate loading induction of FGF21 is associated with the induction of the canonical integrated stress response (ATF3/4, NF-kB), and oxidative metabolism (PPARγ). Together, these data support carbohydrate loading drinks prior to surgery and reveal an essential role of protein dilution via FGF21.

Parkin depletion prevents the age-related alterations in the FGF21 system and the decline in white adipose tissue thermogenic function in mice.

Parkin is an ubiquitin-E3 ligase that is involved in cellular mitophagy and was recently shown to contribute to controlling adipose tissue thermogenic plasticity. We found that Parkin expression is induced in brown (BAT) and white (WAT) adipose tissues of aged mice. We determined the potential role of Parkin in the aging-associated decline in the thermogenic capacity of adipose tissues by analyzing subcutaneous WAT, interscapular BAT, and systemic metabolic and physiological parameters in young (5month-old) and aged (16month-old) mice with targeted invalidation of the Parkin (Park2) gene, and their wild-type littermates. Our data indicate that suppression of Parkin prevented adipose accretion, increased energy expenditure and improved the systemic metabolic derangements, such as insulin resistance, seen in aged mice. This was associated with maintenance of browning and reduction of the age-associated induction of inflammation in subcutaneous WAT. BAT in aged mice was much less affected by Parkin gene invalidation. Such protection was associated with a dramatic prevention of the age-associated induction of fibroblast growth factor-21 (FGF21) levels in aged Parkin-invalidated mice. This was associated with a parallel reduction in FGF21 gene expression in adipose tissues and liver in aged Parkin-invalidated mice. Additionally, Parkin invalidation prevented the protein down-regulation of β-Klotho (a key co-receptor mediating FGF21 responsiveness in tissues) in aged adipose tissues. We conclude that Parkin down-regulation leads to improved systemic metabolism in aged mice, in association with maintenance of adipose tissue browning and FGF21 system functionality.

Dietary protein restriction modulates ‘dessert’ intake after a meal, via fibroblast growth factor 21 (FGF21)

Pharmacological administration of fibroblast growth factor 21 (FGF21) alters food choice, including that it decreases the consumption of sucrose and other sweet tastants. Conversely, endogenous secretion of FGF21 by the liver is modulated by diet, such that plasma FGF21 is increased after eating foods that have a low dietary protein: total energy (P: E) ratio. Together, these findings suggest a strategy to promote healthy eating, in which the macronutrient content of a pre-load diet could reduce the consumption of sweet desserts in sated mice. Here, we tested the prediction that individuals maintained on a low P: E diet, and offered a highly palatable sweet ‘dessert’ following a pre-load meal, would eat less of the sugary snack compared to controls—due to increased FGF21 signaling. In addition to decreasing sweet intake, FGF21 increases the consumption of dietary protein. Thus, we predicted that individuals maintained on the low P: E diet, and offered a very high-protein pellet as ‘dessert’ or snack after a meal, would eat more of the high protein pellet compared to controls, and that this depends on FGF21. We tested this in C57Bl/6J, and liver-specific FGF21-null (FGF21ΔL) null male and female mice and littermate controls. Contrary to expectation, eating a low protein pre-load did not reduce the later consumption of a sweet solution in either males or females, despite robustly increasing plasma FGF21. Rather, eating the low protein pre-load increased later consumption of a high protein pellet. This was more apparent among males and was abrogated in the FGF21ΔL mice. We conclude that physiologic induction of hepatic FGF21 by a low protein pre-load diet is not sufficient to reduce the consumption of sweet desserts, though it effectively increases the subsequent intake of dietary protein in male mice.

Association of NAFLD with FGF21 Polygenic Hazard Score, and Its Interaction with Protein Intake Level in Korean Adults.

Fibroblast growth factor 21 (FGF21) is a hormone that participates in the regulation of energy homeostasis and is induced by dietary protein restriction. Preclinical studies have suggested that FGF21 induction exerts a protective effect against non-alcoholic fatty liver disease (NAFLD), while human studies have revealed elevated levels of and potential resistance to FGF21 in patients with NAFLD. However, whether the FGF21 pathway also contributes to NAFLD risk at the genetic level remains uncertain. A few attempts to investigate the impact of individual genetic variants at the loci encoding FGF21 and its receptors on NAFLD risk have failed to establish a clear association due to a limited effect size. Therefore, this study aimed to (1) develop a polygenic hazard score (PHS) for FGF21-related loci that are associated with NAFLD risk and (2) investigate the effect of its interaction with protein intake level on NAFLD risk. Data on 3501 participants of the Korean Genome Epidemiology Study (Ansan-Ansung) were analyzed. Eight single-nucleotide polymorphisms of fibroblast growth factor receptors and beta-klotho were selected for PHS determination using forward stepwise analysis. The association between the PHS and NAFLD was validated (p-trend: 0.0171 for men and <0.0001 for women). Moreover, the association was significantly modulated by the protein intake level in all participants as well as women (p-interaction = 0.0189 and 0.0131, respectively) but not in men. In particular, the women with the lowest PHS values and a protein intake lower than the recommended nutrient intake (RNI) exhibited a greater NAFLD risk (HR = 2.021, p-trend = 0.0016) than those with an intake equal to or greater than the RNI; however, those with higher PHS values had a high risk, regardless of protein intake level. These findings demonstrate the contribution of FGF21-related genetic variants and restricted protein intake to NAFLD incidence.

Modulation of GCN2/eIF2α/ATF4 Pathway in the Liver and Induction of FGF21 in Young Goats Fed a Protein- and/or Phosphorus-Reduced Diet.

Mammals respond to amino acid (AA) deficiency by initiating an AA response pathway (AAR) that involves the activation of general control nonderepressible 2 (GCN2), phosphorylation of eukaryotic translation initiation factor 2α (eIF2α), and activation of transcription factor 4 (ATF4). In this study, the effects of protein (N) and/or phosphorus (P) restriction on the GCN2/eIF2α/ATF4 pathway in the liver and the induction of fibroblast growth factor 21 (FGF21) in young goats were investigated. An N-reduced diet resulted in a decrease in circulating essential AA (EAA) and an increase in non-essential AA (NEAA), as well as an increase in hepatic mRNA expression of GCN2 and ATF4 and protein expression of GCN2. Dietary N restriction robustly increased both hepatic FGF21 mRNA expression and circulating FGF21 levels. Accordingly, numerous significant correlations demonstrated the effects of the AA profile on the AAR pathway and confirmed an association. Furthermore, activation of the AAR pathway depended on the sufficient availability of P. When dietary P was restricted, the GCN2/eIF2α/ATF4 pathway was not initiated, and no increase in FGF21 was observed. These results illustrate how the AAR pathway responds to N- and/or P-reduced diets in ruminants, thus demonstrating the complexity of dietary component changes.

FOXO1 represses PPARα-Mediated induction of FGF21 gene expression

Fibroblast growth factor 21 (FGF21) has emerged as a metabolic regulator that exerts potent anti-diabetic and lipid-lowering effects in animal models of obesity and type 2 diabetes, showing a protective role in fatty liver disease and hepatocellular carcinoma progression. Hepatic expression of FGF21 is regulated by PPARα and is induced by fasting. Ablation of FoxO1 in liver has been shown to increase FGF21 expression in hyperglycemia. To better understand the role of FOXO1 in the regulation of FGF21 expression we have modified HepG2 human hepatoma cells to overexpress FoxO1 and PPARα. Here we show that FoxO1 represses PPARα-mediated FGF21 induction, and that the repression acts on the FGF21 gene promoter without affecting other PPARα target genes. Additionally, we demonstrate that FoxO1 physically interacts with PPARα and that FoxO1/3/4 depletion in skeletal muscle contributes to increased Fgf21 tissue levels. Taken together, these data indicate that FOXO1 is a PPARα-interacting protein that antagonizes PPARα activity on the FGF21 promoter. Because other PPARα target genes remained unaffected, these results suggest a highly specific mechanism implicated in FGF21 regulation. We conclude that FGF21 can be specifically modulated by FOXO1 in a PPARα-dependent manner.

Zonated leucine sensing by Sestrin-mTORC1 in the liver controls the response to dietary leucine.

The mechanistic target of rapamycin complex 1 (mTORC1) kinase controls growth in response to nutrients, including the amino acid leucine. In cultured cells, mTORC1 senses leucine through the leucine-binding Sestrin proteins, but the physiological functions and distribution of Sestrin-mediated leucine sensing in mammals are unknown. We find that mice lacking Sestrin1 and Sestrin2 cannot inhibit mTORC1 upon dietary leucine deprivation and suffer a rapid loss of white adipose tissue (WAT) and muscle. The WAT loss is driven by aberrant mTORC1 activity and fibroblast growth factor 21 (FGF21) production in the liver. Sestrin expression in the liver lobule is zonated, accounting for zone-specific regulation of mTORC1 activity and FGF21 induction by leucine. These results establish the mammalian Sestrins as physiological leucine sensors and reveal a spatial organization to nutrient sensing by the mTORC1 pathway.

Hepatic CPT1A Facilitates Liver-Adipose Cross-Talk via Induction of FGF21 in Mice.

Hepatosteatosis, defined as excessive intrahepatic lipid accumulation, represents the first step of NAFLD. When combined with additional cellular stress, this benign status progresses to local and systemic pathological conditions such as NASH and insulin resistance. However, the molecular events directly caused by hepatic lipid build-up, in terms of its impact on liver biology and peripheral organs, remain unclear. Carnitine palmitoyltransferase 1A (CPT1A) is the rate limiting enzyme for long chain fatty acid beta-oxidation in the liver. Here we utilise hepatocyte-specific Cpt1a knockout (LKO) mice to investigate the physiological consequences of abolishing hepatic long chain fatty acid metabolism. Compared to the wild-type (WT) littermates, high fat diet (HFD)-fed LKO mice displayed more severe hepatosteatosis but were otherwise protected against diet-induced weight gain, insulin resistance, hepatic ER stress, inflammation and damage. Interestingly, increased energy expenditure was observed in LKO mice, accompanied by enhanced adipose tissue browning. RNAseq analysis revealed that the peroxisome proliferator activator alpha (PPARα)- fibroblast growth factor 21 (FGF21) axis was activated in liver of LKO mice. Importantly, antibody-mediated neutralization of FGF21 abolished the healthier metabolic phenotype and adipose browning in LKO mice, indicating that the elevation of FGF21 contributes to the improved liver pathology and adipose browning in HFD-treated LKO mice. Liver with deficient CPT1A expression adopts a healthy steatotic status that protects against HFD-evoked liver damage and potentiates adipose browning in an FGF21-dependent manner. Inhibition of hepatic CPT1A may serve as a viable strategy for the treatment of obesity and NAFLD.

Transmembrane G protein-coupled receptor 5 signaling stimulates fibroblast growth factor 21 expression concomitant with up-regulation of the transcription factor nuclear receptor Nr4a1

Fibroblast growth factor 21 (FGF21) acts as an endocrine factor, playing important roles in the regulation of energy homeostasis, glucose and lipid metabolism. It is induced by diverse metabolic and cellular stresses, such as starvation and cold challenge, which in turn facilitate adaptation to the stress environment. The pharmacological action of FGF21 has received much attention, because the administration of FGF21 or its analogs has been shown to have an anti-obesity effect in rodent models. In the present study, we found that 3-O-acetyloleanolic acid, an active constituent isolated from the fruits of Forsythia suspensa, stimulated FGF21 production concomitant with the up-regulation of a transcription factor, nuclear receptor Nr4a1, in C2C12 myotubes. Additionally, significant increases in mFgf21 promoter activity were observed in C2C12 cells overexpressing TGR5 receptor in response to 3-O-acetyloleanolic acid treatment. Treatment with the p38 MAPK inhibitor SB203580 was effective at suppressing these stimulatory effects of 3-O-acetyloleanolic acid. Pretreatment with SB203580 also significantly repressed FGF21 mRNA abundance and FGF21 secretion in C2C12 myotubes after 3-O-acetyloleanolic acid stimulation, suggesting that p38 activation is required for the induction of FGF21 by ligand-activated TGR5 in C2C12 myotubes. These findings collectively indicated that TGR5 receptor signaling drives FGF21 expression via p38 activation, at least partly, by mediating Nr4a1 expression. Thus, the novel biological function of 3-O-acetyloleanolic acid as an agent having anti-obesity effects is likely to be mediated through the activation of TGR5 receptors.

Th2 Cytokines Increase the Expression of Fibroblast Growth Factor 21 in the Liver.

Interleukin-4 (IL-4) and IL-13 are the major T helper 2 (Th2) cytokines, and they are involved in the regulation of metabolism in the adipose tissue. The liver contains diverse innate and adaptive immune cells, but it remains to be determined whether Th2 cytokines modulate energy metabolism in the liver. Here, using gene expression data from the Gene Expression Omnibus (GEO) and the BXD mouse reference population, we determined that the Th2 cytokines IL-4 and IL-13 increase the secretion of fibroblast growth factor 21 (FGF21) in the liver. In vitro experiments confirmed that FGF21 was highly expressed in response to IL-4 and IL-13, and this response was abolished by the Janus kinase (JAK)-signal transducer and activator of transcription 6 (STAT6) blockade. Moreover, FGF21 expression in response to Th2 cytokines was augmented by selective peroxisome proliferator-activated receptor α (PPARα) inhibition. In vivo administration of IL-4 increased FGF21 protein levels in the liver in a STAT6-dependent manner, but FGF21 secretion in response to IL-4 was not observed in the epididymal white adipose tissue (eWAT) despite the activation of STAT6. Intraperitoneal administration of IL-33, an activator of type 2 immune responses, significantly increased the level of FGF21 in the serum and liver after 24 h, but repeated administration of IL-33 attenuated this effect. Taken together, these data demonstrate that the IL-4/IL-13–STAT6 axis regulates metabolic homeostasis through the induction of FGF21 in the liver.

Ahnak deficiency attenuates high-fat diet-induced fatty liver in mice through FGF21 induction

The AHNAK nucleoprotein has been determined to exert an anti-obesity effect in adipose tissue and further inhibit adipogenic differentiation. In this study, we examined the role of AHNAK in regulating hepatic lipid metabolism to prevent diet-induced fatty liver. Ahnak KO mice have reportedly exhibited reduced fat accumulation in the liver and decreased serum triglyceride (TG) levels when provided with either a normal chow diet or a high-fat diet (HFD). Gene expression profiling was used to identify novel factors that could be modulated by genetic manipulation of the Ahnak gene. The results revealed that fibroblast growth factor 21 (FGF21) was markedly increased in the livers of Ahnak KO mice compared with WT mice fed a HFD. Ahnak knockdown in hepatocytes reportedly prevented excessive lipid accumulation induced by palmitate treatment and was associated with increased secretion of FGF21 and the expression of genes involved in fatty acid oxidation, which are primarily downstream of PPARα. These results indicate that pronounced obesity and hepatic steatosis are attenuated in HFD-fed Ahnak KO mice. This may be attributed, in part, to the induction of FGF21 and regulation of lipid metabolism, which are considered to be involved in increased fatty acid oxidation and reduced lipogenesis in the liver. These findings suggest that targeting AHNAK may have beneficial implications in preventing or treating hepatic steatosis.

Diagnostic value of serum biomarkers FGF21 and GDF15 compared to muscle sample in mitochondrial disease.

The aim of this study was to compare the value of serum biomarkers, fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15), with histological analysis of muscle in the diagnosis of mitochondrial disease. We collected 194 serum samples from patients with a suspected or known mitochondrial disease. Biomarkers were analyzed blinded using enzyme-labeled immunosorbent assay. Clinical data were collected using a structured questionnaire. Only 39% of patients with genetically verified mitochondrial disease had mitochondrial pathology in their muscle histology. In contrast, biomarkers were elevated in 62% of patients with genetically verified mitochondrial disease. Those with both biomarkers elevated had a muscle manifesting disorder and a defect affecting mitochondrial DNA expression. If at least one of the biomarkers was induced and the patient had a myopathic disease, a mitochondrial DNA expression disease was the cause with 94% probability. Among patients with biomarker analysis and muscle biopsy taken <12 months apart, a mitochondrial disorder would have been identified in 70% with analysis of FGF21 and GDF15 compared to 50% of patients whom could have been identified with muscle biopsy alone. Muscle findings were nondiagnostic in 72% (children) and 45% (adults). Induction of FGF21 and GDF15 suggest a mitochondrial etiology as an underlying cause of a muscle manifesting disease. Normal biomarker values do not, however, rule out a mitochondrial disorder, especially if the disease does not manifest in muscle. We suggest that FGF21 and GDF15 together should be first-line diagnostic investigations in mitochondrial disease complementing muscle biopsy.

MiR-22 inhibition reduces hepatic steatosis via FGF21 and FGFR1 induction.

Background & AimsMetabolism supports cell proliferation and growth. Surprisingly, the tumor suppressor miR-22 is induced by metabolic stimulators like bile acids. Thus, this study examines whether miR-22 could be a metabolic silencer.MethodsThe relationship between miR-22 and the expression of fibroblast growth factor 21 (FGF21) and its receptor FGFR1 was studied in cells and fatty livers obtained from patients and mouse models. We evaluated the effect of an miR-22 inhibitor alone and in combination with obeticholic acid (OCA) for the treatment of steatosis.ResultsThe levels of miR-22 were inversely correlated with those of FGF21, FGFR1, and PGC1α in human and mouse fatty livers, suggesting that hepatic miR-22 acts as a metabolic silencer. Indeed, miR-22 reduced FGFR1 by direct targeting and decreased FGF21 by reducing the recruitment of PPARα and PGC1α to their binding motifs. In contrast, an miR-22 inhibitor increases hepatic FGF21 and FGFR1, leading to AMPK and ERK1/2 activation, which was effective in treating alcoholic steatosis in mouse models. The farnesoid x receptor-agonist OCA induced FGF21 and FGFR1, as well as their inhibitor miR-22. An miR-22 inhibitor and OCA were effective in treating diet-induced steatosis, both alone and in combination. The combined treatment was the most effective at improving insulin sensitivity, releasing glucagon-like peptide 1, and reducing hepatic triglyceride in obese mice.ConclusionThe simultaneous induction of miR-22, FGF21 and FGFR1 by metabolic stimulators may maintain FGF21 homeostasis and restrict ERK1/2 activation. Reducing miR-22 enhances hepatic FGF21 and activates AMPK, which could be a novel approach to treat steatosis and insulin resistance.Lay summaryThis study examines the metabolic role of a tumor suppressor, miR-22, that can be induced by metabolic stimulators such as bile acids. Our novel data revealed that the metabolic silencing effect of miR-22 occurs as a result of reductions in metabolic stimulators, which likely contribute to the development of fatty liver. Consistent with this finding, an miR-22 inhibitor effectively reversed both alcohol- and diet-induced fatty liver; miR-22 inhibition is a promising therapeutic option which could be used in combination with obeticholic acid.

301-LB: Effects of Amino Acid Restriction on Development of Type 2 Diabetes in NZO Mice by FGF21 Secretion

Dietary protein restriction (PR) is emerging as an alternative approach to treat obesity and glucose intolerance since it increases plasma fibroblast growth factor 21 (FGF-21) levels. Also, dietary methionine restriction (MR) is known to mimic the metabolic effects of PR by increasing FGF-21 and inducing beneficial effects. Therefore, we tested in New Zealand Obese (NZO) mice, a model of polygenic obesity and type 2 diabetes, whether a moderate PR or a MR protects against diabetes. Moreover, we investigated whether a decreased methionine intake caused by vegetarian and vegan diets modulates plasma FGF-21 in humans. NZO mice were placed on high-fat diets that provided protein at control (18 gm%), low levels (4 gm%), or on high-fat diets (protein, 18 gm%) that provided methionine at control (0.86 gm%) or low levels (0.17 gm%) for up to 9 weeks. Changes in glucose homeostasis and energy expenditure were assessed. Among humans, plasma FGF-21 levels were investigated by comparing vegetarians and vegans to omnivores, and the effect of short-term vegetarian diet on FGF-21 induction was evaluated. PR prevented the onset of hyperglycemia only when protein was substituted by fat. When protein was substituted by carbohydrates, mice developed hyperglycemia two weeks later than the control, despite elevated plasma FGF-21 levels and increased energy expenditure. MR elevated plasma FGF-21 levels and prevented the onset of hyperglycemia. Human plasma FGF-21 levels were higher in vegans and vegetarians compared to omnivores. Interestingly, already a short-term switch to a vegetarian diet increased plasma FGF-21 in omnivores. Thus, restriction of dietary protein and methionine elevates plasma FGF-21 levels, which protect from hyperglycemia, an effect compromised by high dietary carbohydrates in NZO mice. Patients at high risk of developing type 2 diabetes may benefit from dietary changes in favor of methionine restriction, via increased circulating levels of FGF-21, without protein and calorie restriction. Disclosure T. Castaño-Martinez: None. W. Jonas: None. D. Weber: None. C. Weikert: None. T. Laeger: None. Funding Deutsche Forschungsgemeinschaft

Sterol 12α-Hydroxylase Aggravates Dyslipidemia by Activating the Ceramide/mTORC1/SREBP-1C Pathway via FGF21 and FGF15.

Sterol 12α-hydroxylase (CYP8B1) is required for the synthesis of cholic acid in the classic bile acid synthesis pathway and plays a role in dyslipidemia and insulin resistance. However, the mechanism of the involvement of Cyp8b1 in dyslipidemia and insulin resistance is not known. CYP8B1 mRNA and protein expression are elevated in diabetic and obese (db/db) mouse liver. In this study adenovirus-mediated transduction of CYP8B1 was used to study the effect of Cyp8b1 on lipid metabolism in mice. Results show that Ad-Cyp8b1 increased 12α-hydroxylated bile acids and induced sterol regulatory element-binding protein 1c (Srebp-1c)-mediated lipogenic gene expression. Interestingly, Ad-Cyp8b1 increased ceramide synthesis and activated hepatic mechanistic target of rapamycin complex 1 (mTORC1)-p70S6K signaling cascade and inhibited AKT/insulin signaling in mice. Ad-Cyp8b1 increased free fatty acid uptake into mouse primary hepatocytes. Ceramides stimulated S6K phosphorylation in both mouse and human primary hepatocytes. In high-fat diet-fed mice, Ad-Cyp8b1 reduced fibroblast growth factor 21 (FGF21), activated intestinal farnesoid X receptor (FXR) target gene expression, increased serum ceramides, VLDL secretion, and LDL cholesterol. In high-fat diet-induced obese (DIO) mice, Cyp8b1 ablation by adenovirus-mediated shRNA improved oral glucose tolerance, increased FGF21, and reduced liver triglycerides, inflammatory cytokine expression, nuclear localization of Srebp-1c and phosphorylation of S6K. In conclusion, this study unveiled a novel mechanism linking CYP8B1 to ceramide synthesis and mTORC1 signaling in dyslipidemia and insulin resistance, via intestinal FXR-mediated induction of FGF15 and liver FGF21. Reducing cholic acid synthesis may be a potential therapeutic strategy to treat dyslipidemia and nonalcoholic fatty liver disease.

Methionine restriction prevents onset of type 2 diabetes in NZO mice

Dietary methionine restriction (MR) is well known to reduce body weight by increasing energy expenditure (EE) and insulin sensitivity. An elevated concentration of circulating fibroblast growth factor 21 (FGF21) has been implicated as a potential underlying mechanism. The aims of our study were to test whether dietary MR in the context of a high-fat regimen protects against type 2 diabetes in mice and to investigate whether vegan and vegetarian diets, which have naturally low methionine levels, modulate circulating FGF21 in humans. New Zealand obese (NZO) mice, a model for polygenic obesity and type 2 diabetes, were placed on isocaloric high-fat diets (protein, 16 kcal%; carbohydrate, 52 kcal%; fat, 32 kcal%) that provided methionine at control (Con; 0.86% methionine) or low levels (0.17%) for 9 wk. Markers of glucose homeostasis and insulin sensitivity were analyzed. Among humans, low methionine intake and circulating FGF21 levels were investigated by comparing a vegan and a vegetarian diet to an omnivore diet and evaluating the effect of a short-term vegetarian diet on FGF21 induction. In comparison with the Con group, MR led to elevated plasma FGF21 levels and prevented the onset of hyperglycemia in NZO mice. MR-fed mice exhibited increased insulin sensitivity, higher plasma adiponectin levels, increased EE, and up-regulated expression of thermogenic genes in subcutaneous white adipose tissue. Food intake and fat mass did not change. Plasma FGF21 levels were markedly higher in vegan humans compared with omnivores, and circulating FGF21 levels increased significantly in omnivores after 4 d on a vegetarian diet. These data suggest that MR induces FGF21 and protects NZO mice from high-fat diet–induced glucose intolerance and type 2 diabetes. The normoglycemic phenotype in vegans and vegetarians may be caused by induced FGF21. MR akin to vegan and vegetarian diets in humans may offer metabolic benefits via increased circulating levels of FGF21 and merits further investigation.—Castaño-Martinez, T., Schumacher, F., Schumacher, S., Kochlik, B., Weber, D., Grune, T., Biemann, R., McCann, A., Abraham, K., Weikert, C., Kleuser, B., Schürmann, A., Laeger, T. Methionine restriction prevents onset of type 2 diabetes in NZO mice.

Liver Derived FGF21 Maintains Core Body Temperature During Acute Cold Exposure

Fibroblast Growth Factor 21 (FGF21) elicits an array of metabolic effects. However, the physiological role of FGF21 during thermal challenges is not clear. In this study, we assessed the tissue source of FGF21 and its site of action to regulate core body temperature in response to cold. Using mice lacking FGF21 specifically in the liver (FGF21 LivKO) or adipose tissues (FGF21 AdipoKO), we performed a series of cold exposure studies to examine the tissue specific induction of FGF21 in response to cold. We also examined the physiological site of FGF21 action during cold exposure by impairing FGF21 signaling to adipose tissues or the central nervous system (CNS) using genetic ablation of the FGF21 co-receptor β-klotho in adipose tissues (KLB AdipoKO) or pharmacological blockage of FGF21 signaling. We found that only liver-derived FGF21 enters circulation during acute cold exposure and is critical for thermoregulation. While FGF21 signaling directly to adipose tissues during cold is dispensable for thermoregulation, central FGF21 signaling is necessary for maximal sympathetic drive to brown adipose tissue to maintain thermoregulation during cold. These data demonstrate a previously unrecognized role for FGF21 in the maintenance of body temperature in response to cold.

Glucagon-Like Peptide 1 Increases β-Cell Regeneration by Promoting α- to β-Cell Transdifferentiation.

Glucagon-like peptide 1 (GLP-1) can increase pancreatic β-cells, and α-cells could be a source for new β-cell generation. We investigated whether GLP-1 increases β-cells through α-cell transdifferentiation. New β-cells originating from non-β-cells were significantly increased in recombinant adenovirus expressing GLP-1 (rAd-GLP-1)-treated RIP-CreER;R26-YFP mice. Proliferating α-cells were increased in islets of rAd-GLP-1-treated mice and αTC1 clone 9 (αTC1-9) cells treated with exendin-4, a GLP-1 receptor agonist. Insulin+glucagon+ cells were significantly increased by rAd-GLP-1 or exendin-4 treatment in vivo and in vitro. Lineage tracing to label the glucagon-producing α-cells showed a higher proportion of regenerated β-cells from α-cells in rAd-GLP-1-treated Glucagon-rtTA;Tet-O-Cre;R26-YFP mice than rAd producing β-galactosidase-treated mice. In addition, exendin-4 increased the expression and secretion of fibroblast growth factor 21 (FGF21) in αTC1-9 cells and β-cell-ablated islets. FGF21 treatment of β-cell-ablated islets increased the expression of pancreatic and duodenal homeobox-1 and neurogenin-3 and significantly increased insulin+glucagon+ cells. Generation of insulin+glucagon+ cells by exendin-4 was significantly reduced in islets transfected with FGF21 small interfering RNA or islets of FGF21 knockout mice. Generation of insulin+ cells by rAd-GLP-1 treatment was significantly reduced in FGF21 knockout mice compared with wild-type mice. We suggest that GLP-1 has an important role in α-cell transdifferentiation to generate new β-cells, which might be mediated, in part, by FGF21 induction.

Corrigendum to "ATF4- and CHOP-Dependent Induction of FGF21 through Endoplasmic Reticulum Stress".

[This corrects the article DOI: 10.1155/2014/807874.].

Deficiency of fibroblast growth factor 21 (FGF21) promotes hepatocellular carcinoma (HCC) in mice on a long term obesogenic diet

ObjectiveNon-alcoholic fatty liver (NAFL) associated with obesity is a major cause of liver diseases which can progress to non-alcoholic steatohepatitis, cirrhosis, and hepatocellular carcinoma (HCC). Fibroblast growth factor 21 (FGF21) plays an important role in liver metabolism and is also a potential marker for NAFL. Here we aimed to test the effect of FGF21 deficiency on liver pathology in mice consuming a conventional high fat, high sucrose (HFHS) obesogenic diet for up to 52 weeks. MethodsC57BL6 WT and FGF21 KO mice were fed a conventional obesogenic diet and were evaluated at 16 and 52 weeks. Evaluation included metabolic assessment, liver pathology, and transcriptomic analysis. ResultsWith consumption of HFHS diet, FGF21 deficient mice (FGF21 KO) develop excess fatty liver within 16 weeks. Hepatic pathology progresses and at 52 weeks FGF21 KO mice show significantly worse fibrosis and 78% of mice develop HCC; in contrast only 6% of WT mice develop HCC. Well differentiated hepatocellular carcinomas in FGF21 KO mice were characterized by expanded hepatic plates, loss of reticulin network, cytologic atypia, and positive immunostaining for glutamine synthetase. Microarray analysis reveals enrichment of several fibroblast growth factor signaling pathways in the tumors. ConclusionsIn addition to attenuating inflammation and fibrosis in mice under a number of dietary challenges, we show here that FGF21 is required to limit the progression from NAFL to HCC in response to prolonged exposure to an obesogenic diet. The induction of hepatic FGF21 in response to the high fat, high sucrose obesogenic diet may play an important role in limiting progression of liver pathology from NAFL to HCC.