Targeting the FGF19-FGFR4 pathway for cholestatic, metabolic, and cancerous diseases.

Human fibroblast growth factor 19 (FGF19, or FGF15 in rodents) plays a central role in controlling bile acid (BA) synthesis through a negative feedback mechanism. This process involves a postprandial crosstalk between the BA-activated ileal farnesoid X receptor and the hepatic Klotho beta (KLB) coreceptor complexed with fibrobalst growth factor receptor 4 (FGFR4) kinase. Additionally, FGF19 regulates glucose, lipid, and energy metabolism by coordinating responses from functional KLB and FGFR1-3 receptor complexes on the periphery. Pharmacologically, native FGF19 or its analogs decrease elevated BA levels, fat content, and collateral tissue damage. This makes them effective in treating both cholestatic diseases such as primary biliary or sclerosing cholangitis (PBC or PSC) and metabolic abnormalities such as nonalcoholic steatohepatitis (NASH). However, chronic administration of FGF19 drives oncogenesis in mice by activating the FGFR4-dependent mitogenic or hepatic regenerative pathway, which could be a concern in humans. Agents that block FGF19 or FGFR4 signaling have shown great potency in preventing FGF19-responsive hepatocellular carcinoma (HCC) development in animal models. Recent phase 1/2 clinical trials have demonstrated promising results for several FGF19-based agents in selectively treating patients with PBC, PSC, NASH, or HCC. This review aims to provide an update on the clinical development of both analogs and antagonists targeting the FGF19-FGFR4 signaling pathway for patients with cholestatic, metabolic, and cancer diseases. We will also analyze potential safety and mechanistic concerns that should guide future research and advanced trials.

FGF21 regulates PGC-1α and browning of white adipose tissues in adaptive thermogenesis.

Certain white adipose tissue (WAT) depots are readily able to convert to a "brown-like" state with prolonged cold exposure or exposure to ß-adrenergic compounds. This process is characterized by the appearance of pockets of uncoupling protein 1 (UCP1)-positive, multilocular adipocytes and serves to increase the thermogenic capacity of the organism. We show here that fibroblast growth factor 21 (FGF21) plays a physiologic role in this thermogenic recruitment of WATs. In fact, mice deficient in FGF21 display an impaired ability to adapt to chronic cold exposure, with diminished browning of WAT. Adipose-derived FGF21 acts in an autocrine/paracrine manner to increase expression of UCP1 and other thermogenic genes in fat tissues. FGF21 regulates this process, at least in part, by enhancing adipose tissue PGC-1α protein levels independently of mRNA expression. We conclude that FGF21 acts to activate and expand the thermogenic machinery in vivo to provide a robust defense against hypothermia.

Cholic Acid Supplementation of a High-Fat Obesogenic Diet Suppresses Hepatic Triacylglycerol Accumulation in Mice via a Fibroblast Growth Factor 21-Dependent Mechanism.

Background: Supplementation of a high-fat obesogenic diet (HFD) with cholic acid (CA) suppresses the development of obesity, insulin resistance, and hepatic steatosis in mice. Objective: We investigated the role of fibroblast growth factor 21 (FGF21) in mediating the beneficial actions of CA on metabolic syndrome. Methods: Male 7-wk-old wild-type (WT) mice and FGF21 knockout (FGF21KO) mice were fed an HFD for 12 wk followed by a 4-wk period in which the mice were fed the HFD alone or supplemented with 0.5% CA. Body composition, gross energy efficiency, glucose tolerance, homeostasis model assessment of insulin resistance (HOMA-IR), and hepatic triacylglycerol (TG) concentrations were measured. Results: CA administration improved glucose tolerance and decreased total body fat accretion, gross energy efficiency, fasting blood glucose concentrations, and HOMA-IR in both WT mice and FGF21KO mice. The extent of the effect of CA on glucose tolerance, fasting blood glucose concentrations, and HOMA-IR was similar in both mouse strains, whereas the extent of the effect of CA on total body fat accretion and gross energy efficiency was 4.2- to 4.4-fold greater in FGF21KO mice than in WT mice. Further analyses showed that CA decreased hepatic TG concentrations in WT mice (49%) but had no effect on hepatic TG concentrations in FGF21KO mice. CA decreased the activation state of hepatic acetyl-CoA carboxylase 1 (ACC1) and adipose tissue hormone-sensitive lipase (HSL) in WT mice but was not effective in decreasing the activation of ACC1 and HSL in FGF21KO mice. Conclusions: FGF21 signaling is required for the beneficial effect of CA on hepatic TG accumulation in mice fed an HFD. We propose that FGF21 signaling potentiates the ability of CA to decrease the activation of ACC1 and HSL, key enzymes controlling the supply of long-chain fatty acid precursors for hepatic TG synthesis.

The Nuclear Receptor Rev-erbα Regulates Adipose Tissue-specific FGF21 Signaling.

FGF21 is an atypical member of the FGF family that functions as a hormone to regulate carbohydrate and lipid metabolism. Here we demonstrate that the actions of FGF21 in mouse adipose tissue, but not in liver, are modulated by the nuclear receptor Rev-erbα, a potent transcriptional repressor. Interrogation of genes induced in the absence of Rev-erbα for Rev-erbα-binding sites identified ßKlotho, an essential coreceptor for FGF21, as a direct target gene of Rev-erbα in white adipose tissue but not liver. Rev-erbα ablation led to the robust elevated expression of ßKlotho. Consequently, the effects of FGF21 were markedly enhanced in the white adipose tissue of mice lacking Rev-erbα. A major Rev-erbα-controlled enhancer at the Klb locus was also bound by the adipocytic transcription factor peroxisome proliferator-activated receptor (PPAR) γ, which regulates its activity in the opposite direction. These findings establish Rev-erbα as a specific modulator of FGF21 signaling in adipose tissue.

Hepatic SIRT1 attenuates hepatic steatosis and controls energy balance in mice by inducing fibroblast growth factor 21.

BACKGROUND & AIMS: The hepatocyte-derived hormone fibroblast growth factor 21 (FGF21) is a hormone-like regulator of metabolism. The nicotinamide adenine dinucleotide-dependent deacetylase SIRT1 regulates fatty acid metabolism through multiple nutrient sensors. Hepatic overexpression of SIRT1 reduces steatosis and glucose intolerance in obese mice. We investigated mechanisms by which SIRT1 controls hepatic steatosis in mice. METHODS: Liver-specific SIRT1 knockout (SIRT1 LKO) mice and their wild-type littermates (controls) were divided into groups that were placed on a normal chow diet, fasted for 24 hours, or fasted for 24 hours and then fed for 6 hours. Liver tissues were collected and analyzed by histologic examination, gene expression profiling, and real-time polymerase chain reaction assays. Human HepG2 cells were incubated with pharmacologic activators of SIRT1 (resveratrol or SRT1720) and mitochondrion oxidation consumption rate and immunoblot analyses were performed. FGF21 was overexpressed in SIRT1 LKO mice using an adenoviral vector. Energy expenditure was assessed by indirect calorimetry. RESULTS: Prolonged fasting induced lipid deposition in livers of control mice, but severe hepatic steatosis in SIRT1 LKO mice. Gene expression analysis showed that fasting up-regulated FGF21 in livers of control mice but not in SIRT1 LKO mice. Decreased hepatic and circulating levels of FGF21 in fasted SIRT1 LKO mice were associated with reduced hepatic expression of genes involved in fatty acid oxidation and ketogenesis, and increased expression of genes that control lipogenesis, compared with fasted control mice. Resveratrol or SRT1720 each increased the transcriptional activity of the FGF21 promoter (-2070/+117) and levels of FGF21 messenger RNA and protein in HepG2 cells. Surprisingly, SIRT1 LKO mice developed late-onset obesity with impaired whole-body energy expenditure. Hepatic overexpression of FGF21 in SIRT1 LKO mice increased the expression of genes that regulate fatty acid oxidation, decreased fasting-induced steatosis, reduced obesity, increased energy expenditure, and promoted browning of white adipose tissue. CONCLUSIONS: SIRT1-mediated activation of FGF21 prevents liver steatosis caused by fasting. This hepatocyte-derived endocrine signaling appears to regulate expression of genes that control a brown fat-like program in white adipose tissue, energy expenditure, and adiposity. Strategies to activate SIRT1 or FGF21 could be used to treat fatty liver disease and obesity.

Fibroblast growth factor 21 limits lipotoxicity by promoting hepatic fatty acid activation in mice on methionine and choline-deficient diets.

BACKGROUND & AIMS: Nonalcoholic fatty liver disease is a common consequence of human and rodent obesity. Disruptions in lipid metabolism lead to accumulation of triglycerides and fatty acids, which can promote inflammation and fibrosis and lead to nonalcoholic steatohepatitis. Circulating levels of fibroblast growth factor (FGF)21 increase in patients with nonalcoholic fatty liver disease or nonalcoholic steatohepatitis; therefore, we assessed the role of FGF21 in the progression of murine fatty liver disease, independent of obesity, caused by methionine and choline deficiency. METHODS: C57BL/6 wild-type and FGF21-knockout (FGF21-KO) mice were placed on methionine- and choline-deficient (MCD), high-fat, or control diets for 8-16 weeks. Mice were weighed, and serum and liver tissues were collected and analyzed for histology, levels of malondialdehyde and liver enzymes, gene expression, and lipid content. RESULTS: The MCD diet increased hepatic levels of FGF21 messenger RNA more than 50-fold and serum levels 16-fold, compared with the control diet. FGF21-KO mice had more severe steatosis, fibrosis, inflammation, and peroxidative damage than wild-type C57BL/6 mice. FGF21-KO mice had reduced hepatic fatty acid activation and ß-oxidation, resulting in increased levels of free fatty acid. FGF21-KO mice given continuous subcutaneous infusions of FGF21 for 4 weeks while on an MCD diet had reduced steatosis and peroxidative damage, compared with mice not receiving FGF21. The expression of genes that regulate inflammation and fibrosis were reduced in FGF21-KO mice given FGF21, similar to those of wild-type mice. CONCLUSIONS: FGF21 regulates fatty acid activation and oxidation in livers of mice. In the absence of FGF21, accumulation of inactivated fatty acids results in lipotoxic damage and increased steatosis.

Increased expression of fibroblast growth factor 21 (FGF21) during chronic undernutrition causes growth hormone insensitivity in chondrocytes by inducing leptin receptor overlapping transcript (LEPROT) and leptin receptor overlapping transcript-like 1 (LEPROTL1) expression.

During calorie restriction in mice, increased expression of FGF21 causes growth attenuation and growth hormone (GH) insensitivity. Previous evidence also indicates that fasting-associated increased expression of leptin receptor overlapping transcript (LEPROT) and LEPROT-like 1 (LEPROTL1) (two proteins that regulate intracellular protein trafficking) reduces GH receptor cell-surface expression in the liver. Thus, we hypothesized that FGF21 causes GH insensitivity through regulation of LEPROT and/or LEPROTL1 expression. After 4 weeks of food restriction, LEPROT and LEPROTL1 mRNA expression in the liver and in the tibial growth plate of wild-type (WT) mice was increased compared with WT mice fed ad libitum. In Fgf21 knock-out (KO) mice, LEPROT and LEPROTL1 mRNA expression in food-restricted and fed ad libitum was similar, with the exception of a subgroup of food-restricted Fgf21 KO mice treated with recombinant human (rh) FGF21 that experienced increased LEPROT and LEPROTL1 mRNA expression compared with untreated food-restricted Fgf21 KO mice. In cultured growth plate chondrocytes, FGF21 stimulated LEPROT and LEPROTL1 mRNA expression, with such effect being prevented in chondrocytes transfected with FGFR1 siRNA or ERK1 siRNA. In cells transfected with control siRNA, GH increased [(3)H]thymidine incorporation, collagen X, and IGF-1 mRNA expression, with all effects being prevented by rhFGF21. In addition, rhFGF21 decreased (125)I-GH binding. In LEPROT siRNA- and/or LEPROTL1 siRNA-transfected cells, rhFGF21 did not prevent the GH stimulatory effects on thymidine incorporation, collagen X, and IGF-1 expression; furthermore, rhFGF21 did not prevent (125)I-GH binding. Consistent with the effects of rhFGF21, LEPROT overexpression in chondrocytes resulted in the inhibition of GH action. Our findings indicate that the increased expression of FGF21 during chronic undernutrition inhibits GH action on chondrocytes by activating LEPROT and LEPROTL1.

Silencing of the Fibroblast growth factor 21 gene is an underlying cause of acinar cell injury in mice lacking MIST1.

Fibroblast growth factor 21 (FGF21) is a key regulator of metabolism under conditions of stress such as starvation, obesity, and hypothermia. Rapid induction of FGF21 is also observed in experimental models of pancreatitis, and FGF21 reduces tissue damage observed in these models, suggesting a nonmetabolic function. Pancreatitis is a debilitating disease with significant morbidity that greatly increases the risk of pancreatic ductal adenocarcinoma. The goals of this study were to examine the regulation and function of FGF21 in acinar cell injury, specifically in a mouse model of pancreatic injury (Mist1(-/-)). Mist1(-/-) mice exhibit acinar cell disorganization, decreased acinar cell communication and exocytosis, and increased sensitivity to cerulein-induced pancreatitis (CIP). Examination of Fgf21 expression in Mist1(-/-) mice by qRT-PCR, Northern blot, and Western blot analyses showed a marked decrease in pancreatic Fgf21 expression before and after induction of CIP compared with C57Bl/6 mice. To determine whether the loss of FGF21 accounted for the Mist1(-/-) phenotypes, we generated Mist1(-/-) mice overexpressing human FGF21 from the ApoE promoter (Mist1(-/-)ApoE-FGF21). Reexpression of FGF21 partially mitigated pancreatic damage in Mist1(-/-) tissue based on reduced intrapancreatic enzyme activation, reduced expression of genes involved in fibrosis, and restored cell-cell junctions. Interestingly, alteration of Fgf21 expression in Mist1(-/-) tissue was not simply due to a loss of direct transcriptional regulation by MIST1. Chromatin immunopreciptation indicated that the loss of Fgf21 in the Mist1(-/-) pancreas is due, in part, to epigenetic silencing. Thus, our studies identify a new role for FGF21 in reducing acinar cell injury and uncover a novel mechanism for regulating Fgf21 gene expression.

Fibroblast growth factor (Fgf) 21 is a novel target gene of the aryl hydrocarbon receptor (AhR).

The toxic effects of dioxins, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), mainly through activation of the aryl hydrocarbon receptor (AhR) are well documented. Fibroblast growth factor (Fgf) 21 plays critical roles in metabolic adaptation to fasting by increasing lipid oxidation and ketogenesis in the liver. The present study was performed to determine whether activation of the AhR induces Fgf21 expression. In mouse liver, TCDD increased Fgf21 mRNA in both dose- and time-dependent manners. In addition, TCDD markedly increased Fgf21 mRNA expression in cultured mouse and human hepatocytes. Moreover, TCDD increased mRNA (in liver) and protein levels (in both liver and serum) of Fgf21 in wild-type mice, but not in AhR-null mice. Chromatin immunoprecipitation assays showed that TCDD increased AhR protein binding to the Fgf21 promoter (-105/+1 base pair). Fgf21-null mice administered 200µg/kg of TCDD died within 20days, whereas wild-type mice receiving the same treatment were still alive at one month after administration. This indicates that TCDD-induced Fgf21 expression protects against TCDD toxicity. Diethylhexylphthalate (DEHP) pretreatment attenuated TCDD-induced Fgf21 expression in mouse liver and white adipose tissue, which may explain a previous report that DEHP pretreatment decreases TCDD-induced wasting. In conclusion, Fgf21 appears to be a target gene of AhR-signaling pathway in mouse and human liver.

Photoperiodic regulation of FGF21 production in the Siberian hamster.

This article is part of a Special Issue "Energy Balance". FGF21 is an endocrine member of the fibroblast growth factor superfamily that has been shown to play an important role in the physiological response to nutrient deprivation. Food restriction enhances hepatic FGF21 production, which serves to engage an integrated response to energy deficit. Specifically, elevated FGF21 levels lead to reduced gluconeogenesis and increased hepatic ketogenesis. However, circulating FGF21 concentrations also paradoxically rise in states of metabolic dysfunction such as obesity. Furthermore, multiple peripheral tissues also produce FGF21 in addition to the liver, raising questions as to its endocrine and paracrine roles in the control of energy metabolism. The objectives of this study were to measure plasma FGF21 concentrations in the Siberian hamster, a rodent which undergoes a seasonal cycle of fattening and body weight gain in the long days (LD) of summer, followed by reduction of appetite and fat catabolism in the short days (SD) of winter. Groups of adult male hamsters were raised in long days, and then exposed to SD for up to 12 weeks. Chronic exposure of LD animals to SD led to a significant increase in circulating FGF21 concentrations. This elevation of circulating FGF21 was preceded by an increase in liver FGF21 protein production evident as early as 4 weeks of exposure to SD. FGF21 protein abundance was also increased significantly in interscapular brown adipose tissue, with a positive correlation between plasma levels of FGF21 and BAT protein abundance throughout the experimental period. Epididymal white adipose tissue and skeletal muscle (gastrocnemius) also produced FGF21, but levels did not change in response to a change in photoperiod. In summary, a natural programmed state of fat catabolism was associated with increased FGF21 production in the liver and BAT, consistent with the view that FGF21 has a role in adapting hamsters to the hypophagic winter state.

Fibroblast growth factor 21 (FGF21) inhibits chondrocyte function and growth hormone action directly at the growth plate.

Fibroblast growth factor 21 (FGF21) modulates glucose and lipid metabolism during fasting. In addition, previous evidence indicates that increased expression of FGF21 during chronic food restriction is associated with reduced bone growth and growth hormone (GH) insensitivity. In light of the inhibitory effects on growth plate chondrogenesis mediated by other FGFs, we hypothesized that FGF21 causes growth inhibition by acting directly at the long bones' growth plate. We first demonstrated the expression of FGF21, FGFR1 and FGFR3 (two receptors known to be activated by FGF21) and ß-klotho (a co-receptor required for the FGF21-mediated receptor binding and activation) in fetal and 3-week-old mouse growth plate chondrocytes. We then cultured mouse growth plate chondrocytes in the presence of graded concentrations of rhFGF21 (0.01-10 µg/ml). Higher concentrations of FGF21 (5 and 10 µg/ml) inhibited chondrocyte thymidine incorporation and collagen X mRNA expression. 10 ng/ml GH stimulated chondrocyte thymidine incorporation and collagen X mRNA expression, with both effects prevented by the addition in the culture medium of FGF21 in a concentration-dependent manner. In addition, FGF21 reduced GH binding in cultured chondrocytes. In cells transfected with FGFR1 siRNA or ERK 1 siRNA, the antagonistic effects of FGF21 on GH action were all prevented, supporting a specific effect of this growth factor in chondrocytes. Our findings suggest that increased expression of FGF21 during food restriction causes growth attenuation by antagonizing the GH stimulatory effects on chondrogenesis directly at the growth plate. In addition, high concentrations of FGF21 may directly suppress growth plate chondrocyte proliferation and differentiation.

Activity-balanced GLP-1/GDF15 dual agonist reduces body weight and metabolic disorder in mice and non-human primates.

Obesity is a considerable health concern with limited pharmacotherapy options of low efficacy. Here, we develop a GLP-1/GDF15 fusion protein and explore its weight-lowering potential in animals. The molecule, QL1005, is engineered via fusing GLP-1 and GDF15 analogs by a peptide linker and conjugating it to a fatty acid for time-action extension. In vitro, the potency of QL1005 is superior to the GLP-1 analog semaglutide. In obese mice, QL1005 induces reductions in body weight, food intake, insulin, fasting glucose, and triglycerides. Notably, these metabolic effects come as a result of activities emanating from both GLP-1 and GDF15, in an individual pathway-balanced fashion. In a cynomolgus monkey model of obesity, QL1005 reduces body weight, food intake, insulin, and glucose in a dose-dependent manner with limited incidence of GI side effects. Altogether, this long-acting, dual GLP-1/GDF15 molecule demonstrates the promise of poly-pharmaceutical approaches in metabolic drug discovery and development.

Hormone-like fibroblast growth factors and metabolic regulation.

The family of fibroblast growth factors (FGFs) consisting now of 22 members is generally considered to control a wide range of biological functions such as development, differentiation and survival. However, research during the past decade provided substantial evidence that a so called "hormone-like" subgroup of FGFs, comprised of FGF19, FGF21 and FGF23, is involved in the regulation of diverse metabolic pathways to control glucose, lipid, bile acid, phosphate and vitamin D metabolism. The unique properties of these FGFs include predominant production of the factors in selective tissues, their abundance in the blood due to the lack of extracellular heparin-mediated sequestration, and highly specific tissue-targeted action via engagement of their respective co-receptors. The important metabolic context of FGF19, FGF21, and FGF23 actions has revealed important novel roles for FGFs and provided significant means to explore an opportunity for therapeutic targeting of these factors and their corresponding pathways.

FGF21 as a therapeutic reagent.

The prevalence of obesity and diabetes has been dramatically increasing during the last decade suggesting a greater patient need for more efficacious and safer drugs. Large molecule therapy has played an important role in diabetes since the discovery of insulin. This legacy was continued upon the introduction of Humulin (first recombinant insulin), Humalog (first engineered insulin) and Byetta (first incretin mimetic). Several other protein therapeutics, such as leptin, adiponectin, bone morphogenic protein-9 and others, are currently in or considered for therapeutic development. Among them, FGF21 is one of the most promising candidates given its outstanding pharmacologic benefits for nearly each and every abnormality of a metabolic disease and lack of apparent side effects in a variety of animal models. Thus, FGF21 represents a novel and appealing therapeutic reagent for Type 2 diabetes mellitus, obesity, dyslipidemia, cardiovascular and fatty liver diseases. The in vitro biology, genetic animal models and in vivo pharmacology of FGF21 will be discussed in this chapter.

Direct effects of FGF21 on glucose uptake in human skeletal muscle: implications for type 2 diabetes and obesity.

BACKGROUND: Fibroblast growth factor (FGF) 21, a novel member of the FGF family, plays a role in a variety of endocrine functions, including regulation of glucose and lipid metabolism. The role of FGF21 in skeletal muscle is currently not known. METHODS: Serum levels and skeletal muscle mRNA of FGF21 were determined in normal glucose tolerant (n = 40) and type 2 diabetic (T2D; n = 40) subjects. We determined whether FGF21 has direct effects on glucose metabolism in cultured myotubes (n = 8) and extensor digitorum longus skeletal muscle. RESULTS: Serum FGF21 levels increased 20% in T2D versus normal glucose tolerant subjects (p < 0.05), whereas skeletal muscle mRNA expression was unaltered. Fasting insulin, homeostatic model assessment of insulin resistance (HOMA-IR), waist circumference, and body mass index (BMI) significantly correlated with serum FGF21 levels in T2D (p < 0.01), but not in normal glucose tolerant subjects. Serum FGF21 concentrations were greater in T2D patients in the highest tertile of fasting insulin (p < 0.05) and BMI (p < 0.05). Stepwise regression analysis identified BMI as the strongest independent variable correlating with FGF21. FGF21 exposure increased basal and insulin-stimulated glucose uptake in human myotubes, coincident with increased glucose transporter 1 mRNA, and enhanced glucose transporter 1 abundance at the plasma membrane. In isolated extensor digitorum longus muscle, FGF21 potentiated insulin-stimulated glucose transport, without altering phosphorylation of Akt or AMP-activated protein kinase. CONCLUSIONS: Plasma FGF21 is increased in T2D patients, and positively correlated with fasting insulin and BMI. However, FGF21 has direct effects in enhancing skeletal muscle glucose uptake, providing additional points of regulation that may contribute to the beneficial effects of FGF21 on glucose homeostasis. Whether increased plasma FGF21 in T2D is a compensatory mechanism to increase glucose metabolism remains to be determined.

FGF19 and FGF21: In NASH we trust.

OBJECTIVE: FGF19 and FGF21 have shown therapeutic promise since their discovery, attested by the fact there are at least 5 assets that activate the FGFR/KLB pathway and one FGF19 analog in clinical development. METHODS: We performed a detailed analyses of published preclinical and clinical data to offer insights into the mechanism of action, as well as PK/PD and efficacy data of the clinical assets. RESULTS: Scouring the literature, we offer mechanistic insights from preclinical data using rodents and non-human primates and pharmacodynamic data from clinical studies. CONCLUSION: The basic and applied science around endocrine FGFs has evolved exponentially over the years with FGF19 and FGF21 analogs are now entering Phase 3 clinical research.

Glucagon receptor signaling regulates weight loss via central KLB receptor complexes.

Glucagon regulates glucose and lipid metabolism and promotes weight loss. Thus, therapeutics stimulating glucagon receptor (GCGR) signaling are promising for obesity treatment; however, the underlying mechanism(s) have yet to be fully elucidated. We previously identified that hepatic GCGR signaling increases circulating fibroblast growth factor 21 (FGF21), a potent regulator of energy balance. We reported that mice deficient for liver Fgf21 are partially resistant to GCGR-mediated weight loss, implicating FGF21 as a regulator of glucagon's weight loss effects. FGF21 signaling requires an obligate coreceptor (ß-Klotho, KLB), with expression limited to adipose tissue, liver, pancreas, and brain. We hypothesized that the GCGR-FGF21 system mediates weight loss through a central mechanism. Mice deficient for neuronal Klb exhibited a partial reduction in body weight with chronic GCGR agonism (via IUB288) compared with controls, supporting a role for central FGF21 signaling in GCGR-mediated weight loss. Substantiating these results, mice with central KLB inhibition via a pharmacological KLB antagonist, 1153, also displayed partial weight loss. Central KLB, however, is dispensable for GCGR-mediated improvements in plasma cholesterol and liver triglycerides. Together, these data suggest GCGR agonism mediates part of its weight loss properties through central KLB and has implications for future treatments of obesity and metabolic syndrome.

Fibroblast growth factor 21 reduces the severity of cerulein-induced pancreatitis in mice.

BACKGROUND & AIMS: Fibroblast growth factor 21 (FGF21) acts as a hormonal regulator during fasting and is involved in lipid metabolism. Fgf21 gene expression is regulated by peroxisome proliferator-activated receptor (PPAR)-dependent pathways, which are enhanced during pancreatitis. Therefore, the aim of this study was to investigate FGF21's role in pancreatic injury. METHODS: Fgf21 expression was quantified during cerulein-induced pancreatitis (CIP) or following mechanical or thapsigargin-induced stress through Northern blot analysis, in situ hybridization, and quantitative reverse transcription polymerase chain reaction. FGF21 protein was quantified by Western blot analysis. Isolated acinar cells or AR42J acinar cells were treated with recombinant FGF21 protein, and extracellular regulated kinase 1/2 activation was examined. The severity of CIP was compared between wild-type mice and mice overexpressing FGF21 (FGF21Tg) or harboring a targeted deletion of Fgf21 (Fgf21(-/-)). RESULTS: Acinar cell Fgf21 expression markedly increased during CIP and following injury in vitro. Purified FGF21 activated the extracellular regulated kinase 1/2 pathway in pancreatic acinar cells. The severity of CIP is inversely correlated to FGF21 expression because FGF21Tg mice exhibited decreased serum amylase and decreased pancreatic stellate cell activation, whereas Fgf21(-/-) mice had increased serum amylase and tissue damage. The expression of Fgf21 was also inversely correlated to expression of Early growth response 1, a proinflammatory and profibrotic transcription factor. CONCLUSIONS: These studies suggest a novel function for Fgf21 as an immediate response gene protecting pancreatic acini from overt damage.

Optimization of Peptide Inhibitors of ß-Klotho as Antagonists of Fibroblast Growth Factors 19 and 21.

Fibroblast growth factors 19 and 21 (FGF19 and FGF21) have biological actions that render them promising clinical candidates for treatment of metabolic diseases, particularly dyslipidemia and nonalcoholic steatohepatitis (NASH). These two atypical endocrine FGFs employ an accessory receptor ß-klotho (KLB) to signal through classical FGF receptors (FGFRs). FGF19 and FGF21 bind to KLB via their C-terminus, to orient the N-terminus for productive interaction with FGFRs. The C-terminal peptides have been shown to competitively inhibit this biological agonism. We report here an assessment of the structural relationship in the C-terminal sequences of FGF19 and FGF21 that led to the identification of a sustained-acting peptide optimized for pharmacological use. It demonstrates high potency and selectivity to antagonize FGF19 and FGF21 in cells coexpressing FGFRs and KLB. This peptide was also effective in blocking FGF19 and FGF21 mediated downstream gene expression (i.e., Fos and Egr1) in vivo. In DIO mice, this antagonist alters metabolic function as assessed by changes in body weight, food intake, and plasma insulin. Thus, the selective inhibition of KLB could constitute a medicinal approach to treat diseases associated with excess FGF19 or 21 activity and separately serve as an effective tool to promote a deeper assessment of atypical FGF biology.