Endogenous Fibroblast Growth Factor 21 Research Articles

Fibroblast growth factor 21 attenuates pulmonary ischemia/reperfusion injury via inhibiting endoplasmic reticulum stress-induced ferroptosis though FGFR1/PPARδ signaling pathway

BackgroundAcute lung injury is a critical life-threatening complication of pulmonary and cardiac surgery with a high rate of morbidity and mortality. Fibroblast growth factor 21 (FGF21) has been reported to play an important role in protecting vital organs from damage. This study aims to investigate the potential protective role and mechanism of FGF21 in pulmonary ischemia/reperfusion (I/R)-induced acute lung injury. MethodsA pulmonary epithelial cell line was treated with hypoxia/regeneration (H/R) in vitro and a mouse model of acute lung injury was induced with pulmonary I/R in vivo. Lung injury after pulmonary I/R was compared between FGF21-konckout (KO) mice and wild-type (WT) mice. Recombinant FGF21 was administrated in vivo and in vitro to determine its therapeutic effect. ResultsCirculating levels of FGF21 in mice with pulmonary I/R injury were significantly higher than in those without pulmonary I/R injury. Lung injury was aggravated in FGF21-KO mice compared with WT mice and the administration of FGF21 alleviated lung injury in mouse treated with I/R and pulmonary epithelial cell injury treated with H/R. FGF21 treatment decreased endoplasmic reticulum (ER) stress, Fe2+ and lipid reactive oxygen species (ROS) contents and GPX4 expression and increased PTGS2 levels. Mechanistically, FGF21 upregulated the expression of FGFR1 and PPARδ, ameliorated ER stress and ER stress induced-ferroptosis. Furthermore, FGF21 increased the expression level of PPARδ in pulmonary epithelial cell exposed to H/R, which was inhibited by FGFR1 inhibitor (PD173074). The protective effects of FGF21 were abolished by co-treatment with PPARδ inhibitor (GSK0660), indicating FGF21 attenuated ER stress-induced ferroptosis by dependent on FGFR1/PPARδ signaling pathway. ConclusionOur study reveals that FGF21 protects against pulmonary I/R injury via inhibiting ER stress-induced ferroptosis though FGFR1/PPARδ signaling pathway. Boosting endogenous FGF21 or the administration of recombinant FGF21 could be promising therapeutic strategies for pulmonary IRI.

Aortic Injury Induced by Benzo(a)pyrene and Atherogenic Diet Increased Hepatic FGF21 Expression in C57BL/6J Mice.

Benzo(a)pyrene (BaP), an environmental toxicant and endocrine disruptor, has been shown to exacerbate atherosclerosis when combined with a high-fat diet. Fibroblast Growth Factor-21 (FGF21), a novel hormone with anti-atherosclerotic properties, is associated with the presence of atherosclerosis and reduces plaque formation in experimental animals. The present study aimed to investigate the chronic effect of BaP injection on hepatic FGF21 expression, as an anti-atherosclerotic hormone, in mice fed with or without an atherogenic diet (AtD). Eighteen C57BL/6J male mice (6 weeks) were randomly divided into six groups based on the dosage and diet. Blood samples were collected, and serum cholesterol, triglyceride, HDL-C, LDL-C, and glucose levels were measured. FGF21 expression was assessed by quantitative real-time PCR. Atherosclerotic lesions in mice were studied with Oil Red O (ORO) staining. Benzo(a)pyrene causes a significant increase in liver FGF21 expression in a dose-dependent manner, and BaP co-exposure with AtD leads to a further increase in FGF21 expression. Additionally, the addition of BaP to AtD significantly increased the serum glucose, cholesterol, and LDL-C levels and accelerated the formation of atherosclerotic lesions. Besides, our findings showed that there is a significant positive correlation between FGF21 expression and glucose, cholesterol, LDL-C, and ORO-positive areas. Our findings revealed that BaP increases the expression of endogenous FGF21 in treated animals as a compensatory response to protect the heart from atherosclerosis induced by BaP and AtD.

Fructose-induced FGF21 secretion does not activate brown adipose tissue in Japanese young men: randomized cross-over and randomized controlled trials

BackgroundHuman brown adipose tissue (BAT) activity is associated with lower body fatness and favorable glucose metabolism. Previous studies reported that oral fructose loading induces postprandial fibroblast growth factor 21 (FGF21) secretion. FGF21 is a known inducer of adipose tissue thermogenesis; however, the effects of diet-induced FGF21 secretion on BAT thermogenesis remain to be elucidated.MethodsThe effects of both single load and daily consumption of fructose on BAT activity were examined using a randomized cross-over trial and a 2-week randomized controlled trial (RCT), respectively. In the cross-over trial, 15 young men consumed a single dose of fructose solution or water and then consumed the other on a subsequent day. The RCT enrolled 22 young men, and the participants were allocated to a group that consumed fructose and a group that consumed water daily for 2 weeks. BAT activity was analyzed using thermography with cold exposure. Plasma FGF21 level was determined by enzyme-linked immunosorbent assay.ResultsIn the cross-over single-load trial, plasma FGF21 levels were significantly increased at 2 h after oral fructose load (p < 0.01); however, there was no significant difference in BAT activity between the fructose load and drinking water. The 2-week RCT revealed that both plasma FGF21 levels and BAT activity were not significantly increased by daily fructose consumption compared to water. Correlation analyses revealed that BAT activity at the baseline and the final measurements were strongly and positively associated with the RCT (r = 0.869, p < 0.001). Changes in BAT activity were significantly and negatively correlated with changes in plasma glucose levels during the 2-week intervention (r = − 0.497, p = 0.022).ConclusionsOral fructose load induces a temporary increase in circulating FGF21 levels; however, this does not activate BAT thermogenesis in healthy young men. Further studies are needed to elucidate the effect of endogenous FGF21 on physiological function.Trial registrationThis study is registered with the University Hospital Medical Information Network in Japan (number 000051761, registered 1 August 2023, retrospectively registered, https://center6.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000052680).

FGF21 and autophagy coordinately counteract kidney disease progression during aging and obesity

ABSTRACT Chronic kidney disease (CKD) has reached epidemic proportions worldwide, partly due to the increasing population of elderly and obesity. Macroautophagy/autophagy counteracts CKD progression, whereas autophagy is stagnated owing to lysosomal overburden during aging and obesity, which promotes CKD progression. Therefore, for preventing CKD progression during aging and obesity, it is important to elucidate the compensation mechanisms of autophagy stagnation. We recently showed that FGF21 (fibroblast growth factor 21), which is a prolongevity and metabolic hormone, is induced by autophagy deficiency in kidney proximal tubular epithelial cells (PTECs); however, its pathophysiological role remains uncertain. Here, we investigated the interplay between FGF21 and autophagy and the direct contribution of endogenous FGF21 in the kidney during aging and obesity using PTEC-specific fgf21- and/or atg5-deficient mice at 24 months (aged) or under high-fat diet (obese) conditions. PTEC-specific FGF21 deficiency in young mice increased autophagic flux due to increased demand of autophagy, whereas fgf21-deficient aged or obese mice exacerbated autophagy stagnation due to severer lysosomal overburden caused by aberrant autophagy. FGF21 was robustly induced by autophagy deficiency, and aged or obese PTEC-specific fgf21- and atg5-double deficient mice deteriorated renal histology compared with atg5-deficient mice. Mitochondrial function was severely disturbed concomitant with exacerbated oxidative stress and downregulated TFAM (transcription factor A, mitochondrial) in double-deficient mice. These results indicate that FGF21 is robustly induced by autophagy disturbance and protects against CKD progression during aging and obesity by alleviating autophagy stagnation and maintaining mitochondrial homeostasis, which will pave the way to a novel treatment for CKD.

Double knockout of FFAR4 and FGF21 aggravates metabolic disorders in mice

Several investigations have examined the involvement of free fatty acid receptor 4 (FFAR4) in metabolic disorders, but its action remains controversial. To investigate whether endogenous fibroblast growth factor 21 (FGF21)-mediated signaling controls the metabolic status in FFAR4-deficient mice, we generated FFAR4/FGF21 double knockout (DKO) mice. We also evaluated the role of FGF21 on glucose and lipid metabolism in FFAR4 KO mice fed a high-fat diet. Levels of FGF21 were significantly increased in FFAR4-deficient mice and double deletion of FGF21 and FFAR4 led to severe metabolic disorders. Additionally, FFAR4/FGF21 DKO mice displayed metabolic abnormalities that may be caused by decreased energy expenditure. Collectively, this study characterized the effects of endogenous FGF21, which acts as a master feedback regulator in the absence of FFAR4.

1651-P: Elevated FGF21 Levels after Total Pancreatectomy and in Response to Single-Dose Glucagon Receptor Antagonism in Humans

Fibroblast growth factor 21 (FGF21) is a liver-secreted peptide hormone reportedly improving metabolic homeostasis, partly via reduced hunger for sugar, fat, protein and alcohol. Exogenous glucagon has been shown to increase circulating FGF21 levels, but the role of endogenous glucagon for the control of FGF21 secretion remains unknown. To elucidate the relationship between endogenous glucagon and FGF21 in humans, we investigated the effect of chronic pancreatic glucagon depletion and acute glucagon receptor antagonism, respectively, on FGF21 levels. Nine totally pancreatectomized subjects (7 men, 2 women, age 61.3 ± 10.3 years, BMI 22.6 ± 4.8 kg/m2) and 9 matched control subjects (6 men, 3 women, age 65.9 ± 8.8 years, BMI 23.9 ± 2.7 kg/m2) underwent two randomized, double-blinded test days 24 hours after single-dose oral administration of either the glucagon receptor antagonist LY2409021 (300 mg) or placebo. FGF21 levels were measured both in the fasting state and in response to an oral glucose tolerance test (OGTT). The pancreatectomized patients exhibited significantly increased mean fasting FGF21 levels compared to the control subjects (493 ± 429 vs 108 ± 58 pg/mL, P=0.02). In the control subjects, administration of LY2409021 significantly increased mean fasting levels of FGF21 (216 ± 117 vs 108 ± 58 pg/mL, P=0.004) whereas fasting FGF21 levels in the pancreatectomized patients were unaffected by LY2409021. In both groups, FGF21 levels increased in response to the OGTT, with no significant treatment effect of LY2409021. Our results suggest that both chronic glucagon depletion and acute antagonism of the glucagon receptor mediate an increase in FGF21 levels in humans, pointing to direct or indirect effects of glucagon as important regulators of FGF21 secretion. Disclosure M.F.G.Grøndahl: Speaker's Bureau; Novo Nordisk A/S. T.Vilsbøll: Consultant; AstraZeneca, Boehringer Ingelheim Inc., Gilead Sciences, Inc., Eli Lilly and Company, Mundipharma, Merck &amp; Co., Inc., Novo Nordisk A/S, Sanofi, Sun Pharmaceutical Industries Ltd., Bristol-Myers Squibb Company. F.K.Knop: Advisory Panel; AstraZeneca, Boehringer Ingelheim International GmbH, Eli Lilly and Company, Novo Nordisk, Sanofi, Consultant; AstraZeneca, Boehringer Ingelheim International GmbH, Eli Lilly and Company, Novo Nordisk, Sanofi, Research Support; Novo Nordisk, Zealand Pharma A/S, Speaker's Bureau; AstraZeneca, Boehringer Ingelheim International GmbH, Eli Lilly and Company, Novo Nordisk, Sanofi, Lundbeck. C.T.Juel: None. A.Lund: Speaker's Bureau; Novo Nordisk. S.Haedersdal: Consultant; Novo Nordisk. M.M.Andersen: None. J.S.Svenningsen: None. M.Gillum: None. B.Hartmann: Stock/Shareholder; Bainan Biotech. J.J.Holst: Advisory Panel; Novo Nordisk A/S, Eli Lilly and Company, Board Member; Bainan Biotech, Antag Therapeutics, Consultant; Alphasights, Eli Lilly and Company, ShouTi Pharma Inc., Zealand Pharma A/S, Other Relationship; Novo Nordisk, Novo Nordisk Pharma, Mayo Clinic, Boehringer-Ingelheim, Scohia Pharma Inc., Research Support; ARLA, European Union, Novo Nordisk Foundation. Funding Aase and Ejnar Danielsen's Foundation; Novo Nordisk Foundation (LY2409021); Eli Lilly and Company

CCE and EODF as two distinct non-shivering thermogenesis models inducing weight loss.

Increasing energy expenditure and reducing energy intake are considered two classical methods to induce weight loss. Weight loss through physical methods instead of drugs has been a popular research topic nowadays, but how these methods function in adipose and cause weight loss in body remains unclear. In this study, we set up chronic cold exposure (CCE) and every-other-day fasting (EODF) as two distinct models in long-term treatment to induce weight loss, recording their own characteristics in changes of body temperature and metabolism. We investigated the different types of non-shivering thermogenesis induced by CCE and EODF in white and brown adipose tissue through sympathetic nervous system (SNS), creatine-driven pathway, and fibroblast growth factor 21 (FGF21)-adiponectin axis. CCE and EODF could reduce body weight, lipid composition, increase insulin sensitivity, promote the browning of white fat, and increase the expression of endogenous FGF21 in adipose tissue. CCE stimulated the SNS and increased the thermogenic function of brown fat, and EODF increased the activity of protein kinase in white fat. In this study, we further explained the thermogenic mechanism function in adipose and metabolic benefits of the stable phenotype through physical treatments used for weight loss, providing more details for the literature on weight loss models. The influence on metabolism, non-shivering thermogenesis, endogenous FGF21, and ADPN changes in the long-term treatment of distinct methods (increasing energy expenditure and decreasing energy intake) to induce weight loss.

Endogenous FGF21 attenuates blood-brain barrier disruption in penumbra after delayed recanalization in MCAO rats through FGFR1/PI3K/Akt pathway.

Restoration of blood circulation within "time window" is the principal treating goal for treating acute ischemic stroke. Previous studies revealed that delayed recanalization might cause serious ischemia/reperfusion injury. However, plenty of evidences showed delayed recanalization improved neurological outcomes in acute ischemic stroke. This study aims to explore the role of delayed recanalization on blood-brain barrier (BBB) in the penumbra (surrounding ischemic core) and neurological outcomes after middle cerebral artery occlusion (MCAO). Recanalization was performed on the 3rd day after MCAO. BBB disruption was tested by Western blotting, Evans blue dye, and immunofluorescence staining. Infarct volume and neurological outcomes were evaluated on the 7th day after MCAO. The expression of fibroblast growth factor 21 (FGF21), fibroblast growth factor receptor 1 (FGFR1), phosphatidylinositol-3-kinase (PI3K), and serine/threonine kinase (Akt) in the penumbra were observed by immunofluorescence staining and/or Western blotting. The extraversion of Evans blue, IgG, and albumin increased surrounding ischemic core after MCAO, but significantly decreased after recanalization. The expression of Claudin-5, Occludin, and zona occludens 1 (ZO-1) decreased surrounding ischemic core after MCAO, but significantly increased after recanalization. Infarct volume reduced and neurological outcomes improved following recanalization (on the 7th day after MCAO). The expressions of Claudin-5, Occludin, and ZO-1 decreased surrounding ischemic core following MCAO, which were up-regulated corresponding to the increases of FGF21, p-FGFR1, PI3K, and p-Akt after recanalization. Intra-cerebroventricular injection of FGFR1 inhibitor SU5402 down-regulated the expression of PI3K, p-Akt, Occludin, Claudin-5, and ZO-1 in the penumbra, which weakened the beneficial effects of recanalization on neurological outcomes after MCAO. Delayed recanalization on the 3rd day after MCAO increases endogenous FGF21 in the penumbra and activates FGFR1/PI3K/Akt pathway, which attenuates BBB disruption in the penumbra and improves neurobehavior in MCAO rats.

Fibroblast growth factor 21 attenuates ventilator-induced lung injury by inhibiting the NLRP3/caspase-1/GSDMD pyroptotic pathway

BackgroundVentilator-induced lung injury (VILI) is caused by overdistension of the alveoli by the repetitive recruitment and derecruitment of alveolar units. This study aims to investigate the potential role and mechanism of fibroblast growth factor 21 (FGF21), a metabolic regulator secreted by the liver, in VILI development.MethodsSerum FGF21 concentrations were determined in patients undergoing mechanical ventilation during general anesthesia and in a mouse VILI model. Lung injury was compared between FGF21-knockout (KO) mice and wild-type (WT) mice. Recombinant FGF21 was administrated in vivo and in vitro to determine its therapeutic effect.ResultsSerum FGF21 levels in patients and mice with VILI were significantly higher than in those without VILI. Additionally, the increment of serum FGF21 in anesthesia patients was positively correlated with the duration of ventilation. VILI was aggravated in FGF21-KO mice compared with WT mice. Conversely, the administration of FGF21 alleviated VILI in both mouse and cell models. FGF21 reduced Caspase-1 activity, suppressed the mRNA levels of Nlrp3, Asc, Il-1β, Il-18, Hmgb1 and Nf-κb, and decreased the protein levels of NLRP3, ASC, IL-1β, IL-18, HMGB1 and the cleaved form of GSDMD.ConclusionsOur findings reveal that endogenous FGF21 signaling is triggered in response to VILI, which protects against VILI by inhibiting the NLRP3/Caspase-1/GSDMD pyroptosis pathway. These results suggest that boosting endogenous FGF21 or the administration of recombinant FGF21 could be promising therapeutic strategies for the treatment of VILI during anesthesia or critical care.

FGF21 modulates hippocampal cold-shock proteins and CA2-subregion proteins in neonatal mice with hypoxia-ischemia.

Fibroblast growth factor 21 (FGF21) is a neuroprotectant with cognitive enhancing effects but with poorly characterized mechanism(s) of action, particularly in females. Prior studies suggest that FGF21 may regulate cold-shock proteins (CSPs) and CA2-marker proteins in the hippocampus but empirical evidence is lacking. We assessed in normothermic postnatal day (PND) 10 female mice, if hypoxic-ischemic (HI) brain injury (25 min 8% O2/92% N2) altered endogenous levels of FGF21 in serum or in the hippocampus, or its receptor β-klotho. We also tested if systemic administration of FGF21 (1.5 mg/kg) modulated hippocampal CSPs or CA2 proteins. Finally, we measured if FGF21 therapy altered markers of acute hippocampal injury. HI increased endogenous serum FGF21 (24 h), hippocampal tissue FGF21 (4d), and decreased hippocampal β-klotho levels (4d). Exogenous FGF21 therapy modulated hippocampal CSP levels, and dynamically altered hippocampal CA2 marker expression (24 h and 4d). Finally, FGF21 ameliorated neuronal damage markers at 24 h but did not affect GFAP (astrogliosis) or Iba1 (microgliosis) levels at 4d. FGF21 therapy modulates CSP and CA2 protein levels in the injured hippocampus. These proteins serve different biological functions, but our findings suggest that FGF21 administration modulates them in a homeostatic manner after HI. Hypoxic-ischemic (HI) injury in female post-natal day (PND) 10 mice decreases hippocampal RNA binding motif 3 (RBM3) levels in the normothermic newborn brain. HI injury in normothermic newborn female mice alters serum and hippocampal fibroblast growth factor 21 (FGF21) levels 24 h post-injury. HI injury in normothermic newborn female mice alters hippocampal levels of N-terminal EF-hand calcium binding protein 2 (NECAB2) in a time-dependent manner. Exogenous FGF21 therapy ameliorates the HI-mediated loss of hippocampal cold-induced RNA-binding protein (CIRBP). Exogenous FGF21 therapy modulates hippocampal levels of CA2-marker proteins after HI.

The potential function and clinical application of FGF21 in metabolic diseases.

As an endocrine hormone, fibroblast growth factor 21 (FGF21) plays a crucial role in regulating lipid, glucose, and energy metabolism. Endogenous FGF21 is generated by multiple cell types but acts on restricted effector tissues, including the brain, adipose tissue, liver, heart, and skeletal muscle. Intervention with FGF21 in rodents or non-human primates has shown significant pharmacological effects on a range of metabolic dysfunctions, including weight loss and improvement of hyperglycemia, hyperlipidemia, insulin resistance, cardiovascular disease, and non-alcoholic fatty liver disease (NAFLD). Due to the poor pharmacokinetic and biophysical characteristics of native FGF21, long-acting FGF21 analogs and FGF21 receptor agonists have been developed for the treatment of metabolic dysfunction. Clinical trials of several FGF21-based drugs have been performed and shown good safety, tolerance, and efficacy. Here we review the actions of FGF21 and summarize the associated clinical trials in obesity, type 2 diabetes mellitus (T2DM), and NAFLD, to help understand and promote the development of efficient treatment for metabolic diseases via targeting FGF21.

Obesity-resistance of UCP1-deficient mice associates with sustained FGF21 sensitivity in inguinal adipose tissue.

Metabolic diseases represent the major health burden of our modern society. With the need of novel therapeutic approaches, fibroblast growth factor 21 (FGF21) is a promising target, based on metabolic improvements upon FGF21 administration in mice and humans. Endogenous FGF21 serum levels, however, are increased during obesity-related diseases, suggesting the development of FGF21 resistance during obesity and thereby lowering FGF21 efficacy. In uncoupling protein 1 knockout (UCP1 KO) mice, however, elevated endogenous FGF21 levels mediate resistance against diet-induced obesity. Here, we show that after long-term high fat diet feeding (HFD), circulating FGF21 levels become similarly high in obese wildtype and obesity-resistant UCP1 KO mice, suggesting improved FGF21 sensitivity in UCP1 KO mice. To test this hypothesis, we injected FGF21 after long-term HFD and assessed the metabolic and molecular effects. The UCP1 KO mice lost weight directly upon FGF21 administration, whereas body weights of WT mice resisted weight loss in the initial phase of the treatment. The FGF21 treatment induced expression of liver Pck1, a typical FGF21-responsive gene, in both genotypes. In iWAT, FGF21-responsive genes were selectively induced in UCP1 KO mice, strongly associating FGF21-sensitivity in iWAT with healthy body weights. Thus, these data support the concept that FGF21-sensitivity in adipose tissue is key for metabolic improvements during obesogenic diets.

Central FGF21 production regulates memory but not peripheral metabolism.

SUMMARYFibroblast growth factor 21 (FGF21) is a liver-derived endocrine hormone that functions to regulate energy homeostasis and macronutrient intake. Recently, FGF21 was reported to be produced and secreted from hypothalamic tanycytes, to regulate peripheral lipid metabolism; however, rigorous investigation of FGF21 expression in the brain has yet to be accomplished. Using a mouse model that drives CRE recombinase in FGF21-expressing cells, we demonstrate that FGF21 is not expressed in the hypothalamus, but instead is produced from the retrosplenial cortex (RSC), an essential brain region for spatial learning and memory. Furthermore, we find that central FGF21 produced in the RSC enhances spatial memory but does not regulate energy homeostasis or sugar intake. Finally, our data demonstrate that administration of FGF21 prolongs the duration of long-term potentiation in the hippocampus and enhances activation of hippocampal neurons. Thus, endogenous and pharmacological FGF21 appear to function in the hippocampus to enhance spatial memory.

Methionine Restriction Affects Metabolic Parameters in a Fibroblast Growth Factor 21- and Sex-Dependent Manner

ObjectivesIn rodents, dietary restriction of the amino acid methionine produces profound protection against obesity and obesity-related comorbidities. Fibroblast growth factor 21 (FGF21) is now recognized as an important mediator of methionine restriction's (MR) metabolic benefits. Most preclinical work investigating the impact of diet on weight gain and metabolism has been conducted in males, leaving a gap in our understanding of female responses to dietary changes. This study aimed to examine the impact of high-fat diet (HFD) feeding and MR on body weight and adiposity in male and female mice. Furthermore, we sought to determine the sex-dependent role of endogenous FGF21 in mediating metabolic responses to HFD and MR.MethodsMale and female wild-type (WT) and Fgf21 knockout (Fgf21−/−) mice were fed low-fat diet (LFD) or HFD versions of control (0.86% methionine) or MR (0.17% methionine) diets for 5 weeks. Average body weight (BW) and food intake were recorded weekly. Insulin tolerance tests were performed at week 4. After 5 weeks, mice were euthanized, and adipose depots were collected.ResultsNeither HFD nor MR significantly altered BW of female mice regardless of genotype. However, while HFD did not significantly affect BW, MR significantly reduced BW of both WT and Fgf21−/− males (p < 0.0001). Neither HFD nor MR significantly altered adiposity (gonadal adipose tissue weight/body weight) in female mice regardless of genotype. However, HFD significantly increased adiposity in male WT and Fgf21−/− mice, and MR prevented this increase in both genotypes. MR increased energy intake in LFD- and HFD-fed WT mice. The ability of MR to increase energy intake was abolished in LFD- and HFD-fed Fgf21−/− mice.ConclusionsThe effects of MR on BW and adiposity are sex-dependent, but FGF21-independent. Short-term HFD feeding affects adiposity differently in males and females. The effects of MR on energy intake are dependent upon FGF21. As the field progresses towards developing FGF21 as a therapeutic agent, it will be essential to understand its impact on both sexes.Funding SourcesSources Center for Neuroinflammation and Cardiometabolic Diseases Seed Grant.

Acute Deletion of the FOXO1-dependent Hepatokine FGF21 Does not Alter Basal Glucose Homeostasis or Lipolysis in Mice.

The hepatic transcription factor forkhead box O1 (FOXO1) is a critical regulator of hepatic and systemic insulin sensitivity. Previous work by our group and others demonstrated that genetic inhibition of FOXO1 improves insulin sensitivity both in genetic and dietary mouse models of metabolic disease. Mechanistically, this is due in part to cell nonautonomous control of adipose tissue insulin sensitivity. However, the mechanisms mediating this liver-adipose tissue crosstalk remain ill defined. One candidate hepatokine controlled by hepatic FOXO1 is fibroblast growth factor 21 (FGF21). Preclinical and clinical studies have explored the potential of pharmacological FGF21 as an antiobesity and antidiabetic therapy. In this manuscript, we performed acute loss-of-function experiments to determine the role of hepatocyte-derived FGF21 in glucose homeostasis and insulin tolerance both in control and mice lacking hepatic insulin signaling. Surprisingly, acute deletion of FGF21 did not alter glucose tolerance, insulin tolerance, or adipocyte lipolysis in either liver-specific FGF21KO mice or mice lacking hepatic AKT-FOXO1-FGF21, suggesting a permissive role for endogenous FGF21 in the regulation of systemic glucose homeostasis and insulin tolerance in mice. In addition, these data indicate that liver FOXO1 controls glucose homeostasis independently of liver-derived FGF21.

The Nuanced Metabolic Functions of Endogenous FGF21 Depend on the Nature of the Stimulus, Tissue Source, and Experimental Model.

Fibroblast growth factor 21 (FGF21) is a hormone that is involved in the regulation of lipid, glucose, and energy metabolism. Pharmacological FGF21 administration promotes weight loss and improves insulin sensitivity in rodents, non-human primates, and humans. However, pharmacologic effects of FGF21 likely differ from its physiological effects. Endogenous FGF21 is produced by many cell types, including hepatocytes, white and brown adipocytes, skeletal and cardiac myocytes, and pancreatic beta cells, and acts on a diverse array of effector tissues such as the brain, white and brown adipose tissue, heart, and skeletal muscle. Different receptor expression patterns dictate FGF21 function in these target tissues, with the primary effect to coordinate responses to nutritional stress. Moreover, different nutritional stimuli tend to promote FGF21 expression from different tissues; i.e., fasting induces hepatic-derived FGF21, while feeding promotes white adipocyte-derived FGF21. Target tissue effects of FGF21 also depend on its capacity to enter the systemic circulation, which varies widely from known FGF21 tissue sources in response to various stimuli. Due to its association with obesity and non-alcoholic fatty liver disease, the metabolic effects of endogenously produced FGF21 during the pathogenesis of these conditions are not well known. In this review, we will highlight what is known about endogenous tissue-specific FGF21 expression and organ cross-talk that dictate its diverse physiological functions, with particular attention given to FGF21 responses to nutritional stress. The importance of the particular experimental design, cellular and animal models, and nutritional status in deciphering the diverse metabolic functions of endogenous FGF21 cannot be overstated.

Roles of fibroblast growth factor 21 in the control of depression-like behaviours after social defeat stress in male rodents.

Fibroblast growth factor 21 (FGF21) modulates energy metabolism and neuroendocrine stress responses. FGF21 synthesis is increased after environmental or metabolic challenges. Detailed roles of FGF21 in the control of behavioural disturbances under stressful conditions remain to be clarified. Here, we examined the roles of FGF21 in the control of behavioural changes after social defeat stress in male rodents. Central administration of FGF21 increased the number of tyrosine hydroxylase‐positive catecholaminergic cells expressing c‐Fos protein, an activity marker of neurones, in the nucleus tractus solitarius and area postrema. Double in situ hybridisation showed that some catecholaminergic neurones in the dorsal medulla oblongata expressed β‐Klotho, an essential co‐receptor for FGF21, in male mice. Social defeat stress increased FGF21 concentrations in the plasma of male mice. FGF21‐deficient male mice showed social avoidance in a social avoidance test with C57BL/6J mice (background strain of FGF21‐deficient mice) and augmented immobility behaviour in a forced swimming test after social defeat stress. On the other hand, overexpression of FGF21 by adeno‐associated virus vectors did not significantly change behaviours either in wild‐type male mice or FGF21‐deficient male mice. The present data are consistent with the view that endogenous FGF21, possibly during the developmental period, has an inhibitory action on stress‐induced depression‐like behaviour in male rodents.

Generation of Affinity Purified Antibody Reagents for Specific Determination of Efruxifermin in Biological Matrices

Efruxifermin (EFX) is a novel Fc-fusion analog of human fibroblast growth factor 21 (FGF21), currently in clinical development as a potential treatment for non-alcoholic steatohepatitis (NASH). Each molecule of EFX consists of two modified FGF21 molecules, each attached at their N-termini to a human IgG1 Fc domain by a short polyglycine-serine linker. The FGF21 moiety of EFX incorporates three amino acid substitutions (L98R, P171G, and A180E relative to native FGF21). Two of these are proximal to the C-terminus (P171G and A180E), and reduce cleavage and inactivation by an endogenous protease, fibroblast activation protein (FAP), thereby prolonging its half-life. Fusion to human IgG1 Fc domain further extends circulating half-life, enabling once-weekly subcutaneous dosing. Accordingly, to support on-going clinical development of EFX, a specific assay is needed to distinguish intact EFX from both endogenous FGF21 and any in vivo biotransformation products of EFX that display reduced pharmacology. To maximize the antigenicity of EFX, FGF21 amino acid sequences were compared across species. Based on this, an antibody generation campaign was initiated in both rabbits and chickens. Comparison of titer responses against EFX and human FGF21 suggested that antisera from chickens was superior to rabbit antisera. Following a scaled-up, 12-week antibody campaign, antisera were purified by a combination of batch and column chromatographic procedures. By exploiting differences in structure and amino acid sequence of EFX relative to human FGF21, a purification strategy was designed to isolate chicken antibodies with increased specificity for EFX unique sequences. This reagent is being used as a capture antibody in the development of a noncompetitive ECLIA employing chemiluminescence detection. Presently, a number of different antibodies are being evaluated for potential pairing with the specific capture. We conclude that application of affinity purified chicken anti-EFX IgY will enable sensitive and specific determination of EFX in biological matrices with decreased cross-reactivity from endogenous hFGF21 and EFX metabolites.

The therapeutic potential of FGF21 in metabolic diseases: from bench to clinic.

Fibroblast growth factor 21 (FGF21) is a stress-inducible hormone that has important roles in regulating energy balance and glucose and lipid homeostasis through a heterodimeric receptor complex comprising FGF receptor 1 (FGFR1) and β-klotho. Administration of FGF21 to rodents or non-human primates causes considerable pharmacological benefits on a cluster of obesity-related metabolic complications, including a reduction in fat mass and alleviation of hyperglycaemia, insulin resistance, dyslipidaemia, cardiovascular disorders and non-alcoholic steatohepatitis (NASH). However, native FGF21 is unsuitable for clinical use owing to poor pharmacokinetic and biophysical properties. A large number of long-acting FGF21 analogues and agonistic monoclonal antibodies for the FGFR1-β-klotho receptor complexes have been developed. Several FGF21 analogues and mimetics have progressed to early phases of clinical trials in patients with obesity, type 2 diabetes mellitus and NASH. In these trials, the primary end points of glycaemic control have not been met, whereas substantial improvements were observed in dyslipidaemia, hepatic fat fractions and serum markers of liver fibrosis in patients with NASH. The complexity and divergence in pharmacology and pathophysiology of FGF21, interspecies variations in FGF21 biology, the possible existence of obesity-related FGF21 resistance and endogenous FGF21 inactivation enzymes represent major obstacles to clinical implementation of FGF21-based pharmacotherapies for metabolic diseases.

Adapting to the Cold: A Role for Endogenous Fibroblast Growth Factor 21 in Thermoregulation?

Fibroblast growth factor 21 (FGF21) is in biomedical focus as a treatment option for metabolic diseases, given that administration improves metabolism in mice and humans. The metabolic effects of exogenous FGF21 administration are well-characterized, but the physiological role of endogenous FGF21 has not been fully understood yet. Despite cold-induced FGF21 expression and increased circulating levels in some studies, which co-occur with brown fat thermogenesis, recent studies in cold-acclimated mice demonstrate the dispensability of FGF21 for maintenance of body temperature, thereby questioning FGF21's role for thermogenesis. Here we discuss the evidence either supporting or opposing the role of endogenous FGF21 for thermogenesis based on the current literature. FGF21, secreted by brown fat or liver, is likely not required for energy homeostasis in the cold, but the nutritional conditions could modulate the interaction between FGF21, energy metabolism, and thermoregulation.