Very low-density lipoprotein receptor increases in a liver-specific manner due to protein deficiency but does not affect fatty liver in mice.

Very low-density lipoprotein receptor (VLDLR) is a member of the LDL receptor family that is involved in the uptake of VLDL into cells. Increased hepatic VLDLR under endoplasmic reticulum (ER) stress has been shown to cause fatty liver. In this study, the effect of dietary protein restriction on hepatic VLDLR and the role of VLDLR in fatty liver were investigated using Vldlr knockout (KO) mice. Growing wild-type (WT) and KO mice were fed a control diet containing 20% ​​protein or a low protein diet containing 3% protein for 11 days. In WT mice, the amount of hepatic Vldlr mRNA and VLDLR protein increased by approximately 8- and 7-fold, respectively, due to protein restriction. Vldlr mRNA and protein levels increased in both type 1 and type 2 VLDLR. However, neither Vldlr mRNA nor protein levels were significantly increased in heart, muscle, and adipose tissue, demonstrating that VLDLR increase due to protein restriction occurred in a liver-specific manner. Increased liver triglyceride levels during protein restriction occurred in KO mice to the same extent as in WT mice, indicating that increased VLDLR during protein restriction was not the main cause of fatty liver, which was different from the case of ER stress.

The adverse metabolic effects of branched-chain amino acids are mediated by isoleucine and valine.

Low-protein diets promote metabolic health in rodents and humans, and the benefits of low-protein diets are recapitulated by specifically reducing dietary levels of the three branched-chain amino acids (BCAAs), leucine, isoleucine, and valine. Here, we demonstrate that each BCAA has distinct metabolic effects. A low isoleucine diet reprograms liver and adipose metabolism, increasing hepatic insulin sensitivity and ketogenesis and increasing energy expenditure, activating the FGF21-UCP1 axis. Reducing valine induces similar but more modest metabolic effects, whereas these effects are absent with low leucine. Reducing isoleucine or valine rapidly restores metabolic health to diet-induced obese mice. Finally, we demonstrate that variation in dietary isoleucine levels helps explain body mass index differences in humans. Our results reveal isoleucine as a key regulator of metabolic health and the adverse metabolic response to dietary BCAAs and suggest reducing dietary isoleucine as a new approach to treating and preventing obesity and diabetes.

The role of increased FGF21 in VLDL-TAG secretion and thermogenic gene expression in mice under protein malnutrition.

Protein malnutrition promotes hepatic lipid accumulation in growing animals. In these animals, fibroblast growth factor 21 (FGF21) rapidly increases in the liver and circulation and plays a protective role in hepatic lipid accumulation. To investigate the mechanism by which FGF21 protects against liver lipid accumulation under protein malnutrition, we determined whether upregulated FGF21 promotes the thermogenesis or secretion of very-low-density lipoprotein (VLDL)-triacylglycerol (TAG). The results showed that protein malnutrition decreased VLDL-TAG secretion, but the upregulation of FGF21 did not oppose this effect. In addition, protein malnutrition increased expression of the thermogenic gene uncoupling protein 1 in inguinal white adipose and brown adipose tissue in an FGF21-dependent manner. However, surgically removing inguinal white adipose tissue did not affect liver triglyceride levels in protein-malnourished mice. These data suggest that FGF21 stimulates thermogenesis under protein malnutrition, but this is not the causative factor underlying the protective role of FGF21 against liver lipid accumulation.

Pubertal FGF21 deficit is central in the metabolic pathophysiology of an ovine model of polycystic ovary syndrome.

Polycystic ovary syndrome (PCOS), affecting over 10% of women, is associated with insulin resistance, obesity, dyslipidaemia, fatty liver and adipose tissue dysfunction. Its pathogenesis is poorly understood and consequently treatment remains suboptimal. Prenatally androgenized (PA) sheep, a clinically realistic model of PCOS, recapitulate the metabolic problems associated with PCOS. Fibroblast Growth Factor 21 (FGF21) is a metabolic hormone regulating lipid homeostasis, insulin sensitivity, energy balance and adipose tissue function. We therefore investigated the role of FGF21 in the metabolic phenotype of PA sheep. In adolescence PA sheep had decreased hepatic expression and circulating concentrations of FGF21. Adolescent PA sheep show decreased FGF21 signalling in subcutaneous adipose tissue, increased hepatic triglyceride content, trend towards reduced fatty acid oxidation capacity and increased hepatic expression of inflammatory markers. These data parallel studies on FGF21 deficiency, suggesting that FGF21 therapy during adolescence may represent a treatment strategy to mitigate metabolic problems associated with PCOS.

Ionic Mechanisms of Impulse Propagation Failure in the FHF2-Deficient Heart.

RATIONALE: FHFs (fibroblast growth factor homologous factors) are key regulators of sodium channel (NaV) inactivation. Mutations in these critical proteins have been implicated in human diseases including Brugada syndrome, idiopathic ventricular arrhythmias, and epileptic encephalopathy. The underlying ionic mechanisms by which reduced Nav availability in Fhf2 knockout (Fhf2KO) mice predisposes to abnormal excitability at the tissue level are not well defined. OBJECTIVE: Using animal models and theoretical multicellular linear strands, we examined how FHF2 orchestrates the interdependency of sodium, calcium, and gap junctional conductances to safeguard cardiac conduction. METHODS AND RESULTS: Fhf2KO mice were challenged by reducing calcium conductance (gCaV) using verapamil or by reducing gap junctional conductance (Gj) using carbenoxolone or by backcrossing into a cardiomyocyte-specific Cx43 (connexin 43) heterozygous background. All conditions produced conduction block in Fhf2KO mice, with Fhf2 wild-type (Fhf2WT) mice showing normal impulse propagation. To explore the ionic mechanisms of block in Fhf2KO hearts, multicellular linear strand models incorporating FHF2-deficient Nav inactivation properties were constructed and faithfully recapitulated conduction abnormalities seen in mutant hearts. The mechanisms of conduction block in mutant strands with reduced gCaV or diminished Gj are very different. Enhanced Nav inactivation due to FHF2 deficiency shifts dependence onto calcium current (ICa) to sustain electrotonic driving force, axial current flow, and action potential (AP) generation from cell-to-cell. In the setting of diminished Gj, slower charging time from upstream cells conspires with accelerated Nav inactivation in mutant strands to prevent sufficient downstream cell charging for AP propagation. CONCLUSIONS: FHF2-dependent effects on Nav inactivation ensure adequate sodium current (INa) reserve to safeguard against numerous threats to reliable cardiac impulse propagation.

Fasting-induced FGF21 signaling activates hepatic autophagy and lipid degradation via JMJD3 histone demethylase.

Autophagy is essential for cellular survival and energy homeostasis under nutrient deprivation. Despite the emerging importance of nuclear events in autophagy regulation, epigenetic control of autophagy gene transcription remains unclear. Here, we report fasting-induced Fibroblast Growth Factor-21 (FGF21) signaling activates hepatic autophagy and lipid degradation via Jumonji-D3 (JMJD3/KDM6B) histone demethylase. Upon FGF21 signaling, JMJD3 epigenetically upregulates global autophagy-network genes, including Tfeb, Atg7, Atgl, and Fgf21, through demethylation of histone H3K27-me3, resulting in autophagy-mediated lipid degradation. Mechanistically, phosphorylation of JMJD3 at Thr-1044 by FGF21 signal-activated PKA increases its nuclear localization and interaction with the nuclear receptor PPARα to transcriptionally activate autophagy. Administration of FGF21 in obese mice improves defective autophagy and hepatosteatosis in a JMJD3-dependent manner. Remarkably, in non-alcoholic fatty liver disease patients, hepatic expression of JMJD3, ATG7, LC3, and ULK1 is substantially decreased. These findings demonstrate that FGF21-JMJD3 signaling epigenetically links nutrient deprivation with hepatic autophagy and lipid degradation in mammals.

Pancreatitis is an FGF21-deficient state that is corrected by replacement therapy.

The exocrine pancreas expresses the highest concentrations of fibroblast growth factor 21 (FGF21) in the body, where it maintains acinar cell proteostasis. Here, we showed in both mice and humans that acute and chronic pancreatitis is associated with a loss of FGF21 expression due to activation of the integrated stress response (ISR) pathway. Mechanistically, we found that activation of the ISR in cultured acinar cells and mouse pancreata induced the expression of ATF3, a transcriptional repressor that directly bound to specific sites on the Fgf21 promoter and resulted in loss of FGF21 expression. These ATF3 binding sites are conserved in the human FGF21 promoter. Consistent with the mouse studies, we also observed the reciprocal expression of ATF3 and FGF21 in the pancreata of human patients with pancreatitis. Using three different mouse models of pancreatitis, we showed that pharmacologic replacement of FGF21 mitigated the ISR and resolved pancreatitis. Likewise, inhibition of the ISR with an inhibitor of the PKR-like endoplasmic reticulum kinase (PERK) also restored FGF21 expression and alleviated pancreatitis. These findings highlight the importance of FGF21 in preserving exocrine pancreas function and suggest its therapeutic use for prevention and treatment of pancreatitis.

Physiology of FGF23 and overview of genetic diseases associated with renal phosphate wasting.

Phosphate is a cornerstone of several physiological pathways including skeletal development, bone mineralization, membrane composition, nucleotide structure, maintenance of plasma pH, and cellular signaling. The kidneys have a key role in phosphate homeostasis with three hormones having important functions in renal phosphate handling or intestinal absorption: parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), and 1-25-dihydroxyvitamin D (1,25(OH)2D). FGF23 is mainly synthesized by osteocytes; it is a direct phosphaturic factor that also inhibits 1,25(OH)2D and PTH. In addition to crucial effects on phosphate and calcium metabolism, FGF23 also has 'off-target' effects notably on the cardiovascular, immune and central nervous systems. Genetic diseases may affect the FGF23 pathway, resulting in either increased FGF23 levels leading to hypophosphatemia (such as in X-linked hypophosphatemia) or defective secretion/action of intact FGF23 inducing hyperphosphatemia (such as in familial tumoral calcinosis). The aim of this review is to provide an overview of FGF23 physiology and pathophysiology in X-linked hypophosphatemia, with a focus on FGF23-associated genetic diseases.

Fibroblast growth factor 21 is required for the therapeutic effects of Lactobacillus rhamnosus GG against fructose-induced fatty liver in mice.

OBJECTIVES: High fructose feeding changes fibroblast growth factor 21 (FGF21) regulation. Lactobacillus rhamnosus GG (LGG) supplementation reduces fructose-induced non-alcoholic fatty liver disease (NAFLD). The aim of this study was to determine the role of FGF21 and underlying mechanisms in the protective effects of LGG. METHODS: FGF21 knockout (KO) mice and C57BL/6 wild type (WT) mice were fed 30% fructose for 12 weeks. LGG was administered to the mice in the last 4 weeks during fructose feeding. FGF21-adiponectin (ADPN)-mediated hepatic lipogenesis and inflammation were investigated. RESULTS: FGF21 expression was robustly increased after 5-weeks of feeding and significantly decreased after 12-weeks of feeding in fructose-induced NAFLD mice. LGG administration reversed the depressed FGF21 expression, increased adipose production of ADPN, and reduced hepatic fat accumulation and inflammation in the WT mice but not in the KO mice. Hepatic nuclear carbohydrate responsive-element binding protein (ChREBP) was increased by fructose and reduced by LGG, resulting in a reduction in the expression of lipogenic genes. The methylated form of protein phosphatase 2A (PP2A) C, which dephosphorylates and activates ChREBP, was upregulated by fructose and normalized by LGG. Leucine carboxyl methyltransferase-1, which methylates PP2AC, was also increased by fructose and decreased by LGG. However, those beneficial effects of LGG were blunted in the KO mice. Hepatic dihydrosphingosine-1-phosphate, which inhibits PP2A, was markedly increased by LGG in the WT mice but attenuated in the KO mice. LGG decreased adipose hypertrophy and increased serum levels of ADPN, which regulates sphingosine metabolism. This beneficial effect was decreased in the KO mice. CONCLUSION: LGG administration increases hepatic FGF21 expression and serum ADPN concentration, resulting in a reduced ChREBP activation through dihydrosphingosine-1-phosphate-mediated PP2A deactivation, and subsequently reversed fructose-induced NAFLD. Thus, our data suggest that FGF21 is required for the beneficial effects of LGG in reversal of fructose-induced NAFLD.

Fibroblast growth factor 21 protects against lipotoxicity-induced pancreatic ß-cell dysfunction via regulation of AMPK signaling and lipid metabolism.

Fibroblast growth factor 21 (FGF21) is known as a potent metabolic regulator but its protective mechanisms against lipotoxicity-induced ß-cell dysfunction and apoptosis remain elusive. Here, we aimed to examine the regulatory pathways whereby FGF21 mediates islet lipid metabolism in lipotoxicity-treated cells and animal models. Rat ß-cell line (INS-1E cells) and islets isolated from C57/BL6J mice were exposed to palmitic acid (PA) with/without FGF21, mimicking lipotoxic conditions. Resultant insulin secretion and intracellular signaling were analyzed with Western blotting and RNA-seq. C57/BL6J and global FGF21 knockout (KO) mice were fed with a high-fat diet (HFD) to induce lipotoxicity and given with a long-acting mimetic of FGF21. Insulin resistance and ß-cell function were then assessed using homeostasis model assessment of insulin resistance (HOMA-IR) and insulinogenic index. FGF21 ameliorated PA-induced lipid accumulation, reversed cell apoptosis, and enhanced glucose-stimulated insulin secretion (GSIS) as impaired by lipotoxicity in islet ß-cells. Mechanistically, FGF21 exerted its beneficial effects through activation of AMPK-ACC (acetyl-CoA carboxylase) pathway and peroxisome proliferation-activated receptors (PPARs) δ/γ signaling, thus increasing the levels of carnitine palmitoyltransferase-1A (CPT1A) and leading to increased fatty acid (FA) oxidation and reduced lipid deposition in ß-cells. Interestingly, FGF21 reduced PA-induced cell death via restoration of the expression of apoptosis inhibitor Birc3. In vivo studies further showed that FGF21 is critical for islet insulinogenic capacity and normal function in the context of HFD-treated animals. FGF21 down-regulates islet cell lipid accumulation, probably via activation of AMPK-ACC and PPARδ/γ signaling, and reduces cell death under lipotoxicity, indicating that FGF21 is protective against lipotoxicity-induced ß-cell dysfunction and apoptosis.

FGF19 sustains the high proliferative ability of keratinocytes in psoriasis through the regulation of Wnt/GSK-3ß/ß-catenin signalling via FGFR4.

Accumulating evidence has shown that fibroblast growth factor 19 (FGF19) plays an important role in regulating cell proliferation. Psoriasis is characterized by the hyperproliferation of keratinocytes in skin lesions. However, whether FGF19 regulates the proliferation of keratinocytes in psoriasis remains unknown. In this study, we aimed to explore the potential relevance of FGF19 in psoriasis. We found that FGF19 was highly expressed in psoriatic skin from psoriasis patients, as well as keratinocytes that were stimulated with a cocktail of cytokines (M5), which is an in vitro model of psoriasis. Functional experiments demonstrated that FGF19 overexpression promoted the growth and proliferation of keratinocytes, while FGF19 knockdown showed opposite effect. Moreover, we found that FGF19 increased the phosphorylation of glycogen synthase kinase (GSK)-3ß and promoted the expression of ß-catenin and the activation of T cell factor 4 (TCF4) transcriptional activity. Notably, blocking Wnt/ß-catenin signalling by silencing ß-catenin partially reversed FGF19-mediated promotional effects on keratinocyte proliferation. In addition, FGFR4 inhibition significantly blocked the promotional effect of FGF19 on keratinocyte proliferation and GSK-3ß/ß-catenin/TCF4 signalling. Taken together, our results demonstrated that FGF19 contributes to sustaining the high proliferative ability of keratinocytes through promoting Wnt/GSK-3ß/ß-catenin signalling via FGFR4, highlighting the importance of FGF19 in the pathogenesis of psoriasis. Our study suggests that FGF19 may serve as a novel and potential therapeutic target for psoriasis.

Phosphorylation of hepatic farnesoid X receptor by FGF19 signaling-activated Src maintains cholesterol levels and protects from atherosclerosis.

The bile acid (BA) nuclear receptor, farnesoid X receptor (FXR/NR1H4), maintains metabolic homeostasis by transcriptional control of numerous genes, including an intestinal hormone, fibroblast growth factor-19 (FGF19; FGF15 in mice). Besides activation by BAs, the gene-regulatory function of FXR is also modulated by hormone or nutrient signaling-induced post-translational modifications. Recently, phosphorylation at Tyr-67 by the FGF15/19 signaling-activated nonreceptor tyrosine kinase Src was shown to be important for FXR function in BA homeostasis. Here, we examined the role of this FXR phosphorylation in cholesterol regulation. In both hepatic FXR-knockout and FXR-knockdown mice, reconstitution of FXR expression up-regulated cholesterol transport genes for its biliary excretion, including scavenger receptor class B member 1 (Scarb1) and ABC subfamily G member 8 (Abcg5/8), decreased hepatic and plasma cholesterol levels, and increased biliary and fecal cholesterol levels. Of note, these sterol-lowering effects were blunted by substitution of Phe for Tyr-67 in FXR. Moreover, consistent with Src's role in phosphorylating FXR, Src knockdown impaired cholesterol regulation in mice. In hypercholesterolemic apolipoprotein E-deficient mice, expression of FXR, but not Y67F-FXR, ameliorated atherosclerosis, whereas Src down-regulation exacerbated it. Feeding or treatment with an FXR agonist induced Abcg5/8 and Scarb1 expression in WT, but not FGF15-knockout, mice. Furthermore, FGF19 treatment increased occupancy of FXR at Abcg5/8 and Scarb1, expression of these genes, and cholesterol efflux from hepatocytes. These FGF19-mediated effects were blunted by the Y67F-FXR substitution or Src down-regulation or inhibition. We conclude that phosphorylation of hepatic FXR by FGF15/19-induced Src maintains cholesterol homeostasis and protects against atherosclerosis.

Fibroblast growth factor 21 deficiency aggravates obesity-induced hypothalamic inflammation and impairs thermogenic response.

OBJECTIVE AND DESIGN: Hypothalamic inflammation is closely associated with metabolic dysregulation. Fibroblast growth factor 21 (FGF21) is known to be an important metabolic regulator with anti-inflammatory properties. In this study, we investigated the effects of FGF21 deficiency on obesity-induced hypothalamic inflammation and thermogenic responses. MATERIALS AND METHODS: FGF21-deficient mice and/or wild-type (WT) mice were fed a high-fat diet (HFD) for 12 weeks. RESULTS: FGF21-deficient mice fed an HFD showed increased levels of inflammatory cytokines compared with WT obese control, and this was accompanied by upregulation of gliosis markers in the hypothalamus. Expression of heat-shock protein 72, a marker of neuronal damage, was increased in the FGF21-deficient obese mice, and the expression of hypothalamic neuronal markers involved in anti-thermogenic or thermogenic responses was altered. Moreover, the protein level of uncoupling protein 1 and other thermogenic genes were markedly reduced in the brown adipose tissue of the FGF21-deficient obese mice. CONCLUSIONS: These findings suggest that FGF21 deficiency aggravates obesity-induced hypothalamic inflammation and neuronal injury, leading to alterations in hypothalamic neural circuits accompanied by a reduction of the thermogenic response.

FGF-23 Deficiency Impairs Hippocampal-Dependent Cognitive Function.

Fibroblast growth factor receptor (FGFR) and α-Klotho transduce FGF-23 signaling in renal tubules to maintain systemic phosphate/vitamin D homeostasis. Mice deficient for either the ligand, FGF-23, or the co-receptor, Klotho, are phenocopies with both showing rapid and premature development of multiple aging-like abnormalities. Such similarity in phenotype, suggests that FGF-23 and Klotho have co-dependent systemic functions. Recent reports revealed inverse central nervous system (CNS) effects of Klotho deficiency or Klotho overexpression on hippocampal synaptic, neurogenic, and cognitive functions. However, it is unknown whether FGF-23 deficiency effects function of the hippocampus. We report that, similar to Klotho-deficient mice, FGF-23-deficient mice develop dose-dependent, hippocampal-dependent cognitive impairment. However, FGF-23-deficient brains had no gross structural or developmental defects, no change in hippocampal synaptic plasticity, and only minor impairment to postnatal hippocampal neurogenesis. Together, these data provide evidence that FGF-23 deficiency impairs hippocampal-dependent cognition but otherwise results in a brain phenotype that is distinct from the KL-deficient mouse.

Activation of hepatic estrogen receptor-α increases energy expenditure by stimulating the production of fibroblast growth factor 21 in female mice.

OBJECTIVE: The endogenous estrogen 17ß-estradiol (E2) promotes metabolic homeostasis in premenopausal women. In a mouse model of post-menopausal metabolic syndrome, we reported that estrogens increased energy expenditure, thus preventing estrogen deficiency-induced adiposity. Estrogens' prevention of fat accumulation was associated with increased serum concentrations of fibroblast growth factor 21 (FGF21), suggesting that FGF21 participates in estrogens' promotion of energy expenditure. METHODS: We studied the effect of E2 on FGF21 production and the role of FGF21 in E2 stimulation of energy expenditure and prevention of adiposity, using female estrogen receptor (ER)- and FGF21-deficient mice fed a normal chow and a cohort of ovariectomized women from the French E3N prospective cohort study. RESULTS: E2 acting on the hepatocyte ERα increases hepatic expression and production of FGF21 in female mice. In vivo activation of ERα increases the transcription of Fgf21 via an estrogen response element outside the promoter of Fgf21. Treatment with E2 increases oxygen consumption and energy expenditure and prevents whole body fat accumulation in ovariectomized female WT mice. The effect of E2 on energy expenditure is not observed in FGF21-deficient mice. While E2 treatment still prevents fat accumulation in FGF21-deficient mice, this effect is decreased compared to WT mice. In an observational cohort of ovariectomized women, E2 treatment was associated with lower serum FGF21 concentrations, which may reflect a healthier metabolic profile. CONCLUSIONS: In female mice, E2 action on the hepatocyte ERα increases Fgf21 transcription and FGF21 production, thus promoting energy expenditure and partially decreasing fat accumulation.

Fibroblast growth factor-21 protects against fibrosis in hypertensive heart disease.

FGF21 is an endocrine factor that contributes to multiple pathophysiological processes, mainly via its action as a metabolic regulator and cardioprotective agent. Recent studies have shown increased circulating FGF21 levels in hypertensive patients and in mouse models of hypertension. However, the relevance of FGF21 in hypertensive heart disease has not been addressed. Hypertension was induced by treating 4-month old WT and Fgf21-/- mice with angiotensin II (AngII) for 1 week, resulting in a similar increase in blood pressure in both genotypes. Plasma FGF21 levels and expression in heart and liver were significantly increased in hypertensive WT mice relative to controls, an effect that was associated with increased expression levels of ß-klotho specifically in the heart. Fgf21-/- mice developed a greater degree of hypertensive heart disease than WT mice, notably characterized by extensive cardiac dysfunction and fibrosis. In vitro and in vivo studies further showed that FGF21 exerted a marked protective effect against cardiac fibrosis. Finally, left ventricle biopsies from human hypertensive heart donors, especially those developing cardiomyopathy, showed a significant increase in FGF21expression compared with normotensive controls, a finding that was associated with significantly enhanced cardiac hypertrophy and fibrosis. We conclude that during hypertension, both systemic and cardiac-produced FGF21 are induced and act on the heart, protecting it from hypertensive heart disease. Thus, FGF21 acts as key factor in the fibrogenesis associated with hypertensive heart disease. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

FGF21 Alleviates Hepatic Endoplasmic Reticulum Stress under Physiological Conditions.

Fibroblast growth factor 21 (FGF21), mainly synthesized and secreted from the liver, is an endocrine FGF that regulates glucose and fatty acid metabolism to maintain whole body energy homeostasis. Gene expression of FGF21 was previously reported to be induced by endoplasmic reticulum (ER) stress through activating transcription factor 4 (ATF4). It has been reported that drug-induced ER stress is reduced by overexpression of FGF21. However, the function of endogenous FGF21 under physiological conditions such as the postprandial state remains unknown. Here, we examined the effects of both endogenous and exogenous FGF21 on postprandial hepatic ER stress. In mice, postprandial and tunicamycin-induced ER stress was significantly reduced by overexpression of FGF21 using a recombinant adenovirus. FGF21-deficient mice exhibited a more considerable increase in drug-induced ER stress target gene expression than wild-type mice. Following refeeding after fasting, FGF21 deficiency caused severe ER stress in the liver. The postprandial ER stress response was significantly reduced when hepatic FGF21 gene expression was increased by feeding a diet containing the soy protein ß-conglycinin which activates ATF4. Together, these results demonstrate that FGF21 reduces the increased expression of a subset of genes in the liver in response to ER stress and may correct metabolic disorders caused by ER stress.

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

OBJECTIVE: Non-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. METHODS: C57BL6 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. RESULTS: With 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. CONCLUSIONS: In 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.

Autophagic control of cardiac steatosis through FGF21 in obesity-associated cardiomyopathy.

OBJECTIVE: High-fat diet-induced obesity leads to the development of hypertrophy and heart failure through poorly understood molecular mechanisms. We have recently shown that fibroblast growth factor-21 (FGF21) is produced by the heart and exerts protective effects that prevent cardiac hypertrophy development and oxidative stress. The aim of this study was to determine the effects of FGF21 on the cardiomyopathy associated with obesity development. RESULTS: Fgf21-/- mice showed an enhanced increase in the heart weight/tibia length (HW/TL) ratio in response to the high-fat diet. In keeping with this, echocardiographic measurements confirmed enhanced cardiac hypertrophy in Fgf21-/- mice. At the cellular level, the area of cardiomyocytes was increased in Fgf21-/- mice fed a high-fat diet. Furthermore, a high-fat diet induced fatty acid oxidation in the hearts of Fgf21-/- mice accompanied by an increase in cardiac oxidative stress. Oil-red O staining revealed the presence of higher amounts of lipid droplets in the hearts of Fgf21-/- mice fed a high-fat diet relative to wt mice fed this same diet. Finally, Fgf21-/- mice fed a high-fat diet showed impaired cardiac autophagy and signs of inactive cardiac lipophagy, suggesting that FGF21 promotes autophagy in cardiomyocytes. CONCLUSIONS: Our data indicate that a lack of FGF21 enhances the susceptibility of mice to the development of obesity-related cardiomyopathy. Furthermore, we demonstrate that this cardiac dysfunction is associated with deleterious lipid accumulation in the heart. An impaired ability of FGF21 to promote autophagy/lipophagy may contribute to lipid accumulation and cardiac derangements.

CMPF, a Metabolite Formed Upon Prescription Omega-3-Acid Ethyl Ester Supplementation, Prevents and Reverses Steatosis.

Prescription ω-3 fatty acid ethyl ester supplements are commonly used for the treatment of hypertriglyceridemia. However, the metabolic profile and effect of the metabolites formed by these treatments remain unknown. Here we utilized unbiased metabolomics to identify 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) as a significant metabolite of the ω-3-acid ethyl ester prescription Lovaza™ in humans. Administration of CMPF to mice before or after high-fat diet feeding at exposures equivalent to those observed in humans increased whole-body lipid metabolism, improved insulin sensitivity, increased beta-oxidation, reduced lipogenic gene expression, and ameliorated steatosis. Mechanistically, we find that CMPF acutely inhibits ACC activity, and induces long-term loss of SREBP1c and ACC1/2 expression. This corresponds to an induction of FGF21, which is required for long-term steatosis protection, as FGF21KO mice are refractory to the improved metabolic effects. Thus, CMPF treatment in mice parallels the effects of human Lovaza™ supplementation, revealing that CMPF may contribute to the improved metabolic effects observed with ω-3 fatty acid prescriptions.