Fgf21 Gene Research Articles

Pyruvate kinase M2 represses thermogenic gene expression in brown adipocytes.

Utilizing the thermogenic capacity of brown adipose tissue is a potential anti-obesity strategy; therefore, the mechanisms controlling expression of thermogenesis-related genes are of interest. Pyruvate kinase (PK) catalyzes the last step of glycolysis and exists as four isoenzymes: PK, liver, PK, red blood cell, PK, muscle (PKM1 and PKM2). PKM2 has both glycolytic and nuclear functions. Here, we report that PKM2 is enriched in brown adipose compared with white adipose tissue. Specific knockdown of PKM2 in mature brown adipocytes demonstrates that silencing of PKM2 does not lead to a decrease in PK activity, but causes a robust upregulation of thermogenic uncoupling protein 1 (Ucp1) and fibroblast growth factor 21 (Fgf21) gene expression. This increase is not mediated by any of the known mechanisms for PKM2-regulated gene expression, thus implying the existence of a novel mechanism for PKM2-dependent effects on gene expression.

Sex Differences in Liver, Adipose Tissue, and Muscle Transcriptional Response to Fasting and Refeeding in Mice.

Fasting is often used for obesity correction but the “refeeding syndrome” limits its efficiency, and molecular mechanisms underlying metabolic response to different food availability are under investigation. Sex was shown to affect hormonal and metabolic reactions to fasting/refeeding. The aim of this study was to evaluate hormonal and transcriptional responses to fasting and refeeding in male and female C57Bl/6J mice. Sex asymmetry was observed both at the hormonal and transcriptional levels. Fasting (24 h) induced increase in hepatic Fgf21 gene expression, which was associated with elevation of plasma FGF21 and adiponectin levels, and the upregulation of expression of hepatic (Pparα, Cpt1α) and muscle (Cpt1β, Ucp3) genes involved in fatty acid oxidation. These changes were more pronounced in females. Refeeding (6 h) evoked hyperinsulinemia and increased hepatic expression of gene related to lipogenesis (Fasn) only in males and hyperleptinemia and increase in Fgf21 gene expression in muscles and adipose tissues only in females. The results suggest that in mice, one of the molecular mechanisms underlying sex asymmetry in hepatic Pparα, Cpt1α, muscle Cpt1β, and Ucp3 expression during fasting is hepatic Fgf21 expression, and the reason for sex asymmetry in hepatic Fasn expression during refeeding is male-specific hyperinsulinemia.

Abstract 567: Fgf21 as a Biomarker for Metabolic Stress in Heart Failure

FGF21, an important metabolic regulator, has recently been suggested as a biomarker for heart failure (HF). FGF21 is involved in the integrated mitochondrial stress response, and has been shown to be upregulated with mitochondrial DNA damage, which occurs more frequently in dilated cardiomyopathy. In this study, we investigated whether FGF21 can be used as a biomarker for metabolic stress in HF. We collected blood and cardiac tissue samples from ischemic and non-ischemic HF patients who have undergone VAD transplantation. We also collected blood and tissue from mice with HF due to 1) combination of transverse aortic constriction and coronary artery ligation (TAC+Lig) or 2) cardiac-specific knockout of the mitochondrial transcription factor A (Tfam). Serum FGF21 levels were measured using Enzyme-linked immunosorbent assay (ELISA). Messenger RNA was extracted from the tissue and FGF21 gene expression was measured using real-time quantitative PCR (qPCR). Immunohistochemical staining was performed on tissue sections (either paraffin embedded or frozen) to observe FGF21 levels. Serum FGF21 was elevated in human HF patients compared to healthy controls, as well as in both mouse models of HF. In human patients, cardiac FGF21 gene expression was upregulated 2.2-fold compared to donors. In the TAC+Lig mouse model we observed a 3.37-fold increase, while the Tfam knockout model which has severe mitochondrial damage exhibited a 218-fold increase in cardiac FGF21 gene expression. Further qPCR assays revealed changes in FGF21 gene expression in the liver and white fat of TFAM-KO, indicating metabolic stress on other organs resulting from HF. In conclusion, serum FGF21 is elevated in multiple models of HF, and appears to have both cardiac and extra cardiac sources. Future work will investigate 1) whether there is a correlation between FGF21 levels and mitochondrial damage, and 2) the signaling pathway resulting in metabolic stress to other organs in HF.

Association of the 3'UTR polymorphism (rs11665896) in the FGF21 gene with metabolic status and nutrient intake in children with obesity.

Background Fibroblast growth factor 21 (FGF21) is considered an important regulator of lipid and glucose metabolism. However, the role of FGF21 in macronutrient intake and metabolic disease, particularly in pediatric population, still needs further clarification. This study aimed to evaluate the association of rs11665896 in the FGF21 gene with metabolic status and macronutrient intake in a cohort of Mexican children with obesity. Methods Eighty-four lean children and 113 children with obesity, from 8 to 11 years of age, were recruited. FGF21 rs11665896 was genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Somatometric evaluations, nutrient intake, glucose, lipids, insulin and FGF21 serum levels were measured in the obesity group. Results The T allele of rs11665896 in the FGF21 gene was associated with obesity (odds ratio [OR] = 1.99, 95% confidence interval [CI] = 1.14-3.46; p = 0.0151). Subjects with obesity carrying the TT genotype consumed less lipids and more carbohydrates compared to other genotypes. Circulating FGF21 levels correlated negatively with carbohydrate intake (r = -0.232, p = 0.022) and positively with body weight (r = 0.269, p = 0.007), waist (r = 0.242, p = 0.016) and hip girth (r = 0.204, p = 0.042). FGF21 levels were lower in carriers of at least one T allele. Conclusions Genetic variants in FGF21 could influence metabolic status, food preferences and qualitative changes in nutritional behavior in children.

299-LB: Endothelial Regulation of Pancreatic ß-Cell Homeostasis in Diabetes

Diabetes is the result of having an inadequate supply of functional insulin-producing β-cells. Efforts in research and development that focused on using systemic pathway to induce β-cell regeneration have had limited clinical success. Emerging studies implicate local islet molecular and cellular factors in pancreatic β-cell homeostasis. Intraislet endothelial cells (IECs), a key ally of pancreatic β-cells, secrete factors that could affect β-cell survival and insulin production. Fibroblast growth factor (FGF) 21 is an endocrine hormone that regulates energy homeostasis and insulin sensitivity. The function of endogenous FGF-21 derived from ECs is undefined in diabetes. With a loss-of-function approach, this study sought to determine the role of EC-FGF-21 in pancreatic β-cell homeostasis in STZ-induced diabetic mice and high-fat diet (HFD)-induced obese mice. Mice with EC-specific deletion of FGF-21 gene (EC-FKO) were generated by crossing Tie2-Cre mice with FGF-21loxP mice. In 8-to-10-week-old male mice (n=15/group) treated with STZ (50 mg/kg, i.p. for consecutive 5d and killed 4 weeks later), EC-FKO vs. wild type C57BL/6J (WT) mice displayed more severe hyperglycemia, degeneration of insulin-producing β-cells, and expansion of glucagon-producing α-cells. Both groups showed similar changes in pancreatic Glut2 and PARP1 protein levels and vascular density. In 8-to-10-week-old WT male mice (n=15/group) fed an HFD (TestDiet: 60% energy from fat) for 16 weeks, obesity and insulin resistance developed, along with lipid accumulation in the islet and compensatory expansion of β-cell mass, all of which were worsened, except for less β-cell mass expansion, in EC-FKO mice. Our latest immunofluorescent data showed a significant reduction of IEC-FGF-21 protein staining in WT mice treated with STZ or HFD vs. non-treated mice. Our findings suggest that EC-FGF-21 is required to maintain β-cell homeostasis under stress conditions. Loss of IEC-FGF-21 may contribute, at least in part, to β-cell degeneration in diabetes. Disclosure M. Li: None. M. Qian: None. J. Xu: None. Funding National Institutes of Health

Fibroblast growth factor 21 secretion enhances glucose uptake in mono(2-ethylhexyl)phthalate-treated adipocytes

Previous studies revealed that cellular accumulation of mono(2-ethylhexyl)phthalate (MEHP) disturbed energy metabolism in adipocytes, where glucose uptake was significantly increased. The present study aimed to determine the mechanisms underlying the increased glucose uptake. MEHP-treated 3T3-L1 adipocytes exhibited a significantly increased glucose uptake activity. Immunoblot analysis suggested that the insulin-induced signals were not responsible for the increased glucose uptake. qPCR analysis revealed that both Glut1 and Glut4 genes were highly expressed during adipogenesis; Glut1 mRNA levels in MEHP-treated adipocytes were significantly increased. Moreover, MEHP-treated adipocytes exhibited significantly increased levels of fibroblast growth factor 21 (FGF21) in both mRNA and secreted protein. FGF21 is a peptide hormone with pleiotropic effects on regulation of insulin sensitivity and glucose/lipid homeostasis. We found that MEHP, FGF21, and lactate in culture medium together enhanced Fgf21 gene expression in MEHP-treated adipocytes. FGF21 signaling requires fibroblast growth factor receptor (FGFR) and βKlotho. Fgfr family and βKlotho genes were actively expressed during adipogenesis; mRNA levels of Fgfr3 and Fgfr4 genes in MEHP-treated adipocytes were significantly increased. Roles of FGF21/FGFR and phosphoinositide 3-kinase (PI3K)/AKT signal axes in regulation of glucose uptake were determined. We demonstrated that FGF21/FGFR signals played the major roles in up-regulation of the basal glucose uptake in MEHP-treated adipocytes. The in vitro evidence suggests that cellular FGF21 secretion enhances the basal glucose uptake in MEHP-treated adipocytes.

Micro RNA in Degenerative Disorders

Obesity and type 2 diabetes mellitus considered as the most risk criteria in metabolic syndrome. Twenty four male albino rats, 3 months age weighting (120±15) gm at the beginning of the experiment, were purchased from animal house in our University. The rats were kept at a suitable conditions with a temperature of 23-25°C with 12 hours light-dark cycle and free availability of water and diet. The rats were kept for 2 weeks for accommodation, then randomly divided into 2 main groups the first one was a control group (8 rats) kept on a standard diet with free access to drinking water. The second group (16 rats) kept on high fat high fructose diet (HFHF), 8 rats kept for 7 weeks (considered as obese group G2) and the other 8 rats were kept for 12 week to be diabetic with type II according to (De Castro et al., 2013)and considered as diabetic group (G 3). Grossly, feeding HFHF diet resulted in marked increase in body weight in both obese and diabetic group, this increase was stopped between 7th and 8th week the body weight started to decrease. Laboratory, feeding HFHF diet resulted in decreasing the expression levels of insulin hormone gene which reflected on the increase in the expression levels of FGF-21, IL-1β, IL-6 and TNF-α genes. This increase was more in the diabetic group in IL-1β, and the same in both groups in IL-6 and TNF-α but higher in obese group in FGF-21 gene. The expression levels of miRNA 146a, miRNA 126, FGF 21 and some cytokines may be a good early indicators for obesity and diabetes mellitus type II, having a major role in the mechanism of incidence and may have a great role in the treatment and follow-up the disease.

Sex Dimorphism in the Fgf21 Gene Expression in Liver and Adipose Tissues is Dependent on the Metabolic Condition

Fibroblast growth factor-21 (FGF21) beneficially affects carbohydrate and lipid metabolism. Previously, a sex-specific activation of Fgf21 expression was observed in humans and animals with metabolic diseases. It is unknown whether the sex differences in the Fgf21 expression are manifested in response to the natural physiological situations of fasting and refeeding. The aim of this work was to determine liver, White Adipose Tissue (WAT) and Brown Adipose Tissue (BAT) expression of genes related to FGF21 signaling in response to 24 h fasting, 6 h refeeding (after 24 h fasting) and Diet-Induced Obesity (DIO) in C57Bl mice of both sexes. Obesity was induced by the consumption of palatable food for 10 weeks. mRNA levels of peroxisome proliferator-activated receptor-a and -γ (Pparα, Pparγ), FGF21 (Fgf21), coactivator of FGF receptors (Klb) and transcriptional coactivator (Pgc-1α) were measured by RT-PCR. The study showed that the fasting-induced increases in hepatic Fgf21 gene expression and circulating FGF21 levels, as well as refeeding-induced increases in local WAT and BAT Fgf21 gene expression, were biased toward females. DIO-induced increase in circulating FGF21 levels, as well as in Fgf21 gene expression in the liver and BAT, were biased toward males. Considering that FGF21 is a novel metabolic regulator of energy homeostasis, sex differences in the responses to anabolic and catabolic stimulus could have translational implications for novel therapeutic outcomes.

Changes in Liver Gene Expression and Plasma Concentration of Rbp4, Fetuin-A, and Fgf21 in Sprague-Dawley Rats Subjected to Different Dietary Interventions and Bariatric Surgery.

Purpose To study the effect of duodenal-jejunal omega switch (DJOS) in combination with different dietary patterns on the retinol-binding protein (RBP4), fetuin-A, and fibroblast growth factor 21 (FGF21) plasma levels and their hepatic gene expressions in rats. Methods A high-fat diet (HF) was given to 28 rats and 28 more were fed with a control diet (CD) for 2 months. After that, half of each group underwent either DJOS or SHAM surgery. For the next 2 months, half of the animals in each operation group were kept on the same diet as before and half of them had the diet changed. After 16 weeks of the experiment RBP4, fetuin-A, and FGF21 plasma levels as well as liver Rbp4, Ahsg, and Fgf21 gene expressions were measured. Results DJOS had a reductive impact on plasma levels of RBP4, fetuin-A, and FGF21 and Rbp4, Ahsg, and Fgf21 relative gene expression in the liver when compared to SHAM. The HF/HF group expressed significantly higher RBP4 and fetuin-A plasma levels in comparison to the control. The HF diet used before and/or after surgery led to upregulation of Rbp4, Ahsg, and Fgf21 relative gene expression. The lowest levels of analyzed parameters were observed in the CD/CD group. Conclusions The efficiency of DJOS surgery, measured by hepatokines' plasma levels and their gene expressions in the liver, depends on the type of diet applied before and after surgery. Manipulation of dietary patterns can lead to marked improvements in metabolic profile after DJOS surgery.

A Common Allele in FGF21 Associated with Sugar Intake Is Associated with Body Shape, Lower Total Body-Fat Percentage, and Higher Blood Pressure

SummaryFibroblast growth factor 21 (FGF21) is a hormone that has insulin-sensitizing properties. Some trials of FGF21 analogs show weight loss and lipid-lowering effects. Recent studies have shown that a common allele in the FGF21 gene alters the balance of macronutrients consumed, but there was little evidence of an effect on metabolic traits. We studied a common FGF21 allele (A:rs838133) in 451,099 people from the UK Biobank study, aiming to use the human allele to inform potential adverse and beneficial effects of targeting FGF21. We replicated the association between the A allele and higher percentage carbohydrate intake. We then showed that this allele is more strongly associated with higher blood pressure and waist-hip ratio, despite an association with lower total body-fat percentage, than it is with BMI or type 2 diabetes. These human phenotypes of variation in the FGF21 gene will inform research into FGF21’s mechanisms and therapeutic potential.

Translational Control of FGF21 mRNA Expression is Responsive to Nutritional Stress

FGF21 is an endocrine hormone associated with diseases such as non‐alcoholic fatty liver disease (NAFLD), Type‐2‐Diabetes, and obesity. Remarkably, in studies where obese rodents were treated with FGF21, not only was obesity attenuated, but complications such as hepatic steatosis were largely resolved. Because the majority of circulating FGF21 is produced by the liver, understanding the molecular mechanisms that regulate hepatic expression is critical. In part, FGF21 expression is regulated through changes in FGF21 gene transcription. However, recent studies show that production of FGF21 by hepatocytes is stimulated by glucagon treatment independent of changes in FGF21 mRNA expression, suggesting translational control of the FGF21 mRNA. However, the mechanism(s) involved in such regulation are as yet unexplored. Thus, the aim of the present study was to explore translational control of FGF21 mRNA in a rodent model of obesity. Moreover, because translation of many mRNAs is regulated through modulation of the protein kinase activity of mTOR in complex 1 (mTORC1), we hypothesized that translational control of FGF21 mRNA is in part due to an attenuation of mTORC1 activity.Two studies have been completed thus far. In the first study, obesity‐prone male Sprague Dawley rats were fasted overnight. The next morning one‐half of the rats were randomly re‐fed for 1 hr, and livers were removed and homogenized. Homogenates were centrifuged through sucrose density gradients, and the gradients were fractionated while the absorbance at 254 nm was measured. RNA was isolated from each fraction, and analyzed by qRT‐PCR and RNA‐Seq analyses. In the second study, obesity‐prone rats were fed a high‐fat diet (HFD; 42% calories from fat) or a low‐fat control diet (5.2% fat) ad libitum, for 2 weeks. Rats were weighed every other day, blood glucose concentrations were measured 16‐h prior to sacrifice following a 5‐h fast, and livers were subjected to polysome profile analysis.Results from the first study show that re‐feeding resulted in a dramatic activation of mTORC1 in the liver as assessed by increased phosphorylation of its direct targets, 4E‐BP1 and p70S6K1. There was also a shift in distribution of mRNAs from smaller (i.e. fewer ribosomes attached) to heavier (i.e. more ribosomes attached) polysomes in response to refeeding. Importantly, although expression of the FGF21 mRNA was upregulated in response to refeeding, there was a shift in the polysome distribution of the FGF21 mRNA from heavy to light polysomes, indicating that refeeding led to downregulation of FGF21 mRNA translation. In the second study, there was no effect of diet on FGF21 mRNA expression, however the proportion of FGF21 mRNA in heavy compared to light polysomes was greater in rats consuming the Western compared to the control diet. Furthermore, body weight and fasting blood glucose concentrations were the same in rats fed a Western compared to a control diet, suggesting that the rats had not yet developed insulin resistance.The results show that the FGF21 mRNA is translationally controlled in response to fasting and refeeding in association with changes in mTORC1 activity. Moreover, short‐term consumption of a Western diet enhances translation of the FGF21 mRNA without altering expression of its mRNA. Studies are in progress to explore possible regulatory mechanisms controlling FGF21 mRNA translation, e.g. identification of regulatory elements in the 5′‐UTR of the mRNA.Support or Funding Information(Supported by NIH grant DK13499)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Construction of FGF21 knockout mouse models by the CRISPR/Cas9 system.

Fibroblast growth factors (FGFs) are multifunctional signal molecules between cells, regulating the various physiological functions of the organism. FGF21 is a regulatory factor of the FGF family and has been postulated to play important roles in hair follicle development and hair follicle growth cycle. To evaluate the roles of FGF21, we had established a FGF21 knockout mouse model, using the CRISPR/Cas9 technology. We had constructed a FGF21 targeting vector and microinjected it with Cas9 mRNA and gRNA into fertilized ova of FVB mice. The gRNA was designed to target the exon 1 of the endogenous mouse FGF21 gene. Three lines of Fgf21 -/- mice were obtained from these experiments, and confirmed to harbor Fgf21 -/- genotypes and null expression phenotype, using DNA sequencing, qRT-PCR and Western blotting. FGF21 mRNA and FGF21 protein were not detected in tissues of these Fgf21 -/- mice. Depilation and histochemistry analyses showed that the Fgf21 -/- mice had lower body weight, slower hair regrowth and poorer hair quantities and smaller hair follicles diameters, as compared to WT mice. The Fgf21 -/- mice reported here could provide a useful genetic model for future studies of FGF21 functions in hair follicle development and hair follicle growth cycle.

Glucagon and Insulin Cooperatively Stimulate Fibroblast Growth Factor 21 Gene Transcription by Increasing the Expression of Activating Transcription Factor 4

Previous studies have shown that glucagon cooperatively interacts with insulin to stimulate hepatic FGF21 gene expression. Here we investigated the mechanism by which glucagon and insulin increased FGF21 gene transcription in primary hepatocyte cultures. Transfection analyses demonstrated that glucagon plus insulin induction of FGF21 transcription was conferred by two activating transcription factor 4 (ATF4) binding sites in the FGF21 gene. Glucagon plus insulin stimulated a 5-fold increase in ATF4 protein abundance, and knockdown of ATF4 expression suppressed the ability of glucagon plus insulin to increase FGF21 expression. In hepatocytes incubated in the presence of insulin, treatment with a PKA-selective agonist mimicked the ability of glucagon to stimulate ATF4 and FGF21 expression. Inhibition of PKA, PI3K, Akt, and mammalian target of rapamycin complex 1 (mTORC1) suppressed the ability of glucagon plus insulin to stimulate ATF4 and FGF21 expression. Additional analyses demonstrated that chenodeoxycholic acid (CDCA) induced a 6-fold increase in ATF4 expression and that knockdown of ATF4 expression suppressed the ability of CDCA to increase FGF21 gene expression. CDCA increased the phosphorylation of eIF2α, and inhibition of eIF2α signaling activity suppressed CDCA regulation of ATF4 and FGF21 expression. These results demonstrate that glucagon plus insulin increases FGF21 transcription by stimulating ATF4 expression and that activation of cAMP/PKA and PI3K/Akt/mTORC1 mediates the effect of glucagon plus insulin on ATF4 expression. These results also demonstrate that CDCA regulation of FGF21 transcription is mediated at least partially by an eIF2α-dependent increase in ATF4 expression.

Low-protein diet induces, whereas high-protein diet reduces hepatic FGF21 production in mice, but glucose and not amino acids up-regulate FGF21 in cultured hepatocytes

Fibroblast growth factor 21 (FGF21) is a polypeptide secreted by the liver and involved in several metabolic processes such as thermogenesis and lipid oxidation. The nutritional mechanisms controlling FGF21 production are poorly understood. This study aimed to investigate how dietary carbohydrates and proteins impact FGF21 production and how in turn, FGF21 is involved in the metabolic adaptation to changes in the carbohydrate and protein contents of the diet. For that purpose, we fed 25 male C57BL/6 mice diets composed of different protein and carbohydrate contents (normal-protein and carbohydrate diet (N=9, NPNC), low-protein high-carbohydrate diet (N=8, LPHC), high-protein low-carbohydrate diet (N=8, HPLC) for 3 weeks. We measured liver Fgf21 gene expression, synthesis and secretion as well as different parameters related to energy and glucose metabolism. We also investigated the direct role of amino acids and glucose in the control of Fgf21 gene expression in hepatocyte primary cultures (n=6).In vivo, FGF21 responds acutely to LPHC intake whereas under an HPLC diet, plasma FGF21 circulating levels are low in the fasted and refed states. In hepatocytes, Fgf21 expression was controlled by glucose but not amino acids. Both diets increased the thermic effect of feeding (TEF) and ketogenesis was increased in fasted HPLC mice. The results presented suggest that dietary glucose, rather than amino acids, directly controls FGF21 secretion, and that FGF21 may be involved in the increased TEF response to LPHC. The effects of the HPLC diet on ketogenesis and TEF are probably controlled by other metabolic pathways.

The regulation of FGF21 gene expression by metabolic factors and nutrients.

Fibroblast growth factor 21 (FGF21) gene expression is altered by a wide array of physiological, metabolic, and environmental factors. Among dietary factors, high dextrose, low protein, methionine restriction, short-chain fatty acids (butyric acid and lipoic acid), and all-trans-retinoic acid were repeatedly shown to induce FGF21 expression and circulating levels. These effects are usually more pronounced in liver or isolated hepatocytes than in adipose tissue or isolated fat cells. Although peroxisome proliferator-activated receptor α (PPARα) is a key mediator of hepatic FGF21 expression and function, including the regulation of gluconeogenesis, ketogenesis, torpor, and growth inhibition, there is increasing evidence of PPARα-independent transactivation of the FGF21 gene by dietary molecules. FGF21 expression is believed to follow the circadian rhythm and be placed under the control of first order clock-controlled transcription factors, retinoic acid receptor-related orphan receptors (RORs) and nuclear receptors subfamily 1 group D (REV-ERBs), with FGF21 rhythm being anti-phase to REV-ERBs. Key metabolic hormones such as glucagon, insulin, and thyroid hormone have presumed or clearly demonstrated roles in regulating FGF21 transcription and secretion. The control of the FGF21 gene by glucagon and insulin appears more complex than first anticipated. Some discrepancies are noted and will need continued studies. The complexity in assessing the significance of FGF21 gene expression resides in the difficulty to ascertain (i) when transcription results in local or systemic increase of FGF21 protein; (ii) if FGF21 is among the first or second order genes upregulated by physiological, metabolic, and environmental stimuli, or merely an epiphenomenon; and (iii) whether FGF21 may have some adverse effects alongside beneficial outcomes.

Correction to: Rejuvenation Res 2016;19:90-93.

It has come to our attention that our recent publication Thymus Maintenance and Regeneration by Specific Molecular Factors contains errors. The following sentence from the article was misattributed to Reis et al. Immun Ageing. 2015;12:18]: This FGF21 resistance was due to epigenomic changes at the FGF21 gene, specifically increased DNA methylation. Moreover, the sentence is inaccurate. For clarity, this sentence should be modified: This FGF21 resistance, which is associated with metabolic syndrome and non-alcoholic fatty liver disease (NAFLD) may be due to epigenomic changes in DNA and/or histone methylation due to altered methionine metabolism affecting FGF21 expression ( (Inagaki, Front Endocrinol (Lausanne). 2015 6:147). One possible mechanism is that diet-related DNA methylation changes at the PPARalpha locus in the liver (Contreras et al Adv Nutr, 2013; 4: 439-452) may alter FGF21 expression, because PPARalpha is a key regulator of FGF21 expression involved in insulin resistance, dyslipidemia (...

Valproic Acid and Other HDAC Inhibitors Upregulate FGF21 Gene Expression and Promote Process Elongation in Glia by Inhibiting HDAC2 and 3.

Background:Fibroblast growth factor 21, a novel regulator of glucose and lipid metabolism, has robust protective properties in neurons. However, its expression and function in glia are unknown. Valproic acid, a mood stabilizer and anticonvulsant, is a histone deacetylase inhibitor and a dynamic gene regulator. We investigated whether histone deacetylase inhibition by valproic acid and other inhibitors upregulates fibroblast growth factor 21 expression and, if so, sought to identify the histone deacetylase isoform(s) involved and their role in altering glial cell morphology.Methods:C6 glioma or primary cortical glial cultures were treated with histone deacetylase inhibitors, and fibroblast growth factor 21 levels and length of cell processes were subsequently measured. Histone deacetylase 1, 2, or 3 was also knocked down to detect which isoform was involved in regulating fibroblast growth factor 21 mRNA levels. Finally, knockdown and overexpression of fibroblast growth factor 21 were performed to determine whether it played a role in regulating cell process length.Results:Treatment of C6 cells or primary glial cultures with valproic acid elevated fibroblast growth factor 21 mRNA levels, extended cell process length, and markedly increased acetylated histone-H3 levels. Other histone deacetylase inhibitors including pan- and class I-specific inhibitors, or selective knockdown of histone deacetylase 2 or 3 isoform produced similar effects. Knockdown or overexpression of fibroblast growth factor 21 significantly decreased or increased C6 cell process length, respectively.Conclusions:In glial cell line and primary glia, using pharmacological inhibition and selective gene silencing of histone deacetylases to boost fibroblast growth factor 21 mRNA levels results in elongation of cell processes. Our study provides a new mechanism via which histone deacetylase 2 and 3 participate in upregulating fibroblast growth factor 21 transcription and extending process outgrowth in glia.

Fibroblast Growth Factor 21 Mediates Glycemic Regulation by Hepatic JNK.

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

Fibroblast Growth Factor 21 (Fgf21) Gene Expression Is Elevated in the Liver of Mice Fed a High-Carbohydrate Liquid Diet and Attenuated by a Lipid Emulsion but Is Not Upregulated in the Liver of Mice Fed a High-Fat Obesogenic Diet

Background:Fibroblast growth factor 21 (FGF21) is a regulator of carbohydrate and lipid metabolism; however, the regulation of Fgf21 gene expression by diet remains incompletely understood.Objective:We investigated the effect of a high-carbohydrate (HC) liquid diet, with and without supplementation with a lipid emulsion (LE), and of a high-fat diet (HFD) compared with a low-fat diet (LFD) on the regulation of Fgf21 gene expression in the liver of intact mice.Methods:C57BL/6 male mice were fed standard feed pellets (SFPs), a purified HC liquid diet (adequate in calories and protein), or an HC liquid diet containing an LE at either 4% or 13.5% of energy for 5 wk (Expt. 1) or 1 wk (Expt. 2). In Expt. 3, mice were fed a purified LFD (∼10% fat) or HFD (∼60% fat) or were fed an HFD and given access to a running wheel for voluntary exercise for 16 wk.Results:Fgf21 mRNA in liver and FGF21 protein in plasma were increased by 3.5- to 7-fold in HC mice compared with SFP mice (P < 0.001), whereas the LE dose-dependently attenuated the induction of Fgf21 expression (P < 0.05). After 16 wk, hepatic Fgf21 mRNA did not differ between LFD and HFD mice but was dramatically reduced in the HFD+exercise group to <20% of the level in the HFD group (P < 0.0001).Conclusions: In mice, hepatic Fgf21 expression was upregulated by 1 and 5 wk of feeding a lipogenic HC diet but not by 16 wk of feeding an obesogenic HFD, whereas the addition of fat as an LE to the HC formula significantly reduced Fgf21 gene expression and the plasma FGF21 protein concentration. Our results support a strong and reversible response of hepatic Fgf21 expression to shifts in dietary glucose intake.

Perilipin 5-Driven Lipid Droplet Accumulation in Skeletal Muscle Stimulates the Expression of Fibroblast Growth Factor 21.

Perilipin 5 (PLIN5) is a lipid droplet protein and is highly expressed in oxidative tissue. Expression of the PLIN5 gene is regulated by peroxisome proliferator–activated receptor-α, fasting, and exercise. However, the effect of increased muscle PLIN5 expression on whole-body energy homeostasis remains unclear. To examine this, we developed a mouse line with skeletal muscle PLIN5 overexpression (MCK-Plin5). We show that MCK-Plin5 mice have increased energy metabolism and accumulate more intramyocellular triacylglycerol but have normal glucose and insulin tolerance. MCK-Plin5 mice fed high-fat chow manifest lower expression of inflammatory markers in their liver and increased expression of “browning” factors in adipose tissue. This muscle-driven phenotype is, at least in part, mediated by myokines; the MCK-Plin5 mice have 80-fold higher FGF21 gene expression in muscle and increased serum FGF21 concentration. The increase in FGF21 occurs mainly in muscles with a predominance of fast-twitch fibers, suggesting that fiber type–specific lipid storage may be part of the mechanism conferring metabolic protection in MCK-Plin5 mice. In conclusion, upregulating the PLIN5 level in skeletal muscle drives expression of the FGF21 gene in fast-twitch fibers and is metabolically protective. These findings provide insight into the physiology of PLIN5 and the potential contribution of its upregulation during exercise.