The Correlation Between Serum Fibroblast Growth Factor 21 and the Severity and Occurrence of Coronary Artery Disease

BACKGROUND

The burden of cardiovascular diseases (CVDs) is increasing worldwide with CVD being one of the leading causes of death, including atherosclerosis, myocardial infarction, cardiomyopathy, and heart failure (HF). Fibroblast growth factor 21 (FGF21) is an endocrine hormone that regulates carbohydrate and lipid metabolism. It exerts direct effects on the cardiovascular system and can serve as an early indicator of CVDs. FGF21's therapeutic properties include reducing obesity, dyslipidaemia, and hyperglycemia, which can help treat metabolic disorders, autophagy, and apoptosis. Atherosclerosis is developed due to chronic inflammatory conditions, and the immune system's reaction to oxidized lipoproteins is mainly responsible for the development of atherosclerosis. FGF21's precise role in the pathogenesis of coronary artery disease (CAD) remains elusive.  Aim: This study aimed to assess the role of FGF21 in predicting the severity and magnitude of CAD in individuals diagnosed with stable angina pectoris (SAP).

MATERIALS AND METHODS

A prospective cross-sectional study was conducted on 110 consecutive patients with SAP reported to the cardiology department of the Indira Gandhi Institute of Medical Sciences (IGIMS), Patna, India. They were divided into two groups based on coronary angiography findings. Control groups included patients not showing any atherosclerotic lesions and case groups with atherosclerotic lesions. The SYNTAX score is a grading system that measures the location and complexity of coronary arteries using anatomical principles. The Gensini score assessment technique was employed to determine the severity of CAD. We compared serum FGF21 levels,left ventricular ejection fraction (LVEF), and inflammatory biomarker C-reactive protein (CRP) levels between the two groups. Moreover, we examined the correlation between the serum FGF21 level and the SYNTAX and Gensini scores. The statistical analysis was done using Version 23.0 of SPSS Statistics. P-values below 0.05 were considered statistically significant.

RESULTS

The study found that the case group had a higher average age and a higher proportion of male patients. The case group had considerably higher levels of FGF21 (166.59 ± 94.49791 pg/mL) compared to the control group (54.13 ± 48.467 pg/mL) (p=0.034). The LVEF exhibited a significant difference between the case and control groups, with mean values of 50.3056 ± 7.8242% and 56.078 ± 5.3987%, respectively (p=0.031). CRP levels were comparable in both groups. The case group had mean values of SYNTAX and Gensini scores of 23.19±7.43 and 50.03±27.30, respectively. We found that there was no statistically significant association between the risk assessments for CAD severity and the levels of serum FGF21 (correlation coefficient r=0.14070, p>0.05, and r=0.206415, p>0.05, respectively) Conclusions: FGF21 is gaining recognition as a prospective addition to the FGF family, potentially playing a significant role in cardiovascular disease, particularly atherosclerosis. A statistically significant difference was seen in the serum FGF21 levels between the case and control groups, indicating that it can help in the diagnosis of CAD. However, there was no apparent correlation found between the serum FGF21 levels and the SYNTAX and Gensini scores. The role of FGF21 in the development of atherosclerosis and whether FGF21 could serve as a reliable marker need to be studied further.

miR-26b-5p promotes osteogenesis of bone mesenchymal stem cells via suppressing FGF21

BACKGROUND

miR-26b-5p actively participates in the osteogenic differentiation of bone mesenchymal stem cells (BMSCs). The database showed that fibroblast growth factor (FGF)-21 is a potential binding site of miR-26b-5p. This study aimed to investigate the molecular osteogenic mechanisms of miR-26b-5p targeting FGF21.

METHODS

Bone marrow was aspirated from the anterior superior iliac spine during bone marrow puncture. BMSCs were used to establish an in vitro cell model, and BMSCs markers were analyzed by flow cytometry. miR-26b-5p were overexpressed for 48 hours, and then placed in an osteogenic induction medium for osteogenic induction culture, the expression of RNA was detected using RT-qPCR. On day 7 of induction, RT-qPCR was used to measure Runx2, Osterix (Osx), and target gene FGF21 expression levels in each group. RT-qPCR, the dual-luciferase reporter gene system and western blot were used to verify that FGF21 was a direct target of miR-26b-5p.

RESULTS

BMSCs were identified according to the antigenic characteristics. miR-26b-5p expression was significantly upregulated after the expression of miR-26b-5p mimics, and FGF21 expression was downregulated; in miR-26b-5p inhibitor, the opposite results were revealed. After overexpression of miR-26b-5p, the alkaline phosphatase activity and nodules of Alizarin red S in the culture medium was increased; the opposite results were revealed in miR-26b-5p inhibitor. The expressions of Runx2 and Osx in the miR-26b-5p group were also significantly higher; in the miR-26b-5p inhibitor group, the opposite results were revealed. Luciferase reporter assays demonstrated that FGF21 was a direct target of miR-26b-5p. The western blotting analysis showed that FGF21 expression was significantly downregulated in the miR-26b-5p overexpressed group. Finally, the expressions of the characteristic osteogenic factors in the miR-26b-5p control + FGF21 group was significantly lower, but then increased significantly in the miR-26b-5p mimics + FGF21 group; the expressions of the characteristic osteogenic factors in the miR-26b-5p control + si-FGF21 group was significantly higher.

CONCLUSIONS

miR-26b-5p can regulate the osteogenic differentiation of BMSCs and participate in PMOP pathogenesis via suppressing FGF21.

Fibroblast Growth Factor 21 as a Marker of Prediabetes in Patients with Non-alcoholic Fatty Liver Disease

BACKGROUND

Fibroblast growth factor 21 is a peptide primarily secreted by the liver in response to peroxisome proliferator-activated receptor-α activation which plays an important role in regulating carbohydrate and lipid metabolism. This study investigated the association between fibroblast growth factor 21 and prediabetes in obese patients with non-alcoholic fatty liver disease in adult population.

METHODS

A total of 85 obese non-alcoholic fatty liver disease patients without (n = 49) and with prediabetes (n = 36) were included. Serum fibroblast growth factor 21 levels were determined by enzyme-linked immunosorbent assay.

RESULTS

Higher fibroblast growth factor 21 serum levels were observed in patients with prediabetes, metabolic syndrome, dyslipidemia, and insulin resistance. There were significant correlations between fibroblast growth factor 21 and waist-to-stature ratio, visceral adiposity index, triglycerides, very low-density lipoproteins, alanine aminotransferase (ALT), gamma-glutamyl transferase (GGT), Quantitative Insulin Sensitivity Check Index, and Stumvoll index of insulin sensitivity. Fibroblast growth factor 21 level ≥320 pg/mL was associated with a 4.2-fold higher risk of prediabetes and ≥270 pg/mL for metabolic syndrome approximately 4 times.

CONCLUSION

Fibroblast growth factor 21 is associated with increased risk for prediabetes, metabolic syndrome, and insulin resistance in obese patients with non-alcoholic fatty liver disease.

Dietary Methionine Restriction Signals to the Brain Through Fibroblast Growth Factor 21 to Regulate Energy Balance and Remodeling of Adipose Tissue

OBJECTIVE

Restricting dietary methionine to 0.17% in mice increases energy expenditure (EE), reduces fat deposition, and improves metabolic health by increasing hepatic fibroblast growth factor 21 (FGF21). The goal of this study was to compare each of these responses in mice with the coreceptor for FGF21 deleted in either adipose tissue or the brain.

METHODS

Methionine-restriction (MR) diets were fed to age-matched cohorts of mice with the coreceptor for FGF21 deleted in either adipose tissue or the brain. The physiological and transcriptional responses to MR were compared in the respective cohorts.

RESULTS

Tissue-specific deletion of the FGF21 coreceptor in adipose tissue did not abrogate the ability of dietary MR to increase  EE and reduce fat deposition. Tissue-specific deletion of the FGF21 coreceptor from the brain produced mice that were unable to respond to the effects of MR on  EE or the remodeling of adipose tissue.

CONCLUSIONS

The increase in FGF21 produced by dietary MR acts primarily in the brain to produce its physiological effects on energy balance. In contrast, the effects of MR on hepatic gene expression were intact in both models, supporting a mechanism that directly links detection of reduced methionine in the liver to transcriptional mechanisms that alter gene expression in the liver.

Higher increase degree of FGF21 post long-term interdisciplinary weight loss therapy preserves the free fat mass and rest metabolic rate in adolescents with obesity

Objective Fibroblast growth factor 21 (FGF21) is among the activators that can stimulate thermogenesis in the white adipose tissue and brown adipose tissue. People with obesity have elevated blood levels of FGF21, but also develop resistance to its action, impairing its beneficial role. Inversely, clinical treatments to weight loss has been pointed out as an important therapy for increasing and recovering sensitivity to FGF21. The aim was to analyse the effect of long-term weight loss interdisciplinary intervention on FGF21 and body composition. Subjects and methods Eighty-six post-pubertal obese adolescents (14-19 years-old), were submitted to 20 weeks of weight loss therapy (clinical, nutritional, psychological and physical exercise support). Anthropometric measures, body composition and rest metabolic rate (RMR) by bioelectrical impedance, and serum FGF21 sample by ELISA were evaluated. The adolescents were grouped according to FGF21 individual delta variations after therapy: Higher Increase (HI); lower increase (LI); lower decrease (LD); higher decrease (HD). Results All groups present weight loss. Only in FGF21 ≥ 76,5 pg/mL variation the free-fat-mass and rest metabolic rate were preserved and to others group these variables were significantly reduced. Conclusion High increase in FGF21 can contribute to preservation of FFM and RMR after weight loss therapy, could have important implications for energy balance regulation. Future studies are necessary to continue determining the role of magnitude effects of FGF21 levels in obesity to improve clinical practice, especially in paediatrics population.

Fibroblast growth factor 21 (FGF21) in children and adolescents with chronic kidney disease

Fibroblast growth factor 21 (FGF21) is one of the members of endocrine arm of FGF family. Its actions as a glucose and lipids metabolism regulator are widely known. Although the mechanism of FGF21 action in kidneys is still under investigation, FGF21 was considered as a marker of early kidney function decline. While many researchers focused on adult subjects in this matter, there are no data regarding children. Therefore, we have investigated the relationship between plasma or urine FGF21 levels and kidney function in a group of 42 pediatric patients with chronic kidney disease (CKD). Anthropometrical parameters and blood pressure were taken, routine biochemical tests were performed. The concentration of FGF21 in serum and urine was determined by enzyme immunoassay. The results revealed significantly higher serum FGF21 concentration among children from CKD group. However, serum FGF21 level was not related to gender, proteinuria, eGFR or renal replacement therapy. Urine FGF21 concentration correlated negatively with albuminuria and positively with eGFR. Documented negative correlation of FGF21 fractional excretion and eGFR is not enough to support the role of FGF21 as a biomarker for predicting kidney disease progression in children and adolescents. Other mechanisms including local kidney FGF21 production or enhanced excretion due to higher extrarenal production may result in higher urine FGF21 concentrations.

Weight Loss and Concomitant Adipose Autophagy in Methionine-Restricted Obese Mice is Not Dependent on Adiponectin or FGF21

OBJECTIVE

Identifying novel approaches to combat obesity is important to improve health span. It was hypothesized that methionine restriction (MR) will induce weight loss in obese mice by reducing adipose tissue mass caused by increased energy expenditure and reprogramming of adipose tissue homeostasis. The roles of adiponectin (ADIPOQ) and fibroblast growth factor 21 (FGF21) during weight loss in MR mice were also tested.

METHODS

Diet-induced obese (DIO) male C57BL/6J (wild type), Adipoq-deficient (Adipoq knockout [KO]), Fgf21-KO, and Adipoq-Fgf21 double-KO mice were used. Following a switch to high-fat control (DIO-CF, 60% fat/0.86% methionine) or MR (DIO-MR, 60% fat/0.12% methionine) diet, physiological parameters were measured, and inguinal and perigonadal adipose tissues were examined.

RESULTS

Obese mice subjected to MR showed loss of body weight and adiposity, increased energy expenditure, and improved glucose tolerance that were independent of the actions of ADIPOQ and FGF21. MR induced reduction of circulating lipids, glucose, insulin, leptin, and insulin like growth factor 1 and increased β-hydroxybutyrate, ADIPOQ, and FGF21 concentrations. In fat, MR upregulated protein levels of adipose triglyceride lipase, apoptosis-inducing factor, lysosomal-associated membrane proteins 1 and 2, autophagy-related protein 5, beclin-1, and light chain 3B I and II.

CONCLUSIONS

MR reduction of adipose tissue mass in obese mice is associated with elevated lipolysis, apoptosis, and autophagy and occurs independently of the actions of ADIPOQ and FGF21.

Sexually Dimorphic Effects of Dietary Methionine Restriction are Dependent on Age when the Diet is Introduced

OBJECTIVE

Restricting dietary methionine to 0.17% in male mice increases energy expenditure, reduces fat deposition, and improves metabolic health. The goal of this work was to compare each of these responses in postweaning male and female mice and in physically mature male and female mice.

METHODS

Methionine-restricted (MR) diets were fed to age-matched cohorts of male and female mice for 8 to 10 weeks beginning at 8 weeks of age or beginning at 4 months of age. The physiological and transcriptional responses to MR were compared in the respective cohorts.

RESULTS

Dietary MR produced sexually dimorphic changes in body composition in young growing animals, with males preserving lean at the expense of fat and females preserving fat at the expense of lean. The effects of MR on energy balance were comparable between sexes when the diet was initiated after attainment of physical maturity (4 months), and metabolic and endocrine responses were also comparable between males and females after 8 weeks on the MR diet.

CONCLUSIONS

The sexually dimorphic effects of MR are limited to nutrient partitioning between lean and fat tissue deposition in young, growing mice. Introduction of the diet after physical maturity produced comparable effects on growth and metabolic responses in male and female mice.

Dietary Methionine Restriction Reduces Inflammation Independent of FGF21 Action

OBJECTIVE

Methionine restriction (MR) decreases inflammation and improves markers of metabolic disease in rodents. MR also increases hepatic and circulating concentrations of fibroblast growth factor 21 (FGF21). Emerging evidence has suggested that FGF21 exerts anti-inflammatory effects. The purpose of this study was to determine the role of FGF21 in mediating the MR-induced reduction in inflammation.

METHODS

Wild-type and Fgf21^-/- mice were fed a high-fat (HF) control or HF-MR diet for 8 weeks. In a separate experiment, mice were fed a HF diet (HFD) for 10 weeks. Vehicle or recombinant FGF21 (13.6 µg/d) was administered via osmotic minipump for an additional 2 weeks. Inflammation and metabolic parameters were measured.

RESULTS

Fgf21^-/- mice were more susceptible to HFD-induced inflammation, and MR reduced inflammation in white adipose tissue (WAT) and liver of Fgf21^-/- mice. MR downregulated activity of signal transducer and activator of transcription 3 in WAT of both genotypes. FGF21 administration reduced hepatic lipids and blood glucose concentrations. However, there was little effect of FGF21 on inflammatory gene expression in liver or adipose tissue or circulating cytokines.

CONCLUSIONS

MR reduces inflammation independent of FGF21 action. Endogenous FGF21 is important to protect against the development of HFD-induced inflammation in liver and WAT, yet administration of low-dose FGF21 has little effect on markers of inflammation.

Fibroblast growth factors in control of lipid metabolism: from biological function to clinical application

PURPOSE OF REVIEW

Several members of the fibroblast growth factor (FGF) family have been identified as key regulators of energy metabolism in rodents and nonhuman primates. Translational studies show that their metabolic actions are largely conserved in humans, which led to the development of various FGF-based drugs, including FGF21-mimetics LY2405319, PF-05231023, and pegbelfermin, and the FGF19-mimetic NGM282. Recently, a number of clinical trials have been published that examined the safety and efficacy of these novel therapeutic proteins in the treatment of obesity, type 2 diabetes (T2D), nonalcoholic steatohepatitis (NASH), and cholestatic liver disease. In this review, we discuss the current understanding of FGFs in metabolic regulation and their clinical potential.

RECENT FINDINGS

FGF21-based drugs induce weight loss and improve dyslipidemia in patients with obesity and T2D, and reduce steatosis in patients with NASH. FGF19-based drugs reduce steatosis in patients with NASH, and ameliorate bile acid-induced liver damage in patients with cholestasis. In contrast to their potent antidiabetic effects in rodents and nonhuman primates, FGF-based drugs do not appear to improve glycemia in humans. In addition, various safety concerns, including elevation of low-density lipoprotein cholesterol, modulation of bone homeostasis, and increased blood pressure, have been reported as well.

SUMMARY

Clinical trials with FGF-based drugs report beneficial effects in lipid and bile acid metabolism, with clinical improvements in dyslipidemia, steatosis, weight loss, and liver damage. In contrast, glucose-lowering effects, as observed in preclinical models, are currently lacking.

FGF21 Is Associated with Metabolic Effects and Treatment Response in Depressed Bipolar II Disorder Patients Treated with Valproate

BACKGROUND

Patients with bipolar disorder are at high risk of metabolic disturbance after mood stabilizer treatment. However, the mediators linking the two conditions remain unknown. In this study, we investigated whether fibroblast growth factor-21 (FGF21) was associated with metabolic effects and treatment response in depressed bipolar disorder patients.

METHODS

We recruited 78 community-dwelling controls and 137 bipolar disorder patients; the latter were interviewed using the Chinese Version of the Modified Schedule of Affective Disorder and Schizophrenia-Life Time. Upon study entry, the bipolar disorder patients were all in a major depressive status, with 17-item Hamilton Depression Rating Scale (HDRS) scores >15. They received valproate (500-1000 mg daily) for 12 weeks, and fluoxetine 20 mg daily was permitted to treat depressive symptoms. Fasting plasma level of FGF21, lipid profiles, and body weight were collected at baseline and after 12 weeks of treatment.

RESULTS

At baseline, the demographic characteristics, FGF21 level, and metabolic indices did not differ significantly between the controls and bipolar disorder patients. After 12 weeks of treatment, the FGF21 level (167.7±122.0 to 207.1±162.3 pg/mL, P=.001), body weight and waist circumference had increased significantly (P<.001 and P=.028, respectively). Moreover, the change in FGF21 level was significantly correlated with the changes in HDRS score (r=0.393, P=.002), total cholesterol (r=-0.344, P=.008), and low-density lipoprotein (r=-0.347, P=.007).

CONCLUSIONS

The central and peripheral mediating effects of FGF21 on bipolar disorder depression treatment might be opposite. High peripheral FGF21 levels might link regulation of metabolic effect and resistance to treatment in bipolar disorder.

Fasting-induced hormonal regulation of lysosomal function

Lysosomes are centers for nutrient sensing and recycling that allow mammals to adapt to starvation. Regulation of lysosome dynamics by internal nutrient signaling is well described, but the mechanisms by which external cues modulate lysosomal function are unclear. Here, we describe an essential role of the fasting-induced hormone fibroblast growth factor 21 (FGF21) in lysosome homeostasis in mice. Fgf21 deficiency impairs hepatic lysosomal function by blocking transcription factor EB (TFEB), a master regulator of lysosome biogenesis and autophagy. FGF21 induces mobilization of calcium from the endoplasmic reticulum, which activates the transcriptional repressor downstream regulatory element antagonist modulator (DREAM), and thereby inhibits expression of Mid1 (encoding the E3 ligase Midline-1). Protein phosphatase PP2A, a substrate of MID1, accumulates and dephosphorylates TFEB, thereby upregulating genes involved in lysosome biogenesis, autophagy and lipid metabolism. Thus, an FGF21-TFEB signaling axis links lysosome homeostasis with extracellular hormonal signaling to orchestrate lipid metabolism during fasting.

Concentration-dependent linkage of dietary methionine restriction to the components of its metabolic phenotype

OBJECTIVE

Restricting dietary methionine to 0.17% produces a series of physiological responses through coordinated transcriptional effects in liver and adipose tissue. The goal of the present work was to determine the threshold concentrations above and below 0.17% at which the beneficial responses to 0.17% dietary methionine are preserved.

METHODS

Diets were formulated to restrict methionine to different degrees, followed by evaluation of the transcriptional and physiological responses to the different diets.

RESULTS

Restriction of dietary methionine to 0.25%, but not 0.34%, was partially effective in reproducing the metabolic phenotype produced by restriction of methionine to 0.17%, while restriction of methionine to 0.12% reproduced the responses produced by restriction to 0.17% but failed to support growth and caused excessive weight loss. Restriction beyond 0.12% initiated responses characteristic of essential amino acid deprivation including food aversion and rapid weight loss.

CONCLUSIONS

Restriction of dietary methionine to levels above 0.25% was without effect, while restriction to levels below 0.12% produced responses characteristic of essential amino acid deprivation. In addition, although restriction of dietary methionine to 0.12% did not evoke essential amino acid deprivation responses, it provided insufficient methionine to support growth. The ideal range of dietary methionine restriction was from 0.17% to 0.25%.

Adipose-derived circulating miRNAs regulate gene expression in other tissues

Adipose tissue is a major site of energy storage and has a role in the regulation of metabolism through the release of adipokines. Here we show that mice with an adipose-tissue-specific knockout of the microRNA (miRNA)-processing enzyme Dicer (ADicerKO), as well as humans with lipodystrophy, exhibit a substantial decrease in levels of circulating exosomal miRNAs. Transplantation of both white and brown adipose tissue-brown especially-into ADicerKO mice restores the level of numerous circulating miRNAs that are associated with an improvement in glucose tolerance and a reduction in hepatic Fgf21 mRNA and circulating FGF21. This gene regulation can be mimicked by the administration of normal, but not ADicerKO, serum exosomes. Expression of a human-specific miRNA in the brown adipose tissue of one mouse in vivo can also regulate its 3' UTR reporter in the liver of another mouse through serum exosomal transfer. Thus, adipose tissue constitutes an important source of circulating exosomal miRNAs, which can regulate gene expression in distant tissues and thereby serve as a previously undescribed form of adipokine.

Prophylactic and abundant intake of α-lipoic acid causes hepatic steatosis and should be reconsidered in usage as an anti-aging drug

The majority of research has suggested that α-lipoic acid (ALA) is a potential therapeutic agent for chronic diseases associated with oxidative stress, including atherosclerosis, diabetes, and neurodegeneration. Therefore, a nutritional supplementation with ALA is recommended although the effects of a short- and long-term intake of ALA on central organs in healthy individuals are not studied in detail yet. Therefore, liver tissue of 4 and 74 weeks ALA-treated healthy C57BL6/J mice with respect to lipid metabolism was analyzed. In doing so, it was shown that short-term and long-term ALA treatment caused a marked increase of β-oxidation, as indicated by a significant rise of mRNA expression of fgf21, pparα, and its target genes, for example, acox1, cpt1α, and cpt2, as well as of Fgf21 plasma concentration. Glycolytic activity, as assessed by pklr1 mRNA expression and pyruvate kinase activity, was also found increased. In addition, it was shown that both short- and long-term ALA treatment increased cholesterol content, induced systemic triglyceridemia, and enhanced rxrα and lxrα mRNA expression. Despite the fact that short-term ALA intake reduced lipogenesis, as given by significant declines of fas and srebp1c mRNA expression, and that a long-term ALA intake induced a significant rise of these lipogenic genes, both treatment regimen caused fat accumulation. This, however, was more pronounced upon long-term ALA intake, leading to hepatic steatosis and liver injury, as indicated by increased inflammation and disruption of the general hepatic architecture. In summary, the prophylactic and abundant use of ALA under healthy conditions should be considered with caution.

Unliganded fibroblast growth factor receptor 1 forms density-independent dimers

Fibroblast growth factors receptors (FGFRs) are thought to initiate intracellular signaling cascades upon ligand-induced dimerization of the extracellular domain. Although the existence of unliganded FGFR1 dimers on the surface of living cells has been proposed, this notion remains rather controversial. Here, we employed time-resolved Förster resonance energy transfer combined with SNAP- and ACP-tag labeling in COS7 cells to monitor dimerization of full-length FGFR1 at the cell-surface with or without the coreceptor βKlotho. Using this approach we observed homodimerization of unliganded FGFR1 that is independent of its surface density. The homo-interaction signal observed for FGFR1 was indeed as robust as that obtained for epidermal growth factor receptor (EGFR) and was further increased by the addition of activating ligands or pathogenic mutations. Mutational analysis indicated that the kinase and the transmembrane domains, rather than the extracellular domain, mediate the ligand-independent FGFR1 dimerization. In addition, we observed a formation of a higher order ligand-independent complex by the c-spliced isoform of FGFR1 and βKlotho. Collectively, our approach provides novel insights into the assembly and dynamics of the full-length FGFRs on the cell surface.

Placental fibroblast growth factor 21 is not altered in late-onset preeclampsia

BACKGROUND

Preeclampsia (PE) is associated with alterations of placental function. The incidence of PE is higher in insulin resistant states. Women with PE have high circulating levels of the metabolic regulator fibroblast growth factor 21 (FGF21). FGF21 is synthesized in the placenta. The aim of this study was to compare the expression of FGF21, its receptors, downstream targets and transcriptional regulators in placental tissue from pregnancies with and without late-onset PE. Circulating FGF21 in maternal and cord blood was also studied.

METHODS

mRNA expression was determined by semi-quantitative real-time PCR and normalized for cellular composition in 17 women with and 20 without PE. Protein expression was quantified by Western Blot. FGF21 levels were measured by ELISA in maternal and cord serum of ten mother-baby dyads per condition.

RESULTS

Placental FGF21 mRNA and protein expression were similar in PE compared with control. Placental mRNA expression of the FGF receptors (1-4) and the co-receptor beta-Klotho was not different between the groups. There was no difference in the expression of the glucose transporters GLUT1, 3 or 4. PPAR-alpha but not PPAR-gamma expression was decreased in PE. Maternal FGF21 serum levels were not significantly different in PE. FGF21 was detected in cord blood of 6 infants (4 PE, 2 controls) but was undetectable in 14 infants.

CONCLUSIONS

Late-onset PE is not associated with major changes to the expression of FGF21, its receptors or metabolic targets.

Increased HO-1 levels ameliorate fatty liver development through a reduction of heme and recruitment of FGF21

OBJECTIVE

Obese leptin deficient (ob/ob) mice are a model of adiposity that displays increased levels of fat, glucose, and liver lipids. Our hypothesis is that HO-1 overexpression ameliorates fatty liver development.

METHODS

Obese mice were administered cobalt protoporphyrin (CoPP) and stannic mesoporphyrin (SnMP) for 6 weeks. Heme, HO-1, HO activity, PGC1α, FGF21, glycogen content, and lipogenesis were assessed.

RESULTS

CoPP administration increased hepatic HO-1 protein levels and HO activity, decreased hepatic heme, body weight gain, glucose levels, and resulted in decreased steatosis. Increased levels of HO-1 produced a decrease in lipid droplet size, Fatty acid synthase (FAS) levels involving recruitment of FGF21, PPARα, and Glut 1. These beneficial effects were reversed by inhibition of HO activity.

CONCLUSION

Increased levels of HO-1 and HO activity reduced the levels of obesity by reducing hepatic heme and lipid accumulation. These changes were manifested by decreases in cellular heme, increases in FGF21, glycogen content, and fatty liver. The beneficial effect of HO-1 induction results from an increase in PPARα and FGF21 levels and a decrease in PGC1α, levels they were reversed by SnMP. Low levels of HO-1 and HO activity are responsible for fatty liver.

Irisin and FGF21 are cold-induced endocrine activators of brown fat function in humans

Rediscovery of cold-activated brown adipose tissue (BAT) in humans has boosted research interest in identifying BAT activators for metabolic benefits. Of particular interest are cytokines capable of fat browning. Irisin, derived from FNDC5, is an exercise-induced myokine that drives brown-fat-like thermogenesis in murine white fat. Here we explored whether cold exposure is an afferent signal for irisin secretion in humans and compared it with FGF21, a brown adipokine in rodents. Cold exposure increased circulating irisin and FGF21. We found an induction of irisin secretion proportional to shivering intensity, in magnitude similar to exercise-stimulated secretion. FNDC5 and/or FGF21 treatment upregulated human adipocyte brown fat gene/protein expression and thermogenesis in a depot-specific manner. These results suggest exercise-induced irisin secretion could have evolved from shivering-related muscle contraction, serving to augment brown fat thermogenesis in concert with FGF21. Irisin-mediated muscle-adipose crosstalk may represent a thermogenic, cold-activated endocrine axis that is exploitable in obesity therapeutics development.

Fibroblast growth factor 21 (FGF21) and bone: is there a relationship in humans?

In animals, high fibroblast growth factor 21 (FGF21) states improve insulin resistance but induce bone loss. Whether FGF21 relates to bone mineral density (BMD) is unknown in humans. Contrary to prediction from animal findings, we found higher FGF21 levels associating with greater BMD in women, independent of age and body composition.

INTRODUCTION

Recent laboratory studies suggest that FGF21 is involved in reciprocal regulation of bone and energy homeostasis. Systemic administration of FGF21 protects animals from obesity and diabetes but causes severe bone loss, smothering the enthusiasm over FGF21 as a potential antiobesity therapeutic. To date, there is no information on whether FGF21 relates to BMD in humans. We thus studied the relationship between plasma FGF21 levels and BMD in healthy adults.

METHODS

Fasting plasma FGF21 levels were measured by enzyme-linked immunosorbent assay and body composition by dual-energy X-ray absorptiometry.

RESULTS

Among 40 healthy volunteers (age 32 ± 10 year, 16 women), men had significantly higher lean body mass (p < 0.01) and total BMD (p < 0.05), and lower percent body fat than women (p < 0.01). Median plasma FGF21 levels were not different between the sexes. While there was no association between FGF21 concentrations and body composition in men, FGF21 levels correlated positively with fat mass (p < 0.01) in women. In men, no significant correlation between FGF21 with BMD was observed. However, in women, FGF21 correlated positively with total BMD (R (2) = 0.69, p = 0.003) and spine BMD (R (2) = 0.76, p = 0.001); the correlation remained significant after adjusting for age, ethnicity, and body composition.

CONCLUSIONS

This study reveals for the first time a strong positive association between plasma FGF21 levels and BMD in healthy women, suggesting the association between bone loss and high FGF21 states in animals may not be directly translated to humans in physiologic states. We hypothesize that FGF21 may increase bone mass particularly in women through paracrine mechanisms in the bone-adipose interface.

Endocrine fibroblast growth factors 15/19 and 21: from feast to famine

We review the physiology and pharmacology of two atypical fibroblast growth factors (FGFs)-FGF15/19 and FGF21-that can function as hormones. Both FGF15/19 and FGF21 act on multiple tissues to coordinate carbohydrate and lipid metabolism in response to nutritional status. Whereas FGF15/19 is secreted from the small intestine in response to feeding and has insulin-like actions, FGF21 is secreted from the liver in response to extended fasting and has glucagon-like effects. FGF21 also acts in an autocrine fashion in several tissues, including adipose. The pharmacological actions of FGF15/19 and FGF21 make them attractive drug candidates for treating metabolic disease.

Exenatide decreases hepatic fibroblast growth factor 21 resistance in non-alcoholic fatty liver disease in a mouse model of obesity and in a randomised controlled trial

AIMS/HYPOTHESIS

Systemic fibroblast growth factor (FGF)21 levels and hepatic FGF21 production are increased in non-alcoholic fatty liver disease patients, suggesting FGF21 resistance. We examined the effects of exenatide on FGF21 in patients with type 2 diabetes and in a diet-induced mouse model of obesity (DIO).

METHODS

Type 2 diabetes mellitus patients (n = 24) on diet and/or metformin were randomised (using a table of random numbers) to receive additional treatment consisting of pioglitazone 45 mg/day or combined therapy with pioglitazone (45 mg/day) and exenatide (10 μg twice daily) for 12 months in an open label parallel study at the Baylor Clinic.

RESULTS

Twenty-one patients completed the entire study and were included in the analysis. Pioglitazone treatment (n = 10) reduced hepatic fat as assessed by magnetic resonance spectroscopy, despite a significant increase in body weight (Δ = 3.7 kg); plasma FGF21 levels did not change (1.9  ±  0.6 to 2.2  ±  0.6 ng/ml [mean ± SEM]). However, combined pioglitazone and exenatide therapy (n = 11) was associated with a significant reduction of FGF21 levels (2.3  ±  0.5 to 1.1  ±  0.3 ng/ml) and a greater decrease in hepatic fat. Besides weight gain observed in the pioglitazone-treated patients, lower extremity oedema was observed as a side effect in two of the ten patients. Three patients who received pioglitazone and exenatide combination therapy complained of significant nausea that was self-limiting and did not require them to leave the study. In DIO mice, exendin-4 for 4 weeks significantly reduced hepatic triacylglycerol content, decreased hepatic FGF21 protein and mRNA, and enhanced phosphorylation of hepatic AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase, although no significant difference in weight and body fat was observed. Hepatic FGF21 correlated inversely with hepatic AMPK phosphorylation

CONCLUSIONS/INTERPRETATION

In type 2 diabetes mellitus, combined pioglitazone and exenatide therapy is associated with a reduction in plasma FGF21 levels, as well as a greater decrease in hepatic fat than that achieved with pioglitazone therapy. In DIO mice, exendin-4 treatment reduces hepatic triacylglycerol and FGF21 protein, and enhances hepatic AMPK phosphorylation, suggesting an improvement of hepatic FGF21 resistance.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov NCT 01432405.

A high-fat, ketogenic diet causes hepatic insulin resistance in mice, despite increasing energy expenditure and preventing weight gain

Low-carbohydrate, high-fat ketogenic diets (KD) have been suggested to be more effective in promoting weight loss than conventional caloric restriction, whereas their effect on hepatic glucose and lipid metabolism and the mechanisms by which they may promote weight loss remain controversial. The aim of this study was to explore the role of KD on liver and muscle insulin sensitivity, hepatic lipid metabolism, energy expenditure, and food intake. Using hyperinsulinemic-euglycemic clamps, we studied insulin action in mice fed a KD or regular chow (RC). Body composition was assessed by ¹H magnetic resonance spectroscopy. Despite being 15% lighter (P < 0.001) than RC-fed mice because of a 17% increase in energy expenditure (P < 0.001), KD-fed mice manifested severe hepatic insulin resistance, as reflected by decreased suppression (0% vs. 100% in RC-fed mice, P < 0.01) of endogenous glucose production during the clamp. Hepatic insulin resistance could be attributed to a 350% increase in hepatic diacylglycerol content (P < 0.001), resulting in increased activation of PKCε (P < 0.05) and decreased insulin receptor substrate-2 tyrosine phosphorylation (P < 0.01). Food intake was 56% (P < 0.001) lower in KD-fed mice, despite similar caloric intake, and could partly be attributed to a more than threefold increase (P < 0.05) in plasma N-acylphosphatidylethanolamine concentrations. In conclusion, despite preventing weight gain in mice, KD induces hepatic insulin resistance secondary to increased hepatic diacylglycerol content. Given the key role of nonalcoholic fatty liver disease in the development of type 2 diabetes and the widespread use of KD for the treatment of obesity, these results may have potentially important clinical implications.

Separating mitogenic and metabolic activities of fibroblast growth factor 19 (FGF19)

FGF19 and FGF21 are distinctive members of the FGF family that function as endocrine hormones. Their potent effects on normalizing glucose, lipid, and energy homeostasis in disease models have made them an interesting focus of research for combating the growing epidemics of diabetes and obesity. Despite overlapping functions, FGF19 and FGF21 have many discrete effects, the most important being that FGF19 has both metabolic and proliferative effects, whereas FGF21 has only metabolic effects. Here we identify the structural determinants dictating differential receptor interactions that explain and distinguish these two physiological functions. We also have generated FGF19 variants that have lost the ability to induce hepatocyte proliferation but that still are effective in lowering plasma glucose levels and improving insulin sensitivity in mice. Our results add valuable insight into the structure-function relationship of FGF19/FGF21 and identify the structural basis underpinning the distinct proliferative feature of FGF19 compared with FGF21. In addition, these studies provide a road map for engineering FGF19 as a potential therapeutic candidate for treating diabetes and obesity.

Increased fibroblast growth factor 21 in obesity and nonalcoholic fatty liver disease

BACKGROUND & AIMS

Fibroblast growth factor 21 (FGF21) is an hepatic protein that plays a critical role in metabolism, stimulating fatty acid oxidation in liver and glucose uptake in fat. Systemic administration to obese rodents and diabetic monkeys leads to improved glucose homeostasis and weight loss. In rodents, FGF21 increases with fasting and consumption of a ketogenic diet (KD). In humans, FGF21 correlates with body mass index (BMI), but studies evaluating other parameters show inconsistent results. We examined FGF21 serum levels in lean and obese individuals and in response to dietary manipulation. We also evaluated FGF21 serum levels and liver messenger RNA (mRNA) expression in nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH).

METHODS

Serum FGF21 was measured after an overnight fast in individuals with BMI ranging from normal to obese. Volunteers fasted for 16 or 72 hours and then ate a standard meal. Another group consumed KD for 12 days. Serum FGF21 and hepatic mRNA expression were measured in obese individuals with NAFLD or NASH.

RESULTS

There was a positive correlation between BMI and FGF21. There was no change in FGF21 in response to a short fast or KD. A nonstatistically significant fall in FGF21 levels was seen after a 72-hour fast. Hepatic FGF21 mRNA expression was significantly elevated in NAFLD, which correlated with a substantial increase in serum FGF21. In NASH, serum FGF21 but not liver mRNA was increased.

CONCLUSIONS

FGF21 correlates with BMI and may be a novel biomarker for NAFLD, but is not nutritionally regulated in humans.

The fasting polypeptide FGF21 can enter brain from blood

FGF21 recently has been proposed as a missing link in the biology of fasting, raising the question of whether it directly reaches the brain. We used multiple time-regression analysis to quantify the influx rate of this polypeptide across the blood-brain barrier (BBB), size-exclusion chromatography to examine degradation, capillary depletion to differentiate entry into brain parenchyma from retention in the microvasculature, and measurement of efflux rate to determine a possible confounding effect on measurement of entry. FGF21 was 94% intact in serum and 75% in brain 10 min after intravenous bolus delivery. Its influx rate was 0.23+/-0.12 microl/g-min, nearly four times faster than that of the vascular marker albumin. At 10 min, about 0.5% of the administered FGF21 was present in a gram of brain tissue. Of this, 70% reached the parenchyma of the brain. Co-injection of excess FGF21 failed to inhibit the influx, showing a lack of saturation. Efflux, which occurred at the same rate as the bulk reabsorption of cerebrospinal fluid, also was not saturable. In summary, FGF21 shows significant, non-saturable, unidirectional influx across the BBB.