FGF21 as a Therapeutic Reagent

Structural basis for FGF hormone signalling

α/βKlotho coreceptors simultaneously engage fibroblast growth factor (FGF) hormones (FGF19, FGF21 and FGF23)^1,2 and their cognate cell-surface FGF receptors (FGFR1-4) thereby stabilizing the endocrine FGF-FGFR complex^3-6. However, these hormones still require heparan sulfate (HS) proteoglycan as an additional coreceptor to induce FGFR dimerization/activation and hence elicit their essential metabolic activities⁶. To reveal the molecular mechanism underpinning the coreceptor role of HS, we solved cryo-electron microscopy structures of three distinct 1:2:1:1 FGF23-FGFR-αKlotho-HS quaternary complexes featuring the 'c' splice isoforms of FGFR1 (FGFR1c), FGFR3 (FGFR3c) or FGFR4 as the receptor component. These structures, supported by cell-based receptor complementation and heterodimerization experiments, reveal that a single HS chain enables FGF23 and its primary FGFR within a 1:1:1 FGF23-FGFR-αKlotho ternary complex to jointly recruit a lone secondary FGFR molecule leading to asymmetric receptor dimerization and activation. However, αKlotho does not directly participate in recruiting the secondary receptor/dimerization. We also show that the asymmetric mode of receptor dimerization is applicable to paracrine FGFs that signal solely in an HS-dependent fashion. Our structural and biochemical data overturn the current symmetric FGFR dimerization paradigm and provide blueprints for rational discovery of modulators of FGF signalling² as therapeutics for human metabolic diseases and cancer.

Glucagon receptor signaling regulates weight loss via central KLB receptor complexes

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

Incendiary Leptin

Leptin is a hormone released by adipose tissue that plays a key role in the control of energy homeostasis through its binding to leptin receptors (LepR), mainly expressed in the hypothalamus. Most scientific evidence points to leptin’s satiating effect being due to its dual capacity to promote the expression of anorexigenic neuropeptides and to reduce orexigenic expression in the hypothalamus. However, it has also been demonstrated that leptin can stimulate (i) thermogenesis in brown adipose tissue (BAT) and (ii) the browning of white adipose tissue (WAT). Since the demonstration of the importance of BAT in humans 10 years ago, its study has aroused great interest, mainly in the improvement of obesity-associated metabolic disorders through the induction of thermogenesis. Consequently, several strategies targeting BAT activation (mainly in rodent models) have demonstrated great potential to improve hyperlipidemias, hepatic steatosis, insulin resistance and weight gain, leading to an overall healthier metabolic profile. Here, we review the potential therapeutic ability of leptin to correct obesity and other metabolic disorders, not only through its satiating effect, but by also utilizing its thermogenic properties.

Berberine stimulates fibroblast growth factor 21 by modulating the molecular clock component brain and muscle Arnt-like 1 in brown adipose tissue

Fibroblast growth factor 21 (FGF21), a member of the FGF subfamily that acts through the FGF receptor 1 with the co-receptor β-Klotho, functions as an important metabolic regulator of peripheral glucose tolerance and lipid homeostasis in an endocrine or autocrine and/or paracrine manner. Previous studies showed that FGF21 ameliorated and prevented the development of metabolic disorders, such as obesity and diabetes mellitus. In the present study, we demonstrated that berberine, a naturally occurring compound, stimulated FGF21 expression in brown adipose tissue (BAT). Furthermore, the up-regulated expression of FGF21 in brown adipocytes in response to berberine was due, at least in part, to the activation of the AMP-activated protein kinase pathway. We also found that berberine reversed high-fat diet-induced obesity concomitant with its regulation of the expression of Fgf21 and the core clock component brain and muscle Arnt-like 1 (Bmal1) in BAT. Berberine significantly up-regulated the gene expression and production of FGF21 in a dose-dependent manner in C3H10T1/2 brown adipocytes. Furthermore, the knockdown of Bmal1 prevented the up-regulated expression of FGF21 in response to berberine in C3H10T1/2 brown adipocytes, suggesting that Bmal1 links the regulatory mechanisms of FGF21 in response to berberine. The present results suggest that berberine stimulates the expression of FGF21 by modulating molecular clock Bmal1 in BAT, which may, in turn, attenuate diet-induced obesity. They also indicate the potential of berberine as a therapeutic agent for obesity and obesity-associated metabolic disorders related to circadian misalignments.

Plasma fibroblast growth factor 21 levels increase with ectopic fat accumulation and its receptor levels are decreased in the visceral fat of patients with type 2 diabetes

BACKGROUND

Fibroblast growth factor 21 (FGF21) is a novel metabolic regulator that has beneficial effects on glucose and lipid metabolism. However, plasma FGF21 levels are paradoxically increased in type 2 diabetes mellitus (T2DM) and obesity, suggesting resistance to this ligand. FGF21 acts mainly on adipose tissue and ectopic fat accumulation is a typical feature in metabolic deterioration such as diabetes, metabolic syndrome, and cardiovascular disease.

OBJECTIVE

To investigate the relationship between FGF21 resistance and ectopic fat accumulation.

RESEARCH DESIGN AND METHODS

Subjects who underwent 64-slice multidetector CT (MDCT) were enrolled (n=190). Plasma FGF21 levels and MDCT data of ectopic fats at various sites were analyzed. Human visceral and subcutaneous fat tissues from abdominal and coronary artery bypass surgery were obtained. FGF21 receptor expression and postreceptor signaling in different fat deposits of both control and T2DM subjects were analyzed.

RESULTS

Plasma FGF21 levels were significantly associated with body mass index, triglyceride, homeostatic model assessment of insulin resistance, and Matsuda index. Plasma FGF21 levels were significantly higher in patients with T2DM than in the pre-diabetes and normal glucose tolerance groups. The ectopic fat phenotypes (visceral, epicardial, intrahepatic, and intramuscular fat) of T2DM were significantly higher than controls. Plasma FGF21 levels were elevated and exhibited a strong positive correlation with ectopic fat accumulation in T2DM. The expression of genes comprising the FGF21 signaling pathway was also lower in visceral fat than in subcutaneous fat in this disease.

CONCLUSIONS

Human FGF21 resistance in T2DM could result from increases in FGF21-resistant ectopic fat accumulation. Our study provides novel clinical evidence linking FGF21 resistance and T2DM pathogenesis.

Role of fibroblast growth factor 21 in gestational diabetes mellitus: A mini-review

Gestational diabetes mellitus (GDM) is defined as glucose intolerance with onset or first diagnosis during pregnancy, but not to the level of being diagnostic for diabetes in a nonpregnant adult. In GDM, whole-body insulin-dependent glucose disposal decreases by 40%-60% which necessitates a 200%-250% increase in insulin secretion to maintain normoglycaemia. GDM develops when a pregnant woman does not produce sufficient insulin to compensate for the reduced glucose disposal. Fibroblast growth factor 21 (FGF21) is a hormone that is expressed predominantly in the liver, but also in other metabolically active tissues such as pancreas, skeletal muscle and adipose tissue. In animals, FGF21 lowers blood glucose levels and inhibits glucagon secretion. In humans, circulating FGF21 levels are increased in insulin-resistant morbidities such as obesity and type 2 diabetes mellitus (T2DM). An elevated FGF21 level is also an independent predictor of T2DM. GDM and T2DM are proposed to have similar underlying pathophysiologies, raising the question of whether a similar relationship exists between FGF21 and GDM as it does with T2DM. There are a limited number of studies investigating FGF21 levels in patients with GDM. Moreover, recent clinical trials investigating the therapeutic potential of FGF21 have highlighted a major gap in our understanding of the biology of FGF21. This review evaluates what is currently known about FGF21 and GDM and highlights important gaps that warrant further research.

Hepatic Sel1L-Hrd1 ER-associated degradation (ERAD) manages FGF21 levels and systemic metabolism via CREBH

Fibroblast growth factor 21 (Fgf21) is a liver-derived, fasting-induced hormone with broad effects on growth, nutrient metabolism, and insulin sensitivity. Here, we report the discovery of a novel mechanism regulating Fgf21 expression under growth and fasting-feeding. The Sel1L-Hrd1 complex is the most conserved branch of mammalian endoplasmic reticulum (ER)-associated degradation (ERAD) machinery. Mice with liver-specific deletion of Sel1L exhibit growth retardation with markedly elevated circulating Fgf21, reaching levels close to those in Fgf21 transgenic mice or pharmacological models. Mechanistically, we show that the Sel1L-Hrd1 ERAD complex controls Fgf21 transcription by regulating the ubiquitination and turnover (and thus nuclear abundance) of ER-resident transcription factor Crebh, while having no effect on the other well-known Fgf21 transcription factor Pparα. Our data reveal a physiologically regulated, inverse correlation between Sel1L-Hrd1 ERAD and Crebh-Fgf21 levels under fasting-feeding and growth. This study not only establishes the importance of Sel1L-Hrd1 ERAD in the liver in the regulation of systemic energy metabolism, but also reveals a novel hepatic "ERAD-Crebh-Fgf21" axis directly linking ER protein turnover to gene transcription and systemic metabolic regulation.

HDAC3 inhibition in diabetic mice may activate Nrf2 preventing diabetes-induced liver damage and FGF21 synthesis and secretion leading to aortic protection

Vascular complications are common pathologies associated with type 1 diabetes. In recent years, histone deacetylation enzyme (HDAC) inhibitors have been shown to be successful in preventing atherosclerosis. To investigate the mechanism for HDAC3 inhibition in preventing diabetic aortic pathologies, male OVE26 type 1 diabetic mice and age-matched wild-type (FVB) mice were given the HDAC3-specific inhibitor RGFP-966 or vehicle for 3 mo. These mice were then euthanized immediately or maintained for an additional 3 mo without treatment. Levels of aortic inflammation and fibrosis and plasma and fibroblast growth factor 21 (FGF21) levels were determined. Because the liver is the major organ for FGF21 synthesis in diabetic animals, the effects of HDAC3 inhibition on hepatic FGF21 synthesis were examined. Additionally, hepatic miR-200a and kelch-like ECH-associated protein 1 (Keap1) expression and nuclear factor erythroid 2-related factor 2 (Nrf2) nuclear translocation were measured. HDAC3 inhibition significantly reduced aortic fibrosis and inflammation in OVE26 mice at both 3 and 6 mo. Plasma FGF21 levels were significantly higher in RGFP-966-treated OVE26 mice compared with vehicle-treated mice at both time points. It also significantly reduced hepatic pathologies associated with diabetes, accompanied by increased FGF21 mRNA and protein expression. HDAC3 inhibition also increased miR-200a expression, reduced Keap1 protein levels, and increased Nrf2 nuclear translocation with an upregulation of antioxidant gene and FGF21 transcription. Our results support a model where HDAC3 inhibition may promote Nrf2 activity by increasing miR-200a expression with a concomitant decrease in Keap1 to preserve hepatic FGF21 synthesis. The preservation of hepatic FGF21 synthesis ultimately leads to a reduction in diabetes-induced aorta pathologies.

A systematic dissection of sequence elements determining β-Klotho and FGF interaction and signaling

Endocrine fibroblast growth factors (FGFs) require Klotho transmembrane proteins as necessary co-receptors to activate FGF receptor (FGFR) signaling. In particular, FGF19 and FGF21 function through β-Klotho to regulate glucose and lipid metabolism. Recent research has focused on elucidating how these two FGFs interact with β-Klotho and FGFRs to activate downstream signaling. In this study, using hydrogen deuterium exchange coupled to mass spectrometry (HDX-MS), we identified regions on the β-Klotho protein that likely participate in ligand interaction, and vice versa. Alanine and arginine mutagenesis were carried out to further probe the contributions of individual residues to receptor/ligand interactions. Using biochemical and cell-based signaling assays with full-length proteins, we show that both the KL1 and KL2 domains of β-Klotho participate in ligand interaction, and these binding sites on β-Klotho are shared by FGF19 and FGF21. In addition, we show that two highly conserved regions in the C-terminal tail of FGF19 and FGF21 are responsible for interaction with the co-receptor. Our results are consistent with recent publications on the crystal structures of the Klotho proteins and provide insight into how endocrine FGFs interact with co-receptors for signal transduction.

Treatment of CIA Mice with FGF21 Down-regulates TH17-IL-17 Axis

Recently, FGF21 was reported to play an important role in anti-inflammation. The aim of the study is to explore the mechanism for FGF21 alleviating inflammation of CIA. CIA mice were injected with FGF21 once a day for 28 days after first booster immunization. The results showed that FGF21 alleviates arthritis severity and decreases serum anti-CII antibodies levels in CIA mice. Compared with CIA model, the number of the splenic TH17 cells was significantly decreased in FGF21-treated mice. FGF21 treatment reduced the mRNA expression of IL-17, TNF-α, IL-1β, IL-6, IL-8, and MMP3 and increased level of IL-10 in the spleen tissue. The expression of STAT3 and phosphorylated STAT3 was suppressed in FGF21-treated group. The mRNA expression of RORγt and IL-23 also decreased. In conclusion, these findings suggest that the beneficial effects of FGF21 on CIA mice were achieved by down-regulating Th17-IL-17 axis through STAT3/RORγt pathway. Modulating of Th17-mediated inflammatory response may be one of the mechanisms for FGF21 attenuating inflammation in CIA.

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 deletion aggravates diabetes-induced pathogenic changes in the aorta in type 1 diabetic mice

Fibroblast growth factor 21 (FGF21) is an important regulator in glucose and lipid metabolism, and has been considered as a potential therapy for diabetes. The effect of FGF21 on the development and progression of diabetes-induced pathogenic changes in the aorta has not currently been addressed. To characterize these effects, type 1 diabetes was induced in both FGF21 knockout (FGF21KO) and C57BL/6 J wild type (WT) mice via multiple-dose streptozotocin injection. FGF21KO diabetic mice showed both earlier and more severe aortic remodeling indicated by aortic thickening, collagen accumulation and fibrotic mediator connective tissue growth factor expression. This was accompanied by significant aortic cell apoptosis than in WT diabetic mice. Further investigation found that FGF21 deletion exacerbated aortic inflammation and oxidative stress reflected by elevated expression of tumor necrosis factor α and transforming growth factor β, and the accumulation of 3-nitrotyrocine and 4-Hydroxynonenal. FGF21 administration can reverse the pathologic changes in FGF21KO diabetic mice. These findings demonstrate that FGF21 deletion aggravates aortic remodeling and cell death probably via exacerbation of aortic inflammation and oxidative stress. This marks FGF21 as a potential therapy for the treatment of aortic damage due to diabetes.

FGF21 deletion exacerbates diabetic cardiomyopathy by aggravating cardiac lipid accumulation

Fibroblast growth factor 21 (FGF21) plays an important role in energy homoeostasis. The unaddressed question of FGF21’s effect on the development and progression of diabetic cardiomyopathy (DCM) is investigated here with FGF21 knockout (FGF21KO) diabetic mice. Type 1 diabetes was induced in both FGF21KO and C57BL/6J wild-type (WT) mice via streptozotocin. At 1, 2 and 4 months after diabetes onset, the plasma FGF21 levels were significantly decreased in WT diabetic mice compared to controls. There was no significant difference between FGF21KO and WT diabetic mice in blood glucose and triglyceride levels. FGF21KO diabetic mice showed earlier and more severe cardiac dysfunction, remodelling and oxidative stress, as well as greater increase in cardiac lipid accumulation than WT diabetic mice. Western blots showed that increased cardiac lipid accumulation was accompanied by further increases in the expression of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and its target protein CD36, along with decreases in the phosphorylation of AMP-activated protein kinase and the expression of hexokinase II and peroxisome proliferator-activated receptor gamma co-activator 1α in the heart of FGF21KO diabetic mice compared to WT diabetic mice. Our results demonstrate that FGF21 deletion-aggravated cardiac lipid accumulation is likely mediated by cardiac Nrf2-driven CD36 up-regulation, which may contribute to the increased cardiac oxidative stress and remodelling, and the eventual development of DCM. These findings suggest that FGF21 may be a therapeutic target for the treatment of DCM.

The brain and brown fat

Brown adipose tissue (BAT) is a specialized organ responsible for thermogenesis, a process required for maintaining body temperature. BAT is regulated by the sympathetic nervous system (SNS), which activates lipolysis and mitochondrial uncoupling in brown adipocytes. For many years, BAT was considered to be important only in small mammals and newborn humans, but recent data have shown that BAT is also functional in adult humans. On the basis of this evidence, extensive research has been focused on BAT function, where new molecules, such as irisin and bone morphogenetic proteins, particularly BMP7 and BMP8B, as well as novel central factors and new regulatory mechanisms, such as orexins and the canonical ventomedial nucleus of the hypothalamus (VMH) AMP- activated protein kinase (AMPK)-SNS-BAT axis, have been discovered and emerged as potential drug targets to combat obesity. In this review we provide an overview of the complex central regulation of BAT and how different neuronal cell populations co-ordinately work to maintain energy homeostasis.

Fibroblast growth factor 21 expressions in white blood cells and sera of patients with gestational diabetes mellitus during gestation and postpartum

Fibroblast growth factor 21 (FGF21), a recently discovered regulatory factor, plays an important role in glucose and lipid metabolism. In this study, we firstly found the FGF21 expression in white blood cells (WBCs). Then, we enrolled 51 women with gestational diabetes mellitus (GDM) and 50 pregnant women with normal blood glucose levels to determine the FGF21 levels in the WBCs and the sera at the 28th week of pregnancy, and tracked the dynamic changes of FGF21 in these women until the 7th day postpartum. Repeated Measures analysis of variance (ANOVA) revealed that there was a significant interaction effect between group and time on FGF21 levels (P < 0.05). FGF21 levels were significantly higher in the GDM patients than those in the controls at the 28th week of pregnancy. The 7th day after the delivery, the FGF21 levels decreased in the WBCs and the sera in both groups. The D values (the difference between pregnancy and postpartum) for FGF21 levels were significantly higher in the GDM group (P < 0.05). Serum FGF21 level during gestation positively correlated with leptin, triglyceride, and HDL-cholesterol, and FGF21 may act as a glucose and lipid metabolism compensatory regulatory factor to improve glucose and lipid metabolism during the period of pregnancy. Further, FGF21 level in the WBCs (during pregnancy and the D values for FGF21) was chiefly influenced by GDM.

Circulating FGF21 is liver derived and enhances glucose uptake during refeeding and overfeeding

Fibroblast growth factor (FGF)21 is an endocrine hormone that is expressed in multiple tissues and functions physiologically to maintain energy homeostasis. FGF21 is being pursued as a therapeutic target for diabetes and obesity because of its rapid and potent effects on improving insulin sensitivity. However, whether FGF21 enhances insulin sensitivity under physiologic conditions remains unclear. Here, we show that liver-derived FGF21 enters the circulation during fasting but also remains present and functional during the early stage of refeeding. After a prolonged fast, FGF21 acts as an insulin sensitizer to overcome the peripheral insulin resistance induced by fasting, thereby maximizing glucose uptake. Likewise, FGF21 is produced from the liver during overfeeding and mitigates peripheral insulin resistance. DIO FGF21 liver-specific knockout, but not FGF21 adipose-specific knockout, mice have increased insulin resistance and decreased brown adipose tissue-mediated glucose disposal. These data are compatible with the concept that FGF21 functions physiologically as an insulin sensitizer under conditions of acute refeeding and overfeeding.

Fibroblast growth factor receptor 4 (FGFR4) deficiency improves insulin resistance and glucose metabolism under diet-induced obesity conditions

The role of fibroblast growth factor receptor 4 (FGFR4) in regulating bile acid synthesis has been well defined; however, its reported role on glucose and energy metabolism remains unresolved. Here, we show that FGFR4 deficiency in mice leads to improvement in glucose metabolism, insulin sensitivity, and reduction in body weight under high fat conditions. Mechanism of action studies in FGFR4-deficient mice suggest that the effects are mediated in part by increased plasma levels of adiponectin and the endocrine FGF factors FGF21 and FGF15, the latter of which increase in response to an elevated bile acid pool. Direct actions of increased bile acids on bile acid receptors, and other potential indirect mechanisms, may also contribute to the observed metabolic changes. The results described herein suggest that FGFR4 antagonists alone, or in combination with other agents, could serve as a novel treatment for diabetes.

Exendin-4 regulates lipid metabolism and fibroblast growth factor 21 in hepatic steatosis

OBJECTIVE

Hepatokine fibroblast growth factor (FGF) 21 takes part in the regulation of lipid metabolism in the liver and adipose tissue. We investigated whether exendin-4 regulates the expression of FGF21 in the liver, and whether the effects of exendin-4 on the regulation of FGF21 expression are mediated via silent mating type information regulation 2 homolog (SIRT) 1 or SIRT6.

MATERIALS/METHODS

The C57BL/6J mice were fed a low fat diet, high fat diet, or high fat diet with 1 nmol/kg/day exendin-4 intraperitoneal injection for 10 weeks. HepG2 used in vitro study was treated with palmitic aicd (0.4 mM) with or without exendin-4 (100 nM) and FGF21 (50 nM) for 24 hours. The change of FGF21 and its receptors expression by exendin-4 were measured using quantitative real-time RT-PCR and Western blot. The intracellular lipid content in HepG2 cells was evaluated by Oil Red O staining. Inhibition of FGF21, SIRT1 and SIRT6, by 10 nM siRNA was performed to establish the signaling pathway of exendin-4 action in hepatic lipid metabolism.

RESULTS

Exendin-4 increased the expression of FGF21 and its receptors in high fat diet-induced obese mice. In addition, recombinant FGF21 treatment reduced lipid content in palmitic acid-treated HepG2 cells. We also observed significantly decreased expression of peroxisomal proliferator-activated receptor (PPAR) α and medium-chain acyl-coenzyme A dehydrogenase (MCAD) in hepatocytes transfected with FGF21 siRNA. In cells treated with exendin-4, inhibition of SIRT1, but not SIRT6, by siRNA significantly repressed the expression of FGF21 mRNA, whereas decreased SIRT1 expression by inhibition of FGF21 was not observed.

CONCLUSIONS

These data suggest that exendin-4 could improve fatty liver by increasing SIRT1-mediated FGF21.

Perinatal exposure of mice to the pesticide DDT impairs energy expenditure and metabolism in adult female offspring

Dichlorodiphenyltrichloroethane (DDT) has been used extensively to control malaria, typhus, body lice and bubonic plague worldwide, until countries began restricting its use in the 1970s. Its use in malaria control continues in some countries according to recommendation by the World Health Organization. Individuals exposed to elevated levels of DDT and its metabolite dichlorodiphenyldichloroethylene (DDE) have an increased prevalence of diabetes and insulin resistance. Here we hypothesize that perinatal exposure to DDT disrupts metabolic programming leading to impaired metabolism in adult offspring. To test this, we administered DDT to C57BL/6J mice from gestational day 11.5 to postnatal day 5 and studied their metabolic phenotype at several ages up to nine months. Perinatal DDT exposure reduced core body temperature, impaired cold tolerance, decreased energy expenditure, and produced a transient early-life increase in body fat in female offspring. When challenged with a high fat diet for 12 weeks in adulthood, female offspring perinatally exposed to DDT developed glucose intolerance, hyperinsulinemia, dyslipidemia, and altered bile acid metabolism. Perinatal DDT exposure combined with high fat feeding in adulthood further impaired thermogenesis as evidenced by reductions in core temperature and in the expression of numerous RNA that promote thermogenesis and substrate utilization in the brown adipose tissue of adult female mice. These observations suggest that perinatal DDT exposure impairs thermogenesis and the metabolism of carbohydrates and lipids which may increase susceptibility to the metabolic syndrome in adult female offspring.

The nonhuman primate as a model for type 2 diabetes

PURPOSE OF THE REVIEW

Although rodent models provide insight into the mechanisms underlying type 2 diabetes mellitus (T2DM), they are limited in their translatability to humans. The nonhuman primate (NHP) shares important metabolic similarities with the human, making it an ideal model for the investigation of type 2 diabetes and use in preclinical trials. This review highlights the key contributions in the field over the last year using the NHP model.

RECENT FINDINGS

The NHP has not only provided novel insight into the normal and pathological processes that occur within the islet, but has also allowed for the preclinical testing of novel pharmaceutical targets for obesity and T2DM. Particularly, administration of fibroblast growth factor-21 in the NHP resulted in weight loss and improvements in metabolic health, supporting rodent studies and recent clinical trials. In addition, the NHP was used to demonstrate that a novel melanocortin-4 receptor agonist did not cause adverse cardiovascular effects. Finally, this model has been used to provide evidence that glucagon-like peptide-1-based therapies do not induce pancreatitis in the healthy NHP.

SUMMARY

The insight gained from studies using the NHP model has allowed for a better understanding of the processes driving T2DM and has promoted the development of well tolerated and effective treatments.

Tissue-selective estrogen complexes with bazedoxifene prevent metabolic dysfunction in female mice

Pairing the selective estrogen receptor modulator bazedoxifene (BZA) with estrogen as a tissue-selective estrogen complex (TSEC) is a novel menopausal therapy. We investigated estrogen, BZA and TSEC effects in preventing diabetisity in ovariectomized mice during high-fat feeding. Estrogen, BZA or TSEC prevented fat accumulation in adipose tissue, liver and skeletal muscle, and improved insulin resistance and glucose intolerance without stimulating uterine growth. Estrogen, BZA and TSEC improved energy homeostasis by increasing lipid oxidation and energy expenditure, and promoted insulin action by enhancing insulin-stimulated glucose disposal and suppressing hepatic glucose production. While estrogen improved metabolic homeostasis, at least partially, by increasing hepatic production of FGF21, BZA increased hepatic expression of Sirtuin1, PPARα and AMPK activity. The metabolic benefits of BZA were lost in estrogen receptor-α deficient mice. Thus, BZA alone or in TSEC produces metabolic signals of fasting and caloric restriction and improves energy and glucose homeostasis in female mice.

Artemisia scoparia extract attenuates non-alcoholic fatty liver disease in diet-induced obesity mice by enhancing hepatic insulin and AMPK signaling independently of FGF21 pathway

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) is a common liver disease which has no standard treatment. In this regard, we sought to evaluate the effects of extracts of Artemisia santolinaefolia (SANT) and Artemisia scoparia (SCO) on hepatic lipid deposition and cellular signaling in a diet-induced obesity (DIO) animal model.

MATERIALS/METHODS

DIO C57/B6J mice were randomly divided into three groups, i.e. HFD, SANT and SCO. Both extracts were incorporated into HFD at a concentration of 0.5% (w/w). Fasting plasma glucose, insulin, adiponectin, and FGF21 concentrations were measured.

RESULTS

At the end of the 4-week intervention, liver tissues were collected for analysis of insulin, AMPK, and FGF21 signaling. SANT and SCO supplementation significantly increased plasma adiponectin levels when compared with the HFD mice (P<0.001). Fasting insulin levels were significantly lower in the SCO than HFD mice, but not in SANT group. Hepatic H&E staining showed fewer lipid droplets in the SCO group than in the other two groups. Cellular signaling data demonstrated that SCO significantly increased liver IRS-2 content, phosphorylation of IRS-1, IR β, Akt1 and Akt2, AMPK α1 and AMPK activity and significantly reduced PTP 1B abundance when compared with the HFD group. SCO also significantly decreased fatty acid synthase (FAS), HMG-CoA Reductase (HMGR), and Sterol regulatory element-binding protein 1c (SREBP1c), but not Carnitine palmitoyltransferase I (CPT-1) when compared with HFD group. Neither SANT nor SCO significantly altered plasma FGF21 concentrations and liver FGF21 signaling.

CONCLUSION

This study suggests that SCO may attenuate liver lipid accumulation in DIO mice. Contributing mechanisms were postulated to include promotion of adiponectin expression, inhibition of hepatic lipogenesis, and/or enhanced insulin and AMPK signaling independent of FGF21 pathway.

The adipokine/ceramide axis: key aspects of insulin sensitization

Until recently, sphingolipid physiology was primarily the domain of oncologists and immunologists. However, mounting evidence implicates ceramides and their derivatives in various aspects of metabolism via directly impacting the insulin receptor as well as modulating cell survival and proliferation. More recent observations suggest a strong link between a number of adipokines and ceramide catabolism. Here, we aim to briefly review the available data on the established metabolic effects of sphingolipids in various cell types and will discuss how adipokines exert a critical influence on the steady state levels of these lipid mediators.

Adipose tissue, hormones, and treatment of type 1 diabetes

Type 1 diabetes (T1D) is a serious disease with increasing incidence worldwide, with fatal consequences if untreated. Traditional therapies require direct or indirect insulin replacement, which involves numerous limitations and complications. While insulin is the major regulator of blood glucose, recent reports demonstrate the ability of several extra-pancreatic hormones to decrease blood glucose and improve metabolic homeostasis. Such hormones mainly include adipokines originating from adipose tissue (AT), while specific factors from the gut and liver also contribute to glucose homeostasis. Correction of T1D with adipokines is progressively becoming a realistic option, with the potential to overcome many problems associated with insulin replacement. Several recent studies demonstrate insulin-independent reversal or amelioration of T1D through administration of specific adipokines. Our recent work demonstrates the ability of healthy AT to compensate for the function of endocrine pancreas in long-term correction of T1D. This review discusses the potential of AT-related therapies for T1D as viable alternatives to insulin replacement.

Biological role, clinical significance, and therapeutic possibilities of the recently discovered metabolic hormone fibroblastic growth factor 21

Fibroblast growth factor 21 (FGF21), a 181 amino acid circulating protein, is a member of the FGF superfamily, with relevant metabolic actions. It acts through the interaction with specific FGF receptors and a cofactor called β-Klotho, whose expression is predominantly detected in metabolically active organs. FGF21 stimulates glucose uptake in adipocytes via the induction of glucose transporter-1. This action is additive and independent of insulin. β-Cell function and survival are preserved, and glucagon secretion is reduced by this protein, thus decreasing hepatic glucose production and improving insulin sensitivity. Lipid profile has been shown to be improved by FGF21 in several animal models. FGF21 increases energy expenditure in rodents and induces weight loss in diabetic nonhuman primates. It also exerts favorable effects on hepatic steatosis and reduces tissue lipid content in rodents. Adaptive metabolic responses to fasting, including stimulation of ketogenesis and fatty acid oxidation, seem to be partially mediated by FGF21. In humans, serum FGF21 concentrations have been found elevated in insulin-resistant states, such as impaired glucose tolerance and type 2 diabetes. FGF21 levels are correlated with hepatic insulin resistance index, fasting blood glucose, HbA1c, and blood glucose after an oral glucose tolerance test. A relationship between FGF21 levels and long-term diabetic complications, such as nephropathy and carotid atheromatosis, has been reported. FGF21 levels decreased in diabetic patients after starting therapy with insulin or oral agents. Increased FGF21 serum levels have also been found to be associated with obesity. In children, it is correlated with BMI and leptin levels, whereas in adults, FGF21 levels are mainly related to several components of the metabolic syndrome. Serum FGF21 levels have been found to be elevated in patients with ischemic heart disease. In patients with renal disease, FGF21 levels exhibited a progressive increase as renal function deteriorates. Circulating FGF21 levels seem to be related to insulin resistance and inflammation in dialysis patients. In summary, FGF21 is a recently identified hormone with antihyperglycemic, antihyperlipidemic, and thermogenic properties. Direct or indirect potentiation of its effects might be a potential therapeutic target in insulin-resistant states.