Cell biology. FGF21 takes a fat bite

Fibroblast growth factor 21: An emerging pleiotropic regulator of lipid metabolism and the metabolic network

Fibroblast growth factor 21 (FGF21) was originally identified as an important metabolic regulator which plays a crucial physiological role in regulating a variety of metabolic parameters through the metabolic network. As a novel multifunctional endocrine growth factor, the role of FGF21 in the metabolic network warrants extensive exploration. This insight was obtained from the observation that the FGF21-dependent mechanism that regulates lipid metabolism, glycogen transformation, and biological effectiveness occurs through the coordinated participation of the liver, adipose tissue, central nervous system, and sympathetic nerves. This review focuses on the role of FGF21-uncoupling protein 1 (UCP1) signaling in lipid metabolism and how FGF21 alleviates non-alcoholic fatty liver disease (NAFLD). Additionally, this review reveals the mechanism by which FGF21 governs glucolipid metabolism. Recent research on the role of FGF21 in the metabolic network has mostly focused on the crucial pathway of glucolipid metabolism. FGF21 has been shown to have multiple regulatory roles in the metabolic network. Since an adequate understanding of the concrete regulatory pathways of FGF21 in the metabolic network has not been attained, this review sheds new light on the metabolic mechanisms of FGF21, explores how FGF21 engages different tissues and organs, and lays a theoretical foundation for future in-depth research on FGF21-targeted treatment of metabolic diseases.

Fibroblast growth factor-21 alleviates proteasome injury via activation of autophagy flux in Parkinson's disease

Parkinson's disease (PD) is one of the most common and complex Neurodegeneration, with an inherited metabolic disorder. Fibroblast growth factor 21 (FGF21), an endocrine hormone that belongs to the fibroblast growth factor superfamily, plays an extensive role in metabolic regulation. However, our understandings of the specific function and mechanisms of FGF21 on PD are still quite limited. Here, we aimed to elucidate the actions and the underlying mechanisms of FGF21 on dopaminergic neurodegeneration using cellular models of parkinsonism. To investigate the effects of FGF21 on dopaminergic neurodegeneration in vitro, proteasome impairment models of PD were utilized. Human dopaminergic neuroblastoma SH-SY5Y cells were treated with the proteasome inhibitor lactacystin (5 μmol/L) for 12 h, then with 50 ng/ml FGF-21 with or without 5 mmol/L of 3-methyladenine.The cells were dissected to assess alterations in autophagy using immunofluorescence, immunoblotting and electron microscopy assays. Our data indicate that FGF21 prevents dopaminergic neuron loss and shows beneficial effects against proteasome impairment induced PD syndrome, indicating it might be a potent candidate for developing novel drugs to deal with PD.

The ketogenic diet prevents steatosis and insulin resistance by reducing lipogenesis, diacylglycerol accummulation, and PKC activity in male rat liver

KEY POINTS

The accumulation of diacylglycerol (DAG), ceramides and inflammation are key factors that cause insulin resistance and nonalcoholic fatty liver (NAFLD). This study provides evidence that a ketogenic diet (KD) rich in fat and devoid of carbohydrate reduced DAG content and preserved insulin signalling in the liver. The KD shifted metabolism away from lipogenesis by enhancing genes involved in mitochondrial biogenesis and fatty acid oxidations in the liver. The KD also promoted the production of beneficial very long-chain ceramides instead of potentially harmful long-chain ceramides. Through multiple mechanisms, the KD exerted anti-steatogenic and insulin-sensitizing effects in the liver, which supports the use of this dietary intervention to treat NAFLD.

ABSTRACT

Obesity-associated insulin resistance plays a major role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). The accumulation of diacylglycerol (DAG), ceramides and inflammation are key factors that cause NAFLD. In recent years, the ketogenic diet (KD) has emerged as an effective non-pharmacological intervention for the treatment of NAFLD and other obesity-related metabolic disorders. What remains undetermined is how the KD affects DAG and ceramides content and insulin sensitivity in the liver. Thus, this research was designed to assess these variables, as well as glucose and fat metabolism and markers of inflammation in livers of rats exposed for 8 weeks to one of the following diets: standard chow (SC), obesogenic high-fat, sucrose-enriched diet (HFS), or a KD. Despite having a higher fat content than the HFS diet, the KD did not cause steatosis and preserved hepatic insulin signalling. The KD reduced DAG content and protein kinase C epsilon (PKCε) activity, but markedly increased liver ceramides content. However, whereas the KD increased ceramide synthase 2 (CerS2) expression, it suppressed CerS6 expression, an effect that promoted the production of beneficial very long-chain ceramides instead of harmful long-chain ceramides. The KD also enhanced the liver expression of key genes involved in mitochondrial biogenesis and fatty acid oxidation (Pgc-1α and Fgf21), suppressed inflammatory genes (Tnfα, Nf-kb, Tlr4, and Il6), and shifted substrate away from de-novo lipogenesis. Thus, through multiple mechanisms the KD exerted anti-steatogenic and insulin-sensitizing effects in the liver, which supports the use of this dietary intervention to treat NAFLD. Abstract figure legend This article is protected by copyright. All rights reserved.

Leucine, but not isoleucine or valine, affects serum lipid profiles and browning of WAT in mice

Branched chain amino acids (BCAA), especially leucine (Leu), have been reported to decrease fat deposition. However, opposite effects of BCAA on lipid metabolism have been observed. To determine the role of BCAA in lipid metabolism, an amino acid-defined diet was formulated and C57BL/6J mice were assigned into the following groups: amino acid-defined control diet and control diet supplemented with Leu, isoleucine, or valine. Nitrogen was balanced by proportionally mixed amino acids except BCAA. Results showed that dietary Leu supplementation significantly increased the levels of serum triglycerides, total cholesterol, low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol and urea nitrogen. Metabolomics showed that biosynthesis of unsaturated fatty acids was altered by Leu supplementation. Leu treatment up-regulated the expression of genes related to fat synthesis and down-regulated the expression of genes related to fatty acid synthesis. Furthermore, the genes and proteins of selective markers involved in browning of white adipose tissue (WAT) were up-regulated by dietary supplementation with Leu. This study indicated that dietary supplementation with Leu, but not isoleucine or valine, significantly affected lipid metabolism by regulating lipid metabolism-related genes and serum fatty acid concentration, providing a new tool in the management of obesity and metabolic disorders.

Skeletal Muscle and Bone - Emerging Targets of Fibroblast Growth Factor-21

Fibroblast growth factor 21 (FGF21) is an atypical member of the FGF family, which functions as a powerful endocrine and paracrine regulator of glucose and lipid metabolism. In addition to liver and adipose tissue, recent studies have shown that FGF21 can also be produced in skeletal muscle. As the most abundant tissue in the human body, skeletal muscle has become increasingly recognized as a major site of metabolic activity and an important modulator of systemic metabolic homeostasis. The function and mechanism of action of muscle-derived FGF21 have recently gained attention due to the findings of considerably increased expression and secretion of FGF21 from skeletal muscle under certain pathological conditions. Recent reports regarding the ectopic expression of FGF21 from skeletal muscle and its potential effects on the musculoskeletal system unfolds a new chapter in the story of FGF21. In this review, we summarize the current knowledge base of muscle-derived FGF21 and the possible functions of FGF21 on homeostasis of the musculoskeletal system with a focus on skeletal muscle and bone.

Fibroblast growth factor 21 and autophagy: A complex interplay in Parkinson disease

Parkinson disease (PD) is the second common neurodegenerative disorder after Alzheimer's disease (AD). The predominant pathological hallmark is progressive loss of dopaminergic (DA) neurones in the substantia nigra (SN) complicated by aggregation of misfolded forms of alpha-synuclein (α-syn). α-syn is a cytosolic synaptic protein localized in the presynaptic neuron under normal circumstances. What drives misfolding of this protein is largely unknown. However, recent studies suggest that autophagy might be an important risk factor for contributing towards PD. Autophagy is an evolutionarily conserved mechanism that causes the clearance or degradation of misfolded, mutated and damaged proteins, organelles etc. However, in an aging individual this process might deteriorate which could possibly lead to the accumulation of damaged proteins. Hence, autophagy modulation might provide some interesting cues for the treatment of PD. Additionally, Fibroblast growth factor 21 (FGF21) which is known for its role as a potent regulator of glucose and energy metabolism has also proved to be neuroprotective in various neurodegenerative conditions possibly via mediation of autophagy.

Leucine and isoleucine have similar effects on reducing lipid accumulation, improving insulin sensitivity and increasing the browning of WAT in high-fat diet-induced obese mice

Leucine (Leu) and isoleucine (Ile) have similar effects in the management of obesity and related disorders.

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.

Improvement of Lipid and Glucose Metabolism by Capsiate in Palmitic Acid-Treated HepG2 Cells via Activation of the AMPK/SIRT1 Signaling Pathway

Capsiate, a nonpungent ingredient of CH-19 Sweet, exhibits anti-obesity effects on animals and humans. This study investigated the effects and molecular mechanism of capsiate on lipid and glucose metabolism in PA-treated HepG2 cells. Results showed that compared with the PA-alone group, 100 μM capsiate inhibited lipid accumulation, decreased TG (0.0562 ± 0.0142 vs 0.0381 ± 0.0055 mmol/g of protein; P = 0.024) and TC (0.1087 ± 0.0037 vs 0.0359 ± 0.0059 mmol/g of protein; P = 0.000) levels, and increased the HDL-C level (0.0189 ± 0.0067 vs 0.1050 ± 0.0106 mmol/g of protein; P = 0.000) and glycogen content (0.0065 ± 0.0007 vs 0.0146 ± 0.0008 mg/10⁶ cells; P = 0.000) of PA-treated HepG2 cells; 100 μM capsiate also upregulated the level of CD36 ( P = 0.000), phosphorylation of ACC ( P = 0.034), and expression of CPT1 ( P = 0.013) in PA-treated HepG2 cells, leading to an enhancement of lipid metabolism. Meanwhile, 100 μM capsiate upregulated the levels of GLUT1, GLUT4, GK, and phosphorylation of GS ( P = 0.001, 0.029, 0.000, and 0.045, respectively) and downregulated the PEPCK level ( P = 0.001) to improve glucose metabolism in PA-treated HepG2 cells. Furthermore, the levels of phosphorylation of AMPK and expression of SIRT1 in HepG2 cells were increased by a 100 μM capsiate treatment ( P = 0.001 and 0.000, respectively), while the FGF21 level was decreased ( P = 0.003). Most of these effects were reversed by pretreatment with compound C, a selective AMPK inhibitor. Thus, capsiate might improve lipid and glucose metabolism in HepG2 cells by activating the AMPK/SIRT1 signaling pathway.

The relationship between serum levels of fibroblast growth factor 21 and diabetic retinopathy

Fibroblast growth factor 21 (FGF21) is a major metabolic regulator that has been shown to be elevated in a number of metabolic disturbances including type 2 diabetes mellitus (T2DM) and the metabolic syndrome, but few studies about the relationship between serum FGF21 and the complications of diabetes have been done. Since the association between FGF21 and diabetic retinopathy is not clear, this study was conducted to investigate this relationship. In this cross-sectional study, 61 subjects (14 healthy controls, 22 diabetic patients without retinopathy, and 25 patients with diabetic retinopathy) were evaluated. All patients in the study were examined for the presence of diabetic retinopathy. Various clinical and biochemical parameters including FGF21 were evaluated and analyzed and compared between the study groups. Serum levels of FGF21 showed a significant difference between the three groups (P=0.003) but the difference between diabetic patients with and without retinopathy was not significant (P=0.122). Regression model was used to evaluate the role of FGF21 in predicting diabetic retinopathy. In the multivariate logistic regression model after adjustment of systolic blood pressure and fasting blood glucose, the level of FGF21 was not associated with diabetic retinopathy. In the multivariate model, only fasting blood glucose was associated with diabetic retinopathy (P=0.009). According to the results of this study, serum levels of FGF21 in diabetic patients was higher than the control group but these raised levels could not predict the presence of diabetic retinopathy.

Histone Deacetylase 3 Deletion in Mesenchymal Progenitor Cells Hinders Long Bone Development

Long bone formation is a complex process that requires precise transcriptional control of gene expression programs in mesenchymal progenitor cells. Histone deacetylases (Hdacs) coordinate chromatin structure and gene expression by enzymatically removing acetyl groups from histones and other proteins. Hdac inhibitors are used clinically to manage mood disorders, cancers, and other conditions but are teratogenic to the developing skeleton and increase fracture risk in adults. In this study, the functions of Hdac3, one of the enzymes blocked by current Hdac inhibitor therapies, in skeletal mesenchymal progenitor cells were determined. Homozygous deletion of Hdac3 in Prrx1-expressing cells prevented limb lengthening, altered pathways associated with endochondral and intramembranous bone development, caused perinatal lethality, and slowed chondrocyte and osteoblast differentiation in vitro. Transcriptomic analysis revealed that Hdac3 regulates vastly different pathways in mesenchymal cells expressing the Prxx1-Cre driver than those expressing the Col2-CreERT driver. Notably, Fgf21 was elevated in Hdac3-CKO_Prrx1 limbs as well as in chondrogenic cells exposed to Hdac3 inhibitors. Elevated expression of Mmp3 and Mmp10 transcripts was also observed. In conclusion, Hdac3 regulates distinct pathways in mesenchymal cell populations and is required for mesenchymal progenitor cell differentiation and long bone development. © 2017 American Society for Bone and Mineral Research.

Fibroblast growth factor-21 restores insulin sensitivity but induces aberrant bone microstructure in obese insulin-resistant rats

Fibroblast growth factor (FGF)-21 is a potent endocrine factor that improves insulin resistance and obesity-associated metabolic disorders. However, concomitant activation of peroxisome proliferator-activated receptor-γ by FGF-21 makes bone susceptible to osteopenia and fragility fracture. Since an increase in body weight often induced adaptive change in bone by making it resistant to fracture, it was unclear whether FGF-21 would still induce bone defects in overweight rats. Therefore, the present study aimed to investigate bone microstructure and its mechanical properties in high fat diet (HF)-fed rats treated with 0.1 mg/kg/day FGF-21. Eighteen male rats were divided into two groups to receive either a normal diet or HF for 12 weeks. HF rats were then divided into two subgroups to receive either vehicle or FGF-21 for 4 weeks. The results showed that HF led to obesity, dyslipidemia and insulin resistance, as indicated by hyperinsulinemia with euglycemia. In HF rats, there was an increase in tibial yield displacement (an indicator of ability to be deformed without losing toughness, as determined by 3-point bending) without changes in tibial trabecular volumetric bone mineral density (vBMD) or cortical bone parameters, e.g., cortical thickness and bone area. FGF-21 treatment strongly improved the metabolic parameters and increased insulin sensitivity in HF rats. However, FGF-21-treated HF rats showed lower yield displacement, trabecular vBMD, trabecular bone volume, trabecular thickness, and osteoblast surface compared with vehicle-treated HF rats. These findings suggest that, despite being a potent antagonist of insulin resistance and visceral fat accumulation, FGF-21 is associated with bone defects in HF rats.

PPARs in the central nervous system: roles in neurodegeneration and neuroinflammation

Over 25 years have passed since peroxisome proliferators-activated receptors (PPARs), were first described. Like other members of the nuclear receptors superfamily, PPARs have been defined as critical sensors and master regulators of cellular metabolism. Recognized as ligand-activated transcription factors, they are involved in lipid, glucose and amino acid metabolism, taking part in different cellular processes, including cellular differentiation and apoptosis, inflammatory modulation and attenuation of acute and chronic neurological damage in vivo and in vitro. Interestingly, PPAR activation can simultaneously reprogram the immune response, stimulate metabolic and mitochondrial functions, promote axonal growth, induce progenitor cells to differentiate into myelinating oligodendrocytes, and improve brain clearance of toxic molecules such as β-amyloid peptide. Although the molecular mechanisms and cross-talk with different molecular pathways are still the focus of intense research, PPARs are considered potential therapeutic targets for several neuropathological conditions, including degenerative disorders such as Alzheimer's, Parkinson's and Huntington's disease. This review considers recent advances regarding PPARs, as well as new PPAR agonists. We focus on the mechanisms behind the neuroprotective effects exerted by PPARs and summarise the roles of PPARs in different pathologies of the central nervous system, especially those associated with degenerative and inflammatory mechanisms.

Growth Factors in the Pathogenesis of Retinal Neurodegeneration in Diabetes Mellitus

Neurodegeneration is an initial process in the development of diabetic retinopathy (DR).

High quantities of glutamate, oxidative stress, induction of the renin-angiotensin system (RAS) and elevated levels of RAGE are crucial elements in the retinal neurodegeneration caused by diabetes mellitus. At least, there is emerging proof to indicate that the equilibrium between the neurotoxic and neuroprotective components will affect the state of the retinal neurons.

Somatostatin (SST), pigment epithelium-derived factor (PEDF), and erythropoietin (Epo) are endogenous neuroprotective peptides that are decreased in the eye of diabetic persons and play an essential role in retinal homeostasis. On the other hand, insulin-like growth factor 1 (IGF-1), and vascular endothelial growth factor (VEGF) are pivotal proteins which participate in the development of new capillaries and finally cause damage to the retinal neurons. During recent years, our knowledge about the function of growth factors in the pathogenesis of retinal neurodegeneration has increased. However, intensive investigations are needed to clarify the basic processes that contribute to retinal neurodegeneration and its association with damage to the capillary blood vessels. The objective of this review article is to show new insights on the role of neurotransmitters and growth factors in the pathogenesis of diabetic retinopathy. The information contained in this manuscript may provide the basis for novel strategies based on the factors of neurodegeneration to diagnose, prevent and treat DR in its earliest phases.

Nuclear factor E2-related factor 2 knockdown enhances glucose uptake and alters glucose metabolism in AML12 hepatocytes

Nuclear factor E2-related factor 2 (Nrf2) is a transcription factor known to induce the expression of a variety of antioxidant and detoxification genes. Recently, increasing evidence has revealed roles for Nrf2 in glucose, lipid, and energy metabolism; however, the exact functions of Nrf2 in hepatocyte biology are largely unclear. In the current study, the transient knockdown of Nrf2 via siRNA transfection enhanced the glucose uptake of fasting AML12 hepatocytes to 325.3 ± 11.1% ( P < 0.05) of that of untransfected control cells. The impacts of Nrf2 knockdown (NK) on the antioxidant system, inflammatory response, and glucose metabolism were then examined in AML12 cells under both high-glucose (33 mmol/L) and low-glucose (4.5 mmol/L) conditions. NK lowered the gene and protein expression of the anti-oxidases heme oxygenase-1 and NAD(P)H: quinone oxidoreductase 1 and increased p-eukaryotic initiation factor-2α^S51, p-nuclear factor-κB p65^S276, and its downstream proinflammatory factors, including interleukin-1 beta, tumor necrosis factor-α, matrix metalloproteinase 2, and matrix metalloproteinase 9, at the protein level. NK also altered the protein expression of fibroblast growth factor 21, glucose transporter type 4, insulin-like growth factor 1, forkhead box protein O1, p-AKT^S473, and p-GSK3α/β^Y279/Y216, which are involved in glucose uptake, glycogenesis, and gluconeogenesis in AML12 cells. Our results provide a comprehensive understanding of the central role of Nrf2 in the regulation of glucose metabolism in AML12 hepatocytes, in addition to its classical roles in the regulation of redox signaling, endoplasmic reticulum stress and proinflammatory responses, and support the potential of Nrf2 as a therapeutic target for the prevention and treatment of obesity and other associated metabolic syndromes. Impact statement Increasing evidence supports the complexity of Nrf2 functions beyond the antioxidant and detoxification response. Previous in vivo studies employing either Nrf2-knockout or Nrf2-activated mice have achieved a similar endpoint: protection against an obese and insulin-resistant phenotype that includes impaired lipogenesis and gluconeogenesis in the liver. These apparently paradoxical observations led us to evaluate the impact of Nrf2 in liver cells in the absence of any influence from the systemic environment, including changes in the secretion of adipokines and proinflammatory cytokines by adipose tissues. In the present study, Nrf2 knockdown was sufficient to induce fundamental changes in the glucose metabolism of AML12 hepatocytes in addition to its classical cytoprotective functions. We also discuss similarities and differences between our in vitro study and previous in vivo studies, which may be helpful to dissect and better understand in vivo data that represents the culmination of both local and systemic alterations.

Treatment with FGFR2-IIIc monoclonal antibody suppresses weight gain and adiposity in KKAy mice

Expression of β-Kotho, fibroblast growth factor receptor (FGFR)-1c and 2c, which bind FGF21, is decreased in the white adipose tissue of obese mice. The aim of the present study was to determine the role of FGFR2c in the development of obesity and diabetes in KKA^y mice. Treatment with mouse monoclonal FGFR2-IIIc antibody (0.5 mg kg⁻¹) significantly suppressed body weight gain and epididymal white adipose tissue weight in individually housed KKA^y mice while having no effect on daily food intake. In addition, treatment with FGFR2-IIIc antibody significantly increased plasma-free fatty acid levels while having no effect on blood glucose or plasma FGF21 levels. Moreover, treatment with FGFR2-IIIc antibody had no significant effect on the expression of uncoupling protein-1, uncoupling protein-2 or peroxisome proliferator-activated receptor-γ coactivator 1α in the epididymal white adipose tissue. The treatment with FGFR2-IIIc antibody had no significant effects on daily food intake and body weight gain in individually housed KK mice. These findings suggest that FGFR2-IIIc upregulates the adiposity induced by social isolation in KKA^y mice, and that decreased expression and/or function of FGFR2c might be a compensatory response to enhanced adiposity. Inhibition of FGFR2-IIIc function might be a novel therapeutic approach for obesity.

Macronutrient Intake-Associated FGF21 Genotype Modifies Effects of Weight-Loss Diets on 2-Year Changes of Central Adiposity and Body Composition: The POUNDS Lost Trial

OBJECTIVE

Fibroblast growth factor 21 (FGF21) is involved in the regulation of energy balance and adipose metabolism. Our previous genome-wide association study identified genetic variants in the FGF21 region associated with macronutrient intake preference. We investigated whether the FGF21 genotype modified effects of weight-loss diets varying in macronutrient intake on changes in adiposity in a 2-year randomized diet intervention trial.

RESEARCH DESIGN AND METHODS

We genotyped FGF21 rs838147 in 715 overweight or obese individuals who were assigned to one of four diets varying in macronutrient contents. A DEXA scan was performed to evaluate body composition.

RESULTS

We observed a significant interaction between the FGF21 genotype and carbohydrate/fat intake on 2-year changes in waist circumference (WC), percentage of total fat mass, and percentage of trunk fat (P = 0.049, P = 0.001, and P = 0.003 for interaction, respectively). In response to the low-carbohydrate/high-fat diet, carrying the carbohydrate intake-decreasing C allele of rs838147 was marginally associated with less reduction in WC (P = 0.08) and significantly associated with less reduction of total fat mass (P = 0.01) and trunk fat (P = 0.02). Opposite genetic associations with these outcomes were observed among the high-carbohydrate/low-fat diet group; carrying the C allele was associated with a greater reduction of WC, total body fat mass, and trunk fat.

CONCLUSIONS

Our data suggest that FGF21 genotypes may interact with dietary carbohydrate/fat intake on changes in central adiposity and body fat composition. A low-calorie, high-carbohydrate/low-fat diet was beneficial for overweight or obese individuals carrying the carbohydrate intake-decreasing allele of the FGF21 variant to improve body composition and abdominal obesity.

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.

Current disease modifying approaches to treat Parkinson's disease

Parkinson's disease (PD is a progressive neurological disorder characterized by the degeneration and death of midbrain dopamine and non-dopamine neurons in the brain leading to motor dysfunctions and other symptoms, which seriously influence the quality of life of PD patients. The drug L-dopa can alleviate the motor symptoms in PD, but so far there are no rational therapies targeting the underlying neurodegenerative processes. Despite intensive research, the molecular mechanisms causing neuronal loss are not fully understood which has hampered the development of new drugs and disease-modifying therapies. Neurotrophic factors are by virtue of their survival promoting activities attract candidates to counteract and possibly halt cell degeneration in PD. In particular, studies employing glial cell line-derived neurotrophic factor (GDNF) and its family member neurturin (NRTN), as well as the recently described cerebral dopamine neurotrophic factor (CDNF) and the mesencephalic astrocyte-derived neurotrophic factor (MANF) have shown positive results in protecting and repairing dopaminergic neurons in various models of PD. Other substances with trophic actions in dopaminergic neurons include neuropeptides and small compounds that target different pathways impaired in PD, such as increased cell stress, protein handling defects, dysfunctional mitochondria and neuroinflammation. In this review, we will highlight the recent developments in this field with a focus on trophic factors and substances having the potential to beneficially influence the viability and functions of dopaminergic neurons as shown in preclinical or in animal models of PD.

Bone marrow adipose tissue: formation, function and regulation

The human body requires an uninterrupted supply of energy to maintain metabolic homeostasis and energy balance. To sustain energy balance, excess consumed calories are stored as glycogen, triglycerides and protein, allowing the body to continue to function in states of starvation and increased energy expenditure. Adipose tissue provides the largest natural store of excess calories as triglycerides and plays an important role as an endocrine organ in energy homeostasis and beyond. This short review is intended to detail the current knowledge of the formation and role of bone marrow adipose tissue (MAT), a largely ignored adipose depot, focussing on the role of MAT as an endocrine organ and highlighting the pharmacological agents that regulate MAT.

MicroRNA-34a and Impaired FGF19/21 Signaling in Obesity

The obesity epidemic and the urgent need for effective and safe drugs to treat obesity-related diseases have greatly increased research interest in the metabolic hormones, fibroblast growth factor-19 (FGF19, FGF15 in mice), and FGF21. FGF19 and FGF21 function as endocrine hormones that play key roles in energy metabolism and counteract obesity. Importantly, in obese humans and lab animals, circulating FGF19 and FGF21 levels are elevated, and metabolic actions of these hormones are impaired but the underlying mechanisms remained unknown. Recent microRNA (miR) studies have revealed that aberrantly elevated miR-34a in obesity directly targets β-Klotho, the obligate coreceptor for both FGF19 and FGF21, and attenuates metabolic signaling of these hormones. In this review, we will discuss recent findings in the miR and FGF19/21 fields, emphasizing the novel function of obesity-associated miR-34a in attenuation of FGF19/21 metabolic actions, and further discuss miRs, including miR-34a, as potential drug targets for obesity-related diseases.

Lactate induces FGF21 expression in adipocytes through a p38-MAPK pathway

FGF21 (fibroblast growth factor 21), first described as a main fasting-responsive molecule in the liver, has been shown to act as a true metabolic regulator in additional tissues, including muscle and adipose tissues. In the present study, we found that the expression and secretion of FGF21 was very rapidly increased following lactate exposure in adipocytes. Using different pharmacological and knockout mice models, we demonstrated that lactate regulates Fgf21 expression through a NADH/NAD-independent pathway, but requires active p38-MAPK (mitogen activated protein kinase) signalling. We also demonstrated that this effect is not restricted to lactate as additional metabolites including pyruvate and ketone bodies also activated the FGF21 stress response. FGF21 release by adipose cells in response to an excess of intermediate metabolites may represent a physiological mechanism by which the sensing of environmental metabolic conditions results in the release of FGF21 to improve metabolic adaptations.

Fibroblast Growth Factor 21 Suppresses Adipogenesis in Pig Intramuscular Fat Cells

Fibroblast growth factor 21 (FGF21) plays an important role in the treatment of disease associated with muscle insulin resistance which is characterized by various factors, such as intramuscular triglyceride (IMT) content. Studies have also shown that FGF21 inhibits triglyceride synthesis in vivo. However, the precise mechanism whereby FGF21 regulates triglyceride metabolism in intramuscular fat (IMF), which may influence the muscle insulin sensitivity, is not clearly understood. In order to understand the role of FGF21 in IMF deposition, we performed FGF21 overexpression in IMF cells by stable transfection. Our results showed that FGF21 inhibited the key adipogenesis gene mRNA expression of peroxisome proliferator-activated receptor gamma (PPARG), CCAAT/enhancer-binding protein (CEBP) family by reducing lysine-specific demethylase 1 (LSD1) expression which led to significant decline in lipid accumulation, and the result was confirmed by Western blot. Moreover, triggered by FGF21, parts of the adipokines—fatty acid-binding protein 4 (FABP4), glucose transporter 4 (GLUT4), adiponectin (ADIPOQ), and perilipin (PLIN1)—were also down-regulated. Furthermore, FGF21 gene expression was suppressed by transcription factor CEBP beta (CEBPB) which contributed strongly to triglyceride synthesis. Taken together, our study is the first to experimentally demonstrate FGF21 emerging as an efficient blockade of adipogenesis in IMF, thus also providing a new understanding of the mechanism whereby FGF21 improves insulin sensitivity.

A Liver-Bone Endocrine Relay by IGFBP1 Promotes Osteoclastogenesis and Mediates FGF21-Induced Bone Resorption

Fibroblast growth factor 21 (FGF21) promotes insulin sensitivity but causes bone loss. It elevates bone resorption by an undefined non-osteoclast-autonomous mechanism. We have detected a pro-osteoclastogenic activity in the hepatic secretome that is increased by FGF21 and largely attributed to insulin-like growth factor binding protein 1 (IGFBP1). Ex vivo osteoclast differentiation and in vivo bone resorption are both enhanced by recombinant IGFBP1 but suppressed by an IGFBP1-blocking antibody. Anti-IGFBP1 treatment attenuates ovariectomy-induced osteoporosis and abolishes FGF21-induced bone loss while maintaining its insulin-sensitizing metabolic benefit. Mechanistically, IGFBP1 functions via its RGD domain to bind to its receptor integrin β1 on osteoclast precursors, thereby potentiating RANKL-stimulated Erk-phosphorylation and NFATc1 activation. Consequently, osteoclastic integrin β1 deletion confers resistance to the resorption-enhancing effects of both IGFBP1 and FGF21. Therefore, the hepatokine IGFBP1 is a critical liver-bone hormonal relay that promotes osteoclastogenesis and bone resorption as well as an essential mediator of FGF21-induced bone loss.

Growth differentiation factor 15 as a useful biomarker for mitochondrial disorders

Objective

The diagnosis of mitochondrial disorders (MDs) is occasionally difficult because patients often present with solitary, or a combination of, symptoms caused by each organ insufficiency, which may be the result of respiratory chain enzyme deficiency. Growth differentiation factor 15 (GDF‐15) has been reported to be elevated in serum of patients with MDs. In this study, we investigated whether GDF‐15 is a more useful biomarker for MDs than several conventional biomarkers.

Methods

We measured the serum levels of GDF‐15 and fibroblast growth factor 21 (FGF‐21), as well as other biomarkers, in 48 MD patients and in 146 healthy controls in Japan. GDF‐15 and FGF‐21 concentrations were measured by enzyme‐linked immunosorbant assay and compared with lactate, pyruvate, creatine kinase, and the lactate‐to‐pyruvate ratio. We calculated sensitivity and specificity and also evaluated the correlation based on two rating scales, including the Newcastle Mitochondrial Disease Rating Scale (NMDAS).

Results

Mean GDF‐15 concentration was 6‐fold higher in MD patients compared to healthy controls (2,711 ± 2,459 pg/ml vs 462.5 ± 141.0 pg/mL; p < 0.001). Using a receiver operating characteristic curve, the area under the curve was significantly higher for GDF‐15 than FGF‐21 and other conventional biomarkers. Our date suggest that GDF‐15 is the most useful biomarker for MDs of the biomarkers examined, and it is associated with MD severity.

Interpretation

Our results suggest that measurement of GDF‐15 is the most useful first‐line test to indicate the patients who have the mitochondrial respiratory chain deficiency. Ann Neurol 2015;78:Ann Neurol 2015;78:679–696

Single-cell transcriptomics and functional target validation of brown adipocytes show their complex roles in metabolic homeostasis

Brown adipocytes (BAs) are specialized for adaptive thermogenesis and, upon sympathetic stimulation, activate mitochondrial uncoupling protein (UCP)-1 and oxidize fatty acids to generate heat. The capacity for brown adipose tissue (BAT) to protect against obesity and metabolic disease is recognized, yet information about which signals activate BA, besides β3-adrenergic receptor stimulation, is limited. Using single-cell transcriptomics, we confirmed the presence of mRNAs encoding traditional BAT markers (i.e., UCP1, expressed in 100% of BAs Adrb3, expressed in <50% of BAs) in mouse and have shown single-cell variability (>1000-fold) in their expression at both the mRNA and protein levels. We further identified mRNAs encoding novel markers, orphan GPCRs, and many receptors that bind the classic neurotransmitters, neuropeptides, chemokines, cytokines, and hormones. The transcriptome variability between BAs suggests a much larger range of responsiveness of BAT than previously recognized and that not all BAs function identically. We examined the in vivo functional expression of 12 selected receptors by microinjecting agonists into live mouse BAT and analyzing the metabolic response. In this manner, we expanded the number of known receptors on BAs at least 25-fold, while showing that the expression of classic BA markers is more complex and variable than previously thought.

Endogenous ways to stimulate brown adipose tissue in humans

Obesity is the result of disequilibrium between energy intake and energy expenditure (EE). Successful long-term weight loss is difficult to achieve with current strategies for the correction of this caloric imbalance. Non-shivering thermogenesis (NST) in brown adipose tissue (BAT) is a possible therapeutic target for the prevention and treatment of obesity and associated metabolic diseases. In recent years, more knowledge about the function and stimulation of bat has been obtained. The sympathetic nervous system (SNS) is currently seen as the main effector for brown fat function. Also, interplay between the thyroid axis and SNS plays an important role in BAT thermogenesis. Almost daily new pathways for the induction of BAT thermogenesis and 'browning' of white adipose tissue (WAT) are identified. Especially the activation of BAT via endogenous pathways has received strong scientific attention. Here we will discuss the relevance of several pathways in activating BAT and their implications for the treatment of obesity. In this review we will focus on the discussion of the most promising endocrine and paracrine pathways to stimulate BAT, by factors and pathways that naturally occur in the human body.

FGF-21, a novel metabolic regulator, has a robust neuroprotective role and is markedly elevated in neurons by mood stabilizers

Fibroblast growth factor-21 (FGF-21) is a new member of the FGF super-family and an important endogenous regulator of glucose and lipid metabolism. It has been proposed as a therapeutic target for diabetes and obesity. Its function in the central nervous system (CNS) remains unknown. Previous studies from our laboratory demonstrated that aging primary neurons are more vulnerable to glutamate-induced excitotoxicity, and that co-treatment with the mood stabilizers lithium and valproic acid (VPA) induces synergistic neuroprotective effects. This study sought to identify molecule(s) involved in these synergistic effects. We found that FGF-21 mRNA was selectively and markedly elevated by co-treatment with lithium and VPA in primary rat brain neurons. FGF-21 protein levels were also robustly increased in neuronal lysates and culture medium following lithium-VPA co-treatment. Combining glycogen synthase kinase-3 (GSK-3) inhibitors with VPA or histone deacetylase (HDAC) inhibitors with lithium synergistically increased FGF-21 mRNA levels, supporting that synergistic effects of lithium and VPA are mediated via GSK-3 and HDAC inhibition, respectively. Exogenous FGF-21 protein completely protected aging neurons from glutamate challenge. This neuroprotection was associated with enhanced Akt-1 activation and GSK-3 inhibition. Lithium-VPA co-treatment markedly prolonged lithium-induced Akt-1 activation and augmented GSK-3 inhibition. Akt-1 knockdown markedly decreased FGF-21 mRNA levels and reduced the neuroprotection induced by FGF-21 or lithium-VPA co-treatment. In addition, FGF-21 knockdown reduced lithium-VPA co-treatment-induced Akt-1 activation and neuroprotection against excitotoxicity. Together, our novel results suggest that FGF-21 is a key mediator of the effects of these mood stabilizers and a potential new therapeutic target for CNS disorders.

Exercise-induced myokines in health and metabolic diseases

Skeletal muscle has been emerging as a research field since the past 2 decades. Contraction of a muscle, which acts as a secretory organ, stimulates production, secretion, and expression of cytokines or other muscle fiber-derived peptides, i.e., myokines. Exercise-induced myokines influence crosstalk between different organs in an autocrine, endocrine, or paracrine fashion. Myokines are recently recognized as potential candidates for treating metabolic diseases through their ability to stimulate AMP-activated protein kinase signaling, increase glucose uptake, and improve lipolysis. Myokines may have positive effects on metabolic disorders, type 2 diabetes, or obesity. Numerous studies on myokines suggested that myokines offer a potential treatment option for preventing metabolic diseases. This review summarizes the current understanding of the positive effects of exercise-induced myokines, such as interleukin-15, brain-derived neurotrophic factor, leukemia inhibitory factor, irisin, fibroblast growth factor 21, and secreted protein acidic and rich in cysteine, on metabolic diseases.

MicroRNA 34a inhibits beige and brown fat formation in obesity in part by suppressing adipocyte fibroblast growth factor 21 signaling and SIRT1 function

Brown fat generates heat through uncoupled respiration, protecting against hypothermia and obesity. Adult humans have brown fat, but the amounts and activities are substantially decreased in obesity, by unknown mechanisms. Here we show that elevated microRNA 34a (miR-34a) in obesity inhibits fat browning in part by suppressing the browning activators fibroblast growth factor 21 (FGF21) and SIRT1. Lentivirus-mediated downregulation of miR-34a in mice with diet-induced obesity reduced adiposity, improved serum profiles, increased the mitochondrial DNA copy number, and increased oxidative function in adipose tissue in both BALB/c and C57BL/6 mice. Remarkably, downregulation of miR-34a increased coexpression of the beige fat-specific marker CD137 and the browning marker UCP1 in all types of white fat, including visceral fat, and promoted additional browning in brown fat. Mechanistically, downregulation of miR-34a increased expression of the FGF21 receptor components, FGFR1 and βKL, and also that of SIRT1, resulting in FGF21/SIRT1-dependent deacetylation of PGC-1α and induction of the browning genes Ucp1, Pgc-1α, and Prdm16. Importantly, anti-miR-34a-mediated beneficial effects, including decreased adiposity, are likely from multiple tissues, since downregulation of miR-34a also improves hepatic FGF21 signaling and lipid oxidation. This study identifies miR-34a as an inhibitor of beige and brown fat formation, providing a potential target for treating obesity-related diseases.

Skeletal muscle mitochondrial uncoupling drives endocrine cross-talk through the induction of FGF21 as a myokine

UCP1-Tg mice with ectopic expression of uncoupling protein 1 (UCP1) in skeletal muscle (SM) are a model of improved substrate metabolism and increased longevity. Analysis of myokine expression showed an induction of fibroblast growth factor 21 (FGF21) in SM, resulting in approximately fivefold elevated circulating FGF21 in UCP1-Tg mice. Despite a reduced muscle mass, UCP1-Tg mice showed no evidence for a myopathy or muscle autophagy deficiency but an activation of integrated stress response (ISR; eIF2α/ATF4) in SM. Targeting mitochondrial function in vitro by treating C2C12 myoblasts with the uncoupler FCCP resulted in a dose-dependent activation of ISR, which was associated with increased expression of FGF21, which was also observed by treatment with respiratory chain inhibitors antimycin A and myxothiazol. The cofactor required for FGF21 action, β-klotho, was expressed in white adipose tissue (WAT) of UCP1-Tg mice, which showed an increased browning of WAT similar to what occurred in altered adipocyte morphology, increased brown adipocyte markers (UCP1, CIDEA), lipolysis (HSL phosphorylation), and respiratory capacity. Importantly, treatment of primary white adipocytes with serum of transgenic mice resulted in increased UCP1 expression. Additionally, UCP1-Tg mice showed reduced body length through the suppressed IGF-I-GH axis and decreased bone mass. We conclude that the induction of FGF21 as a myokine is coupled to disturbance of mitochondrial function and ISR activation in SM. FGF21 released from SM has endocrine effects leading to increased browning of WAT and can explain the healthy metabolic phenotype of UCP1-Tg mice. These results confirm muscle as an important endocrine regulator of whole body metabolism.

Serum fibroblast growth factor 21 levels are correlated with the severity of diabetic retinopathy

The aim of the study was to assess serum fibroblast growth factor 21 (FGF21) concentrations in Chinese type 2 diabetic patients with and without retinopathy and to assess the association between FGF21 and the severity of retinopathy. 117 diabetic patients were compared with 68 healthy controls. Fasting blood glucose, serum total cholesterol, serum triglycerides, serum insulin, and serum FGF21 levels were estimated. FGF21 concentrations in the patients were significantly higher than those in control. In the patient group there was a significant positive correlation between FGF21, insulin level, and homeostasis model assessment index. Serum FGF21 concentrations in patients with proliferative diabetic retinopathy or nonproliferative diabetic retinopathy were significantly higher than those in patients without diabetic retinopathy. When the presence of diabetes was defined as the final variable in the conditional logistic regression model with the FGF21 concentration as the continuous variable, FGF21 was significantly involved in the model. This study shows that the increase in serum concentration of FGF21 was associated with the severity of diabetic retinopathy and suggests that FGF21 may play a role in the pathogenesis of diabetic retinopathy and its degree.

Selective peroxisome proliferator-activated receptor α modulators (SPPARMα): the next generation of peroxisome proliferator-activated receptor α-agonists

Dyslipidemia is a major risk factor for cardiovascular (CV) disease – the primary cause of death, worldwide. Although reducing levels of low-density lipoprotein-cholesterol can significantly reduce CV risk, a high level of residual risk persists, especially in people with obesity-related conditions, such as metabolic syndrome and type 2 diabetes mellitus. Peroxisome proliferator-activated receptor alpha- (PPARα-) agonists (e.g. fibrates), play a central role in the reduction of macro- and microvascular risk in these patients. However, the currently available fibrates are weak (PPARα-agonists) with limited efficacy due to dose-related adverse effects. To address this problem, a new generation of highly potent and selective PPARα-modulators (SPPARMα) is being developed that separate the benefits of the PPARα-agonists from their unwanted side effects. Among these, aleglitazar (a dual PPARα/γ agonist) and GFT505 (a dual PPAR α/δ agonist) have recently entered late-phase development. Although both compounds are more potent PPARα-activators than fenofibrate in vitro, only aleglitezar is more effective in lowering triglycerides and raising high-density lipoprotein-cholesterol (HDL-C) in humans. However, it is also associated with a potential risk of adverse effects. More recently, a highly potent, specific PPARα-agonist (K-877) has emerged with SPPARMα characteristics. Compared to fenofibrate, K-877 has more potent PPARα-activating efficacy in vitro, greater effects on triglycerides- and HDL-C levels in humans, and a reduced risk of adverse effects. If successful, K-877 has the potential to supersede the fibrates as the treatment of choice for patients with residual CV risk associated with metabolic syndrome and type 2 diabetes.

Mechanisms of hepatic triglyceride accumulation in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is characterized by hepatic lipid accumulation in the absence of excess alcohol intake. NAFLD is the most common chronic liver disease, and ongoing research efforts are focused on understanding the underlying pathobiology of hepatic steatosis with the anticipation that these efforts will identify novel therapeutic targets. Under physiological conditions, the low steady-state triglyceride concentrations in the liver are attributable to a precise balance between acquisition by uptake of non-esterified fatty acids from the plasma and by de novo lipogenesis, versus triglyceride disposal by fatty acid oxidation and by the secretion of triglyceride-rich lipoproteins. In NAFLD patients, insulin resistance leads to hepatic steatosis by multiple mechanisms. Greater uptake rates of plasma non-esterified fatty acids are attributable to increased release from an expanded mass of adipose tissue as a consequence of diminished insulin responsiveness. Hyperinsulinemia promotes the transcriptional upregulation of genes that promote de novo lipogenesis in the liver. Increased hepatic lipid accumulation is not offset by fatty acid oxidation or by increased secretion rates of triglyceride-rich lipoproteins. This review discusses the molecular mechanisms by which hepatic triglyceride homeostasis is achieved under normal conditions, as well as the metabolic alterations that occur in the setting of insulin resistance and contribute to the pathogenesis of NAFLD.

Novel aspects of brown adipose tissue biology

During the last decades, obesity research has focused on food intake regulation, whereas energy expenditure has been mainly measured based on whole-body oxygen consumption. With the renaissance of brown adipose tissue (BAT) thermogenesis as a potential drug target in humans, more thought is put into alternative heat-producing mechanisms. Also, the interaction of peripheral and central components to regulate thermogenesis requires further studies. Certainly, several of the novel molecular genetic tools available now, compared with 40 years ago, will be helpful to gain new insights in BAT-controlled energy homeostasis and promises new approaches to pharmacologically control body weight.

Fibroblast growth factor-21 serum concentrations are associated with metabolic and hepatic markers in humans

Rather than a traditional growth factor, fibroblast growth factor-21 (FGF21) is considered to be a metabolic hormone. In the current study, we investigated serum FGF21 levels in the self-contained population of Sorbs. Serum FGF21 concentrations were quantified by ELISA and correlated with IGF1 as well as metabolic, renal, hepatic, inflammatory, and cardiovascular parameters in 913 Sorbs from Germany. Moreover, human IGF1 protein secretion was investigated in FGF21-stimulated HepG2 cells. Median FGF21 serum concentrations were 2.1-fold higher in subjects with type 2 diabetes mellitus (141.8 ng/l) compared with controls (66.7 ng/l). Furthermore, nondiabetic subjects with FGF21 levels below the detection limit of the ELISA showed a more beneficial metabolic profile compared with subjects with measurable FGF21. Moreover, FGF21 was significantly lower in female compared with male subjects after adjustment for age and BMI. In multiple regression analyses, circulating FGF21 concentrations remained independently and positively associated with gender, systolic blood pressure, triglycerides, and γ glutamyl transferase whereas a negative association was observed with IGF1 in nondiabetic subjects. Notably, FGF21 significantly inhibited IGF1 secretion into HepG2 cell culture supernatants in preliminary in vitro experiments. FGF21 serum concentrations are associated with facets of the metabolic syndrome, hepatocellular function, as well as GH status.

Mild cold exposure modulates fibroblast growth factor 21 (FGF21) diurnal rhythm in humans: relationship between FGF21 levels, lipolysis, and cold-induced thermogenesis

CONTEXT

Cold exposure stimulates fibroblast growth factor 21 (FGF21) secretion in animals, enhancing the cold-induced thermogenesis (CIT) response through browning of white adipose tissue. In humans, the effects of cold exposure on circulating FGF21 levels are unknown.

OBJECTIVE

Our objective was to evaluate the effects of mild cold exposure on circulating FGF21 and its relationship with CIT and lipolysis in humans.

DESIGN AND SETTING

We conducted a randomized, single-blind, crossover intervention study at the National Institutes of Health Clinical Center.

PARTICIPANTS

Participants were healthy adults.

INTERVENTION

Subjects were exposed to a 12-h exposure to 24 or 19 C in a whole-room indirect calorimeter.

OUTCOME MEASURES

Energy expenditure, plasma FGF 21, nonesterified fatty acid, and adipose tissue microdialysis glycerol concentrations were evaluated.

RESULTS

At 24 C, plasma FGF21 exhibited a diurnal rhythm, peaking at 0800 h [110 (59-178) pg/ml], and progressively dropped to a nadir at 1700 h [41 (21-71) pg/ml, P < 0.0001] before rising at 1900 h [60 (11-81) pg/ml, P < 0.0001]. Exposure at 19 C lessened the diurnal reduction of FGF21 observed at 24 C from 0800-1700 h and augmented overall FGF21 levels by 37 ± 45% (P = 0.01). The change in area under the curve plasma FGF21 between 19 and 24 C correlated positively with the change in area under the curve adipose microdialysate glycerol (R(2) = 0.35, P = 0.04) but not with nonesterified fatty acid. Cold-induced increase in FGF21 predicted greater rise in energy expenditure during cold exposure (β = 0.66, P = 0.027), independent of age, gender, fat mass, and lean mass.

CONCLUSIONS

Mild cold exposure increased circulating FGF21 levels, predicting greater lipolysis and CIT. A small reduction in environmental temperature is sufficient to modulate FGF21 diurnal rhythm in humans, which may mediate cold-induced metabolic changes similar to those in animals.

Bone marrow mesenchymal stem cells: fat on and blast off by FGF21

Bone marrow mesenchymal stem cells (BMMSCs) are multipotent marrow stromal cells with the ability to differentiate into a variety of cell types required for tissue regeneration including osteoblasts and chondrocytes. Thus, they hold tremendous potential as powerful therapeutic strategies for the prevention and treatment of degenerative disorders including osteoporosis and osteoarthritis. The differentiation of BMMSCs into competing lineages such as osteoblasts and marrow adipocytes is regulated by various environmental cues and intrinsic signaling pathways. Here I highlight recent advances in the understanding of BMMSC function and regulation, including the interaction between BMMSCs with the hematopoietic/immune system, and the identification of novel modulators of BMMSC differentiation such as the metabolic hormone fibroblast growth factor 21 (FGF21). These new findings will further elucidate the dynamic regulation of BMMSCs in the pathophysiological control of skeletal homeostasis, and facilitate the clinical applications of BMMSCs in regenerative medicine.