Fibroblast growth factor 21, assisted by elevated glucose, activates paraventricular nucleus NUCB2/Nesfatin-1 neurons to produce satiety under fed states

FGF21 as a mediator of adaptive changes in food intake and macronutrient preference in response to protein restriction

Free-feeding animals navigate complex nutritional landscapes in which food availability, cost, and nutritional value can vary markedly. Animals have thus developed neural mechanisms that enable the detection of nutrient restriction, and these mechanisms engage adaptive physiological and behavioral responses that limit or reverse this nutrient restriction. This review focuses specifically on dietary protein as an essential and independently defended nutrient. Adequate protein intake is required for life, and ample evidence exists to support an active defense of protein that involves behavioral changes in food intake, food preference, and food motivation, likely mediated by neural changes that increase the reward value of protein foods. Available evidence also suggests that the circulating hormone fibroblast growth factor 21 (FGF21) acts in the brain to coordinate these adaptive changes in food intake, making it a unique endocrine signal that drives changes in macronutrient preference in the context of protein restriction. This article is part of the Special Issue on "Food intake and feeding states".

Fibroblast growth factor 21 alleviates diabetes-induced cognitive decline

Diabetes mellitus (DM) causes damage to the central nervous system, resulting in cognitive impairment. Fibroblast growth factor 21 (FGF21) exhibits the potential to alleviate neurodegeneration. However, the therapeutic effect of intracerebroventricular (i.c.v) FGF21 infusion on diabetes-induced cognitive decline (DICD) and its potential mechanisms remain unclear. In this study, the impact of FGF21 on DICD was explored, and 1H nuclear magnetic resonance (NMR)-based metabolomics plus 13C NMR spectroscopy in combine with intravenous [1-13C]-glucose infusion were used to investigate the underlying metabolic mechanism. Results revealed that i.c.v FGF21 infusion effectively improved learning and memory performance of DICD mice; neuron loss and apoptosis in hippocampus and cortex were significantly blocked, suggesting a potential neuroprotective role of FGF21 in DICD. Metabolomics results revealed that FGF21 modulated DICD metabolic alterations related to glucose and neurotransmitter metabolism, which are characterized by distinct recovered enrichment of [3-13C]-lactate, [3-13C]-aspartate, [4-13C]-glutamine, [3-13C]-glutamine, [4-13C]-glutamate, and [4-13C]- γ-aminobutyric acid (GABA) from [1-13C]-glucose. Moreover, diabetes-induced neuron injury and metabolic dysfunctions might be mediated by PI3K/AKT/GSK-3β signaling pathway inactivation in the hippocampus and cortex, which were activated by i.c.v injection of FGF21. These findings indicate that i.c.v FGF21 infusion exerts its neuroprotective effect on DICD by remodeling cerebral glucose and neurotransmitter metabolism by activating the PI3K/AKT/GSK-3β signaling pathway.

The Novel GlycoPEGylated FGF21 Analog Pegozafermin Activates Human FGF Receptors and Improves Metabolic and Liver Outcomes in Diabetic Monkeys and Healthy Human Volunteers

Pegozafermin (also known as BIO89-100) is a glycoPEGylated analog of fibroblast growth factor 21 (FGF21) under development to treat nonalcoholic steatohepatitis (NASH) and severe hypertriglyceridemia (SHTG). In cell-based assays, pegozafermin had a similar receptor engagement profile as recombinant FGF21, with approximately eightfold higher potency at fibroblast growth factor receptor 1c (FGFR1c). In diabetic monkeys, once-weekly and once-every-2-weeks regimens of subcutaneous pegozafermin provided rapid and robust benefits for an array of metabolic biomarkers, including triglycerides, cholesterol, fasting glucose, glycated hemoglobin, adiponectin, alanine aminotransferase, food intake, and body weight. In a single ascending dose study in healthy volunteers, subcutaneously administered pegozafermin was associated with statistically significant improvements in triglycerides, low- and high-density lipoprotein-cholesterol, and adiponectin, an insulin-sensitizing and anti-inflammatory adipokine. Pharmacokinetic half-lives ranged from 55 to 100 hours over the clinically relevant dose range, consistent with the expected half-life extension by glycoPEGylation. These findings provide evidence that pegozafermin is a promising candidate molecule for the treatment of patients with NASH or SHTG. SIGNIFICANCE STATEMENT: Fibroblast growth factor 21 (FGF21) is a stress-inducible hormone that has important roles in regulating energy balance and glucose and lipid homeostasis. Studies presented here demonstrate that a novel long-acting FGF21 analog, pegozafermin, has similar pharmacologic properties as FGF21 and that repeated, subcutaneous dosing of pegozafermin in diabetic monkeys and healthy humans improves lipid metabolism, glucose metabolism, weight, and liver transaminases. These results support future development of pegozafermin for the treatment of metabolic diseases, including nonalcoholic steatohepatitis and severe hypertriglyceridemia.

Development and Characterization of a Cancer Cachexia Rat Model Transplanted with Cells of the Rat Lung Adenocarcinoma Cell Line Sato Lung Cancer (SLC)

Cancer cachexia is a complex malnutrition syndrome that causes progressive dysfunction. This syndrome is accompanied by protein and energy losses caused by reduced nutrient intake and the development of metabolic disorders. As many as 80% of patients with advanced cancer develop cancer cachexia; however, an effective targeted treatment remains to be developed. In this study, we developed a novel rat model that mimics the human pathology during cancer cachexia to elucidate the mechanism underlying the onset and progression of this syndrome. We subcutaneously transplanted rats with SLC cells, a rat lung adenocarcinoma cell line, and evaluated the rats' pathophysiological characteristics. To ensure that our observations were not attributable to simple starvation, we evaluated the characteristics under tube feeding. We observed that SLC-transplanted rats exhibited severe anorexia, weight loss, muscle atrophy, and weakness. Furthermore, they showed obvious signs of cachexia, such as anemia, inflammation, and low serum albumin. The rats also exhibited weight and muscle losses despite sufficient nutrition delivered by tube feeding. Our novel cancer cachexia rat model is a promising tool to elucidate the pathogenesis of cancer cachexia and to conduct further research on the development of treatments and supportive care for patients with this disease.

Potential Correlation between Changes in Serum FGF21 Levels and Lenvatinib-Induced Appetite Loss in Patients with Unresectable Hepatocellular Carcinoma

Lenvatinib, used for unresectable hepatocellular carcinoma (HCC), causes appetite loss, but the underlying mechanisms, clinical impact, and predictive factors have been unclear. The endocrine factor FGF21 modulates appetite and is involved in cachexia. We evaluated the association between FGF21 level changes during lenvatinib treatment for unresectable HCC and appetite loss. Sixty-three eligible unresectable HCC patients who started lenvatinib treatment between 2018 and 2021 were included. We analyzed FGF21 levels at baseline; 1, 2, and 4 weeks after lenvatinib initiation, and before the onset of appetite loss. Grade ≥ 2 lenvatinib-induced appetite loss led to liver functional reserve deterioration at disease progression and a poor prognosis. Baseline characteristics and serum FGF21 levels were similar between patients with and without appetite loss. However, the serum FGF21 change rate increased significantly at 4 weeks post-lenvatinib initiation in patients with grade ≥ 2 appetite loss, as compared to those without appetite loss. Similar significant increases in the serum FGF21 level change rate were observed prior to grade ≥ 2 appetite loss onset. This suggests that changes in FGF21 levels can be used to predict patients with a greater risk of marked appetite loss and provides insights into the mechanisms underlying lenvatinib-induced appetite loss in patients with HCC.

1,5-Anhydro-D-Fructose Exhibits Satiety Effects via the Activation of Oxytocin Neurons in the Paraventricular Nucleus

1,5-Anhydro-D-fructose (1,5-AF) is a bioactive monosaccharide that is produced by the glycogenolysis in mammalians and is metabolized to 1,5-anhydro-D-glucitol (1,5-AG). 1,5-AG is used as a marker of glycemic control in diabetes patients. 1,5-AF has a variety of physiological activities, but its effects on energy metabolism, including feeding behavior, are unclarified. The present study examined whether 1,5-AF possesses the effect of satiety. Peroral administration of 1,5-AF, and not of 1,5-AG, suppressed daily food intake. Intracerebroventricular (ICV) administration of 1,5-AF also suppressed feeding. To investigate the neurons targeted by 1,5-AF, we investigated c-Fos expression in the hypothalamus and brain stem. ICV injection of 1,5-AF significantly increased c-Fos positive oxytocin neurons and mRNA expression of oxytocin in the paraventricular nucleus (PVN). Moreover, 1,5-AF increased cytosolic Ca²⁺ concentration of oxytocin neurons in the PVN. Furthermore, the satiety effect of 1,5-AF was abolished in oxytocin knockout mice. These findings reveal that 1,5-AF activates PVN oxytocin neurons to suppress feeding, indicating its potential as the energy storage monitoring messenger to the hypothalamus for integrative regulation of energy metabolism.

The Origins, Evolution, and Future of Dietary Methionine Restriction

The original description of dietary methionine restriction (MR) used semipurified diets to limit methionine intake to 20% of normal levels, and this reduction in dietary methionine increased longevity by ∼30% in rats. The MR diet also produces paradoxical increases in energy intake and expenditure and limits fat deposition while reducing tissue and circulating lipids and enhancing overall insulin sensitivity. In the years following the original 1993 report, a comprehensive effort has been made to understand the nutrient sensing and signaling systems linking reduced dietary methionine to the behavioral, physiological, biochemical, and transcriptional components of the response. Recent work has shown that transcriptional activation of hepatic fibroblast growth factor 21 (FGF21) is a key event linking the MR diet to many but not all components of its metabolic phenotype. These findings raise the interesting possibility of developing therapeutic, MR-based diets that produce the beneficial effects of FGF21 by nutritionally modulating its transcription and release.

Spatial distribution of beta-klotho mRNA in the mouse hypothalamus, hippocampal region, subiculum, and amygdala

Beta-klotho (KLB) is a co-receptor required for endocrine fibroblast growth factor (FGF) 15/19 and FGF21 signaling in the brain. Klb is prominent within the hypothalamus, which is consistent with its metabolic functions, but diverse roles for Klb are now emerging. Central Klb expression is low but discrete and may govern FGF-targeted sites. However, given its low expression, it is unclear if Klb mRNA is more widespread. We performed in situ hybridization to label Klb mRNA to generate spatial maps capturing the distribution and level of Klb within the mouse hypothalamus, hippocampal region, subiculum, and amygdala. Semi-quantitative analysis revealed that Klb-labeled cells may express low, medium, or high levels of Klb mRNA. Hypothalamic Klb hybridization was heterogeneous and varied rostrocaudally within the same region. Most Klb-labeled cells were found in the lateral hypothalamic zone, but the periventricular hypothalamic region, including the suprachiasmatic nucleus, contained the greatest proportion of cells expressing medium or high Klb levels. We also found heterogeneous Klb hybridization in the amygdala and subiculum, where Klb was especially distinct within the central amygdalar nucleus and ventral subiculum, respectively. By contrast, Klb-labeled cells in the hippocampal region only expressed low levels of Klb and were typically found in the pyramidal layer of Ammon's horn or dentate gyrus. The Klb-labeled regions identified in this study are consistent with reported roles of Klb in metabolism, taste preference, and neuroprotection. However, additional identified sites, including within the hypothalamus and amygdala, may suggest novel roles for FGF15/19 or FGF21 signaling. The central expression of beta-klotho (Klb) is essential for the physiological actions of endocrine fibroblast growth factors. Klb mRNA was widely expressed throughout the hypothalamus, hippocampus, and amygdala. However, the level of Klb expression varied between cells and contributed to a distinctive pattern of distribution within each brain structure. This article is protected by copyright. All rights reserved.

AgRP/NPY and POMC neurons in the arcuate nucleus and their potential role in treatment of obesity

Obesity is a major health crisis affecting over a third of the global population. This multifactorial disease is regulated via interoceptive neural circuits in the brain, whose alteration results in excessive body weight. Certain central neuronal populations in the brain are recognised as crucial nodes in energy homeostasis; in particular, the hypothalamic arcuate nucleus (ARC) region contains two peptide microcircuits that control energy balance with antagonistic functions: agouti-related peptide/neuropeptide-Y (AgRP/NPY) signals hunger and stimulates food intake; and pro-opiomelanocortin (POMC) signals satiety and reduces food intake. These neuronal peptides levels react to energy status and integrate signals from peripheral ghrelin, leptin, and insulin to regulate feeding and energy expenditure. To manage obesity comprehensively, it is crucial to understand cellular and molecular mechanisms of information processing in ARC neurons, since these regulate energy homeostasis. Importantly, a specific strategy focusing on ARC circuits needs to be devised to assist in treating obese patients and maintaining weight loss with minimal or no side effects. The aim of this review is to elucidate the recent developments in the study of AgRP-, NPY- and POMC-producing neurons, specific to their role in controlling metabolism. The impact of ghrelin, leptin, and insulin signalling via action of these neurons is also surveyed, since they also impact energy balance through this route. Lastly, we present key proteins, targeted genes, compounds, drugs, and therapies that actively work via these neurons and could potentially be used as therapeutic targets for treating obesity conditions.

Circadian Clock Component BMAL1 in the Paraventricular Nucleus Regulates Glucose Metabolism

It is suggested that clock genes link the circadian rhythm to glucose and lipid metabolism. In this study, we explored the role of the clock gene Bmal1 in the hypothalamic paraventricular nucleus (PVN) in glucose metabolism. The Sim1-Cre-mediated deletion of Bmal1 markedly reduced insulin secretion, resulting in impaired glucose tolerance. The pancreatic islets' responses to glucose, sulfonylureas (SUs) and arginine vasopressin (AVP) were well maintained. To specify the PVN neuron subpopulation targeted by Bmal1, the expression of neuropeptides was examined. In these knockout (KO) mice, the mRNA expression of Avp in the PVN was selectively decreased, and the plasma AVP concentration was also decreased. However, fasting suppressed Avp expression in both KO and Cre mice. These results demonstrate that PVN BMAL1 maintains Avp expression in the PVN and release to the circulation, possibly providing islet β-cells with more AVP. This action helps enhance insulin release and, consequently, glucose tolerance. In contrast, the circadian variation of Avp expression is regulated by feeding, but not by PVN BMAL1.

A comparative account of nesfatin-1 in vertebrates

Nesfatin-1 was discovered as an anorexigenic peptide derived from proteolytic cleavage of the prepropeptide, nucleobindin 2 (NUCB2). It is widely expressed in central as well as peripheral tissues and is known to have pleiotropic effects such as regulation of feeding, reproduction, cardiovascular functions and maintenance of glucose homeostasis. In order to execute its multifaceted role, nesfatin-1 employs diverse signaling pathways though its receptor has not been identified till date. Further, nesfatin-1 is reported to be under the regulatory effect of feeding state, nutritional status as well as several metabolic and reproductive hormones. This peptide has also been associated with variety of human diseases, especially metabolic, reproductive, cardiovascular and mental disorders. The current review is aimed to present a consolidated picture and highlight lacunae for further investigation in order to develop a deeper comprehensive understanding on physiological significance of nesfatin-1 in vertebrates.

A pyrexic effect of FGF21 independent of energy expenditure and UCP1

OBJECTIVE

Administration of FGF21 to mice reduces body weight and increases body temperature. The increase in body temperature is generally interpreted as hyperthermia, i.e. a condition secondary to the increase in energy expenditure (heat production). Here, we examine an alternative hypothesis: that FGF21 has a direct pyrexic effect, i.e. FGF21 increases body temperature independently of any effect on energy expenditure.

METHODS

We studied the effects of FGF21 treatment on body temperature and energy expenditure in high-fat-diet-fed and chow-fed mice exposed acutely to various ambient temperatures, in high-fat diet-fed mice housed at 30 °C (i.e. at thermoneutrality), and in mice lacking uncoupling protein 1 (UCP1).

RESULTS

In every model studied, FGF21 increased body temperature, but energy expenditure was increased only in some models. The effect of FGF21 on body temperature was more (not less, as expected in hyperthermia) pronounced at lower ambient temperatures. Effects on body temperature and energy expenditure were temporally distinct (daytime versus nighttime). FGF21 enhanced UCP1 protein content in brown adipose tissue (BAT); there was no measurable UCP1 protein in inguinal brite/beige adipose tissue. FGF21 increased energy expenditure through adrenergic stimulation of BAT. In mice lacking UCP1, FGF21 did not increase energy expenditure but increased body temperature by reducing heat loss, e.g. a reduced tail surface temperature.

CONCLUSION

The effect of FGF21 on body temperature is independent of UCP1 and can be achieved in the absence of any change in energy expenditure. Since elevated body temperature is a primary effect of FGF21 and can be achieved without increasing energy expenditure, only limited body weight-lowering effects of FGF21 may be expected.

Severe protein deficiency induces hepatic expression and systemic level of FGF21 but inhibits its hypothalamic expression in growing rats

To study, in young growing rats, the consequences of different levels of dietary protein deficiency on food intake, body weight, body composition, and energy balance and to assess the role of FGF21 in the adaptation to a low protein diet. Thirty-six weanling rats were fed diets containing 3%, 5%, 8%, 12%, 15% and 20% protein for three weeks. Body weight, food intake, energy expenditure and metabolic parameters were followed throughout this period. The very low-protein diets (3% and 5%) induced a large decrease in body weight gain and an increase in energy intake relative to body mass. No gain in fat mass was observed because energy expenditure increased in proportion to energy intake. As expected, Fgf21 expression in the liver and plasma FGF21 increased with low-protein diets, but Fgf21 expression in the hypothalamus decreased. Under low protein diets (3% and 5%), the increase in liver Fgf21 and the decrease of Fgf21 in the hypothalamus induced an increase in energy expenditure and the decrease in the satiety signal responsible for hyperphagia. Our results highlight that when dietary protein decreases below 8%, the liver detects the low protein diet and responds by activating synthesis and secretion of FGF21 in order to activate an endocrine signal that induces metabolic adaptation. The hypothalamus, in comparison, responds to protein deficiency when dietary protein decreases below 5%.

Neuroendocrine Peptides of the Gut and Their Role in the Regulation of Food Intake

The regulation of food intake encompasses complex interplays between the gut and the brain. Among them, the gastrointestinal tract releases different peptides that communicate the metabolic state to specific nuclei in the hindbrain and the hypothalamus. The present overview gives emphasis on seven peptides that are produced by and secreted from specialized enteroendocrine cells along the gastrointestinal tract in relation with the nutritional status. These established modulators of feeding are ghrelin and nesfatin-1 secreted from gastric X/A-like cells, cholecystokinin (CCK) secreted from duodenal I-cells, glucagon-like peptide 1 (GLP-1), oxyntomodulin, and peptide YY (PYY) secreted from intestinal L-cells and uroguanylin (UGN) released from enterochromaffin (EC) cells. © 2021 American Physiological Society. Compr Physiol 11:1679-1730, 2021.

The Effect of FGF21 and Its Genetic Variants on Food and Drug Cravings, Adipokines and Metabolic Traits

Fibroblast growth factor 21 (FGF21) is a regulator of addictive behavior. Increasing evidence suggests an impact of FGF21 on eating behavior, food and drug cravings and on other adipokines like insulin-like growth factor 1 (IGF-1) or adiponectin. We investigated the association of serum FGF21 and genetic variants with aspects of food and drug craving and obesity related metabolic parameters including serum adipokine levels. Standardized questionnaires, blood samples and anthropometric data of the Sorbs cohort (n = 1046) were analyzed using SPSS. For genetic analyses, the FGF21-locus ±10 kb was genotyped and analyzed using PLINK. Validation was conducted in a second independent cohort (n = 704). FGF21 was significantly associated with alcohol and coffee consumption, smoking and eating behavior (disinhibition). We confirmed correlations of FGF21 serum levels with IGF-1, adiponectin, pro-enkephalin, adipocyte fatty-acid-binding protein, chemerin and progranulin. FGF21 genetic variants were associated with anthropometric and metabolic parameters, adipokines, food and drug craving while strongest evidence was seen with low-density lipoprotein cholesterol (LDL-C). We highlight the potential role of FGF21 in food and drug cravings and provide new insights regarding the link of FGF21 with other adipokines as well as with metabolic traits, in particular those related to lipid metabolism (LDL-C).

The Nuanced Metabolic Functions of Endogenous FGF21 Depend on the Nature of the Stimulus, Tissue Source, and Experimental Model

Fibroblast growth factor 21 (FGF21) is a hormone that is involved in the regulation of lipid, glucose, and energy metabolism. Pharmacological FGF21 administration promotes weight loss and improves insulin sensitivity in rodents, non-human primates, and humans. However, pharmacologic effects of FGF21 likely differ from its physiological effects. Endogenous FGF21 is produced by many cell types, including hepatocytes, white and brown adipocytes, skeletal and cardiac myocytes, and pancreatic beta cells, and acts on a diverse array of effector tissues such as the brain, white and brown adipose tissue, heart, and skeletal muscle. Different receptor expression patterns dictate FGF21 function in these target tissues, with the primary effect to coordinate responses to nutritional stress. Moreover, different nutritional stimuli tend to promote FGF21 expression from different tissues; i.e., fasting induces hepatic-derived FGF21, while feeding promotes white adipocyte-derived FGF21. Target tissue effects of FGF21 also depend on its capacity to enter the systemic circulation, which varies widely from known FGF21 tissue sources in response to various stimuli. Due to its association with obesity and non-alcoholic fatty liver disease, the metabolic effects of endogenously produced FGF21 during the pathogenesis of these conditions are not well known. In this review, we will highlight what is known about endogenous tissue-specific FGF21 expression and organ cross-talk that dictate its diverse physiological functions, with particular attention given to FGF21 responses to nutritional stress. The importance of the particular experimental design, cellular and animal models, and nutritional status in deciphering the diverse metabolic functions of endogenous FGF21 cannot be overstated.

Nutritional Regulation of Hepatic FGF21 by Dietary Restriction of Methionine

FGF21 is a potent metabolic regulator of energy balance, body composition, lipid metabolism, and glucose homeostasis. Initial studies reported that it was increased by fasting and the associated increase in ketones, but more recent work points to the importance of dietary protein and sensing of essential amino acids in FGF21 regulation. For example, dietary restriction of methionine produces a rapid transcriptional activation of hepatic FGF21 that results in a persistent 5- to 10-fold increase in serum FGF21. Although FGF21 is a component of a complex transcriptional program activated by methionine restriction (MR), loss-of-function studies show that FGF21 is an essential mediator of the resulting effects of the MR diet on energy balance, remodeling of adipose tissue, and enhancement of insulin sensitivity. These studies also show that FGF21 signaling in the brain is required for the MR diet-induced increase in energy expenditure (EE) and reduction of adiposity. Collectively, the evidence supports the view that the liver functions as a sentinel to detect and respond to changes in dietary amino acid composition, and that the resulting mobilization of hepatic FGF21 is a key element of the homeostatic response. These findings raise the interesting possibility that therapeutic diets could be developed that produce sustained, biologically effective increases in FGF21 by nutritionally modulating its transcription and release.

Disease-specific plasma levels of mitokines FGF21, GDF15, and Humanin in type II diabetes and Alzheimer's disease in comparison with healthy aging

Fibroblast Growth Factor 21 (FGF21), Growth Differentiation Factor 15 (GDF15), and Humanin (HN) are mitochondrial stress-related mitokines, whose role in health and disease is still debated. In this study, we confirmed that their plasma levels are positively correlated with age in healthy subjects. However, when looking at patients with type 2 diabetes (T2D) or Alzheimer's disease (AD), two age-related diseases sharing a mitochondrial impairment, we found that GDF15 is elevated in T2D but not in AD and represents a risk factor for T2D complications, while FGF21 and HN are lower in AD but not in T2D. Moreover, FGF21 reaches the highest levels in centenarian' offspring, a model of successful aging. As a whole, these data indicate that (i) the adaptive mitokine response observed in healthy aging is lost in age-related diseases, (ii) a common expression pattern of mitokines does not emerge in T2D and AD, suggesting an unpredicted complexity and disease-specificity, and (iii) FGF21 emerges as a candidate marker of healthy aging.

Endogenous NUCB2/Nesfatin-1 Regulates Energy Homeostasis Under Physiological Conditions in Male Rats

Nesfatin-1 is the proteolytic cleavage product of Nucleobindin 2, which is expressed both in a number of brain nuclei (e. g., the paraventricular nucleus of the hypothalamus) and peripheral tissues. While Nucleobindin 2 acts as a calcium binding protein, nesfatin-1 was shown to affect energy homeostasis upon central nervous administration by decreasing food intake and increasing thermogenesis. In turn, Nucleobindin 2 mRNA expression is downregulated in starvation and upregulated in the satiated state. Still, knowledge about the physiological role of endogenous Nucleobindin 2/nesfatin-1 in the control of energy homeostasis is limited and since its receptor has not yet been identified, rendering pharmacological blockade impossible. To overcome this obstacle, we tested and successfully established an antibody-based experimental model to antagonize the action of nesfatin-1. This model was then employed to investigate the physiological role of endogenous Nucleobindin 2/nesfatin-1. To this end, we applied nesfatin-1 antibody into the paraventricular nucleus of satiated rats to antagonize the presumably high endogenous Nucleobindin 2/nesfatin-1 levels in this feeding condition. In these animals, nesfatin-1 antibody administration led to a significant decrease in thermogenesis, demonstrating the important role of endogenous Nucleobindin 2/nesfatin-1in the regulation of energy expenditure. Additionally, food and water intake were significantly increased, confirming and complementing previous findings. Moreover, neuropeptide Y was identified as a major downstream target of endogenous Nucleobindin 2/nesfatin-1.

FGF21 Signals Protein Status to the Brain and Adaptively Regulates Food Choice and Metabolism

Reduced dietary protein intake induces adaptive physiological changes in macronutrient preference, energy expenditure, growth, and glucose homeostasis. We demonstrate that deletion of the FGF21 co-receptor βKlotho (Klb) from the brain produces mice that are unable to mount a physiological response to protein restriction, an effect that is replicated by whole-body deletion of FGF21. Mice forced to consume a low-protein diet exhibit reduced growth, increased energy expenditure, and a resistance to diet-induced obesity, but the loss of FGF21 signaling in the brain completely abrogates that response. When given access to a higher protein alternative, protein-restricted mice exhibit a shift toward protein-containing foods, and central FGF21 signaling is essential for that response. FGF21 is an endocrine signal linking the liver and brain, which regulates adaptive, homeostatic changes in metabolism and feeding behavior during protein restriction.

NUCB2/nesfatin-1 - Inhibitory effects on food intake, body weight and metabolism

Since its discovery in 2006 by Oh-I and colleagues, NUCB2/nesfatin-1 encoded by nucleobindin-2 (NUCB2) has drawn sustained attention as reflected in over 500 publications. Among those, more than half focused on the alterations of food intake, body weight and metabolism (glucose, fat) induced by nesfatin-1 and/or NUCB2/nesfatin-1. In the current review we discuss the existing literature focusing on NUCB2/nesfatin-1's influence on food intake, body weight and glucose as well as fat metabolism and highlight gaps in knowledge.

ARCAgRP/NPY Neuron Activity Is Required for Acute Exercise-Induced Food Intake in Un-Trained Mice

While much is known about the role of agouti-regulated peptide/neuropeptide Y (AgRP/NPY) and pro-opiomelanocortin (POMC) neurons to regulate energy homeostasis, little is known about how forced energy expenditure, such as exercise, modulates these neurons and if these neurons are involved in post-exercise feeding behaviors. We utilized multiple mouse models to investigate the effects of acute, moderate-intensity exercise on food intake and neuronal activity in the arcuate nucleus (ARC) of the hypothalamus. NPY-GFP reporter mice were utilized for immunohistochemistry and patch-clamp electrophysiology experiments investigating neuronal activation immediately after acute treadmill exercise. Additionally, ARC^AgRP/NPY neuron inhibition was performed using the Designer Receptors Exclusively Activated by Designer Drugs (DREADD) system in AgRP-Cre transgenic mice to investigate the importance of AgRP/NPY neurons in post-exercise feeding behaviors. Our experiments revealed that acute moderate-intensity exercise significantly increased food intake, ARC^AgRP/NPY neuron activation, and PVN^Sim1 neuron activation, while having no effect on ARC^POMC neurons. Strikingly, this exercise-induced refeeding was completely abolished when ARC^AgRP/NPY neuron activity was inhibited. While acute exercise also increased PVN^Sim1 neuron activity, inhibition of ARC^AgRP/NPY neurons had no effect on PVN^Sim1 neuronal activation. Overall, our results reveal that ARC^AgRP/NPY activation is required for acute exercise induced food intake in mice, thus providing insight into the critical role of ARC^AgRP/NPY neurons in maintaining energy homeostasis in cases of exercise-mediated energy deficit.

FGF21 and the Physiological Regulation of Macronutrient Preference

The ability to respond to variations in nutritional status depends on regulatory systems that monitor nutrient intake and adaptively alter metabolism and feeding behavior during nutrient restriction. There is ample evidence that the restriction of water, sodium, or energy intake triggers adaptive responses that conserve existing nutrient stores and promote the ingestion of the missing nutrient, and that these homeostatic responses are mediated, at least in part, by nutritionally regulated hormones acting within the brain. This review highlights recent research that suggests that the metabolic hormone fibroblast growth factor 21 (FGF21) acts on the brain to homeostatically alter macronutrient preference. Circulating FGF21 levels are robustly increased by diets that are high in carbohydrate but low in protein, and exogenous FGF21 treatment reduces the consumption of sweet foods and alcohol while alternatively increasing the consumption of protein. In addition, while control mice adaptively shift macronutrient preference and increase protein intake in response to dietary protein restriction, mice that lack either FGF21 or FGF21 signaling in the brain fail to exhibit this homeostatic response. FGF21 therefore mediates a unique physiological niche, coordinating adaptive shifts in macronutrient preference that serve to maintain protein intake in the face of dietary protein restriction.

Circulating FGF21 Levels in Human Health and Metabolic Disease

Human fibroblast growth factor 21 (FGF21) is primarily produced and secreted by the liver as a hepatokine. This hormone circulates to its target tissues (e. g., brain, adipose tissue), which requires two components, one of the preferred FGF receptor isoforms (FGFR1c and FGFR3c) and the co-factor beta-Klotho (KLB) to trigger downstream signaling pathways. Although targeting FGF21 signaling in humans by analogues and receptor agonists results in beneficial effects, e. g., improvements in plasma lipids and decreased body weight, it failed to recapitulate the improvements in glucose handling shown for many mouse models. FGF21's role and metabolic effects in mice and its therapeutic potential have extensively been reviewed elsewhere. In this review we focus on circulating FGF21 levels in humans and their associations with disease and clinical parameters, focusing primarily on obesity and obesity-associated diseases such as type-2 diabetes. We provide a comprehensive overview on human circulating FGF21 levels under normal physiology and metabolic disease. We discuss the emerging field of inactivating FGF21 in human blood by fibroblast activation protein (FAP) and its potential clinical implications.

Fibroblast growth factor 21: an endocrine inhibitor of sugar and alcohol appetite

Fibroblast growth factor 21 (FGF21) is a liver-derived hormone with pleiotropic metabolic effects. Its production is induced by various dietary imbalances in mice (including low-protein and ketogenic diets, fructose feeding and ethanol), hinting that it might influence food preference given the role of the liver in maintaining homeostatic levels of circulating nutrients. In 2016, it was shown that FGF21 selectively inhibits consumption of sugars and the primary product of their fermentation, ethanol, but not intake of fat, protein or complex carbohydrates. Since then, studies have sought to unravel this selectivity, its physiological purpose and translational relevance, as well as delineate the neural mechanisms involved. Initially found to impact ingestive behaviours in mice and non-human primates, FGF21 is also induced in humans by sugars and, far more dramatically, by acute alcohol intake. Genetic studies have revealed that patterns of weekly candy and alcohol consumption are associated with genetic variants in FGF21 and its co-receptor β-klotho (KLB), suggesting that liking for sugar, and fermented sugar, may be influenced by natural variation in FGF21 signal strength in humans. Herein, we discuss our nascent understanding of FGF21 as a selective negative regulator of sugar and alcohol appetite as well as reasons why such a peculiar system may have evolved in mammals. Uncovering the regulatory network governing sugar, and fermented sugar, intake could provide new opportunities to improve dietary choices in a population suffering from Western diet-induced diseases fuelled in part by a runaway sweet - and alcohol - tooth.

Effects of central FGF21 infusion on the hypothalamus-pituitary-thyroid axis and energy metabolism in rats

The aim of this study was to evaluate the impact of intracerebroventricular chronic fibroblast growth factor 21 (FGF21) infusion on hypothalamic-pituitary-thyroid (HPT) axis, energy metabolism, food intake and body weight. Thirty male Wistar albino rats were used and divided into three groups including control, sham (vehicle) and FGF21 infused groups (n = 10). Intracerebroventricularly, FGF21 and vehicle groups were infused for 7 days with FGF21 (0.72 µg/day) and artificial cerebrospinal fluid, respectively. During the experimental period, changes in food intake and body weight were recorded daily. Serum thyroid stimulating hormone (TSH), Triiodothyronine (T3) and thyroxine (T4) levels were measured using ELISA. TRH and uncoupling protein 1 (UCP1) gene expressions were analyzed by using RT-PCR in hypothalamus and adipose tissues, respectively. Chronic infusion of FGF21 significantly increased serum TSH (p < 0.05), T3 (p < 0.05) and T4 (p < 0.001) levels. Additionally, hypothalamic TRH (p < 0.05) and UCP1 gene expressions (p < 0.05) in white adipose tissue were found to be higher than in the vehicle and control groups. While FGF21 infusion did not cause a significant change in food consumption, it caused a reduction in the body weight of rats (p < 0.05). Our findings indicate that FGF21 may have an effect on energy metabolism via the HPT axis.

Current Understanding of the Role of Nesfatin-1

Nesfatin-1 was discovered in 2006 and implicated in the regulation of food intake. Subsequently, its widespread central and peripheral distribution gave rise to additional effects. Indeed, a multitude of actions were described, including modulation of gastrointestinal functions, glucose and lipid metabolism, thermogenesis, mediation of anxiety and depression, as well as cardiovascular and reproductive functions. Recent years have witnessed a great increase in our knowledge of these effects and their underlying mechanisms, which will be discussed in the present review. Lastly, gaps in knowledge will be highlighted to foster further studies.

Protective role of AgRP neuron's PDK1 against salt-induced hypertension

In the hypothalamic arcuate nucleus (ARC), orexigenic agouti-related peptide (AgRP) neurons regulate feeding behavior and energy homeostasis. The 3-phosphoinositide-dependent protein kinase-1 (PDK1) in AgRP neurons serves as a major signaling molecule for leptin and insulin, the hormones regulating feeding behavior, energy homeostasis and circulation. However, it is unclear whether PDK1 in AGRP neurons is also involved in regulation of blood pressure. This study explored it by generating and analyzing AgRP neuron-specific PDK1 knockout (Agrp-Pdk1^flox/flox) mice and effect of high salt diet on blood pressure in KO and WT mice was analyzed. Under high salt diet feeding, systolic blood pressure (SBP) of Agrp-Pdk1^flox/flox mice was significantly elevated compared to Agrp-Cre mice. When the high salt diet was switched to control low salt diet, SBP of Agrp-Pdk1^flox/flox mice returned to the basal level observed in Agrp-Cre mice within 1 week. In Agrp-Pdk1^flox/flox mice, urinary noradrenalin excretion and NUCB2 mRNA expression in hypothalamic paraventricular nucleus (PVN) were markedly upregulated. Moreover, silencing of NUCB2 in the PVN counteracted the rises in urinary noradrenalin excretions and SBP. These results demonstrate a novel role of PDK1 in AgRP neurons to counteract the high salt diet-induced hypertension by preventing hyperactivation of PVN nesfatin-1 neurons.

Electroacupuncture Reduces Weight in Diet-Induced Obese Rats via Hypothalamic Tsc1 Promoter Demethylation and Inhibition of the Activity of mTORC1 Signaling Pathway

Subject

The study aimed to investigate the mechanism of electroacupuncture reducing weight via tuberous sclerosis complex 1 (Tsc1) promoter methylation, inhibiting the mammalian target of rapamycin complex 1 (mTORC1) pathway.

Materials and Methods

Male Sprague-Dawley rats were divided into chow-fed group (chow group) or high-fat diet group (HF group) for 14 weeks. The obesity rats in HF group were randomly divided into electroacupuncture group (EA group) and diet-induced obesity (DIO) group, which received EA stimulation on bilateral ST25, RN12, SP6, and ST36 for 4 weeks or no further treatment, respectively. Methylation of the Tsc1 gene promoter and expression of agouti-related protein (AgRP), neuropeptide Y (NPY), and proopiomelanocortin (PoMC) were detected at the 18th week.

Results

At week 18, weight, body fat, and the body fat rate in DIO group were significantly higher than those of the chow and EA group. Compared with the chow group, the DIO group had increased methylation of the Tsc1 gene promoter and expression of mTORC1, AgRP, and NPY gene and decreased PoMC in the hypothalamus; after EA, methylation of the Tsc1 gene promoter, mRNA, and protein of the mTORC1 and expression of AgRP and NPY gene decreased and PoMC increased significantly.

Conclusions

Our study could shed light on the potential pathway where EA exerts effects on the mechanism of EA treatment for obesity through the hypothalamic Tsc1 promoter demethylation and inhibition of the activity of mTORC1 signaling pathway.

α-MSH Influences the Excitability of Feeding-Related Neurons in the Hypothalamus and Dorsal Vagal Complex of Rats

Alpha-melanocyte-stimulating hormone (α-MSH) is processed from proopiomelanocortin (POMC) and acts on the melanocortin receptors, MC3 and MC4. α-MSH plays a key role in energy homeostasis. In the present study, to shed light on the mechanisms by which α-MSH exerts its anorectic effects, extracellular neuronal activity was recorded in the hypothalamus and the dorsal vagal complex (DVC) of anesthetized rats. We examined the impact of α-MSH on glucose-sensing neurons and gastric distension (GD) sensitive neurons. In the lateral hypothalamus (LHA), α-MSH inhibited 75.0% of the glucose-inhibited (GI) neurons. In the ventromedial nucleus (VMN), most glucose-sensitive neurons were glucose-excited (GE) neurons, which were mainly activated by α-MSH. In the paraventricular nucleus (PVN), α-MSH suppressed the majority of GI neurons and excited most GE neurons. In the DVC, among the 20 GI neurons examined for a response to α-MSH, 1 was activated, 16 were depressed, and 3 failed to respond. Nineteen of 24 GE neurons were activated by α-MSH administration. Additionally, among the 42 DVC neurons examined for responses to GD, 23 were excited (GD-EXC) and 19 were inhibited (GD-INH). Fifteen of 20 GD-EXC neurons were excited, whereas 11 out of 14 GD-INH neurons were suppressed by α-MSH. All these responses were abolished by pretreatment with the MC3/4R antagonist, SHU9119. In conclusion, the activity of glucose-sensitive neurons and GD-sensitive neurons in the hypothalamus and DVC can be modulated by α-MSH.

Low protein-induced increases in FGF21 drive UCP1-dependent metabolic but not thermoregulatory endpoints

Dietary protein restriction increases adipose tissue uncoupling protein 1 (UCP1), energy expenditure and food intake, and these effects require the metabolic hormone fibroblast growth factor 21 (FGF21). Here we test whether the induction of energy expenditure during protein restriction requires UCP1, promotes a resistance to cold stress, and is dependent on the concomitant hyperphagia. Wildtype, Ucp1-KO and Fgf21-KO mice were placed on control and low protein (LP) diets to assess changes in energy expenditure, food intake and other metabolic endpoints. Deletion of Ucp1 blocked LP-induced increases in energy expenditure and food intake, and exacerbated LP-induced weight loss. While LP diet increased energy expenditure and Ucp1 expression in an FGF21-dependent manner, neither LP diet nor the deletion of Fgf21 influenced sensitivity to acute cold stress. Finally, LP-induced energy expenditure occurred even in the absence of hyperphagia. Increased energy expenditure is a primary metabolic effect of dietary protein restriction, and requires both UCP1 and FGF21 but is independent of changes in food intake. However, the FGF21-dependent increase in UCP1 and energy expenditure by LP has no effect on the ability to acutely respond to cold stress, suggesting that LP-induced increases in FGF21 impact metabolic but not thermogenic endpoints.