FGF21 contributes to neuroendocrine control of female reproduction

Effects of Intermittent Fasting on Female Reproductive Function: A Review of Animal and Human Studies

PURPOSE OF REVIEW

Intermittent fasting has gained significant attention, yet a comprehensive understanding of its impact on female reproductive health is lacking. This review aims to fill this gap by examining various intermittent fasting regimens and their effects on female reproductive function, along with potential mechanisms.

RECENT FINDINGS

In healthy non-overweight/obese or pregnant animal models, alternate-day fasting (ADF) and an 8-h time-restricted feeding (TRF) window may have adverse effects on reproductive function. However, these regimens show potential to mitigate negative consequences induced by a high-fat diet (HFD) or environmental exposure. A 10-h TRF demonstrates benefits in improving fertility in both normal-weight and HFD-fed animal models. In women with overweight/obesity or polycystic ovary syndrome (PCOS), the 5:2 diet and TRF significantly reduce the free androgen index while elevating sex hormone binding globulin, promising improvements in menstrual regulation. For pregnant Muslim women, available data do not strongly indicate adverse effects of Ramadan fasting on preterm delivery, but potential downsides to maternal weight gain, neonatal birthweight, and long-term offspring health need consideration. Factors linking intermittent fasting to female reproductive health include the circadian clock, gut microbiota, metabolic regulators, and modifiable lifestyles. Drawing definitive conclusions remains challenging in this evolving area. Nonetheless, our findings underscore the potential utility of intermittent fasting regimens as a therapeutic approach for addressing menstruation irregularities and infertility in women with obesity and PCOS. On the other hand, pregnant women should remain cognizant of potential risks associated with intermittent fasting practices.

Fibroblast growth factor 21

Fibroblast growth factor 21 (FGF21) belongs to the FGF19 subfamily and acts systemically, playing a key role in inter-organ crosstalk. Ranging from metabolism, reproduction, and immunity, FGF21 is a pleiotropic hormone which contributes to various physiological processes. Although most of its production across species stems from hepatic tissues, expression of FGF21 in mice has also been identified in adipose tissue, thymus, heart, pancreas, and skeletal muscle. Elevated FGF21 levels are affiliated with various diseases and conditions, such as obesity, type 2 diabetes, preeclampsia, as well as cancer. Murine knockout models are viable and show modest weight gain, while overexpression and gain-of-function models display resistance to weight gain, altered bone volume, and enhanced immunity. In addition, FGF21-based therapies are at the forefront of biopharmaceutical strategies aimed at treating metabolic dysfunction-associated steatotic liver disease.

Metabolic disorder: the dark side of ovarian aging

Ovarian aging plays an important role in the aging process of the whole body. It has been reported that metabolic disorder may significantly contribute to ovarian aging. This article highlights recent advances in metabolic regulation of ovarian aging and highlights key issues in the field.

Development of Zalfermin, a Long-Acting Proteolytically Stabilized FGF21 Analog

Here, we describe the development of the FGF21 analog zalfermin (NNC0194-0499, 15), intended for once-weekly sc dosing. Protein engineering was needed to address inherent druggability issues of the natural FGF21 hormone. Thus, deamidation of Asp121 was solved by mutation to glutamine, and oxidation of Met168 was solved by mutation to leucine. N-terminal region degradation by dipeptidyl peptidase IV was prevented by alanine residue elongation. To prevent inactivating metabolism by fibroblast activation protein and carboxypeptidase-like activity in the C-terminal region, and to achieve t1/2 extension (53 h in cynomolgus monkeys), we introduced a C18 fatty diacid at the penultimate position 180. The fatty diacid binds albumin in a reversible manner, such that the free fraction of zalfermin potently activates the FGF-receptor complex and retains receptor selectivity compared with FGF21, providing strong efficacy on body weight loss in diet-induced obese mice. Zalfermin is currently being clinically evaluated for the treatment of metabolic dysfunction-associated steatohepatitis.

Metabolic Crosstalk between Liver and Brain: From Diseases to Mechanisms

Multiple organs and tissues coordinate to respond to dietary and environmental challenges. It is interorgan crosstalk that contributes to systemic metabolic homeostasis. The liver and brain, as key metabolic organs, have their unique dialogue to transmit metabolic messages. The interconnected pathogenesis of liver and brain is implicated in numerous metabolic and neurodegenerative disorders. Recent insights have positioned the liver not only as a central metabolic hub but also as an endocrine organ, capable of secreting hepatokines that transmit metabolic signals throughout the body via the bloodstream. Metabolites from the liver or gut microbiota also facilitate a complex dialogue between liver and brain. In parallel to humoral factors, the neural pathways, particularly the hypothalamic nuclei and autonomic nervous system, are pivotal in modulating the bilateral metabolic interplay between the cerebral and hepatic compartments. The term "liver-brain axis" vividly portrays this interaction. At the end of this review, we summarize cutting-edge technical advancements that have enabled the observation and manipulation of these signals, including genetic engineering, molecular tracing, and delivery technologies. These innovations are paving the way for a deeper understanding of the liver-brain axis and its role in metabolic homeostasis.

Fibroblast growth factor 21 alleviates idiopathic pulmonary fibrosis by inhibiting PI3K-AKT-mTOR signaling and stimulating autophagy

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive pulmonary disease with an unclear pathogenesis and no available specific drug treatment. The principal etiological factors are lung inflammation caused by environmental factors, damage to alveolar epithelial cells, leading to epithelial-mesenchymal transition (EMT), and the abnormal proliferation of fibroblasts. Here, we have demonstrated that fibroblast growth factor 21 (FGF21) ameliorates IPF via the autophagy pathway. We administered FGF21 to bleomycin (BLM)-treated mice, which ameliorated their defects in lung function, reduced the accumulation of collagen, restored tissue structure, reduced the deposition of hydroxyproline, reduced the expression of collagen I and α-SMA and increased the expression of E-cadherin. The expression of LC3BII and the number of autophagosomes were significantly higher in the lungs. The expression of AKT and mTOR was significantly reduced by FGF21 treatment. We also determined the effects of FGF21 in A549 cells treated with TGF-β, and found that FGF21 significantly inhibits activation of the AKT signaling pathway, thereby reducing TGF-β-induced EMT and preventing the uncontrolled proliferation of fibroblasts. We conclude that FGF21 ameliorates IPF by inhibiting the PI3K-AKT-mTOR signaling pathway and activating autophagy, which provides a theoretical basis for FGF21 to be used for the treatment of IPF.

Expanding the genetics and phenotypes of ocular congenital cranial dysinnervation disorders

Purpose

To identify genetic etiologies and genotype/phenotype associations for unsolved ocular congenital cranial dysinnervation disorders (oCCDDs).

Methods

We coupled phenotyping with exome or genome sequencing of 467 pedigrees with genetically unsolved oCCDDs, integrating analyses of pedigrees, human and animal model phenotypes, and de novo variants to identify rare candidate single nucleotide variants, insertion/deletions, and structural variants disrupting protein-coding regions. Prioritized variants were classified for pathogenicity and evaluated for genotype/phenotype correlations.

Results

Analyses elucidated phenotypic subgroups, identified pathogenic/likely pathogenic variant(s) in 43/467 probands (9.2%), and prioritized variants of uncertain significance in 70/467 additional probands (15.0%). These included known and novel variants in established oCCDD genes, genes associated with syndromes that sometimes include oCCDDs (e.g., MYH10, KIF21B, TGFBR2, TUBB6), genes that fit the syndromic component of the phenotype but had no prior oCCDD association (e.g., CDK13, TGFB2), genes with no reported association with oCCDDs or the syndromic phenotypes (e.g., TUBA4A, KIF5C, CTNNA1, KLB, FGF21), and genes associated with oCCDD phenocopies that had resulted in misdiagnoses.

Conclusion

This study suggests that unsolved oCCDDs are clinically and genetically heterogeneous disorders often overlapping other Mendelian conditions and nominates many candidates for future replication and functional studies.

Circadian Regulation of Endocrine Fibroblast Growth Factors on Systemic Energy Metabolism

The circadian clock is an endogenous biochemical timing system that coordinates the physiology and behavior of organisms to earth's ∼24-hour circadian day/night cycle. The central circadian clock synchronized by environmental cues hierarchically entrains peripheral clocks throughout the body. The circadian system modulates a wide variety of metabolic signaling pathways to maintain whole-body metabolic homeostasis in mammals under changing environmental conditions. Endocrine fibroblast growth factors (FGFs), namely FGF15/19, FGF21, and FGF23, play an important role in regulating systemic metabolism of bile acids, lipids, glucose, proteins, and minerals. Recent evidence indicates that endocrine FGFs function as nutrient sensors that mediate multifactorial interactions between peripheral clocks and energy homeostasis by regulating the expression of metabolic enzymes and hormones. Circadian disruption induced by environmental stressors or genetic ablation is associated with metabolic dysfunction and diurnal disturbances in FGF signaling pathways that contribute to the pathogenesis of metabolic diseases. Time-restricted feeding strengthens the circadian pattern of metabolic signals to improve metabolic health and prevent against metabolic diseases. Chronotherapy, the strategic timing of medication administration to maximize beneficial effects and minimize toxic effects, can provide novel insights into linking biologic rhythms to drug metabolism and toxicity within the therapeutical regimens of diseases. Here we review the circadian regulation of endocrine FGF signaling in whole-body metabolism and the potential effect of circadian dysfunction on the pathogenesis and development of metabolic diseases. We also discuss the potential of chrononutrition and chronotherapy for informing the development of timing interventions with endocrine FGFs to optimize whole-body metabolism in humans. SIGNIFICANCE STATEMENT: The circadian timing system governs physiological, metabolic, and behavioral functions in living organisms. The endocrine fibroblast growth factor (FGF) family (FGF15/19, FGF21, and FGF23) plays an important role in regulating energy and mineral metabolism. Endocrine FGFs function as nutrient sensors that mediate multifactorial interactions between circadian clocks and metabolic homeostasis. Chronic disruption of circadian rhythms increases the risk of metabolic diseases. Chronological interventions such as chrononutrition and chronotherapy provide insights into linking biological rhythms to disease prevention and treatment.

Metabolic control of puberty: 60 years in the footsteps of Kennedy and Mitra's seminal work

An individual's nutritional status has a powerful effect on sexual maturation. Puberty onset is delayed in response to chronic energy insufficiency and is advanced under energy abundance. The consequences of altered pubertal timing for human health are profound. Late puberty increases the chances of cardiometabolic, musculoskeletal and neurocognitive disorders, whereas early puberty is associated with increased risks of adult obesity, type 2 diabetes mellitus, cardiovascular diseases and various cancers, such as breast, endometrial and prostate cancer. Kennedy and Mitra's trailblazing studies, published in 1963 and using experimental models, were the first to demonstrate that nutrition is a key factor in puberty onset. Building on this work, the field has advanced substantially in the past decade, which is largely due to the impressive development of molecular tools for experimentation and population genetics. In this Review, we discuss the latest advances in basic and translational sciences underlying the nutritional and metabolic control of pubertal development, with a focus on perspectives and future directions.

Growth factors and female reproduction in vertebrates

Female reproductive efficiency is influenced by the outcomes of various processes, including folliculogenesis, apoptosis, response to gonadotropin signaling, oocyte maturation, and ovulation. The role of hormones in regulating these processes and other reproductive activities has been well established. It is becoming increasingly evident that in addition to well-characterized hormones, growth factors play vital roles in regulating some of these reproductive activities. Growth factors and their receptors are widely distributed in vertebrate ovaries at different stages of ovarian development, indicating their involvement in intraovarian reproductive functions. In the ovary, cell surface receptors allow growth factors to regulate intraovarian reproductive activities. Understanding these actions in the reproductive axis would provide a tool to target growth factors and/or their receptors to yield desirable reproductive outcomes. These include enrichment of in vitro maturation and fertilization culture media, and management of infertility. This review discusses some widely characterized growth factors belonging to the TGF, EGF, IGF, FGF, and BDNF family of peptides and their role in female reproduction in vertebrates, with a focus on mammals.

Adropin may regulate corpus luteum formation and its function in adult mouse ovary

BACKGROUND

Adropin, a unique peptide hormone, has been associated with the regulation of several physiological processes, including glucose homeostasis, fatty acid metabolism, and neovascularization. However, its possible role in ovarian function is not understood. Our objective was to examine the expression of adropin and its putative receptor, GPR19, in the ovaries of mice at various phases of the estrous cycle.

METHODS

Immunohistochemistry and western blot analysis were performed to explore the localization and changes in expression of adropin and GPR19 in the ovaries during different phases of the estrous cycle in mice. Hormonal assays were performed with ELISA. An in vitro study was performed to examine the direct effect of adropin (10, 100 ng/ml) on ovarian function.

RESULTS

A western blot study showed that adropin and GPR19 proteins were maximum during the estrus phase of the estrous cycle. Interestingly, adropin and GPR19 displayed intense immunoreactivity in granulosa cells of large antral follicles and corpus luteum. This suggested the possible involvement of adropin in corpus luteum formation. Adropin treatment stimulated progesterone synthesis by increasing GPR19, StAR, CYP11A1, and 3β-HSD expressions, while it decreased estrogen synthesis by inhibiting 17β-HSD and aromatase protein expressions. Moreover, adropin treatment upregulated the cell cycle arrest-CDK inhibitor 1B (p27kip1), pERK1/2, and angiogenic protein (EG VEGF) that are involved in the process of luteinization.

CONCLUSIONS

Adropin GPR19 signaling promotes the synthesis of progesterone and upregulates the expression of p27kip1, EG VEGF, and erk1/2, resulting in cell cycle arrest and neovascularization, which ultimately leads to corpus luteum formation.

The pan-liver network theory: From traditional chinese medicine to western medicine

In traditional Chinese medicine (TCM), the liver is the "general organ" that is responsible for governing/maintaining the free flow of qi over the entire body and storing blood. According to the classic five elements theory, zang-xiang theory, yin-yang theory, meridians and collaterals theory, and the five-viscera correlation theory, the liver has essential relationships with many extrahepatic organs or tissues, such as the mother-child relationships between the liver and the heart, and the yin-yang and exterior-interior relationships between the liver and the gallbladder. The influences of the liver to the extrahepatic organs or tissues have been well-established when treating the extrahepatic diseases from the perspective of modulating the liver by using the ancient classic prescriptions of TCM and the acupuncture and moxibustion. In modern medicine, as the largest solid organ in the human body, the liver has the typical functions of filtration and storage of blood; metabolism of carbohydrates, fats, proteins, hormones, and foreign chemicals; formation of bile; storage of vitamins and iron; and formation of coagulation factors. The liver also has essential endocrine function, and acts as an immunological organ due to containing the resident immune cells. In the perspective of modern human anatomy, physiology, and pathophysiology, the liver has the organ interactions with the extrahepatic organs or tissues, for example, the gut, pancreas, adipose, skeletal muscle, heart, lung, kidney, brain, spleen, eyes, skin, bone, and sexual organs, through the circulation (including hemodynamics, redox signals, hepatokines, metabolites, and the translocation of microbiota or its products, such as endotoxins), the neural signals, or other forms of pathogenic factors, under normal or diseases status. The organ interactions centered on the liver not only influence the homeostasis of these indicated organs or tissues, but also contribute to the pathogenesis of cardiometabolic diseases (including obesity, type 2 diabetes mellitus, metabolic [dysfunction]-associated fatty liver diseases, and cardio-cerebrovascular diseases), pulmonary diseases, hyperuricemia and gout, chronic kidney disease, and male and female sexual dysfunction. Therefore, based on TCM and modern medicine, the liver has the bidirectional interaction with the extrahepatic organ or tissue, and this established bidirectional interaction system may further interact with another one or more extrahepatic organs/tissues, thus depicting a complex "pan-hepatic network" model. The pan-hepatic network acts as one of the essential mechanisms of homeostasis and the pathogenesis of diseases.

Fibroblast Growth Factor 21 Has a Diverse Role in Energetic and Reproductive Physiological Functions of Female Beef Cattle

Fibroblast growth factor 21 (FGF21) has been identified in multiple mammalian species as a molecular marker of energy metabolism while also providing negative feedback to the gonads. However, the role of FGF21 in regulating the energetic and reproductive physiology of beef heifers and cows has yet to be characterized. Herein, we investigated the temporal concentrations of FGF21 in female beef cattle from the prepubertal period to early lactation. Circulating concentrations of FGF21, non-esterified fatty acids, plasma urea nitrogen, glucose, and progesterone were assessed. Ultrasonography was employed to determine the onset of puberty and resumption of postpartum ovarian cyclicity as well as to measure backfat thickness. Finally, cows and calves underwent the weigh-suckle-weigh technique to estimate rate of milk production. We have revealed that FGF21 has an expansive role in the physiology of female beef cattle, including pubertal onset, adaptation to nutritional transition, rate of body weight gain, circulating markers of metabolism, and rate of milk production. In conclusion, FGF21 plays a role in physiological functions in beef cattle that can be applied to advance the understanding of basic scientific processes governing the nutritional regulation of reproductive function but also provides a novel means for beef cattle producers to select parameters of financial interest.

Feto-maternal cholesterol transport regulated by β-Klotho-FGF15 axis is essential for fetal growth

β-Klotho (β-KL) is indispensable to regulate lipid, glucose, and energy metabolism in adult animals. β-KL is highly expressed in the yolk sac, but its role in the developmental stages has not been established. We hypothesized that β-KL is required for metabolic regulation in the embryo and aimed to clarify the role of β-KL during development. Here, we show that β-KL regulates feto-maternal cholesterol transport through the yolk sac by mediating FGF 15 signaling, and also that impairment of the β-KL-FGF15 axis causes fetal growth restriction (FGR). Embryos of β- kl knockout (β-kl-/-) mice were morphologically normal but exhibited FGR before placental maturation. The body weight of β-kl-/- mice remained lower after birth. β-KL deletion reduced cholesterol supply from the maternal blood and led to lipid shortage in the embryos. These phenotypes were similar to those of embryos lacking FGF15, indicating that β-KL-FGF15 axis is essential for growth and lipid regulation in the embryonic stages. Our findings suggest that lipid abnormalities in early gestation provoke FGR, leading to reduced body size in later life.

Dietary Protein Regulates Female Estrous Cyclicity Partially via Fibroblast Growth Factor 21

Fibroblast growth factor 21 (FGF21), a hormone predominantly released in the liver, has emerged as a critical endocrine signal of dietary protein intake, but its role in the control of estrous cyclicity by dietary protein remains uncertain. To investigated the role of FGF21 and hypothalamic changes in the regulation of estrous cyclicity by dietary protein intake, female adult Sprague-Dawley rats with normal estrous cycles were fed diets with protein contents of 4% (P4), 8% (P8), 13% (P13), 18% (P18), and 23% (P23). FGF21 liver-specific knockout or wild-type mice were fed P18 or P4 diets to examine the role of liver FGF21 in the control of estrous cyclicity. Dietary protein restriction resulted in no negative effects on estrous cyclicity or ovarian follicular development when the protein content was greater than 8%. Protein restriction at 4% resulted in decreased bodyweight, compromised Kiss-1 expression in the hypothalamus, disturbed estrous cyclicity, and inhibited uterine and ovarian follicular development. The disturbed estrous cyclicity in rats that received the P4 diet was reversed after feeding with the P18 diet. Liver Fgf21 mRNA expressions and serum FGF21 levels were significantly increased as dietary protein content decreased, and loss of hepatic FGF21 delayed the onset of cyclicity disruption in rats fed with the P4 diet, possibly due to the regulation of insulin-like growth factor-1. Collectively, severe dietary protein restriction results in the cessation of estrous cyclicity and ovarian follicle development, and hepatic FGF21 and hypothalamic Kiss-1 were partially required for this process.

Hyperphagia of female UCP1-deficient mice blunts anti-obesity effects of FGF21

Increasing energy expenditure through uncoupling protein 1 (UCP1) activity in thermogenic adipose tissue is widely investigated to correct diet-induced obesity (DIO). Paradoxically, UCP1-deficient male mice are resistant to DIO at room temperature. Recently, we uncovered a key role for fibroblast growth factor 21 (FGF21), a promising drug target for treatment of metabolic disease, in this phenomenon. As the metabolic action of FGF21 is so far understudied in females, we aim to investigate potential sexual dimorphisms. Here, we confirm that male UCP1 KO mice display resistance to DIO in mild cold, without significant changes in metabolic parameters. Surprisingly, females gained the same amount of body fat as WT controls. Molecular regulation was similar between UCP1 KO males and females, with an upregulation of serum FGF21, coinciding with beiging of inguinal white adipose tissue and induced lipid metabolism. While energy expenditure did not display significant differences, UCP1 KO females significantly increased their food intake. Altogether, our results indicate that hyperphagia is likely counteracting the beneficial effects of FGF21 in female mice. This underlines the importance of sex-specific studies in (pre)clinical research for personalized drug development.

Central and peripheral mechanisms involved in the control of GnRH neuronal function by metabolic factors

Gonadotropin-releasing hormone (GnRH) neurons are the final output pathway for the brain control of reproduction. The activity of this neuronal population, mainly located at the preoptic area of the hypothalamus, is controlled by a plethora of metabolic signals. However, it has been documented that most of these signal impact on GnRH neurons through indirect neuronal circuits, Kiss1, proopiomelanocortin, and neuropeptide Y/agouti-related peptide neurons being some of the most prominent mediators. In this context, compelling evidence has been gathered in recent years on the role of a large range of neuropeptides and energy sensors in the regulation of GnRH neuronal activity through both direct and indirect mechanisms. The present review summarizes some of the most prominent recent advances in our understanding of the peripheral factors and central mechanisms involved in the metabolic control of GnRH neurons.

Biological and pharmacological functions of the FGF19- and FGF21-coreceptor beta klotho

Beta klotho (KLB) is a fundamental component in fibroblast growth factor receptor (FGFR) signaling as it serves as an obligatory coreceptor for the endocrine hormones fibroblast growth factor 19 (FGF19) and fibroblast growth factor 21 (FGF21). Through the development of FGF19- and FGF21 mimetics, KLB has emerged as a promising drug target for treating various metabolic diseases, such as type 2 diabetes (T2D), non-alcoholic fatty liver disease (NAFLD), and cardiovascular disease. While rodent studies have significantly increased our understanding of KLB function, current clinical trials that test the safety and efficacy of KLB-targeting drugs raise many new scientific questions about human KLB biology. Although most KLB-targeting drugs can modulate disease activity in humans, individual patient responses differ substantially. In addition, species-specific differences in KLB tissue distribution may explain why the glucose-lowering effects that were observed in preclinical studies are not fully replicated in clinical trials. Besides, the long-term efficacy of KLB-targeting drugs might be limited by various pathophysiological conditions known to reduce the expression of KLB. Moreover, FGF19/FGF21 administration in humans is also associated with gastrointestinal side effects, which are currently unexplained. A better understanding of human KLB biology could help to improve the efficacy and safety of existing or novel KLB/FGFR-targeting drugs. In this review, we provide a comprehensive overview of the current understanding of KLB biology, including genetic variants and their phenotypic associations, transcriptional regulation, protein structure, tissue distribution, subcellular localization, and function. In addition, we will highlight recent developments regarding the safety and efficacy of KLB-targeting drugs in clinical trials. These insights may direct the development and testing of existing and future KLB-targeting drugs.

Circadian and kisspeptin regulation of the preovulatory surge

Fertility in mammals is ultimately controlled by a small population of neurons - the gonadotropin-releasing hormone (GnRH) neurons - located in the ventral forebrain. GnRH neurons control gonadal function through the release of GnRH, which in turn stimulates the secretion of the anterior pituitary gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH). In spontaneous ovulators, ovarian follicle maturation eventually stimulates, via sex steroid feedback, the mid-cycle surge in GnRH and LH secretion that causes ovulation. The GnRH/LH surge is initiated in many species just before the onset of activity through processes controlled by the central circadian clock, ensuring that the neuroendocrine control of ovulation and sex behavior are coordinated. This review aims to give an overview of anatomical and functional studies that collectively reveal some of the mechanisms through which the central circadian clock regulates GnRH neurons and their afferent circuits to drive the preovulatory surge.

FGF-21 Conducts a Liver-Brain-Kidney Axis to Promote Renal Cell Carcinoma

Metabolic homeostasis is one of the most exquisitely tuned systems in mammalian physiology. Metabolic homeostasis requires multiple redundant systems to cooperate to maintain blood glucose concentrations in a narrow range, despite a multitude of physiological and pathophysiological pressures. Cancer is one of the canonical pathophysiological settings in which metabolism plays a key role. In this study, we utilized REnal Gluconeogenesis Analytical Leads (REGAL), a liquid chromatography-mass spectrometry/mass spectrometry-based stable isotope tracer method that we developed to show that in conditions of metabolic stress, the fasting hepatokine fibroblast growth factor-21 (FGF-21)1,2 coordinates a liver-brain-kidney axis to promote renal gluconeogenesis. FGF-21 promotes renal gluconeogenesis by enhancing β2 adrenergic receptor (Adrb2)-driven, adipose triglyceride lipase (ATGL)-mediated intrarenal lipolysis. Further, we show that this liver-brain-kidney axis promotes gluconeogenesis in the renal parenchyma in mice and humans with renal cell carcinoma (RCC). This increased gluconeogenesis is, in turn, associated with accelerated RCC progression. We identify Adrb2 blockade as a new class of therapy for RCC in mice, with confirmatory data in human patients. In summary, these data reveal a new metabolic function of FGF-21 in driving renal gluconeogenesis, and demonstrate that inhibition of renal gluconeogenesis by FGF-21 antagonism deserves attention as a new therapeutic approach to RCC.

The care of patients with secondary hypothalamic amenorrhoea

Secondary hypothalamic amenorrhoea is a common menstrual disorder affecting women of reproductive age. In some cases, periods become absent due to prolonged stress on the body, caused by undereating, overexercising and psychological stress. Secondary hypothalamic amenorrhoea is often underdiagnosed and undertreated, and patients may be prescribed oral contraception, which can mask the problem. This article will mainly focus on lifestyle factors associated with this condition and its association with disordered eating.

BCAA insufficiency leads to premature ovarian insufficiency via ceramide-induced elevation of ROS

Premature ovarian insufficiency (POI) is a disease featured by early menopause before 40 years of age, accompanied by an elevation of follicle-stimulating hormone. Though POI affects many aspects of women's health, its major causes remain unknown. Many clinical studies have shown that POI patients are generally underweight, indicating a potential correlation between POI and metabolic disorders. To understand the pathogenesis of POI, we performed metabolomics analysis on serum and identified branch-chain amino acid (BCAA) insufficiency-related metabolic disorders in two independent cohorts from two clinics. A low BCAA diet phenotypically reproduced the metabolic, endocrine, ovarian, and reproductive changes of POI in young C57BL/6J mice. A mechanism study revealed that the BCAA insufficiency-induced POI is associated with abnormal activation of the ceramide-reactive oxygen species (ROS) axis and consequent impairment of ovarian granulosa cell function. Significantly, the dietary supplement of BCAA prevented the development of ROS-induced POI in female mice. The results of this pathogenic study will lead to the development of specific therapies for POI.

Fibroblast Growth Factor-Based Pharmacotherapies for the Treatment of Obesity-Related Metabolic Complications

The fibroblast growth factor (FGF) family, which comprises 22 structurally related proteins, plays diverse roles in cell proliferation, differentiation, development, and metabolism. Among them, two classical members (FGF1 and FGF4) and two endocrine members (FGF19 and FGF21) are important regulators of whole-body energy homeostasis, glucose/lipid metabolism, and insulin sensitivity. Preclinical studies have consistently demonstrated the therapeutic benefits of these FGFs for the treatment of obesity, diabetes, dyslipidemia, and nonalcoholic steatohepatitis (NASH). Several genetically engineered FGF19 and FGF21 analogs with improved pharmacodynamic and pharmacokinetic properties have been developed and progressed into various stages of clinical trials. These FGF analogs are effective in alleviating hepatic steatosis, steatohepatitis, and liver fibrosis in biopsy-confirmed NASH patients, whereas their antidiabetic and antiobesity effects are mildand vary greatly in different clinical trials. This review summarizes recent advances in biopharmaceutical development of FGF-based therapies against obesity-related metabolic complications, highlights major challenges in clinical implementation, and discusses possible strategies to overcome these hurdles.

Dual Role of Fibroblast Growth Factor Pathways in Sleep Regulation

Sleep plays an important function in neuro-immuno-endocrine homeostasis. Sleep disorders have been associated with an increased risk of metabolic and cognitive impairments. Among different factors that have an effect on sleep metabolism, a growing body of literature has investigated growth factors in the course of sleep quality and disorders. A good example of growth factors is fibroblast growth factors (FGFs), which are a large family of polypeptide growth factors. Evidence has shown that FGFs are involved in the modulation of sleep-wake behavior by their receptor subtypes and ligands, e.g., FFG1 plays an important role in the quality of sleep through somnogenic effects, while the high level of FGF23 is associated with secondary disorders in shift workers. Therefore, a controversial effect of FGFs can be seen in the course of sleep in physiologic and pathologic conditions. Further investigation on this topic would help us to understand the role of FGFs in sleep disorders as a therapeutic option and biomarker.

Targeting FGF21 in cardiovascular and metabolic diseases: from mechanism to medicine

Cardiovascular and metabolic disease (CVMD) is becoming increasingly prevalent in developed and developing countries with high morbidity and mortality. In recent years, fibroblast growth factor 21 (FGF21) has attracted intensive research interest due to its purported role as a potential biomarker and critical player in CVMDs, including atherosclerosis, coronary artery disease, myocardial infarction, hypoxia/reoxygenation injury, heart failure, type 2 diabetes, obesity, and nonalcoholic steatohepatitis. This review summarizes the recent developments in investigating the role of FGF21 in CVMDs and explores the mechanism whereby FGF21 regulates the development of CVMDs. Novel molecular targets and related pathways of FGF21 (adenosine 5'-monophosphate-activated protein kinase, silent information regulator 1, autophagy-related molecules, and gut microbiota-related molecules) are highlighted in this review. Considering the poor pharmacokinetics and biophysical properties of native FGF21, the development of new generations of FGF21-based drugs has tremendous therapeutic potential. Related preclinical and clinical studies are also summarized in this review to foster clinical translation. Thus, our review provides a timely and insightful overview of the physiology, biomarker potential, molecular targets, and therapeutic potential of FGF21 in CVMDs.

The potential function and clinical application of FGF21 in metabolic diseases

As an endocrine hormone, fibroblast growth factor 21 (FGF21) plays a crucial role in regulating lipid, glucose, and energy metabolism. Endogenous FGF21 is generated by multiple cell types but acts on restricted effector tissues, including the brain, adipose tissue, liver, heart, and skeletal muscle. Intervention with FGF21 in rodents or non-human primates has shown significant pharmacological effects on a range of metabolic dysfunctions, including weight loss and improvement of hyperglycemia, hyperlipidemia, insulin resistance, cardiovascular disease, and non-alcoholic fatty liver disease (NAFLD). Due to the poor pharmacokinetic and biophysical characteristics of native FGF21, long-acting FGF21 analogs and FGF21 receptor agonists have been developed for the treatment of metabolic dysfunction. Clinical trials of several FGF21-based drugs have been performed and shown good safety, tolerance, and efficacy. Here we review the actions of FGF21 and summarize the associated clinical trials in obesity, type 2 diabetes mellitus (T2DM), and NAFLD, to help understand and promote the development of efficient treatment for metabolic diseases via targeting FGF21.

Fibroblast growth factor 21 (FGF21) promotes porcine granulosa cell estradiol production and proliferation via PI3K/AKT/mTOR signaling

The proliferation and steroidogenesis of mammalian ovarian granulosa cells (GCs) are related to follicular development. Previous studies found that fibroblast growth factor 21 (FGF21) regulated female fertility through the hypothalamic-pituitary-gonad axis. However, FGF21 receptors are expressed on GCs, so we speculate that it might affect female reproduction by regulating their physiological activities. Here, we showed that FGF21, fibroblast growth factor receptor-1(FGFR1), and beta-klotho (KLB) were expressed in porcine GCs. ELISA assays showed that estradiol (E₂) production was increased significantly when treating GCs with recombinant FGF21 (rFGF21). In addition, rFGF21 upregulated the mRNA and protein levels of E₂ synthesis-related genes including StAR, CYP11A1, and CYP19A1 in porcine GCs. Correspondingly, FGF21 siRNA inhibited E₂ levels and its synthesis-related gene expression. After rFGF21 treatment, CCK8 showed increased cell viability, and flow cytometry showed that the number of S phase increased, and cycle-related genes also increased. However, treatment with FGF21 siRNA to porcine GCs suppressed the cell cycle, viability, and EdU positive cell number. Consequently, FGF21/FGFR1/KLB forms a complex to activate the phosphatidylinositol-3-kinase (PI3K)/AKT/mTOR signaling pathway and further promote the proliferation and E₂ synthesis in porcine GCs. Collectively, these findings suggests that FGF21 regulates porcine ovarian folliculogenesis.

Glial cells as integrators of peripheral and central signals in the regulation of energy homeostasis

Communication between the periphery and the brain is key for maintaining energy homeostasis. To do so, peripheral signals from the circulation reach the brain via the circumventricular organs (CVOs), which are characterized by fenestrated vessels lacking the protective blood-brain barrier (BBB). Glial cells, by virtue of their plasticity and their ideal location at the interface of blood vessels and neurons, participate in the integration and transmission of peripheral information to neuronal networks in the brain for the neuroendocrine control of whole-body metabolism. Metabolic diseases, such as obesity and type 2 diabetes, can disrupt the brain-to-periphery communication mediated by glial cells, highlighting the relevance of these cell types in the pathophysiology of such complications. An improved understanding of how glial cells integrate and respond to metabolic and humoral signals has become a priority for the discovery of promising therapeutic strategies to treat metabolic disorders. This Review highlights the role of glial cells in the exchange of metabolic signals between the periphery and the brain that are relevant for the regulation of whole-body energy homeostasis.

Translation Reprogramming as a Novel Therapeutic Target in MAFLD

Approved pharmacotherapies for metabolic-dysfunction-associated fatty liver disease (MAFLD) are lacking. Novel approaches and therapeutic targets that are likely to translate to clinical benefit are required. Targeting components of the translation machinery hold promise as a novel therapeutic approach that can overcome the well-known disease heterogeneity, as dysregulation of mRNA translation is a common feature independent of the MAFLD drivers. In this perspective, recent advances in understanding the role of mRNA translation in MAFLD are discussed, with a particular focus on the potential implications and challenges to "translate" these findings to the clinic, and an overview of similar recent efforts in other diseases is provided.

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.

Endocrine Fibroblast Growth Factors in Relation to Stress Signaling

Fibroblast growth factors (FGFs) play important roles in various growth signaling processes, including proliferation, development, and differentiation. Endocrine FGFs, i.e., atypical FGFs, including FGF15/19, FGF21, and FGF23, function as endocrine hormones that regulate energy metabolism. Nutritional status is known to regulate the expression of endocrine FGFs through nuclear hormone receptors. The increased expression of endocrine FGFs regulates energy metabolism processes, such as fatty acid metabolism and glucose metabolism. Recently, a relationship was found between the FGF19 subfamily and stress signaling during stresses such as endoplasmic reticulum stress and oxidative stress. This review focuses on endocrine FGFs and the recent progress in FGF studies in relation to stress signaling. In addition, the relevance of the stress-FGF pathway to disease and human health is discussed.

Exposure of male mice to perfluorooctanoic acid induces anxiety-like behaviors by increasing corticotropin-releasing factor in the basolateral amygdala complex

Perfluorooctanoic acid (PFOA), a hazardous environmental pollutant, has been found to enhance hepatic synthesis of fibroblast growth factor 21 (FGF21). FGF21 can enter the brain and increase the expression of corticotropin-releasing factor (CRF) in the paraventricular nucleus (PVN). In this study, adult male mice were orally administered PFOA to evaluate how it regulates emotion. Exposure of mice to PFOA (1 mg kg-1 bw) for 10 consecutive days (PFOA-mice) caused anxiety-like behaviors and a peroxisome proliferator-activated receptor α (PPARα)-dependent increase in hepatic FGF21 synthesis. The levels of CRF expression in not only PVN but also basolateral amygdala complex (BLA) neurons of PFOA-mice were increased via FGF receptor 1 (FGF-R1) activation. However, the microinjection of FGF-R1 or CRF 1 receptor (CRF-R1) antagonist in the BLA rather than the PVN of PFOA-mice could relieve their anxiety-like behaviors. In addition, external capsule-BLA synaptic transmission in PFOA-mice was enhanced by increasing CRF-R1-mediated presynaptic glutamate release, which was corrected by the blockade of PPARα, FGF-R1 and CRF-R1 or the inhibition of PKA. Furthermore, the threshold of frequency-dependent long-term potentiation (LTP) induction was decreased in the BLA of PFOA-mice, which depended on the activation of PPARα, FGF-R1, CRF-R1, PKA and NMDA receptor (NMDAR), whereas long-term depression (LTD) induction was unchanged. Thus, the results indicate that the exposure of male mice to PFOA (1 mg kg-1 bw) enhances CRF expression in BLA neurons by increasing hepatic FGF21 synthesis, which then enhances CRF-R1-mediated presynaptic glutamate release to facilitate NMDAR-dependent BLA-LTP induction, leading to the production of anxiety-like behaviors.

Mice with high FGF21 serum levels had a reduced preference for morphine and an attenuated development of acute antinociceptive tolerance and physical dependence

Because of increased opioid misuse, there is a need to identify new targets for minimizing opioid tolerance, and physical and psychological dependence. Previous studies showed that fibroblast growth factor 21 (FGF21) decreased alcohol and sweet preference in mice. In this study, FGF21-transgenic (FGF21-Tg) mice, expressing high FGF21 serum levels, and wildtype (WT) C57BL/6J littermates were treated with morphine and saline to determine if differences exist in their physiological and behavioral responses to opioids. FGF21-Tg mice displayed reduced preference for morphine in the conditioned place preference assay compared to WT littermates. Similarly, FGF21-Tg mice had an attenuation of the magnitude and rate of acute morphine antinociceptive tolerance development, and acute and chronic morphine physical dependence, but exhibited no change in chronic morphine antinociceptive tolerance. The ED50 values for morphine-induced antinociception in the 55 °C hot plate and the 55 °C warm-water tail withdrawal assays were similar in both strains of mice. Likewise, FGF21-Tg and WT littermates had comparable responses to morphine-induced respiratory depression. Overall, FGF21-Tg mice had a decrease in the development of acute analgesic tolerance, and the development of physical dependence, and morphine preference. FGF21 and its receptor have therapeutic potential for reducing opioid withdrawal symptoms and craving, and augmenting opioid therapeutics for acute pain patients to minimize tolerance development.

Protein Appetite at the Interface between Nutrient Sensing and Physiological Homeostasis

Feeding behavior is guided by multiple competing physiological needs, as animals must sense their internal nutritional state and then identify and consume foods that meet nutritional needs. Dietary protein intake is necessary to provide essential amino acids and represents a specific, distinct nutritional need. Consistent with this importance, there is a relatively strong body of literature indicating that protein intake is defended, such that animals sense the restriction of protein and adaptively alter feeding behavior to increase protein intake. Here, we argue that this matching of food consumption with physiological need requires at least two concurrent mechanisms: the first being the detection of internal nutritional need (a protein need state) and the second being the discrimination between foods with differing nutritional compositions. In this review, we outline various mechanisms that could mediate the sensing of need state and the discrimination between protein-rich and protein-poor foods. Finally, we briefly describe how the interaction of these mechanisms might allow an animal to self-select between a complex array of foods to meet nutritional needs and adaptively respond to changes in either the external environment or internal physiological state.

Hepatic FGF21 preserves thermoregulation and cardiovascular function during bacterial inflammation

Sickness behaviors, including anorexia, are evolutionarily conserved responses to acute infections. Inflammation-induced anorexia causes dramatic metabolic changes, of which components critical to survival are unique depending on the type of inflammation. Glucose supplementation during the anorectic period induced by bacterial inflammation suppresses adaptive fasting metabolic pathways, including fibroblast growth factor 21 (FGF21), and decreases survival. Consistent with this observation, FGF21-deficient mice are more susceptible to mortality from endotoxemia and polybacterial peritonitis. Here, we report that increased circulating FGF21 during bacterial inflammation is hepatic derived and required for survival through the maintenance of thermogenesis, energy expenditure, and cardiac function. FGF21 signaling downstream of its obligate coreceptor, β-Klotho (KLB), is required in bacterial sepsis. However, FGF21 modulates thermogenesis and chronotropy independent of the adipose, forebrain, and hypothalamus, which are operative in cold adaptation, suggesting that in bacterial inflammation, either FGF21 signals through a novel, undescribed target tissue or concurrent signaling of multiple KLB-expressing tissues is required.

Circulating fibroblast growth factor 21 as a potential biomarker for missed abortion in humans

OBJECTIVE

To investigate whether serum levels of fibroblast growth factor 21 (FGF21) and fatty acid-binding protein-4 (FABP4) are associated with missed abortion (MA) in humans.

DESIGN

Cross-sectional study.

SETTING

University-affiliated hospital.

PATIENT(S)

Patients with MA at 8-12 weeks of gestation.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURES(S)

Serum levels of FGF21 and FABP4 were tested by enzyme-linked immunosorbent assay. Placental samples were collected during dilation and curettage surgery, and the expression of FGF21 and its related genes were measured using quantitative polymerase chain reaction.

RESULT(S)

In the discovery cohort, 78 patients with MA and 79 healthy pregnant women matched for maternal age and body mass index were nested from a prospective cohort. Circulating levels of FGF21 and FABP4 were significantly and independently elevated in patients with MA relative to the levels in the healthy controls. A single measurement of FGF21 serum level effectively discriminated MA with an area under the receiver operating characteristics curve of 0.80 (95% confidence interval: 0.73-0.87). Importantly, in our external validation cohort that comprised subjects with MA (n = 34) or induced abortion (n = 27), the FGF21 serum levels achieved an area under the receiver operating characteristics curve of 0.85 (95% confidence interval: 0.75-0.96) when identifying those with MA. Nevertheless, expression of FGF21 in the placenta was not associated with its serum concentration. Placental tissues from patients with MA exhibited impaired FGF21 signaling.

CONCLUSION(S)

Our results suggested that serum levels of FGF21 and FABP4 were associated with MA. Circulating FGF21 may serve as a potential biomarker for the recognition of MA.

Fibroblast growth factor 21 in dairy cows: current knowledge and potential relevance

Fibroblast growth factor 21 (FGF21) has been identified as an important regulator of carbohydrate and lipid metabolism, which plays an important role for metabolic regulation, particularly under conditions of energy deprivation or stress conditions. Dairy cows are subjected to a negative energy balance and various kinds of stress particularly during the periparturient phase and during early lactation. It has been shown that the plasma concentration of FGF21 in dairy cows is dramatically increased at parturition and remains high during the first weeks of lactation. This finding suggests that FGF21 might exert similar functions in dairy cows than in other species, such as mice or humans. However, the role of FGF21 in dairy cows has been less investigated so far. Following a brief summary of the previous findings about the function of FGF21 in humans and mice, the present review aims to present the current state of knowledge about the role of FGF21 in dairy cows. The first part of the review deals with the tissue localization of FGF21 and with conditions leading to an upregulation of FGF21 expression in the liver of dairy cows. In the second part, the influence of nutrition on FGF21 expression and the role of FGF21 for metabolic diseases in dairy cows is addressed. In the third part, findings of exogenous FGF21 application on metabolism in dairy cows are reported. Finally, the potential relevance of FGF21 in dairy cows is discussed. It is concluded that FGF21 might be of great importance for metabolic adaptation to negative energy balance and stress conditions in dairy cows. However, further studies are needed for a better understanding of the functions of FGF21 in dairy cows.

Skeletal endocrinology: where evolutionary advantage meets disease

The regulation of whole-body homeostasis by the skeleton is mediated by its capacity to secrete endocrine signaling molecules. Although bone-derived hormones confer several adaptive benefits, their physiological functions also involve trade-offs, thus eventually contributing to disease. In this manuscript, we discuss the origins and functions of two of the best-studied skeletal mediators, fibroblast growth factor 23 and osteocalcin, in an evolutionary context. Moreover, we provide a theoretical framework seeking to explain the broad involvement of these two hormones in amniote physiology as well as their potential to fuel the development and progression of diseases. Vice versa, we outline which perturbations might be amenable to manipulation of these systems and discuss limitations and ongoing challenges in skeletal endocrine research. Finally, we summarize unresolved questions and potential future studies in this thriving field.

Prenatal exposure of female mice to perfluorononanoic acid delays pubertal activation of the reproductive endocrine axis through enhanced hepatic FGF21 production

The developmental toxicity of perfluorononanoic acid (PFNA), a ubiquitous environmental contaminant, has been associated with the activation of PPARα. This study investigated influence of prenatal exposure to PFNA in pubertal activation of reproductive endocrine axis in female mice and explored underlying molecular mechanisms. Herein, we show that when PFNA (3 mg kg^-1 body weight) was orally administered during gestational days 1-18, dams showed an increase in liver weight and hepatic FGF21 synthesis via PPARα activation, and their female offspring (PFNA mice) showed an increase in liver weight and hepatic FGF21 synthesis from postnatal day (PND) 1 to PND21, which were corrected by the administration of the PPARα antagonist GW6471 from PND1-14 (pup-GW). Expression of vasopressin (VAP) in the hypothalamic suprachiasmatic nucleus (SCN) was reduced in PND14-30 PFNA mice, and could be rescued by pup-GW. Pubertal activation of kisspeptin neurons in anteroventral periventricular nucleus (AVPV) and hypothalamic GnRH neurons in PND21-30 PFNA mice was obviously suppressed, but were recovered by pup-GW or PND21-30 application of VAP. The times of vaginal opening and first estrus were delayed in PFNA mice with a decrease in ovary size and the numbers of primary, secondary and antral follicles, and corpora lutea, which were relieved by pup-GW or application of VAP. The findings indicate that prenatal exposure to PFNA through increased FGF21 production in postnatal female offspring impedes postnatal activation of SCN-VAP neurons, which suppresses pubertal onset in AVPV-kisspeptin neurons and reproductive endocrine axis, leading to delayed puberty and dysfunction of ovaries.

Sexually dimorphic roles for the type 2 diabetes-associated C2cd4b gene in murine glucose homeostasis

AIMS/HYPOTHESIS

Variants close to the VPS13C/C2CD4A/C2CD4B locus are associated with altered risk of type 2 diabetes in genome-wide association studies. While previous functional work has suggested roles for VPS13C and C2CD4A in disease development, none has explored the role of C2CD4B.

METHODS

CRISPR/Cas9-induced global C2cd4b-knockout mice and zebrafish larvae with c2cd4a deletion were used to study the role of this gene in glucose homeostasis. C2 calcium dependent domain containing protein (C2CD)4A and C2CD4B constructs tagged with FLAG or green fluorescent protein were generated to investigate subcellular dynamics using confocal or near-field microscopy and to identify interacting partners by mass spectrometry.

RESULTS

Systemic inactivation of C2cd4b in mice led to marked, but highly sexually dimorphic changes in body weight and glucose homeostasis. Female C2cd4b mice displayed unchanged body weight compared with control littermates, but abnormal glucose tolerance (AUC, p = 0.01) and defective in vivo, but not in vitro, insulin secretion (p = 0.02). This was associated with a marked decrease in follicle-stimulating hormone levels as compared with wild-type (WT) littermates (p = 0.003). In sharp contrast, male C2cd4b null mice displayed essentially normal glucose tolerance but an increase in body weight (p < 0.001) and fasting blood glucose (p = 0.003) after maintenance on a high-fat and -sucrose diet vs WT littermates. No metabolic disturbances were observed after global inactivation of C2cd4a in mice, or in pancreatic beta cell function at larval stages in C2cd4a null zebrafish. Fasting blood glucose levels were also unaltered in adult C2cd4a-null fish. C2CD4B and C2CD4A were partially localised to the plasma membrane, with the latter under the control of intracellular Ca2+. Binding partners for both included secretory-granule-localised PTPRN2/phogrin.

CONCLUSIONS/INTERPRETATION

Our studies suggest that C2cd4b may act centrally in the pituitary to influence sex-dependent circuits that control pancreatic beta cell function and glucose tolerance in rodents. However, the absence of sexual dimorphism in the impact of diabetes risk variants argues for additional roles for C2CD4A or VPS13C in the control of glucose homeostasis in humans.

DATA AVAILABILITY

The datasets generated and/or analysed during the current study are available in the Biorxiv repository ( www.biorxiv.org/content/10.1101/2020.05.18.099200v1 ). RNA-Seq (GSE152576) and proteomics (PXD021597) data have been deposited to GEO ( www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE152576 ) and ProteomeXchange ( www.ebi.ac.uk/pride/archive/projects/PXD021597 ) repositories, respectively.

Pseudo-Starvation Driven Energy Expenditure Negatively Affects Ovarian Follicle Development

In the present investigation, we examined whether a change in whole body energy fluxes could affect ovarian follicular development, employing mice ectopically expressing uncoupling protein 1 in skeletal muscle (UCP1-TG). Female UCP1-TG and wild-type (WT) mice were dissected at the age of 12 weeks. Energy intake and expenditure, activity, body weight and length, and body composition were measured. Plasma insulin, glucose, leptin, plasma fibroblast growth factor 21 (FGF21) and plasma insulin-like growth factor 1 (IGF1) levels were analyzed and ovarian follicle and corpus luteum numbers were counted. IGF1 signaling was analyzed by immunohistochemical staining for the activation of insulin receptor substrate 1/2 (IRS1/2) and AKT. UCP1-TG female mice had increased energy expenditure, reduced body size, maintained adiposity, and decreased IGF1 concentrations compared to their WT littermates, while preantral and antral follicle numbers were reduced by 40% and 60%, respectively. Corpora lutea were absent in 40% of the ovaries of UCP1-TG mice. Phospho-IRS1, phospho-AKT -Ser473 and -Thr308 immunostaining was present in the granulosa cells of antral follicles in WT ovaries, but faint to absent in the antral follicles of UCP1-TG mice. In conclusion, the reduction in circulating IGF1 levels due to the ectopic expression of UCP1 is associated with reduced immunostaining of the IRS1-PI3/AKT pathway, which may negatively affect ovarian follicle development and ovulation.

A randomised trial examining inflammatory signaling in acutely induced hyperinsulinemia and hyperlipidemia in normal weight women-the reprometabolic syndrome

Context

Obesity, is a state of chronic inflammation, characterized by elevated lipids, insulin resistance and relative hypogonadotropic hypogonadism. We have defined the accompanying decreased Luteinizing Hormone (LH), Follicle-Stimulating Hormone (FSH), ovarian steroids and reduced pituitary response to Gonadotropin-releasing Hormone (GnRH) as Reprometabolic syndrome, a phenotype that can be induced in healthy normal weight women (NWW) by acute infusion of free fatty acids and insulin.

Objective

To identify potential mediators of insulin and lipid-related reproductive endocrine dysfunction.

Design, setting, participants

Secondary analysis of crossover study of eumenorrheic reproductive aged women of normal Body Mass Index (BMI) (<25 kg/m²) at an academic medical center.

Intervention

Participants underwent 6-hour infusions of either saline/heparin or insulin plus fatty acids (Intralipid plus heparin), in the early follicular phase of sequential menstrual cycles, in random order. Euglycemia was maintained by glucose infusion. Frequent blood samples were obtained.

Main outcome measures

Pooled serum from each woman was analyzed for cytokines, interleukins, chemokines, adipokines, Fibroblast Growth Factor-21 (FGF-21) and markers of endoplasmic reticulum (ER) stress (CHOP and GRP78). Wilcoxon signed-rank tests were used to compare results across experimental conditions.

Results

Except for Macrophage Inflammatory Protein-1β (MIP-1β), no significant differences were observed in serum levels of any of the inflammatory signaling or ER stress markers tested.

Conclusion

Acute infusion of lipid and insulin, to mimic the metabolic syndrome of obesity, was not associated with an increase in inflammatory markers. These results imply that the endocrine disruption and adverse reproductive outcomes of obesity are not a consequence of the ambient inflammatory environment but may be mediated by direct lipotoxic effects on the hypothalamic-pituitary-ovarian (HPO) axis.

[How a metabolic hormone, FGF21 (fibroblast growth factor 21) impacts reproduction]

Obesity or insulin resistance are the major non-infectious diseases that continue to progress worldwide. They promote diabetes and cardiovascular diseases, but also lead to a decrease in fertility in both sexes. FGF21, discovered in the 2000s, is a hormone closely linked to the energy status and has the ability to decrease insulin resistance. Its action through the FGFR1c, 3c & 4 receptors modulates tissues involved in energy-related metabolism but also the brain and the gonads. Recent data favor a role of FGF21 in female and male fertility, but raise the question about the role of FGF21 on reproductive function. In this review, we have scanned the different FGF21 actions on the reproductive axis, suggesting a potential therapeutic role in case of infertility.

Advances in Biological Functions and Clinical Studies of FGF21

Fibroblast growth factor 21 (FGF21) regulates many crucial biological processes in human and mammals, particularly metabolic modulation and protective effect after injury. Therefore, determining complex regulatory mechanisms and elucidating the signaling pathway may greatly promote the prevention, diagnosis, and treatment of related injury and metabolic diseases. This review focused on the metabolic modulation and protective effect of FGF21 and summarized the molecular mechanisms and clinical research developments.

Association of fibroblast growth factor 21 with alcohol consumption and alcohol liver cirrhosis

BACKGROUND

Fibroblast growth factor 21 (FGF21) is produced in the liver and binds to different complex receptor/coreceptor systems. Besides many other processes, FGF21 regulates the intake of simple sugars and alcohol. Increased levels of FGF21 decrease harmful alcohol intake in mice. To increase our understanding on the relationship between FGF21 and alcohol intake in humans, we aimed to measure FGF21 levels in patients with alcoholic liver cirrhosis (ALC) in comparison to patients with nonalcoholic liver cirrhosis (NALC) and healthy persons based on their present alcohol consumption.

METHODS

Alcohol intake was verified by urinary ethyl glucuronide (uETG) levels, eating and drinking behaviour by a Food Frequency Questionnaire and FGF 21 plasma levels were determined by ELISA in 96 persons (ALC n = 41; NALC n = 34; healthy n = 21).

RESULTS

Both ALC and NALC patients with elevated ETG levels (≥0.5 μg/ml; indicating alcohol consumption in the last 12-72 h) showed significantly higher FGF21 plasma levels in comparison to patients with negative ETG levels. Eating behaviour did not have an impact on FGF21 plasma levels.

CONCLUSIONS

Increased FGF21 levels in patients with recent alcohol consumption (verified by ETG) confirmed the first part of the liver-brain endocrine axis: alcohol consumption was associated with increased FGF21 levels. We could not confirm that elevated FGF21 levels were associated with reduced alcohol intake as a result. That points towards a pathology in this pathway, which might be caused by a malfunction of β‑Klotho or FGF receptors according to other studies and chronic alcohol dependency. Further research is required to clarify these pathologies, which may open new pharmacological treatment for patients with alcohol use disorder and alcohol dependence.

FGF21 in obesity and cancer: New insights

The endocrine FGF21 was discovered as a novel metabolic regulator in 2005 with new functions bifurcating from the canonic heparin-binding FGFs that directly promote cell proliferation and growth independent of a co-receptor. Early studies have demonstrated that FGF21 is a stress sensor in the liver and possibly, several other endocrine and metabolic tissues. Hepatic FGF21 signals via endocrine routes to quench episodes of metabolic derangements, promoting metabolic homeostasis. The convergence of mouse and human studies shows that FGF21 promotes lipid catabolism, including lipolysis, fatty acid oxidation, mitochondrial oxidative activity, and thermogenic energy dissipation, rather than directly regulating insulin and appetite. The white and brown adipose tissues and, to some extent, the hypothalamus, all of which host a transmembrane receptor binary complex of FGFR1 and co-receptor KLB, are considered the essential tissue and molecular targets of hepatic or pharmacological FGF21. On the other hand, a growing body of work has revealed that pancreatic acinar cells form a constitutive high-production site for FGF21, which then acts in an autocrine or paracrine mode. Beyond regulation of macronutrient metabolism and physiological energy expenditure, FGF21 appears to function in forestalling the development of fatty pancreas, steato-pancreatitis, fatty liver, and steato-hepatitis, thereby preventing the development of advanced pathologies such as pancreatic ductal adenocarcinoma or hepatocellular carcinoma. This review is intended to provide updates on these new discoveries that illuminate the protective roles of FGF21-FGFR1-KLB signal pathway in metabolic anomalies-associated severe tissue damage and malignancy, and to inform potential new preventive or therapeutic strategies for obesity-inflicted cancer patients via reducing metabolic risks and inflammation.

Time-restricted feeding improves the reproductive function of female mice via liver fibroblast growth factor 21

Background

There has been a significant increase, to epidemic levels, of obese and overweight women of reproductive age, causing impairments to reproductive health. Time‐restricted feeding (TRF) including isocaloric intake has shown to be preventive of obesity‐related disorders. However, its therapeutic ability to improve the reproductive function of female remains largely unknown.

Methods

Here, we investigated the ability of TRF to improve the reproductive function in wild‐type and liver‐specific FGF21 knockout female mice. To study fertility, a continuous and a short‐term fertility test, gonadotropin releasing‐hormone (GnRH), and Kisspeptin test were performed. Immortalized GnRH neuron was used to examine the direct role of liver fibroblast growth factor 21 (FGF21) on GnRH secretion.

Results

We found that TRF rescues female mice from bodyweight gain and glucose intolerance, as well as ovarian follicle loss and dysfunction of estrus cyclicity induced by high‐fat diet. Furthermore, the beneficial effects of the TRF regimen on the reproductive performance were also observed in mice fed both chow and high‐fat diet. However, those beneficial effects of TRF on metabolism and reproduction were absent in liver‐specific FGF21 knockout mice. In vitro, FGF21 directly acted on GnRH neurons to modulate GnRH secretion via extracellular regulated protein kinases (ERK_1/2) pathway.

Conclusions

Overall, time‐restricted feeding improves the reproductive function of female mice and liver FGF21 signaling plays a key role in GnRH neuron activity in female mice.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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