FGF21 induces PGC-1alpha and regulates carbohydrate and fatty acid metabolism during the adaptive starvation response

Acetylated cellulose suppresses body mass gain through gut commensals consuming host-accessible carbohydrates

Effective approaches to preventing and treating obesity are urgently needed. Although current strategies primarily focus on direct modulation of host metabolism, another promising approach may involve limiting nutrient availability through regulation of the gut microbiota, which links diet and host physiology. Here, we report that acetylated cellulose (AceCel), which markedly alters gut bacterial composition and function, reduces body mass gain in both wild-type and obese mice. AceCel limits carbohydrate oxidation and promotes fatty acid oxidation in the host liver in a microbiota-dependent manner. We further show that acetate enhances carbohydrate fermentation by the gut commensal Bacteroides thetaiotaomicron, depleting host-accessible simple sugars in the gut of AceCel-fed mice. These findings highlight the potential of AceCel as a prebiotic that regulates carbohydrate metabolism in both bacteria and host, offering promise as a therapeutic strategy for obesity.

FGF21 reverses MASH through coordinated actions on the CNS and liver

Metabolic dysfunction-associated steatotic liver disease (MASLD) and its progressive form, metabolic dysfunction-associated steatohepatitis (MASH), represent a growing public health burden with limited therapeutic options. Recent studies have revealed that fibroblast growth factor 21 (FGF21)-based analogs can significantly improve MASH, but the mechanisms for this effect are not well understood. Here, we demonstrate that the beneficial metabolic effects of FGF21 to reverse MASH are mediated through distinct mechanisms to independently lower hepatic triglyceride and cholesterol levels. Specifically, FGF21 signaling directly to glutamatergic neurons in the central nervous system (CNS) stimulates hepatic triglyceride reduction and reversal of fibrosis, whereas FGF21 signaling directly to hepatocytes is necessary and sufficient to reduce hepatic cholesterol levels in mice. Mechanistically, we show that FGF21 acts in the CNS to increase sympathetic nerve activity to the liver, which suppresses hepatic de novo lipogenesis. These results provide critical insights into a promising pharmacological target to treat MASH.

TSG attenuated NAFLD and facilitated weight loss in HFD-fed mice via activating the RUNX1/FGF21 signaling axis

Non-alcoholic fatty liver disease (NAFLD) is a chronic liver disease characterized by steatosis in hepatocytes and is now becoming the major cause of liver-related mortality. Fibroblast growth factor 21 (FGF21) is an endocrine hormone mainly secreted by the liver, which can bind to its receptor (FGFR) and co-receptor beta klotho (KLB) to form a receptor complex, exerting its lipid-lowering function. 2,3,5,4'-Tetrahydroxy-stilbene-2-O-β-D-glucoside (TSG), a natural compound isolated from Polygonum multiflorum Thunb, has shown excellent activity in lowering lipid content and efficacy in improving NAFLD. In this study we investigated whether FGF21 was implicated in the therapeutic effect of TSG in NAFLD mice. NAFLD was induced in mice by feeding with a high-fat diet (HFD) for 12 weeks, and treated with TSG (20, 40 mg·kg-1·d-1, i.g.) during the last 4 weeks. We showed that TSG treatment significantly alleviated NAFLD in HFD-fed mice evidenced by reduced hepatic triglyceride (TG) and non-esterified fatty acids (NEFA), diminished lipid droplets and decreased NAFLD activity score (NAS) in liver tissues. We demonstrated that TSG treatment significantly increased the mRNA and protein levels of FGF21 in vitro and in vivo, and reduced lipid accumulation in both the liver and adipose tissues. Transcriptomics analysis revealed that TSG treatment significantly increased the nuclear translocation of a transcription factor RUNX1. Knockdown of Runx1 in HFD-fed mice eliminated the efficacy of TSG in alleviating NAFLD, reducing hepatic lipid accumulation and regulating FGF21 signaling pathway in liver and adipose tissues. In conclusion, TSG alleviates NAFLD by enhancing the FGF21-mediated lipid metabolism in a RUNX1-dependent manner.

MOB1 deletion in murine mature adipocytes ameliorates obesity and diabetes

There is currently a global epidemic of obesity and obesity-related diseases such as type 2 diabetes due to decreased physical activity, excessive food intake, and/or genetic predisposition. The Hippo-YAP1 pathway has attracted attention as a potential therapeutic target because YAP1/TAZ activation in murine immature adipocytes in vitro suppresses their differentiation by inhibiting PPARγ activity. However, the role of YAP1 activation in mature adipocytes in vivo remains unclear. MOB1, whose expression is increased in obesity, is the hub of the Hippo core molecule complex and negatively regulates YAP1/TAZ activation. Therefore, we generated aMob1DKO mutant mice, which feature deficiency of Mob1a/b specifically in mature adipocytes. Compared to controls, aMob1DKO mice subjected to a high-fat diet showed beneficial changes consistent with resistance to diet-induced obesity. The mutants exhibited increases in basal lipolysis, "beiging," and energy expenditure, as well as suppression of ROS production and inflammation in white adipose tissue. Insulin sensitivity and glucose tolerance were improved, and ectopic fat accumulation was reduced. Most of these changes were dependent on the YAP1 activation observed in mature white adipose tissue of aMob1DKO mice. FGF21, which improves lipid metabolism, was upregulated directly via YAP1 activation, and many of the phenotypes seen in aMob1DKO mice were also dependent on FGF21. Thus, the aMob1DKO mouse is an interesting model for the study of the metabolic effects of diet-induced obesity and protection against diabetes. Our work suggests that a YAP1-FGF21 axis exists in adipocytes that may be a potential therapeutic target for obesity.

Daily Complementary Feeding With Eggs Improves Fibroblast Growth Factor 21 in Infants

This secondary analysis of the Eggcel-growth study investigated the effect of daily egg intake for 6 months in infants aged 6-9 months on environmental enteric dysfunction (EED) biomarkers and the association of EED markers with growth faltering. A randomised controlled trial was conducted in Jouberton, South Africa, among 500 infants randomly assigned equally to either an intervention group receiving a daily chicken egg or a control group. Both groups were followed up for 6 months. Data on infant and maternal sociodemographic information and anthropometric status of infants were collected. EED and inflammatory markers were analysed using Q-Plex Human EED (11-Plex) assay. There was a significant reduction in fibroblast growth factor 21 (FGF21) concentration in the intervention group (B = -0.132; 95% CI -0.255, -0.010; p = 0.035). Baseline, insulin-like growth factor 1 (IGF-1) was positively associated with endpoint length-for-age z-score (LAZ), weight-for-age z-score (WAZ) and weight-for-length z-score (WLZ) and there was an inverse relationship between baseline FGF21 and intestinal fatty acid-binding protein (I-FABP) with endpoint growth indicators. Baseline IGF-1 was positively associated with reduced odds of wasting, stunting and being underweight (p < 0.001) and baseline FGF21 was associated with increased odds of stunting (p = 0.002), wasting (p = 0.031) and being underweight (p = 0.035). There was a 20% increased odds of stunting with baseline I-FABP (p = 0.045) and a 30% increased odds of being underweight with baseline soluble CD14 (p = 0.039). Complementary feeding with eggs decreased growth hormone resistance (reduced FGF21 levels); however, FGF21 and I-FABP levels were linked to increased growth faltering. Trial Registration: ClinicalTrials.gov: NCT05168085.

FGF21 Ameliorates Fibroblasts Activation and Systemic Sclerosis by Inhibiting CK2α/GLI2 Signaling Axis

Systemic sclerosis is a typical fibrotic disease of unknown etiology that is characterized by abnormal fibroblast activation and excessive deposition of extracellular matrix. Unfortunately, effective therapeutic approaches are lacking. FGF21 plays a key role in mediating a variety of biological activities. However, its specific function in systemic sclerosis is unclear. In this study, we found that the expression of FGF21 was significantly downregulated in fibrotic skin tissue and in TGF-β-stimulated fibroblasts. Furthermore, our studies demonstrated that treatment with recombinant FGF21 in the skin significantly alleviated bleomycin-induced and TBRI-activated fibrosis and inhibited the activation of fibroblasts, whereas skin fibrosis was exacerbated by deletion of FGF21. Mechanistically, FGF21 inhibits the activity of CK2α and promotes the degradation of GLI2. In conclusion, these results indicate that FGF21 attenuates skin fibrosis through the CK2α/GLI2 signaling pathway and therefore may be a potential therapeutic target for systemic sclerosis.

Fibroblast growth factor 21: update on genetics and molecular biology

PURPOSE OF REVIEW

Since its discovery, most research on fibroblast growth factor 21 (FGF21) has focused on its antihyperglycemia properties. However, attention has recently shifted towards elucidating the ability of FGF21 to lower circulating lipid levels and ameliorate liver inflammation and steatosis. We here discuss the physiology of FGF21 and its role in lipid metabolism, with a focus on genetics, which has up until now not been fully appreciated.

RECENT FINDINGS

New developments have uncovered associations of common small-effect variants of the FGF21 gene, such as the single nucleotide polymorphisms rs2548957 and rs838133, with numerous physiological, biochemical and behavioural phenotypes linked to energy metabolism and liver function. In addition, rare loss-of-function variants of the cellular receptors for FGF21 have been recently associated with severe endocrine and metabolic phenotypes. These associations corroborate the findings from basic studies and preliminary clinical investigations into the therapeutic potential of FGF21 for the treatment of metabolic dysfunction-associated steatotic liver disease (MASLD) and hypertriglyceridemia. Furthermore, recent breakthrough research has begun to dissect mechanisms of a potential FGF21 brain-adipose axis. Such inter-organ communication would be comparable to that seen with other potent metabolic hormones. A deeper understanding of FGF21 could prove to be further beneficial for drug development.

SUMMARY

FGF21 is a potent regulator of lipid and energy homeostasis and its physiology is currently at the centre of investigative efforts to develop agents targeting hypertriglyceridemia and MASLD.

Protocol to evaluate fasting metabolism and its relationship to the core circadian clock in mice

To investigate the role of hepatocyte genes in fasting metabolism, it is essential to analyze their expression across the entire 24-h circadian cycle. Here, we present a protocol to evaluate fasting metabolism and its relationship to the core circadian clock in mice. We describe steps for time-course fasting/feeding experiment setup and performing staggered fasting and refeeding for 24 h. We then detail procedures for evaluating oxidative substrate selection and rescuing defective oxidative metabolism through FGF21 and CPI-613 injections. For complete details on the use and execution of this protocol, please refer to Sun et al.1.

Functions of FGF21 and its role in cardiac hypertrophy

BACKGROUND

FGF21 is a stress-inducible hormone that operates in the autocrine or paracrine manner. Recent reports have revealed that FGF21 is highly expressed in cardiac hypertrophy to protect against heart injury and dysfunction. FGF21 is used to treat cardiac hypertrophy in mouse models. However, preclinical and clinical trials are restricted.

AIM OF REVIEW

This review mainly elucidates the diverse functions of FGF21 and explores the relationship between these functions and cardiac hypertrophy. It also discusses challenges and future perspectives in treating cardiac hypertrophy with FGF21.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review first illustrates the functions of FGF21, including energy metabolism, inflammation, oxidative stress, apoptosis, and autophagy. We also summarize vital functions and the underlying mechanisms through which FGF21 regulates the initiation and development of cardiac hypertrophy, connecting energy metabolism, inflammation, oxidative stress, apoptosis, and autophagy. Finally, we propose that FGF21 may be a potential therapeutic strategy for cardiac hypertrophy.

Aerobic Exercise Activates Fibroblast Growth Factor 21 and Alleviates Cardiac Ischemia/Reperfusion-induced Neuronal Oxidative Stress and Ferroptosis in Paraventricular Nucleus

Cardiac ischemia/reperfusion (I/R) induces systemic oxidative stress, which in turn gives rise to the development of multiple organ abnormalities, including brain injury. The paraventricular nucleus (PVN) of the hypothalamus is a cardiovascular regulatory center. Aerobic exercise is an effective intervention to protect the heart against I/R injury. However, the effect of aerobic exercise on cardiac I/R-induced neuronal injury in the PVN has not been fully elucidated. The aim of this study is to investigate whether aerobic exercise can up-regulate fibroblast growth factor 21 (FGF21) and alleviate neuronal oxidative stress and ferroptosis in the PVN caused by cardiac I/R. In vivo, after six weeks of aerobic exercise, the cardiac I/R model was established by ligating the left anterior descending (LAD) coronary artery for 30 min, followed by 2 h of reperfusion. Cardiac function and heart rate variability (HRV) were measured. Morphological changes, oxidative stress, expression of FGF21 and its downstream signaling molecules, as well as ferroptosis-related indicators in the PVN, were evaluated. In vitro, HT22 cells were exposed to oxygen-glucose deprivation and reoxygenation (OGD/R) and treated with recombinant human FGF21 (rhFGF21) and compound C to elucidate the potential mechanism. Cardiac I/R induced iron deposition, elevated expression of lipid peroxidation drivers, and impaired antioxidant capacity in the PVN, which collectively contributed to neuronal ferroptosis. Aerobic exercise up-regulated the expression of FGF21, FGFR1, and PGC-1α, maintained the phosphorylation of AMPKα, enhanced antioxidant capacity, reduced ROS and lipid peroxidation, regulated iron homeostasis, and effectively attenuated neuronal ferroptosis induced by cardiac I/R. In addition, rhFGF21 protected HT22 cells against OGD/R-induced oxidative stress and ferroptosis, which was blocked by AMPK inhibition. FGF21 plays a pivotal role in regulating neuronal oxidative stress and ferroptosis. Aerobic exercise could increase the expression of FGF21, FGFR1, and PGC-1α, maintain the phosphorylation of AMPKα, and alleviate cardiac I/R-induced neuronal oxidative stress and ferroptosis. These results confirm the protective effect of aerobic exercise against cardiac I/R-induced brain injury and provide an experimental basis for studying the relationship between exercise and the "heart-brain axis."

A comparative genomic study across 396 liver biopsies provides deep insight into FGF21 mode of action as a therapeutic agent in metabolic dysfunction-associated steatotic liver disease

BACKGROUND

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a systemic disease with insulin resistance at its core. It affects one-third of the world population. Fibroblast growth factor (FGF21)-based therapies are effective in lowering hepatic fat content and fibrosis resolution; yet, its molecular functions remain uncertain. To gain insight into FGF21 mode of action (MoA), we investigated the transcriptomes of MASLD liver biopsies in relation to FGF21 expression.

METHODS

We compared N = 66 healthy controls with 396 MASLD patients and considered clinical characteristics relative to NAS disease activity scores (steatosis, lobular inflammation and ballooning), fibrosis grades and sex. We performed comparative genomics to identify FGF21-responsive DEGs, utilised information from FGF21-transgenic and FGF21-knockout mice and evaluated DEGs following FGF21 treatment of MASLD animal models. Eventually, we explored 188 validated FGF21 targets, and for ≥10 patients showing the same changes, we constructed MASLD-associated networks to determine the effects of FGF21 in reverting metabolic dysfunction.

RESULTS

We identified patients with increased 30% (N = 117), decreased 40% (N = 159) or unchanged 30% (N = 120) FGF21 expression, and the differences are caused by changes in FGF21 transcriptional control with ATF4 functioning as a key regulator. Based on comparative genomics, we discovered molecular circuitries of FGF21 in MASLD, notably FGF21-dependent induction of autophagy and oxidative phosphorylation/mitochondrial respiration. Conversely, FGF21 repressed hepatic glycogen-storage, its glucose release and gluconeogenesis, and therefore reduced glucose flux in conditions of insulin resistance. Furthermore, FGF21 repressed lipid transporters, and acetyl-CoA carboxylase-β to attenuate hepatic lipid overload and lipogenesis. Strikingly, FGF21 dampened immune response by repressing complement factors, MARCO, CD163, MRC1/CD206, CD4, CD45 and pro-inflammatory cytokine receptors. It also reverted procoagulant imbalance in MASLD, stimulated extracellular matrix degradation, repressed TGFβ- and integrin-signalling and lessened liver sinusoidal endothelial cell defenestration in support of fibrosis resolution.

CONCLUSIONS

We gained deep insight into FGF21-MoA in MASLD. However, heterogeneity in FGF21 expression calls for molecular stratifications as to identify patients which likely benefit from FGF21-based therapies.

KEY POINTS

Performed comprehensive genomics across liver biopsies of 396 MASLD patients and identified patients with increased, decreased and unchanged FGF21 expression. Used genomic data from FGF21 transgenic, knock-out and animal MASLD models treated with synthetic FGF21 analogues to identify FGF21-mode-of-action and metabolic networks in human MASLD. Given the significant heterogeneity in FGF21 expression, not all patients will benefit from FGF21-based therapies.

Bile acid sequestrant inhibits gluconeogenesis via inducing hepatic cysteine dioxygenase type 1 to reduce cysteine availability

Bile acid sequestrants such as cholestyramine (ChTM) are gut-restricted bile acid-binding resins that block intestine bile acid absorption and attenuate hepatic bile acid signaling. Bile acid sequestrants induce hepatic bile acid synthesis to promote cholesterol catabolism and are cholesterol-lowering drugs. Bile acid sequestrants also reduce blood glucose in clinical trials and are approved drugs for treating hyperglycemia in type-2 diabetes. However, the mechanisms mediating the glucose-lowering effect of bile acid sequestrants are still incompletely understood. Here we showed that ChTM treatment decreased hepatic glucose production in Western diet-fed mice with paradoxically induced hepatic gluconeogenic genes. Cysteine dioxygenase type 1 (CDO1) mediates cysteine conversion to taurine and its expression is repressed by bile acids. We show that ChTM induced hepatic CDO1 and selectively reduced hepatic cysteine availability. Knockdown of liver CDO1 increased liver cysteine and glucose production in mice, whereas hepatocytes cultured in cystine-deficient medium showed reduced glucose production. By using dietary protein-restricted and cystine-modified Western diets that selectively alter hepatic cysteine availability, we found that reduced hepatic cysteine availability strongly inhibited glucose production in mice. Interestingly, chronic dietary protein restriction also prevented Western diet-induced obesity, which was fully reversed by restoring dietary cystine intake alone. Consistently, reduced cysteine availability dose-dependently inhibited adipogenesis in vitro. In conclusion, we report that the glucose-lowering effect of bile acid sequestrants is mediated by a CDO1-induced hepatic cysteine restriction mimetic effect. Furthermore, the anti-obesity effect of dietary protein restriction is largely mediated by reduced dietary cysteine intake.NEW & NOTEWORTHY Hepatic cysteine availability is a key driver of hepatic gluconeogenesis. Bile acid sequestrant inhibits gluconeogenesis by inducing CDO1-mediated cysteine catabolism to reduce cysteine availability. Dietary protein restriction causes hepatic cysteine deficiency without overall amino acid deficiency. The glucose-lowering effect of dietary protein restriction is largely mediated by lower dietary cysteine intake. The anti-obesity effect of chronic dietary protein restriction is largely mediated by lower dietary cysteine intake.

The Role of microRNA-22 in Metabolism

microRNA-22 (miR-22) plays a pivotal role in the regulation of metabolic processes and has emerged as a therapeutic target in metabolic disorders, including obesity, type 2 diabetes, and metabolic-associated liver diseases. While miR-22 exhibits context-dependent effects, promoting or inhibiting metabolic pathways depending on tissue and condition, current research highlights its therapeutic potential, particularly through inhibition strategies using chemically modified antisense oligonucleotides. This review examines the dual regulatory functions of miR-22 across key metabolic pathways, offering perspectives on its integration into next-generation diagnostic and therapeutic approaches while acknowledging the complexities of its roles in metabolic homeostasis.

Impaired Fibroblast Growth Factor 21 (FGF21) Associated with Visceral Adiposity Leads to Insulin Resistance: The Core Defect in Diabetes Mellitus

The Central nervous system (CNS) is the prime regulator of signaling pathways whose function includes regulation of food intake (consumption), energy expenditure, and other metabolic responses like glycolysis, gluconeogenesis, fatty acid oxidation, and thermogenesis that have been implicated in chronic inflammatory disorders. Type 2 diabetes mellitus (T2DM) and obesity are two metabolic disorders that are linked together and have become an epidemic worldwide, thus raising significant public health concerns. Fibroblast growth factor 21 (FGF21) is an endocrine hormone with pleiotropic metabolic effects that increase insulin sensitivity and energy expenditure by elevating thermogenesis in brown or beige adipocytes, thus reducing body weight and sugar intake. In contrast, during starvation conditions, FGF21 induces its expression in the liver to initiate glucose homeostasis. Insulin resistance is one of the main anomalies caused by impaired FGF21 signaling, which also causes abnormal regulation of other signaling pathways. Tumor necrosis factor alpha (TNF-α), the cytokine released by adipocytes and inflammatory cells in response to chronic inflammation, is regarded major factor that reduces the expression of FGF21 and modulates underlying insulin resistance that causes imbalanced glucose homeostasis. This review aims to shed light on the mechanisms underlying the development of insulin resistance in obese individuals as well as the fundamental flaw in type 2 diabetes, which is malfunctioning obese adipose tissue.

FGF21 acts in the brain to drive macronutrient-specific changes in behavioral motivation and brain reward signaling

OBJECTIVE

Dietary protein restriction induces adaptive changes in food preference, increasing protein consumption over carbohydrates or fat. We investigated whether motivation and reward signaling underpin these preferences.

METHODS AND RESULTS

In an operant task, protein-restricted male mice responded more for liquid protein rewards, but not carbohydrate, fat, or sweet rewards compared to non-restricted mice. When the number of responses required to access protein reward varied, protein-restricted mice exhibited higher operant responses at moderate to high response requirements. The protein restriction-induced increase in operant responding for protein was absent in Fgf21-KO mice and mice with neuron-specific deletion of the FGF21 co-receptor beta-Klotho (KlbCam2ka). Fiber photometry recording of VTA dopamine neurons revealed that oral delivery of maltodextrin triggered a larger dopamine neuron activation than casein in control diet-fed mice, while casein triggered a larger activation in low-protein diet-fed mice. This restriction-induced shift in nutrient-specific VTA dopamine signaling was lost in Fgf21-KO mice.

CONCLUSION

These data suggest that the increased FGF21 during protein restriction acts in the brain to induce a protein-specific appetite by specifically enhancing the reward value of protein-containing foods and the motivation to consume them.

Glycerol-3-phosphate activates ChREBP, FGF21 transcription and lipogenesis in Citrin Deficiency

Citrin Deficiency (CD) is caused by inactivation of SLC25A13, a mitochondrial membrane protein required to move electrons from cytosolic NADH to the mitochondrial matrix in hepatocytes. People with CD do not like sweets. We discovered that SLC25A13 loss causes accumulation of glycerol-3-phosphate (G3P), which activates carbohydrate response element binding protein (ChREBP) to transcribe FGF21, which acts in the brain to restrain intake of sweets and alcohol, and to transcribe key genes of de novo lipogenesis. Mouse and human data establish G3P-ChREBP as a new mechanistic component of the Randle Cycle that contributes to metabolic dysfunction-associated steatotic liver disease (MASLD) and forms part of a system that communicates metabolic states from liver to brain in a manner that alters food and alcohol choices. The data provide a framework for understanding FGF21 induction in varied conditions, suggest ways to develop FGF21-inducing drugs, and drug candidates for both lean MASLD and support of urea cycle function in CD.

Novel FGF21 analogues through structure-based optimization for therapeutic development

Fibroblast growth factor 21 (FGF21) plays a pivotal role in regulating metabolic processes and energy homeostasis, making it a promising therapeutic avenue for various obesity-related conditions. However, its therapeutic efficacy faces challenges due to its suboptimal pharmacokinetics and bioactivity. To overcome these limitations, we adapt a strategy in which key amino acid residues responsible for enhanced activity are pinpointed through sequence alignment and comparative analysis to develop long-acting FGF21 analogs. The mutant FGF21 analogs are fused with the Fc fragment. Here, we report the design, identification, and characterization of two distinct Fc-fused FGF21 analogs, Fc-FGF21(P119R) and Fc-FGF21(H125R), with significantly augmented potency. These findings hold promise for clinical applications, offering potential interventions for obesity-related metabolic disorders.

Lipid sensing by PPARα: Role in controlling hepatocyte gene regulatory networks and the metabolic response to fasting

Peroxisome proliferator-activated receptors (PPARs) constitute a small family of three nuclear receptors that act as lipid sensors, and thereby regulate the transcription of genes having key roles in hepatic and whole-body energy homeostasis, and in other processes (e.g., inflammation), which have far-reaching health consequences. Peroxisome proliferator-activated receptor isotype α (PPARα) is expressed in oxidative tissues, particularly in the liver, carrying out critical functions during the adaptive fasting response. Advanced omics technologies have provided insight into the vast complexity of the regulation of PPAR expression and activity, as well as their downstream effects on the physiology of the liver and its associated metabolic organs. Here, we provide an overview of the gene regulatory networks controlled by PPARα in the liver in response to fasting. We discuss impacts on liver metabolism, the systemic repercussions and benefits of PPARα-regulated ketogenesis and production of fibroblast growth factor 21 (FGF21), a fasting- and stress-inducible metabolic hormone. We also highlight current challenges in using novel methods to further improve our knowledge of PPARα in health and disease.

Oxidative phosphorylation and fatty acid oxidation in slow-aging mice

Oxidative metabolism declines with aging in humans leading to multiple metabolic ailments and subsequent inflammation. In mice, there is evidence of age-related suppression of fatty acid oxidation and oxidative phosphorylation in the liver, heart, and muscles. Many interventions that extend healthy lifespan of mice have been developed, including genetic, pharmacological, and dietary interventions. In this article, we review the literature on oxidative metabolism changes in response to those interventions. We also discuss the molecular pathways that mediate those changes, and their potential as targets for future longevity interventions.

Effects of central FGF21 infusion on the glucose homeostasis in rats (brain-pancreas axis)

INTRODUCTION

Glucose homeostasis is a physiological process mediated by a variety of hormones. Fibroblast growth factor (FGF) 21 is a protein expressed in the liver, adipose tissue, muscle and pancreas and exerts actions in multiple targets including adipose, liver, pancreas and hypothalamus. The aim of this study was to examine the possible involvement of FGF21 in pancreatic and central control of glucose by measuring reflective changes in the release of insulin and glucagon.

METHODS

Thirty adult male Wistar Albino rats were divided; Control, PD + aCSF, PD + FGF21 groups (n = 10). Effects of intracerebroventricular (icv) FGF21 administration to pancreatic denervated (PD) rats. Agouti-related protein (AgRP), Pro-opiomelanocortin (POMC) levels and blood glucose homeostasis were investigated.

RESULTS

Administration of FGF21 to 3rd ventricle increased food consumption but body weight didn't change significantly. AgRP level increased, pancreatic insulin levels increased, and glucagon level decreased.

CONCLUSION

Central FGF21 administration is effective in regulating blood glucose homeostasis by increasing the amount and efficiency of insulin and changing glucose use.

Endocrine fibroblast growth factors in domestic animals

Fibroblast growth factors (FGFs) are a group of structurally homologous yet functionally pleiotropic proteins. Canonical and intracellular FGFs have primarily autocrine or paracrine effects. However, the FGF19 subfamily, composed of FGF15/19, FGF21, and FGF23, act as endocrine hormones that regulate bile acid, metabolic, and phosphorus homeostasis, respectively. Current research in human and rodent models demonstrates the potential of these endocrine FGFs to target various diseases, including disorders of inherited hypophosphatemia, chronic liver disease, obesity, and insulin resistance. Many diseases targeted for therapeutic use in humans have pathophysiological overlaps in domestic animals. Despite the potential clinical and economic impact, little is known about endocrine FGFs and their signaling pathways in major domestic animal species compared with humans and laboratory animals. This review aims to describe the physiology of these endocrine FGFs, discuss their current therapeutic use, and summarize the contemporary literature regarding endocrine FGFs in domestic animals, focusing on potential future directions.

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".

FGF21 acts in the brain to drive macronutrient-specific changes in behavioral motivation and brain reward signaling

Dietary protein restriction induces adaptive changes in food preference, increasing protein consumption over carbohydrates or fat. We investigated whether motivation and reward signaling underpin these preferences. In an operant task, protein-restricted male mice responded more for liquid protein rewards, but not carbohydrate, fat, or sweet rewards compared to non-restricted mice. The protein restriction-induced increase in operant responding for protein was absent in Fgf21-KO mice and mice with neuron-specific deletion of the FGF21 co-receptor beta-Klotho (Klb Cam2ka ) mice. Fiber photometry recording of VTA dopamine neurons revealed that oral delivery of maltodextrin triggered a larger activation as compared to casein in control-fed mice, whereas casein triggered a larger activation in protein-restricted mice. This restriction-induced shift in nutrient-specific VTA dopamine signaling was lost in Fgf21-KO mice. These data strongly suggest that the increased FGF21 during protein restriction acts in the brain to induce a protein-specific appetite by specifically enhancing the reward value of protein-containing foods and the motivation to consume them.

Exploring endocrine FGFs - structures, functions and biomedical applications

The family of fibroblast growth factors (FGFs) consists of 22 members with diverse biological functions in cells, from cellular development to metabolism. The family can be further categorized into three subgroups based on their three modes of action. FGF19, FGF21, and FGF23 are endocrine FGFs that act in a hormone-like/endocrine manner to regulate various metabolic activities. However, all three members of the endocrine family require both FGF receptors (FGFRs) and klotho co-receptors to elicit their functions. α-klotho and β-klotho act as scaffolds to bring endocrine FGFs closer to their receptors (FGFRs) to form active complexes. Numerous novel studies about metabolic FGFs' structures, mechanisms, and physiological insights have been published to further understand the complex molecular interactions and physiological activities of endocrine FGFs. Herein, we aim to review the structures, physiological functions, binding mechanisms to cognate receptors, and novel biomedical applications of endocrine FGFs in recent years.

Team players in the pathogenesis of metabolic dysfunctions-associated steatotic liver disease: The basis of development of pharmacotherapy

Nutrient metabolism is regulated by several factors. Social determinants of health with or without genetics are the primary regulator of metabolism, and an unhealthy lifestyle affects all modulators and mediators, leading to the adaptation and finally to the exhaustion of cellular functions. Hepatic steatosis is defined by presence of fat in more than 5% of hepatocytes. In hepatocytes, fat is stored as triglycerides in lipid droplet. Hepatic steatosis results from a combination of multiple intracellular processes. In a healthy individual nutrient metabolism is regulated at several steps. It ranges from the selection of nutrients in a grocery store to the last step of consumption of ATP as an energy or as a building block of a cell as structural component. Several hormones, peptides, and genes have been described that participate in nutrient metabolism. Several enzymes participate in each nutrient metabolism as described above from ingestion to generation of ATP. As of now several publications have revealed very intricate regulation of nutrient metabolism, where most of the regulatory factors are tied to each other bidirectionally, making it difficult to comprehend chronological sequence of events. Insulin hormone is the primary regulator of all nutrients' metabolism both in prandial and fasting states. Insulin exerts its effects directly and indirectly on enzymes involved in the three main cellular function processes; metabolic, inflammation and repair, and cell growth and regeneration. Final regulators that control the enzymatic functions through stimulation or suppression of a cell are nuclear receptors in especially farnesoid X receptor and peroxisome proliferator-activated receptor/RXR ligands, adiponectin, leptin, and adiponutrin. Insulin hormone has direct effect on these final modulators. Whereas blood glucose level, serum lipids, incretin hormones, bile acids in conjunction with microbiota are intermediary modulators which are controlled by lifestyle. The purpose of this review is to overview the key players in the pathogenesis of metabolic dysfunction-associated steatotic liver disease (MASLD) that help us understand the disease natural course, risk stratification, role of lifestyle and pharmacotherapy in each individual patient with MASLD to achieve personalized care and target the practice of precision medicine. PubMed and Google Scholar databases were used to identify publication related to metabolism of carbohydrate and fat in states of health and disease states; MASLD, cardiovascular disease and cancer. More than 1000 publications including original research and review papers were reviewed.

FGF21 mediating the Sex-dependent Response to Dietary Macronutrients

Sex is key variable influencing body composition and substrate utilization. At rest, females maintain greater adiposity than males and resist the mobilization of fat. Males maintain greater lean muscle mass and mobilize fat readily. Determining the mechanisms that direct these sex-dependent effects is important for both reproductive and metabolic health. Here, we highlight the fundamental importance of sex in shaping metabolic physiology and assess growing evidence that the hepatokine fibroblast growth factor-21 (FGF21) plays a mechanistic role to facilitate sex-dependent responses to a changing nutritional environment. First, we examine the importance of sex in modulating body composition and substrate utilization. We summarize new data that point toward sex-biased effects of pharmacologic FGF21 administration on these endpoints. When energy is not limited, metabolic responses to FGF21 mirror broader sex differences; FGF21-treated males conserve lean mass at the expense of increased lipid catabolism, whereas FGF21-treated females conserve fat mass at the expense of reduced lean mass. Next, we examine the importance of sex in modulating the endogenous secretion of FGF21 in response to changing macronutrient and energy availability. During the resting state when energy is not limited, macronutrient imbalance increases the secretion of FGF21 more so in males than females. When energy is limited, the effect of sex on both the secretion of FGF21 and its metabolic actions may be reversed. Altogether, we argue that a growing literature supports FGF21 as a plausible mechanism contributing to the sex-dependent mobilization vs preservation of lipid storage and highlight the need for further research.

Pathophysiological Relationship between Type 2 Diabetes Mellitus and Metabolic Dysfunction-Associated Steatotic Liver Disease: Novel Therapeutic Approaches

Type 2 diabetes mellitus (T2DM), often featuring hyperglycemia or insulin resistance, is a global health concern that is increasing in prevalence in the United States and worldwide. A common complication is metabolic dysfunction-associated steatotic liver disease (MASLD), the hepatic manifestation of metabolic syndrome that is also rapidly increasing in prevalence. The majority of patients with T2DM will experience MASLD, and likewise, individuals with MASLD are at an increased risk for developing T2DM. These two disorders may act synergistically, in part due to increased lipotoxicity and inflammation within the liver, among other causes. However, the pathophysiological mechanisms by which this occurs are unclear, as is how the improvement of one disorder can ameliorate the other. This review aims to discuss the pathogenic interactions between T2D and MASLD, and will highlight novel therapeutic targets and ongoing clinical trials for the treatment of these diseases.

Hepatic function of glucagon-like peptide-1 and its based diabetes drugs

Incretins are gut-produced peptide-hormones that potentiate insulin secretion, especially after food intake. The concept of incretin was formed more than 100 years ago, even before insulin was isolated and utilized in the treatment of subjects with type 1 diabetes. The first incretin, glucose-dependent insulinotropic polypeptide (GIP), was identified during later 1960's and early 1970's; while the second one, known as glucagon-like peptide-1 (GLP-1), was recognized during 1980's. Today, GLP-1-based therapeutic agents [also known as GLP-1 receptor (GLP-1R) agonists, GLP-1RAs] are among the first line drugs for type 2 diabetes. In addition to serving as incretin, extra-pancreatic functions of GLP-1RAs have been broadly recognized, including those in the liver, despite the absence of GLP-1R in hepatic tissue. The existence of insulin-independent or gut-pancreas-liver axis-independent hepatic function of GLP-1RAs explains why those therapeutic agents are effective in subjects with insulin resistance and their profound effect on lipid homeostasis. Following a brief review on the discovery of GLP-1, we reviewed literature on the exploration of hepatic function of GLP-1 and GLP-1RAs and discussed recent studies on the role of hepatic hormone fibroblast growth factor 21 (FGF21) in mediating function of GLP-1RAs in animal models. This was followed by presenting our perspective views.

Weighing in on the role of brown adipose tissue for treatment of obesity

Brown adipose tissue (BAT) activation is an emerging target for obesity treatments due to its thermogenic properties stemming from its ability to shuttle energy through uncoupling protein 1 (Ucp1). Recent rodent studies show how BAT and white adipose tissue (WAT) activity can be modulated to increase the expression of thermogenic proteins. Consequently, these alterations enable organisms to endure cold-temperatures and elevate energy expenditure, thereby promoting weight loss. In humans, BAT is less abundant in obese subjects and impacts of thermogenesis are less pronounced, bringing into question whether energy expending properties of BAT seen in rodents can be translated to human models. Our review will discuss pharmacological, hormonal, bioactive, sex-specific and environmental activators and inhibitors of BAT to determine the potential for BAT to act as a therapeutic strategy. We aim to address the feasibility of utilizing BAT modulators for weight reduction in obese individuals, as recent studies suggest that BAT's contributions to energy expenditure along with Ucp1-dependent and -independent pathways may or may not rectify energy imbalance characteristic of obesity.

New advances in drug development for metabolic dysfunction-associated diseases and alcohol-associated liver disease

Metabolic disorders are currently threatening public health worldwide. Discovering new targets and developing promising drugs will reduce the global metabolic-related disease burden. Metabolic disorders primarily consist of lipid and glucose metabolic disorders. Specifically, metabolic dysfunction-associated steatosis liver disease (MASLD) and alcohol-associated liver disease (ALD) are two representative lipid metabolism disorders, while diabetes mellitus is a typical glucose metabolism disorder. In this review, we aimed to summarize the new drug candidates with promising efficacy identified in clinical trials for these diseases. These drug candidates may provide alternatives for patients with metabolic disorders and advance the progress of drug discovery for the large disease burden.

A novel fatty acid mimetic with pan-PPAR partial agonist activity inhibits diet-induced obesity and metabolic dysfunction-associated steatotic liver disease

OBJECTIVE

The prevalence of metabolic diseases is increasing globally at an alarming rate; thus, it is essential that effective, accessible, low-cost therapeutics are developed. Peroxisome proliferator-activated receptors (PPARs) are transcription factors that tightly regulate glucose homeostasis and lipid metabolism and are important drug targets for the treatment of type 2 diabetes and dyslipidemia. We previously identified LDT409, a fatty acid-like compound derived from cashew nut shell liquid, as a novel pan-active PPARα/γ/δ compound. Herein, we aimed to assess the efficacy of LDT409 in vivo and investigate the molecular mechanisms governing the actions of the fatty acid mimetic LDT409 in diet-induced obese mice.

METHODS

C57Bl/6 mice (6-11-month-old) were fed a chow or high fat diet (HFD) for 4 weeks; mice thereafter received once daily intraperitoneal injections of vehicle, 10 mg/kg Rosiglitazone, 40 mg/kg WY14643, or 40 mg/kg LDT409 for 18 days while continuing the HFD. During treatments, body weight, food intake, glucose and insulin tolerance, energy expenditure, and intestinal lipid absorption were measured. On day 18 of treatment, tissues and plasma were collected for histological, molecular, and biochemical analysis.

RESULTS

We found that treatment with LDT409 was effective at reversing HFD-induced obesity and associated metabolic abnormalities in mice. LDT409 lowered food intake and hyperlipidemia, while improving insulin tolerance. Despite being a substrate of both PPARα and PPARγ, LDT409 was crucial for promoting hepatic fatty acid oxidation and reducing hepatic steatosis in HFD-fed mice. We also highlighted a role for LDT409 in white and brown adipocytes in vitro and in vivo where it decreased fat accumulation, increased lipolysis, induced browning of WAT, and upregulated thermogenic gene Ucp1. Remarkably, LDT409 reversed HFD-induced weight gain back to chow-fed control levels. We determined that the LDT409-induced weight-loss was associated with a combination of increased energy expenditure (detectable before weight loss was apparent), decreased food intake, increased systemic fat utilization, and increased fecal lipid excretion in HFD-fed mice.

CONCLUSIONS

Collectively, LDT409 represents a fatty acid mimetic that generates a uniquely favorable metabolic response for the treatment of multiple abnormalities including obesity, dyslipidemia, metabolic dysfunction-associated steatotic liver disease, and diabetes. LDT409 is derived from a highly abundant natural product-based starting material and its development could be pursued as a therapeutic solution to the global metabolic health crisis.

Hepatic IRE1α-XBP1 signaling promotes GDF15-mediated anorexia and body weight loss in chemotherapy

Platinum-based chemotherapy drugs can lead to the development of anorexia, a detrimental effect on the overall health of cancer patients. However, managing chemotherapy-induced anorexia and subsequent weight loss remains challenging due to limited effective therapeutic strategies. Growth differentiation factor 15 (GDF15) has recently gained significant attention in the context of chemotherapy-induced anorexia. Here, we report that hepatic GDF15 plays a crucial role in regulating body weight in response to chemo drugs cisplatin and doxorubicin. Cisplatin and doxorubicin treatments induce hepatic Gdf15 expression and elevate circulating GDF15 levels, leading to hunger suppression and subsequent weight loss. Mechanistically, selective activation by chemotherapy of hepatic IRE1α-XBP1 pathway of the unfolded protein response (UPR) upregulates Gdf15 expression. Genetic and pharmacological inactivation of IRE1α is sufficient to ameliorate chemotherapy-induced anorexia and body weight loss. These results identify hepatic IRE1α as a molecular driver of GDF15-mediated anorexia and suggest that blocking IRE1α RNase activity offers a therapeutic strategy to alleviate the adverse anorexia effects in chemotherapy.

Loss of flavin-containing monooxygenase 3 modulates dioxin-like polychlorinated biphenyl 126-induced oxidative stress and hepatotoxicity

Dioxin-like pollutants (DLPs), such as polychlorinated biphenyl 126 (PCB 126), are synthetic chemicals classified as persistent organic pollutants. They accumulate in adipose tissue and have been linked to cardiometabolic disorders, including fatty liver disease. The toxicity of these compounds is associated with activation of the aryl hydrocarbon receptor (Ahr), leading to the induction of phase I metabolizing enzyme cytochrome P4501a1 (Cyp1a1) and the subsequent production of reactive oxygen species (ROS). Recent research has shown that DLPs can also induce the xenobiotic detoxification enzyme flavin-containing monooxygenase 3 (FMO3), which plays a role in metabolic homeostasis. We hypothesized whether genetic deletion of Fmo3 could protect mice, particularly in the liver, where Fmo3 is most inducible, against PCB 126 toxicity. To test this hypothesis, male C57BL/6 wild-type (WT) mice and Fmo3 knockout (Fmo3 KO) mice were exposed to PCB 126 or vehicle (safflower oil) during a 12-week study, at weeks 2 and 4. Various analyses were performed, including hepatic histology, RNA-sequencing, and quantitation of PCB 126 and F2-isoprostane concentrations. The results showed that PCB 126 exposure caused macro and microvesicular fat deposition in WT mice, but this macrovesicular fatty change was absent in Fmo3 KO mice. Moreover, at the pathway level, the hepatic oxidative stress response was significantly different between the two genotypes, with the induction of specific genes observed only in WT mice. Notably, the most abundant F2-isoprostane, 8-iso-15-keto PGE2, increased in WT mice in response to PCB 126 exposure. The study's findings also demonstrated that hepatic tissue concentrations of PCB 126 were higher in WT mice compared to Fmo3 KO mice. In summary, the absence of FMO3 in mice led to a distinctive response to dioxin-like pollutant exposure in the liver, likely due to alterations in lipid metabolism and storage, underscoring the complex interplay of genetic factors in the response to environmental toxins.

Exercise enhances hepatic mitochondrial structure and function while preventing endoplasmic reticulum stress and metabolic dysfunction-associated steatotic liver disease in mice fed a high-fat diet

Metabolic dysfunction-associated steatotic liver disease (MASLD) has attracted increasing attention from the scientific community because of its severe but silent progression and the lack of specific treatment. Glucolipotoxicity triggers endoplasmic reticulum (ER) stress with decreased beta-oxidation and enhanced lipogenesis, promoting the onset of MASLD, whereas regular physical exercise can prevent MASLD by preserving ER and mitochondrial function. Thus, the hypothesis of this study was that high-intensity interval training (HIIT) could prevent the development of MASLD in high-fat (HF)-fed C57BL/6J mice by maintaining insulin sensitivity, preventing ER stress, and promoting beta-oxidation. Forty male C57BL/6J mice (3 months old) comprised 4 experimental groups: the control (C) diet group, the C diet + HIIT (C-HIIT) group, the HF diet group, and the HF diet + HIIT (HF-HIIT) group. HIIT sessions lasted 12 minutes and were performed 3 times weekly by trained mice. The diet and exercise protocols lasted for 10 weeks. The HIIT protocol prevented weight gain and maintained insulin sensitivity in the HF-HIIT group. A chronic HF diet increased ER stress-related gene and protein expression, but HIIT helped to maintain ER homeostasis, preserve mitochondrial ultrastructure, and maximize beta-oxidation. The increased sirtuin-1/peroxisome proliferator-activated receptor-gamma coactivator 1-alpha expression implies that HIIT enhanced mitochondrial biogenesis and yielded adequate mitochondrial dynamics. High hepatic fibronectin type III domain containing 5/irisin agreed with the antilipogenic and anti-inflammatory effects observed in the HF-HIIT group, reinforcing the antisteatotic effects of HIIT. Thus, we confirmed that practicing HIIT 3 times per week maintained insulin sensitivity, prevented ER stress, and enhanced hepatic beta-oxidation, impeding MASLD development in this mouse model even when consuming high energy intake from saturated fatty acids.

Rab30 facilitates lipid homeostasis during fasting

To facilitate inter-tissue communication and the exchange of proteins, lipoproteins, and metabolites with the circulation, hepatocytes have an intricate and efficient intracellular trafficking system regulated by small Rab GTPases. Here, we show that Rab30 is induced in the mouse liver by fasting, which is amplified in liver-specific carnitine palmitoyltransferase 2 knockout mice (Cpt2L-/-) lacking the ability to oxidize fatty acids, in a Pparα-dependent manner. Live-cell super-resolution imaging and in vivo proximity labeling demonstrates that Rab30-marked vesicles are highly dynamic and interact with proteins throughout the secretory pathway. Rab30 whole-body, liver-specific, and Rab30; Cpt2 liver-specific double knockout (DKO) mice are viable with intact Golgi ultrastructure, although Rab30 deficiency in DKO mice suppresses the serum dyslipidemia observed in Cpt2L-/- mice. Corresponding with decreased serum triglyceride and cholesterol levels, DKO mice exhibit decreased circulating but not hepatic ApoA4 protein, indicative of a trafficking defect. Together, these data suggest a role for Rab30 in the selective sorting of lipoproteins to influence hepatocyte and circulating triglyceride levels, particularly during times of excessive lipid burden.

Exploring exercise-driven exerkines: unraveling the regulation of metabolism and inflammation

Exercise has many beneficial effects that provide health and metabolic benefits. Signaling molecules are released from organs and tissues in response to exercise stimuli and are widely termed exerkines, which exert influence on a multitude of intricate multi-tissue processes, such as muscle, adipose tissue, pancreas, liver, cardiovascular tissue, kidney, and bone. For the metabolic effect, exerkines regulate the metabolic homeostasis of organisms by increasing glucose uptake and improving fat synthesis. For the anti-inflammatory effect, exerkines positively influence various chronic inflammation-related diseases, such as type 2 diabetes and atherosclerosis. This review highlights the prospective contribution of exerkines in regulating metabolism, augmenting the anti-inflammatory effects, and providing additional advantages associated with exercise. Moreover, a comprehensive overview and analysis of recent advancements are provided in this review, in addition to predicting future applications used as a potential biomarker or therapeutic target to benefit patients with chronic diseases.

Role of liver FGF21-KLB signaling in ketogenic diet-induced amelioration of hepatic steatosis

BACKGROUND

The effectiveness of ketogenic diet (KD) in ameliorating fatty liver has been established, although its mechanism is under investigation. Fibroblast growth factor 21 (FGF21) positively regulates obesity-associated metabolic disorders and is elevated by KD. FGF21 conventionally initiates its intracellular signaling via receptor β-klotho (KLB). However, the mechanistic role of FGF21-KLB signaling for KD-ameliorated fatty liver remains unknown. This study aimed to delineate the critical role of FGF21 signaling in the ameliorative effects of KD on hepatic steatosis.

METHODS

Eight-week-old C57BL/6 J mice were fed a chow diet (CD), a high-fat diet (HFD), or a KD for 16 weeks. Adeno-associated virus-mediated liver-specific KLB knockdown mice and control mice were fed a KD for 16 weeks. Phenotypic assessments were conducted during and after the intervention. We investigated the mechanism underlying KD-alleviated hepatic steatosis using multi-omics and validated the expression of key genes.

RESULTS

KD improved hepatic steatosis by upregulating fatty acid oxidation and downregulating lipogenesis. Transcriptional analysis revealed that KD dramatically activated FGF21 pathway, including KLB and fibroblast growth factor receptor 1 (FGFR1). Impairing liver FGF21 signaling via KLB knockdown diminished the beneficial effects of KD on ameliorating fatty liver, insulin resistance, and regulating lipid metabolism.

CONCLUSION

KD demonstrates beneficial effects on diet-induced metabolic disorders, particularly on hepatic steatosis. Liver FGF21-KLB signaling plays a critical role in the KD-induced amelioration of hepatic steatosis.

Pegbelfermin for reducing transaminase levels in patients with non-alcoholic steatohepatitis: a dose-response meta-analysis of randomized controlled trials

Background

The efficacy of Pegbelfermin (PGBF) in treating non-alcoholic steatohepatitis (NASH) remains controversial. Therefore, we conducted a dose-response meta-analysis to explore the effect and pattern of PGBF at different dosages and treatment durations on transaminase reduction in NASH patients.

Methods

We conducted searches on PubMed, Embase, Cochrane Library, Web of Science, and ClinicalTrials.gov, and supplemented the search with gray literature and manual searches. Randomized controlled trials (RCTs) evaluating the efficacy of PGBF in NASH patients were included. Risk of bias was assessed by Cochrane Risk of Bias Tool 2.0. We used random-effects models, generalized least squares regression, constrained maximum likelihood, and restricted cubic splines to explore the dose-response relationship. Egger's linear regression was employed to assess publication bias. The study is registered with PROSPERO, CRD42023448024.

Results

Four RCT studies from the period 2018-2023, involving 546 participants, were included. No participants discontinued PGBF treatment due to adverse events. High-dose PGBF treatment significantly reduced transaminase levels in NASH patients compared to the low-dose group (ALT %: MD = 14.94, 95% CI = 2.11-27.77; AST %: MD = 9.05, 95% CI = 3.17-14.92). Longer treatment duration further decreased transaminase levels (ALT%: MD = 8.81, 95% CI = 4.07-13.56; AST%: MD = 6.72, 95% CI = 2.62-10.81). Egger's test did not reveal significant publication bias (p > 0.05). Further investigation indicated a ceiling effect of PGBF dosage on transaminase reduction at 30 mg/week, and NASH patients experienced a rebound in transaminase levels after 28 weeks of continuous treatment.

Conclusion

There is a positive correlation between PGBF dosage and transaminase reduction within a certain range, showing an overall non-linear dose-response relationship. This finding provides guidance for the clinical application of PGBF. Clinicians should be mindful of the dosage ceiling at 30 mg/week and monitor changes in transaminase levels after 28 weeks for timely adjustments in PGBF dosage.

Systematic review registration

PROSPERO, CRD42023448024. https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=448024.

mTORC1 in energy expenditure: consequences for obesity

In eukaryotic cells, the mammalian target of rapamycin complex 1 (sometimes referred to as the mechanistic target of rapamycin complex 1; mTORC1) orchestrates cellular metabolism in response to environmental energy availability. As a result, at the organismal level, mTORC1 signalling regulates the intake, storage and use of energy by acting as a hub for the actions of nutrients and hormones, such as leptin and insulin, in different cell types. It is therefore unsurprising that deregulated mTORC1 signalling is associated with obesity. Strategies that increase energy expenditure offer therapeutic promise for the treatment of obesity. Here we review current evidence illustrating the critical role of mTORC1 signalling in the regulation of energy expenditure and adaptive thermogenesis through its various effects in neuronal circuits, adipose tissue and skeletal muscle. Understanding how mTORC1 signalling in one organ and cell type affects responses in other organs and cell types could be key to developing better, safer treatments targeting this pathway in obesity.

Tumor-secreted FGF21 acts as an immune suppressor by rewiring cholesterol metabolism of CD8+T cells

Tumors employ diverse strategies for immune evasion. Unraveling the mechanisms by which tumors suppress anti-tumor immunity facilitates the development of immunotherapies. Here, we have identified tumor-secreted fibroblast growth factor 21 (FGF21) as a pivotal immune suppressor. FGF21 is upregulated in multiple types of tumors and promotes tumor progression. Tumor-secreted FGF21 significantly disrupts anti-tumor immunity by rewiring cholesterol metabolism of CD8+T cells. Mechanistically, FGF21 sustains the hyperactivation of AKT-mTORC1-sterol regulatory-element-binding protein 1 (SREBP1) signal axis in the activated CD8+T cells, resulting in the augment of cholesterol biosynthesis and T cell exhaustion. FGF21 knockdown or blockade using a neutralizing antibody normalizes AKT-mTORC1 signaling and reduces excessive cholesterol accumulation in CD8+T cells, thus restoring CD8+T cytotoxic function and robustly suppressing tumor growth. Our findings reveal FGF21 as a "secreted immune checkpoint" that hampers anti-tumor immunity, suggesting that inhibiting FGF21 could be a valuable strategy to enhance the cancer immunotherapy efficacy.

Spermidine activates adipose tissue thermogenesis through autophagy and fibroblast growth factor 21

Spermidine exerts protective roles in obesity, while the mechanism of spermidine in adipose tissue thermogenesis remains unclear. The present study first investigated the effect of spermidine on cold-stimulation and β3-adrenoceptor agonist-induced thermogenesis in lean and high-fat diet-induced obese mice. Next, the role of spermidine on glucose and lipid metabolism in different types of adipose tissue was determined. Here, we found that spermidine supplementation did not affect cold-stimulated thermogenesis in lean mice, while significantly promoting the activation of adipose tissue thermogenesis under cold stimulation and β3-adrenergic receptor agonist treatment in obese mice. Spermidine treatment markedly enhanced glucose and lipid metabolism in adipose tissues, and these results were associated with the activated autophagy pathway. Moreover, spermidine up-regulated fibroblast growth factor 21 (FGF21) signaling and its downstream pathway, including PI3K/AKT and AMPK pathways in vivo and in vitro. Knockdown of Fgf21 or inhibition of PI3K/AKT and AMPK pathways in brown adipocytes abolished the thermogenesis-promoting effect of spermidine, suggesting that the effect of spermidine on adipose tissue thermogenesis might be regulated by FGF21 signaling via the PI3K/AKT and AMPK pathways. The present study provides new insight into the mechanism of spermidine on obesity and its metabolic complications, thereby laying a theoretical basis for the clinical application of spermidine.

Sotagliflozin attenuates liver-associated disorders in cystic fibrosis rabbits

Mutations in the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) gene lead to CF, a life-threating autosomal recessive genetic disease. While recently approved Trikafta dramatically ameliorates CF lung diseases, there is still a lack of effective medicine to treat CF-associated liver disease (CFLD). To address this medical need, we used a recently established CF rabbit model to test whether sotagliflozin, a sodium-glucose cotransporter 1 and 2 (SGLT1/2) inhibitor drug that is approved to treat diabetes, can be repurposed to treat CFLD. Sotagliflozin treatment led to systemic benefits to CF rabbits, evidenced by increased appetite and weight gain as well as prolonged lifespan. For CF liver-related phenotypes, the animals benefited from normalized blood chemistry and bile acid parameters. Furthermore, sotagliflozin alleviated nonalcoholic steatohepatitis-like phenotypes, including liver fibrosis. Intriguingly, sotagliflozin treatment markedly reduced the otherwise elevated endoplasmic reticulum stress responses in the liver and other affected organs of CF rabbits. In summary, our work demonstrates that sotagliflozin attenuates liver disorders in CF rabbits and suggests sotagliflozin as a potential drug to treat CFLD.

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.

Growth differentiation factor-15 is an IFN-γ regulated mediator of infection-induced weight loss and the hepatic FGF21 response

Infections are often accompanied by weight loss caused by alterations in host behavior and metabolism, also known as sickness behaviors. Recent studies have revealed that sickness behaviors can either promote or impede survival during infections depending on factors such as the type of infectious pathogen. Nevertheless, we have an incomplete understanding of the underlying mechanisms of sickness behaviors. Furthermore, although the host immune responses to infections have long been known to contribute to the induction of sickness behaviors, recent studies have identified emerging cytokines that are also key regulators of host metabolism during infection and inflammation, such as growth differentiation factor 15 (GDF-15). GDF-15 is a distant member of the TGF-β superfamily that causes weight loss by suppressing appetite and food consumption and causing emesis. These effects require activation of neurons that express the only known GDF-15 receptor, the GFRAL receptor. GDF-15 also functions in the periphery including the induction of ketogenesis and immunoregulation. Nevertheless, the functions and regulation of GDF-15 during live infections is not yet known. Murine infection with avirulent Toxoplasma gondii is an established model to understand infection-induced weight loss. Past studies have determined that acute T. gondii infection causes weight loss due to diminished food consumption and increased energy expenditure through unknown mechanisms. Additionally, our lab previously demonstrated that T. gondii causes upregulation in serum GDF-15 in an IFN-γ-dependent manner during the post-acute phase of the infection. In this study, we interrogated the in-vivo functions and immune regulation of GDF-15 during Toxoplasma gondii infection. First, we found that in wild-type mice, acute T. gondii infection caused a significant weight loss that is preceded by elevation of serum levels of IFN-γ and GDF-15. To determine whether IFN-γ regulates GDF-15, we neutralized IFN-γ on days 5 and 6 and measured GDF-15 on day 7 and found that serum but not tissue levels of GDF-15 decreased after IFN-γ neutralization. Additionally, exogenous IFN-γ was sufficient to elevate serum GDF-15 in the absence of infection. Next, we compared the outcomes of T. gondii infection between WT and Gdf15-/- mice. We observed that the weight trajectories were declining in WT mice while they were increasing in Gdf15-/-mice during the acute phase of the infection. This difference in trajectories extended throughout the chronic infection resulting to an overall weight loss relative to initial weights in WT mice but not Gdf15-/-mice. Then, we determined that GDF-15 is not essential for survival and immunoregulation during T. gondii infection. We also demonstrated that GDF-15 is required for the induction of FGF21, stress-induced cytokine with prominent roles in regulating host metabolism. Finally, we discovered a cytokine cascade IFN-γ-GDF-15-FGF21 that is likely involved in the regulation of host metabolism. Overall, our study provides evidence that IFN-γ contributes to the regulation of host metabolism during infection by inducing GDF-15 and FGF21. GDF-15 orchestrates changes in host metabolism that supports the host immune response in clearing the infection. These physiological alterations induce FGF21, which in turn, orchestrates the adaptive responses to the effects of GDF-15, which can be detrimental when protracted.

Fibroblast Growth Factor 21 Relieves Lipopolysaccharide-Induced Acute Lung Injury by Suppressing JAK2/STAT3 Signaling Pathway

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a life-threatening disease without an effective drug at present. Fibroblast growth factor 21 (FGF21) was reported to be protective against inflammation in metabolic disease in recent studies. However, the role of FGF21 in ALI has been rarely investigated. In this study, it was found that the expression of FGF21 was markedly increased in lung tissue under lipopolysaccharide (LPS) stimulation in vivo, whereas it was decreased in lung epithelial cells under LPS stimulation in vitro. Therefore, our research aimed to elucidate the potential role of FGF21 in LPS-induced ALI and to detect possible underlying mechanisms. The results revealed that the deficiency of FGF21 aggravated pathological damage, inflammatory infiltration, and pulmonary function in LPS-induced ALI, while exogenous administration of FGF21 improved these manifestations. Moreover, through RNA sequencing and enrichment analysis, it was unveiled that FGF21 might play a protective role in LPS-induced ALI via JAK2/STAT3 signaling pathway. The therapeutic effect of FGF21 was weakened after additional usage of JAK2 activator in vivo. Further investigation revealed that FGF21 significantly inhibited STAT3 phosphorylation and impaired the nuclear translocation of STAT3 in vitro. In addition, the aggravation of inflammation caused by silencing FGF21 can be alleviated by JAK2 inhibitor in vitro. Collectively, these findings unveil a potent protective effect of FGF21 against LPS-induced ALI by inhibiting the JAK2/STAT3 pathway, implying that FGF21 might be a novel and effective therapy for ALI.

Lipid metabolism reprogramming in cardiac fibrosis

Cardiac fibrosis is a critical pathophysiological process that occurs with diverse types of cardiac injury. Lipids are the most important bioenergy substrates for maintaining optimal heart performance and act as second messengers to transduce signals within cardiac cells. However, lipid metabolism reprogramming is a double-edged sword in the regulation of cardiomyocyte homeostasis and heart function. Moreover, lipids can exert diverse effects on cardiac fibrosis through different signaling pathways. In this review, we provide a brief overview of aberrant cardiac lipid metabolism and recent progress in pharmacological research targeting lipid metabolism alterations in cardiac fibrosis.

ATF4 expression in thermogenic adipocytes is required for cold-induced thermogenesis in mice via FGF21-independent mechanisms

In brown adipose tissue (BAT), short-term cold exposure induces the activating transcription factor 4 (ATF4), and its downstream target fibroblast growth factor 21 (FGF21). Induction of ATF4 in BAT in response to mitochondrial stress is required for thermoregulation, partially by increasing FGF21 expression. In the present study, we tested the hypothesis that Atf4 and Fgf21 induction in BAT are both required for BAT thermogenesis under physiological stress by generating mice selectively lacking either Atf4 (ATF4 BKO) or Fgf21 (FGF21 BKO) in UCP1-expressing adipocytes. After 3 days of cold exposure, core body temperature was significantly reduced in ad-libitum-fed ATF4 BKO mice, which correlated with Fgf21 downregulation in brown and beige adipocytes, and impaired browning of white adipose tissue. Conversely, despite having reduced browning, FGF21 BKO mice had preserved core body temperature after cold exposure. Mechanistically, ATF4, but not FGF21, regulates amino acid import and metabolism in response to cold, likely contributing to BAT thermogenic capacity under ad libitum-fed conditions. Importantly, under fasting conditions, both ATF4 and FGF21 were required for thermogenesis in cold-exposed mice. Thus, ATF4 regulates BAT thermogenesis under fed conditions likely in a FGF21-independent manner, in part via increased amino acid uptake and metabolism.

FGF21 Induces Skeletal Muscle Atrophy and Increases Amino Acids in Female Mice: A Potential Role for Glucocorticoids

Fibroblast growth factor-21 (FGF21) is an intercellular signaling molecule secreted by metabolic organs, including skeletal muscle, in response to intracellular stress. FGF21 crosses the blood-brain barrier and acts via the nervous system to coordinate aspects of the adaptive starvation response, including increased lipolysis, gluconeogenesis, fatty acid oxidation, and activation of the hypothalamic-pituitary-adrenocortical (HPA) axis. Given its beneficial effects for hepatic lipid metabolism, pharmaceutical FGF21 analogues are used in clinical trials treatment of fatty liver disease. We predicted pharmacologic treatment with FGF21 increases HPA axis activity and skeletal muscle glucocorticoid signaling and induces skeletal muscle atrophy in mice. Here we found a short course of systemic FGF21 treatment decreased muscle protein synthesis and reduced tibialis anterior weight; this was driven primarily by its effect in female mice. Similarly, intracerebroventricular FGF21 reduced tibialis anterior muscle fiber cross-sectional area; this was more apparent among female mice than male littermates. In agreement with the reduced muscle mass, the topmost enriched metabolic pathways in plasma collected from FGF21-treated females were related to amino acid metabolism, and the relative abundance of plasma proteinogenic amino acids was increased up to 3-fold. FGF21 treatment increased hypothalamic Crh mRNA, plasma corticosterone, and adrenal weight, and increased expression of glucocorticoid receptor target genes known to reduce muscle protein synthesis and/or promote degradation. Given the proposed use of FGF21 analogues for the treatment of metabolic disease, the study is both physiologically relevant and may have important clinical implications.

Endocrine FGFs and their signaling in the brain: Relevance for energy homeostasis

Since their discovery in 2000, there has been a continuous expansion of studies investigating the physiology, biochemistry, and pharmacology of endocrine fibroblast growth factors (FGFs). FGF19, FGF21, and FGF23 comprise a subfamily with attributes that distinguish them from typical FGFs, as they can act as hormones and are, therefore, referred to as endocrine FGFs. As they participate in a broad cross-organ endocrine signaling axis, endocrine FGFs are crucial lipidic, glycemic, and energetic metabolism regulators during energy availability fluctuations. They function as powerful metabolic signals in physiological responses induced by metabolic diseases, like type 2 diabetes and obesity. Pharmacologically, FGF19 and FGF21 cause body weight loss and ameliorate glucose homeostasis and energy expenditure in rodents and humans. In contrast, FGF23 expression in mice and humans has been linked with insulin resistance and obesity. Here, we discuss emerging concepts in endocrine FGF signaling in the brain and critically assess their putative role as therapeutic targets for treating metabolic disorders.

Fibroblast growth factor 21 ameliorates cholestatic liver injury via a hepatic FGFR4-JNK pathway

Cholestasis is characterized by hepatic accumulation of cytotoxic bile acids (BAs), which often subsequently leads to liver injury, inflammation, fibrosis, and liver cirrhosis. Fibroblast growth factor 21 (FGF21) is a liver-secreted hormone with pleiotropic effects on the homeostasis of glucose, lipid, and energy metabolism. However, whether hepatic FGF21 plays a role in cholestatic liver injury remains elusive. We found that serum and hepatic FGF21 levels were significantly increased in response to cholestatic liver injury. Hepatocyte-specific deletion of Fgf21 exacerbated hepatic accumulation of BAs, further accentuating liver injury. Consistently, administration of rFGF21 ameliorated cholestatic liver injury caused by α-naphthylisothiocyanate (ANIT) treatment and Mdr2 deficiency. Mechanically, FGF21 activated a hepatic FGFR4-JNK signaling pathway to decrease Cyp7a1 expression, thereby reducing hepatic BAs pool. Our study demonstrates that hepatic FGF21 functions as an adaptive stress-responsive signal to downregulate BA biosynthesis, thereby ameliorating cholestatic liver injury, and FGF21 analogs may represent a candidate therapy for cholestatic liver diseases.