The GDF15-GFRAL Pathway in Health and Metabolic Disease: Friend or Foe?

GDF15 is a cell activation and stress response cytokine of the glial cell line-derived neurotrophic factor family within the TGF-ß superfamily. It acts through a recently identified orphan member of the GFRα family called GFRAL and signals through the Ret coreceptor. Cell stress and disease lead to elevated GDF15 serum levels, causing anorexia, weight loss, and alterations to metabolism, largely by actions on regions of the hindbrain. These changes restore homeostasis and, in the case of obesity, cause a reduction in adiposity. In some diseases, such as advanced cancer, serum GDF15 levels can rise by as much as 10-100-fold, leading to an anorexia-cachexia syndrome, which is often fatal. This review discusses how GDF15 regulates appetite and metabolism, the role it plays in resistance to obesity, and how this impacts diseases such as diabetes, nonalcoholic fatty liver disease, and anorexia-cachexia syndrome. It also discusses potential therapeutic applications of targeting the GDF15-GFRAL pathway and lastly suggests some potential unifying hypotheses for its biological role.

Lung Epithelium Releases Growth Differentiation Factor 15 in Response to Pathogen-mediated Injury.

GDF15 (growth differentiation factor 15) is a stress cytokine with several proposed roles, including support of stress erythropoiesis. Higher circulating GDF15 levels are prognostic of mortality during acute respiratory distress syndrome, but the cellular sources and downstream effects of GDF15 during pathogen-mediated lung injury are unclear. We quantified GDF15 in lower respiratory tract biospecimens and plasma from patients with acute respiratory failure. Publicly available data from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection were reanalyzed. We used mouse models of hemorrhagic acute lung injury mediated by Pseudomonas aeruginosa exoproducts in wild-type mice and mice genetically deficient for Gdf15 or its putative receptor, Gfral. In critically ill humans, plasma levels of GDF15 correlated with lower respiratory tract levels and were higher in nonsurvivors. SARS-CoV-2 infection induced GDF15 expression in human lung epithelium, and lower respiratory tract GDF15 levels were higher in coronavirus disease (COVID-19) nonsurvivors. In mice, intratracheal P. aeruginosa type II secretion system exoproducts were sufficient to induce airspace and plasma release of GDF15, which was attenuated with epithelial-specific deletion of Gdf15. Mice with global Gdf15 deficiency had decreased airspace hemorrhage, an attenuated cytokine profile, and an altered lung transcriptional profile during injury induced by P. aeruginosa type II secretion system exoproducts, which was not recapitulated in mice deficient for Gfral. Airspace GDF15 reconstitution did not significantly modulate key lung cytokine levels but increased circulating erythrocyte counts. Lung epithelium releases GDF15 during pathogen injury, which is associated with plasma levels in humans and mice and can increase erythrocyte counts in mice, suggesting a novel lung-blood communication pathway.

Total and H-specific growth/differentiation factor 15 levels are unaffected by liraglutide or naltrexone/bupropion administration.

AIM: To investigate growth/differentiation factor 15 (GDF-15) levels in response to antiobesity medications, namely, liraglutide (Lira) and naltrexone/bupropion (N/B), in individuals with overweight or obesity. MATERIALS AND METHODS: This was a prospective, non-randomized clinical trial with a two-arm, parallel design. A total of 42 individuals with overweight or obesity without type 1 or type 2 diabetes mellitus were enrolled. The participants received either Lira 3 mg or N/B 32/360 mg, along with diet and exercise, according to comorbidities, cost and method of administration. Participants underwent clinical and laboratory measurements at baseline, as well as at the 3- and 6-month time points. Anthropometric measurements and body composition analysis via bioelectrical impendence analysis were performed. Total blood samples for GDF-15 and H-specific GDF-15 were collected in the fasting state and every 30 min for 3 h after the consumption of a standardized mixed meal. RESULTS: Overall, participants' weight was reduced by 9.29 ± 5.34 kg at Month 3 and 11.52 ± 7.52 kg at Month 6. Total and H-specific GDF-15 levels did not show significant changes during the mixed meal compared to values before the meal when all participants were examined at baseline, and at 3 and 6 month follow-ups. No statistical significance was found when participants were examined by subgroup (Lira vs. N/B). No significant differences between treatment groups in postprandial area under the curve (AUC) or incremental AUC values were found at baseline or in the follow-up months with regard to total and H-specific GDF-15 levels. CONCLUSION: Neither total nor H-specific GDF-15 levels are affected by Lira or N/B treatment in patients with overweight or obesity.

GFRAL-expressing neurons suppress food intake via aversive pathways.

The TGFß cytokine family member, GDF-15, reduces food intake and body weight and represents a potential treatment for obesity. Because the brainstem-restricted expression pattern of its receptor, GDNF Family Receptor α-like (GFRAL), presents an exciting opportunity to understand mechanisms of action for area postrema neurons in food intake; we generated GfralCre and conditional GfralCreERT mice to visualize and manipulate GFRAL neurons. We found infection or pathophysiologic states (rather than meal ingestion) stimulate GFRAL neurons. TRAP-Seq analysis of GFRAL neurons revealed their expression of a wide range of neurotransmitters and neuropeptides. Artificially activating GfralCre -expressing neurons inhibited feeding, decreased gastric emptying, and promoted a conditioned taste aversion (CTA). GFRAL neurons most strongly innervate the parabrachial nucleus (PBN), where they target CGRP-expressing (CGRPPBN) neurons. Silencing CGRPPBN neurons abrogated the aversive and anorexic effects of GDF-15. These findings suggest that GFRAL neurons link non-meal-associated pathophysiologic signals to suppress nutrient uptake and absorption.

Unexpected structures formed by the kinase RET C634R mutant extracellular domain suggest potential oncogenic mechanisms in MEN2A.

The RET receptor tyrosine kinase plays a pivotal role in cell survival, proliferation, and differentiation, and its abnormal activation leads to cancers through receptor fusions or point mutations. Mutations that disrupt the disulfide network in the extracellular domain (ECD) of RET drive multiple endocrine neoplasia type 2A (MEN2A), a hereditary syndrome associated with the development of thyroid cancers. However, structural details of how specific mutations affect RET are unclear. Here, we present the first structural insights into the ECD of the RET(C634R) mutant, the most common mutation in MEN2A. Using electron microscopy, we demonstrate that the C634R mutation causes ligand-independent dimerization of the RET ECD, revealing an unusual tail-to-tail conformation that is distinct from the ligand-induced signaling dimer of WT RET. Additionally, we show that the RETC634R ECD dimer can form complexes with at least two of the canonical RET ligands and that these complexes form very different structures than WT RET ECD upon ligand binding. In conclusion, this structural analysis of cysteine-mutant RET ECD suggests a potential key mechanism of cancer induction in MEN2A, both in the absence and presence of its native ligands, and may offer new targets for therapeutic intervention.

The GDF15-GFRAL axis mediates chemotherapy-induced fatigue in mice.

Cancer-related fatigue is defined as a distressing persistent subjective sense of physical, emotional, and/or cognitive tiredness or exhaustion related to cancer or cancer treatment that is not proportional to recent activity and that interferes with usual functioning. This form of fatigue is highly prevalent during cancer treatment and in some patients, it can persist for years after treatment has ended. An understanding of the mechanisms that drive cancer-related fatigue is still lacking, which hampers the identification of effective treatment options. Various chemotherapeutic agents including cisplatin are known to induce mitochondrial dysfunction and this effect is known to mediate chemotherapy-induced peripheral neuropathy and cognitive dysfunction. Mitochondrial dysfunction results in the release of mitokines that act locally and at distance to promote metabolic and behavioral adjustments to this form of cellular stress. One of these mitokines, growth differentiation factor 15 (GDF15) and its receptor, glial cell line-derived neurotrophic factor family receptor α-like (GFRAL), have received special attention in oncology as activation of GFRAL mediates the anorexic response that is responsible for cancer anorexia. The present study was initiated to determine whether GDF15 and GFRAL are involved in cisplatin-induced fatigue. We first tested the ability of cisplatin to increase circulating GDF15 in mice before assessing whether GDF15 can induce behavioral fatigue measured by decreased wheel running in healthy mice and increase behavioral fatigue induced by cisplatin. Mice administered a long acting form of GDF15, mGDF15-fc, decreased their voluntary wheel running activity. When the same treatment was administered to mice receiving cisplatin, it increased the amplitude and duration of cisplatin-induced decrease in wheel running. To determine whether endogenous GDF15 mediates the behavioral fatigue induced by cisplatin, we then administered a neutralizing monoclonal antibody to GFRAL to mice injected with cisplatin. The GFRAL neutralizing antibody mostly prevented cisplatin-induced decrease in wheel running and accelerated recovery. Taken together these findings demonstrate for the first time the role of the GDF15/GFRAL axis in cisplatin-induced behaviors and indicate that this axis could be a promising therapeutic target for the treatment of cancer-related fatigue.

LPS induces rapid increase in GDF15 levels in mice, rats, and humans but is not required for anorexia in mice.

Growth differentiation factor 15 (GDF15), a TGFß superfamily cytokine, acts through its receptor, cell line-derived neurotrophic factorfamily receptor α-like (GFRAL), to suppress food intake and promote nausea. GDF15 is broadly expressed at low levels but increases in states of disease such as cancer, cachexia, and sepsis. Whether GDF15 is necessary for inducing sepsis-associated anorexia and body weight loss is currently unclear. To test this we used a model of moderate systemic infection in GDF15KO and GFRALKO mice with lipopolysaccharide (LPS) treatment to define the role of GDF15 signaling in infection-mediated physiologic responses. Since physiological responses to LPS depend on housing temperature, we tested the effects of subthermoneutral and thermoneutral conditions on eliciting anorexia and inducing GDF15. Our data demonstrate a conserved LPS-mediated increase in circulating GDF15 levels in mouse, rat, and human. However, we did not detect differences in LPS-induced anorexia between WT and GDF15KO or GFRALKO mice. Furthermore, there were no differences in anorexia or circulating GDF15 levels at either thermoneutral or subthermoneutral housing conditions in LPS-treated mice. These data demonstrate that GDF15 is not necessary to drive food intake suppression in response to moderate doses of LPS.NEW & NOTEWORTHY Although many responses to LPS depend on housing temperature, the anorexic response to LPS does not. LPS results in a potent and rapid increase in circulating levels of GDF15 in mice, rats, and humans. Nevertheless, GDF15 and its receptor (GFRAL) are not required for the anorexic response to systemic LPS administration. The anorexic response to LPS likely involves a myriad of complex physiological alterations.

Macrophage inhibitory cytokine-1 promotes angiogenesis by eliciting the GFRAL-mediated endothelial cell signaling.

Macrophage inhibitory cytokine-1 (MIC-1) is a cytokine with pleotropic actions and its expression is markedly increased by inflammation and cardiac injury and in cancers. In particular, MIC-1 production after cardiac ischemia injury is associated with enhanced cardiac angiogenesis as well as myocardial protection. However, it remains uncertain whether MIC-1 itself has proangiogenic activity. In this study, we tried to determine the precise role of MIC-1 in physiological and pathological angiogenesis. Human microvessel endothelial cells responded to MIC-1 with enhanced angiogenic behaviors. Employing various angiogenesis assays, MIC-1 was found to promote vessel formation and development with a potency similar to that of vascular endothelial growth factor (VEGF). MIC-1 transgenic (Tg) mice also displayed enhanced neovascularization in both developing embryos and neonatal mouse retinas, compared with wild-type mice. Furthermore, endothelial cells (ECs) isolated from MIC-1 Tg mouse lung exhibited higher angiogenic potential than ECs from wild-type lung. MIC-1-induced angiogenesis was also observed in the recovery or healing processes of injuries such as hindlimb ischemia and skin wounds in mice. However, unlike VEGF, MIC-1 induced neither endothelial inflammation nor increased vascular permeability. In ECs, the MIC-1 signal exerted proangiogenic actions via the MEK/extracellular signal-regulated kinase- and phosphatidylinositol 3-kinase/Akt-dependent pathways. Notably, these MIC-1 signaling events in ECs were abrogated by small interfering RNA-mediated knockdown of GFRAL, suggesting that GFRAL is an EC receptor for MIC-1. In summary, we here show a novel role of MIC-1 as a potent EC activator, which promotes both normal and injury-related angiogenesis.

GDF15, an update of the physiological and pathological roles it plays: a review.

Growth differentiation factor 15 (GDF15) is a peptide hormone, and a divergent member of the transforming growth factor beta (TGFß) superfamily. In normal physiology, GDF15 is expressed in multiple tissues at a low concentration. GDF15 is overexpressed during and following many pathological conditions such as tissue injury and inflammation in order to play a protective role. However, GDF15 appears to promote tumour growth in the later stages of malignant cancer. The recently identified endogenous receptor for GDF15, GDNF family receptor a-like (GFRAL), has allowed elucidation of a physiological pathway in which GDF15 regulates energy homeostasis and body weight, primarily via appetite suppression. The anorectic effect of GDF15 provides some therapeutic potential in management of cancer-related anorexia/cachexia and obesity. Despite the identification of GFRAL as a GDF15 receptor, there appears to be other signalling mechanisms utilized by GDF15 that further increase the possibility of development of therapeutic treatments, should these pathways be fully characterized. In this review, GDF15 function in both physiological and pathological conditions in various tissues will be discussed.

ARRB1 inhibits non-alcoholic steatohepatitis progression by promoting GDF15 maturation.

BACKGROUND & AIMS: Non-alcoholic steatohepatitis (NASH) is associated with the dysregulation of lipid metabolism and hepatic inflammation. The causal mechanism underlying NASH is not fully elucidated. This study investigated the role of ß-Arrestin1 (ARRB1) in the progression of NASH. METHODS: Liver tissue from patients with NASH and controls were obtained to evaluate ARRB1 expression. NASH models were established in Arrb1-knockout and wild-type mice fed either a high-fat diet (HFD) for 26 weeks or a methionine/choline-deficient (MCD) diet for 6 weeks. RESULTS: ARRB1 expression was reduced in liver samples from patients with NASH. Reduced Arrb1 levels were also detected in murine NASH models. Arrb1 deficiency accelerated steatohepatitis development in HFD-/MCD-fed mice (accompanied by the upregulation of lipogenic genes and downregulation of ß-oxidative genes). Intriguingly, ARRB1 was found to interact with growth differentiation factor 15 (GDF15) and facilitated the transportation of GDF15 precursor (pro-GDF15) to the Golgi apparatus for cleavage and maturation. Treatment with recombinant GDF15 ablated the lipid accumulation in the presence of Arrb1 deletion both in vitro and in vivo. Re-expression of Arrb1 in the NASH models ameliorated the liver disease, and this effect was greater in the presence of pro-GDF15 overexpression. By contrast, the effect of pro-GDF15 overexpression alone was impaired in Arrb1-deficient mice. In addition, the severity of liver disease in patients with NASH was negatively correlated with ARRB1 expression. CONCLUSION: ARRB1 acts as a vital regulator in the development of NASH by facilitating the translocation of GDF15 to the Golgi apparatus and its subsequent maturation. Thus, ARRB1 is a potential therapeutic target for the treatment of NASH. LAY SUMMARY: Non-alcoholic steatohepatitis (NASH) is associated with the progressive dysfunction of lipid metabolism and a consequent inflammatory response. Decreased ARRB1 is observed in patients with NASH and murine NASH models. Re-expression of Arrb1 in the murine NASH model ameliorated liver disease, an effect which was more pronounced in the presence of pro-GDF15 overexpression, highlighting a promising strategy for NASH therapy.

GFRAL Is Widely Distributed in the Brain and Peripheral Tissues of Mice.

In 2017, four independent publications described the glial cell-derived neurotrophic factor (GDNF) receptor alpha-like (GFRAL) as receptor for the growth differentiation factor 15 (GDF15, also MIC-1, NAG-1) with an expression exclusively in the mice brainstem area postrema (AP) and nucleus tractus solitarii (NTS) where it mediates effects of GDF15 on reduction of food intake and body weight. GDF15 is a cell stress cytokine with a widespread expression and pleiotropic effects, which both seem to be in contrast to the reported highly specialized localization of its receptor. This discrepancy prompts us to re-evaluate the expression pattern of GFRAL in the brain and peripheral tissues of mice. In this detailed immunohistochemical study, we provide evidence for a more widespread distribution of this receptor. Apart from the AP/NTS region, GFRAL-immunoreactivity was found in the prefrontal cortex, hippocampus, nucleus arcuatus and peripheral tissues including liver, small intestine, fat, kidney and muscle tissues. This widespread receptor expression, not taken into consideration so far, may explain the multiple effects of GDF-15 that are not yet assigned to GFRAL. Furthermore, our results could be relevant for the development of novel pharmacological therapies for physical and mental disorders related to body image and food intake, such as eating disorders, cachexia and obesity.

Overview of growth differentiation factor 15 (GDF15) in metabolic diseases.

GDF15 is a stress response cytokine and a distant member of the transforming growth factor beta (TGFß) superfamily, its levels increase in response to cell stress and certain diseases in the serum. To exert its effects, GDF15 binds to glial-derived neurotrophic factor (GDNF) receptor alpha-like (GFRAL), which was firstly identified in 2017 and highly expressed in the brain stem. Many studies have demonstrated that elevated serum GDF15 is associated with anorexia and weight loss. Herein, we focus on the biology of GDF15, specifically how this circulating protein regulates appetite and metabolism in influencing energy homeostasis through its actions on hindbrain neurons to shed light on its impact on diseases such as obesity and anorexia/cachexia syndromes. It works as an endocrine factor and transmits metabolic signals leading to weight reduction effects by directly reducing appetite and indirectly affecting food intake through complex mechanisms, which could be a promising target for the treatment of energy-intake disorders.

Preventing obesity, insulin resistance and type 2 diabetes by targeting MT1-MMP.

Obesity is one of the predominant risk factors for type 2 diabetes. Despite all the modern advances in medicine, an effective drug treatment for obesity without overt side effects has not yet been found. The discovery of growth and differentiation factor 15 (GDF15), an appetite-regulating hormone, created hopes for the treatment of obesity. However, an insufficient understanding of the physiological regulation of GDF15 has been a major obstacle to mitigating GDF15-centric treatment of obesity. Our recent studies revealed how a series of proteolytic events predominantly mediated by membrane-type 1 matrix metalloproteinase (MT1-MMP/MMP14), a key cell-surface metalloproteinase involved in extracellular remodeling, contribute to the pathogenesis of metabolic disorders, including obesity and diabetes. The MT1-MMP-mediated cleavage of the GDNF family receptor-α-like (GFRAL), a key neuronal receptor of GDF15, controls the satiety center in the hindbrain, thereby regulating non-homeostatic appetite and bodyweight changes. Furthermore, increased activation of MT1-MMP does not only lead to increased risk of obesity, but also causes age-associated insulin resistance by cleaving Insulin Receptor in major metabolic tissues. Importantly, inhibition of MT1-MMP effectively protects against obesity and diabetes, revealing the therapeutic potential of targeting MT1-MMP for the management of metabolic disorders.

Comprehensive Role of GDF15 in Inhibiting Adipogenesis and Hyperlipidemia, Enhancing Cardiovascular Health and Alleviating Inflammation in Metabolic Disorders.

Growth Differentiation Factor 15 (GDF15) has emerged as a pivotal signaling molecule implicated in diverse physiological processes, spanning metabolic regulation, inflammation, and cardiovascular health. This studyprovides a comprehensive exploration of GDF15's multifaceted role, primarily focusing on its association with obesity-related complications and therapeutic potential. GDF15's involvement in energy homeostasis, specifically its regulation of body weight and appetite through hindbrain neuron activation and the GFRAL-RET signaling pathway, underscores its significance as an appetite-regulating hormone. GDF15's intricate modulation within adipose tissue dynamics in response to dietary changes and obesity, coupled with its influence on insulin sensitivity, highlights its critical role in metabolic health. The manuscript delves into the intricate crosstalk between GDF15 and pathways related to insulin sensitivity, macrophage polarization, and adipose tissue function, elucidating its potential as a therapeutic target for metabolic disorders associated with obesity. GDF15's association with chronic low-grade inflammation and its impact on cardiovascular health, particularly during hyperlipidemia and ischemic events, are explored. The intricate relationship between GDF15 and cardiovascular diseases, including its effects on endothelial function, cardiac hypertrophy, and heart failure, emphasizes its multifaceted nature in maintaining overall cardiovascular well-being. Challenges regarding the therapeutic application of GDF15, such as long-term safety concerns and ongoing clinical investigations, are discussed. Lastly, future research directions exploring GDF15's potential in addressing obesity-related complications and cardiovascular risks are proposed, highlighting its promising role as a therapeutic target in reshaping treatment strategies for obesity and associated health conditions.

Growth/differentiation factor 15 controls ependymal and stem cell number in the V-SVZ.

The expression of growth/differentiation factor (GDF) 15 increases in the ganglionic eminence (GE) late in neural development, especially in neural stem cells (NSCs). However, GDF15 function in this region remains unknown. We report that GDF15 receptor is expressed apically in the GE and that GDF15 ablation promotes proliferation and cell division in the embryonic GE and in the adult ventricular-subventricular zone (V-SVZ). This causes a transient generation of additional neuronal progenitors, compensated by cell death, and a lasting increase in the number of ependymal cells and apical NSCs. Finally, both GDF15 receptor and the epidermal growth factor receptor (EGFR) were expressed in progenitors and mutation of GDF15 affected EGFR signaling. However, only exposure to exogenous GDF15, but not to EGF, normalized proliferation and the number of apical progenitors. Thus, GDF15 regulates proliferation of apical progenitors in the GE, thereby affecting the number of ependymal cells and NSCs.

Activation of GFRAL+ neurons induces hypothermia and glucoregulatory responses associated with nausea and torpor.

GFRAL-expressing neurons actuate aversion and nausea, are targets for obesity treatment, and may mediate metformin effects by long-term GDF15-GFRAL agonism. Whether GFRAL+ neurons acutely regulate glucose and energy homeostasis is, however, underexplored. Here, we report that cell-specific activation of GFRAL+ neurons using a variety of techniques causes a torpor-like state, including hypothermia, the release of stress hormones, a shift from glucose to lipid oxidation, and impaired insulin sensitivity, glucose tolerance, and skeletal muscle glucose uptake but augmented glucose uptake in visceral fat. Metabolomic analysis of blood and transcriptomics of muscle and fat indicate alterations in ketogenesis, insulin signaling, adipose tissue differentiation and mitogenesis, and energy fluxes. Our findings indicate that acute GFRAL+ neuron activation induces endocrine and gluco- and thermoregulatory responses associated with nausea and torpor. While chronic activation of GFRAL signaling promotes weight loss in obesity, these results show that acute activation of GFRAL+ neurons causes hypothermia and hyperglycemia.

GDNF family receptor alpha-like antagonist antibody alleviates chemotherapy-induced cachexia in melanoma-bearing mice.

BACKGROUND: Patients with cancer undergoing chemotherapy experience cachexia with anorexia, body weight loss, and the depletion of skeletal muscles and adipose tissues. Effective treatment strategies for chemotherapy-induced cachexia are scarce. The growth differentiation factor 15 (GDF15)/GDNF family receptor alpha-like (GFRAL)/rearranged during transfection (RET) axis is a critical signalling pathway in chemotherapy-induced cachexia. In this study, we developed a fully human GFRAL antagonist antibody and investigated whether it inhibits the GDF15/GFRAL/RET axis, thereby alleviating chemotherapy-induced cachexia in tumour-bearing mice. METHODS: Anti-GFRAL antibodies were selected via biopanning, using a human combinatorial antibody phage library. The potent GFRAL antagonist antibody A11 was selected via a reporter cell assay and its inhibitory activity of GDF15-induced signalling was evaluated using western blotting. To investigate the in vivo function of A11, a tumour-bearing mouse model was established by inoculating 8-week-old male C57BL/6 mice with B16F10 cells (n = 10-16 mice per group). A11 was administered subcutaneously (10 mg/kg) 1 day before intraperitoneal treatment with cisplatin (10 mg/kg). Animals were assessed for changes in food intake, body weight, and tumour volume. Plasma and key metabolic tissues such as skeletal muscles and adipose tissues were collected for protein and mRNA expression analysis. RESULTS: A11 reduced serum response element-luciferase reporter activity up to 74% (P < 0.005) in a dose-dependent manner and blocked RET phosphorylation up to 87% (P = 0.0593), AKT phosphorylation up to 28% (P = 0.0593) and extracellular signal regulatory kinase phosphorylation up to 75% (P = 0.0636). A11 inhibited the action of cisplatin-induced GDF15 on the brainstem and decreased GFRAL-positive neuron population expressing c-Fos in the area postrema and nucleus of the solitary tract by 62% in vivo (P < 0.05). In a melanoma mouse model treated with cisplatin, A11 recovered anorexia by 21% (P < 0.05) and tumour-free body weight loss by 13% (P < 0.05). A11 significantly improved the cisplatin-induced loss of skeletal muscles (quadriceps: 21%, gastrocnemius: 9%, soleus: 13%, P < 0.05) and adipose tissues (epididymal white adipose tissue: 37%, inguinal white adipose tissue: 51%, P < 0.05). CONCLUSIONS: Our study suggests that GFRAL antagonist antibody may alleviate chemotherapy-induced cachexia, providing a novel therapeutic approach for patients with cancer experiencing chemotherapy-induced cachexia.

Identification of GDF15 peptide fragments inhibiting GFRAL receptor signaling.

Growth differentiation factor 15 (GDF15) is believed to be a major causative factor for cancer-induced cachexia. Recent elucidation of the central circuits involved in GDF15 function and its signaling through the glial cell-derived neurotrophic factor family receptor α-like (GFRAL) has prompted the interest of targeting the GDF15-GFRAL signaling for energy homeostasis and body weight regulation. Here, we applied advanced peptide technologies to identify GDF15 peptide fragments inhibiting GFRAL signaling. SPOT peptide arrays revealed binding of GDF15 C-terminal peptide fragments to the extracellular domain of GFRAL. Parallel solid-phase peptide synthesis allowed for generation of complementary GDF15 peptide libraries and their subsequent functional evaluation in cells expressing the GFRAL/RET receptor complex. We identified a series of C-terminal fragments of GDF15 inhibiting GFRAL activity in the micromolar range. These novel GFRAL peptide inhibitors could serve as valuable tools for further development of peptide therapeutics towards the treatment of cachexia and other wasting disorders.

GDF15 is a major determinant of ketogenic diet-induced weight loss.

A ketogenic diet (KD) has been promoted as an obesity management diet, yet its underlying mechanism remains elusive. Here we show that KD reduces energy intake and body weight in humans, pigs, and mice, accompanied by elevated circulating growth differentiation factor 15 (GDF15). In GDF15- or its receptor GFRAL-deficient mice, these effects of KD disappeared, demonstrating an essential role of GDF15-GFRAL signaling in KD-mediated weight loss. Gdf15 mRNA level increases in hepatocytes upon KD feeding, and knockdown of Gdf15 by AAV8 abrogated the obesity management effect of KD in mice, corroborating a hepatic origin of GDF15 production. We show that KD activates hepatic PPARγ, which directly binds to the regulatory region of Gdf15, increasing its transcription and production. Hepatic Pparγ-knockout mice show low levels of plasma GDF15 and significantly diminished obesity management effects of KD, which could be restored by either hepatic Gdf15 overexpression or recombinant GDF15 administration. Collectively, our study reveals a previously unexplored GDF15-dependent mechanism underlying KD-mediated obesity management.

GDF15 increases insulin action in the liver and adipose tissue via a ß-adrenergic receptor-mediated mechanism.

Growth differentiation factor 15 (GDF15) induces weight loss and increases insulin action in obese rodents. Whether and how GDF15 improves insulin action without weight loss is unknown. Obese rats were treated with GDF15 and displayed increased insulin tolerance 5 h later. Lean and obese female and male mice were treated with GDF15 on days 1, 3, and 5 without weight loss and displayed increased insulin sensitivity during a euglycemic hyperinsulinemic clamp on day 6 due to enhanced suppression of endogenous glucose production and increased glucose uptake in WAT and BAT. GDF15 also reduced glucagon levels during clamp independently of the GFRAL receptor. The insulin-sensitizing effect of GDF15 was completely abrogated in GFRAL KO mice and also by treatment with the ß-adrenergic antagonist propranolol and in ß1,ß2-adrenergic receptor KO mice. GDF15 activation of the GFRAL receptor increases ß-adrenergic signaling, in turn, improving insulin action in the liver and white and brown adipose tissue.