GDF15 Provides an Endocrine Signal of Nutritional Stress in Mice and Humans

Transcoronary study of biomarkers in patients with heart failure: Insights into intracardiac production

AIMS

Biomarkers are pivotal in the management of heart failure (HF); however, their lack of cardiac specificity could limit clinical utility. This study aimed to investigate the transcoronary changes and intracardiac production of these biomarkers.

METHODS

Transcoronary gradients for B-type natriuretic peptide (BNP) and five novel biomarkers-galectin-3 (Gal-3), soluble suppression of tumourigenicity 2 (sST2), tissue inhibitor of metalloproteinase 1 (TIMP-1), growth differentiation factor 15 (GDF-15) and myeloperoxidase (MPO)-were determined using femoral artery (FA) and coronary sinus (CS) samples from 30 HF patients and 10 non-HF controls. Intracardiac biomarker production was assessed in an HF canine model using real-time quantitative PCR (qPCR) and western blot (WB) analysis.

RESULTS

Compared with the control group, levels of all detected biomarkers were significantly elevated in the HF group, while transcoronary gradients were only observed for BNP, Gal-3 and TIMP-1 levels in the HF group (BNP: FA: 841.5 ± 727.2 ng/mL vs. CS: 1132.0 ± 959.1 ng/mL, P = 0.005; Gal-3: FA: 9.5 ± 3.0 ng/mL vs. CS: 19.7 ± 16.4 ng/mL, P = 0.002; and TIMP-1: FA: 286.7 ± 68.9 ng/mL vs. CS: 377.3 ± 108.9 ng/mL, P = 0.001). Real-time qPCR and WB analysis revealed significant elevation of BNP, Gal-3 and TIMP-1 in the cardiac tissues of the HF group relative to other groups.

CONCLUSIONS

This study provided evidence of transcoronary changes in BNP, Gal-3 and TIMP-1 levels in HF patients, offering insights into their intracardiac production. These findings enhance the understanding of the biology of these biomarkers and may inform their clinical application.

Unravelling cysteine-deficiency-associated rapid weight loss

Around 40% of the US population and 1 in 6 individuals worldwide have obesity, with the incidence surging globally1,2. Various dietary interventions, including carbohydrate, fat and, more recently, amino acid restriction, have been explored to combat this epidemic3-6. Here we investigated the impact of removing individual amino acids on the weight profiles of mice. We show that conditional cysteine restriction resulted in the most substantial weight loss when compared to essential amino acid restriction, amounting to 30% within 1 week, which was readily reversed. We found that cysteine deficiency activated the integrated stress response and oxidative stress response, which amplify each other, leading to the induction of GDF15 and FGF21, partly explaining the phenotype7-9. Notably, we observed lower levels of tissue coenzyme A (CoA), which has been considered to be extremely stable10, resulting in reduced mitochondrial functionality and metabolic rewiring. This results in energetically inefficient anaerobic glycolysis and defective tricarboxylic acid cycle, with sustained urinary excretion of pyruvate, orotate, citrate, α-ketoglutarate, nitrogen-rich compounds and amino acids. In summary, our investigation reveals that cysteine restriction, by depleting GSH and CoA, exerts a maximal impact on weight loss, metabolism and stress signalling compared with other amino acid restrictions. These findings suggest strategies for addressing a range of metabolic diseases and the growing obesity crisis.

Age-Associated Increase in Growth Differentiation Factor 15 Levels Correlates With Central Arterial Stiffness and Predicts All-Cause Mortality in a Sardinian Population Cohort

BACKGROUND

Growth differentiation factor 15 (GDF-15) levels are emerging as a candidate biomarker of aging. The present study aimed to: (1) characterize the association of GDF-15 with the continuum of arterial stiffening, assessed as carotid-femoral pulse wave velocity, as age increases; (2) determine the predictive role of serum GDF-15 levels on mortality; and (3) identify genetic determinants of serum GDF-15 levels.

METHODS AND RESULTS

Serum levels of GDF-15 and established cardiovascular risk factors, including pulse wave velocity, were assessed in a large (4736 individual) Sardinian population. Serum levels of GDF-15, which can be reliably measured repeatedly over time, increase with age; are associated with a stiffer aorta; "mediate" a large proportion of the age-associated increase in arterial stiffness; pose risks because of their association with greater mortality; and are significantly associated with the variant rs11549407, which causes thalassemia major in homozygosity.

CONCLUSIONS

Because of its consistent ability to predict functional and clinical outcomes, including all-cause mortality, we conclude that GDF-15 serum levels serve as a robust biomarker for the continuum from health to the emergence of clinical disease during aging and, subsequently, to the likelihood of mortality.

Association between exposure to perfluoroalkyl substances (PFASs) and risk of hyperemesis gravidarum

The fluctuation of endocrine hormones during early pregnancy plays an important role in the pathogenesis of hyperemesis gravidarum (HG). As an endocrine disrupting chemical (EDC), perfluoroalkyl substances (PFASs) exert an impact on pregnancy-related complications by altering hormone balances throughout gestation. Despite this potential impact, the relationship between serum PFAS levels in early pregnancy and the risk of HG has not been previously investigated. A total of 98 HG cases and 495 controls were included in this study from the Xi'an Birth Cohort Study. In total, serum levels of 10 PFASs were measured using High Performance Liquid Chromatography with tandem Mass Spectrometry (HPLC-MS/MS) during early pregnancy. Binary logistic models were applied to evaluate the associations between individual PFAS levels and HG. Weighted quantile sum (WQS) regression models and Bayesian kernel machine regression (BKMR) models were performed to test the overall effect of the PFAS mixture on HG. After adjusting for confounding variables, the highest tertile concentrations of perfluoroundecanoic acid (PFUnDA) (OR: 3.49, 95 %CI: 1.31-9.29), and perfluorododecanoic acid (PFDoA) (OR: 3.13, 95 % CI: 1.40-6.98) were significantly associated with a higher risk of HG, while highest tertile of perfluorohexanoic acid (PFHxA) (OR: 0.34; 95 % CI: 0.16-0.73), and PFOS (OR: 0.35; 95 % CI: 0.13-0.97) were inversely associated with HG. The WQS index showed a positive correlation with HG risk (β = 0.80; 95 % CI: 0.02, 1.57), with notable contributions from PFDoA (0.952), PFUnDA (0.159), and perfluorobutanoic acid (PFBA) (0.146). In addition, the joint effect of the PFAS mixture was positively associated with HG, with PFDoA (posterior inclusion probability (PIP) = 0.78) and PFUnDA (PIP = 0.75) being identified as the primary contributors. Our findings indicate that exposure to PFAS mixture during early pregnancy was associated with an increased risk of HG, with PFDoA and PFUnDA being the major contributors.

Defeating lethal cancer: Interrupting the ecologic and evolutionary basis of death from malignancy

Despite the advances in cancer prevention, early detection, and treatments, all of which have led to improved cancer survival, globally, there is an increased incidence in cancer-related deaths. Although each patient and each tumor is wholly unique, the tipping point to incurable disease is common across all patients: the dual capacity for cancers to metastasize and resist systemic treatment. The discovery of genetic mutations and epigenetic variation that emerges during cancer progression highlights that evolutionary and ecology principles can be used to understand how cancer evolves to a lethal phenotype. By applying such an eco-evolutionary framework, the authors reinterpret our understanding of the metastatic process as one of an ecologic invasion and define the eco-evolutionary paths of evolving therapy resistance. With this understanding, the authors draw from successful strategies optimized in evolutionary ecology to define strategic interventions with the goal of altering the evolutionary trajectory of lethal cancer. Ultimately, studying, understanding, and treating cancer using evolutionary ecology principles provides an opportunity to improve the lives of patients with cancer.

GDF15 links adipose tissue lipolysis with anxiety

Psychological stress changes both behaviour and metabolism to protect organisms. Adrenaline is an important driver of this response. Anxiety correlates with circulating free fatty acid levels and can be alleviated by a peripherally restricted β-blocker, suggesting a peripheral signal linking metabolism with behaviour. Here we show that adrenaline, the β3 agonist CL316,243 and acute restraint stress induce growth differentiation factor 15 (GDF15) secretion in white adipose tissue of mice. Genetic inhibition of adipose triglyceride lipase or genetic deletion of β-adrenergic receptors blocks β-adrenergic-induced increases in GDF15. Increases in circulating GDF15 require lipolysis-induced free fatty acid stimulation of M2-like macrophages within white adipose tissue. Anxiety-like behaviour elicited by adrenaline or restraint stress is eliminated in mice lacking the GDF15 receptor GFRAL. These data provide molecular insights into the mechanisms linking metabolism and behaviour and suggest that inhibition of GDF15-GFRAL signalling might reduce acute anxiety.

The association between serum growth differentiation factor 15 and insulin resistance in women diagnosed with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is strongly associated with metabolic abnormalities, with 50-70% of patients exhibiting insulin resistance (IR), which significantly impacts the reproductive health of women in their reproductive years. Growth differentiation factor 15 (GDF15), a hormone responsive to nutritional stress, has been implicated in several diseases. This study sought to clarify the relationship between GDF15 levels and IR condition in PCOS patients. Based on the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), patients were categorized into an IR-PCOS group (n = 124) and a non-insulin-resistant group (non-IR-PCOS group, n = 109). Fasting blood samples were collected to measure GDF15 concentrations. To assess metabolic complications in relation to GDF15 levels, patients were also classified into high and normal GDF15 groups. Serum GDF15 levels were significantly higher in IR-PCOS patients (median 772.94 pg/ml) compared to non-IR-PCOS patients (median 575.80 pg/ml, P < 0.05). The high GDF15 group showed more severe metabolic and lipid abnormalities than the normal GDF15 group. Spearman correlation analysis revealed a correlation between increased GDF15 levels and impaired glucose metabolism. Logistic regression analysis identified GDF15, HDL-C, and prolactin as risk factors for IR in PCOS, and the fully adjusted regression coefficient for GDF15 levels and IR prevalence was 4.490 (95% CI 1.541 to 13.088). Restricted cubic spline analysis confirmed a positive association between GDF15 levels and IR within a specific range. The combined predictive probability of GDF15, prolactin, and HDL-C for IR was 0.763 (95% CI 0.701 to 0.826) according to ROC analysis. Elevated GDF15 levels may be associated with IR in PCOS patients, suggesting a potential role for GDF15 in the pathophysiology of IR in this condition.

Growth differentiation factor 15: a valuable biomarker for the diagnosis and prognosis of late-onset form of multiple Acyl-CoA dehydrogenation deficiency

BACKGROUND

Multiple acyl-CoA Dehydrogenation Deficiency (MADD) is a hereditary metabolic disorder affecting the metabolism of fatty acids, amino acids, and choline, typically presenting with fat accumulation and mitochondrial abnormalities in muscle pathology. Growth differentiation factor 15 (GDF15) is a stress-responsive cytokine implicated in energy metabolism. Therefore, this study aimed to assess the level of GDF15 in patients with late-onset MADD and to evaluate its potential as a reliable biomarker for diagnosing symptoms and determining the severity of late-onset MADD.

METHODS

In this study, consecutive patients with MADD mitochondrial diseases were recruited from the Neuromuscular Center of Qilu Hospital, Shandong University, between April 2015 and October 2021. We measured serum GDF15 levels in patients with late-onset MADD and healthy controls. Additionally, we analyzed the messenger RNA(mRNA) expression of GDF15 and integrated stress response (ISR)-related factors, including CHOP, ATF5, and TRIB3, in the muscles.

RESULTS

Serum GDF15 levels in patients with late-onset MADD were 18.8 times higher than those in healthy controls. GDF15 levels decreased as the disease progressed, and its elecated levels correlated with anorexia symptoms. The mRNA expression of GDF15 and ISR-related factors in the muscles was higher in patients with late-onset MADD than in controls.

CONCLUSION

GDF15 levels were significantly elevated in symptomatic patients with late-onset MADD, likely due to mitochondrial dysfunction activating the ISR pathway. These findings suggest that GDF15 is a valuable biomarker for monitoring disease severity and symptomatology in patients with late-onset MADD.

Circulating and hepatic levels of growth differentiation factor 15 in patients with metabolic dysfunction-associated steatotic liver disease

AIM

Increased growth differentiation factor 15 (GDF15) may reflect impaired metabolic health and an inflammatory state in metabolic dysfunction-associated steatotic liver disease (MASLD). We investigated the role of GDF15 in histologically verified MASLD in a meal test (discovery) cohort (n = 20) and a prospective (validation) cohort with 2 years of follow-up (n = 276).

METHODS

Participants were evaluated clinically and histologically in both cohorts. Fibrosis severity was classified as no/mild (F0/F1) or significant (F2-4). Plasma GDF15 was measured by enzyme-linked immunosorbent assays and the SOMAScan platform. Hepatic GDF15 mRNA expression was analyzed by RNA in situ hybridization and bulk RNA-sequencing. In addition, we used data from public single-nucleus RNA-sequencing datasets.

RESULTS

In both cohorts, plasma GDF15 was increased in MASLD compared with healthy controls (p < 0.0001) with the highest levels in patients with significant fibrosis (area under the curve 0.83; 95% confidence interval [CI], 0.76-0.91). The GDF15 levels were unaffected by a standardized meal and there was no difference in peripheral or hepatic venous concentrations. After 2 years, the increase in GDF15 levels was reduced in patients treated with glucagon-like peptide receptor agonists (GLP-1-RA) compared to patients receiving lifestyle advice (-28%; 95% CI, -44 to -8; p = 0.01). Plasma GDF15 was associated with circulating insulin-like growth factor 1 and related proteins. Hepatic GDF15 mRNA was mainly expressed in hepatocytes and in cholangiocytes in fibrotic areas and was increased in MASLD (p = 0.02) with the highest expression in the group with steatohepatitis (p = 0.009).

CONCLUSIONS

Increased hepatic and circulating GDF15 are found in MASLD. Treatment with GLP-1-RA may reduce GDF15, possibly reflecting beneficial metabolic and inflammatory effects.

Skeletal muscle mitochondrial dysfunction is associated with increased Gdf15 expression and circulating GDF15 levels in aged mice

Growth differentiation factor-15 (GDF15) is a biomarker of multiple disease states and circulating GDF15 levels are increased during aging in both pre-clinical animal models and human studies. Accordingly, multiple stressors have been identified, including mitochondrial dysfunction, that lead to induction of Gdf15 expression downstream of the integrated stress response (ISR). For some disease states, the source of increased circulating GDF15 is evident based on the specific pathology. Aging, however, presents a less tractable system for understanding the source of increased plasma GDF15 levels in that cellular dysfunction with aging can be pleiotropic and heterogeneous. To better understand which organ or organs contribute to increased circulating GDF15 levels with age, and whether changes in metabolic and mitochondrial dysfunction were associated with these potential changes, we compared young 12-week-old and middle-aged 52-week-old C57BL/6 J mice using a series of metabolic phenotyping studies and by comparing circulating levels of GDF15 and tissue-specific patterns of Gdf15 expression. Overall, we found that Gdf15 expression was increased in skeletal muscle but not liver, white or brown adipose tissue, kidney or heart of middle-aged mice, and that insulin sensitivity and mitochondrial respiratory capacity were impaired in middle-aged mice. These data suggest that early changes in skeletal muscle mitochondrial function and metabolism contribute to increased circulating GDF15 levels observed during aging.

Central mechanisms of emesis: A role for GDF15

BACKGROUND

Nausea and emesis are ubiquitously reported medical conditions and often present as treatment side effects along with polymorbidities contributing to detrimental life-threatening outcomes, such as poor nutrition, lower quality of life, and unfavorable patient prognosis. Growth differentiation factor 15 (GDF15) is a stress response cytokine secreted by a wide variety of cell types in response to a broad range of stressors. Circulating GDF15 levels are elevated in a range of medical conditions characterized by cachexia and malaise. In recent years, GDF15 has gained scientific and translational prominence with the discovery that its receptor, GDNF family receptor α-like (GFRAL), is expressed exclusively in the hindbrain. GFRAL activation may results in profound anorexia and body weight loss, effects which have attracted interest for the pharmacological treatment of obesity.

PURPOSE

This review highlights compelling emerging evidence indicating that GDF15 causes anorexia through the induction of nausea, emesis, and food aversions, which encourage a perspective on GDF15 system function in physiology and behavior beyond homeostatic energy regulation contexts. This highlights the potential role of GDF15 in the central mediation of nausea and emesis following a variety of physiological, and pathophysiological conditions such as chemotherapy-induced emesis, hyperemesis gravidarum, and cyclic vomiting syndrome.

What is the pipeline for future medications for obesity?

Obesity is a chronic disease associated with increased risk of obesity-related complications and mortality. Our better understanding of the weight regulation mechanisms and the role of gut-brain axis on appetite has led to the development of safe and effective entero-pancreatic hormone-based treatments for obesity such as glucagon-like peptide-1 (GLP-1) receptor agonists (RA). Semaglutide 2.4 mg once weekly, a subcutaneously administered GLP-1 RA approved for obesity treatment in 2021, results in 15-17% mean weight loss (WL) with evidence of cardioprotection. Oral GLP-1 RA are also under development and early data shows similar WL efficacy to semaglutide 2.4 mg. Looking to the next generation of obesity treatments, combinations of GLP-1 with other entero-pancreatic hormones with complementary actions and/or synergistic potential (such as glucose-dependent insulinotropic polypeptide (GIP), glucagon, and amylin) are under investigation to enhance the WL and cardiometabolic benefits of GLP-1 RA. Tirzepatide, a dual GLP-1/GIP receptor agonist has been approved for glycaemic control in type 2 diabetes as well as for obesity management leading in up to 22.5% WL in phase 3 obesity trials. Other combinations of entero-pancreatic hormones including cagrisema (GLP-1/amylin RA) and the triple agonist retatrutide (GLP-1/GIP/glucagon RA) have also progressed to phase 3 trials as obesity treatments and early data suggests that may lead to even greater WL than tirzepatide. Additionally, agents with different mechanisms of action to entero-pancreatic hormones (e.g. bimagrumab) may improve the body composition during WL and are in early phase clinical trials. We are in a new era for obesity pharmacotherapy where combinations of entero-pancreatic hormones approach the WL achieved with bariatric surgery. In this review, we present the efficacy and safety data for the pipeline of obesity pharmacotherapies with a focus on entero-pancreatic hormone-based treatments and we consider the clinical implications and challenges that the new era in obesity management may bring.

Autophagy-related 7 (ATG7) regulates food intake and liver health during asparaginase exposure

Amino acid starvation by the chemotherapy agent asparaginase is a potent activator of the integrated stress response (ISR) in the liver and can upregulate autophagy in some cell types. We hypothesized that autophagy-related 7 (ATG7), a protein that is essential for autophagy and an ISR target gene, was necessary during exposure to asparaginase to maintain liver health. We knocked down Atg7 systemically (Atg7Δ/Δ) or in hepatocytes only (ls-Atg7KO) in mice before exposure to pegylated asparaginase for 5 days. Intact mice injected with asparaginase lost body weight due to reduced food intake and increased energy expenditure. Systemic Atg7 ablation reduced liver protein synthesis and increased liver injury in vehicle-injected mice but did not further reduce liver protein synthesis, exacerbate steatosis or liver injury, or alter energy expenditure following 5 days of asparaginase exposure. Atg7Δ/Δ mice were unexpectantly protected from asparaginase-induced anorexia and weight loss. This protection corresponded with reduced phosphorylation of hepatic GCN2 and blunted increases in ISR gene targets including growth differentiation factor 15 (GDF15), a negative regulator of food intake. Interestingly, asparaginase elevated serum GDF15 and reduced food intake in ls-Atg7KO mice, similar to intact mice. Liver triglycerides and production of the hepatokine fibroblast growth factor 21, another ISR gene target, were suppressed in asparaginase-exposed Atg7Δ/Δ and ls-Atg7KO mice. This work identifies a bidirectional relationship between autophagy and the ISR in the liver during asparaginase, affecting food intake and liver health.

Growth Differentiation Factor-15 Is Associated With Congestion-Related Anorexia and Weight Loss in Advanced Heart Failure

BACKGROUND

Growth differentiation factor (GDF)-15 is a pleiotropic cytokine that is associated with appetite-suppressing effects and weight loss in patients with malignancy.

OBJECTIVES

This study aims to investigate the relationships between GDF-15 levels, anorexia, cachexia, and clinical outcomes in patients with advanced heart failure with reduced ejection fraction (HFrEF).

METHODS

In this observational, retrospective analysis, a total of 344 patients with advanced HFrEF (age 58 ± 10 years, 85% male, 67% NYHA functional class III), underwent clinical and echocardiographic examination, body composition evaluation by skinfolds and dual-energy x-ray absorptiometry, circulating metabolite assessment, Minnesota Living with Heart Failure Questionnaire, and right heart catheterization.

RESULTS

The median GDF-15 level was 1,503 ng/L (Q1-Q3: 955-2,332 ng/L) (reference range: <1,200 ng/L). Higher GDF-15 levels were associated with more prevalent anorexia and cachexia. Patients with higher GDF-15 had increased circulating free fatty acids and beta-hydroxybutyrate, lower albumin, cholesterol, and insulin/glucagon ratio, consistent with a catabolic state. Patients with higher GDF-15 had worse congestion and more severe right ventricular dysfunction. In multivariable Cox analysis, elevated GDF-15 was independently associated with risk of the combined endpoint of death, urgent transplantation, or left ventricular assist device implantation, even after adjusting for coexisting anorexia and cachexia (T3 vs T1 HR: 2.31 [95% CI: 1.47-3.66]; P < 0.001).

CONCLUSIONS

In patients with advanced HFrEF, elevated circulating GDF-15 levels are associated with a higher prevalence of anorexia and cachexia, right ventricular dysfunction, and congestion, as well as an independently increased risk of adverse events. Further studies are warranted to determine whether therapies altering GDF-15 signaling pathways can affect metabolic status and clinical outcomes in advanced HFrEF.

Neurotensin-neurotensin receptor 2 signaling in adipocytes suppresses food intake through regulating ceramide metabolism

Neurotensin (NTS) is a secretory peptide produced by lymphatic endothelial cells. Our previous study revealed that NTS suppressed the activity of brown adipose tissue via interactions with NTSR2. In the current study, we found that the depletion of Ntsr2 in white adipocytes upregulated food intake, while the local treatment of NTS suppressed food intake. Our mechanistic study revealed that suppression of NTS-NTSR2 signaling enhanced the phosphorylation of ceramide synthetase 2, increased the abundance of its products ceramides C20-C24, and downregulated the production of GDF15 in white adipose tissues, which was responsible for the elevation of food intake. We discovered a potential causal and positive correlation between serum C20-C24 ceramide levels and human food intake in four populations with different ages and ethnic backgrounds. Together, our study shows that NTS-NTSR2 signaling in white adipocytes can regulate food intake via its direct control of lipid metabolism and production of GDF15. The ceramides C20-C24 are key factors regulating food intake in mammals.

GDF15-GFRAL signaling drives weight loss and lipid metabolism in mouse model of amyotrophic lateral sclerosis

Weight loss is a common early sign in amyotrophic lateral sclerosis (ALS) patients and negatively correlates with survival. In different cancers and metabolic disorders, high levels of serum growth differentiation factor 15 (GDF15) contribute to a decrease of food intake and body weight, acting through GDNF family receptor alpha-like (GFRAL). Here we report that GDF15 is highly expressed in the peripheral blood of ALS patients and in the hSOD1G93A mouse model and that GFRAL is upregulated in the brainstem of hSOD1G93A mice. We demonstrate that the localized GFRAL silencing by shRNA in the area postrema/nucleus tractus solitarius of hSOD1G93A mice induces weight gain, reduces adipose tissue wasting, ameliorates the motor function and muscle atrophy and prolongs the survival time. We report that microglial cells could be involved in mediating these effects because their depletion with PLX5622 reduces brainstem GDF15 expression, weight loss and the expression of lipolytic genes in adipose tissue. Altogether these results reveal a key role of GDF15-GFRAL signaling in regulating weight loss and the alteration of and lipid metabolism in the early phases of ALS.

Palmitate potentiates the SMAD3-PAI-1 pathway by reducing nuclear GDF15 levels

Nuclear growth differentiation factor 15 (GDF15) reduces the binding of the mothers' against decapentaplegic homolog (SMAD) complex to its DNA-binding elements. However, the stimuli that control this process are unknown. Here, we examined whether saturated fatty acids (FA), particularly palmitate, regulate nuclear GDF15 levels and the activation of the SMAD3 pathway in human skeletal myotubes and mouse skeletal muscle, where most insulin-stimulated glucose use occurs in the whole organism. Human LHCN-M2 myotubes and skeletal muscle from wild-type and Gdf15-/- mice fed a standard (STD) or a high-fat (HFD) diet were subjected to a series of studies to investigate the involvement of lipids in nuclear GDF15 levels and the activation of the SMAD3 pathway. The saturated FA palmitate, but not the monounsaturated FA oleate, increased the expression of GDF15 in human myotubes and, unexpectedly, decreased its nuclear levels. This reduction was prevented by the nuclear export inhibitor leptomycin B. The decrease in nuclear GDF15 levels caused by palmitate was accompanied by increases in SMAD3 protein levels and in the expression of its target gene SERPINE1, which encodes plasminogen activator inhibitor 1 (PAI-1). HFD-fed Gdf15-/- mice displayed aggravated glucose intolerance compared to HFD-fed WT mice, with increased levels of SMAD3 and PAI-1 in the skeletal muscle. The increased PAI-1 levels in the skeletal muscle of HFD-fed Gdf15-/- mice were accompanied by a reduction in one of its targets, hepatocyte growth factor (HGF)α, a cytokine involved in glucose metabolism. Interestingly, PAI-1 acts as a ligand of signal transducer and activator of transcription 3 (STAT3) and the phosphorylation of this transcription factor was exacerbated in HFD-fed Gdf15-/- mice compared to HFD-fed WT mice. At the same time, the protein levels of insulin receptor substrate 1 (IRS-1) were reduced. These findings uncover a potential novel mechanism through which palmitate induces the SMAD3-PAI-1 pathway to promote insulin resistance in skeletal muscle by reducing nuclear GDF15 levels.

Effects of Acute Exercise and Carbohydrate Intake on Plasma GDF-15 Levels and Its Association With Appetite Regulation

Background

Growth differentiation factor 15 (GDF-15) is a potential therapeutic target for obesity due to its role in appetite suppression. Although acute exercise stimulates GDF-15 secretion, its relationship with appetite regulation remains unclear. It is also unknown whether preexercise carbohydrate intake would affect GDF-15 responses. This study aimed to examine the effects of acute exercise and carbohydrate intake on GDF-15 secretion and its potential links to appetite regulation.

Methods

In a secondary analysis of a randomized crossover trial, 12 healthy males completed four 120-minute trial conditions: (1) control (water) with rest, (2) control with exercise (0-30 minutes at ∼75% of maximal oxygen uptake), (3) carbohydrate (75 g maltodextrin) with rest, and (4) carbohydrate with exercise. Plasma GDF-15 levels were measured at 0, 30, 60, and 120 minutes, alongside subjective appetite ratings using visual analog scales. Energy intake was measured at the end of each trial condition with an ad libitum meal.

Results

Time-averaged area under the curve analysis showed that neither exercise [34 pg/mL (95% confidence interval [CI], -2-69 pg/mL); P = .062) nor carbohydrate intake [10 pg/mL (95% CI, -39-58 pg/mL); P = .673] independently or interactively (P = .283) affected GDF-15 levels. Exercise induced a delayed independent increase in GDF-15 at 120 minutes [55 pg/mL (95% CI, 18-94 pg/mL); P = .008]. No significant associations were found between GDF-15 levels and subjective appetite ratings or energy intake.

Conclusion

A 30-minute bout of high-intensity exercise induces a delayed increase in GDF-15 levels, which is not affected by carbohydrate intake. Physiological GDF-15 responses to acute exercise display no association with markers of appetite regulation.

Effects of seven days' fasting on physical performance and metabolic adaptation during exercise in humans

Humans have, throughout history, faced periods of starvation necessitating increased physical effort to gather food. To explore adaptations in muscle function, 13 participants (7 males and 6 females) fasted for seven days. They lost 4.6 ± 0.3 kg lean and 1.4 ± 0.1 kg fat mass. Maximal isometric and isokinetic strength remained unchanged, while peak oxygen uptake decreased by 13%. Muscle glycogen was halved, while expression of electron transport chain proteins was unchanged. Pyruvate dehydrogenase kinase 4 (PDK4) expression increased 13-fold, accompanied by inhibitory pyruvate dehydrogenase phosphorylation, reduced carbohydrate oxidation and decreased exercise endurance capacity. Fasting had no impact on 5' AMP-activated protein kinase (AMPK) activity, challenging its proposed role in muscle protein degradation. The participants maintained muscle strength and oxidative enzymes in skeletal muscle during fasting but carbohydrate oxidation and high-intensity endurance capacity were reduced.

GDF15 antagonism limits severe heart failure and prevents cardiac cachexia

AIMS

Heart failure and associated cachexia is an unresolved and important problem. This study aimed to determine the factors that contribute to cardiac cachexia in a new model of heart failure in mice that lack the integrated stress response (ISR) induced eIF2α phosphatase, PPP1R15A.

METHODS AND RESULTS

Mice were irradiated and reconstituted with bone marrow cells. Mice lacking functional PPP1R15A, exhibited dilated cardiomyopathy and severe weight loss following irradiation, whilst wild-type mice were unaffected. This was associated with increased expression of Gdf15 in the heart and increased levels of GDF15 in circulation. We provide evidence that the blockade of GDF15 activity prevents cachexia and slows the progression of heart failure. We also show the relevance of GDF15 to lean mass and protein intake in patients with heart failure.

CONCLUSION

Our data suggest that cardiac stress mediates a GDF15-dependent pathway that drives weight loss and worsens cardiac function. Blockade of GDF15 could constitute a novel therapeutic option to limit cardiac cachexia and improve clinical outcomes in patients with severe systolic heart failure.

Brainstem BDNF neurons are downstream of GFRAL/GLP1R signalling

Growth differentiation factor 15, GDF15, and glucagon-like peptide-1 (GLP-1) analogues act through brainstem neurons that co-localise their receptors, GDNF-family receptor α-like (GFRAL) and GLP1R, to reduce food intake and body weight. However, their use as clinical treatments is partially hampered since both can also induce sickness-like behaviours, including aversion, that are mediated through a well-characterised pathway via the exterolateral parabrachial nucleus. Here, in mice, we describe a separate pathway downstream of GFRAL/GLP1R neurons that involves a distinct population of brain-derived neurotrophic factor (BDNF) cells in the medial nucleus of the tractus solitarius. Thus, BDNFmNTS neurons are required for the weight-reducing actions of both GDF15 and the GLP1RA, Exendin-4. Moreover, acute activation of BDNFmNTS neurons is sufficient to reduce food intake and drive fatty acid oxidation and might provide a route for longer-term weight loss.

A systematic review of the neuroprotective role and biomarker potential of GDF15 in neurodegeneration

Neurodegeneration is characteristically multifaceted, with limited therapeutic options. One of the chief pathophysiological mechanisms driving these conditions is neuroinflammation, prompting increasing clinical interest in immunomodulatory agents. Growth differentiation factor 15 (GDF15; previously also called macrophage inhibitory cytokine-1 or MIC-1), an anti-inflammatory cytokine with established neurotrophic properties, has emerged as a promising therapeutic agent in recent decades. However, methodological challenges and the delayed identification of its specific receptor GFRAL have hindered research progress. This review systematically examines literature about GDF15 in neurodegenerative diseases and neurotrauma. The evidence collated in this review indicates that GDF15 expression is upregulated in response to neurodegenerative pathophysiology and increasing its levels in preclinical models typically improves outcomes. Key knowledge gaps are addressed for future investigations to foster a more comprehensive understanding of the neuroprotective effects elicited by GDF15.

Metformin inhibits migration and epithelial-to-mesenchymal transition in non-small cell lung cancer cells through AMPK-mediated GDF15 induction

The growth differentiation factor 15 (GDF15) may serve as a biomarker of metformin, which mediates the bodyweight lowering effect of metformin. However, whether GDF15 also serves as a molecular target of metformin to inhibit carcinogenesis remains largely unknown. This study examined the role and molecular mechanisms of GDF15 in the anticancer effects of metformin in non-small cell lung cancer (NSCLC) cells, which has never been reported before. We found that metformin significantly inhibited the migration of NSCLC A549 and NCI-H460 cells and reduced the expression of epithelial-to-mesenchymal transition (EMT)-related molecules, including neuro-cadherin (N-cadherin), matrix metalloproteinase 2 (MMP2), and the zinc finger transcription factor Snail, but increased epithelial cadherin (E-cadherin) expression. Furthermore, metformin increased GDF15 and its upstream transcription factors activated transcription factor 4 (ATF4) and C/EBP-homologous protein (CHOP) expressions and increased AMP-activated protein kinase (AMPK) phosphorylation in NSCLC cells. GDF15 siRNA partially reverses the inhibitory effect of metformin on NSCLC cell migration. Moreover, metformin-induced increases in GDF15, CHOP, and ATF4 expression and the inhibition of migration were partially reversed by treatment with Compound C, a specific AMPK inhibitor. Meanwhile, metformin significantly inhibited NCI-H460 xenograft tumor growth in nude mice, increased GDF15 expression, and regulated EMT- and migration-related protein expression in xenograft tumors. In conclusion, our results provide novel insights into revealing that GDF15 can serve as a potential molecular target of metformin owing to its anti-cancer effect in NSCLC, which is mediated by AMPK activation.

Alterations in Biomarkers Associated with Cardiovascular Health and Obesity with Short-Term Lifestyle Changes in Overweight Women: The Role of Exercise and Diet

Background and Objectives: In this study, the effects of an eight-week exercise and nutrition program on blood lipids, glucose, insulin, insulin resistance (HOMA-IR), leptin, ghrelin, irisin, malondialdehyde (MDA), and Growth Differentiation Factor 15 (GDF15) in overweight women were investigated. Materials and Methods: A total of 48 women volunteers participated in this study. The participants were randomly divided into four groups: control (C), exercise (E), nutrition (N), exercise + nutrition (E + N). While no intervention was applied to group C, the other groups participated in the predetermined programs for 8 weeks. At the beginning and end of this study, body composition was measured and blood samples were taken. Results: It was determined that the body composition components, lipid profile indicators, insulin, glucose, insulin resistance, leptin, ghrelin, irisin, and MDA parameters examined in this study showed positive changes in the intervention groups. Group E had a greater effect on body muscle percentage, MDA, and irisin levels, while group N had a greater effect on blood lipids and ghrelin levels. Conclusions: As a result, it is thought that lifestyle changes are important to improve cardiovascular health and combat obesity, and that maintaining a healthy diet together with exercise may be more effective.

GDF15/MIC-1: a stress-induced immunosuppressive factor which promotes the aging process

The GDF15 protein, a member of the TGF-β superfamily, is a stress-induced multifunctional protein with many of its functions associated with the regulation of the immune system. GDF15 signaling provides a defence against the excessive inflammation induced by diverse stresses and tissue injuries. Given that the aging process is associated with a low-grade inflammatory state, called inflammaging, it is not surprising that the expression of GDF15 gradually increases with aging. In fact, the GDF15 protein is a core factor secreted by senescent cells, a state called senescence-associated secretory phenotype (SASP). Many age-related stresses, e.g., mitochondrial and endoplasmic reticulum stresses as well as inflammatory, metabolic, and oxidative stresses, induce the expression of GDF15. Although GDF15 signaling is an effective anti-inflammatory modulator, there is robust evidence that it is a pro-aging factor promoting the aging process. GDF15 signaling is not only an anti-inflammatory modulator but it is also a potent immunosuppressive enhancer in chronic inflammatory states. The GDF15 protein can stimulate immune responses either non-specifically via receptors of the TGF-β superfamily or specifically through the GFRAL/HPA/glucocorticoid pathway. GDF15 signaling stimulates the immunosuppressive network activating the functions of MDSCs, Tregs, and M2 macrophages and triggering inhibitory immune checkpoint signaling in senescent cells. Immunosuppressive responses not only suppress chronic inflammatory processes but they evoke many detrimental effects in aged tissues, such as cellular senescence, fibrosis, and tissue atrophy/sarcopenia. It seems that the survival functions of GDF15 go awry in persistent inflammation thus promoting the aging process and age-related diseases.

Targeting the GDF15 Signalling for Obesity Treatment: Recent Advances and Emerging Challenges

The growth differentiation factor 15 (GDF15)-glial cell-derived neurotrophic factor family receptor alpha-like (GFRAL) pathway plays a crucial role in the regulation of metabolism, appetite and body weight control. Obesity is an increasingly prevalent chronic disease worldwide, necessitating effective treatment strategies. Recent preclinical and clinical studies have highlighted that targeting the GDF15-GFRAL signalling pathway is a promising approach for treating obesity, particularly because it has minimal impact on skeletal muscle mass, which is essential to preserve during weight loss. Given its distinctive mechanisms, the GDF15-GFRAL axis represents an attractive target for addressing various metabolic disorders, especially obesity. In this review, we will explore how the GDF15-GFRAL axis is regulated, its distribution in the body and its role in the regulation of metabolism, appetite and obesity. Additionally, we will discuss recent advances and potential challenges in targeting the GDF15-GFRAL axis for obesity treatment.

GDF15 associates with, but is not responsible for, exercise-induced increases in corticosterone and indices of lipid utilization in mice

Growth differentiation factor 15 (GDF15) is a stress-induced cytokine that increases with exercise and is thought to increase corticosterone and lipid utilization. How postexercise nutrient availability impacts GDF15 and the physiological role that GDF15 plays during and/or in the recovery from exercise has not been elucidated. The purpose of this investigation was to examine how postexercise nutrient availability impacts GDF15 and to use this as a model to explore associations between GDF15, corticosterone, and indices of lipid and carbohydrate metabolism. In addition, we explored the causality of these relationships using GDF15-deficient mice. Male and female C57BL/6J mice ran for 2 hours on a treadmill and were euthanized immediately or 3 hours after exercise with or without access to a chow diet. In both sexes, circulating concentrations of GDF15, corticosterone, nonesterified fatty acids (NEFA), and beta-hydroxybutyrate (BHB) were higher immediately postexercise and remained elevated when food was withheld during the recovery period. While serum GDF15 was positively associated with corticosterone, BHB, and NEFA, increases in these factors were similar in wild-type and GDF15-/- mice following exercise. The lack of a genotype effect was not explained by differences in insulin, glucagon, or epinephrine after exercise. Our findings provide evidence that while GDF15 is associated with increases in corticosterone and indices of lipid utilization this is not a causal relationship.NEW & NOTEWORTHY Circulating growth differentiation factor 15 (GDF15) increases during exercise, but the physiological role that it plays has not been elucidated. Recent data suggest that GDF15 regulates corticosterone and lipid utilization. Here we demonstrate that postexercise nutrient availability influences GDF15 in the recovery from exercise and GDF15 is associated with corticosterone and indices of lipid utilization. However, the associations were not causal as exercise-induced increases in fatty acids, beta-hydroxybutyrate, and corticosterone were intact in GDF15-/- mice.

Curcumol effectively improves obesity through GDF15 induction via activation of endoplasmic reticulum stress response

The escalating prevalence of obesity presents a formidable global health challenge, underscoring the imperative for efficacious pharmacotherapeutic interventions. However, current anti-obesity medications often exhibit limited efficacy and adverse effects, necessitating the exploration of alternative therapeutic approaches. Growth differentiation factor 15 (GDF15) has emerged as a promising target for obesity management, given its crucial role in appetite control and metabolic regulation. In this study, we aimed to investigate the efficacy of curcumol, a sesquiterpene compound derived from plants of the Zingiberaceae family, in obesity treatment. Our findings demonstrate that curcumol effectively induces the expression of GDF15 through the activation of the endoplasmic reticulum stress pathway. To confirm the role of GDF15 as a critical target for curcumol's function, we compared the effects of curcumol in wild-type mice and Gdf15-knockout mice. Using a high-fat diet-induced obese murine model, we observed that curcumol led to reduced appetite and altered dietary preferences mediated by GDF15. Furthermore, chronic curcumol intervention resulted in promising anti-obesity effects. Additionally, curcumol administration improved glucose tolerance and lipid metabolism in the obese mice. These findings highlight the potential of curcumol as a GDF15 inducer and suggest innovative strategies for managing obesity and its associated metabolic disorders. In conclusion, our study provides evidence for the efficacy of curcumol in obesity treatment by inducing GDF15 expression. The identified effects of curcumol on appetite regulation, dietary preferences, glucose tolerance, and lipid metabolism emphasize its potential as a therapeutic agent for combating obesity and related metabolic disorders.

Daily GDF15 treatment has sex-specific effects on body weight and food intake and does not enhance the effects of voluntary physical activity in mice

Growth differentiation factor 15 (GDF15) is a stress-induced cytokine that suppresses food intake and causes weight loss. GDF15 also reduces voluntary physical activity and, thus, it is not clear whether combining GDF15 with exercise will be beneficial or if reductions in food intake would be offset by decreases in physical activity. We investigated how GDF15 treatment combined with voluntary wheel running (VWR) would impact weight gain, food intake, adiposity and indices of metabolic health in mice. High-fat fed male and female mice underwent daily GDF15 treatments and were given access to voluntary running wheels, or not, for 11 days. In both sexes, VWR prevented weight gain. In males, GDF15 reduced food intake, as well as attenuated weight gain and the accumulation of adipose tissue, with no additional effect of VWR. In female mice, GDF15 did not impact body weight gain or body composition. GDF15 acutely reduced food intake in female mice but this was followed by a period of rebound hyperphagia and consequently GDF15 did not reduce total food intake in female mice. GDF15 treatment reduced wheel running distance in both sexes. There were main effects of VWR to improve glucose tolerance in female but not male mice. These findings show that GDF15 has sex-specific effects on food intake and consequently weight gain and adiposity. There is no added benefit of combining GDF15 and voluntary physical activity for weight loss. Adaptive responses to acute caloric restriction induced by GDF15 might limit its effectiveness as a weight loss tool in females. KEY POINTS: GDF15 is a stress-induced signalling factor that reduces food intake and voluntary physical activity. It is not known whether combining GDF15 treatment with voluntary wheel running would impart beneficial combined effects in attenuating weight gain and the accumulation of adipose tissue. In the present study, we demonstrate that GDF15 reduces food intake and prevents weight gain in male but not female mice consuming a high-fat diet and also that combining GDF15 with voluntary wheel running (VWR) does not lead to a greater dampening of weight gain. In female mice, GDF15 acutely reduced food intake, but this was followed by a period of rebound hyperphagia resulting in no differences in total food intake. In both sexes, VWR was equivalent, or superior to GDF15 in preventing weight gain.

Cancer cachexia: multilevel metabolic dysfunction

Cancer cachexia is a complex metabolic disorder marked by unintentional body weight loss or 'wasting' of body mass, driven by multiple aetiological factors operating at various levels. It is associated with many malignancies and significantly contributes to cancer-related morbidity and mortality. With emerging recognition of cancer as a systemic disease, there is increasing awareness that understanding and treatment of cancer cachexia may represent a crucial cornerstone for improved management of cancer. Here, we describe the metabolic changes contributing to body wasting in cachexia and explain how the entangled action of both tumour-derived and host-amplified processes induces these metabolic changes. We discuss energy homeostasis and possible ways that the presence of a tumour interferes with or hijacks physiological energy conservation pathways. In that context, we highlight the role played by metabolic cross-talk mechanisms in cachexia pathogenesis. Lastly, we elaborate on the challenges and opportunities in the treatment of this devastating paraneoplastic phenomenon that arise from the complex and multifaceted metabolic cross-talk mechanisms and provide a status on current and emerging therapeutic approaches.

Health implications of racial differences in serum growth differentiation factor levels among men with obesity

Growth differentiation factor (GDF15) has been considered a biomarker and recently a hormonal driver for diseases in different populations. However, the role of GDF15 as a biomarker of health outcomes in obese men from different racial/ethnic background has not been evaluated. The objective of this study was to investigate the racial/ethnic differences on the relationship between GDF15 and markers of glucometabolic status, hormonal profile, body composition and bone mineral density (BMD) in obese men. One hundred ninety-three obese men from diverse racial/ethnic backgrounds were enrolled. BMD and body composition were measured by dual energy X-ray absorptiometry. Serum GDF15, osteocalcin, C-terminal telopeptide, sclerostin, adiponectin, leptin, estradiol, testosterone, follicle-stimulating hormone, luteinizing hormone, 25-hydroxyvitamin D, lipid profile, and hemoglobin A1C (A1C) were measured. Non-African Americans (NAA) had significantly higher GDF15 level than African Americans (AA). Level was also higher in patients with type 2 diabetes (T2DM). In both the groups GDF15 correlated with A1C and lean mass. However. GDF15 correlated  with body fat, LDL total cholesterol and femoral neck BMD only in NAA and with appendicular lean mass only in AA. Ethnicity, total cholesterol and T2DM were found to be independent predictors of GDF15. We conclude that GDF15 may influence glucometabolic status, body composition and bone parameters which may affect cardiovascular risk and osteoporosis  between races.

The Energetic Stress Marker GDF15 is Induced by Acute Psychosocial Stress

GDF15 (growth differentiation factor 15) is a marker of cellular and mitochondrial energetic stress linked to physical-mental illness, aging, and mortality. Here, we describe the psychobiological regulation of plasma and saliva GDF15 in four human studies including 3,599 samples from 148 healthy individuals. We report two main observations establishing GDF15 as a novel tractable biomarker of psychosocial stress. 1) In two experimental laboratory studies, socio-evaluative stress rapidly elevates GDF15 and lactate, two molecular markers of energetic/reductive stress. 2) Similar to other stress-related metabolic hormones, we also find that saliva GDF15 exhibit a robust awakening response, being highest at the time of waking up and declining by ~42-92% within 30-45 minutes. These data position GDF15 as a dynamic biomarker of psychosocial stress accessible in human blood and saliva, pointing towards a shared psychobiological pathway linking mental and mitochondrial energetic stress. These foundational observations open the door to large-scale studies using GDF15 to non-invasively probe how acute psychosocial factors promote cellular and mitochondrial and energetic stress contributing to the stress-disease cascade across the lifespan.

Diversity of Microglia-Derived Molecules with Neurotrophic Properties That Support Neurons in the Central Nervous System and Other Tissues

Microglia, the brain immune cells, support neurons by producing several established neurotrophic molecules including glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF). Modern analytical techniques have identified numerous phenotypic states of microglia, each associated with the secretion of a diverse set of substances, which likely include not only canonical neurotrophic factors but also other less-studied molecules that can interact with neurons and provide trophic support. In this review, we consider the following eight such candidate cytokines: oncostatin M (OSM), leukemia inhibitory factor (LIF), activin A, colony-stimulating factor (CSF)-1, interleukin (IL)-34, growth/differentiation factor (GDF)-15, fibroblast growth factor (FGF)-2, and insulin-like growth factor (IGF)-2. The available literature provides sufficient evidence demonstrating murine cells produce these cytokines and that they exhibit neurotrophic activity in at least one neuronal model. Several distinct types of neurotrophic activity are identified that only partially overlap among the cytokines considered, reflecting either their distinct intrinsic properties or lack of comprehensive studies covering the full spectrum of neurotrophic effects. The scarcity of human-specific studies is another significant knowledge gap revealed by this review. Further studies on these potential microglia-derived neurotrophic factors are warranted since they may be used as targeted treatments for diverse neurological disorders.

GDF15 research from bench to bedside

Pre-clinical data suggest that increased circulating growth differentiation factor 15 (GDF15) is a cause of both anorexia/cachexia syndromes and hyperemesis gravidarum in pregnancy, serious conditions with no highly effective treatment. A phase 2 study of a therapeutic GDF15 monoclonal antibody in the New England Journal of Medicine suggests that effective treatment of anorexia/cachexia in cancer may be approaching.

GDF15 is required for maintaining subcutaneous adipose tissue lipid metabolic signature

Recent research has identified growth differentiation factor 15 (GDF15) as a crucial factor in various physiological and pathological processes, particularly in energy balance regulation. While the role of GDF15 in modulating energy metabolism through hindbrain GDNF family receptor alpha-like (GFRAL) signaling has been extensively studied, emerging evidence suggests direct peripheral metabolic actions of GDF15. Using knockout mouse models, we investigated GDF15 and GFRAL's roles in adipose tissue metabolism. Our findings indicate that C57BL/6/129/SvJ Gdf15-KO mice exhibit impaired expression of de novo lipogenesis enzymes in subcutaneous adipose tissue (sWAT). In contrast, C57BL/6J Gfral-KO mice showed no impairments compared to wild-type (WT) littermates. RNA-Seq analysis of sWAT in Gdf15-KO mice revealed a broad downregulation of genes involved in lipid metabolism. Importantly, our study uncovered sex-specific effects, with females being more affected by GDF15 loss than males. Additionally, we observed a fasting-induced upregulation of GDF15 gene expression in sWAT of both mice and humans, reinforcing this factor's role in adipose tissue lipid metabolism. In conclusion, our research highlights an essential role for GDF15 in sWAT lipid metabolic homeostasis. These insights enhance our understanding of GDF15's functions in adipose tissue physiology and underscore its potential as a therapeutic target for metabolic disorders.

BATokines in metabolic liver disease: good cops or bad cops?

Recent work identifies PCPE-1 as a brown-adipose tissue-derived systemic mediator of liver fibrosis in metabolic dysfunction-associated steatohepatitis.

GDF15 Knockout Does Not Substantially Impact Perinatal Body Weight or Neonatal Outcomes in Mice

Growth differentiation factor-15 (GDF15) increases in circulation during pregnancy and has been implicated in food intake, weight loss, complications of pregnancy, and metabolic illness. We used a Gdf15 knockout mouse model (Gdf15-/-) to assess the role of GDF15 in body weight regulation and food intake during pregnancy. We found that Gdf15-/- dams consumed a similar amount of food and gained comparable weight during the course of pregnancy compared with Gdf15+/+ dams. Insulin sensitivity on gestational day 16.5 was also similar between genotypes. In the postnatal period, litter size and survival rates were similar between genotypes. There was a modest reduction in birth weight of Gdf15-/- pups, but this difference was no longer evident from postnatal day 3.5 to 14.5. We observed no detectable differences in milk volume production or milk fat percentage. These data suggest that GDF15 is dispensable for changes in food intake, and body weight as well as insulin sensitivity during pregnancy in a mouse model.

The area postrema: a critical mediator of brain-body interactions

The dorsal vagal complex contains three structures: the area postrema, the nucleus tractus solitarii, and the dorsal motor nucleus of the vagus. These structures are tightly linked, both anatomically and functionally, and have important yet distinct roles in not only conveying peripheral bodily signals to the rest of the brain but in the generation of behavioral and physiological responses. Reports on the new discoveries in these structures were highlights of the symposium. In this outlook, we focus on the roles of the area postrema in mediating brain-body interactions and its potential utility as a therapeutic target, especially in cancer cachexia.

Hepatocyte-specific GDF15 overexpression improves high-fat diet-induced obesity and hepatic steatosis in mice via hepatic FGF21 induction

GDF15 and FGF21, stress-responsive cytokines primarily secreted from the liver, are promising therapeutic targets for metabolic dysfunction-associated steatotic liver disease (MASLD). However, the interaction between GDF15 and FGF21 remains unclear. We examined the effects of hepatocyte-specific GDF15 or FGF21 overexpression in high-fat diet (HFD)-fed mice for 8 weeks. Hydrodynamic injection of GDF15 or FGF21 sustained high circulating levels of GDF15 or FGF21, respectively, resulting in marked reductions in body weight, epididymal fat mass, insulin resistance, and hepatic steatosis. In addition, GDF15 treatment led to early reduction in body weight despite no change in food intake, indicating the role of GDF15 other than appetite loss. GDF15 treatment increased liver-derived serum FGF21 levels, whereas FGF21 treatment did not affect GDF15 expression. GDF15 promoted eIF2α phosphorylation and XBP1 splicing, leading to FGF21 induction. In murine AML12 hepatocytes treated with free fatty acids (FFAs), GDF15 overexpression upregulated Fgf21 mRNA levels and promoted eIF2α phosphorylation and XBP1 splicing. Overall, continuous exposure to excess FFAs resulted in a gradual increase of β-oxidation-derived reactive oxygen species and endoplasmic reticulum stress, suggesting that GDF15 enhanced this pathway and induced FGF21 expression. GDF15- and FGF21-related crosstalk is an important pathway for the treatment of MASLD.

Growth differentiation factor 15: Emerging role in liver diseases

Growth differentiation factor 15 (GDF15) is a cell stress-response cytokine within the transforming growth factor-β (TGFβ) superfamily. It is known to exert diverse effects on many metabolic pathways through its receptor GFRAL, which is expressed in the hindbrain, and transduces signals through the downstream receptor tyrosine kinase Ret. Since the liver is the core organ of metabolism, summarizing the functions of GDF15 is highly important. In this review, we assessed the relevant literature regarding the main metabolic, inflammatory, fibrogenic, tumorigenic and other effects of GDF15 on different liver diseases, including Metabolic dysfunction-associated steatotic liver disease(MASLD), alcohol and drug-induced liver injury, as well as autoimmune and viral hepatitis, with a particular focus on the pathogenesis of MASLD progression from hepatic steatosis to MASH, liver fibrosis and even hepatocellular carcinoma (HCC). Finally, we discuss the prospects of the clinical application potential of GDF15 along with its research and development progress. With better knowledge of GDF15, increasing in-depth research will lead to a new era in the field of liver diseases.

Bitter-tasting drugs tune GDF15 and GLP-1 expression via bitter taste or motilin receptors in the intestine of patients with obesity

OBJECTIVE

Growth differentiation factor 15 (GDF15), a stress related cytokine, was recently identified as a novel satiety signal acting via the GFRAL receptor located in the hindbrain. Bitter compounds are known to induce satiety via the release of glucagon-like peptide 1 (GLP-1) through activation of bitter taste receptors (TAS2Rs, 25 subtypes) on enteroendocrine cells in the gut. This study aimed to investigate whether and how bitter compounds induce a stress response in intestinal epithelial cells to affect GDF15 expression in patients with obesity, thereby facilitating satiety signaling from the gut.

METHODS

The acute effect of oral intake of the bitter-containing medication Plaquenil (hydroxychloroquine sulfate) on plasma GDF15 levels was evaluated in a placebo-controlled, double-blind, randomized, two-visit crossover study in healthy volunteers. Primary crypts isolated from the jejunal mucosa from patients with obesity were stimulated with vehicle or bitter compounds, and the effect on GDF15 expression was evaluated using RT-qPCR or ELISA. Immunofluorescence colocalization studies were performed between GDF15, epithelial cell type markers and TAS2Rs. The role of TAS2Rs was tested by 1) pretreatment with a TAS2R antagonist, GIV3727; 2) determining TAS2R4/43 polymorphisms that affect taste sensitivity to TAS2R4/43 agonists.

RESULTS

Acute intake of hydroxychloroquine sulfate increased GDF15 plasma levels, which correlated with reduced hunger scores and plasma ghrelin levels in healthy volunteers. This effect was mimicked in primary jejunal cultures from patients with obesity. GDF15 was expressed in enteroendocrine and goblet cells with higher expression levels in patients with obesity. Various bitter-tasting compounds (medicinal, plant extracts, bacterial) either increased or decreased GDF15 expression, with some also affecting GLP-1. The effect was mediated by specific intestinal TAS2R subtypes and the unfolded protein response pathway. The bitter-induced effect on GDF15/GLP-1 expression was influenced by the existence of TAS2R4 amino acid polymorphisms and TAS2R43 deletion polymorphisms that may predict patient's therapeutic responsiveness. However, the effect of the bitter-tasting antibiotic azithromycin on GDF15 release was mediated via the motilin receptor, possibly explaining some of its aversive side effects.

CONCLUSIONS

Bitter chemosensory and pharmacological receptors regulate the release of GDF15 from human gut epithelial cells and represent potential targets for modulating metabolic disorders or cachexia.

A detective story of intermittent fasting effect on immunity

Intermittent fasting (IF) refers to periodic fasting routines, that caloric intake is minimized not by meal portion size reduction but by intermittently eliminating ingestion of one or several consecutive meals. IF can instigate comprehensive and multifaceted alterations in energy metabolism, these metabolic channels may aboundingly function as primordial mechanisms that interface with the immune system, instigating intricate immune transformations. This review delivers a comprehensive understanding of IF, paying particular attention to its influence on the immune system, thus seeking to bridge these two research domains. We explore how IF effects lipid metabolism, hormonal levels, circadian rhythm, autophagy, oxidative stress, gut microbiota, and intestinal barrier integrity, and conjecture about the mechanisms orchestrating the intersect between these factors and the immune system. Moreover, the review includes research findings on the implications of IF on the immune system and patients burdened with autoimmune diseases.

Identification and characterization of human GDF15 knockouts

Growth differentiation factor 15 (GDF15) is a secreted protein that regulates food intake, body weight and stress responses in pre-clinical models1. The physiological function of GDF15 in humans remains unclear. Pharmacologically, GDF15 agonism in humans causes nausea without accompanying weight loss2, and GDF15 antagonism is being tested in clinical trials to treat cachexia and anorexia. Human genetics point to a role for GDF15 in hyperemesis gravidarum, but the safety or impact of complete GDF15 loss, particularly during pregnancy, is unknown3-7. Here we show the absence of an overt phenotype in human GDF15 loss-of-function carriers, including stop gains, frameshifts and the fully inactivating missense variant C211G3. These individuals were identified from 75,018 whole-exome/genome-sequenced participants in the Pakistan Genomic Resource8,9 and recall-by-genotype studies with family-based recruitment of variant carrier probands. We describe 8 homozygous ('knockouts') and 227 heterozygous carriers of loss-of-function alleles, including C211G. GDF15 knockouts range in age from 31 to 75 years, are fertile, have multiple children and show no consistent overt phenotypes, including metabolic dysfunction. Our data support the hypothesis that GDF15 is not required for fertility, healthy pregnancy, foetal development or survival into adulthood. These observations support the safety of therapeutics that block GDF15.

The brain-body energy conservation model of aging

Aging involves seemingly paradoxical changes in energy metabolism. Molecular damage accumulation increases cellular energy expenditure, yet whole-body energy expenditure remains stable or decreases with age. We resolve this apparent contradiction by positioning the brain as the mediator and broker in the organismal energy economy. As somatic tissues accumulate damage over time, costly intracellular stress responses are activated, causing aging or senescent cells to secrete cytokines that convey increased cellular energy demand (hypermetabolism) to the brain. To conserve energy in the face of a shrinking energy budget, the brain deploys energy conservation responses, which suppress low-priority processes, producing fatigue, physical inactivity, blunted sensory capacities, immune alterations and endocrine 'deficits'. We term this cascade the brain-body energy conservation (BEC) model of aging. The BEC outlines (1) the energetic cost of cellular aging, (2) how brain perception of senescence-associated hypermetabolism may drive the phenotypic manifestations of aging and (3) energetic principles underlying the modifiability of aging trajectories by stressors and geroscience interventions.

Increased serum carboxylesterase-1 levels are associated with metabolic dysfunction associated steatotic liver disease and metabolic syndrome in children with obesity

BACKGROUND

Carboxylesterase 1(CES1) is expressed mainly in the liver and adipose tissue and is highly hypothesized to play an essential role in metabolism. Our study aimed to investigate the association between CES1 and metabolic syndrome (MetS) and metabolic dysfunction associated steatotic liver disease (MASLD) in children with obesity in China.

METHODS

This study included 72 children with obesity aged 6-13years (including 25(35%) diagnosed as MetS and 36(50%) diagnosed as MASLD). All subjects were measured in anthropometry, serum level of biochemical parameters related to obesity, circumstance levels of insulin-like growth factor1, adipokines (adiponectin, leptin and growth differentiation factor 15) and CES1.

RESULTS

Higher serum CES1 level were found in the MetS group (P = 0.004) and the MASLD group (P < 0.001) of children with obesity. Serum CES1 levels were positively correlated with alanine aminotransferase, aspartate aminotransferase, triglyceride, cholesterol, low-density lipoprotein cholesterol, GDF15, Leptin and negatively correlated with high-density lipoprotein cholesterol, adiponectin and IGF1. We also found a multivariable logistic regression analysis of MASLD and MetS predicted by CES1 significantly (MASLD P < 0.01, MetS P < 0.05). The combination of CES1, sex, age and BMI Z-score showed a sensitivity and specificity of 92.7% for the identification of MASLD and 78.6% for the identification of MetS. The cutoff for CES1 of MASLD is 56.30 ng/mL and of MetS is 97.79 ng/mL.

CONCLUSIONS

CES1 is associated with an increasing risk of MetS and MASLD and can be established as a biomarker for metabolic syndrome and MASLD of children with obesity.

Aerobic exercise elevates perceived appetite but does not modify energy intake over a 3-day postexercise period: A pilot study

While a low degree of energy compensation is typically reported over the 24 h following a session of exercise, the prolonged impact of a bout of exercise on energy intake remains unclear. To overcome the challenge associated with accurately measuring energy intake in a free-living environment, this study employed the use of a meal replacement beverage to assess the 3 day impact of an exercise session on energy intake. In a randomized, crossover study, 14 participants (8 male, 6 female) completed two trials: (1) EX: 75 min exercise on a motorized treadmill (75% VO2peak); and (2) SED: 75 min sedentary control session. Each condition was followed by 3 days of exclusive ad libitum consumption of a meal replacement beverage. Appetite-regulating hormones, subjective appetite, energy intake, and energy expenditure were assessed. Exercise transiently suppressed the orexigenic hormone acyl-ghrelin (p < 0.05) and elevated the appetite-supressing hepatokine GDF-15 (p < 0.05). Despite these acute changes, overall perceived appetite was elevated over the 3 day assessment period with exercise (p < 0.05). No increase in energy intake or change in postexercise physical activity patterns were observed. One acute session of moderate to vigorous exercise is unlikely to affect short-term, three-day energy balance in healthy individuals.

Housing mice near vs. below thermoneutrality affects drug-induced weight loss but does not improve prediction of efficacy in humans

Evaluation of weight loss drugs is usually performed in diet-induced obese mice housed at ∼22°C. This is a cold stress that increases energy expenditure by ∼35% compared to thermoneutrality (∼30°C), which may overestimate drug-induced weight loss. We investigated five anti-obesity mechanisms that have been in clinical development, comparing weight loss in mice housed at 22°C vs. 30°C. Glucagon-like peptide-1 (GLP-1), human fibroblast growth factor 21 (hFGF21), and melanocortin-4 receptor (MC4R) agonist induced similar weight losses. Peptide YY elicited greater vehicle-subtracted weight loss at 30°C (7.2% vs. 1.4%), whereas growth differentiation factor 15 (GDF15) was more effective at 22°C (13% vs. 6%). Independent of ambient temperature, GLP-1 and hFGF21 prevented the reduction in metabolic rate caused by weight loss. There was no simple rule for a better prediction of human drug efficacy based on ambient temperature, but since humans live at thermoneutrality, drug testing using mice should include experiments near thermoneutrality.