The cytokine GDF15 signals through a population of brainstem cholecystokinin neurons to mediate anorectic signalling

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.

Comprehensive insights into emerging advances in the Neurobiology of anorexia

BACKGROUND

Anorexia is a complex eating disorder influenced by genetic, environmental, psychological, and socio-cultural factors. Research into its molecular mechanisms and neural circuits has deepened our understanding of its pathogenesis. Recent advances in neuroscience, molecular biology, and genetics have revealed key molecular and neural circuit mechanisms underlying anorexia.

AIM OF REVIEW

Clarify the peripheral and central molecular mechanisms regulating various types of anorexia, identify key cytokines and neural circuits, and propose new strategies for its treatment. Key scientific concepts of review: Anorexia animal models, including activity-induced, genetic mutation, and inflammation-induced types, are explored for their relevance to studying the disorder. Anorexic behavior is regulated by cytokines, hormones (like GDF15, GLP-1, and leptin), and neural circuits such as AgRP, serotonergic, dopaminergic, and glutamatergic pathways. Disruptions in these pathways, including GABAergic signaling in AgRP neurons and 5-HT2C and D2 receptors, contribute to anorexia. Potential therapies target neurotransmitter receptors, ghrelin receptors, and the GDF15-GFRAL pathway, offering insights for treating anorexia, immune responses, and obesity.

The interplay between hypothalamic and brainstem nuclei in homeostatic control of energy balance

Energy balance and body weight are tightly regulated by homeostatic and hedonic systems of the brain. These systems are ultimately finely tuned by hypothalamic and extrahypothalamic neurocircuitry that modulate feeding and the appetite signalling cascade. The hypothalamus has been extensively researched and its role in homeostatic regulation of energy balance is well established. Later on, evidence indicated that extrahypothalamic signalling also has a critical role in regulation of body mass across the lifespan. One of these brain regions was the brainstem and specifically the dorsal vagal complex (DVC), which comprises of the area postrema (AP), nucleus of the solitary tract (NTS) and dorsal motor complex of the vagus (DMV). These brain stem nuclei were shown to also finely tune feeding behaviour through catecholaminergic, glutamatergic, and GABAergic signals. Moreover, these nuclei also receive afferent signals from the viscera through the gut, as well as humoral input from the bloodstream. Therefore, these brain stem nuclei are deemed as the port of entry where initial appetite-related signals are first conveyed and then modulated to the forebrain to hypothalamic and extrahypothalamic regions such as the arcuate nucleus (ARC) and parabrachial nucleus (PBN). Understanding the intricate interactions and projections between hypothalamic and brainstem nuclei is instrumental to comprehend energy balance regulation as a whole and to potentially address metabolic conditions such as diabetes and obesity. Further research in this area may lead to the development of targeted pharmacological and lifestyle intervention strategies that could lead to mitigation of metabolic disorders and/or promote a healthier body mass across the life span.

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.

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.

Associations between prenatal distress, mitochondrial health, and gestational age: findings from two pregnancy studies in the USA and Turkey

Objective

This study examined associations between mitochondrial markers-circulating cell-free mitochondrial DNA (cf-mtDNA) and Growth Differentiation Factor-15 (GDF15)-with maternal distress and pregnancy outcomes.

Method

Participants were drawn from two pregnancy studies, EPI (N=187, USA) and BABIP (N=198, Turkey). Plasma cf-mtDNA and GDF15 levels were quantified using qPCR and ELISA assays.

Results

Plasma cf-mtDNA levels did not significantly vary across pregnancy, while plasma GDF15 levels increased from early to late pregnancy and decreased postpartum. Late 2nd trimester plasma GDF15 was negatively correlated with pre-pregnancy BMI (p=0.035) and gestational age (p=0.0048) at birth. Early 2nd trimester maternal distress was associated with lower cf-mtDNA (p<0.05) and a trend for lower GDF15. Higher pre-pregnancy BMI and late-pregnancy maternal distress were linked to smaller postpartum GDF15 declines in EPI (p<0.05).

Conclusion

This study reveals distinct plasma cf-mtDNA and GDF15 patterns during the perinatal period, linking mitochondrial markers to maternal distress and pregnancy outcomes.

A β-hydroxybutyrate shunt pathway generates anti-obesity ketone metabolites

β-Hydroxybutyrate (BHB) is an abundant ketone body. To date, all known pathways of BHB metabolism involve the interconversion of BHB and primary energy intermediates. Here, we identify a previously undescribed BHB secondary metabolic pathway via CNDP2-dependent enzymatic conjugation of BHB and free amino acids. This BHB shunt pathway generates a family of anti-obesity ketone metabolites, the BHB-amino acids. Genetic ablation of CNDP2 in mice eliminates tissue amino acid BHB-ylation activity and reduces BHB-amino acid levels. The most abundant BHB-amino acid, BHB-Phe, is a ketosis-inducible congener of Lac-Phe that activates hypothalamic and brainstem neurons and suppresses feeding. Conversely, CNDP2-KO mice exhibit increased food intake and body weight following exogenous ketone ester supplementation or a ketogenic diet. CNDP2-dependent amino acid BHB-ylation and BHB-amino acid metabolites are also conserved in humans. Therefore, enzymatic amino acid BHB-ylation defines a ketone shunt pathway and bioactive ketone metabolites linked to energy balance.

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.

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.

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.

The implicated role of GDF15 in gastrointestinal cancer

BACKGROUND

Growth differentiation factor 15 (GDF15), a stress-responsive cytokine from transforming growth factor superfamily, is highly expressed in mammalian tissues, including pancreas, stomach and intestine under pathological conditions. In particular, elevated levels of GDF15 might play an important role in the development and progression of various gastrointestinal cancers (GCs), suggesting its potential as a promising target for disease prediction and treatment.

METHODS

In this review, systematic reviews addressing the role of GDF15 in GCs were updated, along with the latest clinical trials focussing on the GDF15-associated digestive malignancies.

RESULTS

The multiple cellular pathways through which GDF15 is involved in the regulation of physiological and pathological conditions were first summarized. Then, GDF15 was also established as a valuable clinical index, functioning as a predictive marker in diverse GCs. Notably, latest clinical treatments targeting GDF15 were also highlighted, demonstrating its promising potential in mitigating and curing digestive malignancies.

CONCLUSIONS

This review unveils the pivotal roles of GDF15 and its potential as a promising target in the pathogenesis of GCs, which may provide insightful directions for future investigations.

The effects of acute aerobic exercise on appetite-regulating parameters and energy intake in males with obesity

Objective

To investigate the effects of moderate-intensity aerobic exercise on appetite control parameters, appetite perceptions, and energy intake in sedentary males with obesity.

Design

Eleven males with obesity (body fat percentage 36.5 ± 2.5%, body mass index 35.3 ± 4.2 kg/m2, V̇O2peak 29 ± 3.1 mL·kg-1·min-1) completed two experimental sessions: (1) no exercise (CTRL) and (2) 60 min of moderate-intensity cycling exercise at 60% V̇O2peak (MICT) in a crossover design. Blood analysis included growth differentiation factor 15 (GDF-15), total ghrelin, peptide tyrosine tyrosine3-36 (PYY3-36), total glucagon-like peptide-1 (GLP-1), insulin, and glucose, as well as subjective appetite perceptions were measured in specific intervals. A standard breakfast at 0 h and an ad libitum meal postexercise was provided.

Result

GDF-15 (95% confidence interval [CI]: [2.48-27.28] ng/L, p = 0.021) increased immediately following MICT compared to CTRL. However, there were no differences for PYY3-36 (p = 0.480,η p 2 = 0.025 ), total ghrelin (p = 0.646,η p 2 = 0.011 ), and total GLP-1 (p = 0.451,η p 2 = 0.029 ) between sessions. Appetite perceptions (95% CI: [(-20.38)-(-6.16)] mm, p = 0.001) were suppressed following MICT though energy intake was not different between the sessions (95% CI: [(-1904.9)-928.1] kJ, p = 0.480).

Conclusion

Sixty minutes of MICT increased GDF-15 while suppressing appetite perceptions in individuals with obesity. There was no energy compensation postexercise.

Neutralizing antibody against GDF15 for treatment of cancer-associated cachexia

GDF15 (growth differentiation factor 15), also known as macrophage inhibitory cytokine 1 (MIC-1), is a circulating protein involved in the regulation of energy balance and weight control. Elevated levels of GDF15 have been associated with cachexia and reduced survival rates in cancer patients. Through the activation of the GFRAL (GDNF-family receptor α-like)-RET (Rearranged during Transfection) signaling pathway, GDF15 can induce weight loss, making it a potential target for treating cachexia. Currently, there are no approved antibody drugs specifically targeting GDF15 for cancer cachexia treatment. However, efforts have been made to develop antibody-based therapeutics against this emerging target. In this study, we generated a monoclonal antibody KY-NAb-GDF15 against GDF15 that effectively blocks downstream signaling mediated by GFRAL upon stimulation by GDF15. This antibody demonstrates robust neutralizing activity and exhibits high binding specificity. Importantly, our findings indicate that this antibody holds promise in alleviating cancer-induced cachexia and mitigating chemotherapy-induced weight loss, thereby offering significant therapeutic potential for managing cancer cachexia.

Regulation of Energy and Glucose Homeostasis by the Nucleus of the Solitary Tract and the Area Postrema

The central nervous system regulates feeding, weight and glucose homeostasis in rodents and humans, but the site-specific mechanisms remain unclear. The dorsal vagal complex in the brainstem that contains the nucleus of the solitary tract (NTS) and area postrema (AP) emerges as a regulatory center that impacts energy and glucose balance by monitoring hormonal and nutrient changes. However, the specific mechanistic metabolic roles of the NTS and AP remain elusive. This mini-review highlights methods to study their distinct roles and recent findings on their metabolic differences and similarities of growth differentiation factor 15 (GDF15) action and glucose sensing in the NTS and AP. In summary, future research aims to characterize hormonal and glucose sensing mechanisms in the AP and/or NTS carries potential to unveil novel targets that lower weight and glucose levels in obesity and diabetes.

Growth differentiation factor 15 is not modified after weight loss induced by liraglutide in South Asians and Europids with type 2 diabetes mellitus

Glucagon-like peptide-1 receptor (GLP-1R) agonists induce weight loss in patients with type 2 diabetes mellitus (T2DM), but the underlying mechanism is unclear. Recently, the mechanism by which metformin induces weight loss could be explained by an increase in growth differentiation factor 15 (GDF15), which suppresses appetite. Therefore, we aimed to investigate whether the GLP-1R agonist liraglutide modifies plasma GDF15 levels in patients with T2DM. GDF15 levels were measured in plasma samples obtained from Dutch Europids and Dutch South Asians with T2DM before and after 26 weeks of treatment with daily liraglutide (n = 44) or placebo (n = 50) added to standard care. At baseline, circulating GDF15 levels did not differ between South Asians and Europids with T2DM. Treatment with liraglutide, compared to placebo, decreased body weight, but did not modify plasma GDF15 levels in all patients, or when data were split by ethnicity. Also, the change in plasma GDF15 levels after treatment with liraglutide did not correlate with changes in body weight or HbA1c levels. In addition, the dose of metformin used did not correlate with baseline plasma GDF15 levels. Compared to placebo, liraglutide treatment for 26 weeks does not modify plasma GDF15 levels in Dutch Europid or South Asian patients with T2DM. Thus, the weight loss induced by liraglutide is likely explained by other mechanisms beyond the GDF15 pathway. HIGHLIGHTS: What is the central question of this study? Growth differentiation factor 15 (GDF15) suppresses appetite and is increased by metformin: does the GLP-1R agonist liraglutide modify plasma GDF15 levels in patients with type 2 diabetes mellitus (T2DM)? What is the main finding and its importance? Plasma GDF15 levels did not differ between South Asians and Europids with T2DM and were not modified by 26 weeks of liraglutide in either ethnicity. Moreover, there was no correlation between the changes in plasma GDF15 levels and dosage of metformin administered, changes in body weight or HbA1c levels. The appetite-suppressing effect of liraglutide is likely exerted via pathways other than GDF15.

Serum growth differentiation factor 15 as a biomarker for malnutrition in patients with acute exacerbation of chronic obstructive pulmonary disease

Background

Chronic obstructive pulmonary disease (COPD) is a common respiratory disease that often coexists with malnutrition during acute exacerbation (AECOPD) and significantly affects the prognosis. Previous studies have shown that growth differentiation factor 15 (GDF15) levels promote appetite suppression, weight loss, and muscle weakness, and are markedly high in peripheral blood following inflammatory stimulation. However, it is still unknown whether serum GDF15 levels can be used to predict malnutrition in patients with AECOPD.

Methods

A total of 142 patients admitted to the Department of Respiratory Medicine at Anshun People's Hospital between December 2022 and August 2023 were selected for this study. The participants were divided into two groups: malnutrition group (n = 44) and non-malnutrition group (n = 98) based on a body mass index (BMI) < 18.5 kg/m2, according to the Global Leadership Initiative on Malnutrition (GLIM) criteria. Serum GDF15 levels were measured using the enzyme-linked immunosorbent assay (ELISA) and compared between the two groups. Spearman correlation analysis was used to examine the association between serum GDF15 levels, baseline data, and clinical indicators. Binary logistic regression was used to identify the independent risk factors for AECOPD combined with malnutrition. The predictive value of serum GDF15, albumin (ALB), and a combination of these was evaluated to identify malnutrition in patients with AECOPD using a receiver operating characteristic (ROC) curve.

Results

Serum GDF15 levels in patients with malnutrition and AECOPD were significantly higher than those in patients without malnutrition, whereas the serum ALB levels were significantly lower than those in patients without malnutrition (p < 0.001). Moreover, serum GDF15 levels were negatively correlated with BMI (r = -0.562, p < 0.001), mid-arm circumference (r = -0.505, p < 0.001), calf circumference (r = -0.490, p < 0.001), total protein (r = -0.486, p < 0.001), ALB (r = -0.445, p < 0.001), and prognostic nutritional index (r = -0.276, p = 0.001), and positively correlated with C-reactive protein (r = 0.318, p < 0.001), COPD assessment test score (r = 0.286, p = 0.001), modified medical research council classification (r = 0.310, p < 0.001), and global initiative for chronic obstructive pulmonary disease grade (r = 0.177, p = 0.035). Furthermore, serum GDF15 levels were an independent risk factor for malnutrition in patients with AECOPD (OR = 1.010, 95% CI, 1.003∼1.016). The optimal cut-off value of serum GDF15 level was 1,092.885 pg/mL, with a sensitivity of 65.90% and a specificity of 89.80%, while the serum ALB level was 36.15 g/L, with a sensitivity of 86.40% and a specificity of 65.00%, as well as a combined sensitivity of 84.10% and a specificity of 73.90%. Serum GDF15 and serum ALB levels had a good predictive ability (AUC = 0.856, AUC = 0.887), and the ROC revealed a greater combined prediction value for the two (AUC = 0.935).

Conclusion

Serum GDF15 levels could be used as a potential biomarker in the prediction of malnutrition in patients with AECOPD, offering a guidance for future clinical evaluation of malnutrition.

Identification and utility exploration of a highly potent and long-acting bullfrog GLP-1 analogue in GLP-1 and amylin combination therapy

This study assesses the efficacy of an innovative therapeutic approach that combines GLP-1 and amylin analogues for weight reduction. Focusing on GLP-1 analogues from bullfrog (Rana catesbeiana), we designed ten bGLP-1 analogues with various modifications. Among them, bGLP-10 showed high potency in binding and activating GLP-1 receptors, with superior albumin affinity. In diet-induced obesity (DIO) mice fed a high-fat diet, bGLP-10 demonstrated significant superiority over semaglutide in reducing blood sugar and food intake at a dose of 10 nmol/kg (P < 0.001). Notably, in a chronic study involving DIO mice, the combination of bGLP-10 with the amylin analogue cagrilintide led to a more substantial weight loss (-38.4%, P < 0.001) compared to either the semaglutide-cagrilintide combination (-23.0%) or cagrilintide (-5.7%), bGLP-10 (-16.1%), and semaglutide (-10.9%) alone. Furthermore, the bGLP-10 and cagrilintide combination exhibited superior glucose control and liver lipid management compared to the semaglutide-cagrilintide combination (P < 0.001). These results highlight bGLP-10's potential in GLP-1 and amylin-based therapies and suggest exploring more GLP-1 analogues from natural sources for anti-obesity and anti-diabetic treatments.

Stress relief of chemo illness

New studies (Tang et al. 2024. J. Exp. Med.https://doi.org/10.1084/jem.20231395) describe a liver stress pathway that is activated by certain chemotherapeutic drugs, which in turn induces a peptide hormone which partially mediates the lower food intake and body weight loss during chemotherapy treatment.

A new experimental rat model of nocebo-related nausea involving double mechanisms of observational learning and conditioning

AIM

The nocebo effect, such as nausea and vomiting, is one of the major reasons patients discontinue therapy. The underlying mechanisms remain unknown due to a lack of reliable experimental models. The goal of this study was to develop a new animal model of nocebo-related nausea by combining observational learning and Pavlovian conditioning paradigms.

METHODS

Male Sprague-Dawley rats with nitroglycerin-induced migraine were given 0.9% saline (a placebo) or LiCl (a nausea inducer) following headache relief, according to different paradigms.

RESULTS

Both strategies provoked nocebo nausea responses, with the conditioning paradigm having a greater induction impact. The superposition of two mechanisms led to a further increase in nausea responses. A preliminary investigation of the underlying mechanism revealed clearly raised peripheral and central cholecystokinin (CCK) levels, as well as specific changes in the 5-hydroxytryptamine and cannabinoid systems. Brain networks related to emotion, cognition, and visceral sense expressed higher c-Fos-positive neurons, including the anterior cingulate cortex (ACC), insula, basolateral amygdala (BLA), thalamic paraventricular nucleus (PVT), hypothalamic paraventricular nucleus (PVN), nucleus tractus solitarius (NTS), periaqueductal gray (PAG), and dorsal raphe nucleus-dorsal part (DRD). We also found that nausea expectances in the model could last for at least 12 days.

CONCLUSION

The present study provides a useful experimental model of nocebo nausea that might be used to develop potential molecular pathways and therapeutic strategies for nocebo.

Research Progress on the Role and Mechanism of GDF15 in Body Weight Regulation

BACKGROUND

Growth differentiation factor-15 (GDF15) is a member of the growth differentiation factor subfamily in the transforming growth factor beta superfamily. GDF15 has multiple functions and can regulate biological processes. High levels of GDF15 in the circulation can affect metabolic processes. Studies have shown that GDF15 is associated with changes in body weight.

SUMMARY

This review reviews the current knowledge on the relationship between GDF15 and body weight change, focusing on the role and mechanism of GDF15 in body weight regulation. GDF15 plays an important role in reducing food intake, improving insulin resistance, and breaking down fat, suggesting that GDF15 has an important regulatory effect on body weight. The mechanism by which GDF15 causes reduced food intake may be related to changes in food preference, delayed gastric emptying, and conditioned taste aversion. GDF15 can combat insulin resistance induced by inflammation or protect β cell from apoptosis. GDF15 probably promotes lipolysis through a brain-somatic tissue circuit. Several factors and related signaling pathways are also mentioned that can contribute to the effects of GDF15 on reducing weight.

KEY MESSAGE

GDF15 plays an important role in weight regulation and provides a new direction for the treatment of obesity. Its effects on resisting obesity are of great significance to inhibiting the progression of metabolic diseases. It is expected to become a new target for regulating body weight, improving obesity, and treating metabolic diseases such as diabetes.

Engineering a potent and long-acting GLP-1/Y2 receptor dual agonist as a multi-agonist therapy for diabetes and obesity

Novel dual agonists for the glucagon-like peptide-1 (GLP-1) and Y2 receptor hold the potential for enhanced efficacy over GLP-1 receptor (GLP-1R) agonists in treating obesity and diabetes. In this study, we aimed to improve the stability and increase the drug development success rate of our previously identified GLP-1/Y2 receptor dual agonist, 6q. To achieve this, we first optimized the structure of the linker within 6q. Additionally, we explored various fatty acid albumin binders to further enhance the stability of 6q. These binders were mainly selected from approved or clinically developed GLP-1R agonists or GLP-1-based multi-agonists. Through this process, we were able to identify a lead peptide, xGLP/PYY-6, that exhibited comparable in vitro potency toward the GLP-1 and Y2 receptors as 6q but with significantly improved stability compared to 6q. In Kunming and DIO mice, xGLP/PYY-6 showed a comparable hypoglycemic effect to semaglutide, and a significantly better effect on inhibiting food intake than semaglutide. In a chronic study in DIO mice, xGLP/PYY-6 exhibited significant metabolic benefits, as reflected by regulation of lipid levels, improved glucose tolerance, weight loss, decreased hepatocellular vacuolation, and the reversal of steatosis effects caused by xGLP/PYY-6. These results indicate the potential of developing xGLP/PYY-6 as an antiobesity, lipid regulation, antisteatotic, and antidiabetic agent.

Chemotherapy-induced gastrointestinal toxicity: Pathogenesis and current management

Chemotherapy is the most common treatment for malignant tumors. However, chemotherapy-induced gastrointestinal toxicity (CIGT) has been a major concern for cancer patients, which reduces their quality of life and leads to treatment intolerance and even cessation. Nevertheless, prevention and treatment for CIGT are challenging, due to the prevalence and complexity of the condition. Chemotherapeutic drugs directly damage gastrointestinal mucosa to induce CIGT, including nausea, vomiting, anorexia, gastrointestinal mucositis, and diarrhea, etc. The pathogenesis of CIGT involves multiple factors, such as gut microbiota disorders, inflammatory responses and abnormal neurotransmitter levels, that synergistically contribute to its occurrence and development. In particular, the dysbiosis of gut microbiota is usually linked to abnormal immune responses that increases inflammatory cytokines' expression, which is a common characteristic of many types of CIGT. Chemotherapy-induced intestinal neurotoxicity is also a vital concern in CIGT. Currently, modern medicine is the dominant treatment of CIGT, however, traditional Chinese medicine (TCM) has attracted interest as a complementary and alternative therapy that can greatly alleviate CIGT. Accordingly, this review aimed to comprehensively summarize the pathogenesis and current management of CIGT using PubMed and Google Scholar databases, and proposed that future research for CIGT should focus on the gut microbiota, intestinal neurotoxicity, and promising TCM therapies, which may help to develop more effective interventions and optimize managements of CIGT.

Growth differentiation factor 15 (GDF-15) in endocrinology

Human growth differentiation factor 15 (GDF-15) is a widely distributed protein that has shown to play multiple roles in both physiological and pathological conditions. In healthy individuals, GDF-15 is mainly expressed in the placenta, followed by the prostate, although low levels of expression have also been detected in different organs. GDF-15 acts through a recently identified receptor called glial-derived neurotrophic factor (GDNF) receptor alpha-like (GFRAL) which signals through the rearranged during transfection (RET) tyrosine kinase receptor. The effects of GDF-15 are pleiotropic and include appetite regulation, and actions on metabolism, pregnancy, cell survival, immune response, and inflammation. GDF-15 also plays different roles in the pathophysiology of cardiovascular disease, autoimmunity, cancer-associated anorexia/cachexia, and diabetes. In recent years, several studies have reported a link between GDF-15 and the endocrine system. In this review, we up-date and summarize the relevant investigations of the relationships between GDF-15 and different endocrine conditions. We also assess the potential pathogenic role and potential therapeutic applications of GDF-15 in the field of endocrinology.

Screening study of anti-emetics to improve GDF15-induced malaise and anorexia: Implications for emesis control

Considerable preclinical and clinical attention has focused on the food intake and body weight suppressive effects of growth differentiation factor 15 (GDF15) and its elevated blood levels as a consequence of disease states and disease treatment therapeutics. We have previously reported that exogenous administration of GDF15 induces anorexia through nausea and emesis in multiple species. Importantly, GDF15 signaling as a meditator of chemotherapy-induced anorexia and emesis has recently been demonstrated in both murine and nonhuman primate models. The mechanism, however, by which GDF15 induces malaise and the utility of existing therapeutic targets to counteract its effects remain largely unknown. Using a dose of GDF15 that mimics stimulated levels following chemotherapy administration and reliably induces malaise, we sought to screen anti-emetics that represent distinct pharmacotherapeutic classes hypothesized to reduce GDF15-induced effects in rats. Strikingly, our results showed that none of the tested compounds were effective at preventing GDF15-induced malaise. These results illustrate the complexity of GDF15 signaling mechanism and may have important implications for medical conditions characterized by elevated GDF15 levels and incomplete symptom control, such as chemotherapy-induced nausea and vomiting.

Metformin triggers a kidney GDF15-dependent area postrema axis to regulate food intake and body weight

Metformin, the most widely prescribed medication for obesity-associated type 2 diabetes (T2D), lowers plasma glucose levels, food intake, and body weight in rodents and humans, but the mechanistic site(s) of action remain elusive. Metformin increases plasma growth/differentiation factor 15 (GDF15) levels to regulate energy balance, while GDF15 administration activates GDNF family receptor α-like (GFRAL) that is highly expressed in the area postrema (AP) and the nucleus of the solitary tract (NTS) of the hindbrain to lower food intake and body weight. However, the tissue-specific contribution of plasma GDF15 levels after metformin treatment is still under debate. Here, we found that metformin increased plasma GDF15 levels in high-fat (HF) fed male rats through the upregulation of GDF15 synthesis in the kidney. Importantly, the kidney-specific knockdown of GDF15 expression as well as the AP-specific knockdown of GFRAL expression negated the ability of metformin to lower food intake and body weight gain. Taken together, we unveil the kidney as a target of metformin to regulate energy homeostasis through a kidney GDF15-dependent AP axis.

Discovery, development, and clinical proof of mechanism of LY3463251, a long-acting GDF15 receptor agonist

GDF15 and its receptor GFRAL/RET form a non-homeostatic system that regulates food intake and body weight in preclinical species. Here, we describe a GDF15 analog, LY3463251, a potent agonist at the GFRAL/RET receptor with prolonged pharmacokinetics. In rodents and obese non-human primates, LY3463251 decreased food intake and body weight with no signs of malaise or emesis. In a first-in-human study in healthy participants, single subcutaneous LY3463251 injections showed a safety and pharmacokinetic profile supporting further clinical development with dose-dependent nausea and emesis in a subset of individuals. A subsequent 12-week multiple ascending dose study in overweight and obese participants showed that LY3463251 induced significant decreases in food intake and appetite scores associated with modest body weight reduction independent of nausea and emesis (clinicaltrials.gov: NCT03764774). These observations demonstrate that agonism of the GFRAL/RET system can modulate energy balance in humans, though the decrease in body weight is surprisingly modest, suggesting challenges in leveraging the GDF15 system for clinical weight-loss applications.

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.

Immune sensing of food allergens promotes aversive behaviour

In addition to its canonical function in protecting from pathogens, the immune system can also promote behavioural alterations ^1â€"3 . The scope and mechanisms of behavioural modifications by the immune system are not yet well understood. Using a mouse food allergy model, here we show that allergic sensitization drives antigen-specific behavioural aversion. Allergen ingestion activates brain areas involved in the response to aversive stimuli, including the nucleus of tractus solitarius, parabrachial nucleus, and central amygdala. Food aversion requires IgE antibodies and mast cells but precedes the development of gut allergic inflammation. The ability of allergen-specific IgE and mast cells to promote aversion requires leukotrienes and growth and differentiation factor 15 (GDF15). In addition to allergen-induced aversion, we find that lipopolysaccharide-induced inflammation also resulted in IgE-dependent aversive behaviour. These findings thus point to antigen-specific behavioural modifications that likely evolved to promote niche selection to avoid unfavourable environments.

Mitochondrial stress-induced GFRAL signaling controls diurnal food intake and anxiety-like behavior

Growth differentiation factor 15 (GDF15) is a mitochondrial stress-induced cytokine that modulates energy balance in an endocrine manner. However, the importance of its brainstem-restricted receptor GDNF family receptor alpha-like (GFRAL) to mediate endocrine GDF15 signaling to the brain upon mitochondrial dysfunction is still unknown. Using a mouse model with muscle-specific mitochondrial dysfunction, we here show that GFRAL is required for activation of systemic energy metabolism via daytime-restricted anorexia but not responsible for muscle wasting. We further find that muscle mitochondrial stress response involves a GFRAL-dependent induction of hypothalamic corticotropin-releasing hormone, without elevated corticosterone levels. Finally, we identify that GFRAL signaling governs an anxiety-like behavior in male mice with muscle mitochondrial dysfunction, with females showing a less robust GFRAL-dependent anxiety-like phenotype. Together, we here provide novel evidence of a mitochondrial stress-induced muscle–brain crosstalk via the GDF15-GFRAL axis to modulate food intake and anxiogenic behavior.

The GDF15-GFRAL pathway is dispensable for the effects of metformin on energy balance

Metformin is a blood-glucose-lowering medication with physiological effects that extend beyond its anti-diabetic indication. Recently, it was reported that metformin lowers body weight via induction of growth differentiation factor 15 (GDF15), which suppresses food intake by binding to the GDNF family receptor α-like (GFRAL) in the hindbrain. Here, we corroborate that metformin increases circulating GDF15 in mice and humans, but we fail to confirm previous reports that the GDF15-GFRAL pathway is necessary for the weight-lowering effects of metformin. Instead, our studies in wild-type, GDF15 knockout, and GFRAL knockout mice suggest that the GDF15-GFRAL pathway is dispensable for the effects of metformin on energy balance. The data presented here question whether metformin is a sufficiently strong stimulator of GDF15 to drive anorexia and weight loss and emphasize that additional work is needed to untangle the relationship among metformin, GDF15, and energy balance.

Circulating total and intact GDF-15 levels are not altered in response to weight loss induced by liraglutide or lorcaserin treatment in humans with obesity

BACKGROUND

Growth differentiation factor 15 (GDF-15) is a stress-response cytokine proposed to be associated with body weight regulation.

AIMS

The primary aim was to investigate changes of circulating intact GDF-15 (wildtype, non-carrier of the rs1058587 polymorphism coding for the H2O2D mutation) and total GDF-15 (measured irrespective of the mutation) in response to liraglutide (GLP-1 receptor agonist) and lorcaserin (5-HT2C receptor agonist), two pharmacologic agents that induce food intake and weight reduction. In addition, we perform exploratory correlations of total and intact GDF-15 with clinical, hormonal and metabolo-lipidomic parameters in humans with obesity.

MATERIALS AND METHODS

We utilized two studies: 1) Study 1, a randomized, double-blinded, cross-over trial of liraglutide and placebo administration for 5 weeks in subjects with obesity (n = 20; BMI = 35.6 ± 5.9 kg/m2), in escalating doses starting at 0.6 mg/day on week 1 and increased every week, up to the highest dose of 3.0 mg/day during week 5. b) Study 2, a randomized, double-blinded trial of lorcaserin 10 mg twice daily, or placebo for 12-weeks in humans with obesity (n = 34 BMI = 37.4 ± 6.1 kg/m2). Total and intact GDF-15 levels were measured with novel enzyme-linked immunosorbent assays and the metabolomics and lipidomics analysis was performed with nuclear magnetic resonance spectroscopy.

RESULTS

Total and intact GDF-15 were positively correlated with diabetes risk index and trimethylamine N-oxide and negatively with eGFR. Despite significant changes in body weight, total and intact GDF-15 were not altered in response to liraglutide or lorcaserin treatment in subjects with obesity.

CONCLUSIONS

Total and intact GDF-15 levels are not altered in response to liraglutide or lorcaserin therapy and are thus not directly involved in the metabolic feedback loop pathways downstream of GLP1 or 5-HT2C receptor agonists. Since neither total nor intact GDF-15 levels were altered in response to weight loss, future studies are needed to elucidate the pathways activated by GDF-15 in humans and its role, if any, in body weight regulation and energy homeostasis.

Hindbrain circuits in the control of eating behaviour and energy balance

Body weight and adiposity represent biologically controlled parameters that are influenced by a combination of genetic, developmental and environmental variables. Although the hypothalamus plays a crucial role in matching caloric intake with energy expenditure to achieve a stable body weight, it is now recognized that neuronal circuits in the hindbrain not only serve to produce nausea and to terminate feeding in response to food consumption or during pathological states, but also contribute to the long-term control of body weight. Additionally, recent work has identified hindbrain neurons that are capable of suppressing food intake without producing aversive responses like those associated with nausea. Here we review recent advances in our understanding of the hindbrain neurons that control feeding, particularly those located in the area postrema and the nucleus tractus solitarius. We frame this information in the context of new atlases of hindbrain neuronal populations and develop a model of the hindbrain circuits that control food intake and energy balance, suggesting important areas for additional research.

GIPR Agonism Inhibits PYY-Induced Nausea-Like Behavior

The induction of nausea and emesis is a major barrier to maximizing the weight loss profile of obesity medications, and therefore, identifying mechanisms that improve tolerability could result in added therapeutic benefit. The development of peptide YY (PYY)-based approaches to treat obesity are no exception, as PYY receptor agonism is often accompanied by nausea and vomiting. Here, we sought to determine whether glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) agonism reduces PYY-induced nausea-like behavior in mice. We found that central and peripheral administration of a GIPR agonist reduced conditioned taste avoidance (CTA) without affecting hypophagia mediated by a PYY analog. The receptors for GIP and PYY (Gipr and Npy2r) were found to be expressed by the same neurons in the area postrema (AP), a brainstem nucleus involved in detecting aversive stimuli. Peripheral administration of a GIPR agonist induced neuronal activation (cFos) in the AP. Further, whole-brain cFos analyses indicated that PYY-induced CTA was associated with augmented neuronal activity in the parabrachial nucleus (PBN), a brainstem nucleus that relays aversive/emetic signals to brain regions that control feeding behavior. Importantly, GIPR agonism reduced PYY-mediated neuronal activity in the PBN, providing a potential mechanistic explanation for how GIPR agonist treatment reduces PYY-induced nausea-like behavior. Together, the results of our study indicate a novel mechanism by which GIP-based therapeutics may have benefit in improving the tolerability of weight loss agents.

Single-cell transcriptomic analysis of neuroepithelial cells and other cell types of the gills of zebrafish (Danio rerio) exposed to hypoxia

The fish gill is a multifunctional organ involved in numerous physiological processes, such as gas exchange and sensing of hypoxia by respiratory chemoreceptors, called neuroepithelial cells (NECs). Many studies have focused on zebrafish (Danio rerio) to investigate the structure, function and development of the gills, yet the transcriptomic profile of most gill cells remains obscure. We present the results of a comprehensive transcriptomic analysis of the gills of zebrafish using single-cell RNA sequencing (scRNA‐seq). Gill cells from ETvmat2:EGFP zebrafish were individually labelled before scRNA‐seq library construction using 10× Genomics Chromium technology. 12,819 cells were sequenced with an average depth of over 27,000 reads per cell. We identified a median of 485 genes per cell and 16 cell clusters, including NECs, neurons, pavement cells, endothelial cells and mitochondrion-rich cells. The identity of NECs was confirmed by expression of slc18a2, encoding the vesicular monoamine transporter, Vmat2. Highly differentially-expressed genes in NECs included tph1a, encoding tryptophan hydroxylase, sv2 (synaptic vesicle protein), and proteins implicated in O₂ sensing (ndufa4l2a, cox8al and epas1a). In addition, NECs and neurons expressed genes encoding transmembrane receptors for serotonergic, cholinergic or dopaminergic neurotransmission. Differential expression analysis showed a clear shift in the transcriptome of NECs following 14 days of acclimation to hypoxia. NECs in the hypoxia group showed high expression of genes involved in cell cycle control and proliferation. The present article provides a complete cell atlas for the zebrafish gill and serves as a platform for future studies investigating the molecular biology and physiology of this organ.

Growth differentiation factor 15 (GDF15) and semaglutide inhibit food intake and body weight through largely distinct, additive mechanisms

AIMS

To evaluate whether the potent hypophagic and weight-suppressive effects of growth differentiation factor-15 (GDF15) and semaglutide combined would be a more efficacious antiobesity treatment than either treatment alone by examining whether the neural and behavioural mechanisms contributing to their anorectic effects were common or disparate.

MATERIALS/METHODS

Three mechanisms were investigated to determine how GDF15 and semaglutide induce anorexia: the potentiation of the intake suppression by gastrointestinal satiation signals; the reduction in motivation to feed; and the induction of visceral malaise. We then compared the effects of short-term, combined GDF15 and semaglutide treatment on weight loss to the individual treatments. Rat pharmaco-behavioural experiments assessed whether GDF15 or semaglutide added to the satiating effects of orally gavaged food and exogenous cholecystokinin (CCK). A progressive ratio operant paradigm was used to examine whether GDF15 or semaglutide reduced feeding motivation. Pica behaviour (ie, kaolin intake) and conditioned affective food aversion testing were used to evaluate visceral malaise. Additionally, fibre photometry studies were conducted in agouti-related protein (AgRP)-Cre mice to examine whether GDF15 or semaglutide, alone or in combination with CCK, modulate calcium signalling in hypothalamic AgRP neurons.

RESULTS

Semaglutide reduced food intake by amplifying the feeding-inhibitory effect of CCK or ingested food, inhibited the activity of AgRP neurons when combined with CCK, reduced feeding motivation and induced malaise. GDF15 induced visceral malaise but, strikingly, did not affect feeding motivation, the satiating effect of ingested food or CCK signal processing. Combined GDF15 and semaglutide treatment produced greater food intake and body weight suppression than did either treatment alone, without enhancing malaise.

CONCLUSIONS

GDF15 and semaglutide reduce food intake and body weight through largely distinct processes that produce greater weight loss and feeding suppression when combined.

Liujunzi Decoction ameliorated cisplatin-induced anorexia by inhibiting the JAK-STAT signaling pathway and coordinating anorexigenic and orexigenic neuropeptides in rats

ETHNOPHARMACOLOGICAL RELEVANCE

As a traditional Chinese formula, Liujunzi Decoction (LJZD) originated from the Yi Xue Zheng Zhuan, and has a promising effect in treating chemotherapy-induced anorexia (CIA).

AIM OF THE STUDY

The present study aims to investigate whether LJZD acts on interleukin-6 (IL-6)/leptin mediated janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway that regulates hypothalamus anorexigenic and orexigenic peptides to ameliorate CIA, and also elucidates the potential mechanism by metabolomic analysis.

MATERIALS AND METHODS

Network pharmacology analyses were conducted to screen out potential targets and pathways. The CIA rat model was established via an intraperitoneal injection of cisplatin. The histological changes of gastric antrum, liver and ileum were observed by HE staining. The serum levels of leptin, ghrelin, IL-6 and growth differentiation factor 15 (GDF15) were measured by ELISA. The JAK1/2 and STAT levels in gastric antrum and hypothalamus were detected by Western blot. The transcriptions of gastric antrum and hypothalamus IL-6R mRNA, and hypothalamus cocaine- and amphetamine-regulated transcript (CART), pro-opiomelanocortin (POMC), thyrotropin-releasing hormone (TRH), upregulated orexigenic peptides neuropeptide Y (NPY), and agouti-related protein (AGRP) mRNA were assessed by RT-qPCR. The blood samples of control, model and high dose LJZD groups were analyzed by metabolomic.

RESULTS

Network pharmacology highlighted the IL-6/leptin mediated JAK-STAT signaling pathway, which regulated downstream anorexigenic and orexigenic peptides in hypothalamus. LJZD ameliorated CIA via stimulating food intake and water consumption in rats. Cisplatin-induced gastric antrum, liver, ileum injuries were ameliorated, serum leptin level reduction was elevated, and ghrelin, IL-6, GDF15 level increases were decreased after LJZD treatments. In gastric antrum and hypothalamus, LJZD inhibited cisplatin-induced activation of JAK-STAT signaling pathway, downregulated the transcriptions of downstream anorexigenic peptides CART, POMC, TRH, and upregulated orexigenic peptides NPY, AGRP in hypothalamus. Importantly, the effect of LJZD in treating CIA might partly relate to the improvements of 23 abnormal metabolites.

CONCLUSION

This study implies that inhibiting JAK-STAT signaling pathway, regulating the expressions of anorexigenic and orexigenic peptides, and mediating various metabolic pathways might be potential mechanisms of LJZD's effect against CIA.

GDF15, an emerging key player in human aging

Growth differentiation factor 15 (GDF15) is recently emerging not only as a stress-related mitokine, but also as a key player in the aging process, being one of the most up-regulated protein with age and associated with a variety of age-related diseases (ARDs). Many data indicate that GDF15 has protective roles in several tissues during different stress and aging, thus playing a beneficial role in apparent contrast with the observed association with many ARDs. A possible detrimental role for this protein is then hypothesized to emerge with age. Therefore, GDF15 can be considered as a pleiotropic factor with beneficial activities that can turn detrimental in old age possibly when it is chronically elevated. In this review, we summarize the current knowledge on the biology of GDF15 during aging. We also propose GDF15 as a part of a dormancy program, where it may play a role as a mediator of defense processes aimed to protect from inflammatory damage and other stresses, according to the life history theory.

Body weight regulation via MT1-MMP-mediated cleavage of GFRAL

GDNF-family receptor a-like (GFRAL) has been identified as the cognate receptor of growth/differentiation factor 15 (GDF15/MIC-1), considered a key signaling axis in energy homeostasis and body weight regulation. Currently, little is known about the physiological regulation of the GDF15-GFRAL signaling pathway. Here we show that membrane-bound matrix metalloproteinase 14 (MT1-MMP/MMP14) is an endogenous negative regulator of GFRAL in the context of obesity. Overnutrition-induced obesity increased MT1-MMP activation, which proteolytically inactivated GFRAL to suppress GDF15-GFRAL signaling, thus modulating the anorectic effects of the GDF15-GFRAL axis in vivo. Genetic ablation of MT1-MMP specifically in GFRAL+ neurons restored GFRAL expression, resulting in reduced weight gain, along with decreased food intake in obese mice. Conversely, depletion of GFRAL abolished the anti-obesity effects of MT1-MMP inhibition. MT1-MMP inhibition also potentiated GDF15 activity specifically in obese phenotypes. Our findings identify a negative regulator of GFRAL for the control of non-homeostatic body weight regulation, provide mechanistic insights into the regulation of GDF15 sensitivity, highlight negative regulators of the GDF15-GFRAL pathway as a therapeutic avenue against obesity and identify MT1-MMP as a promising target.

GDF15 in Appetite and Exercise: Essential Player or Coincidental Bystander?

Growth differentiation factor 15 (GDF15) has recently moved to the forefront of metabolism research. When administered pharmacologically, GDF15 reduces food intake and lowers body weight via the hindbrain-situated receptor GFRAL (glial cell-derived neurotrophic factor family receptor alpha-like). Endogenous GDF15 is a ubiquitous cellular stress signal that can be produced and secreted by a variety of cell types. Circulating levels are elevated in a series of disease states, but also in response to exogenous agents such as metformin, colchicine, AICAR, and cisplatin. Recently, exercise has emerged as a relevant intervention to interrogate GDF15 physiology. Prolonged endurance exercise increases circulating GDF15 to levels otherwise associated with certain pathological states and in response to metformin treatment. The jury is still out on whether GDF15 is a functional "exerkine" mediating organ-to-brain crosstalk or whether it is a coincidental bystander. In this review, we discuss the putative physiological implication of exercise-induced GDF15, focusing on the potential impact on appetite and metabolism.

Hypophagia induced by salmon calcitonin, but not by amylin, is partially driven by malaise and is mediated by CGRP neurons

Objective

The behavioral mechanisms and the neuronal pathways mediated by amylin and its long-acting analog sCT (salmon calcitonin) are not fully understood and it is unclear to what extent sCT and amylin engage overlapping or distinct neuronal subpopulations to reduce food intake. We here hypothesize that amylin and sCT recruit different neuronal population to mediate their anorectic effects.

Methods

Viral approaches were used to inhibit calcitonin gene-related peptide (CGRP) lateral parabrachial nucleus (LPBN) neurons and assess their role in amylin’s and sCT’s ability to decrease food intake in mice. In addition, to test the involvement of LPBN CGRP neuropeptidergic signaling in the mediation of amylin and sCT’s effects, a LPBN site-specific knockdown was performed in rats. To deeper investigate whether the greater anorectic effect of sCT compared to amylin is due do the recruitment of additional neuronal pathways related to malaise multiple and distinct animal models tested whether amylin and sCT induce conditioned avoidance, nausea, emesis, and conditioned affective taste aversion.

Results

Our results indicate that permanent or transient inhibition of CGRP neurons in LPBN blunts sCT-, but not amylin-induced anorexia and neuronal activation. Importantly, sCT but not amylin induces behaviors indicative of malaise including conditioned affective aversion, nausea, emesis, and conditioned avoidance; the latter mediated by CGRP^LPBN neurons.

Conclusions

Together, the present study highlights that although amylin and sCT comparably decrease food intake, sCT is distinctive from amylin in the activation of anorectic neuronal pathways associated with malaise.

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CGRP neurons mediate the effect of the amylin agonist salmon calcitonin (sCT) on food intake.

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Amylin's hypophagic effect does not require CGRP neurons.

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sCT-induced anorexia but not amylin is associated with malaise.

Chrono-communication and cardiometabolic health: The intrinsic relationship and therapeutic nutritional promises

Circadian rhythm, an innate 24-h biological clock, regulates several mammalian physiological activities anticipating daily environmental variations and optimizing available energetic resources. The circadian machinery is a complex neuronal and endocrinological network primarily organized into a central clock, suprachiasmatic nucleus (SCN), and peripheral clocks. Several small molecules generate daily circadian fluctuations ensuring inter-organ communication and coordination between external stimuli, i.e., light, food, and exercise, and body metabolism. As an orchestra, this complex network can be out of tone. Circadian disruption is often associated with obesity development and, above all, with diabetes and cardiovascular disease onset. Moreover, accumulating data highlight a bidirectional relationship between circadian misalignment and cardiometabolic disease severity. Food intake abnormalities, especially timing and composition of meal, are crucial cause of circadian disruption, but evidence from preclinical and clinical studies has shown that food could represent a unique therapeutic approach to promote circadian resynchronization. In this review, we briefly summarize the structure of circadian system and discuss the role playing by different molecules [from leptin to ghrelin, incretins, fibroblast growth factor 21 (FGF-21), growth differentiation factor 15 (GDF15)] to guarantee circadian homeostasis. Based on the recent data, we discuss the innovative nutritional interventions aimed at circadian re-synchronization and, consequently, improvement of cardiometabolic health.

Insights Into Acute and Delayed Cisplatin-Induced Emesis From a Microelectrode Array, Radiotelemetry and Whole-Body Plethysmography Study of Suncus murinus (House Musk Shrew)

Purpose: Cancer patients receiving cisplatin therapy often experience side-effects such as nausea and emesis, but current anti-emetic regimens are suboptimal. Thus, to enable the development of efficacious anti-emetic treatments, the mechanisms of cisplatin-induced emesis must be determined. We therefore investigated these mechanisms in Suncus murinus, an insectivore that is capable of vomiting.

Methods: We used a microelectrode array system to examine the effect of cisplatin on the spatiotemporal properties of slow waves in stomach antrum, duodenum, ileum and colon tissues isolated from S. murinus. In addition, we used a multi-wire radiotelemetry system to record conscious animals’ gastric myoelectric activity, core body temperature, blood pressure (BP) and heart rate viability over 96-h periods. Furthermore, we used whole-body plethysmography to simultaneously monitor animals’ respiratory activity. At the end of in vivo experiments, the stomach antrum was collected and immunohistochemistry was performed to identify c-Kit and cluster of differentiation 45 (CD45)-positive cells.

Results: Our acute in vitro studies revealed that cisplatin (1–10 μM) treatment had acute region-dependent effects on pacemaking activity along the gastrointestinal tract, such that the stomach and colon responded oppositely to the duodenum and ileum. S. murinus treated with cisplatin for 90 min had a significantly lower dominant frequency (DF) in the ileum and a longer waveform period in the ileum and colon. Our 96-h recordings showed that cisplatin inhibited food and water intake and caused weight loss during the early and delayed phases. Moreover, cisplatin decreased the DF, increased the percentage power of bradygastria, and evoked a hypothermic response during the acute and delayed phases. Reductions in BP and respiratory rate were also observed. Finally, we demonstrated that treatment with cisplatin caused inflammation in the antrum of the stomach and reduced the density of the interstitial cells of Cajal (ICC).

Conclusion: These studies indicate that cisplatin treatment of S. murinus disrupted ICC networking and viability and also affected general homeostatic mechanisms of the cardiovascular system and gastrointestinal tract. The effect on the gastrointestinal tract appeared to be region-specific. Further investigations are required to comprehensively understand these mechanistic effects of cisplatin and their relationship to emesis.

Single nuclei RNA sequencing of the rat AP and NTS following GDF15 treatment

Objective

Growth differentiation factor 15 (GDF15) is known to play a role in feeding, nausea, and body weight, with action through the GFRAL-RET receptor complex in the area postrema (AP) and nucleus tractus solitarius (NTS). To further elucidate the underlying cell type-specific molecular mechanisms downstream of GDF15 signaling, we used a single nuclei RNA sequencing (snRNAseq) approach to profile AP and NTS cellular subtype-specific transcriptomes after systemic GDF15 treatment.

Methods

AP and NTS micropunches were used for snRNAseq from Sprague Dawley rats 6 h following GDF15 or saline injection, and Seurat was used to identify cellular subtypes and cell type-specific alterations in gene expression that were due to the direct and secondary effects of systemic GDF15 treatment.

Results

Using the transcriptome profile of ∼35,000 individual AP/NTS nuclei, we identified 19 transcriptomically distinct cellular subtypes, including a single population Gfral and Ret positive excitatory neurons, representing the primary site of action for GDF15. A total of ∼600 cell type-specific differential expression events were identified in neurons and glia, including the identification of transcriptome alterations specific to the direct effects of GDF15 in the Gfral-Ret positive excitatory neurons and shared transcriptome alterations across neuronal and glial cell types. Downstream analyses identified shared and cell type-specific alterations in signaling pathways and upstream regulatory mechanisms of the observed transcriptome alterations.

Conclusions

These data provide a considerable advance in our understanding of AP and NTS cell type-specific molecular mechanisms associated with GDF15 signaling. The identified cellular subtype-specific regulatory mechanism and signaling pathways likely represent important targets for future pharmacotherapies.

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GDF15 directly alters transcription in Gfral- and Ret-positive excitatory neurons.

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GDF15 indirectly alters transcription in other neuronal and glial populations.

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Cell type-specific expression changes identify regulatory and signaling mechanisms.

Human intestinal bitter taste receptors regulate innate immune responses and metabolic regulators in obesity

Bitter taste receptors (taste 2 receptors, TAS2Rs) serve as warning sensors in the lingual system against the ingestion of potentially poisonous food. Here, we investigated the functional role of TAS2Rs in the human gut and focused on their potential to trigger an additional host defense pathway in the intestine. Human jejunal crypts, especially those from individuals with obesity, responded to bitter agonists by inducing the release of antimicrobial peptides (α-defensin 5 and regenerating islet–derived protein 3 α [REG3A]) but also regulated the expression of other innate immune factors (mucins, chemokines) that affected E. coli growth. We found that the effect of aloin on E. coli growth and on the release of the mucus glycoprotein CLCA1, identified via proteomics, was affected by TAS2R43 deletion polymorphisms and thus confirmed a role for TAS2R43. RNA-Seq revealed that denatonium benzoate induced an NRF2-mediated nutrient stress response and an unfolded protein response that increased the expression of the mitokine GDF15 but also ADM2 and LDLR, genes that are involved in anorectic signaling and lipid homeostasis. In conclusion, TAS2Rs in the intestine constitute a promising target for treating diseases that involve disturbances in the innate immune system and body weight control. TAS2R polymorphisms may be valuable genetic markers to predict therapeutic responses.

The Role of GDF15 as a Myomitokine

Growth differentiation factor 15 (GDF15) is a cytokine best known for affecting systemic energy metabolism through its anorectic action. GDF15 expression and secretion from various organs and tissues is induced in different physiological and pathophysiological states, often linked to mitochondrial stress, leading to highly variable circulating GDF15 levels. In skeletal muscle and the heart, the basal expression of GDF15 is very low compared to other organs, but GDF15 expression and secretion can be induced in various stress conditions, such as intense exercise and acute myocardial infarction, respectively. GDF15 is thus considered as a myokine and cardiokine. GFRAL, the exclusive receptor for GDF15, is expressed in hindbrain neurons and activation of the GDF15–GFRAL pathway is linked to an increased sympathetic outflow and possibly an activation of the hypothalamic-pituitary-adrenal (HPA) stress axis. There is also evidence for peripheral, direct effects of GDF15 on adipose tissue lipolysis and possible autocrine cardiac effects. Metabolic and behavioral outcomes of GDF15 signaling can be beneficial or detrimental, likely depending on the magnitude and duration of the GDF15 signal. This is especially apparent for GDF15 production in muscle, which can be induced both by exercise and by muscle disease states such as sarcopenia and mitochondrial myopathy.

GDF15: emerging biology and therapeutic applications for obesity and cardiometabolic disease

Growth differentiation factor 15 (GDF15) is a member of the TGFβ superfamily whose expression is increased in response to cellular stress and disease as well as by metformin. Elevations in GDF15 reduce food intake and body mass in animal models through binding to glial cell-derived neurotrophic factor family receptor alpha-like (GFRAL) and the recruitment of the receptor tyrosine kinase RET in the hindbrain. This effect is largely independent of other appetite-regulating hormones (for example, leptin, ghrelin or glucagon-like peptide 1). Consistent with an important role for the GDF15-GFRAL signalling axis, some human genetic studies support an interrelationship with human obesity. Furthermore, findings in both mice and humans have shown that metformin and exercise increase circulating levels of GDF15. GDF15 might also exert anti-inflammatory effects through mechanisms that are not fully understood. These unique and distinct mechanisms for suppressing food intake and inflammation makes GDF15 an appealing candidate to treat many metabolic diseases, including obesity, type 2 diabetes mellitus, non-alcoholic fatty liver disease, cardiovascular disease and cancer cachexia. Here, we review the mechanisms regulating GDF15 production and secretion, GDF15 signalling in different cell types, and how GDF15-targeted pharmaceutical approaches might be effective in the treatment of metabolic diseases.

Weight loss from caloric restriction vs Roux-en-Y gastric bypass surgery differentially regulates systemic and portal vein GDF15 levels in obese Zucker fatty rats

Weight loss from caloric restriction (i.e. dieting) tends to be modest and short-lived, whereas from bariatric surgeries such as Roux-en-Y gastric bypass (RYGB) is pronounced and generally sustained. The reasons behind these opposing outcomes between interventions remain unclear, but likely involve differential effects on gut-brain communication. Growth differentiation factor 15 (GDF15) is a ubiquitously-induced, centrally-acting, anorexigenic cytokine whose systemic levels are elevated under a variety of conditions associated with a negative energy balance, including in patients following RYGB. We therefore asked whether systemic and portal vein GDF15 levels differ between obese Zucker fatty rats that experienced similar weight loss from RYGB or from forced caloric restriction (CR). Compared with ad libitum fed (ALF) controls, body weight, visceral adiposity and food intake of RYGB and CR rats were markedly lower during the postoperative observation period. Both systemic and portal vein GDF15 levels in RYGB rats at postoperative day 28 were higher compared with ALF rats and particularly compared with CR rats. Further, systemic and portal vein GDF15 levels negatively correlated with body weight and food intake specifically in RYGB rats. These findings provide evidence that, unlike dieting, RYGB might achieve sustained weight loss and appetite suppression partly through increased GDF15 release from epithelial cells of the gastrointestinal tract.

Activation of the hypothalamic-pituitary-adrenal axis by exogenous and endogenous GDF15

An acute increase in the circulating concentration of glucocorticoid hormones is essential for the survival of severe somatic stresses. Circulating concentrations of GDF15, a hormone that acts in the brain to reduce food intake, are frequently elevated in stressful states. We now report that GDF15 potently activates the hypothalamic-pituitary-adrenal (HPA) axis in mice and rats. A blocking antibody to the GDNF-family receptor α-like receptor completely prevented the corticosterone response to GDF15 administration. In wild-type mice exposed to a range of stressful stimuli, circulating levels of both corticosterone and GDF15 rose acutely. In the case of Escherichia coli or lipopolysaccharide injections, the vigorous proinflammatory cytokine response elicited was sufficient to produce a near-maximal HPA response, regardless of the presence or absence of GDF15. In contrast, the activation of the HPA axis seen in wild-type mice in response to the administration of genotoxic or endoplasmic reticulum toxins, which do not provoke a marked rise in cytokines, was absent in Gdf15 ^-/- mice. In conclusion, consistent with its proposed role as a sentinel hormone, endogenous GDF15 is required for the activation of the protective HPA response to toxins that do not induce a substantial cytokine response. In the context of efforts to develop GDF15 as an antiobesity therapeutic, these findings identify a biomarker of target engagement and a previously unrecognized pharmacodynamic effect, which will require monitoring in human studies.

Growth differentiation factor 15 increases in both cerebrospinal fluid and serum during pregnancy

Aim

Growth differentiation factor 15 (GDF15) increases in serum during pregnancy to levels not seen in any other physiological state and is suggested to be involved in pregnancy-induced nausea, weight regulation and glucose metabolism. The main action of GDF15 is regulated through a receptor of the brainstem, i.e., through exposure of GDF15 in both blood and cerebrospinal fluid (CSF). The aim of the current study was to measure GDF15 in both CSF and serum during pregnancy, and to compare it longitudinally to non-pregnant levels.

Methods

Women were sampled at elective caesarean section (n = 45, BMI = 28.1±5.0) and were followed up 5 years after pregnancy (n = 25). GDF15, insulin and leptin were measured in CSF and serum. Additional measurements included plasma glucose, and serum adiponectin and Hs-CRP.

Results

GDF15 levels were higher during pregnancy compared with follow-up in both CSF (385±128 vs. 115±32 ng/l, P<0.001) and serum (73789±29198 vs. 404±102 ng/l, P<0.001). CSF levels correlated with serum levels during pregnancy (P<0.001), but not in the non-pregnant state (P = 0.98). Both CSF and serum GDF15 were highest in women carrying a female fetus (P<0.001). Serum GDF15 correlated with the homeostatic model assessment for beta-cell function and placental weight, and CSF GDF15 correlated inversely with CSF insulin levels.

Conclusion

This, the first study to measure CSF GDF15 during pregnancy, demonstrated increased GDF15 levels in both serum and CSF during pregnancy. The results suggest that effects of GDF15 during pregnancy can be mediated by increases in both CSF and serum levels.