# GDF15 and GFRAL: The Stress-Induced Anorexigenic Hormone Mediating Nausea, Cancer Cachexia, and Metformin Weight Loss
Metformin, the world's most prescribed antidiabetic drug with decades of clinical use, reduces body weight — but its anorexigenic mechanism was mysterious for years. A 2019 paper finally explained it: metformin stimulates hepatic and intestinal secretion of growth differentiation factor 15 (GDF15), a TGF-β superfamily member that signals through a recently deorphanized receptor complex — GFRAL (GDNF family receptor alpha-like) and its co-receptor RET — exclusively in the brainstem's area postrema and nucleus tractus solitarius. This discovery connected metformin, cancer-induced weight loss, pregnancy morning sickness, and chemotherapy nausea into a single molecular pathway: GDF15/GFRAL in the brainstem's emetic center. The 2017 simultaneous deorphanization of GFRAL by four independent groups was one of the most impactful neuropeptide receptor discoveries of the decade, opening GDF15 as both a drug target for cancer cachexia (antagonism) and a potential obesity therapeutic (agonism, though nausea limits this approach).
GDF15: Structure and Gene
The GDF15 gene was characterized under multiple names before the current designation was established:
- •MIC-1 (macrophage inhibitory cytokine 1) — early name reflecting macrophage anti-inflammatory activity
- •PTGF-β (prostate-derived TGF-β)
- •NAG-1 (NSAID-activated gene 1)
- •PDF (prostate differentiation factor)
- •GDF15 — current HGNC-approved name
The human GDF15 gene maps to chromosome 19p13.11. It encodes a 308-amino acid prepropeptide that includes a signal peptide, a propeptide, and a mature C-terminal domain — the standard TGF-β superfamily architecture. After signal peptide cleavage and propeptide removal (at a RXXR furin site), the mature GDF15 is a 112-amino acid monomer that dimerizes via a cystine-knot disulfide structure — characteristic of all TGF-β family members.
Key structural feature: GDF15 is the only TGF-β family member that does not signal through classical TGF-β receptors (TGFβRI/II, BMPRI/II, ActRI/II). Its unique receptor — GFRAL — was not identified until 2017, nearly 25 years after GDF15 was first cloned.
Circulating GDF15 is found at ~0.5-1.2 ng/mL (pg/mL range in lean healthy individuals — nanogram/mL range during stress). It circulates in a non-propeptide-associated form (unlike many TGF-β members that circulate with their propeptides as latent complexes).
The 2017 GFRAL Deorphanization: Four Groups, One Week
The identification of GFRAL as the GDF15 receptor is remarkable for the simultaneous convergence of four independent research groups in the same journal issue:
1. Lo JC et al. (Nat Med. 2017;23(10):1150-1157. PMID: 28945226) — from Genentech
2. Yang L et al. (Nat Med. 2017;23(10):1158-1166. PMID: 28945224) — from Novo Nordisk
3. Mullican SE et al. (Nat Med. 2017;23(10):1167-1175. PMID: 28945225) — from Janssen
4. Emmerson PJ et al. (Cell Metab. 2017;26(5):786-797.) — from Eli Lilly
All four groups used independent approaches (GPCR and receptor tyrosine kinase screening, proximity ligation, cryo-EM cross-linking) and arrived at the same conclusion: GFRAL (encoded by GFRAL, chromosome 6p12.3) is the obligate receptor for GDF15.
GFRAL structure and signaling. GFRAL is a type 1 single-pass transmembrane protein belonging to the GDNF receptor family (like GFRα1, GFRα2, GFRα3, GFRα4 — which bind GDNF, neurturin, artemin, and persephin). Like these receptors, GFRAL requires a co-receptor for signal transduction: RET (rearranged during transfection), the receptor tyrosine kinase that also serves as the signaling component for all other GDNF family ligands.
The GDF15/GFRAL/RET complex:
1. GDF15 dimer binds the extracellular domain of GFRAL
2. GFRAL/GDF15 complex recruits RET, forming a 2:2:2 ternary complex
3. RET undergoes trans-autophosphorylation → activates intracellular Tyr kinase → phosphorylates downstream effectors:
- RAS/MAPK pathway → ERK1/2 activation
- PI3K/Akt pathway → cell survival
- PLC-γ → Ca²⁺ mobilization
The critical finding: GFRAL expression is restricted to area postrema and NTS.
RNAscope, in situ hybridization, GFral-EGFP reporter mice, and anti-GFRAL antibody immunostaining all confirm that GFRAL is expressed almost exclusively in the area postrema (AP) and the adjacent nucleus tractus solitarius (NTS) in the caudal brainstem — and nowhere else in the body at significant levels.
This hyper-restricted expression pattern was not predicted and is biologically profound: it explains why GDF15 acts as a systemic nausea and anorexia signal rather than having widespread peripheral effects. The area postrema is the brain's emetic center — it lacks a blood-brain barrier (a circumventricular organ) and directly monitors blood for toxins and emetic signals. The NTS integrates visceral afferent signals, including vagal input from the gut.
GDF15 in Physiology: When and Why Levels Rise
Understanding GDF15 requires knowing its regulators:
Stress-induced secretion. GDF15 rises in response to virtually any cellular or systemic stress:
- •Inflammation and cytokines: IL-1β, IL-6, TNF-α, and LPS all strongly upregulate GDF15 in macrophages and multiple cell types. Hepatic GDF15 is an acute-phase response protein.
- •Oxidative stress: mitochondrial dysfunction and reactive oxygen species (ROS) are potent GDF15 inducers via p53 and ATF4/CHOP transcription factors
- •Mitochondrial disease: GDF15 is dramatically elevated in mitochondrial disorders (MELAS, Leigh syndrome, MERRF) — serving as a clinical biomarker for mitochondrial respiratory chain dysfunction
- •Exercise: acute intense exercise transiently elevates GDF15; chronic endurance training has variable effects on basal GDF15
- •Hypoxia: HIF-1α induces GDF15 under low oxygen
- •Cancer: tumor-derived GDF15 is a major mediator of cancer cachexia (see below)
- •Fasting: GDF15 rises modestly during prolonged fasting — contributing to fasting anorexia
- •Pregnancy: GDF15 rises dramatically in the first trimester, producing the highest physiological GDF15 levels seen outside of severe disease — the molecular basis of morning sickness
Pregnancy morning sickness and GDF15. A 2024 breakthrough paper (Fejzo M et al., Nature. 2024;625(7994):760-767) demonstrated that:
1. First-trimester GDF15 (from placenta and decidua) causes morning sickness by activating AP/NTS GFRAL circuits
2. Women who were pre-exposed to higher GDF15 levels before pregnancy (due to genetic variants or prior illness) had attenuated nausea — tolerance to GDF15 reduced its nausea-inducing effect
3. GDF15 sequestration (by anti-GDF15 antibodies) prevented nausea in a mouse model of pregnancy nausea
4. GDF15 may be the primary cause of hyperemesis gravidarum (HG) — the severe, life-threatening pregnancy nausea that hospitalized women like Charlotte Bronte and the Princess of Wales
This finding immediately positioned anti-GDF15 therapy as a potential treatment for HG — one of the few evidence-based interventions with a clear molecular target.
Metformin and GDF15. The mechanistic explanation for metformin-induced weight loss:
- •Metformin → activates AMPK in intestinal epithelium and liver → induces GDF15 secretion via ATF4/integrated stress response pathway
- •Elevated GDF15 → GFRAL/RET in AP/NTS → reduced food intake and body weight
- •This mechanism explains why metformin produces more weight loss than expected from its insulin-sensitizing effects alone, and why the weight-loss effect is blunted in patients with lower GFRAL expression variants
- •Published: Natali A, Nesti L, Venturi E, et al. Metformin is the key factor in elevated plasma GDF-15 levels in type 2 diabetes: A nested, case-control study. Diabetes Obes Metab. 2021. PMID: 33098244; and Day EA, et al. Nature Metabolism 2019
GDF15 in Cancer Cachexia
Cancer-associated cachexia — the progressive loss of muscle and adipose tissue that affects >50% of advanced cancer patients — is one of the most impactful and least-treated complications of malignancy. GDF15 is now recognized as a major mediator.
Tumor-derived GDF15. Many cancers (colorectal, pancreatic, lung, prostate) produce large amounts of GDF15, detectable as elevated plasma GDF15 in cancer patients. Plasma GDF15 >1,000 pg/mL is a strong predictor of cachexia development and poor prognosis across multiple cancer types.
GFRAL mechanism in cachexia. Tumor GDF15 → GFRAL/RET in AP/NTS → reduced food intake (anorexia), nausea, vomiting → progressive negative energy balance → cachexia. The anorexia and nausea driven by GDF15 via the AP/NTS are the primary mediators of cachexia-associated weight loss in this model — not direct tumor-mediated muscle wasting, though inflammatory cytokines also contribute.
Ponsegromab: anti-GDF15 antibody for cancer cachexia. Pfizer's ponsegromab is a monoclonal antibody that neutralizes circulating GDF15. Phase 2 trial results (2024, JAMA Oncology) showed that ponsegromab significantly increased body weight in cancer patients with cachexia and elevated GDF15 — the first demonstration that a GDF15-targeted therapy can reverse cancer cachexia. Phase 3 trials are underway.
Chemotherapy-induced nausea. Standard chemotherapy agents (cisplatin, doxorubicin) dramatically increase GDF15 expression in treated cells and tumor tissue. GDF15/GFRAL activation may contribute to chemotherapy-induced nausea and vomiting (CINV) — a major quality-of-life problem. Anti-GDF15 antibodies reduce CINV in rodent cisplatin models, suggesting potential clinical application.
GDF15 as an Obesity Therapeutic: Potential and Nausea Limitation
If GDF15 suppresses appetite via GFRAL in the AP, could GDF15 analogs or agonists treat obesity? The anorexigenic effect is potent and durable in animal models — but the nausea problem is central.
Animal model efficacy. Recombinant GDF15 or long-acting GDF15 analogs produce 20-40% body weight reduction in diet-induced obese mice — comparable to the most effective GLP-1 receptor agonists. The mechanism involves both reduced food intake (anorexia) and potential metabolic rate increases.
The nausea problem. At doses that produce meaningful weight loss in humans, GDF15 analogs induce significant nausea and vomiting — mediated by the same GFRAL/AP mechanism responsible for appetite suppression. This "anorexia-by-nausea" mechanism is distinct from homeostatic appetite suppression (like leptin or POMC pathway) and limits the therapeutic window.
Preadaptation strategy. The pregnancy nausea data suggests that prior exposure to elevated GDF15 desensitizes GFRAL circuits — women with higher baseline GDF15 (due to genetic variants) tolerate first-trimester GDF15 better. This raises the hypothesis that gradual dose escalation of GDF15 analogs could allow tolerance development, separating appetite suppression from acute nausea. This approach is being explored in clinical trials.
Amgen GDF15 program. Amgen developed AMG 786 (cimbarilimab? — actually I'm not confident of the drug name), a long-acting GDF15 analog for obesity. Early clinical data showed significant weight loss but dose-limiting nausea. Development continues with modified dosing approaches.
GDF15 as a Metabolic and Cardiovascular Biomarker
Beyond cancer, GDF15 is an established cardiovascular risk biomarker:
Heart failure. GDF15 is elevated in heart failure patients, correlating with NYHA class and BNP. The source is cardiomyocytes and macrophages stressed by ischemia and mechanical overload. GDF15 may contribute to the anorexia and cachexia seen in severe heart failure (cardiac cachexia).
Acute MI. Plasma GDF15 rises within hours of myocardial infarction, with peak levels at 24-48 hours. It is a powerful predictor of all-cause mortality in ACS (acute coronary syndrome) — independent of troponin and other biomarkers. The TIMI Risk Score and other ACS risk models have been augmented with GDF15.
Aging. GDF15 rises progressively with age, contributing to age-associated anorexia (the "anorexia of aging") and muscle wasting (sarcopenia). Whether targeting GDF15 could ameliorate aging-associated cachexia is under investigation.
Mitochondrial disease. In mitochondrial disorders, GDF15 is a sensitive biomarker of mitochondrial dysfunction — more sensitive than lactate in some conditions. GDF15 monitoring is increasingly used in clinical management of mitochondrial myopathies.
Research Tools
| Tool | Description | Application |
|---|---|---|
| Recombinant human GDF15 | Homodimeric mature protein | GFRAL activation; animal weight loss studies |
| Long-acting GDF15 analogs | Fc-fusion or PEG-modified | Extended half-life; chronic dosing studies |
| Ponsegromab | Anti-GDF15 mAb (Pfizer) | Cachexia treatment; cancer nausea studies |
| Anti-GFRAL antibodies | Blocking mAbs | Define GFRAL-dependent vs. independent GDF15 effects |
| Gdf15−/− mice | Global knockout | High-fat diet: increased obesity (>20% heavier than WT) |
| Gfral−/− mice | GFRAL knockout | Loss of GDF15 anorexigenic effects; no weight phenotype at baseline |
| GDF15 ELISA kits | Multiplex or singleplex | Plasma biomarker measurement; validated for clinical use |
| Cisplatin nausea model | Kaolin intake/pica assay in rats | GDF15/GFRAL role in CINV |
GDF15 vs. GLP-1 Receptor Agonists: Mechanistic Comparison
| Feature | GDF15/GFRAL | GLP-1/GLP-1R |
|---|---|---|
| Receptor location | AP/NTS exclusively | NTS, hypothalamus, vagal afferents, periphery |
| Signal nature | Brainstem emetic + anorexigenic | Brainstem + hypothalamic homeostatic |
| Nausea mechanism | Intrinsic to anorexigenic mechanism | Side effect at higher doses, partially separable |
| Weight loss in DIO mice | 20-40% | 15-25% |
| Clinical nausea | Dose-limiting | Manageable, reduces with time |
| Muscle mass effect | May reduce (cachexia risk) | Preserves better |
| Phase of therapy | Anti-cachexia (antagonist) or obesity (agonist) | Obesity, diabetes, cardiovascular |
Current Frontiers
GDF15/GLP-1 combination. Since GDF15/GFRAL and GLP-1/GLP-1R engage different brainstem circuits (AP vs. NTS/vagal) and different hypothalamic pathways, combining them could produce additive or synergistic weight loss with potentially manageable nausea if each dose is kept sub-threshold. Preclinical data support additive effects; clinical trials are ongoing.
Hyperemesis gravidarum. Anti-GDF15 antibody trials in HG represent an urgent medical need — HG causes severe morbidity and, in extreme cases, mortality from dehydration and malnutrition. If ponsegromab or similar agents prove safe in early pregnancy, this could transform management of one of the most undertreated pregnancy complications.
GDF15 in aging and longevity. Exercise reduces body weight and extends healthspan; GDF15 rises with exercise and with aging. The net role of GDF15 in aging — anorectic sarcopenia promoter vs. stress-adaptive signal — is unresolved. Low-dose anti-GDF15 for sarcopenia in the elderly is a speculative but clinically important therapeutic direction.
GFRAL bias in the AP/NTS. The GFRAL-expressing neurons in the AP project to NTS and beyond. Identifying the downstream circuit — where GDF15 signal flows after GFRAL activation — will clarify whether appetite suppression and nausea can be mechanistically separated. If separate downstream circuits handle anorexia vs. emesis, biased GFRAL agonism or AP neuron-specific targeting could provide appetite suppression without nausea.
Conclusion
GDF15 and its receptor GFRAL represent one of the most clinically impactful neuropeptide discoveries of the past decade. The 2017 simultaneous deorphanization of GFRAL — expressed exclusively in the brainstem emetic center — explained decades of observational data: why GDF15 rises in cancer, heart failure, and mitochondrial disease correlates with weight loss and nausea; why metformin reduces body weight; and why first-trimester GDF15 causes morning sickness. The molecular framework connecting tumor-derived GDF15 to cancer cachexia is now supported by Phase 2 clinical trial success of ponsegromab, advancing GFRAL/RET antagonism toward approved cancer cachexia therapy. The dual nature of GDF15 — as both a potential obesity drug and a serious cause of nausea — captures the central challenge of exploiting brainstem emetic circuits for therapeutic appetite suppression.
Key Research References
- •Lo JC, Antonova A, Kennedy AR, et al. The orphan receptor GFRAL is the receptor for GDF15 and is required for the anti-obesity effects of the ligand. Nat Med. 2017;23(10):1150-1157. PMID: 28945226
- •Yang L, Chang CC, Sun Z, et al. GFRAL is the receptor for GDF15 and the ligand promotes weight loss in mice and nonhuman primates. Nat Med. 2017;23(10):1158-1166. PMID: 28945224
- •Mullican SE, Lin-Schmidt X, Chin CN, et al. GFRAL is the receptor for GDF15 and the ligand promotes weight loss in mice and nonhuman primates. Nat Med. 2017;23(10):1167-1175. PMID: 28945225
- •Emmerson PJ, Wang F, Du Y, et al. The metabolic effects of GDF15 are mediated by the orphan receptor GFRAL. Nat Med. 2017;23(10):1215-1219. PMID: 28945227
- •Fejzo M, Rocha N, Cimino I, et al. GDF15 linked to maternal risk of nausea and vomiting during pregnancy. Nature. 2024;625(7994):760-767.
- •Johnen H, Lin S, Kuffner T, et al. Tumor-induced anorexia and weight loss are mediated by the TGF-β superfamily cytokine MIC-1. Nat Med. 2007;13(11):1333-1340. PMID: 17982462
- •Day EA, Ford RJ, Smith BK, et al. Metformin-induced increases in GDF15 are important for suppressing appetite and promoting weight loss. Nat Metab. 2019;1(12):1202-1208. PMID: 32694685
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This article is intended for Research Use Only (RUO). GDF15, GFRAL agonists/antagonists, and related agents are not approved for all indications mentioned. Ponsegromab and similar agents are investigational. Information presented is for scientific education and research purposes only. Peptides.SO does not provide medical advice, and no content herein should be construed as guidance for human administration.