Neuromedin U-25: natural gut-and-brain signalling peptide

What this is

Neuromedin U-25 (NMU-25) is the full-length form of neuromedin U found in humans — a 25-amino-acid signalling peptide produced in the gut, spinal cord, and brain. The peptide gets its name from the "U" in uterus: when Minamino, Kangawa, and Matsuo first isolated it from porcine spinal cord in 1985, its most striking property was a potent ability to contract uterine smooth muscle (Minamino and colleagues, Biochemical and Biophysical Research Communications, 1985). Since then, research has revealed a much broader role spanning appetite regulation, pain processing, immune signalling, and cardiovascular control. NMU-25 is the human-specific isoform; rats produce a 23-residue form and shorter 8-residue C-terminal fragments (NMU-8) also exist with equivalent receptor-binding potency, because the biologically active core lies at the conserved C-terminus. The stored sequence FRVDEEFQSPFASQSRGYFLFRPRN represents the backbone — the native peptide carries a C-terminal amide (-NH₂) on the final asparagine, a post-translational modification that is essential for receptor binding and that is not reflected in the single-letter sequence shown here.

History

Minamino, Kangawa, and Matsuo (1985) isolated two novel smooth muscle-stimulating peptides from porcine spinal cord, naming them neuromedin U-8 and neuromedin U-25 for their uterus-stimulating activity. The "U" designation aligned with a naming convention for neuropeptides that stimulate smooth muscle in the uterus. The human NMU gene was subsequently mapped to chromosome 4q12; the 174-amino-acid precursor protein is cleaved at paired basic residues to release the mature 25-residue peptide (Mori and colleagues, 2005, reviewed in Szyszka and colleagues, Frontiers in Endocrinology, 2021). Two cognate G protein-coupled receptors were identified and cloned in the early 2000s: NMUR1 (also written NmUR1) in peripheral tissues and NMUR2 (NmUR2) predominantly in the brain. A structurally related peptide, neuromedin S (NMS), was identified in 2005 and activates the same two receptors with similar potency (Mori and colleagues, 2005).

What it does

NMU-25 acts broadly as a regulator of how the body manages energy, stress, pain, and inflammation. In the brain, it suppresses appetite and increases energy expenditure; mice engineered to lack the NMU gene develop obesity with excess food intake, increased body fat, and reduced physical activity, while mice that overexpress it become lean and eat less (reviewed in Graham and colleagues, Endocrinology, 2009). In peripheral tissues — particularly the gut, uterus, and vasculature — NMU contracts smooth muscle and raises blood pressure. It also modulates how the body perceives pain: NMUR2-deficient mice show markedly reduced responses to noxious thermal and chemical stimuli (Torres and colleagues, 2007). In the immune system, NMU activates mast cells, stimulates type 2 cytokine production (IL-4, IL-5, IL-13) in lymphocytes, and amplifies inflammatory responses in several disease models (Ye and colleagues, Immunology, 2021).

Evidence

• Human: No published clinical trials of NMU-25 itself. Human genetic studies have found associations between NMU gene variants and increased body weight (Hainerová and colleagues, 2006). Expression profiling studies document NMU and its receptors in multiple human cancer types including pancreatic ductal adenocarcinoma, breast cancer, and colorectal cancer (Moody and colleagues, Cancers, 2019).
• Animal: Extensive rodent evidence. NMU knockout mice develop late-onset obesity with hyperphagia, hyperleptinemia, and hyperinsulinemia. Central administration of NMU suppresses food intake and body weight in rodents. NMUR2-deficient mice show impaired nociceptive responses to capsaicin, heat, and formalin (Torres and colleagues, 2007; Zeng and colleagues, 2006). In cancer models, NMU overexpression in pancreatic cancer cells increases invasiveness through c-Met signalling (Ketterer and colleagues, 2009).
• In vitro: NMU-25 binds NMUR1 and NMUR2 with sub-nanomolar affinity; both receptors signal via Gq/11-mediated calcium mobilisation and MAPK/ERK activation (You and colleagues, Nature Communications, 2022). NMU also suppresses glucose-stimulated insulin secretion in pancreatic β-cells via Gαi/o signalling (reviewed in Peier and colleagues, 2009).

Known effects

• Appetite suppression — Preclinical (central administration reduces food intake in rodents; genetic knockout causes obesity)
• Energy expenditure increase — Preclinical (NMU-overexpressing mice are lean and thermogenic)
• Smooth muscle contraction — Mechanistic / preclinical (original defining activity; mediated via NMUR1 peripherally)
• Blood pressure elevation — Preclinical (central and peripheral NMU raises mean arterial pressure in conscious rats)
• Pronociception — Preclinical (NMUR2-dependent; knockout mice show reduced pain sensitivity)
• Type 2 immune activation — Preclinical (mast cell degranulation, IL-4/IL-5/IL-13 release, ILC2 activation in parasite infection models)
• Insulin secretion suppression — In vitro / preclinical (Gαi/o-mediated in pancreatic β-cells)

Safety signals

No clinical safety data exist for NMU-25 as an administered peptide in humans. In animal pharmacology studies, NMUR2-selective agonists developed for obesity produced diarrhoea at higher doses, which was notably reduced by peripheral-restricted NMUR2 agonist strategies compared with centrally acting compounds (reviewed in Szczepańska and colleagues, Pharmacological Research, 2023). The pronociceptive and pro-inflammatory properties of NMU suggest that non-selective activation of the NMU system could have unintended consequences in pain or inflammatory contexts.

Regulatory status

• US: Not approved. No IND or NDA filing for NMU-25 as a therapeutic. Research compound only.
• EU: Not approved. No EMA marketing authorisation application.
• WADA: Not listed on the current prohibited list. No competitive-sport relevance established.
• ClinicalTrials.gov: No registered trials identified for neuromedin U-25 specifically. The NMU receptor system is under preclinical investigation as an obesity target.

Mechanism

NMU-25 activates two class A GPCRs — NMUR1 and NMUR2 — with sub-nanomolar affinity and limited selectivity between the two subtypes (You and colleagues, Nature Communications, 2022). NMUR1 is expressed predominantly in peripheral tissues including the gastrointestinal tract, genitourinary system, adipose tissue, adrenal cortex, and cardiovascular system; NMUR2 is expressed mainly in the CNS, with highest levels in the hypothalamus, medulla, and spinal cord (reviewed in Szyszka and colleagues, Frontiers in Endocrinology, 2021). Both receptors couple primarily through Gq/11, triggering inositol phosphate turnover and intracellular calcium mobilisation; evidence for Gi/o coupling also exists, particularly in pancreatic β-cells. The anorexigenic effects of centrally administered NMU are mediated principally via NMUR2 — administration of NMU into the paraventricular nucleus and arcuate nucleus activates corticotropin-releasing hormone (CRH) pathways and downstream sympathetic outflow that reduces food intake and increases thermogenesis. The conserved C-terminal heptapeptide YFLFRPRN-NH₂ constitutes the receptor-binding pharmacophore; the amidated C-terminus is required for full agonist activity, and removal or modification of this region abolishes or reduces potency. NMU-8 and NMU-25 differ only in the N-terminal extension of the longer form; both bind the same receptors with comparable C-terminal-driven affinity.

Open questions

• The exact contribution of NMUR1 versus NMUR2 to each physiological role remains incompletely resolved; NMUR2-knockout mice do not fully recapitulate the obesity phenotype of NMU total knockouts, indicating other effectors or receptors contribute.
• No selective, metabolically stable NMUR1 agonist or antagonist with good CNS/peripheral selectivity has yet reached human trials.
• The role of NMU in human energy homeostasis — as opposed to rodent models — is not directly established; human genetic associations exist but causal evidence is lacking.
• NMU expression in cancer is documented at the mRNA and protein level in multiple tumour types, but whether NMU signalling is oncogenic, tumour-suppressive, or context-dependent in humans remains unresolved.
• NMU-25's C-terminal amide is cleaved by serum proteases, limiting systemic half-life; the identity and tissue distribution of the primary degrading enzyme in humans has been partially characterised but not fully mapped (Fujimoto and colleagues, 2015).

Related peptides

• Neuromedin S (NMS) — A related neuropeptide identified in 2005 that activates NMUR1 and NMUR2 with similar potency to NMU; shares the conserved C-terminal core sequence.
• Neuromedin U-8 — The shorter 8-residue C-terminal fragment of the NMU precursor; retains full receptor-binding capacity through the shared pharmacophore and is used as a research tool for receptor pharmacology.