{"gene":"PYY","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":2002,"finding":"PYY(3-36) inhibits food intake via the NPY Y2 receptor (Y2R) in the arcuate nucleus: peripheral injection inhibits feeding in wild-type but not Y2r-null mice, increases c-Fos in the arcuate nucleus, decreases hypothalamic NPY mRNA, inhibits electrical activity of NPY nerve terminals thereby activating adjacent POMC neurons, and intra-arcuate injection of PYY(3-36) inhibits food intake.","method":"Y2r knockout mice (genetic epistasis), peripheral and intra-arcuate injection, c-Fos immunoreactivity, in situ hybridization, electrophysiology, human infusion study","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including genetic null mice, electrophysiology, neuronal activation, and human infusion; highly replicated landmark paper","pmids":["12167864"],"is_preprint":false},{"year":1993,"finding":"Dipeptidyl peptidase IV (DPP-IV) cleaves the N-terminal dipeptide Tyr-Pro from PYY(1-36) to generate PYY(3-36), converting a non-selective Y1/Y2 agonist into a highly selective Y2 receptor agonist; DPP-IV is present on endothelial surfaces and brush border membranes and is the only enzyme tested capable of performing this cleavage.","method":"In vitro enzymatic assay with purified DPP-IV and PYY substrate; receptor binding assays","journal":"Medizinische Klinik","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro enzymatic assay with receptor binding confirmation; finding corroborated by multiple subsequent studies","pmids":["8097274"],"is_preprint":false},{"year":1994,"finding":"Two endogenous molecular forms of PYY exist in vivo—PYY(1-36) and PYY(3-36)—with distinct receptor selectivity: PYY(1-36) is an unselective Y1/Y2 agonist whereas PYY(3-36) is a highly selective Y2 agonist, demonstrating that proteolytic processing controls receptor subtype selectivity.","method":"Peptide purification from rabbit intestinal mucosa, primary structure determination (sequencing), receptor binding displacement assays","journal":"Peptides","confidence":"High","confidence_rationale":"Tier 1 — direct biochemical purification and receptor pharmacology; confirmed across species","pmids":["7984499"],"is_preprint":false},{"year":2000,"finding":"PYY(1-36), [Pro34]PYY (Y1-selective), and PYY(3-36) (Y2-selective) adopt distinct solution conformations (differing helicities by CD and NMR) that correlate with their receptor subtype binding affinities, suggesting conformation contributes to Y receptor subtype selectivity.","method":"Circular dichroism, 1H-NMR, sedimentation equilibrium, receptor binding (Y1- and Y2-transfected cells)","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"High","confidence_rationale":"Tier 1 — multiple structural methods combined with functional receptor binding assays in single study","pmids":["10898754"],"is_preprint":false},{"year":2004,"finding":"PYY adopts the PP-fold in solution but binds to Y receptors from a membrane-associated (micelle-bound) state in which the N-terminus is free and the C-terminal helix is stabilized; micelle-bound pPYY and pNPY are structurally much more similar than their solution structures, explaining their similar receptor binding profiles at Y1/Y2 receptors.","method":"NMR structure of pPYY in solution and bound to DPC micelles; heteronuclear NOE, generalized order parameters S2","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — rigorous NMR structural study with functional interpretation based on receptor binding profiles","pmids":["15178255"],"is_preprint":false},{"year":2005,"finding":"The anorectic effect of peripherally administered PYY(3-36) is not dependent on the vagus nerve, but activates neurons in the area postrema and nucleus tractus solitarius (brainstem areas mediating aversive stimuli) and produces conditioned taste aversion in mice, suggesting its food-intake inhibition partly involves induction of an aversive response.","method":"Vagotomy, c-Fos immunoreactivity, conditioned taste aversion assay in mice","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 2 — clean surgical ablation with defined behavioral readout, multiple endpoints","pmids":["16054059"],"is_preprint":false},{"year":1997,"finding":"PYY and the Y2-selective agonist PYY(13-36) directly inhibit approximately 50% of dorsal motor nucleus of the vagus (DMN) neurons via Y2 receptors, including under synaptic blockade, providing a direct mechanism by which circulating PYY suppresses vagally mediated digestive functions.","method":"In vivo and in vitro brain stem slice electrophysiology, synaptic blockade, Y2-selective agonist pharmacology","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 1 — direct electrophysiological recordings in two experimental systems with receptor-selective agonist","pmids":["9249552"],"is_preprint":false},{"year":1997,"finding":"PYY controls gastric motility via differential action at Y1 and Y2 receptors in the dorsal vagal complex (DVC): Y2 agonist applied to the DVC suppresses TRH-stimulated gastric motility (mimicking peripheral PYY), while Y1 agonist stimulates motility from basal conditions, indicating receptor-specific bidirectional control.","method":"Microinjection into DVC, gastric motility recording, Y1 and Y2 selective agonists","journal":"Neurogastroenterology and motility","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological dissection with receptor-selective agonists in vivo; single lab","pmids":["9198086"],"is_preprint":false},{"year":2009,"finding":"NPY and PYY modulate GABAergic inhibitory synaptic transmission onto dorsal motor nucleus of the vagus (DMV) neurons via presynaptic Y1 and Y2 receptors, but only when intracellular cAMP levels are elevated (by forskolin, CCK-8s, TRH, or vagal deafferentation); under low resting cAMP, neither peptide inhibits evoked IPSCs.","method":"Whole-cell patch-clamp recordings from identified DMV neurons, cAMP manipulation, spontaneous and miniature current analysis, receptor-selective agonists","journal":"Neurogastroenterology and motility","confidence":"High","confidence_rationale":"Tier 1 — rigorous electrophysiology with pharmacological dissection; mechanistic dependency on cAMP demonstrated","pmids":["19622099"],"is_preprint":false},{"year":2004,"finding":"PYY slows intestinal transit via serotonergic (5-HT) neurotransmission that is coupled to a downstream opioid (naloxone-sensitive) pathway; both pathways are localized to the efferent (proximal gut) limb and 5-HT-induced slowing of transit is itself naloxone-reversible.","method":"Fistulated dog model with compartmentalized gut perfusion, selective receptor antagonists (ondansetron, naloxone), intestinal transit measurement","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological pathway dissection in a controlled in vivo model; single lab","pmids":["15010361"],"is_preprint":false},{"year":1991,"finding":"PYY receptors in rat pancreas are Y1-type receptors localized predominantly on vascular smooth muscle cells (and to a lesser extent endothelial cells), as shown by autoradiography with 125I-Tyr36-PYY and displacement by the Y1-selective agonist [Leu31,Pro34]NPY.","method":"Slide-mount autoradiography, collagenase-isolated vascular fractions, competitive binding, light- and electron-microscopic autoradiography","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 1 — ultrastructural localization combined with pharmacological receptor characterization","pmids":["1847590"],"is_preprint":false},{"year":2014,"finding":"Propionate stimulates PYY and GLP-1 secretion from colonic L cells via free fatty acid receptor 2 (FFA2/GPR43): propionate-induced gut hormone release is significantly attenuated in FFA2-knockout mice both in primary colonic crypt cultures and in vivo (portal and jugular vein measurements after intra-colonic infusion).","method":"FFA2 knockout mice, primary murine colonic crypt cultures (in vitro), in vivo intra-colonic infusion with portal/jugular vein sampling","journal":"International journal of obesity (2005)","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout with in vitro and in vivo validation, multiple measurement sites","pmids":["25109781"],"is_preprint":false},{"year":2016,"finding":"Fermentable carbohydrate (inulin) acts via FFAR2 to drive an 87% increase in PYY-producing cell density in the colon, reducing food intake and preventing diet-induced obesity; this effect is absent in Ffar2-knockout mice.","method":"Ffar2 knockout mice, dietary supplementation, enteroendocrine cell density measurement, intestinal organoids and colonic cultures","journal":"Molecular metabolism","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout plus in vitro organoid validation, multiple orthogonal readouts","pmids":["28123937"],"is_preprint":false},{"year":2018,"finding":"SCFAs (propionate and butyrate) strongly increase PYY gene expression and hormone secretion in human enteroendocrine cells predominantly via histone deacetylase (HDAC) inhibitory activity, with minor contribution of FFA2 (GPR43); this transcriptional stimulation is specific to human-derived cell models and not reproduced in murine primary cultures due to differences in PYY gene structure.","method":"Human cell lines and intestinal primary cultures, HDAC inhibition assays, FFA2 pharmacology, gene expression and secretion measurements","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — mechanistic dissection with HDAC inhibitors and FFA2 agonists, human vs mouse comparison; single lab","pmids":["29311617"],"is_preprint":false},{"year":2016,"finding":"TLR stimulation increases PYY expression in enteroendocrine L cells via an NF-κB-dependent pathway, additive to butyrate effects; butyrate also upregulates TLR expression (including TLR4), enhancing the NF-κB response to TLR stimulation and thus linking microbiota sensing to PYY production.","method":"Human L-cell model with NF-κB reporter, TLR agonists, butyrate treatment, gene expression analysis","journal":"Cellular microbiology","confidence":"Medium","confidence_rationale":"Tier 2 — reporter assay plus expression data in defined cell model; single lab","pmids":["27405092"],"is_preprint":false},{"year":2006,"finding":"The taste-signaling G protein α-gustducin co-localizes with PYY and GLP-1 in enteroendocrine L cells of the human colon; stimulation with the bitter compound phenylthiocarbamide (a hT2R38 ligand) induces rapid intracellular Ca2+ increases in human intestinal endocrine cell lines, indicating gustducin-coupled chemosensory receptors mediate PYY secretion signals.","method":"Double-labeling immunofluorescence, serial section immunostaining, RT-PCR, intracellular Ca2+ imaging","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"Medium","confidence_rationale":"Tier 2 — co-localization plus functional Ca2+ signaling assay; single lab","pmids":["16728727"],"is_preprint":false},{"year":2011,"finding":"The intestinal sweet taste receptor T1R2/T1R3 (coupled through α-gustducin) is functionally involved in glucose-stimulated PYY and GLP-1 secretion in humans: blockade with the T1R2/T1R3 antagonist lactisole significantly reduces postprandial PYY and GLP-1 release after intragastric and intraduodenal glucose administration.","method":"Randomized double-blind placebo-controlled crossover human study, lactisole pharmacology, plasma hormone measurement","journal":"American journal of physiology. Endocrinology and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 — controlled human intervention with receptor antagonist; single study","pmids":["21540445"],"is_preprint":false},{"year":2016,"finding":"Angiotensin II stimulates PYY and GLP-1 secretion from colonic L cells via the Ang II type 1 receptor (AT1R), which is exclusively expressed in colonic L cells; AT1R activation raises intracellular calcium in L cells, and the released PYY acts on epithelial Y1 receptors to reduce ion transport (short-circuit current), thereby limiting fluid secretion into the colonic lumen.","method":"Primary cultures of mouse and human colon, candesartan antagonist, live-cell GCaMP3 calcium imaging, Ussing chamber electrophysiology, Y1 receptor antagonist","journal":"Endocrinology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (Ca2+ imaging, Ussing chamber, receptor antagonists) in mouse and human tissue","pmids":["27447725"],"is_preprint":false},{"year":2016,"finding":"Elevated circulating PYY following Roux-en-Y gastric bypass (RYGB) restores normal glucose regulation of glucagon and insulin secretion and normalizes islet morphology in diabetic GK rats; serum from RYGB animals mimics these effects on isolated islets, and this is reversed by PYY neutralization but not GLP-1 receptor antagonism.","method":"GK rat RYGB model, isolated islet culture with RYGB serum, PYY neutralization, GLP-1 receptor antagonist, chronic PYY in vitro exposure","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — humoral factor identification by neutralization, in vitro recapitulation with GLP-1 receptor antagonist control","pmids":["27117413"],"is_preprint":false},{"year":2017,"finding":"Intra-islet PYY (localized in alpha-cells) is regulated by DPP-IV activity; DPP-IV inhibition by sitagliptin enhances glucose-stimulated insulin secretion (GSIS) via local PYY rather than GLP-1; chronic PYY application directly enhances GSIS in rodent and diabetic human islets; RYGB strongly increases islet PYY content.","method":"Immunohistochemistry, gene expression, DPP-IV inhibition with sitagliptin, islet secretion studies, radioimmunoassay","journal":"Diabetes, obesity & metabolism","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological dissection with GLP-1/PYY distinction, rodent and human islets; single lab","pmids":["28892258"],"is_preprint":false},{"year":2015,"finding":"Pancreatic islet beta-cell-derived PYY improves glucose homeostasis by increasing beta-cell mass and insulin secretion; transgenic overexpression of PYY in beta-cells (Pyy-tg/Rip-Cre mice) leads to elevated serum insulin, improved glucose tolerance, increased beta-cell proliferation, and altered expression of genes important for beta-cell function.","method":"Transgenic mouse model (Rip-Cre driven PYY overexpression), glucose tolerance tests, beta-cell mass quantification, gene expression analysis","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 — clean transgenic gain-of-function with defined metabolic phenotype; single lab","pmids":["26125465"],"is_preprint":false},{"year":1988,"finding":"PYY secretion from primary colonic L cells is stimulated by sodium oleate (fatty acid) in a dose-dependent manner, as well as by bombesin, epinephrine, and forskolin (cAMP elevation), but not by carbachol, establishing fatty acids and cAMP-linked pathways as direct secretagogues.","method":"Primary culture of canine colonic PYY cells on collagen, elutriation-based enrichment, secretion assay with pharmacological agents","journal":"The American journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 — direct primary cell secretion assay with multiple pharmacological agents; single lab","pmids":["3377082"],"is_preprint":false},{"year":1997,"finding":"PYY upregulates intestinal fatty acid-binding protein (I-FABP) transcripts specifically in differentiated enterocytes via high-affinity PYY receptors (IC50 5-50 pM), acting through a post-transcriptional or transcriptional mechanism that is confined to terminally differentiated villar cells and does not affect mRNA in proliferating cells.","method":"Quantitative in situ hybridization on intestinal epithelial hybrid cell lines, competitive binding autoradiography, ribonuclease protection assay, BrdU incorporation","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — receptor identification combined with cell-type-specific transcriptional readout; single lab","pmids":["9139712"],"is_preprint":false},{"year":1998,"finding":"PYY stimulates intestinal apolipoprotein AIV (apo AIV) synthesis and lymphatic secretion by a post-transcriptional mechanism: intravenous PYY (75-200 pmol/kg/h) increases apo AIV output up to 3.5-fold and raises jejunal mucosal apo AIV synthesis by 60% without affecting apo AIV mRNA levels.","method":"Mesenteric lymph fistula rat model, intravenous PYY infusion, apo AIV protein output measurement in lymph, mucosal synthesis assay, mRNA analysis","journal":"The American journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo dose-response with parallel protein and mRNA measurements establishing post-transcriptional mechanism; single lab","pmids":["9756495"],"is_preprint":false},{"year":2007,"finding":"After peripheral (i.p.) injection, PYY(3-36) distributes to the area postrema (and subfornical organ and median eminence) in the brain, with near-background signals in all other brain structures including hypothalamic nuclei, suggesting the anorectic effect of peripheral PYY(3-36) is mediated primarily through circumventricular organs rather than direct hypothalamic action.","method":"Whole-body autoradiography and brain section autoradiography after i.p. and i.v. injection of 125I-labeled PYY(3-36) and analogs in rats","journal":"Journal of molecular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — direct radiolabeled biodistribution study with brain regional analysis; single lab","pmids":["17952639"],"is_preprint":false},{"year":2010,"finding":"The anorectic effect of peripheral PYY(3-36) requires intact area postrema (AP) and subfornical organ (SFO) acting redundantly (ablation of either alone is insufficient), and also partially requires subdiaphragmatic vagal input; vagotomy further reveals that AP and SFO neuronal activation by peripheral PYY is partly vagally driven.","method":"Lesion of AP, SFO, or both combined; subdiaphragmatic vagotomy; c-fos mRNA brain mapping; food intake measurement in rats","journal":"The European journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — multiple surgical ablations with defined behavioral and neuronal activation readouts; mechanistic pathway delineated","pmids":["20646064"],"is_preprint":false},{"year":2007,"finding":"PYY(3-36) activates neurons in the arcuate nucleus (ARC), commissural and gelatinous NTS, and area postrema; approximately 10% of Fos+ neurons in the cmNTS are catecholaminergic (TH+), indicating that PYY(3-36) inhibits feeding partly through activation of ARC neurons and hindbrain catecholaminergic circuits.","method":"Peripheral PYY(3-36) injection in rats, c-Fos immunoreactivity in multiple brain regions, tyrosine hydroxylase double-labeling","journal":"Peptides","confidence":"Medium","confidence_rationale":"Tier 2 — c-Fos neuronal mapping with catecholaminergic co-labeling after defined dose; single lab","pmids":["18082288"],"is_preprint":false},{"year":2008,"finding":"Central PYY-immunoreactive neurons are located exclusively in the gigantocellular reticular nucleus (Gi) of the rostral medulla in mouse, rat, and monkey; their axonal projections concentrate in the nucleus tractus solitarius, dorsal motor nucleus of the vagus, and hypoglossal nucleus, and they receive input from orexin and MCH fibers, suggesting a role in energy homeostasis via visceral and autonomic circuits.","method":"Immunohistochemistry in NPY-knockout mouse (to eliminate NPY crossreactivity), NPY-preabsorbed antibody in rat, cross-species comparison, projection mapping","journal":"The Journal of comparative neurology","confidence":"Medium","confidence_rationale":"Tier 2 — rigorous antibody controls (NPY KO mice), multi-species, anatomical circuit mapping; single lab","pmids":["18022952"],"is_preprint":false},{"year":1993,"finding":"PYY receptors in human adipocytes mediate antilipolytic effects; PYY (10^-7 M) inhibits lipolysis by 58% in femoral and 14% in pericolonic fat cells, correlating with regional PYY receptor density; this is an inhibitory system alongside the alpha2-adrenergic system.","method":"Radioligand binding (125I-PYY) on adipocyte membranes from multiple depots, lipolysis assay on isolated adipocytes","journal":"The American journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 — receptor characterization combined with functional lipolysis assay across multiple depots; single lab","pmids":["8393293"],"is_preprint":false},{"year":2013,"finding":"Endogenous PYY released from colonic L cells acts in a paracrine fashion via Y1 receptors to inhibit epithelial ion transport: L-glutamine-stimulated PYY release produces slow reductions in short-circuit current (Isc) in colonic and jejunal mucosa that are absent in PYY-/- tissue and blocked by Y1 receptor antagonist; the initial GLP-1-mediated Isc increase can be partially attributed to GLP-1 receptor activation.","method":"Ussing chamber voltage-clamp of mouse intestinal mucosae, PYY knockout tissue, selective Y1 and GLP-1 receptor antagonists, CaSR inhibitor","journal":"British journal of pharmacology","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout combined with pharmacological receptor dissection; multiple receptor antagonists and tissue regions tested","pmids":["23992397"],"is_preprint":false},{"year":2022,"finding":"GIP receptor (GIPR) agonism reduces PYY(3-36)-induced conditioned taste aversion (CTA) without affecting PYY-mediated hypophagia; GIPR and NPY2R are co-expressed on the same neurons in the area postrema; peripheral GIPR agonism reduces PYY-induced neuronal activity in the parabrachial nucleus (PBN), providing a mechanistic basis for reduced nausea.","method":"Conditioned taste avoidance in mice, central and peripheral administration, cFos whole-brain analysis, receptor co-expression in area postrema neurons","journal":"Diabetes","confidence":"Medium","confidence_rationale":"Tier 2 — behavioral assay with neuroanatomical receptor co-localization and brain-wide cFos mapping; single lab","pmids":["35499381"],"is_preprint":false},{"year":2009,"finding":"PYY(3-36) (Y2 receptor agonist) inhibits diarrhea by two mechanisms: reducing intestinal fluid secretion and slowing colonic transit, both demonstrated in mouse models using a selective Y2 agonist alongside PYY(3-36).","method":"Mouse diarrhea models (dimethyl-PGE2, 5-HT, castor oil), intestinal fluid accumulation assay, colonic transit (fecal output) measurement, Y2-selective agonist comparison","journal":"Peptides","confidence":"Medium","confidence_rationale":"Tier 2 — multiple in vivo disease models with receptor-selective pharmacology; single lab","pmids":["19925840"],"is_preprint":false},{"year":1996,"finding":"PYY mRNA is transiently expressed in all early pancreatic endocrine cell types during embryogenesis (E12 onward), co-localizing with glucagon and insulin in multipotent precursor cells; PYY expression precedes NPY and PP, and actively-dividing triple-positive (insulin+glucagon+PYY) cells are consistent with a precursor role for PYY-positive endocrine cells.","method":"Immunohistochemistry, BrdU S-phase labeling, developmental staging in rat and mouse pancreas","journal":"The journal of histochemistry and cytochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — systematic developmental staging with BrdU cell-cycle analysis; single lab","pmids":["8756753"],"is_preprint":false},{"year":2015,"finding":"GLP-1 and PYY are co-stored in separate secretory granules from neurotensin in intestinal L cells, yet all three peptides are co-secreted together from perfused small intestines and colonic crypt cultures in response to metabolite, neuropeptide, and hormonal stimuli; neurotensin acts synergistically with GLP-1 and PYY to decrease food intake and inhibit gastric emptying.","method":"FACS-sorted cell analysis, laser capture, confocal fluorescence microscopy, perfused intestine and crypt culture secretion assays, cell ablation studies, feeding and gastric emptying assays","journal":"Endocrinology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (ultrastructural, secretion, cell ablation, pharmacological) in single comprehensive study","pmids":["26469136"],"is_preprint":false}],"current_model":"PYY is released from intestinal L cells postprandially (stimulated by fatty acids, SCFAs via FFA2/HDAC mechanisms, sweet taste receptors, amino acids, and angiotensin II via AT1R), undergoes DPP-IV–mediated cleavage of its N-terminal dipeptide to generate the Y2-selective form PYY(3-36), which inhibits food intake primarily through Y2 receptors in the hypothalamic arcuate nucleus (suppressing NPY neurons and activating POMC neurons) and circumventricular organs (area postrema, subfornical organ), with additional peripheral actions including direct inhibition of vagal motor neurons in the dorsal motor nucleus via Y2 receptors (modulated by cAMP levels), slowing of intestinal transit via serotonergic-opioid pathways, antilipolysis in adipocytes via Y1 receptors, paracrine inhibition of colonic fluid secretion via Y1 receptors, regulation of pancreatic islet insulin secretion and beta-cell mass, and stimulation of intestinal apolipoprotein AIV secretion by a post-transcriptional mechanism."},"narrative":{"teleology":[{"year":1988,"claim":"Establishing how PYY secretion is directly regulated resolved a key question about the physiological triggers for this L-cell hormone: fatty acids and cAMP-linked pathways were identified as direct secretagogues.","evidence":"Primary canine colonic L-cell cultures with pharmacological stimulation","pmids":["3377082"],"confidence":"Medium","gaps":["Signaling cascade downstream of fatty acid sensing not identified","Relevance to human L cells not tested"]},{"year":1991,"claim":"Identifying the receptor subtype mediating PYY actions in the pancreas revealed that PYY signals through Y1 receptors on pancreatic vascular smooth muscle, suggesting a vascular rather than direct endocrine mechanism.","evidence":"Autoradiographic receptor localization and competitive binding with Y1-selective agonist in rat pancreas","pmids":["1847590"],"confidence":"High","gaps":["Direct islet cell receptor expression not characterized","Functional consequence of vascular Y1 activation on islet blood flow not measured"]},{"year":1993,"claim":"Two discoveries established that DPP-IV-mediated cleavage generates a Y2-selective form PYY(3-36), and that PYY receptors in adipocytes mediate regional antilipolytic effects, defining both a key processing step and a peripheral metabolic action.","evidence":"In vitro DPP-IV enzymatic assay with receptor binding [PMID:8097274]; radioligand binding and lipolysis assay on human adipocytes from multiple depots [PMID:8393293]","pmids":["8097274","8393293"],"confidence":"High","gaps":["In vivo DPP-IV processing kinetics not measured","Y receptor subtype mediating adipocyte antilipolysis not definitively assigned"]},{"year":1994,"claim":"Purification of both PYY(1-36) and PYY(3-36) from intestinal tissue and demonstration of their distinct receptor selectivities confirmed that proteolytic processing is a physiological mechanism controlling receptor subtype engagement.","evidence":"Peptide purification from rabbit intestinal mucosa with receptor binding displacement assays","pmids":["7984499"],"confidence":"High","gaps":["Relative circulating concentrations of both forms in fed versus fasted states not quantified"]},{"year":1996,"claim":"Demonstrating transient PYY co-expression with insulin and glucagon in dividing embryonic pancreatic cells suggested PYY marks multipotent endocrine precursors, opening the question of whether PYY has a developmental function.","evidence":"Immunohistochemistry with BrdU S-phase labeling across developmental stages in rat and mouse pancreas","pmids":["8756753"],"confidence":"Medium","gaps":["No loss-of-function test for PYY in pancreatic development","Whether PYY expression is functionally required or merely a lineage marker is unresolved"]},{"year":1997,"claim":"Electrophysiological and pharmacological studies revealed that PYY directly inhibits vagal motor neurons via Y2 receptors and bidirectionally controls gastric motility via Y1/Y2 in the dorsal vagal complex, establishing central autonomic circuits as key effector pathways.","evidence":"Brain stem slice electrophysiology with synaptic blockade and Y2-selective agonist [PMID:9249552]; DVC microinjection with gastric motility recording [PMID:9198086]","pmids":["9249552","9198086"],"confidence":"High","gaps":["Whether circulating PYY achieves sufficient concentrations at the DVC to reproduce these effects physiologically was not established"]},{"year":1997,"claim":"Discovery that PYY upregulates intestinal fatty acid-binding protein and stimulates apolipoprotein AIV secretion post-transcriptionally extended PYY's role beyond motility/appetite to intestinal lipid handling.","evidence":"In situ hybridization in intestinal hybrid cells [PMID:9139712]; mesenteric lymph fistula rat model with mRNA/protein comparison [PMID:9756495]","pmids":["9139712","9756495"],"confidence":"Medium","gaps":["Receptor subtype mediating apo AIV stimulation not identified","Post-transcriptional mechanism (mRNA stability vs. translational) not resolved"]},{"year":2000,"claim":"Structural studies revealed that PYY(1-36) and PYY(3-36) adopt distinct solution conformations correlated with Y1/Y2 selectivity, and that the functional receptor-binding state is membrane-associated with a stabilized C-terminal helix.","evidence":"CD, NMR, and sedimentation equilibrium on PYY variants [PMID:10898754]; NMR of micelle-bound pPYY [PMID:15178255]","pmids":["10898754","15178255"],"confidence":"High","gaps":["No receptor-bound co-crystal or cryo-EM structure","How N-terminal truncation alters membrane association and receptor docking at atomic detail remains unknown"]},{"year":2002,"claim":"The landmark demonstration that PYY(3-36) inhibits food intake via arcuate nucleus Y2 receptors—suppressing NPY neurons and activating POMC neurons—established the central satiety mechanism.","evidence":"Y2r knockout mice, peripheral and intra-arcuate injection, electrophysiology, c-Fos mapping, and human infusion in a single study","pmids":["12167864"],"confidence":"High","gaps":["Whether Y2R in the arcuate is sufficient versus necessary for the full anorectic response was not resolved by this study alone"]},{"year":2005,"claim":"Vagotomy and brain mapping studies revealed that PYY(3-36) anorexia does not require the vagus but involves brainstem aversive circuits (area postrema, NTS), while subsequent lesion studies showed the area postrema and subfornical organ act redundantly as central access points.","evidence":"Vagotomy with c-Fos and conditioned taste aversion [PMID:16054059]; combinatorial AP/SFO lesions with vagotomy and c-fos mapping [PMID:20646064]; radiolabeled PYY biodistribution [PMID:17952639]","pmids":["16054059","20646064","17952639"],"confidence":"High","gaps":["Relative contribution of aversive versus homeostatic satiety signaling to total food intake reduction remains unquantified","Neuronal cell types in area postrema responding to PYY not fully characterized"]},{"year":2006,"claim":"Co-localization of gustducin with PYY in colonic L cells and functional bitter taste receptor signaling in these cells revealed that chemosensory taste pathways regulate PYY secretion, later extended to sweet taste receptor T1R2/T1R3 in humans.","evidence":"Immunofluorescence co-localization and Ca2+ imaging in human intestinal endocrine cells [PMID:16728727]; randomized controlled human study with T1R2/T1R3 antagonist lactisole [PMID:21540445]","pmids":["16728727","21540445"],"confidence":"Medium","gaps":["Quantitative contribution of taste receptor pathways versus nutrient transporters to total postprandial PYY release is unknown","Downstream signaling cascade from gustducin to granule exocytosis not delineated"]},{"year":2009,"claim":"The finding that PYY modulation of vagal GABAergic transmission requires elevated cAMP revealed a gating mechanism: PYY's inhibition of vagal circuits is context-dependent, only operative when neurons are already activated by other signals.","evidence":"Whole-cell patch-clamp of DMV neurons with forskolin and physiological cAMP elevators (CCK, TRH)","pmids":["19622099"],"confidence":"High","gaps":["In vivo confirmation that cAMP-dependent gating determines PYY efficacy on vagal output is lacking","Whether this gating extends to other brain regions expressing Y2R is untested"]},{"year":2013,"claim":"Using PYY knockout tissue and receptor antagonists, paracrine PYY signaling through epithelial Y1 receptors was shown to inhibit colonic ion transport, establishing PYY as a local regulator of fluid secretion in addition to its endocrine roles.","evidence":"Ussing chamber on PYY-/- mouse colonic and jejunal mucosa with Y1 antagonist","pmids":["23992397"],"confidence":"High","gaps":["Whether this paracrine axis is dysregulated in inflammatory bowel disease is unknown","Quantitative contribution to whole-body fluid balance not assessed"]},{"year":2014,"claim":"SCFA-driven PYY secretion was mechanistically dissected: propionate acts through FFA2 in mice, while in human cells SCFAs primarily induce PYY gene transcription via HDAC inhibition; fermentable carbohydrates expand PYY-producing cell populations via FFAR2.","evidence":"FFA2 knockout mice with in vivo and crypt culture validation [PMID:25109781]; HDAC inhibitor studies in human L-cell models [PMID:29311617]; Ffar2 KO with dietary inulin and organoids [PMID:28123937]","pmids":["25109781","29311617","28123937"],"confidence":"High","gaps":["Relative importance of FFA2 versus HDAC pathways in intact human gut in vivo is unresolved","Chromatin targets of SCFA-mediated HDAC inhibition at the PYY locus not mapped"]},{"year":2016,"claim":"Multiple studies expanded PYY's regulatory inputs and outputs: angiotensin II via AT1R on L cells triggers PYY release that limits colonic fluid secretion via Y1; TLR/NF-κB signaling enhances PYY expression; and elevated PYY after gastric bypass normalizes islet function independently of GLP-1.","evidence":"AT1R agonism with Ca2+ imaging and Ussing chamber in mouse/human colon [PMID:27447725]; NF-κB reporter in human L-cell model [PMID:27405092]; GK rat RYGB with PYY neutralization and GLP-1R antagonist [PMID:27117413]","pmids":["27447725","27405092","27117413"],"confidence":"High","gaps":["Whether AT1R-PYY axis is physiologically relevant in hypertension or ACE-inhibitor therapy is untested","Molecular mechanism by which PYY normalizes islet morphology is not defined"]},{"year":2017,"claim":"Intra-islet PYY localized in alpha cells was shown to enhance insulin secretion and beta-cell mass, with DPP-IV processing controlling local PYY activity, revealing an autocrine/paracrine islet circuit distinct from gut-derived PYY.","evidence":"Immunohistochemistry, sitagliptin DPP-IV inhibition, islet secretion in rodent and human islets [PMID:28892258]; transgenic beta-cell PYY overexpression with glucose tolerance and beta-cell proliferation [PMID:26125465]","pmids":["28892258","26125465"],"confidence":"Medium","gaps":["Y receptor subtype mediating islet PYY effects not definitively identified","Whether intra-islet PYY contributes meaningfully to glycemic control in non-surgical settings is unclear","Single-lab findings for intra-islet circuit"]},{"year":2022,"claim":"The finding that GIPR agonism reduces PYY(3-36)-induced conditioned taste aversion via co-expressed GIPR/NPY2R neurons in the area postrema dissociated PYY's aversive from its hypophagic signaling, with therapeutic implications for incretin-based anti-obesity drugs.","evidence":"Conditioned taste avoidance in mice, cFos whole-brain analysis, receptor co-expression mapping in area postrema","pmids":["35499381"],"confidence":"Medium","gaps":["Whether GIPR-NPY2R interaction occurs at the intracellular signaling level or involves separate downstream circuits is unknown","Human translation of the GIPR–PYY interaction not confirmed"]},{"year":null,"claim":"Key unresolved questions include the atomic-resolution structure of PYY bound to Y2R, the precise chromatin and transcriptional regulation of the PYY gene in L cells, the relative physiological contribution of aversive versus homeostatic pathways to PYY-mediated satiety in humans, and the mechanism by which PYY promotes beta-cell proliferation.","evidence":"","pmids":[],"confidence":"Low","gaps":["No receptor-bound structural model of PYY–Y2R complex","Transcriptional regulation of the PYY gene locus largely unmapped","Mechanism of PYY-driven beta-cell proliferation unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,2,3,6]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,8,17,29]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,1,2,21,23]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[33]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,6,8,17,29]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[0,5,6,8,25,26]},{"term_id":"R-HSA-8963743","term_label":"Digestion and absorption","supporting_discovery_ids":[9,23,31]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[22,23,28]}],"complexes":[],"partners":["NPY2R","NPY1R","DPP4","FFAR2","AGTR1","GNAT3","TAS1R2"],"other_free_text":[]},"mechanistic_narrative":"PYY is a gut-derived anorexigenic peptide hormone released from intestinal L cells in response to luminal nutrients (fatty acids, glucose, amino acids), short-chain fatty acids (via FFA2 receptors and HDAC inhibition), sweet/bitter taste receptor signaling (T1R2/T1R3 and gustducin-coupled pathways), and angiotensin II (via AT1R), and is proteolytically converted by DPP-IV from the non-selective Y1/Y2 agonist PYY(1-36) to the Y2-selective form PYY(3-36) [PMID:8097274, PMID:7984499, PMID:25109781, PMID:21540445, PMID:27447725]. PYY(3-36) inhibits food intake centrally by acting on Y2 receptors in the hypothalamic arcuate nucleus—suppressing NPY neurons and disinhibiting POMC neurons—and in circumventricular organs (area postrema, subfornical organ), with redundant vagal and humoral input pathways contributing to brainstem neuronal activation and conditioned taste aversion [PMID:12167864, PMID:16054059, PMID:20646064]. Peripherally, PYY exerts Y2-mediated direct inhibition of vagal motor neurons in the dorsal motor nucleus (gated by intracellular cAMP levels), slows intestinal transit through serotonergic-opioid pathways, and acts in a paracrine Y1-dependent manner to suppress colonic epithelial ion transport and fluid secretion [PMID:9249552, PMID:19622099, PMID:15010361, PMID:23992397]. PYY also functions as an intra-islet regulator—expressed in alpha cells and beta cells—where it enhances glucose-stimulated insulin secretion and promotes beta-cell mass, and it exerts antilipolytic effects in adipocytes via Y1 receptors [PMID:27117413, PMID:26125465, PMID:8393293]."},"prefetch_data":{"uniprot":{"accession":"P10082","full_name":"Peptide YY","aliases":["PYY-I","Peptide tyrosine tyrosine"],"length_aa":97,"mass_kda":11.1,"function":"This gut peptide inhibits exocrine pancreatic secretion, has a vasoconstrictory action and inhibitis jejunal and colonic mobility","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/P10082/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PYY","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PYY","total_profiled":1310},"omim":[{"mim_id":"606638","title":"PANCREATIC POLYPEPTIDE 2; PPY2","url":"https://www.omim.org/entry/606638"},{"mim_id":"606637","title":"PEPTIDE YY, 2; PYY2","url":"https://www.omim.org/entry/606637"},{"mim_id":"601790","title":"PANCREATIC POLYPEPTIDE RECEPTOR 1; PPYR1","url":"https://www.omim.org/entry/601790"},{"mim_id":"601770","title":"NEUROPEPTIDE Y RECEPTOR Y6; NPY6R","url":"https://www.omim.org/entry/601770"},{"mim_id":"601665","title":"OBESITY","url":"https://www.omim.org/entry/601665"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"intestine","ntpm":66.2}],"url":"https://www.proteinatlas.org/search/PYY"},"hgnc":{"alias_symbol":["PYY1"],"prev_symbol":[]},"alphafold":{"accession":"P10082","domains":[{"cath_id":"-","chopping":"9-79","consensus_level":"medium","plddt":75.6534,"start":9,"end":79}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P10082","model_url":"https://alphafold.ebi.ac.uk/files/AF-P10082-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P10082-F1-predicted_aligned_error_v6.png","plddt_mean":71.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PYY","jax_strain_url":"https://www.jax.org/strain/search?query=PYY"},"sequence":{"accession":"P10082","fasta_url":"https://rest.uniprot.org/uniprotkb/P10082.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P10082/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P10082"}},"corpus_meta":[{"pmid":"12167864","id":"PMC_12167864","title":"Gut hormone PYY(3-36) physiologically inhibits food intake.","date":"2002","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/12167864","citation_count":1697,"is_preprint":false},{"pmid":"25109781","id":"PMC_25109781","title":"The short chain fatty acid propionate stimulates GLP-1 and PYY secretion via free fatty acid receptor 2 in rodents.","date":"2014","source":"International journal of obesity (2005)","url":"https://pubmed.ncbi.nlm.nih.gov/25109781","citation_count":611,"is_preprint":false},{"pmid":"29311617","id":"PMC_29311617","title":"SCFAs strongly stimulate PYY production in human enteroendocrine cells.","date":"2018","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/29311617","citation_count":330,"is_preprint":false},{"pmid":"18796545","id":"PMC_18796545","title":"Dietary resistant starch upregulates total GLP-1 and PYY in a sustained day-long manner through fermentation in rodents.","date":"2008","source":"American journal of physiology. 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(genetic epistasis), peripheral and intra-arcuate injection, c-Fos immunoreactivity, in situ hybridization, electrophysiology, human infusion study\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including genetic null mice, electrophysiology, neuronal activation, and human infusion; highly replicated landmark paper\",\n      \"pmids\": [\"12167864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Dipeptidyl peptidase IV (DPP-IV) cleaves the N-terminal dipeptide Tyr-Pro from PYY(1-36) to generate PYY(3-36), converting a non-selective Y1/Y2 agonist into a highly selective Y2 receptor agonist; DPP-IV is present on endothelial surfaces and brush border membranes and is the only enzyme tested capable of performing this cleavage.\",\n      \"method\": \"In vitro enzymatic assay with purified DPP-IV and PYY substrate; receptor binding assays\",\n      \"journal\": \"Medizinische Klinik\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro enzymatic assay with receptor binding confirmation; finding corroborated by multiple subsequent studies\",\n      \"pmids\": [\"8097274\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Two endogenous molecular forms of PYY exist in vivo—PYY(1-36) and PYY(3-36)—with distinct receptor selectivity: PYY(1-36) is an unselective Y1/Y2 agonist whereas PYY(3-36) is a highly selective Y2 agonist, demonstrating that proteolytic processing controls receptor subtype selectivity.\",\n      \"method\": \"Peptide purification from rabbit intestinal mucosa, primary structure determination (sequencing), receptor binding displacement assays\",\n      \"journal\": \"Peptides\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct biochemical purification and receptor pharmacology; confirmed across species\",\n      \"pmids\": [\"7984499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"PYY(1-36), [Pro34]PYY (Y1-selective), and PYY(3-36) (Y2-selective) adopt distinct solution conformations (differing helicities by CD and NMR) that correlate with their receptor subtype binding affinities, suggesting conformation contributes to Y receptor subtype selectivity.\",\n      \"method\": \"Circular dichroism, 1H-NMR, sedimentation equilibrium, receptor binding (Y1- and Y2-transfected cells)\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple structural methods combined with functional receptor binding assays in single study\",\n      \"pmids\": [\"10898754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PYY adopts the PP-fold in solution but binds to Y receptors from a membrane-associated (micelle-bound) state in which the N-terminus is free and the C-terminal helix is stabilized; micelle-bound pPYY and pNPY are structurally much more similar than their solution structures, explaining their similar receptor binding profiles at Y1/Y2 receptors.\",\n      \"method\": \"NMR structure of pPYY in solution and bound to DPC micelles; heteronuclear NOE, generalized order parameters S2\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — rigorous NMR structural study with functional interpretation based on receptor binding profiles\",\n      \"pmids\": [\"15178255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The anorectic effect of peripherally administered PYY(3-36) is not dependent on the vagus nerve, but activates neurons in the area postrema and nucleus tractus solitarius (brainstem areas mediating aversive stimuli) and produces conditioned taste aversion in mice, suggesting its food-intake inhibition partly involves induction of an aversive response.\",\n      \"method\": \"Vagotomy, c-Fos immunoreactivity, conditioned taste aversion assay in mice\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean surgical ablation with defined behavioral readout, multiple endpoints\",\n      \"pmids\": [\"16054059\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"PYY and the Y2-selective agonist PYY(13-36) directly inhibit approximately 50% of dorsal motor nucleus of the vagus (DMN) neurons via Y2 receptors, including under synaptic blockade, providing a direct mechanism by which circulating PYY suppresses vagally mediated digestive functions.\",\n      \"method\": \"In vivo and in vitro brain stem slice electrophysiology, synaptic blockade, Y2-selective agonist pharmacology\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct electrophysiological recordings in two experimental systems with receptor-selective agonist\",\n      \"pmids\": [\"9249552\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"PYY controls gastric motility via differential action at Y1 and Y2 receptors in the dorsal vagal complex (DVC): Y2 agonist applied to the DVC suppresses TRH-stimulated gastric motility (mimicking peripheral PYY), while Y1 agonist stimulates motility from basal conditions, indicating receptor-specific bidirectional control.\",\n      \"method\": \"Microinjection into DVC, gastric motility recording, Y1 and Y2 selective agonists\",\n      \"journal\": \"Neurogastroenterology and motility\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological dissection with receptor-selective agonists in vivo; single lab\",\n      \"pmids\": [\"9198086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"NPY and PYY modulate GABAergic inhibitory synaptic transmission onto dorsal motor nucleus of the vagus (DMV) neurons via presynaptic Y1 and Y2 receptors, but only when intracellular cAMP levels are elevated (by forskolin, CCK-8s, TRH, or vagal deafferentation); under low resting cAMP, neither peptide inhibits evoked IPSCs.\",\n      \"method\": \"Whole-cell patch-clamp recordings from identified DMV neurons, cAMP manipulation, spontaneous and miniature current analysis, receptor-selective agonists\",\n      \"journal\": \"Neurogastroenterology and motility\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — rigorous electrophysiology with pharmacological dissection; mechanistic dependency on cAMP demonstrated\",\n      \"pmids\": [\"19622099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PYY slows intestinal transit via serotonergic (5-HT) neurotransmission that is coupled to a downstream opioid (naloxone-sensitive) pathway; both pathways are localized to the efferent (proximal gut) limb and 5-HT-induced slowing of transit is itself naloxone-reversible.\",\n      \"method\": \"Fistulated dog model with compartmentalized gut perfusion, selective receptor antagonists (ondansetron, naloxone), intestinal transit measurement\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological pathway dissection in a controlled in vivo model; single lab\",\n      \"pmids\": [\"15010361\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"PYY receptors in rat pancreas are Y1-type receptors localized predominantly on vascular smooth muscle cells (and to a lesser extent endothelial cells), as shown by autoradiography with 125I-Tyr36-PYY and displacement by the Y1-selective agonist [Leu31,Pro34]NPY.\",\n      \"method\": \"Slide-mount autoradiography, collagenase-isolated vascular fractions, competitive binding, light- and electron-microscopic autoradiography\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — ultrastructural localization combined with pharmacological receptor characterization\",\n      \"pmids\": [\"1847590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Propionate stimulates PYY and GLP-1 secretion from colonic L cells via free fatty acid receptor 2 (FFA2/GPR43): propionate-induced gut hormone release is significantly attenuated in FFA2-knockout mice both in primary colonic crypt cultures and in vivo (portal and jugular vein measurements after intra-colonic infusion).\",\n      \"method\": \"FFA2 knockout mice, primary murine colonic crypt cultures (in vitro), in vivo intra-colonic infusion with portal/jugular vein sampling\",\n      \"journal\": \"International journal of obesity (2005)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with in vitro and in vivo validation, multiple measurement sites\",\n      \"pmids\": [\"25109781\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Fermentable carbohydrate (inulin) acts via FFAR2 to drive an 87% increase in PYY-producing cell density in the colon, reducing food intake and preventing diet-induced obesity; this effect is absent in Ffar2-knockout mice.\",\n      \"method\": \"Ffar2 knockout mice, dietary supplementation, enteroendocrine cell density measurement, intestinal organoids and colonic cultures\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout plus in vitro organoid validation, multiple orthogonal readouts\",\n      \"pmids\": [\"28123937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SCFAs (propionate and butyrate) strongly increase PYY gene expression and hormone secretion in human enteroendocrine cells predominantly via histone deacetylase (HDAC) inhibitory activity, with minor contribution of FFA2 (GPR43); this transcriptional stimulation is specific to human-derived cell models and not reproduced in murine primary cultures due to differences in PYY gene structure.\",\n      \"method\": \"Human cell lines and intestinal primary cultures, HDAC inhibition assays, FFA2 pharmacology, gene expression and secretion measurements\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic dissection with HDAC inhibitors and FFA2 agonists, human vs mouse comparison; single lab\",\n      \"pmids\": [\"29311617\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"TLR stimulation increases PYY expression in enteroendocrine L cells via an NF-κB-dependent pathway, additive to butyrate effects; butyrate also upregulates TLR expression (including TLR4), enhancing the NF-κB response to TLR stimulation and thus linking microbiota sensing to PYY production.\",\n      \"method\": \"Human L-cell model with NF-κB reporter, TLR agonists, butyrate treatment, gene expression analysis\",\n      \"journal\": \"Cellular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reporter assay plus expression data in defined cell model; single lab\",\n      \"pmids\": [\"27405092\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The taste-signaling G protein α-gustducin co-localizes with PYY and GLP-1 in enteroendocrine L cells of the human colon; stimulation with the bitter compound phenylthiocarbamide (a hT2R38 ligand) induces rapid intracellular Ca2+ increases in human intestinal endocrine cell lines, indicating gustducin-coupled chemosensory receptors mediate PYY secretion signals.\",\n      \"method\": \"Double-labeling immunofluorescence, serial section immunostaining, RT-PCR, intracellular Ca2+ imaging\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-localization plus functional Ca2+ signaling assay; single lab\",\n      \"pmids\": [\"16728727\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The intestinal sweet taste receptor T1R2/T1R3 (coupled through α-gustducin) is functionally involved in glucose-stimulated PYY and GLP-1 secretion in humans: blockade with the T1R2/T1R3 antagonist lactisole significantly reduces postprandial PYY and GLP-1 release after intragastric and intraduodenal glucose administration.\",\n      \"method\": \"Randomized double-blind placebo-controlled crossover human study, lactisole pharmacology, plasma hormone measurement\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — controlled human intervention with receptor antagonist; single study\",\n      \"pmids\": [\"21540445\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Angiotensin II stimulates PYY and GLP-1 secretion from colonic L cells via the Ang II type 1 receptor (AT1R), which is exclusively expressed in colonic L cells; AT1R activation raises intracellular calcium in L cells, and the released PYY acts on epithelial Y1 receptors to reduce ion transport (short-circuit current), thereby limiting fluid secretion into the colonic lumen.\",\n      \"method\": \"Primary cultures of mouse and human colon, candesartan antagonist, live-cell GCaMP3 calcium imaging, Ussing chamber electrophysiology, Y1 receptor antagonist\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (Ca2+ imaging, Ussing chamber, receptor antagonists) in mouse and human tissue\",\n      \"pmids\": [\"27447725\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Elevated circulating PYY following Roux-en-Y gastric bypass (RYGB) restores normal glucose regulation of glucagon and insulin secretion and normalizes islet morphology in diabetic GK rats; serum from RYGB animals mimics these effects on isolated islets, and this is reversed by PYY neutralization but not GLP-1 receptor antagonism.\",\n      \"method\": \"GK rat RYGB model, isolated islet culture with RYGB serum, PYY neutralization, GLP-1 receptor antagonist, chronic PYY in vitro exposure\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — humoral factor identification by neutralization, in vitro recapitulation with GLP-1 receptor antagonist control\",\n      \"pmids\": [\"27117413\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Intra-islet PYY (localized in alpha-cells) is regulated by DPP-IV activity; DPP-IV inhibition by sitagliptin enhances glucose-stimulated insulin secretion (GSIS) via local PYY rather than GLP-1; chronic PYY application directly enhances GSIS in rodent and diabetic human islets; RYGB strongly increases islet PYY content.\",\n      \"method\": \"Immunohistochemistry, gene expression, DPP-IV inhibition with sitagliptin, islet secretion studies, radioimmunoassay\",\n      \"journal\": \"Diabetes, obesity & metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological dissection with GLP-1/PYY distinction, rodent and human islets; single lab\",\n      \"pmids\": [\"28892258\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Pancreatic islet beta-cell-derived PYY improves glucose homeostasis by increasing beta-cell mass and insulin secretion; transgenic overexpression of PYY in beta-cells (Pyy-tg/Rip-Cre mice) leads to elevated serum insulin, improved glucose tolerance, increased beta-cell proliferation, and altered expression of genes important for beta-cell function.\",\n      \"method\": \"Transgenic mouse model (Rip-Cre driven PYY overexpression), glucose tolerance tests, beta-cell mass quantification, gene expression analysis\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean transgenic gain-of-function with defined metabolic phenotype; single lab\",\n      \"pmids\": [\"26125465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"PYY secretion from primary colonic L cells is stimulated by sodium oleate (fatty acid) in a dose-dependent manner, as well as by bombesin, epinephrine, and forskolin (cAMP elevation), but not by carbachol, establishing fatty acids and cAMP-linked pathways as direct secretagogues.\",\n      \"method\": \"Primary culture of canine colonic PYY cells on collagen, elutriation-based enrichment, secretion assay with pharmacological agents\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct primary cell secretion assay with multiple pharmacological agents; single lab\",\n      \"pmids\": [\"3377082\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"PYY upregulates intestinal fatty acid-binding protein (I-FABP) transcripts specifically in differentiated enterocytes via high-affinity PYY receptors (IC50 5-50 pM), acting through a post-transcriptional or transcriptional mechanism that is confined to terminally differentiated villar cells and does not affect mRNA in proliferating cells.\",\n      \"method\": \"Quantitative in situ hybridization on intestinal epithelial hybrid cell lines, competitive binding autoradiography, ribonuclease protection assay, BrdU incorporation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — receptor identification combined with cell-type-specific transcriptional readout; single lab\",\n      \"pmids\": [\"9139712\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"PYY stimulates intestinal apolipoprotein AIV (apo AIV) synthesis and lymphatic secretion by a post-transcriptional mechanism: intravenous PYY (75-200 pmol/kg/h) increases apo AIV output up to 3.5-fold and raises jejunal mucosal apo AIV synthesis by 60% without affecting apo AIV mRNA levels.\",\n      \"method\": \"Mesenteric lymph fistula rat model, intravenous PYY infusion, apo AIV protein output measurement in lymph, mucosal synthesis assay, mRNA analysis\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo dose-response with parallel protein and mRNA measurements establishing post-transcriptional mechanism; single lab\",\n      \"pmids\": [\"9756495\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"After peripheral (i.p.) injection, PYY(3-36) distributes to the area postrema (and subfornical organ and median eminence) in the brain, with near-background signals in all other brain structures including hypothalamic nuclei, suggesting the anorectic effect of peripheral PYY(3-36) is mediated primarily through circumventricular organs rather than direct hypothalamic action.\",\n      \"method\": \"Whole-body autoradiography and brain section autoradiography after i.p. and i.v. injection of 125I-labeled PYY(3-36) and analogs in rats\",\n      \"journal\": \"Journal of molecular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct radiolabeled biodistribution study with brain regional analysis; single lab\",\n      \"pmids\": [\"17952639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The anorectic effect of peripheral PYY(3-36) requires intact area postrema (AP) and subfornical organ (SFO) acting redundantly (ablation of either alone is insufficient), and also partially requires subdiaphragmatic vagal input; vagotomy further reveals that AP and SFO neuronal activation by peripheral PYY is partly vagally driven.\",\n      \"method\": \"Lesion of AP, SFO, or both combined; subdiaphragmatic vagotomy; c-fos mRNA brain mapping; food intake measurement in rats\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple surgical ablations with defined behavioral and neuronal activation readouts; mechanistic pathway delineated\",\n      \"pmids\": [\"20646064\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PYY(3-36) activates neurons in the arcuate nucleus (ARC), commissural and gelatinous NTS, and area postrema; approximately 10% of Fos+ neurons in the cmNTS are catecholaminergic (TH+), indicating that PYY(3-36) inhibits feeding partly through activation of ARC neurons and hindbrain catecholaminergic circuits.\",\n      \"method\": \"Peripheral PYY(3-36) injection in rats, c-Fos immunoreactivity in multiple brain regions, tyrosine hydroxylase double-labeling\",\n      \"journal\": \"Peptides\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — c-Fos neuronal mapping with catecholaminergic co-labeling after defined dose; single lab\",\n      \"pmids\": [\"18082288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Central PYY-immunoreactive neurons are located exclusively in the gigantocellular reticular nucleus (Gi) of the rostral medulla in mouse, rat, and monkey; their axonal projections concentrate in the nucleus tractus solitarius, dorsal motor nucleus of the vagus, and hypoglossal nucleus, and they receive input from orexin and MCH fibers, suggesting a role in energy homeostasis via visceral and autonomic circuits.\",\n      \"method\": \"Immunohistochemistry in NPY-knockout mouse (to eliminate NPY crossreactivity), NPY-preabsorbed antibody in rat, cross-species comparison, projection mapping\",\n      \"journal\": \"The Journal of comparative neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — rigorous antibody controls (NPY KO mice), multi-species, anatomical circuit mapping; single lab\",\n      \"pmids\": [\"18022952\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"PYY receptors in human adipocytes mediate antilipolytic effects; PYY (10^-7 M) inhibits lipolysis by 58% in femoral and 14% in pericolonic fat cells, correlating with regional PYY receptor density; this is an inhibitory system alongside the alpha2-adrenergic system.\",\n      \"method\": \"Radioligand binding (125I-PYY) on adipocyte membranes from multiple depots, lipolysis assay on isolated adipocytes\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — receptor characterization combined with functional lipolysis assay across multiple depots; single lab\",\n      \"pmids\": [\"8393293\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Endogenous PYY released from colonic L cells acts in a paracrine fashion via Y1 receptors to inhibit epithelial ion transport: L-glutamine-stimulated PYY release produces slow reductions in short-circuit current (Isc) in colonic and jejunal mucosa that are absent in PYY-/- tissue and blocked by Y1 receptor antagonist; the initial GLP-1-mediated Isc increase can be partially attributed to GLP-1 receptor activation.\",\n      \"method\": \"Ussing chamber voltage-clamp of mouse intestinal mucosae, PYY knockout tissue, selective Y1 and GLP-1 receptor antagonists, CaSR inhibitor\",\n      \"journal\": \"British journal of pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout combined with pharmacological receptor dissection; multiple receptor antagonists and tissue regions tested\",\n      \"pmids\": [\"23992397\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GIP receptor (GIPR) agonism reduces PYY(3-36)-induced conditioned taste aversion (CTA) without affecting PYY-mediated hypophagia; GIPR and NPY2R are co-expressed on the same neurons in the area postrema; peripheral GIPR agonism reduces PYY-induced neuronal activity in the parabrachial nucleus (PBN), providing a mechanistic basis for reduced nausea.\",\n      \"method\": \"Conditioned taste avoidance in mice, central and peripheral administration, cFos whole-brain analysis, receptor co-expression in area postrema neurons\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — behavioral assay with neuroanatomical receptor co-localization and brain-wide cFos mapping; single lab\",\n      \"pmids\": [\"35499381\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PYY(3-36) (Y2 receptor agonist) inhibits diarrhea by two mechanisms: reducing intestinal fluid secretion and slowing colonic transit, both demonstrated in mouse models using a selective Y2 agonist alongside PYY(3-36).\",\n      \"method\": \"Mouse diarrhea models (dimethyl-PGE2, 5-HT, castor oil), intestinal fluid accumulation assay, colonic transit (fecal output) measurement, Y2-selective agonist comparison\",\n      \"journal\": \"Peptides\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple in vivo disease models with receptor-selective pharmacology; single lab\",\n      \"pmids\": [\"19925840\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"PYY mRNA is transiently expressed in all early pancreatic endocrine cell types during embryogenesis (E12 onward), co-localizing with glucagon and insulin in multipotent precursor cells; PYY expression precedes NPY and PP, and actively-dividing triple-positive (insulin+glucagon+PYY) cells are consistent with a precursor role for PYY-positive endocrine cells.\",\n      \"method\": \"Immunohistochemistry, BrdU S-phase labeling, developmental staging in rat and mouse pancreas\",\n      \"journal\": \"The journal of histochemistry and cytochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic developmental staging with BrdU cell-cycle analysis; single lab\",\n      \"pmids\": [\"8756753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"GLP-1 and PYY are co-stored in separate secretory granules from neurotensin in intestinal L cells, yet all three peptides are co-secreted together from perfused small intestines and colonic crypt cultures in response to metabolite, neuropeptide, and hormonal stimuli; neurotensin acts synergistically with GLP-1 and PYY to decrease food intake and inhibit gastric emptying.\",\n      \"method\": \"FACS-sorted cell analysis, laser capture, confocal fluorescence microscopy, perfused intestine and crypt culture secretion assays, cell ablation studies, feeding and gastric emptying assays\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (ultrastructural, secretion, cell ablation, pharmacological) in single comprehensive study\",\n      \"pmids\": [\"26469136\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PYY is released from intestinal L cells postprandially (stimulated by fatty acids, SCFAs via FFA2/HDAC mechanisms, sweet taste receptors, amino acids, and angiotensin II via AT1R), undergoes DPP-IV–mediated cleavage of its N-terminal dipeptide to generate the Y2-selective form PYY(3-36), which inhibits food intake primarily through Y2 receptors in the hypothalamic arcuate nucleus (suppressing NPY neurons and activating POMC neurons) and circumventricular organs (area postrema, subfornical organ), with additional peripheral actions including direct inhibition of vagal motor neurons in the dorsal motor nucleus via Y2 receptors (modulated by cAMP levels), slowing of intestinal transit via serotonergic-opioid pathways, antilipolysis in adipocytes via Y1 receptors, paracrine inhibition of colonic fluid secretion via Y1 receptors, regulation of pancreatic islet insulin secretion and beta-cell mass, and stimulation of intestinal apolipoprotein AIV secretion by a post-transcriptional mechanism.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PYY is a gut-derived anorexigenic peptide hormone released from intestinal L cells in response to luminal nutrients (fatty acids, glucose, amino acids), short-chain fatty acids (via FFA2 receptors and HDAC inhibition), sweet/bitter taste receptor signaling (T1R2/T1R3 and gustducin-coupled pathways), and angiotensin II (via AT1R), and is proteolytically converted by DPP-IV from the non-selective Y1/Y2 agonist PYY(1-36) to the Y2-selective form PYY(3-36) [PMID:8097274, PMID:7984499, PMID:25109781, PMID:21540445, PMID:27447725]. PYY(3-36) inhibits food intake centrally by acting on Y2 receptors in the hypothalamic arcuate nucleus—suppressing NPY neurons and disinhibiting POMC neurons—and in circumventricular organs (area postrema, subfornical organ), with redundant vagal and humoral input pathways contributing to brainstem neuronal activation and conditioned taste aversion [PMID:12167864, PMID:16054059, PMID:20646064]. Peripherally, PYY exerts Y2-mediated direct inhibition of vagal motor neurons in the dorsal motor nucleus (gated by intracellular cAMP levels), slows intestinal transit through serotonergic-opioid pathways, and acts in a paracrine Y1-dependent manner to suppress colonic epithelial ion transport and fluid secretion [PMID:9249552, PMID:19622099, PMID:15010361, PMID:23992397]. PYY also functions as an intra-islet regulator—expressed in alpha cells and beta cells—where it enhances glucose-stimulated insulin secretion and promotes beta-cell mass, and it exerts antilipolytic effects in adipocytes via Y1 receptors [PMID:27117413, PMID:26125465, PMID:8393293].\",\n  \"teleology\": [\n    {\n      \"year\": 1988,\n      \"claim\": \"Establishing how PYY secretion is directly regulated resolved a key question about the physiological triggers for this L-cell hormone: fatty acids and cAMP-linked pathways were identified as direct secretagogues.\",\n      \"evidence\": \"Primary canine colonic L-cell cultures with pharmacological stimulation\",\n      \"pmids\": [\"3377082\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Signaling cascade downstream of fatty acid sensing not identified\", \"Relevance to human L cells not tested\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Identifying the receptor subtype mediating PYY actions in the pancreas revealed that PYY signals through Y1 receptors on pancreatic vascular smooth muscle, suggesting a vascular rather than direct endocrine mechanism.\",\n      \"evidence\": \"Autoradiographic receptor localization and competitive binding with Y1-selective agonist in rat pancreas\",\n      \"pmids\": [\"1847590\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct islet cell receptor expression not characterized\", \"Functional consequence of vascular Y1 activation on islet blood flow not measured\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Two discoveries established that DPP-IV-mediated cleavage generates a Y2-selective form PYY(3-36), and that PYY receptors in adipocytes mediate regional antilipolytic effects, defining both a key processing step and a peripheral metabolic action.\",\n      \"evidence\": \"In vitro DPP-IV enzymatic assay with receptor binding [PMID:8097274]; radioligand binding and lipolysis assay on human adipocytes from multiple depots [PMID:8393293]\",\n      \"pmids\": [\"8097274\", \"8393293\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo DPP-IV processing kinetics not measured\", \"Y receptor subtype mediating adipocyte antilipolysis not definitively assigned\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Purification of both PYY(1-36) and PYY(3-36) from intestinal tissue and demonstration of their distinct receptor selectivities confirmed that proteolytic processing is a physiological mechanism controlling receptor subtype engagement.\",\n      \"evidence\": \"Peptide purification from rabbit intestinal mucosa with receptor binding displacement assays\",\n      \"pmids\": [\"7984499\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative circulating concentrations of both forms in fed versus fasted states not quantified\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Demonstrating transient PYY co-expression with insulin and glucagon in dividing embryonic pancreatic cells suggested PYY marks multipotent endocrine precursors, opening the question of whether PYY has a developmental function.\",\n      \"evidence\": \"Immunohistochemistry with BrdU S-phase labeling across developmental stages in rat and mouse pancreas\",\n      \"pmids\": [\"8756753\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No loss-of-function test for PYY in pancreatic development\", \"Whether PYY expression is functionally required or merely a lineage marker is unresolved\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Electrophysiological and pharmacological studies revealed that PYY directly inhibits vagal motor neurons via Y2 receptors and bidirectionally controls gastric motility via Y1/Y2 in the dorsal vagal complex, establishing central autonomic circuits as key effector pathways.\",\n      \"evidence\": \"Brain stem slice electrophysiology with synaptic blockade and Y2-selective agonist [PMID:9249552]; DVC microinjection with gastric motility recording [PMID:9198086]\",\n      \"pmids\": [\"9249552\", \"9198086\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether circulating PYY achieves sufficient concentrations at the DVC to reproduce these effects physiologically was not established\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Discovery that PYY upregulates intestinal fatty acid-binding protein and stimulates apolipoprotein AIV secretion post-transcriptionally extended PYY's role beyond motility/appetite to intestinal lipid handling.\",\n      \"evidence\": \"In situ hybridization in intestinal hybrid cells [PMID:9139712]; mesenteric lymph fistula rat model with mRNA/protein comparison [PMID:9756495]\",\n      \"pmids\": [\"9139712\", \"9756495\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor subtype mediating apo AIV stimulation not identified\", \"Post-transcriptional mechanism (mRNA stability vs. translational) not resolved\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Structural studies revealed that PYY(1-36) and PYY(3-36) adopt distinct solution conformations correlated with Y1/Y2 selectivity, and that the functional receptor-binding state is membrane-associated with a stabilized C-terminal helix.\",\n      \"evidence\": \"CD, NMR, and sedimentation equilibrium on PYY variants [PMID:10898754]; NMR of micelle-bound pPYY [PMID:15178255]\",\n      \"pmids\": [\"10898754\", \"15178255\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No receptor-bound co-crystal or cryo-EM structure\", \"How N-terminal truncation alters membrane association and receptor docking at atomic detail remains unknown\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"The landmark demonstration that PYY(3-36) inhibits food intake via arcuate nucleus Y2 receptors—suppressing NPY neurons and activating POMC neurons—established the central satiety mechanism.\",\n      \"evidence\": \"Y2r knockout mice, peripheral and intra-arcuate injection, electrophysiology, c-Fos mapping, and human infusion in a single study\",\n      \"pmids\": [\"12167864\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Y2R in the arcuate is sufficient versus necessary for the full anorectic response was not resolved by this study alone\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Vagotomy and brain mapping studies revealed that PYY(3-36) anorexia does not require the vagus but involves brainstem aversive circuits (area postrema, NTS), while subsequent lesion studies showed the area postrema and subfornical organ act redundantly as central access points.\",\n      \"evidence\": \"Vagotomy with c-Fos and conditioned taste aversion [PMID:16054059]; combinatorial AP/SFO lesions with vagotomy and c-fos mapping [PMID:20646064]; radiolabeled PYY biodistribution [PMID:17952639]\",\n      \"pmids\": [\"16054059\", \"20646064\", \"17952639\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of aversive versus homeostatic satiety signaling to total food intake reduction remains unquantified\", \"Neuronal cell types in area postrema responding to PYY not fully characterized\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Co-localization of gustducin with PYY in colonic L cells and functional bitter taste receptor signaling in these cells revealed that chemosensory taste pathways regulate PYY secretion, later extended to sweet taste receptor T1R2/T1R3 in humans.\",\n      \"evidence\": \"Immunofluorescence co-localization and Ca2+ imaging in human intestinal endocrine cells [PMID:16728727]; randomized controlled human study with T1R2/T1R3 antagonist lactisole [PMID:21540445]\",\n      \"pmids\": [\"16728727\", \"21540445\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Quantitative contribution of taste receptor pathways versus nutrient transporters to total postprandial PYY release is unknown\", \"Downstream signaling cascade from gustducin to granule exocytosis not delineated\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"The finding that PYY modulation of vagal GABAergic transmission requires elevated cAMP revealed a gating mechanism: PYY's inhibition of vagal circuits is context-dependent, only operative when neurons are already activated by other signals.\",\n      \"evidence\": \"Whole-cell patch-clamp of DMV neurons with forskolin and physiological cAMP elevators (CCK, TRH)\",\n      \"pmids\": [\"19622099\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo confirmation that cAMP-dependent gating determines PYY efficacy on vagal output is lacking\", \"Whether this gating extends to other brain regions expressing Y2R is untested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Using PYY knockout tissue and receptor antagonists, paracrine PYY signaling through epithelial Y1 receptors was shown to inhibit colonic ion transport, establishing PYY as a local regulator of fluid secretion in addition to its endocrine roles.\",\n      \"evidence\": \"Ussing chamber on PYY-/- mouse colonic and jejunal mucosa with Y1 antagonist\",\n      \"pmids\": [\"23992397\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this paracrine axis is dysregulated in inflammatory bowel disease is unknown\", \"Quantitative contribution to whole-body fluid balance not assessed\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"SCFA-driven PYY secretion was mechanistically dissected: propionate acts through FFA2 in mice, while in human cells SCFAs primarily induce PYY gene transcription via HDAC inhibition; fermentable carbohydrates expand PYY-producing cell populations via FFAR2.\",\n      \"evidence\": \"FFA2 knockout mice with in vivo and crypt culture validation [PMID:25109781]; HDAC inhibitor studies in human L-cell models [PMID:29311617]; Ffar2 KO with dietary inulin and organoids [PMID:28123937]\",\n      \"pmids\": [\"25109781\", \"29311617\", \"28123937\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative importance of FFA2 versus HDAC pathways in intact human gut in vivo is unresolved\", \"Chromatin targets of SCFA-mediated HDAC inhibition at the PYY locus not mapped\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Multiple studies expanded PYY's regulatory inputs and outputs: angiotensin II via AT1R on L cells triggers PYY release that limits colonic fluid secretion via Y1; TLR/NF-κB signaling enhances PYY expression; and elevated PYY after gastric bypass normalizes islet function independently of GLP-1.\",\n      \"evidence\": \"AT1R agonism with Ca2+ imaging and Ussing chamber in mouse/human colon [PMID:27447725]; NF-κB reporter in human L-cell model [PMID:27405092]; GK rat RYGB with PYY neutralization and GLP-1R antagonist [PMID:27117413]\",\n      \"pmids\": [\"27447725\", \"27405092\", \"27117413\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether AT1R-PYY axis is physiologically relevant in hypertension or ACE-inhibitor therapy is untested\", \"Molecular mechanism by which PYY normalizes islet morphology is not defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Intra-islet PYY localized in alpha cells was shown to enhance insulin secretion and beta-cell mass, with DPP-IV processing controlling local PYY activity, revealing an autocrine/paracrine islet circuit distinct from gut-derived PYY.\",\n      \"evidence\": \"Immunohistochemistry, sitagliptin DPP-IV inhibition, islet secretion in rodent and human islets [PMID:28892258]; transgenic beta-cell PYY overexpression with glucose tolerance and beta-cell proliferation [PMID:26125465]\",\n      \"pmids\": [\"28892258\", \"26125465\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Y receptor subtype mediating islet PYY effects not definitively identified\", \"Whether intra-islet PYY contributes meaningfully to glycemic control in non-surgical settings is unclear\", \"Single-lab findings for intra-islet circuit\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The finding that GIPR agonism reduces PYY(3-36)-induced conditioned taste aversion via co-expressed GIPR/NPY2R neurons in the area postrema dissociated PYY's aversive from its hypophagic signaling, with therapeutic implications for incretin-based anti-obesity drugs.\",\n      \"evidence\": \"Conditioned taste avoidance in mice, cFos whole-brain analysis, receptor co-expression mapping in area postrema\",\n      \"pmids\": [\"35499381\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether GIPR-NPY2R interaction occurs at the intracellular signaling level or involves separate downstream circuits is unknown\", \"Human translation of the GIPR–PYY interaction not confirmed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the atomic-resolution structure of PYY bound to Y2R, the precise chromatin and transcriptional regulation of the PYY gene in L cells, the relative physiological contribution of aversive versus homeostatic pathways to PYY-mediated satiety in humans, and the mechanism by which PYY promotes beta-cell proliferation.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No receptor-bound structural model of PYY–Y2R complex\", \"Transcriptional regulation of the PYY gene locus largely unmapped\", \"Mechanism of PYY-driven beta-cell proliferation unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 2, 3, 6]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 8, 17, 29]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 1, 2, 21, 23]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [33]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0162582\", \"supporting_discovery_ids\": [0, 6, 8, 17, 29]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 6, 8, 17, 29]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [0, 5, 6, 8, 25, 26]},\n      {\"term_id\": \"R-HSA-8963743\", \"supporting_discovery_ids\": [9, 23, 31]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [22, 23, 28]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"NPY2R\",\n      \"NPY1R\",\n      \"DPP4\",\n      \"FFAR2\",\n      \"AGTR1\",\n      \"GNAT3\",\n      \"TAS1R2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}