{"gene":"RAMP2","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":1999,"finding":"RAMP2 forms a functional adrenomedullin (AM) receptor complex with the calcitonin receptor-like receptor (CRLR/CLR), mediating AM-induced cAMP elevation in human endothelial and vascular smooth muscle cells; RAMP2 but not RAMP1 or RAMP3 mRNA is expressed in these cells.","method":"Co-expression of RAMP2 and CRLR in HeLa EBNA and 293 EBNA cells; cAMP assay; RT-PCR","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 — functional reconstitution in heterologous cells with cAMP readout, replicated across multiple cell lines","pmids":["10217420"],"is_preprint":false},{"year":2001,"finding":"Seven amino acids in the extracellular N-terminal domain of RAMP2 (residues 86–92) are critical for high-affinity AM binding and AM-evoked cAMP production at the CRLR/RAMP2 receptor; deletion or alanine substitution of individual residues within this segment attenuates receptor function without disrupting cell-surface expression of the heterodimer.","method":"RAMP chimera and deletion mutant co-expression with CRLR in HEK293 cells; 125I-AM radioligand binding; cAMP assay; FACS for surface expression","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis with orthogonal binding and functional assays in same study","pmids":["11591721"],"is_preprint":false},{"year":2001,"finding":"AM signaling in rat cardiomyocytes requires both CRLR and RAMP2 to constitute functional AM receptors; overexpression of CRLR and RAMP2 together additively potentiated AM-induced CRE-luciferase activity ~4-fold, and this response was abolished by the antagonist CGRP(8–37) or CRLR antisense.","method":"Transient transfection of cardiomyocytes with CRE-luciferase reporter; RT-PCR for RAMP2/CRLR expression; antagonist inhibition","journal":"Peptides","confidence":"Medium","confidence_rationale":"Tier 2 — functional overexpression and antagonist validation in primary cardiomyocytes","pmids":["11754972"],"is_preprint":false},{"year":2003,"finding":"CL/RAMP2 and CL/RAMP3 produce pharmacologically distinct AM receptors: AM22-52 is selective for CL/RAMP2 over CL/RAMP3, while CGRP8-37 shows the opposite selectivity in mixed-species combinations; BIBN4096BS does not antagonize AM at either receptor.","method":"Transient expression in Cos-7 cells and endogenous expression in Rat2 and L6 cells; cAMP antagonism assays with pA2 calculations","journal":"British journal of pharmacology","confidence":"High","confidence_rationale":"Tier 1 — quantitative pharmacological assays across multiple receptor combinations and cell lines","pmids":["12970090"],"is_preprint":false},{"year":2008,"finding":"RAMP2 is essential for vascular integrity and angiogenesis in vivo: RAMP2−/− embryos die at midgestation with vascular fragility, severe edema, hemorrhage, deformed endothelial cells detached from basement membrane, and disrupted arterial multilayer structure; expression of tight junction, adherence junction, and basement membrane molecules by ECs was diminished; in adults, reduced RAMP2 causes vascular hyperpermeability and impaired neovascularization, while EC overexpression of RAMP2 enhances capillary formation and tight junctions.","method":"RAMP2 knockout and heterozygous mouse models; EC-specific overexpression; histology; immunofluorescence; permeability assays","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — germline KO, heterozygous, and overexpression models with multiple orthogonal phenotypic readouts; >160 citations","pmids":["18097473"],"is_preprint":false},{"year":2013,"finding":"The endothelial AM-RAMP2 system regulates vascular integrity by controlling the Rac1-GTP/RhoA-GTP ratio and cortical actin formation; loss of endothelial RAMP2 causes actin disarrangement and EC detachment, leading to vascular leakage, organ fibrosis, oxidative stress, and accelerated vascular senescence.","method":"Endothelial cell-specific RAMP2 KO mice (E-RAMP2−/−) and drug-inducible KO (DI-E-RAMP2−/−); Rac1/RhoA activity assays; in vitro actin imaging; permeability assays; histopathology","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 2 — cell-specific KO with defined molecular mechanism (Rac1/RhoA ratio) and multiple orthogonal readouts","pmids":["23355623"],"is_preprint":false},{"year":2013,"finding":"The AM-RAMP2 system is crucially involved in retinal angiogenesis: heterozygous RAMP2 KO mice show reduced pathological neovascularization with decreased VEGF and eNOS expression in OIR; inducible endothelial RAMP2 deletion causes abnormal retinal vascular patterning; AM promotes retinal EC proliferation and migration via RAMP2.","method":"RAMP2+/− and DI-E-RAMP2−/− mouse OIR model; in vitro EC proliferation/migration assays; intravitreal anti-ADM antibody treatment; RT-PCR","journal":"The American journal of pathology","confidence":"High","confidence_rationale":"Tier 2 — multiple mouse genetic models plus in vitro mechanistic validation","pmids":["23562442"],"is_preprint":false},{"year":2014,"finding":"RAMP2 and RAMP3 have distinct functional roles in vascular biology: RAMP2 KO is embryonically lethal (essential for blood vessel development), while RAMP3 KO mice are viable but show defective lymphatic drainage and lymphatic endothelial cell migration; the AM-RAMP3 system specifically regulates lymphatic vessel function.","method":"RAMP2−/− and RAMP3−/− mouse generation; ICG lymphangiography; tail lymphedema model; scratch-wound migration assay of isolated lymphatic ECs","journal":"Journal of molecular and cellular cardiology","confidence":"High","confidence_rationale":"Tier 2 — comparative KO models with orthogonal in vivo and in vitro assays demonstrating functional differentiation","pmids":["25264174"],"is_preprint":false},{"year":2014,"finding":"The AM-RAMP2 system suppresses ER stress-induced tubule cell death: in renal proximal tubule cells, AM via RAMP2 suppresses PERK activation and downstream CHOP-induced apoptosis; in RAMP2+/− kidneys, tunicamycin-induced ER stress causes greater tubular damage and exogenous AM fails to rescue injury.","method":"RAMP2+/− mice; streptozotocin and tunicamycin injury models; PERK/CHOP western blotting in human RPTECs; AM rescue experiment","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo haploinsufficiency plus in vitro mechanistic pathway (PERK/CHOP) validated with loss-of-rescue experiment","pmids":["24505304"],"is_preprint":false},{"year":2015,"finding":"RAMP2 modulates glucagon receptor (GCGR) pharmacology by altering ligand selectivity and G protein preference; RAMP2 interaction abolishes cross-reactivity of GLP-1 receptor agonists at GCGR.","method":"Yeast reporter assays; mammalian cell functional assays; co-expression of RAMP2 with GCGR; multiple ligand competition assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — orthogonal yeast and mammalian assay systems; pharmacological characterization across multiple ligands","pmids":["26198634"],"is_preprint":false},{"year":2016,"finding":"Endothelial RAMP2 deletion promotes vascular permeability, endothelial-mesenchymal transition (EndMT)-like changes, and formation of pre-metastatic niches; RAMP2 loss leads to inflammatory cell infiltration and expression of chemotactic factors S100A8/9 and SAA3 in lung vessels, enhancing tumor metastasis; conversely, RAMP2 overexpression suppresses tumor cell adhesion to endothelial cells.","method":"DI-E-RAMP2−/− inducible KO mice; sarcoma and melanoma transplant/metastasis models; vascular permeability assays; gene expression analysis","journal":"Cardiovascular research","confidence":"High","confidence_rationale":"Tier 2 — inducible endothelial-specific KO with defined molecular mediators and gain/loss-of-function in vivo","pmids":["27307317"],"is_preprint":false},{"year":2017,"finding":"RAMP2 co-expression with the glucagon receptor (GCGR) reduces GCGR cell-surface expression by causing its intracellular redistribution; RAMP2 influences Gαs and Gαq pathway signaling and β-arrestin recruitment at GCGR.","method":"Confocal microscopy; cell-surface ELISA; competition binding; Gαs/Gαq functional assays; β-arrestin recruitment assays; siRNA knockdown of RAMP2","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods in one study; trafficking and signaling both addressed","pmids":["28586439"],"is_preprint":false},{"year":2017,"finding":"The AM-RAMP2 system in endothelial cells exerts vasoprotective effects after vascular injury: RAMP2+/− and DI-E-RAMP2−/− mice show enhanced neointima formation, increased macrophage infiltration, oxidative stress, and impaired re-endothelialization; the AM-RAMP2 system also augments proliferation and migration of endothelial progenitor cells.","method":"Wire-induced vascular injury model in RAMP2+/− and DI-E-RAMP2−/− mice; bone marrow transplant experiments; histomorphometry; EPC proliferation/migration assays","journal":"Endocrinology","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic models plus bone marrow transplant establishing cell-autonomous contribution","pmids":["28324104"],"is_preprint":false},{"year":2019,"finding":"RAMP2 interacts with CRFR1α and CRFR1β (but not CRFR2β) to enhance their cell-surface expression; CRF stimulation causes loss of cell-surface RAMP2 when co-expressed with CRFR1 subtypes; molecular modelling identifies a smaller contact interface between RAMP2 and CRF receptors compared to CLR, and a specific residue difference (Glu vs. His) may impair CRFR2β:RAMP2 interaction.","method":"Cell-surface FLAG-RAMP2 detection across four cell lines; RT-PCR; molecular modelling","journal":"Biochimica et biophysica acta. Biomembranes","confidence":"Medium","confidence_rationale":"Tier 3 — cell-surface expression assay in multiple lines with computational modelling support; no direct binding assay","pmids":["30826286"],"is_preprint":false},{"year":2019,"finding":"Pathogenic RAMP2 variants cause POAG by disrupting the AM-RAMP2/CRLR-cAMP signaling pathway; mutant RAMP2 proteins aggregate in transfected cells; heterozygous Ramp2 KO in mice reduces cAMP and leads to retinal ganglion cell death.","method":"Exome sequencing; Sanger sequencing; transfection of mutant RAMP2 constructs; cAMP assays; heterozygous Ramp2 KO mouse retinal histology","journal":"Genetics in medicine","confidence":"Medium","confidence_rationale":"Tier 2 — human genetics combined with in vitro mutant characterization and in vivo KO model with defined cellular phenotype","pmids":["31000793"],"is_preprint":false},{"year":2021,"finding":"RAMP2 alters GCGR trafficking in hepatocytes by inducing GCGR internalisation both basally and after agonist stimulation; intracellular retention of GCGR by RAMP2 biases signaling away from β-arrestin-2 recruitment toward increased Gαs activation at endosomes, producing increased short-term cAMP but enhanced lysosomal degradation long-term.","method":"Confocal microscopy; radioligand binding; WASH-complex KO MEFs; monensin trafficking inhibition; NanoBiT complementation; cAMP assays; hepatocyte-targeted AAV in lean/obese mice","journal":"Molecular metabolism","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal trafficking and signaling assays plus genetic tools (WASH KO cells, AAV in vivo) in one study","pmids":["34271220"],"is_preprint":false},{"year":2021,"finding":"Cardiomyocyte-specific RAMP2 KO mice show cardiac hypertrophy, decreased ejection fraction, increased fibrosis, reduced ventricular contractility/relaxation, and impaired mitochondrial function (fewer viable mitochondria, reduced membrane potential and respiratory capacity) after pressure overload; thus AM-RAMP2 regulates early cardiac adaptation to stress through mitochondrial homeostasis.","method":"Cardiomyocyte-specific RAMP2−/− mice; transverse aortic constriction; echocardiography; pressure-volume loops; mitochondrial membrane potential and respiratory capacity assays; isoproterenol treatment of isolated cardiomyocytes","journal":"Endocrinology","confidence":"High","confidence_rationale":"Tier 2 — cell-type-specific KO with defined molecular mechanism (mitochondrial regulation) and multiple orthogonal readouts","pmids":["33545715"],"is_preprint":false},{"year":2022,"finding":"RAMP2 acts as a specific allosteric modulator of the parathyroid hormone 1 receptor (PTH1R), shifting it to a preactivated state that permits faster activation in a ligand-specific manner; RAMP2 increases PTH-mediated Gi3 signaling sensitivity and increases β-arrestin2 recruitment triggered by both PTH and PTHrP.","method":"Optical FRET/BRET biosensors for PTH1R activation and downstream signaling; RAMP2 co-expression; homology modelling","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — multiple optical biosensors measuring receptor conformational states and downstream pathway activation with computational structural modelling","pmids":["35914163"],"is_preprint":false},{"year":2023,"finding":"RAMP2 acts as a negative allosteric modulator of the glucagon receptor (GCGR): RAMP2 directly interacts with GCGR, broadly inhibiting receptor-induced downstream signaling; HDX-MS shows RAMP2 enhances local flexibility in the receptor ECD and 6th transmembrane helix; smFRET demonstrates ECD disorder inhibits active and intermediate intracellular states; cryo-EM at 2.9 Å of the GCGR-Gs-RAMP2 complex shows RAMP2 does not interact with GCGR in an ordered manner but ECD is disordered with rearranged intracellular activation hallmarks.","method":"HDX-MS; smFRET; cryo-EM structure at 2.9 Å; signaling assays","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structure plus HDX-MS and smFRET providing orthogonal mechanistic validation in one study","pmids":["37001505"],"is_preprint":false},{"year":2023,"finding":"In the ARDS model, endothelial RAMP2 deletion reduces Epac1 expression (a regulator of vascular endothelial barrier function), impairing endothelial barrier integrity; RAMP2 primarily contributes to circulation-regulating effects of AM, while RAMP3 contributes more to inflammation regulation.","method":"DI-E-RAMP2−/− and RAMP3−/− mice; intratracheal LPS ARDS model; transcriptomic analysis; Epac1 expression assays","journal":"Peptides","confidence":"Medium","confidence_rationale":"Tier 2 — inducible endothelial KO with transcriptomic mechanistic characterization; single study","pmids":["38012983"],"is_preprint":false},{"year":2023,"finding":"In hepatocytes, downregulation of Gata3 combined with upregulation of Ramp2 promotes proliferation of liver sinusoidal endothelial cells and hepatic revascularization after hepatectomy by shifting expression from PEDF to VEGFA.","method":"Alb-Cre-CRISPR/Cas9 AAV screening in partial hepatectomy mouse model; endothelial precursor transfusion; ALPPS model; hepatic organoids with Gata3 inhibitor; patient biopsy expression analysis","journal":"Journal of hepatology","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo AAV-CRISPR screen with multiple model systems; RAMP2 role in hepatocytes is paracrine (on LSECs) via PEDF/VEGFA shift","pmids":["37918568"],"is_preprint":false},{"year":2025,"finding":"AM/RAMP2 signaling enhances vascular barrier integrity, anti-inflammatory phenotype, and endothelial homeostasis in human pulmonary endothelial cells under shear stress; blockade of RAMP2 completely attenuates the ADM-induced upregulation of endothelial homeostatic markers (CDH5, NOS3, TEK, S1PR1), anti-coagulation (THBD increase, F3 decrease), and aerocyte marker EDNRB.","method":"ECIS and XperT permeability assays; shear stress perfusion system (15 dynes/cm2); RAMP2 blockade; gene expression analysis","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 — functional in vitro assays with receptor blockade validation; single study","pmids":["41597226"],"is_preprint":false}],"current_model":"RAMP2 is a single-pass transmembrane accessory protein that heterodimerizes with calcitonin receptor-like receptor (CLR/CRLR) to form the primary high-affinity adrenomedullin (AM) receptor, with seven extracellular N-terminal residues (86–92) critical for AM binding; the AM-RAMP2 system controls vascular integrity and angiogenesis through regulation of the Rac1-GTP/RhoA-GTP balance and cortical actin formation in endothelial cells, while also functioning as a negative allosteric modulator of the glucagon receptor (GCGR) by disordering its extracellular domain to broadly inhibit downstream signaling, and modulating additional Family B GPCRs including PTH1R (shifting it to a preactivated, faster-activating state) and CRFR1, thereby exerting pleiotropic roles in cardiovascular homeostasis, endocrine signaling, and organ protection."},"narrative":{"teleology":[{"year":1999,"claim":"Established that RAMP2, when co-expressed with CRLR, constitutes a functional AM receptor that couples to cAMP — resolving how AM selectivity is determined at the receptor level.","evidence":"Co-expression in HeLa EBNA and HEK293 EBNA cells with cAMP measurement; RT-PCR for endogenous expression in ECs and VSMCs","pmids":["10217420"],"confidence":"High","gaps":["Structural basis of RAMP2 vs RAMP1 selectivity for AM vs CGRP unknown","Endogenous stoichiometry and trafficking of the complex not examined"]},{"year":2001,"claim":"Identified a minimal seven-residue segment (86–92) in the RAMP2 N-terminal ectodomain as critical for AM binding and signaling, separating the ligand-recognition determinant from the receptor trafficking function.","evidence":"RAMP chimeras, deletion mutants, and alanine scanning co-expressed with CRLR in HEK293 cells; radioligand binding and cAMP assays with FACS surface-expression controls","pmids":["11591721"],"confidence":"High","gaps":["No crystal or cryo-EM structure of AM–RAMP2–CLR to map contacts at atomic resolution","Contribution of CLR residues to AM selectivity not dissected"]},{"year":2003,"claim":"Demonstrated that CLR/RAMP2 and CLR/RAMP3 form pharmacologically distinct AM receptors with differing antagonist profiles, establishing the AM1/AM2 receptor nomenclature.","evidence":"Quantitative cAMP antagonism assays with pA2 calculations across Cos-7, Rat2, and L6 cells using AM22-52, CGRP8-37, and BIBN4096BS","pmids":["12970090"],"confidence":"High","gaps":["Downstream signaling bias differences between AM1 and AM2 not characterized","Physiological contexts where AM2 substitutes for AM1 unclear"]},{"year":2008,"claim":"Revealed that RAMP2 is indispensable for vascular development and integrity in vivo — its complete loss causes midgestation lethality with vascular fragility, hemorrhage, and endothelial detachment, while haploinsufficiency impairs adult angiogenesis.","evidence":"RAMP2 knockout mice (lethal), heterozygous mice, and EC-specific RAMP2 overexpression; histology, immunofluorescence, permeability assays","pmids":["18097473"],"confidence":"High","gaps":["Molecular pathway downstream of AM-RAMP2 mediating junction/basement-membrane gene expression not defined","Whether RAMP2 KO lethality is entirely AM-dependent or involves other CLR ligands unresolved"]},{"year":2013,"claim":"Defined the intracellular mechanism by which endothelial AM-RAMP2 maintains vascular barrier: control of the Rac1-GTP/RhoA-GTP balance and cortical actin organization; loss of this system triggers vascular leakage, fibrosis, and accelerated senescence.","evidence":"Endothelial-specific and drug-inducible endothelial RAMP2 KO mice; Rac1/RhoA activity assays; actin imaging; permeability measurements","pmids":["23355623"],"confidence":"High","gaps":["Whether RAMP2 regulates Rac1/RhoA through Epac, PI3K, or another intermediate not resolved","Contribution of β-arrestin-dependent vs G-protein-dependent pathways to barrier function unknown"]},{"year":2013,"claim":"Extended the vascular role to retinal angiogenesis, showing RAMP2 haploinsufficiency reduces pathological neovascularization and VEGF/eNOS expression in oxygen-induced retinopathy.","evidence":"RAMP2+/− and DI-E-RAMP2−/− mice in OIR model; EC proliferation/migration assays; intravitreal anti-ADM antibody","pmids":["23562442"],"confidence":"High","gaps":["Whether AM-RAMP2 directly transcribes VEGF or acts upstream via HIF not determined","Therapeutic window for targeting AM-RAMP2 in retinal disease undefined"]},{"year":2015,"claim":"Expanded RAMP2's receptor repertoire beyond CLR by showing it modulates glucagon receptor pharmacology — altering GCGR ligand selectivity and G-protein coupling preference.","evidence":"RAMP2-GCGR co-expression in yeast reporter and mammalian cell functional assays with multiple ligands","pmids":["26198634"],"confidence":"Medium","gaps":["Direct physical interaction between RAMP2 and GCGR not confirmed by co-IP or structural data at this point","Physiological tissues where RAMP2-GCGR interaction occurs not identified"]},{"year":2017,"claim":"Showed RAMP2 causes intracellular redistribution of GCGR, reducing its surface expression and modulating both Gαs/Gαq signaling and β-arrestin recruitment — providing a trafficking-based mechanism for GCGR modulation.","evidence":"Confocal microscopy, cell-surface ELISA, competition binding, Gαs/Gαq assays, β-arrestin recruitment, siRNA knockdown","pmids":["28586439"],"confidence":"Medium","gaps":["Whether RAMP2-induced GCGR internalization is constitutive or regulated not fully dissected","Structural interface between RAMP2 and GCGR undefined"]},{"year":2019,"claim":"Identified pathogenic RAMP2 variants as a cause of primary open-angle glaucoma (POAG), linking disrupted AM-RAMP2/CRLR-cAMP signaling and mutant protein aggregation to retinal ganglion cell death.","evidence":"Exome and Sanger sequencing of POAG families; transfection of mutant RAMP2; cAMP assays; RAMP2+/− mouse retinal histology","pmids":["31000793"],"confidence":"Medium","gaps":["Number of POAG families carrying RAMP2 variants is small; replication in larger cohorts needed","Mechanism of mutant RAMP2 aggregation (misfolding vs ER retention) not characterized"]},{"year":2021,"claim":"Resolved the mechanism of RAMP2's GCGR modulation in hepatocytes: RAMP2 drives constitutive and agonist-stimulated GCGR internalization, biasing signaling toward endosomal Gαs/cAMP and away from β-arrestin-2, with long-term lysosomal degradation of GCGR.","evidence":"Confocal microscopy, radioligand binding, WASH-complex KO MEFs, monensin trafficking inhibition, NanoBiT complementation, cAMP assays, hepatocyte-targeted AAV in lean/obese mice","pmids":["34271220"],"confidence":"High","gaps":["In vivo metabolic consequences of hepatic RAMP2-GCGR interaction in disease models not fully explored","Whether RAMP2-directed lysosomal degradation of GCGR is ubiquitin-dependent not tested"]},{"year":2021,"claim":"Demonstrated that cardiomyocyte AM-RAMP2 signaling maintains mitochondrial homeostasis under pressure overload, with cardiomyocyte-specific RAMP2 deletion causing cardiac hypertrophy, fibrosis, and impaired mitochondrial membrane potential and respiration.","evidence":"Cardiomyocyte-specific RAMP2 KO mice; TAC; echocardiography; PV loops; mitochondrial assays","pmids":["33545715"],"confidence":"High","gaps":["Pathway linking AM-RAMP2-cAMP to mitochondrial biogenesis or quality control (e.g. PGC-1α, mitophagy) not identified","Whether cardiomyocyte RAMP2 also modulates other GPCRs in the heart not explored"]},{"year":2022,"claim":"Established that RAMP2 allosterically modulates PTH1R by shifting it to a preactivated conformation that accelerates activation and enhances Gi3 signaling and β-arrestin2 recruitment in a ligand-specific manner — broadening RAMP2's role to parathyroid hormone signaling.","evidence":"FRET/BRET biosensors for PTH1R conformational states and downstream signaling; RAMP2 co-expression; homology modelling","pmids":["35914163"],"confidence":"High","gaps":["Structural basis of RAMP2-PTH1R interaction at atomic resolution not available","In vivo relevance to calcium/phosphate homeostasis or bone biology not tested"]},{"year":2023,"claim":"Provided the first near-atomic structural insight into RAMP2's allosteric mechanism at GCGR: cryo-EM, HDX-MS, and smFRET showed RAMP2 disorders the GCGR ECD and rearranges intracellular activation hallmarks, acting as a negative allosteric modulator that broadly inhibits downstream signaling.","evidence":"Cryo-EM at 2.9 Å of GCGR-Gs-RAMP2 complex; HDX-MS; smFRET; signaling assays","pmids":["37001505"],"confidence":"High","gaps":["No ordered RAMP2-GCGR interface resolved — mechanism of ECD disordering is inferred rather than structurally mapped","Whether similar allosteric disordering occurs at PTH1R or CRFR1 unknown"]},{"year":2023,"claim":"Linked endothelial RAMP2 to Epac1 expression as a downstream effector maintaining vascular barrier integrity in ARDS, distinguishing RAMP2's vascular regulation role from RAMP3's anti-inflammatory role.","evidence":"DI-E-RAMP2−/− and RAMP3−/− mice in intratracheal LPS ARDS model; transcriptomic and Epac1 expression analysis","pmids":["38012983"],"confidence":"Medium","gaps":["Direct transcriptional regulation of Epac1 by AM-RAMP2-cAMP pathway not demonstrated","Single disease model; generalizability to other forms of acute lung injury not established"]},{"year":null,"claim":"Key unresolved questions include the high-resolution structural basis of AM recognition by the RAMP2-CLR complex, the full spectrum of Family B GPCRs modulated by RAMP2 in vivo, the signaling intermediates connecting AM-RAMP2 to mitochondrial homeostasis in cardiomyocytes, and whether RAMP2 allosteric mechanisms (ECD disordering) are generalizable across its non-CLR GPCR partners.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of the full AM–RAMP2–CLR signaling complex","Tissue-specific RAMP2 interactome beyond CLR, GCGR, PTH1R, CRFR1 not systematically mapped","Downstream pathway from AM-RAMP2 to mitochondrial function in cardiomyocytes undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,9,11,15,17,18]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,13]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,11,13]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[15]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,3,9,11,15,17,18]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[4,6]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[10,14]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[11,15]}],"complexes":["AM1 receptor (CLR-RAMP2)"],"partners":["CALCRL","GCGR","PTH1R","CRHR1","RAPGEF3"],"other_free_text":[]},"mechanistic_narrative":"RAMP2 is a single-pass transmembrane accessory protein that serves as an obligate co-receptor for the calcitonin receptor-like receptor (CLR/CRLR), forming the principal high-affinity adrenomedullin (AM) receptor (AM1 receptor) that signals through cAMP, and additionally functions as an allosteric modulator of multiple Family B GPCRs including the glucagon receptor (GCGR) and parathyroid hormone 1 receptor (PTH1R) [PMID:10217420, PMID:37001505, PMID:35914163]. Seven N-terminal extracellular residues (86–92) are critical for AM binding specificity, and the RAMP2–CLR complex is pharmacologically distinct from the RAMP3–CLR (AM2) receptor [PMID:11591721, PMID:12970090]. Through endothelial AM–RAMP2 signaling, RAMP2 maintains vascular integrity and barrier function by regulating the Rac1-GTP/RhoA-GTP balance, cortical actin organization, tight/adherens junction expression, and Epac1 levels; genetic ablation causes embryonic lethality with severe vascular fragility, and postnatal endothelial deletion leads to vascular hyperpermeability, organ fibrosis, accelerated senescence, and pre-metastatic niche formation [PMID:18097473, PMID:23355623, PMID:27307317, PMID:38012983]. Pathogenic RAMP2 variants that disrupt AM–RAMP2/CRLR–cAMP signaling cause primary open-angle glaucoma (POAG), with mutant proteins aggregating intracellularly and heterozygous Ramp2 knockout mice exhibiting retinal ganglion cell death [PMID:31000793]."},"prefetch_data":{"uniprot":{"accession":"O60895","full_name":"Receptor activity-modifying protein 2","aliases":["Calcitonin-receptor-like receptor activity-modifying protein 2","CRLR activity-modifying protein 2"],"length_aa":175,"mass_kda":19.6,"function":"Accessory protein that interacts with and modulates the function of G-protein coupled receptors including calcitonin gene-related peptide type 1 receptor (CALCRL) and calcitonin receptor (CALCR) (PubMed:9620797). Required for the transport of CALCRL to the plasma membrane (PubMed:9620797). Together with CALCRL, form a receptor complex for adrenomedullin/ADM (PubMed:22102369, PubMed:32296767, PubMed:9620797). Together with CALCR, act as a receptor complex for calcitonin/CT/CALC (PubMed:35324283). Together with CALCR, also act as a receptor complex for amylin/IAPP (PubMed:35324283)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/O60895/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RAMP2","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/RAMP2","total_profiled":1310},"omim":[{"mim_id":"618773","title":"LYMPHATIC MALFORMATION 8; LMPHM8","url":"https://www.omim.org/entry/618773"},{"mim_id":"605155","title":"RECEPTOR ACTIVITY-MODIFYING PROTEIN 3; RAMP3","url":"https://www.omim.org/entry/605155"},{"mim_id":"605154","title":"RECEPTOR ACTIVITY-MODIFYING PROTEIN 2; RAMP2","url":"https://www.omim.org/entry/605154"},{"mim_id":"605153","title":"RECEPTOR ACTIVITY-MODIFYING PROTEIN 1; RAMP1","url":"https://www.omim.org/entry/605153"},{"mim_id":"114190","title":"CALCITONIN RECEPTOR-LIKE RECEPTOR; CALCRL","url":"https://www.omim.org/entry/114190"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/RAMP2"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"O60895","domains":[{"cath_id":"1.10.150.510","chopping":"93-133","consensus_level":"medium","plddt":96.142,"start":93,"end":133}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O60895","model_url":"https://alphafold.ebi.ac.uk/files/AF-O60895-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O60895-F1-predicted_aligned_error_v6.png","plddt_mean":80.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RAMP2","jax_strain_url":"https://www.jax.org/strain/search?query=RAMP2"},"sequence":{"accession":"O60895","fasta_url":"https://rest.uniprot.org/uniprotkb/O60895.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O60895/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O60895"}},"corpus_meta":[{"pmid":"18097473","id":"PMC_18097473","title":"The GPCR modulator protein RAMP2 is 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RAMP2 but not RAMP1 or RAMP3 mRNA is expressed in these cells.\",\n      \"method\": \"Co-expression of RAMP2 and CRLR in HeLa EBNA and 293 EBNA cells; cAMP assay; RT-PCR\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — functional reconstitution in heterologous cells with cAMP readout, replicated across multiple cell lines\",\n      \"pmids\": [\"10217420\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Seven amino acids in the extracellular N-terminal domain of RAMP2 (residues 86–92) are critical for high-affinity AM binding and AM-evoked cAMP production at the CRLR/RAMP2 receptor; deletion or alanine substitution of individual residues within this segment attenuates receptor function without disrupting cell-surface expression of the heterodimer.\",\n      \"method\": \"RAMP chimera and deletion mutant co-expression with CRLR in HEK293 cells; 125I-AM radioligand binding; cAMP assay; FACS for surface expression\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with orthogonal binding and functional assays in same study\",\n      \"pmids\": [\"11591721\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"AM signaling in rat cardiomyocytes requires both CRLR and RAMP2 to constitute functional AM receptors; overexpression of CRLR and RAMP2 together additively potentiated AM-induced CRE-luciferase activity ~4-fold, and this response was abolished by the antagonist CGRP(8–37) or CRLR antisense.\",\n      \"method\": \"Transient transfection of cardiomyocytes with CRE-luciferase reporter; RT-PCR for RAMP2/CRLR expression; antagonist inhibition\",\n      \"journal\": \"Peptides\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional overexpression and antagonist validation in primary cardiomyocytes\",\n      \"pmids\": [\"11754972\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"CL/RAMP2 and CL/RAMP3 produce pharmacologically distinct AM receptors: AM22-52 is selective for CL/RAMP2 over CL/RAMP3, while CGRP8-37 shows the opposite selectivity in mixed-species combinations; BIBN4096BS does not antagonize AM at either receptor.\",\n      \"method\": \"Transient expression in Cos-7 cells and endogenous expression in Rat2 and L6 cells; cAMP antagonism assays with pA2 calculations\",\n      \"journal\": \"British journal of pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative pharmacological assays across multiple receptor combinations and cell lines\",\n      \"pmids\": [\"12970090\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"RAMP2 is essential for vascular integrity and angiogenesis in vivo: RAMP2−/− embryos die at midgestation with vascular fragility, severe edema, hemorrhage, deformed endothelial cells detached from basement membrane, and disrupted arterial multilayer structure; expression of tight junction, adherence junction, and basement membrane molecules by ECs was diminished; in adults, reduced RAMP2 causes vascular hyperpermeability and impaired neovascularization, while EC overexpression of RAMP2 enhances capillary formation and tight junctions.\",\n      \"method\": \"RAMP2 knockout and heterozygous mouse models; EC-specific overexpression; histology; immunofluorescence; permeability assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — germline KO, heterozygous, and overexpression models with multiple orthogonal phenotypic readouts; >160 citations\",\n      \"pmids\": [\"18097473\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The endothelial AM-RAMP2 system regulates vascular integrity by controlling the Rac1-GTP/RhoA-GTP ratio and cortical actin formation; loss of endothelial RAMP2 causes actin disarrangement and EC detachment, leading to vascular leakage, organ fibrosis, oxidative stress, and accelerated vascular senescence.\",\n      \"method\": \"Endothelial cell-specific RAMP2 KO mice (E-RAMP2−/−) and drug-inducible KO (DI-E-RAMP2−/−); Rac1/RhoA activity assays; in vitro actin imaging; permeability assays; histopathology\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-specific KO with defined molecular mechanism (Rac1/RhoA ratio) and multiple orthogonal readouts\",\n      \"pmids\": [\"23355623\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The AM-RAMP2 system is crucially involved in retinal angiogenesis: heterozygous RAMP2 KO mice show reduced pathological neovascularization with decreased VEGF and eNOS expression in OIR; inducible endothelial RAMP2 deletion causes abnormal retinal vascular patterning; AM promotes retinal EC proliferation and migration via RAMP2.\",\n      \"method\": \"RAMP2+/− and DI-E-RAMP2−/− mouse OIR model; in vitro EC proliferation/migration assays; intravitreal anti-ADM antibody treatment; RT-PCR\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple mouse genetic models plus in vitro mechanistic validation\",\n      \"pmids\": [\"23562442\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"RAMP2 and RAMP3 have distinct functional roles in vascular biology: RAMP2 KO is embryonically lethal (essential for blood vessel development), while RAMP3 KO mice are viable but show defective lymphatic drainage and lymphatic endothelial cell migration; the AM-RAMP3 system specifically regulates lymphatic vessel function.\",\n      \"method\": \"RAMP2−/− and RAMP3−/− mouse generation; ICG lymphangiography; tail lymphedema model; scratch-wound migration assay of isolated lymphatic ECs\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — comparative KO models with orthogonal in vivo and in vitro assays demonstrating functional differentiation\",\n      \"pmids\": [\"25264174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The AM-RAMP2 system suppresses ER stress-induced tubule cell death: in renal proximal tubule cells, AM via RAMP2 suppresses PERK activation and downstream CHOP-induced apoptosis; in RAMP2+/− kidneys, tunicamycin-induced ER stress causes greater tubular damage and exogenous AM fails to rescue injury.\",\n      \"method\": \"RAMP2+/− mice; streptozotocin and tunicamycin injury models; PERK/CHOP western blotting in human RPTECs; AM rescue experiment\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo haploinsufficiency plus in vitro mechanistic pathway (PERK/CHOP) validated with loss-of-rescue experiment\",\n      \"pmids\": [\"24505304\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"RAMP2 modulates glucagon receptor (GCGR) pharmacology by altering ligand selectivity and G protein preference; RAMP2 interaction abolishes cross-reactivity of GLP-1 receptor agonists at GCGR.\",\n      \"method\": \"Yeast reporter assays; mammalian cell functional assays; co-expression of RAMP2 with GCGR; multiple ligand competition assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — orthogonal yeast and mammalian assay systems; pharmacological characterization across multiple ligands\",\n      \"pmids\": [\"26198634\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Endothelial RAMP2 deletion promotes vascular permeability, endothelial-mesenchymal transition (EndMT)-like changes, and formation of pre-metastatic niches; RAMP2 loss leads to inflammatory cell infiltration and expression of chemotactic factors S100A8/9 and SAA3 in lung vessels, enhancing tumor metastasis; conversely, RAMP2 overexpression suppresses tumor cell adhesion to endothelial cells.\",\n      \"method\": \"DI-E-RAMP2−/− inducible KO mice; sarcoma and melanoma transplant/metastasis models; vascular permeability assays; gene expression analysis\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — inducible endothelial-specific KO with defined molecular mediators and gain/loss-of-function in vivo\",\n      \"pmids\": [\"27307317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"RAMP2 co-expression with the glucagon receptor (GCGR) reduces GCGR cell-surface expression by causing its intracellular redistribution; RAMP2 influences Gαs and Gαq pathway signaling and β-arrestin recruitment at GCGR.\",\n      \"method\": \"Confocal microscopy; cell-surface ELISA; competition binding; Gαs/Gαq functional assays; β-arrestin recruitment assays; siRNA knockdown of RAMP2\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in one study; trafficking and signaling both addressed\",\n      \"pmids\": [\"28586439\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The AM-RAMP2 system in endothelial cells exerts vasoprotective effects after vascular injury: RAMP2+/− and DI-E-RAMP2−/− mice show enhanced neointima formation, increased macrophage infiltration, oxidative stress, and impaired re-endothelialization; the AM-RAMP2 system also augments proliferation and migration of endothelial progenitor cells.\",\n      \"method\": \"Wire-induced vascular injury model in RAMP2+/− and DI-E-RAMP2−/− mice; bone marrow transplant experiments; histomorphometry; EPC proliferation/migration assays\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic models plus bone marrow transplant establishing cell-autonomous contribution\",\n      \"pmids\": [\"28324104\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"RAMP2 interacts with CRFR1α and CRFR1β (but not CRFR2β) to enhance their cell-surface expression; CRF stimulation causes loss of cell-surface RAMP2 when co-expressed with CRFR1 subtypes; molecular modelling identifies a smaller contact interface between RAMP2 and CRF receptors compared to CLR, and a specific residue difference (Glu vs. His) may impair CRFR2β:RAMP2 interaction.\",\n      \"method\": \"Cell-surface FLAG-RAMP2 detection across four cell lines; RT-PCR; molecular modelling\",\n      \"journal\": \"Biochimica et biophysica acta. Biomembranes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — cell-surface expression assay in multiple lines with computational modelling support; no direct binding assay\",\n      \"pmids\": [\"30826286\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Pathogenic RAMP2 variants cause POAG by disrupting the AM-RAMP2/CRLR-cAMP signaling pathway; mutant RAMP2 proteins aggregate in transfected cells; heterozygous Ramp2 KO in mice reduces cAMP and leads to retinal ganglion cell death.\",\n      \"method\": \"Exome sequencing; Sanger sequencing; transfection of mutant RAMP2 constructs; cAMP assays; heterozygous Ramp2 KO mouse retinal histology\",\n      \"journal\": \"Genetics in medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — human genetics combined with in vitro mutant characterization and in vivo KO model with defined cellular phenotype\",\n      \"pmids\": [\"31000793\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"RAMP2 alters GCGR trafficking in hepatocytes by inducing GCGR internalisation both basally and after agonist stimulation; intracellular retention of GCGR by RAMP2 biases signaling away from β-arrestin-2 recruitment toward increased Gαs activation at endosomes, producing increased short-term cAMP but enhanced lysosomal degradation long-term.\",\n      \"method\": \"Confocal microscopy; radioligand binding; WASH-complex KO MEFs; monensin trafficking inhibition; NanoBiT complementation; cAMP assays; hepatocyte-targeted AAV in lean/obese mice\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal trafficking and signaling assays plus genetic tools (WASH KO cells, AAV in vivo) in one study\",\n      \"pmids\": [\"34271220\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cardiomyocyte-specific RAMP2 KO mice show cardiac hypertrophy, decreased ejection fraction, increased fibrosis, reduced ventricular contractility/relaxation, and impaired mitochondrial function (fewer viable mitochondria, reduced membrane potential and respiratory capacity) after pressure overload; thus AM-RAMP2 regulates early cardiac adaptation to stress through mitochondrial homeostasis.\",\n      \"method\": \"Cardiomyocyte-specific RAMP2−/− mice; transverse aortic constriction; echocardiography; pressure-volume loops; mitochondrial membrane potential and respiratory capacity assays; isoproterenol treatment of isolated cardiomyocytes\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific KO with defined molecular mechanism (mitochondrial regulation) and multiple orthogonal readouts\",\n      \"pmids\": [\"33545715\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"RAMP2 acts as a specific allosteric modulator of the parathyroid hormone 1 receptor (PTH1R), shifting it to a preactivated state that permits faster activation in a ligand-specific manner; RAMP2 increases PTH-mediated Gi3 signaling sensitivity and increases β-arrestin2 recruitment triggered by both PTH and PTHrP.\",\n      \"method\": \"Optical FRET/BRET biosensors for PTH1R activation and downstream signaling; RAMP2 co-expression; homology modelling\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple optical biosensors measuring receptor conformational states and downstream pathway activation with computational structural modelling\",\n      \"pmids\": [\"35914163\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"RAMP2 acts as a negative allosteric modulator of the glucagon receptor (GCGR): RAMP2 directly interacts with GCGR, broadly inhibiting receptor-induced downstream signaling; HDX-MS shows RAMP2 enhances local flexibility in the receptor ECD and 6th transmembrane helix; smFRET demonstrates ECD disorder inhibits active and intermediate intracellular states; cryo-EM at 2.9 Å of the GCGR-Gs-RAMP2 complex shows RAMP2 does not interact with GCGR in an ordered manner but ECD is disordered with rearranged intracellular activation hallmarks.\",\n      \"method\": \"HDX-MS; smFRET; cryo-EM structure at 2.9 Å; signaling assays\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structure plus HDX-MS and smFRET providing orthogonal mechanistic validation in one study\",\n      \"pmids\": [\"37001505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In the ARDS model, endothelial RAMP2 deletion reduces Epac1 expression (a regulator of vascular endothelial barrier function), impairing endothelial barrier integrity; RAMP2 primarily contributes to circulation-regulating effects of AM, while RAMP3 contributes more to inflammation regulation.\",\n      \"method\": \"DI-E-RAMP2−/− and RAMP3−/− mice; intratracheal LPS ARDS model; transcriptomic analysis; Epac1 expression assays\",\n      \"journal\": \"Peptides\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — inducible endothelial KO with transcriptomic mechanistic characterization; single study\",\n      \"pmids\": [\"38012983\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In hepatocytes, downregulation of Gata3 combined with upregulation of Ramp2 promotes proliferation of liver sinusoidal endothelial cells and hepatic revascularization after hepatectomy by shifting expression from PEDF to VEGFA.\",\n      \"method\": \"Alb-Cre-CRISPR/Cas9 AAV screening in partial hepatectomy mouse model; endothelial precursor transfusion; ALPPS model; hepatic organoids with Gata3 inhibitor; patient biopsy expression analysis\",\n      \"journal\": \"Journal of hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo AAV-CRISPR screen with multiple model systems; RAMP2 role in hepatocytes is paracrine (on LSECs) via PEDF/VEGFA shift\",\n      \"pmids\": [\"37918568\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"AM/RAMP2 signaling enhances vascular barrier integrity, anti-inflammatory phenotype, and endothelial homeostasis in human pulmonary endothelial cells under shear stress; blockade of RAMP2 completely attenuates the ADM-induced upregulation of endothelial homeostatic markers (CDH5, NOS3, TEK, S1PR1), anti-coagulation (THBD increase, F3 decrease), and aerocyte marker EDNRB.\",\n      \"method\": \"ECIS and XperT permeability assays; shear stress perfusion system (15 dynes/cm2); RAMP2 blockade; gene expression analysis\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional in vitro assays with receptor blockade validation; single study\",\n      \"pmids\": [\"41597226\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RAMP2 is a single-pass transmembrane accessory protein that heterodimerizes with calcitonin receptor-like receptor (CLR/CRLR) to form the primary high-affinity adrenomedullin (AM) receptor, with seven extracellular N-terminal residues (86–92) critical for AM binding; the AM-RAMP2 system controls vascular integrity and angiogenesis through regulation of the Rac1-GTP/RhoA-GTP balance and cortical actin formation in endothelial cells, while also functioning as a negative allosteric modulator of the glucagon receptor (GCGR) by disordering its extracellular domain to broadly inhibit downstream signaling, and modulating additional Family B GPCRs including PTH1R (shifting it to a preactivated, faster-activating state) and CRFR1, thereby exerting pleiotropic roles in cardiovascular homeostasis, endocrine signaling, and organ protection.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"RAMP2 is a single-pass transmembrane accessory protein that serves as an obligate co-receptor for the calcitonin receptor-like receptor (CLR/CRLR), forming the principal high-affinity adrenomedullin (AM) receptor (AM1 receptor) that signals through cAMP, and additionally functions as an allosteric modulator of multiple Family B GPCRs including the glucagon receptor (GCGR) and parathyroid hormone 1 receptor (PTH1R) [PMID:10217420, PMID:37001505, PMID:35914163]. Seven N-terminal extracellular residues (86–92) are critical for AM binding specificity, and the RAMP2–CLR complex is pharmacologically distinct from the RAMP3–CLR (AM2) receptor [PMID:11591721, PMID:12970090]. Through endothelial AM–RAMP2 signaling, RAMP2 maintains vascular integrity and barrier function by regulating the Rac1-GTP/RhoA-GTP balance, cortical actin organization, tight/adherens junction expression, and Epac1 levels; genetic ablation causes embryonic lethality with severe vascular fragility, and postnatal endothelial deletion leads to vascular hyperpermeability, organ fibrosis, accelerated senescence, and pre-metastatic niche formation [PMID:18097473, PMID:23355623, PMID:27307317, PMID:38012983]. Pathogenic RAMP2 variants that disrupt AM–RAMP2/CRLR–cAMP signaling cause primary open-angle glaucoma (POAG), with mutant proteins aggregating intracellularly and heterozygous Ramp2 knockout mice exhibiting retinal ganglion cell death [PMID:31000793].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Established that RAMP2, when co-expressed with CRLR, constitutes a functional AM receptor that couples to cAMP — resolving how AM selectivity is determined at the receptor level.\",\n      \"evidence\": \"Co-expression in HeLa EBNA and HEK293 EBNA cells with cAMP measurement; RT-PCR for endogenous expression in ECs and VSMCs\",\n      \"pmids\": [\"10217420\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of RAMP2 vs RAMP1 selectivity for AM vs CGRP unknown\", \"Endogenous stoichiometry and trafficking of the complex not examined\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identified a minimal seven-residue segment (86–92) in the RAMP2 N-terminal ectodomain as critical for AM binding and signaling, separating the ligand-recognition determinant from the receptor trafficking function.\",\n      \"evidence\": \"RAMP chimeras, deletion mutants, and alanine scanning co-expressed with CRLR in HEK293 cells; radioligand binding and cAMP assays with FACS surface-expression controls\",\n      \"pmids\": [\"11591721\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal or cryo-EM structure of AM–RAMP2–CLR to map contacts at atomic resolution\", \"Contribution of CLR residues to AM selectivity not dissected\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrated that CLR/RAMP2 and CLR/RAMP3 form pharmacologically distinct AM receptors with differing antagonist profiles, establishing the AM1/AM2 receptor nomenclature.\",\n      \"evidence\": \"Quantitative cAMP antagonism assays with pA2 calculations across Cos-7, Rat2, and L6 cells using AM22-52, CGRP8-37, and BIBN4096BS\",\n      \"pmids\": [\"12970090\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling bias differences between AM1 and AM2 not characterized\", \"Physiological contexts where AM2 substitutes for AM1 unclear\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Revealed that RAMP2 is indispensable for vascular development and integrity in vivo — its complete loss causes midgestation lethality with vascular fragility, hemorrhage, and endothelial detachment, while haploinsufficiency impairs adult angiogenesis.\",\n      \"evidence\": \"RAMP2 knockout mice (lethal), heterozygous mice, and EC-specific RAMP2 overexpression; histology, immunofluorescence, permeability assays\",\n      \"pmids\": [\"18097473\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular pathway downstream of AM-RAMP2 mediating junction/basement-membrane gene expression not defined\", \"Whether RAMP2 KO lethality is entirely AM-dependent or involves other CLR ligands unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Defined the intracellular mechanism by which endothelial AM-RAMP2 maintains vascular barrier: control of the Rac1-GTP/RhoA-GTP balance and cortical actin organization; loss of this system triggers vascular leakage, fibrosis, and accelerated senescence.\",\n      \"evidence\": \"Endothelial-specific and drug-inducible endothelial RAMP2 KO mice; Rac1/RhoA activity assays; actin imaging; permeability measurements\",\n      \"pmids\": [\"23355623\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether RAMP2 regulates Rac1/RhoA through Epac, PI3K, or another intermediate not resolved\", \"Contribution of β-arrestin-dependent vs G-protein-dependent pathways to barrier function unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Extended the vascular role to retinal angiogenesis, showing RAMP2 haploinsufficiency reduces pathological neovascularization and VEGF/eNOS expression in oxygen-induced retinopathy.\",\n      \"evidence\": \"RAMP2+/− and DI-E-RAMP2−/− mice in OIR model; EC proliferation/migration assays; intravitreal anti-ADM antibody\",\n      \"pmids\": [\"23562442\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether AM-RAMP2 directly transcribes VEGF or acts upstream via HIF not determined\", \"Therapeutic window for targeting AM-RAMP2 in retinal disease undefined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Expanded RAMP2's receptor repertoire beyond CLR by showing it modulates glucagon receptor pharmacology — altering GCGR ligand selectivity and G-protein coupling preference.\",\n      \"evidence\": \"RAMP2-GCGR co-expression in yeast reporter and mammalian cell functional assays with multiple ligands\",\n      \"pmids\": [\"26198634\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct physical interaction between RAMP2 and GCGR not confirmed by co-IP or structural data at this point\", \"Physiological tissues where RAMP2-GCGR interaction occurs not identified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showed RAMP2 causes intracellular redistribution of GCGR, reducing its surface expression and modulating both Gαs/Gαq signaling and β-arrestin recruitment — providing a trafficking-based mechanism for GCGR modulation.\",\n      \"evidence\": \"Confocal microscopy, cell-surface ELISA, competition binding, Gαs/Gαq assays, β-arrestin recruitment, siRNA knockdown\",\n      \"pmids\": [\"28586439\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether RAMP2-induced GCGR internalization is constitutive or regulated not fully dissected\", \"Structural interface between RAMP2 and GCGR undefined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified pathogenic RAMP2 variants as a cause of primary open-angle glaucoma (POAG), linking disrupted AM-RAMP2/CRLR-cAMP signaling and mutant protein aggregation to retinal ganglion cell death.\",\n      \"evidence\": \"Exome and Sanger sequencing of POAG families; transfection of mutant RAMP2; cAMP assays; RAMP2+/− mouse retinal histology\",\n      \"pmids\": [\"31000793\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Number of POAG families carrying RAMP2 variants is small; replication in larger cohorts needed\", \"Mechanism of mutant RAMP2 aggregation (misfolding vs ER retention) not characterized\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Resolved the mechanism of RAMP2's GCGR modulation in hepatocytes: RAMP2 drives constitutive and agonist-stimulated GCGR internalization, biasing signaling toward endosomal Gαs/cAMP and away from β-arrestin-2, with long-term lysosomal degradation of GCGR.\",\n      \"evidence\": \"Confocal microscopy, radioligand binding, WASH-complex KO MEFs, monensin trafficking inhibition, NanoBiT complementation, cAMP assays, hepatocyte-targeted AAV in lean/obese mice\",\n      \"pmids\": [\"34271220\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo metabolic consequences of hepatic RAMP2-GCGR interaction in disease models not fully explored\", \"Whether RAMP2-directed lysosomal degradation of GCGR is ubiquitin-dependent not tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrated that cardiomyocyte AM-RAMP2 signaling maintains mitochondrial homeostasis under pressure overload, with cardiomyocyte-specific RAMP2 deletion causing cardiac hypertrophy, fibrosis, and impaired mitochondrial membrane potential and respiration.\",\n      \"evidence\": \"Cardiomyocyte-specific RAMP2 KO mice; TAC; echocardiography; PV loops; mitochondrial assays\",\n      \"pmids\": [\"33545715\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Pathway linking AM-RAMP2-cAMP to mitochondrial biogenesis or quality control (e.g. PGC-1α, mitophagy) not identified\", \"Whether cardiomyocyte RAMP2 also modulates other GPCRs in the heart not explored\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Established that RAMP2 allosterically modulates PTH1R by shifting it to a preactivated conformation that accelerates activation and enhances Gi3 signaling and β-arrestin2 recruitment in a ligand-specific manner — broadening RAMP2's role to parathyroid hormone signaling.\",\n      \"evidence\": \"FRET/BRET biosensors for PTH1R conformational states and downstream signaling; RAMP2 co-expression; homology modelling\",\n      \"pmids\": [\"35914163\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of RAMP2-PTH1R interaction at atomic resolution not available\", \"In vivo relevance to calcium/phosphate homeostasis or bone biology not tested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Provided the first near-atomic structural insight into RAMP2's allosteric mechanism at GCGR: cryo-EM, HDX-MS, and smFRET showed RAMP2 disorders the GCGR ECD and rearranges intracellular activation hallmarks, acting as a negative allosteric modulator that broadly inhibits downstream signaling.\",\n      \"evidence\": \"Cryo-EM at 2.9 Å of GCGR-Gs-RAMP2 complex; HDX-MS; smFRET; signaling assays\",\n      \"pmids\": [\"37001505\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No ordered RAMP2-GCGR interface resolved — mechanism of ECD disordering is inferred rather than structurally mapped\", \"Whether similar allosteric disordering occurs at PTH1R or CRFR1 unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Linked endothelial RAMP2 to Epac1 expression as a downstream effector maintaining vascular barrier integrity in ARDS, distinguishing RAMP2's vascular regulation role from RAMP3's anti-inflammatory role.\",\n      \"evidence\": \"DI-E-RAMP2−/− and RAMP3−/− mice in intratracheal LPS ARDS model; transcriptomic and Epac1 expression analysis\",\n      \"pmids\": [\"38012983\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct transcriptional regulation of Epac1 by AM-RAMP2-cAMP pathway not demonstrated\", \"Single disease model; generalizability to other forms of acute lung injury not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the high-resolution structural basis of AM recognition by the RAMP2-CLR complex, the full spectrum of Family B GPCRs modulated by RAMP2 in vivo, the signaling intermediates connecting AM-RAMP2 to mitochondrial homeostasis in cardiomyocytes, and whether RAMP2 allosteric mechanisms (ECD disordering) are generalizable across its non-CLR GPCR partners.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of the full AM–RAMP2–CLR signaling complex\", \"Tissue-specific RAMP2 interactome beyond CLR, GCGR, PTH1R, CRFR1 not systematically mapped\", \"Downstream pathway from AM-RAMP2 to mitochondrial function in cardiomyocytes undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 9, 11, 15, 17, 18]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 11, 13]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 3, 9, 11, 15, 17, 18]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [4, 6]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [10, 14]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [11, 15]}\n    ],\n    \"complexes\": [\n      \"AM1 receptor (CLR-RAMP2)\"\n    ],\n    \"partners\": [\n      \"CALCRL\",\n      \"GCGR\",\n      \"PTH1R\",\n      \"CRHR1\",\n      \"RAPGEF3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}