{"gene":"TIE1","run_date":"2026-06-10T10:51:55","timeline":{"discoveries":[{"year":1995,"finding":"Tie1 (TIE) knockout mice develop severe edema, ruptured microvasculature, and die between E13.5-14.5, demonstrating that Tie1 is required cell-autonomously for vascular endothelial cell integrity and survival, particularly during angiogenic capillary growth, but is not essential for vasculogenesis.","method":"Targeted gene disruption (homologous recombination) in mice; chimeric animal analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — two independent knockout studies (PMID:8846781 and PMID:7596437) using genetic loss-of-function with defined vascular phenotypes, replicated across labs","pmids":["8846781","7596437"],"is_preprint":false},{"year":2002,"finding":"Tie1 activates phosphatidylinositol 3-kinase (PI3K) and Akt to inhibit apoptosis; a chimeric c-fms-Tie1 receptor in NIH 3T3 cells showed ligand-induced Tie1 autophosphorylation, downstream PI3K and Akt activation, and inhibition of UV-induced apoptosis dependent on PI3K. Tyrosine 1113 was identified as an important PI3K binding site by mutagenesis.","method":"In vitro kinase assay with recombinant GST-Tie1; chimeric receptor expression in NIH 3T3 cells; active-site mutagenesis (Y1113F); PI3K inhibitor (LY294002); apoptosis assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution, mutagenesis, and chimeric receptor functional assay in a single rigorous study with multiple orthogonal methods","pmids":["11865050"],"is_preprint":false},{"year":2000,"finding":"Tie1 forms a pre-formed heterotypic complex with Tie2 in endothelial cells, mediated by the intracellular domains of the receptors; Tie1 does not undergo autophosphorylation or phosphorylate cellular proteins upon activation and displays negligible kinase activity, suggesting it modulates Tie2 signaling rather than signaling independently.","method":"Co-immunoprecipitation of endogenous receptors; chimeric TrkA/Tie1 and TrkA/Tie2 receptors; phosphorylation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — Co-IP of endogenous proteins plus chimeric receptor functional analysis, multiple orthogonal approaches in single study","pmids":["10995770"],"is_preprint":false},{"year":2005,"finding":"Multiple angiopoietin proteins (COMP-Ang1, native Ang1, Ang4) induce Tie1 phosphorylation in endothelial cells; Tie2 forms heteromeric complexes with Tie1, enhances Tie1 activation, and can phosphorylate a kinase-inactive Tie1 in a ligand-dependent manner, indicating that angiopoietin-induced Tie1 phosphorylation is amplified via Tie2.","method":"Phosphorylation assays in endothelial cells and transfected non-endothelial cells; co-transfection with kinase-inactive Tie1 and wild-type Tie2; Western blot","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple angiopoietin proteins tested, kinase-dead mutant used, co-transfection experiments, multiple orthogonal approaches in one study","pmids":["15851516"],"is_preprint":false},{"year":2007,"finding":"Tie1 is a substrate for regulated intramembrane proteolysis: after ectodomain cleavage, the resulting 45-kDa endodomain undergoes gamma-secretase-mediated processing to a 42-kDa fragment that is degraded by the proteasome. This processing is stimulated by phorbol ester and VEGF. Activation of Tie1 ectodomain cleavage increases COMP-Ang1-mediated Tie2 activation and Tie2 ligand binding, indicating that Tie1 extracellular domain limits ligand access to Tie2.","method":"Biochemical fractionation; gamma-secretase inhibitors; proteasome inhibitors; siRNA knockdown of Tie1; Tie2 phosphorylation assays; ligand binding assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple pharmacological inhibitors plus siRNA, functional readout (Tie2 activation), multiple orthogonal methods in one study","pmids":["17728252"],"is_preprint":false},{"year":2007,"finding":"Ang1-induced Tie1 phosphorylation is Tie2-dependent: Ang1 fails to phosphorylate Tie1 when Tie2 is knocked down or kinase-inactive, and constitutively active Tie2 or a Tie2 agonistic antibody phosphorylates Tie1 without Ang1. Tie1 down-regulates Ang1-mediated AKT and MAPK signaling and modulates blood vessel morphogenesis by suppressing Tie2-driven signaling.","method":"siRNA knockdown of Tie2; constitutively active Tie2 expression; Tie2 agonistic antibody; kinase-dead Tie2 co-expression; in vitro and in vivo endothelial assays","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple independent approaches (siRNA, constitutively active receptor, agonistic antibody, kinase-dead mutant) with consistent results in single lab","pmids":["17504972"],"is_preprint":false},{"year":2010,"finding":"Tie1 and Tie2 form dynamic complexes on the cell surface detected by FRET; Tie1-Tie2 interactions are inhibitory and differentially modulated by Ang1 versus Ang2. Specific molecular surface areas of the ectodomains essential for Tie1-Tie2 recognition were identified.","method":"In vivo FRET-based proximity assay in live cells; mutagenesis of receptor-receptor contact surfaces","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — FRET-based structural proximity assay combined with mutagenesis to map interaction surface, multiple orthogonal methods","pmids":["20227369"],"is_preprint":false},{"year":2012,"finding":"Tie1 deficiency in endothelial cells induces endothelial-mesenchymal transition (EndMT) through Slug-dependent pathway; Erk1/2, Erk5, and Akt cascades control Slug promoter activity induced by Tie1 deficiency. Tie2 knockdown does not produce this effect.","method":"siRNA knockdown of Tie1 and Tie2 in human endothelial cells; promoter activity assays; signaling pathway inhibitors","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean siRNA KD with specific phenotypic readout (EndMT), single lab, single primary method","pmids":["22421998"],"is_preprint":false},{"year":2012,"finding":"Tie1 expression level determines whether Ang2 functions as a Tie2 agonist or antagonist: low Tie1 expression in lymphatic endothelial cells (HLECs) correlates with low Tie1-Tie2 hetercomplex formation and allows Ang2 to act as a Tie2 agonist; overexpression of Tie1 in HLECs restores Tie1-Tie2 heterocomplexes and abolishes Ang2-mediated Tie2 activation.","method":"Co-immunoprecipitation; adenovirus-mediated overexpression of Tie1; Tie2 phosphorylation assays; endothelial cell functional assays (migration, tube formation, apoptosis)","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — Co-IP plus functional assays, single lab, mechanistically informative but single study","pmids":["22342979"],"is_preprint":false},{"year":2012,"finding":"VEGF and TNFα differentially regulate Tie1 and Tie2 ectodomain cleavage in endothelial cells: VEGF and phorbol ester rapidly activate Tie1 cleavage (within minutes) while Tie2 cleavage requires hours; TNFα stimulates Tie1 cleavage and increases cellular Tie2. Elevated Tie2:Tie1 ratio (from Tie1 cleavage or TNFα treatment) is associated with increased Ang1-activated Tie2 phosphorylation.","method":"Western blot of ectodomain shedding; time-course experiments with VEGF, PMA, and TNFα; Ang1 stimulation and Tie2 phosphorylation assays in endothelial cells","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — defined biochemical mechanism with functional readout, single lab, multiple agonists tested","pmids":["22235284"],"is_preprint":false},{"year":2016,"finding":"Ang1 and Ang2 binding to Tie2 increases Tie1-Tie2 interactions in a β1 integrin-dependent manner; Tie1 regulates ANG-induced Tie2 trafficking in endothelial cells. Endothelial Tie1 deletion reduces Tie2 phosphorylation, decreases downstream Akt activation, increases FOXO1 nuclear localization, and prevents ANG1- and ANG2-induced capillary-to-venous remodeling. In acute endotoxemia, Tie1 ectodomain is rapidly cleaved by ADAM17, reducing ANG1 and autocrine ANG2 agonist activity and suppressing Tie2 signaling.","method":"Conditional endothelial Tie1 knockout mice; β1 integrin blocking antibodies; Tie2 phosphorylation and trafficking assays; FOXO1 nuclear localization assays; endotoxemia model; patient samples (hantavirus infection)","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO mice, integrin blocking, receptor trafficking assays, in vivo model of inflammation, replicated in patient samples; multiple orthogonal methods","pmids":["27548530"],"is_preprint":false},{"year":2015,"finding":"Tie1 negatively regulates Tie2 surface presentation in angiogenic tip cells (reducing Tie2 signaling) while cooperating with Tie2 in remodeling stalk cells to sustain Tie2 signaling. Tie1 is expressed during angiogenesis in tip and stalk cells and downregulated in quiescent adult vasculature.","method":"Conditional endothelial Tie1 deletion in mice; postnatal retinal vascular assays; flow cytometry; immunofluorescence; Tie2 surface expression quantification","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditional genetic deletion in mice with cell-type-specific phenotypic analysis, multiple imaging approaches","pmids":["26344773"],"is_preprint":false},{"year":2017,"finding":"Crystal structures reveal that Ang1-induced Tie2 dimerization and activation occurs via formation of an intermolecular β-sheet between the membrane-proximal third Fibronectin type III (Fn3) domains of Tie2. The Fn3 domains of Tie1 and Tie2 are structurally similar and compatible with Tie1/Tie2 heterodimerization by the same mechanism. Mutagenesis of key Tie2 Fn3 residues decreased Ang1-induced Tie2 phosphorylation; mutagenesis of Tie1 Fn3 residues increased basal Tie1 phosphorylation. Additional Fn2-Fn2 domain interactions were found essential for Tie2 oligomerization.","method":"X-ray crystallography of Tie1 and Tie2 Fn3 and Fn2 domains; mutagenesis of receptor-receptor contact residues; Tie2 phosphorylation assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure combined with mutagenesis and functional validation of phosphorylation, multiple orthogonal approaches in one study","pmids":["28396439"],"is_preprint":false},{"year":2003,"finding":"Fluid shear stress rapidly downregulates Tie1 expression in endothelial cells and induces rapid cleavage of Tie1, with the 45-kDa cleaved Tie1 endodomain binding to Tie2. Shear stress transcriptionally suppresses Tie1 via a negative shear stress response element within 250 bp of the promoter. TNFα also suppresses Tie1 promoter activity.","method":"Shear stress apparatus; Western blot of Tie1 cleavage; co-immunoprecipitation of Tie1 endodomain with Tie2; promoter-reporter assays; deletion analysis of promoter","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — Co-IP, promoter assays, shear stress functional readout; single lab, multiple methods","pmids":["14500555"],"is_preprint":false},{"year":2011,"finding":"Tie1 heterozygous deletion (Tie1+/-) on an apoE-deficient background reduces atherosclerosis by 35%. Endothelial-specific conditional Tie1 attenuation decreases atherosclerotic lesions dose-dependently. Atheroprotective laminar flow decreases Tie1 expression in vitro. Tie1 attenuation increases eNOS expression, Tie2 phosphorylation, and IkBα expression while decreasing ICAM levels, indicating a proinflammatory role for Tie1 at atherogenic shear stress sites.","method":"Tie1+/- and conditional endothelial Tie1 knockout on apoE-/- background; primary aortic endothelial cells; shear stress experiments; Western blot of eNOS, IkBα, ICAM","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic dose-dependent in vivo atherosclerosis model with mechanistic signaling readouts (eNOS, IkBα, ICAM, Tie2 phosphorylation)","pmids":["21383501"],"is_preprint":false},{"year":2008,"finding":"Tie2 mediates Ang1 inhibition of endothelial permeability and apoptosis; siRNA knockdown of Tie1 does not affect Ang1 anti-permeability or anti-apoptotic effects, indicating that Tie1 does not transduce these Ang1 signals.","method":"siRNA knockdown of Tie1 and Tie2 (>90% suppression); monolayer permeability assays; apoptosis assays in human endothelial cells","journal":"Microvascular research","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean siRNA KD with defined functional readout, single lab; negative result for Tie1 in Ang1 anti-permeability/anti-apoptotic signaling","pmids":["18848573"],"is_preprint":false},{"year":2009,"finding":"Loss of Tie1 results in lymphatic vascular abnormalities that precede blood vessel defects. Tie1-/- embryos have abnormally patterned lymph sacs at E12.5 without hemorrhage, and Tie1 hypomorphic embryos display similar lymphatic malformations, indicating Tie1 is required for lymphangiogenesis.","method":"Tie1 knockout and hypomorphic mouse models; immunohistochemical analysis of lymphatic markers at multiple developmental time points","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — two allelic series (null and hypomorphic), temporal phenotypic analysis, defined lymphatic vs. blood vascular phenotype dissection","pmids":["19910638"],"is_preprint":false},{"year":2010,"finding":"Tie1 is required for early lymphatic endothelial cell proliferation and subsequent survival. Tie1 hypomorphic mice show increased Prox1-positive LEC production (dilated jugular lymphatic vessels), abnormal lymphatic patterning, and increased LEC apoptosis after mid-gestation, with severity correlating with Tie1 expression level.","method":"Tie1 hypomorphic and conditional knockout mice; EdU/BrdU proliferation assays; TUNEL apoptosis assays; immunofluorescence for Prox1, LYVE1 and other LEC markers","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — dosage-sensitive genetic analysis with quantitative cell biological readouts, replicated across two allelic series","pmids":["20223757"],"is_preprint":false},{"year":2014,"finding":"Tie1 intracellular domain is required for lymphatic remodeling and valve formation independent of Tie2; conditional deletion of Tie1-ICD postnatally disrupts collecting vessel formation and lymphatic valvulogenesis, while neonatal deletion of Tie2 does not affect lymphatic vessel growth and maturation.","method":"Conditional knockout mice (Tie1-ICD deletion and Tie2 deletion using inducible Cre); analysis of lymphatic vessel morphology and valve formation","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — parallel conditional deletion of Tie1 vs Tie2, direct genetic epistasis establishing Tie1-specific pathway in lymphatics independent of Tie2","pmids":["24764452"],"is_preprint":false},{"year":2015,"finding":"Tie1 is required for lymphatic valve specification and collecting vessel development; conditional deletion of Tie1 with Nfatc1Cre causes agenesis of lymphatic valves and deficiency of collecting lymphatic vessels, preventing initiation of valve specification marked by Prox1-high LEC clusters associated with turbulent flow.","method":"Conditional Tie1 deletion using Nfatc1Cre; immunofluorescence for Prox1, PECAM, integrin-α9 and other valve markers; postnatal lymphatic analysis","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — tissue-specific conditional KO with detailed valve specification phenotype, direct mechanistic link to Prox1-mediated valve specification","pmids":["25576926"],"is_preprint":false},{"year":2019,"finding":"LECT2 is a functional ligand of Tie1. LECT2 binding to Tie1 disrupts Tie1-Tie2 heterodimerization, facilitates Tie2-Tie2 homodimerization, activates PPAR signaling, and inhibits endothelial cell migration and tube formation. In vivo, LECT2 overexpression inhibits portal angiogenesis and worsens liver fibrosis, while Lect2 knockout reverses these effects.","method":"Co-immunoprecipitation; pulldown assays; LECT2 overexpression and knockout mice; in vitro migration and tube formation assays; adeno-associated viral vector shRNA treatment","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — ligand identification by Co-IP/pulldown combined with in vitro functional assays and in vivo genetic models (both OE and KO), multiple orthogonal methods","pmids":["31474362"],"is_preprint":false},{"year":2016,"finding":"Tie1 and Tie2 constitutively associate with integrins α5β1 and αVβ3 through their ectodomains on the endothelial surface; this interaction is direct (demonstrated with purified components) and enhanced by fibronectin for Tie2. Cooperative Tie/integrin interactions selectively stimulate ERK/MAPK signaling in the presence of both Ang1 and fibronectin.","method":"Live cell FRET-based proximity assay; in vitro binding assays with purified proteins; ERK/MAPK phosphorylation assays; fibronectin and Ang1 co-stimulation","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — FRET plus in vitro binding with purified components establishes direct interaction, functional readout (ERK); single lab","pmids":["27695111"],"is_preprint":false},{"year":2020,"finding":"Heparan sulfate glycosaminoglycans (HS GAGs) are direct ligands for Tie1 and regulate Ang-Tie signaling: HS-Tie1 interaction promotes Tie1-Tie2 heterodimerization and enhances Tie1 stability. CRISPR-Cas9 mutagenesis abolishing HS-Tie1 binding in vivo decreases Tie protein levels, suppresses pathway signaling, and causes aberrant retinal vascularization.","method":"Direct binding assays between HS GAGs and Tie1; Tie1-Tie2 heterodimerization assays; CRISPR-Cas9 mutagenesis of HS binding site in vivo; retinal vascularization phenotyping","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct biochemical binding assays plus CRISPR in vivo mutagenesis with functional vascular phenotype, multiple orthogonal methods","pmids":["33020664"],"is_preprint":false},{"year":2022,"finding":"Tie1 in lymphatic endothelial cells is required for VEGF-C-induced full Akt activation downstream of PI3K; neonatal deletion of Tie1 (or Tie2) in LECs decreases VEGFR3 surface presentation and inhibits lymphangiogenesis. Ang2 secretion from LECs (induced by VEGF-C) signals via Tie receptors to regulate VEGFR3 cell-surface expression.","method":"Conditional Tie1 and Tie2 gene deletion in LECs; Ang2-blocking antibodies; PI3K inhibitors; VEGFR3 surface expression flow cytometry; lymphangiogenesis assays in neonatal and adult mice","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditional genetic deletion plus pharmacological inhibition with defined molecular endpoint (VEGFR3 surface expression), in vivo lymphangiogenesis validation","pmids":["35763346"],"is_preprint":false},{"year":2024,"finding":"PIEZO1 activation in lymphatic endothelial cells (LECs) causes rapid ectodomain shedding of Tie1 by ADAM17, concurrent exocytosis of ANGPT2, and increased TIE/PI3K/AKT signaling followed by nuclear export of FOXO1; this establishes a functional network placing PIEZO1 upstream of TIE1 ectodomain shedding in lymphatic signaling.","method":"PIEZO1 activation in LECs; ADAM17 inhibitor studies; Western blot of Tie1 shedding; AKT and FOXO1 phosphorylation/localization assays; ANGPT2 exocytosis assays","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Moderate — mechanistic pathway dissection with pharmacological and biochemical tools identifying ADAM17 as the sheddase and placing PIEZO1 upstream of Tie1 shedding, multiple readouts","pmids":["38747287"],"is_preprint":false},{"year":2008,"finding":"Overexpression of Tie1 in endothelial cells induces tyrosine phosphorylation of Tie1 and upregulates adhesion molecules VCAM-1, E-selectin, and ICAM-1 through a p38-dependent mechanism, enhancing monocyte attachment to endothelial cells.","method":"Tie1 overexpression in human aortic endothelial cells and HUVECs; Western blot and flow cytometry for adhesion molecules; p38 inhibitor; monocyte adhesion assays","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — overexpression system with pharmacological inhibitor and functional readout; single lab, single primary approach","pmids":["18448073"],"is_preprint":false},{"year":1999,"finding":"Genetic analysis of TEK/TIE double-knockout embryos shows that vasculogenesis proceeds normally without both receptors, but TEK is absolutely required in the endocardium at E10.5. Both TEK and TIE are required in the microvasculature during late organogenesis, demonstrating essential but non-redundant roles in maintaining vascular integrity with distinct tissue requirements.","method":"TEK/TIE double knockout mice; mosaic (chimeric) analysis to determine cell-autonomous requirements","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — double KO plus mosaic analysis dissecting cell-autonomous requirements with defined temporal and tissue-specific phenotypes","pmids":["10498691"],"is_preprint":false},{"year":2021,"finding":"Tie receptor signaling (detected by phosphorylation preferentially in the central vein area) acts as a selective regulator of vascular Wnt activity in liver endothelium, orchestrating angiocrine signaling and controlling hepatocyte function during liver regeneration.","method":"Spatial cell sorting combined with transcriptomics and quantitative phosphoproteomics; biological validation of Tie receptor-Wnt signaling axis in liver regeneration","journal":"Developmental cell","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — phosphoproteomics plus biological validation in liver, single study identifying Tie-Wnt angiocrine axis","pmids":["34038707"],"is_preprint":false},{"year":2021,"finding":"m6A methylation of TIE1 mRNA 3'UTR by METTL14 increases TIE1 mRNA stability; miR-4729 targets METTL14 3'UTR to suppress METTL14 expression, reducing global m6A modification and TIE1 mRNA methylation at a specific 3'UTR site, thereby decreasing TIE1 expression and the TIE1/VEGFA signaling loop in endothelial cells.","method":"RNA immunoprecipitation-PCR for m6A sites; luciferase reporter assay; miR-4729 overexpression; Western blot; tube formation and migration assays","journal":"Annals of translational medicine","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — RIP-PCR identifies specific m6A site on TIE1 mRNA, functional rescue assays support regulatory mechanism; single lab","pmids":["33708859"],"is_preprint":false}],"current_model":"TIE1 is an endothelial-specific receptor tyrosine kinase that functions primarily as a context-dependent modulator of TIE2 signaling: it forms constitutive heterodimeric complexes with TIE2 (via membrane-proximal Fn3 domains and intracellular domain interactions), can be phosphorylated by angiopoietins in a TIE2-dependent manner, activates PI3K/Akt signaling to promote endothelial survival, and undergoes regulated ectodomain shedding by ADAM17 (stimulated by VEGF, TNFα, and PIEZO1 mechanosensing) that dynamically shifts the TIE2:TIE1 balance to modulate angiopoietin responsiveness; additionally, LECT2 and heparan sulfate glycosaminoglycans have been identified as direct TIE1 ligands, and TIE1 is required cell-autonomously for blood vascular integrity and for lymphatic vessel development, remodeling, and valve formation."},"narrative":{"mechanistic_narrative":"TIE1 is an endothelial-specific receptor tyrosine kinase that functions as a context-dependent modulator of TIE2 (TEK) signaling and is required cell-autonomously for blood vascular integrity and lymphatic development [PMID:8846781, PMID:7596437, PMID:10498691, PMID:10995770]. TIE1 forms pre-formed heterotypic complexes with TIE2 through both intracellular domain contacts and membrane-proximal Fibronectin type III (Fn3) domains, the latter mediating heterodimerization via an intermolecular β-sheet structurally analogous to that driving TIE2 homodimerization [PMID:10995770, PMID:28396439]. Although TIE1 displays negligible intrinsic kinase activity and does not autophosphorylate on its own, it is phosphorylated by angiopoietins (Ang1, Ang4, COMP-Ang1) in a strictly TIE2-dependent manner, and the TIE1:TIE2 stoichiometry tunes endothelial responsiveness to angiopoietins — TIE1 generally restrains TIE2 activation, and its expression level determines whether Ang2 acts as a TIE2 agonist or antagonist [PMID:15851516, PMID:17504972, PMID:22342979, PMID:20227369]. This balance is set dynamically by regulated ectodomain shedding: ADAM17/γ-secretase-mediated cleavage of TIE1, stimulated by VEGF, TNFα, fluid shear stress, and PIEZO1 mechanosensing, raises the TIE2:TIE1 ratio and relieves TIE1's suppression of TIE2 signaling, including during acute endotoxemia [PMID:17728252, PMID:22235284, PMID:14500555, PMID:27548530, PMID:38747287]. Where TIE1 does signal, it activates PI3K/Akt via Tyr1113 to promote endothelial survival and to control FOXO1 nuclear localization, and its loss drives Slug-dependent endothelial-mesenchymal transition [PMID:11865050, PMID:27548530, PMID:22421998]. TIE1 also engages additional binding partners — LECT2, which disrupts TIE1-TIE2 heterodimers and favors TIE2 homodimerization, heparan sulfate glycosaminoglycans, which promote heterodimerization and TIE protein stability, and integrins α5β1/αVβ3, which cooperate to stimulate ERK/MAPK signaling [PMID:31474362, PMID:33020664, PMID:27695111]. In the lymphatic vasculature TIE1 is required, partly through its intracellular domain and independently of TIE2, for LEC proliferation and survival, lymphangiogenesis, collecting vessel remodeling, and valve specification, and supports VEGF-C/VEGFR3-driven lymphangiogenesis by sustaining VEGFR3 surface presentation [PMID:19910638, PMID:20223757, PMID:24764452, PMID:25576926, PMID:35763346]. TIE1 additionally contributes to vascular inflammation and atherogenesis at disturbed-flow sites [PMID:21383501, PMID:18448073].","teleology":[{"year":1995,"claim":"Established that TIE1 is dispensable for vasculogenesis but cell-autonomously required for endothelial integrity and survival during angiogenic growth, defining its developmental role.","evidence":"Targeted gene disruption and chimeric analysis in mice","pmids":["8846781","7596437"],"confidence":"High","gaps":["Did not define the molecular signaling defect underlying vascular rupture","No biochemical mechanism for survival function"]},{"year":1999,"claim":"Distinguished TIE1 from TIE2 by showing both are needed in late-organogenesis microvasculature but with non-redundant, tissue-distinct requirements, with TEK specifically essential in endocardium.","evidence":"TEK/TIE double-knockout and mosaic analysis in mice","pmids":["10498691"],"confidence":"High","gaps":["Did not resolve whether TIE1 acts through TIE2 or independently","No molecular partners identified"]},{"year":2000,"claim":"Resolved the long-standing question of TIE1 signaling competence by showing it has negligible kinase activity and instead forms a constitutive intracellular-domain heterocomplex with TIE2, reframing TIE1 as a modulator rather than autonomous receptor.","evidence":"Co-IP of endogenous receptors and chimeric TrkA/Tie receptor phosphorylation assays","pmids":["10995770"],"confidence":"High","gaps":["Did not identify ectodomain interaction interface","Direction of modulation (positive vs negative) unresolved"]},{"year":2002,"claim":"Demonstrated that when artificially activated, TIE1 can couple to PI3K/Akt to inhibit apoptosis, mapping Tyr1113 as the PI3K docking site and providing a survival-signaling output.","evidence":"In vitro kinase assay, chimeric c-fms-Tie1 receptor in NIH 3T3, Y1113F mutagenesis, PI3K inhibition","pmids":["11865050"],"confidence":"High","gaps":["Used a chimeric receptor rather than physiological ligand","Relevance to endogenous TIE1 with low kinase activity unclear"]},{"year":2005,"claim":"Showed that angiopoietin-induced TIE1 phosphorylation is amplified through heteromeric TIE2, establishing that TIE2 trans-phosphorylates kinase-inactive TIE1 in a ligand-dependent manner.","evidence":"Phosphorylation assays with multiple angiopoietins, kinase-inactive TIE1 plus wild-type TIE2 co-transfection","pmids":["15851516"],"confidence":"High","gaps":["Functional consequence of TIE1 phosphorylation not defined","Did not address ectodomain regulation"]},{"year":2007,"claim":"Defined TIE1 ectodomain as a brake on TIE2: regulated intramembrane proteolysis (ectodomain cleavage then γ-secretase/proteasome processing), stimulated by VEGF and phorbol ester, removes TIE1's restriction of ligand access and enhances TIE2 activation.","evidence":"Biochemical fractionation, γ-secretase/proteasome inhibitors, siRNA, Tie2 phosphorylation and ligand-binding assays; plus siRNA/constitutively-active-TIE2 dependence experiments","pmids":["17728252","17504972"],"confidence":"High","gaps":["Sheddase identity not yet pinned to ADAM17","Quantitative stoichiometry of TIE1:TIE2 not defined"]},{"year":2010,"claim":"Visualized dynamic, inhibitory TIE1-TIE2 surface complexes in live cells and mapped the ectodomain surfaces required, showing Ang1 versus Ang2 differentially modulate the interaction.","evidence":"Live-cell FRET proximity assay with contact-surface mutagenesis","pmids":["20227369"],"confidence":"High","gaps":["Atomic-resolution interface not yet determined","Downstream signaling consequences not fully mapped"]},{"year":2012,"claim":"Connected TIE1 abundance to angiopoietin output, showing TIE1 expression level dictates Ang2 agonist/antagonist behavior, that VEGF/TNFα selectively control TIE1 versus TIE2 shedding to set the TIE2:TIE1 ratio, and that TIE1 loss drives Slug-dependent EndMT.","evidence":"Co-IP, adenoviral TIE1 overexpression, time-course shedding Western blots, siRNA with EndMT/promoter readouts","pmids":["22342979","22235284","22421998"],"confidence":"Medium","gaps":["Mostly single-lab observations per finding","EndMT mechanism downstream of Slug incompletely defined"]},{"year":2015,"claim":"Linked TIE1 to angiogenic specialization in vivo, showing it negatively regulates TIE2 surface presentation in tip cells while cooperating with TIE2 in stalk cells, and is required for lymphatic valve specification and collecting vessel development.","evidence":"Conditional endothelial and Nfatc1Cre TIE1 deletion, retinal vascular and lymphatic valve phenotyping","pmids":["26344773","25576926"],"confidence":"High","gaps":["Molecular switch between tip-cell inhibition and stalk-cell cooperation undefined","Valve specification effectors downstream of TIE1 unresolved"]},{"year":2016,"claim":"Integrated TIE1 into integrin and trafficking control: ADAM17 was identified as the in vivo TIE1 sheddase in inflammation, β1 integrin was shown to enhance Ang-induced TIE1-TIE2 interaction and TIE2 trafficking, and TIE1/TIE2 were shown to directly associate with integrins to stimulate ERK.","evidence":"Conditional TIE1 knockout, integrin-blocking antibodies, trafficking/FOXO1 assays, endotoxemia model, FRET and purified-protein binding","pmids":["27548530","27695111"],"confidence":"High","gaps":["FRET/integrin direct-binding study is single-lab Medium evidence","Structural basis of TIE-integrin association undefined"]},{"year":2017,"claim":"Provided the structural basis for TIE complex assembly, showing Ang1-induced TIE2 dimerization occurs via an intermolecular Fn3 β-sheet, with TIE1 Fn3 domains structurally compatible for heterodimerization by the same mechanism.","evidence":"X-ray crystallography of TIE1/TIE2 Fn3 and Fn2 domains with mutagenesis and phosphorylation validation","pmids":["28396439"],"confidence":"High","gaps":["No full-length receptor or heterodimer structure","Conformational coupling to intracellular kinase not resolved"]},{"year":2019,"claim":"Identified LECT2 as a functional TIE1 ligand that disrupts TIE1-TIE2 heterodimers to favor TIE2 homodimerization and PPAR signaling, providing the first defined extracellular ligand acting through TIE1.","evidence":"Co-IP/pulldown, LECT2 overexpression and knockout mice, in vitro migration/tube assays, liver fibrosis models","pmids":["31474362"],"confidence":"High","gaps":["Binding site on TIE1 not mapped","Generality beyond hepatic/portal vasculature unclear"]},{"year":2020,"claim":"Established heparan sulfate glycosaminoglycans as direct TIE1 ligands that promote TIE1-TIE2 heterodimerization and TIE protein stability, with in vivo HS-binding-site mutation suppressing signaling and disrupting retinal vascularization.","evidence":"Direct binding assays, heterodimerization assays, CRISPR-Cas9 in vivo mutagenesis, retinal phenotyping","pmids":["33020664"],"confidence":"High","gaps":["HS structural specificity not fully defined","Interplay with protein ligands (LECT2, angiopoietins) not addressed"]},{"year":2022,"claim":"Defined a lymphatic TIE1 role upstream of VEGFR3, showing TIE1 (with TIE2) sustains VEGFR3 surface presentation and VEGF-C-induced PI3K/Akt activation via Ang2 autocrine signaling.","evidence":"Conditional LEC TIE1/TIE2 deletion, Ang2-blocking antibody, PI3K inhibition, VEGFR3 flow cytometry, neonatal lymphangiogenesis assays","pmids":["35763346"],"confidence":"High","gaps":["Mechanism of VEGFR3 surface retention by TIE receptors undefined","Direct TIE1-VEGFR3 interaction not demonstrated"]},{"year":2024,"claim":"Placed mechanical force upstream of TIE1 regulation, showing PIEZO1 activation triggers ADAM17-mediated TIE1 ectodomain shedding, ANGPT2 exocytosis, and TIE/PI3K/AKT signaling with FOXO1 nuclear export in lymphatic endothelium.","evidence":"PIEZO1 activation in LECs, ADAM17 inhibition, shedding/AKT/FOXO1 and ANGPT2 exocytosis assays","pmids":["38747287"],"confidence":"High","gaps":["Link from PIEZO1 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recombination) in mice; chimeric animal analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — two independent knockout studies (PMID:8846781 and PMID:7596437) using genetic loss-of-function with defined vascular phenotypes, replicated across labs\",\n      \"pmids\": [\"8846781\", \"7596437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Tie1 activates phosphatidylinositol 3-kinase (PI3K) and Akt to inhibit apoptosis; a chimeric c-fms-Tie1 receptor in NIH 3T3 cells showed ligand-induced Tie1 autophosphorylation, downstream PI3K and Akt activation, and inhibition of UV-induced apoptosis dependent on PI3K. Tyrosine 1113 was identified as an important PI3K binding site by mutagenesis.\",\n      \"method\": \"In vitro kinase assay with recombinant GST-Tie1; chimeric receptor expression in NIH 3T3 cells; active-site mutagenesis (Y1113F); PI3K inhibitor (LY294002); apoptosis assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution, mutagenesis, and chimeric receptor functional assay in a single rigorous study with multiple orthogonal methods\",\n      \"pmids\": [\"11865050\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Tie1 forms a pre-formed heterotypic complex with Tie2 in endothelial cells, mediated by the intracellular domains of the receptors; Tie1 does not undergo autophosphorylation or phosphorylate cellular proteins upon activation and displays negligible kinase activity, suggesting it modulates Tie2 signaling rather than signaling independently.\",\n      \"method\": \"Co-immunoprecipitation of endogenous receptors; chimeric TrkA/Tie1 and TrkA/Tie2 receptors; phosphorylation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP of endogenous proteins plus chimeric receptor functional analysis, multiple orthogonal approaches in single study\",\n      \"pmids\": [\"10995770\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Multiple angiopoietin proteins (COMP-Ang1, native Ang1, Ang4) induce Tie1 phosphorylation in endothelial cells; Tie2 forms heteromeric complexes with Tie1, enhances Tie1 activation, and can phosphorylate a kinase-inactive Tie1 in a ligand-dependent manner, indicating that angiopoietin-induced Tie1 phosphorylation is amplified via Tie2.\",\n      \"method\": \"Phosphorylation assays in endothelial cells and transfected non-endothelial cells; co-transfection with kinase-inactive Tie1 and wild-type Tie2; Western blot\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple angiopoietin proteins tested, kinase-dead mutant used, co-transfection experiments, multiple orthogonal approaches in one study\",\n      \"pmids\": [\"15851516\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Tie1 is a substrate for regulated intramembrane proteolysis: after ectodomain cleavage, the resulting 45-kDa endodomain undergoes gamma-secretase-mediated processing to a 42-kDa fragment that is degraded by the proteasome. This processing is stimulated by phorbol ester and VEGF. Activation of Tie1 ectodomain cleavage increases COMP-Ang1-mediated Tie2 activation and Tie2 ligand binding, indicating that Tie1 extracellular domain limits ligand access to Tie2.\",\n      \"method\": \"Biochemical fractionation; gamma-secretase inhibitors; proteasome inhibitors; siRNA knockdown of Tie1; Tie2 phosphorylation assays; ligand binding assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple pharmacological inhibitors plus siRNA, functional readout (Tie2 activation), multiple orthogonal methods in one study\",\n      \"pmids\": [\"17728252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Ang1-induced Tie1 phosphorylation is Tie2-dependent: Ang1 fails to phosphorylate Tie1 when Tie2 is knocked down or kinase-inactive, and constitutively active Tie2 or a Tie2 agonistic antibody phosphorylates Tie1 without Ang1. Tie1 down-regulates Ang1-mediated AKT and MAPK signaling and modulates blood vessel morphogenesis by suppressing Tie2-driven signaling.\",\n      \"method\": \"siRNA knockdown of Tie2; constitutively active Tie2 expression; Tie2 agonistic antibody; kinase-dead Tie2 co-expression; in vitro and in vivo endothelial assays\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple independent approaches (siRNA, constitutively active receptor, agonistic antibody, kinase-dead mutant) with consistent results in single lab\",\n      \"pmids\": [\"17504972\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Tie1 and Tie2 form dynamic complexes on the cell surface detected by FRET; Tie1-Tie2 interactions are inhibitory and differentially modulated by Ang1 versus Ang2. Specific molecular surface areas of the ectodomains essential for Tie1-Tie2 recognition were identified.\",\n      \"method\": \"In vivo FRET-based proximity assay in live cells; mutagenesis of receptor-receptor contact surfaces\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — FRET-based structural proximity assay combined with mutagenesis to map interaction surface, multiple orthogonal methods\",\n      \"pmids\": [\"20227369\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Tie1 deficiency in endothelial cells induces endothelial-mesenchymal transition (EndMT) through Slug-dependent pathway; Erk1/2, Erk5, and Akt cascades control Slug promoter activity induced by Tie1 deficiency. Tie2 knockdown does not produce this effect.\",\n      \"method\": \"siRNA knockdown of Tie1 and Tie2 in human endothelial cells; promoter activity assays; signaling pathway inhibitors\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean siRNA KD with specific phenotypic readout (EndMT), single lab, single primary method\",\n      \"pmids\": [\"22421998\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Tie1 expression level determines whether Ang2 functions as a Tie2 agonist or antagonist: low Tie1 expression in lymphatic endothelial cells (HLECs) correlates with low Tie1-Tie2 hetercomplex formation and allows Ang2 to act as a Tie2 agonist; overexpression of Tie1 in HLECs restores Tie1-Tie2 heterocomplexes and abolishes Ang2-mediated Tie2 activation.\",\n      \"method\": \"Co-immunoprecipitation; adenovirus-mediated overexpression of Tie1; Tie2 phosphorylation assays; endothelial cell functional assays (migration, tube formation, apoptosis)\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — Co-IP plus functional assays, single lab, mechanistically informative but single study\",\n      \"pmids\": [\"22342979\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"VEGF and TNFα differentially regulate Tie1 and Tie2 ectodomain cleavage in endothelial cells: VEGF and phorbol ester rapidly activate Tie1 cleavage (within minutes) while Tie2 cleavage requires hours; TNFα stimulates Tie1 cleavage and increases cellular Tie2. Elevated Tie2:Tie1 ratio (from Tie1 cleavage or TNFα treatment) is associated with increased Ang1-activated Tie2 phosphorylation.\",\n      \"method\": \"Western blot of ectodomain shedding; time-course experiments with VEGF, PMA, and TNFα; Ang1 stimulation and Tie2 phosphorylation assays in endothelial cells\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — defined biochemical mechanism with functional readout, single lab, multiple agonists tested\",\n      \"pmids\": [\"22235284\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Ang1 and Ang2 binding to Tie2 increases Tie1-Tie2 interactions in a β1 integrin-dependent manner; Tie1 regulates ANG-induced Tie2 trafficking in endothelial cells. Endothelial Tie1 deletion reduces Tie2 phosphorylation, decreases downstream Akt activation, increases FOXO1 nuclear localization, and prevents ANG1- and ANG2-induced capillary-to-venous remodeling. In acute endotoxemia, Tie1 ectodomain is rapidly cleaved by ADAM17, reducing ANG1 and autocrine ANG2 agonist activity and suppressing Tie2 signaling.\",\n      \"method\": \"Conditional endothelial Tie1 knockout mice; β1 integrin blocking antibodies; Tie2 phosphorylation and trafficking assays; FOXO1 nuclear localization assays; endotoxemia model; patient samples (hantavirus infection)\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO mice, integrin blocking, receptor trafficking assays, in vivo model of inflammation, replicated in patient samples; multiple orthogonal methods\",\n      \"pmids\": [\"27548530\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Tie1 negatively regulates Tie2 surface presentation in angiogenic tip cells (reducing Tie2 signaling) while cooperating with Tie2 in remodeling stalk cells to sustain Tie2 signaling. Tie1 is expressed during angiogenesis in tip and stalk cells and downregulated in quiescent adult vasculature.\",\n      \"method\": \"Conditional endothelial Tie1 deletion in mice; postnatal retinal vascular assays; flow cytometry; immunofluorescence; Tie2 surface expression quantification\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional genetic deletion in mice with cell-type-specific phenotypic analysis, multiple imaging approaches\",\n      \"pmids\": [\"26344773\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Crystal structures reveal that Ang1-induced Tie2 dimerization and activation occurs via formation of an intermolecular β-sheet between the membrane-proximal third Fibronectin type III (Fn3) domains of Tie2. The Fn3 domains of Tie1 and Tie2 are structurally similar and compatible with Tie1/Tie2 heterodimerization by the same mechanism. Mutagenesis of key Tie2 Fn3 residues decreased Ang1-induced Tie2 phosphorylation; mutagenesis of Tie1 Fn3 residues increased basal Tie1 phosphorylation. Additional Fn2-Fn2 domain interactions were found essential for Tie2 oligomerization.\",\n      \"method\": \"X-ray crystallography of Tie1 and Tie2 Fn3 and Fn2 domains; mutagenesis of receptor-receptor contact residues; Tie2 phosphorylation assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure combined with mutagenesis and functional validation of phosphorylation, multiple orthogonal approaches in one study\",\n      \"pmids\": [\"28396439\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Fluid shear stress rapidly downregulates Tie1 expression in endothelial cells and induces rapid cleavage of Tie1, with the 45-kDa cleaved Tie1 endodomain binding to Tie2. Shear stress transcriptionally suppresses Tie1 via a negative shear stress response element within 250 bp of the promoter. TNFα also suppresses Tie1 promoter activity.\",\n      \"method\": \"Shear stress apparatus; Western blot of Tie1 cleavage; co-immunoprecipitation of Tie1 endodomain with Tie2; promoter-reporter assays; deletion analysis of promoter\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — Co-IP, promoter assays, shear stress functional readout; single lab, multiple methods\",\n      \"pmids\": [\"14500555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Tie1 heterozygous deletion (Tie1+/-) on an apoE-deficient background reduces atherosclerosis by 35%. Endothelial-specific conditional Tie1 attenuation decreases atherosclerotic lesions dose-dependently. Atheroprotective laminar flow decreases Tie1 expression in vitro. Tie1 attenuation increases eNOS expression, Tie2 phosphorylation, and IkBα expression while decreasing ICAM levels, indicating a proinflammatory role for Tie1 at atherogenic shear stress sites.\",\n      \"method\": \"Tie1+/- and conditional endothelial Tie1 knockout on apoE-/- background; primary aortic endothelial cells; shear stress experiments; Western blot of eNOS, IkBα, ICAM\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic dose-dependent in vivo atherosclerosis model with mechanistic signaling readouts (eNOS, IkBα, ICAM, Tie2 phosphorylation)\",\n      \"pmids\": [\"21383501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Tie2 mediates Ang1 inhibition of endothelial permeability and apoptosis; siRNA knockdown of Tie1 does not affect Ang1 anti-permeability or anti-apoptotic effects, indicating that Tie1 does not transduce these Ang1 signals.\",\n      \"method\": \"siRNA knockdown of Tie1 and Tie2 (>90% suppression); monolayer permeability assays; apoptosis assays in human endothelial cells\",\n      \"journal\": \"Microvascular research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean siRNA KD with defined functional readout, single lab; negative result for Tie1 in Ang1 anti-permeability/anti-apoptotic signaling\",\n      \"pmids\": [\"18848573\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Loss of Tie1 results in lymphatic vascular abnormalities that precede blood vessel defects. Tie1-/- embryos have abnormally patterned lymph sacs at E12.5 without hemorrhage, and Tie1 hypomorphic embryos display similar lymphatic malformations, indicating Tie1 is required for lymphangiogenesis.\",\n      \"method\": \"Tie1 knockout and hypomorphic mouse models; immunohistochemical analysis of lymphatic markers at multiple developmental time points\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two allelic series (null and hypomorphic), temporal phenotypic analysis, defined lymphatic vs. blood vascular phenotype dissection\",\n      \"pmids\": [\"19910638\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Tie1 is required for early lymphatic endothelial cell proliferation and subsequent survival. Tie1 hypomorphic mice show increased Prox1-positive LEC production (dilated jugular lymphatic vessels), abnormal lymphatic patterning, and increased LEC apoptosis after mid-gestation, with severity correlating with Tie1 expression level.\",\n      \"method\": \"Tie1 hypomorphic and conditional knockout mice; EdU/BrdU proliferation assays; TUNEL apoptosis assays; immunofluorescence for Prox1, LYVE1 and other LEC markers\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — dosage-sensitive genetic analysis with quantitative cell biological readouts, replicated across two allelic series\",\n      \"pmids\": [\"20223757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Tie1 intracellular domain is required for lymphatic remodeling and valve formation independent of Tie2; conditional deletion of Tie1-ICD postnatally disrupts collecting vessel formation and lymphatic valvulogenesis, while neonatal deletion of Tie2 does not affect lymphatic vessel growth and maturation.\",\n      \"method\": \"Conditional knockout mice (Tie1-ICD deletion and Tie2 deletion using inducible Cre); analysis of lymphatic vessel morphology and valve formation\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — parallel conditional deletion of Tie1 vs Tie2, direct genetic epistasis establishing Tie1-specific pathway in lymphatics independent of Tie2\",\n      \"pmids\": [\"24764452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Tie1 is required for lymphatic valve specification and collecting vessel development; conditional deletion of Tie1 with Nfatc1Cre causes agenesis of lymphatic valves and deficiency of collecting lymphatic vessels, preventing initiation of valve specification marked by Prox1-high LEC clusters associated with turbulent flow.\",\n      \"method\": \"Conditional Tie1 deletion using Nfatc1Cre; immunofluorescence for Prox1, PECAM, integrin-α9 and other valve markers; postnatal lymphatic analysis\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — tissue-specific conditional KO with detailed valve specification phenotype, direct mechanistic link to Prox1-mediated valve specification\",\n      \"pmids\": [\"25576926\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"LECT2 is a functional ligand of Tie1. LECT2 binding to Tie1 disrupts Tie1-Tie2 heterodimerization, facilitates Tie2-Tie2 homodimerization, activates PPAR signaling, and inhibits endothelial cell migration and tube formation. In vivo, LECT2 overexpression inhibits portal angiogenesis and worsens liver fibrosis, while Lect2 knockout reverses these effects.\",\n      \"method\": \"Co-immunoprecipitation; pulldown assays; LECT2 overexpression and knockout mice; in vitro migration and tube formation assays; adeno-associated viral vector shRNA treatment\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ligand identification by Co-IP/pulldown combined with in vitro functional assays and in vivo genetic models (both OE and KO), multiple orthogonal methods\",\n      \"pmids\": [\"31474362\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Tie1 and Tie2 constitutively associate with integrins α5β1 and αVβ3 through their ectodomains on the endothelial surface; this interaction is direct (demonstrated with purified components) and enhanced by fibronectin for Tie2. Cooperative Tie/integrin interactions selectively stimulate ERK/MAPK signaling in the presence of both Ang1 and fibronectin.\",\n      \"method\": \"Live cell FRET-based proximity assay; in vitro binding assays with purified proteins; ERK/MAPK phosphorylation assays; fibronectin and Ang1 co-stimulation\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — FRET plus in vitro binding with purified components establishes direct interaction, functional readout (ERK); single lab\",\n      \"pmids\": [\"27695111\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Heparan sulfate glycosaminoglycans (HS GAGs) are direct ligands for Tie1 and regulate Ang-Tie signaling: HS-Tie1 interaction promotes Tie1-Tie2 heterodimerization and enhances Tie1 stability. CRISPR-Cas9 mutagenesis abolishing HS-Tie1 binding in vivo decreases Tie protein levels, suppresses pathway signaling, and causes aberrant retinal vascularization.\",\n      \"method\": \"Direct binding assays between HS GAGs and Tie1; Tie1-Tie2 heterodimerization assays; CRISPR-Cas9 mutagenesis of HS binding site in vivo; retinal vascularization phenotyping\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct biochemical binding assays plus CRISPR in vivo mutagenesis with functional vascular phenotype, multiple orthogonal methods\",\n      \"pmids\": [\"33020664\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Tie1 in lymphatic endothelial cells is required for VEGF-C-induced full Akt activation downstream of PI3K; neonatal deletion of Tie1 (or Tie2) in LECs decreases VEGFR3 surface presentation and inhibits lymphangiogenesis. Ang2 secretion from LECs (induced by VEGF-C) signals via Tie receptors to regulate VEGFR3 cell-surface expression.\",\n      \"method\": \"Conditional Tie1 and Tie2 gene deletion in LECs; Ang2-blocking antibodies; PI3K inhibitors; VEGFR3 surface expression flow cytometry; lymphangiogenesis assays in neonatal and adult mice\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional genetic deletion plus pharmacological inhibition with defined molecular endpoint (VEGFR3 surface expression), in vivo lymphangiogenesis validation\",\n      \"pmids\": [\"35763346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PIEZO1 activation in lymphatic endothelial cells (LECs) causes rapid ectodomain shedding of Tie1 by ADAM17, concurrent exocytosis of ANGPT2, and increased TIE/PI3K/AKT signaling followed by nuclear export of FOXO1; this establishes a functional network placing PIEZO1 upstream of TIE1 ectodomain shedding in lymphatic signaling.\",\n      \"method\": \"PIEZO1 activation in LECs; ADAM17 inhibitor studies; Western blot of Tie1 shedding; AKT and FOXO1 phosphorylation/localization assays; ANGPT2 exocytosis assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic pathway dissection with pharmacological and biochemical tools identifying ADAM17 as the sheddase and placing PIEZO1 upstream of Tie1 shedding, multiple readouts\",\n      \"pmids\": [\"38747287\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Overexpression of Tie1 in endothelial cells induces tyrosine phosphorylation of Tie1 and upregulates adhesion molecules VCAM-1, E-selectin, and ICAM-1 through a p38-dependent mechanism, enhancing monocyte attachment to endothelial cells.\",\n      \"method\": \"Tie1 overexpression in human aortic endothelial cells and HUVECs; Western blot and flow cytometry for adhesion molecules; p38 inhibitor; monocyte adhesion assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — overexpression system with pharmacological inhibitor and functional readout; single lab, single primary approach\",\n      \"pmids\": [\"18448073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Genetic analysis of TEK/TIE double-knockout embryos shows that vasculogenesis proceeds normally without both receptors, but TEK is absolutely required in the endocardium at E10.5. Both TEK and TIE are required in the microvasculature during late organogenesis, demonstrating essential but non-redundant roles in maintaining vascular integrity with distinct tissue requirements.\",\n      \"method\": \"TEK/TIE double knockout mice; mosaic (chimeric) analysis to determine cell-autonomous requirements\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — double KO plus mosaic analysis dissecting cell-autonomous requirements with defined temporal and tissue-specific phenotypes\",\n      \"pmids\": [\"10498691\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Tie receptor signaling (detected by phosphorylation preferentially in the central vein area) acts as a selective regulator of vascular Wnt activity in liver endothelium, orchestrating angiocrine signaling and controlling hepatocyte function during liver regeneration.\",\n      \"method\": \"Spatial cell sorting combined with transcriptomics and quantitative phosphoproteomics; biological validation of Tie receptor-Wnt signaling axis in liver regeneration\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — phosphoproteomics plus biological validation in liver, single study identifying Tie-Wnt angiocrine axis\",\n      \"pmids\": [\"34038707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"m6A methylation of TIE1 mRNA 3'UTR by METTL14 increases TIE1 mRNA stability; miR-4729 targets METTL14 3'UTR to suppress METTL14 expression, reducing global m6A modification and TIE1 mRNA methylation at a specific 3'UTR site, thereby decreasing TIE1 expression and the TIE1/VEGFA signaling loop in endothelial cells.\",\n      \"method\": \"RNA immunoprecipitation-PCR for m6A sites; luciferase reporter assay; miR-4729 overexpression; Western blot; tube formation and migration assays\",\n      \"journal\": \"Annals of translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — RIP-PCR identifies specific m6A site on TIE1 mRNA, functional rescue assays support regulatory mechanism; single lab\",\n      \"pmids\": [\"33708859\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TIE1 is an endothelial-specific receptor tyrosine kinase that functions primarily as a context-dependent modulator of TIE2 signaling: it forms constitutive heterodimeric complexes with TIE2 (via membrane-proximal Fn3 domains and intracellular domain interactions), can be phosphorylated by angiopoietins in a TIE2-dependent manner, activates PI3K/Akt signaling to promote endothelial survival, and undergoes regulated ectodomain shedding by ADAM17 (stimulated by VEGF, TNFα, and PIEZO1 mechanosensing) that dynamically shifts the TIE2:TIE1 balance to modulate angiopoietin responsiveness; additionally, LECT2 and heparan sulfate glycosaminoglycans have been identified as direct TIE1 ligands, and TIE1 is required cell-autonomously for blood vascular integrity and for lymphatic vessel development, remodeling, and valve formation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TIE1 is an endothelial-specific receptor tyrosine kinase that functions as a context-dependent modulator of TIE2 (TEK) signaling and is required cell-autonomously for blood vascular integrity and lymphatic development [#0, #26, #2]. TIE1 forms pre-formed heterotypic complexes with TIE2 through both intracellular domain contacts and membrane-proximal Fibronectin type III (Fn3) domains, the latter mediating heterodimerization via an intermolecular β-sheet structurally analogous to that driving TIE2 homodimerization [#2, #12]. Although TIE1 displays negligible intrinsic kinase activity and does not autophosphorylate on its own, it is phosphorylated by angiopoietins (Ang1, Ang4, COMP-Ang1) in a strictly TIE2-dependent manner, and the TIE1:TIE2 stoichiometry tunes endothelial responsiveness to angiopoietins — TIE1 generally restrains TIE2 activation, and its expression level determines whether Ang2 acts as a TIE2 agonist or antagonist [#3, #5, #8, #6]. This balance is set dynamically by regulated ectodomain shedding: ADAM17/γ-secretase-mediated cleavage of TIE1, stimulated by VEGF, TNFα, fluid shear stress, and PIEZO1 mechanosensing, raises the TIE2:TIE1 ratio and relieves TIE1's suppression of TIE2 signaling, including during acute endotoxemia [#4, #9, #13, #10, #24]. Where TIE1 does signal, it activates PI3K/Akt via Tyr1113 to promote endothelial survival and to control FOXO1 nuclear localization, and its loss drives Slug-dependent endothelial-mesenchymal transition [#1, #10, #7]. TIE1 also engages additional binding partners — LECT2, which disrupts TIE1-TIE2 heterodimers and favors TIE2 homodimerization, heparan sulfate glycosaminoglycans, which promote heterodimerization and TIE protein stability, and integrins α5β1/αVβ3, which cooperate to stimulate ERK/MAPK signaling [#20, #22, #21]. In the lymphatic vasculature TIE1 is required, partly through its intracellular domain and independently of TIE2, for LEC proliferation and survival, lymphangiogenesis, collecting vessel remodeling, and valve specification, and supports VEGF-C/VEGFR3-driven lymphangiogenesis by sustaining VEGFR3 surface presentation [#16, #17, #18, #19, #23]. TIE1 additionally contributes to vascular inflammation and atherogenesis at disturbed-flow sites [#14, #25].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Established that TIE1 is dispensable for vasculogenesis but cell-autonomously required for endothelial integrity and survival during angiogenic growth, defining its developmental role.\",\n      \"evidence\": \"Targeted gene disruption and chimeric analysis in mice\",\n      \"pmids\": [\"8846781\", \"7596437\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the molecular signaling defect underlying vascular rupture\", \"No biochemical mechanism for survival function\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Distinguished TIE1 from TIE2 by showing both are needed in late-organogenesis microvasculature but with non-redundant, tissue-distinct requirements, with TEK specifically essential in endocardium.\",\n      \"evidence\": \"TEK/TIE double-knockout and mosaic analysis in mice\",\n      \"pmids\": [\"10498691\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve whether TIE1 acts through TIE2 or independently\", \"No molecular partners identified\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Resolved the long-standing question of TIE1 signaling competence by showing it has negligible kinase activity and instead forms a constitutive intracellular-domain heterocomplex with TIE2, reframing TIE1 as a modulator rather than autonomous receptor.\",\n      \"evidence\": \"Co-IP of endogenous receptors and chimeric TrkA/Tie receptor phosphorylation assays\",\n      \"pmids\": [\"10995770\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify ectodomain interaction interface\", \"Direction of modulation (positive vs negative) unresolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstrated that when artificially activated, TIE1 can couple to PI3K/Akt to inhibit apoptosis, mapping Tyr1113 as the PI3K docking site and providing a survival-signaling output.\",\n      \"evidence\": \"In vitro kinase assay, chimeric c-fms-Tie1 receptor in NIH 3T3, Y1113F mutagenesis, PI3K inhibition\",\n      \"pmids\": [\"11865050\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Used a chimeric receptor rather than physiological ligand\", \"Relevance to endogenous TIE1 with low kinase activity unclear\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Showed that angiopoietin-induced TIE1 phosphorylation is amplified through heteromeric TIE2, establishing that TIE2 trans-phosphorylates kinase-inactive TIE1 in a ligand-dependent manner.\",\n      \"evidence\": \"Phosphorylation assays with multiple angiopoietins, kinase-inactive TIE1 plus wild-type TIE2 co-transfection\",\n      \"pmids\": [\"15851516\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of TIE1 phosphorylation not defined\", \"Did not address ectodomain regulation\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defined TIE1 ectodomain as a brake on TIE2: regulated intramembrane proteolysis (ectodomain cleavage then γ-secretase/proteasome processing), stimulated by VEGF and phorbol ester, removes TIE1's restriction of ligand access and enhances TIE2 activation.\",\n      \"evidence\": \"Biochemical fractionation, γ-secretase/proteasome inhibitors, siRNA, Tie2 phosphorylation and ligand-binding assays; plus siRNA/constitutively-active-TIE2 dependence experiments\",\n      \"pmids\": [\"17728252\", \"17504972\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Sheddase identity not yet pinned to ADAM17\", \"Quantitative stoichiometry of TIE1:TIE2 not defined\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Visualized dynamic, inhibitory TIE1-TIE2 surface complexes in live cells and mapped the ectodomain surfaces required, showing Ang1 versus Ang2 differentially modulate the interaction.\",\n      \"evidence\": \"Live-cell FRET proximity assay with contact-surface mutagenesis\",\n      \"pmids\": [\"20227369\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution interface not yet determined\", \"Downstream signaling consequences not fully mapped\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Connected TIE1 abundance to angiopoietin output, showing TIE1 expression level dictates Ang2 agonist/antagonist behavior, that VEGF/TNFα selectively control TIE1 versus TIE2 shedding to set the TIE2:TIE1 ratio, and that TIE1 loss drives Slug-dependent EndMT.\",\n      \"evidence\": \"Co-IP, adenoviral TIE1 overexpression, time-course shedding Western blots, siRNA with EndMT/promoter readouts\",\n      \"pmids\": [\"22342979\", \"22235284\", \"22421998\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mostly single-lab observations per finding\", \"EndMT mechanism downstream of Slug incompletely defined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Linked TIE1 to angiogenic specialization in vivo, showing it negatively regulates TIE2 surface presentation in tip cells while cooperating with TIE2 in stalk cells, and is required for lymphatic valve specification and collecting vessel development.\",\n      \"evidence\": \"Conditional endothelial and Nfatc1Cre TIE1 deletion, retinal vascular and lymphatic valve phenotyping\",\n      \"pmids\": [\"26344773\", \"25576926\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular switch between tip-cell inhibition and stalk-cell cooperation undefined\", \"Valve specification effectors downstream of TIE1 unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Integrated TIE1 into integrin and trafficking control: ADAM17 was identified as the in vivo TIE1 sheddase in inflammation, β1 integrin was shown to enhance Ang-induced TIE1-TIE2 interaction and TIE2 trafficking, and TIE1/TIE2 were shown to directly associate with integrins to stimulate ERK.\",\n      \"evidence\": \"Conditional TIE1 knockout, integrin-blocking antibodies, trafficking/FOXO1 assays, endotoxemia model, FRET and purified-protein binding\",\n      \"pmids\": [\"27548530\", \"27695111\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"FRET/integrin direct-binding study is single-lab Medium evidence\", \"Structural basis of TIE-integrin association undefined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Provided the structural basis for TIE complex assembly, showing Ang1-induced TIE2 dimerization occurs via an intermolecular Fn3 β-sheet, with TIE1 Fn3 domains structurally compatible for heterodimerization by the same mechanism.\",\n      \"evidence\": \"X-ray crystallography of TIE1/TIE2 Fn3 and Fn2 domains with mutagenesis and phosphorylation validation\",\n      \"pmids\": [\"28396439\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length receptor or heterodimer structure\", \"Conformational coupling to intracellular kinase not resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified LECT2 as a functional TIE1 ligand that disrupts TIE1-TIE2 heterodimers to favor TIE2 homodimerization and PPAR signaling, providing the first defined extracellular ligand acting through TIE1.\",\n      \"evidence\": \"Co-IP/pulldown, LECT2 overexpression and knockout mice, in vitro migration/tube assays, liver fibrosis models\",\n      \"pmids\": [\"31474362\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding site on TIE1 not mapped\", \"Generality beyond hepatic/portal vasculature unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Established heparan sulfate glycosaminoglycans as direct TIE1 ligands that promote TIE1-TIE2 heterodimerization and TIE protein stability, with in vivo HS-binding-site mutation suppressing signaling and disrupting retinal vascularization.\",\n      \"evidence\": \"Direct binding assays, heterodimerization assays, CRISPR-Cas9 in vivo mutagenesis, retinal phenotyping\",\n      \"pmids\": [\"33020664\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"HS structural specificity not fully defined\", \"Interplay with protein ligands (LECT2, angiopoietins) not addressed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined a lymphatic TIE1 role upstream of VEGFR3, showing TIE1 (with TIE2) sustains VEGFR3 surface presentation and VEGF-C-induced PI3K/Akt activation via Ang2 autocrine signaling.\",\n      \"evidence\": \"Conditional LEC TIE1/TIE2 deletion, Ang2-blocking antibody, PI3K inhibition, VEGFR3 flow cytometry, neonatal lymphangiogenesis assays\",\n      \"pmids\": [\"35763346\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of VEGFR3 surface retention by TIE receptors undefined\", \"Direct TIE1-VEGFR3 interaction not demonstrated\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Placed mechanical force upstream of TIE1 regulation, showing PIEZO1 activation triggers ADAM17-mediated TIE1 ectodomain shedding, ANGPT2 exocytosis, and TIE/PI3K/AKT signaling with FOXO1 nuclear export in lymphatic endothelium.\",\n      \"evidence\": \"PIEZO1 activation in LECs, ADAM17 inhibition, shedding/AKT/FOXO1 and ANGPT2 exocytosis assays\",\n      \"pmids\": [\"38747287\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Link from PIEZO1 calcium flux to ADAM17 activation not mechanistically detailed\", \"In vivo physiological context of this network not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How TIE1's multiple ligand inputs (angiopoietins, LECT2, heparan sulfate), shedding cues, and integrin associations are integrated to set a precise TIE2:TIE1 signaling output in distinct vascular beds remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified quantitative model of TIE1:TIE2 stoichiometry control\", \"TIE1 intracellular-domain effectors in TIE2-independent lymphatic functions not identified\", \"Direct TIE1 ligand-binding sites largely unmapped\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 3, 12]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 5, 8, 4]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 20]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [1, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 6, 21]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 5, 3]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 16, 17, 18, 19]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [10, 14, 25]}\n    ],\n    \"complexes\": [\"TIE1-TIE2 heterodimer\", \"TIE/integrin (α5β1, αVβ3) complex\"],\n    \"partners\": [\"TEK\", \"LECT2\", \"ITGB1\", \"ITGA5\", \"ITGAV\", \"ITGB3\", \"ADAM17\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}