{"gene":"GPIHBP1","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":2002,"finding":"GPIHBP1 (GPI-HBP1) was identified as a novel GPI-anchored protein that binds HDL with high affinity (Kd = 2–3 µg/mL) and mediates selective lipid uptake but not HDL protein uptake, and lacks HDL-dependent cholesterol efflux activity. It is susceptible to phosphatidylinositol-specific phospholipase C treatment, confirming GPI anchorage. Highest expression was found in the heart.","method":"Expression cloning with fluorescent-labeled HDL; lipid uptake assays; PIPL-C treatment; in situ hybridization","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — expression cloning with functional lipid uptake assays and biochemical validation in a single lab","pmids":["12496272"],"is_preprint":false},{"year":2007,"finding":"GPIHBP1-deficient mice develop severe chylomicronemia (plasma TG up to ~5000 mg/dL even on low-fat diet). GPIHBP1 is expressed on the luminal surface of capillary endothelial cells in heart, skeletal muscle, and adipose tissue. Cells transfected with GPIHBP1 bind both LPL and chylomicrons avidly, establishing GPIHBP1 as a platform for LPL-mediated lipolysis.","method":"GPIHBP1 knockout mouse model; fluorescence microscopy; cell transfection binding assays","journal":"Current opinion in lipidology","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockout mouse phenotype combined with cell-based binding assays, replicated across multiple subsequent studies","pmids":["17620854"],"is_preprint":false},{"year":2008,"finding":"The acidic domain of GPIHBP1 (amino acids 38–48, enriched in Asp/Glu) is required for binding LPL and chylomicrons. Polyaspartate and polyglutamate peptides block LPL and chylomicron binding; alanine substitution of acidic residues 38–48 eliminates binding. Electrostatic interactions are key: mutation of positively charged heparin-binding domains in LPL and apoAV abolished their binding to GPIHBP1.","method":"Cell-based binding assays with CHO cells overexpressing GPIHBP1; blocking experiments with polyaspartate/polyglutamate peptides; alanine scanning mutagenesis; anti-acidic domain antiserum blocking","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis of specific residues with functional binding readout, multiple orthogonal blocking approaches in one rigorous study","pmids":["18713736"],"is_preprint":false},{"year":2008,"finding":"N-glycosylation of GPIHBP1 at Asn-76 within the Ly6 domain is critical for trafficking GPIHBP1 to the cell surface. Mutation of the N-glycosylation site causes GPIHBP1 to accumulate in the ER and markedly reduces cell-surface expression; cells expressing non-glycosylated GPIHBP1 lack the ability to bind LPL or chylomicrons.","method":"N-glycosidase F / endoglycosidase H/F digestion; site-directed mutagenesis of glycosylation site; immunofluorescence and cell-based LPL/chylomicron binding assays","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis of specific glycosylation site with multiple orthogonal methods (enzymatic deglycosylation, ER localization, functional binding assays)","pmids":["18340083"],"is_preprint":false},{"year":2008,"finding":"In GPIHBP1-deficient mice, post-heparin plasma LPL levels peak very slowly (over 15 min) rather than rapidly (within 1 min as in wild-type), and plasma triglycerides fall negligibly within the first 15 min after heparin. Intralipid injection releases LPL in wild-type but not GPIHBP1-deficient mice, despite similar tissue LPL stores. These findings establish that GPIHBP1 represents an important LPL-binding site in vivo.","method":"Heparin injection kinetics; plasma LPL measurement; Intralipid injection; comparison of Gpihbp1−/− vs. control mice","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo heparin-release kinetics experiment with multiple readouts in knockout vs. wild-type mice","pmids":["18845532"],"is_preprint":false},{"year":2008,"finding":"GPIHBP1 expression in heart, adipose tissue, and skeletal muscle is upregulated by fasting and by PPARγ agonists (but not PPARα or PPARδ agonists). A PPARγ binding site upstream of exon 1 exhibits activity in a luciferase reporter assay. Conditional knockout of endothelial PPARγ reduces Gpihbp1 expression in adipose tissue in vivo.","method":"Quantitative RT-PCR; luciferase reporter assay; PPARγ agonist treatment; endothelial-specific PPARγ knockout mice","journal":"Molecular endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — luciferase reporter and in vivo conditional knockout, single lab with multiple methods","pmids":["18787041"],"is_preprint":false},{"year":2009,"finding":"A homozygous Q115P missense mutation in GPIHBP1 identified in a chylomicronemia patient abolishes the ability of GPIHBP1 to bind LPL and chylomicrons without affecting cell-surface expression. The corresponding mouse mutation (Q114P) also cannot bind LPL, establishing this residue as critical for LPL binding.","method":"Patient genetic sequencing; cell-based binding assays in CHO cells expressing wild-type vs. Q115P GPIHBP1; mouse GPIHBP1 Q114P mutagenesis","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — disease mutation validated by cell-based binding assays in both human and mouse GPIHBP1, replicated in multiple subsequent studies","pmids":["19304573"],"is_preprint":false},{"year":2009,"finding":"Conserved cysteines in the Ly6 domain of GPIHBP1 (C65, C68 in humans; C65S, C68G mutations found in chylomicronemia patients) are essential for LPL binding. Cysteine mutants reach the cell surface but are defective in LPL binding in both cell-based and cell-free binding assays, demonstrating that a structurally intact Ly6 domain is required.","method":"Site-directed mutagenesis; cell-based LPL binding assay; cell-free LPL binding assay using GPIHBP1 immobilized on antibody-coated agarose beads; PIPL-C cell-surface release assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis of specific cysteines validated in both cell-based and cell-free assays, findings replicated by independent patient mutation studies","pmids":["19726683"],"is_preprint":false},{"year":2009,"finding":"Compound heterozygous cysteine mutations in GPIHBP1 Ly6 domain (C65S and C68G) identified in familial chylomicronemia. Mutant GPIHBP1 proteins reach the cell surface but fail to bind LPL in cell-based and cell-free assays. LPL mass and activity in adipose tissue biopsies appear normal, consistent with defective LPL transport rather than synthesis.","method":"Family genetics; cell-based and cell-free LPL binding assays; adipose tissue biopsy LPL activity; [35S]methionine incorporation","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 2 / Strong — disease mutations functionally validated by multiple binding assays in clinical pedigree study","pmids":["20026666"],"is_preprint":false},{"year":2009,"finding":"GPIHBP1 stabilizes LPL activity and protects it from inhibition by ANGPTL4 and ANGPTL3 in vitro. ANGPTL4 potently inhibits non-stabilized LPL and heparin-stabilized LPL but not GPIHBP1-stabilized LPL. In vivo, Angptl4−/−/Gpihbp1−/− double knockout mice had lower plasma TG than Gpihbp1−/− mice, approaching wild-type levels, confirming the physiological relevance of this protection.","method":"In vitro LPL activity assay with GPIHBP1, ANGPTL3, ANGPTL4; double-knockout mouse models; ANGPTL-neutralizing antibody treatment in Gpihbp1−/− mice","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic assays combined with in vivo genetic epistasis in double-knockout mice and antibody rescue experiments","pmids":["19542565"],"is_preprint":false},{"year":2010,"finding":"GPIHBP1 binds LPL but does not bind other members of the lipase family (endothelial lipase, hepatic lipase, pancreatic lipase). GPIHBP1 binds apoAV (dependent on the acidic domain, independent of the Ly6 domain). The ability of GPIHBP1-expressing cells to bind chylomicrons is entirely mediated by LPL captured from the medium; GPIHBP1 does not bind chylomicrons directly in the absence of LPL.","method":"Cell-based and cell-free binding assays; antibody blocking; cells expressing GPIHBP1 with acidic domain mutations","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — comprehensive specificity study using multiple binding assays with domain mutants, single lab but multiple orthogonal methods","pmids":["20966398"],"is_preprint":false},{"year":2010,"finding":"Homozygous GPIHBP1 C65Y mutation causes chylomicronemia; the mutant protein reaches the cell surface but cannot bind LPL. Patients with homozygous C65Y or Q115P mutations have very low LPL in post-heparin plasma, demonstrating that GPIHBP1 is required for efficient LPL entry into plasma after heparin, consistent with its role in LPL transport.","method":"Patient clinical studies; cell-surface expression assays; cell-based LPL binding assay; post-heparin LPL measurement; prolonged heparin infusion in Q115P patient","journal":"Circulation. Cardiovascular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — disease mutation validated by cell-based assays and in vivo heparin-release studies in human patients","pmids":["20124439"],"is_preprint":false},{"year":2010,"finding":"PET scanning with radiolabeled GPIHBP1-specific antibodies revealed that GPIHBP1 is expressed at unexpectedly high levels in lung and liver capillary endothelium, not only in heart/skeletal muscle/adipose tissue. LPL protein was detected in lung despite very low Lpl transcript levels, suggesting GPIHBP1 in the lung captures LPL produced elsewhere. Lung LPL levels were lower in Gpihbp1−/− mice.","method":"PET imaging with radiolabeled anti-GPIHBP1 antibodies; immunofluorescence microscopy; tissue LPL quantification in knockout mice; Lpl−/− mice expressing human LPL only in muscle","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo imaging with functional validation in knockout mice and transgenic model, multiple orthogonal methods","pmids":["20889497"],"is_preprint":false},{"year":2011,"finding":"GPIHBP1 transports LPL from the subendothelial space across endothelial cells to the capillary lumen. LPL binding to GPIHBP1 requires only LPL's C-terminal domain (residues 298–448); the C-terminal fragment binds GPIHBP1 avidly independent of the N-terminal catalytic domain or full-length homodimer formation. C418Y and E421K mutations in LPL eliminate GPIHBP1 binding without affecting catalytic activity.","method":"Cell-based and cell-free LPL-GPIHBP1 binding assays; LPL deletion mutants; furin cleavage mapping; alanine scanning of LPL C-terminal residues","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — domain dissection by deletion and mutagenesis with cell-based and cell-free binding assays, identifying minimal binding domain","pmids":["21518912"],"is_preprint":false},{"year":2011,"finding":"Within the Ly6 domain three-fingered structure of GPIHBP1, alanine scanning identified 12 residues (aside from conserved cysteines) required for LPL binding, with 9 clustered in finger 2. Mutant GPIHBP1 proteins that cannot bind LPL also lack the ability to transport LPL from the basolateral to the apical surface of endothelial cells.","method":"Comprehensive alanine-scanning mutagenesis; immunofluorescence cell-surface expression assay; Western blot LPL binding assay; endothelial transcytosis assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — comprehensive alanine scanning of entire Ly6 domain with functional transport assay in endothelial cells","pmids":["21478160"],"is_preprint":false},{"year":2011,"finding":"Homozygous GPIHBP1 deletion (17.5 kb) causes complete GPIHBP1 deficiency and severe chylomicronemia. Intravenous heparin failed to raise LPL in plasma of GPIHBP1-deficient patients (unlike controls), demonstrating that GPIHBP1 is required for heparin-releasable LPL in the human vascular compartment.","method":"Array-based copy number analysis; Sanger sequencing; heparin bolus LPL release in GPIHBP1-null patients vs. controls","journal":"Journal of inherited metabolic disease","confidence":"High","confidence_rationale":"Tier 2 / Strong — complete genetic deletion with in vivo physiological validation of LPL transport function in human patients","pmids":["22008945"],"is_preprint":false},{"year":2012,"finding":"TRL margination along heart capillaries depends on GPIHBP1 and specifically on LPL bound to GPIHBP1. In Gpihbp1−/− mice, TRLs do not marginate along capillaries. Expression of LPL by endothelial cells (binding to HSPGs) in Gpihbp1−/− mice does not restore TRL margination, demonstrating that GPIHBP1-bound LPL is the primary determinant of TRL margination.","method":"Fluorescence microscopy; infrared-dye-labeled lipoprotein quantitative margination assays; EM tomography; cell-culture and in vivo studies with Gpihbp1−/− mice expressing endothelial LPL","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal imaging methods (fluorescence, quantitative IR, EM tomography) in knockout and rescue models","pmids":["24726386"],"is_preprint":false},{"year":2012,"finding":"GPIHBP1 and LPL move bidirectionally across capillary endothelial cells in vesicles. Transport of LPL across endothelial cells is inhibited by dynasore and genistein (dynamin inhibitor/vesicular transport blockers). EM and dual-axis EM tomography show GPIHBP1 and LPL in membrane invaginations and vesicles. Transport is efficient in the absence of caveolin-1.","method":"Live-cell bidirectional transport assays; dynasore/genistein pharmacological inhibition; transmission EM and dual-axis EM tomography; caveolin-1 knockout endothelial cells and in vivo studies","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (live imaging, pharmacological inhibition, EM ultrastructure) with genetic caveolin-1 KO controls","pmids":["23008484"],"is_preprint":false},{"year":2012,"finding":"LPL's C-terminal domain (residues 298–448) is sufficient for GPIHBP1 binding; the N-terminal catalytic domain is dispensable. Full-length homodimers are not required for GPIHBP1 binding. C-terminal fragments of LPL with C418Y or E421K mutations cannot bind GPIHBP1. After denaturation, the C-terminal fragment refolds and restores GPIHBP1 binding.","method":"LPL truncation/deletion constructs; furin cleavage mapping; cell-based and cell-free GPIHBP1 binding assays; denaturation/refolding experiment","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 1 / Strong — domain dissection with multiple deletion constructs plus refolding experiment establishing C-terminal domain sufficiency","pmids":["22493000"],"is_preprint":false},{"year":2014,"finding":"Many GPIHBP1 Ly6 domain missense mutations (including disease-causing mutations) cause GPIHBP1 to form disulfide-linked dimers and multimers. Only GPIHBP1 monomers—not dimers or multimers—are capable of binding LPL. W109S mutation abolishes LPL binding without promoting multimerization, suggesting W109 plays a direct role in LPL binding rather than only through structural integrity.","method":"Expression in CHO, rat and human endothelial cells, and Drosophila S2 cells; Western blot under non-reducing conditions; cell-based and cell-free LPL binding assays; systematic W109 mutagenesis to 8 other amino acids","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 / Strong — multimerization mechanism tested across multiple expression systems with systematic mutagenesis, clear functional correlation with LPL binding loss","pmids":["25387803"],"is_preprint":false},{"year":2014,"finding":"GPIHBP1-S107C mutation (serine-to-cysteine substitution creating an extra cysteine) causes nearly all cell-surface GPIHBP1 to form disulfide-linked dimers and multimers, abolishing LPL binding. Functional studies confirmed only GPIHBP1 monomers bind LPL. Three homozygous patients with this mutation have very low preheparin plasma LPL.","method":"Patient genetic analysis; cell-based and insect-cell expression; non-reducing Western blot; cell-based and cell-free LPL binding assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — disease mutation mechanistically explained by multimerization assay in two independent expression systems with in vivo patient data","pmids":["24847059"],"is_preprint":false},{"year":2015,"finding":"ANGPTL4 can bind and inactivate LPL when LPL is complexed with GPIHBP1 on endothelial cell surfaces. Once inactivated by ANGPTL4, LPL dissociates from GPIHBP1. ANGPTL4-inactivated LPL is incapable of re-binding GPIHBP1. The N-terminal coiled-coil domain of ANGPTL4 alone is more potent in inactivating GPIHBP1-bound LPL than full-length ANGPTL4.","method":"Cell-based LPL binding and inactivation assays using endothelial cells; ANGPTL4 domain constructs; temperature-dependent binding experiments (4°C vs. 37°C)","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-based assays with endogenous-context LPL-GPIHBP1 complex, single lab, multiple conditions tested","pmids":["25809481"],"is_preprint":false},{"year":2015,"finding":"GPIHBP1 has two distinct binding sites for LPL: the acidic N-terminal domain forms a tight but short-lived complex (fast on/off rates, salt-sensitive, heparin-displaceable), while the Ly6 domain forms a slower but longer-lasting complex (heparin-resistant). LPL bound to the acidic domain retains affinity for the Ly6 domain and retains capacity to interact with lipoproteins, whereas LPL bound to the Ly6 domain does not.","method":"Surface plasmon resonance (SPR); comparative binding studies with isolated N-terminal peptide, Ly6 domain, full-length GPIHBP1, and Q114P mutant; salt and heparin competition assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — biophysical SPR measurements with domain fragments and mutants establishing distinct kinetic signatures for two binding sites","pmids":["25873395"],"is_preprint":false},{"year":2016,"finding":"GPIHBP1's intrinsically disordered acidic N-terminal domain stabilizes LPL catalytic activity by mitigating global unfolding of LPL's catalytic domain. Biophysical studies using hydrogen-deuterium exchange/mass spectrometry (HDX-MS) demonstrated that the acidic domain reduces spontaneous unfolding of LPL's hydrolase domain. The LU domain and acidic domain serve distinct roles: the LU domain mediates binding kinetics while the acidic domain prevents unfolding.","method":"Hydrogen-deuterium exchange/mass spectrometry (HDX-MS); surface plasmon resonance (SPR); zero-length cross-linking; LPL catalytic activity assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple biophysical methods (HDX-MS, SPR, cross-linking) with functional validation of stabilization mechanism in single rigorous study","pmids":["26725083"],"is_preprint":false},{"year":2016,"finding":"ANGPTL4 inactivates LPL by catalyzing the unfolding of its hydrolase domain (not simply by binding). Binding of LPL to GPIHBP1 renders LPL largely refractory to ANGPTL4-catalyzed inactivation. Both the LU domain and the intrinsically disordered acidic domain of GPIHBP1 are required for this protective effect. A common ANGPTL4 polymorphic variant (associated with lower plasma TG) is less efficient at catalyzing LPL unfolding and its substitution destabilizes its N-terminal α-helix.","method":"HDX-MS measuring unfolding of LPL hydrolase domain; LPL activity assays in presence of ANGPTL4 with/without GPIHBP1; GPIHBP1 domain mutants; biophysical analysis of ANGPTL4 variant","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 / Strong — mechanistic HDX-MS measurements combined with functional activity assays and domain mutants establishing the unfolding mechanism","pmids":["27929370"],"is_preprint":false},{"year":2016,"finding":"LPL bound to HSPGs in interstitial spaces is mobile and can detach to move to GPIHBP1 on capillaries. LPL moves from HSPGs on cultured cells to: soluble GPIHBP1 in medium; GPIHBP1-coated agarose beads; and nearby GPIHBP1-expressing cells. Movement requires an intact GPIHBP1 Ly6 domain (W109S mutation blocks transfer) but is largely independent of the acidic domain. In vivo, LPL moves rapidly from adipocyte HSPGs to GPIHBP1-coated beads injected into adipose tissue of Gpihbp1−/− mice.","method":"Cell culture LPL transfer assays; GPIHBP1-coated bead capture; in vivo bead injection into brown adipose tissue of Gpihbp1−/− mice; Ly6 domain mutant (W109S) and acidic domain mutant GPIHBP1","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vitro and in vivo approaches with domain mutant controls establishing HSPG-to-GPIHBP1 LPL transfer mechanism","pmids":["27811232"],"is_preprint":false},{"year":2016,"finding":"Monoclonal antibodies targeting GPIHBP1's Ly6 domain (RE3 and RG3) abolish LPL binding, whereas an antibody against the acidic domain (RF4) does not. Both RE3 and RG3 bind with reduced affinity to GPIHBP1-W109S (an Ly6 mutant that abolishes LPL binding), linking the W109 region to the LPL binding interface. Immunohistochemistry confirmed that human GPIHBP1 is expressed exclusively in capillary endothelial cells.","method":"Monoclonal antibody development; cell-based LPL binding blocking assays; affinity measurements with Ly6 domain mutants; immunohistochemistry of human tissues","journal":"Journal of lipid research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — antibody blocking assays with domain mutants in single lab, functional and localization data","pmids":["27875259"],"is_preprint":false},{"year":2017,"finding":"GPIHBP1 autoantibodies (identified in 6 patients with chylomicronemia) block the binding of LPL to GPIHBP1, thereby preventing LPL transport into capillaries, reducing plasma LPL levels, and causing severe hypertriglyceridemia. The autoantibody-mediated chylomicronemia phenotype mirrors genetic GPIHBP1 deficiency. Maternal autoantibodies transferred to a neonate caused transient chylomicronemia.","method":"ELISA; Western blot; immunocytochemistry; LPL-GPIHBP1 binding blocking assay with patient plasma","journal":"The New England journal of medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — mechanistic blocking assay confirming autoantibodies inhibit LPL-GPIHBP1 interaction, replicated across multiple patients including neonatal transfer case","pmids":["28402248"],"is_preprint":false},{"year":2017,"finding":"ApoC-III potently inhibits triglyceride hydrolysis specifically when LPL is bound to GPIHBP1. TRLs from APOC3 transgenic mice bind normally to GPIHBP1-bound LPL on cells and in vivo, but triglycerides are hydrolyzed more slowly. The inhibitory effect of apoC-III is greater when LPL is bound to GPIHBP1 compared to free LPL. A loss-of-function apoC-III variant (A23T) associated with low plasma TG shows reduced capacity to inhibit both free and GPIHBP1-bound LPL.","method":"Cell-based lipolysis assays using GPIHBP1-bound LPL; GPIHBP1-coated agarose bead lipolysis assay; in vivo margination assay in mice; recombinant apoC-III variants","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-based and bead-based lipolysis assays with in vivo confirmation, natural apoC-III variant as functional control","pmids":["28694296"],"is_preprint":false},{"year":2017,"finding":"Mutating a conserved cysteine in mouse GPIHBP1 (C63Y) abolishes LPL binding and causes severe chylomicronemia in vivo, with ~70% reduction in GPIHBP1 levels at the endothelial cell surface. The mutant GPIHBP1 is predominantly monomeric, contrasting with cell culture studies where cysteine mutations cause multimerization.","method":"Knock-in mouse model (CRISPR/Cas9 was not stated explicitly but mice harboring C63Y were created); immunohistochemistry; plasma TG measurement; LPL localization","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo mouse model with specific GPIHBP1 mutation, functional and expression readouts","pmids":["28476858"],"is_preprint":false},{"year":2018,"finding":"X-ray crystal structure of the LPL-GPIHBP1 complex was solved at 2.5–3.0 Å. GPIHBP1's LU domain binds to LPL's C-terminal lipid-binding domain largely through hydrophobic interactions. LPL contains a large basic patch spanning its N- and C-terminal domains, positioned to interact with GPIHBP1's acidic domain. In the complex, LPL can be active as a 1:1 monomer rather than requiring a homodimer.","method":"X-ray crystallography; co-expression of LPL, soluble GPIHBP1, and LMF1; inhibitor-bound structure resolving LPL lid region; biochemical activity assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure at 2.5–3.0 Å with functional validation of LPL monomer activity, confirmed in parallel independent structural study (PMID 31072929)","pmids":["30559189","31072929"],"is_preprint":false},{"year":2018,"finding":"A conserved tyrosine in the middle of GPIHBP1's intrinsically disordered acidic domain undergoes posttranslational O-sulfation. This tyrosine sulfation increases the affinity of GPIHBP1-LPL interactions and enhances GPIHBP1's ability to protect LPL against ANGPTL4-catalyzed unfolding. The acidic IDR also increases the probability of GPIHBP1-LPL encounters via electrostatic steering, increasing the association rate constant (kon) for LPL binding by >250-fold.","method":"Mass spectrometry identification of sulfotyrosine; surface plasmon resonance (kon/koff measurements); LPL activity protection assays; biophysical characterization of IDR conformation","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — PTM identified by mass spectrometry with quantitative SPR binding kinetics and functional LPL protection assays","pmids":["29899144"],"is_preprint":false},{"year":2018,"finding":"An upstream enhancer element located ~3.6 kb upstream from exon 1 of mouse Gpihbp1 regulates tissue-specific Gpihbp1 expression. Deletion of this enhancer (CRISPR/Cas9) reduced Gpihbp1 expression by >90% in liver and ~50% in heart/brown adipose tissue. Reduced GPIHBP1 caused partial LPL mislocalization (increased LPL in interstitial spaces) in compound heterozygotes, but did not cause hypertriglyceridemia.","method":"CRISPR/Cas9 enhancer deletion; quantitative RT-PCR; immunofluorescence microscopy for LPL localization; plasma TG measurement","journal":"Journal of lipid research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR-based enhancer deletion in vivo with functional readouts, single lab","pmids":["30598475"],"is_preprint":false},{"year":2019,"finding":"GPIHBP1 is expressed in glioma capillaries (unlike normal brain capillaries, which lack GPIHBP1) and captures locally produced LPL. GPIHBP1 in glioma capillaries enables margination of TRLs along glioma capillaries, and NanoSIMS imaging confirmed uptake of TRL-derived lipid nutrients by surrounding glioma cells, providing a source of lipid energy for tumors.","method":"Immunohistochemistry of mouse and human glioma; NanoSIMS isotope imaging; TRL margination assay in glioma-bearing mice; LPL capture by GPIHBP1 in glioma capillaries","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — NanoSIMS imaging with functional TRL margination data in glioma model, single lab","pmids":["31169500"],"is_preprint":false},{"year":2020,"finding":"In a NanoBiT split-luciferase assay monitoring LPL-GPIHBP1 binding on endothelial cells in real time, ANGPTL4 and ANGPTL3-ANGPTL8 complexes disrupt LPL-GPIHBP1 interactions. Chylomicrons can dissociate LPL from GPIHBP1, and this dissociation is mediated in part by fatty acids produced during lipolysis. Exogenous inhibitors (tyloxapol, poloxamer-407, tetrahydrolipstatin) did not disrupt LPL-GPIHBP1 binding.","method":"NanoBiT split-luciferase real-time binding assay on endothelial cells; ANGPTL4, ANGPTL3-8 complex, and chylomicron addition assays; fatty acid competition","journal":"Journal of lipid research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — novel real-time assay with validated specificity and multiple inhibitor/substrate conditions, single lab","pmids":["32029511"],"is_preprint":false},{"year":2022,"finding":"GPIHBP1's acidic domain (AD) serves three distinct functions established experimentally: (1) it accelerates LPL binding kinetics via electrostatic steering; (2) it preserves LPL catalytic activity by preventing unfolding of LPL's catalytic domain; and (3) by sheathing LPL's basic patch, the AD enables LPL-GPIHBP1 complexes to move across endothelial cells to the capillary lumen—without the AD, GPIHBP1-bound LPL is trapped by interactions with heparan sulfate proteoglycans on the abluminal surface.","method":"Biophysical binding assays; LPL activity measurements; in vivo mouse studies with AD-mutant GPIHBP1; HSPG interaction studies","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — three distinct functions experimentally demonstrated in vitro and in vivo with clear molecular mechanism, published in high-quality journal","pmids":["36037340"],"is_preprint":false},{"year":2023,"finding":"LPL transported into capillaries by GPIHBP1 can detach from GPIHBP1 and move into the endothelial glycocalyx. By confocal microscopy, immunogold EM, and NanoSIMS, LPL detected by a GPIHBP1-binding-blocking antibody (88B8, which cannot detect GPIHBP1-bound LPL) is located in the glycocalyx, distant from GPIHBP1 on the plasma membrane. This glycocalyx-localized LPL mediates TRL margination and is active in TRL processing, delivering lipids to adjacent parenchymal cells.","method":"Monoclonal antibody 88B8 (GPIHBP1-binding-blocking epitope); confocal microscopy; immunogold electron microscopy; NanoSIMS imaging; in vivo functional lipid delivery assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — three orthogonal imaging methods with functional validation, identifies a novel post-GPIHBP1 step in LPL trafficking","pmids":["37871217"],"is_preprint":false},{"year":2015,"finding":"VEGF, secreted by cardiomyocytes in response to hyperglycemia-triggered heparanase release, induces GPIHBP1 expression in endothelial cells via Notch signaling (Delta-like ligand 4 augmentation and nuclear translocation of the Notch intracellular domain), thereby increasing LPL shuttling across endothelial cells in the diabetic heart.","method":"High-glucose EC culture; heparanase treatment; VEGF neutralizing antibody; Notch pathway inhibition; cardiomyocyte-EC co-culture; in vivo severely diabetic animal model with VEGF attenuation","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic pathway (heparanase→VEGF→Notch→GPIHBP1) established by multiple cell-based and in vivo experiments, single lab","pmids":["26586663"],"is_preprint":false}],"current_model":"GPIHBP1 is a GPI-anchored protein of capillary endothelial cells with two functional domains: an intrinsically disordered, sulfotyrosine-containing acidic N-terminal domain that accelerates LPL capture by electrostatic steering, shields LPL's basic patch to enable transcytosis past abluminal heparan sulfate proteoglycans, and stabilizes LPL's catalytic domain against spontaneous and ANGPTL4-catalyzed unfolding; and a three-fingered Ly6/LU domain that makes stable hydrophobic contacts with LPL's C-terminal lipid-binding domain. GPIHBP1 picks up LPL secreted into the subendothelial space, transports it bidirectionally across endothelial cells in vesicles to the capillary lumen, where GPIHBP1-bound LPL can also transfer into the glycocalyx to mediate margination and lipolysis of triglyceride-rich lipoproteins; loss of GPIHBP1 strands LPL in the interstitial space and causes severe chylomicronemia."},"narrative":{"mechanistic_narrative":"GPIHBP1 is a GPI-anchored protein of capillary endothelial cells that functions as the dedicated platform and transporter for lipoprotein lipase (LPL), enabling intravascular triglyceride lipolysis [PMID:17620854, PMID:18845532]. It is built from two functional modules: an intrinsically disordered, acidic (Asp/Glu-rich) N-terminal domain that engages LPL through electrostatic interactions, and a three-fingered Ly6/LU domain that forms a stable, longer-lived contact with LPL's C-terminal lipid-binding domain (residues 298–448) [PMID:18713736, PMID:21518912, PMID:25873395]. The acidic domain accelerates LPL capture by electrostatic steering—an effect enhanced by O-sulfation of a conserved tyrosine that raises the LPL association rate constant >250-fold—and it sheathes LPL's basic patch so that LPL–GPIHBP1 complexes can cross the endothelial cell rather than being trapped by abluminal heparan sulfate proteoglycans [PMID:29899144, PMID:36037340]. GPIHBP1 picks up LPL released from interstitial HSPGs and shuttles it bidirectionally across the endothelium in dynamin-dependent vesicles to the capillary lumen, where GPIHBP1-bound LPL drives margination and lipolysis of triglyceride-rich lipoproteins, and from which LPL can transfer into the glycocalyx [PMID:21478160, PMID:24726386, PMID:23008484, PMID:27811232, PMID:37871217]. Binding requires a structurally intact Ly6 domain: conserved cysteines, N-glycosylation at Asn-76, and the monomeric state of GPIHBP1 are all essential, and mutations that disrupt these (or autoantibodies against the Ly6 domain) abolish LPL binding [PMID:18340083, PMID:19726683, PMID:25387803, PMID:28402248]. Beyond capture and transport, GPIHBP1 stabilizes LPL's catalytic domain against spontaneous and ANGPTL4-catalyzed unfolding, protecting enzyme activity [PMID:26725083, PMID:27929370]. A crystal structure shows the LU domain binding LPL's C-terminal domain through hydrophobic contacts, with LPL active as a 1:1 monomer [PMID:30559189, PMID:31072929]. Loss-of-function mutations, gene deletion, and neutralizing autoantibodies all strand LPL in the interstitium and cause severe chylomicronemia in humans [PMID:19304573, PMID:22008945, PMID:28402248].","teleology":[{"year":2002,"claim":"GPIHBP1 was first identified as a GPI-anchored cell-surface protein with high-affinity HDL binding and lipid-uptake activity, establishing it as a lipid-handling membrane protein before its LPL role was known.","evidence":"Expression cloning with fluorescent HDL, lipid uptake assays, and PIPL-C sensitivity in a single lab","pmids":["12496272"],"confidence":"Medium","gaps":["HDL binding role not reconciled with later LPL-centric function","physiological ligand and tissue context not yet defined"]},{"year":2007,"claim":"Knockout mice and binding assays established GPIHBP1 as a luminal endothelial platform for LPL-mediated lipolysis, answering whether it has an essential role in triglyceride metabolism.","evidence":"Gpihbp1 knockout mouse phenotype with severe chylomicronemia, plus cell-transfection LPL/chylomicron binding assays","pmids":["17620854"],"confidence":"High","gaps":["which GPIHBP1 domain mediates LPL binding not yet mapped","mechanism of chylomicron capture unresolved"]},{"year":2008,"claim":"Domain dissection assigned LPL/apoAV/chylomicron binding to the acidic N-terminal domain via electrostatic interactions and showed N-glycosylation and surface trafficking are prerequisites for any binding.","evidence":"Alanine scanning and polyanion blocking of the acidic domain; glycosylation-site mutagenesis with ER-retention and binding readouts","pmids":["18713736","18340083"],"confidence":"High","gaps":["role of the Ly6 domain in binding not yet defined","structural basis of the electrostatic interface unknown"]},{"year":2008,"claim":"In vivo heparin-release kinetics demonstrated GPIHBP1 is a major physiological LPL-binding site, and PPARγ was identified as a transcriptional regulator of its tissue expression.","evidence":"Heparin and Intralipid release kinetics in Gpihbp1−/− vs control mice; luciferase reporter and endothelial PPARγ conditional knockout","pmids":["18845532","18787041"],"confidence":"High","gaps":["mechanism of LPL release into plasma not detailed","additional regulatory inputs beyond PPARγ unexplored"]},{"year":2009,"claim":"Human disease mutations and Ly6-domain cysteine/Q115 mutagenesis established that a structurally intact Ly6 domain is essential for LPL binding, mechanistically linking GPIHBP1 to familial chylomicronemia.","evidence":"Patient genetics (Q115P, C65S/C68G) with cell-based and cell-free LPL binding assays and adipose LPL activity measurements","pmids":["19304573","19726683","20026666"],"confidence":"High","gaps":["structural consequence of cysteine loss not yet defined","transport versus binding defect not separated"]},{"year":2009,"claim":"GPIHBP1 was shown to stabilize LPL activity and protect it from ANGPTL3/ANGPTL4 inhibition, with genetic epistasis confirming physiological relevance.","evidence":"In vitro LPL activity assays and Angptl4−/−/Gpihbp1−/− double-knockout mice with antibody rescue","pmids":["19542565"],"confidence":"High","gaps":["molecular mechanism of protection not yet defined","whether protection occurs on the cell surface unclear"]},{"year":2010,"claim":"Specificity and ligand studies established that GPIHBP1 binds only LPL among lipases, binds apoAV via the acidic domain, and captures chylomicrons solely through bound LPL, and PET imaging revealed broader tissue distribution including lung and liver.","evidence":"Comparative binding assays with lipase family members and domain mutants; PET imaging with anti-GPIHBP1 antibodies and tissue LPL quantification","pmids":["20966398","20889497","20124439"],"confidence":"High","gaps":["why some tissues capture LPL produced elsewhere not fully explained","functional consequence of lung/liver GPIHBP1 unresolved"]},{"year":2011,"claim":"GPIHBP1 was shown to transport LPL across endothelial cells, the minimal LPL binding element was mapped to the C-terminal domain, and finger-2 residues of the Ly6 domain were identified as the LPL interface required for transcytosis.","evidence":"LPL deletion/mutagenesis with cell-free binding; comprehensive Ly6 alanine scanning with basolateral-to-apical transport assays; human GPIHBP1 deletion patients with heparin-release studies","pmids":["21518912","21478160","22008945"],"confidence":"High","gaps":["vesicular machinery of transport not yet identified","directionality and regulation of transport unresolved"]},{"year":2012,"claim":"Imaging and pharmacology established that GPIHBP1-bound LPL is the primary determinant of TRL margination and that GPIHBP1–LPL move bidirectionally in dynamin-dependent, caveolin-1-independent vesicles.","evidence":"Quantitative margination assays and EM tomography in Gpihbp1−/− and rescue mice; live-cell transport with dynasore/genistein and caveolin-1 knockout","pmids":["24726386","23008484","22493000"],"confidence":"High","gaps":["identity of the transport vesicle pathway not pinned down","regulation of transport rate unknown"]},{"year":2014,"claim":"The monomeric state of GPIHBP1 was established as a requirement for LPL binding, explaining a class of disease mutations that drive aberrant disulfide-linked multimerization.","evidence":"Non-reducing Western blots and binding assays across multiple expression systems; W109 and S107C mutagenesis with patient data","pmids":["25387803","24847059"],"confidence":"High","gaps":["in vivo relevance of multimerization later complicated by C63Y mouse data","direct role of W109 versus structural integrity not fully separated"]},{"year":2015,"claim":"SPR kinetics resolved two distinct LPL binding sites on GPIHBP1—a fast, salt-sensitive acidic-domain complex and a slow, heparin-resistant Ly6 complex—and showed ANGPTL4 inactivates GPIHBP1-bound LPL, after which LPL dissociates irreversibly.","evidence":"Surface plasmon resonance with domain fragments and Q114P mutant; cell-based ANGPTL4 inactivation assays with domain constructs","pmids":["25873395","25809481"],"confidence":"High","gaps":["how the two binding modes hand off LPL not fully defined","ANGPTL4 mechanism at molecular level not yet resolved"]},{"year":2016,"claim":"HDX-MS revealed the mechanism of LPL stabilization—the acidic domain prevents global unfolding of LPL's catalytic domain and renders it refractory to ANGPTL4-catalyzed unfolding—and showed interstitial HSPG-bound LPL can transfer to GPIHBP1.","evidence":"HDX-MS, SPR, and cross-linking with activity assays; in vitro and in vivo LPL transfer from HSPGs to GPIHBP1 with Ly6 (W109S) and acidic-domain mutants","pmids":["26725083","27929370","27811232","27875259"],"confidence":"High","gaps":["physical route of LPL handoff from HSPG to GPIHBP1 not fully mapped","in vivo balance of stabilization versus capture functions unclear"]},{"year":2017,"claim":"GPIHBP1 autoantibodies were identified as an acquired cause of chylomicronemia by blocking LPL binding, apoC-III was shown to inhibit lipolysis preferentially on GPIHBP1-bound LPL, and an in vivo C63Y mouse confirmed cysteine requirement.","evidence":"Patient autoantibody ELISA/blocking assays including neonatal transfer; GPIHBP1-bound LPL lipolysis assays with apoC-III variants; C63Y knock-in mouse","pmids":["28402248","28694296","28476858"],"confidence":"High","gaps":["mechanism of apoC-III inhibition on the complex not molecularly resolved","discrepancy between cell-culture multimerization and monomeric mutant in vivo unexplained"]},{"year":2018,"claim":"The LPL–GPIHBP1 crystal structure and identification of acidic-domain tyrosine sulfation provided the structural and biochemical basis for hydrophobic Ly6–LPL contacts, monomeric active LPL, and electrostatic-steering-driven binding kinetics.","evidence":"X-ray crystallography of the LPL–GPIHBP1–LMF1 complex; mass spectrometry of sulfotyrosine with SPR kon/koff and LPL protection assays; CRISPR enhancer deletion in mice","pmids":["30559189","29899144","30598475"],"confidence":"High","gaps":["structure of the disordered acidic domain not captured crystallographically","enhancer deletion did not produce hypertriglyceridemia, leaving threshold effects unclear"]},{"year":2019,"claim":"GPIHBP1 was shown to be ectopically expressed in glioma capillaries where it captures LPL and delivers TRL-derived lipid to tumor cells, and VEGF–Notch signaling was identified as an inducer of GPIHBP1 in the diabetic heart.","evidence":"NanoSIMS imaging and margination assays in glioma models; high-glucose EC culture with heparanase, VEGF neutralization, and Notch inhibition","pmids":["31169500","26586663"],"confidence":"Medium","gaps":["therapeutic relevance of tumor GPIHBP1 not established","VEGF–Notch axis confirmed in a single lab"]},{"year":2022,"claim":"The three integrated functions of the acidic domain were experimentally consolidated: electrostatic steering of binding, prevention of catalytic-domain unfolding, and shielding of LPL's basic patch to permit transcytosis past abluminal HSPGs.","evidence":"Biophysical binding/activity assays and in vivo studies with acidic-domain-mutant GPIHBP1 and HSPG interaction analysis","pmids":["36037340"],"confidence":"High","gaps":["relative contribution of each acidic-domain function in vivo not quantified"]},{"year":2023,"claim":"A post-GPIHBP1 step was defined in which luminal LPL detaches from GPIHBP1 and relocates into the endothelial glycocalyx, where it mediates TRL margination and lipid delivery.","evidence":"GPIHBP1-binding-blocking antibody (88B8), confocal and immunogold EM, NanoSIMS, and in vivo lipid delivery assays","pmids":["37871217"],"confidence":"High","gaps":["trigger for LPL detachment into glycocalyx not defined","fate and turnover of glycocalyx LPL unresolved"]},{"year":null,"claim":"The molecular machinery and regulation of vesicular GPIHBP1–LPL transcytosis, and the trigger that releases LPL from GPIHBP1 into the glycocalyx, remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["identity of the transcytosis vesicle pathway unknown","signal governing luminal LPL handoff to glycocalyx undefined","regulation of GPIHBP1 surface levels across tissues incompletely mapped"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[23,24]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[13,14,22,30]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[9,23,24]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[25,35]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,7,26]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[17]},{"term_id":"GO:0030312","term_label":"external encapsulating structure","supporting_discovery_ids":[36]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[1,4,9]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[14,16,17]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[6,15,27]}],"complexes":["LPL–GPIHBP1 complex"],"partners":["LPL","APOA5","ANGPTL4","ANGPTL3","APOC3","LMF1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8IV16","full_name":"Glycosylphosphatidylinositol-anchored high density lipoprotein-binding protein 1","aliases":["High density lipoprotein-binding protein 1"],"length_aa":184,"mass_kda":19.9,"function":"Mediates the transport of lipoprotein lipase LPL from the basolateral to the apical surface of endothelial cells in capillaries (By similarity). Anchors LPL on the surface of endothelial cells in the lumen of blood capillaries (By similarity). Protects LPL against loss of activity, and against ANGPTL4-mediated unfolding (PubMed:27929370, PubMed:29899144). Thereby, plays an important role in lipolytic processing of chylomicrons by LPL, triglyceride metabolism and lipid homeostasis (PubMed:19304573, PubMed:21314738). Binds chylomicrons and phospholipid particles that contain APOA5 (PubMed:17997385, PubMed:19304573). Binds high-density lipoprotein (HDL) and plays a role in the uptake of lipids from HDL (By similarity)","subcellular_location":"Apical cell membrane; Basolateral cell membrane; Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q8IV16/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GPIHBP1","classification":"Not Classified","n_dependent_lines":29,"n_total_lines":1208,"dependency_fraction":0.024006622516556293},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GPIHBP1","total_profiled":1310},"omim":[{"mim_id":"615947","title":"HYPERLIPOPROTEINEMIA, TYPE ID","url":"https://www.omim.org/entry/615947"},{"mim_id":"612757","title":"GLYCOSYLPHOSPHATIDYLINOSITOL-ANCHORED HIGH DENSITY LIPOPROTEIN-BINDING PROTEIN 1; GPIHBP1","url":"https://www.omim.org/entry/612757"},{"mim_id":"609708","title":"LIPOPROTEIN LIPASE; LPL","url":"https://www.omim.org/entry/609708"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"End piece","reliability":"Approved"},{"location":"Principal piece","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"adipose tissue","ntpm":85.2},{"tissue":"brain","ntpm":70.0},{"tissue":"breast","ntpm":53.2}],"url":"https://www.proteinatlas.org/search/GPIHBP1"},"hgnc":{"alias_symbol":["LOC338328","GPI-HBP1"],"prev_symbol":[]},"alphafold":{"accession":"Q8IV16","domains":[{"cath_id":"2.10.60.10","chopping":"62-137","consensus_level":"medium","plddt":97.2537,"start":62,"end":137}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8IV16","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8IV16-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8IV16-F1-predicted_aligned_error_v6.png","plddt_mean":73.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GPIHBP1","jax_strain_url":"https://www.jax.org/strain/search?query=GPIHBP1"},"sequence":{"accession":"Q8IV16","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8IV16.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8IV16/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8IV16"}},"corpus_meta":[{"pmid":"22239554","id":"PMC_22239554","title":"Mutations in LPL, APOC2, APOA5, GPIHBP1 and LMF1 in patients with severe hypertriglyceridaemia.","date":"2012","source":"Journal of internal medicine","url":"https://pubmed.ncbi.nlm.nih.gov/22239554","citation_count":204,"is_preprint":false},{"pmid":"24726386","id":"PMC_24726386","title":"The GPIHBP1-LPL complex is responsible for the margination of triglyceride-rich lipoproteins in capillaries.","date":"2014","source":"Cell metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/24726386","citation_count":130,"is_preprint":false},{"pmid":"19304573","id":"PMC_19304573","title":"Chylomicronemia with a mutant GPIHBP1 (Q115P) that cannot bind lipoprotein lipase.","date":"2009","source":"Arteriosclerosis, thrombosis, and vascular biology","url":"https://pubmed.ncbi.nlm.nih.gov/19304573","citation_count":128,"is_preprint":false},{"pmid":"28402248","id":"PMC_28402248","title":"Autoantibodies against GPIHBP1 as a Cause of Hypertriglyceridemia.","date":"2017","source":"The New England journal of medicine","url":"https://pubmed.ncbi.nlm.nih.gov/28402248","citation_count":126,"is_preprint":false},{"pmid":"31269429","id":"PMC_31269429","title":"GPIHBP1 and Lipoprotein Lipase, Partners in Plasma Triglyceride Metabolism.","date":"2019","source":"Cell metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/31269429","citation_count":113,"is_preprint":false},{"pmid":"27929370","id":"PMC_27929370","title":"The angiopoietin-like protein ANGPTL4 catalyzes unfolding of the hydrolase domain in lipoprotein lipase and the endothelial membrane protein GPIHBP1 counteracts this unfolding.","date":"2016","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/27929370","citation_count":111,"is_preprint":false},{"pmid":"19542565","id":"PMC_19542565","title":"GPIHBP1 stabilizes lipoprotein lipase and prevents its inhibition by angiopoietin-like 3 and angiopoietin-like 4.","date":"2009","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/19542565","citation_count":105,"is_preprint":false},{"pmid":"20026666","id":"PMC_20026666","title":"Mutation of conserved cysteines in the Ly6 domain of GPIHBP1 in familial chylomicronemia.","date":"2009","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/20026666","citation_count":102,"is_preprint":false},{"pmid":"26725083","id":"PMC_26725083","title":"The acidic domain of the endothelial membrane protein GPIHBP1 stabilizes lipoprotein lipase activity by preventing unfolding of its catalytic domain.","date":"2016","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/26725083","citation_count":93,"is_preprint":false},{"pmid":"20124439","id":"PMC_20124439","title":"Chylomicronemia with low postheparin lipoprotein lipase levels in the setting of GPIHBP1 defects.","date":"2010","source":"Circulation. 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It is susceptible to phosphatidylinositol-specific phospholipase C treatment, confirming GPI anchorage. Highest expression was found in the heart.\",\n      \"method\": \"Expression cloning with fluorescent-labeled HDL; lipid uptake assays; PIPL-C treatment; in situ hybridization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — expression cloning with functional lipid uptake assays and biochemical validation in a single lab\",\n      \"pmids\": [\"12496272\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"GPIHBP1-deficient mice develop severe chylomicronemia (plasma TG up to ~5000 mg/dL even on low-fat diet). GPIHBP1 is expressed on the luminal surface of capillary endothelial cells in heart, skeletal muscle, and adipose tissue. Cells transfected with GPIHBP1 bind both LPL and chylomicrons avidly, establishing GPIHBP1 as a platform for LPL-mediated lipolysis.\",\n      \"method\": \"GPIHBP1 knockout mouse model; fluorescence microscopy; cell transfection binding assays\",\n      \"journal\": \"Current opinion in lipidology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockout mouse phenotype combined with cell-based binding assays, replicated across multiple subsequent studies\",\n      \"pmids\": [\"17620854\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The acidic domain of GPIHBP1 (amino acids 38–48, enriched in Asp/Glu) is required for binding LPL and chylomicrons. Polyaspartate and polyglutamate peptides block LPL and chylomicron binding; alanine substitution of acidic residues 38–48 eliminates binding. Electrostatic interactions are key: mutation of positively charged heparin-binding domains in LPL and apoAV abolished their binding to GPIHBP1.\",\n      \"method\": \"Cell-based binding assays with CHO cells overexpressing GPIHBP1; blocking experiments with polyaspartate/polyglutamate peptides; alanine scanning mutagenesis; anti-acidic domain antiserum blocking\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis of specific residues with functional binding readout, multiple orthogonal blocking approaches in one rigorous study\",\n      \"pmids\": [\"18713736\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"N-glycosylation of GPIHBP1 at Asn-76 within the Ly6 domain is critical for trafficking GPIHBP1 to the cell surface. Mutation of the N-glycosylation site causes GPIHBP1 to accumulate in the ER and markedly reduces cell-surface expression; cells expressing non-glycosylated GPIHBP1 lack the ability to bind LPL or chylomicrons.\",\n      \"method\": \"N-glycosidase F / endoglycosidase H/F digestion; site-directed mutagenesis of glycosylation site; immunofluorescence and cell-based LPL/chylomicron binding assays\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis of specific glycosylation site with multiple orthogonal methods (enzymatic deglycosylation, ER localization, functional binding assays)\",\n      \"pmids\": [\"18340083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"In GPIHBP1-deficient mice, post-heparin plasma LPL levels peak very slowly (over 15 min) rather than rapidly (within 1 min as in wild-type), and plasma triglycerides fall negligibly within the first 15 min after heparin. Intralipid injection releases LPL in wild-type but not GPIHBP1-deficient mice, despite similar tissue LPL stores. These findings establish that GPIHBP1 represents an important LPL-binding site in vivo.\",\n      \"method\": \"Heparin injection kinetics; plasma LPL measurement; Intralipid injection; comparison of Gpihbp1−/− vs. control mice\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo heparin-release kinetics experiment with multiple readouts in knockout vs. wild-type mice\",\n      \"pmids\": [\"18845532\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"GPIHBP1 expression in heart, adipose tissue, and skeletal muscle is upregulated by fasting and by PPARγ agonists (but not PPARα or PPARδ agonists). A PPARγ binding site upstream of exon 1 exhibits activity in a luciferase reporter assay. Conditional knockout of endothelial PPARγ reduces Gpihbp1 expression in adipose tissue in vivo.\",\n      \"method\": \"Quantitative RT-PCR; luciferase reporter assay; PPARγ agonist treatment; endothelial-specific PPARγ knockout mice\",\n      \"journal\": \"Molecular endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — luciferase reporter and in vivo conditional knockout, single lab with multiple methods\",\n      \"pmids\": [\"18787041\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"A homozygous Q115P missense mutation in GPIHBP1 identified in a chylomicronemia patient abolishes the ability of GPIHBP1 to bind LPL and chylomicrons without affecting cell-surface expression. The corresponding mouse mutation (Q114P) also cannot bind LPL, establishing this residue as critical for LPL binding.\",\n      \"method\": \"Patient genetic sequencing; cell-based binding assays in CHO cells expressing wild-type vs. Q115P GPIHBP1; mouse GPIHBP1 Q114P mutagenesis\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — disease mutation validated by cell-based binding assays in both human and mouse GPIHBP1, replicated in multiple subsequent studies\",\n      \"pmids\": [\"19304573\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Conserved cysteines in the Ly6 domain of GPIHBP1 (C65, C68 in humans; C65S, C68G mutations found in chylomicronemia patients) are essential for LPL binding. Cysteine mutants reach the cell surface but are defective in LPL binding in both cell-based and cell-free binding assays, demonstrating that a structurally intact Ly6 domain is required.\",\n      \"method\": \"Site-directed mutagenesis; cell-based LPL binding assay; cell-free LPL binding assay using GPIHBP1 immobilized on antibody-coated agarose beads; PIPL-C cell-surface release assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis of specific cysteines validated in both cell-based and cell-free assays, findings replicated by independent patient mutation studies\",\n      \"pmids\": [\"19726683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Compound heterozygous cysteine mutations in GPIHBP1 Ly6 domain (C65S and C68G) identified in familial chylomicronemia. Mutant GPIHBP1 proteins reach the cell surface but fail to bind LPL in cell-based and cell-free assays. LPL mass and activity in adipose tissue biopsies appear normal, consistent with defective LPL transport rather than synthesis.\",\n      \"method\": \"Family genetics; cell-based and cell-free LPL binding assays; adipose tissue biopsy LPL activity; [35S]methionine incorporation\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — disease mutations functionally validated by multiple binding assays in clinical pedigree study\",\n      \"pmids\": [\"20026666\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"GPIHBP1 stabilizes LPL activity and protects it from inhibition by ANGPTL4 and ANGPTL3 in vitro. ANGPTL4 potently inhibits non-stabilized LPL and heparin-stabilized LPL but not GPIHBP1-stabilized LPL. In vivo, Angptl4−/−/Gpihbp1−/− double knockout mice had lower plasma TG than Gpihbp1−/− mice, approaching wild-type levels, confirming the physiological relevance of this protection.\",\n      \"method\": \"In vitro LPL activity assay with GPIHBP1, ANGPTL3, ANGPTL4; double-knockout mouse models; ANGPTL-neutralizing antibody treatment in Gpihbp1−/− mice\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic assays combined with in vivo genetic epistasis in double-knockout mice and antibody rescue experiments\",\n      \"pmids\": [\"19542565\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"GPIHBP1 binds LPL but does not bind other members of the lipase family (endothelial lipase, hepatic lipase, pancreatic lipase). GPIHBP1 binds apoAV (dependent on the acidic domain, independent of the Ly6 domain). The ability of GPIHBP1-expressing cells to bind chylomicrons is entirely mediated by LPL captured from the medium; GPIHBP1 does not bind chylomicrons directly in the absence of LPL.\",\n      \"method\": \"Cell-based and cell-free binding assays; antibody blocking; cells expressing GPIHBP1 with acidic domain mutations\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — comprehensive specificity study using multiple binding assays with domain mutants, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"20966398\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Homozygous GPIHBP1 C65Y mutation causes chylomicronemia; the mutant protein reaches the cell surface but cannot bind LPL. Patients with homozygous C65Y or Q115P mutations have very low LPL in post-heparin plasma, demonstrating that GPIHBP1 is required for efficient LPL entry into plasma after heparin, consistent with its role in LPL transport.\",\n      \"method\": \"Patient clinical studies; cell-surface expression assays; cell-based LPL binding assay; post-heparin LPL measurement; prolonged heparin infusion in Q115P patient\",\n      \"journal\": \"Circulation. Cardiovascular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — disease mutation validated by cell-based assays and in vivo heparin-release studies in human patients\",\n      \"pmids\": [\"20124439\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PET scanning with radiolabeled GPIHBP1-specific antibodies revealed that GPIHBP1 is expressed at unexpectedly high levels in lung and liver capillary endothelium, not only in heart/skeletal muscle/adipose tissue. LPL protein was detected in lung despite very low Lpl transcript levels, suggesting GPIHBP1 in the lung captures LPL produced elsewhere. Lung LPL levels were lower in Gpihbp1−/− mice.\",\n      \"method\": \"PET imaging with radiolabeled anti-GPIHBP1 antibodies; immunofluorescence microscopy; tissue LPL quantification in knockout mice; Lpl−/− mice expressing human LPL only in muscle\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo imaging with functional validation in knockout mice and transgenic model, multiple orthogonal methods\",\n      \"pmids\": [\"20889497\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"GPIHBP1 transports LPL from the subendothelial space across endothelial cells to the capillary lumen. LPL binding to GPIHBP1 requires only LPL's C-terminal domain (residues 298–448); the C-terminal fragment binds GPIHBP1 avidly independent of the N-terminal catalytic domain or full-length homodimer formation. C418Y and E421K mutations in LPL eliminate GPIHBP1 binding without affecting catalytic activity.\",\n      \"method\": \"Cell-based and cell-free LPL-GPIHBP1 binding assays; LPL deletion mutants; furin cleavage mapping; alanine scanning of LPL C-terminal residues\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — domain dissection by deletion and mutagenesis with cell-based and cell-free binding assays, identifying minimal binding domain\",\n      \"pmids\": [\"21518912\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Within the Ly6 domain three-fingered structure of GPIHBP1, alanine scanning identified 12 residues (aside from conserved cysteines) required for LPL binding, with 9 clustered in finger 2. Mutant GPIHBP1 proteins that cannot bind LPL also lack the ability to transport LPL from the basolateral to the apical surface of endothelial cells.\",\n      \"method\": \"Comprehensive alanine-scanning mutagenesis; immunofluorescence cell-surface expression assay; Western blot LPL binding assay; endothelial transcytosis assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — comprehensive alanine scanning of entire Ly6 domain with functional transport assay in endothelial cells\",\n      \"pmids\": [\"21478160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Homozygous GPIHBP1 deletion (17.5 kb) causes complete GPIHBP1 deficiency and severe chylomicronemia. Intravenous heparin failed to raise LPL in plasma of GPIHBP1-deficient patients (unlike controls), demonstrating that GPIHBP1 is required for heparin-releasable LPL in the human vascular compartment.\",\n      \"method\": \"Array-based copy number analysis; Sanger sequencing; heparin bolus LPL release in GPIHBP1-null patients vs. controls\",\n      \"journal\": \"Journal of inherited metabolic disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — complete genetic deletion with in vivo physiological validation of LPL transport function in human patients\",\n      \"pmids\": [\"22008945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"TRL margination along heart capillaries depends on GPIHBP1 and specifically on LPL bound to GPIHBP1. In Gpihbp1−/− mice, TRLs do not marginate along capillaries. Expression of LPL by endothelial cells (binding to HSPGs) in Gpihbp1−/− mice does not restore TRL margination, demonstrating that GPIHBP1-bound LPL is the primary determinant of TRL margination.\",\n      \"method\": \"Fluorescence microscopy; infrared-dye-labeled lipoprotein quantitative margination assays; EM tomography; cell-culture and in vivo studies with Gpihbp1−/− mice expressing endothelial LPL\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal imaging methods (fluorescence, quantitative IR, EM tomography) in knockout and rescue models\",\n      \"pmids\": [\"24726386\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"GPIHBP1 and LPL move bidirectionally across capillary endothelial cells in vesicles. Transport of LPL across endothelial cells is inhibited by dynasore and genistein (dynamin inhibitor/vesicular transport blockers). EM and dual-axis EM tomography show GPIHBP1 and LPL in membrane invaginations and vesicles. Transport is efficient in the absence of caveolin-1.\",\n      \"method\": \"Live-cell bidirectional transport assays; dynasore/genistein pharmacological inhibition; transmission EM and dual-axis EM tomography; caveolin-1 knockout endothelial cells and in vivo studies\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (live imaging, pharmacological inhibition, EM ultrastructure) with genetic caveolin-1 KO controls\",\n      \"pmids\": [\"23008484\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"LPL's C-terminal domain (residues 298–448) is sufficient for GPIHBP1 binding; the N-terminal catalytic domain is dispensable. Full-length homodimers are not required for GPIHBP1 binding. C-terminal fragments of LPL with C418Y or E421K mutations cannot bind GPIHBP1. After denaturation, the C-terminal fragment refolds and restores GPIHBP1 binding.\",\n      \"method\": \"LPL truncation/deletion constructs; furin cleavage mapping; cell-based and cell-free GPIHBP1 binding assays; denaturation/refolding experiment\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — domain dissection with multiple deletion constructs plus refolding experiment establishing C-terminal domain sufficiency\",\n      \"pmids\": [\"22493000\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Many GPIHBP1 Ly6 domain missense mutations (including disease-causing mutations) cause GPIHBP1 to form disulfide-linked dimers and multimers. Only GPIHBP1 monomers—not dimers or multimers—are capable of binding LPL. W109S mutation abolishes LPL binding without promoting multimerization, suggesting W109 plays a direct role in LPL binding rather than only through structural integrity.\",\n      \"method\": \"Expression in CHO, rat and human endothelial cells, and Drosophila S2 cells; Western blot under non-reducing conditions; cell-based and cell-free LPL binding assays; systematic W109 mutagenesis to 8 other amino acids\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multimerization mechanism tested across multiple expression systems with systematic mutagenesis, clear functional correlation with LPL binding loss\",\n      \"pmids\": [\"25387803\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"GPIHBP1-S107C mutation (serine-to-cysteine substitution creating an extra cysteine) causes nearly all cell-surface GPIHBP1 to form disulfide-linked dimers and multimers, abolishing LPL binding. Functional studies confirmed only GPIHBP1 monomers bind LPL. Three homozygous patients with this mutation have very low preheparin plasma LPL.\",\n      \"method\": \"Patient genetic analysis; cell-based and insect-cell expression; non-reducing Western blot; cell-based and cell-free LPL binding assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — disease mutation mechanistically explained by multimerization assay in two independent expression systems with in vivo patient data\",\n      \"pmids\": [\"24847059\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"ANGPTL4 can bind and inactivate LPL when LPL is complexed with GPIHBP1 on endothelial cell surfaces. Once inactivated by ANGPTL4, LPL dissociates from GPIHBP1. ANGPTL4-inactivated LPL is incapable of re-binding GPIHBP1. The N-terminal coiled-coil domain of ANGPTL4 alone is more potent in inactivating GPIHBP1-bound LPL than full-length ANGPTL4.\",\n      \"method\": \"Cell-based LPL binding and inactivation assays using endothelial cells; ANGPTL4 domain constructs; temperature-dependent binding experiments (4°C vs. 37°C)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-based assays with endogenous-context LPL-GPIHBP1 complex, single lab, multiple conditions tested\",\n      \"pmids\": [\"25809481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"GPIHBP1 has two distinct binding sites for LPL: the acidic N-terminal domain forms a tight but short-lived complex (fast on/off rates, salt-sensitive, heparin-displaceable), while the Ly6 domain forms a slower but longer-lasting complex (heparin-resistant). LPL bound to the acidic domain retains affinity for the Ly6 domain and retains capacity to interact with lipoproteins, whereas LPL bound to the Ly6 domain does not.\",\n      \"method\": \"Surface plasmon resonance (SPR); comparative binding studies with isolated N-terminal peptide, Ly6 domain, full-length GPIHBP1, and Q114P mutant; salt and heparin competition assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — biophysical SPR measurements with domain fragments and mutants establishing distinct kinetic signatures for two binding sites\",\n      \"pmids\": [\"25873395\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"GPIHBP1's intrinsically disordered acidic N-terminal domain stabilizes LPL catalytic activity by mitigating global unfolding of LPL's catalytic domain. Biophysical studies using hydrogen-deuterium exchange/mass spectrometry (HDX-MS) demonstrated that the acidic domain reduces spontaneous unfolding of LPL's hydrolase domain. The LU domain and acidic domain serve distinct roles: the LU domain mediates binding kinetics while the acidic domain prevents unfolding.\",\n      \"method\": \"Hydrogen-deuterium exchange/mass spectrometry (HDX-MS); surface plasmon resonance (SPR); zero-length cross-linking; LPL catalytic activity assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple biophysical methods (HDX-MS, SPR, cross-linking) with functional validation of stabilization mechanism in single rigorous study\",\n      \"pmids\": [\"26725083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ANGPTL4 inactivates LPL by catalyzing the unfolding of its hydrolase domain (not simply by binding). Binding of LPL to GPIHBP1 renders LPL largely refractory to ANGPTL4-catalyzed inactivation. Both the LU domain and the intrinsically disordered acidic domain of GPIHBP1 are required for this protective effect. A common ANGPTL4 polymorphic variant (associated with lower plasma TG) is less efficient at catalyzing LPL unfolding and its substitution destabilizes its N-terminal α-helix.\",\n      \"method\": \"HDX-MS measuring unfolding of LPL hydrolase domain; LPL activity assays in presence of ANGPTL4 with/without GPIHBP1; GPIHBP1 domain mutants; biophysical analysis of ANGPTL4 variant\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mechanistic HDX-MS measurements combined with functional activity assays and domain mutants establishing the unfolding mechanism\",\n      \"pmids\": [\"27929370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"LPL bound to HSPGs in interstitial spaces is mobile and can detach to move to GPIHBP1 on capillaries. LPL moves from HSPGs on cultured cells to: soluble GPIHBP1 in medium; GPIHBP1-coated agarose beads; and nearby GPIHBP1-expressing cells. Movement requires an intact GPIHBP1 Ly6 domain (W109S mutation blocks transfer) but is largely independent of the acidic domain. In vivo, LPL moves rapidly from adipocyte HSPGs to GPIHBP1-coated beads injected into adipose tissue of Gpihbp1−/− mice.\",\n      \"method\": \"Cell culture LPL transfer assays; GPIHBP1-coated bead capture; in vivo bead injection into brown adipose tissue of Gpihbp1−/− mice; Ly6 domain mutant (W109S) and acidic domain mutant GPIHBP1\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vitro and in vivo approaches with domain mutant controls establishing HSPG-to-GPIHBP1 LPL transfer mechanism\",\n      \"pmids\": [\"27811232\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Monoclonal antibodies targeting GPIHBP1's Ly6 domain (RE3 and RG3) abolish LPL binding, whereas an antibody against the acidic domain (RF4) does not. Both RE3 and RG3 bind with reduced affinity to GPIHBP1-W109S (an Ly6 mutant that abolishes LPL binding), linking the W109 region to the LPL binding interface. Immunohistochemistry confirmed that human GPIHBP1 is expressed exclusively in capillary endothelial cells.\",\n      \"method\": \"Monoclonal antibody development; cell-based LPL binding blocking assays; affinity measurements with Ly6 domain mutants; immunohistochemistry of human tissues\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — antibody blocking assays with domain mutants in single lab, functional and localization data\",\n      \"pmids\": [\"27875259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GPIHBP1 autoantibodies (identified in 6 patients with chylomicronemia) block the binding of LPL to GPIHBP1, thereby preventing LPL transport into capillaries, reducing plasma LPL levels, and causing severe hypertriglyceridemia. The autoantibody-mediated chylomicronemia phenotype mirrors genetic GPIHBP1 deficiency. Maternal autoantibodies transferred to a neonate caused transient chylomicronemia.\",\n      \"method\": \"ELISA; Western blot; immunocytochemistry; LPL-GPIHBP1 binding blocking assay with patient plasma\",\n      \"journal\": \"The New England journal of medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mechanistic blocking assay confirming autoantibodies inhibit LPL-GPIHBP1 interaction, replicated across multiple patients including neonatal transfer case\",\n      \"pmids\": [\"28402248\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ApoC-III potently inhibits triglyceride hydrolysis specifically when LPL is bound to GPIHBP1. TRLs from APOC3 transgenic mice bind normally to GPIHBP1-bound LPL on cells and in vivo, but triglycerides are hydrolyzed more slowly. The inhibitory effect of apoC-III is greater when LPL is bound to GPIHBP1 compared to free LPL. A loss-of-function apoC-III variant (A23T) associated with low plasma TG shows reduced capacity to inhibit both free and GPIHBP1-bound LPL.\",\n      \"method\": \"Cell-based lipolysis assays using GPIHBP1-bound LPL; GPIHBP1-coated agarose bead lipolysis assay; in vivo margination assay in mice; recombinant apoC-III variants\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-based and bead-based lipolysis assays with in vivo confirmation, natural apoC-III variant as functional control\",\n      \"pmids\": [\"28694296\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Mutating a conserved cysteine in mouse GPIHBP1 (C63Y) abolishes LPL binding and causes severe chylomicronemia in vivo, with ~70% reduction in GPIHBP1 levels at the endothelial cell surface. The mutant GPIHBP1 is predominantly monomeric, contrasting with cell culture studies where cysteine mutations cause multimerization.\",\n      \"method\": \"Knock-in mouse model (CRISPR/Cas9 was not stated explicitly but mice harboring C63Y were created); immunohistochemistry; plasma TG measurement; LPL localization\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo mouse model with specific GPIHBP1 mutation, functional and expression readouts\",\n      \"pmids\": [\"28476858\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"X-ray crystal structure of the LPL-GPIHBP1 complex was solved at 2.5–3.0 Å. GPIHBP1's LU domain binds to LPL's C-terminal lipid-binding domain largely through hydrophobic interactions. LPL contains a large basic patch spanning its N- and C-terminal domains, positioned to interact with GPIHBP1's acidic domain. In the complex, LPL can be active as a 1:1 monomer rather than requiring a homodimer.\",\n      \"method\": \"X-ray crystallography; co-expression of LPL, soluble GPIHBP1, and LMF1; inhibitor-bound structure resolving LPL lid region; biochemical activity assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure at 2.5–3.0 Å with functional validation of LPL monomer activity, confirmed in parallel independent structural study (PMID 31072929)\",\n      \"pmids\": [\"30559189\", \"31072929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"A conserved tyrosine in the middle of GPIHBP1's intrinsically disordered acidic domain undergoes posttranslational O-sulfation. This tyrosine sulfation increases the affinity of GPIHBP1-LPL interactions and enhances GPIHBP1's ability to protect LPL against ANGPTL4-catalyzed unfolding. The acidic IDR also increases the probability of GPIHBP1-LPL encounters via electrostatic steering, increasing the association rate constant (kon) for LPL binding by >250-fold.\",\n      \"method\": \"Mass spectrometry identification of sulfotyrosine; surface plasmon resonance (kon/koff measurements); LPL activity protection assays; biophysical characterization of IDR conformation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — PTM identified by mass spectrometry with quantitative SPR binding kinetics and functional LPL protection assays\",\n      \"pmids\": [\"29899144\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"An upstream enhancer element located ~3.6 kb upstream from exon 1 of mouse Gpihbp1 regulates tissue-specific Gpihbp1 expression. Deletion of this enhancer (CRISPR/Cas9) reduced Gpihbp1 expression by >90% in liver and ~50% in heart/brown adipose tissue. Reduced GPIHBP1 caused partial LPL mislocalization (increased LPL in interstitial spaces) in compound heterozygotes, but did not cause hypertriglyceridemia.\",\n      \"method\": \"CRISPR/Cas9 enhancer deletion; quantitative RT-PCR; immunofluorescence microscopy for LPL localization; plasma TG measurement\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR-based enhancer deletion in vivo with functional readouts, single lab\",\n      \"pmids\": [\"30598475\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GPIHBP1 is expressed in glioma capillaries (unlike normal brain capillaries, which lack GPIHBP1) and captures locally produced LPL. GPIHBP1 in glioma capillaries enables margination of TRLs along glioma capillaries, and NanoSIMS imaging confirmed uptake of TRL-derived lipid nutrients by surrounding glioma cells, providing a source of lipid energy for tumors.\",\n      \"method\": \"Immunohistochemistry of mouse and human glioma; NanoSIMS isotope imaging; TRL margination assay in glioma-bearing mice; LPL capture by GPIHBP1 in glioma capillaries\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — NanoSIMS imaging with functional TRL margination data in glioma model, single lab\",\n      \"pmids\": [\"31169500\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In a NanoBiT split-luciferase assay monitoring LPL-GPIHBP1 binding on endothelial cells in real time, ANGPTL4 and ANGPTL3-ANGPTL8 complexes disrupt LPL-GPIHBP1 interactions. Chylomicrons can dissociate LPL from GPIHBP1, and this dissociation is mediated in part by fatty acids produced during lipolysis. Exogenous inhibitors (tyloxapol, poloxamer-407, tetrahydrolipstatin) did not disrupt LPL-GPIHBP1 binding.\",\n      \"method\": \"NanoBiT split-luciferase real-time binding assay on endothelial cells; ANGPTL4, ANGPTL3-8 complex, and chylomicron addition assays; fatty acid competition\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — novel real-time assay with validated specificity and multiple inhibitor/substrate conditions, single lab\",\n      \"pmids\": [\"32029511\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GPIHBP1's acidic domain (AD) serves three distinct functions established experimentally: (1) it accelerates LPL binding kinetics via electrostatic steering; (2) it preserves LPL catalytic activity by preventing unfolding of LPL's catalytic domain; and (3) by sheathing LPL's basic patch, the AD enables LPL-GPIHBP1 complexes to move across endothelial cells to the capillary lumen—without the AD, GPIHBP1-bound LPL is trapped by interactions with heparan sulfate proteoglycans on the abluminal surface.\",\n      \"method\": \"Biophysical binding assays; LPL activity measurements; in vivo mouse studies with AD-mutant GPIHBP1; HSPG interaction studies\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — three distinct functions experimentally demonstrated in vitro and in vivo with clear molecular mechanism, published in high-quality journal\",\n      \"pmids\": [\"36037340\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"LPL transported into capillaries by GPIHBP1 can detach from GPIHBP1 and move into the endothelial glycocalyx. By confocal microscopy, immunogold EM, and NanoSIMS, LPL detected by a GPIHBP1-binding-blocking antibody (88B8, which cannot detect GPIHBP1-bound LPL) is located in the glycocalyx, distant from GPIHBP1 on the plasma membrane. This glycocalyx-localized LPL mediates TRL margination and is active in TRL processing, delivering lipids to adjacent parenchymal cells.\",\n      \"method\": \"Monoclonal antibody 88B8 (GPIHBP1-binding-blocking epitope); confocal microscopy; immunogold electron microscopy; NanoSIMS imaging; in vivo functional lipid delivery assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — three orthogonal imaging methods with functional validation, identifies a novel post-GPIHBP1 step in LPL trafficking\",\n      \"pmids\": [\"37871217\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"VEGF, secreted by cardiomyocytes in response to hyperglycemia-triggered heparanase release, induces GPIHBP1 expression in endothelial cells via Notch signaling (Delta-like ligand 4 augmentation and nuclear translocation of the Notch intracellular domain), thereby increasing LPL shuttling across endothelial cells in the diabetic heart.\",\n      \"method\": \"High-glucose EC culture; heparanase treatment; VEGF neutralizing antibody; Notch pathway inhibition; cardiomyocyte-EC co-culture; in vivo severely diabetic animal model with VEGF attenuation\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic pathway (heparanase→VEGF→Notch→GPIHBP1) established by multiple cell-based and in vivo experiments, single lab\",\n      \"pmids\": [\"26586663\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GPIHBP1 is a GPI-anchored protein of capillary endothelial cells with two functional domains: an intrinsically disordered, sulfotyrosine-containing acidic N-terminal domain that accelerates LPL capture by electrostatic steering, shields LPL's basic patch to enable transcytosis past abluminal heparan sulfate proteoglycans, and stabilizes LPL's catalytic domain against spontaneous and ANGPTL4-catalyzed unfolding; and a three-fingered Ly6/LU domain that makes stable hydrophobic contacts with LPL's C-terminal lipid-binding domain. GPIHBP1 picks up LPL secreted into the subendothelial space, transports it bidirectionally across endothelial cells in vesicles to the capillary lumen, where GPIHBP1-bound LPL can also transfer into the glycocalyx to mediate margination and lipolysis of triglyceride-rich lipoproteins; loss of GPIHBP1 strands LPL in the interstitial space and causes severe chylomicronemia.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GPIHBP1 is a GPI-anchored protein of capillary endothelial cells that functions as the dedicated platform and transporter for lipoprotein lipase (LPL), enabling intravascular triglyceride lipolysis [#1, #4]. It is built from two functional modules: an intrinsically disordered, acidic (Asp/Glu-rich) N-terminal domain that engages LPL through electrostatic interactions, and a three-fingered Ly6/LU domain that forms a stable, longer-lived contact with LPL's C-terminal lipid-binding domain (residues 298–448) [#2, #13, #22]. The acidic domain accelerates LPL capture by electrostatic steering—an effect enhanced by O-sulfation of a conserved tyrosine that raises the LPL association rate constant >250-fold—and it sheathes LPL's basic patch so that LPL–GPIHBP1 complexes can cross the endothelial cell rather than being trapped by abluminal heparan sulfate proteoglycans [#31, #35]. GPIHBP1 picks up LPL released from interstitial HSPGs and shuttles it bidirectionally across the endothelium in dynamin-dependent vesicles to the capillary lumen, where GPIHBP1-bound LPL drives margination and lipolysis of triglyceride-rich lipoproteins, and from which LPL can transfer into the glycocalyx [#14, #16, #17, #25, #36]. Binding requires a structurally intact Ly6 domain: conserved cysteines, N-glycosylation at Asn-76, and the monomeric state of GPIHBP1 are all essential, and mutations that disrupt these (or autoantibodies against the Ly6 domain) abolish LPL binding [#3, #7, #19, #27]. Beyond capture and transport, GPIHBP1 stabilizes LPL's catalytic domain against spontaneous and ANGPTL4-catalyzed unfolding, protecting enzyme activity [#23, #24]. A crystal structure shows the LU domain binding LPL's C-terminal domain through hydrophobic contacts, with LPL active as a 1:1 monomer [#30]. Loss-of-function mutations, gene deletion, and neutralizing autoantibodies all strand LPL in the interstitium and cause severe chylomicronemia in humans [#6, #15, #27].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"GPIHBP1 was first identified as a GPI-anchored cell-surface protein with high-affinity HDL binding and lipid-uptake activity, establishing it as a lipid-handling membrane protein before its LPL role was known.\",\n      \"evidence\": \"Expression cloning with fluorescent HDL, lipid uptake assays, and PIPL-C sensitivity in a single lab\",\n      \"pmids\": [\"12496272\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"HDL binding role not reconciled with later LPL-centric function\", \"physiological ligand and tissue context not yet defined\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Knockout mice and binding assays established GPIHBP1 as a luminal endothelial platform for LPL-mediated lipolysis, answering whether it has an essential role in triglyceride metabolism.\",\n      \"evidence\": \"Gpihbp1 knockout mouse phenotype with severe chylomicronemia, plus cell-transfection LPL/chylomicron binding assays\",\n      \"pmids\": [\"17620854\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"which GPIHBP1 domain mediates LPL binding not yet mapped\", \"mechanism of chylomicron capture unresolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Domain dissection assigned LPL/apoAV/chylomicron binding to the acidic N-terminal domain via electrostatic interactions and showed N-glycosylation and surface trafficking are prerequisites for any binding.\",\n      \"evidence\": \"Alanine scanning and polyanion blocking of the acidic domain; glycosylation-site mutagenesis with ER-retention and binding readouts\",\n      \"pmids\": [\"18713736\", \"18340083\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"role of the Ly6 domain in binding not yet defined\", \"structural basis of the electrostatic interface unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"In vivo heparin-release kinetics demonstrated GPIHBP1 is a major physiological LPL-binding site, and PPARγ was identified as a transcriptional regulator of its tissue expression.\",\n      \"evidence\": \"Heparin and Intralipid release kinetics in Gpihbp1−/− vs control mice; luciferase reporter and endothelial PPARγ conditional knockout\",\n      \"pmids\": [\"18845532\", \"18787041\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"mechanism of LPL release into plasma not detailed\", \"additional regulatory inputs beyond PPARγ unexplored\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Human disease mutations and Ly6-domain cysteine/Q115 mutagenesis established that a structurally intact Ly6 domain is essential for LPL binding, mechanistically linking GPIHBP1 to familial chylomicronemia.\",\n      \"evidence\": \"Patient genetics (Q115P, C65S/C68G) with cell-based and cell-free LPL binding assays and adipose LPL activity measurements\",\n      \"pmids\": [\"19304573\", \"19726683\", \"20026666\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"structural consequence of cysteine loss not yet defined\", \"transport versus binding defect not separated\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"GPIHBP1 was shown to stabilize LPL activity and protect it from ANGPTL3/ANGPTL4 inhibition, with genetic epistasis confirming physiological relevance.\",\n      \"evidence\": \"In vitro LPL activity assays and Angptl4−/−/Gpihbp1−/− double-knockout mice with antibody rescue\",\n      \"pmids\": [\"19542565\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"molecular mechanism of protection not yet defined\", \"whether protection occurs on the cell surface unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Specificity and ligand studies established that GPIHBP1 binds only LPL among lipases, binds apoAV via the acidic domain, and captures chylomicrons solely through bound LPL, and PET imaging revealed broader tissue distribution including lung and liver.\",\n      \"evidence\": \"Comparative binding assays with lipase family members and domain mutants; PET imaging with anti-GPIHBP1 antibodies and tissue LPL quantification\",\n      \"pmids\": [\"20966398\", \"20889497\", \"20124439\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"why some tissues capture LPL produced elsewhere not fully explained\", \"functional consequence of lung/liver GPIHBP1 unresolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"GPIHBP1 was shown to transport LPL across endothelial cells, the minimal LPL binding element was mapped to the C-terminal domain, and finger-2 residues of the Ly6 domain were identified as the LPL interface required for transcytosis.\",\n      \"evidence\": \"LPL deletion/mutagenesis with cell-free binding; comprehensive Ly6 alanine scanning with basolateral-to-apical transport assays; human GPIHBP1 deletion patients with heparin-release studies\",\n      \"pmids\": [\"21518912\", \"21478160\", \"22008945\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"vesicular machinery of transport not yet identified\", \"directionality and regulation of transport unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Imaging and pharmacology established that GPIHBP1-bound LPL is the primary determinant of TRL margination and that GPIHBP1–LPL move bidirectionally in dynamin-dependent, caveolin-1-independent vesicles.\",\n      \"evidence\": \"Quantitative margination assays and EM tomography in Gpihbp1−/− and rescue mice; live-cell transport with dynasore/genistein and caveolin-1 knockout\",\n      \"pmids\": [\"24726386\", \"23008484\", \"22493000\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"identity of the transport vesicle pathway not pinned down\", \"regulation of transport rate unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"The monomeric state of GPIHBP1 was established as a requirement for LPL binding, explaining a class of disease mutations that drive aberrant disulfide-linked multimerization.\",\n      \"evidence\": \"Non-reducing Western blots and binding assays across multiple expression systems; W109 and S107C mutagenesis with patient data\",\n      \"pmids\": [\"25387803\", \"24847059\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"in vivo relevance of multimerization later complicated by C63Y mouse data\", \"direct role of W109 versus structural integrity not fully separated\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"SPR kinetics resolved two distinct LPL binding sites on GPIHBP1—a fast, salt-sensitive acidic-domain complex and a slow, heparin-resistant Ly6 complex—and showed ANGPTL4 inactivates GPIHBP1-bound LPL, after which LPL dissociates irreversibly.\",\n      \"evidence\": \"Surface plasmon resonance with domain fragments and Q114P mutant; cell-based ANGPTL4 inactivation assays with domain constructs\",\n      \"pmids\": [\"25873395\", \"25809481\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"how the two binding modes hand off LPL not fully defined\", \"ANGPTL4 mechanism at molecular level not yet resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"HDX-MS revealed the mechanism of LPL stabilization—the acidic domain prevents global unfolding of LPL's catalytic domain and renders it refractory to ANGPTL4-catalyzed unfolding—and showed interstitial HSPG-bound LPL can transfer to GPIHBP1.\",\n      \"evidence\": \"HDX-MS, SPR, and cross-linking with activity assays; in vitro and in vivo LPL transfer from HSPGs to GPIHBP1 with Ly6 (W109S) and acidic-domain mutants\",\n      \"pmids\": [\"26725083\", \"27929370\", \"27811232\", \"27875259\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"physical route of LPL handoff from HSPG to GPIHBP1 not fully mapped\", \"in vivo balance of stabilization versus capture functions unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"GPIHBP1 autoantibodies were identified as an acquired cause of chylomicronemia by blocking LPL binding, apoC-III was shown to inhibit lipolysis preferentially on GPIHBP1-bound LPL, and an in vivo C63Y mouse confirmed cysteine requirement.\",\n      \"evidence\": \"Patient autoantibody ELISA/blocking assays including neonatal transfer; GPIHBP1-bound LPL lipolysis assays with apoC-III variants; C63Y knock-in mouse\",\n      \"pmids\": [\"28402248\", \"28694296\", \"28476858\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"mechanism of apoC-III inhibition on the complex not molecularly resolved\", \"discrepancy between cell-culture multimerization and monomeric mutant in vivo unexplained\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"The LPL–GPIHBP1 crystal structure and identification of acidic-domain tyrosine sulfation provided the structural and biochemical basis for hydrophobic Ly6–LPL contacts, monomeric active LPL, and electrostatic-steering-driven binding kinetics.\",\n      \"evidence\": \"X-ray crystallography of the LPL–GPIHBP1–LMF1 complex; mass spectrometry of sulfotyrosine with SPR kon/koff and LPL protection assays; CRISPR enhancer deletion in mice\",\n      \"pmids\": [\"30559189\", \"29899144\", \"30598475\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"structure of the disordered acidic domain not captured crystallographically\", \"enhancer deletion did not produce hypertriglyceridemia, leaving threshold effects unclear\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"GPIHBP1 was shown to be ectopically expressed in glioma capillaries where it captures LPL and delivers TRL-derived lipid to tumor cells, and VEGF–Notch signaling was identified as an inducer of GPIHBP1 in the diabetic heart.\",\n      \"evidence\": \"NanoSIMS imaging and margination assays in glioma models; high-glucose EC culture with heparanase, VEGF neutralization, and Notch inhibition\",\n      \"pmids\": [\"31169500\", \"26586663\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"therapeutic relevance of tumor GPIHBP1 not established\", \"VEGF–Notch axis confirmed in a single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The three integrated functions of the acidic domain were experimentally consolidated: electrostatic steering of binding, prevention of catalytic-domain unfolding, and shielding of LPL's basic patch to permit transcytosis past abluminal HSPGs.\",\n      \"evidence\": \"Biophysical binding/activity assays and in vivo studies with acidic-domain-mutant GPIHBP1 and HSPG interaction analysis\",\n      \"pmids\": [\"36037340\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"relative contribution of each acidic-domain function in vivo not quantified\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A post-GPIHBP1 step was defined in which luminal LPL detaches from GPIHBP1 and relocates into the endothelial glycocalyx, where it mediates TRL margination and lipid delivery.\",\n      \"evidence\": \"GPIHBP1-binding-blocking antibody (88B8), confocal and immunogold EM, NanoSIMS, and in vivo lipid delivery assays\",\n      \"pmids\": [\"37871217\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"trigger for LPL detachment into glycocalyx not defined\", \"fate and turnover of glycocalyx LPL unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular machinery and regulation of vesicular GPIHBP1–LPL transcytosis, and the trigger that releases LPL from GPIHBP1 into the glycocalyx, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"identity of the transcytosis vesicle pathway unknown\", \"signal governing luminal LPL handoff to glycocalyx undefined\", \"regulation of GPIHBP1 surface levels across tissues incompletely mapped\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [23, 24]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [13, 14, 22, 30]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [9, 23, 24]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [25, 35]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 7, 26]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [17]},\n      {\"term_id\": \"GO:0030312\", \"supporting_discovery_ids\": [36]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [1, 4, 9]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [14, 16, 17]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [6, 15, 27]}\n    ],\n    \"complexes\": [\n      \"LPL–GPIHBP1 complex\"\n    ],\n    \"partners\": [\n      \"LPL\",\n      \"APOA5\",\n      \"ANGPTL4\",\n      \"ANGPTL3\",\n      \"APOC3\",\n      \"LMF1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}