{"gene":"LRAT","run_date":"2026-04-28T18:30:27","timeline":{"discoveries":[{"year":2005,"finding":"LRAT is the predominant enzyme responsible for physiological esterification of retinol in liver, lung, and kidney; Lrat-/- mice lack retinyl ester stores in these tissues and hepatic stellate cell lipid droplets, confirming LRAT's essential role. In adipose tissue, an acyl-CoA-dependent acyl-CoA:retinol acyltransferase (ARAT) compensates, as evidenced by the fatty acyl composition of chylomicron retinyl esters in Lrat-/- mice.","method":"Lrat knockout mouse model with tissue retinoid quantification, electron microscopy of stellate cells, and fatty acid composition analysis of retinyl esters","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — clean KO with multiple orthogonal readouts (biochemical quantification, EM, lipid analysis), replicated across tissues","pmids":["16115871"],"is_preprint":false},{"year":2014,"finding":"A specific LRAT-specific domain (LRAT-LD) confers substrate specificity to N1pC/P60 family enzymes. When swapped into HRASLS3, this domain causes three-dimensional domain-swapping dimerization and slows hydrolysis of the thioester catalytic intermediate, enabling efficient acyl transfer to retinol rather than phospholipid hydrolysis. A 2.2-Å crystal structure of the chimeric enzyme in a thioester intermediate state revealed the structural basis for this catalytic diversity.","method":"Gain-of-function domain-swap chimera, 2.2-Å crystal structure of thioester intermediate, in vitro enzymatic assays","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1 — crystal structure of catalytic intermediate combined with mutagenesis/chimera and in vitro activity assays","pmids":["25383759"],"is_preprint":false},{"year":2007,"finding":"LRAT is not required for the membrane association of RPE65 or its palmitoylation; RPE65 membrane affinity is similar in wild-type and Lrat-/- mice. LRAT is required for isomerase activity only insofar as it synthesizes the retinyl ester substrate: with all-trans-retinyl palmitate as substrate, isomerase activity is equivalent in both genotypes, but with all-trans-retinol, isomerase activity is undetectable in Lrat-/- RPE because retinyl esters are absent.","method":"Lrat-/- mouse biochemical fractionation, isomerase activity assays with defined substrates, mass spectrometry for palmitoylation, 2-bromopalmitate inhibition","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (KO mice, substrate-defined assays, MS, chemical inhibitor) in single rigorous study","pmids":["17504753"],"is_preprint":false},{"year":1998,"finding":"In bovine RPE, LRAT activity is exclusively localized to endoplasmic reticulum-enriched membranes, whereas 11-cis retinyl ester hydrolase (REH) is predominantly in plasma membrane fractions, establishing compartmentalized retinoid processing within RPE subcellular membranes.","method":"Subcellular membrane fractionation with ER and PM marker enrichment, enzymatic activity assays on fractions","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 — direct fractionation with functional enzyme assays, single lab","pmids":["9767084"],"is_preprint":false},{"year":2001,"finding":"Both LRAT and acyl-CoA:retinol acyltransferase (ARAT) activities are induced during conversion of hepatic stellate cell myofibroblasts to lipocytes. LRAT induction is dependent on retinoic acid, whereas ARAT induction depends on the overall fat-storing phenotype, demonstrating distinct transcriptional regulation of the two retinol esterifying enzymes.","method":"Microsomal enzyme kinetics, [3H]retinol metabolite analysis in GRX cell line and primary HSCs, retinoic acid treatment","journal":"The Journal of nutritional biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — enzyme kinetics in microsomal fractions with pharmacological dissection of LRAT vs. ARAT, single lab","pmids":["12031254"],"is_preprint":false},{"year":2007,"finding":"RPE-specific somatic ablation of Lrat strongly reduces all-trans retinyl ester synthesis in RPE cells and diminishes ERG light responses, confirming that LRAT in the RPE is the primary source of retinyl ester substrate for the visual cycle.","method":"Conditional Cre-lox knockout (Tyrp1-Cre driving RPE-specific Lrat deletion), retinoid HPLC quantification, ERG recordings","journal":"Investigative ophthalmology & visual science","confidence":"High","confidence_rationale":"Tier 2 — tissue-specific KO with biochemical and functional (ERG) readouts","pmids":["18055784"],"is_preprint":false},{"year":2013,"finding":"LRAT-catalyzed esterification of retinol is necessary for STRA6-mediated activation of JAK2/STAT5 signaling by holo-RBP. By maintaining an inward retinol concentration gradient, LRAT enables STRA6-mediated retinol transport, which in turn supports STRA6 cytokine receptor function. LRAT-null mice are protected from holo-RBP-induced suppression of insulin signaling.","method":"LRAT-null mice, cell-based STRA6/JAK2/STAT5 signaling assays, insulin response measurements","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 — genetic KO combined with defined signaling pathway readouts and in vivo metabolic phenotype","pmids":["24036882"],"is_preprint":false},{"year":2021,"finding":"LRAT's catalytic sequestration of retinol into retinyl esters coordinates the negative-feedback regulation of intestinal β-carotene conversion to vitamin A. In LRAT-deficient mice, the transcription factor ISX becomes hypersensitive to dietary vitamin A and suppresses β-carotene oxygenase-1, leading to β-carotene accumulation and extrahepatic vitamin A deficiency. Pharmacological inhibition of retinoid signaling or Isx gene deletion restores retinoid biosynthesis.","method":"Lrat-/- mice, pharmacological retinoid signaling inhibition, Isx-/- genetic epistasis, tissue retinoid quantification","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 2 — genetic and pharmacological epistasis with multiple KO models and biochemical endpoints","pmids":["33631212"],"is_preprint":false},{"year":2016,"finding":"In the absence of LRAT, quiescent hepatic stellate cells retain the capacity to synthesize retinyl esters via DGAT1, but lipid droplets are significantly smaller (median 1080 nm vs. 1618 nm in WT). During HSC activation, the cell shifts retinyl ester synthesis from LRAT to DGAT1, as shown by exogenous fatty acid incorporation into retinyl ester species.","method":"Lrat-/- primary HSC cultures, LC-MS/MS MRM quantification of retinyl ester species, lipid droplet size measurement","journal":"Biochimica et biophysica acta. Molecular and cell biology of lipids","confidence":"High","confidence_rationale":"Tier 1-2 — quantitative lipidomics with MRM, KO cells, morphometric analysis","pmids":["27815220"],"is_preprint":false},{"year":2017,"finding":"The LCA-associated E14L mutation in LRAT destabilizes the protein and causes accelerated proteasomal degradation. Despite reduced protein levels, some visual chromophore production persists in a cell-based assay. Instead, E14L expression leads to rapid increase in cellular retinoic acid upon retinoid supplementation, implicating retinoic acid toxicity in the disease pathology.","method":"Bicistronic LRAT(E14L)-EGFP expression for protein stability, proteasome inhibitor experiments, cell-based chromophore production assay, HPLC retinoid quantification","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — multiple biochemical methods in single lab; mutation in N-terminal membrane-interacting helix mechanistically characterized","pmids":["28758396"],"is_preprint":false},{"year":2015,"finding":"LRAT overexpression in murine melanoma B16F10 cells increases retinyl ester levels, reduces intracellular all-trans-retinol and ATRA, decreases RAR-regulated Cyp26a1 expression, and diminishes the antiproliferative effects of retinoid treatment, establishing that LRAT-catalyzed esterification diverts retinol away from retinoic acid signaling.","method":"Stable LRAT overexpression in B16F10 cells, HPLC retinoid quantification, cell viability assays, RT-PCR for Cyp26a1","journal":"Skin pharmacology and physiology","confidence":"Medium","confidence_rationale":"Tier 2-3 — overexpression with biochemical (HPLC) and functional readouts, single lab","pmids":["25721651"],"is_preprint":false},{"year":2024,"finding":"During early hepatic stellate cell activation, LRAT activity and retinyl ester formation are maintained while retinyl ester levels decline due to enhanced breakdown (hydrolysis). Only upon prolonged activation is LRAT activity lost, at which point residual retinyl ester synthesis shifts to DGAT1.","method":"HSCs cultured in soft gel (quiescent) vs. stiff plastic (activated), Lrat mRNA/protein quantification, LC-MS/MS retinyl ester analysis, comparison of RE synthesis and breakdown rates","journal":"Biochimica et biophysica acta. Molecular and cell biology of lipids","confidence":"Medium","confidence_rationale":"Tier 2 — quantitative lipidomics and gene expression in controlled culture model with clear temporal resolution","pmids":["39068984"],"is_preprint":false},{"year":2009,"finding":"Transcriptional regulation of the rat Lrat gene by retinoic acid (RA) requires a proximal promoter region (~300 bp upstream of TSS) containing essential basic elements (TATA box, SP3 site, AP-1 site, CAAT box); nuclear run-on assays confirmed transcriptional (not post-transcriptional) activation by RA. RAR/RXR receptors drive Lrat expression via this region despite absence of canonical retinoid response elements.","method":"Nuclear run-on transcription assay, luciferase reporter deletions in HEK293T and HepG2 cells, electrophoretic mobility shift assay with nuclear extracts","journal":"Archives of biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 2 — nuclear run-on confirms transcriptional mechanism; multiple promoter deletion constructs with EMSA","pmids":["19665987"],"is_preprint":false},{"year":2026,"finding":"LRAT enriches DHRS3 at endoplasmic reticulum–lipid droplet interfaces juxtaposed to mitochondria after irradiation; loss of LRAT disperses these organelle contacts, mislocalizes DHRS3, and impairs retinoid and NADPH buffering, contributing to radioresistance in esophageal squamous cell carcinoma.","method":"Spatial imaging (ER-LD-mitochondria contacts), LRAT knockdown/overexpression, DHRS3 mitochondrial targeting rescue, NADP+/NADPH measurement, ROS quantification, clonogenic survival","journal":"Free radical biology & medicine","confidence":"Low","confidence_rationale":"Tier 3 — mechanistic context is new (organelle contact scaffold role) but from single lab; imaging and biochemical evidence without structural validation","pmids":["41579973"],"is_preprint":false}],"current_model":"LRAT is an ER-membrane-localized N1pC/P60 thioester-intermediate acyltransferase that esterifies all-trans-retinol to retinyl esters using phosphatidylcholine as acyl donor; this activity is the predominant physiological route for vitamin A storage in liver, RPE, and other tissues, supplies the retinyl ester substrate required for the RPE65 visual cycle isomerase, supports STRA6/JAK2/STAT5 signaling by maintaining the intracellular retinol gradient, coordinates negative-feedback control of intestinal β-carotene conversion via ISX, and in hepatic stellate cells organizes lipid droplet size and retinoid homeostasis, with substrate specificity within the family determined by a discrete LRAT-specific domain that stabilizes the thioester intermediate to favor acyl transfer over hydrolysis."},"narrative":{"teleology":[{"year":1998,"claim":"Establishing that LRAT activity resides exclusively in ER membranes of RPE provided the first subcellular framework for compartmentalized retinoid processing in the visual cycle.","evidence":"Subcellular membrane fractionation with ER/PM markers and enzymatic activity assays in bovine RPE","pmids":["9767084"],"confidence":"Medium","gaps":["Single tissue source (bovine RPE); generalizability to other LRAT-expressing tissues not tested","Protein identity not confirmed by immunodetection in fractions"]},{"year":2001,"claim":"Demonstrating that LRAT induction in hepatic stellate cells is retinoic acid-dependent and distinct from ARAT regulation established that two retinol-esterifying activities are under separate transcriptional control during lipocyte differentiation.","evidence":"Microsomal enzyme kinetics and [³H]retinol metabolite analysis in GRX cells and primary HSCs with retinoic acid treatment","pmids":["12031254"],"confidence":"Medium","gaps":["Transcriptional mechanism not defined; no promoter analysis performed","ARAT molecular identity not established at this time"]},{"year":2005,"claim":"The Lrat knockout mouse resolved a long-standing question by showing that LRAT is the predominant retinol esterifying enzyme in vivo, with near-complete loss of retinyl ester stores in liver, lung, kidney, and stellate cell lipid droplets; an alternative ARAT pathway compensates only in adipose tissue.","evidence":"Lrat-/- mice with multi-tissue retinoid HPLC quantification, electron microscopy of stellate cells, fatty acid composition analysis","pmids":["16115871"],"confidence":"High","gaps":["Molecular identity of the compensatory ARAT activity not resolved","Contribution of LRAT to retinyl ester formation in intestine not fully defined"]},{"year":2007,"claim":"Two complementary studies established that LRAT is required for the visual cycle solely as the source of the retinyl ester substrate for RPE65 isomerase, not for RPE65 membrane association, and that RPE-specific Lrat ablation diminishes ERG responses.","evidence":"Lrat-/- biochemical fractionation with substrate-defined isomerase assays; conditional RPE-specific Lrat knockout with ERG and retinoid HPLC","pmids":["17504753","18055784"],"confidence":"High","gaps":["Whether residual non-LRAT esterification in RPE can sustain any visual cycle flux remains unclear","Kinetic coupling between LRAT and RPE65 at the ER membrane not characterized"]},{"year":2009,"claim":"Identification of the proximal promoter elements driving retinoic acid-dependent Lrat transcription showed that RAR/RXR activate Lrat through non-canonical regulatory elements (SP3, AP-1, CAAT) rather than classical retinoid response elements.","evidence":"Nuclear run-on, luciferase reporter deletions, and EMSA in HEK293T and HepG2 cells","pmids":["19665987"],"confidence":"Medium","gaps":["Intermediary factors bridging RAR/RXR to the proximal promoter not identified","In vivo chromatin occupancy not tested"]},{"year":2013,"claim":"Linking LRAT to STRA6/JAK2/STAT5 signaling expanded its role beyond retinoid storage to active signal transduction: LRAT-driven retinol uptake is required for STRA6 to function as a cytokine receptor, and Lrat-null mice are protected from holo-RBP-induced insulin resistance.","evidence":"Lrat-null mice, cell-based STRA6/JAK2/STAT5 signaling assays, and insulin response measurements","pmids":["24036882"],"confidence":"High","gaps":["Whether LRAT physically associates with STRA6 or acts purely through metabolic gradient not resolved","Tissue-specific contribution of LRAT to STRA6 signaling beyond the examined systems unknown"]},{"year":2014,"claim":"A 2.2-Å crystal structure of a LRAT-domain chimera in the thioester intermediate state revealed how a discrete LRAT-specific domain confers acyltransferase specificity within the N1pC/P60 family by promoting domain-swapping dimerization that slows thioester hydrolysis.","evidence":"Gain-of-function domain-swap chimera (LRAT-LD into HRASLS3), 2.2-Å crystal structure, in vitro enzymatic assays","pmids":["25383759"],"confidence":"High","gaps":["Structure is of a chimeric protein, not full-length LRAT; native LRAT structure unavailable","Membrane-associated conformation and retinol binding geometry not determined"]},{"year":2015,"claim":"Demonstrating that LRAT overexpression diverts retinol away from retinoic acid synthesis confirmed a metabolic branch-point function: LRAT activity attenuates RAR-regulated gene expression and the antiproliferative effects of retinoids.","evidence":"Stable LRAT overexpression in B16F10 melanoma cells, HPLC retinoid quantification, RT-PCR for Cyp26a1","pmids":["25721651"],"confidence":"Medium","gaps":["Overexpression system; physiological relevance of the branch-point ratio in non-transformed cells not established","No loss-of-function complement in the same system"]},{"year":2016,"claim":"Quantitative lipidomics in Lrat-/- hepatic stellate cells showed that DGAT1 provides a compensatory retinyl ester synthesis pathway but produces smaller lipid droplets, establishing that LRAT determines lipid droplet size and the specific retinyl ester species profile.","evidence":"Lrat-/- primary HSC cultures, LC-MS/MS MRM retinyl ester quantification, lipid droplet morphometry","pmids":["27815220"],"confidence":"High","gaps":["Mechanism by which LRAT-derived esters promote larger droplets (biophysical or protein-scaffolding) not defined","In vivo hepatic stellate cell activation dynamics not captured in culture"]},{"year":2017,"claim":"Characterization of the LCA-associated E14L mutation showed it destabilizes LRAT protein via proteasomal degradation and paradoxically increases retinoic acid accumulation, suggesting that disease pathology involves retinoic acid toxicity rather than simple loss of chromophore production.","evidence":"Bicistronic LRAT(E14L)-EGFP stability assays, proteasome inhibitor experiments, cell-based chromophore production and HPLC retinoid quantification","pmids":["28758396"],"confidence":"Medium","gaps":["Retinoic acid toxicity mechanism not validated in vivo","Whether other LCA-associated LRAT mutations share this gain-of-toxicity pathomechanism unknown"]},{"year":2021,"claim":"Genetic epistasis between Lrat and Isx revealed that LRAT-mediated retinol sequestration coordinates intestinal β-carotene absorption through a negative-feedback loop: without LRAT, ISX becomes hypersensitive to dietary vitamin A and suppresses β-carotene oxygenase, causing extrahepatic vitamin A deficiency.","evidence":"Lrat-/- mice, Isx-/- double-knockout epistasis, pharmacological retinoid signaling inhibition, tissue retinoid quantification","pmids":["33631212"],"confidence":"High","gaps":["Whether LRAT in enterocytes directly esterifies retinol or acts indirectly through circulating retinoid pool not fully separated","Quantitative contribution of this feedback loop relative to hepatic retinoid homeostasis not established"]},{"year":2024,"claim":"Temporal profiling of stellate cell activation resolved that early activation maintains LRAT activity while increasing retinyl ester hydrolysis, with LRAT loss and DGAT1 compensation occurring only during prolonged activation.","evidence":"HSCs cultured on soft gel vs. stiff substrates, Lrat mRNA/protein kinetics, LC-MS/MS retinyl ester analysis","pmids":["39068984"],"confidence":"Medium","gaps":["In vivo validation of the two-phase model in liver fibrosis progression not performed","Identity of the hydrolase(s) responsible for early retinyl ester breakdown not determined"]},{"year":null,"claim":"A full-length structure of membrane-embedded LRAT, the identity and regulation of the retinyl ester hydrolase(s) that oppose LRAT activity, and whether LRAT has a direct protein-scaffolding role at ER–lipid droplet contacts remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structure of full-length, membrane-associated LRAT is available","Retinyl ester hydrolase opposing LRAT in stellate cells and RPE molecularly unidentified","Proposed ER–lipid droplet contact site scaffolding role (PMID:41579973) is from a single study and awaits independent confirmation"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1,2,5,8]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[3]},{"term_id":"GO:0005811","term_label":"lipid droplet","supporting_discovery_ids":[0,8]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,1,2,7,8]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6]},{"term_id":"R-HSA-9709957","term_label":"Sensory Perception","supporting_discovery_ids":[2,5]}],"complexes":[],"partners":["RPE65","STRA6","DGAT1","ISX","DHRS3","HRASLS3"],"other_free_text":[]},"mechanistic_narrative":"LRAT is an endoplasmic reticulum-localized acyltransferase of the N1pC/P60 thioester-intermediate family that catalyzes the esterification of all-trans-retinol using phosphatidylcholine as acyl donor, serving as the predominant physiological route for vitamin A storage in liver, lung, kidney, and retinal pigment epithelium [PMID:16115871, PMID:18055784]. Its catalytic specificity arises from a discrete LRAT-specific domain that promotes domain-swapping dimerization and stabilizes the thioester intermediate to favor acyl transfer over hydrolysis [PMID:25383759]. By generating retinyl esters, LRAT supplies the obligate substrate for the RPE65 visual-cycle isomerase [PMID:17504753], maintains the retinol concentration gradient required for STRA6/JAK2/STAT5 signaling [PMID:24036882], coordinates ISX-mediated negative-feedback control of intestinal β-carotene conversion [PMID:33631212], and governs lipid droplet size and retinoid homeostasis in hepatic stellate cells [PMID:27815220, PMID:39068984]. Loss-of-function mutations such as E14L cause Leber congenital amaurosis through protein destabilization and aberrant retinoic acid accumulation [PMID:28758396]."},"prefetch_data":{"uniprot":{"accession":"O95237","full_name":"Lecithin retinol acyltransferase","aliases":["Phosphatidylcholine--retinol O-acyltransferase"],"length_aa":230,"mass_kda":25.7,"function":"Transfers the acyl group from the sn-1 position of phosphatidylcholine to all-trans retinol, producing all-trans retinyl esters (PubMed:9920938). Retinyl esters are storage forms of vitamin A (Probable). LRAT plays a critical role in vision (Probable). It provides the all-trans retinyl ester substrates for the isomerohydrolase which processes the esters into 11-cis-retinol in the retinal pigment epithelium; due to a membrane-associated alcohol dehydrogenase, 11 cis-retinol is oxidized and converted into 11-cis-retinaldehyde which is the chromophore for rhodopsin and the cone photopigments (Probable). Required for the survival of cone photoreceptors and correct rod photoreceptor cell morphology (By similarity)","subcellular_location":"Endoplasmic reticulum membrane; Rough endoplasmic reticulum; Endosome, multivesicular body; Cytoplasm, perinuclear region","url":"https://www.uniprot.org/uniprotkb/O95237/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/LRAT","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/LRAT","total_profiled":1310},"omim":[{"mim_id":"613341","title":"LEBER CONGENITAL AMAUROSIS 14; LCA14","url":"https://www.omim.org/entry/613341"},{"mim_id":"611474","title":"PHOSPHOLIPASE A AND ACYLTRANSFERASE 5; PLAAT5","url":"https://www.omim.org/entry/611474"},{"mim_id":"611234","title":"LRAT DOMAIN-CONTAINING PROTEIN 1; LRATD1","url":"https://www.omim.org/entry/611234"},{"mim_id":"610745","title":"STIMULATED BY RETINOIC ACID 6; STRA6","url":"https://www.omim.org/entry/610745"},{"mim_id":"610113","title":"ADAMTS-LIKE PROTEIN 4; ADAMTSL4","url":"https://www.omim.org/entry/610113"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Endoplasmic reticulum","reliability":"Approved"},{"location":"Golgi apparatus","reliability":"Approved"},{"location":"Plasma membrane","reliability":"Additional"},{"location":"Basal body","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"brain","ntpm":1.9},{"tissue":"liver","ntpm":2.0}],"url":"https://www.proteinatlas.org/search/LRAT"},"hgnc":{"alias_symbol":["LCA14"],"prev_symbol":[]},"alphafold":{"accession":"O95237","domains":[{"cath_id":"3.90.1720.10","chopping":"40-175","consensus_level":"high","plddt":92.4093,"start":40,"end":175},{"cath_id":"1.10.287","chopping":"191-228","consensus_level":"high","plddt":82.9987,"start":191,"end":228}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O95237","model_url":"https://alphafold.ebi.ac.uk/files/AF-O95237-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O95237-F1-predicted_aligned_error_v6.png","plddt_mean":83.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=LRAT","jax_strain_url":"https://www.jax.org/strain/search?query=LRAT"},"sequence":{"accession":"O95237","fasta_url":"https://rest.uniprot.org/uniprotkb/O95237.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O95237/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O95237"}},"corpus_meta":[{"pmid":"16115871","id":"PMC_16115871","title":"Retinoid absorption and storage is impaired in mice lacking lecithin:retinol acyltransferase (LRAT).","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16115871","citation_count":249,"is_preprint":false},{"pmid":"26656277","id":"PMC_26656277","title":"Safety and Proof-of-Concept Study of Oral QLT091001 in Retinitis Pigmentosa Due to Inherited Deficiencies of Retinal Pigment Epithelial 65 Protein (RPE65) or Lecithin:Retinol Acyltransferase (LRAT).","date":"2015","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/26656277","citation_count":58,"is_preprint":false},{"pmid":"25383759","id":"PMC_25383759","title":"LRAT-specific domain facilitates vitamin A metabolism by domain swapping in HRASLS3.","date":"2014","source":"Nature chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/25383759","citation_count":49,"is_preprint":false},{"pmid":"19700416","id":"PMC_19700416","title":"Acidic retinoids synergize with vitamin A to enhance retinol uptake and STRA6, LRAT, and CYP26B1 expression in neonatal lung.","date":"2009","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/19700416","citation_count":44,"is_preprint":false},{"pmid":"17504753","id":"PMC_17504753","title":"Role of LRAT on the retinoid isomerase activity and membrane association of Rpe65.","date":"2007","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17504753","citation_count":40,"is_preprint":false},{"pmid":"22559933","id":"PMC_22559933","title":"A homozygous frameshift mutation in LRAT causes retinitis punctata albescens.","date":"2012","source":"Ophthalmology","url":"https://pubmed.ncbi.nlm.nih.gov/22559933","citation_count":37,"is_preprint":false},{"pmid":"22570351","id":"PMC_22570351","title":"Early onset retinal dystrophy due to mutations in LRAT: molecular analysis and detailed phenotypic study.","date":"2012","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/22570351","citation_count":35,"is_preprint":false},{"pmid":"17011878","id":"PMC_17011878","title":"Screening genes of the retinoid metabolism: novel LRAT mutation in leber congenital amaurosis.","date":"2006","source":"American journal of ophthalmology","url":"https://pubmed.ncbi.nlm.nih.gov/17011878","citation_count":34,"is_preprint":false},{"pmid":"27815220","id":"PMC_27815220","title":"Hepatic stellate cells retain the capacity to synthesize retinyl esters and to store neutral lipids in small lipid droplets in the absence of LRAT.","date":"2016","source":"Biochimica et biophysica acta. Molecular and cell biology of lipids","url":"https://pubmed.ncbi.nlm.nih.gov/27815220","citation_count":30,"is_preprint":false},{"pmid":"33631212","id":"PMC_33631212","title":"LRAT coordinates the negative-feedback regulation of intestinal retinoid biosynthesis from β-carotene.","date":"2021","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/33631212","citation_count":29,"is_preprint":false},{"pmid":"18055784","id":"PMC_18055784","title":"Somatic ablation of the Lrat gene in the mouse retinal pigment epithelium drastically reduces its retinoid storage.","date":"2007","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/18055784","citation_count":27,"is_preprint":false},{"pmid":"24036882","id":"PMC_24036882","title":"The retinol esterifying enzyme LRAT supports cell signaling by retinol-binding protein and its receptor STRA6.","date":"2013","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/24036882","citation_count":23,"is_preprint":false},{"pmid":"9767084","id":"PMC_9767084","title":"Distribution of 11-cis LRAT, 11-cis RD and 11-cis REH in bovine retinal pigment epithelium membranes.","date":"1998","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/9767084","citation_count":22,"is_preprint":false},{"pmid":"12031254","id":"PMC_12031254","title":"Acyl-CoA: retinol acyltransferase (ARAT) and lecithin:retinol acyltransferase (LRAT) activation during the lipocyte phenotype induction in hepatic stellate cells.","date":"2001","source":"The Journal of nutritional biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12031254","citation_count":22,"is_preprint":false},{"pmid":"19665987","id":"PMC_19665987","title":"An essential set of basic DNA response elements is required for receptor-dependent transcription of the lecithin:retinol acyltransferase (Lrat) gene.","date":"2009","source":"Archives of biochemistry and biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/19665987","citation_count":19,"is_preprint":false},{"pmid":"31448181","id":"PMC_31448181","title":"Long-Term Follow-Up of Retinal Degenerations Associated With LRAT Mutations and Their Comparability to Phenotypes Associated With RPE65 Mutations.","date":"2019","source":"Translational vision science & technology","url":"https://pubmed.ncbi.nlm.nih.gov/31448181","citation_count":18,"is_preprint":false},{"pmid":"12524014","id":"PMC_12524014","title":"Retinoid metabolism (LRAT, REH) in the yolk-sac membrane of Japanese quail eggs and effects of mono-ortho-PCBs.","date":"2003","source":"Comparative biochemistry and physiology. Toxicology & pharmacology : CBP","url":"https://pubmed.ncbi.nlm.nih.gov/12524014","citation_count":16,"is_preprint":false},{"pmid":"21268677","id":"PMC_21268677","title":"Why some photoreceptors die, while others remain dormant: lessons from RPE65 and LRAT associated retinal dystrophies.","date":"2011","source":"Ophthalmic genetics","url":"https://pubmed.ncbi.nlm.nih.gov/21268677","citation_count":15,"is_preprint":false},{"pmid":"33052059","id":"PMC_33052059","title":"Vitamin A deficiency indicating as low expression of LRAT may be a novel biomarker of primary hypertension.","date":"2020","source":"Clinical and experimental hypertension (New York, N.Y. : 1993)","url":"https://pubmed.ncbi.nlm.nih.gov/33052059","citation_count":15,"is_preprint":false},{"pmid":"29973277","id":"PMC_29973277","title":"A novel LRAT mutation affecting splicing in a family with early onset retinitis pigmentosa.","date":"2018","source":"Human genomics","url":"https://pubmed.ncbi.nlm.nih.gov/29973277","citation_count":14,"is_preprint":false},{"pmid":"12739853","id":"PMC_12739853","title":"Retinoids, LRAT and REH activities in eggs of Japanese quail following maternal and in ovo exposures to 3,3',4,4'-tetrachlorobiphenyl.","date":"2003","source":"Ecotoxicology (London, England)","url":"https://pubmed.ncbi.nlm.nih.gov/12739853","citation_count":14,"is_preprint":false},{"pmid":"16234259","id":"PMC_16234259","title":"Evidence that sequence homologous region in LRAT-like proteins possesses anti-proliferative activity and DNA binding properties: translational implications and mechanism of action.","date":"2005","source":"Carcinogenesis","url":"https://pubmed.ncbi.nlm.nih.gov/16234259","citation_count":13,"is_preprint":false},{"pmid":"28758396","id":"PMC_28758396","title":"Impact of LCA-Associated E14L LRAT Mutation on Protein Stability and Retinoid Homeostasis.","date":"2017","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/28758396","citation_count":12,"is_preprint":false},{"pmid":"34281288","id":"PMC_34281288","title":"The Lrat-/- Rat: CRISPR/Cas9 Construction and Phenotyping of a New Animal Model for Retinitis Pigmentosa.","date":"2021","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/34281288","citation_count":11,"is_preprint":false},{"pmid":"25260806","id":"PMC_25260806","title":"High incidence of LRAT promoter hypermethylation in colorectal cancer correlates with tumor stage.","date":"2014","source":"Medical oncology (Northwood, London, England)","url":"https://pubmed.ncbi.nlm.nih.gov/25260806","citation_count":11,"is_preprint":false},{"pmid":"23890161","id":"PMC_23890161","title":"Hepatic stellate cells that coexpress LRAT and CRBP-1 partially contribute to portal fibrogenesis in patients with human viral hepatitis.","date":"2013","source":"Liver international : official journal of the International Association for the Study of the Liver","url":"https://pubmed.ncbi.nlm.nih.gov/23890161","citation_count":11,"is_preprint":false},{"pmid":"36181700","id":"PMC_36181700","title":"Emergence of highly profibrotic and proinflammatory Lrat+Fbln2+ HSC subpopulation in alcoholic hepatitis.","date":"2022","source":"Hepatology (Baltimore, Md.)","url":"https://pubmed.ncbi.nlm.nih.gov/36181700","citation_count":9,"is_preprint":false},{"pmid":"25721651","id":"PMC_25721651","title":"LRAT overexpression diminishes intracellular levels of biologically active retinoids and reduces retinoid antitumor efficacy in the murine melanoma B16F10 cell line.","date":"2015","source":"Skin pharmacology and physiology","url":"https://pubmed.ncbi.nlm.nih.gov/25721651","citation_count":9,"is_preprint":false},{"pmid":"38002575","id":"PMC_38002575","title":"Fundus Albipunctatus Associated with Biallelic LRAT Gene Mutation: A Case Report with Long-Term Follow-Up.","date":"2023","source":"Journal of clinical medicine","url":"https://pubmed.ncbi.nlm.nih.gov/38002575","citation_count":4,"is_preprint":false},{"pmid":"39068984","id":"PMC_39068984","title":"Early activation of hepatic stellate cells induces rapid initiation of retinyl ester breakdown while maintaining lecithin:retinol acyltransferase (LRAT) activity.","date":"2024","source":"Biochimica et biophysica acta. Molecular and cell biology of lipids","url":"https://pubmed.ncbi.nlm.nih.gov/39068984","citation_count":4,"is_preprint":false},{"pmid":"36768627","id":"PMC_36768627","title":"The BCO2 Genotype and the Expression of BCO1, BCO2, LRAT, and TTPA Genes in the Adipose Tissue and Brain of Rabbits Fed a Diet with Marigold Flower Extract.","date":"2023","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/36768627","citation_count":3,"is_preprint":false},{"pmid":"25317684","id":"PMC_25317684","title":"Transgenic reporter mice with promoter region of murine LRAT specifically marks lens and meiosis spermatocytes.","date":"2014","source":"Physiological research","url":"https://pubmed.ncbi.nlm.nih.gov/25317684","citation_count":2,"is_preprint":false},{"pmid":"40394841","id":"PMC_40394841","title":"Genetic detection of a novel LRAT pathogenic variant in patients with early-onset severe retinal dystrophy.","date":"2025","source":"Ophthalmic genetics","url":"https://pubmed.ncbi.nlm.nih.gov/40394841","citation_count":0,"is_preprint":false},{"pmid":"41044262","id":"PMC_41044262","title":"tRF-34-86J8WPMN1E8Y2Q promotes the occurrence and development of gastric cancer by combining with LRAT.","date":"2025","source":"Journal of cancer research and clinical oncology","url":"https://pubmed.ncbi.nlm.nih.gov/41044262","citation_count":0,"is_preprint":false},{"pmid":"41542649","id":"PMC_41542649","title":"Lrat-Cre Exhibits Widespread Expression Beyond Hepatic Stellate Cells Across Multiple Tissues.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41542649","citation_count":0,"is_preprint":false},{"pmid":"41807804","id":"PMC_41807804","title":"AAV-mediated gene replacement therapy for LRAT-associated retinitis pigmentosa: a proof-of-concept study in a patient-based rat model.","date":"2026","source":"Gene therapy","url":"https://pubmed.ncbi.nlm.nih.gov/41807804","citation_count":0,"is_preprint":false},{"pmid":"41579973","id":"PMC_41579973","title":"YTHDF2-m6A regulation of DHRS3 at LRAT-organized organelle contacts orchestrates redox to drive radioresistance in esophageal squamous cell carcinoma.","date":"2026","source":"Free radical biology & medicine","url":"https://pubmed.ncbi.nlm.nih.gov/41579973","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":20939,"output_tokens":3695,"usd":0.059121},"stage2":{"model":"claude-opus-4-6","input_tokens":7100,"output_tokens":3279,"usd":0.176212},"total_usd":0.235333,"stage1_batch_id":"msgbatch_01Mgbec4vM6c9vXht7JVJzss","stage2_batch_id":"msgbatch_01JkuuH5RB2BdJNsgnhjbC6s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2005,\n      \"finding\": \"LRAT is the predominant enzyme responsible for physiological esterification of retinol in liver, lung, and kidney; Lrat-/- mice lack retinyl ester stores in these tissues and hepatic stellate cell lipid droplets, confirming LRAT's essential role. In adipose tissue, an acyl-CoA-dependent acyl-CoA:retinol acyltransferase (ARAT) compensates, as evidenced by the fatty acyl composition of chylomicron retinyl esters in Lrat-/- mice.\",\n      \"method\": \"Lrat knockout mouse model with tissue retinoid quantification, electron microscopy of stellate cells, and fatty acid composition analysis of retinyl esters\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple orthogonal readouts (biochemical quantification, EM, lipid analysis), replicated across tissues\",\n      \"pmids\": [\"16115871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"A specific LRAT-specific domain (LRAT-LD) confers substrate specificity to N1pC/P60 family enzymes. When swapped into HRASLS3, this domain causes three-dimensional domain-swapping dimerization and slows hydrolysis of the thioester catalytic intermediate, enabling efficient acyl transfer to retinol rather than phospholipid hydrolysis. A 2.2-Å crystal structure of the chimeric enzyme in a thioester intermediate state revealed the structural basis for this catalytic diversity.\",\n      \"method\": \"Gain-of-function domain-swap chimera, 2.2-Å crystal structure of thioester intermediate, in vitro enzymatic assays\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure of catalytic intermediate combined with mutagenesis/chimera and in vitro activity assays\",\n      \"pmids\": [\"25383759\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"LRAT is not required for the membrane association of RPE65 or its palmitoylation; RPE65 membrane affinity is similar in wild-type and Lrat-/- mice. LRAT is required for isomerase activity only insofar as it synthesizes the retinyl ester substrate: with all-trans-retinyl palmitate as substrate, isomerase activity is equivalent in both genotypes, but with all-trans-retinol, isomerase activity is undetectable in Lrat-/- RPE because retinyl esters are absent.\",\n      \"method\": \"Lrat-/- mouse biochemical fractionation, isomerase activity assays with defined substrates, mass spectrometry for palmitoylation, 2-bromopalmitate inhibition\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (KO mice, substrate-defined assays, MS, chemical inhibitor) in single rigorous study\",\n      \"pmids\": [\"17504753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"In bovine RPE, LRAT activity is exclusively localized to endoplasmic reticulum-enriched membranes, whereas 11-cis retinyl ester hydrolase (REH) is predominantly in plasma membrane fractions, establishing compartmentalized retinoid processing within RPE subcellular membranes.\",\n      \"method\": \"Subcellular membrane fractionation with ER and PM marker enrichment, enzymatic activity assays on fractions\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct fractionation with functional enzyme assays, single lab\",\n      \"pmids\": [\"9767084\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Both LRAT and acyl-CoA:retinol acyltransferase (ARAT) activities are induced during conversion of hepatic stellate cell myofibroblasts to lipocytes. LRAT induction is dependent on retinoic acid, whereas ARAT induction depends on the overall fat-storing phenotype, demonstrating distinct transcriptional regulation of the two retinol esterifying enzymes.\",\n      \"method\": \"Microsomal enzyme kinetics, [3H]retinol metabolite analysis in GRX cell line and primary HSCs, retinoic acid treatment\",\n      \"journal\": \"The Journal of nutritional biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — enzyme kinetics in microsomal fractions with pharmacological dissection of LRAT vs. ARAT, single lab\",\n      \"pmids\": [\"12031254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"RPE-specific somatic ablation of Lrat strongly reduces all-trans retinyl ester synthesis in RPE cells and diminishes ERG light responses, confirming that LRAT in the RPE is the primary source of retinyl ester substrate for the visual cycle.\",\n      \"method\": \"Conditional Cre-lox knockout (Tyrp1-Cre driving RPE-specific Lrat deletion), retinoid HPLC quantification, ERG recordings\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — tissue-specific KO with biochemical and functional (ERG) readouts\",\n      \"pmids\": [\"18055784\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"LRAT-catalyzed esterification of retinol is necessary for STRA6-mediated activation of JAK2/STAT5 signaling by holo-RBP. By maintaining an inward retinol concentration gradient, LRAT enables STRA6-mediated retinol transport, which in turn supports STRA6 cytokine receptor function. LRAT-null mice are protected from holo-RBP-induced suppression of insulin signaling.\",\n      \"method\": \"LRAT-null mice, cell-based STRA6/JAK2/STAT5 signaling assays, insulin response measurements\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO combined with defined signaling pathway readouts and in vivo metabolic phenotype\",\n      \"pmids\": [\"24036882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"LRAT's catalytic sequestration of retinol into retinyl esters coordinates the negative-feedback regulation of intestinal β-carotene conversion to vitamin A. In LRAT-deficient mice, the transcription factor ISX becomes hypersensitive to dietary vitamin A and suppresses β-carotene oxygenase-1, leading to β-carotene accumulation and extrahepatic vitamin A deficiency. Pharmacological inhibition of retinoid signaling or Isx gene deletion restores retinoid biosynthesis.\",\n      \"method\": \"Lrat-/- mice, pharmacological retinoid signaling inhibition, Isx-/- genetic epistasis, tissue retinoid quantification\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic and pharmacological epistasis with multiple KO models and biochemical endpoints\",\n      \"pmids\": [\"33631212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In the absence of LRAT, quiescent hepatic stellate cells retain the capacity to synthesize retinyl esters via DGAT1, but lipid droplets are significantly smaller (median 1080 nm vs. 1618 nm in WT). During HSC activation, the cell shifts retinyl ester synthesis from LRAT to DGAT1, as shown by exogenous fatty acid incorporation into retinyl ester species.\",\n      \"method\": \"Lrat-/- primary HSC cultures, LC-MS/MS MRM quantification of retinyl ester species, lipid droplet size measurement\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular and cell biology of lipids\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — quantitative lipidomics with MRM, KO cells, morphometric analysis\",\n      \"pmids\": [\"27815220\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The LCA-associated E14L mutation in LRAT destabilizes the protein and causes accelerated proteasomal degradation. Despite reduced protein levels, some visual chromophore production persists in a cell-based assay. Instead, E14L expression leads to rapid increase in cellular retinoic acid upon retinoid supplementation, implicating retinoic acid toxicity in the disease pathology.\",\n      \"method\": \"Bicistronic LRAT(E14L)-EGFP expression for protein stability, proteasome inhibitor experiments, cell-based chromophore production assay, HPLC retinoid quantification\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple biochemical methods in single lab; mutation in N-terminal membrane-interacting helix mechanistically characterized\",\n      \"pmids\": [\"28758396\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"LRAT overexpression in murine melanoma B16F10 cells increases retinyl ester levels, reduces intracellular all-trans-retinol and ATRA, decreases RAR-regulated Cyp26a1 expression, and diminishes the antiproliferative effects of retinoid treatment, establishing that LRAT-catalyzed esterification diverts retinol away from retinoic acid signaling.\",\n      \"method\": \"Stable LRAT overexpression in B16F10 cells, HPLC retinoid quantification, cell viability assays, RT-PCR for Cyp26a1\",\n      \"journal\": \"Skin pharmacology and physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — overexpression with biochemical (HPLC) and functional readouts, single lab\",\n      \"pmids\": [\"25721651\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"During early hepatic stellate cell activation, LRAT activity and retinyl ester formation are maintained while retinyl ester levels decline due to enhanced breakdown (hydrolysis). Only upon prolonged activation is LRAT activity lost, at which point residual retinyl ester synthesis shifts to DGAT1.\",\n      \"method\": \"HSCs cultured in soft gel (quiescent) vs. stiff plastic (activated), Lrat mRNA/protein quantification, LC-MS/MS retinyl ester analysis, comparison of RE synthesis and breakdown rates\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular and cell biology of lipids\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — quantitative lipidomics and gene expression in controlled culture model with clear temporal resolution\",\n      \"pmids\": [\"39068984\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Transcriptional regulation of the rat Lrat gene by retinoic acid (RA) requires a proximal promoter region (~300 bp upstream of TSS) containing essential basic elements (TATA box, SP3 site, AP-1 site, CAAT box); nuclear run-on assays confirmed transcriptional (not post-transcriptional) activation by RA. RAR/RXR receptors drive Lrat expression via this region despite absence of canonical retinoid response elements.\",\n      \"method\": \"Nuclear run-on transcription assay, luciferase reporter deletions in HEK293T and HepG2 cells, electrophoretic mobility shift assay with nuclear extracts\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — nuclear run-on confirms transcriptional mechanism; multiple promoter deletion constructs with EMSA\",\n      \"pmids\": [\"19665987\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"LRAT enriches DHRS3 at endoplasmic reticulum–lipid droplet interfaces juxtaposed to mitochondria after irradiation; loss of LRAT disperses these organelle contacts, mislocalizes DHRS3, and impairs retinoid and NADPH buffering, contributing to radioresistance in esophageal squamous cell carcinoma.\",\n      \"method\": \"Spatial imaging (ER-LD-mitochondria contacts), LRAT knockdown/overexpression, DHRS3 mitochondrial targeting rescue, NADP+/NADPH measurement, ROS quantification, clonogenic survival\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — mechanistic context is new (organelle contact scaffold role) but from single lab; imaging and biochemical evidence without structural validation\",\n      \"pmids\": [\"41579973\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"LRAT is an ER-membrane-localized N1pC/P60 thioester-intermediate acyltransferase that esterifies all-trans-retinol to retinyl esters using phosphatidylcholine as acyl donor; this activity is the predominant physiological route for vitamin A storage in liver, RPE, and other tissues, supplies the retinyl ester substrate required for the RPE65 visual cycle isomerase, supports STRA6/JAK2/STAT5 signaling by maintaining the intracellular retinol gradient, coordinates negative-feedback control of intestinal β-carotene conversion via ISX, and in hepatic stellate cells organizes lipid droplet size and retinoid homeostasis, with substrate specificity within the family determined by a discrete LRAT-specific domain that stabilizes the thioester intermediate to favor acyl transfer over hydrolysis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"LRAT is an endoplasmic reticulum-localized acyltransferase of the N1pC/P60 thioester-intermediate family that catalyzes the esterification of all-trans-retinol using phosphatidylcholine as acyl donor, serving as the predominant physiological route for vitamin A storage in liver, lung, kidney, and retinal pigment epithelium [PMID:16115871, PMID:18055784]. Its catalytic specificity arises from a discrete LRAT-specific domain that promotes domain-swapping dimerization and stabilizes the thioester intermediate to favor acyl transfer over hydrolysis [PMID:25383759]. By generating retinyl esters, LRAT supplies the obligate substrate for the RPE65 visual-cycle isomerase [PMID:17504753], maintains the retinol concentration gradient required for STRA6/JAK2/STAT5 signaling [PMID:24036882], coordinates ISX-mediated negative-feedback control of intestinal β-carotene conversion [PMID:33631212], and governs lipid droplet size and retinoid homeostasis in hepatic stellate cells [PMID:27815220, PMID:39068984]. Loss-of-function mutations such as E14L cause Leber congenital amaurosis through protein destabilization and aberrant retinoic acid accumulation [PMID:28758396].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Establishing that LRAT activity resides exclusively in ER membranes of RPE provided the first subcellular framework for compartmentalized retinoid processing in the visual cycle.\",\n      \"evidence\": \"Subcellular membrane fractionation with ER/PM markers and enzymatic activity assays in bovine RPE\",\n      \"pmids\": [\"9767084\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single tissue source (bovine RPE); generalizability to other LRAT-expressing tissues not tested\",\n        \"Protein identity not confirmed by immunodetection in fractions\"\n      ]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Demonstrating that LRAT induction in hepatic stellate cells is retinoic acid-dependent and distinct from ARAT regulation established that two retinol-esterifying activities are under separate transcriptional control during lipocyte differentiation.\",\n      \"evidence\": \"Microsomal enzyme kinetics and [³H]retinol metabolite analysis in GRX cells and primary HSCs with retinoic acid treatment\",\n      \"pmids\": [\"12031254\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Transcriptional mechanism not defined; no promoter analysis performed\",\n        \"ARAT molecular identity not established at this time\"\n      ]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"The Lrat knockout mouse resolved a long-standing question by showing that LRAT is the predominant retinol esterifying enzyme in vivo, with near-complete loss of retinyl ester stores in liver, lung, kidney, and stellate cell lipid droplets; an alternative ARAT pathway compensates only in adipose tissue.\",\n      \"evidence\": \"Lrat-/- mice with multi-tissue retinoid HPLC quantification, electron microscopy of stellate cells, fatty acid composition analysis\",\n      \"pmids\": [\"16115871\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular identity of the compensatory ARAT activity not resolved\",\n        \"Contribution of LRAT to retinyl ester formation in intestine not fully defined\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Two complementary studies established that LRAT is required for the visual cycle solely as the source of the retinyl ester substrate for RPE65 isomerase, not for RPE65 membrane association, and that RPE-specific Lrat ablation diminishes ERG responses.\",\n      \"evidence\": \"Lrat-/- biochemical fractionation with substrate-defined isomerase assays; conditional RPE-specific Lrat knockout with ERG and retinoid HPLC\",\n      \"pmids\": [\"17504753\", \"18055784\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether residual non-LRAT esterification in RPE can sustain any visual cycle flux remains unclear\",\n        \"Kinetic coupling between LRAT and RPE65 at the ER membrane not characterized\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identification of the proximal promoter elements driving retinoic acid-dependent Lrat transcription showed that RAR/RXR activate Lrat through non-canonical regulatory elements (SP3, AP-1, CAAT) rather than classical retinoid response elements.\",\n      \"evidence\": \"Nuclear run-on, luciferase reporter deletions, and EMSA in HEK293T and HepG2 cells\",\n      \"pmids\": [\"19665987\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Intermediary factors bridging RAR/RXR to the proximal promoter not identified\",\n        \"In vivo chromatin occupancy not tested\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Linking LRAT to STRA6/JAK2/STAT5 signaling expanded its role beyond retinoid storage to active signal transduction: LRAT-driven retinol uptake is required for STRA6 to function as a cytokine receptor, and Lrat-null mice are protected from holo-RBP-induced insulin resistance.\",\n      \"evidence\": \"Lrat-null mice, cell-based STRA6/JAK2/STAT5 signaling assays, and insulin response measurements\",\n      \"pmids\": [\"24036882\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether LRAT physically associates with STRA6 or acts purely through metabolic gradient not resolved\",\n        \"Tissue-specific contribution of LRAT to STRA6 signaling beyond the examined systems unknown\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"A 2.2-Å crystal structure of a LRAT-domain chimera in the thioester intermediate state revealed how a discrete LRAT-specific domain confers acyltransferase specificity within the N1pC/P60 family by promoting domain-swapping dimerization that slows thioester hydrolysis.\",\n      \"evidence\": \"Gain-of-function domain-swap chimera (LRAT-LD into HRASLS3), 2.2-Å crystal structure, in vitro enzymatic assays\",\n      \"pmids\": [\"25383759\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structure is of a chimeric protein, not full-length LRAT; native LRAT structure unavailable\",\n        \"Membrane-associated conformation and retinol binding geometry not determined\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Demonstrating that LRAT overexpression diverts retinol away from retinoic acid synthesis confirmed a metabolic branch-point function: LRAT activity attenuates RAR-regulated gene expression and the antiproliferative effects of retinoids.\",\n      \"evidence\": \"Stable LRAT overexpression in B16F10 melanoma cells, HPLC retinoid quantification, RT-PCR for Cyp26a1\",\n      \"pmids\": [\"25721651\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Overexpression system; physiological relevance of the branch-point ratio in non-transformed cells not established\",\n        \"No loss-of-function complement in the same system\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Quantitative lipidomics in Lrat-/- hepatic stellate cells showed that DGAT1 provides a compensatory retinyl ester synthesis pathway but produces smaller lipid droplets, establishing that LRAT determines lipid droplet size and the specific retinyl ester species profile.\",\n      \"evidence\": \"Lrat-/- primary HSC cultures, LC-MS/MS MRM retinyl ester quantification, lipid droplet morphometry\",\n      \"pmids\": [\"27815220\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism by which LRAT-derived esters promote larger droplets (biophysical or protein-scaffolding) not defined\",\n        \"In vivo hepatic stellate cell activation dynamics not captured in culture\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Characterization of the LCA-associated E14L mutation showed it destabilizes LRAT protein via proteasomal degradation and paradoxically increases retinoic acid accumulation, suggesting that disease pathology involves retinoic acid toxicity rather than simple loss of chromophore production.\",\n      \"evidence\": \"Bicistronic LRAT(E14L)-EGFP stability assays, proteasome inhibitor experiments, cell-based chromophore production and HPLC retinoid quantification\",\n      \"pmids\": [\"28758396\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Retinoic acid toxicity mechanism not validated in vivo\",\n        \"Whether other LCA-associated LRAT mutations share this gain-of-toxicity pathomechanism unknown\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Genetic epistasis between Lrat and Isx revealed that LRAT-mediated retinol sequestration coordinates intestinal β-carotene absorption through a negative-feedback loop: without LRAT, ISX becomes hypersensitive to dietary vitamin A and suppresses β-carotene oxygenase, causing extrahepatic vitamin A deficiency.\",\n      \"evidence\": \"Lrat-/- mice, Isx-/- double-knockout epistasis, pharmacological retinoid signaling inhibition, tissue retinoid quantification\",\n      \"pmids\": [\"33631212\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether LRAT in enterocytes directly esterifies retinol or acts indirectly through circulating retinoid pool not fully separated\",\n        \"Quantitative contribution of this feedback loop relative to hepatic retinoid homeostasis not established\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Temporal profiling of stellate cell activation resolved that early activation maintains LRAT activity while increasing retinyl ester hydrolysis, with LRAT loss and DGAT1 compensation occurring only during prolonged activation.\",\n      \"evidence\": \"HSCs cultured on soft gel vs. stiff substrates, Lrat mRNA/protein kinetics, LC-MS/MS retinyl ester analysis\",\n      \"pmids\": [\"39068984\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"In vivo validation of the two-phase model in liver fibrosis progression not performed\",\n        \"Identity of the hydrolase(s) responsible for early retinyl ester breakdown not determined\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A full-length structure of membrane-embedded LRAT, the identity and regulation of the retinyl ester hydrolase(s) that oppose LRAT activity, and whether LRAT has a direct protein-scaffolding role at ER–lipid droplet contacts remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No structure of full-length, membrane-associated LRAT is available\",\n        \"Retinyl ester hydrolase opposing LRAT in stellate cells and RPE molecularly unidentified\",\n        \"Proposed ER–lipid droplet contact site scaffolding role (PMID:41579973) is from a single study and awaits independent confirmation\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1, 2, 5, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0005811\", \"supporting_discovery_ids\": [0, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 1, 2, 7, 8]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"R-HSA-9709957\", \"supporting_discovery_ids\": [2, 5]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"RPE65\",\n      \"STRA6\",\n      \"DGAT1\",\n      \"ISX\",\n      \"DHRS3\",\n      \"HRASLS3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}