{"gene":"TTR","run_date":"2026-04-28T21:43:00","timeline":{"discoveries":[{"year":1974,"finding":"Human plasma prealbumin (TTR) was determined to be a tetramer of identical subunits with a defined amino acid sequence, establishing the primary structure of the protein.","method":"Protein sequencing of cyanogen bromide and tryptic peptides","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — direct protein sequencing, foundational structural determination","pmids":["4607556"],"is_preprint":false},{"year":1978,"finding":"X-ray crystallography at 1.8 Å resolution revealed that TTR (prealbumin) forms a β-strand-rich homo-tetramer with two thyroxine (T4) binding sites located at the dimer-dimer interface, defining the secondary, tertiary, and quaternary structure of the protein.","method":"X-ray crystallography, Fourier refinement at 1.8 Å","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure, foundational and widely replicated","pmids":["671542"],"is_preprint":false},{"year":1983,"finding":"The amyloid fibril protein in familial amyloidotic polyneuropathy (Japanese type) was identified as a variant of TTR (prealbumin) in which valine at position 30 is replaced by methionine (Val30Met), establishing TTR as the precursor of familial amyloid in FAP.","method":"Peptide mapping, cyanogen bromide fragment comparison, sequence analysis of amyloid fibril protein versus normal prealbumin","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — direct protein sequencing and peptide mapping, foundational discovery","pmids":["6651852"],"is_preprint":false},{"year":1986,"finding":"TTR mRNA is synthesized specifically by choroid plexus epithelial cells within the CNS, with no expression in cerebellum or cerebral cortex, and TTR protein is produced de novo by the choroid plexus for secretion into CSF, establishing choroid plexus as the site of CNS TTR production.","method":"Northern blot analysis of postmortem brain homogenates, in vitro translation assay of choroid plexus mRNA, immunocytochemistry, in situ hybridization in rat brain","journal":"Neurology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Northern, IHC, ISH, in vitro translation), replicated across human and rat","pmids":["3714052"],"is_preprint":false},{"year":1987,"finding":"The human TTR (prealbumin, PALB) gene was assigned to chromosome region 18q11.2-q12.1 by somatic cell hybrid analysis and in situ hybridization, establishing the chromosomal locus for the gene responsible for familial amyloidotic polyneuropathy.","method":"Somatic cell hybrid analysis with human genomic probe, in situ hybridization","journal":"Human genetics","confidence":"High","confidence_rationale":"Tier 2 — two orthogonal mapping methods, confirmed chromosomal location","pmids":["3028932"],"is_preprint":false},{"year":1990,"finding":"Amyloid fibrils in senile systemic amyloidosis (SSA) are derived from wild-type (normal primary structure) TTR, demonstrating that TTR amyloidogenesis does not require coding mutations and that factors other than primary sequence drive wild-type TTR misfolding.","method":"Protein sequencing of amyloid fibril protein isolated from SSA patients; comparison with normal TTR sequence","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — direct protein sequencing of fibril material, foundational finding","pmids":["2320592"],"is_preprint":false},{"year":1991,"finding":"Site-directed mutagenesis of hepatocyte nuclear factor (HNF) binding sites in the TTR promoter revealed that the high-affinity HNF-3-S site (−106 to −94) is absolutely required for TTR promoter activity, and that synergistic cooperation between factors binding the promoter and distal enhancer is necessary for tissue-specific TTR expression in hepatoma cells.","method":"Site-directed mutagenesis of promoter elements, transfection into hepatoma cells, reporter gene assays","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis of each HNF binding site with functional readout in hepatoma cells","pmids":["1870969"],"is_preprint":false},{"year":1991,"finding":"In vivo genomic footprinting of the mouse TTR promoter and enhancer in liver revealed liver-specific occupancy of certain DNA binding sites and identified additional protein-binding sites not previously detected in transfection studies, indicating that not all in vitro demonstrable sites are occupied during active transcription in vivo.","method":"In vivo genomic footprinting using biotinylated riboprobe purification and single primer extension with Taq polymerase in mouse liver","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — direct in vivo footprinting method in native liver tissue, novel technique with functional implications","pmids":["1989908"],"is_preprint":false},{"year":1993,"finding":"The TTR Met119 variant (Thr119Met substitution) increases serum TTR concentration and T4 binding capacity, with increased T4 binding attributable to higher TTR levels rather than an increased association constant; elevated RBP (retinol-binding protein) in carriers also confirmed that TTR normally facilitates RBP retention in plasma.","method":"Serum dialysis with stepwise saturation, cyanogen bromide peptide mapping, DNA restriction fragment length polymorphism, family study","journal":"The Journal of clinical endocrinology and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 — direct biochemical binding assay with mechanistic conclusion; single lab but multiple methods","pmids":["8102146"],"is_preprint":false},{"year":1995,"finding":"X-ray crystallography at 3.1 Å resolution of the TTR–retinol-binding protein (RBP) complex showed that one TTR tetramer binds two RBP molecules, both interacting with the same TTR dimer, with contacts near the retinol-binding site of RBP; the other two potential binding sites of the TTR tetramer were blocked by this arrangement.","method":"X-ray crystallography of the TTR–RBP co-crystal at 3.1 Å resolution","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure of protein complex, defines molecular basis of TTR–RBP interaction","pmids":["7754382"],"is_preprint":false},{"year":1997,"finding":"Retinol uptake from the RBP–TTR complex by primary rat hepatocytes (parenchymal and nonparenchymal cells) was approximately twofold greater than from RBP alone, uptake was inhibitable by excess free TTR, and nonparenchymal (stellate) cells converted most incorporated retinol to retinyl ester; these data indicate TTR acts as a positive regulator of RBP-bound retinol delivery, possibly via a membrane receptor.","method":"Primary cultured rat hepatocyte incubation with [3H]retinol-RBP or [3H]retinol-RBP-TTR, competitive inhibition assays, HPLC analysis of retinol metabolites","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 — direct radiotracer uptake assay with competition controls; single lab","pmids":["9260907"],"is_preprint":false},{"year":2000,"finding":"The non-pathogenic TTR R104H variant, like TTR T119M, stabilizes the TTR tetramer against dissociation into monomers in compound heterozygotes carrying Val30Met, providing a molecular explanation for the protective effect of R104H on FAP progression; however, stability and T4 binding affinity are not obligatorily linked, as R104H shows increased stability but lower T4 binding affinity than T119M.","method":"Stability assays (resistance to dissociation into monomers), thyroxine binding studies comparing TTR variants","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — direct biochemical assays on purified variants; single lab, moderate evidence","pmids":["10772944"],"is_preprint":false},{"year":2000,"finding":"Crystal structures of TTR complexed with several small-molecule inhibitors (flufenamic acid, diclofenac, flurbiprofen, resveratrol) at the T4-binding sites revealed the structural basis for stabilization of the native tetramer; structure-based drug design led to identification of ortho-trifluoromethylphenyl anthranilic acid and N-(meta-trifluoromethylphenyl) phenoxazine 4,6-dicarboxylic acid as potent, selective TTR fibril formation inhibitors.","method":"X-ray crystallography of TTR–ligand complexes, in vitro fibril formation inhibition assays, structure-based drug design","journal":"Nature structural biology","confidence":"High","confidence_rationale":"Tier 1 — crystal structures plus in vitro functional assays, multiple compounds tested","pmids":["10742177"],"is_preprint":false},{"year":2001,"finding":"Incorporation of one or more T119M TTR subunits into a predominantly V30M TTR tetramer strongly stabilizes the mixed tetramer against dissociation, providing the molecular mechanism for intragenic trans-suppression of FAP amyloidosis; tetramer dissociation is required for amyloid formation, so stabilization by T119M subunits prevents V30M-driven aggregation.","method":"Biophysical analysis of mixed V30M/T119M TTR tetramers; dissociation assays under denaturing conditions; analytical ultracentrifugation","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — reconstituted mixed tetramers with direct dissociation measurements; mechanistic explanation for a genetic phenomenon","pmids":["11577236"],"is_preprint":false},{"year":2003,"finding":"Kinetic stabilization of the native TTR tetramer by small molecules raises the kinetic barrier to misfolding and prevents amyloidogenesis; the protective T119M trans-suppressor mutation likewise acts through kinetic stabilization rather than thermodynamic stabilization, establishing kinetic stabilization of the native state as a valid therapeutic strategy.","method":"In vitro TTR amyloidogenesis inhibition assays, rate constant measurements for tetramer dissociation, comparison of small molecules and the T119M variant","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro kinetic measurements plus comparison with genetic suppressor, mechanistically rigorous","pmids":["12560553"],"is_preprint":false},{"year":2004,"finding":"TTR monomers and small non-native oligomers (≤6 subunits, <100 kDa) are the major cytotoxic species to neural lineage cells; TTR amyloid fibrils and large soluble aggregates (>100 kDa) are not toxic; small molecules that stabilize the native tetramer prevent this toxicity, supporting a model in which tetramer dissociation → misfolded monomer → small aggregates is the cytotoxic pathway.","method":"Cell viability assays with size-fractionated TTR quaternary structures (size-exclusion chromatography, SDS-PAGE), small molecule rescue experiments in cell culture","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — multiple quaternary states tested, mechanistic rescue with stabilizers, rigorous controls","pmids":["14981241"],"is_preprint":false},{"year":2011,"finding":"Natural polyphenols curcumin, NDGA, and EGCG bind TTR and modulate fibrillogenesis by distinct mechanisms: curcumin and NDGA stabilize the TTR tetramer, while curcumin generates small off-pathway oligomers, EGCG maintains protein in a non-aggregated soluble form, and both curcumin and EGCG can disaggregate pre-formed TTR amyloid fibrils.","method":"In vitro TTR fibril formation assays, binding studies, transmission electron microscopy, disaggregation assays","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 — multiple compounds and assays; single lab, moderate evidence","pmids":["21740906"],"is_preprint":false},{"year":2012,"finding":"Nearly 200 X-ray crystal structures of TTR have revealed that TTR forms two T4-binding sites at the dimer-dimer interface and holo-RBP binding sites on both faces of the tetramer; structural studies define the mechanistic role of specific structural elements in TTR misfolding and amyloid formation, and guide rational inhibitor design targeting tetramer stabilization.","method":"Review and synthesis of X-ray crystallographic data from ~200 TTR structures and ligand complexes","journal":"Current medicinal chemistry","confidence":"High","confidence_rationale":"Tier 1 — synthesis of extensive crystallographic evidence across many studies","pmids":["22471981"],"is_preprint":false},{"year":2014,"finding":"TTR expression in neuronal cells (SH-SY5Y, primary hippocampal neurons, and APP23 mouse hippocampus) is upregulated by heat shock factor 1 (HSF1), which directly occupies heat shock elements in the TTR promoter in neurons but not in liver, HepG2 hepatoma cells, or cardiomyocytes; this neuron-specific transcriptional regulation by HSF1 is triggered by heat shock or HSF1 stimulator celastrol and is blocked by HSF1 antisense.","method":"Chromatin immunoprecipitation (ChIP) assays in vivo and in cell culture, HSF1 overexpression/knockdown, celastrol treatment, Northern/Western blot analysis","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — ChIP in multiple cell types and in vivo, gain- and loss-of-function, multiple orthogonal methods","pmids":["24849358"],"is_preprint":false},{"year":2014,"finding":"TTR Y114C mutation leads to increased monomeric TTR and impaired autophagy (as shown by autophagic marker accumulation); curcumin treatment significantly decreases monomeric TTR by recovering autophagic flux in a cell model of FAP, implicating autophagy impairment in TTR FAP pathogenesis.","method":"Cell model with TTR Y114C transfection, autophagy flux assays (LC3, p62 markers), curcumin treatment, Western blot","journal":"Drug design, development and therapy","confidence":"Medium","confidence_rationale":"Tier 3 — cell-based assays with pharmacological rescue; single lab, limited mechanistic depth","pmids":["25382970"],"is_preprint":false},{"year":2016,"finding":"TTR V30M aggregates cause partial impairment of autophagic machinery (p62 accumulation) in cell culture while early autophagic steps remain intact; in TTR V30M transgenic mice, tauroursodeoxycholic acid (TUDCA) and curcumin reverse p62 accumulation in the gastrointestinal tract, demonstrating that both compounds modulate autophagy in addition to mitigating apoptosis.","method":"Cell culture autophagy flux assays (p62, LC3, autophagosome quantification), in vivo TTR V30M transgenic mouse model, TUDCA and curcumin treatment, immunohistochemistry","journal":"Clinical science","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro and in vivo evidence, multiple markers; single lab","pmids":["27382986"],"is_preprint":false},{"year":2018,"finding":"TTR stabilizers act at the TTR dimer-dimer interface to prevent dissociation of TTR tetramers into amyloidogenic monomers, representing the mechanistic basis for their therapeutic action in TTR cardiac amyloidosis.","method":"Retrospective clinical study with mechanistic framing; mechanism cited from prior biochemical studies","journal":"Circulation. Heart failure","confidence":"Low","confidence_rationale":"Tier 4 — mechanism cited from prior work, not directly demonstrated in this study","pmids":["29615436"],"is_preprint":false},{"year":2019,"finding":"Hydrophilic extract of Centella asiatica (CAB) bound to human TTR, stabilized the native homo-tetramer against acid/urea-mediated denaturation, and prevented TTR fibrillation in vitro; the binding was demonstrated by NBT redox-cycling and ANS displacement assays, with phenolics and terpenoids identified as likely active components.","method":"Acid/urea denaturation stability assays, transmission electron microscopy of fibrils, NBT redox-cycling assay, ANS displacement assay, HPLC-QTOF-MS for chemical profiling","journal":"Biomolecules","confidence":"Medium","confidence_rationale":"Tier 2 — multiple binding and stability assays; single lab, moderate evidence","pmids":["30934952"],"is_preprint":false},{"year":2024,"finding":"TNF-α stimulation of rheumatoid arthritis synoviocytes upregulates TTR and RAGE protein expression via NF-κB pathway activation; apigenin reduces p65, TTR, and RAGE levels both in vitro and in vivo in an RA model, indicating that TTR expression in synoviocytes is NF-κB-dependent and modulated by anti-inflammatory compounds.","method":"TNF-α stimulation of human RA synovial fibroblasts, apigenin treatment, in-silico docking, Western blot (p65, TTR, RAGE), in vivo RA mouse model","journal":"Cytokine","confidence":"Medium","confidence_rationale":"Tier 3 — Western blot with in vitro and in vivo validation; single lab, pharmacological rather than genetic manipulation","pmids":["38626647"],"is_preprint":false}],"current_model":"TTR is a β-strand-rich homo-tetramer synthesized primarily by the liver and choroid plexus that transports thyroxine (via two binding sites at the dimer-dimer interface) and retinol (via association with retinol-binding protein on both faces of the tetramer); tetramer dissociation into non-native monomers is the rate-limiting step in amyloidogenesis, with monomers and small oligomers (<100 kDa) constituting the major cytotoxic species, while tetramer stabilization—achieved either by kinetic stabilizer small molecules or by trans-suppressor mutations such as T119M—prevents amyloid formation; neuronal TTR expression is additionally regulated by HSF1 occupancy of promoter heat shock elements in a cell-type-specific manner distinct from hepatic regulation."},"narrative":{"teleology":[{"year":1974,"claim":"Determination of the complete primary structure of human TTR established it as a homo-tetramer of identical subunits, enabling all subsequent structure–function work.","evidence":"Protein sequencing of cyanogen bromide and tryptic peptides from plasma prealbumin","pmids":["4607556"],"confidence":"High","gaps":["No tertiary or quaternary structural detail yet available","No information on ligand binding sites"]},{"year":1978,"claim":"The 1.8 Å crystal structure revealed a β-sheet-rich tetramer with two T4-binding sites at the dimer–dimer interface, defining the architectural framework for understanding both transport function and amyloidogenesis.","evidence":"X-ray crystallography with Fourier refinement at 1.8 Å resolution","pmids":["671542"],"confidence":"High","gaps":["RBP binding geometry unknown","No structural basis for why TTR misfolds"]},{"year":1983,"claim":"Identification of the Val30Met substitution in amyloid fibrils from FAP patients established TTR as the direct precursor of hereditary amyloid, linking a specific point mutation to systemic amyloidosis.","evidence":"Peptide mapping and sequence analysis of amyloid fibril protein versus normal prealbumin","pmids":["6651852"],"confidence":"High","gaps":["Whether wild-type TTR can also form amyloid was unknown","Mechanism by which Val30Met destabilizes TTR not defined"]},{"year":1986,"claim":"Demonstration that TTR mRNA is synthesized specifically by choroid plexus epithelial cells in the CNS established this tissue as the source of CSF TTR, distinct from hepatic production.","evidence":"Northern blot, in situ hybridization, immunocytochemistry, and in vitro translation in rat and human brain tissue","pmids":["3714052"],"confidence":"High","gaps":["Regulatory elements controlling choroid plexus versus hepatic expression not yet dissected","Neuronal expression not yet identified"]},{"year":1990,"claim":"Sequencing of amyloid fibrils from senile systemic amyloidosis patients revealed wild-type TTR as the precursor, proving that amyloidogenesis does not require a coding mutation and implicating age-related destabilization.","evidence":"Protein sequencing of fibril material from SSA patients compared with normal TTR","pmids":["2320592"],"confidence":"High","gaps":["Factors that drive wild-type TTR destabilization with age remain undefined","No structural comparison of wild-type versus mutant fibril architecture"]},{"year":1991,"claim":"Systematic mutagenesis and in vivo footprinting of the TTR promoter identified an essential HNF-3 binding site and revealed liver-specific transcription factor occupancy, explaining tissue-restricted expression.","evidence":"Site-directed mutagenesis with reporter assays in hepatoma cells; in vivo genomic footprinting in mouse liver","pmids":["1870969","1989908"],"confidence":"High","gaps":["Choroid plexus and neuronal promoter regulation not yet addressed","Enhancer–promoter communication mechanism not resolved"]},{"year":1995,"claim":"The crystal structure of the TTR–RBP complex showed two RBP molecules bind the same TTR dimer face, defining the molecular basis for retinol transport and explaining the 2:1 RBP:TTR stoichiometry.","evidence":"X-ray crystallography of the TTR–RBP co-crystal at 3.1 Å resolution","pmids":["7754382"],"confidence":"High","gaps":["Mechanism of retinol transfer from RBP–TTR complex to target cells not defined","Whether RBP binding modulates TTR stability unknown"]},{"year":2001,"claim":"Reconstitution of mixed V30M/T119M tetramers demonstrated that incorporation of T119M subunits strongly stabilizes the tetramer against dissociation, providing the molecular mechanism for intragenic trans-suppression of FAP.","evidence":"Biophysical analysis of reconstituted mixed tetramers, dissociation assays under denaturing conditions, analytical ultracentrifugation","pmids":["11577236"],"confidence":"High","gaps":["Whether other trans-suppressor variants act by the same mechanism was only partly addressed","In vivo kinetics of mixed tetramer formation not measured"]},{"year":2003,"claim":"Kinetic (not thermodynamic) stabilization of the TTR tetramer was established as the operative mechanism by which both the T119M mutation and small-molecule inhibitors prevent amyloidogenesis, validating kinetic stabilization as a therapeutic strategy.","evidence":"In vitro rate constant measurements for tetramer dissociation comparing small molecules and T119M variant","pmids":["12560553"],"confidence":"High","gaps":["In vivo pharmacokinetic validation of small-molecule stabilizers not shown here","Whether kinetic stabilization fully prevents oligomer toxicity in vivo unknown"]},{"year":2004,"claim":"Size-fractionation experiments identified monomers and small oligomers (<100 kDa) as the cytotoxic species to neural cells, while mature fibrils and large aggregates were non-toxic, shifting the pathogenic model from fibril deposition to pre-fibrillar intermediates.","evidence":"Cell viability assays with SEC-fractionated TTR quaternary structures and rescue by tetramer-stabilizing small molecules","pmids":["14981241"],"confidence":"High","gaps":["Specific receptors or cellular pathways mediating oligomer toxicity not identified","In vivo relevance of size fractions not directly tested"]},{"year":2014,"claim":"HSF1 was shown to directly occupy heat shock elements in the TTR promoter in neurons but not in hepatocytes or cardiomyocytes, revealing a cell-type-specific transcriptional circuit for neuronal TTR upregulation distinct from hepatic HNF-driven expression.","evidence":"Chromatin immunoprecipitation in SH-SY5Y cells, primary hippocampal neurons, and APP23 mouse hippocampus; gain- and loss-of-function for HSF1","pmids":["24849358"],"confidence":"High","gaps":["Functional consequence of neuronal TTR upregulation for neuroprotection not causally demonstrated","Other neuron-specific co-regulators not identified"]},{"year":2016,"claim":"TTR V30M aggregates impair late-stage autophagic flux (p62 accumulation) in cell and transgenic mouse models, and pharmacological agents (curcumin, TUDCA) rescue this defect, implicating autophagy dysfunction as a secondary pathogenic mechanism downstream of TTR aggregation.","evidence":"Autophagy flux assays in vitro (LC3, p62) and in TTR V30M transgenic mouse gastrointestinal tissue with curcumin/TUDCA rescue","pmids":["27382986","25382970"],"confidence":"Medium","gaps":["Whether autophagy impairment is cause or consequence of cytotoxicity not resolved","Molecular target through which TTR aggregates impair autophagy not identified","Replicated only in gastrointestinal tissue in vivo"]},{"year":null,"claim":"The cellular receptor(s) or signaling pathways through which TTR monomers and small oligomers exert cytotoxicity, and the precise mechanism by which TTR aggregates impair autophagy, remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No receptor for oligomer-mediated toxicity identified","Structural basis of oligomer versus fibril differential toxicity not determined","In vivo contribution of neuronal TTR to neuroprotection versus liver-derived TTR not delineated"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[1,8,9,10,17]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[9,10]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,3,5,8]}],"pathway":[{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[1,8,9,10]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[2,5,13,14,15]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[19,20]}],"complexes":["TTR homo-tetramer","TTR-RBP complex"],"partners":["RBP4","HSF1"],"other_free_text":[]},"mechanistic_narrative":"TTR (transthyretin) is a β-strand-rich homo-tetrameric transport protein, synthesized primarily by the liver and choroid plexus, that carries thyroxine (T4) via two binding sites at its dimer–dimer interface and retinol via association with retinol-binding protein (RBP) on both faces of the tetramer [PMID:671542, PMID:7754382]. Tetramer dissociation into non-native monomers is the rate-limiting step in amyloidogenesis: monomers and small oligomers (<100 kDa) constitute the principal cytotoxic species, while mature fibrils are comparatively inert [PMID:14981241]. Kinetic stabilization of the tetramer—achieved pharmacologically by small molecules occupying the T4-binding channels or genetically by the trans-suppressor mutation T119M—raises the dissociation barrier and prevents amyloid formation, providing the mechanistic basis for therapy in both hereditary (Val30Met) and wild-type TTR amyloidosis [PMID:12560553, PMID:11577236]. Missense mutations in TTR (notably Val30Met) cause familial amyloidotic polyneuropathy, whereas wild-type TTR forms amyloid fibrils in senile systemic amyloidosis without any coding mutation [PMID:6651852, PMID:2320592]."},"prefetch_data":{"uniprot":{"accession":"P02766","full_name":"Transthyretin","aliases":["ATTR","Prealbumin","TBPA"],"length_aa":147,"mass_kda":15.9,"function":"Thyroid hormone-binding protein. 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Nearly 200 X-ray crystal structures have characterized this architecture and the mechanistic role of structural components in TTR function and misfolding.\",\n      \"method\": \"X-ray crystallography (structural review of ~200 crystal structures with functional validation)\",\n      \"journal\": \"Current medicinal chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — extensive structural data from ~200 crystal structures replicated across many labs, with functional implications validated\",\n      \"pmids\": [\"22471981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The TTR T119M variant (and similarly R104H) confers increased resistance to dissociation into monomers (tetramer stabilization) and higher thyroxine binding affinity compared to normal TTR, demonstrating that tetramer stability is mechanistically linked to amyloidogenicity. Compound heterozygotes carrying both an amyloidogenic mutation (V30M) and T119M show slower disease progression, establishing a protective trans-suppression mechanism.\",\n      \"method\": \"In vitro stability assays (urea/acid denaturation), thyroxine binding assays, serum protein analysis in human carriers\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal biochemical assays with genotype-phenotype correlation, replicated across related publications\",\n      \"pmids\": [\"10772944\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"The TTR Met119 variant increases T4 binding to TTR due to higher TTR serum concentration rather than an increased association constant; TTR Met119 also elevates plasma retinol-binding protein levels, consistent with TTR's role in stabilizing RBP in circulation.\",\n      \"method\": \"Serum dialysis with stepwise saturation of iodothyronine binding sites, cyanogen bromide peptide mapping, DNA restriction fragment length polymorphism analysis\",\n      \"journal\": \"The Journal of clinical endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple biochemical methods in a single study with human carriers, moderate evidence\",\n      \"pmids\": [\"8102146\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"TTR positively regulates retinol uptake from RBP into hepatocytes and non-parenchymal cells; retinol uptake from the RBP-TTR complex was approximately twofold greater than from RBP alone, and excess free TTR inhibits uptake, suggesting TTR facilitates receptor-mediated delivery of RBP-bound retinol.\",\n      \"method\": \"Primary rat hepatocyte culture with [3H]retinol-RBP and [3H]retinol-RBP-TTR complexes; HPLC analysis; competitive inhibition assays\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct in vitro uptake assay with competitive inhibition, single study\",\n      \"pmids\": [\"9260907\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Natural polyphenols inhibit TTR fibrillogenesis via distinct mechanisms: curcumin and NDGA bind TTR and stabilize the tetramer; NDGA slightly reduced aggregation; curcumin strongly suppressed amyloid fibril formation by generating small 'off-pathway' oligomers; EGCG maintained protein in a non-aggregated soluble form. Both EGCG and curcumin also disaggregated pre-formed TTR amyloid fibrils.\",\n      \"method\": \"In vitro TTR fibrillogenesis assays, binding assays (TTR-polyphenol interactions), transmission electron microscopy\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution with multiple orthogonal assays, single study\",\n      \"pmids\": [\"21740906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"TTR plays a critical role in modulating amyloid-beta (Aβ) deposition in vivo; hemizygous deletion of TTR in APPswe/PS1deltaE9 transgenic mice accelerated Aβ deposition and increased soluble and insoluble Aβ levels in hippocampus and cortex, demonstrating that TTR modulates Aβ aggregation in vivo.\",\n      \"method\": \"Genetic mouse model (TTR+/- hemizygous deletion crossed with APPswe/PS1deltaE9 transgenic mice); ELISA for Aβ levels; immunohistochemical analysis of amyloid deposition\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic loss-of-function in vivo with quantitative biochemical and histological readouts\",\n      \"pmids\": [\"17596449\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In neurons, TTR expression is regulated by heat shock factor 1 (HSF1), which directly occupies heat shock elements in the TTR promoter; this regulation is neuron-specific (not seen in liver, hepatoma, or cardiomyocyte cells) and is activated by heat shock or the HSF1 stimulator celastrol.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), transfection with HSF1 constructs, shHSF1 antisense knockdown, in vivo celastrol treatment of APP23 mice\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ChIP demonstrating direct promoter occupancy, in vivo validation, multiple orthogonal methods in a single study\",\n      \"pmids\": [\"24849358\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"The TTR promoter requires HNF-3 (specifically the high-affinity HNF-3-S site at -106 to -94) for transcriptional activity; this site is absolutely required for TTR promoter activity. Cooperation between factors binding the promoter and distal enhancer regions is necessary for tissue-specific expression, involving HNF1, HNF3, HNF4, C/EBP, and AP-1/cJun binding sites.\",\n      \"method\": \"Site-directed mutagenesis of HNF binding sites, transfection in hepatoma cells, reporter gene assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution by mutagenesis in cell-based reporter system with multiple mutant constructs and rigorous controls\",\n      \"pmids\": [\"1870969\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"In vivo genomic footprinting of the TTR promoter and enhancer in mouse liver revealed high liver-specific occupancy of specific DNA elements, including sites not previously identified by transfection studies, indicating that only a subset of demonstrable binding sites are occupied during active transcription in vivo.\",\n      \"method\": \"In vivo genomic footprinting using biotinylated riboprobe purification and Taq DNA polymerase primer extension\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — direct in vivo footprinting, single study, established tissue-specific protein-DNA interactions\",\n      \"pmids\": [\"1989908\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"The human TTR (prealbumin/PALB) gene was mapped to chromosome region 18q11.2-q12.1 by somatic cell hybrid analysis and in situ hybridization, establishing the chromosomal locus of the gene responsible for familial amyloidotic polyneuropathy.\",\n      \"method\": \"Somatic cell hybrid analysis, in situ hybridization with human genomic probe\",\n      \"journal\": \"Human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — two orthogonal methods confirming chromosomal localization\",\n      \"pmids\": [\"3028932\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TTR stabilizers (tafamidis, diflunisal) act at the dimer-dimer interface to prevent tetramer dissociation into monomers, thereby inhibiting amyloid fibril formation; clinical use of these stabilizers was associated with reduced risk of death or heart transplant in TTR cardiac amyloidosis patients.\",\n      \"method\": \"Retrospective clinical cohort study with Cox proportional hazards modeling; mechanism established by prior structural/biochemical studies\",\n      \"journal\": \"Circulation. Heart failure\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — clinical association study citing established mechanism; mechanistic basis from structural studies in other papers\",\n      \"pmids\": [\"29615436\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TTR V30M aggregates impair autophagic flux in cells (measured by p62 accumulation), and this impairment can be reversed in vivo by TUDCA and curcumin in transgenic mice, establishing a link between TTR aggregation and autophagy disruption as a pathogenic mechanism.\",\n      \"method\": \"Cell culture with TTR V30M aggregates, p62 immunoblotting, LC3 turnover assay, autophagosome counting; in vivo treatment of TTR V30M transgenic mice with TUDCA/curcumin\",\n      \"journal\": \"Clinical science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in vitro and in vivo, single lab\",\n      \"pmids\": [\"27382986\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TTR Y114C mutation leads to increased monomeric TTR and impaired autophagy in cells; curcumin treatment reduces monomeric TTR by recovering autophagic flux.\",\n      \"method\": \"Cell culture model with TTR Y114C expression, autophagy markers, curcumin treatment\",\n      \"journal\": \"Drug design, development and therapy\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single method, single lab, limited mechanistic detail\",\n      \"pmids\": [\"25382970\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Iododiflunisal (IDIF), a TTR tetramer-stabilizing compound, enhances blood-brain barrier (BBB) permeability of TTR and itself when administered as a TTR-IDIF complex in mice, increasing brain concentrations of both TTR and IDIF, potentially augmenting Aβ sequestration in the CNS.\",\n      \"method\": \"Radioiodine labeling of IDIF and TTR; biodistribution by ex vivo and in vivo PET imaging in mice after intravenous administration\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct in vivo biodistribution measurement with labeled compounds, single study\",\n      \"pmids\": [\"31541162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TNF-α stimulation of rheumatoid arthritis synoviocytes upregulates TTR and RAGE expression via NF-κB pathway activation; apigenin treatment reduces p65, TTR, and RAGE levels, suggesting TTR expression is regulated by inflammatory NF-κB signaling in synovial fibroblasts.\",\n      \"method\": \"In vitro TNF-α stimulation of RA synoviocytes, Western blot for TTR/RAGE/p65, in-silico binding analysis, in vivo arthritis model\",\n      \"journal\": \"Cytokine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, limited mechanistic depth for TTR-specific findings\",\n      \"pmids\": [\"38626647\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TTR is a homotetrameric β-strand-rich protein produced primarily by the liver (and choroid plexus) that transports thyroxine via two binding sites at the dimer-dimer interface and stabilizes retinol-binding protein (RBP) in circulation; tetramer dissociation into non-native monomers initiates misfolding and amyloid fibril formation underlying familial amyloid polyneuropathy, cardiomyopathy, and senile systemic amyloidosis, and TTR also modulates amyloid-beta aggregation in the brain. Hepatocyte-specific expression is controlled by cooperative binding of HNF transcription factors to the promoter and enhancer, while in neurons TTR is additionally regulated by HSF1 binding to promoter heat shock elements. Small-molecule kinetic stabilizers that bind at the dimer-dimer interface prevent tetramer dissociation and inhibit fibrillogenesis, and TTR aggregates impair autophagy as an additional pathogenic mechanism.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper and extract discoveries only from KEEP papers.\n\n**Classification summary:**\n- KEEP: Papers about human/mammalian TTR (transthyretin) protein\n- EXCLUDE (alias collision): Papers about CTS1/CTS2 (chitinase genes in fungi), CTS (leukemic cell line), CTS1 (p53 chimera), CTS-1027 (MMP inhibitor), lncRNA-CTS, Cts1 in Cryptococcus/Ustilago, Ace2p/CTS1 in yeast, CTS scaffolds (chitosan), C. elegans TTR-52 (different protein/organism with distinct function), HIV cPPT/CTS, PalB, etc.\n- EXCLUDE (not mechanistic): Pure clinical/epidemiological papers\n\n**KEEP papers with mechanistic findings:**\n- PMID:671542, 7754382, 2320592, 12560553, 10742177, 14981241, 11577236, 4607556, 3714052, 6651852, 1870969, 1989908, 20526330 (C. elegans TTR-52 — borderline; this is a transthyretin-LIKE protein in C. elegans with distinct function — EXCLUDE as symbol collision/alt-locus), 21740906, 10772944, 8102146, 9260907, 24849358, 38626647, 30934952, 25382970, 27382986, 22471981\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1974,\n      \"finding\": \"Human plasma prealbumin (TTR) was determined to be a tetramer of identical subunits with a defined amino acid sequence, establishing the primary structure of the protein.\",\n      \"method\": \"Protein sequencing of cyanogen bromide and tryptic peptides\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct protein sequencing, foundational structural determination\",\n      \"pmids\": [\"4607556\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1978,\n      \"finding\": \"X-ray crystallography at 1.8 Å resolution revealed that TTR (prealbumin) forms a β-strand-rich homo-tetramer with two thyroxine (T4) binding sites located at the dimer-dimer interface, defining the secondary, tertiary, and quaternary structure of the protein.\",\n      \"method\": \"X-ray crystallography, Fourier refinement at 1.8 Å\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure, foundational and widely replicated\",\n      \"pmids\": [\"671542\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1983,\n      \"finding\": \"The amyloid fibril protein in familial amyloidotic polyneuropathy (Japanese type) was identified as a variant of TTR (prealbumin) in which valine at position 30 is replaced by methionine (Val30Met), establishing TTR as the precursor of familial amyloid in FAP.\",\n      \"method\": \"Peptide mapping, cyanogen bromide fragment comparison, sequence analysis of amyloid fibril protein versus normal prealbumin\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct protein sequencing and peptide mapping, foundational discovery\",\n      \"pmids\": [\"6651852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"TTR mRNA is synthesized specifically by choroid plexus epithelial cells within the CNS, with no expression in cerebellum or cerebral cortex, and TTR protein is produced de novo by the choroid plexus for secretion into CSF, establishing choroid plexus as the site of CNS TTR production.\",\n      \"method\": \"Northern blot analysis of postmortem brain homogenates, in vitro translation assay of choroid plexus mRNA, immunocytochemistry, in situ hybridization in rat brain\",\n      \"journal\": \"Neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Northern, IHC, ISH, in vitro translation), replicated across human and rat\",\n      \"pmids\": [\"3714052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"The human TTR (prealbumin, PALB) gene was assigned to chromosome region 18q11.2-q12.1 by somatic cell hybrid analysis and in situ hybridization, establishing the chromosomal locus for the gene responsible for familial amyloidotic polyneuropathy.\",\n      \"method\": \"Somatic cell hybrid analysis with human genomic probe, in situ hybridization\",\n      \"journal\": \"Human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — two orthogonal mapping methods, confirmed chromosomal location\",\n      \"pmids\": [\"3028932\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"Amyloid fibrils in senile systemic amyloidosis (SSA) are derived from wild-type (normal primary structure) TTR, demonstrating that TTR amyloidogenesis does not require coding mutations and that factors other than primary sequence drive wild-type TTR misfolding.\",\n      \"method\": \"Protein sequencing of amyloid fibril protein isolated from SSA patients; comparison with normal TTR sequence\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct protein sequencing of fibril material, foundational finding\",\n      \"pmids\": [\"2320592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"Site-directed mutagenesis of hepatocyte nuclear factor (HNF) binding sites in the TTR promoter revealed that the high-affinity HNF-3-S site (−106 to −94) is absolutely required for TTR promoter activity, and that synergistic cooperation between factors binding the promoter and distal enhancer is necessary for tissue-specific TTR expression in hepatoma cells.\",\n      \"method\": \"Site-directed mutagenesis of promoter elements, transfection into hepatoma cells, reporter gene assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis of each HNF binding site with functional readout in hepatoma cells\",\n      \"pmids\": [\"1870969\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"In vivo genomic footprinting of the mouse TTR promoter and enhancer in liver revealed liver-specific occupancy of certain DNA binding sites and identified additional protein-binding sites not previously detected in transfection studies, indicating that not all in vitro demonstrable sites are occupied during active transcription in vivo.\",\n      \"method\": \"In vivo genomic footprinting using biotinylated riboprobe purification and single primer extension with Taq polymerase in mouse liver\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct in vivo footprinting method in native liver tissue, novel technique with functional implications\",\n      \"pmids\": [\"1989908\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"The TTR Met119 variant (Thr119Met substitution) increases serum TTR concentration and T4 binding capacity, with increased T4 binding attributable to higher TTR levels rather than an increased association constant; elevated RBP (retinol-binding protein) in carriers also confirmed that TTR normally facilitates RBP retention in plasma.\",\n      \"method\": \"Serum dialysis with stepwise saturation, cyanogen bromide peptide mapping, DNA restriction fragment length polymorphism, family study\",\n      \"journal\": \"The Journal of clinical endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct biochemical binding assay with mechanistic conclusion; single lab but multiple methods\",\n      \"pmids\": [\"8102146\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"X-ray crystallography at 3.1 Å resolution of the TTR–retinol-binding protein (RBP) complex showed that one TTR tetramer binds two RBP molecules, both interacting with the same TTR dimer, with contacts near the retinol-binding site of RBP; the other two potential binding sites of the TTR tetramer were blocked by this arrangement.\",\n      \"method\": \"X-ray crystallography of the TTR–RBP co-crystal at 3.1 Å resolution\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure of protein complex, defines molecular basis of TTR–RBP interaction\",\n      \"pmids\": [\"7754382\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Retinol uptake from the RBP–TTR complex by primary rat hepatocytes (parenchymal and nonparenchymal cells) was approximately twofold greater than from RBP alone, uptake was inhibitable by excess free TTR, and nonparenchymal (stellate) cells converted most incorporated retinol to retinyl ester; these data indicate TTR acts as a positive regulator of RBP-bound retinol delivery, possibly via a membrane receptor.\",\n      \"method\": \"Primary cultured rat hepatocyte incubation with [3H]retinol-RBP or [3H]retinol-RBP-TTR, competitive inhibition assays, HPLC analysis of retinol metabolites\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct radiotracer uptake assay with competition controls; single lab\",\n      \"pmids\": [\"9260907\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The non-pathogenic TTR R104H variant, like TTR T119M, stabilizes the TTR tetramer against dissociation into monomers in compound heterozygotes carrying Val30Met, providing a molecular explanation for the protective effect of R104H on FAP progression; however, stability and T4 binding affinity are not obligatorily linked, as R104H shows increased stability but lower T4 binding affinity than T119M.\",\n      \"method\": \"Stability assays (resistance to dissociation into monomers), thyroxine binding studies comparing TTR variants\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct biochemical assays on purified variants; single lab, moderate evidence\",\n      \"pmids\": [\"10772944\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Crystal structures of TTR complexed with several small-molecule inhibitors (flufenamic acid, diclofenac, flurbiprofen, resveratrol) at the T4-binding sites revealed the structural basis for stabilization of the native tetramer; structure-based drug design led to identification of ortho-trifluoromethylphenyl anthranilic acid and N-(meta-trifluoromethylphenyl) phenoxazine 4,6-dicarboxylic acid as potent, selective TTR fibril formation inhibitors.\",\n      \"method\": \"X-ray crystallography of TTR–ligand complexes, in vitro fibril formation inhibition assays, structure-based drug design\",\n      \"journal\": \"Nature structural biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures plus in vitro functional assays, multiple compounds tested\",\n      \"pmids\": [\"10742177\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Incorporation of one or more T119M TTR subunits into a predominantly V30M TTR tetramer strongly stabilizes the mixed tetramer against dissociation, providing the molecular mechanism for intragenic trans-suppression of FAP amyloidosis; tetramer dissociation is required for amyloid formation, so stabilization by T119M subunits prevents V30M-driven aggregation.\",\n      \"method\": \"Biophysical analysis of mixed V30M/T119M TTR tetramers; dissociation assays under denaturing conditions; analytical ultracentrifugation\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted mixed tetramers with direct dissociation measurements; mechanistic explanation for a genetic phenomenon\",\n      \"pmids\": [\"11577236\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Kinetic stabilization of the native TTR tetramer by small molecules raises the kinetic barrier to misfolding and prevents amyloidogenesis; the protective T119M trans-suppressor mutation likewise acts through kinetic stabilization rather than thermodynamic stabilization, establishing kinetic stabilization of the native state as a valid therapeutic strategy.\",\n      \"method\": \"In vitro TTR amyloidogenesis inhibition assays, rate constant measurements for tetramer dissociation, comparison of small molecules and the T119M variant\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro kinetic measurements plus comparison with genetic suppressor, mechanistically rigorous\",\n      \"pmids\": [\"12560553\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"TTR monomers and small non-native oligomers (≤6 subunits, <100 kDa) are the major cytotoxic species to neural lineage cells; TTR amyloid fibrils and large soluble aggregates (>100 kDa) are not toxic; small molecules that stabilize the native tetramer prevent this toxicity, supporting a model in which tetramer dissociation → misfolded monomer → small aggregates is the cytotoxic pathway.\",\n      \"method\": \"Cell viability assays with size-fractionated TTR quaternary structures (size-exclusion chromatography, SDS-PAGE), small molecule rescue experiments in cell culture\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple quaternary states tested, mechanistic rescue with stabilizers, rigorous controls\",\n      \"pmids\": [\"14981241\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Natural polyphenols curcumin, NDGA, and EGCG bind TTR and modulate fibrillogenesis by distinct mechanisms: curcumin and NDGA stabilize the TTR tetramer, while curcumin generates small off-pathway oligomers, EGCG maintains protein in a non-aggregated soluble form, and both curcumin and EGCG can disaggregate pre-formed TTR amyloid fibrils.\",\n      \"method\": \"In vitro TTR fibril formation assays, binding studies, transmission electron microscopy, disaggregation assays\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple compounds and assays; single lab, moderate evidence\",\n      \"pmids\": [\"21740906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Nearly 200 X-ray crystal structures of TTR have revealed that TTR forms two T4-binding sites at the dimer-dimer interface and holo-RBP binding sites on both faces of the tetramer; structural studies define the mechanistic role of specific structural elements in TTR misfolding and amyloid formation, and guide rational inhibitor design targeting tetramer stabilization.\",\n      \"method\": \"Review and synthesis of X-ray crystallographic data from ~200 TTR structures and ligand complexes\",\n      \"journal\": \"Current medicinal chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — synthesis of extensive crystallographic evidence across many studies\",\n      \"pmids\": [\"22471981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TTR expression in neuronal cells (SH-SY5Y, primary hippocampal neurons, and APP23 mouse hippocampus) is upregulated by heat shock factor 1 (HSF1), which directly occupies heat shock elements in the TTR promoter in neurons but not in liver, HepG2 hepatoma cells, or cardiomyocytes; this neuron-specific transcriptional regulation by HSF1 is triggered by heat shock or HSF1 stimulator celastrol and is blocked by HSF1 antisense.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) assays in vivo and in cell culture, HSF1 overexpression/knockdown, celastrol treatment, Northern/Western blot analysis\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP in multiple cell types and in vivo, gain- and loss-of-function, multiple orthogonal methods\",\n      \"pmids\": [\"24849358\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TTR Y114C mutation leads to increased monomeric TTR and impaired autophagy (as shown by autophagic marker accumulation); curcumin treatment significantly decreases monomeric TTR by recovering autophagic flux in a cell model of FAP, implicating autophagy impairment in TTR FAP pathogenesis.\",\n      \"method\": \"Cell model with TTR Y114C transfection, autophagy flux assays (LC3, p62 markers), curcumin treatment, Western blot\",\n      \"journal\": \"Drug design, development and therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — cell-based assays with pharmacological rescue; single lab, limited mechanistic depth\",\n      \"pmids\": [\"25382970\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"TTR V30M aggregates cause partial impairment of autophagic machinery (p62 accumulation) in cell culture while early autophagic steps remain intact; in TTR V30M transgenic mice, tauroursodeoxycholic acid (TUDCA) and curcumin reverse p62 accumulation in the gastrointestinal tract, demonstrating that both compounds modulate autophagy in addition to mitigating apoptosis.\",\n      \"method\": \"Cell culture autophagy flux assays (p62, LC3, autophagosome quantification), in vivo TTR V30M transgenic mouse model, TUDCA and curcumin treatment, immunohistochemistry\",\n      \"journal\": \"Clinical science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and in vivo evidence, multiple markers; single lab\",\n      \"pmids\": [\"27382986\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TTR stabilizers act at the TTR dimer-dimer interface to prevent dissociation of TTR tetramers into amyloidogenic monomers, representing the mechanistic basis for their therapeutic action in TTR cardiac amyloidosis.\",\n      \"method\": \"Retrospective clinical study with mechanistic framing; mechanism cited from prior biochemical studies\",\n      \"journal\": \"Circulation. Heart failure\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — mechanism cited from prior work, not directly demonstrated in this study\",\n      \"pmids\": [\"29615436\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Hydrophilic extract of Centella asiatica (CAB) bound to human TTR, stabilized the native homo-tetramer against acid/urea-mediated denaturation, and prevented TTR fibrillation in vitro; the binding was demonstrated by NBT redox-cycling and ANS displacement assays, with phenolics and terpenoids identified as likely active components.\",\n      \"method\": \"Acid/urea denaturation stability assays, transmission electron microscopy of fibrils, NBT redox-cycling assay, ANS displacement assay, HPLC-QTOF-MS for chemical profiling\",\n      \"journal\": \"Biomolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple binding and stability assays; single lab, moderate evidence\",\n      \"pmids\": [\"30934952\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TNF-α stimulation of rheumatoid arthritis synoviocytes upregulates TTR and RAGE protein expression via NF-κB pathway activation; apigenin reduces p65, TTR, and RAGE levels both in vitro and in vivo in an RA model, indicating that TTR expression in synoviocytes is NF-κB-dependent and modulated by anti-inflammatory compounds.\",\n      \"method\": \"TNF-α stimulation of human RA synovial fibroblasts, apigenin treatment, in-silico docking, Western blot (p65, TTR, RAGE), in vivo RA mouse model\",\n      \"journal\": \"Cytokine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Western blot with in vitro and in vivo validation; single lab, pharmacological rather than genetic manipulation\",\n      \"pmids\": [\"38626647\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TTR is a β-strand-rich homo-tetramer synthesized primarily by the liver and choroid plexus that transports thyroxine (via two binding sites at the dimer-dimer interface) and retinol (via association with retinol-binding protein on both faces of the tetramer); tetramer dissociation into non-native monomers is the rate-limiting step in amyloidogenesis, with monomers and small oligomers (<100 kDa) constituting the major cytotoxic species, while tetramer stabilization—achieved either by kinetic stabilizer small molecules or by trans-suppressor mutations such as T119M—prevents amyloid formation; neuronal TTR expression is additionally regulated by HSF1 occupancy of promoter heat shock elements in a cell-type-specific manner distinct from hepatic regulation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TTR is a homotetrameric transport protein that carries thyroxine (T4) via two binding sites at the dimer–dimer interface and stabilizes retinol-binding protein (RBP) in circulation, additionally facilitating receptor-mediated retinol uptake into hepatocytes [PMID:22471981, PMID:9260907]. Rate-limiting tetramer dissociation into non-native monomers initiates misfolding and amyloid fibril formation underlying familial amyloid polyneuropathy and cardiomyopathy, while naturally occurring trans-suppressor variants such as T119M stabilize the tetramer and slow disease progression in compound heterozygotes [PMID:10772944, PMID:22471981]. Hepatocyte-specific transcription requires cooperative binding of HNF-3, HNF-1, HNF-4, C/EBP, and AP-1 to the promoter and distal enhancer, whereas neuron-specific expression is driven by HSF1 occupancy of heat shock elements in the TTR promoter [PMID:1870969, PMID:24849358]. TTR also suppresses amyloid-β deposition in the brain, as demonstrated by accelerated Aβ accumulation upon hemizygous TTR deletion in Alzheimer-model mice, and aggregated mutant TTR impairs autophagic flux as an additional pathogenic mechanism [PMID:17596449, PMID:27382986].\",\n  \"teleology\": [\n    {\n      \"year\": 1987,\n      \"claim\": \"Mapping TTR to chromosome 18q11.2–q12.1 established the genetic locus underlying familial amyloidotic polyneuropathy, enabling subsequent mutation–phenotype studies.\",\n      \"evidence\": \"Somatic cell hybrid analysis and in situ hybridization with a human genomic probe\",\n      \"pmids\": [\"3028932\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No coding mutations identified in this study\", \"Choroid plexus vs. liver expression regulation not addressed\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Identification of the HNF-3-S site as absolutely required for TTR promoter activity, together with cooperative enhancer–promoter interactions involving HNF-1/3/4, C/EBP, and AP-1, explained liver-specific transcriptional control.\",\n      \"evidence\": \"Site-directed mutagenesis of HNF binding sites and reporter gene assays in hepatoma cells; in vivo genomic footprinting in mouse liver\",\n      \"pmids\": [\"1870969\", \"1989908\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Choroid plexus-specific regulatory elements not defined\", \"Relative contribution of each HNF factor not quantified in vivo\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Demonstrating that the Met119 variant elevates serum TTR concentration (rather than binding affinity) and correspondingly raises plasma RBP levels clarified that TTR stabilizes RBP in circulation through a mass-action mechanism.\",\n      \"evidence\": \"Serum dialysis with iodothyronine saturation, cyanogen bromide peptide mapping, and RFLP analysis in human carriers\",\n      \"pmids\": [\"8102146\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of TTR clearance rate differences not identified\", \"RBP–TTR stoichiometry in vivo not measured\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Showing that the RBP–TTR complex delivers retinol to hepatocytes approximately twofold more efficiently than RBP alone established a functional role for TTR beyond simple RBP stabilization — it actively facilitates receptor-mediated retinol uptake.\",\n      \"evidence\": \"Primary rat hepatocyte uptake assays with radiolabeled retinol-RBP ± TTR and competitive inhibition with free TTR\",\n      \"pmids\": [\"9260907\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the cell-surface receptor mediating RBP–TTR uptake not determined\", \"Relevance to retinol delivery in extrahepatic tissues not tested\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Biochemical proof that the T119M variant resists urea/acid-induced tetramer dissociation and that V30M/T119M compound heterozygotes show slower disease progression established the principle that kinetic stabilization of the TTR tetramer is protective against amyloidogenesis.\",\n      \"evidence\": \"In vitro urea and acid denaturation assays, thyroxine binding measurements, and genotype–phenotype analysis in human carriers\",\n      \"pmids\": [\"10772944\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of T119M stabilization at atomic resolution not shown in this study\", \"Whether all amyloidogenic variants are equally suppressible unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Hemizygous TTR deletion in Alzheimer-model mice accelerated Aβ deposition, providing in vivo genetic evidence that TTR is a physiological modulator of amyloid-β aggregation in the brain.\",\n      \"evidence\": \"TTR+/- crossed with APPswe/PS1ΔE9 transgenic mice; ELISA and immunohistochemistry for Aβ levels\",\n      \"pmids\": [\"17596449\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of Aβ sequestration by TTR (direct binding vs. indirect clearance) not resolved\", \"Whether TTR tetramers or monomers interact with Aβ unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Comprehensive structural analysis of ~200 TTR crystal structures unified the understanding of two T4 binding channels at the dimer–dimer interface, RBP binding on both tetramer faces, and the conformational pathway from tetramer dissociation through monomer misfolding to fibril formation.\",\n      \"evidence\": \"Review and synthesis of ~200 X-ray crystal structures with functional validation\",\n      \"pmids\": [\"22471981\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structures of early misfolded monomeric intermediates largely lacking\", \"Full fibril architecture at atomic resolution not determined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Discovery that HSF1 directly occupies heat shock elements in the TTR promoter in neurons — but not in hepatocytes or cardiomyocytes — revealed a neuron-specific transcriptional regulatory axis distinct from the hepatic HNF-dependent program.\",\n      \"evidence\": \"ChIP for HSF1 at TTR promoter, shHSF1 knockdown, celastrol treatment in APP23 mice\",\n      \"pmids\": [\"24849358\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether HSF1-driven TTR induction is sufficient to reduce Aβ load long-term not established\", \"Epigenetic basis of neuron-specific HSF1 access not explored\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstration that V30M TTR aggregates impair autophagic flux (p62 accumulation, reduced LC3 turnover) added autophagy disruption as a downstream pathogenic mechanism of TTR amyloidosis, reversible by TUDCA and curcumin in vivo.\",\n      \"evidence\": \"TTR V30M aggregate treatment of cells, p62/LC3 immunoblotting, autophagosome counting; V30M transgenic mice treated with TUDCA/curcumin\",\n      \"pmids\": [\"27382986\", \"25382970\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether autophagy impairment is aggregate species–specific (oligomers vs. fibrils) not determined\", \"Direct molecular target of TTR aggregates in the autophagy pathway unknown\", \"Y114C data from a single lab with limited mechanistic depth\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Clinical evidence that tafamidis and diflunisal — small-molecule kinetic stabilizers binding at the dimer–dimer T4 site — reduce mortality in TTR cardiac amyloidosis validated the therapeutic principle of pharmacological tetramer stabilization in humans.\",\n      \"evidence\": \"Retrospective clinical cohort study with Cox proportional hazards modeling\",\n      \"pmids\": [\"29615436\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Observational design limits causal inference\", \"Relative contribution of tetramer stabilization vs. anti-inflammatory effects of diflunisal not disentangled\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the atomic structure of cytotoxic TTR oligomeric intermediates, the identity of the cell-surface receptor mediating RBP–TTR retinol delivery, the molecular basis by which TTR sequesters Aβ, and whether neuron-derived TTR contributes significantly to neuroprotection independently of hepatic TTR.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of toxic oligomeric intermediates not solved\", \"RBP–TTR uptake receptor identity unknown\", \"Direct TTR–Aβ interaction mechanism unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [0, 2, 3]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 1, 2, 3, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 2, 3]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [11, 12]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [1, 10, 11]}\n    ],\n    \"complexes\": [\n      \"TTR homotetramer\",\n      \"RBP-TTR complex\"\n    ],\n    \"partners\": [\n      \"RBP4\",\n      \"HSF1\",\n      \"HNF3A\",\n      \"HNF1A\",\n      \"HNF4A\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"TTR (transthyretin) is a β-strand-rich homo-tetrameric transport protein, synthesized primarily by the liver and choroid plexus, that carries thyroxine (T4) via two binding sites at its dimer–dimer interface and retinol via association with retinol-binding protein (RBP) on both faces of the tetramer [PMID:671542, PMID:7754382]. Tetramer dissociation into non-native monomers is the rate-limiting step in amyloidogenesis: monomers and small oligomers (<100 kDa) constitute the principal cytotoxic species, while mature fibrils are comparatively inert [PMID:14981241]. Kinetic stabilization of the tetramer—achieved pharmacologically by small molecules occupying the T4-binding channels or genetically by the trans-suppressor mutation T119M—raises the dissociation barrier and prevents amyloid formation, providing the mechanistic basis for therapy in both hereditary (Val30Met) and wild-type TTR amyloidosis [PMID:12560553, PMID:11577236]. Missense mutations in TTR (notably Val30Met) cause familial amyloidotic polyneuropathy, whereas wild-type TTR forms amyloid fibrils in senile systemic amyloidosis without any coding mutation [PMID:6651852, PMID:2320592].\",\n  \"teleology\": [\n    {\n      \"year\": 1974,\n      \"claim\": \"Determination of the complete primary structure of human TTR established it as a homo-tetramer of identical subunits, enabling all subsequent structure–function work.\",\n      \"evidence\": \"Protein sequencing of cyanogen bromide and tryptic peptides from plasma prealbumin\",\n      \"pmids\": [\"4607556\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No tertiary or quaternary structural detail yet available\", \"No information on ligand binding sites\"]\n    },\n    {\n      \"year\": 1978,\n      \"claim\": \"The 1.8 Å crystal structure revealed a β-sheet-rich tetramer with two T4-binding sites at the dimer–dimer interface, defining the architectural framework for understanding both transport function and amyloidogenesis.\",\n      \"evidence\": \"X-ray crystallography with Fourier refinement at 1.8 Å resolution\",\n      \"pmids\": [\"671542\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"RBP binding geometry unknown\", \"No structural basis for why TTR misfolds\"]\n    },\n    {\n      \"year\": 1983,\n      \"claim\": \"Identification of the Val30Met substitution in amyloid fibrils from FAP patients established TTR as the direct precursor of hereditary amyloid, linking a specific point mutation to systemic amyloidosis.\",\n      \"evidence\": \"Peptide mapping and sequence analysis of amyloid fibril protein versus normal prealbumin\",\n      \"pmids\": [\"6651852\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether wild-type TTR can also form amyloid was unknown\", \"Mechanism by which Val30Met destabilizes TTR not defined\"]\n    },\n    {\n      \"year\": 1986,\n      \"claim\": \"Demonstration that TTR mRNA is synthesized specifically by choroid plexus epithelial cells in the CNS established this tissue as the source of CSF TTR, distinct from hepatic production.\",\n      \"evidence\": \"Northern blot, in situ hybridization, immunocytochemistry, and in vitro translation in rat and human brain tissue\",\n      \"pmids\": [\"3714052\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Regulatory elements controlling choroid plexus versus hepatic expression not yet dissected\", \"Neuronal expression not yet identified\"]\n    },\n    {\n      \"year\": 1990,\n      \"claim\": \"Sequencing of amyloid fibrils from senile systemic amyloidosis patients revealed wild-type TTR as the precursor, proving that amyloidogenesis does not require a coding mutation and implicating age-related destabilization.\",\n      \"evidence\": \"Protein sequencing of fibril material from SSA patients compared with normal TTR\",\n      \"pmids\": [\"2320592\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Factors that drive wild-type TTR destabilization with age remain undefined\", \"No structural comparison of wild-type versus mutant fibril architecture\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Systematic mutagenesis and in vivo footprinting of the TTR promoter identified an essential HNF-3 binding site and revealed liver-specific transcription factor occupancy, explaining tissue-restricted expression.\",\n      \"evidence\": \"Site-directed mutagenesis with reporter assays in hepatoma cells; in vivo genomic footprinting in mouse liver\",\n      \"pmids\": [\"1870969\", \"1989908\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Choroid plexus and neuronal promoter regulation not yet addressed\", \"Enhancer–promoter communication mechanism not resolved\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"The crystal structure of the TTR–RBP complex showed two RBP molecules bind the same TTR dimer face, defining the molecular basis for retinol transport and explaining the 2:1 RBP:TTR stoichiometry.\",\n      \"evidence\": \"X-ray crystallography of the TTR–RBP co-crystal at 3.1 Å resolution\",\n      \"pmids\": [\"7754382\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of retinol transfer from RBP–TTR complex to target cells not defined\", \"Whether RBP binding modulates TTR stability unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Reconstitution of mixed V30M/T119M tetramers demonstrated that incorporation of T119M subunits strongly stabilizes the tetramer against dissociation, providing the molecular mechanism for intragenic trans-suppression of FAP.\",\n      \"evidence\": \"Biophysical analysis of reconstituted mixed tetramers, dissociation assays under denaturing conditions, analytical ultracentrifugation\",\n      \"pmids\": [\"11577236\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other trans-suppressor variants act by the same mechanism was only partly addressed\", \"In vivo kinetics of mixed tetramer formation not measured\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Kinetic (not thermodynamic) stabilization of the TTR tetramer was established as the operative mechanism by which both the T119M mutation and small-molecule inhibitors prevent amyloidogenesis, validating kinetic stabilization as a therapeutic strategy.\",\n      \"evidence\": \"In vitro rate constant measurements for tetramer dissociation comparing small molecules and T119M variant\",\n      \"pmids\": [\"12560553\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo pharmacokinetic validation of small-molecule stabilizers not shown here\", \"Whether kinetic stabilization fully prevents oligomer toxicity in vivo unknown\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Size-fractionation experiments identified monomers and small oligomers (<100 kDa) as the cytotoxic species to neural cells, while mature fibrils and large aggregates were non-toxic, shifting the pathogenic model from fibril deposition to pre-fibrillar intermediates.\",\n      \"evidence\": \"Cell viability assays with SEC-fractionated TTR quaternary structures and rescue by tetramer-stabilizing small molecules\",\n      \"pmids\": [\"14981241\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific receptors or cellular pathways mediating oligomer toxicity not identified\", \"In vivo relevance of size fractions not directly tested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"HSF1 was shown to directly occupy heat shock elements in the TTR promoter in neurons but not in hepatocytes or cardiomyocytes, revealing a cell-type-specific transcriptional circuit for neuronal TTR upregulation distinct from hepatic HNF-driven expression.\",\n      \"evidence\": \"Chromatin immunoprecipitation in SH-SY5Y cells, primary hippocampal neurons, and APP23 mouse hippocampus; gain- and loss-of-function for HSF1\",\n      \"pmids\": [\"24849358\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of neuronal TTR upregulation for neuroprotection not causally demonstrated\", \"Other neuron-specific co-regulators not identified\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"TTR V30M aggregates impair late-stage autophagic flux (p62 accumulation) in cell and transgenic mouse models, and pharmacological agents (curcumin, TUDCA) rescue this defect, implicating autophagy dysfunction as a secondary pathogenic mechanism downstream of TTR aggregation.\",\n      \"evidence\": \"Autophagy flux assays in vitro (LC3, p62) and in TTR V30M transgenic mouse gastrointestinal tissue with curcumin/TUDCA rescue\",\n      \"pmids\": [\"27382986\", \"25382970\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether autophagy impairment is cause or consequence of cytotoxicity not resolved\", \"Molecular target through which TTR aggregates impair autophagy not identified\", \"Replicated only in gastrointestinal tissue in vivo\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The cellular receptor(s) or signaling pathways through which TTR monomers and small oligomers exert cytotoxicity, and the precise mechanism by which TTR aggregates impair autophagy, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No receptor for oligomer-mediated toxicity identified\", \"Structural basis of oligomer versus fibril differential toxicity not determined\", \"In vivo contribution of neuronal TTR to neuroprotection versus liver-derived TTR not delineated\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [1, 8, 9, 10, 17]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [9, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 3, 5, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [1, 8, 9, 10]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [2, 5, 13, 14, 15]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [19, 20]}\n    ],\n    \"complexes\": [\n      \"TTR homo-tetramer\",\n      \"TTR-RBP complex\"\n    ],\n    \"partners\": [\n      \"RBP4\",\n      \"HSF1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}