{"gene":"TRDN","run_date":"2026-06-10T10:51:55","timeline":{"discoveries":[{"year":2003,"finding":"Human triadin isoforms Trisk 51 and Trisk 95 are alternative splice variants of the same TRDN gene. Trisk 51 is the major isoform expressed in human skeletal muscle, whereas Trisk 95 is below detection level.","method":"Gene cloning, RT-PCR, Western blot, genomic sequence alignment","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct cloning and protein expression experiments in two orthogonal methods (RT-PCR + Western blot), single lab","pmids":["12659871"],"is_preprint":false},{"year":2005,"finding":"Overexpression of Trisk 95 (but not Trisk 51) in rat skeletal myotubes almost abolishes depolarization-induced calcium release without affecting caffeine-induced release or dihydropyridine receptor activation curves, indicating that Trisk 95 levels specifically regulate the excitation-contraction coupling step of the calcium release complex.","method":"Adenovirus-mediated overexpression, antisense rescue, calcium imaging, electrophysiology, immunofluorescence co-localization","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (overexpression, antisense rescue, calcium imaging, electrophysiology), specific functional phenotype with controls","pmids":["16176928"],"is_preprint":false},{"year":2011,"finding":"Trisk 32 (TRDN isoform) co-localizes and co-immunoprecipitates with IP3 receptors in rat skeletal myoblasts, and its overexpression enhances IP3-mediated calcium release stimulated by bradykinin or vasopressin; ryanodine receptors are not involved in this effect.","method":"Stable transfection/overexpression, immunocytochemistry, co-immunoprecipitation, intracellular calcium measurement, pharmacological exclusion of RyR involvement","journal":"Pflugers Archiv : European journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP and functional calcium assays, single lab, two orthogonal methods","pmids":["21811790"],"is_preprint":false},{"year":2016,"finding":"Three lysine residues (K218, K220, K224) in the luminal domain of Trisk 95 (residues 200–232) are required together for binding to RyR1 and activating RyR1 ion channel activity in vitro; neutralization of all three by alanine substitution abolishes binding and activation, whereas single or double substitutions do not. The same residues are required for calsequestrin (CSQ) binding, suggesting Trisk 95 monomers cannot simultaneously bind RyR1 and CSQ.","method":"Peptide-based in vitro binding assay, alanine-scanning mutagenesis, single-channel electrophysiology (bilayer recordings)","journal":"Pflugers Archiv : European journal of physiology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with mutagenesis and channel activity assay, single lab but multiple orthogonal methods","pmids":["27595738"],"is_preprint":false},{"year":2019,"finding":"A homozygous missense mutation p.L56P in TRDN alters the dynamics of the cardiac triadin isoform TRISK32 and reduces caffeine-induced calcium release when co-expressed with RyR2 in heterologous systems, establishing a pathogenic mechanism for arrhythmia.","method":"GFP-tagged mutant protein expression in heterologous cells, caffeine-induced calcium release assay, co-expression with RyR2","journal":"Heart rhythm","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional calcium assay with mutant vs wild-type in heterologous system, single lab, single method for the core mechanistic claim","pmids":["31437535"],"is_preprint":false},{"year":2020,"finding":"A novel deep intronic TRDN variant (c.484+1189G>A) disrupts splicing of a previously unrecognized alternative exon 6a-containing TRDN transcript and also abolishes the canonical 8-exon cardiac triadin 1 transcript, resulting in loss of triadin protein in patient-derived iPSC-derived cardiomyocytes.","method":"Genome sequencing, RT-PCR, Western blot in patient-specific iPSC-derived cardiomyocytes","journal":"Heart rhythm","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RT-PCR and Western blot on patient-derived cells confirming splicing and protein loss, single lab, two orthogonal methods","pmids":["32402482"],"is_preprint":false},{"year":2020,"finding":"Trisk 95 expression in skin is induced at the transcriptional level by elevated glucose independently of insulin signaling, and Trisk 95 knockout abolishes both the glucose-induced intracellular calcium flux and associated mitochondrial fragmentation in skin cells.","method":"Luciferase reporter assay, Fluo-4AM calcium imaging, knockout mouse model, proteomics screen","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO with defined phenotypic readout (calcium flux, mitochondrial morphology), luciferase reporter for transcriptional mechanism, single lab","pmids":["32699238"],"is_preprint":false}],"current_model":"TRDN (triadin) encodes multiple alternatively spliced isoforms (Trisk 95, Trisk 51, Trisk 32) that reside within the calcium release complex of muscle sarcoplasmic reticulum; Trisk 95 directly binds and activates RyR1 through luminal-domain lysine residues (K218, K220, K224) and regulates excitation-contraction coupling in skeletal muscle, while Trisk 32 associates with and potentiates IP3 receptor-mediated calcium release; recessive loss-of-function or missense mutations in TRDN reduce RyR2-mediated calcium release in cardiomyocytes, causing triadin knockout syndrome with malignant arrhythmias."},"narrative":{"mechanistic_narrative":"TRDN encodes triadin, a sarcoplasmic reticulum protein of the muscle calcium release complex that is expressed as multiple alternatively spliced isoforms (Trisk 51, Trisk 95, Trisk 32) from a single gene [PMID:12659871]. Within skeletal muscle, Trisk 95 is the functionally decisive isoform for excitation-contraction coupling: its overexpression specifically abolishes depolarization-induced calcium release without altering caffeine-induced release or dihydropyridine receptor activation, identifying it as a direct regulator of the calcium release step [PMID:16176928]. This regulation is mediated by three lysine residues (K218, K220, K224) in the luminal domain of Trisk 95, which are jointly required for binding and activating the RyR1 channel; the same residues mediate calsequestrin binding, so a single triadin monomer cannot simultaneously engage RyR1 and calsequestrin [PMID:27595738]. A distinct isoform, Trisk 32, instead associates with IP3 receptors and potentiates IP3-mediated calcium release independently of ryanodine receptors [PMID:21811790]. In the heart, loss-of-function and missense TRDN mutations impair RyR2-mediated calcium release: a homozygous p.L56P substitution alters cardiac TRISK32 dynamics and reduces caffeine-induced calcium release when co-expressed with RyR2 [PMID:31437535], and a deep intronic variant disrupts cardiac triadin splicing to abolish triadin protein in patient-derived iPSC cardiomyocytes [PMID:32402482], establishing TRDN as a cause of recessive arrhythmia (triadin knockout syndrome). Triadin also functions outside striated muscle, where Trisk 95 is transcriptionally induced by glucose and is required for glucose-evoked calcium flux and mitochondrial fragmentation in skin cells [PMID:32699238].","teleology":[{"year":2003,"claim":"Established that human TRDN produces multiple triadin isoforms by alternative splicing, defining the molecular repertoire whose individual roles would later be dissected.","evidence":"Gene cloning, RT-PCR and Western blot of human skeletal muscle","pmids":["12659871"],"confidence":"Medium","gaps":["Did not assign distinct functions to Trisk 51 versus Trisk 95","Cardiac isoform expression not addressed"]},{"year":2005,"claim":"Showed that Trisk 95, not Trisk 51, specifically governs the excitation-contraction coupling step, resolving which isoform regulates depolarization-induced calcium release.","evidence":"Adenoviral overexpression with antisense rescue, calcium imaging and electrophysiology in rat myotubes","pmids":["16176928"],"confidence":"High","gaps":["Did not define the molecular interface with RyR1","Mechanism of the EC-coupling-specific effect unresolved"]},{"year":2011,"claim":"Demonstrated that a separate isoform, Trisk 32, links triadin to IP3-receptor signaling rather than ryanodine receptors, revealing isoform-specific channel partnerships.","evidence":"Overexpression, reciprocal co-immunoprecipitation and calcium measurement with RyR pharmacological exclusion in myoblasts","pmids":["21811790"],"confidence":"Medium","gaps":["Binding interface on Trisk 32 not mapped","Single lab, physiological role of IP3R potentiation untested in vivo"]},{"year":2016,"claim":"Identified the luminal lysine cluster (K218/K220/K224) as the structural determinant for Trisk 95 binding and activation of RyR1, and showed it is shared with calsequestrin binding, defining mutually exclusive engagement.","evidence":"Peptide binding assays, alanine-scanning mutagenesis and single-channel bilayer recordings","pmids":["27595738"],"confidence":"High","gaps":["Functional competition between RyR1 and CSQ not demonstrated in intact cells","Structural basis of triadin oligomerization not resolved"]},{"year":2019,"claim":"Connected a TRDN missense mutation to arrhythmia mechanism by showing p.L56P alters cardiac TRISK32 and reduces RyR2-coupled calcium release.","evidence":"GFP-tagged mutant expression and caffeine-induced calcium release assay with RyR2 co-expression in heterologous cells","pmids":["31437535"],"confidence":"Medium","gaps":["Single functional readout for the core claim","Effect on native cardiomyocyte calcium handling not shown"]},{"year":2020,"claim":"Defined a non-coding pathogenic mechanism in which a deep intronic variant disrupts cardiac triadin splicing and eliminates triadin protein, plus a non-muscle role for glucose-induced Trisk 95.","evidence":"Genome sequencing, RT-PCR and Western blot in patient iPSC-cardiomyocytes; luciferase reporter, calcium imaging and knockout mouse in skin cells","pmids":["32402482","32699238"],"confidence":"Medium","gaps":["Mechanism linking triadin loss to arrhythmia at tissue level not fully resolved","Transcription factors driving glucose induction of Trisk 95 unidentified"]},{"year":null,"claim":"How the distinct triadin isoforms are coordinated within a single calcium release complex and how loss of triadin produces malignant cardiac arrhythmia mechanistically remain open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No integrated structural model of the triadin-RyR-calsequestrin complex","In vivo arrhythmia mechanism downstream of triadin loss not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,3,2]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[3]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[1,3]}],"pathway":[],"complexes":["calcium release complex"],"partners":["RYR1","CASQ1","ITPR","RYR2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q13061","full_name":"Triadin","aliases":[],"length_aa":729,"mass_kda":81.6,"function":"Contributes to the regulation of lumenal Ca2+ release via the sarcoplasmic reticulum calcium release channels RYR1 and RYR2, a key step in triggering skeletal and heart muscle contraction. Required for normal organization of the triad junction, where T-tubules and the sarcoplasmic reticulum terminal cisternae are in close contact (By similarity). Required for normal skeletal muscle strength. Plays a role in excitation-contraction coupling in the heart and in regulating the rate of heart beats","subcellular_location":"Cell membrane; Sarcoplasmic reticulum membrane","url":"https://www.uniprot.org/uniprotkb/Q13061/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TRDN","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TRDN","total_profiled":1310},"omim":[{"mim_id":"615950","title":"SPEG COMPLEX LOCUS; SPEG","url":"https://www.omim.org/entry/615950"},{"mim_id":"615441","title":"CARDIAC ARRHYTHMIA SYNDROME, WITH OR WITHOUT SKELETAL MUSCLE WEAKNESS; CARDAR","url":"https://www.omim.org/entry/615441"},{"mim_id":"604772","title":"VENTRICULAR TACHYCARDIA, CATECHOLAMINERGIC POLYMORPHIC, 1, WITH OR WITHOUT ATRIAL DYSFUNCTION AND/OR DILATED CARDIOMYOPATHY; CPVT1","url":"https://www.omim.org/entry/604772"},{"mim_id":"603283","title":"TRIADIN; TRDN","url":"https://www.omim.org/entry/603283"},{"mim_id":"600582","title":"ASPARTATE BETA-HYDROXYLASE; ASPH","url":"https://www.omim.org/entry/600582"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"heart muscle","ntpm":394.7},{"tissue":"skeletal muscle","ntpm":1819.8},{"tissue":"tongue","ntpm":951.2}],"url":"https://www.proteinatlas.org/search/TRDN"},"hgnc":{"alias_symbol":["TRISK"],"prev_symbol":[]},"alphafold":{"accession":"Q13061","domains":[{"cath_id":"1.20.5","chopping":"48-81","consensus_level":"medium","plddt":81.9038,"start":48,"end":81}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q13061","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q13061-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q13061-F1-predicted_aligned_error_v6.png","plddt_mean":47.59},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TRDN","jax_strain_url":"https://www.jax.org/strain/search?query=TRDN"},"sequence":{"accession":"Q13061","fasta_url":"https://rest.uniprot.org/uniprotkb/Q13061.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q13061/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q13061"}},"corpus_meta":[{"pmid":"12659871","id":"PMC_12659871","title":"Human skeletal muscle triadin: gene organization and cloning of the major isoform, Trisk 51.","date":"2003","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/12659871","citation_count":33,"is_preprint":false},{"pmid":"16176928","id":"PMC_16176928","title":"Triadin (Trisk 95) overexpression blocks excitation-contraction coupling in rat skeletal myotubes.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16176928","citation_count":30,"is_preprint":false},{"pmid":"12955494","id":"PMC_12955494","title":"Expression of Trisk 51, agrin and nicotinic-acetycholine receptor epsilon-subunit during muscle development in a novel three-dimensional muscle-neuronal co-culture system.","date":"2003","source":"Cell and tissue research","url":"https://pubmed.ncbi.nlm.nih.gov/12955494","citation_count":29,"is_preprint":false},{"pmid":"26196381","id":"PMC_26196381","title":"Common Variants in TRDN and CALM1 Are Associated with Risk of Sudden Cardiac Death in Chronic Heart Failure Patients in Chinese Han Population.","date":"2015","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/26196381","citation_count":25,"is_preprint":false},{"pmid":"31437535","id":"PMC_31437535","title":"A novel homozygous mutation in the TRDN gene causes a severe form of pediatric malignant ventricular arrhythmia.","date":"2019","source":"Heart rhythm","url":"https://pubmed.ncbi.nlm.nih.gov/31437535","citation_count":17,"is_preprint":false},{"pmid":"32402482","id":"PMC_32402482","title":"Phenotype-guided whole genome analysis in a patient with genetically elusive long QT syndrome yields a novel TRDN-encoded triadin pathogenetic substrate for triadin knockout syndrome and reveals a novel primate-specific cardiac TRDN transcript.","date":"2020","source":"Heart rhythm","url":"https://pubmed.ncbi.nlm.nih.gov/32402482","citation_count":13,"is_preprint":false},{"pmid":"34415104","id":"PMC_34415104","title":"Novel cases of pediatric sudden cardiac death secondary to TRDN mutations presenting as long QT syndrome at rest and catecholaminergic polymorphic ventricular tachycardia during exercise: The TRDN arrhythmia syndrome.","date":"2021","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/34415104","citation_count":12,"is_preprint":false},{"pmid":"24026879","id":"PMC_24026879","title":"Synthesis, properties, and remarkable 2 D Self-Assembly at the Liquid/Solid interface of a series of triskele-shaped 5,11,17-triazatrinaphthylenes (TrisK).","date":"2013","source":"Chemistry (Weinheim an der Bergstrasse, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/24026879","citation_count":7,"is_preprint":false},{"pmid":"33692971","id":"PMC_33692971","title":"Pediatric Malignant Arrhythmias Caused by Rare Homozygous Genetic Variants in TRDN: A Comprehensive Interpretation.","date":"2021","source":"Frontiers in pediatrics","url":"https://pubmed.ncbi.nlm.nih.gov/33692971","citation_count":6,"is_preprint":false},{"pmid":"27595738","id":"PMC_27595738","title":"Three residues in the luminal domain of triadin impact on Trisk 95 activation of skeletal muscle ryanodine receptors.","date":"2016","source":"Pflugers Archiv : European journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/27595738","citation_count":6,"is_preprint":false},{"pmid":"39821729","id":"PMC_39821729","title":"Cardiomyocyte-specific long noncoding RNA Trdn-as induces mitochondrial calcium overload by promoting the m6A modification of calsequestrin 2 in diabetic cardiomyopathy.","date":"2025","source":"Frontiers of medicine","url":"https://pubmed.ncbi.nlm.nih.gov/39821729","citation_count":5,"is_preprint":false},{"pmid":"37589058","id":"PMC_37589058","title":"Acute aerobic exercise regulation of myocardial calcium homeostasis involves CASQ1, CASQ2, and TRDN.","date":"2023","source":"Journal of applied physiology (Bethesda, Md. : 1985)","url":"https://pubmed.ncbi.nlm.nih.gov/37589058","citation_count":3,"is_preprint":false},{"pmid":"21811790","id":"PMC_21811790","title":"Trisk 32 regulates IP(3) receptors in rat skeletal myoblasts.","date":"2011","source":"Pflugers Archiv : European journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/21811790","citation_count":3,"is_preprint":false},{"pmid":"32699238","id":"PMC_32699238","title":"Trisk 95 as a novel skin mirror for normal and diabetic systemic glucose level.","date":"2020","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/32699238","citation_count":2,"is_preprint":false},{"pmid":"39528282","id":"PMC_39528282","title":"[Clinical and genetic analysis of a case of Triadin knockout syndrome due to variant of TRDN gene and a literature review].","date":"2024","source":"Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/39528282","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.09.25.24314371","title":"Refined selection of individuals for preventive cardiovascular disease treatment with a Transformer-based risk model","date":"2024-09-26","source":"bioRxiv","url":"https://doi.org/10.1101/2024.09.25.24314371","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.01.13.632728","title":"RBM20-variants induce distinct calcium handling and metabolic phenotypes in patient-specific stem cell models of dilated and non-compaction cardiomyopathy","date":"2025-01-14","source":"bioRxiv","url":"https://doi.org/10.1101/2025.01.13.632728","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.09.16.25335490","title":"A novel truncating variant c.1222DupC in <i>RBM20</i> causes cardiomyopathy through haploinsufficiency","date":"2025-09-18","source":"bioRxiv","url":"https://doi.org/10.1101/2025.09.16.25335490","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12534,"output_tokens":1779,"usd":0.032143,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8637,"output_tokens":2490,"usd":0.052718,"stage2_stop_reason":"end_turn"},"total_usd":0.084861,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2003,\n      \"finding\": \"Human triadin isoforms Trisk 51 and Trisk 95 are alternative splice variants of the same TRDN gene. Trisk 51 is the major isoform expressed in human skeletal muscle, whereas Trisk 95 is below detection level.\",\n      \"method\": \"Gene cloning, RT-PCR, Western blot, genomic sequence alignment\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct cloning and protein expression experiments in two orthogonal methods (RT-PCR + Western blot), single lab\",\n      \"pmids\": [\"12659871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Overexpression of Trisk 95 (but not Trisk 51) in rat skeletal myotubes almost abolishes depolarization-induced calcium release without affecting caffeine-induced release or dihydropyridine receptor activation curves, indicating that Trisk 95 levels specifically regulate the excitation-contraction coupling step of the calcium release complex.\",\n      \"method\": \"Adenovirus-mediated overexpression, antisense rescue, calcium imaging, electrophysiology, immunofluorescence co-localization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (overexpression, antisense rescue, calcium imaging, electrophysiology), specific functional phenotype with controls\",\n      \"pmids\": [\"16176928\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Trisk 32 (TRDN isoform) co-localizes and co-immunoprecipitates with IP3 receptors in rat skeletal myoblasts, and its overexpression enhances IP3-mediated calcium release stimulated by bradykinin or vasopressin; ryanodine receptors are not involved in this effect.\",\n      \"method\": \"Stable transfection/overexpression, immunocytochemistry, co-immunoprecipitation, intracellular calcium measurement, pharmacological exclusion of RyR involvement\",\n      \"journal\": \"Pflugers Archiv : European journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP and functional calcium assays, single lab, two orthogonal methods\",\n      \"pmids\": [\"21811790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Three lysine residues (K218, K220, K224) in the luminal domain of Trisk 95 (residues 200–232) are required together for binding to RyR1 and activating RyR1 ion channel activity in vitro; neutralization of all three by alanine substitution abolishes binding and activation, whereas single or double substitutions do not. The same residues are required for calsequestrin (CSQ) binding, suggesting Trisk 95 monomers cannot simultaneously bind RyR1 and CSQ.\",\n      \"method\": \"Peptide-based in vitro binding assay, alanine-scanning mutagenesis, single-channel electrophysiology (bilayer recordings)\",\n      \"journal\": \"Pflugers Archiv : European journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with mutagenesis and channel activity assay, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"27595738\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A homozygous missense mutation p.L56P in TRDN alters the dynamics of the cardiac triadin isoform TRISK32 and reduces caffeine-induced calcium release when co-expressed with RyR2 in heterologous systems, establishing a pathogenic mechanism for arrhythmia.\",\n      \"method\": \"GFP-tagged mutant protein expression in heterologous cells, caffeine-induced calcium release assay, co-expression with RyR2\",\n      \"journal\": \"Heart rhythm\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional calcium assay with mutant vs wild-type in heterologous system, single lab, single method for the core mechanistic claim\",\n      \"pmids\": [\"31437535\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A novel deep intronic TRDN variant (c.484+1189G>A) disrupts splicing of a previously unrecognized alternative exon 6a-containing TRDN transcript and also abolishes the canonical 8-exon cardiac triadin 1 transcript, resulting in loss of triadin protein in patient-derived iPSC-derived cardiomyocytes.\",\n      \"method\": \"Genome sequencing, RT-PCR, Western blot in patient-specific iPSC-derived cardiomyocytes\",\n      \"journal\": \"Heart rhythm\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RT-PCR and Western blot on patient-derived cells confirming splicing and protein loss, single lab, two orthogonal methods\",\n      \"pmids\": [\"32402482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Trisk 95 expression in skin is induced at the transcriptional level by elevated glucose independently of insulin signaling, and Trisk 95 knockout abolishes both the glucose-induced intracellular calcium flux and associated mitochondrial fragmentation in skin cells.\",\n      \"method\": \"Luciferase reporter assay, Fluo-4AM calcium imaging, knockout mouse model, proteomics screen\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO with defined phenotypic readout (calcium flux, mitochondrial morphology), luciferase reporter for transcriptional mechanism, single lab\",\n      \"pmids\": [\"32699238\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TRDN (triadin) encodes multiple alternatively spliced isoforms (Trisk 95, Trisk 51, Trisk 32) that reside within the calcium release complex of muscle sarcoplasmic reticulum; Trisk 95 directly binds and activates RyR1 through luminal-domain lysine residues (K218, K220, K224) and regulates excitation-contraction coupling in skeletal muscle, while Trisk 32 associates with and potentiates IP3 receptor-mediated calcium release; recessive loss-of-function or missense mutations in TRDN reduce RyR2-mediated calcium release in cardiomyocytes, causing triadin knockout syndrome with malignant arrhythmias.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TRDN encodes triadin, a sarcoplasmic reticulum protein of the muscle calcium release complex that is expressed as multiple alternatively spliced isoforms (Trisk 51, Trisk 95, Trisk 32) from a single gene [#0]. Within skeletal muscle, Trisk 95 is the functionally decisive isoform for excitation-contraction coupling: its overexpression specifically abolishes depolarization-induced calcium release without altering caffeine-induced release or dihydropyridine receptor activation, identifying it as a direct regulator of the calcium release step [#1]. This regulation is mediated by three lysine residues (K218, K220, K224) in the luminal domain of Trisk 95, which are jointly required for binding and activating the RyR1 channel; the same residues mediate calsequestrin binding, so a single triadin monomer cannot simultaneously engage RyR1 and calsequestrin [#3]. A distinct isoform, Trisk 32, instead associates with IP3 receptors and potentiates IP3-mediated calcium release independently of ryanodine receptors [#2]. In the heart, loss-of-function and missense TRDN mutations impair RyR2-mediated calcium release: a homozygous p.L56P substitution alters cardiac TRISK32 dynamics and reduces caffeine-induced calcium release when co-expressed with RyR2 [#4], and a deep intronic variant disrupts cardiac triadin splicing to abolish triadin protein in patient-derived iPSC cardiomyocytes [#5], establishing TRDN as a cause of recessive arrhythmia (triadin knockout syndrome). Triadin also functions outside striated muscle, where Trisk 95 is transcriptionally induced by glucose and is required for glucose-evoked calcium flux and mitochondrial fragmentation in skin cells [#6].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established that human TRDN produces multiple triadin isoforms by alternative splicing, defining the molecular repertoire whose individual roles would later be dissected.\",\n      \"evidence\": \"Gene cloning, RT-PCR and Western blot of human skeletal muscle\",\n      \"pmids\": [\"12659871\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Did not assign distinct functions to Trisk 51 versus Trisk 95\", \"Cardiac isoform expression not addressed\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Showed that Trisk 95, not Trisk 51, specifically governs the excitation-contraction coupling step, resolving which isoform regulates depolarization-induced calcium release.\",\n      \"evidence\": \"Adenoviral overexpression with antisense rescue, calcium imaging and electrophysiology in rat myotubes\",\n      \"pmids\": [\"16176928\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Did not define the molecular interface with RyR1\", \"Mechanism of the EC-coupling-specific effect unresolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrated that a separate isoform, Trisk 32, links triadin to IP3-receptor signaling rather than ryanodine receptors, revealing isoform-specific channel partnerships.\",\n      \"evidence\": \"Overexpression, reciprocal co-immunoprecipitation and calcium measurement with RyR pharmacological exclusion in myoblasts\",\n      \"pmids\": [\"21811790\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Binding interface on Trisk 32 not mapped\", \"Single lab, physiological role of IP3R potentiation untested in vivo\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified the luminal lysine cluster (K218/K220/K224) as the structural determinant for Trisk 95 binding and activation of RyR1, and showed it is shared with calsequestrin binding, defining mutually exclusive engagement.\",\n      \"evidence\": \"Peptide binding assays, alanine-scanning mutagenesis and single-channel bilayer recordings\",\n      \"pmids\": [\"27595738\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Functional competition between RyR1 and CSQ not demonstrated in intact cells\", \"Structural basis of triadin oligomerization not resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Connected a TRDN missense mutation to arrhythmia mechanism by showing p.L56P alters cardiac TRISK32 and reduces RyR2-coupled calcium release.\",\n      \"evidence\": \"GFP-tagged mutant expression and caffeine-induced calcium release assay with RyR2 co-expression in heterologous cells\",\n      \"pmids\": [\"31437535\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Single functional readout for the core claim\", \"Effect on native cardiomyocyte calcium handling not shown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined a non-coding pathogenic mechanism in which a deep intronic variant disrupts cardiac triadin splicing and eliminates triadin protein, plus a non-muscle role for glucose-induced Trisk 95.\",\n      \"evidence\": \"Genome sequencing, RT-PCR and Western blot in patient iPSC-cardiomyocytes; luciferase reporter, calcium imaging and knockout mouse in skin cells\",\n      \"pmids\": [\"32402482\", \"32699238\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Mechanism linking triadin loss to arrhythmia at tissue level not fully resolved\", \"Transcription factors driving glucose induction of Trisk 95 unidentified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the distinct triadin isoforms are coordinated within a single calcium release complex and how loss of triadin produces malignant cardiac arrhythmia mechanistically remain open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"No integrated structural model of the triadin-RyR-calsequestrin complex\", \"In vivo arrhythmia mechanism downstream of triadin loss not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 3, 2]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [1, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0397014\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"complexes\": [\"calcium release complex\"],\n    \"partners\": [\"RYR1\", \"CASQ1\", \"ITPR\", \"RYR2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}