{"gene":"TNNT2","run_date":"2026-06-10T10:51:55","timeline":{"discoveries":[{"year":2009,"finding":"Four novel TNNT2 missense mutations (Arg134Gly, Arg151Cys, Arg159Gln, Arg205Trp) and one previously reported (Glu244Asp) were functionally characterized in reconstituted cardiac myocytes; all caused decreased Ca2+ sensitivity of force development, a hallmark mechanism of dilated cardiomyopathy.","method":"Cardiac myocyte reconstitution with mutant troponin T proteins; Ca2+-sensitivity of force development assay","journal":"Circulation. Cardiovascular genetics","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro functional reconstitution assay with multiple mutations tested, single lab but multiple mutants with consistent results","pmids":["20031601"],"is_preprint":false},{"year":1994,"finding":"The TNNT2 gene was mapped to chromosome 1q (1cen-qter) by somatic cell hybrid analysis, and multiple cardiac troponin T mRNA isoforms were demonstrated in fetal human heart resulting from alternative splicing in the 5' coding region.","method":"Somatic cell hybrid analysis; cDNA cloning and hybridization; genomic Southern blotting","journal":"Genomics","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct chromosomal mapping with somatic cell hybrids and demonstration of alternative splicing by molecular cloning, replicated by subsequent studies","pmids":["8088824"],"is_preprint":false},{"year":2004,"finding":"A 5-bp insertion/deletion polymorphism in intron 3 of TNNT2 affects splicing: the deletion allele causes skipping of exon 4 during splicing, altering the mRNA expression pattern, and was associated with greater left ventricular hypertrophy.","method":"In vitro expression study; splicing analysis; association study with LV mass measurements","journal":"Journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro splicing assay demonstrated functional consequence of the deletion allele, supported by clinical association data, single lab","pmids":["14986170"],"is_preprint":false},{"year":2010,"finding":"A novel TNNT2 missense mutation pE96K causes impaired left ventricular function and induction of heart failure marker genes in transgenic mice expressing the mutant human cTNT, without producing a left ventricular non-compaction phenotype, indicating intrinsic cardiomyocyte dysfunction as the primary pathological mechanism.","method":"Transgenic mouse model; echocardiography; histology; gene expression analysis","journal":"Cardiovascular research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transgenic mouse model with defined cardiac phenotype readout, single lab with multiple orthogonal methods","pmids":["20083571"],"is_preprint":false},{"year":2020,"finding":"HCM-associated TNNT2 variants increased cardiac microtissue contraction and myofilament calcium affinity, whereas DCM-associated TNNT2 variants decreased contraction and calcium affinity; both disease classes induced graded transcriptomic changes including MAPK signaling targets and NPPB, which correlated directly with sarcomere functional changes.","method":"CRISPR/Cas9-engineered hiPSC-derived cardiomyocytes; cardiac microtissue contraction assay; thin filament calcium reporter; RNA sequencing; NPPB transcriptional reporter","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal methods (functional assays, calcium reporter, transcriptomics, reporter engineering) across 51 variants in isogenic hiPSC-CM platform","pmids":["33025817"],"is_preprint":false},{"year":2021,"finding":"The HCM-associated TNNT2 variant I79N significantly increases myofilament Ca2+ sensitivity and decreases the Ca2+ off-rate constant (koff) in reconstituted human cardiac thin filaments; in heterozygous I79N+/- hiPSC-CMs, enhanced cytosolic Ca2+ buffering reduced Ca2+ transients, causing beat-to-beat instability, action potential triangulation, and voltage/Ca2+ alternans at higher stimulation frequencies, mechanistically linking the variant to arrhythmogenesis.","method":"Reconstituted human cardiac thin filaments with steady-state and stopped-flow fluorescence; CRISPR/Cas9-generated I79N+/- hiPSC-CMs; voltage and Ca2+ transient measurement; NanoString transcriptomics","journal":"Frontiers in cell and developmental biology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro reconstitution with biophysical assays plus isogenic hiPSC-CM model with multiple functional readouts, single lab but multiple orthogonal methods","pmids":["34977031"],"is_preprint":false},{"year":2022,"finding":"The TNNT2 Δ160E mutation causes sarcomeric calcium retention, prolonged calcium decay, relaxation impairment, and cardiomyocyte hypertrophy in isogenic hiPSC-CMs in a dose-dependent manner; the mutation promotes hypertrophic signaling via NFATc1 nuclear translocation and increased CaMKIIδ and phospholamban phosphorylation; calcium desensitization with epigallocatechin-3-gallate rescues the prolonged calcium decay phenotype.","method":"CRISPR/Cas9 isogenic iPSC-CMs (hetero- and homozygous); calcium transient measurement; high-content imaging of NFATc1 nuclear translocation; western blotting for CaMKIIδ and phospholamban phosphorylation; R-GECO-fused mutant troponin T overexpression","journal":"Circulation. Genomic and precision medicine","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — isogenic hiPSC-CM model with multiple orthogonal assays (calcium imaging, signaling pathway analysis, pharmacological rescue), single lab","pmids":["35861968"],"is_preprint":false},{"year":2022,"finding":"The TNNT2 K280N mutation increases myofilament Ca2+ sensitivity independently of phosphorylation status (not corrected by alkaline phosphatase or PKA treatment); as little as 14% mutant cTnT-K280N in troponin exchange experiments is sufficient to elevate Ca2+ sensitivity; homozygous K280N hiPSC-CMs show elevated diastolic Ca2+, enhanced contractility, and impaired relaxation.","method":"Force measurements in isolated cardiomyocytes from homozygous K280N patient; troponin exchange experiments; alkaline phosphatase and PKA treatment; CRISPR/Cas9 isogenic hiPSC-CMs; Ca2+ transient and cell shortening assays","journal":"Journal of molecular and cellular cardiology plus","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal methods including human patient tissue, troponin exchange titration, and isogenic hiPSC-CM model","pmids":["37159677"],"is_preprint":false},{"year":2022,"finding":"DYRK1A overexpression in iPSC-derived cardiomyocytes increases the abundance of TNNT2 fetal splice variants by ~58% and decreases the adult cTnT3 variant by ~27%, with increased SRSF6 phosphorylation (~25-65%), establishing that DYRK1A regulates TNNT2 alternative splicing through phosphorylation of the splicing factor SRSF6.","method":"iPSC-derived cardiomyocytes with DYRK1A overexpression; RT-PCR for TNNT2 splice variants; phospho-SRSF6 western blotting","journal":"Cardiovascular toxicology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct functional demonstration of DYRK1A-SRSF6-TNNT2 splicing pathway in human cardiomyocytes, single lab, two orthogonal methods","pmids":["35596909"],"is_preprint":false},{"year":2019,"finding":"In zebrafish, tnnt2a is expressed not only in myocardial cells but also in a novel group of myl7-negative smooth muscle cells on the outflow tract (OFT); restoration of tnnt2a expression in myocardial tissue alone (via myl7 promoter) was insufficient to recover normal heart function and circulation, whereas combinatorial rescue in both myocardial and OFT cells fully restored cardiac function, demonstrating that TNNT2 expression in OFT smooth muscle cells is indispensable for normal cardiac mechanical dynamics.","method":"CRISPR/Cas9 tnnt2a zebrafish mutants; conditional/inducible promoter-driven rescue; RNA-seq; immunofluorescence; cardiac function imaging","journal":"Biology open","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic rescue experiments with defined functional readout in zebrafish, supported by RNA-seq and immunofluorescence, single lab","pmids":["31796423"],"is_preprint":false},{"year":2021,"finding":"XIN protein expression is reduced in TNNT2-ΔK210 hESC-derived cardiomyocytes and mouse heart tissues; overexpression of XINB decreases myofilament disorganization and increases cell contractility in TNNT2-ΔK210 cardiomyocytes; AAV9-mediated cardiac XINB overexpression in TNNT2-ΔK210 mice partially reversed cardiac dilation, systolic dysfunction, and fibrosis.","method":"hESC-derived cardiomyocytes; TNNT2-ΔK210 mouse model; AAV9 cardiac overexpression; echocardiography; histology","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo rescue experiment with AAV9 and defined phenotypic readouts, single lab with multiple methods","pmids":["34222259"],"is_preprint":false},{"year":2019,"finding":"In Down syndrome myocardium, the DYRK1A-SRSF6-TNNT2 pathway is dysregulated: phosphorylated SRSF6 levels are 2.6-fold higher in trisomic myocardium, and fetal TNNT2 splice variants are more highly expressed, consistent with trisomy 21 gene dosage effects driving aberrant TNNT2 splicing via SRSF6 hyperphosphorylation.","method":"Western blotting for phospho-DYRK1A, phospho-SRSF6; RT-PCR/analysis of TNNT2 fetal isoforms in human myocardial tissue samples","journal":"Experimental and molecular pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct protein measurements in human myocardial tissue with functional pathway inference, single lab","pmids":["31201803"],"is_preprint":false},{"year":2022,"finding":"The HCM-linked TNNT2 mutation R92Q causes increased myofilament calcium sensitivity in atrial muscle, leading to reduced inotropic reserve, slower twitch kinetics, and increased spontaneous beats and triggered contractions representing an intrinsic atrial arrhythmogenic mechanism; by contrast, the E163R mutation increases energy cost of tension generation in atrial muscle without causing atrial arrhythmic propensity, establishing genotype-specific atrial pathomechanisms.","method":"HCM mouse models (R92Q and E163R); atrial trabecula functional assays (twitch amplitude, kinetics, ATP consumption, myofilament calcium sensitivity); echocardiography","journal":"Frontiers in physiology","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — ex vivo functional assays on atrial trabeculae from two distinct mouse models with orthogonal measurements, single lab","pmids":["35514357"],"is_preprint":false},{"year":2023,"finding":"The HCM-linked TNNT2 mutation R92L allosterically repositions the N-terminus of cTnI closer to cTnC (measured by TR-FRET), creates additional electrostatic interactions at the PKA consensus sequence, and reduces cTnI phosphorylation at that site, thereby impairing PKA-mediated regulation of myofilament relaxation and causing early-onset diastolic dysfunction; constitutive phosphomimetic cTnI (D23D24) rescued diastolic function only for R92L but not Δ160E.","method":"In vivo mouse models; ex vivo hemodynamics; stopped-flow kinetics; time-resolved FRET (TR-FRET); molecular dynamics simulations; western blotting; 2D echocardiography","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — multiple orthogonal methods including TR-FRET structural measurement and kinetics, but preprint (not peer-reviewed), single lab","pmids":["37503299"],"is_preprint":true},{"year":2026,"finding":"The TNNT2-R151W mutation causes sarcomere disarray, attenuated Ca2+ transient amplitude, prolonged time to peak, and delayed decay tau in patient-derived iPSC-CMs, with substantially decreased contractile force in pillar-based engineered heart tissue; overexpression of wild-type TNNT2 rescued all these phenotypes, providing functional evidence that the mutation causes pediatric DCM through sarcomere insufficiency and Ca2+ handling disturbances.","method":"Patient-derived iPSC-CMs; pillar-based engineered heart tissue (EHT) contractile force assay; Ca2+ transient imaging; wild-type TNNT2 overexpression rescue","journal":"Bioengineering & translational medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patient iPSC-CM model with EHT functional assay and rescue experiment, multiple orthogonal methods, single lab","pmids":["42016857"],"is_preprint":false},{"year":2024,"finding":"The TNNT2 R141W mutation (modeled as Tnnt2 R154W in mice) causes LVNC through loss of a salt bridge between TNNT2(R141W) and E-257 in tropomyosin (identified by 3D protein structural modeling), decreasing cardiac contraction; furthermore, nuclear TNNT2 functions as an HDAC1 sponge in cardiomyocyte nuclei, and the R141W mutation compromises this nuclear TNNT2-HDAC1 association, causing epigenetic perturbation and transcriptional dysregulation; simvastatin restores the nuclear TNNT2(R141W)-HDAC1 association and recovers cardiac function.","method":"Knock-in mice (Tnnt2 R154W); iPSC-derived cardiomyocytes from LVNC patients; 3D protein structure modeling; co-immunoprecipitation (nuclear TNNT2-HDAC1); omics analysis; pharmacological rescue with simvastatin, pan-HDAC inhibitor, TGFβR1 inhibitor, EZH2 inhibitor","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP for nuclear interaction plus multiple in vivo/in vitro models and pharmacological rescue, but preprint (not peer-reviewed), novel nuclear function claim requires independent replication","pmids":[],"is_preprint":true},{"year":2023,"finding":"TNNT2 protein physically interacts with EGFR in colorectal cancer cells (demonstrated by co-immunoprecipitation); TNNT2 overexpression upregulates EGFR and HER2 expression, decreases E-cadherin, and increases Vimentin and N-cadherin, promoting EMT; knockdown reverses these effects, suggesting TNNT2 promotes CRC invasion through an EGFR/HER2/EMT signaling axis.","method":"Co-immunoprecipitation; western blotting; CCK-8; colony formation; Transwell assay; qPCR","journal":"Cancer cell international","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP in cancer cell line for a non-canonical TNNT2 function; single lab, novel context with no independent replication","pmids":["37481519"],"is_preprint":false},{"year":2025,"finding":"In hiPSC-CMs bearing HCM (hypercontractile) or DCM (hypocontractile) TNNT2 pathogenic variants, impaired contractile transients alter lamin A/C expression and nuclear stiffness (nuclear lamina remodeling); treatment with myosin modulators Mavacamten (for HCM) or Omecamtiv Mecarbil (for DCM) rescued these changes in nuclear stiffness, establishing a causal link between sarcomere contractility and nuclear mechanics.","method":"hiPSC-CMs with TNNT2 pathogenic variants; transcriptomics; nuclear stiffness measurements; pharmacological rescue with Mavacamten and Omecamtiv Mecarbil","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct nuclear mechanics measurement with pharmacological rescue in isogenic hiPSC-CM models, single lab with multiple orthogonal methods","pmids":["41321620"],"is_preprint":false}],"current_model":"TNNT2 encodes cardiac troponin T, a thin filament protein that regulates Ca2+-dependent actomyosin interactions; HCM-causing variants increase myofilament Ca2+ sensitivity and contractility (driving hypertrophy, diastolic dysfunction, and arrhythmia risk), while DCM-causing variants decrease Ca2+ sensitivity and contractile force; TNNT2 alternative splicing is regulated by the DYRK1A-SRSF6 kinase-splicing factor pathway; the protein also has a nuclear role as an HDAC1 sponge that, when disrupted by mutation, causes epigenetic perturbation; mechanosensory force transmission from mutant sarcomeres to the nuclear lamina remodels lamin A/C and nuclear stiffness; and in the outflow tract, TNNT2 expression in smooth muscle cells is required for normal cardiac mechanical dynamics."},"narrative":{"mechanistic_narrative":"TNNT2 encodes cardiac troponin T, a thin-filament protein that couples cytosolic Ca2+ to actomyosin contraction in cardiomyocytes, and whose missense variants produce divergent cardiomyopathies through opposite shifts in myofilament Ca2+ handling [PMID:20031601, PMID:33025817]. In isogenic hiPSC-derived cardiomyocytes and reconstituted thin filaments, HCM-associated variants raise myofilament Ca2+ affinity and contraction, while DCM-associated variants lower Ca2+ sensitivity and contractile force, and both classes drive graded transcriptomic responses including MAPK targets and NPPB induction that scale with the functional change [PMID:33025817, PMID:20031601]. At the biophysical level, individual HCM variants slow the Ca2+ off-rate and raise diastolic Ca2+ to cause relaxation impairment, beat-to-beat instability, and Ca2+/voltage alternans that link the protein to arrhythmogenesis [PMID:34977031, PMID:37159677], with downstream hypertrophic signaling through NFATc1 nuclear translocation and CaMKIIδ/phospholamban phosphorylation [PMID:35861968]; variant-specific effects extend to allosteric repositioning of cTnI that impairs PKA-mediated relaxation control [PMID:37503299]. Beyond the sarcomere, altered contractile transients from pathogenic variants remodel lamin A/C and nuclear stiffness, a change rescued by myosin modulators, establishing mechanotransmission from sarcomere to nucleus [PMID:41321620]. TNNT2 is also subject to developmentally regulated alternative splicing that is controlled by DYRK1A-dependent phosphorylation of the splicing factor SRSF6, a pathway dysregulated in trisomic (Down syndrome) myocardium [PMID:35596909, PMID:31201803, PMID:8088824]. A reported nuclear role for TNNT2 as an HDAC1 sponge and a physical interaction with EGFR in colorectal cancer fall outside the validated sarcomeric mechanism in the current corpus.","teleology":[{"year":1994,"claim":"Established the gene's chromosomal location and that cardiac troponin T is expressed as multiple developmentally regulated isoforms, setting up alternative splicing as a feature of TNNT2 biology.","evidence":"Somatic cell hybrid mapping and cDNA cloning/hybridization in fetal human heart","pmids":["8088824"],"confidence":"High","gaps":["Functional consequences of individual isoforms not defined","Regulators of the splicing not identified at this stage"]},{"year":2004,"claim":"Linked a TNNT2 intronic polymorphism to altered splicing (exon 4 skipping) and to left ventricular hypertrophy, connecting splice regulation to a structural cardiac phenotype.","evidence":"In vitro splicing assay plus clinical association with LV mass","pmids":["14986170"],"confidence":"Medium","gaps":["Association does not establish causation of hypertrophy","Mechanism connecting exon 4 skipping to LV mass unresolved"]},{"year":2009,"claim":"Defined the unifying biophysical mechanism for DCM-causing variants — decreased Ca2+ sensitivity of force development — across multiple mutations.","evidence":"Cardiac myocyte reconstitution with mutant troponin T and Ca2+-sensitivity of force assays","pmids":["20031601"],"confidence":"High","gaps":["In vitro reconstitution does not capture intact-cell or in vivo remodeling","Downstream signaling consequences not addressed"]},{"year":2010,"claim":"Showed in vivo that a pathogenic variant produces intrinsic cardiomyocyte dysfunction and heart-failure gene induction, arguing the primary defect is cell-autonomous rather than developmental.","evidence":"Transgenic mouse expressing mutant human cTnT with echocardiography, histology, and gene expression","pmids":["20083571"],"confidence":"Medium","gaps":["Single variant in transgenic (non-knock-in) context","Calcium-handling mechanism not directly measured"]},{"year":2020,"claim":"Resolved the bidirectional genotype-phenotype rule at scale: HCM variants increase, and DCM variants decrease, both contraction and Ca2+ affinity, with transcriptomic output scaling to sarcomere function.","evidence":"CRISPR-engineered isogenic hiPSC-CMs (51 variants), microtissue contraction, Ca2+ reporter, RNA-seq, NPPB reporter","pmids":["33025817"],"confidence":"High","gaps":["Mechanism converting sarcomere change to MAPK/NPPB transcription not dissected","Long-term remodeling not captured in microtissue timeframe"]},{"year":2021,"claim":"Connected an HCM variant's biophysical signature (slowed Ca2+ off-rate, raised Ca2+ sensitivity) to a cellular arrhythmogenic phenotype, providing a mechanistic chain to arrhythmia risk.","evidence":"Reconstituted thin filaments with stopped-flow kinetics plus I79N+/- hiPSC-CMs with voltage/Ca2+ transient measurement","pmids":["34977031"],"confidence":"High","gaps":["Arrhythmia demonstrated in cellular model, not whole heart","Single variant"]},{"year":2022,"claim":"Extended the mechanism downstream to hypertrophic signaling, showing a Ca2+-retaining variant activates NFATc1 and CaMKIIδ/phospholamban phosphorylation, with pharmacological Ca2+ desensitization rescuing relaxation.","evidence":"Isogenic hiPSC-CMs with Ca2+ imaging, NFATc1 translocation imaging, signaling western blots, EGCG rescue","pmids":["35861968"],"confidence":"High","gaps":["Causal ordering of Ca2+ retention versus signaling activation not fully resolved","In vivo relevance of EGCG rescue untested here"]},{"year":2022,"claim":"Demonstrated that elevated Ca2+ sensitivity is phosphorylation-independent and dominant at low mutant fraction, clarifying how heterozygous variants exert outsized effects.","evidence":"Patient cardiomyocyte force measurements, troponin exchange titration, phosphatase/PKA treatment, isogenic hiPSC-CMs","pmids":["37159677"],"confidence":"High","gaps":["Generalizability of the 14% threshold to other variants unknown","Atrial versus ventricular differences not addressed"]},{"year":2022,"claim":"Established genotype-specific atrial pathomechanisms, distinguishing a Ca2+-sensitizing arrhythmogenic variant from an energetic-cost variant lacking arrhythmic propensity.","evidence":"R92Q and E163R HCM mouse models with atrial trabecula functional assays and echocardiography","pmids":["35514357"],"confidence":"Medium","gaps":["Two variants do not define the full genotypic spectrum of atrial risk","Molecular basis of energy-cost increase not detailed"]},{"year":2022,"claim":"Identified DYRK1A-SRSF6 phosphorylation as the regulatory pathway controlling the developmental fetal-to-adult TNNT2 splice transition.","evidence":"DYRK1A overexpression in iPSC-CMs with RT-PCR splice quantification and phospho-SRSF6 western blot","pmids":["35596909"],"confidence":"Medium","gaps":["Direct SRSF6 binding to TNNT2 pre-mRNA not shown","Functional consequence of fetal isoform shift not measured"]},{"year":2019,"claim":"Provided disease-context validation of the splicing pathway, showing SRSF6 hyperphosphorylation and fetal TNNT2 isoform enrichment in trisomy 21 myocardium.","evidence":"Phospho-DYRK1A/SRSF6 western blotting and TNNT2 isoform RT-PCR in human trisomic myocardial tissue","pmids":["31201803"],"confidence":"Medium","gaps":["Correlative tissue measurement, not causal manipulation","Functional cardiac consequence in Down syndrome not established"]},{"year":2019,"claim":"Revealed a non-myocardial requirement for TNNT2, showing outflow-tract smooth muscle expression is indispensable for normal cardiac mechanical dynamics.","evidence":"tnnt2a zebrafish mutants with tissue-specific promoter rescue, RNA-seq, and cardiac function imaging","pmids":["31796423"],"confidence":"Medium","gaps":["Mammalian conservation of the OFT smooth muscle role not shown","Molecular function of TNNT2 in smooth muscle cells undefined"]},{"year":2021,"claim":"Identified XIN/XINB as a modifier that can partially rescue a DCM variant phenotype, pointing to candidate therapeutic targets downstream of sarcomere dysfunction.","evidence":"TNNT2-ΔK210 hESC-CMs and mice with AAV9 XINB overexpression, echocardiography, histology","pmids":["34222259"],"confidence":"Medium","gaps":["Mechanism of XIN reduction by ΔK210 not defined","Rescue is partial; durability unknown"]},{"year":2023,"claim":"Provided a structural-allosteric explanation for diastolic dysfunction, showing a variant repositions cTnI to impair PKA phosphorylation of the relaxation-regulating site.","evidence":"Mouse models, ex vivo hemodynamics, stopped-flow kinetics, TR-FRET, MD simulation, phosphomimetic rescue (preprint)","pmids":["37503299"],"confidence":"Medium","gaps":["Preprint, not peer-reviewed","Variant-specific rescue (R92L not Δ160E) limits generality"]},{"year":2024,"claim":"Proposed a non-canonical nuclear function for TNNT2 as an HDAC1 sponge whose disruption causes epigenetic dysregulation, expanding the mechanism beyond sarcomere mechanics.","evidence":"Knock-in mice, LVNC patient iPSC-CMs, structural modeling, nuclear TNNT2-HDAC1 co-IP, pharmacological rescue (preprint)","pmids":[],"confidence":"Medium","gaps":["Preprint with no PMID; novel nuclear claim awaits independent replication","Single Co-IP for the nuclear interaction","Reciprocal validation and stoichiometry of the sponge model not established"]},{"year":2025,"claim":"Established a causal sarcomere-to-nucleus mechanotransmission axis, linking variant-altered contractile transients to lamin A/C and nuclear stiffness changes reversible by myosin modulators.","evidence":"hiPSC-CMs with HCM/DCM TNNT2 variants, transcriptomics, nuclear stiffness measurement, Mavacamten/Omecamtiv Mecarbil rescue","pmids":["41321620"],"confidence":"Medium","gaps":["Molecular link from contractility to lamin remodeling not detailed","In vivo nuclear mechanics not assessed"]},{"year":null,"claim":"It remains unresolved whether the reported non-sarcomeric roles of TNNT2 — nuclear HDAC1 sponging and EGFR-driven EMT in cancer — represent bona fide physiological functions and how they integrate with the established thin-filament regulatory role.","evidence":"","pmids":[],"confidence":"Low","gaps":["Nuclear and cancer functions rest on single-lab/preprint or Low-confidence evidence","No reciprocal or independent validation of non-sarcomeric interactions","Physiological stoichiometry and context unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,4,5,7]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,4,5,7]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[4,14]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,4,14]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[15]}],"pathway":[{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[0,4,5,7]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[1,8,11]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,4,6]}],"complexes":["cardiac troponin complex","cardiac thin filament"],"partners":["TNNI3","TNNC1","TPM1","HDAC1","EGFR","XIRP2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P45379","full_name":"Troponin T, cardiac muscle","aliases":["Cardiac muscle troponin T","cTnT"],"length_aa":298,"mass_kda":35.9,"function":"Troponin T is the tropomyosin-binding subunit of troponin, the thin filament regulatory complex which confers calcium-sensitivity to striated muscle actomyosin ATPase activity","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/P45379/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/TNNT2","classification":"Common Essential","n_dependent_lines":394,"n_total_lines":1208,"dependency_fraction":0.326158940397351},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TNNT2","total_profiled":1310},"omim":[{"mim_id":"621216","title":"PLAQUE-ENRICHED LONG NONCODING RNA IN ATHEROSCLEROTIC AND INFLAMMATORY BOWEL MACROPHAGE REGULATION; PELATON","url":"https://www.omim.org/entry/621216"},{"mim_id":"615396","title":"LEFT VENTRICULAR NONCOMPACTION 10; LVNC10","url":"https://www.omim.org/entry/615396"},{"mim_id":"613874","title":"CARDIOMYOPATHY, FAMILIAL HYPERTROPHIC, 18; CMH18","url":"https://www.omim.org/entry/613874"},{"mim_id":"613251","title":"CARDIOMYOPATHY, FAMILIAL HYPERTROPHIC, 14; CMH14","url":"https://www.omim.org/entry/613251"},{"mim_id":"612681","title":"CUGBP- AND ELAV-LIKE FAMILY, MEMBER 6; CELF6","url":"https://www.omim.org/entry/612681"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Uncertain","locations":[{"location":"Nucleoplasm","reliability":"Uncertain"},{"location":"Nucleoli","reliability":"Uncertain"},{"location":"Focal adhesion sites","reliability":"Additional"},{"location":"Microtubules","reliability":"Additional"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"heart muscle","ntpm":8731.9}],"url":"https://www.proteinatlas.org/search/TNNT2"},"hgnc":{"alias_symbol":["CMPD2"],"prev_symbol":["CMH2","CMD1D"]},"alphafold":{"accession":"P45379","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P45379","model_url":"https://alphafold.ebi.ac.uk/files/AF-P45379-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P45379-F1-predicted_aligned_error_v6.png","plddt_mean":78.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TNNT2","jax_strain_url":"https://www.jax.org/strain/search?query=TNNT2"},"sequence":{"accession":"P45379","fasta_url":"https://rest.uniprot.org/uniprotkb/P45379.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P45379/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P45379"}},"corpus_meta":[{"pmid":"19412328","id":"PMC_19412328","title":"Coding sequence mutations identified in MYH7, TNNT2, SCN5A, CSRP3, LBD3, and TCAP from 313 patients with familial or idiopathic dilated cardiomyopathy.","date":"2008","source":"Clinical and translational science","url":"https://pubmed.ncbi.nlm.nih.gov/19412328","citation_count":159,"is_preprint":false},{"pmid":"20031601","id":"PMC_20031601","title":"Clinical and functional characterization of TNNT2 mutations identified in patients with dilated cardiomyopathy.","date":"2009","source":"Circulation. Cardiovascular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/20031601","citation_count":94,"is_preprint":false},{"pmid":"8088824","id":"PMC_8088824","title":"Human cardiac troponin T: identification of fetal isoforms and assignment of the TNNT2 locus to chromosome 1q.","date":"1994","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/8088824","citation_count":67,"is_preprint":false},{"pmid":"19150014","id":"PMC_19150014","title":"[Mutations in sarcomeric genes MYH7, MYBPC3, TNNT2, TNNI3, and TPM1 in patients with hypertrophic cardiomyopathy].","date":"2009","source":"Revista espanola de cardiologia","url":"https://pubmed.ncbi.nlm.nih.gov/19150014","citation_count":59,"is_preprint":false},{"pmid":"20083571","id":"PMC_20083571","title":"Severe familial left ventricular non-compaction cardiomyopathy due to a novel troponin T (TNNT2) mutation.","date":"2010","source":"Cardiovascular 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Cardiovascular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro functional reconstitution assay with multiple mutations tested, single lab but multiple mutants with consistent results\",\n      \"pmids\": [\"20031601\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"The TNNT2 gene was mapped to chromosome 1q (1cen-qter) by somatic cell hybrid analysis, and multiple cardiac troponin T mRNA isoforms were demonstrated in fetal human heart resulting from alternative splicing in the 5' coding region.\",\n      \"method\": \"Somatic cell hybrid analysis; cDNA cloning and hybridization; genomic Southern blotting\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct chromosomal mapping with somatic cell hybrids and demonstration of alternative splicing by molecular cloning, replicated by subsequent studies\",\n      \"pmids\": [\"8088824\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"A 5-bp insertion/deletion polymorphism in intron 3 of TNNT2 affects splicing: the deletion allele causes skipping of exon 4 during splicing, altering the mRNA expression pattern, and was associated with greater left ventricular hypertrophy.\",\n      \"method\": \"In vitro expression study; splicing analysis; association study with LV mass measurements\",\n      \"journal\": \"Journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro splicing assay demonstrated functional consequence of the deletion allele, supported by clinical association data, single lab\",\n      \"pmids\": [\"14986170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"A novel TNNT2 missense mutation pE96K causes impaired left ventricular function and induction of heart failure marker genes in transgenic mice expressing the mutant human cTNT, without producing a left ventricular non-compaction phenotype, indicating intrinsic cardiomyocyte dysfunction as the primary pathological mechanism.\",\n      \"method\": \"Transgenic mouse model; echocardiography; histology; gene expression analysis\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transgenic mouse model with defined cardiac phenotype readout, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"20083571\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"HCM-associated TNNT2 variants increased cardiac microtissue contraction and myofilament calcium affinity, whereas DCM-associated TNNT2 variants decreased contraction and calcium affinity; both disease classes induced graded transcriptomic changes including MAPK signaling targets and NPPB, which correlated directly with sarcomere functional changes.\",\n      \"method\": \"CRISPR/Cas9-engineered hiPSC-derived cardiomyocytes; cardiac microtissue contraction assay; thin filament calcium reporter; RNA sequencing; NPPB transcriptional reporter\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal methods (functional assays, calcium reporter, transcriptomics, reporter engineering) across 51 variants in isogenic hiPSC-CM platform\",\n      \"pmids\": [\"33025817\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The HCM-associated TNNT2 variant I79N significantly increases myofilament Ca2+ sensitivity and decreases the Ca2+ off-rate constant (koff) in reconstituted human cardiac thin filaments; in heterozygous I79N+/- hiPSC-CMs, enhanced cytosolic Ca2+ buffering reduced Ca2+ transients, causing beat-to-beat instability, action potential triangulation, and voltage/Ca2+ alternans at higher stimulation frequencies, mechanistically linking the variant to arrhythmogenesis.\",\n      \"method\": \"Reconstituted human cardiac thin filaments with steady-state and stopped-flow fluorescence; CRISPR/Cas9-generated I79N+/- hiPSC-CMs; voltage and Ca2+ transient measurement; NanoString transcriptomics\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro reconstitution with biophysical assays plus isogenic hiPSC-CM model with multiple functional readouts, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"34977031\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The TNNT2 Δ160E mutation causes sarcomeric calcium retention, prolonged calcium decay, relaxation impairment, and cardiomyocyte hypertrophy in isogenic hiPSC-CMs in a dose-dependent manner; the mutation promotes hypertrophic signaling via NFATc1 nuclear translocation and increased CaMKIIδ and phospholamban phosphorylation; calcium desensitization with epigallocatechin-3-gallate rescues the prolonged calcium decay phenotype.\",\n      \"method\": \"CRISPR/Cas9 isogenic iPSC-CMs (hetero- and homozygous); calcium transient measurement; high-content imaging of NFATc1 nuclear translocation; western blotting for CaMKIIδ and phospholamban phosphorylation; R-GECO-fused mutant troponin T overexpression\",\n      \"journal\": \"Circulation. Genomic and precision medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — isogenic hiPSC-CM model with multiple orthogonal assays (calcium imaging, signaling pathway analysis, pharmacological rescue), single lab\",\n      \"pmids\": [\"35861968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The TNNT2 K280N mutation increases myofilament Ca2+ sensitivity independently of phosphorylation status (not corrected by alkaline phosphatase or PKA treatment); as little as 14% mutant cTnT-K280N in troponin exchange experiments is sufficient to elevate Ca2+ sensitivity; homozygous K280N hiPSC-CMs show elevated diastolic Ca2+, enhanced contractility, and impaired relaxation.\",\n      \"method\": \"Force measurements in isolated cardiomyocytes from homozygous K280N patient; troponin exchange experiments; alkaline phosphatase and PKA treatment; CRISPR/Cas9 isogenic hiPSC-CMs; Ca2+ transient and cell shortening assays\",\n      \"journal\": \"Journal of molecular and cellular cardiology plus\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal methods including human patient tissue, troponin exchange titration, and isogenic hiPSC-CM model\",\n      \"pmids\": [\"37159677\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"DYRK1A overexpression in iPSC-derived cardiomyocytes increases the abundance of TNNT2 fetal splice variants by ~58% and decreases the adult cTnT3 variant by ~27%, with increased SRSF6 phosphorylation (~25-65%), establishing that DYRK1A regulates TNNT2 alternative splicing through phosphorylation of the splicing factor SRSF6.\",\n      \"method\": \"iPSC-derived cardiomyocytes with DYRK1A overexpression; RT-PCR for TNNT2 splice variants; phospho-SRSF6 western blotting\",\n      \"journal\": \"Cardiovascular toxicology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct functional demonstration of DYRK1A-SRSF6-TNNT2 splicing pathway in human cardiomyocytes, single lab, two orthogonal methods\",\n      \"pmids\": [\"35596909\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In zebrafish, tnnt2a is expressed not only in myocardial cells but also in a novel group of myl7-negative smooth muscle cells on the outflow tract (OFT); restoration of tnnt2a expression in myocardial tissue alone (via myl7 promoter) was insufficient to recover normal heart function and circulation, whereas combinatorial rescue in both myocardial and OFT cells fully restored cardiac function, demonstrating that TNNT2 expression in OFT smooth muscle cells is indispensable for normal cardiac mechanical dynamics.\",\n      \"method\": \"CRISPR/Cas9 tnnt2a zebrafish mutants; conditional/inducible promoter-driven rescue; RNA-seq; immunofluorescence; cardiac function imaging\",\n      \"journal\": \"Biology open\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic rescue experiments with defined functional readout in zebrafish, supported by RNA-seq and immunofluorescence, single lab\",\n      \"pmids\": [\"31796423\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"XIN protein expression is reduced in TNNT2-ΔK210 hESC-derived cardiomyocytes and mouse heart tissues; overexpression of XINB decreases myofilament disorganization and increases cell contractility in TNNT2-ΔK210 cardiomyocytes; AAV9-mediated cardiac XINB overexpression in TNNT2-ΔK210 mice partially reversed cardiac dilation, systolic dysfunction, and fibrosis.\",\n      \"method\": \"hESC-derived cardiomyocytes; TNNT2-ΔK210 mouse model; AAV9 cardiac overexpression; echocardiography; histology\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo rescue experiment with AAV9 and defined phenotypic readouts, single lab with multiple methods\",\n      \"pmids\": [\"34222259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In Down syndrome myocardium, the DYRK1A-SRSF6-TNNT2 pathway is dysregulated: phosphorylated SRSF6 levels are 2.6-fold higher in trisomic myocardium, and fetal TNNT2 splice variants are more highly expressed, consistent with trisomy 21 gene dosage effects driving aberrant TNNT2 splicing via SRSF6 hyperphosphorylation.\",\n      \"method\": \"Western blotting for phospho-DYRK1A, phospho-SRSF6; RT-PCR/analysis of TNNT2 fetal isoforms in human myocardial tissue samples\",\n      \"journal\": \"Experimental and molecular pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct protein measurements in human myocardial tissue with functional pathway inference, single lab\",\n      \"pmids\": [\"31201803\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The HCM-linked TNNT2 mutation R92Q causes increased myofilament calcium sensitivity in atrial muscle, leading to reduced inotropic reserve, slower twitch kinetics, and increased spontaneous beats and triggered contractions representing an intrinsic atrial arrhythmogenic mechanism; by contrast, the E163R mutation increases energy cost of tension generation in atrial muscle without causing atrial arrhythmic propensity, establishing genotype-specific atrial pathomechanisms.\",\n      \"method\": \"HCM mouse models (R92Q and E163R); atrial trabecula functional assays (twitch amplitude, kinetics, ATP consumption, myofilament calcium sensitivity); echocardiography\",\n      \"journal\": \"Frontiers in physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — ex vivo functional assays on atrial trabeculae from two distinct mouse models with orthogonal measurements, single lab\",\n      \"pmids\": [\"35514357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"The HCM-linked TNNT2 mutation R92L allosterically repositions the N-terminus of cTnI closer to cTnC (measured by TR-FRET), creates additional electrostatic interactions at the PKA consensus sequence, and reduces cTnI phosphorylation at that site, thereby impairing PKA-mediated regulation of myofilament relaxation and causing early-onset diastolic dysfunction; constitutive phosphomimetic cTnI (D23D24) rescued diastolic function only for R92L but not Δ160E.\",\n      \"method\": \"In vivo mouse models; ex vivo hemodynamics; stopped-flow kinetics; time-resolved FRET (TR-FRET); molecular dynamics simulations; western blotting; 2D echocardiography\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — multiple orthogonal methods including TR-FRET structural measurement and kinetics, but preprint (not peer-reviewed), single lab\",\n      \"pmids\": [\"37503299\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"The TNNT2-R151W mutation causes sarcomere disarray, attenuated Ca2+ transient amplitude, prolonged time to peak, and delayed decay tau in patient-derived iPSC-CMs, with substantially decreased contractile force in pillar-based engineered heart tissue; overexpression of wild-type TNNT2 rescued all these phenotypes, providing functional evidence that the mutation causes pediatric DCM through sarcomere insufficiency and Ca2+ handling disturbances.\",\n      \"method\": \"Patient-derived iPSC-CMs; pillar-based engineered heart tissue (EHT) contractile force assay; Ca2+ transient imaging; wild-type TNNT2 overexpression rescue\",\n      \"journal\": \"Bioengineering & translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patient iPSC-CM model with EHT functional assay and rescue experiment, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"42016857\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The TNNT2 R141W mutation (modeled as Tnnt2 R154W in mice) causes LVNC through loss of a salt bridge between TNNT2(R141W) and E-257 in tropomyosin (identified by 3D protein structural modeling), decreasing cardiac contraction; furthermore, nuclear TNNT2 functions as an HDAC1 sponge in cardiomyocyte nuclei, and the R141W mutation compromises this nuclear TNNT2-HDAC1 association, causing epigenetic perturbation and transcriptional dysregulation; simvastatin restores the nuclear TNNT2(R141W)-HDAC1 association and recovers cardiac function.\",\n      \"method\": \"Knock-in mice (Tnnt2 R154W); iPSC-derived cardiomyocytes from LVNC patients; 3D protein structure modeling; co-immunoprecipitation (nuclear TNNT2-HDAC1); omics analysis; pharmacological rescue with simvastatin, pan-HDAC inhibitor, TGFβR1 inhibitor, EZH2 inhibitor\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP for nuclear interaction plus multiple in vivo/in vitro models and pharmacological rescue, but preprint (not peer-reviewed), novel nuclear function claim requires independent replication\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"TNNT2 protein physically interacts with EGFR in colorectal cancer cells (demonstrated by co-immunoprecipitation); TNNT2 overexpression upregulates EGFR and HER2 expression, decreases E-cadherin, and increases Vimentin and N-cadherin, promoting EMT; knockdown reverses these effects, suggesting TNNT2 promotes CRC invasion through an EGFR/HER2/EMT signaling axis.\",\n      \"method\": \"Co-immunoprecipitation; western blotting; CCK-8; colony formation; Transwell assay; qPCR\",\n      \"journal\": \"Cancer cell international\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP in cancer cell line for a non-canonical TNNT2 function; single lab, novel context with no independent replication\",\n      \"pmids\": [\"37481519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In hiPSC-CMs bearing HCM (hypercontractile) or DCM (hypocontractile) TNNT2 pathogenic variants, impaired contractile transients alter lamin A/C expression and nuclear stiffness (nuclear lamina remodeling); treatment with myosin modulators Mavacamten (for HCM) or Omecamtiv Mecarbil (for DCM) rescued these changes in nuclear stiffness, establishing a causal link between sarcomere contractility and nuclear mechanics.\",\n      \"method\": \"hiPSC-CMs with TNNT2 pathogenic variants; transcriptomics; nuclear stiffness measurements; pharmacological rescue with Mavacamten and Omecamtiv Mecarbil\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct nuclear mechanics measurement with pharmacological rescue in isogenic hiPSC-CM models, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"41321620\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TNNT2 encodes cardiac troponin T, a thin filament protein that regulates Ca2+-dependent actomyosin interactions; HCM-causing variants increase myofilament Ca2+ sensitivity and contractility (driving hypertrophy, diastolic dysfunction, and arrhythmia risk), while DCM-causing variants decrease Ca2+ sensitivity and contractile force; TNNT2 alternative splicing is regulated by the DYRK1A-SRSF6 kinase-splicing factor pathway; the protein also has a nuclear role as an HDAC1 sponge that, when disrupted by mutation, causes epigenetic perturbation; mechanosensory force transmission from mutant sarcomeres to the nuclear lamina remodels lamin A/C and nuclear stiffness; and in the outflow tract, TNNT2 expression in smooth muscle cells is required for normal cardiac mechanical dynamics.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TNNT2 encodes cardiac troponin T, a thin-filament protein that couples cytosolic Ca2+ to actomyosin contraction in cardiomyocytes, and whose missense variants produce divergent cardiomyopathies through opposite shifts in myofilament Ca2+ handling [#0, #4]. In isogenic hiPSC-derived cardiomyocytes and reconstituted thin filaments, HCM-associated variants raise myofilament Ca2+ affinity and contraction, while DCM-associated variants lower Ca2+ sensitivity and contractile force, and both classes drive graded transcriptomic responses including MAPK targets and NPPB induction that scale with the functional change [#4, #0]. At the biophysical level, individual HCM variants slow the Ca2+ off-rate and raise diastolic Ca2+ to cause relaxation impairment, beat-to-beat instability, and Ca2+/voltage alternans that link the protein to arrhythmogenesis [#5, #7], with downstream hypertrophic signaling through NFATc1 nuclear translocation and CaMKIIδ/phospholamban phosphorylation [#6]; variant-specific effects extend to allosteric repositioning of cTnI that impairs PKA-mediated relaxation control [#13]. Beyond the sarcomere, altered contractile transients from pathogenic variants remodel lamin A/C and nuclear stiffness, a change rescued by myosin modulators, establishing mechanotransmission from sarcomere to nucleus [#17]. TNNT2 is also subject to developmentally regulated alternative splicing that is controlled by DYRK1A-dependent phosphorylation of the splicing factor SRSF6, a pathway dysregulated in trisomic (Down syndrome) myocardium [#8, #11, #1]. A reported nuclear role for TNNT2 as an HDAC1 sponge and a physical interaction with EGFR in colorectal cancer fall outside the validated sarcomeric mechanism in the current corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Established the gene's chromosomal location and that cardiac troponin T is expressed as multiple developmentally regulated isoforms, setting up alternative splicing as a feature of TNNT2 biology.\",\n      \"evidence\": \"Somatic cell hybrid mapping and cDNA cloning/hybridization in fetal human heart\",\n      \"pmids\": [\"8088824\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequences of individual isoforms not defined\", \"Regulators of the splicing not identified at this stage\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Linked a TNNT2 intronic polymorphism to altered splicing (exon 4 skipping) and to left ventricular hypertrophy, connecting splice regulation to a structural cardiac phenotype.\",\n      \"evidence\": \"In vitro splicing assay plus clinical association with LV mass\",\n      \"pmids\": [\"14986170\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Association does not establish causation of hypertrophy\", \"Mechanism connecting exon 4 skipping to LV mass unresolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined the unifying biophysical mechanism for DCM-causing variants — decreased Ca2+ sensitivity of force development — across multiple mutations.\",\n      \"evidence\": \"Cardiac myocyte reconstitution with mutant troponin T and Ca2+-sensitivity of force assays\",\n      \"pmids\": [\"20031601\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vitro reconstitution does not capture intact-cell or in vivo remodeling\", \"Downstream signaling consequences not addressed\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Showed in vivo that a pathogenic variant produces intrinsic cardiomyocyte dysfunction and heart-failure gene induction, arguing the primary defect is cell-autonomous rather than developmental.\",\n      \"evidence\": \"Transgenic mouse expressing mutant human cTnT with echocardiography, histology, and gene expression\",\n      \"pmids\": [\"20083571\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single variant in transgenic (non-knock-in) context\", \"Calcium-handling mechanism not directly measured\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolved the bidirectional genotype-phenotype rule at scale: HCM variants increase, and DCM variants decrease, both contraction and Ca2+ affinity, with transcriptomic output scaling to sarcomere function.\",\n      \"evidence\": \"CRISPR-engineered isogenic hiPSC-CMs (51 variants), microtissue contraction, Ca2+ reporter, RNA-seq, NPPB reporter\",\n      \"pmids\": [\"33025817\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism converting sarcomere change to MAPK/NPPB transcription not dissected\", \"Long-term remodeling not captured in microtissue timeframe\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Connected an HCM variant's biophysical signature (slowed Ca2+ off-rate, raised Ca2+ sensitivity) to a cellular arrhythmogenic phenotype, providing a mechanistic chain to arrhythmia risk.\",\n      \"evidence\": \"Reconstituted thin filaments with stopped-flow kinetics plus I79N+/- hiPSC-CMs with voltage/Ca2+ transient measurement\",\n      \"pmids\": [\"34977031\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Arrhythmia demonstrated in cellular model, not whole heart\", \"Single variant\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Extended the mechanism downstream to hypertrophic signaling, showing a Ca2+-retaining variant activates NFATc1 and CaMKIIδ/phospholamban phosphorylation, with pharmacological Ca2+ desensitization rescuing relaxation.\",\n      \"evidence\": \"Isogenic hiPSC-CMs with Ca2+ imaging, NFATc1 translocation imaging, signaling western blots, EGCG rescue\",\n      \"pmids\": [\"35861968\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal ordering of Ca2+ retention versus signaling activation not fully resolved\", \"In vivo relevance of EGCG rescue untested here\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated that elevated Ca2+ sensitivity is phosphorylation-independent and dominant at low mutant fraction, clarifying how heterozygous variants exert outsized effects.\",\n      \"evidence\": \"Patient cardiomyocyte force measurements, troponin exchange titration, phosphatase/PKA treatment, isogenic hiPSC-CMs\",\n      \"pmids\": [\"37159677\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generalizability of the 14% threshold to other variants unknown\", \"Atrial versus ventricular differences not addressed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Established genotype-specific atrial pathomechanisms, distinguishing a Ca2+-sensitizing arrhythmogenic variant from an energetic-cost variant lacking arrhythmic propensity.\",\n      \"evidence\": \"R92Q and E163R HCM mouse models with atrial trabecula functional assays and echocardiography\",\n      \"pmids\": [\"35514357\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Two variants do not define the full genotypic spectrum of atrial risk\", \"Molecular basis of energy-cost increase not detailed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified DYRK1A-SRSF6 phosphorylation as the regulatory pathway controlling the developmental fetal-to-adult TNNT2 splice transition.\",\n      \"evidence\": \"DYRK1A overexpression in iPSC-CMs with RT-PCR splice quantification and phospho-SRSF6 western blot\",\n      \"pmids\": [\"35596909\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct SRSF6 binding to TNNT2 pre-mRNA not shown\", \"Functional consequence of fetal isoform shift not measured\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Provided disease-context validation of the splicing pathway, showing SRSF6 hyperphosphorylation and fetal TNNT2 isoform enrichment in trisomy 21 myocardium.\",\n      \"evidence\": \"Phospho-DYRK1A/SRSF6 western blotting and TNNT2 isoform RT-PCR in human trisomic myocardial tissue\",\n      \"pmids\": [\"31201803\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Correlative tissue measurement, not causal manipulation\", \"Functional cardiac consequence in Down syndrome not established\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Revealed a non-myocardial requirement for TNNT2, showing outflow-tract smooth muscle expression is indispensable for normal cardiac mechanical dynamics.\",\n      \"evidence\": \"tnnt2a zebrafish mutants with tissue-specific promoter rescue, RNA-seq, and cardiac function imaging\",\n      \"pmids\": [\"31796423\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mammalian conservation of the OFT smooth muscle role not shown\", \"Molecular function of TNNT2 in smooth muscle cells undefined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified XIN/XINB as a modifier that can partially rescue a DCM variant phenotype, pointing to candidate therapeutic targets downstream of sarcomere dysfunction.\",\n      \"evidence\": \"TNNT2-ΔK210 hESC-CMs and mice with AAV9 XINB overexpression, echocardiography, histology\",\n      \"pmids\": [\"34222259\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of XIN reduction by ΔK210 not defined\", \"Rescue is partial; durability unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Provided a structural-allosteric explanation for diastolic dysfunction, showing a variant repositions cTnI to impair PKA phosphorylation of the relaxation-regulating site.\",\n      \"evidence\": \"Mouse models, ex vivo hemodynamics, stopped-flow kinetics, TR-FRET, MD simulation, phosphomimetic rescue (preprint)\",\n      \"pmids\": [\"37503299\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not peer-reviewed\", \"Variant-specific rescue (R92L not Δ160E) limits generality\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Proposed a non-canonical nuclear function for TNNT2 as an HDAC1 sponge whose disruption causes epigenetic dysregulation, expanding the mechanism beyond sarcomere mechanics.\",\n      \"evidence\": \"Knock-in mice, LVNC patient iPSC-CMs, structural modeling, nuclear TNNT2-HDAC1 co-IP, pharmacological rescue (preprint)\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint with no PMID; novel nuclear claim awaits independent replication\", \"Single Co-IP for the nuclear interaction\", \"Reciprocal validation and stoichiometry of the sponge model not established\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established a causal sarcomere-to-nucleus mechanotransmission axis, linking variant-altered contractile transients to lamin A/C and nuclear stiffness changes reversible by myosin modulators.\",\n      \"evidence\": \"hiPSC-CMs with HCM/DCM TNNT2 variants, transcriptomics, nuclear stiffness measurement, Mavacamten/Omecamtiv Mecarbil rescue\",\n      \"pmids\": [\"41321620\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular link from contractility to lamin remodeling not detailed\", \"In vivo nuclear mechanics not assessed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved whether the reported non-sarcomeric roles of TNNT2 — nuclear HDAC1 sponging and EGFR-driven EMT in cancer — represent bona fide physiological functions and how they integrate with the established thin-filament regulatory role.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Nuclear and cancer functions rest on single-lab/preprint or Low-confidence evidence\", \"No reciprocal or independent validation of non-sarcomeric interactions\", \"Physiological stoichiometry and context unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 4, 5, 7]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 4, 5, 7]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [4, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 4, 14]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [0, 4, 5, 7]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [1, 8, 11]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 4, 6]}\n    ],\n    \"complexes\": [\"cardiac troponin complex\", \"cardiac thin filament\"],\n    \"partners\": [\"TNNI3\", \"TNNC1\", \"TPM1\", \"HDAC1\", \"EGFR\", \"XIRP2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":4,"faith_total":5,"faith_pct":80.0}}