{"gene":"TNNI3","run_date":"2026-06-10T10:51:55","timeline":{"discoveries":[{"year":1996,"finding":"The human TNNI3 gene comprises eight exons within 6.2 kb of genomic DNA. A 2300-bp 5'-flanking region drives expression in cardiac myocytes and skeletal muscle cells but not fibroblasts, indicating it is insufficient to confer cardiac-specific expression alone. Several conserved putative cis-acting elements were identified in the proximal promoter.","method":"Genomic cloning, sequencing, and transfection assays in cardiac myocytes, skeletal muscle cells, and fibroblasts","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct transfection with defined promoter constructs in multiple cell types, single lab","pmids":["8661099"],"is_preprint":false},{"year":2004,"finding":"PKC phosphorylation of cTnI at Ser43 and Ser45 (primarily via PKC-epsilon) slows cardiac contraction and relaxation rates in vivo. Transgenic mice with alanine substitutions at these sites showed ~30% greater +dP/dt and ~18% greater -dP/dt at baseline, with negligible response to isoproterenol or phenylephrine. Mutation of PKC sites was also associated with enhanced PKA-dependent phosphorylation of cTnI, demonstrating interdependence of the phosphorylation sites.","method":"Transgenic mouse model with Ser43Ala/Ser45Ala cTnI substitutions; in situ hemodynamics; back-phosphorylation assay","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo transgenic model with multiple hemodynamic readouts and biochemical back-phosphorylation assay; mechanistically defines PKC sites","pmids":["14726296"],"is_preprint":false},{"year":2006,"finding":"DSCR1L2 (Down syndrome critical region gene 1-like 2) protein physically interacts with human cardiac troponin I (TNNI3). The interaction was identified by yeast two-hybrid screening of a human heart cDNA library and confirmed by yeast co-transformation and GST pulldown. Exon 2 of DSCR1L2 was identified as critical for binding to TNNI3.","method":"Yeast two-hybrid (human heart cDNA library), yeast co-transformation, GST fusion protein pulldown assay","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — two orthogonal binding assays (yeast two-hybrid + GST pulldown), single lab, no functional consequence established","pmids":["16516408"],"is_preprint":false},{"year":2008,"finding":"Expression of the HCM-associated cTnI-R145G mutation in adult rat cardiomyocytes significantly decreased baseline sarcomere shortening. Upon beta-adrenergic stimulation with isoproterenol, rates of shortening and relengthening were depressed in cTnI-R145G-expressing cells, indicating that the R145G mutation in the inhibitory peptide region impairs the beta-adrenergic contractile response in a receptor-subtype-dependent manner.","method":"Adenovirus-driven expression of cTnI-R145G in adult rat cardiomyocytes; sarcomere shortening measurements with/without beta-adrenergic stimulation","journal":"Pflugers Archiv : European journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct functional readout in primary cardiomyocytes with adenoviral overexpression; single lab, one cell model","pmids":["18548271"],"is_preprint":false},{"year":2010,"finding":"PAK3-mediated phosphorylation of cTnI at Ser151 (studied via S151E phosphomimic) increases Ca2+-sensitivity of cardiac thin filaments by shortening inter-site distances between cTnC and cTnI and reducing kinetic rates of Ca2+ dissociation-induced structural change. The effects mimic those of strong crossbridges on cTnI structural changes.","method":"Steady-state and time-resolved FRET; stopped-flow kinetics using reconstituted thin filaments containing cTnI(S151E)","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with multiple orthogonal methods (FRET + kinetics), single lab","pmids":["20540949"],"is_preprint":false},{"year":2013,"finding":"Phosphorylation of cTnI at serines 23/24 by PKA is a key regulator of length-dependent force generation (Frank-Starling mechanism) in striated muscle. Exchange of unphosphorylated recombinant cTn into permeabilized rat cardiac myocytes yielded shallow length-tension relationships; PKA treatment or use of cTnI S23D/S24D phosphomimic shifted relationships to steep, recapitulating the length-dependence seen with full PKA treatment.","method":"Troponin exchange into permeabilized rat cardiac myocytes and slow-twitch skeletal muscle fibers; length-tension relationship measurements; PKA treatment; S23D/S24D phosphomimic cTnI","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution in living permeabilized cells with phosphomimic mutagenesis and PKA treatment as orthogonal confirmations; mechanistically definitive","pmids":["23836688"],"is_preprint":false},{"year":2014,"finding":"The HCM mutation cTnI-R145G in the inhibitory peptide stabilizes Ca2+-coordinating interactions in cTnC but blunts intrasubunit interactions between the cTnI N-terminal extension (which is phosphorylated at S23/S24 by PKA) and the inhibitory peptide itself. This explains how R145G reduces modulation of troponin function during beta-adrenergic stimulation.","method":"Molecular dynamics simulations (triplicate 150 ns) of cTnI-R145G, cTnI-R145G/S23D/S24D, and cTnI-R145G/PS23/PS24 constructs of cTnC(1-161)-cTnI(1-172)-cTnT(236-285)","journal":"Biophysical journal","confidence":"Low","confidence_rationale":"Tier 4 / Weak — computational only (molecular dynamics), no in vitro or in vivo validation in this paper","pmids":["25606687"],"is_preprint":false},{"year":2014,"finding":"The Ca2+-regulatory function of the cTnI inhibitory peptide (Ip) is aided by the C-terminus of cTnT. The HCM mutation cTnI-R145G (in the Ip) and cTnT-R278C together showed that the cTnT mutant rescued some deleterious effects of the cTnI mutant at high Ca2+, but exacerbated loss of thin filament switching-off at low Ca2+, demonstrating functional interaction between these two troponin subunits.","method":"In vitro motility assays with reconstituted troponin complexes containing cTnI-R145G and/or cTnT-R278C, varying [Ca2+], temperature, and HMM density","journal":"Archives of biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with functional motility assay and multiple conditions; single lab","pmids":["24418317"],"is_preprint":false},{"year":2016,"finding":"The HCM-associated cTnI-G203S mutation leads to impaired functional communication between the L-type Ca2+ channel (ICa-L) and mitochondria via the cytoskeletal network (involving decreased F-actin-myosin movement and block of the mitochondrial voltage-dependent anion channel), resulting in a 'hypermetabolic' mitochondrial state with greater ICa-L inactivation rate and higher mitochondrial membrane potential. This was observed in pre-cardiomyopathic mice, suggesting it is an early event.","method":"Patch clamp electrophysiology; mitochondrial membrane potential measurement; metabolic activity assay; L-type Ca2+ channel antagonist treatment in cTnI-G203S transgenic mouse cardiomyocytes","journal":"The Journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple electrophysiological and metabolic readouts in transgenic mouse model, single lab","pmids":["27062056"],"is_preprint":false},{"year":2017,"finding":"Low cTnI expression in aging hearts is regulated by histone acetylation. EGCG treatment inhibited HDAC1 and HDAC3 binding at the cTnI promoter, increased AcH3K9 levels at the promoter, and increased binding of transcription factors GATA4 and Mef2c to the cTnI promoter, thereby restoring cTnI expression and improving cardiac diastolic function in aged mice.","method":"ChIP assay for HDAC1/HDAC3 binding and AcH3K9 at cTnI promoter; Western blot and RT-PCR for cTnI expression; echocardiography in aged mice treated with EGCG","journal":"Journal of cellular and molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP assays with functional cardiac readout in vivo; single lab, multiple methods","pmids":["28382690"],"is_preprint":false},{"year":2019,"finding":"cTnI is modified by arginine methylation in human myocardium. PRMT1 methylates an extended cTnI inhibitory peptide at R146 and R148 in vitro. Mutations at R145 (associated with HCM) impaired R146/R148 methylation by PRMT1 in vitro. H9c2 cells transfected with methylation-deficient R146A/R148A cTnI showed a 32% increase in cell size (hypertrophy). Reduced cTnI arginine methylation was observed in human hypertrophic cardiomyopathy vs. dilated cardiomyopathy biopsies and in rat cardiac hypertrophy.","method":"Western blot for arginine methylation; mass spectrometry identification of methylation sites (R74/R79, R146/R148); in vitro PRMT1 methylation assay with extended inhibitory peptide; H9c2 cell transfection with R146A/R148A cTnI and cell size measurement","journal":"International journal of cardiology","confidence":"High","confidence_rationale":"Tier 1 / Strong — mass spectrometry site identification, in vitro enzymatic assay with PRMT1, cell-based loss-of-function phenotype, and human tissue validation; multiple orthogonal methods","pmids":["30772011"],"is_preprint":false},{"year":2019,"finding":"cTnI (both wild-type and RCM-mutant 193His) is present in the nucleus of cardiomyocytes and interacts with histone-modifying enzymes HDAC1 and SMYD1. In RCM mice with the cTnI-193His mutation, PDE4d was downregulated, associated with enhanced acetylation of H3K4 and H3K9 and decreased tri-methylation of H3K4 at the PDE4d promoter. Overexpression of mutated cTnI in cultured cardiomyocytes reduced PDE4d expression.","method":"Immunofluorescent labeling and Western blot for nuclear cTnI; co-immunoprecipitation of cTnI with HDAC1 and SMYD1; ChIP assay for histone modifications at PDE4d promoter in cTnI193His transgenic hearts; cardiomyocyte overexpression","journal":"Science China. Life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ChIP, subcellular fractionation, and functional overexpression; single lab, multiple methods","pmids":["30900165"],"is_preprint":false},{"year":2019,"finding":"Complete loss of TNNI3 protein (due to homozygous truncating mutation) in pediatric cardiomyopathy is associated with upregulation of the fetal slow skeletal troponin I isoform TNNI1, as confirmed by protein and transcript-level analysis of heart biopsies. This demonstrates a compensatory fetal isoform switch upon TNNI3 loss.","method":"Western blot and transcript analysis of heart biopsies from patient with homozygous TNNI3 c.24+2T>A truncating variant","journal":"Clinical genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct protein/transcript analysis from patient biopsy tissue, single case with orthogonal protein and mRNA methods","pmids":["31568572"],"is_preprint":false},{"year":2020,"finding":"cTnI-R170G and R170W mutations (located in the regulatory C-terminus of cTnI) strongly enhanced Ca2+-sensitivity of skinned fibers and increased troponin affinity for tropomyosin (with differential effects on actin binding), destabilized reconstituted thin filament structure (wavy/broken filaments by EM), and disrupted the interaction between troponin and cMyBPC-C0C2. Direct cTnI/cTnT (but not cTnC) binding to cMyBPC-C0C2 was demonstrated by microscale thermophoresis. R170G reduced cTn affinity for cMyBPC-C0C2 and abolished the cMyBPC-C0C2-dependent increase in thin filament activation cooperativity.","method":"Skinned fiber Ca2+-sensitivity measurements; electron microscopy of reconstituted thin filaments; cosedimentation/binding assays for troponin-actin/tropomyosin; microscale thermophoresis for troponin-cMyBPC-C0C2 interaction","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal in vitro methods (functional assays, EM, binding assays, thermophoresis) in single study; mechanistically comprehensive","pmids":["32182250"],"is_preprint":false},{"year":2020,"finding":"miR-449 regulates cTnI gene expression by sponging HDAC1. HDAC1-mediated deacetylation of H3K4 and H3K9 at the cTnI promoter reduces cTnI transcription and impairs GATA4 transcription factor binding. miR-449 agomiR treatment in aged mice with low cTnI expression improved cardiac function through this mechanism.","method":"Dual-luciferase reporter assay (miR-449/HDAC1 binding); ChIP assay (H3K4, H3K9 acetylation at cTnI promoter; GATA4 binding); in vivo miR-449 agomiR treatment in aged mice with echocardiography","journal":"European review for medical and pharmacological sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple methods (luciferase, ChIP, in vivo functional assay); single lab","pmids":["33378032"],"is_preprint":false},{"year":2021,"finding":"A de novo cTnI-D127Y mutation causes severe infantile restrictive cardiomyopathy. In reconstituted thin filaments, cTnI-D127Y increased Ca2+-sensitivity in skinned fibers, impaired troponin-actin interactions, reduced thin filament structural integrity, and affected inter-subunit troponin interactions. The troponin-targeting agents levosimendan and EGCg partially stabilized thin filament structure and improved contractile function in vitro.","method":"Skinned cardiomyocyte/fiber force measurements; reconstituted thin filament binding and structural assays; patient myocardial tissue protein quality control analysis; levosimendan/EGCg treatment in vitro","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — reconstituted thin filament assays and skinned fiber measurements; single lab, multiple readouts","pmids":["34502534"],"is_preprint":false},{"year":2016,"finding":"HDAC5 binds to the cTnI promoter and mediates histone deacetylation (reduced H3K9ac) leading to decreased cTnI transcription. Estrogen treatment increased HDAC5 binding at the cTnI promoter in neonatal mouse hearts, while SAHA (HDAC inhibitor) increased H3K9ac and restored cTnI expression.","method":"Chromatin immunoprecipitation (ChIP) for HDAC5 at cTnI promoter; HDAC/HAT activity assays; RT-PCR and Western blot for cTnI expression; in vivo estrogen/SAHA treatment","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP with functional in vivo readout; single lab","pmids":["27379430"],"is_preprint":false},{"year":2005,"finding":"During cardioplegic arrest, cTnI undergoes site-specific N-terminal proteolysis early and C-terminal proteolysis later, with concomitant dissociation of cTnI from other myofibrillar proteins. Adenosine supplementation of cardioplegic solution significantly attenuated the C-terminal proteolysis and apparent cTnI dissociation from myofibrils, but had no effect on early N-terminal proteolysis.","method":"Western blot with region-specific anti-cTnI antibodies on isolated perfused rat hearts subjected to cardioplegic arrest ± adenosine; cellular fractionation","journal":"The Journal of surgical research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined proteolytic cleavage sites using region-specific antibodies in controlled ex vivo model; single lab","pmids":["15652960"],"is_preprint":false},{"year":2022,"finding":"A TNNI3 synonymous variant (c.24G>A, p.Ala8Ala) causes intron retention (c.24+1_24+45ins) through aberrant cryptic splicing of intron 2, as demonstrated by minigene splicing analysis. Compound heterozygosity with a full gene deletion caused lethal infantile dilated cardiomyopathy.","method":"Trio whole-exome sequencing; Sanger sequencing; minigene splicing assay","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — minigene functional splicing assay directly demonstrates molecular mechanism of synonymous variant; single lab","pmids":["36565796"],"is_preprint":false},{"year":2024,"finding":"The cTnI-R170W mutation (causing RCM) in iPSC-derived cardiomyocytes and engineered heart tissues caused impaired relaxation (prolonged tau, increased relaxation-to-contractile force ratio) that was reversed by CRISPR/Cas9 isogenic correction. Overexpression of wild-type TNNI3 in R170W-iPSC-CMs and EHTs effectively rescued impaired relaxation, demonstrating that the mutation acts dominantly via a gain-of-function mechanism amenable to WT cTnI supplementation.","method":"iPSC-derived cardiomyocytes and engineered heart tissue from patient with TNNI3-R170W; CRISPR/Cas9 isogenic correction; wild-type TNNI3 overexpression; calcium kinetics; contractile force measurements","journal":"Development, growth & differentiation","confidence":"High","confidence_rationale":"Tier 1 / Strong — isogenic CRISPR correction plus overexpression rescue with functional mechanical readout; multiple orthogonal approaches in single study","pmids":["38193576"],"is_preprint":false},{"year":2024,"finding":"Patient-specific iPSC-derived cardiomyocytes with heterozygous or homozygous TNNI3-R170W exhibited impaired diastolic function (cell motion analysis) without significant changes in intracellular Ca2+ oscillation or troponin I immunocytochemistry or myofibril/mitochondrial ultrastructure. RNA sequencing revealed altered pathways in cardiac muscle development/contraction, ECM-receptor interaction, and TGF-β signaling in RCM-iPSC-CMs.","method":"iPSC-derived cardiomyocytes (heterozygous and homozygous TNNI3-R170W vs isogenic correction); cell motion analysis; calcium imaging; immunocytochemistry; electron microscopy; RNA sequencing","journal":"Journal of the American Heart Association","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (functional, structural, transcriptomic) with isogenic control; single lab","pmids":["38497452"],"is_preprint":false},{"year":2024,"finding":"The HCM mutation cTnI-R79Cys (TNNI3 c.235C>T) in AC16 human cardiomyocytes upregulates hypertrophy markers ANP, BNP, and MYH7, increases cardiomyocyte size, activates the ERK signaling pathway, impairs mitochondrial function, disrupts cardiomyocyte metabolism, and increases cellular autophagy and apoptosis.","method":"Mutant plasmid transfection into AC16 human cardiomyocytes; gene expression analysis; cell size measurement; ERK pathway Western blot; mitochondrial function and metabolic assays; autophagy/apoptosis assays","journal":"International journal of cardiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple cellular assays in human cardiomyocyte cell line; single lab, no isogenic control","pmids":["39426416"],"is_preprint":false},{"year":2024,"finding":"The R92L-cTnT HCM mutation causes early diastolic dysfunction via allosterically mediated structural changes at the cTnC-cTnI interface that impair PKA accessibility to cTnI (reduced cTnI phosphorylation at S23/S24 region). Time-resolved FRET revealed repositioning of the cTnI N-terminus closer to cTnC with decreased distance distributions flanking the PKA consensus sequence. Constitutive phosphorylation of cTnI (cTnI-D23D24) was sufficient to rescue diastolic function only for R92L-cTnT, not Δ160E-cTnT.","method":"2D echocardiography; Western blot for cTnI phosphorylation; ex vivo hemodynamics; stopped-flow kinetics; time-resolved FRET; molecular dynamics simulations with FRET distance constraints","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods (FRET, kinetics, in vivo, MD) demonstrating structural basis for impaired PKA accessibility to cTnI; single rigorous study","pmids":["39328062"],"is_preprint":false},{"year":2025,"finding":"High-throughput iPSC-CM measurements of contractile force and calcium cycling distinguished pathogenic from non-pathogenic TNNI3 variants. Clustering by quantitative physiological phenotypes (including diastolic function measures) identified subgroups correlating with age of disease onset in a patient cohort. Increased calcium sensitivity accurately predicted pathogenicity but did not correlate with disease severity, while normalized diastolic function correlated with age of onset (R2=0.6).","method":"High-throughput imaging of hiPSC-CMs expressing multiple TNNI3 variants; contractile force measurement; calcium handling analysis; correlation with clinical cohort outcomes","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic functional characterization of multiple variants with clinical correlation; preprint, single lab","pmids":["41446209"],"is_preprint":true}],"current_model":"TNNI3 encodes cardiac troponin I (cTnI), the inhibitory subunit of the troponin complex, which regulates cardiac muscle contraction and relaxation by Ca2+-dependent modulation of thin filament activity; its function is fine-tuned by multiple post-translational modifications including PKA phosphorylation at Ser23/Ser24 (which controls length-dependent force generation and beta-adrenergic responsiveness by repositioning the cTnI N-terminus relative to cTnC), PKC phosphorylation at Ser43/Ser45 (which slows contraction/relaxation rates and cross-talks with PKA sites), PAK3 phosphorylation at Ser151 (which increases Ca2+-sensitivity by altering cTnC-cTnI distances), and PRMT1-mediated arginine methylation at R146/R148 in the inhibitory/switch peptide boundary (loss of which causes cardiomyocyte hypertrophy); cTnI also localizes to the cardiomyocyte nucleus where it interacts with HDAC1 and SMYD1 to epigenetically regulate gene expression, and its own transcription is regulated by HDAC1/HDAC3/HDAC5-mediated histone deacetylation and GATA4/Mef2c binding at its promoter; disease-causing mutations in the inhibitory peptide (R145G), C-terminal regulatory region (R170G/W), and elsewhere alter Ca2+-sensitivity, thin filament stability, cMyBPC-C0C2 interactions, and beta-adrenergic responsiveness, collectively explaining the molecular basis of HCM, RCM, and DCM caused by TNNI3 mutations."},"narrative":{"mechanistic_narrative":"TNNI3 encodes cardiac troponin I (cTnI), the inhibitory subunit of the cardiac thin-filament troponin complex that governs Ca2+-dependent regulation of contraction and relaxation [PMID:23836688, PMID:32182250]. Its inhibitory/switch-peptide region and C-terminus are central regulatory elements: phosphorylation of the cTnI N-terminal extension at Ser23/Ser24 by PKA tunes length-dependent force generation (the Frank-Starling response) by repositioning the cTnI N-terminus relative to cTnC [PMID:23836688, PMID:39328062], while PKC phosphorylation at Ser43/Ser45 slows contraction and relaxation and is functionally interdependent with the PKA sites [PMID:14726296], and PAK3 phosphorylation at Ser151 raises Ca2+-sensitivity by shortening cTnC–cTnI inter-site distances [PMID:20540949]. cTnI is additionally arginine-methylated by PRMT1 at R146/R148 within the extended inhibitory peptide; loss of this methylation drives cardiomyocyte hypertrophy, and the HCM mutation at R145 impairs it [PMID:30772011]. Beyond the sarcomere, cTnI localizes to the cardiomyocyte nucleus, where it associates with HDAC1 and SMYD1 to influence histone modification and target-gene expression [PMID:30900165], and its own promoter is repressed by HDAC1/HDAC3/HDAC5-mediated histone deacetylation and activated by GATA4/Mef2c binding [PMID:28382690, PMID:27379430, PMID:33378032]. Disease-causing mutations cluster in the inhibitory peptide (R145G) and the regulatory C-terminus (R170G/W, D127Y, G203S), altering Ca2+-sensitivity, thin-filament structural integrity, troponin–tropomyosin and troponin–cMyBPC interactions, and beta-adrenergic responsiveness, providing the molecular basis for hypertrophic, restrictive, and dilated cardiomyopathies, with biallelic loss-of-function producing infantile cardiomyopathy and a compensatory fetal TNNI1 isoform switch [PMID:18548271, PMID:32182250, PMID:34502534, PMID:31568572, PMID:36565796].","teleology":[{"year":1996,"claim":"Defined the genomic structure and transcriptional control region of human TNNI3, establishing that proximal promoter elements drive striated-muscle but not strictly cardiac-specific expression.","evidence":"Genomic cloning, sequencing, and transfection of 5'-flanking constructs in cardiac myocytes, skeletal muscle, and fibroblasts","pmids":["8661099"],"confidence":"Medium","gaps":["Did not identify the elements conferring cardiac-restricted expression","No trans-acting factors mapped to the conserved cis-elements"]},{"year":2004,"claim":"Established PKC phosphorylation of cTnI at Ser43/Ser45 as an in vivo brake on contraction/relaxation kinetics that cross-talks with PKA phosphorylation, revealing interdependence among cTnI phospho-sites.","evidence":"Ser43Ala/Ser45Ala transgenic mouse with in situ hemodynamics and back-phosphorylation assay","pmids":["14726296"],"confidence":"High","gaps":["Mechanism of PKC/PKA site cross-talk at the structural level unresolved","Phospho-occupancy under physiological signaling not quantified"]},{"year":2005,"claim":"Showed cTnI is degraded by region-specific N- then C-terminal proteolysis during ischemic arrest, linking C-terminal cleavage to myofibrillar dissociation and identifying adenosine as protective.","evidence":"Region-specific anti-cTnI Western blotting and fractionation in perfused rat hearts under cardioplegia ± adenosine","pmids":["15652960"],"confidence":"Medium","gaps":["Protease responsible not identified","Functional consequence of dissociation not directly measured"]},{"year":2006,"claim":"Identified a candidate physical partner (DSCR1L2) of cTnI, raising the possibility of regulatory interactions beyond the troponin core.","evidence":"Yeast two-hybrid screen of human heart cDNA with GST pulldown confirmation; exon 2 mapped as binding determinant","pmids":["16516408"],"confidence":"Medium","gaps":["No functional consequence established","Interaction not validated in cardiomyocytes or in vivo"]},{"year":2010,"claim":"Defined PAK3-mediated Ser151 phosphorylation as a Ca2+-sensitizing modification that shortens cTnC–cTnI distances, expanding the kinase repertoire tuning thin-filament activation.","evidence":"Steady-state/time-resolved FRET and stopped-flow kinetics on reconstituted thin filaments with cTnI(S151E) phosphomimic","pmids":["20540949"],"confidence":"High","gaps":["In vivo PAK3 phosphorylation of cTnI and its physiological trigger not demonstrated","Phosphomimic may not fully replicate genuine phosphorylation"]},{"year":2013,"claim":"Established that PKA phosphorylation of cTnI Ser23/Ser24 is a key determinant of length-dependent force generation, mechanistically linking cTnI to the Frank-Starling response.","evidence":"Troponin exchange into permeabilized rat myocytes with PKA treatment and S23D/S24D phosphomimic; length-tension measurements","pmids":["23836688"],"confidence":"High","gaps":["Structural basis for how N-terminal phosphorylation alters length sensing left to later studies","Contribution of other myofilament PKA substrates not isolated"]},{"year":2008,"claim":"Demonstrated that the HCM inhibitory-peptide mutation R145G impairs the beta-adrenergic contractile response, connecting a disease mutation to depressed adrenergic reserve.","evidence":"Adenoviral cTnI-R145G expression in adult rat cardiomyocytes with sarcomere shortening ± isoproterenol","pmids":["18548271"],"confidence":"Medium","gaps":["Single cell model with overexpression rather than endogenous knock-in","Structural mechanism not resolved here"]},{"year":2014,"claim":"Provided structural and functional mechanism for R145G: it stabilizes Ca2+ coordination in cTnC while blunting N-terminus–inhibitory-peptide coupling and functionally interacts with the cTnT C-terminus to alter thin-filament switching.","evidence":"Molecular dynamics simulations and in vitro motility assays of cTnI-R145G ± cTnT-R278C","pmids":["25606687","24418317"],"confidence":"Medium","gaps":["MD predictions of N-terminus repositioning lack direct in vitro/in vivo validation","Subunit cross-talk quantified only in reconstituted systems"]},{"year":2016,"claim":"Revealed dual nuclear/metabolic axes of cTnI biology: HDAC5-mediated promoter deacetylation represses TNNI3 transcription, and an HCM mutation (G203S) impairs Ca2+-channel–mitochondria communication as an early pre-cardiomyopathic event.","evidence":"ChIP of HDAC5 at the cTnI promoter with estrogen/SAHA treatment; patch-clamp and mitochondrial assays in cTnI-G203S transgenic cardiomyocytes","pmids":["27379430","27062056"],"confidence":"Medium","gaps":["Direct connection between cTnI mutation and mitochondrial coupling mechanism incompletely defined","Promoter regulation studied in neonatal/aging contexts only"]},{"year":2017,"claim":"Extended epigenetic control of TNNI3 to aging hearts, showing HDAC1/HDAC3 occupancy and GATA4/Mef2c recruitment set cTnI expression and diastolic function.","evidence":"ChIP for HDAC1/HDAC3 and AcH3K9, transcription-factor binding, and echocardiography in aged mice ± EGCG","pmids":["28382690"],"confidence":"Medium","gaps":["Causal hierarchy among HDACs not dissected","EGCG acts pleiotropically beyond the cTnI promoter"]},{"year":2019,"claim":"Established three new dimensions of cTnI regulation and pathology: PRMT1 arginine methylation at R146/R148 restraining hypertrophy, nuclear cTnI partnering with HDAC1/SMYD1 to control PDE4d via histone marks, and a fetal TNNI1 isoform switch upon complete TNNI3 loss.","evidence":"Mass spectrometry, in vitro PRMT1 assays and H9c2 hypertrophy readout; nuclear Co-IP and ChIP in cTnI-193His mice; protein/transcript analysis of a homozygous truncating patient biopsy","pmids":["30772011","30900165","31568572"],"confidence":"High","gaps":["How methylation loss mechanistically drives hypertrophy not fully defined","Nuclear cTnI translocation signals and DNA-targeting specificity unknown","Isoform switch documented in a single patient"]},{"year":2020,"claim":"Mapped how C-terminal regulatory mutations (R170G/W) destabilize thin filaments and disrupt cTnI/cTnT–cMyBPC-C0C2 interactions, and showed miR-449 controls TNNI3 transcription by sponging HDAC1.","evidence":"Skinned-fiber Ca2+-sensitivity, EM, binding assays and microscale thermophoresis for R170 mutants; luciferase, ChIP and in vivo agomiR for miR-449/HDAC1","pmids":["32182250","33378032"],"confidence":"High","gaps":["Physiological consequence of disrupted cMyBPC coupling in vivo not measured","miR-449 regulation tested mainly in aged hearts"]},{"year":2021,"claim":"Showed a de novo C-terminal mutation (D127Y) causes infantile restrictive cardiomyopathy through Ca2+-sensitization and thin-filament destabilization, and that troponin-targeting agents can partially restore filament structure.","evidence":"Skinned-fiber force, reconstituted thin-filament structural/binding assays, and levosimendan/EGCg treatment in vitro","pmids":["34502534"],"confidence":"Medium","gaps":["In vivo or cell-based validation absent","Drug effects shown only in vitro"]},{"year":2024,"claim":"Used human iPSC-CM and engineered-tissue models with isogenic correction and WT supplementation to show R170W acts as a dominant gain-of-function causing impaired relaxation, and demonstrated a generalizable structural mechanism by which a partner-subunit mutation impairs PKA access to cTnI Ser23/Ser24.","evidence":"CRISPR-corrected and WT-overexpressing R170W iPSC-CM/EHT with mechanical readouts and RNA-seq; 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Cardiomyopathy.","date":"2024","source":"Journal of the American Heart Association","url":"https://pubmed.ncbi.nlm.nih.gov/38497452","citation_count":4,"is_preprint":false},{"pmid":"27379430","id":"PMC_27379430","title":"Suberoylanilide Hydroxamic Acid Restores Estrogen Reduced-cTnI Expression in Neonatal Hearts of Mice.","date":"2016","source":"Journal of cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/27379430","citation_count":4,"is_preprint":false},{"pmid":"30208128","id":"PMC_30208128","title":"Correlations of inhaled NO with the cTnI levels and the plasma clotting factor in rabbits with acute massive pulmonary embolism.","date":"2018","source":"Acta cirurgica brasileira","url":"https://pubmed.ncbi.nlm.nih.gov/30208128","citation_count":4,"is_preprint":false},{"pmid":"23220502","id":"PMC_23220502","title":"Effects of the glucose-lowering rate on cTnI and hs-CRP serum levels in type 2 diabetics.","date":"2012","source":"Human immunology","url":"https://pubmed.ncbi.nlm.nih.gov/23220502","citation_count":4,"is_preprint":false},{"pmid":"38924380","id":"PMC_38924380","title":"Homozygous TNNI3 frameshift variant in a consanguineous family with lethal infantile dilated cardiomyopathy.","date":"2024","source":"Molecular genetics & genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/38924380","citation_count":3,"is_preprint":false},{"pmid":"34365612","id":"PMC_34365612","title":"[Identification of variants in TNNI3 gene in two children with restrictive cardiomyopathy].","date":"2021","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/34365612","citation_count":3,"is_preprint":false},{"pmid":"34798544","id":"PMC_34798544","title":"Generation of three induced pluripotent stem cell lines from hypertrophic cardiomyopathy patients carrying TNNI3 mutations.","date":"2021","source":"Stem cell 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cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/39426416","citation_count":2,"is_preprint":false},{"pmid":"37782550","id":"PMC_37782550","title":"A carbon quantum layer modified BiVO4 photoelectrochemical aptamer biosensor for ultra-sensitive cTnI biomarker detection based on the interface nephelauxetic effect and heterojunction assistance.","date":"2023","source":"Journal of materials chemistry. 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A 2300-bp 5'-flanking region drives expression in cardiac myocytes and skeletal muscle cells but not fibroblasts, indicating it is insufficient to confer cardiac-specific expression alone. Several conserved putative cis-acting elements were identified in the proximal promoter.\",\n      \"method\": \"Genomic cloning, sequencing, and transfection assays in cardiac myocytes, skeletal muscle cells, and fibroblasts\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct transfection with defined promoter constructs in multiple cell types, single lab\",\n      \"pmids\": [\"8661099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PKC phosphorylation of cTnI at Ser43 and Ser45 (primarily via PKC-epsilon) slows cardiac contraction and relaxation rates in vivo. Transgenic mice with alanine substitutions at these sites showed ~30% greater +dP/dt and ~18% greater -dP/dt at baseline, with negligible response to isoproterenol or phenylephrine. Mutation of PKC sites was also associated with enhanced PKA-dependent phosphorylation of cTnI, demonstrating interdependence of the phosphorylation sites.\",\n      \"method\": \"Transgenic mouse model with Ser43Ala/Ser45Ala cTnI substitutions; in situ hemodynamics; back-phosphorylation assay\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo transgenic model with multiple hemodynamic readouts and biochemical back-phosphorylation assay; mechanistically defines PKC sites\",\n      \"pmids\": [\"14726296\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"DSCR1L2 (Down syndrome critical region gene 1-like 2) protein physically interacts with human cardiac troponin I (TNNI3). The interaction was identified by yeast two-hybrid screening of a human heart cDNA library and confirmed by yeast co-transformation and GST pulldown. Exon 2 of DSCR1L2 was identified as critical for binding to TNNI3.\",\n      \"method\": \"Yeast two-hybrid (human heart cDNA library), yeast co-transformation, GST fusion protein pulldown assay\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — two orthogonal binding assays (yeast two-hybrid + GST pulldown), single lab, no functional consequence established\",\n      \"pmids\": [\"16516408\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Expression of the HCM-associated cTnI-R145G mutation in adult rat cardiomyocytes significantly decreased baseline sarcomere shortening. Upon beta-adrenergic stimulation with isoproterenol, rates of shortening and relengthening were depressed in cTnI-R145G-expressing cells, indicating that the R145G mutation in the inhibitory peptide region impairs the beta-adrenergic contractile response in a receptor-subtype-dependent manner.\",\n      \"method\": \"Adenovirus-driven expression of cTnI-R145G in adult rat cardiomyocytes; sarcomere shortening measurements with/without beta-adrenergic stimulation\",\n      \"journal\": \"Pflugers Archiv : European journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct functional readout in primary cardiomyocytes with adenoviral overexpression; single lab, one cell model\",\n      \"pmids\": [\"18548271\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PAK3-mediated phosphorylation of cTnI at Ser151 (studied via S151E phosphomimic) increases Ca2+-sensitivity of cardiac thin filaments by shortening inter-site distances between cTnC and cTnI and reducing kinetic rates of Ca2+ dissociation-induced structural change. The effects mimic those of strong crossbridges on cTnI structural changes.\",\n      \"method\": \"Steady-state and time-resolved FRET; stopped-flow kinetics using reconstituted thin filaments containing cTnI(S151E)\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with multiple orthogonal methods (FRET + kinetics), single lab\",\n      \"pmids\": [\"20540949\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Phosphorylation of cTnI at serines 23/24 by PKA is a key regulator of length-dependent force generation (Frank-Starling mechanism) in striated muscle. Exchange of unphosphorylated recombinant cTn into permeabilized rat cardiac myocytes yielded shallow length-tension relationships; PKA treatment or use of cTnI S23D/S24D phosphomimic shifted relationships to steep, recapitulating the length-dependence seen with full PKA treatment.\",\n      \"method\": \"Troponin exchange into permeabilized rat cardiac myocytes and slow-twitch skeletal muscle fibers; length-tension relationship measurements; PKA treatment; S23D/S24D phosphomimic cTnI\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution in living permeabilized cells with phosphomimic mutagenesis and PKA treatment as orthogonal confirmations; mechanistically definitive\",\n      \"pmids\": [\"23836688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The HCM mutation cTnI-R145G in the inhibitory peptide stabilizes Ca2+-coordinating interactions in cTnC but blunts intrasubunit interactions between the cTnI N-terminal extension (which is phosphorylated at S23/S24 by PKA) and the inhibitory peptide itself. This explains how R145G reduces modulation of troponin function during beta-adrenergic stimulation.\",\n      \"method\": \"Molecular dynamics simulations (triplicate 150 ns) of cTnI-R145G, cTnI-R145G/S23D/S24D, and cTnI-R145G/PS23/PS24 constructs of cTnC(1-161)-cTnI(1-172)-cTnT(236-285)\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — computational only (molecular dynamics), no in vitro or in vivo validation in this paper\",\n      \"pmids\": [\"25606687\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The Ca2+-regulatory function of the cTnI inhibitory peptide (Ip) is aided by the C-terminus of cTnT. The HCM mutation cTnI-R145G (in the Ip) and cTnT-R278C together showed that the cTnT mutant rescued some deleterious effects of the cTnI mutant at high Ca2+, but exacerbated loss of thin filament switching-off at low Ca2+, demonstrating functional interaction between these two troponin subunits.\",\n      \"method\": \"In vitro motility assays with reconstituted troponin complexes containing cTnI-R145G and/or cTnT-R278C, varying [Ca2+], temperature, and HMM density\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with functional motility assay and multiple conditions; single lab\",\n      \"pmids\": [\"24418317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The HCM-associated cTnI-G203S mutation leads to impaired functional communication between the L-type Ca2+ channel (ICa-L) and mitochondria via the cytoskeletal network (involving decreased F-actin-myosin movement and block of the mitochondrial voltage-dependent anion channel), resulting in a 'hypermetabolic' mitochondrial state with greater ICa-L inactivation rate and higher mitochondrial membrane potential. This was observed in pre-cardiomyopathic mice, suggesting it is an early event.\",\n      \"method\": \"Patch clamp electrophysiology; mitochondrial membrane potential measurement; metabolic activity assay; L-type Ca2+ channel antagonist treatment in cTnI-G203S transgenic mouse cardiomyocytes\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple electrophysiological and metabolic readouts in transgenic mouse model, single lab\",\n      \"pmids\": [\"27062056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Low cTnI expression in aging hearts is regulated by histone acetylation. EGCG treatment inhibited HDAC1 and HDAC3 binding at the cTnI promoter, increased AcH3K9 levels at the promoter, and increased binding of transcription factors GATA4 and Mef2c to the cTnI promoter, thereby restoring cTnI expression and improving cardiac diastolic function in aged mice.\",\n      \"method\": \"ChIP assay for HDAC1/HDAC3 binding and AcH3K9 at cTnI promoter; Western blot and RT-PCR for cTnI expression; echocardiography in aged mice treated with EGCG\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP assays with functional cardiac readout in vivo; single lab, multiple methods\",\n      \"pmids\": [\"28382690\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"cTnI is modified by arginine methylation in human myocardium. PRMT1 methylates an extended cTnI inhibitory peptide at R146 and R148 in vitro. Mutations at R145 (associated with HCM) impaired R146/R148 methylation by PRMT1 in vitro. H9c2 cells transfected with methylation-deficient R146A/R148A cTnI showed a 32% increase in cell size (hypertrophy). Reduced cTnI arginine methylation was observed in human hypertrophic cardiomyopathy vs. dilated cardiomyopathy biopsies and in rat cardiac hypertrophy.\",\n      \"method\": \"Western blot for arginine methylation; mass spectrometry identification of methylation sites (R74/R79, R146/R148); in vitro PRMT1 methylation assay with extended inhibitory peptide; H9c2 cell transfection with R146A/R148A cTnI and cell size measurement\",\n      \"journal\": \"International journal of cardiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mass spectrometry site identification, in vitro enzymatic assay with PRMT1, cell-based loss-of-function phenotype, and human tissue validation; multiple orthogonal methods\",\n      \"pmids\": [\"30772011\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"cTnI (both wild-type and RCM-mutant 193His) is present in the nucleus of cardiomyocytes and interacts with histone-modifying enzymes HDAC1 and SMYD1. In RCM mice with the cTnI-193His mutation, PDE4d was downregulated, associated with enhanced acetylation of H3K4 and H3K9 and decreased tri-methylation of H3K4 at the PDE4d promoter. Overexpression of mutated cTnI in cultured cardiomyocytes reduced PDE4d expression.\",\n      \"method\": \"Immunofluorescent labeling and Western blot for nuclear cTnI; co-immunoprecipitation of cTnI with HDAC1 and SMYD1; ChIP assay for histone modifications at PDE4d promoter in cTnI193His transgenic hearts; cardiomyocyte overexpression\",\n      \"journal\": \"Science China. Life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ChIP, subcellular fractionation, and functional overexpression; single lab, multiple methods\",\n      \"pmids\": [\"30900165\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Complete loss of TNNI3 protein (due to homozygous truncating mutation) in pediatric cardiomyopathy is associated with upregulation of the fetal slow skeletal troponin I isoform TNNI1, as confirmed by protein and transcript-level analysis of heart biopsies. This demonstrates a compensatory fetal isoform switch upon TNNI3 loss.\",\n      \"method\": \"Western blot and transcript analysis of heart biopsies from patient with homozygous TNNI3 c.24+2T>A truncating variant\",\n      \"journal\": \"Clinical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct protein/transcript analysis from patient biopsy tissue, single case with orthogonal protein and mRNA methods\",\n      \"pmids\": [\"31568572\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"cTnI-R170G and R170W mutations (located in the regulatory C-terminus of cTnI) strongly enhanced Ca2+-sensitivity of skinned fibers and increased troponin affinity for tropomyosin (with differential effects on actin binding), destabilized reconstituted thin filament structure (wavy/broken filaments by EM), and disrupted the interaction between troponin and cMyBPC-C0C2. Direct cTnI/cTnT (but not cTnC) binding to cMyBPC-C0C2 was demonstrated by microscale thermophoresis. R170G reduced cTn affinity for cMyBPC-C0C2 and abolished the cMyBPC-C0C2-dependent increase in thin filament activation cooperativity.\",\n      \"method\": \"Skinned fiber Ca2+-sensitivity measurements; electron microscopy of reconstituted thin filaments; cosedimentation/binding assays for troponin-actin/tropomyosin; microscale thermophoresis for troponin-cMyBPC-C0C2 interaction\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal in vitro methods (functional assays, EM, binding assays, thermophoresis) in single study; mechanistically comprehensive\",\n      \"pmids\": [\"32182250\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"miR-449 regulates cTnI gene expression by sponging HDAC1. HDAC1-mediated deacetylation of H3K4 and H3K9 at the cTnI promoter reduces cTnI transcription and impairs GATA4 transcription factor binding. miR-449 agomiR treatment in aged mice with low cTnI expression improved cardiac function through this mechanism.\",\n      \"method\": \"Dual-luciferase reporter assay (miR-449/HDAC1 binding); ChIP assay (H3K4, H3K9 acetylation at cTnI promoter; GATA4 binding); in vivo miR-449 agomiR treatment in aged mice with echocardiography\",\n      \"journal\": \"European review for medical and pharmacological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple methods (luciferase, ChIP, in vivo functional assay); single lab\",\n      \"pmids\": [\"33378032\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A de novo cTnI-D127Y mutation causes severe infantile restrictive cardiomyopathy. In reconstituted thin filaments, cTnI-D127Y increased Ca2+-sensitivity in skinned fibers, impaired troponin-actin interactions, reduced thin filament structural integrity, and affected inter-subunit troponin interactions. The troponin-targeting agents levosimendan and EGCg partially stabilized thin filament structure and improved contractile function in vitro.\",\n      \"method\": \"Skinned cardiomyocyte/fiber force measurements; reconstituted thin filament binding and structural assays; patient myocardial tissue protein quality control analysis; levosimendan/EGCg treatment in vitro\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted thin filament assays and skinned fiber measurements; single lab, multiple readouts\",\n      \"pmids\": [\"34502534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"HDAC5 binds to the cTnI promoter and mediates histone deacetylation (reduced H3K9ac) leading to decreased cTnI transcription. Estrogen treatment increased HDAC5 binding at the cTnI promoter in neonatal mouse hearts, while SAHA (HDAC inhibitor) increased H3K9ac and restored cTnI expression.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) for HDAC5 at cTnI promoter; HDAC/HAT activity assays; RT-PCR and Western blot for cTnI expression; in vivo estrogen/SAHA treatment\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP with functional in vivo readout; single lab\",\n      \"pmids\": [\"27379430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"During cardioplegic arrest, cTnI undergoes site-specific N-terminal proteolysis early and C-terminal proteolysis later, with concomitant dissociation of cTnI from other myofibrillar proteins. Adenosine supplementation of cardioplegic solution significantly attenuated the C-terminal proteolysis and apparent cTnI dissociation from myofibrils, but had no effect on early N-terminal proteolysis.\",\n      \"method\": \"Western blot with region-specific anti-cTnI antibodies on isolated perfused rat hearts subjected to cardioplegic arrest ± adenosine; cellular fractionation\",\n      \"journal\": \"The Journal of surgical research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined proteolytic cleavage sites using region-specific antibodies in controlled ex vivo model; single lab\",\n      \"pmids\": [\"15652960\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A TNNI3 synonymous variant (c.24G>A, p.Ala8Ala) causes intron retention (c.24+1_24+45ins) through aberrant cryptic splicing of intron 2, as demonstrated by minigene splicing analysis. Compound heterozygosity with a full gene deletion caused lethal infantile dilated cardiomyopathy.\",\n      \"method\": \"Trio whole-exome sequencing; Sanger sequencing; minigene splicing assay\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — minigene functional splicing assay directly demonstrates molecular mechanism of synonymous variant; single lab\",\n      \"pmids\": [\"36565796\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The cTnI-R170W mutation (causing RCM) in iPSC-derived cardiomyocytes and engineered heart tissues caused impaired relaxation (prolonged tau, increased relaxation-to-contractile force ratio) that was reversed by CRISPR/Cas9 isogenic correction. Overexpression of wild-type TNNI3 in R170W-iPSC-CMs and EHTs effectively rescued impaired relaxation, demonstrating that the mutation acts dominantly via a gain-of-function mechanism amenable to WT cTnI supplementation.\",\n      \"method\": \"iPSC-derived cardiomyocytes and engineered heart tissue from patient with TNNI3-R170W; CRISPR/Cas9 isogenic correction; wild-type TNNI3 overexpression; calcium kinetics; contractile force measurements\",\n      \"journal\": \"Development, growth & differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — isogenic CRISPR correction plus overexpression rescue with functional mechanical readout; multiple orthogonal approaches in single study\",\n      \"pmids\": [\"38193576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Patient-specific iPSC-derived cardiomyocytes with heterozygous or homozygous TNNI3-R170W exhibited impaired diastolic function (cell motion analysis) without significant changes in intracellular Ca2+ oscillation or troponin I immunocytochemistry or myofibril/mitochondrial ultrastructure. RNA sequencing revealed altered pathways in cardiac muscle development/contraction, ECM-receptor interaction, and TGF-β signaling in RCM-iPSC-CMs.\",\n      \"method\": \"iPSC-derived cardiomyocytes (heterozygous and homozygous TNNI3-R170W vs isogenic correction); cell motion analysis; calcium imaging; immunocytochemistry; electron microscopy; RNA sequencing\",\n      \"journal\": \"Journal of the American Heart Association\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (functional, structural, transcriptomic) with isogenic control; single lab\",\n      \"pmids\": [\"38497452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The HCM mutation cTnI-R79Cys (TNNI3 c.235C>T) in AC16 human cardiomyocytes upregulates hypertrophy markers ANP, BNP, and MYH7, increases cardiomyocyte size, activates the ERK signaling pathway, impairs mitochondrial function, disrupts cardiomyocyte metabolism, and increases cellular autophagy and apoptosis.\",\n      \"method\": \"Mutant plasmid transfection into AC16 human cardiomyocytes; gene expression analysis; cell size measurement; ERK pathway Western blot; mitochondrial function and metabolic assays; autophagy/apoptosis assays\",\n      \"journal\": \"International journal of cardiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple cellular assays in human cardiomyocyte cell line; single lab, no isogenic control\",\n      \"pmids\": [\"39426416\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The R92L-cTnT HCM mutation causes early diastolic dysfunction via allosterically mediated structural changes at the cTnC-cTnI interface that impair PKA accessibility to cTnI (reduced cTnI phosphorylation at S23/S24 region). Time-resolved FRET revealed repositioning of the cTnI N-terminus closer to cTnC with decreased distance distributions flanking the PKA consensus sequence. Constitutive phosphorylation of cTnI (cTnI-D23D24) was sufficient to rescue diastolic function only for R92L-cTnT, not Δ160E-cTnT.\",\n      \"method\": \"2D echocardiography; Western blot for cTnI phosphorylation; ex vivo hemodynamics; stopped-flow kinetics; time-resolved FRET; molecular dynamics simulations with FRET distance constraints\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods (FRET, kinetics, in vivo, MD) demonstrating structural basis for impaired PKA accessibility to cTnI; single rigorous study\",\n      \"pmids\": [\"39328062\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"High-throughput iPSC-CM measurements of contractile force and calcium cycling distinguished pathogenic from non-pathogenic TNNI3 variants. Clustering by quantitative physiological phenotypes (including diastolic function measures) identified subgroups correlating with age of disease onset in a patient cohort. Increased calcium sensitivity accurately predicted pathogenicity but did not correlate with disease severity, while normalized diastolic function correlated with age of onset (R2=0.6).\",\n      \"method\": \"High-throughput imaging of hiPSC-CMs expressing multiple TNNI3 variants; contractile force measurement; calcium handling analysis; correlation with clinical cohort outcomes\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic functional characterization of multiple variants with clinical correlation; preprint, single lab\",\n      \"pmids\": [\"41446209\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"TNNI3 encodes cardiac troponin I (cTnI), the inhibitory subunit of the troponin complex, which regulates cardiac muscle contraction and relaxation by Ca2+-dependent modulation of thin filament activity; its function is fine-tuned by multiple post-translational modifications including PKA phosphorylation at Ser23/Ser24 (which controls length-dependent force generation and beta-adrenergic responsiveness by repositioning the cTnI N-terminus relative to cTnC), PKC phosphorylation at Ser43/Ser45 (which slows contraction/relaxation rates and cross-talks with PKA sites), PAK3 phosphorylation at Ser151 (which increases Ca2+-sensitivity by altering cTnC-cTnI distances), and PRMT1-mediated arginine methylation at R146/R148 in the inhibitory/switch peptide boundary (loss of which causes cardiomyocyte hypertrophy); cTnI also localizes to the cardiomyocyte nucleus where it interacts with HDAC1 and SMYD1 to epigenetically regulate gene expression, and its own transcription is regulated by HDAC1/HDAC3/HDAC5-mediated histone deacetylation and GATA4/Mef2c binding at its promoter; disease-causing mutations in the inhibitory peptide (R145G), C-terminal regulatory region (R170G/W), and elsewhere alter Ca2+-sensitivity, thin filament stability, cMyBPC-C0C2 interactions, and beta-adrenergic responsiveness, collectively explaining the molecular basis of HCM, RCM, and DCM caused by TNNI3 mutations.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TNNI3 encodes cardiac troponin I (cTnI), the inhibitory subunit of the cardiac thin-filament troponin complex that governs Ca2+-dependent regulation of contraction and relaxation [#5, #13]. Its inhibitory/switch-peptide region and C-terminus are central regulatory elements: phosphorylation of the cTnI N-terminal extension at Ser23/Ser24 by PKA tunes length-dependent force generation (the Frank-Starling response) by repositioning the cTnI N-terminus relative to cTnC [#5, #22], while PKC phosphorylation at Ser43/Ser45 slows contraction and relaxation and is functionally interdependent with the PKA sites [#1], and PAK3 phosphorylation at Ser151 raises Ca2+-sensitivity by shortening cTnC–cTnI inter-site distances [#4]. cTnI is additionally arginine-methylated by PRMT1 at R146/R148 within the extended inhibitory peptide; loss of this methylation drives cardiomyocyte hypertrophy, and the HCM mutation at R145 impairs it [#10]. Beyond the sarcomere, cTnI localizes to the cardiomyocyte nucleus, where it associates with HDAC1 and SMYD1 to influence histone modification and target-gene expression [#11], and its own promoter is repressed by HDAC1/HDAC3/HDAC5-mediated histone deacetylation and activated by GATA4/Mef2c binding [#9, #16, #14]. Disease-causing mutations cluster in the inhibitory peptide (R145G) and the regulatory C-terminus (R170G/W, D127Y, G203S), altering Ca2+-sensitivity, thin-filament structural integrity, troponin–tropomyosin and troponin–cMyBPC interactions, and beta-adrenergic responsiveness, providing the molecular basis for hypertrophic, restrictive, and dilated cardiomyopathies, with biallelic loss-of-function producing infantile cardiomyopathy and a compensatory fetal TNNI1 isoform switch [#3, #13, #15, #12, #18].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Defined the genomic structure and transcriptional control region of human TNNI3, establishing that proximal promoter elements drive striated-muscle but not strictly cardiac-specific expression.\",\n      \"evidence\": \"Genomic cloning, sequencing, and transfection of 5'-flanking constructs in cardiac myocytes, skeletal muscle, and fibroblasts\",\n      \"pmids\": [\"8661099\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not identify the elements conferring cardiac-restricted expression\", \"No trans-acting factors mapped to the conserved cis-elements\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Established PKC phosphorylation of cTnI at Ser43/Ser45 as an in vivo brake on contraction/relaxation kinetics that cross-talks with PKA phosphorylation, revealing interdependence among cTnI phospho-sites.\",\n      \"evidence\": \"Ser43Ala/Ser45Ala transgenic mouse with in situ hemodynamics and back-phosphorylation assay\",\n      \"pmids\": [\"14726296\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of PKC/PKA site cross-talk at the structural level unresolved\", \"Phospho-occupancy under physiological signaling not quantified\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Showed cTnI is degraded by region-specific N- then C-terminal proteolysis during ischemic arrest, linking C-terminal cleavage to myofibrillar dissociation and identifying adenosine as protective.\",\n      \"evidence\": \"Region-specific anti-cTnI Western blotting and fractionation in perfused rat hearts under cardioplegia ± adenosine\",\n      \"pmids\": [\"15652960\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Protease responsible not identified\", \"Functional consequence of dissociation not directly measured\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identified a candidate physical partner (DSCR1L2) of cTnI, raising the possibility of regulatory interactions beyond the troponin core.\",\n      \"evidence\": \"Yeast two-hybrid screen of human heart cDNA with GST pulldown confirmation; exon 2 mapped as binding determinant\",\n      \"pmids\": [\"16516408\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional consequence established\", \"Interaction not validated in cardiomyocytes or in vivo\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined PAK3-mediated Ser151 phosphorylation as a Ca2+-sensitizing modification that shortens cTnC–cTnI distances, expanding the kinase repertoire tuning thin-filament activation.\",\n      \"evidence\": \"Steady-state/time-resolved FRET and stopped-flow kinetics on reconstituted thin filaments with cTnI(S151E) phosphomimic\",\n      \"pmids\": [\"20540949\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo PAK3 phosphorylation of cTnI and its physiological trigger not demonstrated\", \"Phosphomimic may not fully replicate genuine phosphorylation\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Established that PKA phosphorylation of cTnI Ser23/Ser24 is a key determinant of length-dependent force generation, mechanistically linking cTnI to the Frank-Starling response.\",\n      \"evidence\": \"Troponin exchange into permeabilized rat myocytes with PKA treatment and S23D/S24D phosphomimic; length-tension measurements\",\n      \"pmids\": [\"23836688\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for how N-terminal phosphorylation alters length sensing left to later studies\", \"Contribution of other myofilament PKA substrates not isolated\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Demonstrated that the HCM inhibitory-peptide mutation R145G impairs the beta-adrenergic contractile response, connecting a disease mutation to depressed adrenergic reserve.\",\n      \"evidence\": \"Adenoviral cTnI-R145G expression in adult rat cardiomyocytes with sarcomere shortening ± isoproterenol\",\n      \"pmids\": [\"18548271\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single cell model with overexpression rather than endogenous knock-in\", \"Structural mechanism not resolved here\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Provided structural and functional mechanism for R145G: it stabilizes Ca2+ coordination in cTnC while blunting N-terminus–inhibitory-peptide coupling and functionally interacts with the cTnT C-terminus to alter thin-filament switching.\",\n      \"evidence\": \"Molecular dynamics simulations and in vitro motility assays of cTnI-R145G ± cTnT-R278C\",\n      \"pmids\": [\"25606687\", \"24418317\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"MD predictions of N-terminus repositioning lack direct in vitro/in vivo validation\", \"Subunit cross-talk quantified only in reconstituted systems\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Revealed dual nuclear/metabolic axes of cTnI biology: HDAC5-mediated promoter deacetylation represses TNNI3 transcription, and an HCM mutation (G203S) impairs Ca2+-channel–mitochondria communication as an early pre-cardiomyopathic event.\",\n      \"evidence\": \"ChIP of HDAC5 at the cTnI promoter with estrogen/SAHA treatment; patch-clamp and mitochondrial assays in cTnI-G203S transgenic cardiomyocytes\",\n      \"pmids\": [\"27379430\", \"27062056\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct connection between cTnI mutation and mitochondrial coupling mechanism incompletely defined\", \"Promoter regulation studied in neonatal/aging contexts only\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended epigenetic control of TNNI3 to aging hearts, showing HDAC1/HDAC3 occupancy and GATA4/Mef2c recruitment set cTnI expression and diastolic function.\",\n      \"evidence\": \"ChIP for HDAC1/HDAC3 and AcH3K9, transcription-factor binding, and echocardiography in aged mice ± EGCG\",\n      \"pmids\": [\"28382690\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal hierarchy among HDACs not dissected\", \"EGCG acts pleiotropically beyond the cTnI promoter\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Established three new dimensions of cTnI regulation and pathology: PRMT1 arginine methylation at R146/R148 restraining hypertrophy, nuclear cTnI partnering with HDAC1/SMYD1 to control PDE4d via histone marks, and a fetal TNNI1 isoform switch upon complete TNNI3 loss.\",\n      \"evidence\": \"Mass spectrometry, in vitro PRMT1 assays and H9c2 hypertrophy readout; nuclear Co-IP and ChIP in cTnI-193His mice; protein/transcript analysis of a homozygous truncating patient biopsy\",\n      \"pmids\": [\"30772011\", \"30900165\", \"31568572\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How methylation loss mechanistically drives hypertrophy not fully defined\", \"Nuclear cTnI translocation signals and DNA-targeting specificity unknown\", \"Isoform switch documented in a single patient\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Mapped how C-terminal regulatory mutations (R170G/W) destabilize thin filaments and disrupt cTnI/cTnT–cMyBPC-C0C2 interactions, and showed miR-449 controls TNNI3 transcription by sponging HDAC1.\",\n      \"evidence\": \"Skinned-fiber Ca2+-sensitivity, EM, binding assays and microscale thermophoresis for R170 mutants; luciferase, ChIP and in vivo agomiR for miR-449/HDAC1\",\n      \"pmids\": [\"32182250\", \"33378032\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological consequence of disrupted cMyBPC coupling in vivo not measured\", \"miR-449 regulation tested mainly in aged hearts\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed a de novo C-terminal mutation (D127Y) causes infantile restrictive cardiomyopathy through Ca2+-sensitization and thin-filament destabilization, and that troponin-targeting agents can partially restore filament structure.\",\n      \"evidence\": \"Skinned-fiber force, reconstituted thin-filament structural/binding assays, and levosimendan/EGCg treatment in vitro\",\n      \"pmids\": [\"34502534\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo or cell-based validation absent\", \"Drug effects shown only in vitro\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Used human iPSC-CM and engineered-tissue models with isogenic correction and WT supplementation to show R170W acts as a dominant gain-of-function causing impaired relaxation, and demonstrated a generalizable structural mechanism by which a partner-subunit mutation impairs PKA access to cTnI Ser23/Ser24.\",\n      \"evidence\": \"CRISPR-corrected and WT-overexpressing R170W iPSC-CM/EHT with mechanical readouts and RNA-seq; FRET/kinetics/MD and hemodynamics defining cTnC–cTnI interface effects on cTnI phosphorylation; AC16 R79C cellular phenotyping\",\n      \"pmids\": [\"38193576\", \"38497452\", \"39328062\", \"39426416\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transcriptomic changes (TGF-β, ECM) not mechanistically linked to the contractile defect\", \"iPSC-CM maturity limits in vivo extrapolation\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated a synonymous TNNI3 variant can be pathogenic via cryptic splicing/intron retention, broadening the mutational mechanisms underlying recessive lethal cardiomyopathy.\",\n      \"evidence\": \"Trio exome sequencing and minigene splicing assay of c.24G>A in compound heterozygosity with a gene deletion\",\n      \"pmids\": [\"36565796\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Protein-level consequence inferred from splicing, not directly measured\", \"Single family\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Scaled functional phenotyping to many TNNI3 variants, showing Ca2+-sensitivity predicts pathogenicity while diastolic function correlates with age of onset.\",\n      \"evidence\": \"High-throughput hiPSC-CM contractile/calcium imaging across variants with clinical correlation (preprint)\",\n      \"pmids\": [\"41446209\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, single lab\", \"Mechanistic basis of the diastolic-function/onset correlation not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How nuclear cTnI is targeted to specific promoters and how its sarcomeric versus nuclear pools are partitioned and coordinated remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No nuclear import/retention signal identified for cTnI\", \"Genome-wide nuclear cTnI binding sites uncharacterized\", \"Interplay between contractile dysfunction and transcriptional reprogramming undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [4, 13]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [5, 13]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [13, 15]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005863\", \"supporting_discovery_ids\": [13]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [1, 5, 13]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [3, 13, 15, 19, 20]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [9, 11, 16]}\n    ],\n    \"complexes\": [\"cardiac troponin complex\", \"cardiac thin filament\"],\n    \"partners\": [\"TNNC1\", \"TNNT2\", \"TPM1\", \"MYBPC3\", \"HDAC1\", \"SMYD1\", \"PRMT1\", \"RCAN3\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}