{"gene":"NEXN","run_date":"2026-06-10T05:19:52","timeline":{"discoveries":[{"year":1998,"finding":"Nexilin (b-nexilin and s-nexilin) are F-actin binding proteins isolated from rat brain and fibroblasts. b-Nexilin has two F-actin-binding domains (ABDs) at NH2-terminal and middle regions and shows F-actin cross-linking activity; s-nexilin has one ABD at the middle region and lacks cross-linking activity. s-Nexilin colocalizes with vinculin, talin, and paxillin at cell-matrix adherens junctions and focal contacts.","method":"Protein purification, in vitro F-actin binding assay, F-actin cross-linking assay, immunofluorescence microscopy","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical reconstitution with purified protein, domain-level mutagenesis (deletion of ABD1), and orthogonal localization by immunofluorescence","pmids":["9832551"],"is_preprint":false},{"year":2009,"finding":"Nexilin is a Z-disk protein in cardiac and skeletal muscle; loss of nexilin in zebrafish disrupts Z-disk stability and causes heart failure. Expression of disease-associated NEXN mutant alleles in zebrafish induces Z-disk damage in a dominant-negative manner. Increased mechanical strain aggravates Z-disk damage in nexilin-deficient skeletal muscle, indicating nexilin protects Z-disks from mechanical trauma.","method":"Zebrafish morpholino knockdown, transgenic expression of mutant NEXN alleles, electron microscopy of Z-disk ultrastructure, genetic association study","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function (morpholino), gain-of-dominant-negative function, electron microscopy of Z-disk phenotype, replicated across human and zebrafish","pmids":["19881492"],"is_preprint":false},{"year":2005,"finding":"NELIN (human nexilin) product associates with F-actin in cells. Stable transfection of NELIN into HeLa cells increases cell migration by ~2-fold and adhesion by ~1.7-fold compared to empty vector controls.","method":"Immunofluorescence, immunoprecipitation, stable transfection, migration and adhesion assays","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP and functional overexpression assay in single lab; two orthogonal methods (IP + functional assay)","pmids":["15823560"],"is_preprint":false},{"year":2010,"finding":"Two HCM-associated NEXN missense mutations (Q131E and R279C) cause local accumulations of nexilin in cells. The Q131E mutation abolishes F-actin binding of the actin-binding domain fragment and decreases binding of full-length NEXN to α-actin as demonstrated by co-immunoprecipitation.","method":"Cellular transfection, immunofluorescence, co-immunoprecipitation, F-actin binding assay in C2C12 cells","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct F-actin binding assay + Co-IP with mutation-function correlation, single lab","pmids":["20970104"],"is_preprint":false},{"year":2013,"finding":"Nexilin binds preferentially to IRS1 (over IRS2) in L6 skeletal muscle myotubes under basal conditions, and this complex is disassembled by insulin. Functional silencing of nexilin enhances recruitment of p85α to IRS1, increases PI-3,4,5-P3 formation, and enhances AKT activation and glucose uptake, while nexilin overexpression inhibits IRS1-to-AKT signaling. Disruption of actin with Latrunculin B abolishes the nexilin–IRS1 spatial association.","method":"Co-immunoprecipitation, siRNA knockdown, nexilin overexpression, PI3K activity assay, AKT phosphorylation immunoblot, glucose uptake assay in L6 myotubes","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, functional KD and OE with signaling readouts, single lab","pmids":["23383252"],"is_preprint":false},{"year":2014,"finding":"NEXN inhibits cardiac differentiation by suppressing GATA4 expression. Cardiac-selective NEXN transgenic mice develop atrial septal defects. Disease-associated NEXN mutations (K199E, L227S) also inhibit GATA4 expression, establishing NEXN as a negative regulator of GATA4-dependent cardiac development.","method":"Knockdown, overexpression, and rescue experiments in P19cl6 cells; transgenic mouse model; GATA4 expression analysis","journal":"Cardiovascular research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal approaches (KD, OE, rescue, in vivo transgenic) in single lab establishing NEXN-GATA4 regulatory axis","pmids":["24866383"],"is_preprint":false},{"year":2015,"finding":"Constitutive Nexn knockout mice develop rapidly progressive dilated cardiomyopathy with left ventricular dilation, wall thinning, systolic dysfunction, and collagen/elastin deposits (endomyocardial fibroelastosis) by postnatal day 6, establishing an essential role of nexilin in cardiac structure and function.","method":"Constitutive knockout mouse model, echocardiography, histology, immunostaining","journal":"Basic research in cardiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — cardiomyocyte-specific KO with defined morphological and functional cardiac phenotype, multiple time-point analyses","pmids":["26659360"],"is_preprint":false},{"year":2018,"finding":"Nexilin localizes to dense bodies and dense bands in smooth muscle cells (analogous to Z-discs). NEXN expression in SMCs is controlled by actin polymerization state and by transcriptional coactivators MRTF (MYOCD, MKL1, MKL2) and YAP/TAZ. Silencing NEXN reduces actin polymerization, cell migration, and smooth muscle marker expression, indicating a positive feedback loop between nexilin and actin dynamics.","method":"Immunofluorescence, immunoelectron microscopy, Latrunculin B treatment, NEXN knockdown/overexpression, MRTF/YAP overexpression, promoter assay","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (immunoelectron microscopy, functional knockdown/overexpression, promoter reporter) in single lab","pmids":["30158653"],"is_preprint":false},{"year":2019,"finding":"NEXN is a component of junctional membrane complexes at cardiac dyads. Loss of Nexn in global and cardiomyocyte-specific knockout mice causes dilated cardiomyopathy. NEXN interacts with junctional sarcoplasmic reticulum proteins, is essential for optimal calcium transients, and is required for initiation and formation of T-tubule invagination.","method":"Global and cardiomyocyte-specific KO mice, electron microscopy, confocal microscopy, calcium transient measurements, RNA sequencing, mass spectrometry","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 2 / Strong — cardiomyocyte-specific KO with multiple orthogonal analyses (EM ultrastructure, calcium imaging, MS interaction proteomics) in single rigorous study","pmids":["30982350"],"is_preprint":false},{"year":2019,"finding":"NEXN (nexilin) exerts a protective role against atherosclerosis; NEXN protein inhibits TLR4 oligomerization and downstream NF-κB activity, reducing expression of adhesion molecules and inflammatory cytokines in endothelial cells. The anti-inflammatory/anti-atherosclerotic effects of the lncRNA NEXN-AS1 are abolished by NEXN knockdown, placing NEXN downstream of NEXN-AS1 in this pathway. In ApoE-KO mice, NEXN deficiency promotes atherosclerosis while augmented NEXN expression deters it.","method":"In vitro knockdown/overexpression, TLR4 oligomerization assay, NF-κB reporter, monocyte adhesion assay, ApoE-KO mouse model with NEXN manipulation","journal":"The Journal of clinical investigation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — TLR4 oligomerization assay + NF-κB reporter + in vivo mouse model, single lab","pmids":["30589415"],"is_preprint":false},{"year":2020,"finding":"Inducible adult cardiomyocyte-specific loss of Nexn in mice causes dilated cardiomyopathy, impairs calcium handling, and leads to a 40% reduction in the transverse tubular component, demonstrating that NEXN is required not only for T-tubule formation during development but also for maintenance of the transverse-axial tubular architecture in adult cardiomyocytes.","method":"Inducible cardiomyocyte-specific KO mice, confocal microscopy, electron microscopy, calcium transient and myocyte shortening studies, echocardiography","journal":"Circulation. Heart failure","confidence":"High","confidence_rationale":"Tier 2 / Strong — inducible adult-specific KO with quantitative T-tubule morphometry, calcium imaging, and functional cardiac measurements","pmids":["32635769"],"is_preprint":false},{"year":2022,"finding":"CDC-like kinase 4 (CLK4) directly phosphorylates nexilin (NEXN). CLK4 knockdown induces pathological cardiomyocyte hypertrophy, while overexpression of a phosphorylation-mimic NEXN mutant is sufficient to reverse CLK4 knockdown-induced hypertrophy. Restoring NEXN phosphorylation ameliorates myocardial hypertrophy in cardiac-specific Clk4-knockout mice, establishing CLK4 as the kinase writer for NEXN phosphorylation in cardiac hypertrophy regulation.","method":"Kinase substrate assay, cardiomyocyte-specific Clk4 KO mice, phosphorylation-mimic NEXN mutant overexpression, echocardiography, cardiomyocyte size measurements","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct kinase substrate identification + phospho-mimic rescue in both cell and mouse model, multiple orthogonal methods in one rigorous study","pmids":["35907876"],"is_preprint":false},{"year":2015,"finding":"NELIN (nexilin) promotes vascular smooth muscle cells (VSMCs) toward a contractile phenotype by activating RhoA, which drives SRF nuclear translocation and SMα-actin expression. NELIN knockdown shifts VSMCs to a synthetic phenotype with decreased RhoA and SRF nuclear localization; the RhoA kinase inhibitor Y-27632 abolishes the NELIN-induced contractile phenotype.","method":"Lentiviral overexpression and siRNA knockdown in VSMCs, Western blot for RhoA/SRF/SMα-actin, nuclear translocation assay, Rho kinase inhibitor treatment","journal":"Molecular medicine reports","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — overexpression and knockdown with pharmacological inhibitor validation, single lab, two methods","pmids":["26458985"],"is_preprint":false},{"year":2025,"finding":"NEXN interacts with SERCA2 in vascular smooth muscle cells, enhancing SERCA2 SUMOylation, stability, and function. VSMC-specific NEXN knockout exacerbates vascular calcification, while NEXN overexpression alleviates it, operating through the NEXN-SERCA2 interaction and SERCA2 SUMOylation axis.","method":"VSMC-specific KO and overexpression mouse models, co-immunoprecipitation for NEXN-SERCA2 interaction, SUMOylation assay, multi-transcriptomics analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — VSMC-specific KO + OE animal models + Co-IP + SUMOylation biochemical assay demonstrating mechanistic interaction in one study","pmids":["40883305"],"is_preprint":false},{"year":2025,"finding":"NEXN deficiency in VSMCs promotes phenotypic transition and neointimal hyperplasia through endoplasmic reticulum (ER) stress and Krüppel-like factor 4 (KLF4) signaling. Inhibiting ER stress ameliorates VSMC phenotypic transition and proliferation caused by NEXN deficiency.","method":"VSMC-specific lineage-tracing mice, NEXN KO, integrative transcriptomics, ER stress inhibitor treatment, cell proliferation and phenotypic marker assays","journal":"JCI insight","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — VSMC-specific KO mouse model with pharmacological rescue (ER stress inhibitor), single lab","pmids":["40440261"],"is_preprint":false},{"year":2025,"finding":"Nexilin binds directly to the C-terminal intracellular loop of GABAA receptor γ-subunits. This interaction regulates cell-surface expression of extrasynaptic γ2-containing GABAA receptors in hippocampal neurons; nexilin upregulation increases surface GABAA receptor numbers and synaptic currents, while the effect requires the actin-binding domain of nexilin (its deletion abolishes the effect). Nexilin also interacts with Rab7b and the lysosomal calcium channel TRPML1, and promotes calcium-dependent fission of late endosomes/lysosomes required for retrograde transport.","method":"Pulldown, array-based peptide mapping, deep-mutational scanning, siRNA knockdown and overexpression in hippocampal neurons, electrophysiology (GABA-mediated currents), surface GABAA receptor quantification, actin-binding domain deletion mutant","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding mapping (array + deep-mutational scan) + domain deletion + functional electrophysiology, single lab","pmids":["40812511"],"is_preprint":false},{"year":2026,"finding":"Nexilin regulates late endosome/lysosome (LE/Lys) fission and retrograde transport. Depletion of nexilin causes LE/Lys enlargement due to inhibited fission. Nexilin interacts with the small GTPase Rab7b and the lysosomal calcium channel TRPML1; TRPML1 activation rescues LE/Lys enlargement caused by nexilin depletion, indicating nexilin mediates the interaction between LE/Lys and the acto-myosin cytoskeleton for calcium-dependent organelle fission.","method":"siRNA screen, live imaging of LE/Lys size, Co-immunoprecipitation for Rab7b and TRPML1, TRPML1 agonist rescue experiment, retrograde transport assay","journal":"Cell communication and signaling : CCS","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA screen + Co-IP + pharmacological rescue, single lab, multiple orthogonal methods","pmids":["41514273"],"is_preprint":false},{"year":2012,"finding":"Nexilin is required for efficient Listeria monocytogenes invasion; siRNA-mediated nexilin knockdown significantly reduces intracellular bacterial levels. Nexilin is a component of L. monocytogenes actin comet tails and EPEC pedestals, accumulating at the distal portion of motile bacterial actin structures. Nexilin knockdown impairs comet tail formation (malformed comet tails) but is dispensable for EPEC pedestal generation.","method":"siRNA knockdown, immunofluorescence colocalization, bacterial invasion assay (intracellular bacteria quantification), comet tail morphology analysis","journal":"Cellular microbiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA functional knockdown with specific phenotypic readout (bacterial invasion + comet tail formation), single lab, two orthogonal assays","pmids":["22381134"],"is_preprint":false},{"year":2025,"finding":"NEXN overexpression in hepatocellular carcinoma cells reduces β-catenin nuclear accumulation and inhibits EMT. NEXN binds to MYOCD, and together they co-regulate EMT via the WNT/β-catenin signaling pathway. Diminished NEXN expression leads to β-catenin nuclear accumulation and enhanced EMT-driven metastasis.","method":"Overexpression in HCC cell lines, β-catenin nuclear localization assay, Co-immunoprecipitation for NEXN-MYOCD interaction, in vivo tumor formation, EMT marker Western blot","journal":"iScience","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP and overexpression with mechanistic follow-up, single lab, no reconstitution or mutagenesis","pmids":["41399508"],"is_preprint":false},{"year":2024,"finding":"AAV-mediated systemic delivery of Nexn restores cardiac function and extends lifespan in both global Nexn knockout mice and mice carrying the human equivalent G645del mutation, demonstrating that exogenous full-length nexilin can functionally rescue loss-of-function DCM and identifying functional components of nexilin sufficient for this rescue.","method":"AAV gene delivery (systemic intravenous injection), echocardiography, immunoblot, Nexn global KO and G645del knock-in mouse models","journal":"Genome biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo gene rescue in two independent mouse models with functional cardiac readout, single lab","pmids":["38783323"],"is_preprint":false},{"year":2025,"finding":"NEXN homozygous knockout human iPSC-derived cardiomyocytes show disordered junctional membrane complexes, abnormal excitation-contraction coupling, increased oxidative stress, and decreased energy metabolism, confirming that nexilin is a structural component of junctional membrane complexes essential for excitation-contraction coupling.","method":"CRISPR/Cas9 knockout in hiPSCs, directed differentiation to cardiomyocytes, electron microscopy, calcium imaging, oxidative stress assays, metabolic assays","journal":"Stem cell research & therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR KO in human iPSC-derived cardiomyocytes with multiple orthogonal functional readouts, single lab","pmids":["40713745"],"is_preprint":false},{"year":2024,"finding":"Novel nexilin splice variants exist in mouse and human tissues segregating into myocyte-specific and epithelial-specific isoforms. Heart-specific isoforms differ between atria and ventricles. Different isoforms exhibit distinct self-interaction properties in recombinant protein interaction studies, and critical exons in ABD1 and ABD2 differ between isoforms.","method":"RT-PCR, tissue expression analysis, recombinant protein interaction studies (pulldown), isoform mapping","journal":"Cells","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, recombinant protein pulldown without full reconstitution or in vivo functional validation of isoform-specific differences","pmids":["39682766"],"is_preprint":false}],"current_model":"Nexilin (NEXN) is an F-actin-binding protein with multiple ABDs that localizes to sarcomeric Z-discs/dense bodies in striated and smooth muscle and to cell-matrix adherens junctions in non-muscle cells; it is an essential structural component of cardiac junctional membrane complexes required for T-tubule formation and maintenance, optimal calcium transients, and excitation-contraction coupling, while also functioning as a substrate of CLK4 kinase (whose phosphorylation of NEXN regulates cardiac hypertrophy), an inhibitor of TLR4 oligomerization and NF-κB signaling in endothelial cells, an interactor with SERCA2 that promotes its SUMOylation and stability to prevent vascular calcification, a regulator of VSMC phenotypic switching via RhoA/SRF and ER stress/KLF4 pathways, a regulator of IRS1 scaffold signaling in skeletal muscle, and a regulator of extrasynaptic GABAA receptor surface expression and late endosome/lysosome fission in neurons."},"narrative":{"mechanistic_narrative":"Nexilin (NEXN) is an F-actin-binding cytoskeletal protein that organizes contractile and adhesive actin structures and serves as an essential structural component of the cardiac sarcomere and dyad [PMID:9832551, PMID:19881492, PMID:30982350]. It contains multiple actin-binding domains, cross-links F-actin, and localizes to cell-matrix adherens junctions in non-muscle cells and to the Z-disk—and the smooth-muscle equivalent dense bodies—in striated and smooth muscle [PMID:9832551, PMID:19881492, PMID:30158653]. At the Z-disk, nexilin protects against mechanical strain, and its loss destabilizes Z-disk ultrastructure and causes heart failure, with disease-associated mutant alleles acting dominant-negatively and abolishing actin binding [PMID:19881492, PMID:20970104]. Nexilin is a component of junctional membrane complexes at cardiac dyads, where it interacts with junctional sarcoplasmic reticulum proteins and is required for both developmental formation and adult maintenance of the transverse-tubular system, optimal calcium transients, and excitation-contraction coupling; its loss in mice and human iPSC-derived cardiomyocytes produces dilated cardiomyopathy with disordered dyads, impaired calcium handling, and metabolic stress [PMID:30982350, PMID:32635769, PMID:40713745]. Loss-of-function cardiomyopathy is rescuable by AAV-delivered full-length nexilin in knockout and human-equivalent G645del mutant mice, establishing NEXN as a causative dilated/hypertrophic cardiomyopathy gene [PMID:38783323, PMID:19881492]. NEXN activity is post-translationally tuned by CLK4, which directly phosphorylates it to restrain pathological cardiomyocyte hypertrophy [PMID:35907876]. Beyond the heart, nexilin governs vascular smooth muscle phenotype—promoting the contractile state via RhoA/SRF and protecting against calcification through a SERCA2 interaction that enhances SERCA2 SUMOylation and stability [PMID:26458985, PMID:40883305]. Additional context-specific roles include scaffolding insulin/IRS1 signaling in skeletal myotubes [PMID:23383252], inhibiting TLR4 oligomerization and NF-κB-driven endothelial inflammation [PMID:30589415], and, in non-muscle cells, mediating actin-dependent organelle dynamics including late endosome/lysosome fission via Rab7b and TRPML1 and surface trafficking of γ2-containing GABAA receptors in neurons [PMID:40812511, PMID:41514273].","teleology":[{"year":1998,"claim":"Established the founding biochemical identity of nexilin as an F-actin-binding and cross-linking protein with distinct domain architectures and junctional localization, defining the molecular basis for all later cytoskeletal roles.","evidence":"Protein purification with in vitro F-actin binding/cross-linking assays and immunofluorescence in rat brain and fibroblasts","pmids":["9832551"],"confidence":"High","gaps":["No tissue-level or in vivo function established","Physiological consequences of cross-linking activity unaddressed"]},{"year":2005,"claim":"First linked nexilin to cell behavior, showing its overexpression promotes migration and adhesion, extending its actin association to functional motility.","evidence":"Co-IP and stable overexpression with migration/adhesion assays in HeLa cells","pmids":["15823560"],"confidence":"Medium","gaps":["Overexpression-only; no loss-of-function","Mechanism connecting actin binding to migration not defined"]},{"year":2009,"claim":"Identified nexilin as a Z-disk protein essential for sarcomere stability and protection against mechanical strain, and connected human NEXN mutations to cardiomyopathy via dominant-negative Z-disk damage.","evidence":"Zebrafish morpholino knockdown, mutant allele expression, Z-disk electron microscopy, human genetic association","pmids":["19881492"],"confidence":"High","gaps":["Molecular partners at the Z-disk not defined","Mechanism of strain protection unresolved"]},{"year":2010,"claim":"Showed disease-associated NEXN missense mutations mechanistically impair F-actin/α-actin binding and cause protein mislocalization, tying genotype to a defined biochemical defect.","evidence":"Transfection, immunofluorescence, Co-IP, F-actin binding assay in C2C12 cells","pmids":["20970104"],"confidence":"Medium","gaps":["Single-lab in vitro correlation","In vivo consequence of each mutation not tested"]},{"year":2013,"claim":"Revealed a metabolic scaffolding role in which nexilin binds IRS1 in an actin-dependent, insulin-regulated manner to restrain PI3K/AKT signaling and glucose uptake in muscle.","evidence":"Reciprocal Co-IP, siRNA/overexpression, PI3K and AKT readouts, glucose uptake in L6 myotubes","pmids":["23383252"],"confidence":"Medium","gaps":["Single-lab cell model only","In vivo metabolic relevance untested"]},{"year":2014,"claim":"Identified a developmental signaling role whereby NEXN negatively regulates GATA4 and cardiac differentiation, with disease mutations recapitulating GATA4 suppression.","evidence":"Knockdown/overexpression/rescue in P19cl6 cells and cardiac-selective transgenic mice","pmids":["24866383"],"confidence":"Medium","gaps":["Mechanism of GATA4 suppression unknown","Relationship to structural Z-disk role unclear"]},{"year":2015,"claim":"Defined nexilin as a driver of smooth muscle phenotype, promoting the contractile state through RhoA-dependent SRF nuclear translocation.","evidence":"Lentiviral OE/siRNA in VSMCs with RhoA/SRF/SMα-actin blots and Y-27632 inhibitor","pmids":["26458985"],"confidence":"Medium","gaps":["Direct RhoA regulatory mechanism not defined","Single-lab pharmacological inference"]},{"year":2015,"claim":"Demonstrated an essential in vivo cardiac requirement, with constitutive Nexn knockout producing early, rapidly progressive dilated cardiomyopathy.","evidence":"Constitutive KO mouse, echocardiography, histology, immunostaining","pmids":["26659360"],"confidence":"High","gaps":["Cell-autonomous vs developmental contribution not separated","Molecular cause of DCM not yet mechanistic"]},{"year":2018,"claim":"Placed NEXN within a transcriptional feedback circuit in smooth muscle, controlled by actin state and MRTF/YAP-TAZ coactivators and feeding back on actin polymerization.","evidence":"Immunoelectron microscopy, Latrunculin B, KD/OE, MRTF/YAP overexpression, promoter assay","pmids":["30158653"],"confidence":"Medium","gaps":["Direct promoter occupancy not shown","In vivo SMC relevance untested"]},{"year":2019,"claim":"Resolved the dilated-cardiomyopathy mechanism by identifying NEXN as a junctional membrane complex component required for T-tubule formation, calcium transients, and excitation-contraction coupling.","evidence":"Global and cardiomyocyte-specific KO mice with EM, calcium imaging, RNA-seq, and interaction mass spectrometry","pmids":["30982350"],"confidence":"High","gaps":["Specific jSR-binding partners not individually validated","How nexilin nucleates T-tubule invagination mechanistically unresolved"]},{"year":2019,"claim":"Uncovered a vascular protective, anti-inflammatory function in which NEXN inhibits TLR4 oligomerization and NF-κB signaling downstream of lncRNA NEXN-AS1.","evidence":"KD/OE, TLR4 oligomerization assay, NF-κB reporter, monocyte adhesion, ApoE-KO mouse model","pmids":["30589415"],"confidence":"Medium","gaps":["Direct TLR4 binding not structurally defined","Link to cytoskeletal function unclear"]},{"year":2020,"claim":"Showed NEXN is required not only for developmental T-tubule formation but for ongoing maintenance of tubular architecture in adult cardiomyocytes.","evidence":"Inducible adult cardiomyocyte-specific KO with quantitative T-tubule morphometry, calcium imaging, echocardiography","pmids":["32635769"],"confidence":"High","gaps":["Turnover mechanism of tubular maintenance unresolved","Reversibility upon re-expression not tested here"]},{"year":2022,"claim":"Identified CLK4 as the kinase that directly phosphorylates nexilin to restrain pathological hypertrophy, defining a post-translational control layer for NEXN.","evidence":"Kinase substrate assay, cardiomyocyte-specific Clk4 KO mice, phospho-mimic NEXN rescue, cardiomyocyte size measurements","pmids":["35907876"],"confidence":"High","gaps":["Phosphosite-specific structural consequence not mapped","Whether phosphorylation alters actin or dyad function unknown"]},{"year":2024,"claim":"Demonstrated therapeutic sufficiency, with AAV-delivered full-length nexilin rescuing cardiac function and lifespan in KO and G645del mutant mice and defining minimal functional components.","evidence":"Systemic AAV gene delivery, echocardiography, immunoblot in two mouse models","pmids":["38783323"],"confidence":"Medium","gaps":["Durability and dosing not fully characterized","Single-lab rescue"]},{"year":2025,"claim":"Confirmed in a human system that NEXN is required for junctional membrane complex integrity and excitation-contraction coupling, linking its loss to oxidative and metabolic stress.","evidence":"CRISPR KO in human iPSC-derived cardiomyocytes with EM, calcium imaging, oxidative stress and metabolic assays","pmids":["40713745"],"confidence":"Medium","gaps":["Single-lab hiPSC model","Causal order of metabolic vs structural defects unresolved"]},{"year":2025,"claim":"Expanded NEXN's vascular role by showing it stabilizes SERCA2 via enhanced SUMOylation to prevent calcification, and that its deficiency drives VSMC phenotypic transition through ER stress/KLF4 signaling.","evidence":"VSMC-specific KO/OE mice, Co-IP, SUMOylation assay, lineage tracing, ER stress inhibitor rescue","pmids":["40883305","40440261"],"confidence":"High","gaps":["Direct SERCA2 binding interface not mapped","How NEXN promotes SUMOylation mechanistically unresolved"]},{"year":2025,"claim":"Extended nexilin function to neuronal and organelle biology, mapping direct binding to GABAA receptor γ-subunits and to Rab7b/TRPML1 for actin-dependent surface receptor trafficking and late endosome/lysosome fission.","evidence":"Peptide array mapping, deep-mutational scanning, ABD-deletion mutants, electrophysiology, Co-IP, TRPML1 agonist rescue in neurons and cells","pmids":["40812511","41514273"],"confidence":"Medium","gaps":["In vivo neuronal relevance untested","How actin binding couples to organelle fission not fully defined"]},{"year":null,"claim":"It remains unresolved how nexilin's single actin-binding scaffold is repurposed across such divergent contexts (sarcomere/dyad, vascular SERCA2 stabilization, IRS1/TLR4 signaling, organelle fission) and whether tissue-specific isoforms partition these functions.","evidence":"No discovery in the corpus directly tests cross-tissue functional partitioning or isoform-specific in vivo roles","pmids":[],"confidence":"Low","gaps":["Isoform-specific functions only mapped at recombinant/expression level [#21]","No unifying structural mechanism linking actin binding to signaling roles"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,1,3,7]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4,15]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[9,11,13]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,1,7]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[8,10]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[15,16]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[8,14]}],"pathway":[{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[1,8,10]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[9,11,12]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[5,7]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[16]}],"complexes":["cardiac junctional membrane complex (dyad)","Z-disk","smooth muscle dense bodies"],"partners":["IRS1","SERCA2","CLK4","MYOCD","TLR4","RAB7B","TRPML1","GABRG2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q0ZGT2","full_name":"Nexilin","aliases":["F-actin-binding protein","Nelin"],"length_aa":675,"mass_kda":80.7,"function":"Involved in regulating cell migration through association with the actin cytoskeleton. Has an essential role in the maintenance of Z line and sarcomere integrity","subcellular_location":"Cytoplasm, cytoskeleton; Cell junction, adherens junction; Cytoplasm, myofibril, sarcomere, Z line","url":"https://www.uniprot.org/uniprotkb/Q0ZGT2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/NEXN","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CALD1","stoichiometry":0.2},{"gene":"CAPZB","stoichiometry":0.2},{"gene":"CTTN","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/NEXN","total_profiled":1310},"omim":[{"mim_id":"621261","title":"CARDIOMYOPATHY, DILATED, 2M; CMD2M","url":"https://www.omim.org/entry/621261"},{"mim_id":"618370","title":"NEXN ANTISENSE RNA 1, NONCODING; NEXNAS1","url":"https://www.omim.org/entry/618370"},{"mim_id":"613876","title":"CARDIOMYOPATHY, FAMILIAL HYPERTROPHIC, 20; 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cell-matrix adherens junctions and focal contacts.\",\n      \"method\": \"Protein purification, in vitro F-actin binding assay, F-actin cross-linking assay, immunofluorescence microscopy\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical reconstitution with purified protein, domain-level mutagenesis (deletion of ABD1), and orthogonal localization by immunofluorescence\",\n      \"pmids\": [\"9832551\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Nexilin is a Z-disk protein in cardiac and skeletal muscle; loss of nexilin in zebrafish disrupts Z-disk stability and causes heart failure. Expression of disease-associated NEXN mutant alleles in zebrafish induces Z-disk damage in a dominant-negative manner. Increased mechanical strain aggravates Z-disk damage in nexilin-deficient skeletal muscle, indicating nexilin protects Z-disks from mechanical trauma.\",\n      \"method\": \"Zebrafish morpholino knockdown, transgenic expression of mutant NEXN alleles, electron microscopy of Z-disk ultrastructure, genetic association study\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function (morpholino), gain-of-dominant-negative function, electron microscopy of Z-disk phenotype, replicated across human and zebrafish\",\n      \"pmids\": [\"19881492\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"NELIN (human nexilin) product associates with F-actin in cells. Stable transfection of NELIN into HeLa cells increases cell migration by ~2-fold and adhesion by ~1.7-fold compared to empty vector controls.\",\n      \"method\": \"Immunofluorescence, immunoprecipitation, stable transfection, migration and adhesion assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP and functional overexpression assay in single lab; two orthogonal methods (IP + functional assay)\",\n      \"pmids\": [\"15823560\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Two HCM-associated NEXN missense mutations (Q131E and R279C) cause local accumulations of nexilin in cells. The Q131E mutation abolishes F-actin binding of the actin-binding domain fragment and decreases binding of full-length NEXN to α-actin as demonstrated by co-immunoprecipitation.\",\n      \"method\": \"Cellular transfection, immunofluorescence, co-immunoprecipitation, F-actin binding assay in C2C12 cells\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct F-actin binding assay + Co-IP with mutation-function correlation, single lab\",\n      \"pmids\": [\"20970104\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Nexilin binds preferentially to IRS1 (over IRS2) in L6 skeletal muscle myotubes under basal conditions, and this complex is disassembled by insulin. Functional silencing of nexilin enhances recruitment of p85α to IRS1, increases PI-3,4,5-P3 formation, and enhances AKT activation and glucose uptake, while nexilin overexpression inhibits IRS1-to-AKT signaling. Disruption of actin with Latrunculin B abolishes the nexilin–IRS1 spatial association.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, nexilin overexpression, PI3K activity assay, AKT phosphorylation immunoblot, glucose uptake assay in L6 myotubes\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, functional KD and OE with signaling readouts, single lab\",\n      \"pmids\": [\"23383252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"NEXN inhibits cardiac differentiation by suppressing GATA4 expression. Cardiac-selective NEXN transgenic mice develop atrial septal defects. Disease-associated NEXN mutations (K199E, L227S) also inhibit GATA4 expression, establishing NEXN as a negative regulator of GATA4-dependent cardiac development.\",\n      \"method\": \"Knockdown, overexpression, and rescue experiments in P19cl6 cells; transgenic mouse model; GATA4 expression analysis\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal approaches (KD, OE, rescue, in vivo transgenic) in single lab establishing NEXN-GATA4 regulatory axis\",\n      \"pmids\": [\"24866383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Constitutive Nexn knockout mice develop rapidly progressive dilated cardiomyopathy with left ventricular dilation, wall thinning, systolic dysfunction, and collagen/elastin deposits (endomyocardial fibroelastosis) by postnatal day 6, establishing an essential role of nexilin in cardiac structure and function.\",\n      \"method\": \"Constitutive knockout mouse model, echocardiography, histology, immunostaining\",\n      \"journal\": \"Basic research in cardiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cardiomyocyte-specific KO with defined morphological and functional cardiac phenotype, multiple time-point analyses\",\n      \"pmids\": [\"26659360\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Nexilin localizes to dense bodies and dense bands in smooth muscle cells (analogous to Z-discs). NEXN expression in SMCs is controlled by actin polymerization state and by transcriptional coactivators MRTF (MYOCD, MKL1, MKL2) and YAP/TAZ. Silencing NEXN reduces actin polymerization, cell migration, and smooth muscle marker expression, indicating a positive feedback loop between nexilin and actin dynamics.\",\n      \"method\": \"Immunofluorescence, immunoelectron microscopy, Latrunculin B treatment, NEXN knockdown/overexpression, MRTF/YAP overexpression, promoter assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (immunoelectron microscopy, functional knockdown/overexpression, promoter reporter) in single lab\",\n      \"pmids\": [\"30158653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"NEXN is a component of junctional membrane complexes at cardiac dyads. Loss of Nexn in global and cardiomyocyte-specific knockout mice causes dilated cardiomyopathy. NEXN interacts with junctional sarcoplasmic reticulum proteins, is essential for optimal calcium transients, and is required for initiation and formation of T-tubule invagination.\",\n      \"method\": \"Global and cardiomyocyte-specific KO mice, electron microscopy, confocal microscopy, calcium transient measurements, RNA sequencing, mass spectrometry\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cardiomyocyte-specific KO with multiple orthogonal analyses (EM ultrastructure, calcium imaging, MS interaction proteomics) in single rigorous study\",\n      \"pmids\": [\"30982350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"NEXN (nexilin) exerts a protective role against atherosclerosis; NEXN protein inhibits TLR4 oligomerization and downstream NF-κB activity, reducing expression of adhesion molecules and inflammatory cytokines in endothelial cells. The anti-inflammatory/anti-atherosclerotic effects of the lncRNA NEXN-AS1 are abolished by NEXN knockdown, placing NEXN downstream of NEXN-AS1 in this pathway. In ApoE-KO mice, NEXN deficiency promotes atherosclerosis while augmented NEXN expression deters it.\",\n      \"method\": \"In vitro knockdown/overexpression, TLR4 oligomerization assay, NF-κB reporter, monocyte adhesion assay, ApoE-KO mouse model with NEXN manipulation\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — TLR4 oligomerization assay + NF-κB reporter + in vivo mouse model, single lab\",\n      \"pmids\": [\"30589415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Inducible adult cardiomyocyte-specific loss of Nexn in mice causes dilated cardiomyopathy, impairs calcium handling, and leads to a 40% reduction in the transverse tubular component, demonstrating that NEXN is required not only for T-tubule formation during development but also for maintenance of the transverse-axial tubular architecture in adult cardiomyocytes.\",\n      \"method\": \"Inducible cardiomyocyte-specific KO mice, confocal microscopy, electron microscopy, calcium transient and myocyte shortening studies, echocardiography\",\n      \"journal\": \"Circulation. Heart failure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — inducible adult-specific KO with quantitative T-tubule morphometry, calcium imaging, and functional cardiac measurements\",\n      \"pmids\": [\"32635769\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CDC-like kinase 4 (CLK4) directly phosphorylates nexilin (NEXN). CLK4 knockdown induces pathological cardiomyocyte hypertrophy, while overexpression of a phosphorylation-mimic NEXN mutant is sufficient to reverse CLK4 knockdown-induced hypertrophy. Restoring NEXN phosphorylation ameliorates myocardial hypertrophy in cardiac-specific Clk4-knockout mice, establishing CLK4 as the kinase writer for NEXN phosphorylation in cardiac hypertrophy regulation.\",\n      \"method\": \"Kinase substrate assay, cardiomyocyte-specific Clk4 KO mice, phosphorylation-mimic NEXN mutant overexpression, echocardiography, cardiomyocyte size measurements\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct kinase substrate identification + phospho-mimic rescue in both cell and mouse model, multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"35907876\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"NELIN (nexilin) promotes vascular smooth muscle cells (VSMCs) toward a contractile phenotype by activating RhoA, which drives SRF nuclear translocation and SMα-actin expression. NELIN knockdown shifts VSMCs to a synthetic phenotype with decreased RhoA and SRF nuclear localization; the RhoA kinase inhibitor Y-27632 abolishes the NELIN-induced contractile phenotype.\",\n      \"method\": \"Lentiviral overexpression and siRNA knockdown in VSMCs, Western blot for RhoA/SRF/SMα-actin, nuclear translocation assay, Rho kinase inhibitor treatment\",\n      \"journal\": \"Molecular medicine reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — overexpression and knockdown with pharmacological inhibitor validation, single lab, two methods\",\n      \"pmids\": [\"26458985\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NEXN interacts with SERCA2 in vascular smooth muscle cells, enhancing SERCA2 SUMOylation, stability, and function. VSMC-specific NEXN knockout exacerbates vascular calcification, while NEXN overexpression alleviates it, operating through the NEXN-SERCA2 interaction and SERCA2 SUMOylation axis.\",\n      \"method\": \"VSMC-specific KO and overexpression mouse models, co-immunoprecipitation for NEXN-SERCA2 interaction, SUMOylation assay, multi-transcriptomics analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — VSMC-specific KO + OE animal models + Co-IP + SUMOylation biochemical assay demonstrating mechanistic interaction in one study\",\n      \"pmids\": [\"40883305\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NEXN deficiency in VSMCs promotes phenotypic transition and neointimal hyperplasia through endoplasmic reticulum (ER) stress and Krüppel-like factor 4 (KLF4) signaling. Inhibiting ER stress ameliorates VSMC phenotypic transition and proliferation caused by NEXN deficiency.\",\n      \"method\": \"VSMC-specific lineage-tracing mice, NEXN KO, integrative transcriptomics, ER stress inhibitor treatment, cell proliferation and phenotypic marker assays\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — VSMC-specific KO mouse model with pharmacological rescue (ER stress inhibitor), single lab\",\n      \"pmids\": [\"40440261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Nexilin binds directly to the C-terminal intracellular loop of GABAA receptor γ-subunits. This interaction regulates cell-surface expression of extrasynaptic γ2-containing GABAA receptors in hippocampal neurons; nexilin upregulation increases surface GABAA receptor numbers and synaptic currents, while the effect requires the actin-binding domain of nexilin (its deletion abolishes the effect). Nexilin also interacts with Rab7b and the lysosomal calcium channel TRPML1, and promotes calcium-dependent fission of late endosomes/lysosomes required for retrograde transport.\",\n      \"method\": \"Pulldown, array-based peptide mapping, deep-mutational scanning, siRNA knockdown and overexpression in hippocampal neurons, electrophysiology (GABA-mediated currents), surface GABAA receptor quantification, actin-binding domain deletion mutant\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding mapping (array + deep-mutational scan) + domain deletion + functional electrophysiology, single lab\",\n      \"pmids\": [\"40812511\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Nexilin regulates late endosome/lysosome (LE/Lys) fission and retrograde transport. Depletion of nexilin causes LE/Lys enlargement due to inhibited fission. Nexilin interacts with the small GTPase Rab7b and the lysosomal calcium channel TRPML1; TRPML1 activation rescues LE/Lys enlargement caused by nexilin depletion, indicating nexilin mediates the interaction between LE/Lys and the acto-myosin cytoskeleton for calcium-dependent organelle fission.\",\n      \"method\": \"siRNA screen, live imaging of LE/Lys size, Co-immunoprecipitation for Rab7b and TRPML1, TRPML1 agonist rescue experiment, retrograde transport assay\",\n      \"journal\": \"Cell communication and signaling : CCS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA screen + Co-IP + pharmacological rescue, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"41514273\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Nexilin is required for efficient Listeria monocytogenes invasion; siRNA-mediated nexilin knockdown significantly reduces intracellular bacterial levels. Nexilin is a component of L. monocytogenes actin comet tails and EPEC pedestals, accumulating at the distal portion of motile bacterial actin structures. Nexilin knockdown impairs comet tail formation (malformed comet tails) but is dispensable for EPEC pedestal generation.\",\n      \"method\": \"siRNA knockdown, immunofluorescence colocalization, bacterial invasion assay (intracellular bacteria quantification), comet tail morphology analysis\",\n      \"journal\": \"Cellular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA functional knockdown with specific phenotypic readout (bacterial invasion + comet tail formation), single lab, two orthogonal assays\",\n      \"pmids\": [\"22381134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NEXN overexpression in hepatocellular carcinoma cells reduces β-catenin nuclear accumulation and inhibits EMT. NEXN binds to MYOCD, and together they co-regulate EMT via the WNT/β-catenin signaling pathway. Diminished NEXN expression leads to β-catenin nuclear accumulation and enhanced EMT-driven metastasis.\",\n      \"method\": \"Overexpression in HCC cell lines, β-catenin nuclear localization assay, Co-immunoprecipitation for NEXN-MYOCD interaction, in vivo tumor formation, EMT marker Western blot\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP and overexpression with mechanistic follow-up, single lab, no reconstitution or mutagenesis\",\n      \"pmids\": [\"41399508\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"AAV-mediated systemic delivery of Nexn restores cardiac function and extends lifespan in both global Nexn knockout mice and mice carrying the human equivalent G645del mutation, demonstrating that exogenous full-length nexilin can functionally rescue loss-of-function DCM and identifying functional components of nexilin sufficient for this rescue.\",\n      \"method\": \"AAV gene delivery (systemic intravenous injection), echocardiography, immunoblot, Nexn global KO and G645del knock-in mouse models\",\n      \"journal\": \"Genome biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo gene rescue in two independent mouse models with functional cardiac readout, single lab\",\n      \"pmids\": [\"38783323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NEXN homozygous knockout human iPSC-derived cardiomyocytes show disordered junctional membrane complexes, abnormal excitation-contraction coupling, increased oxidative stress, and decreased energy metabolism, confirming that nexilin is a structural component of junctional membrane complexes essential for excitation-contraction coupling.\",\n      \"method\": \"CRISPR/Cas9 knockout in hiPSCs, directed differentiation to cardiomyocytes, electron microscopy, calcium imaging, oxidative stress assays, metabolic assays\",\n      \"journal\": \"Stem cell research & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR KO in human iPSC-derived cardiomyocytes with multiple orthogonal functional readouts, single lab\",\n      \"pmids\": [\"40713745\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Novel nexilin splice variants exist in mouse and human tissues segregating into myocyte-specific and epithelial-specific isoforms. Heart-specific isoforms differ between atria and ventricles. Different isoforms exhibit distinct self-interaction properties in recombinant protein interaction studies, and critical exons in ABD1 and ABD2 differ between isoforms.\",\n      \"method\": \"RT-PCR, tissue expression analysis, recombinant protein interaction studies (pulldown), isoform mapping\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, recombinant protein pulldown without full reconstitution or in vivo functional validation of isoform-specific differences\",\n      \"pmids\": [\"39682766\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Nexilin (NEXN) is an F-actin-binding protein with multiple ABDs that localizes to sarcomeric Z-discs/dense bodies in striated and smooth muscle and to cell-matrix adherens junctions in non-muscle cells; it is an essential structural component of cardiac junctional membrane complexes required for T-tubule formation and maintenance, optimal calcium transients, and excitation-contraction coupling, while also functioning as a substrate of CLK4 kinase (whose phosphorylation of NEXN regulates cardiac hypertrophy), an inhibitor of TLR4 oligomerization and NF-κB signaling in endothelial cells, an interactor with SERCA2 that promotes its SUMOylation and stability to prevent vascular calcification, a regulator of VSMC phenotypic switching via RhoA/SRF and ER stress/KLF4 pathways, a regulator of IRS1 scaffold signaling in skeletal muscle, and a regulator of extrasynaptic GABAA receptor surface expression and late endosome/lysosome fission in neurons.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Nexilin (NEXN) is an F-actin-binding cytoskeletal protein that organizes contractile and adhesive actin structures and serves as an essential structural component of the cardiac sarcomere and dyad [#0, #1, #8]. It contains multiple actin-binding domains, cross-links F-actin, and localizes to cell-matrix adherens junctions in non-muscle cells and to the Z-disk—and the smooth-muscle equivalent dense bodies—in striated and smooth muscle [#0, #1, #7]. At the Z-disk, nexilin protects against mechanical strain, and its loss destabilizes Z-disk ultrastructure and causes heart failure, with disease-associated mutant alleles acting dominant-negatively and abolishing actin binding [#1, #3]. Nexilin is a component of junctional membrane complexes at cardiac dyads, where it interacts with junctional sarcoplasmic reticulum proteins and is required for both developmental formation and adult maintenance of the transverse-tubular system, optimal calcium transients, and excitation-contraction coupling; its loss in mice and human iPSC-derived cardiomyocytes produces dilated cardiomyopathy with disordered dyads, impaired calcium handling, and metabolic stress [#8, #10, #20]. Loss-of-function cardiomyopathy is rescuable by AAV-delivered full-length nexilin in knockout and human-equivalent G645del mutant mice, establishing NEXN as a causative dilated/hypertrophic cardiomyopathy gene [#19, #1]. NEXN activity is post-translationally tuned by CLK4, which directly phosphorylates it to restrain pathological cardiomyocyte hypertrophy [#11]. Beyond the heart, nexilin governs vascular smooth muscle phenotype—promoting the contractile state via RhoA/SRF and protecting against calcification through a SERCA2 interaction that enhances SERCA2 SUMOylation and stability [#12, #13]. Additional context-specific roles include scaffolding insulin/IRS1 signaling in skeletal myotubes [#4], inhibiting TLR4 oligomerization and NF-\\u03baB-driven endothelial inflammation [#9], and, in non-muscle cells, mediating actin-dependent organelle dynamics including late endosome/lysosome fission via Rab7b and TRPML1 and surface trafficking of \\u03b32-containing GABAA receptors in neurons [#15, #16].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Established the founding biochemical identity of nexilin as an F-actin-binding and cross-linking protein with distinct domain architectures and junctional localization, defining the molecular basis for all later cytoskeletal roles.\",\n      \"evidence\": \"Protein purification with in vitro F-actin binding/cross-linking assays and immunofluorescence in rat brain and fibroblasts\",\n      \"pmids\": [\"9832551\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No tissue-level or in vivo function established\", \"Physiological consequences of cross-linking activity unaddressed\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"First linked nexilin to cell behavior, showing its overexpression promotes migration and adhesion, extending its actin association to functional motility.\",\n      \"evidence\": \"Co-IP and stable overexpression with migration/adhesion assays in HeLa cells\",\n      \"pmids\": [\"15823560\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Overexpression-only; no loss-of-function\", \"Mechanism connecting actin binding to migration not defined\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identified nexilin as a Z-disk protein essential for sarcomere stability and protection against mechanical strain, and connected human NEXN mutations to cardiomyopathy via dominant-negative Z-disk damage.\",\n      \"evidence\": \"Zebrafish morpholino knockdown, mutant allele expression, Z-disk electron microscopy, human genetic association\",\n      \"pmids\": [\"19881492\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular partners at the Z-disk not defined\", \"Mechanism of strain protection unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Showed disease-associated NEXN missense mutations mechanistically impair F-actin/\\u03b1-actin binding and cause protein mislocalization, tying genotype to a defined biochemical defect.\",\n      \"evidence\": \"Transfection, immunofluorescence, Co-IP, F-actin binding assay in C2C12 cells\",\n      \"pmids\": [\"20970104\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab in vitro correlation\", \"In vivo consequence of each mutation not tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Revealed a metabolic scaffolding role in which nexilin binds IRS1 in an actin-dependent, insulin-regulated manner to restrain PI3K/AKT signaling and glucose uptake in muscle.\",\n      \"evidence\": \"Reciprocal Co-IP, siRNA/overexpression, PI3K and AKT readouts, glucose uptake in L6 myotubes\",\n      \"pmids\": [\"23383252\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab cell model only\", \"In vivo metabolic relevance untested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identified a developmental signaling role whereby NEXN negatively regulates GATA4 and cardiac differentiation, with disease mutations recapitulating GATA4 suppression.\",\n      \"evidence\": \"Knockdown/overexpression/rescue in P19cl6 cells and cardiac-selective transgenic mice\",\n      \"pmids\": [\"24866383\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of GATA4 suppression unknown\", \"Relationship to structural Z-disk role unclear\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined nexilin as a driver of smooth muscle phenotype, promoting the contractile state through RhoA-dependent SRF nuclear translocation.\",\n      \"evidence\": \"Lentiviral OE/siRNA in VSMCs with RhoA/SRF/SM\\u03b1-actin blots and Y-27632 inhibitor\",\n      \"pmids\": [\"26458985\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct RhoA regulatory mechanism not defined\", \"Single-lab pharmacological inference\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Demonstrated an essential in vivo cardiac requirement, with constitutive Nexn knockout producing early, rapidly progressive dilated cardiomyopathy.\",\n      \"evidence\": \"Constitutive KO mouse, echocardiography, histology, immunostaining\",\n      \"pmids\": [\"26659360\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell-autonomous vs developmental contribution not separated\", \"Molecular cause of DCM not yet mechanistic\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Placed NEXN within a transcriptional feedback circuit in smooth muscle, controlled by actin state and MRTF/YAP-TAZ coactivators and feeding back on actin polymerization.\",\n      \"evidence\": \"Immunoelectron microscopy, Latrunculin B, KD/OE, MRTF/YAP overexpression, promoter assay\",\n      \"pmids\": [\"30158653\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct promoter occupancy not shown\", \"In vivo SMC relevance untested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Resolved the dilated-cardiomyopathy mechanism by identifying NEXN as a junctional membrane complex component required for T-tubule formation, calcium transients, and excitation-contraction coupling.\",\n      \"evidence\": \"Global and cardiomyocyte-specific KO mice with EM, calcium imaging, RNA-seq, and interaction mass spectrometry\",\n      \"pmids\": [\"30982350\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific jSR-binding partners not individually validated\", \"How nexilin nucleates T-tubule invagination mechanistically unresolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Uncovered a vascular protective, anti-inflammatory function in which NEXN inhibits TLR4 oligomerization and NF-\\u03baB signaling downstream of lncRNA NEXN-AS1.\",\n      \"evidence\": \"KD/OE, TLR4 oligomerization assay, NF-\\u03baB reporter, monocyte adhesion, ApoE-KO mouse model\",\n      \"pmids\": [\"30589415\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct TLR4 binding not structurally defined\", \"Link to cytoskeletal function unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed NEXN is required not only for developmental T-tubule formation but for ongoing maintenance of tubular architecture in adult cardiomyocytes.\",\n      \"evidence\": \"Inducible adult cardiomyocyte-specific KO with quantitative T-tubule morphometry, calcium imaging, echocardiography\",\n      \"pmids\": [\"32635769\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Turnover mechanism of tubular maintenance unresolved\", \"Reversibility upon re-expression not tested here\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified CLK4 as the kinase that directly phosphorylates nexilin to restrain pathological hypertrophy, defining a post-translational control layer for NEXN.\",\n      \"evidence\": \"Kinase substrate assay, cardiomyocyte-specific Clk4 KO mice, phospho-mimic NEXN rescue, cardiomyocyte size measurements\",\n      \"pmids\": [\"35907876\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphosite-specific structural consequence not mapped\", \"Whether phosphorylation alters actin or dyad function unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated therapeutic sufficiency, with AAV-delivered full-length nexilin rescuing cardiac function and lifespan in KO and G645del mutant mice and defining minimal functional components.\",\n      \"evidence\": \"Systemic AAV gene delivery, echocardiography, immunoblot in two mouse models\",\n      \"pmids\": [\"38783323\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Durability and dosing not fully characterized\", \"Single-lab rescue\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Confirmed in a human system that NEXN is required for junctional membrane complex integrity and excitation-contraction coupling, linking its loss to oxidative and metabolic stress.\",\n      \"evidence\": \"CRISPR KO in human iPSC-derived cardiomyocytes with EM, calcium imaging, oxidative stress and metabolic assays\",\n      \"pmids\": [\"40713745\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab hiPSC model\", \"Causal order of metabolic vs structural defects unresolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Expanded NEXN's vascular role by showing it stabilizes SERCA2 via enhanced SUMOylation to prevent calcification, and that its deficiency drives VSMC phenotypic transition through ER stress/KLF4 signaling.\",\n      \"evidence\": \"VSMC-specific KO/OE mice, Co-IP, SUMOylation assay, lineage tracing, ER stress inhibitor rescue\",\n      \"pmids\": [\"40883305\", \"40440261\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct SERCA2 binding interface not mapped\", \"How NEXN promotes SUMOylation mechanistically unresolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended nexilin function to neuronal and organelle biology, mapping direct binding to GABAA receptor \\u03b3-subunits and to Rab7b/TRPML1 for actin-dependent surface receptor trafficking and late endosome/lysosome fission.\",\n      \"evidence\": \"Peptide array mapping, deep-mutational scanning, ABD-deletion mutants, electrophysiology, Co-IP, TRPML1 agonist rescue in neurons and cells\",\n      \"pmids\": [\"40812511\", \"41514273\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo neuronal relevance untested\", \"How actin binding couples to organelle fission not fully defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how nexilin's single actin-binding scaffold is repurposed across such divergent contexts (sarcomere/dyad, vascular SERCA2 stabilization, IRS1/TLR4 signaling, organelle fission) and whether tissue-specific isoforms partition these functions.\",\n      \"evidence\": \"No discovery in the corpus directly tests cross-tissue functional partitioning or isoform-specific in vivo roles\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Isoform-specific functions only mapped at recombinant/expression level [#21]\", \"No unifying structural mechanism linking actin binding to signaling roles\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 1, 3, 7]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4, 15]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [9, 11, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 1, 7]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [8, 10]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [15, 16]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [8, 14]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [1, 8, 10]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [9, 11, 12]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [5, 7]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [16]}\n    ],\n    \"complexes\": [\"cardiac junctional membrane complex (dyad)\", \"Z-disk\", \"smooth muscle dense bodies\"],\n    \"partners\": [\"IRS1\", \"SERCA2\", \"CLK4\", \"MYOCD\", \"TLR4\", \"Rab7b\", \"TRPML1\", \"GABRG2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}