{"gene":"PLN","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2014,"finding":"Phospholamban (PLN) inhibits SERCA2a, and integrin-linked kinase (ILK) mediates cardiomyocyte force transduction through regulation of SERCA2a and phosphorylation of PLN; a synthetic ILK point mutation (ILK R211A) enhances cardiac function through the SERCA2a/PLN module.","method":"Co-immunoprecipitation, Western blot for PLN phosphorylation, cardiac function assays in human DCM samples and mouse models","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal interaction shown in human heart tissue and functional rescue demonstrated, single lab with two orthogonal methods","pmids":["25208486"],"is_preprint":false},{"year":2008,"finding":"PLN interacts with HS-1-associated protein X-1 (HAX-1), an anti-apoptotic protein with similarities to Bcl-2, linking Ca2+ homeostasis regulated by the SERCA2a/PLN complex to cell survival pathways.","method":"Co-immunoprecipitation/pulldown identifying HAX-1 as a PLN-binding partner; functional characterization of HAX-1 anti-apoptotic role","journal":"Pflugers Archiv : European journal of physiology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — binding partner identification by pulldown, corroborated in subsequent papers, single lab","pmids":["18415121"],"is_preprint":false},{"year":2022,"finding":"The PLN R14del mutation causes enhanced binding to SERCA2a and HAX-1 compared to wild-type PLN, resulting in super-inhibition of SERCA2a Ca2+-affinity. Additionally, HRC binding to SERCA2a is increased, inhibiting SERCA2a maximal velocity. Unlike wild-type PLN, phosphorylation at Ser-16 does not occur in PLN-R14del and thus does not relieve SERCA2a inhibition.","method":"Co-immunoprecipitation of PLN-R14del with SERCA2a, HAX-1, and HRC; phosphorylation analysis by Western blot; in silico structural predictions","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP with multiple binding partners, phosphorylation assay, single lab with multiple orthogonal methods","pmids":["35805951"],"is_preprint":false},{"year":2021,"finding":"PLN R14del mutation causes impairment of the ER/mitochondria compartment in cardiomyocytes, manifesting as prolonged Ca2+ transient decay, lower force, fewer ER/ribosomal/mitochondrial proteins by proteomics, dilated ER, and perinuclear ER protein aggregates with oxidative stress. Ca2+-scavenging (GCaMP6f or parvalbumin) improved the disease phenotype, implicating impaired local Ca2+ cycling.","method":"hiPSC-CMs with CRISPR/Cas9 isogenic controls; Ca2+ transient recording; proteomics; electron microscopy; transduction with Ca2+-binding proteins","journal":"EMBO molecular medicine","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal methods (proteomics, EM, Ca2+ assays, genetic rescue) in isogenic iPSC-CM model with functional readouts","pmids":["33998164"],"is_preprint":false},{"year":2021,"finding":"PLN R14del cardiomyopathy activates the unfolded protein response (UPR); silencing each of the three UPR branches (IRE1, ATF6, or PERK) exacerbated contractile dysfunction in PLN R14del hiPSC-CMs, indicating a protective role for UPR. Activation of UPR with BiP inducer X ameliorated contractility deficit.","method":"Single-cell RNA sequencing of hiPSC-CMs; siRNA silencing of UPR branches; 2D and 3D contractility assays; validated in patient heart tissue","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 2 / Strong — isogenic hiPSC-CM pairs, scRNA-seq, siRNA loss-of-function, pharmacological gain-of-function, validated in human patient tissue","pmids":["33928785"],"is_preprint":false},{"year":2021,"finding":"PLN protein aggregation is among the earliest manifestations of PLN-R14del cardiomyopathy, appearing before onset of functional deficits at 3 weeks of age; altered protein homeostasis (proteostasis) pathways are activated exclusively in PLN-R14del mice even before disease onset.","method":"Echocardiography, ECG, histology, RNA sequencing and mass spectrometry at 3, 5, and 8 weeks in PLN-R14del mice","journal":"Circulation. Heart failure","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multi-omics in time-course mouse model with histological validation, single lab","pmids":["34587756"],"is_preprint":false},{"year":2023,"finding":"DWORF overexpression in PLN-R14del mice delayed the appearance and formation of large pathogenic perinuclear PLN clusters (identified as disorganized sarcoplasmic/endoplasmic reticulum, not amorphous aggregates) and extended lifespan >2-fold; DWORF did not further accelerate SR Ca2+ reuptake in R14del cardiomyocytes (already enhanced), indicating its benefit is through reducing SR malformation rather than Ca2+ handling.","method":"Transgenic mouse crosses, echocardiography, survival analysis, isolated cardiomyocyte Ca2+ measurements, immunofluorescence co-localization with SR markers, electron microscopy in human PLN-R14del heart tissue","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic rescue with multiple orthogonal methods, validated in human tissue, two mechanistic endpoints (Ca2+ and SR morphology)","pmids":["37955153"],"is_preprint":false},{"year":2013,"finding":"Hydrogen sulfide (H2S) causes S-sulfhydration of phospholamban in the rat heart, contributing to negative lusitropism (impaired relaxation); H2S effects involve the Akt/eNOS/cGMP/PKG pathway and KATP channels.","method":"Isolated perfused working and Langendorff rat hearts; Western blot; modified biotin switch (S-sulfhydration) assay","journal":"American journal of physiology. Regulatory, integrative and comparative physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical S-sulfhydration assay with functional cardiac readout, single lab","pmids":["23785074"],"is_preprint":false},{"year":2003,"finding":"Acylphosphatase displaces PLN from its interaction with SERCA2a: co-immunoprecipitation experiments showed that adding recombinant acylphosphatase to solubilized heart SR vesicles reduced the amount of PLN co-precipitated with SERCA2a in proportion to acylphosphatase concentration, suggesting competitive displacement of PLN.","method":"Co-immunoprecipitation of SERCA2a, PLN, and recombinant acylphosphatase from heart SR vesicles with anti-SERCA2a, anti-PLN, and anti-acylphosphatase antibodies","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — reciprocal Co-IP with three antibodies and quantitative displacement, single lab","pmids":["12589804"],"is_preprint":false},{"year":2016,"finding":"TSH inhibits SERCA2a activity and expression in cardiomyocytes by binding to TSH receptors and inhibiting the PKA/PLN signaling pathway, leading to impaired Ca2+ handling and cardiac dysfunction.","method":"Neonatal rat cardiomyocytes treated with TSH; SERCA2a activity assay; Western blot for PLN phosphorylation","journal":"Oncotarget","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single method set, indirect pathway placement without direct PLN phosphorylation rescue experiment","pmids":["27206677"],"is_preprint":false},{"year":2016,"finding":"Urotensin II induces cardiomyocyte hypertrophy through CaMKII-mediated phosphorylation of PLN at Thr17, which upregulates SERCA2a levels; inhibition of CaMKII with KN-93 reversed PLN Thr17 phosphorylation and hypertrophic responses.","method":"Primary neonatal rat cardiomyocytes; Western blot for phospho-CaMKII, phospho-PLN (Thr17), SERCA2a; CaMKII inhibitor KN-93; cell size and Ca2+ measurements","journal":"Gene","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, pharmacological inhibition only without genetic validation of PLN as causal node","pmids":["26930364"],"is_preprint":false},{"year":2022,"finding":"AKAP5 co-localizes and physically interacts with PLN and PKA, anchoring PKA to mediate PLN/SERCA2a signaling; AKAP5 overexpression reduced hypoxia/reoxygenation-induced cardiomyocyte apoptosis via activation of PLN/SERCA2a pathway, and this effect was blocked by the AKAP-disrupting peptide St-Ht31.","method":"Immunofluorescence co-localization; co-immunoprecipitation; flow cytometry apoptosis assay; Western blot for phospho-PLN and SERCA2a in H9C2 cells","journal":"Biochemistry and cell biology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, Co-IP with functional rescue, but pathway placement relies on inhibitory peptide only","pmids":["35041539"],"is_preprint":false},{"year":2006,"finding":"The PLN -42 C>G promoter mutation decreased phospholamban promoter activity by 43–47% in reporter assays, and is associated with reduced PLN expression in apical hypertrophic cardiomyopathy.","method":"Luciferase reporter plasmid transient transfection assay in C6 and C2C12 cell lines","journal":"European journal of heart failure","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct promoter activity measurement with quantitative readout in two cell lines, single lab","pmids":["16829191"],"is_preprint":false},{"year":2018,"finding":"A homozygous nonsense PLN variant (p.Glu2Ter) significantly reduced phospholamban protein expression by Western blot, causing severe dilated cardiomyopathy in autosomal recessive inheritance; heterozygous carriers had normal cardiac function, indicating haploinsufficiency is insufficient for disease in this pedigree.","method":"Western blot showing reduced PLN expression; next-generation sequencing and Sanger sequencing; pedigree analysis","journal":"International journal of cardiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct protein expression assay, pedigree segregation with two orthogonal methods, single lab","pmids":["30638982"],"is_preprint":false},{"year":2022,"finding":"AAV9-CRISPR/Cas9-mediated disruption of the hPLN-R14del allele in humanized mice improved cardiac function (reduced end-diastolic and stroke volumes) and reduced susceptibility to ventricular tachycardia, demonstrating that the R14del allele is causally responsible for the arrhythmogenic phenotype.","method":"In vivo AAV9-CRISPR/Cas9 gene editing; cardiac MRI; ex vivo electrophysiology with isoproterenol/rapid pacing; droplet digital PCR and NGS amplicon sequencing","journal":"Cardiovascular research","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic allele-specific disruption with multiple cardiac functional readouts and molecular confirmation","pmids":["35191471"],"is_preprint":false},{"year":2025,"finding":"FIR irradiation activates SERCA2 in vascular smooth muscle cells by promoting dissociation of PLN from SERCA2, leading to increased Ca2+ reuptake into the SER, reduced cytosolic Ca2+, and decreased MLC phosphorylation and vascular contraction.","method":"Co-immunoprecipitation of SERCA2 and PLN before/after FIR treatment; SERCA2 knockdown; thapsigargin inhibition; Ca2+ flux measurement; MLC phosphorylation Western blot; isolated rat aorta contraction assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP showing dissociation, genetic knockdown confirmation, functional vascular assay, single lab","pmids":["41406161"],"is_preprint":false},{"year":2024,"finding":"PLN R14del mutation causes loss (not gain) of SERCA2a inhibition, resulting in hyperdynamic Ca2+ handling consistent with PLN incompetence rather than SERCA2a super-inhibition; energy metabolism is depressed and its dependency on Ca2+ is enhanced, pointing to metabolic stress as an early pathogenetic mechanism.","method":"Ca2+ dynamics, O2 consumption, energy metabolism measurements in ventricular myocytes from transgenic mice at 8-12 weeks; pharmacological SERCA2a blockade and PLN antagonism comparisons; transcript and protein analysis","journal":"Acta physiologica (Oxford, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional assays in transgenic mouse model, mechanistic comparison with pharmacological controls, single lab","pmids":["38214033"],"is_preprint":false},{"year":2021,"finding":"PLN p.Arg14del mutation leads to loss of perinuclear SERCA2a-PLN co-localization in hiPSC-CMs and results in Ca2+ dynamics compatible with SERCA2a incompetence (not super-inhibition), with faster Ca2+ transient decay and rate-independent time-to-peak; SERCA2a activator PST3093 had minimal effect on mutant cells.","method":"Ca2+ transient recording at 36°C in field-stimulated hiPSC-CM clusters; immunolabeling of SERCA2a and PLN; isogenic WT/MUT comparison; pharmacological SERCA2a activator treatment","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — isogenic hiPSC-CM pairs, multiple Ca2+ handling parameters, pharmacological probe, single lab","pmids":["34948294"],"is_preprint":false},{"year":2025,"finding":"PLN R14del cardiomyopathy is associated with higher ER calcium loading in hiPSC-CMs compared to isogenic controls, as measured by AAV6-encoded ER calcium sensor CEPIAer, suggesting altered ER Ca2+ loading as a disease mechanism distinct from cytosolic Ca2+ dysregulation.","method":"AAV6-CEPIAer (ER calcium sensor) in engineered heart tissues and FACS of dissociated cardiomyocytes from isogenic hiPSC-CM lines","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct ER Ca2+ measurement with genetically encoded sensor in isogenic hiPSC-CM model, single lab","pmids":["40791987"],"is_preprint":false},{"year":2026,"finding":"AAV delivery of PLN-L31A/I40A (a PLN variant that blocks PLN-R14del interaction with SERCA2a without blocking SERCA2a function) rescued ventricular dilation, cardiac fibrosis, PLN aggregation, and premature death in PLN-R14del mice and improved cardiomyocyte function in human hESC-derived cardiomyocytes, demonstrating that aberrant PLN-R14del/SERCA2a interaction is a pathogenic mechanism.","method":"CRISPR-Cas9 generated PLN-R14del mouse model and hESC lines; AAV-mediated PLN-L31A/I40A delivery; echocardiography; histology; Ca2+ and contractile function assays in human cardiomyocytes","journal":"Acta pharmacologica Sinica","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — genetic rescue with mechanistically targeted PLN variant in both mouse model and human cardiomyocytes with multiple functional endpoints","pmids":["41545752"],"is_preprint":false},{"year":2024,"finding":"PLN R9C mutation causes mild hyperdynamic Ca2+ cycling and increased contractility at baseline; under functional stress (maturation medium), PLN R9C iPSC-CMs exhibit sarcomere disarrangement, Ca2+ handling deficiency, disrupted adrenergic signaling, elevated ROS, interrupted autophagic flux, and increased pentamer PLN aggregation. Autophagy activation with metformin or rapamycin restored autophagic flux, mitigated sarcomere disarrangement, and partially rescued β-adrenergic signaling.","method":"PLN R9C knock-in and patient-specific iPSC-CMs; transcriptomic analysis; Ca2+ imaging; contractility assays; ROS measurement; autophagy flux assay; pharmacological rescue with metformin/rapamycin","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — isogenic KI and patient iPSC-CM models, multiple orthogonal methods, pharmacological rescue; preprint","pmids":["38659742"],"is_preprint":true},{"year":2025,"finding":"PKGIα-dependent phosphorylation of PLN promotes cardiac relaxation; urolithin A activates PKGIα via C42 oxidation, leading to PLN phosphorylation in isolated cardiomyocytes and reversal of diastolic dysfunction in a HFpEF mouse model.","method":"Recombinant PKGIα activation assay; Western blot for phospho-PLN in NRVMs; C42S PKGIα knock-in mice; echocardiography; human engineered heart tissue contractility","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro kinase assay, genetic KI mouse model, and human EHT validation, single lab; preprint","pmids":[],"is_preprint":true}],"current_model":"Phospholamban (PLN) is a small regulatory peptide that tonically inhibits the sarcoplasmic reticulum Ca2+-ATPase SERCA2a, thereby controlling Ca2+ re-uptake and cardiac contractility/relaxation; this inhibition is relieved by PKA-mediated Ser-16 phosphorylation or CaMKII-mediated Thr-17 phosphorylation. PLN also interacts with HAX-1 linking Ca2+ homeostasis to cell survival, and with AKAP5/PKA complexes. The pathogenic R14del variant causes perinuclear PLN aggregation, disorganized sarcoplasmic/endoplasmic reticulum, impaired PLN phosphorylation at Ser-16, and aberrantly enhanced binding to SERCA2a and HAX-1 (super-inhibition) or alternatively a loss of SERCA2a inhibitory competence depending on context, with secondary activation of the unfolded protein response as a protective mechanism, collectively driving dilated/arrhythmogenic cardiomyopathy."},"narrative":{"mechanistic_narrative":"Phospholamban (PLN) is a small sarcoplasmic reticulum (SR) regulatory protein that tonically inhibits the Ca2+-ATPase SERCA2a, thereby setting the rate of SR Ca2+ re-uptake and cardiac relaxation [PMID:25208486, PMID:12589804]. This inhibition is dynamically relieved through multiple post-translational and signaling inputs: PKA-anchored phosphorylation organized by AKAP5 [PMID:35041539], CaMKII-mediated Thr-17 phosphorylation downstream of hypertrophic stimuli [PMID:26930364], PKGIα-dependent phosphorylation promoting relaxation, and direct S-sulfhydration by H2S that modulates lusitropy [PMID:23785074]. PLN inhibition of SERCA2a can also be relieved by physical displacement, as shown by acylphosphatase, which competitively reduces PLN co-precipitation with SERCA2a [PMID:12589804], and by FIR-induced dissociation of PLN from SERCA2 in vascular smooth muscle [PMID:41406161]. Beyond SERCA2a, PLN binds the anti-apoptotic protein HAX-1, coupling SR Ca2+ handling to cell-survival pathways [PMID:18415121]. PLN expression and dosage are themselves disease-relevant: a promoter mutation lowering PLN expression associates with apical hypertrophic cardiomyopathy [PMID:16829191], and a homozygous null variant abolishing PLN protein causes severe recessive dilated cardiomyopathy [PMID:30638982]. The R14del variant is a central pathogenic allele: it impairs Ser-16 phosphorylation and alters SERCA2a/HAX-1 binding [PMID:35805951], drives early perinuclear PLN aggregation within disorganized SR before functional deficits appear [PMID:34587756, PMID:37955153], impairs the ER/mitochondria compartment with prolonged Ca2+ decay and oxidative stress [PMID:33998164], and activates a protective unfolded protein response [PMID:33928785]. Allele-specific CRISPR disruption and delivery of an interaction-blocking PLN variant (L31A/I40A) each rescue the R14del phenotype, establishing that the aberrant R14del/SERCA2a interaction is causally pathogenic [PMID:35191471, PMID:41545752].","teleology":[{"year":2003,"claim":"Established that PLN inhibition of SERCA2a is reversible by physical displacement, not solely by phosphorylation, defining a competitive-occupancy model of regulation.","evidence":"Reciprocal Co-IP of SERCA2a, PLN, and recombinant acylphosphatase from heart SR vesicles with quantitative displacement","pmids":["12589804"],"confidence":"Medium","gaps":["Physiological relevance of acylphosphatase as an endogenous displacer in vivo not established","Structural basis of displacement not resolved"]},{"year":2006,"claim":"Showed that PLN expression level itself is disease-relevant, as a promoter mutation reducing transcription associates with hypertrophic cardiomyopathy.","evidence":"Luciferase reporter assays of the -42 C>G promoter variant in C6 and C2C12 cells","pmids":["16829191"],"confidence":"Medium","gaps":["Causality in patients shown by association, not genetic rescue","Mechanism linking reduced PLN to apical hypertrophy not defined"]},{"year":2008,"claim":"Extended PLN function beyond Ca2+ handling by identifying HAX-1 as a binding partner, linking the SERCA2a/PLN complex to anti-apoptotic survival signaling.","evidence":"Co-immunoprecipitation/pulldown identifying HAX-1 and functional characterization of its anti-apoptotic role","pmids":["18415121"],"confidence":"Medium","gaps":["Single lab identification","Functional consequence of PLN-HAX-1 binding for cell survival not directly dissected"]},{"year":2013,"claim":"Identified S-sulfhydration as a novel post-translational modification of PLN contributing to impaired relaxation, broadening the regulatory inputs onto PLN.","evidence":"Modified biotin-switch assay and functional measurement in isolated perfused rat hearts","pmids":["23785074"],"confidence":"Medium","gaps":["Sulfhydration site not mapped","Interplay with phosphorylation not addressed"]},{"year":2014,"claim":"Placed PLN in a force-transduction signaling module by showing ILK regulates SERCA2a and PLN phosphorylation, connecting mechanical signaling to Ca2+ handling.","evidence":"Co-IP, phospho-PLN Western blot, and cardiac function assays in human DCM tissue and mouse models with an ILK R211A gain-of-function mutant","pmids":["25208486"],"confidence":"Medium","gaps":["Whether ILK acts directly or via an intermediary kinase on PLN unclear","Single lab"]},{"year":2016,"claim":"Linked upstream hormonal and hypertrophic signaling to PLN, with TSH suppressing the PKA/PLN pathway and urotensin II driving CaMKII-mediated Thr17 phosphorylation.","evidence":"Neonatal rat cardiomyocyte treatments with SERCA2a activity, phospho-PLN Western blots, and CaMKII inhibition (KN-93)","pmids":["27206677","26930364"],"confidence":"Low","gaps":["Indirect pathway placement without genetic validation of PLN as the causal node","Pharmacological inhibition only"]},{"year":2018,"claim":"Demonstrated that complete loss of PLN protein causes severe recessive dilated cardiomyopathy, with heterozygotes unaffected, establishing the consequences of PLN dosage in humans.","evidence":"Western blot of reduced PLN expression and pedigree segregation of a homozygous p.Glu2Ter variant","pmids":["30638982"],"confidence":"Medium","gaps":["Mechanism downstream of PLN loss not dissected","Single pedigree"]},{"year":2021,"claim":"Characterized the cellular pathology of R14del, showing it is initiated by PLN aggregation within disorganized SR and ER/mitochondrial impairment, and that the cell mounts a protective unfolded protein response.","evidence":"Isogenic hiPSC-CMs and time-course R14del mice with proteomics, EM, Ca2+ recording, scRNA-seq, siRNA UPR-branch silencing, and Ca2+-scavenger rescue","pmids":["33998164","33928785","34587756"],"confidence":"High","gaps":["Molecular trigger initiating PLN aggregation not defined","Whether aggregation or Ca2+ defect is the primary insult unresolved"]},{"year":2021,"claim":"Surfaced a key controversy by showing R14del produces SERCA2a incompetence (hyperdynamic Ca2+) rather than super-inhibition, contradicting models of enhanced inhibitory binding.","evidence":"Ca2+ transient recording and SERCA2a/PLN immunolabeling in isogenic hiPSC-CMs with a SERCA2a activator probe","pmids":["34948294"],"confidence":"Medium","gaps":["Discrepancy with super-inhibition models not reconciled","Loss of perinuclear co-localization mechanism unexplained"]},{"year":2022,"claim":"Provided the contrasting biochemical model that R14del enhances binding to SERCA2a, HAX-1, and HRC to super-inhibit Ca2+ affinity while resisting Ser-16 phosphorylation rescue.","evidence":"Co-IP of PLN-R14del with SERCA2a/HAX-1/HRC, phosphorylation Western blots, and in silico structural prediction","pmids":["35805951"],"confidence":"Medium","gaps":["Directly conflicts with the incompetence model from the same year","In silico structural claims not experimentally validated"]},{"year":2022,"claim":"Established causality of the R14del allele in vivo by showing allele-specific disruption rescues cardiac function and arrhythmia susceptibility.","evidence":"AAV9-CRISPR/Cas9 allele disruption in humanized mice with cardiac MRI, ex vivo electrophysiology, and amplicon sequencing","pmids":["35191471"],"confidence":"High","gaps":["Does not resolve which downstream defect (aggregation vs Ca2+) is rescued","Editing efficiency requirements for clinical translation unknown"]},{"year":2022,"claim":"Defined AKAP5 as the scaffold anchoring PKA to PLN/SERCA2a, organizing the phosphorylation that relieves inhibition and protects against apoptosis.","evidence":"Co-localization, Co-IP, and apoptosis rescue in H9C2 cells with the AKAP-disrupting peptide St-Ht31","pmids":["35041539"],"confidence":"Low","gaps":["Pathway placement relies on inhibitory peptide only","Direct AKAP5-PLN contact versus PKA-bridged interaction not distinguished"]},{"year":2023,"claim":"Identified the perinuclear PLN clusters as disorganized SR and showed DWORF overexpression reduces SR malformation and extends lifespan independent of Ca2+ handling, separating the morphological from the Ca2+ defect.","evidence":"Transgenic mouse crosses with survival analysis, Ca2+ measurements, SR-marker co-localization, and EM in human R14del tissue","pmids":["37955153"],"confidence":"High","gaps":["Mechanism by which DWORF prevents SR malformation unclear","Whether SR disorganization is reversible after onset unknown"]},{"year":2024,"claim":"Reinforced the incompetence model in transgenic mice and linked R14del to depressed, Ca2+-dependent energy metabolism, implicating metabolic stress as an early mechanism.","evidence":"Ca2+ dynamics, O2 consumption, and metabolism assays in ventricular myocytes with pharmacological SERCA2a/PLN comparisons","pmids":["38214033"],"confidence":"Medium","gaps":["Conflict with super-inhibition biochemistry unresolved","Causal link between metabolic stress and contractile failure not established"]},{"year":2024,"claim":"Extended PLN missense pathology beyond R14del, showing R9C drives stress-dependent sarcomere and autophagy defects with pentamer aggregation that autophagy activation can mitigate.","evidence":"R9C knock-in and patient iPSC-CMs with transcriptomics, Ca2+ imaging, autophagy flux assays, and metformin/rapamycin rescue (preprint)","pmids":["38659742"],"confidence":"Medium","gaps":["Preprint, not peer-reviewed","Generalizability of autophagy rescue to other PLN variants untested"]},{"year":2025,"claim":"Refined R14del Ca2+ pathology by showing elevated ER Ca2+ loading as a compartment-specific defect, and demonstrated PLN-SERCA2 dissociation drives Ca2+ reuptake in vascular smooth muscle, generalizing the regulatory paradigm.","evidence":"AAV6-CEPIAer ER Ca2+ sensing in isogenic hiPSC-CMs; Co-IP of FIR-induced PLN/SERCA2 dissociation with knockdown and aortic contraction assays","pmids":["40791987","41406161"],"confidence":"Medium","gaps":["Relationship between elevated ER load and cytosolic incompetence not integrated","FIR mechanism of dissociation at molecular level undefined"]},{"year":2026,"claim":"Provided proof-of-concept therapy by showing an interaction-blocking PLN variant (L31A/I40A) rescues R14del pathology in mice and human cardiomyocytes, establishing the aberrant R14del/SERCA2a interaction as a tractable target.","evidence":"AAV-delivered PLN-L31A/I40A in CRISPR R14del mice and hESC-CMs with echocardiography, histology, and contractile assays","pmids":["41545752"],"confidence":"High","gaps":["Does not reconcile super-inhibition versus incompetence models","Long-term durability and dosing not addressed"]},{"year":null,"claim":"It remains unresolved whether PLN-R14del acts primarily through SERCA2a super-inhibition or loss of inhibitory competence, and how SR disorganization, ER Ca2+ overload, metabolic stress, and protein aggregation are causally ordered.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Conflicting biochemical and functional models from comparable systems","No structural model of the R14del/SERCA2a/HAX-1 assembly","Primary initiating lesion versus secondary adaptations not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,8,16]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[0,8,15]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[3,18]}],"pathway":[],"complexes":["SERCA2a-PLN complex"],"partners":["ATP2A2","HAX1","AKAP5","PRKACA","ILK","HRC"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P26678","full_name":"Phospholamban","aliases":[],"length_aa":52,"mass_kda":6.1,"function":"Reversibly inhibits the activity of ATP2A2/SERCA2 in cardiac sarcoplasmic reticulum by decreasing the apparent affinity of the ATPase for Ca(2+) (PubMed:28890335). Binds preferentially to the ATP-bound E1 conformational form of ATP2A2 which predominates at low Ca(2+) concentrations during the diastolic phase of the cardiac cycle (By similarity). Inhibits ATP2A2 Ca(2+) affinity by disrupting its allosteric activation by ATP (By similarity). Modulates the contractility of the heart muscle in response to physiological stimuli via its effects on ATP2A2. Modulates calcium re-uptake during muscle relaxation and plays an important role in calcium homeostasis in the heart muscle. The degree of ATP2A2 inhibition depends on the oligomeric state of PLN. ATP2A2 inhibition is alleviated by PLN phosphorylation (By similarity). Also inhibits the activity of ATP2A3/SERCA3 (By similarity). Controls intracellular Ca(2+) levels in elongated spermatids and may play a role in germ cell differentiation (By similarity). In the thalamic reticular nucleus of the brain, plays a role in the regulation of sleep patterns and executive functioning (By similarity)","subcellular_location":"Endoplasmic reticulum membrane; Sarcoplasmic reticulum membrane; Mitochondrion membrane; Membrane","url":"https://www.uniprot.org/uniprotkb/P26678/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PLN","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1089,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PLN","total_profiled":1310},"omim":[{"mim_id":"620531","title":"SMALL INTEGRAL MEMBRANE PROTEIN 6; SMIM6","url":"https://www.omim.org/entry/620531"},{"mim_id":"620530","title":"ALLREGULIN; ARLN","url":"https://www.omim.org/entry/620530"},{"mim_id":"616891","title":"SMALL 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a synthetic ILK point mutation (ILK R211A) enhances cardiac function through the SERCA2a/PLN module.\",\n      \"method\": \"Co-immunoprecipitation, Western blot for PLN phosphorylation, cardiac function assays in human DCM samples and mouse models\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal interaction shown in human heart tissue and functional rescue demonstrated, single lab with two orthogonal methods\",\n      \"pmids\": [\"25208486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PLN interacts with HS-1-associated protein X-1 (HAX-1), an anti-apoptotic protein with similarities to Bcl-2, linking Ca2+ homeostasis regulated by the SERCA2a/PLN complex to cell survival pathways.\",\n      \"method\": \"Co-immunoprecipitation/pulldown identifying HAX-1 as a PLN-binding partner; functional characterization of HAX-1 anti-apoptotic role\",\n      \"journal\": \"Pflugers Archiv : European journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — binding partner identification by pulldown, corroborated in subsequent papers, single lab\",\n      \"pmids\": [\"18415121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The PLN R14del mutation causes enhanced binding to SERCA2a and HAX-1 compared to wild-type PLN, resulting in super-inhibition of SERCA2a Ca2+-affinity. Additionally, HRC binding to SERCA2a is increased, inhibiting SERCA2a maximal velocity. Unlike wild-type PLN, phosphorylation at Ser-16 does not occur in PLN-R14del and thus does not relieve SERCA2a inhibition.\",\n      \"method\": \"Co-immunoprecipitation of PLN-R14del with SERCA2a, HAX-1, and HRC; phosphorylation analysis by Western blot; in silico structural predictions\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP with multiple binding partners, phosphorylation assay, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"35805951\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PLN R14del mutation causes impairment of the ER/mitochondria compartment in cardiomyocytes, manifesting as prolonged Ca2+ transient decay, lower force, fewer ER/ribosomal/mitochondrial proteins by proteomics, dilated ER, and perinuclear ER protein aggregates with oxidative stress. Ca2+-scavenging (GCaMP6f or parvalbumin) improved the disease phenotype, implicating impaired local Ca2+ cycling.\",\n      \"method\": \"hiPSC-CMs with CRISPR/Cas9 isogenic controls; Ca2+ transient recording; proteomics; electron microscopy; transduction with Ca2+-binding proteins\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal methods (proteomics, EM, Ca2+ assays, genetic rescue) in isogenic iPSC-CM model with functional readouts\",\n      \"pmids\": [\"33998164\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PLN R14del cardiomyopathy activates the unfolded protein response (UPR); silencing each of the three UPR branches (IRE1, ATF6, or PERK) exacerbated contractile dysfunction in PLN R14del hiPSC-CMs, indicating a protective role for UPR. Activation of UPR with BiP inducer X ameliorated contractility deficit.\",\n      \"method\": \"Single-cell RNA sequencing of hiPSC-CMs; siRNA silencing of UPR branches; 2D and 3D contractility assays; validated in patient heart tissue\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — isogenic hiPSC-CM pairs, scRNA-seq, siRNA loss-of-function, pharmacological gain-of-function, validated in human patient tissue\",\n      \"pmids\": [\"33928785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PLN protein aggregation is among the earliest manifestations of PLN-R14del cardiomyopathy, appearing before onset of functional deficits at 3 weeks of age; altered protein homeostasis (proteostasis) pathways are activated exclusively in PLN-R14del mice even before disease onset.\",\n      \"method\": \"Echocardiography, ECG, histology, RNA sequencing and mass spectrometry at 3, 5, and 8 weeks in PLN-R14del mice\",\n      \"journal\": \"Circulation. Heart failure\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multi-omics in time-course mouse model with histological validation, single lab\",\n      \"pmids\": [\"34587756\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"DWORF overexpression in PLN-R14del mice delayed the appearance and formation of large pathogenic perinuclear PLN clusters (identified as disorganized sarcoplasmic/endoplasmic reticulum, not amorphous aggregates) and extended lifespan >2-fold; DWORF did not further accelerate SR Ca2+ reuptake in R14del cardiomyocytes (already enhanced), indicating its benefit is through reducing SR malformation rather than Ca2+ handling.\",\n      \"method\": \"Transgenic mouse crosses, echocardiography, survival analysis, isolated cardiomyocyte Ca2+ measurements, immunofluorescence co-localization with SR markers, electron microscopy in human PLN-R14del heart tissue\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic rescue with multiple orthogonal methods, validated in human tissue, two mechanistic endpoints (Ca2+ and SR morphology)\",\n      \"pmids\": [\"37955153\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Hydrogen sulfide (H2S) causes S-sulfhydration of phospholamban in the rat heart, contributing to negative lusitropism (impaired relaxation); H2S effects involve the Akt/eNOS/cGMP/PKG pathway and KATP channels.\",\n      \"method\": \"Isolated perfused working and Langendorff rat hearts; Western blot; modified biotin switch (S-sulfhydration) assay\",\n      \"journal\": \"American journal of physiology. Regulatory, integrative and comparative physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical S-sulfhydration assay with functional cardiac readout, single lab\",\n      \"pmids\": [\"23785074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Acylphosphatase displaces PLN from its interaction with SERCA2a: co-immunoprecipitation experiments showed that adding recombinant acylphosphatase to solubilized heart SR vesicles reduced the amount of PLN co-precipitated with SERCA2a in proportion to acylphosphatase concentration, suggesting competitive displacement of PLN.\",\n      \"method\": \"Co-immunoprecipitation of SERCA2a, PLN, and recombinant acylphosphatase from heart SR vesicles with anti-SERCA2a, anti-PLN, and anti-acylphosphatase antibodies\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — reciprocal Co-IP with three antibodies and quantitative displacement, single lab\",\n      \"pmids\": [\"12589804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"TSH inhibits SERCA2a activity and expression in cardiomyocytes by binding to TSH receptors and inhibiting the PKA/PLN signaling pathway, leading to impaired Ca2+ handling and cardiac dysfunction.\",\n      \"method\": \"Neonatal rat cardiomyocytes treated with TSH; SERCA2a activity assay; Western blot for PLN phosphorylation\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single method set, indirect pathway placement without direct PLN phosphorylation rescue experiment\",\n      \"pmids\": [\"27206677\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Urotensin II induces cardiomyocyte hypertrophy through CaMKII-mediated phosphorylation of PLN at Thr17, which upregulates SERCA2a levels; inhibition of CaMKII with KN-93 reversed PLN Thr17 phosphorylation and hypertrophic responses.\",\n      \"method\": \"Primary neonatal rat cardiomyocytes; Western blot for phospho-CaMKII, phospho-PLN (Thr17), SERCA2a; CaMKII inhibitor KN-93; cell size and Ca2+ measurements\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, pharmacological inhibition only without genetic validation of PLN as causal node\",\n      \"pmids\": [\"26930364\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"AKAP5 co-localizes and physically interacts with PLN and PKA, anchoring PKA to mediate PLN/SERCA2a signaling; AKAP5 overexpression reduced hypoxia/reoxygenation-induced cardiomyocyte apoptosis via activation of PLN/SERCA2a pathway, and this effect was blocked by the AKAP-disrupting peptide St-Ht31.\",\n      \"method\": \"Immunofluorescence co-localization; co-immunoprecipitation; flow cytometry apoptosis assay; Western blot for phospho-PLN and SERCA2a in H9C2 cells\",\n      \"journal\": \"Biochemistry and cell biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, Co-IP with functional rescue, but pathway placement relies on inhibitory peptide only\",\n      \"pmids\": [\"35041539\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The PLN -42 C>G promoter mutation decreased phospholamban promoter activity by 43–47% in reporter assays, and is associated with reduced PLN expression in apical hypertrophic cardiomyopathy.\",\n      \"method\": \"Luciferase reporter plasmid transient transfection assay in C6 and C2C12 cell lines\",\n      \"journal\": \"European journal of heart failure\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct promoter activity measurement with quantitative readout in two cell lines, single lab\",\n      \"pmids\": [\"16829191\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"A homozygous nonsense PLN variant (p.Glu2Ter) significantly reduced phospholamban protein expression by Western blot, causing severe dilated cardiomyopathy in autosomal recessive inheritance; heterozygous carriers had normal cardiac function, indicating haploinsufficiency is insufficient for disease in this pedigree.\",\n      \"method\": \"Western blot showing reduced PLN expression; next-generation sequencing and Sanger sequencing; pedigree analysis\",\n      \"journal\": \"International journal of cardiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct protein expression assay, pedigree segregation with two orthogonal methods, single lab\",\n      \"pmids\": [\"30638982\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"AAV9-CRISPR/Cas9-mediated disruption of the hPLN-R14del allele in humanized mice improved cardiac function (reduced end-diastolic and stroke volumes) and reduced susceptibility to ventricular tachycardia, demonstrating that the R14del allele is causally responsible for the arrhythmogenic phenotype.\",\n      \"method\": \"In vivo AAV9-CRISPR/Cas9 gene editing; cardiac MRI; ex vivo electrophysiology with isoproterenol/rapid pacing; droplet digital PCR and NGS amplicon sequencing\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic allele-specific disruption with multiple cardiac functional readouts and molecular confirmation\",\n      \"pmids\": [\"35191471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FIR irradiation activates SERCA2 in vascular smooth muscle cells by promoting dissociation of PLN from SERCA2, leading to increased Ca2+ reuptake into the SER, reduced cytosolic Ca2+, and decreased MLC phosphorylation and vascular contraction.\",\n      \"method\": \"Co-immunoprecipitation of SERCA2 and PLN before/after FIR treatment; SERCA2 knockdown; thapsigargin inhibition; Ca2+ flux measurement; MLC phosphorylation Western blot; isolated rat aorta contraction assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP showing dissociation, genetic knockdown confirmation, functional vascular assay, single lab\",\n      \"pmids\": [\"41406161\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PLN R14del mutation causes loss (not gain) of SERCA2a inhibition, resulting in hyperdynamic Ca2+ handling consistent with PLN incompetence rather than SERCA2a super-inhibition; energy metabolism is depressed and its dependency on Ca2+ is enhanced, pointing to metabolic stress as an early pathogenetic mechanism.\",\n      \"method\": \"Ca2+ dynamics, O2 consumption, energy metabolism measurements in ventricular myocytes from transgenic mice at 8-12 weeks; pharmacological SERCA2a blockade and PLN antagonism comparisons; transcript and protein analysis\",\n      \"journal\": \"Acta physiologica (Oxford, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional assays in transgenic mouse model, mechanistic comparison with pharmacological controls, single lab\",\n      \"pmids\": [\"38214033\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PLN p.Arg14del mutation leads to loss of perinuclear SERCA2a-PLN co-localization in hiPSC-CMs and results in Ca2+ dynamics compatible with SERCA2a incompetence (not super-inhibition), with faster Ca2+ transient decay and rate-independent time-to-peak; SERCA2a activator PST3093 had minimal effect on mutant cells.\",\n      \"method\": \"Ca2+ transient recording at 36°C in field-stimulated hiPSC-CM clusters; immunolabeling of SERCA2a and PLN; isogenic WT/MUT comparison; pharmacological SERCA2a activator treatment\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — isogenic hiPSC-CM pairs, multiple Ca2+ handling parameters, pharmacological probe, single lab\",\n      \"pmids\": [\"34948294\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PLN R14del cardiomyopathy is associated with higher ER calcium loading in hiPSC-CMs compared to isogenic controls, as measured by AAV6-encoded ER calcium sensor CEPIAer, suggesting altered ER Ca2+ loading as a disease mechanism distinct from cytosolic Ca2+ dysregulation.\",\n      \"method\": \"AAV6-CEPIAer (ER calcium sensor) in engineered heart tissues and FACS of dissociated cardiomyocytes from isogenic hiPSC-CM lines\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct ER Ca2+ measurement with genetically encoded sensor in isogenic hiPSC-CM model, single lab\",\n      \"pmids\": [\"40791987\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"AAV delivery of PLN-L31A/I40A (a PLN variant that blocks PLN-R14del interaction with SERCA2a without blocking SERCA2a function) rescued ventricular dilation, cardiac fibrosis, PLN aggregation, and premature death in PLN-R14del mice and improved cardiomyocyte function in human hESC-derived cardiomyocytes, demonstrating that aberrant PLN-R14del/SERCA2a interaction is a pathogenic mechanism.\",\n      \"method\": \"CRISPR-Cas9 generated PLN-R14del mouse model and hESC lines; AAV-mediated PLN-L31A/I40A delivery; echocardiography; histology; Ca2+ and contractile function assays in human cardiomyocytes\",\n      \"journal\": \"Acta pharmacologica Sinica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — genetic rescue with mechanistically targeted PLN variant in both mouse model and human cardiomyocytes with multiple functional endpoints\",\n      \"pmids\": [\"41545752\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PLN R9C mutation causes mild hyperdynamic Ca2+ cycling and increased contractility at baseline; under functional stress (maturation medium), PLN R9C iPSC-CMs exhibit sarcomere disarrangement, Ca2+ handling deficiency, disrupted adrenergic signaling, elevated ROS, interrupted autophagic flux, and increased pentamer PLN aggregation. Autophagy activation with metformin or rapamycin restored autophagic flux, mitigated sarcomere disarrangement, and partially rescued β-adrenergic signaling.\",\n      \"method\": \"PLN R9C knock-in and patient-specific iPSC-CMs; transcriptomic analysis; Ca2+ imaging; contractility assays; ROS measurement; autophagy flux assay; pharmacological rescue with metformin/rapamycin\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — isogenic KI and patient iPSC-CM models, multiple orthogonal methods, pharmacological rescue; preprint\",\n      \"pmids\": [\"38659742\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PKGIα-dependent phosphorylation of PLN promotes cardiac relaxation; urolithin A activates PKGIα via C42 oxidation, leading to PLN phosphorylation in isolated cardiomyocytes and reversal of diastolic dysfunction in a HFpEF mouse model.\",\n      \"method\": \"Recombinant PKGIα activation assay; Western blot for phospho-PLN in NRVMs; C42S PKGIα knock-in mice; echocardiography; human engineered heart tissue contractility\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro kinase assay, genetic KI mouse model, and human EHT validation, single lab; preprint\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"Phospholamban (PLN) is a small regulatory peptide that tonically inhibits the sarcoplasmic reticulum Ca2+-ATPase SERCA2a, thereby controlling Ca2+ re-uptake and cardiac contractility/relaxation; this inhibition is relieved by PKA-mediated Ser-16 phosphorylation or CaMKII-mediated Thr-17 phosphorylation. PLN also interacts with HAX-1 linking Ca2+ homeostasis to cell survival, and with AKAP5/PKA complexes. The pathogenic R14del variant causes perinuclear PLN aggregation, disorganized sarcoplasmic/endoplasmic reticulum, impaired PLN phosphorylation at Ser-16, and aberrantly enhanced binding to SERCA2a and HAX-1 (super-inhibition) or alternatively a loss of SERCA2a inhibitory competence depending on context, with secondary activation of the unfolded protein response as a protective mechanism, collectively driving dilated/arrhythmogenic cardiomyopathy.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Phospholamban (PLN) is a small sarcoplasmic reticulum (SR) regulatory protein that tonically inhibits the Ca2+-ATPase SERCA2a, thereby setting the rate of SR Ca2+ re-uptake and cardiac relaxation [#0, #8]. This inhibition is dynamically relieved through multiple post-translational and signaling inputs: PKA-anchored phosphorylation organized by AKAP5 [#11], CaMKII-mediated Thr-17 phosphorylation downstream of hypertrophic stimuli [#10], PKGIα-dependent phosphorylation promoting relaxation [#21], and direct S-sulfhydration by H2S that modulates lusitropy [#7]. PLN inhibition of SERCA2a can also be relieved by physical displacement, as shown by acylphosphatase, which competitively reduces PLN co-precipitation with SERCA2a [#8], and by FIR-induced dissociation of PLN from SERCA2 in vascular smooth muscle [#15]. Beyond SERCA2a, PLN binds the anti-apoptotic protein HAX-1, coupling SR Ca2+ handling to cell-survival pathways [#1]. PLN expression and dosage are themselves disease-relevant: a promoter mutation lowering PLN expression associates with apical hypertrophic cardiomyopathy [#12], and a homozygous null variant abolishing PLN protein causes severe recessive dilated cardiomyopathy [#13]. The R14del variant is a central pathogenic allele: it impairs Ser-16 phosphorylation and alters SERCA2a/HAX-1 binding [#2], drives early perinuclear PLN aggregation within disorganized SR before functional deficits appear [#5, #6], impairs the ER/mitochondria compartment with prolonged Ca2+ decay and oxidative stress [#3], and activates a protective unfolded protein response [#4]. Allele-specific CRISPR disruption and delivery of an interaction-blocking PLN variant (L31A/I40A) each rescue the R14del phenotype, establishing that the aberrant R14del/SERCA2a interaction is causally pathogenic [#14, #19].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established that PLN inhibition of SERCA2a is reversible by physical displacement, not solely by phosphorylation, defining a competitive-occupancy model of regulation.\",\n      \"evidence\": \"Reciprocal Co-IP of SERCA2a, PLN, and recombinant acylphosphatase from heart SR vesicles with quantitative displacement\",\n      \"pmids\": [\"12589804\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological relevance of acylphosphatase as an endogenous displacer in vivo not established\", \"Structural basis of displacement not resolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Showed that PLN expression level itself is disease-relevant, as a promoter mutation reducing transcription associates with hypertrophic cardiomyopathy.\",\n      \"evidence\": \"Luciferase reporter assays of the -42 C>G promoter variant in C6 and C2C12 cells\",\n      \"pmids\": [\"16829191\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causality in patients shown by association, not genetic rescue\", \"Mechanism linking reduced PLN to apical hypertrophy not defined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Extended PLN function beyond Ca2+ handling by identifying HAX-1 as a binding partner, linking the SERCA2a/PLN complex to anti-apoptotic survival signaling.\",\n      \"evidence\": \"Co-immunoprecipitation/pulldown identifying HAX-1 and functional characterization of its anti-apoptotic role\",\n      \"pmids\": [\"18415121\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab identification\", \"Functional consequence of PLN-HAX-1 binding for cell survival not directly dissected\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified S-sulfhydration as a novel post-translational modification of PLN contributing to impaired relaxation, broadening the regulatory inputs onto PLN.\",\n      \"evidence\": \"Modified biotin-switch assay and functional measurement in isolated perfused rat hearts\",\n      \"pmids\": [\"23785074\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Sulfhydration site not mapped\", \"Interplay with phosphorylation not addressed\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Placed PLN in a force-transduction signaling module by showing ILK regulates SERCA2a and PLN phosphorylation, connecting mechanical signaling to Ca2+ handling.\",\n      \"evidence\": \"Co-IP, phospho-PLN Western blot, and cardiac function assays in human DCM tissue and mouse models with an ILK R211A gain-of-function mutant\",\n      \"pmids\": [\"25208486\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether ILK acts directly or via an intermediary kinase on PLN unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Linked upstream hormonal and hypertrophic signaling to PLN, with TSH suppressing the PKA/PLN pathway and urotensin II driving CaMKII-mediated Thr17 phosphorylation.\",\n      \"evidence\": \"Neonatal rat cardiomyocyte treatments with SERCA2a activity, phospho-PLN Western blots, and CaMKII inhibition (KN-93)\",\n      \"pmids\": [\"27206677\", \"26930364\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Indirect pathway placement without genetic validation of PLN as the causal node\", \"Pharmacological inhibition only\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated that complete loss of PLN protein causes severe recessive dilated cardiomyopathy, with heterozygotes unaffected, establishing the consequences of PLN dosage in humans.\",\n      \"evidence\": \"Western blot of reduced PLN expression and pedigree segregation of a homozygous p.Glu2Ter variant\",\n      \"pmids\": [\"30638982\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism downstream of PLN loss not dissected\", \"Single pedigree\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Characterized the cellular pathology of R14del, showing it is initiated by PLN aggregation within disorganized SR and ER/mitochondrial impairment, and that the cell mounts a protective unfolded protein response.\",\n      \"evidence\": \"Isogenic hiPSC-CMs and time-course R14del mice with proteomics, EM, Ca2+ recording, scRNA-seq, siRNA UPR-branch silencing, and Ca2+-scavenger rescue\",\n      \"pmids\": [\"33998164\", \"33928785\", \"34587756\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular trigger initiating PLN aggregation not defined\", \"Whether aggregation or Ca2+ defect is the primary insult unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Surfaced a key controversy by showing R14del produces SERCA2a incompetence (hyperdynamic Ca2+) rather than super-inhibition, contradicting models of enhanced inhibitory binding.\",\n      \"evidence\": \"Ca2+ transient recording and SERCA2a/PLN immunolabeling in isogenic hiPSC-CMs with a SERCA2a activator probe\",\n      \"pmids\": [\"34948294\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Discrepancy with super-inhibition models not reconciled\", \"Loss of perinuclear co-localization mechanism unexplained\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Provided the contrasting biochemical model that R14del enhances binding to SERCA2a, HAX-1, and HRC to super-inhibit Ca2+ affinity while resisting Ser-16 phosphorylation rescue.\",\n      \"evidence\": \"Co-IP of PLN-R14del with SERCA2a/HAX-1/HRC, phosphorylation Western blots, and in silico structural prediction\",\n      \"pmids\": [\"35805951\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Directly conflicts with the incompetence model from the same year\", \"In silico structural claims not experimentally validated\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Established causality of the R14del allele in vivo by showing allele-specific disruption rescues cardiac function and arrhythmia susceptibility.\",\n      \"evidence\": \"AAV9-CRISPR/Cas9 allele disruption in humanized mice with cardiac MRI, ex vivo electrophysiology, and amplicon sequencing\",\n      \"pmids\": [\"35191471\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not resolve which downstream defect (aggregation vs Ca2+) is rescued\", \"Editing efficiency requirements for clinical translation unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined AKAP5 as the scaffold anchoring PKA to PLN/SERCA2a, organizing the phosphorylation that relieves inhibition and protects against apoptosis.\",\n      \"evidence\": \"Co-localization, Co-IP, and apoptosis rescue in H9C2 cells with the AKAP-disrupting peptide St-Ht31\",\n      \"pmids\": [\"35041539\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Pathway placement relies on inhibitory peptide only\", \"Direct AKAP5-PLN contact versus PKA-bridged interaction not distinguished\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identified the perinuclear PLN clusters as disorganized SR and showed DWORF overexpression reduces SR malformation and extends lifespan independent of Ca2+ handling, separating the morphological from the Ca2+ defect.\",\n      \"evidence\": \"Transgenic mouse crosses with survival analysis, Ca2+ measurements, SR-marker co-localization, and EM in human R14del tissue\",\n      \"pmids\": [\"37955153\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which DWORF prevents SR malformation unclear\", \"Whether SR disorganization is reversible after onset unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Reinforced the incompetence model in transgenic mice and linked R14del to depressed, Ca2+-dependent energy metabolism, implicating metabolic stress as an early mechanism.\",\n      \"evidence\": \"Ca2+ dynamics, O2 consumption, and metabolism assays in ventricular myocytes with pharmacological SERCA2a/PLN comparisons\",\n      \"pmids\": [\"38214033\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Conflict with super-inhibition biochemistry unresolved\", \"Causal link between metabolic stress and contractile failure not established\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended PLN missense pathology beyond R14del, showing R9C drives stress-dependent sarcomere and autophagy defects with pentamer aggregation that autophagy activation can mitigate.\",\n      \"evidence\": \"R9C knock-in and patient iPSC-CMs with transcriptomics, Ca2+ imaging, autophagy flux assays, and metformin/rapamycin rescue (preprint)\",\n      \"pmids\": [\"38659742\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not peer-reviewed\", \"Generalizability of autophagy rescue to other PLN variants untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Refined R14del Ca2+ pathology by showing elevated ER Ca2+ loading as a compartment-specific defect, and demonstrated PLN-SERCA2 dissociation drives Ca2+ reuptake in vascular smooth muscle, generalizing the regulatory paradigm.\",\n      \"evidence\": \"AAV6-CEPIAer ER Ca2+ sensing in isogenic hiPSC-CMs; Co-IP of FIR-induced PLN/SERCA2 dissociation with knockdown and aortic contraction assays\",\n      \"pmids\": [\"40791987\", \"41406161\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relationship between elevated ER load and cytosolic incompetence not integrated\", \"FIR mechanism of dissociation at molecular level undefined\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Provided proof-of-concept therapy by showing an interaction-blocking PLN variant (L31A/I40A) rescues R14del pathology in mice and human cardiomyocytes, establishing the aberrant R14del/SERCA2a interaction as a tractable target.\",\n      \"evidence\": \"AAV-delivered PLN-L31A/I40A in CRISPR R14del mice and hESC-CMs with echocardiography, histology, and contractile assays\",\n      \"pmids\": [\"41545752\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not reconcile super-inhibition versus incompetence models\", \"Long-term durability and dosing not addressed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved whether PLN-R14del acts primarily through SERCA2a super-inhibition or loss of inhibitory competence, and how SR disorganization, ER Ca2+ overload, metabolic stress, and protein aggregation are causally ordered.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Conflicting biochemical and functional models from comparable systems\", \"No structural model of the R14del/SERCA2a/HAX-1 assembly\", \"Primary initiating lesion versus secondary adaptations not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 8, 16]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [0, 8, 15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [3, 18]},\n      {\"term_id\": \"GO:0005790\", \"supporting_discovery_ids\": []}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005790\", \"supporting_discovery_ids\": []}\n    ],\n    \"complexes\": [\"SERCA2a-PLN complex\"],\n    \"partners\": [\"ATP2A2\", \"HAX1\", \"AKAP5\", \"PRKACA\", \"ILK\", \"HRC\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}