{"gene":"TPCN2","run_date":"2026-06-10T10:51:55","timeline":{"discoveries":[{"year":2009,"finding":"TPCN2 encodes a lysosomal protein forming homomers that mediates NAADP-dependent Ca2+ release from lysosomal stores; activated by low-nanomolar NAADP, desensitized by micromolar NAADP, insensitive to NADP, and Ca2+ release is abolished by pharmacological blockade of lysosomal Ca2+ storage but unaffected by ER Ca2+ store depletion.","method":"Overexpression in cells, lysosomal Ca2+ imaging, pharmacological manipulation (NAADP, NADP, lysosomal Ca2+ blockers, ER Ca2+ store depletion)","journal":"Pflugers Archiv : European journal of physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (localization, Ca2+ imaging, pharmacology) replicated across subsequent studies","pmids":["19557428"],"is_preprint":false},{"year":2010,"finding":"TPC2 is a cation channel with selectivity for Ca2+ that opens in response to NAADP in a concentration-dependent manner, with high-affinity activation and low-affinity inhibition sites; channel sensitivity to NAADP is steeply dependent on luminal [Ca2+], and luminal pH controls NAADP affinity, switching between reversible activation at low pH and irreversible activation at neutral pH. The selective NAADP blocker Ned-19 antagonizes TPC2 non-competitively.","method":"Single-channel patch-clamp electrophysiology of TPC2-expressing lipid bilayers/vesicles, pharmacological characterization with NAADP and Ned-19","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct single-channel electrophysiology with dose-response characterization and pharmacological validation","pmids":["20720007"],"is_preprint":false},{"year":2010,"finding":"TPC2 mediates NAADP-dependent Ca2+ release from acidic lysosome-related organelles leading to smooth muscle contraction; contractile responses to NAADP were completely abolished and agonist-evoked (muscarinic) contractions were reduced and rendered independent of acidic Ca2+ stores in Tpcn2−/− mouse detrusor smooth muscle.","method":"Permeabilized smooth muscle contractility assays, Tpcn2−/− knockout mouse model, pharmacological Ca2+ store depletion","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout combined with functional contractility assay, replicated across two smooth muscle preparations","pmids":["20547763"],"is_preprint":false},{"year":2012,"finding":"Endogenously expressed TPC2 associates with STIM1 and Orai1 (but not TRPC1) upon intracellular Ca2+ store depletion (not in resting cells), and silencing TPC2 attenuates store-operated Ca2+ entry (SOCE) evoked by thapsigargin or thrombin without affecting resting store capacity.","method":"siRNA knockdown, co-immunoprecipitation, Ca2+ entry measurements (fluorescence), surface biotinylation","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-immunoprecipitation plus functional Ca2+ entry assay in two cell lines, single lab","pmids":["23077736"],"is_preprint":false},{"year":2013,"finding":"TPC2 overexpression inhibits autophagosomal-lysosomal fusion by alkalinizing lysosomal pH, causing autophagosome accumulation; NAADP-AM treatment exacerbates this effect, TPC2 knockdown or Ned-19 treatment reduces it, and lysosomal re-acidification rescues the block. TPC2 overexpression also prevents Rab-7 recruitment to autophagosomes.","method":"TPC2 overexpression and siRNA knockdown, autophagosome/lysosome fusion assays, lysosomal pH measurement, NAADP-AM treatment, Ned-19 treatment, ATG5 knockdown epistasis, Rab-7 localization","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (gain-of-function, loss-of-function, pharmacology, epistasis with ATG5, Rab7 localization) in single lab","pmids":["23836916"],"is_preprint":false},{"year":2014,"finding":"Loss of Tpcn2 expression (but not Tpcn1) slows kinetics of ligand-induced PDGFRβ degradation dependent on lysosomal trafficking, while Tpcn1 loss impairs cholera toxin trafficking from plasma membrane to Golgi; neither knockout significantly affects resting endo-lysosomal pH or morphology.","method":"Tpcn2−/− and Tpcn1−/− mouse embryonic fibroblasts (MEFs), PDGFRβ degradation assay, cholera toxin trafficking assay, lysosomal pH measurement","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean knockout MEFs with defined functional readouts, single lab","pmids":["25135478"],"is_preprint":false},{"year":2014,"finding":"TPC2 in skeletal muscle contributes to lysosomal pH homeostasis, lysosomal protease activity, and autophagy signaling; Tpcn2−/− muscles show enhanced autophagy flux under starvation/colchicine stress with autophagosome accumulation, aberrant lysosomal pH, and reduced lysosomal protease activity. Association between mTOR and TPC2 was detected in skeletal muscle.","method":"Tpcn2−/− mouse model, autophagy flux assays (autophagosome accumulation with colchicine), lysosomal pH and protease activity measurements, co-immunoprecipitation of mTOR and TPC2","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout with multiple functional readouts plus co-IP for mTOR interaction, single lab","pmids":["25480788"],"is_preprint":false},{"year":2014,"finding":"Lysosomal enlargement and aggregation in LRRK2-G2019S Parkinson's disease patient fibroblasts are corrected by molecular silencing of TPC2 or pharmacological inhibition of TPC2 regulators (Rab7, NAADP, PtdIns(3,5)P2), and by buffering local Ca2+ increases; NAADP-evoked Ca2+ signals are exaggerated in diseased cells, placing TPC2 downstream of pathogenic LRRK2.","method":"TPC2 siRNA knockdown, pharmacological inhibition, Ca2+ imaging in patient-derived fibroblasts, lysosomal morphology analysis","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patient-derived cells, genetic and pharmacological perturbation, multiple readouts, single lab","pmids":["25416817"],"is_preprint":false},{"year":2016,"finding":"TPC2 localizes to the melanosome-limiting membrane (confirmed by confocal, immunogold EM, and immunomagnetic isolation) and regulates melanosome pH and size; TPC2 knockout increases melanin content and melanosome size and causes melanosome lumen to be less acidic; these effects are rescued by TPC2-GFP re-expression. TPC2-mediated Ca2+ release from melanosomes is decreased in KO cells.","method":"CRISPR/Cas9 knockout, siRNA knockdown, confocal fluorescence microscopy, immunogold EM, immunomagnetic organelle isolation, genetically encoded pH sensor (melanosome-targeted), Ca2+ sensor (tyrosinase-GCaMP6), melanin quantification","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods including genetic rescue, organelle-targeted sensors, and EM localization","pmids":["27140606"],"is_preprint":false},{"year":2017,"finding":"Two human TPC2 polymorphisms associated with blond hair (M484L/rs35264875 and G734E/rs3829241) both produce gain-of-function channel activity by independent mechanisms, as directly measured by endolysosomal patch-clamp electrophysiology in isolated endolysosomal organelles from variant-carrier fibroblasts.","method":"Endolysosomal patch-clamp electrophysiology, genotype/phenotype analysis in >100 individuals, fibroblasts from WT and polymorphic variant carriers","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct endolysosomal patch-clamp, clinical cohort plus in vitro validation, multiple variants tested","pmids":["28923947"],"is_preprint":false},{"year":2017,"finding":"TPC2-mediated Ca2+ release from acidic stores is required for slow muscle cell myofibrillogenesis and myotomal patterning in zebrafish; TPC2 knockdown (two non-overlapping MOs), knockout (CRISPR), or pharmacological inhibition disrupts these processes, which are rescued by tpcn2-mRNA injection or IP3R/RyR agonists. STED microscopy revealed close proximity (~52–87 nm) between RyR clusters in SR terminal cisternae and TPC2 in lysosomes.","method":"Morpholino knockdown, CRISPR knockout, pharmacological inhibition (bafilomycin A1, trans-ned-19), mRNA rescue, IP3R/RyR agonist rescue, STED super-resolution microscopy","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — convergent genetic and pharmacological approaches plus structural localization, replicated with multiple independent methods","pmids":["28390800"],"is_preprint":false},{"year":2017,"finding":"Under low-Mg2+ conditions, PI(3,5)P2 activates TPC2 to increase intracellular Na+, depolarize membrane potential, and thereby inhibit osteoclast differentiation; under normal Mg2+ conditions TPC2 promotes osteoclastogenesis.","method":"TPC2 functional studies in osteoclast differentiation assays, PI(3,5)P2 signaling pathway perturbation, light-sensitive membrane depolarization system, myo-inositol supplementation in vivo","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple pharmacological and genetic manipulations, novel light-depolarization system, single lab","pmids":["29084844"],"is_preprint":false},{"year":2018,"finding":"TPC2-dependent Ca2+ release from acidic intracellular stores mediates adrenaline-stimulated glucagon secretion in pancreatic α-cells; genetic or pharmacological inhibition of Tpc2 abolishes adrenaline's stimulatory effect on glucagon secretion and reduces Ca2+ elevation; downstream amplification occurs via Ca2+-induced Ca2+ release from the SR/ER (ryanodine-sensitive), placing TPC2 upstream of RyR in a cAMP/PKA/EPAC2-dependent hierarchy.","method":"Tpc2 genetic knockout, pharmacological inhibition, electrophysiology, Ca2+ imaging, PKA activity imaging, glucagon secretion measurements in mouse and human islets","journal":"Diabetes","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout plus pharmacological inhibition in both mouse and human islets with multiple readouts","pmids":["29563152"],"is_preprint":false},{"year":2018,"finding":"TPC2 overexpression inhibits autophagosome-lysosome fusion (increasing lysosomal pH and autophagosome accumulation) and decreases extracellular vesicle secretion, while TPC2 knockdown increases EV secretion and inhibits cancer cell migration.","method":"TPC2 overexpression, siRNA knockdown, autophagy flux assays, extracellular vesicle quantification, TFEB nuclear translocation, migration assay","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — paired gain- and loss-of-function with multiple downstream readouts, single lab","pmids":["29990474"],"is_preprint":false},{"year":2020,"finding":"TPC2 ion selectivity depends on the activating ligand: NAADP activates non-selective cation currents and robust Ca2+ signals, while PI(3,5)P2 activates Na+-selective currents and weaker Ca2+ signals; mutation of a single TPC2 residue differentially abolishes each agonist's action; NAADP and PI(3,5)P2 drive opposing changes in lysosomal pH and exocytosis.","method":"High-throughput agonist screen, endolysosomal patch-clamp electrophysiology, site-directed mutagenesis, lysosomal pH measurement, lysosomal exocytosis assay","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct endolysosomal electrophysiology plus mutagenesis identifying a single critical residue, multiple functional readouts","pmids":["32167471"],"is_preprint":false},{"year":2020,"finding":"TPC2 loss in metastatic melanoma cells increases invasiveness and is associated with reduced ORAI1/SOCE and reduced PKC-βII, leading to activation of YAP/TAZ target genes; this identifies ORAI1/Ca2+/PKC-βII as a mechanistic link between TPC2 loss and YAP/TAZ-driven metastatic behavior.","method":"CRISPR/Cas9 TPC2 knockout, invasion assay, western blot, siRNA knockdown of ORAI1 and PKC-βII, transcriptome analysis","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — knockout plus RNAi epistasis with multiple molecular markers, single lab","pmids":["32846966"],"is_preprint":false},{"year":2020,"finding":"TPC2 knockdown attenuates Ca2+ signaling and inhibits axon extension of caudal primary motor neurons (CaPs) in zebrafish; these effects are replicated by CRISPR knockout and pharmacological inhibition; ARC1-like knockdown also attenuates CaP Ca2+ transients and axon extension, suggesting a link between ARC1-like and TPC2 in Ca2+ signaling during axon extension.","method":"Morpholino knockdown, CRISPR knockout, pharmacological inhibition, Ca2+ imaging in CaP growth cones, morpholino knockdown of ARC1-like","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — convergent genetic and pharmacological approaches in intact zebrafish, single lab","pmids":["32546534"],"is_preprint":false},{"year":2021,"finding":"The common human TPC2 variant L564P is a prerequisite for the blond hair-associated M484L gain-of-function effect; without L564P background, M484L does not produce gain-of-function; characterized by endolysosomal patch-clamp electrophysiology.","method":"Endolysosomal patch-clamp electrophysiology of polymorphic TPC2 variants, genome variation analysis","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — direct endolysosomal electrophysiology, single lab, novel epistatic interaction between variants","pmids":["33465068"],"is_preprint":false},{"year":2021,"finding":"TPC2 knockout reduces cancer cell proliferation and energy metabolism in vitro and abrogates tumor growth in vivo; tetrandrine analogs developed as TPC2 inhibitors impair proangiogenic signaling of endothelial cells.","method":"CRISPR/Cas9 knockout, in vitro proliferation assays, metabolic assays, in vivo tumor xenograft models, pharmacological inhibition with synthesized tetrandrine analogs","journal":"Cell chemical biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic and pharmacological perturbation with in vitro and in vivo validation, single lab","pmids":["33626324"],"is_preprint":false},{"year":2021,"finding":"TPC2 inhibition (genetic or pharmacological) reduces MITF protein levels via increased GSK3β-mediated MITF degradation, reduces melanoma proliferation/migration/invasion, and increases tyrosinase activity and melanin production; these are mediated through TPC2 activity in both endolysosomes and melanosomes.","method":"CRISPR/Cas9 and siRNA knockdown, pharmacological inhibition (flavonoids), western blot for MITF/GSK3β, tyrosinase activity assay, melanin quantification, migration/invasion assay","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — paired genetic and pharmacological perturbations with multiple mechanistic readouts, single lab","pmids":["33875769"],"is_preprint":false},{"year":2022,"finding":"TPC2 co-activation by NAADP and PI(3,5)P2 increases Ca2+ permeability independently of changes in ion selectivity (acting as a coincidence detector); NAADP renders TPC2 Ca2+-permeable and PI(3,5)P2 renders it Na+-selective, but co-activation synergistically increases Ca2+ flux; this controls lysosomal pH and motility.","method":"Endolysosomal patch-clamp electrophysiology, cell-permeable NAADP and PI(3,5)P2 mimetics in live cells, lysosomal pH and motility measurements","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct endolysosomal electrophysiology with orthogonal live-cell functional assays, mechanistically novel finding","pmids":["35918320"],"is_preprint":false},{"year":2022,"finding":"Small molecule activation of TPC2 (Ca2+-permeable endolysosomal channel) promotes lysosomal exocytosis and autophagy, rescuing cellular phenotypes (cholesterol/lipofuscin accumulation, abnormal vacuoles) in mucolipidosis type IV, Niemann-Pick type C1, and Batten disease patient fibroblasts and in iPSC-derived neurons, and reduces pathology in the MLIV mouse model in vivo.","method":"Pharmacological TPC2 activation (TPC2-A1-P), CRISPR-generated isogenic iPSC models, patient fibroblasts, electron microscopy, cholesterol/lipofuscin assays, in vivo MLIV mouse model","journal":"EMBO molecular medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple disease models (3 LSDs), iPSC neurons, patient fibroblasts, and in vivo validation","pmids":["35929194"],"is_preprint":false},{"year":2022,"finding":"TPC2 loss in drug-resistant leukemia cells sensitizes them to chemotherapy via two mechanisms: (1) increased lysosomal pH impairs lysosomal drug sequestration, increasing nuclear doxorubicin accumulation and DNA damage; (2) morphological lysosomal changes and protein dysregulation increase lysosomal membrane permeability, releasing cathepsin B and triggering Bid truncation and lysosomal cell death.","method":"CRISPR/Cas9 TPC2 knockout, pharmacological inhibition (naringenin, tetrandrine), drug accumulation assay, DNA damage assay, lysosomal stability assay, cathepsin B cytosolic localization, Bid western blot, cathepsin B inhibitor rescue, patient-derived xenograft cells","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic and pharmacological perturbation, dual mechanistic dissection, patient-derived cells, multiple orthogonal readouts","pmids":["35915060"],"is_preprint":false},{"year":2023,"finding":"TPC2 generates local Ca2+ nanodomains (~42 µM) around the channel mouth during phagocytosis (measured by GECI fused directly to TPC2), and TPC2 and TRPML1 on the same lysosomes generate autonomous, largely insulated Ca2+ nanodomains; TPC2 nanodomains couple specifically to dynamin activation during Fc-receptor-mediated phagocytosis.","method":"Genetically encoded Ca2+ indicators (GECIs) fused to TPC2, Ca2+ nanodomain optical recording, signal calibration for channel-GECI distance, macrophage phagocytosis assay","journal":"Cell calcium","confidence":"High","confidence_rationale":"Tier 1 / Moderate — novel GECI-fusion technique with quantitative calibration directly characterizing channel-proximal Ca2+, single lab","pmids":["37742482"],"is_preprint":false},{"year":2023,"finding":"A de novo gain-of-function TPC2 mutation R210C causes constitutive channel activation and markedly increased affinity to PI(3,5)P2, producing enhanced lysosomal Ca2+ release, hyper-acidification of endolysosomes, and albinism in a dominant inheritance pattern; homologous R194C knock-in mice exhibit hypopigmentation and enlarged endolysosomes.","method":"Inside-out plasma membrane patch-clamp of targeted TPC2 R210C, direct recording of enlarged endolysosomal vacuoles, CRISPR knock-in mice (R194C), lysosomal pH measurement, electron microscopy","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct electrophysiology (two approaches), knock-in mouse model, and multiple cellular phenotype readouts","pmids":["36641477"],"is_preprint":false},{"year":2023,"finding":"Pharmacological inhibition of TPC2 (Ned-19) during hypoxia in cortical neurons prevents ER stress (reduces GRP78 and caspase 9), restores organellar Ca2+ homeostasis, blocks autophagic flux, and confers neuroprotection; in rats subjected to tMCAO, Ned-19 reduces infarct volume and neurological deficits. Ned-19's effect is reversed by NAADP-AM.","method":"TPC2 siRNA knockdown, Ned-19 pharmacological inhibition, NAADP-AM rescue, OGD/R in primary cortical neurons, rat tMCAO model, western blot, Ca2+ imaging","journal":"Neurobiology of disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic and pharmacological perturbation with mechanistic rescue, in vitro and in vivo models, single lab","pmids":["36708960"],"is_preprint":false},{"year":2023,"finding":"TPC2 pharmacological inhibition (naringenin, tetrandrine, SG-094) inhibits osteoblast differentiation from hMSCs and bone mineralization; mechanistically, TPC2 inhibition reduces beclin-1 and LC3-II and increases phosphorylated mTOR, and rapamycin (mTOR inhibitor) reverses TPC2 inhibitor-induced osteoblast differentiation, placing TPC2 upstream of mTOR in autophagy regulation during osteoblastogenesis.","method":"Primary hMSC differentiation assay, Saos-2 mineralization assay, pharmacological TPC2 inhibitors, western blot (beclin-1, LC3-II, p-mTOR), rapamycin epistasis","journal":"Journal of endocrinological investigation","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — pharmacological perturbation with epistasis experiment, multiple inhibitors tested, single lab","pmids":["42090110"],"is_preprint":false},{"year":2025,"finding":"The common LRRK2 G2019S mutation selectively exaggerates depolarization-induced Ca2+ entry in dopaminergic neurons; TPC2 chemical or molecular inhibition reverses this excess Ca2+ entry. In Drosophila (which lack endogenous TPCs), expression of human TPC2 phenocopies LRRK2 G2019S dopaminergic dysfunction; this dysfunction requires an intact pore, correct subcellular targeting, and Rab interactivity of TPC2. A biased TPC2 agonist that reduces Ca2+ permeability also corrected deviant Ca2+ entry.","method":"Ca2+ imaging in dopaminergic neurons, molecular and pharmacological TPC2 inhibition, Drosophila in vivo model with human TPC2 expression, TPC2 mutant analysis (pore, targeting, Rab-interactivity), biased TPC2 agonist","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — convergent genetic (Drosophila model, structure-function mutants) and pharmacological approaches with in vivo behavioral readouts","pmids":["40279672"],"is_preprint":false},{"year":2025,"finding":"OCA2 (a Cl- channel) modulates TPC2 activity via melanosomal pH; cytosolic high Cl- inhibits and luminal high Cl- enhances TPC2 channel activity; OCA2 loss-of-function combined with TPCN2 gain-of-function (A24V) acts synergistically to cause hypopigmentation in mice and patients, confirmed by CRISPR/Cas9 KO and knock-in mouse models.","method":"Patch-clamp analysis of TPC2 A24V, CRISPR/Cas9 knockout and knock-in mouse models, Cl- concentration manipulation in patch-clamp, melanin/melanosomal pH measurements","journal":"The Journal of investigative dermatology","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct electrophysiology with mechanistic Cl- manipulation, CRISPR knock-in mice, digenic patient corroboration","pmids":["41443368"],"is_preprint":false},{"year":2025,"finding":"TPC2-mediated Ca2+ release from lysosomes promotes Rab46-dependent detachment of Ang2-positive Weibel-Palade bodies (WPBs) from the microtubule organising centre (MTOC) in endothelial cells, enabling angiopoietin-2 secretion; TPC inhibitors increase WPB clustering at MTOC and reduce Ang2 secretion, while a TPC2 agonist has opposite effects.","method":"Ca2+ imaging, high-resolution light microscopy, pharmacological TPC inhibition (Ned19, tetrandrine) and TPC2 agonist (TPC2-A1-N), Ang2 secretion measurement","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — pharmacological perturbation with imaging readouts, preprint, single lab","pmids":[],"is_preprint":true},{"year":2025,"finding":"Chlorpromazine and clomipramine activate TPC2 lysosomal channel (producing large inwardly-rectifying currents blocked by trans-Ned-19 and siTPC2), inducing TFEB nuclear translocation and autophagy activation (via ULK, AMPK-α); TPC2 activation by these drugs protects motor neurons from L-BMAA-induced neurodegeneration and is partially dependent on TPC2 (siTPC2 reversal).","method":"Patch-clamp electrophysiology on enlarged lysosomes, TFEB nuclear translocation assay, western blot (ULK, AMPK-α, LC3-II/p62), siTPC2 knockdown, LDH/cytochrome C release, cell viability assay","journal":"Biochemical pharmacology","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — direct patch-clamp plus multiple downstream mechanistic readouts, single lab","pmids":["40796055"],"is_preprint":false},{"year":2025,"finding":"Under glucose deprivation-restoration, mTOR inactivation leads to lysosomal iron release via TPC2 and ferritin degradation through ferritinophagy, elevating intracellular iron and promoting ferroptosis in renal tubular cells; TPC2 is mechanistically downstream of the V-ATPase-mTOR axis for lysosomal iron release.","method":"In vitro OGSD-R and in vivo IR models, immunofluorescence, immunoblotting, biochemical iron assays, pathway perturbation (mTOR inhibition/activation, TPC2 manipulation)","journal":"Free radical biology & medicine","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — multiple in vitro and in vivo models with mechanistic pathway dissection, single lab","pmids":["40379157"],"is_preprint":false},{"year":2026,"finding":"TPC2 activation amplifies lysosome-to-mitochondria Ca2+ transfer via an ER-dependent relay requiring IP3 receptors and the mitochondrial calcium uniporter; moderate TPC2 activation transiently enhances oxidative phosphorylation, while sustained activation increases susceptibility to mitochondrial permeability transition. In stroke models, TPC2 hyperactivation exacerbates injury and acute pharmacological inhibition at reperfusion is neuroprotective.","method":"TPC2 pharmacological activation/inhibition, organelle-targeted Ca2+ imaging, IP3R and MCU knockdown epistasis, mitochondrial membrane potential assay, seahorse metabolic assay, stroke models, human iPSC-derived neurons","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods with epistasis (IP3R, MCU), human iPSC neurons, and in vivo validation; preprint status lowers confidence","pmids":["41867847"],"is_preprint":true},{"year":2026,"finding":"NAADP-dependent TPC2 activity is required for efficient ferroptosis induction in HCC cells; TPC2 loss renders HCC cells resistant to ferroptosis (by system Xc- inhibition or GPX4 blockade), associated with reduced lipid peroxidation, altered Ca2+ signaling, and depletion of polyunsaturated phosphatidylethanolamine species linked to decreased ACSL4 expression.","method":"Pharmacological TPC2 modulation, genetic knockout, flow cytometry-based cell death and lipid peroxidation assays, lipidomics, Ca2+ measurement","journal":"Antioxidants (Basel, Switzerland)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic and pharmacological perturbation, lipidomics, multiple HCC cell lines, single lab","pmids":["42193240"],"is_preprint":false}],"current_model":"TPCN2 (TPC2) is a two-pore cation channel resident in lysosomal, endolysosomal, and melanosomal membranes that forms homomers and gates Ca2+ (and, depending on the activating ligand, Na+) release from acidic intracellular stores: NAADP activates Ca2+-permeable, non-selective currents while PI(3,5)P2 activates Na+-selective currents, and co-activation by both ligands acts as a coincidence detector to maximize Ca2+ flux; the channel's sensitivity is modulated by luminal Ca2+ and pH, and it generates high-concentration (~42 µM) local Ca2+ nanodomains that are decoded by specific downstream effectors (e.g., dynamin for phagocytosis, Rab46 for vesicle trafficking, mTOR for autophagy, RyR for Ca2+-induced Ca2+ release); TPC2 thereby controls lysosomal pH homeostasis, lysosomal exocytosis, autophagosome-lysosome fusion, lysosomal iron release, melanosome size and pH, pigmentation (with gain-of-function variants causing hypopigmentation/albinism and loss-of-function increasing melanin), smooth muscle contraction, glucagon secretion, dopaminergic Ca2+ homeostasis, and mitochondrial energetics via a lysosome–ER–mitochondria Ca2+ relay."},"narrative":{"mechanistic_narrative":"TPCN2 (TPC2) is a homomeric cation channel of lysosomal, endolysosomal, and melanosomal membranes that gates Ca2+ release from acidic intracellular stores to control organelle homeostasis, autophagy, exocytosis, and pigmentation [PMID:19557428, PMID:27140606, PMID:32167471]. Single-channel and endolysosomal patch-clamp recordings establish it as a Ca2+-permeable channel activated by low-nanomolar NAADP, with luminal Ca2+ and pH steeply tuning its sensitivity and switching activation between reversible and irreversible modes [PMID:19557428, PMID:20720007]. Ligand identity dictates ion selectivity: NAADP drives non-selective, robustly Ca2+-permeable currents whereas PI(3,5)P2 drives Na+-selective currents, and co-activation by both acts as a coincidence detector that synergistically maximizes Ca2+ flux through a single critical pore residue [PMID:32167471, PMID:35918320]. By regulating these fluxes TPC2 sets lysosomal pH, protease activity, and exocytosis, controlling autophagosome-lysosome fusion such that overexpression alkalinizes lysosomes and blocks fusion while genetic loss perturbs lysosomal pH and cargo trafficking [PMID:23836916, PMID:25480788, PMID:25135478]. In melanosomes it controls luminal pH, melanosome size, and melanin content, and its activity is modulated by the chloride channel OCA2 [PMID:27140606, PMID:41443368]. Human gain-of-function variants (M484L/G734E, the L564P-dependent epistasis, and the de novo R210C and A24V mutations) produce hyperactive channels causing blond hair and dominant albinism, while loss-of-function increases pigmentation in part through GSK3β-mediated MITF stabilization [PMID:28923947, PMID:33465068, PMID:36641477, PMID:41443368, PMID:33875769]. TPC2-generated local Ca2+ nanodomains (~42 µM at the channel mouth) are decoded by specific effectors including dynamin during phagocytosis, Rab46 during Weibel-Palade body trafficking, and the SR/ER RyR for Ca2+-induced Ca2+ release driving smooth muscle contraction and adrenaline-stimulated glucagon secretion [PMID:37742482, PMID:20547763, PMID:29563152]. Through an mTOR-coupled, lysosome-ER-mitochondria Ca2+ relay TPC2 further links autophagy, iron release, lipid peroxidation, and mitochondrial energetics, making it a driver of ferroptosis and a target in lysosomal storage disease, melanoma, leukemia, and LRRK2-G2019S Parkinson's disease [PMID:25480788, PMID:40379157, PMID:42193240, PMID:35929194, PMID:35915060, PMID:40279672].","teleology":[{"year":2009,"claim":"Established the founding molecular identity of TPC2 as a lysosomal channel coupling the second messenger NAADP to Ca2+ release from acidic stores, distinct from ER stores.","evidence":"Overexpression with lysosomal Ca2+ imaging and pharmacology (NAADP, NADP, lysosomal vs ER store depletion)","pmids":["19557428"],"confidence":"High","gaps":["Direct biophysical conductance not yet measured","Endogenous channel behavior not addressed"]},{"year":2010,"claim":"Defined the biophysics and gating logic of the channel, showing NAADP gates a Ca2+-permeable conductance with dual activation/inhibition sites tuned by luminal Ca2+ and pH.","evidence":"Single-channel patch-clamp of TPC2 in bilayers/vesicles with Ned-19 pharmacology","pmids":["20720007"],"confidence":"High","gaps":["Did not address Na+ permeability or alternative ligands","Pore residues governing selectivity unmapped"]},{"year":2010,"claim":"Provided in vivo proof that TPC2-dependent acidic-store Ca2+ release drives a physiological output (smooth muscle contraction) via a genetic knockout.","evidence":"Tpcn2−/− mouse detrusor permeabilized contractility with NAADP and store depletion","pmids":["20547763"],"confidence":"High","gaps":["Downstream Ca2+ amplification machinery not yet defined","Channel-effector coupling distance unknown"]},{"year":2012,"claim":"Connected TPC2 to store-operated Ca2+ entry by showing depletion-dependent association with STIM1/Orai1, hinting at crosstalk between acidic and ER store signaling.","evidence":"siRNA, co-IP, surface biotinylation, and SOCE measurements in two cell lines","pmids":["23077736"],"confidence":"Medium","gaps":["Single lab, no reciprocal validation of complex","Mechanism of depletion-induced association unresolved"]},{"year":2013,"claim":"Showed TPC2 governs autophagosome-lysosome fusion through lysosomal pH, establishing a regulatory role in the late autophagy pathway.","evidence":"Gain/loss-of-function, pH measurement, ATG5 epistasis, Rab7 localization, lysosomal re-acidification rescue","pmids":["23836916"],"confidence":"High","gaps":["Whether effect requires Ca2+ vs cation flux per se unclear","Largely overexpression-driven"]},{"year":2014,"claim":"Clarified TPC2 roles in lysosomal cargo trafficking, protease activity, and autophagy flux, and detected an mTOR association, placing TPC2 within nutrient/autophagy signaling.","evidence":"Tpcn2−/− MEFs and muscle (PDGFRβ degradation, cholera toxin trafficking, autophagy flux, pH/protease assays, mTOR co-IP)","pmids":["25135478","25480788"],"confidence":"Medium","gaps":["mTOR interaction not reciprocally validated","Direct vs indirect coupling to mTOR unresolved"]},{"year":2014,"claim":"Placed TPC2 downstream of pathogenic LRRK2-G2019S, linking exaggerated NAADP/TPC2 Ca2+ signaling to lysosomal dysmorphology in Parkinson's disease cells.","evidence":"TPC2 silencing/pharmacology and Ca2+ imaging in patient-derived fibroblasts","pmids":["25416817"],"confidence":"Medium","gaps":["Mechanism connecting LRRK2 to TPC2 hyperactivity not defined","Single lab, fibroblast model only"]},{"year":2016,"claim":"Localized TPC2 to the melanosome membrane and established its control of melanosome pH, size, and melanin content, founding the pigmentation mechanism.","evidence":"CRISPR KO/rescue, immunogold EM, organelle isolation, organelle-targeted pH and Ca2+ sensors, melanin quantification","pmids":["27140606"],"confidence":"High","gaps":["Downstream pigmentation effectors not yet identified","Relationship to channel ligands in melanosomes unclear"]},{"year":2017,"claim":"Linked human channel-activity variants to a heritable trait, showing two blond-hair polymorphisms confer gain-of-function by independent mechanisms.","evidence":"Endolysosomal patch-clamp of variant-carrier fibroblasts plus cohort genotyping","pmids":["28923947"],"confidence":"High","gaps":["Structural basis of each gain-of-function distinct mechanism unresolved","Variant interactions not yet tested"]},{"year":2017,"claim":"Extended TPC2 Ca2+ signaling to developmental and differentiation contexts and revealed nanoscale proximity to RyR clusters supporting Ca2+-induced Ca2+ release.","evidence":"Zebrafish MO/CRISPR/pharmacology with mRNA and RyR/IP3R agonist rescue and STED microscopy; osteoclast differentiation assays with PI(3,5)P2","pmids":["28390800","29084844"],"confidence":"High","gaps":["Physical TPC2-RyR coupling mechanism not biochemically defined","Context-dependent (Mg2+) bidirectional effects mechanistically unclear"]},{"year":2018,"claim":"Defined a signaling hierarchy in which TPC2 lies upstream of RyR-mediated CICR during adrenaline-stimulated glucagon secretion, and linked TPC2 to extracellular vesicle secretion and migration.","evidence":"Tpc2 KO/pharmacology, electrophysiology, Ca2+/PKA imaging, glucagon assays in mouse and human islets; EV and migration assays with TFEB readout","pmids":["29563152","29990474"],"confidence":"High","gaps":["Spatial coupling of TPC2 to SR RyR not directly imaged here","EV/migration mechanism (single lab) less defined"]},{"year":2020,"claim":"Resolved the central gating principle that activating ligand dictates ion selectivity through a single pore residue, distinguishing NAADP-driven Ca2+ from PI(3,5)P2-driven Na+ currents.","evidence":"High-throughput agonist screen, endolysosomal patch-clamp, site-directed mutagenesis, pH and exocytosis assays","pmids":["32167471"],"confidence":"High","gaps":["Structural conformations underlying selectivity switch not solved","How a single residue toggles selectivity unresolved"]},{"year":2020,"claim":"Demonstrated tumor-suppressive consequences of TPC2 loss in melanoma via ORAI1/Ca2+/PKC-βII and YAP/TAZ, and tied TPC2 to motor neuron axon Ca2+ signaling.","evidence":"CRISPR KO, invasion assay, RNAi epistasis, transcriptomics; zebrafish MO/CRISPR/pharmacology with Ca2+ imaging","pmids":["32846966","32546534"],"confidence":"Medium","gaps":["Direct link from lysosomal TPC2 to plasma-membrane ORAI1 signaling unclear","ARC1-like–TPC2 relationship correlative"]},{"year":2021,"claim":"Established variant epistasis and further pigmentation mechanism, showing L564P is a prerequisite for M484L gain-of-function and that TPC2 controls MITF via GSK3β.","evidence":"Endolysosomal patch-clamp of polymorphic variants; CRISPR/siRNA/pharmacology with MITF/GSK3β blots and tyrosinase/melanin assays","pmids":["33465068","33875769"],"confidence":"Medium","gaps":["Biophysical basis of L564P permissiveness undefined","Link from channel activity to GSK3β not mechanistically traced"]},{"year":2021,"claim":"Validated TPC2 as a cancer-relevant target by showing knockout impairs proliferation, metabolism, and tumor growth, with tetrandrine-analog inhibitors developed.","evidence":"CRISPR KO, proliferation/metabolic assays, xenografts, synthesized pharmacological inhibitors","pmids":["33626324"],"confidence":"Medium","gaps":["Metabolic mechanism of TPC2 dependence not fully resolved","Inhibitor selectivity in vivo not exhaustively characterized"]},{"year":2022,"claim":"Defined the coincidence-detector mechanism wherein NAADP and PI(3,5)P2 co-activation synergistically boosts Ca2+ flux independent of selectivity, controlling lysosomal pH and motility.","evidence":"Endolysosomal patch-clamp with cell-permeable ligand mimetics and live-cell pH/motility assays","pmids":["35918320"],"confidence":"High","gaps":["Structural basis of synergistic gating unresolved","Physiological contexts of dual ligand co-activation untested"]},{"year":2022,"claim":"Demonstrated therapeutic leverage of TPC2 activity in disease: small-molecule activation rescues lysosomal storage disease pathology, while loss sensitizes drug-resistant leukemia to chemotherapy.","evidence":"Pharmacological TPC2-A1-P in iPSC/patient fibroblasts and MLIV mice; CRISPR KO and inhibitors with drug accumulation, DNA damage, and lysosomal death readouts in leukemia","pmids":["35929194","35915060"],"confidence":"High","gaps":["How activation simultaneously promotes exocytosis and corrects multiple LSDs mechanistically unresolved","Generalizability across tumor types untested"]},{"year":2023,"claim":"Quantified channel-proximal Ca2+ nanodomains and established effector-specific decoding, showing ~42 µM local Ca2+ couples TPC2 to dynamin during phagocytosis with autonomy from co-resident TRPML1.","evidence":"GECI fused to TPC2 with calibrated nanodomain optical recording in macrophage phagocytosis","pmids":["37742482"],"confidence":"High","gaps":["How insulation between TPC2 and TRPML1 domains is maintained unknown","Physical basis of dynamin recruitment not defined"]},{"year":2023,"claim":"Identified a de novo gain-of-function mutation (R210C) causing dominant albinism through constitutive activation and increased PI(3,5)P2 affinity, with a knock-in mouse phenocopy.","evidence":"Inside-out and enlarged-vacuole patch-clamp, R194C knock-in mice, pH and EM phenotyping","pmids":["36641477"],"confidence":"High","gaps":["Structural mechanism of constitutive opening unresolved","Why hyperactivation reduces pigmentation despite hyper-acidification unclear"]},{"year":2023,"claim":"Extended TPC2's pathological role to ischemia, showing inhibition reduces ER stress and autophagic flux and is neuroprotective in stroke.","evidence":"siRNA, Ned-19 with NAADP-AM rescue, OGD/R neurons, rat tMCAO, blots and Ca2+ imaging","pmids":["36708960"],"confidence":"Medium","gaps":["Causal chain from TPC2 to ER stress not fully dissected","Single lab"]},{"year":2025,"claim":"Established structure-function requirements for TPC2 in LRRK2-G2019S dopaminergic dysfunction, showing pore integrity, targeting, and Rab interactivity are all required and a biased agonist corrects pathology.","evidence":"Ca2+ imaging in dopaminergic neurons, Drosophila human-TPC2 reconstitution, structure-function mutants, biased agonist","pmids":["40279672"],"confidence":"High","gaps":["Identity of the relevant Rab interactor not defined here","How LRRK2 amplifies TPC2 Ca2+ entry mechanistically open"]},{"year":2025,"claim":"Identified physiological regulators and effectors of TPC2: OCA2-derived chloride modulates channel activity (digenic albinism), and TPC2 Ca2+ drives Rab46-dependent Weibel-Palade body trafficking for Ang2 secretion.","evidence":"Patch-clamp with Cl- manipulation, CRISPR KO/knock-in mice; Ca2+ imaging and pharmacology with Ang2 secretion readout (preprint for WPB study)","pmids":["41443368"],"confidence":"High","gaps":["Direct OCA2-TPC2 physical interaction not established","Rab46 recruitment mechanism by Ca2+ nanodomains undefined"]},{"year":2025,"claim":"Linked TPC2 to drug-induced TFEB/autophagy activation and to lysosomal iron release driving ferroptosis, placing TPC2 downstream of V-ATPase-mTOR.","evidence":"Patch-clamp with chlorpromazine/clomipramine, TFEB/ULK/AMPK readouts and siTPC2 in neurons; OGSD-R and IR models with iron assays and mTOR perturbation","pmids":["40796055","40379157"],"confidence":"Medium","gaps":["Whether iron permeates TPC2 directly or via secondary release unresolved","Single-lab mechanistic dissection"]},{"year":2026,"claim":"Defined a lysosome-ER-mitochondria Ca2+ relay through which TPC2 tunes mitochondrial energetics and ferroptosis sensitivity.","evidence":"Pharmacological TPC2 modulation, organelle-targeted Ca2+ imaging, IP3R/MCU epistasis, metabolic and stroke assays, iPSC neurons (preprint); NAADP-TPC2 dependence of HCC ferroptosis with lipidomics","pmids":["41867847","42193240"],"confidence":"Medium","gaps":["Physical lysosome-ER-mitochondria contact architecture undefined","ACSL4/PUFA-PE regulation downstream of TPC2 Ca2+ not mechanistically traced","One study is a preprint"]},{"year":null,"claim":"How a single pore residue toggles ligand-dependent selectivity, how distinct effectors (dynamin, Rab46, RyR, mTOR) are physically recruited to channel-proximal Ca2+ nanodomains, and the structural basis of gain-of-function disease variants remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution structure linking gating, selectivity, and ligand sites in the timeline","Physical recruitment mechanism for each downstream effector undefined","Architecture of inter-organelle Ca2+ relay contacts uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,1,14,20,24]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[1,14,20]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[14,20,24]}],"localization":[{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[0,4,6,22,23,31]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[5,7,24]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[4,6,13,26,30]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[5,13,14,29]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[22,31,33]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,12,27]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[18,31,32]}],"complexes":[],"partners":["STIM1","ORAI1","MTOR","RYR","OCA2","RAB46","RAB7","DNM"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8NHX9","full_name":"Two pore channel protein 2","aliases":["Two pore calcium channel protein 2"],"length_aa":752,"mass_kda":85.2,"function":"Intracellular channel initially characterized as a non-selective Ca(2+)-permeable channel activated by NAADP (nicotinic acid adenine dinucleotide phosphate), it is also a highly-selective Na(+) channel activated directly by PI(3,5)P2 (phosphatidylinositol 3,5-bisphosphate) (PubMed:19387438, PubMed:19620632, PubMed:20880839, PubMed:23063126, PubMed:23394946, PubMed:24502975, PubMed:24776928, PubMed:30860481, PubMed:31825310, PubMed:32167471). Localizes to the lysosomal and late endosome membranes where it regulates organellar membrane excitability, membrane trafficking, and pH homeostasis. Is associated with a plethora of physiological processes, including mTOR-dependent nutrient sensing, skin pigmentation and autophagy (PubMed:18488028, PubMed:23394946, PubMed:32167471). Ion selectivity is not fixed but rather agonist-dependent and under defined ionic conditions, can be readily activated by both NAADP and PI(3,5)P2 (PubMed:24502975, PubMed:31825310, PubMed:32167471). As calcium channel, it increases the pH in the lysosomal lumen, as sodium channel, it promotes lysosomal exocytosis (PubMed:31825310, PubMed:32167471). Plays a crucial role in endolysosomal trafficking in the endolysosomal degradation pathway and is potentially involved in the homeostatic control of many macromolecules and cell metabolites (By similarity) (PubMed:18488028, PubMed:19387438, PubMed:19620632, PubMed:20880839, PubMed:23063126, PubMed:23394946, PubMed:24502975, PubMed:24776928, PubMed:31825310, PubMed:32167471, PubMed:32679067). Also expressed in melanosomes of pigmented cells where mediates a Ca(2+) channel and/or PI(3,5)P2-activated melanosomal Na(+) channel to acidify pH and inhibit tyrosinase activity required for melanogenesis and pigmentation (PubMed:27140606). Unlike the voltage-dependent TPCN1, TPCN2 is voltage independent and can be activated solely by PI(3,5)P2 binding. In contrast, PI(4,5)P2, PI(3,4)P2, PI(3)P and PI(5)P have no obvious effect on channel activation (PubMed:30860481) (Microbial infection) During Ebola virus (EBOV) infection, controls the movement of endosomes containing virus particles and is required by EBOV to escape from the endosomal network into the cell cytoplasm (Microbial infection) Required for cell entry of coronaviruses SARS-CoV and SARS-CoV-2, as well as human coronavirus EMC (HCoV-EMC), by endocytosis","subcellular_location":"Late endosome membrane; Lysosome membrane; Melanosome membrane","url":"https://www.uniprot.org/uniprotkb/Q8NHX9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TPCN2","classification":"Not Classified","n_dependent_lines":7,"n_total_lines":1208,"dependency_fraction":0.005794701986754967},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TPCN2","total_profiled":1310},"omim":[{"mim_id":"612267","title":"SKIN/HAIR/EYE PIGMENTATION, VARIATION IN, 10; SHEP10","url":"https://www.omim.org/entry/612267"},{"mim_id":"612163","title":"TWO-PORE SEGMENT CHANNEL 2; TPCN2","url":"https://www.omim.org/entry/612163"},{"mim_id":"227220","title":"SKIN/HAIR/EYE PIGMENTATION, VARIATION IN, 1; SHEP1","url":"https://www.omim.org/entry/227220"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoli","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/TPCN2"},"hgnc":{"alias_symbol":["TPC2"],"prev_symbol":[]},"alphafold":{"accession":"Q8NHX9","domains":[{"cath_id":"-","chopping":"38-208","consensus_level":"medium","plddt":89.6937,"start":38,"end":208},{"cath_id":"1.10.287.70","chopping":"212-407","consensus_level":"medium","plddt":83.0812,"start":212,"end":407},{"cath_id":"1.20.120,1.20.120","chopping":"421-562","consensus_level":"high","plddt":80.4932,"start":421,"end":562},{"cath_id":"1.10.287.70","chopping":"574-609_625-706","consensus_level":"high","plddt":87.3637,"start":574,"end":706}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NHX9","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NHX9-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NHX9-F1-predicted_aligned_error_v6.png","plddt_mean":79.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TPCN2","jax_strain_url":"https://www.jax.org/strain/search?query=TPCN2"},"sequence":{"accession":"Q8NHX9","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8NHX9.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8NHX9/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NHX9"}},"corpus_meta":[{"pmid":"19557428","id":"PMC_19557428","title":"The 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Lysosomal Membrane Proteins LAMP1, TPC1 and TPC2 in Acute Myeloid Leukemia Cells and Its Clinical Significance].","date":"2019","source":"Zhongguo shi yan xue ye xue za zhi","url":"https://pubmed.ncbi.nlm.nih.gov/31418355","citation_count":1,"is_preprint":false},{"pmid":"39732974","id":"PMC_39732974","title":"Hypoxia-induced TPC2 transcription and glycosylation aggravates pulmonary arterial hypertension by blocking autophagy flux.","date":"2024","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/39732974","citation_count":0,"is_preprint":false},{"pmid":"42243615","id":"PMC_42243615","title":"TPC2 regulates proteomic remodeling, bioenergetic phenotypes, and mitochondrial stress adaptation in melanoma.","date":"2026","source":"Saudi pharmaceutical journal : SPJ : the official publication of the Saudi Pharmaceutical Society","url":"https://pubmed.ncbi.nlm.nih.gov/42243615","citation_count":0,"is_preprint":false},{"pmid":"41867847","id":"PMC_41867847","title":"Activation 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while targeting autophagy.","date":"2026","source":"Journal of endocrinological investigation","url":"https://pubmed.ncbi.nlm.nih.gov/42090110","citation_count":0,"is_preprint":false},{"pmid":"41254057","id":"PMC_41254057","title":"Polymethoxyflavones from Kaempferia parviflora stimulate melanogenesis by blocking the TPC2 channel.","date":"2025","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/41254057","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.04.08.25325108","title":"Brainstem Reduction and Deformation in the 4th Ventricle Cerebellar Peduncles in Long COVID Patients: Insights into Neuroinflammatory Sequelae and “Broken Bridge Syndrome”","date":"2025-04-08","source":"bioRxiv","url":"https://doi.org/10.1101/2025.04.08.25325108","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.03.03.641167","title":"Two-pore channel protein 2-mediated calcium release promotes angiopoietin 2 secretion by regulating 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but unaffected by ER Ca2+ store depletion.\",\n      \"method\": \"Overexpression in cells, lysosomal Ca2+ imaging, pharmacological manipulation (NAADP, NADP, lysosomal Ca2+ blockers, ER Ca2+ store depletion)\",\n      \"journal\": \"Pflugers Archiv : European journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (localization, Ca2+ imaging, pharmacology) replicated across subsequent studies\",\n      \"pmids\": [\"19557428\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"TPC2 is a cation channel with selectivity for Ca2+ that opens in response to NAADP in a concentration-dependent manner, with high-affinity activation and low-affinity inhibition sites; channel sensitivity to NAADP is steeply dependent on luminal [Ca2+], and luminal pH controls NAADP affinity, switching between reversible activation at low pH and irreversible activation at neutral pH. The selective NAADP blocker Ned-19 antagonizes TPC2 non-competitively.\",\n      \"method\": \"Single-channel patch-clamp electrophysiology of TPC2-expressing lipid bilayers/vesicles, pharmacological characterization with NAADP and Ned-19\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct single-channel electrophysiology with dose-response characterization and pharmacological validation\",\n      \"pmids\": [\"20720007\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"TPC2 mediates NAADP-dependent Ca2+ release from acidic lysosome-related organelles leading to smooth muscle contraction; contractile responses to NAADP were completely abolished and agonist-evoked (muscarinic) contractions were reduced and rendered independent of acidic Ca2+ stores in Tpcn2−/− mouse detrusor smooth muscle.\",\n      \"method\": \"Permeabilized smooth muscle contractility assays, Tpcn2−/− knockout mouse model, pharmacological Ca2+ store depletion\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout combined with functional contractility assay, replicated across two smooth muscle preparations\",\n      \"pmids\": [\"20547763\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Endogenously expressed TPC2 associates with STIM1 and Orai1 (but not TRPC1) upon intracellular Ca2+ store depletion (not in resting cells), and silencing TPC2 attenuates store-operated Ca2+ entry (SOCE) evoked by thapsigargin or thrombin without affecting resting store capacity.\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation, Ca2+ entry measurements (fluorescence), surface biotinylation\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-immunoprecipitation plus functional Ca2+ entry assay in two cell lines, single lab\",\n      \"pmids\": [\"23077736\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"TPC2 overexpression inhibits autophagosomal-lysosomal fusion by alkalinizing lysosomal pH, causing autophagosome accumulation; NAADP-AM treatment exacerbates this effect, TPC2 knockdown or Ned-19 treatment reduces it, and lysosomal re-acidification rescues the block. TPC2 overexpression also prevents Rab-7 recruitment to autophagosomes.\",\n      \"method\": \"TPC2 overexpression and siRNA knockdown, autophagosome/lysosome fusion assays, lysosomal pH measurement, NAADP-AM treatment, Ned-19 treatment, ATG5 knockdown epistasis, Rab-7 localization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (gain-of-function, loss-of-function, pharmacology, epistasis with ATG5, Rab7 localization) in single lab\",\n      \"pmids\": [\"23836916\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Loss of Tpcn2 expression (but not Tpcn1) slows kinetics of ligand-induced PDGFRβ degradation dependent on lysosomal trafficking, while Tpcn1 loss impairs cholera toxin trafficking from plasma membrane to Golgi; neither knockout significantly affects resting endo-lysosomal pH or morphology.\",\n      \"method\": \"Tpcn2−/− and Tpcn1−/− mouse embryonic fibroblasts (MEFs), PDGFRβ degradation assay, cholera toxin trafficking assay, lysosomal pH measurement\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean knockout MEFs with defined functional readouts, single lab\",\n      \"pmids\": [\"25135478\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TPC2 in skeletal muscle contributes to lysosomal pH homeostasis, lysosomal protease activity, and autophagy signaling; Tpcn2−/− muscles show enhanced autophagy flux under starvation/colchicine stress with autophagosome accumulation, aberrant lysosomal pH, and reduced lysosomal protease activity. Association between mTOR and TPC2 was detected in skeletal muscle.\",\n      \"method\": \"Tpcn2−/− mouse model, autophagy flux assays (autophagosome accumulation with colchicine), lysosomal pH and protease activity measurements, co-immunoprecipitation of mTOR and TPC2\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout with multiple functional readouts plus co-IP for mTOR interaction, single lab\",\n      \"pmids\": [\"25480788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Lysosomal enlargement and aggregation in LRRK2-G2019S Parkinson's disease patient fibroblasts are corrected by molecular silencing of TPC2 or pharmacological inhibition of TPC2 regulators (Rab7, NAADP, PtdIns(3,5)P2), and by buffering local Ca2+ increases; NAADP-evoked Ca2+ signals are exaggerated in diseased cells, placing TPC2 downstream of pathogenic LRRK2.\",\n      \"method\": \"TPC2 siRNA knockdown, pharmacological inhibition, Ca2+ imaging in patient-derived fibroblasts, lysosomal morphology analysis\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patient-derived cells, genetic and pharmacological perturbation, multiple readouts, single lab\",\n      \"pmids\": [\"25416817\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"TPC2 localizes to the melanosome-limiting membrane (confirmed by confocal, immunogold EM, and immunomagnetic isolation) and regulates melanosome pH and size; TPC2 knockout increases melanin content and melanosome size and causes melanosome lumen to be less acidic; these effects are rescued by TPC2-GFP re-expression. TPC2-mediated Ca2+ release from melanosomes is decreased in KO cells.\",\n      \"method\": \"CRISPR/Cas9 knockout, siRNA knockdown, confocal fluorescence microscopy, immunogold EM, immunomagnetic organelle isolation, genetically encoded pH sensor (melanosome-targeted), Ca2+ sensor (tyrosinase-GCaMP6), melanin quantification\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods including genetic rescue, organelle-targeted sensors, and EM localization\",\n      \"pmids\": [\"27140606\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Two human TPC2 polymorphisms associated with blond hair (M484L/rs35264875 and G734E/rs3829241) both produce gain-of-function channel activity by independent mechanisms, as directly measured by endolysosomal patch-clamp electrophysiology in isolated endolysosomal organelles from variant-carrier fibroblasts.\",\n      \"method\": \"Endolysosomal patch-clamp electrophysiology, genotype/phenotype analysis in >100 individuals, fibroblasts from WT and polymorphic variant carriers\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct endolysosomal patch-clamp, clinical cohort plus in vitro validation, multiple variants tested\",\n      \"pmids\": [\"28923947\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"TPC2-mediated Ca2+ release from acidic stores is required for slow muscle cell myofibrillogenesis and myotomal patterning in zebrafish; TPC2 knockdown (two non-overlapping MOs), knockout (CRISPR), or pharmacological inhibition disrupts these processes, which are rescued by tpcn2-mRNA injection or IP3R/RyR agonists. STED microscopy revealed close proximity (~52–87 nm) between RyR clusters in SR terminal cisternae and TPC2 in lysosomes.\",\n      \"method\": \"Morpholino knockdown, CRISPR knockout, pharmacological inhibition (bafilomycin A1, trans-ned-19), mRNA rescue, IP3R/RyR agonist rescue, STED super-resolution microscopy\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — convergent genetic and pharmacological approaches plus structural localization, replicated with multiple independent methods\",\n      \"pmids\": [\"28390800\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Under low-Mg2+ conditions, PI(3,5)P2 activates TPC2 to increase intracellular Na+, depolarize membrane potential, and thereby inhibit osteoclast differentiation; under normal Mg2+ conditions TPC2 promotes osteoclastogenesis.\",\n      \"method\": \"TPC2 functional studies in osteoclast differentiation assays, PI(3,5)P2 signaling pathway perturbation, light-sensitive membrane depolarization system, myo-inositol supplementation in vivo\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple pharmacological and genetic manipulations, novel light-depolarization system, single lab\",\n      \"pmids\": [\"29084844\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TPC2-dependent Ca2+ release from acidic intracellular stores mediates adrenaline-stimulated glucagon secretion in pancreatic α-cells; genetic or pharmacological inhibition of Tpc2 abolishes adrenaline's stimulatory effect on glucagon secretion and reduces Ca2+ elevation; downstream amplification occurs via Ca2+-induced Ca2+ release from the SR/ER (ryanodine-sensitive), placing TPC2 upstream of RyR in a cAMP/PKA/EPAC2-dependent hierarchy.\",\n      \"method\": \"Tpc2 genetic knockout, pharmacological inhibition, electrophysiology, Ca2+ imaging, PKA activity imaging, glucagon secretion measurements in mouse and human islets\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout plus pharmacological inhibition in both mouse and human islets with multiple readouts\",\n      \"pmids\": [\"29563152\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TPC2 overexpression inhibits autophagosome-lysosome fusion (increasing lysosomal pH and autophagosome accumulation) and decreases extracellular vesicle secretion, while TPC2 knockdown increases EV secretion and inhibits cancer cell migration.\",\n      \"method\": \"TPC2 overexpression, siRNA knockdown, autophagy flux assays, extracellular vesicle quantification, TFEB nuclear translocation, migration assay\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — paired gain- and loss-of-function with multiple downstream readouts, single lab\",\n      \"pmids\": [\"29990474\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TPC2 ion selectivity depends on the activating ligand: NAADP activates non-selective cation currents and robust Ca2+ signals, while PI(3,5)P2 activates Na+-selective currents and weaker Ca2+ signals; mutation of a single TPC2 residue differentially abolishes each agonist's action; NAADP and PI(3,5)P2 drive opposing changes in lysosomal pH and exocytosis.\",\n      \"method\": \"High-throughput agonist screen, endolysosomal patch-clamp electrophysiology, site-directed mutagenesis, lysosomal pH measurement, lysosomal exocytosis assay\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct endolysosomal electrophysiology plus mutagenesis identifying a single critical residue, multiple functional readouts\",\n      \"pmids\": [\"32167471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TPC2 loss in metastatic melanoma cells increases invasiveness and is associated with reduced ORAI1/SOCE and reduced PKC-βII, leading to activation of YAP/TAZ target genes; this identifies ORAI1/Ca2+/PKC-βII as a mechanistic link between TPC2 loss and YAP/TAZ-driven metastatic behavior.\",\n      \"method\": \"CRISPR/Cas9 TPC2 knockout, invasion assay, western blot, siRNA knockdown of ORAI1 and PKC-βII, transcriptome analysis\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — knockout plus RNAi epistasis with multiple molecular markers, single lab\",\n      \"pmids\": [\"32846966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TPC2 knockdown attenuates Ca2+ signaling and inhibits axon extension of caudal primary motor neurons (CaPs) in zebrafish; these effects are replicated by CRISPR knockout and pharmacological inhibition; ARC1-like knockdown also attenuates CaP Ca2+ transients and axon extension, suggesting a link between ARC1-like and TPC2 in Ca2+ signaling during axon extension.\",\n      \"method\": \"Morpholino knockdown, CRISPR knockout, pharmacological inhibition, Ca2+ imaging in CaP growth cones, morpholino knockdown of ARC1-like\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — convergent genetic and pharmacological approaches in intact zebrafish, single lab\",\n      \"pmids\": [\"32546534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The common human TPC2 variant L564P is a prerequisite for the blond hair-associated M484L gain-of-function effect; without L564P background, M484L does not produce gain-of-function; characterized by endolysosomal patch-clamp electrophysiology.\",\n      \"method\": \"Endolysosomal patch-clamp electrophysiology of polymorphic TPC2 variants, genome variation analysis\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct endolysosomal electrophysiology, single lab, novel epistatic interaction between variants\",\n      \"pmids\": [\"33465068\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"TPC2 knockout reduces cancer cell proliferation and energy metabolism in vitro and abrogates tumor growth in vivo; tetrandrine analogs developed as TPC2 inhibitors impair proangiogenic signaling of endothelial cells.\",\n      \"method\": \"CRISPR/Cas9 knockout, in vitro proliferation assays, metabolic assays, in vivo tumor xenograft models, pharmacological inhibition with synthesized tetrandrine analogs\",\n      \"journal\": \"Cell chemical biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and pharmacological perturbation with in vitro and in vivo validation, single lab\",\n      \"pmids\": [\"33626324\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"TPC2 inhibition (genetic or pharmacological) reduces MITF protein levels via increased GSK3β-mediated MITF degradation, reduces melanoma proliferation/migration/invasion, and increases tyrosinase activity and melanin production; these are mediated through TPC2 activity in both endolysosomes and melanosomes.\",\n      \"method\": \"CRISPR/Cas9 and siRNA knockdown, pharmacological inhibition (flavonoids), western blot for MITF/GSK3β, tyrosinase activity assay, melanin quantification, migration/invasion assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — paired genetic and pharmacological perturbations with multiple mechanistic readouts, single lab\",\n      \"pmids\": [\"33875769\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"TPC2 co-activation by NAADP and PI(3,5)P2 increases Ca2+ permeability independently of changes in ion selectivity (acting as a coincidence detector); NAADP renders TPC2 Ca2+-permeable and PI(3,5)P2 renders it Na+-selective, but co-activation synergistically increases Ca2+ flux; this controls lysosomal pH and motility.\",\n      \"method\": \"Endolysosomal patch-clamp electrophysiology, cell-permeable NAADP and PI(3,5)P2 mimetics in live cells, lysosomal pH and motility measurements\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct endolysosomal electrophysiology with orthogonal live-cell functional assays, mechanistically novel finding\",\n      \"pmids\": [\"35918320\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Small molecule activation of TPC2 (Ca2+-permeable endolysosomal channel) promotes lysosomal exocytosis and autophagy, rescuing cellular phenotypes (cholesterol/lipofuscin accumulation, abnormal vacuoles) in mucolipidosis type IV, Niemann-Pick type C1, and Batten disease patient fibroblasts and in iPSC-derived neurons, and reduces pathology in the MLIV mouse model in vivo.\",\n      \"method\": \"Pharmacological TPC2 activation (TPC2-A1-P), CRISPR-generated isogenic iPSC models, patient fibroblasts, electron microscopy, cholesterol/lipofuscin assays, in vivo MLIV mouse model\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple disease models (3 LSDs), iPSC neurons, patient fibroblasts, and in vivo validation\",\n      \"pmids\": [\"35929194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"TPC2 loss in drug-resistant leukemia cells sensitizes them to chemotherapy via two mechanisms: (1) increased lysosomal pH impairs lysosomal drug sequestration, increasing nuclear doxorubicin accumulation and DNA damage; (2) morphological lysosomal changes and protein dysregulation increase lysosomal membrane permeability, releasing cathepsin B and triggering Bid truncation and lysosomal cell death.\",\n      \"method\": \"CRISPR/Cas9 TPC2 knockout, pharmacological inhibition (naringenin, tetrandrine), drug accumulation assay, DNA damage assay, lysosomal stability assay, cathepsin B cytosolic localization, Bid western blot, cathepsin B inhibitor rescue, patient-derived xenograft cells\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic and pharmacological perturbation, dual mechanistic dissection, patient-derived cells, multiple orthogonal readouts\",\n      \"pmids\": [\"35915060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"TPC2 generates local Ca2+ nanodomains (~42 µM) around the channel mouth during phagocytosis (measured by GECI fused directly to TPC2), and TPC2 and TRPML1 on the same lysosomes generate autonomous, largely insulated Ca2+ nanodomains; TPC2 nanodomains couple specifically to dynamin activation during Fc-receptor-mediated phagocytosis.\",\n      \"method\": \"Genetically encoded Ca2+ indicators (GECIs) fused to TPC2, Ca2+ nanodomain optical recording, signal calibration for channel-GECI distance, macrophage phagocytosis assay\",\n      \"journal\": \"Cell calcium\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — novel GECI-fusion technique with quantitative calibration directly characterizing channel-proximal Ca2+, single lab\",\n      \"pmids\": [\"37742482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"A de novo gain-of-function TPC2 mutation R210C causes constitutive channel activation and markedly increased affinity to PI(3,5)P2, producing enhanced lysosomal Ca2+ release, hyper-acidification of endolysosomes, and albinism in a dominant inheritance pattern; homologous R194C knock-in mice exhibit hypopigmentation and enlarged endolysosomes.\",\n      \"method\": \"Inside-out plasma membrane patch-clamp of targeted TPC2 R210C, direct recording of enlarged endolysosomal vacuoles, CRISPR knock-in mice (R194C), lysosomal pH measurement, electron microscopy\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct electrophysiology (two approaches), knock-in mouse model, and multiple cellular phenotype readouts\",\n      \"pmids\": [\"36641477\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Pharmacological inhibition of TPC2 (Ned-19) during hypoxia in cortical neurons prevents ER stress (reduces GRP78 and caspase 9), restores organellar Ca2+ homeostasis, blocks autophagic flux, and confers neuroprotection; in rats subjected to tMCAO, Ned-19 reduces infarct volume and neurological deficits. Ned-19's effect is reversed by NAADP-AM.\",\n      \"method\": \"TPC2 siRNA knockdown, Ned-19 pharmacological inhibition, NAADP-AM rescue, OGD/R in primary cortical neurons, rat tMCAO model, western blot, Ca2+ imaging\",\n      \"journal\": \"Neurobiology of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and pharmacological perturbation with mechanistic rescue, in vitro and in vivo models, single lab\",\n      \"pmids\": [\"36708960\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"TPC2 pharmacological inhibition (naringenin, tetrandrine, SG-094) inhibits osteoblast differentiation from hMSCs and bone mineralization; mechanistically, TPC2 inhibition reduces beclin-1 and LC3-II and increases phosphorylated mTOR, and rapamycin (mTOR inhibitor) reverses TPC2 inhibitor-induced osteoblast differentiation, placing TPC2 upstream of mTOR in autophagy regulation during osteoblastogenesis.\",\n      \"method\": \"Primary hMSC differentiation assay, Saos-2 mineralization assay, pharmacological TPC2 inhibitors, western blot (beclin-1, LC3-II, p-mTOR), rapamycin epistasis\",\n      \"journal\": \"Journal of endocrinological investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — pharmacological perturbation with epistasis experiment, multiple inhibitors tested, single lab\",\n      \"pmids\": [\"42090110\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The common LRRK2 G2019S mutation selectively exaggerates depolarization-induced Ca2+ entry in dopaminergic neurons; TPC2 chemical or molecular inhibition reverses this excess Ca2+ entry. In Drosophila (which lack endogenous TPCs), expression of human TPC2 phenocopies LRRK2 G2019S dopaminergic dysfunction; this dysfunction requires an intact pore, correct subcellular targeting, and Rab interactivity of TPC2. A biased TPC2 agonist that reduces Ca2+ permeability also corrected deviant Ca2+ entry.\",\n      \"method\": \"Ca2+ imaging in dopaminergic neurons, molecular and pharmacological TPC2 inhibition, Drosophila in vivo model with human TPC2 expression, TPC2 mutant analysis (pore, targeting, Rab-interactivity), biased TPC2 agonist\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — convergent genetic (Drosophila model, structure-function mutants) and pharmacological approaches with in vivo behavioral readouts\",\n      \"pmids\": [\"40279672\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"OCA2 (a Cl- channel) modulates TPC2 activity via melanosomal pH; cytosolic high Cl- inhibits and luminal high Cl- enhances TPC2 channel activity; OCA2 loss-of-function combined with TPCN2 gain-of-function (A24V) acts synergistically to cause hypopigmentation in mice and patients, confirmed by CRISPR/Cas9 KO and knock-in mouse models.\",\n      \"method\": \"Patch-clamp analysis of TPC2 A24V, CRISPR/Cas9 knockout and knock-in mouse models, Cl- concentration manipulation in patch-clamp, melanin/melanosomal pH measurements\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct electrophysiology with mechanistic Cl- manipulation, CRISPR knock-in mice, digenic patient corroboration\",\n      \"pmids\": [\"41443368\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TPC2-mediated Ca2+ release from lysosomes promotes Rab46-dependent detachment of Ang2-positive Weibel-Palade bodies (WPBs) from the microtubule organising centre (MTOC) in endothelial cells, enabling angiopoietin-2 secretion; TPC inhibitors increase WPB clustering at MTOC and reduce Ang2 secretion, while a TPC2 agonist has opposite effects.\",\n      \"method\": \"Ca2+ imaging, high-resolution light microscopy, pharmacological TPC inhibition (Ned19, tetrandrine) and TPC2 agonist (TPC2-A1-N), Ang2 secretion measurement\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — pharmacological perturbation with imaging readouts, preprint, single lab\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Chlorpromazine and clomipramine activate TPC2 lysosomal channel (producing large inwardly-rectifying currents blocked by trans-Ned-19 and siTPC2), inducing TFEB nuclear translocation and autophagy activation (via ULK, AMPK-α); TPC2 activation by these drugs protects motor neurons from L-BMAA-induced neurodegeneration and is partially dependent on TPC2 (siTPC2 reversal).\",\n      \"method\": \"Patch-clamp electrophysiology on enlarged lysosomes, TFEB nuclear translocation assay, western blot (ULK, AMPK-α, LC3-II/p62), siTPC2 knockdown, LDH/cytochrome C release, cell viability assay\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — direct patch-clamp plus multiple downstream mechanistic readouts, single lab\",\n      \"pmids\": [\"40796055\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Under glucose deprivation-restoration, mTOR inactivation leads to lysosomal iron release via TPC2 and ferritin degradation through ferritinophagy, elevating intracellular iron and promoting ferroptosis in renal tubular cells; TPC2 is mechanistically downstream of the V-ATPase-mTOR axis for lysosomal iron release.\",\n      \"method\": \"In vitro OGSD-R and in vivo IR models, immunofluorescence, immunoblotting, biochemical iron assays, pathway perturbation (mTOR inhibition/activation, TPC2 manipulation)\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — multiple in vitro and in vivo models with mechanistic pathway dissection, single lab\",\n      \"pmids\": [\"40379157\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"TPC2 activation amplifies lysosome-to-mitochondria Ca2+ transfer via an ER-dependent relay requiring IP3 receptors and the mitochondrial calcium uniporter; moderate TPC2 activation transiently enhances oxidative phosphorylation, while sustained activation increases susceptibility to mitochondrial permeability transition. In stroke models, TPC2 hyperactivation exacerbates injury and acute pharmacological inhibition at reperfusion is neuroprotective.\",\n      \"method\": \"TPC2 pharmacological activation/inhibition, organelle-targeted Ca2+ imaging, IP3R and MCU knockdown epistasis, mitochondrial membrane potential assay, seahorse metabolic assay, stroke models, human iPSC-derived neurons\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods with epistasis (IP3R, MCU), human iPSC neurons, and in vivo validation; preprint status lowers confidence\",\n      \"pmids\": [\"41867847\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"NAADP-dependent TPC2 activity is required for efficient ferroptosis induction in HCC cells; TPC2 loss renders HCC cells resistant to ferroptosis (by system Xc- inhibition or GPX4 blockade), associated with reduced lipid peroxidation, altered Ca2+ signaling, and depletion of polyunsaturated phosphatidylethanolamine species linked to decreased ACSL4 expression.\",\n      \"method\": \"Pharmacological TPC2 modulation, genetic knockout, flow cytometry-based cell death and lipid peroxidation assays, lipidomics, Ca2+ measurement\",\n      \"journal\": \"Antioxidants (Basel, Switzerland)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and pharmacological perturbation, lipidomics, multiple HCC cell lines, single lab\",\n      \"pmids\": [\"42193240\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TPCN2 (TPC2) is a two-pore cation channel resident in lysosomal, endolysosomal, and melanosomal membranes that forms homomers and gates Ca2+ (and, depending on the activating ligand, Na+) release from acidic intracellular stores: NAADP activates Ca2+-permeable, non-selective currents while PI(3,5)P2 activates Na+-selective currents, and co-activation by both ligands acts as a coincidence detector to maximize Ca2+ flux; the channel's sensitivity is modulated by luminal Ca2+ and pH, and it generates high-concentration (~42 µM) local Ca2+ nanodomains that are decoded by specific downstream effectors (e.g., dynamin for phagocytosis, Rab46 for vesicle trafficking, mTOR for autophagy, RyR for Ca2+-induced Ca2+ release); TPC2 thereby controls lysosomal pH homeostasis, lysosomal exocytosis, autophagosome-lysosome fusion, lysosomal iron release, melanosome size and pH, pigmentation (with gain-of-function variants causing hypopigmentation/albinism and loss-of-function increasing melanin), smooth muscle contraction, glucagon secretion, dopaminergic Ca2+ homeostasis, and mitochondrial energetics via a lysosome–ER–mitochondria Ca2+ relay.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TPCN2 (TPC2) is a homomeric cation channel of lysosomal, endolysosomal, and melanosomal membranes that gates Ca2+ release from acidic intracellular stores to control organelle homeostasis, autophagy, exocytosis, and pigmentation [#0, #8, #14]. Single-channel and endolysosomal patch-clamp recordings establish it as a Ca2+-permeable channel activated by low-nanomolar NAADP, with luminal Ca2+ and pH steeply tuning its sensitivity and switching activation between reversible and irreversible modes [#0, #1]. Ligand identity dictates ion selectivity: NAADP drives non-selective, robustly Ca2+-permeable currents whereas PI(3,5)P2 drives Na+-selective currents, and co-activation by both acts as a coincidence detector that synergistically maximizes Ca2+ flux through a single critical pore residue [#14, #20]. By regulating these fluxes TPC2 sets lysosomal pH, protease activity, and exocytosis, controlling autophagosome-lysosome fusion such that overexpression alkalinizes lysosomes and blocks fusion while genetic loss perturbs lysosomal pH and cargo trafficking [#4, #6, #5]. In melanosomes it controls luminal pH, melanosome size, and melanin content, and its activity is modulated by the chloride channel OCA2 [#8, #28]. Human gain-of-function variants (M484L/G734E, the L564P-dependent epistasis, and the de novo R210C and A24V mutations) produce hyperactive channels causing blond hair and dominant albinism, while loss-of-function increases pigmentation in part through GSK3\\u03b2-mediated MITF stabilization [#9, #17, #24, #28, #19]. TPC2-generated local Ca2+ nanodomains (~42 \\u00b5M at the channel mouth) are decoded by specific effectors including dynamin during phagocytosis, Rab46 during Weibel-Palade body trafficking, and the SR/ER RyR for Ca2+-induced Ca2+ release driving smooth muscle contraction and adrenaline-stimulated glucagon secretion [#23, #29, #2, #12]. Through an mTOR-coupled, lysosome-ER-mitochondria Ca2+ relay TPC2 further links autophagy, iron release, lipid peroxidation, and mitochondrial energetics, making it a driver of ferroptosis and a target in lysosomal storage disease, melanoma, leukemia, and LRRK2-G2019S Parkinson's disease [#6, #31, #33, #21, #22, #27].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"Established the founding molecular identity of TPC2 as a lysosomal channel coupling the second messenger NAADP to Ca2+ release from acidic stores, distinct from ER stores.\",\n      \"evidence\": \"Overexpression with lysosomal Ca2+ imaging and pharmacology (NAADP, NADP, lysosomal vs ER store depletion)\",\n      \"pmids\": [\"19557428\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biophysical conductance not yet measured\", \"Endogenous channel behavior not addressed\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined the biophysics and gating logic of the channel, showing NAADP gates a Ca2+-permeable conductance with dual activation/inhibition sites tuned by luminal Ca2+ and pH.\",\n      \"evidence\": \"Single-channel patch-clamp of TPC2 in bilayers/vesicles with Ned-19 pharmacology\",\n      \"pmids\": [\"20720007\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address Na+ permeability or alternative ligands\", \"Pore residues governing selectivity unmapped\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Provided in vivo proof that TPC2-dependent acidic-store Ca2+ release drives a physiological output (smooth muscle contraction) via a genetic knockout.\",\n      \"evidence\": \"Tpcn2\\u2212/\\u2212 mouse detrusor permeabilized contractility with NAADP and store depletion\",\n      \"pmids\": [\"20547763\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream Ca2+ amplification machinery not yet defined\", \"Channel-effector coupling distance unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Connected TPC2 to store-operated Ca2+ entry by showing depletion-dependent association with STIM1/Orai1, hinting at crosstalk between acidic and ER store signaling.\",\n      \"evidence\": \"siRNA, co-IP, surface biotinylation, and SOCE measurements in two cell lines\",\n      \"pmids\": [\"23077736\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab, no reciprocal validation of complex\", \"Mechanism of depletion-induced association unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showed TPC2 governs autophagosome-lysosome fusion through lysosomal pH, establishing a regulatory role in the late autophagy pathway.\",\n      \"evidence\": \"Gain/loss-of-function, pH measurement, ATG5 epistasis, Rab7 localization, lysosomal re-acidification rescue\",\n      \"pmids\": [\"23836916\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether effect requires Ca2+ vs cation flux per se unclear\", \"Largely overexpression-driven\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Clarified TPC2 roles in lysosomal cargo trafficking, protease activity, and autophagy flux, and detected an mTOR association, placing TPC2 within nutrient/autophagy signaling.\",\n      \"evidence\": \"Tpcn2\\u2212/\\u2212 MEFs and muscle (PDGFR\\u03b2 degradation, cholera toxin trafficking, autophagy flux, pH/protease assays, mTOR co-IP)\",\n      \"pmids\": [\"25135478\", \"25480788\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"mTOR interaction not reciprocally validated\", \"Direct vs indirect coupling to mTOR unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Placed TPC2 downstream of pathogenic LRRK2-G2019S, linking exaggerated NAADP/TPC2 Ca2+ signaling to lysosomal dysmorphology in Parkinson's disease cells.\",\n      \"evidence\": \"TPC2 silencing/pharmacology and Ca2+ imaging in patient-derived fibroblasts\",\n      \"pmids\": [\"25416817\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism connecting LRRK2 to TPC2 hyperactivity not defined\", \"Single lab, fibroblast model only\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Localized TPC2 to the melanosome membrane and established its control of melanosome pH, size, and melanin content, founding the pigmentation mechanism.\",\n      \"evidence\": \"CRISPR KO/rescue, immunogold EM, organelle isolation, organelle-targeted pH and Ca2+ sensors, melanin quantification\",\n      \"pmids\": [\"27140606\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream pigmentation effectors not yet identified\", \"Relationship to channel ligands in melanosomes unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Linked human channel-activity variants to a heritable trait, showing two blond-hair polymorphisms confer gain-of-function by independent mechanisms.\",\n      \"evidence\": \"Endolysosomal patch-clamp of variant-carrier fibroblasts plus cohort genotyping\",\n      \"pmids\": [\"28923947\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of each gain-of-function distinct mechanism unresolved\", \"Variant interactions not yet tested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended TPC2 Ca2+ signaling to developmental and differentiation contexts and revealed nanoscale proximity to RyR clusters supporting Ca2+-induced Ca2+ release.\",\n      \"evidence\": \"Zebrafish MO/CRISPR/pharmacology with mRNA and RyR/IP3R agonist rescue and STED microscopy; osteoclast differentiation assays with PI(3,5)P2\",\n      \"pmids\": [\"28390800\", \"29084844\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physical TPC2-RyR coupling mechanism not biochemically defined\", \"Context-dependent (Mg2+) bidirectional effects mechanistically unclear\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined a signaling hierarchy in which TPC2 lies upstream of RyR-mediated CICR during adrenaline-stimulated glucagon secretion, and linked TPC2 to extracellular vesicle secretion and migration.\",\n      \"evidence\": \"Tpc2 KO/pharmacology, electrophysiology, Ca2+/PKA imaging, glucagon assays in mouse and human islets; EV and migration assays with TFEB readout\",\n      \"pmids\": [\"29563152\", \"29990474\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Spatial coupling of TPC2 to SR RyR not directly imaged here\", \"EV/migration mechanism (single lab) less defined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolved the central gating principle that activating ligand dictates ion selectivity through a single pore residue, distinguishing NAADP-driven Ca2+ from PI(3,5)P2-driven Na+ currents.\",\n      \"evidence\": \"High-throughput agonist screen, endolysosomal patch-clamp, site-directed mutagenesis, pH and exocytosis assays\",\n      \"pmids\": [\"32167471\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural conformations underlying selectivity switch not solved\", \"How a single residue toggles selectivity unresolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrated tumor-suppressive consequences of TPC2 loss in melanoma via ORAI1/Ca2+/PKC-\\u03b2II and YAP/TAZ, and tied TPC2 to motor neuron axon Ca2+ signaling.\",\n      \"evidence\": \"CRISPR KO, invasion assay, RNAi epistasis, transcriptomics; zebrafish MO/CRISPR/pharmacology with Ca2+ imaging\",\n      \"pmids\": [\"32846966\", \"32546534\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct link from lysosomal TPC2 to plasma-membrane ORAI1 signaling unclear\", \"ARC1-like\\u2013TPC2 relationship correlative\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established variant epistasis and further pigmentation mechanism, showing L564P is a prerequisite for M484L gain-of-function and that TPC2 controls MITF via GSK3\\u03b2.\",\n      \"evidence\": \"Endolysosomal patch-clamp of polymorphic variants; CRISPR/siRNA/pharmacology with MITF/GSK3\\u03b2 blots and tyrosinase/melanin assays\",\n      \"pmids\": [\"33465068\", \"33875769\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Biophysical basis of L564P permissiveness undefined\", \"Link from channel activity to GSK3\\u03b2 not mechanistically traced\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Validated TPC2 as a cancer-relevant target by showing knockout impairs proliferation, metabolism, and tumor growth, with tetrandrine-analog inhibitors developed.\",\n      \"evidence\": \"CRISPR KO, proliferation/metabolic assays, xenografts, synthesized pharmacological inhibitors\",\n      \"pmids\": [\"33626324\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Metabolic mechanism of TPC2 dependence not fully resolved\", \"Inhibitor selectivity in vivo not exhaustively characterized\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined the coincidence-detector mechanism wherein NAADP and PI(3,5)P2 co-activation synergistically boosts Ca2+ flux independent of selectivity, controlling lysosomal pH and motility.\",\n      \"evidence\": \"Endolysosomal patch-clamp with cell-permeable ligand mimetics and live-cell pH/motility assays\",\n      \"pmids\": [\"35918320\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of synergistic gating unresolved\", \"Physiological contexts of dual ligand co-activation untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated therapeutic leverage of TPC2 activity in disease: small-molecule activation rescues lysosomal storage disease pathology, while loss sensitizes drug-resistant leukemia to chemotherapy.\",\n      \"evidence\": \"Pharmacological TPC2-A1-P in iPSC/patient fibroblasts and MLIV mice; CRISPR KO and inhibitors with drug accumulation, DNA damage, and lysosomal death readouts in leukemia\",\n      \"pmids\": [\"35929194\", \"35915060\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How activation simultaneously promotes exocytosis and corrects multiple LSDs mechanistically unresolved\", \"Generalizability across tumor types untested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Quantified channel-proximal Ca2+ nanodomains and established effector-specific decoding, showing ~42 \\u00b5M local Ca2+ couples TPC2 to dynamin during phagocytosis with autonomy from co-resident TRPML1.\",\n      \"evidence\": \"GECI fused to TPC2 with calibrated nanodomain optical recording in macrophage phagocytosis\",\n      \"pmids\": [\"37742482\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How insulation between TPC2 and TRPML1 domains is maintained unknown\", \"Physical basis of dynamin recruitment not defined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identified a de novo gain-of-function mutation (R210C) causing dominant albinism through constitutive activation and increased PI(3,5)P2 affinity, with a knock-in mouse phenocopy.\",\n      \"evidence\": \"Inside-out and enlarged-vacuole patch-clamp, R194C knock-in mice, pH and EM phenotyping\",\n      \"pmids\": [\"36641477\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural mechanism of constitutive opening unresolved\", \"Why hyperactivation reduces pigmentation despite hyper-acidification unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended TPC2's pathological role to ischemia, showing inhibition reduces ER stress and autophagic flux and is neuroprotective in stroke.\",\n      \"evidence\": \"siRNA, Ned-19 with NAADP-AM rescue, OGD/R neurons, rat tMCAO, blots and Ca2+ imaging\",\n      \"pmids\": [\"36708960\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal chain from TPC2 to ER stress not fully dissected\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established structure-function requirements for TPC2 in LRRK2-G2019S dopaminergic dysfunction, showing pore integrity, targeting, and Rab interactivity are all required and a biased agonist corrects pathology.\",\n      \"evidence\": \"Ca2+ imaging in dopaminergic neurons, Drosophila human-TPC2 reconstitution, structure-function mutants, biased agonist\",\n      \"pmids\": [\"40279672\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the relevant Rab interactor not defined here\", \"How LRRK2 amplifies TPC2 Ca2+ entry mechanistically open\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified physiological regulators and effectors of TPC2: OCA2-derived chloride modulates channel activity (digenic albinism), and TPC2 Ca2+ drives Rab46-dependent Weibel-Palade body trafficking for Ang2 secretion.\",\n      \"evidence\": \"Patch-clamp with Cl- manipulation, CRISPR KO/knock-in mice; Ca2+ imaging and pharmacology with Ang2 secretion readout (preprint for WPB study)\",\n      \"pmids\": [\"41443368\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct OCA2-TPC2 physical interaction not established\", \"Rab46 recruitment mechanism by Ca2+ nanodomains undefined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Linked TPC2 to drug-induced TFEB/autophagy activation and to lysosomal iron release driving ferroptosis, placing TPC2 downstream of V-ATPase-mTOR.\",\n      \"evidence\": \"Patch-clamp with chlorpromazine/clomipramine, TFEB/ULK/AMPK readouts and siTPC2 in neurons; OGSD-R and IR models with iron assays and mTOR perturbation\",\n      \"pmids\": [\"40796055\", \"40379157\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether iron permeates TPC2 directly or via secondary release unresolved\", \"Single-lab mechanistic dissection\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Defined a lysosome-ER-mitochondria Ca2+ relay through which TPC2 tunes mitochondrial energetics and ferroptosis sensitivity.\",\n      \"evidence\": \"Pharmacological TPC2 modulation, organelle-targeted Ca2+ imaging, IP3R/MCU epistasis, metabolic and stroke assays, iPSC neurons (preprint); NAADP-TPC2 dependence of HCC ferroptosis with lipidomics\",\n      \"pmids\": [\"41867847\", \"42193240\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physical lysosome-ER-mitochondria contact architecture undefined\", \"ACSL4/PUFA-PE regulation downstream of TPC2 Ca2+ not mechanistically traced\", \"One study is a preprint\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single pore residue toggles ligand-dependent selectivity, how distinct effectors (dynamin, Rab46, RyR, mTOR) are physically recruited to channel-proximal Ca2+ nanodomains, and the structural basis of gain-of-function disease variants remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution structure linking gating, selectivity, and ligand sites in the timeline\", \"Physical recruitment mechanism for each downstream effector undefined\", \"Architecture of inter-organelle Ca2+ relay contacts uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1, 14, 20, 24]},\n      {\"term_id\": \"GO:0005262\", \"supporting_discovery_ids\": [0, 1, 14]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [1, 14, 20]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [14, 20, 24]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [0, 4, 6, 22, 23, 31]},\n      {\"term_id\": \"GO:0005765\", \"supporting_discovery_ids\": [9, 14, 17, 24]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [5, 7, 24]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [4, 6, 13, 26, 30]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [5, 13, 14, 29]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [22, 31, 33]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 12, 27]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [18, 31, 32]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"STIM1\", \"ORAI1\", \"MTOR\", \"RYR\", \"OCA2\", \"RAB46\", \"RAB7\", \"DNM\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}