{"gene":"PLA2G6","run_date":"2026-04-28T19:45:44","timeline":{"discoveries":[{"year":1999,"finding":"Human PLA2G6 (iPLA2β) gene on chromosome 22q13.1 produces two catalytically active isoforms (85-kDa short and 88-kDa long) via exon-skipping alternative splicing of exon 8; both are active without Ca2+ and inhibited by bromoenol lactone, but only the long isoform is activated by ATP.","method":"cDNA cloning from human pancreatic islets, recombinant protein expression, in vitro phospholipase assay, alternative splicing analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstitution of recombinant proteins with in vitro enzymatic assays and molecular characterization","pmids":["10092647"],"is_preprint":false},{"year":2001,"finding":"iPLA2β (PLA2G6) amplifies glucose-stimulated insulin secretion in pancreatic β-cells; cAMP-elevating agents promote translocation of iPLA2β to perinuclear/nuclear compartments, consistent with a signaling rather than housekeeping role.","method":"Stable overexpression in INS-1 insulinoma cells, insulin secretion assay, immunocytofluorescence, BEL inhibitor studies","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (overexpression, pharmacological inhibition, imaging) in same study","pmids":["11278673"],"is_preprint":false},{"year":2002,"finding":"iPLA2β (PLA2G6), but not iPLA2γ, mediates arginine vasopressin-induced arachidonic acid release from A-10 smooth muscle cells, demonstrated using enantioselective inhibitors (S-BEL selective for iPLA2β, R-BEL selective for iPLA2γ).","method":"Enantioselective BEL inhibition in intact A-10 cells, arachidonic acid release assay, chiral HPLC separation of BEL enantiomers","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — mechanistic discrimination using enantioselective inhibitors with IC50 quantification","pmids":["12089145"],"is_preprint":false},{"year":2002,"finding":"Stimulation of insulin secretion promotes time-dependent nuclear accumulation of iPLA2β in INS-1 cells; nuclear accumulation correlates with increased nuclear iPLA2β enzymatic activity and is attenuated by inhibitors of protein phosphorylation and glycosylation.","method":"Immunofluorescence, immunoaffinity fractionation, enzymatic activity assay in nuclear fractions, pharmacological inhibition","journal":"American journal of physiology. Endocrinology and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 — multiple methods but single lab","pmids":["11882502"],"is_preprint":false},{"year":2003,"finding":"Pancreatic islets and 832/13 INS-1 insulinoma cells express a novel ~70 kDa isoform of iPLA2β not generated by alternative splicing, which retains catalytic activity and participates in insulin secretion but not membrane phospholipid remodeling.","method":"Western blotting, mass spectrometry of tryptic peptides, BEL inhibition of insulin secretion, arachidonic acid incorporation assay","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — mass spectrometry peptide identification plus functional enzyme and secretion assays","pmids":["14636061"],"is_preprint":false},{"year":2004,"finding":"ER stress-induced apoptosis of insulin-secreting cells is amplified by iPLA2β overexpression and suppressed by BEL inhibition; ER stress activates iPLA2β, causes its perinuclear accumulation, and triggers caspase-3-mediated cleavage of 84 kDa iPLA2β to a 62 kDa nuclear fragment; ceramide accumulation is also iPLA2β-dependent.","method":"INS-1 cell overexpression, BEL inhibition, caspase activity assay, immunofluorescence, ceramide measurement","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including proteolytic processing identification and subcellular localization with functional consequence","pmids":["14744135"],"is_preprint":false},{"year":2004,"finding":"FcγRI activation in human monocytic U937 cells couples specifically to iPLA2β (not cPLA2α) for arachidonic acid release and generation of leukotriene B4 and prostaglandin E2; iPLA2β activation in this pathway is protein kinase C-dependent.","method":"BEL inhibition, siRNA/antisense knockdown, arachidonic acid release assay, eicosanoid measurement","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological and genetic inhibition with defined lipid mediator readouts","pmids":["15007079"],"is_preprint":false},{"year":2005,"finding":"ER-localized iPLA2 activity in kidney, heart, and brain microsomes is attributable to iPLA2γ (group VIB), not iPLA2β, based on isoform-selective BEL enantiomers and immunoblot analysis.","method":"Subcellular fractionation, iPLA2 activity assay, immunoblotting, RT-PCR, BEL enantiomer inhibition","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — distinguishes iPLA2β from γ at the ER using multiple methods, single lab","pmids":["15629460"],"is_preprint":false},{"year":2006,"finding":"Mitochondrial Ca2+-independent phospholipase A2 (iPLA2β) is activated during sustained mitochondrial membrane depolarization and Ca2+ accumulation; sustained activity promotes outer mitochondrial membrane rupture and spontaneous cytochrome c release; BEL inhibition of this phospholipase attenuates the mitochondrial permeability transition.","method":"Isolated mitochondria, membrane potential measurement, BEL inhibition, cytochrome c release assay, permeability transition pore assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with isolated mitochondria plus pharmacological intervention","pmids":["16407316"],"is_preprint":false},{"year":2007,"finding":"iPLA2β (PLA2G6) plays a pivotal role in angiotensin II-induced transcriptional upregulation of RGS2 in vascular smooth muscle cells; both arachidonic acid and lysophosphatidylcholine (products of iPLA2β) induce RGS2 mRNA, and the pathway is abolished by pharmacological inhibition, antisense knockdown, or genetic deletion of iPLA2β.","method":"BEL inhibition, antisense oligonucleotides, iPLA2β-null mice VSMCs, adenoviral re-expression, RGS2 mRNA/protein measurement, iPLA2 enzymatic activity assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — three independent approaches (pharmacological, genetic KO, reconstitution by adenovirus) with consistent results","pmids":["17613534"],"is_preprint":false},{"year":2007,"finding":"iPLA2β (PLA2G6) overexpression in pancreatic β-cells in vivo lowers blood glucose and amplifies glucose-induced insulin secretion; iPLA2β-null islets show blunted insulin secretion and impaired glucose tolerance; iPLA2β reduces Kv2.1 delayed rectifier current and prolongs glucose-induced action potentials and cytosolic Ca2+ elevations.","method":"Transgenic RIP-iPLA2β mice, iPLA2β-null mice, glucose tolerance test, patch-clamp electrophysiology, Ca2+ imaging, insulin secretion assay","journal":"American journal of physiology. Endocrinology and metabolism","confidence":"High","confidence_rationale":"Tier 1-2 — gain- and loss-of-function in vivo models with electrophysiological mechanism","pmids":["17895289"],"is_preprint":false},{"year":2008,"finding":"ER stress induces iPLA2β accumulation in mitochondria, opening of mitochondrial permeability transition pore, and loss of mitochondrial membrane potential in INS-1 cells; iPLA2β-mediated ceramide generation via sphingomyelin hydrolysis mediates mitochondrial dysfunction and cytochrome c release in the apoptotic cascade.","method":"Subcellular fractionation, mitochondrial membrane potential assay, cytochrome c release, ceramide measurement, iPLA2β overexpression, BEL and NSMase inhibition","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods establishing subcellular localization and mechanism in same study","pmids":["18936091"],"is_preprint":false},{"year":2010,"finding":"Human PLA2G6 enzyme hydrolyzes both phospholipids and lysophospholipids to release free fatty acids; INAD/NBIA mutations cause loss of enzymatic activity (<20% of WT), while dystonia-parkinsonism mutations do not impair catalytic activity and two produce increased specific activity for phospholipid substrates.","method":"Purified recombinant WT and mutant human PLA2G6, in vitro phospholipase and lysophospholipase assays with radiolabeled lipid substrates","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro enzymatic assay with purified recombinant proteins and multiple disease-associated mutants","pmids":["20886109"],"is_preprint":false},{"year":2010,"finding":"iPLA2β undergoes endogenous proteolytic processing to generate N-terminally truncated isoforms that localize differentially to subcellular organelles; secretagogues and ER stress promote differential redistribution of iPLA2β variants among subcellular compartments.","method":"EGFP fusion protein stable expression, dual fluorescence organelle tracking, immunoblotting, mass spectrometry of N-terminal variants","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 — mass spectrometry identification of processing plus live-cell localization, single lab","pmids":["20132906"],"is_preprint":false},{"year":2010,"finding":"iPLA2β deficiency in mice reduces brain DHA metabolism and DHA-dependent signaling in vivo at baseline and following muscarinic M1,3,5 receptor activation, consistent with iPLA2β selectively hydrolyzing DHA from phospholipids.","method":"iPLA2β-/- and +/- mice, intravenous [1-14C]DHA infusion, quantitative autoradiography of 81 brain regions, cholinergic agonist challenge","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 2 — in vivo imaging with genetic KO and pharmacological challenge, quantitative across 81 brain regions","pmids":["20686114"],"is_preprint":false},{"year":2015,"finding":"Knockout of the Drosophila PLA2G6 homolog iPLA2-VIA causes mitochondrial respiratory chain dysfunction, reduced ATP synthesis, abnormal mitochondrial morphology, and elevated mitochondrial lipid peroxidation; similar mitochondrial lipid peroxidation and membrane defects occur in fibroblasts from PLA2G6-mutant patients; deuterated PUFAs that inhibit lipid peroxidation partially rescue locomotor deficits.","method":"Drosophila iPLA2-VIA knockout, respirometry, ATP assay, electron microscopy, lipid peroxidation assay, patient fibroblast analysis, pharmacological rescue with deuterated PUFAs","journal":"Brain : a journal of neurology","confidence":"High","confidence_rationale":"Tier 2 — fly KO + patient fibroblast validation + pharmacological rescue with multiple orthogonal readouts","pmids":["26001724"],"is_preprint":false},{"year":2015,"finding":"iPLA2β modulates Bcl-x pre-mRNA 5'-splice site selection to suppress anti-apoptotic Bcl-xL in β-cells; iPLA2β inactivation or knockdown augments the Bcl-xL/Bcl-xS ratio, whereas iPLA2β overexpression reduces it; the bioactive lipid 5(S)-HETE augments Bcl-xL/Bcl-xS by 15.5-fold.","method":"Chemical inactivation and siRNA knockdown of iPLA2β, transgenic and KO mouse islets, Bcl-x splice isoform quantitation by RT-PCR, exogenous lipid treatments","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — multiple genetic and pharmacological approaches in islets and cell lines, single lab","pmids":["25762722"],"is_preprint":false},{"year":2015,"finding":"In PLA2G6 knockout mice, mitochondria with damaged inner membranes appear early in neurons and move anterogradely into distal axons; inner mitochondrial membrane degeneration precedes axonal spheroid formation; presynaptic membrane abnormalities also develop, leading to axon terminal degeneration containing tubulovesicular structures.","method":"PLA2G6 KO mouse neuropathology, electron microscopy, immunohistochemistry, axonal transport analysis","journal":"Neuropathology : official journal of the Japanese Society of Neuropathology","confidence":"Medium","confidence_rationale":"Tier 2 — detailed ultrastructural analysis in genetic KO model with temporal progression","pmids":["25950622"],"is_preprint":false},{"year":2016,"finding":"PLA2G6 deficiency impairs store-operated Ca2+ entry signaling; genetic or molecular impairment of PLA2G6-dependent Ca2+ signaling triggers autophagic dysfunction and progressive loss of dopaminergic neurons in substantia nigra pars compacta; this sequence is recapitulated in a Pla2g6 exon2 knockout mouse model.","method":"Patient-derived cells (idiopathic PD), PLA2g6 exon2 KO mouse, Ca2+ imaging, autophagy assays, dopaminergic neuron counting, L-DOPA behavioral rescue","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — human patient cells corroborated by genetic mouse model with mechanistic pathway (Ca2+ → autophagy → neurodegeneration)","pmids":["26755131"],"is_preprint":false},{"year":2016,"finding":"PLA2G6 deficiency causes elevated α-synuclein expression in neurons; phosphorylated α-synuclein accumulates in mitochondrial outer membrane-positive (TOM20+) granules in PLA2G6-KO mice; α-synuclein localizes to degenerated inner mitochondrial membranes, suggesting a role in stabilizing damaged mitochondrial membranes.","method":"PLA2G6 KO mouse, PLA2G6 knockdown cells, immunohistochemistry with TOM20 co-staining, immunofluorescence, electron microscopy, quantitative Lewy body analysis in PLAN and PD patients","journal":"Acta neuropathologica communications","confidence":"Medium","confidence_rationale":"Tier 2 — KO mouse and patient tissue with multiple markers, single lab","pmids":["27030050"],"is_preprint":false},{"year":2018,"finding":"Loss of iPLA2-VIA (Drosophila PLA2G6 homolog) does not alter phospholipid composition of brain tissue but causes elevation in ceramide levels; iPLA2-VIA physically binds retromer subunits Vps35 and Vps26, enhancing retromer function to promote protein and lipid recycling; loss of iPLA2-VIA impairs retromer function, progressively increasing ceramide levels that in turn impair membrane fluidity and retromer function in a positive feedback loop.","method":"Drosophila iPLA2-VIA KO, lipidomics, co-immunoprecipitation of Vps35/Vps26, pharmacological ceramide reduction (myriocin, desipramine), genetic epistasis with vps26/vps35 mutants","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 1-2 — co-IP of retromer binding, lipidomics, genetic epistasis, and pharmacological rescue in same study","pmids":["29909971"],"is_preprint":false},{"year":2018,"finding":"PARK14 mutant PLA2G6 proteins (D331Y, G517C, T572I, R632W, N659S, R741Q) fail to prevent rotenone-induced mitochondrial membrane potential loss, mitochondrial superoxide increase, complex I activity reduction, mitophagy impairment, and cytochrome c release, while WT PLA2G6 rescues all these defects.","method":"SH-SY5Y cell overexpression of WT and mutant PLA2G6, rotenone model, mitochondrial membrane potential assay, ROS measurement, complex I activity assay, ATP measurement, cytochrome c release, mitophagy markers","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 — multiple mitochondrial readouts with multiple disease mutants, single lab","pmids":["29108286"],"is_preprint":false},{"year":2019,"finding":"iPLA2-VIA loss in Drosophila shortens acyl-chain length of phospholipids, causing ER stress through membrane lipid disequilibrium; WT human iPLA2-VIA or the mitochondria-ER contact site protein C19orf12 rescue altered lipid composition, ER stress, and DA neurodegeneration; disease-associated iPLA2-VIA A80T mutant fails to rescue; linoleic acid supplementation corrects brain lipid composition and suppresses α-synuclein aggregation caused by iPLA2-VIA loss.","method":"Drosophila iPLA2-VIA KO, lipid analysis by mass spectrometry, ER stress markers, DA neuron counting, transgenic rescue with WT and A80T mutant, linoleic acid supplementation","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — lipidomics + ER stress + genetic rescue + disease mutant comparison + pharmacological rescue","pmids":["31548400"],"is_preprint":false},{"year":2020,"finding":"PLA2G6 (iPLA2β/PNPLA9) metabolizes hydroperoxy-arachidonoyl- and adrenoyl-phosphatidylethanolamine (Hp-PE) to lyso-PE and oxidized fatty acid, attenuating ferroptotic injury; PLA2G6 protects human trophoblasts and mouse placenta from ferroptosis induced by GPX4 inhibition or hypoxia/reoxygenation.","method":"Primary human trophoblast cultures, mouse pregnancy model, GPX4 inhibitor (RSL3), hypoxia/reoxygenation, lipid mass spectrometry, PLA2G6 knockdown","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro and in vivo models with lipidomic substrate identification and genetic knockdown","pmids":["33087576"],"is_preprint":false},{"year":2021,"finding":"iPLA2β (PLA2G6) hydrolyzes 15-HpETE-PE (the ferroptotic death signal generated by 15-LOX/PEBP1 complex) to avert ferroptosis; genetic or pharmacological inactivation of iPLA2β sensitizes cells to ferroptosis; patient fibroblasts with PD-associated mutation (R747W) show selectively decreased 15-HpETE-PE-hydrolyzing activity and elevated 15-HpETE-PE; Pnpla9 R748W knock-in mice develop progressive parkinsonian motor deficits with 15-HpETE-PE accumulation.","method":"Lipidomics (15-HpETE-PE quantification), CRISPR-Cas9 knock-in mouse (R748W), patient fibroblast assays, genetic and pharmacological iPLA2β inactivation, rotenone rat and SncaA53T mouse models","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1 — substrate identified by lipidomics, enzymatic activity in patient cells, CRISPR knock-in mouse model with motor phenotype, replicated in multiple animal models","pmids":["33542532"],"is_preprint":false},{"year":2021,"finding":"iPLA2β (PLA2G6) acts as a major ferroptosis repressor independent of GPX4 by detoxifying peroxidized lipids; iPLA2β-mediated removal of oxidized acyl tails from phospholipids suppresses p53-driven ferroptosis under ROS stress; iPLA2β loss has no obvious effect on normal development but is essential for regulating ferroptosis upon ROS-induced stress.","method":"GPX4-null cells, iPLA2β overexpression and inhibition, p53-driven ferroptosis assay, xenograft tumor model, lipid peroxidation measurement","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 — GPX4-null cells isolate iPLA2β mechanism, xenograft in vivo model, multiple cancer cell lines","pmids":["34131139"],"is_preprint":false},{"year":2015,"finding":"PLA2G6 loss causes disruption of Golgi morphology and defects in protein O-linked glycosylation and sialylation in patient fibroblasts; lentiviral re-expression of WT PLA2G6 rescues these Golgi and glycosylation abnormalities.","method":"Patient fibroblast cultures (INAD and dystonia-parkinsonism), HPLC and MALDI-TOF/MS glycosylation analysis, immunofluorescence of Golgi morphology, lentiviral WT PLA2G6 rescue","journal":"Journal of medical genetics","confidence":"Medium","confidence_rationale":"Tier 2 — functional rescue with WT protein plus multiple analytical methods, single lab","pmids":["26668131"],"is_preprint":false},{"year":2008,"finding":"iPLA2β (PLA2G6)-null mice show accelerated age-related bone loss associated with increased bone marrow adipogenesis and decreased osteogenesis; bone marrow stromal cells from KO mice express higher PPARγ and lower Runx2 mRNA, indicating that iPLA2β regulates mesenchymal stem cell lineage commitment.","method":"iPLA2β-null mice, bone morphometry, bone strength testing, osteoclast/osteoblast quantification, BMSC differentiation assays, gene expression analysis","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with multiple skeletal phenotypic readouts and molecular mechanism, single lab","pmids":["18349124"],"is_preprint":false},{"year":2008,"finding":"iPLA2β activity is required for skeletal muscle fatty acid oxidation through an acyl-CoA thioesterase activity (distinct from its phospholipase activity) that liberates CoA-SH to facilitate fatty acid transport into mitochondria; iPLA2β-null mice show reduced palmitate oxidation and reduced acyl-CoA thioesterase activity.","method":"iPLA2β-null mice, palmitate oxidation assay, palmitoyl-CoA and acetyl-CoA oxidation assays, ATP and calmodulin column chromatography, BEL inhibition of thioesterase activity","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — novel enzymatic activity identified with genetic KO and biochemical fractionation, single lab","pmids":["18937505"],"is_preprint":false},{"year":2017,"finding":"PLA2G6 protein accumulates in the cores of brainstem-type Lewy bodies in PARK14 and idiopathic Parkinson's disease patients, but not in cortical Lewy bodies, multiple system atrophy, or Alzheimer's disease.","method":"Immunohistochemistry and immunoblotting on post-mortem brain tissue from PARK14, idiopathic PD, DLB, MSA, and AD","journal":"Neuroscience letters","confidence":"Medium","confidence_rationale":"Tier 3 — direct localization in human tissue with disease-specificity, single lab","pmids":["28213071"],"is_preprint":false},{"year":2009,"finding":"A point mutation in the ankyrin repeat domain of Pla2g6 (generated by ENU mutagenesis in mice) produces a protein with no glycerophospholipid-catalyzing enzyme activity and causes early-onset (7-8 weeks) INAD with widespread spheroid formation containing tubulovesicular membranes, demonstrating that loss of catalytic activity is sufficient for disease.","method":"ENU mutagenesis mouse model, neuropathology with electron microscopy, biochemical assay of iPLA2β enzyme activity","journal":"The American journal of pathology","confidence":"High","confidence_rationale":"Tier 1-2 — point mutation knock-in with biochemical activity measurement and neuropathological validation","pmids":["19893029"],"is_preprint":false},{"year":2018,"finding":"PARK14 D331Y knockin mice develop early-onset degeneration of substantia nigra dopaminergic neurons with Lewy body pathology, mitochondrial cristae disruption, mitochondrial dysfunction, elevated ROS, ER stress (upregulated GRP78, IRE1, PERK, CHOP), and impaired mitophagy (reduced parkin and BNIP3).","method":"PLA2G6 D331Y/D331Y knockin mouse, dopaminergic neuron counting, electron microscopy, mitochondrial membrane potential, ROS measurement, ER stress protein immunoblot, mitophagy protein expression, behavioral testing","journal":"Molecular neurobiology","confidence":"High","confidence_rationale":"Tier 2 — knockin mouse with multiple orthogonal mechanistic readouts demonstrating convergent pathways","pmids":["30088174"],"is_preprint":false},{"year":2021,"finding":"iPLA2β translocates to the ER upon myocardial ischemia/reperfusion injury; this translocation promotes ER stress and cardiomyocyte apoptosis; iPLA2β knockout or siRNA knockdown ameliorates ER stress and decreases cell death during I/R.","method":"iPLA2β KO mice, siRNA knockdown, I/R model in vivo and in vitro, cell surface protein biotinylation, immunofluorescence localization, ER stress markers, apoptosis assays","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 — localization to ER upon stress with genetic KO confirmation and functional consequence, single lab","pmids":["34207793"],"is_preprint":false}],"current_model":"PLA2G6 encodes a Ca2+-independent phospholipase A2 (iPLA2β) that cleaves acyl chains (preferentially oxidized/peroxidized fatty acids including 15-HpETE-PE and DHA) from the sn-2 position of glycerophospholipids, generating free fatty acids and lysophospholipids; it also possesses acyl-CoA thioesterase activity; it functions in membrane phospholipid remodeling, mitochondrial membrane integrity maintenance, ER function, retromer-mediated lipid recycling (via direct binding to Vps35/Vps26), store-operated Ca2+ entry signaling, insulin secretion amplification in β-cells, and ferroptosis suppression by eliminating peroxidized phospholipid death signals, with disease-causing mutations in the INAD/NBIA spectrum abolishing catalytic activity while dystonia-parkinsonism mutations selectively impair 15-HpETE-PE hydrolysis and alter substrate preferences without globally eliminating activity."},"narrative":{"teleology":[{"year":1999,"claim":"Molecular cloning established that PLA2G6 encodes a Ca²⁺-independent phospholipase A2 with two catalytically active splice isoforms differing in ATP responsiveness, defining the enzyme's fundamental identity and regulatory properties.","evidence":"cDNA cloning from human pancreatic islets with recombinant protein expression and in vitro phospholipase assays","pmids":["10092647"],"confidence":"High","gaps":["Three-dimensional structure not determined","Endogenous substrate specificity in vivo not yet defined","Oligomeric state and regulation by ankyrin repeats not characterized"]},{"year":2001,"claim":"Demonstration that iPLA2β amplifies glucose-stimulated insulin secretion and translocates to perinuclear compartments upon cAMP signaling established a regulated signaling role beyond housekeeping phospholipid remodeling.","evidence":"Overexpression in INS-1 cells, BEL inhibition, immunocytofluorescence, and insulin secretion assays","pmids":["11278673","11882502"],"confidence":"High","gaps":["Identity of lipid mediators linking iPLA2β to secretory machinery unknown","Mechanism of cAMP-induced translocation unresolved"]},{"year":2002,"claim":"Enantioselective inhibitor studies discriminated iPLA2β from iPLA2γ in intact cells, showing iPLA2β specifically mediates receptor-coupled arachidonic acid release in smooth muscle, establishing isoform-selective signaling.","evidence":"S-BEL vs R-BEL enantiomers in A-10 cells with arachidonic acid release measurement","pmids":["12089145"],"confidence":"High","gaps":["Downstream eicosanoid products of iPLA2β-released AA in smooth muscle not fully mapped","Whether iPLA2γ compensates in iPLA2β absence not tested"]},{"year":2006,"claim":"Identification that iPLA2β activates during mitochondrial membrane depolarization and promotes outer membrane rupture and cytochrome c release revealed a direct role in mitochondrial permeability transition, linking the enzyme to apoptotic signaling.","evidence":"Isolated mitochondria assays with BEL inhibition, membrane potential measurement, and cytochrome c release","pmids":["16407316","18936091"],"confidence":"High","gaps":["Whether iPLA2β acts on specific mitochondrial phospholipid species (e.g., cardiolipin) not determined","Mechanism of iPLA2β activation by depolarization unknown"]},{"year":2007,"claim":"Gain- and loss-of-function mouse models proved iPLA2β amplifies insulin secretion in vivo by suppressing Kv2.1 currents and prolonging Ca²⁺ oscillations, defining an electrophysiological mechanism for its β-cell function.","evidence":"RIP-iPLA2β transgenic and iPLA2β-null mice with patch-clamp electrophysiology, Ca²⁺ imaging, and glucose tolerance tests","pmids":["17895289"],"confidence":"High","gaps":["Specific lipid mediator that modulates Kv2.1 not identified","Whether this mechanism operates in human islets not confirmed"]},{"year":2008,"claim":"Discovery of an acyl-CoA thioesterase activity distinct from phospholipase activity expanded iPLA2β's enzymatic repertoire and linked it to mitochondrial fatty acid oxidation in skeletal muscle.","evidence":"iPLA2β-null mice with palmitate oxidation assays and chromatographic separation of thioesterase activity","pmids":["18937505"],"confidence":"Medium","gaps":["Structural basis for dual enzymatic activities not resolved","Relative contribution of thioesterase vs phospholipase activity in different tissues unknown","Not independently replicated"]},{"year":2009,"claim":"An ENU-generated point mutation in the ankyrin repeat domain that abolished catalytic activity was sufficient to produce INAD with tubulovesicular spheroids, proving that loss of enzymatic function—not a structural scaffolding defect—drives disease.","evidence":"ENU mutagenesis mouse with neuropathology, electron microscopy, and biochemical activity assay","pmids":["19893029"],"confidence":"High","gaps":["Whether ankyrin repeat mutations also disrupt protein-protein interactions not tested","Specific lipid substrates accumulating in INAD not identified"]},{"year":2010,"claim":"Biochemical analysis of disease-associated mutations revealed a genotype-activity correlation: INAD/NBIA mutations ablate catalytic activity while dystonia-parkinsonism mutations preserve or even increase it, suggesting distinct pathomechanisms for the two disease spectra.","evidence":"Purified recombinant WT and mutant PLA2G6 with in vitro phospholipase and lysophospholipase assays","pmids":["20886109"],"confidence":"High","gaps":["Substrate specificity differences between dystonia-parkinsonism mutants not yet explored with oxidized lipid substrates","In vivo lipid profiles of dystonia-parkinsonism mutants not determined"]},{"year":2015,"claim":"Cross-species studies in Drosophila and patient fibroblasts established that PLA2G6 loss causes mitochondrial respiratory chain dysfunction, elevated lipid peroxidation, and Golgi/glycosylation defects, with deuterated PUFAs providing partial rescue—identifying lipid peroxidation as a druggable pathogenic driver.","evidence":"Drosophila iPLA2-VIA KO with respirometry, patient fibroblasts with glycosylation analysis, and deuterated PUFA rescue","pmids":["26001724","26668131"],"confidence":"High","gaps":["Whether Golgi defects are secondary to lipid peroxidation or an independent pathway unclear","Mechanism by which PLA2G6 maintains Golgi morphology not defined"]},{"year":2016,"claim":"Demonstration that PLA2G6 deficiency impairs store-operated Ca²⁺ entry, causing autophagic dysfunction and progressive dopaminergic neuron loss, established a Ca²⁺ signaling–autophagy axis as a central pathogenic mechanism in PLA2G6-associated parkinsonism.","evidence":"Patient-derived cells and Pla2g6 exon2 KO mouse with Ca²⁺ imaging, autophagy assays, and dopaminergic neuron counting","pmids":["26755131"],"confidence":"High","gaps":["Molecular mechanism by which iPLA2β regulates SOCE channels not identified","Whether Ca²⁺ and ferroptosis pathways converge or operate independently unknown"]},{"year":2018,"claim":"Discovery that iPLA2β physically binds retromer subunits Vps35/Vps26 and that its loss triggers a ceramide-driven positive feedback loop impairing retromer function revealed a non-enzymatic scaffolding role in membrane trafficking.","evidence":"Drosophila iPLA2-VIA KO with co-immunoprecipitation, lipidomics, genetic epistasis with vps26/vps35, and pharmacological ceramide reduction","pmids":["29909971"],"confidence":"High","gaps":["Whether the retromer interaction requires iPLA2β catalytic activity not determined","Binding interface between iPLA2β and retromer not mapped","Whether this interaction occurs in mammalian neurons not confirmed"]},{"year":2019,"claim":"Lipidomic analysis showed iPLA2-VIA loss shortens phospholipid acyl chains causing ER stress, and that linoleic acid supplementation corrects lipid composition and suppresses α-synuclein aggregation, directly linking membrane lipid remodeling to synucleinopathy.","evidence":"Drosophila KO with mass spectrometry lipidomics, ER stress markers, transgenic rescue with WT vs A80T mutant, and linoleic acid supplementation","pmids":["31548400"],"confidence":"High","gaps":["Whether acyl-chain shortening occurs in mammalian PLA2G6-deficient neurons not confirmed","Mechanism by which altered lipid composition promotes α-synuclein aggregation not defined"]},{"year":2021,"claim":"Identification of 15-HpETE-PE as the specific ferroptotic substrate of iPLA2β, and demonstration that the PD-associated R747W mutation selectively impairs its hydrolysis causing 15-HpETE-PE accumulation and parkinsonian motor deficits in knock-in mice, unified the ferroptosis-suppression and neurodegeneration functions into a single molecular mechanism.","evidence":"Lipidomics, CRISPR knock-in R748W mouse, patient fibroblast enzymatic assays, GPX4-null cell models, and xenograft tumor models","pmids":["33542532","34131139","33087576"],"confidence":"High","gaps":["Whether ferroptosis is the dominant cell death mode in all PLA2G6-associated diseases or only in parkinsonism not resolved","Structural basis for substrate selectivity of PD mutants unknown","Therapeutic window for ferroptosis inhibitors in PLA2G6 disease not established"]},{"year":null,"claim":"Key unresolved questions include the structural basis for iPLA2β's dual enzymatic activities and substrate selectivity, the precise relationship between its retromer-binding, Ca²⁺-signaling, and anti-ferroptotic functions in dopaminergic neurons, and whether these represent parallel or convergent pathogenic axes.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No crystal structure of full-length iPLA2β available","Relative contribution of ferroptosis vs autophagy vs ER stress to neurodegeneration not delineated","No therapeutic strategy validated in human PLA2G6-associated disease"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,2,12,14,23,24]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[23,24,22]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[10,18,25]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[8,11,15,17,21,31]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[22,32]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1,3,5]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[26]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,9]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,2,14,22,23,24,28]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[5,8,11,24,25]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[18,21]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,10,18]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[20]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[5,22,31,32]}],"complexes":["retromer (via Vps35/Vps26 binding)"],"partners":["VPS35","VPS26","KCNB1"],"other_free_text":[]},"mechanistic_narrative":"PLA2G6 encodes calcium-independent phospholipase A2β (iPLA2β), a multifunctional lipid-metabolizing enzyme that cleaves sn-2 acyl chains—with preference for oxidized and polyunsaturated fatty acids including 15-HpETE-PE and DHA—from glycerophospholipids and also possesses acyl-CoA thioesterase activity, serving as a critical guardian of membrane lipid homeostasis and a major suppressor of ferroptosis [PMID:10092647, PMID:33542532, PMID:18937505]. iPLA2β maintains mitochondrial inner membrane integrity, supports retromer-mediated lipid and protein recycling through direct interaction with Vps35/Vps26, regulates store-operated Ca²⁺ entry, and modulates ER stress responses; its loss leads to ceramide accumulation, mitochondrial cristae degeneration, impaired autophagy, and progressive neurodegeneration [PMID:29909971, PMID:26755131, PMID:25950622, PMID:16407316]. In pancreatic β-cells, iPLA2β amplifies glucose-stimulated insulin secretion by suppressing Kv2.1 delayed rectifier currents and prolonging Ca²⁺ oscillations [PMID:17895289, PMID:11278673]. Loss-of-function mutations in PLA2G6 cause infantile neuroaxonal dystrophy (INAD) and neurodegeneration with brain iron accumulation, while dystonia-parkinsonism (PARK14) mutations selectively impair hydrolysis of the ferroptotic death signal 15-HpETE-PE, leading to its accumulation and progressive dopaminergic neuron loss [PMID:20886109, PMID:33542532, PMID:30088174]."},"prefetch_data":{"uniprot":{"accession":"O60733","full_name":"85/88 kDa calcium-independent phospholipase A2","aliases":["2-lysophosphatidylcholine acylhydrolase","Group VI phospholipase A2","GVI PLA2","Intracellular membrane-associated calcium-independent phospholipase A2 beta","iPLA2-beta","Palmitoyl-CoA hydrolase","Patatin-like phospholipase domain-containing protein 9","PNPLA9"],"length_aa":806,"mass_kda":89.9,"function":"Calcium-independent phospholipase involved in phospholipid remodeling with implications in cellular membrane homeostasis, mitochondrial integrity and signal transduction. Hydrolyzes the ester bond of the fatty acyl group attached at sn-1 or sn-2 position of phospholipids (phospholipase A1 and A2 activity respectively), producing lysophospholipids that are used in deacylation-reacylation cycles (PubMed:10092647, PubMed:10336645, PubMed:20886109, PubMed:9417066). Hydrolyzes both saturated and unsaturated long fatty acyl chains in various glycerophospholipid classes such as phosphatidylcholines, phosphatidylethanolamines and phosphatidates, with a preference for hydrolysis at sn-2 position (PubMed:10092647, PubMed:10336645, PubMed:20886109). Can further hydrolyze lysophospholipids carrying saturated fatty acyl chains (lysophospholipase activity) (PubMed:20886109). Upon oxidative stress, contributes to remodeling of mitochondrial phospholipids in pancreatic beta cells, in a repair mechanism to reduce oxidized lipid content (PubMed:23533611). Preferentially hydrolyzes oxidized polyunsaturated fatty acyl chains from cardiolipins, yielding monolysocardiolipins that can be reacylated with unoxidized fatty acyls to regenerate native cardiolipin species (By similarity). Hydrolyzes oxidized glycerophosphoethanolamines present in pancreatic islets, releasing oxidized polyunsaturated fatty acids such as hydroxyeicosatetraenoates (HETEs) (By similarity). Has thioesterase activity toward fatty-acyl CoA releasing CoA-SH known to facilitate fatty acid transport and beta-oxidation in mitochondria particularly in skeletal muscle (PubMed:20886109). Plays a role in regulation of membrane dynamics and homeostasis. Selectively hydrolyzes sn-2 arachidonoyl group in plasmalogen phospholipids, structural components of lipid rafts and myelin (By similarity). Regulates F-actin polymerization at the pseudopods, which is required for both speed and directionality of MCP1/CCL2-induced monocyte chemotaxis (PubMed:18208975). Targets membrane phospholipids to produce potent lipid signaling messengers. Generates lysophosphatidate (LPA, 1-acyl-glycerol-3-phosphate), which acts via G-protein receptors in various cell types (By similarity). Has phospholipase A2 activity toward platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine), likely playing a role in inactivation of this potent pro-inflammatory signaling lipid (By similarity). In response to glucose, amplifies calcium influx in pancreatic beta cells to promote INS secretion (By similarity) Lacks the catalytic domain and may act as a negative regulator of the catalytically active isoforms Lacks the catalytic domain and may act as a negative regulator of the catalytically active isoforms","subcellular_location":"Cytoplasm; Cell membrane; Mitochondrion; Cell projection, pseudopodium","url":"https://www.uniprot.org/uniprotkb/O60733/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PLA2G6","classification":"Not Classified","n_dependent_lines":13,"n_total_lines":1208,"dependency_fraction":0.01076158940397351},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PLA2G6","total_profiled":1310},"omim":[{"mim_id":"615787","title":"NAD KINASE 2, MITOCHONDRIAL; NADK2","url":"https://www.omim.org/entry/615787"},{"mim_id":"612953","title":"PARKINSON DISEASE 14, AUTOSOMAL RECESSIVE; PARK14","url":"https://www.omim.org/entry/612953"},{"mim_id":"612123","title":"PATATIN-LIKE PHOSPHOLIPASE DOMAIN-CONTAINING PROTEIN 8; PNPLA8","url":"https://www.omim.org/entry/612123"},{"mim_id":"610217","title":"NEURODEGENERATION WITH BRAIN IRON ACCUMULATION 2B; NBIA2B","url":"https://www.omim.org/entry/610217"},{"mim_id":"608507","title":"MITOFUSIN 2; MFN2","url":"https://www.omim.org/entry/608507"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"},{"location":"Nuclear speckles","reliability":"Additional"},{"location":"Microtubules","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PLA2G6"},"hgnc":{"alias_symbol":["iPLA2","PNPLA9","PARK14","iPLA2beta","NBIA2"],"prev_symbol":[]},"alphafold":{"accession":"O60733","domains":[{"cath_id":"1.25.40.20","chopping":"186-282","consensus_level":"medium","plddt":93.2526,"start":186,"end":282},{"cath_id":"1.25.40.20","chopping":"291-416","consensus_level":"medium","plddt":91.4244,"start":291,"end":416},{"cath_id":"3.40.1090.10","chopping":"481-531_553-608_625-700_734-805","consensus_level":"high","plddt":94.1524,"start":481,"end":805}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O60733","model_url":"https://alphafold.ebi.ac.uk/files/AF-O60733-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O60733-F1-predicted_aligned_error_v6.png","plddt_mean":86.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PLA2G6","jax_strain_url":"https://www.jax.org/strain/search?query=PLA2G6"},"sequence":{"accession":"O60733","fasta_url":"https://rest.uniprot.org/uniprotkb/O60733.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O60733/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O60733"}},"corpus_meta":[{"pmid":"18570303","id":"PMC_18570303","title":"Characterization of PLA2G6 as a locus for dystonia-parkinsonism.","date":"2009","source":"Annals of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/18570303","citation_count":347,"is_preprint":false},{"pmid":"34131139","id":"PMC_34131139","title":"iPLA2β-mediated lipid detoxification controls p53-driven ferroptosis independent of GPX4.","date":"2021","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/34131139","citation_count":288,"is_preprint":false},{"pmid":"33542532","id":"PMC_33542532","title":"Phospholipase iPLA2β averts ferroptosis by eliminating a redox lipid death signal.","date":"2021","source":"Nature chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/33542532","citation_count":279,"is_preprint":false},{"pmid":"20669327","id":"PMC_20669327","title":"Early-onset L-dopa-responsive parkinsonism with pyramidal signs due to ATP13A2, PLA2G6, FBXO7 and spatacsin mutations.","date":"2010","source":"Movement disorders : official journal of the Movement Disorder Society","url":"https://pubmed.ncbi.nlm.nih.gov/20669327","citation_count":188,"is_preprint":false},{"pmid":"18443314","id":"PMC_18443314","title":"Phenotypic spectrum of neurodegeneration associated with mutations in the PLA2G6 gene (PLAN).","date":"2008","source":"Neurology","url":"https://pubmed.ncbi.nlm.nih.gov/18443314","citation_count":172,"is_preprint":false},{"pmid":"20619503","id":"PMC_20619503","title":"Widespread Lewy body and tau accumulation in childhood and adult onset dystonia-parkinsonism cases with PLA2G6 mutations.","date":"2010","source":"Neurobiology of aging","url":"https://pubmed.ncbi.nlm.nih.gov/20619503","citation_count":164,"is_preprint":false},{"pmid":"33087576","id":"PMC_33087576","title":"PLA2G6 guards placental trophoblasts against ferroptotic injury.","date":"2020","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/33087576","citation_count":163,"is_preprint":false},{"pmid":"26001724","id":"PMC_26001724","title":"Loss of PLA2G6 leads to elevated mitochondrial lipid peroxidation and mitochondrial dysfunction.","date":"2015","source":"Brain : a journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/26001724","citation_count":158,"is_preprint":false},{"pmid":"12089145","id":"PMC_12089145","title":"Identification of calcium-independent phospholipase A2 (iPLA2) beta, and not iPLA2gamma, as the mediator of arginine vasopressin-induced arachidonic acid release in A-10 smooth muscle cells. 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both are active without Ca2+ and inhibited by bromoenol lactone, but only the long isoform is activated by ATP.\",\n      \"method\": \"cDNA cloning from human pancreatic islets, recombinant protein expression, in vitro phospholipase assay, alternative splicing analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution of recombinant proteins with in vitro enzymatic assays and molecular characterization\",\n      \"pmids\": [\"10092647\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"iPLA2β (PLA2G6) amplifies glucose-stimulated insulin secretion in pancreatic β-cells; cAMP-elevating agents promote translocation of iPLA2β to perinuclear/nuclear compartments, consistent with a signaling rather than housekeeping role.\",\n      \"method\": \"Stable overexpression in INS-1 insulinoma cells, insulin secretion assay, immunocytofluorescence, BEL inhibitor studies\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (overexpression, pharmacological inhibition, imaging) in same study\",\n      \"pmids\": [\"11278673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"iPLA2β (PLA2G6), but not iPLA2γ, mediates arginine vasopressin-induced arachidonic acid release from A-10 smooth muscle cells, demonstrated using enantioselective inhibitors (S-BEL selective for iPLA2β, R-BEL selective for iPLA2γ).\",\n      \"method\": \"Enantioselective BEL inhibition in intact A-10 cells, arachidonic acid release assay, chiral HPLC separation of BEL enantiomers\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mechanistic discrimination using enantioselective inhibitors with IC50 quantification\",\n      \"pmids\": [\"12089145\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Stimulation of insulin secretion promotes time-dependent nuclear accumulation of iPLA2β in INS-1 cells; nuclear accumulation correlates with increased nuclear iPLA2β enzymatic activity and is attenuated by inhibitors of protein phosphorylation and glycosylation.\",\n      \"method\": \"Immunofluorescence, immunoaffinity fractionation, enzymatic activity assay in nuclear fractions, pharmacological inhibition\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods but single lab\",\n      \"pmids\": [\"11882502\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Pancreatic islets and 832/13 INS-1 insulinoma cells express a novel ~70 kDa isoform of iPLA2β not generated by alternative splicing, which retains catalytic activity and participates in insulin secretion but not membrane phospholipid remodeling.\",\n      \"method\": \"Western blotting, mass spectrometry of tryptic peptides, BEL inhibition of insulin secretion, arachidonic acid incorporation assay\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mass spectrometry peptide identification plus functional enzyme and secretion assays\",\n      \"pmids\": [\"14636061\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"ER stress-induced apoptosis of insulin-secreting cells is amplified by iPLA2β overexpression and suppressed by BEL inhibition; ER stress activates iPLA2β, causes its perinuclear accumulation, and triggers caspase-3-mediated cleavage of 84 kDa iPLA2β to a 62 kDa nuclear fragment; ceramide accumulation is also iPLA2β-dependent.\",\n      \"method\": \"INS-1 cell overexpression, BEL inhibition, caspase activity assay, immunofluorescence, ceramide measurement\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including proteolytic processing identification and subcellular localization with functional consequence\",\n      \"pmids\": [\"14744135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"FcγRI activation in human monocytic U937 cells couples specifically to iPLA2β (not cPLA2α) for arachidonic acid release and generation of leukotriene B4 and prostaglandin E2; iPLA2β activation in this pathway is protein kinase C-dependent.\",\n      \"method\": \"BEL inhibition, siRNA/antisense knockdown, arachidonic acid release assay, eicosanoid measurement\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological and genetic inhibition with defined lipid mediator readouts\",\n      \"pmids\": [\"15007079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"ER-localized iPLA2 activity in kidney, heart, and brain microsomes is attributable to iPLA2γ (group VIB), not iPLA2β, based on isoform-selective BEL enantiomers and immunoblot analysis.\",\n      \"method\": \"Subcellular fractionation, iPLA2 activity assay, immunoblotting, RT-PCR, BEL enantiomer inhibition\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — distinguishes iPLA2β from γ at the ER using multiple methods, single lab\",\n      \"pmids\": [\"15629460\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Mitochondrial Ca2+-independent phospholipase A2 (iPLA2β) is activated during sustained mitochondrial membrane depolarization and Ca2+ accumulation; sustained activity promotes outer mitochondrial membrane rupture and spontaneous cytochrome c release; BEL inhibition of this phospholipase attenuates the mitochondrial permeability transition.\",\n      \"method\": \"Isolated mitochondria, membrane potential measurement, BEL inhibition, cytochrome c release assay, permeability transition pore assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with isolated mitochondria plus pharmacological intervention\",\n      \"pmids\": [\"16407316\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"iPLA2β (PLA2G6) plays a pivotal role in angiotensin II-induced transcriptional upregulation of RGS2 in vascular smooth muscle cells; both arachidonic acid and lysophosphatidylcholine (products of iPLA2β) induce RGS2 mRNA, and the pathway is abolished by pharmacological inhibition, antisense knockdown, or genetic deletion of iPLA2β.\",\n      \"method\": \"BEL inhibition, antisense oligonucleotides, iPLA2β-null mice VSMCs, adenoviral re-expression, RGS2 mRNA/protein measurement, iPLA2 enzymatic activity assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — three independent approaches (pharmacological, genetic KO, reconstitution by adenovirus) with consistent results\",\n      \"pmids\": [\"17613534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"iPLA2β (PLA2G6) overexpression in pancreatic β-cells in vivo lowers blood glucose and amplifies glucose-induced insulin secretion; iPLA2β-null islets show blunted insulin secretion and impaired glucose tolerance; iPLA2β reduces Kv2.1 delayed rectifier current and prolongs glucose-induced action potentials and cytosolic Ca2+ elevations.\",\n      \"method\": \"Transgenic RIP-iPLA2β mice, iPLA2β-null mice, glucose tolerance test, patch-clamp electrophysiology, Ca2+ imaging, insulin secretion assay\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — gain- and loss-of-function in vivo models with electrophysiological mechanism\",\n      \"pmids\": [\"17895289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"ER stress induces iPLA2β accumulation in mitochondria, opening of mitochondrial permeability transition pore, and loss of mitochondrial membrane potential in INS-1 cells; iPLA2β-mediated ceramide generation via sphingomyelin hydrolysis mediates mitochondrial dysfunction and cytochrome c release in the apoptotic cascade.\",\n      \"method\": \"Subcellular fractionation, mitochondrial membrane potential assay, cytochrome c release, ceramide measurement, iPLA2β overexpression, BEL and NSMase inhibition\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods establishing subcellular localization and mechanism in same study\",\n      \"pmids\": [\"18936091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Human PLA2G6 enzyme hydrolyzes both phospholipids and lysophospholipids to release free fatty acids; INAD/NBIA mutations cause loss of enzymatic activity (<20% of WT), while dystonia-parkinsonism mutations do not impair catalytic activity and two produce increased specific activity for phospholipid substrates.\",\n      \"method\": \"Purified recombinant WT and mutant human PLA2G6, in vitro phospholipase and lysophospholipase assays with radiolabeled lipid substrates\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro enzymatic assay with purified recombinant proteins and multiple disease-associated mutants\",\n      \"pmids\": [\"20886109\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"iPLA2β undergoes endogenous proteolytic processing to generate N-terminally truncated isoforms that localize differentially to subcellular organelles; secretagogues and ER stress promote differential redistribution of iPLA2β variants among subcellular compartments.\",\n      \"method\": \"EGFP fusion protein stable expression, dual fluorescence organelle tracking, immunoblotting, mass spectrometry of N-terminal variants\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mass spectrometry identification of processing plus live-cell localization, single lab\",\n      \"pmids\": [\"20132906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"iPLA2β deficiency in mice reduces brain DHA metabolism and DHA-dependent signaling in vivo at baseline and following muscarinic M1,3,5 receptor activation, consistent with iPLA2β selectively hydrolyzing DHA from phospholipids.\",\n      \"method\": \"iPLA2β-/- and +/- mice, intravenous [1-14C]DHA infusion, quantitative autoradiography of 81 brain regions, cholinergic agonist challenge\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo imaging with genetic KO and pharmacological challenge, quantitative across 81 brain regions\",\n      \"pmids\": [\"20686114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Knockout of the Drosophila PLA2G6 homolog iPLA2-VIA causes mitochondrial respiratory chain dysfunction, reduced ATP synthesis, abnormal mitochondrial morphology, and elevated mitochondrial lipid peroxidation; similar mitochondrial lipid peroxidation and membrane defects occur in fibroblasts from PLA2G6-mutant patients; deuterated PUFAs that inhibit lipid peroxidation partially rescue locomotor deficits.\",\n      \"method\": \"Drosophila iPLA2-VIA knockout, respirometry, ATP assay, electron microscopy, lipid peroxidation assay, patient fibroblast analysis, pharmacological rescue with deuterated PUFAs\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — fly KO + patient fibroblast validation + pharmacological rescue with multiple orthogonal readouts\",\n      \"pmids\": [\"26001724\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"iPLA2β modulates Bcl-x pre-mRNA 5'-splice site selection to suppress anti-apoptotic Bcl-xL in β-cells; iPLA2β inactivation or knockdown augments the Bcl-xL/Bcl-xS ratio, whereas iPLA2β overexpression reduces it; the bioactive lipid 5(S)-HETE augments Bcl-xL/Bcl-xS by 15.5-fold.\",\n      \"method\": \"Chemical inactivation and siRNA knockdown of iPLA2β, transgenic and KO mouse islets, Bcl-x splice isoform quantitation by RT-PCR, exogenous lipid treatments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic and pharmacological approaches in islets and cell lines, single lab\",\n      \"pmids\": [\"25762722\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"In PLA2G6 knockout mice, mitochondria with damaged inner membranes appear early in neurons and move anterogradely into distal axons; inner mitochondrial membrane degeneration precedes axonal spheroid formation; presynaptic membrane abnormalities also develop, leading to axon terminal degeneration containing tubulovesicular structures.\",\n      \"method\": \"PLA2G6 KO mouse neuropathology, electron microscopy, immunohistochemistry, axonal transport analysis\",\n      \"journal\": \"Neuropathology : official journal of the Japanese Society of Neuropathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — detailed ultrastructural analysis in genetic KO model with temporal progression\",\n      \"pmids\": [\"25950622\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PLA2G6 deficiency impairs store-operated Ca2+ entry signaling; genetic or molecular impairment of PLA2G6-dependent Ca2+ signaling triggers autophagic dysfunction and progressive loss of dopaminergic neurons in substantia nigra pars compacta; this sequence is recapitulated in a Pla2g6 exon2 knockout mouse model.\",\n      \"method\": \"Patient-derived cells (idiopathic PD), PLA2g6 exon2 KO mouse, Ca2+ imaging, autophagy assays, dopaminergic neuron counting, L-DOPA behavioral rescue\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — human patient cells corroborated by genetic mouse model with mechanistic pathway (Ca2+ → autophagy → neurodegeneration)\",\n      \"pmids\": [\"26755131\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PLA2G6 deficiency causes elevated α-synuclein expression in neurons; phosphorylated α-synuclein accumulates in mitochondrial outer membrane-positive (TOM20+) granules in PLA2G6-KO mice; α-synuclein localizes to degenerated inner mitochondrial membranes, suggesting a role in stabilizing damaged mitochondrial membranes.\",\n      \"method\": \"PLA2G6 KO mouse, PLA2G6 knockdown cells, immunohistochemistry with TOM20 co-staining, immunofluorescence, electron microscopy, quantitative Lewy body analysis in PLAN and PD patients\",\n      \"journal\": \"Acta neuropathologica communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse and patient tissue with multiple markers, single lab\",\n      \"pmids\": [\"27030050\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Loss of iPLA2-VIA (Drosophila PLA2G6 homolog) does not alter phospholipid composition of brain tissue but causes elevation in ceramide levels; iPLA2-VIA physically binds retromer subunits Vps35 and Vps26, enhancing retromer function to promote protein and lipid recycling; loss of iPLA2-VIA impairs retromer function, progressively increasing ceramide levels that in turn impair membrane fluidity and retromer function in a positive feedback loop.\",\n      \"method\": \"Drosophila iPLA2-VIA KO, lipidomics, co-immunoprecipitation of Vps35/Vps26, pharmacological ceramide reduction (myriocin, desipramine), genetic epistasis with vps26/vps35 mutants\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — co-IP of retromer binding, lipidomics, genetic epistasis, and pharmacological rescue in same study\",\n      \"pmids\": [\"29909971\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PARK14 mutant PLA2G6 proteins (D331Y, G517C, T572I, R632W, N659S, R741Q) fail to prevent rotenone-induced mitochondrial membrane potential loss, mitochondrial superoxide increase, complex I activity reduction, mitophagy impairment, and cytochrome c release, while WT PLA2G6 rescues all these defects.\",\n      \"method\": \"SH-SY5Y cell overexpression of WT and mutant PLA2G6, rotenone model, mitochondrial membrane potential assay, ROS measurement, complex I activity assay, ATP measurement, cytochrome c release, mitophagy markers\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple mitochondrial readouts with multiple disease mutants, single lab\",\n      \"pmids\": [\"29108286\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"iPLA2-VIA loss in Drosophila shortens acyl-chain length of phospholipids, causing ER stress through membrane lipid disequilibrium; WT human iPLA2-VIA or the mitochondria-ER contact site protein C19orf12 rescue altered lipid composition, ER stress, and DA neurodegeneration; disease-associated iPLA2-VIA A80T mutant fails to rescue; linoleic acid supplementation corrects brain lipid composition and suppresses α-synuclein aggregation caused by iPLA2-VIA loss.\",\n      \"method\": \"Drosophila iPLA2-VIA KO, lipid analysis by mass spectrometry, ER stress markers, DA neuron counting, transgenic rescue with WT and A80T mutant, linoleic acid supplementation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — lipidomics + ER stress + genetic rescue + disease mutant comparison + pharmacological rescue\",\n      \"pmids\": [\"31548400\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PLA2G6 (iPLA2β/PNPLA9) metabolizes hydroperoxy-arachidonoyl- and adrenoyl-phosphatidylethanolamine (Hp-PE) to lyso-PE and oxidized fatty acid, attenuating ferroptotic injury; PLA2G6 protects human trophoblasts and mouse placenta from ferroptosis induced by GPX4 inhibition or hypoxia/reoxygenation.\",\n      \"method\": \"Primary human trophoblast cultures, mouse pregnancy model, GPX4 inhibitor (RSL3), hypoxia/reoxygenation, lipid mass spectrometry, PLA2G6 knockdown\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro and in vivo models with lipidomic substrate identification and genetic knockdown\",\n      \"pmids\": [\"33087576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"iPLA2β (PLA2G6) hydrolyzes 15-HpETE-PE (the ferroptotic death signal generated by 15-LOX/PEBP1 complex) to avert ferroptosis; genetic or pharmacological inactivation of iPLA2β sensitizes cells to ferroptosis; patient fibroblasts with PD-associated mutation (R747W) show selectively decreased 15-HpETE-PE-hydrolyzing activity and elevated 15-HpETE-PE; Pnpla9 R748W knock-in mice develop progressive parkinsonian motor deficits with 15-HpETE-PE accumulation.\",\n      \"method\": \"Lipidomics (15-HpETE-PE quantification), CRISPR-Cas9 knock-in mouse (R748W), patient fibroblast assays, genetic and pharmacological iPLA2β inactivation, rotenone rat and SncaA53T mouse models\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — substrate identified by lipidomics, enzymatic activity in patient cells, CRISPR knock-in mouse model with motor phenotype, replicated in multiple animal models\",\n      \"pmids\": [\"33542532\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"iPLA2β (PLA2G6) acts as a major ferroptosis repressor independent of GPX4 by detoxifying peroxidized lipids; iPLA2β-mediated removal of oxidized acyl tails from phospholipids suppresses p53-driven ferroptosis under ROS stress; iPLA2β loss has no obvious effect on normal development but is essential for regulating ferroptosis upon ROS-induced stress.\",\n      \"method\": \"GPX4-null cells, iPLA2β overexpression and inhibition, p53-driven ferroptosis assay, xenograft tumor model, lipid peroxidation measurement\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — GPX4-null cells isolate iPLA2β mechanism, xenograft in vivo model, multiple cancer cell lines\",\n      \"pmids\": [\"34131139\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PLA2G6 loss causes disruption of Golgi morphology and defects in protein O-linked glycosylation and sialylation in patient fibroblasts; lentiviral re-expression of WT PLA2G6 rescues these Golgi and glycosylation abnormalities.\",\n      \"method\": \"Patient fibroblast cultures (INAD and dystonia-parkinsonism), HPLC and MALDI-TOF/MS glycosylation analysis, immunofluorescence of Golgi morphology, lentiviral WT PLA2G6 rescue\",\n      \"journal\": \"Journal of medical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional rescue with WT protein plus multiple analytical methods, single lab\",\n      \"pmids\": [\"26668131\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"iPLA2β (PLA2G6)-null mice show accelerated age-related bone loss associated with increased bone marrow adipogenesis and decreased osteogenesis; bone marrow stromal cells from KO mice express higher PPARγ and lower Runx2 mRNA, indicating that iPLA2β regulates mesenchymal stem cell lineage commitment.\",\n      \"method\": \"iPLA2β-null mice, bone morphometry, bone strength testing, osteoclast/osteoblast quantification, BMSC differentiation assays, gene expression analysis\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with multiple skeletal phenotypic readouts and molecular mechanism, single lab\",\n      \"pmids\": [\"18349124\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"iPLA2β activity is required for skeletal muscle fatty acid oxidation through an acyl-CoA thioesterase activity (distinct from its phospholipase activity) that liberates CoA-SH to facilitate fatty acid transport into mitochondria; iPLA2β-null mice show reduced palmitate oxidation and reduced acyl-CoA thioesterase activity.\",\n      \"method\": \"iPLA2β-null mice, palmitate oxidation assay, palmitoyl-CoA and acetyl-CoA oxidation assays, ATP and calmodulin column chromatography, BEL inhibition of thioesterase activity\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — novel enzymatic activity identified with genetic KO and biochemical fractionation, single lab\",\n      \"pmids\": [\"18937505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PLA2G6 protein accumulates in the cores of brainstem-type Lewy bodies in PARK14 and idiopathic Parkinson's disease patients, but not in cortical Lewy bodies, multiple system atrophy, or Alzheimer's disease.\",\n      \"method\": \"Immunohistochemistry and immunoblotting on post-mortem brain tissue from PARK14, idiopathic PD, DLB, MSA, and AD\",\n      \"journal\": \"Neuroscience letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — direct localization in human tissue with disease-specificity, single lab\",\n      \"pmids\": [\"28213071\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"A point mutation in the ankyrin repeat domain of Pla2g6 (generated by ENU mutagenesis in mice) produces a protein with no glycerophospholipid-catalyzing enzyme activity and causes early-onset (7-8 weeks) INAD with widespread spheroid formation containing tubulovesicular membranes, demonstrating that loss of catalytic activity is sufficient for disease.\",\n      \"method\": \"ENU mutagenesis mouse model, neuropathology with electron microscopy, biochemical assay of iPLA2β enzyme activity\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — point mutation knock-in with biochemical activity measurement and neuropathological validation\",\n      \"pmids\": [\"19893029\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PARK14 D331Y knockin mice develop early-onset degeneration of substantia nigra dopaminergic neurons with Lewy body pathology, mitochondrial cristae disruption, mitochondrial dysfunction, elevated ROS, ER stress (upregulated GRP78, IRE1, PERK, CHOP), and impaired mitophagy (reduced parkin and BNIP3).\",\n      \"method\": \"PLA2G6 D331Y/D331Y knockin mouse, dopaminergic neuron counting, electron microscopy, mitochondrial membrane potential, ROS measurement, ER stress protein immunoblot, mitophagy protein expression, behavioral testing\",\n      \"journal\": \"Molecular neurobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — knockin mouse with multiple orthogonal mechanistic readouts demonstrating convergent pathways\",\n      \"pmids\": [\"30088174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"iPLA2β translocates to the ER upon myocardial ischemia/reperfusion injury; this translocation promotes ER stress and cardiomyocyte apoptosis; iPLA2β knockout or siRNA knockdown ameliorates ER stress and decreases cell death during I/R.\",\n      \"method\": \"iPLA2β KO mice, siRNA knockdown, I/R model in vivo and in vitro, cell surface protein biotinylation, immunofluorescence localization, ER stress markers, apoptosis assays\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — localization to ER upon stress with genetic KO confirmation and functional consequence, single lab\",\n      \"pmids\": [\"34207793\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PLA2G6 encodes a Ca2+-independent phospholipase A2 (iPLA2β) that cleaves acyl chains (preferentially oxidized/peroxidized fatty acids including 15-HpETE-PE and DHA) from the sn-2 position of glycerophospholipids, generating free fatty acids and lysophospholipids; it also possesses acyl-CoA thioesterase activity; it functions in membrane phospholipid remodeling, mitochondrial membrane integrity maintenance, ER function, retromer-mediated lipid recycling (via direct binding to Vps35/Vps26), store-operated Ca2+ entry signaling, insulin secretion amplification in β-cells, and ferroptosis suppression by eliminating peroxidized phospholipid death signals, with disease-causing mutations in the INAD/NBIA spectrum abolishing catalytic activity while dystonia-parkinsonism mutations selectively impair 15-HpETE-PE hydrolysis and alter substrate preferences without globally eliminating activity.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PLA2G6 encodes calcium-independent phospholipase A2β (iPLA2β), a multifunctional lipid-metabolizing enzyme that cleaves sn-2 acyl chains—with preference for oxidized and polyunsaturated fatty acids including 15-HpETE-PE and DHA—from glycerophospholipids and also possesses acyl-CoA thioesterase activity, serving as a critical guardian of membrane lipid homeostasis and a major suppressor of ferroptosis [PMID:10092647, PMID:33542532, PMID:18937505]. iPLA2β maintains mitochondrial inner membrane integrity, supports retromer-mediated lipid and protein recycling through direct interaction with Vps35/Vps26, regulates store-operated Ca²⁺ entry, and modulates ER stress responses; its loss leads to ceramide accumulation, mitochondrial cristae degeneration, impaired autophagy, and progressive neurodegeneration [PMID:29909971, PMID:26755131, PMID:25950622, PMID:16407316]. In pancreatic β-cells, iPLA2β amplifies glucose-stimulated insulin secretion by suppressing Kv2.1 delayed rectifier currents and prolonging Ca²⁺ oscillations [PMID:17895289, PMID:11278673]. Loss-of-function mutations in PLA2G6 cause infantile neuroaxonal dystrophy (INAD) and neurodegeneration with brain iron accumulation, while dystonia-parkinsonism (PARK14) mutations selectively impair hydrolysis of the ferroptotic death signal 15-HpETE-PE, leading to its accumulation and progressive dopaminergic neuron loss [PMID:20886109, PMID:33542532, PMID:30088174].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Molecular cloning established that PLA2G6 encodes a Ca²⁺-independent phospholipase A2 with two catalytically active splice isoforms differing in ATP responsiveness, defining the enzyme's fundamental identity and regulatory properties.\",\n      \"evidence\": \"cDNA cloning from human pancreatic islets with recombinant protein expression and in vitro phospholipase assays\",\n      \"pmids\": [\"10092647\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Three-dimensional structure not determined\", \"Endogenous substrate specificity in vivo not yet defined\", \"Oligomeric state and regulation by ankyrin repeats not characterized\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Demonstration that iPLA2β amplifies glucose-stimulated insulin secretion and translocates to perinuclear compartments upon cAMP signaling established a regulated signaling role beyond housekeeping phospholipid remodeling.\",\n      \"evidence\": \"Overexpression in INS-1 cells, BEL inhibition, immunocytofluorescence, and insulin secretion assays\",\n      \"pmids\": [\"11278673\", \"11882502\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of lipid mediators linking iPLA2β to secretory machinery unknown\", \"Mechanism of cAMP-induced translocation unresolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Enantioselective inhibitor studies discriminated iPLA2β from iPLA2γ in intact cells, showing iPLA2β specifically mediates receptor-coupled arachidonic acid release in smooth muscle, establishing isoform-selective signaling.\",\n      \"evidence\": \"S-BEL vs R-BEL enantiomers in A-10 cells with arachidonic acid release measurement\",\n      \"pmids\": [\"12089145\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream eicosanoid products of iPLA2β-released AA in smooth muscle not fully mapped\", \"Whether iPLA2γ compensates in iPLA2β absence not tested\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identification that iPLA2β activates during mitochondrial membrane depolarization and promotes outer membrane rupture and cytochrome c release revealed a direct role in mitochondrial permeability transition, linking the enzyme to apoptotic signaling.\",\n      \"evidence\": \"Isolated mitochondria assays with BEL inhibition, membrane potential measurement, and cytochrome c release\",\n      \"pmids\": [\"16407316\", \"18936091\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether iPLA2β acts on specific mitochondrial phospholipid species (e.g., cardiolipin) not determined\", \"Mechanism of iPLA2β activation by depolarization unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Gain- and loss-of-function mouse models proved iPLA2β amplifies insulin secretion in vivo by suppressing Kv2.1 currents and prolonging Ca²⁺ oscillations, defining an electrophysiological mechanism for its β-cell function.\",\n      \"evidence\": \"RIP-iPLA2β transgenic and iPLA2β-null mice with patch-clamp electrophysiology, Ca²⁺ imaging, and glucose tolerance tests\",\n      \"pmids\": [\"17895289\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific lipid mediator that modulates Kv2.1 not identified\", \"Whether this mechanism operates in human islets not confirmed\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Discovery of an acyl-CoA thioesterase activity distinct from phospholipase activity expanded iPLA2β's enzymatic repertoire and linked it to mitochondrial fatty acid oxidation in skeletal muscle.\",\n      \"evidence\": \"iPLA2β-null mice with palmitate oxidation assays and chromatographic separation of thioesterase activity\",\n      \"pmids\": [\"18937505\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis for dual enzymatic activities not resolved\", \"Relative contribution of thioesterase vs phospholipase activity in different tissues unknown\", \"Not independently replicated\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"An ENU-generated point mutation in the ankyrin repeat domain that abolished catalytic activity was sufficient to produce INAD with tubulovesicular spheroids, proving that loss of enzymatic function—not a structural scaffolding defect—drives disease.\",\n      \"evidence\": \"ENU mutagenesis mouse with neuropathology, electron microscopy, and biochemical activity assay\",\n      \"pmids\": [\"19893029\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ankyrin repeat mutations also disrupt protein-protein interactions not tested\", \"Specific lipid substrates accumulating in INAD not identified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Biochemical analysis of disease-associated mutations revealed a genotype-activity correlation: INAD/NBIA mutations ablate catalytic activity while dystonia-parkinsonism mutations preserve or even increase it, suggesting distinct pathomechanisms for the two disease spectra.\",\n      \"evidence\": \"Purified recombinant WT and mutant PLA2G6 with in vitro phospholipase and lysophospholipase assays\",\n      \"pmids\": [\"20886109\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrate specificity differences between dystonia-parkinsonism mutants not yet explored with oxidized lipid substrates\", \"In vivo lipid profiles of dystonia-parkinsonism mutants not determined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Cross-species studies in Drosophila and patient fibroblasts established that PLA2G6 loss causes mitochondrial respiratory chain dysfunction, elevated lipid peroxidation, and Golgi/glycosylation defects, with deuterated PUFAs providing partial rescue—identifying lipid peroxidation as a druggable pathogenic driver.\",\n      \"evidence\": \"Drosophila iPLA2-VIA KO with respirometry, patient fibroblasts with glycosylation analysis, and deuterated PUFA rescue\",\n      \"pmids\": [\"26001724\", \"26668131\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Golgi defects are secondary to lipid peroxidation or an independent pathway unclear\", \"Mechanism by which PLA2G6 maintains Golgi morphology not defined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstration that PLA2G6 deficiency impairs store-operated Ca²⁺ entry, causing autophagic dysfunction and progressive dopaminergic neuron loss, established a Ca²⁺ signaling–autophagy axis as a central pathogenic mechanism in PLA2G6-associated parkinsonism.\",\n      \"evidence\": \"Patient-derived cells and Pla2g6 exon2 KO mouse with Ca²⁺ imaging, autophagy assays, and dopaminergic neuron counting\",\n      \"pmids\": [\"26755131\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which iPLA2β regulates SOCE channels not identified\", \"Whether Ca²⁺ and ferroptosis pathways converge or operate independently unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Discovery that iPLA2β physically binds retromer subunits Vps35/Vps26 and that its loss triggers a ceramide-driven positive feedback loop impairing retromer function revealed a non-enzymatic scaffolding role in membrane trafficking.\",\n      \"evidence\": \"Drosophila iPLA2-VIA KO with co-immunoprecipitation, lipidomics, genetic epistasis with vps26/vps35, and pharmacological ceramide reduction\",\n      \"pmids\": [\"29909971\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the retromer interaction requires iPLA2β catalytic activity not determined\", \"Binding interface between iPLA2β and retromer not mapped\", \"Whether this interaction occurs in mammalian neurons not confirmed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Lipidomic analysis showed iPLA2-VIA loss shortens phospholipid acyl chains causing ER stress, and that linoleic acid supplementation corrects lipid composition and suppresses α-synuclein aggregation, directly linking membrane lipid remodeling to synucleinopathy.\",\n      \"evidence\": \"Drosophila KO with mass spectrometry lipidomics, ER stress markers, transgenic rescue with WT vs A80T mutant, and linoleic acid supplementation\",\n      \"pmids\": [\"31548400\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether acyl-chain shortening occurs in mammalian PLA2G6-deficient neurons not confirmed\", \"Mechanism by which altered lipid composition promotes α-synuclein aggregation not defined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identification of 15-HpETE-PE as the specific ferroptotic substrate of iPLA2β, and demonstration that the PD-associated R747W mutation selectively impairs its hydrolysis causing 15-HpETE-PE accumulation and parkinsonian motor deficits in knock-in mice, unified the ferroptosis-suppression and neurodegeneration functions into a single molecular mechanism.\",\n      \"evidence\": \"Lipidomics, CRISPR knock-in R748W mouse, patient fibroblast enzymatic assays, GPX4-null cell models, and xenograft tumor models\",\n      \"pmids\": [\"33542532\", \"34131139\", \"33087576\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ferroptosis is the dominant cell death mode in all PLA2G6-associated diseases or only in parkinsonism not resolved\", \"Structural basis for substrate selectivity of PD mutants unknown\", \"Therapeutic window for ferroptosis inhibitors in PLA2G6 disease not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis for iPLA2β's dual enzymatic activities and substrate selectivity, the precise relationship between its retromer-binding, Ca²⁺-signaling, and anti-ferroptotic functions in dopaminergic neurons, and whether these represent parallel or convergent pathogenic axes.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No crystal structure of full-length iPLA2β available\", \"Relative contribution of ferroptosis vs autophagy vs ER stress to neurodegeneration not delineated\", \"No therapeutic strategy validated in human PLA2G6-associated disease\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 2, 12, 14, 23, 24]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [23, 24, 22]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [10, 18, 25]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [8, 11, 15, 17, 21, 31]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [22, 32]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 3, 5]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [26]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 2, 14, 22, 23, 24, 28]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [5, 8, 11, 24, 25]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [18, 21]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 10, 18]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [20]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [5, 22, 31, 32]}\n    ],\n    \"complexes\": [\n      \"retromer (via Vps35/Vps26 binding)\"\n    ],\n    \"partners\": [\n      \"VPS35\",\n      \"VPS26\",\n      \"KCNB1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}