{"gene":"PLA2G6","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2006,"finding":"PLA2G6 encodes a calcium-independent phospholipase A2 (iPLA2β) that catalyzes hydrolysis of glycerophospholipids; loss-of-function mutations in PLA2G6 cause infantile neuroaxonal dystrophy (INAD), establishing the enzyme's essential role in neuronal membrane homeostasis.","method":"Homozygosity mapping, mutational analysis, and identification of PLA2G6 mutations in INAD patients; corroborated by neuropathological findings of axonal spheroids","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic mapping with mutation identification in patients, single lab, no direct in vitro enzymatic reconstitution in this paper","pmids":["17033970"],"is_preprint":false},{"year":1999,"finding":"Human PLA2G6 (iPLA2β) gene on chromosome 22q13.1 produces two catalytically active isoforms (85 kDa and 88 kDa) via exon-skipping alternative splicing; the long isoform (LH-iPLA2) is activated by ATP whereas the short isoform (SH-iPLA2) is not, demonstrating isoform-specific regulatory differences.","method":"cDNA cloning from human pancreatic islets, recombinant protein expression, in vitro phospholipase assays with bromoenol lactone inhibition, chromosomal mapping","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro enzymatic characterization of recombinant proteins with functional distinction between isoforms, replicated in two cell types","pmids":["10092647"],"is_preprint":false},{"year":2002,"finding":"iPLA2β (PLA2G6), but not iPLA2γ, is the primary mediator of arginine vasopressin-induced arachidonic acid release from A-10 smooth muscle cells; established using enantioselective inhibition showing (S)-BEL selectively inhibits iPLA2β (IC50 ~2 µM) while (R)-BEL preferentially inhibits iPLA2γ.","method":"Chiral HPLC separation of BEL enantiomers, pharmacological inhibition in intact cells, arachidonic acid release assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — enantioselective mechanism-based inhibitors used in intact cells with rigorous pharmacological discrimination of two enzyme isoforms","pmids":["12089145"],"is_preprint":false},{"year":2001,"finding":"iPLA2β overexpression in INS-1 insulinoma cells amplifies glucose- and cAMP-stimulated insulin secretion without affecting arachidonic acid incorporation into phosphatidylcholine, indicating a signaling rather than housekeeping (phospholipid remodeling) role; cAMP-elevating agents cause perinuclear accumulation of iPLA2β.","method":"Stable retroviral overexpression in INS-1 cells, insulin secretion assays, ESI-MS lipid analysis, immunocytofluorescence","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (secretion assays, lipid MS, immunolocalization), overexpression and pharmacological inhibition in same system","pmids":["11278673"],"is_preprint":false},{"year":2004,"finding":"iPLA2β mediates ER stress-induced apoptosis in insulin-secreting INS-1 cells; overexpression amplifies thapsigargin-induced apoptosis and ceramide accumulation, inhibition suppresses it, and ER stress triggers caspase-3-catalyzed cleavage of 84 kDa iPLA2β to a 62 kDa product that associates with nuclei.","method":"iPLA2β overexpression in INS-1 cells, BEL pharmacological inhibition, flow cytometry for apoptosis, ceramide measurement, immunofluorescence","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — overexpression and pharmacological inhibition with multiple functional readouts (apoptosis, ceramide, caspase cleavage, nuclear translocation) in same study","pmids":["14744135"],"is_preprint":false},{"year":2007,"finding":"iPLA2β (PLA2G6) plays a pivotal role in angiotensin II-induced RGS2 mRNA upregulation in vascular smooth muscle cells; demonstrated by three independent approaches (BEL inhibition, antisense oligonucleotides, iPLA2β-null mice); Ang II stimulates iPLA2 enzymatic activity in VSMC; downstream products arachidonic acid and lysophosphatidylcholine induce RGS2 via lipoxygenase pathway.","method":"Pharmacological inhibition (BEL), antisense oligonucleotide knockdown, iPLA2β knockout mice, adenovirus-mediated gene rescue, iPLA2 enzymatic activity assays, real-time PCR","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — three independent genetic/pharmacological approaches with gene rescue in null cells, multiple orthogonal methods","pmids":["17613534"],"is_preprint":false},{"year":2008,"finding":"Upon MCP-1 stimulation, iPLA2β translocates to the membrane-enriched pseudopod in monocytes and controls directionality and actin polymerization during chemotaxis; antisense knockdown of iPLA2β reduces migration speed, directionality, and abolishes in vivo peritoneal migration.","method":"Antisense oligonucleotide knockdown, immunofluorescence localization, in vitro chemotaxis assays, adoptive transfer in vivo migration assay","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vitro and in vivo evidence with subcellular localization and functional knockdown, multiple readouts","pmids":["18208975"],"is_preprint":false},{"year":2008,"finding":"iPLA2β mediates ER stress-induced apoptosis via a ceramide-mitochondria axis: ER stress promotes iPLA2β accumulation in mitochondria, ceramide generation via sphingomyelin hydrolysis, mitochondrial permeability transition pore opening, loss of mitochondrial membrane potential, cytochrome c/Smac release, and caspase-3 activation; these are amplified by iPLA2β overexpression and inhibited by iPLA2β inactivation or NSMase inhibition.","method":"iPLA2β overexpressing INS-1 cells (OE), BEL inhibition, subcellular fractionation, ceramide measurement in ER and mitochondria fractions, mitochondrial membrane potential assay, cytochrome c/Smac immunoblotting","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — subcellular fractionation demonstrating mitochondrial translocation plus multiple functional endpoints, overexpression and pharmacological inhibition","pmids":["18936091"],"is_preprint":false},{"year":2007,"finding":"iPLA2β-dependent activation of store-operated Ca2+ channels (SOC) is required for agonist-induced Ca2+ influx and vasoconstriction in cerebral, mesenteric, and carotid arteries; iPLA2β inhibition abolishes phenylephrine-induced Ca2+ entry without affecting K+-induced (voltage-gated L-type channel-dependent) vasoconstriction.","method":"Pharmacological inhibition of iPLA2β (BEL) in intact pressurized vessels, simultaneous measurement of intracellular Ca2+ and vessel diameter","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct functional assay in intact vessels, pharmacological inhibitor only, single lab","pmids":["18156193"],"is_preprint":false},{"year":2009,"finding":"A point mutation in the ankyrin repeat domain of Pla2g6 completely abolishes glycerophospholipid-catalyzing enzyme activity while allowing protein expression, demonstrating that the ankyrin repeat domain is required for catalytic function and that loss of iPLA2β enzymatic activity causes INAD neuropathology.","method":"ENU mutagenesis mouse model, biochemical enzyme activity assay on mutant protein, neuropathological examination (axonal spheroids with tubulovesicular membranes)","journal":"The American journal of pathology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct enzymatic assay demonstrating zero activity of mutant protein, with in vivo phenotypic validation","pmids":["19893029"],"is_preprint":false},{"year":2010,"finding":"PLA2G6 mutations associated with INAD/NBIA cause loss of enzyme activity (<20% residual activity for both phospholipase and lysophospholipase substrates), while mutations associated with dystonia-parkinsonism do not impair catalytic activity and two mutations increase specific activity for phospholipid substrates, indicating distinct disease mechanisms.","method":"Purified recombinant wildtype and mutant human PLA2G6 proteins, in vitro phospholipase and lysophospholipase assays with radiolabeled lipid substrates","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro enzymatic reconstitution with multiple disease-associated mutants tested against two substrate classes","pmids":["20886109"],"is_preprint":false},{"year":2010,"finding":"iPLA2β deficiency in mice reduces brain DHA metabolism and signaling both at baseline and following muscarinic receptor activation, consistent with iPLA2β selectively hydrolyzing DHA from phospholipids in vivo.","method":"iPLA2β knockout mice, quantitative autoradiography with [1-14C]DHA intravenous infusion, measurement of DHA incorporation coefficients in 81 brain regions","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 2 / Strong — quantitative in vivo imaging with isotope tracer in knockout vs. wildtype across three genotypes, multiple brain regions","pmids":["20686114"],"is_preprint":false},{"year":2011,"finding":"Homozygous PLA2G6 D331Y mutation causes ~70% reduction in iPLA2β enzyme activity in vitro, linking reduced catalytic activity to autosomal recessive early-onset parkinsonism.","method":"Direct sequencing for mutation identification, in vitro enzyme activity assay of D331Y mutant vs. wildtype PLA2G6","journal":"Neurology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — direct enzymatic assay, single lab, one mutation tested","pmids":["21700586"],"is_preprint":false},{"year":2011,"finding":"iPLA2β is activated upstream of p38 MAPK in pancreatic β-cells: glucose and thapsigargin stimulate p38 MAPK phosphorylation in an iPLA2β-dependent manner; p38 MAPK inhibition prevents insulin secretion and apoptosis downstream of iPLA2β; iPLA2β product arachidonic acid activates p38 MAPK.","method":"iPLA2β overexpressing INS-1 cells and knockout mice islets, BEL pharmacological inhibition, p38 MAPK inhibitor PD169316, phosphorylation immunoblotting, insulin secretion assay, apoptosis assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — epistasis established with pharmacological and genetic tools across multiple cell systems, multiple orthogonal endpoints","pmids":["22194610"],"is_preprint":false},{"year":2012,"finding":"Three PLA2G6 frameshift and missense mutations found in PD patients reduce iPLA2β phospholipase activity (P.His597fx69: <6% residual activity; Leu656Val: 55% residual; Leu693Val: 65% residual), extending the genotype-activity relationship in PD-associated PLA2G6 mutations.","method":"Sequencing in patient cohort, in vitro phospholipase assay with recombinant mutant proteins","journal":"Parkinsonism & related disorders","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — direct enzymatic assay with recombinant proteins, single lab, limited patient numbers","pmids":["23182313"],"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 were confirmed in fibroblasts from human PLA2G6 mutation patients; deuterated PUFAs (inhibiting lipid peroxidation) partially rescued locomotor deficits and restored mitochondrial membrane potential.","method":"Drosophila iPLA2-VIA knockout, mitochondrial respiratory chain assays, ATP measurement, electron microscopy, lipid peroxidation assays; patient-derived fibroblast studies; deuterated PUFA rescue experiment","journal":"Brain : a journal of neurology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods in two model systems (fly and human cells), with mechanistic rescue experiment","pmids":["26001724"],"is_preprint":false},{"year":2016,"finding":"PLA2G6-dependent Ca2+ signaling activates store-operated Ca2+ entry (SOCE); genetic or molecular impairment of PLA2g6-dependent Ca2+ signaling in a PLA2g6 exon2 knockout mouse triggers autophagic dysfunction and progressive loss of dopaminergic neurons in substantia nigra pars compacta with age-dependent L-DOPA-sensitive motor dysfunction.","method":"PLA2g6 exon2 knockout mouse model, Ca2+ signaling measurements, autophagy assays, dopaminergic neuron counting, behavioral motor tests","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout mouse with multiple cellular and behavioral phenotypic readouts establishing pathway position","pmids":["26755131"],"is_preprint":false},{"year":2018,"finding":"iPLA2-VIA (Drosophila PLA2G6 homolog) binds retromer subunits Vps35 and Vps26 and enhances retromer function to promote protein and lipid recycling; loss of iPLA2-VIA does not alter phospholipid composition but causes elevation of ceramides leading to lysosomal stress and neurodegeneration; reducing ceramides with myriocin or desipramine alleviates neurodegeneration.","method":"Co-immunoprecipitation/pulldown of iPLA2-VIA with Vps35/Vps26, lipidomics of fly brain tissue, pharmacological ceramide reduction (myriocin, desipramine), Drosophila genetic loss-of-function","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — binding partner identified by Co-IP, lipidomics, and pharmacological rescue with multiple readouts in single rigorous study","pmids":["29909971"],"is_preprint":false},{"year":2019,"finding":"Loss of iPLA2-VIA in Drosophila shortens acyl-chain length of phospholipids, causing ER stress through membrane lipid disequilibrium; wild-type human iPLA2-VIA or the mitochondria-ER contact site protein C19orf12 rescues lipid composition, ER stress, and DA neurodegeneration, while disease-associated A80T mutant fails to rescue; linoleic acid supplementation corrects brain lipid composition and suppresses α-synuclein aggregation.","method":"iPLA2-VIA-deficient Drosophila, lipid mass spectrometry of brain tissue, ER stress markers, transgenic rescue with wildtype vs. mutant human iPLA2-VIA, linoleic acid supplementation, α-synuclein aggregation assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods including lipidomics, genetic rescue with wildtype vs. disease mutant, and lipid supplementation rescue","pmids":["31548400"],"is_preprint":false},{"year":2020,"finding":"PLA2G6 (iPLA2β) hydrolyzes ferroptotic death signal 15-HpETE-PE (hydroperoxy-arachidonoyl-phosphatidylethanolamine) in placental trophoblasts, attenuating ferroptosis induced by GPX4 inhibition or hypoxia/reoxygenation injury in vivo.","method":"Primary human trophoblast cell culture, mouse pregnancy model, GPX4 inhibition, lipid peroxidation assays, in vitro and in vivo ferroptosis endpoints","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — both in vitro and in vivo mechanistic evidence with defined lipid substrate (15-HpETE-PE) and functional ferroptosis readouts","pmids":["33087576"],"is_preprint":false},{"year":2021,"finding":"iPLA2β hydrolyzes 15-HpETE-PE (generated by 15-LOX/PEBP1 complexes) to avert ferroptosis; genetic or pharmacological inactivation sensitizes cells to ferroptosis; a PD-associated patient mutation (R747W) selectively reduces 15-HpETE-PE-hydrolyzing activity, causes 15-HpETE-PE accumulation, and elevates ferroptosis sensitivity; CRISPR-Cas9 Pnpla9R748W/R748W mice develop progressive parkinsonian motor deficits with 15-HpETE-PE accumulation.","method":"Biochemical lipid peroxidase assay with purified iPLA2β, patient-derived fibroblasts (fPDR747W), CRISPR-Cas9 knockin mice, lipidomics (15-HpETE-PE quantification), motor behavior tests, rotenone rat model, SncaA53T mice","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct enzymatic assay with defined substrate, patient cells, CRISPR knockin mouse, multiple animal models, replicated across several systems","pmids":["33542532"],"is_preprint":false},{"year":2021,"finding":"iPLA2β suppresses p53-driven ferroptosis upon ROS-induced stress by detoxifying peroxidized lipids, even in GPX4-null cells; inhibition of endogenous iPLA2β sensitizes tumor cells to p53-driven ferroptosis and promotes p53-dependent tumor suppression in xenograft models; loss of iPLA2β has no obvious effect on normal cell viability.","method":"GPX4-null cell lines, iPLA2β inhibition and overexpression, ROS-induced stress assays, ferroptosis cell death assays, xenograft mouse tumor models","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple cell systems including GPX4-null cells, in vivo xenograft model, demonstrating GPX4-independent mechanism","pmids":["34131139"],"is_preprint":false},{"year":2015,"finding":"PLA2G6 loss-of-function causes Golgi morphology disruption and defects in protein O-linked glycosylation and sialylation in patient-derived fibroblasts; these defects are rescued by lentiviral overexpression of wild-type PLA2G6, establishing PLA2G6 as required for normal Golgi function.","method":"Patient-derived fibroblasts, HPLC and MALDI-TOF/MS glycosylation analysis, immunofluorescence for Golgi morphology, lentiviral wildtype PLA2G6 rescue","journal":"Journal of medical genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — rescue experiment with wildtype gene, multiple analytical methods, single lab","pmids":["26668131"],"is_preprint":false},{"year":2015,"finding":"In PLA2G6 knockout mice, mitochondria with damaged inner membranes appear early before symptom onset and move anterogradely into distal axons; inner mitochondrial membrane collapse accompanies axonal injury near impaired mitochondria; presynaptic membranes expand and rupture causing axon terminal degeneration; both processes generate tubulovesicular structures, the ultrastructural marker of INAD.","method":"PLA2G6 knockout mouse neuropathological analysis, electron microscopy, axonal transport studies","journal":"Neuropathology : official journal of the Japanese Society of Neuropathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — detailed ultrastructural analysis in genetic knockout, mechanistic description of degeneration sequence, single lab","pmids":["25950622"],"is_preprint":false},{"year":2016,"finding":"In PLA2G6-knockout mouse neurons, elevated α-synuclein/phosphorylated α-synuclein expression occurs early in mitochondria with degenerated inner membranes (TOM20-positive granules); in PLAN patient neurons, phospho-α-synuclein-positive inclusions with TOM20-positive edges cluster into Lewy bodies, suggesting PLA2G6 deficiency-induced mitochondrial damage drives α-synuclein accumulation and Lewy body formation.","method":"PLA2G6 knockout mouse brain immunohistochemistry, iPLA2β knockdown cell lines, human PLAN brain tissue immunohistochemistry, electron microscopy, quantitative neuronal analysis","journal":"Acta neuropathologica communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — convergent evidence from knockout mouse, knockdown cells, and human tissue, but mechanistic link is correlative","pmids":["27030050"],"is_preprint":false},{"year":2017,"finding":"PLA2G6 protein accumulates in the cores of brainstem-type Lewy bodies in both PARK14 and idiopathic Parkinson's disease patients but not in cortical Lewy bodies or other synucleinopathies, establishing a physical association between PLA2G6 and Lewy body pathology.","method":"Immunohistochemistry and Western blotting of human brain tissue from PARK14, idiopathic PD, DLB, MSA, and normal controls using anti-PLA2G6 antibodies","journal":"Neuroscience letters","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct protein localization in human tissue replicated across multiple disease groups, but purely observational without functional manipulation","pmids":["28213071"],"is_preprint":false},{"year":2018,"finding":"PARK14 (D331Y) PLA2G6 knockin mice develop early-onset death of substantia nigra dopaminergic neurons with disrupted mitochondrial cristae, mitochondrial dysfunction, elevated ROS, ER stress (elevated GRP78, IRE1, PERK, CHOP), mitophagy impairment (reduced Parkin and BNIP3), and transcriptional dysregulation; Lewy body pathology was found in substantia nigra.","method":"Knockin mouse model (PLA2G6D331Y/D331Y), dopaminergic neuron counting, electron microscopy of mitochondria, mitochondrial function assays, ER stress marker immunoblotting, motor behavior tests","journal":"Molecular neurobiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockin model with multiple mechanistic readouts establishing pathway connections between D331Y mutation and neuronal death","pmids":["30088174"],"is_preprint":false},{"year":2012,"finding":"iPLA2β in smooth muscle cells participates in vascular inflammation and neointima formation; smooth muscle-specific iPLA2β transgenic mice show exacerbated ligation-induced neointima with enhanced cytokine production and macrophage infiltration; Ang II-, arachidonic acid-, and TNF-α-induced IL-6/TNF-α expression in VSMC is suppressed by iPLA2β inhibition/deletion; downstream 12/15-lipoxygenase pathway mediates these effects.","method":"iPLA2β knockout and smooth muscle-specific transgenic mice, carotid artery ligation model, BEL pharmacological inhibition, antisense oligonucleotides, cultured VSMC with cytokine assays, 12/15-lipoxygenase genetic/pharmacological inhibition","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function, gain-of-function transgenic, and pharmacological inhibition with in vivo and in vitro endpoints","pmids":["22637477"],"is_preprint":false},{"year":2007,"finding":"iPLA2 associated with endosomal and exosomal membranes in reticulocytes is activated by reactive oxygen species produced during 15-lipoxygenase-induced mitochondria degeneration, leading to lysophosphatidylcholine generation on exosome surfaces that enables IgM antibody binding and complement-mediated clearance.","method":"Reticulocyte maturation model, subcellular fractionation (endosomal/exosomal), ROS measurement, lipid analysis, IgM binding assay, C3 deposition detection","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — subcellular localization with functional consequence (lysophosphatidylcholine generation), but indirect iPLA2 identification; gene not directly confirmed as PLA2G6","pmids":["17666570"],"is_preprint":false},{"year":2008,"finding":"iPLA2β mediates FcγRI-triggered arachidonic acid release and leukotriene B4/prostaglandin E2 generation in human monocytic cells (U937); this is protein kinase C-dependent, whereas platelet-activating factor activates cPLA2α through MAPK, demonstrating selective coupling of different stimuli to distinct PLA2 isoforms.","method":"BEL pharmacological inhibition, selective receptor agonists, eicosanoid measurement, PKC inhibitor studies in U937 cells","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — pharmacological inhibition demonstrating selective coupling, single lab, no genetic confirmation","pmids":["15007079"],"is_preprint":false},{"year":2008,"finding":"iPLA2β exhibits thioesterase activity that hydrolyzes fatty acyl-CoAs; skeletal muscle from iPLA2β-null mice shows reduced acyl-CoA thioesterase activity and reduced capacity to oxidize palmitate (but not palmitoyl-CoA or acetyl-CoA), revealing a novel function distinct from phospholipase activity that contributes to fatty acid oxidation.","method":"iPLA2β-null mouse skeletal muscle, sequential ATP/calmodulin affinity chromatography, palmitate oxidation assay, acyl-CoA thioesterase activity assay, BEL inhibition","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — biochemical enzymatic characterization plus genetic knockout validation of novel thioesterase activity in specific tissue","pmids":["18937505"],"is_preprint":false},{"year":2015,"finding":"iPLA2β inhibition blocks corticostriatal long-term potentiation (LTP) and depotentiation; acute application of docosahexaenoic acid (DHA) restores LTP after iPLA2β inhibition, indicating iPLA2β-mediated DHA release is required for corticostriatal synaptic plasticity.","method":"Acute BEL application to rat brain slices, field potential electrophysiology, DHA rescue experiment","journal":"Brain research bulletin","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — electrophysiological LTP assay with pharmacological inhibition and substrate rescue, but uses non-selective inhibitor BEL","pmids":["25562715"],"is_preprint":false},{"year":2015,"finding":"iPLA2β modulates Bcl-x pre-mRNA 5' splice site selection in β-cells; ER stress shifts splicing toward pro-apoptotic Bcl-x(S) in an iPLA2β-dependent manner; iPLA2β inactivation or knockout increases anti-apoptotic Bcl-x(L)/Bcl-x(S) ratio; 5(S)-HETE (a lipoxygenase metabolite of arachidonic acid) augments Bcl-x(L)/Bcl-x(S) ratio 15.5-fold, identifying a lipid mediator mechanism.","method":"Chemical inactivation, knockdown, RIP-iPLA2β transgenic and iPLA2β knockout mouse islets, RT-PCR splice variant quantification, exogenous lipid treatment","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic and pharmacological tools in multiple model systems, novel mechanism (alternative splicing) with lipid mediator identification","pmids":["25762722"],"is_preprint":false},{"year":2021,"finding":"iPLA2β expression increases during myocardial ischemia/reperfusion injury and the protein translocates to the ER upon I/R; iPLA2β knockout mice and siRNA knockdown reduce ER stress and cardiomyocyte apoptosis during I/R injury, demonstrating iPLA2β promotes ER stress-induced apoptosis by translocating to ER.","method":"iPLA2β knockout mice, siRNA knockdown, in vivo mouse I/R model, cell surface protein biotinylation, immunofluorescence localization to ER, ER stress markers, apoptosis assays","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout and knockdown with ER localization confirmed by two methods, in vitro and in vivo, single lab","pmids":["34207793"],"is_preprint":false}],"current_model":"PLA2G6 encodes iPLA2β, a calcium-independent phospholipase A2 that hydrolyzes the sn-2 acyl chain of glycerophospholipids (releasing fatty acids such as arachidonic acid and DHA), lysophospholipids, and fatty acyl-CoAs (thioesterase activity); it produces two catalytically active isoforms via alternative splicing (with the long isoform being ATP-activated); it preferentially cleaves oxidized/peroxidized phospholipids including the ferroptotic death signal 15-HpETE-PE to suppress ferroptosis in a GPX4-independent manner; it physically associates with retromer subunits Vps35/Vps26 to promote membrane recycling and prevent ceramide accumulation; it translocates to pseudopods during monocyte chemotaxis, to the perinucleus during insulin secretion, and to the ER/mitochondria during ER stress-induced apoptosis, acting upstream of p38 MAPK and ceramide generation to regulate β-cell apoptosis and Bcl-x splicing; in neurons, loss of iPLA2β causes phospholipid acyl-chain shortening, ER stress, mitochondrial membrane degeneration, and α-synuclein accumulation leading to dopaminergic neurodegeneration, while disease-causing mutations in PLA2G6 either abolish enzymatic activity (causing INAD/NBIA) or selectively impair peroxidized lipid hydrolysis (causing Parkinson's disease via ferroptosis sensitization)."},"narrative":{"mechanistic_narrative":"PLA2G6 encodes iPLA2β, a calcium-independent phospholipase A2 that hydrolyzes the sn-2 acyl chain of glycerophospholipids and is central to neuronal membrane homeostasis, lipid signaling, and protection from peroxidation-driven cell death [PMID:17033970, PMID:10092647]. The gene produces two catalytically active isoforms by alternative splicing, with the long isoform being ATP-activated, and its activity requires an intact ankyrin repeat domain [PMID:10092647, PMID:19893029]. Beyond canonical phospholipase activity, iPLA2β possesses fatty acyl-CoA thioesterase activity that supports fatty acid oxidation [PMID:18937505], and it selectively hydrolyzes DHA-containing phospholipids in vivo to supply DHA for brain signaling and corticostriatal synaptic plasticity [PMID:20686114, PMID:25562715]. As a signaling enzyme, iPLA2β generates arachidonic acid and lysophospholipids that act through lipoxygenase pathways to drive RGS2 induction, vascular inflammation, and store-operated Ca2+ entry, and it couples specific stimuli (vasopressin, MCP-1, FcγRI) to lipid mediator production and directional cell behaviors including monocyte chemotaxis [PMID:12089145, PMID:17613534, PMID:18208975, PMID:18156193, PMID:22637477]. In pancreatic β-cells iPLA2β amplifies insulin secretion and, under ER stress, translocates to the ER and mitochondria to drive a ceramide–mitochondrial permeability transition–caspase axis acting upstream of p38 MAPK, while also shifting Bcl-x pre-mRNA splicing toward the pro-apoptotic isoform [PMID:11278673, PMID:14744135, PMID:18936091, PMID:22194610, PMID:25762722]; an analogous ER-translocation and apoptotic role operates in myocardial ischemia/reperfusion injury [PMID:34207793]. A major protective function is the hydrolysis of the ferroptotic death signal 15-HpETE-PE, by which iPLA2β suppresses ferroptosis in a GPX4-independent manner and limits p53-driven and oxidative-stress-induced death [PMID:33087576, PMID:33542532, PMID:34131139]. iPLA2β physically associates with the retromer subunits Vps35 and Vps26 to promote membrane recycling and prevent ceramide accumulation, and maintains phospholipid acyl-chain length to avert ER stress [PMID:29909971, PMID:31548400]. Loss-of-function mutations that abolish enzyme activity cause infantile neuroaxonal dystrophy/NBIA, whereas mutations that spare general activity but selectively impair peroxidized-lipid hydrolysis cause Parkinson's disease through ferroptosis sensitization; the resulting pathology features mitochondrial inner-membrane degeneration, lipid peroxidation, and α-synuclein/Lewy body accumulation [PMID:19893029, PMID:20886109, PMID:26001724, PMID:33542532, PMID:27030050].","teleology":[{"year":1999,"claim":"Established that PLA2G6 encodes a functional calcium-independent phospholipase A2 existing as two splice isoforms with distinct ATP regulation, defining the enzyme's basic biochemistry.","evidence":"cDNA cloning from human pancreatic islets, recombinant expression, in vitro phospholipase assays with BEL inhibition","pmids":["10092647"],"confidence":"High","gaps":["Physiological substrate selectivity in vivo not yet defined","Functional significance of ATP activation of long isoform unresolved"]},{"year":2006,"claim":"Linked PLA2G6 loss-of-function to infantile neuroaxonal dystrophy, establishing the enzyme as essential for neuronal membrane homeostasis in humans.","evidence":"Homozygosity mapping and mutational analysis in INAD patients with neuropathological correlation","pmids":["17033970"],"confidence":"Medium","gaps":["No in vitro enzymatic reconstitution of mutants in this study","Molecular pathway from enzyme loss to axonal spheroids not defined"]},{"year":2009,"claim":"Demonstrated that the ankyrin repeat domain is required for catalytic activity and that abolished activity drives INAD pathology, mapping structure to function and disease.","evidence":"ENU mutagenesis mouse model with biochemical enzyme assay and ultrastructural neuropathology","pmids":["19893029"],"confidence":"High","gaps":["Mechanism by which ankyrin domain supports catalysis unresolved","Link between activity loss and tubulovesicular membrane formation indirect"]},{"year":2010,"claim":"Resolved that INAD/NBIA mutations cause near-complete activity loss whereas parkinsonism mutations spare or increase activity, establishing distinct enzymatic mechanisms for the two disease spectra.","evidence":"Purified recombinant wildtype/mutant proteins assayed against phospholipid and lysophospholipid substrates","pmids":["20886109","21700586","23182313"],"confidence":"High","gaps":["Why activity-preserving mutations cause parkinsonism not explained by general phospholipase activity","Substrate-specific defects not assayed in this work"]},{"year":2010,"claim":"Showed iPLA2β selectively liberates DHA from brain phospholipids in vivo, defining a specific lipid-signaling substrate relevant to neuronal function.","evidence":"Knockout mice with [14C]DHA tracer autoradiography across brain regions; corticostriatal LTP electrophysiology with DHA rescue","pmids":["20686114","25562715"],"confidence":"High","gaps":["Mechanistic link from DHA release to synaptic plasticity not fully defined","Inhibitor used for LTP studies is non-selective"]},{"year":2008,"claim":"Identified a non-phospholipase fatty acyl-CoA thioesterase activity of iPLA2β contributing to fatty acid oxidation, broadening its enzymatic repertoire.","evidence":"Knockout mouse skeletal muscle with affinity-purified enzyme, palmitate oxidation and thioesterase assays","pmids":["18937505"],"confidence":"High","gaps":["Relative physiological weight of thioesterase vs phospholipase activity unclear","Tissue specificity beyond muscle not established"]},{"year":2008,"claim":"Defined iPLA2β as a stimulus-selective signaling enzyme coupling specific agonists and receptors to arachidonic-acid/lysophospholipid mediator production and directional cell behavior.","evidence":"Pharmacological/antisense/knockout approaches across smooth muscle, monocytes, and U937 cells with eicosanoid, migration, and Ca2+ readouts","pmids":["12089145","17613534","18208975","18156193","15007079"],"confidence":"High","gaps":["Mechanism of agonist-specific iPLA2β recruitment unresolved","Some studies rely on non-selective BEL inhibition"]},{"year":2008,"claim":"Established that under ER stress iPLA2β translocates to ER/mitochondria and drives a ceramide–mitochondrial-permeability-transition–caspase apoptotic axis, positioning it in stress-induced cell death.","evidence":"Overexpression and BEL inhibition in INS-1 cells with subcellular fractionation, ceramide and mitochondrial membrane potential measurements, caspase/cytochrome c assays","pmids":["14744135","18936091"],"confidence":"High","gaps":["Mechanism of iPLA2β translocation to mitochondria not defined","Link between lipid hydrolysis and ceramide generation indirect"]},{"year":2013,"claim":"Placed iPLA2β upstream of p38 MAPK and showed it controls insulin secretion and Bcl-x splicing, integrating its lipid mediators into β-cell signaling and survival decisions.","evidence":"Overexpression/knockout islet and INS-1 systems with p38 inhibitor epistasis, secretion assays, and RT-PCR splice variant quantification with lipid treatment","pmids":["11278673","22194610","25762722"],"confidence":"High","gaps":["How a lipid metabolite controls splice-site selection mechanistically unresolved","Direct vs indirect activation of p38 by arachidonic acid not separated"]},{"year":2016,"claim":"Genetic mouse models established that PLA2G6 deficiency causes age-dependent dopaminergic neurodegeneration with autophagic/Ca2+ dysfunction, ER stress, mitochondrial damage, and α-synuclein/Lewy body accumulation, linking enzyme loss to parkinsonian pathology.","evidence":"Exon2 and D331Y knockin/knockout mice plus patient tissue with neuronal counting, Ca2+/autophagy assays, EM, ER stress markers, and α-synuclein immunohistochemistry","pmids":["26755131","30088174","25950622","27030050","28213071"],"confidence":"High","gaps":["Causal ordering of mitochondrial damage vs α-synuclein accumulation correlative","Direct molecular trigger of dopaminergic vulnerability unresolved"]},{"year":2018,"claim":"Revealed that iPLA2β maintains phospholipid acyl-chain length and binds retromer (Vps35/Vps26) to promote membrane recycling and prevent ceramide-driven lysosomal/ER stress, providing a membrane-homeostasis mechanism for neurodegeneration.","evidence":"Drosophila iPLA2-VIA loss-of-function with Co-IP, brain lipidomics, ER-stress markers, transgenic rescue with wildtype vs mutant human protein, and lipid/ceramide-modulating rescue","pmids":["29909971","31548400"],"confidence":"High","gaps":["Reciprocal validation and direct interface of retromer binding not detailed","Relationship between recycling defect and catalytic activity unresolved"]},{"year":2021,"claim":"Identified hydrolysis of the ferroptotic signal 15-HpETE-PE as a key protective activity, defining a GPX4-independent ferroptosis-suppressing function whose selective loss causes Parkinson's disease.","evidence":"Purified-enzyme peroxidase assays, GPX4-null cells, patient fibroblasts, CRISPR R748W knockin mice, multiple PD models, and xenograft tumor studies with ferroptosis endpoints","pmids":["33087576","33542532","34131139"],"confidence":"High","gaps":["Structural basis for selective peroxidized-lipid recognition not defined","Connection between ferroptosis suppression and earlier mitochondrial/α-synuclein phenotypes not unified"]},{"year":2021,"claim":"Showed iPLA2β translocates to the ER during myocardial ischemia/reperfusion to promote ER-stress apoptosis, extending its stress-apoptotic role beyond β-cells.","evidence":"Knockout and siRNA approaches in vivo and in cells with biotinylation/immunofluorescence ER localization and apoptosis readouts","pmids":["34207793"],"confidence":"Medium","gaps":["Single lab; signal triggering ER translocation unknown","Relationship to ceramide axis in heart not tested"]},{"year":null,"claim":"How a single enzyme reconciles its protective peroxidized-lipid-detoxifying role with its pro-apoptotic ER/mitochondrial functions, and what determines context-specific outcomes, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model linking substrate selectivity to disease-specific mutant phenotypes","Mechanism of regulated subcellular translocation across contexts unknown","Unified pathway from enzyme loss to dopaminergic neurodegeneration not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,1,9,10,19,20,30]},{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[19,20,21]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[1,11,19]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[30]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[7,18,33]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[7,24]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[3,4]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[6]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[22]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[28]}],"pathway":[{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[4,7,19,20,21,33]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[11,30]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5,8,13]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[6,27,29]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[17]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,16,20,26]}],"complexes":["retromer (Vps35/Vps26)"],"partners":["VPS35","VPS26"],"other_free_text":[]}},"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":352,"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":296,"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":287,"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":"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":170,"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":168,"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":161,"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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loss-of-function mutations in PLA2G6 cause infantile neuroaxonal dystrophy (INAD), establishing the enzyme's essential role in neuronal membrane homeostasis.\",\n      \"method\": \"Homozygosity mapping, mutational analysis, and identification of PLA2G6 mutations in INAD patients; corroborated by neuropathological findings of axonal spheroids\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic mapping with mutation identification in patients, single lab, no direct in vitro enzymatic reconstitution in this paper\",\n      \"pmids\": [\"17033970\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Human PLA2G6 (iPLA2β) gene on chromosome 22q13.1 produces two catalytically active isoforms (85 kDa and 88 kDa) via exon-skipping alternative splicing; the long isoform (LH-iPLA2) is activated by ATP whereas the short isoform (SH-iPLA2) is not, demonstrating isoform-specific regulatory differences.\",\n      \"method\": \"cDNA cloning from human pancreatic islets, recombinant protein expression, in vitro phospholipase assays with bromoenol lactone inhibition, chromosomal mapping\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro enzymatic characterization of recombinant proteins with functional distinction between isoforms, replicated in two cell types\",\n      \"pmids\": [\"10092647\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"iPLA2β (PLA2G6), but not iPLA2γ, is the primary mediator of arginine vasopressin-induced arachidonic acid release from A-10 smooth muscle cells; established using enantioselective inhibition showing (S)-BEL selectively inhibits iPLA2β (IC50 ~2 µM) while (R)-BEL preferentially inhibits iPLA2γ.\",\n      \"method\": \"Chiral HPLC separation of BEL enantiomers, pharmacological inhibition in intact cells, arachidonic acid release assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — enantioselective mechanism-based inhibitors used in intact cells with rigorous pharmacological discrimination of two enzyme isoforms\",\n      \"pmids\": [\"12089145\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"iPLA2β overexpression in INS-1 insulinoma cells amplifies glucose- and cAMP-stimulated insulin secretion without affecting arachidonic acid incorporation into phosphatidylcholine, indicating a signaling rather than housekeeping (phospholipid remodeling) role; cAMP-elevating agents cause perinuclear accumulation of iPLA2β.\",\n      \"method\": \"Stable retroviral overexpression in INS-1 cells, insulin secretion assays, ESI-MS lipid analysis, immunocytofluorescence\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (secretion assays, lipid MS, immunolocalization), overexpression and pharmacological inhibition in same system\",\n      \"pmids\": [\"11278673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"iPLA2β mediates ER stress-induced apoptosis in insulin-secreting INS-1 cells; overexpression amplifies thapsigargin-induced apoptosis and ceramide accumulation, inhibition suppresses it, and ER stress triggers caspase-3-catalyzed cleavage of 84 kDa iPLA2β to a 62 kDa product that associates with nuclei.\",\n      \"method\": \"iPLA2β overexpression in INS-1 cells, BEL pharmacological inhibition, flow cytometry for apoptosis, ceramide measurement, immunofluorescence\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — overexpression and pharmacological inhibition with multiple functional readouts (apoptosis, ceramide, caspase cleavage, nuclear translocation) in same study\",\n      \"pmids\": [\"14744135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"iPLA2β (PLA2G6) plays a pivotal role in angiotensin II-induced RGS2 mRNA upregulation in vascular smooth muscle cells; demonstrated by three independent approaches (BEL inhibition, antisense oligonucleotides, iPLA2β-null mice); Ang II stimulates iPLA2 enzymatic activity in VSMC; downstream products arachidonic acid and lysophosphatidylcholine induce RGS2 via lipoxygenase pathway.\",\n      \"method\": \"Pharmacological inhibition (BEL), antisense oligonucleotide knockdown, iPLA2β knockout mice, adenovirus-mediated gene rescue, iPLA2 enzymatic activity assays, real-time PCR\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — three independent genetic/pharmacological approaches with gene rescue in null cells, multiple orthogonal methods\",\n      \"pmids\": [\"17613534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Upon MCP-1 stimulation, iPLA2β translocates to the membrane-enriched pseudopod in monocytes and controls directionality and actin polymerization during chemotaxis; antisense knockdown of iPLA2β reduces migration speed, directionality, and abolishes in vivo peritoneal migration.\",\n      \"method\": \"Antisense oligonucleotide knockdown, immunofluorescence localization, in vitro chemotaxis assays, adoptive transfer in vivo migration assay\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vitro and in vivo evidence with subcellular localization and functional knockdown, multiple readouts\",\n      \"pmids\": [\"18208975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"iPLA2β mediates ER stress-induced apoptosis via a ceramide-mitochondria axis: ER stress promotes iPLA2β accumulation in mitochondria, ceramide generation via sphingomyelin hydrolysis, mitochondrial permeability transition pore opening, loss of mitochondrial membrane potential, cytochrome c/Smac release, and caspase-3 activation; these are amplified by iPLA2β overexpression and inhibited by iPLA2β inactivation or NSMase inhibition.\",\n      \"method\": \"iPLA2β overexpressing INS-1 cells (OE), BEL inhibition, subcellular fractionation, ceramide measurement in ER and mitochondria fractions, mitochondrial membrane potential assay, cytochrome c/Smac immunoblotting\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — subcellular fractionation demonstrating mitochondrial translocation plus multiple functional endpoints, overexpression and pharmacological inhibition\",\n      \"pmids\": [\"18936091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"iPLA2β-dependent activation of store-operated Ca2+ channels (SOC) is required for agonist-induced Ca2+ influx and vasoconstriction in cerebral, mesenteric, and carotid arteries; iPLA2β inhibition abolishes phenylephrine-induced Ca2+ entry without affecting K+-induced (voltage-gated L-type channel-dependent) vasoconstriction.\",\n      \"method\": \"Pharmacological inhibition of iPLA2β (BEL) in intact pressurized vessels, simultaneous measurement of intracellular Ca2+ and vessel diameter\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct functional assay in intact vessels, pharmacological inhibitor only, single lab\",\n      \"pmids\": [\"18156193\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"A point mutation in the ankyrin repeat domain of Pla2g6 completely abolishes glycerophospholipid-catalyzing enzyme activity while allowing protein expression, demonstrating that the ankyrin repeat domain is required for catalytic function and that loss of iPLA2β enzymatic activity causes INAD neuropathology.\",\n      \"method\": \"ENU mutagenesis mouse model, biochemical enzyme activity assay on mutant protein, neuropathological examination (axonal spheroids with tubulovesicular membranes)\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct enzymatic assay demonstrating zero activity of mutant protein, with in vivo phenotypic validation\",\n      \"pmids\": [\"19893029\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PLA2G6 mutations associated with INAD/NBIA cause loss of enzyme activity (<20% residual activity for both phospholipase and lysophospholipase substrates), while mutations associated with dystonia-parkinsonism do not impair catalytic activity and two mutations increase specific activity for phospholipid substrates, indicating distinct disease mechanisms.\",\n      \"method\": \"Purified recombinant wildtype and mutant human PLA2G6 proteins, in vitro phospholipase and lysophospholipase assays with radiolabeled lipid substrates\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro enzymatic reconstitution with multiple disease-associated mutants tested against two substrate classes\",\n      \"pmids\": [\"20886109\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"iPLA2β deficiency in mice reduces brain DHA metabolism and signaling both at baseline and following muscarinic receptor activation, consistent with iPLA2β selectively hydrolyzing DHA from phospholipids in vivo.\",\n      \"method\": \"iPLA2β knockout mice, quantitative autoradiography with [1-14C]DHA intravenous infusion, measurement of DHA incorporation coefficients in 81 brain regions\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — quantitative in vivo imaging with isotope tracer in knockout vs. wildtype across three genotypes, multiple brain regions\",\n      \"pmids\": [\"20686114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Homozygous PLA2G6 D331Y mutation causes ~70% reduction in iPLA2β enzyme activity in vitro, linking reduced catalytic activity to autosomal recessive early-onset parkinsonism.\",\n      \"method\": \"Direct sequencing for mutation identification, in vitro enzyme activity assay of D331Y mutant vs. wildtype PLA2G6\",\n      \"journal\": \"Neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — direct enzymatic assay, single lab, one mutation tested\",\n      \"pmids\": [\"21700586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"iPLA2β is activated upstream of p38 MAPK in pancreatic β-cells: glucose and thapsigargin stimulate p38 MAPK phosphorylation in an iPLA2β-dependent manner; p38 MAPK inhibition prevents insulin secretion and apoptosis downstream of iPLA2β; iPLA2β product arachidonic acid activates p38 MAPK.\",\n      \"method\": \"iPLA2β overexpressing INS-1 cells and knockout mice islets, BEL pharmacological inhibition, p38 MAPK inhibitor PD169316, phosphorylation immunoblotting, insulin secretion assay, apoptosis assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — epistasis established with pharmacological and genetic tools across multiple cell systems, multiple orthogonal endpoints\",\n      \"pmids\": [\"22194610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Three PLA2G6 frameshift and missense mutations found in PD patients reduce iPLA2β phospholipase activity (P.His597fx69: <6% residual activity; Leu656Val: 55% residual; Leu693Val: 65% residual), extending the genotype-activity relationship in PD-associated PLA2G6 mutations.\",\n      \"method\": \"Sequencing in patient cohort, in vitro phospholipase assay with recombinant mutant proteins\",\n      \"journal\": \"Parkinsonism & related disorders\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — direct enzymatic assay with recombinant proteins, single lab, limited patient numbers\",\n      \"pmids\": [\"23182313\"],\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 were confirmed in fibroblasts from human PLA2G6 mutation patients; deuterated PUFAs (inhibiting lipid peroxidation) partially rescued locomotor deficits and restored mitochondrial membrane potential.\",\n      \"method\": \"Drosophila iPLA2-VIA knockout, mitochondrial respiratory chain assays, ATP measurement, electron microscopy, lipid peroxidation assays; patient-derived fibroblast studies; deuterated PUFA rescue experiment\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods in two model systems (fly and human cells), with mechanistic rescue experiment\",\n      \"pmids\": [\"26001724\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PLA2G6-dependent Ca2+ signaling activates store-operated Ca2+ entry (SOCE); genetic or molecular impairment of PLA2g6-dependent Ca2+ signaling in a PLA2g6 exon2 knockout mouse triggers autophagic dysfunction and progressive loss of dopaminergic neurons in substantia nigra pars compacta with age-dependent L-DOPA-sensitive motor dysfunction.\",\n      \"method\": \"PLA2g6 exon2 knockout mouse model, Ca2+ signaling measurements, autophagy assays, dopaminergic neuron counting, behavioral motor tests\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout mouse with multiple cellular and behavioral phenotypic readouts establishing pathway position\",\n      \"pmids\": [\"26755131\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"iPLA2-VIA (Drosophila PLA2G6 homolog) binds retromer subunits Vps35 and Vps26 and enhances retromer function to promote protein and lipid recycling; loss of iPLA2-VIA does not alter phospholipid composition but causes elevation of ceramides leading to lysosomal stress and neurodegeneration; reducing ceramides with myriocin or desipramine alleviates neurodegeneration.\",\n      \"method\": \"Co-immunoprecipitation/pulldown of iPLA2-VIA with Vps35/Vps26, lipidomics of fly brain tissue, pharmacological ceramide reduction (myriocin, desipramine), Drosophila genetic loss-of-function\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — binding partner identified by Co-IP, lipidomics, and pharmacological rescue with multiple readouts in single rigorous study\",\n      \"pmids\": [\"29909971\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Loss of iPLA2-VIA in Drosophila shortens acyl-chain length of phospholipids, causing ER stress through membrane lipid disequilibrium; wild-type human iPLA2-VIA or the mitochondria-ER contact site protein C19orf12 rescues lipid composition, ER stress, and DA neurodegeneration, while disease-associated A80T mutant fails to rescue; linoleic acid supplementation corrects brain lipid composition and suppresses α-synuclein aggregation.\",\n      \"method\": \"iPLA2-VIA-deficient Drosophila, lipid mass spectrometry of brain tissue, ER stress markers, transgenic rescue with wildtype vs. mutant human iPLA2-VIA, linoleic acid supplementation, α-synuclein aggregation assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods including lipidomics, genetic rescue with wildtype vs. disease mutant, and lipid supplementation rescue\",\n      \"pmids\": [\"31548400\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PLA2G6 (iPLA2β) hydrolyzes ferroptotic death signal 15-HpETE-PE (hydroperoxy-arachidonoyl-phosphatidylethanolamine) in placental trophoblasts, attenuating ferroptosis induced by GPX4 inhibition or hypoxia/reoxygenation injury in vivo.\",\n      \"method\": \"Primary human trophoblast cell culture, mouse pregnancy model, GPX4 inhibition, lipid peroxidation assays, in vitro and in vivo ferroptosis endpoints\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — both in vitro and in vivo mechanistic evidence with defined lipid substrate (15-HpETE-PE) and functional ferroptosis readouts\",\n      \"pmids\": [\"33087576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"iPLA2β hydrolyzes 15-HpETE-PE (generated by 15-LOX/PEBP1 complexes) to avert ferroptosis; genetic or pharmacological inactivation sensitizes cells to ferroptosis; a PD-associated patient mutation (R747W) selectively reduces 15-HpETE-PE-hydrolyzing activity, causes 15-HpETE-PE accumulation, and elevates ferroptosis sensitivity; CRISPR-Cas9 Pnpla9R748W/R748W mice develop progressive parkinsonian motor deficits with 15-HpETE-PE accumulation.\",\n      \"method\": \"Biochemical lipid peroxidase assay with purified iPLA2β, patient-derived fibroblasts (fPDR747W), CRISPR-Cas9 knockin mice, lipidomics (15-HpETE-PE quantification), motor behavior tests, rotenone rat model, SncaA53T mice\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct enzymatic assay with defined substrate, patient cells, CRISPR knockin mouse, multiple animal models, replicated across several systems\",\n      \"pmids\": [\"33542532\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"iPLA2β suppresses p53-driven ferroptosis upon ROS-induced stress by detoxifying peroxidized lipids, even in GPX4-null cells; inhibition of endogenous iPLA2β sensitizes tumor cells to p53-driven ferroptosis and promotes p53-dependent tumor suppression in xenograft models; loss of iPLA2β has no obvious effect on normal cell viability.\",\n      \"method\": \"GPX4-null cell lines, iPLA2β inhibition and overexpression, ROS-induced stress assays, ferroptosis cell death assays, xenograft mouse tumor models\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple cell systems including GPX4-null cells, in vivo xenograft model, demonstrating GPX4-independent mechanism\",\n      \"pmids\": [\"34131139\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PLA2G6 loss-of-function causes Golgi morphology disruption and defects in protein O-linked glycosylation and sialylation in patient-derived fibroblasts; these defects are rescued by lentiviral overexpression of wild-type PLA2G6, establishing PLA2G6 as required for normal Golgi function.\",\n      \"method\": \"Patient-derived fibroblasts, HPLC and MALDI-TOF/MS glycosylation analysis, immunofluorescence for Golgi morphology, lentiviral wildtype PLA2G6 rescue\",\n      \"journal\": \"Journal of medical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — rescue experiment with wildtype gene, multiple analytical methods, single lab\",\n      \"pmids\": [\"26668131\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"In PLA2G6 knockout mice, mitochondria with damaged inner membranes appear early before symptom onset and move anterogradely into distal axons; inner mitochondrial membrane collapse accompanies axonal injury near impaired mitochondria; presynaptic membranes expand and rupture causing axon terminal degeneration; both processes generate tubulovesicular structures, the ultrastructural marker of INAD.\",\n      \"method\": \"PLA2G6 knockout mouse neuropathological analysis, electron microscopy, axonal transport studies\",\n      \"journal\": \"Neuropathology : official journal of the Japanese Society of Neuropathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — detailed ultrastructural analysis in genetic knockout, mechanistic description of degeneration sequence, single lab\",\n      \"pmids\": [\"25950622\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In PLA2G6-knockout mouse neurons, elevated α-synuclein/phosphorylated α-synuclein expression occurs early in mitochondria with degenerated inner membranes (TOM20-positive granules); in PLAN patient neurons, phospho-α-synuclein-positive inclusions with TOM20-positive edges cluster into Lewy bodies, suggesting PLA2G6 deficiency-induced mitochondrial damage drives α-synuclein accumulation and Lewy body formation.\",\n      \"method\": \"PLA2G6 knockout mouse brain immunohistochemistry, iPLA2β knockdown cell lines, human PLAN brain tissue immunohistochemistry, electron microscopy, quantitative neuronal analysis\",\n      \"journal\": \"Acta neuropathologica communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — convergent evidence from knockout mouse, knockdown cells, and human tissue, but mechanistic link is correlative\",\n      \"pmids\": [\"27030050\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PLA2G6 protein accumulates in the cores of brainstem-type Lewy bodies in both PARK14 and idiopathic Parkinson's disease patients but not in cortical Lewy bodies or other synucleinopathies, establishing a physical association between PLA2G6 and Lewy body pathology.\",\n      \"method\": \"Immunohistochemistry and Western blotting of human brain tissue from PARK14, idiopathic PD, DLB, MSA, and normal controls using anti-PLA2G6 antibodies\",\n      \"journal\": \"Neuroscience letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct protein localization in human tissue replicated across multiple disease groups, but purely observational without functional manipulation\",\n      \"pmids\": [\"28213071\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PARK14 (D331Y) PLA2G6 knockin mice develop early-onset death of substantia nigra dopaminergic neurons with disrupted mitochondrial cristae, mitochondrial dysfunction, elevated ROS, ER stress (elevated GRP78, IRE1, PERK, CHOP), mitophagy impairment (reduced Parkin and BNIP3), and transcriptional dysregulation; Lewy body pathology was found in substantia nigra.\",\n      \"method\": \"Knockin mouse model (PLA2G6D331Y/D331Y), dopaminergic neuron counting, electron microscopy of mitochondria, mitochondrial function assays, ER stress marker immunoblotting, motor behavior tests\",\n      \"journal\": \"Molecular neurobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockin model with multiple mechanistic readouts establishing pathway connections between D331Y mutation and neuronal death\",\n      \"pmids\": [\"30088174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"iPLA2β in smooth muscle cells participates in vascular inflammation and neointima formation; smooth muscle-specific iPLA2β transgenic mice show exacerbated ligation-induced neointima with enhanced cytokine production and macrophage infiltration; Ang II-, arachidonic acid-, and TNF-α-induced IL-6/TNF-α expression in VSMC is suppressed by iPLA2β inhibition/deletion; downstream 12/15-lipoxygenase pathway mediates these effects.\",\n      \"method\": \"iPLA2β knockout and smooth muscle-specific transgenic mice, carotid artery ligation model, BEL pharmacological inhibition, antisense oligonucleotides, cultured VSMC with cytokine assays, 12/15-lipoxygenase genetic/pharmacological inhibition\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function, gain-of-function transgenic, and pharmacological inhibition with in vivo and in vitro endpoints\",\n      \"pmids\": [\"22637477\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"iPLA2 associated with endosomal and exosomal membranes in reticulocytes is activated by reactive oxygen species produced during 15-lipoxygenase-induced mitochondria degeneration, leading to lysophosphatidylcholine generation on exosome surfaces that enables IgM antibody binding and complement-mediated clearance.\",\n      \"method\": \"Reticulocyte maturation model, subcellular fractionation (endosomal/exosomal), ROS measurement, lipid analysis, IgM binding assay, C3 deposition detection\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — subcellular localization with functional consequence (lysophosphatidylcholine generation), but indirect iPLA2 identification; gene not directly confirmed as PLA2G6\",\n      \"pmids\": [\"17666570\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"iPLA2β mediates FcγRI-triggered arachidonic acid release and leukotriene B4/prostaglandin E2 generation in human monocytic cells (U937); this is protein kinase C-dependent, whereas platelet-activating factor activates cPLA2α through MAPK, demonstrating selective coupling of different stimuli to distinct PLA2 isoforms.\",\n      \"method\": \"BEL pharmacological inhibition, selective receptor agonists, eicosanoid measurement, PKC inhibitor studies in U937 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — pharmacological inhibition demonstrating selective coupling, single lab, no genetic confirmation\",\n      \"pmids\": [\"15007079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"iPLA2β exhibits thioesterase activity that hydrolyzes fatty acyl-CoAs; skeletal muscle from iPLA2β-null mice shows reduced acyl-CoA thioesterase activity and reduced capacity to oxidize palmitate (but not palmitoyl-CoA or acetyl-CoA), revealing a novel function distinct from phospholipase activity that contributes to fatty acid oxidation.\",\n      \"method\": \"iPLA2β-null mouse skeletal muscle, sequential ATP/calmodulin affinity chromatography, palmitate oxidation assay, acyl-CoA thioesterase activity assay, BEL inhibition\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — biochemical enzymatic characterization plus genetic knockout validation of novel thioesterase activity in specific tissue\",\n      \"pmids\": [\"18937505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"iPLA2β inhibition blocks corticostriatal long-term potentiation (LTP) and depotentiation; acute application of docosahexaenoic acid (DHA) restores LTP after iPLA2β inhibition, indicating iPLA2β-mediated DHA release is required for corticostriatal synaptic plasticity.\",\n      \"method\": \"Acute BEL application to rat brain slices, field potential electrophysiology, DHA rescue experiment\",\n      \"journal\": \"Brain research bulletin\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — electrophysiological LTP assay with pharmacological inhibition and substrate rescue, but uses non-selective inhibitor BEL\",\n      \"pmids\": [\"25562715\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"iPLA2β modulates Bcl-x pre-mRNA 5' splice site selection in β-cells; ER stress shifts splicing toward pro-apoptotic Bcl-x(S) in an iPLA2β-dependent manner; iPLA2β inactivation or knockout increases anti-apoptotic Bcl-x(L)/Bcl-x(S) ratio; 5(S)-HETE (a lipoxygenase metabolite of arachidonic acid) augments Bcl-x(L)/Bcl-x(S) ratio 15.5-fold, identifying a lipid mediator mechanism.\",\n      \"method\": \"Chemical inactivation, knockdown, RIP-iPLA2β transgenic and iPLA2β knockout mouse islets, RT-PCR splice variant quantification, exogenous lipid treatment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic and pharmacological tools in multiple model systems, novel mechanism (alternative splicing) with lipid mediator identification\",\n      \"pmids\": [\"25762722\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"iPLA2β expression increases during myocardial ischemia/reperfusion injury and the protein translocates to the ER upon I/R; iPLA2β knockout mice and siRNA knockdown reduce ER stress and cardiomyocyte apoptosis during I/R injury, demonstrating iPLA2β promotes ER stress-induced apoptosis by translocating to ER.\",\n      \"method\": \"iPLA2β knockout mice, siRNA knockdown, in vivo mouse I/R model, cell surface protein biotinylation, immunofluorescence localization to ER, ER stress markers, apoptosis assays\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout and knockdown with ER localization confirmed by two methods, in vitro and in vivo, single lab\",\n      \"pmids\": [\"34207793\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PLA2G6 encodes iPLA2β, a calcium-independent phospholipase A2 that hydrolyzes the sn-2 acyl chain of glycerophospholipids (releasing fatty acids such as arachidonic acid and DHA), lysophospholipids, and fatty acyl-CoAs (thioesterase activity); it produces two catalytically active isoforms via alternative splicing (with the long isoform being ATP-activated); it preferentially cleaves oxidized/peroxidized phospholipids including the ferroptotic death signal 15-HpETE-PE to suppress ferroptosis in a GPX4-independent manner; it physically associates with retromer subunits Vps35/Vps26 to promote membrane recycling and prevent ceramide accumulation; it translocates to pseudopods during monocyte chemotaxis, to the perinucleus during insulin secretion, and to the ER/mitochondria during ER stress-induced apoptosis, acting upstream of p38 MAPK and ceramide generation to regulate β-cell apoptosis and Bcl-x splicing; in neurons, loss of iPLA2β causes phospholipid acyl-chain shortening, ER stress, mitochondrial membrane degeneration, and α-synuclein accumulation leading to dopaminergic neurodegeneration, while disease-causing mutations in PLA2G6 either abolish enzymatic activity (causing INAD/NBIA) or selectively impair peroxidized lipid hydrolysis (causing Parkinson's disease via ferroptosis sensitization).\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PLA2G6 encodes iPLA2β, a calcium-independent phospholipase A2 that hydrolyzes the sn-2 acyl chain of glycerophospholipids and is central to neuronal membrane homeostasis, lipid signaling, and protection from peroxidation-driven cell death [#0, #1]. The gene produces two catalytically active isoforms by alternative splicing, with the long isoform being ATP-activated, and its activity requires an intact ankyrin repeat domain [#1, #9]. Beyond canonical phospholipase activity, iPLA2β possesses fatty acyl-CoA thioesterase activity that supports fatty acid oxidation [#30], and it selectively hydrolyzes DHA-containing phospholipids in vivo to supply DHA for brain signaling and corticostriatal synaptic plasticity [#11, #31]. As a signaling enzyme, iPLA2β generates arachidonic acid and lysophospholipids that act through lipoxygenase pathways to drive RGS2 induction, vascular inflammation, and store-operated Ca2+ entry, and it couples specific stimuli (vasopressin, MCP-1, FcγRI) to lipid mediator production and directional cell behaviors including monocyte chemotaxis [#2, #5, #6, #8, #27]. In pancreatic β-cells iPLA2β amplifies insulin secretion and, under ER stress, translocates to the ER and mitochondria to drive a ceramide–mitochondrial permeability transition–caspase axis acting upstream of p38 MAPK, while also shifting Bcl-x pre-mRNA splicing toward the pro-apoptotic isoform [#3, #4, #7, #13, #32]; an analogous ER-translocation and apoptotic role operates in myocardial ischemia/reperfusion injury [#33]. A major protective function is the hydrolysis of the ferroptotic death signal 15-HpETE-PE, by which iPLA2β suppresses ferroptosis in a GPX4-independent manner and limits p53-driven and oxidative-stress-induced death [#19, #20, #21]. iPLA2β physically associates with the retromer subunits Vps35 and Vps26 to promote membrane recycling and prevent ceramide accumulation, and maintains phospholipid acyl-chain length to avert ER stress [#17, #18]. Loss-of-function mutations that abolish enzyme activity cause infantile neuroaxonal dystrophy/NBIA, whereas mutations that spare general activity but selectively impair peroxidized-lipid hydrolysis cause Parkinson's disease through ferroptosis sensitization; the resulting pathology features mitochondrial inner-membrane degeneration, lipid peroxidation, and α-synuclein/Lewy body accumulation [#9, #10, #15, #20, #24].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Established that PLA2G6 encodes a functional calcium-independent phospholipase A2 existing as two splice isoforms with distinct ATP regulation, defining the enzyme's basic biochemistry.\",\n      \"evidence\": \"cDNA cloning from human pancreatic islets, recombinant expression, in vitro phospholipase assays with BEL inhibition\",\n      \"pmids\": [\"10092647\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological substrate selectivity in vivo not yet defined\", \"Functional significance of ATP activation of long isoform unresolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Linked PLA2G6 loss-of-function to infantile neuroaxonal dystrophy, establishing the enzyme as essential for neuronal membrane homeostasis in humans.\",\n      \"evidence\": \"Homozygosity mapping and mutational analysis in INAD patients with neuropathological correlation\",\n      \"pmids\": [\"17033970\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No in vitro enzymatic reconstitution of mutants in this study\", \"Molecular pathway from enzyme loss to axonal spheroids not defined\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrated that the ankyrin repeat domain is required for catalytic activity and that abolished activity drives INAD pathology, mapping structure to function and disease.\",\n      \"evidence\": \"ENU mutagenesis mouse model with biochemical enzyme assay and ultrastructural neuropathology\",\n      \"pmids\": [\"19893029\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which ankyrin domain supports catalysis unresolved\", \"Link between activity loss and tubulovesicular membrane formation indirect\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Resolved that INAD/NBIA mutations cause near-complete activity loss whereas parkinsonism mutations spare or increase activity, establishing distinct enzymatic mechanisms for the two disease spectra.\",\n      \"evidence\": \"Purified recombinant wildtype/mutant proteins assayed against phospholipid and lysophospholipid substrates\",\n      \"pmids\": [\"20886109\", \"21700586\", \"23182313\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why activity-preserving mutations cause parkinsonism not explained by general phospholipase activity\", \"Substrate-specific defects not assayed in this work\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Showed iPLA2β selectively liberates DHA from brain phospholipids in vivo, defining a specific lipid-signaling substrate relevant to neuronal function.\",\n      \"evidence\": \"Knockout mice with [14C]DHA tracer autoradiography across brain regions; corticostriatal LTP electrophysiology with DHA rescue\",\n      \"pmids\": [\"20686114\", \"25562715\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanistic link from DHA release to synaptic plasticity not fully defined\", \"Inhibitor used for LTP studies is non-selective\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identified a non-phospholipase fatty acyl-CoA thioesterase activity of iPLA2β contributing to fatty acid oxidation, broadening its enzymatic repertoire.\",\n      \"evidence\": \"Knockout mouse skeletal muscle with affinity-purified enzyme, palmitate oxidation and thioesterase assays\",\n      \"pmids\": [\"18937505\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative physiological weight of thioesterase vs phospholipase activity unclear\", \"Tissue specificity beyond muscle not established\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Defined iPLA2β as a stimulus-selective signaling enzyme coupling specific agonists and receptors to arachidonic-acid/lysophospholipid mediator production and directional cell behavior.\",\n      \"evidence\": \"Pharmacological/antisense/knockout approaches across smooth muscle, monocytes, and U937 cells with eicosanoid, migration, and Ca2+ readouts\",\n      \"pmids\": [\"12089145\", \"17613534\", \"18208975\", \"18156193\", \"15007079\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of agonist-specific iPLA2β recruitment unresolved\", \"Some studies rely on non-selective BEL inhibition\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Established that under ER stress iPLA2β translocates to ER/mitochondria and drives a ceramide–mitochondrial-permeability-transition–caspase apoptotic axis, positioning it in stress-induced cell death.\",\n      \"evidence\": \"Overexpression and BEL inhibition in INS-1 cells with subcellular fractionation, ceramide and mitochondrial membrane potential measurements, caspase/cytochrome c assays\",\n      \"pmids\": [\"14744135\", \"18936091\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of iPLA2β translocation to mitochondria not defined\", \"Link between lipid hydrolysis and ceramide generation indirect\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Placed iPLA2β upstream of p38 MAPK and showed it controls insulin secretion and Bcl-x splicing, integrating its lipid mediators into β-cell signaling and survival decisions.\",\n      \"evidence\": \"Overexpression/knockout islet and INS-1 systems with p38 inhibitor epistasis, secretion assays, and RT-PCR splice variant quantification with lipid treatment\",\n      \"pmids\": [\"11278673\", \"22194610\", \"25762722\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How a lipid metabolite controls splice-site selection mechanistically unresolved\", \"Direct vs indirect activation of p38 by arachidonic acid not separated\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Genetic mouse models established that PLA2G6 deficiency causes age-dependent dopaminergic neurodegeneration with autophagic/Ca2+ dysfunction, ER stress, mitochondrial damage, and α-synuclein/Lewy body accumulation, linking enzyme loss to parkinsonian pathology.\",\n      \"evidence\": \"Exon2 and D331Y knockin/knockout mice plus patient tissue with neuronal counting, Ca2+/autophagy assays, EM, ER stress markers, and α-synuclein immunohistochemistry\",\n      \"pmids\": [\"26755131\", \"30088174\", \"25950622\", \"27030050\", \"28213071\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal ordering of mitochondrial damage vs α-synuclein accumulation correlative\", \"Direct molecular trigger of dopaminergic vulnerability unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Revealed that iPLA2β maintains phospholipid acyl-chain length and binds retromer (Vps35/Vps26) to promote membrane recycling and prevent ceramide-driven lysosomal/ER stress, providing a membrane-homeostasis mechanism for neurodegeneration.\",\n      \"evidence\": \"Drosophila iPLA2-VIA loss-of-function with Co-IP, brain lipidomics, ER-stress markers, transgenic rescue with wildtype vs mutant human protein, and lipid/ceramide-modulating rescue\",\n      \"pmids\": [\"29909971\", \"31548400\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Reciprocal validation and direct interface of retromer binding not detailed\", \"Relationship between recycling defect and catalytic activity unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified hydrolysis of the ferroptotic signal 15-HpETE-PE as a key protective activity, defining a GPX4-independent ferroptosis-suppressing function whose selective loss causes Parkinson's disease.\",\n      \"evidence\": \"Purified-enzyme peroxidase assays, GPX4-null cells, patient fibroblasts, CRISPR R748W knockin mice, multiple PD models, and xenograft tumor studies with ferroptosis endpoints\",\n      \"pmids\": [\"33087576\", \"33542532\", \"34131139\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for selective peroxidized-lipid recognition not defined\", \"Connection between ferroptosis suppression and earlier mitochondrial/α-synuclein phenotypes not unified\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed iPLA2β translocates to the ER during myocardial ischemia/reperfusion to promote ER-stress apoptosis, extending its stress-apoptotic role beyond β-cells.\",\n      \"evidence\": \"Knockout and siRNA approaches in vivo and in cells with biotinylation/immunofluorescence ER localization and apoptosis readouts\",\n      \"pmids\": [\"34207793\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; signal triggering ER translocation unknown\", \"Relationship to ceramide axis in heart not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single enzyme reconciles its protective peroxidized-lipid-detoxifying role with its pro-apoptotic ER/mitochondrial functions, and what determines context-specific outcomes, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model linking substrate selectivity to disease-specific mutant phenotypes\", \"Mechanism of regulated subcellular translocation across contexts unknown\", \"Unified pathway from enzyme loss to dopaminergic neurodegeneration not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 1, 9, 10, 19, 20, 30]},\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [19, 20, 21]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [1, 11, 19]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [30]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [7, 18, 33]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [7, 24]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [22]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [28]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [4, 7, 19, 20, 21, 33]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [11, 30]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 8, 13]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [6, 27, 29]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [17]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 16, 20, 26]}\n    ],\n    \"complexes\": [\"retromer (Vps35/Vps26)\"],\n    \"partners\": [\"VPS35\", \"VPS26\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}