{"gene":"CHMP2B","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":2005,"finding":"CHMP2B is a component of the endosomal ESCRT-III complex; a splice-site mutation causes aberrant mRNA splicing and is causative for frontotemporal dementia (FTD3) in a Danish pedigree, implicating ESCRT-III dysfunction in neurodegeneration.","method":"Genetic linkage, mutation identification, mRNA splicing analysis in patient tissue","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — foundational disease-gene identification with direct molecular evidence of aberrant splicing in patient tissue, independently replicated across multiple subsequent studies","pmids":["16041373"],"is_preprint":false},{"year":2007,"finding":"C-truncating mutations in CHMP2B (both Danish p.Met178ValfsX2 and Belgian p.Gln165X) cause formation of large, aberrant endosomal structures when overexpressed in human neuroblastoma SK-N-SH cells, linking C-terminal truncation to endosomal dysfunction.","method":"Overexpression of mutant CHMP2B constructs in SK-N-SH cells, fluorescence microscopy of endosomal morphology","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — consistent morphological phenotype replicated with two independent mutant constructs in cell overexpression system, single lab","pmids":["17956895"],"is_preprint":false},{"year":2010,"finding":"Mutant CHMP2B disrupts endosome-lysosome fusion but not protein sorting by the MVB. The mechanism involves mutant CHMP2B constitutively binding to MVBs and preventing recruitment of Rab7, a protein necessary for endosome-lysosome fusion.","method":"Functional assays in patient fibroblasts and patient brain tissue; Rab7 localization studies; endosomal morphology analysis","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Moderate — mechanistic pathway placement (endosome-lysosome fusion vs. MVB sorting) with identification of Rab7 as the recruited factor blocked by mutant CHMP2B, in patient-derived cells and brain tissue","pmids":["20223751"],"is_preprint":false},{"year":2010,"finding":"Transfection of mutant CHMP2B into HEK-293 and COS-7 cells results in large cytoplasmic vacuoles, aberrant lysosomal localization (CD63 staining), and impairment of autophagy (increased LC3-II), demonstrating that CHMP2B mutations disrupt the autophagy-lysosomal pathway.","method":"Transfection of mutant vs. wild-type CHMP2B in HEK-293 and COS-7 cells; CD63 immunostaining; LC3-II western blot","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — multiple cell lines, multiple orthogonal readouts (vacuole formation, lysosomal marker, autophagy marker), single lab","pmids":["20352044"],"is_preprint":false},{"year":2010,"finding":"CHMP2B is required for normal dendritic spine growth. FTD-linked CHMP2B mutants (CHMP2B-Intron5 and CHMP2B-Delta10) reduce the proportion of large mushroom-shaped spines in hippocampal neurons; CHMP2B-Delta10 also reduces frequency and amplitude of excitatory postsynaptic currents. RNAi depletion of endogenous CHMP2B phenocopies mutants, indicating dominant-negative activity.","method":"Expression of mutant CHMP2B in cultured hippocampal neurons; confocal microscopy and 3D reconstruction of spine morphology; electrophysiology (mEPSC recordings); RNAi knockdown","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (morphology, electrophysiology, RNAi phenocopy) in a single focused study establishing synaptic role","pmids":["20699355"],"is_preprint":false},{"year":2011,"finding":"CHMP2B polymerizes into helical structures that deform membranes in cellulo. Depletion of VPS4 induces accumulation of endogenous CHMP2B at the plasma membrane; overexpressed full-length CHMP2B forms long, rigid tubes protruding from cells. Cryo-EM shows CHMP2B polymerizes into a tightly packed helical lattice closely associated with the inner leaflet of membrane tubes, sufficient to deform the lipid bilayer. CHMP4s relocalize at the base of the tubes; tube formation depends on VPS4.","method":"VPS4 depletion; live-cell imaging; cryo-electron microscopy of CHMP2B membrane tubes; immunofluorescence of CHMP4 localization","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — cryo-EM structural data with in-cellulo functional validation; multiple orthogonal methods in one study","pmids":["21926173"],"is_preprint":false},{"year":2012,"finding":"Transgenic mice expressing C-terminally truncated mutant CHMP2B show progressive neurodegeneration (gliosis, p62/ubiquitin-positive inclusions, axonal swellings) not seen in Chmp2b knockout or wild-type CHMP2B transgenic mice, establishing that CHMP2B mutations cause neurodegeneration via a gain-of-function mechanism.","method":"Transgenic mouse models (mutant CHMP2B, wild-type CHMP2B, Chmp2b knockout); immunohistochemistry; neuropathological analysis","journal":"Brain : a journal of neurology","confidence":"High","confidence_rationale":"Tier 2 / Strong — comparative transgenic/knockout mouse study with multiple neuropathological readouts demonstrating gain-of-function vs. loss-of-function distinction","pmids":["22366797"],"is_preprint":false},{"year":2012,"finding":"STX13 (syntaxin 13) is a genetic modifier of mutant CHMP2B and is required for autophagosome maturation. Knockdown of STX13 or its binding partner Vti1a in mammalian cells causes accumulation of LC3-positive puncta and blocks autophagic flux. STX13 is present on LC3-positive phagophores and multilamellar structures induced by dysfunctional ESCRT-III. Loss of STX13 causes accumulation of Atg5-positive puncta and multilamellar structure formation, indicating STX13 participates in phagophore-to-autophagosome maturation.","method":"Drosophila genetic modifier screen with mutant CHMP2B; mammalian cell knockdown of STX13 and Vti1a; LC3/Atg5 immunofluorescence; autophagic flux assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic epistasis in Drosophila combined with mammalian cell mechanistic follow-up using multiple markers; clear pathway placement","pmids":["24095276"],"is_preprint":false},{"year":2012,"finding":"CHMP2B missense mutant T104N accumulates in Rab5- and Rab7-positive endosomes, causes delayed EGFR degradation, shows reduced association with Vps4 ATPase and increased association with Snf7-2 (ESCRT-III core component), and causes autophagosome accumulation in post-mitotic neurons — indicating defects in ESCRT dissociation from endosomes.","method":"Transfection of missense mutant CHMP2B in post-mitotic neurons; Rab5/Rab7 co-localization; EGFR degradation assay; Co-immunoprecipitation with Vps4 and Snf7-2; LC3 autophagosome accumulation assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — multiple readouts in neurons, Co-IP data for Vps4 binding, single lab","pmids":["22521643"],"is_preprint":false},{"year":2013,"finding":"Expression of CHMP2B-Intron5 in Drosophila causes accumulation of Notch in enlarged endosomes and upregulation of Notch signaling activity; partial loss of Notch activity rescues eye deformities and behavioral defects, demonstrating that mutant CHMP2B disrupts Notch receptor trafficking and signaling.","method":"Drosophila genetics (eyeless-Gal4 driver); Notch immunofluorescence; epistasis with Notch loss-of-function; phototactic behavior assay","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis demonstrating pathway relationship between CHMP2B dysfunction and Notch signaling, with rescue experiment","pmids":["24158394"],"is_preprint":false},{"year":2015,"finding":"Neuronal Chmp2b concentrates beneath the perisynaptic membrane of dendritic spines (by quantitative immuno-EM). Depletion of endogenous Chmp2b reduces dendritic branching, decreases excitatory synapse density in vitro and in vivo, and abolishes activity-induced spine enlargement and synaptic potentiation. Co-immunoprecipitation and mass spectrometry show Chmp2b is part of a stable complex containing other Chmp family members and postsynaptic scaffolds, corresponding to a stable ESCRT-III form at synapses.","method":"Quantitative immuno-electron microscopy; Chmp2b depletion (in vitro and in vivo); synaptic plasticity assays; co-immunoprecipitation + mass spectrometry","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (ultrastructural localization, KD phenotype in vitro and in vivo, CoIP-MS) establishing synaptic ESCRT-III complex and function","pmids":["25698751"],"is_preprint":false},{"year":2015,"finding":"Mice expressing FTD-causative mutant CHMP2B at physiological levels develop lysosomal storage pathology characterized by large neuronal autofluorescent aggregates derived from the endolysosomal system (confirmed by ultrastructural analysis and immuno-gold labeling), not seen in wild-type CHMP2B mice. Similar aggregates are found in CHMP2B patient brains, identifying lysosomal storage pathology as the major neuronal pathology in CHMP2B-FTD.","method":"Transgenic mice at physiological expression levels; autofluorescence imaging; ultrastructural analysis (EM); immuno-gold labeling; human patient brain analysis","journal":"Acta neuropathologica","confidence":"High","confidence_rationale":"Tier 2 / Strong — physiological-level transgenic model with ultrastructural validation and human patient confirmation; multiple orthogonal methods","pmids":["26358247"],"is_preprint":false},{"year":2015,"finding":"TMEM106B (T185 risk variant) associates more strongly with CHMP2B than S185 variant by co-immunoprecipitation, and is more localized to Rab7-positive endosomes. T185 enhances EGFR accumulation, autophagic flux impairment, and neurotoxicity caused by CHMP2B-Intron5, suggesting functional interaction between TMEM106B and CHMP2B in the ESCRT/endolysosomal pathway.","method":"Co-immunoprecipitation of TMEM106B variants with CHMP2B; Rab5/Rab7 localization; EGFR degradation assay; autophagy flux assay; cell viability","journal":"Molecular brain","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP and multiple functional readouts but single lab, overexpression system","pmids":["26651479"],"is_preprint":false},{"year":2017,"finding":"FTD3 patient iPSC-derived cortical neurons show abnormal endosomes, defective mitochondrial cristae formation, reduced mitochondrial respiration, increased reactive oxygen species, and perturbed iron homeostasis. All phenotypes are rescued in CRISPR/Cas9-corrected isogenic controls, directly linking mutant CHMP2B to mitochondrial and endosomal dysfunction in human neurons.","method":"Patient iPSC differentiation into cortical neurons; CRISPR/Cas9 isogenic correction; electron microscopy of mitochondria; Seahorse respirometry; ROS measurement; iron homeostasis assays","journal":"Stem cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — isogenic CRISPR correction as gold-standard control; multiple orthogonal phenotypic readouts in patient-derived neurons","pmids":["28216144"],"is_preprint":false},{"year":2018,"finding":"Physiological levels of mutant CHMP2B cause stable incorporation onto neuronal endolysosomes, rendering them unable to traffic within dendrites. This defect is due to inability of mutant CHMP2B to recruit VPS4, which is required for CHMP2B release from endosomal membranes. Antisense oligonucleotides targeting TMEM106B rescue both impaired endolysosomal trafficking and increased dendritic branching.","method":"Transgenic mice at physiological expression levels; live imaging of endolysosomal trafficking in dendrites; VPS4 recruitment assay; ASO treatment and rescue","journal":"Brain : a journal of neurology","confidence":"High","confidence_rationale":"Tier 2 / Strong — mechanistic identification of VPS4 recruitment failure as the cause of endolysosomal immobility, with pharmacological rescue; physiological expression levels","pmids":["30496365"],"is_preprint":false},{"year":2018,"finding":"CHMP2B preferentially binds to membranes containing PI(4,5)P2 (phosphatidylinositol 4,5-bisphosphate). CHMP2B (both full-length and C-terminal deletion ΔC) preferentially accumulates at the neck of membrane nanotubes and prevents diffusion of PI(4,5)P2 lipids and membrane-bound proteins across the tube neck, functioning as a diffusion barrier at membrane necks.","method":"Reconstituted GUV-nanotube system; purified CHMP2B protein; lipid diffusion assay; fluorescence microscopy","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with purified protein on biomimetic membranes; direct measurement of diffusion barrier function","pmids":["29967034"],"is_preprint":false},{"year":2009,"finding":"In a Drosophila model of FTD3, a genome-wide genetic screen identified Serpin5 (Spn5) as a suppressor of mutant CHMP2B toxicity. Spn5 is a negative regulator of the Toll pathway, functioning extracellularly by blocking proteolytic activation of Spaetzle (Toll receptor ligand). Spn5 inhibited Toll pathway activation by mutant CHMP2B, identifying the Toll pathway as a major signaling pathway misregulated by mutant CHMP2B in vivo.","method":"Drosophila model expressing CHMP2B-Intron5; genome-wide genetic modifier screen; epistasis analysis with Toll pathway components","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — unbiased genome-wide screen with epistasis validation; Drosophila model; single lab","pmids":["19581577"],"is_preprint":false},{"year":2021,"finding":"CHMP2B downregulation reduces TDP-43 phosphorylation and toxicity in flies and mammalian cells independently of autophagy. Inhibition of CK1 (casein kinase 1) abolishes CHMP2B's modifying effect on TDP-43 phosphorylation. CHMP2B modulates CK1 protein levels by negatively regulating ubiquitination and proteasome-mediated turnover of CK1, revealing an autophagy-independent role for CHMP2B in regulating CK1 abundance.","method":"Drosophila genetic screen; mammalian cell knockdown/overexpression; TDP-43 phosphorylation assays; CK1 inhibitor treatment; ubiquitination assay; proteasome inhibition experiment","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods across two model systems; specific kinase identified and mechanistically linked; autophagy-independence confirmed by direct autophagy perturbation","pmids":["34726688"],"is_preprint":false},{"year":2021,"finding":"CHMP2B binding is enhanced in the presence of PI(4,5)P2 lipids, whereas CHMP2A does not display lipid specificity and requires CHMP3 for membrane binding. CHMP2B forms a reticular membrane structure and strongly rigidifies membranes upon polymerization; CHMP2A (+CHMP3) binds homogeneously and has no significant effect on membrane rigidity, demonstrating distinct biophysical properties of the two CHMP2 isoforms.","method":"Purified recombinant proteins; biomimetic membrane systems (GUVs, lipid bilayers); biolayer interferometry; membrane mechanics measurements; fluorescence microscopy","journal":"BMC biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with purified proteins; multiple biophysical techniques; direct comparison of two isoforms","pmids":["33832485"],"is_preprint":false},{"year":2021,"finding":"Expression of C-terminally truncated mutant CHMP2B in mice causes selective retention of presynaptic SV (synaptic vesicle) trafficking proteins with significant loss of postsynaptic proteins. Ultrastructural analysis reveals increased presynaptic endosomes; neurons expressing mutant CHMP2B display defective SV recycling and altered functional SV pools, identifying CHMP2B FTD as a novel synaptopathy.","method":"Aged mutant CHMP2B transgenic mice; immunohistochemistry for pre- and postsynaptic markers; electron microscopy; SV recycling assays in primary cortical cultures","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transgenic mouse model with ultrastructural validation and functional SV recycling assay; single lab","pmids":["34855215"],"is_preprint":false},{"year":2022,"finding":"SIRT6 negatively regulates CHMP2B accumulation in aged hearts. SIRT6 decreases acetylation of FoxO1, promoting its transcriptional function on Atrogin-1 (a muscle-specific E3 ubiquitin ligase), which subsequently enhances proteasomal degradation of CHMP2B. CHMP2B accumulation in aged hearts impairs autophagic flux, worsening myocardial ischemia-reperfusion injury.","method":"Myocardial-specific SIRT6 heterozygous knockout mice; SIRT6 activation pharmacology; FoxO1 acetylation assays; Atrogin-1 transcription assays; ubiquitination of CHMP2B; autophagic flux measurement","journal":"Journal of cardiovascular translational research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multi-step pathway established in vivo with genetic and pharmacological tools; multiple orthogonal methods; single lab","pmids":["35235147"],"is_preprint":false},{"year":2022,"finding":"Mutant CHMP2B-Intron5 binds spastin with greater affinity than wild-type CHMP2B, and colocalizes with CHMP2B-Intron5 in p62-positive aggregates. In cells expressing CHMP2B-Intron5, cytoplasmic soluble spastin decreases while insoluble spastin increases. Genetic knockdown of spastin enhances CHMP2B-Intron5 toxicity in Drosophila, demonstrating functional interaction.","method":"Co-immunoprecipitation; immunofluorescence co-localization; soluble/insoluble fractionation; Drosophila genetic epistasis (spastin knockdown)","journal":"Acta neuropathologica communications","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP and fractionation with Drosophila genetic validation; multiple methods but single lab","pmids":["36414997"],"is_preprint":false},{"year":2024,"finding":"CHMP2B promotes CHMP7-mediated nuclear pore complex (NPC) injury in sporadic ALS iPSC-derived neurons. CHMP2B-dependent sustained 'activation' contributes to pathologic CHMP7 nuclear accumulation and POM121 reduction at NPCs. Partial knockdown of CHMP2B alleviates NPC injury and downstream TDP-43 dysfunction in sALS neurons.","method":"iPSC-derived neurons from sALS patients; partial CHMP2B knockdown; super-resolution microscopy; NPC composition analysis (POM121); TDP-43 localization","journal":"Acta neuropathologica communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — human iPSC neuron model with genetic perturbation and multiple molecular readouts; single lab","pmids":["39709457"],"is_preprint":false},{"year":2025,"finding":"CHMP2B axonal transport and recruitment to presynaptic boutons are regulated by neuronal activity and depend on kinesin-binding protein (KBP). The FTD-causative CHMP2B-Intron5 mutant shows little processive movement or presynaptic localization; its transport vesicles exhibit oscillatory (tug-of-war) behavior due to deficient binding to kinesin-binding protein, which normally regulates CHMP2B transport.","method":"Live imaging of CHMP2B axonal trafficking in neurons; neuronal activity manipulation; KBP binding assays; comparison of WT vs. CHMP2B-Intron5 transport dynamics","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — live imaging with mechanistic identification of KBP as transport regulator and specific binding defect of mutant; single lab, recent publication","pmids":["40021219"],"is_preprint":false},{"year":2026,"finding":"Wild-type CHMP2B contains a nuclear export signal (NES) in its C-terminus that is necessary and sufficient for CRM1-dependent nuclear export. The FTD3-causative CHMP2B-Intron5 mutation removes this NES, causing mislocalization of CHMP2B to the nucleus of iPSC-derived cortical neurons. Site-directed mutagenesis of key hydrophobic NES residues confirms the NES is required for nuclear export.","method":"iPSC-derived cortical neurons; CRM1 inhibition (leptomycin B); site-directed mutagenesis of NES residues; immunofluorescence localization; functional export assays","journal":"Acta neuropathologica communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — NES identified by mutagenesis and CRM1 inhibition in human neurons; multiple orthogonal validation methods; single lab","pmids":["41559796"],"is_preprint":false},{"year":2023,"finding":"CHMP2B with the T104N (FTD/ALS7-associated) mutation accumulates preferentially in the Golgi body rather than ESCRT-III structures, activates Arf4-mediated Golgi stress signaling, and inhibits neuronal process elongation. Knockdown of Arf4 recovers the neuronal process elongation inhibited by the T104N mutation.","method":"N1E-115 neuronal cell line differentiation; immunofluorescence of CHMP2B T104N localization; Arf4 pathway analysis; Arf4 siRNA knockdown rescue","journal":"Neurology international","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — novel Golgi mis-targeting mechanism with siRNA rescue; single lab, cell line model","pmids":["37606396"],"is_preprint":false},{"year":2020,"finding":"Partial loss of function of Ik2 (fly TBK1 homologue) enhances CHMP2B-Intron5 toxicity in fly eye, while Ik2 overexpression suppresses it. Loss of Spn-F (downstream Ik2 phosphorylation target) also enhances CHMP2B-Intron5 toxicity. Interactome analysis identified a network including Spn-F, Ik2, dynein light chain, and Hook (early endosome transport adaptor). Partial loss of dynein light chain or Hook enhances mutant CHMP2B toxicity, implicating early endosome transport as a contributing pathway.","method":"Drosophila genetic epistasis; Ik2/Spn-F loss-of-function and overexpression; protein interactome analysis; Hook and dynein light chain loss-of-function","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis in Drosophila with interactome data; multiple genetic modifiers tested; single lab","pmids":["32848189"],"is_preprint":false},{"year":2024,"finding":"CHMP2B and CHMP4B are recruited to Leishmania donovani parasitophorous vacuoles (LdLPVs) together with VPS4a and TSG101, demonstrating CHMP2B participates in ESCRT-III assembly at pathological membrane compartments beyond its canonical endosomal role.","method":"Immunofluorescence of ESCRT components at LdLPVs in infected macrophages; dominant-negative VPS4a expression","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single immunofluorescence observation in a preprint; not directly focused on CHMP2B mechanism; no functional perturbation of CHMP2B specifically","pmids":[],"is_preprint":true},{"year":2024,"finding":"CHMP2B acts after Annexin-mediated membrane sealing in a sequential 'sealing and healing' membrane repair pathway. FTD- and ALS-associated mutations in CHMP2B compromise the repair process (ESCRT-III-mediated shedding of damaged membranes).","method":"Temporal recruitment analysis of ESCRT-III and Annexins to membrane damage sites; CHMP2B mutant functional analysis in membrane repair assay","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — preprint, single lab, functional assay for membrane repair; mechanistic ordering is novel but awaits peer review","pmids":[],"is_preprint":true},{"year":2025,"finding":"In CHMP2A knockout cells, CHMP2B localization at the abscission site is minimally disrupted during cytokinesis, whereas CHMP4B, CHMP3, and CHMP1B show progressively severe organization defects, indicating CHMP2B is relatively independent of CHMP2A for cytokinetic abscission site targeting.","method":"CHMP2A knockout; live cell imaging; structured illumination microscopy (SIM); correlative light-electron microscopy (CLEM)","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — preprint, negative/minimal result for CHMP2B specifically; finding is about CHMP2A's role with CHMP2B as a comparator","pmids":[],"is_preprint":true}],"current_model":"CHMP2B is a core ESCRT-III subunit that polymerizes into helical filaments to deform and remodel membranes; it preferentially binds PI(4,5)P2-containing membranes and can act as a diffusion barrier at membrane necks. Its C-terminal domain contains a nuclear export signal (NES) enabling CRM1-dependent cytoplasmic retention, and its activity requires VPS4-mediated release from membranes — a step blocked by FTD-causative C-terminal truncation mutations, leading to stable aberrant membrane association that disrupts endosome-lysosome fusion (by preventing Rab7 recruitment), impairs autophagic flux, blocks axonal endolysosomal trafficking, and causes lysosomal storage pathology; at synapses, CHMP2B-containing ESCRT-III complexes regulate dendritic spine growth, synaptic plasticity, and presynaptic vesicle recycling, while its axonal transport to presynaptic boutons is regulated by neuronal activity through kinesin-binding protein — with loss of these functions collectively driving the neurodegeneration seen in FTD3 and ALS."},"narrative":{"mechanistic_narrative":"CHMP2B is a core ESCRT-III subunit that polymerizes into helical membrane-deforming lattices and underlies endolysosomal, autophagic, and synaptic membrane remodeling, with its dysfunction causing frontotemporal dementia (FTD3) and contributing to ALS [PMID:16041373, PMID:21926173]. Purified CHMP2B preferentially binds PI(4,5)P2-containing membranes, assembles into a tightly packed helical coat that rigidifies and tubulates the bilayer, and concentrates at membrane necks where it acts as a diffusion barrier to lipids and membrane proteins [PMID:21926173, PMID:29967034, PMID:33832485]. Productive turnover of the polymer requires VPS4-mediated release from membranes [PMID:21926173]. FTD3-causative C-terminal truncations (e.g. CHMP2B-Intron5) act through a gain of function: the mutant protein fails to recruit VPS4, becomes stably trapped on endosomal membranes, blocks Rab7 recruitment and thereby endosome-lysosome fusion, impairs autophagic flux, and produces enlarged endolysosomes and neuronal lysosomal storage pathology [PMID:20223751, PMID:20352044, PMID:22366797, PMID:26358247, PMID:30496365]. In neurons CHMP2B is part of a stable perisynaptic ESCRT-III complex required for dendritic spine growth, excitatory synapse density, activity-dependent potentiation, and presynaptic vesicle recycling, and its activity-regulated axonal transport to boutons depends on kinesin-binding protein [PMID:20699355, PMID:25698751, PMID:34855215, PMID:40021219]. Beyond canonical ESCRT functions, CHMP2B regulates CK1 abundance to control TDP-43 phosphorylation independently of autophagy [PMID:34726688], and sustained CHMP2B activity promotes CHMP7-mediated nuclear pore complex injury in sporadic ALS neurons [PMID:39709457]. Disease severity is modulated by physical and genetic interactors including TMEM106B and spastin [PMID:26651479, PMID:36414997], and the C-terminus also encodes a CRM1-dependent nuclear export signal lost upon the FTD3 truncation [PMID:41559796].","teleology":[{"year":2005,"claim":"Established CHMP2B as a disease gene, linking ESCRT-III dysfunction to neurodegeneration for the first time.","evidence":"Genetic linkage and splice-site mutation analysis in a Danish FTD3 pedigree showing aberrant mRNA splicing in patient tissue","pmids":["16041373"],"confidence":"High","gaps":["Did not define the cellular mechanism of toxicity","Did not distinguish loss- vs gain-of-function"]},{"year":2007,"claim":"Connected C-terminal truncation specifically to endosomal morphological dysfunction.","evidence":"Overexpression of two independent truncation mutants in SK-N-SH neuroblastoma cells with fluorescence microscopy of endosomes","pmids":["17956895"],"confidence":"Medium","gaps":["Overexpression artifact possible","Molecular step disrupted not identified"]},{"year":2010,"claim":"Defined where in the endolysosomal pathway mutant CHMP2B acts, identifying Rab7 recruitment failure as the block to endosome-lysosome fusion, and showed disruption of the autophagy-lysosomal pathway.","evidence":"Patient fibroblasts/brain Rab7 localization assays; transfection of mutant CHMP2B in HEK-293/COS-7 with CD63 and LC3-II readouts","pmids":["20223751","20352044"],"confidence":"High","gaps":["Did not show how mutant remains membrane-bound","MVB sorting itself intact"]},{"year":2012,"claim":"Distinguished gain-of-function from loss-of-function, establishing that the truncation mutant, not loss of CHMP2B, drives neurodegeneration.","evidence":"Comparative transgenic (mutant vs WT) and Chmp2b knockout mice with neuropathological analysis","pmids":["22366797"],"confidence":"High","gaps":["Did not define the molecular trapping mechanism","Cell-type selectivity unexplained"]},{"year":2011,"claim":"Provided the structural basis for CHMP2B function, showing it forms a VPS4-dependent helical membrane-deforming polymer.","evidence":"Cryo-EM of CHMP2B membrane tubes plus VPS4 depletion and CHMP4 relocalization in cells","pmids":["21926173"],"confidence":"High","gaps":["Physiological membrane target not defined","Lipid specificity not yet measured"]},{"year":2012,"claim":"Placed CHMP2B-linked autophagy defects in a maturation pathway via genetic modifiers and probed ESCRT dissociation defects of a missense mutant.","evidence":"Drosophila modifier screen identifying STX13/Vti1a; missense T104N Co-IP with VPS4/Snf7-2 and EGFR degradation assays in neurons","pmids":["24095276","22521643"],"confidence":"Medium","gaps":["STX13-CHMP2B physical link not shown","T104N Co-IP single lab without reciprocal validation"]},{"year":2010,"claim":"Identified a physiological synaptic role for CHMP2B in spine growth and excitatory transmission, with mutants acting dominant-negatively.","evidence":"Mutant expression and RNAi in hippocampal neurons with spine morphometry and mEPSC recordings","pmids":["20699355"],"confidence":"High","gaps":["Molecular mechanism at spines not defined","Relation to ESCRT membrane activity unclear"]},{"year":2015,"claim":"Defined CHMP2B as part of a stable perisynaptic ESCRT-III complex required for synapse formation and plasticity in vivo, and identified lysosomal storage as the major neuronal pathology.","evidence":"Immuno-EM, CoIP-MS, depletion phenotypes in vitro/in vivo; physiological-level transgenic mice with ultrastructure and patient brain confirmation","pmids":["25698751","26358247"],"confidence":"High","gaps":["Composition of synaptic complex only partially resolved","Link between storage pathology and synaptic loss unresolved"]},{"year":2015,"claim":"Identified TMEM106B as a physical and functional modifier of CHMP2B toxicity in the endolysosomal pathway.","evidence":"Co-IP of TMEM106B risk variants with CHMP2B plus EGFR/autophagy/viability assays in overexpression","pmids":["26651479"],"confidence":"Medium","gaps":["Overexpression system","Direct vs indirect interaction not resolved"]},{"year":2017,"claim":"Demonstrated mitochondrial and endosomal dysfunction in patient neurons attributable to the mutation using isogenic correction.","evidence":"FTD3 patient iPSC cortical neurons with CRISPR isogenic controls; EM, respirometry, ROS and iron assays","pmids":["28216144"],"confidence":"High","gaps":["Mechanistic link between ESCRT defect and mitochondrial phenotype unclear","Iron homeostasis pathway not detailed"]},{"year":2018,"claim":"Identified the proximate molecular defect: mutant CHMP2B cannot recruit VPS4, becoming stably trapped and immobilizing dendritic endolysosomes, with TMEM106B knockdown providing rescue.","evidence":"Physiological-level transgenic mice, dendritic endolysosome live imaging, VPS4 recruitment assays, TMEM106B ASO rescue","pmids":["30496365"],"confidence":"High","gaps":["How truncation abolishes VPS4 recruitment structurally not shown","Whether trafficking arrest fully accounts for degeneration unknown"]},{"year":2018,"claim":"Defined CHMP2B's membrane biophysics: PI(4,5)P2 preference and diffusion-barrier function at membrane necks.","evidence":"Reconstituted GUV-nanotube system with purified CHMP2B and lipid diffusion assays","pmids":["29967034"],"confidence":"High","gaps":["In vivo relevance of barrier function not established","Relationship to scission unresolved"]},{"year":2021,"claim":"Distinguished CHMP2B from CHMP2A biophysically, showing CHMP2B uniquely binds PI(4,5)P2 and rigidifies membranes without requiring CHMP3.","evidence":"Purified recombinant proteins on biomimetic membranes; biolayer interferometry and membrane mechanics","pmids":["33832485"],"confidence":"High","gaps":["Functional consequence of isoform divergence in cells unresolved"]},{"year":2021,"claim":"Revealed an autophagy-independent role: CHMP2B controls CK1 abundance via ubiquitin-proteasome turnover to modulate TDP-43 phosphorylation and toxicity.","evidence":"Drosophila and mammalian cell knockdown/overexpression; CK1 inhibition, ubiquitination and proteasome assays","pmids":["34726688"],"confidence":"High","gaps":["Direct CHMP2B-CK1 interaction not defined","Connection to ESCRT activity unclear"]},{"year":2021,"claim":"Characterized CHMP2B-FTD as a synaptopathy involving presynaptic vesicle recycling defects, and identified spastin as a mutation-enhanced binding partner.","evidence":"Aged transgenic mice with synaptic marker IHC, EM and SV recycling assays; Co-IP, fractionation and Drosophila epistasis for spastin","pmids":["34855215","36414997"],"confidence":"Medium","gaps":["Causal chain from sequestration to synaptic failure incomplete","Spastin interaction single lab"]},{"year":2024,"claim":"Extended CHMP2B's pathological reach to nuclear pore injury in sporadic ALS, where sustained CHMP2B activation drives CHMP7 accumulation and TDP-43 dysfunction.","evidence":"sALS iPSC neurons with partial CHMP2B knockdown, super-resolution microscopy and NPC composition analysis","pmids":["39709457"],"confidence":"Medium","gaps":["Mechanism of CHMP2B 'activation' undefined","Single lab iPSC model"]},{"year":2025,"claim":"Showed activity-dependent axonal transport of CHMP2B to presynaptic boutons depends on kinesin-binding protein, with the FTD mutant failing transport.","evidence":"Live imaging of CHMP2B axonal trafficking with KBP binding assays comparing WT vs Intron5","pmids":["40021219"],"confidence":"Medium","gaps":["KBP-CHMP2B binding interface not mapped","Single lab"]},{"year":2026,"claim":"Identified a C-terminal CRM1-dependent nuclear export signal lost in the FTD3 mutant, causing nuclear mislocalization.","evidence":"iPSC cortical neurons with leptomycin B and NES site-directed mutagenesis; 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disease","url":"https://pubmed.ncbi.nlm.nih.gov/31837425","citation_count":3,"is_preprint":false},{"pmid":"27558613","id":"PMC_27558613","title":"Generation of a human induced pluripotent stem cell line via CRISPR-Cas9 mediated integration of a site-specific heterozygous mutation in CHMP2B.","date":"2016","source":"Stem cell research","url":"https://pubmed.ncbi.nlm.nih.gov/27558613","citation_count":3,"is_preprint":false},{"pmid":"40316175","id":"PMC_40316175","title":"Truncation mutation of CHMP2B disrupts late endosome function but reduces TDP-43 aggregation through HSP70 upregulation.","date":"2025","source":"Neurochemistry international","url":"https://pubmed.ncbi.nlm.nih.gov/40316175","citation_count":2,"is_preprint":false},{"pmid":"33583303","id":"PMC_33583303","title":"Differential levels of CHMP2B, LLPH, and SLC25A51 proteins in secondary renal amyloidosis.","date":"2021","source":"Expert review of 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FTD3-associated mutant CHMP2B to the nucleus of human neurons due to loss of a nuclear export signal.","date":"2026","source":"Acta neuropathologica communications","url":"https://pubmed.ncbi.nlm.nih.gov/41559796","citation_count":0,"is_preprint":false},{"pmid":"40244880","id":"PMC_40244880","title":"A Novel CHMP2B Splicing Variant in Atypical Presentation of Familial Frontotemporal Lobar Degeneration.","date":"2025","source":"Annals of clinical and translational neurology","url":"https://pubmed.ncbi.nlm.nih.gov/40244880","citation_count":0,"is_preprint":false},{"pmid":"38392208","id":"PMC_38392208","title":"Modulating Golgi Stress Signaling Ameliorates Cell Morphological Phenotypes Induced by CHMP2B with Frontotemporal Dementia-Associated p.Asp148Tyr.","date":"2024","source":"Current issues in molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/38392208","citation_count":0,"is_preprint":false},{"pmid":"42143939","id":"PMC_42143939","title":"CHMP2B exacerbates renal tubular 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analysis in patient tissue\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — foundational disease-gene identification with direct molecular evidence of aberrant splicing in patient tissue, independently replicated across multiple subsequent studies\",\n      \"pmids\": [\"16041373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"C-truncating mutations in CHMP2B (both Danish p.Met178ValfsX2 and Belgian p.Gln165X) cause formation of large, aberrant endosomal structures when overexpressed in human neuroblastoma SK-N-SH cells, linking C-terminal truncation to endosomal dysfunction.\",\n      \"method\": \"Overexpression of mutant CHMP2B constructs in SK-N-SH cells, fluorescence microscopy of endosomal morphology\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — consistent morphological phenotype replicated with two independent mutant constructs in cell overexpression system, single lab\",\n      \"pmids\": [\"17956895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Mutant CHMP2B disrupts endosome-lysosome fusion but not protein sorting by the MVB. The mechanism involves mutant CHMP2B constitutively binding to MVBs and preventing recruitment of Rab7, a protein necessary for endosome-lysosome fusion.\",\n      \"method\": \"Functional assays in patient fibroblasts and patient brain tissue; Rab7 localization studies; endosomal morphology analysis\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic pathway placement (endosome-lysosome fusion vs. MVB sorting) with identification of Rab7 as the recruited factor blocked by mutant CHMP2B, in patient-derived cells and brain tissue\",\n      \"pmids\": [\"20223751\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Transfection of mutant CHMP2B into HEK-293 and COS-7 cells results in large cytoplasmic vacuoles, aberrant lysosomal localization (CD63 staining), and impairment of autophagy (increased LC3-II), demonstrating that CHMP2B mutations disrupt the autophagy-lysosomal pathway.\",\n      \"method\": \"Transfection of mutant vs. wild-type CHMP2B in HEK-293 and COS-7 cells; CD63 immunostaining; LC3-II western blot\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — multiple cell lines, multiple orthogonal readouts (vacuole formation, lysosomal marker, autophagy marker), single lab\",\n      \"pmids\": [\"20352044\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"CHMP2B is required for normal dendritic spine growth. FTD-linked CHMP2B mutants (CHMP2B-Intron5 and CHMP2B-Delta10) reduce the proportion of large mushroom-shaped spines in hippocampal neurons; CHMP2B-Delta10 also reduces frequency and amplitude of excitatory postsynaptic currents. RNAi depletion of endogenous CHMP2B phenocopies mutants, indicating dominant-negative activity.\",\n      \"method\": \"Expression of mutant CHMP2B in cultured hippocampal neurons; confocal microscopy and 3D reconstruction of spine morphology; electrophysiology (mEPSC recordings); RNAi knockdown\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (morphology, electrophysiology, RNAi phenocopy) in a single focused study establishing synaptic role\",\n      \"pmids\": [\"20699355\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CHMP2B polymerizes into helical structures that deform membranes in cellulo. Depletion of VPS4 induces accumulation of endogenous CHMP2B at the plasma membrane; overexpressed full-length CHMP2B forms long, rigid tubes protruding from cells. Cryo-EM shows CHMP2B polymerizes into a tightly packed helical lattice closely associated with the inner leaflet of membrane tubes, sufficient to deform the lipid bilayer. CHMP4s relocalize at the base of the tubes; tube formation depends on VPS4.\",\n      \"method\": \"VPS4 depletion; live-cell imaging; cryo-electron microscopy of CHMP2B membrane tubes; immunofluorescence of CHMP4 localization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — cryo-EM structural data with in-cellulo functional validation; multiple orthogonal methods in one study\",\n      \"pmids\": [\"21926173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Transgenic mice expressing C-terminally truncated mutant CHMP2B show progressive neurodegeneration (gliosis, p62/ubiquitin-positive inclusions, axonal swellings) not seen in Chmp2b knockout or wild-type CHMP2B transgenic mice, establishing that CHMP2B mutations cause neurodegeneration via a gain-of-function mechanism.\",\n      \"method\": \"Transgenic mouse models (mutant CHMP2B, wild-type CHMP2B, Chmp2b knockout); immunohistochemistry; neuropathological analysis\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — comparative transgenic/knockout mouse study with multiple neuropathological readouts demonstrating gain-of-function vs. loss-of-function distinction\",\n      \"pmids\": [\"22366797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"STX13 (syntaxin 13) is a genetic modifier of mutant CHMP2B and is required for autophagosome maturation. Knockdown of STX13 or its binding partner Vti1a in mammalian cells causes accumulation of LC3-positive puncta and blocks autophagic flux. STX13 is present on LC3-positive phagophores and multilamellar structures induced by dysfunctional ESCRT-III. Loss of STX13 causes accumulation of Atg5-positive puncta and multilamellar structure formation, indicating STX13 participates in phagophore-to-autophagosome maturation.\",\n      \"method\": \"Drosophila genetic modifier screen with mutant CHMP2B; mammalian cell knockdown of STX13 and Vti1a; LC3/Atg5 immunofluorescence; autophagic flux assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis in Drosophila combined with mammalian cell mechanistic follow-up using multiple markers; clear pathway placement\",\n      \"pmids\": [\"24095276\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CHMP2B missense mutant T104N accumulates in Rab5- and Rab7-positive endosomes, causes delayed EGFR degradation, shows reduced association with Vps4 ATPase and increased association with Snf7-2 (ESCRT-III core component), and causes autophagosome accumulation in post-mitotic neurons — indicating defects in ESCRT dissociation from endosomes.\",\n      \"method\": \"Transfection of missense mutant CHMP2B in post-mitotic neurons; Rab5/Rab7 co-localization; EGFR degradation assay; Co-immunoprecipitation with Vps4 and Snf7-2; LC3 autophagosome accumulation assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — multiple readouts in neurons, Co-IP data for Vps4 binding, single lab\",\n      \"pmids\": [\"22521643\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Expression of CHMP2B-Intron5 in Drosophila causes accumulation of Notch in enlarged endosomes and upregulation of Notch signaling activity; partial loss of Notch activity rescues eye deformities and behavioral defects, demonstrating that mutant CHMP2B disrupts Notch receptor trafficking and signaling.\",\n      \"method\": \"Drosophila genetics (eyeless-Gal4 driver); Notch immunofluorescence; epistasis with Notch loss-of-function; phototactic behavior assay\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis demonstrating pathway relationship between CHMP2B dysfunction and Notch signaling, with rescue experiment\",\n      \"pmids\": [\"24158394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Neuronal Chmp2b concentrates beneath the perisynaptic membrane of dendritic spines (by quantitative immuno-EM). Depletion of endogenous Chmp2b reduces dendritic branching, decreases excitatory synapse density in vitro and in vivo, and abolishes activity-induced spine enlargement and synaptic potentiation. Co-immunoprecipitation and mass spectrometry show Chmp2b is part of a stable complex containing other Chmp family members and postsynaptic scaffolds, corresponding to a stable ESCRT-III form at synapses.\",\n      \"method\": \"Quantitative immuno-electron microscopy; Chmp2b depletion (in vitro and in vivo); synaptic plasticity assays; co-immunoprecipitation + mass spectrometry\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (ultrastructural localization, KD phenotype in vitro and in vivo, CoIP-MS) establishing synaptic ESCRT-III complex and function\",\n      \"pmids\": [\"25698751\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Mice expressing FTD-causative mutant CHMP2B at physiological levels develop lysosomal storage pathology characterized by large neuronal autofluorescent aggregates derived from the endolysosomal system (confirmed by ultrastructural analysis and immuno-gold labeling), not seen in wild-type CHMP2B mice. Similar aggregates are found in CHMP2B patient brains, identifying lysosomal storage pathology as the major neuronal pathology in CHMP2B-FTD.\",\n      \"method\": \"Transgenic mice at physiological expression levels; autofluorescence imaging; ultrastructural analysis (EM); immuno-gold labeling; human patient brain analysis\",\n      \"journal\": \"Acta neuropathologica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — physiological-level transgenic model with ultrastructural validation and human patient confirmation; multiple orthogonal methods\",\n      \"pmids\": [\"26358247\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"TMEM106B (T185 risk variant) associates more strongly with CHMP2B than S185 variant by co-immunoprecipitation, and is more localized to Rab7-positive endosomes. T185 enhances EGFR accumulation, autophagic flux impairment, and neurotoxicity caused by CHMP2B-Intron5, suggesting functional interaction between TMEM106B and CHMP2B in the ESCRT/endolysosomal pathway.\",\n      \"method\": \"Co-immunoprecipitation of TMEM106B variants with CHMP2B; Rab5/Rab7 localization; EGFR degradation assay; autophagy flux assay; cell viability\",\n      \"journal\": \"Molecular brain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP and multiple functional readouts but single lab, overexpression system\",\n      \"pmids\": [\"26651479\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"FTD3 patient iPSC-derived cortical neurons show abnormal endosomes, defective mitochondrial cristae formation, reduced mitochondrial respiration, increased reactive oxygen species, and perturbed iron homeostasis. All phenotypes are rescued in CRISPR/Cas9-corrected isogenic controls, directly linking mutant CHMP2B to mitochondrial and endosomal dysfunction in human neurons.\",\n      \"method\": \"Patient iPSC differentiation into cortical neurons; CRISPR/Cas9 isogenic correction; electron microscopy of mitochondria; Seahorse respirometry; ROS measurement; iron homeostasis assays\",\n      \"journal\": \"Stem cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — isogenic CRISPR correction as gold-standard control; multiple orthogonal phenotypic readouts in patient-derived neurons\",\n      \"pmids\": [\"28216144\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Physiological levels of mutant CHMP2B cause stable incorporation onto neuronal endolysosomes, rendering them unable to traffic within dendrites. This defect is due to inability of mutant CHMP2B to recruit VPS4, which is required for CHMP2B release from endosomal membranes. Antisense oligonucleotides targeting TMEM106B rescue both impaired endolysosomal trafficking and increased dendritic branching.\",\n      \"method\": \"Transgenic mice at physiological expression levels; live imaging of endolysosomal trafficking in dendrites; VPS4 recruitment assay; ASO treatment and rescue\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mechanistic identification of VPS4 recruitment failure as the cause of endolysosomal immobility, with pharmacological rescue; physiological expression levels\",\n      \"pmids\": [\"30496365\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CHMP2B preferentially binds to membranes containing PI(4,5)P2 (phosphatidylinositol 4,5-bisphosphate). CHMP2B (both full-length and C-terminal deletion ΔC) preferentially accumulates at the neck of membrane nanotubes and prevents diffusion of PI(4,5)P2 lipids and membrane-bound proteins across the tube neck, functioning as a diffusion barrier at membrane necks.\",\n      \"method\": \"Reconstituted GUV-nanotube system; purified CHMP2B protein; lipid diffusion assay; fluorescence microscopy\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with purified protein on biomimetic membranes; direct measurement of diffusion barrier function\",\n      \"pmids\": [\"29967034\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In a Drosophila model of FTD3, a genome-wide genetic screen identified Serpin5 (Spn5) as a suppressor of mutant CHMP2B toxicity. Spn5 is a negative regulator of the Toll pathway, functioning extracellularly by blocking proteolytic activation of Spaetzle (Toll receptor ligand). Spn5 inhibited Toll pathway activation by mutant CHMP2B, identifying the Toll pathway as a major signaling pathway misregulated by mutant CHMP2B in vivo.\",\n      \"method\": \"Drosophila model expressing CHMP2B-Intron5; genome-wide genetic modifier screen; epistasis analysis with Toll pathway components\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — unbiased genome-wide screen with epistasis validation; Drosophila model; single lab\",\n      \"pmids\": [\"19581577\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CHMP2B downregulation reduces TDP-43 phosphorylation and toxicity in flies and mammalian cells independently of autophagy. Inhibition of CK1 (casein kinase 1) abolishes CHMP2B's modifying effect on TDP-43 phosphorylation. CHMP2B modulates CK1 protein levels by negatively regulating ubiquitination and proteasome-mediated turnover of CK1, revealing an autophagy-independent role for CHMP2B in regulating CK1 abundance.\",\n      \"method\": \"Drosophila genetic screen; mammalian cell knockdown/overexpression; TDP-43 phosphorylation assays; CK1 inhibitor treatment; ubiquitination assay; proteasome inhibition experiment\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods across two model systems; specific kinase identified and mechanistically linked; autophagy-independence confirmed by direct autophagy perturbation\",\n      \"pmids\": [\"34726688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CHMP2B binding is enhanced in the presence of PI(4,5)P2 lipids, whereas CHMP2A does not display lipid specificity and requires CHMP3 for membrane binding. CHMP2B forms a reticular membrane structure and strongly rigidifies membranes upon polymerization; CHMP2A (+CHMP3) binds homogeneously and has no significant effect on membrane rigidity, demonstrating distinct biophysical properties of the two CHMP2 isoforms.\",\n      \"method\": \"Purified recombinant proteins; biomimetic membrane systems (GUVs, lipid bilayers); biolayer interferometry; membrane mechanics measurements; fluorescence microscopy\",\n      \"journal\": \"BMC biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with purified proteins; multiple biophysical techniques; direct comparison of two isoforms\",\n      \"pmids\": [\"33832485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Expression of C-terminally truncated mutant CHMP2B in mice causes selective retention of presynaptic SV (synaptic vesicle) trafficking proteins with significant loss of postsynaptic proteins. Ultrastructural analysis reveals increased presynaptic endosomes; neurons expressing mutant CHMP2B display defective SV recycling and altered functional SV pools, identifying CHMP2B FTD as a novel synaptopathy.\",\n      \"method\": \"Aged mutant CHMP2B transgenic mice; immunohistochemistry for pre- and postsynaptic markers; electron microscopy; SV recycling assays in primary cortical cultures\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transgenic mouse model with ultrastructural validation and functional SV recycling assay; single lab\",\n      \"pmids\": [\"34855215\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SIRT6 negatively regulates CHMP2B accumulation in aged hearts. SIRT6 decreases acetylation of FoxO1, promoting its transcriptional function on Atrogin-1 (a muscle-specific E3 ubiquitin ligase), which subsequently enhances proteasomal degradation of CHMP2B. CHMP2B accumulation in aged hearts impairs autophagic flux, worsening myocardial ischemia-reperfusion injury.\",\n      \"method\": \"Myocardial-specific SIRT6 heterozygous knockout mice; SIRT6 activation pharmacology; FoxO1 acetylation assays; Atrogin-1 transcription assays; ubiquitination of CHMP2B; autophagic flux measurement\",\n      \"journal\": \"Journal of cardiovascular translational research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multi-step pathway established in vivo with genetic and pharmacological tools; multiple orthogonal methods; single lab\",\n      \"pmids\": [\"35235147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Mutant CHMP2B-Intron5 binds spastin with greater affinity than wild-type CHMP2B, and colocalizes with CHMP2B-Intron5 in p62-positive aggregates. In cells expressing CHMP2B-Intron5, cytoplasmic soluble spastin decreases while insoluble spastin increases. Genetic knockdown of spastin enhances CHMP2B-Intron5 toxicity in Drosophila, demonstrating functional interaction.\",\n      \"method\": \"Co-immunoprecipitation; immunofluorescence co-localization; soluble/insoluble fractionation; Drosophila genetic epistasis (spastin knockdown)\",\n      \"journal\": \"Acta neuropathologica communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP and fractionation with Drosophila genetic validation; multiple methods but single lab\",\n      \"pmids\": [\"36414997\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CHMP2B promotes CHMP7-mediated nuclear pore complex (NPC) injury in sporadic ALS iPSC-derived neurons. CHMP2B-dependent sustained 'activation' contributes to pathologic CHMP7 nuclear accumulation and POM121 reduction at NPCs. Partial knockdown of CHMP2B alleviates NPC injury and downstream TDP-43 dysfunction in sALS neurons.\",\n      \"method\": \"iPSC-derived neurons from sALS patients; partial CHMP2B knockdown; super-resolution microscopy; NPC composition analysis (POM121); TDP-43 localization\",\n      \"journal\": \"Acta neuropathologica communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — human iPSC neuron model with genetic perturbation and multiple molecular readouts; single lab\",\n      \"pmids\": [\"39709457\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CHMP2B axonal transport and recruitment to presynaptic boutons are regulated by neuronal activity and depend on kinesin-binding protein (KBP). The FTD-causative CHMP2B-Intron5 mutant shows little processive movement or presynaptic localization; its transport vesicles exhibit oscillatory (tug-of-war) behavior due to deficient binding to kinesin-binding protein, which normally regulates CHMP2B transport.\",\n      \"method\": \"Live imaging of CHMP2B axonal trafficking in neurons; neuronal activity manipulation; KBP binding assays; comparison of WT vs. CHMP2B-Intron5 transport dynamics\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — live imaging with mechanistic identification of KBP as transport regulator and specific binding defect of mutant; single lab, recent publication\",\n      \"pmids\": [\"40021219\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Wild-type CHMP2B contains a nuclear export signal (NES) in its C-terminus that is necessary and sufficient for CRM1-dependent nuclear export. The FTD3-causative CHMP2B-Intron5 mutation removes this NES, causing mislocalization of CHMP2B to the nucleus of iPSC-derived cortical neurons. Site-directed mutagenesis of key hydrophobic NES residues confirms the NES is required for nuclear export.\",\n      \"method\": \"iPSC-derived cortical neurons; CRM1 inhibition (leptomycin B); site-directed mutagenesis of NES residues; immunofluorescence localization; functional export assays\",\n      \"journal\": \"Acta neuropathologica communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — NES identified by mutagenesis and CRM1 inhibition in human neurons; multiple orthogonal validation methods; single lab\",\n      \"pmids\": [\"41559796\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CHMP2B with the T104N (FTD/ALS7-associated) mutation accumulates preferentially in the Golgi body rather than ESCRT-III structures, activates Arf4-mediated Golgi stress signaling, and inhibits neuronal process elongation. Knockdown of Arf4 recovers the neuronal process elongation inhibited by the T104N mutation.\",\n      \"method\": \"N1E-115 neuronal cell line differentiation; immunofluorescence of CHMP2B T104N localization; Arf4 pathway analysis; Arf4 siRNA knockdown rescue\",\n      \"journal\": \"Neurology international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — novel Golgi mis-targeting mechanism with siRNA rescue; single lab, cell line model\",\n      \"pmids\": [\"37606396\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Partial loss of function of Ik2 (fly TBK1 homologue) enhances CHMP2B-Intron5 toxicity in fly eye, while Ik2 overexpression suppresses it. Loss of Spn-F (downstream Ik2 phosphorylation target) also enhances CHMP2B-Intron5 toxicity. Interactome analysis identified a network including Spn-F, Ik2, dynein light chain, and Hook (early endosome transport adaptor). Partial loss of dynein light chain or Hook enhances mutant CHMP2B toxicity, implicating early endosome transport as a contributing pathway.\",\n      \"method\": \"Drosophila genetic epistasis; Ik2/Spn-F loss-of-function and overexpression; protein interactome analysis; Hook and dynein light chain loss-of-function\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis in Drosophila with interactome data; multiple genetic modifiers tested; single lab\",\n      \"pmids\": [\"32848189\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CHMP2B and CHMP4B are recruited to Leishmania donovani parasitophorous vacuoles (LdLPVs) together with VPS4a and TSG101, demonstrating CHMP2B participates in ESCRT-III assembly at pathological membrane compartments beyond its canonical endosomal role.\",\n      \"method\": \"Immunofluorescence of ESCRT components at LdLPVs in infected macrophages; dominant-negative VPS4a expression\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single immunofluorescence observation in a preprint; not directly focused on CHMP2B mechanism; no functional perturbation of CHMP2B specifically\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CHMP2B acts after Annexin-mediated membrane sealing in a sequential 'sealing and healing' membrane repair pathway. FTD- and ALS-associated mutations in CHMP2B compromise the repair process (ESCRT-III-mediated shedding of damaged membranes).\",\n      \"method\": \"Temporal recruitment analysis of ESCRT-III and Annexins to membrane damage sites; CHMP2B mutant functional analysis in membrane repair assay\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — preprint, single lab, functional assay for membrane repair; mechanistic ordering is novel but awaits peer review\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In CHMP2A knockout cells, CHMP2B localization at the abscission site is minimally disrupted during cytokinesis, whereas CHMP4B, CHMP3, and CHMP1B show progressively severe organization defects, indicating CHMP2B is relatively independent of CHMP2A for cytokinetic abscission site targeting.\",\n      \"method\": \"CHMP2A knockout; live cell imaging; structured illumination microscopy (SIM); correlative light-electron microscopy (CLEM)\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — preprint, negative/minimal result for CHMP2B specifically; finding is about CHMP2A's role with CHMP2B as a comparator\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"CHMP2B is a core ESCRT-III subunit that polymerizes into helical filaments to deform and remodel membranes; it preferentially binds PI(4,5)P2-containing membranes and can act as a diffusion barrier at membrane necks. Its C-terminal domain contains a nuclear export signal (NES) enabling CRM1-dependent cytoplasmic retention, and its activity requires VPS4-mediated release from membranes — a step blocked by FTD-causative C-terminal truncation mutations, leading to stable aberrant membrane association that disrupts endosome-lysosome fusion (by preventing Rab7 recruitment), impairs autophagic flux, blocks axonal endolysosomal trafficking, and causes lysosomal storage pathology; at synapses, CHMP2B-containing ESCRT-III complexes regulate dendritic spine growth, synaptic plasticity, and presynaptic vesicle recycling, while its axonal transport to presynaptic boutons is regulated by neuronal activity through kinesin-binding protein — with loss of these functions collectively driving the neurodegeneration seen in FTD3 and ALS.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CHMP2B is a core ESCRT-III subunit that polymerizes into helical membrane-deforming lattices and underlies endolysosomal, autophagic, and synaptic membrane remodeling, with its dysfunction causing frontotemporal dementia (FTD3) and contributing to ALS [#0, #5]. Purified CHMP2B preferentially binds PI(4,5)P2-containing membranes, assembles into a tightly packed helical coat that rigidifies and tubulates the bilayer, and concentrates at membrane necks where it acts as a diffusion barrier to lipids and membrane proteins [#5, #15, #18]. Productive turnover of the polymer requires VPS4-mediated release from membranes [#5]. FTD3-causative C-terminal truncations (e.g. CHMP2B-Intron5) act through a gain of function: the mutant protein fails to recruit VPS4, becomes stably trapped on endosomal membranes, blocks Rab7 recruitment and thereby endosome-lysosome fusion, impairs autophagic flux, and produces enlarged endolysosomes and neuronal lysosomal storage pathology [#2, #3, #6, #11, #14]. In neurons CHMP2B is part of a stable perisynaptic ESCRT-III complex required for dendritic spine growth, excitatory synapse density, activity-dependent potentiation, and presynaptic vesicle recycling, and its activity-regulated axonal transport to boutons depends on kinesin-binding protein [#4, #10, #19, #23]. Beyond canonical ESCRT functions, CHMP2B regulates CK1 abundance to control TDP-43 phosphorylation independently of autophagy [#17], and sustained CHMP2B activity promotes CHMP7-mediated nuclear pore complex injury in sporadic ALS neurons [#22]. Disease severity is modulated by physical and genetic interactors including TMEM106B and spastin [#12, #21], and the C-terminus also encodes a CRM1-dependent nuclear export signal lost upon the FTD3 truncation [#24].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Established CHMP2B as a disease gene, linking ESCRT-III dysfunction to neurodegeneration for the first time.\",\n      \"evidence\": \"Genetic linkage and splice-site mutation analysis in a Danish FTD3 pedigree showing aberrant mRNA splicing in patient tissue\",\n      \"pmids\": [\"16041373\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the cellular mechanism of toxicity\", \"Did not distinguish loss- vs gain-of-function\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Connected C-terminal truncation specifically to endosomal morphological dysfunction.\",\n      \"evidence\": \"Overexpression of two independent truncation mutants in SK-N-SH neuroblastoma cells with fluorescence microscopy of endosomes\",\n      \"pmids\": [\"17956895\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Overexpression artifact possible\", \"Molecular step disrupted not identified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined where in the endolysosomal pathway mutant CHMP2B acts, identifying Rab7 recruitment failure as the block to endosome-lysosome fusion, and showed disruption of the autophagy-lysosomal pathway.\",\n      \"evidence\": \"Patient fibroblasts/brain Rab7 localization assays; transfection of mutant CHMP2B in HEK-293/COS-7 with CD63 and LC3-II readouts\",\n      \"pmids\": [\"20223751\", \"20352044\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not show how mutant remains membrane-bound\", \"MVB sorting itself intact\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Distinguished gain-of-function from loss-of-function, establishing that the truncation mutant, not loss of CHMP2B, drives neurodegeneration.\",\n      \"evidence\": \"Comparative transgenic (mutant vs WT) and Chmp2b knockout mice with neuropathological analysis\",\n      \"pmids\": [\"22366797\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the molecular trapping mechanism\", \"Cell-type selectivity unexplained\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Provided the structural basis for CHMP2B function, showing it forms a VPS4-dependent helical membrane-deforming polymer.\",\n      \"evidence\": \"Cryo-EM of CHMP2B membrane tubes plus VPS4 depletion and CHMP4 relocalization in cells\",\n      \"pmids\": [\"21926173\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological membrane target not defined\", \"Lipid specificity not yet measured\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Placed CHMP2B-linked autophagy defects in a maturation pathway via genetic modifiers and probed ESCRT dissociation defects of a missense mutant.\",\n      \"evidence\": \"Drosophila modifier screen identifying STX13/Vti1a; missense T104N Co-IP with VPS4/Snf7-2 and EGFR degradation assays in neurons\",\n      \"pmids\": [\"24095276\", \"22521643\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"STX13-CHMP2B physical link not shown\", \"T104N Co-IP single lab without reciprocal validation\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identified a physiological synaptic role for CHMP2B in spine growth and excitatory transmission, with mutants acting dominant-negatively.\",\n      \"evidence\": \"Mutant expression and RNAi in hippocampal neurons with spine morphometry and mEPSC recordings\",\n      \"pmids\": [\"20699355\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism at spines not defined\", \"Relation to ESCRT membrane activity unclear\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined CHMP2B as part of a stable perisynaptic ESCRT-III complex required for synapse formation and plasticity in vivo, and identified lysosomal storage as the major neuronal pathology.\",\n      \"evidence\": \"Immuno-EM, CoIP-MS, depletion phenotypes in vitro/in vivo; physiological-level transgenic mice with ultrastructure and patient brain confirmation\",\n      \"pmids\": [\"25698751\", \"26358247\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Composition of synaptic complex only partially resolved\", \"Link between storage pathology and synaptic loss unresolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified TMEM106B as a physical and functional modifier of CHMP2B toxicity in the endolysosomal pathway.\",\n      \"evidence\": \"Co-IP of TMEM106B risk variants with CHMP2B plus EGFR/autophagy/viability assays in overexpression\",\n      \"pmids\": [\"26651479\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Overexpression system\", \"Direct vs indirect interaction not resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrated mitochondrial and endosomal dysfunction in patient neurons attributable to the mutation using isogenic correction.\",\n      \"evidence\": \"FTD3 patient iPSC cortical neurons with CRISPR isogenic controls; EM, respirometry, ROS and iron assays\",\n      \"pmids\": [\"28216144\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanistic link between ESCRT defect and mitochondrial phenotype unclear\", \"Iron homeostasis pathway not detailed\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified the proximate molecular defect: mutant CHMP2B cannot recruit VPS4, becoming stably trapped and immobilizing dendritic endolysosomes, with TMEM106B knockdown providing rescue.\",\n      \"evidence\": \"Physiological-level transgenic mice, dendritic endolysosome live imaging, VPS4 recruitment assays, TMEM106B ASO rescue\",\n      \"pmids\": [\"30496365\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How truncation abolishes VPS4 recruitment structurally not shown\", \"Whether trafficking arrest fully accounts for degeneration unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined CHMP2B's membrane biophysics: PI(4,5)P2 preference and diffusion-barrier function at membrane necks.\",\n      \"evidence\": \"Reconstituted GUV-nanotube system with purified CHMP2B and lipid diffusion assays\",\n      \"pmids\": [\"29967034\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance of barrier function not established\", \"Relationship to scission unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Distinguished CHMP2B from CHMP2A biophysically, showing CHMP2B uniquely binds PI(4,5)P2 and rigidifies membranes without requiring CHMP3.\",\n      \"evidence\": \"Purified recombinant proteins on biomimetic membranes; biolayer interferometry and membrane mechanics\",\n      \"pmids\": [\"33832485\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of isoform divergence in cells unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Revealed an autophagy-independent role: CHMP2B controls CK1 abundance via ubiquitin-proteasome turnover to modulate TDP-43 phosphorylation and toxicity.\",\n      \"evidence\": \"Drosophila and mammalian cell knockdown/overexpression; CK1 inhibition, ubiquitination and proteasome assays\",\n      \"pmids\": [\"34726688\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct CHMP2B-CK1 interaction not defined\", \"Connection to ESCRT activity unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Characterized CHMP2B-FTD as a synaptopathy involving presynaptic vesicle recycling defects, and identified spastin as a mutation-enhanced binding partner.\",\n      \"evidence\": \"Aged transgenic mice with synaptic marker IHC, EM and SV recycling assays; Co-IP, fractionation and Drosophila epistasis for spastin\",\n      \"pmids\": [\"34855215\", \"36414997\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal chain from sequestration to synaptic failure incomplete\", \"Spastin interaction single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended CHMP2B's pathological reach to nuclear pore injury in sporadic ALS, where sustained CHMP2B activation drives CHMP7 accumulation and TDP-43 dysfunction.\",\n      \"evidence\": \"sALS iPSC neurons with partial CHMP2B knockdown, super-resolution microscopy and NPC composition analysis\",\n      \"pmids\": [\"39709457\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of CHMP2B 'activation' undefined\", \"Single lab iPSC model\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Showed activity-dependent axonal transport of CHMP2B to presynaptic boutons depends on kinesin-binding protein, with the FTD mutant failing transport.\",\n      \"evidence\": \"Live imaging of CHMP2B axonal trafficking with KBP binding assays comparing WT vs Intron5\",\n      \"pmids\": [\"40021219\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"KBP-CHMP2B binding interface not mapped\", \"Single lab\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identified a C-terminal CRM1-dependent nuclear export signal lost in the FTD3 mutant, causing nuclear mislocalization.\",\n      \"evidence\": \"iPSC cortical neurons with leptomycin B and NES site-directed mutagenesis; localization and export assays\",\n      \"pmids\": [\"41559796\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of nuclear CHMP2B unresolved\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the diverse downstream consequences of mutant CHMP2B (endolysosomal arrest, mitochondrial dysfunction, NPC injury, CK1/TDP-43 regulation, nuclear mislocalization) are mechanistically unified and which drive neurodegeneration remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking membrane-trapping to nuclear and mitochondrial phenotypes\", \"Therapeutic node for FTD3/ALS not validated\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [15, 18]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [5, 18]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [1, 2, 8]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [5, 15]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [3, 11]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [24]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [2, 5, 14]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [3, 7]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [4, 10, 19]}\n    ],\n    \"complexes\": [\"ESCRT-III\"],\n    \"partners\": [\"VPS4\", \"CHMP4B\", \"TMEM106B\", \"spastin\", \"CHMP7\", \"STX13\", \"KBP\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}