| CHMP2B — Charged Multivesicular Body Protein 2B | |
|---|---|
| Symbol | CHMP2B |
| Full Name | Charged Multivesicular Body Protein 2B |
| Chromosome | 3p11.2 |
| NCBI Gene | 25978 |
| Ensembl | ENSG00000083937 |
| OMIM | 609512 |
| UniProt | Q9UQN3 |
| Diseases | Frontotemporal Dementia (FTD-3), ALS |
| Expression | Cerebral cortex (frontal, temporal), Hippocampus, Cerebellum, Spinal cord |
| Key Mutations | |
| Intron5 splice mutation (Danish FTD-3) Gln165X — nonsense (Belgian) Thr104Asn — missense (ALS) Asn143Ser — missense (CBD) |
|
Chmp2B — Charged Multivesicular Body Protein 2B is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
CHMP2B (Charged Multivesicular Body Protein 2B) is a gene located on chromosome 3p11.2 that encodes a core subunit of the ESCRT-III (Endosomal Sorting Complex Required for Transport-III) complex. CHMP2B mutations were first identified in 2005 as the cause of [frontotemporal dementia[/diseases/ftd linked to chromosome 3 (FTD-3) in a large Danish family. The gene has since been associated with a spectrum of neurodegenerative disorders including [amyotrophic lateral sclerosis[/diseases/als (ALS) and Corticobasal Degeneration (CBD).
CHMP2B-associated disease provided one of the earliest demonstrations that endosomal-lysosomal trafficking dysfunction directly causes neurodegeneration, establishing the ESCRT pathway as a fundamental mechanism in the FTD-ALS disease spectrum. The gene is catalogued as NCBI Gene ID [25978] and OMIM [609512].
CHMP2B is a component of the ESCRT-III complex, the executory arm of the ESCRT machinery that catalyzes membrane scission events in multiple cellular processes. The ESCRT pathway consists of four sequential complexes (ESCRT-0, -I, -II, -III) plus associated factors:
CHMP2B, together with CHMP4B (Snf7), forms the core ESCRT-III filament. CHMP2B undergoes a conformational switch from an autoinhibited "closed" state in the cytosol to an "open" active state on endosomal membranes, where its C-terminal autoinhibitory domain releases to allow polymerization.
The primary function of ESCRT-III/CHMP2B is to sort ubiquitinated transmembrane proteins into intraluminal vesicles of MVBs (late endosomes). When MVBs fuse with lysosomes, ILV contents are degraded. This pathway is essential for:
ESCRT-III/CHMP2B is required for the fusion of autophagosomes with late endosomes/lysosomes (amphisome formation). CHMP2B dysfunction blocks autophagic flux, leading to accumulation of autophagosomes and undegraded cargo — including ubiquitin-positive protein aggregates.
Beyond endolysosomal sorting, ESCRT-III/CHMP2B participates in:
CHMP2B is broadly expressed in the central nervous system with particularly high levels in:
Expression data is available from the Allen Human Brain Atlas.
The landmark identification of CHMP2B mutations in FTD came from a large Danish family in which autosomal dominant dementia had been mapped to chromosome 3p11.2 (designated FTD-3). In 2005, Skibinski et al. identified a mutation in the splice acceptor site of exon 6, producing two aberrant transcripts:
Both truncated proteins lack the C-terminal autoinhibitory domain, locking CHMP2B in a constitutively "open" (active) state that dominantly poisons ESCRT-III function.
Clinical features of CHMP2B-FTD:
CHMP2B mutations have been identified in patients with [ALS[/diseases/als, supporting the genetic and mechanistic overlap between FTD and ALS. Key ALS-associated variants include:
ALS-associated CHMP2B mutations tend to be missense variants rather than truncating mutations, suggesting they may cause subtler functional impairment than the FTD-causing splice mutations.
A missense mutation (Asn143Ser) was identified in a patient with familial Corticobasal Degeneration, expanding the clinical spectrum of CHMP2B-related neurodegeneration.
The neuropathology of CHMP2B-FTD is classified as frontotemporal lobar degeneration with ubiquitin-proteasome system markers (FTLD-[UPS). Key features include:
The [TDP-43[/entities/tdp-43-negative, FUS-negative pathology is distinctive and suggests that CHMP2B mutations cause neurodegeneration through a mechanism independent of the [TDP-43[/proteins/tdp-43 and [FUS[/proteins/fus-protein proteinopathies that characterize most other forms of FTLD.
Detailed neuropathological studies have revealed widespread neuronal lysosomal storage pathology in CHMP2B-FTD, with accumulation of electron-dense material in enlarged lysosomes throughout the brain. This lysosomal pathology is consistent with the loss of ESCRT-III-mediated endolysosomal sorting.
CHMP2B-FTD operates through a dominant gain-of-function mechanism. The C-terminally truncated CHMP2B protein:
Expression of CHMP2B truncation mutants causes:
CHMP2B mutants impair maturation of dendritic spines in [neurons[/entities/neurons, leading to increased filopodia-like protrusions and reduced mushroom-type mature spines. This synaptic pathology may contribute to the early cognitive and behavioral symptoms in CHMP2B-FTD.
Recent research (2025) has revealed that truncated CHMP2B (CHMP2BIntron5), while disrupting late endosome trafficking, paradoxically reduces [TDP-43[/proteins/tdp-43 aggregation through upregulation of [HSP70[/proteins/hsp70-protein chaperones. This finding provides insight into why CHMP2B-FTD pathology is [TDP-43[/entities/tdp-43-negative despite occurring in the FTD-ALS spectrum.
Cerebrospinal fluid [neurofilament light chain[/proteins/neurofilament-light ([NfL[/entities/neurofilament-light is elevated in presymptomatic CHMP2B mutation carriers up to 5 years before expected symptom onset, suggesting it may serve as a preclinical biomarker. Serum [NfL[/entities/neurofilament-light levels also show promise for tracking disease progression.
Approaches to restore or compensate for ESCRT-III dysfunction include:
Because autophagic flux is blocked in CHMP2B disease, pharmacological activation of autophagy upstream of the MVB fusion step may not be therapeutic. Instead, strategies that bypass the MVB bottleneck — such as enhancing direct lysosomal targeting — may be more effective.
For the dominant gain-of-function mutations, allele-specific knockdown of mutant CHMP2B using antisense oligonucleotides represents a potential therapeutic strategy, analogous to approaches being developed for other dominant neurodegenerative diseases.
The study of Chmp2B — Charged Multivesicular Body Protein 2B has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.