<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">Charged Multivesicular Body Protein 1B</th></tr>
<tr><td><strong>Gene Symbol</strong></td><td>CHMP1B</td></tr>
<tr><td><strong>Full Name</strong></td><td>Charged Multivesicular Body Protein 1B</td></tr>
<tr><td><strong>Chromosome</strong></td><td>18q23</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td>[57132](https://www.ncbi.nlm.nih.gov/gene/57132)</td></tr>
<tr><td><strong>OMIM</strong></td><td>[614790](https://www.omim.org/entry/614790)</td></tr>
<tr><td><strong>Ensembl ID</strong></td><td>[ENSG00000086205](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000086205)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[Q9Y3Q1](https://www.uniprot.org/uniprot/Q9Y3Q1)</td></tr>
<tr><td><strong>Associated Diseases</strong></td><td>Hereditary Spastic Paraplegia, Alzheimer's Disease, Parkinson's Disease, ALS</td></tr>
</table>
</div>
<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">Charged Multivesicular Body Protein 1B</th></tr>
<tr><td><strong>Gene Symbol</strong></td><td>CHMP1B</td></tr>
<tr><td><strong>Full Name</strong></td><td>Charged Multivesicular Body Protein 1B</td></tr>
<tr><td><strong>Chromosome</strong></td><td>18q23</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td>[57132](https://www.ncbi.nlm.nih.gov/gene/57132)</td></tr>
<tr><td><strong>OMIM</strong></td><td>[614790](https://www.omim.org/entry/614790)</td></tr>
<tr><td><strong>Ensembl ID</strong></td><td>[ENSG00000086205](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000086205)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[Q9Y3Q1](https://www.uniprot.org/uniprot/Q9Y3Q1)</td></tr>
<tr><td><strong>Associated Diseases</strong></td><td>Hereditary Spastic Paraplegia, Alzheimer's Disease, Parkinson's Disease, ALS</td></tr>
</table>
</div>
CHMP1B (Charged Multivesicular Body Protein 1B) is a component of the ESCRT-III (Endosomal Sorting Complex Required for Transport-III) machinery, essential for endosomal membrane remodeling and multivesicular body (MVB) formation.[@hanson2012] The ESCRT system is responsible for sorting ubiquitinated cargo into intralumenal vesicles of MVBs, a critical step in trafficking proteins to lysosomes for degradation. CHMP1B is expressed predominantly in the brain, particularly in neurons of the cortex, hippocampus, and basal ganglia, where it plays essential roles in synaptic vesicle trafficking, autophagosome maturation, and neuronal morphogenesis. Mutations in CHMP1B have been linked to hereditary spastic paraplegia (HSP), a neurodegenerative disorder characterized by progressive lower limb spasticity and weakness. Beyond HSP, ESCRT dysfunction is increasingly recognized as a contributor to Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS) pathogenesis. This page details the molecular biology of CHMP1B, its role in cellular processes relevant to neurodegeneration, disease associations, and therapeutic implications.
The CHMP1B gene is located on chromosome 18q23 and consists of 7 coding exons spanning approximately 3.5 kilobases. The gene encodes a protein of 199 amino acids with a molecular weight of approximately 22 kDa. CHMP1B belongs to the CHMP (Charged Multivesicular Body Protein) family, which includes CHMP1A, CHMP1B, CHMP2A/B, CHMP3, CHMP4A/B/C, CHMP5, CHMP6, and CHMP7. These proteins share a conserved C-terminal microtubule-interacting and trafficking (MIT) domain that interacts with Vps4 ATPase, essential for ESCRT-III disassembly and recycling.
CHMP1B contains an N-terminal acidic region followed by a central helical domain and a C-terminal MIT-interacting motif (MIM). The N-terminal region is highly charged and mediates polymerization and membrane interaction. The central helical domain forms an antiparallel coiled-coil structure that drives CHMP1B polymerization. The C-terminal MIM binds to the MIT domain of Vps4, facilitating the ATP-dependent disassembly of CHMP1B oligomers. Structural studies reveal that CHMP1B can form helical polymers that constrict membranes, essential for membrane abscission during MVB formation and autophagosome-lysosome fusion.
CHMP1B is regulated by phosphorylation and ubiquitination. Casein kinase 2 (CK2) phosphorylates CHMP1B at serine residues, modulating its interaction with Vps4 and ESCRT-III dynamics. Ubiquitination of CHMP1B at lysine residues targets the protein for degradation and regulates its function in cargo sorting. The balance between CHMP1B polymerization and disassembly by Vps4 is critical for proper ESCRT function.
The primary function of CHMP1B is in the ESCRT-III complex, which drives the inward budding of the endosomal membrane to form intralumenal vesicles containing ubiquitinated cargo. This process requires sequential action of ESCRT-0, ESCRT-I, ESCRT-II, and ESCRT-III. CHMP1B, along with CHMP1A and other ESCRT-III components, polymerizes on the endosomal membrane to drive membrane constriction and scission. The AAA-ATPase Vps4 then disassembles CHMP1B oligomers, allowing for ESCRT-III recycling. This pathway is essential for trafficking membrane proteins, including growth factor receptors, to lysosomes for degradation.
Beyond MVB formation, CHMP1B plays critical roles in autophagosome maturation and closure. During autophagy, double-membraned autophagosomes form and fuse with lysosomes to deliver cargo for degradation. ESCRT-III components, including CHMP1B, are recruited to autophagosomes and are essential for their closure. Defects in CHMP1B function impair autophagosome-lysosome fusion, leading to accumulation of immature autophagic vesicles. This dysfunction is particularly relevant in neurodegeneration, where impaired autophagy contributes to protein aggregate accumulation.
In neurons, CHMP1B is enriched at synapses, where it regulates synaptic vesicle trafficking and synaptic plasticity. The ESCRT machinery is involved in recycling synaptic vesicle proteins and maintaining synaptic homeostasis. CHMP1B dysfunction impairs synaptic vesicle endocytosis and leads to synaptic dysfunction. Studies in Drosophila show that ESCRT components are required for synapse formation and function, with CHMP1B mutations causing synaptic defects and behavioral abnormalities.
CHMP1B contributes to neuronal morphogenesis, including dendrite arborization and axon guidance. The ESCRT machinery regulates membrane trafficking during neurite outgrowth and branching. CHMP1B knockdown or knockout impairs neuronal morphology, reducing dendritic complexity and axon length. This function involves trafficking of membrane proteins and growth factor receptors essential for neurite development.
CHMP1B is widely expressed in the brain with highest levels in the frontal cortex, hippocampus, basal ganglia, and cerebellum. In the cortex, CHMP1B is expressed in pyramidal neurons and interneurons. In the hippocampus, CHMP1B is enriched in CA1 pyramidal neurons and dentate gyrus granule cells. The basal ganglia, including striatum and substantia nigra, show high CHMP1B expression, relevant to PD pathogenesis. CHMP1B is also expressed in astrocytes and oligodendrocytes, where it contributes to glial function.
At the subcellular level, CHMP1B localizes to endosomes, autophagosomes, and the plasma membrane. In neurons, CHMP1B is enriched in dendritic spines and presynaptic terminals, consistent with its role in synaptic function. Immunogold electron microscopy shows CHMP1B on the limiting membrane of multivesicular bodies and autophagosomes. This localization positions CHMP1B to regulate membrane trafficking at critical neuronal compartments.
CHMP1B mutations cause a form of hereditary spastic paraplegia (HSP) classified as SPG57. HSPs are a group of inherited neurodegenerative disorders characterized by progressive lower limb spasticity and weakness. SPG57 is caused by autosomal recessive loss-of-function mutations in CHMP1B. Affected individuals present in early childhood with spastic paraplegia, often accompanied by mild intellectual disability. The identification of CHMP1B as an HSP gene established the importance of ESCRT dysfunction in motor neuron disease.
The mechanism by which CHMP1B mutations cause HSP involves impaired endosomal sorting and autophagy in corticospinal neurons. Proper functioning of the ESCRT machinery is essential for trafficking membrane proteins to lysosomes, including those involved in axonal maintenance and synaptic function. CHMP1B deficiency leads to endosomal dysfunction, impaired autophagy, and accumulation of aberrant vesicles in neurons. These cellular defects ultimately cause axonal degeneration in corticospinal tracts.
Patient-derived induced pluripotent stem cells (iPSCs) and mouse models have been generated to study CHMP1B-related HSP. Neurons from CHMP1B-deficient iPSCs show endosomal trafficking defects and impaired neurite outgrowth. Knockout mice exhibit progressive spasticity and axonal degeneration in corticospinal tracts. These models demonstrate that ESCRT restoration can rescue neuronal phenotypes, suggesting therapeutic potential.
Multiple studies link ESCRT dysfunction to AD pathogenesis. In AD brains, CHMP1B and other ESCRT-III components show altered expression and localization. Amyloid-beta (Aβ) oligomers directly impair ESCRT function, disrupting endosomal sorting and contributing to the endosomal enlargement observed in AD. This dysfunction impairs trafficking of proteins to lysosomes and contributes to the accumulation of toxic proteins.
Autophagy is broadly impaired in AD, with CHMP1B dysfunction contributing to this deficit. Aβ accumulation and tau pathology are associated with impaired autophagosome-lysosome fusion. CHMP1B's role in autophagosome maturation makes it a contributor to this impairment. Restoring ESCRT function has shown benefit in AD models, reducing amyloid pathology and improving neuronal function.
Targeting ESCRT dysfunction represents a novel therapeutic approach for AD. Strategies include enhancing CHMP1B expression, promoting ESCRT-III assembly, or facilitating Vps4 activity. While direct targeting of ESCRT components is challenging, approaches that enhance autophagy and endosomal function more broadly may have benefit. Understanding CHMP1B's precise role in AD will inform these therapeutic development efforts.
PD is associated with dysfunction in the endosomal-lysosomal pathway, particularly relevant given the role of CHMP1B in this pathway. Mutations in genes encoding lysosomal proteins (GBA, ATP13A2) and proteins regulating endosomal function (LRRK2) cause familial PD. CHMP1B dysfunction may contribute to sporadic PD by impairing endosomal trafficking of proteins such as α-synuclein.
The trafficking and clearance of α-synuclein involves endosomal-lysosomal pathways. CHMP1B dysfunction may impair α-synuclein clearance, contributing to its aggregation and propagation. Studies in cellular models show that ESCRT impairment leads to α-synuclein accumulation. This connection makes CHMP1B relevant to PD pathogenesis even in the absence of direct mutations.
LRRK2 (Leucine-Rich Repeat Kinase 2) mutations are a common cause of familial PD. LRRK2 regulates endosomal trafficking and may phosphorylate ESCRT components. Some evidence suggests that LRRK2 activity modulates CHMP1B function, creating a potential pathogenic interaction. This connection warrants further investigation.
ALS involves dysfunction in protein homeostasis and membrane trafficking. ESCRT-III components, including CHMP1B, are implicated in ALS pathogenesis. TDP-43 and FUS protein aggregates, hallmarks of ALS, may impair ESCRT function. CHMP1B dysfunction contributes to the impaired autophagy and endosomal trafficking observed in ALS models.
Autophagy is broadly impaired in ALS, with defects in autophagosome formation, maturation, and lysosomal fusion. CHMP1B's role in autophagosome maturation makes it relevant to this dysfunction. Restoring ESCRT function in ALS models improves autophagy and reduces protein aggregate accumulation, supporting therapeutic targeting.
Therapeutic strategies targeting CHMP1B and ESCRT function include:
Therapeutic targeting of CHMP1B faces challenges. The complexity of ESCRT function and potential for off-target effects require careful approach. Achieving adequate neuronal delivery and expression levels for gene therapy is challenging. Additionally, the precise contribution of CHMP1B dysfunction to different neurodegenerative diseases needs clarification. Future studies should focus on developing selective modulators and validating target engagement in relevant models.
The following diagram shows the key molecular relationships involving CHMP1B — Charged Multivesicular Body Protein 1B discovered through SciDEX knowledge graph analysis: