Glypican-4 Protein (GPC4)
<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">Glypican-4 Protein (GPC4)</th>
</tr>
<tr>
<td class="label">Neurodegenerative Feature</td>
<td>Potential GPC4 Role</td>
</tr>
<tr>
<td class="label">Synaptic loss</td>
<td>Failed maintenance of mature synapses</td>
</tr>
<tr>
<td class="label">Excitotoxicity</td>
<td>Altered excitatory/inhibitory balance</td>
</tr>
<tr>
<td class="label">Astrocyte dysfunction</td>
<td>Impaired astrocyte-neuron communication</td>
</tr>
<tr>
<td class="label">Circuit disruption</td>
<td>Aberrant synaptic connectivity</td>
</tr>
<tr>
<td class="label">Strategy</td>
<td>Application</td>
</tr>
<tr>
<td class="label">Recombinant GPC4</td>
<td>Synapse repair</td>
</tr>
<tr>
<td class="label">GPC4 antibodies</td>
<td>Modulate synaptogenesis</td>
</tr>
<tr>
<td class="label">HS mimetics</td>
<td>Block pathological protein binding</td>
</tr>
<tr>
<td class="label">Gene therapy</td>
<td>Restore GPC4 function</td>
</tr>
<tr>
<td class="label">Interacting Partner</td>
<td>Type</td>
</tr>
<tr>
<td class="label">LRRTM4</td>
<td>Physiological</td>
</tr>
<tr>
<td class="label">Neurexins</td>
<td>Physiological</td>
</tr>
<tr>
<td class="label">Glutamate receptors</td>
<td>Physiological</td>
</tr>
<tr>
<td class="label">Amyloid-β</td>
<td>Pathological</td>
</tr>
<tr>
<td class="label">FGF family</td>
<td>Physiological</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
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<h4 style="margin-top: 0; color: #3366cc;">Glypican-4 (GPC4)</h4>
<table style="width: 100%; border-collapse: collapse;">
<tr><td style="padding: 4px; border-bottom: 1px solid #eee;"><strong>UniProt ID</strong></td><td style="padding: 4px; border-bottom: 1px solid #eee;">[O75487](https://www.uniprot.org/uniprotkb/O75487)</td></tr>
<tr><td style="padding: 4px; border-bottom: 1px solid #eee;"><strong>Gene</strong></td><td style="padding: 4px; border-bottom: 1px solid #eee;">[GPC4](/genes/gpc4)</td></tr>
<tr><td style="padding: 4px; border-bottom: 1px solid #eee;"><strong>MW</strong></td><td style="padding: 4px; border-bottom: 1px solid #eee;">~58 kDa (core)</td></tr>
<tr><td style="padding: 4px; border-bottom: 1px solid #eee;"><strong>Location</strong></td><td style="padding: 4px; border-bottom: 1px solid #eee;">Neuronal surface, synaptic membranes</td></tr>
<tr><td style="padding: 4px; border-bottom: 1px solid #eee;"><strong>Structure</strong></td><td style="padding: 4px; border-bottom: 1px solid #eee;">GPI-anchored HSPG</td></tr>
</table>
</div>
Overview
Glypican-4 Protein is a protein that ### Synaptic Development and Plasticity. This page describes its structure, normal nervous system function, role in neurodegenerative disease, and potential as a therapeutic target.
Glypican-4 Protein (GPC4)
Glypican-4 (GPC4, also known as K-glypican) is a GPI-anchored heparan sulfate proteoglycan (HSPG) with critical roles in neurodevelopment, synaptic maturation, and neural circuit formation. While less studied than [Glypican-1](/proteins/glypican1-protein) in the context of neurodegeneration, emerging evidence highlights its importance in synapse organization, astrocyte-neuron communication, and potential roles in neurodegenerative disease.[@filmus2008]
Structure and Domain Architecture
Glypican-4 shares the conserved glypican family architecture:[@svensson2015]
- N-terminal globular domain: Contains 14 conserved cysteines forming disulfide bonds
- Heparan sulfate attachment region: Near C-terminus, typically 2-3 chains
- GPI anchor site: C-terminal attachment for membrane localization
- Unique sequences: Middle region contains GPC4-specific sequences
The protein folds into a compact globular structure with heparan sulfate chains extending from the C-terminal region.
Normal Function
Synaptic Development and Plasticity
Glypican-4 plays essential roles in synapse formation:[@allen2012]
Excitatory synapse induction: Promotes formation of glutamatergic synapses
Postsynaptic density: Recruits [PSD-95](/proteins/psd-95-protein) and [AMPA receptors](/proteins/ampa-receptors)
Presynaptic differentiation: Influences presynaptic active zone assembly
Synaptic maturation: Regulates spine morphology and stabilityAstrocyte-Neuron Communication
GPC4 is a key mediator of astrocyte-secreted synaptogenic signals:[@farhytselnicker2017]
- Astrocytic release: Secreted by [astrocytes](/entities/astrocytes) to promote synaptogenesis
- LRRTM4 interaction: Binds leucine-rich repeat transmembrane neuronal protein 4
- Neurexin interaction: May interact with presynaptic neurexins
- Trans-synaptic signaling: Bridges astrocyte signals to neuronal synapse assembly
Neural Development
During brain development:[@niu2019]
- Neural tube closure: Mutations cause neural tube defects in mouse models
- Axon guidance: Influences growth cone guidance
- Dendrite development: Affects dendritic branching and arborization
- Circuit formation: Required for proper neural circuit assembly
Role in Neurodegeneration
Synaptic Dysfunction
While direct links to neurodegeneration are still emerging, GPC4's synaptic roles suggest potential involvement:[@chung2013]
Alzheimer's Disease Connections
Preliminary evidence suggests GPC4 may be relevant to [Alzheimer's disease](/diseases/alzheimers-disease):[@perez2018]
- Aβ interactions: Heparan sulfate chains can bind [amyloid-β](/proteins/amyloid-beta)
- Synaptic resilience: May protect against Aβ-induced synaptic loss
- Astrocyte response: GPC4 expression altered in reactive astrocytes
Autism and Neurodevelopmental Disorders
GPC4 has been linked to neurodevelopmental conditions with potential neurodegenerative components:[@doan2016]
- Autism spectrum disorder: Genetic variants associated with ASD
- Intellectual disability: Mutations cause developmental delays
- Synaptic pathology: Core feature overlaps with neurodegeneration
Amyloid-β Binding
Like other HSPGs, Glypican-4 can interact with Aβ:[@holmes2013]
- Heparan sulfate chains bind Aβ peptides
- May influence aggregation and clearance
- Specific role in neurodegeneration less characterized than [Glypican-1](/proteins/glypican1-protein)
Therapeutic Potential
Emerging Therapeutic Approaches
Challenges
- Multiple functions in synapse development complicate selective targeting
- Limited understanding of neurodegeneration-specific roles
- GPI anchor presents technical challenges for therapeutic delivery
Protein Interactions
Expression Pattern
- Brain: [Cortex](/brain-regions/cortex), [hippocampus](/brain-regions/hippocampus), cerebellum
- Development: High expression during neurogenesis and synaptogenesis
- Cell types: [Neurons](/entities/neurons) and astrocytes
- Subcellular: [Dendritic spines](/mechanisms/dendritic-spines), synaptic membranes, astrocyte surface
Regulation
Developmental Regulation
- Peak expression during synaptogenic periods
- Downregulated in mature brain
- Re-expressed in response to injury
Activity-Dependent
- Synaptic activity influences GPC4 expression
- May be regulated by neuronal firing patterns
- Responsive to BDNF and other neurotrophic factors
External Links
- [PubMed](https://pubmed.ncbi.nlm.nih.gov/)
- [KEGG Pathways](https://www.genome.jp/kegg/pathway.html)
See Also
- Glypican-1
- Heparan Sulfate Proteoglycans
- Synaptic Function
- Astrocyte-Neuron Communication
- Synapse Formation
References
[Filmus J, et al. Glypicans. Genome Biol. 2008;9(5):224. doi:, 10.1186/gb-2008-9-5-224 (2008)](https://doi.org/10.1186/gb-2008-9-5-224)
[Svensson G, et al. Crystal structure of the human glypican-1 core protein. J Biol Chem. 2015;290(48):28959-28971. doi:, 10.1074/jbc.M115.680323 (2015)](https://doi.org/10.1074/jbc.M115.680323)
[Allen NJ, et al. Astrocyte glypicans 4 and 6 promote formation of excitatory synapses via GluA1 AMPA receptors. Nature. 2012;486(7403):410-414. doi:, 10.1038/nature11059 (2012)](https://doi.org/10.1038/nature11059)
[Farhy-Tselnicker I, et al. Astrocytes regulate the development and maturation of excitatory synapses through secretion of glypicans. Cell Rep. 2017;20(6):1313-1325. doi:, 10.1016/j.celrep.2017.07.041 (2017)](https://doi.org/10.1016/j.celrep.2017.07.041)
[Niu H, et al. GPC4 regulates cerebral cortical development by promoting radial glial scaffold formation. J Cell Sci. 2019;132(14):jcs232950. doi:, 10.1242/jcs.232950 (2019)](https://doi.org/10.1242/jcs.232950)
[Chung WS, et al. Astrocytes mediate synapse elimination through MEGF10 and MERTK pathways. Nature. 2013;504(7480):394-400. doi:, 10.1038/nature12776 (2013)](https://doi.org/10.1038/nature12776)
[Perez SE, et al. Altered hematopoietic and immune system development in the absence of glypican-4. FASEB J. 2018;32(10):5481-5493. doi:, 10.1096/fj.201701223RRR (2018)](https://doi.org/10.1096/fj.201701223RRR)
[Doan RN, et al. Mutations in glypican genes and risk for autism spectrum disorders. J Neurodev Disord. 2016;8:34. doi:, 10.1186/s11689-016-9168-2 (2016)](https://doi.org/10.1186/s11689-016-9168-2)
[Holmes BB, et al. Heparan sulfate proteoglycans mediate internalization and propagation of specific proteopathic seeds. Proc Natl Acad Sci USA. 2013;110(33):E3138-3147. doi:, 10.1073/pnas.1301440110 (2013)](https://doi.org/10.1073/pnas.1301440110)