AQP4 Protein
Overview
AQP4 (Aquaporin-4) is the principal water channel protein expressed in the central nervous system, primarily in astrocytic end-feet that surround blood vessels and the pial surface. It plays a critical role in brain water homeostasis, cerebrospinal fluid circulation, and neuroinflammation.
Structure
Protein Infobox
<div class="infobox infobox-protein">
<table>
<tr><th colspan="2">AQP4 Protein</th></tr>
<tr><td><b>Protein Name</b></td><td>Aquaporin-4</td></tr>
<tr><td><b>Gene</b></td><td>[AQP4](/genes/aqp4)</td></tr>
<tr><td><b>UniProt ID</b></td><td>[P55064](https://www.uniprot.org/uniprot/P55064)</td></tr>
<tr><td><b>PDB Structures</b></td><td>1xzx, 2d57</td></tr>
<tr><td><b>Molecular Weight</b></td><td>34 kDa</td></tr>
<tr><td><b>Subcellular Localization</b></td><td>Plasma membrane (astrocytic end-feet), basolateral membrane</td></tr>
<tr><td><b>Protein Family</b></td><td>Aquaporin (MIP) family</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/ad" style="color:#ef9a9a">AD</a>, <a href="/wiki/ali" style="color:#ef9a9a">ALI</a>, <a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">ALZHEIMER</a>, <a href="/wiki/alzheimer's" style="color:#ef9a9a">ALZHEIMER'S</a></td>
</tr>
<tr>
<td class="label">SciDEX Hypotheses</td>
<td><a href="/hypothesis/h-807d7a82" style="color:#ce93d8" title="Score: 0.60">SASP-Driven Aquaporin-4 Dysregulation...</a><br><a href="/hypothesis/h-62e56eb9" style="color:#ce93d8" title="Score: 0.53">Glymphatic System-Enhanced Antibody Clea...</a><br><a href="/hypothesis/h-c8ccbee8" style="color:#ce93d8" title="Score: 0.46">Aquaporin-4 Polarization Rescue...</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">924 edges</a></td>
</tr>
</table>
</div>
Domain Architecture
AQP4 is a monomeric water channel that assembles as a tetramer. Each monomer contains six transmembrane alpha-helices with both N- and C-termini facing the cytosol. The protein has two half-helices that form the pore, with conserved NPA (Asn-Pro-Ala) motifs in the middle of the transmembrane helices that are characteristic of aquaporins.
Normal Function in the Nervous System
AQP4 is the dominant water channel in the brain and plays several essential roles:
Brain Water Homeostasis: Regulates water flow across the [blood-brain barrier](/entities/blood-brain-barrier) and between intracellular and extracellular compartments
Cerebrospinal Fluid Circulation: Facilitates CSF flow through the ventricular system and subarachnoid space
Astrocytic Function: Expressed in astrocytic end-feet surrounding cerebral blood vessels, forming the glia limitans perivascularis
Potassium Buffering: Cooperates with Kir4.1 potassium channels in astrocytic potassium homeostasis
Neurovascular Coupling: Links neuronal activity to changes in cerebral blood flow through astrocytic signalingRole in Neurodegeneration
Alzheimer's Disease
- AQP4 expression is altered in AD brain, with mislocalization from perivascular to somatic membranes
- Impaired perivascular AQP4 leads to reduced glymphatic clearance of [amyloid-beta](/proteins/amyloid-beta)
- Loss of polar AQP4 distribution correlates with reduced interstitial fluid clearance
- AQP4 deficiency accelerates amyloid plaque deposition in mouse models
Parkinson's Disease
- AQP4 upregulation in PD substantia nigra may contribute to neuroinflammation
- Altered water homeostasis affects dopaminergic neuron survival
- Potential role in Lewy body formation through impaired protein clearance
Amyotrophic Lateral Sclerosis
- AQP4 expression changes in motor [cortex](/brain-regions/cortex) and spinal cord
- Dysregulated water homeostasis contributes to excitotoxicity
- Astrocyte reactivity involves AQP4 redistribution
Multiple Sclerosis
- AQP4 is the target of neuromyelitis optica (NMO) autoantibodies
- Loss of AQP4 in NMO leads to extensive astrocyte damage
- Role in blood-brain barrier breakdown and demyelination
Traumatic Brain Injury
- AQP4 upregulation contributes to cytotoxic edema
- Dysregulated water flux exacerbates secondary neuronal damage
Therapeutic Targeting
Small Molecule Modulators
- AQP4 inhibitors: TGN-020 and AqB013 are experimental AQP4 blockers under investigation
- Anti-edema agents: AQP4 modulators being explored for traumatic brain injury
Gene Therapy Approaches
- Viral vector-mediated AQP4 modulation for neuroprotection
- CRISPR-based editing to restore proper AQP4 localization
Biomarkers
- AQP4 autoantibodies serve as diagnostic marker for neuromyelitis optica
- Cerebrospinal fluid AQP4 levels as potential neurodegeneration biomarker
Key Publications
[Nico et al., AQP4 in brain edema (2003)](https://doi.org/10.1016/s0301-0082(03)00101-6)
[Iliff et al., Glymphatic clearance (2012)](https://doi.org/10.1126/science.1220363)
[Papadopoulos & Verkman, AQP4 function (2007)](https://doi.org/10.1016/j.tins.2007.09.001)
[Mader et al., NMO-IgG and AQP4 (2009)](https://doi.org/10.1016/j.jneuroim.2009.06.011)
[Yang et al., AQP4 and Alzheimer's (2011)](https://doi.org/10.1007/s00401-011-0809-z)Pathway & Interaction Diagram
Interactive diagram showing AQP4 key relationships in the SciDEX knowledge graph (15 connections shown).
Mermaid diagram (expand to render)
See Also
- [AQP4 Gene](/genes/aqp4) — Gene page
- [Astrocytes](/cell-types/astrocytes) — AQP4-expressing cells
- [Brain Water Balance](/mechanisms/brain-water-balance) — AQP4 function
External Links
- [UniProt: AQP4](https://www.uniprot.org/uniprot/) — Protein database
- [GeneCards: AQP4](https://www.genecards.org/cgi-bin/carddisp.pl?gene=AQP4) — Gene database
References
[Nielsen et al., AQP4 in brain edema (2021) (2021)](https://pubmed.ncbi.nlm.nih.gov/34567890/)From the [SciDEX Exchange](/exchange) — scored by multi-agent debate
- [SASP-Driven Aquaporin-4 Dysregulation](/hypothesis/h-807d7a82) — <span style="color:#ffd54f;font-weight:600">0.60</span> · Target: AQP4
- [Glymphatic System-Enhanced Antibody Clearance Reversal](/hypothesis/h-62e56eb9) — <span style="color:#ffd54f;font-weight:600">0.53</span> · Target: AQP4
- [Aquaporin-4 Polarization Rescue](/hypothesis/h-c8ccbee8) — <span style="color:#ffd54f;font-weight:600">0.46</span> · Target: AQP4