HAPLN1 Protein

HAPLN1 Protein

HAPLN1 Protein — Hyaluronan and Proteoglycan Link Protein 1

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8;">HAPLN1 Protein</th></tr>
<tr><td><b>Gene</b></td><td>[HAPLN1](/genes/hapln1)</td></tr>
<tr><td><b>UniProt ID</b></td><td>[P10915](https://www.uniprot.org/uniprot/P10915)</td></tr>
<tr><td><b>Molecular Weight</b></td><td>~40 kDa ( mature), ~50 kDa (precursor)</td></tr>
<tr><td><b>Subcellular Localization</b></td><td>Extracellular matrix, secreted</td></tr>
<tr><td><b>Protein Family</b></td><td>HAPLN/RLIP family (hyaluronan and proteoglycan link proteins)</td></tr>
<tr><td><b>PDB Structures</b></td><td>[1V42](https://www.ebi.ac.uk/pdbe/entry/pdb/1v42), [2J8U](https://www.ebi.ac.uk/pdbe/entry/pdb/2j8u)</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>

Introduction

HAPLN1 (Hyaluronan and Proteoglycan Link Protein 1), also known as Cartilage Link Protein (CRTL1), is an extracellular matrix protein that plays a critical role in stabilizing the perineuronal net (PNN) and maintaining synaptic plasticity. It is essential for proper brain development and is implicated in neurodegenerative diseases where PNN integrity is compromised.

Structure

HAPLN1 is a modular secreted protein:

HAPLN1 Protein

HAPLN1 Protein — Hyaluronan and Proteoglycan Link Protein 1

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8;">HAPLN1 Protein</th></tr>
<tr><td><b>Gene</b></td><td>[HAPLN1](/genes/hapln1)</td></tr>
<tr><td><b>UniProt ID</b></td><td>[P10915](https://www.uniprot.org/uniprot/P10915)</td></tr>
<tr><td><b>Molecular Weight</b></td><td>~40 kDa ( mature), ~50 kDa (precursor)</td></tr>
<tr><td><b>Subcellular Localization</b></td><td>Extracellular matrix, secreted</td></tr>
<tr><td><b>Protein Family</b></td><td>HAPLN/RLIP family (hyaluronan and proteoglycan link proteins)</td></tr>
<tr><td><b>PDB Structures</b></td><td>[1V42](https://www.ebi.ac.uk/pdbe/entry/pdb/1v42), [2J8U](https://www.ebi.ac.uk/pdbe/entry/pdb/2j8u)</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>

Introduction

HAPLN1 (Hyaluronan and Proteoglycan Link Protein 1), also known as Cartilage Link Protein (CRTL1), is an extracellular matrix protein that plays a critical role in stabilizing the perineuronal net (PNN) and maintaining synaptic plasticity. It is essential for proper brain development and is implicated in neurodegenerative diseases where PNN integrity is compromised.

Structure

HAPLN1 is a modular secreted protein:

• N-terminal domain: Link module that binds hyaluronan
• Core protein: Central region with multiple glycosylation sites
• C-terminal domain: Binds to chondroitin sulfate proteoglycans (CSPGs)
• Link module family: Shares homology with other link proteins (HAPLN2-5)

Normal Function in the Nervous System

HAPLN1 performs critical functions in the central nervous system:

HAPLN1 is expressed in the [cortex](/brain-regions/cortex), [hippocampus](/brain-regions/hippocampus), and cerebellum during development and persists in adult brain, particularly in regions with high synaptic plasticity.

Role in Neurodegenerative Diseases

Alzheimer's Disease

HAPLN1 is downregulated in AD and contributes to disease pathology:

• Perineuronal net degradation: Early loss of PNN integrity in AD
• Synaptic dysfunction: Loss of synaptic stabilization
• Memory impairment: Critical period-like plasticity deficits
• Amyloid interaction: [A-beta](/proteins/amyloid-beta) disrupts HAPLN1-CSPG interactions
• Therapeutic potential: Restoring HAPLN1 may improve synaptic function

Parkinson's Disease

• PNN alterations observed in PD models
• May affect dopaminergic neuron survival
• Potential target for restoring plasticity

Multiple Sclerosis

• Demyelination involves PNN degradation
• HAPLN1 may be involved in repair mechanisms
• Therapeutic opportunity for remyelination therapies

Therapeutic Targeting

HAPLN1 represents a promising therapeutic target:

Interactions

HAPLN1 interacts with key extracellular matrix components:

• Hyaluronan (HA): Primary binding partner via link module
• CSPGs: Aggrecan, versican, neuroglycan-C
• Tenascin-R: Forms complexes in PNNs
• Matrix metalloproteinases (MMPs): Degrades HAPLN1
• Integrins: Mediates cell-matrix signaling

Key Publications

Cross-References

• [HAPLN1 Gene](/genes/hapln1)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Perineuronal Nets](/mechanisms/perineuronal-nets)
• [Synaptic Plasticity](/mechanisms/synaptic-plasticity)
• [Extracellular Matrix](/mechanisms/extracellular-matrix)
• [CSPGs](/proteins/cspg-proteins)

See Also

• HAPLN1 Gene
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Perineuronal Nets](/mechanisms/perineuronal-nets)
• [Synaptic Plasticity](/mechanisms/synaptic-plasticity)
• [Extracellular Matrix](/mechanisms/extracellular-matrix)

External Links

• [UniProt: P10915](https://www.uniprot.org/uniprot/P10915)
• [PDB structures](https://www.rcsb.org/search?q=uniprot:P10915)
• [GeneCards: HAPLN1](https://www.genecards.org/cgi-bin/carddisp.pl?gene=HAPLN1)

References