VLDL Receptor

VLDL Receptor

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">VLDL Receptor</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>[VLDLR](/genes/vldlr)</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/P98155" target="_blank">P98155</a></td>
</tr>
<tr>
<td class="label">PDB</td>
<td><a href="https://www.rcsb.org/structure/7D73" target="_blank">7D73</a></td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>105 kDa</td>
</tr>
<tr>
<td class="label">Localization</td>
<td>Cell membrane, Postsynaptic density</td>
</tr>
<tr>
<td class="label">Family</td>
<td>LDLR family</td>
</tr>
<tr>
<td class="label">Ligands</td>
<td>Reelin, Apolipoprotein E</td>
</tr>
<tr>
<td class="label">Brain Expression</td>
<td>Cortex, Hippocampus, Cerebellum</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">2 edges</a></td>
</tr>
</table>

VLDL Receptor (VLDLR)

Overview

VLDL Receptor

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">VLDL Receptor</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>[VLDLR](/genes/vldlr)</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/P98155" target="_blank">P98155</a></td>
</tr>
<tr>
<td class="label">PDB</td>
<td><a href="https://www.rcsb.org/structure/7D73" target="_blank">7D73</a></td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>105 kDa</td>
</tr>
<tr>
<td class="label">Localization</td>
<td>Cell membrane, Postsynaptic density</td>
</tr>
<tr>
<td class="label">Family</td>
<td>LDLR family</td>
</tr>
<tr>
<td class="label">Ligands</td>
<td>Reelin, Apolipoprotein E</td>
</tr>
<tr>
<td class="label">Brain Expression</td>
<td>Cortex, Hippocampus, Cerebellum</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">2 edges</a></td>
</tr>
</table>

VLDL Receptor (VLDLR)

Overview

The VLDL Receptor (VLDLR) is a 105 kDa cell surface receptor belonging to the low-density lipoprotein receptor (LDLR) family. It is encoded by the VLDLR gene and plays crucial roles in the developing and adult nervous system. VLDLR binds [Reelin](/proteins/reelin-protein), a large extracellular matrix protein essential for neuronal migration, synaptic plasticity, and memory formation.[@herz2008] In the adult brain, VLDLR continues to mediate Reelin signaling at synapses, where it regulates NMDA receptor trafficking, dendritic spine morphology, and long-term potentiation.[@xu2014]

VLDLR is expressed throughout the brain with particularly high levels in the [hippocampus](/cell-types/hippocampus), cerebral cortex, and [cerebellum](/cell-types/cerebellum). Dysregulation of VLDLR-mediated signaling has been implicated in Alzheimer's Disease, cerebellar ataxia, and various neurodevelopmental disorders.[@ishii2016]

The receptor belongs to the LDLR superfamily, which includes multiple related receptors involved in lipid metabolism and cell signaling. Unlike other LDLR family members that primarily function in peripheral tissue lipid uptake, VLDLR has evolved specialized functions in the central nervous system, where it mediates the extracellular signaling of Reelin—a critical guidance molecule for neuronal development and synaptic function.

Evolutionary Perspective

VLDLR emerged as a specialized receptor during vertebrate evolution, with orthologs present in all jawed vertebrates. The receptor's extracellular domain contains multiple copies of LDLR class A (LA) repeats, which were likely acquired through gene duplication events. This domain architecture allows for high-affinity binding to Reelin while maintaining the endocytic properties characteristic of the LDLR family.

In mammals, VLDLR is highly conserved, with >90% amino acid identity between mouse and human orthologs. This conservation underscores the receptor's essential function in brain development and function. Knockout mouse studies have revealed that VLDLR is dispensable for embryonic survival but critical for postnatal brain development and cognitive function.

Structure and Ligand Binding

VLDLR is a type I transmembrane receptor with the following structural features:

Extracellular Domain

The extracellular domain of VLDLR (~792 amino acids) contains multiple functional modules:

• LDLR class A (LA) repeats (7 copies): These ~40-residue motifs contain conserved cysteine residues and form the ligand-binding region. Each LA repeat can bind one molecule of Reelin, with the full extracellular domain capable of binding multiple Reelin molecules. The affinity of individual LA repeats for Reelin varies, with the first two repeats contributing most significantly to high-affinity binding.
• Epidermal growth factor (EGF) repeats (3 copies): These ~40-residue repeats are interspersed between the LA repeats and the β-propeller domain. The EGF repeats are involved in receptor recycling by facilitating the release of ligand in acidic endosomes.
• β-propeller domain: This unique structure within the LDLR family serves as a pH-dependent "gate" that regulates ligand release. At neutral pH (extracellular environment), the β-propeller is open and allows ligand binding. At acidic pH (endosomal lumen), the β-propeller closes, displacing the ligand for degradation or recycling.
• O-linked sugar domain: Located between the EGF repeats and the transmembrane domain, this region contains multiple threonine and serine residues that undergo O-linked glycosylation. The O-linked sugars contribute to proper folding and stability of the receptor.

Transmembrane Domain

• Single-pass α-helical transmembrane segment (22 amino acids) that anchors the receptor in the plasma membrane
• The transmembrane domain also plays a role in receptor dimerization, which may enhance ligand binding avidity

Cytoplasmic Domain

• NPXY motif (Asn-Pro-X-Tyr): Located at residues 831-834, this internalization signal recruits clathrin adapter proteins (e.g., ARH, Dab2) for clathrin-mediated endocytosis
• NPXY motif 2 (residues 871-874): A second endocytosis signal that ensures efficient receptor internalization
• PDZ-binding motif (Ser-Ser-Val-Leu at residues 876-879): Interacts with PSD-95 and other synaptic scaffolding proteins at postsynaptic densities

Ligand Binding

VLDLR binds two primary ligands with distinct physiological roles:

Structural Insights from PDB

The crystal structure of the VLDLR extracellular domain (PDB: 7D73) has revealed:

• The LA repeats form an extended, curved structure that can accommodate multiple Reelin molecules
• The β-propeller domain adopts a "closed" conformation at neutral pH
• EGF repeats connect the LA repeats and β-propeller with flexible linkers

Normal Physiological Function

Neuronal Migration During Development

During brain development, VLDLR plays an essential role in neuronal migration, the process by which neurons travel from their birthplace to their final position in the developing brain:

The mechanism of Reelin-VLDLR-mediated neuronal migration involves:

• Reelin secretion by Cajal-Retzius cells in the marginal zone
• VLDLR activation on migrating neurons
• Downstream phosphorylation of Disabled-1 (DAB1) by Src family kinases
• Activation of downstream effectors including PI3K/Akt and Crk/CrkL
• Cytoskeletal reorganization driving neuronal movement

Synaptic Function in the Adult Brain

In the adult brain, VLDLR continues to play important synaptic roles beyond its developmental function in neuronal migration:

Reelin Signaling Pathway

Upon Reelin binding, VLDLR triggers a complex intracellular cascade:

Reelin → VLDLR/ApoER2 → DAB1 phosphorylation → Src family kinases
↓
PI3K/Akt → GSK-3β inhibition → Microtubule stabilization
↓
Crk/CrkL → Rap1 → NMDA receptor trafficking
↓
Limk1 → Cofilin → Actin dynamics

This pathway regulates:

• Cytoskeletal dynamics through Akt-mediated phosphorylation of GSK-3β
• Cell adhesion through integrin and cadherin signaling
• Synaptic plasticity through NMDA receptor modulation
• Neuronal survival through PI3K/Akt anti-apoptotic signaling

Additional Physiological Functions

VLDLR also plays roles in:

• White matter development: VLDLR signaling in oligodendrocyte precursor cells regulates myelination
• Neurovascular unit function: VLDLR is expressed on endothelial cells and pericytes, where it may regulate blood-brain barrier function
• Inner ear development: VLDLR is required for proper development of the vestibular system
• Retinal development: VLDLR contributes to retinal ganglion cell survival and visual system development
• Astrocyte function: Reelin-VLDLR signaling modulates astrocyte morphology and function

Role in Disease

Alzheimer's Disease

VLDLR has been increasingly implicated in AD pathogenesis through multiple mechanisms:

Cerebellar Ataxia

VLDLR mutations cause cerebellar ataxia through disrupted Reelin signaling:

• Cerebellar ataxia
• Quadrupedal gait
• Intellectual disability
• Structural brain abnormalities including cerebellar hypoplasia

The mechanism involves disrupted Reelin signaling leading to abnormal cerebellar layering and connectivity. Patients with VLDLR mutations show characteristic neuroimaging findings including cerebellar vermis hypoplasia and cortical atrophy.

Neurodevelopmental Disorders

VLDLR is implicated in several neurodevelopmental conditions:

• Lissencephaly: In utero disruption of neuronal migration due to VLDLR dysfunction can result in lissencephaly (smooth brain)
• Miller-Dieker syndrome: Shares phenotypic features with VLDLR deficiency due to overlapping molecular pathways
• Autism spectrum disorder: Some patients carry VLDLR variants that may contribute to neurodevelopmental phenotypes
• Intellectual disability: VLDLR mutations are associated with varying degrees of cognitive impairment

Psychiatric Disorders

• Schizophrenia: Altered VLDLR expression and Reelin signaling has been reported in postmortem brain studies
• Bipolar disorder: VLDLR genetic variants may influence disease risk
• Depression: VLDLR may play a role in stress-responsive signaling
• Addiction: VLDLR is expressed in reward-related brain regions and may modulate dopaminergic signaling

Signaling Pathway Diagram

Therapeutic Implications

VLDLR represents a therapeutic target for multiple neurological conditions:

Challenges and Considerations

• Blood-brain barrier: Therapeutic delivery to the CNS is challenging
• Receptor saturation: Overactivation may have adverse effects
• Isoform-specific targeting: ApoER2 shares signaling mechanisms with VLDLR
• Developmental vs. adult function: Timing of intervention may be critical

Interacting Partners

| Partner | Interaction Type | Functional Significance |
|---------|-----------------|------------------------|
| Reelin | Primary extracellular ligand | Neuronal migration, synaptic plasticity |
| ApoER2 | Coreceptor | Enhanced signaling, receptor crosstalk |
| DAB1 | Adapter protein | Primary signaling partner, recruits downstream effectors |
| Src family kinases | Phosphorylation | DAB1 phosphorylation, downstream activation |
| PSD-95 | PDZ interaction | Synaptic scaffolding, NMDAR organization |
| NMDA receptors | Modulation | Synaptic plasticity regulation |
| Apolipoprotein E | Competition | Lipid transport, AD risk factor |
| Disabled-2 (Dab2) | Endocytosis | Receptor internalization |
| ARH | Endocytosis | Clathrin adapter for endocytosis |
| PI3K | Signaling | Akt activation, cell survival |
| Crk/CrkL | Signaling | Rap1 activation, cytoskeletal regulation |

Animal Models

Knockout Mouse Models

• VLDLR knockout mice: Show cerebellar ataxia, inverted cortical layering, and memory deficits
• Conditional knockouts: Brain-specific deletion reveals adult-onset phenotypes
• Humanized mice: Expressing human VLDLR variants

Phenotypic Findings

• Abnormal cerebellar development
• Cortical layer inversion
• Reduced hippocampal LTP
• Spatial memory deficits
• Altered GABAergic signaling

Research Highlights

Key Studies

Ongoing Research

• VLDLR as a biomarker for AD progression
• Small molecule VLDLR activators
• Gene therapy approaches
• Understanding VLDLR-ApoE interactions

Summary

The VLDL Receptor (VLDLR) is a critical signaling receptor in the developing and adult nervous system. Through its interaction with Reelin, VLDLR regulates neuronal migration during development and synaptic plasticity in the adult brain. VLDLR dysfunction contributes to multiple neurological conditions, including Alzheimer's disease, cerebellar ataxia, and neurodevelopmental disorders.

The receptor's structure, with multiple LDLR class A repeats and a pH-dependent β-propeller, enables high-affinity Reelin binding and regulated signaling. Downstream pathways including DAB1, PI3K/Akt, and Crk/CrkL mediate the diverse effects of VLDLR signaling on cytoskeletal dynamics, synaptic function, and neuronal survival.

Therapeutic targeting of VLDLR offers potential for treating Alzheimer's disease and other conditions, though challenges remain in delivering therapeutics to the CNS and achieving appropriate receptor activation.

See Also

• [VLDLR Gene](/genes/vldlr)
• [Reelin Protein](/proteins/reelin-protein)
• [ApoER2 Protein](/proteins/apoer2-protein)
• [Disabled-1 (DAB1) Protein](/proteins/dab1-protein)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Cerebellar Ataxia](/diseases/cerebellar-ataxia)
• [Hippocampus](/cell-types/hippocampus)
• [Neuronal Migration](/mechanisms/neuronal-migration)

External Links

• UniProt: [https://www.uniprot.org/uniprot/P98155](https://www.uniprot.org/uniprot/P98155)
• AlphaFold: [VLDL Receptor](https://alphafold.ebi.ac.uk/entry/P98155)
• PDB: [7D73](https://www.rcsb.org/structure/7D73)
• GeneCards: [VLDLR](https://www.genecards.org/cgi-bin/carddisp.pl?gene=VLDLR)
• OMIM: [VLDLR](https://www.omim.org/entry/192977)

References