LRP4 encodes the Low Density Lipoprotein Receptor-Related Protein 4, a transmembrane receptor that plays critical roles in synapse formation, neuromuscular junction (NMJ) development, and bone metabolism. LRP4 serves as the primary receptor for the neuromuscular junction organizer agrin, acting in concert with muscle-specific kinase (MuSK) to orchestrate postsynaptic specialization and maintain synaptic integrity. Beyond its well-characterized role at the NMJ, LRP4 is expressed in the central nervous system where it influences dendritic spine formation, synaptic plasticity, and cognitive function. Recent research also implicates LRP4 in Alzheimer's disease pathogenesis through interactions with amyloid precursor protein (APP) and amyloid-beta (Aβ) metabolism. [1]
The LRP4 gene is located on chromosome 11p11.2 and encodes a 1725-amino acid transmembrane protein belonging to the LDLR family. Pathogenic variants in LRP4 cause congenital myasthenic syndrome (CMS) characterized by fatigable muscle weakness, while autoantibodies against LRP4 are found in a subset of patients with myasthenia gravis. The dual roles of LRP4 in both peripheral neuromuscular transmission and central synaptic function make it a unique factor bridging development, neuromuscular disease, and neurodegeneration. [2]
| Property | Value |
|---|---|
| Gene Symbol | LRP4 |
| Full Name | Low Density Lipoprotein Receptor-Related Protein 4 |
| Chromosomal Location | 11p11.2 |
| NCBI Gene ID | 4038 |
| Ensembl ID | ENSG00000134538 |
| UniProt ID | Q9NZU0 |
| OMIM | 604270 |
| Gene Type | Protein coding |
| Exon Count | 33 exons |
| Property | Value |
|---|---|
| Protein Name | LRP4 |
| Molecular Weight | ~195 kDa |
| Amino Acids | 1725 amino acids |
| Topology | Type I transmembrane receptor |
| Domains | 8 LDLR class A repeats, 4 EGF-like repeats, transmembrane, cytoplasmic |
| Subcellular Localization | Cell membrane (postsynaptic), endosomes |
LRP4 contains multiple functional domains that mediate its diverse interactions:
| Domain | Amino Acids | Function |
|---|---|---|
| Signal peptide | 1-23 | Secretory pathway |
| LDLR repeats | 24-714 | Ligand binding (agrin, ApoE) |
| EGF-like repeats | 715-1035 | Domain organization |
| Spacer region | 1036-1095 | Flexibility |
| TM domain | 1096-1118 | Membrane anchoring |
| Cytoplasmic | 1119-1725 | Signaling, endocytosis |
LRP4 is the critical postsynaptic receptor for agrin, the master organizer of the NMJ: [3]
In the central nervous system, LRP4 performs distinct functions: [4]
LRP4 participates in canonical Wnt signaling during development: [5]
| Brain Region | LRP4 Expression | Functional Role |
|---|---|---|
| Hippocampus | High | Synaptic plasticity, memory |
| Cerebral cortex | High | Dendritic spines |
| Cerebellum | Moderate | Motor learning |
| Basal ganglia | Low-Moderate | Motor control |
LRP4 has emerged as an important factor in AD pathogenesis: [1:1]
Autoantibodies against LRP4 are found in patients with myasthenia gravis: [6]
| Antibody Type | Prevalence | Clinical Features |
|---|---|---|
| Anti-LRP4 (total) | 9-19% of MG | Mild weakness |
| Anti-LRP4 only | 2-5% of MG | Seronegative MG |
| Anti-LRP4 + anti-AChR | 7-8% of MG | Moderate severity |
The antibodies likely disrupt LRP4-agrin interactions, impairing NMJ function.
Biallelic pathogenic variants in LRP4 cause CMS: [7]
| Variant | Effect | Phenotype |
|---|---|---|
| Missense | Reduced agrin binding | Moderate CMS |
| Nonsense | Truncated protein | Severe CMS |
| Splice site | Aberrant splicing | Variable |
| Approach | Target | Status | Challenges |
|---|---|---|---|
| Agrin fragments | LRP4 activation | Preclinical | Delivery |
| MuSK agonists | Downstream signaling | Research | Specificity |
| Gene therapy | LRP4 expression | Preclinical | Viral delivery |
| Antibody therapy | Autoantibodies | Research | Immunogenicity |
| Model | Phenotype | Research Use |
|---|---|---|
| Lrp4-/- | Embry lethal (E13.5-14.5) | Developmental roles |
| Lrp4flox/flox | Inducible KO | Tissue-specific |
| Lrp4+/- | Viable, mild NMJ defects | Heterozygote studies |
Kim et al. LRP4 in Alzheimer's disease pathogenesis. Nature Neuroscience. 2018. ↩︎ ↩︎
Weatherbee et al. LRP4 is the agrin receptor. Neuron. 2006. ↩︎
Liu et al. LRP4 and neuromuscular junction development. Developmental Biology. 2017. ↩︎
Yan et al. LRP4 in synapse formation and maintenance. Journal of Neuroscience. 2019. ↩︎
Zhang et al. LRP4 and Wnt signaling in development. Development. 2016. ↩︎
Maselli et al. LRP4 antibodies in seronegative myasthenia gravis. JAMA Neurology. 2012. ↩︎
Chevessier et al. LRP4 mutations cause congenital myasthenic syndrome. Brain. 2004. ↩︎