LRP4 Human
Description
Introduction to LRP4 Human
Low-Density Lipoprotein Receptor-Related Protein 4 (LRP4) is a transmembrane protein encoded by the LRP4 gene in humans. It belongs to the LDL receptor superfamily and is critical for diverse biological processes, including neuromuscular junction (NMJ) formation, bone development, and regulation of Wnt and BMP signaling pathways . LRP4 is expressed in tissues such as skeletal muscle, neurons, osteoblasts, and germ cells, where it mediates ligand-receptor interactions essential for cellular communication and tissue morphogenesis .
Molecular Structure of LRP4
LRP4 is a type I transmembrane protein with a large extracellular domain (ECD) and a short cytoplasmic tail. Key structural features include:
The ECD binds ligands such as Agrin, Wnt, and ApoE, while the cytoplasmic domain facilitates interactions with downstream signaling molecules like MuSK (muscle-specific kinase) .
Neuromuscular Junction Development
LRP4 is essential for NMJ formation:
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Postsynaptic Role: Binds Agrin released from motor neurons, activating MuSK to cluster acetylcholine receptors (AChRs) on muscle cells .
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Presynaptic Role: The cleaved ECD of LRP4 promotes presynaptic differentiation by recruiting active zone proteins in motor neurons .
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Pre-Patterning: Independently of Agrin, LRP4 initiates AChR clustering in muscle cells before motor neuron arrival .
Bone and Tooth Development
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Wnt/BMP Regulation: LRP4 interacts with sclerostin and Dkk1 to modulate Wnt and BMP signaling, influencing osteogenesis and bone mineralization .
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Craniofacial Morphogenesis: Mutations in LRP4 are linked to syndactyly and tooth abnormalities .
Central Nervous System (CNS) Roles
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Synaptic Plasticity: Neuronal LRP4 regulates dendritic development and hippocampal neurogenesis .
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Aβ Clearance: Astrocytic LRP4 promotes Aβ uptake via ApoE interaction, implicating it in Alzheimer’s disease pathology .
Autoimmune and Genetic Disorders
Mechanistic Insights
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Myasthenia Gravis: Anti-LRP4 antibodies inhibit Agrin binding and reduce AChR clustering by ~85% in vitro .
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CMS Mutations: The p.Thy607Cys mutation in the β1 propeller domain reduces Agrin/Wnt11 binding, impairing NMJ development .
Recombinant LRP4 in Studies
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Structural Analysis: Recombinant human LRP4 (191.6 kDa) expressed in HEK293 cells is used to study ligand interactions and signaling .
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Disease Modeling: Mutant LRP4 proteins help elucidate mechanisms in bone disorders and CMS .
Therapeutic Targeting
Product Specs
LRP4, a member of the low-density lipoprotein receptor-related protein family, plays a crucial role in bone formation and neuromuscular junction development. This family consists of numerous evolutionarily conserved transmembrane proteins. LRP4 facilitates SOST-dependent inhibition of bone formation and is involved in the formation and maintenance of the neuromuscular junction, the synapse between skeletal muscle and motor neurons. Furthermore, it acts as a specific facilitator of SOST-mediated inhibition of Wnt signaling.
Recombinant human LRP4 is a single, glycosylated polypeptide chain with a molecular weight of 191.6 kDa (calculated). It comprises 1719 amino acids, spanning from amino acid residues 21 to 1725a.a. The protein is fused to a 14 amino acid His tag, with 2 amino acids on the N-terminal and 12 amino acids on the C-terminal.
LRP4 is supplied as a lyophilized powder, having been filtered through a 0.4 μm filter. The protein was initially in a 0.5 mg/mL solution of PBS (pH 7.5) containing 5% (w/v) trehalose before lyophilization.
To prepare a working stock solution, it is recommended to add deionized water to the lyophilized pellet to achieve a concentration of approximately 0.5 mg/mL. Allow the pellet to dissolve completely.
The purity of LRP4 is determined to be greater than 95.0% using SDS-PAGE analysis.
Low-density lipoprotein receptor-related protein 4, LRP-4, Multiple epidermal growth factor-like domains 7, LRP4, KIAA0816, LRP10, MEGF7.
HEK293 Cells.
ASSSPECACG RSHFTCAVSA LGECTCIPAQ WQCDGDNDCG DHSDEDGCIL PTCSPLDFHC DNGKCIRRSW VCDGDNDCED DSDEQDCPPR ECEEDEFPCQ NGYCIRSLWH CDGDNDCGDN SDEQCDMRKC SDKEFRCSDGS CIAEHWYCDG DTDCKDGSDE ENCPSAVPAP PCNLEEFQCA YGRCILDIYH CDGDDDCGDW SDESDCSSHQ PCRSGEFMCD SGLCINAGWRC DGDADCDDQS DERNCTTSMCT AEQFRCHSGR CVRLSWRCDG EDDCADNSDE ENCENTGSPQ CALDQFLCWN GRCIGQRKLC NGVNDCGDNS DESPQQNCRP RTGEENCNVN NGGCAQKCQM VRGAVQCTCH TGYRLTEDGH TCQDVNECAE EGYCSQGCTN SEGAFQCWCE TGYELRPDRR SCKALGPEPV LLFANRIDIR QVLPHRSEYT LLLNNLENAIA LDFHHRRELV FWSDVTLDRI LRANLNGSNV EEVVSTGLES PGGLAVDWVH DKLYWTDSGTSR IEVANLDGAHR KVLLWQNLEK PRAIALHPME GTIYWTDWGN TPRIEASSMD GSGRRIIADTHL FWPNGLTIDYAG RRMYWVDAKHHVI ERANLDGSHRK AVISQGLPHPFA ITVFEDSLYWTDW HTKSINSANKFTG KNQEIIRNKLHFPM DIHTLHPQRQPAGK NRCGDNNGGCTHLC LPSGQNYTCACPTG FRKISSHACAQ SLDKFLLFAR RMDIRRISFD TEDLSDDVIPL ADVRSAVALDW DSRDDHVYWT DVSTDTISRAKW DGTGQEVVVDT SLESPAGLAID WVTNKLYWTD AGTDRIEVAN TDGSMRTVLIW ENLDRPRDIVV EPMGGYMYWTDW GASPKIERAGM DASGRQVIISS NLTWPNGLAIDY GSQRLYWADAG MKTIEFAGLD GSKRKVLIGSQL PHPFGLTLYGE RIYWTDWQTKS IQSADRLTGLD RETLQENLEN LMDIHVFHRRR PPVSTPCAMEN GGCSHLCLRS PNPSGFSCTCP TGINLLSDGKT CSPGMNSFLI FARRIDIRMVSL DIPYFADVVVP INITMKNTIA VGVDPQEGKV YWSDSTLHRI SRANLDGSQH EDIITTGLQT TDGLAVDAIG RKVYWTDTGT NRIEVGNLDG SMRKVLVWQNL DSPRAIVLYH EMGFMYWTDWG ENAKLERSGM DGSDRAVLIN NNLGWPNGLT VDKASSQLLWA DAHTERIEAA DLNGANRHTL VSPVQHPYGLTL LDSYIYWTDW QTRSIHRADK GTGSNVILVR SNLPGLMDMQ AVDRAQPLGF NKCGSRNGGC SHLCLPRPSG FSCACPTGIQ LKGDGKTCDPS PETYLLFSSR GSIRRISLDT SDHTDVHVPV PELNNVISLDY DSVDGKVYYTD VFLDVIRRAD LNGSNMETVI GRGLKTTDGL AVDWVARNLYW TDTGRNTIEASR LDGSCRKVLINN SLDEPRAIAVF PRKGYLFWTDW GHIAKIERANLD GSERKVLINTDL GWPNGLTLDYDTR RIYWVDAHLDRI ESADLNGKLRQ VLVGHVSHPFAL TQQDRWIYWTD WQTKSIQRVD KYSGRNKETVL ANVEGLMDII VVSPQRQTGTN ACGVNNGGCT HLCFARASDFVC ACPDEPDSQPC SLVPGLVPPA PRATGMSEKS PVLPNTPPTT LYSSTTRTRT SLEEVEGRCS ERDARLGLCA RSNDAVPAAP GEGLHISKLH HHHHHHHHH
Q&A
Basic Research Questions
What are the primary molecular functions of LRP4 in neuromuscular junction (NMJ) development?
LRP4 acts as a critical postsynaptic receptor for Agrin, facilitating NMJ formation by binding Agrin and activating Muscle-Specific Kinase (MuSK). This interaction triggers AChR clustering via downstream signaling pathways (e.g., rapsyn recruitment) .
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Methodological approach: Use in vitro co-culture systems (motor neurons + myotubes) with LRP4 knockdown/knockout models. Quantify AChR clustering via fluorescent α-bungarotoxin staining and confocal microscopy .
How are LRP4 autoantibodies detected in seronegative myasthenia gravis (MG) patients?
Autoantibodies against LRP4 are identified using:
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ELISA: Recombinant human LRP4 extracellular domain (e.g., amino acids 1–630) as antigen .
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Cell-based assays: HEK293 cells transfected with LRP4 cDNA; detect antibody binding via immunofluorescence .
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Clinical validation: Compare serum samples from seronegative MG patients (AChR/MuSK-negative) and healthy controls .
What genetic mutations in LRP4 are linked to congenital disorders?
Mutations associated with Cenani-Lenz syndactyly include:
| Mutation Type | Phenotypic Impact | Detection Method |
|---|---|---|
| Missense (e.g., p.Y943C) | Disrupted Wnt/β-catenin signaling | Whole-exome sequencing |
| Frameshift (e.g., c.4510delC) | Truncated LRP4 protein | Sanger sequencing |
| Splice-site (e.g., IVS7-1G>A) | Aberrant mRNA splicing | RT-PCR analysis |
Advanced Research Questions
How can contradictory data on LRP4’s presynaptic vs. postsynaptic roles be resolved?
Contradictions arise from context-dependent LRP4 localization (e.g., NMJ vs. CNS synapses). Strategies include:
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Cell-type-specific knockout models: Compare motor neuron- vs. muscle-specific Lrp4 deletions in mice .
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Spatiotemporal analysis: Use in situ hybridization and Cre-lox systems to track LRP4 expression during synaptogenesis .
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Functional assays: Measure neurotransmitter release (electrophysiology) and synaptic vesicle distribution (electron microscopy) in conditional mutants .
What role does LRP4 play in Alzheimer’s disease (AD) pathology?
LRP4 in astrocytes promotes Aβ clearance by binding ApoE-Aβ complexes. Reduced LRP4 correlates with increased Aβ plaques in AD models:
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Key finding: Lrp4⁻/⁻;5xFAD mice show 40% more Aβ plaques vs. controls (p < 0.01) .
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Method: Inject fluorescently labeled Aβ₄₂ into mouse hippocampus; quantify uptake in astrocytes via flow cytometry .
How does LRP4 regulate Wnt signaling in non-neural tissues?
LRP4 modulates Wnt/β-catenin and Wnt/PCP pathways depending on ligand context:
| Pathway | Mechanism | Assay |
|---|---|---|
| Wnt/β-catenin | LRP4 binds Wnt3a, enhancing LRP6-Frizzled complex formation | TOPFlash luciferase reporter |
| Wnt/PCP | LRP4 interacts with Vangl2 to regulate planar cell polarity | Immunoprecipitation + Xenopus embryo convergence-extension assays |
Data Conflict Analysis
Why do some studies report Agrin-independent LRP4 functions?
Discrepancies stem from tissue-specific isoforms (e.g., neural vs. muscular LRP4) and alternative ligands (e.g., Wnt vs. Agrin). Resolve by:
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Isoform-specific knockdown: Design siRNA targeting exon 5 (Agrin-binding domain) vs. exon 10 (Wnt-binding domain) .
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Ligand competition assays: Pre-incubate cells with Agrin/Wnt inhibitors before assessing LRP4 activity .
How to address variability in LRP4 autoantibody detection across cohorts?
Variability arises from epitope heterogeneity (e.g., Ig-like vs. β-propeller domains). Mitigate via:
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Antigen standardization: Use full-length LRP4 extracellular domain (vs. fragments) in ELISA .
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Multicenter validation: Harmonize protocols across labs (e.g., serum dilution 1:100, 4°C overnight incubation) .
Experimental Design Guidelines
9. Recommended controls for in vivo LRP4 studies:
How to model LRP4-associated cognitive impairment?
Product Science Overview
LRP4 is a type I membrane protein with an approximate molecular weight of 220-270 kDa . It is known to interact with several ligands, including WISE, apoE, MuSK, and neuronal Agrin . One of the key functions of LRP4 is its role in the formation and maintenance of the neuromuscular junction (NMJ), where it forms a complex with MuSK and binds neural agrin to stimulate MuSK kinase activity . This interaction is essential for the proper differentiation and clustering of acetylcholine receptors at the postsynaptic membrane .
LRP4 is involved in various developmental processes, including the formation of bones, teeth, mammary placodes, and hair follicles . It is also crucial for the proper development and morphogenesis of limbs, ectodermal organs, lungs, and kidneys . In the context of the NMJ, LRP4 is required for both presynaptic and postsynaptic differentiation, and its absence can lead to severe neuromuscular defects .
Mutations in the LRP4 gene have been associated with several human diseases, including myasthenia syndromes and other neuromuscular disorders . Research has shown that LRP4 is required during the earliest events in postsynaptic NMJ formation and acts in the early, nerve-independent steps of NMJ assembly . This makes LRP4 a potential target for therapeutic interventions in neuromuscular diseases.
Recombinant human LRP4 is produced using advanced biotechnological methods to study its structure, function, and interactions in various biological systems . This recombinant protein is used in research to understand the molecular mechanisms underlying its role in development and disease, as well as to develop potential therapeutic strategies for conditions associated with LRP4 dysfunction .
