Agrin Binds to the N-terminal Region of Lrp4 Protein and Stimulates Association between Lrp4 and the First Immunoglobulin-like Domain in Muscle-specific Kinase (MuSK)

Zhang, Wei; Coldefy, Anne-Sophie; Hubbard, Stevan R.; Burden, Steven J.

doi:10.1074/jbc.m111.279307

Cited by 137 publications

(182 citation statements)

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“…We measured binding between Lrp4 and MuSK using a solid-phase binding assay in which the extracellular region of MuSK, fused to Fc (ectoMuSK-Fc), was adsorbed to protein A plates. The extracellular region of Lrp4 (ecto-Lrp4), fused to human alkaline phosphatase (AP), binds specifically but weakly to ecto-MuSK in the absence of neural Agrin; neural Agrin binds Lrp4 and stimulates strong and specific binding of AP-ecto-Lrp4 to ecto-MuSK (20). We tested IgG4 as well as IgG1-3 antibodies from seven MuSK MG patients and found that the IgG4 autoantibodies from all MuSK MG patients strongly inhibited binding between Lrp4 and MuSK, reducing binding by as much as 80-100%, in a dose-dependent manner ( Fig.…”

Section: Resultsmentioning

confidence: 99%

“…We measured binding between patient antibodies, bound to a protein A plate, and AP-ecto MuSK or AP-ecto MuSK I96A, in triplicate, using an ELISA. Binding between MuSK and Lrp4 was measured using a solid-phase binding assay, as described previously (20), except that we used human rather than rat MuSK (SI Materials and Methods). To determine the effect of IgG on MuSK-Lrp4 binding, 10 nM Agrin and 10 nM Lrp4-AP were coincubated with 8.3 μM purified IgG, which is within the reported normal range for IgG4 (0.05-9 μM); moreover, IgG4 levels can be elevated more than 20-fold in IgG4 autoimmune diseases (53).…”

Section: Methodsmentioning

confidence: 99%

“…AChR clustering and synapse formation are orchestrated by neuronally released Agrin, which binds to low-density lipoprotein receptor-related protein 4 (Lrp4), a member of the lipoprotein receptor-related protein family, causing Lrp4 to bind and activate MuSK (18)(19)(20). Once tyrosine-phosphorylated, MuSK recruits Dok-7, an adaptor protein that becomes phosphorylated and recruits additional signaling molecules essential for synapse formation (21)(22)(23).…”

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confidence: 99%

“…The first Ig-like domain in MuSK is required for MuSK to bind Lrp4. Mutation of a single residue, I96, on a solvent-exposed surface of the first Ig-like domain, prevents MuSK from binding Lrp4 and responding to Agrin (20,24). A hydrophobic surface on the opposite side of the first Ig-like domain mediates MuSK homodimerization, which is essential for MuSK transphosphorylation (24).…”

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MuSK IgG4 autoantibodies cause myasthenia gravis by inhibiting binding between MuSK and Lrp4

Huijbers¹,

Zhang

Klooster³

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Myasthenia gravis (MG) is a severely debilitating autoimmune disease that is due to a decrease in the efficiency of synaptic transmission at neuromuscular synapses. MG is caused by antibodies against postsynaptic proteins, including (i) acetylcholine receptors, the neurotransmitter receptor, (ii) muscle-specific kinase (MuSK), a receptor tyrosine kinase essential for the formation and maintenance of neuromuscular synapses, and (iii)

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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confidence: 99%

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MuSK IgG4 autoantibodies cause myasthenia gravis by inhibiting binding between MuSK and Lrp4

Huijbers¹,

Zhang

Klooster³

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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252

207

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“…Reduced muscle strength and body weight in Dox-treated imKO mice LRP4 is a receptor of agrin and critical for NMJ formation (Weatherbee et al, 2006;Kim et al, 2008;Zhang et al, 2011;Wu et al, 2012b;Zong et al, 2012;Ahn et al, 2013;Shen et al, 2013). LRP4 mutant mice die prematurely (Weatherbee et al, 2006), which prevents investigating the role of LRP4 in NMJ stability.…”

Section: Resultsmentioning

confidence: 99%

LRP4 Is Critical for Neuromuscular Junction Maintenance

et al. 2014

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The neuromuscular junction (NMJ) is a synapse between motor neurons and skeletal muscle fibers, and is critical for control of muscle contraction. Its formation requires neuronal agrin that acts by binding to LRP4 to stimulate MuSK. Mutations have been identified in agrin, MuSK, and LRP4 in patients with congenital myasthenic syndrome, and patients with myasthenia gravis develop antibodies against agrin, LRP4, and MuSK. However, it remains unclear whether the agrin signaling pathway is critical for NMJ maintenance because null mutation of any of the three genes is perinatal lethal. In this study, we generated imKO mice, a mutant strain whose LRP4 gene can be deleted in muscles by doxycycline (Dox) treatment. Ablation of the LRP4 gene in adult muscle enabled studies of its role in NMJ maintenance. We demonstrate that Dox treatment of P30 mice reduced muscle strength and compound muscle action potentials. AChR clusters became fragmented with diminished junctional folds and synaptic vesicles. The amplitude and frequency of miniature endplate potentials were reduced, indicating impaired neuromuscular transmission and providing cellular mechanisms of adult LRP4 deficiency. We showed that LRP4 ablation led to the loss of synaptic agrin and the 90 kDa fragments, which occurred ahead of other prejunctional and postjunctional components, suggesting that LRP4 may regulate the stability of synaptic agrin. These observations demonstrate that LRP4 is essential for maintaining the structural and functional integrity of the NMJ and that loss of muscle LRP4 in adulthood alone is sufficient to cause myasthenic symptoms.

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Molecular Genetics of Congenital Myasthenic Syndromes

Ohno

Ohkawara

Ito

et al. 2014

Encyclopedia of Life Sciences

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Congenital myasthenic syndromes (CMS) are heterogeneous disorders caused by congenital defects of molecules expressed at the neuromuscular junctions. Clinical features include fatigable muscle weakness, amyotrophy and minor facial anomalies. Mutations have been identified in 18 genes encoding acetylcholine receptor (AChR) subunits ( CHRNA1 , CHRNB1 , CHRND and CHRNE ); skeletal muscle sodium channel ( SCN4A ); signalling molecules driving AChR clustering and subserving maintenance and differentiation of the postsynaptic region ( AGRN, LRP4, MUSK and DOK7 ); postsynaptic structural proteins ( RAPSN and PLEC ); synaptic β2 laminin, which promotes presynaptic differentiation, and synaptic collagen Q; presynaptic choline acetyltransferase and enzymes in subserving protein glycosylation ( GFPT1 , DPAGT1 , ALG14 , and ALG2 ). The CMS are caused by recessive mutations except for the slow‐channel CMS. The recent development of the exome sequencing has speeded identification of causative mutations. Mutations in glycosylation genes were recently discovered, but the mechanisms by which they impair neuromuscular signal transmission have not been fully elucidated. Key Concepts: Congenital myasthenic syndromes are caused by germline mutations in molecules expressed at the neuromuscular junction (NMJ). Muscle nicotinic acetylcholine receptor (AChR) is a pentameric ligand‐gated ion channel in the stoichiometry of α 2 βδϵ subunits. Missense mutations in AChR subunit genes can cause abnormally long and brief ion channel openings resulting in slow‐ and fast‐channel myasthenic syndromes, respectively. Primary endplate AChR deficiency can be due to low‐expressor or null mutations in the AChR ϵ subunit. The phenotype in case of biallelic low‐expressor or null mutations in the ϵ subunit is rescued by expression of the foetal γ subunit. Biallelic null mutations in non‐ϵ are embryonic lethal mutations. A second group of endplate AChR deficiency is caused by mutations in signalling molecules including agrin, LRP4, MuSK, Dok‐7, which drive AChR clustering. The third group of endplate AChR deficiency stems from mutations in the postsynaptic structural proteins of rapsyn or plectin. Mutations in enzymes subserving the N ‐glycosylation pathway of GFPT1, DPAGT1, ALG14 and ALG2 cause limb‐girdle CMS with tubular aggregates. Endplate acetylcholinesterase (AChE) deficiency is caused by mutations in collagen Q (ColQ), which anchors AChE to the synaptic basal lamina. Protein‐anchoring therapy, in which ectopically expressed AChE/ColQ complex is specifically anchored to the neuromuscular junction using the proprietary binding motifs, markedly ameliorates myasthenic symptoms of Colq ‐knockout mice. Mutations in choline acetyltransferase (ChAT) cause defective resynthesis of ACh at the nerve terminal and a CMS associated with frequent episodic apnoea.

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Agrin Binds to the N-terminal Region of Lrp4 Protein and Stimulates Association between Lrp4 and the First Immunoglobulin-like Domain in Muscle-specific Kinase (MuSK)

Cited by 137 publications

References 42 publications

MuSK IgG4 autoantibodies cause myasthenia gravis by inhibiting binding between MuSK and Lrp4

MuSK IgG4 autoantibodies cause myasthenia gravis by inhibiting binding between MuSK and Lrp4

LRP4 Is Critical for Neuromuscular Junction Maintenance

Molecular Genetics of Congenital Myasthenic Syndromes

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