LRP4 third β-propeller domain mutations cause novel congenital myasthenia by compromising agrin-mediated MuSK signaling in a position-specific manner.
Congenital myasthenic syndromes (CMS) are heterogeneous disorders in which the safety margin of neuromuscular transmission is compromised by one or more specific mechanisms. Using Sanger and exome sequencing in a CMS patient, we identified two heteroallelic mutations, p.Glu1233Lys and p.Arg1277His, in LRP4 coding for the postsynaptic low-density lipoprotein receptor-related protein 4. LRP4, expressed on the surface of the postsynaptic membrane of the neuromuscular junction, is a receptor for neurally secreted agrin, and LRP4 bound by agrin activates MuSK. Activated MuSK in concert with Dok-7 stimulates rapsyn to concentrate and anchor AChR on the postsynaptic membrane and interacts with other proteins implicated in the assembly and maintenance of the neuromuscular junction. LRP4 also functions as an inhibitor of Wnt/beta-catenin signaling. The identified mutations in LRP4 are located at the edge of its 3rd beta-propeller domain and decrease binding affinity of LRP4 for both MuSK and agrin. Mutations in the LRP4 3rd beta-propeller domain were previously reported to impair Wnt signaling and cause bone diseases including Cenani-Lenz syndactyly syndrome and sclerosteosis-2. By analyzing naturally occurring and artificially introduced mutations in the LRP4 3rd beta-propeller domain, we show that the edge of the domain regulates the MuSK signaling whereas its central cavity governs Wnt signaling. We conclude that LRP4 is a new CMS disease gene and that the 3rd beta propeller domain of LRP4 mediates the two signaling pathways in a position-specific manner.
Division of Neurogenetics, Center for Neurological Diseases and Cancer and.
Bisei
B
Ohkawara
Macarena
M
Cabrera-Serrano
Tomohiko
T
Nakata
Margherita
M
Milone
Nobuyuki
N
Asai
Kenyu
K
Ito
Mikako
M
Ito
Akio
A
Masuda
Yasutomo
Y
Ito
Andrew G
AG
Engel
Kinji
K
Ohno
D000293:Adolescent; D018171:Agrin / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D018679:Cholinergic Agonists / Q000627:therapeutic use; D002800:Cholinesterase Inhibitors / Q000627:therapeutic use; D004491:Edrophonium / Q000627:therapeutic use; D004789:Enzyme Activation / Q000235:genetics; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D026502:LDL-Receptor Related Proteins / Q000235:genetics*; D051379:Mice; D009124:Muscle Proteins / Q000378:metabolism; D009154:Mutation; D020294:Myasthenic Syndromes, Congenital / Q000235:genetics*; D009469:Neuromuscular Junction / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011729:Pyridostigmine Bromide / Q000627:therapeutic use; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D011950:Receptors, Cholinergic / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D051153:Wnt Proteins / Q000037:antagonists & inhibitors; D060449:Wnt Signaling Pathway / Q000235:genetics; D051176:beta Catenin / Q000037:antagonists & inhibitors
D018171:Agrin; D018679:Cholinergic Agonists; D002800:Cholinesterase Inhibitors; C511692:DOK7 protein, human; D026502:LDL-Receptor Related Proteins; C551781:LRP4 protein, human; D009124:Muscle Proteins; D011950:Receptors, Cholinergic; D051153:Wnt Proteins; D051176:beta Catenin; C051609:peripheral membrane protein 43K; D004491:Edrophonium; C095714:MUSK protein, human; D020794:Receptor Protein-Tyrosine Kinases; D011729:Pyridostigmine Bromide