Proteolytic ectodomain shedding of muscle-specific tyrosine kinase in myasthenia gravis

Shuuichi Mori, Shigeaki Suzuki, Tetsuro Konishi, Naoki Kawaguchi, Masahiko Kishi, Satoshi Kuwabara, Kei Ishizuchi, Heying Zhou, Futoshi Shibasaki, Hiroki Tsumoto, Takuya Omura, Yuri Miura, Seijiro Mori, Mana Higashihara, Shigeo Murayama, Kazuhiro Shigemoto

Research output: Contribution to journalArticlepeer-review


Autoantibodies to muscle-specific tyrosine kinase (MuSK) proteins at the neuromuscular junction (NMJ) cause refractory generalized myasthenia gravis (MG) with dyspnea more frequently than other MG subtypes. However, the mechanisms via which MuSK, a membrane protein locally expressed on the NMJ of skeletal muscle, is supplied to the immune system as an autoantigen remains unknown. Here, we identified MuSK in both mouse and human serum, with the amount of MuSK dramatically increasing in mice with motor nerve denervation and in MG model mice. Peptide analysis by liquid chromatography-tandem-mass spectrometry (LC-MS/MS) confirmed the presence of MuSK in both human and mouse serum. Furthermore, some patients with MG have significantly higher amounts of MuSK in serum than healthy controls. Our results indicated that the secretion of MuSK proteins from muscles into the bloodstream was induced by ectodomain shedding triggered by neuromuscular junction failure. The results may explain why MuSK-MG is refractory to treatments and causes rapid muscle atrophy in some patients due to the denervation associated with Ab-induced disruption of neuromuscular transmission at the NMJ. Such discoveries pave the way for new MG treatments, and MuSK may be used as a biomarker for other neuromuscular diseases in preclinical studies, clinical diagnostics, therapeutics, and drug discovery.

Original languageEnglish
Article number114300
JournalExperimental Neurology
Publication statusPublished - 2023 Mar


  • Animal model
  • Biomarker
  • Denervation
  • Extracellular domain
  • Mass spectrometry
  • Matrix protease
  • Muscle-specific kinase
  • Myasthenia gravis
  • Reinnervation
  • Shedding

ASJC Scopus subject areas

  • Neurology
  • Developmental Neuroscience


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