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Change of voltage-gated sodium channel repertoire in skeletal muscle of a MuSK myasthenia gravis mouse model
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  • Olena Butenko,
  • Stine Jensen,
  • Yvonne Fillié-Grijpma,
  • Robyn Verpalen,
  • Jan Verschuuren,
  • Silvère van der Maarel,
  • Maartje Huijbers,
  • Jaap Plomp
Olena Butenko
Leiden University Medical Center

Corresponding Author:o.butenko@lumc.nl

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Stine Jensen
Leiden University Medical Center
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Yvonne Fillié-Grijpma
Leiden University Medical Center
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Robyn Verpalen
Leiden University Medical Center
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Jan Verschuuren
Leiden University Medical Center
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Silvère van der Maarel
Leiden University Medical Center
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Maartje Huijbers
Leiden University Medical Center
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Jaap Plomp
Leiden University Medical Center
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Abstract

Muscle-specific kinase myasthenia gravis (MuSK MG) is caused by autoantibodies against MuSK in the neuromuscular junction (NMJ). MuSK MG patients have fluctuating, fatigable weakness, in particular of bulbar muscles. Severity differs greatly between patients, in spite of comparable autoantibody levels. One explanation for inter-patient and inter-muscle variability in sensitivity might be variations in compensatory muscle responses. Previously, we developed a passive transfer mouse model for MuSK MG. In preliminary ex vivo experiments we observed that muscle contraction, in particular of mice with milder myasthenia, had become partially insensitive to μ-Conotoxin-GIIIB, a blocker of skeletal muscle NaV1.4 voltage-gated sodium channels. We hypothesized that changes in NaV channel expression profile, possibly co-expression of (μ-Conotoxin-GIIIB insensitive) NaV1.5 type channels, might lower the muscle fibre’s firing threshold and facilitate neuromuscular synaptic transmission. To test this, we here performed passive transfer in mice, using ‘high’, ‘intermediate’ and ‘low’ dosing regimens of purified MuSK MG patient IgG4 and compared myasthenia levels, μ-Conotoxin-GIIIB resistance, muscle fibre action potential characteristics and firing thresholds. High- and intermediate-dosed mice showed clear, progressive myasthenia, not seen in low-dosed animals. However, diaphragm NMJ electrophysiology demonstrated almost equal myasthenic severities amongst all regimens. Nonetheless, low-dosed mouse diaphragms showed a much higher degree of μ-Conotoxin-GIIIB resistance. This was not explained by upregulation of Scn5a (the NaV1.5 gene), lowered muscle fibre firing thresholds or histologically detectable upregulated NaV1.5 channels. It remains to be established which factors are responsible for the μ-Conotoxin-GIIIB insensitivity and whether the NaV repertoire change is compensatory beneficial, or a bystander effect.
15 Sep 2023Submitted to European Journal of Neuroscience
15 Sep 2023Submission Checks Completed
15 Sep 2023Assigned to Editor
18 Sep 2023Review(s) Completed, Editorial Evaluation Pending
19 Sep 2023Reviewer(s) Assigned
02 Feb 20241st Revision Received
02 Feb 2024Assigned to Editor
02 Feb 2024Submission Checks Completed
03 Feb 2024Reviewer(s) Assigned
23 Feb 2024Review(s) Completed, Editorial Evaluation Pending
28 Feb 2024Editorial Decision: Revise Major
11 Mar 20242nd Revision Received
13 Mar 2024Submission Checks Completed
13 Mar 2024Assigned to Editor
13 Mar 2024Review(s) Completed, Editorial Evaluation Pending