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MuSK cysteine-rich domain antibodies are pathogenic in a mouse model of autoimmune myasthenia gravis

Marius Halliez,¹ Steve Cottin,¹ Axel You,¹ Céline Buon,¹ Antony Grondin,¹ Léa S. Lippens,¹ Megane Lemaitre,² Jérome Ezan,³ Charlotte Isch,³ Yann Rufin,⁴ Mireille Montcouquiol,³ Nathalie Sans,³ Bertrand Fontaine,¹ Julien Messéant,¹ Rozen Le Panse,¹ and Laure Strochlic¹

Published June 12, 2025 - More info

The neuromuscular junction (NMJ), synapse between the motor neuron terminal and a skeletal muscle fiber is crucial, throughout life, in maintaining the reliable neurotransmission required for functional motricity. Disruption of this system leads to neuromuscular disorders, such as auto-immune myasthenia gravis (MG), the most common form of NMJ diseases. MG is caused by autoantibodies directed mostly against the acetylcholine receptor (AChR) or the muscle-specific kinase MuSK. Several studies report immunoreactivity to the Frizzled-like cysteine-rich Wnt-binding domain of MuSK (CRD) in patients, although the pathogenicity of the antibodies involved remains unknown. We showed here that the immunoreactivity to MuSK CRD induced by the passive transfer of anti-MuSK^CRD antibodies in mice led to typical MG symptoms, characterized by a loss of body weight and a locomotor deficit. The functional and morphological integrity of the NMJ was compromised with a progressive decay of neurotransmission and disruption of the structure of pre- and post-synaptic compartments. We found that anti-MuSK^CRD antibodies completely abolished Agrin-mediated AChR clustering by decreasing the Lrp4-MuSK interaction. These results provide the first demonstration of the role of the MuSK CRD in MG pathogenesis and improve our understanding of the underlying pathophysiological mechanisms.

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