Abstract
Epilepsy is one of the most common and intractable brain disorders. Mutations in the human gene LGI1, encoding a neuronal secreted protein, cause autosomal dominant lateral temporal lobe epilepsy (ADLTE). However, the pathogenic mechanisms of LGI1 mutations remain unclear. We classified 22 reported LGI1 missense mutations as either secretion defective or secretion competent, and we generated and analyzed two mouse models of ADLTE encoding mutant proteins representative of the two groups. The secretion-defective LGI1E383A protein was recognized by the ER quality-control machinery and prematurely degraded, whereas the secretable LGI1S473L protein abnormally dimerized and was selectively defective in binding to one of its receptors, ADAM22. Both mutations caused a loss of function, compromising intracellular trafficking or ligand activity of LGI1 and converging on reduced synaptic LGI1-ADAM22 interaction. A chemical corrector, 4-phenylbutyrate (4PBA), restored LGI1E383A folding and binding to ADAM22 and ameliorated the increased seizure susceptibility of the LGI1E383A model mice. This study establishes LGI1-related epilepsy as a conformational disease and suggests new therapeutic options for human epilepsy.
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Acknowledgements
We thank J.L. Noebels and Y. Takahashi for helpful discussion. We thank A. Maas for kind assistance with Adam22 and Adam23 KO mice, S. Okamoto for technical guidance, M. Ohashi for sharing laboratory equipment, and Y. Kawabe and the members of the Fukata laboratory for their technical assistance. We also thank D. Monard (Friedrich Miescher Institute for Biomedical Research, Switzerland) for the kind gift of a Thy1 expression cassette. N.Y. was supported by the Japan Society for the Promotion of Science (22-2876) and Ministry of Education, Culture, Sports, Science and Technology (MEXT) (25890021). Y.F. is supported by grants from MEXT (25110733) and Ministry of Health, Labour and Welfare (MHLW) (Intramural Research Grant (24-12) for Neurological and Psychiatric Disorder of Japan National Center of Neurology and Psychiatry). D.M. and M.J. are supported by grants from the Dutch government to the Netherlands Institute for Regenerative Medicine (FES0908), the VICI (918.66.616) and the European Union (Neuron-Glia Interactions in Nerve Development and Disease, FP7 HEALTH-F2-2008-201535). M.W. is supported by a grant from MEXT (Comprehensive Brain Science Network). M.F. was supported by a grant from the Funding Program for Next Generation World-Leading Researchers (LS123).
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N.Y. designed and performed most of experiments and analyzed data. Y.F. conceived and supervised the project, performed experiments and analyzed data. D.K. performed experiments on characterization of mutant mice. T.M. performed experiments, analyzed data and wrote the parts of the manuscript on electron microscopic analysis. M.J. produced Adam22 and Adam23 KO mice. T.O. produced reagents. N.T. performed experiments on mouse breeding, genotyping and measurement of seizure frequency. H.I., Y.M. and T.H. produced the LGI1 monoclonal antibody. K.I. provided expert advice on LGI1 seizure phenotypes. D.M. produced the Adam22 and Adam23 KO mice and provided advice and wrote the part of the manuscript on these mice. M.W. produced guinea pig antibody to LGI1 and rabbit antibody to ADAM23, performed immunohistochemical experiments to compare KO mice and wrote the part of the manuscript on immunohistochemical analysis. M.F. conceived and supervised the project, performed experiments and analyzed data. N.Y., Y.F. and M.F. wrote the manuscript.
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Supplementary Text and Figures
Supplementary Figures 1–5, Supplementary Tables 1–5 and Supplementary Discussion (PDF 6712 kb)
Supplementary Video 1
Epileptic phenotype of Lgi1−/− mice. A P17 Lgi1−/− mouse shows a spontaneous generalized seizure with a sudden onset of limb jerks and/or wild running/jumping, followed by limb clonus and full tonic limb extension. This epileptic phenotype of Lgi1−/− mice was already reported (Fukata, Y. et al., Proc. Natl. Acad. Sci. USA 107, 3799–3804, 2010), and is shown as a control of the epileptic phenotype of Lgi1−/−;Lgi1-TgE383A3 or Lgi1−/−;Lgi1-TgS473L mice (Supplementary Videos 2 and 3). (MOV 2713 kb)
Supplementary Video 2
Epileptic phenotype of Lgi1−/−;Lgi1-TgE383A3 mice. A P21 Lgi1−/−;Lgi1-TgE383A3 mouse shows a spontaneous generalized seizure as the Lgi1−/− mouse does (Supplementary Video 1). (MOV 2726 kb)
Supplementary Video 3
Epileptic phenotype of Lgi1−/−;Lgi1-TgS473L mice. A P17 Lgi1−/−;Lgi1-TgS473L mouse shows a spontaneous generalized seizure as the Lgi1−/− mouse does (Supplementary Video 1). (MOV 2228 kb)
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Yokoi, N., Fukata, Y., Kase, D. et al. Chemical corrector treatment ameliorates increased seizure susceptibility in a mouse model of familial epilepsy. Nat Med 21, 19–26 (2015). https://doi.org/10.1038/nm.3759
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DOI: https://doi.org/10.1038/nm.3759
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