Axonopathies are a group of clinically diverse disorders characterized by the progressive degeneration of the axons of specific neurons. In hereditary spastic paraplegia (HSP), the axons of cortical motor neurons degenerate and cause a spastic movement disorder. HSP is linked to mutations in several loci known collectively as the spastic paraplegia genes (SPGs). We identified a heterozygous receptor accessory protein 1 (REEP1) exon 2 deletion in a patient suffering from the autosomal dominantly inherited HSP variant SPG31. We generated the corresponding mouse model to study the underlying cellular pathology. Mice with heterozygous deletion of exon 2 in Reep1 displayed a gait disorder closely resembling SPG31 in humans. Homozygous exon 2 deletion resulted in the complete loss of REEP1 and a more severe phenotype with earlier onset. At the molecular level, we demonstrated that REEP1 is a neuron-specific, membrane-binding, and membrane curvature–inducing protein that resides in the ER. We further show that Reep1 expression was prominent in cortical motor neurons. In REEP1-deficient mice, these neurons showed reduced complexity of the peripheral ER upon ultrastructural analysis. Our study connects proper neuronal ER architecture to long-term axon survival.
Christian Beetz, Nicole Koch, Mukhran Khundadze, Geraldine Zimmer, Sandor Nietzsche, Nicole Hertel, Antje-Kathrin Huebner, Rizwan Mumtaz, Michaela Schweizer, Elisabeth Dirren, Kathrin N. Karle, Andrey Irintchev, Victoria Alvarez, Christoph Redies, Martin Westermann, Ingo Kurth, Thomas Deufel, Michael M. Kessels, Britta Qualmann, Christian A. Hübner
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