title: Pharmacologic rescue of axon growth defects in a human iPSC model of hereditary spastic paraplegia SPG3A.
abstract: Hereditary spastic paraplegias are a large, diverse group of neurological disorders (SPG1-71) with the unifying feature of prominent lower extremity spasticity, owing to a length-dependent axonopathy of corticospinal motor neurons. The most common early-onset form of pure, autosomal dominant hereditary spastic paraplegia is caused by mutation in the ATL1 gene encoding the atlastin-1 GTPase, which mediates homotypic fusion of ER tubules to form the polygonal ER network. We have identified a p.Pro342Ser mutation in a young girl with pure SPG3A. This residue is in a critical hinge region of atlastin-1 between its GTPase and assembly domains, and it is conserved in all known eukaryotic atlastin orthologs. We produced induced pluripotent stem cells from skin fibroblasts and differentiated these into forebrain neurons to generate a human neuronal model for SPG3A. Axons of these SPG3A neurons showed impaired growth, recapitulating axonal defects in atlastin-1-depleted rat cortical neurons and impaired root hair growth in loss-of-function mutants of the ATL1 ortholog rhd3 in the plant Arabidopsis. Both the microtubule cytoskeleton and tubular ER are important for mitochondrial distribution and function within cells, and SPG3A neurons showed alterations in mitochondrial motility. Even so, it is not clear whether this change is involved in disease pathogenesis. The SPG3A axon growth defects could be rescued with microtubule-binding agents, emphasizing the importance of tubular ER interactions with the microtubule cytoskeleton in hereditary spastic paraplegia pathogenesis. The prominent alterations in axon growth in SPG3A neurons may represent a particularly attractive target for suppression in screens for novel pharmacologic agents.
authors.affiliation: Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Peng-Peng
authors.initials: PP
authors.lastname: Zhu
authors.affiliation: Department of Neuroscience and.
authors.forename: Kyle R
authors.initials: KR
authors.lastname: Denton
authors.affiliation: Departments of Pediatrics and Neurology and the Regenerative Medicine Institute, Cedars-Sinai Medical Center, Los Angeles, CA 90048, USA.
authors.forename: Tyler Mark
authors.initials: TM
authors.lastname: Pierson
authors.affiliation: Department of Neuroscience and The Stem Cell Institute, University of Connecticut Health Center, Farmington, CT 06030, USA and xjli@uchc.edu.
authors.forename: Xue-Jun
authors.initials: XJ
authors.lastname: Li
authors.affiliation: Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Craig
authors.initials: C
authors.lastname: Blackstone
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001369:Axons / Q000187:drug effects* / Q000378:metabolism* / Q000473:pathology; D002454:Cell Differentiation; D002460:Cell Line; D002675:Child, Preschool; D004252:DNA Mutational Analysis; D005260:Female; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics*; D006579:Heterozygote; D006801:Humans; D057026:Induced Pluripotent Stem Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D011487:Protein Conformation; D021381:Protein Transport; D016415:Sequence Alignment; D015419:Spastic Paraplegia, Hereditary / Q000235:genetics*; D050257:Tubulin Modulators / Q000494:pharmacology
chemical_list: D008565:Membrane Proteins; D050257:Tubulin Modulators; C440006:ATL1 protein, human; D019204:GTP-Binding Proteins