title: Excitation-induced ataxin-3 aggregation in neurons from patients with Machado-Joseph disease.
abstract: Machado-Joseph disease (MJD; also called spinocerebellar ataxia type 3) is a dominantly inherited late-onset neurodegenerative disorder caused by expansion of polyglutamine (polyQ)-encoding CAG repeats in the MJD1 gene (also known as ATXN3). Proteolytic liberation of highly aggregation-prone polyQ fragments from the protective sequence of the MJD1 gene product ataxin 3 (ATXN3) has been proposed to trigger the formation of ATXN3-containing aggregates, the neuropathological hallmark of MJD. ATXN3 fragments are detected in brain tissue of MJD patients and transgenic mice expressing mutant human ATXN3(Q71), and their amount increases with disease severity, supporting a relationship between ATXN3 processing and disease progression. The formation of early aggregation intermediates is thought to have a critical role in disease initiation, but the precise pathogenic mechanism operating in MJD has remained elusive. Here we show that L-glutamate-induced excitation of patient-specific induced pluripotent stem cell (iPSC)-derived neurons initiates Ca(2+)-dependent proteolysis of ATXN3 followed by the formation of SDS-insoluble aggregates. This phenotype could be abolished by calpain inhibition, confirming a key role of this protease in ATXN3 aggregation. Aggregate formation was further dependent on functional Na(+) and K(+) channels as well as ionotropic and voltage-gated Ca(2+) channels, and was not observed in iPSCs, fibroblasts or glia, thereby providing an explanation for the neuron-specific phenotype of this disease. Our data illustrate that iPSCs enable the study of aberrant protein processing associated with late-onset neurodegenerative disorders in patient-specific neurons.
authors: Institute of Reconstructive Neurobiology, Life and Brain Center, University of Bonn and Hertie Foundation, 53127 Bonn, Germany.
authors: Philipp
authors: P
authors: Koch
authors: Peter
authors: P
authors: Breuer
authors: Michael
authors: M
authors: Peitz
authors: Johannes
authors: J
authors: Jungverdorben
authors: Jaideep
authors: J
authors: Kesavan
authors: Daniel
authors: D
authors: Poppe
authors: Jonas
authors: J
authors: Doerr
authors: Julia
authors: J
authors: Ladewig
authors: Jerome
authors: J
authors: Mertens
authors: Thomas
authors: T
authors: Tüting
authors: Per
authors: P
authors: Hoffmann
authors: Thomas
authors: T
authors: Klockgether
authors: Bernd O
authors: BO
authors: Evert
authors: Ullrich
authors: U
authors: Wüllner
authors: Oliver
authors: O
authors: Brüstle
mesh_terms: D000067699:Ataxin-3; D002118:Calcium / Q000378:metabolism; D002154:Calpain / Q000378:metabolism; D002478:Cells, Cultured; D018846:Excitatory Amino Acids / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D006801:Humans; D017827:Machado-Joseph Disease / Q000473:pathology*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism*
chemical_list: D018846:Excitatory Amino Acids; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; D018698:Glutamic Acid; C092341:ATXN3 protein, human; D000067699:Ataxin-3; D002154:Calpain; D002118:Calcium