title: Rab7 induces clearance of α-synuclein aggregates.
abstract: Parkinson's disease can be caused by mutations in the α-synuclein gene and is characterized by aggregates of α-synuclein protein. Aggregates are degraded by the autophago-lysosomal pathway. Since Rab7 has been shown to regulate trafficking of late endosomes and autophagosomes, we hypothesized that over-expressing Rab7 might be beneficial in Parkinson's disease. To test this hypothesis, we expressed the pathogenic A53T mutant of α-synuclein in HEK293 cells and Drosophila melanogaster. In HEK293 cells, EGFP-Rab7-decorated vesicles contain α-synuclein. Rab7 over-expression reduced the percentage of cells with α-synuclein particles and the amount of α-synuclein protein. Time-lapse microscopy confirmed that particles frequently disappeared with Rab7 over-expression. Clearance of α-synuclein is explained by the increased occurrence of acidified α-synuclein vesicles with Rab7 over-expression, presumably representing autolysosomes. Rab7 over-expression reduced apoptosis and the percentage of dead cells in trypan blue staining. In the fly model, Rab7 rescued the locomotor deficit induced by neuronal expression of A53T-α-synuclein. These beneficial effects were not produced by Rab7 missense mutations causing Charcot Marie Tooth neuropathy, or by the related GTPases Rab5, Rab9, or Rab23. Using mass spectrometry, we identified Rab7 in neuromelanin granules purified from human substantia nigra, indicating that Rab7 might be involved in the biogenesis of these possibly protective, autophagosome-like organelles in dopaminergic neurons. Taken together, Rab7 increased the clearance of α-synuclein aggregates, reduced cell death, and rescued the phenotype in a fly model of Parkinson's disease. These findings indicate that Rab7 is rate-limiting for aggregate clearance, and that Rab7 activation may offer a therapeutic strategy for Parkinson's disease. Cells over-expressing aggregation-prone A53T alpha-synuclein develop cytoplasmic aggregates mimicking changes observed in Parkinson's disease. When following cells in time-lapse microscopy, some few cells are able to remove these aggregates (Opazo et al. 2008). We now show that the percentage of cells clearing all aggregates from their cytosol is greatly increased with Rab7 over-expression, indicating that availability of Rab7 is rate-limiting for autophagic clearance of aggregates. The functional significance of this effect in neurons was confirmed in a Drosophila melanogaster model of Parkinson's disease.
authors.affiliation: Department of Neurology, RWTH University Aachen, Aachen, Germany.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Dinter
authors.affiliation: Department of Neurology, RWTH University Aachen, Aachen, Germany.
authors.forename: Theodora
authors.initials: T
authors.lastname: Saridaki
authors.affiliation: Department of Neurology, RWTH University Aachen, Aachen, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Nippold
authors.affiliation: Medizinisches Proteom-Center, Ruhr-Universität Bochum, Bochum, Germany.
authors.forename: Sarah
authors.initials: S
authors.lastname: Plum
authors.affiliation: Department of Neurology, RWTH University Aachen, Aachen, Germany.
authors.forename: Leonie
authors.initials: L
authors.lastname: Diederichs
authors.affiliation: Department of Neurology, RWTH University Aachen, Aachen, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Komnig
authors.affiliation: Department of Neurology, RWTH University Aachen, Aachen, Germany.
authors.forename: Luisa
authors.initials: L
authors.lastname: Fensky
authors.affiliation: Medizinisches Proteom-Center, Ruhr-Universität Bochum, Bochum, Germany.
authors.forename: Caroline
authors.initials: C
authors.lastname: May
authors.affiliation: Medizinisches Proteom-Center, Ruhr-Universität Bochum, Bochum, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Marcus
authors.affiliation: Department of Neurology, RWTH University Aachen, Aachen, Germany.
authors.forename: Aaron
authors.initials: A
authors.lastname: Voigt
authors.affiliation: Department of Neurology, RWTH University Aachen, Aachen, Germany.|JARA BRAIN Institute II, FZ Jülich and RWTH Aachen, Aachen, Germany.
authors.forename: Jörg B
authors.identifier: 0000-0002-8903-0593
authors.initials: JB
authors.lastname: Schulz
authors.affiliation: Department of Neurology, RWTH University Aachen, Aachen, Germany.|JARA BRAIN Institute II, FZ Jülich and RWTH Aachen, Aachen, Germany.
authors.forename: Björn H
authors.initials: BH
authors.lastname: Falkenburger
mesh_terms: D000818:Animals; D001343:Autophagy / Q000187:drug effects; D059290:Dopaminergic Neurons / Q000378:metabolism; D004331:Drosophila melanogaster / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D008543:Melanins / Q000378:metabolism; D010588:Phagosomes / Q000378:metabolism; D013378:Substantia Nigra / Q000378:metabolism*; D051844:alpha-Synuclein / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000378:metabolism*; D000090802:rab7 GTP-Binding Proteins
chemical_list: D008543:Melanins; D051844:alpha-Synuclein; C014121:neuromelanin; D000090802:rab7 GTP-Binding Proteins; C000716463:rab7 GTP-binding proteins, human; D020691:rab GTP-Binding Proteins
keywords: Rab7; acidification; autophagy; time-lapse microscopy; α-synuclein