Interactions among alpha-synuclein, dopamine, and biomembranes: some clues for understanding neurodegeneration in Parkinson's disease.
Parkinson's disease (PD) is a neurologic disorder resulting from the loss of dopaminergic neurons in the brain. Two lines of evidence suggest that the protein alpha-synuclein plays a role in the pathogenesis of PD: Fibrillar alpha-synuclein is a major component of Lewy bodies in diseased neurons, and two mutations in alpha-synuclein are linked to early-onset disease. Accordingly, the fibrillization of alpha-synuclein is proposed to contribute to neurodegeneration in PD. In this report, we provide evidence that oligomeric intermediates of the alpha-synuclein fibrillization pathway, termed protofibrils, might be neurotoxic. Analyses of protofibrillar alpha-synuclein by atomic force microscopy and electron microscopy indicate that the oligomers consist of spheres, chains, and rings. alpha-Synuclein protofibrils permeabilize synthetic vesicles and form pore-like assemblies on the surface of brain-derived vesicles. Dopamine reacts with alpha-synuclein to form a covalent adduct that slows the conversion of protofibrils to fibrils. This finding suggests that cytosolic dopamine in dopaminergic neurons promotes the accumulation of toxic alpha-synuclein protofibrils, which might explain why these neurons are most vulnerable to degeneration in PD. Finally, we note that aggregation of alpha-synuclein likely occurs via different mechanisms in the cell versus the test tube. For example, the binding of alpha-synuclein to cellular membranes might influence its self-assembly. To address this point, we have developed a yeast model that might enable the selection of random alpha-synuclein mutants with different membrane-binding affinities. These variants might be useful to test whether membrane binding by alpha-synuclein is necessary for neurodegeneration in transgenic animal models of PD.
Rochet
Jean-Christophe
JC
Center for Neurologic Diseases, Brigham and Women's Hospital, Department of Neurology, Harvard Medical School, Cambridge, MA 02139, USA. rochet@pharmacy.purdue.edu
Outeiro
Tiago Fleming
TF
Conway
Kelly A
KA
Ding
Tomas T
TT
Volles
Michael J
MJ
Lashuel
Hilal A
HA
Bieganski
Robert M
RM
Lindquist
Susan L
SL
Lansbury
Peter T
PT
D000818:Animals; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism*; D006801:Humans; D008954:Models, Biological; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009454:Neurofibrils / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D009474:Neurons / Q000378:metabolism* / Q000473:pathology; D010300:Parkinson Disease / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D011485:Protein Binding / Q000235:genetics; D051843:Synucleins; D051844:alpha-Synuclein
D009419:Nerve Tissue Proteins; C497604:SNCA protein, human; D051843:Synucleins; D051844:alpha-Synuclein; D004298:Dopamine