title: Alpha-synuclein overexpression in PC12 and chromaffin cells impairs catecholamine release by interfering with a late step in exocytosis.
abstract: Alpha-synuclein (alpha-syn), a protein implicated in Parkinson's disease pathogenesis, is a presynaptic protein suggested to regulate transmitter release. We explored how alpha-syn overexpression in PC12 and chromaffin cells, which exhibit low endogenous alpha-syn levels relative to neurons, affects catecholamine release. Overexpression of wild-type or A30P mutant alpha-syn in PC12 cell lines inhibited evoked catecholamine release without altering calcium threshold or cooperativity of release. Electron micrographs revealed that vesicular pools were not reduced but that, on the contrary, a marked accumulation of morphologically "docked" vesicles was apparent in the alpha-syn-overexpressing lines. We used amperometric recordings from chromaffin cells derived from mice that overexpress A30P or wild-type (WT) alpha-syn, as well as chromaffin cells from control and alpha-syn null mice, to determine whether the filling of vesicles with the transmitter was altered. The quantal size and shape characteristics of amperometric events were identical for all mouse lines, suggesting that overexpression of WT or mutant alpha-syn did not affect vesicular transmitter accumulation or the kinetics of vesicle fusion. The frequency and number of exocytotic events per stimulus, however, was lower for both WT and A30P alpha-syn-overexpressing cells. The alpha-syn-overexpressing cells exhibited reduced depression of evoked release in response to repeated stimuli, consistent with a smaller population of readily releasable vesicles. We conclude that alpha-syn overexpression inhibits a vesicle "priming" step, after secretory vesicle trafficking to "docking" sites but before calcium-dependent vesicle membrane fusion.
authors.affiliation: Department of Neurology, Columbia University School of Medicine, New York, New York 10032, USA.
authors.forename: Kristin E
authors.initials: KE
authors.lastname: Larsen
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Schmitz
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Troyer
authors.forename: Eugene
authors.initials: E
authors.lastname: Mosharov
authors.forename: Paula
authors.initials: P
authors.lastname: Dietrich
authors.forename: Abrar Z
authors.initials: AZ
authors.lastname: Quazi
authors.forename: Magali
authors.initials: M
authors.lastname: Savalle
authors.forename: Venu
authors.initials: V
authors.lastname: Nemani
authors.forename: Farrukh A
authors.initials: FA
authors.lastname: Chaudhry
authors.forename: Robert H
authors.initials: RH
authors.lastname: Edwards
authors.forename: Leonidas
authors.initials: L
authors.lastname: Stefanis
authors.forename: David
authors.initials: D
authors.lastname: Sulzer
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology; D002395:Catecholamines / Q000378:metabolism*; D019439:Chromaffin Cells / Q000378:metabolism* / Q000648:ultrastructure; D004195:Disease Models, Animal; D004298:Dopamine / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology*; D005260:Female; D008297:Male; D008561:Membrane Fusion / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009474:Neurons / Q000378:metabolism* / Q000648:ultrastructure; D016716:PC12 Cells; D020734:Parkinsonian Disorders / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology; D051381:Rats; D022142:Secretory Vesicles / Q000378:metabolism / Q000648:ultrastructure; D013570:Synaptic Membranes / Q000378:metabolism / Q000648:ultrastructure; D009435:Synaptic Transmission / Q000502:physiology*; D013572:Synaptic Vesicles / Q000378:metabolism / Q000648:ultrastructure; D013997:Time Factors; D051844:alpha-Synuclein / Q000235:genetics / Q000378:metabolism*
chemical_list: D002395:Catecholamines; D051844:alpha-Synuclein; D002118:Calcium; D004298:Dopamine