Article

α-Synuclein mediates alterations in membrane conductance: A potential role for α-synuclein oligomers in cell vulnerability

Department of Neuroscience, Georgetown University Medical Center, Washington, DC 20057, USA.
European Journal of Neuroscience (Impact Factor: 3.18). 07/2010; 32(1):10-7. DOI: 10.1111/j.1460-9568.2010.07266.x
Source: PubMed

ABSTRACT

alpha-Synuclein has been linked to the pathogenesis of Parkinson's disease and other synucleinopathies through its propensity to form toxic oligomers. The exact mechanism for oligomeric synuclein-directed cell vulnerability has not been fully elucidated, but one hypothesis portends the formation of synuclein-containing pores within cell membranes leading to leak channel-mediated calcium influx and subsequent cell death. Here we demonstrate synuclein-induced formation of sodium dodecyl sulfate-stable oligomers, intracellular synuclein-positive aggregates, alterations in membrane conductance reminiscent of leak channels and subsequent cytotoxicity in a dopaminergic-like cell line. Furthermore we demonstrate that the synuclein-induced membrane conductance changes are blocked by direct extracellular application of an anti-synuclein antibody. The work presented here confirms that synuclein overexpression leads to membrane conductance changes and demonstrates for the first time through antibody-blocking studies that synuclein plays a direct role in the formation of leak channels.

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    • "Feng et al. used a dopaminergic-like cell model with regulated Syn expression, reporting an increase in membrane permeability and conductance due to pore formation. More importantly, they show for the first time that the extracellular application of an anti-Syn antibody reverts the effects on membrane permeability, suggesting an Syn interaction with the outer surface of the cell membrane [126]. Danzer et al. entered more in detail about Syn species and showed that different aggregation conditions produce heterogeneous populations of Syn oligomers, which can be differentiated on the basis of their biophysical properties and cellular effects. "
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    ABSTRACT: Mutations and duplication/triplication of the alpha-synuclein (αSyn)-coding gene have been found to cause familial Parkinson's disease (PD), while genetic polymorphisms in the region controlling the expression level and stability of αSyn have been identified as risk factors for idiopathic PD, pointing to the importance of wild-type (wt) αSyn dosage in the disease. Evidence that αSyn is present in the cerebrospinal fluid and interstitial brain tissue and that healthy neuronal grafts transplanted into PD patients often degenerate suggests that extracellularly-released αSyn plays a role in triggering the neurodegenerative process. αSyn's role in neurotransmission has been shown in various cell culture models in which the protein was upregulated or deleted and in knock out and transgenic animal, with different results on αSyn's effect on synaptic vesicle pool size and mobilization, αSyn being proposed as a negative or positive regulator of neurotransmitter release. In this review, we discuss the effect of αSyn on pre- and post-synaptic compartments in terms of synaptic vesicle trafficking, calcium entry and channel activity, and we focus on the process of exocytosis and internalization of αSyn and on the spreading of αSyn-driven effects due to the presence of the protein in the extracellular milieu.
    Full-text · Article · Jun 2015
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    • "the presence of extracellular a-syn, suggesting that the neurotoxic effects of a-syn might also occur in the extracellular space through unknown mechanisms (El-Agnaf et al. 2003, 2006; Paleologou et al. 2009; Tokuda et al. 2010; Bidinosti et al. 2012). Previous studies have shown that a-syn alters membrane permeability through the formation of ion permeable pores (Volles and Lansbury 2002, 2003; Quist et al. 2005; Tsigelny et al. 2007, 2012; Zakharov et al. 2007; Kostka et al. 2008; Kim et al. 2009; Feng et al. 2010; van Rooijen et al. 2010; Schmidt et al. 2012). Although this is an attractive idea to explain part of the associated neurotoxicity of a-syn, it has never been demonstrated to occur in neuronal membranes exposed directly to extracellular a-syn oligomers (Tsigelny et al. 2012; Lashuel et al. 2013). "
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    ABSTRACT: It has been postulated that the accumulation of extracellular α-synuclein (α-syn) might alter the neuronal membrane by formation of "pore-like structures" that will lead to alterations in ionic homeostasis. However, this has never been demonstrated to occur in brain neuronal plasma membranes. In this study, we show that α-syn oligomers rapidly associate to hippocampal membranes in a punctate fashion, resulting in increased membrane conductance (5 fold over control) and the influx of both calcium and a fluorescent glucose analogue. The enhancement in intracellular calcium (1.7 fold over control) caused a large increase in the frequency of synaptic transmission (2.5 fold over control), calcium transients (3 fold over control) and synaptic vesicle release. Both primary hippocampal and dissociated nigral neurons showed rapid increases in membrane conductance by α-syn oligomers. In addition, we show here that α-syn caused synaptotoxic failure associated to a decrease in SV2, a membrane protein of synaptic vesicles associated to neurotransmitter release. In conclusion, extracellular α-syn oligomers facilitates the perforation of the neuronal plasma membrane, thus explaining, in part, the synaptotoxicity observed in neurodegenerative diseases characterized by its extracellular accumulation. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Full-text · Article · Feb 2015 · Journal of Neurochemistry
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    • "Considering the ability of αsyn to bind to membranes characterized by different lipid compositions [57], a " scaffolding effect " may be envisioned, partially due to the localization of αsyn oligomers at the numerous membranous structures present in the cell cytoplasm and at the plasma membrane. This interpretation is supported by a model for αsyn aggregation where the early αsyn oligomers are formed not only in the cell cytoplasm but also at the membranes [32] [58], which can lead to calcium leakage [59] and to synaptic vesicles homeostasis disruption in neurons [60]. Another explanation for this pattern is the sequestration of the toxic oligomeric species by lysosomes. "
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    ABSTRACT: Background Alpha-synuclein oligomerization is associated to Parkinson's disease etiopathogenesis. The study of alpha-synuclein oligomerization properties in live cell and the definition of their effects on cellular viability are among fields expected to provide the knowledge required to unravel the mechanism(s) of toxicity that lead to the disease. Methods We used Number and Brightness method, which is a method based on fluorescence fluctuation analysis, to monitor alpha-synuclein tagged with EGFP aggregation in living SH-SY5Y cells. The presence of alpha-synuclein oligomers detected with this method was associated with intracellular structure conditions, evaluated by fluorescence confocal imaging. Results Cells overexpressing alpha-synuclein-EGFP present a heterogeneous ensemble of oligomers constituted by less than 10 monomers, when the protein approaches a threshold concentration value of about 90 nM in the cell cytoplasm. We show that the oligomeric species are partially sequestered by lysosomes and that the mitochondria morphology is altered in cells presenting oligomers, suggesting that these mitochondria may be dysfunctional. Conclusions We showed that alpha-synuclein overexpression in SH-SY5Y causes the formation of alpha-synuclein oligomeric species, whose presence is associated with mitochondrial fragmentation and autophagic-lysosomal pathway activation in live cells. General significance The unique capability provided by the Number and Brightness analysis to study alpha-synuclein oligomers distribution and properties, and the study their association to intracellular components in single live cells is important to forward our understanding of the molecular mechanisms Parkinson’s disease and it may be of general significance when applied to the study of other aggregating proteins in cellular models.
    Full-text · Article · Jun 2014 · Biochimica et Biophysica Acta (BBA) - General Subjects
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