Ca2+ is a key factor in α-synuclein-induced neurotoxicity

Abstract

Aggregation of α-synuclein leads to the formation of oligomeric intermediates that can interact with membranes to form pores. However, it is unknown how this leads to cell toxicity in Parkinson's disease. We investigated the species-specific effects of α-synuclein on Ca2+ signalling in primary neurons and astrocytes using live neuronal imaging and electrophysiology on artificial membranes. We demonstrate that α-synuclein induces an increase in basal intracellular Ca2+ in its unfolded monomeric state as well as in its oligomeric state. Electrophysiology of artificial membranes demonstrated that α-synuclein monomers induce irregular ionic currents, whereas α-synuclein oligomers induce rare discrete channel formation events. Despite the ability of monomeric α-synuclein to affect Ca2+ signalling, it is only the oligomeric form of α-synuclein that induces cell death. Oligomer-induced cell death was abolished by the exclusion of extracellular Ca2+, which prevented the α-synuclein-induced Ca2+ dysregulation. The findings of this study confirm that α-synuclein interacts with membranes to affect Ca2+ signalling in a structure-specific manner and the oligomeric β-sheet-rich α-synuclein species ultimately leads to Ca2+ dysregulation and Ca2+-dependent cell death.

Crucial role of protein oligomerization in the pathogenesis of Alzheimer's and Parkinson's diseases

“…Calcium is the most pleiotropic ion that is capable of triggering intracellular pathways in response to external stimuli [5,63,64]. We have reported that a-syn oligomers induce cytosolic calcium influx in neurons, and this results in an increase in cytosolic calcium before inducing cell death; cell toxicity is rescued by exclusion of extracellular calcium [5], confirming the importance of oligomer-induced membrane disruption in inducing neuronal toxicity. We have reported that a-syn oligomers induce cytosolic calcium influx in neurons, and this results in an increase in cytosolic calcium before inducing cell death; cell toxicity is rescued by exclusion of extracellular calcium [5], confirming the importance of oligomer-induced membrane disruption in inducing neuronal toxicity.…”

“…Furthermore, once oligomers are formed, they are able to disrupt membranes and this is due to their structural composition, with a high lipophilic component promoting membrane interaction, and the cross b-sheet structure leading to integration into the lipid bilayer [62]. Calcium is the most pleiotropic ion that is capable of triggering intracellular pathways in response to external stimuli [5,63,64]. Calcium is the most pleiotropic ion that is capable of triggering intracellular pathways in response to external stimuli [5,63,64].…”

“…During misfolding, intrinsically disordered monomeric proteins (such as Ab and tau in AD, and a-syn in PD), undergo conformational changes from their native states into highly ordered b-sheet rich fibrillar amyloid structures [1]. Direct application of In vitro formed a-syn oligomers, or overexpression of a-syn mutants induces a range of cellular damage affecting membrane integrity, mitochondria, ER, autophagy, and synaptic transmission, and ultimately leading to cell toxicity [3][4][5]. As the presence of intracellular and extracellular fibril deposition is seen predominantly in disease, it is this insoluble end-stage species of protein aggregation that has traditionally defined disease.…”

Signal transduction in astrocytes: Localization and release of inorganic polyphosphate

“…Primary cell cocultures of neurons and astrocytes were prepared as described in detail previously (Angelova, Ludtmann, et al, 2016; Turovsky et al, 2016) with modifications, from the midbrains and cerebral cortices of Sprague‐Dawley P3 rat pups or wildtype and LRRK2 knockout C57BL/6 mice (UCL breeding colony). Experimental procedures were performed in compliance with the United Kingdom Animals (Scientific Procedures) Act of 1986.…”

Calcium: Alpha-Synuclein Interactions in Alpha-Synucleinopathies

“…Furthermore, secreted α-syn induced an increase in capacitive Ca(II) entry in differentiated SH-SY5Y cells (Melachroinou et al, 2013). Transmembrane entry of Ca(II) or other cations may be via α-syn pore-like oligomers (Pountney et al, 2005; Mironov, 2015) and can mediate cytotoxicity (Angelova et al, 2016). Transgenic mice over-expressing human WT α-syn showed that α-syn transgenic mice exhibited augmented, long-lasting Ca(II) transients characterized by considerable deviation from the exponential decay.…”