Different Species of α-Synuclein Oligomers Induce Calcium Influx and Seeding

Abstract

Aggregation of ␣-synuclein (␣-syn) has been linked to the pathogenesis of Parkinson's disease (PD) and other neurodegenerative diseases. Increasing evidence suggests that prefibrillar oligomers and protofibrils, rather than mature fibrils of ␣-syn, are the pathogenic species in PD. Despite extensive effort on studying oligomerization of ␣-syn, no studies have compared different oligomer species directly on a single-particle level and investigated their biological effects on cells. In this study, we applied a novel highly sensitive single molecule detection system that allowed a direct comparison of different oligomer types. Furthermore, we studied biological effects of different oligomer types on cells. For this purpose, we developed new oligomerization protocols, that enabled the use of these different oligomers in cell culture. We found that all of our three aggregation protocols resulted in heterogeneous populations of oligomers. Some types of oligomers induced cell death via disruption of cellular ion homeostasis by a presumably pore-forming mechanism. Other oligomer types could directly enter the cell resulting in increased ␣-syn aggregation. Based on our results, we propose that under various physiological conditions, heterogeneous populations of oligomeric forms will coexist in an equilibrium. These different oligomer types lead directly or indirectly to cell damage. Our data indicate that inhibition of early ␣-syn aggregation events would consequently prevent all ␣-syn oligomer related toxicities. This has important implications for the development of disease-modifying drugs for the treatment of PD and other synucleinopathies.

Mechanism of Membrane Interaction and Disruption by α-Synuclein

“…18 Thus, it was suggested that oligomeric intermediates of α-Syn generated in the process of amyloidogenic aggregation could be the species responsible for cell death. 19,38,54,55 In addition, the mechanism of toxicity is also unknown. It has been proposed, that α-Syn oligomers may penetrate the cell membrane generating voltage-gated channels.…”

Distinct higher-order α-synuclein oligomers induce intracellular aggregation

“…Oligomer preparation of both seeding-and pore-forming-type oligomers used as positive controls is fully described in the Supplementary Online Data and in [6]. To make the MS-compatible oligomers (i.e.…”

“…Growing evidence suggests that soluble oligomeric forms of α-syn, which precede amyloid formation, are causative triggers for the dopaminergic cell loss occurring in PD [4,5]. The morphology and associated mode of toxicity displayed by alternative types of α-syn oligomers are largely dependent on the environmental conditions under which they have been prepared [6][7][8][9][10][11]. Numerous in vitro and in vivo studies on α-syn oligomers have demonstrated that a toxic gain-offunction occurs in the disease state via two main mechanisms: (i) Ca 2 + imbalances caused by the formation of pore-like complexes within lipid membranes, and (ii) transmembrane seeding that then results in intracellular aggregation [1].…”

“…Ion mobility measurements, accompanied by molecular modelling, permit the assignment of possible geometries for unknown protein complexes, and this gives valuable insights into the topology of the oligomers [27,28]. In the present study, oligomeric forms of α-syn [6,29] have been solubilized under MS-compatible conditions by the use of ammonium acetate as a buffer to enable ESI-IMS-MS analysis. Ion mobility experiments and molecular modelling demonstrate that the oligomeric species present encompass dimers to hexamers with various morphologies and suggest that assembly follows an isotropic growth pathway.…”

Immunotherapeutic Approaches Targeting Amyloid-β, α-Synuclein, and Tau for the Treatment of Neurodegenerative Disorders

“…Numerous strategies directed at reducing the accumulation of these proteins have been developed, including the use of small interfering RNA, antisense RNA [39][40][41][42][43], degrading enzymes (e.g., cathepsin D, neurosin, neprilysin) [44][45][46], chaperonelike molecules that modulate aggregation state (e.g., Hsp70, β-syn) [47][48][49][50], anti-aggregation compounds (e.g., polyphenols) [51][52][53], and immunotherapy (passive, active, and Tcell-based) [54]. Moreover, the recent discovery that toxic oligomeric forms of α-syn and tau accumulate in the plasma membrane and are secreted to the extracellular environment has provided further rationale for the development of immunotherapeutic approaches for PD, DLB, MSA, FTD, and other neurodegenerative disorders characterized by the abnormal accumulation of these proteins [24,26,[55][56][57][58].…”