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Article type: Research Article
Authors: Dos Santos, Altair B.a | Skaanning, Line K.a | Mikkelsen, Eyda | Romero-Leguizamón, Cesar R.a | Kristensen, Morten P.b | Klein, Anders B.a; c | Thaneshwaran, Siganyaa | Langkilde, Annette E.a | Kohlmeier, Kristi A.a; *
Affiliations: [a] Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark | [b] Academic Services International, Værløse, Denmark | [c] Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
Correspondence: [*] Correspondence to: Kristi A. Kohlmeier, PhD, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Jagtvej 160, 2100 Copenhagen, Denmark. E-mail: [email protected].
Abstract: Background:Parkinson’s disease (PD) is a neurodegenerative disorder associated with insoluble pathological aggregates of the protein α-synuclein. While PD is diagnosed by motor symptoms putatively due to aggregated α-synuclein-mediated damage to substantia nigra (SN) neurons, up to a decade before motor symptom appearance, patients exhibit sleep disorders (SDs). Therefore, we hypothesized that α-synuclein, which can be present in monomeric, fibril, and other forms, has deleterious cellular actions on sleep-control nuclei. Objective:We investigated whether native monomer and fibril forms of α-synuclein have effects on neuronal function, calcium dynamics, and cell-death-induction in two sleep-controlling nuclei: the laterodorsal tegmentum (LDT), and the pedunculopontine tegmentum (PPT), as well as the motor-controlling SN. Methods:Size exclusion chromatography, Thioflavin T fluorescence assays, and circular dichroism spectroscopy were used to isolate structurally defined forms of recombinant, human α-synuclein. Neuronal and viability effects of characterized monomeric and fibril forms of α-synuclein were determined on LDT, PPT, and SN neurons using electrophysiology, calcium imaging, and neurotoxicity assays. Results:In LDT and PPT neurons, both forms of α-synuclein induced excitation and increased calcium, and the monomeric form heightened putatively excitotoxic neuronal death, whereas, in the SN, we saw inhibition, decreased intracellular calcium, and monomeric α-synuclein was not associated with heightened cell death. Conclusion:Nucleus-specific differential effects suggest mechanistic underpinnings of SDs’ prodromal appearance in PD. While speculative, we hypothesize that the monomeric form of α-synuclein compromises functionality of sleep-control neurons, leading to the presence of SDs decades prior to motor dysfunction.
Keywords: Biomarkers, excessive daytime sleepiness, mechanism of disease, neurodegenerative diseases, neuronal alterations, prodromal phase, REM sleep behavior disorder
DOI: 10.3233/JPD-212554
Journal: Journal of Parkinson's Disease, vol. 11, no. 4, pp. 1773-1790, 2021
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