α-Synuclein Responses in the Laterodorsal Tegmentum, the Pedunculopontine Tegmentum, and the Substantia Nigra: Implications for Early Appearance of Sleep Disorders in Parkinson’s Disease

Article type: Research Article

Authors: Dos Santos, Altair B.^a | Skaanning, Line K.^a | Mikkelsen, Eyd^a | Romero-Leguizamón, Cesar R.^a | Kristensen, Morten P.^b | Klein, Anders B.^{a; c} | Thaneshwaran, Siganya^a | 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: kak1@sund.ku.dk.

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