Identification of distinct pathological signatures induced by patient-derived -synuclein structures in nonhuman primates

©. This manuscript version is made available under the CC BY-NC 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ This document is the Submitted, Accepted, Published, version of a Published Work that appeared in final form in Science Advances To access the final edited and published work see http://dx.doi.org/10.5281/zenodo.1240558Dopaminergic neuronal cell death, associated with intracellular -synuclein (-syn)–rich protein aggregates [termed “Lewy bodies” (LBs)], is a well-established characteristic of Parkinson’s disease (PD). Much evidence, accumulated from multiple experimental models, has suggested that -syn plays a role in PD pathogenesis, not only as a trigger of pathology but also as a mediator of disease progression through pathological spreading. Here, we have used a machine learning–based approach to identify unique signatures of neurodegeneration in monkeys induced by distinct -syn pathogenic structures derived from patients with PD. Unexpectedly, our results show that, in nonhuman primates, a small amount of singular -syn aggregates is as toxic as larger amyloid fibrils present in the LBs, thus reinforcing the need for preclinical research in this species. Furthermore, our results provide evidence supporting the true multifactorial nature of PD, as multiple causes can induce a similar outcome regarding dopaminergic neurodegeneration

NMDA receptor GluN2D subunit participates to levodopa-induced dyskinesia pathophysiology

In the striatum, specific N-methyl-D-aspartate receptor (NMDAR) subtypes are found in different neuronal cells. Spiny projection neurons (SPNs) are characterized by NMDARs expressing GluN2A and GluN2B subunits, while GluN2D is exclusively detected in striatal cholinergic interneurons (ChIs). In Parkinson's disease (PD), dopamine depletion and prolonged treatment with levodopa (L-DOPA) trigger adaptive changes in the glutamatergic transmission from the cortex to the striatum, also resulting in the aberrant function of striatal NMDARs. While modifications of GluN2A- and GluN2B-NMDARs in SPNs have been extensively documented, only few studies report GluN2D dysfunction in PD and no data are available in L-DOPA-induced dyskinesia (LID). Here we investigate the contribution of a specific NMDAR subtype (GluN2D-NMDAR) to PD and LID, and whether this receptor could represent a candidate for future pharmacological interventions. Our results show that GluN2D synaptic abundance is selectively augmented in the striatum of L-DOPA-treated male parkinsonian rats displaying a dyskinetic phenotype. This event is associated to a dramatic increase in GluN2D binding to the postsynaptic protein scaffold PSD-95. Moreover, immunohistochemistry and electrophysiology experiments reveal that GluN2D-NMDARs are expressed not only by striatal ChIs but also by SPNs in dyskinetic rats. Notably, in vivo treatment with a well-characterized GluN2D antagonist ameliorates the severity of established dyskinesia in L-DOPA-treated animals. Our findings support a role for GluN2D-NMDARs in LID, and they confirm that cell-type and subunit specific modifications of NMDARs underlie the pathophysiology of LID