Parkinson's disease (PD) is the most common representative of a group of disorders known as synucleinopathies, in which misfolding and aggregation of α-synuclein (a-syn) in various brain regions is the major pathological hallmark. Indeed, the motor symptoms in PD are caused by a heterogeneous degeneration of brain neurons not only in substantia nigra pars compacta but also in other extrastriatal areas of the brain. In addition to the well known motor dysfunction in PD patients, cognitive deficits and memory impairment are also an important part of the disorder, probably due to disruption of synaptic transmission and plasticity in extrastriatal areas, including the hippocampus.Here, we investigated the impact of a-syn aggregation on AMPA and NMDA receptor-mediated rat hippocampal (CA3-CA1) synaptic transmission and long-term potentiation (LTP), the neurophysiological basis for learning and memory. Our data show that prolonged exposure to a-syn oligomers, but not monomers or fibrils, increases basal synaptic transmission through NMDA receptor activation, triggering enhanced contribution of calcium-permeable AMPA receptors. Slices treated with a-syn oligomers were unable to respond with further potentiation to theta-burst stimulation, leading to impaired LTP. Prior delivery of a low-frequency train reinstated the ability to express LTP, implying that exposure to a-syn oligomers drives the increase of glutamatergic synaptic transmission, preventing further potentiation by physiological stimuli.Our novel findings provide mechanistic insight on how a-syn oligomers may trigger neuronal dysfunction and toxicity in PD and other synucleinopathies.

α-Synuclein misfolding and aggregation is a hallmark in Parkinson’s disease and in several other neurodegenerative diseases known as synucleinopathies. The toxic properties of α-synuclein are conserved from yeast to man, but the precise underpinnings of the cellular pathologies associated are still elusive, complicating the development of effective therapeutic strategies. Combining molecular genetics with target-based approaches, we established that glycation, an unavoidable age-associated post-translational modification, enhanced α-synuclein toxicity in vitro and in vivo, in Drosophila and in mice. Glycation affected primarily the N-terminal region of α-synuclein, reducing membrane binding, impaired the clearance of α-synuclein, and promoted the accumulation of toxic oligomers that impaired neuronal synaptic transmission. Strikingly, using glycation inhibitors, we demonstrated that normal clearance of α-synuclein was re-established, aggregation was reduced, and motor phenotypes in Drosophila were alleviated. Altogether, our study demonstrates glycation constitutes a novel drug target that can be explored in synucleinopathies as well as in other neurodegenerative conditions.

Sirtuin genes have been associated with aging and are known to affect multiple cellular pathways. Sirtuin 2 was previously shown to modulate proteotoxicity associated with age-associated neurodegenerative disorders such as Alzheimer and Parkinson disease (PD). However, the precise molecular mechanisms involved remain unclear. Here, we provide mechanistic insight into the interplay between sirtuin 2 and α-synuclein, the major component of the pathognomonic protein inclusions in PD and other synucleinopathies. We found that α-synuclein is acetylated on lysines 6 and 10 and that these residues are deacetylated by sirtuin 2. Genetic manipulation of sirtuin 2 levels in vitro and in vivo modulates the levels of α-synuclein acetylation, its aggregation, and autophagy. Strikingly, mutants blocking acetylation exacerbate α-synuclein toxicity in vivo, in the substantia nigra of rats. Our study identifies α-synuclein acetylation as a key regulatory mechanism governing α-synuclein aggregation and toxicity, demonstrating the potential therapeutic value of sirtuin 2 inhibition in synucleinopathies. Parkinson disease is an age-associated neurodegenerative disorder characterized by the loss of dopamine-producing neurons from a region in the brain known as the substantia nigra and by the accumulation of the protein alpha-synuclein in intracellular clumps called inclusions. Whether these inclusions are the cause or a consequence of the pathological processes is still unclear. Sirtuin proteins are considered master regulators of the ageing process and have previously been associated with neurodegeneration. In this study, we investigated the interplay between sirtuin 2 and alpha-synuclein in order to dissect the molecular mechanisms associated with protection against alpha-synuclein toxicity. We found that sirtuin 2 interacted with and removed acetyl groups from alpha-synuclein. By decreasing the levels of sirtuin 2, or by expressing mutant versions of alpha-synuclein that modulate its acetylation status, we found that acetylation reduces the aggregation of alpha-synuclein and its cytotoxicity in vitro. Next, we evaluated whether genetic inhibition of sirtuin 2 could prevent the deleterious effects of alpha-synuclein in vivo and found that, in two different models of Parkinson disease, deletion of sirtuin 2 was neuroprotective. Our data therefore suggest that strategies aimed at decreasing sirtuin 2 activity might prove valuable therapeutic avenues for intervention in Parkinson disease and other synucleinopathies.

Cell-to-cell propagation of aggregated alpha synuclein (aSyn) has been suggested to play an important role in the progression of alpha synucleinopathies. A critical step for the propagation process is the accumulation of extracellular aSyn within recipient cells. Here, we investigated the trafficking of distinct exogenous aSyn forms and addressed the mechanisms influencing their accumulation in recipient cells. The aggregated aSyn species (oligomers and fibrils) exhibited more pronounced accumulation within recipient cells than aSyn monomers. In particular, internalized extracellular aSyn in the aggregated forms was able to seed the aggregation of endogenous aSyn. Following uptake, aSyn was detected along endosome-to-lysosome and autophagosome-to-lysosome routes. Intriguingly, aggregated aSyn resulted in lysosomal activity impairment, accompanied by the accumulation of dilated lysosomes. Moreover, analysis of autophagy-related protein markers suggested decreased autophagosome clearance. In contrast, the endocytic pathway, proteasome activity, and mitochondrial homeostasis were not substantially affected in recipient cells. Our data suggests that extracellularly added aggregated aSyn primarily impairs lysosomal activity, consequently leading to aSyn accumulation within recipient cells. Importantly, the autophagy inducer trehalose prevented lysosomal alterations and attenuated aSyn accumulation within aSyn-exposed cells. Our study underscores the importance of lysosomes for the propagation of aSyn pathology, thereby proposing these organelles as interventional targets.