Alpha-synuclein (a-Syn) is a key protein involved in Parkinson's disease (PD) pathology. PD is characterized by the loss of dopaminergic neuronal cells in the substantia nigra pars compacta and the abnormal accumulation and aggregation of a-Syn in the form of Lewy bodies and Lewy neurites. More precisely, the aggregation of a-Syn is associated with the dysfunctionality and degeneration of neurons in PD. Moreover, mutations in the SNCA gene, which encodes a-Syn, cause familial forms of PD and are the basis of sporadic PD risk. Given the role of the a-Syn protein in the pathology of PD, animal models that reflect the dopaminergic neuronal loss and the widespread and progressive formation of a-Syn aggregates in different areas of the brain constitute a valuable tool. Indeed, animal models of PD are important for understanding the molecular mechanisms of the disease and might contribute to the development and validation of new therapies. In the absence of animal models that faithfully reproduce human PD, in recent years, numerous animal models of PD based on a-Syn have been generated. In this review, we summarize the main features of the a-Syn pre-formed fibrils (PFFs) model and recombinant adenoassociated virus vector (rAAV) mediated a-Syn overexpression models, providing a detailed comparative analysis of both models. Here, we discuss how each model has contributed to our understanding of PD pathology and the advantages and weakness of each of them. Significance: Here, we show that injection of a-Syn PFFs and overexpression of a-Syn mediated by rAAV lead to a different pattern of PD pathology in rodents. First, a-Syn PFFs models trigger the Lewy body-like inclusions formation in brain regions directly interconnected with the injection site, suggesting that there is an inter-neuronal transmission of the a-Syn pathology. In contrast, rAAV-mediated a-Syn overexpression in the brain limits the a-Syn aggregates within the transduced neurons. Second, phosphorylated a-Syn inclusions obtained with rAAV are predominantly nuclear with a punctate appearance that becomes diffuse along the neuronal fibers, whereas a-Syn PFFs models lead to the formation of cytoplasmic aggregates of phosphorylated a-Syn reminiscent of Lewy bodies and Lewy neurites.

IntroductionParkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons as well as the presence of proteinaceous inclusions named Lewy bodies. α-synuclein (α-syn) is a major constituent of Lewy bodies, and the first disease-causing protein characterized in PD. Several α-syn-based animal models of PD have been developed to investigate the pathophysiology of PD, but none of them recapitulate the full picture of the disease. Ageing is the most compelling and major risk factor for developing PD but its impact on α-syn toxicity remains however unexplored. In this study, we developed and exploited a recombinant adeno-associated viral (AAV) vector of serotype 9 overexpressing mutated α-syn to elucidate the influence of ageing on the dynamics of PD-related neurodegeneration associated with α-syn pathology in different mammalian species.ResultsIdentical AAV pseudotype 2/9 vectors carrying the DNA for human mutant p.A53T α-syn were injected into the substantia nigra to induce neurodegeneration and synucleinopathy in mice, rats and monkeys. Rats were used first to validate the ability of this serotype to replicate α-syn pathology and second to investigate the relationship between the kinetics of α-syn-induced nigrostriatal degeneration and the progressive onset of motor dysfunctions, strikingly reminiscent of the impairments observed in PD patients. In mice, AAV2/9-hα-syn injection into the substantia nigra was associated with accumulation of α-syn and phosphorylated hα-syn, regardless of mouse strain. However, phenotypic mutants with either accelerated senescence or resistance to senescence did not display differential susceptibility to hα-syn overexpression. Of note, p-α-syn levels correlated with nigrostriatal degeneration in mice. In monkeys, hα-syn-induced degeneration of the nigrostriatal pathway was not affected by the age of the animals. Unlike mice, monkeys did not exhibit correlations between levels of phosphorylated α-syn and neurodegeneration.ConclusionsIn conclusion, AAV2/9-mediated hα-syn induces robust nigrostriatal neurodegeneration in mice, rats and monkeys, allowing translational comparisons among species. Ageing, however, neither exacerbated nigrostriatal neurodegeneration nor α-syn pathology per se. Our unprecedented multi-species investigation thus favours the multiple-hit hypothesis for PD wherein ageing would merely be an aggravating, additive, factor superimposed upon an independent disease process.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-015-0222-2) contains supplementary material, which is available to authorized users.

Running title:C-terminal truncation: a master regulator of α-syn inclusion formation and LB biogenesis. AbstractAlthough converging evidence point to α-synuclein (α-syn) aggregation and Lewy body (LB) formation as central events in Parkinson's disease (PD), the molecular mechanisms that regulate these processes and their role in disease pathogenesis remain poorly understood.Herein, we applied an integrative biochemical, structural and imaging approach to elucidate the sequence, molecular and cellular mechanisms that regulate LB formation in primary neurons. Our results establish that post-fibrillization C-terminal truncation mediated by calpains 1 and 2 and potentially other enzymes, plays critical roles in regulating α-syn seeding, fibrillization and orchestrates many of the events associated with LB formation and maturation.These findings combined with the abundance of α-syn truncated species in LBs and pathological α-syn aggregates have significant implications for ongoing efforts to develop therapeutic strategies based on targeting the C-terminus of α-syn or proteolytic processing of this region.

Immunotargeting of extracellular tau could slow the prion-like spreading of neurodegeneration. Albert et al. report that antibodies that recognize a central epitope on tau are the most effective at blocking both seeding and propagation of tau pathological species in transgenic mouse models seeded by materials derived from Alzheimer’s disease brains.

Agonists at dopamine D2 and D3 receptors are important therapeutic agents in the treatment of Parkinson's disease. Compared with the use of agonists, allosteric potentiators offer potential advantages such as temporal, regional, and phasic potentiation of natural signaling, and that of receptor subtype selectivity. We report the identification of a stereoselective interaction of a benzothiazol racemic compound that acts as a positive allosteric modulator (PAM) of the rat and human dopamine D2 and D3 receptors. The R isomer did not directly stimulate the dopamine D2 receptor but potentiated the effects of dopamine. In contrast the S isomer attenuated the effects of the PAM and the effects of dopamine. In radioligand binding studies, these compounds do not compete for binding of orthosteric ligands, but indeed the R isomer increased the number of high-affinity sites for [ 3 H]-dopamine without affecting K d . We went on to identify a more potent PAM for use in native receptor systems. This compound potentiated the effects of D2/D3 signaling in vitro in electrophysiologic studies on dissociated striatal neurons and in vivo on the effects of L-dopa in the 6OHDA (6-hydroxydopamine) contralateral turning model. These PAMs

Levetiracetam (LEV) (Keppra; UCB Pharma, Brussels, Belgium) has recently been reported to have antidyskinetic activity against levodopa (L-DOPA)-induced dyskinesia in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset and macaque models of Parkinson's disease. Amantadine is frequently used as adjunctive therapy for L-DOPA-induced dyskinesia, but adverse effects limit its clinical utility. The current study was designed to investigate whether LEV can potentiate the antidyskinetic action of amantadine. The antiparkinsonian and antidyskinetic effects of LEV (13 and 60 mg/kg) and amantadine (0.01, 0.03, 0.1, and 0.3 mg/kg), administered alone and in combination, were assessed in the MPTP-lesioned marmoset model of L-DOPA-induced dyskinesia (n ϭ 12). LEV (60 mg/kg) and amantadine (0.3 mg/kg) administered alone significantly reduced L-DO-PA-induced dyskinesia without compromising the antiparkinsonian action of L-DOPA. Lower doses were without any significant effects. The combination of LEV (60 mg/kg) and amantadine (0.01, 0.03, 0.1, and 0.3 mg/kg) significantly decreased dyskinesia severity, without compromising the antiparkinsonian action of L-DOPA, more efficaciously than LEV or amantadine monotherapy. These results support the concept that normalization of different pathophysiological mechanisms (i.e., altered synchronization between neurons and enhanced N-methyl-

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