Expression of human A53T alpha-synuclein in the rat substantia nigra using a novel AAV1/2 vector produces a rapidly evolving pathology with protein aggregation, dystrophic neurite architecture and nigrostriatal degeneration with potential to model the pathology of Parkinson's disease

Abstract

BackgroundThe pathological hallmarks of Parkinson's disease (PD) include the presence of alpha-synuclein (α-syn) rich Lewy bodies and neurites and the loss of dopaminergic (DA) neurons of the substantia nigra (SN). Animal models of PD based on viral vector-mediated over-expression of α-syn have been developed and show evidence of DA toxicity to varying degrees depending on the type of virus used, its concentration, and the serotype of vector employed. To date these models have been variable, difficult to reproduce, and slow in their evolution to achieve a desired phenotype, hindering their use as a model for testing novel therapeutics. To address these issues we have taken a novel vector in this context, that can be prepared in high titer and which possesses an ability to produce neuronally-directed expression, with expression dynamics optimised to provide a rapid rise in gene product expression. Thus, in the current study, we have used a high titer chimeric AAV1/2 vector, to express human A53T α-syn, an empty vector control (EV), or green fluorescent protein (GFP), the latter to control for the possibility that high levels of protein in themselves might contribute to damage.ResultsWe show that following a single 2 μl injection into the rat SN there is near complete coverage of the structure and expression of A53T α-syn or GFP appears throughout the striatum. Within 3 weeks of SN delivery of their respective vectors, aggregations of insoluble α-syn were observed in SN DA neurons. The numbers of DA neurons in the SN were significantly reduced by expression of A53T α-syn (52%), and to a lesser extent by GFP (24%), compared to EV controls (both P < 0.01). At the level of the striatum, AAV1/2-A53T α-syn injection produced dystrophic neurites and a significant reduction in tyrosine hydroxylase levels (by 53%, P < 0.01), this was not seen in the AAV1/2-GFP condition.ConclusionsIn the current implementation of the model, we recapitulate the primary pathological hallmarks of PD, although a proportion of the SN damage may relate to general protein overload and may not be specific for A53T α-syn. Future studies will thus be required to optimise the dose of AAV1/2 employed before fully characterizing this model. The dynamics of the evolution of the pathology however, provide advantages over current models with respect to providing an initial screen to assess efficacy of novel treatments that might prevent/reverse α-syn aggregation.

Mimicking Phosphorylation at Serine 87 Inhibits the Aggregation of Human α-Synuclein and Protects against Its Toxicity in a Rat Model of Parkinson's Disease

“…It is worth noting that after induction of 25-30% of THϩ neuron loss, we observed a significant effect on the animal motor performance, suggesting that a moderate dopaminergic lesion is sufficient to induce a motor impairment in rats. This result is in agreement with a recent report by Koprich et al (2010) demonstrating that overexpression of A53T ␣-syn in the rat SN resulted in an impairment in striatal DA release and significant motor behavior deficits despite the fact that only a moderate dopaminergic lesion (28%) was observed. Together, our results demonstrate that the serine-to-glutamic acid substitution reduces ␣-syn-induced neuronal toxicity, fiber pathology, and motor deficits and suggest that phosphorylation at this site would block ␣-syn toxicity in vivo.…”

“…Human ␣-syn WT and S87A mutant induce striatal fiber pathology, but the S87E mutant does not Neuropathological observations in synucleinopathy-diseased brains (Irizarry et al, 1998;Braak and Braak, 2000;Duda et al, 2000) and animal models of PD (Kirik et al, 2002b;Koprich et al, 2010) describe the presence of striatal dystrophic neurites. To determine whether the overexpression of ␣-syn WT and S87 mutants induces fiber pathology in the striatum, we performed a dopaminergic terminal staining using TH antibody.…”

Inflammation and Adaptive Immunity in Parkinson's Disease

“…Abnormal species of a-syn found in PD patients are also present in LBs of other synucleinopathy-affected brains, including AD and multiple-system atrophy (MSA) (Duda et al 2000;Giasson et al 2000;Cavallarin et al 2010). These observations are supported by in vitro data and animal models of PD in which overexpression of native or mutated forms of a-syn show that aberrant species have an increased propensity to aggregate (Parihar et al 2009;Koprich et al 2010). Aggregation of a-syn is also caused by genetic mutations.…”

Subthalamic nucleus deep brain stimulation is neuroprotective in the A53T α‐synuclein Parkinson's disease rat model

“…Thus, in order to evaluate the disease‐modifying potential of DBS in a context where SN neurons are accumulating and under duress from pathological aSyn, we utilized a rat model for PD that is based on a vector driven (adeno‐associated virus [AAV] 1/2) overexpression of mutated A53T α‐synuclein (A53T‐aSyn) in dopaminergic neurons of the SN that leads to progressive and reliable neurodegeneration and motor impairment 20, 21. This model mimics the neurobiological hallmarks of PD much closer than toxin models and is thus more suitable for the investigation of DBS mechanisms of action.…”