Targeted overexpression of the parkin substrate Pael-R in the nigrostriatal system of adult rats to model Parkinson's disease
Loss of function of parkin, an ubiquitin ligase, is responsible for autosomal recessive juvenile parkinsonism (AR-JP). Parkin-associated endothelin receptor-like receptor (Pael-R) was identified as an authentic substrate of parkin and is thought to accumulate abnormally following loss of parkin activity, causing neurodegeneration of nigral dopaminergic neurons in AR-JP patients. Our aim is therefore to generate a model of AR-JP through overexpression of Pael-R in the nigrostriatal system of adult rats. Using recombinant adeno-associated virus pseudotyped with the serotype 6 capsid (rAAV2/6) as a gene delivery tool, we achieved targeted and robust overexpression of rat Pael-R in nigral neurons and their striatal terminals. Overexpressed Pael-R was shown to accumulate very rapidly in an insoluble form. Accumulation of the receptor triggered a rapid and severe loss of nigral neurons and nigrostriatal fibers and terminals. No cell recovery was observed for up to 6 months post-injection. GABAergic neurons of the globus pallidus were unaffected by Pael-R overexpression, highlighting the selective vulnerability of nigral dopaminergic neurons to abnormal levels of Pael-R. Pael-R-induced degeneration also led to a depletion of striatal dopamine resulting in spontaneous motor impairments, as measured in the cylinder and stepping tests for forelimb akinesia. Interestingly, behavioral deficits of individual animals were correlated with the extent of the nigrostriatal lesion. Insoluble accumulation of Pael-R in the nigrostriatal system of adult rats represents, therefore, a chronic, rapidly progressing and specific model of AR-JP, which recapitulates major pathological hallmarks of the disease.