Analysis of α-Synuclein Pathology in PINK1 Knockout Rat Brains

Mutations in PTEN induced kinase 1 (PINK1) cause autosomal recessive Parkinson's disease (PD). The main pathological hallmarks of PD are loss of dopaminergic neurons in the substantia nigra pars compacta and the formation of protein aggregates containing alpha-synuclein. Previous studies of PINK1 knockout (PINK1-/-) rats have reported mitochondrial dysfunction, locomotor behavioral deficits, loss of neurons in the substantia nigra and alpha-synuclein aggregates in various brain regions. We sought to characterize PINK1-/- rats in more detail specifically with respect to alpha-synuclein pathology because abnormal alpha-synuclein has been implicated genetically, biophysically and neuropathologically as a mechanism of PD pathogenesis. Moreover, the spontaneous formation of alpha-synuclein aggregates without alpha-synuclein overexpression, injection or toxin administration is a rare and important characteristic for an animal model of PD or other synucleinopathies, such as dementia with Lewy bodies and multiple system atrophy. We observed alpha-synuclein-immunoreactive aggregates in various brain regions of PINK1-/- rats including cortex, thalamus, striatum and ventral midbrain, but nowhere in wild-type (WT) rats. Co-immunofluorescence showed that the alpha-synuclein-immunoreactive aggregates are both thioflavin S and ubiquitin positive. Many cells in the brains of PINK1-/- rats but not WT rats contained protease-resistant alpha-synuclein. Total synuclein protein levels were unchanged; however, biochemical fractionation showed a significant shift of alpha-synuclein from the cytosolic fraction to the synaptic vesicle-enriched fraction of PINK1-/- brain homogenates compared to WT. This data indicates that PINK1 deficiency results in abnormal alpha-synuclein localization, protease resistance and aggregation in vivo. The PINK1-/- rat could be a useful animal model to study the role of abnormal alpha-synuclein in PD-related neurodegeneration.