A progressive dopaminergic phenotype associated with neurotoxic conversion of α-synuclein in BAC-transgenic rats.

Conversion of soluble alpha-synuclein into insoluble and fibrillar inclusions is a hallmark of Parkinson's disease and other synucleinopathies. Accumulating evidence points towards a relationship between its generation at nerve terminals and structural synaptic pathology. Little is known about the pathogenic impact of alpha-synuclein conversion and deposition at nigrostriatal dopaminergic synapses in transgenic mice, mainly owing to expression limitations of the alpha-synuclein construct. Here, we explore whether both the rat as a model and expression of the bacterial artificial chromosome construct consisting of human full-length wild-type alpha-synuclein could exert dopaminergic neuropathological effects. We found that the human promoter induced a pan-neuronal expression, matching the rodent alpha-synuclein expression pattern, however, with prominent C-terminally truncated fragments. Ageing promoted conversion of both full-length and C-terminally truncated alpha-synuclein species into insolube and proteinase K-resistant fibres, with strongest accumulation in the striatum, resembling biochemical changes seen in human Parkinson's disease. Transgenic rats develop early changes in novelty-seeking, avoidance and smell before the progressive motor deficit. Importantly, the observed pathological changes were associated with severe loss of the dopaminergic integrity, thus resembling more closely the human pathology.