Abnormal α-Synuclein Interactions with Rab Proteins in α-Synuclein A30P Transgenic Mice

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Abstract
Mutation A30P in the α-synuclein gene is a cause of familial Parkinson disease. Transgenic mice expressing wild mouse and mutant human A30P α-synuclein, Tg5093 mice (Tg), show a progressive motor disorder characterized by tremor, rigidity, and dystonia, accompanied by accumulation of α-synuclein in the soma and neurites and by a conspicuous gliosis beginning in the hippocampal formation at the age of 7 to 8 months and spreading throughout the CNS. Impaired short-term changes in synaptic strength have also been documented in hippocampal slices from Tg mice. α-synuclein aggregates of approximately 34 and 70 kDa, in addition to the band of 17 kDa, corresponding to the molecular weight of α-synuclein, were recovered in the PBS-soluble fraction of brain homogenates from Tg mice but not from brain samples from age-matched wildtype littermates. MPTP-treated Tg and wildtype mice produced α-synuclein aggregates in the PBS-, deoxycholate-, and SDS-soluble fractions. Aggregates of α-synuclein, although with different molecular weights, were also observed in rotenone- treated Tg and wildtype mice. Pull-down studies with members of the Rab protein family have shown that α-synuclein from Tg mice interacts with Rab3a, Rab5, and Rab8. This binding is not due to the amount of α-synuclein (levels of which are higher in Tg mice) and it is not dependent on the amount of Rab protein used in the assay. Rather, α-synuclein interactions with Rab proteins are due to mutant α-synuclein as demonstrated in Rab pull-down assays with recombinant of wildtype and mutant A30P human α-synuclein. Since Rab3a, Rab5, and Rab8 are important proteins involved in synaptic vesicle trafficking and exocytosis at the synapse, vesicle endocytosis, and trans-Golgi transport, respectively, it can be suggested that these functions are impaired in Tg mice. This rationale is consistent with previous data showing that short-term hippocampal synaptic plasticity is altered and that α-synuclein accumulates in the cytoplasm of neurons in Tg mice.