Blood-Derived α-Synuclein Aggregated in the Substantia Nigra of Parabiotic Mice

As a pathological biomarker of Parkinson’s disease, α-synuclein is thought to be a prion-like protein, but evidence for the transmission of α-synuclein from blood to the brain is unclear. The goals of this study were to determine whether blood-derived α-synuclein could enter the brains of mice and whether α-synuclein in the brain could be cleared by parabiosis. Heterochronic parabiosis was performed on SNCA(A53T) transgenic mice (A53T mice) and wildtype mice. The levels of human α-synuclein in the blood and substantia nigra of wildtype mice were significantly increased after 4-month parabiosis with A53T mice. Moreover, the expression of α-synuclein filament, but not of total α-synuclein, was significantly increased in the substantia nigra of wildtype mice that were paired with A53T mice. However, the levels of human α-synuclein displayed no significant change in the serum, blood, or substantia nigra of A53T mice. These results provide direct evidence that pathological α-synuclein can be transmitted from blood to the brain in the heterochronic parabiosis system; however, it appears to be difficult to clear it from the brain in a short period of time.