Proteinase K-resistant α-synuclein is deposited in presynapses in human Lewy body disease and A53T α-synuclein transgenic mice
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Abnormally modified α-synuclein is a pathological hallmark of Parkinson’s disease and the other α-synucleinopathies. Since proteinase K (PK) treatment is known to enhance the immunoreactivity of abnormal α-synuclein, we immunohistochemically examined the brain of transgenic (Tg) mice expressing human mutant A53T α-synuclein using this retrieval method. PK treatment abolished the immunoreactivity of α-synuclein in abnormal inclusions as well as of endogenous α-synuclein in Tg mice, whereas PK-resistant α-synuclein was found in the presynaptic nerve terminals, especially in the hippocampus and temporal cortex. In human Lewy body disease, PK-resistant α-synuclein was deposited in Lewy bodies and Lewy neurites, as well as in the presynapses in distinct brain regions, including the hippocampus, temporal cortex and substantia nigra. Biochemical analysis revealed that PK-resistant α-synuclein was detected in the presynaptic fraction in Tg mice and human Lewy body disease. Although PK-resistant α-synuclein was found in the presynapse in Tg mice even at 1 week of age, it was not phosphorylated until at least 8 months of age. Moreover, PK-resistant α-synuclein in the presynapse was not phosphorylated in human Lewy body disease. These findings suggest that phosphorylation is not necessary to cause the conversion of soluble form to PK-resistant α-synuclein. Considering that native α-synuclein is a soluble protein localized to the presynaptic terminals, our findings suggest that PK-resistant α-synuclein may disturb the neurotransmission in α-synucleinopathies.
Keywordsα-Synuclein Dementia with Lewy bodies Parkinson’s disease Presynapse Proteinase K Transgenic mice
This work was supported by Grants-in-Aid 20590335 (K.T.), 20591361 (F.M.) and 20300123 (K.W.) for Scientific Research from the Ministry of Education, Culture, Sports, Science, and Technology, Japan, a Grant for Hirosaki University Institutional Research (K.W.), a Hirosaki University Grant for Exploratory Research by Young Scientists (K.T.), and a Grant-in-Aid for Studies on the Development of Diagnostic Technique and Therapies for Lewy Body Disease, the Ministry of Health, Labour and Welfare, Japan (K.W.). The authors wish to express their gratitude to M. Nakata for her technical assistance.
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