Abstract
Mutations in the alpha-synuclein (alphaSYN) gene are associated with rare cases of familial Parkinson's disease, and alphaSYN is a major component of Lewy bodies and Lewy neurites. Here we have investigated the localization of wild-type and mutant [A30P]alphaSYN as well as betaSYN at the cellular and subcellular level. Our direct comparative study demonstrates extensive synaptic colocalization of alphaSYN and betaSYN in human and mouse brain. In a sucrose gradient equilibrium centrifugation assay, a portion of betaSYN floated into lower density fractions, which also contained the synaptic vesicle marker synaptophysin. Likewise, wild-type and [A30P]alphaSYN were found in floating fractions. Subcellular fractionation of mouse brain revealed that both alphaSYN and betaSYN were present in synaptosomes. In contrast to synaptophysin, betaSYN and alphaSYN were recovered from the soluble fraction upon lysis of the synaptosomes. Synaptic colocalization of alphaSYN and betaSYN was directly visualized by confocal microscopy of double-stained human brain sections. The Parkinson's disease-associated human mutant [A30P]alphaSYN was found to colocalize with betaSYN and synaptophysin in synapses of transgenic mouse brain. However, in addition to their normal presynaptic localization, transgenic wild-type and [A30P]alphaSYN abnormally accumulated in neuronal cell bodies and neurites throughout the brain. Thus, mutant [A30P]alphaSYN does not fail to be transported to synapses, but its transgenic overexpression apparently leads to abnormal cellular accumulations.
Highlights
Mutations in the ␣-synuclein (␣SYN) gene are associated with rare cases of familial Parkinson’s disease, and ␣SYN is a major component of Lewy bodies and Lewy neurites
Full-length ␣SYN has been subsequently found in Lewy bodies (LBs), pale bodies, and Lewy neurites of patients with Parkinson’s disease (PD) and dementia with LBs, as well as in cytoplasmic inclusions characteristic for multiple system atrophy (Spillantini et al, 1997; Arima et al, 1998; Baba et al, 1998; Spillantini et al, 1998; Takeda et al, 1998a; Tu et al, 1998; Wakabayashi et al, 1998; Culvenor et al, 1999)
In brains of transgenic mice expressing human mutant [A30P]␣SYN, a synaptic colocalization with SYN was found, suggesting that the mutation does not interfere with anterograde transport of ␣SYN to synapses
Summary
Mutations in the ␣-synuclein (␣SYN) gene are associated with rare cases of familial Parkinson’s disease, and ␣SYN is a major component of Lewy bodies and Lewy neurites. In brains of transgenic mice expressing human mutant [A30P]␣SYN, a synaptic colocalization with SYN was found, suggesting that the mutation does not interfere with anterograde transport of ␣SYN to synapses. Sucrose gradient floatation assays (Jensen et al, 1998) were performed with material prepared from wild-type and transgenic mouse and human brain.
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