Abstract
Mutations in alpha-synuclein gene cause familial form of Parkinson disease, and deposition of wild-type alpha-synuclein as Lewy bodies occurs as a hallmark lesion of sporadic Parkinson disease and dementia with Lewy bodies, implicating alpha-synuclein in the pathogenesis of Parkinson disease and related neurodegenerative diseases. Dopamine neurons in substantia nigra are the major site of neurodegeneration associated with alpha-synuclein deposition in Parkinson disease. Here we establish transgenic Caenorhabditis elegans (TG worms) that overexpresses wild-type or familial Parkinson mutant human alpha-synuclein in dopamine neurons. The TG worms exhibit accumulation of alpha-synuclein in the cell bodies and neurites of dopamine neurons, and EGFP labeling of dendrites is often diminished in TG worms expressing familial Parkinson disease-linked A30P or A53T mutant alpha-synuclein, without overt loss of neuronal cell bodies. Notably, TG worms expressing A30P or A53T mutant alpha-synuclein show failure in modulation of locomotory rate in response to food, which has been attributed to the function of dopamine neurons. This behavioral abnormality was accompanied by a reduction in neuronal dopamine content and was treatable by administration of dopamine. These phenotypes were not seen upon expression of beta-synuclein. The present TG worms exhibit dopamine neuron-specific dysfunction caused by accumulation of alpha-synuclein, which would be relevant to the genetic and compound screenings aiming at the elucidation of pathological cascade and therapeutic strategies for Parkinson disease.
Highlights
We examined whether phosphorylation of ␣-synuclein at Ser-129, which is characteristic of ␣-synuclein deposited in Lewy bodies and other synucleinopathy lesions in human [30] as well as in transgenic mice [33, 34] brains, occurs in the dopamine neurons of transgenic C. elegans
No dopamine neurons were positive for anti-PSer129 in 3- or 9-day-old worms, whereas a subfraction of dopamine neurons (1.90, 2.26, and 7.09% of dopamine neurons in TG worms expressing wt, A30P, and A53T mt ␣-synuclein, respectively; n ϭ 105–141) showed positive reaction in 15-day-old worms, which was most prominent in TG worms expressing A53T FPD mt ␣-synuclein (Fig. 1I)
We further examined the ultrastructure of the ␣-synuclein accumulated within the cell bodies and dendrites of dopamine neurons by immunoelectron microscopy. ␣-Synuclein immunoreactivities detected by LB509 were diffusely distributed within the cytoplasm of dopamine neurons without formation of abnormal fibrils or aggregates (Fig. 1J), as well as in dendritic cytoplasm where they were detected between microtubular arrays (Fig. 1K, arrows)
Summary
Glial cytoplasmic inclusions in the brains of patients with multiple system atrophy, another major sporadic neurodegenerative disease, or dystrophic neurites in Hallervorden-Spatz disease were shown to be composed of ␣-synuclein, and these neurodegenerative diseases characterized by deposition of ␣-synuclein are collectively designated “synucleinopathies” [2]. Taken together with the gene dosage effects of ␣-synuclein in a subset of FPD (i.e. duplication and triplication), transgenic overexpression of ␣-synuclein in neurons would be a rational strategy to model neurodegeneration in PD. We describe a transgenic C. elegans model in which human ␣-synuclein overexpressed in dopamine neurons causes an abnormal phenotype in food-sensing behavior that has been attributed to the function of C. elegans dopamine neurons [25], in a manner dependent on FPD-linked mutations, through reduction of neuronal dopamine
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