Nigrostriatal overabundance of α-synuclein leads to decreased vesicle density and deficits in dopamine release that correlate with reduced motor activity


α-Synuclein (α-syn) is a presynaptic protein present at most nerve terminals, but its function remains largely unknown. The familial forms of Parkinson’s disease associated with multiplications of the α-syn gene locus indicate that overabundance of this protein might have a detrimental effect on dopaminergic transmission. To investigate this hypothesis, we use adeno-associated viral (AAV) vectors to overexpress human α-syn in the rat substantia nigra. Moderate overexpression of either wild-type (WT) or A30P α-syn differs in the motor phenotypes induced, with only the WT form generating hemiparkinsonian impairments. Wild-type α-syn causes a reduction of dopamine release in the striatum that exceeds the loss of dopaminergic neurons, axonal fibers, and the reduction in total dopamine. At the ultrastructural level, the reduced dopamine release corresponds to a decreased density of dopaminergic vesicles and synaptic contacts in striatal terminals. Interestingly, the membrane-binding-deficient A30P mutant does neither notably reduce dopamine release nor it cause ultrastructural changes in dopaminergic axons, showing that α-syn’s membrane-binding properties are critically involved in the presynaptic defects. To further determine if the affinity of the protein for membranes determines the extent of motor defects, we compare three forms of α-syn in conditions leading to pronounced degeneration. While membrane-binding α-syns (wild-type and A53T) induce severe motor impairments, an N-terminal deleted form with attenuated affinity for membranes is inefficient in inducing motor defects. Overall, these results demonstrate that α-syn overabundance is detrimental to dopamine neurotransmission at early stages of the degeneration of nigrostriatal dopaminergic axons.

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The authors thank Vivianne Padrun, Fabienne Pidoux, Christel Sadeghi, Philippe Colin and Martial Mbefo Kamdem for their excellent technical assistance, and Gürdal Sahin and Prof. Deniz Kirik for the HPLC analysis. The authors are grateful to Alexandre Froidevaux for his help with the 3D-reconstruction from electron microscopic data. This work was supported by the Merck-Serono EPFL Alliance, the Swiss National Science Foundation Grant No 31003A_120653, the European Community’s FP7 under grant agreement no. HEALTH-F5-2008-222925 (Neugene), the Michael J Fox Foundation (Target Validation 2005), and a grant from the Synapsis Foundation (to R.S.).

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Correspondence to Patrick Aebischer or Bernard Laurent Schneider.

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Supplementary Movie 1. Movie showing 80 serial images taken from a subregion within a full image series. Image z spacing is 13 nm. The horizontal field width is 3.1 μm. DA dopaminergic axon. X type-x axon. glut glutamatergic axon. Asterisks mark zones of synaptic specialization.

Supplementary material 1 (AVI 1385 kb)

Supplementary material 1 (AVI 1385 kb)

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Gaugler, M.N., Genc, O., Bobela, W. et al. Nigrostriatal overabundance of α-synuclein leads to decreased vesicle density and deficits in dopamine release that correlate with reduced motor activity. Acta Neuropathol 123, 653–669 (2012).

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  • α-Synuclein
  • Neurotransmission
  • Dopamine
  • Substantia nigra
  • Motor behavior
  • Electron microscopy