Regulation of nigrostriatal dopamine neurotransmission by gamma-synuclein: down- and over-expression mouse models

Trabajo presentado en el Alpha-synuclein & Parkinson’s disease Conference: Lessons from the past 20 years, celebrado en la Universitat de Barcelona los días 11 y 12 de mayo de 2017Synucleins are small proteins in vertebrates, especially abundant in neurons and presynaptic terminals. Mutations in α-synuclein gene have been reported in inherited forms of Parkinson’s disease, but far less is known about β- and γsynucleins, which have been implicated in some neurodegenerative diseases and synucleinopathies. Here, we examined the distribution and cellular localization of γ-synuclein in the mouse brain using in situ hybridization and immunohistochemistry procedures, and evaluated its functional role in nigrostriatal dopamine (DA) neurotransmission in vivo. We used two different models with: 1) down-regulated γ-synuclein expression in DA neurons of substantia nigra compacta/ventral tegmental area (SNc/VTA) by small interfering RNA molecules (siRNA), or 2) over-expressed γ-synuclein in SNc/VTA DA neurons using AAV10-CMV-mouse-γ-synuclein vector. In C57BL/6J control mice, abundant levels of γ-synuclein mRNA were found in monoaminergic nuclei (SNc/VTA, raphe nuclei and locus coeruleus). Double in situ hybridization and immunohistochemistry showed a specific colocalization of γ-synuclein in TH-positive DA neurons. Unilateral infusion of three siRNA sequences targeting γ-synuclein decreased its mRNA levels in DA neurons of SNc (50% of aCSF-treated mice 24h post-infusion). Furthermore, γ-synuclein suppression displayed an enhanced striatal DA tone using intracerebral microdialysis, which is reflected in higher extracellular DA levels in siRNAtreated mice during local veratridine, nomifensine and amphetamine administrations and lower levels with quinpirole; meanwhile, γ-synuclein overexpression led to lower levels during nomifensine administration. In conclusion, these results confirm that γ-synuclein is a negative regulator of DA neurotransmission and suggest that siRNA-induced γ-synuclein suppression in midbrain dopaminergic neurons may lead to new therapies for synucleinopathies.Peer reviewe