Endogenous alpha-synuclein influences the number of dopaminergic neurons in mouse substantia nigra

Abstract

The presynaptic protein α-synuclein is central to the pathogenesis of α-synucleinopathies. We show that the presence of endogenous mouse α-synuclein leads to higher number of dopaminergic neurons in the substantia nigra of wild-type C57Bl/6J mice compared with C57Bl/6S mice with a spontaneous deletion of the α-synuclein gene or C57Bl/6J mice with a targeted deletion of the α-synuclein gene. This effect of α-synuclein on dopaminergic neuron occurs during development between E10.5 and E13.5 and persists in adult life supporting the involvement of α-synuclein in the development of a subset of dopaminergic neurons.

Keywords: Dopaminergic; Embryonic development; Parkinson's disease; Transgenic mouse; α-Synuclein.

Figure 1. Western blot analysis of olfactory bulb (OB) extract demonstrates the expression of truncated human 1-120 α-synuclein in the presence of endogenous α-synuclein in α-syn (1-120)E mice.

Quantification was performed by analyzing the relative optic density of the western blot bands from 3 animals (A); Staining with anti-TH antibody in the substantia nigra of C57Bl/6S control (B), α-syn (1-120) mice (C), and homozygous α-syn(1-120)E mice (D) shows an increase in stereologically quantified TH⁺ cell numbers in Syn (1-120)E mice (E), scale bar 100 μm, *p < 0.05, **p < 0.01; (F) Stereological quantification of TH⁺ neurons in the substantia nigra of 6 month-old wt C57BL/6J, C57Bl/6S mice and C57Bl/6J α-synuclein knockout mice. *p < 0.05, ns not significant; (G) HPLC analysis does not show a significant difference in striatal dopamine and dopamine metabolite levels between α-syn (1-120)E and α-syn (1-120) mice with and without endogenous α-synuclein; TH⁺ cells in ventral mesencephalic areas (substantia nigra) of C57Bl/6J and C57Bl/6S wild type mice embryos at E10.5 and E13.5 days of gestation (H), as well as α-synuclein heterozygous (+/−) and homozygous (−/−) knockout mouse embryos at E10.5 and E13.5 days of gestation (I). Cell numbers were quantified stereologically and presented as percentage of control groups. The statistically significant difference was observed between C57Bl/6J and C57Bl/6S embryos at E13.5 (n = 3, p = 0.0143, two tailed t-test) and in the group of α-synuclein +/+, α-synuclein −/− and α-synuclein +/− (n = 4, 6 and 4 respectively, ** and *** by one-way ANOVA).