Endogenous state of α-synuclein protein alters susceptibility to Lewy-like pathology
Background and aims: Two human mutations affecting the α-synuclein protein confer the most clinical severity in Parkinson’s disease; endogenous αSyn over-expression due to gene multiplication and αSynG51D due to a missense mutation. The main hypotheses include 1) αSyn over-expression may affect cortical neuronal differentiation, 2) αSyn over-expression influences vulnerability to Lewy-like pathology in human cortical neurons, and 3) the SNCAG51D mutation alters susceptibility to Lewy-like pathology in a novel rat model of PD.Methods: Transgenic human embryonic stem cells (hESCs) over-expressing αSyn were differentiated into cortical neurons and analysed for gene expression. Cortical neurons were challenged with recombinant human wild-type αSyn monomers or pre-formed fibrils (PFFs) for 1 week. Subsequent analysis for phosphorylated αSyn (pS129-αSyn), an early disease marker, was performed two to three weeks later. In the second model, novel CRISPR-edited SNCAG51D/G51D rats and SNCA+/+ control rats received unilateral intracortical injections of αSyn PFFs, and pS129-αSyn structures were quantified at six months.Results: Transcriptomic analysis of hESCs and immature cortical neurons, as well as mature cortical neuron counts, showed αSyn over-expression did not impair cortical neurogenesis. Mature cortical neurons with high endogenous αSyn that were challenged with αSyn PFFs, but not αSyn monomers or unseeded neurons, readily formed pS129-αSyn inclusions (p < 0.001). In the SNCAG51D/G51D rats, αSyn PFF-injection led to defined, mature-appearing, Lewy-like (pS129-αSyn) inclusions with a predilection for the striatum in mutant rats, although not statistically significant. PFF-injected SNCA+/+ rats had diffuse pS129-αSyn pathology in similar interconnected regions to PFF-injected mutant rats. Conclusion: αSyn over-expression in hESCs did not impair differentiation into cortical neurons, which helps to clarify conflicting data in the literature on the role of αSyn in neurogenesis. Secondly, exposure to αSyn PFFs in human cortical neurons with high endogenous αSyn expression produced significantly more pS129-αSyn inclusions than neurons with wild-type levels of αSyn expression. Finally, the SNCAG51D/G51D rats developed more defined Lewy-like pathology in PD-vulnerable regions than controls after PFF-injection. These two accelerated disease models may provide further mechanistic insight in PD.