α-Synuclein Alters Notch-1 Expression and Neurogenesis in Mouse Embryonic Stem Cells and in the Hippocampus of Transgenic Mice

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Abstract
Altered expression and mutations in α-synuclein (α-syn) have been linked to Parkinson9s disease (PD) and related disorders. The neurological alterations in PD patients have been associated with degeneration of dopaminergic cells and other neuronal populations. Moreover, recent studies in murine models have shown that alterations in neurogenesis might also contribute to the neurodegenerative phenotype. However, the mechanisms involved and the effects of α-syn expression on neurogenesis are not yet clear. To this end, murine embryonic stem (mES) cells were infected with lentiviral (LV) vectors expressing wild-type (WT) and mutant α-syn. Compared with mES cells infected with LV–green fluorescent protein (GFP), cells expressing WT and mutant α-syn showed reduced proliferation as indicated by lower 5-bromo-2′-deoxyuridine uptake, increased apoptosis, and reduced expression of neuronal markers such as neuron specific enolase and β-III tubulin. The alterations in neurogenesis in α-syn-expressing mES cells were accompanied by a reduction in Notch-1 and Hairy and enhancer of split-5 (Hes-5) mRNA and protein levels. Moreover, levels of total Notch-1 and Notch intracellular domain (NICD) were lower in mES cells expressing WT and mutant α-syn compared with GFP controls. The reduced survival of α-syn-expressing mES cells was reverted by overexpressing constitutively active NICD. Similarly, in α-syn transgenic mice, the alterations in neurogenesis in the hippocampal subgranular zone were accompanied by decreased Notch-1, NICD, and Hes-5 expression. Together, these results suggest that accumulation of α-syn might impair survival of NPCs by interfering with the Notch signaling pathway. Similar mechanisms could be at play in PD and Lewy body disease.