α-synuclein knockdown protects differentiated human neurons from MPP+ toxicity. Differentiated SH-SY5Y and MESC2.10 cells were transfected with SNCA1 (knockdown) or a scrambled version of SNCA1 (scram control) and differentiated as normal. At the end of differentiation, cells were exposed to different concentrations of MPP+ for 16 hours and then live cells were stained green using calcein AM and dead cells red using ethidium homodimer-1. Representative photographs are shown of differentiated (A) SH-SY5Y and (B) MESC2.10 cells exposed to normal media or 1mM MPP+ with or without α-synuclein knockdown. 20x objective. (C) Viability was determined by counting live cells in six random 20x fields of view for each condition. Results are from 3 separate experiments performed in triplicate (± SEM). Survival of differentiated SH-SY5Y cells exposed to MPP+ was significantly improved by α-synuclein knockdown (two-way ANOVA, siRNA effect, p < 0.001). (D) MESC2.10 cells were also significantly protected by α-synuclein knockdown from MPP+ exposure (two-way ANOVA, siRNA effect, p < 0.001).