Polyethylenimine Nanoparticle-Mediated siRNA Delivery to Reduce α-Synuclein Expression in a Model of Parkinson's Disease.

RNA interference (RNAi)-based strategies that mediate the specific knockdown of target genes by administration of small interfering RNAs (siRNAs) could be applied for treatment of presently incurable neurodegenerative diseases such as Parkinson's disease. However, inefficient delivery of siRNA into neurons hampers in vivo application of RNAi. We have previously established the 4-12 kDa branched polyethylenimine (PEI) F25-LMW with superior transfection efficacy for delivery of siRNA in vivo. Here, we present that siRNA complexed with this PEI extensively distributes across the CNS down to the lumbar spinal cord after a single intracerebroventricular infusion. siRNA against α-synuclein (SNCA), a pre-synaptic protein that aggregates in Parkinson's disease, was complexed with PEI F25-LMW and injected into the lateral ventricle of mice overexpressing human wild-type SNCA (Thy1-aSyn mice). Five days after the single injection of 0.75 μg PEI/siRNA, SNCA mRNA expression in the striatum was reduced by 65%, accompanied by reduction of SNCA protein by ∼50%. Mice did not show signs of toxicity or adverse effects. Moreover, ependymocytes and brain parenchyma were completely preserved and free of immune cell invasion, astrogliosis, or microglial activation. Our results support the efficacy and safety of PEI nanoparticle-mediated delivery of siRNA to the brain for therapeutic intervention.