Identification of Allele-Specific RNAi Effectors Targeting Genetic Forms of Parkinson's Disease

Parkinson's disease (PD) is a progressive neurological disorder affecting an estimated 5–10 million people worldwide. Recent evidence has implicated several genes that directly cause or increase susceptibility to PD. As well as advancing understanding of the genetic aetiology of PD these findings suggest new ways to modify the disease course, in some cases through genetic manipulation. Here we generated a ‘walk-through’ series of RNA Pol III-expressed shRNAs targeting both the α-synuclein A30P and LRRK2 G2019S PD-associated mutations. Allele-specific discrimination of the α-synuclein A30P mutation was achieved with alignments at position 10, 13 and 14 in two model systems, including a heterozygous model mimicking the disease setting, whilst 5′RACE was used to confirm stated alignments. Discrimination of the most common PD-linked LRRK2 G2019S mutation was assessed in hemizygous dual-luciferase assays and showed that alignment of the mutation opposite position 4 of the antisense species produced robust discrimination of alleles at all time points studied. Discrimination at this position was subsequently confirmed using siRNAs, where up to 10-fold discrimination was seen. The results suggest that RNAi-mediated silencing of PD-associated autosomal dominant genes could be a novel therapeutic approach for the treatment of the relevant clinical cases of PD in future

Resistance to MPTP-Neurotoxicity in α-Synuclein Knockout Mice Is Complemented by Human α-Synuclein and Associated with Increased β-Synuclein and Akt Activation

Genetic and biochemical abnormalities of α-synuclein are associated with the pathogenesis of Parkinson's disease. In the present study we investigated the in vivo interaction of mouse and human α-synuclein with the potent parkinsonian neurotoxin, MPTP. We find that while lack of mouse α-synuclein in mice is associated with reduced vulnerability to MPTP, increased levels of human α-synuclein expression is not associated with obvious changes in the vulnerability of dopaminergic neurons to MPTP. However, expressing human α-synuclein variants (human wild type or A53T) in the α-synuclein null mice completely restores the vulnerability of nigral dopaminergic neurons to MPTP. These results indicate that human α-synuclein can functionally replace mouse α-synuclein in regard to vulnerability of dopaminergic neurons to MPTP-toxicity. Significantly, α-synuclein null mice and wild type mice were equally sensitive to neurodegeneration induced by 2′NH2-MPTP, a MPTP analog that is selective for serotoninergic and noradrenergic neurons. These results suggest that effects of α-synuclein on MPTP like compounds are selective for nigral dopaminergic neurons. Immunoblot analysis of β-synuclein and Akt levels in the mice reveals selective increases in β-synuclein and phosphorylated Akt levels in ventral midbrain, but not in other brain regions, of α-synuclein null mice, implicating the α-synuclein-level dependent regulation of β-synuclein expression in modulation of MPTP-toxicity by α-synuclein. Together these findings provide new mechanistic insights on the role α-synuclein in modulating neurodegenerative phenotypes by regulation of Akt-mediated cell survival signaling in vivo