A major known risk factor in Parkinson’s disease is the misfolding, aggregation and abnormal accumulation of the protein alpha-synuclein. The goal of the proposed work is to pursue efforts in drug discovery using the molecular events associated with alpha-synuclein cytotoxicity and aggregation as a target. We recently discovered that pharmacological inhibition of SIRT2 deacetylase activity modulates alpha-synuclein aggregation and reduces its cytotoxicity. As a subsequent step in the drug discovery process, SIRT2 deacetylase must be further validated as a useful therapeutic target for Parkinson’s disease.
To assess the therapeutic potential of SIRT2 inhibition we will employ a powerful genetic approach, based on RNA interference. Using the phenomenon of RNA interference, which specifically silences gene expression, we expect to confirm the efficacy of selective SIRT2 inhibition in Parkinson’s disease models. Alpha-synuclein, when overexpressed in human cells, causes cell toxicity which is associated with the formation of protein inclusions. We propose to design specific SIRT2 RNA-targeting constructs and use modern viral delivery systems to inoculate cells and primary dopamine-positive neurons and investigate the protective effects against alpha-synuclein toxicity and aggregation. Using the same approach we propose to determine the efficacy of SIRT2 silencing in primary dopaminergic neurons, which are affected in Parkinson’s disease. Expression of mutant alpha-synuclein or treatment with MPP+ causes cell-death of those dopamine positive neurons. We expect to rescue the dying neurons by silencing SIRT2 expression.
Relevance to Diagnosis/Treatment of Parkinson’s Disease:
We previously identified a lead-series of small molecule SIRT2 inhibitors, representing eight structurally diverse scaffolds. Upon genetic validation of SIRT2 target, we plan to optimize the compound potencies and drug like properties and test the candidates in efficacy trials, using alpha-synuclein rodent models of Parkinson’s disease. The efficacious molecules, emerging from the animal trials, will be subjected for further medicinal chemistry optimization to expedite the development of pre-clinical candidates and conducting phase I human trials.
We expect to confirm our preliminary results suggesting potential therapeutic benefits of inhibition of SIRT2 activity in Parkinson’s disease models. The proposed approach provides justification for future orchestrated efforts for the development of therapeutics based on small molecule SIRT2 inhibitors. The proposed line of investigation might lead to the identification of new therapeutic targets or provide clues about alpha-synuclein-dependent mechanism(s) of neurodegeneration. Lastly, the relationship between sirtuin proteins (SIRT1, SIRT2, SIRT3), implicated in aging and neurodegenerative processes will be assessed.
The researchers showed that SIRT2 inhibition was modestly protective in a cell culture model of alpha-synuclein toxicity. However, they also unexpectedly saw modulated expression levels of other sirtuins -- possibly cell compensatory responses. The SIRT2-dependent changes to SIRT1 and SIRT3 expression levels may contribute negatively or positively to toxicity read-out, and remain to be elucidated. Thus, the results from the selected RNAi target-validation approach was not conclusive, but in general supported previous observations on efficacy of SIRT2 inhibition in PD models.