Objective/Rationale:
Recent studies indicate that degenerative changes seen in Parkinson´s disease (PD) may be linked to impairments in the cells´ ability to degrade toxic proteins, such as misfolded alpha-synuclein, by the so-called autophagy-lysosome pathway. Defective lysosome function has been shown to result in impaired clearance of alpha-synuclein and accumulation of alpha-synuclein aggregates, suggesting that methods aimed at enhancing lysosomal function is an interesting therapeutic strategy. The purpose of this project is to develop a gene transfer approach to boost lysosomal function and protect the affected dopamine neurons from alpha-synuclein-induced toxicity.
Project Description:
Transcription factor EB (TFEB) is a master regulator of the autophagy-lysosome pathway, and its associated micro-RNA, miR-128, the action of which has been identified as diminishing TFEB activity. The aim of our project is to investigate if enhancement of TFEB activity, obtained either by overexpression of TFEB or by blockade of miR-128, has the potential to prevent and reverse alpha-synuclein-induced toxicity.
The studies will be performed in the pre-clinical AAV-alpha-synuclein model, where human alpha-synuclein is overexpressed in midbrain dopamine neurons. In this model, alpha-synuclein overexpression is accompanied by extensive neuropathological changes, including alpha-synuclein aggregates, axonal damage, and cell death, that develops progressively over the first 2 months after vector injection. This provides excellent opportunities to monitor changes in alpha-synuclein toxicity induced by altered expression of TFEB.
Relevance to Diagnosis/Treatment of Parkinson’s Disease:
Studies of brains from PD patients have shown a reduction of markers related to protein degradation in surviving nigral dopamine neurons, most pronounced in neurons containing alpha-synuclein inclusions. Similar impairments in the autophagy-lysosome pathway have been observed in alpha-synuclein overexpressing dopamine neurons in the AAV-alpha-synuclein model used in the present study. Taken together, these experimental and clinical data suggest that methods aimed at enhancing lysosomal function may provide an interesting therapeutic strategy for PD.
Anticipated Outcome:
TFEB may be an ideal target for neuroprotection in PD. Enhancement of lysosomal function by TFEB has previously been shown to block protein aggregation in cells expressing mutated huntingtin. If similar effects can be obtained by TFEB upregulation also in the AAV-alpha-synuclein model used here, this will provide further support for the central role of impaired autophagy-lysosome function in PD and open up for an interesting new disease-modifying therapeutic strategy based on miR-128 silencing. The AAV-sponge vector developed here may be an ideal tool for this purpose.
Final Outcome
Alpha-synuclein aggregation is a key pathological event that leads to the loss of nigral dopamine neurons in PD. We hypothesized that stimulation of alpha-synuclein clearance through the autophagy-lysosomal pathway may provide a protection to nigral neurons in the AAV-alpha-synuclein rat model of PD. We found that, in the early phase of neuronal degeneration, alpha-synuclein interferes with the autophagy pathway by impairing the function of the key transcription factor TFEB. In addition, examination of post-mortem midbrain tissue from PD and control patients revealed changes in TFEB expression in nigral dopaminergic neurons. Genetic or pharmacological activation of TFEB provided robust protection and disease modifying effect of against alpha-synuclein toxicity. Conversely, overexpression of miR-128 resulted in the increased vulnerability of nigral and VTA dopamine neurons to alpha-synuclein toxicity. The study provides compelling evidence that stimulation of autophagy may represent an interesting therapeutic approach in PD.