Protein misfolding and aggregation characterizes the development of a number of neurodegenerative diseases, such as Parkinson’s, Alzheimer’s and Huntington’s disease. The hallmark of Parkinson’s disease is the formation of proteinaceous inclusions, which consist primarily of α-synuclein (α-syn), a natively unstructured protein with propensity to misfold and aggregate. Cells have evolved sophisticated systems of protein quality control to prevent accumulation of non-native proteins and maintain protein homeostasis. However, the load of misfolded α-syn typically exceeds the capacity of the quality control system. Aberrant accumulation of misfolded α-syn leads to proteotoxic stress, eventually resulting in neurodegeneration.
The objective of this project is to investigate chemical and genetic approaches to modulate the protein quality control system and reduce the accumulation of aberrant α-syn species. Studying α-syn aggregation in cells presents a number of challenges mainly due to the limited availability of tools to quantitatively distinguish between different α-syn conformational species within the cellular environment. To address this need, we engineered an in vitro model system based on neuroglioma cells that accumulate α-syn aggregates and developed a set of analytical tools based on the use of aggregation responsive probes to quantify α-syn aggregation in cells. To test whether modulating the protein quality control system affects the accumulation of α-syn aggregates, we investigated a series of complementary approaches aimed at i) enhancing the innate cellular chaperone machinery, which promotes folding and prevents aggregation, and ii) upregulating the autophagy pathway, which mediates clearance of aggregated proteins. We demonstrated that chemical modulation of Hsp70, a ubiquitously expressed molecular chaperone, affects the accumulation of α-syn aggregates. Particularly, the Hsp70 upregulator carbenoxolone was found to reduce α-syn aggregation and prevent α-syn-induced cytotoxicity via activation of the heat shock response. We also found that activation of the transcription factor EB (TFEB), a master regulator of the autophagy-lysosomal pathway, results in enhanced autophagic clearance of α-syn aggregates. We demonstrated that cell treatment with 2-hydroxypropyl-β-cyclodextrin reduces the accumulation of aggregated α-syn specifically by upregulating TFEB-mediated autophagic clearance. These findings lay the foundation for the development of pharmacological strategies to reduce the accumulation of misfolded and aggregated α-syn for the treatment of Parkinson’s disease.