Objective/Rationale:
A characteristic feature of Parkinson’s disease (PD) is the buildup of the protein, alpha-synuclein, and overproduction of this protein can trigger PD. Therefore, it is important to understand the mechanisms that degrade alpha-synuclein in neurons and prevent its accumulation normally. Dr. Goldberg’s lab has identified an enzyme that targets alpha-synuclein for rapid degradation. The goal of this study is to prove that it helps protect against PD and to learn more about its regulation in normal and diseased brains. It’s a member of the well-studied family of ubiquitin ligases, which attach a chain of proteins and target them for destruction by the proteasome or the lysosome. Their evidence shows that this enzyme may help protect yeast from toxic effects of alpha-synuclein.
Project Description:
We have identified an enzyme that attaches a tag to alpha-synuclein that targets them to the proteasome for destruction. We shall carry out biochemical studies 1) of the pure enzyme to learn how it recognizes and modifies alpha-synuclein, 2) with neurons in culture to see if raising their content of this enzyme protects them against alpha-synuclein or if lowering its level enhances their sensitivity, 3) in rat and human brain to localize this enzymes and learn how its content changes in PD.
Relevance to Diagnosis/Treatment of Parkinson’s Disease:
These recent discoveries emphasize the importance of obtaining further information about how this enzyme recognizes alpha-synuclein and targets it for degradation and how important this enzyme is in showing the onset and progression of Parkinson’s disease. If further work supports these promising findings, then we would undertake a search for agents that induce or activate this enzyme.
Anticipated Outcome:
These studies should yield valuable insights concerning the mechanisms that determine the onset and progression of PD. Specifically they should clarify what determines the brain’s content of alpha-synuclein, a critical factor in the development of PD. Moreover, by clarifying how alpha-syncuclein is destroyed in different regions of the brain and how this process may protect cells, these studies may lay the basis for the development of novel therapies that enhance degradation of this potentially toxic protein.
Final Outcome
We have shown that the enzyme Nedd4 (a ubiquitin ligase) catalyzes alpha-synuclein ubiquitination (attachment of ubiquitin molecules) and the degradation of alpha-synuclein by lysosomes. In yeast models of PD, disruption of the Nedd4 gene, Rsp5p, decreased alpha-synuclein degradation and enhanced the formation of alpha-synuclein aggregates and toxicity. In human dopaminergic cells, Nedd4 overexpression enhanced alpha-synuclein clearance via lysosomes, while Nedd4 down-regulation increased alpha-synuclein content. Thus Nedd4 appears to target alpha-synuclein to the lysosomal pathway, reducing alpha-synuclein content, which may help protect against the pathogenesis of PD and other alpha-synucleinpathies.