All ETDs from UAB

Advisory Committee Chair

Jianhua Zhang

Advisory Committee Members

Steven Carroll

Kevin A Roth

David G Standaert

Aimee Landar

Document Type

Dissertation

Date of Award

2012

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Parkinson's disease (PD) is the most commonly occurring neurodegenerative movement disorder, and aberrant accumulation of the protein α-synuclein is thought to be a major contributing factor in disease development. Dysfunction of the autophagy lysosome pathway (ALP) has been implicated in PD pathogenesis. Our lab and others have shown that the lysosomal enzyme cathepsin D (CD) is an important regulator of α-synuclein degradation. The primary focus of this thesis is probing the structure/function dynamic that exists between α-synuclein and CD. We have found that lentiviral-mediated over expression of wild type CD (wtCD) leads to subtle alterations in the ALP in a dopaminergic cell line. Surprisingly, over expression of a catalytically dead mutant CD (mtCD) led to significant accumulation of endogenous α-synuclein, despite up regulation of another lysosomal enzyme cathepsin B (CB). We demonstrated that endogenous CD activity was significantly reduced in response to over expression of mtCD, revealing one mechanism for mtCD's effect on endogenous α-synuclein levels. We have also shown that pharmacologic inhibition of CD with pepstatin A (PepA) led to increases in α-synuclein, though not the same extent as mtCD over expression. However, CD inhibition with PepA did result in significant increases in CB activity, suggesting that CB activity increases as a response to inhibition of CD. These iii studies provide evidence that perturbations of CD function may promote the development of synucleinopathy. After our lab showed that CD null mice exhibited dramatic α-synuclein aggregation in several brain regions, we examined whether CD haploinsufficient mice exhibit differential sensitivity to the dopaminergic toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a PD model which is dependent upon the presence of α-synuclein. There were no differences in neurotoxicity between CD wild type and mutant mice after MPTP administration. However, CD heterozygous mice have significantly higher levels of the monoamine dopamine (DA) and its metabolites, a phenomenon which is abolished by MPTP treatment. These data imply that elevated monoamine content does not convey protection from dopaminergic insults.

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