Abstract
alpha-Synuclein (alpha-syn) is a small protein of unknown function that is found aggregated in Lewy bodies, the histopathological hallmark of sporadic Parkinson disease and other synucleinopathies. Mutations in the alpha-syn gene and a triplication of its gene locus have been identified in early onset familial Parkinson disease. alpha-Syn turnover can be mediated by the proteasome pathway. A survey of published data may lead to the suggestion that overexpression of alpha-syn wild type, and/or their variants (A53T and A30P), may produce a decrease in proteasome activity and function, contributing to alpha-syn aggregation. To investigate the relationship between synuclein expression and proteasome function we have studied proteasome peptidase activities and proteasome subunit expression (alpha, beta-constitutive, and inducible) in mice either lacking alpha-syn (knock-out mice) or transgenic for human alpha-syn A30P (under control of PrP promoter, at a time when no clear gliosis can be observed). Similar studies are presented in PC12 cells overexpressing enhanced yellow fluorescent protein fusion constructs of human wild type, A30P, and A53T alpha-syn. In these cell lines we have also analyzed the assembly of 20 S proteasome complex and the degradation rate of a well known substrate of the proteasome pathway, Ikappabalpha. Overall the data obtained led us to the conclusion that alpha-synuclein expression levels by themselves have no significant effect on proteasome peptidase activity, subunit expression, and proteasome complex assembly and function. These results strengthen the suggestion that other mechanisms resulting in synuclein aggregation (not simply expression levels) may be the key to understand the possible effect of aggregated synuclein on proteasome function.
Highlights
Idiopathic Parkinson disease (PD),1 dementia with Lewy bodies, a Lewy body variant of Alzheimer’s disease, and multiple system atrophy are characterized pathologically by proteinaceous inclusions commonly referred to as Lewy pathology in postmortem brain tissue samples [1, 2]
Proteasome Activity and Expression in PC12 Cells and Stable PC12 Transfectants with EYFP, EYFPsyn wt, EYFPsyn A30P, and EYFPsyn A53T— we investigated proteasome peptidase activities and subunit expression in PC12 cell lines transfected with EYFP-␣-synucleins and their respective controls
In the present work we have evaluated the hypothesis that ␣-synuclein expression levels may alter proteasome activity and function
Summary
Idiopathic Parkinson disease (PD), dementia with Lewy bodies, a Lewy body variant of Alzheimer’s disease, and multiple system atrophy are characterized pathologically by proteinaceous inclusions commonly referred to as Lewy pathology in postmortem brain tissue samples [1, 2]. Supporting the above conclusion several reports have described that proteasome inhibitors promote ␣-syn aggregation in neurons (14 –16), neuronal-like cell lines [12, 17,18,19], and nonneuronal cell lines [20, 21] These results by themselves are not unexpected, as many different pathogenic proteins aggregate when they are overexpressed in cells as a consequence of proteasome inhibition (see for example Ref. 22). Other authors have found no change of proteasome peptidase activity in human brain regions with dementia with Lewy bodies pathology [26] Another line of circumstantial evidence is the report by several groups that synuclein overexpression produces a decrease of proteasome peptidase activity when assayed in crude extracts obtained from stably transfected cell lines [17, 19, 27], and in. The data obtained clearly suggest that synuclein expression levels by themselves have no significant effect on proteasome expression and function
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