Comparative analyses of alpha-synuclein expression levels in rat brain tissues and transfected cells

alpha-Synuclein may have a role in the genesis of Parkinson's disease (PD) and other neurodegenerative diseases, and overexpression of alpha-synuclein in endogenously expressing systems and transfected cell lines has been linked to its cytotoxicity. Because there is no definition of what constitutes normal or high expression levels of alpha-synuclein, the current studies were undertaken. Protein levels of alpha-synuclein, and its binding partner, the dopamine transporter (DAT), were examined and semi-quantified in different rat brain regions and compared to the amounts of alpha-synuclein expressed in Ltk(-) cells after transfection with known amounts of DNA. Of the regions tested, alpha-synuclein expression was lowest in dopamine-producing brain areas, substantia nigra and ventral tegmental area; conversely, the expression of DAT was the highest in these tissues. Areas that do not normally degenerate in PD, such as cerebellum, nucleus accumbens and thalamus, expressed the highest levels of alpha-synuclein and very low DAT. Expression of DAT and alpha-synuclein to levels similar to those observed in rat substantia nigra were obtained after transfection of Ltk(-) cells with 1-2 microg each of alpha-synuclein and DAT DNAs, indicating that such transfection conditions produce normal expression levels of these proteins.