Elevated α-synuclein mRNA levels in individual UV-laser-microdissected dopaminergic substantia nigra neurons in idiopathic Parkinson's disease

The presynaptic protein alpha-synuclein is involved in several neurodegenerative diseases, including Parkinsons disease (PD). In rare familial forms of PD, causal mutations (PARK1) as well as multiplications (PARK4) of the -synuclein gene have been identified. In sporadic, idiopathic PD, abnormal accumulation and deposition of alpha-synuclein might also cause degeneration of dopaminergic midbrain neurons, the clinically most relevant neuronal population in PD. Thus, cell-specific quantification of alpha-synuclein expression-levels in dopaminergic neurons from idiopathic PD patients in comparison to controls would provide essential information about contributions of alpha-synuclein to the etiology of PD. However, a number of previous studies addressing this question at the tissue-level yielded varying results regarding alpha-synuclein expression. To increase specificity, we developed a cell-specific approach for mRNA quantification that also took into account the important issue of variable RNA integrities of the individual human postmortem brain samples. We demonstrate that PCR amplicon size can confound quantitative gene-expression analysis, in particular of partly degraded RNA. By combining optimized UV-laser microdissection- and quantitative RTPCR-techniques with suitable PCR assays, we detected significantly elevated alpha-synuclein mRNA levels in individual, surviving neuromelanin- and tyrosine hydroxylase-positive substantia nigra dopaminergic neurons from idiopathic PD brains compared to controls. These results strengthen the pathophysiologic role of transcriptional dysregulation of the alpha-synuclein gene in sporadic PD.