Disease-oriented Genome Networks Diseases of the Nervous System Network: Systematic Gene Identification and Functional Analyses in Common CNS Disorders Project: Functional Analyses in Genetic Mouse Model of Parkinson’s Disease

Introduction In 1997, based on linkage analyses of Italian and Greek families, alpha-synuclein was identified first as a gene involved in the pathogenesis of autosomal-dominantly inherited, early-onset Parkinson’s disease (PD). A nucleotide transition at position 209 from guanosine to adenosine (G209A), resulting in an alanine to threonine substitution at position 53 (A53T) on the amino acid level [1], is causal for the disease. The physiological function of alpha-synuclein is still poorly understood, but seems to relate to lipid and vesicle control in the presynaptic compartment according to preliminary evidence [2, 3]. On the molecular and cellular level, diagnostic hallmarks of both autosomal-dominant and sporadic PD are protein aggregates called Lewy bodies and neurites, which contain alpha-synuclein as main component [4]. Crucial pathogenetic events of PD appear to include the ubiquitination and aggregation of alpha-synuclein on the molecular level, consequent oxidative stress / dysfunction / degeneration of dopaminergic neurons in the substantia nigra on the cellular level, resulting in clinical deficits such as slowed movements and muscular rigidity in the organism [5]. Our investigations focus on the A53T-alpha-synuclein mutation. Three alpha-synuclein mouse mutants are employed, where an alteration of striatal dopamine steadystate levels was observed at old age a typical finding of PD (unpublished). In the transgenic mouse lines PrPmtA and PrPmtB, human A53T-alpha-synuclein is expressed under the control of the neuronal prion promoter. While no aggregates of alphasynuclein are detectable in both transgenic lines, there is progressive reduction of spontaneous movement [6]. In addition, striatal dopamine levels are elevated in PrPmtA as well as in PrPmtB by the age of 18 months (unpublished). The Snca -/mouse line with a knock-out of alpha-synuclein shows a progressive reduction of spontaneous movement, too (unpublished). Opposite to the observations in the employed transgenic mouse lines PrPmtA and PrPmtB, Snca -/mice exhibit reduced striatal dopamine steady state levels at the age of 15 months (unpublished). Taken together, a direct influence of the alpha-synuclein dosage on dopamine neurotransmission at old age has been observed by us, in both transgenic PrPmtA and PrPmtB mouse lines as well as in Snca -/mice, without concomitant loss of neurons or alpha-synuclein aggregates. This selective dysfunction is clearly reminiscent of human PD criteria. The striatal dopamine alteration in the mouse mutants may serve as biomarker at early disease stages where experimental preventive therapies may have the best chance of success. By crossing the transgenic PrPmtA line with the Snca -/line, the double mutant mouse line -/-A53T was generated. These mice have only the pathogenic human A53T-alpha-synuclein and lack the murine wildtype alpha-synuclein. -/-A53T mice display a progressive paralysis with reduced survival rate. In addition, alpha-synuclein aggregates can be detected in the sciatic nerve / spinal cord with Wallerian axon degeneration [7]. In the hope to understand the mechanisms of PD, we want to investigate pathogenic and compensatory effects of the A53T-alpha-synuclein mutation, both by systematic surveys of the transcriptome and proteome, and assays for known biochemical and behavioural markers of the human disease. At different ages – at least at 6 months and 18 months, prior to and after the onset of the alpha-synuclein mutation-related phenotype – markers of dopamine homeostasis, Lewy body formation and oxidative stress will be investigated in comparison between the four mentioned alpha-synuclein mouse mutants and their wildtype littermates.