Mutations in the parkin gene are the major cause of early-onset familial Parkinson's disease (PD). We previously reported the generation and analysis of a knockout mouse carrying a deletion of exon 3 in the parkin gene. F1 hybrid pa+/- mice were backcrossed to wild-type C57Bl/6 for three more generations to establish a pa-/-(F4) mouse line. The appearance of tyrosine hydroxylase-positive neurons was normal in young and aged pa-/- (F4) animals. Loss of parkin function in mice did not enhance vulnerability of dopaminergic neurons to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxicity. However, the pa-/- (F4) mice displayed impaired exploration and habituation to a new environment and exhibited thigmotaxis behaviour in the open field and Morris water maze. Abnormal anxiety-related behaviour of pa-/- (F4) mice was also observed in the light/dark exploration test paradigm. Dopamine metabolism was enhanced in the striatum of pa-/- (F4) mice, as revealed by increased homovanillic acid (HVA) content and a reduced ratio of dihydroxyphenylacetic acid (DOPAC)/HVA. The alterations found in the dopaminergic system could be responsible for the behavioural impairments of pa-/- (F4) mice. Consistent with a recent observation of cognitive dysfunction in parkin-linked patients with PD, our findings provide evidence of a physiological role of parkin in non-motor behaviour, possibly representing a disease stage that precedes dopaminergic neuron loss.
Parkinson's disease (PD) is a common neurodegenerative disorder, characterized by the progressive loss of dopaminergic neurons in the substantia nigra. Although valuable animal models have been developed, our knowledge of the aetiology and pathogenic factors implicated in PD is still insufficient to develop causal therapeutic strategies aimed at halting its progression. The neurotoxicity induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is one of the most valuable models for analysing pathological aspects of PD. In this paper we studied the gene expression patterns underlying the pathogenesis of MPTP-induced neurodegeneration. We treated young and old C57BL/6 mice with different schedules of MPTP to induce degenerative processes that vary in intensity and time-course. During the first week after intoxication we used nonradioactive in situ-hybridization to investigate the expression patterns of genes associated with (i) dopamine metabolism and signalling; (ii) familial forms of PD; (iii) protein folding and (iv) energy metabolism. MPTP injections induced different severities of neuronal injury depending on the age of the animals and the schedule of administration as well as a significant degeneration in the striatum. In situ hybridization showed that MPTP intoxication initiated a number of gene expression changes that (i) were restricted to the neurons of the substantia nigra pars compacta; (ii) were correlated in intensity and number of changes with the age of the animals and the severity of histopathological disturbances; (iii) displayed in each a significant down-regulation by the end of one week after the last MPTP injection, but (iv) varied within one MPTP regimen in expression levels during the observation period. The subacute injection of MPTP into one-year-old mice induced the most severe changes in gene expression. All genes investigated were affected. However, alpha-synuclein was the only gene that was exclusively up-regulated in MPTP-treated animals displaying cell death.
Two missense mutations (A53T and A30P) in the gene encoding the presynaptic protein α-synuclein (asyn) are associated with rare, dominantly inherited forms of Parkinson’s disease (PD) and its accumulation in Lewy bodies and Lewy neurites. As an initial step in investigating the role of asyn in the pathogenesis of PD, we have generated C57BL/6 transgenic mice overexpressing the doubly mutated human asyn under the control of three different promoters; the chicken β-actin (chβactin), the mouse tyrosine hydroxylase 9.6 kb (msTH) and the mouse prion protein (msprp). In this study we compared the regional and cellular expression pattern of the transgenic protein in the brain and peripheral organs of various transgenic mouse lines. Western blot analysis and immunohistochemistry consistently showed that all three promoters successfully drive the expression of the transgene. The msprp promoter was found to give the highest level of transgene expression. All promoters directed the expression into the brain and specific neuron types. However, the promoters differed with respect to (i) the expression pattern in peripheral organs, (ii) the number and (iii) the regional distribution of expressing cells in the brain. Furthermore, remarkable line-to-line variation of expression patterns was observed in mouse lines carrying the same construct. Future studies will analyze how the variations in transgene expression affect the pathogenesis in the animals.
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