Parkinson's disease (PD) is one of the most common progressive neurodegenerative disorders, characterized by resting tremor, rigidity, bradykinesia, and postural instability. These symptoms are associated with massive loss of tyrosine hydroxylase-positive neurons in the substantia nigra (SN) causing an estimated 70-80% depletion of dopamine (DA) in the striatum, where their projections are located. Although the etiology of PD is unknown, mitochondrial dysfunctions have been associated with the disease pathophysiology. We used a mouse model expressing a mitochondria-targeted restriction enzyme, PstI or mito-PstI, to damage mitochondrial DNA (mtDNA) in dopaminergic neurons. The expression of mito-PstI induces double-strand breaks in the mtDNA, leading to an oxidative phosphorylation deficiency, mostly due to mtDNA depletion. Taking advantage of a dopamine transporter (DAT) promoter-driven tetracycline transactivator protein (tTA), we expressed mito-PstI exclusively in dopaminergic neurons, creating a novel PD transgenic mouse model (PD-mito-PstI mouse). These mice recapitulate most of the major features of PD: they have a motor phenotype that is reversible with L-DOPA treatment, a progressive neurodegeneration of the SN dopaminergic population, and striatal DA depletion. Our results also showed that behavioral phenotypes in PD-mito-PstI mice were associated with striatal dysfunctions preceding SN loss of tyrosine hydroxylase-positive neurons and that other neurotransmitter systems [noradrenaline (NE) and serotonin (5-HT)] were increased after the disruption of DA neurons, potentially as a compensatory mechanism. This transgenic mouse model provides a novel model to study the role of mitochondrial defects in the axonal projections of the striatum in the pathophysiology of PD.
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