Abstract
Parkinson's disease (PD) pathology is characterized by the formation of intra-neuronal inclusions called Lewy bodies, which are comprised of alpha-synuclein (α-syn). Duplication, triplication or genetic mutations in α-syn (A53T, A30P and E46K) are linked to autosomal dominant PD; thus implicating its role in the pathogenesis of PD. In both PD patients and mouse models, there is increasing evidence that neuronal dysfunction occurs before the accumulation of protein aggregates (i.e., α-syn) and neurodegeneration. Characterization of the timing and nature of symptomatic dysfunction is important for understanding the impact of α-syn on disease progression. Furthermore, this knowledge is essential for identifying pathways and molecular targets for therapeutic intervention. To this end, we examined various functional and morphological endpoints in the transgenic mouse model expressing the human A53T α-syn variant directed by the mouse prion promoter at specific ages relating to disease progression (2, 6 and 12 months of age). Our findings indicate A53T mice develop fine, sensorimotor, and synaptic deficits before the onset of age-related gross motor and cognitive dysfunction. Results from open field and rotarod tests show A53T mice develop age-dependent changes in locomotor activity and reduced anxiety-like behavior. Additionally, digigait analysis shows these mice develop an abnormal gait by 12 months of age. A53T mice also exhibit spatial memory deficits at 6 and 12 months, as demonstrated by Y-maze performance. In contrast to gross motor and cognitive changes, A53T mice display significant impairments in fine- and sensorimotor tasks such as grooming, nest building and acoustic startle as early as 1–2 months of age. These mice also show significant abnormalities in basal synaptic transmission, paired-pulse facilitation and long-term depression (LTD). Combined, these data indicate the A53T model exhibits early- and late-onset behavioral and synaptic impairments similar to PD patients and may provide useful endpoints for assessing novel therapeutic interventions for PD.
Highlights
Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized pathologically by the loss of dopamine neurons in the substantia nigra and the formation of intraneuronal inclusions called Lewy bodies, which are mainly comprised of alpha-synuclein (a-syn) [1]. a-syn is a small 140 amino acid protein that is ubiquitously expressed in brain, but concentrated primarily in presynaptic vesicles [2]
Previous studies have shown that duplication [5], triplication [6] or missense mutations (A53T [7], A30P [8] and E46K [9]) in the a-syn gene are linked to autosomal dominant PD; implicating its role in the pathogenesis of PD
The human A53T mouse model studied here has been previously characterized in the context of a-syn accumulation and aggregation [13,14,23,32]; the course of age-related phenotypic deficits has not been characterized in detail
Summary
Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized pathologically by the loss of dopamine neurons in the substantia nigra and the formation of intraneuronal inclusions called Lewy bodies, which are mainly comprised of alpha-synuclein (a-syn) [1]. a-syn is a small 140 amino acid (aa) protein that is ubiquitously expressed in brain, but concentrated primarily in presynaptic vesicles [2]. Previous studies show significant behavioral and synaptic impairment in mice over-expressing wild type [18,19,20] or mutant a-syn [13,14,21,22,23]; a majority of these studies evaluate behavioral function at a finite time point, usually late in the course of disease when behavioral alterations are apparent These studies help to further our understanding of how over-expressed or mutant a-syn can alter normal behavior and synaptic plasticity in animal models of PD, they do not fully characterize the onset or extent of symptoms that develop as the disease progresses. It is important to thoroughly examine the extent of symptoms within a-syn animal models as phenotypic changes that occur prior to the onset of motor dysfunction may increase our understanding of the role a-syn plays in the disease process and provide useful endophenotypes and biomarkers to assess potential disease-modifying therapies
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