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Characterisation of the new Vps35 p.D620N KI mouse model of Parkinson's disease Cataldi, Stefano


Vacuolar protein sorting 35 (VPS35) is a core component of the retromer trimer required for endosomal membrane-associated protein trafficking. The discovery of a missense mutation, Vps35 p.D620N, implicates retromer dysfunction in the pathogenesis of Parkinson’s disease (PD). Our group have generated and characterized a knock-in mouse with a Vps35 p.D620N substitution (herein referred to as VKI) from 3 to 18 months of age. Stereological counting of tyrosine hydroxylase (TH)-positive nigral neurons was comparable between mutant and wild-type animals. Quantification of extracellular dopamine by striatal microdialysis of freely moving animals, and high performance liquid chromatography, was comparable across genotypes at all ages. However, dopamine metabolites appear increased in young VKI mice, suggesting increase dopamine turnover. Assessment of nigrostriatal function by ex-vivo fast scan cyclic voltammetry (FSCV) revealed an increase in dopamine release in brain slices from 3-month-old VKI, and a reduction in older animals. Western blot analysis of VKI striata revealed increased in the vesicular monoamine transporter 2 (VMAT2), and decreased in dopamine transporter (DAT) levels, at 3 and 18 months of age. These results were supported by confocal imaging of the dorsolateral striatum, showing an increase in the size of VMAT2-positive synaptic structures, and a significant loss of DAT cluster density in VKI mice. Standardized behavioural testing failed to observe overt movement disorder. Cognitive evaluation showed altered exploratory behaviour and perseveration in both young and old VKI animals. These alterations in dopaminergic activity and behaviour are reminiscent of prodromal PD. Together these results implicate retromer in dopaminergic function and early PD stage symptoms and provide a molecular mechanism for dopamine dysregulation in VPS35 p.D620N parkinsonism.

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