Objective: To explore the therapeutic potential of LRRK2 kinase inhibitors in a Vps35 p.D620N mouse model of Parkinsonsim.

Background: The discovery of a missense mutation, Vps35 p.D620N implicates retromer, an endosomal membrane-associated protein trafficking complex, in the pathogenesis of Parkinson’s disease (PD). Our previous work characterizing a novel Vps35 p.D620N knock-in (VKI) mouse revealed increased dopamine release in VKI striatal slices and increased dopamine turnover in VKI homozygous mice. Biochemical and imaging analysis revealed a genotype-dependent decreases in dopamine transporter (DAT) along with an increase in vesicular monoamine transporter 2 (VMAT2), suggestive of profound alterations to dopaminergic pre-synaptic terminals in VKI mice. Most recently, biochemical evidence suggests a membrane bound macromolecular complex comprised of LRRK2 and retromer and increased LRRK2 kinase activity in Vps35 p.D620N mice.

Method: WT and heterozygous VKI mice are injected once daily for a total of 7 days with 10mg/kg of the commercially available LRRK2 kinase inhibitor, MLi-2, or vehicle control. One hour after the final injection, mice are sacrificed and processed for fast scan cyclic voltammetry, biochemical or immunhistochemical analysis.

Results: Heterozygous VKI mice that receive the LRRK2 kinase inhibitor MLi-2 show a rescue of increased dopamine release when compared to genotype and age-matched littermates that were given vehicle control. No difference in the levels of evoked dopamine release is observed in WT mice following MLi-2 administration. In addition, the previously reported impairment in dopamine re-uptake observed in VKI mice is corrected following MLi-2 treatment, suggesting a re-population of synaptic machinery needed for dopamine clearance. Western blot analysis of striatal tissue subjected to sucrose-based fractionation are being explored to investigate  the total level along with the synaptic enriched population of dopamine transporter (DAT), vesicular monoamine transporter 2 (VMAT2), Tyrosine hydroxylase (TH), alpha-synuclien and retromer subunits in WT and VKI following drug MLi-2 or vehicle control are ongoing.

Conclusion: LRRK2 kinase inhibitors correct synaptic phenotypes induced by Vps35 p.D620N expression and may provide the first therapeutic intervention for intervention in genetically confirmed (D620N) Parkinsonism in man.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/therapeutic-intervention-of-lrrk2-kinase-inhibitors-in-vps35-p-d620n-parkinsonism/