Objective: To understand the role of the retromer complex in the central nervous system(CNS), and its link to Parkinson’s disease (PD) susceptibility.

Background: Mutations in VPS35 cause autosomal dominant, late-onset PD. However, how retromer dysfunction contributes to PD pathogenesis remains elusive. The retromer core consists of a conserved, heterotrimeric complex including VPS35, VPS26, and VPS29, that mediates the recycling of cargo proteins from the endosome. Tissue-specific loss of Vps35 or Vps26 in the Drosophila eye causes progressive retinal degeneration, but embryonic lethality has hindered systematic studies of retromer dysfunction in the CNS.

Methods: Using CRISPR/Cas9 technology, we generated a Vps29 null allele, in which the entire coding sequence is deleted. Since Vps29 null homozygotes are adult viable, we evaluated age-dependent survival, startle-induced negative geotaxis, electroretinograms (ERG), and CNS histology analysis to reveal evidence of potential neurodegeneration. Western blotting and immunofluorescence were also performed to evaluate other retromer components and the integrity/function of the endolysosomal system.

Results: Vps29 null animals exhibit reduced survival and age-dependent locomotor defects, and these phenotypes are dominantly enhanced in a Vps35 heterozygous genetic background. Based on ERG, loss of Vps29 causes progressive loss of photoreceptor depolarization and transient potentials, similar to the Vps35-mutant phenotype. Consistent with this, histology revealed extensive retinal vacuolar degeneration in aged Vps29 mutants. Using a rapid stimulation paradigm, ERG transients are progressively diminished in Vps29 null mutants, suggestive of defects in synaptic vesicle recycling. All observed phenotypes were rescued by a Vps29 genomic transgenic construct or via targeted expression in neurons. Interestingly, while loss of Vps29 did not significantly affect Vps35 protein level, Vps35 showed an aberrant perinuclear localization co-localizing with Rab7 GTPase, potentially consistent with impaired retromer turnover and endolysosomal dysfunction.

Conclusions: Loss of Vps29 in Drosophila causes progressive synaptic dysfunction, impaired locomotor behavior, and neurodegeneration, thus recapitulating salient features of PD, and establishing a valuable model for studying the role of the retromer and associated endolysosomal system in the aging, adult nervous system.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/loss-of-vps29-disrupts-retromer-function-and-synaptic-transmission-leading-to-neurodegeneration-in-drosophila/