According to the Alzheimer’s Association 2012 report, 13% of Americans over 65 years of age, and approximately half of Americans over the age of 85, suffer from Alzheimer’s Disease (AD), resulting in an estimated cost of 200 billion dollars for related health care. Additionally, AD is the most prevalent dementia, and the sixth leading cause of death in the United States. Thus, investigating mechanisms of pathophysiology and identifying potential therapeutic targets for AD is significant.
AD is characterized by the formation of plaques, composed primarily of the amyloid-β 1-42 (Aβ) peptide in the brain, resulting in neurodegeneration. Our lab has observed that over-expression of human VPS41 in C. elegans provides neuroprotection from Aβ toxicity, and that depletion of VPS41 in worms expressing Aβ increases the neurotoxicity of Aβ. In yeast, VPS41 has been demonstrated to function in the tethering of vesicles, late endosomes, and AP-3-coated vesicles from the late Golgi, to the lysosome for degradation. Previously, our lab has shown that over-expression of human VPS41 is neuroprotective in a transgenic worm model of Parkinson’s Disease, wherein dopaminergic neurodegeneration is induced by α-synuclein overexpression (Harrington et al., 2012, J. Neurosci.). VPS41-mediated neuroprotection from α-synuclein-based degeneration was abolished by mutation of putative phosphorylation sites in VPS41 and was dependent on its interactions with AP-3δ, RAB7, VPS core proteins, and VPS39. Thus, VPS41 has a role in lysosomal trafficking that impacts neuron survival.
The objective of this study is to determine how this specifically relates to cellular processing and ameliorates the impact of neurotoxic proteinaceous products. Here we report the results of a systematic RNAi screen whereby we knocked down the core components involved in lysosomal trafficking and categorized their requirement for Aβ protein toxicity. Our results indicate that the ARF-like GTPase arl-8 mitigates endocytic Aβ neurodegeneration in a VPS41-dependent manner, rather than through rab-7 and AP-3-coated vesicles from the late Golgi as with α-synuclein. Additionally, we suggest that the GABARAP homologue, lgg-2, plays a critical role in Aβ toxicity with arl-8. In this regard, further analysis of functional effectors of Aβ protein processing via the lysosomal pathway, along with subsequent evaluation in our worm neuronal model of AD (Treusch et al, 2011, Science), will assist in the elucidation of the underlying mechanism involving VPS-41-mediated neuroprotection.