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Dis Model Mech. 2019 Jan 11. pii: dmm.033803. doi: 10.1242/dmm.033803. [Epub ahead of print]

SOD1 activity threshold and TOR signalling modulate VAP(P58S) aggregation via ROS-induced proteasomal degradation in a Drosophila model of Amyotrophic Lateral Sclerosis.

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Department of Biology, Indian Institute of Science Education & Research, Pune 411008, INDIA.
Oxford Nanoimaging Ltd, Oxford, UK.
Department of Biology, Indian Institute of Science Education & Research, Pune 411008, INDIA


Familial Amyotrophic Lateral Sclerosis (F-ALS) is an incurable, late onset motor neuron disease, linked strongly to various causative genetic loci. ALS8 codes for a missense mutation, P56S, in VAMP-associated Protein B (VAPB) that causes the protein to misfold and form cellular aggregates. Uncovering genes and mechanisms that affect aggregation dynamics would greatly help increase our understanding of the disease and lead to potential therapeutics.We developed a quantitative high-throughput, Drosophila S2R+ cell-based kinetic assay coupled with fluorescent microscopy to score for genes involved in the modulation of aggregates of fly ortholog, VAP(P58S), fused with GFP. A targeted RNAi screen against 900 genes identified 150 hits that modify aggregation, including the ALS loci SOD1, TDP43 and also genes belonging to the TOR pathway. Further, a system to measure the extent of VAP(P58S) aggregation in the Drosophila larval brain was developed in order to validate the hits from the cell based screen. In the larval brain, we find that reduction of SOD1 level or decreased TOR signalling reduces aggregation, presumably by increasing levels of cellular reactive oxygen species (ROS). The mechanism of aggregate clearance is, primarily, proteasomal degradation which appears to be triggered by an increase in ROS.We have thus uncovered an interesting interplay between SOD1, ROS and TOR signalling that regulates the dynamics of VAP aggregation. Mechanistic processes underlying such cellular regulatory networks will lead us to a better understanding of initiation and progression of ALS.


ALS; Aggregate; Autophagy; MG132; Rapamycin; UPS

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