PgmNr D183: Defects in synaptic vesicle endocytosis are caused by TDP-43 dependent translation inhibition in a Drosophila model of ALS.

Authors:
A. Coyne; J. Johannesmeyer; D. Zarnescu


Institutes
University of Arizona, Tucson, AZ.


Keyword: neural degeneration

Abstract:

Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative disease affecting upper and lower motor neurons. TDP-43, an RNA binding protein linked to the majority of ALS cases, is involved in several aspects of RNA metabolism. Using a Drosophila model of ALS based on TDP-43 we have previously identified a role for TDP-43 in the translation regulation of specific mRNA targets. Here we use a combination of genetic, molecular, and imaging approaches to show that TDP-43G298S but not TDP-43WT regulates the translation of hsc70-4 mRNA. Hsc70 is a molecular chaperone that functions at multiple steps in the synaptic vesicle cycle. FM1-43 dye uptake experiments reveal defects in endocytosis and a reduction in the size of the readily releasable and recycling vesicle pools in both TDP-43WT and TDP-43G298S variants. However, upon overexpression of Hsc70, endocytosis is restored specifically only in the disease associated mutant. Genetic interaction approaches reveal the ability of synaptic proteins namely cysteine string protein (CSP), dynamin, clathrin, lap, and auxilin to modulate TDP-43 mediated locomotor dysfunction. The results of these experiments suggest that synaptic vesicle cycling defects resulting from TDP-43 expression occur during early endocytic events at the presynaptic membrane. In addition, overexpression of Hsc70 in the context of TDP-43 mitigates multiple aspects of TDP-43 toxicity including locomotor dysfunction and reduced lifespan. Notably, this rescue is dependent on both the chaperone and membrane bending activities of Hsc70 as evidenced by genetic interactions with Hsc70 ATPase or membrane binding mutants, respectively. Thus, both chaperone and membrane bending activities, both of which contribute to the maintenance of synaptic protein pools, are affected upon TDP-43 overexpression and contribute to ALS phenotypes and toxicity. Our results provide the first evidence for TDP-43 regulating the synaptic vesicle cycle through the translational regulation of its synaptic mRNA targets. Thus, altered ribostasis, a key event in the progression of ALS, contributes to synaptic failure preceding neurodegeneration in ALS pathogenesis.