Alyssa N. Coyne Abstracts
Alyssa N. Coyne
Ph.D. Candidate
Neuroscience GIDP
Society for Neuroscience Annual Meeting
Chicago, Illinois
October 17-21, 2016
TDP-43 influences synaptic function through translational regulation of synaptic mRNA targets.
Authors: Alyssa N Coyne1,2, Jeffrey Johannesmeyer1, Daniela C Zarnescu1,2,3
1 – Department of Molecular and Cellular Biology, University of Arizona 2 – Department of Neuroscience, University of Arizona 3 – Department of Neurology, University of Arizona, Tucson, AZ 85721
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, imaging, and electrophysiology approaches to show that TDP-43 regulates the translation of hsc70 mRNA in a variant dependent manner. Hsc70 is a molecular chaperone that functions at multiple steps in the synaptic vesicle cycle. 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 the chaperone activity of Hsc70 as evidenced by genetic interactions with an Hsc70 ATPase mutant that no longer rescues TDP-43 dependent phenotypes. In addition, Hsc70 overexpression restores synaptic vesicle cycling, specifically in the context of disease associated mutant TDP-43. 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-43 variants. However, upon overexpression of Hsc70, endocytosis is restored specifically only in the disease associated mutant. Furthermore, overexpression of Hsc70 reduces the amount of insoluble TDP-43 in a variant dependent manner. Our results provide evidence for TDP-43 regulating synaptic function and the synaptic vesicle cycle through the translational regulation of its synaptic mRNA targets. Ultimately, this dysregulation of translation may lead to depletion of key synaptic proteins at the neuromuscular junction and synaptic failure preceding neurodegeneration. Additionally, our results provide evidence for differential regulation of mRNA targets by disease associated mutant TDP-43 and dysregulation of synaptic function through altered ribostasis, a key event in the progression of ALS.
Amyotrophic Lateral Sclerosis (ALS), or Lou Gherig’s disease, is a progressive and
universally fatal neurodegenerative disease caused by death of motor neurons. TAR DNA-binding protein (TDP-43) is an RNA binding protein linked to the vast majority of ALS cases. Using a fruit fly model of ALS based on TDP-43, we have previously identified a role for TDP-43 the regulation of the process that translates specific mRNA “messages” to functional proteins. I am currently using this model to investigate how TDP-43 affects the ability of neurons to communicate with muscles during the progression of ALS.
Here, we use a combination of different experimental approaches to show that TDP-43 regulates the translation of hsc70 mRNA in a TDP-43 variant dependent manner. Hsc70 is a gene involved in multiple steps of the process that allows neurons to communicate with muscles, a process severely altered in ALS pathology. Overexpression of Hsc70 in the context of TDP-43 alleviates multiple aspects of toxicity such as the ability of fruit fly to move. Additionally, overexpression of Hsc70 rescues defects in the processes that allow neurons to communicate with muscles, specifically in the context of ALS associated mutant TDP-43.
Moreover, Hsc70 also plays a role in ridding the cell of non-functional proteins that are improperly folded or have accumulated, thus rendering them unable to perform their typical cellular functions. Overexpression of Hsc70 reduces the amount of pathologically accumulated TDP-43 in a variant dependent manner.
Our results provide evidence for TDP-43 regulating the ability of neurons to communicate with muscle through translational regulation of genes involved in this process. Ultimately, a dysregulation of translation may deplete the neuromuscular junction, the contact point where neurons communicate with muscles, of these key proteins. This will in turn lead to a failure in communication which is proposed to be one of the first steps initiation neuron death in ALS. Furthermore, our results provide evidence for differential regulation of gene targets by TDP-43. This finding begins to pinpoint differences in the progression of ALS that arises from mutations in TDP-43 and the over 95% of ALS cases with wildtype TDP-43 pathology.