Date of Award
2024
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Molecular Physiology and Biophysics
First Advisor
Christopher L. Berger
Abstract
Frontotemporal Dementia (FTD) is classified as a Tauopathy, a group of heterogenous neurodegenerative disorders characterized by the abnormal functioning of a microtubule associated protein (MAP), Tau. Microtubules, an integral cytoskeletal component in neurons, are thought to be stabilized by Tau. In disease states such as FTD, a reduction in binding affinity of Tau for the microtubule is believed to lead to intraneural Tau deposition and aggregation, which subsequently causes microtubule instability. Consequently, neuronal health is compromised and an array of brain functions decline creating the symptomology seen in FTD. However, it is now known that Tau has a myriad of other functions within the neuron, indicating that its role as a microtubule stabilizer is simplistic at best. Tau interacts with microtubules in dynamic ways through nucleation of tubulin, assembly of microtubules, bundling of adjacent microtubules, and regulation of axonal transport by molecular motor proteins including multiple kinesin family members and cytoplasmic dynein. Therefore, the decline of neuronal integrity observed in disorders such as FTD is likely more nuanced than simply a lack of microtubule stability provided by Tau.
Traditionally, there are two distinct pathological mechanisms that give rise to dysfunctional Tau: hyperphosphorylation and pathological point mutations in the protein. Both mechanisms typically decrease the binding affinity of Tau for microtubules, thereby decreasing Tau’s ability to interact with microtubules. Many point mutations associated with the neurodegeneration observed in FTD are in the C-terminal region of Tau, known as the microtubule binding repeat (MTBR) region, sites where Tau binds directly to the microtubule surface. While most pathological point mutations located in the MTBR region show a reduced binding affinity for microtubules, not all Tau mutations express this pathogenic phenotype. Here, we examine a MTBR region point mutation, E342V, implicated in FTD that has been shown to promote microtubule assembly like wild-type (WT) Tau, suggesting normal interactions with the microtubule surface.
Due to previous findings demonstrating E342V’s ability to increase tubulin polymerization, we hypothesized that E342V does not decrease microtubule binding affinity when compared with WT 4RL Tau. Using total internal reflection fluorescence (TIRF) microscopy, E342V Tau’s microtubule binding affinity was compared with WT 4RL Tau. Quantitating average fluorescence intensity across an increasing range of Tau concentrations, no change in binding affinity was observed between E342V and WT 4RL-Tau. We conclude that the point mutation E342V is not directly pathogenic itself. Instead, we propose E342V contributes to the pathology of FTD via a different mechanism. E342V could behave like intronic mutations, which increase the mRNA splicing of exon 10, leading to the transcription of more 4-Repeat (4R) Tau isoforms relative to 3-Repeat (3R) Tau isoforms. We explore the potential implications of the upregulation of 4-Repeat Tau isoforms in the pathogenicity of FTD through the lens of point mutation E342V. We conclude with describing a potential novel molecular mechanism of how E342V and its assumed intronic function contribute to axonal transport dysregulation.
Language
en
Number of Pages
76 p.
Recommended Citation
Clancy, Liam, "Characterization Of A Pathological Tau Point Mutation, E342v, Implicated In Frontotemporal Dementia" (2024). Graduate College Dissertations and Theses. 1828.
https://scholarworks.uvm.edu/graddis/1828