Project Summary/Abstract
Alzheimer’s disease (AD) is the leading cause of dementia worldwide and its impact will increase exponentially
as the population ages. New therapeutic approaches are desperately needed to treat AD. The microtubule-
associated protein Tau is has been heavily studies because it aggregates into neurofibrillary tangles within
neurons, one of the hallmarks of AD. Genetic knockout of Tau is protective in several models of AD, highlighting
its potential as a therapeutic target for AD. Interestingly, Tau reduction also prevents network hyperexcitability,
which occurs early in AD and may contribute to neurodegeneration, in these models. Similarly, in a primary
neuron culture system, Tau reduction prevents amyloid-ß (Aß) toxicity and glutamate or NMDA-induced
excitotoxicity. In short, Tau reduction is protective in a variety of systems, but the mechanism by which it
does so is currently unknown. Tau’s central proline-rich region, which is hyperphosphorylated in AD, has
several PxxP motifs that mediate binding with SH3 domain–containing proteins including the nonreceptor
tyrosine kinase Fyn. Fyn is also an important mediator of network hyperexcitability, as it phosphorylates AMPA
and NMDA receptors to strengthen their signaling and regulates dendritic spine dynamics. Exogenous Aß
activates Fyn at the postsynaptic density, leading to NMDAR phosphorylation and excitotoxicity in neurons.
Diverse evidence indicates that Tau’s interaction with Fyn could be a critical mediator of Aß toxicity. Genetic
knockout of either Tau or Fyn prevents Aß toxicity in primary neurons, hyperphosphorylated Tau has a higher
affinity for Fyn, and Tau mediates trafficking of Fyn to dendrites in vivo, leading to Aß-induced cognitive deficits
and network hyperexcitability. However, the idea that the Tau-Fyn interaction is a critical mediator of Aß toxicity
has not been directly tested, which is the goal of this project. My overarching hypothesis is that the Tau-Fyn
interaction is a critical mediator of Aß-induced structural and functional abnormalities. I will test this
hypothesis using a peptide inhibitor of the Tau-Fyn interaction, Tau-PxxP5/6, developed by previous members of
the Roberson lab. I developed a proximity ligation-based assay to confirm that Tau-PxxP5/6 inhibits endogenous
Tau-Fyn interaction in situ and found that it prevents Aß-induced neurite degeneration and membrane trafficking
dysfunction. Here, I will determine if Tau-PxxP5/6 prevents Aß-induced deficits in dendritic spine morphology
using 3D morphometric analysis and Aß- and gabazine-induced network hyperexcitability using multi-electrode
arrays. I will also determine if the Fyn-binding region of Tau is the critical region of Tau that mediates Aß toxicity
by transducing Tau knockout neurons with different mutated Tau constructs to prevent Fyn binding. In addition
to in vitro studies, I will determine if Tau-PxxP5/6 prevents cognitive deficits, epileptiform activity and seizure
susceptibility in vivo using the hAPPJ20 mouse model of AD. The proposed work will provide insights into the
molecular mechanisms of Aß toxicity and could provide a promising therapeutic strategy to treat AD.