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-? (A?) 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 A? 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 A? toxicity. Genetic knockout of either Tau or Fyn prevents A? toxicity in primary neurons, hyperphosphorylated Tau has a higher affinity for Fyn, and Tau mediates trafficking of Fyn to dendrites in vivo, leading to A?-induced cognitive deficits and network hyperexcitability. However, the idea that the Tau-Fyn interaction is a critical mediator of A? 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 A?-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 A?-induced neurite degeneration and membrane trafficking dysfunction. Here, I will determine if Tau-PxxP5/6 prevents A?-induced deficits in dendritic spine morphology using 3D morphometric analysis and A?- 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 A? 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 A? toxicity and could provide a promising therapeutic strategy to treat AD.
Alzheimer?s disease (AD) is the leading cause of dementia and familial AD is caused by mutations proteins involved in processing amyloid-? (A?). Tau reduction prevents A?-induced dysfunction in multiple models of AD, but the mechanism by which it does so is unknown. Diverse evidence suggests that Tau?s interaction with Fyn may be a critical mediator of A? toxicity, so this project will investigate the role of the Tau-Fyn interaction in A?- induced dysfunction and AD.