Dissertations, Theses, and Capstone Projects

Date of Degree

9-2022

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biology

Advisor

Alejandra del Carmen Alonso

Committee Members

Abdeslem El Idrissi

Christopher Corbo

Jimmie Fata

Zaghloul Ahmed

Frida Kleiman

Subject Categories

Molecular and Cellular Neuroscience

Keywords

Tau, neurodegeneration

Abstract

One of the characteristics of Alzheimer’s disease and associated tauopathies is the accumulation and aggregation of hyperphosphorylated tau protein. The biological activity of tau is to bind to tubulin and promote its assembly into microtubules with subsequent stabilization of the latter. When tau gets hyperphosphorylated it cannot bind to tubulin and carry on its function, instead, it binds to normal tau and sequesters it from microtubules leading to disruption of microtubular assembly and ultimately to the death of neurons. Our lab had previously shown that tau phosphorylation sites 199, 212, 231, and 262, combined with the FTDP-17 mutation R406W (Pathological Human tau or PH-Tau) are critical for inducing a conformational change in the protein similar to the abnormally hyperphosphorylated tau from AD brain. Moreover, it was proposed that hyperphosphorylated tau can transfer between the cells in a prion fashion leading to more microtubular disruption. This research was designed to investigate the role of phosphorylated tau in the mechanism of tau transfer from one cell to another in vitro and in vivo and its effect on memory. I found that tau can be taken up by the cells and neurons when added to the cell media and this uptake is mediated by the M1 and M3 muscarinic receptors. M1 muscarinic receptor inhibitor Pirenzipine similarly to Atropine, a broad muscarinic receptor antagonist is able to block almost 80 percent of tau uptake, while PTX and AF-DX116, M2 antagonist, and M2 and M4 downstream blockers respectively, had no impact on tau PH-PH-Tau uptake, Moreover, once again I confirmed that effect of PH-Tau on primary neuronal cultures is very similar to tau isolated from the brain of the patient with Alzheimer disease and leads to almost complete disruption of neurites and microglial activation. On the other hand, the incubation of primary cultures with tau resulted in enhanced growth of neurites. I also found that all the tau isoforms can be taken up by the neurons and preincubation with atropine significantly reduces their uptake. However, the highest uptake I observed was with the largest tau isoforms, and this uptake was significantly reduced with the isoforms with an absent 2N domain. The intracranial hippocampal injections of PH-Tau lead to cognitive decline in CD1 mice within 6 months after the injection. Furthermore, Direct Current (DC) stimulation is the technique that was shown to upregulate chaperone proteins. These proteins are involved in targeting misfolded proteins and aggregates. Here I investigated the effect of DC stimulation on human cells and primary neuronal cultures that were exposed to pathological tau and the brain of our transgenic mice expressing high amounts of hyperphosphorylated tau. I found that DC stimulation resulted in an increase in HSP70 proteins in vitro and in vivo. I also found the reduction in PH-Tau in vitro and in vivo most likely due to the upregulation of the degradation pathway.

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