Date of Award

Fall 2020

Document Type

Open Access Dissertation

Department

Pharmacology, Physiology and Neuroscience

First Advisor

Jun Zhu

Abstract

Despite the success of combinatorial antiretroviral therapy (cART) in controlling peripheral HIV infection and improving the lives of HIV-1 patients, roughly 50% of this population continues to develop a group of neurological complications including cognitive dysfunction, motor deficits, and dementia collectively referred to as HIV-associated neurocognitive disorders (HAND). The continuing presence of the transactivator of transcription (Tat) protein in cART-treated HIV-1 patients has been suggested to play a crucial role in the neurotoxicity and cognitive impairment evident in HAND. HIV-1 Tat protein has been detected in dopamine (DA) -rich brain areas, and long-term viral protein exposure has been found to accelerate damage to the mesocorticolimbic DA system. Previous reports from our laboratory indicate that HIV-1 Tat-mediated damage to the dopaminergic system involves a direct allosteric interaction between HIV-1 Tat and the DA transporter (DAT). Importantly, in the central nervous system, in addition to the DAT, the norepinephrine (NE) transporter (NET) is also responsible for maintaining DA homeostasis. Due to its high level of homology with the DAT it is possible that HIV-1 Tat may induce DA dysregulation through interactions with this transporter as well. Based on these findings, this research project investigated the hypothesis that via direct inhibitory allosteric interactions with the dopamine and norepinephrine transporters, the HIV-1 Tat protein dysregulates dopamine homeostasis, resulting in the neuropsychiatric dysfunction prominently featured in HAND.

First, the possibility that HIV-1 Tat inhibition of DA uptake involves both DAT and NET was investigated. Via site-directed mutagenesis of the Tyrosine467 (Y467) residue of the NET to a phenylalanine (Y467F) or a histidine (Y467H), which correlates with Tyrosine470 on the DAT, it was determined that not only is HIV-1 Tat capable of inhibiting DA uptake through NET, but that this interaction involved similar residues as the HIV-1 Tat/DAT interaction. Building on this finding, the next step was to establish if HIV-1 Tat-mediated inhibition of the DA and NE transporters could be replicated in an animal model of HAND. Utilizing an inducible HIV-1 Tat transgenic mouse model (iTat-tg), it was determined that HIV-1 Tat inhibited both the DA and NE transporters to a similar extent in the prefrontal cortex (PFC) of the iTat-tg mice. The critical question following these findings was if HIV-1 Tat-mediated dysregulation of the dopaminergic system could be prevented, what effect would this have on the development of cognitive deficits observed in HAND? This possibility was investigated via generation of a mutant Tyrosine88 to phenylalanine (Y88F) DAT mouse model, which was crossed with the iTat-tg mouse. The Y88F DAT mutation proved capable of both preventing HIV-1 Tat-mediated inhibition of the DAT in the PFC, as well as learning and memory deficits which had been previously reported in the iTat-tg mice. These results demonstrate that prevention of the HIV-1 Tat/DAT interaction is sufficient to prevent DA dysregulation and associated neurocognitive deficits in HAND.

Furthermore, this interaction is highlighted as a potential target for the development of novel therapies which may serve as adjunct therapy to improve the lives of HIV-1 infected patients.

Available for download on Saturday, December 31, 2022

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