Graduation Date

Summer 8-14-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Pharmacology and Experimental Neuroscience

First Advisor

Jialin Zheng

Abstract

Glutaminase is the enzyme that converts glutamine into glutamate, which serves as a key excitatory neurotransmitter and one of the energy providers for cellular metabolism. Glutamate is essential for proper brain functioning but at excess levels, it is neurotoxic and has a key role in the pathogenesis of various neurodegenerative diseases, including HIV-1 associated neurocognitive disorders (HAND). However, the detailed mechanism of glutamate-mediated neurotoxicity remains unclear. In part I, we identified the regulation of glutaminase 1 (GLS1) in the central nervous system (CNS) of HAND animal models including HIV-Tat transgenic (Tg) mouse and HIVE-SCID mouse, since GLS1 is the dominant isoform of glutaminase in mammalian brains. Interestingly, examinations of both animals revealed an upregulation of GLS1 in correlation with the increase of brain inflammation and cognitive impairment. As our previous data revealed an upregulation of glutaminase C (GAC) in the postmortem brain tissues of patients with HIV dementia by protein analysis, suggesting a critical role of GAC in the instigation of primary dysfunction and subsequent neuronal damage in HAND, thus in part II we hypothesize that GAC dysregulation in brain is sufficient to induce brain inflammation and dementia in relevance to HAND. Using a brain GAC overexpression mouse model (which has the overexpression of GAC confined in the brain), we found that the expressions of the marker for brain inflammation, the glial fibrillary acidic protein (GFAP), were increased in the brains of GAC-overexpression mice, suggesting increased reactive astrogliosis. To study the functional impact of GAC overexpression, we performed Morris Water Maze (MWM) test and Contextual Fear Conditioning (CFC) test to determine the learning and memory of mice. GAC-overexpression mice perfomed poorer in both tests, indicating that overexpressing GAC in mouse brain impaired the learning and memory of the animals. Moreover, pathological and physiologial examinations revealed synaptic damage and increased apoptosis in Nestin-GAC mouse brain. Together, these data suggest that dysregulated GAC has a causal relationship with prolonged inflammation and dementia relevant to HAND. In part III, we evaluated the feasibility of genetically knocking down GLS1 in CNS to treat HAND using human primary neural progenitor cell (NPC) culture. However, we have found that GLS1 is essential for the survival, proliferation and differentiation of human NPC. This suggests that more-advanced genetic methods capable of targeting GLS1 in specific cell types of CNS ought to be developed for the therapeutic purpose.

In summary, we report that GLS1 is dysregulated in the brains of HAND murine models in correlation with increased brain inflammation and cognitive impairment. Moreover, overexpressed GAC in mouse brains has a causal relationship to prolonged brain inflammation and dementia of these animals, suggesting a pathologenic role of dysregulated brain GLS1 in relevance to HAND.

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