Date of Award

1-1-2006

Embargo Period

4-21-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biochemistry and Molecular Biology

College

College of Graduate Studies

First Advisor

Mark S. Kindy

Second Advisor

Lotta Granholm-Bentley

Third Advisor

Maurizio Del Poeta

Fourth Advisor

Daniel Fernandes

Fifth Advisor

Eleanor Spicer

Abstract

Alzheimer's disease is named after Alois Alzheimer, the German psychiatrist and neuropathologist who identified it in 1907. Alzheimer's disease (AD) is the most common form of dementia and accounts for at least half of all dementias (Owen et al., 1994). The disease moved from eighth to seventh place among the leading causes of death in 2004, with 65,829 deaths in the United States (Minifio et al., 2006). In an attempt to solve the mystery of this disease, scientists have discovered brain changes in people with AD that lead to dementia. Nerve cells die in areas of the brain that are vital to memory and other mental abilities, such as the cortex and hippocampus, and connections between nerve cells are disrupted. There also are lower levels of some of the chemicals (neurotransmitters) in the brain that carry messages back and forth between nerve cells and increased levels of inflammatory and oxidative stress products. In recent years, studies have suggested that accumulation of amyloid beta peptide in the brain plays a key role in the development of AD (Estus et al., 2002). Amyloid beta (AP) peptide is a physiological peptide, of unknown function that is produced throughout the body's cells. The steady state level of AP peptide in the brain is determined by the rate of its production from amyloid precursor protein via P- and y-secretases and its degradation by the activity of several enzymes. Neprilysin (NEP), a membrane-associated neutral endopeptidase, appears to be the most potent AP peptide-degrading enzyme in the brain (Iwata et al., 2000). Decreasing the activity of NEP ( due to genetic mutations, age, or diseases that alter the expression or activity of NEP) may lead to accumulation of the neurotoxic AP peptide in the brain; in tum, this leads to inflammatory and oxidative stress responses, neuronal loss, and ,thus, AD. In fact, NEP has been reported to be down vu regulated at early stages of AD and with agmg m areas vulnerable to AP peptide accumulation and plaque fonnation (Russo et al. , 2005; Yasojima et al., 2001a). Thus, NEP levels in the brain appear to play a significant role in regulating the cerebral AP peptide levels and AD pathogenesis. All transgenic mice used to evaluate potential therapeutic interventions to lower AP peptide level in the brain have been APP transgenic mice or APP/PS (presenilins) bigenic mice because they provide good models for AD in which both amyloid deposition and progressive memory loss have been shown. However, these mice do not develop the full spectrum of the disease, such as significant neuronal loss and neurofibrillary tangles formation ( deposition of hyperphosphorylated tau protein) in the brain. Therefore, we investigated the efficacy of lentivirus-mediated over-expression of human NEP to protect neuronal cells from AP peptide toxicity in vitro. Incubation of hippocampal neuronal cells (HT22) that stably over-express human NEP with the monomeric forms of AP peptide decreased the AP peptide toxicity on the cells, as measured through cell viability. In addition, we investigated the effects of human NEP gene transfer in the brain of a young animal model of AD on reducing the accumulation of AP peptide level and its down-stream effects (i.e. inflammation, oxidative stress, and memory impairment). The results indicate that over-expression of human NEP in the right cortex/hippocampal area by lentiviral vector at early stage of the disease resulted in attenuation of amyloid load, oxidative stress, and inflammatory responses in both brain hemispheres as well as a marked decrease in the memory impairment compared to control mice. We conclude that restoring NEP levels in the affected areas and at early stages of the disease is an effective tool to decrease neuronal loss and prevent or treat the disease progression and pathology.

Rights

Copyright is held by the author. All rights reserved.

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