Degree Name

PhD (Doctor of Philosophy)

Program

Biomedical Sciences

Date of Award

12-2014

Committee Chair or Co-Chairs

Meng-Yang Zhu

Committee Members

Phillip R. Musich, Gregory A. Ordway, Antonio E. Rusiñol, Yue Zou

Abstract

It has been reported that locus coeruleus (LC) degeneration precedes the degeneration of other neurons in the brain in some neurodegenerative diseases like Alzheimer’s disease (AD) and Parkinson’s disease (PD). However, the precise mechanisms of neurodegeneration remain to be elucidated. N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) has been widely used as a noradrenergic neurotoxin in the development of AD and PD animal models for specific LC degeneration. However, the precise mechanism of action of DSP4 remains unclear. An increased systemic DNA damage caused by neurotoxin or oxidative stress has been found to be related to the pathogenic development of neurodegeneration. The process of neurodegeneration is not well understood, so current therapeutic approaches are limited to disease management and symptoms relief, such as using antidepressants for depression symptoms, which often accompany neurodegenerative disorders. To date, few studies have explained why different groups of antidepressants have similar clinical effects on relieving depression. Our data demonstrate that DSP4 induces the DNA damage response (DDR) and results in down-regulation of dopamine β-hydroxylase (DBH) and the norepinephrine transporter (NET), which are 2 noradrenergic phenotypes. DSP4 results in cell cycle arrest in S and G2/M phases, which is reversible. The comet assays verify that DSP4 induces single-strand DNA breaks (SSBs). Furthermore, the neurotoxins camptothecin (CPT) and DSP4 were used to induce the DDR in SH-SY5Y cells, fibroblast cells, and primary cultured neurons. Data show that both CPT and DSP4 induce the DDR in SH-SY5Y cells and primary cultured LC neurons. Compared to fibroblast cells, SH-SY5Y cells and LC neurons are more sensitive to the accumulation of DNA damage when treated with CPT or DSP4. Persistent phosphorylated H2AX (γH2AX) and p53 (p-p53ser15) levels indicate a deficient repair in noradrenergic SH-SY5Y cells and LC neurons. In addition, the current study demonstrates that some antidepressants reduce the DDR induced by DSP4 or CPT in SH-SY5Y cells. Flow cytometry data show that selective antidepressants protect cells from being arrested in S-phase. Together, these effects suggest that blocking DNA damage is one important pharmacologic characteristic of antidepressants, which may explain why different antidepressants could alleviate depression symptoms in neurodegenerative patients.

Document Type

Dissertation - unrestricted

Copyright

Copyright by the authors.

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