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THE HUMAN LON PROTEASE IN MITOCHONDRIAL STRESS
PROTECTION AND AGING
by
Jenny Kathleen Ngo
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
in Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(MOLECULAR & COMPUTATIONAL BIOLOGY)
August 2008
Copyright 2008 Jenny Kathleen Ngo
Object Description
| Title | The human Lon protease in mitochondrial stress protection and aging |
| Author | Ngo, Jenny Kathleen |
| Author email | jngo@usc.edu |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Molecular Biology |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2008-05-05 |
| Date submitted | 2008 |
| Restricted until | Unrestricted |
| Date published | 2008-07-02 |
| Advisor (committee chair) | Davies, Kelvin J.A. |
| Advisor (committee member) |
Pike, Christian Goodman, Steven Finkel, Steven |
| Abstract | The mitochondrial Lon protease was discovered in our laboratory to be the major protease that degrades oxidized mitochondrial proteins, specifically oxidized aconitase. Published work from a number of laboratories shows that Lon-mediated proteolysis is important not only for the degradation of abnormal proteins, but can affect many important cellular processes in E.coli and yeast. In light of this, for my thesis project, I studied human cells in culture to determine the significance of Lon in mitochondrial maintenance, cellular protection, and potential affects in aging.; The first chapter of this dissertation provides a brief history of our understanding of the Lon protease, gives background information on the Lon gene and protein, and provides insight into how Lon may be involved in mitochondrial homeostasis based on current published data.; In the second chapter, I look into the possibility that Lon may be a stress responsive protein. I know from published data that in lower organisms such as bacteria and yeast that Lon is required for the degradation of damaged proteins, as well as proteins that can turn on and off the SOS response system. In addition, Lon can bind to DNA, for a currently undetermined reason. This suggests that Lon is a multifunctional protein, which may be very important for the mitochondria under conditions of stress. Our results indicate that Lon is indeed a stress responsive protein that provides protection to the cell.; In the third part of my thesis, I show that human Lon binds to the mitochondrial promoter in vivo, as shown previously by other laboratories in vitro. I then silenced the same cells with Lon siRNA and show that these cells start to make less mitochondrial mRNA when Lon is absent, and this is not due to the loss of mitochondrial DNA template. These data suggest that the presence of Lon may affect mitochondrial DNA transcription, possibly from Lon DNA binding.; The fourth chapter of my thesis was done in collaboration with Daniela Bota. Here we determined the effects of Lon down-regulation in human lung fibroblasts. We silenced Lon with antisense RNA and through various biochemical assays, determined the affects on mitochondrial function, structure, and type of cell death. We conclude that the Lon protease is required to maintain mitochondrial function, and when silenced, leads to massive cell death.; Chapter five of my thesis examines the level of Lon from young to aged human cells. Published data indicate that Lon protease expression is significantly lowered in aged rodent models, and my previous work indicates that Lon is important for mitochondrial maintenance and stress response. I determined that the overall level of Lon in replicative senescent cells is significantly lower than in younger cells. In addition, the ability for Lon to be induced in response to oxidativestress is delayed and maximal induction level is low compared to young cells. Overall, senescent cells exhibit high levels of oxidative protein damage with low levels of Lon. I propose that the decline of Lon protein and induction ability contributes to the accumulation of oxidized proteins found in senescent cells.; Chapter six is a review that relates to the significance of the Lon protease and potential affects in aging cells. In addition to the data represented in this thesis, there is an emerging body of evidence that indicates that Lon may contribute to the aging process. Studies from prokaryotes to mammalian systems suggest that Lon is important for the degradation of damaged proteins, however, in aging animals, expression and overall activity of Lon declines, while protein oxidation by-products accumulate. We also propose in this chapter, from previous work in our laboratory and current published work that the Lon protease may be working in conjunction with aconitase to maintain mitochondrial homeostasis under conditions of stress.; In conclusion, I find that the Lon protease is protective against metabolic stresses, but it is also down-regulated in senescent cells. Cells that have higher levels of Lon display protection against oxidative protein damage, with increased cell viability and mitochondrial function after a toxic insult. On the other hand, cells that are silenced with Lon no longer exhibit protection during oxidative stress, instead, start to lose mitochondria, mitochondrial function, leading to cell death. We propose that Lon is protective against metabolic stress, and its decline may contribute to the loss of mitochondrial function and the accumulation of damaged proteins typically observed in aging human cells. |
| Keyword | mitochondria; proteolysis; aging |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Type | texts |
| Legacy record ID | usctheses-m1314 |
| Rights | Ngo, Jenny Kathleen |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | http://www.usc.edu/isd/libraries/services/ask_a_librarian/email/ |
| Filename | etd-Ngo-20080702 |
| Archival file | uscthesesreloadpub_Volume29/etd-Ngo-20080702.pdf |
Description
| Title | Page 1 |
| Full text | THE HUMAN LON PROTEASE IN MITOCHONDRIAL STRESS PROTECTION AND AGING by Jenny Kathleen Ngo A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA in Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (MOLECULAR & COMPUTATIONAL BIOLOGY) August 2008 Copyright 2008 Jenny Kathleen Ngo |
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