The Non-Coding RNA gadd7 is a Feed-Forward Regulator of Oxidative Stress
Date of Award
Doctor of Philosophy (PhD)
In obesity and diabetes, an imbalance in fatty acid uptake and fatty acid utilization leads to excess accumulation of lipid in non-adipose tissues. This lipid overload is associated with cellular dysfunction and cell death contributing to organ and tissue failure, a phenomenon termed lipotoxicity. While lipotoxicity is implicated in several complications of obesity and type 2 diabetes, the molecular mechanisms involved in lipotoxic stress are not fully understood. Here we describe the non-coding RNA (ncRNA) gadd7 as a key regulator involved in the response to metabolic stress.
To elucidate the molecular mechanisms of lipid-mediated cell death, we generated and characterized a mutant Chinese hamster ovary (CHO) cell line that is resistant to fatty acid-induced cell death. In this mutant, random insertion of a retroviral promoter trap has disrupted the gene for the ncRNA gadd7. Here we report that gadd7 is induced by lipid overload in a reactive oxygen species (ROS)-dependent fashion and is necessary for both lipid- and general oxidative stress-mediated cell death. In vitro depletion of gadd7 by mutagenesis or short hairpin RNA knockdown in CHO cells significantly reduces lipid and non-lipidinduced ROS. Furthermore, depletion of gadd7 delays and diminishes ROSinduced endoplasmic reticulum stress.
Gadd7 has only been identified in the hamster species. The lack of disease models in the hamster makes investigating the pathophysiological significance of gadd7 difficult. Therefore, we extended our studies of gadd7 into the murine species, for which there exist several models of metabolic stress. We identified and characterized mouse gadd7 orthologs in murine fibroblasts and show that, like gadd7, the mouse orthologs participate in a feed-forward loop with ROS in response to lipid-induced oxidative stress. We investigated the pathophysiological role of gadd7 and show that expression is induced during cerebral ischemia and liver injury, pathophysiologic processes in which oxidative stress is a known contributor.
Our data are the first to describe a ncRNA involved in the feed-forward regulation of oxidative stress. Further study into the pathophysiological significance of gadd7 will provide valuable insight into the propagation of oxidative stress in disease and may enable the development of novel therapeutic approaches.
Chair and Committee
Kathleen Hall, Rakesh Nagarajan, Daniel Ory, Alan Permutt, John Russell
Brookheart, Rita Thomas, "The Non-Coding RNA gadd7 is a Feed-Forward Regulator of Oxidative Stress" (2009). Arts & Sciences Electronic Theses and Dissertations. 101.