Oxidative Stress and G6PDH Expression

Western Michigan University, Kalamazoo MI

Investigators

Abstract

Reactive oxygen species (ROS) are produced inside the cell during normal oxidative metabolism. Tight control of this process is crucial for numerous biological events to occur, including enzyme activation, cell cycle regulation and programmed cell death. Abnormal production of ROS can lead to an imbalance in redox homeostasis known as oxidative stress. Often times exposure to environmental agents, including, UV irradiation, ozone, herbicides, pesticides and metals can produce additional ROS that lead to this imbalance. Upon exposure to these agents, this elevated level of ROS can cause damage to proteins, nucleic acids and lipids, as well as, alter physiological responses such as signal transduction and gene expression. Long term consequences of oxidative stress have also been associated with the pathogenesis of a variety of toxicities and diseases. Under some circumstances, cells can utilize an antioxidant defense system in order to cope with the excess ROS produced during oxidative stress. However, the mechanism by which some key components in the antioxidant defense system work is not completely known. For example, NADPH is a critical biological cofactor that helps to maintain a balance between the prooxidant and antioxidant status of the cell. The pentose phosphate pathway through the activities of glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase generates most of the NADPH needed by the cell. G6PDH is the key rate-limiting enzyme in this pathway and thus not only regulates the flow of carbon through this pathway, but also the production of NADPH. Since NADPH is necessary for maintaining the cell's redox balance and G6PDH is important for its production then it seems reasonable to conclude that the redox state of the cell would influence the expression of this important enzyme. Indeed, studies from this laboratory and others have suggested that expression of the gene for G6PDH is regulated by the oxidative status of the cell. However, the mechanism by which this regulation occurs is unknown. Therefore, this research is aimed at testing the hypothesis that the environmental contaminant cadmium, which influences the oxidative state of a cell by decreasing levels of glutathione, regulates the expression of G6PDH through a redox sensitive transcriptional event. Cadmium is generating a great deal of environmental concern due to its accumulation from such industrial practices as production of plastics, materials, batteries, tobacco, electroplating, welding and smelting. Organisms are easily exposed to cadmium due to its relatively high vapor pressure, which accounts for its high solubility in water. The studies will be done in primary rat hepatocytes in culture. The liver is the major target organ for acute inorganic Cd exposure. Additionally, hepatocytes are attractive to use as a model since the metabolic responses to hormones, nutrients or environmental agents consistently mimic those observed in vivo. These studies would represent the first of this kind and add significantly to our understanding of the role of the oxidative state of the cell on the expression of enzymes involved in major biochemical pathways such as the pentose phosphate pathway. These studies would also add valuable information about how a cell protects itself from damage induced from environmental agents such as metals. A team learning environment will facilitate the completion of the work by the PI and students.