Compensatory responses to oxidant stresses in vitro and in vivo

2013 Fall.Includes bibliographical references.Emerging evidence shows that reactive oxygen species (ROS) are not merely damaging agents causing random destruction to cell structure and function, but that they act as modulators of physiological processes (such as cell adaptation to physical exercise) by regulating gene transcription and protein synthesis. The exact redox signaling pathways involved in cell adaptations to oxidative stress are unknown. Since various stimuli can induce oxidative stress under different conditions in vivo and in vitro, different models are warranted to study the cell signaling pathways involved in compensatory responses to oxidative stress. The following investigation comprises a series of experiments with the overall aim of elucidating the role of redox sensitive pathways in inducing cellular responses to oxidative stress in vitro and in vivo. The experiments tested the general hypothesis that changes in the redox state of the cell, through hypoxia, contractile activity or direct application of hydrogen peroxide (H2O2), would cause antioxidant compensatory responses and cell adaptations. The specific aims of the experimental series were: 1) to determine whether pulmonary edema, evoked by cerebral hypoxia in the presence of systemic normoxia, will be accompanied by sympathetic activation, increased oxidative stress, and upregulation of endogenous antioxidant pathways, 2) to determine whether electrical stimulation (Es) induced contractile activity of cultured murine myotubes would induce energetic stress, redox sensitive signaling, and mitochondrial biogenesis, and 3) to determine whether treatment with H2O2 would result in a greater rate of mitochondrial biogenesis compared to control, and whether the increase would be maintained during co-treatment with either an exogenous antioxidant (vitamin C) or a nuclear erythroid 2 -related factor 2 (Nrf2) activator that increases transcription of endogenous antioxidants. Studies in aim 1 demonstrated that under pathologic conditions such as isolated cerebral hypoxia with systemic normoxia, tissue specific patterns of compensatory responses to the hypoxic stressor exist. Further, this study showed that the differences in lung and brain redox signaling pathways during hypoxia can have different systemic outcomes through modulation of the sympathetic nervous system (SNS). Studies in aim 2 demonstrated a unique model of contractile activity in vitro, which was successful in simulating the cellular adaptations to a single bout of endurance exercise such as greater rate of cytosolic protein synthesis, upregulation of antioxidants and mitochondrial protein markers as well as AMP activated protein kinase (AMPK). Studies in aim 3 demonstrated that H2O2 did not increase mitochondrial biogenesis. Further, increasing Nrf2 activation maintained the rate of mitochondrial protein synthesis during H2O2 treatment, while treatment with the exogenous antioxidant failed to restore the H2O2 induced decreases in mitochondrial biogenesis during H2O2 treatment. Collectively, we have used different models of oxidative stress in vitro and in vivo to evaluate some of the mechanisms involved in cell adaptations responses. Findings from these experiments provide insight into understanding the role of redox signaling in pathologic and non-pathologic circumstances and can help future therapeutic recommendations for battling the consequences of oxidative stress on health