Browsing by Subject "Oxidative stress"
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Item ERK5/KLF4 SIGNALING IS A SHARED PATHWAY UNDERLYING THE NEUROPROTECTIVE EFFECTS OF H2O2 PRECONDITIONING AND NGF(2013-04-12) Su, ChangPurpose: Oxidative stress has long been implicated in the pathogenesis of various neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. While high levels of oxidative stress is generally associated with neuronal death, a slight rise of reactive oxygen species (ROS) levels can be protective by "preconditioning" cells to develop a resistance against subsequent challenges. However, the mechanisms underlying such a preconditioning (PC)-induced protection are still poorly understood. One clue stems from the observation that the mitogen-activated protein (MAP) kinase ERK5 is recruited both under conditions of H2O2 - induced neuronal preconditioning (PC) as well as following application of the application of the neuroprotectant, Nerve Growth Factor (NGF). This project tests the hypothesis that the ERK5-dependent signaling cascade may function as a convergence point for various protective signals to counteract oxidative stress-induced neuronal death. Methods: We used PC12 cells as our model to study the effect of oxidative stress. Activity of the ERK5 signaling pathway was enhanced by over-expression of active upstream kinease, or blocked by pharmacological inhibitors or RNAi. Cell viability was determined by Calcein Assay. Results: Over-expression of a constitutively active form of MEK5, the upstream activator of ERK5, partially rescued PC12 cells from H2O2-caused death, while inhibition of ERK5 by pharmacological inhibitors or RNAi abolished NGF or PC-induced protection.Furthermore, both NGF and PC increased the expression of the transcription factor, KLF4, which can initiate an anti-apoptotic response in various cell types. Induction of KLF4 by NGF or PC in PC12 cells is blocked by siERK5, suggesting that ERK5 is required in this process. Finally, siKLF4 can also attenuate NGF- or PC-induced neuroprotection. Conclusions: Taken together, our data suggest that ERK5/KLF4 cascade is a common signaling pathway shared by multiple mechanisms to protect neurons from oxidative stress-induced cell death. Since oxidative stress is thought to be a major player in many aging-associated diseases, KLF4 may serve as a therapeutic target, that when activated, counteracts oxidative stress under such conditions.Item Membrane androgen receptor-induced oxidative stress: mechanism involved in neurodegeneration(2019-05) Tenkorang, Mavis A. A.; Cunningham, Rebecca L.; O'Bryant, Sid; Schreihofer, Derek; Barber, Robert C.Oxidative stress-associated neurodegenerative diseases, such as Parkinson's disease (PD), affect millions of people worldwide. Although aging is the greatest risk factor for PD, other significant factors may be implicated, such as sex hormones that can mediate sex differences. Men have a higher incidence and prevalence of PD than women. Therefore, testosterone, a primary male sex hormone and a known oxidative stressor, is implicated in PD pathophysiology. Since androgens can have negative effects on dopaminergic cells, it is imperative to understand the underlying mechanisms in order to determine what mediates the observed sex differences in PD prevalence. NADPH Oxidase 1 and 2 are major oxidative stress generators in the brain, thus potential targets for testosterone-induced oxidative stress and cell death. This dissertation project therefore investigates the role of androgens and membrane androgen receptor activation on NOX1/2. We hypothesize that in dopaminergic cells, testosterone activates the membrane androgen receptor (AR45) that is complexed with NOX1/2 to increase oxidative stress. In an oxidative stress environment, androgen activation of this AR45-NOX complex leads to cell death. Results indicate that classical androgen receptor (AR) antagonists do not block testosterone's negative actions in an oxidative stress environment. The effects of AR45-NOX complex on cell viability can be blocked by either degrading AR45 protein or blocking NOX activation by apocynin. Further, these results show that testosterone's detrimental effect on cells is via a non-genomic mechanism, specifically via a novel membrane androgen receptor, AR45. The findings of this study help identify key players in testosterone-induced neurodegeneration, which could serve as potential therapeutic targets for PD. Ultimately, this project provides novel mechanisms to explain thought provoking questions on male sex bias in PD.Item NANOPARTICLES-MEDIATED CATALASE DELIVERY PROTECTS HUMAN NEURONS FROM OXIDATIVE STRESS(2013-04-12) Ashutosh, FNUPurpose: Several brain injuries and neurodegenerative diseases implicate excessive production of reactive oxygen species, such as hydrogen peroxide (H2O2) in disease pathogenesis. Catalase, an H2O2 degrading enzyme, is a well-known antioxidant target for therapeutic intervention. However, medical use of catalase is restricted by its labile nature and inadequate delivery to central nervous system. Methods: Here, a nanotechnology approach was evaluated that utilizes catalase-loaded, poly(lactic-co-glycolic acid) nanoparticles (NPs) to deliver catalase in order to protect human neurons from oxidative damage. Results: This study shows highly efficient catalase encapsulation capable of retaining ~ 99% enzymatic activity. NPs released catalase rapidly and antioxidant activity was sustained for over a month. Human neurons took up NPs rapidly and without toxicity. While human neurons are highly sensitive to H2O2, nanoparticle-mediated catalase delivery protected neuronal cultures from H2O2-induced oxidative stress. Catalase-loaded NPs significantly reduced H2O2-induced protein oxidation, DNA damage, mitochondrial membrane transition pore opening, loss of cell membrane integrity and restored cell morphology, neurite network and microtubule-associated protein-2 expression in neuronal cultures. Further, catalase-loaded NPs showed better neuronal recovery from H2O2 pre-exposure than non-encapsulated catalase enzyme, suggesting possible applications in ameliorating stroke relevant oxidative stress. Conclusions: Brain targeting of catalase-loaded NPs may find wide therapeutic applications for oxidative stress-associated acute and chronic neurodegenerative disorders.Item Neuroprotective and neurotoxic outcomes of androgens and estrogens in an oxidative stress environment(BioMed Central Ltd., 2020-03-29) Duong, Phong; Tenkorang, Mavis A. A.; Trieu, Jenny; McCuiston, Clayton; Rybalchenko, Nataliya; Cunningham, Rebecca L.BACKGROUND: The role of sex hormones on cellular function is unclear. Studies show androgens and estrogens are protective in the CNS, whereas other studies found no effects or damaging effects. Furthermore, sex differences have been observed in multiple oxidative stress-associated CNS disorders, such as Alzheimer's disease, depression, and Parkinson's disease. The goal of this study is to examine the relationship between sex hormones (i.e., androgens and estrogens) and oxidative stress on cell viability. METHODS: N27 and PC12 neuronal and C6 glial phenotypic cell lines were used. N27 cells are female rat derived, whereas PC12 cells and C6 cells are male rat derived. These cells express estrogen receptors and the membrane-associated androgen receptor variant, AR45, but not the full-length androgen receptor. N27, PC12, and C6 cells were exposed to sex hormones either before or after an oxidative stressor to examine neuroprotective and neurotoxic properties, respectively. Estrogen receptor and androgen receptor inhibitors were used to determine the mechanisms mediating hormone-oxidative stress interactions on cell viability. Since the presence of AR45 in the human brain tissue was unknown, we examined the postmortem brain tissue from men and women for AR45 protein expression. RESULTS: Neither androgens nor estrogens were protective against subsequent oxidative stress insults in glial cells. However, these hormones exhibited neuroprotective properties in neuronal N27 and PC12 cells via the estrogen receptor. Interestingly, a window of opportunity exists for sex hormone neuroprotection, wherein temporary hormone deprivation blocked neuroprotection by sex hormones. However, if sex hormones are applied following an oxidative stressor, they exacerbated oxidative stress-induced cell loss in neuronal and glial cells. CONCLUSIONS: Sex hormone action on cell viability is dependent on the cellular environment. In healthy neuronal cells, sex hormones are protective against oxidative stress insults via the estrogen receptor, regardless of sex chromosome complement (XX, XY). However, in unhealthy (e.g., high oxidative stress) cells, sex hormones exacerbated oxidative stress-induced cell loss, regardless of cell type or sex chromosome complement. The non-genomic AR45 receptor, which is present in humans, mediated androgen's damaging effects, but it is unknown which receptor mediated estrogen's damaging effects. These differential effects of sex hormones that are dependent on the cellular environment, receptor profile, and cell type may mediate the observed sex differences in oxidative stress-associated CNS disorders.Item Oxidative Stress Alters IP3 Receptor Function in the Neuronal Cell Line HT22(2008-05-01) Longoria, Sandra; Peter Koulen; Kati Prokai; Tina MachuSandra Longoria., Oxidative Stress Alters IP3 Receptor Function in the Neuronal Cell Line HT22, Master of Science (Biomedical Sciences), May 2008, 72 pp., 25 Figures. Oxidative stress contributes to the genesis of several neurodegenerative disorders such as Alzheimer’s Disease (AD). Oxidants such as, tert-butyl hydrogen peroxide (tBHP), have been used in in vitro models of neurodegeneration to induce oxidative stress. Small changes in the regulation of the intracellular calcium (Ca2+) concentration can contribute to brain aging and increase vulnerability of neurons to cellular and functional damage in neurodegenerative diseases. In neurons, inositol 1, 4, 5-trisphosphate (IP3) is a second messenger that is generated through receptor activity at the plasma membrane. IP3 receptors (IP3R) are located on endoplasmic reticulum (ER) membranes and are intracellular calcium channels (ICC) that release Ca2+ into the cytoplasm in response to activation by their ligand IP3. The goal of the present study was to measure the contribution of ICCs to Ca2+ dysregulation in neurons experiencing oxidative stress. I tested the hypothesis that oxidative stress induced with tBHP causes increased intracellular Ca2+ release via activation of IP3 receptors. I used the murine hippocampal cell line HT22, as a model for neuronal oxidative stress. Immunocytochemistry and Ca2+ imaging experiments were performed to identify areas of altered IP3R expression and activity under normal conditions and induced oxidative stress. tBHP treatment increased expression and Ca2+ release activity of neuronal IP3 receptors. My findings support that oxidative stress as seen in a number of neurodegenerative diseases negatively affects regulation of Ca2+ release through increased expression and activity of IP3 receptors.