Theses and Dissertations
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Browsing Theses and Dissertations by Subject "17beta-estradiol"
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Item 17Beta-Estradiol Suppresses Hydrogen Peroxide-Induced Nuclear Factor Kappa B Activation in HT22 Cells(2008-05-01) Kim, Pil J.; Simpkins; Singh; Yang, ShaohuaKim, Pil J., 17beta-estradiol suppresses hydrogen peroxide-induced nuclear factor κappa B activation in HT22 cells. Master of Science (Biomedical Sciences), May, 2008, 78pp., 20 illustrations, 66 titles. Reactive oxygen species (ROS) are natural byproducts of normal cellular reactions. They are oxygen ions, free (non)radicals, and peroxides that are highly reactive with normal macromolecules, such as lipids, DNA, and proteins. Cells are normally able to defend against the damages of ROS via enzymes that neutralize them into water. However, when cells are not able to cope with the accumulation of ROS, distributions in signaling pathways and gene transcription will occur, which will ultimately lead to cell death. It is now widely accepted that increased oxidative stress-induced damage in the brain is a major cause of neurodegenerative diseases, such as Alzheimer’s disease (AD). Nuclear factor κappa-B (NFκB) is not only a ubiquitously expressed transcription factor but also a signaling protein that is activated by ROS-induced oxidative stress. Our laboratory has demonstrated the neuroprotective effects of 17β-estradiol (E2) are elicited via an anti-oxidant effect. The purpose of this project was to determine the role of NFκB activation in E2-mediated neuroprotection against hydrogen peroxide (H2O2)-induced oxidative stress. HT-22, a murine immortalized hippocampal neuronal cell line, was utilized to determine whether NFκB is activated by hydrogen peroxide-induced oxidative stress and whether E2 suppresses H2O2-induced NFκB activation. We observed that H2O2 activated NFκB by phosphorylation of IκBα (pIκBα), one of the NFκB inhibitor proteins, reduction of total IκBα, and induction of NFκB (p65) nuclear translocation. In contrast, E2 suppressed H2O2-induced NFκB activation by dramatic reducing pIκBα, increasing total IκBα, and inhibiting p65 nuclear translocation. Our results show that one of the mechanisms by which estrogens are neuroprotective against oxidative stress is through the attenuation of H2O2-induced NFκB activation.Item Estrogen-induced Signaling Links Structural and Functional Synaptic Plasticity(2009-05-01) Logan, Shaun M.; Simpkins, James W.It is well documented that of its many roles, estrogen can acutely alter the intrinsic and synaptic physiology of neuronal circuits in various regions of the brain. However, the molecular and cellular mechanisms by which estrogen couples electrophysiology to plasticity and memory are still not fully understood. Our data suggests a new possible mechanism by which estrogen, via L-type voltage-gated calcium channel (L-type VGCC) potentiation, modulates memory related synaptic plasticity. The rapid onset of 17β-estradiol (E2) action (less than one second) supports the hypothesis that E2 directly interacts with the channel protein. Several techniques allowed us to confirm that not only does E2 bind with high affinity to the L-type VGCC, but that it binds at a domain that overlaps with the dihydropyridine (DHP) site. Further, to determine whether E2-induced biochemical signaling mechanistically links synaptic plasticity, we studied the phosphorylation patterns of structural and functional plasticity related proteins (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors [AMPAR], AMPA-type glutamate receptor subunit 1 [GluR1], calcium/calmodulin-dependent protein kinase II [CaMKII], and extracellular signal-related kinase [ERK]). E2 rapidly increased phosphorylation of CaMKII, ERK, and AMPAR in primary cortical neurons and in vivo in the cortex. The CaMKII inhibitor (KN-93) decreased phosphorylation levels of GluR1 in primary cortical neurons. We also determined that soluble amyloid-beta (Aβ)1-42 oligomers abrogated, while E2 ameliorated phosphorylation of GluR1 at its CaMKII site. Aβ treatment also inhibited GluR1 trafficking, but E2 prevented this inhibition. Due to our observation that E2 treatment rapidly increased spine number and ameliorated Aβ-induced spine loss, we concluded that estrogen-induced signaling does in fact mechanistically link structural and functional plasticity. In comparison with the cortical data (in vitro and in vivo), we found that E2 treatment in hippocampal slice culture ameliorated Aβ oligomer-induced inhibition of CaMKII and AMPAR phosphorylation, reduction of dendritic spine density, and abnormalities in LTP-induced spine growth. Taken together, these results suggest that acute estrogen treatment has the potential to prevent Aβ oligomer-induced synaptic dysfunction.