Browsing by Subject "neurons"
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Item Mechanisms by which 17β-Estradiol (E2) suppress neuronal cox-2 expression(2015-12-01) Stacey, Winfred; Rosalie M. Uht; Rebecca L. Cunningham; Eric B. GonzalesData from animal models indicate that 17β-estradiol (E2) deprivation increases susceptibility to neurodegenerative diseases. E2 attenuates inflammatory response by suppressing expression of pro-inflammatory genes; however, the mechanisms by which E2 suppress neuronal pro-inflammatory genes are not well established. Histological analyses of postmortem human brains suggest that neuronal cyclooxygenase-2 (COX-2) is upregulated in early stages of Alzheimer’s disease (AD) and in Parkinson’s disease (PD). Given that COX-2 is selectively expressed in a subset of neurons in the hippocampus, cerebral cortex, and amygdala, we investigated mechanisms by which E2 could down-regulate cox-2 expression in a neuronal system. To characterize the effect of E2 on cox 2 in a neuronal system, we used the AR-5 and N27 rat neuronal cell line models. Our data indicate that E2 and ERβ agonist diarylpropionitrile (DPN) suppress COX-2 pre-mRNA and mRNA levels to the same extent in AR-5 but not in N27. Furthermore, PHTPP, a selective ERβ antagonist, reversed the effect of both E2 and DPN in AR-5. Because the cox-2 promoter lacks palindromic estrogen response elements (EREs), we targeted a proximal promoter region with a nuclear factor- ĸB (NF-ĸB) response element implicated in cox-2 regulation. E2 and DPN failed to increase ERβ occupancy at the cox-2 promoter. Rather, DPN decreased promoter occupancy of p65 NF-κB subunit and acetylation of histone 4 (Ac-H4). Treatment with the non-specific HDAC inhibitor Trichostatin A (TSA) counteracted DPN’s repressive effects on cox-2 expression. In keeping with the effect of TSA, E2 and DPN increase HDAC1 promoter occupancy; however recruitment of HDAC3 was unchanged. HDAC1 is known to form a complex with Swi-independent A (Sin3A); E2 and DPN increased Sin3A occupancy. The recruitment of HDAC1 seems to correlate with decreased acetylation of histone 4 (H4) and not histone 3 (H3). Furthermore E2 alone increased methylation status in the cox-2 proximal promoter. Taken together, these data suggest that E2 suppresses neuronal cox-2 expression through ERβ-mediated recruitment of HDAC1, Sin3A and a concomitant reduction of p65 and H4 levels. Here we conclude that E2 suppresses neuronal cox-2 expression through a mechanism that involves a combination of decreasing activator and increasing repressor recruitment to the cox-2 promoter.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.Item Regulation of intracellular calcium channels by their associated proteins homer 1 and presenilin 1(2006-05-01) Hwang, Sung-Yong; Koulen, Peter; Dillon, Glenn; Singh, MeharvanSung-Yong, Hwang, Regulation of intracellular calcium channels by their associated proteins homer 1 and presenilin 1. Doctor of Philosophy (Pharmacology and Neuroscience), May, 2006, 184 pp., 4 tables, 20 illustrations, 74 titles. In neurons, Calcium (CA2+) serves as a critical intracellular messenger that regulates a variety of cellular processes such as gene expression, neurotransmitter release, cell death, and synaptic plasticity. Therefore, it is essential for neurons to control their Ca2+ levels tightly. Ca2+ is released within the cell from intracellular stores such as the endoplasmic reticulum by activation of intracellular Ca2+ channels (ICCs) such as the inositol 1,4,5-triphosphate (IP3) receptors (IP3Rs) and ryanodine receptors (RyRs). Each of these two groups of ICC has three isoforms. A number of associated proteins of these two ICCs that were shown to modulate activity of the respective channel have been identified. Homer 1, a synaptic scaffolding protein not only physically associated with IP3R type1 (IP3R1), but also changes the activity of IP3R1, suggesting that Homer 1 is involved in intracellular Ca2+ signaling. Based on the similarity in amino acid sequence and molecular and physiological properties among IP3R isoforms and the fact that IP3R type 3 (IP3R3) contains the proline-rich motif (PPxxFr) that is required for the interaction with Homer, it was hypothesized that Homer 1 associates with IP3R3, leading to changes in the channel activity. Presenilin 1 (PS1) is a transmembrane protein, being expressed in cell body, dendrites, and axon in the neuron. Mutations in PS1 account for most cases of early-onset familial Alzheimer’s disease (AD). PS1 was shown to associate with RyRs and to modulate their channel activity. Therefore, it was hypothesized that specific regions of PS-1 bind to RyR type 2 (RyR2), a major isoform in the brain, resulting in changes in the channel activity. Homer 1c was shown to associate with IP3R3, leading to a decrease in channel activity. A specific region of PS1 that interacts with RyR2 was identified to increase the channel activity of RyR2. Results of the present study contributed to the understanding of the nature of intracellular Ca2+ signaling as well as the mechanisms of action by which ICCs are regulated by their associated proteins. These findings provide the rationale for novel strategies to study neurological disorders including AD and epilepsy that are mediated by Ca2+ dysregulation.