The effect of estrogen on the vasculature is mediated in part by influences on NO bioavailability. Nitric oxide (NO) is a potent vasodilator which is synthesized in endothelial cell by endothelial nitric oxide synthase (eNOS) catalyzed conversion of L-arginine to L-citrulline. Although estrogen has been shown to increase eNOS expression and/or activity, the mechanism of estrogen-mediated increased eNOS activity in endothelial cells remains elusive. The Ca 2+ /calmodulin complex is known to aid in eNOS activation by dissociating eNOS from the membrane bound protein, caveolin-1. We investigated the role of estrogen on the Ca 2+ homeostasis of the human endothelial cell line, EA.hy926, using thapsigargin (TG), a sarco(endo)plasmic reticulum Ca 2+ -ATPase, or ATP, a purinergic receptor agonist, to evoke increased intracellular calcium concentration ([Ca 2+ ] i ). [Ca 2+ ] i in Fura 2-AM-loaded EA.hy926 cell populations were measured by fluorescence spectrophotometry. Treatment of cells with 17 β-estradiol (E 2 , 1 μM, 24 hours) showed an increased agonist-evoked [Ca 2+ ] i increase due to both higher Ca 2+ release and Ca 2+ influx, which accompanied an increased eNOS protein expression. Both increased [Ca 2+ ] i and eNOS expression were attenuated with the nonselective estrogen receptor (ER) inhibitor, ICI 182,780. We further analyzed the role of ER in E 2 - mediated effects using ERα-knockdown cells. ERα-knockdown was achieved by transfecting the cells with ERα-specific siRNA. E 2 did not influence agonist-evoked [Ca 2+ ] i increase in the ERα-knockdown cells, indicating that the E 2 -mediated effects were ERα-dependent. In the vasculature, both the genomic and nongenomic effects of estrogen are mediated via ERα. In the current study, the effect of E 2 on agonist-evoked [Ca 2+ ] i increase was only observed in chronically treated (1 μM, 24 hours) cells and not acutely treated (1 μM, 5 minutes) cells, suggesting a genomic action of E 2 . The genomic action was verified by treating cells with E 2 in the presence of actinomycin D, a transcription inhibitor. Actinomycin D attenuated the effect of E 2 on agonist-evoked [Ca 2+ ] i increase. The present work revealed a transcription-dependent and ERα-mediated modulation of Ca 2+ homeostasis in human endothelial cells treated with estrogen for the long-term. This data suggests a novel mechanism by which estrogen-mediated NO release may occur in endothelial cells.
| Identifer | oai:union.ndltd.org:pacific.edu/oai:scholarlycommons.pacific.edu:uop_etds-3396 |
| Date | 01 January 2009 |
| Creators | Thor, Der |
| Publisher | Scholarly Commons |
| Source Sets | University of the Pacific |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | University of the Pacific Theses and Dissertations |
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