Mitochondrial Effects of Estrogen Are Mediated by Estrogen Receptor in Brain Endothelial Cells

Department of Pharmacology, School of Medicine, University of California, Irvine, CA 92697-4625, USA.
Journal of Pharmacology and Experimental Therapeutics (Impact Factor: 3.97). 07/2008; 325(3):782-90. DOI: 10.1124/jpet.107.134072
Source: PubMed


Mitochondrial reactive oxygen species (ROS) and endothelial dysfunction are key contributors to cerebrovascular pathophysiology. We previously found that 17beta-estradiol profoundly affects mitochondrial function in cerebral blood vessels, enhancing efficiency of energy production and suppressing mitochondrial oxidative stress. To determine whether estrogen specifically affects endothelial mitochondria through receptor mechanisms, we used cultured human brain microvascular endothelial cells (HBMECs). 17beta-Estradiol treatment for 24 h increased mitochondrial cytochrome c protein and mRNA; use of silencing RNA for estrogen receptors (ERs) showed that this effect involved ERalpha, but not ERbeta. Mitochondrial ROS were determined by measuring the activity of aconitase, an enzyme with an iron-sulfur center inactivated by mitochondrial superoxide. 17beta-Estradiol increased mitochondrial aconitase activity in HBMECs, indicating a reduction in ROS. Direct measurement of mitochondrial superoxide with MitoSOX Red showed that 17beta-estradiol, but not 17alpha-estradiol, significantly decreased mitochondrial superoxide production, an effect blocked by the ER antagonist, ICI-182,780 (fulvestrant). Selective ER agonists demonstrated that the decrease in mitochondrial superoxide was mediated by ERalpha, not ERbeta. The selective estrogen receptor modulators, raloxifene and 4-hydroxy-tamoxifen, differentially affected mitochondrial superoxide production, with raloxifene acting as an agonist but 4-hydroxy-tamoxifen acting as an estrogen antagonist. Changes in superoxide by 17beta-estradiol could not be explained by changes in manganese superoxide dismutase. Instead, ERalpha-mediated decreases in mitochondrial ROS may depend on the concomitant increase in mitochondrial cytochrome c, previously shown to act as an antioxidant. Mitochondrial protective effects of estrogen in cerebral endothelium may contribute to sex differences in the occurrence of stroke and other age-related neurodegenerative diseases.

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Available from: Vincent Procaccio, Jun 13, 2015
    • "This is in line with other results showing that neuroprotection involves attenuation of NADPH oxidase activation and superoxide production via an ERα-mediated nongenomic signaling cascade (Zhang et al., 2009). In human brain microvascular endothelial cells physiological levels of 17β-Estradiol but not its enantiomer 17α-Estradiol suppressed mitochondrial superoxide production mediated through ERα receptor (Razmara et al., 2008). The failure of 17α-Estradiol, which does not activate ER but shares antioxidant properties, underlines the irrelevance of estradiol's direct antioxidant activity at physiological levels. "
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    ABSTRACT: Introduction 17β-estradiol (E2) is neuroprotective in experimental models of stroke. While some postulate a mainly antioxidative action due to E2’s free C3 hydroxyl group at its A-ring, others suggest that neuroprotection is mediated by a hormonal, receptor mediated effect. The aim of the current study was to clarify this issue by testing whether E2 analogues lacking hormonal activity are also neuroprotective following cerebral ischemia. Material & Methods Focal cerebral ischemia was induced in male C57/BL6 mice by laser-Doppler-controlled endovascular occlusion of the middle cerebral artery for 40 min. Mice received either 1) memantine, a NMDA-receptor antagonist, as a positive control, 2) E2 (1400 µg/kg b.w.), or 3) 2,4,6-trimethylphenol (TMP), an E2 analogue without hormonal activity (1400, 140, or 14 µg/kg b.w.). Motor function was tested 3 h and 24 h after ischemia. Thereafter mice were sacrificed and brain damage was quantified by histomorphometry. Results Treatment with memantine or E2 significantly reduced infarct volume by >40% and significantly improved neurological function while treatment with TMP had no effect. Conclusion E2 is equally neuroprotective as antagonization of NMDA receptors while E2 analogues without hormonal activity are not neuroprotective. Therefore the current data suggest that the neuroprotection activity of E2 is independent of its free-radical scavenging properties.
    No preview · Article · Nov 2014 · Brain Research
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    • "However, existing data suggest the interactions of estrogen with its cognate receptors may be beneficial. During early post-ischemic conditions ER-α can maintain mitochondrial biogenesis [28], suppress free radical formation and lessen inflammation [28]. Estrogen has been shown to modulate endothelium-dependent dilation via processes that involve nitric oxide (NO), prostacyclin I2 and endothelium dependent hyperpolarizing factor [12], [29]–[31]. "
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    ABSTRACT: Background Several studies demonstrate that estrogen treatment improves cerebral blood flow in ischemic brain regions of young ovariectomized (OVX) rats. Estrogen receptor-α (ER-α) may mediate estrogen’s beneficial actions via its effects on the cerebral microvasculature. However, estrogen-derived benefit may be attenuated in aged, reproductively senescent (RS) rats. Our goal was to determine the effects of aging, estrogen deprivation and estrogen repletion with oral conjugated estrogens (CE) on postischemic cerebral microvascular protein expression of ER-α and ER-β. Methods Fisher-344 (n = 37) female rats were randomly divided into the following groups: OVX, OVX CE-treated, RS untreated, and RS CE-treated. After 30 days pretreatment with CE (0.01 mg/kg) rats were subjected to15 min. transient global cerebral ischemia. Non-ischemic naïve, OVX and RS rats were used as controls. Expression of ER-α and ER-β in isolated cortical cerebral microvessels (20 to 100 µm in diameter) was assessed using Western blot and immunohistochemistry techniques. Results Age and reproductive status blunted nonischemic ER-α expression in microvessels of OVX rats (0.31±0.05) and RS rats (0.33±0.06) compared to naïve rats (0.45±0.02). Postischemic microvascular expression of ER-α in OVX rats (0.01±0.0) was increased by CE treatment (0.04±0.01). Expression of ER-α in microvessels of RS rats (0.03±0.02) was unaffected by CE treatment (0.01±0.02). Western blot data are presented as a ratio of ER-α or ER-β proteins to β-actin and. Oral CE treatment had no effect on ER-β expression in postischemic microvessels of OVX and RS rats. Statistical analysis was performed by One-Way ANOVA and a Newman-Keuls or Student’s post-hoc test. Conclusion Chronic treatment with CE increases ER-α but not ER-β expression in cerebral microvessels of OVX rats. Aging appears to reduce the normal ability of estrogen to increase ER-α expression in postischemic cerebral microvessels.
    Full-text · Article · Jul 2014 · PLoS ONE
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    • "Endocrine disrupters may also be involved in different estrogenic intervention processes, such as the glycolytic pathway and during the regulation of glucose transporters with compounds like BPA, 4-nonylphenol (NP), 4-octylphenol (OP), and 4-propylphenol [116, 153, 154]. Endocrine disruption using these substances also interferes with tricarboxylic acid metabolism by decreasing key enzymes in mitochondrial activity, which could be partially related to obesity (Figure 4). "
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    ABSTRACT: Sex hormones strongly influence body fat distribution and adipocyte differentiation. Estrogens and testosterone differentially affect adipocyte physiology, but the importance of estrogens in the development of metabolic diseases during menopause is disputed. Estrogens and estrogen receptors regulate various aspects of glucose and lipid metabolism. Disturbances of this metabolic signal lead to the development of metabolic syndrome and a higher cardiovascular risk in women. The absence of estrogens is a clue factor in the onset of cardiovascular disease during the menopausal period, which is characterized by lipid profile variations and predominant abdominal fat accumulation. However, influence of the absence of these hormones and its relationship to higher obesity in women during menopause are not clear. This systematic review discusses of the role of estrogens and estrogen receptors in adipocyte differentiation, and its control by the central nervous systemn and the possible role of estrogen-like compounds and endocrine disruptors chemicals are discussed. Finally, the interaction between the decrease in estrogen secretion and the prevalence of obesity in menopausal women is examined. We will consider if the absence of estrogens have a significant effect of obesity in menopausal women.
    Full-text · Article · Mar 2014
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