Effect of estradiol on low density lipoprotein uptake by bovine aortic endothelial cells

Identification of authentic estrogen receptor in cultured endothelial cells. A potential mechanism for steroid hormone regulation of endothelial function

BACKGROUND

Estrogen plays a major role in the delayed expression of coronary heart disease (CHD) in women, and recent data indicate that postmenopausal estrogen therapy reduces the incidence of CHD by > 40%. The mechanism or mechanisms through which estrogen exerts this benefit are unknown, although effects on blood pressure, carbohydrate and lipid metabolism, and coagulation have been suggested. We hypothesized that at least part of the effect of estrogen in reducing the incidence of CHD is due to an effect on endothelial cell function.

METHODS AND RESULTS

In the present study, we examined human aortic and umbilical vein endothelial cells and bovine aortic endothelial cells for the presence of estrogen receptors (ERs) through immunoblot and mRNA analyses. Electrophoretic mobility shift assays were also performed to determine the DNA-binding properties of the putative ERs. Nuclear extracts from all three endothelial cell types were found to contain a 67-kD protein that reacted with anti-ER monoclonal antibodies specific to different domains of the ERs. Each of these types of cells expresses proteins that bind specifically to consensus estrogen-responsive elements. Finally, Northern blots verified that endothelial cells express abundant amount of mRNA for the ER.

CONCLUSIONS

These data indicate that endothelial cells constitutively possess the potential for transcriptional regulation of target genes by estrogen. The evolutionary conservation of this receptor in bovine and human endothelial cells suggests a common mechanism for estrogen regulation of endothelial function.

17 beta-Estradiol inhibits flow- and acute hypoxia-induced prostacyclin release from perfused endocardial endothelial cells

BACKGROUND

Because of the marked difference in the incidence and severity of cardiovascular diseases between men and premenopausal women, several groups have studied the effect of sex steroids, particularly estrogen, on vascular endothelial prostacyclin (PGI2) release. No previous studies have addressed the effect of estrogen on endocardial endothelial cells (EECs), which are involved in the modulation of the myocardium and potentially in downstream pulmonary and systemic vascular tone. Furthermore, all previous studies of estrogen effects on cultured endothelial cell function have used cells grown under standard static cell culture conditions, thereby ignoring the contribution of flow, the ubiquitous environmental endothelial stimulus.

METHODS AND RESULTS

The effect of 17 beta-estradiol pretreatment (100 ng/mL, 72 hours) on cultured sheep EEC PGI2 release in response to multiple physiologically relevant stimuli was studied. EECs were grown in six-well plates (static conditions) or on microcarrier beads and perfused at a constant flow with normoxic (PO2 = 150 mm Hg, PCO2 = 35 mm Hg) or hypoxic (PO2 = 35 mm Hg, PCO2 = 35 mm Hg) Krebs solution. The stable metabolite of PGI2, 6-keto-PGF1 alpha, was determined in samples from both static and perfusion experiments by direct radioimmunoassay. 17 beta-Estradiol pretreatment did not alter basal or stimulated (arachidonic acid, 1 mumol/L, 10 mumol/L; A23187, 10 mumol/L; and bradykinin, 1 mumol/L) PGI2 release in static conditions. Untreated and acutely treated (100 ng/mL added to perfusate) EECs responded to flow with a time-dependent increase in PGI2 release that plateaued between 60 and 100 minutes. In contrast, 17 beta-estradiol-pretreated, perfused EECs did not increase PGI2 release over time. During perfusion, acute hypoxia increased PGI2 release: 140 +/- 65 (normoxia) to 296 +/- 113 pg (hypoxia) 6-keto-PGF1 alpha/mg per minute. 17 beta-Estradiol inhibited hypoxia-induced PGI2 release: 296 +/- 113 pg (untreated EECs, hypoxia) versus 159 +/- 60 pg (17 beta-estradiol pretreated, hypoxia) 6-keto-PGF1 alpha/mg per minute.

CONCLUSIONS

This study demonstrates for the first time an inhibitory effect of 17 beta-estradiol on flow- and acute hypoxia-induced increase in PGI2 release from perfused EECs in the absence of any effect on pharmacologically stimulated PGI2 release from static cultures. These effects of 17 beta-estradiol may explain in part the well-recognized gender and estrogen effects in cardiovascular diseases and highlight the importance of flow in studies of endothelial cell function.

Postmenopausal hormone replacement therapy--clinical implications

The menopause is defined as cessation of menstruation, ending the fertile period. The hormonal changes are a decrease in progesterone level, followed by a marked decrease in estrogen production. Symptoms associated with these hormonal changes may advocate for hormonal replacement therapy. This review is based on the English-language literature on the effect of estrogen therapy and estrogen plus progestin therapy on postmenopausal women. The advantages of hormone replacement therapy are regulation of dysfunctional uterine bleeding, relief of hot flushes, and prevention of atrophic changes in the urogenital tract. Women at risk of osteoporosis will benefit from hormone replacement therapy. The treatment should start as soon after menopause as possible and it is possible that it should be maintained for life. The treatment may be supplemented with extra calcium intake, vitamin D, and maybe calcitonin. Physical activity should be promoted, and cigarette smoking reduced if possible. Women at risk of cardiovascular disease will also benefit from hormone replacement therapy. There is overwhelming evidence that hormone therapy will protect against both coronary heart disease and stroke, and there is no increased risk of venous thrombosis or hypertension. A disadvantage of hormone replacement therapy is an increased risk of forming gall-bladder stones and undergoing cholecystectomy. Unopposed estrogen therapy gives a higher incidence of endometrial cancer in women with an intact uterus, but the contribution of progestins for about 10 days every month excludes this risk. Breast cancer in relation to estrogen-progestogen therapy has been given much concern, and the problem is still not fully solved. If there is a risk, it is small, and only after prolonged use of estrogen (15-20 years). The decision whether or not to use hormone replacement therapy should, of course, be taken by the individual woman in question, but her decision should be based on the available scientific information. It is the opinion of the authors that the advantages of hormone replacement therapy far exceed the disadvantages. We suggest that every woman showing any signs of hormone deprivation should be treated with hormone replacement therapy. This includes women with subjective or objective vaso-motor symptoms, genito-urinary symptoms, women at risk of osteoporosis (fast bone losers), and women at risk of cardiovascular diseases.

Estradiol enhances leukocyte binding to tumor necrosis factor (TNF)-stimulated endothelial cells via an increase in TNF-induced adhesion molecules E-selectin, intercellular adhesion molecule type 1, and vascular cell adhesion molecule type 1

Adhesion of leukocytes to endothelial cells is a critical step in the development of acute and chronic inflammatory lesions. We report here that estradiol treatment of cultured human umbilical vein endothelial cells stimulated up to a twofold increase in TNF-induced adhesion of both polymorphonuclear leukocytes and PMA-activated peripheral blood mononuclear cells. This effect was more evident (threefold increase) when endothelial cells were cultured on the basement membrane glycoprotein laminin. Progesterone, but not testosterone, had a similar stimulatory effect. Estradiol also promoted a slight increase in interferon gamma-stimulated endothelial cell adherence for peripheral blood mononuclear cells, but no effect of estradiol was observed when adhesion of leukocytes to endothelial cells was stimulated with IL-1 or IL-4. The estradiol-induced increase in leukocyte binding to human umbilical vein endothelial cells was partially blocked by antibodies to the adhesion molecules E-selectin, intercellular adhesion molecule type 1 (ICAM-1), and vascular cell adhesion molecule type 1 (VCAM-1). Indirect immunofluorescence techniques showed that estradiol produces an increase in TNF-induced cell surface expression of these molecules. Northern blot analysis demonstrated a transient increase in TNF-induced expression of mRNA for E-selectin, ICAM-1, and VCAM-1 in endothelial cells treated with estradiol. Our data demonstrate that estradiol has important regulatory functions in promoting leukocyte-endothelial cell interactions that might contribute to the observed predominance in females of some autoimmune inflammatory diseases.