Estrogen increases apoptosis in the arterial wall in a murine atherosclerosis model

The interaction of estrogen and CSE/H2S pathway in the development of atherosclerosis

Both estrogen and hydrogen sulfide (H₂S) have been shown to inhibit the development of atherosclerosis. We previously reported that cystathionine γ-lyase knockout (CSE-KO) male mice develop atherosclerosis earlier than male wild-type (WT) mice. The present study investigated the interaction of CSE/H₂S pathway and estrogen on the development of atherosclerosis in female mice. Plasma estrogen levels were significantly lower in female CSE-KO mice than in female WT mice. NaHS treatment had no effect on plasma estrogen levels in both WT and CSE-KO female mice. After CSE-KO and WT female mice were fed with atherogenic diet for 12 wk, plasma lipid levels were significantly increased and triglyceride levels decreased compared with those of control diet-fed mice. Atherogenic diet induced more atherosclerotic lesion, oxidative stress, intracellular adhesion molecule-1 (ICAM-1), and NF-κB in CSE-KO mice than in WT mice. Estrogen treatment of atherogenic diet-fed WT mice attenuated hypercholesterolemia, oxidative stress, ICAM-1 expression, and NF-κB in WT mice but not in atherogenic diet-fed CSE-KO mice. Furthermore, H₂S production in both the liver and vascular tissues was enhanced by estrogen in WT mice but not in CSE-KO mice. It is concluded that the antiatherosclerotic effect of estrogen is mediated by CSE-generated H₂S. This study provides new insights into the interaction of H₂S and estrogen signaling pathways on the regulation of cardiovascular functions.NEW & NOTEWORTHY Female cystathionine γ-lyase (CSE)-knockout mice have significantly lower plasma estrogen levels and more severe early atherosclerotic lesion than female wild-type mice. H₂S production in liver and vascular tissues is enhanced by estrogen via its stimulatory effect on CSE activity. The antiatherosclerotic effect of estrogen is mediated by CSE-generated H₂S.

Molecular mechanisms of hormone resistance of breast cancer

More than 70% malignant mammary tumors contain steroid hormone receptors; this suggests the possibility of hormone therapy in the majority of patients with breast cancer (BC). The main cause of inefficiency of hormone therapy in BC is hormone resistance (tumor resistance to hormonal cytostatics). Here we discuss the main mechanisms of hormone resistance of BC and the mechanisms underlying the formation of hormone resistance of the tumors are analyzed at the molecular level. The data on the signal pathways of estrogen receptors (ER), the key regulators of BC cell proliferation, are presented. The most important factors of BC hormone resistance are: high activity/expression of receptor tyrosine kinases; high activity of proteins regulating cell defense mechanisms (Akt PI3K, mTOR); changes in the activities of cell cycle regulator proteins (Myc, c-Fos, Cyclin D1). Our experiments have demonstrated that estrogen-independent BC cell growth is supported by VEGF/VEGFR2 and EGF/EGFR mitogenic signal pathways. Our data indicate that NF-kappaB transcription factor is directly involved in the regulation of hormone-resistant BC cell growth and survival, while NF-kappaB suppression determines cell sensitivity to apoptotic activity of antitumor compounds. On the whole, the results indicate good prospects of using EGFR, HER-2/neu, mTOR, VEGFR, PI3K/Akt molecular pathways as targets for BC therapy, including therapy for BC resistant forms.

Acute exposure to high-fat diets increases hepatic expression of genes related to cell repair and remodeling in female rats

High-fat diets (HFD) promote the development of both obesity and fatty liver disease through the up-regulation of hepatic lipogenesis. Insulin resistance, a hallmark of both conditions, causes dysfunctional fuel partitioning and increases in lipogenesis. Recent work has demonstrated that systemic insulin resistance occurs in as little as the first 72 hours of an HFD, suggesting the potential for hepatic disruption with HFD at this time point. The current study sought to determine differences in expression of lipogenic genes between sexes in 3-month-old male and female Long-Evans rats after 72 hours of a 40% HFD or a 17% fat (chow) diet. Owing to the response of estrogen on hepatic signaling, we hypothesized that a sexual dimorphic response would occur in the expression of lipogenic enzymes, inflammatory cytokines, apoptotic, and cell repair and remodeling genes. Both sexes consumed more energy when fed an HFD compared with their low fat-fed controls. However, only the males fed the HFD had a significant increase in body fat. Regardless of sex, HFD caused down-regulation of lipogenic and inflammatory genes. Interestingly, females fed an HFD had up-regulated expression of apoptotic and cell repair-related genes compared with the males. This may suggest that females are more responsive to the acute hepatic injury effects caused by HFDs. In summary, neither male nor female rats displayed disrupted hepatic metabolic pathways after 72 hours of the HFD treatment. In addition, female rats appear to have protection from increases in fat deposition, possibly due to increased caloric expenditure; male rats fed an HFD were less active, as demonstrated by distance traveled in their home cage.

Actions of 17β-estradiol and testosterone in the mitochondria and their implications in aging

A decline in the mitochondrial functions and aging are two closely related processes. The presence of estrogen and androgen receptors and hormone-responsive elements in the mitochondria represents the starting point for the investigation of the effects of 17β-estradiol and testosterone on the mitochondrial functions and their relationships with aging. Both steroids trigger a complex molecular mechanism that involves crosstalk between the mitochondria, nucleus, and plasma membrane, and the cytoskeleton plays a key role in these interactions. The result of this signaling is mitochondrial protection. Therefore, the molecular components of the pathways activated by the sexual steroids could represent targets for anti-aging therapies. In this review, we discuss previous studies that describe the estrogen- and testosterone-dependent actions on the mitochondrial processes implicated in aging.

Estrogens and atherosclerosis: insights from animal models and cell systems

Estrogens not only play a pivotal role in sexual development but are also involved in several physiological processes in various tissues including vasculature. While several epidemiological studies documented an inverse relationship between plasma estrogen levels and the incidence of cardiovascular disease and related it to the inhibition of atherosclerosis, an interventional trial showed an increase in cardiovascular events among postmenopausal women on estrogen treatment. The development of atherosclerotic lesions involves complex interplay between various pro- or anti-atherogenic processes that can be effectively studied only in vivo in appropriate animal models. With the advent of genetic engineering, transgenic mouse models of atherosclerosis have supplemented classical dietary cholesterol-induced disease models such as the cholesterol-fed rabbit. In the last two decades, these models were widely applied along with in vitro cell systems to specifically investigate the influence of estrogens on the development of early and advanced atherosclerotic lesions. The present review summarizes the results of these studies and assesses their contribution toward better understanding of molecular mechanisms underlying anti- and/or pro-atherogenic effects of estrogens in humans.

Role of 17β-estradiol and testosterone in apoptosis

17β-Estradiol (E2) and Testosterone (T) exert actions in most animal tissues, in addition to the reproductive system. Thus, both sex steroid hormones affect growth and different cell functions in several organs. Accordingly, the nuclear estrogen (ER) and androgen (AR) receptors are ubiquitously expressed. Moreover, ER and AR may have non-classical intracellular localizations, e.g. plasma membrane, mitochondria and endoplasmic reticulum, raising additional complexity to the functional roles of E2 and T. In addition to the modulation of gene transcription by direct interaction with their cognate nuclear receptors, the steroids can rapidly activate signaling pathways by a non-genomic mechanism mediated by receptors identical to or different from known steroid receptors. Among various functions, E2 and T can regulate apoptosis through those pathways. In mitochondria, the presence of ER and AR and actions of estrogen and androgen have been shown, in keeping with the organelle being a control point of apoptosis. The most recurrent action for each steroid hormone is the protection of mitochondria against different insults, resulting in antiapoptosis. This review summarizes the molecular basis of the modulation of programmed cell death by E2 and T in several tissues.

Participation of HSP27 in the antiapoptotic action of 17beta-estradiol in skeletal muscle cells

Exposure to 17beta-estradiol prior to induction of apoptosis protects skeletal muscle cells against damage. The mechanism involved in this protective action of the hormone is poorly understood. In the present study, using the murine muscle cell line C2C12, evidence was obtained that inhibition of H(2)O(2)-induced apoptosis by the estrogen requires the participation of heat shock protein 27 (HSP27). Reverse transcriptase polymerase chain reaction, Western blot, and immunocytochemistry assays showed that 17beta-estradiol induces a time-dependent (5-60 min) increase in the expression of HSP27. In addition, in presence of quercetin, an inhibitor of HSPs, the antiapoptotic effect of the hormone was diminished. More specifically, blockage experiments with short interference RNA targeting HSP27 confirmed the role of this chaperone in the protective effect of the steroid. 17beta-Estradiol abolished caspase-3 cleavage elicited by H(2)O(2). Coimmunoprecipitation assays suggested physical interaction of HSP27 with caspase-3 in presence of estradiol. Furthermore, we observed that this chaperone interacts with estrogen receptors (ER) beta in mitochondria. Then, this study suggests that HSP27 plays a new role in the antiapoptotic action triggered by 17beta-estradiol by modulating caspase-3 activity and stabilizing ERbeta in skeletal muscle cells.

Research into Specific Modulators of Vascular Sex Hormone Receptors in the Management of Postmenopausal Cardiovascular Disease

Cardiovascular disease (CVD) is more common in men and postmenopausal women than premenopausal women, suggesting vascular benefits of female sex hormones. Studies on the vasculature have identified estrogen receptors ERα, ERβ and a novel estrogen binding membrane protein GPR30, that mediate genomic and/or non-genomic effects. Estrogen promotes endothelium-dependent relaxation by inducing the production/activity of nitric oxide, prostacyclin, and hyperpolarizing factor, and inhibits the mechanisms of vascular smooth muscle contraction including [Ca(2+)](i), protein kinase C, Rho kinase and mitogen-activated protein kinase. Additional effects of estrogen on the cytoskeleton, matrix metalloproteinases and inflammatory factors contribute to vascular remodeling. However, the experimental evidence did not translate into vascular benefits of menopausal hormone therapy (MHT), and the HERS, HERS-II and WHI clinical trials demonstrated adverse cardiovascular events. The discrepancy has been partly related to delayed MHT and potential changes in the vascular ER amount, integrity, affinity, and downstream signaling pathways due to the subjects' age and preexisting CVD. The adverse vascular effects of MHT also highlighted the need of specific modulators of vascular sex hormone receptors. The effectiveness of MHT can be improved by delineating the differences in phramcokinetics and pharmacodynamics of natural, synthetic, and conjugated equine estrogens. Estriol, "hormone bioidenticals" and phytoestrogens are potential estradiol substitutes. The benefits of low dose MHT, and transdermal or vaginal estrogens over oral preparations are being evaluated. Specific ER modulators (SERMs) and ER agonists are being developed to maximize the effects on vascular ERs. Also, the effects of estrogen are being examined in the context of the whole body hormonal environment and the levels of progesterone and androgens. Thus, the experimental vascular benefits of estrogen can be translated to the outcome of MHT in postmenopausal CVD, as more specific modulators of sex hormone receptors become available and are used at the right dose, route of administration and timing, depending on the subject's age and preexisting cardiovascular condition.

Estradiol-mediated ERK phosphorylation and apoptosis in vascular smooth muscle cells requires GPR 30

Recent studies suggest that the rapid and nongenomic effects of estradiol may be mediated through the G protein-coupled receptor dubbed GPR30 receptor. The present study examines the role of GPR30 versus a classical estrogen receptor (ERalpha) in mediating the growth regulatory effects of estradiol. GPR30 is readily detectable in freshly isolated vascular tissue but barely detectable in cultured vascular smooth muscle cells (VSMC). In freshly isolated aortic tissue, estradiol stimulated extracellular signal-regulated kinases (ERK) phosphorylation. In contrast, in cultured VSMC, where GPR30 expression is significantly reduced, estradiol inhibits ERK phosphorylation. Transfer of the genes encoding GPR30 led to estradiol stimulation of ERK phosphorylation, which is opposite the effects of estradiol in the primary culture of VSMCs. Transduction of the mineralocorticoid receptor (MR) had no effect on estradiol effects on ERK. Estradiol-mediated stimulation of ERK subsequent to heterologous GPR30 expression was pertussis toxin sensitive and phosphoinositide 3-kinase (PI3 kinase) dependent; under these conditions, estradiol also inhibited protein kinase A (PKA). In contrast, in the absence of GPR30 expression in cultured VSMC, estradiol stimulated PKA activity and inhibited ERK phosphorylation. To determine the functional effect of GPR30 (vs. estrogen receptor expression), we assessed estradiol-mediated apoptosis. In the absence of GPR30 expression, estradiol inhibited apoptosis. This effect was enhanced with ERalpha expression. In contrast, with GPR30 expression, estradiol stimulated apoptosis in an ERK-dependent manner. Thus the effect of estradiol on vascular smooth muscle cell apoptosis is likely dependent on the balance between ER-mediated PKA activation and GPR30-mediated PKA inhibition and PI3 kinase activation. Taken together, we postulate that modulation of GPR30 expression or activity may be an important determinant of the effects of estradiol in the vasculature.

Other Transgenic Animal Models Used in Cardiovascular Studies

Previous chapters have described a large number of transgenic animal models used to study specific cardiovascular syndromes. This chapter will fill in some gaps. Many of these transgenic animals were developed to study normal and/or abnormal physiological responses in other organ systems, or to study basic biochemical and molecular reactions or pathways. These models were then discovered to also have effects on the cardiovascular system, some of them unanticipated.

A word of caution, particularly when highly inbred mouse strains are used to develop transgenic models - not all strains of a particular species are created equal. When cardiovascular parameters of age- and sex-matched A/J and C57BL/6J inbred mice were compared the C57BL/6J mice demonstrated eccentric physiologic ventricular hypertrophy, increased ventricular function, lower heart rates, and increased exercise endurance.¹