Genetic knockdown of estrogen receptor-alpha in the subfornical organ augments ANG II-induced hypertension in female mice

The adverse role of endocrine disrupting chemicals in the reproductive system

Reproductive system diseases pose prominent threats to human physical and mental well-being. Besides being influenced by genetic material regulation and changes in lifestyle, the occurrence of these diseases is closely connected to exposure to harmful substances in the environment. Endocrine disrupting chemicals (EDCs), characterized by hormone-like effects, have a wide range of influences on the reproductive system. EDCs are ubiquitous in the natural environment and are present in a wide range of industrial and everyday products. Currently, thousands of chemicals have been reported to exhibit endocrine effects, and this number is likely to increase as the testing for potential EDCs has not been consistently required, and obtaining data has been limited, partly due to the long latency of many diseases. The ability to avoid exposure to EDCs, especially those of artificially synthesized origin, is increasingly challenging. While EDCs can be divided into persistent and non-persistent depending on their degree of degradation, due to the recent uptick in research studies in this area, we have chosen to focus on the research pertaining to the detrimental effects on reproductive health of exposure to several EDCs that are widely encountered in daily life over the past six years, specifically bisphenol A (BPA), phthalates (PAEs), polychlorinated biphenyls (PCBs), parabens, pesticides, heavy metals, and so on. By focusing on the impact of EDCs on the hypothalamic-pituitary-gonadal (HPG) axis, which leads to the occurrence and development of reproductive system diseases, this review aims to provide new insights into the molecular mechanisms of EDCs' damage to human health and to encourage further in-depth research to clarify the potentially harmful effects of EDC exposure through various other mechanisms. Ultimately, it offers a scientific basis to enhance EDCs risk management, an endeavor of significant scientific and societal importance for safeguarding reproductive health.

Loss of the Protective Effect of Estrogen Contributes to Maternal Gestational Hypertension-Induced Hypertensive Response Sensitization Elicited by Postweaning High-Fat Diet in Female Offspring

Background

A recent study conducted in male offspring demonstrated that maternal gestational hypertension (MHT) induces hypertensive response sensitization (HTRS) elicited by postweaning high‐fat diet (HFD). In this study, we investigated the sensitizing effect of MHT on postweaning HFD‐induced hypertensive response in female rat offspring and assessed the protective role of estrogen in HTRS.

Methods and Results

The results showed that MHT also induced a sensitized HFD‐elicited hypertensive response in intact female offspring. However, compared with male offspring, this MHT‐induced HTRS was sex specific in that intact female offspring exhibited an attenuated increase in blood pressure. Ovariectomy significantly enhanced the HFD‐induced increase in blood pressure and the pressor response to centrally administered angiotensin II or tumor necrosis factor‐α in offspring of normotensive dams, which was accompanied by elevated centrally driven sympathetic activity, upregulated mRNA expression of prohypertensive components, and downregulated expression of antihypertensive components in the hypothalamic paraventricular nucleus. However, when compared with HFD‐fed ovariectomized offspring of normotensive dams, the MHT‐induced HTRS and pressor responses to centrally administered angiotensin II or tumor necrosis factor‐α in HFD‐fed intact offspring of MHT dams were not potentiated by ovariectomy, but the blood pressure and elicited pressor responses as well as central sympathetic tone remained higher.

Conclusions

The results indicate that in adult female offspring MHT induced HTRS elicited by HFD. Estrogen normally plays a protective role in antagonizing HFD prohypertensive effects, and MHT compromises this normal protective action of estrogen by augmenting brain reactivity and centrally driven sympathetic activity.

Central CYP1B1 (Cytochrome P450 1B1)-Estradiol Metabolite 2-Methoxyestradiol Protects From Hypertension and Neuroinflammation in Female Mice

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Previously, we showed that peripheral administration of 2-ME (2-methoxyestradiol), a CYP1B1 (cytochrome P450 1B1)-catechol-O-methyltransferase (COMT) generated metabolite of E2 (17β-Estradiol), protects against angiotensin II-induced hypertension in female mice. The demonstration that central E2 inhibits angiotensin II-induced hypertension, together with the expression of CYP1B1 in the brain, led us to hypothesize that E2-CYP1B1 generated metabolite 2-ME in the brain mediates its protective action against angiotensin II-induced hypertension in female mice. To test this hypothesis, we examined the effect of intracerebroventricularly (ICV) administered E2 in ovariectomized (OVX)-wild-type (Cyp1b1^+/+) and OVX-Cyp1b1^−/− mice on the action of systemic angiotensin II. ICV-E2 attenuated the angiotensin II-induced increase in mean arterial blood pressure, impairment of baroreflex sensitivity, and sympathetic activity in OVX-Cyp1b1^+/+ but not in ICV-injected short interfering (si)RNA-COMT or OVX-Cyp1b1^−/− mice. ICV-2-ME attenuated the angiotensin II-induced increase in blood pressure in OVX-Cyp1b1^−/− mice; this effect was inhibited by ICV-siRNA estrogen receptor-α (ERα) and G protein-coupled estrogen receptor 1 (GPER1). ICV-E2 in OVX-Cyp1b1^+/+ but not in OVX-Cyp1b1^−/− mice and 2-ME in the OVX-Cyp1b1^−/− inhibited angiotensin II-induced increase in reactive oxygen species production in the subfornical organ and paraventricular nucleus, activation of microglia and astrocyte, and neuroinflammation in paraventricular nucleus. Furthermore, central CYP1B1 gene disruption in Cyp1b1^+/+ mice by ICV-adenovirus-GFP (green fluorescence protein)-CYP1B1-short hairpin (sh)RNA elevated, while reconstitution by adenovirus-GFP-CYP1B1-DNA in the paraventricular nucleus but not in subfornical organ in Cyp1b1^−/− mice attenuated the angiotensin II-induced increase in systolic blood pressure. These data suggest that E2-CYP1B1-COMT generated metabolite 2-ME, most likely in the paraventricular nucleus via estrogen receptor-α and GPER1, protects against angiotensin II-induced hypertension and neuroinflammation in female mice.

Genetic knockdown of brain-derived neurotrophic factor in the nervous system attenuates angiotensin II-induced hypertension in mice

Introduction:

Brain-derived neurotropic factor (BDNF) is expressed throughout the central nervous system and peripheral organs involved in the regulation of blood pressure, but the systemic effects of BDNF in the control of blood pressure are not well elucidated.

Materials and methods:

We utilized loxP flanked BDNF male mice to cross with nestin-Cre female mice to generate nerve system BDNF knockdown mice, nestin-BDNF (+/–), or injected Cre adenovirus into the subfornical organ to create subfornical organ BDNF knockdown mice. Histochemistry was used to verify injection location. Radiotelemetry was employed to determine baseline blood pressure and pressor response to angiotensin II (1000 ng/kg/min). Real-time polymerase chain reaction was used to measure the expression of renin–angiotensin system components in the laminal terminalis and peripheral organs.

Results:

Nestin-BDNF (+/–) mice had lower renin–angiotensin system expression in the laminal terminalis and peripheral organs including the gonadal fat pad, and a lower basal blood pressure. They exhibited an attenuated hypertensive response and a weak or similar modification of renin–angiotensin system component expression to angiotensin II infusion. Subfornical organ BDNF knockdown was sufficient for the attenuation of angiotensin II-induced hypertension.

Conclusion:

Central BDNF, especially subfornical organ BDNF is involved in the maintenance of basal blood pressure and in augmentation of hypertensive response to angiotensin II through systemic regulation of the expression of renin–angiotensin system molecules.

Roles of oestradiol receptor alpha and beta against hypertension and brain mitochondrial dysfunction under intermittent hypoxia in female rats

AIM

Chronic intermittent hypoxia (CIH) induces systemic (hypertension) and central alterations (mitochondrial dysfunction underlying cognitive deficits). We hypothesized that agonists of oestradiol receptors (ER) α and β prevent CIH-induced hypertension and brain mitochondrial dysfunction.

METHODS

Ovariectomized female rats were implanted with osmotic pumps delivering vehicle (Veh), the ERα agonist propylpyraoletriol (PPT - 30 μg/kg/day) or the ERβ agonist diarylpropionitril (DPN - 100 μg/kg/day). Animals were exposed to CIH (21%-10% F_I O₂ - 10 cycles/hour - 8 hours/day - 7 days) or normoxia. Arterial blood pressure was measured after CIH or normoxia exposures. Mitochondrial respiration and H₂ O₂ production were measured in brain cortex with high-resolution respirometry, as well as activity of complex I and IV of the electron transport chain, citrate synthase, pyruvate, and lactate dehydrogenase (PDH and LDH).

RESULTS

Propylpyraoletriol but not DPN prevented the rise of arterial pressure induced by CIH. CIH exposures decreased O₂ consumption, complex I activity, and increased H₂ O₂ production. CIH had no effect on citrate synthase activity, but decreased PDH activity and increased LDH activity indicating higher anaerobic glycolysis. Propylpyraoletriol and DPN treatments prevented all these alterations.

CONCLUSIONS

We conclude that in OVX female rats, the ERα agonist prevents from CIH-induced hypertension while both ERα and ERβ agonists prevent the brain mitochondrial dysfunction and metabolic switch induced by CIH. These findings may have implications for menopausal women suffering of sleep apnoea regarding hormonal therapy.

Sex differences in the central and peripheral manifestations of ischemia-induced heart failure in rats

Sex differences in the presentation, outcome, and responses to treatment of systolic heart failure (HF) have been reported. In the present study, we examined the effect of sex on central neural mechanisms contributing to neurohumoral excitation and its peripheral manifestations in rats with HF. Male and female Sprague-Dawley rats underwent coronary artery ligation (CL) to induce HF. Age-matched rats served as controls. Ischemic zone and left ventricular function were similar 24 h and 4 wk after CL. Female rats with HF had a lower mortality rate and less hemodynamic compromise, pulmonary congestion, and right ventricular remodeling 4 wk after CL. Plasma angiotensin II (ANG II), arginine vasopressin (AVP), and norepinephrine levels were increased in HF rats in both sexes, but AVP and norepinephrine levels increased less in female rats. In the hypothalamic paraventricular nucleus, a key cardiovascular-related nucleus contributing to neurohumoral excitation in HF, mRNA levels for the proinflammatory cytokines tumor necrosis factor-α and interleukin-1β as well as cyclooxygenase-2 and the ANG II type 1a receptor were increased in HF rats of both sexes, but less so in female rats. Angiotensin-converting enzyme 2 protein levels increased in female HF rats but decreased in male HF rats. mRNA levels of AVP were lower in female rats in both control and HF groups compared with the respective male groups. Activation of extracellular signal-regulated protein kinases 1 and 2 increased similarly in both sexes in HF. The results suggest that female HF rats have less central neural excitation and less associated hemodynamic compromise than male HF rats with the same degree of initial ischemic cardiac injury. NEW & NOTEWORTHY Sex differences in the presentation and responses to treatment of heart failure (HF) are widely recognized, but the underlying mechanisms are poorly understood. The present study describes sex differences in the central nervous system mechanisms that drive neurohumoral excitation in ischemia-induced HF. Female rats had a less intense central neurochemical response to HF and experienced less hemodynamic compromise. Sex hormones may contribute to these differences in the central and peripheral adaptations to HF.

Nestin Improves Preeclampsia-Like Symptoms by Inhibiting Activity of Cyclin-Dependent Kinase 5

BACKGROUND/AIMS

Preeclampsia (PE) is a pregnancy-specific hypertensive disorder that is characterised by a high incidence of hypertension and proteinuria. Podocytes are involved in the formation of a split membrane, which is the last barrier preventing the leakage of protein into the urine. Nestin, a cytoskeleton protein, is expressed stably in podocytes. However, the association between the Nestin concentration in urine and the progression of PE and the role of Nestin in PE remains unclear.

METHODS

In the present study, a mouse podocyte cell line, PE-like animal model and PE patients' urine samples were used. Eilsa kits were used to detect the levels of proteins expression in urine samples from patients and animal models. Western Blotting and immunofluorescence were used to detect proteins expression levels in cell samples and animal tissue samples. Flow cytometry was used to detect the level of apoptosis in cells. Tunel assay was used to detect the levels of apoptosis in animal tissue samples.

RESULTS

Nestin levels were significantly increased in PE patients than in hypertensive patients and healthy subjects, and positively correlated with proteinuria and podocalyxin. Ang II treatment decreased the expression of Nestin and Podocin in a time- and dose- dependent manner in podocytes. Restoration of the Nestin levels could reverse Ang II-induced F-actin degradation and attenuate Ang II-mediated podocyte apoptosis, while knockdown of the Nestin level exhibited the opposite. Moreover, the protective role of Nestin on podocytes is mediated by inhibition of the kinase activity of CDK5. In PE-like animal model induced by L-NAME injection, restoration of Nestin lowered the pressure and proteinuria concentration, attenuated the loss of podocytes, and decreased the expression of p35, p53 and the activity of CDK5 kinase, as compared with the control.

CONCLUSIONS

Our findings suggest that Nestin could improve preeclampsia-like symptoms by inhibiting the activity of CDK5, and Nestin may become a new prognostic factor and a potential therapy target for PE.

The proinflammatory cytokine tumor necrosis factor-α excites subfornical organ neurons

Tumor necrosis factor-α (TNF-α) is a proinflammatory cytokine implicated in cardiovascular and autonomic regulation via actions in the central nervous system. TNF-α^-/- mice do not develop angiotensin II (ANG II)-induced hypertension, and administration of TNF-α into the bloodstream of rats increases blood pressure and sympathetic tone. Recent studies have shown that lesion of the subfornical organ (SFO) attenuates the hypertensive and autonomic effects of TNF-α, while direct administration of TNF-α into the SFO increases blood pressure, suggesting the SFO to be a key site for the actions of TNF-α. Therefore, we used patch-clamp techniques to examine both acute and long-term effects of TNF-α on the excitability of Sprague-Dawley rat SFO neurons. It was observed that acute bath application of TNF-α depolarized SFO neurons and subsequently increased action potential firing rate. Furthermore, the magnitude of depolarization and the proportion of depolarized SFO neurons were concentration dependent. Interestingly, following 24-h incubation with TNF-α, the basal firing rate of the SFO neurons was increased and the rheobase was decreased, suggesting that TNF-α elevates SFO neuron excitability. This effect was likely mediated by the transient sodium current, as TNF-α increased the magnitude of the current and lowered its threshold of activation. In contrast, TNF-α did not appear to modulate either the delayed rectifier potassium current or the transient potassium current. These data suggest that acute and long-term TNF-α exposure elevates SFO neuron activity, providing a basis for TNF-α hypertensive and sympathetic effects.NEW & NOTEWORTHY Considerable recent evidence has suggested important links between inflammation and the pathological mechanisms underlying hypertension. The present study describes cellular mechanisms through which acute and long-term exposure of tumor necrosis factor-α (TNF-α) influences the activity of subfornical organ neurons by modulating the voltage-gated transient Na⁺ current. This provides critical new information regarding the specific pathological mechanisms through which inflammation and TNF-α in particular may result in the development of hypertension.

Endoplasmic reticulum stress in the brain subfornical organ contributes to sex differences in angiotensin-dependent hypertension in rats

AIM

Endoplasmic reticulum (ER) stress in the brain subfornical organ (SFO), a key cardiovascular regulatory centre, has been implicated in angiotensin (ANG) II-induced hypertension in males; however, the contribution of ER stress to ANG II-induced hypertension in females is unknown. Female hormones have been shown to prevent ER stress in the periphery. We tested the hypothesis that females are less susceptible to ANG II-induced SFO ER stress than males, leading to sex differences in hypertension.

METHODS

Male, intact and ovariectomized (OVX) female rats received a continuous 2-week subcutaneous infusion of ANG II or saline. Additional male, intact and OVX female rats received intracerebroventricular (ICV) injection of ER stress inducer tunicamycin.

RESULTS

ANG II, but not saline, increased blood pressure (BP) in both males and females, but intact females exhibited smaller increase in BP and less depressor response to ganglionic blockade compared with males or OVX females. Molecular studies revealed that ANG II elevated expression of ER stress biomarkers and Fra-like activity in the SFO in both males and females; however, elevations in these parameters were less in intact females than in males or OVX females. Moreover, ICV tunicamycin induced smaller elevation in BP and less increase in expression of ER stress biomarkers in the SFO in intact females compared with males or OVX females.

CONCLUSION

The results suggest that differences in ANG II-induced brain ER stress between males and females contribute to sex differences in ANG II-mediated hypertension and that oestrogen protects females against ANG II-induced brain ER stress.

Divergent effects of ERα and ERβ on fluid intake by female rats are not dependent on concomitant changes in AT1R expression or body weight

Estradiol (E2) decreases both water and saline intakes by female rats. The ERα and ERβ subtypes are expressed in areas of the brain that control fluid intake; however, the role that these receptors play in E2's antidipsogenic and antinatriorexigenic effects have not been examined. Accordingly, we tested the hypothesis that activation of ERα and ERβ decreases water and saline intakes by female rats. We found a divergence in E2's inhibitory effect on intake: activation of ERα decreased water intake, whereas activation of ERβ decreased saline intake. E2 decreases expression of the angiotensin II type 1 receptor (AT1R), a receptor with known relevance to water and salt intakes, in multiple areas of the brain where ERα and ERβ are differentially expressed. Therefore, we tested for agonist-induced changes in AT1R mRNA expression by RT-PCR and protein expression by analyzing receptor binding to test the hypothesis that the divergent effects of these ER subtypes are mediated by region-specific changes in AT1R expression. Although we found no changes in AT1R mRNA or binding in areas of the brain known to control fluid intake associated with agonist treatment, the experimental results replicate and extend previous findings that body weight changes mediate alterations in AT1R expression in distinct brain regions. Together, the results reveal selective effects of ER subtypes on ingestive behaviors, advancing our understanding of E2's inhibitory role in the controls of fluid intake by female rats.

Recent advances in central cardiovascular control: sex, ROS, gas and inflammation

The central nervous system (CNS) in concert with the heart and vasculature is essential to maintaining cardiovascular (CV) homeostasis. In recent years, our understanding of CNS control of blood pressure regulation (and dysregulation leading to hypertension) has evolved substantially to include (i) the actions of signaling molecules that are not classically viewed as CV signaling molecules, some of which exert effects at CNS targets in a non-traditional manner, and (ii) CNS locations not traditionally viewed as central autonomic cardiovascular centers. This review summarizes recent work implicating immune signals and reproductive hormones, as well as gasotransmitters and reactive oxygen species in the pathogenesis of hypertension at traditional CV control centers. Additionally, recent work implicating non-conventional CNS structures in CV regulation is discussed.

Estrogen Receptor α Is Required for Maintaining Baseline Renin Expression

Enzymatic cleavage of angiotensinogen by renin represents the critical rate-limiting step in the production of angiotensin II, but the mechanisms regulating the initial expression of the renin gene remain incomplete. The purpose of this study is to unravel the molecular mechanism controlling renin expression. We identified a subset of nuclear receptors that exhibited an expression pattern similar to renin by reanalyzing a publicly available microarray data set. Expression of some of these nuclear receptors was similarly regulated as renin in response to physiological cues, which are known to regulate renin. Among these, only estrogen receptor α (ERα) and hepatic nuclear factor α have no known function in regulating renin expression. We determined that ERα is essential for the maintenance of renin expression by transfection of small interfering RNAs targeting Esr1, the gene encoding ERα, in renin-expressing As4.1 cells. We also observed that previously characterized negative regulators of renin expression, Nr2f2 and vitamin D receptor, exhibited elevated expression in response to ERα inhibition. Therefore, we tested whether ERα regulates renin expression through an interaction with Nr2f2 and vitamin D receptor. Renin expression did not return to baseline when we concurrently suppressed both Esr1 and Nr2f2 or Esr1 and vitamin D receptor mRNAs, strongly suggesting that Esr1 regulates renin expression independent of Nr2f2 and vitamin D receptor. ERα directly binds to the hormone response element within the renin enhancer region. We conclude that ERα is a previously unknown regulator of renin that directly binds to the renin enhancer hormone response element sequence and is critical in maintaining renin expression in renin-expressing As4.1 cells.

Sex, the brain and hypertension: brain oestrogen receptors and high blood pressure risk factors

Hypertension is a major contributor to worldwide morbidity and mortality rates related to cardiovascular disease. There are important sex differences in the onset and rate of hypertension in humans. Compared with age-matched men, premenopausal women are less likely to develop hypertension. However, after age 60, the incidence of hypertension increases in women and even surpasses that seen in older men. It is thought that changes in levels of circulating ovarian hormones as women age may be involved in the increase in hypertension in older women. One of the key mechanisms involved in the development of hypertension in both men and women is an increase in sympathetic nerve activity (SNA). Brain regions important for the regulation of SNA, such as the subfornical organ, the paraventricular nucleus and the rostral ventral lateral medulla, also express specific subtypes of oestrogen receptors. Each of these brain regions has also been implicated in mechanisms underlying risk factors for hypertension such as obesity, stress and inflammation. The present review brings together evidence that links actions of oestrogen at these receptors to modulate some of the common brain mechanisms involved in the ability of hypertensive risk factors to increase SNA and blood pressure. Understanding the mechanisms by which oestrogen acts at key sites in the brain for the regulation of SNA is important for the development of novel, sex-specific therapies for treating hypertension.

Estrogen Replacement Reduces Oxidative Stress in the Rostral Ventrolateral Medulla of Ovariectomized Rats

Cardiovascular disease prevalence rises rapidly after menopause, which is believed to be derived from the loss of estrogen. It is reported that sympathetic tone is increased in postmenopause. The high level of oxidative stress in the rostral ventrolateral medulla (RVLM) contributes to increased sympathetic outflow. The focus of this study was to determine if estrogen replacement reduces oxidative stress in the RVLM and sympathetic outflow in the ovariectomized (OVX) rats. The data of this study showed that OVX rat increased oxidative stress in the RVLM and sympathetic tone; estrogen replacement improved cardiovascular functions but also reduced the level of oxidative stress in the RVLM. These findings suggest that estrogen replacement decreases blood pressure and sympathoexcitation in the OVX rats, which may be associated with suppression in oxidative stress in the RVLM through downregulation of protein expression of NADPHase (NOX4) and upregulation of protein expression of SOD1. The data from this study is beneficial for our understanding of the mechanism of estrogen exerting cardiovascular protective effects on postmenopause.