The effects of 17β-estradiol on blood brain barrier integrity in the absence of the estrogen receptor alpha; an in-vitro model

Gender-based research underscores sex differences in biological processes, clinical disorders and pharmacological interventions

Earlier research has presumed that the male and female biology is similar in most organs except the reproductive system, leading to major misconceptions in research interpretations and clinical implications, with serious disorders being overlooked or misdiagnosed. Careful research has now identified sex differences in the cardiovascular, renal, endocrine, gastrointestinal, immune, nervous, and musculoskeletal systems. Also, several cardiovascular, immunological, and neurological disorders have shown differences in prevalence and severity between males and females. Genetic variations in the sex chromosomes have been implicated in several disorders at young age and before puberty. The levels of the gonadal hormones estrogen, progesterone and testosterone and their receptors play a role in the sex differences between adult males and premenopausal women. Hormonal deficiencies and cell senescence have been implicated in differences between postmenopausal and premenopausal women. Specifically, cardiovascular disorders are more common in adult men vs premenopausal women, but the trend is reversed with age with the incidence being greater in postmenopausal women than age-matched men. Gender-specific disorders in females such as polycystic ovary syndrome, hypertension-in-pregnancy and gestational diabetes have attained further research recognition. Other gender-related research areas include menopausal hormone therapy, the "Estrogen Paradox" in pulmonary arterial hypertension being more predominant but less severe in young females, and how testosterone may cause deleterious effects in the kidney while having vasodilator effects in the coronary circulation. This has prompted the National Institutes of Health (NIH) initiative to consider sex as a biological variable in research. The NIH and other funding agencies have provided resources to establish state-of-the-art centers for women health and sex differences in biology and disease in several academic institutions. Scientific societies and journals have taken similar steps to organize specialized conferences and publish special issues on gender-based research. These combined efforts should promote research to enhance our understanding of the sex differences in biological systems beyond just the reproductive system, and provide better guidance and pharmacological tools for the management of various clinical disorders in a gender-specific manner.

CmPn/CmP Signaling Networks in the Maintenance of the Blood Vessel Barrier

Cerebral cavernous malformations (CCMs) arise when capillaries within the brain enlarge abnormally, causing the blood-brain barrier (BBB) to break down. The BBB serves as a sophisticated interface that controls molecular interactions between the bloodstream and the central nervous system. The neurovascular unit (NVU) is a complex structure made up of neurons, astrocytes, endothelial cells (ECs), pericytes, microglia, and basement membranes, which work together to maintain blood-brain barrier (BBB) permeability. Within the NVU, tight junctions (TJs) and adherens junctions (AJs) between endothelial cells play a critical role in regulating the permeability of the BBB. Disruptions to these junctions can compromise the BBB, potentially leading to a hemorrhagic stroke. Understanding the molecular signaling cascades that regulate BBB permeability through EC junctions is, therefore, essential. New research has demonstrated that steroids, including estrogens (ESTs), glucocorticoids (GCs), and metabolites/derivatives of progesterone (PRGs), have multifaceted effects on blood-brain barrier (BBB) permeability by regulating the expression of tight junctions (TJs) and adherens junctions (AJs). They also have anti-inflammatory effects on blood vessels. PRGs, in particular, have been found to play a significant role in maintaining BBB integrity. PRGs act through a combination of its classic and non-classic PRG receptors (nPR/mPR), which are part of a signaling network known as the CCM signaling complex (CSC). This network couples both nPR and mPR in the CmPn/CmP pathway in endothelial cells (ECs).

Nuclear receptor ligand screening in an iPSC-derived in vitro blood-brain barrier model identifies new contributors to leptin transport

BACKGROUND

The hormone leptin exerts its function in the brain to reduce food intake and increase energy expenditure to prevent obesity. However, most obese subjects reflect the resistance to leptin even with elevated serum leptin. Considering that leptin must cross the blood-brain barrier (BBB) in several regions to enter the brain parenchyma, altered leptin transport through the BBB might play an important role in leptin resistance and other biological conditions. Here, we report the use of a human induced pluripotent stem cell (iPSC)-derived BBB model to explore mechanisms that influence leptin transport.

METHODS

iPSCs were differentiated into brain microvascular endothelial cell (BMEC)-like cells using standard methods. BMEC-like cells were cultured in Transwell filters, treated with ligands from a nuclear receptor agonist library, and assayed for leptin transport using an enzyme-linked immune sorbent assay. RNA sequencing was further used to identify differentially regulated genes and pathways. The role of a select hit in leptin transport was tested with the competitive substrate assay and after gene knockdown using CRISPR techniques.

RESULTS

Following a screen of 73 compounds, 17β-estradiol was identified as a compound that could significantly increase leptin transport. RNA sequencing revealed many differentially expressed transmembrane transporters after 17β-estradiol treatment. Of these, cationic amino acid transporter-1 (CAT-1, encoded by SLC7A1) was selected for follow-up analyses due to its high and selective expression in BMECs in vivo. Treatment of BMEC-like cells with CAT-1 substrates, as well as knockdown of CAT-1 expression via CRISPR-mediated epigenome editing, yielded significant increases in leptin transport.

CONCLUSIONS

A major female sex hormone, as well as an amino acid transporter, were revealed as regulators of leptin BBB transport in the iPSC-derived BBB model. Outcomes from this work provide insights into regulation of hormone transport across the BBB.

Estradiol Inhibits Human Brain Vascular Pericyte Migration Activity: A Functional and Transcriptomic Analysis

Stroke is the third leading cause of mortality in women and it kills twice as many women as breast cancer. A key role in the pathophysiology of stroke plays the disruption of the blood–brain barrier (BBB) within the neurovascular unit. While estrogen induces vascular protective actions, its influence on stroke remains unclear. Moreover, experiments assessing its impact on endothelial cells to induce barrier integrity are non-conclusive. Since pericytes play an active role in regulating BBB integrity and function, we hypothesize that estradiol may influence BBB by regulating their activity. In this study using human brain vascular pericytes (HBVPs) we investigated the impact of estradiol on key pericyte functions known to influence BBB integrity. HBVPs expressed estrogen receptors (ER-α, ER-β and GPER) and treatment with estradiol (10 nM) inhibited basal cell migration but not proliferation. Since pericyte migration is a hallmark for BBB disruption following injury, infection and inflammation, we investigated the effects of estradiol on TNFα-induced PC migration. Importantly, estradiol prevented TNFα-induced pericyte migration and this effect was mimicked by PPT (ER-α agonist) and DPN (ER-β agonist), but not by G1 (GPR30 agonist). The modulatory effects of estradiol were abrogated by MPP and PHTPP, selective ER-α and ER-β antagonists, respectively, confirming the role of ER-α and ER-β in mediating the anti-migratory actions of estrogen. To delineate the intracellular mechanisms mediating the inhibitory actions of estradiol on PC migration, we investigated the role of AKT and MAPK activation. While estradiol consistently reduced the TNFα-induced MAPK and Akt phosphorylation, only the inhibition of MAPK, but not Akt, significantly abrogated the migratory actions of TNFα. In transendothelial electrical resistance measurements, estradiol induced barrier function (TEER) in human brain microvascular endothelial cells co-cultured with pericytes, but not in HBMECs cultured alone. Importantly, transcriptomics analysis of genes modulated by estradiol in pericytes showed downregulation of genes known to increase cell migration and upregulation of genes known to inhibit cell migration. Taken together, our findings provide the first evidence that estradiol modulates pericyte activity and thereby improves endothelial integrity.

Sensory Neurons, Neuroimmunity, and Pain Modulation by Sex Hormones

The inclusion of women in preclinical pain studies has become more commonplace in the last decade as the National Institutes of Health (NIH) released its "Sex as a Biological Variable" mandate. Presumably, basic researchers have not had a comprehensive understanding about neuroimmune interactions in half of the population and how hormones play a role in this. To date, we have learned that sex hormones contribute to sexual differentiation of the nervous system and sex differences in behavior throughout the lifespan; however, the cycling of sex hormones does not always explain these differences. Here, we highlight recent advances in our understanding of sex differences and how hormones and immune interactions influence sensory neuron activity to contribute to physiology and pain. Neuroimmune mechanisms may be mediated by different cell types in each sex, as the actions of immune cells are sexually dimorphic. Unfortunately, the majority of studies assessing neuronal contributions to immune function have been limited to males, so it is unclear if the mechanisms are similar in females. Finally, pathways that control cellular metabolism, like nuclear receptors, have been shown to play a regulatory role both in pain and inflammation. Overall, communication between the neuroimmune and endocrine systems modulate pain signaling in a sex-dependent manner, but more research is needed to reveal nuances of these mechanisms.

Sex hormones regulate NHE1 functional expression and brain endothelial proteome to control paracellular integrity of the blood endothelial barrier

BACKGROUND

Sex hormones have been implicated in pH regulation of numerous physiological systems. One consistent factor of these studies is the sodium-hydrogen exchanger 1 (NHE1). NHE1 has been associated with pH homeostasis at epithelial barriers. Hormone fluctuations have been implicated in protection and risk for breaches in blood brain barrier (BBB)/blood endothelial barrier (BEB) integrity. Few studies, however, have investigated BBB/BEB integrity in neurological disorders in the context of sex-hormone regulation of pH homeostasis.

METHODS//RESULTS

Physiologically relevant concentrations of 17-β-estradiol (E2, 294 pM), progesterone (P, 100 nM), and testosterone (T,3.12 nM) were independently applied to cultured immortalized bEnd.3 brain endothelial cells to study the BEB. Individual gonadal hormones showed preferential effects on extracellular pH (E2), 14C-sucrose uptake (T), stimulated paracellular breaches (P) with dependence on functional NHE1 expression without impacting transendothelial resistance (TEER) or total protein expression. While total NHE1 expression was not changed as determined via whole cell lysate and subcellular fractionation experiment, biotinylation of NHE1 for surface membrane expression showed E2 reduced functional expression. Quantitative proteomic analysis revealed divergent effects of 17-β-estradiol and testosterone on changes in protein abundance in bEnd.3 endothelial cells as compared to untreated controls.

CONCLUSIONS

These data suggest that circulating levels of sex hormones may independently control BEB integrity by 1) regulating pH homeostasis through NHE1 functional expression and 2) modifying the endothelial proteome.

Tamoxifen suppresses brain metastasis of estrogen receptor-deficient breast cancer by skewing microglia polarization and enhancing their immune functions

Background

Brain metastasis of breast cancer exhibits exceedingly poor prognosis, and both triple negative (TN) and Her2⁺ subtypes have the highest incidence of brain metastasis. Although estrogen blockers are considered to be ineffective for their treatment, recent evidence indicates that estrogen blockade using tamoxifen showed certain efficacy. However, how estrogen affects brain metastasis of triple negative breast cancer (TNBC) remains elusive.

Methods

To examine the effect of estrogen on brain metastasis progression, nude mice were implanted with brain metastatic cells and treated with either estrogen supplement, tamoxifen, or ovariectomy for estrogen depletion. For clinical validation study, brain metastasis specimens from pre- and post-menopause breast cancer patients were examined for microglia polarization by immunohistochemistry. To examine the estrogen-induced M2 microglia polarization, microglia cells were treated with estrogen, and the M1/M2 microglia polarization was detected by qRT-PCR and FACS. The estrogen receptor-deficient brain metastatic cells, SkBrM and 231BrM, were treated with conditioned medium (CM) derived from microglia that were treated with estrogen in the presence or absence of tamoxifen. The effect of microglia-derived CM on tumor cells was examined by colony formation assay and sphere forming ability.

Results

We found that M2 microglia were abundantly infiltrated in brain metastasis of pre-menopausal breast cancer patients. A similar observation was made in vivo, when we treated mice systemically with estrogen. Blocking of estrogen signaling either by tamoxifen treatment or surgical resection of mice ovaries suppressed M2 microglial polarization and decreased the secretion of C-C motif chemokine ligand 5, resulting in suppression of brain metastasis. The estrogen modulation also suppressed stemness in TNBC cells in vitro. Importantly, estrogen enhanced the expression of signal regulatory protein α on microglia and restricted their phagocytic ability.

Conclusions

Our results indicate that estrogen promotes brain metastasis by skewing polarity of M2 microglia and inhibiting their phagocytic ability, while tamoxifen suppresses brain metastasis by blocking the M2 polarization of microglia and increasing their anti-tumor phagocytic ability. Our results also highlight a potential therapeutic utility of tamoxifen for treating brain metastasis of hormone receptor-deficient breast cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13058-021-01412-z.

An electrochemiluminescence sensor for 17β-estradiol detection based on resonance energy transfer in α-FeOOH@CdS/Ag NCs

An electrochemiluminescence (ECL) resonance energy transfer system is constructed for 17β-estradiol (E2) detection using α-FeOOH@CdS nanospheres as the ECL-active substrates and Ag NCs as an efficient quencher. CdS QDs loaded onto three-dimensional (3D) urchin-like α-FeOOH nanospheres (α-FeOOH@CdS nanospheres) exhibited excellent ECL responses, which is attributed to dual-amplification of α-FeOOH frameworks. The 3D hierarchical structure of the α-FeOOH nanospheres provided abundant sites for loading ECL-active species, thus significantly improving the ECL performance of substrates; While Fe³⁺ presented on surface of α-FeOOH nanospheres could be reduced to Fe²⁺ in negative potentials, after which might activate persulfate in a Fenton-like process, resulting in more sulfate free radicals for more effective ECL responses via electron transfer reactions. Additionally, Ag nanoclusters (Ag NCs) stabilized by single stranded oligonucleotide were introduced as quenching probes for CdS QDs owing to the well-matched donor-acceptor spectrum for efficient energy transfer, which makes them appropriate for detection of E2. The proposed strategy displayed a desirable dynamic range from 0.01 to 10 pg mL^-1 with a limit of detection of 0.003 pg mL^-1. The proposed strategy based on the ECL-RET strategy offered an ideal way for E2 detection, and also revealed an alternative platform for detection of other small molecules.

Blood-brain barrier integrity in the pathogenesis of Alzheimer's disease

The blood-brain barrier (BBB) tightly controls the molecular exchange between the brain parenchyma and blood. Accumulated evidence from transgenic animal Alzheimer's disease (AD) models and human AD patients have demonstrated that BBB dysfunction is a major player in AD pathology. In this review, we discuss the role of the BBB in maintaining brain integrity and how this is mediated by crosstalk between BBB-associated cells within the neurovascular unit (NVU). We then discuss the role of the NVU, in particular its endothelial cell, pericyte, and glial cell constituents, in AD pathogenesis. The effect of substances released by the neuroendocrine system in modulating BBB function and AD pathogenesis is also discussed. We perform a systematic review of currently available AD treatments specifically targeting pericytes and BBB glial cells. In summary, this review provides a comprehensive overview of BBB dysfunction in AD and a new perspective on the development of therapeutics for AD.

Reusable chemiluminescent fiber optic aptasensor for the determination of 17β-estradiol in water samples

A reusable fiber optic chemiluminescent aptasensor (FOCA) is reported for the rapid and sensitive on-site detection of 17β-estradiol (E2), an endocrine-disrupting compound frequently found in water samples. The E2-ovalbumin conjugate (E2-OVA) was covalently immobilized onto the optical fiber as a biorecognition element as well as a transducer. The affinity constant of the E2/aptamer complex was determined to be 1.35 × 10⁶ M^-1 using the FOCA. An indirect competitive assay was then developed for E2 detection. A certain concentration of HRP-E2 aptamers pre-reacted with samples containing E2 in various concentrations. Part of HRP-E2 aptamers specially bound to the sensor surface after introduction of the mixture. This catalyzed the chemiluminescece reaction of a chemiluminescent system composed of luminol and H₂O₂. A higher concentration of E2 led to less HRP-E2 aptamer bound to the biosensor surface, thus resulting in less chemiluminescence. Highly sensitive detection of E2 was achieved under optimal conditions, and the limit of detection is 48 ng ·L^-1 (0.18 nM). The whole analytical process, including measurement and regeneration, can be performed in <15 min. The robustness of the biosensor allows its application to multiple assays with little activity loss. The selectivity, recovery, and accuracy of the sensor was demonstrated by evaluating its response to potentially interfering endocrine disruptors in spiked water samples. Graphical abstract Schematic diagram of the fiber optic chemiluminescent aptasensor system (A), detection mechanism of 17β-estradiol (B), and its application for detection of 17β-estradiol with rapidity and sensitivity (C and D).

Effect of enriched environment and predictable chronic stress on spatial memory in adolescent rats: Predominant expression of BDNF, nNOS, and interestingly malondialdehyde in the right hippocampus

Little is known about the mechanisms that promote divergence of function between left and right in the hippocampus, which is most affected by external factors and critical for spatial memory. We investigated the levels of memory-related mediators in the left and right hippocampus and spatial memory in rats exposed to predictable chronic stress (PCS) and an enriched environment (EE) during adolescence. Twenty-eight-day-old Sprague-Dawley rats were divided into control (standard cages), PCS (15 min/day immobilization stress for four weeks), and EE (one hour/day environmentally enriched cages for four weeks) groups. After the applications, spatial memory was tested with the Morris water maze, and the serum levels of corticosterone were evaluated. The levels of brain-derived neurotrophic factor (BDNF) and neuronal nitric oxide synthase (nNOS), which are critical for synaptic plasticity; malondialdehyde (MDA; lipid-peroxidation indicator); protein carbonyl (protein-oxidation indicator); and superoxide dismutase (antioxidant enzyme) were evaluated in the left and right hippocampus. Corticosterone levels in both the PCS and EE groups did not change compared with control. In both the PCS and EE groups, spatial memory improved and BDNF was increased in both halves of the hippocampus, still there was an asymmetry. nNOS levels were increased in the dentate gyrus and CA1 regions of the right hippocampus in both PCS and EE groups. MDA levels were increased but PCO levels were decreased in the right hippocampus in both the PCS and EE groups, but SOD did not change in either half of the hippocampus. Our results suggest that both PCS and EE improved spatial memory by increasing BDNF and nNOS in the right hippocampus and that, interestingly; MDA could be the physiological signal molecule in the right hippocampus for spatial memory process.

Progesterone decreases gut permeability through upregulating occludin expression in primary human gut tissues and Caco-2 cells

Progesterone plays a protective role in preventing inflammation and preterm delivery during pregnancy. However, the mechanism involved is unknown. Microbial product translocation from a permeable mucosa is demonstrated as a driver of inflammation. To study the mechanism of the protective role of progesterone during pregnancy, we investigated the effect of physiologic concentrations of progesterone on tight junction protein occludin expression and human gut permeability in vitro and systemic microbial translocation in pregnant women in vivo. Plasma bacterial lipopolysaccharide (LPS), a representative marker of in vivo systemic microbial translocation was measured. We found that plasma LPS levels were significantly decreased during 24 to 28 weeks of gestation compared to 8 to 12 weeks of gestation. Moreover, plasma LPS levels were negatively correlated with plasma progesterone levels but positively correlated with plasma tumor necrosis factor-alpha (TNF-α) levels at 8 to 12 weeks of gestation but not at 24 to 28 weeks of gestation. Progesterone treatment increased intestinal trans-epithelial electrical resistance (TEER) in primary human colon tissues and Caco-2 cells in vitro through upregulating tight junction protein occludin expression. Furthermore, progesterone exhibited an inhibitory effect on nuclear factor kappa B (NF-κB) activation following LPS stimulation in Caco-2 cells. These results reveal a novel mechanism that progesterone may play an important role in decreasing mucosal permeability, systemic microbial translocation, and inflammation during pregnancy.

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.

Elevated systemic microbial translocation in pregnant HIV-infected women compared to HIV-uninfected women, and its inverse correlations with plasma progesterone levels

In HIV infection, increased adverse perinatal outcomes reported among HIV-associated pregnancies are not fully understood. Currently, microbial product translocation (MT) from a permeable mucosa is demonstrated as a driver of inflammation, and may contribute to preterm delivery in HIV. Here, our results showed that plasma LPS levels (a representative marker of MT) were increased in HIV-infected women in the first and second trimester. Progesterone levels were significantly decreased in HIV-infected subjects in the first trimester and second trimester. There were significant inverse correlations between plasma LPS and progesterone in the first and second trimester. These results suggested heightened systemic MT and decreased plasma progesterone levels in HIV-infected pregnant women may play a role in increased incidence of preterm delivery.

Increased systemic microbial translocation is associated with depression during early pregnancy

Plasma level of microbial translocation is a marker of mucosal permeability. Increased mucosal permeability ignites elevated microbial translocation and as a consequence of systemic inflammation. Pregnant women with depression have higher levels of inflammatory markers relative to pregnant women without depression, however, no studies have reported whether systemic microbial translocation will change in depressed women during pregnancy. In this study, we examined the plasma LPS level of depressed women during pregnancy. The results showed that the plasma LPS level was significantly increased in depressed mothers during their 8-12 weeks gestation compared to healthy controls. Compared to 8-12 weeks gestation, the plasma LPS levels were significantly decreased at 24-28 weeks gestation and 6-8 weeks postpartum in both depressed subjects and healthy controls. Furthermore, the plasma levels of pro-inflammatory cytokines (TNF-α and MCP/CCL2) associated with microbial translocation were significantly increased in depressed subjects during 8-12 weeks gestation compared to healthy controls. These results indicate that the level of microbial translocation is increased in depressed women during early pregnancy.