Age and 17β-estradiol effects on blood-brain barrier tight junction and estrogen receptor proteins in ovariectomized rats

Menopause and Alzheimer's disease susceptibility: Exploring the potential mechanisms

Alzheimer's Disease (AD), responsible for 62% of all dementia cases, is a progressive neurodegenerative condition that leads to cognitive dysfunction. The prevalence of AD is consistently higher in women suggesting they are disproportionately affected by this disease. Despite this, our understanding of this female AD vulnerability remains limited. Menopause has been identified as a potential contributing factor to AD in women, with earlier menopause onset associated with greater AD risk. However, the underlying mechanisms responsible for this increased risk are not fully understood. This review examines the potential role of menopause in the development of Alzheimer's Disease providing a mechanistic overview of the available literature from hormones to pathology. While literature is now emerging that indicates a role of hormonal shifts, gut dysbiosis, lipid dysregulation and inflammation, more research is needed to fully elucidate the mechanisms involved.

Young blood-mediated cerebromicrovascular rejuvenation through heterochronic parabiosis: enhancing blood-brain barrier integrity and capillarization in the aged mouse brain

Age-related cerebromicrovascular changes, including blood-brain barrier (BBB) disruption and microvascular rarefaction, play a significant role in the development of vascular cognitive impairment (VCI) and neurodegenerative diseases. Utilizing the unique model of heterochronic parabiosis, which involves surgically joining young and old animals, we investigated the influence of systemic factors on these vascular changes. Our study employed heterochronic parabiosis to explore the effects of young and aged systemic environments on cerebromicrovascular aging in mice. We evaluated microvascular density and BBB integrity in parabiotic pairs equipped with chronic cranial windows, using intravital two-photon imaging techniques. Our results indicate that short-term exposure to young systemic factors leads to both functional and structural rejuvenation of cerebral microcirculation. Notably, we observed a marked decrease in capillary density and an increase in BBB permeability to fluorescent tracers in the cortices of aged mice undergoing isochronic parabiosis (20-month-old C57BL/6 mice [A-(A)]; 6 weeks of parabiosis), compared to young isochronic parabionts (6-month-old, [Y-(Y)]). However, aged heterochronic parabionts (A-(Y)) exposed to young blood exhibited a significant increase in cortical capillary density and restoration of BBB integrity. In contrast, young mice exposed to old blood from aged parabionts (Y-(A)) rapidly developed cerebromicrovascular aging traits, evidenced by reduced capillary density and increased BBB permeability. These findings underscore the profound impact of systemic factors in regulating cerebromicrovascular aging. The rejuvenation observed in the endothelium, following exposure to young blood, suggests the existence of anti-geronic elements that counteract microvascular aging. Conversely, pro-geronic factors in aged blood appear to accelerate cerebromicrovascular aging. Further research is needed to assess whether the rejuvenating effects of young blood factors could extend to other age-related cerebromicrovascular pathologies, such as microvascular amyloid deposition and increased microvascular fragility.

Estrogen-immuno-neuromodulation disorders in menopausal depression

A significant decrease in estrogen levels puts menopausal women at high risk for major depression, which remains difficult to cure despite its relatively clear etiology. With the discovery of abnormally elevated inflammation in menopausal depressed women, immune imbalance has become a novel focus in the study of menopausal depression. In this paper, we examined the characteristics and possible mechanisms of immune imbalance caused by decreased estrogen levels during menopause and found that estrogen deficiency disrupted immune homeostasis, especially the levels of inflammatory cytokines through the ERα/ERβ/GPER-associated NLRP3/NF-κB signaling pathways. We also analyzed the destruction of the blood-brain barrier, dysfunction of neurotransmitters, blockade of BDNF synthesis, and attenuation of neuroplasticity caused by inflammatory cytokine activity, and investigated estrogen-immuno-neuromodulation disorders in menopausal depression. Current research suggests that drugs targeting inflammatory cytokines and NLRP3/NF-κB signaling molecules are promising for restoring homeostasis of the estrogen-immuno-neuromodulation system and may play a positive role in the intervention and treatment of menopausal depression.

Estrogenic regulation of claudin 5 and tight junction protein 1 gene expression in zebrafish: A role on blood-brain barrier?

The blood-brain barrier (BBB) is a physical interface between the blood and the brain parenchyma, playing key roles in brain homeostasis. In mammals, the BBB is established thanks to tight junctions between cerebral endothelial cells, involving claudin, occludin, and zonula occludens proteins. Estrogens have been documented to modulate BBB permeability. Interestingly, in the brain of zebrafish, the estrogen-synthesizing activity is strong due to the high expression of Aromatase B protein, encoded by the cyp19a1b gene, in radial glial cells (neural stem cells). Given the roles of estrogens in BBB function, we investigated their impact on the expression of genes involved in BBB tight junctions. We treated zebrafish embryos and adult males with 17β-estradiol and observed an increased cerebral expression of tight junction and claudin 5 genes in adult males only. In females, treatment with the nuclear estrogen receptor antagonist (ICI182,780 ) had no impact. Interestingly, telencephalic injuries performed in males decreased tight junction gene expression that was partially reversed with 17β-estradiol. This was further confirmed by extravasation experiments of Evans blue showing that estrogenic treatment limits BBB leakage. We also highlighted the intimate links between endothelial cells and neural stem cells, suggesting that cholesterol and peripheral steroids could be taken up by endothelial cells and used as precursors for estrogen synthesis by neural stem cells. Together, our results show that zebrafish provides an alternative model to further investigate the role of steroids on the expression of genes involved in BBB integrity, both in constitutive and regenerative physiological conditions. The link we described between capillaries endothelial cells and steroidogenic neural cells encourages the use of this model in understanding the mechanisms by which peripheral steroids get into neural tissue and modulate neurogenic activity.

Stabilizing the neural barrier - A novel approach in pain therapy

Chronic and neuropathic pain are a widespread burden. Incomplete understanding of underlying pathomechanisms is one crucial factor for insufficient treatment. Recently, impairment of the blood nerve barrier (BNB) has emerged as one key aspect of pain initiation and maintenance. In this narrative review, we discuss several mechanisms and putative targets for novel treatment strategies. Cells such as pericytes, local mediators like netrin-1 and specialized proresolving mediators (SPMs), will be covered as well as circulating factors including the hormones cortisol and oestrogen and microRNAs. They are crucial in either the BNB or similar barriers and associated with pain. While clinical studies are still scarce, these findings might provide valuable insight into mechanisms and nurture development of therapeutic approaches.

Biological agents and the aging brain: glial inflammation and neurotoxic signaling

Neuroinflammation is a universal characteristic of brain aging and neurological disorders, irrespective of the disease state. Glial inflammation mediates this signaling, through astrocyte and microglial polarization from neuroprotective to neurotoxic phenotypes. Glial reactivity results in the loss of homeostasis, as these cells no longer provide support to neurons, in addition to the production of chronically toxic pro-inflammatory mediators. These glial changes initiate an inflammatory brain state that injures the central nervous system (CNS) over time. As the brain ages, glia are altered, including increased glial cell numbers, morphological changes, and either a pre-disposition or inability to become reactive. These alterations induce age-related neuropathologies, ultimately leading to neuronal degradation and irreversible damage associated with disorders of the aged brain, including Alzheimer's Disease (AD) and other related diseases. While the complex interactions of these glial cells and the brain are well studied, the role additional stressors, such as infectious agents, play on age-related neuropathology has not been fully elucidated. Both biological agents in the periphery, such as bacterial infections, or in the CNS, including viral infections like SARS-CoV-2, push glia into neuroinflammatory phenotypes that can exacerbate pathology within the aging brain. These biological agents release pattern associated molecular patterns (PAMPs) that bind to pattern recognition receptors (PRRs) on glial cells, beginning an inflammatory cascade. In this review, we will summarize the evidence that biological agents induce reactive glia, which worsens age-related neuropathology.

Menopause causes metabolic and cognitive impairments in a chronic cerebral hypoperfusion model of vascular contributions to cognitive impairment and dementia

BACKGROUND

The vast majority of women with dementia are post-menopausal. Despite clinical relevance, menopause is underrepresented in rodent models of dementia. Before menopause, women are less likely than men to experience strokes, obesity, and diabetes-known risk factors for vascular contributions to cognitive impairment and dementia (VCID). During menopause, ovarian estrogen production stops and the risk of developing these dementia risk factors spikes. Here, we aimed to determine if menopause worsens cognitive impairment in VCID. We hypothesized that menopause would cause metabolic dysfunction and increase cognitive impairment in a mouse model of VCID.

METHODS

We performed a unilateral common carotid artery occlusion surgery to produce chronic cerebral hypoperfusion and model VCID in mice. We used 4-vinylcyclohexene diepoxide to induce accelerated ovarian failure and model menopause. We evaluated cognitive impairment using behavioral tests including novel object recognition, Barnes maze, and nest building. To assess metabolic changes, we measured weight, adiposity, and glucose tolerance. We explored multiple aspects of brain pathology including cerebral hypoperfusion and white matter changes (commonly observed in VCID) as well as changes to estrogen receptor expression (which may mediate altered sensitivity to VCID pathology post-menopause).

RESULTS

Menopause increased weight gain, glucose intolerance, and visceral adiposity. VCID caused deficits in spatial memory regardless of menopausal status. Post-menopausal VCID specifically led to additional deficits in episodic-like memory and activities of daily living. Menopause did not alter resting cerebral blood flow on the cortical surface (assessed by laser speckle contrast imaging). In the white matter, menopause decreased myelin basic protein gene expression in the corpus callosum but did not lead to overt white matter damage (assessed by Luxol fast blue). Menopause did not significantly alter estrogen receptor expression (ERα, ERβ, or GPER1) in the cortex or hippocampus.

CONCLUSIONS

Overall, we have found that the accelerated ovarian failure model of menopause caused metabolic impairment and cognitive deficits in a mouse model of VCID. Further studies are needed to identify the underlying mechanism. Importantly, the post-menopausal brain still expressed estrogen receptors at normal (pre-menopausal) levels. This is encouraging for any future studies attempting to reverse the effects of estrogen loss by activating brain estrogen receptors.

The Blood-Brain Barrier: Implications for Experimental Cancer Therapeutics

The blood-brain barrier is critically important for the treatment of both primary and metastatic cancers of the central nervous system (CNS). Clinical outcomes for patients with primary CNS tumors are poor and have not significantly improved in decades. As treatments for patients with extracranial solid tumors improve, the incidence of CNS metastases is on the rise due to suboptimal CNS exposure of otherwise systemically active agents. Despite state-of-the art surgical care and increasingly precise radiation therapy, clinical progress is limited by the ability to deliver an effective dose of a therapeutic agent to all cancerous cells. Given the tremendous heterogeneity of CNS cancers, both across cancer subtypes and within a single tumor, and the range of diverse therapies under investigation, a nuanced examination of CNS drug exposure is needed. With a shared goal, common vocabulary, and interdisciplinary collaboration, the field is poised for renewed progress in the treatment of CNS cancers.

iPSCs-derived mesenchymal stromal cells mitigate anxiety and neuroinflammation in aging female mice

Perimenopause is a natural transition to menopause, when hormone disturbance can result in both short-term mental disorders, such as anxiety, and long-term neuroinflammation due to blood-brain barrier (BBB) impairment, which may lead to more serious neurological disorders later on, such as dementia. Effective treatments may prevent both short-term and long-term neurological sequela, which formed the aim of this study. In aged female C57BL/6 mice (16-18 months of age), mesenchymal stromal cells (MSCs) differentiated from human-induced pluripotent stem cells (iPSCs), were administered via tail vein injection. Mice showed increased blood estrogen levels, alleviated anxiety and neuroinflammation, and improved BBB integrity. Interestingly, transplanted MSCs were located close to ovarian sympathetic nerves and decreased ovarian norepinephrine levels, which in turn increased ovarian estrogen secretion. Moreover, the administration of anastrozole, an inhibitor of estrogen synthesis, diminished the therapeutic effects of MSCs in vivo, suggesting the effect to be estrogen-dependent. In vitro study confirmed the impact of MSCs on sympathetic nerves via mitochondria exchange. In conclusion, iPSC-derived MSCs may provide a novel option to manage perimenopause-related hormonal dysregulation and neurological disorders during the female aging process.

Regulation of Tight Junctions by Sex Hormones in Goat Mammary Epithelial Cells

Simple Summary

How ovarian hormones affect goat lactation by regulating cell–cell junctions is still unclear. Through the in vivo and in vitro assays, we found that ovarian hormones could elevate cell–cell junction protein expression, which may affect the intercellular space and molecule transportation between the goat mammary epithelial cells. Our assessment suggests that ovarian hormones may affect goat milk production by regulating the cell–cell junction protein expression between mammary epithelial cells.

Abstract

The sex hormones of estrogen and progesterone (P₄) play a vital role in mammary gland development and milk lactation in ruminants. The tight junction (TJ) between adjacent secretory epithelial cells is instrumental in establishing the mammary blood–milk barrier. However, whether estrogen and P₄ exert their effect on mammary function via regulating TJ remain unclear. Here, to clarify the role of 17-β estradiol (E₂) and P₄ in the regulation of TJ in goat mammary gland, we first explored the relationships between the concentrations of E₂, P₄, and the protein expression of claudin-1, claudin-3, occludin, and ZO-1 during the mammary gland development in goat. Then, we further explored the mRNA and protein expression of claudin-1, claudin-3, occludin, and ZO-1 in the goat mammary epithelial cells (GMECs) in vitro under different concentrations of E₂ and P₄. The results demonstrated that the protein expression of claudin-1 decreased, but occludin and ZO-1 increased with the decline in E₂ and P₄ during the transition from pregnancy to lactation. In the in vitro studies, E₂ exerted a positive effect on the mRNA expression of claudin-1, and accelerated the proteins’ expression of claudin-1 and ZO-1 in GMECs; P₄ upregulated the mRNA expression of claudin-1, claudin-3, occludin, and ZO-1, and also improved the protein expression of claudin-1, claudin-3, and ZO-1 in the GMECs. The results demonstrated that E₂ and P₄ play an important role in regulating the expression of the mammary TJ components, which may ultimately affect the mammary gland development and milk lactation.

Effects and underlying cellular pathway involved in the impairment of the neurovascular unit following exposure of adult male mice to low doses of di(2-ethylhexyl) phthalate alone or in an environmental phthalate mixture

We have previously shown that adult male mice exposure to low doses of di (2-ethylhexyl)phthalate (DEHP) impacts the blood-brain barrier (BBB) integrity and surrounding parenchyma in the medial preoptic area (mPOA), a key hypothalamic area involved in the male sexual behavior. BBB leakage was associated with a decrease in the endothelial tight junction accessory protein, zona occludens-1, and caveolae protein Cav-1, added to an inflammatory profile including glial activation accompanied by enhanced expression of inducible nitric oxide synthase. As this failure of BBB functionality in the mPOA could participate, at least in part, in reported alteration of sexual behavior following DEHP exposure, we explored the cellular pathway connecting cerebral capillaries and neurons. Two-month-old C57BL/6J male mice were orally exposed for 6 weeks to DEHP alone (5 and 50 μg/kg/day) or to DEHP (5 μg/kg/day) in an environmental phthalate mixture. The presence of androgen receptor (AR) and estrogen receptor-α (ERα) were first evidenced in brain capillaries. Protein levels of AR but not of ERα were reduced in cerebral capillaries after phthalate exposure. The amounts of basement membrane and cell-matrix interaction components were decreased, while matrix metalloprotease MMP-2 and MMP-9 activities were increased. Fluorojade® labelling suggested that exposure to phthalates also lead to a neurodegenerative process in the mPOA. Altogether, the data suggest that environmental exposure to endocrine disruptors such as phthalates, could alter AR/Cav-1 interaction, impacting a Cav-1/nitric oxide/MMP pathway. This would lead to disruption of the glio-neurovascular coupling which is essential to neuronal functioning.

β-Amyloid Formation, Memory, and Learning Decline Following Long-term Ovariectomy and Its Inhibition by Systemic Administration of Apigenin and β-Estradiol

Introduction:

The increasing cases of Alzheimer Disease (AD) has caused numerous problems. The risk of developing AD increases in menopausal women, too. Apigenin and β-estradiol are effective antioxidant and neuroprotective agents. We conducted the present study to explore their combined effects on β-amyloid plaque formation, memory, and learning in ovariectomized rats.

Methods:

Forty-two Wistar rats were randomly assigned into 6 groups: 1) ovariectomized (OVX), 2) OVX + apigenin, 3) OVX + β-estradiol, 4) OVX + apigenin + β-estradiol, 5 &6) vehicle shams for E2 and API, and 7) surgical sham. Treatment was done with apigenin and β-estradiol. Then, we studied the formation of β-amyloid plaques, neuronal density in the hippocampus area, apoptosis, memory, and learning.

Results:

Findings showed the significant formation of β-amyloid plaques in the hippocampus of OVX animals and their memory impairment. Apigenin and β-estradiol significantly reduced the number of β-amyloid plaques, as well as the symptoms of memory impairment and learning, and decreased the expression of caspase-3 in treated animals.

Conclusion:

Accordingly, β-estradiol and apigenin could have more potent therapeutic effects on AD.

Disruption of the blood-brain barrier and its close environment following adult exposure to low doses of di(2-ethylhexyl)phthalate alone or in an environmental phthalate mixture in male mice

We have previously shown that adult male mice exposure to low doses of di(2-ethylhexyl)phthalate (DEHP) alters neural function and behaviour. Whether such exposure also affects the integrity and function of the blood-brain barrier (BBB) remained to be explored. The impact of adult exposure to low doses of DEHP alone or in an environmental phthalate mixture on the BBB integrity and surrounding parenchyma was studied in male mice. Two-month-old C57BL/6J males were orally exposed for 6 weeks to DEHP alone (5, and 50 μg/kg/day) or to DEHP (5 μg/kg/day) in an environmental phthalate mixture. BBB permeability, glial activation and neuroinflammation were investigated in the hypothalamic medial preoptic area (mPOA) and hippocampus involved, respectively on the reproductive and cognitive functions. Exposure to DEHP alone or in a phthalate mixture increased BBB permeability and affected the endothelial accessory tight junction protein zona occludens-1 and caveolae protein Cav-1 in the mPOA and the hippocampal CA1 and CA3 areas. This was associated with an inflammatory profile including astrocyte activation accompanied by enhanced expression of inducible nitric oxide synthase in the mPOA, and a microglial activation in the mPOA and the hippocampal CA1 and CA3 areas. The protein levels of the inflammatory molecule cyclooxygenase-2 were increased in activated microglial cells of the exposed mPOA. None of the major effects induced by DEHP alone or in a mixture was detected in the hippocampal dendate gyrus. The data highlight that environmental exposure to endocrine disruptors such as phthalates, could represent a risk factor for the cerebrovascular function.

Age-related ultrastructural neurovascular changes in the female mouse cortex and hippocampus

Blood-brain barrier (BBB) breakdown occurs in aging and neurodegenerative diseases. Although age-associated alterations have previously been described, most studies focused in male brains; hence, little is known about BBB breakdown in females. This study measured ultrastructural features in the aging female BBB using transmission electron microscopy and 3-dimensional reconstruction of cortical and hippocampal capillaries from 6- and 24-month-old female C57BL/6J mice. Aged cortical capillaries showed more changes than hippocampal capillaries. Specifically, the aged cortex showed thicker basement membrane, higher number and volume of endothelial pseudopods, decreased endothelial mitochondrial number, larger pericyte mitochondria, higher pericyte-endothelial cell contact, and increased tight junction tortuosity compared with young animals. Only increased basement membrane thickness and pericyte mitochondrial volume were observed in the aged hippocampus. Regional comparison revealed significant differences in endothelial pseudopods and tight junctions between the cortex and hippocampus of 24-month-old mice. Therefore, the aging female BBB shows region-specific ultrastructural alterations that may lead to oxidative stress and abnormal capillary blood flow and barrier stability, potentially contributing to cerebrovascular diseases, particularly in postmenopausal women.

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.

Involvement of Testosterone Signaling in the Integrity of the Neurovascular Unit in the Male: Review of Evidence, Contradictions, and Hypothesis

Age-related central nervous system function decline and increased susceptibility of females compared to males with respect to prevalence of several neurodegenerative and neuropsychiatric diseases are both based on the principle that hormonal factors could be involved. These cerebral disorders are characterized by an alteration of blood-brain barrier (BBB) properties and chronic neuroinflammation, which lead to disease progression. Neuroinflammation, in turn, contributes to BBB dysfunction. The BBB and its environment, called the neurovascular unit (NVU), are crucial for cerebral homeostasis and neuronal function. Interestingly, sex steroids influence BBB properties and modulate neuroinflammatory responses. To date however, the majority of work reported has focused on the effects of estrogens on BBB function and neuroinflammation in female mammals. In contrast, the effects of testosterone signaling on the NVU in males are still poorly studied. The aim of this review was to summarize and discuss the literature, providing insights and contradictions to highlight hypothesis and the need for further investigations.

Claudin-5: gatekeeper of neurological function

Tight junction proteins of the blood–brain barrier are vital for maintaining integrity of endothelial cells lining brain blood vessels. The presence of these protein complexes in the space between endothelial cells creates a dynamic, highly regulated and restrictive microenvironment that is vital for neural homeostasis. By limiting paracellular diffusion of material between blood and brain, tight junction proteins provide a protective barrier preventing the passage of unwanted and potentially damaging material. Simultaneously, this protective barrier hinders the therapeutic effectiveness of central nervous system acting drugs with over 95% of small molecule therapeutics unable to bypass the blood–brain barrier. At the blood–brain barrier, claudin-5 is the most enriched tight junction protein and its dysfunction has been implicated in neurodegenerative disorders such as Alzheimer’s disease, neuroinflammatory disorders such as multiple sclerosis as well as psychiatric disorders including depression and schizophrenia. By regulating levels of claudin-5, it is possible to abrogate disease symptoms in many of these disorders. This review will give an overview of the blood–brain barrier and the role of tight junction complexes in maintaining blood–brain barrier integrity before focusing on the role of claudin-5 and its regulation in homeostatic and pathological conditions. We will also summarise therapeutic strategies to restore integrity of cerebral vessels by targeting tight junction protein complexes.

Contributions of sex to cerebrovascular function and pathology

Sex differences exist in how cerebral blood vessels function under both physiological and pathological conditions, contributing to observed sex differences in risk and outcomes of cerebrovascular diseases (CBVDs), such as vascular contributions to cognitive impairment and dementia (VCID) and stroke. Throughout most of the lifespan, women are protected from CBVDs; however, risk increases following menopause, suggesting sex hormones may play a significant role in this protection. The cerebrovasculature is a target for sex hormones, including estrogens, progestins, and androgens, where they can influence numerous vascular functions and pathologies. While there is a plethora of information on estrogen, the effects of progestins and androgens on the cerebrovasculature are less well-defined. Estrogen decreases cerebral tone and increases cerebral blood flow, while androgens increase tone. Both estrogens and androgens enhance angiogenesis/cerebrovascular remodeling. While both estrogens and androgens attenuate cerebrovascular inflammation, pro-inflammatory effects of androgens under physiological conditions have also been demonstrated. Sex hormones exert additional neuroprotective effects by attenuating oxidative stress and maintaining integrity and function of the blood brain barrier. Most animal studies utilize young, healthy, gonadectomized animals, which do not mimic the clinical conditions of aging individuals likely to get CBVDs. This is also concerning, as sex hormones appear to mediate cerebrovascular function differently based on age and disease state (e.g. metabolic syndrome). Through this review, we hope to inspire others to consider sex as a key biological variable in cerebrovascular research, as greater understanding of sex differences in cerebrovascular function will assist in developing personalized approaches to prevent and treat CBVDs.

Platelet glycoprotein receptor Ib blockade ameliorates experimental cerebral ischemia-reperfusion injury by strengthening the blood-brain barrier function and anti-thrombo-inflammatory property

Blood-brain barrier (BBB) disruption, thrombus formation and immune-mediated inflammation are important steps in the pathophysiology of cerebral ischemia-reperfusion injury but are still inaccessible to therapeutic interventions. Recent studies have provided increasing evidence that blocking of platelet glycoprotein (GP) receptor Ib might represent a novel target in treating acute ischemic stroke. This research was conducted to explore the therapeutic efficacy and potential mechanisms of GPIbα inhibitor (anfibatide) in a model of brain ischemia-reperfusion injury in mice. Male mice underwent 90 min of right middle cerebral artery occlusion (MCAO) followed by 24 h of reperfusion. Anfibatide (1, 2, 4 ug/kg) or tirofiban were administered intravenously 1 h after reperfusion. The results showed that anfibatide could significantly reduce infarct volumes, increase the number of intact neuronal cells and improve neurobehavioral function. Moreover, anfibatide could reduce post ischemic BBB damage by attenuating increased paracellular permeability in the ischemia hemisphere significantly. Stroke-induced increases in activity and protein expression of macrophage-1 antigen (MAC-1) and P-selectin were also reduced by anfibatide intervention. Finally, anfibatide exerted antithrombotic effects upon stroke by decreased the number of microthrombi formation. This is the first demonstration of anfibatide's efficacy in protecting the BBB integrity and decreasing neutrophil inflammation response mediated by MAC-1 besides microthrombus formation inhibition in the brain during reperfusion. Anfibatide, as a promising anti-thrombo-inflammation agent, could be beneficial for the treatment of ischemic stroke.

Chronic depletion of gonadal testosterone leads to blood-brain barrier dysfunction and inflammation in male mice

A dysfunction in the blood-brain barrier (BBB) is associated with many neurological and metabolic disorders. Although sex steroid hormones have been shown to impact vascular tone, endothelial function, oxidative stress, and inflammatory responses, there are still no data on the role of testosterone in the regulation of BBB structure and function. In this context, we investigated the effects of gonadal testosterone depletion on the integrity of capillary BBB and the surrounding parenchyma in male mice. Our results show increased BBB permeability for different tracers and endogenous immunoglobulins in chronically testosterone-depleted male mice. These results were associated with disorganization of tight junction structures shown by electron tomography and a lower amount of tight junction proteins such as claudin-5 and ZO-1. BBB leakage was also accompanied by activation of astrocytes and microglia, and up-regulation of inflammatory molecules such as inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX-2), interleukin 1 beta (IL-1β), and tumor necrosis factor (TNF). Supplementation of castrated male mice with testosterone restored BBB selective permeability, tight junction integrity, and almost completely abrogated the inflammatory features. The present demonstration that testosterone transiently impacts cerebrovascular physiology in adult male mice should help gain new insights into neurological and metabolic diseases linked to hypogonadism in men of all ages.

Activation of G protein-coupled estrogen receptor 1 (GPER-1) ameliorates blood-brain barrier permeability after global cerebral ischemia in ovariectomized rats

G protein-coupled estrogen receptor 1 (GPER-1) plays important roles in estrogen-mediated neuroprotection. However, protective effects of GPER-1 on blood-brain barrier (BBB) after ischemic stroke have not been determined. The aim of present study was to determine whether GPER-1 activation ameliorates BBB permeability in ovariectomized rats with induced global cerebral ischemia (GCI). GCI was induced by 4-vessel occlusion for 20 min followed by 24 h reperfusion period. The GPER-1 agonist (G1) was bilaterally administered immediately upon reperfusion by intracerebroventricular (icv) injection. We found that the GPER-1 agonist could significantly decrease immunoglobulin G (IgG) extravasation and increase the levels of tight junctions (occludin and claudin-5) in the CA1 at 24 h of reperfusion after GCI. Further, protein levels of vascular endothelial growth factor A (VEGF-A) was significantly decreased in the ischemic CA1 by G1. Our results suggest that GPER-1 activation reduce tight junctions disruption via inhibition of VEGF-A expression after ischemic injury.

Activation of classical estrogen receptor subtypes reduces tight junction disruption of brain endothelial cells under ischemia/reperfusion injury

Ischemic stroke, which induces oxidative stress in the brain, disrupts tight junctions (TJs) between brain endothelial cells, resulting in blood-brain barrier (BBB) breakdown and brain edema. Estrogen reduces oxidative stress and protects brain endothelial cells from ischemic insult. The aim of this study was to determine the protective effects of estrogen on TJ disruption and to examine the roles of classical estrogen receptor (ER) subtypes, ERα- and ERβ, in estrogen effects in brain endothelial cells (bEnd.3) exposed to oxygen-glucose deprivation/reperfusion (OGD/R) injury. Estrogen pretreatment prevented OGD/R-induced decreases in cell viability and TJ protein levels. ERα- and ERβ-specific agonists also reduced TJ disruption. Knockdown of ERα or ERβ expression partially inhibited the effects of estrogen, but completely reversed the effects of corresponding ER subtype-specific agonists on the outcomes of OGD/R. During the early reperfusion period, activation of extracellular signal-regulated kinase1/2 and hypoxia-inducible factor 1α/vascular endothelial growth factor was associated with decreased expression of occludin and claudin-5, respectively, and these changes in TJ protein levels were differentially regulated by ER subtype-specific agonists. Our results suggest that ERα and ERβ activation reduce TJ disruption via inhibition of signaling molecules after ischemic injury and that targeting each ER subtype can be a useful strategy for protecting the BBB from ischemic stroke in postmenopausal women.

How Hormones Influence Composition and Physiological Function of the Brain-Blood Barrier

Hormones exert many actions in the brain. Their access and effects in the brain are regulated by the blood-brain barrier (BBB). Hormones as other substances may enter the brain and vice versa either by paracellular way requiring breaching tight junctions stitching the endothelial cells composing the BBB, or by passage through the cells (transcellular way). Hormones influence both ways through their receptors, both membrane and intracellular, present on/in the BBB. In the review the main examples are outlined how hormones influence the expression and function of proteins forming the tight junctions, as well as how they regulate expression and function of major protein transporters mediating transport of various substances including hormone themselves.

Hormones and the blood-brain barrier

Hormones exert many actions in the brain, and brain cells are also hormonally active. To reach their targets in brain structures, hormones must overcome the blood-brain barrier (BBB). The BBB is a unique device selecting desired/undesired molecules to reach or leave the brain, and it is composed of endothelial cells forming the brain vasculature. These cells differ from other endothelial cells in their almost impermeable tight junctions and in possessing several membrane structures such as receptors, transporters, and metabolically active molecules, ensuring their selection function. The main ways how compounds pass through the BBB are briefly outlined in this review. The main part concerns the transport of major classes of hormones: steroids, including neurosteroids, thyroid hormones, insulin, and other peptide hormones regulating energy homeostasis, growth hormone, and also various cytokines. Peptide transporters mediating the saturable transport of individual classes of hormones are reviewed. The last paragraph provides examples of how hormones affect the permeability and function of the BBB either at the level of tight junctions or by various transporters.

17β-Estradiol attenuates hematoma expansion through estrogen receptor α/silent information regulator 1/nuclear factor-kappa b pathway in hyperglycemic intracerebral hemorrhage mice

BACKGROUND AND PURPOSE

17β-estradiol (E2) has been reported to reduce bleeding and brain injury in experimental intracerebral hemorrhage (ICH) model. However, it is not clear if E2 can prevent early hematoma expansion (HE) induced by hyperglycemia in acute ICH. The aim of this study is to evaluate the effects of E2 on HE and its potential mechanisms in hyperglycemic ICH mice.

METHODS

Two hundred, 8-week-old male CD1 mice were used. ICH was performed by collagenase injection. 50% dextrose (8 mL/kg) was injected intraperitoneally 3 hours after ICH to induce acute HE (normal saline was used as control). The time course of HE was measured 6, 24, and 72 hours after ICH. Two dosages (100 and 300 μg/kg) of E2 were administrated 1 hour after ICH intraperitoneally. Neurobehavioral deficits, hemorrhage volume, blood glucose level, and blood-brain barrier disruption were measured. To study the mechanisms of E2, estrogen receptor α (ERα) inhibitor methyl-piperidino-pyrazole, silent information regulator 1 (Sirt1) siRNA was administered, respectively. Protein expression of ERα, Sirt1, and acetylated nuclear factor-kappa B, and activity of matrix metalloproteinases-9 were detected.

RESULTS

Hyperglycemia enhanced HE and deteriorated neurological deficits after ICH from 6 hours after ICH. E2 treatment prevented blood-brain barrier disruption and improved neurological deficits 24 and 72 hours after ICH. E2 reduced HE by activating its receptor ERα, decreasing the expression of Sirt1, deacelylation of nuclear factor-kappa B, and inhibiting the activity of matrix metalloproteinases-9. ERα inhibitor methyl-piperidino-pyrazole and Sirt1 siRNA removed these effects of E2.

CONCLUSIONS

E2 treatment prevented hyperglycemia-enhanced HE and improved neurological deficits in ICH mice mediated by ERα/Sirt1/nuclear factor-kappa B pathway. E2 may serve as an alternative treatment to decrease early HE after ICH.

Estrogen receptor-mediated resveratrol actions on blood-brain barrier of ovariectomized mice

To test whether resveratrol provides benefits via estrogen receptors (ERs) in the blood-brain barrier of estrogen-deficient females, ovariectomized mice were treated with resveratrol then were subjected to transient middle cerebral artery occlusion (MCAO). Compared with vehicle treatment, resveratrol reduced infarct volume and neurologic deficits after MCAO. Basal tight junction (TJ) protein levels in the brain were increased by resveratrol. After MCAO, blood-brain barrier breakdown reduced levels of TJ proteins, and induction of HIF-1α and VEGF were attenuated by resveratrol. These effects were reversed by the ERs antagonist, ICI182,780. In mouse brain, endothelial cells (bEnd.3) exposed to hypoxia, resveratrol treatment protected the cells against cytotoxicity, increases of paracellular permeability and changes in levels of TJ protein and HIF-1α/VEGF proteins. These effects were reversed by ICI182,780 but not by specific ERα or ERβ antagonists, indicating nonspecific ER mediated effects. Altogether, these results showed that neuroprotective effects of resveratrol in ovariectomized mice were mediated by ERs and associated with tightening of blood-brain barrier, suggesting that resveratrol can be an alternative to estrogens to protect the brains of estrogen-deficient females against ischemic insult.

Steroids and the blood-brain barrier: therapeutic implications

Steroids have a wide spectrum of impact, serving as fundamental regulators of nearly every physiological process within the human body. Therapeutic applications of steroids are equally broad, with a diverse range of medications and targets. Within the central nervous system (CNS), steroids influence development, memory, behavior, and disease outcomes. Moreover, steroids are well recognized as to their impact on the vascular endothelium. The blood-brain barrier (BBB) at the level of the brain microvascular endothelium serves as the principle interface between the peripheral circulation and the brain. Steroids have been identified to impact several critical properties of the BBB, including cellular efflux mechanisms, nutrient uptake, and tight junction integrity. Such actions not only influence brain homeostasis but also the delivery of CNS-targeted therapeutics. A greater understanding of the respective steroid-BBB interactions may shed further light on the differential treatment outcomes observed across CNS pathologies. In this chapter, we examine the current therapeutic implications of steroids respective to BBB structure and function, with emphasis on glucocorticoids and estrogens.

Reproductive senescence blunts response of estrogen receptor-α expression to estrogen treatment in rat post-ischemic cerebral microvessels

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 to 15 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.

Vascular hyperpermeability and aging

Vascular hyperpermeability, the excessive leakage of fluid and proteins from blood vessels to the interstitial space, commonly occurs in traumatic and ischemic injuries. This hyperpermeability causes tissue vasogenic edema, which often leads to multiple organ failure resulting in patient death. Vascular hyperpermeability occurs most readily in small blood vessels as their more delicate physical constitution makes them an easy target for barrier dysfunction. A single layer of endothelial cells, linked to one another by cell adhesion molecules, covers the interior surface of each blood vessel. The cell adhesion molecules play a key role in maintaining barrier functions like the regulation of permeability. Aging is a major risk factor for microvascular dysfunction and hyperpermeability. Apart from age-related remodeling of the vascular wall, endothelial barrier integrity and function declines with the advancement of age. Studies that address the physiological and molecular basis of vascular permeability regulation in aging are currently very limited. There have been many cellular and molecular mechanisms proposed to explain aging-related endothelial dysfunction but their true relationship to barrier dysfunction and hyperpermeability is not clearly known. Among the several mechanisms that promote vascular dysfunction and hyperpermeability, the following are considered major contributors: oxidative stress, inflammation, and the activation of apoptotic signaling pathways. In this review we highlighted (a) the physiological, cellular and molecular changes that occur in the vascular system as a product of aging; (b) the potential mechanisms by which aging leads to barrier dysfunction and vascular hyperpermeability in the peripheral and the blood-brain barrier; (c) the mechanisms by which the age-related increases in oxidative stress, inflammatory markers and apoptotic signaling etc. cause endothelial dysfunction and their relationship to hyperpermeability; and (d) the relationship between aging, vascular permeability and traumatic injuries.

Triggers and effectors of oxidative stress at blood-brain barrier level: relevance for brain ageing and neurodegeneration

As fundamental research advances, it is becoming increasingly clear that a clinically expressed disease implies a mixture of intertwining molecular disturbances. Oxidative stress is one of such pathogenic pathways involved in virtually all central nervous system pathologies, infectious, inflammatory, or degenerative in nature. Since brain homeostasis largely depends on integrity of blood-brain barrier (BBB), many studies focused lately on BBB alteration in a wide spectrum of brain diseases. The proper two-way molecular transfer through BBB depends on several factors, including the functional status of its tight junction (TJ) complexes of proteins sealing neighbour endothelial cells. Although there is abundant experimental work showing that oxidative stress associates BBB permeability alteration, less is known about its implications, at molecular level, in TJ protein expression or TJ-related cell signalling. In this paper, oxidative stress is presented as a common pathway for different brain pathogenic mechanisms which lead to BBB dysregulation. We revise here oxidative-induced molecular mechanisms of BBB disruption and TJ protein expression alteration, in relation to ageing and neurodegeneration.

Onion (Allium cepa) extract attenuates brain edema

OBJECTIVE

This study investigated the potential beneficial effects of onion extract on brain ischemia-induced edema and blood-brain barrier (BBB) dysfunction. The possible underlying mechanisms are investigated, especially those linked to the antioxidant effects of the onion extract.

METHODS

Brain ischemia was induced by middle cerebral artery occlusion (MCAO) for 2 h followed by reperfusion in mice. Mice were treated intravenously with onion extract 30 min before MCAO. Brain edema and BBB hyperpermeability were evaluated by the measurement of the brain water content and Evans blue extravasation, respectively. The disruption of tight junction proteins was examined by immunohistochemical staining. The level of malondialdehyde was determined using the thiobarbituric acid method. The activities of glutathione peroxidase and catalase were determined by spectrophotometric assay.

RESULTS

Brain water content in the ischemic hemisphere was significantly reduced by treatment with onion extract. Onion extract also had a significant effect on both the decrease in Evans blue extravasation and the inhibition of zonula occludens-1 and occludin disruption caused by brain ischemia. In addition, onion extract significantly prevented brain ischemia-induced reduction in catalase and glutathione peroxidase activities and elevation of malondialdehyde level in the brain tissue.

CONCLUSION

The results from this study demonstrate that onion extract prevents brain edema, BBB hyperpermeability, and tight junction proteins disruption, possibly through its antioxidant effects in the mouse MCAO model. This study suggests that onion extract may be a beneficial nutrient for the prevention of BBB function during brain ischemia.

Tight junction in blood-brain barrier: an overview of structure, regulation, and regulator substances

Blood-brain barrier (BBB) is a dynamic interference that regulates the nutrition and toxic substance in and out of the central nervous system (CNS), and plays a crucial role in maintaining a stable circumstance of the CNS. Tight junctions among adjacent cells form the basic structure of BBB to limiting paracellular permeability. In the present review, the constituents of tight junction proteins are depicted in detail, together with the regulation of tight junction under stimulation and in pathological conditions. Tight junction modulators are also discussed.

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.

Dopaminergic neuroprotection of hormonal replacement therapy in young and aged menopausal rats: role of the brain angiotensin system

There is a lack of consensus about the effects of the type of menopause (surgical or natural) and of oestrogen replacement therapy on Parkinson's disease. The effects of the timing of replacement therapy and the female's age may explain the observed differences in such effects. However, the mechanisms involved are poorly understood. The renin-angiotensin system mediates the beneficial effects of oestrogen in several tissues, and we have previously shown that dopaminergic cell loss is enhanced by angiotensin via type 1 receptors, which is activated by ageing. In rats, we compared the effects of oestrogen replacement therapy on 6-hydroxydopamine-induced dopaminergic degeneration, nigral renin-angiotensin system activity, activation of the nicotinamide adenine dinucleotide phosphate oxidase complex and levels of the proinflammatory cytokine interleukin-1β in young (surgical) menopausal rats and aged menopausal rats. In young surgically menopausal rats, the renin-angiotensin system activity was higher (i.e. higher angiotensin converting enzyme activity, higher angiotensin type-1 receptor expression and lower angiotensin type-2 receptor expression) than in surgically menopausal rats treated with oestrogen; the nicotinamide adenine dinucleotide phosphate oxidase activity and interleukin-1β expression were also higher in the first group than in the second group. In aged menopausal rats, the levels of nigral renin-angiotensin and nicotinamide adenine dinucleotide phosphate oxidase activity were similar to those observed in surgically menopausal rats. However, oestrogen replacement therapy significantly reduced 6-hydroxydopamine-induced dopaminergic cell loss in young menopausal rats but not in aged rats. Treatment with oestrogen also led to a more marked reduction in nigral renin-angiotensin and nicotinamide adenine dinucleotide phosphate oxidase activity in young surgically menopausal rats (treated either immediately or after a period of hypo-oestrogenicity) than in aged menopausal rats. Interestingly, treatment with the angiotensin type-1 receptor antagonist candesartan led to remarkable reduction in renin-angiotensin system activity and dopaminergic neuron loss in both groups of menopausal rats. This suggests that manipulation of the brain renin-angiotensin system may be an efficient approach for the prevention or treatment of Parkinson's disease in oestrogen-deficient females, together with or instead of oestrogen replacement therapy.