Estrogens are neuroprotective factors for hypertensive encephalopathy

Cerebrolysin treatment improved short-term memory deficits while simultaneously increasing hippocampal spine density in hypertensive female rats

Hypertension, if untreated, can disrupt the blood-brain-barrier (BBB) and reduce cerebral flow in the central nervous system (CNS) inducing hippocampal atrophy, potentially leading to cognitive deficits and vascular dementia. Spontaneous hypertensive rats (SHR) demonstrated neuroplastic alterations in the hippocampus, hyperlocomotion and memory deficits in males. Cerebrolysin (CBL), a neuropeptide preparation, induces synaptic and neuronal plasticity in various populations of neurons and repairs the integrity of the BBB. This research aims to investigate the behavioral outcomes in locomotion and recognition memory in the Novel Object Recognition Test (NORT) and assess the neuroreparative effect of CBL on the cytoarchitecture of neurons and the spine density in pyramidal neurons of the prefrontal cortex (PFC), the entorhinal cortex (EC) and the CA1 region of the dorsal hippocampus, as well as spheroidal neurons of the dentate gyrus (DG). Our findings indicate that SHR exhibited elevated diastolic and systolic pressures, and increased locomotion. Importantly, CBL treatment improved recognition memory in SHR strain. Hypertension led to reduced arborization in the EC, CA1, and DG regions. Moreover, CBL treatment increased arborization in both normotensive and hypertensive rats in the CA1, and DG regions of hippocampus and EC and selectively increased spine density in the hippocampus of hypertensive rats. These findings suggest that CBL neurotrophic treatment enhances recognition memory and promotes dendritic growth or spine density, depending on the neurochemical environment within the brain.

The phytoestrogen genistein improves hippocampal neurogenesis and cognitive impairment and decreases neuroinflammation in an animal model of metabolic syndrome

Metabolic syndrome (MS) is the medical term for the combination of at least three of the following factors: obesity, hyperlipidemia, hyperglycemia, insulin resistance, and hypertension. The spontaneously hypertensive rat (SHR) is an accepted animal model for the study of human MS that reveals all the features of the syndrome when fed high-fat, high-carbohydrate diets. The intake of high-fat diets in rats has been shown to produce brain neuropathology. In humans, MS increases the risk of cognitive impairment, dementia, and Alzheimer's disease. Genistein (GEN) is a phytoestrogen found in soy that lacks feminizing and carcinogenic effects and was found to have neuroprotective and anti-inflammatory effects in many pathological conditions. Considering that multiple data support that natural phytoestrogens may be therapeutic options for CNS maladies, we aim to elucidate if these properties also apply to a rat model of MS. Thus, GEN effects on neuroinflammation, neurogenesis, and cognition were evaluated in SHR eating a fat/carbohydrate-enriched diet. To characterize the neuropathology and cognitive dysfunction of MS we fed SHR with a high-fat diet (4520 kcal/kg) along with a 20% sucrose solution to drink. MS rats displayed a significant increase in body weight, BMI and obesity indexes along with an increased in fasting glucose levels, glucose intolerance, high blood pressure, and high blood triglyceride levels. MS rats were injected with GEN during 2 weeks a dose of 10 mg/kg. We found that MS rats showed a decreased number of DCX+ neural progenitors in the dentate gyrus and treatment with GEN increased this parameter. Expression of GFAP was increased in the DG and CA1 areas of the hippocampus and treatment decreased astrogliosis in all of them. We measured the expression of IBA1+ microglia in the same regions and classified microglia according to their morphology: we found that MS rats presented an increased proportion of the hypertrophied phenotype and GEN produced a shift in microglial phenotypes toward a ramified type. Furthermore, colocalization of IBA1 with the proinflammatory marker TNFα showed increased proportion of proinflammatory microglia in MS and a reduction with GEN treatment. On the other hand, colocalization with the anti-inflammatory marker Arg1 showed that MS has decreased proportion of anti-inflammatory microglia and GEN treatment increased this parameter. Cognitive dysfunction was evaluated in rats with MS using a battery of behavioral tests that assessed hippocampus-dependent spatial and working memory, such as the novel object recognition test (NOR), the novel object location test (NOL), and the free-movement pattern Y-maze (FMP-YMAZE) and the d-YMAZE. In all of them, MS performed poorly and GEN was able to improve cognitive impairments. These results indicate that GEN was able to exert neuroprotective actions increasing neurogenesis and improving cognitive impairments while decreasing astrogliosis, microgliosis, and neuroinflammatory environment in MS rats. Together, these results open an interesting possibility for proposing this phytoestrogen as a neuroprotective therapy for MS.

Evidence for the contribution of vasopressin V1B receptors in the pathophysiology of depression

Depression is a chronic and recurrent psychiatric condition characterised by depressed mood, loss of interest or pleasure, poor sleep, low appetite, and poor concentration. Research has shown that both heritable and environmental risk factors are involved in the pathogenesis of depression. In addition, several studies have indicated that dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis is implicated in the development of depression in adulthood. However, the mechanism underlying the activation of HPA axis-induced depression remains unclear. Arginine vasopressin (AVP), also known as vasopressin (VP), is a hormone synthesised in the hypothalamus that plays important roles in numerous biological functions in mammals, including the regulation of stress and anxiety, and has been implicated in the pathogenesis of many disorders. VP regulates pituitary corticotroph function by binding to the plasma membrane G-protein receptors of the V1B receptor (V1BR), which are coupled to calcium-phospholipid signalling. V1BR, a receptor subtype of VP, plays a pivotal role in HPA axis abnormalities observed in depression. In animals, V1BR antagonists reduce plasma stress hormone levels and have been shown to have antidepressant activity. However, the precise mechanism of V1BR in modulating HPA axis activity remains unclear. We therefore reviewed and integrated the clinical and preclinical literature pertinent to the role of V1BR in depression, while emphasising the effect of V1BR antagonists on attenuating the hyperactivity of the HPA axis. In addition, therapy for depression through the regulation of the HPA axis is briefly discussed. Although effective antidepressants are available, a large proportion of patients do not respond to initial treatment. Therefore, this review describes the exact mechanisms of V1BR in depression and contributes to the development of new therapeutic strategies for this disease.

Hippocampus under Pressure: Molecular Mechanisms of Development of Cognitive Impairments in SHR Rats

Data from clinical trials and animal experiments demonstrate relationship between chronic hypertension and development of cognitive impairments. Here, we review structural and biochemical alterations in the hippocampus of SHR rats with genetic hypertension, which are used as a model of essential hypertension and vascular dementia. In addition to hypertension, dysfunction of the hypothalamic-pituitary-adrenal system observed in SHR rats already at an early age may be a key factor of changes in the hippocampus at the structural and molecular levels. Global changes at the body level, such as hypertension and neurohumoral dysfunction, are associated with the development of vascular pathology and impairment of the blood-brain barrier. Changes in multiple biochemical glucocorticoid-dependent processes in the hippocampus, including dysfunction of steroid hormones receptors, impairments of neurotransmitter systems, BDNF deficiency, oxidative stress, and neuroinflammation are accompanied by the structural alterations, such as cellular signs of neuroinflammation micro- and astrogliosis, impairments of neurogenesis in the subgranular neurogenic zone, and neurodegenerative processes at the level of synapses, axons, and dendrites up to the death of neurons. The consequence of this is dysfunction of hippocampus, a key structure of the limbic system necessary for cognitive functions. Taking into account the available results at various levels starting from the body and brain structure (hippocampus) levels to molecular one, we can confirm translational validity of SHR rats for modeling mechanisms of vascular dementia.

Post-Traumatic Expressions of Aromatase B, Glutamine Synthetase, and Cystathionine-Beta-Synthase in the Cerebellum of Juvenile Chum Salmon, Oncorhynchus keta

In adult fish, neurogenesis occurs in many areas of the brain, including the cerebellum, with the ratio of newly formed cells relative to the total number of brain cells being several orders of magnitude greater than in mammals. Our study aimed to compare the expressions of aromatase B (AroB), glutamine synthetase (GS), and cystathionine-beta-synthase (CBS) in the cerebellum of intact juvenile chum salmon, Oncorhynchus keta. To identify the dynamics that determine the involvement of AroB, GS, and CBS in the cellular mechanisms of regeneration, we performed a comprehensive assessment of the expressions of these molecular markers during a long-term primary traumatic brain injury (TBI) and after a repeated acute TBI to the cerebellum of O. keta juveniles. As a result, in intact juveniles, weak or moderate expressions of AroB, GS, and CBS were detected in four cell types, including cells of the neuroepithelial type, migrating, and differentiated cells (graphic abstract, A). At 90 days post injury, local hypercellular areas were found in the molecular layer containing moderately labeled AroB+, GS+, and CBS+ cells of the neuroepithelial type and larger AroB+, GS+, and CBS+ cells (possibly analogous to the reactive glia of mammals); patterns of cells migration and neovascularization were also observed. A repeated TBI caused the number of AroB+, GS+, and CBS+ cells to further increase; an increased intensity of immunolabeling was recorded from all cell types (graphic abstract, C). Thus, the results of this study provide a better understanding of adult neurogenesis in teleost fishes, which is expected to clarify the issue of the reactivation of adult neurogenesis in mammalian species.

The effects of peripheral hormone responses to exercise on adult hippocampal neurogenesis

Over the last decade, a considerable amount of new data have revealed the beneficial effects of exercise on hippocampal neurogenesis and the maintenance or improvement of cognitive function. Investigations with animal models, as well as human studies, have yielded novel understanding of the mechanisms through which endocrine signaling can stimulate neurogenesis, as well as the effects of exercise on acute and/or chronic levels of these circulating hormones. Considering the effects of aging on the decline of specific endocrine factors that affect brain health, insights in this area of research are particularly important. In this review, we discuss how different forms of exercise influence the peripheral production of specific endocrine factors, with particular emphasis on brain-derived neurotrophic factor, growth hormone, insulin-like growth factor-1, ghrelin, estrogen, testosterone, irisin, vascular endothelial growth factor, erythropoietin, and cortisol. We also describe mechanisms through which these endocrine responses to exercise induce cellular changes that increase hippocampal neurogenesis and improve cognitive function.

Beneficial effects of the phytoestrogen genistein on hippocampal impairments of spontaneously hypertensive rats (SHR)

Hippocampal neuropathology is a recognized feature of the spontaneously hypertensive rat (SHR). The hippocampal alterations associate with cognitive impairment. We have shown that hippocampal abnormalities are reversed by 17β-estradiol, a steroid binding to intracellular receptors (estrogen receptor α and β subtypes) or the membrane-located G-protein coupled estradiol receptor. Genistein (GEN) is a neuroprotective phytoestrogen which binds to estrogen receptor β and G-protein coupled estradiol receptor. Here, we investigated whether GEN neuroprotection extends to SHR. For this purpose, we treated 5-month-old SHR for 2 weeks with 10 mg kg^-1 daily s.c injections of GEN. We analyzed the expression of doublecortin+ neuronal progenitors, glial fibrillary acidic protein+ astrocytes and ionized calcium-binding adapter molecule 1+ microglia in the CA1 region and dentate gyrus of the hippocampus using immunocytochemistry, whereas a quantitative real-time polymerase chain reaction was used to measure the expression of pro- and anti-inflammatory factors tumor necrosis factor α, cyclooxygenase-2 and transforming growth factor β. We also evaluated hippocampal dependent memory using the novel object recognition test. The results showed a decreased number of doublecortin+ neural progenitors in the dentate gyrus of SHR that was reversed with GEN. The number of glial fibrillary acidic protein+ astrocytes in the dentate gyrus and CA1 was increased in SHR but significantly decreased by GEN treatment. Additionally, GEN shifted microglial morphology from the predominantly activated phenotype present in SHR, to the more surveillance phenotype found in normotensive rats. Furthermore, treatment with GEN decreased the mRNA of the pro-inflammatory factors tumor necrosis factor α and cyclooxygenase-2 and increased the mRNA of the anti-inflammatory factor transforming growth factor β. Discrimination index in the novel object recognition test was decreased in SHR and treatment with GEN increased this parameter. Our results indicate important neuroprotective effects of GEN at the neurochemical and behavioral level in SHR. Our data open an interesting possibility for proposing this phytoestrogen as an alternative therapy in hypertensive encephalopathy.

Immune regulation based on sex differences in ischemic stroke pathology

Ischemic stroke is one of the world's leading causes of death and disability. It has been established that gender differences in stroke outcomes prevail, and the immune response after stroke is an important factor affecting patient outcomes. However, gender disparities lead to different immune metabolic tendencies closely related to immune regulation after stroke. The present review provides a comprehensive overview of the role and mechanism of immune regulation based on sex differences in ischemic stroke pathology.

Sex-Associated Differences in Neurovascular Dysfunction During Ischemic Stroke

Neurovascular units (NVUs) are basic functional units in the central nervous system and include neurons, astrocytes and vascular compartments. Ischemic stroke triggers not only neuronal damage, but also dissonance of intercellular crosstalk within the NVU. Stroke is sexually dimorphic, but the sex-associated differences involved in stroke-induced neurovascular dysfunction are studied in a limited extend. Preclinical studies have found that in rodent models of stroke, females have less neuronal loss, stronger repairing potential of astrocytes and more stable vascular conjunction; these properties are highly related to the cerebroprotective effects of female hormones. However, in humans, these research findings may be applicable only to premenopausal stroke patients. Women who have had a stroke usually have poorer outcomes compared to men, and because stoke is age-related, hormone replacement therapy for postmenopausal women may exacerbate stroke symptoms, which contradicts the findings of most preclinical studies. This stark contrast between clinical and laboratory findings suggests that understanding of neurovascular differences between the sexes is limited. Actually, apart from gonadal hormones, differences in neuroinflammation as well as genetics and epigenetics promote the sexual dimorphism of NVU functions. In this review, we summarize the confirmed sex-associated differences in NVUs during ischemic stroke and the possible contributing mechanisms. We also describe the gap between clinical and preclinical studies in terms of sexual dimorphism.

IGF1 Gene Therapy Reversed Cognitive Deficits and Restored Hippocampal Alterations After Chronic Spinal Cord Injury

The hippocampus is implicated in the generation of memory and learning, processes which involve extensive neuroplasticity. The generation of hippocampal adult-born neurons is particularly regulated by glial cells of the neurogenic niche and the surrounding microenvironment. Interestingly, recent evidence has shown that spinal cord injury (SCI) in rodents leads to hippocampal neuroinflammation, neurogenesis reduction, and cognitive impairments. In this scenario, the aim of this work was to evaluate whether an adenoviral vector expressing IGF1 could reverse hippocampal alterations and cognitive deficits after chronic SCI. SCI caused neurogenesis reduction and impairments of both recognition and working memories. We also found that SCI increased the number of hypertrophic arginase-1 negative microglia concomitant with the decrease of the number of ramified surveillance microglia in the hilus, molecular layer, and subgranular zone of the dentate gyrus. RAd-IGF1 treatment restored neurogenesis and improved recognition and working memory impairments. In addition, RAd-IGF1 gene therapy modulated differentially hippocampal regions. In the hilus and molecular layer, IGF1 gene therapy recovered the number of surveillance microglia coincident with a reduction of hypertrophic microglia cell number. However, in the neurogenic niche, IGF1 reduced the number of ramified microglia and increased the number of hypertrophic microglia, which as a whole expressed arginase-1. In summary, RAd-IGF1 gene therapy might surge as a new therapeutic strategy for patients with hippocampal microglial alterations and cognitive deficits such as those with spinal cord injury and other neurodegenerative diseases.

Activation of the G Protein-Coupled Estrogen Receptor (GPER) Increases Neurogenesis and Ameliorates Neuroinflammation in the Hippocampus of Male Spontaneously Hypertensive Rats

It is known that spontaneously hypertensive rats (SHR) present a marked encephalopathy, targeting vulnerable regions such as the hippocampus. Abnormalities of the hippocampus of SHR include decreased neurogenesis in the dentate gyrus (DG), partial loss of neurons in the hilus of the DG, micro and astrogliosis and inflammation. It is also known that 17β-estradiol (E2) exert neuroprotective effects and prevent hippocampal abnormalities of SHR. The effects of E2 may involve a variety of mechanisms, including intracellular receptors of the ERα and ERβ subtypes or membrane-located receptors, such as the G protein-coupled estradiol receptor (GPER). We have now investigated the protective role of GPER in SHR employing its synthetic agonist G1. To accomplish this objective, 5 month-old male SHR received 150 μg/day of G1 during 2 weeks. At the end of this period, we analyzed neuronal progenitors by staining for doublecortin (DCX), and counted the number of glial fibrillary acidic protein (GFAP)-labeled astrocytes and Iba1-stained microglial cells by computerized image analysis. We found that G1 activation of GPER increased DCX+ cells in the DG and reduced GFAP+ astrogliosis and Iba1+ microgliosis in the CA1 region of hippocampus. We also found that the high expression of proinflammatory makers IL1β and cyclooxygenase 2 (COX2) of SHR was decreased after G1 treatment, which correlated with a change of microglia phenotype from the activated to a resting morphology. Additionally, G1 treatment increased the anti-inflammatory factor TGFβ in SHR hippocampus. Altogether, our results suggest that activation of GPER plays a neuroprotective role on the encephalopathy of SHR, an outcome resembling E2 effects but avoiding secondary effects of the natural hormone.

Molecular mechanisms and cellular events involved in the neuroprotective actions of estradiol. Analysis of sex differences

Estradiol, either from peripheral or central origin, activates multiple molecular neuroprotective and neuroreparative responses that, being mediated by estrogen receptors or by estrogen receptor independent mechanisms, are initiated at the membrane, the cytoplasm or the cell nucleus of neural cells. Estrogen-dependent signaling regulates a variety of cellular events, such as intracellular Ca²⁺ levels, mitochondrial respiratory capacity, ATP production, mitochondrial membrane potential, autophagy and apoptosis. In turn, these molecular and cellular actions of estradiol are integrated by neurons and non-neuronal cells to generate different tissue protective responses, decreasing blood-brain barrier permeability, oxidative stress, neuroinflammation and excitotoxicity and promoting synaptic plasticity, axonal growth, neurogenesis, remyelination and neuroregeneration. Recent findings indicate that the neuroprotective and neuroreparative actions of estradiol are different in males and females and further research is necessary to fully elucidate the causes for this sex difference.

Sexually Dimorphic Effects of Aromatase on Neurobehavioral Responses

Aromatase is the enzyme responsible for converting testosterone to estradiol. In mammals, aromatase is expressed in the testes, ovaries, brain, and other tissues. While estrogen is traditionally associated with reproduction and sexual behavior in females, our current understanding broadens this perspective to include such biological functions as metabolism and cognition. It is now well-recognized that aromatase plays a vital lifetime role in brain development and neurobehavioral function in both sexes. Thus, ongoing investigations seek to highlight potentially vital sex differences in the role of aromatase, particularly regarding its centrally mediated effects. To characterize the role of aromatase in mediating such functions, effects of aromatase inhibitor (AI) treatments on humans and animal models have been determined. Aromatase knockout (ArKO) mice that systemically lack the enzyme have also been employed. Humans possessing mutations in the gene encoding aromatase, CYP19, have also provided critical insight into how aromatase affects brain function in a possible sex-dependent manner. A better understanding of how AIs, used to treat breast cancer and other clinical conditions, may detrimentally affect neurobehavioral responses will likely promote development of future therapies to combat these effects. Herein, we will provide a critical review of the current knowledge of sex differences in aromatase regulation of various neurobehavioral functions. Although many species have been used to better understand the functions of aromatase, this review focuses on rodent models and humans. Critical gaps in our present understanding of this area will be considered, and important future research directions will be discussed.

Choline ameliorates cardiovascular damage by improving vagal activity and inhibiting the inflammatory response in spontaneously hypertensive rats

Autonomic dysfunction and abnormal immunity lead to systemic inflammatory responses, which result in cardiovascular damage in hypertension. The aim of this report was to investigate the effects of choline on cardiovascular damage in hypertension. Eight-week-old male spontaneously hypertensive rats (SHRs) and Wistar-Kyoto rats were intraperitoneally injected with choline or vehicle (8 mg/kg/day). After 8 weeks, choline restored the cardiac function of the SHRs, as evidenced by decreased heart rate, systolic blood pressure, left ventricle systolic pressure, and ±dp/dt_max and increased ejection fraction and fractional shortening. Choline also ameliorated the cardiac hypertrophy of the SHRs, as indicated by reduced left ventricle internal dimensions and decreased cardiomyocyte cross-sectional area. Moreover, choline improved mesenteric arterial function and preserved endothelial ultrastructure in the SHRs. Notably, the protective effect of choline may be due to its anti-inflammatory effect. Choline downregulated expression of interleukin (IL)-6 and tumour necrosis factor-α and upregulated IL-10 in the mesenteric arteries of SHRs, possibly because of the inhibition of Toll-like receptor 4. Furthermore, choline restored baroreflex sensitivity and serum acetylcholine level in SHRs, thus indicating that choline improved vagal activity. This study suggests that choline elicits cardiovascular protective effects and may be useful as a potential adjunct therapeutic approach for hypertension.

Role of aromatase and radial glial cells in neurotoxin-induced dopamine neuron degeneration and regeneration

Radial glial cells (RGCs) in teleost brain are progenitor cells that express aromatase B and produce estrogens. Controversial data suggest that estrogens are critical for brain repair and neurogenesis in teleosts. Using a goldfish model for neurotoxin-induced Parkinson-like syndrome, we investigated the possible roles of RGCs, especially estrogen synthetic function, in the processes underlying dopamine neuron regeneration. The data indicate that dopamine neuron degeneration and aromatase activity inhibition could be respectively achieved in vivo with treatments with the neurotoxin 1-methyl-1,2,3,6-tetrahydropyridine (MPTP) and fadrozole in female goldfish. The expression of genes in the telencephalon and hypothalamus related to RGC functions including gfap, gdnf and bdnf as well as genes related to mature dopamine neuron functions including th, slc6a3 and pitx3 are under modulation of estrogens. Together these results revealed that the activation of radial glial cells and dopamine neuron recovery after MPTP insult is aromatase-dependent. Findings in this study provide support for the hypothesis that endogenous estrogens are neuroprotective in goldfish. Future studies focus on the molecular pathways for enhancing protective functions of estrogens and understanding global effects of estrogens in the central nervous system.

Dehydroabietic acid cytotoxicity in goldfish radial glial cells in vitro

Dehydroabietic acid (DHAA) is a resin acid present in aquatic environments shown to induce cellular and molecular damage in aquatic animals. In this study, the cytotoxicity of DHAA on primary cultured goldfish radial glial cells (RGCs), an important component of the central nervous system, was evaluated. Here, it is reported that a concentration of 20mg/L DHAA affected cellular morphology and expression of genes involved in RGC steroidogenesis and metabolism. Higher concentration exposures of DHAA (40mg/L) lead to RGC death based on a lactate dehydrogenase leakage assay. Together, these data have implications in understanding the effects of DHAA on an integral central nervous system cell type important for neurogenesis, steroidogenesis and structural support. Due to the continuous presence of DHAA into water systems, results from this study provide indications as to the potential impacts of DHAA and demonstrate the importance of this class of chemicals on aquatic organisms.

Selective Oestrogen Receptor Agonists Rescued Hippocampus Parameters in Male Spontaneously Hypertensive Rats

Spontaneously hypertensive rats (SHR) show pronounced hippocampus alterations, including low brain-derived neurotrophic factor (BDNF) expression, reduced neurogenesis, astrogliosis and increased aromatase expression. These changes are reverted by treatment with 17β-oestradiol. To determine which oestradiol receptor (ER) type is involved in these neuroprotective effects, we used agonists of the ERα [propylpyrazole triol (PPT)] and the ERβ [diarylpropionitrite (DPN)] given over 2 weeks to 4-month-old male SHR. Wistar Kyoto normotensive rats served as controls. Using immunocytochemistry, we determined glial fibrillary protein (GFAP)+ astrocytes in the CA1, CA3 and hilus of the dentate gyrus of the hippocampus, aromatase immunostaining in the hilus, and doublecortin (DCX)+ neuronal progenitors in the inner granular zone of the dentate gyrus. Brain-derived neurotrophic factor mRNA was also measured in the hippocampus by the quantitative polymerase chain reaction. In SHR, PPT had no effect on blood pressure, decreased astrogliosis, slightly increased BDNF mRNA, had no effect on the number of DCX+ progenitors, and increased aromatase staining. Treatment with DPN decreased blood pressure, decreased astrogliosis, increased BDNF mRNA and DCX+ progenitors, and did not modify aromatase staining. We hypothesise that, although both receptor types may participate in the previously reported beneficial effects of 17β-oestradiol in SHR, receptor activation with DPN may preferentially facilitate BDNF mRNA expression and neurogenesis. The results of the present study may help in the design of ER-based neuroprotection for the encephalopathy of hypertension.

GnRH and GnRH receptors in the pathophysiology of the human female reproductive system

BACKGROUND

Human reproduction depends on an intact hypothalamic-pituitary-gonadal (HPG) axis. Hypothalamic gonadotrophin-releasing hormone (GnRH) has been recognized, since its identification in 1971, as the central regulator of the production and release of the pituitary gonadotrophins that, in turn, regulate the gonadal functions and the production of sex steroids. The characteristic peculiar development, distribution and episodic activity of GnRH-producing neurons have solicited an interdisciplinary interest on the etiopathogenesis of several reproductive diseases. The more recent identification of a GnRH/GnRH receptor (GnRHR) system in both the human endometrium and ovary has widened the spectrum of action of the peptide and of its analogues beyond its hypothalamic function.

METHODS

An analysis of research and review articles published in international journals until June 2015 has been carried out to comprehensively summarize both the well established and the most recent knowledge on the physiopathology of the GnRH system in the central and peripheral control of female reproductive functions and diseases.

RESULTS

This review focuses on the role of GnRH neurons in the control of the reproductive axis. New knowledge is accumulating on the genetic programme that drives GnRH neuron development to ameliorate the diagnosis and treatment of GnRH deficiency and consequent delayed or absent puberty. Moreover, a better understanding of the mechanisms controlling the episodic release of GnRH during the onset of puberty and the ovulatory cycle has enabled the pharmacological use of GnRH itself or its synthetic analogues (agonists and antagonists) to either stimulate or to block the gonadotrophin secretion and modulate the functions of the reproductive axis in several reproductive diseases and in assisted reproduction technology. Several inputs from other neuronal populations, as well as metabolic, somatic and age-related signals, may greatly affect the functions of the GnRH pulse generator during the female lifespan; their modulation may offer new possible strategies for diagnostic and therapeutic interventions. A GnRH/GnRHR system is also expressed in female reproductive tissues (e.g. endometrium and ovary), both in normal and pathological conditions. The expression of this system in the human endometrium and ovary supports its physiological regulatory role in the processes of trophoblast invasion of the maternal endometrium and embryo implantation as well as of follicular development and corpus luteum functions. The GnRH/GnRHR system that is expressed in diseased tissues of the female reproductive tract (both benign and malignant) is at present considered an effective molecular target for the development of novel therapeutic approaches for these pathologies. GnRH agonists are also considered as a promising therapeutic approach to counteract ovarian failure in young female patients undergoing chemotherapy.

CONCLUSIONS

Increasing knowledge about the regulation of GnRH pulsatile release, as well as the therapeutic use of its analogues, offers interesting new perspectives in the diagnosis, treatment and outcome of female reproductive disorders, including tumoral and iatrogenic diseases.

Sex Steroids Influence Brain-Derived Neurotropic Factor Secretion From Human Airway Smooth Muscle Cells

Brain derived neurotropic factor (BDNF) is emerging as an important player in airway inflammation, remodeling, and hyperreactivity. Separately, there is increasing evidence that sex hormones contribute to pathophysiology in the lung. BDNF and sex steroid signaling are thought to be intricately linked in the brain. There is currently little information on BDNF and sex steroid interactions in the airway but is relevant to understanding growth factor signaling in the context of asthma in men versus women. In this study, we assessed the effect of sex steroids on BDNF expression and secretion in human airway smooth muscle (ASM). Human ASM was treated with estrogen (E2 ) or testosterone (T, 10 nM each) and intracellular BDNF and secreted BDNF measured. E2 and T significantly reduced secretion of BDNF; effects prevented by estrogen and androgen receptor inhibitor, ICI 182,780 (1 μM), and flutamide (10 μM), respectively. Interestingly, no significant changes were observed in intracellular BDNF mRNA or protein expression. High affinity BDNF receptor, TrkB, was not altered by E2 or T. E2 (but not T) significantly increased intracellular cyclic AMP levels. Notably, Epac1 and Epac2 expression were significantly reduced by E2 and T. Furthermore, SNARE complex protein SNAP25 was decreased. Overall, these novel data suggest that physiologically relevant concentrations of E2 or T inhibit BDNF secretion in human ASM, suggesting a potential interaction of sex steroids with BDNF in the airway that is different from brain. The relevance of sex steroid-BDNF interactions may lie in their overall contribution to airway diseases such as asthma.