Aromatase promoter I.f is regulated by estrogen receptor alpha (ESR1) in mouse hypothalamic neuronal cell lines

Mutation of brain aromatase disrupts spawning behavior and reproductive health in female zebrafish

Aromatase (Cyp19a1) is the steroidogenic enzyme that converts androgens into bioactive estrogens, and hence is in a pivotal position to mediate reproduction and sexual behavior. In teleosts, there are two aromatase paralogs: cyp19a1a that is highly expressed in granulosa and Leydig cells in the gonads with critical function in sexual differentiation of the ovary, and cyp19a1b that is highly expressed in radial glial cells in the brain with unknown roles in reproduction. Cyp19a1 ^-/- mutant zebrafish lines were used to investigate the importance of the cyp19a1 paralogs for spawning behavior and offspring survival and early development. Mutation of cyp19a1b was found to increase the latency to the first oviposition in females. Mutation of cyp19a1b in females also increased the number of eggs spawned; however, significantly more progeny died during early development resulting in no net increase in female fecundity. This finding suggests a higher metabolic cost of reproduction in cyp19a1b ^-/- mutant females. In males, the combined mutation of both cyp19a1 paralogs resulted in significantly lower progeny survival rates, indicating a critical function of cyp19a1 during early larval development. These data establish the specific importance of cyp19a1b for female spawning behavior and the importance of the cyp19a1 paralogs for early larval survival.

Anti-Inflammatory Actions of G-Protein-Coupled Estrogen Receptor 1 (GPER) and Brain-Derived Estrogen Following Cerebral Ischemia in Ovariectomized Rats

Global cerebral ischemia can elicit rapid innate neuroprotective mechanisms that protect against delayed neuronal death. Brain-derived 17β-estradiol (BDE2), an endogenous neuroprotectant, is synthesized from testosterone by the enzyme aromatase (Aro) and is upregulated by brain ischemia and inflammation. Our recent study revealed that G1, a specific G-protein-coupled estrogen receptor 1 (GPER) agonist, exerts anti-inflammatory and anti-apoptotic roles after global cerebral ischemia (GCI). Herein, we aimed to elucidate whether G1 modulates the early inflammatory process and the potential underlying mechanisms in the ovariectomized rat hippocampal CA1 region. G1 was found to markedly reduce pro-inflammatory (iNOS, MHCII, and CD68) and to enhance anti-inflammatory (CD206, Arginase 1, IL1RA, PPARγ, and BDNF) markers after 1 and 3 days of reperfusion after GCI. Intriguingly, the neuroprotection of G1 was blocked by the Aro inhibitor, letrozole. Conversely, the GPER antagonist, G36, inhibited Aro-BDE2 signaling and exacerbated neuronal damage. As a whole, this work demonstrates a novel anti-inflammatory role of GPER, involving a synergistic mediation with BDE2 during the early stage of GCI.

Integrated network-based multiple computational analyses for identification of co-expressed candidate genes associated with neurological manifestations of COVID-19

'Tripartite network' (TN) and 'combined gene network' (CGN) were constructed and their hub-bottleneck and driver nodes (44 genes) were evaluated as 'target genes' (TG) to identify 21 'candidate genes' (CG) and their relationship with neurological manifestations of COVID-19. TN was developed using neurological symptoms of COVID-19 found in literature. Under query genes (TG of TN), co-expressed genes were identified using pair-wise mutual information to genes available in RNA-Seq autopsy data of frontal cortex of COVID-19 victims. CGN was constructed with genes selected from TN and co-expressed in COVID-19. TG and their connecting genes of respective networks underwent functional analyses through findings of their enrichment terms and pair-wise 'semantic similarity scores' (SSS). A new integrated 'weighted harmonic mean score' was formulated assimilating values of SSS and STRING-based 'combined score' of the selected TG-pairs, which provided CG-pairs with properties of CGs as co-expressed and 'indispensable nodes' in CGN. Finally, six pairs sharing seven 'prevalent CGs' (ADAM10, ADAM17, AKT1, CTNNB1, ESR1, PIK3CA, FGFR1) showed linkages with the phenotypes (a) directly under neurodegeneration, neurodevelopmental diseases, tumour/cancer and cellular signalling, and (b) indirectly through other CGs under behavioural/cognitive and motor dysfunctions. The pathophysiology of 'prevalent CGs' has been discussed to interpret neurological phenotypes of COVID-19.

Transcriptional regulation of CYP19A1 expression in chickens: ESR1, ESR2 and NR5A2 form a functional network

Aromatase, encoded by CYP19A1, is responsible for the conversion of androgen to estrogen, which plays a vital role in the development and function of the ovary and functions in many other physiological processes in both sexes. Instead of being expressed in ovarian granulosa cells, as in mammals, CYP19A1 is expressed in chickens in the theca cells of ovarian follicles, and the mechanism of CYP19A1 expression regulation remains unknown. Here, using immunofluorescence and western blotting assay, we first confirmed that CYP19A1 and FOXL2 (Forkheadbox L2) were coexpressed in pre-granulosa cells of female chicken embryonic gonads, while FOXL2 did not affect aromatase expression at embryonic stages. Second, our research showed that CYP19A1, ESR1 (estrogen receptor alpha), ESR2 (estrogen receptor beta) and NR5A2 (liver receptor homologue-1) were coexpressed in the theca cell layers of chicken small yellow follicles. There was cross-talk between CYP19A1 and candidate transcription factors (ESR1, ESR2 and NR5A2), which was identified by generating a reliable theca cell culture model. Using luciferase assays in theca cells and chicken embryonic fibroblast (DF-1) cells, the results suggested that ESR1 and NR5A2 had potential effects on CYP19A1 promoter activity in chickens. Overexpression of ESR1, ESR2 and NR5A2 in chicken embryonic fibroblast (DF-1) cells upregulated the protein expression of CYP19A1, mutually restricted each other and formed a potential regulatory network to coordinate the expression of CYP19A1. To conclude, our results indicated that FOXL2 cannot regulate the expression of CYP19A1 at chicken embryonic stages and after sexual maturity, ESR1, ESR2 and NR5A2 form a functional network to affect the expression of CYP19A1. These results laid a foundation for further research on the transcriptional regulation of chicken aromatase.

Neuron-Derived Estrogen-A Key Neuromodulator in Synaptic Function and Memory

In addition to being a steroid hormone, 17β-estradiol (E₂) is also a neurosteroid produced in neurons in various regions of the brain of many species, including humans. Neuron-derived E₂ (NDE₂) is synthesized from androgen precursors via the action of the biosynthetic enzyme aromatase, which is located at synapses and in presynaptic terminals in neurons in both the male and female brain. In this review, we discuss evidence supporting a key role for NDE₂ as a neuromodulator that regulates synaptic plasticity and memory. Evidence supporting an important neuromodulatory role of NDE₂ in the brain has come from studies using aromatase inhibitors, aromatase overexpression in neurons, global aromatase knockout mice, and the recent development of conditional forebrain neuron-specific knockout mice. Collectively, these studies demonstrate a key role of NDE₂ in the regulation of synapse and spine density, efficacy of excitatory synaptic transmission and long-term potentiation, and regulation of hippocampal-dependent recognition memory, spatial reference memory, and contextual fear memory. NDE₂ is suggested to achieve these effects through estrogen receptor-mediated regulation of rapid kinase signaling and CREB-BDNF signaling pathways, which regulate actin remodeling, as well as transcription, translation, and transport of synaptic proteins critical for synaptic plasticity and function.

Brain-derived estrogen and neural function

Although classically known as an endocrine signal produced by the ovary, 17β-estradiol (E₂) is also a neurosteroid produced in neurons and astrocytes in the brain of many different species. In this review, we provide a comprehensive overview of the localization, regulation, sex differences, and physiological/pathological roles of brain-derived E₂ (BDE₂). Much of what we know regarding the functional roles of BDE₂ has come from studies using specific inhibitors of the E₂ synthesis enzyme, aromatase, as well as the recent development of conditional forebrain neuron-specific and astrocyte-specific aromatase knockout mouse models. The evidence from these studies support a critical role for neuron-derived E₂ (NDE₂) in the regulation of synaptic plasticity, memory, socio-sexual behavior, sexual differentiation, reproduction, injury-induced reactive gliosis, and neuroprotection. Furthermore, we review evidence that astrocyte-derived E₂ (ADE₂) is induced following brain injury/ischemia, and plays a key role in reactive gliosis, neuroprotection, and cognitive preservation. Finally, we conclude by discussing the key controversies and challenges in this area, as well as potential future directions for the field.

Efficacy of a novel orally active SERD AZD9496 against hormone dependent post-menopausal breast cancer depends on inhibition of cellular aromatase activity

Treatment of hormone sensitive breast cancer tumors with endocrine therapy such as antiestrogens or aromatase inhibitors has improved the outcome significantly. Studies including our own have shown that downregulation of ERα with pure antiestrogen fulvestrant in combination with aromatase inhibitors may prolong responsiveness of the tumors to endocrine therapy. Fulvestrant has been studied as second line or first line treatment for post-menopausal hormone receptor positive breast cancers as a single agent or in combination with AIs. Studies have also suggested that further escalation of dose may improve benefit. However, dose escalation of fulvestrant, which is administered via intramuscular injection, is difficult due to its poor solubility. To overcome this shortcoming of an injectable drug, a novel orally active antiestrogen, AZD9496 was developed. In addition to being orally active, AZD9496 is designed as a selective ERα downregulator (SERD). In the current study, we compared the effect of AZD9496 and fulvestrant on the growth of MCF-7Ca (human estrogen receptor positive MCF-7 cells stably transfected with human placental aromatase gene) xenografts grown in ovariectomized athymic nude mice. AZD9496 was also compared to fulvestrant in vitro as a single agent or in combination with anastrozole. Our current study shows that AZD9496 is equally effective as fulvestrant at controlling the growth of hormone sensitive human breast cancer tumors. Similar to fulvestrant, AZD9496 inhibits cellular aromatase activity through ERα mediated signaling. However, unlike fulvestrant, combination of AZD9496 with anastrozole did not produce increased tumor inhibition. Our results show that AZD9496 was significantly better at inhibiting cellular aromatase which contributed to its anticancer activity. Next, we measured the effect of AZD9496 on the mouse uterus. Uterine weight of mice treated with AZD9496 was significantly lower than that for mice treated with androstenedione. This reduction in uterine weight was due to AZD9496 mediated inhibition of aromatase activity and not a direct effect on uterine ERα expression. We also observed that anti-cancer efficacy of AZD9496 depended on its ability to inhibit cellular aromatase. These results suggest that AZD9496 may be a better alternative to fulvestrant due to its selectivity for mammary ER and ability to inhibit aromatase in addition of downregulating ERα that can be obtained upon oral administration. As such, AZD9496 may prove to be a better option than fulvestrant for the treatment of hormone sensitive human breast cancer.

Aromatase (CYP19A1) gene variants, sex steroid levels, and late-life depression

BACKGROUND

Sex differences in psychiatric disorders are common and could involve sex steroids. Aromatase, the product of the CYP19A1 gene, is the key enzyme in the conversion of androgen to estrogen. Whether CYP19A1 variants could be associated with depression differently in men and women has not been examined.

METHODS

This population-based study included 405 men and 602 women aged ≥65 years. A clinical level of depression (DEP) was defined as having a score ≥16 on the Center for Epidemiology Studies Depression scale or a diagnosis of current major depression based on the Mini-International Neuropsychiatric Interview and according to DSM-IV criteria. Seven single-nucleotide polymorphisms (SNPs) spanning the CYP19A1 gene were genotyped and circulating levels of estradiol and testosterone were determined. Multivariable analyses were adjusted for age, body mass index, ischemic pathologies, cognitive impairment, and anxiety.

RESULTS

Five SNPs were associated with DEP in women specifically and this varied according to a history of major depression (p-values .01 to .0005). Three SNPs were associated with an increased risk of late-life DEP in women without a history of major depression, while two SNPs were associated with a decreased DEP risk in women with a history of major depression and were also associated with higher estradiol levels.

CONCLUSIONS

Variants of the CYP19A1 gene appear to be susceptibility factors for late-life depression in a sex-specific manner. The polymorphisms decreasing the risk of recurrent depression in postmenopausal women also influence estradiol levels.

ARP-1 Regulates the Transcriptional Activity of the Aromatase Gene in the Mouse Brain

An important function of aromatase in the brain is conversion of testosterone secreted from the testis into estradiol. Estradiol produced in the brain is thought to be deeply involved in the formation of sexually dimorphic nuclei and sexual behavior as a neurosteroid. We analyzed the brain-specific promoter to elucidate the control mechanisms of brain aromatase expression that may be highly involved in sexual differentiation of the brain. The 202-bp upstream region of the brain-specific exon 1 has three types of cis-acting elements, aro-AI, AII, and B. We isolated ARP-1 as an aro-AII-binding protein by yeast one-hybrid screening from a cDNA library of mouse fetal brains. ARP-1 is a member of the nuclear receptor superfamily and functions as an orphan-type transcription factor. ARP-1 protein synthesized in vitro showed the same binding property to the aro-AII site as nuclear extract from fetal brains. To determine how the promoter is involved in brain-specific transcription of the aromatase gene, we first detected the in vivo occupancy of the aro-AII site by ARP-1 using chromatin immunoprecipitation assays. Diencephalic regions of fetal brains at embryonic day 16 were analyzed, which revealed ARP-1 recruitment to the aro-AII site. To analyze the effects of ARP-1 on transcriptional regulation of the brain-specific aromatase promoter, a luciferase reporter plasmid driven by the brain-specific promoter was transfected into CV-1 cells together with a plasmid expressing ARP-1 protein. These analyses revealed that ARP-1 induced promoter activity in a dose-dependent manner. Furthermore, to determine whether ARP-1 is required for aromatase expression in neurons, ARP-1 knockdown was conducted in neuronal cell primary culture. Knockdown of ARP-1 significantly suppressed the increase in aromatase mRNA observed in cultured neurons. These results indicate that ARP-1 is involved in the transcriptional regulation of the brain-specific promoter of the aromatase gene.

Aromatase/Seladin-1 Interactions in Human Neuronal Cell Culture, the Hippocampus of Healthy Rats and Transgenic Alzheimer’s Disease Mice

Background/Aims: Decreasing levels of aromatase and seladin-1 could be one of the molecular mechanisms of Alzheimer’s disease (AD). Aromatase is an enzyme that catalyzes estrogen biosynthesis from androgen precursors, and seladin-1 is an enzyme that converts desmosterol to cholesterol, which is the precursor of all hormones. Verifying the potential relationship between these proteins and accordingly determining new therapeutic targets constitute the aims of this study. Methods: Changes in protein levels were compared in vitro in aromatase and seladin-1 inhibitor-administered human neuroblastoma (SH-SY5Y) cells in vivo in intracerebroventricular (icv) aromatase or seladin-1 inhibitor-administered rats, as well as in transgenic AD mice in which the genes encoding these proteins were knocked out. Results and Conclusions: In the cell cultures, we observed that seladin-1 protein levels increased after aromatase enzyme inhibition. The hippocampal aromatase protein levels decreased following chronic seladin-1 inhibition in icv inhibitor-administered rats; however, the aromatase levels in the dentate gyrus of seladin-1 knockout (SelKO) AD male mice increased. These findings indicate a partial relationship between these proteins and their roles in AD pathology.

Hormonal and genetic factors interact to control aromatase expression in the developing brain

Brain expression of the enzyme P450-aromatase has been studied extensively. Subsequent to the aromatisation hypothesis having established brain aromatase as a key factor to convert gonadal testosterone to oestradiol, several studies have investigated the regulation of aromatase during the critical period of brain sexual differentiation. We review previous and recent findings concerning regulation of aromatase. The role of gonadal hormones, sex chromosome genes and neurosteroids is analysed in terms of their contribution to aromatase expression, as well as implications for the organisational effect of steroids during development.

Regulation of aromatase expression in the anterior amygdala of the developing mouse brain depends on ERβ and sex chromosome complement

During development sex differences in aromatase expression in limbic regions of mouse brain depend on sex chromosome factors. Genes on the sex chromosomes may affect the hormonal regulation of aromatase expression and this study was undertaken to explore that possibility. Male E15 anterior amygdala neuronal cultures expressed higher levels of aromatase (mRNA and protein) than female cultures. Furthermore, treatment with oestradiol (E2) or dihydrotestosterone (DHT) increased Cyp19a1 expression and aromatase protein levels only in female neuronal cultures. The effect of E2 on aromatase expression was not imitated by oestrogen receptor (ER) α agonist PPT or the GPER agonist G1, but it was fully reproduced by DPN, a specific ligand of ERβ. By contrast, the effect of DHT on aromatase expression was not blocked by the anti-androgen flutamide, but completely abrogated by the ERβ antagonist PHTPP. Experiments using the four core genotype model showed a sex chromosome effect in ERβ expression (XY > XX) and regulation by E2 or DHT (only XX respond) in amygdala neurons. In conclusion, sex chromosome complement governs the hormonal regulation of aromatase expression through activation of ERβ in developing mouse brain.

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.

Control of aromatase in hippocampal neurons

Our knowledge on estradiol-induced modulation of synaptic function in the hippocampus is widely based on results following the application of the steroid hormone to either cell cultures, or after the treatment of gonadectomized animals, thus ignoring local neuronal estrogen synthesis. We and others, however, have shown that hippocampus-derived estradiol also controls synaptic plasticity in the hippocampus. Estradiol synthesis in the hippocampus is regulated by several mechanisms, which are reviewed in this report. The regulation of the activity of aromatase, the final enzyme of estrogen biosynthesis, by Ca(2+) transients, is of particular interest. Aromatase becomes inactivated as soon as it is phosphorylated by Ca(2+)-dependent kinases upon calcium release from internal stores. Accordingly, thapsigargin dephosphorylates aromatase and stimulates estradiol synthesis by depletion of internal Ca(2+) stores. Vice versa, letrozole, an aromatase inhibitor, phosphorylates aromatase and reduces estradiol synthesis. Treatment of the cultures with 17β-estradiol results in phosphorylation of the enzyme and increased aromatase protein expression, which suggests that estradiol synthesis in hippocampal neurons is regulated in an autocrine manner.

Aromatase Expression in the Hippocampus of AD Patients and 5xFAD Mice

Numerous studies show that 17β-estradiol (E2) protects against Alzheimer's disease (AD) induced neurodegeneration. The E2-synthesizing enzyme aromatase is expressed in healthy hippocampi, but although the hippocampus is severely affected in AD, little is known about the expression of hippocampal aromatase in AD. To better understand the role of hippocampal aromatase in AD, we studied its expression in postmortem material from patients with AD and in a mouse model for AD (5xFAD mice). In human hippocampi, aromatase-immunoreactivity was observed in the vast majority of principal neurons and signal quantification revealed higher expression of aromatase protein in AD patients compared to age- and sex-matched controls. The tissue-specific first exons of aromatase I.f, PII, I.3, and I.6 were detected in hippocampi of controls and AD patients by RT-PCR. In contrast, 3-month-old, female 5xFAD mice showed lower expression of aromatase mRNA and protein (measured by qRT-PCR and semiquantitative immunohistochemistry) than WT controls; no such differences were observed in male mice. Our findings stress the importance of hippocampal aromatase expression in neurodegenerative diseases.

Estrogens are neuroprotective factors for hypertensive encephalopathy

Estrogens are neuroprotective factors for brain diseases, including hypertensive encephalopathy. In particular, the hippocampus is highly damaged by high blood pressure, with several hippocampus functions being altered in humans and animal models of hypertension. Working with a genetic model of primary hypertension, the spontaneously hypertensive rat (SHR), we have shown that SHR present decreased dentate gyrus neurogenesis, astrogliosis, low expression of brain derived neurotrophic factor (BDNF), decreased number of neurons in the hilus of the dentate gyrus, increased basal levels of the estrogen-synthesizing enzyme aromatase, and atrophic dendritic arbor with low spine density in the CA1 region compared to normotensive Wistar Kyoto (WKY) ratsl. Changes also occur in the hypothalamus of SHR, with increased expression of the hypertensinogenic peptide arginine vasopressin (AVP) and its V1b receptor. Following chronic estradiol treatment, SHR show decreased blood pressure, enhanced hippocampus neurogenesis, decreased the reactive astrogliosis, increased BDNF mRNA and protein expression in the dentate gyrus, increased neuronal number in the hilus of the dentate gyrus, further increased the hyperexpression of aromatase and replaced spine number with remodeling of the dendritic arbor of the CA1 region. We have detected by qPCR the estradiol receptors ERα and ERβ in hippocampus from both SHR and WKY rats, suggesting direct effects of estradiol on brain cells. We hypothesize that a combination of exogenously given estrogens plus those locally synthesized by estradiol-stimulated aromatase may better alleviate the hippocampal and hypothalamic encephalopathy of SHR. This article is part of a Special Issue entitled "Sex steroids and brain disorders".

Membrane-initiated non-genomic signaling by estrogens in the hypothalamus: cross-talk with glucocorticoids with implications for behavior

The estrogen receptor and glucocorticoid receptor are members of the nuclear receptor superfamily that can signal using both non-genomic and genomic transcriptional modes. Though genomic modes of signaling have been well characterized and several behaviors attributed to this signaling mechanism, the physiological significance of non-genomic modes of signaling has not been well understood. This has partly been due to the controversy regarding the identity of the membrane ER (mER) or membrane GR (mGR) that may mediate rapid, non-genomic signaling and the downstream signaling cascades that may result as a consequence of steroid ligands binding the mER or the mGR. Both estrogens and glucocorticoids exert a number of actions on the hypothalamus, including feedback. This review focuses on the various candidates for the mER or mGR in the hypothalamus and the contribution of non-genomic signaling to classical hypothalamically driven behaviors and changes in neuronal morphology. It also attempts to categorize some of the possible functions of non-genomic signaling at both the cellular level and at the organismal level that are relevant for behavior, including some behaviors that are regulated by both estrogens and glucocorticoids in a potentially synergistic manner. Lastly, it attempts to show that steroid signaling via non-genomic modes may provide the organism with rapid behavioral responses to stimuli.

17α-Oestradiol-induced neuroprotection in the brain of spontaneously hypertensive rats

17β-oestradiol is a powerful neuroprotective factor for the brain abnormalities of spontaneously hypertensive rats (SHR). 17α-Oestradiol, a nonfeminising isomer showing low affinity for oestrogen receptors, is also endowed with neuroprotective effects in vivo and in vitro. We therefore investigated whether treatment with 17α-oestradiol prevented pathological changes of the hippocampus and hypothalamus of SHR. We used 20-week-old male SHR with a blood pressure of approximately 170 mmHg receiving s.c. a single 800 μg pellet of 17α-oestradiol dissolved in cholesterol or vehicle only for 2 weeks Normotensive Wistar-Kyoto (WKY) rats were used as controls. 17α-Oestradiol did not modify blood pressure, serum prolactin, 17β-oestradiol levels or the weight of the testis and pituitary of SHR. In the brain, we analysed steroid effects on hippocampus Ki67+ proliferating cells, doublecortin (DCX) positive neuroblasts, glial fibrillary acidic protein (GFAP)+ astrocyte density, aromatase immunostaining and brain-derived neurotrophic factor (BDNF) mRNA. In the hypothalamus, we determined arginine vasopressin (AVP) mRNA. Treatment of SHR with 17α-oestradiol enhanced the number of Ki67+ in the subgranular zone and DCX+ cells in the inner granule cell layer of the dentate gyrus, increased BDNF mRNA in the CA1 region and gyrus dentatus, decreased GFAP+ astrogliosis in the CA1 subfield, and decreased hypothalamic AVP mRNA. Aromatase expression was unmodified. By contrast to SHR, normotensive WKY rats were unresponsive to 17α-oestradiol. These data indicate a role for 17α-oestradiol as a protective factor for the treatment of hypertensive encephalopathy. Furthermore, 17α-oestradiol is weakly oestrogenic in the periphery and can be used in males.

C-fos down-regulation inhibits testosterone-dependent male sexual behavior and the associated learning

Environmental stimulation results in an increased expression of transcription factors called immediate early genes (IEGs) in specific neuronal populations. In male Japanese quail, copulation with a female increases the expression of the IEGs zenk and c-fos in the medial pre-optic nucleus (POM), a key nucleus controlling male sexual behavior. The functional significance of this increased IEG expression that follows performance of copulatory behavior is unknown. We addressed this question by repeatedly quantifying the performance of appetitive (learned social proximity response) and consummatory (actual copulation) sexual behavior in castrated, testosterone-treated males that received daily intra-cerebroventricular injection of an antisense oligodeoxynucleotide targeting c-fos or control vehicle. Daily antisense injections significantly inhibited the expression of copulatory behavior as well as the acquisition of the learned social proximity response. A strong reduction of the proximity response was still observed in antisense-treated birds that copulated with a female, ruling out the indirect effect of the absence of interactions with females on the learning process. After a 2-day interruption of behavioral testing but not of antisense injections, birds were submitted to a final copulatory test that confirmed the behavioral inhibition in antisense-injected birds. Brains were collected at 90 min after the behavioral testing for quantification of c-fos-immunoreactive cells. A significant reduction of the number of c-fos-positive cells in the POM but not in other brain regions was observed following antisense injection. Taken together, the data suggest that c-fos expression in the POM modulates copulatory behavior and sexual learning in male quail.

LIM-homeodomain transcription factor, Lhx2, is involved in transcriptional control of brain-specific promoter/exon 1f of the mouse aromatase gene

Neurosteroidal oestrogen has been proposed to play important roles in a variety of reproductive behaviours. Aromatase, a key enzyme in oestrogen synthesis, is localised in neural nuclei of specific brain regions and is developmentally regulated, with a transient expression peak at the perinatal period. The brain-specific promoter of the aromatase gene was analysed aiming to determine the transcriptional control mechanisms that could help explain the spatiotemporal expression. We previously reported that a 202-bp sequence, which is upstream from the transcriptional initiation site, is essential for the basal transcriptional activity. The 202-bp upstream region of brain-specific exon 1 comprises at least three types of cis-acting elements: aro-AI (Arom-Aα), aro-AII (Arom-Aβ) and aro-B (Arom-B). To identify the binding proteins for the cis-acting elements, a yeast one-hybrid screen was performed with these cis-element sequences using a mouse foetal cDNA library. Lhx2, a LIM-homeodomain protein, was identified as one of the aro-B binding proteins. The identification was further confirmed using the gel shift assay, which demonstrated binding competition of nuclear proteins to the aro-B element with a typical Lhx2-binding element. In addition, a chromatin immunoprecipitation assay with an anti-Lhx2 antibody demonstrated that Lhx2 bound to the aro-B site in vivo. A reporter assay of the brain-specific promoter demonstrated increased Lhx2-dependent promoter activity. Furthermore, the time-dependent increase in aromatase mRNA in primary cultured foetal neurones was suppressed by an small-interfering RNA-mediated knockdown of Lhx2 expression. These results show that Lhx2 is involved in the transcriptional regulation of aromatase in the rodent brain.

Glucocorticoid-induction of hypothalamic aromatase via its brain-specific promoter

In the brain, a 36-kb distal promoter (I.f) regulates the Cyp19a1 gene that encodes aromatase, the key enzyme for estrogen biosynthesis. Local estrogen production in the brain regulates critical functions such as gonadotropin secretion and sexual behavior. The mechanisms that control brain aromatase production are not well understood. Here we show that the glucocorticoid dexamethasone robustly increases aromatase mRNA and protein by up to 98-fold in mouse hypothalamic cell lines in a dose- and time-dependent fashion. Using deletion mutants of the brain-specific promoter I.f and chromatin immunoprecipitation-PCR, we isolated a distinct region (-500/-200 bp) which becomes enriched in bound glucocorticoid receptor upon dexamethasone stimulation. A glucocorticoid antagonist or siRNA based knockdown of glucocorticoid receptor ablated dexamethasone stimulation of aromatase expression. Our findings demonstrate how glucocorticoids alter aromatase expression in the hypothalamus and might indicate a mechanism whereby glucocorticoid action modifies gonadotropin pulses and the menstrual cycle.

Neuroestrogen, rapid action of estradiol, and GnRH neurons

Estradiol plays a pivotal role in the control of GnRH neuronal function, hence female reproduction. A series of recent studies in our laboratory indicate that rapid excitatory actions of estradiol directly modify GnRH neuronal activity in primate GnRH neurons through GPR30 and STX-sensitive receptors. Similar rapid direct actions of estradiol through estrogen receptor beta are also described in mouse GnRH neurons. In this review, we propose two novel hypotheses as a possible physiological role of estradiol in primates. First, while ovarian estradiol initiates the preovulatory GnRH surge through interneurons expressing estrogen receptor alpha, rapid direct membrane-initiated action of estradiol may play a role in sustaining GnRH surge release for many hours. Second, locally produced neuroestrogens may contribute to pulsatile GnRH release. Either way, estradiol synthesized in interneurons in the hypothalamus may play a significant role in the control of the GnRH surge and/or pulsatility of GnRH release.

Location, location, location: genetic regulation of neural sex differences

Sex differences in many behaviors such as cognition, mood, and motor skills are well-documented in animals and humans and are regulated by many neural circuits. Sexual dimorphisms within cell populations in these circuits play critical roles in the production of these behavioral dichotomies. Here we focus on three proteins that have well described sexual dimorphisms; calbindin-D28k, a calcium binding protein, tyrosine hydroxylase, the rate limiting enzyme involved in dopamine synthesis and vasopressin, a neuropeptide with central and peripheral sites of action. We describe the sex differences in subpopulations of these proteins, with particular emphasis on laboratory mice. Our thrust is to examine genetic bases of sex differences and how the use of genetically modified models has advanced our understanding of this topic. Regional sex differences in the expression of these three proteins are driven by sex chromosome complement, steroid receptors or in some instances both. While studies of sex differences attributable to sex chromosome genes are still few in number it is exciting to note that this variable factors into expression differences for all three of these proteins. Different genetic mechanisms, which elaborate sex differences, may be employed stochastically in different cell populations. Alternately, general patterns involving the timing of differentiation of the sex differences, relative to the "critical period" in hormonal differences between males and female neonates may emerge. In conclusion, future directions in this area should include examination of the importance of location, timing, steroidal receptor/sex chromosome gene synergy and epigenetics in molding neural sex differences.

Differential regulation of the expression of cytochrome P450 aromatase, estrogen and androgen receptor subtypes in the brain-pituitary-ovarian axis of the Japanese eel (Anguilla japonica) reveals steroid dependent and independent mechanisms

This study aimed at investigating the role of sexual steroids in the regulation of the expression of the single aromatase gene and steroid receptor subtypes in the brain-pituitary-ovarian axis of the Japanese eel. Unlike other teleosts, which possess duplicated genes for aromatase, cyp19a1a and cyp19a1b, expressed in the gonads and in the brain, respectively, eel species possess a single cyp19a1. Phylogenetic analysis indicated that eel brain/gonadal cyp19a1 branches at the basis of both teleost gonadal cyp19a1a and brain cyp19a1b clades. Female eels treated with catfish pituitary homogenate (CPH) to induce sexual maturation showed an increase in the expression of cyp19a1 and aromatase enzymatic activity in the brain and in the ovaries. Treatments with sex steroids (estradiol-17β, E(2) or testosterone, T) revealed that the increase in cyp19a1 expression in the brain may result from E(2)-specific induction. In contrast, the increase in cyp19a1 expression in the ovaries of CPH-treated eels is a result of steroid-independent control, probably from a direct effect of gonadotropins contained in the pituitary extract. Analysis of the expression of estrogen and androgen receptor subtypes, esr-α, esr-β, ar-α and ar-β, in eels treated with CPH or sex steroids revealed differential regulations. In CPH-treated eels, the expression of esr-α and ar-α was significantly increased in the brain, while the expression of ar-α and ar-β was increased in the ovaries. No change was observed in esr-β in any organ. Steroid treatments induced an upregulation by E(2) of esr-α, but not esr-β expression, in the brain, pituitary and ovaries, while no autoregulation by T of its own receptors could be observed. These results reveal both steroid-dependent and -independent mechanisms in the regulation of cyp19a1 and steroid receptor subtype expression in the eel.

Molecular bases and phenotypic determinants of aromatase excess syndrome

Aromatase excess syndrome (AEXS) is a rare autosomal dominant disorder characterized by gynecomastia. This condition is caused by overexpression of CYP19A1 encoding aromatase, and three types of cryptic genomic rearrangement around CYP19A1, that is, duplications, deletions, and inversions, have been identified in AEXS. Duplications appear to have caused CYP19A1 overexpression because of an increased number of physiological promoters, whereas deletions and inversions would have induced wide CYP19A1 expression due to the formation of chimeric genes consisting of a noncoding exon(s) of a neighboring gene and CYP19A1 coding exons. Genotype-phenotype analysis implies that phenotypic severity of AEXS is primarily determined by the expression pattern of CYP19A1 and the chimeric genes and by the structural property of the fused exons with a promoter function (i.e., the presence or the absence of a natural translation start codon). These results provide novel information about molecular mechanisms of human genetic disorders and biological function of estrogens.

Aromatase promoter I.f is regulated by progesterone receptor in mouse hypothalamic neuronal cell lines

Aromatase catalyzes the conversion of C(19) steroids to estrogens. Aromatase and progesterone, both of which function at different steps of steroidogenesis, are crucial for the sexually dimorphic development of the fetal brain and the regulation of gonadotropin secretion and sexual interest in adults. The aromatase gene (Cyp19a1) is selectively expressed in distinct neurons of the mouse hypothalamus through a distal brain-specific promoter, I.f, located ∼40 kb upstream of the coding region. However, the regulation of aromatase expression in the brain is not well understood. In this study, we investigated a short feedback effect of progesterone analogues on aromatase mRNA expression and enzyme activity in estrogen receptor α (Esr1)-positive or -negative mouse embryonic hypothalamic neuronal cell lines that express aromatase via promoter I.f. In a hypothalamic neuronal cell line that highly expresses aromatase, progesterone receptor (Pgr), and Esr1, a progesterone agonist, R5020, inhibited aromatase mRNA level and enzyme activity. The inhibitory effect of R5020 was reversed by its antagonist, RU486. Deletion mutants of promoter I.f suggested that inhibition of aromatase expression by progesterone is conferred by the nt -1000/-500 region, and R5020 enhanced binding of Pgr to the nt -800/-600 region of promoter I.f. Small interfering RNA knockdown of Pgr eliminated progesterone-dependent inhibition of aromatase mRNA and enzyme activity. Taken together, progesterone enhances recruitment of Pgr to specific regions of the promoter I.f of Cyp19a1 and regulates aromatase expression in hypothalamic neurons.

Perimenopausal regulation of steroidogenesis in the nonhuman primate

Human aging is characterized by a marked decrease in circulating levels of dehydroepiandrosterone (DHEA) and DHEA-sulfate (DHEAS), hormonal changes associated with cognitive decline. Despite beneficial effects of DHEA supplementation in rodents, studies in elderly humans have generally failed to show cognitive improvement after treatment. In the present study we evaluate the effects of age and estradiol supplementation on expression of genes involved in the de novo synthesis of DHEA and its conversion to estradiol in the rhesus macaque hippocampus. Using reverse transcription polymerase chain reaction (RT-PCR) we demonstrate the expression of genes associated with this synthesis in several areas of the rhesus brain. Furthermore, real-time PCR reveals an age-related attenuation of hippocampal expression level of the genes CYP17A1, STS, and 3BHSD1/2. Additionally, short-term administration of estradiol is associated with decreased expression of CYP17A1, STS, SULT2B1, and AROMATASE, consistent with a downregulation not only of estrogen synthesis from circulating DHEA, but also of de novo DHEA synthesis within the hippocampus. These findings suggest a decline in neurosteroidogenesis may account for the inefficacy of DHEA supplementation in elderly humans, and that central steroidogenesis may be a function of circulating hormones and menopausal status.

Protective effect of estrogens on the brain of rats with essential and endocrine hypertension

Estrogen neuroprotection has been shown in pathological conditions damaging the hippocampus, such as trauma, aging, neurodegeneration, excitotoxicity, oxidative stress, hypoglycemia, amyloid-β peptide exposure and ischemia. Hypertensive encephalopathy also targets the hippocampus; therefore, hypertension seems an appropriate circumstance to evaluate steroid neuroprotection. Two experimental models of hypertension, spontaneously hypertensive rats (SHR) and deoxycorticosterone (DOCA)-salt hypertensive rats, develop hippocampal abnormalities, which include decreased neurogenesis in the dentate gyrus, astrogliosis, low expression of brain-derived neurotrophic factor (BDNF) and decreased number of neurons in the hilar region, with respect of their normotensive strains Wistar Kyoto (WKY) and Sprague-Dawley rats. After estradiol was given for 2 weeks to SHR and DOCA-treated rats, both hypertensive models normalized their faulty hippocampal parameters. Thus, estradiol treatment positively modulated neurogenesis in the dentate gyrus of the hippocampus, according to bromodeoxyuridine incorporation and doublecortin immunocytochemistry, decreased reactive astrogliosis, increased BDNF mRNA and protein expression in the dentate gyrus and increased neuronal number in the hilar region of the dentate gyrus. A role of local estrogen biosynthesis is suggested in SHR, because basal aromatase mRNA in the hippocampus and immunoreactive aromatase protein in cell processes of the dentate gyrus were highly expressed in these rats. Estradiol further stimulated aromatase-related parameters in SHR but not in WKY. These observations strongly support that a combination of exogenous estrogens to those locally synthesized might better alleviate hypertensive encephalopathy. These studies broaden estrogen neuroprotective functions to the hippocampus of hypertensive rat models.