Visualisation and characterisation of oestrogen receptor α-positive neurons expressing green fluorescent protein under the control of the oestrogen receptor α promoter

Functions of habenula in reproduction and socio-reproductive behaviours

Habenula is an evolutionarily conserved structure in the brain of vertebrates. Recent reports have drawn attention to the habenula as a processing centre for emotional decision-making and its role in psychiatric disorders. Emotional decision-making process is also known to be closely associated with reproductive conditions. The habenula receives innervations from reproductive centres within the brain and signals from key reproductive neuroendocrine regulators such as gonadal sex steroids, gonadotropin-releasing hormone (GnRH), and kisspeptin. In this review, based on morphological, biochemical, physiological, and pharmacological evidence we discuss an emerging role of the habenula in reproduction. Further, we discuss the modulatory role of reproductive endocrine factors in the habenula and their association with socio-reproductive behaviours such as mating, anxiety and aggression.

Estrogen receptor alpha in the brain mediates tamoxifen-induced changes in physiology in mice

Adjuvant tamoxifen therapy improves survival in breast cancer patients. Unfortunately, long-term treatment comes with side effects that impact health and quality of life, including hot flashes, changes in bone density, and fatigue. Partly due to a lack of proven animal models, the tissues and cells that mediate these negative side effects are unclear. Here, we show that mice undergoing tamoxifen treatment experience changes in temperature, bone, and movement. Single-cell RNA sequencing reveals that tamoxifen treatment induces widespread gene expression changes in the hypothalamus and preoptic area (hypothalamus-POA). These expression changes are dependent on estrogen receptor alpha (ERα), as conditional knockout of ERα in the hypothalamus-POA ablates or reverses tamoxifen-induced gene expression. Accordingly, ERα-deficient mice do not exhibit tamoxifen-induced changes in temperature, bone, or movement. These findings provide mechanistic insight into the effects of tamoxifen on the hypothalamus-POA and indicate that ERα mediates several physiological effects of tamoxifen treatment in mice.

Effects of puerarin on estrogen-regulated gene expression in gonadotropin-releasing hormone pulse generator of ovariectomized rats

Effects of puerarin on the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator function is investigated, for the first time, in ovariectomized rats at the level of mRNA expression of estrogen-responsive genes, e.g., estrogen receptor (ER), GnRH and its receptor (GnRHR). Rats were treated orally for 90 days either with a soy-free diet containing two different doses of puerarin (low dose of 600 mg/kg and high dose of 3000 mg/kg) or estradiol benzoate (E2B) at either low dose (4.3 mg/kg) or high dose (17.3 mg/kg). Levels of mRNA expression in the medial preoptic area/anterior hypothalamus (MPOA/AH), mediobasal hypothalamus/median eminence (MBH/ME) and adenohypophysis were measured by quantitative TaqMan® real-time RT-PCR. Plasma levels of luteinizing hormone (LH) and prolactin (PRL) were measured by radioimmunoassay. In the MPOA/AH, both puerarin and E2B decreased ERα mRNA levels without any significant changes in ERβ and GnRH mRNA levels. Both puerarin and E2B did not significantly alter the expression levels of ERα, ERβ and GnRHR in the MBH/ME. E2B exerted significant effects on the down-regulation of adenohypophyseal GnRHR mRNA transcripts and serum LH levels. Puerarin did not cause significant changes in pituitary GnRHR mRNA transcripts and serum LH and PRL levels. This is the first study to demonstrate that in ovariectomized rat models of ovarian hormone deprivation, puerarin acted as a weak estrogen-active compound in the hypothalamic GnRH pulse generator through the downregulation of MPOA/AH ERα mRNA expression.

Immunohistochemical profiling of estrogen-related receptor gamma in rat brain and colocalization with estrogen receptor alpha in the preoptic area

Estrogen-related receptor (ERR) is a member of the nuclear receptor superfamily that has strong homology with estrogen receptor (ER) α. Despite the lack of endogenous ligands, ERR serves as transcription factors through their constitutively active structure with or without interaction with ERα. Among the three subtypes of ERR (α, β, and γ), ERRγ is highly expressed in brain, but the distribution of ERRγ is poorly characterized. Therefore, we investigated ERRγ immunoreactivity throughout the rostro-caudal axis in rat brain. Immunohistochemistry revealed localization of ERRγ protein in the cell nucleus, and a ubiquitous distribution of ERRγ in brain regions including the olfactory bulb, cerebrum, brain stem, and cerebellum. Selective intense immunoreactivity was observed in the reticular thalamic nucleus, zona incerta, circular nucleus, interpeduncular nucleus, pontine nucleus, and parasolitary nucleus. Most ERRγ-immunoreactive (ir) regions were also positive for ERα and/or ERβ, which suggests that ERRγ is involved in modulation of estrogen signaling in adult rat brain. Double immunofluorescence demonstrated colocalization of ERRγ with ERα within the anteroventral periventricular nucleus of the preoptic area (AVPV) and medial preoptic nucleus (MPO), which are major target sites for estrogen action. The results of this study suggest that ERRγ function in the brain is affected by estrogens through an interaction with ERα. The findings also provide basic information on brain region-specific ERRγ function.

A Sexually Dimorphic Area of the Dorsal Hypothalamus in Mice and Common Marmosets

We found a novel sexually dimorphic area (SDA) in the dorsal hypothalamus (DH) of mice. The SDA-DH was sandwiched between 2 known male-biased sexually dimorphic nuclei, the principal nucleus of the bed nucleus of the stria terminalis and the calbindin-sexually dimorphic nucleus, and exhibited a female-biased sex difference in neuronal cell density. The density of neurons in the SDA-DH was increased in male mice by orchidectomy on the day of birth and decreased in female mice by treatment with testosterone, dihydrotestosterone, or estradiol within 5 days after birth. These findings indicate that the SDA-DH is defeminized under the influence of testicular testosterone, which acts via both directly by binding to the androgen receptor, and indirectly by binding to the estrogen receptor after aromatization. We measured the activity of SDA-DH neurons with c-Fos, a neuronal activity marker, in female mice during maternal and sexual behaviors. The number of c-Fos-expressing neurons in the SDA-DH of female mice was negatively correlated with maternal behavior performance. However, the number of c-Fos-expressing neurons did not change during female sexual behavior. These findings suggest that the SDA-DH contains a neuronal cell population, the activity of which decreases in females exhibiting higher performance of maternal behavior, but it may contribute less to female sexual behavior. Additionally, we examined the brain of common marmosets and found an area that appears to be homologous with the mouse SDA-DH. The sexually dimorphic structure identified in this study is not specific to mice and may be found in other species.

Visualizing estrogen receptor-α-expressing neurons using a new ERα-ZsGreen reporter mouse line

BACKGROUND

A variety of biological functions of estrogens, including regulation of energy metabolism, are mediated by neurons expressing estrogen receptor-α (ERα) in the brain. However, complex intracellular processes in these ERα-expressing neurons are difficult to unravel, due to the lack of strategy to visualize ERα-expressing neurons, especially in unfixed brain tissues.

RESULTS AND CONCLUSIONS

Here we generated a novel ERα-ZsGreen reporter mouse line in which expression of a green fluorescent reporter protein, ZsGreen, is driven by a 241kb ERα gene promoter. We validated that ZsGreen is highly colocalized with endogenous ERα in the brain. Native ZsGreen signals were visualized in unfixed brain tissue, and were used to assist single cell collection and electrophysiological recordings. Finally, we demonstrated that this ERα-ZsGreen mouse allele can be used in combination with other genetic reporter alleles to allow experiments in highly selective neural populations.

Effects of postnatal estrogen manipulations on juvenile alloparental behavior

Sex- and species-specific patterns of estrogen receptor (ER)-α expression are established early in development, which may contribute to sexual differentiation of behavior and determine male social organization. The current study investigated the effects of ERα and ERβ activation during the second postnatal week on subsequent alloparental behavior and ERα expression in juvenile prairie voles. Male and female pups were treated daily with 17β-estradiol (E2, ERα/ERβ agonist), PPT (selective ERα agonist), DPN (selective ERβ agonist), or the oil vehicle on postnatal days (PD) 8-14. Alloparental behavior and ERα expression were examined at PD21. PPT treatment inhibited prosocial motivation in males and increased pup-directed aggression in both sexes. E2 and DPN had no apparent effect on behavior in either sex. PPT-treated males had increased ERα expression in the medial preoptic area (MPN), medial amygdala (MEApd) and bed nucleus of the stria terminalis (BSTpr). DPN treatment also increased ERα expression in males, but only in the BSTpr. Female ERα expression was unaffected by treatment. These results support the hypothesis that ERα activation in early life is associated with less prosocial patterns of central ERα expression and alloparental behavior in males. The lack of an effect of E2 on behavior suggests that ERβ may antagonize the effects of ERα on alloparental behavior. The results in DPN-treated males suggest that ERα in the MEApd, and not the BSTpr, may be a primary determinant of alloparental behavior in males.

Progress in the molecular understanding of central regulation of body weight by estrogens

OBJECTIVE

Estrogens can act in the brain to prevent body weight gain. Tremendous research efforts have been focused on estrogen physiology in the brain in the context of body weight control; estrogen receptors and the related signals have been attractive targets for development of new obesity therapies. The objective is to review recent findings on these aspects.

METHODS

Recent studies that used conventional and conditional knockout mouse strains to delineate the cellular and molecular mechanisms for the beneficial effects of estrogens on body weight balance are reviewed. Emerging genetic tools that could further benefit the field of estrogen research and a newly developed estrogen-based regimen that produces body weight-lowering benefits also are discussed.

RESULTS

The body weight-lowering effects of estrogens are mediated by multiple forms of estrogen receptors in different brain regions through distinct but coordinated mechanisms. Both rapid signals and "classic" nuclear receptor actions of estrogen receptors appear to contribute to estrogenic regulation of body weight.

CONCLUSIONS

Estrogen receptors and associated signal networks are potential targets for obesity treatment, and further investigations are warranted.

Estrogen receptors regulate innate immune cells and signaling pathways

Humans show strong sex differences in immunity to infection and autoimmunity, suggesting sex hormones modulate immune responses. Indeed, receptors for estrogens (ER) regulate cells and pathways in the innate and adaptive immune system, as well as immune cell development. ERs are ligand-dependent transcription factors that mediate long-range chromatin interactions and form complexes at gene regulatory elements, thus promoting epigenetic changes and transcription. ERs also participate in membrane-initiated steroid signaling to generate rapid responses. Estradiol and ER activity show profound dose- and context-dependent effects on innate immune signaling pathways and myeloid cell development. While estradiol most often promotes the production of type I interferon, innate pathways leading to pro-inflammatory cytokine production may be enhanced or dampened by ER activity. Regulation of innate immune cells and signaling by ERs may contribute to the reported sex differences in innate immune pathways. Here we review the recent literature and highlight several molecular mechanisms by which ERs regulate the development or functional responses of innate immune cells.