Estrogen actions in the brain

Early postnatal genistein administration permanently affects nitrergic and vasopressinergic systems in a sex-specific way

Genistein (GEN) is a natural xenoestrogen (isoflavonoid) that may interfere with the development of estrogen-sensitive neural circuits. Due to the large and increasing use of soy-based formulas for babies (characterized by a high content of GEN), there are some concerns that this could result in an impairment of some estrogen-sensitive neural circuits and behaviors. In a previous study, we demonstrated that its oral administration to female mice during late pregnancy and early lactation induced a significant decrease of nitric oxide synthase-positive cells in the amygdala of their male offspring. In the present study, we have used a different experimental protocol mimicking, in mice, the direct precocious exposure to GEN. Mice pups of both sexes were fed either with oil, estradiol or GEN from birth to postnatal day 8. Nitric oxide synthase and vasopressin neural systems were analyzed in adult mice. Interestingly, we observed that GEN effect was time specific (when compared to our previous study), sex specific, and not always comparable to the effects of estradiol. This last observation suggests that GEN may act through different intracellular pathways. Present results indicate that the effect of natural xenoestrogens on the development of the brain may be highly variable: a plethora of neuronal circuits may be affected depending on sex, time of exposure, intracellular pathway involved, and target cells. This raises concern on the possible long-term effects of the use of soy-based formulas for babies, which may be currently underestimated.

Nudging oligodendrocyte intrinsic signaling to remyelinate and repair: Estrogen receptor ligand effects

Demyelination in multiple sclerosis (MS) leads to significant, progressive axonal and neuronal degeneration. Currently existing immunosuppressive and immunomodulatory therapies alleviate MS symptoms and slow, but fail to prevent or reverse, disease progression. Restoration of damaged myelin sheath by replenishment of mature oligodendrocytes (OLs) should not only restore saltatory axon conduction, but also provide a major boost to axon survival. Our previous work has shown that therapeutic treatment with the modestly selective generic estrogen receptor (ER) β agonist diarylpropionitrile (DPN) confers functional neuroprotection in a chronic experimental autoimmune encephalomyelitis (EAE) mouse model of MS by stimulating endogenous remyelination. Recently, we found that the more potent, selective ERβ agonist indazole-chloride (Ind-Cl) improves clinical disease and motor performance. Importantly, electrophysiological measures revealed improved corpus callosal conduction and reduced axon refractoriness. This Ind-Cl treatment-induced functional remyelination was attributable to increased OL progenitor cell (OPC) and mature OL numbers. At the intracellular signaling level, transition of early to late OPCs requires ERK1/2 signaling, and transition of immature to mature OLs requires mTOR signaling; thus, the PI3K/Akt/mTOR pathway plays a major role in the late stages of OL differentiation and myelination. Indeed, therapeutic treatment of EAE mice with various ERβ agonists results in increased brain-derived neurotrophic factor (BDNF) and phosphorylated (p) Akt and p-mTOR levels. It is notable that while DPN's neuroprotective effects occur in the presence of peripheral and central inflammation, Ind-Cl is directly neuroprotective, as demonstrated by remyelination effects in the cuprizone-induced demyelination model, as well as immunomodulatory. Elucidating the mechanisms by which ER agonists and other directly remyelinating agents modulate endogenous OPC and OL regulatory signaling is critical to the development of effective remyelinating drugs. The discovery of signaling targets to induce functional remyelination will valuably contribute to the treatment of demyelinating neurological diseases, including MS, stroke, and traumatic brain and spinal cord injury.

Transcriptional interaction of an estrogen receptor splice variant and ErbB4 suggests convergence in gene susceptibility pathways in schizophrenia

Mounting evidence from clinical and basic research suggests that estrogen signaling may be altered in the brains of people with schizophrenia. Previously, we found that DNA sequence variation in the estrogen receptor (ER) alpha gene, lower ERalpha mRNA levels, and/or blunted ERalpha signaling is associated with schizophrenia. In this study, we asked whether the naturally occurring truncated ERalpha isoform, Delta7, which acts as a dominant negative, can attenuate gene expression induced by the wild-type (WT) receptor in an estrogen-dependent manner in neuronal (SHSY5Y) and non-neuronal (CHOK1 and HeLa) cells. In addition, we determined the extent to which ERalpha interacts with NRG1-ErbB4, a leading schizophrenia susceptibility pathway. Reductions in the transcriptionally active form of ErbB4 comprising the intracytoplasmic domain (ErbB4-ICD) have been found in schizophrenia, and we hypothesized that ERalpha and ErbB4 may converge to control gene expression. In the present study, we show that truncated Delta7-ERalpha attenuates WT-ERalpha-driven gene expression across a wide range of estrogen concentrations in cells that express functional ERalpha at base line or upon co-transfection of full-length ERalpha. Furthermore, we find that ErbB4-ICD can potentiate the transcriptional activity of WT-ERalpha at EREs in two cell lines and that this potentiation effect is abolished by the presence of Delta7-ERalpha. Immunofluorescence microscopy revealed nuclear co-localization of WT-ERalpha, Delta7-ERalpha, and ErbB4-ICD, whereas immunoprecipitation assays showed direct interaction. Our findings demonstrate convergence between ERalpha and ErbB4-ICD in the transcriptional control of ERalpha-target gene expression and suggest that this may represent a convergent pathway that may be disrupted in schizophrenia.

Estradiol-17beta-induced human neural progenitor cell proliferation is mediated by an estrogen receptor beta-phosphorylated extracellularly regulated kinase pathway

Estradiol-17beta (E(2)) induces rodent hippocampal neural progenitor cell (NPC) proliferation in vitro, in vivo, and after brain injury. The purpose of the present investigation was to determine whether E(2)-induced proliferation observed in rodent model systems generalized to cells of human neural origin and the signaling pathway by which E(2) promotes mitosis of human NPCs (hNPCs). Results of these analyses indicate that E(2) induced a significant increase in hNPC proliferation in a time- and dose-dependent manner. E(2)-induced hNPC DNA replication was paralleled by elevated cell cycle protein expression and centrosome amplification, which was associated with augmentation of total cell number. To determine whether estrogen receptor (ER) and which ER subtype were required for E(2)-induced hNPC proliferation, ER expression was first determined by real-time RT-PCR, followed by Western blot analysis, and subsequently verified pharmacologically using ERalpha or beta-selective ligands. Results of these analyses indicated that ERbeta expression was predominant relative to ERalpha, which was barely detectable in hNPCs. Activation of ERbeta by the ERbeta-selective ligand, diarylpropionitrile, led to an increase in phosphorylated extracellular signal-regulated kinase, and subsequent centrosome amplification and hNPC proliferation, which were blocked by the MEKK antagonist, UO126, but not its inactive analog, UO124. These findings, for the first time, demonstrate the molecular cascade and related cell biology events involved in E(2)-induced hNPC proliferation in vitro. Therapeutic implications of these findings relevant to hormone therapy and prevention of neurodegenerative disease are discussed.

Structural and biochemical characterization of human orphan DHRS10 reveals a novel cytosolic enzyme with steroid dehydrogenase activity

To this day, a significant proportion of the human genome remains devoid of functional characterization. In this study, we present evidence that the previously functionally uncharacterized product of the human DHRS10 gene is endowed with 17beta-HSD (17beta-hydroxysteroid dehydrogenase) activity. 17beta-HSD enzymes are primarily involved in the metabolism of steroids at the C-17 position and also of other substrates such as fatty acids, prostaglandins and xenobiotics. In vitro, DHRS10 converts NAD+ into NADH in the presence of oestradiol, testosterone and 5-androstene-3beta,17beta-diol. Furthermore, the product of oestradiol oxidation, oestrone, was identified in intact cells transfected with a construct plasmid encoding the DHRS10 protein. In situ fluorescence hybridization studies have revealed the cytoplasmic localization of DHRS10. Along with tissue expression data, this suggests a role for DHRS10 in the local inactivation of steroids in the central nervous system and placenta. The crystal structure of the DHRS10 apoenzyme exhibits secondary structure of the SDR (short-chain dehydrogenase/reductase) family: a Rossmann-fold with variable loops surrounding the active site. It also reveals a broad and deep active site cleft into which NAD+ and oestradiol can be docked in a catalytically competent orientation.

Reduced urocortin 1 immunoreactivity in the non-preganglionic Edinger-Westphal nucleus during late pregnancy in rats

Pregnancy is accompanied by an array of adaptive changes that play an important role in pre- and postnatal events. In rats, urocortin 1, a corticotropin-releasing factor-like peptide, is expressed mainly in the non-preganglionic Edinger-Westphal nucleus. We investigated the number of neurons immunoreactive for urocortin 1 at three different levels of the Edinger-Westphal nucleus in female rats by immunohistochemistry. The number of urocortin 1 immunoreactive cells was found to be decreased in pregnant rats compared to virgin rats. These results indicate that the hormonal status of the female rat affects urocortin 1 immunoreactive neurons in the non-preganglionic Edinger-Westphal nucleus and its signaling to target brain areas.

Estrogen receptor beta expression in the embryonic brain regulates development of calretinin-immunoreactive GABAergic interneurons

Our previous studies with estrogen receptor beta knockout (ERbeta(-/-)) mice demonstrated that ERbeta is necessary for embryonic development of the brain as early as embryonic day 14.5 (E14.5) and is involved in neuronal migration. Such early effects of ER were unexpected because estradiol synthesis and action in the brain occur at E18.5. In the present study, we examined the distribution of ERbeta in the developing brain and identified a population of ERbeta-regulated interneurons. ERbeta appears in the brain at E12.5, mainly localized in the wall of the midbrain, neuromere, hypothalamus, thalamus, and basal plate of pons. At E15.5 and E16.5, ERbeta expression increased in the hypothalamus, thalamus, and midbrain and appeared in the limbic forebrain. At E18.5, ERbeta expression was strongly expressed throughout the brain, including the cerebellum and striatum, whereas there were very few positive cells in the ventricular region. In the paraventricular thalamic nucleus and parafascicular nucleus, most of the calretinin-immunopositive interneurons expressed ERbeta. In ERbeta(-/-) mice, calretinin expression was markedly lower than in WT mice in the hippocampus, thalamus, and amygdala both at E16.5 and at E18.5. Epidermal growth factor receptor expression was lower in the cortex of ERbeta(-/-) than in WT mice at E15.5 and, unlike WT mice, was absent from the superficial marginal zone. These findings suggest that ERbeta in the embryonic brain is necessary for the development of calretinin-immunoreactive GABAergic interneurons and for neuronal migration in the cortex through modulating epidermal growth factor receptor expression at middle and later embryonic stages.