Rapid estrogen signaling in the brain

Functional interaction of DYX1C1 with estrogen receptors suggests involvement of hormonal pathways in dyslexia

Dyslexia, or specific reading disability, is the unexpected failure in learning to read and write when intelligence and senses are normal. One of the susceptibility genes, DYX1C1, has been implicated in neuronal migration, but little is known about its interactions and functions. As DYX1C1 was suggested to interact with the U-box protein CHIP (carboxy terminus of Hsc70-interacting protein), which also participates in the degradation of estrogen receptors alpha (ERalpha) and beta (ERbeta), we hypothesized that the effects of DYX1C1 might be at least in part mediated through the regulation of ERs. ERs have shown to be important in brain development and cognitive functions. Indeed, we show that DYX1C1 interacts with both ERs in the presence of 17beta-estradiol, as determined by co-localization, co-immunoprecipitation and proximity ligation assays. Protein levels of endogenous ERalpha or exogenous ERbeta were reduced upon over-expression of DYX1C1, resulting in decreased transcriptional responses to 17beta-estradiol. Furthermore, we detected in vivo complexes of DYX1C1 with ERalpha or ERbeta at endogenous levels along neurites of primary rat hippocampal neurons. Taken together, our data suggest that DYX1C1 is involved in the regulation of ERalpha and ERbeta, and may thus affect the brain development and regulate cognitive functions. These findings provide novel insights into the function of DYX1C1 and link neuronal migration and developmental dyslexia to the estrogen-signaling effects in the brain.

17beta-Estradiol-induced enhancement of estrogen receptor biosynthesis via MAPK pathway in mouse skeletal muscle myoblasts

The skeletal muscle is one of the important target tissues for the actions of estrogen via both nuclear and extranuclear (non-genomic) pathways. However, there is a paucity of information about the receptor (ER) involved. The aim of this study was thus to explore the ER expression in skeletal muscle, and the influence of estrogen on it, by using C2C12 myoblasts derived from mouse skeletal muscle. Significant expression of a approximately 66-kD protein immunoreactive to ER type alpha (ERalpha) monoclonal antibody, which was comparable to that in ovary, was detected in the whole-cell (total) and nucleus-free (nonnuclear) fractions of C2C12 myoblasts. The expression level of these ER proteins increased in several hours with treatment with 17beta-estradiol (E2), which was preceded by the elevation of the ER mRNA level. This increase appeared to reflect the acceleration of de novo synthesis of ER protein, as proved by the (35)S-methionine immunoprecipitation method. A similar extent of fast increase in ER expression was also induced by a membrane-impermeable, BSA-conjugated estradiol (E2-BSA). Unexpectedly, the E2-induced increases in total and nonnuclear ER were further enhanced by the classic ER antagonists tamoxifen and ICI182,780 in a wide concentration range, implying some structural difference of the involved ER from the classical one. Treatment with the ERK1/2 inhibitor, PD98059 (10 microM), or the p38 MAPK-specific inhibitor, SB203580 (10 microM), greatly inhibited the E2-induced ER increase, while the protein kinase C (PKC) activator TPA (1 microM) enhanced it. These results collectively suggest that C2C12 skeletal myoblasts express a high level of ER, a considerable part of which is extranuclear. Further, the expression of ER in these cells may be significantly upregulated by estrogen itself via increased biosynthesis linked to membrane-bound ER and downstream MAPK-mediated signaling pathways.

17beta-estradiol-mediated neuroprotection and ERK activation require a pertussis toxin-sensitive mechanism involving GRK2 and beta-arrestin-1

17-beta-Estradiol (E2) is a steroid hormone involved in numerous bodily functions, including several brain functions. In particular, E2 is neuroprotective against excitotoxicity and other forms of brain injuries, a property that requires the extracellular signal-regulated kinase (ERK) pathway and possibly that of other signaling molecules. The mechanism and identity of the receptor(s) involved remain unclear, although it has been suggested that E2 receptor alpha (ERalpha) and G proteins are involved. We, therefore, investigated whether E2-mediated neuroprotection and ERK activation were linked to pertussis toxin (PTX)-sensitive G-protein-coupled effector systems. Biochemical and image analysis of organotypic hippocampal slices and cortical neuronal cultures showed that E2-mediated neuroprotection as well as E2-induced ERK activation were sensitive to PTX. The sensitivity to PTX suggested a possible role of G-protein- and beta-arrestin-mediated mechanisms. Western immunoblots from E2-treated cortical neuronal cultures revealed an increase in phosphorylation of both G-protein-coupled receptor-kinase 2 and beta-arrestin-1, a G-protein-coupled receptor adaptor protein. Transfection of neurons with beta-arrestin-1 small interfering RNA prevented E2-induced ERK activation. Coimmunoprecipitation experiments indicated that E2 increased the recruitment of beta-arrestin-1 and c-Src to ERalpha. These findings suggested that ERalpha is regulated by a mechanism associated with receptor desensitization and downregulation. In support of this idea, we found that E2 treatment of cortical synaptoneurosomes resulted in internalization of ERalpha, whereas treatment of cortical neurons with the ER agonists E-6-BSA-FITC [beta-estradiol-6-(O-carboxymethyl)oxime-bovine serum albumin conjugated with fluorescein isothiocyanate] and E-6-biotin [1,3,5(10)-estratrien-3,17beta-diol-6-one-6-carboxymethloxime-NH-propyl-biotin] resulted in agonist internalization. These results demonstrate that E2-mediated neuroprotection and ERK activation involve ERalpha activation of G-protein- and beta-arrestin-mediated mechanisms.

Estrogen and tamoxifen protect against Mn-induced toxicity in rat cortical primary cultures of neurons and astrocytes

Chronic exposure to manganese (Mn) leads to a neurological disorder, manganism, which shares multiple common features with idiopathic Parkinson disease (IPD). 17beta-Estradiol (E2) and some selective estrogen receptor modulators, including tamoxifen (TX), afford neuroprotection in various experimental models of neurodegeneration. However, the neuroprotective effects and mechanisms of E2/TX in Mn-induced toxicity have yet to be documented. Herein, we studied the ability of E2/TX to protect rat cortical primary neuronal and astroglial cultures from Mn-induced toxicity. Cell viability, Western blot, and reactive oxygen species (ROS) generation were assessed. Results established that both E2 (10nM) and TX (1 microM) attenuated Mn-induced toxicity. The protective effects of E2/TX were more pronounced in astrocytes versus neurons. The E2-mediated attenuation of Mn-induced ROS generation in astrocytes at 6-h treatment (where no cell death was detected) was mediated by a classical estrogen receptor (ER) pathway and the TX-mediated effect on Mn-induced ROS generation was not mediated via classical ER-dependent mechanisms and likely by its antioxidant properties. The phosphatidylinositol-3 kinase (PI3K)/Akt signaling pathway was involved in both E2- and TX-induced attenuation of Mn-induced ROS formation (6 h) in astrocytes. Treatments with Mn for a longer duration (24 h) led to significant cell death, and the protective effects of E2 and TX were (1) not mediated by a classical ER pathway and (2) associated with activation of both mitogen-activated protein kinase/extracellular signal-regulated kinase and PI3K/Akt signaling pathways. Taken together, the results suggest that both E2 and TX offer effective therapeutic means for neuroprotection against Mn-induced toxicity.

Calmodulin effects on steroids-regulated plasma membrane calcium pump activity

It is now generally accepted that non-genomic steroids action precedes their genomic effects by modulation of intracellular signaling pathways within seconds after application. Ca(2+) is a very potent and ubiquitous ion in all cells, and its concentration is precisely regulated. The most sensitive on Ca(2+) increase is ATP-consuming plasma membrane calcium pump (PMCA). The enzyme is coded by four genes, but isoforms diversity was detected in excitable and non-excitable cells. It is the only ion pump stimulated directly by calmodulin (CaM). We examined the role of PMCA isoforms composition and CaM effect in regulation of Ca(2+) uptake by estradiol, dehydroepiandrosterone (DHEA), pregnenolone (PREG), and their sulfates in a concentration range from 10(-9) to 10(-6) M, using the membranes from rat cortical synaptosomes, differentiated PC12 cells, and human erythrocytes. In excitable membranes with full set of PMCAs steroids apparently increased Ca(2+) uptake, although to a variable extent. In most of the cases, CaM decreased transport by 30-40% below controls. Erythrocyte PMCA was regulated by the steroids somewhat differently than excitable cells. CaM strongly increased the potency for Ca(2+) extrusion in membranes incubated with 17-beta-estradiol and PREG. Our results indicated that steroids may sufficiently control cytoplasmic calcium concentration within physiological and therapeutic range. The response depended on the cell type, PMCA isoforms expression profile, CaM presence, and the steroids structure.

Different forms of oestrogen rapidly upregulate cell proliferation in the dentate gyrus of adult female rats

Oestrogens are known to exert significant structural and functional effects in the hippocampus of adult rodents. The dentate gyrus of the hippocampus retains the ability to produce neurones throughout adulthood and 17beta-oestradiol has been shown to influence hippocampal neurogenesis in adult female rats. The effects of other oestrogens, such as oestrone and 17alpha-oestradiol, on neurogenesis have not been investigated. The present study aimed to investigate the effects of 17beta-oestradiol, oestradiol benzoate, oestrone, and 17alpha-oestradiol on cell proliferation in ovariectomised adult female rats at two different time points. Young ovariectomised female rats were injected with one of the oestrogens at one of three doses. In Experiment 1, rats were exposed to the hormone for 4 h and, in Experiment 2, rats were exposed to the hormone for 30 min prior to 5-bromo-2-deoxyuridine injection to label proliferating cells and their progeny. We found that young ovariectomised females responded with increased cell proliferation to most oestrogens, except oestradiol benzoate, after 30 min of exposure. However, administration of oestrogens for a longer time interval was ineffective at increasing cell proliferation. After 30 min, 17beta-oestradiol and oestrone increased cell proliferation at low (0.3 microg) and high (10 microg) doses, whereas 17alpha-oestradiol increased cell proliferation at medium (1 microg) and high doses. The results of the present study indicate that different oestrogens rapidly increase cell proliferation in a dose-dependent manner, possibly through a nonclassical, nongenomic mechanism. Future experiments should focus on further elucidating the specific pathways utilised by each oestrogen. These results have important therapeutic implications because it may be possible to use 17alpha-oestradiol and lower doses of oestrogens in hormone replacement therapies.

Estrogenic control of mitochondrial function and biogenesis

Estrogens have cell-specific effects on a variety of physiological endpoints including regulation of mitochondrial biogenesis and activity. Estrogens regulate gene transcription by the classical genomic mechanism of binding to estrogen receptors alpha and beta (ERalpha and ERbeta) as well as the more recently described nongenomic pathways involving plasma membrane-associated ERs that activate intracellular protein kinase-mediated phosphorylation signaling cascades. Here I will review the rapid and longer-term effects of estrogen on mitochondrial function. The identification of ERalpha and ERbeta within mitochondria of various cells and tissues is discussed with a model of estrogen regulation of the transcription of nuclear respiratory factor-1 (NRF-1, NRF1). NRF-1 subsequently promotes transcription of mitochondrial transcription factor Tfam (mtDNA maintenance factor, also called mtTFA) and then Tfam targets mtDNA-encoded genes. The nuclear effects of estrogens on gene expression directly controlling mitochondrial biogenesis, oxygen consumption, mtDNA transcription, and apoptosis are reviewed. Overall, we are just beginning to evaluate the many direct and indirect effects of estrogens on mitochondrial activities.

Interaction of estrogen receptor alpha transactivation domain with MTA1 decreases in old mouse brain

We have reported earlier that estrogen receptor (ER) alpha-transactivation domain (TAD) interacted with four nuclear proteins of 100 kD, 80 kD, 68 kD, and 50 kD of mouse brain and identified 68 kD as p68 RNA helicase and 50 kD as beta-tubulin. In this paper, we describe the identification of 80 kD nuclear protein as metastasis associated protein 1 (MTA1) and its interaction and expression in the brain of aging mice. Far-Western blotting and immunoprecipitation data revealed lower interaction of MTA1 in old than adult mice of both sexes. Furthermore, adult male showed lower expression of protein as compared to adult female. Altogether these findings suggest that age-dependent decrease in the expression of MTA1 and its interaction with ERalpha-TAD may influence the estrogen-mediated signaling pathway during aging of mouse brain.

Modulation of estrogen receptors during development inhibits neurogenesis of precursors to GnRH-1 neurones: in vitro studies with explants of ovine olfactory placode

The aim of the present study was to explore the putative effects of agonists and antagonists of the estradiol receptor on the early phase of GnRH-1 neuron development. To address this question we used an in vitro model of GnRH-1 neurons using cultured olfactory placode from sheep embryos on day 26 of gestation. Previous studies on this model have shown that in vitro the development of GnRH-1 neurons mimics in vivo development up to the start of pulsatile GnRH-1 secretion, To address the effects of modulating the estrogen receptor, cultures were treated with the endogenous and synthetic ligands of estradiol receptors: 17beta-estradiol, 17alpha-estradiol and tamoxifen. Neurogenesis was measured by incorporation of [(3)H]-thymidine. Morphometric parameters were evaluated by image analysis. The main results are that antagonism of estradiol receptors induced an important decrease in neurogenesis but had little effect on morphometric parameters, suggesting that during this early phase of development, maternal estrogens are important to achieve correct development of the GnRH-1 neuronal network.