Dopaminergic phenotype induced by oestrogens in a human neuroblastoma cell line

Rapid and acute effects of estrogen on time perception in male and female rats

Sex differences in the rapid and acute effects of estradiol on time perception were investigated in adult male and female Sprague-Dawley rats. Because estradiol has been shown to increase striatal dopamine release, it may be able to modify time perception and timed performance by increasing the speed of an internal clock in a manner similar to indirect dopamine agonists such as amphetamine and cocaine. Two groups of females (neonatally estradiol-treated/adult ovariectomized and neonatally oil-treated/adult ovariectomized) and two groups of males (neonatally castrated and adult castrated) were trained in a 2 vs. 8-s duration bisection procedure and tested using intermediate signal durations. After obtaining oil-injected baseline psychometric functions over several days, rats were administered 5 μg of estradiol for 4 days and behaviorally evaluated 30 min following each injection. This oil-estradiol administration cycle was subsequently repeated three times following the re-establishment of baseline training. Results revealed significant sex differences in the initial baseline functions that were not modifiable by organizational hormones, with males' duration bisection functions shifted horizontally to the left of females'. Upon the first administration of estradiol, females, but not males, showed a significant, transient leftward shift in their bisection functions, indicative of an increase in clock speed. After extensive retraining in the duration bisection procedure, rats that were exposed to gonadal hormones during the first week of life showed a significant rightward shift in their bisection functions on the fourth day of estradiol administration during each cycle, suggesting a decrease in clock speed. Taken together, our results support the view that there are multiple mechanisms of estrogens' action in the striatum that modulate dopaminergic activity and are differentially organized by gonadal steroids during early brain development.

Gender-specific role of mitochondria in the vulnerability of 6-hydroxydopamine-treated mesencephalic neurons

Many neurodegenerative diseases, such as Morbus Parkinson, exhibit a gender-dependency showing a higher incidence in men than women. Most of the neurodegenerative disorders involve either causally or consequently a dysfunction of mitochondria. Therefore, neuronal mitochondria may demonstrate a gender-specificity with respect to structural and functional characteristics of these organelles during toxic and degenerative processes. The application of 6-OHDA (6-hydroxydopamine) in vitro and in vivo represents a well-accepted experimental model of Parkinson's disease causing Parkinsonian symptoms. Besides the known effects of 6-OHDA on mitochondria and neuronal survivability, we aimed to demonstrate that the mitochondrial neurotoxin affects the morphology and survival of primary dopaminergic and non-dopaminergic neurons in the mesencephalon in a gender-specific manner by influencing the transcription of mitochondrial genes, ATP and reactive oxygen species production. Our data suggest that cell death in response to 6-OHDA is primarily caused due to increased oxidative stress which is more pronounced in male than in female mesencephalic neurons.

The SIRT1 activator resveratrol protects SK-N-BE cells from oxidative stress and against toxicity caused by alpha-synuclein or amyloid-beta (1-42) peptide

Human sirtuins are a family of seven conserved proteins (SIRT1-7). The most investigated is the silent mating type information regulation-2 homolog (SIRT1, NM_012238), which was associated with neuroprotection in models of polyglutamine toxicity or Alzheimer's disease (AD) and whose activation by the phytocompound resveratrol (RES) has been described. We have examined the neuroprotective role of RES in a cellular model of oxidative stress, a common feature of neurodegeneration. RES prevented toxicity triggered by hydrogen peroxide or 6-hydroxydopamine (6-OHDA). This action was likely mediated by SIRT1 activation, as the protection was lost in the presence of the SIRT1 inhibitor sirtinol and when SIRT1 expression was down-regulated by siRNA approach. RES was also able to protect SK-N-BE from the toxicity arising from two aggregation-prone proteins, the AD-involved amyloid-beta (1-42) peptide (Abeta42) and the familiar Parkinson's disease linked alpha-synuclein(A30P) [alpha-syn(A30P)]. Alpha-syn(A30P) toxicity was restored by sirtinol addition, while a partial RES protective effect against Abeta42 was found even in presence of sirtinol, thus suggesting a direct RES effect on Abeta42 fibrils. We conclude that SIRT1 activation by RES can prevent in our neuroblastoma model the deleterious effects triggered by oxidative stress or alpha-syn(A30P) aggregation, while RES displayed a SIRT1-independent protective action against Abeta42.

Estradiol promotes proliferation of dopaminergic precursors resulting in a higher proportion of dopamine neurons derived from mouse embryonic stem cells

Estradiol protects dopamine neurons of the substantia nigra from toxic insults. Such neurons succumb in Parkinson's disease; one strategy for restoring dopamine deficiency is cell therapy with neurons differentiated from embryonic stem cells. We investigated the effects of 17beta-estradiol on dopaminergic induction of embryonic stem cells using the 5-stage protocol. Cells were incubated with different steroid concentrations during the proliferation (stage 4) or differentiation (stage 5) phases. Estradiol added at nM concentrations only during stage 4 increases the proliferation of dopaminergic precursors expressing Lmx1a, inducing a higher proportion of dopamine neurons at stage 5. These actions were mediated by activation of estrogen receptors, because co-incubation of cells with estradiol and ICI 182,780 completely abolished the positive effect on both proliferation of committed precursors, and subsequent differentiation to dopaminergic neurons. Our results suggest that estradiol should be useful in producing higher proportions of dopamine neurons from embryonic stem cells aimed for treating Parkinson's disease.

Estrogen downregulates the proximal tubule type IIa sodium phosphate cotransporter causing phosphate wasting and hypophosphatemia

Estrogen treatment causes significant hypophosphatemia in patients. To determine the mechanisms responsible for this effect, we injected ovariectomized rats with either 17beta-estradiol or vehicle for three days. Significant renal phosphate wasting and hypophosphatemia occurred in estrogen-treated rats despite a decrease in their food intake. The mRNA and protein levels of the renal proximal tubule sodium phosphate cotransporter (NaPi-IIa) were significantly decreased in estradiol-treated ad-libitum or pair-fed groups. Estrogen did not affect NaPi-III or NaPi-IIc expression. In ovariectomized and parathyroidectomized rats, 17beta-estradiol caused a significant decrease in NaPi-IIa mRNA and protein expression compared to vehicle. Estrogen receptor alpha isoform blocker significantly blunted the anorexic effect of 17beta-estradiol but did not affect the downregulation of NaPi-IIa. Our studies show that renal phosphate wasting and hypophosphatemia induced by estrogen are secondary to downregulation of NaPi-IIa in the proximal tubule. These effects are independent of food intake or parathyroid hormone levels and likely not mediated through the activation of estrogen receptor alpha subtype.

Astrocyte-like cells as a main target for estrogen action during neuronal differentiation

Neurospheres from the subventricular zone of adult mice were used as an experimental model to analyse the early differential effects of 17beta-estradiol (17beta-E2). Both floating and differentiating neurospheres expressed estrogen receptors (ERs) alpha and beta. The initial phases of differentiation coincided with a peak of ERalpha expression as by Western blot analysis. Treatment with 10 nM 17beta-E2 induced a significant increase in the glial fibrillary acidic protein (GFAP)-positive population and a greater expression of GFAP, an effect sensitive to the estrogen receptor antagonist ICI 182,780. The GFAP-positive cell population induced by 17beta-E2 was characterized by a highly differentiated phenotype and intense immunostaining as by immunocytochemistry and flow cytometry. These cells co-expressed ERalpha and were positive to BrdU. 17beta-E2 also affected neuronal differentiation by rapidly and transiently increasing the percentage of polysialylated-neural cell adhesion molecule (PSA-NCAM)-positive progenitors, and by accelerating the appearance of a mature neuronal phenotype, as evaluated by microtubule-associated protein 2 (MAP2) staining. Our results point to a key role for ERalpha during initial phases of differentiation of brain cells and to an effect of 17beta-E2 that sequentially involves both glia and neurons.

Aging of Brain: Role of Estrogen

The brain undergoes many structural and functional changes during aging. Some of these changes are regulated by estrogens which act mainly through their intracellular receptors, estrogen receptor ERalpha and ERbeta. The expression of these receptors is regulated by several factors including their own ligand estrogen, and others such as growth hormone and thyroid hormone. The levels of these factors decrease during aging which in turn influence estrogen signaling leading to alterations in brain functions. In the present paper, we review the effects of aging on brain structure and function, and estrogen action and signaling during brain aging. The findings suggest key role of estrogen in the maintenance of brain functions during aging.

Beauty product-related exposures and childhood brain tumors in seven countries: results from the SEARCH International Brain Tumor Study

Data from 1218 cases of childhood brain tumors (CBT) diagnosed between 1976 and 1994 and 2223 matched controls from the general population were included in an analysis of maternal beauty product exposure and beauty-related employment in 9 centers in 7 countries. A 50% increased odds ratio (OR) [95% confidence interval (CI) = 1.0-2.1] for CBT was observed among children of mothers who were exposed via personal use of and/or possible ambient contact with beauty products during the 5 years preceding the index child's birth compared with children of mothers never exposed to beauty products during this time period. Overall maternal personal use of hair-coloring agents in the month before or during the pregnancy of the index child's birth was not associated with CBT (OR = 1.0, CI = 0.83-1.3) or with astroglial (OR = 1.1, CI = 0.85-1.4), PNET (OR = 1.0, CI = 0.71-1.5) and other glial subtypes (OR = 1.0, CI = 0.62-1.0). Similarly, no statistically increased ORs or discernable pattern of risk estimates were observed for period of use or for number of applications per year for maternal personal use of hair-coloring agents overall or by histologic type. Among children born on or after 1980, increased ORs for CBT were associated with maternal non-work-related exposure to any beauty products (OR = 2.6, CI = 1.2-5.9), hair-dyes (OR = 11, CI = 1.2-90), and hair sprays (OR = 3.4, CI = 1.0-11). No overall increased OR for CBT was observed among children of mothers employed in beauty-related jobs during the 5 years preceding the index child's birth compared with those who reported no beauty-related employment. In general, other specific beauty product-related exposures were not associated with increased ORs for CBT. Data from our study provide little evidence of an increased risk for CBT with mothers' exposures to beauty products.

Estrogen receptor alpha, a molecular switch converting transforming growth factor-alpha-mediated proliferation into differentiation in neuroblastoma cells

Transforming growth factor-alpha (TGF-alpha) is known to promote both proliferation and differentiation of neural cell progenitors. Using the human neuroblastoma cell line SK-N-BE that is induced to proliferate by TGF-alpha, we demonstrated that the expression of a single transcription factor, the estrogen receptor-alpha (ER alpha), can reroute the TGF-alpha mitogenic signaling toward a path leading to differentiation. With selected mutations in ER alpha and signal transducer and activator of transcription 3 (Stat3), we demonstrated that the blockade of TGF-alpha mitotic potential was not dependent on ER alpha DNA binding activity but required a transcriptionally active Stat3. In neuroblastoma cells, 17 beta-estradiol treatment induced a transient increase in the transcription of estrogen-responsive element-containing promoters including those regulating TGF-alpha and prothymosin alpha synthesis. Based on the data presented, we hypothesized that in the presence of prothymosin alpha, ER alpha activates its direct target genes and increases cell proliferation, whereas in the presence of high levels of TGF-alpha, ER alpha preferentially interacts with Stat3 and causes cell differentiation. Our results reveal a novel form of "end-product" regulation of an intracellular receptor that occurs through recruitment of membrane receptors and their signaling effector system. Cross-coupling between membrane and intracellular receptors has been described by several laboratories. This study proves the relevance of these interactions in cellular responses to growth factors.

Estrogen stimulates brain-derived neurotrophic factor expression in embryonic mouse midbrain neurons through a membrane-mediated and calcium-dependent mechanism

We have provided evidence that 17beta-estradiol (E) synthesized in the midbrain promotes the differentiation of midbrain dopamine neurons through nonclassical steroid action. Because these developmental effects resemble those reported for brain-derived neurotrophic factor (BDNF), we hypothesized that E influences dopaminergic cell differentiation through a BDNF-dependent mechanism. Competitive RT-PCR and ELISA techniques were employed to study first the developmental pattern of BDNF and trkB expression in the mouse midbrain. BDNF protein/mRNA levels peaked postnatally, whereas trkB did not fluctuate perinatally. To prove the hypothesis that E regulates BDNF expression in vivo, fetuses and newborns were treated with the aromatase antagonist CGS 16949A. CGS 16949A exposure reduced midbrain BDNF mRNA/protein levels. The coapplication of CGS 16949A and E abolished this effect. Midbrain cultures from mouse fetuses were used to investigate intracellular signaling mechanisms involved in transmitting E effects. Estrogen increased expression of BDNF but not of other neurotrophins. As concerns the related signaling mechanism, these effects were antagonized by interrupting intracellular Ca(2+) signaling with BAPTA and thapsigargin but not by the estrogen receptor antagonist ICI 182,780. Insofar as E effects on BDNF mRNA expression were inhibited by cycloheximide, it appears likely that other, not yet characterized intermediate proteins take part in the estrogenic regulation of BDNF expression. We conclude that E exerts its stimulatory effect on the differentiation of dopaminergic neurons by coordinating BDNF expression. This particular E effect appears to be transmitted through Ca(2+)-dependent signaling cascades upon activation of putative membrane estrogen receptors.

Classical and nonclassical estrogen action in the developing midbrain

There is widespread acceptance that estrogen is involved in various steps of cellular differentiation during brain development. In the past years, we have demonstrated such a developmental role for estrogen in the rodent midbrain. Precisely, estrogen affects midbrain dopamine neurons with respect to functional and morphological maturation. On the cellular level, estrogen may act classically by binding and activating its respective nuclear receptors, thereby controlling the transcription of target genes. On the other hand, many estrogen effects in the CNS are transmitted nonclassically by interactions with putative membrane receptors and by stimulating distinct intracellular signaling cascades. In the midbrain, classical and nonclassical estrogen signaling routes operate side by side to ensure the proper development of dopaminergic cells. In the present report, we detail some of the cellular and molecular events which are activated by estrogen and are thought to take part in the estrogen-mediated stimulation of dopamine neuron differentiation.

Estrogens, apoptosis and cells of neural origin

In view of the relevant complexity of estradiol actions in the nervous system, we have proposed to utilize a reductionist approach and gain an insight on its role in neural cells via the identification of the genes target for this hormone. Once obtained a biochemical footprint of the responses elicited by E2 in the neural target cells we believe that the physiological effects exerted by this hormone will be more easily elucidated; in addition, we might find novel targets for drugs aimed at mimicking or blocking E2 effects. We here summarize preliminary results obtained in the cell line SK-ER3 appropriately engineered by us to express the ERalpha. We show that nip-2, one of the genes found to be regulated by E2, is involved in the mechanisms leading to cell death. This finding led us to investigate on estrogen effects on SK-ER3 apoptosis. We found that E2 has a significant anti-apoptotic activity in SKER3 cells. These results are in line with the recent reports from other laboratories indicating that E2 may prevent death of neural cells exposed to toxic stimuli. We conclude that these initial studies seem to support the strategy of our research and underline the strength of inverse genetics in the study of the physiology of sex hormone activities.

Morphological abnormalities in the brains of estrogen receptor beta knockout mice

Estrogen receptor beta (ERbeta) is expressed at high levels in both neurons and glial cells of the central nervous system. The development of ERbeta knockout (BERKO) mice has provided a model to study the function of this nuclear receptor in the brain. We have found that the brains of BERKO mice show several morphological abnormalities. There is a regional neuronal hypocellularity in the brain, with a severe neuronal deficit in the somatosensory cortex, especially layers II, III, IV, and V, and a remarkable proliferation of astroglial cells in the limbic system but not in the cortex. These abnormalities are evident as early as 2 mo of age in BERKO mice. As BERKO mice age, the neuronal deficit becomes more pronounced, and, by 2 yr of age, there is degeneration of neuronal cell bodies throughout the brain. This is particularly evident in the substantia nigra. We conclude that ERbeta is necessary for neuronal survival and speculate that this gene could have an important influence on the development of degenerative diseases of the central nervous system, such as Alzheimer's disease and Parkinson's disease, as well as those resulting from trauma and stroke in the brain.

Estrogen stimulates the mitogen-activated protein kinase pathway in midbrain astroglia

Estrogen stimulates the development of midbrain dopamine neurons predominantly by acting through membrane receptors coupled to Ca(2+)-signaling. In this report, we describe that estrogen activates extracellular signal-regulated kinases (ERK1/2) in midbrain astrocytes but not neurons. This effect was inhibited by BAPTA which interrupts Ca(2+)-signaling but not by antagonists specific for other signaling pathways. The activation of the MAP kinase pathway suggests a potential role for astrocytes in mediating estrogen effects in the midbrain.

Identification of estrogen target genes in human neural cells

In mammals, estrogens have a multiplicity of effects ranging from control of differentiation of selected brain nuclei, reproductive functions, sexual behavior. In addition, these hormones influence the manifestation of disorders like depression and Alzheimer's. Study of the cells target for the hormone has shown that estrogen receptors (ERs) are expressed in all known neural cells, including microglia. In view of the potential interest in the use of estrogens in the therapy of several pathologies of the nervous system, it would be of interest to fully understand the mechanism of estrogen activity in the various neural target cells and get an insight on the molecular means allowing the hormone to display such a variety of effects. We have proposed the use of a reductionist approach for the systematic understanding of the estrogen activities in each specific type of target cell. Thus, we have generated a model system in which to study the activation of one of the known (ERs), estrogen receptor alpha. This system allowed us to identify a number of novel genes which expression may be influenced following the activation of this receptor subtype by estradiol (E(2)). We here report on data recently obtained by the study of one of these target genes, nip2, which encodes a proapoptotic protein product. We hypothesize that nip2 might be an important molecular determinant for estrogen anti-apoptotic activity in cells of neural origin and represents a potential target for drugs aimed at mimicking the E(2) beneficial effects in neural cells.

Oestrogen prevention of neural cell death correlates with decreased expression of mRNA for the pro-apoptotic protein nip-2

We have recently identified nip-2 as a gene target for 17beta-oestradiol activity in the neuroblastoma SK-ER3 cells expressing the oestrogen receptor (ER) alpha. Here we show 17beta-oestradiol treatment of neuroblastoma and rat embryo neurones in culture blocks the increase in nip-2 mRNA induced by apoptotic stimuli and prevents cell death as indicated by cell counting, 3,(4,5-dimethylthiazol-2-yl)2,5-diphenil-tetrazoliumbromi de and DNA fragmentation assays. Neither of these effects are observed in the presence of the specific ER antagonist ICI 182,780, and are absent in neuroblastoma cells not expressing ER. We propose that nip-2 plays a relevant role in neural cell apoptosis and that a decrease in its expression is instrumental for the oestrogen anti-apoptotic effect described here. The experimental evidence presented supports the recent hypothesis of a protective role of oestrogens in neurodegenerative diseases such as Alzheimer's disease and highlights the importance of the development of new ER ligands for the prevention of neural cell damage.

Expression of the estrogen-regulated gene Nip2 during rat brain maturation

The present study stems from previous observations demonstrating that in the neuroblastoma cell line SK-ER3 the mRNA content of the pro-apoptotic gene Nip2 is decreased following treatment with estradiol. We investigate the content of Nip2 mRNA during the maturation of rat embryo brain and we show that Nip2 mRNA is very low at embryo day 15 and steadily increases up to day 20. At day 21 Nip2 mRNA is decreased almost to the low levels observed in the mature brain. Studies in neurons from rat embryo at day 18 show that Nip2 mRNA content is significantly decreased by exposure to estradiol at 1 nM concentration demonstrating that the observations previously done in the SK-ER3 neuroblastoma cell line can be reproduced in neurons in culture. The finding that estrogens may modulate the activity of Nip2 gene activity may be of relevance not only with regard to the effects of estradiol on brain maturation, but also for the understanding of the neuroprotective effects recently described for this hormone.

Ontogenetic expression and splicing of estrogen receptor-alpha and beta mRNA in the rat midbrain

Several studies have shown that estrogen is important for the differentiation of midbrain dopaminergic neurons. This is supported by the previous demonstration of estrogen synthesis in the perinatal ventral midbrain. The present study attempts to characterize the expression pattern of nuclear estrogen receptors (ER-alpha/beta) mRNAs in the ventral rat midbrain during development. By applying primers specific for the hormone-binding domain, ER-alpha mRNA was detected from embryonic day (E) 14 until postnatal day (P) 20, whereas considerable levels of ER-beta mRNA were found from P3 to P20. In contrast, primers spanning the DNA-binding domain demonstrated the presence of transcripts for ER-alpha as well as ER-beta after birth. These findings indicate that both ERs are expressed in the developing midbrain. The presence of ER-alpha transcripts devoid of the DNA-binding region is discussed in the context of 'non-genomic' estrogen signaling possibly by membrane receptors.

Estrogen receptor-dependent regulation of sensory neuron survival in developing dorsal root ganglion

Estrogen is known to influence different functions in brain tissue ranging from neuronal development to plasticity and survival, but the mechanisms involved have not been defined clearly. Previous studies have shown the presence of the two estrogen receptors (ERs), ERalpha and ERbeta, in several brain areas, but less is known about the role of estrogen in the peripheral nervous system. Here we demonstrate that dorsal root ganglion (DRG) neurons express ERalpha and ERbeta during early postnatal development and in culture, and that the ERs localize mainly to neuronal cell nuclei. Studying the role of estrogen in DRG, we observed that low concentrations of 17beta-estradiol increased survival of cultured DRG neurons deprived of nerve growth factor. 17beta-Estradiol up-regulated the expression of the antiapoptotic molecule Bcl-x without affecting that of Bax, suggesting a mechanism by which the hormone counteracted neuronal death. Antiestrogens abolished the action of 17beta-estradiol in the DRG neurons, which demonstrates an involvement of ERs. The results show that estrogen and ERs play an important role in the development and survival of DRG neurons.

Effects and metabolism of steroid hormones in human neuroblastoma cells

The development of the central nervous system is influenced by sex steroids and by their metabolites. However, little information on the possible effects of steroid hormones on neuroblastoma cells is available. Human neuroblastoma cell lines have been used as a model of human neuroblasts in vitro to study the metabolism of steroid hormones; in addition, the effects of steroids and steroid antagonists on neuroblastoma cell growth have also been investigated. The results obtained show that SH-SY5Y human neuroblastoma cells may actively metabolize testosterone and progesterone to their respective 5 alpha-reduced metabolites and that differentiation of neuroblastoma cells is paralleled by a significant increase in expression of the type-1 5 alpha-reductase and of the formation of steroid metabolites. All these data are suggestive of a potential role of steroid 5 alpha-reduced metabolites in the biology of neuroblastoma cells. Studies performed to analyze the role of steroid hormones on neuroblastoma cell proliferation show that progesterone at low doses may induce minor stimulation, and at higher doses, a toxic effect on the neuroblastoma cell line SK-N-SH is seen. Moreover, the antiprogestin 17 beta-hydroxy-11 beta-(4-dimethylamino-phenyl-1)-17-(prop-1-ynyl)estra-4,9-dien+ ++-3-one (RU486) decreases the proliferation of these cells in a dose-dependent manner. The effect of RU486 is not antagonized by either progesterone or dexamethasone, a result that seems to exclude the action of RU486 via classic intracellular steroid hormone receptors.

Identification of estrogen-responsive genes in neuroblastoma SK-ER3 cells

To evaluate the role of estrogen receptor in the differentiation of cells of neural origin, we developed a molecular approach aimed at the identification of estrogen target genes by mRNA differential display PCR (ddPCR) in human neuroblastoma SK-ER3 cells. More than 3000 RNAs were examined, a few of which displayed a differential regulation pattern in response to 17beta-estradiol (E2). Sequence analysis of three differentially amplified ddPCR products showed homology with the growth-associated nuclear protein prothymosin-alpha (PTMA), the Bcl2-interacting protein Nip2, and one mRNA previously described by others in fetal human brain. Two ddPCR products, referred to as P4 and P10, corresponded to new DNA sequences. Northern analysis confirmed that estrogen treatment of SK-ER3 cells resulted in the upregulation and downregulation of expression of these messages. In particular, PTMA was found to accumulate at both 1 and 17 hr after E2 treatment, whereas P10 product accumulated only at 1 hr. Conversely, P4, Nip2, and the fetal brain-related mRNAs were significantly decreased by the treatment. Further time course analysis of PTMA and Nip2 mRNAs levels indicated that the hormone exerted a marked biphasic regulatory effect on expression of both messages during the course of cell differentiation. In the present study we report for the first time the identification of a panel of estrogen target genes in neural cells that provide new insights in the molecular mechanism of action of E2 in cells of neural origin.