Spontaneous fetal loss caused by placental thrombosis in estrogen sulfotransferase-deficient mice

Triclosan: environmental exposure, toxicity and mechanisms of action

Triclosan [5-chloro-2-(2,4-dichlorophenoxy)phenol; TCS] is a broad spectrum antibacterial agent used in personal care, veterinary, industrial and household products. TCS is commonly detected in aquatic ecosystems, as it is only partially removed during the wastewater treatment process. Sorption, biodegradation and photolytic degradation mitigate the availability of TCS to aquatic biota; however the by-products such as methyltriclosan and other chlorinated phenols may be more resistant to degradation and have higher toxicity than the parent compound. The continuous exposure of aquatic organisms to TCS, coupled with its bioaccumulation potential, have led to detectable levels of the antimicrobial in a number of aquatic species. TCS has been also detected in breast milk, urine and plasma, with levels of TCS in the blood correlating with consumer use patterns of the antimicrobial. Mammalian systemic toxicity studies indicate that TCS is neither acutely toxic, mutagenic, carcinogenic, nor a developmental toxicant. Recently, however, concern has been raised over TCS's potential for endocrine disruption, as the antimicrobial has been shown to disrupt thyroid hormone homeostasis and possibly the reproductive axis. Moreover, there is strong evidence that aquatic species such as algae, invertebrates and certain types of fish are much more sensitive to TCS than mammals. TCS is highly toxic to algae and exerts reproductive and developmental effects in some fish. The potential for endocrine disruption and antibiotic cross-resistance highlights the importance of the judicious use of TCS, whereby the use of TCS should be limited to applications where it has been shown to be effective.

Estrogen sulfotransferase inhibits adipocyte differentiation

The estrogen sulfotransferase (EST) is a phase II drug-metabolizing enzyme known to catalyze the sulfoconjugation of estrogens. EST is highly expressed in the white adipose tissue of male mice, but the role of EST in the development and function of adipocytes remains largely unknown. In this report, we showed that EST played an important role in adipocyte differentiation. EST was highly expressed in 3T3-L1 preadipocytes and primary mouse preadipocytes. The expression of EST was dramatically reduced in differentiated 3T3-L1 cells and mature primary adipocytes. Overexpression of EST in 3T3-L1 cells prevented adipocyte differentiation. In contrast, preadipocytes isolated from EST knockout (EST-/-) mice exhibited enhanced differentiation. The inhibitory effect of EST on adipogenesis likely resulted from the sustained activation of ERK1/2 MAPK and inhibition of insulin signaling, leading to a failure of switch from clonal expansion to differentiation. The enzymatic activity of EST was required for the inhibitory effect of EST on adipogenesis, because an enzyme-dead EST mutant failed to inhibit adipocyte differentiation. In vivo, overexpression of EST in the adipose tissue of female transgenic mice resulted in smaller adipocyte size. Taken together, our results suggest that EST functions as a negative regulator of adipogenesis.

Liganded pregnane X receptor represses the human sulfotransferase SULT1E1 promoter through disrupting its chromatin structure

Pregnane X receptor (PXR), acting as a xenobiotic-activated transcription factor, regulates the hepatic metabolism of therapeutics as well as endobiotics such as steroid hormones. Given our finding that PXR activation by rifampicin (RIF) represses the estrogen sulfotransferase (SULT1E1) gene in human primary hepatocytes and hepatocellular carcinoma Huh7 cells, here we have investigated the molecular mechanism of this repression. First the PXR-responsive enhancer was delineated to a 100 bp sequence (−1000/−901), which contains three half sites that constitute the overlapping direct repeat 1 (DR1) and direct repeat 2 (DR2) motifs and two forkhead factor binding sites. siRNA knockdown, chromatin immunoprecipitation and chromatin conformation capture assays were employed to demonstrate that hepatocyte nuclear factor 4α (HNF4α) bound to the PXR-responsive enhancer, and activated the enhancer by looping its position close to the proximal promoter. Upon activation by RIF, PXR indirectly interacted with the enhancer, decreasing the interaction with HNF4α and dissolving the looped SULT1E1 promoter with deacetylation of histone 3. Removal of the DR sites from the enhancer hampers the ability of HNF4α to loop the promoter and that of PXR to repress the promoter activity. Thus, PXR represses human SULT1E1, possibly attenuating the inactivation of estrogen.

Biological activity of oestradiol sulphate in an oviparous amniote: implications for maternal steroid effects

Understanding the many factors that underlie phenotypic variation is of profound importance to evolutionary biologists. The embryonic endocrine environment is one such factor that has received much attention. In placental amniotes, the dynamic interaction of maternal and embryonic steroid production and metabolism is critical to regulating the endocrine environment. Less is known about how embryos of oviparous amniotes regulate their endocrine environment because most studies have focused on relating initial steroid levels in the yolk at oviposition to offspring phenotype. We tested the hypothesis that embryos of oviparous amniotes regulate their endocrine environment by conjugating maternal steroids and subsequently using the metabolites as precursors for steroid production later in development. Using the red-eared slider turtle (Trachemys scripta), we first characterized the conjugation of exogenous oestradiol to either oestradiol glucuronide or oestradiol sulphate (E(2)-S) in ovo during the first 15 days of development. Results show that oestradiol is primarily conjugated to E(2)-S. We then examined whether E(2)-S influenced sex determination and report that E(2)-S increases the production of female offspring. These data demonstrate that oviparous amniotes can both sulphonate steroids and respond to sulphonated steroids during embryonic development in a manner similar to placental amniotes.

Garlic extract diallyl sulfide (DAS) activates nuclear receptor CAR to induce the Sult1e1 gene in mouse liver

Constituent chemicals in garlic extract are known to induce phase I and phase II enzymes in rodent livers. Here we have utilized Car(+/+) and Car(-/-) mice to demonstrate that the nuclear xenobiotic receptor CAR regulated the induction of the estrogen sulfotransferase Sult1e1 gene by diallyl sulfide (DAS) treatment in mouse liver. DAS treatment caused CAR accumulation in the nucleus, resulting in a remarkable increase of SULT1E1 mRNA (3,200 fold) and protein in the livers of Car(+/+) females but not of Car(-/-) female mice. DAS also induced other CAR-regulated genes such as Cyp2b10, Cyp3a11 and Gadd45β. Compared with the rapid increase of these mRNA levels, which began as early as 6 hours after DAS treatment, the levels of SULT1E1 mRNA began increasing after 24 hours. This slow response to DAS suggested that CAR required an additional factor to activate the Sult1e1 gene or that this activation was indirect. Despite the remarkable induction of SULT1E1, there was no decrease in the serum levels of endogenous E2 or increase of estrone sulfate while the clearance of exogenously administrated E2 was accelerated in DAS treated mice.

Sulfate in fetal development

Sulfate (SO(4)(2-)) is an important nutrient for human growth and development, and is obtained from the diet and the intra-cellular metabolism of sulfur-containing amino acids, including methionine and cysteine. During pregnancy, fetal tissues have a limited capacity to produce sulfate, and rely on sulfate obtained from the maternal circulation. Sulfate enters and exits placental and fetal cells via transporters on the plasma membrane, which maintain a sufficient intracellular supply of sulfate and its universal sulfonate donor 3'-phosphoadenosine 5'-phosphosulfate (PAPS) for sulfate conjugation (sulfonation) reactions to function effectively. Sulfotransferases mediate sulfonation of numerous endogenous compounds, including proteins and steroids, which biotransforms their biological activities. In addition, sulfonation of proteoglycans is important for maintaining normal structure and development of tissues, as shown for reduced sulfonation of cartilage proteoglycans that leads to developmental dwarfism disorders and four different osteochondrodysplasias (diastrophic dysplasia, atelosteogenesis type II, achondrogenesis type IB and multiple epiphyseal dysplasia). The removal of sulfate via sulfatases is an important step in proteoglycan degradation, and defects in several sulfatases are linked to perturbed fetal bone development, including mesomelia-synostoses syndrome and chondrodysplasia punctata 1. In recent years, interest in sulfate and its role in developmental biology has expanded following the characterisation of sulfate transporters, sulfotransferases and sulfatases and their involvement in fetal growth. This review will focus on the physiological roles of sulfate in fetal development, with links to human and animal pathophysiologies.

Fetal loss and hyposulfataemia in pregnant NaS1 transporter null mice

Sulfate is important for growth and development, and is supplied from mother to fetus throughout pregnancy. We used NaS1 sulfate transporter null (Nas1(-/-)) mice to investigate the role of NaS1 in maintaining sulfate homeostasis during pregnancy and to determine the physiological consequences of maternal hyposulfataemia on fetal, placental and postnatal growth. We show that maternal serum (≤0.5 mM), fetal serum (<0.1 mM) and amniotic fluid (≤0.5 mM) sulfate levels were significantly lower in pregnant Nas1(-/-) mice when compared with maternal serum (≍2.0 mM), fetal serum (≍1.5 mM) and amniotic fluid (≍1.7 mM) sulfate levels in pregnant Nas1(+/+) mice. After 12 days of pregnancy, fetal reabsorptions led to markedly reduced (by ≥50%) fetal numbers in Nas1(-/-) mice. Placental labyrinth and spongiotrophoblast layers were increased (by ≍140%) in pregnant Nas1(-/-) mice when compared to pregnant Nas1(+/+) mice. Birth weights of progeny from female Nas1(-/-) mice were increased (by ≍7%) when compared to progeny of Nas1(+/+) mice. These findings show that NaS1 is essential to maintain high maternal and fetal sulfate levels, which is important for maintaining pregnancy, placental development and normal birth weight.

The molecular biology, biochemistry, and physiology of human steroidogenesis and its disorders

Steroidogenesis entails processes by which cholesterol is converted to biologically active steroid hormones. Whereas most endocrine texts discuss adrenal, ovarian, testicular, placental, and other steroidogenic processes in a gland-specific fashion, steroidogenesis is better understood as a single process that is repeated in each gland with cell-type-specific variations on a single theme. Thus, understanding steroidogenesis is rooted in an understanding of the biochemistry of the various steroidogenic enzymes and cofactors and the genes that encode them. The first and rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone by a single enzyme, P450scc (CYP11A1), but this enzymatically complex step is subject to multiple regulatory mechanisms, yielding finely tuned quantitative regulation. Qualitative regulation determining the type of steroid to be produced is mediated by many enzymes and cofactors. Steroidogenic enzymes fall into two groups: cytochrome P450 enzymes and hydroxysteroid dehydrogenases. A cytochrome P450 may be either type 1 (in mitochondria) or type 2 (in endoplasmic reticulum), and a hydroxysteroid dehydrogenase may belong to either the aldo-keto reductase or short-chain dehydrogenase/reductase families. The activities of these enzymes are modulated by posttranslational modifications and by cofactors, especially electron-donating redox partners. The elucidation of the precise roles of these various enzymes and cofactors has been greatly facilitated by identifying the genetic bases of rare disorders of steroidogenesis. Some enzymes not principally involved in steroidogenesis may also catalyze extraglandular steroidogenesis, modulating the phenotype expected to result from some mutations. Understanding steroidogenesis is of fundamental importance to understanding disorders of sexual differentiation, reproduction, fertility, hypertension, obesity, and physiological homeostasis.

Triclosan is a potent inhibitor of estradiol and estrone sulfonation in sheep placenta

The personal care product Triclosan, 5-chloro-2(2,4-dichlorophenoxy)-phenol, is widely used in consumer products as an antibacterial agent and is increasingly found in the environment as a contaminant of sewage sludge and wastewater. This compound has been identified in plasma and urine of people in the United States, Sweden and Australia. Triclosan is known to inhibit sulfonation of phenolic xenobiotics and is structurally related to inhibitors of estrogen sulfotransferase, such as polychlorobiphenylols. In pregnancy, the placenta is an important source of estrogen, which is needed for normal fetal development and successful parturition, and estrogen sulfotransferase is thought to play an important role in regulation of estrogen availability. In this study, we examined the effect of Triclosan on sheep placental cytosolic sulfotransferase activity with 17-beta-estradiol and estrone as substrates. For comparison, we studied the effects of 4-hydroxy-3,3',4',5-tetrachlorobiphenyl and 2'-hydroxytriclocarban on estradiol sulfonation. The apparent K(m) for placental cytosolic sulfotransferase activity with estradiol as substrate was 0.27 ± 0.06 nM (mean ± S.D., n = 3 individuals) and with estrone as substrate was 1.86 ± 0.22 nM. Partial substrate inhibition was observed with estradiol at concentrations higher than 10-20 nM, as is typical of estrogen sulfotransferases (SULT1E1) in other species. Studies of the effect of Triclosan on estrogen sulfotransferase activity were conducted with several concentrations (0.1-6 nM) of estradiol and with 2 nM estrone. Triclosan was a very potent inhibitor of both estradiol and estrone sulfonation. For estradiol the inhibition was shown to be mixed competitive/uncompetitive, with K(ic) of 0.09 ± 0.01 nM and K(iu) of 5.2 ± 2.9 nM. The IC(50) for inhibition of estrone sulfonation was 0.60 ± 0.06 nM. At an environmentally relevant concentration of 1 µM, Triclosan was not a substrate for glucuronidation in sheep placental microsomes. Triclosan could be sulfonated in placental cytosol with K(m) 1.14 ± 0.18 µM and V(max) 160 ± 26 pmol/min/mg protein, however the calculated rates of Triclosan sulfonation were negligible at the low nM concentrations that potently inhibit estrogen sulfonation. The high potency of Triclosan as an inhibitor of estrogen sulfotransferase activity raises concern about its possible effects on the ability of the placenta to supply estrogen to the fetus, and in turn on fetal growth and development.

Drug-metabolizing enzyme, transporter, and nuclear receptor genetically modified mouse models

Determining the in vivo significance of a specific enzyme, transporter, or xenobiotic receptor in drug metabolism and pharmacokinetics may be hampered by gene multiplicity and complexity, levels of expression, and interaction between various components involved. The development of knockout (loss-of-function) and transgenic (gain-of-function) mouse models opens the door to the improved understanding of gene function in a whole-body system. There is also growing interest in the development of humanized mice to overcome species differences in drug metabolism and disposition. This review, therefore, aims to summarize and discuss some successful examples of drug-metabolizing enzyme, transporter, and nuclear-receptor genetically modified mouse models. These genetically modified mouse models have been proven as invaluable models for understanding in vivo function of drug-metabolizing enzymes, transporters, and xenobiotic receptors in drug metabolism and transport, as well as predicting potential drug-drug interaction and toxicity in humans. Nevertheless, concerns remain about interpretation of data obtained from such genetically modified mouse models, in which the expression of related genes is altered significantly.

Progesterone metabolites, "xenobiotic-sensing" nuclear receptors, and the metabolism of maternal steroids

During development, embryos utilize steroid signals to direct sexual differentiation of tissues necessary for reproduction. Disruption of these signals by exogenous substances (both natural and synthetic) frequently produce phenotypic effects that can persist into adulthood and influence reproduction. This paper reviews the evidence that during embryonic development, progesterone metabolites and xenobiotic-sensing nuclear receptors may interact to increase the expression of numerous enzymes responsible for steroid metabolism in oviparous and placental amniotes. In these groups, embryonic development is characterized by (1) elevated progesterone concentrations, (2) 5 beta reduction being the primary metabolic pathway of progesterone, (3) the presence of xenobiotic-sensing nuclear receptors that can bind 5 beta metabolites of progesterone, and (4) increased expression of a suite of enzymes responsible for the metabolism of multiple steroids. We propose that xenobiotic-sensing nuclear receptors initially evolved to buffer the developing embryo from the potentially adverse effects of various maternal steroids on sexual differentiation.

Regulation of sulfotransferase and UDP-glucuronosyltransferase gene expression by the PPARs

During phase II metabolism, a substrate is rendered more hydrophilic through the covalent attachment of an endogenous molecule. The cytosolic sulfotransferase (SULT) and UDP-glucuronosyltransferase (UGT) families of enzymes account for the majority of phase II metabolism in humans and animals. In general, phase II metabolism is considered to be a detoxication process, as sulfate and glucuronide conjugates are more amenable to excretion and elimination than are the parent substrates. However, certain products of phase II metabolism (e.g., unstable sulfate conjugates) are genotoxic. Members of the nuclear receptor superfamily are particularly important regulators of SULT and UGT gene transcription. In metabolically active tissues, increasing evidence supports a major role for lipid-sensing transcription factors, such as peroxisome proliferator-activated receptors (PPARs), in the regulation of rodent and human SULT and UGT gene expression. This review summarizes current information regarding the regulation of these two major classes of phase II metabolizing enzyme by PPARs.

Assisted reproduction technologies impair placental steroid metabolism

The placenta plays a vital role in pregnancy by facilitating steroid passage from maternal to fetal circulation and/or direct production of hormones. Using a murine model, we demonstrated the differences in placental steroid metabolism between pregnancies conceived naturally and with assisted reproduction technologies (ART): in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). While the ovarian steroid production was similar (estrone, 17beta-estradiol) or higher (estriol) in ART pregnancies compared to mating, the levels of placental estriol were significantly lower in ART group. Placentas from ART had significantly higher activities of the steroid metabolizing enzymes UDP-glucuronosyltransferase (UGT) and sulfotransferase (SULT), which in ICSI were also coupled with decreased activity of the steroid regenerating enzymes beta-glucuronidase (beta-G) and aryl sulfatase (AS). Levels of steroid metabolites androstane-3alpha-17beta-diol glucuronide and dehydroepiandrosterone sulfate were higher in fetal compared to maternal blood in ART, but not in mating. This study demonstrates that in murine ART pregnancies, higher metabolism and clearance of steroids by the placenta may seriously affect the passage of essential hormones to the fetus. If a similar phenomenon exists in humans, this could provide a plausible explanation for obstetric and neonatal complications associated with ART, including the higher incidence of low birth weight babies.

Androgen synthesis in adrenarche

The enzymes and pathways of steroidogenesis are central to an understanding of adrenarche. The quantitative regulation of steroidogenesis occurs at the first step, the conversion of cholesterol to pregnenolone. Chronic quantitative regulation is principally at the level of transcription of the CYP11A1 gene encoding P450scc, which is the enzymatically rate-limiting step. Acute regulation is mediated by the steroidogenic acute regulatory protein (StAR), which facilitates the rapid influx of cholesterol into mitochondria, where P450scc resides. Qualitative regulation, which determines the type of steroid produced in a cell, is principally at the level of P450c17 (CYP17). In the absence of P450c17 in the zona glomerulosa, C21 deoxy steroids are produced, leading to the mineralocorticoid, aldosterone. In the presence of the 17alpha-hydroxylase but not the 17,20 lyase activity of P450c17 in the zona fasciculata, C21, 17-hydroxy steroids are produced, leading to the glucocorticoid, cortisol. When both the 17alpha-hydroxylase and 17,20 lyase activities of P450c17 are present in the zona reticularis, the androgen precursor DHEA is produced. The discrimination between 17alpha-hydroxylase and 17,20 lyase activities is regulated by two post-translational events, the serine phosphorylation of P450c17 and the allosteric action of cytochrome b5, both of which act to optimize the interaction of P450c17 with its obligatory electron donor, P450 oxidoreductase. In the adrenal zona reticularis, the abundant expression of P450 oxidoreductase and cytochrome b5, and the low expression of 3beta-hydroxysteroid dehydrogenase (HSD3B2) result in the production of the large amounts of DHEA that characterize adrenarche.

Gender-specific expression and mechanism of regulation of estrogen sulfotransferase in adipose tissues of the mouse

Although primarily regarded as a sex steroid, estrogen plays an important role in many other physiological processes including adipose development and disposition. Estrogen sulfotransferase (EST) regulates estrogen activity by catalyzing the sulfoconjugation and inactivation of estrogens. In the present study, we report the gender-specific expression of EST in adipose tissues of the mouse and describe contrasting mechanisms of EST regulation in the fat and liver. EST is expressed in the white adipose tissues of the male but not female mouse. Within the various fat depots of male mice, it is most abundantly expressed in the epididymal fat pad, with variable levels in other white fats and no expression in the brown fat. Fractionation of epididymal fat cells showed EST to be predominantly associated with stromal vascular cells (preadipocyte). EST expression in male mouse adipose tissues is dependent on testosterone as castration ablated, and administration of exogenous testosterone restored, EST expression. Furthermore, testosterone treatment induced abnormal EST expression in the parametrial fat of female mice. EST induction by testosterone in female mice is tissue specific because testosterone treatment had no effect on liver EST expression. Conversely, the liver X receptor agonist TO-901317 induced EST expression in female mouse liver but not in their adipose tissues. Finally, we demonstrate that male EST knockout mice developed increased epididymal fat accumulation with enlarged adipocyte size. We conclude that EST is expressed in adipose tissues in a sexually dimorphic manner, is regulated by testosterone, and plays a physiological role in regulating adipose tissue accumulation in male mice.

Glucocorticoids antagonize estrogens by glucocorticoid receptor-mediated activation of estrogen sulfotransferase

Glucocorticoids and estrogens are two classes of steroid hormones that have essential but distinct physiologic functions. Estrogens also represent a risk factor for breast cancer. It has been suggested that glucocorticoids can attenuate estrogen responses, but the mechanism by which glucocorticoids inhibit estrogenic activity is unknown. In this study, we show that activation of glucocorticoid receptor (GR) by dexamethasone (DEX) induced the expression and activity of estrogen sulfotransferase (SULT1E1 or EST), an enzyme important for the metabolic deactivation of estrogens, because sulfonated estrogens fail to activate the estrogen receptor. Treatment with DEX lowered circulating estrogens, compromised uterine estrogen responses, and inhibited estrogen-dependent breast cancer growth in vitro and in a xenograft model. We further showed that the mouse and human SULT1E1 genes are transcriptional targets of GR and deletion of Sult1e1/Est in mice abolished the DEX effect on estrogen responses. These findings have revealed a novel nuclear receptor-mediated and metabolism-based mechanism of estrogen deprivation, which may have implications in therapeutic development for breast cancers. Because glucocorticoids and estrogens are widely prescribed drugs, our results also urge caution in avoiding glucocorticoid-estrogen interactions in patients.

Liver receptor homolog 1 is essential for ovulation

Female fertility requires normal ovarian follicular growth and ovulation. The nuclear receptor liver receptor homolog 1 has been implicated in processes as diverse as bile acid metabolism, steroidogenesis, and cell proliferation. In the ovary, Lrh1 is expressed exclusively in granulosa and luteal cells. Using somatic targeted mutagenesis, we show that mice lacking Lrh1 in granulosa cells are sterile, due to anovulation. The preovulatory stimulus fails to elicit cumulus expansion, luteinization, and follicular rupture in these mice. Multiple defects, including severely reduced transactivation of the Lrh1 target gene, nitric oxide synthase 3, leads to increased intrafollicular estradiol levels in the absence of Lrh1. This further causes dysfunction of prostaglandin and hyaluronic acid cascades and interrupts cumulus expansion. Lack of Lrh1 also interferes with progesterone synthesis because of failure of normal expression of the Lrh1 targets, steroidogenic acute regulatory protein and cytochrome P450 side-chain cleavage. In addition, expression of extracellular matrix proteases essential for ovulation is compromised. These results demonstrate that Lrh1 is a regulator of multiple mechanisms essential for maturation of ovarian follicles and for ovulation. Lrh1 is therefore a key modulator of female fertility and a potential target for contraception.

Placenta defects and embryonic lethality resulting from disruption of mouse hydroxysteroid (17-beta) dehydrogenase 2 gene

Hydroxysteroid (17-beta) dehydrogenase 2 (HSD17B2) is a member of aldo-keto reductase superfamily, known to catalyze the inactivation of 17beta-hydroxysteroids to less active 17-keto forms and catalyze the conversion of 20alpha-hydroxyprogesterone to progesterone in vitro. To examine the role of HSD17B2 in vivo, we generated mice deficient in Hsd17b2 [HSD17B2 knockout (KO)] by a targeted gene disruption in embryonic stem cells. From the homozygous mice carrying the disrupted Hsd17b2, 70% showed embryonic lethality appearing at the age of embryonic d 11.5 onward. The embryonic lethality was associated with reduced placental size measured at embryonic d 17.5. The HSD17B2KO mice placentas presented with structural abnormalities in all three major layers: the decidua, spongiotrophoblast, and labyrinth. Most notable was the disruption of the spongiotrophoblast and labyrinthine layers, together with liquid-filled cysts in the junctional region and the basal layer. Treatments with an antiestrogen or progesterone did not rescue the embryonic lethality or the placenta defect in the homozygous mice. In hybrid background used, 24% of HSD17B2KO mice survived through the fetal period but were born growth retarded and displayed a phenotype in the brain with enlargement of ventricles, abnormal laminar organization, and increased cellular density in the cortex. Furthermore, the HSD17B2KO mice had unilateral renal degeneration, the affected kidney frequently appearing as a fluid-filled sac. Our results provide evidence for a role for HSD17B2 enzyme in the cellular organization of the mouse placenta.

Estrogen Deprivation and Inhibition of Breast Cancer Growth in Vivo through Activation of the Orphan Nuclear Receptor Liver X Receptor

Estrogen plays an important role in normal physiology. It is also a risk factor for breast cancer, and antiestrogen therapies have been shown to be effective in the treatment and prevention of breast cancers. The liver is important for estrogen metabolism, and a compromised liver function has been linked to hyperestrogenism in patients. In this report, we showed that the liver X receptor (LXR) controls estrogen homeostasis by regulating the basal and inducible hepatic expression of estrogen sulfotransferase (Est, or Sult1e1), an enzyme critical for metabolic estrogen deactivation. Genetic or pharmacological activation of LXR resulted in Est induction, which in turn inhibited estrogen-dependent uterine epithelial cell proliferation and gene expression, as well as breast cancer growth in a nude mouse model of tumorigenicity. We further established that Est is a transcriptional target of LXR, and deletion of the Est gene in mice abolished the LXR effect on estrogen deprivation. Interestingly, Est regulation by LXR appeared to be liver specific, further underscoring the role of liver in estrogen metabolism. Activation of LXR failed to induce other major estrogen-metabolizing enzymes, suggesting that the LXR effect on estrogen metabolism is Est specific. In summary, our results have revealed a novel mechanism controlling estrogen homeostasis in vivo and may have implications for drug development in the treatment of breast cancer and other estrogen-related cancerous endocrine disorders.

Low salinity acclimation and thyroid hormone metabolizing enzymes in gilthead seabream (Sparus auratus)

We investigated the effect of acclimation to low salinity water of gilthead seabream (Sparus auratus), a euryhaline seawater teleost, on the activities of thyroid hormone-metabolizing enzymes in gills, kidney, and liver. Following acclimation to low salinity water, the plasma free thyroxine (T(4)) concentration increases 2.5-fold, and outer ring deiodination activities towards T(4), 3,5,3'-triiodothyronine (T(3)) and 3,3',5'-triiodothyronine (reverse T(3), rT(3)) in the gills are reduced by 20-32%. Conjugation (catalyzed by sulfotransferase and UDP-glucuronyltransferase) and deconjugation pathways (arylsulfatase, beta-glucuronidase) play a role in the biological activity of native and conjugated thyroid hormones. Branchial, renal, and hepatic activities of the enzymes involved in these metabolic pathways respond differentially to low salinity conditions. The results substantiate that thyroid hormones are involved in S. auratus osmoregulation, and that the gills are well equipped to play an important role in the modulation of plasma hormone titers.

Platelet adhesion onto immobilized fibrinogen under arterial and venous in-vitro flow conditions does not significantly differ between men and women

Background

Gender-related differences in incidence of arterial thrombosis have been a focus of interest for years. The platelet integrin αIIbβ3 is primarily responsible for the interaction between platelets and fibrinogen and consecutive thrombus growth. In this study, we evaluated platelet adhesion onto immobilized fibrinogen under venous and arterial flow conditions in men and women.

Methods

Platelets in whole anticoagulated blood were labelled with the fluorescence dye Mepacrine and perfused through the rectangular flow chamber over glass cover slips coated with fibrinogen (shear rates of 50 s^-1, 500 s^-1 and 1500 s^-1). A fluorescence laser-scan microscope was used for visualisation and quantification of platelet adhesion at 15 seconds, 1 and 5 minutes after the start of perfusion.

Results

During perfusion, the platelet adhesion linearly increased in regard to exposition time and shear rate. After five minutes of perfusion the platelet adhesion onto immobilized fibrinogen showed no significant gender related difference, neither at 50 s^-1 nor at 500 s^-1 and 1500 s^-1 (p > 0.05), respectively. No significant difference in platelet adhesion onto immobilized fibrinogen, in regard to the menopausal status, was either observed (p > 0.05).

Conclusion

In our in vitro experimental system, hormonal differences between men and women did not influence platelet adhesion onto immobilized fibrinogen, neither under venous nor under arterial rheological conditions.

Molecular and biochemical characterization of two brassinosteroid sulfotransferases from Arabidopsis, AtST4a (At2g14920) and AtST1 (At2g03760)

Mammalian sulfotransferases (EC 2.8.2) are involved in many important facets of steroid hormone activity and metabolism. In this study, Arabidopsis AtST4a and AtST1 were identified and characterized as brassinosteroid sulfotransferases that appear to be involved in different aspects of hormone regulation. The two proteins share 44% identity in amino acid sequence, and belong to different plant sulfotransferase families. AtST4a was specific for biologically active end products of the brassinosteroid pathway. The enzyme sulfated brassinosteroids with diverse side-chain structures, including 24-epibrassinosteroids and the naturally occurring (22R, 23R)-28-homobrassinosteroids. AtST4a belongs to a small subfamily of sulfotransferases having two other members, AtST4b and -c. Among the three recombinant enzymes, only AtST4a was catalytically active with brassinosteroids. Transcript expression of AtST4 subfamily members was largely specific to the root. AtST4b- and -c transcript levels were induced by treatment with trans-zeatin, while AtST4a was repressed under the same conditions, supporting a divergent function of AtST4a. Co-regulation of AtST4b and -c correlated with their location in tandem on chromosome 1. AtST1 was stereospecific for 24-epibrassinosteroids, with a substrate preference for the metabolic precursor 24-epicathasterone, and exhibited catalytic activity with hydroxysteroids and estrogens. To gain more insight into this dual activity with plant and mammalian steroids, enzymatic activities of human steroid sulfotransferases toward brassinosteroids were characterized. The dehydroepiandrosterone sulfotransferase SULT2A1 displayed catalytic activity with a selected set of 24-epibrassinolide precursors, including 24-epicathasterone, with specific activities comparable to that measured for the endogenous substrate dehydroepiandrosterone. The comparable activity profiles of AtST1 and SULT2A1 suggest a similar architecture of the acceptor-binding site between the two enzymes, and may potentially reflect a common ability to conjugate certain xenobiotics.

Low expression of COX-2, reduced cumulus expansion, and impaired ovulation in SULT1E1-deficient mice

The SULT1E1-encoded estrogen sulfotransferase (EST) catalyzes sulfation of estrogen, resulting in its inactivation. Reduced fertility observed in SULT1E1 knockout (KO) female mice has previously been attributed to the deleterious effect of chronic exposure to high levels of circulating estrogen on placental function. We herein suggest that, in addition to placental dysfunction, this phenotype demonstrates that an excess of estrogen impairs ovulation. The role of SULT1E1 in ovulation is suggested by the substantially low ovulatory response in hCG-treated SULT1E1 KO mice; a similar effect was observed when 17beta-estradiol was administered to wild-type (WT) females. The normal rate of ovulation in SULT1E1 KO females may be restored by PGE2. Along this line, ovaries of human Chorionic Gonadotropin (hCG)-treated SULT1E1 KO mice expressed low levels of cyclooxygenase-2 (COX-2) and its downstream TSG6; moreover, their ovaries contained a reduced number of expanded cumuli. Our results demonstrate, for the first time, that estrogen inactivation may allow the expression of COX-2 and subsequent cumulus expansion, enabling normal ovulation. Our findings may be applied to novel treatments of human ovulatory failure.

Molecular cloning and characterization of the mouse Na+ sulfate cotransporter gene (Slc13a4): Structure and expression

Sulfate is an essential ion required for numerous functions in mammalian physiology. Due to its hydrophilic nature, cells require sulfate transporters on their plasma membranes to allow entry of sulfate into cells. In this study, we identified a new mouse Na(+)-sulfate cotransporter (mNaS2), characterized its tissue distribution and determined its cDNA and gene (Slc13a4) structures. mNaS2 mRNA was expressed in placenta, brain, lung, eye, heart, testis, thymus and liver. The mouse NaS2 cDNA spans 3384 nucleotides and its open frame encodes a protein of 624 amino acids. Slc13a4 maps to mouse chromosome 6B1 and contains 16 exons, spanning over 40 kb in length. Its 5'-flanking region contains CAAT- and GC-box motifs and a number of putative transcription factor binding sites, including GATA-1, MTF-1, STAT6 and HNF4 consensus sequences. This is the first study to define the tissue distribution of mNaS2 and resolve its cDNA and gene structures, which will allow us to investigate mNaS2 gene expression in vivo and determine its role in mammalian physiology.

Enzymatic reduction of oxysterols impairs LXR signaling in cultured cells and the livers of mice

Liver X receptors (LXRs) are nuclear receptors that play crucial roles in lipid metabolism in vivo and are activated by oxysterol ligands in vitro. The identity of the ligand that activates LXRs in vivo is uncertain. Here we provide two lines of evidence that oxysterols are LXR ligands in vitro and in vivo. First, overexpression of an oxysterol catabolic enzyme, cholesterol sulfotransferase, inactivates LXR signaling in several cultured mammalian cell lines but does not alter receptor response to the nonsterol agonist T0901317. Adenovirus-mediated expression of the enzyme in mice prevents dietary induction of hepatic LXR target genes by cholesterol but not by T0901317. Second, triple-knockout mice deficient in the biosynthesis of three oxysterol ligands of LXRs, 24S-hydroxycholesterol, 25-hydroxycholesterol, and 27-hydroxycholesterol, respond to dietary T0901317 by inducing LXR target genes in liver but show impaired responses to dietary cholesterol. We conclude that oxysterols are in vivo ligands for LXR.

Cellular Localization Studies on Human Estrogen Sulfotransferase SULT1E1 in Human Embryonic Kidney 293 Cells

Human cytosolic sulfotransferase SULT1E1 catalyzes the sulfation of endogenous estrogens as well as xenobiotic estrogen-like chemicals. This reaction increases the water solubility of the molecule, which may affect its cellular distribution and biological activity. This could alter estrogen signaling to the estrogen receptor in human estrogen receptor-positive cells. The current work characterized the cellular distribution of SULT1E1 in the human embryonic kidney 293 (HEK293) cell line using green fluorescent protein (GFP) tagging and immunochemistry methods. The GFP-tagged recombinant SULT1E1 protein was expressed and localized in the cytoplasm of HEK293 cells. By using a commercial anti-SULT1E1 peptide antibody, a 35.7-kDa protein was detected in HEK293 cells via Western blot. The molecular mass of the protein detected suggested that it may be related to native SULT1E1 protein. However, reverse transcription-polymerase chain reaction (RT-PCR) with gene-specific primers could not confirm the presence of the SULT1E1 transcript in the total RNA sample of HEK293 cells. The discrepancy between protein and transcript data could be due to the instability of SULT1E1 mRNA or the specificity of the anti-SULT1E1 antibody used. In the present work, RT-PCR analysis with gene-specific primers also identified a transcript fragment of human estrogen-related receptor gamma. Future studies on the functional relationship between estrogen-related receptors and sulfotransferases are expected to provide additional insights into the physiological and toxicological roles of human estrogen sulfotransferases.

Placental thrombosis and spontaneous fetal death in mice deficient in ethanolamine kinase 2

Ethanolamine kinase catalyzes the first step in the CDP-ethanolamine pathway for the formation of the major membrane phospholipid phosphatidylethanolamine (PtdEtn). In this work, the predicted Etnk2 cDNA was established as a soluble protein with ethanolamine-specific kinase activity that was most highly expressed in liver. Mice with an inactivated Etnk2 gene were derived, and its absence reduced the rate of PtdEtn synthesis from exogenous ethanolamine in hepatocytes. PtdEtn is a major precursor to phosphatidylcholine in liver; however, Etnk2(-/-) mice did not have reduced amounts of either PtdEtn or phosphatidylcholine or an altered phospholipid molecular species distribution. The knock-out animals were able to adapt to a choline-deficient diet. The Etnk2(-/-) mice exhibited a maternal-specific intrauterine growth retardation phenotype that resulted in a 33% reduction in litter size and frequent perinatal death. Histological analysis of pregnant Etnk2(-/-) females showed that fetal development failed at the late stage of pregnancy in a significant percentage of embryos because of the appearance of extensive placental thrombosis. These results illustrate a non-redundant role for EtnK2 expression in regulating placental hemostasis.

Thrombophilia and Recurrent Pregnancy Loss

Many unanswered questions regarding thrombophilia and recurrent pregnancy loss exist. For example, does a true association exist? Are thrombotic mechanisms relevant? Is a second messenger necessary to cause the manifestation of thrombosis? At present it seems that thrombophilia are associated with and may even cause some cases of pregnancy loss. The role of treatment remains to be determined. Although the aim of physicians working in this field is entirely laudable, to allow childless couples to have children, it is necessary to have good evidence of effect before treatment is given to all patients. A serious ethical dilemma remains, however, namely should treatment that may be effective be denied to patients who have prior pregnancy losses? Denial of treatment is extremely distressing for the patient and the physician. The author's own practice is to offer treatment after a full explanation, particularly because treatment is generally prescribed in the antiphospholipid syndrome and justified in hereditary thrombophilias according to the report of Carp and colleagues, showing a 25% improvement in live birth rates in treated patients. When treatment fails, however, the embryo should be karyotyped to exclude chromosomal aberrations.

Transcriptional profile reveals altered hepatic lipid and cholesterol metabolism in hyposulfatemic NaS1 null mice

Sulfate plays an essential role in human growth and development, and its circulating levels are maintained by the renal Na+-SO42- cotransporter, NaS1. We previously generated a NaS1 knockout (Nas1-/-) mouse, an animal model for hyposulfatemia, that exhibits reduced growth and liver abnormalities including hepatomegaly. In this study, we investigated the hepatic gene expression profile of Nas1-/- mice using oligonucleotide microarrays. The mRNA expression levels of 92 genes with known functional roles in metabolism, cell signaling, cell defense, immune response, cell structure, transcription, or protein synthesis were increased (n = 51) or decreased (n = 41) in Nas1-/- mice when compared with Nas1+/+ mice. The most upregulated transcript levels in Nas1-/- mice were found for the sulfotransferase genes, Sult3a1 (approximately 500% increase) and Sult2a2 (100% increase), whereas the metallothionein-1 gene, Mt1, was among the most downregulated genes (70% decrease). Several genes involved in lipid and cholesterol metabolism, including Scd1, Acly, Gpam, Elov16, Acsl5, Mvd, Insig1, and Apoa4, were found to be upregulated (> or = 30% increase) in Nas1-/- mice. In addition, Nas1-/- mice exhibited increased levels of hepatic lipid (approximately 16% increase), serum cholesterol (approximately 20% increase), and low-density lipoprotein (approximately 100% increase) and reduced hepatic glycogen (approximately 50% decrease) levels. In conclusion, these data suggest an altered lipid and cholesterol metabolism in the hyposulfatemic Nas1-/- mouse and provide new insights into the metabolic state of the liver in Nas1-/- mice.

Variation in commercial rodent diets induces disparate molecular and physiological changes in the mouse uterus

Although ovarian estrogen, estradiol-17beta, is a key modulator of normal reproductive functions, natural and synthetic compounds with estrogen-like activities can further influence reproductive functions. Plant-derived phytoestrogens specifically have received much attention because of associated health benefits. However, a comprehensive understanding of the beneficial and/or detrimental impacts of phytoestrogen consumption through commercial rodent diets on uterine biology and early pregnancy at the molecular level remains largely unexplored. Using multiple approaches, we demonstrate here that exposure of adult female mice to a commercial rodent diet with higher phytoestrogen levels facilitates uterine growth in the presence or absence of ovarian estrogen, alters uterine expression of estrogen-responsive genes, and advances the timing of implantation compared with a diet with lower phytoestrogen levels. The finding that variability in phytoestrogen content in commercial rodent diets, both within and between brands, influences experimental results stresses the importance of this investigation and raises caution for investigators using rodents as animal models.