Hormonal regulation of rat 17 beta-hydroxysteroid dehydrogenase type 1 in cultured rat granulosa cells: effects of recombinant follicle-stimulating hormone, estrogens, androgens, and epidermal growth factor

The Nrf2/ARE pathway as a potential target to ameliorate atrazine-induced endocrine disruption in granulosa cells

Atrazine (ATR) is widely used worldwide as a commercial herbicide, Diaminochlorotriazine (DACT) is the main metabolite of ATR in the organism. Both of them disrupt the production of steroids and induce abnormal reproductive development. The granulosa cells (GCs) are important for growth and reproduction of animals. However, the toxicity of ATR on the GCs of birds is not well clarified. To evaluate the effect of the environmental pollutant ATR on bird GCs. The quail GCs were allotted into 7 groups, C (The medium of M199), A20 (20 µM ATR), A100 (100 µM ATR), A250 (250 µM ATR), D20 (20 µM DACT), D100 (100 µM DACT) and D200 (200 µM DACT). The results demonstrated that ATR reduced the viability of GCs, disrupted mitochondrial structure (including mitochondrial cristae fragmentation and the mitochondrial morphology disappearance) and decreased mitochondrial membrane potential. Meanwhile, ATR interfered with the expression of key factors in the steroid synthesis pathway, inducing the secretion of the sex hormones E2 and P in GCs. which in turn induced apoptosis. Furthermore, the Nrf2/ARE pathway as a potential target to ameliorate ATR-induced endocrine disruption in GCs for proper reproductive functions. Our research provides a new perspective for understanding the effects of ATR on reproductive functions in birds.

Transcriptome analysis during 4-vinylcyclohexene diepoxide exposure-induced premature ovarian insufficiency in mice

The occupational chemical 4-Vinylcyclohexene diepoxide (VCD) is a reproductively toxic environmental pollutant that causes follicular failure, leading to premature ovarian insufficiency (POI), which significantly impacts a woman's physical health and fertility. Investigating VCD's pathogenic mechanisms can offer insights for the prevention of ovarian impairment and the treatment of POI. This study established a mouse model of POI through intraperitoneal injection of VCD into female C57BL/6 mice for 15 days. The results were then compared with those of the control group, including a comparison of phenotypic characteristics and transcriptome differences, at two time points: day 15 and day 30. Through a comprehensive analysis of differentially expressed genes (DEGs), key genes were identified and validated some using RT-PCR. The results revealed significant impacts on sex hormone levels, follicle number, and the estrous cycle in VCD-induced POI mice on both day 15 and day 30. The DEGs and enrichment results obtained on day 15 were not as significant as those obtained on day 30. The results of this study provide a preliminary indication that steroid hormone synthesis, DNA damage repair, and impaired oocyte mitosis are pivotal in VCD-mediated ovarian dysfunction. This dysfunction may have been caused by VCD damage to the primordial follicular pool, impairing follicular development and aggravating ovarian damage over time, making it gradually difficult for the ovaries to perform their normal functions.

Alterations of estrous cycle, 3β hydroxysteroid dehydrogenase activity and progesterone synthesis in female rats after exposure to hypobaric hypoxia

The underlying mechanism regulating hypoxia induced alteration in female steroid hormones is first time explored in this study. To understand the mechanistic approach, female Sprague- Dawley rats were exposed to acute and chronic hypobaric hypoxia (282 mm-Hg, ~7620 m, 6 hours, 3 and 7 days). Estrous cycle, body weight, plasma progesterone and estradiol levels, morphology, histology and two key steroidogenic enzymes: 3ß hydroxysteroid dehydrogenase (HSD) and 17ß HSD activity of ovary and adrenal gland were studied. A persistent diestrous phase and a significant decrease in body weight were found in chronic hypoxia groups. Histological study suggested degenerative changes in ovarian corpus luteum of 7 days chronic hypobaric hypoxia (7CHH) group and a declined percentage of adrenocortical cells in 3 days chronic hypobaric hypoxia (3CHH) and 7CHH groups. Plasma estradiol level was unaltered, but progesterone level was decreased significantly in all hypoxic groups. Ovarian 3ß HSD activity was decreased significantly with increasing days of hypoxic treatment along with a significantly low adrenal 3ß HSD activity in 7CHH. In conclusion, hypobaric hypoxia causes a state of low circulatory progesterone level in females likely due to the degenerative changes in the female ovarian and adrenal tissues together with low steroidogenic 3ß HSD enzyme activity.

Role of hydroxysteroid (17beta) dehydrogenase type 1 in reproductive tissues and hormone-dependent diseases

Abnormal synthesis and metabolism of sex steroids is involved in the pathogenesis of various human diseases, such as endometriosis and cancers arising from the breast and uterus. Steroid biosynthesis is a multistep enzymatic process proceeding from cholesterol to highly active sex steroids via different intermediates. Human Hydroxysteroid (17beta) dehydrogenase 1 (HSD17B1) enzyme shows a high capacity to produce the highly active estrogen, estradiol, from a precursor hormone, estrone. However, the enzyme may also play a role in other steps of the steroid biosynthesis pathway. In this article, we have reviewed the literature on HSD17B1, and summarize the role of the enzyme in hormone-dependent diseases in women as evidenced by preclinical studies.

Expression of genes controlling steroid metabolism and action in granulosa-lutein cells of women with polycystic ovaries

INTRODUCTION

Aberrant function of granulosa cells has been implicated in the pathophysiology of PCOS.

MATERIALS & METHODS

Granulosa lutein (GL) cells were collected during oocyte retrieval for IVF/ICSI. RT-qPCR was used to compare gene expression between 12 control women, 12 with ovulatory PCO and 12 with anovulatory PCOS. To examine which genes are directly regulated by androgens, GL cells from an additional 12 control women were treated in-vitro with 10 nM dihydrotestosterone (DHT).

RESULTS

GL cells from women with PCOS showed reduced expression of CYP11A1 3-fold (p = 0.005), HSD17B1 1.8-fold (p = 0.02) and increased expression of SULT1E1 7-fold (p = 0.0003). Similar results were seen in ovulatory women with PCO. GL cells treated with 10 nM DHT showed a 4-fold (p = 0.03) increase in expression of SULT1E1 and a 5-fold reduction in SRD5A1 (p = 0.03).

CONCLUSIONS

These findings support the notion that aberrant regulation of steroid metabolism or action play a part in ovarian dysfunction in PCOS.

Di-(2-ethylhexyl) phthalate (DEHP) inhibits steroidogenesis and induces mitochondria-ROS mediated apoptosis in rat ovarian granulosa cells

Increased oxidative stress (OS) due to ubiquitous exposure to di-(2-ethylhexyl) phthalate (DEHP) can affect the quality of oocytes by inducing apoptosis and hampering granulosa cell mediated steroidogenesis. This study was carried out to investigate whether DEHP induced OS affects steroidogenesis and induces apoptosis in rat ovarian granulosa cells. OS was induced by exposing granulosa cells to various concentrations of DEHP (0.0, 100, 200, 400 and 800 μM) for 72 h in vitro. Intracellular reactive oxygen species (ROS), oxidative stress (OS), mitochondrial membrane potential, cellular senescence, apoptosis, steroid hormones (estradiol & progesterone) and gene expression were analyzed. The results showed that an effective dose of DEHP (400 μg) significantly increased OS by elevating the ROS level, mitochondrial membrane potential, and β-galactosidase activity with higher mRNA expression levels of apoptotic genes (Bax, cytochrome-c and caspase3) and a lower level of an anti-apoptotic gene (Bcl₂) as compared to the control. Further, DEHP significantly (P > 0.05) decreased the level of steroid hormones (estradiol and progesterone) in a conditioned medium and this effect was reciprocated with a lower expression (P > 0.05) of steroidogenic responsive genes (Cyp11a1, Cyp19A1, Star, ERβ1) in treated granulosa cells. Furthermore, co-treatment with N-Acetyl-Cysteine (NAC) rescues the effects of DEHP on OS, ROS, β-galactosidase levels and gene expression activities. Altogether, these results suggest that DEHP induces oxidative stress via ROS generation and inhibits steroid synthesis via modulating steroidogenic responsive genes, which leads to the induction of apoptosis through the activation of Bax/Bcl-2-cytochrome-c and the caspase-3-mediated mitochondrial apoptotic pathway in rat granulosa cells.

Estrogen biosynthesis in breast adipose tissue during menstrual cycle in women with and without breast cancer

Circulating estrogens fluctuate during the menstrual cycle but it is not known whether this fluctuation is related to local hormone levels in adipose tissue. We analyzed estrogen concentrations and gene expression of estrogen-regulating enzymes in breast subcutaneous adipose tissue in premenopausal women with (n = 11) and without (n = 17) estrogen receptor-positive breast cancer. Estrone (E₁) was the predominant estrogen in premenopausal breast adipose tissue, and E₁ and mRNA expression of CYP19A1 in adipose tissue correlated positively with BMI. Adipose tissue estradiol (E₂) concentrations fluctuated during the menstrual cycle, similarly to the serum concentrations. In women with breast cancer median adipose tissue E₁ (1519 vs. 3244, p < .05) and E₂ (404 vs. 889 pmol/kg, p < .05) levels were lower in the follicular than in the luteal phase whereas in control women no significant differences were observed. In the follicular phase, mRNA expressions of HSD17B1 (median 0.06; interquartile range 0.05-0.07 vs. 0.17; 0.03-0.2, p = .010) and CYP19A1 (0.08; 0.07-0.14 vs. 0.22; 0.09-0.54, p = .025) were lower in women with breast cancer than in controls. In conclusion, the changes in adipose tissue E₁ and E₂ concentrations and the estrogen-regulating CYP19A1 and HSD17B1 during the menstrual cycle may be related to dysfunctional local estrogen metabolism in women with breast cancer.

Deleting the mouse Hsd17b1 gene results in a hypomorphic Naglu allele and a phenotype mimicking a lysosomal storage disease

HSD17B1 is a steroid metabolising enzyme. We have previously generated knockout mice that had the entire coding region of Hsd17b1 replaced with lacZ-neo cassette (Hsd17b1-LacZ/Neo mice). This resulted in a 90% reduction of HSD17B1 activity, associated with severe subfertility in the knockout females. The present study indicates that Hsd17b1-LacZ/Neo male mice have a metabolic phenotype, including reduced adipose mass, increased lean mass and lipid accumulation in the liver. During the characterisation of this metabolic phenotype, it became evident that the expression of the Naglu gene, located closely upstream of Hsd17b1, was severely reduced in all tissues analysed. Similar results were obtained from Hsd17b1-LacZ mice after removing the neo cassette from the locus or by crossing the Hsd17b1-LacZ/Neo mice with transgenic mice constitutively expressing human HSD17B1. The deficiency of Naglu caused the accumulation of glycosaminoglycans in all studied mouse models lacking the Hsd17b1 gene. The metabolic phenotypes of the Hsd17b1 knockout mouse models were recapitulated in Naglu knockout mice. Based on the data we propose that the Hsd17b1 gene includes a regulatory element controlling Naglu expression and the metabolic phenotype in mice lacking the Hsd17b1 genomic region is caused by the reduced expression of Naglu rather than the lack of Hsd17b1.

Diethylstilbestrol administration inhibits theca cell androgen and granulosa cell estrogen production in immature rat ovary

Diethylstilbestrol (DES), a strong estrogenic compound, is well-known to affect the reproductive system. In this study, we investigated the effects of DES administration on gonadotropin levels and ovarian steroidogenesis in prepubertal rats. DES treatment acutely reduced serum LH levels, followed by a reduction in the expression of various steroidogenesis-related genes in theca cells. Serum FSH levels were almost unaffected by DES-treatment, even though Cyp19a1 expression was markedly reduced. Serum progesterone, testosterone and estradiol levels were also declined at this time. LH levels recovered from 12 h after DES-treatment and gradually increased until 96 h with a reduction of ERα expression observed in the pituitary. Steroidogenesis-related genes were also up-regulated during this time, except for Cyp17a1 and Cyp19a1. Consistent with observed gene expression pattern, serum testosterone and estradiol concentrations were maintained at lower levels, even though progesterone levels recovered. DES-treatment induced the inducible nitric oxide synthase (iNOS) in granulosa cells, and a nitric oxide generator markedly repressed Cyp19a1 expression in cultured granulosa cells. These results indicate that DES inhibits thecal androgen production via suppression of pituitary LH secretion and ovarian Cyp17a1 expression. In addition, DES represses Cyp19a1 expression by inducing iNOS gene expression for continuous inhibition of estrogen production in granulosa cells.

rFSH in medically assisted procreation: Evidence for ovarian follicular hyperplasia and interest of mass spectrometry to measure 17-hydroxyprogesterone and Δ4-androstenedione in serum

Ovarian monitoring requires the determination of serum estradiol and progesterone levels. We investigated whole follicular steroidogenesis under rFSH in medically assisted procreation (MAP: 26 IVF, 24 ICSI) compared to 11 controls (IUI). Estrone, estradiol, Δ4-androstenedione, testosterone, progesterone and 17-hydroxyprogesterone were measured by immunoassay and mass spectrometry except for estrogens. At the start of a spontaneous or induced cycle, steroids levels fluctuated within normal ranges: estradiol (314-585 pmol/L), estrone (165-379 pmol/L) testosterone (1.3-1.6 nmol/L), Δ4-androstenedione (4.5-5.6 nmol/L), 17-hydroxyprogesterone (2.1-2.2 nmol/L) and progesterone (1.8-1.9 nmol/L). 17-hydroxyprogesterone, Δ 4-androstenedione and estradiol predominated. Then estradiol and oestrone levels rise, but less markedly for oestrone in IUI. In MAP, rFSH injections induce a sharp increase in estrogens associated with a rise in 17-hydroxyprogesterone and Δ4-androstenedione levels, disrupting oestrogen/androgen ratios. rFSH stimulation induces an ovarian hyperplasia and Δ4pathway which could become abnormal. Determining 17-hydroxyprogesterone and Δ4-androstenedione levels with LC-MS/MS may therefore be useful in managing recurrent MAP failures.

Reproductive and Developmental Toxicity of Arsenic in Rodents: A Review

Arsenic is a recognized reproductive toxicant in humans and induces malformations, especially neural tube defects, in laboratory animals. Early studies showed that murine malformations occurred only when a high dose of inorganic arsenic was given by intravenous or intraperitoneal injection in early gestation. Oral gavage of inorganic arsenic at maternally toxic doses caused reduced fetal body weight and increased resorptions. Recently, arsenic reproductive and developmental toxicity has been studied in situations more similar to human exposures and using broader endpoints, such as behavioral changes and gene expression. For the general population, exposure to arsenic is mostly oral, particularly via drinking water, repeated and prolonged over time. In mice and rats, methylated or inorganic arsenic via drinking water or by repeated oral gavage induced male and female reproductive and developmental toxicities. Furthermore, at nonmaternally toxic levels, inorganic arsenic given to pregnant dams via drinking water affected fetal brain development and postnatal behaviors. However, arsenic given by repeated oral gavage to pregnant mice and rats was not morphologically teratogenic. In this review of arsenic reproductive and developmental toxicity in rats and mice, the authors summarize recent in vivo studies and discuss possible underlying mechanisms. The influences of folate, selenium, zinc, and arsenic methylation on arsenic reproductive and developmental toxicity are also discussed.

The impact of testosterone, tibolone and black cohosh on purified mammary and placental 17β-hydroxysteroid dehydrogenase type 1

CONTEXT

Mammary and placental 17β-hydroxysteroid dehydrogenase type 1 (17βHSD1).

OBJECTIVE

To assess the impact of testosterone, tibolone, and black cohosh on purified mammary and placental 17βHSD1.

MATERIALS AND METHODS

17βHSD1 was purified from human mammary gland and placenta by column chromatography, its activity was monitored by a radioactive activity assay, and the degree of purification was determined by gel electrophoresis. Photometric cofactor transformation analysis was performed to assess 17βHSD1 activity without or in presence of testosterone, tibolone and black cohosh.

RESULTS

17βHSD1 from both sources displayed a comparable basal activity. Testosterone and tibolone metabolites inhibited purified mammary and placental 17βHSD1 activity to a different extent, whereas black cohosh had no impact.

DISCUSSION

Studies on purified enzymes reveal the individual action of drugs on local regulatory mechanisms thus helping to develop more targeted therapeutic intervention.

CONCLUSION

Testosterone, tibolone and black cohosh display a beneficial effect on local mammary estrogen metabolism by not affecting or decreasing local estradiol exposure.

Dioxin exposure reduces the steroidogenic capacity of mouse antral follicles mainly at the level of HSD17B1 without altering atresia

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent ovarian toxicant. Previously, we demonstrated that in vitro TCDD (1nM) exposure decreases production/secretion of the sex steroid hormones progesterone (P4), androstenedione (A4), testosterone (T), and 17β-estradiol (E2) in mouse antral follicles. The purpose of this study was to determine the mechanism by which TCDD inhibits steroidogenesis. Specifically, we examined the effects of TCDD on the steroidogenic enzymes, atresia, and the aryl hydrocarbon receptor (AHR) protein. TCDD exposure for 48h increased levels of A4, without changing HSD3B1 protein, HSD17B1 protein, estrone (E1), T or E2 levels. Further, TCDD did not alter atresia ratings compared to vehicle at 48h. TCDD, however, did down regulate the AHR protein at 48h. TCDD exposure for 96h decreased transcript levels for Cyp11a1, Cyp17a1, Hsd17b1, and Cyp19a1, but increased Hsd3b1 transcript. TCDD exposure particularly lowered both Hsd17b1 transcript and HSD17B1 protein. However, TCDD exposure did not affect levels of E1 in the media nor atresia ratings at 96h. TCDD, however, decreased levels of the proapoptotic factor Bax. Collectively, these data suggest that TCDD exposure causes a major block in the steroidogenic enzyme conversion of A4 to T and E1 to E2 and that it regulates apoptotic pathways, favoring survival over death in antral follicles. Finally, the down-regulation of the AHR protein in TCDD exposed follicles persisted at 96h, indicating that the activation and proteasomal degradation of this receptor likely plays a central role in the impaired steroidogenic capacity and altered apoptotic pathway of exposed antral follicles.

The molecular control of corpus luteum formation, function, and regression

The corpus luteum (CL) is one of the few endocrine glands that forms from the remains of another organ and whose function and survival are limited in scope and time. The CL is the site of rapid remodeling, growth, differentiation, and death of cells originating from granulosa, theca, capillaries, and fibroblasts. The apparent raison d'etre of the CL is the production of progesterone, and all the structural and functional features of this gland are geared toward this end. Because of its unique importance for successful pregnancies, the mammals have evolved a complex series of checks and balances that maintains progesterone at appropriate levels throughout gestation. The formation, maintenance, regression, and steroidogenesis of the CL are among the most significant and closely regulated events in mammalian reproduction. During pregnancy, the fate of the CL depends on the interplay of ovarian, pituitary, and placental regulators. At the end of its life span, the CL undergoes a process of regression leading to its disappearance from the ovary and allowing the initiation of a new cycle. The generation of transgenic, knockout and knockin mice and the development of innovative technologies have revealed a novel role of several molecules in the reprogramming of granulosa cells into luteal cells and in the hormonal and molecular control of the function and demise of the CL. The current review highlights our knowledge on these key molecular events in rodents.

The intraovarian actions of estrogen receptor-alpha are necessary to repress the formation of morphological and functional Leydig-like cells in the female gonad

The predisposition of the testis and ovary to primarily synthesize testosterone (T) and estradiol (E2), respectively, is due to gonadal-specific cell types that differentially express the various hydroxysteroid (17beta) dehydrogenase (HSD17B) isoforms. In testes, Leydig cells rely on LH stimulation to maintain expression of the type 3 (HSD17B3) isoform, which specifically converts androstenedione to T. In ovaries, thecal interstitial (TI) cells also rely on LH to induce androgen synthesis but lack HSD17B3 and therefore secrete androgens of low biological activity. Therefore, thecal cells may possess a mechanism to repress the Leydig cell phenotype and HSD17B3 expression. E2 is known to inhibit experimentally Leydig cell function and proliferation. In the current study, we provide evidence that E2 prevents the development of functional Leydig-like cells in the murine ovary and that this action is mediated by estrogen receptor (ER) alpha. ERalpha-null (alphaERKO) female mice exhibit testis-like levels of Hsd17b3 expression in the ovaries and male-like levels of plasma T. Herein, we demonstrate that: 1) Hsd17b3 expression in alphaERKO ovaries is a primary effect of the loss of intraovarian ERalpha actions; 2) alphaERKO ovarian cells produce substantial levels of T in vitro, and this is blocked by a HSD17B3-specific inhibitor; 3) Hsd17b3 expression in alphaERKO ovaries is LH regulated and localized to the secondary interstitial (SI)/TI cells; and 4) alphaERKO SI/TI cells possess Leydig-like ultrastructural features. These data indicate that intraovarian ERalpha actions are required to repress Hsd17b3 expression in the ovary and may be important to maintaining a female phenotype in SI/TI cells.

The effects of estrogen on the expression of genes underlying the differentiation of somatic cells in the murine gonad

Estrogen (17beta-estradiol, E2)-deficient aromatase knockout (ArKO) mice develop Sertoli and Leydig cells at puberty. We hypothesized that estrogen, directly or indirectly, regulates genes responsible for somatic cell differentiation and steroidogenesis. ArKO ovaries expressed estrogen receptors alpha and beta, and LH receptor, indices of estrogen responsiveness in the ovary. Wild-type (Wt) and ArKO mice received either E2 or placebo for 3 wk, from 7-10 wk of age. E2 decreased serum FSH and LH and increased uterine weights of 10-wk-old ArKO mice. We measured mRNA expression of Sertoli cell, Sry-like HMG box protein 9 (Sox9); three upstream transcription factors, liver receptor homolog-1 (Lrh-1), steroidogenic factor 1, and dosage-sensitive sex reversal adrenal hypoplasia congenital critical region on the X chromosome gene 1; and one downstream factor, Müllerian-inhibiting substance. Placebo-treated ArKO ovaries have increased Sox9 (15-fold; P < 0.001), Müllerian-inhibiting substance (2.9-fold), Lrh-1 (7.7-fold), and dosage-sensitive sex reversal adrenal hypoplasia congenital critical region on the X chromosome gene 1 (12-fold) expression compared with Wt at 10 wk. Steroidogenic factor 1 was similar to Wt. Consistent with increased serum T levels and Leydig cells in their ovaries, placebo-treated ArKO ovaries had increased 17alpha-hydroxylase, 17beta-hydroxysteroid dehydrogenase type-3, and 17beta-hydroxysteroid dehydrogenase type-1 expression compared with Wt at 10 wk. E2 treatment for 3 wk improved the ovarian phenotype, decreased development of Sertoli cells, decreased the expression of Sox9, Lrh-1, and the steroidogenic enzymes in ArKO ovaries, and induced ovulation in some cases. In conclusion, the expression of the genes regulating somatic cell differentiation is directly or indirectly responsive to estrogen.

Characterization of the hypothalamic-pituitary-gonadal axis in estrogen receptor (ER) Null mice reveals hypergonadism and endocrine sex reversal in females lacking ERalpha but not ERbeta

To determine the role of each estrogen receptor (ER) form (ERalpha, ERbeta) in mediating the estrogen actions necessary to maintain proper function of the hypothalamic-pituitary-gonadal axis, we have characterized the hypothalamic-pituitary-gonadal axis in female ER knockout (ERKO) mice. Evaluation of pituitary function included gene expression assays for Gnrhr, Cga, Lhb, Fshb, and Prl. Evaluation of ovarian steroidogenic capacity included gene expression assays for the components necessary for estradiol synthesis: i.e. Star, Cyp11a, Cyp17, Cyp19, Hsd3b1, and Hsd17b1. These data were corroborated by assessing plasma levels of the respective peptide and steroid hormones. alphaERKO and alphabetaERKO females exhibited increased pituitary Cga and Lhb expression and increased plasma LH levels, whereas both were normal in betaERKO. Pituitary Fshb expression and plasma FSH were normal in all three ERKOs. In the ovary, all three ERKOs exhibited normal expression of Star, Cyp11a, and Hsd3b1. In contrast, Cyp17 and Cyp19 expression were elevated in alphaERKO but normal in betaERKO and alphabetaERKO. Plasma steroid levels in each ERKO mirrored the steroidogenic enzyme expression, with only the alphaERKO exhibiting elevated androstenedione and estradiol. Elevated plasma testosterone in alphaERKO and alphabetaERKO females was attributable to aberrant expression of Hsd17b3 in the ovary, representing a form of endocrine sex reversal, as this enzyme is unique to the testes. Enhanced steroidogenic capacity in alphaERKO ovaries was erased by treatment with a GnRH antagonist, indicating these phenotypes to be the indirect result of excess LH stimulation that follows the loss of ERalpha in the hypothalamic-pituitary axis. Overall, these findings indicate that ERalpha, but not ERbeta, is indispensable to the negative-feedback effects of estradiol that maintain proper LH secretion from the pituitary. The subsequent hypergonadism is illustrated as increased Cyp17, Cyp19, Hsd17b1, and ectopic Hsd17b3 expression in the ovary.

Bone morphogenetic protein-15 inhibits follicle-stimulating hormone (FSH) action by suppressing FSH receptor expression

We have recently reported that oocyte-derived bone morphogenetic protein-15 (BMP-15) can directly modulate follicle-stimulating hormone (FSH) action in rat granulosa cells. Here, we investigate underlying mechanisms of this BMP-15 effect. Treatment with BMP-15 alone exerted no significant effect on the basal expression of mRNAs encoding steroidogenic acute regulatory protein, P450 side chain cleavage enzyme, P450 aromatase, 3beta-hydroxysteroid dehydrogenase, luteinization hormone receptor, and inhibin/activin subunits. However, BMP-15 markedly inhibited the FSH-induced increases in these messages. In striking contrast, BMP-15 did not change the forskolin-induced levels of these transcripts. Thus, the inhibitory effect of BMP-15 on FSH action must be upstream of cAMP signaling. We next examined changes in FSH receptor mRNA expression. Interestingly, BMP-15 severely reduced the levels of FSH receptor mRNA in both basal and FSH-stimulated cells. To determine whether this effect was at the level of FSH function, we investigated the effect of BMP-15 on FSH bioactivity. Consistent with the mRNA data, BMP-15 inhibited the biological response of FSH, but not that of forskolin. Based on these results, we propose that BMP-15 is an important determinant of FSH action through its ability to inhibit FSH receptor expression. Because FSH plays an essential role in follicle growth and development, our findings could have new implications for understanding how oocyte growth factors contribute to folliculogenesis.

Developmental regulation of effect of epidermal growth factor on porcine oocyte-cumulus cell complexes: nuclear maturation, expansion, and F-actin remodeling

Epidermal growth factor (EGF) efficiently stimulates expansion of mouse and rat oocyte-cumulus complexes (OCC). Contradictory data have been published by several laboratories about the ability of EGF to stimulate expansion of porcine OCC. We assumed that these contradictions may have resulted from heterogeneous conditions used for isolation, culture, and assessment of OCC. The present experiments were designed to test the hypothesis that porcine OCC acquire the ability to synthesize hyaluronic acid (HA) and undergo expansion following EGF-stimulation gradually during the growth of follicles. For this reason, we isolated OCC from follicles of different sizes and assessed quantity of produced HA and proportions of expanding OCC after stimulation by EGF. In addition, we assessed in those OCC changes in morphology of cumulus cells and assembly of F-actin microfilaments, which are necessary for expansion to occur. Finally, nuclear maturation of EGF-stimulated OCC was assessed and its relationship with occurrence of expansion was evaluated. In all experiments, OCC stimulated with FSH were used as positive controls. The results showed that EGF did not stimulate production of HA, rearrangement of F-actin and expansion in OCC isolated from small follicles (<4 mm in diameter). OCC isolated from large preovulatory follicles (6-7 mm in diameter and PMSG-stimulated follicles) underwent efficient expansion when stimulated by EGF (93% and 100%, respectively). EGF dramatically stimulated total production of HA in these OCC and its retention in extracellular matrix of the expanding cumulus. Cumulus cells of the large OCC underwent essential changes of their morphology and extensive rearrangement of F-actin microfilaments following stimulation with EGF. Interestingly, EGF enhanced nuclear maturation of OCC isolated from both small and large follicles, which suggest diversity of signaling pathways controlling maturation and expansion. FSH caused cumulus expansion, F-actin remodeling, and enhancement of oocyte nuclear maturation in OCC originated from both small and large follicles. We conclude that EGF can stimulate expansion of porcine OCC in vitro; however, only of those isolated from large follicles. This indicates that EGF may have a physiological role in regulation of porcine cumulus expansion in preovulatory follicles, presumably as a mediator of signals elicited by the LH surge.

Identification of essential subelements in the hHSD17B1 enhancer: difference in function of the enhancer and that of the hHSD17BP1 analog is due to -480C and -486G

The function of the gene encoding human 17beta-hydroxysteroid dehydrogenase (17HSD) type 1, the hHSD17B1 gene, is regulated by a cell-specific enhancer at position -662 to -392. The adjacent hHSD17BP1 gene, whose function is not known, contains an analogous region in its 5'-flanking region. The identity between the hHSD17B1 enhancer and the hHSD17BP1 equivalent is as high as 98%, i.e. they differ by only five nucleotides. Results from reporter gene analyses showed that the hHSD17BP1 analog, a pseudoenhancer, has only 10% the activity of the hHSD17B1 enhancer. Furthermore, the results indicate that the reduced function of the pseudoenhancer is a consequence of the presence of G and A at positions -480 and -486, whereas the hHSD17B1 enhancer contains -480C and -486G. In addition, three protected areas were localized to regions -495/-485 (FP1), -544/-528 (FP2), and -589/-571 (FP3) in deoxyribonuclease I footprinting analysis of the hHSD17B1 enhancer. Replacement of the footprinted regions with a nonsense sequence demonstrated that the FP2 region is the most critical for enhancer activity. Mutations of FP2 or a short palindromic region within it led to almost complete abolishment of enhancer activity. We have identified several subelements that are essential for appropriate function of the hHSD17B1 enhancer. The results also show that the hHSD17B1 and hHSD17BP1 genes operate differently despite the high homology between them.

Diverse effects of tyrosine kinase inhibitors on follicle-stimulating hormone-stimulated estradiol and progesterone production from rat granulosa cells in serum-containing medium and serum-free medium containing epidermal growth factor

Epidermal growth factor (EGF) has been shown to influence FSH-stimulated estradiol (E2) and progesterone (P4) production from granulosa cells. RG 50810, a tyrosine kinase inhibitor (TKI), has previously been shown to inhibit the EGF-receptor tyrosine kinase. RG 50810 has also been shown to inhibit FSH-stimulated increases in mRNA for steroidogenic enzymes, implying a functional role of tyrosine kinases in FSH action in granulosa cells. However, inhibition of FSH-stimulated steroidogenesis by TKIs has not been evaluated in connection with the effects of EGF in granulosa cells. In the present studies, FSH-stimulated E2 production was inhibited similarly by inhibitors of protein kinase A (H-89) and protein kinase C (calphostin C) and by TKIs, and none of the inhibitors were capable of reversing the EGF-induced inhibition of FSH-stimulated E2 production. FSH-stimulated P4 production was enhanced dramatically in serum-containing medium with concentrations of TKI that were near previously reported IC50s. The enhancing effect of TKIs was less evident in serum-free medium. Addition of EGF to serum-free medium enhanced FSH-stimulated P4 production, and the TKIs reversed EGF-enhanced P4 production, but in a manner similar to that of protein kinase A inhibitor H-89. Compared to results in serum-free medium, the potency of RG 50810 and genistein to inhibit the effects of EGF on P4 production was 3- to 8-fold greater relative to H-89. These studies have demonstrated that TKIs RG 50810 and genistein selectively inhibit the effects of EGF on FSH-stimulated P4 production in granulosa cell cultures. In contrast, these studies have demonstrated nonselective inhibition of FSH-stimulated E2 and P4 production by TKIs in serum-free medium, in which it is not clear which enzyme system is affected by the compounds tested.

Oxidative activity of the type 2 isozyme of 17beta-hydroxysteroid dehydrogenase (17beta-HSD) predominates in human sebaceous glands

Sebum production is regulated by the opposing effects of androgens and estrogens. The intracrine activity of steroid metabolizing enzymes is important in regulating sebum production because these enzymes can convert weak steroids from the serum into potent androgens and estrogens within the sebaceous gland (SG). 17Beta-hydroxysteroid dehydrogenase (17beta-HSD) interconverts weak and potent sex steroids via redox reactions. In this regard, it may function as a gatekeeping enzyme regulating the hormonal milieu of the SG. Six isozymes of 17beta-HSD have been identified that differ in their substrate preference and their preference to produce weak or potent sex steroids via oxidation or reduction, respectively. The goals of this study are: (i) to identify which isozyme (s) of 17beta-HSD is active in SG; (ii) to determine if its activity differs in facial skin compared with nonacne-prone skin that may account for the regional differences in sebum production; (iii) to compare the activity of 17beta-HSD in intact glands and in SG homogenates; and (iv) to determine if 13-cis retinoic acid inhibits 17beta-HSD activity. Human SG were assayed for 17beta-HSD activity using estrogens, androgens, and progestins as substrates. Oxidative activity of the type 2 isozyme predominated in all samples tested. Although transcripts for the types 1, 2, 3, and 4 isozymes were detected using reverse transcriptase-polymerase chain reaction, only mRNA for the predominant type 2 isozyme and the type 4 isozyme were detected in northern analysis. Greater reductive activity of 17beta-HSD was noted in SG from facial areas compared with nonacne-prone areas, suggesting an increased net production of potent androgens in facial areas. Oxidation was more predominant over reduction in intact SG compared with homogenized SG, thus supporting the hypothesis that 17beta-HSD protects against the effects of potent androgens in vivo. Activity of the type 2 17beta-HSD was not inhibited by 13-cis retinoic acid. In conclusion, SG possess the cellular machinery needed to transcribe the genes for the type 1-4 isozymes of 17beta-HSD. At the protein level, however, oxidative activity of the type 2 isozyme predominates, suggesting that 17beta-HSD isozyme activity may be translationally regulated.

Steroid hormone-dependent overexpression of cytochromes P450 2A in liver tumors of TGF alpha transgenic male mice

To clarify the mechanism underlying the male preference of liver tumor in transforming growth factor (TGF) alpha transgenic mice, we analyzed the sexually dimorphic expression of two P450s, i.e., female-specific mouse 15 alpha hydroxylase P450 (2A4) and coumarin 7-hydroxylase P450 (2A5). The expression of 2A4 mRNA in the livers of both transgenic and nontransgenic males was low compared with that in females. P450 2A5 mRNA in the transgenic males was slightly elevated in the adjacent non-tumorous tissues and dramatically elevated in the tumor compared with that in nontransgenic male liver. The activity of P450 2A5 was higher in females than in males in control and transgenic mice but the difference was smaller in the transgenic mice. The activity of P450 2A5 was exceptionally high in liver tumors of transgenic males, as indicated by mRNA expression. These results suggest that female-specific P450 2A5 is induced in the livers of TGF alpha transgenic male mice, particularly in liver tumors of transgenic male mice overexpressing TGF alpha, and may be useful as a marker for mouse hepatocarcinogenesis.

Cloning of mouse 17beta-hydroxysteroid dehydrogenase type 2, and analysing expression of the mRNAs for types 1, 2, 3, 4 and 5 in mouse embryos and adult tissues

17beta-Hydroxysteroid dehydrogenases (17HSDs) are responsible for the conversion of low-activity sex steroids to more potent forms, and vice versa. 17HSD activity is essential for the biosynthesis of sex steroids in the gonads, and it is also one of the key factors regulating the availability of active ligands for sex-steroid receptors in various extragonadal tissues. In this study, we have characterized mouse 17HSD type 2 cDNA, and analysed the relative expression of 17HSD types 1, 2, 3, 4 and 5 mRNAs in mouse embryos and adult male and female tissues. The cDNA characterized has a open reading frame of 1146 bp, and encodes a protein of 381 amino acids with a predicted molecular mass of 41837 kDa. Northern-blot analysis of adult mouse tissues revealed that, of the different 17HSDs, the type 2 enzyme is most abundantly expressed. High expression of the enzyme, which oxidizes both testosterone and oestradiol, in several large organs of both sexes indicates that it is the isoform having the most substantial role in the metabolism of sex steroids. Interestingly, four of the five 17HSD enzymes were also detected by Northern blots of whole mouse embryos, and each of the enzymes showed a unique pattern of expression. The oestradiol-synthesizing type 1 enzyme predominates in early days of development embryonic day 7, but after that the oxidative type 2 enzyme becomes the predominant form of all 17HSDs. The data therefore suggest that there is transient oestradiol production in the early days of embryonic development, after which inactivation of sex steroids predominates in the fetus and placenta.

Regulation of oestrogen action: role of 17 beta-hydroxysteroid dehydrogenases

The target cell responses to steroid hormones, such as oestrogens, are dependent on the expression of their receptors. Apart from receptor concentration, another key regulatory factor in steroid hormone action is the intracellular hormone concentration, which is affected by three main variables: the concentration of the steroid in plasma, local production and local conversion into metabolites. During the reproductive years the main source of oestrogens is the ovarian follicle, but in postmenopausal women most of the oestrogens are formed in peripheral tissues. The present overview deals with the formation of active oestrogens in steroidogenic tissues and in oestrogen target tissues, and the main focus is on 17 beta-hydroxysteroid dehydrogenases, which catalyse the interconversion between oestradiol and oestrone. It is evident that different 17 beta-hydroxysteroid dehydrogenase isoenzymes are responsible for the oxidation/reduction of oestradiol or oestrone in oestrogen target cells. Because these enzymes are involved in the biosynthesis and metabolism of oestrogens, they have an important physiological significance for the growth of oestrogen-dependent tissues and, hence, the growth and progression of hormone-dependent tumours.