Steroids control the aromatase gene expression in purified germ cells from the adult male rat

Venlafaxine-induced adrenergic signaling stimulates Leydig cells steroidogenesis via Nur77 overexpression: a possible role of EGF

Venlafaxine, a norepinephrine and serotonin reuptake inhibitor, impairs rat sperm parameters, spermatogenesis and causes high intratesticular estrogen and testosterone levels, indicating that Leydig cells (LCs) may be a venlafaxine target. We evaluated the effect of venlafaxine treatment on LCs in vivo, focusing on adrenergic signaling, EGF immunoexpression and steroidogenesis. Germ cells mitotic/meiotic activity and UCHL1 levels were also evaluated in the seminiferous epithelium. Adult male rats received venlafaxine (30 mg/kg) or distilled water. In testicular sections, the seminiferous tubules, epithelium and the LCs nuclear areas were measured, and the immunoexpression of Ki-67, UCHL1, StAR, EGF, c-Kit and 17β-HSD was evaluated. UCHL1, StAR and EGF protein levels and Adra1a, Nur77 and Ndrg2 expression were analyzed. MDA and nitrite testicular levels, and serum estrogen and testosterone levels were measured. Venlafaxine induced LCs hypertrophy and Ndrg2 upregulation, in parallel to increased number of Ki-67, c-Kit- and 17β-HSD-positive interstitial cells, indicating that this antidepressant stimulates LCs lineage proliferation and differentiation. Upregulation of Adra1a and Nur77 could explain the high levels of StAR and testosterone levels, as well as aromatization. Enhanced EGF immunoexpresion in LCs suggests that this growth fact is involved in adrenergically-induced steroidogenesis, likely via upregulation of Nur77. Slight tubular atrophy and weak Ki-67 immunoexpression in germ cells, in association with high UCHL1 levels, indicate that spermatogenesis is likely impaired by this enzyme under supraphysiological estrogen levels. These data corroborate the unchanged MDA and nitrite levels. Therefore, venlafaxine stimulates LCs steroidogenesis via adrenergic signaling, and EGF may be involved in this process.

Venlafaxine-induced damage to seminiferous epithelium, spermiation, and sperm parameters in rats: A correlation with high estrogen levels

BACKGROUND

Venlafaxine (selective serotonin and norepinephrine reuptake inhibitor) use has increased worldwide. However, the impact of venlafaxine on testes and sperm parameters has not been investigated.

OBJECTIVES

We evaluated venlafaxine impact on testicular and sperm parameters and verified whether the changes are reversible.

METHODS

Animals from venlafaxine-35 days and venlafaxine-65 days groups received 30 mg/kg of venlafaxine for 35 days. Control-35 days and control-65 days received distilled water. In control-65 days and venlafaxine-65 days, the treatment was interrupted for 30 days. Sperm concentration, morphology, motility, and mitochondrial activity were analyzed. Number of step 19 spermatids (NLS), frequency of tubules with spermiation failure, Sertoli cells number, and TUNEL-positive germ cells were quantified. Testicular aromatase, connexin 43 (Cx43) immunoexpression, Cx43 protein levels, and Cx43 expression were evaluated. Either intratesticular testosterone or estrogen levels were measured.

RESULTS

Venlafaxine impaired sperm morphology, reduced sperm concentration, mitochondrial activity, and sperm motility. The frequency of tubules with spermiation failure and NLS increased in parallel to increased Cx43 immunoexpression; mRNA and protein levels; and aromatase, testosterone, and estrogen levels. An increase in germ cell death and decreased Sertoli cells number were observed. In venlafaxine-65 days, except for sperm motility, mitochondrial activity, Sertoli cells number, and germ cell death, all other parameters were partially or totally recovered.

CONCLUSION

Venlafaxine increases testosterone aromatization and Cx43. This drug, via high estrogen levels, disturbs Sertoli cells, induces germ cell death, and impairs spermiation and sperm parameters. The restoration of spermiation associated with the decreased Cx43 and hormonal levels in venlafaxine-65 days reinforces that high estrogen levels are related to venlafaxine-induced changes. The presence of damaged Sertoli cells, germ cell death, and low sperm motility in venlafaxine-65 days indicates that interruption of treatment for 30 days was insufficient for testicular recovery and points to a long-term estrogen impact on the seminiferous epithelium.

Androstenedione and 17α-methyltestosterone induce early ovary development of Anguilla japonica

Endocrine effects as 11-ketotestosterone (11-KT), an unaromatizable androgen, regulating the follicles growth in the previtellogenic stage of eel reproduction have been widely elucidated. However, the influence of aromatizable androgens on the brain-pituitary-gonad axis during oogenesis in A. japonica has not been clearly elaborated. In the study, androstenedione (AD) and 17α-methyltestosterone (MT) were employed together to induce ovary development of seven-year-old female Anguilla japonica through feeding or exposure in the migration season. After female A. japonica had been fed with commercial diet containing 5 mg AD and MT kg d^-1 body weight respectively for 45 d in fresh water (Trial I), the development of oocytes still remained at the oil droplet stage, but the GSI and follicle diameter increased significantly. The serum 11-KT level and expression of liver vitellogenin mRNA were significantly elevated. After female fish had been exposed to seawater containing 50 μg L^-1 AD and MT respectively for 45 d (Trial II), the ovaries of A. japonica almost reached midvitellogenic stage and the GSI and follicle diameter increased significantly. Yolk granular layer was observed in the peripheral ooplasm. The serum 11-KT level maintained consistently low, and the serum E2 level declined significantly to a relatively low level. The expression levels of ovarian arα and cyp19a1, brain (with pituitary together) mGnRH and lhβ increased significantly. The results showed that A. japonica in Trial II appeared a higher ovarian development than those in Trial I. These findings indicated that AD and MT increased the oil droplet and enlarged follicle diameter in previtellogenic stage, while the vitellogenesis and gonadotropin release did not occur in Trial I. In Trial II, AD and MT promoted vitellogenesis by stimulating the ovary expression of arα and by up-regulating brain mGnRH and pituitary lhβ expression.

Dehydroepiandrosterone reduces accumulation of lipid droplets in primary chicken hepatocytes by biotransformation mediated via the cAMP/PKA-ERK1/2 signaling pathway

Dehydroepiandrosterone (DHEA) is commonly used as a nutritional supplement to control fat deposition, but the mechanism of this action is poorly understood. In this study, we demonstrated that DHEA increased phosphorylation of AMP-activated protein kinase (p-AMPK). Elevated p-AMPK levels resulted in reduced expression of sterol regulatory element binding protein-1c, acetyl CoA carboxylase, fatty acid synthase and enhanced expression of peroxisome proliferators-activated receptor α and carnitine palmitoyl transferase-I, ultimately leading to the reduction of lipid droplet accumulation in primary chicken hepatocytes. We found that DHEA activates the cyclic adenosine 3', 5'-monophosphate/protein kinase A - extracellular signal-regulated kinase 1/2 (cAMP/PKA-ERK1/2) signaling pathway, which regulates the conversion of DHEA into testosterone and estradiol by increasing the 17β-hydroxysteroid dehydrogenase and aromatase protein expression. Importantly, the fat-reducing effects of DHEA are more closely associated with the conversion of DHEA into estradiol than with the action of DHEA itself as an active biomolecule, or to its alternative metabolite, testosterone. Taken together, our results indicate that DHEA is converted into active hormones through activation of the cAMP/PKA-ERK1/2 signaling pathway; the fat-reducing effects of DHEA are achieved through its conversion into estradiol, not testosterone, and not through direct action of DHEA itself, which led to the activation of the p-AMPK in primary chicken hepatocytes. These data provide novel insight into the mechanisms underlying the action of DHEA in preventing fat deposition, and suggest potential applications for DHEA treatment to control fat deposition or as an agent to treat disorders related to lipid metabolism in animals and humans.

Control of aromatase in hippocampal neurons

Our knowledge on estradiol-induced modulation of synaptic function in the hippocampus is widely based on results following the application of the steroid hormone to either cell cultures, or after the treatment of gonadectomized animals, thus ignoring local neuronal estrogen synthesis. We and others, however, have shown that hippocampus-derived estradiol also controls synaptic plasticity in the hippocampus. Estradiol synthesis in the hippocampus is regulated by several mechanisms, which are reviewed in this report. The regulation of the activity of aromatase, the final enzyme of estrogen biosynthesis, by Ca(2+) transients, is of particular interest. Aromatase becomes inactivated as soon as it is phosphorylated by Ca(2+)-dependent kinases upon calcium release from internal stores. Accordingly, thapsigargin dephosphorylates aromatase and stimulates estradiol synthesis by depletion of internal Ca(2+) stores. Vice versa, letrozole, an aromatase inhibitor, phosphorylates aromatase and reduces estradiol synthesis. Treatment of the cultures with 17β-estradiol results in phosphorylation of the enzyme and increased aromatase protein expression, which suggests that estradiol synthesis in hippocampal neurons is regulated in an autocrine manner.

Ample Evidence: Dehydroepiandrosterone (DHEA) Conversion into Activated Steroid Hormones Occurs in Adrenal and Ovary in Female Rat

Dehydroepiandrosterone (DHEA) is important for human health, especially for women. All estrogens and practically half of androgens are synthesized from DHEA in peripheral tissues. However, the mechanism and exact target tissues of DHEA biotransformation in the female are not fully clear. The present study showed that maximal content of androstenedione (AD) and testosterone (T) were observed at 3h after DHEA administration in female rats, which was 264% and 8000% above the control, respectively. Estradiol (E2) content significantly increased at 6h after DHEA administration, which was 113% higher than that in control group. Gavage with DHEA could significantly reduce 3β-hydroxysteroid dehydrogenase (3β-HSD) mRNA level at 3-12h and 17β-hydroxysteroid dehydrogenase (17β-HSD) mRNA level at 12h in ovary, while increasing aromatase mRNA levels at 6, 24, and 48h. It is interesting that administration of DHEA caused a significant increase of 17β-HSD, 3β-HSD and aromatase mRNA levels in adrenal. The AD and T contents also markedly increased by 537% and 2737% after DHEA administration in ovariectomised rats, in company with a significant increase in 17β-HSD and 3β-HSD mRNA levels and decreased aromatase mRNA level in adrenal. However, DHEA administration did not restore the decreased E2, estrone (E1), and progesterone (P) caused by the removal of the ovaries in females. These results clearly illustrated that exogenous DHEA is preferentially converted into androgens in adrenal, while its conversion to estrogens mainly happens in the ovary through steroidogenic enzyme in female rats.

Estrogens are neuroprotective factors for hypertensive encephalopathy

Estrogens are neuroprotective factors for brain diseases, including hypertensive encephalopathy. In particular, the hippocampus is highly damaged by high blood pressure, with several hippocampus functions being altered in humans and animal models of hypertension. Working with a genetic model of primary hypertension, the spontaneously hypertensive rat (SHR), we have shown that SHR present decreased dentate gyrus neurogenesis, astrogliosis, low expression of brain derived neurotrophic factor (BDNF), decreased number of neurons in the hilus of the dentate gyrus, increased basal levels of the estrogen-synthesizing enzyme aromatase, and atrophic dendritic arbor with low spine density in the CA1 region compared to normotensive Wistar Kyoto (WKY) ratsl. Changes also occur in the hypothalamus of SHR, with increased expression of the hypertensinogenic peptide arginine vasopressin (AVP) and its V1b receptor. Following chronic estradiol treatment, SHR show decreased blood pressure, enhanced hippocampus neurogenesis, decreased the reactive astrogliosis, increased BDNF mRNA and protein expression in the dentate gyrus, increased neuronal number in the hilus of the dentate gyrus, further increased the hyperexpression of aromatase and replaced spine number with remodeling of the dendritic arbor of the CA1 region. We have detected by qPCR the estradiol receptors ERα and ERβ in hippocampus from both SHR and WKY rats, suggesting direct effects of estradiol on brain cells. We hypothesize that a combination of exogenously given estrogens plus those locally synthesized by estradiol-stimulated aromatase may better alleviate the hippocampal and hypothalamic encephalopathy of SHR. This article is part of a Special Issue entitled "Sex steroids and brain disorders".

Regulation of aromatase expression by 1α,25(OH)2 vitamin D3 in rat testicular cells

It is well known that the vitamin D endocrine system is involved in physiological and biochemical events in numerous tissues, especially gut, bone and kidney but also testis. Therefore, in this study the effect and mechanisms of action of 1α,25(OH)2 vitamin D3 (1,25D) on aromatase gene expression in immature rat Sertoli cells were evaluated. Vitamin D receptor transcripts were present in immature Sertoli cells as well as in adult testicular germ cells and somatic cells. The treatment of immature Sertoli cells with 100 nM 1,25D increased the amount of aromatase transcript, mainly in 30-day-old rats. The protein kinase A (PKA) blocker, H89, partially inhibited the 1,25D effect. The stimulation of aromatase gene expression in 30-day-old Sertoli cells by the agonist 1α,25(OH)2 lumisterol3, and the suppression of the 1,25D effect by the antagonists 1β,25(OH)2 vitamin D3 and (23S)-25-dehydro-1α (OH)-vitamin D3-26,23-lactone suggested, besides a genomic effect of 1,25D, the existence of non-genomic activation of the membrane-bound vitamin D receptor involving the PKA pathway.

Protective effect of estrogens on the brain of rats with essential and endocrine hypertension

Estrogen neuroprotection has been shown in pathological conditions damaging the hippocampus, such as trauma, aging, neurodegeneration, excitotoxicity, oxidative stress, hypoglycemia, amyloid-β peptide exposure and ischemia. Hypertensive encephalopathy also targets the hippocampus; therefore, hypertension seems an appropriate circumstance to evaluate steroid neuroprotection. Two experimental models of hypertension, spontaneously hypertensive rats (SHR) and deoxycorticosterone (DOCA)-salt hypertensive rats, develop hippocampal abnormalities, which include decreased neurogenesis in the dentate gyrus, astrogliosis, low expression of brain-derived neurotrophic factor (BDNF) and decreased number of neurons in the hilar region, with respect of their normotensive strains Wistar Kyoto (WKY) and Sprague-Dawley rats. After estradiol was given for 2 weeks to SHR and DOCA-treated rats, both hypertensive models normalized their faulty hippocampal parameters. Thus, estradiol treatment positively modulated neurogenesis in the dentate gyrus of the hippocampus, according to bromodeoxyuridine incorporation and doublecortin immunocytochemistry, decreased reactive astrogliosis, increased BDNF mRNA and protein expression in the dentate gyrus and increased neuronal number in the hilar region of the dentate gyrus. A role of local estrogen biosynthesis is suggested in SHR, because basal aromatase mRNA in the hippocampus and immunoreactive aromatase protein in cell processes of the dentate gyrus were highly expressed in these rats. Estradiol further stimulated aromatase-related parameters in SHR but not in WKY. These observations strongly support that a combination of exogenous estrogens to those locally synthesized might better alleviate hypertensive encephalopathy. These studies broaden estrogen neuroprotective functions to the hippocampus of hypertensive rat models.

Expression of estrogen related proteins in hormone refractory prostate cancer: association with tumor progression

PURPOSE

Despite increasing evidence that estrogen signaling has a key role in prostate cancer development and progression, few studies have focused on the estrogen pathway in the transition from hormone sensitive to hormone refractory tumors. We investigated the expression of proteins related to androgen and estrogen metabolism in paired prostate cancer samples collected before androgen deprivation therapy and after hormonal relapse.

MATERIALS AND METHODS

The study included 55 patients treated for prostate cancer only with androgen deprivation therapy and in whom tissue was available before treatment induction and after recurrence. Immunohistochemistry was performed using tissue microarray with antibodies directed against androgen receptor, phosphorylated androgen receptor, estrogen receptor α, estrogen receptor β, 5α-reductase 1 and 2, aromatase, BCAR1 and the proliferation marker Ki67.

RESULTS

Compared to hormone sensitive samples, tissues collected after hormonal relapse were characterized by increased expression of Ki67, androgen receptor, phosphorylated androgen receptor (p <0.001) and BCAR (p = 0.03), and by lower staining for 5α-reductase 2 (p = 0.002), estrogen receptor β (p = 0.016) and aromatase (p <0.001). Shorter time to hormonal relapse was associated with high expression of aromatase and BCAR1 on diagnostic biopsy, together with low staining for estrogen receptor α in stromal cells. Overall survival was significantly shorter when tissues collected after relapse showed a high proliferation index and low estrogen receptor α expression.

CONCLUSIONS

Results revealed dysregulation of proteins involved in androgen pathways, and in estrogen synthesis and signaling during the development of hormone refractory prostate cancer.

Glyphosate-based herbicides are toxic and endocrine disruptors in human cell lines

Glyphosate-based herbicides are the most widely used across the world; they are commercialized in different formulations. Their residues are frequent pollutants in the environment. In addition, these herbicides are spread on most eaten transgenic plants, modified to tolerate high levels of these compounds in their cells. Up to 400 ppm of their residues are accepted in some feed. We exposed human liver HepG2 cells, a well-known model to study xenobiotic toxicity, to four different formulations and to glyphosate, which is usually tested alone in chronic in vivo regulatory studies. We measured cytotoxicity with three assays (Alamar Blue, MTT, ToxiLight), plus genotoxicity (comet assay), anti-estrogenic (on ERalpha, ERbeta) and anti-androgenic effects (on AR) using gene reporter tests. We also checked androgen to estrogen conversion by aromatase activity and mRNA. All parameters were disrupted at sub-agricultural doses with all formulations within 24h. These effects were more dependent on the formulation than on the glyphosate concentration. First, we observed a human cell endocrine disruption from 0.5 ppm on the androgen receptor in MDA-MB453-kb2 cells for the most active formulation (R400), then from 2 ppm the transcriptional activities on both estrogen receptors were also inhibited on HepG2. Aromatase transcription and activity were disrupted from 10 ppm. Cytotoxic effects started at 10 ppm with Alamar Blue assay (the most sensitive), and DNA damages at 5 ppm. A real cell impact of glyphosate-based herbicides residues in food, feed or in the environment has thus to be considered, and their classifications as carcinogens/mutagens/reprotoxics is discussed.

Effects of sex, age, and season on plasma steroids in free-ranging Texas horned lizards (Phrynosoma cornutum)

The Texas horned lizard (Phrynosoma cornutum) is protected in several states due to its apparently declining numbers; information on its physiology is therefore of interest from both comparative endocrine and applied perspectives. We collected blood samples from free-ranging P. cornutum in Oklahoma from April to September 2005, spanning their complete active period. We determined plasma concentrations of the steroids, progesterone (P), testosterone (T), and corticosterone (CORT) by radioimmunoassay following chromatographic separation and 17beta-estradiol (E2) by direct radioimmunoassay. T concentrations in breeding males were significantly higher than in non-breeding males. P showed no significant seasonal variation within either sex. CORT was significantly higher during the egg-laying season compared to breeding and non-breeding seasons for adult females and it was marginally higher in breeding than in non-breeding males (P=0.055). CORT concentrations also significantly increased with handling in non-breeding males and egg-laying females. Perhaps most surprisingly, there were no significant sex differences in plasma concentrations of P and E2. Furthermore, with respect to seasonal differences, plasma E2 concentrations were significantly higher in breeding females than in egg-laying or non-breeding females, and they were significantly higher in breeding than in non-breeding males. During the non-breeding season, yearling males exhibited higher E2 concentrations than adult males; no other differences between the steroid concentrations of yearlings and adults were detected. In comparison to other vertebrates, the seasonal steroid profile of P. cornutum exhibited both expected and unexpected patterns, and our results illustrate the value of collecting such baseline data as a springboard for appropriate questions for future research.

Interference of endocrine disrupting chemicals with aromatase CYP19 expression or activity, and consequences for reproduction of teleost fish

Many natural and synthetic compounds present in the environment exert a number of adverse effects on the exposed organisms, leading to endocrine disruption, for which they were termed endocrine disrupting chemicals (EDCs). A decrease in reproduction success is one of the most well-documented signs of endocrine disruption in fish. Estrogens are steroid hormones involved in the control of important reproduction-related processes, including sexual differentiation, maturation and a variety of others. Careful spatial and temporal balance of estrogens in the body is crucial for proper functioning. At the final step of estrogen biosynthesis, cytochrome P450 aromatase, encoded by the cyp19 gene, converts androgens into estrogens. Modulation of aromatase CYP19 expression and function can dramatically alter the rate of estrogen production, disturbing the local and systemic levels of estrogens. In the present review, the current progress in CYP19 characterization in teleost fish is summarized and the potential of several classes of EDCs to interfere with CYP19 expression and activity is discussed. Two cyp19 genes are present in most teleosts, cyp19a and cyp19b, primarily expressed in the ovary and brain, respectively. Both aromatase CYP19 isoforms are involved in the sexual differentiation and regulation of the reproductive cycle and male reproductive behavior in diverse teleost species. Alteration of aromatase CYP19 expression and/or activity, be it upregulation or downregulation, may lead to diverse disturbances of the above mentioned processes. Prediction of multiple transcriptional regulatory elements in the promoters of teleost cyp19 genes suggests the possibility for several EDC classes to affect cyp19 expression on the transcriptional level. These sites include cAMP responsive elements, a steroidogenic factor 1/adrenal 4 binding protein site, an estrogen-responsive element (ERE), half-EREs, dioxin-responsive elements, and elements related to diverse other nuclear receptors (peroxisome proliferator activated receptor, retinoid X receptor, retinoic acid receptor). Certain compounds including phytoestrogens, xenoestrogens, fungicides and organotins may modulate aromatase CYP19 activity on the post-transcriptional level. As is shown in this review, diverse EDCs may affect the expression and/or activity of aromatase cyp19 genes through a variety of mechanisms, many of which need further characterization in order to improve the prediction of risks posed by a contaminated environment to teleost fish population.

The expression of aromatase in gonadotropes is regulated by estradiol and gonadotropin-releasing hormone in a manner that differs from the regulation of luteinizing hormone

The role of estrogens is dual: they suppress basal expression of gonadotropins and enhance GnRH responsiveness at the time of the LH surge. Estrogens are synthesized by cytochrome P450 aromatase (P450arom), encoded by the cyp19 gene. We focused on the cyp19 gene in rat and showed that it is expressed in gonadotropes through promoters PII and PI.f, using RT-PCR and dual fluorescence labeling with anti-P450arom and -LH antibodies. Real-time PCR quantification revealed that aromatase mRNA levels varied during the estrous cycle and were significantly increased after ovariectomy. This effect is prevented by estradiol (E2) as well as GnRH antagonist administration, suggesting that GnRH may mediate the steroid effect. Interestingly, the long-acting GnRH agonist that induces LH desensitization does not modify aromatase expression in ovariectomized rats. Administration of E2 in ovariectomized rats receiving either GnRH agonist or GnRH antagonist clearly demonstrated that E2 also reduces cyp19 expression at the pituitary level. The selective estrogen receptor-alpha ligand propyl pyrazole triol and the selective estrogen receptor-beta ligand diarylpropionitrile both mimic the E2 effects. By contrast, propyl pyrazole triol reduces LH beta expression whereas diarylpropionitrile does not. In addition, using transient transfection assays in an L beta T2 gonadotrope cell line, we provided evidence that GnRH agonist stimulated, in a dose-dependant manner, cyp19 promoters PII and PI.f and that E2 decreased the GnRH stimulation. In conclusion, our data demonstrate that GnRH is an important signal in the regulation of cyp19 in gonadotrope cells. Both common and specific intracellular factors were responsible for dissociated variations of LH beta and cyp19 expression.

Conversion from testosterone to oestradiol is required to modulate respiratory long-term facilitation in male rats

Sex hormones modulate plasticity in the central nervous system, including respiratory long-term facilitation (LTF), a form of serotonin-dependent respiratory plasticity induced by intermittent hypoxia. Since gonadectomy (GDX) attenuates LTF in male rats, we tested the hypotheses that: (1) testosterone replenishment restores LTF in gonadectomized male rats, and (2) that the conversion of testosterone to oestradiol (under the influence of aromatase) is required for these effects. Intact and sham operated male F344 rats were compared to gonadectomized rats implanted with Silastic tubing containing testosterone (T), T plus an aromatase inhibitor (ADT), or 5alpha-dihydrotestosterone (DHT), a form of testosterone not converted to oestradiol. Seven days postsurgery, LTF was studied in anaesthetized, neuromuscularly blocked and ventilated rats while monitoring integrated phrenic and hypoglossal (XII) motor output. LTF was elicited by three 5 min hypoxic episodes (P(a,O(2)) = 35 - 45 mmHg). Although significant phrenic and XII LTF were observed in all rat groups, GDX reduced both phrenic and XII LTF, an effect reversed by T. In contrast, LTF was not restored in T + ADT or DHT-treated gonadectomized rats. We conclude that the conversion of testosterone to oestradiol modulates phrenic and XII LTF in male F344 rats.

Expression of functional aromatase in the epididymis: role of androgens and LH in modulation of expression and activity

The primary source of 17beta-estradiol (E2) in the male is the testis, which expresses the enzyme complex aromatase that is involved in E2 biosynthesis. However, recent evidences suggest that the epididymis is also capable of E2 biosynthesis. Our results demonstrate the presence of cytochrome P450 aromatase (P450(AROM)) and 17beta-hydroxysteroid dehydrogenase I messenger ribonucleic acid (mRNA) in the caput and cauda regions of rat epididymis. The androgenic substrates testosterone and androstenedione could be utilized by the rat epididymal aromatase for E2 biosynthesis as assessed by radioimmunoassay. P450(AROM) expression is transcriptionally regulated in a tissue-specific manner by various factors including androgens and luteinizing hormone (LH). Androgens could positively modulate epididymal P450(AROM) mRNA levels as assessed by castration studies, treatment with flutamide or in vitro incubation of tissue minces with 5 alpha-dihydrotestosterone (DHT). Several extra-gonadal tissues including the epididymis are known to express LH receptors (LHR). Our study revealed a higher level of LHR mRNA expression in the cauda region compared to the caput. Caudal membrane extracts could bind human chorionic gonadotropin (hCG), which resulted in the production of cAMP. Interestingly, hCG could also regulate P450(AROM) mRNA expression in vitro and enhance E2 biosynthesis. Together our results highlight the presence of a functional aromatase in the epididymis that is subject to regulation by LH and androgens.

Apoptotic effects of 25-hydroxycholesterol in immature rat Sertoli cells: Prevention by 17β-estradiol

The aim of the present study was to determine whether or not apoptosis occurs in Sertoli cells in presence of 25-hydroxycholesterol, an oxysterol derived from cholesterol-containing foods or endogenous oxidation. Here, we provide evidence that 25-hydroxycholesterol can induce cultured Sertoli cells of immature rat to undergo apoptosis. The cell death was identified by analysis of fragmented DNA detected using enzyme-immunoassay. After 48 h of treatment with 50 microM of 25-hydroxycholesterol, apoptosis increased by 70% in Sertoli cells. Moreover, 50 microM of 25-hydroxycholesterol inhibited the incorporation of [14C] acetate into cholesterol by 70%. Addition of mevanolate to prevent isoprenoid deficiency do not inhibit the apoptosis generated by 25-hydroxycholesterol. In contrast, this increase of DNA fragmentation was reversed by addition of caspase-3 inhibitors as Ac-DEVD-CHO or Ac-ESMD-CHO. Bcl-2 mRNA level in the Sertoli cells decreased by 60% after 24 h exposure to 25-hydroxycholesterol. In parallel, Bax mRNA level increased by 40% in the Sertoli cells incubated in presence of 50 microM of 25-hydroxycholesterol. Physiological concentrations of 17beta-estradiol (10 or 100 nM) elicited a significant protection on apoptosis generated by 25-hydroxycholesterol in Sertoli cells. Our results show that the 25-hydroxycholesterol would control the cholesterol synthesis without toxic effect in immature rat Sertoli cells, these cells being able to protect themselves by estradiol production.

Effects of estradiol on spatial learning, hippocampal cytochrome P450 19, and estrogen alpha and beta mRNA levels in ovariectomized female mice

The brain is an important target organ for peripherally synthesized estrogen but it also has its own steroid biosynthesis producing estrogen from testosterone catalyzed by the aromatase enzyme. This study examined the effects of estrogen treatment in two spatial memory tasks, one-arm-baited radial arm maze and a position discrimination task in the T-maze in ovariectomized female mice. Hippocampal cytochrome P450 19 (encoding aromatase), and estrogen receptor alpha and beta gene expressions were also measured using real time quantitative polymerase chain reaction analysis. Estrogen (17beta-estradiol) was administered either tonically via s.c. minipellets or phasically via daily i.p. injections. In ovariectomized mice, the tonic estrogen decreased the number of reference memory errors in radial arm maze. Tonic estrogen treatment also up-regulated the expression of cytochrome P450 19 and estrogen receptors. In contrast, estrogen injections decreased the expression of cytochrome P450 19 and estrogen receptor alpha genes. The number of reference memory errors correlated negatively with estrogen receptor alpha expression. These findings indicate that peripheral estrogen levels affect neuronal estrogen synthesis by regulating the cytochrome P450 19 gene expression and also influence estrogen receptor alpha expression. The results also suggest that tonic rather than cyclic estrogen treatment might be more beneficial for cognitive functions.

Estrogen regulation of testicular function

Evidence supporting a role for estrogen in male reproductive tract development and function has been collected from rodents and humans. These studies fall into three categories: i) localization of aromatase and the target protein for estrogen (ER-alpha and ER-beta) in tissues of the reproductive tract; ii) analysis of testicular phenotypes in transgenic mice deficient in aromatase, ER-alpha and/or ER-beta gene; and, iii) investigation of the effects of environmental chemicals on male reproduction. Estrogen is thought to have a regulatory role in the testis because estrogen biosynthesis occurs in testicular cells and the absence of ERs caused adverse effects on spermatogenesis and steroidogenesis. Moreover, several chemicals that are present in the environment, designated xenoestrogens because they have the ability to bind and activate ERs, are known to affect testicular gene expression. However, studies of estrogen action are confounded by a number of factors, including the inability to dissociate estrogen-induced activity in the hypothalamus and pituitary from action occurring directly in the testis and expression of more than one ER subtype in estrogen-sensitive tissues. Use of tissue-specific knockout animals and administration of antiestrogens and/or aromatase inhibitors in vivo may generate additional data to advance our understanding of estrogen and estrogen receptor biology in the developing and mature testis.

Aromatase in testis: expression and role in male reproduction

The mammalian testis serves two main functions: production of spermatozoa and synthesis of steroids, among them estrogens are the end products obtained from the irreversible transformation of androgens by aromatase (P450arom). In the rat the pattern of P450arom expression differs among the testicular somatic cell types according to age; in addition, we have shown that gonocytes, spermatogonia, spermatocytes (preleptotene, pachytene), spermatids and spermatozoa, represent an important source of estrogens; the expression of aromatase is three-fold higher in pachytene spermatocyte (PS) compared to gonocytes. In man both Leydig cells and immature germ cells (PS and round spermatids, RS) as well as ejaculated spermatozoa expressed a biologically active aromatase revealed as a single band of 49 kDa on western blots. Up today P450arom has been demonstrated in male germ cells of all mammals so far studied (mice, bank vole, bear and monkey). The aromatase gene is highly conserved and is unique in humans; its expression is regulated in a cell-specific manner via the alternative use of various promoters located in the first exon. Nevertheless, data concerning the regulation of P450arom especially in germ cells are scarce. We have demonstrated that TGFbeta inhibits the expression of Cyp19 in PS and RS via the SMAD pathway although TNFalpha exerts a stimulatory role in PS, which is amplified in presence of dexamethasone. It is noteworthy that dexamethasone alone exerts a positive effect on Cyp19 expression in PS and a negative one in RS. Cyclic AMP is also a positive regulator of P450arom gene expression in germ cells. In addition, we have shown that androgens and estrogens modulate Cyp19 gene expression, whatever the testicular cell type studied, which favored the presence of androgens and estrogens responsive elements on the Cyp19 gene promoter(s). Moreover, in presence of seminiferous tubules conditioned media, the amount of aromatase transcripts is increased in Leydig cells, therefore, suggesting that other locally produced modulators are involved in the regulation of the aromatase gene expression and among them the liver receptor homolog-1 (LRH-1) from germ cells origin is concerned. Using RACE-PCR we have confirmed that promoter II directs the expression of aromatase gene, whatever the testicular cell type studied in the rat but the involvement of another promoter, such as PI.4 is suggested. Finally, the aromatase gene is constitutively expressed both in somatic and germ cells of the testis and the identification of the promoter(s) concerned as well as their detailed regions which direct(s) the expression of Cyp19 gene is obviously very important but largely unknown especially according to the ontogeny of the male gonad.

Testicular germ cell tumors exhibit evidence of hormone dependence

The aim of this investigation was to test the hypothesis that testicular germ cell tumors (TGCTs) are hormone-dependent cancers. Human TGCT cells were implanted in the left testis of male severe combined immunodeficient mice receiving either no treatment or hormone manipulation treatment [blockade of gonadotropin-releasing hormone secretion and/or signaling using leuprolide or leuprolide plus exogenous testosterone]. Real-time RT-PCR analysis was used to determine the expression profiles of hormone pathway-associated genes. Tumor burden was significantly smaller in mice receiving both leuprolide and testosterone. Real-time RT-PCR analysis of follicle-stimulating hormone (FSH) receptor, luteinizing hormone (LH) receptor and P450 aromatase revealed changes in expression in normal testis tissue related to presence of xenograft tumors and manipulation of hormone levels but a complete absence of expression of these genes in tumor cells themselves. This was confirmed in human specimens of TGCT. Reduced TGCT growth in vivo was associated with significant downregulation of LH receptor and P450 aromatase expression in normal testes. In conclusion, manipulation of hormone levels influenced the growth of TGCT in vivo, while the presence of xenografted tumors influenced the expression of hormone-related genes in otherwise untreated animals. Human TGCTs, both in the animal model and in clinical specimens, appear not to express receptors for FSH or LH. Similarly, expression of the P450 aromatase gene is absent in TGCTs. Impaired estrogen synthesis and/or signaling may be at least partly responsible for inhibition of TGCT growth in the animal model.

Inhibition of testicular steroidogenesis by the xenoestrogen bisphenol A is associated with reduced pituitary luteinizing hormone secretion and decreased steroidogenic enzyme gene expression in rat Leydig cells

Exposure of humans to bisphenol A (BPA), a monomer in polycarbonate plastics and a constituent of resins used in food packaging and dentistry, is significant. In this report exposure of rats to 2.4 microg/kg.d (a dose that approximates BPA levels in the environment) from postnatal d 21-35 suppressed serum LH (0.21 +/- 0.05 ng/ml; vs. control, 0.52 +/- 0.04; P < 0.01) and testosterone (T) levels (1.62 +/- 0.16 ng/ml; vs. control, 2.52 +/- 0.21; P < 0.05), in association with decreased LHbeta and increased estrogen receptor beta pituitary mRNA levels as measured by RT-PCR. Treatment of adult Leydig cells with 0.01 nm BPA decreased T biosynthesis by 25% as a result of decreased expression of the steroidogenic enzyme 17alpha-hydroxylase/17-20 lyase. BPA decreased serum 17beta-estradiol levels from 0.31 +/- 0.02 ng/ml (control) to 0.22 +/- 0.02, 0.19 +/- 0.02, and 0.23 +/- 0.03 ng/ml in rats exposed to 2.4 microg, 10 microg, or 100 mg/kg.d BPA, respectively, from 21-35 d of age (P < 0.05) due to its ability to inhibit Leydig cell aromatase activity. Exposures of pregnant and nursing dams, i.e. from gestation d 12 to postnatal d 21, decreased T levels in the testicular interstitial fluid from 420 +/- 34 (control) to 261 +/- 22 (P < 0.05) ng/ml in adulthood, implying that the perinatal period is a sensitive window of exposure to BPA. As BPA has been measured in several human populations, further studies are warranted to assess the effects of BPA on male fertility.