Alternative 5'-untranslated first exons of the mouse Cyp19A1 (aromatase) gene

Effect of Cycas pectinata Seed Extract on Testicular Steroidogenesis in a Mouse Model

The seed of Cycas pectinata is widely used in traditional practices in the Northeastern region of India for diverse purposes along with improving testicular functions. Thus, it may be hypothesized that the phytochemicals of C. pectinata seed could modulate testicular steroidogenesis. Therefore, we have investigated the effects of C. Pectinata seed extract (CPE) on testicular steroidogenesis by using in vivo and in vitro approaches. We have also performed the molecular docking of phytochemicals with some steroidogenic markers based on the identified phytochemicals from our previous study. The in vivo treatment of CPE increased the circulating estrogen and decreased circulating testosterone. The in vitro treatment of CPE also showed increased secretion of estrogen which can be suggested due to an increase in the aromatase (CYP19A1) activity. Our results also showed that the expression and localization of CYP19A1 were elevated by the CPE. The treatment of CPE also showed an accumulation of cholesterol in the testis, which could enhance testicular steroidogenesis. The other steroidogenic markers like 3βHSD, StAR, and LHR were upregulated by the CPE. Twelve compounds exhibited binding energy in the range of -10.0 to -8.0 kcal/mol with CYP19A1. Our data from in vitro, in vivo, and docking studies, showed that phytochemicals of CPE could modulate testicular steroidogenesis.

Metabolic pathways in obesity-related breast cancer

This Review focuses on the mechanistic evidence for a link between obesity, dysregulated cellular metabolism and breast cancer. Strong evidence now links obesity with the development of 13 different types of cancer, including oestrogen receptor-positive breast cancer in postmenopausal women. A number of local and systemic changes are hypothesized to support this relationship, including increased circulating levels of insulin and glucose as well as adipose tissue-derived oestrogens, adipokines and inflammatory mediators. Metabolic pathways of energy production and utilization are dysregulated in tumour cells and this dysregulation is a newly accepted hallmark of cancer. Dysregulated metabolism is also hypothesized to be a feature of non-neoplastic cells in the tumour microenvironment. Obesity-associated factors regulate metabolic pathways in both breast cancer cells and cells in the breast microenvironment, which provides a molecular link between obesity and breast cancer. Consequently, interventions that target these pathways might provide a benefit in postmenopausal women and individuals with obesity, a population at high risk of breast cancer.

The Tumor Promotional Role of Adipocytes in the Breast Cancer Microenvironment and Macroenvironment

The role of the adipocyte in the tumor microenvironment has received significant attention as a critical mediator of the obesity-cancer relationship. Current estimates indicate that 650 million adults have obesity, and thirteen cancers, including breast cancer, are estimated to be associated with obesity. Even in people with a normal body mass index, adipocytes are key players in breast cancer progression because of the proximity of tumors to mammary adipose tissue. Outside the breast microenvironment, adipocytes influence metabolic and immune function and produce numerous signaling molecules, all of which affect breast cancer development and progression. The current epidemiologic data linking obesity, and importantly adipose tissue, to breast cancer risk and prognosis, focusing on metabolic health, weight gain, and adipose distribution as underlying drivers of obesity-associated breast cancer is presented here. Bioactive factors produced by adipocytes, both normal and cancer associated, such as cytokines, growth factors, and metabolites, and the potential mechanisms through which adipocytes influence different breast cancer subtypes are highlighted.

Progesterone and Breast Cancer

Synthetic progestogens (progestins) have been linked to increased breast cancer risk; however, the role of endogenous progesterone in breast physiology and carcinogenesis is less clearly defined. Mechanistic studies using cell culture, tissue culture, and preclinical models implicate progesterone in breast carcinogenesis. In contrast, limited epidemiologic data generally do not show an association of circulating progesterone levels with risk, and it is unclear whether this reflects methodologic limitations or a truly null relationship. Challenges related to defining the role of progesterone in breast physiology and neoplasia include: complex interactions with estrogens and other hormones (eg, androgens, prolactin, etc.), accounting for timing of blood collections for hormone measurements among cycling women, and limitations of assays to measure progesterone metabolites in blood and progesterone receptor isotypes (PRs) in tissues. Separating the individual effects of estrogens and progesterone is further complicated by the partial dependence of PR transcription on estrogen receptor (ER)α-mediated transcriptional events; indeed, interpreting the integrated interaction of the hormones may be more essential than isolating independent effects. Further, many of the actions of both estrogens and progesterone, particularly in "normal" breast tissues, are driven by paracrine mechanisms in which ligand binding to receptor-positive cells evokes secretion of factors that influence cell division of neighboring receptor-negative cells. Accordingly, blood and tissue levels may differ, and the latter are challenging to measure. Given conflicting data related to the potential role of progesterone in breast cancer etiology and interest in blocking progesterone action to prevent or treat breast cancer, we provide a review of the evidence that links progesterone to breast cancer risk and suggest future directions for filling current gaps in our knowledge.

The transcription factor SMAD4 and miR-10b contribute to E2 release and cell apoptosis in ovarian granulosa cells by targeting CYP19A1

The cytochrome P450 family 19 subfamily A member 1 (CYP19A1) gene, encodes aromatase, a key enzyme in estradiol (E2) synthesis, and is down-regulated during porcine follicular atresia. However, its role in and the mechanism of transcriptional repression in follicular atresia is largely unknown. In the present study, we show that the CYP19A1 gene stimulates E2 release and inhibits cell apoptosis in porcine granulosa cells (GCs). SMAD4, an anti-apoptotic moderator, was identified as a transcription factor of the porcine CYP19A1 gene and enhanced the expression and function of CYP19A1 in porcine GCs through direct binding to a SMAD4-binding element (SBE) within the promoter region of CYP19A1 gene. Moreover, we found that miR-10b, a pro-apoptotic factor, directly interacted with 3'-UTR of the porcine CYP19A1 mRNA, inhibiting its expression and function in porcine GCs. Collectively, we demonstrated that CYP19A1 is an inhibitor of follicular atresia and is regulated by both SMAD4 and miR-10b. These findings provide further insight into the mechanisms of CYP19A1 in steroid hormone synthesis and GC apoptosis and provide molecular targets for exploring methods of treatment for steroid-dependent reproductive disorders.

TCF21 is related to testis growth and development in broiler chickens

Background

Large amounts of fat deposition often lead to loss of reproductive efficiency in humans and animals. We used broiler chickens as a model species to conduct a two-directional selection for and against abdominal fat over 19 generations, which resulted in a lean and a fat line. Direct selection for abdominal fat content also indirectly resulted in significant differences (P < 0.05) in testis weight (TeW) and in TeW as a percentage of total body weight (TeP) between the lean and fat lines.

Results

A total of 475 individuals from the generation 11 (G₁₁) were genotyped. Genome-wide association studies revealed two regions on chicken chromosomes 3 and 10 that were associated with TeW and TeP. Forty G₁₆ individuals (20 from each line), were further profiled by focusing on these two chromosomal regions, to identify candidate genes with functions that may be potentially related to testis growth and development. Of the nine candidate genes identified with database mining, a significant association was confirmed for one gene, TCF21, based on mRNA expression analysis. Gene expression analysis of the TCF21 gene was conducted again across 30 G₁₉ individuals (15 individuals from each line) and the results confirmed the findings on the G₁₆ animals.

Conclusions

This study revealed that the TCF21 gene is related to testis growth and development in male broilers. This finding will be useful to guide future studies to understand the genetic mechanisms that underlie reproductive efficiency.

Electronic supplementary material

The online version of this article (doi:10.1186/s12711-017-0299-0) contains supplementary material, which is available to authorized users.

Modifications of Western-type diet regarding protein, fat and sucrose levels as modulators of steroid metabolism and activity in liver

The aim of the study was to evaluate whether the modification of the Western-type diet (high-fat, high-sucrose diet rich in saturated fatty acids) considering macronutrients content would influence hepatic metabolism and activity of steroids. For 3 weeks Wistar rat were fed the Western-type diet (21% fat, 35% sucrose, 19% protein, lard) and its modifications regarding dietary protein (10 and 19%), fat (5 and 21%) and sucrose (0 and 35%) levels. The steroid 5α-reductase type 1 (Srd5a1) and androgen receptor (Ar) gene expression as well as testosterone (T) conversion towards 5α-reduced derivatives in liver were positively correlated with body weight gain. The Western-type diets with decreased protein content regardless of the sucrose level exerted the most negative effect on the antioxidant system decreasing catalase (Cat), sodium dismutase (Sod1) and glutathione peroxidase (Gpx1) gene expression as well as Cat and Gpx activity and total antioxidant status, simultaneously intensifying lipid peroxidation. The impaired antioxidant system was accompanied by decreased level of hepatic T metabolism towards estrogens: 17β-estradiol (E2) and estriol, and increased estrogen receptor type 1 (Esr1) gene expression. Liver Esr1 mRNA level was differently correlated with T (positively) and E2 (negatively) plasma levels. Whereas the fat reduction in Western-type diet restored the plasma proportion between T and E2. In conclusion it could be stated that Western-type diet modification relating to protein, sucrose and fat content can influence hepatic steroid metabolism and activity; however the estrogens and androgens metabolism in liver would be connected with impairment of liver function or catabolic activity, respectively.

Aromatase expression and regulation in breast and endometrial cancer

Long-term exposure to excess estrogen increases the risk of breast cancer and type 1 endometrial cancer. Most of the estrogen in premenopausal women is synthesized by the ovaries, while extraovarian subcutaneous adipose tissue is the predominant tissue source of estrogen after menopause. Estrogen and its metabolites can cause hyperproliferation and neoplastic transformation of breast and endometrial cells via increased proliferation and DNA damage. Several genetically modified mouse models have been generated to help understand the physiological and pathophysiological roles of aromatase and estrogen in the normal breast and in the development of breast cancers. Aromatase, the key enzyme for estrogen production, is comprised of at least ten partially tissue-selective and alternatively used promoters. These promoters are regulated by distinct signaling pathways to control aromatase expression and estrogen formation via recruitment of various transcription factors to their cis-regulatory elements. A shift in aromatase promoter use from I.4 to I.3/II is responsible for the excess estrogen production seen in fibroblasts surrounding malignant epithelial cells in breast cancers. Targeting these distinct pathways and/or transcription factors to modify aromatase activity may lead to the development of novel therapeutic remedies that inhibit estrogen production in a tissue-specific manner.

A Preclinical Model for ERα-Positive Breast Cancer Points to the Epithelial Microenvironment as Determinant of Luminal Phenotype and Hormone Response

Seventy-five percent of breast cancers are estrogen receptor α positive (ER⁺). Research on these tumors is hampered by lack of adequate in vivo models; cell line xenografts require non-physiological hormone supplements, and patient-derived xenografts (PDXs) are hard to establish. We show that the traditional grafting of ER⁺ tumor cells into mammary fat pads induces TGFβ/SLUG signaling and basal differentiation when they require low SLUG levels to grow in vivo. Grafting into the milk ducts suppresses SLUG; ER⁺ tumor cells develop, like their clinical counterparts, in the presence of physiological hormone levels. Intraductal ER⁺ PDXs are retransplantable, predictive, and appear genomically stable. The model provides opportunities for translational research and the study of physiologically relevant hormone action in breast carcinogenesis.

Obesity-related proliferative diseases: the interaction between adipose tissue and estrogens in post-menopausal women

Epidemiological studies have shown that overweight and cancer are closely related, even though obesity alone does not apparently heighten cancer risk by the same amount. Given the low overall risk of all cancers with obesity, it is unlikely that obesity alone causes cancer, but should instead be considered as a tumor promoter. There are three main hypotheses that could explain how obesity might contribute to cancer development and growth: the inflammatory cytokines from adipose tissue hypothesis, the insulin resistance and hyperinsulinemia hypothesis, and the unopposed estrogen cancer hypothesis. The link between obesity and cancer is that adipocytes constitute a major component of the tumor microenvironment for breast and abdominally metastasizing cancers, promoting tumor growth. This review will mainly focus attention on the relationship between adipose tissue, estrogens, and cancer risk.

Expression and localization of aromatase during fetal mouse testis development

BACKGROUND

Both androgens and estrogens are necessary to ensure proper testis development and function. Studies on endocrine disruptors have highlighted the importance of maintaining the balance between androgens and estrogens during fetal development, when testis is highly sensitive to environmental disturbances. This balance is regulated mainly through an enzymatic cascade that converts irreversibly androgens into estrogens. The most important and regulated component of this cascade is its terminal enzyme: the cytochrome p450 19A1 (aromatase hereafter). This study was conducted to improve our knowledge about its expression during mouse testis development.

FINDINGS

By RT-PCR and western blotting, we show that full-length aromatase is expressed as early as 12.5 day post-coitum (dpc) with maximal expression at 17.5 dpc. Two additional truncated transcripts were also detected by RT-PCR. Immunostaining of fetal testis sections and of gonocyte-enriched cell cultures revealed that aromatase is strongly expressed in fetal Leydig cells and at variable levels in gonocytes. Conversely, it was not detected in Sertoli cells.

CONCLUSIONS

This study shows for the first time that i) aromatase is expressed from the early stages of fetal testis development, ii) it is expressed in mouse gonocytes suggesting that fetal germ cells exert an endocrine function in this species and that the ratio between estrogens and androgens may be higher inside gonocytes than in the interstitial fluid. Furthermore, we emphasized a species-specific cell localization. Indeed, previous works found that in the rat aromatase is expressed both in Sertoli and Leydig cells. We propose to take into account this species difference as a new concept to better understand the changes in susceptibility to Endocrine Disruptors from one species to another.

Expression profile of the aromatase enzyme in the Xenopus brain and localization of estradiol and estrogen receptors in each tissue

Estradiol (E2) with the strongest bioactivity of the estrogens, is synthesized by the cytochrome p450 aromatase enzyme and plays a key role in sex differentiation of the vertebrate's gonads. In Xenopus, aromatase mRNA is highly expressed in the brain rather than in the gonad during sex differentiation. In this study, we analyzed the stage change, tissue specificity, and localization of the aromatase expression in the Xenopus brain. Regardless of the sex difference, expression level of aromatase was remarkably higher in the brain than in other tissues during the early stages of brain morphogenesis and was observed in the formation regions of the choroid plexus of cerebral ventricle and the paleocortex and olfactory bulb of the prosencephalon. However, E2 concentrations in each tissue indicated a different localization of aromatase and were seen in the heart at almost double the level as seen in the brain. In addition, while aromatase expression level in the brain was increasing, E2 in the whole body began to increase at the same stage. Since the expression level of estrogen receptor α also corresponded to localization of E2, these results may imply that the E2 synthesized by the high aromatase expression in the choroid plexus, which generates cerebrospinal fluid, circulates to the heart and acts through ERα.

Sertoli cell androgen receptor expression regulates temporal fetal and adult Leydig cell differentiation, function, and population size

We recently created a mouse model displaying precocious Sertoli cell (SC) and spermatogenic development induced by SC-specific transgenic androgen receptor expression (TgSCAR). Here we reveal that TgSCAR regulates the development, function, and absolute number of Leydig cells (LCs). Total fetal and adult type LC numbers were reduced in postnatal and adult TgSCAR vs control testes, despite normal circulating LH levels. Normal LC to SC ratios found in TgSCAR testes indicate that SC androgen receptor (SCAR)-mediated activity confers a quorum-dependent relationship between total SC and LC numbers. TgSCAR enhanced LC differentiation, shown by elevated ratios of advanced to immature LC types, and reduced LC proliferation in postnatal TgSCAR vs control testes. Postnatal TgSCAR testes displayed up-regulated expression of coupled ligand-receptor transcripts (Amh-Amhr2, Dhh-Ptch1, Pdgfa-Pdgfra) for potential SCAR-stimulated paracrine pathways, which may coordinate LC differentiation. Neonatal TgSCAR testes displayed normal T and dihydrotestosterone levels despite differential changes to steroidogenic gene expression, with down-regulated Star, Cyp11a1, and Cyp17a1 expression contrasting with up-regulated Hsd3b1, Hsd17b3, and Srd5a1 expression. TgSCAR males also displayed elevated postnatal and normal adult serum testosterone levels, despite reduced LC numbers. Enhanced adult-type LC steroidogenic output was revealed by increased pubertal testicular T, dihydrotestosterone, 3α-diol and 3β-diol levels per LC and up-regulated steroidogenic gene (Nr5a1, Lhr, Cyp11a1, Cyp17a1, Hsd3b6, Srd5a1) expression in pubertal or adult TgSCAR vs control males, suggesting regulatory mechanisms maintain androgen levels independently of absolute LC numbers. Our unique gain-of-function TgSCAR model has revealed that SCAR activity controls temporal LC differentiation, steroidogenic function, and population size.

Progesterone signalling in breast cancer: a neglected hormone coming into the limelight

Understanding the biology of the breast and how ovarian hormones impinge on it is key to rational new approaches in breast cancer prevention and therapy. Because of the success of selective oestrogen receptor modulators (SERMs), such as tamoxifen, and aromatase inhibitors in breast cancer treatment, oestrogens have long received the most attention. Early progesterone receptor (PR) antagonists, however, were dismissed because of severe side effects, but awareness is now increasing that progesterone is an important hormone in breast cancer. Oestrogen receptor-α (ERα) signalling and PR signalling have distinct roles in normal mammary gland biology in mice; both ERα and PR delegate many of their biological functions to distinct paracrine mediators. If the findings in the mouse model translate to humans, new preventive and therapeutic perspectives might open up.

Brain-specific promoter/exon I.f of the cyp19a1 (aromatase) gene in Xenopus laevis

Aromatase, encoded by the cyp19a1 gene, is the key enzyme for estrogen biosynthesis. Exon I.f of aromatase transcripts in the Xenopus brain is driven in a brain-specific manner. In this study, we cloned brain aromatase with a 5'-end of various lengths by 5'-RACE and detected the expression pattern of the aromatase mRNA. In Xenopus at the larval stage, the brain aromatase mRNA expression was five-fold higher than those in the gonad and liver, and was upregulated from stage 42 to stage 50. After isolating the brain-specific promoter I.f, which was located ∼6.5 kb upstream from gonad-specific exon PII, we observed this promoter in a potential cis-elements for several transcriptional factors, such as Oct-1, c-Myc, the GATA gene family, C/EBPalpha, Sox5, p300, XFD-1, AP1, the STAT gene family, FOXD3, and the Smad gene family. In addition, the core promoter elements of two initiators and an atypical TATA box were found around the 5'-RACE products. In the 5'-flanking region of exon I.f, the binding sites for nuclear extracts suggested that the followings are important: the STAT gene family, a 38-bp conserved region among five species, FOXD3, and the Smad gene family within the region 200 bp upstream from the transcription initiation site. Real-time RT-PCR analysis showed that the foxd3, smad2 and smad4.1/4.2 mRNAs are specifically expressed in the brain. Furthermore, the expression change of foxd3, which has been reported as a repressor, indicated that expression decreased to stage 50 from stage 42, contrary to that of aromatase mRNA. These results may imply that foxd3 expression decreases and aromatase expression increases as a result of the contribution to promoter I.f by transcriptional activators such as smads. However, since these putative cis-elements and transcription initiation sites are not conserved in the brain-specific promoter of other species, this transcriptional regulatory mechanism of exon I.f may be characteristic of Xenopus.

Semen quality is influenced by androgen receptor and aromatase gene synergism

STUDY QUESTION

Does synergism between AR(CAG)(n) and CYP19(TTTA)(n) polymorphisms influence the quality of sperm?

SUMMARY ANSWER

AR(CAG)(n) and CYP19(TTTA)(n) polymorphisms had a synergistic effect on sperm concentration and motility.

WHAT IS KNOWN ALREADY

Androgens exert their action in the testicular tissue by binding to androgen receptor (AR), while their action is mediated by the aromatase P450 enzyme (CYP19). AR(CAG)(n) alleles are associated with sperm motility and CYP19(TTTA)(n) allelic variants have implications for sperm concentration and motility.

STUDY DESIGN, SIZE, DURATION

Two hundred oligozoospermic and 250 normozoospermic men who presented for infertility investigation were examined during a period of 2 years.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Conventional semen analysis was performed. DNA was extracted from spermatozoa and both polymorphisms were genotyped by polymerase chain reaction. Serum hormone levels were determined.

MAIN RESULTS AND THE ROLE OF CHANCE

Six combined genotypes were identified between the 18 AR(CAG)(n) alleles with 12-32 repeats and the 6 CYP19(TTTA)(n) alleles with 7-12 repeats. A gradual reduction in the sperm concentration (10(6)/ml) and motility (%) from long AR allele-non-CYP19(TTTA)(7) allele carriers to long AR allele-CYP19(TTTA)(7) homozygotes and from short AR allele-non-CYP19(TTTA)(7) carriers to short AR allele-CYP19(TTTA)(7) homozygotes was observed in normozoospermic men (means ± SD; concentration: 93 ± 53.1 versus 65 ± 48.6 and 85 ± 60.1 versus 37 ± 17.2l, P < 0.002; motility: 63 ± 10.3 versus 55 ± 14.5 and 52 ± 19.6 versus 41 ± 13.7, P < 0.001, respectively). Similar associations were observed in oligozoospermic men (concentration: 10 ± 4.2 versus 9 ± 5.9 and 10 ± 6.3 versus 6 ± 3.1, P < 0.03; motility: 47 ± 17.1 versus 39 ± 6.2 and 39 ± 22 versus 27 ± 18.3, P < 0.003, respectively). The above associations of the combined genotypes with sperm concentration and motility were confirmed in the total study population (P < 0.006 and P < 0.001, respectively).

LIMITATIONS, REASONS FOR CAUTION

Our study population was limited to Greek Caucasian adult males, residents of Northwest Greece.

WIDER IMPLICATIONS OF THE FINDINGS

The confirmation of our findings in other populations would verify the significance of AR and CYP19 genes for spermatogenesis.

STUDY FUNDING/COMPETING INTERESTS

This study did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector. The authors declare no conflicts of interest.

The aromatase gene CYP19A1: several genetic and functional lines of evidence supporting a role in reading, speech and language

Inspired by the localization, on 15q21.2 of the CYP19A1 gene in the linkage region of speech and language disorders, and a rare translocation in a dyslexic individual that was brought to our attention, we conducted a series of studies on the properties of CYP19A1 as a candidate gene for dyslexia and related conditions. The aromatase enzyme is a member of the cytochrome P450 super family, and it serves several key functions: it catalyzes the conversion of androgens into estrogens; during early mammalian development it controls the differentiation of specific brain areas (e.g. local estrogen synthesis in the hippocampus regulates synaptic plasticity and axonal growth); it is involved in sexual differentiation of the brain; and in songbirds and teleost fishes, it regulates vocalization. Our results suggest that variations in CYP19A1 are associated with dyslexia as a categorical trait and with quantitative measures of language and speech, such as reading, vocabulary, phonological processing and oral motor skills. Variations near the vicinity of its brain promoter region altered transcription factor binding, suggesting a regulatory role in CYP19A1 expression. CYP19A1 expression in human brain correlated with the expression of dyslexia susceptibility genes such as DYX1C1 and ROBO1. Aromatase-deficient mice displayed increased cortical neuronal density and occasional cortical heterotopias, also observed in Robo1-/- mice and human dyslexic brains, respectively. An aromatase inhibitor reduced dendritic growth in cultured rat neurons. From this broad set of evidence, we propose CYP19A1 as a candidate gene for human cognitive functions implicated in reading, speech and language.

Tissue physiology and pathology of aromatase

Aromatase is expressed in multiple tissues, indicating a crucial role for locally produced oestrogens in the differentiation, regulation and normal function of several organs and processes. This review is an overview of the role of aromatase in different tissues under normal physiological conditions and its contribution to the development of some oestrogen-related pathologies.

Inhibitory effects of calcitriol on the growth of MCF-7 breast cancer xenografts in nude mice: selective modulation of aromatase expression in vivo

Calcitriol (1,25-dihydroxyvitamin D(3)), the hormonally active metabolite of vitamin D, exerts many anticancer effects in breast cancer (BCa) cells. We have previously shown using cell culture models that calcitriol acts as a selective aromatase modulator (SAM) and inhibits estrogen synthesis and signaling in BCa cells. We have now examined calcitriol effects in vivo on aromatase expression, estrogen signaling, and tumor growth when used alone and in combination with aromatase inhibitors (AIs). In immunocompromised mice bearing MCF-7 xenografts, increasing doses of calcitriol exhibited significant tumor inhibitory effects (~50% to 70% decrease in tumor volume). At the suboptimal doses tested, anastrozole and letrozole also caused significant tumor shrinkage when used individually. Although the combinations of calcitriol and the AIs caused a statistically significant increase in tumor inhibition in comparison to the single agents, the cooperative interaction between these agents appeared to be minimal at the doses tested. Calcitriol decreased aromatase expression in the xenograft tumors. Importantly, calcitriol also acted as a SAM in the mouse, decreasing aromatase expression in the mammary adipose tissue, while increasing it in bone marrow cells and not altering it in the ovaries and uteri. As a result, calcitriol significantly reduced estrogen levels in the xenograft tumors and surrounding breast adipose tissue. In addition, calcitriol inhibited estrogen signaling by decreasing tumor ERα levels. Changes in tumor gene expression revealed the suppressive effects of calcitriol on inflammatory and growth signaling pathways and demonstrated cooperative interactions between calcitriol and AIs to modulate gene expression. We hypothesize that cumulatively these calcitriol actions would contribute to a beneficial effect when calcitriol is combined with an AI in the treatment of BCa.

Aromatase (CYP19) gene variants influence ovarian response to standard gonadotrophin stimulation

PURPOSE

The association of cytochrome P450 aromatase gene CYP19(TTTA) ( n ) polymorphism with ovarian response to FSH stimulation was explored.

METHODS

Three hundred women undergoing medically assisted reproduction and 300 women with at least one spontaneous pregnancy participated in the study. CYP19(TTTA) ( n ) polymorphism was genotyped, while serum hormones were determined. During oocyte retrieval, the follicular size, the follicle and oocyte numbers were recorded.

RESULTS

Six CYP19(TTTA) ( n ) alleles with 7 to 12 repeats were revealed. Women homozygous for long CYP19(TTTA) ( n ) alleles presented with lower serum FSH levels at the third day of the menstrual cycle (p < 0.001) and higher large follicle numbers (p < 0.01), compared to women homozygous for short CYP19(TTTA) ( n ) alleles. The CYP19(TTTA) ( 7 ) allele was associated with higher serum FSH levels (p < 0.003), with lower total follicle (p < 0.02) and large follicle numbers (p < 0.03), while CYP19(TTTA) ( 7 ) allele-carriers presented more frequently with small follicles than CYP19(TTTA) ( 7 ) allele-non carriers (p < 0.01).

CONCLUSIONS

CYP19 genetic variants were associated with ovarian reserve and response to standard gonadotrophin stimulation of women undergoing in vitro fertilization.

Evolutionary origins of the estrogen signaling system: insights from amphioxus

Classically, the estrogen signaling system has two core components: cytochrome P450 aromatase (CYP19), the enzyme complex that catalyzes the rate limiting step in estrogen biosynthesis; and estrogen receptors (ERs), ligand activated transcription factors that interact with the regulatory region of target genes to mediate the biological effects of estrogen. While the importance of estrogens for regulation of reproduction, development and physiology has been well-documented in gnathostome vertebrates, the evolutionary origins of estrogen as a hormone are still unclear. As invertebrates within the phylum Chordata, cephalochordates (e.g., the amphioxus of the genus Branchiostoma) are among the closest invertebrate relatives of the vertebrates and can provide critical insight into the evolution of vertebrate-specific molecules and pathways. To address this question, this paper briefly reviews relevant earlier studies that help to illuminate the history of the aromatase and ER genes, with a particular emphasis on insights from amphioxus and other invertebrates. We then present new analyses of amphioxus aromatase and ER sequence and function, including an in silico model of the amphioxus aromatase protein, and CYP19 gene analysis. CYP19 shares a conserved gene structure with vertebrates (9 coding exons) and moderate sequence conservation (40% amino acid identity with human CYP19). Modeling of the amphioxus aromatase substrate binding site and simulated docking of androstenedione in comparison to the human aromatase shows that the substrate binding site is conserved and predicts that androstenedione could be a substrate for amphioxus CYP19. The amphioxus ER is structurally similar to vertebrate ERs, but differs in sequence and key residues of the ligand binding domain. Consistent with results from other laboratories, amphioxus ER did not bind radiolabeled estradiol, nor did it modulate gene expression on an estrogen-responsive element (ERE) in the presence of estradiol, 4-hydroxytamoxifen, diethylstilbestrol, bisphenol A or genistein. Interestingly, it has been shown that a related gene, the amphioxus "steroid receptor" (SR), can be activated by estrogens and that amphioxus ER can repress this activation. CYP19, ER and SR are all primarily expressed in gonadal tissue, suggesting an ancient paracrine/autocrine signaling role, but it is not yet known how their expression is regulated and, if estrogen is actually synthesized in amphioxus, whether it has a role in mediating any biological effects. Functional studies are clearly needed to link emerging bioinformatics and in vitro molecular biology results with organismal physiology to develop an understanding of the evolution of estrogen signaling. This article is part of a Special Issue entitled 'Marine organisms'.

Aromatase promoter I.f is regulated by progesterone receptor in mouse hypothalamic neuronal cell lines

Aromatase catalyzes the conversion of C(19) steroids to estrogens. Aromatase and progesterone, both of which function at different steps of steroidogenesis, are crucial for the sexually dimorphic development of the fetal brain and the regulation of gonadotropin secretion and sexual interest in adults. The aromatase gene (Cyp19a1) is selectively expressed in distinct neurons of the mouse hypothalamus through a distal brain-specific promoter, I.f, located ∼40 kb upstream of the coding region. However, the regulation of aromatase expression in the brain is not well understood. In this study, we investigated a short feedback effect of progesterone analogues on aromatase mRNA expression and enzyme activity in estrogen receptor α (Esr1)-positive or -negative mouse embryonic hypothalamic neuronal cell lines that express aromatase via promoter I.f. In a hypothalamic neuronal cell line that highly expresses aromatase, progesterone receptor (Pgr), and Esr1, a progesterone agonist, R5020, inhibited aromatase mRNA level and enzyme activity. The inhibitory effect of R5020 was reversed by its antagonist, RU486. Deletion mutants of promoter I.f suggested that inhibition of aromatase expression by progesterone is conferred by the nt -1000/-500 region, and R5020 enhanced binding of Pgr to the nt -800/-600 region of promoter I.f. Small interfering RNA knockdown of Pgr eliminated progesterone-dependent inhibition of aromatase mRNA and enzyme activity. Taken together, progesterone enhances recruitment of Pgr to specific regions of the promoter I.f of Cyp19a1 and regulates aromatase expression in hypothalamic neurons.

A doxycycline-inducible, tissue-specific aromatase-expressing transgenic mouse

Aromatase converts androgens to estrogens and it is expressed in gonads and non-reproductive tissues (e.g. brain and adipose tissues). As circulating levels of estrogens in males are low, we hypothesize that local estrogen production is important for the regulation of physiological functions (e.g. metabolism) and pathological development (e.g. breast and prostate cancers) by acting in a paracrine and/or intracrine manner. We generated a tissue-specific doxycycline-inducible, aromatase transgenic mouse to test this hypothesis. The transgene construct (pTetOAROM) consists of a full-length human aromatase cDNA (hAROM) and a luciferase gene under the control of a bi-directional tetracycline-responsive promoter (pTetO), which is regulated by transactivators (rtTA or tTA) and doxycycline. Our in vitro studies using MBA-MB-231tet cells stably expressing rtTA, showed that doxycycline treatment induced transgene expression of hAROM transcripts by 17-fold (P = 0.01), aromatase activity by 26-fold, (P = 0.0008) and luciferase activity by 9.6-fold (P = 0.0006). Pronuclear microinjection of the transgene generated four pTetOAROM founder mice. A male founder was bred with a female mammary gland-specific rtTA mouse (MMTVrtTA) to produce MMTVrtTA-pTetOAROM double-transgenic mice. Upon doxycycline treatment via drinking water, human aromatase expression was detected by RT-PCR, specifically in mammary glands, salivary glands and seminal vesicles of double-stransgenic mice. Luciferase expression and activity was detected in these tissues by in vivo bioluminescence imaging, in vitro luciferase assay and RT-PCR. In summary, we generated a transgenic mouse model that expresses the human aromatase transgene in a temporal- and spatial-specific manner, which will be a useful model to study the physiological importance of local estrogen production.

The association of aromatase (CYP19) gene variants with sperm concentration and motility

The irreversible transformation of androgens into oestrogens is catalysed by cytochrome P450 aromatase. In the present study, we explored the contribution of the (TTTA)(n) polymorphism in the aromatase gene (CYP19) to sperm concentration and motility. Ninety normozoospermic and 60 oligospermic men were examined during infertility examinations. DNA was extracted from spermatozoa, and the CYP19 (TTTA)(n) polymorphism was genotyped by PCR. Genotype analysis revealed six CYP19 (TTTA)(n) alleles with 7-12 repeats. The allelic distribution of the CYP19 (TTTA)(n) polymorphism differed between normozoospermic and oligospermic men (P<0.01). Oligospermic men less frequently had long CYP19 alleles than did normozoospermic men (25 and 37.8%, respectively; P<0.02). The higher frequency of short CYP19 alleles in oligospermic men compared to normozoospermic men (43.3 and 28.3%, respectively; P<0.01) was primarily due to the distribution of the CYP19 (TTTA)(7) allele. The CYP19 (TTTA)(7) allele was associated with lower sperm concentration in normozoospermic men (P<0.01) and in the total study population (P<0.01); it was also associated with lower sperm motility in normozoospermic men (P<0.05) and in the total study population (P<0.01). In conclusion, the CYP19 (TTTA)(7) allele probably impairs aromatase activity, which in turn alters aromatase and oestrogen levels in the testis, leading to decreased sperm concentration and motility. These findings support the significance of cytochrome P450 aromatase in human spermatogenesis and consequently in semen quality.

Neuroendocrine effects of endocrine disruptors in teleost fish

Because a large proportion of potential endocrine disruptors (EDC) end up in surface waters, aquatic species are particularly vulnerable to their potential adverse effects. Recent studies identified a number of brain targets for EDC commonly present in environmentally relevant concentrations in surface waters. Among those neuronal systems disrupted by EDC are the gonadotropin-releasing hormone (GnRH) neurons, the dopaminergic and serotoninergic circuits, and more recently the Kiss/GPR54 system, which regulates gonadotropin release. However, one of the most striking effects of EDC, notably estrogen mimics, is their impact on the cyp19a1b gene that encodes the brain aromatase isoform in fish. Moreover, this is the only example in which the molecular basis of endocrine disruption is fully understood. The aims of this review were to (1) synthesize the most recent discoveries concerning the EDC effects upon neuroendocrine systems of fish and (2) provide, when possible, the underlying molecular basis of disruption for each system concerned. The potential adverse effects of EDC on neurogenesis, puberty, and brain sexualization are also described. It is important to point out the future environmental, social, and economical issues arising from endocrine disruption studies in the context of risk assessment.

Diverse and active roles for adipocytes during mammary gland growth and function

The mammary gland is unique in its requirement to develop in close association with a depot of adipose tissue that is commonly referred to as the mammary fat pad. As discussed throughout this issue, the mammary fat pad represents a complex stromal microenvironment that includes a variety of cell types. In this article we focus on adipocytes as local regulators of epithelial cell growth and their function during lactation. Several important considerations arise from such a discussion. There is a clear and close interrelationship between different stromal tissue types within the mammary fat pad and its adipocytes. Furthermore, these relationships are both stage- and species-dependent, although many questions remain unanswered regarding their roles in these different states. Several lines of evidence also suggest that adipocytes within the mammary fat pad may function differently from those in other fat depots. Finally, past and future technologies present a variety of opportunities to model these complexities in order to more precisely delineate the many potential functions of adipocytes within the mammary glands. A thorough understanding of the role for this cell type in the mammary glands could present numerous opportunities to modify both breast cancer risk and lactation performance.

Genomic and neural analysis of the estradiol-synthetic pathway in the zebra finch

Background

Steroids are small molecule hormones derived from cholesterol. Steroids affect many tissues, including the brain. In the zebra finch, estrogenic steroids are particularly interesting because they masculinize the neural circuit that controls singing and their synthesis in the brain is modulated by experience. Here, we analyzed the zebra finch genome assembly to assess the content, conservation, and organization of genes that code for components of the estrogen-synthetic pathway and steroid nuclear receptors. Based on these analyses, we also investigated neural expression of a cholesterol transport protein gene in the context of song neurobiology.

Results

We present sequence-based analysis of twenty steroid-related genes using the genome assembly and other resources. Generally, zebra finch genes showed high homology to genes in other species. The diversity of steroidogenic enzymes and receptors may be lower in songbirds than in mammals; we were unable to identify all known mammalian isoforms of the 3β-hydroxysteroid dehydrogenase and 17β-hydroxysteroid dehydrogenase families in the zebra finch genome assembly, and not all splice sites described in mammals were identified in the corresponding zebra finch genes. We did identify two factors, Nobox and NR1H2-RXR, that may be important for coordinated transcription of multiple steroid-related genes. We found very little qualitative overlap in predicted transcription factor binding sites in the genes for two cholesterol transport proteins, the 18 kDa cholesterol transport protein (TSPO) and steroidogenic acute regulatory protein (StAR). We therefore performed in situ hybridization for TSPO and found that its mRNA was not always detected in brain regions where StAR and steroidogenic enzymes were previously shown to be expressed. Also, transcription of TSPO, but not StAR, may be regulated by the experience of hearing song.

Conclusions

The genes required for estradiol synthesis and action are represented in the zebra finch genome assembly, though the complement of steroidogenic genes may be smaller in birds than in mammals. Coordinated transcription of multiple steroidogenic genes is possible, but results were inconsistent with the hypothesis that StAR and TSPO mRNAs are co-regulated. Integration of genomic and neuroanatomical analyses will continue to provide insights into the evolution and function of steroidogenesis in the songbird brain.

The multiple roles of estrogens and the enzyme aromatase

Aromatase is the enzyme that catalyzes the last step of estrogen biosynthesis. It is expressed in many tissues such as the gonads, brain and adipose tissue. The regulation of the level and activity of aromatase determines the levels of estrogens that have endocrine, paracrine and autocrine effects on tissues. Estrogens play many roles in the body, regulating reproduction, metabolism and behavior. In the brain, cell survival and the activity of neurons are affected by estrogens and hence aromatase.