Characterization of the fertility of male aromatase knockout mice

Previous studies employing the male aromatase knockout (ArKO) mouse have indicated that local expression of estrogens appears to be important for the progression of spermatogenesis. In the absence of estrogen biosynthesis round spermatids are observed to undergo apoptosis and thus fail to differentiate into mature, elongated spermatids. This lesion appears to arise between the ages of 18 weeks and 1 year. To ultimately determine if the disruption to spermatogenesis arises earlier than 18 weeks, we performed an intensive study to examine the fertility of younger male ArKO mice. This involved an analysis of their mating capacity together with an extensive stereological analysis, determination of the in vitro potential of mature sperm, and sexual behavior. ArKO and wild-type (w/t) males at 7 weeks of age were placed with w/t females for 7 weeks. At age 14 weeks, the males were killed and the testes removed. ArKO mice were observed to sire significantly fewer litters than the w/t mice; 5 out of the 10 sired no litters at all. Stereological analysis performed on the removed testes found a significant decrease in round spermatid numbers between w/t and ArKO mice at this age; however, there were no differences in all other germ cells and Sertoli cell numbers. When mature spermatozoa were analyzed, sperm from 15-week-old ArKO mice had a significant reduction in motility. This was further reduced by 1 year of age with a decrease in concentration. A preliminary examination of sexual behavior found that ArKO mice did not attempt to mount the females, in contrast to the w/t mice, which mounted consistently during the time period. In conclusion, we observed that ArKO mice have reduced fertility at age 14 weeks. This may be due in part to a disruption in spermatogenesis because the phenotype does appear to arise earlier than 18 weeks, possibly leading to abnormalities in the mature spermatozoa. Or, in part, this may be attributable to an impairment in the development of copulatory behavior, which is consistent with the available evidence that points to a crucial role for estrogens in the neural development and initiation of male sexual behavior.

Elevated androgens and prolactin in aromatase-deficient mice cause enlargement, but not malignancy, of the prostate gland

Although androgens are the main steroids controlling the growth of the mammalian prostate, increasing evidence demonstrates that estrogens also regulate prostate development and growth. This study describes the effects of estrogen deficiency using aromatase knockout mice (ArKO) with targeted disruption of the cyp19 gene. Serum and tissue testosterone and 5alpha-dihydrotestosterone as well as serum PRL levels are significantly (P < 0.05) elevated in mature male ArKO mice. Histological, stereological, and immunohistochemical studies demonstrated enlargement of the ventral, anterior, and dorsolateral lobes of the prostate in young and older ArKO mice. Hyperplasia of the epithelial, interstitial, and luminal compartments was identified and associated with up-regulation of androgen receptors. There was no evidence of malignancy as the animals aged (up to 56 weeks). The changes observed in the prostates of ArKO mice were unaffected by maintaining mice on regular or soy-free diets. It is concluded in ArKO mice that, despite the long-term elevation of androgens and PRL, the absence of estrogen in these animals does not result in induction of malignancy in the prostate gland.

Estrogen and spermatogenesis

Although it has been known for many years that estrogen administration has deleterious effects on male fertility, data from transgenic mice deficient in estrogen receptors or aromatase point to an essential physiological role for estrogen in male fertility. This review summarizes the current knowledge on the localization of estrogen receptors and aromatase in the testis in an effort to understand the likely sites of estrogen action. The review also discusses the many studies that have used models employing the administration of estrogenic substances to show that male fertility is responsive to estrogen, thus providing a mechanism by which inappropriate exposure to estrogenic substances may cause adverse effects on spermatogenesis and male fertility. The reproductive phenotypes of mice deficient in estrogen receptors alpha and/or beta and aromatase are also compared to evaluate the physiological role of estrogen in male fertility. The review focuses on the effects of estrogen administration or deprivation, primarily in rodents, on the hypothalamo-pituitary-testis axis, testicular function (including Leydig cell, Sertoli cell, and germ cell development and function), and in the development and function of the efferent ductules and epididymis. The requirement for estrogen in normal male sexual behavior is also reviewed, along with the somewhat limited data on the fertility of men who lack either the capacity to produce or respond to estrogen. This review highlights the ability of exogenous estrogen exposure to perturb spermatogenesis and male fertility, as well as the emerging physiological role of estrogens in male fertility, suggesting that, in this local context, estrogenic substances should also be considered "male hormones."

Collaborative ocular melanoma study (COMS) randomized trial of I-125 brachytherapy for medium choroidal melanoma. I. Visual acuity after 3 years COMS report no. 16

OBJECTIVE

To report visual acuity during the first three years after iodine 125 (I(125)) brachytherapy for medium-sized choroidal melanoma and to identify important baseline and treatment factors associated with posttreatment visual acuity in a group of patients who were treated and observed prospectively as part of a large, randomized clinical trial.

DESIGN

Observational case series within a randomized, multicenter study.

PARTICIPANTS

Patients enrolled in the Collaborative Ocular Melanoma Study randomized trial of I(125) brachytherapy versus enucleation had choroidal melanoma of at least 2.5 mm but no more than 10.0 mm in apical height, and no more than 16.0 mm in largest basal dimension. One thousand three hundred seventeen patients enrolled from February 1987 through July 1998; 657 patients were assigned to I(125) brachytherapy. Visual acuity data for 623 patients who received I(125) brachytherapy as randomly assigned and who have been observed for at least 1 year were analyzed for this report.

METHODS

Under study protocol, an ophthalmic evaluation, including best-corrected visual acuity measurement of each eye, was performed at baseline, every 6 months thereafter for 5 years, and once yearly thereafter. Two poor vision outcomes, visual acuity of 20/200 or worse that was confirmed at the next follow-up examination and loss of six lines or more of visual acuity from baseline that was confirmed at the next follow-up examination, were analyzed to identify baseline and treatment characteristics that were associated with posttreatment visual acuity.

RESULTS

At baseline, median visual acuity in the eye with choroidal melanoma was 20/32, with 70% of eyes having 20/40 or better and 10% of eyes having 20/200 or worse visual acuity. Three years after I(125) brachytherapy, median visual acuity was 20/125, with 34% having 20/40 or better and 45% having 20/200 or worse visual acuity, including eyes that were enucleated within 3 years of treatment. Life-table estimates of percentages of patients who lost six or more lines of visual acuity from baseline, a quadrupling of the minimum angle of resolution, with this finding confirmed at the next 6-month follow-up examination, were 18% by 1 year, 34% by 2 years, and 49% by 3 years after treatment. Life-table estimates of percentages of patients with baseline visual acuity better than 20/200 whose visual acuity decreased to 20/200 or worse, confirmed at the next follow-up examination, were 17% by 1 year, 33% by 2 years, and 43% by 3 years after treatment. As soon as a poor vision outcome was observed, improvement of visual acuity to a level that no longer met the definition for a poor vision outcome was rare. Greater baseline tumor apical height and shorter distance between the tumor and the foveal avascular zone (FAZ) were the factors most strongly associated with loss of six or more lines of visual acuity after treatment. These two factors and baseline visual acuity also were strongly associated with visual acuity 20/200 or worse after treatment. Patient history of diabetes, presence of tumor-associated retinal detachment, and tumors that were not dome shaped also were associated with greater risk for both of the poor vision outcomes.

CONCLUSIONS

Forty-three percent to 49% of treated eyes had substantial impairment in visual acuity by 3 years after I(125) brachytherapy, defined as a loss of six or more lines of visual acuity from the pretreatment level (49% of eyes) or visual acuity of 20/200 or worse (43% of eyes) that was confirmed at the next 6-month examination. Patients with a history of diabetes and patients whose eyes had thicker tumors, tumors close to or beneath the FAZ, tumor-associated retinal detachment, or tumors that were not dome shaped were those most likely to have a poor visual acuity outcome within 3 years after I(125) brachytherapy.

Aromatase-deficient (ArKO) mice have a phenotype of increased adiposity

The aromatase-knockout (ArKO) mouse provides a useful model to examine the role that estrogens play in development and homeostasis in mammals. Lacking a functional Cyp19 gene, which encodes aromatase, the ArKO mouse cannot synthesize endogenous estrogens. We examined the adipose depots of male and female ArKO mice, observing that these animals progressively accumulate significantly more intraabdominal adipose tissue than their wild-type (WT) littermates, reflected in increased adipocyte volume at gonadal and infrarenal sites. This increased adiposity was not due to hyperphagia or reduced resting energy expenditure, but was associated with reduced spontaneous physical activity levels, reduced glucose oxidation, and a decrease in lean body mass. Elevated circulating levels of leptin and cholesterol were present in 1-year-old ArKO mice compared with WT controls, as were elevated insulin levels, although blood glucose levels were unchanged. Associated with these changes, a striking accumulation of lipid droplets was observed in the livers of ArKO animals. Our findings demonstrate an important role for estrogen in the maintenance of lipid homeostasis in both males and females.

Oestrogens in male reproduction

The role of oestrogens in male reproductive physiology is rapidly being redefined. While cases of oestrogen deficiency or insensitivity are rare among humans, insights are being gained from the development of mouse models in which oestrogen action has been abolished. Four knockout mouse models are currently available. The three oestrogen receptor knockout models-the oestrogen receptor-alpha (alphaERKO), -beta (betaERKO) and -alphabeta (alphabetaERKO) double knockout mice-are providing valuable information on the loss of action of oestrogen receptors and the way in which either or both isoforms of the receptor are employed in any given action. On the other hand, the generation of the aromatase knockout (ArKO) mouse has produced animals unable to synthesize endogenous oestrogen. Fundamental perturbations that affect male fertility in these models include a disruption of testis morphology, an arrest of spermatogenesis at the stage of early spermiogenesis, a reduction in sperm concentration, motility and the ability to fertilize, severe dilatation of the efferent ductules and significant alterations to the normal hormone profile. The continuing accumulation of evidence from these animal models demonstrates that oestrogen plays an essential and direct role in the development and maintenance of male fertility.

Aromatase in aging women

Cessation of ovarian estrogen secretion is the key event during the climacteric. An enzyme termed aromatase in a number of human tissues and cells, including ovarian granulosa cells, the placental syncytiotrophoblast, adipose and skin fibroblasts, bone, and the brain, catalyzes the conversion of C19 steroids to estrogens. Aromatase expression in adipose tissue and possibly the skin primarily accounts for the extraglandular (peripheral) formation of estrogen and increases as a function of body weight and advancing age. Sufficient circulating levels of the biologically active estrogen, estradiol, can be produced as a result of extraglandular aromatization of androstenedione to estrone, which is subsequently reduced to estradiol in peripheral tissues, to cause uterine bleeding and endometrial hyperplasia and cancer in obese anovulatory or postmenopausal women. Extraglandular aromatase expression in adipose tissue and skin (via increasing circulating levels of estradiol) and bone (via increasing local estrogen concentrations) is of paramount importance in slowing the rate of postmenopausal bone loss. Moreover, excessive or inappropriate aromatase expression was demonstrated in adipose fibroblasts surrounding a breast carcinoma, endometriosis-derived stromal cells, and stromal cells in endometrial cancer and gave rise to increased local estrogen concentrations in these tissues. Whether systemically delivered or locally produced, elevated estrogen levels promote the growth of these steroid-responsive tissues. Finally, local estrogen biosynthesis by aromatase activity in the brain may be important in the regulation of various cognitive and hypothalamic functions. The regulation of aromatase expression in human cells via alternatively used promoters, which can be activated or inhibited by various hormones, increases the complexity of estrogen biosynthesis in the human body. Aromatase expression is under the control of the classically located proximal promoter II in the ovary and a far distal promoter I.1 (40 kb upstream of the translation initiation site) in the placenta. In adipose tissue, two other promoters (I.4 and I.3) located between I.1 and II are used in addition to the ovarian-type promoter II. To add a further twist, promoter use in adipose fibroblasts switches between promoters II/I.3 and I.4 upon treatment of these cells with prostaglandin E2 (PGE2) versus glucocorticoids plus cytokines. Moreover, the presence of a carcinoma in breast adipose tissue causes a switch of promoter use from I.4 to II/I.3. Molecular and cellular mechanisms responsible for estrogen formation and their physiologic and clinical relevance will be reviewed in this article.

Biology of aromatase in the mammary gland

While the ovaries are the principal source of systemic estrogen in the premenopausal nonpregnant woman, other sites of estrogen biosynthesis are present throughout the body and these become the major sources of estrogen beyond menopause. These sites include the mesenchymal cells of the adipose tissue and skin, osteoblasts, and perhaps chondrocytes in bone, vascular endothelial and aortic smooth muscle cells, as well as a number of sites in the brain including the medial preoptic/anterior hypothalamus, the medial basal hypothalamus and the amygdala. These extragonadal sites of estrogen biosynthesis possess several fundamental features which differ from those of the ovaries. Principally, the estrogen synthesized within these compartments is probably only biologically active at a local tissue level in a paracrine or 'intracrine' fashion. Thus the total amount of estrogen synthesized by these extragonadal sites may be small, but the local tissue concentrations achieved are probably quite high, and exert significant biological influence locally. Thus these sources of estrogen play an important but hitherto largely unrecognized, physiological and pathophysiological role.

An age-related ovarian phenotype in mice with targeted disruption of the Cyp 19 (aromatase) gene

With the development of a mouse model of estrogen insufficiency due to targeted disruption of the aromatase gene [the aromatase knockout (ArKO) mouse], a new opportunity exists to examine the role of estrogen in ovarian follicular development. Ovaries and serum were collected from wild-type, heterozygous, and ArKO mice at 10-12 and 21-23 weeks and 1 yr of age. The ovaries were assessed histologically and stereologically, with primary, secondary, and antral follicles and corpora lutea counted. The uteri were hypoestrogenic, and serum levels of LH and FSH in ArKO females were elevated above those in heterozygote and wild-type animals at all ages studied. Although estrogen was not a prerequisite for reinitiation of follicle growth, there was a block of follicular development, and no corpora lutea were present in ArKO ovaries. Thus, the ArKO mouse was infertile as a consequence of disrupted folliculogenesis and a failure to ovulate. Hemorrhagic cystic follicles were present by 21-23 weeks of age. The ovarian phenotype degenerated with age, such that by 1 yr there were no secondary or antral follicles, and the primary follicles present were atretic. Extensive interstitial tissue remodeling occurred, exemplified by an influx of macrophages and collagen deposition, coincident with the loss of follicles. In conclusion, the ovarian environment in ArKO mice does not allow the characteristic development of follicles that culminates in ovulation and demonstrates an in vivo requirement of estrogen for normal ovarian function in the mouse.

The roles of activins, inhibins and estrogen in early committed follicles

The hypothesis that activin and inhibin are autocrine/paracrine mediators of ovarian folliculogenesis has a solid basis. In mouse and rat models, granulosa cells (GC) of committed follicles express mRNA and protein for the activin/inhibin subunits and mRNA for the activin receptors (type I and II). Dimeric inhibin-A and -B are produced by postnatal ovarian cell dispersates and (GC) in culture. Similar levels of inhibin-A and -B are produced by postnatal ovarian cells, but thereafter as the ovary develops, inhibin-A becomes the predominant form. Activin was more effective than transforming growth factor-beta (TGF-beta) in enhancing follicle stimulating hormone (FSH)-stimulated inhibin production by ovarian cells. Evidence for a local regulatory role of estrogen in the ovary is also accumulating. Murine models of estrogen receptor (ERalpha or ERbeta) disruption produce mice with abnormal ovarian phenotypes. Female mice, which lack the capacity to produce estrogen (ArKO mice), have arrested folliculogenesis, no corpora lutea, elevated levels of luteinising hormone (LH), FSH and testosterone and are infertile. These data are consistent with autocrine/paracrine actions of activin in the early growth of committed follicles and estrogen in follicular maturation.

Upregulation of estrogen receptors in the forebrain of aromatase knockout (ArKO) mice

Estrogens have numerous reproductive and nonreproductive functions in brain. The actions of estrogens are mediated by estrogen receptors (ERs), and estrogens are believed to down-regulate their own receptors in many tissues. Assuming this to be true, if estrogens are removed there should be an upregulation of ERs. We have developed a mouse model in which estrogen synthesis is completely eliminated by homologous recombination to delete the gene encoding aromatase cytochrome P450 (P450(arom)). The P450(arom) enzyme catalyzes the synthesis of estrogens from androgens in the brain. The localization and density of ERs was studied in the brains of aromatase knockout (ArKO) and wild type male mice by using immunohistochemistry with a peptide antibody to ERalpha (ER-21) and computer imaging. In the wild-type animals a high density of ERalpha was found in a small number of hypothalamic cells; in the medial preoptic area, periventricular, arcuate, and ventromedial nuclei. A low and medium density of ERalpha was observed in cells of the lateral preoptic area, supraoptic, bed nucleus of the stria terminalis, and in central, medial and anterior cortical amygdaloid nuclei. The number of cells containing ERalpha-immunoreactivity was significantly increased (244%) in the medial preoptic area of the ArKO mice. In neither wild type nor ArKO animals was immunoreactivity observed in the cerebral cortex or striatum. There was intense ER-immunostaining in the nucleus of neurons in both wild type and ArKO mice. These data indicate that in the absence of estrogens there is as much as a 2-fold increase in the number of cells with ERalpha-immunoreactivity in certain hypothalamic and limbic regions. Thus, estrogens can down-regulate ERalpha in brain.

Peroxisome proliferator-activated receptor gamma ligands inhibit estrogen biosynthesis in human breast adipose tissue: possible implications for breast cancer therapy

Estrogen biosynthesis is catalyzed by aromatase cytochrome P-450 (the product of the CYP19 gene). Adipose tissue is the major site of estrogen biosynthesis in postmenopausal women, with the local production of estrogen in breast adipose tissue implicated in the development of breast cancer. In human adipose tissue, aromatase is primarily expressed in the mesenchymal stromal cells and is a marker of the undifferentiated preadipocyte phenotype. Aromatase expression in adipose tissue is regulated via the distal promoter I.4, under the control of glucocorticoids and class I cytokines such as oncostatin M, interleukin 6, and interleukin 11, as well as tumor necrosis factor alpha. These cytokines, which are expressed in adipose, also inhibit adipocyte differentiation. Therefore, we hypothesized that factors which stimulate adipocyte differentiation should inhibit aromatase expression. These factors include synthetic peroxisome proliferator-activated receptor gamma (PPARgamma) ligands such as thiazolidinediones, e.g., troglitazone and rosiglitazone (BRL49653) and the endogenous PPARgamma ligand 15-deoxy-delta12,14-prostaglandin J2. We have demonstrated by measurement of aromatase activity and by reverse transcription-PCR/Southern blotting that these PPARgamma ligands inhibit aromatase expression in cultured breast adipose stromal cells stimulated with oncostatin M or tumor necrosis factor alpha plus dexamethasone in a concentration-dependent manner, whereas a metabolite of troglitazone that does not activate PPARgamma has no effect. We have also shown that troglitazone inhibits luciferase activity of reporter constructs containing various lengths of the upstream region of promoter I.4 transfected into mouse 3T3-L1 preadipocyte mesenchymal cells, whereas the troglitazone metabolite does not. Because local estrogen production in breast fat is implicated in breast cancer development in postmenopausal women, the actions of PPARgamma ligands suggest that they may have potential therapeutic benefit in the treatment and management of breast cancer.

Bone has a sexually dimorphic response to aromatase deficiency

Aromatase synthesizes estrogen from androgen precursors. To better understand the role of estrogen in skeletal metabolism and growth, we have assessed long bone growth and histomorphometry in aromatase-deficient (ArKO) mice. The age range for the animals was 5-7 months. At this age mice have already achieved peak bone density but continue slow bone growth. Femur length, an index of long bone growth, showed decreased growth in ArKO males compared with wild-type (wt) littermates but no significant difference in females. Radiographically, compared with age- and sex- matched littermates both ArKO males and females showed osteopenia in the lumbar spine. Histologically, both ArKO males and females showed an osteoporotic-type picture, characterized by significant decreases in trabecular bone volume and trabecular thickness. However, compared with wt littermates female ArKO animals showed a bone remodeling picture consistent with increased bone turnover, much like early postmenopausal osteoporosis in humans. On the other hand, male ArKO animals showed decreases in both osteoblastic and osteoclastic surfaces compared with wt littermates, similar to age-related osteopenia. These findings suggest that osteoporosis seen in aromatase-deficient mice may arise from different bone remodeling activities between males and females. These results also show that the ArKO model exhibits the expected results of estrogen deficiency and may be a good model for investigating sex-specific responses to estrogen deficiency. Furthermore, they imply that estrogen is important for attaining peak bone mass in male as well as in female mice.

TGF-beta1 stimulates expression of the aromatase (CYP19) gene in human osteoblast-like cells and THP-1 cells

Recent evidence has shown that bone is not only a target of estrogen action but also a source of local estrogen production. Bone cells such as osteoblasts express aromatase (P450arom) and the expression of P450arom in osteoblasts is positively regulated in a tissue specific fashion, as in the case of other tissues which express P450arom. To clarify the physiological factors regulating expression of P450arom in bone, we tested TGF-beta1 using osteoblast-like cells obtained from human fetuses as well as THP-1 cells. TGF-beta1 increased IL-1beta+DEX- induced aromatase activity in osteoblast-like cells, while it inhibited activity in skin fibroblasts. Similar enhancement of aromatase activity by TGF-beta1 was found in DEX-stimulated THP-1 cells and this cell line was used for further experiments. In THP-1 cells, TGF-beta1 enhanced DEX-induced aromatase activity almost linearly by 12 h and thereafter. Increased levels of P450arom transcripts were also demonstrated by RT-PCR at 3 h of TGF-beta1 treatment and thereafter. Cyclohexamide abolished enhancement of activity but did not inhibit the accumulation of P450arom transcripts induced by TGF-beta1. Increase in P450arom expression by TGF-beta1 was attributable to expression driven by promoter I.4. TGF-beta1 did not change the half life of P450arom transcripts. To identify the cis-acting elements responsible for TGF-beta1 action on aromatase expression, transient transfection assays were performed using a series of deletion constructs for promoter I.4 (P450-I.4/Luc). Two constructs (-410/+14 and-340/+14) that contain a functional glucocorticoid response element (GRE) and downstream sequence showed significant increase of luciferase activity in response to TGF-beta1. Deletion and mutation of the GRE in P450-I.4/Luc (-340/+14) abolished the TGF-beta1. The luciferase activity of a (GRE)(1)-SV40/Luc construct was also stimulated by TGF-beta1. These results indicate that TGF-beta1 increases the expression of P450arom at the level of transcription through promoter I.4, at least in part via an enhancement of transactivation activity of the GR in THP-1 cells. TGF-beta1 is suggested to be one of the physiological up-regulatory factors of bone aromatase.

Genetic mutations resulting in loss of aromatase activity in humans and mice

Aromatase enzyme is the product of the CYP19 gene. Human aromatase deficiency is a rare disorder and is usually caused by single base-pair changes resulting in amino acid substitution or premature stop codons. In most cases, the affected mother presents with virilization in the third trimester of pregnancy. Affected female newborns have pseudohemaphrodism with clitoromegaly and hypospadias. The cause of these presentations in pregnancy is the inability to convert fetal dehydroepiandrosterone to estrogen in the placenta and subsequent conversion to androgens in the periphery. Affected male newborns present with tall stature secondary to failed epiphyseal fusion. They also have delayed bone age, osteopenia, and undermineralization, which can be corrected with the addition of estrogen, highlighting estrogen's critical role in men as well as women. The aromatase knock-out male mouse (ArKO) has shortened femur length and bone undermineralization. Female ArKO mice at 10-12 weeks have multiple ovarian follicles arrested in the antral phase and stromal hyperplasia. By 1 year the ovaries become grossly dysmorphic with numerous cystic follicles and fibrous stroma. Male ArKO mice testes demonstrate arrest of spermatogenesis at the level of round spermatids and Leydig cell hyperplasia. ArKO mice also exhibit evidence of insulin resistance and visceral adiposity.

Phytoestrogens in health and disease

Phytoestrogens are compounds found in a wide variety of plant foods that historically are said to exhibit estrogen-like activity and, more recently, have been reported to display both estrogenic and anti-estrogenic effects. Population-based studies have been interpreted to suggest that consumption of a phytoestrogen-rich diet is protective against breast, prostate, and bowel cancer and cardiovascular disease and ameliorates estrogen-deficiency symptoms in postmenopausal women. Consequently, there is a global movement towards increased consumption of phytoestrogen-rich foods and tabletized concentrated isoflavone extracts are being heavily promoted. Evaluating the effects and hence the potential benefits and risks of phytoestrogens is a complex task. The interindividual diversity and complexity in dietary phytoestrogen absorption and metabolism make the bioactivity of these compounds unpredictable. Epidemiological studies of relationships between phytoestrogens and cancer and cardiovascular disease that take into account confounding factors are scarce. Results of many of the in vitro and in vivo studies are conflicting and confusing. These compounds do not simply mimic the effects of human steroidal estrogen but rather demonstrate both similar and divergent actions. The ultimate actions of these compounds in specific cells are determined by many factors, including the relative levels of estrogen receptor (ER) alpha and ER beta and the diverse cocktail of co-activators and co-repressors present in any given cell type. Therefore, effects vary according to the phytoestrogen studied, cell line, tissue, species, and response being evaluated. Overall, it is naive to assume that exposure to these compounds is always good; inappropriate or excessive exposure may be detrimental. Extensive documentation of the specific intracellular effects of the various phytoestrogens in different tissues, the relationships between timing and duration of exposure and disease, and results from prospective randomized studies in humans of their clinical effects and potential side effects are essential. Only then can widespread recommendations regarding the dietary and pharmacological intake of these compounds be made.

Molecular mechanism for cooperation between Sp1 and steroidogenic factor-1 (SF-1) to regulate bovine CYP11A gene expression

Bovine cholesterol side-chain cleavage cytochrome P450 (P450scc; product of the CYP11A gene) gene expression is regulated by gonadotropins via cAMP in the ovary, and by ACTH via cAMP in adrenal cortical cells. Previously, we characterized response elements located at -57/-32 and at -111/-101 bp in the 5'-flanking region of the bovine CYP11A gene required for cAMP-stimulated transcription in both mouse Y-1 adrenal tumor cells and bovine ovarian cells in primary culture, which bind SF-1 (or Ad4-BP) and Sp1, respectively. The role of these transcription factors in CYP11A transcription was further confirmed by deletion and mutation analyses. In addition, results obtained employing a double mutation of the Sp1- and SF-1-binding sites and a mammalian two-hybrid system indicate that Sp1 and SF-1 function cooperatively in the transactivation of the bovine CYP11A promoter in both bovine luteal cells and Y-1 cells. Here we report that SF-1 and Sp1 are able to associate with one another in vitro and in vivo. The NH2-terminal region of SF-1, especially the DNA-binding domain, is the binding site for Sp1. In addition, as CBP is a common coactivator required for the transcriptional activity of numerous transcription factors including nuclear receptors, we investigated whether CBP functions as a cofactor for the regulation of bovine CYP11A promoter activity. We show here that CBP enhanced the PKA-induced CYP11A promoter activity, while a double mutation of both Sp1 and SF-1 sites within the CYP11A promoter region abolished CBP-induced activity. Furthermore, CBP stimulated Sp1-dependent transactivation, and a CBP/Sp1 complex in vivo was demonstrated by a co-immunoprecipitation assay. Also, CBP potentiated the transcriptional activity of GAL4-SF-1 in the presence of PKA. Thus, the cooperation between SF-1 and Sp1, required for the regulation of bovine CYP11A gene expression, is mediated by a direct protein-protein interaction and/or the common coactivator CBP.

Impairment of spermatogenesis in mice lacking a functional aromatase (cyp 19) gene

It is well established that spermatogenesis is controlled by gonadotrophins and testosterone. However, a role for estrogens in male reproduction recently was suggested in adult mice deficient in estrogen receptor alpha. These mice became infertile primarily because of an interruption of fluid reabsorption by the efferent ductules of the epididymis, thus leading to a disruption of the seminiferous epithelium [Hess, R. A., Bunick, D., Lee, K. H., Bahr, J., Taylor, J. A., Korach, K. S., and Lubahn, D. B. (1997) Nature (London) 390, 509-512]. Despite the demonstration of the aromatase enzyme, which converts androgens to estrogens, and estrogen receptors within the rodent seminiferous epithelium, the role of aromatase and estrogen in germ cell development is unknown. We have investigated spermatogenesis in mice that lack aromatase because of the targeted disruption of the cyp19 gene (ArKO). Male mice deficient in aromatase were initially fertile but developed progressive infertility, until their ability to sire pups was severely impaired. The mice deficient in aromatase developed disruptions to spermatogenesis between 4.5 months and 1 year, despite no decreases in gonadotrophins or androgens. Spermatogenesis primarily was arrested at early spermiogenic stages, as characterized by an increase in apoptosis and the appearance of multinucleated cells, and there was a significant reduction in round and elongated spermatids, but no changes in Sertoli cells and earlier germ cells. In addition, Leydig cell hyperplasia/hypertrophy was evident, presumably as a consequence of increased circulating luteinizing hormone. Our findings indicate that local expression of aromatase is essential for spermatogenesis and provide evidence for a direct action of estrogen on male germ cell development and thus fertility.

Genetic mutations resulting in estrogen insufficiency in the male

The biosynthesis of estrogens is catalyzed by an enzyme known as aromatase (aromatase cytochrome P450; P450 arom; the product of the CYP19 gene). In recent years a number of patients have been described suffering from aromatase deficiency due to mutations in the CYP19 gene, resulting in the synthesis of a non-functional gene product and a resulting failure to synthesize estrogens. Males with this condition have sustained linear growth into adulthood resulting from failure of epiphyseal closure. Osteopenia and reduced bone mineral density and bone age are also characteristic. Lack of circulating estrogens is accompanied by elevated testosterone and gonadotropins. One of the men had macroorchidism with testicular volumes in excess of 25 ml (Morishima et al. J. Clin. Endocrinol. Metab. 80, 3689, 1995). Semen analysis was not performed on this patient, but it is of note that the one patient described with estrogen insensitivity due to a mutation in the estrogen receptor had a normal sperm count, although motility was decreased (Smith et al., New England J. Med. 331. 1056, 1994). By contrast, the other man with aromatase deficiency had testicular volumes of only 8 ml per testes, and was infertile. Sperm analysis revealed a count of 1 million/ml with 100% immotile sperm (Carani et al. New England J. Med. 337, 91, 1997). However, his clinical picture is confused by the fact that another male sibling has azoospermia, but has no CYP19 mutation, suggesting that the infertility problem may be due to a second genetic condition in this consanguineous family. Recently mice have been generated in which the aromatase (CYP19) gene and the gene encoding the estrogen receptor-alpha have been inactivated by targeted disruption (ArKO and ERKO mice, respectively). Male ERKO mice are infertile with atrophy of the testes and seminiferous tubule dysmorphogenesis resulting in decreased spermatogenesis and inacive sperm. By contrast the ArKO mice are initially fertile and sire litters of normal size ad frequency, however with advancing age the number of litters sired decreases relative to those of wild type litter ates. In contrast to the ERKO mice, light microscopic analysis of the testes of the ArKO mice reveals no gross morphological abnormalties and the testes are of normal size. Following recent observations that the estrogen receptor-beta isoform is highly expressed in seminiferous epthelium, spermatids and spermatocytes, it is conceivable that the relatively high levels of estrogens present in the ERKO mice can act through the ER-beta to cause infertility by a direct action on the testes. In this context it is well known that administration of high levels of estrogen to men results in infertility. It is apparent that studies of human and mouse models with disruptions of aromatase and the estrogen receptor have as yet failed to clarify the role of estrogens in male fertility and testicular function. Development of an ER-beta knockout mouse, or else a double, or even triple, knockout model, may be required in order to resolve these issues.

Characterization of mice deficient in aromatase (ArKO) because of targeted disruption of the cyp19 gene

The formation of estrogens from C19 steroids is catalyzed by aromatase cytochrome P450 (P450arom), the product of the cyp19 gene. The actions of estrogen include dimorphic anatomical, functional, and behavioral effects on the development of both males and females, considerations that prompted us to examine the consequences of deficiency of aromatase activity in mice. Mice lacking a functional aromatase enzyme (ArKO) were generated by targeted disruption of the cyp19 gene. Male and female ArKO mice were born with the expected Mendelian frequency from F1 parents and grew to adulthood. Female ArKO mice at 9 weeks of age displayed underdeveloped external genitalia and uteri. Ovaries contained numerous follicles with abundant granulosa cells and evidence of antrum formation that appeared arrested before ovulation. No corpora lutea were present. Additionally the stroma were hyperplastic with structures that appeared to be atretic follicles. Development of the mammary glands approximated that of a prepubertal female. Examination of male ArKO mice of the same age revealed essentially normal internal anatomy but with enlargement of the male accessory sex glands because of increased content of secreted material. The testes appeared normal. Male ArKO mice are capable of breeding and produce litters of approximately average size. Whereas serum estradiol levels were at the limit of detection, testosterone levels were elevated, as were the levels of follicle-stimulating hormone and luteinizing hormone. The phenotype of these animals differs markedly from that of the previously reported ERKO mice, in which the estrogen receptor alpha is deleted by targeted disruption.

Molecular basis of severe gynecomastia associated with aromatase expression in a fibrolamellar hepatocellular carcinoma

This report represents the first study in the literature linking development of severe gynecomastia, in a 17 1/2-yr-old boy, to high levels of aromatase expression in a large fibrolamellar hepatocellular carcinoma, which gave rise to extremely elevated serum levels of estrone (1200 pg/mL) and estradiol-17 beta (312 pg/mL) that suppressed FSH and LH (1.3 and 2.8 IU/L, respectively), and consequently testosterone (1.53 ng/mL). After removal of a 1.5-kg hepatocellular carcinoma, gynecomastia partially regressed, and essentially, normal hormone levels were restored (estradiol-17 beta, < 50 pg/mL; estrone, 74 pg/mL; testosterone, 6.85 ng/mL; and FSH/LH, 6.3/3.7 mIU/mL). Conversion of C19 steroids to estrogens occurs in a number of human tissues and is catalyzed by aromatase P450 (P450arom), the product of the CYP19 gene in a number of human tissues. Tissue-specific promoters are used to regulate P450arom gene transcription in adult human tissues, e.g. promoters I.4 and I.3 in adipose fibroblasts, and promoter II in the gonads. Human fetal liver uses promoter I.4 to express markedly high levels of P450arom, whereas hepatic P450arom expression normally becomes undetectable in postnatal life. Using immunohistochemistry, diffuse intracytoplasmic aromatase expression was detected in the liver cancer cells from this severely feminized boy. Northern analysis indicated the presence of P450arom transcripts in total RNA from the hepatocellular cancer but not in the adjacent liver nor in disease-free adult liver samples. Promoter use for aromatase expression was determined by a specific RT-PCR method. Promoters I.3 and II were used for P450arom gene expression in the hepatocellular cancer tissue. Because aromatase is not expressed in the disease-free adult liver, the presence of extremely high levels of aromatase expression in this fibrolamellar hepatocellular carcinoma tissue is intriguing, particularly because there is preferential use of the proximally located P450arom promoters I.3 and II by the tumor, instead of the much more distally located fetal liver-type promoter I.4.