Sari Mäkelä

Altered Structure and Function of Reproductive Organs in Transgenic Male Mice Overexpressing Human Aromatase1

Aromatization of androgens is a key step in estrogen production, and it regulates the delicate balance between estrogens and androgens in the gonads and sex steroid target tissues. In the present study, we generated transgenic mice (AROM(+)) bearing the human ubiquitin C promoter/human P450 aromatase fusion gene. AROM(+) male mice are characterized by an imbalance in sex hormone metabolism, resulting in elevated serum E(2) concentrations, combined with significantly reduced testosterone and FSH levels, and elevated levels of PRL and corticosterone. AROM(+) males present a multitude of severe structural and functional alterations in the reproductive organs, such as cryptorchidism associated with Leydig cell hyperplasia, dysmorphic seminiferous tubules, and disrupted spermatogenesis. The males also have small or rudimentary accessory sex glands with abnormal morphology; a prominent prostatic utricle with squamous epithelial metaplasia, and edema in the ejaculatory ducts and vas deferens. In addition, the abdominal muscle wall is thin, and the adrenal glands are enlarged, with cortical hyperplasia. Some of the abnormalities, such as undescended testes and undeveloped prostate, resemble those observed in animals exposed perinatally to high levels of exogenous estrogen, indicating that the elevated aromatase activity results in excessive estrogen exposure during early phases of development. Some of the disorders in the reproductive organs, furthermore, can be explained by the fact that AROM(+) males are hypoandrogenic, and have elevated levels of serum PRL and corticosterone. Thus, the AROM(+) mouse model provides a novel tool to investigate the consequences of a prolonged increase in conversion of androgens to estrogens which results in complex hormonal disturbances altering the structure and function of various male reproductive organs.

A Role for the Androgen Receptor in Follicular Atresia of Estrogen Receptor Beta Knockout Mouse Ovary

Abstract Estrogen receptor beta (ERβ) is highly expressed, but ERα is not detectable in granulosa cells in the mouse ovary. In ERβ knockout (BERKO) mice, there is abnormal follicular development and very reduced fertility. At 3 wk of age, no significant morphologic differences were discernable between wild type (WT) and BERKO mouse ovaries, but by 5 mo of age, atretic follicles were abundant in BERKO mice and there were very few healthy late antral follicles or corpora lutea. At 2 yr of age, unlike the ovaries of their WT littermates, BERKO mouse ovaries were devoid of healthy follicles but had numerous large, foamy lipid-filled stromal cells. The late antral and atretic follicles in BERKO mice were characterized by a high level of expression of the androgen receptor (AR) and IGF-1 receptor. These proteins were abundantly expressed in granulosa cells of preantral and early antral follicles in both genotypes, but their expression was extinguished in late antral follicles of WT mice. Healthy late antral follicles and corpora lutea were restored in BERKO ovaries after 15 days of treatment of mice with the antiandrogen flutamide. The results suggest that in the absence of ERβ there was a loss of regulation of AR. Because androgens enhance recruitment of primordial follicles into the growth pool and cause atresia of late antral follicles, the inappropriately high level of AR probably is related to the follicular atresia and to the early exhaustion of follicles in BERKO mice.

Differential expression of estrogen receptors α and β in adult rat accessory sex glands and lower urinary tract

Abstract Estrogens induce pronounced structural and functional changes in male accessory sex glands and the lower urinary tract in both sexes, but the exact mechanisms of estrogen action are not fully understood. This study was undertaken to localise the tissue cell types that express estrogen receptor in adult rats, and to determine the receptor subtype (ERα and ERβ) in order to identify sites that may respond directly to estrogens. In the male accessory sex glands (seminal vesicles, prostatic lobes and ampullary glands), ERβ mRNA and protein were strongly expressed in the epithelium but not in the stroma, while ERα mRNA was present only in the fibromuscular tissue surrounding the prostatic collecting ducts in the posterior periurethral region and in ampullary gland stroma. In the epithelium of the urinary bladder and urethra of both sexes, high level of ERβ mRNA and protein, but no ERα mRNA, was detected. The connective tissue in urinary bladder of both males and females, as well as that in prostatic urethra in males expressed ERα mRNA. The neural cells in the autonomic ganglia of the prostatic plexus were strongly positive for ERβ mRNA, but were completely devoid of ERα. We conclude that ERβ is the predominant ER subtype in the epithelium of adult male rat accessory sex glands and the lower urinary tract of both males and females, as well as in the prostatic neural plexus regulating the function of the lower urinary tract in males, while ERα is present only in the stromal compartment of distinct sites. These results indicate that in these tissues in intact adults there are multiple targets for direct estrogen action. Furthermore, the differential or complementary expression of the two ER subtypes suggests that they may have specific functions, and may explain the complex structural and functional changes induced by estrogens.

GENISTEIN EXERTS ESTROGEN-LIKE EFFECTS IN MALE MOUSE REPRODUCTIVE TRACT

The aim of this study was to evaluate the estrogenicity of genistein in the neonatal and adult male mouse reproductive tract. In intact adults, genistein (2.5 mg s.c./kg of body weight/day for 9 days) reduced testicular and serum testosterone concentrations, pituitary LH-content and prostate weight. In castrated adults, genistein (0.025-2.5 mg s.c./kg of body weight) increased expression of c-fos gene in prostatic urethra. In adult, neonatally estrogenized mice showing an increased estrogen sensitivity, a 10-day treatment with genistein (2.5 mg s.c./kg of body weight) induced development of squamous epithelial metaplasia in prostatic collecting ducts. Neonatally, only a very high dose of genistein (1 mg/pup per day; i.e. approximately 500 mg/kg of body weight) induced persistent structural changes, similar to those seen in mice treated neonatally with diethylstilbestrol, in the urethroprostatic complex. These results suggest that in adult males, genistein induces the typical estrogenic effects in doses comparable to those present in soy-based diets, while in neonatal animals, considerably higher doses are required to show estrogen-like activity.

Estrogen and progesterone receptors in ovarian epithelial tumors.

Epidemiological studies have indicated a relationship between ovarian cancer and gonadal steroid hormones. In the present study immunohistochemical localization in combination with morphometry were used to characterize changes in the pattern of expression for estrogen receptor alpha (ERalpha), estrogen receptor beta (ERbeta), and progesterone receptor (PR), in epithelial cells of normal ovaries, and in benign, borderline and malignant ovarian tumors of different types (n=53). Positive correlations with immunoreactivity of the cell proliferation-marker, Ki67, and the apoptosis-related marker of genetic instability, p53, between the different tumor types were also found. A simultaneous expression of ERalpha, ERbeta and PR in epithelial cells of all histopathological tumor types was noted, with the notable exception of all mucinous tumors who remained ERbeta-positive, but ERalpha- and PR-negative. Epithelial cells in ovarian cancer tissue showed significantly lower mean immunoreactivity of ERbeta and PR, but not ERalpha, than in normal ovarian tissue. These novel findings may provide a rationale for the development of new diagnostic and possibly therapeutic strategies.

Dietary phytoestrogens and their role in hormonally dependent disease

Epidemiological studies suggest that diets rich in phytoestrogens (plant estrogens), particularly soy and unrefined grain products, may be associated with low risk of breast and prostate cancer. It has also been proposed that dietary phytoestrogens could play a role in the prevention of other estrogen-related conditions, namely cardiovascular disease, menopausal symptoms and post-menopausal osteoporosis. However, there is no direct evidence for the beneficial effects of phytoestrogens in humans. All information is based on consumption of phytoestrogen-rich diets, and the causal relationship and the mechanisms of phytoestrogen action in humans still remain to be demonstrated. In addition, the possible adverse effects of phytoestrogens have not been evaluated. It is plausible that phytoestrogens, as any exogenous hormonally active agent, might also cause adverse effects in the endocrine system, i.e. act as endocrine disrupters.

Multiple Structural and Functional Abnormalities in the P450 Aromatase Expressing Transgenic Male Mice Are Ameliorated by a P450 Aromatase Inhibitor

The present study was undertaken to analyze the effect of a P450 aromatase inhibitor (finrozole) on 4-month-old transgenic mice expressing human P450 aromatase (P450arom) under the human ubiquitin C promoter (AROM+). AROM+ mice present several dysfunctions, such as adrenal and pituitary hyperplasia, cryptorchidism, Leydig cell hypertrophy and hyperplasia, and gynecomastia. The present study demonstrates that these abnormalities were efficiently treated by administration of a P450arom inhibitor, finrozole. The treatment normalized the reduced intratesticular and serum testosterone levels, while those of estradiol were decreased. The body weight and several affected organ weights were normalized with the treatment. Histological analysis revealed that both the pituitary and adrenal hyperplasia were diminished. Furthermore, the cryptorchid testes present in the untreated AROM+ males descended to scrotum, 4 to 15 days after inhibitor treatment. In addition, the disrupted spermatogenesis was recovered and qualitatively complete spermatogenesis appeared with the inhibitor treatment. This was associated with normalized structure of the interstitial tissue, as analyzed by immunohistochemical staining for Leydig cells and macrophages. One of the features was that the Leydig cell hypertrophy was markedly diminished in the treated mice. AROM+ mice also present with severe gynecomastia, while the development and differentiation of the mammary gland in AROM+ males was markedly diminished with the inhibitor treatment. Interestingly, the mammary gland involution was associated with the induction of androgen receptor in the epithelial cells, while estrogen receptors were still detectable in the epithelium. The data show that AROM+ mouse model is a novel tool to further analyze the use of P450arom inhibitors in the treatment of the dysfunctions in males associated with misbalanced estrogen to androgen ratio, such as pituitary adenoma, testicular dysfunction, and gynecomastia.

Phenotype characteristics of transgenic male mice expressing human aromatase under ubiquitin C promoter.

To study the significance of the increased ratio of the estrogen/androgen concentration for the male reproductive functions, we have generated transgenic mice expressing human P450 aromatase under a promoter providing ubiquitous and permanent transgene expression (AROM+ mice). AROM+ male mice are characterized by elevated serum estradiol and prolactin (Prl) concentrations, combined with markedly reduced testosterone levels. The mice are present with a multitude of structural and functional alterations in the reproductive organs such as cryptorchidism, Leydig cell hyperplasia, disrupted spermatogenesis and infertility. Furthermore, the mice develop infravesical obstruction associated with the rhabdosphincter atrophy and rudimentary accessory sex glands. Interestingly, the mammary gland in AROM+ males undergo a ductal and alveolar development morphologically resembling terminally differentiated female mammary glands, and express several signaling proteins typical for female mammary glands. Some of the abnormalities seen in AROM+ mice are similar to those described in both mice and humans exposed to diethylstilbestrol (DES) in utero. The importance of the AROM+ model may lie in its predictability, i.e. the model suggests which abnormalities of the human reproductive functions may be associated with the increased ratio of estrogen/androgen concentrations in early life and at adult age as well.

Receptors mediating toxicity and their involvement in endocrine disruption

Many toxic compounds exert their harmful effects by activating of certain receptors, which in turn leads to dysregulation of transcription. Some of these receptors are so called xenosensors. They are activated by external chemicals and evoke a cascade of events that lead to the elimination of the chemical from the system. Other receptors that are modulated by toxic substances are hormone receptors, particularly the ones of the nuclear receptor family. Some environmental chemicals resemble endogenous hormones and can falsely activate these receptors, leading to undesired activity in the cell. Furthermore, excessive activation of the xenosensors can lead to disturbances of the integrity of the system as well. In this chapter, the concepts of receptor-mediated toxicity and hormone disruption are introduced. We start by describing environmental chemicals that can bind to xenosensors and nuclear hormone receptors. We then describe the receptors most commonly targeted by environmental chemicals. Finally, the mechanisms by which receptor-mediated events can disrupt the system are depicted.

Sex specific expression of progesterone receptor in mouse lower urinary tract

Progesterone receptor (PR) was investigated immunohistochemically in the lower urinary tract of the male and female mouse. Estrogen receptor (ER)-subtype-deficient mice (ERKO, BERKO) were used to determine the possible regulation of PR expression in an ER-subtype-specific manner. PR was found to be co-expressed with ERalpha in cell nuclei of urothelium, lamina propria fibroblasts and smooth muscle cells in the female urethra. Only few PR positive cells were seen in female ERKO mice. Ovariectomy reduced and estrogen treatment restored the urethral PR expression in female wild type and BERKO mice. Thus, the expression of PR in the female urethra is estrogen-inducible via ERalpha. In male urethra, PR was co-expressed with ERbeta in the rhabdosphincter. In male, no evidence was obtained for the ER-linked control of the PR expression. No PR-positive cells were observed in the body of the bladder of either sex or any strain.