Sex steroids reduce DNaseI accessibility of androgen receptor promoter in adult male mice brain

Activation of androgen receptors protects intact male mice from memory impairments caused by aromatase inhibition

Although 17β-estradiol (E₂) is known to regulate hippocampal function, the specific contributions of hippocampally-synthesized E₂ remain unclear. Infusion of the aromatase inhibitor letrozole into the dorsal hippocampus (DH) of ovariectomized mice disrupts object recognition and object placement memory consolidation, suggesting that DH-synthesized E₂ is essential for memory. However, the role of DH-synthesized E₂ in memory among male rodents is unknown. Here, we examined effects of aromatase inhibition on memory consolidation in male mice. Intact and gonadectomized mice were infused with vehicle or letrozole into the DH immediately post-training in object placement and object recognition tasks. Letrozole blocked memory in both tasks among gonadectomized males only, suggesting that circulating androgens, or a rise in hippocampal androgens due to aromatase inhibition, may support memory consolidation in intact males. To test this hypothesis, intact males were infused with the androgen receptor antagonist flutamide into the DH after object training. A dose-dependent impairment was observed in both tasks, indicating that blocking androgen signaling can impair memory consolidation. To test if hippocampal androgen receptor activation protected intact males from the impairing effects of letrozole, a non-impairing dose of flutamide was co-infused with letrozole. Co-administration of both drugs blocked object placement and object recognition memory consolidation, demonstrating that letrozole impairs memory in intact males only if androgen receptors are blocked. Together, these data suggest that DH-synthesized E₂ and androgen receptor activation may work in concert to mediate memory consolidation in intact males, such that androgen receptor activation protects against memory impairments caused by aromatase inhibition.

The role of androgens and the androgen receptor in cycling endometrium

Androgens and the androgen receptor (AR) are not only required for male reproductive function, they are also essential for female reproductive physiology. Widely expressed in female reproductive tissues, AR levels fluctuate in a regulated manner in the cycling endometrium. Female androgen production depends on the adrenal glands and expression of key enzymes in the endometrium that facilitate local androgen biosynthesis and conversion. Moreover, levels of circulating androgens, in women of reproductive age, fluctuate in a cycle-dependent manner and a mid-cycle peak is associated with conception. AR and androgen signalling have a decisive role in the differentiation of human endometrial stromal cells into decidual cells. Compelling evidence for androgen signalling in the regulation of endometrial function pertaining to implantation and pregnancy is provided by epidemiological studies demonstrating a strong association between polycystic ovary syndrome, premature ovarian failure or advanced maternal age and adverse pregnancy outcome. Thus, androgen signalling is an essential component of normal endometrial physiology and its perturbation is associated with reproductive failure.

Epigenetic setting for long-term expression of estrogen receptor α and androgen receptor in cells

Epigenetic regulation of the nuclear estrogen and androgen receptors, ER and AR, constitutes the molecular basis for the long-lasting effects of sex steroids on gene expression in cells. The effects prevail at hundreds of gene loci in the proximity of estrogen- and androgen-responsive elements and many more such loci through intra- and even inter-chromosomal level regulation. Such a memory system should be active in a flexible manner during the early development of vertebrates, and later replaced to establish more stable marks on genomic DNA. In mammals, DNA methylation is utilized as a very stable mark for silencing of the ERα and AR isoform expression during cancer cell and normal brain development. The factors affecting the DNA methylation of the ERα and AR genes in cells include estrogen and androgen. Since testosterone induces brain masculinization through its aromatization to estradiol in a narrow time window of the perinatal stage in rodents, the autoregulation of estrogen receptors, especially the predominant form of ERα, at the level of DNA methylation to set up the "cell memory" affecting the sexually differentiated status of brain function has been attracting increasing attention. The alternative usage of the androgen-AR system for brain masculinization and estrogenic regulation of AR expression in some species imply that the DNA methylation pattern of the AR gene can be established by closely related but different systems for sex steroid-induced phenomena, including brain masculinization.

Binding of estrogen receptor alpha promoter to nuclear proteins of mouse cerebral cortex: effect of age, sex, and gonadal steroids

Majority of estrogen actions in the brain are mediated by estrogen receptor (ER) alpha which in turn is regulated by several factors like circulating levels of gonadal steroid hormones 17beta-estradiol and testosterone, sex and age of the organism. The expression of ERalpha is regulated through interaction between cis-elements of its promoter and proteins present in the nuclei. Here, we have used electrophoretic mobility shift assay (EMSA) to analyze the effect of age, sex, 17beta-estradiol, and testosterone on the binding of ERalpha promoter (-91 to +46 bp) to nuclear proteins from the mouse cerebral cortex. EMSA revealed the formation of three specific complexes in all groups. However, the intensity of these complexes varied as a function of age, sex and treatment with 17beta-estradiol and testosterone. Nuclear proteins from the cerebral cortex of both sexes showed reduced binding with promoter fragment in old mice. Further, competition analysis indicated stronger binding in females than males of both ages. The extent of binding was reduced by 17beta-estradiol and testosterone treatment in both ages and sexes. Thus, these findings demonstrate differential binding of nuclear proteins to mouse ERalpha promoter which may account for different functions of estrogen in the brain.

Comparative anti-androgenic actions of vinclozolin and flutamide on transgenerational adult onset disease and spermatogenesis

Exposure of gestating female rats to the anti-androgenic endocrine disruptor vinclozolin has been shown to induce transgenerational adult onset disease phenotypes. The current study, was designed to compare the actions of vinclozolin to the known anti-androgenic compound flutamide. The gestating female rats were exposed to intraperitoneal injections during embryonic day 8-14 (E8-E14) to 100mg/kg/day vinclozolin or flutamide at either 5mg or 20mg/kg/day. As previously observed, vinclozolin induced a transgenerational testis phenotype of increased spermatogenic cell apoptosis and decreased epididymal sperm number. In contrast, the flutamide exposures resulted in a testis phenotype of increased spermatogenic cell apoptosis and decreased epididymal sperm numbers in the F1 generation only, and not the F2 and F3 generation adult males. Interestingly, some of the low dose (5mg/kg) flutamide F2 generation offspring developed spinal agenesis and supernummery development (polymelia) of limbs. Although the actions of vinclozolin and flutamide appear similar in the F1 generation males, the transgenerational effects of vinclozolin do not appear to be acting through the same anti-androgenic mechanism as flutamide.

17Beta-estradiol modulates age-dependent binding of 40 kDa nuclear protein to androgen receptor promoter in mouse cerebral cortex

Androgen influences the function of central and peripheral nervous system and plays a crucial role in maintaining reproductive behaviors and neuroendocrine regulation. Such action is mediated by interaction of androgen receptor (AR) promoter with nuclear proteins, which are involved in transcriptional regulation of androgen responsive genes. We have analyzed the binding of AR core promoter to nuclear proteins from the cerebral cortex of adult and old mice of both sexes by electrophoretic mobility shift assay (EMSA) and characterized the bound protein by Southwestern blotting. EMSA showed that the binding of nuclear proteins declined in the cerebral cortex of intact old mice as compared to adult. Following gonadectomy, the binding was reduced in old male and adult female but increased in old female. In contrast, estradiol supplementation increased the binding in old male and adult female but decreased in old female. Southwestern blotting analysis revealed that a 40 kDa nuclear protein bound to the promoter and the binding pattern was similar to that observed in EMSA. Further characterization of this protein may help to explore the intricate mechanism that underlies the transcriptional regulation of androgen responsive genes during aging.

Transgenerational effect of the endocrine disruptor vinclozolin on male spermatogenesis

The current study was designed to examine the actions of a model endocrine disruptor on embryonic testis development and male fertility. Pregnant rats (F0) that received a transient embryonic exposure to an environmental endocrine disruptor, vinclozolin, had male offspring (F1) with reduced spermatogenic capacity. The reduced spermatogenetic capacity observed in the F1 male offspring was transmitted to the subsequent generations (F2-F4). The administration of vinclozolin, an androgen receptor antagonist, at 100 mg/kg/day from embryonic day 8-14 (E8-E14) of pregnancy to only the F0 dam resulted in a transgenerational phenotype in the subsequent male offspring in the F1-F4 generations. The litter size and male/female sex ratios were similar in controls and the vinclozolin generations. The average testes/body weight index of the postnatal day 60 (P60) males was not significantly different in the vinclozolin-treated generations compared to the controls. However, the testicular spermatid number, as well as the epididymal sperm number and motility, were significantly reduced in the vinclozolin generations compared to the control animals. Postnatal day 20 (P20) testis from the vinclozolin F2 generation had no morphological abnormalities, but did have an increase in spermatogenic cell apoptosis. Although the P60 testis morphology was predominantly normal, the germ cell apoptosis was significantly increased in the testes cross sections of animals from the vinclozolin generations. The increase in apoptosis was stage-specific in the testis, with tubules at stages IX-XIV having the highest increase in apoptotic germ cells. The tubules at stages I-V also had an increase in apoptotic germ cells compared to the control samples, but tubules at stages VI-VIII had no increase in apoptotic germ cells. An outcross of a vinclozolin generation male with a wild-type female demonstrated that the reduced spermatogenic cell phenotype was transmitted through the male germ line. An outcross with a vinclozolin generation female with a wild-type male had no phenotype. A similar phenotype was observed in outbred Sprague Dawley and inbred Fisher rat strains. Observations demonstrate that a transient exposure at the time of male sex determination to the antiandrogenic endocrine disruptor vinclozolin can induce an apparent epigenetic transgenerational phenotype with reduced spermatogenic capacity.

In the cerebral cortex of female and male mice, amyloid precursor protein (APP) promoter methylation is higher in females and differentially regulated by sex steroids

The over-expression of amyloid precursor protein (APP) gene in certain areas of the brain indicates abnormalities in gene regulation as an important factor for the development of Alzheimer's disease (AD). We have reported recently that APP mRNA expression is lower in female as compared to male and is regulated by sex steroids. As methylation of promoter is crucial for such regulation, we have used isoschizomeric restriction enzymes MspI and HpaII to analyze the pattern of APP promoter methylation in the cerebral cortex of intact, gonadectomized, testosterone- and estradiol-treated adult and old mice of both sexes. Southern blots of DNA digested with HindIII/MspI or HindIII/HpaII from different groups of mice were probed with a 1.27-kb DIG-11-dUTP labeled APP promoter fragment. The results revealed four distinct bands of 315 bp, 596 bp, 911 bp, and 2.6 kb by MspI, a single band of 2.6 kb by HpaII in all groups and an additional 2.9 kb in intact and estradiol treated old male and testosterone-treated adult female mice. The intensity of 2.6-kb band was relatively lower in intact female as compared to male and varied with different treatments in both ages, indicating the modulation of methylation. Thus, these findings showed that APP promoter methylation is higher in female and differentially regulated by sex steroids in the mice cerebral cortex, suggesting a strong correlation between promoter methylation and transcriptional silencing of APP.