Proceedings: Hormonal regulation of breast development and activity

Critical Review on Physiological and Molecular Features during Bovine Mammary Gland Development: Recent Advances

The mammary gland is a unique organ with the ability to undergo repeated cyclic changes throughout the life of mammals. Among domesticated livestock species, ruminants (cattle and buffalo) constitute a distinct class of livestock species that are known milk producers. Cattle and buffalo contribute to 51 and 13% of the total milk supply in the world, respectively. They also play an essential role in the development of the economy for farming communities by providing milk, meat, and draft power. The development of the ruminant mammary gland is highly dynamic and multiphase in nature. There are six developmental stages: embryonic, prepubertal, pubertal, pregnancy, lactation, and involution. There has been substantial advancement in our understanding of the development of the mammary gland in both mouse and human models. Until now, there has not been a thorough investigation into the molecular processes that underlie the various stages of cow udder development. The current review sheds light on the morphological and molecular changes that occur during various developmental phases in diverse species, with a particular focus on the cow udder. It aims to explain the physiological differences between cattle and non-ruminant mammalian species such as humans, mice, and monkeys. Understanding the developmental biology of the mammary gland in molecular detail, as well as species-specific variations, will facilitate the researchers working in this area in further studies on cellular proliferation, differentiation, apoptosis, organogenesis, and carcinogenesis. Additionally, in-depth knowledge of the mammary gland will promote its use as a model organ for research work and promote enhanced milk yield in livestock animals without affecting their health and welfare.

Estrogens: Two nuclear receptors, multiple possibilities

Much is known about estrogen action in experimental animal models and in human physiology. This article reviews the mechanisms of estrogen activity in animals and humans and the role of its two receptors α and β in terms of structure and mechanisms of action in various tissues in health and in relationship with human pathologies (e.g., osteoporosis). Recently, the spectrum of clinical pictures of estrogen resistance caused by estrogen receptors gene variants has been widened by our description of a woman with β-receptor defect, which could be added to the already known descriptions of α-receptor defect in women and men and β-receptor defect in men. The essential role of the β-receptor in the development of the gonad stands out. We summarize the clinical pictures due to estrogen resistance in men and women and focus on long-term follow-up of two women, one with α- and the other with β-receptor resistance. Some open questions remain on the complex interactions between the two receptors on bone metabolism and hypothalamus-pituitary-gonadal axis, which need further deepening and research.

Colostrogenesis: Role and Mechanism of the Bovine Fc Receptor of the Neonate (FcRn)

Colostrogenesis is a separate and unique phase of mammary epithelial cell activity occurring in the weeks before parturition and rather abruptly ending after birth in the bovine. It has been the focus of research to define what controls this process and how it produces high concentrations of specific biologically active components important for the neonate. In this review we consider colostrum composition and focus upon components that appear in first milked colostrum in concentrations exceeding that in blood serum. The Fc Receptor of the Neonate (FcRn) is recognized as the major immunoglobulin G (IgG) and albumin binding protein that accounts for the proteins' long half-lives. We integrate the action of the pinocytotic (fluid phase) uptake of extracellular components and merge them with FcRn in sorting endosomes. We define and explore the means of binding, sorting, and the transcytotic delivery of IgG1 while recycling IgG2 and albumin. We consider the means of releasing the ligands from the receptor within the endosome and describe a new secretion mechanism of cargo release into colostrum without the appearance of FcRn itself in colostrum. We integrate the insulin-like growth factor family, some of which are highly concentrated bioactive components of colostrum, with the mechanisms related to FcRn endosome action. In addition to secretion, we highlight the recent findings of a role of the FcRn in phagocytosis and antigen presentation and relate its significant and abrupt change in cellular location after parturition to a role in the prevention and resistance to mastitis infections.

Microenvironmental control of cell fate decisions in mammary gland development and cancer

Cell fate decisions are critical for adequate tissue development, maintenance and regeneration. In the mammary gland, epithelial cell fates are tightly controlled by the microenvironment. Here, we review how cell fate decisions are regulated by components of the microenvironment during mammary gland development and how pathological changes in the microenvironment can alter cell fates, leading to malignancy. Specifically, we describe the current understanding of how mammary cell fate is controlled and directed by three elements: the extracellular matrix, the immune microenvironment, and hormones-and how these elements can converge to create microenvironments that promote a fourth element: DNA damage.

Chronic stress caused by maternal separation is a possible risk factor for the development of 7,12-dimethyl benzo anthracene-induced breast tumors in rats

BACKGROUND

Chronic stress has been investigated as a risk factor for breast cancer. Maternal separation (MS) of rats has been used as a chronic stress model that alters certain systemic functions, such as the immune response.

OBJECTIVE

The aim of this study was to determine the possible effect of MS on the development of breast tumors induced by 7,12-dimethyl benzo anthracene (DMBA).

METHODOLOGY

postnatal day (PND) 1 female Wistar rats were divided into four experimental groups that either were or were not subjected to MS and either received or did not receive DMBA. For MS, PND 1 to 21 pups were separated from their mothers for 360 min/day. On PND 30, carcinomas were induced in mammary glands using DMBA. Body weight was evaluated, and the injected region was palpated. In addition, the mammary glands were subjected to histological examination, and corticosterone levels were determined in all groups.

RESULTS

DMBA-induced groups had significantly lower body weight gain compared with the non-DMBA-induced groups. Maternal separation increased the incidence of preneoplastic changes and breast carcinogenesis in DMBA-treated animals compared with control animals. Corticosterone levels were increased in both DMBA-induced and MS groups without interaction.

CONCLUSION

MS is a possible risk factor for DMBA-induced preneoplastic changes and breast tumors in rats.

The Role of Estradiol in Traumatic Brain Injury: Mechanism and Treatment Potential

Patients surviving traumatic brain injury (TBI) face numerous neurological and neuropsychological problems significantly affecting their quality of life. Extensive studies over the past decades have investigated pharmacological treatment options in different animal models, targeting various pathological consequences of TBI. Sex and gender are known to influence the outcome of TBI in animal models and in patients, respectively. Apart from its well-known effects on reproduction, 17β-estradiol (E2) has a neuroprotective role in brain injury. Hence, in this review, we focus on the effect of E2 in TBI in humans and animals. First, we discuss the clinical classification and pathomechanism of TBI, the research in animal models, and the neuroprotective role of E2. Based on the results of animal studies and clinical trials, we discuss possible E2 targets from early to late events in the pathomechanism of TBI, including neuroinflammation and possible disturbances of the endocrine system. Finally, the potential relevance of selective estrogenic compounds in the treatment of TBI will be discussed.

Effect of Estradiol on Neurotrophin Receptors in Basal Forebrain Cholinergic Neurons: Relevance for Alzheimer's Disease

The basal forebrain is home to the largest population of cholinergic neurons in the brain. These neurons are involved in a number of cognitive functions including attention, learning and memory. Basal forebrain cholinergic neurons (BFCNs) are particularly vulnerable in a number of neurological diseases with the most notable being Alzheimer's disease, with evidence for a link between decreasing cholinergic markers and the degree of cognitive impairment. The neurotrophin growth factor system is present on these BFCNs and has been shown to promote survival and differentiation on these neurons. Clinical and animal model studies have demonstrated the neuroprotective effects of 17β-estradiol (E2) on neurodegeneration in BFCNs. It is believed that E2 interacts with neurotrophin signaling on cholinergic neurons to mediate these beneficial effects. Evidence presented in our recent study confirms that altering the levels of circulating E2 levels via ovariectomy and E2 replacement significantly affects the expression of the neurotrophin receptors on BFCN. However, we also showed that E2 differentially regulates neurotrophin receptor expression on BFCNs with effects depending on neurotrophin receptor type and neuroanatomical location. In this review, we aim to survey the current literature to understand the influence of E2 on the neurotrophin system, and the receptors and signaling pathways it mediates on BFCN. In addition, we summarize the physiological and pathophysiological significance of E2 actions on the neurotrophin system in BFCN, especially focusing on changes related to Alzheimer's disease.

Estrogen therapy to treat retinopathy in newborn mice

The aim of the present study was to treat retinopathy of prematurity (ROP) with estrogen (E₂) so as to elucidate the role of E₂ in the pathogenesis of ROP. A total of 120 postnatal 7-day-old (P7) C57BL/6J mice were selected and raised in a high-oxygen environment (75% oxygen) for 5 days, followed by 5 days in normal room air. Different doses of E₂ or normal saline (NS) were injected intraperitoneally during different time-periods, and the mice were divided into 14 groups according dose of E₂ injection (0.5-1.5 µg/0.05 ml) and dosing time. Blood vessel changes and hyperplasia were evaluated in flat-mounted retina and retinal slices. All mice that were exposed to room air, whether they were administered E₂ or NS, showed good vascular development in the flat-mounted retina at P17. No increase in the number of endothelial cell nuclei in the new blood vessels was observed. In ascending order of E₂ dose the numbers of cell nuclei were as follows: 0.18±0.129, 0.28±0.086 and 0.55±0.110. The number in the NS group was 2.12±0.373. When the results of the room-air groups were compared with those of the hyperoxia groups, a highly significant difference was found in each comparison (P<0.0001). All mice showed varying degrees of neovascularization and vascular obstruction in the flat-mounted retina at P17, and it was difficult to compare the blood vessels morphologically among these groups. The number of endothelial cell nuclei decreased following E₂ injection, and the difference from the NS group exposed to hyperoxia was highly significant (P<0.0001). For all dose levels, the number of cell nuclei was the lowest when the drug was administered during P7-16, and the difference from the other two time-periods was statistically significant (P<0.05). When E₂ was administered during P7-16, the number of cell nuclei was 15.5±1.993 in the 0.5-µg group, 14.23±2.49 in the 1.0-µg group and 18.05±1.62 in the 1.5-µg group. No significant difference was found among these three groups (P>0.05). In conclusion, E₂ treatment during the development of retinopathy can improve symptoms in neonatal mice, suggesting that E₂ plays an important role at the two initial stages in the pathogenesis of ROP. This may indicate new pharmacological measures to prevent and treat ROP.

Hydrocortisone down-regulates the tumor suppressor gene BRCA1 in mammary cells: a possible molecular link between stress and breast cancer

Psychological stress has been correlated with breast cancer development in numerous epidemiological studies. However, physiological and molecular models which may account for this association are not readily available. We have found that the stress hormone hydrocortisone (cortisol) down-regulates the expression of the breast cancer susceptibility gene BRCA1 in the nonmalignant mouse mammary cell line EPH4. This effect is concentration-dependent, is reliant on the continuous presence of hydrocortisone, and is not affected by the addition of lactogenic hormones, or growth conditions. Hydrocortisone was also found to negate a known positive effect of estrogen on BRCA1 expression and, therefore, may interfere with estrogen-related signaling in mammary epithelial cells. The repressive effect of hydrocortisone is diminished or lost in the mouse mammary lines HC-11 and SP1, respectively, suggesting regulation of the BRCA1 may differ between lines. We have uncovered two promoter regulatory sites, which are involved in BRCA1 regulation by hydrocortisone, namely the RIBS and UP regulatory elements. Binding of the transcription factor GABP to both sites is lost upon hydrocortisone addition, though the levels of these factors are not altered by hydrocortisone treatment. Because BRCA1 activity is important for a number of intracellular pathways involved in prevention of tumorigenesis, its observed down-regulation may represent a novel molecular mechanism for cortisol's involvement in breast cancer development.

Novel identification of UDP-glucuronosyltransferase 1A10 as an estrogen-regulated target gene

Recently, we have shown that UGT1A10 is actively involved in the inactivation of E(1), E(2), and their 2- and 4-hydroxylated derivatives. In the present study, we show for the first time that treatment of the MCF-7 ER-positive breast cancer cell line with E(2) produces a dose-dependent up-regulation of UGT1A10 mRNA levels, followed by a steady down-regulation. In contrast, E(2) did not stimulate mRNA expression in the MDA-MB-231 (ER)-negative breast cancer cell line. Expression of UGT1A10 mRNA was blocked by the antiestrogen, ICI 182,780, but not by the transcriptional inhibitor, actinomycin-d. These findings suggest that regulation of UGT1A10 mRNA might be a primary transcriptional response mediated through the ER. Expression of UGT1A10 mRNA was also stimulated by other estrogenic compounds including propylpyrazoletriol (PPT) and genistein (Gen). Exposure of MCF-7 cells to 0.1nM E(2) up-regulated, and then down-regulated, UGT1A protein and enzymatic activity toward E(2) at 10nM E(2) as determined by Western blot and glucuronidation activity assays. Collectively, these results suggest that induction of UGT1A10 mRNA expression by E(2) might be mediated through ER, and that this isoform is a novel, estrogen-regulated target gene in MCF-7, ER-positive human breast cancer cells. The finding of E(2)-induced expression of UGT1A10 mRNA, followed by the down-regulation of UGT1A10 at pharmacological concentrations of E(2), might have a significant moderating effect on E(2) availability for ER and estrogen clearance, thereby promoting the signaling of E(2) in breast cancer cells.

Tools for making correct decisions regarding hormone therapy. Part II. organ response and clinical applications

OBJECTIVE

To review existing scientific knowledge of the complicated and variable behavior and response to hormone therapy (HT) of different organs during aging, and to summarize long-term consequences on human health.

DESIGN

A MEDLINE computer search was performed to identify relevant articles.

RESULT(S)

Five body organs were evaluated. [1]. Physiologic aging of the bone has deleterious consequences on women's health and quality of life. Bone fractures could be attributed to the combination of estrogen depletion and osteoporosis, mechanisms of applied forces, and disturbed brain function, partially reversible by timely estrogen administration. [2]. Estrogen seems to have a profound neuroprotective effect. As physiologic aging of the brain is an unhealthy phenomenon, possible intervention is justified. The therapeutic time window seems crucial. [3]. The differentiation between response of a healthy or already damaged organ to sex hormones is the key factor to understanding the possible cardioprotective effects. [4]. Based on doubling time of tumor cells, intracrinology, epidemiological data on breast cancer, and behavior of breast cancer survivors in response to estrogen treatment, estrogen seems to be mainly a promoter and even a protector of breast cancer survivors. [5]. Colon cancer appears to be an estrogen-dependent tumor with a wide therapeutic window, as every report regardless of age and dose demonstrates protective effects.

CONCLUSION(S)

Knowledge of each organ's response to aging and sex hormone substitutions demonstrates that the organs could benefit from properly designed intervention. In the wake of the publication of the Women's Health Initiative study, which shocked the medical community, we suggest that the results be reevaluated according to the aforementioned principles, and that menopausal medicine could play an important role.

An evaluation of three methods used to assess the gestational age of aboriginal neonates

Many Aboriginal women do not recall their last menstrual period date, so alternative methods of estimating gestational age are necessary for optimal obstetric and neonatal care. In this retrospective review of 605 Aboriginal infants born at the Royal Darwin Hospital, the gestational age was estimated by the Dubowitz method and compared with available gestational age estimates from first fundal height and first ultrasound measurement. There was good agreement between the Dubowitz and ultrasound estimates of gestational age with best agreement occurring when ultrasound was done in the first trimester and worst agreement in the third trimester. Agreement between fundal height and Dubowitz estimates was poor but the measurement of fundal height was not standardized. When accurate last menstrual period information is absent, these findings suggest that good estimates of gestational age in Aboriginal neonates can be determined from the Dubowitz assessment at birth and from ultrasound measurements taken in the first trimester.

Organization and growth of mammary epithelia in the mammary gland fat pad

Mammary gland development consists of a series of very highly ordered events involving interactions among a number of distinct cell types. An important aspect of mammary gland development is that the mammary gland consists of a fat pad of mesodermal origin into which epithelial cells of ectodermal origin proliferate. This proliferation of epithelial cells into the mammary fat pad is the subject of this review. The nature of the stroma into which epithelial cells proliferate is of considerable importance in determining the structure of the resulting gland. In mice, white adipose tissue appears to be required for normal mammary development. Transplantation of mammary epithelia to other types of stroma does not support epithelial growth or result in abnormal growth. To date, a synthetic substratum capable of mimicking white adipose tissue has not been developed. Although collagen gel cultures are generally considered superior to glass or plastic substratum in supporting near normal epithelial growth, the technique has not advanced to the point that the in vivo growth pattern is duplicated. Recent research on the generation of chimeric mammary tissue (by transplanting mammary epithelia from rats, cows, and women to the mammary fat pads of athymic nude mice) suggests that there are important species differences in the stromal requirements for mammary gland development. In particular, extensive and expansive growth of rat mammary tissue is observed in mouse mammary fat pads. However, the mouse mammary fat pad appears incapable of supporting expansive growth of bovine or human mammary epithelia. The reason for this difference is not clear. However, human and bovine mammary epithelia may require the presence of more fibrous (collagenous) tissue than rodent mammary epithelia for normal proliferation.

Estradiol/progesterone interaction in normal and pathologic breast cells

In most target cells of the female genital tract, adequate cell differentiation is obtained via the successive and synergistic actions of estradiol (E2) and progesterone (P). This mainly due to the fact that progesterone receptor (PR) synthesis involves the prior action of estradiol through its receptor (ER). In normal breast, E2 stimulates the growth of the ductal system whereas lobular development depends on progesterone secretion. In other words E2 + P, when secreted in an adequate balance, permit the complete and proper development of the mammary gland. On the other hand progesterone may also have an antagonistic action against E2. The antiestrogen activity of progesterone is mediated through a decrease in the replenishment of E2 receptor and the synthesis of 17 beta-hydroxysteroid dehydrogenase, which leads to an accelerated metabolism of E2 to E1 in the target organ itself. These biochemical events, which have been well documented in the endometrium, have also been shown in cultures of normal breast epithelial cells as well as in differentiated fibroadenomas with high cellular density. In addition, data from the literature show that E2 added to human breast cells increases cell multiplication by means, eventually, of the synthesis of growth factors. Progesterone and progestins have a reverse effect. Data from our laboratory indicate that in normal cultured cells E2 and progestins are also antagonists with regard to cell multiplication. From these different data, it is postulated that in human beings, long periods of a luteal-phase defect leading to an unopposed estrogen effect might be a promoter of carcinogenesis in the breast.

The effects of relaxin on the mouse mammary gland. II. The epithelium

The study deals with the effects of relaxin (RLX) on epithelial cells of the mammary ducts in ovariectomized virgin mice, evaluated by light and electron microscopy. One microgram (3 GPU) pure porcine RLX (NIH-RXN-P1) was administered either alone or after pretreatment with estrogen. The possibility of a non specific binding of RLX to insulin receptors on the mammary epithelial cells was excluded by comparing the effects of the administration of the two hormones at the same doses. Our findings indicate that RLX greatly enhances the growth of the mammary duct epithelial cells, as demonstrated by the extensive branching and elongation of the ducts, and by the rather frequent occurrence of mitoses in the epithelial cell precursors and of the intermediate stages of their differentiation into mature duct cells. Three GPU RLX, administered alone, had only an inconstant and slight effect on the epithelial cell growth, a priming dose with estrogen being necessary to obtain the highest levels of duct growth. Moreover the treatment with 1 microgram of insulin for the same time showed a very inconstant and lesser effect in comparison to RLX. We did not find any evidence of alveolar maturation and milk secretion in the RLX-treated mice. The recognition of a stimulatory role of RLX on the proliferation and growth of the mammary duct epithelium may be of a certain importance in the understanding of hormonal control of the mammary development in physiological conditions and the genesis and growth of mammary neoplasms.

Paracrine regulation of mammary gland growth

The growth and differentiation of the mammary gland is a complex process involving the interactions of various steroid and polypeptide hormones. The mammary growth occurs in a discontinued way during five distinct phases, i.e. fetal, prepubertal, postpubertal, pregnancy, and early lactation periods. The gland expresses its differentiated function by producing milk during the period of lactation. Although the mammary gland has been regarded as one of the well-known target tissues for various types of hormones, evidence has been accumulating in recent years indicating the involvement of other factors and substances in the process of mammary growth and differentiation. In this chapter the importance of the mesenchymal component in mammary epithelial cell growth has been documented. This component, including embryonic mesenchyme and adipocytes in adult tissue, play an essential role by not only serving as a structural entity of the gland but also by producing extracellular matrix substances and various factors that promote the growth, morphologic development and differentiation of mammary epithelium in a paracrine fashion. Other possible paracrine peptide factors for mammary cell growth have been isolated from several other sources including mammary tumors and milk. Thus, it is possible that paracrine growth factors play a role in mammary tumorigenesis. Since most of these factors are present in minute amounts, it is difficult to obtain pure forms of these factors in sufficient amounts for detailed physicochemical characterization. Moreover, further studies are needed to assess the physiological importance of these growth factors, their mode of action, and the mechanism of regulation relating to their production. It is conceivable that some mammary paracrine agents interact with each other or with endocrine agents in promoting the normal and neoplastic growth of mammary cells. Furthermore, the possibility exists that the production and release of paracrine factors are under the endocrine control. In view of the rapid progress and great interest in this area, these questions may be answered before long, along with the discovery of some other new growth regulating agents in this system. Clearly such information is important for understanding the complex process of normal and neoplastic growth of the mammary gland.

A comparative study of the effect of oestrogen substitution therapy on breast development in girls with hypo- and hypergonadotrophic hypogonadism

During treatment of girls with oestrogen deficiency we observed different patterns of breast development in response to therapy. The forty-five girls studied fell into four groups: Group A, gonadal dysgenesis; Group B, isolated gonadotrophin deficiency; Group C, multiple pituitary hormone deficiencies; Group D, congenital adrenal hyperplasia (17-alpha-hydroxylase deficiency). Treatment with oestrogen was given in an identical manner to all. In the patients with gonadal dysgenesis, in whom the hypothalamic-pituitary function was normal, treatment led to full breast development. In isolated gonadotrophin deficiency and multiple pituitary hormone deficiency breast development was incomplete even after 3 years or more of oestrogen treatment. The conspicuous difference in the hormonal status is that the latter two groups lack gonadotrophins, while in gonadal dysgenesis these hormones are grossly elevated. Our conclusion is that gonadotrophins play an important role in mammary gland development, a finding not previously described. In the girl with 17-alpha-hydroxylase deficiency we observed that cortisol was necessary, in addition to sex hormones, for normal breast development.

Prolactin, maternal oestrogens, and breast development in the newborn

To investigate the influence of maternal oestrogens on the fetal breast development, maternal urinary oestriol excretion, maternal plasma oestriol concentrations, and cord venous plasma oestradiol and oestriol concentrations were related to the size of the neonatal breast. A significant positive association between oestriol excretion and neonatal breast size was demonstrated, but the relationship was not strong and might be due to both measures having a positive relationship with birthweight. The infants' circulating concentrations of prolactin at birth and during the first weeks of life were also related to breast size. There was no cord venous-arterial difference in prolactin concentrations, and neither related to breast diameter. However there was a strong association between breast size and prolactin concentrations in mature infants aged between 5 and 7 days. In preterm infants breast tissue often develops after birth. Prolactin levels in preterm infants were higher between 2 and 6 weeks than they were in the first week of life. It would appear that the early development of the breast is influenced more by the infants's than the mother's endocrine activity.

Triamcinolone-induced mammary activation in virgin mice

Intact ICR mice receiving Triamcinolone showed extensive proliferation within the mammary gland. Galactophores and ducts were enlarged. In contrast with the non-treated animals, those treated with Triamcinolone had an evident lobuloalveolar system. Triamcinolone failed to activate the glands of oophorectomized animals. It is thus evident that systemic administration of Triamcinolone to young virgin mice causes mammary stimulation and that this effect only occurs in the presence of the ovary.