Progesterone stimulates mammary gland ductal morphogenesis by synergizing with and enhancing insulin-like growth factor-I action

Branching morphogenesis of the mouse mammary gland after exposure to benzophenone-3

Pubertal mammary branching morphogenesis is a hormone-regulated process susceptible to exposure to chemicals with endocrine disruptive capacity, such as the UV-filter benzophenone-3 (BP3). Our aim was to assess whether intrauterine or in vitro exposure to BP3 modified the branching morphogenesis of the female mouse mammary gland. For this, pregnant mice were dermally exposed to BP3 (0.15 or 50 mg/kg/day) from gestation day (GD) 8.5 to GD18.5. Sesame oil treatment served as control. Changes of the mammary glands of the offspring were studied on postnatal day 45. Further, mammary organoids from untreated mice were cultured under branching induction conditions and exposed for 9 days to BP3 (1 × 10-6 M, 1 × 10-9 M, or 1 × 10-12 M with 0.01% ethanol as control) to evaluate the branching progression. Mice that were exposed to BP3 in utero showed decreased mRNA levels of progesterone receptor (PR) and WNT4. However, estradiol and progesterone serum levels, mammary histomorphology, proliferation, and protein expression of estrogen receptor alpha (ESR1) and PR were not significantly altered. Interestingly, direct exposure to BP3 in vitro also decreased the mRNA levels of PR, RANKL, and amphiregulin without affecting the branching progression. Most effects were found after exposure to 50 mg/kg/day or 1 × 10-6 M of BP3, both related to sunscreen application in humans. In conclusion, exposure to BP3 does not impair mammary branching morphogenesis in our models. However, BP3 affects PR transcriptional expression and its downstream mediators, suggesting that exposure to BP3 might affect other developmental stages of the mammary gland.

Single-Cell Transcription Mapping of Murine and Human Mammary Organoids Responses to Female Hormones

During female adolescence and pregnancy, rising levels of hormones result in a cyclic source of signals that control the development of mammary tissue. While such alterations are well understood from a whole-gland perspective, the alterations that such hormones bring to organoid cultures derived from mammary glands have yet to be fully mapped. This is of special importance given that organoids are considered suitable systems to understand cross species breast development. Here we utilized single-cell transcriptional profiling to delineate responses of murine and human normal breast organoid systems to female hormones across evolutionary distinct species. Collectively, our study represents a molecular atlas of epithelial dynamics in response to estrogen and pregnancy hormones.

Transcriptome analysis of the Bactrian camel (Camelus bactrianus) reveals candidate genes affecting milk production traits

BACKGROUND

Milk production traits are complex traits with vital economic importance in the camel industry. However, the genetic mechanisms regulating milk production traits in camels remain poorly understood. Therefore, we aimed to identify candidate genes and metabolic pathways that affect milk production traits in Bactrian camels.

METHODS

We classified camels (fourth parity) as low- or high-yield, examined pregnant camels using B-mode ultrasonography, observed the microscopic changes in the mammary gland using hematoxylin and eosin (HE) staining, and used RNA sequencing to identify differentially expressed genes (DEGs) and pathways.

RESULTS

The average standard milk yield over the 300 days during parity was recorded as 470.18 ± 9.75 and 978.34 ± 3.80 kg in low- and high-performance camels, respectively. Nine female Junggar Bactrian camels were subjected to transcriptome sequencing, and 609 and 393 DEGs were identified in the low-yield vs. high-yield (WDL vs. WGH) and pregnancy versus colostrum period (RSQ vs. CRQ) comparison groups, respectively. The DEGs were compared with genes associated with milk production traits in the Animal Quantitative Trait Loci database and in Alashan Bactrian camels, and 65 and 46 overlapping candidate genes were obtained, respectively. Functional enrichment and protein-protein interaction network analyses of the DEGs and candidate genes were conducted. After comparing our results with those of other livestock studies, we identified 16 signaling pathways and 27 core candidate genes associated with maternal parturition, estrogen regulation, initiation of lactation, and milk production traits. The pathways suggest that emerged milk production involves the regulation of multiple complex metabolic and cellular developmental processes in camels. Finally, the RNA sequencing results were validated using quantitative real-time PCR; the 15 selected genes exhibited consistent expression changes.

CONCLUSIONS

This study identified DEGs and metabolic pathways affecting maternal parturition and milk production traits. The results provides a theoretical foundation for further research on the molecular mechanism of genes related to milk production traits in camels. Furthermore, these findings will help improve breeding strategies to achieve the desired milk yield in camels.

Pre- and post-weaning nutrition status affects sheep mammary gland morphology and promotes differential gene expression

Little is known about how varying the plane of nutrition before and after weaning can influence gene expression that drives mammary gland development (MGD). Therefore, the aim of this study was to investigate this paradigm in a seasonal sheep breed. Forty pre-weaning 30-day old Kurdish female lambs were fed either a low-nutrient and protein (L; 2.0 Mcal ME/kg DM; 8.70% crude protein [CP]) or high-nutrient and protein diet (H; 2.5 Mcal ME/kg DM; 14.80% CP). At d 120 (weaning), lambs were allocated into a 2 × 2 arrangement based on pre- and post-weaning diets, resulting in four groups (LL, LH, HL, HH). On d 210, mammary biopsy samples were taken for histomorphological and gene expression studies. Alveoli were larger in HH compared with all other groups (p < 0.05). Whilst estrogen receptor-alpha, progesterone receptor, growth hormone receptor and insulin-like growth factor binding protein-1 gene expression was modulated depending on pre- or post-weaning nutritional levels (p < 0.01). Overall, a consistent high plane of nutrition promoted MGD, with more a complex relationship evident between the expression of genes critical for mammary gland function and development. These findings provide scope for future tailored nutritional strategies to optimize both liveweight gain and MGD.

Single-cell transcription mapping of murine and human mammary organoids responses to female hormones

During female adolescence and pregnancy, rising levels of hormones result in a cyclic source of signals that control the development of mammary tissue. While such alterations are well understood from a whole-gland perspective, the alterations that such hormones bring to organoid cultures derived from mammary glands have yet to be fully mapped. This is of special importance given that organoids are considered suitable systems to understand cross species breast development. Here we utilized single-cell transcriptional profiling to delineate responses of murine and human normal breast organoid systems to female hormones across evolutionary distinct species. Collectively, our study represents a molecular atlas of epithelial dynamics in response to estrogen and pregnancy hormones.

Unveiling the Role of Hormonal Imbalance in Breast Cancer Development: A Comprehensive Review

Breast cancer is a complex and multifactorial disease with a significant global impact. Hormonal imbalance has emerged as a crucial factor in breast cancer development, highlighting the importance of understanding the intricate interplay between hormones and breast tissue. This comprehensive review aims to unveil the role of hormonal imbalance in breast cancer by exploring the involvement of key hormones, including estrogen and progesterone, and their receptors in tumor development. The review delves into how hormonal imbalance impacts breast tissue, emphasizing the significance of hormone receptor status in guiding treatment decisions. Furthermore, the review investigates the influence of other hormones, such as insulin and growth factors, and their cross-talk with hormone pathways in breast cancer progression. The implications of hormonal imbalance assessment in breast cancer risk assessment and the importance of hormone testing in diagnosis and treatment decisions are also discussed. Moreover, the review provides an overview of the various hormonal therapies used in breast cancer treatment, their benefits, limitations, and ongoing research efforts to optimize their efficacy and overcome resistance. Future directions in hormonal therapy research, including developing novel therapies and personalized medicine approaches, are explored. This review underscores the need for a comprehensive understanding of hormonal imbalance in breast cancer to enhance prevention, diagnosis, and treatment strategies, ultimately improving outcomes for individuals affected by this disease.

Hormonal regulation of mammary gland development and lactation

Lactation is critical to infant short-term and long-term health and protects mothers from breast cancer, ovarian cancer and type 2 diabetes mellitus. The mammary gland is a dynamic organ, regulated by the coordinated actions of reproductive and metabolic hormones. These hormones promote gland development from puberty onwards and induce the formation of a branched, epithelial, milk-secreting organ by the end of pregnancy. Progesterone withdrawal following placental delivery initiates lactation, which is maintained by increased pituitary secretion of prolactin and oxytocin, and stimulated by infant suckling. After weaning, local cytokine production and decreased prolactin secretion trigger large-scale mammary cell loss, leading to gland involution. Here, we review advances in the molecular endocrinology of mammary gland development and milk synthesis. We discuss the hormonal functions of the mammary gland, including parathyroid hormone-related peptide secretion that stimulates maternal calcium mobilization for milk synthesis. We also consider the hormonal composition of human milk and its associated effects on infant health and development. Finally, we highlight endocrine and metabolic diseases that cause lactation insufficiency, for example, monogenic disorders of prolactin and prolactin receptor mutations, maternal obesity and diabetes mellitus, interventions during labour and delivery, and exposure to endocrine-disrupting chemicals such as polyfluoroalkyl substances in consumer products and other oestrogenic compounds.

Effects of Hormones on Breast Development and Breast Cancer Risk in Transgender Women

Transgender women experience gender dysphoria due to a gender assignment at birth that is incongruent with their gender identity. Transgender people undergo different surgical procedures and receive sex steroids hormones to reduce psychological distress and to induce and maintain desired physical changes. These persons on feminizing hormones represent a unique population to study the hormonal effects on breast development, to evaluate the risk of breast cancer and perhaps to better understand the precise role played by different hormonal components. In MTF (male to female) patients, hormonal treatment usually consists of antiandrogens and estrogens. Exogenous hormones induce breast development with the formation of ducts and lobules and an increase in the deposition of fat. A search of the existing literature dedicated to hormone regimens for MTF patients, their impact on breast tissue (incidence and type of breast lesions) and breast cancer risk provided the available information for this review. The evaluation of breast cancer risk is currently complicated by the heterogeneity of administered treatments and a lack of long-term follow-up in the great majority of studies. Large studies with longer follow-up are required to better evaluate the breast cancer risk and to understand the precise mechanisms on breast development of each exogenous hormone.

The Mammary Gland: Basic Structure and Molecular Signaling during Development

The mammary gland is a compound, branched tubuloalveolar structure and a major characteristic of mammals. The mammary gland has evolved from epidermal apocrine glands, the skin glands as an accessory reproductive organ to support postnatal survival of offspring by producing milk as a source of nutrition. The mammary gland development begins during embryogenesis as a rudimentary structure that grows into an elementary branched ductal tree and is embedded in one end of a larger mammary fat pad at birth. At the onset of ovarian function at puberty, the rudimentary ductal system undergoes dramatic morphogenetic change with ductal elongation and branching. During pregnancy, the alveolar differentiation and tertiary branching are completed, and during lactation, the mature milk-producing glands eventually develop. The early stages of mammary development are hormonal independent, whereas during puberty and pregnancy, mammary gland development is hormonal dependent. We highlight the current understanding of molecular regulators involved during different stages of mammary gland development.

Chemical Effects on Breast Development, Function, and Cancer Risk: Existing Knowledge and New Opportunities

Population studies show worrisome trends towards earlier breast development, difficulty in breastfeeding, and increasing rates of breast cancer in young women. Multiple epidemiological studies have linked these outcomes with chemical exposures, and experimental studies have shown that many of these chemicals generate similar effects in rodents, often by disrupting hormonal regulation. These endocrine-disrupting chemicals (EDCs) can alter the progression of mammary gland (MG) development, impair the ability to nourish offspring via lactation, increase mammary tissue density, and increase the propensity to develop cancer. However, current toxicological approaches to measuring the effects of chemical exposures on the MG are often inadequate to detect these effects, impairing our ability to identify exposures harmful to the breast and limiting opportunities for prevention. This paper describes key adverse outcomes for the MG, including impaired lactation, altered pubertal development, altered morphology (such as increased mammographic density), and cancer. It also summarizes evidence from humans and rodent models for exposures associated with these effects. We also review current toxicological practices for evaluating MG effects, highlight limitations of current methods, summarize debates related to how effects are interpreted in risk assessment, and make recommendations to strengthen assessment approaches. Increasing the rigor of MG assessment would improve our ability to identify chemicals of concern, regulate those chemicals based on their effects, and prevent exposures and associated adverse health effects.

Key to Life: Physiological Role and Clinical Implications of Progesterone

The most recent studies of progesterone research provide remarkable insights into the physiological role and clinical importance of this hormone. Although the name progesterone itself means “promoting gestation”, this steroid hormone is far more than a gestational agent. Progesterone is recognized as a key physiological component of not only the menstrual cycle and pregnancy but also as an essential steroidogenic precursor of other gonadal and non-gonadal hormones such as aldosterone, cortisol, estradiol, and testosterone. Based on current findings, progesterone and novel progesterone-based drugs have many important functions, including contraception, treatment of dysfunctional uterine bleeding, immune response, and prevention of cancer. Considering the above, reproduction and life are not possible without progesterone; thus, a better understanding of this essential molecule could enable safe and effective use of this hormone in many clinical conditions.

The molecular basis of mammary gland development and epithelial differentiation

Our understanding of the molecular events underpinning the development of mammalian organ systems has been increasing rapidly in recent years. With the advent of new and improved next-generation sequencing methods, we are now able to dig deeper than ever before into the genomic and epigenomic events that play critical roles in determining the fates of stem and progenitor cells during the development of an embryo into an adult. In this review, we detail and discuss the genes and pathways that are involved in mammary gland development, from embryogenesis, through maturation into an adult gland, to the role of pregnancy signals in directing the terminal maturation of the mammary gland into a milk producing organ that can nurture the offspring. We also provide an overview of the latest research in the single-cell genomics of mammary gland development, which may help us to understand the lineage commitment of mammary stem cells (MaSCs) into luminal or basal epithelial cells that constitute the mammary gland. Finally, we summarize the use of 3D organoid cultures as a model system to study the molecular events during mammary gland development. Our increased investigation of the molecular requirements for normal mammary gland development will advance the discovery of targets to predict breast cancer risk and the development of new breast cancer therapies.

Advanced Approaches to Breast Cancer Classification and Diagnosis

The International Agency for Research on Cancer (IARC) has recently reported a 66% increase in the global number of cancer deaths since 1960. In the US alone, about one in eight women is expected to develop invasive breast cancer(s) (breast cancer) at some point in their lifetime. Traditionally, a BC diagnosis includes mammography, ultrasound, and some high-end molecular bioimaging. Unfortunately, these techniques detect BC at a later stage. So early and advanced molecular diagnostic tools are still in demand. In the past decade, various histological and immuno-molecular studies have demonstrated that BC is highly heterogeneous in nature. Its growth pattern, cytological features, and expression of key biomarkers in BC cells including hormonal receptor markers can be utilized to develop advanced diagnostic and therapeutic tools. A cancer cell's progression to malignancy exhibits various vital biomarkers, many of which are still underrepresented in BC diagnosis and treatment. Advances in genetics have also enabled the development of multigene assays to detect genetic heterogeneity in BC. However, thus far, the FDA has approved only four such biomarkers-cancer antigens (CA); CA 15-3, CA 27-29, Human epidermal growth factor receptor 2 (HER2), and circulating tumor cells (CTC) in assessing BC in body fluids. An adequately structured portable-biosensor with its non-invasive and inexpensive point-of-care analysis can quickly detect such biomarkers without significantly compromising its specificity and selectivity. Such advanced techniques are likely to discriminate between BC and a healthy patient by accurately measuring the cell shape, structure, depth, intracellular and extracellular environment, and lipid membrane compositions. Presently, BC treatments include surgery and systemic chemo- and targeted radiation therapy. A biopsied sample is then subjected to various multigene assays to predict the heterogeneity and recurrence score, thus guiding a specific treatment by providing complete information on the BC subtype involved. Thus far, we have seven prognostic multigene signature tests for BC providing a risk profile that can avoid unnecessary treatments in low-risk patients. Many comparative studies on multigene analysis projected the importance of integrating clinicopathological information with genomic-imprint analysis. Current cohort studies such as MINDACT, TAILORx, Trans-aTTOM, and many more, are likely to provide positive impact on long-term patient outcome. This review offers consolidated information on currently available BC diagnosis and treatment options. It further describes advanced biomarkers for the development of state-of-the-art early screening and diagnostic technologies.

Reproductive hormones during pubertal transition in girls with transient Thelarche

CONTEXT

Transient thelarche (TT), that is, the appearance, regression and subsequent reappearance of breast buds, is a frequent phenomenon, but little is known about pubertal transition in these girls.

OBJECTIVE

To describe pubertal progression, growth, genotypes, reproductive hormones and growth factors in girls with TT compared to those who do not present TT (non-TT).

DESIGN

Retrospective analysis of a longitudinal population-based study.

PATIENTS OR OTHER PARTICIPANTS

Girls (n = 508) of the Chilean Growth and Obesity cohort.

MEASUREMENTS

Pubertal progression, reproductive hormones, follicle stimulating hormone (FSH) beta subunit/FSH receptor gene single nucleotide polymorphisms and growth.

RESULTS

Thirty-seven girls (7.3%) were presented TT. These girls entered puberty by pubarche more frequently (51%) than girls with normal progression (non-TT; n = 471; 23%, P = .005). Girls with TT who were under 8 years old had lower androgens, anti-Müllerian hormone (AMH), luteinizing hormone (LH) and oestradiol (all P < .05) than older girls with TT. At the time of Tanner breast stage 2 (B2), girls with TT had higher androgens, LH, FSH, IGF1, LH, insulin and oestradiol (P < .01) than at the time of TT. TT girls were older at B2 (10.3 ± 1.1 vs. 9.2 ± 1.2 years, P < .001) and menarche (12.3 ± 0.8 vs. 12.0 ± 1.0 years, P = .040) than their counterparts (non-TT). No differences in anthropometric variables or FSHB/FSHR genotypes were detected.

CONCLUSION

Transient thelarche is a frequent phenomenon that does not appear to be mediated by hypothalamic-pituitary-gonadal axis activation or by adiposity. Hormonal differences between earlier TT and later TT suggest that their mechanisms are different.

Effects of hormones and hormone therapy on breast tissue in transgender patients: a concise review

PURPOSE

Hormone replacement therapy (HRT) has become a mainstay medical treatment option for management of gender dysphoria in transgender patients of both biologic sexes. Very little is known about the long-term effects of steroid hormone modulation on breast tissue in this population. Most of the data available on the effects of HRT on breast and reproductive tissues come from studies of postmenopausal cisgender women. Therapeutic regimens are often provider-dependent, and there, are no uniform guidelines in place for cancer surveillance in transgender patients. In this review, we present what forms of hormone therapy and hormone modulation are available to transgender patients, what is known about their effects on male and female breast tissue, and what other endogenous and exogenous factors contribute to the macroscopic and cellular changes observed.

METHODS

A search for the existing literature focusing on therapeutic regimens and the effects of HRT on breast tissue provided the most current information available for this review. Recent evidence-based reports (since the year 2000) and reviews were given priority over anecdotal evidence and expert opinions when conflicting information was encountered. Older resources were considered when primary sources were needed. Given the paucity of available articles on this subject, all resources were given careful consideration.

RESULTS

Information about the risks associated with HRT in the current literature and in this setting is limited and often conflicting, due to a scarcity of long-term studies tracking breast pathology among transgender men and women.

CONCLUSIONS

We conclude that the long-term effects of off-label pharmaceutical use for modulation of hormone levels and sexual characteristics in transgender patients have not been well studied. The tendency of steroid hormones to promote the growth of certain cancers also raises questions about the safety of differing doses and drug combinations. Further clinical and laboratory study is needed to better establish safety and dosing guidelines in transgender patients.

Growth factor genes and change in mammographic density after stopping combined hormone therapy in the California Teachers Study

Background

The contribution of genetic polymorphisms to the large inter-individual variation in mammographic density (MD) changes following starting and stopping use of estrogen and progestin combined therapy (EPT) has not been well-studied. Previous studies have shown that circulating levels of insulin-like growth factors are associated with MD and cross-talk between estrogen signaling and growth factors is necessary for cell proliferation in the breast. We evaluated single nucleotide polymorphisms (SNPs) in growth factor genes in association with MD changes after women stop EPT use.

Methods

We genotyped 191 SNPs in 13 growth factor pathway genes in 284 non-Hispanic white California Teachers Study participants who previously used EPT and collected their mammograms before and after quitting EPT. Percent MD was assessed using a computer-assisted method. Change in percent MD was calculated by subtracting percent MD of an ‘off-EPT’ mammogram from percent MD of an ‘on-EPT’ (i.e. baseline) mammogram. We used multivariable linear regression analysis to investigate the association between SNPs and change in percent MD. We calculated P-values corrected for multiple testing within a gene (P_adj).

Results

Rs1983210 in INHA and rs35539615 in IGFBP1/3 showed the strongest associations. Per minor allele of rs1983210, the absolute change in percent MD after stopping EPT use decreased by 1.80% (a difference in absolute change in percent MD) (P_adj= 0.021). For rs35539615, change in percent MD increased by 1.79% per minor allele (P_adj= 0.042). However, after applying a Bonferroni correction for the number of genes tested, these associations were no longer statistically significant.

Conclusions

Genetic variation in growth factor pathway genes INHA and IGFBP1/3 may predict longitudinal MD change after women quit EPT. The observed differences in EPT-associated changes in percent MD in association with these genetic polymorphisms are modest but may be clinically significant considering that the magnitude of absolute increase in percent MD reported from large clinical trials of EPT ranged from 3% to 7%.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4981-6) contains supplementary material, which is available to authorized users.

Long-Chain Omega-3 Polyunsaturated Fatty Acids Modulate Mammary Gland Composition and Inflammation

Studies in rodents have shown that dietary modifications as mammary glands (MG) develop, regulates susceptibility to mammary tumor initiation. However, the effects of dietary PUFA composition on MGs in adult life, remains poorly understood. This study investigated morphological alterations and inflammatory microenvironments in the MGs of adult mice fed isocaloric and isolipidic liquid diets with varying compositions of omega (ω)-6 and long-chain (Lc)-ω3FA that were pair-fed. Despite similar consumption levels of the diets, mice fed the ω-3 diet had significantly lower body-weight gains, and abdominal-fat and mammary fat pad (MFP) weights. Fatty acid analysis showed significantly higher levels of Lc-ω-3FAs in the MFPs of mice on the ω-3 diet, while in the MFPs from the ω-6 group, Lc-ω-3FAs were undetectable. Our study revealed that MGs from ω-3 group had a significantly lower ductal end-point density, branching density, an absence of ductal sprouts, a thinner ductal stroma, fewer proliferating epithelial cells and a lower transcription levels of estrogen receptor 1 and amphiregulin. An analysis of the MFP and abdominal-fat showed significantly smaller adipocytes in the ω-3 group, which was accompanied by lower transcription levels of leptin, IGF1, and IGF1R. Further, MFPs from the ω-3 group had significantly decreased numbers and sizes of crown-like-structures (CLS), F4/80+ macrophages and decreased expression of proinflammatory mediators including Ptgs2, IL6, CCL2, TNFα, NFκB, and IFNγ. Together, these results support dietary Lc-ω-3FA regulation of MG structure and density and adipose tissue inflammation with the potential for dietary Lc-ω-3FA to decrease the risk of mammary gland tumor formation.

TRIENNIAL LACTATION SYMPOSIUM/BOLFA: Plasticity of mammary development in the prepubertal bovine mammary gland

Although peripubertal mammary development represents only a small fraction of the total mass of mammary parenchyma present in the udder at the end of gestation and into lactation, there is increasing evidence that the tissue foundations created in early life can affect future mammary development and function. Studies on expression of estrogen and progesterone receptors seem to confirm the relevance of these steroids in prepubertal mammary development, but connections with other growth factors, hormones, and local tissue factors remain elusive. Enhanced preweaning feeding in the bovine appears to enhance the capacity of mammary tissue to response to mammogenic stimulation. This suggests the possibility that improved early nutrition might allow for creation of stem or progenitor cell populations to better support the massive ductal growth and lobulo-alveolar development during gestation. Increasing evidence that immune cells are involved in mammary development suggests there are unexpected and poorly understood connections between the immune system and mammary development. This is nearly unexplored in ruminants. Development of new tools to identify, isolate, and characterize cell populations within the developing bovine mammary gland offer the possibility of identifying and perhaps altering populations of mammary stem cells or selected progenitor cells to modulate mammary development and, possibly, mammary function.

TRIENNIAL LACTATION SYMPOSIUM/BOLFA: Dietary regulation of allometric ductal growth in the mammary glands

Although mammary gland growth and development in females is a lifelong process, it builds on isometric and allometric phases of mammary growth to establish a complex ductal network before and during puberty. Only then can other phases of branching and alveologenesis, differentiation, lactation, and involution proceed. Although the ductal network of various species differs in its histomorphology, all glands undergo a common phase of allometric growth when the mammary ducts penetrate into the supporting stromal microenvironment. Perhaps not surprisingly, different aspects of diet and nutrition can influence this allometric growth, either directly or indirectly. In this review, we outline some of the fundamental aspects of how allometric ductal growth in the mammary glands of various species is influenced by diet and nutrition and identify opportunities and questions for future investigation.

The Terminal End Bud: the Little Engine that Could

The mammary gland is one of the most regenerative organs in the body, with the majority of development occurring postnatally and in the adult mammal. Formation of the ductal tree is orchestrated by a specialized structure called the terminal end bud (TEB). The TEB is responsible for the production of mature cell types leading to the elongation of the subtending duct. The TEB is also the regulatory control point for basement membrane deposition, branching, angiogenesis, and pattern formation. While the hormonal control of TEB growth is well characterized, the local regulatory factors are less well understood. Recent studies of pubertal outgrowth and ductal elongation have yielded surprising details in regards to ongoing processes in the TEB. Here we summarize the current understanding of TEB biology, discuss areas of future study, and discuss the use of the TEB as a model for the study of breast cancer.

A Convenient Method for Evaluating Epithelial Cell Proliferation in the Whole Mammary Glands of Female Mice

The mammary glands (MG) undergo rapid expansion of the ductal network during puberty in response to endocrine cues including the potent mitogenic effects of estrogen. The proliferation of mammary epithelial cells occurs in a spatially distinctive manner, where terminal end buds located at the ductal termini are the primary site of cell division. Here, we present a relatively high throughput approach to spatially assess epithelial cell proliferation in whole mouse MG using histochemical detection of 5-ethynyl-2'-deoxyuridine in conjunction with a standard curve-based data deconvolution technique to semiquantitatively measure proliferation via wide-field epifluorescent microscopy. This approach was validated against the "gold standard" of counting labeled nuclei from confocal images utilizing computer-assisted image analysis. Our method proved sensitive enough to describe the significant and spatially variable proliferative response to low-dose estrogen after 108 hours. This flexible method presents a timely and economical approach to obtaining spatial information regarding epithelial cell proliferation in the mouse MG.

The Rat Mammary Gland: Morphologic Changes as an Indicator of Systemic Hormonal Perturbations Induced by Xenobiotics

The development and morphology of the rat mammary gland are dependent upon several hormones including estrogens, androgens, progesterone, growth hormone and prolactin. In toxicology studies, treatment with xenobiotics may alter these hormones resulting in changes in the morphology of reproductive tissues such as the mammary gland. In the rat, male and female mammary glands exhibit striking morphologic differences that can be altered secondary to hormonal perturbations. Recognizing these morphologic changes can help the pathologist predict potential xenobiotic-induced perturbations in the systemic hormonal milieu. This review examines the development of the rat mammary gland and the influence of sex hormones on the morphology of the adult male and female rat mammary gland. Specific case examples from the literature and data from our laboratory highlight the dynamic nature of the rat mammary gland in response to hormonal changes.

Pesticide chlorpyrifos acts as an endocrine disruptor in adult rats causing changes in mammary gland and hormonal balance

Endocrine disruptors (EDs) are compounds that interfere with hormone regulation and influence mammary carcinogenesis. We have previously demonstrated that the pesticide chlorpyrifos (CPF) acts as an ED in vitro, since it induces human breast cancer cells proliferation through estrogen receptor alpha (ERα) pathway. In this work, we studied the effects of CPF at environmental doses (0.01 and 1mg/kg/day) on mammary gland, steroid hormone receptors expression and serum steroid hormone levels. It was carried out using female Sprague-Dawley 40-days-old rats exposed to the pesticide during 100 days. We observed a proliferating ductal network with a higher number of ducts and alveolar structures. We also found an increased number of benign breast diseases, such as hyperplasia and adenosis. CPF enhanced progesterone receptor (PgR) along with the proliferating cell nuclear antigen (PCNA) in epithelial ductal cells. On the other hand, the pesticide reduced the expression of co-repressors of estrogen receptor activity REA and SMRT and it decreased serum estradiol (E2), progesterone (Pg) and luteinizing hormone (LH) levels. Finally, we found a persistent decrease in LH levels among ovariectomized rats exposed to CPF. Therefore, CPF alters the endocrine balance acting as an ED in vivo. These findings warn about the harmful effects that CPF exerts on mammary gland, suggesting that this compound may act as a risk factor for breast cancer.

Mammary gland development--It's not just about estrogen

The mammary gland (MG) is one of a few organs that undergoes most of its growth after birth. Much of this development occurs concurrently with specific reproductive states, such that the ultimate goal of milk synthesis and secretion is coordinated with the nutritional requirements of the neonate. Central to the reproductive-MG axis is its endocrine regulation, and pivotal to this regulation is the ovarian secretion of estrogen (E). Indeed, it is widely accepted that estrogens are essential for growth of the MG to occur, both for ductal elongation during puberty and for alveolar development during gestation. As the factors regulating MG development continually come to light from the fields of developmental biology, lactation physiology, and breast cancer research, a growing body of evidence serves as a reminder that the MG are not as exclusively dependent on estrogens as might have been thought. The objective of this review is to summarize the state of information regarding our understanding of how estrogen (E) has been implicated as the key regulator of MG development, and to highlight some of the alternative E-independent mechanisms that have been discovered. In particular, we review our findings that dietary trans-10,cis-12 conjugated linoleic acid promotes ductal elongation and that the combination of progesterone (P) and prolactin (PRL) can stimulate branching morphogenesis in the absence of E. Ultimately, these examples stand as a healthy challenge to the question of just how important estrogens are for MG development. Answers to this question, in turn, increase our understanding of MG development across all mammals and the ways in which it can affect milk production.

Targeted DNA Methylation Screen in the Mouse Mammary Genome Reveals a Parity-Induced Hypermethylation of Igf1r That Persists Long after Parturition

The most effective natural prevention against breast cancer is an early first full-term pregnancy. Understanding how the protective effect is elicited will inform the development of new prevention strategies. To better understand the role of epigenetics in long-term protection, we investigated parity-induced DNA methylation in the mammary gland. FVB mice were bred or remained nulliparous and mammary glands harvested immediately after involution (early) or 6.5 months following involution (late), allowing identification of both transient and persistent changes. Targeted DNA methylation (109 Mb of Ensemble regulatory features) analysis was performed using the SureSelectXT Mouse Methyl-seq assay and massively parallel sequencing. Two hundred sixty-nine genes were hypermethylated and 128 hypomethylated persistently at both the early and late time points. Pathway analysis of the persistently differentially methylated genes revealed Igf1r to be central to one of the top identified signaling networks, and Igf1r itself was one of the most significantly hypermethylated genes. Hypermethylation of Igf1r in the parous mammary gland was associated with a reduction of Igf1r mRNA expression. These data suggest that the IGF pathway is regulated at multiple levels during pregnancy and that its modification might be critical in the protective role of pregnancy. This supports the approach of lowering IGF action for prevention of breast cancer, a concept that is currently being tested clinically.

Abnormal Mammary Development in 129:STAT1-Null Mice is Stroma-Dependent

Female 129:Stat1-null mice (129S6/SvEvTac-Stat1^tm1Rds homozygous) uniquely develop estrogen-receptor (ER)-positive mammary tumors. Herein we report that the mammary glands (MG) of these mice have altered growth and development with abnormal terminal end buds alongside defective branching morphogenesis and ductal elongation. We also find that the 129:Stat1-null mammary fat pad (MFP) fails to sustain the growth of 129S6/SvEv wild-type and Stat1-null epithelium. These abnormalities are partially reversed by elevated serum progesterone and prolactin whereas transplantation of wild-type bone marrow into 129:Stat1-null mice does not reverse the MG developmental defects. Medium conditioned by 129:Stat1-null epithelium-cleared MFP does not stimulate epithelial proliferation, whereas it is stimulated by medium conditioned by epithelium-cleared MFP from either wild-type or 129:Stat1-null females having elevated progesterone and prolactin. Microarrays and multiplexed cytokine assays reveal that the MG of 129:Stat1-null mice has lower levels of growth factors that have been implicated in normal MG growth and development. Transplanted 129:Stat1-null tumors and their isolated cells also grow slower in 129:Stat1-null MG compared to wild-type recipient MG. These studies demonstrate that growth of normal and neoplastic 129:Stat1-null epithelium is dependent on the hormonal milieu and on factors from the mammary stroma such as cytokines. While the individual or combined effects of these factors remains to be resolved, our data supports the role of STAT1 in maintaining a tumor-suppressive MG microenvironment.

Insulin-like growth factor-I inhibition with pasireotide decreases cell proliferation and increases apoptosis in pre-malignant lesions of the breast: a phase 1 proof of principle trial

INTRODUCTION

Estrogen inhibition is effective in preventing breast cancer in only up to 50% of women with precancerous lesions and many experience side effects that are poorly tolerated. As insulin-like growth factor I (IGF-I) underlies both estrogen and progesterone actions and has other direct effects on mammary development and carcinogenesis, we hypothesized that IGF-I inhibition might provide a novel approach for breast cancer chemoprevention.

METHODS

In total, 13 women with core breast biopsies diagnostic of atypical hyperplasia (AH) were treated for 10 days with pasireotide, a somatostatin analog which uniquely inhibits IGF-I action in the mammary gland. They then had excision biopsies. 12 patients also had proliferative lesions and one a ductal carcinoma in situ (DCIS). Primary outcomes were changes in cell proliferation and apoptosis after treatment. Expression of estrogen receptor (ER), progesterone receptor (PR), and phosphorylated Insulin-like growth factor I receptor (IGF-1R), protein kinase B (AKT) and extracellular signal-regulated kinases 1/2 (ERK1/2) were also assessed. Core and excision biopsies from 14 untreated patients served as non-blinded controls. Hyperglycemia and other side effects were carefully monitored.

RESULTS

Pasireotide decreased proliferation and increased apoptosis in all AH (from 3.6 ± 2.6% to 1.3 ± 1.2% and from 0.3 ± 0.2% to 1.5 ± 1.6%, respectively) and proliferative lesions (from 3.8 ± 2.5% to 1.8 ± 1.8% and from 0.3 ± 0.2% to 1.3 ± 0.6%, respectively). The DCIS responded similarly. ER and PR were not affected by pasireotide, while IGF-1R, ERK1/2 and AKT phosphorylation decreased significantly. In contrast, tissue from untreated controls showed no change in cell proliferation or phosphorylation of IGF-1R, AKT or ERK 1/2. Mild to moderate hyperglycemia associated with reduced insulin levels was found. Glucose fell into the normal range after discontinuing treatment. Pasireotide was well tolerated and did not cause symptoms of estrogen deprivation.

CONCLUSIONS

IGF-I inhibition by pasireotide, acting through the IGF-1R, was associated with decreased proliferation and increased apoptosis in pre-malignant breast lesions and one DCIS. Assuming hyperglycemia can be controlled, these data suggest that inhibiting the IGF-I pathway may prove an effective alternative for breast cancer chemoprevention.

TRIAL REGISTRATION

NCT01372644 Trial date: July 1, 2007.

Gynaecomastia--pathophysiology, diagnosis and treatment

Gynaecomastia (enlargement of the male breast tissue) is a common finding in the general population. Most cases of gynaecomastia are benign and of cosmetic, rather than clinical, importance. However, the condition might cause local pain and tenderness, could occasionally be the result of a serious underlying illness or a medication, or be inherited. Breast cancer in men is much less common than benign gynaecomastia, and the two conditions can usually be distinguished by a careful physical examination. Estrogens are known to stimulate the growth of breast tissue, whereas androgens inhibit it; most cases of gynaecomastia result from deficient androgen action or excessive estrogen action in the breast tissue. In some cases, such as pubertal gynaecomastia, the breast enlargement resolves spontaneously. In other situations, more active treatment might be required to correct an underlying condition (such as hyperthyroidism or a benign Leydig cell tumour of the testis) or medications that could cause breast enlargement (such as spironolactone) might need to be discontinued. For men with hypogonadism, administration of androgens might be helpful, as might antiestrogen therapy in men with endogenous overproduction of estrogens. Surgery to remove the enlarged breast tissue might be necessary when gynaecomastia does not resolve spontaneously or with medical therapy.

Assessment of the proliferative capacity of the flavanones 8-prenylnaringenin, 6-(1.1-dimethylallyl)naringenin and naringenin in MCF-7 cells and the rat mammary gland

8-Prenylnaringenin (8-PN) and naringenin (Nar) are phytoestrogens found in food items and nutritional supplements, while 6-(1.1-dimethylallyl)naringenin (6-DMAN) is a component of an African plant. Besides their assumed beneficial effects they may promote mammary and endometrial cancer. We therefore assessed their proliferative and estrogenic potential on the mammary gland in vitro and in vivo. In competitive estrogen receptor (ER) ligand binding assays 8-PN displayed a high relative binding affinity for both ERs with a preference for ERα and had the strongest mitotic effect on MCF-7 cells among the test substances. In a three day exposure in young adult ovariectomized female rats 15 mg/kg 8-PN had the highest capacity to increase the number of terminal end buds (TEB) in the mammary gland and stimulated expression of proliferation markers in epithelial ductal cells, followed by 6-DMAN and Nar, but overall their capacity to stimulate proliferation was weak in comparison to 17β-Estradiol (E2).

Detection of expressional changes induced by intrauterine growth restriction in the developing rat mammary gland via exploratory pathways analysis

Background

Intrauterine growth restriction (IUGR) is thought to lead to fetal programming that in turn contributes to developmental changes of many organs postnatally. There is evidence that IUGR is a risk factor for the development of metabolic and cardiovascular disease later in life. A higher incidence of breast cancer was also observed after IUGR. This could be due to changes in mammary gland developmental pathways. We sought to characterise IUGR-induced alterations of the complex pathways of mammary development at the level of the transcriptome in a rat model of IUGR, using pathways analysis bioinformatics.

Methodology/Principal Findings

We analysed the mammary glands of Wistar rats with IUGR induced by maternal low protein (LP) diet at the beginning (d21) and the end (d28) of pubertal ductal morphogenesis. Mammary glands of the LP group were smaller in size at d28, however did not show morphologic changes. We identified multiple differentially expressed genes in the mammary gland using Agilent SurePrint arrays at d21 and d28. In silico analysis was carried out using Ingenuity Pathways Analysis. In mammary gland tissue of LP rats at d21 of life a prominent upregulation of WT1 and CDKN1A (p21) expression was observed. Differentially regulated genes were associated with the extracellular regulated kinase (ERK)-1/-2 pathway. Western Blot analysis showed reduced levels of phosphorylated ERK-1/-2 in the mammary glands of the LP group at d21. To identify possible changes in circulating steroid levels, serum LC-Tandem mass-spectrometry was performed. LP rats showed higher serum progesterone levels and an increased corticosterone/dehydrocorticosterone-ratio at d28.

Conclusions/Significance

Our data obtained from gene array analysis support the hypothesis that IUGR influences pubertal development of the rat mammary gland. We identified prominent differential regulation of genes and pathways for factors regulating cell cycle and growth. Moreover, we detected new pathways which appear to be programmed by IUGR.

Breast cancer risk in BRCA1 mutation carriers: insight from mouse models

Since its identification 20 years ago, the biological basis for the high breast cancer risk in women who have germline BRCA1 mutations has been an area of intense study for three reasons. First, BRCA1 was the first gene shown to associate with breast cancer risk, and therefore serves as model for understanding genetic susceptibility. Second, the type of breast cancer that occurs in these women has specific features that have engendered new hypotheses about the cancer biology. Third, it is hoped that understanding the origins of this disease may provide the means to prevent disease. Resolving this question has proven extremely challenging because the biology controlled by BRCA1 is complex. Our working model is that the high frequency of basal-like breast cancer in BRCA1 mutation carriers is the result of a self-perpetuating triad of cellular phenotypes consisting of: (i) intrinsic defects in DNA repair and centrosome regulation that lead to genomic instability and increases spontaneous transformation; (ii) aberrant lineage commitment; and (iii) increased proliferation due to in large part to increased IGF-1 activity. We propose that the last is key and is a potential entree for preventing breast cancer in BRCA1 mutation carriers.

IGF-I retards proper development of acinar structures formed by bovine mammary epithelial cells via sustained activation of Akt kinase

Insulin-like growth factor-I is involved in mammary gland development, promoting proliferation and inhibiting apoptosis of mammary epithelial cells (MECs). Mitogenic actions of IGF-I are mainly mediated by the phosphatidylinositol-3 kinase (PI3K)/Akt signaling pathway. We have found that in the presence of IGF-I bovine BME-UV1 MECs cultured on reconstituted basement membrane form large spheroids with disrupted polarity and no cavity in the center. These cells showed enhanced phosphorylation of Akt, decreased level of cleaved caspase-3, and sustained proliferative activity throughout the 16-d period of 3-dimensional culture. Inhibition of the PI3K/Akt pathway by a specific inhibitor of PI3K, LY294002, resulted in the restoration of the normal acinar phenotype. However, this effect was noted only when LY294002 was added in the second week of 3-dimensional culture, which corresponded with the time of cell cycle arrest and polarity formation under control conditions. Normal development of acini was also obtained when BME-UV1 cells were treated simultaneously with IGF-I and 17β-estradiol. The addition of 17β-estradiol regulated Akt activation, enabling the subsequent initiation of polarization processes. 17β-Estradiol also increased the level of IGFBP-3 protein in MECs cultured on Matrigel in the presence of IGF-I. The presented results indicate important interactions between signaling pathways activated by estrogen and IGF-I, which regulate alveologenesis in bovine mammary gland.

Hormonal control of stem cell systems

Many organs respond to physiological challenges by changing tissue size or composition. Such changes may originate from tissue-specific stem cells and their supportive environment (niche). The endocrine system is a major effector and conveyor of physiological changes and as such could alter stem cell behavior in various ways. In this review, we examine how hormones affect stem cell biology in four different organs: the ovary, intestine, hematopoietic system, and mammary gland. Hormones control every stage of stem cell life, including establishment, expansion, maintenance, and differentiation. The effects can be cell autonomous or non-cell autonomous through the niche. Moreover, a single hormone can affect different stem cells in different ways or affect the same stem cell differently at various developmental times. The vast complexity and diversity of stem cell responses to hormonal cues allow hormones to coordinate the body's reaction to physiological challenges.

Amphiregulin mediates progesterone-induced mammary ductal development during puberty

Introduction

Puberty is a period of increased susceptibility to factors that cause increased breast cancer risk in adulthood. Mammary end buds (EBs) that develop during puberty are believed to be the targets of breast cancer initiation. Whereas the role of estrogen (E) has been extensively studied in pubertal mammary gland development, the role of progesterone (P) during puberty is less defined.

Methods

Pubertal and prepubertal ovariectomized mice were treated with vehicle control (C), E, P, or E+P. Mammary glands from these mice were analyzed for changes in morphology, proliferation, and expression of the downstream targets amphiregulin (AREG) and receptor activator of NF-κB ligand (RANKL).

Results

P, acting specifically through the progesterone receptor, induced increases in mammary gland proliferation and EB formation that were associated with increased AREG expression in ducts and EBs. E, acting specifically through the estrogen receptor, produced similar responses also mediated by AREG. Blocking AREG action by treatment with an EGFR inhibitor completely abrogated the effect of P on EB formation and proliferation and significantly reduced proliferation within ducts. P also increased expression of RANKL, primarily in ducts. Treatment with RANK-Fc, an inhibitor of RANKL, reduced P-dependent proliferation in ducts and to a lesser extent in EB, but did not cause EB regression.

Conclusions

These results demonstrate a novel P-specific effect through AREG to cause EB formation and proliferation in the developing mammary gland both before and during puberty. Thus, hormones and/or factors in addition to E that upregulate AREG can promote mammary gland development and have the potential to affect breast cancer risk associated with pubertal mammary gland development.

Impaired mouse mammary gland growth and development is mediated by melatonin and its MT1G protein-coupled receptor via repression of ERα, Akt1, and Stat5

To determine whether melatonin, via its MT(1)  G protein-coupled receptor, impacts mouse mammary gland development, we generated a mouse mammary tumor virus (MMTV)-MT1-Flag-mammary gland over-expressing (MT1-mOE) transgenic mouse. Increased expression of the MT(1) -Flag transgene was observed in the mammary glands of pubescent MT1-mOE transgenic female mice, with further significant increases during pregnancy and lactation. Mammary gland whole mounts from MT1-mOE mice showed significant reductions in ductal growth, ductal branching, and terminal end bud formation. Elevated MT(1) receptor expression in pregnant and lactating female MT1-mOE mice was associated with reduced lobulo-alveolar development, inhibition of mammary epithelial cell proliferation, and significant reductions in body weights of suckling pups. Elevated MT(1) expression in pregnant and lactating MT1-mOE mice correlated with reduced mammary gland expression of Akt1, phospho-Stat5, Wnt4, estrogen receptor alpha, progesterone receptors A and B, and milk proteins β-casein and whey acidic protein. Estrogen- and progesterone-stimulated mammary gland development was repressed by elevated MT(1) receptor expression and exogenous melatonin administration. These studies demonstrate that the MT(1) melatonin receptor and its ligand melatonin play an important regulatory role in mammary gland development and lactation in mice through both growth suppression and alteration of developmental paradigms.

Diet-induced metabolic change induces estrogen-independent allometric mammary growth

Lifetime breast cancer risk reflects an unresolved combination of early life factors including diet, body mass index, metabolic syndrome, obesity, and age at first menses. In parallel, the onset of allometric growth by the mammary glands around puberty is widely held to be estrogen (E)-dependent. Here we report that several physiological changes associated with metabolic syndrome in response to a diet supplemented with the trans-10, cis-12 isomer of conjugated linoleic acid lead to ovary-independent allometric growth of the mammary ducts. The E-independence of this diet-induced growth was highlighted by the fact that it occurred both in male mice and with pharmacological inhibition of either E receptor function or E biosynthesis. Reversal of the metabolic phenotype with the peroxisome proliferator-activated receptor-γ agonist rosiglitazone abrogated diet-induced mammary growth. A role for hyperinsulinemia and increased insulin-like growth factor-I receptor (IGF-IR) expression during mammary growth induced by the trans-10, cis-12 isomer of conjugated linoleic acid was confirmed by its reversal upon pharmacological inhibition of IGF-IR function. Diet-stimulated ductal growth also increased mammary tumorigenesis in ovariectomized polyomavirus middle T-antigen mice. Our data demonstrate that diet-induced metabolic dysregulation, independently of ovarian function, stimulates allometric growth within the mammary glands via an IGF-IR-dependent mechanism.

The biology of human breast epithelial progenitors

Current evidence suggests that similar to other tissues in the human body mammary epithelia cells are being maintained by the unique properties of stem cells, undifferentiated as well as lineage-restricted progenitors. Because of their longevity, proliferation and differentiation potentials these primitive breast epithelial cells are likely targets of transforming mutations that can cause them to act as cancer initiating cells. In this context, understanding the molecular mechanisms that regulate the normal functions of the human breast epithelial stem cells and progenitors and how alterations to these same mechanisms can confer a cancer stem cell phenotype on these rare cell populations is crucial to the development of new and more effective therapies again breast cancer. This review article will examine the current state of knowledge about the isolation and characterization of human breast epithelial progenitors and their relevance to breast cancer research.

Gynecomastia: physiopathology, evaluation and treatment

Gynecomastia (GM) is characterized by enlargement of the male breast, caused by glandular proliferation and fat deposition. GM is common and occurs in adolescents, adults and in old age. The aim of this review is to discuss the pathophysiology, etiology, evaluation and therapy of GM. A hormonal imbalance between estrogens and androgens is the key hallmark of GM generation. The etiology of GM is attributable to physiological factors, endocrine tumors or dysfunctions, non-endocrine diseases, drug use or idiopathic causes. Clinical evaluation must address diagnostic confirmation, search for an etiological factor and classify GM into severity grades to guide the treatment. A proposal for tailored therapy is presented. Weight loss, reassurance, pharmacotherapy with tamoxifen and surgical correction are the therapeutic options. For long-standing GM, the best results are generally achieved through surgery, combining liposuction and mammary adenectomy.

Alcohol exposure in utero leads to enhanced prepubertal mammary development and alterations in mammary IGF and estradiol systems

Exposure to alcohol during fetal development increases susceptibility to mammary cancer in adult rats. This study determined if early changes in mammary morphology and the insulin-like growth factor (IGF)/estradiol axis are involved in the mechanisms that underlie this increased susceptibility. Pregnant Sprague-Dawley rats were fed a liquid diet containing 6.7% ethanol (alcohol), an isocaloric liquid diet (pair-fed), or rat chow ad libitum from days 11 to 21 of gestation. At birth, female pups were cross-fostered to ad libitum-fed control dams. Offspring were euthanized at postnatal days (PND) 20, 40, or 80. Animals were injected with BrdU before euthanasia, then mammary glands, serum, and livers were collected. Mammary glands from animals exposed to alcohol in utero displayed increased epithelial cell proliferation and aromatase expression at PND 20 and 40. Mammary IGF-I mRNA was higher in alcohol-exposed animals relative to controls at PND 20, while mammary IGFBP-5 mRNA was lower in this group at PND 40. Hepatic IGF-I mRNA expression was increased at all time points in alcohol-exposed animals, however, circulating IGF-I levels were not altered. These data indicate that alcohol exposure in utero may advance mammary development via the IGF and estradiol systems, which could contribute to increased susceptibility to mammary cancer later in life.

The pivotal role of insulin-like growth factor I in normal mammary development

Mammary development begins in puberty in response to an estrogen (E(2)) surge. E(2) does not act alone. It relies on pituitary growth hormone (GH) to induce insulin-like growth factor I (IGF-I) production in the mammary stromal compartment. In turn, IGF-I permits E(2) (and progesterone) action. During puberty, E(2) and IGF-I synergize for ductal morphogenesis. During pregnancy, progesterone joins IGF-I and E(2) to stimulate secretory differentiation necessary to produce milk. Prolactin stimulates milk production, while transforming growth factor-β inhibits proliferation. The orchestrated action of hormones, growth factors, and receptors necessary for mammary development and function are also critical in breast cancer.

Decreased IGF type 1 receptor signaling in mammary epithelium during pregnancy leads to reduced proliferation, alveolar differentiation, and expression of insulin receptor substrate (IRS)-1 and IRS-2

The IGFs and the IGF type 1 receptor (IGF-1R) are essential mediators of normal mammary gland development in mice. IGF-I and the IGF-1R have demonstrated functions in formation and proliferation of terminal end buds and in ductal outgrowth and branching during puberty. To study the functions of IGF-1R during pregnancy and lactation, we established transgenic mouse lines expressing a human dominant-negative kinase dead IGF-1R (dnhIGF-1R) under the control of the whey acidic protein promoter. We provide evidence that the IGF-1R pathway is necessary for normal epithelial proliferation and alveolar formation during pregnancy. Furthermore, we demonstrate that the whey acidic protein-dnhIGF-1R transgene causes a delay in alveolar differentiation including lipid droplet formation, lumen expansion, and β-casein protein expression. Analysis of IGF-1R signaling pathways showed a decrease in P-IGF-1R and P-Akt resulting from expression of the dnhIGF-1R. We further demonstrate that disruption of the IGF-1R decreases mammary epithelial cell expression of the signaling intermediates insulin receptor substrate (IRS)-1 and IRS-2. No alterations were observed in downstream signaling targets of prolactin and progesterone, suggesting that activation of the IGF-1R may directly regulate expression of IRS-1/2 during alveolar development and differentiation. These data show that IGF-1R signaling is necessary for normal alveolar proliferation and differentiation, in part, through induction of signaling intermediates that mediate alveolar development.

Mammary gland reprogramming: metalloproteinases couple form with function

The adult mammary structure provides for the rapid growth, development, and immunological protection of the live-born young of mammals through its production of milk. The dynamic remodeling of the branched epithelial structure of the mammary gland in response to physiological stimuli that allow its programmed branching morphogenesis at puberty, cyclical turnover during the reproductive cycle, differentiation into a secretory organ at parturition, postlactational involution, and ultimately, regression with age is critical for these processes. Extracellular metalloproteinases are essential for the remodeling programs that operate in the tissue microenvironment at the interface of the epithelium and the stroma, coupling form with function. Deregulated proteolytic activity drives the transition of a physiological mammary microenvironment into a tumor microenvironment, facilitating malignant transformation.

Prevention of breast cancer: the case for studying inhibition of IGF-1 actions

Measures to prevent breast cancer are receiving particular attention by women at high risk from either clinico-pathologic findings or genetic susceptibility. Life-style and nutritional interventions have been difficult to quantify, but merit further study. Chemoprevention with tamoxifen and subsequently with the related raloxifene demonstrates some efficacy, but may be not be applicable to premenopausal women (with regard to raloxifene), or have low acceptance (with regard to tamoxifen). Based on the importance of the insulin-like growth factor-1 pathway in mammary gland development, and the availability of a potent inhibitor, pilot studies are ongoing to evaluate such an inhibitor in women with demonstrable high risk to develop breast cancer. Short-term interventions with the inhibitor have been completed, and subsequent interventions are planned.

Pasireotide, an IGF-I action inhibitor, prevents growth hormone and estradiol-induced mammary hyperplasia

Mammary hyperplasia increases breast cancer risk. Tamoxifen prevents breast cancer in women with atypical hyperplasia, but has serious side effects. As estradiol action requires IGF-I, direct inhibition of IGF-I action theoretically might be an efficacious alternative to tamoxifen. After hypophysectomy and oophorectomy, 21-day-old female rats were treated with GH and E₂. After 7 days all terminal end buds (TEBs) and 75% of ducts became hyperplastic. Co-treatment with pasireotide, a somatostatin analog that blocks GH secretion and IGF-I action in the mammary gland, prevented hormone-induced hyperplasia. The number and size of TEBs and moderately or floridly hyperplastic ducts was reduced by pasireotide (P < 0.01). In contrast, the same concentration of octreotide, which has a more selective somatostatin receptor subtype binding profile, was less effective than pasireotide. Tamoxifen inhibited hyperplasia when used alone with GH + E₂, but did not add to the inhibitory effect of pasireotide when the two treatments were combined. Both pasireotide and tamoxifen acted via the IGF-I receptor signaling pathway and both were found to inhibit mammary cell proliferation and stimulate apoptosis. The number of epithelial cells expressing phosphorylated insulin receptor substrate (IRS)-1 in response to GH and E₂ was reduced by pasireotide, as was staining intensity. These results support the concept that IGF-I inhibition, in this case by pasireotide, inhibits E₂ and GH-induced mammary hyperplasia. As tamoxifen did not further increase the inhibitory effect of pasireotide, the peptide appears to be at least as effective as tamoxifen in preventing GH + E₂-induced mammary hyperplasia.

Loss of transcription factor AP-2gamma/TFAP2C impairs branching morphogenesis of the murine mammary gland

Extensive development of the mammary gland occurs during puberty, when rising levels of ovarian hormones induce the formation of highly proliferative terminal end buds (TEBs) at the tips of mammary ducts. TEBs consist of an outer layer of cap cells and of inner body cells. TEBs invade the adipose stroma and bifurcate while extending the ducts to generate an arborized ductal network. We show that in murine mammary glands transcription factor AP-2gamma is strongly expressed in the cap cell layer and in a subset of body cells of TEBs. To decipher AP-2gamma functions during mammary development we generated AP-2gamma-deficient mice. Their mammary glands displayed impaired ductal branching and elongation. Cellular proliferation within TEBs was reduced. Although estrogen receptor was expressed, exogenously administered ovarian hormones could not restore normal development. Therefore, AP-2gamma is functionally involved in branching morphogenesis of the mammary epithelium, possibly by controlling genetic processes downstream of ovarian hormones.