Postmenopausal hormone replacement therapy: effects on normal mammary gland in humans and in a mouse postmenopausal model

Macronutrient-differential dietary pattern impacts on body weight, hepatic inflammation, and metabolism

Introduction

Obesity is a multi-factorial disease frequently associated with poor nutritional habits and linked to many detrimental health outcomes. Individuals with obesity are more likely to have increased levels of persistent inflammatory and metabolic dysregulation. The goal of this study was to compare four dietary patterns differentiated by macronutrient content in a postmenopausal model. Dietary patterns were high carbohydrate (HC), high fat (HF), high carbohydrate plus high fat (HCHF), and high protein (HP) with higher fiber.

Methods

Changes in body weight and glucose levels were measured in female, ovariectomized C57BL/6 mice after 15 weeks of feeding. One group of five mice fed the HCHF diet was crossed over to the HP diet on day 84, modeling a 21-day intervention. In a follow-up study comparing the HCHF versus HP dietary patterns, systemic changes in inflammation, using an 80-cytokine array and metabolism, by untargeted liquid chromatography-mass spectrometry (LCMS)-based metabolomics were evaluated.

Results

Only the HF and HCHF diets resulted in obesity, shown by significant differences in body weights compared to the HP diet. Body weight gains during the two-diet follow-up study were consistent with the four-diet study. On Day 105 of the 4-diet study, glucose levels were significantly lower for mice fed the HP diet than for those fed the HC and HF diets. Mice switched from the HCHF to the HP diet lost an average of 3.7 grams by the end of the 21-day intervention, but this corresponded with decreased food consumption. The HCHF pattern resulted in dramatic inflammatory dysregulation, as all 80 cytokines were elevated significantly in the livers of these mice after 15 weeks of HCHF diet exposure. Comparatively, only 32 markers changed significantly on the HP diet (24 up, 8 down). Metabolic perturbations in several endogenous biological pathways were also observed based on macronutrient differences and revealed dysfunction in several nutritionally relevant biosynthetic pathways.

Conclusion

Overall, the HCHF diet promoted detrimental impacts and changes linked to several diseases, including arthritis or breast neoplasms. Identification of dietary pattern-specific impacts in this model provides a means to monitor the effects of disease risk and test interventions to prevent poor health outcomes through nutritional modification.

Unique Transcriptomic Changes Underlie Hormonal Interactions During Mammary Histomorphogenesis in Female Pigs

Successful lactation and the risk for developing breast cancer depend on growth and differentiation of the mammary gland (MG) epithelium that is regulated by ovarian steroids (17β-estradiol [E] and progesterone [P]) and pituitary-derived prolactin (PRL). Given that the MG of pigs share histomorphogenic features present in the normal human breast, we sought to define the transcriptional responses within the MG of pigs following exposure to all combinations of these hormones. Hormone-ablated female pigs were administered combinations of E, medroxyprogesterone 17-acetate (source of P), and either haloperidol (to induce PRL) or 2-bromo-α-ergocryptine. We subsequently monitored phenotypic changes in the MG including mitosis, receptors for E and P (ESR1 and PGR), level of phosphorylated STAT5 (pSTAT5), and the frequency of terminal ductal lobular unit (TDLU) subtypes; these changes were then associated with all transcriptomic changes. Estrogen altered the expression of approximately 20% of all genes that were mostly associated with mitosis, whereas PRL stimulated elements of fatty acid metabolism and an inflammatory response. Several outcomes, including increased pSTAT5, highlighted the ability of E to enhance PRL action. Regression of transcriptomic changes against several MG phenotypes revealed 1669 genes correlated with proliferation, among which 29 were E inducible. Additional gene expression signatures were associated with TDLU formation and the frequency of ESR1 or PGR. These data provide a link between the hormone-regulated genome and phenome of the MG in a species having a complex histoarchitecture like that in the human breast, and highlight an underexplored synergy between the actions of E and PRL during MG development.

Cellular mechanisms linking cancers to obesity

Obesity is epidemiologically linked to 13 forms of cancer. The local and systemic obese environment is complex and likely affect tumors through multiple avenues. This includes modulation of cancer cell phenotypes and the composition of the tumor microenvironment. A molecular understanding of how obesity links to cancer holds promise for identifying candidate genes for targeted therapy for obese cancer patient. Herein, we review both the cell-autonomous and non-cell-autonomous mechanisms linking obesity and cancer as well as provide an overview of the mouse model systems applied to study this.

Progesterone receptor antagonism inhibits progestogen-related carcinogenesis and suppresses tumor cell proliferation

PURPOSE

Blockade of the progestogen-progesterone receptor (PR) axis is a novel but untested strategy for breast cancer prevention. We report preclinical data evaluating telapristone acetate (TPA), ulipristal acetate (UPA), and mifepristone.

METHODS

Tumors were induced with medroxyprogesterone acetate (MPA) plus 7,12-dimethylbenz[a]anthracene (DMBA) in mice, and MPA or progesterone plus N-methyl-N-nitrosourea (MNU) in rats. Mammary gland histology, tumor incidence, latency, multiplicity, burden and histology were evaluated, along with immunohistochemical labeling of pHH3 (proliferation), CD34 (angiogenesis), and estrogen and progesterone receptors (ER and PR). A concentration gradient of TPA, UPA, and mifepristone was tested for growth inhibition of T47D spheroids.

RESULTS

In mouse mammary glands, no tumors formed, but TPA opposed the pro-hyperplastic effects of MPA (p = 0.002). In rats, TPA decreased tumor incidence (p = 0.037 for MPA + TPA vs. MPA, and p = 0.032 for progesterone + TPA vs. progesterone) and tumor burden (p = 0.042 for progesterone + TPA vs. progesterone), with significant decreases in pHH3 and CD34 positive cells. TPA and UPA were superior to mifepristone in growth inhibition of T47D spheroids.

CONCLUSION

TPA has consistent anti-tumorigenic effects in several models, which are accompanied by decreases in cell proliferation, angiogenesis, and hormone receptor expression.

Optimizing mouse models for precision cancer prevention

As cancer has become increasingly prevalent, cancer prevention research has evolved towards placing a greater emphasis on reducing cancer deaths and minimizing the adverse consequences of having cancer. 'Precision cancer prevention' takes into account the collaboration of intrinsic and extrinsic factors in influencing cancer incidence and aggressiveness in the context of the individual, as well as recognizing that such knowledge can improve early detection and enable more accurate discrimination of cancerous lesions. However, mouse models, and particularly genetically engineered mouse (GEM) models, have yet to be fully integrated into prevention research. In this Opinion article, we discuss opportunities and challenges for precision mouse modelling, including the essential criteria of mouse models for prevention research, representative success stories and opportunities for more refined analyses in future studies.

Progesterone-induced stimulation of mammary tumorigenesis is due to the progesterone metabolite, 5α-dihydroprogesterone (5αP) and can be suppressed by the 5α-reductase inhibitor, finasteride

Progesterone has long been linked to breast cancer but its actual role as a cancer promoter has remained in dispute. Previous in vitro studies have shown that progesterone is converted to 5α-dihydroprogesterone (5αP) in breast tissue and human breast cell lines by the action of 5α-reductase, and that 5αP acts as a cancer-promoter hormone. Also studies with human breast cell lines in which the conversion of progesterone to 5αP is blocked by a 5α-reductase inhibitor, have shown that the in vitro stimulation in cell proliferation with progesterone treatments are not due to progesterone itself but to the metabolite 5αP. No similar in vivo study has been previously reported. The objective of the current studies was to determine in an in vivo mouse model if the presumptive progesterone-induced mammary tumorigenesis is due to the progesterone metabolite, 5αP. BALB/c mice were challenged with C4HD murine mammary cells, which have been shown to form tumors when treated with progesterone or the progestin, medroxyprogesterone acetate. Cells and mice were treated with various doses and combinations of progesterone, 5αP and/or the 5α-reductase inhibitor, finasteride, and the effects on cell proliferation and induction and growth of tumors were monitored. Hormone levels in serum and tumors were measured by specific RIA and ELISA tests. Proliferation of C4HD cells and induction and growth of tumors was stimulated by treatment with either progesterone or 5αP. The progesterone-induced stimulation was blocked by finasteride and reinstated by concomitant treatment with 5αP. The 5αP-induced tumors expressed high levels of ER, PR and ErbB-2. Hormone measurements showed significantly higher levels of 5αP in serum from mice with tumors than from mice without tumors, regardless of treatments, and 5αP levels were significantly higher (about 4-fold) in tumors than in respective sera, while progesterone levels did not differ between the compartments. The results indicate that the stimulation of C4HD tumor growth in BALB/c mice treated with progesterone is due to the progesterone metabolite 5αP formed at elevated levels in mammary cells as a result of the 5α-reductase action on progesterone. The results provide the first in vivo demonstration that stimulation of breast cell tumorigenesis and tumor growth accompanying progesterone treatment is due to the progesterone metabolite 5αP, and that breast tumorigenesis can be blocked with the 5α-reductase inhibitor, finasteride.

Stearoyl gemcitabine nanoparticles overcome obesity-induced cancer cell resistance to gemcitabine in a mouse postmenopausal breast cancer model

Obesity is associated with increased breast tumor aggressiveness and decreased response to multiple modalities of therapy in postmenopausal women. Delivering cancer chemotherapeutic drugs using nanoparticles has evolved as a promising approach to improve the efficacy of anticancer agents. However, the application of nanoparticles in cancer chemotherapy in the context of obesity has not been studied before. The nucleoside analog gemcitabine is widely used in solid tumor therapy. Previously, we developed a novel stearoyl gemcitabine solid-lipid nanoparticle formulation (GemC18-NPs) and showed that the GemC18-NPs are significantly more effective than gemcitabine in controlling tumor growth in mouse models. In the present study, using ovariectomized diet-induced obese female C57BL/6 mice with orthotopically transplanted MMTV-Wnt-1 mammary tumors as a model of postmenopausal obesity and breast cancer, we discovered that obesity induces tumor cell resistance to gemcitabine. Furthermore, our GemC18-NPs can overcome the obesity-related resistance to gemcitabine chemotherapy. These findings have important clinical implications for cancer chemotherapies involving gemcitabine or other nucleoside analogs in the context of obesity.

Downregulation of the tumor-suppressor miR-16 via progestin-mediated oncogenic signaling contributes to breast cancer development

Introduction

Experimental and clinical evidence points to a critical role of progesterone and the nuclear progesterone receptor (PR) in controlling mammary gland tumorigenesis. However, the molecular mechanisms of progesterone action in breast cancer still remain elusive. On the other hand, micro RNAs (miRNAs) are short ribonucleic acids which have also been found to play a pivotal role in cancer pathogenesis. The role of miRNA in progestin-induced breast cancer is poorly explored. In this study we explored progestin modulation of miRNA expression in mammary tumorigenesis.

Methods

We performed a genome-wide study to explore progestin-mediated regulation of miRNA expression in breast cancer. miR-16 expression was studied by RT-qPCR in cancer cell lines with silenced PR, signal transducer and activator of transcription 3 (Stat3) or c-Myc, treated or not with progestins. Breast cancer cells were transfected with the precursor of miR-16 and proliferation assays, Western blots or in vivo experiments were performed. Target genes of miR-16 were searched through a bioinformatical approach, and the study was focused on cyclin E. Reporter gene assays were performed to confirm that cyclin E 3'UTR is a direct target of miR-16.

Results

We found that nine miRNAs were upregulated and seven were downregulated by progestin in mammary tumor cells. miR-16, whose function as a tumor suppressor in leukemia has already been shown, was identified as one of the downregulated miRNAs in murine and human breast cancer cells. Progestin induced a decrease in miR-16 levels via the classical PR and through a hierarchical interplay between Stat3 and the oncogenic transcription factor c-Myc. A search for miR-16 targets showed that the CCNE1 gene, encoding the cell cycle regulator cyclin E, contains conserved putative miR-16 target sites in its mRNA 3' UTR region. We found that, similar to the molecular mechanism underlying progestin-modulated miR-16 expression, Stat3 and c-Myc participated in the induction of cyclin E expression by progestin. Moreover, overexpression of miR-16 abrogated the ability of progestin to induce cyclin E upregulation, revealing that cyclin E is a novel target of miR-16 in breast cancer. Overexpression of miR-16 also inhibited progestin-induced breast tumor growth in vitro and in vivo, demonstrating for the first time, a role for miR-16 as a tumor suppressor in mammary tumorigenesis. We also found that the ErbB ligand heregulin (HRG) downregulated the expression of miR-16, which then participates in the proliferative activity of HRG in breast tumor cells.

Conclusions

In this study, we reveal the first progestin-regulated miRNA expression profile and identify a novel role for miR-16 as a tumor suppressor in progestin- and growth factor-induced growth in breast cancer.

Age-related changes in the epithelial and stromal compartments of the mammary gland in normocalcemic mice lacking the vitamin D3 receptor

The vitamin D₃ receptor (VDR) serves as a negative growth regulator during mammary gland development via suppression of branching morphogenesis during puberty and modulation of differentiation and apoptosis during pregnancy, lactation and involution. To assess the role of the VDR in the aging mammary gland, we utilized 12, 14, and 16 month old VDR knockout (KO) and wild type (WT) mice for assessment of integrity of the epithelial and stromal compartments, steroid hormone levels and signaling pathways. Our data indicate that VDR ablation is associated with ductal ectasia of the primary mammary ducts, loss of secondary and tertiary ductal branches and atrophy of the mammary fat pad. In association with loss of the white adipose tissue compartment, smooth muscle actin staining is increased in glands from VDR KO mice, suggesting a change in the stromal microenviroment. Activation of caspase-3 and increased Bax expression in mammary tissue of VDR KO mice suggests that enhanced apoptosis may contribute to loss of ductal branching. These morphological changes in the glands of VDR KO mice are associated with ovarian failure and reduced serum 17β-estradiol. VDR KO mice also exhibit progressive loss of adipose tissue stores, hypoleptinemia and increased metabolic rate with age. These developmental studies indicate that, under normocalcemic conditions, loss of VDR signaling is associated with age-related estrogen deficiency, disruption of epithelial ductal branching, abnormal energy expenditure and atrophy of the mammary adipose compartment.

Differential effects of calorie restriction and exercise on the adipose transcriptome in diet-induced obese mice

We tested the hypothesis that obesity reversal by calorie restriction (CR) versus treadmill exercise (EX) differentially modulates adipose gene expression using 48 female C57BL/6 mice administered a diet-induced obesity (DIO) regimen for 8 weeks, then randomized to receive for 8 weeks either: (1) a control (AIN-76A) diet, fed ad libitum (DIO control); (2) a 30% CR regimen; (3) a treadmill EX regimen (with AIN-76A diet fed ad libitum); or (4) continuation of the DIO diet. Relative to the DIO controls, both CR and EX reduced adiposity by 35-40% and serum leptin levels by 80%, but only CR increased adiponectin and insulin sensitivity. Gene expression microarray analysis of visceral white adipose tissue revealed 209 genes responsive to both CR and EX, relative to the DIO group. However, CR uniquely altered expression of an additional 496 genes, whereas only 20 were uniquely affected by EX. Of the genes distinctly responsive to CR, 17 related to carbohydrate metabolism and glucose transport, including glucose transporter (GLUT) 4. Chromatin immunoprecipitation assays of the Glut4 promoter revealed that, relative to the DIO controls, CR significantly increased histone 4 acetylation, suggesting epigenetic regulation may underlie some of the differential effects of CR versus EX on the adipose transcriptome.

Progesterone stimulates mitochondrial activity with subsequent inhibition of apoptosis in MCF-10A benign breast epithelial cells

The effects of progesterone on breast epithelial cells remain poorly defined with observations showing both proliferative and antiproliferative effects. As an example, progesterone levels correlate with increased epithelial cell proliferation, but there is discordance between the dividing cells and the cells with nuclear progesterone receptor expression. The release of paracrine growth factors from nuclear receptor-positive cells has been postulated as a mechanism, since in vitro studies show a lack of growth effect by progesterone in breast epithelial cells lacking nuclear receptors. This study examined possible nongenomic effects of progesterone in breast epithelia by using MCF-10A cells known to lack nuclear progesterone receptor expression. Treatment for 30-60 min with progesterone or the progestin, R5020, increased mitochondrial activity as shown by an increase in mitochondrial membrane potential (hyperpolarization) with a concordant increase in total cellular ATP. The reaction was inhibited by a specific progesterone receptor antagonist and not affected by the translation inhibitor cycloheximide. Progestin treatment inhibited apoptosis induced by activation of the FasL pathway, as shown by a decrease in sub-G(1) cell fraction during fluorescence-activated cell sorting and a decrease in caspase 3/7 levels. Progestin treatment did not alter the cell cycle over 48 h. Our study demonstrates a nongenomic action of progesterone on benign breast epithelial cells, resulting in enhanced cellular respiration and protection from apoptosis.

Progesterone and breast cancer

Progesterone is an ovarian steroid hormone that is essential for normal breast development during puberty and in preparation for lactation and breastfeeding. The actions of progesterone are primarily mediated by its high-affinity receptors, which include the classical progesterone receptor (PR)-A and -B isoforms, located in diverse tissues, including the brain, where progesterone controls reproductive behavior, and the breast and reproductive organs. Progestins are frequently prescribed for contraception or during postmenopausal hormone replacement therapy, in which progestins are combined with estrogen as a means to block estrogen-induced endometrial growth. The role of estrogen as a potent breast mitogen is undisputed, and inhibitors of the estrogen receptor and estrogen-producing enzymes (aromatases) are effective first-line cancer therapies. However, PR action in breast cancer is grossly understudied and remains controversial. Herein, we review existing evidence and discuss the challenges to defining a role for progesterone in breast cancer.

Obesity accelerates mouse mammary tumor growth in the absence of ovarian hormones

Obesity increases incidence and mortality of breast cancer in postmenopausal women. Mechanisms underlying this association are poorly understood. Suitable animal models are needed to elucidate potential mechanisms for this association. To determine the effects of obesity on mammary tumor growth, nonovariectomized and ovariectomized C57BL/6 mice of various body weights (lean, overweight, and obese) were implanted subcutaneously with mammary tumor cells from syngeneic Wnt-1 transgenic mice. In mice, the lean phenotype was associated with reduced Wnt-1 tumor growth regardless of ovarian hormone status. Ovariectomy delayed Wnt-1 tumor growth consistent with the known hormone responsiveness of these tumors. However, obesity accelerated tumor growth in ovariectomized but not in nonovariectomized animals. Diet-induced obesity in a syngeneic mouse model of breast cancer enhanced tumor growth, specifically in the absence of ovarian hormones. These results support epidemiological evidence that obesity is associated with increased breast cancer incidence and mortality in postmenopausal but not premenopausal women. In contrast, maintaining a lean body weight phenotype was associated with reduced Wnt-1 tumor growth regardless of ovarian hormone status.

Challenges to defining a role for progesterone in breast cancer

Progesterone is an ovarian steroid hormone that is essential for normal breast development during puberty and in preparation for lactation. The actions of progesterone are primarily mediated by its high affinity receptors, including the classical progesterone receptor (PR) -A and -B isoforms, located in diverse tissues such as the brain where progesterone controls reproductive behavior, and the breast and reproductive organs. Progestins are frequently prescribed as contraceptives or to alleviate menopausal symptoms, wherein progestin is combined with estrogen as a means to block estrogen-induced endometrial growth. Estrogen is undisputed as a potent breast mitogen, and inhibitors of the estrogen receptor (ER) and estrogen producing enzymes (aromatases) are effective first-line cancer therapies. However, PR action in breast cancer remains controversial. Herein, we review existing evidence from in vitro and in vivo models, and discuss the challenges to defining a role for progesterone in breast cancer.

Estrogen plus progestin and risk of benign proliferative breast disease

Women with benign proliferative breast disease are at increased risk of subsequent breast cancer. Estrogens and progesterone exert proliferative effects on mammary epithelium, and combined hormone replacement therapy has been associated with increased breast cancer risk. We tested the effect of conjugated equine estrogen plus progestin on the risk of benign proliferative breast disease in the Women's Health Initiative (WHI) randomized controlled trial. In the WHI trial of estrogen plus progestin, 16,608 postmenopausal women were randomly assigned either to 0.625 mg/day of conjugated equine estrogen plus 2.5 mg/day of medroxyprogesterone acetate or to placebo. Baseline and annual breast exams and mammograms were required. The trial was terminated early (average follow-up, 5.5 years). We identified women who had had a biopsy for benign breast disease, and subjected histologic sections from the biopsies to standardized review. Overall, 178 incident cases of benign proliferative breast disease were ascertained in the estrogen plus progestin group and 99 in the placebo group. The use of estrogen plus progestin was associated with a 74% increase in the risk of benign proliferative breast disease [hazard ratio, 1.74; 95% confidence interval (CI), 1.35-2.25]. For benign proliferative breast disease without atypia the hazard ratio was 2.00 (95% CI, 1.50-2.66), while for atypical hyperplasia it was 0.76 (95% CI, 0.38-1.52). The risk varied little by levels of baseline characteristics. The results of this study suggest that the use of estrogen plus progestin may increase the risk of benign proliferative breast disease.

Antiproliferative actions of the synthetic androgen, mibolerone, in breast cancer cells are mediated by both androgen and progesterone receptors

Androgen signaling, mediated by the androgen receptor (AR), is a critical factor influencing growth of normal and malignant breast cells. Given the increasing use of exogenous androgens in women, a better understanding of androgen action in the breast is essential. This study compared the effects of 5alpha-dihydrotestosterone (DHT) and a synthetic androgen, mibolerone, on estradiol (E(2))-induced proliferation of breast cancer cells. DHT modestly inhibited E(2)-induced proliferation and mibolerone significantly inhibited proliferation in T-47D cells. The effects of both androgens could be reversed by an AR antagonist, suggesting that their actions were mediated, in part, by AR. Whereas high physiological doses (10-100nM) of DHT reduced E(2)-mediated induction of the estrogen-regulated gene progesterone receptor (PR) to basal levels, mibolerone at lower doses (1nM) eliminated PR expression, suggesting that mibolerone may also act via the PR. In the AR positive, PR-negative MCF-7 cells, mibolerone had modest effects on E(2)-induced proliferation, but was a potent inhibitor of proliferation in the AR positive, PR positive MCF-7M11 PRA cells. The effects of mibolerone in breast cancer cells were similar to those of the progestin, medroxyprogesterone acetate. Our results demonstrate that mibolerone can have both androgenic and progestagenic actions in breast cancer cells.

Integration of progesterone receptor action with rapid signaling events in breast cancer models

Recent discoveries suggest that several protein kinases are rapidly activated in response to ligand binding to cytoplasmic steroid hormone receptors (SRs), including progesterone receptors (PRs). Thus, PRs act as ligand-activated transcription factor "sensors" for growth factor-initiated signaling pathways in hormonally regulated tissues, such as the breast. Induction of rapid signaling upon progestin binding to PR-B provides a means to ensure that receptors and co-regulators are appropriately phosphorylated as part of optimal transcription complexes. Alternatively, PR-B activated kinase cascades provide additional avenues for progestin-regulated gene expression independent of PR nuclear action. Herein, an overview of progesterone/PR and signaling cross-talk in breast cancer models is provided. Kinases are emerging as key mediators of PR action. Cross-talk between SR and membrane-initiated signaling events suggests a mechanism for coordinate regulation of gene subsets by mitogenic stimuli in hormonally responsive normal tissues, and is suspected to contribute to cancer biology.

Progesterone receptor action: translating studies in breast cancer models to clinical insights

Progesterone receptors (PR) are useful prognostic indicators of breast cancers likely to respond to anti-estrogen receptor (ER) therapies. However, the role of progesterone, therapeutic progestins, or unliganded or liganded PRin breast cancer development or progression remains controversial. PR are ligand-activated transcription factors that act in concert with intracellular signaling pathways as "sensors" of multiple growth factor inputs to hormonally regulated tissues, such as the breast. The recently defined induction of rapid signaling events upon progestin-binding to PR-B provides a means to ensure that receptors and coregulators are appropriately phosphorylated as part of optimal transcription complexes. PR-activated kinase cascades may provide additional avenues for progestin-regulated gene expression independent of PR nuclear action. Herein, we present an overview ofprogesterone/PR and signaling cross-talk in breast cancer models and discuss the potential significance ofprogestin/PR action in breast cancer biology using examples from both in vitro and in vivo models, as well as limited clinical data. Kinases are emerging as key mediators of PR action. Cross-talk between PR and membrane-initiated signaling events suggests a mechanism for coordinated regulation ofgene subsets by mitogenic stimuli in hormonally responsive normal tissues. Dysregulation of this cross-talk mechanism may contribute to breast cancer biology; further studies are needed to address the potential for targeting PR in addition to ER and selected protein kinases as part of more effective breast cancer therapies.

Extreme obesity reduces bone mineral density: complementary evidence from mice and women

OBJECTIVE

To evaluate the effects of body adiposity on bone mineral density in the presence and absence of ovarian hormones in female mice and postmenopausal women.

RESEARCH METHODS AND PROCEDURES

We assessed percentage body fat, serum leptin levels, and bone mineral density in ovariectomized and non-ovariectomized C57BL/6 female mice that had been fed various calorically dense diets to induce body weight profiles ranging from lean to very obese. Additionally, we assessed percentage body fat and whole body bone mineral density in 37 overweight and extremely obese postmenopausal women from the Women's Contraceptive and Reproductive Experiences study.

RESULTS

In mice, higher levels of body adiposity (>40% body fat) were associated with lower bone mineral density in ovariectomized C57BL/6 female mice. A similar trend was observed in a small sample of postmenopausal women.

DISCUSSION

The complementary studies in mice and women suggest that extreme obesity in postmenopausal women may be associated with reduced bone mineral density. Thus, extreme obesity (BMI > 40 kg/m2) may increase the risk for osteopenia and osteoporosis. Given the obesity epidemic in the U.S. and in many other countries, and, in particular, the rising number of extremely obese adult women, increased attention should be drawn to the significant and interrelated public health issues of obesity and osteoporosis.

Progesterone receptor isoforms and proliferation in the rat mammary gland during development

Progesterone (P), acting through progesterone receptor (PR) isoforms A and B, plays an important role in normal mammary gland development and is implicated in the etiology of breast cancer. Because of significant similarities between human and rat mammary gland development and hormonal responsiveness of mammary cancers, we investigated P action in the rat mammary gland. By immunohistochemical methods we determined PRA and PRB expression at puberty, sexual maturity, pregnancy, and lactation and after postlactational involution and their functional roles in the regulation of proliferation. PRA expression was restricted to luminal epithelial cells, whereas PRB was expressed in both luminal and myoepithelial cells, indicating a novel role of PRB in myoepithelial cell regulation. The majority of PRA-positive (PRA+) cells coexpressed PRB. In the pubertal and adult virgin mammary gland, PRA+PRB+ cells also expressed nuclear cyclin D1 but did not contain the proliferation marker bromodeoxyuridine. Based on a lack of phosphorylated retinoblastoma protein expression and the expression patterns of the cyclin-dependent kinase inhibitors p21 and p27 in these cells, we conclude that PRA+PRB+ cells appear to be cell cycle arrested and do not proliferate. PRA+ cells were decreased in the adult gland and during and after pregnancy. The percentage of PRB+ cells was relatively constant throughout development, and in a significant proportion of cells, only PRB was detected. During development, and especially during pregnancy, a high percentage of PRB+ cells were positive for bromodeoxyuridine. From this observation, we conclude that these cells proliferate and that P acting through PRB may directly stimulate proliferation.

Integration of Rapid Signaling Events with Steroid Hormone Receptor Action in Breast and Prostate Cancer

Steroid hormone receptors (SRs) are ligand-activated transcription factors and sensors for growth factor-initiated signaling pathways in hormonally regulated tissues, such as the breast or prostate. Recent discoveries suggest that several protein kinases are rapidly activated in response to steroid hormone binding to cytoplasmic SRs. Induction of rapid signaling upon SR ligand binding ensures that receptors and coregulators are appropriately phosphorylated as part of optimal transcription complexes. Alternatively, SR-activated kinase cascades provide additional avenues for SR-regulated gene expression independent of SR nuclear action. We provide an overview of SR and signaling cross talk in breast and prostate cancers, using the human progesterone receptor (PR) and androgen receptor (AR) as models. Kinases are emerging as key mediators of SR action. Cross talk between SR and membrane-initiated signaling events suggests a mechanism for coordinate regulation of gene subsets by mitogenic stimuli in hormonally responsive normal tissues; such cross talk is suspected to contribute to cancer biology.

Postmenopausal hormone replacement therapy: endometrial and breast effects

The history of hormone replacement therapy (HRT) dates back to the late 1800s, when animal extracts of ovaries were first used. With the development of synthetic hormones, widespread use in postmenopausal women extended throughout the industrialized world, so that by the late 1900s roughly one-third to one-half of all postmenopausal women in the United States and Europe were taking HRT. Two events changed the course of use of HRT: the association of an increased rate of endometrial carcinoma with estrogen-only HRT and the association of an increased breast cancer rate with combined estrogen and progestin HRT. This review explores the evidence of the effects of HRT on the endometrium and the breast, with emphasis on the pathologic changes.

Increased tumor growth in mice with diet-induced obesity: impact of ovarian hormones

Obesity increases the risk of many cancers in both males and females. This study describes a link between obesity, obesity-associated metabolic alterations, and the risk of developing cancer in male and female mice. The goal of this study was to evaluate the relationship between gender and obesity and to determine the role of estrogen status in obese females and its effect on tumor growth. We examined the susceptibility of C57BL/6 mice to diet-induced obesity, insulin resistance/glucose intolerance, and tumors. Mice were injected sc with one of two tumorigenic cell lines, Lewis lung carcinoma, or mouse colon 38-adenocarcinoma. Results show that tumor growth rate was increased in obese mice vs. control mice irrespective of the tumor cell type. To investigate the effect of estrogen status on tumor development in obese females, we compared metabolic parameters and tumor growth in ovariectomized (ovx) and intact obese female mice. Obese ovx female mice developed insulin resistance and glucose intolerance similar to that observed in obese males. Our results demonstrate that body adiposity increased in ovx females irrespective of the diet administered and that tumor growth correlated positively with body adiposity. Overall, these data point to more rapid tumor growth in obese mice and suggest that endogenous sex steroids, together with diet, affect adiposity, insulin sensitivity, and tumor growth in female mice.

Different types of postmenopausal hormone therapy and mammographic density in Norwegian women

Postmenopausal hormone therapy (HT) is associated with increased risk of breast cancer. The HTs used in Scandinavia is associated with higher risk estimates than those used in most other countries. Mammographic density is one of the strongest risk factors for breast cancer, and possibly an intermediate marker for breast cancer. We decided to examine the relationship between use of different types of HT and mammographic density in Norwegian women. Altogether, 1,007 postmenopausal participants in the governmental mammographic screening program were asked about current and previous HT use. Mammograms were classified according to percent and absolute mammographic density. Overall, current users of HT had on average 3.6% higher mean percent mammographic density when compared with never users (p < 0.001). After adjustment for age at screening, number of children and BMI in a multivariate model, women using the continuous estradiol (E(2)) plus norethisterone acetate (NETA) combination had a mean percent mammographic density significantly higher than never users (6.1% absolute difference). Those using the continuous E(2) plus NETA combination had an 4.8% (absolute difference) higher mean percent mammographic density after <5 years of use when compared with never users, while the corresponding number for >or=5 years of use was 7% (p-trend < 0.001). We found similar associations when absolute mammographic density was used as the outcome variable. In summary, our study shows a statistical significant positive dose-response association between current use of the continuous E(2) plus NETA combination and both measures of mammographic density.

Progesterone receptor isoforms A and B: temporal and spatial differences in expression during murine mammary gland development

Progesterone is a potent mitogen in the mammary gland. Based on studies using cells and animals engineered to express progesterone receptor (PR) isoforms A or B, PRA and PRB are believed to have different functions. Using an immunohistochemical approach with antibodies specific for PRA only or PRB only, we show that PRA and PRB expression in mammary epithelial cells is temporally and spatially separated during normal mammary gland development in the BALB/c mouse. In the virgin mammary gland when ductal development is active, the only PR protein isoform expressed was PRA. PRA levels were significantly lower during pregnancy, suggesting a minor role at this stage of development. PRB was abundantly expressed only during pregnancy, during alveologenesis. PRA and PRB colocalization occurred in only a small percentage of cells. During pregnancy there was extensive colocalization of PRB with 5-bromo-2'-deoxyuridine (BrdU) and cyclin D1; 95% of BrdU-positive cells and 83% of cyclin D1-positive cells expressed PRB. No colocalization of PRA with either BrdU or cyclin D1 was observed at pregnancy. In the virgin gland, PRA colocalization with BrdU or cyclin D1 was low; only 27% of BrdU-positive cells and 4% of cyclin D1-positive cells expressed PRA. The implication of these findings is that different actions of progesterone are mediated in PRB positive vs. PRA-positive cells in vivo. The spatial and temporal separation of PR isoform expression in mouse mammary gland provides a unique opportunity to determine the specific functions of PRA vs. PRB in vivo.

Endogenous estrogen, androgen, and progesterone concentrations and breast cancer risk among postmenopausal women

BACKGROUND

Levels of endogenous hormones have been associated with the risk of breast cancer among postmenopausal women. Little research, however, has investigated the association between hormone levels and tumor receptor status or invasive versus in situ tumor status. Nor has the relation between breast cancer risk and postmenopausal progesterone levels been investigated. We prospectively investigated these relations in a case-control study nested within the Nurses' Health Study.

METHODS

Blood samples were prospectively collected during 1989 and 1990. Among eligible postmenopausal women, 322 cases of breast cancer (264 invasive, 41 in situ, 153 estrogen receptor [ER]-positive and progesterone receptor [PR]-positive [ER+/PR+], and 39 ER-negative and PR-negative [ER-/PR-] disease) were reported through June 30, 1998. For each case subject, two control subjects (n = 643) were matched on age and blood collection (by month and time of day). Endogenous hormone levels were measured in blood plasma. We used conditional and unconditional logistic regression analyses to assess associations and to control for established breast cancer risk factors.

RESULTS

We observed a statistically significant direct association between breast cancer risk and the level of both estrogens and androgens, but we did not find any (by year) statistically significant associations between this risk and the level of progesterone or sex hormone binding globulin. When we restricted the analysis to case subjects with ER+/PR+ tumors and compared the highest with the lowest fourths of plasma hormone concentration, we observed an increased risk of breast cancer associated with estradiol (relative risk [RR] = 3.3, 95% confidence interval [CI] = 2.0 to 5.4), testosterone (RR = 2.0, 95% CI = 1.2 to 3.4), androstenedione (RR = 2.5, 95% CI = 1.4 to 4.3), and dehydroepiandrosterone sulfate (RR = 2.3, 95% CI = 1.3 to 4.1). In addition, all hormones tended to be associated most strongly with in situ disease.

CONCLUSION

Circulating levels of sex steroid hormones may be most strongly associated with risk of ER+/PR+ breast tumors.

Morphogenesis of mammary gland development

Development of the mammary gland in females is a dynamic, orchestrated process that occurs throughout postnatal development. Initiated during embryogenesis, epithelial cells advance into the underlying stromal matrix to form a primitive rudimentary structure. With the onset of puberty this anlage then responds to hormonal and local cues to rapidly establish a ductal network. Whereas in mice this network is relatively simple, in humans there is significantly more branching morphogenesis to develop terminal duct lobular unit structures. With the onset of pregnancy and associated changes in the hormonal and local environment, alveolar development progresses to establish a gland that is densely filled with alveolar structures by the end of pregnancy. Concomitantly, mammary epithelial cells within the gland begin to attain their unique ability to synthesize various milk constituents, such that by parturition, functional lactogenesis can be realized.

Progesterone involvement in breast development and tumorigenesis--as revealed by progesterone receptor "knockout" and "knockin" mouse models

In light of recent clinical trials, the debate concerning the risks and benefits of progestin-based postmenopausal hormone replacement therapy (HRT) has reached a renewed level of urgency. Irrespective of the position taken, the consensus is that more basic research needs to be performed to address progesterone's fundamental role in mammary development and tumorigenesis. Towards this end, the progesterone receptor knockout (PRKO) mouse demonstrated that progesterone is essential for pregnancy-associated mammary gland ductal side-branching and alveologenesis and that these morphological changes are dependent on progesterone-induced mammary epithelial proliferation. Importantly, the PRKO mouse showed that the progesterone-proliferative signal significantly contributes to mammary tumor susceptibility in an established mammary tumor model. Insight into the cellular mechanism(s) by which progesterone affects mammary morphogenesis has been disclosed by a new PR-LacZ knockin mouse, which revealed that PR's spatial expression pattern undergoes precise choreographed distributional changes that precede key stages in postnatal mammary development. In the case of early pregnancy, the segregation of cells undergoing progesterone-induced proliferation from those that express PR implicates a paracrine mode of action for progesterone-induced mammary epithelial proliferation, whereas the preparturient decline of PR expression underscores the need to remove this signal for full functional differentiation of this tissue. Our findings support the proposal that the mammary gland's normal response to the progesterone-signal is dependent upon specific spatial organizational patterns of PR expression and that derailment in these cellular processes may contribute to abnormal mammary development, including cancer. This review concludes by emphasizing the need to identify the downstream molecular targets that mediate progesterone's effects in this tissue. Identification of such targets will not only enhance our mechanistic understanding of progesterone's role in mammary development and cancer, but may also facilitate the formulation of new design strategies in breast cancer diagnosis and/or treatment.