The neuropeptide galanin augments lobuloalveolar development

RNA-Seq Analysis of Pubertal Mammary Epithelial Cells Reveals Novel n-3 Polyunsaturated Fatty Acid Transcriptomic Changes in the fat-1 Mouse Model

BACKGROUND

The early exposure of nutrients during pubertal mammary gland development may reduce the risk of developing breast cancer later in life. Anticancer n-3 polyunsaturated fatty acids (n-3 PUFA) are shown to modulate pubertal mammary gland development; however, the mechanisms of action remain unclear. Prior work focused on effects at the whole tissue level, and little is known at the cellular level, such as at the level of mammary epithelial cells (MECs), which are implicated in cancer development.

METHODS

This pilot study examined the effects of lifelong n-3 PUFA exposure on the transcriptome by RNA-Seq in the isolated MECs of pubertal (6-8-week-old) female fat-1 transgenic mice capable of de novo n-3 PUFA synthesis. edgeR and DESeq2 were used separately for the differential expression analysis of RNA sequencing data followed by the Benjamani-Hochberg procedure for multiple testing correction.

RESULTS

Nine genes were found concordant and significantly different (p ≤ 0.05) by both the DESeq2 and edgeR methods. These genes were associated with multiple pathways, suggesting that n-3 PUFA stimulates estrogen-related signaling (Mlltl0, Galr3, and Nrip1) and a glycolytic profile (Soga1, Pdpr, and Uso1) while offering protective effects for immune and DNA damage responses (Glpd1, Garre1, and Rpa1) in MECs during puberty.

CONCLUSIONS

This pilot study highlights the utility of RNA-Seq to better understanding the mechanistic effects of specific nutrients such as n-3 PUFA in a cell-specific manner. Thus, further studies are warranted to investigate the cell-specific mechanisms by which n-3 PUFA influences pubertal mammary gland development and breast cancer risk later in life.

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.

Galanin in pregnancy: Is there an association with birth weight and gestational diabetes?

OBJECTIVE

To review the actions of galanin during pregnancy and to examine the existence of an association between galanin and birthweight as well as with gestational diabetes mellitus (GDM).

RESULTS

Galanin concentrations in maternal circulation are similar in pregnant and nonpregnant status and have been correlated with body mass index (BMI). There is evidence of an association between birthweight and galanin concentrations in amniotic fluid during second trimester and galanin concentrations in umbilical cord at term. Moreover, there is a positive correlation between maternal galanin concentrations and existence of GDM. However, galanin concentrations in fetal circulation have not been correlated with neonatal fat mass. Neonatal galanin concentrations do not differ among uncomplicated pregnancies and those complicated by GDM or intrauterine growth retardation (IUGR).

CONCLUSIONS

There is evidence for an association between galanin during pregnancy with birth weight and metabolic processes. Further studies are required in order to elucidate this role. Galanin could serve as a predictor of neonatal body weight, alternations of which contribute to the development of diseases during adulthood.

Thyroid hormone responsive protein Spot14 enhances catalysis of fatty acid synthase in lactating mammary epithelium

Thyroid hormone responsive protein Spot 14 has been consistently associated with de novo fatty acid synthesis activity in multiple tissues, including the lactating mammary gland, which synthesizes large quantities of medium chain fatty acids (MCFAs) exclusively via FASN. However, the molecular function of Spot14 remains undefined during lactation. Spot14-null mice produce milk deficient in total triglyceride and de novo MCFA that does not sustain optimal neonatal growth. The lactation defect was rescued by provision of a high fat diet to the lactating dam. Transgenic mice overexpressing Spot14 in mammary epithelium produced total milk fat equivalent to controls, but with significantly greater MCFA. Spot14-null dams have no diminution of metabolic gene expression, enzyme protein levels, or intermediate metabolites that accounts for impaired de novo MCFA. When [(13)C] fatty acid products were quantified in vitro using crude cytosolic lysates, native FASN activity was 1.6-fold greater in control relative to Spot14-null lysates, and add back of Spot14 partially restored activity. Recombinant FASN catalysis increased 1.4-fold and C = 14:0 yield was enhanced 4-fold in vitro following addition of Spot14. These findings implicate Spot14 as a direct protein enhancer of FASN catalysis in the mammary gland during lactation when maximal MCFA production is needed.

Influence of terminal differentiation and PACAP on the cytokine, chemokine, and growth factor secretion of mammary epithelial cells

Pituitary adenylate cyclase-activating polypeptide (PACAP), a neuropeptide with trophic and cytoprotective effects, has been shown to affect cell survival, proliferation, and also differentiation of various cell types. The high PACAP level in the milk and its changes during lactation suggest a possible effect of PACAP on the differentiation of mammary epithelial cells. Mammary cell differentiation is regulated by hormones, growth factors, cytokines/chemokines, and angiogenic proteins. In this study, differentiation was hormonally induced by lactogenic hormones in confluent cultures of HC11 mouse mammary epithelial cells. We investigated the effect of PACAP on mammary cell differentiation as well as release of cytokines, chemokines, and growth factors. Differentiation was assessed by expression analysis of the milk protein β-casein. Differentiation significantly decreased the secretion of interferon gammainduced protein (IP)-10, "regulated upon activation normal T cell expressed and presumably secreted" (RANTES), insulin-like growth factor-binding protein (IGFBP)-3 and the epidermal growth factor receptor (EGFR) ligands, such as epidermal growth factor (EGF) and amphiregulin (AREG). The changes in the levels of IP-10 and RANTES may be relevant for the alterations in homing of T cells and B cells at different stages of mammary gland development, while the changes of the EGFR ligands may facilitate the switch from proliferative to lactating stage. PACAP did not modulate the expression of β-casein or the activity of hormone-induced pathways as determined by the analysis of phosphorylation of Akt, STAT5, and p38 MAPK. However, PACAP decreased the release of EGF and AREG from non-differentiated cells. This may influence the extracellular signal-related transactivation of EGFR in the non-differentiated mammary epithelium and is considered to have an impact on the modulation of oncogenic EGFR signaling in breast cancer.

Identification of gene sets and pathways associated with lactation performance in mice

Mammary transcriptome analyses across the lactation cycle and transgenic animal studies have identified candidate genes for mammogenesis, lactogenesis and involution; however, there is a lack of information on pathways that contribute to lactation performance. Previously we have shown significant differences in lactation performance, mammary gland histology, and gene expression profiles during lactation [lactation day 9 (L9)] between CBA/CaH (CBA) and the superior performing QSi5 strains of mice. In the present study, we compared these strains at midpregnancy [pregnancy day 12 (P12)] and utilized these data along with data from a 14th generation of intercross (AIL) to develop an integrative analysis of lactation performance. Additional analysis by quantitative reverse transcription PCR examined the correlation between expression profiles of lactation candidate genes and lactation performance across six inbred strains of mice. The analysis demonstrated that the mammary epithelial content per unit area was similar between CBA and QSi5 mice at P12, while differential expression was detected in 354 mammary genes (false discovery rate < 0.1). Gene ontology and functional annotation analyses showed that functional annotation terms associated with cell division and proliferation were the most enriched in the differentially expressed genes between these two strains at P12. Further analysis revealed that genes associated with neuroactive ligand-receptor interaction and calcium signaling pathways were significantly upregulated and positively correlated with lactation performance, while genes associated with cell cycle and DNA replication pathways were downregulated and positively correlated with lactation performance. There was also a significant negative correlation between Grb10 expression and lactation performance. In summary, using an integrative genomic approach we have identified key genes and pathways associated with lactation performance.

Heat shock protein-90-alpha, a prolactin-STAT5 target gene identified in breast cancer cells, is involved in apoptosis regulation

INTRODUCTION

The prolactin-Janus-kinase-2-signal transducer and activator of transcription-5 (JAK2-STAT5) pathway is essential for the development and functional differentiation of the mammary gland. The pathway also has important roles in mammary tumourigenesis. Prolactin regulated target genes are not yet well defined in tumour cells, and we undertook, to the best of our knowledge, the first large genetic screen of breast cancer cells treated with or without exogenous prolactin. We hypothesise that the identification of these genes should yield insights into the mechanisms by which prolactin participates in cancer formation or progression, and possibly how it regulates normal mammary gland development.

METHODS

We used subtractive hybridisation to identify a number of prolactin-regulated genes in the human mammary carcinoma cell line SKBR3. Northern blotting analysis and luciferase assays identified the gene encoding heat shock protein 90-alpha (HSP90A) as a prolactin-JAK2-STAT5 target gene, whose function was characterised using apoptosis assays.

RESULTS

We identified a number of new prolactin-regulated genes in breast cancer cells. Focusing on HSP90A, we determined that prolactin increased HSP90A mRNA in cancerous human breast SKBR3 cells and that STAT5B preferentially activated the HSP90A promoter in reporter gene assays. Both prolactin and its downstream protein effector, HSP90alpha, promote survival, as shown by apoptosis assays and by the addition of the HSP90 inhibitor, 17-allylamino-17-demethoxygeldanamycin (17-AAG), in both untransformed HC11 mammary epithelial cells and SKBR3 breast cancer cells. The constitutive expression of HSP90A, however, sensitised differentiated HC11 cells to starvation-induced wild-type p53-independent apoptosis. Interestingly, in SKBR3 breast cancer cells, HSP90alpha promoted survival in the presence of serum but appeared to have little effect during starvation.

CONCLUSIONS

In addition to identifying new prolactin-regulated genes in breast cancer cells, we found that prolactin-JAK2-STAT5 induces expression of the HSP90A gene, which encodes the master chaperone of cancer. This identifies one mechanism by which prolactin contributes to breast cancer. Increased expression of HSP90A in breast cancer is correlated with increased cell survival and poor prognosis and HSP90alpha inhibitors are being tested in clinical trials as a breast cancer treatment. Our results also indicate that HSP90alpha promotes survival depending on the cellular conditions and state of cellular transformation.

Prolactin regulation of mammary gland development

Mammary morphogenesis is orchestrated with other reproductive events by pituitary-driven changes to the systemic hormone environment, initiating the formation of a mammary ductal network during puberty and the addition of secretory alveoli during pregnancy. Prolactin is the major driver of development during pregnancy via regulation of ovarian progesterone production (in many species) and direct effects on mammary epithelial cells (in all species). Together these hormones regulate two aspects of development that are the subject of intense interest: (1) a genomic regulatory network that integrates many additional spatial and temporal cues to control gene expression and (2), the activity of a stem and progenitor cell hierarchy. Amalgamation of these two aspects will increase our understanding of cell proliferation and differentiation within the mammary gland, with clear application to our attempts to control breast cancer. Here we focus on providing an over-view of prolactin action during development of the model murine mammary gland.

Galanin concentrations in maternal circulation, amniotic fluid and umbilical cord blood during term labor: relationship with maternal body mass and neonatal birth weight

BACKGROUND

Galanin is a hypothalamic regulatory peptide involved in the regulation of appetite. It is synthesized by the nervous system, anterior pituitary gland, adrenal medulla, pancreas, intestine and placenta. Placental secretion of galanin has until now only been investigated in animals. Additionally, galanin concentration has not been assessed in umbilical cord blood and amniotic fluid.

PATIENTS AND METHODS

Galanin concentrations were measured in maternal circulation before term delivery, in cord blood and in amniotic fluid of 45 healthy pregnant women (gestational age 38 - 40 gestational weeks). The control group consisted of 26 normally menstruating healthy women.

RESULTS

Plasma galanin concentrations were found to be similar in pregnant healthy women before term delivery (20.8 +/- 1.9 pg/ml) and non-pregnant women (19.0 +/- 1.7 pg/ml). Galanin concentration in umbilical cord blood (26.5 +/- 2.2 pg/ml) was significantly higher (p < 0.05) than in maternal circulation. Galanin concentration in amniotic fluid (20.4 +/- 1.0 pg/ml) was similar to that observed in maternal plasma, but significantly (p < 0.01) lower than in umbilical cord blood. A significant correlation was found between maternal body mass index and plasma galanin concentration (tau = 0.246; p < 0.05) and between birth weight and cord blood galanin concentration (tau = 0.345; p = 0.01). There was no significant correlation between placental mass and cord blood galanin concentration (tau = 0.124; p = 0.26).

CONCLUSIONS

Plasma galanin concentration in pregnant women before term delivery is similar to that in non-pregnant women. The fetus rather than the placenta is the source of the high galanin concentration in umbilical cord blood. The role of galanin in the regulation of newborn weight is uncertain.

The alveolar switch: coordinating the proliferative cues and cell fate decisions that drive the formation of lobuloalveoli from ductal epithelium

Massive tissue remodelling occurs within the mammary gland during pregnancy, resulting in the formation of lobuloalveoli that are capable of milk secretion. Endocrine signals generated predominantly by prolactin and progesterone operate the alveolar switch to initiate these developmental events. Here we review the current understanding of the components of the alveolar switch and conclude with an examination of the role of the ets transcription factor Elf5. We propose that Elf5 is a key regulator of the alveolar switch.

Ablation of beta1 integrin in mammary epithelium reveals a key role for integrin in glandular morphogenesis and differentiation

Integrin-mediated adhesion regulates the development and function of a range of tissues; however, little is known about its role in glandular epithelium. To assess the contribution of beta1 integrin, we conditionally deleted its gene in luminal epithelia during different stages of mouse mammary gland development and in cultured primary mammary epithelia. Loss of beta1 integrin in vivo resulted in impaired alveologenesis and lactation. Cultured beta1 integrin-null cells displayed abnormal focal adhesion function and signal transduction and could not form or maintain polarized acini. In vivo, epithelial cells became detached from the extracellular matrix but remained associated with each other and did not undergo overt apoptosis. beta1 integrin-null mammary epithelial cells did not differentiate in response to prolactin stimulation because of defective Stat5 activation. In mice where beta1 integrin was deleted after the initiation of differentiation, fewer defects in alveolar morphology occurred, yet major deficiencies were also observed in milk protein and milk fat production and Stat5 activation, indicating a permissive role for beta1 integrins in prolactin signaling. This study demonstrates that beta1 integrin is critical for the alveolar morphogenesis of a glandular epithelium and for maintenance of its differentiated function. Moreover, it provides genetic evidence for the cooperation between integrin and cytokine signaling pathways.

Information networks in the mammary gland

Unique developmental features during puberty, pregnancy, lactation and post-lactation make the mammary gland a prime object to explore genetic circuits that control the specification, proliferation, differentiation, survival and death of cells. Steroids and simple peptide hormones initiate and carry out complex developmental programmes, and reverse genetics has been used to define the underlying mechanistic connections.

Elf5 is essential for early embryogenesis and mammary gland development during pregnancy and lactation

Elf5 is an epithelial-specific ETS factor. Embryos with a null mutation in the Elf5 gene died before embryonic day 7.5, indicating that Elf5 is essential during mouse embryogenesis. Elf5 is also required for proliferation and differentiation of mouse mammary alveolar epithelial cells during pregnancy and lactation. The loss of one functional allele led to complete developmental arrest of the mammary gland in pregnant Elf5 heterozygous mice. A quantitative mRNA expression study and Western blot analysis revealed that decreased expression of Elf5 correlated with the downregulation of milk proteins in Elf5(+/-) mammary glands. Mammary gland transplants into Rag(-/-) mice demonstrated that Elf5(+/-) mammary alveolar buds failed to develop in an Elf5(+/+) mammary fat pad during pregnancy, demonstrating an epithelial cell autonomous defect. Elf5 expression was reduced in Prolactin receptor (Prlr) heterozygous mammary glands, which phenocopy Elf5(+/-) glands, suggesting that Elf5 and Prlr are in the same pathway. Our data demonstrate that Elf5 is essential for developmental processes in the embryo and in the mammary gland during pregnancy.

Endocrinology of lactation

The endocrine control of lactation is one of the most complex physiologic mechanisms of human parturition. Mammogenesis, lactogenesis, galactopoiesis, and galactokinesis are all essential to assure proper lactation. Prolactin is the key hormone of lactation and seems to be the single most important galactopoietic hormone. Oxytocin, serotonin, opioids, histamine, substance P, and arginine-leucine modulate prolactin release by means of an autocrine/paracrine mechanism, whereas estrogen and progesterone hormones can act at the hypothalamic and adenohypophysial levels. Human placental lactogen and growth factors play an essential role to assure successful lactation during pregnancy. Oxytocin is the most powerful galactokinetic hormone.

Using gene expression arrays to elucidate transcriptional profiles underlying prolactin function

Prolactin is an ancient hormone, with different functions in many species. The binding of prolactin to its receptor, a member of the cytokine receptor superfamily, results in the activation of different intracellular signaling pathways, such as JAK2/STAT5, MAP kinase, and PI3K/AKT. How prolactin elicits so many different biological responses remains unclear. Recently, microarray technology has been applied to identify prolactin target genes in different systems. Here, we attempt to summarize and compare the available data. Our comparison of the genes reported to be transcriptionally regulated by prolactin indicates that there are few genes in common between the different tissues. Among the organs studied, mammary and prostate glands displayed the largest number of overlaps in putative prolactin target genes. Some of the candidates have been implicated in tumorigenesis. The relevance and validation of microarray data, as well as comparison of the results obtained by different groups, will be discussed.