In the Murine and Bovine Maternal Mammary Gland Signal Transducer and Activator of Transcription 3 is Activated in Clusters of Epithelial Cells around the Day of Birth

Signal transducers and activators of transcription (STAT) proteins regulate mammary development. Here we investigate the expression of phosphorylated STAT3 (pSTAT3) in the mouse and cow around the day of birth. We present localised colocation analysis, applicable to other mammary studies requiring identification of spatially congregated events. We demonstrate that pSTAT3-positive events are multifocally clustered in a non-random and statistically significant fashion. Arginase-1 expressing cells, consistent with macrophages, exhibit distinct clustering within the periparturient mammary gland. These findings represent a new facet of mammary STAT3 biology, and point to the presence of mammary sub-microenvironments.

Effects of hydrostatic compression on milk production-related signaling pathways in mouse mammary epithelial cells

Mammary epithelial cells (MECs) secrete milk into the mammary alveolar lumen during lactation. The secreted milk accumulates in the alveolar lumen until milk ejection occurs, and excess milk accumulation downregulates milk production in alveolar MECs. Intramammary hydrostatic pressure also increases in the alveolar lumen in a manner dependent on milk accumulation. In this study, we investigated whether high hydrostatic compression directly affects lactating MECs, using a commercial compression device and a lactation culture model of MECs, which have milk production ability and less permeable tight junctions. High hydrostatic compression at 100 kPa for 8 h decreased β-casein and increased claudin-4 levels concurrently with inactivation of STAT5 and glucocorticoid receptor signaling pathways. In addition, high hydrostatic compression for 1 h inactivated STAT5 and activated p38 MAPK signaling. Furthermore, repeated rises and falls of the hourly hydrostatic compression induced activation of positive (Akt, mTOR) and negative (STAT3, NF-κB) signaling pathways for milk production concurrently with stimulation of casein and lactoferrin production in MECs. These results indicate that milk production-related signaling pathways in MECs change in response to hydrostatic compression. Hydrostatic compression of the alveolar lumen may directly regulate milk production in the alveolar MECs of lactating mammary glands.

miR-30a-3p Regulates Autophagy in the Involution of Mice Mammary Glands

The mammary gland undergoes intensive remodeling during the lactation cycle, and the involution process of mammary gland contains extensive epithelial cells involved in the process of autophagy. Our studies of mice mammary glands suggest that miR-30a-3p expression was low during involution compared with its high expression in the mammary glands of lactating mice. Then, we revealed that miR-30a-3p negatively regulated autophagy by autophagy related 12 (Atg12) in mouse mammary gland epithelial cells (MMECs). Restoring ATG12, knocking down autophagy related 5 (Atg5), starvation, and Rapamycin were used to further confirm this conclusion. Overexpression of miR-30a-3p inhibited autophagy and altered mammary structure in the involution of the mammary glands of mice, which was indicative of alteration in mammary remodeling. Taken together, these results elucidated the molecular mechanisms of miR-30a-3p as a key induction mediator of autophagy by targeting Atg12 within the transition period between lactation and involution in mammary glands.

Effect of experimental stress and cortisol release induced by ACTH administration on expression of key genes related to milk synthesis and apoptosis during mammary involution of Saanen goats

This research paper addresses the hypothesis that stress, induced by ACTH administration and cortisol release increases somatic cell count (SCC) in mammary secretion, and improves the effectiveness of dry off in goats. We report indicators of milk synthesis and mammary gland involution during dry off. Thirty Saanen goats were subjected to abrupt dry off and treatments: (1) ACTH administration (ACTH) or (2) placebo (Control) on days 1, 3, 6, 9, 12, 15, 30, and 60 of dry off. The expression of target genes in mammary tissue that are related to milk synthesis and cell survival such as insulin-like growth factor 1 receptor (IGF1R), phosphatidylinositol-3-kinase (PIK3CA), protein kinase B (AKT1) and mechanistic target of rapamycin (MTOR), casein (CSN2), lactalbumin (LALBA) and lactoferrin (LF) were evaluated, and plasma cortisol concentration, SCC, leucocyte count, and microbiological analyses in milk and mammary secretions were assessed. ACTH significantly downregulated the expression of IGF1R and upregulated the expression of PIK3CA in mammary tissue, increased lactoferrin concentration and SCC, and changed immune cell levels in mammary secretions compared to Control. Furthermore, ACTH administration increased the percentage of dry goats compared to the Control (73 vs. 46%, respectively). We conclude that the effect of stress via ACTH administration and cortisol release accelerated mammary involution during the early dry-off period.

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

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

Lactose on the basolateral side of mammary epithelial cells inhibits milk production concomitantly with signal transducer and activator of transcription 5 inactivation

Mammary epithelial cells (MECs) are the only cells capable of synthesizing lactose. During lactation, alveolar MECs secrete lactose through the apical membrane into the alveolar lumen, whereas alveolar tight junctions (TJs) block the leakage of lactose into the basolateral sides of the MECs. However, lactose leaks from the alveolar lumen into the blood plasma in the mastitis and after weaning. This exposes the basolateral membrane of MECs to lactose. The relationship between lactose in blood plasma and milk production has been suggested. The present study determined whether lactose exposure on the basolateral membrane of mouse MECs adversely affects milk production in vitro. Restricted exposure to lactose on the basolateral side of the MECs was performed using a culture model, in which MECs on the cell culture insert exhibit milk production and less-permeable TJs. The results indicated that lactose exposure on the basolateral side inhibited casein and lipid production in the MECs. Interestingly, lactose exposure on the apical side did not show detectable effects on milk production in the MECs. Basolateral lactose exposure also caused the inactivation of STAT5, a primary transcriptional factor for milk production. Furthermore, p38 and JNK were activated by basolateral lactose exposure. The activation of p38 and JNK following anisomycin treatment reduced phosphorylated STAT5, and inhibitors of p38 blocked the reduction of phosphorylated STAT5 by basolateral lactose exposure. These findings suggest that lactose functions as a partial inhibitor for milk production but only when it directly makes contact with the basolateral membrane of MECs.

Isoflavones and their metabolites influence the milk production ability of bovine mammary epithelial cells in a type-specific manner

Dairy cows feed on isoflavones as physiologically active substances present in legumes. However, the influences of isoflavones (biochanin A, genistein, formononetin, and daidzein) and their metabolites (p-ethylphenol and equol) on milk components production, tight junctions (TJs), and their regulatory pathways are unclear in bovine mammary epithelial cells (BMECs). In this study, we investigated the influences of isoflavones and their metabolites in BMECs using an in vitro culture model. The influences of isoflavones on milk components production, TJ proteins, and STAT5/STAT3 signaling pathways were different in a type-specific manner. Biochanin A decreased the mRNA expression and secretion of both β-casein and lactoferrin while a decrease in activated STAT5 and an increase in activated STAT3. In contrast, equol increased claudin-3, which is the main components for less-permeable TJs in lactation, while an increase in activated STAT5. In addition, a mixture of multiple isoflavones based on the intake of red clover increased secretion of lactoferrin, mRNA expression of β-casein, and amount of claudin-3, but a mixture based on soy did not affect the BMECs. Thus, these results indicate that isoflavones in legumes and the metabolic activity of isoflavones in dairy cows when feeding legumes may affect the milk production ability in BMECs.

The role of the IGF system in mammary physiology of ruminants

The IGF system plays a central role in all stages of mammary development, lactation and involution. IGFs exert their effects on the mammary gland through both endocrine and paracrine/autocrine mechanisms and the importance of circulating versus local IGF action remains an open question, especially in ruminants. At the whole organ level, a critical role for IGFs in ductal morphogenesis and lobuloalveolar development has been established, while at the cellular level the ability of IGFs to stimulate cell proliferation and control cell survival contributes to the number of milk-secreting cells in the gland. Much of this work has been conducted in rodents which provide an affordable research model and allow for genetic manipulation of specific components of the IGF system. Research into the role of the IGF system in dairy cows has generally supported information obtained with rodents though large gaps in our knowledge remain and species differences are not well defined. Examples include whether exogenous somatotropin exerts its effects on the mammary gland through local IGF-1 synthesis which is accepted dogma in rodents, what the role of IGF-1 versus IGF-2 is in the mammary gland, and how the IGFBPs regulate IGF bioactivity. This last area is particularly under-investigated in ruminants both at the whole animal and the cellular and molecular levels. Given that the IGF system may underlie many management practices that could contribute to enhancing productive efficiency of lactation, more research into the basic biology of this important system is warranted.

Acute and chronic effects of cortisol on milk yield, the expression of key receptors, and apoptosis of mammary epithelial cells in Saanen goats

Cortisol (CORT) induces mammary development in late gestation and is fundamental to the differentiation of mammary epithelial cells and lactogenesis. The objective of this study was to investigate the relationship between CORT, insulin, prolactin, growth hormone, and insulin-like growth factor-1 in milk as well as the effect of CORT on the expression of receptors of insulin (INSR), prolactin (PRLR), growth hormone (GHR); we also studied the insulin-like growth factor-1 (IGF1R), glucocorticoid (NR3C1), mineralocorticoid (NR3C2), B-cell lymphoma 2 (BCL2), BCL-2-like protein X (BAX) genes, and the apoptosis rate of mammary epithelial cells of lactating Saanen goats in vivo and in vitro. The following experiments were conducted: (1) comparing hormone release in milk and blood after ACTH or a placebo administration; (2) evaluating the effect of acute CORT increases in mammary gland expression and milk yield in vivo; and (3) evaluating the effect of a chronic increase in CORT concentration in epithelial mammary cell apoptosis in vitro. In vivo, ACTH administration significantly increased CORT release but did not affect insulin, prolactin, growth hormone, and insulin-like growth factor-1 release in plasma and milk versus placebo. The results show also that a low CORT release after ACTH administration increased the expression of GHR and PRLR genes in the mammary tissue. Indeed, CORT release significantly increased the milk yield from goats subjected to ACTH versus goats subjected to the placebo. However, a higher amount of CORT added in vitro upregulated the NR3C1, GHR, PRLR, and BAX genes and downregulated the IGF1R and INSR genes, which could negatively modulate the apoptosis of mammary epithelial cells. Finally, the effect of CORT in vivo after ACTH administration demonstrated the increased expression of the PRLR and GHR genes, which may improve epithelial cell responsiveness and be associated with the positive effect of CORT observed on milk yield at mid-end lactation.

Endocrine Signals Altered by Heat Stress Impact Dairy Cow Mammary Cellular Processes at Different Stages of the Dry Period

Simple Summary

Late-gestation heat stress increases blood prolactin and decreases oestrogen concentrations in dry cows. These hormonal alterations may disturb mammary gland remodelling during the dry period, thereby being potentially responsible for the observed production impairments during the subsequent lactation. This project aimed to better understand the molecular mechanisms underlying subsequent impairments in mammary performance after dry period heat stress. For this, we studied the expression of genes encompassing prolactin and oestrogen pathways and key cellular process pathways under different thermal environments and in vitro hormonal milieus. The results of this study revealed that late-gestation heat stress impacted the expression of genes in the mammary gland involved in key cellular processes occurring during the dry period. Furthermore, our results indicated that these modifications are in part modulated by alterations of oestrogen and prolactin signalling.

Abstract

Hormonal alterations occurring under late gestation heat stress may disturb mammary gland remodelling, resulting in a reduced milk yield during the subsequent lactation. We investigated the effects of an altered endocrine environment on mammary gene expression at different stages of the dry period. Mammary gland biopsies from in vivo-cooled (CL) or heat-stressed (HT) cows were collected at d 3 and 35 relative to dry-off and divided into explants. Explants were incubated in vitro for 24 h in one of three media: Basal: no prolactin or estrogen; CL-mimic: Basal + low prolactin + high 17β-estradiol, or HT-mimic: Basal + high prolactin + low 17β-estradiol. Real time qPCR was used to quantify gene expression. We established that late-gestation heat stress changes the expression of prolactin and oestrogen receptors, downregulates genes involved in apoptosis, autophagy and proliferation at d 3 and upregulates genes related to those cellular processes at d 35. Moreover, compared with in vivo treatments, we showed that the expression of fewer genes was impacted by in vitro treatments which aimed to mimic the hormonal response of cows exposed to a different environment. Further research will continue to uncover the mechanisms behind the production impairments caused by late-gestation heat stress.

Comparative mammary gland postnatal development and tumourigenesis in the sheep, cow, cat and rabbit: Exploring the menagerie

Sheep, cows, cats, and rabbits are kept by humans for agricultural purposes and as companion animals. Much of the mammary research in these species has focussed on mastitis in the case of ruminants and rabbits, and mammary tumourigenesis in cats and rabbits. However, similarities with the human breast suggest that these species may be currently underutilised as valuable comparative models of breast development and disease. The mammary gland undergoes cyclical postnatal development that will be considered here in the context of these non-traditional model species, with a focus on the mammary microenvironment at different postnatal developmental stages. The second part of this review will consider mammary tumour development. Ruminants are thought to be relatively 'resistant' to mammary tumourigenesis, likely due to multiple factors including functional properties of ruminant mammary stem/progenitor cells, diet, and/or the fact that production animals undergo a first parity soon after puberty. By contrast, unneutered female cats and rabbits have a propensity to develop mammary neoplasms, and subsets of these may constitute valuable comparative models of breast cancer.

Single-step genome-wide association studies (GWAS) and post-GWAS analyses to identify genomic regions and candidate genes for milk yield in Brazilian Girolando cattle

Milk production is economically important to the Brazilian agribusiness, and the majority of the country's milk production derives from Girolando (Gir × Holstein) cows. This study aimed to identify quantitative trait loci (QTL) and candidate genes associated with 305-d milk yield (305MY) in Girolando cattle. In addition, we investigated the SNP-specific variances for Holstein and Gir breeds of origin within the sequence of candidate genes. A single-step genomic BLUP procedure was used to identify QTL associated with 305MY, and the most likely candidate genes were identified through follow-up analyses. Genomic breeding values specific for Holstein and Gir were estimated in the Girolando animals using a model that uses breed-specific partial relationship matrices, which were converted to breed of origin SNP effects. Differences between breed of origin were evaluated by comparing estimated SNP variances between breeds. From 10 genome regions explaining most additive genetic variance for 305MY in Girolando cattle, 7 candidate genes were identified on chromosomes 1, 4, 6, and 26. Within the sequence of these 7 candidate genes, Gir breed of origin SNP alleles showed the highest genetic variance. These results indicated QTL regions that could be further explored in genomic selection panels and which may also help in understanding the gene mechanisms involved in milk production in the Girolando breed.

Contrasting effects of transforming growth factor β1 on programmed cell death of bovine mammary epithelial cell lines MAC-T and BME-UV1

A previous study in the bovine mammary epithelial cell line BME-UV1 demonstrated that suppression of the phosphatidylinositol-4,5-biphosphate 3 kinase (PI3K)/AKT (somatotropic) signaling pathway was required for transforming growth factor β1 (TGFβ1)-induced programmed cell death (PCD). To investigate whether this is a universal mechanism for TGFβ1 to induce PCD in bovine mammary epithelium, we compared TGFβ1 modulation of PI3K/AKT and its role in PCD in 2 bovine mammary epithelial cell lines: MAC-T and BME-UV1. In MAC-T cells, TGFβ1 promoted cell survival, and this paralleled a reduction in PI3K/AKT activity, rather than an increase. In BME-UV1 cells, TGFβ1 induced PCD, and this was accompanied by a time-dependent effect on PI3K/AKT activity, including an initial significant increase in the phosphorylation of AKT at 3 h, followed by a reduction between 12 and 24 h, and then an increase at 48 h. Inhibition of AKT activity enhanced TGFβ1-induced PCD in BME-UV1 cells but had no effect on MAC-T cells, suggesting that TGFβ1 mediates PCD in BME-UV1 cells through suppression of AKT activity. Inhibition of TGFβ receptor type I (TβRI) kinase activity completely abrogated TGFβ1-induced PCD in BME-UV1 cells but had no effect on TGFβ1-induced suppression of PCD in MAC-T cells, demonstrating that TGFβ1-induced PCD in BME-UV1 cells is dependent on TβRI/SMAD signaling. These and previous observations suggest that the different effects of TGFβ1 on PCD in these cell lines might involve noncanonical signaling pathways other than PI3K/AKT, and may reflect their different lineages. Future studies should address this finding, taking into consideration the effect that different culture conditions might have on cell phenotype.

Chi-miR-3031 regulates beta-casein via the PI3K/AKT-mTOR signaling pathway in goat mammary epithelial cells (GMECs)

BACKGROUND

MicroRNAs can regulate gene expression at the posttranscriptional level through translational repression or target degradation. Our previous investigations examined the differential expression levels of chi-miR-3031 in caprine mammary gland tissues in colostrum and common milk stages.

RESULTS

The present study detected the role of chi-miR-3031 in the lactation mechanisms of GMECs. High-throughput sequencing was used to analyze transcriptomic landscapes of GMECs transfected with chi-miR-3031 mimics (MC) and a mimic negative control (NC). In the MC and NC groups, we acquired 39,793,503 and 36,531,517 uniquely mapped reads, respectively, accounting for 85.85 and 81.66% of total reads. In the MC group, 180 differentially expressed unigenes were downregulated, whereas 157 unigenes were upregulated. KEGG pathway analyses showed that the prolactin, TNF and ErbB signaling pathways, including TGFα, PIK3R3, IGF2, ELF5, IGFBP5 and LHβ genes, played important roles in mammary development and milk secretion. Results from transcriptome sequencing, real-time PCR and western blotting showed that chi-miR-3031 suppressed the expression of IGFBP5 mRNA and protein. The expression levels of β-casein significantly increased in the MC and siRNA-IGFBP5 groups. We observed that the down-regulation of IGFBP5 activated mTOR at the Ser2448 site in GMECs transfected with MC and siRNA-IGFBP5. Previous findings and our results showed that chi-miR-3031 activated the PI3K-AKT-mTOR pathway and increased β-casein expression by down-regulating IGFBP5.

CONCLUSIONS

These findings will afford valuable information for improving milk quality and contribute the development of potential methods for amending lactation performance.

RNA-Seq reveals novel genes and pathways involved in bovine mammary involution during the dry period and under environmental heat stress

The bovine dry period is a dynamic non-lactating phase where the mammary gland undergoes extensive cellular turnover. Utilizing RNA sequencing, we characterized novel genes and pathways involved in this process and determined the impact of dry period heat stress. Mammary tissue was collected before and during the dry period (−3, 3, 7, 14, and 25 days relative to dry-off [day 0]) from heat-stressed (HT, n = 6) or cooled (CL, n = 6) late-gestation Holstein cows. We identified 3,315 differentially expressed genes (DEGs) between late lactation and early involution, and 880 DEGs later in the involution process. DEGs, pathways, and upstream regulators during early involution support the downregulation of functions such as anabolism and milk component synthesis, and upregulation of cell death, cytoskeleton degradation, and immune response. The impact of environmental heat stress was less significant, yet genes, pathways, and upstream regulators involved in processes such as ductal branching morphogenesis, cell death, immune function, and protection against tissue stress were identified. Our research advances understanding of the mammary gland transcriptome during the dry period, and under heat stress insult. Individual genes, pathways, and upstream regulators highlighted in this study point towards potential targets for dry period manipulation and mitigation of the negative consequences of heat stress on mammary function.

The Multifaceted Role of STAT3 in Mammary Gland Involution and Breast Cancer

Since seminal descriptions of signal transducer and activator of transcription 3 (STAT3) as a signal transducer and transcriptional regulator, which is most usually activated by phosphorylation of a specific tyrosine residue, a staggering wealth of research has delineated the key role of this transcription factor as a mediator of mammary gland postlactational regression (involution), and paradoxically, a pro-survival factor in breast cancer and some breast cancer cell lines. STAT3 is a critical regulator of lysosomal-mediated programmed cell death (LM-PCD) during mammary gland involution, where uptake of milk fat globules, and consequent high levels of free fatty acids, cause permeabilisation of lysosomal vesicle membranes, in turn leading to cathepsin protease leakage and cell death. A recent proteomic screen of STAT3-induced changes in lysosomal membrane protein components has highlighted wide-ranging effects of STAT3, which may coordinate LM-PCD via the stimulation of endocytosis, intracellular trafficking, and lysosome biogenesis. In parallel, STAT3 regulates the acute phase response during the first phase of involution, and it contributes to shaping the pro-tumourigenic 'wound healing' signature of the gland during the second phase of this process. STAT3 activation during involution is important across species, although some differences exist in the progression of involution in dairy cows. In breast cancer, a number of upstream regulators can lead to STAT3 activation and the effects of phosphorylation of STAT3 are equally wide-ranging. Recent studies have implicated microRNAs in some regulatory pathways. In this review, we will examine the multifaceted role of STAT3 in mammary gland involution and tumourigenesis, incorporating a review of these fundamental processes in tandem with a discussion of recent developments in this field.

MicroRNA roles in signalling during lactation: an insight from differential expression, time course and pathway analyses of deep sequence data

The study examined microRNA (miRNA) expression and regulatory patterns during an entire bovine lactation cycle. Total RNA from milk fat samples collected at the lactogenesis (LAC, day1 [D1] and D7), galactopoiesis (GAL, D30, D70, D130, D170 and D230) and involution (INV, D290 and when milk production dropped to 5 kg/day) stages from 9 cows was used for miRNA sequencing. A total of 475 known and 238 novel miRNAs were identified. Fifteen abundantly expressed miRNAs across lactation stages play regulatory roles in basic metabolic, cellular and immunological functions. About 344, 366 and 209 miRNAs were significantly differentially expressed (DE) between GAL and LAC, INV and GAL, and INV and LAC stages, respectively. MiR-29b/miR-363 and miR-874/miR-6254 are important mediators for transition signals from LAC to GAL and from GAL to INV, respectively. Moreover, 58 miRNAs were dynamically DE in all lactation stages and 19 miRNAs were significantly time-dependently DE throughout lactation. Relevant signalling pathways for transition between lactation stages are involved in apoptosis (PTEN and SAPK/JNK), intracellular signalling (protein kinase A, TGF-β and ERK5), cell cycle regulation (STAT3), cytokines, hormones and growth factors (prolactin, growth hormone and glucocorticoid receptor). Overall, our data suggest diverse, temporal and physiological signal-dependent regulatory and mediator functions for miRNAs during lactation.