Expression of prolactin mRNA in rat mammary gland during pregnancy and lactation

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.

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.

Patterns of prolactin secretion

Prolactin is pleotropic in nature affecting multiple tissues throughout the body. As a consequence of the broad range of functions, regulation of anterior pituitary prolactin secretion is complex and atypical as compared to other pituitary hormones. Many studies have provided insight into the complex hypothalamic-pituitary networks controlling prolactin secretion patterns in different species using a range of techniques. Here, we review prolactin secretion in both males and females; and consider the different patterns of prolactin secretion across the reproductive cycle in representative female mammals with short versus long luteal phases and in seasonal breeders. Additionally, we highlight changes in the pattern of secretion during pregnancy and lactation, and discuss the wide range of adaptive functions that prolactin may have in these important physiological states.

Autocrine/paracrine roles of extrapituitary growth hormone and prolactin in health and disease: An overview

Growth hormone (GH) and prolactin (PRL) are both endocrines that are synthesized and released from the pituitary gland into systemic circulation. Both are therefore hormones and both have numerous physiological roles mediated through a myriad of target sites and both have pathophysiological consequences when present in excess or deficiency. GH or PRL gene expression is not, however, confined to the anterior pituitary gland and it occurs widely in many of their central and peripheral sites of action. This may reflect "leaky gene" phenomena and the fact that all cells have the potential to express every gene that is present in their genome. However, the presence of GH or PRL receptors in these extrapituitary sites of GH and PRL production suggests that they are autocrine or paracrine sites of GH and PRL action. These local actions often occur prior to the ontogeny of pituitary somatotrophs and lactotrophs and they may complement or differ from the roles of their pituitary counterparts. Many of these local actions are also of physiological significance, since they are impaired by a blockade of local GH or PRL production or by an antagonism of local GH or PRL action. These local actions may also be of pathophysiological significance, since autocrine or paracrine actions of GH and PRL are thought to be causally involved in a number of disease states, particularly in cancer. Autocrine GH for instance, is thought to be more oncogenic than pituitary GH and selective targeting of the autocrine moiety may provide a therapeutic approach to prevent tumor progression. In summary, GH and PRL are not just endocrine hormones, as they have autocrine and/or paracrine roles in health and disease.

Effects of resveratrol on cell growth and prolactin synthesis in GH3 cells

Resveratrol (RE), a phytoestrogen, has antiestrogenic properties. Estrogen plays a key role in the development and progression of pituitary prolactinoma. Moreover, RE is a potent cancer chemopreventive agent that inhibits the initiation, promotion and progression of carcinogenesis. The present study investigated the antitumor effects of RE on GH3 pituitary tumor cells. A concentration- and treatment duration-dependent biphasic effect of RE on the proliferation of the GH3 cells was demonstrated. After three days of treatment, RE stimulated proliferation at low concentrations and inhibited proliferation at high concentrations. However, when the treatment duration was reduced to 6 h, RE inhibited proliferation in a concentration-dependent manner. In addition, RE induced apoptosis with the activation of caspase-3 and -8, and decreased the percentage of prolactin (PRL)-immunopositive GH3 cells. Furthermore, RE suppressed expression of the PRL gene and inhibited the cell proliferation and PRL synthesis induced by 17β-estradiol (E2). In GH3 cells, the proliferation response exhibited higher sensitivity to E2 compared with the PRL response; by contrast, the PRL response was more sensitive to RE than the proliferation response was. These results indicate that RE, an antiestrogenic compound, exerts its antitumor effect on GH3 cells through the suppression of GH3 cell growth and through the inhibition of PRL synthesis. The RE-induced cell apoptosis was shown to be caspase-dependent. Therefore, the present study provides support for the use of RE in the chemoprevention and chemotherapy of pituitary prolactinoma.

Autocrine prolactin induced by the Pten-Akt pathway is required for lactation initiation and provides a direct link between the Akt and Stat5 pathways

Extrapituitary prolactin (Prl) is produced in humans and rodents; however, little is known about its in vivo regulation or physiological function. We now report that autocrine prolactin is required for terminal mammary epithelial differentiation during pregnancy and that its production is regulated by the Pten-PI3K-Akt pathway. Conditional activation of the PI3K-Akt pathway in the mammary glands of virgin mice by either Akt1 expression or Pten deletion rapidly induced terminal mammary epithelial differentiation accompanied by the synthesis of milk despite the absence of lobuloalveolar development. Surprisingly, we found that mammary differentiation was due to the PI3K-Akt-dependent synthesis and secretion of autocrine prolactin and downstream activation of the prolactin receptor (Prlr)-Jak-Stat5 pathway. Consistent with this, Akt-induced mammary differentiation was abrogated in Prl(-/-), Prlr(-/-), and Stat5(-/-) mice. Furthermore, cells treated with conditioned medium from mammary glands in which Akt had been activated underwent rapid Stat5 phosphorylation in a manner that was blocked by inhibition of Jak2, treatment with an anti-Prl antibody, or deletion of the prolactin gene. Demonstrating a physiological requirement for autocrine prolactin, mammary glands from lactation-defective Akt1(-/-);Akt2(+/-) mice failed to express autocrine prolactin or activate Stat5 during late pregnancy despite normal levels of circulating serum prolactin and pituitary prolactin production. Our findings reveal that PI3K-Akt pathway activation is necessary and sufficient to induce autocrine prolactin production in the mammary gland, Stat5 activation, and terminal mammary epithelial differentiation, even in the absence of the normal developmental program that prepares the mammary gland for lactation. Together, these findings identify a function for autocrine prolactin during normal development and demonstrate its endogenous regulation by the PI3K-Akt pathway.

Mammary gland zinc metabolism: regulation and dysregulation

Zinc (Zn) is required for numerous metabolic processes serving both a structural and catalytic role. The mammary gland has a unique Zn requirement resulting from the need to also transfer an extraordinary amount of Zn into milk (~0.5-1 mg Zn/day) during lactation. Impairments in this process can result in severe Zn deficiency in the nursing offspring which has adverse consequences with respect to growth and development. Moreover, dysregulated mammary gland Zn metabolism has recently been implicated in breast cancer transition, progression and metastasis, thus there is a critical need to understand the molecular mechanisms which underlie these observations. Tight regulation of Zn transporting mechanisms is critical to providing an extraordinary amount of Zn for secretion into milk as well as maintaining optimal cellular function. Expression of numerous Zn transporters has been detected in mammary gland or cultured breast cells; however, understanding the molecular mechanisms which regulate mammary Zn metabolism as well as the etiology and downstream consequences resulting from their dysregulation is largely not understood. In this review, we will summarize the current understanding of the regulation of mammary gland Zn metabolism and its regulation by reproductive hormones, with a discussion of the dysregulation of this process in breast cancer.

Molecular regulation of milk trace mineral homeostasis

The regulation of milk trace mineral homeostasis requires the temporal integration of three main processes, (A) mineral uptake into the secretory mammary epithelial cell (MEC); followed by (B) mineral secretion from MEC into the alveoli lumen of the mammary gland for sequestration in milk; and then (C) milk release in response to suckling. Trace mineral requirements of term infants are generally met by exclusive breast-feeding through about the first 6 months of life and although milk zinc (Zn), iron (Fe), and copper (Cu) concentrations are relatively refractory to maternal trace mineral status, they normally decline throughout lactation. Recently, Zn-, Fe- and Cu-specific transporters have been identified that regulate trace element uptake and efflux in various cell types; however, there is currently little information available regarding the processes through which the mammary gland regulates milk trace mineral transport. The homology of trace mineral transporters between species permits the utilization of rodent models to examine the regulation of mammary gland mineral transport. Therefore, we have used the lactating rat to determine changes in mammary gland Zn, Fe and Cu transporter expression and localization that occur throughout lactation and in response to maternal trace mineral deficiency in hope of elucidating some of the changes which occur during mammary gland trace element homeostasis and also may be occurring in lactating women.

Effects of Neonatal Exposure to Diethylstilbestrol, Tamoxifen, and Toremifene on the BALB/c Mouse Mammary Gland1

In this study, we compared the long-term effects of neonatal exposure to diethylstilbestrol (DES, 0.0125-50 microg), tamoxifen (TAM, 0.0125-50 microg), and toremifene (TOR, 53 microg) on mammary gland development and differentiation. Allometric growth of the mammary ducts was stimulated by neonatal DES exposure (12.5 microg) and impaired by exposure to TAM (25 microg). Neonatal treatment with high doses of DES resulted in mammary ducts that displayed extensive dilatation and precocious lactogenesis in postpubertal, nulliparous females. Initiation of this precocious differentiation coincided with the absence of corpora lutea, increased levels of serum prolactin (PRL), and the induction of Prl mRNA expression within the mammary glands. Neonatal exposure to 1.25 microg TAM increased alveolar development in postpubertal, nulliparous females similar to that recorded in females treated with low doses of DES. Lower doses of TAM did not affect alveolar development, whereas branching morphogenesis and alveolar development were impaired by higher doses. Increased alveolar development in females exposed to 1.25 microg TAM was associated with elevated serum progesterone (P) and increased alveolar development in response to exogenous P. Taken together, our findings demonstrate that neonatal exposure to both DES and TAM exerts long-lasting effects on the proliferation and differentiation of the mammary glands in female BALB/c, primarily as the result of endocrine disruption.

Prolactin regulates mammary epithelial cell proliferation via autocrine/paracrine mechanism

Prolactin (PRL) is essential for a number of developmental events in the mammary gland. Work with PRL and PRL receptor knockout mice has shown that PRL indirectly regulates ductal side branching during puberty and directly controls lobuloalveolar development and lactogenesis during pregnancy. Anterior pituitary or placental PRL is thought to be responsible for these functions via an endocrine mechanism; however, PRL is also produced in a number of extrapituitary sites including the mammary gland. The physiologic relevance of mammary PRL remains unknown. In this study we utilized mammary recombination in Rag1(-/-) hosts, to determine whether mammary PRL plays a role in the regulation of mammary gland development. Mammary glands formed with the PRL gene deleted from either the epithelium, stroma, or both displayed normal development, on the basis of whole mount and hematoxylin and eosin histology, during puberty and lactation. At the end of pregnancy, a 2.8-fold decrease in bromodeoxyuridine incorporation was observed in the epithelial cells of mammary glands formed using PRL knockout epithelium compared with those formed using wildtype epithelium. No balancing alteration in the rates of apoptosis was detected. Thus, mammary-derived PRL influences mammary epithelial cell proliferation via an autocrine/paracrine mechanism, establishing a physiologic function for mammary PRL during mammopoiesis.