The ins and outs of calcium signalling in lactation and involution: Implications for breast cancer treatment

Methods for Imaging Intracellular Calcium Signals in the Mouse Mammary Epithelium in Two and Three Dimensions

The mammary gland has a central role in optimal mammalian development and survival. Contractions of smooth muscle-like basal (or myoepithelial) cells in the functionally mature mammary gland in response to oxytocin are essential for milk ejection and are tightly regulated by intracellular calcium (Ca2+). Using mice expressing a genetically encoded Ca2+ indicator (GCaMP6f), we present in this chapter a method to visualize at high spatiotemporal resolution changes in intracellular Ca2+ in mammary epithelial cells, both in vitro (2D) and ex vivo (3D). The procedure to optimally prepare mammary tissue and primary cells is presented in detail.

Cabergoline as a Novel Strategy for Post-Pregnancy Breast Cancer Prevention in Mice and Human

Post-pregnancy breast cancer often carries a poor prognosis, posing a major clinical challenge. The increasing trend of later-life pregnancies exacerbates this risk, highlighting the need for effective chemoprevention strategies. Current options, limited to selective estrogen receptor modulators, aromatase inhibitors, or surgical procedures, offer limited efficacy and considerable side effects. Here, we report that cabergoline, a dopaminergic agonist, reduces the risk of breast cancer post-pregnancy in a Brca1/P53-deficient mouse model, with implications for human breast cancer prevention. We show that a single dose of cabergoline administered post-pregnancy significantly delayed the onset and reduced the incidence of breast cancer in Brca1/P53-deficient mice. Histological analysis revealed a notable acceleration in post-lactational involution over the short term, characterized by increased apoptosis and altered gene expression related to ion transport. Over the long term, histological changes in the mammary gland included a reduction in the ductal component, decreased epithelial proliferation, and a lower presence of recombinant Brca1/P53 target cells, which are precursors of tumors. These changes serve as indicators of reduced breast cancer susceptibility. Additionally, RNA sequencing identified gene expression alterations associated with decreased proliferation and mammary gland branching. Our findings highlight a mechanism wherein cabergoline enhances the protective effect of pregnancy against breast cancer by potentiating postlactational involution. Notably, a retrospective cohort study in women demonstrated a markedly lower incidence of post-pregnancy breast cancer in those treated with cabergoline compared to a control group. Our work underscores the importance of enhancing postlactational involution as a strategy for breast cancer prevention, and identifies cabergoline as a promising, low-risk option in breast cancer chemoprevention. This strategy has the potential to revolutionize breast cancer prevention approaches, particularly for women at increased risk due to genetic factors or delayed childbirth, and has wider implications beyond hereditary breast cancer cases.

L-arginine stimulates the proliferation of mouse mammary epithelial cells and the development of mammary gland in pubertal mice by activating the GPRC6A/PI3K/AKT/mTOR signalling pathway

Amino acids have been shown to affect the development of mammary gland (MG). However, it is unclear whether L-arginine promotes the development of pubertal MG. Therefore, our study aims to explore the effect of L-arginine on the development of MG in pubertal mice. To investigate its internal mechanism of action, we will use mouse mammary epithelial cells (mMECs) line. Whole-mount staining showed that L-arginine can promote the extension of MG duct. In vitro, 0.4 mM L-arginine could activate the G protein-coupled receptor family C, group 6, subtype A (GPRC6A)/phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signalling pathway and increase the phosphorylation of eukaryotic initiation factor 4E binding protein 1 (4EBP1) to promote the synthesis of cell cycle regulatory protein D1 (Cyclin D1), leading to the dissociation of the retinoblastoma tumour suppressor protein (Rb)-E2F1 transcription factor (E2F1) complex in mMECs and releasing E2F1 to promote cell proliferation. Furthermore, GPRC6A was knocked down or inhibition of the PI3K/AKT/mTOR signalling pathway with corresponding inhibitors completely abolished the arginine-induced promotion of mMECs proliferation. In vivo, it was further confirmed that 0.1% L-arginine can activate the PI3K/AKT/mTOR signalling pathway in the MG of pubertal mice. These results were able to indicate that L-arginine stimulates the development of MG in pubertal mice through the GPRC6A/PI3K/AKT/mTOR signalling pathway.

Graduate Student Literature Review: Serotonin and calcium metabolism: A story unfolding

The peripartum period is characterized by dynamic shifts in metabolic, mineral, and immune metabolism as the dairy cow adapts to the demands of lactation. Emphasis over the past decade has been placed on understanding the biology of the large shift in calcium metabolism in particular. Moreover, research has also focused on exploring the role of serotonin during the transition period and lactation and further unraveling its relationship with calcium. This review aimed to demonstrate the integration of calcium physiology during the peripartal period and throughout lactation. More specifically, we sought to discuss the knowledge gained in recent years on calcium metabolism, mammary calcium transport, serotonin metabolism, and the serotonin-calcium axis. Herein we also discuss the challenges and limitations of current research and where that leaves the present understanding of the serotonin-calcium axis as we seek to move forward and continue exploring this interesting relationship.

Mammary mechanobiology - investigating roles for mechanically activated ion channels in lactation and involution

The ability of a mother to produce a nutritionally complete neonatal food source has provided a powerful evolutionary advantage to mammals. Milk production by mammary epithelial cells is adaptive, its release is exquisitely timed, and its own glandular stagnation with the permanent cessation of suckling triggers the cell death and tissue remodeling that enables female mammals to nurse successive progeny. Chemical and mechanical signals both play a role in this process. However, despite this duality of input, much remains unknown about the nature and function of mechanical forces in this organ. Here, we characterize the force landscape in the functionally mature gland and the capacity of luminal and basal cells to experience and exert force. We explore molecular instruments for force-sensing, in particular channel-mediated mechanotransduction, revealing increased expression of Piezo1 in mammary tissue in lactation and confirming functional expression in luminal cells. We also reveal, however, that lactation and involution proceed normally in mice with luminal-specific Piezo1 deletion. These findings support a multifaceted system of chemical and mechanical sensing in the mammary gland, and a protective redundancy that ensures continued lactational competence and offspring survival.

A new molecular risk pathway for postpartum mood disorders: clues from steroid sulfatase-deficient individuals

Postpartum mood disorders develop shortly after childbirth in a significant proportion of women. These conditions are associated with a range of symptoms including abnormally high or low mood, irritability, cognitive disorganisation, disrupted sleep, hallucinations/delusions, and occasionally suicidal or infanticidal ideation; if not treated promptly, they can substantially impact upon the mother's health, mother-infant bonding, and family dynamics. The biological precipitants of such disorders remain unclear, although large changes in maternal immune and hormonal physiology following childbirth are likely to play a role. Pharmacological therapies for postpartum mood disorders can be effective, but may be associated with side effects, concerns relating to breastfeeding, and teratogenicity risks when used prophylactically. Furthermore, most of the drugs that are used to treat postpartum mood disorders are the same ones that are used to treat mood episodes during non-postpartum periods. A better understanding of the biological factors predisposing to postpartum mood disorders would allow for rational drug development, and the identification of predictive biomarkers to ensure that 'at risk' mothers receive earlier and more effective clinical management. We describe new findings relating to the role of the enzyme steroid sulfatase in maternal postpartum behavioural processes, and discuss how these point to a novel molecular risk pathway underlying postpartum mood disorders. Specifically, we suggest that aberrant steroid hormone-dependent regulation of neuronal calcium influx via extracellular matrix proteins and membrane receptors involved in responding to the cell's microenvironment might be important. Testing of this hypothesis might identify novel therapeutic targets and predictive biomarkers.

Got Milk? Identifying and Characterizing Lactation Defects in Genetically-Engineered Mouse Models

The ability to produce and expel milk is important for the health and survival of all mammals. Nevertheless, our understanding of the molecular events underlying the execution of this process remains incomplete. Whilst impaired mammary gland development and lactational competence remains the subject of focused investigations, defects in these events may also be an unintended consequence of genetic manipulation in rodent models. In this technical report, we outline established and emerging methods to characterize lactation phenotypes in genetically-engineered mouse models. We discuss important considerations of common models, optimized conditions for mating and the importance of litter size and standardization. Methods for quantifying milk production and quality, as well as protocols for wholemount preparation, immunohistochemistry and the preparation of RNA and protein lysates are provided. This review is intended to help guide researchers new to the field of mammary gland biology in the systematic analysis of lactation defects and in the preparation of samples for more focused mechanistic investigations.

Developmental Stage-Specific Distribution of Macrophages in Mouse Mammary Gland

Mammary gland development begins in the embryo and continues throughout the reproductive life of female mammals. Tissue macrophages (Mϕs), dependent on signals from the Mϕ colony stimulating factor 1 receptor (CSF1R), have been shown to regulate the generation, regression and regeneration of this organ, which is central for mammalian offspring survival. However, the distribution of Mϕs in the pre- and post-natal mammary gland, as it undergoes distinct phases of development and regression, is unknown or has been inferred from immunostaining of thin tissue sections. Here, we used optical tissue clearing and 3-dimensional imaging of mammary tissue obtained from Csf1r-EGFP mice. Whilst tissue Mϕs were observed at all developmental phases, their abundance, morphology, localization and association with luminal and basal epithelial cells exhibited stage-specific differences. Furthermore, sexual dimorphism was observed at E14.5, when the male mammary bud is severed from the overlying epidermis. These findings provide new insights into the localization and possible functions of heterogeneous tissue Mϕ populations in mammogenesis.