Adipocyte hypertrophy and lipid dynamics underlie mammary gland remodeling after lactation

Exploring the contribution of mammary-derived serotonin on liver and pancreas metabolism during lactation

During lactation, the murine mammary gland is responsible for a significant increase in circulating serotonin. However, the role of mammary-derived serotonin in energy homeostasis during lactation is unclear. To investigate this, we utilized C57/BL6J mice with a lactation and mammary-specific deletion of the gene coding for the rate-limiting enzyme in serotonin synthesis (TPH1, Wap-Cre x TPH1FL/FL) to understand the metabolic contributions of mammary-derived serotonin during lactation. Circulating serotonin was reduced by approximately 50% throughout lactation in Wap-Cre x TPH1FL/FL mice compared to wild-type mice (TPH1FL/FL), with mammary gland and liver serotonin content reduced on L21. The Wap-Cre x TPH1FL/FL mice had less serotonin and insulin immunostaining in the pancreatic islets on L21, resulting in reduced circulating insulin but no changes in glucose. The mammary glands of Wap-Cre x TPH1FL/FL mice had larger mammary alveolar areas, with fewer and smaller intra-lobular adipocytes, and increased expression of milk protein genes (e.g., WAP, CSN2, LALBA) compared to TPH1FL/FL mice. No changes in feed intake, body composition, or estimated milk yield were observed between groups. Taken together, mammary-derived serotonin appears to contribute to the pancreas-mammary cross-talk during lactation with potential implications in the regulation of insulin homeostasis.

Protein Dynamic Landscape during Mouse Mammary Gland Development from Virgin to Pregnant, Lactating, and Involuting Stages

The mammary gland undergoes significant physiological changes as it undergoes a transition from virgin to pregnancy, lactation, and involution. However, the dynamic role of proteins in regulating these processes during mouse mammary gland development has not been thoroughly explored. In this study, we collected mouse mammary gland tissues from mature virgins aged 8-10 weeks (V), day 16 of pregnancy (P16d), day 12 of lactation (L12d), day 1 of forced weaning (FW 1d), and day 3 of forced weaning (FW 3d) stages for analysis using DIA-based quantitative proteomics technology. A total of 3,312 proteins were identified, of which 843 were DAPs that were categorized into nine clusters based on their abundance changes across developmental stages. Notably, DAPs in cluster 2, which peaked at the L12d stage, were primarily associated with mammary gland development and lactation. The protein-protein interaction network revealed that the epidermal growth factor (EGF) was central to this cluster. Our study provides a comprehensive overview of the mouse mammary gland development proteome and identifies some important proteins, such as EGF, Janus kinase 1 (JAK1), and signal transducer and activator of transcription 6 (STAT6) that may serve as potential targets for future research to provide guidelines for a deeper understanding of the developmental biology of mammary glands.

Mutation of SOCS2 induces structural and functional changes in mammary development

Lactation is an essential process for mammals. In sheep, the R96C mutation in suppressor of cytokine signaling 2 (SOCS2) protein is associated with greater milk production and increased mastitis sensitivity. To shed light on the involvement of R96C mutation in mammary gland development and lactation, we developed a mouse model carrying this mutation (SOCS2KI/KI). Mammary glands from virgin adult SOCS2KI/KI mice presented a branching defect and less epithelial tissue, which were not compensated for in later stages of mammary development. Mammary epithelial cell (MEC) subpopulations were modified, with mutated mice having three times as many basal cells, accompanied by a decrease in luminal cells. The SOCS2KI/KI mammary gland remained functional; however, MECs contained more lipid droplets versus fat globules, and milk lipid composition was modified. Moreover, the gene expression dynamic from virgin to pregnancy state resulted in the identification of about 3000 differentially expressed genes specific to SOCS2KI/KI or control mice. Our results show that SOCS2 is important for mammary gland development and milk production. In the long term, this finding raises the possibility of ensuring adequate milk production without compromising animal health and welfare.

Tissue fibrosis associated depletion of lipid-filled cells

Fibrosis is primarily described as the deposition of excessive extracellular matrix, but in many tissues it also involves a loss of lipid or lipid-filled cells. Lipid-filled cells are critical to tissue function and integrity in many tissues including the skin and lungs. Thus, loss or depletion of lipid-filled cells during fibrogenesis, has implications for tissue function. In some contexts, lipid-filled cells can impact ECM composition and stability, highlighting their importance in fibrotic transformation. Recent papers in fibrosis address this newly recognized fibrotic lipodystrophy phenomenon. Even in disparate tissues, common mechanisms are emerging to explain fibrotic lipodystrophy. These findings have implications for fibrosis in tissues composed of fibroblast and lipid-filled cell populations such as skin, lung, and liver. In this review, we will discuss the roles of lipid-containing cells, their reduction/loss during fibrotic transformation, and the mechanisms of that loss in the skin and lungs.

Adipose Tissue in Breast Cancer Microphysiological Models to Capture Human Diversity in Preclinical Models

Female breast cancer accounts for 15.2% of all new cancer cases in the United States, with a continuing increase in incidence despite efforts to discover new targeted therapies. With an approximate failure rate of 85% for therapies in the early phases of clinical trials, there is a need for more translatable, new preclinical in vitro models that include cellular heterogeneity, extracellular matrix, and human-derived biomaterials. Specifically, adipose tissue and its resident cell populations have been identified as necessary attributes for current preclinical models. Adipose-derived stromal/stem cells (ASCs) and mature adipocytes are a normal part of the breast tissue composition and not only contribute to normal breast physiology but also play a significant role in breast cancer pathophysiology. Given the recognized pro-tumorigenic role of adipocytes in tumor progression, there remains a need to enhance the complexity of current models and account for the contribution of the components that exist within the adipose stromal environment to breast tumorigenesis. This review article captures the current landscape of preclinical breast cancer models with a focus on breast cancer microphysiological system (MPS) models and their counterpart patient-derived xenograft (PDX) models to capture patient diversity as they relate to adipose tissue.

SNAT2-mediated regulation of estrogen and progesterone in the proliferation of goat mammary epithelial cells

The development of the goat mammary gland is mainly under the control of ovarian hormones particularly estrogen and progesterone (P4). Amino acids play an essential role in mammary gland development and milk production, and sodium-coupled neutral amino acid transporter 2 (SNAT2) was reported to be expressed in the mammary gland of rats and bovine mammary epithelial cells, which may affect the synthesis of milk proteins or mammary cell proliferation by mediating prolactin, 17β-estradiol (E2) or methionine function. However, whether SNAT2 mediates the regulatory effects of E2 and P4 on the development of the ruminant mammary gland is still unclear. In this study, we show that E2 and P4 could increase the proliferation of goat mammary epithelial cells (GMECs) and regulate SNAT2 mRNA and protein expression in a dose-dependent manner. Further investigation revealed that SNAT2 is abundantly expressed in the mammary gland during late pregnancy and early lactation, while knockdown and overexpression of SNAT2 in GMECs could inhibit or enhance E2- and P4-induced cell proliferation as well as mammalian target of rapamycin (mTOR) signaling. We also found that the accelerated proliferation induced by SNAT2 overexpression in GMECs was suppressed by the mTOR signaling pathway inhibitor rapamycin. This indicates that the regulation of GMECs proliferation mediated by SNAT2 in response to E2 and P4 is dependent on the mTOR signaling pathway. Finally, we found that the total content of the amino acids in GMECs changed after knocking-down and overexpressing SNAT2. In summary, the results demonstrate that the regulatory effects of E2 and P4 on GMECs proliferation may be mediated by the SNAT2-transported amino acid pathway. These results may offer a novel nutritional target for improving the development of the ruminant mammary gland and milk production.

Differentiation of Fibroblasts to Adipocytes in 3D for a Co-culture with Mammary Organoids and Immunohistological Analysis

Mammary epithelial ducts, the main functional compartment of the mammary gland, are embedded in an adipocyte-rich stroma, which is essential for proper mammary gland development, function, and tissue homeostasis. Moreover, the adipocyte compartment has an important role in cancer progression. To better understand cell-to-cell interactions and the role of the adipocytes in the mammary gland, development of proper in vitro models which realistically mimic in vivo conditions has been essential. In this chapter, we describe a simple and effective method for generating mammary gland adipocytes from mammary fibroblasts and their subsequent co-culture with mammary epithelial organoids to further investigate the role of adipocytes in epithelial development and morphogenesis.

Update on Adipose Tissue and Cancer

Adipose tissue is the largest endocrine organ and an accepted contributor to overall energy homeostasis. There is strong evidence linking increased adiposity to the development of 13 types of cancer. With increased adiposity comes metabolic dysfunction and insulin resistance, and increased systemic insulin and glucose support the growth of many cancers, including those of the colon and endometrium. There is also an important direct crosstalk between adipose tissue and various organs. For instance, the healthy development and function of the mammary gland, as well as the development, growth, and progression of breast cancer, are heavily impacted by the breast adipose tissue in which breast epithelial cells are embedded. Cells of the adipose tissue are responsive to external stimuli, including overfeeding, leading to remodeling and important changes in the secretion of factors known to drive the development and growth of cancers. Loss of factors like adiponectin and increased production of leptin, endotrophin, steroid hormones, and inflammatory mediators have been determined to be important mediators of the obesity-cancer link. Obesity is also associated with a structural remodeling of the adipose tissue, including increased localized fibrosis and disrupted angiogenesis that contribute to the development and progression of cancers. Furthermore, tumor cells feed off the adipose tissue, where increased lipolysis within adipocytes leads to the release of fatty acids and stromal cell aerobic glycolysis leading to the increased production of lactate. Both have been hypothesized to support the higher energetic demands of cancer cells. Here, we aim to provide an update on the state of the literature revolving around the role of the adipose tissue in cancer initiation and progression.

A cell transcriptomic profile provides insights into adipocytes of porcine mammary gland across development

BACKGROUND

Studying the composition and developmental mechanisms in mammary gland is crucial for healthy growth of newborns. The mammary gland is inherently heterogeneous, and its physiological function dependents on the gene expression of multiple cell types. Most studies focused on epithelial cells, disregarding the role of neighboring adipocytes.

RESULTS

Here, we constructed the largest transcriptomic dataset of porcine mammary gland cells thus far. The dataset captured 126,829 high-quality nuclei from physiological mammary glands across five developmental stages (d 90 of gestation, G90; d 0 after lactation, L0; d 20 after lactation, L20; 2 d post natural involution, PI2; 7 d post natural involution, PI7). Seven cell types were identified, including epithelial cells, adipocytes, endothelial cells, fibroblasts cells, immune cells, myoepithelial cells and precursor cells. Our data indicate that mammary glands at different developmental stages have distinct phenotypic and transcriptional signatures. During late gestation (G90), the differentiation and proliferation of adipocytes were inhibited. Meanwhile, partly epithelial cells were completely differentiated. Pseudo-time analysis showed that epithelial cells undergo three stages to achieve lactation, including cellular differentiation, hormone sensing, and metabolic activation. During lactation (L0 and L20), adipocytes area accounts for less than 0.5% of mammary glands. To maintain their own survival, the adipocyte exhibited a poorly differentiated state and a proliferative capacity. Epithelial cells initiate lactation upon hormonal stimulation. After fulfilling lactation mission, their undergo physiological death under high intensity lactation. Interestingly, the physiological dead cells seem to be actively cleared by immune cells via CCL21-ACKR4 pathway. This biological process may be an important mechanism for maintaining homeostasis of the mammary gland. During natural involution (PI2 and PI7), epithelial cell populations dedifferentiate into mesenchymal stem cells to maintain the lactation potential of mammary glands for the next lactation cycle.

CONCLUSION

The molecular mechanisms of dedifferentiation, proliferation and redifferentiation of adipocytes and epithelial cells were revealed from late pregnancy to natural involution. This cell transcriptomic profile constitutes an essential reference for future studies in the development and remodeling of the mammary gland at different stages.

She didn't start the fire: Mammary duct epithelial cells suppress adipocyte thermogenesis

Male and female mice display highly divergent responses to cold-induced thermogenic beiging of subcutaneous adipose tissues. Recently in Nature, Patel et al. showed that mammary duct epithelial cells respond to cold-induced sympathetic activity, triggering the secretion of lipocalin 2 (LCN2) to inhibit thermogenic differentiation of adjacent mammary adipocytes.

Mature white adipocyte plasticity during mammary gland remodelling and cancer

Mammary gland growth and differentiation predominantly rely on stromal-epithelial cellular communication. Specifically, mammary adipocytes play a crucial role in ductal morphogenesis, as well as in the proliferation and differentiation of mammary epithelial cells. The process of lactation entails a reduction in the levels of white adipose tissue associated with the MG, allowing for the expansion of milk-producing epithelial cells. Subsequently, during involution and the regression of the milk-producing unit, adipocyte layers resurface, occupying the vacated space. This dynamic phenomenon underscores the remarkable plasticity and expansion of adipose tissue. Traditionally considered terminally differentiated, adipocytes have recently been found to exhibit plasticity in certain contexts. Unraveling the significance of this cell type within the MG could pave the way for novel approaches to reduce the risk of breast cancer and enhance lactation performance. Moreover, a comprehensive understanding of adipocyte trans- and de-differentiation processes holds promise for the development of innovative therapeutic interventions targeting cancer, fibrosis, obesity, type 2 diabetes, and other related diseases. Additionally, adipocytes may find utility in the realm of regenerative medicine. This review article provides a comprehensive examination of recent advancements in our understanding of MG remodelling, with a specific focus on the tissue-specific functions of adipocytes and their role in the development of cancer. By synthesizing current knowledge in this field, it aims to consolidate our understanding of adipocyte biology within the context of mammary gland biology, thereby fostering further research and discovery in this vital area.

Three Dimensional Models of Endocrine Organs and Target Tissues Regulated by the Endocrine System

Immortalized cell lines originating from tumors and cultured in monolayers in vitro display consistent behavior and response, and generate reproducible results across laboratories. However, for certain endpoints, these cell lines behave quite differently from the original solid tumors. Thereby, the homogeneity of immortalized cell lines and two-dimensionality of monolayer cultures deters from the development of new therapies and translatability of results to the more complex situation in vivo. Organoids originating from tissue biopsies and spheroids from cell lines mimic the heterogeneous and multidimensional characteristics of tumor cells in 3D structures in vitro. Thus, they have the advantage of recapitulating the more complex tissue architecture of solid tumors. In this review, we discuss recent efforts in basic and preclinical cancer research to establish methods to generate organoids/spheroids and living biobanks from endocrine tissues and target organs under endocrine control while striving to achieve solutions in personalized medicine.

Targeting adipocyte-immune cell crosstalk to control breast cancer progression

Adipocytes are crucial components of breast cancer and are involved in regulating the progression, therapeutic efficacy, and prognosis of breast cancer patients. Characterized by storing energy and producing a variety of secretory factors, adipocytes are responsible for inducing obesity and regulating the tumor immune activity. Adipocytes communicate with tumor infiltrating immune cells through the secreted adipokines, cytokines, and exosomes in the breast cancer TIME, which shapes the tumor supporting environment to facilitate the immune escape of tumor cells. In-depth studies of the crosstalk between adipocytes and TIME can not only provide a more comprehensive regulatory landscape of TIME, but also be conducive to screening novel targets for future precision targeted therapy. The aim of this review is to discuss recent studies for understanding the role of crosstalk between adipocytes and immune cells in shaping the breast cancer immune microenvironment.

A spatially resolved single-cell genomic atlas of the adult human breast

The adult human breast is comprised of an intricate network of epithelial ducts and lobules that are embedded in connective and adipose tissue1-3. Although most previous studies have focused on the breast epithelial system4-6, many of the non-epithelial cell types remain understudied. Here we constructed the comprehensive Human Breast Cell Atlas (HBCA) at single-cell and spatial resolution. Our single-cell transcriptomics study profiled 714,331 cells from 126 women, and 117,346 nuclei from 20 women, identifying 12 major cell types and 58 biological cell states. These data reveal abundant perivascular, endothelial and immune cell populations, and highly diverse luminal epithelial cell states. Spatial mapping using four different technologies revealed an unexpectedly rich ecosystem of tissue-resident immune cells, as well as distinct molecular differences between ductal and lobular regions. Collectively, these data provide a reference of the adult normal breast tissue for studying mammary biology and diseases such as breast cancer.

Obese Adipocytes Have Altered Redox Homeostasis with Metabolic Consequences

White and brown adipose tissues are organized to form a real organ, the adipose organ, in mice and humans. White adipocytes of obese animals and humans are hypertrophic. This condition is accompanied by a series of organelle alterations and stress of the endoplasmic reticulum. This stress is mainly due to reactive oxygen species activity and accumulation, lending to NLRP3 inflammasome activation. This last causes death of adipocytes by pyroptosis and the formation of large cellular debris that must be removed by macrophages. During their chronic scavenging activity, macrophages produce several secretory products that have collateral consequences, including interference with insulin receptor activity, causing insulin resistance. The latter is accompanied by an increased noradrenergic inhibitory innervation of Langerhans islets with de-differentiation of beta cells and type 2 diabetes. The whitening of brown adipocytes could explain the different critical death size of visceral adipocytes and offer an explanation for the worse clinical consequence of visceral fat accumulation. White to brown transdifferentiation has been proven in mice and humans. Considering the energy-dispersing activity of brown adipose tissue, transdifferentiation opens new therapeutic perspectives for obesity and related disorders.

Mammary adipocyte flow cytometry as a tool to study mammary gland biology

The mammary gland is a vital exocrine organ that has evolved in mammals to secrete milk and provide nutrition to ensure the growth and survival of the neonate The mouse mammary gland displays extraordinary plasticity each time the female undergoes pregnancy and lactation, including a sophisticated process of tertiary branching and alveologenesis to form a branched epithelial tree and subsequently milk-producing alveoli. Upon the cessation of lactation, the gland remodels back to a simple ductal architecture via highly regulated involution processes. At the cellular level, the plasticity is characterised by proliferation of mammary cell populations, differentiation and apoptosis, accompanied by major changes in cell function and morphology. The mammary epithelium requires a specific stromal environment to grow, known as the mammary fat pad. Mammary adipocytes are one of the most prominent cell types in the fat pad, but despite their vast proportion in the tissue and their crucial interaction with epithelial cells, their physiology remains largely unknown. Over the past decade, the need to understand the properties and contribution of mammary adipocytes has become more recognised. However, the development of adequate methods and protocols to study this cellular niche is still lagging, partially due to their fragile nature, the difficulty of isolating them, the lack of reliable cell surface markers and the heterogenous environment in this tissue, which differs from other adipocyte depots. Here, we describe a new rapid and simple flow cytometry protocol specifically designed for the analysis and isolation of mouse mammary adipocytes across mammary gland developmental stages.

The High Level of RANKL Improves IκB/p65/Cyclin D1 Expression and Decreases p-Stat5 Expression in Firm Udder of Dairy Goats

Udder traits, influencing udder health and function, are positively correlated with lactation performance. Among them, breast texture influences heritability and impacts on the milk yield of cattle; however, there is a lack of systematic research on its underlying mechanism in dairy goats in particular. Here, we showed the structure of firm udders with developed connective tissue and smaller acini per lobule during lactation and confirmed that there were lower serum levels of estradiol (E₂) and progesterone (PROG), and higher mammary expression of estrogen nuclear receptor (ER) α and progesterone receptor (PR), in dairy goats with firm udders. The results of transcriptome sequencing of the mammary gland revealed that the downstream pathway of PR, the receptor activator of nuclear factor-kappa B (NF-κB) ligand (RANKL) signal, participated in the formation of firm mammary glands. During the culture of goat mammary epithelial cells (GMECs), high RANKL level additions promote the Inhibitor kappaB (IκB)/p65/Cyclin D1 expression related to cell proliferation and decrease the phosphorylated signal transduction and transcription activator 5 (Stat5) expression related to milk-protein synthesis of GMECs, which is consistent with electron microscope results showing that there are fewer lactoprotein particles in the acinar cavity of a firm mammary. Furthermore, co-culturing with adipocyte-like cells for 7 d is beneficial for the acinar structure formation of GMECs, while there is a slightly negative effect of high RANKL level on it. In conclusion, the results of this study revealed the structure of firm udders structure and confirmed the serum hormone levels and their receptor expression in the mammary glands of dairy goats with firm udders. The underlying mechanism leading to firm udders and a decrease in milk yield were explored preliminarily, which provided an important foundation for the prevention and amelioration of firm udders and improving udder health and milk yield.

Estradiol cycling drives female obesogenic adipocyte hyperplasia

White adipose tissue (WAT) distribution is sex dependent. Adipocyte hyperplasia contributes to WAT distribution in mice driven by cues in the tissue microenvironment, with females displaying hyperplasia in subcutaneous and visceral WAT, while males and ovariectomized females have visceral WAT (VWAT)-specific hyperplasia. However, the mechanism underlying sex-specific hyperplasia remains elusive. Here, transcriptome analysis in female mice shows that high-fat diet (HFD) induces estrogen signaling in adipocyte precursor cells (APCs). Analysis of APCs throughout the estrous cycle demonstrates increased proliferation only when proestrus (high estrogen) coincides with the onset of HFD feeding. We further show that estrogen receptor α (ERα) is required for this proliferation and that estradiol treatment at the onset of HFD feeding is sufficient to drive it. This estrous influence on APC proliferation leads to increased obesity driven by adipocyte hyperplasia. These data indicate that estrogen drives ERα-dependent obesogenic adipocyte hyperplasia in females, exacerbating obesity and contributing to the differential fat distribution between the sexes.

A spatially resolved single cell genomic atlas of the adult human breast

The adult human breast comprises an intricate network of epithelial ducts and lobules that are embedded in connective and adipose tissue. While previous studies have mainly focused on the breast epithelial system, many of the non-epithelial cell types remain understudied. Here, we constructed a comprehensive Human Breast Cell Atlas (HBCA) at single-cell and spatial resolution. Our single-cell transcriptomics data profiled 535,941 cells from 62 women, and 120,024 nuclei from 20 women, identifying 11 major cell types and 53 cell states. These data revealed abundant pericyte, endothelial and immune cell populations, and highly diverse luminal epithelial cell states. Our spatial mapping using three technologies revealed an unexpectedly rich ecosystem of tissue-resident immune cells in the ducts and lobules, as well as distinct molecular differences between ductal and lobular regions. Collectively, these data provide an unprecedented reference of adult normal breast tissue for studying mammary biology and disease states such as breast cancer.

Adipose tissue at single-cell resolution

Adipose tissue exhibits remarkable plasticity with capacity to change in size and cellular composition under physiological and pathophysiological conditions. The emergence of single-cell transcriptomics has rapidly transformed our understanding of the diverse array of cell types and cell states residing in adipose tissues and has provided insight into how transcriptional changes in individual cell types contribute to tissue plasticity. Here, we present a comprehensive overview of the cellular atlas of adipose tissues focusing on the biological insight gained from single-cell and single-nuclei transcriptomics of murine and human adipose tissues. We also offer our perspective on the exciting opportunities for mapping cellular transitions and crosstalk, which have been made possible by single-cell technologies.

Fur removal promotes an earlier expression of involution-related genes in mammary gland of lactating mice

Peak lactation occurs when milk production is at its highest. The factors limiting peak lactation performance have been subject of intense debate. Milk production at peak lactation appears limited by the capacity of lactating females to dissipate body heat generated as a by-product of processing food and producing milk. As a result, manipulations that enhance capacity to dissipate body heat (such as fur removal) increase peak milk production. We investigated the potential correlates of shaving-induced increases in peak milk production in laboratory mice. By transcriptomic profiling of the mammary gland, we searched for the mechanisms underlying experimentally increased milk production and its consequences for mother-young conflict over weaning, manifested by advanced or delayed involution of mammary gland. We demonstrated that shaving-induced increases in milk production were paradoxically linked to reduced expression of some milk synthesis-related genes. Moreover, the mammary glands of shaved mice had a gene expression profile indicative of earlier involution relative to unshaved mice. Once provided with enhanced capacity to dissipate body heat, shaved mice were likely to rear their young to independence faster than unshaved mothers.

Obesity-derived alterations in the lactating mammary gland: Focus on prolactin

Obesity is a modern pandemic with negative consequences in women's reproductive health. Women with overweight and obesity can develop mammary gland alterations that unable exclusive breastfeeding. Obesity associates with a disturbed lactating mammary gland endocrine environment including a decreased action of the hormone prolactin (PRL), the master regulator of lactation. The PRL receptor and the action of PRL are reduced in the mammary gland of lactating rodents fed an obesogenic diet and are contributing factors to impaired lactation in obesity. Also, treatment with PRL improves milk yield in women with lactation insufficiency. This review focuses on the impact of diet-induced obesity in the lactating mammary gland and how obesity impairs the lactogenic action of PRL. Although obesity alters lactation performance in humans and rodents, the responsible mechanisms have been mainly addressed in rodents.

Simultaneous Labeling of Adipogenic and Osteogenic Differentiating Stem Cells for Live Confocal Analysis

Adipocytes and osteoblasts derive from a common mesenchymal progenitor present in a range of connective tissues. Differentiation of the progenitors toward the two cell lineages can be induced in vitro through well-established protocols, and leads to the appearance of lipid-laden adipocytes and osteoblasts embedded in a mineralized matrix. The formation of these two lineages in cell cultures can be monitored using lipophilic dyes such as Oil Red O and substances binding to mineral deposits such as Alizarin Red S, respectively. However, these common staining techniques require cell fixation and are thus incompatible with live analyses. Recently, alternative approaches using vital stains have allowed the dual visualization and fluorescence imaging of adipogenic and osteogenic lineages in live cultures. Here we present the concomitant analysis of cultures containing adipogenic and osteogenic cell types using live staining, combining LipidTox Red and tetracycline with NucRed nuclear counterstain for confocal imaging. This approach can be applied to visualize the kinetics and 3D structure of differentiating mesenchymal cultures over time and highlights the interaction of adipose and mineralized compartments associated with bone marrow stroma.

Neonatal intake of Omega-3 fatty acids enhances lipid oxidation in adipocyte precursors

Establishing metabolic programming begins during fetal and postnatal development, and early-life lipid exposures play a critical role during neonatal adipogenesis. We define how neonatal consumption of a low omega-6 to -3 fatty acid ratio (n6/n3 FA ratio) establishes FA oxidation in adipocyte precursor cells (APCs) before they become adipocytes. In vivo, APCs isolated from mouse pups exposed to the low n6/n3 FA ratio had superior FA oxidation capacity, elevated beige adipocyte mRNAs Ppargc1α, Ucp2, and Runx1, and increased nuclear receptor NR2F2 protein. In vitro, APC treatment with NR2F2 ligand-induced beige adipocyte mRNAs and increased mitochondrial potential but not mass. Single-cell RNA-sequencing analysis revealed low n6/n3 FA ratio yielded more mitochondrial-high APCs and linked APC NR2F2 levels with beige adipocyte signatures and FA oxidation. Establishing beige adipogenesis is of clinical relevance, because fat depots with energetically active, smaller, and more numerous adipocytes improve metabolism and delay metabolic dysfunction.

A tumor-suppressive function for Notch3 in the parous mammary gland

Notch3 promotes mammary luminal cell specification and forced Notch3 activation can induce mammary tumor formation. However, recent studies suggest a tumor-suppressive role for Notch3. Here, we report on Notch3 expression and functional analysis in the mouse mammary gland. Notch3 is expressed in the luminal compartment throughout mammary gland development, but switches to basal cells with initiation of post-lactational involution. Deletion of Notch3 caused a decrease of Notch activation in luminal cells and diminished luminal progenitors at puberty, as well as reduced alveolar progenitors during pregnancy. Parous Notch3−/− mammary glands developed hyperplasia with accumulation of CD24hiCD49flo cells, some of which progressed to invasive tumors with luminal features. Notch3 deletion abolished Notch activation in basal cells during involution, accompanied by altered apoptosis and reduced brown adipocytes, leading to expansion of parity-identified mammary epithelial cells (PI-MECs). Interestingly, the postpartum microenvironment is required for the stem cell activity of Notch3−/− PI-MECs. Finally, high expression of NOTCH3 is associated with prolonged survival in patients with luminal breast cancer. These results highlight an unexpected tumor-suppressive function for Notch3 in the parous mammary gland through restriction of PI-MEC expansion.

Adipocyte plasticity in tissue regeneration, repair, and disease

Mammalian tissue repair forms a scar that fills the injured area with a fibrotic lesion, limiting tissue function. Adipocytes, lipid-filled cells, well-known for energy storage and endocrine functions, can reside adjacent to or within many tissues, and are emerging as critical regulators of tissue repair. In this review, the plasticity and function of adipocytes to tissue repair and fibrosis in four tissues: skin, heart, skeletal muscle, and mammary gland, will be discussed. The dynamic nature of adipocytes as they release bioactive products, lipids, and adipokines, and their ability to form contractile fibroblasts, is emerging as an essential regulator of wound healing and tumorigenesis in multiple tissues. Thus, modulation of adipocytes may provide therapeutic avenues for regenerative medicine and cancer.

A monocyte-leptin-angiogenesis pathway critical for repair post-infection

During infection, inflammatory monocytes are thought to be key for bacterial eradication, but this is hard to reconcile with the large numbers of neutrophils that are recruited for each monocyte that migrates to the afflicted tissue, and the much more robust microbicidal functions of the neutrophils. However, unlike neutrophils, monocytes have the capacity to convert to situationally specific macrophages that may have critical functions beyond infection control^1,2. Here, using a foreign body coated with Staphylococcus aureus and imaging over time from cutaneous infection to wound resolution, we show that monocytes and neutrophils are recruited in similar numbers with low-dose infection but not with high-dose infection, and form a localization pattern in which monocytes surround the infection site, whereas neutrophils infiltrate it. Monocytes did not contribute to bacterial clearance but converted to macrophages that persisted for weeks after infection, regulating hypodermal adipocyte expansion and production of the adipokine hormone leptin. In infected monocyte-deficient mice there was increased persistent hypodermis thickening and an elevated leptin level, which drove overgrowth of dysfunctional blood vasculature and delayed healing, with a thickened scar. Ghrelin, which opposes leptin function³, was produced locally by monocytes, and reduced vascular overgrowth and improved healing post-infection. In sum, we find that monocytes function as a cellular rheostat by regulating leptin levels and revascularization during wound repair.

Identification and profiling of microRNAs involved in the regenerative involution of mammary gland

Regenerative involution is important for the subsequent lactation, but molecular mechanism has not been revealed. The crucial miRNA in tissue development indicates that miRNAs might participate in regenerative involution. In the present study, the mammary tissues of the dairy goats (n = 3) were collected via biopsy at wk-8 (time to dry off), -6, -4, -1, and + 1 relative to lambing for the Hematoxylin and Eosin staining and miRNA sequencing. Alveolar structures collapsed during regenerative involution, but the structures remained intact and distended. Among the 50 miRNA expression trajectories categorized by short time-series expression miner, two significant patterns were clustered. The differentially expressed miRNAs in the two patterns were mainly related to the self-renewal of tissue and enriched in pathways containing vesical-mediated transport, tissue development, tube development, vasculature development and epithelial development. The identification of the miRNA will help in elucidating the regulatory roles of miRNAs in mammary gland development.

Alveolar cells in the mammary gland: lineage commitment and cell death

The mammary gland provides a spectacular example of physiological cell death whereby the cells that produce milk during lactation are removed swiftly, efficiently, and without inducing inflammation upon the cessation of lactation. The milk-producing cells arise primarily during pregnancy and comprise the alveolar lineage that is specified by signalling pathways and factors that are activated in response to pregnancy hormones. There are at least two alveolar sub-lineages, one of which is marked by the presence of binucleate cells that are especially susceptible to programmed cell death during involution. This process of post-lactational regression, or involution, is carefully orchestrated and occurs in two phases, the first results in a rapid switch in cell fate with the secretory epithelial cells becoming phagocytes whereupon they destroy dead and dying cells from milk. This reversible phase is followed by the second phase that is marked by an influx of immune cells and a remodelling of the gland to replace the alveolar cells with re-differentiated adipocytes, resulting in a return to the pre-pregnant state in preparation for any subsequent pregnancies. The mouse mammary gland provides an excellent experimental tool with which to investigate lineage commitment and the mechanisms of programmed cell death that occur in a normal physiological process. Importantly, involution has highlighted a role for lysoptosis, a mechanism of cell death that is mediated by lysosomal cathepsins and their endogenous inhibitors, serpins. In this review, I discuss alveolar lineage commitment during pregnancy and the programmed cell death pathways that destroy these cells during involution.

The immune environment of the mammary gland fluctuates during post-lactational regression and correlates with tumour growth rate

Post-lactational mammary gland regression encompasses extensive programmed cell death and removal of milk-producing epithelial cells, breakdown of extracellular matrix components and redifferentiation of stromal adipocytes. This highly regulated involution process is associated with a transient increased risk of breast cancer in women. Using a syngeneic tumour model, we show that tumour growth is significantly altered depending on the stage of involution at which tumour cells are implanted. Tumour cells injected at day 3 involution grew faster than those in nulliparous mice, whereas tumours initiated at day 6 involution grew significantly slower. These differences in tumour progression correlate with distinct changes in innate immune cells, in particular among F4/80-expressing macrophages and among TCRδ⁺ unconventional T cells. Breast cancer post-pregnancy risk is exacerbated in older first-time mothers and, in our model, initial tumour growth is moderately faster in aged mice compared with young mice. Our results have implications for breast cancer risk and the use of anti-inflammatory therapeutics for postpartum breast cancers.

Summary: Mammary gland involution is associated with dynamic changes in immune cell types and numbers at different stages that correlates with the initial rate of growth of implanted tumour cells.

A microRNA Cluster Controls Fat Cell Differentiation and Adipose Tissue Expansion By Regulating SNCG

The H19X-encoded miR-424(322)/503 cluster regulates multiple cellular functions. Here, it is reported for the first time that it is also a critical linchpin of fat mass expansion. Deletion of this miRNA cluster in mice results in obesity, while increasing the pool of early adipocyte progenitors and hypertrophied adipocytes. Complementary loss and gain of function experiments and RNA sequencing demonstrate that miR-424(322)/503 regulates a conserved genetic program involved in the differentiation and commitment of white adipocytes. Mechanistically, it is demonstrated that miR-424(322)/503 targets γ-Synuclein (SNCG), a factor that mediates this program rearrangement by controlling metabolic functions in fat cells, allowing adipocyte differentiation and adipose tissue enlargement. Accordingly, diminished miR-424(322) in mice and obese humans co-segregate with increased SNCG in fat and peripheral blood as mutually exclusive features of obesity, being normalized upon weight loss. The data unveil a previously unknown regulatory mechanism of fat mass expansion tightly controlled by the miR-424(322)/503 through SNCG.

Fluorescent Genetic Tools for Studying Brown Fat Development and Function in Mice

Techniques to trace and isolate brown adipocyte precursor and adipocytes during development and disease are essential to fully understand brown adipose tissue development and function. Here we report several protocols using the R26R-mTmG reporter mice in thermogenic tissues based on confocal microscopy and fluorescence based flow cytometry. These techniques may be useful to understand the influence of genetic or environmental alterations in brown adipocyte precursors and adipocyte biology.

Short histological kaleidoscope - recent findings in histology. Part I

This article is a review of new advances in histology, concerning either classification or structure of different tissular elements (basement membrane, hemidesmosomes, urothelium, glandular epithelia, adipose tissue, astrocytes), and various organs' constituents (blood-brain barrier, human dental cementum, tubarial salivary glands, hepatic stellate cells, pineal gland, fibroblasts of renal interstitium, Leydig testicular cells, ovarian hilar cells), as well as novel biotechnological techniques (tissue engineering in angiogenesis), recently introduced.

Rhubarb hydroxyanthraquinones act as antiobesity agents to inhibit adipogenesis and enhance lipolysis

Rhubarb as an herbal medicine has been shown to exhibit antiadipogenic activity. This study evaluated and compared the lipid-lowering activity of five rhubarb hydroxyanthraquinones (HAQs), including chrysophanol, aloe emodin, emodin, physcion, and rhein, aiming to identify candidate compounds for obesity treatment. Examination of the antiobesity effects of HAQs in 3T3-L1 adipocytes and high-fat diet (HFD)-induced obese rats showed that these anthraquinone compounds inhibited lipid accumulation in 3T3-L1 cells before and after differentiation. Emodin and rhein showed greater inhibition than the other compounds; dosage at 50 μM reduced intracellular triglyceride (TG) by about 30% in the differentiated adipocytes. Both compounds also revealed lipolytic effects to increase glycerol release from adipocytes. Adipokine overexpression induced by differentiation was downregulated by emodin and rhein through mitogen-activated protein kinase (MAPK) signaling. Despite their structural similarity, emodin and rhein exhibited different mechanisms on adipogenesis and lipid metabolism. Rhein restrained lipid deposition by controlling adipogenic transcriptional factors and lipolytic lipases during differentiation. The lipid-lowering effects of emodin did not use these pathways but reduced levels of lipogenic enzymes. HFD consumption in rats significantly increased body weight, visceral fat mass and adipocyte size, which were attenuated by intraperitoneal delivery of emodin or rhein. Rhein showed greater amelioration of obesity than emodin, decreasing plasma cholesterol by 29% and 14%, respectively. HAQs also suppressed cytokine upregulation in the liver and adipose tissues of obese rats. Rhein is a potential antiobesity agent through its ability to regulate obesity-associated adipogenesis, lipolysis and inflammation.

Bone marrow adiposity and the hematopoietic niche: A historical perspective of reciprocity, heterogeneity, and lineage commitment

PURPOSE

Here we review the current knowledge on bone marrow adipocytes (BMAds) as active contributors to the regulation of the hematopoietic niche, and as potentially pivotal players in the progression of hematological malignancies. We highlight the hierarchical and functional heterogeneity of the adipocyte lineage within the bone marrow, and how potentially different contexts dictate their interactions with hematopoietic populations.

RECENT FINDINGS

Growing evidence associates the adipocyte lineage with important functions in hematopoietic regulation within the BM niche. Initially proposed to serve as negative regulators of the hematopoietic microenvironment, studies have also demonstrated that BMAds positively influence the survival and maintenance of hematopoietic stem cells (HSCs). These seemingly incongruous findings may at least be partially explained by stage-specificity across the adipocytic differentiation axis and by BMAds subtypes, suggesting that the heterogeneity of these populations allows for differential context-based interactions. One such distinction relies on the location of adipocytes. Constitutive bone marrow adipose tissue (cBMAT) historically associates to the "yellow" marrow containing so-called "stable" BMAs larger in size, less responsive to stimuli, and linked to HSC quiescence. On the other hand, regulated bone marrow adipose tissue (rBMAT)-associated adipocytes, also referred to as "labile" are smaller, more responsive to hematopoietic demand and strategically situated in hematopoietically active regions of the skeleton. Here we propose a model where the effect of distinct BM stromal cell populations (BMSC) in hematopoiesis is structured along the BMSC-BMAd differentiation axis, and where the effects on HSC maintenance versus hematopoietic proliferation are segregated. In doing so, it is possible to explain how recently identified, adipocyte-primed leptin receptor-expressing, CXCL12-high adventitial reticular cells (AdipoCARs) and marrow adipose lineage precursor cells (MALPs) best support active hematopoietic cell proliferation, while adipose progenitor cells (APCs) and maturing BMAd gradually lose the capacity to support active hematopoiesis, favoring HSC quiescence. Implicated soluble mediators include MCP-1, PAI-1, NRP1, possibly DPP4 and limiting availability of CXCL12 and SCF. How remodeling occurs within the BMSC-BMAd differentiation axis is yet to be elucidated and will likely unravel a three-way regulation of the hematopoietic, bone, and adipocytic compartments orchestrated by vascular elements. The interaction of malignant hematopoietic cells with BMAds is precisely contributing to unravel specific mechanisms of remodeling.

SUMMARY

BMAds are important operative components of the hematopoietic microenvironment. Their heterogeneity directs their ability to exert a range of regulatory capacities in a manner dependent on their hierarchical, spatial, and biological context. This complexity highlights the importance of (i) developing experimental tools and nomenclature adapted to address stage-specificity and heterogeneity across the BMSC-BMAd differentiation axis when reporting effects in hematopoiesis, (ii) interpreting gene reporter studies within this framework, and (iii) quantifying changes in all three compartments (hematopoiesis, adiposity and bone) when addressing interdependency.

Mammary gland adipocytes in lactation cycle, obesity and breast cancer

The mammary gland (MG) is an exocrine gland present in female mammals responsible for the production and secretion of milk during the process of lactation. It is mainly composed by epithelial cells and adipocytes. Among the features that make the MG unique there are 1) its highly plastic properties displayed during pregnancy, lactation and involution (all steps belonging to the lactation cycle) and 2) its requirement to grow in close association with adipocytes which are absolutely necessary to ensure MG's proper development at puberty and remodeling during the lactation cycle. Although MG adipocytes play such a critical role for the gland development, most of the studies have focused on its epithelial component only, leaving the role of the neighboring adipocytes largely unexplored. In this review we aim to describe evidences regarding MG's adipocytes role and properties in physiologic conditions (gland development and lactation cycle), obesity and breast cancer, emphasizing the existing gaps in the literature which deserve further investigation.

How should we define mammary stem cells?

Mammary stem cells (MaSCs) have been defined by cell surface marker expression and their ability to repopulate a cleared fat pad, a capacity now known to result from reprogramming upon transplantation. Furthermore, lineage-tracing studies have provoked controversy as to whether MaSCs are unipotent or bi/multipotent. Various innovative experimental approaches, including single-cell RNA sequencing (scRNA-Seq), epigenetic analyses, deep tissue and live imaging, and advanced mouse models, have provided new and unexpected insights into stem and progenitor cells; thus, it is now timely to reappraise our concept of the MaSC hierarchy. Here, I highlight misconceptions, suggest definitions of stem and progenitor cells, and propose a way forward in our search for an understanding of MaSCs.

A Robust Mammary Organoid System to Model Lactation and Involution-like Processes

The mammary gland is a highly dynamic tissue that changes throughout reproductive life, including growth during puberty and repetitive cycles of pregnancy and involution. Mammary gland tumors represent the most common cancer diagnosed in women worldwide. Studying the regulatory mechanisms of mammary gland development is essential for understanding how dysregulation can lead to breast cancer initiation and progression. Three-dimensional (3D) mammary organoids offer many exciting possibilities for the study of tissue development and breast cancer. In the present protocol derived from Sumbal et al., we describe a straightforward 3D organoid system for the study of lactation and involution ex vivo. We use primary and passaged mouse mammary organoids stimulated with fibroblast growth factor 2 (FGF2) and prolactin to model the three cycles of mouse mammary gland lactation and involution processes. This 3D organoid model represents a valuable tool to study late postnatal mammary gland development and breast cancer, in particular postpartum-associated breast cancer. Graphic abstract: Mammary gland organoid isolation and culture procedures.

Lipofilling in Breast Oncological Surgery: A Safe Opportunity or Risk for Cancer Recurrence?

Lipofilling (LF) is a largely employed technique in reconstructive and esthetic breast surgery. Over the years, it has demonstrated to be extremely useful for treatment of soft tissue defects after demolitive or conservative breast cancer surgery and different procedures have been developed to improve the survival of transplanted fat graft. The regenerative potential of LF is attributed to the multipotent stem cells found in large quantity in adipose tissue. However, a growing body of pre-clinical evidence shows that adipocytes and adipose-derived stromal cells may have pro-tumorigenic potential. Despite no clear indication from clinical studies has demonstrated an increased risk of cancer recurrence upon LF, these observations challenge the oncologic safety of the procedure. This review aims to provide an updated overview of both the clinical and the pre-clinical indications to the suitability and safety of LF in breast oncological surgery. Cellular and molecular players in the crosstalk between adipose tissue and cancer are described, and heterogeneous contradictory results are discussed, highlighting that important issues still remain to be solved to get a clear understanding of LF safety in breast cancer patients.

Single-cell transcriptomics reveals involution mimicry during the specification of the basal breast cancer subtype

Basal breast cancer is associated with younger age, early relapse, and a high mortality rate. Here, we use unbiased droplet-based single-cell RNA sequencing (RNA-seq) to elucidate the cellular basis of tumor progression during the specification of the basal breast cancer subtype from the luminal progenitor population in the MMTV-PyMT (mouse mammary tumor virus-polyoma middle tumor-antigen) mammary tumor model. We find that basal-like cancer cells resemble the alveolar lineage that is specified upon pregnancy and encompass the acquisition of an aberrant post-lactation developmental program of involution that triggers remodeling of the tumor microenvironment and metastatic dissemination. This involution mimicry is characterized by a highly interactive multicellular network, with involution cancer-associated fibroblasts playing a pivotal role in extracellular matrix remodeling and immunosuppression. Our results may partially explain the increased risk and poor prognosis of breast cancer associated with childbirth.

The Cellular Organization of the Mammary Gland: Insights From Microscopy

Despite rapid advances in our knowledge of the cellular heterogeneity and molecular regulation of the mammary gland, how these relate to 3D cellular organization remains unclear. In addition to hormonal regulation, mammary gland development and function is directed by para- and juxtacrine signaling among diverse cell-types, particularly the immune and mesenchymal populations. Precise mapping of the cellular landscape of the breast will help to decipher this complex coordination. Imaging of thin tissue sections has provided foundational information about cell positioning in the mammary gland and now technological advances in tissue clearing and subcellular-resolution 3D imaging are painting a more complete picture. In particular, confocal, light-sheet and multiphoton microscopy applied to intact tissue can fully capture cell morphology, position and interactions, and have the power to identify spatially rare events. This review will summarize our current understanding of mammary gland cellular organization as revealed by microscopy. We focus on the mouse mammary gland and cover a broad range of immune and stromal cell types at major developmental stages and give insights into important tissue niches and cellular interactions.

Characterization of Gene Expression Signatures for the Identification of Cellular Heterogeneity in the Developing Mammary Gland

The developing mammary gland depends on several transcription-dependent networks to define cellular identities and differentiation trajectories. Recent technological advancements that allow for single-cell profiling of gene expression have provided an initial picture into the epithelial cellular heterogeneity across the diverse stages of gland maturation. Still, a deeper dive into expanded molecular signatures would improve our understanding of the diversity of mammary epithelial and non-epithelial cellular populations across different tissue developmental stages, mouse strains and mammalian species. Here, we combined differential mammary gland fractionation approaches and transcriptional profiles obtained from FACS-isolated mammary cells to improve our definitions of mammary-resident, cellular identities at the single-cell level. Our approach yielded a series of expression signatures that illustrate the heterogeneity of mammary epithelial cells, specifically those of the luminal fate, and uncovered transcriptional changes to their lineage-defined, cellular states that are induced during gland development. Our analysis also provided molecular signatures that identified non-epithelial mammary cells, including adipocytes, fibroblasts and rare immune cells. Lastly, we extended our study to elucidate expression signatures of human, breast-resident cells, a strategy that allowed for the cross-species comparison of mammary epithelial identities. Collectively, our approach improved the existing signatures of normal mammary epithelial cells, as well as elucidated the diversity of non-epithelial cells in murine and human breast tissue. Our study provides a useful resource for future studies that use single-cell molecular profiling strategies to understand normal and malignant breast development.

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.

Effects of Sphingosine-1-Phosphate on Cell Viability, Differentiation, and Gene Expression of Adipocytes

Sphingosine-1-phosphate (S1P) is a highly potent sphingolipid metabolite, which controls numerous physiological and pathological process via its extracellular and intracellular functions. The breast is mainly composed of epithelial cells (mammary gland) and adipocytes (stroma). Adipocytes play an important role in regulating the normal functions of the breast. Compared to the vast amount studies on breast epithelial cells, the functions of S1P in breast adipocytes are much less known. Thus, in the current study, we used human preadipocyte cell lines SGBS and mouse preadipocyte cell line 3T3-L1 as in vitro models to evaluate the effects of S1P on cell viability, differentiation, and gene expression in adipocytes. Our results showed that S1P increased cell viability in SGBS and 3T3-L1 preadipocytes but moderately reduced cell viability in differentiated SGBS and 3T3-L1 adipocytes. S1P was also shown to inhibit adipogenic differentiation of SGBS and 3T3-L1 at concentration higher than 1000 nM. Transcriptome analyses showed that S1P was more influential on gene expression in differentiated adipocytes. Furthermore, our network analysis in mature adipocytes showed that the upregulated DEGs (differentially expressed genes) were related to regulation of lipolysis, PPAR (peroxisome proliferator-activated receptor) signaling, alcoholism, and toll-like receptor signaling, whereas the downregulated DEGs were overrepresented in cytokine-cytokine receptor interaction, focal adhesion, starch and sucrose metabolism, and nuclear receptors pathways. Together previous studies on the functions of S1P in breast epithelial cells, the current study implicated that S1P may play a critical role in modulating the bidirectional regulation of adipocyte-extracellular matrix-epithelial cell axis and maintaining the normal physiological functions of the breast.

Mammary development in the embryo and adult: new insights into the journey of morphogenesis and commitment

The mammary gland is a unique tissue and the defining feature of the class Mammalia. It is a late-evolving epidermal appendage that has the primary function of providing nutrition for the young, although recent studies have highlighted additional benefits of milk including the provision of passive immunity and a microbiome and, in humans, the psychosocial benefits of breastfeeding. In this Review, we outline the various stages of mammary gland development in the mouse, with a particular focus on lineage specification and the new insights that have been gained by the application of recent technological advances in imaging in both real-time and three-dimensions, and in single cell RNA sequencing. These studies have revealed the complexity of subpopulations of cells that contribute to the mammary stem and progenitor cell hierarchy and we suggest a new terminology to distinguish these cells.

Fibroblasts: The grey eminence of mammary gland development

The essential role of mammary gland stroma in the regulation of mammary epithelial development, function, and cancer has long been recognized. Only recently, though, the functions of individual stromal cell populations have begun to become more clarified. Mammary fibroblasts have emerged as master regulators and modulators of epithelial cell behavior through paracrine signaling, extracellular matrix production and remodeling, and through regulation of other stromal cell types. In this review article, we summarize the crucial studies that helped to untangle the roles of fibroblasts in mammary gland development. Furthermore, we discuss the origin, heterogeneity, and plasticity of mammary fibroblasts during mammary development and cancer progression.

Studying Adipose Tissue in the Breast Tumor Microenvironment In Vitro: Progress and Opportunities

BACKGROUND

The breast cancer microenvironment contains a variety of stromal cells that are widely implicated in worse patient outcomes. While many in vitro models of the breast tumor microenvironment have been published, only a small fraction of these feature adipocytes. Adipocytes are a cell type increasingly recognized to have complex functions in breast cancer.

METHODS

In this review, we examine findings from recent examples of in vitro experiments modeling adipocytes within the local breast tumor microenvironment.

RESULTS

Both two-dimensional and three-dimensional models of adipocytes in the breast tumor microenvironment are covered in this review and both have uncovered interesting phenomena related to breast tumor progression.

CONCLUSION

Certain aspects of breast cancer and associated adipocyte biology: extracellular matrix effects, cell-cell contact, and physiological mass transport can only be examined with a three-dimensional culture platform. Opportunities remain for innovative improvements to be made to in vitro models that further increase what is known about adipocytes during breast cancer progression.

Effect of Breast Cancer and Adjuvant Therapy on Adipose-Derived Stromal Cells: Implications for the Role of ADSCs in Regenerative Strategies for Breast Reconstruction

Tissue engineering using Adipose Derived Stromal Cells (ADSCs) has emerged as a novel regenerative medicine approach to replace and reconstruct soft tissue damaged or lost as a result of disease process or therapeutic surgical resection. ADSCs are an attractive cell source for soft tissue regeneration due to the fact that they are easily accessible, multipotent, non-immunogenic and pro-angiogenic. ADSC based regenerative strategies have been successfully translated to the clinical setting for the treatment of Crohn's fistulae, musculoskeletal pathologies, wound healing, and cosmetic breast augmentation (fat grafting). ADSCs are particularly attractive as a source for adipose tissue engineering as they exhibit preferential differentiation to adipocytes and support maintenance of mature adipose graft volume. The potential for reconstruction with an autologous tissue sources and a natural appearance and texture is particularly appealing in the setting of breast cancer; up to 40% of patients require mastectomy for locoregional control and current approaches to post-mastectomy breast reconstruction (PMBR) are limited by the potential for complications at the donor and reconstruction sites. Despite their potential, the use of ADSCs in breast cancer patients is controversial due to concerns regarding oncological safety. These concerns relate to the regeneration of tissue at a site where a malignancy has been treated and the impact this may have on stimulating local disease recurrence or dissemination. Pre-clinical data suggest that ADSCs exhibit pro-oncogenic characteristics and are involved in stimulating progression, and growth of tumour cells. However, there have been conflicting reports on the oncologic outcome, in terms of locoregional recurrence, for breast cancer patients in whom ADSC enhanced fat grafting was utilised as an alternative to reconstruction for small volume defects. A further consideration which may impact the successful translation of ADSC based regenerative strategies for post cancer reconstruction is the potential effects of cancer therapy. This review aims to address the effect of malignant cells, adjuvant therapies and patient-specific factors that may influence the success of regenerative strategies using ADSCs for post cancer tissue regeneration.