Fibroblast-induced mammary epithelial branching depends on fibroblast contractility

Embryonic Mammary Gland Morphogenesis

Embryonic mammary gland development unfolds with the specification of bilateral mammary lines, thereafter progressing through placode, bud, and sprout stages before branching morphogenesis. Extensive epithelial-mesenchymal interactions guide morphogenesis from embryogenesis to adulthood. Two distinct mesenchymal tissues are involved, the primary mammary mesenchyme that harbors mammary inductive capacity, and the secondary mesenchyme, the precursor of the adult stroma. Placode and bud stages are morphologically similar with other ectodermal appendages like the hair follicle, reflecting the mammary gland's assumed evolutionary origin from an ancestral hair follicle-associated glandular unit. The shared features extend to signalling cascades such as the Wnt/β-catenin, fibroblast growth factor (Fgf), and ectodysplasin (Eda) pathways, while pathways unique to mammary gland include parathyroid hormone-like hormone (Pthlh) signalling and Hedgehog activity suppression. Mammary gland branching is highly non-stereotypic, achieved by the dynamic use of two distinct modes of branching: tip bifurcation and side branching and stochastic branch point formation. The cellular mechanisms driving the initial morphogenetic steps are slowly beginning to be unravelled. During placode and bud stages, mammary primordium predominantly grows through cell influx, while sprouting correlates with heightened proliferation. Branch elongation is driven by directional cell migration combined with differential cell motility and proliferation supplying the reservoir of migratory cells, whereas a bifurcating tip is associated with localized repression of the cell cycle and cell motility. Numerous similarities exist between embryonic programs and breast tumorigenesis, spanning cellular plasticity, epithelial-stromal interactions, and molecular regulators. Understanding embryonic mammogenesis may provide insights into how normal developmental processes can go awry, leading to malignancy, or how they can be reversed to prevent cancer progression.

Hormone-responsive progenitors have a unique identity and exhibit high motility during mammary morphogenesis

Hormone-receptor-positive (HR+) luminal cells largely mediate the response to estrogen and progesterone during mammary gland morphogenesis. However, there remains a lack of consensus on the precise nature of the precursor cells that maintain this essential HR+ lineage. Here we refine the identification of HR+ progenitors and demonstrate their unique regenerative capacity compared to mature HR+ cells. HR+ progenitors proliferate but do not expand, suggesting rapid differentiation. Subcellular resolution, 3D intravital microscopy was performed on terminal end buds (TEBs) during puberty to dissect the contribution of each luminal lineage. Surprisingly, HR+ TEB progenitors were highly elongated and motile compared to columnar HR- progenitors and static, conoid HR+ cells within ducts. This dynamic behavior was also observed in response to hormones. Development of an AI model for motility dynamics analysis highlighted stark behavioral changes in HR+ progenitors as they transitioned to mature cells. This work provides valuable insights into how progenitor behavior contributes to mammary morphogenesis.

Differential Effects of Confinement on the Dynamics of Normal and Tumor-Derived Pancreatic Ductal Organoids

Pancreatic ductal adenocarcinoma (PDAC) is a cancer of the epithelia comprising the ductal network of the pancreas. During disease progression, PDAC tumors recruit fibroblasts that promote fibrosis, increasing local tissue stiffness and subjecting epithelial cells to increased compressive forces. Previous in vitro studies have documented cytoskeletal and nuclear adaptation following compressive stresses in two-dimensional (2D) and three-dimensional (3D) environments. However, a comparison of the responses of normal and tumor-derived ductal epithelia to physiologically relevant confinement remains underexplored, especially in 3D organoids. Here we control confinement with an engineered 3D microenvironment composed of Matrigel mixed with a low yield stress granular microgel. Normal and tumor-derived murine pancreas organoids (normal and tumor) were cultured for 48 h within this composite 3D environment or in pure Matrigel to investigate the effects of confinement on morphogenesis and lumen expansion. In confinement, tumor organoids (mT) formed a lumen that expanded rapidly, whereas normal organoids (mN) expanded more slowly. Moreover, a majority of normal organoids in more-confined conditions exhibited an inverted apicobasal polarity compared to those in less-confined conditions. Tumor organoids exhibited a collective "pulsing" behavior that increased in confinement. These pulses generated forces sufficient to locally overcome the yield stress of the microgels in the direction of organoid expansion. Normal organoids more commonly exhibit unidirectional rotation. Our in vitro microgel confinement platform enabled the discovery of two distinct modes of collective force generation in organoids that may shed light on the mutual interactions between tumors and the microenvironment. These insights into in vitro dynamics may deepen our understanding of how the confinement of healthy cells within a fibrotic tumor niche disrupts tissue organization and function in vivo.

Volumetric analysis of the terminal ductal lobular unit architecture and cell phenotypes in the human breast

The major lactiferous ducts of the human breast branch out and end at terminal ductal lobular units (TDLUs). Despite their functional and clinical importance, the three-dimensional (3D) architecture of TDLUs has remained undetermined. Our quantitative and volumetric imaging of healthy human breast tissue demonstrates that highly branched TDLUs, which exhibit increased proliferation, are uncommon in the resting tissue regardless of donor age, parity, or hormonal contraception. Overall, TDLUs have a consistent shape and branch parameters, and they contain a main subtree that dominates in bifurcation events and exhibits a more duct-like keratin expression pattern. Simulation of TDLU branching morphogenesis in three dimensions suggests that evolutionarily conserved mechanisms regulate mammary gland branching in humans and mice despite their anatomical differences. In all, our data provide structural insight into 3D anatomy and branching of the human breast and exemplify the power of volumetric imaging in gaining a deeper understanding of breast biology.

Perimenopausal and Menopausal Mammary Glands In A 4-Vinylcyclohexene Diepoxide Mouse Model

As both perimenopausal and menopausal periods are recognized critical windows of susceptibility for breast carcinogenesis, development of a physiologically relevant model has been warranted. The traditional ovariectomy model causes instant removal of the entire hormonal repertoire produced by the ovary, which does not accurately approximate human natural menopause with gradual transition. Here, we characterized the mammary glands of 4-vinylcyclohexene diepoxide (VCD)-treated animals at different time points, revealing that the model can provide the mammary glands with both perimenopausal and menopausal states. The perimenopausal gland showed moderate regression in ductal structure with no responsiveness to external hormones, while the menopausal gland showed severe regression with hypersensitivity to hormones. Leveraging the findings on the VCD model, effects of a major endocrine disruptor (polybrominated diphenyl ethers, PBDEs) on the mammary gland were examined during and after menopausal transition, with the two exposure modes; low-dose, chronic (environmental) and high-dose, subacute (experimental). All conditions of PBDE exposure did not augment or compromise the macroscopic ductal reorganization resulting from menopausal transition and/or hormonal treatments. Single-cell RNA sequencing revealed that the experimental PBDE exposure during the post-menopausal period caused specific transcriptomic changes in the non-epithelial compartment such as Errfi1 upregulation in fibroblasts. The environmental PBDE exposure resulted in similar transcriptomic changes to a lesser extent. In summary, the VCD mouse model provides both perimenopausal and menopausal windows of susceptibility for the breast cancer research community. PBDEs, including all tested models, may affect the post-menopausal gland including impacts on the non-epithelial compartments.

Application of amphiregulin in IVM culture of immature human oocytes and pre-insemination culture for COCs in IVF cycles

Background

Amphiregulin (AR) is a growth factor that resembles the epidermal growth factor (EGF) and serves various functions in different cells. However, no systematic studies or reports on the role of AR in human oocytes have currently been performed or reported. This study aimed to explore the role of AR in human immature oocytes during in vitro maturation (IVM) and in vitro fertilization (IVF) in achieving better embryonic development and to provide a basis for the development of a pre-insemination culture medium specific for cumulus oocyte complexes (COCs).

Methods

First, we examined the concentration of AR in the follicular fluid (FF) of patients who underwent routine IVF and explored the correlation between AR levels and oocyte maturation and subsequent embryonic development. Second, AR was added to the IVM medium to culture immature oocytes and investigate whether AR could improve the effects of IVM. Finally, we pioneered the use of a fertilization medium supplemented with AR for the pre-insemination culture of COCs to explore whether the involvement of AR can promote the maturation and fertilization of IVF oocytes, as well as subsequent embryonic development.

Results

A total of 609 FF samples were examined, and a positive correlation between AR levels and blastocyst formation was observed. In our IVM study, the development potential and IVM rate of immature oocytes, as well as the fertilization rate of IVM oocytes in the AR-added groups, were ameliorated significantly compared to the control group (All P < 0.05). Only the IVM-50 group had a significantly higher blastocyst formation rate than the control group (P < 0.05). In the final IVF study, the maturation, fertilization, high-quality embryo, blastocyst formation, and high-quality blastocyst rates of the AR-added group were significantly higher than those of the control group (All P < 0.05).

Conclusion

AR levels in the FF positively correlated with blastocyst formation, and AR involvement in pre-insemination cultures of COCs can effectively improve laboratory outcomes in IVF. Furthermore, AR can directly promote the in vitro maturation and developmental potential of human immature oocytes at an optimal concentration of 50 ng/ml.

Fibroblast-Epithelium Co-culture Methods Using Epithelial Organoids and Cell Line-Derived Spheroids

Fibroblasts are an integral cell type of mammary gland stroma, which plays crucial roles in development, homeostasis, and tumorigenesis of mammary epithelium. Fibroblasts produce and remodel extracellular matrix proteins and secrete a plethora of paracrine signals, which instruct both epithelial and other stromal cells of the mammary gland through mechanisms, which have not been fully understood. To enable deciphering of the intricate fibroblast-epithelial interactions, we developed several 3D co-culture methods. In this chapter, we describe methods for establishment of various types of embedded 3D co-cultures of mammary fibroblasts with mammary epithelial organoids, mammary tumor organoids, or breast cancer spheroids to investigate the role of fibroblasts in mammary epithelial development, morphogenesis, and tumorigenesis. The co-culture types include dispersed, aggregated, and transwell cultures.