Three-dimensional mammary primary culture model systems

Insulin regulates human mammosphere development and function

Assessing the role of lactogenic hormones in human mammary gland development is limited due to issues accessing tissue samples and so development of a human in vitro three-dimensional mammosphere model with functions similar to secretory alveoli in the mammary gland can aid to overcome this shortfall. In this study, a mammosphere model has been characterised using human mammary epithelial cells grown on either mouse extracellular matrix or agarose and showed insulin is essential for formation of mammospheres. Insulin was shown to up-regulate extracellular matrix genes. Microarray analysis of these mammospheres revealed an up-regulation of differentiation, cell-cell junctions, and cytoskeleton organisation functions, suggesting mammosphere formation may be regulated through ILK signalling. Comparison of insulin and IGF-1 effects on mammosphere signalling showed that although IGF-1 could induce spherical structures, the cells did not polarise correctly as shown by the absence of up-regulation of polarisation genes and did not induce the expression of milk protein genes. This study demonstrated a major role for insulin in mammary acinar development for secretory differentiation and function indicating the potential for reduced lactational efficiency in women with obesity and gestational diabetes.

Luminal MCF-12A & myoepithelial-like Hs 578Bst cells form bilayered acini similar to human breast

The epithelium's functional unit is the bilayered acinus, made of a layer of luminal cells, surrounded by a layer of basal cells mainly composed of myoepithelial cells.

Aim

The aim of this study was to develop a reproducible and manipulable 3D co-culture model of the bilayered acinus in vitro to study the interactions between the two layers.

Materials & methods

Two different combinations of cell lines were co-cultured in Matrigel: SCp2 and SCg6 mice cells, or MCF-12A and Hs 578Bst human cell lines.

Results

Confocal microscopy analysis showed that only MCF-12A and Hs 578Bst cells could form some bilayered acini. This in vitro bilayered acini model will allow us to understand the role of interactions between luminal and myoepithelial cells in the normal breast development.

Engineering Three-dimensional Epithelial Tissues Embedded within Extracellular Matrix

The architecture of branched organs such as the lungs, kidneys, and mammary glands arises through the developmental process of branching morphogenesis, which is regulated by a variety of soluble and physical signals in the microenvironment. Described here is a method created to study the process of branching morphogenesis by forming engineered three-dimensional (3D) epithelial tissues of defined shape and size that are completely embedded within an extracellular matrix (ECM). This method enables the formation of arrays of identical tissues and enables the control of a variety of environmental factors, including tissue geometry, spacing, and ECM composition. This method can also be combined with widely used techniques such as traction force microscopy (TFM) to gain more information about the interactions between cells and their surrounding ECM. The protocol can be used to investigate a variety of cell and tissue processes beyond branching morphogenesis, including cancer invasion.

Stromal-epithelial cell interactions and alteration of branching morphogenesis in macromastic mammary glands

True macromastia is a rare but disabling condition characterized by massive breast growth. The aetiology and pathogenic mechanisms for this disorder remain largely unexplored because of the lack of in vivo or in vitro models. Previous studies suggested that regulation of epithelial cell growth and development by oestrogen was dependent on paracrine growth factors from the stroma. In this study, a co-culture model containing epithelial and stromal cells was used to investigate the interactions of these cells in macromastia. Epithelial cell proliferation and branching morphogenesis were measured to assess the effect of macromastic stromal cells on epithelial cells. We analysed the cytokines secreted by stromal cells and identified molecules that were critical for effects on epithelial cells. Our results indicated a significant increase in cell proliferation and branching morphogenesis of macromastic and non-macromastic epithelial cells when co-cultured with macromastic stromal cells or in conditioned medium from macromastic stromal cells. Hepatocyte growth factor (HGF) is a key factor in epithelial–stromal interactions of macromastia-derived cell cultures. Blockade of HGF with neutralizing antibodies dramatically attenuated epithelial cell proliferation in conditioned medium from macromastic stromal cells. The epithelial–stromal cell co-culture model demonstrated reliability for studying interactions of mammary stromal and epithelial cells in macromastia. In this model, HGF secreted by macromastic stromal cells was found to play an important role in modifying the behaviour of co-cultured epithelial cells. This model allows further studies to investigate basic cellular and molecular mechanisms in tissue from patients with true breast hypertrophy.

In vitro methods to culture primary human breast epithelial cells

Current evidence suggests that much like leukemia, breast tumors are maintained by a small subpopulation of tumor cells that have stem cell properties. These cancer stem cells are envisaged to be responsible for tumor formation and relapse. Therefore, knowledge about their nature will provide a platform to develop therapies to eliminate these breast cancer stem cells. This concept highlights the need to understand the mechanisms that regulate the normal functions of the breast stem cells and their immediate progeny as alterations to these same mechanisms can cause these primitive cells to act as cancer stem cells. The study of the primitive cell functions relies on the ability to isolate them from primary sources of breast tissue. This chapter describes processing of discarded tissue from reduction mammoplasty samples as sources of normal primary human breast epithelial cells and describes cell culture systems to grow single-cell suspensions prepared from these reduction samples in vitro.

Hormone-responsive 3D multicellular culture model of human breast tissue

A hormone-responsive 3D human tissue-like culture system was developed in which human primary mammary epithelial cells (MECs) were co-cultured with two types of predominant mammary stromal cells on silk protein scaffolds. Silk porous scaffolds with incorporated extracellular matrix provided a compatible environment for epithelial structure morphogenesis and differentiation. The presence of stromal cells promoted MEC proliferation, induced both alveolar and ductal morphogenesis and enhanced casein expression. In contrast, only alveolar structures were observed in monocultures. The alveolar structures generated from the heterotypic cultures in vitro exhibited proper polarity similar to human breast tissue in vivo. Consistent with their phenotypic appearance, more functional differentiation of epithelial cells was also observed in the heterotypic cultures, where casein-α and -β mRNA expression were increased significantly. Additionally, this 3D multicellular culture model displayed an estrogen-responsive physiologically relevant response, evidenced by enhanced cell proliferation, aberrant morphology, changes in gene expression profile and few polarized lumen structures after estrogen treatment. This culture system offers an excellent opportunity to explore the role of cell-cell and cell-substrate interactions during mammary gland development, the consequences of hormone receptor activation on MEC behavior and morphogenesis, as well as their alteration during neoplastic transformation in human breast tissue.

Three-dimensional cultures of mouse mammary epithelial cells

The mammary gland is an ideal "model organism" for studying tissue specificity and gene expression in mammals: it is one of the few organs that develop after birth and it undergoes multiple cycles of growth, differentiation and regression during the animal's lifetime in preparation for the important function of lactation. The basic "functional differentiation" unit in the gland is the mammary acinus made up of a layer of polarized epithelial cells specialized for milk production surrounded by myoepithelial contractile cells, and the two-layered structure is surrounded by basement membrane. Much knowledge about the regulation of mammary gland development has been acquired from studying the physiology of the gland and of lactation in rodents. Culture studies, however, were hampered by the inability to maintain functional differentiation on conventional tissue culture plastic. We now know that the microenvironment, including the extracellular matrix and tissue architecture, plays a crucial role in directing functional differentiation of organs. Thus, in order for culture systems to be effective experimental models, they need to recapitulate the basic unit of differentiated function in the tissue or organ and to maintain its three-dimensional (3D) structure. Mouse mammary culture models evolved from basic monolayers of cells to an array of complex 3D systems that observe the importance of the microenvironment in dictating proper tissue function and structure. In this chapter, we focus on how 3D mouse mammary epithelial cultures have enabled investigators to gain a better understanding of the organization, development and function of the acinus, and to identify key molecular, structural, and mechanical cues important for maintaining mammary function and architecture. The accompanying chapter of Vidi et al. describes 3D models developed for human cells. Here, we describe how mouse primary epithelial cells and cell lines--essentially those we use in our laboratory--are cultured in relevant 3D microenvironments. We focus on the design of functional assays that enable us to understand the intricate signaling events underlying mammary gland biology, and address the advantages and limitations of the different culture settings. Finally we also discuss how advances in bioengineering tools may help towards the ultimate goal of building tissues and organs in culture for basic research and clinical studies.

Lactation stage-dependent expression of transporters in rat whole mammary gland and primary mammary epithelial organoids

Since solute carrier (SLC) and ATP-binding cassette (ABC) transporters play pivotal roles in the transport of both nutrients and drugs into breast milk, drug-nutrient transport interactions at the lactating mammary gland are possible. Our purpose was to characterize lactation stage-dependent changes in transporter expression in rat mammary gland and isolated mammary epithelial organoids (MEO) to provide additional insight for the safe use of maternal medications during breastfeeding. We used quantitative reverse transcription-polymerase chain reaction to assess the temporal expression patterns of SLC and ABC transporters in rat mammary gland and isolated MEO at different stages of lactation. In whole mammary gland five distinct patterns of expression emerged relative to late gestation: (i) decreasing throughout lactation (Mdr1a, Mdr1b, Mrp1, Octn2, Ent2, Ent3, Ncbt2, Mtx1); (ii) prominent increase in early lactation, which may remain elevated or decline with advancing lactation (Octn1, Cnt2, Cnt3, Ent1, Pept1, Pept2); (iii) constant but decreasing later in lactation (Octn3, Dmt1); (iv) increasing until mid-to-late lactation (Oct1, Cnt1); and (v) prominent increase late in lactation (Ncbt1). In isolated MEO (an enriched source of mammary epithelial cells) major differences in expression patterns were noted for Octn3, Ncbt1, and Mtx1, but otherwise were reasonably similar with the whole mammary gland. In conclusion our study augments existing data on transporter expression in the lactating mammary gland. These data should facilitate investigations into lactation-stage dependent changes in drug or nutrient milk-to-serum concentration ratios, the potential for drug- or disease-transporter interactions, and mechanistic studies of transporter function in the lactating mammary gland.

A novel in vitro three-dimensional skeletal muscle model

A novel three-dimensional (3D) skeletal muscle model composed of C2C12 mouse myoblasts is described. This model was generated by cultivating myoblasts in suspension using the rotary cell culture system (RCCS), a unique culture environment. Single-cell suspensions of myoblasts were seeded at 5 x 10(5)/ml in growth medium without exogenous support structures or substrates. Cell aggregation occurred in both RCCS and suspension control (SC) conditions within 12 h but occurred more rapidly in the SC at all time intervals examined. RCCS-cultured myoblasts fused and differentiated into a 3D construct without serum deprivation or alterations. Syncitia were quantified at 3 and 6+ d in stained thin sections. A significantly greater number of syncitia was found at 6+ d in the RCCS cultures compared to the SC. The majority of syncitia were localized to the periphery of the cell constructs for all treatments. The expression of sarcomeric myosin heavy chain (MHC) was localized at or near the periphery of the 3D construct. The majority of MHC was associated with the large cells (syncitia) of the 6+-d aggregates. These results show, for the first time, that myoblasts form syncitia and express MHC in the presence of growth factors and without the use of exogenous supports or substrates. This model test system is useful for investigating initial cell binding, myoblast fusion and syncitia formation, and differentiation processes.

The goat mammary glandular epithelial (GMGE) cell line promotes polyfucosylation and N,N′-diacetyllactosediaminylation of N-glycans linked to recombinant human erythropoietin

We have established a continuous, non-transformed cell line from primary cultures from Capra hircus mammary gland. Low-density cultures showed a homogeneous epithelial morphology without detectable fibroblastic or myoepithelial cells. The culture was responsive to contact inhibition of proliferation and its doubling time was dependent on the presence of insulin and epidermal growth factor (EGF). GMGE cells secrete caseins regardless of the presence or absence of lactogenic hormones in the culture media. Investigation of the total N-glycan pool of human erythropoietin (rhEPO) expressed in GMGE cells by monosaccharide analysis, HPLC profiling, and mass spectrometry, indicated significant differences with respect to the same protein expressed in Chinese hamster ovary (CHO) cells. N-Glycans of rhEPO-GMGE are core-fucosylated, but fucosylation of outer arms was also found. Our results also revealed the presence of low levels of sialylation (>95% Neu5Ac), N,N'-diacetyllactosediamine units, and possibly Gal-Gal non-reducing terminal elements.

NFkappaB1/p50 is not required for tumor necrosis factor-stimulated growth of primary mammary epithelial cells: implications for NFkappaB2/p52 and RelB

Nuclear factor kappaB (NFkappaB) plays an important role in mammary gland development and breast cancer. We previously demonstrated that TNF stimulates growth of mammary epithelial cells (MEC) in a physiologically relevant three-dimensional primary culture system, accompanied by enhanced DNA-binding of the NFkappaB p50 homodimer. To further understand the mechanism of TNF-stimulated growth of primary MEC, the requirement for NFkappaB1/p50, and the role of cyclin D1 in TNF-stimulated growth were examined. TNF induced the formation of DNA-binding complexes of p50 and p52 with their coactivator bcl3 in MEC nuclear extracts. Concomitantly, TNF increased the binding of NFkappaB proteins to the kappaB site on the cyclin D1 promoter, and increased expression of cyclin D1 mRNA and protein. Using MEC from p50 null mice, we found that p50 was not required for TNF-induced growth nor for up-regulation of cyclin D1. However, TNF induced a p52/RelB NFkappaB DNA-binding complex in p50 null MEC nuclear extracts. In addition, we found that in wild-type MEC, TNF stimulated the occupancy of p52 and RelB on the cyclin D1 promoter kappaB site, whereas p50 was present constitutively. These data suggest that in wild-type MEC, TNF stimulates the interaction of bcl3 with p50 and p52, and the binding of p52, as well as RelB, to cyclin D1 promoter kappaB sites, and as a consequence, stimulates the growth of MEC. In the absence of p50, p52 and RelB can compensate for p50 in TNF-stimulated growth and cyclin D1 induction in MEC.

Loss of Alx4, a stromally-restricted homeodomain protein, impairs mammary epithelial morphogenesis

Postnatal development of the mammary gland is determined by reciprocal interactions between the ductal epithelia and adjacent stroma. Alx4 is a mesenchymally restricted homeodomain transcription factor expressed in a number of developing tissues, including skin appendages such as hair follicles, whiskers and teeth. We show here that Alx4 is expressed in a subset of ERalpha-expressing mammary stromal cells adjacent to terminal end buds and alveoli during puberty and pregnancy, respectively. Alx4 expression is induced in mammary stromal cells at the onset of puberty and can be induced in prepubescent mice by administration of 17beta-estradiol. In order to determine the role of Alx4 during mammary gland development, we characterized mammary gland development of mice homozygous for the null allele of Alx4, lst(D). Mammary glands from animals lacking Alx4 activity exhibit profound alterations in ductal morphogenesis. Overall development is delayed, ducts being grossly distorted in size and structure. Terminal end buds are also disoriented, displaying aberrant architecture during bifurcation. Despite the developmental delay, the ductal network typically reaches the limits of the fat pad. However, during puberty and in the adult virgin mice, the frequency and density of branch points is significantly reduced. We show further that the defective ductal morphogenesis is due to defects in stromal cells. Specifically, when injected into the cleared fat pad of wild-type recipients, mixed populations of wild-type epithelial cells and Alx4-deficient stromal cells give rise to retarded ductal morphogenesis. Wild-type stromal cells mixed with Alx4-deficient epithelial cells result in normal progression of ductal development. Defective branching morphogenesis in Alx4-deficient females is not due to a loss in expression of HGF, since the level of HGF message in mammary stromal cells is similar in mutant and wild-type littermates. MMP3 is similarly expressed while a 40% increase in MMP2 and a 50% decrease in MMP9 message levels in Alx4-deficient mice relative to their wild-type littermates is observed. Thus, the activity of the stromally restricted homeodomain factor, Alx4, is required for normal branching morphogenesis of the ductal epithelia during pubescent mammary gland development.

Primary porcine proximal tubular cells as a model for transepithelial drug transport in human kidney

BACKGROUND

Kidney proximal tubular cells play a major role in the transport of endogenous and exogenous compounds. A multitude of different transporters are expressed starting with multidrug ABC transporters (e.g. abcb1, abcc1-6), slc22a6-8 (organic anion transporters) and slc22a1-3 (organic cation transporters). For transport studies of renal drug transport, cell lines like MDCK and LLC-PK1 are often used to overexpress and study one or two transporters, such as abcb1 or abcc1-6. However, the use is limited since under physiological conditions xenobiotics are transported through different transporters at the same time. Therefore, a primary in vitro model expressing functionally different transporters simultaneously, as it is the case in vivo, would be of great benefit.

METHODS

Primary proximal tubular cells were isolated from porcine kidney. Cells were cultured under selective culturing conditions leading to specific growth of primary proximal tubular cells. Expression of important proximal transporters was checked at mRNA level with RT-PCR, at protein level with immunocytochemistry and functionally by transport and uptake assays.

RESULTS

A model of primary proximal tubular cells was established expressing the most important transporters: abcb1, abcc1, abcc2, slc22a8, slco1a2, slc15a1, slc5a2 and slc4a4. In freshly isolated cells, slc22a1 and slc22a6 were expressed, but were down-regulated in culture. Abcb1, abcc1, abcc2 and slc4a4 were detected at protein level with immunostaining. Functional activity was confirmed for abcb1, abcc1/2, slc22a8, slc15a1/2 and slc5a1/2. The tightness of the monolayers of this model was better than in previously established in vitro models.

CONCLUSION

This primary cell culture model might be an interesting tool to investigate proximal tubular transport and to predict toxicity and drug interactions since it expresses functionally several transporters simultaneously.

Method for the generation and cultivation of functional three-dimensional mammary constructs without exogenous extracellular matrix

During puberty, pregnancy, lactation and post-lactation, breast tissue undergoes extensive remodelling and the disruption of these events can lead to cancer. In vitro studies of mammary tissue and its malignant transformation regularly employ mammary epithelial cells cultivated on matrigel or floating collagen rafts. In these cultures, mammary epithelial cells assemble into three-dimensional structures resembling in vivo acini. We present a novel technique for generating functional mammary constructs without the use of matrix substitutes.

Breast cancer cell lines: friend or foe?

The majority of breast cancer research is conducted using established breast cancer cell lines as in vitro models. An alternative is to use cultures established from primary breast tumours. Here, we discuss the pros and cons of using both of these models in translational breast cancer research.

Mechanisms for 2-methoxyestradiol-induced apoptosis of prostate cancer cells

Prostate and breast carcinomas are sex hormone-related carcinomas, which are known to be associated with an over-expression of the proto-oncogene Bcl-2. Here, we report that 2-methoxyestradiol (2-ME), an endogenous metabolite of estrogen that does not bind to nuclear estrogen receptors, effectively induces apoptosis in Bcl-2-expressing human prostate and breast carcinoma cells in vitro and in a rat prostate tumor model in vivo. In several cell lines derived from prostate, breast, liver and colorectal carcinomas, 2-ME treatment led to an activation of c-Jun N-terminal kinase (JNK) and phosphorylation of Bcl-2, which preceded the induction of apoptosis. In summary, our data suggest that 2-ME induces apoptosis in epithelial carcinomas by causing phosphorylation of JNK, which appears to be correlated with phosphorylation of Bcl-2.

Estrogen mediates mammary epithelial cell proliferation in serum-free culture indirectly via mammary stroma-derived hepatocyte growth factor

Epithelial-stromal cell interactions are important for normal development and function of the mouse mammary gland. The steroid hormone estrogen is required for epithelial cell proliferation and ductal development in vivo. Recent studies of estrogen receptor alpha knockout mice indicate that estrogen-induced proliferation is dependent upon the presence of estrogen receptor in mammary stromal cells, but not in epithelial cells. The purpose of the present study was to identify the underlying mechanism of estrogen-dependent stroma-derived effects on mammary epithelium. We have developed a minimally supplemented serum-free medium, collagen gel primary mammary coculture system to address the issue of stroma-derived, estrogen-dependent effects on epithelial cell proliferation. Conditioned medium from mammary fibroblasts or coculture with mammary fibroblasts caused increased epithelial cell proliferation and produced tubular/ductal morphology. Hepatocyte growth factor (HGF) was identified as the mediator of this effect, as the proliferative activity in fibroblast-conditioned medium was completely abolished by neutralizing antibody to HGF, whereas neutralizing antibodies to either epidermal growth factor or IGF-I had no effect. Treatment of mammary fibroblasts with estrogen increased the production of HGF. From these results we conclude that estrogen may indirectly mediate mammary epithelial cell proliferation via the regulation of HGF in mammary stromal cells and that HGF plays a crucial role in estrogen-induced proliferation in vivo.

Hepatocyte growth factor is required for progestin-induced epithelial cell proliferation and alveolar-like morphogenesis in serum-free culture of normal mammary epithelial cells

The steroid hormones, estrogen and progesterone, are required for mammary epithelial cell proliferation and alveolar morphogenesis in vivo. We have developed a minimally supplemented, serum-free medium, collagen gel primary mammary culture system to determine the mechanism of progestin-induced proliferation and alveolar morphogenesis. In epithelial cells cultured alone, treatment with progestin (R5020) alone produced a lumen within the epithelial organoids, but did not stimulate epithelial cell proliferation. The formation of lumens was associated with increased apoptosis, targeted within the organoids. We have previously reported that in our culture system hepatocyte growth factor (HGF) increases epithelial cell proliferation and induces a tubulo-ductal morphological response. In the present report we show that treatment with HGF and progestin (R5020) further increases epithelial proliferation above that with HGF alone and also produces an alveolar-like morphology similar to that observed in vivo in response to progestin treatment. To the best of our knowledge this is the first in vitro demonstration of both progestin-induced proliferation and alveolar-like morphogenesis of normal nonpregnant mouse mammary epithelial cells in vitro. These results suggest that HGF may play a crucial role in progestin-induced proliferation and morphogenesis in vivo.

Functional role of matrix metalloproteinases (MMPs) in mammary epithelial cell development

The extracellular matrix (ECM) is an important regulator of mammary epithelial cell (MEC) function and is remodeled by matrix metalloproteinases (MMPs). To investigate the significance and regulation of MMP activity in normal MEC, we utilized a primary culture model in which rat MEC were grown three dimensionally within a reconstituted basement membrane (RBM) in defined serum-free medium. Zymograms of culture medium demonstrated that five major gelatinases of 97, 80, 74, 69, and 65 kDa were secreted by MEC and were distinct from gelatinases of RBM origin. Based on molecular weight, p-aminophenylmercuric acid activation, immunoblotting with MMP-specific antibodies, inhibition by EDTA, a peptide containing the prodomain sequence of MMP (TMRKPRCGNPDVAN) and two synthetic MMP inhibitors (BB-94 and CGS 27023A), these were classified as inactive and active forms of MMP-9 and MMP-2. The maximal MMP activities occurred when MEC were in a rapid proliferation and branching phase and declined after they underwent functional differentiation. Known regulators of MEC growth and differentiation were evaluated for their ability to modulate gelatinase activity in primary culture. Secretion of one or both MMPs was inhibited by EGF, TGFalpha, prolactin, and hydrocortisone and stimulated by progesterone. Furthermore, the functional significance of MMPs was demonstrated since three MMP inhibitors blocked branching morphogenesis elicited by the absence of hydrocortisone. Additionally, two synthetic MMP inhibitors not only inhibited epithelial cell growth but also inhibited normal alveolar development of the MEC. Finally, these drugs were found to enhance MMP secretion from MEC, although the activity of the secreted MMPs was inhibited as long as the drug was present.

Mammary fibroblasts stimulate growth, alveolar morphogenesis, and functional differentiation of normal rat mammary epithelial cells

Stromal-epithelial interactions play a profound role in regulating normal and tumor development in the mammary gland. The molecular details of these events, however, are incompletely understood. A novel serum-free transwell coculture system was developed to study the natural paracrine interactions between mammary epithelial cells (MEC) and mammary fibroblasts (MFC) isolated from normal rats during puberty. The MEC were cultured within a reconstituted basement membrane (RBM) in transwell inserts with or without MFC in the lower well. The presence of MFC stimulated epithelial cell growth, induced alveolar morphogenesis, and enhanced casein accumulation, a marker of the functional differentiation of MEC, but did not induce ductal morphogenesis. Potent mitogenic, morphogenic, and lactogenic effects were observed when the MFC were cultured either on plastic or within a layer of RBM. Although most MFC maintained on plastic died after 1 wk in serum-free medium, fibroblast survival was enhanced significantly when the MFC were cultured within the RBM. Taken together, this in vitro model effectively reconstitutes a physiologically relevant three-dimensional microenvironment for MEC and MFC, and seems ideal for studying the locally derived factors that regulate the developmental fate of the epithelial and fibroblast compartments of the mammary gland.

Experimental basis for the prevention of breast cancer

Cancer chemoprevention involves intervention in the carcinogenic process by a natural or synthetic chemical that either blocks neoplasia development or arrests malignant phenotype progression. The chemopreventive test agent must experimentally be established as safe before a clinical trial. In our laboratory, inhibition of carcinogen-induced development of precancerous lesions in the mouse mammary gland organ culture model is used as a primary screen to select chemopreventive agents for in vivo efficacy evaluation. A nearly 75% correlation apparently exists between the efficacy observed in vitro and in vivo carcinogenesis. For in vivo experiments, MNU- and DMBA-induced mammary tumours in rats are the models of choice. Numerous agents have been identified and progressed to preclinical toxicity and clinical trials. More recently, combination chemoprevention has received considerable attention, since no known chemopreventive agent sufficiently reduces tumour incidence in rats. The sequence of events for establishing the experimental basis for chemoprevention of breast cancer is described.

Growth and morphogenesis of epithelial cell organoids from peripheral and medial mammary parenchyma of prepubertal heifers

Collagen gel cell cultures were used to test the hypothesis that cells from peripheral parenchymal zones of the developing bovine mammary gland have greater proliferative and morphogenic potential than cells from the medial parenchymal mass. Tritiated thymidine was incorporated to assess cell proliferation. Dose responses for insulin-like growth factor one (IGF-I, 0 to 50 ng/ml) and transforming growth factor beta one (0 to 5 ng/ml) were determined for each cell population. Cells from the peripheral regions were two to three times more sensitive to the mitogenic action of IGF-I or serum. Transforming growth factor beta one concentrations of 12.5 to 500 pg/ml stimulated cell proliferation, but concentrations above 1 ng/ml were inhibitory. Peripheral cells showed a distinct biphasic response to addition of transforming growth factor beta one. Morphology of organoids was evaluated daily during culture and by histologic examination at the end of culture. Peripheral zone cells formed multi-layered cell structures that resembled native mammary parenchyma with serum or mammary gland extract. Our results indicate that epithelial cells of the peripheral and medial parenchymal zones in the ruminant mammary gland can differ in their proliferative and morphogenetic response to growth factor treatment in vitro. These differences likely reflect local tissue regulation necessary for sequential ductular and lobulo-alveolar development in vivo.

Establishment and characterization of a caprine mammary epithelial cell line (CMEC)

We describe the establishment of a continuous, nontransformed cell line obtained from primary culture of a lactating (114 days postparturition) Anglo-Nubian (Capra hircus) goat mammary gland biopsy. These cells (CMEC), have been cultured in the presence of supraphysiologic concentrations of insulin and hydrocortisone for more than 560 population doublings (over 80 passages) without any sign of senescence while maintaining a normal/near-normal diploid chromosome modal number of 2n = 60 and are responsive to contact inhibition of proliferation. Cytoskeletal analysis indicates that CMECs are epithelial, without detectable fibroblastic or myoepithelial cells. When grown at low density on plastic substratum, the cells tend to form island monolayer aggregates with the characteristic cobblestone morphology of epithelial cells. With increasing density, the cells organize into lumen-like structures with various morphology consisting of large and small vacuolized and nonvacuolized cells. Postconfluent cultures form epithelial raised dome-like structures, implying a process of contact-induced differentiation. This is corroborated by positive immunocytochemistry to lactation-specific proteins: beta-casein and alpha-lactalbumin, which were predominantly expressed in dome-forming cells. We also observed an overall modulation of cytokeratin 18/19 expression associated with number of days post subculture and with the expression of lactation-specific proteins. Postconfluent cultures which contain lactation-specific, antibody-reactive, dome-like structures showed a decreased expression of keratin 18 and no (null) expression for keratin 19. Lastly, cells cultured within a collagen matrix show morphological differentiation with the organization of branching duct-like and acini-like structures. This study suggests that CMECs are a useful in vitro model for study of mammary gland development and differentiation, in particular, direct modulation of epithelial cells grown on plastic substratum or extracellular matrix without the influence of stromal elements or the necessity and variability associated with primary cell culture or tissue explants.

Conjugated linoleic acid inhibits proliferation and induces apoptosis of normal rat mammary epithelial cells in primary culture

The trace fatty acid conjugated linoleic acid (CLA) inhibits rat mammary carcinogenesis when fed prior to carcinogen during pubertal mammary gland development or during the promotion phase of carcinogenesis. The following studies were done to investigate possible mechanisms of these effects. Using a physiological model for growth and differentiation of normal rat mammary epithelial cell organoids (MEO) in primary culture, we found that CLA, but not linoleic acid (LA), inhibited growth of MEO and that this growth inhibition was mediated both by a reduction in DNA synthesis and a stimulation of apoptosis. The effects of CLA did not appear to be mediated by changes in epithelial protein kinase C (PKC) since neither total activity nor expression nor localization of PKC isoenzymes alpha, beta II, delta, epsilon, eta, or zeta were altered in the epithelium of CLA-fed rats. In contrast, PKCs delta, epsilon, and eta were specifically upregulated and associated with a lipid-like, but acetone-insoluble, fibrillar material found exclusively in adipocytes from CLA-fed rats. Taken together, these observations demonstrate that CLA can act directly to inhibit growth and induce apoptosis of normal MEO and may thus prevent breast cancer by its ability to reduce mammary epithelial density and to inhibit the outgrowth of initiated MEO. Moreover, the changes in mammary adipocyte PKC expression and lipid composition suggest that the adipose stroma may play an important in vivo role in mediating the ability of CLA to inhibit mammary carcinogenesis.

Adipocyte-epithelial interactions regulate the in vitro development of normal mammary epithelial cells

Mammary epithelial organoids (MEO), isolated from pubescent rats, were cultured within a reconstituted basement membrane in transwell inserts, in the presence or absence of mature mammary adipocytes in the lower well. This system allowed for free medium exchange between the two compartments, without direct cell-to-cell contact. When cultured in serum-free medium supplemented with insulin, prolactin, hydrocortisone, progesterone, and various epidermal growth factor (EGF) concentrations, mammary adipocytes did not affect epithelial cell growth, but enhanced epithelial differentiation. Casein and lipid accumulations were monitored as indicators of functional differentiation of MEO. Mammary adipocytes significantly enhanced casein and lipid accumulation within the MEO, independently of EGF concentration. Furthermore, adipocytes induced MEO to preferentially undergo alveolar morphogenesis, inhibited squamous outgrowth, and increased lumen size. These findings demonstrate that morphological and functional differentiation of mammary epithelial cells is profoundly enhanced by the adipose stroma and that these effects are mediated by diffusible paracrine factors. This new model can be exploited in future studies to define the mechanisms whereby hormones and growth factors regulate mammary gland development and carcinogenesis. Moreover, it could complement in vivo reconstitution/transplantation studies, which are currently employed to evaluate the role of specific gene deletions in the regulation of mammary development.

Transferrin and prolactin transcytosis in the lactating mammary epithelial cell

The mammary epithelial cell ferries constituents originating from blood and from stromal cells, into milk, by transcytosis. Morphological analysis of a membrane marker of transcytosis in the lactating mammary epithelial cell showed that very rapid endocytosis of surface membrane occurs from both the basolateral and the apical side of the cell. In both cases, membrane trafficking between endosomes and the Golgi complex allows communication between the endocytic and the biosynthetic pathways. Transferrin and prolactin are internalized in mammary cells and transported through multivesicular bodies and Golgi stacks. They are released into milk via different types of secretory vesicles, prolactin being carried in secretory vesicles containing casein micelles. Consequences of the intracellular transport of these proteins and physiological benefits for cell function are discussed.

The proliferation of mouse mammary epithelial cells in response to specific mitogens is modulated by the mammary fat pad in vitro

The ability of the murine mammary fat pad to directly stimulate the growth of mammary epithelial cells and to modulate the effects of various mammogenic agents has been investigated in a newly described, hormone- and serum-free coculture system. COMMA-1D mouse mammary epithelial cells were cultured for 5 or 7 d with various supplements in the absence or presence of epithelium-free mammary fat pad explants from virgin female BALB/c mice. Cocultured fat pad stimulated increases in the DNA content of COMMA-1D cultures by two- to threefold or six- to eightfold after 5 or 7 d, respectively. The mitogenic effect was additive to that of 10% fetal calf serum and could not be attributed to the release of prostaglandin E2 or synthesis of prostaglandins by epithelial cells. In addition, bovine serum albumin attenuated (P < 0.05) the mitogenic effect of cocultured mammary fat pad. Added alone, insulinlike growth factor-I, epidermal growth factor, and insulin increased (P < 0.05) total DNA of COMMA-1D cultures by 2.5-, 3.7-, and 2.3-fold, respectively. Cocultured mammary fat pad markedly interacted (P < 0.01) with these mitogens to yield final DNA values that were 21.2-, 13.3-, and 22.1-fold greater than in basal medium only. Associated with this proliferation was the formation of numerous domes above the COMMA-1D monolayer. There was no proliferative response to growth hormone or prolactin in the absence or presence of cocultured fat pad (P > 0.05). Whereas hydrocortisone did not alter cell number, it attenuated (P < 0.05) the mitogenic effect of cocultured mammary fat pad. These results indicate that the murine mammary fat pad is not only a direct source of mitogenic activity, but also modulates the response of mammary epithelial cells to certain mammogens.

Establishment and initial characterization of the ovine mammary epithelial cell line NISH

Analysis of the molecular mechanisms involved in the differentiation and formation of the characteristic three-dimensional structures of the developing mammary gland of the major milk-producing livestock (ducts, end buds, and alveoli) requires in vitro model cell cultures. The few cell lines that have been established from dairy animals do not fully reproduce the entire program of mammary differentiation. Here we present the initial characterization of a unique mammary epithelial cell line derived spontaneously from midpregnant sheep (NISH). These cells form in vitro functional structures resembling ducts, lateral buds, and alveoli that secrete beta-lactoglobulin (BLG) in an ECM (extracellular matrix)-dependent manner. Interestingly, the presence of growth hormone dramatically increased BLG secretion from NISH cells cultured on ECM. It appears that GH is required not only to establish the structural organization but also is continuously needed to maintain BLG expression. Stable transfection of NISH cells with BLG/Human Serum Albumin (HSA) hybrid gene constructs revealed that the relative level of expression was comparable to the in vivo secretion of HSA in transgenic mice carrying these gene sequences. No expression could be detected in cells transfected with hybrid genes carrying either HSA cDNA or the entire HSA gene, and HSA expression was dependent on the presence of intronic sequences. These results demonstrate that NISH cells may prove a useful tool for studying the differentiation and organogenesis of mammary epithelial cells under defined culture conditions. Furthermore, transfected NISH cells may be an alternative for the transgenic mouse model in evaluating the potential of gene constructs to be efficiently expressed in the mammary gland of transgenic farm animals.

Conditional control of gene expression in the mammary gland

Identifying gene function during mammary gland development and function remains a technical challenge. For example, if a gene deletion is lethal during early embryogenesis, there is no opportunity to study its effects on the development or function of the gland. Similarly, if a dominant gain of gene function alters early mammary gland development, then its specific role during lactation cannot be assessed. Conditional gene expression systems can be used to circumvent these problems. Gene deletions or dominant gain experiments can be performed in an organ or cell type specific manner at specific timepoints using inducible gene expression systems. This review focuses on tetracycline responsive transactivation and Cre-lox systems. Other tetracycline regulatable (tet system) or hormone inducible systems and the Flp recombinase system are discussed as alternative approaches. Each system is described. The advantages and disadvantages of each for studying gene function in the mammary gland are discussed. Finally, the role of mammary gland transplantation in these genetic studies is examined.

An in vitro approach to ruminant mammary gland biology

This review discusses both fundamental and applied in vitro studies on ruminant mammary gland biology and summarizes progress made over the last decade in development of in vitro techniques to study growth, function and pathology of the mammary gland. The advantages and limitations of different in vitro systems are considered including explant cultures, primary cell cultures and immortalized lines of mammary-derived cells from cow, sheep and goat. The cell growth, differentiation and response to lactogenic hormones and growth factors are discussed as well as the relevance of the cell behavior in different culture conditions.

The role of TGF-beta in patterning and growth of the mammary ductal tree

Evidence that transforming growth factor beta (TGF-beta) influences pattern formation in the developing mammary gland and negatively regulates ductal growth is reviewed. In the mouse, overexpression of TGF-beta transgenes during puberty reduces the rate of growth of the ductal tree and simplifies the pattern of arborization, while expression during pregnancy also interferes with lactation. Expression studies in the normal mouse gland indicate that TGF-beta is synthesized in the mammary epithelium, with the three isoforms showing somewhat different spatial and temporal distributions. Exogenous TGF-beta applied directly to the gland in situ inhibits epithelial cell division within hours, and strongly stimulates extracellular matrix synthesis over a longer time course. Normal human breast cells as well as certain breast cancer cell lines also secrete TGF-beta and are themselves inhibited by it, suggesting an autoregulatory feedback circuit, that in some cases appears to be modulated by estradiol. Taken together, the evidence suggests a model in which growth and patterning of the mammary ductal tree are regulated, at least in part, by TGF-beta operating through an autocrine feedback mechanism and by paracrine circuits associated with epithelial-stromal interactions.