Post-bioprinting processing methods to improve cell viability and pattern fidelity in heterogeneous tissue test systems

Bioprinted tissue test systems show promise as a powerful tool for studying cell-cell interaction in heterogeneous, tissue-like co-culture. Several challenges were encountered while attempting to consistently fabricate samples with high viability and pattern fidelity. This paper evaluates four methods for processing samples after bioprinting but prior to adding media for incubation. These methods, composed of various combinations of three techniques meant to promote cell hydration, are evaluated with respect to sample viability and pattern preservation. In the best performing method, Hank's Balanced Salt Solution was applied immediately after fabrication and a collagen overlayer was applied one hour thereafter. The success of this method highlights the ability of the collagen substrate to absorb moisture, which promotes cell health without disturbing the cell's printed location. An addendum to the main study is an investigation of the limits of an HP26 print cartridge to deposit cells at a faster rate for the purpose of creating cell layers with densities that approach confluence.

The normal mammary microenvironment suppresses the tumorigenic phenotype of mouse mammary tumor virus-neu-transformed mammary tumor cells

The microenvironment of the mammary gland has been shown to exert a deterministic control over cells from different normal organs during murine mammary gland regeneration in transplantation studies. When mouse mammary tumor virus (MMTV)-neu-induced tumor cells were mixed with normal mammary epithelial cells (MECs) in a dilution series and inoculated into epithelium-free mammary fat pads, they were redirected to non-carcinogenic cell fates by interaction with untransformed MECs during regenerative growth. In the presence of non-transformed MECs (50:1), tumor cells interacted with MECs to generate functional chimeric outgrowths. When injected alone, tumor cells invariably produced tumors. Here, the normal microenvironment redirects MMTV-neu-transformed tumorigenic cells to participate in the regeneration of a normal, functional mammary gland. In addition, the redirected tumor cells show the capacity to differentiate into normal mammary cell types, including luminal, myoepithelial and secretory. The results indicate that signals emanating from a normal mammary microenvironment, comprised of stromal, epithelial and host-mediated signals, combine to suppress the cancer phenotype during glandular regeneration. Clarification of these signals offers improved therapeutic possibilities for the control of mammary cancer growth.

The normal microenvironment directs mammary gland development

Normal development of the mammary gland is a multidimensional process that is controlled in part by its mammary microenvironment. The mammary microenvironment is a defined location that encompasses mammary somatic stem cells, neighboring signaling cells, the basement membrane and extracellular matrix, mammary fibroblasts as well as the intercellular signals produced and received by these cells. These dynamic signals take numerous forms including growth factors, steroids, cell-cell or cell-basement membrane physical interactions. Cellular growth and differentiation of the mammary gland throughout the developmental stages are regulated by changes in these signals and interactions. The purpose of this review is to summarize current information and research regarding the role of the mammary microenvironment during normal glandular development.

Reprogramming human cancer cells in the mouse mammary gland

The tissue microenvironment directs stem/progenitor cell behavior. Cancer cells are also influenced by the microenvironment. It has been shown that, when placed into blastocysts, cancer cells respond to embryonic cues and differentiate according to the tissue type encountered during ontological development. Previously, we showed that the mouse mammary gland was capable of redirecting adult mouse testicular and neural stem/progenitor cells toward a mammary epithelial cell fate during gland regeneration. Here, we report that human embryonal carcinoma cells proliferate and produce differentiated mammary epithelial cell progeny when mixed with mouse mammary epithelial cells and inoculated into the epithelium-free mammary fat pads of athymic nude mice. Fluorescence in situ hybridization confirmed the presence of human cell progeny in the mammary outgrowths for human centromeric DNA, as well as immunochemistry for human-specific breast epithelial cytokeratins and human-specific milk proteins in impregnated transplant hosts. It was found that the number of human cells increased by 66- to 660-fold during mammary epithelial growth and expansion as determined by human cytokeratin expression. All features found in primary outgrowths were recapitulated in the secondary outgrowths from chimeric implants. These results show that human embryonal carcinoma-derived progeny interact with mouse mammary cells during mammary gland regeneration and are directed to differentiate into cells that exhibit diverse mammary epithelial cell phenotypes. This is the first demonstration that human cells are capable of recognizing the signals generated by the mouse mammary gland microenvironment present during gland regeneration in vivo.

ErbB/EGF signaling and EMT in mammary development and breast cancer

Activation of the ErbB family of receptor tyrosine kinases via cognate Epidermal Growth Factor (EGF)-like peptide ligands constitutes a major group of related signaling pathways that control proliferation, survival, angiogenesis and metastasis of breast cancer. In this respect, clinical trials with various ErbB receptor blocking antibodies and specific tyrosine kinase inhibitors have proven to be partially efficacious in the treatment of this heterogeneous disease. Induction of an embryonic program of epithelial-to-mesenchymal transition (EMT) in breast cancer, whereupon epithelial tumor cells convert to a more mesenchymal-like phenotype, facilitates the migration, intravasation, and extravasation of tumor cells during metastasis. Breast cancers which exhibit properties of EMT are highly aggressive and resistant to therapy. Activation of ErbB signaling can regulate EMT-associated invasion and migration in normal and malignant mammary epithelial cells, as well as modulating discrete stages of mammary gland development. The purpose of this review is to summarize current information regarding the role of ErbB signaling in aspects of EMT that influence epithelial cell plasticity during mammary gland development and tumorigenesis. How this information may contribute to the improvement of therapeutic approaches in breast cancer will also be addressed.

Stem cells and the mammary microenvironment

An entire mammary epithelial outgrowth, capable of full secretory differentiation, may comprise the progeny of a single cellular antecedent. This conclusion is based upon the maintenance of retroviral insertion sites within the somatic DNA of successive transplant generations derived from a single mammary fragment. In addition, dissociation of these clonal dominant glands and implantation of dispersed cells at limiting dilution demonstrated that both duct-limited and lobule-limited outgrowths were developed as well as complete, fully differentiated glands. Thus, transplantation has revealed three distinct mammary epithelial progenitors in the mouse. Recently, using cre-lox conditional activation of reporter genes, the lobule-limited progenitor was lineally marked by lacZ expression. In situ, these cells were shown to regenerate secretory lobules upon successive pregnancies. In transplant studies, they demonstrated the capacity for self- renewal and contributed to the new generation of all of the epithelial cell types among mammary secretory lobules. Using this conditional activation model, cells isolated from other tissues of the WAP-Cre/Rosa26/lacZReporter mice, co-mingled with normal wild type mammary epithelial cells and transplanted into epithelium-divested mammary fat pads, were shown to be amenable to redirection of their cell fate by interaction with the mammary microenvironment in vivo. This suggests the ascendancy of the microenvironment over the intrinsic nature of somatic stem cells.

Selective segregation of DNA strands persists in long-label-retaining mammary cells during pregnancy

Introduction

During pregnancy the mammary epithelial compartment undergoes extreme proliferation and differentiation, facilitated by stem/progenitor cells. Mouse mammary epithelium in nonpregnant mice contains long label-retaining epithelial cells (LREC) that divide asymmetrically and retain their template DNA strands. The role of LREC during alveogenesis has not been determined.

Methods

We performed immunohistochemistry and autoradiography on murine mammary glands that had been labeled with 5-bromodeoxyuridine (5BrdU) during allometric ductal growth to investigate the co-expression of DNA label retention and estrogen receptor-α or progesterone receptor during pregnancy. A second DNA label ([³H]-thymidine) was administered during pregnancy to identify label-retaining cells (LRC), which subsequently enter the cell cycle. Use of this methodology allowed us to investigate the co-localization of 5BrdU with smooth muscle actin, CD31, cytokeratin, and desmin in periductal or peri-acinar LRC in mammary tissue from pregnant mice subsequent to a long chase period in order to identify LRC.

Results

Estrogen receptor-α positive and progesterone receptor positive cells represented approximately 30% to 40% of the LREC, which is under 1.0% of the epithelial subpopulation. Pregnancy altered the percentage of LREC expressing estrogen receptor-α. LRC situated in periductal or peri-acinar positions throughout the gland do not express epithelial, endothelial, or myoepithelial markers, and these undefined LRCs persist throughout pregnancy. Additionally, new cycling LREC ([³H]-thymidine retaining) appear during alveologenesis, and LRC found in other tissue types (for example, endothelium and nerve) within the mammary fat pad become double labeled during pregnancy, which indicates that they may also divide asymmetrically.

Conclusions

Our findings support the premise that there is a subpopulation of LREC in the mouse mammary gland that persists during alveologenesis. These cells react to hormonal cues during pregnancy and enter the cell cycle while continuing to retain, selectively, their original template DNA. In addition, nonepithelial LRC are found in periductal or peri-acinar positions. These LRC also enter the cell cycle during pregnancy. During alveologenesis, newly created label-retaining ([³H]-thymidine) epithelial cells appear within the expanding alveoli and continue to cycle and retain their original template DNA ([³H]-thymidine) strands, as determined by a second pulse of 5BrdU.

The mammary microenvironment alters the differentiation repertoire of neural stem cells

A fundamental issue in stem cell biology is whether adult somatic stem cells are capable of accessing alternate tissue sites and continue functioning as stem cells in the new microenvironment. To address this issue relative to neurogenic stem cells in the mouse mammary gland microenvironment, we mixed wild-type mammary epithelial cells (MECs) with bona fide neural stem cells (NSCs) isolated from WAP-Cre/Rosa26R mice and inoculated them into cleared fat pads of immunocompromised females. Hosts were bred 6-8 weeks later and examined postinvolution. This allowed for mammary tissue growth, transient activation of the WAP-Cre gene, recombination, and constitutive expression of LacZ. The NSCs and their progeny contributed to mammary epithelial growth during ductal morphogenesis, and the Rosa26-LacZ reporter gene was activated by WAP-Cre expression during pregnancy. Some NSC-derived LacZ(+) cells expressed mammary-specific functions, including milk protein synthesis, whereas others adopted myoepithelial cell fates. Thus, NSCs and their progeny enter mammary epithelium-specific niches and adopt the function of similarly endowed mammary cells. This result supports the conclusion that tissue-specific signals emanating from the stroma and from the differentiated somatic cells of the mouse mammary gland can redirect the NSCs to produce cellular progeny committed to MEC fates.

Netrin-1 can affect morphogenesis and differentiation of the mouse mammary gland

Netrin-1 has been shown to regulate the function of the EGF-like protein Cripto-1 (Cr-1) and affect mammary gland development. Since Cr-1 is a target gene of Nanog and Oct4, we investigated the relationship between Netrin-1 and Cr-1, Nanog and Oct4 during different stages of development in the mouse mammary gland. Results from histological analysis show that exogenous Netrin-1 was able to induce formation of alveolar-like structures within the mammary gland terminal end buds of virgin transgenic Cripto-1 mice and enhance mammary gland alveologenesis in early pregnant FVB/N mice. Results from immunostaining and Western blot analysis show that Netrin-1, Nanog and Oct4 are expressed in the mouse embryonic mammary anlage epithelium while Cripto-1 is predominantly expressed outside this structure in the surrounding mesenchyme. We find that in lactating mammary glands of postnatal FVB/N mice, Netrin-1 expression is highest while Cripto-1 and Nanog levels are lowest indicating that Netrin-1 may perform a role in the mammary gland during lactation. HC-11 mouse mammary epithelial cells stimulated with lactogenic hormones and exogenous soluble Netrin-1 showed increased beta-casein expression as compared to control thus supporting the potential role for Netrin-1 during functional differentiation of mouse mammary epithelial cells. Finally, mouse ES cells treated with exogenous soluble Netrin-1 showed reduced levels of Nanog and Cripto-1 and higher levels of beta-III tubulin during differentiation. These results suggest that Netrin-1 may facilitate functional differentiation of mammary epithelial cells and possibly affect the expression of Nanog and/or Cripto-1 in multipotent cells that may reside in the mammary gland.

Roles of transforming growth factor-alpha in mammary development and disease

Transforming growth factor-alpha (TGFalpha) is a member of the epidermal growth factor (EGF) family. Expression of TGFalpha is highly regulated in response to exogenous cellular signals including cytokines and other growth factors. The growth factor has been found to be indispensable for proper development of many tissues and organs. TGFalpha has also been implicated in numerous disease states including forms of breast cancer. This minireview summarizes the basic biology of TGFalpha and its actions during normal and pathogenic development of the mammary epithelium.

IL-13-induced proliferation of airway epithelial cells: mediation by intracellular growth factor mobilization and ADAM17

BACKGROUND

The pleiotrophic cytokine interleukin (IL)-13 features prominently in allergic and inflammatory diseases. In allergic asthma, IL-13 is well established as an inducer of airway inflammation and tissue remodeling. We demonstrated previously that IL-13 induces release of transforming growth factor-alpha (TGFalpha) from human bronchial epithelial cells, with proliferation of these cells mediated by the autocrine/paracrine action of this growth factor. TGFalpha exists as an integral membrane protein and requires proteolytic processing to its mature form, with a disintegrin and metalloproteinase (ADAM)17 responsible for this processing in a variety of tissues.

METHODS

In this study, normal human bronchial epithelial (NHBE) cells grown in air/liquid interface (ALI) culture were used to examine the mechanisms whereby IL-13 induces release of TGFalpha and cellular proliferation. Inhibitors and antisense RNA were used to examine the role of ADAM17 in these processes, while IL-13-induced changes in the intracellular expression of TGFalpha and ADAM17 were visualized by confocal microscopy.

RESULTS

IL-13 was found to induce proliferation of NHBE cells, and release of TGFalpha, in an ADAM17-dependent manner; however, this IL-13-induced proliferation did not appear to result solely from ADAM17 activation. Rather, IL-13 induced a change in the location of TGFalpha expression from intracellular to apical regions of the NHBE cells. The apical region was also found to be a site of significant ADAM17 expression, even prior to IL-13 stimulation.

CONCLUSION

Results from this study indicate that ADAM17 mediates IL-13-induced proliferation and TGFalpha shedding in NHBE cells. Furthermore, they provide the first example wherein a cytokine (IL-13) induces a change in the intracellular expression pattern of a growth factor, apparently inducing redistribution of intracellular stores of TGFalpha to the apical region of NHBE cells where expression of ADAM17 is prominent. Thus, IL-13-induced, ADAM17-mediated release of TGFalpha, and subsequent epithelial cell proliferation, could contribute to the epithelial hypertrophy, as well as other features, associated with airway remodeling in allergic asthma.

Interaction with the mammary microenvironment redirects spermatogenic cell fate in vivo

Previously, we characterized a parity-induced mammary epithelial cell population that possessed the properties of pluripotency and self-renewal upon transplantation. These cells were lineally marked by the expression of beta-galactosidase (LacZ) as a result of mammary-specific activation of a reporter gene through Cre-lox recombination during pregnancy. We used this experimental model to determine whether testicular cells would alter their cell fate upon interaction with the mammary gland microenvironment during pregnancy, lactation, and involution. Adult testicular cells, isolated from seminiferous tubules, were mixed with limiting dilutions of dispersed mammary epithelial cells and injected into epithelium-divested mammary fat pads. The host mice were bred 6-8 weeks later and examined 20-30 days postinvolution. This approach allowed for the growth of mammary tissue from the injected cells and transient activation of the whey acidic protein promoter-Cre gene during pregnancy and lactation, leading to Cre-lox recombination and constitutive expression of LacZ from its promoter. Here we show that cells from adult seminiferous tubules interact with mammary epithelial cells during regeneration of the gland. They adopt mammary epithelial progenitor cell properties, including self-renewal and the production of cell progeny, which differentiate into functional mammary epithelial cells. Our results provide evidence for the ascendancy of the tissue microenvironment over the intrinsic nature of cells from an alternative adult tissue.

Estrogen receptor-alpha and progesterone receptor are expressed in label-retaining mammary epithelial cells that divide asymmetrically and retain their template DNA strands

Introduction

Stem cells of somatic tissues are hypothesized to protect themselves from mutation and cancer risk through a process of selective segregation of their template DNA strands during asymmetric division. Mouse mammary epithelium contains label-retaining epithelial cells that divide asymmetrically and retain their template DNA.

Method

Immunohistochemistry was used in murine mammary glands that had been labeled with [³H]thymidine during allometric growth to investigate the co-expression of DNA label retention and estrogen receptor (ER)-α or progesterone receptor (PR). Using the same methods, we investigated the co-localization of [³H]thymidine and ER-α or PR in mammary tissue from mice that had received treatment with estrogen, progesterone, and prolactin subsequent to a long chase period to identify label-retaining cells.

Results

Label-retaining epithelial cells (LRECs) comprised approximately 2.0% of the entire mammary epithelium. ER-α-positive and PR-positive cells represented about 30–40% of the LREC subpopulation. Administration of estrogen, progesterone, and prolactin altered the percentage of LRECs expressing ER-α.

Conclusion

The results presented here support the premise that there is a subpopulation of LRECs in the murine mammary gland that is positive for ER-α and/or PR. This suggests that certain mammary LRECs (potentially stem cells) remain stably positive for these receptors, raising the possibility that LRECs comprise a hierarchy of asymmetrically cycling mammary stem/progenitor cells that are distinguished by the presence or absence of nuclear steroid receptor expression.

Alveolar progenitor cells develop in mouse mammary glands independent of pregnancy and lactation

We have previously described pluripotent, parity-induced mammary epithelial cells (PI-MEC) marked by Rosa26-lacZ expression in the mammary glands of parous females. PI-MEC act as lobule-limited epithelial stem/progenitor cells. To determine whether parity is necessary to generate PI-MEC, we incubated mammary explant cultures from virgin mice in vitro with insulin alone (I), hydrocortisone alone (H), prolactin alone (Prl), or a combination of these lactogenic hormones (IHPrl). Insulin alone activated the WAP-Cre gene. Hydrocortisone and prolactin alone did not. Any combination of hormones that included insulin was effective. Only I, H and Prl together were able to induce secretory differentiation and milk protein synthesis. In addition, EGF, IGF-2 and IGF-1 added individually produced activated (lacZ(+)) PI-MEC in explant cultures. Neither estrogen nor progesterone induced WAP-Cre expression in the explants. None of these positive initiators of WAP-Cre expression in PI-MEC were effective in mammospheres or two-dimensional cultures of mammary epithelium, indicating the indispensability of epithelial-stromal interaction in PI-MEC activation. Like PI-MEC, lacZ(+) cells from virgin explants proliferated and contributed progeny to mammospheres in vitro and to epithelial outgrowths in vivo after transplantation. LacZ(+) cells induced in virgin mouse mammary explants were multipotent (like PI-MEC) in impregnated hosts producing lacZ(+) mammary alveolar structures comprised of both myoepithelial and luminal progeny. These data demonstrate PI-MEC, a mammary epithelial sub-population of lobule-limited progenitor cells, are present in nulliparous female mice before parity and, like the PI-MEC observed following parity, are capable of proliferation, self-renewal and the capacity to produce progeny of diverse epithelial cell fates.

TGFβ1 and TGFα contrarily affect alveolar survival and tumorigenesis in mouse mammary epithelium

Growth factors and hormones are responsible for development of the mammary gland and can contribute to mammary carcinogenesis. The transforming growth factors (TGF) alpha and beta1 demonstrate opposing effects on the mammary epithelium. TGFalpha is a mitogen and survival factor for mammary secretory cells and is often upregulated in cancer, while TGFbeta1 may act as a growth suppressor and has been shown to inhibit alveolar development and lactogenesis. To examine the contradistinct effects of TGFalpha and TGFbeta1 on normal mammary epithelium, we crossed MT-TGFalpha mice with WAP-TGFbeta1 transgenic mice. The newly generated bitransgenic mice failed to nurse their pups and were resistant to mammary tumorigenesis (0% at 12 months of age), compared to single transgenic MT-TGFalpha in which the majority (65% at 12 months of age) of the mice developed hyperplastic alveolar mammary lesions. Transplantation studies showed that bitransgenic tissue was highly resistant to tumor formation even after multiple pregnancies. WAP-TGFbeta1 mammary transplants often failed to grow and fully fill cleared mammary fat pads upon transplantation. This repression of growth was completely reversed in the bitransgenic implants, which grew as well as normal epithelium upon transplantation. In addition, TGF and bitransgenic TGFalpha/TGFbeta1 mice had reduced rates of apoptosis during involution as compared to wild type and TGFbeta1. These data demonstrate that TGFbeta1 and TGFalpha exhibit opposing effects upon the proliferation and survival of mammary epithelium when expressed alone but when expressed together result in reciprocally suppressive effects upon one another in the context of mammary development and tumorigenesis.

Interleukin-13 induces proliferation of human airway epithelial cells in vitro via a mechanism mediated by transforming growth factor-alpha

Remodeling of the airways, as occurs in asthmatic patients, is associated with the continual presence of inflammatory mediators and Th2 cytokines, especially interleukin (IL)-13, during cycles of epithelial injury and repair. In this study, we examined the effect of IL-13 on well-differentiated normal human bronchial epithelial (NHBE) cells maintained in air-liquid interface culture. IL-13 induced proliferation of NHBE cells after 24 h exposure, as reflected by [(3)H]thymidine uptake and cell counts. The effects of IL-13 were mediated through the epidermal growth factor receptor (EGFR), as proliferation was attenuated by AG1478, an EGFR tyrosine kinase inhibitor. Proliferation appeared to be mediated by transforming growth factor (TGF)-alpha, a potent ligand for EGFR, which was released rapidly from NHBE cells in response to IL-13. Neutralizing antibody to TGF-alpha, but not antibodies against other potentially important growth factors (EGF, heparin binding epidermal growth factor-like growth factor [HB-EGF], platelet-derived growth factor [PDGF]), inhibited the mitogenic response to IL-13. This study provides the first experimental evidence that IL-13 can initiate a proliferative response of human airway epithelium in the absence of inflammatory cells or other cell types. The results are consistent with a mechanism whereby IL-13 induces release of TGF-alpha from the epithelial cells, which in turn binds via an autocrine/paracrine-type action to the EGFR, initiating proliferation. IL-13-induced airway remodeling in vivo may involve this epithelium-driven response.

Hypertrophic pulmonary osteoarthropathy and breast cancer

Hypertrophic pulmonary osteoarthropathy is an uncommon, poorly understood syndrome usually seen with bronchogenic carcinomas, and rarely with tumors metastatic to the lungs or mediastinum. In a review of the literature, we have found only 140 cases associated with nonbronchogenic intrathoracic tumors. We have reported a case associated with metastatic breast carcinoma in which surgical resection led to rapid disappearance of the syndrome and prolonged palliation for the patient.

An epizootic of measles in captive silvered leaf-monkeys (Presbytis cristatus) in Malaysia

An epizootic of measles occurred in a group of 31 silvered leaf-monkeys (Presbytis cristatus) that had been in captivity for 4-12 months. Twenty-four of the monkeys exhibited a maculopapular rash that persisted for 6-9 days. A serous to mucopurulent nasal discharge and conjunctivitis were seen in some animals. Eight monkeys died during the epizootic; however, their deaths could not be directly attributed to measles. Serum samples from the surviving monkeys collected 1-2 months prior to, and 5 weeks after, the epizootic were examined by the complement-fixation and hemagglutination-inhibition tests for antibodies to measles virus. The preepizootic complement-fixation titers were all less than 1:4 and hemagglutination-inhibition titers, less than 1:10. The postepizootic complement-fixation titers in 21 of 23 surviving monkeys ranged from 1:8 to 1:128, and hemagglutination-inhibition titers in 22 of 23 monkeys ranged from 1:40 to 1:80 or greater.

Enhancement of infectivity of encephalomyocarditis virus RNA by amphotericin B methyl ester

The methyl ester of amphotericin B (AmBME), a macrolide polyene antibiotic, enhanced the infectivity of encephalomyocarditis (EMC) virus RNA for L929 cells. AmBME alone (100 microgram/ml) resulted in increases in EMC virus RNA infectivity of 10- to 100-fold. Addition of DEAE dextran at concentrations (5 microgram/ml), which alone slightly suppressed EMC virus RNA infectivity, further augmented the effects of AmBME (augmentation in infectivity up to 750-fold). AmBME did not inhibit RNase, did not enhance EMC virus infectivity and increased infectivity of EMC virus RNA which was already cell-associated. The polyenes are probably acting by increasing intracellular penetration of polyribonucleotides.

Increase by calcium in production of interferon by L929 cells induced with polyriboinosinate-polyribocytidylate complex

Calcium chloride (5 to 20 mM) potentiated interferon production induced by rIn:rCn in L929 mouse fibroblasts up to a thousand-fold. Higher concentrations of calcium (20 to 65 mM) mixed with rIn:rCn were associated with increased cytotoxicity and a more acidic medium, but were effective in enhancing interferon production if preparations were adjusted to a uniform pH. Although calcium increased cellular binding of 3H-rCn:rIn, only a partial correlation between binding and interferon production was observed.