Involvement of growth factors in the regulation of pubertal mammary growth in cattle

ERBB Receptors and Their Ligands in the Developing Mammary Glands of Different Species: Fifteen Characters in Search of an Author

The ERBB tyrosine kinase receptors and their ligands belong to a complex family that has diverse biological effects and expression profiles in the developing mammary glands, where its members play an essential role in translating hormone signals into local effects. While our understanding of these processes stems mostly from mouse models, there is the potential for differences in how this family functions in the mammary glands of other species, particularly in light of their unique histomorphological features. Herein we review the postnatal distribution and function of ERBB receptors and their ligands in the mammary glands of rodents and humans, as well as for livestock and companion animals. Our analysis highlights the diverse biology for this family and its members across species, the regulation of their expression, and how their roles and functions might be modulated by varying stromal composition and hormone interactions. Given that ERBB receptors and their ligands have the potential to influence processes ranging from normal mammary development to diseased states such as cancer and/or mastitis, both in human and veterinary medicine, a more complete understanding of their biological functions should help to direct future research and the identification of new therapeutic targets.

MiR-21-3p Centric Regulatory Network in Dairy Cow Mammary Epithelial Cell Proliferation

MicroRNA-mediated gene regulation is important for the development of the mammary gland and the lactating process. A previous study has shown that the expression of microRNA-21 (miR-21) is different in the dry and early lactation period of the dairy cow mammary gland, but the molecular mechanisms underlying the lactation cycle are not fully understood. Here, the function of miR-21-3p on bovine mammary gland epithelial cells (BMECs) was detected by MTT assay and flow cytometry analysis, which showed that miR-21-3p significantly promoted the cell viability and proliferation. Then, the regulating mechanism of miR-21-3p on cell viability and proliferation was elucidated. Dual luciferase assay, RT-qPCR, and Western blot results revealed that IGFBP5 was a target gene of miR-21-3p. It was known that lncRNA could act as a competing endogenous RNA to sequester miRNAs and reduce the regulatory effect of miRNA-targeted genes. Based on our previous lncRNA-seq data and bioinformatics analysis, lncRNA NONBTAT017009.2 was potentially associated with miR-21-3p, and its expression was specifically inhibited with the transfection of miR-21-3p mimic into BMECs. Inversely, the overexpression of NONBTAT017009.2 significantly decreased the expression level of miR-21-3p in BMECs, while the expression of IGFBP5, the target gene of miR-21-3p, was significantly upregulated. In addition, the promoter region of miR-21 contained two STAT3 binding sites, and the dual luciferase reporter assays revealed that the overexpression of STAT3 significantly reduced the promoter activity of miR-21, implying that the transcription factor STAT3 may act as an upstream regulator affecting the regulation process of miR-21-3p. The overexpression of STAT3 significantly inhibited the expression of miR-21-3p, while the mRNA expression of IGFBP5 was significantly increased compared with the control group. Besides, there are no STAT3 binding sites in the promoter region of IGFBP5 as we predicted by gene-regulation and JASPAR software. Therefore, it could infer that STAT3 might regulate the expression of IGFBP5 by miR-21-3p. Taken together, these results established a regulatory network of miR-21-3p to illustrate the regulating mechanism on promoting cow mammary epithelial cell proliferation.

A corn straw-based diet increases release of inflammatory cytokines in peripheral blood mononuclear cells of dairy cows

Recent studies have shown that diet can affect the body's immunity. Roughage of dairy cows consists of a variety of plant materials which make different contributions to health. This study investigated the effect of different roughages on the immunity of dairy cows. Serum, peripheral blood mononuclear cells (PBMCs), and milk samples were collected from 20 multiparous mid-lactation cows fed mixed forage (MF)- or corn straw (CS)-based diets. Expression profile analysis was used to detect the differentially expressed genes (DEGs) from PBMCs. The results showed that milk protein in the MF group increased to 3.22 g/100 ml, while that of the CS group milk was 2.96 g/100 ml; by RNA sequencing, it was found that 1615 genes were differentially expressed between the CS group and the MF group among the 24 027 analyzed probes. Gene ontology (GO) and pathway analysis of DEGs suggested that these genes (especially genes coding cytokines, chemokine and its receptors) are involved in the immune response. Results were confirmed at the protein level via detecting the levels of interleukin-2 (IL-2), IL-6, IL-10, IL-12, leptin (LEP), interferon-γ (IFN-γ), transforming growth factor-β1 (TGF-β1), and tumor necrosis factor-α (TNF-α) in peripheral blood by enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay analysis. Our data supported the conclusions that the protein content in milk of the MF group was higher than that of the CS group, the CS-based diets induced more release of cytokines than the MF-based diets in dairy cows' PBMCs, and milk protein content may be affected by cytokines.

Effects of cinnamaldehyde or monensin on performance of weaned Holstein dairy heifers

The objective of this 70-d study was to determine the effects of the essential oil cinnamaldehyde compared with the ionophore monensin on performance of weaned Holstein dairy heifers. Eighty-four Holstein dairy heifers (91 ± 3.33 d of age; 109 ± 7.55 kg) were housed in a naturally ventilated curtain sidewall, straw-bedded barn in 12 pens with 7 heifers/pen (3.98 m²/head). Heifers were randomly assigned to 1 of 4 treatments in a completely randomized design: (1) control (CON; carrier, 908 g of ground corn), (2) monensin sodium [MON; 1 mg/kg of body weight (BW) + carrier], (3) cinnamaldehyde (CIN1; 1 mg/kg of BW + carrier), or (4) cinnamaldehyde (CIN2; 2 mg/kg of BW + carrier). The treatments were hand-mixed into a 20% crude protein (CP) whole shelled corn and protein pellet mix fed at 2.21 kg/heifer daily. Heifers had access to free-choice hay and water daily. Initial BW and hip heights were taken at the start of the study and every other week thereafter until calves reached 23 wk of age. Blood samples were also taken on each weigh day to determine plasma urea nitrogen, glucose, and insulin-like growth factor-1 concentrations. Fecal samples were taken from the same 3 heifers/pen initially and then at d 28, 56, and 70 of the study for coccidia counts. Cinnamaldehyde had no performance effects on growth, hay intake, hip height, or blood metabolites compared with MON or CON. Average daily gains were 0.98, 0.99, 1.01, and 1.03 kg/d, and average hay intakes per pen were 17.08, 16.34, 18.11, and 17.60 kg/d for CON, MON, CIN1, and CIN2, respectively. Fecal samples by pens indicated the presence of viable coccidia, but the counts were low and not consistent across heifers within each pen. No benefits were associated with supplementing cinnamaldehyde or monensin into grain mixes for weaned heifers.

Short communication: Expression of T-box 2 and 3 in the bovine mammary gland

To increase our understanding of the mechanisms by which growth hormone (GH) and insulin-like growth factor (IGF)-I influence bovine mammary gland development, the potential roles of T-box2 (TBX2) and T-box3 (TBX3) were investigated. Although no information regarding expression of either transcription factor in the bovine mammary gland exists, it is known that TBX3 and its closely related family member, TBX2, are required for mammary gland development in humans and mice. Additionally, TBX3 mutations in humans and mice lead to ulnar mammary syndrome. Evidence is present in bone that TBX3 is required for proliferation and its expression is regulated by GH, an important regulator of mammary gland development and milk production. We hypothesized that TBX2 and TBX3 are expressed in the bovine mammary gland and that GH, IGF-I, or both increase TBX2 and TBX3 expression in bovine mammary epithelial cells (MEC). Bovine mammary gland tissue, MAC-T cells, primary MEC, and fibroblasts were obtained and TBX2 and TBX3 expression was determined by real-time reverse transcription PCR. In addition, TBX2 and TBX3 expression was examined in cells treated with 100 or 500 ng/mL of GH or 100 or 200 ng/mL of IGF-I for 24 or 48 h. Both TBX2 and TBX3 were expressed in bovine mammary tissue. Surprisingly, expression of TBX2 was only detected in mammary fibroblast cells, whereas TBX3 was expressed in all 3 cell types. Growth hormone did not alter TBX3 expression in MAC-T cells or MEC. However, IGF-I increased TBX3 expression in MAC-T, but not in primary MEC. We did not observe a change in TBX2 or TBX3 expression in fibroblasts treated with GH and IGF. Therefore, we concluded that (1) TBX2 and TBX3 are expressed in bovine mammary gland, (2) their expression is cell-type specific, and (3) IGF-I stimulates TBX3 expression in MAC-T cells.

IGF-I retards proper development of acinar structures formed by bovine mammary epithelial cells via sustained activation of Akt kinase

Insulin-like growth factor-I is involved in mammary gland development, promoting proliferation and inhibiting apoptosis of mammary epithelial cells (MECs). Mitogenic actions of IGF-I are mainly mediated by the phosphatidylinositol-3 kinase (PI3K)/Akt signaling pathway. We have found that in the presence of IGF-I bovine BME-UV1 MECs cultured on reconstituted basement membrane form large spheroids with disrupted polarity and no cavity in the center. These cells showed enhanced phosphorylation of Akt, decreased level of cleaved caspase-3, and sustained proliferative activity throughout the 16-d period of 3-dimensional culture. Inhibition of the PI3K/Akt pathway by a specific inhibitor of PI3K, LY294002, resulted in the restoration of the normal acinar phenotype. However, this effect was noted only when LY294002 was added in the second week of 3-dimensional culture, which corresponded with the time of cell cycle arrest and polarity formation under control conditions. Normal development of acini was also obtained when BME-UV1 cells were treated simultaneously with IGF-I and 17β-estradiol. The addition of 17β-estradiol regulated Akt activation, enabling the subsequent initiation of polarization processes. 17β-Estradiol also increased the level of IGFBP-3 protein in MECs cultured on Matrigel in the presence of IGF-I. The presented results indicate important interactions between signaling pathways activated by estrogen and IGF-I, which regulate alveologenesis in bovine mammary gland.

Effect of growth factors and lactogenic hormones on expression of plasminogen activator-related genes and cell proliferation in a bovine mammary epithelial cell line

There is conflicting evidence in the literature as to whether up-regulation of urokinase plasminogen activator (u-PA) expression is related to bovine mammary epithelial cell growth. The role of u-PA receptor (u-PAR) and that of the plasminogen activator inhibitors type 1 and type 2 (PAI-1 and PAI-2) in bovine mammary epithelial cell proliferation is not known. The effect of growth factors and various hormones known to affect mammary function on expression of u-PA, u-PAR, PAI-1, PAI-2 and cell proliferation using the BME-UV1 bovine mammary epithelial cell line was examined. Cell proliferation was measured using the MTT assay and direct cell enumeration. Results showed that both IGF-1 and EGF increased cell proliferation but EGF was a more potent mitogen than IGF-1. Furthermore, IGF-1 increased by 2-fold expression of both u-PA and u-PAR while EGF increased by 3·8-fold the expression of only u-PAR. Both growth factors had no effect on expression of PAI-1 and PAI-2. In a manner consistent with changes in gene expression, EGF and to a lesser extent IGF-1 up-regulated total cell associated, membrane-bound and secreted u-PA activity. Thus, a strong correlation exists between u-PAR gene expression along with the activity of u-PA present on cell membranes and cell proliferation. Dexamethasone, prolactin and surprisingly insulin had no effect on cell proliferation. Dexamethasone alone and when combined with insulin or prolactin up-regulated gene expression of both PAI- and PAI-2 but not that of u-PA and u-PAR. Decreased total cell-associated, membrane-bound and secreted u-PA activity was detected in cells cultured in the presence of dexamethasone when combined with insulin or prolactin. However no such effect was observed in the presence of dexamethasone alone. Thus, dexamethasone acting synergistically with prolactin or insulin inhibits the activation of the plasmin-plasminogen system but this inhibition is not correlated with any changes in cell proliferation.

Human milk proteins: an interactomics and updated functional overview

Milk and milk fractions are characterized by a wide array of proteins, whose concentration spans across several orders of magnitude. By exploiting a combined approach based on functional gene ontology enrichment (FatiGO/Babelomics), hierarchical clustering, and pathway and network analyses, we merged data from literature dealing with protein-oriented studies on human milk. A total of 285 entries defined a nonredundant list upon comparison with the Ingenuity Knowledge Base from the Ingenuity Pathway Analysis software. Results were compared with an inventory of bovine milk proteins gathered from dedicated proteomic studies. A protein core of 106 proteins was found, with most of the entries associated to three main biological functions, namely nutrient transport/lipid metabolism, concretization of the immune system response and cellular proliferation processes. Our analyses confirm and emphasize that the biological role of the human milk proteins is not only limited to the provision of external nutrients and defense molecules against pathogens to the suckling but also to the direct stimulation of the growth of neonate tissues/organs and to the development of a proper independent immune system, both through the induction of a number of molecular cascades associated with cell proliferation/differentiation. The latter aspects were previously investigated by single-molecule dedicated studies, missing the holistic view that results from our analysis.

The bovine milk proteome: cherishing, nourishing and fostering molecular complexity. An interactomics and functional overview

Bovine milk represents an essential source of nutrients for lactating calves and a key raw material for human food preparations. A wealth of data are present in the literature dealing with massive proteomic analyses of milk fractions and independent targeted studies on specific groups of proteins, such as caseins, globulins, hormones and cytokines. In this study, we merged data from previous investigations to compile an exhaustive list of 573 non-redundant annotated protein entries. This inventory was exploited for integrated in silico studies, including functional GO term enrichment (FatiGO/Babelomics), multiple pathway and network analyses. As expected, most of the milk proteins were grouped under pathways/networks/ontologies referring to nutrient transport, lipid metabolism and objectification of the immune system response. Notably enough, another functional family was observed as the most statistically significant one, which included proteins involved in the induction of cellular proliferation processes as well as in anatomical and haematological system development. Although the latter function for bovine milk proteins has long been postulated, studies reported so far mainly focused on a handful of molecules and missed the whole overview resulting from an integrated holistic analysis. A preliminary map of the bovine milk proteins interactome was also built up, which will be refined in future as result of the widespread use of quantitative methods in protein interaction studies and consequent reduction of false-positives within associated databases.

Liver regeneration

Liver regeneration after partial hepatectomy is a very complex and well-orchestrated phenomenon. It is carried out by the participation of all mature liver cell types. The process is associated with signaling cascades involving growth factors, cytokines, matrix remodeling, and several feedbacks of stimulation and inhibition of growth related signals. Liver manages to restore any lost mass and adjust its size to that of the organism, while at the same time providing full support for body homeostasis during the entire regenerative process. In situations when hepatocytes or biliary cells are blocked from regeneration, these cell types can function as facultative stem cells for each other.

Liver regeneration

Liver regeneration after partial hepatectomy is a very complex and well-orchestrated phenomenon. It is carried out by the participation of all mature liver cell types. The process is associated with signaling cascades involving growth factors, cytokines, matrix remodeling, and several feedbacks of stimulation and inhibition of growth related signals. Liver manages to restore any lost mass and adjust its size to that of the organism, while at the same time providing full support for body homeostasis during the entire regenerative process. In situations when hepatocytes or biliary cells are blocked from regeneration, these cell types can function as facultative stem cells for each other.

Localization of Fibroblast Growth Factor I (Acid Fibroblast Growth Factor) and Its mRNA in the Bovine Mammary Gland During Mammogenesis, Lactation and Involution

Growth factors are involved in development and function of the mammary gland. The aim of this study was the localization of fibroblast growth factor 1 (FGF-1) and its mRNA in the bovine mammary gland during different developmental and functional stages. Mammary tissue was obtained from German Brown Swiss cows (n = 23) during defined stages of mammogenesis (before and during pregnancy), lactogenesis, peak lactation and involution. The distribution of FGF-1 mRNA was studied using non-radioactive in situ hybridization, the corresponding FGF-protein was analysed using immunohistochemistry [avidin-biotin peroxidase complex (ABC)-method]. A moderate to distinct staining for FGF-mRNA was found in the epithelium of ducts and developing alveoli during mammogenesis. Post-partum at the same cellular locations, a considerable amount of FGF-1 mRNA, was seen that decreased during lactation. Also during early involution clear staining for FGF-mRNA could still be observed. Immunoreactive FGF-1 was found in considerable concentration in the epithelium of the mammary gland in heifers. The staining intensity generally decreased somewhat during mammogenesis and lactation, but could be always clearly demonstrated in the secretory epithelial cells of alveoli and glandular ducts. Also during the first day after the end of milking, the epithelium displayed a moderate to distinct epithelial immunostaining. Notably, After 4 weeks of involution, in many alveoli a shedding of the FGF-1 positive luminal cell layer was found. In our localization studies, no strict correlation between FGF-1 mRNA and its corresponding protein was found. The various reasons for this finding are discussed.

Leptin Does Not Act Directly on Mammary Epithelial Cells in Prepubertal Dairy Heifers

The mammary gland of prepubertal dairy heifers consists of parenchyma expanding into the stroma, a matrix of connective and adipose tissue. High planes of nutrition increase stromal mass, but inhibit growth of parenchyma. The parenchyma consists of epithelial cells proliferating in response to growth factors such as insulin like growth factor-I (IGF-I). These observations have led to the hypothesis that elevated planes of nutrition increase leptin production, which in turn inhibits IGF-I-mediated epithelial cell proliferation. To assess this possibility, heifers were offered planes of nutrition sustaining average daily gains of 715 g/d (normal; NP) or 1,202 g/d (high; HP) from 42 d of age until slaughter at 240 kg. At slaughter, HP heifers had 2-fold greater plasma leptin concentration and 3-fold greater leptin mRNA abundance in mammary stroma and parenchyma. To assess the causal nature between leptin and parenchymal development, the induction of signaling events and functional responses in the MAC-T cell line and in primary mammary epithelial cells by leptin was examined. Leptin did not induce phosphorylation of signal transducers and activators of transcription (STAT)3, STAT5, extracellular signal-regulated kinase (ERK1/2), or AKT/Protein kinase B. Consistent with its inability to signal, leptin did not alter basal- or IGF-I-stimulated thymidine incorporation or increase suppressors of cytokine signaling 3 (SOCS3) expression in these cells. Transcripts corresponding to the short leptin receptor form were present in mammary tissue, but those corresponding to the long signaling form were not detected in either mammary tissue or cells. In conclusion, elevated planes of nutrition increase leptin synthesis in mammary stroma, but leptin does not act directly on bovine mammary epithelial cells.

Activin and follistatin in rat mammary gland

Mammary gland morphogenesis and differentiation are mediated through the combined activities of systemic hormones and locally synthesized growth factors. Activin, a member of the transforming growth factor (TGF)-beta superfamily, is known to regulate the growth and differentiation of several cell types. In the present study, we investigated the role of activin in rat mammary gland on different stages of development. We found that activin A in vitro inhibits the proliferation of isolated acini, and this effect increases with the development of the gland. This factor also produces in vitro an inhibition of the final differentiation of acini obtained from 19th day pregnant rats. We also report the expression of activin receptors IIA and IIB mRNA in whole rat mammary gland and acini, with decreased levels of expression of type IIA (in both compartments) and IIB (in acini) during pregnancy and lactogenesis. In addition, we show that activin betaB-subunit mRNA decreases throughout pregnancy, and that the mRNA levels of follistatin (Fst) (its ligand protein) are high in cycling rats and at the beginning of pregnancy and diminish thereafter, having the acini higher levels of expression. Our data show that activin betaB-subunit, follistatin and ActRIIA and IIB transcripts are expressed in rat mammary gland at appropriate times and locations during development, allowing an interplay that might regulate activin action on growth and differentiation of the gland.

Exogenous TGF-β1 Promotes Stromal Development in the Heifer Mammary Gland

The objectives of this study were to determine the local effects of transforming growth factor-beta1 (TGF-beta1) on mammary epithelial and stromal cell proliferation and expression of the TGF-beta1 responsive genes c-myc and fibronectin. A single slow-release plastic pellet containing 5 microg of TGF-beta1 and 20 mg of BSA was implanted in the parenchyma of the right rear quarter of the mammary gland of 9-mo-old prepubertal heifers. A control pellet containing 20 mg of BSA was implanted in the left rear quarter of each heifer. All heifers were treated with bromodeoxyuridine (BrdU) at 4, 12.5, and 22 h after the pellets were implanted to label proliferating cells. Two hours after the last BrdU injection, the animals were euthanatized, and their mammary glands were recovered. Proliferation of mammary stromal cells was significantly higher in TGF-beta1-treated quarters than in BSA-treated, control quarters (3.5 vs. 1.8% BrdU-positive cells). This result coincided with a lack of significant effect of TGF-beta1 on proliferation of mammary epithelial cells and apoptosis. By quantitative reverse transcriptase-polymerase chain reaction, we found that c-myc gene expression was unchanged after TGF-beta1 treatment, but fibronectin gene expression was increased 3-fold in TGF-beta1-treated quarters compared with BSA-treated, control quarters. Thus, we concluded that TGF-beta1 selectively acts on the stromal compartment of the bovine mammary gland by increasing cell proliferation and gene expression of the extracellular matrix protein fibronectin.

Clubbed fingers: the claws we lost?

Clubbed digits resemble the human embryonic fingers and toes, which look like the digits of a claw. Clubbed digits, thus, may represent the return of the embryonic claw and may even represent the claws man has lost during evolution, if ontogenesis really recapitulates phylogenesis. We put forward the hypothesis that secondary clubbing, like gynecomastia, is caused by a pathologic condition, which alters hormone levels in the blood, leading to the activation of 'dormant' genes, resulting in the development of an organ. However, the nature of the diseases that cause clubbing suggests that these hormones may actually be cytokines, acting as hormones. The nature of these cytokines is not known. They may be identified by comparing their blood levels or the combination of their blood levels to the presence or absence of clubbing, but also to the degree of clubbing and its disappearance after treatment of the primary disease.

To create the correct microenvironment: three-dimensional heterotypic collagen assays for human breast epithelial morphogenesis and neoplasia

The normal human breast comprises an inner layer of luminal epithelial cells and an outer layer of myoepithelial cells separated from the connective tissue stroma by an intact basement membrane. In breast cancer, tumor cells are in direct contact with the surrounding highly activated collagenous stroma, with little or no discernible myoepithelial fence from the original double-layered structure. To understand the evolution of these two scenarios, we took advantage of a three-dimensional hydrated collagen gel approach. The contribution of myoepithelial cells to normal morphogenesis was studied by ablation and rescue experiments, and genes regulated on tumor cell-fibroblast interaction were identified in a tumor environment assay. In normal breast morphogenesis, the ability to correctly polarize sialomucin to the luminal membrane of emerging acini was used as a criterion for apical polarity and functional differentiation. In the assay of breast neoplasia, the consequence of reciprocal tumor cell-fibroblast interaction was addressed morphologically as well as by a differential display approach. Normal breast epithelial cells were purified immunomagnetically and an established cell line, MCF-7, was used as a surrogate tumor cell. With regard to the importance of myoepithelial cells in normal breast epithelial morphogenesis, the collagen gel assay elucidated the following subtleties: In contrast to culturing in basement membrane gels, luminal epithelial cells when cultured alone made structures that were all inversely polarized. This aberrant polarity could be rescued by co-culture with myoepithelial cells. The molecular activity of myoepithelial cells responsible for correct morphogenesis was narrowed down to the laminin-1 component of the basement membrane. As for the consequence of interaction of tumor cells with connective tissue fibroblasts, the assay allowed us to identify a hitherto undescribed gene referred to as EPSTI1. The relevance of the assay-based identification of regulated genes was confirmed in a series of breast carcinomas in which EPSTI1 was highly upregulated compared with normal breast. Few if any of these observations would have been possible on two-dimensional tissue culture plastic.