Epidermal growth factor in mouse milk during early lactation: lack of dependency on submandibular glands

Milk growth factors and expression of small intestinal growth factor receptors during the perinatal period in mice

BACKGROUND

Growth factors (GFs) are milk bioactive components contributing to the regulation of neonatal small intestinal maturation, and their receptors on the small intestinal epithelium play essential roles in mediating the functions of GFs. There is limited data correlating milk GFs and their receptors in the neonatal small intestine during the perinatal period.

METHODS

Small intestines of C57BL/6N mouse pups were collected at regular intervals during fetal life and up to postnatal day (PD) 60. Gene expression of GF receptors was determined by real-time qPCR. Milk GF concentrations up to PD21 were analyzed by enzyme-linked immunosorbent assay.

RESULTS

The majority of GF receptors showed significantly greater expression in the fetus than in postnatal life, and a sharp decrease occurred from PD14 extending to PD60; solid food restriction (PD14 and PD18) did not affect this decrease. Concentrations of five detected milk GFs demonstrated that GFs and the corresponding small intestinal receptors exhibited different correlations, with only milk transforming growth factor β1 (TGF-β1) having a significant positive correlation with TGF-β receptor 1 mRNA.

CONCLUSION

Gene expression of small intestinal GF receptors is likely a process of neonatal intestinal maturation that is affected concurrently by milk GFs and additional endogenous factors.

Role of 3'-5'-cyclic adenosine monophosphate on the epidermal growth factor dependent survival in mammary epithelial cells

Epidermal growth factor (EGF) has been suggested to play a key role in the maintenance of epithelial cell survival during lactation. Previously, we demonstrated that EGF dependent activation of PI3K pathway prevents apoptosis in confluent murine HC11 cells cultured under low nutrient conditions. The EGF protective effect is associated with increased levels of the antiapoptotic protein Bcl-XL. Here, we identify the EGF-dependent mechanism involved in cell survival that converges in the regulation of bcl-X expression by activated CREB. EGF induces Bcl-XL expression through activation of a unique bcl-X promoter, the P1; being not only the PI3K/AKT signaling pathway but also the increase in cAMP levels and the concomitant PKA/CREB activation necessary for both bcl-XL upregulation and apoptosis avoidance. Results presented in this work suggest the existence of a novel connection between the EGF receptor and the adenylate cyclase that would have an impact in preventing apoptosis under low nutrient conditions.

Newborns prefer the odor of milk and nipples from females matched in lactation age: Comparison of two mouse strains

Newborn mice are attracted to mammary odor cues carried in murine milk and nipple secretions. However, murine milk odor is not equally attractive along lactation. The present study focuses on the differential response of 2day-old mouse pups of C57Bl/6 (C) and Balb/C (B) strains to the odor of milk (Experiment 1) and nipples (Experiment 2) that are matched/unmatched in terms of pup's age or strain. In Experiment 1, C and B pups were tested in a series of tests simultaneously opposing either murine milk and a blank (water), or two milks collected in early and late lactation (lactation days 2 and 15, respectively) from females belonging to their own or the other strain. Results showed that C and B pups were attracted to the odor of the different milks regardless of the lactation age and the strain of the donor female. Nevertheless, C and B pups preferred the odor conveyed by early- than late-lactation milk of either strain. Moreover, early-lactation milk from C females was more attractive than early-lactation milk from B females for pups of either strain. In Experiment 2, differential nipple grasping response of C and B pups was measured when they were exposed to nipples of females in early or late lactation. The proportion of C pups that grasped a nipple was greater when they were exposed to a nipple in early lactation regardless of the strain of the donor females, whereas the proportion of B pups that grasped a nipple was greater when they were exposed to a nipple in early lactation, but only from own strain. Thus, newborn mice prefer the odor of milk and nipples from females that are matched in lactation age. This result is discussed in terms of reciprocally adaptive mechanisms between lactating females and their newborn offspring.

The Mammary Gland in Mucosal and Regional Immunity

The mammary gland (MG) lacks a mucosa but is part of the mucosal immune system because of its role in passive mucosal immunity. The MG is not an inductive site for mucosal immunity. Rather, synthesis of immunoglobulin (Ig)A by plasma cells stimulated at distal inductive sites dominate in the milk of rodents, humans, and swine whereas IgG1 derived from serum predominates in ruminants. Despite the considerable biodiversity in the role of the MG, IgG passively transfers the maternal systemic immunological experience whereas IgA transfers the mucosal immunological experience. Although passive antibodies are protective, they and other lacteal constituents can be immunoregulatory. Immune protection of the MG largely depends on the innate immune system; the monocytes–macrophages group together with intraepithelial lymphocytes is dominant in the healthy gland. An increase in somatic cells (neutrophils) and various interleukins signal infection (mastitis) and a local immune response in the MG. The major role of the MG to mucosal immunity is the passive immunity supplied to the suckling neonate.

The response of newly born mice to odors of murine colostrum and milk: unconditionally attractive, conditionally discriminated

It is a general rule that milk conveys chemosensory cues that are attractive to mammalian neonates. This study investigated whether compositional fluctuations in milk along lactation induce variations in newborn mouse pups' (Mus musculus, strain BALB/c) attraction to milk odor. Pups differing in suckling experience were exposed to the odor of milk sampled from females varying in lactational stage. Immediately after birth, suckling-inexperienced (P0) and suckling-experienced (P0suck ) pups were assayed in a series of paired-choice tests contrasting murine milk [of lactation days 0, 3, 15 (abridged L0, L3, L15, respectively)] and a blank (water) to evaluate olfactory detection and attraction of milk odor. Preference tests further paired these milk two-by-two to assess their relative attraction. Results showed first that P0 and P0suck pups detect and positively orient to any milk odor. When L0 is presented against L15 milk, P0 pups orient for a similar duration towards these odor stimuli, whereas P0suck pups spend more time toward the odor of L0 than of L15 milk. Finally, P0suck pups orient similarly to odors of L0 milk collected before/after the first suckling episode (L0 and L0suck , respectively), but the odor of L0 milk was more attractive than that of L3 milk. Thus, mouse pups' positive orientation toward the odors of murine colostrum (assumed to correspond to L0/L0suck milk) and later-lactation milk appears unconditional of previous suckling experience, whereas their ability to discriminate or display preference between milk differing in lactation stage appears conditional on postnatal exposure effects.

Morphological and functional events associated to weaning in rabbits

It is acknowledged that the most critical period of rabbit post natal development comprises the first 10-15 days after weaning, when the animals are most susceptible to gastrointestinal infections and at greatest risk of a fatal outcome. Detailed information on rabbits' weaning is provided. The advantages and disadvantages of early weaning (under 23 days of age) are summarised. Regardless of the numerous reports, the effects of early weaning on the growth and development of bunnies and the physiological status of rabbit does are contradictory. The morphological changes in rabbit digestive tract related to weaning - development of intestinal mucosa, height of villi, crypt depth and villus height to crypt depth ratio - are described in detail. The review also goes over several functional changes in rabbits' organism during weaning: blood cholesterol, triglycerides, α-amylase, lysozyme, complement, triiodothyronine and thyroxine concentrations, and the time course of epidermal growth factor in the milk of lactating does. Based on published research reports, both ours and of other authors, we suggest that from a physiological point of view, the early weaning of rabbits is not fully justified at present. Nevertheless, the increasing market demand for rabbit meat makes early weaning an attractive alternative for farmers and necessitates further studies on the optimisation of weaning in this species.

The potential physiological significance of milk-borne hormonally active substances for the neonate

This article reviews the presence and potential physiological significance of hormones and hormonally active substances (including growth factors) in human milk. Human milk has been found to contain several nonpeptide hormones and many peptide hormones and growth factors. In contrast to human breast milk, infant formulae lack some hormonally active peptides. There is little data concerning the effects of these agents on human neonates. Studies in immature experimental animals showing effects of orogastically administered hormones are summarized. The problems of supplementation of infant formula are discussed. Since hormones are present in the milk as a "cocktail" of potentially agonistic and antagonistic substances, one question is whether supplementation with a single agent would disturb this balance.

Stability of epidermal growth factor in the gastrointestinal lumen of suckling and weaned pigs

The stability of epidermal growth factor (EGF) in the gastrointestinal humen of 3-day-old suckling and 45-day-old weaned pigs was examined by incubating iodine labeled recombinant human EGF (hEGF) in the gastrointestinal fluids at 37 degrees C and monitoring the generation of acid soluble radioactivity. Chromatographic analysis and receptor binding study were also undertaken. The results showed that hEGF was quite stable in the gastric fluids in both suckling and weaned pigs with less than 20% degradation after 20 min incubation. The degradation rate in the intestinal fluids varied with the region of the small intestine and the age of the animals. At the proximal and mid regions of the small intestine in suckling pigs the degradation rate of hEGF after 20 min incubation was 5 and 20% respectively, while the degradation rate at the distal region was up to 50%. In the small intestinal lumen in weaned pigs the degradation rate of hEGF was much greater than that in suckling pigs, and the degradation rates at the proximal, mid and distal regions were 33, 51 and 56% respectively. Addition of acid soluble or casein fractions of porcine colostrum markedly reduced the degradation of hEGF in the intestinal fluids. These results indicate that milk-borne EGF is stable in the gastric and proximal intestinal humen in suckling pigs, and may play a role in regulating postnatal development in the suckling young.

Development and heterogeneity of prolactin cells

Prolactin (PRL) is synthesized in pituitary cells called mammotrophs (PRL cells). Ample evidence demonstrates that the PRL cell population consists of structurally and functionally heterogeneous PRL cells. Multiple variants of PRL molecules are found in various species. Prolactin cells may be divided into various subtypes in the rat and mouse. Secretory activities differ among the PRL cell population. These heterogeneities may reflect various phases of the maturation process of PRL cells, or the integrated outcome of various functional differences in PRL cells. To clarify the significance of heterogeneities among PRL cells, we present updated reports on the differentiation, proliferation, and development of PRL cells, and discuss factors responsible for the functional differences in PRL cell population. The age-related alteration in PRL secretion in the rat is summarized, because it is one of the most important aspects of the developmental changes in PRL cells. A mammosomatotroph, which secretes growth hormone and PRL, is found in various species. Prolactin cells and somatotrophs are derived from the same lineage. The possible relationship among PRL cells, somatotrophs, and mammosomatotrophs is discussed.

Crossfostering and early development of natural killer cytotoxic activity in various inbred mouse strains

In the present study using crossfostering among three inbred mouse strains (C57BL/6, DBA/2, and Balb/c) we compared the effects of lactation with milk of different compositions on the development of NK cells cytotoxic activity. The results show that the pups from C57BL/6 and DBA/2 mice exhibit a significant early increase of NK cells cytotoxic activity when fostered by Balb/c dams, in comparison to those fostered by natural mothers. The analysis of proteins, lactose, and lipids showed difference among the strains for all components. Strain effects for days of lactation were also observed. The naso-anal length and the body weight of young mice showed differences with the strain of fostering mothers. The results indicate that the characteristic of maternal milk composition interacts with the inbred genetic susceptibility of the pups to elicit the full expression of the level of NK activity.

Role of salivary epidermal growth factor in the pathogenesis of Barrett's columnar lined oesophagus

Epidermal growth factor (EGF) is implicated in the regeneration of epithelial cells at the site of inflammation or ulceration in the gastrointestinal tract. Single parotid EGF concentration and production was studied in 64 patients with Barrett's columnar lined oesophagus (CLO), in 22 patients with severe reflux oesophagitis without columnar metaplasia and in 51 normal controls. In control patients, mean salivary EGF concentration was 2790 pg/ml (median 1450 pg/ml; range 450-16,500 pg/ml) and mean single parotid EGF production was 2550 pg/min (median 1750 pg/min; range 790-18,000 pg/min). Patients with severe reflux oesophagitis had a similar EGF concentration (mean 3112 pg/ml; median 1500 pg/ml; range 300-16,000 pg/ml) and production (mean 3100 pg/min; median 2200 pg/min; range 790-17,950 pg/min) to controls. Patients with CLO had a 62 per cent lower mean EGF concentration (mean 1197 pg/ml; median 640 pg/ml; range 233-4500 pg/ml) (P less than 0.001, Mann-Whitney U test) and a 60 per cent lower EGF production (mean 1254 pg/min; median 800 pg/min; range 170-3125 pg/min) (P less than 0.001, Mann-Whitney U test) than patients with severe reflux oesophagitis. A subpopulation with malignant change in CLO (n = 16) had a similar EGF concentration and production to the CLO group as a whole (mean 1240 and 1300 pg/min, respectively). Low salivary EGF levels are associated with Barrett's CLO but not with severe oesophagitis without columnar metaplasia. EGF levels do not identify those patients who will subsequently develop malignant change.

Changes in concentrations of insulin-like growth factor 1, insulin and growth hormone in bovine mammary gland secretion ante and post partum

Concentrations of insulin-like growth factor 1 (IGF-1), insulin and growth hormone were measured in the secretion of the bovine mammary gland from day 70 ante partum until 6 d post partum. Highest levels were found during the last 2 weeks ante partum followed by a rapid decrease during the first milkings post partum. The association of IGF-1 with its binding proteins in milk was analysed and striking differences were found in the distribution of bound and free IGF-1. IGF-1 appeared mainly in the bound form (91%) at days 40-2 ante partum. Free IGF-1 preponderated in the first milkings post partum (73%) and changed again to about 85% in the bound form after day 4 post partum. A slightly acidic pH (6.3) of the secretion was correlated with high amounts of free IGF-1. Gel filtration experiments revealed a possible pH-dependent mechanism for the binding of IGF-1 to its binding proteins in milk.

Lack of effect of epidermal growth factor treatment in late-pregnant ewes on subsequent lactation

Twin-bearing ewes were treated with epidermal growth factor (EGF) to determine its effect on mammogenesis and resultant milk production and composition. The EGF was infused intravenously at a dose rate of 0.5 mg/d in 300 ml saline between days 117 and 139 of gestation; control animals received placebo infusions of saline. All animals then received continuous infusions of 300 ml/d saline on days 139-144. Following parturition 1-5 d later, ewes were milked by hand for 10 d and thereafter were machine-milked until day 16 of lactation. At this level of treatment, EGF was not detected in the circulation during infusion and feed intake was not affected. All ewes gave birth to healthy twin lambs. There were no effects of EGF on birth weights of lambs, live weights of ewes or lengths of gestation. An EGF-immunoreactive material was detected in the mammary secretions of control ewes at a mean concentration of 2 micrograms/l on day 1 of lactation. Two ewes had detectable levels on day 2, but none was found in the milk thereafter. In the EGF-infused group, concentrations of EGF in colostrum were approximately 10 times higher than in the control ewes on day 1 of lactation and EGF was detected in mammary secretions on day 2 but not in subsequent milk samples. A range of 0.3-0.5% of the EGF infused appeared in mammary secretions over the first 2 d of lactation. No other differences were observed for colostrum composition, subsequent milk yield or composition between the two groups of ewes indicating that mammary gland development and function were unaffected. The levels of EGF observed in the mammary secretions of treated and control ewes indicate that the mammary glands accumulate and store EGF in the pre partum period.

Biologically active polypeptides in milk

Many biologically active polypeptides have been described in the milk of several species. Various functions for these polypeptides in addition to nutrition have been proposed in the maternal body and in the breast-fed infant. These polypeptides are derived from several sources and multiple factors control their secretion into milk as well as their fate in the mother and infant. An increasing body of evidence supports the concept that they may function physiologically.

Specific growth factor activity identifies and predicts murine mammary tumor

In milk from substrains of mice with varying incidences of developing mammary tumor, we have isolated a specific mitogenic activity, which is unique in that it identifies mice with mammary tumor and predicts those mice that will eventually develop mammary tumor. None of the milk samples from control mice, who never developed mammary tumor, contained this specific predictive mitogenic activity. Chemical characterization has shown this specific mitogenic activity to be acid- and heat-stable and resistant to reducing agents. Partial purification, by ion-exchange, high-performance liquid chromatography size-exclusion, and isoelectrofocusing techniques, of this specific mitogenic activity from milk of mice that had or eventually developed mammary tumor identifies several peptide growth factor components in a 6-10 kDa molecular weight range. Of known growth factors, radioassay techniques identify an insulin-like growth factor-1-like peptide as a major component. Small amounts of platelet-derived growth factor and transforming growth factor-beta activities also were present. Our results suggest that a subset of growth factors that are diagnostic of the presence of murine mammary tumor and predictive of eventual tumor development may be early indicators of the transition of a competent cell to a progressively malignant state. Similar studies of a secreted body fluid from women at risk for breast cancer may lead to the identification of a specific biologic tumor marker for breast cancer.

Changes of DNA methylation level during pre- and postnatal periods in mice

DNA methylation in an adult mammalian body shows tissue-specificity. But when and how the specificity is established in the process of development has not yet been elucidated. Here we have investigated age-dependent changes in the amount of 5-methyldeoxycytidine (5mdC) that DNA of various mouse tissues contains during the late-fetal and postnatal periods, using high-performance liquid chromatography. The tissue-specificity in the 5mdC level was observed in the late-fetal stage, and the level continued to change during the subsequent periods. The most pronounced alterations were observed in brain and liver, where similar biphasic changes were seen, but at different ages. At maturation, the 5mdC levels were high in thymus, spleen and brain, intermediate in lung, and low in liver and sperm. The data demonstrate the importance of the peri- and postnatal periods in establishment of tissue-specificity in 5mdC content.

Expression of epidermal growth factor in the kidney and submandibular gland during mouse postnatal development. An immunocytochemical and in situ hybridization study

Earlier work has demonstrated that the salivary glands and kidneys are the major sites of epidermal growth factor (EGF) synthesis in adult mice. The precise timing of the onset of endogenous EGF synthesis in these tissues is not yet clear. In the present study we assessed the ontogenesis of EGF expression in the Swiss-Webster mouse. Paraformaldehyde-fixed frozen sections of neonatal kidneys and salivary glands were probed with proEGF cRNA labelled with 35S for in situ hybridization and with rabbit antisera to mouse EGF for immunocytochemistry. Both EGF mRNA and immunoreactivity were first detected in the developing distal nephron between days 3 and 5 postpartum. Juxtamedullary nephrons underlying the superficial nephrogenic zone were the first to express EGF. During the 2nd week after birth, EGF-expressing tubules became more abundant and distributed to medullary as well as cortical regions, corresponding to the thick ascending limb of Henle and distal convoluted tubule. Initial EGF mRNA and immunoreactivity in the submandibular gland were first detected between days 18 and 20 postpartum and increased notably during the following weeks.

Epidermal growth factor reactivity in rat milk

The concentration of EGF immunoreactivity in rat whey increases from 0.3 pmol/ml at lactation day 1 to 2.0 pmol/ml at lactation day 19. The concentration of EGF is not influenced when the rats undergo sialoadenectomy prior to mating. On S-200 gel chromatography, almost all EGF-reactivity in rat whey elutes as a broad peak corresponding to a Stokes radius of 4.0 nm (an approximate molecular weight of 80 kDa). Almost no 6 kDa EGF is present. Judged by gel filtration of whey pre-incubated with 125I-EGF (6 kDa), no binding protein for EGF is present in rat whey. When rat milk is incubated overnight at 37 degrees C, the 80 kDa EGF is degraded and elutes as a peak with a Stokes radius of 2.7 nm, corresponding to a molecular weight of approximately 35 kDa EGF and as a peak corresponding to 6 kDa EGF. Also, after partial purification by immuno-affinity chromatography, the EGF-reactive material in rat whey behaves as a peptide with a Stokes radius of 2.7 nm, corresponding to a molecular weight of approximately 35 kDa at gel filtration. Comparative binding studies between EGF purified from the submandibular glands and the EGF purified from rat whey confirm differences in the binding to antibodies raised against submandibular EGF, but not in binding to the EGF-receptor. Our results make it unlikely that EGF in rat whey is derived from the submandibular glands.

Identification of a unique biological tumor marker in human breast cyst fluid and breast cancer tissue

Breast cyst fluid from 35 women was stratified into risk groups based on personal and family history of breast cancer. Mitogenic activity in breast cyst fluid of women at highest risk to develop breast cancer was significantly higher than the activity in the lowest-risk group. There was a direct dose-dependent relationship between mitogenic activity and increased risk of developing breast cancer. Size-exclusion chromatography showed that breast cyst fluid from women at highest risk contained two peaks of growth factor activity: less than 6 kilodaltons (kd), identified as human EGF (epidermal growth factor), and 6 to 18 kd. Moderate-risk group samples demonstrated only the single less than 6 kd peak, whereas the lowest-risk group had insignificant growth-promoting activity. Breast cancer tissue analyzed in a similar manner revealed a predominant 6- to 14-kd peak of mitogenic activity demonstrating the same acid- and heat-stability found in breast cyst fluid.

Transepithelial transport of epidermal growth factor by absorptive cells of suckling rat ileum

Epidermal growth factor (EGF), an acid-stable peptide present in rodent and human milk, is absorbed and promotes intestinal growth when fed to suckling rats. To determine whether absorptive cells of suckling rat ileum conduct selective transepithelial transport of EGF, we followed uptake of 125I-EGF from ileal loops by autoradiography and biochemical methods. Specific binding sites for 125I-EGF were localized by electron microscope autoradiography on apical membranes of ileal epithelial sheets in vitro. During uptake in vivo, radiolabeled molecules were concentrated in apical endosomal compartments and were also associated with lysosomal vacuoles, basolateral cell surfaces, and lamina propria. Excess cold EGF reduced basolateral label by 44% and TCA precipitable serum label by 38%. After 30 and 60 min of continuous uptake, radiolabeled molecules in epithelium, denuded mucosa, blood, and liver were analyzed under reducing conditions by reversed-phase high-pressure liquid chromatography (HPLC) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Although considerable degradation of 125I-EGF occurred after uptake from the lumen, a portion of radiolabel in epithelium and mucosa represented 125I-EGF which eluted somewhat more rapidly from C18 HPLC columns and showed a slight decrease in apparent molecular weight by SDS-PAGE. All radiolabel in blood and liver represented breakdown products. Thus, EGF is selectively transported across the ileal epithelium in suckling rats but is modified during transport. Milk EGF may accumulate in the lamina propria where it could influence growth and maturation of the suckling intestine.

Functional and structural characteristics of EGF and its receptor and their relationship to transforming proteins

Epidermal growth factor (EGF) is a peptide which effects the growth and/or differentiated functions of many cell types. Several pieces of evidence indicate that EGF and its receptor may play a role in carcinogenesis. Functional and structural characteristics of EGF and its receptor and their relationship to transforming proteins are discussed. EGF has extensive homology with alpha-transforming growth factor (alpha-TGF), which may actually be an embryonic form of EGF. Nevertheless, both EGF and alpha-TGF elicit transformation-associated phenotypes in target cells under certain conditions. EGF effects are mediated by a receptor present on the plasma membrane. The EGF receptor is a highly complex protein having several functions in addition to binding EGF in a highly specific manner. One of these functions is to phosphorylate tyrosyl residues on certain proteins. This activity is similar to that expressed by the src family of oncogene-encoded proteins. Besides sharing functional homology the EGF receptor also exhibits structural homology to several oncogene-encoded proteins. The v-erb-B-transforming protein has a striking extent of homology (95%) to the cytoplasmic portion of the EGF receptor. These data support the concept that some aspect of EGF-stimulated metabolism is involved in cellular transformation.