Insulin-like growth factor (IGF) system in the bovine mammary gland and milk

Is bovine somatotropin an alternative strategy to overcome the detrimental effects of high-gain diets on prepubertal Holstein × Gyr heifers?

Feeding high-gain diets and an inadequate energy and protein ratio during pre-puberty may lead to impaired growth and mammary gland development of heifers. Thus, frequent application of bovine somatotropin (bST) may prevent future losses in productivity, improve mammary development and animal performance. We aimed to evaluate the effects of bST on digestibility, performance, blood metabolites, mammary gland development, and carcass composition of high-performance prepubertal Holstein × Gyr heifers. Thirty-four Holstein × Gyr heifers with an average initial body weight of 218 ± 49 kg and 14 ± 4 months of age were submitted to an 84-day trial evaluating the effects of no bST or bST injections. Treatments were randomly assigned to each animal within one of the tree blocks. The bST did not influence digestibility or performance parameters. Regarding blood results, IGF1 concentration presented an interaction between treatment and day, where bST heifers had the highest IGF1 concentration. Heifers receiving bST also showed increased ribeye area; however, only an experimental day effect for backfat thickness was observed, with greater accumulation of carcass fat on day 84. Heifers receiving bST had lower pixels/mm² on parenchyma, characteristic of greater parenchymal tissue. Moreover, heifers on bST treatment also had reduced pixels/mm2, characteristic of reduced fat pad tissue. Lastly, bST injections did not influence liver and muscle gene expression, nor most genes evaluated in mammary gland tissue, except for IGFBP3 expression, which was greater for bST heifers. In summary, we confirm the efficacy of bST injections to overcome the detrimental effects of high-gain diets on mammary gland growth and to improve lean carcass gain of prepubertal Holstein × Gyr heifers.

Colostrogenesis: Role and Mechanism of the Bovine Fc Receptor of the Neonate (FcRn)

Colostrogenesis is a separate and unique phase of mammary epithelial cell activity occurring in the weeks before parturition and rather abruptly ending after birth in the bovine. It has been the focus of research to define what controls this process and how it produces high concentrations of specific biologically active components important for the neonate. In this review we consider colostrum composition and focus upon components that appear in first milked colostrum in concentrations exceeding that in blood serum. The Fc Receptor of the Neonate (FcRn) is recognized as the major immunoglobulin G (IgG) and albumin binding protein that accounts for the proteins' long half-lives. We integrate the action of the pinocytotic (fluid phase) uptake of extracellular components and merge them with FcRn in sorting endosomes. We define and explore the means of binding, sorting, and the transcytotic delivery of IgG1 while recycling IgG2 and albumin. We consider the means of releasing the ligands from the receptor within the endosome and describe a new secretion mechanism of cargo release into colostrum without the appearance of FcRn itself in colostrum. We integrate the insulin-like growth factor family, some of which are highly concentrated bioactive components of colostrum, with the mechanisms related to FcRn endosome action. In addition to secretion, we highlight the recent findings of a role of the FcRn in phagocytosis and antigen presentation and relate its significant and abrupt change in cellular location after parturition to a role in the prevention and resistance to mastitis infections.

Structural equation modeling for investigating multi-trait genetic architecture of udder health in dairy cattle

Mastitis is one of the most prevalent and costly diseases in dairy cattle. It results in changes in milk composition and quality which are indicators of udder inflammation in absence of clinical signs. We applied structural equation modeling (SEM) - GWAS aiming to explore interrelated dependency relationships among phenotypes related to udder health, including milk yield (MY), somatic cell score (SCS), lactose (%, LACT), pH and non-casein N (NCN, % of total milk N), in a cohort of 1,158 Brown Swiss cows. The phenotypic network inferred via the Hill-Climbing algorithm was used to estimate SEM parameters. Integration of multi-trait models-GWAS and SEM-GWAS identified six significant SNPs for SCS, and quantified the contribution of MY and LACT acting as mediator traits to total SNP effects. Functional analyses revealed that overrepresented pathways were often shared among traits and were consistent with biological knowledge (e.g., membrane transport activity for pH and MY or Wnt signaling for SCS and NCN). In summary, SEM-GWAS offered new insights on the relationships among udder health phenotypes and on the path of SNP effects, providing useful information for genetic improvement and management strategies in dairy cattle.

Functional analysis of recombinant buffalo lactoferrin and monoferric lobes and their cytotoxic effect on buffalo mammary epithelial cells

Lactoferrin (Lf) has been involved in diverse type of cellular activities and its biochemical properties are species specific. Lf is a bilobal molecule in which each lobe binds with one Fe²⁺/Fe³⁺ ion. A lot of physiological effects of Lf are regulated by its iron binding and release properties; however these properties are species-specific. To understand the iron-binding, thermal stability and cytotoxic effect of buffalo Lf (buLf) and contribution of individual N- and C-terminal lobes therein, buLf and the truncated monoferric lobes were expressed in Kluyveromyces lactis or Pichia pastoris yeast expression systems. The iron-uptake/release behavior and thermal stability of recombinant buLf was observed similar to the Lf purified from buffalo milk. Supplementation of recombinant buLf to the buffalo mammary epithelial cells (BuMEC) culture decreased their proliferation and the cell viability in a dose dependent manner. The cell growth decreased by 37% at 1.0 mg/ml Lf. C-lobe decreased the viability of BuMEC by 15% at 1 mg/ml. The C-lobe showed greater cytotoxic effect against BuMEC in comparison to N-lobe. buLf caused a reduced expression of the casein in BuMEC. At 1.0 mg/ml of buLf, CSN2 transcript level was reduced by 74% and 78% in the normal and hormone free media, respectively. The expression of IL-1β gene in BuMEC increased by 4-5 fold in the presence of 1.0 mg/ml of Lf. The effect was similar to that observed in the involutory mammary gland, suggesting the role of elevated level of Lf in remodeling of buffalo mammary tissue during involution.

Analysis of the IGF-system in milk from farm animals - Occurrence, regulation, and biomarker potential

IGFs and IGF-binding proteins (IGFBPs) are abundantly present in milk and in dairy products. Compared to the IGFs, the IGFBP have received less attention in milk, although truncated IGFBPs and IGFBP-glycosylation have been described in milk. Thereby, complex control of local IGF-effects can be assumed on the levels of IGFBPs, proteases, and protease inhibitors. The present review collects the current knowledge both on presence and regulation of IGFs and IGFBPs in milk particularly from dairy animal species. As a rule higher levels of IGF-I, IGF-II, and IGFBPs are measured around parturition if compared to later time-points of lactation. In all farm animal species included in this review, it is found that the relative abundancies of IGFBPs in milk and serum are similar, with IGFBP-3 and -2 characterized by higher concentrations if compared to IGFBP-4 or -5. The concentrations of IGFs and IGFBPs in milk or dairy products can be altered by hormones, dairy processing, or fermentation. Because milk can be used for non-invasive biomarker research, quality management, and health monitoring, we discuss novel directions of IGF-analysis and potential on-site biomarker research in milk.

The effects of milking frequency on insulin-like growth factor I signaling within the mammary gland of dairy cows

In dairy cows, short-term changes in milking frequency (MF) in early lactation have been shown to produce both an immediate and a long-term effect on milk yield. The effect of MF on milk yield is controlled locally within mammary glands and could be a function of changes in either number or activity of secretory mammary epithelial cells (MEC). Insulin-like growth factor I (IGF-I) signaling is one candidate factor that could mediate these effects, as it can be controlled locally within mammary glands. Both MEC number and activity can be affected by IGF-I signaling by activating the phosphoinositide 3-kinase (PI3K)/Akt and extracellular-signal-regulated kinase (ERK)1/2 pathways. To investigate the relationship between MF and IGF-I signaling, udder halves of 17 dairy cows were milked either 4 times a day (4×) or once a day (1×) for 14 d in early lactation. On d 14, between 3 and 5 h following milking, mammary biopsies were obtained from 10 cows from both udder halves, and changes in the expression of genes associated with IGF-I signaling and the activation of the PI3K/Akt and ERK1/2 pathways were measured. The mRNA abundance of IGF type I receptor, IGF binding protein (IGFBP)-3, and IGFBP-5 were lower following 4× milking relative to 1× milking. However, the mRNA abundance of IGF-I was not affected by MF. Both IGFBP3 and IGFBP5 are thought to inhibit IGF-I; therefore, decreases in their mRNA abundance may serve to stimulate the IGF-I signal in the 4×-milked mammary gland. The activation of PI3K/Akt pathway was lower in response to 4× milking relative to 1×, and the activation of the ERK1/2 was unaffected by MF, suggesting that they do not mediate the effects of MF.

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.

Camel milk ameliorates steatohepatitis, insulin resistance and lipid peroxidation in experimental non-alcoholic fatty liver disease

Background

Camel milk (CM) is gaining increasing recognition due to its beneficial effects in the control and prevention of multiple health problems. The current study aimed to investigate the effects of CM on the hepatic biochemical and cellular alterations induced by a high-fat, cholesterol-rich diet (HCD), specifically, non-alcoholic fatty liver disease (NAFLD).

Methods

Seventy male Wistar rats were divided into four groups: the Control (C) Group fed a standard diet; the Control + camel milk (CCM) Group fed a standard diet and CM, the Cholesterol (Ch) Group fed a HCD with no CM, and the Cholesterol + camel milk (ChM) Group fed a HCD and CM. The following parameters were investigated in the studied groups; basal, weekly random and final fasting blood glucose levels, intraperitoneal glucose tolerance test (GTT) and insulin tolerance test (ITT), serum insulin, serum lipids, liver functions, lipid peroxidation products, the antioxidant activity of catalase (CAT) and the levels of reduced glutathione (GSH). In addition, HOMA-IR as an index of insulin resistance (IR) and the histopathology of the hepatic tissue were assessed.

Results

The Ch Group developed features similar to those of non-alcoholic steatohepatitis (NASH), characterized by hepatic steatosis; inflammatory cellular infiltration in liver tissue; altered liver functions; and increased total cholesterol, triglycerides, low-density lipoprotein cholesterol, very-low-density lipoprotein cholesterol, atherogenic index (AI), blood glucose, IR, and malondialdehyde (MDA) levels. Additionally, feeding the HCD to animals in the Ch Group decreased CAT activity and the GSH and high-density lipoprotein (HDL) cholesterol levels. Camel milk intake for eight weeks decreased hepatic fat accumulation and inflammatory cellular infiltration, preserved liver function, increased the GSH levels and CAT activity, decreased the MDA levels, and ameliorated the changes in the lipid profile, AI, and IR in animals from the ChM Group.

Conclusions

CM has a unique composition that is rich in minerals; vitamins, insulin and insulin-like protein, and it increased HDL-cholesterol and ameliorated the biochemical and cellular features of NAFLD in rats that received a HCD. The antioxidant effect of CM is a likely mechanism for the altered metabolism and absorption of HCD in the presence of CM. Regular consumption of CM could provide a natural way to protect against NAFLD induced by a high-fat diet.

Continuous lactation effects on mammary remodeling during late gestation and lactation in dairy goats

The present study aimed to 1) elucidate whether continuous milking during late gestation in dairy goats negatively affects mammary remodeling and hence milk production in the subsequent lactation, and 2) identify the regulatory factors responsible for changes in cell turnover and angiogenesis in the continuously lactating mammary gland. Nine multiparous dairy goats were used. One udder half was dried off approximately 9 wk prepartum (normal lactation; NL), and the other udder half of the same goat was milked continuously (continuous lactation; CL) until parturition or until the half-udder milk yields had dropped to below 50 g/d. Mammary biopsies were obtained from each udder half just before the NL gland was dried off (before dry period), within the first 2 wk after drying-off (early dry period, samples available only for NL glands), in the mid dry period, within the last 2 wk before parturition (late dry period), and at d 1 (the day of parturition), 3, 10, 60, and 180 of lactation. Mammary morphology was characterized in biopsies by quantitative histology, and cell turnover was determined by immunohistochemistry (terminal deoxynucleotidyl transferase dUTP nick end labeling and Ki-67). Transcription of genes encoding factors involved in mammary epithelial cell (MEC) turnover and vascular function was quantified by quantitative reverse transcription PCR. Results demonstrated that omitting the dry period was possible in goats but was not as easy as claimed before. Renewal of MEC was suppressed in CL glands, which resulted in a smaller MEC population in the subsequent lactation. At the time of parturition (and throughout lactation), the mammary glands subjected to CL had smaller alveoli, more fully differentiated MEC, and a substantially larger capillary fraction compared with NL glands. The continuously lactating gland thus resembled a normally lactating gland in an advanced stage of lactation. None of the studied genomic factors could account for these treatment differences. The described characteristics in CL glands compared with NL glands indicated a gland maintained in lactation for a longer period.

Fat overload induces changes in circulating lactoferrin that are associated with postprandial lipemia and oxidative stress in severely obese subjects

Lactoferrin is an innate immune system protein with anti-inflammatory and antioxidant activities. We aimed to evaluate circulating lactoferrin levels in association with lipid concentrations, and parameters of oxidative stress and inflammation in subjects with morbid obesity after an acute fat intake. The effects of a 60 g fat overload on circulating lactoferrin and antioxidant activities were evaluated in 45 severely obese patients (15 men and 30 women, BMI 53.4 +/- 7.2 kg/m(2)). The change in circulating lactoferrin after fat overload was significantly and inversely associated with the free fatty acid (FFA) change. In those subjects with the highest increase in lactoferrin (in the highest quartile), high-density lipoprotein (HDL)-cholesterol decreased after fat overload to a lesser extent (P = 0.03). In parallel to lipid changes, circulating lactoferrin concentrations were inversely linked to the variations in catalase (CAT) and glutathione reductase (GSH-Rd). Baseline circulating lactoferrin concentration was also inversely associated with the absolute change in antioxidant activity after fat overload, and with the change in C-reactive protein (CRP). Furthermore, those subjects with higher than the median value of homeostasis model assessment of insulin secretion (HOMA(IS)) had significantly increased lactoferrin concentration after fat load (885 +/- 262 vs. 700 +/- 286 ng/ml, P = 0.03). Finally, we further explored the action of lactoferrin in vitro. Lactoferrin (10 micromol/l) led to significantly lower triglyceride (TG) concentrations and lactate dehydrogenase activity (as expression of cell viability) in the media from adipose explants obtained from severely obese subjects. In conclusion, circulating lactoferrin concentrations, both at baseline and fat-stimulated, were inversely associated with postprandial lipemia, and parameters of oxidative stress and fat-induced inflammation in severely obese subjects.

Lactoferrin decreases primary bovine mammary epithelial cell viability and casein expression

The concentration of lactoferrin (LTF) in milk varies during lactation, rising sharply during involution. We proposed that LTF might have a regulatory role in involution and investigated its effects in vitro on the viability of bovine mammary epithelial cells (BMEC) and on casein expression in bovine mammospheres. Mammospheres capable of milk protein expression were formed by culturing primary BMEC on extracellular matrix in the presence of lactogenic hormones. Exogenously added LTF decreased β-casein and κ-casein mRNA expression in mammospheres while transfection of a short interfering RNA (siRNA) to suppress LTF expression resulted in increased casein mRNA expression. We believe that LTF exerts its effect on casein gene expression by up-regulating interleukin-1β (IL-1β) as IL-Iβ gene expression was elevated in mammospheres treated with LTF. LTF also decreased viability of BMEC grown as monolayers and as mammospheres. Interestingly, LTF was only effective in reducing casein mRNA expression and viability in mammospheres when added at concentrations found during early involution but was inactive when used at concentrations found in milk. We suggest that LTF has a regulatory role during early involution, decreasing casein expression and reducing BMEC viability.

Insulin-like growth factors (IGFs), IGF binding proteins, and other endocrine factors in milk: role in the newborn

The role of colostrum and milk in the neonate has been chiefly recognized as a comprehensive nutrient foodstuff. In addition, the provision of colostrum-the first milk-for early immune capacity has been well documented for several species. Colostrum is additionally a rich and concentrated source of various factors that demonstrate biological activity in vitro. Three hypotheses have been proposed for the phenotypic function of these secreted bioactive components: (1) only mammary disposal, (2) mammary cell regulation, and (3) neonatal function [gastrointestinal tract (GIT) or systemic]. Traditionally, it was assumed that the development of the GIT is preprogrammed and not influenced by events occurring in the intestinal lumen. However, a large volume of research has demonstrated that colostrum (or milk-borne) bioactive components can basically contribute to the regulation of GIT growth and differentiation, while their role in postnatal development at physiological concentrations has remained elusive. Much of our current understanding is derived from cell culture and laboratory animals, but experimentation with agriculturally important species is taking place. This chapter provides an overview of work conducted primarily in neonatal calves and secondarily in other species on the effects on neonates of selected peptide endocrine factors (hormones, growth factors, in part cytokines) in colostrum. The primary focus will be on insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) and other bioactive peptides, but new interest and concern about steroids (especially estrogens) in milk are considered as well.

Growth hormone suppresses the expression of IGFBP-5, and promotes the IGF-I-induced phosphorylation of Akt in bovine mammary epithelial cells

Growth hormone (GH) plays a specific role to inhibit apoptosis in the bovine mammary gland through the insulin-like growth factor (IGF)-I system, however, the mechanism of GH action is poorly understood. In this study, we show that GH dramatically inhibits the expression of IGFBP-5, and GH along with IGF-I enhanced the phosphorylation of Akt through the reduction of IGF binding protein (IGFBP)-5. To determine how GH affects Akt through IGF-I in bovine mammary epithelial cells (BMECs), we examined the phosphorylation of Akt in GH treated BMECs and found that IGF-I induced phosphorylation of Akt was significantly enhanced by the treatment with GH. We demonstrated that GH reduces mRNA and protein expression of IGFBP-5 in BMECs, but it does not affect the expression of IGFBP-3. To determine that the enhanced effect of the Akt phosphorylation by the treatment of GH is due to the inhibition of the expression of IGFBP-5, we examined the effect of IGFBP-3 and -5 on the phosphorylation of Akt through IGF-I in the GH-treated BMECs. The phosphorylation of Akt was inhibited in a dose-dependent manner when IGFBP-5 was added at varying concentrations and was also inhibited in the presence of IGFBP-3. The results of this study suggest that GH plays an important role on mammary gland involution in bovine mammary epithelial cells.

Cell Turnover and Activity in Mammary Tissue During Lactation and the Dry Period in Dairy Cows

Milk yield of the dairy cow follows a pattern termed the lactation curve. We have investigated the cellular background for this pattern. Seven mammary biopsies were obtained from each of 10 cows: at the end of lactation (d 347, equal to d 77 before next parturition); during the dry period at d 48 (4 d after dry off); 16 d before parturition; and during lactation at d 14, 42, 88, and 172. The fraction of proliferating (staining positive for Ki-67) alveolar cells was higher during the dry period (8.6%) than during lactation (0.5%). The fraction of apoptotic (staining positive by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling) alveolar cells was higher immediately after dry off (0.37%) and in early lactation (0.76%) than during other periods (0.15%). The enzyme activities of fatty acid synthetase, acetyl CoA-carboxylase, and galactosyl transferase were approximately 12-, 11-, and 4-fold higher, respectively, during lactation than during the dry period. In conclusion, mammary cell proliferation is substantial in a period near parturition but otherwise low, and apoptosis is elevated at dry off and in early lactation. The increase in apoptosis in early lactation may be due to discarding nonfunctional or senescent cells or to removal of a surplus of newly synthesized cells. The activity of selected enzymes central for milk synthesis is probably not limiting for milk production.

Major advances associated with hormone and growth factor regulation of mammary growth and lactation in dairy cows

In recent years, the number of researchers interested in mammary development and mammary function in dairy animals has declined. More importantly this cadre of workers has come to rely more than ever on scientists focused on and funded by breast cancer interests to provide fundamental mechanistic and basic cellular insights. Philosophically and practically this is a risky path to better understand, manipulate, and control a national resource as important as the dairy cow. The efficiency, resourcefulness, and dedication of dairy scientists have mirrored the actions of many dairy producers but there are limits. Many of the applications of research, use of bovine somatotropin, management of transition cows, estrus synchronization techniques, and so on, are based on decades-old scientific principles. Specific to dairy, do rodents or breast cancer cell lines adequately represent the dairy cow? Will these results inspire the next series of lactation-related dairy improvements? These are key unanswered questions. Study of the classic mammogenic and lactogenic hormones has served dairy scientists well. But there is an exciting, and bewildering universe of growth factors, transcription factors, receptors, intracellular signaling intermediates, and extracellular molecules that must ultimately interact to determine the size of the mature udder and the functional capacity of mammary gland in the lactating cow. We can only hope that enough scientific, fiscal, and resource scraps fall from the biomedical research banquet table to allow dairy-focused mammary gland research to continue.

Nutritional physiology of neonatal calves*

The gastrointestinal tract of neonatal calves is relatively mature but still requires morphological and functional changes. The intake of colostrum with its nutrient and non-nutrient components exerts marked effects on gastrointestinal development and function. Colostrum intake provides immunoprotection (passive immunity by immunoglobulins) and is essential for survival of neonates of most species. Furthermore, there are important transient as well as long-lasting systemic effects on the nutritional status, on metabolism, and on various endocrine systems due to intake of nutrient and non-nutrient colostral components that contribute to survival in the stressful postnatal period. Colostrum is much more than just a supplier of immunoglobulins.

Physiology of the periparturient period and its relation to severity of clinical mastitis

Incidence of clinical mastitis is highest at drying off and during the periparturient period. Intramammary Escherichia coli infection in high-yielding cows can show a severe clinical response during the early post-partum period. Severe clinical mastitis is mainly determined by cow factors, in particular the functionality of the circulating polymorphonuclear leukocytes (PMN) which are recruited to the mammary gland during the inflammatory reaction. There is a co-incidence between the periods of highest incidence of clinical mastitis and specific structural changes in the mammary gland. During the periparturient period, marked changes in various systemic and local hormones are related to the secretory state of the mammary gland epithelium (lactogenesis). Estrogen and progesterone induce proliferation of the mammary epithelium throughout gestation and act as survival factors in different tissues, although conflicting data have been reported on their effect on PMN oxidative burst. Somatotropin (STH), responsible for maintenance of lactation in ruminants, has been shown to positively influence innate immunity and a more rapid recovery in milk production of severely affected animals. The concentration of STH, and as a result also IGF-I levels is, however, quite low during early lactation. IGF-I and its regulating binding proteins are associated with cell survival, modulation of apoptosis and functionality of PMN in humans. During early lactation, bio-availability of IGF-I is decreased, which might reduce its stimulating effects on PMN quality and functionality. PRL, concomitantly known as a lactogenic hormone and an immunoregulatory cytokine, has also been associated with modulation of the immune system. It is expected that in periparturient animals, hormone changes could interfere with the immune response and the clinical response of mastitis.

Endocrinology of milk production

The physiology of lactation includes development of the mammary gland from the foetal to the adult stage, further development during pregnancy and onset of lactation, with the accompanying metabolic and behavioural adaptation. At the onset of pregnancy the endocrine system undergoes dramatic changes. The growth of the mammary gland is stimulated by growth hormone and prolactin, adrenocortical steroids, oestrogens and progesterone, and that of the gastrointestinal (GI) tract by gastrin, CCK and secretin. The onset of lactation is accompanied by increases in the blood volume, cardiac output, mammary blood flow and blood flow through the GI-tract and liver, aiming to provide the udder with nutrients and hormones for regulation of milk synthesis. Food intake and distribution of nutrients to the mammary gland are partially regulated by hormones as well as the repartitioning of nutrients away from body stores towards the udder. To improve milk production, administration of growth hormone has been practised, but also much discussed. Besides central mechanisms, local mechanisms within the mammary gland regulate initiation of lactation, maintenance, regulation of blood flow and mammary gland cell apoptosis. Most of the milk in a filled dairy cow udder is stored in the alveolar compartments. The milk ejection reflex must be activated to gain access to the udder milk, i.e. oxytocin contracts the myoepithelial cells. Recent studies show that vasopressin may also elicit milk ejection. More efficient oxytocin release is achieved if the cows are fed during milking. Beyond milk let down, oxytocin influences maternal behaviour and metabolism. Furthermore, it has been indicated that suckling or milking activates a vagal reflex, which may link the milk production to the endocrine system of the GI-tract. The question has been raised whether the mammary gland is a supporting or consuming organ.

Effects of an enhanced vitamin A intake during the dry period on retinoids, lactoferrin, IGF system, mammary gland epithelial cell apoptosis, and subsequent lactation in dairy cows

Studies in vitro show important interactions among vitamin A, lactoferrin, and insulin-like growth factor (IGF) binding proteins (IGFBP) and, thus, the IGF system. As a consequence, mammary gland epithelial cell proliferation and apoptosis during the bovine dry period and potential milk yield may be affected. We have studied effects of feeding vitamin A (550,000 IU/ d) that exceed daily requirements about 8-fold for up to 2 mo to dairy cows during the dry period on concentrations of retinol and its metabolites in plasma and milk, milk lactoferrin, plasma and milk IGF-I and IGFBP-3, lactoferrin and IGF-I mRNA levels in mammary gland tissue, mammary gland apoptosis, and 100-d milk yield in the ensuing lactation. In the group supplemented with vitamin A, the peripartal decrease of plasma retinol was delayed and attenuated, and colostral retinol plus retinylester concentration was enhanced, but colostral beta-carotene concentration decreased. The retinoic acid isomer 9,13-dicis retinoic acid that coeluted with 13-cis retinoic acid, was the predominant circulating retinoic acid and was higher in GrA than the control group. Plasma IGFBP-3 concentrations were positively correlated with plasma retinol concentrations (r = 0.51), but there were no group differences. Numbers of apoptotic epithelial cells in mammary epithelium were higher at drying off and parturition than in the middle of the dry period, coinciding with high concentrations of IGF-I and lactoferrin in mammary secretions. At parturition, numbers of apoptotic cells in mammary gland biopsies in cows supplemented with vitamin A were higher than in control cows. In conclusion, supplementation of dairy cows during the dry period with high amounts of vitamin A did not significantly modify concentrations of lactoferrin, IGFBP-3, and IGF-I in plasma and in mammary secretions, but slightly decreased energy-corrected 100-d milk yield and milk fat yield, possibly because of enhanced apoptic rates of mammary cells.

Effects of Feeding Vitamin A and Lactoferrin on Epithelium of Lymphoid Tissues of Intestine of Neonatal Calves

Circulating levels of vitamin A (retinol) and lactoferrin (Lf) are low in calves at birth. Bovine colostrum contains relatively high amounts of vitamin A and Lf, and both substances are intestinally absorbed by neonatal calves. There is evidence that these compounds interact with insulin-like growth factor binding proteins and thus influence the status and effects of insulin-like growth factor. The hypothesis was therefore tested that vitamin A and Lf influence epithelial growth, development, and absorptive capacity of the small and large intestine and modulate intestinal immune tissues (Peyer's patches; PP). Four groups of calves (n = 7 per group) were fed a milk-based formula with or without vitamin A and (or) Lf. Group F received formula (F) only; group F(A) was fed F supplemented with vitamin A; group F(L) was fed F supplemented with Lf, and group F(AL) received F plus vitamin A plus Lf. An additional group of calves (group C; n = 7) served as positive control and was fed colostrum (C) from pooled milk obtained on d 1, 2, and 3 of lactation. Amounts of nutritive components in formula and colostrum were similar. Blood samples were taken to measure vitamin A and Lf, and plasma xylose (added on d 4 to feeds) was measured postprandially for 8 h as a marker of intestinal absorptive capacity. Plasma vitamin A was low at birth and further decreased in groups F and F(L), but increased in groups F(A), F(AL), and C. Plasma Lf was low at birth and transiently increased up to 4 h after the first meal in group C. Xylose absorption was higher in group C than in other groups. Incorporation of 5-bromo-2'-deoxyuridine into DNA (as a measure of cell proliferation rate) was enhanced in intestinal crypts in groups F and F(L) at all intestinal sites. Ileum villus heights of groups F and F(L) were smaller than of groups F(A) and F(AL). Villus height to crypt depth ratios were smaller in F-fed groups (especially in groups F and F(L)) than in C-fed calves in the duodenum and jejunum. Incorporation of 5-bromo-2'-deoxyuridine into colon crypt cells of group F was greater than in groups F(L) and F(A). Sizes of follicles of PP in the ileum were greater in group F(A) than in group F. In the ileum, vitamin A and Lf tended to interact with PP size. In conclusion, feed supplementation of vitamin A and Lf influenced growth of the ileum and colon. Interactions were observed between vitamin A and Lf on epithelial cell maturation, villus growth, and size of follicles in PP of neonatal calves.

Hematological, Metabolic, and Endocrine Effects of Feeding Vitamin A and Lactoferrin in Neonatal Calves

There are reports of important interactions among vitamin A, lactoferrin (Lf), and components of the insulin-like growth factor (IGF) system. Newborn calves are deficient in vitamin A and have a low Lf status. Colostrum contains vitamin A, Lf, and members of the IGF system, including IGF binding proteins (IGFBP), and these compounds may exert mutual interactions in neonatal calves. Effects of feeding different amounts of vitamin A and Lf on hematological, metabolic, and endocrine traits during the first 5 d of life were studied in neonatal calves. Calves were fed a milk-based formula without (F) or with added vitamin A [F(A); 351, 402, 490, and 490 micromol/kg dry matter (DM) on d 1, 2, 3, and 4, respectively], Lf (F(L); 3850, 1990, 660, and 660 mg/kg DM on d 1, 2, 3, and 4, respectively), or vitamin A + Lf (F(AL)) and colostrum (C). Blood samples were taken preprandially on d 1 to 5 and postprandially on d 1, 2, and 4 for the study of hematological, metabolic, and endocrine traits. As intestinal absorption of Lf in formula-fed calves was obviously lower than in colostrum-fed calves, Lf supplementation did not influence the metabolic and endocrine status. Plasma vitamin A concentrations increased from d 1 to 5 in F(A), F(AL), and C, but remained low in F and F(L). Addition of vitamin A to F affected concentrations of vitamin A from d 2 to 5; hemoglobin and triglycerides on d 3; and tended to influence IGFBP-3 levels on d 5. On d 1, preprandial insulin concentrations in F and F(L) were higher than those in F(A) and F(AL) and growth hormone concentrations on d 3 in F(A) were higher than in F(AL). In C, plasma Lf concentrations increased on d 1 and then decreased until d 5, whereas plasma urea and IGF-I concentrations remained stable. Compared with F-fed calves, C-fed calves had higher plasma concentrations of Lf from d 1 to 4, higher concentrations of vitamin A on d 5, higher concentrations of total protein from d 2 to 5, higher concentrations of triglycerides on d 3 and 4, and higher concentrations of IGF-I on d 4 and 5, but lower urea concentrations on d 4 and 5 and lower basal growth hormone concentrations than in F, F(L), and F(A). In conclusion, metabolite and hormone concentrations were influenced by differences in feeding. Addition of vitamin A influenced concentrations of vitamin A, hemoglobin, and triglycerides and tended to affect IGFBP-3 levels. Lactoferrin and vitamin A did not interact with respect to the IGF-I and IGFBP-3 status.

IGF-binding proteins mediate TGF-beta 1-induced apoptosis in bovine mammary epithelial BME-UV1 cells

TGF-beta 1 is an antiproliferative and apoptogenic factor for mammary epithelial cells (MEC) acting in an auto/paracrine manner and thus considered an important local regulator of mammary tissue involution. However, the apoptogenic signaling pathway induced by this cytokine in bovine MEC remains obscure. The present study was focused on identification of molecules involved in apoptogenic signaling of transforming growth factor-beta 1 (TGF-beta 1) in the model of bovine mammary epithelial cell line (BME-UV1). Laser scanning cytometry (LSC), Western blot and electrophoretic mobility shift assay (EMSA) were used for analysis of expression and activity of TGF-beta 1-related signaling molecules. The earliest response occurring within 1-2 h after TGF-beta 1 administration was an induction and activation of R-Smads (Smad2 and Smad3) and Co-Smad (Smad4). An evident formation of Smad-DNA complexes began from 2nd hour after MEC exposure to TGF-beta 1. Similarly to Smads, proteins of AP1 complex: phosphorylated c-Jun and JunD appeared to be early reactive molecules; however, an increase in their expression was detected only in cytosolic fraction. In the next step, an increase of IGF binding protein-3 (IGFBP-3) and IGFBP-4 expression was observed from 6th hour followed by a decrease in the activity of protein kinase B (PKB/Akt), which occurred after 24 h of MEC exposure to TGF-beta 1. The decrease in PKB/Akt activity coincided in time with the decline of phosphorylated Bad expression (inactive form). Present study supported additional evidence that stimulation of insulin-like growth factor I (IGF-I) was associated with complete abrogation of TGF-beta 1-induced activation of Bad and Bax and in the consequence protection against apoptosis. In conclusion, apoptotic effect of TGF-beta 1 in bovine MEC is mediated by IGFBPs and occurs through IGF-I sequestration, resulting in inhibition of PKB/Akt-dependent survival pathway.

Sex steroids and growth factors in the regulation of mammary gland proliferation, differentiation, and involution

The mammary gland is subjected to major morphological and biochemical changes during the lactation cycle. It is therefore not surprising that this dynamic process is strictly controlled. The importance of the sex steroid hormones 17beta-estradiol and progesterone for normal development of the mammary gland was recognized several decades ago and has been unequivocally confirmed since. Furthermore, it is now also established that the influence of sex steroids is not restricted to mammogenesis, but that these hormones also control involution. Another important regulatory role is played by growth factors that have been shown to modulate survival (epidermal growth factor, amphiregulin, transforming growth factor alpha, insulin like growth factor, and tumor necrosis factor alpha) or apoptosis (tumor necrosis factor alpha, transforming growth factor beta) of mammary cells. However, the molecular mechanism underlying the influence of sex steroid hormones and/or growth factors on the development and function of the mammary gland remains largely unknown to date. Also scarce is information on the interaction between both groups of modulators. Nevertheless, based on the current indications compiled in this review, an important functional role for sex steroid hormones in the lactation cycle in co-operation with growth factors can be suggested.

Purification of bovine IGFBP-3 and the development of an enzyme immunoassay for the protein

Insulin-like growth factor binding protein-3 (IGFBP-3), the most prominent IGF-binding protein in serum, has been demonstrated to modulate the effects of the IGFs but also to exert IGF-independent actions. Quantification of IGFBP-3 in livestock species, in particular ruminants, is commonly limited to blotting methods in spite of the importance of these species. Here we describe the development of a specific homologous enzyme-linked immunosorbent assay (ELISA) to measure bovine IGFBP-3 in bovine plasma, serum and milk. IGFBP-3 purified from bovine serum was used both as standard and also for tracer synthesis. A specific antiserum was raised in rabbits using a synthetic peptide based on the sequence of bovine IGFBP-3. The measuring range of the assay was between 50 and 1000 ng IGFBP-3 per milliliter of plasma or milk. Mean recovery was 97.3% for plasma and 100.1% for milk. Intra- and interassay coefficients of variation were 6.2% and 9.3%, respectively. For the biological verification of the assay, IGFBP-3 was determined in plasma obtained from 12 dairy cows before and after being injected with a depot-formulated growth hormone (GH) preparation. GH, a well-characterized stimulator of IGFBP-3, led to a 1.3-fold increase of basal IGFBP-3 concentrations during days 3 to 19 after the injection. The availability of an ELISA procedure which permits precise and sufficiently sensitive quantification of bovine IGFBP-3 and which can be used on large sample numbers thereby avoiding the need for radioactive labels, should facilitate further research studies.

Co-localization of apoptosis-regulating proteins in mouse mammary epithelial HC11 cells exposed to TGF-beta1

TGF-beta1 is an apoptogenic agent for mammary epithelial cells (MEC). The molecular mechanism of the TGF-beta1-induced apoptosis remains, however, obscure. In the present study we used laser scanning cytometry, confocal microscopy and immunogold electron microscopy to analyze the expression, aggregation and co-localization of caspase-8, Bid, Bax and VDAC-1. These proteins are regarded as the most important factors involved in the regulatory phase of TGF-beta1-induced apoptosis. Apoptosis in HC11 mouse MEC manifested with a simultaneous increase in expression and subcellular aggregation of caspase-8, Bid, Bax and VDAC-1. Confocal microscopy revealed a strong pattern of co-localization of examined proteins during both early and late apoptosis. Experiments with double- and triple-staining immunoelectron microscopy showed a co-localization of Bax/Bid, caspase-8/Bax/Bid, and Bax/VDAC-1, on the membranes of mitochondria, Golgi apparatus, rough endoplasmic reticulum, nuclear envelope, nuclear pore, and within the nucleus. In conclusion, the observed pattern of changes in aggregation and subcellular localization of caspase-8, Bid, Bax and VDAC-1 during TGF-beta1-induced apoptosis in HC11 mouse MEC suggests an interaction between these proteins and formation of multimeric complexes on organellar membranes, thus controlling their permeability for intracellular mediators of apoptosis.

Intestinal morphology, epithelial cell proliferation, and absorptive capacity in neonatal calves fed milk-born insulin-like growth factor-I or a colostrum extract

Concentrations of nonnutritional factors, such as insulin-like growth factor-I (IGF-I), in bovine colostrum are high and can modulate neonatal gastrointestinal tract development and function. In neonatal calves, we have investigated effects on intestinal epithelial cell morphology, proliferation, and absorption of feeding milk-born human IGF-I (hIGF-I) or a bovine colostrum extract. Calves were fed a milk-based formula containing amounts of nutrients comparable to colostrum for the first 3 d and a milk replacer from d 4 on. Formula and milk replacer contained only traces of nonnutritional factors. In experiment 1, supraphysiological amounts of hIGF-I (3.8 mg/L formula; secreted by transgenic rabbits with their milk) were added to the formula. Xylose appearance in blood (after feeding xylose on d 5) and intestinal traits (after euthanasia on d 8) did not differ between groups. In experiment 2, an extract of first-milked bovine colostrum that provided physiological amounts of IGF-I (0.50, 0.15, and 0.09 mg of IGF-I/L formula on d 1, 2, and 3, respectively, and 0.09 mg of IGF-I/L milk replacer on d 4) was added to formula or milk replacer. Plasma xylose concentration in the control group was transiently higher than in calves fed the colostrum extract. On d 5 (after euthanasia), villus circumferences and heights in small intestine, and epithelial cell proliferation rate in intestine were higher in calves fed the colostrum extract than in controls. In conclusion, orally administered hIGF-I from transgenic rabbits had no effect on the intestinal tract. However, feeding a bovine colostrum extract enhanced intestinal villus size, although it appeared to transiently decrease the absorptive capacity.

Bovine lactoferrin binds to insulin-like growth factor-binding protein-3

Insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3) has been shown to have IGF independent actions that appear to be mediated by specific IGFBP-3 binding proteins located on cell membranes. We show here using Western ligand blotting, a number of mammary membrane proteins that bind 125I-labeled rhIGFBP-3. Immunoprecipitation studies demonstrated that the >70 kDa protein was identified from bovine mammary microsomes as bovine lactoferrin (bLf). In addition to being a secretory protein, Lf is tightly associated with cellular membranes. Labeled rhIGFBP-3 was shown to bind to commercially purchased and processed apo- or holo-human or bLf, but not bovine transferrin (bTf). Binding of [125I]rhIGFBP-3 to other positively charged proteins was not detected nor was binding to rhIGFBP-5 or other mammary-secreted IGFBPs observed. Reciprocal specific binding of [125I]bLf to rhIGFBP-3 was shown, but [125I]bTf did not show binding to rhIGFBP-3. While [125I]rhIGF-II does not bind to bLf, unlabeled rhIGF-II was shown to compete with [125I]bLf for rhIGFBP-3 binding. More detailed analysis by dot blot showed that Lf competes (ED(50)=3 microg/ml) or displaces (ED(50)=1mg/ml) bound [125I]rhIGF-II from dot blotted rhIGFBP-3. In vitro studies with a bovine primary mammary epithelial cell culture showed that all-trans-retinoic acid stimulates the appearance of bovine IGFBP-3 and bLf in the conditioned media and that [125I]rhIGFBP-3 could be utilized to detect conditioned media bLf. These findings reveal a novel role for bLf, binding to IGFBP-3 and perhaps disassociating IGFBP-3:IGF when in high concentration.

Antiproliferative and apoptotic effect of TGF-beta 1 in bovine mammary epithelial BME-UV1 cells

Transforming growth factor beta1 (TGF-beta(1)) is regarded as an important auto/paracrine regulator of mammary gland involution, however, its apoptotic effect and inhibition of growth in bovine mammary epithelial cells (MEC) has not been documented. In the present study, laser scanning cytometry, confocal and immunoelectron microscopy techniques were used for quantitative and qualitative analyzes of apoptosis, cell cycle and expression, subcellular redistribution and interactions of apoptosis-related proteins in bovine BME-UV1 MEC exposed to TGF-beta(1). TGF-beta(1) exerted both antiproliferative and apoptotic action. The antiproliferative effect was manifested by increase of cell number in G1 phase with simultaneous decrease of cell number in S and G2/M phases. It resulted in significant increase of G1/S ratio in TGF-beta(1) treated cells, indicating partial cell cycle arrest at the G1-S transition. Apoptosis induced by TGF-beta(1) manifested by characteristic morphological changes. Among biochemical features of TGF-beta(1)-induced apoptosis in BME-UV1 cells we found: (1) an increase of cell number with lowered DNA content and condensed chromatin, (2) enhanced expression of caspase-3 and m-calpain, (3) elevated number of 89 kDa PARP degradation fragments, and (4) aggregation of Bax and its interactions with voltage dependant anion channel-1. In conclusion, antiproliferative and apoptotic action of TGF-beta(1), observed in the culture of BME-UV1 cells, suggests an essential role of this cytokine in the regulation of mammary gland involution in cow.

Lactation persistency: Insights from mammary cell proliferation studies

A persistent lactation is dependent on maintaining the number and activity of milk secreting cells with advancing lactation. When dairy cows are milked twice daily, the increase in milk yield from parturition to peak lactation is due to increased secretory activity per cell rather than to accretion of additional epithelial cells. After peak lactation, declining milk yield is due to loss of mammary epithelial cells by apoptosis. During lactation, only 0.3% of mammary cells proliferate in a 24-h period. Yet this proliferative rate is sufficient to replace most mammary epithelial cells by the end of lactation. Management practices can influence lactation persistency. Administration of bovine somatotropin may enhance persistency by increasing cell proliferation and turnover, or by reducing the rate of apoptosis. Increased photoperiod may also increase persistency of lactation by mechanisms that are as yet undefined. Increased milking frequency during the first weeks of lactation increases milk yield, even after return to less frequent milking, with increases of approximately 8% over the entire lactation. A mammary cell proliferation response to frequent milking during early lactation appears to be involved. Conversely, advanced pregnancy, infrequent milking, and mastitis increase death of epithelial cells by apoptosis. Regulation of mammary cell renewal provides a key to increasing persistency. Investigations to characterize epithelial cells that serve as the proliferative population in the bovine mammary gland have been initiated. Epithelial cells that stain lightly in histological sections are evident through all phases of mammary development and secretion and account for nearly all proliferation in the prepubertal gland. Characterization of these cells may provide a means to regulate mammary cell proliferation and thus to enhance persistency, reduce the effects of mastitis, and decrease the necessity for a dry period.

Cellular actions of the insulin-like growth factor binding proteins

In addition to their roles in IGF transport, the six IGF-binding proteins (IGFBPs) regulate cell activity in various ways. By sequestering IGFs away from the type I IGF receptor, they may inhibit mitogenesis, differentiation, survival, and other IGF-stimulated events. IGFBP proteolysis can reverse this inhibition or generate IGFBP fragments with novel bioactivity. Alternatively, IGFBP interaction with cell or matrix components may concentrate IGFs near their receptor, enhancing IGF activity. IGF receptor-independent IGFBP actions are also increasingly recognized. IGFBP-1 interacts with alpha(5)beta(1) integrin, influencing cell adhesion and migration. IGFBP-2, -3, -5, and -6 have heparin-binding domains and can bind glycosaminoglycans. IGFBP-3 and -5 have carboxyl-terminal basic motifs incorporating heparin-binding and additional basic residues that interact with the cell surface and matrix, the nuclear transporter importin-beta, and other proteins. Serine/threonine kinase receptors are proposed for IGFBP-3 and -5, but their signaling functions are poorly understood. Other cell surface IGFBP-interacting proteins are uncharacterized as functional receptors. However, IGFBP-3 binds and modulates the retinoid X receptor-alpha, interacts with TGFbeta signaling through Smad proteins, and influences other signaling pathways. These interactions can modulate cell cycle and apoptosis. Because IGFBPs regulate cell functions by diverse mechanisms, manipulation of IGFBP-regulated pathways is speculated to offer therapeutic opportunities in cancer and other diseases.

Molecular characterization of mouse gastric epithelial progenitor cells

The adult mouse gastric epithelium undergoes continuous renewal in discrete anatomic units. Lineage tracing studies have previously disclosed the morphologic features of gastric epithelial lineage progenitors (GEPs), including those of the presumptive multipotent stem cell. However, their molecular features have not been defined. Here, we present the results of an analysis of genes and pathways expressed in these cells. One hundred forty-seven transcripts enriched in GEPs were identified using an approach that did not require physical disruption of the stem cell niche. Real-time quantitative RT-PCR studies of laser capture microdissected cells retrieved from this niche confirmed enriched expression of a selected set of genes from the GEP list. An algorithm that allows quantitative comparisons of the functional relatedness of automatically annotated expression profiles showed that the GEP profile is similar to a dataset of genes that defines mouse hematopoietic stem cells, and distinct from the profiles of two differentiated GEP descendant lineages (parietal and zymogenic cell). Overall, our analysis revealed that growth factor response pathways are prominent in GEPs, with insulin-like growth factor appearing to play a key role. A substantial fraction of GEP transcripts encode products required for mRNA processing and cytoplasmic localization, including numerous homologs of Drosophila genes (e.g., Y14, staufen, mago nashi) needed for axis formation during oogenesis. mRNA targeting proteins may help these epithelial progenitors establish differential communications with neighboring cells in their niche.

Dexamethasone changes the composition of insulin-like growth factor binding proteins in the newborn mouse ileum

BACKGROUND

Early postnatal glucocorticoid exposure accelerates the maturation of the bowel mucosa but results in bowel wall thinning in the newborn mouse ileum and increases the risk of focal ileal perforation in extremely premature infants. We have previously demonstrated a redistribution of insulin-like growth factor-I (IGF-I) from the submucosa in control animals to the distal villi of those treated with early postnatal dexamethasone, implicating IGF-I as an important mediator of dexamethasone's capacity to alter tissue growth. To investigate the possibility that IGF binding proteins (IGFBPs) might contribute to this process, we characterized the localization and abundance of IGFBP peptides and mRNAs in the same model.

METHODS

Newborn mice received daily intraperitoneal injections of dexamethasone (l microg/g) or phosphate-buffered saline and then were euthanized on day 3 of life. Their ileums were harvested and prepared for microscopy. Tissue sections of ileum from both treatment conditions were processed in parallel for immunolocalization of each of the six IGFBP peptides and for in situ hybridization of each of the six IGFBP transcripts.

RESULTS

Transcripts for IGFBP-1, -2, and -3 were highly abundant and ubiquitous the ileal mucosa, whereas transcripts for IGFBP-4, -5, and -6 were less abundant in epithelial cells. There were no differences in abundance between control and dexamethasone-treated ileum with regard to mRNA localization or abundance for IGFBP-1, -2, -3, and -6. In contrast, mRNA transcripts for IGFBP-4 and -5 were modestly increased with dexamethasone treatment (although only IGFBP-4 was significant). Strikingly different patterns of IGFBP immunolocalization were observed between control and dexamethasone-treated animals. IGFBP-1, -2, -3, and -5 were not detected in control ileum, whereas IGFBP-4 and -6 were both present in the mucosa. In contrast, dexamethasone treatment resulted in dramatic mucosal increases in IGFBP-2, -3, -4, and -5, paralleling the changing distribution of IGF-I that we previously reported.

CONCLUSION

Taken together, these findings further implicate the IGF system as an important participant in dexamethasone-induced maturation in the newborn mouse ileum.

Colostral and milk insulin-like growth factors and related substances: mammary gland and neonatal (intestinal and systemic) targets

The identification of hormones and regulatory factors in colostrum and milk has led to intensive investigations on their roles in the development and maintenance of the mammary and neonatal tissues. Insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) in transgenic mice influence mammary biology gland towards the end of lactation. In the bovine, IGFBP-3 is the major IGFBP in mammary secretions. In addition to binding IGFs, IGFBP-3 also binds to lactoferrin (Lf). Secreted IGFBP-3 re-enters mammary epithelial cells and with the presence of a nuclear localization sequence, IGFBP-3 and Lf enter the nucleus. Nuclear IGFBP-3 affects apoptotic signaling through the retinoic-x-receptors, while Lf affects apoptotic events through unknown mechanisms. Such interactions likely influence mammary development and involution. Furthermore, ingested colostral bioactive factors can exert regulatory functions in neonates. Intestinal receptors for IGFs and insulin are modified by age and/or diet. Feeding IGF-I had no effect, but colostrum extracts had small intestinal effects (stimulation of proliferation and villus size), suggesting that several factors, rather than one single bioactive factor were responsible. Systemic changes of metabolic and endocrine profiles in neonates depend on composition, amounts, time and duration of feeding colostrum. Early postnatal colostrum intake is not only important for the provision and absorption of immunoglobulins. Thus, in neonatal calves the lack of colostrum intake during the first 24h after birth results in a low immunoglobulin G, beta-carotene and Vitamin A status that persists for weeks and plasma patterns of fatty acids, essential amino acids and the glutamine/glutamate ratios are affected. In calves oral administration of IGF-I had no and feeding of colostrum whey extracts had only minor effects on metabolic and endocrine traits. Thus, mammary secretions influence regulatory functions of mammary and neonatal tissues.