Insulin-Like Growth Factor Binding Proteins: IGF-Dependent and -Independent Effects in the Mammary Gland

The insulin-like growth factor binding proteins (IGFBPs)³ are a family of proteins which bindto the IGFs with high affinity. Their expression within the mammary gland is species specific;it has thus been difficult to determine the biological roles of these binding proteins duringlactation. In this article we propose a role for IGFBP-5 in the mammary gland involving theinitiation of apoptosis induced by sequestration of IGF-1, an important survival factor for themammary gland. We have shown that this binding protein retains its high affinity for IGF-1and that it is present in extremely high concentrations compared with the growth factor. Theseobservations make it likely that IGFBP-5 is capable of preventing interaction of IGF-1 withits receptor on the epithelial cells synthesizing milk. We have also demonstrated thatIGFBP-5 interacts with _s2-casein and that this interaction implicates it in the regulation of plasminogenactivation in the mammary gland. The generation of plasmin is a key initiating event in theremodeling of the extracellular matrix during mammary involution. As such, IGFBP-5 mayplay a key role in coordinating cell death and tissue remodeling processes. Many of themolecules involved in embryological development are also expressed in the developing andinvoluting mammary gland. We believe that our studies may offer mechanistic explanationsfor apoptotic events in a wide variety of tissues. We have recently shown that IGFBP-5 isapoptotic in the chick embryonic limb bud, adding further support to our belief thatIGFBP-5 serves this function in the mammary gland. We hope to be able to explore the role of thisbinding protein in the mammary gland with a transgenic mouse model expressing IGFBP-5on the -lactoglobulin promoter.     

Insulin-like growth factors in milk and mammary gland

Milk contains insulin-like growth factor I and II (IGF-I and IGF-II)³ and four IGF binding proteins (IGFBP). Their concentrations are highest prepartum and early postpartum, coinciding with maximal proliferation of mammary cells and the time when the infant gut is the least developed. This has lead to the suggestion that IGFs may be important for the growth and development of the mammary gland and that IGFs in milk play a role in promoting development of the gastrointestinal tract of the newborn. IGF-I and, to a lesser extent, IGF-II can stimulate milk yield and blood flow in goats when infused directly into the mammary gland, suggesting they may also be important in supporting established lactation. Thus IGFs may have a dual function in the mammary gland, establishing and maintaining the maternal mammary system and, once secreted into milk, supporting gastrointestinal development in the newborn.     

重组人生长激素对肝硬化大鼠肝部分切除术后生长激素/胰岛素样生长因子-1轴的影响

目的探讨rhGH对肝硬化大鼠肝部分切除术后GH/IGF-1轴的影响。方法6只正常大鼠作为正常对照组,24只肝硬化大鼠随机分为术前组6只,肝部分切除术后1d组6只,肝部分切除后行PN5d组6只,肝部分切除术后行rhGH+PN5d组6只。测大鼠肝功能、血糖及血清GH、IGF-1、IGFBP-3水平,用RT-PCR法检测肝ALBmRNA、IGF-1mRNA、IGFBP-3mRNA的表达。肝组织行Ki67免疫组化染色。结果与PN组比较,rhGH+PN组血清ALP显著下降(P<0·05),血清ALB显著升高(P<0·05),血糖显著升高(P<0·05),血清GH、IGF-1、IGFBP-3水平显著升高(P<0·05),肝ALBmRNA、IGF-1mRNA表达水平显著升高(P<0·05),肝Ki67指数也显著升高(P<0·05)。且血清GH水平与血糖呈正相关(P<0·05),血清IGF-1、IGFBP-3水平与血清AST、ALT、ALP呈负相关(P<0·05),与血清ALB量正相关(P<0·05)。结论rhGH可以改善肝硬化大鼠肝部分切除术后GH/IGF-1轴,血清IGF-1、IGFBP-3水平有助于判断营养支持的效果。     

Insulin-Like Growth Factor (IGF) System in the Bovine Mammary Gland and Milk

Primary bovine mammary cells express the two IGF receptors (IGF-IR, IGF-IIR),⁴ insulinreceptor, and four IGFBPs (IGFBP-2, -3, -4, and -5). Examination of the IGF-IR during themammary gland lactation cycle shows that IGF-IR number declines at parturition, a changethat coincides with decreases in the blood level of its ligand, IGF-I. IGF-II and IGF-IIR arelargely unchanged. IGFBP-3 is the predominant mammary IGFBP and its concentration alsodeclines in blood and milk during lactation compared to prepartum and involution periods.Time of lactation and pregnancy were the main determinants of milk but not bloodIGFBP-3 levels. IGFBP-3 binds to membrane proteins of bovine mammary tissue; an IGFBP-3 bindingprotein has been identified as bovine lactoferrin. Lactoferrin has the capacity to compete withIGF binding to IGFBP-3. Appearance of both IGFBP-3 and lactoferrin in conditioned mediaof primary cultures of bovine mammary cells was stimulated by all trans retinoic acid (atRA).Furthermore, atRA was necessary for the entry of exogenously added lactoferrin into themammary cell nucleus, while IGFBP-3 entry into the nuclei of atRA treated cells requiredthe presence of lactoferrin. These findings reveal a novel role for lactoferrin, suggesting thatlactoferrin is critically involved in the regulation of the IGF system during the involution period.     

Serum leptin values in relation to bone density and growth hormone-insulin like growth factors axis in healthy men

A novel action of leptin on bone formation has recently been described in animals. However, in humans, studies provide data, that, are less conclusive. So far, few studies investigated the leptin-bone density association in males. Moreover, it has been suggested that GH, IGF-1 and IGFBP-3 may be major players in the hormonal or paracrine pathways that regulate bone cell metabolism. Also, leptin has been shown to modulate the GH/IGF pathway. The aim of this study was to clarify further this issue by investigating (a) the influence of serum levels of leptin, GH, IGF-1 and IGFBP-3 on bone mass in various skeletal sites and, (b), the relationship between leptin and the GH/IGF axis. 363 healthy individuals were investigated. BMD and serum leptin, GH, IGF-1 and IGFBP-3 serum levels were assessed. Our results indicate that 11% of healthy males had bone density with T scores 相似文献   

Feedback control of milk secretion from milk

Extracellular storage allows biologically-active substances in milk to influence mammary function. Among these factors is one which regulates the rate of milk secretion acutely according to frequency or completeness of milk removal in each mammary gland. The active factor in goat's milk has been identified by screening milk constituents for their ability to inhibit milk constituent secretion in tissue and cell culture bioassays, and found to be a novel milk protein. The proteins identified by bioassayin vitro, also inhibited milk secretion in lactating goats in a reversible, concentration-dependent manner. This protein, termed FIL (feedback inhibitor of lactation), acts by reversible blockade of constitutive secretion in the mammary epithelial cell. As the inhibitor is synthesized in the same epithelial cells, feedback inhibition is, therefore, an autocrine mechanism. FIL's unusual mechanism of action also influences other aspects of mammary function. Acute disruption of mammary membrane trafficking is associated with downregulation of prolactin receptors and followed by a decrease in epithelial cell differentiation. Thus, in addition to acutely-regulating milk secretion, FIL may induce the adaptation in mammary cell differentiation which actsin vivo to sustain the secretory response to a sustained change in milk removal. In the long term, matching of milk output to demand is achieved by a change in mammary cell number. This developmental response is also local in nature. Whether it too is due to autocrine modulation by FIL of mechanisms influencing cell proliferation or survival, or elicited by another milk-borne factor, remains to be determined.     

Role of Prolactin in Promotion of Immune Cell Migration into the Mammary Gland

Immune cells in the mammary gland play a number of important roles, including protection against infection during lactation and, after passing into milk, modulation of offspring immunity. However, little is known about the mechanism of recruitment of immune cells to the lactating gland in the absence of infection. Given the importance of prolactin to other aspects of lactation, we hypothesized it would also play a role in immune cell recruitment. Prolactin treatment of adult female mice for a period equivalent to pregnancy and the first week of lactation increased immune cell flux through the mammary gland, as reflected in the number of immune cells in mammary gland-draining, but not other lymph nodes. Conditioned medium from luminal mammary epithelial HC11 cell cultures was chemo-attractive to CD4+ and CD8+ T cells, CD4+ and CD8+ memory T cells, B cells, macrophages, monocytes, eosinophils, and neutrophils. Prolactin did not act as a direct chemo-attractant, but through effects on luminal mammary epithelial cells, increased the chemo-attractant properties of conditioned medium. Macrophages and neutrophils constitute the largest proportion of cells in milk from healthy glands. Depletion of CCL2 and CXCL1 from conditioned medium reduced chemo-attraction of monocytes and neutrophils, and prolactin increased expression of these two chemokines in mammary epithelial cells. We conclude that prolactin is an important player in the recruitment of immune cells to the mammary gland both through its activities to increase epithelial cell number as well as production of chemo-attractants on a per cell basis.     

Course of Epidermal Growth Factor (EGF) and Insulin‐like Growth Factor I (IGF‐I) in Mammary Secretions of the Goat during End‐Pregnancy and Early Lactation

The epidermal growth factor (EGF) plays a crucial role in mammogenesis in many species. In ruminants, studies are limited, as EGF does not occur in peripheral plasma and specific analytical systems do not exist. Therefore a heterologous radioimmunoassay based on rhEGF was set up to monitor EGF in mammary gland secretions from goats during end‐pregnancy and early lactation. IGF‐I was measured with an established radioimmunoassay. Samples were collected from 13 goats for 25 days ante‐partum and 25 days post‐partum. Mammary gland secretions were obtained ante‐partum by removing a small amount of the udder secretions (control half) or milking (stimulated half). Post‐partum normal milk samples were collected. Blood samples were drawn by jugular venipuncture for the same period. EGF was found to occur in different molecular weight forms in the mammary glands. For routine measurements these proteins were extracted with acetone and not further separated. IGF‐I and EGF concentrations in mammary secretions and similarly IGF‐I in blood were high ante‐partum and decreased slightly towards birth. IGF‐I but not EGF is found in the peripheral plasma. Whereas IGF‐I concentrations in blood were quite constant post‐partum, IGF‐I and EGF dropped in mammary secretions close to the detection limits. The decrease was more pronounced in the stimulated half than in the control half. The data support a synergistic role for EGF and IGF‐I for mammogenesis. Both factors are further influenced by the milking stimulus and thus the functional state of the udder.     

Differential distribution of insulin-like growth factor-1 and insulin-like growth factor binding proteins in experimental diabetic rat kidney

Insulin-like growth factor-1 (IGF-1) is a peptide growth factor, and its activity is modulated by interaction with the family of IGF binding proteins (IGFBP-1 to 6). IGF-1 is detected in rat kidney and has metabolic and growth effects. To explore the possible involvement of IGFBPs in glomerular hypertrophy in streptozotocin (STZ)-induced diabetic rat, the immunolocalization of IGF-1 and IGFBPs were investigated. IGF-1 was gradually increased in the glomeruli of diabetic rats and correlated with glomerular hypertrophy. IGFBP-1 was transiently increased at 1 week after the STZ injection and declined to control level during the following period. In contrast, IGFBP-4 was increased in the diabetic glomeruli throughout the observation period. With insulin treatment, the levels of IGF-1, IGFBP-1 and 4 were normalized and glomerular hypertrophy was prevented. Initial glomerular hypertrophy of diabetic nephropathy is a related IGF-1 action, which may be modulated by IGFBP-1 and 4.     

术后应用肠外营养对肝细胞癌合并肝硬化病人的影响

目的探讨肝细胞癌合并肝硬化病人术后的营养支持。方法24例行根治性切除的肝癌病人随机分为PN组（n=12）和rhGH＋PN组（n=12）。术前、术后1d和术后6d测肝功能、血糖、AFP、血清前白蛋白、转铁蛋白及血清GH、IGF-1、IGFBP-3，用RT—PCR法检测肝组织（包括癌组织，癌旁组织和术后6d肝穿刺组织）ALBmRNA、IGF-1mRNA、IGFBP-3mRNA的表达，肝组织行Ki67免疫组织化染色。同时选12例因胆石症或肝血管瘤行手术的病人作为正常对照。结果肝细胞癌合并肝硬化病人血清前白蛋白，转铁蛋白低于正常对照组，血清GH水平高于正常对照组，而血清IGF-1、IGFBP-3水平低于正常对照组；术后6d，rhGH＋PN组血糖、血清前白蛋白、转铁蛋白、血清GH、IGF-1、IGFBP-3水平、肝ALBmRNA、IGF—1mRNA、IGFBP-3mRNA表达水平、肝Ki67指数均高于PN组。血清GH水平与血糖呈正相关，血清IGF1、IGFBP-3水平与血清AST、ALT、TBIL呈负相关，与血清ALB、前白蛋白，转铁蛋白呈正相关。结论rhGH＋PN有利于肝细胞癌合并肝硬化病人术后生长激素／胰岛素样生长因子-1轴的恢复，检测血清IGF-1、IGFBP-3水平有助于了解短期营养支持的效果和选择营养素。     

不同配方肠外营养对肝硬化大鼠生长激素/胰岛素样生长因子-1轴的影响

目的探讨不同配方肠外营养对肝硬化大鼠肝部分切除术后生长激素/胰岛素样生长因子-1轴的影响。方法正常大鼠作为对照组,肝硬化大鼠随机分为肝硬化术前组,肝硬化肝部分切除术后1 d组,术后行Novamin肠外营养5 d组,术后行Hepa肠外营养5 d组,各组n=6。测大鼠肝功能、血糖及血清GHI、GF-1I、GFBP-3水平,用RT-PCR法检测肝ALBmRNAI、GF-1 mRNA、IG-FBP-3mRNA的表达,肝组织行Ki67免疫组化染色。结果Hepa组肠外营养5 d后血清ALT、ALP、GH分别为(103±23)IU/L(、571±92)IU/L、(1.55±0.12)ng/ml,均比Novamin组明显降低,而血清IGF-1I、GFPB-3分别为(966.4±54.7)ng/ml(、6.9±0.2)ng/ml,均明显升高,肝ALBmRNA、IGF-1mRNAI、GFBP-3mRNA表达水平分别为(1.24±0.06)、(0.85±0.00)、(0.69±0.02),也明显升高,但肝Ki67指数(4.8%±0.3%vs 4.4%±0.4%)却无显著性差异。血清IGF-1I、GFPB-3与血清AST、ALT、ALP水平呈负相关,与血清ALB呈正相关。结论肝硬化大鼠不同配方肠外营养均可反映在生长激素/胰岛素样生长因子-1轴的变化,检测血清IGF-1,IGFBP-3水平有助于营养素的选择。     

Castration rapidly decreases local insulin-like growth factor-1 levels and inhibits its effects in the ventral prostate in mice

BACKGROUND: The mechanisms by which castration induces prostate involution are largely unknown. METHODS: Early responses to castration in mouse ventral prostate (VP) were explored by quantitative microscopy, cDNA array expression, quantitative RT-PCR, and Western blot analysis. As several changes occurred in the insulin-like growth factor (IGF) system this was studied in more detail. Laser micro-dissection was used to localize sites of IGF-1 and IGF-1 receptor (IGF-R1) production. IGF-1 protein levels and IGF-R1 mediated signaling via insulin regulated substrate 1 and 2 (IRS-1 and 2) were examined. IGF-1 was injected into the VP in intact, and castrated mice and effects studied 1 day later. RESULTS: IGF-1 and IGF binding protein 2 (IGFBP-2) mRNA were rapidly reduced whereas IGFBP-3 and IGF-R1 mRNA were increased after castration. IGF-1 was principally produced in the stromal compartment, while IGF-R1 was produced in both epithelial and stromal cells. IGF-1 and IRS-1 protein levels were decreased 1 and 3 days after castration, respectively, while IRS-2 was unchanged. Inactivating phosphorylation of IRS-1 at serine 307 was increased 1 day after castration, and activating phosphorylation at tyrosine 612 was decreased 2 days later. These changes were accompanied by decreased cell proliferation and increased cell death in the glandular and vascular compartment. Local injection of IGF-1 increased vascular density and epithelial cell proliferation in intact mice, but had no effect in castrated animals. CONCLUSION: Decreased IGF-1 levels and action may mediate some of the key features of castration-induced prostate involution.     

Insulin-like growth factor binding protein-2 modulates podocyte mitogenesis

To study the role of insulin-like growth factors (IGF) in podocyte maturation, we isolated and characterized fetal visceral glomerular epithelial cells from human kidneys obtained at 8–18 weeks gestation. Cells were identified as podocyte lineage by their cobblestone morphology and immunoreactivity with synaptopodin, Wilms tumor-1 suppressor gene product (WT-1), complement receptor CR1, and cytoskeletal proteins smooth muscle actin and vimentin. Stimulation of the podocyte cell monolayers with IGF-II resulted in a slight increase in mitogenesis, an effect that was concentration and time dependent and abrogated by co-incubation with exogenous IGF binding protein 2 (IGFBP-2). Western blot analysis of conditioned media revealed that cultured podocytes expressed endogenous IGFBP-2 exclusively. IGF-II stimulation enhanced IGFBP-2 production in a dose- and time-dependent fashion and was associated with an increase in IGFBP-2 mRNA production. These data demonstrate that IGF-II-stimulated IGFBP-2 production appears to inhibit the mitogenic effect of IGF-II, and may have an autocrine effect on the maturation, differentiation, and survival of fetal podocytes.     

Serum levels of IGF-1 and IGFBP-3 during adjuvant chemotherapy for primary breast cancer

High serum concentrations of insulin-like growth factor-1 (IGF-1) are associated with an increased risk of breast, prostate, colorectal, and lung cancer whereas IGF binding protein-3 (IGFBP-3) seems to exert a protective effect. Therefore, patients may benefit from low IGF-1 levels and high IGFBP-3 levels. This study evaluated whether adjuvant anthracycline-containing chemotherapy modulates IGF-1 and/or IGFBP-3 serum levels in breast cancer patients. In 18 patients undergoing adjuvant treatment for primary breast cancer, IGF-1 and IGFBP-3 serum levels were measured with immunoassays during chemotherapy regimens of either 5-fluorouracil, epirubicin and cyclophosphamide (FEC) or epirubicin and cyclophosphamide (EC). Mean pre-treatment values of IGF-1 and IGFBP-3 were 124+/-13 and 3698+/-186 ng/ml, respectively. No significant changes in IGF-1 and IGFBP-3 serum concentrations were observed during adjuvant anthracycline-containing chemotherapy. IGF-1 levels significantly correlated with IGFBP-3 levels before and during chemotherapy. In conclusion, these chemotherapy regimens do not seem to modulate IGF-1 or IGFBP-3 levels in a favourable or unfavourable way.     

mRNA expression of the IGF system in the kidney of the hypersomatotropic rat

AIM: To examine the response of the insulinlike growth factor (IGF) system in the kidney during a state of extreme growth. METHODS: We studied the mRNA expression of IGF-I, IGF-I receptor, and IGF-binding proteins (BP) using sensitive RNase protection assays following subcutaneous implantation of growth hormone pituitary cells (GH(3)) in rats. RESULTS: Within 5 weeks, the serum GH levels increased from 18.0 +/- (SE) 5.0 ng/ml in control animals to 389.8 +/- 30.3 ng/ml in GH(3) rats (n = 5, p < 0.001). The circulating IGF-I levels were also elevated. The kidney weights increased from 0.74 +/- 0.01 g in controls to 1.06 +/- 0.03 g in GH(3) animals (n = 5, p < 0.001). Similar changes were observed at week 10. The renal IGF-I mRNA averaged 1.0 +/- (SD) 0.33 relative densitometry units in controls (n = 4) and increased to 2.11 +/- 0.13 relative densitometry units in GH(3) rats (n = 5, p < 0.001). On the other hand, mRNA for the type I IGF receptor decreased in hypersomatotropic rats. Messenger RNAs for IGFBP-1 and IGFBP-4, which have been localized to renal tubules, both decreased significantly following growth induction, while IGFBP-3, the mRNA of which has an interstitial localization, was increased at week 10. CONCLUSION: These data suggest that there is a dynamic relationship between tubular and interstitial compartments with regard to the IGF system in the kidney which may be important in the regulation of the cell mass.     

Recombinant insulin-like growth factor-1 as a therapy for IGF-1 deficiency in renal failure

Renal disease in children disrupts the growth hormone (GH) and insulin-like growth factor (IGF) axis and causes growth failure. Although GH therapy stimulates growth in these children, their short stature is likely due to a form of IGF-1 deficiency (IGFD) rather than GH deficiency. Recent experimental data have caused us to reconsider the importance of IGF-1 and IGFD to human growth. Pharmacology studies in rodents, as well as studies in patients with no functional GH receptors and primary IGFD, have shown that IGF-1 is an effective growth-promoting therapy. Gene knockout studies in mice have shown that IGF-1, rather than GH, is the major hormone controlling growth. In addition, both pharmacological and genetic studies have shown that there are effects of GH and IGF-1 that require their combined presence. In children with primary IGFD, where there is no GH signaling, recombinant human (rh)IGF-1 produces a large growth response, while in children who are GH and IGF-1 deficient, treatment with rhGH is the most-appropriate therapy. Children with short stature due to renal failure are GH sufficient and have some GH receptor signaling capacity, so that rhIGF-1, or rhIGF-1 plus rhGH, are logical therapeutic options and merit clinical testing.This work was presented in part at the IPNA Seventh Symposium on Growth and Development in Children with Chronic Kidney Disease: The Molecular Basis of Skeletal Growth, 1–3 April 2004, Heidelberg, Germany     

IGFBP-2 is a negative predictor of cold-induced brown fat and bone mineral density in young non-obese women

Recent studies have shown a positive correlation between brown adipose tissue (BAT) and bone mineral density (BMD). However, mechanisms underlying this relationship are unknown. Insulin-like growth factor 1 (IGF-1) is an important regulator of stem cell differentiation promoting bone formation. IGF binding protein 2 (IGFBP-2) binds IGF-1 in the circulation and has been reported to inhibit bone formation in humans. IGF-1 is also a crucial regulator of brown adipocyte differentiation. We hypothesized that IGFBP-2 is a negative and IGF-1 a positive regulator of BAT-mediated osteoblastogenesis. We therefore investigated a cohort of 15 women (mean age 27.7 ± 5.7 years): 5 with anorexia nervosa (AN) in whom IGF-1 levels were low due to starvation, 5 recovered AN (AN-R), and 5 women of normal weight. All subjects underwent assessment of cold-activated BAT by PET/CT, BMD of the spine, hip, femoral neck, and total body by DXA, thigh muscle area by MRI, IGF-1 and IGFBP-2. There was a positive correlation between BAT and BMD and an inverse association between IGFBP-2 and both BAT and BMD. There was no association between IGF-1 and BAT. We show for the first time that IGFBP-2 is a negative predictor of cold-induced BAT and BMD in young non-obese women, suggesting that IGFBP-2 may serve as a regulator of BAT-mediated osteoblastogenesis.     

Effects of growth hormone on growth factors after renal transplantation

Growth retardation occurs frequently in renal transplanted children (RTx) and can be improved by growth hormone (GH) treatment. This study retrospectively examines the insulin-like growth factor-1 (IGF-1) and IGF binding protein (IGFBP) profile of ten growth-retarded children previously given renal allografts, after 1 year of GH treatment period. Ten prepubertal patients (nine boys and one girl) were investigated. They had a mean chronological age (CA) of 11.4±1.1 years and a mean bone age (BA) of 7.3±0.9 years. Mean height was –3.9±0.4 SD units below the mean for CA. The mean body mass index (BMI) was 16.9±0.6 and the mean inulin clearance was 36.5±4.9 ml/min/1.73 m². Recombinant hGH was given at 4 IU/m²/day. Plasma GH, total and free IGF-1, IGFBP-2 and -3 were measured by specific radioimmunoassay (RIA). IGFBPs were characterized by SDS PAGE techniques and ligand and immunoblot analyses. Mean velocity was markedly increased (P<0.01) after 1 year of GH therapy, expressed as SD score for BA. The range of growth response was wide. The total and free plasma IGF-1 increased (P<0.01) by about 100% (mean values after GH therapy: 95.9± 2.1 nM and 165±29 pM, respectively). Plasma IGFBP-3 concentrations increased by about 40% (mean value: 148±18 pM, P<0.01), with a concomitant increase in both intact IGFBP-3 and its 30-kDa proteolytic fragment. There was no change in plasma IGFBP-2 concentration. Both mean values of inulin clearance and BMI were unchanged during the treatment. In view of the IGF-1/IGFBP concentration changes, there should have been an even better growth response to GH therapy in these patients. This strongly suggests IGF-1 insensitivity, probably as a result of corticosteroid therapy. Received: 12 April 2000 / Revised: 31 July 2000 / Accepted: 1 August 2000