Gender differences in the insulin-like growth factor axis response to a glucose load

AIMS

The insulin-like growth factors (IGFs) are thought to contribute to glucose homeostasis. The aim of our study was to examine the response of the IGFs and their binding proteins to an intravenous load of glucose in a cohort of young men and women with normal glucose tolerance.

METHODS

The intravenous glucose tolerance test (IVGTT) was used to quantify insulin sensitivity and insulin secretion in 160 adults aged 20-21 years in Adelaide, Australia. Serum IGF-I, IGF-II, IGF-binding protein (IGFBP)-1 and IGFBP-3 were measured during the IVGTT.

RESULTS

Women were less insulin sensitive than men with higher fasting insulin (women 55.6 +/- 4.4, men 44.1 +/- 3.6 pmol L(-1), P = 0.001) and first phase insulin secretion (women 3490 +/- 286, men 3038 +/- 271 pmol L(-1) min, P = 0.042). Women showed lower fasting free IGF-I (women 0.29 +/- 0.02, men 0.36 +/- 0.02 mug L(-1), P = 0.004) but higher IGFBP-3 (women 46.3 +/- 0.53, men 43.3 +/- 0.58 mg dL(-1), P = 0.001) and higher IGFBP-1 concentrations (women 37.0 +/- 2.9, men 24.8 +/- 2.3 mug L(-1), P = 0.012). IGFBP-1 fell by 5 min and remained suppressed. IGFBP-3 and total IGF-I fell until 60 min rising again by 2 h. IGF and IGFBP values were all higher in women. IGFBP-1 showed a negative association with fasting and stimulated insulin concentrations in both genders. First phase insulin secretion however showed positive correlations with IGFBP-3 (r = 0.321, P = 0.004) and IGF-I (r = 0.339 P = 0.002) in men but not women.

CONCLUSION

Our data show that IGFBP-1, IGFBP-3 and IGF-I show acute changes following a glucose load and there are marked gender differences in these responses.

Endoplasmic Reticulum Stress Induction of Insulin-like Growth Factor-binding Protein-1 Involves ATF4

Endoplasmic reticulum (ER) stress is sensed by cells in different physiopathological conditions in which there is an accumulation of unfolded proteins in the ER. A coordinated adaptive program called the unfolded protein response is triggered and includes translation inhibition, transcriptional activation of a set of genes encoding mostly intracellular proteins, and ultimately apoptosis. Here we show that insulin-like growth factor (IGF)-binding protein-1 (IGFBP-1), a secreted protein that modulates IGF bioavailability and has other IGF-independent effects, is potently induced during ER stress in human hepatocytes. Various ER stress-inducing agents were able to increase IGFBP-1 mRNA levels, as well as cellular and secreted IGFBP-1 protein up to 20-fold. A distal regulatory region of the human IGFBP-1 gene (-6682/-6384) containing an activating transcription factor 4 (ATF4) composite site was required for promoter activation upon ER stress. Mutation of the ATF4 composite site led to the loss of IGFBP-1 regulation. Electrophoretic mobility shift assay revealed an ER stress-inducible complex that was displaced by an ATF4 antibody. Knockdown of ATF4 expression using two specific small interfering RNAs impaired up-regulation of IGFBP-1 mRNA, which highlights the relevance of ATF4 in endogenous IGFBP-1 gene induction. In addition to intracellular proteins involved in secretory and metabolic pathways, we conclude that ER stress induces the synthesis of secreted proteins. Increased secretion of IGFBP-1 during hepatic ER stress may thus constitute a signal to modulate cell growth and metabolism and induce a systemic adaptive response.

Human chorionic gonadotropin inhibits insulin-like growth factor–binding protein-1 and prolactin in decidualized human endometrial stromal cells

Recent data clearly show that hCG, as one of the first hormonal signals of the embryo, is involved in the modulation of endometrial receptivity in the secretory phase. Here we report a significant dose- and time-dependent inhibition of insulin-like growth factor-binding protein-1 and prolactin by hCG in human endometrial stromal cells after decidualization in vitro-findings that further underline the role of hCG in the endometrial milieu during early implantation.

Endocrine regulation of HOX genes

Hox genes have a well-characterized role in embryonic development, where they determine identity along the anteroposterior body axis. Hox genes are expressed not only during embryogenesis but also in the adult, where they are necessary for functional differentiation. Despite the known function of these genes as transcription factors, few regulatory mechanisms that drive Hox expression are known. Recently, several hormones and their cognate receptors have been shown to regulate Hox gene expression and thereby mediate development in the embryo as well as functional differentiation in the adult organism. Estradiol, progesterone, testosterone, retinoic acid, and vitamin D have been shown to regulate Hox gene expression. In the embryo, the endocrine system directs axial Hox gene expression; aberrant Hox gene expression due to exposure to endocrine disruptors contributes to the teratogenicity of these compounds. In the adult, endocrine regulation of Hox genes is necessary to enable such diverse functions as hematopoiesis and reproduction; endocrinopathies can result in dysregulated HOX gene expression affecting physiology. By regulating HOX genes, hormonal signals utilize a conserved mechanism that allows generation of structural and functional diversity in both developing and adult tissues. This review discusses endocrine Hox regulation and its impact on physiology and human pathology.

Regulation of hepatic insulin-like growth factor-binding protein-1 gene expression by insulin: central role for mammalian target of rapamycin independent of forkhead box O proteins

The expression of IGF-binding protein-1 (IGFBP-1) is induced in rat liver by dexamethasone and glucagon and is completely inhibited by 100 nM insulin. Various studies have implicated phosphatidylinositol 3-kinase, protein kinase B (Akt), phosphorylation of the transcription factors forkhead in rhabdomyosarcoma 1 (Foxo1)/Foxo3, and the mammalian target of rapamycin (mTOR) in insulin's effect. In this study we examined insulin regulation of IGFBP-1 in both subconfluent and confluent hepatocytes. In subconfluent hepatocytes, insulin inhibition of IGFBP-1 mRNA levels was blocked by inhibiting PI3 kinase activation, and there was a corresponding inhibition of Foxo1/Foxo3 phosphorylation. In these same cells, inhibition of the insulin effect by rapamycin occurred in the presence of insulin-induced Foxo1/Foxo3 phosphorylation. In confluent hepatocytes, insulin could not activate the phosphatidylinositol 3-kinase (PI3 kinase)-Akt-Foxo1/Foxo3 pathway, but still inhibited IGFBP-1 gene expression in an mTOR-dependent manner. In subconfluent hepatocytes, the serine/threonine phosphatase inhibitor okadaic acid (100 nM) partially inhibited IGFBP-1 gene expression by 40%, but did not produce phosphorylation of either Akt or Foxo proteins. In contrast, 1 nm insulin inhibited the IGFBP-1 mRNA level by 40% and correspondingly activated Akt and Foxo1/Foxo3 phosphorylation to a level comparable to that observed with 100 nM insulin. These results suggest a potential role for a serine/threonine phosphatase(s) in the regulation of IGFBP-1 gene transcription, which is not downstream of mTOR and is independent of Akt. In conclusion, we have found that in rat liver, insulin inhibition of IGFBP-1 mRNA levels can occur in the absence of the phosphorylation of Foxo1/Foxo3, whereas activation of the mTOR pathway is both necessary and sufficient.

Stromal cells from endometriotic lesions and endometrium from women with endometriosis have reduced decidualization capacity

OBJECTIVE

To evaluate the phenotype, proliferative, and differentiation capacities in vitro of stromal cells derived from peritoneal, ovarian, and deeply infiltrating endometriosis.

DESIGN

Experimental study using phase contrast microscopy, immunocytochemistry, and functional bioassays.

SETTING

University-based laboratory.

PATIENT(S)

Women with and without endometriosis undergoing surgery for benign indications.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The stability in vitro of stromal cells derived from peritoneal (n = 18), ovarian (n = 29), and deeply infiltrating (n = 14) endometriotic lesions, as well as endometrium from women with (n = 5) and without endometriosis (n = 5) was evaluated by detection of endometrial markers. The proliferative and differentiation capacity of the cells was assessed by the use of cell doubling estimation and in vitro decidualization assays.

RESULT(S)

The expression of the progesterone receptor and CD10 in stromal cells derived from the three types of endometriotic lesions is retained in culture up to passage 10. The doubling time of stromal cells from deeply infiltrating lesions is lower than that of endometrial stromal cells. Levels of prolactin and insulin-like growth factor binding protein-1 (IGFBP-1) are reduced in supernatants from stromal cells derived from the three types of lesions and from the endometrium of women with endometriosis.

CONCLUSION(S)

The peritoneal, ovarian, and deeply infiltrating endometriotic stromal cell lines we describe retain in vivo tissue markers. Loss of differentiation capacity of the endometriotic cell lines and endometrial cells from women with endometriosis may influence the capacity for proliferation and survival of these cells in the ectopic environment.

Effects of betaine on ethanol-stimulated secretion of IGF-I and IGFBP-1 in rat primary hepatocytes: Involvement of p42/44 MAPK activation

AIM: To evaluate the effects of betaine on the ethanol-induced secretion of IGF-I and IGFBP-1 using radioimmunoassay and Western blotting, respectively, in primary cultured rat hepatocytes.

METHODS: Hepatocytes isolated from male Sprague-Dawley rats were incubated with various concentrations of ethanol and PD98059 procedures. The hepatocytes were also treated with different doses of betaine (10^-5, 10^-4, and 10^-3 mol/L). We measured IGF-I and IGFBP-1 using radioimmunoassay and Western blotting, respectively.

RESULTS: The ethanol-induced inhibition of IGF-I secretion was attenuated by betaine in a concentration-dependent manner in primary cultured rat hepatocytes. At 10^-3 mol/L, betaine significantly increased IGF-I secretion but decreased IGFBP-1 secretion. In addition, p42/44 mitogen-activated protein kinase (MAPK) activity was accelerated significantly from 10 min to 5 h after treatment with 10^-3 mol/L betaine. Furthermore, the changes in IGF-1 and IGFBP-1 secretion resulting from the increased betaine-induced p42/44 MAPK activity in primary cultured rat hepatocytes was blocked by treatment with the MAPK inhibitor PD98059. Betaine treatment blocked the ethanol-induced inhibition of IGF-I secretion and p42/44 MAPK activity, and the ethanol-induced increase in IGFBP-1 secretion.

CONCLUSION: Betaine modulates the secretion of IGF-I and IGFBP-1 via the activation of p42/44 MAPK in primary cultured rat hepatocytes. Betaine also alters the MAPK activations induced by ethanol.

Alessi D, Sutherland C. Analysis of hepatic gene transcription in mice expressing insulin-insensitive GSK3

GSK3 (glycogen synthase kinase-3) regulation is proposed to play a key role in the hormonal control of many cellular processes. Inhibition of GSK3 in animal models of diabetes leads to normalization of blood glucose levels, while high GSK3 activity has been reported in Type II diabetes. Insulin inhibits GSK3 by promoting phosphorylation of a serine residue (Ser-21 in GSK3alpha, Ser-9 in GSK3beta), thereby relieving GSK3 inhibition of glycogen synthesis in muscle. GSK3 inhibition in liver reduces expression of the gluconeogenic genes PEPCK (phosphoenolpyruvate carboxykinase), G6Pase (glucose-6-phosphatase), as well as IGFBP1 (insulin-like growth factor binding protein-1). Overexpression of GSK3 in cells antagonizes insulin regulation of these genes. In the present study we demonstrate that regulation of these three genes by feeding is normal in mice that express insulin-insensitive GSK3. Therefore inactivation of GSK3 is not a prerequisite for insulin repression of these genes, despite the previous finding that GSK3 activity is absolutely required for maintaining their expression. Interestingly, insulin injection of wild-type mice, which activates PKB (protein kinase B) and inhibits GSK3 to a greater degree than feeding (50% versus 25%), does not repress these genes. We suggest for the first time that although pharmacological inhibition of GSK3 reduces hepatic glucose production even in insulin-resistant states, feeding can repress the gluconeogenic genes without inhibiting GSK3.

Involvement of the tyrosine phosphatase early gene of liver regeneration (PRL-1) in cell cycle and in liver regeneration and fibrosis effect of halofuginone

Tyrosine phosphatase PRL-1 is one of the immediate-early genes up-regulated during liver regeneration and is apparently involved in cell proliferation. Previously, we have demonstrated that halofuginone, an inhibitor of collagen type I synthesis, prevents liver fibrosis and improves cirrhotic liver regeneration. In this study, we evaluated the effect of halofuginone on PRL-1 expression, its cellular localization in vitro and during liver regeneration, and fibrosis progression in vivo. In culture, halofuginone increased PRL-1 expression in primary rat hepatocytes and in hepatocellular carcinoma (HCC) cell lines, the former being more sensitive to halofuginone. The halofuginone-dependent increase in PRL-1 gene expression was correlated with an increase in the transcription factor early growth response-1 (Egr-1) and inversely correlated with the inhibition of cell proliferation. Halofuginone arrested HepG2 and Huh7 cell lines at the G1 phase, whereas Hep3B cells were arrested at G2/M, probably because of a reduction in the synthesis of cyclins D1 and B1 in all HCC cells and increased cyclin A in Hep3B cells. Halofuginone also affected the PRL-1 sub-cellular localization that was cell-cycle-dependent. In addition, halofuginone augmented PRL-1 expression in the remnant liver after partial hepatectomy and in chemically induced fibrosis in rats; this was accompanied by increased expression of insulin-like growth factor binding protein 1 (IGFBP-1), another immediate-early gene of regeneration. The regulation of the expression of the early genes of regeneration such as PRL-1 and IGFBP-1 is thus part of the mode of action of halofuginone and results in the prevention of liver fibrosis and improved cirrhotic liver regeneration.

Chemical Genetic Identification of the IGF-Linked Pathway that Is Mediated by STAT6 and MFP2

Insulin-like growth factor 2 (IGF2) is a potent mitogen whose deregulation plays a role in developing liver, breast, and prostate cancers. Here, we take a small-molecule approach to investigate molecular pathways that modulate IGF2 signaling, by using chromeceptin, a synthetic molecule that selectively impairs the viability and growth of IGF2-overexpressing hepatocellular carcinoma cells. Affinity purification revealed that chromeceptin binds to multifunctional protein 2 (MFP-2), a seemingly multifunctional enzyme implicated in peroxisomal beta-oxidation. The small molecule-protein interaction stimulates the expression of IGF binding protein 1 (IGFBP-1) and suppressor of cytokine signaling-3 (SOCS-3), two cellular attenuators of the IGF signals, through activation of signal transducers and activators of transcription 6 (STAT6). The results underline the importance of STATs in IGF/insulin regulation, and they implicate a new pathway for STAT6 activation that is amenable to small-molecule intervention.

The serum levels of proinsulin and their relationship with IGFBP-1 in obese children

AIM

Serum proinsulin (PI) levels were investigated in obese children to determine whether PI is a sensitive indicator of insulin resistance, as previously shown in adults with type 2 diabetes mellitus (DM), and to evaluate their relationship with insulin-like growth factor-binding protein-1 (IGFBP-1) known as a predictor of the development of cardiovascular disease in diabetic adults.

SUBJECTS AND METHODS

Forty-two obese children without DM (age, 12.1 +/- 1.5 year) and 42 age-matched control children were included in the study. The serum levels of PI, immunoreactive insulin (IRI), IGFBP-1 and free insulin-like growth factor-1 (IGF-1) were measured in the fasting state.

RESULTS

The fasting levels of serum PI and IRI were significantly higher in obese children than in controls (PI, 10.5 +/- 6.8 vs. 5.6 +/- 2.0 pmol/l, p < 0.001; IRI, 72.0 +/- 41.8 vs. 32.7 +/- 19.5 pmol/l, p < 0.001). Serum IGFBP-1 levels were significantly lower in obese children than in controls (37.7 +/- 24.6 vs. 76.3 +/- 26.5 microg/l, p < 0.001). The ratio of PI to IRI (calculated as molar ratios) did not differ significantly between obese and control subjects (0.16 +/- 0.08 vs. 0.19 +/- 0.11, p = 0.08). For the whole group, serum PI levels correlated positively with IRI and inversely with IGFBP-1 (IRI, r = 0.67, p < 0.001; IGFBP-1, r = -0.49, p < 0.001). Serum IGFBP-1 levels correlated inversely with both BMI and IRI (BMI, r = -0.73, p < 0.001; IRI, r = -0.60, p < 0.001). Multiple regression analysis revealed that the best predictive parameters for IGFBP-1 were BMI and PI (R2 = 0.57, p < 0.001 and p < 0.05, respectively).

CONCLUSION

These findings suggest that fasting serum PI levels may be a better predictor than fasting insulin levels for the future development of type 2 DM and cardiovascular disease in obese children, and PI, in addition to insulin, contributes to the suppression of hepatic IGFBP-1 production.

[Effect and risk analysis of misoprostol in stimulating cervical maturity for post-term pregnancy]

OBJECTIVE

To evaluate the effect and risk of misoprostol for stimulating cervical maturity in women with post-term pregnancy negative for insulin-like growth factor binding protein-1 (IGFBP-1) in cervical secretion with modified Bishop score less than 3.

METHODS

Seventy-one women with post-term pregnancy randomized into misoprostol group (n=37) and control group (n=34) received misoprostol placement at the posterior vaginal fornix and routine intravenous oxytocin infusion, respectively, to stimulate cervical maturity. Failure to respond to the treatment within the initial 24 h necessitated a repeated administration for no more than 3 times in all. Modified Bishop score was recorded and fetal heart monitored once every 24 h, and IGFBP-1 in the cervical secretion was detected at 24 and 48 h after drug administration.

RESULTS

The misoprostol group showed better effect of cervical maturity stimulation than the control group (P<0.001), and the positivity rates of IGFBP-1 24 and 48 h after drug administration were significantly higher than that of the control group (P<0.01 and 0.001). The number of cases with indication for cesarean section was significant higher in the control group (P<0.001). There were no significant differences in postpartum hemorrhage, excessive uterine contraction, incidence of fecal contamination of the amniotic fluid or Apgar score of the newborn between the two groups (P>0.05).

CONCLUSIONS

Misoprostol is safe and effective for stimulating cervical maturity in women with post-term pregnancy who have modified Bishop score lower than 3 and are negative for IGPBF-1 in cervical secretion. Oxytocin is not advised for use in such gravida for stimulating cervical maturity. IGFBP-1 in cervical secretion may serve as an important index for evaluating the cervical maturity.

Oxygen-dependent modulation of insulin-like growth factor binding protein biosynthesis in primary cultures of rat hepatocytes

Higher levels of IGF-binding protein 1 (IGFBP-1) mRNA are expressed in the less aerobic perivenous zone of the liver. Because gradients in oxygen tension (pO(2)) may contribute to zonated gene expression, the influence of arterial and venous pO(2) on IGFBP-1 biosynthesis was studied in primary cultures of rat hepatocytes. Maximal IGFBP-1 mRNA and protein levels were observed under venous pO(2), whereas less than 30% of maximal levels were observed under arterial pO(2). In contrast, the expression of IGFBP-4 was greatest under arterial pO(2), indicating that this effect of hypoxia on IGFBP-1 gene expression is specific. The response to hypoxia appears to involve reactive oxygen species, because treatment with H(2)O(2) results in a dose-dependent decrease of IGFBP-1 mRNA levels under venous pO(2), whereas IGFBP-1 mRNA expression under arterial pO(2) was not affected. Inhibition of the hypoxia-dependent IGFBP-1 mRNA induction by actinomycin D indicates that this effect is mediated at the level of gene transcription, and inhibition of IGFBP-1 mRNA by the iron chelator desferrioxamine under both venous and arterial pO(2) suggested the involvement of hypoxia-inducible transcription factors (HIF). Transfection experiments demonstrated that especially HIF-3alpha and HIF-2alpha, and to a lesser extent HIF-1alpha, contribute to the induction of IGFBP-1 mRNA expression in isolated hepatocytes, whereas experiments with vectors for the HIF prolyl hydroxylases (PHD) indicated a major role of PHD-2 in destabilization of HIFs, attenuating the induction of IGFBP-1 under venous pO(2). Reporter gene studies indicate that hypoxia stimulates IGFBP-1 expression through a putative HIF response element located approximately 250 bp upstream from the transcription initiation site. Together, these results support the concept that iron, radical oxygen species, and the HIF-2 and -3 as well as the PHD pathways play important roles in mediating effects of hypoxia on IGFBP-1 gene expression in the liver.

Insulin-like growth factor-1 and insulin-like growth factor binding protein-1 and 3 in the follicular fluid of infertile patients submitted to in vitro fertilization

PURPOSE

In the present article we propose to evaluate IGF-1, IGFBP-1 and 3 in the follicular fluid of infertile patients submitted to in vitro fertilization.

METHODS

We performed a case-control study with 53 infertile patients submitted to the first in vitro fertilization attempt. We compared their follicular fluid concentration of IGF-1, IGFBP-1 and IGFBP-3 between the patients who became pregnant (n = 11) versus those nonpregnant (n = 42).

RESULTS

The clinical characteristics of patients from the two groups were similar in terms of age and body mass index. Data related to the analysis of ovulation induction was not different regarding length of induction in days, number of retrieved oocytes, fertilization rate, and number of transferred embryos. Furthermore, the number of FSH units required for ovarian induction was also similar between the studied groups. IGF-1 and IGFBP-1 were not significantly different between the groups (p > 0.05). However, those patients that became pregnant presented a lower follicular fluid concentration of IGFBP-3, 2237.10 +/- 582.73 pg/ml and 2657.64 +/- 584.15 ng/ml, respectively (p = 0.038).

CONCLUSIONS

We demonstrated an association of a lower follicular fluid IGFBP-3 in individuals that became pregnant compared to subjects that did not after in vitro fertilization.

In vivo infusion of interleukin-1beta and chorionic gonadotropin induces endometrial changes that mimic early pregnancy events in the baboon

Both human chorionic gonadotropin (hCG) and IL-1beta induce changes in the endometrium that are associated with the establishment of pregnancy. We investigated the synergistic effect of these two embryonic signals on endometrial function using a baboon model of simulated pregnancy. Recombinant hCG (30 IU/d) was infused between d 6 and 10 post ovulation (PO) to mimic blastocyst transit. On the expected day of implantation (d 10 PO), IL-1beta (12 ng/d) or IL-1 receptor antagonist (IL-1Ra; 12 ng/d) was infused for an additional 5 d. Endometria were harvested on d 15 PO. Both hCG and hCG plus IL-1beta induced marked differences in the distribution of alpha-smooth muscle actin, proliferation marker Ki67, decidualization marker IGF-binding protein-1, and cyclooxygenase-1. The most marked effect of IL-1beta was the induction of IGF-binding protein-1 protein in stromal cells close to the apical surface, whereas cyclooxygenase-1 was down-regulated in the glandular epithelium. Protein arrays of uterine flushings showed significant suppression of death receptors, Fas and TNF receptor 1, in the hCG- with or without IL-1beta-treated groups, suggesting an inhibition of apoptosis. Additionally, cytotoxic T lymphocyte antigen-4, matrix metalloproteinase-3, and IL-4 were suppressed in treated animals compared with controls. However, no differences were observed in cytokine profile between hCG-treated and hCG- plus IL-1beta-treated baboons. This study confirms that in preparation for pregnancy, the primate endometrium undergoes both morphological and functional changes, which are modulated by hCG and IL-1beta, that lead to the inhibition of apoptosis and the development of an immunotolerant environment. These changes suggest that infusion of IL-1beta at the time of implantation into the nonpregnant baboon treated with hCG synergizes with hCG and mimics the early endometrial events associated with the presence of an embryo.

Posttranslational modifications of decidual IGFBP-1 by steroid hormones in vitro

Insulin-like growth factor binding protein-1 (IGFBP-1) appears to regulate insulin-like growth factors (IGFs; IGF-I and IGF-II) biological activity within the local environment of human placenta by modulating IGFs interaction with their receptors. Considering that posttranslational modifications of IGFBP-1 such as phosphorylation and proteolysis affect its affinity for IGFs, this study was undertaken to identify the role of estrogen and progesterone in this regard. The conditioned media of steroid hormone-treated decidual cells were evaluated using different approaches using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and non-denaturing PAGE following immunoblotting as well as zymographys that contained gelatin and IGFBP-1 as substrates. Our results demonstrated that medroxy progesterone acetate (MPA) treatment increased both phosphorylated and non-phosphorylated decidual-secreted IGFBP-1, whereas 17beta-estradiol (E2) treatment attenuated its phosphorylated forms. Furthermore, the results of zymography revealed that steroid hormones regulated the activity of decidual-secreted matrix metalloproteinases (MMP)-2 and -9, in which E2 treatment up-regulated the MMP-9 activity. Finally, it was demonstrated in our study that decidual-secreted MMP-9 was capable of degrading human amniotic fluid-derived IGFBP-1. In conclusion, our data implicate steroid hormones in the control of IGF system activities at the embryo-maternal interface, at least in part, through their effects on the post-translation changes of decidual-secreted IGFBP-1 such as its phosphorylation and/or proteolysis.

Insulin-like growth factor binding protein-1 detection in preterm labor: evaluation of a bedside test

Phosphorylated insulin-like growth factor binding protein-1 (phIGFBP-1) is secreted by decidual cells and may leak into cervical secretions during detachment of the fetal membrane. The aim of this study was to determine whether a rapid bedside test for phIGFBP-1 predicts preterm birth in women with preterm uterine contractions. This was a prospective study of pregnant women who sought medical care for symptoms of preterm labor. Cervical swabs were assayed for the presence of phIGFBP-1 by a rapid bedside test. Sixty-four patients were enrolled. Eleven of them (17%) delivered preterm (< 35 weeks). phIGFBP-1 in cervical secretions predicted preterm birth with a sensitivity of 72.7%, a specificity of 83.0%, a positive predictive value of 47.0%, and negative predictive value of 93.6%. Positive phIGFBP-1 bedside test in women with preterm uterine contractions may indicate a significant risk for subsequent preterm birth. The absence of phIGBP-1 is a reassuring sign that the likelihood of preterm birth is low.

The effect of submaximal exercise on immuno- and bioassayable IGF-I activity in patients with GH-deficiency and healthy subjects

OBJECTIVE

Growth hormone (GH) increases during exercise, but the response of the insulin-like growth factor (IGF) system has not been as definitive. Therefore, we investigated the effect of the exercise-induced GH response on the circulating IGF-system in GH-deficient (GHD) and intact adults.

DESIGN

Eight GHD adults were studied on 2 occasions, with (+GH) and without (-GH) GH administered (0.4 IU) during exercise (45 min of cycle ergometer exercise at the lactate threshold). Eight age-matched controls were only studied on one occasion. Blood samples were drawn at baseline, during and post-exercise. IGFBP-3 proteolysis was measured by an in vitro proteolytic activity assay, IGF-I bioactivity by novel IGF-I kinase receptor activation assay (KIRA) and other hormones by immunoassay.

RESULTS

GH administration to GHD adults resulted in a serum GH peak similar to the exercise-stimulated GH response in GH intact controls, but exercise had only a small impact on the IGF system. IGF-I concentration was lower in controls but was only significantly lower than the +GH day. Neither IGF-I nor -II levels changed over time. IGFBP-1 demonstrated a time effect (P<0.01) in all groups, and a time x group interaction (P<0.01) with a rise at 75 min post-exercise, which was greater in the GHD subjects than controls. IGFBP-2 and -3 increased significantly (P<0.01) over time in the GHD subjects, but not in the controls. No change in IGFBP-3 proteolysis or IGF-I bioactivity was found during exercise or recovery in either group.

CONCLUSION

Submaximal exercise induced minor changes in IGFBP-1, -2 and -3, without affecting IGFBP-3 proteolysis and IGF-I bioavailability. Thus the metabolic status during submaximal exercise does not require a change in plasma IGF-I bioavailability. Administration of GH to GHD adults does not result in changes in proteolysis or bioavailability.

Amniotic IGF-I supplementation of growth-restricted fetal sheep alters IGF-I and IGF receptor type 1 mRNA and protein levels in placental and fetal tissues

We have previously reported that chronic intra-amniotic supplementation of the late gestation growth-restricted (IUGR) ovine fetus with IGF-I (20 microg/day) increased gut growth but reduced liver weight and circulating IGF-I concentrations. Here we report mRNA and protein levels of IGF-I, the type 1 IGF receptor (IGF-1R) and IGF-binding proteins (IGFBP)-1, -2 and -3 in fetal gut, liver, muscle and placenta from fetuses in that earlier study in an attempt to explain these contrasting results. mRNA and protein were extracted from tissues obtained at post mortem at 131 days of gestation (term, 145 days) from three groups of fetuses (control, IUGR+saline and IUGR+IGF-I, n=9 per group). Control fetuses were unembolised and untreated. In the IUGR groups, growth restriction was induced from 113 to 120 days by placental embolisation; from 120 to 130 days fetuses were treated with daily intra-amniotic injections of either saline or 20 microg IGF-I. mRNA was measured by RT-PCR or real-time RT-PCR, and protein by Western blot. In liver, muscle and placenta, IGF-I mRNA and protein levels were reduced by between 8 and 30% in IGF-I-treated fetuses compared with saline-treated fetuses and controls with no change in IGF-1R mRNA or protein levels. In contrast, in the gut, IGF-I mRNA and protein levels were not significantly altered with IGF-I treatment, but IGF-1R levels were increased, especially in the jejunum. Immunolocalisation demonstrated that IGF-1R expression was confined to the luminal aspect of the gut. mRNA levels of all three IGFBPs were reduced in the gut of IGF-I-treated fetuses, but hepatic expression was significantly increased. These data demonstrated tissue-specific regulation of IGF-I, IGF-1R and IGFBPs-1, -2 and -3 in response to intra-amniotic IGF-I supplementation, though the underlying mechanisms remain obscure.

Role of FOXO1A in the regulation of insulin-like growth factor-binding protein-1 in human endometrial cells: interaction with progesterone receptor

Insulin-like growth factor-binding protein-1 (IGFBP1) is a major secretory product of the decidualized endometrium. In the present study, we investigated the role of two transcription factors, progesterone receptor (PGR) and a member of the forkhead box class O family of transcription factors (FOXO1A), in the regulation of the IGFBP1 gene in endometrial cells. Human endometrial fibroblasts (HuF) expressed FOXO1A, progesterone receptor A (PGRA), and progesterone receptor B (PGRB) proteins, whereas the endometrial adenocarcinoma cell line, HEC-1B cells, expressed only FOXO1A and no detectable PGR proteins. When FOXO1A expression was silenced using small interference RNA, IGFBP1 expression decreased in both HuF and HEC-1B cells. Using the chromatin immunoprecipitation technique, we demonstrated that liganded PGR was recruited to the IGFBP1 promoter region (-358 to -49). In addition, immunoprecipitation of HuF nuclear proteins with a PGR antibody followed by immunoblotting with anti-FOXO1A revealed that these two proteins interact in these cells. Reporter studies demonstrated that whereas liganded PGRA or PGRB increased a progesterone response element-linked reporter construct, pPRE/ GRE.E1b.Luc, coexpression of FOXO1A inhibited the PGRB response in HuF and synergistically increased PGRA and PGRB response in HEC-1B cells. Furthermore, in HEC-1B cells, FOXO1A increased IGFBP1 promoter activity, and coexpression of PGRA or PGRB further increased the promoter activity in a cooperative manner. In HuF, the response to FOXO1A and PGR was not additive; in fact, it was lower than the sum of the individual responses. Thus, FOXO1A and PGR associate with one another, and each influences the transactivating potential of the other. The cell type-dependent responses strongly implicate the involvement of other cofactors.

Insulin and human chorionic gonadotropin cause a shift in the balance of sterol regulatory element-binding protein (SREBP) isoforms toward the SREBP-1c isoform in cultures of human granulosa cells

The isoforms of sterol regulatory element-binding proteins (SREBP) (1a, 1c, and 2) are key transcriptional regulators of lipid biosynthesis. We examined their regulation by gonadotropin and insulin in human granulosa cells. After removal of leukocytes, granulosa cells were exposed to hormonal additions for 16 h starting on d 2 of culture. Progesterone, lactate, and IGF binding protein-1 were measured in culture medium and cellular mRNA measured by competitive RT-PCR. Addition of human chorionic gonadotropin (hCG) (100 ng/ml) stimulated progesterone production (7.0-fold, P < 0.001 vs. control), whereas lactate was increased by hCG (1.6-fold, P < 0.001) and insulin (1.4-fold, P < 0.001; 1000 ng/ml). Insulin decreased IGF binding protein-1 production by 85% (P < 0.001). There were no significant effects on the expression of SREBP-1a but significant increases in mRNA for SREBP-1c with insulin (6.3-fold), hCG (10.4-fold) and in combination (15.2-fold; P < 0.01 for all comparisons). No consistent effects on SREBP-2 were observed. The expression of mRNA for fatty acid synthase, a target gene for SREBP-1c, was increased by hCG (24-fold, P = 0.006) and insulin (19-fold, P = 0.024), which also increased the level of cellular, total fatty acid (1.34-fold; P = 0.03). Thus, hCG and insulin cause a switch toward expression of the SREBP-1c isoform with consequent effects on fatty acid synthesis. We suggest that high circulating insulin, associated with clinically defined insulin resistance, may up-regulate SREBP-1c expression in the ovary.

Human growth hormone responses to repeated bouts of sprint exercise with different recovery periods between bouts

This study examined the growth hormone (GH) response to repeated bouts of sprint cycling. Eight healthy men completed three trials consisting of two 30-s sprints on a cycle ergometer separated by either 60 min (Trial A) or 240 min (Trial B) of recovery and a single 30-s sprint carried out the day after Trial B (Trial C). Trials A and B were separated by at least 7 days. Blood samples were obtained at rest and during recovery from each sprint. In Trial A, GH was elevated immediately before sprint 2, and there was no further increase in GH following the second sprint [area under the curve: 460 (SD 348) vs. 226 min.mug(-1).l(-1) (SD 182), P = 0.05]. Free insulin-like growth factor I tended to be lower immediately before sprint 2 than sprint 1 (P = 0.06). Serum free fatty acids were not different immediately before each of the sprints. In Trial B, there was a trend for a smaller GH response to the second sprint [GH area under the curve: 512 (SD 396) vs. 242 min.mug(-1).l(-1) (SD 190), P = 0.09]. Free insulin-like growth factor I tended to be lower (P = 0.06), and serum free fatty acids were higher (P = 0.01) immediately before sprint 2 than sprint 1. There was no difference in the GH response to sprinting on consecutive days (Trials B and C). In conclusion, repeated bouts of sprint cycling on the same day result in an attenuation or even ablation of the exercise-induced increase in GH, depending on the recovery interval between sprints.

Kidney growth in normal and diabetic mice is not affected by human insulin-like growth factor binding protein-1 administration

Insulin-like growth factor I (IGF-I) accumulates in the kidney following the onset of diabetes, initiating diabetic renal hypertrophy. Increased renal IGF-I protein content, which is not reflected in messenger RNA (mRNA) levels, suggests that renal IGF-I accumulation is due to sequestration of circulating IGF-I rather than to local synthesis. It has been suggested that IGF-I is trapped in the kidney by IGF binding protein 1 (IGFBP-1). We administered purified human IGFBP-1 (hIGFBP-1) to nondiabetic and diabetic mice as three daily sc injections for 14 days, starting 6 days after induction of streptozotocin diabetes when the animals were overtly diabetic. Markers of early diabetic renal changes (i.e., increased kidney weight, glomerular volume, and albuminuria) coincided with accumulation of renal cortical IGF-I despite decreased mRNA levels in 20-day diabetic mice. Human IGFBP-1 administration had no effect on increased kidney weight or albuminuria in early diabetes, although it abolished renal cortical IGF-I accumulation and glomerular hypertrophy in diabetic mice. Increased IGF-I levels in kidneys of normal mice receiving hIGFBP-1 were not reflected on kidney parameters. IGFBP-1 administration in diabetic mice had only minor effects on diabetic renal changes. Accordingly, these results did not support the hypothesis that IGFBP-1 plays a major role in early renal changes in diabetes.

The production of interleukin-11 and decidualization are compromised in endometrial stromal cells derived from patients with infertility

IL-11 signaling is critical for decidualization of the endometrial stroma in early pregnancy in the mouse. In this study, we investigate the function of IL-11 signaling in cAMP-induced decidualization of human endometrial stromal cells. We show that treatment of endometrial stromal cells with 8-bromo-cAMP (8-Br-cAMP) results in an increase in the levels of secreted IL-11, whereas levels of cell surface IL-11 receptor alpha are similar with or without 8-Br-cAMP treatment. The production of IL-11 correlates with the production of molecular markers of decidualization, prolactin and IGF-binding protein-1. The expression of these markers is inhibited when IL-11 signaling is specifically blocked in decidualizing endometrial stromal cells by the IL-11 antagonist W147A. We demonstrate that 8-Br-cAMP-induced endometrial stromal cells derived from patients with primary infertility produce lower levels of prolactin, IGF-binding protein-1, and IL-11 than cells derived from fertile women. Our results suggest that IL-11 expression is critically important during decidualization in the human endometrium, and that aberrant regulation of endometrial IL-11 production may be associated with some types of infertility.

Dose-dependent insulin regulation of insulin-like growth factor binding protein-1 in human endometrial stromal cells is mediated by distinct signaling pathways

IGF binding protein-1 (IGFBP-1) is a major product of decidualized human endometrial stromal cells and decidua, and as a modulator of IGF action and/or by independent mechanisms, it regulates cell growth and differentiation and embryonic implantation in these tissues. IGFBP-1 secretion is primarily stimulated by progesterone and cAMP and is inhibited by insulin and IGFs. The signaling pathways mediating the latter are not well defined, and the current study was conducted to determine which pathways mediate the effects of insulin on IGFBP-1 mRNA and protein expression by human endometrial stromal cells decidualized in vitro by progesterone. Cells were cultured and treated with different combinations of insulin; wortmannin, an inhibitor of the phosphatidylinositide-3-kinase (PI3-kinase) pathway; and PD98059, an inhibitor of the MAPK pathway. IGFBP-1 mRNA was determined by real-time PCR, and protein secretion in the conditioned medium was measured by ELISA. Activation of the PI3-kinase and the MAPK pathways was assessed by the detection of phosphorylated AKT and ERK in Western blots, respectively. Insulin inhibited IGFBP-1 mRNA and protein secretion in a dose-dependent fashion, with an ED(50) for the latter 0.127 ng/ml (21.6 pm). Inhibitor studies revealed that at low doses, insulin acts through the PI3-kinase pathway, whereas at higher levels it also activates the MAPK pathway in the inhibition of IGFBP-1. The data demonstrate that human endometrium is a target for insulin action in the regulation of IGFBP-1. At physiological levels insulin likely plays a homeostatic role for energy metabolism in the endometrium, and in hyperinsulinemic states, insulin action on the endometrium may activate cellular mitosis via the MAPK pathway and perhaps predispose this tissue to hyperplasia and/or cancer.