Effect of maternal diabetes on phosphorylation of insulin-like growth factor binding protein-1 in cord serum

Fetal growth regulation via insulin-like growth factor axis in normal and diabetic pregnancy

OBJECTIVES

Diabetes mellitus (DM) in pregnancy and gestational diabetes remain a considerable cause of pregnancy complications, and fetal macrosomia is among them. Insulin, insulin-like growth factors (IGFs), and components of their signal-transduction axes belong to the predominant growth regulators and are implicated in glucose homeostasis. This study aimed to evaluate the available evidence on the association between the IGF axis and fetal anthropometric parameters in human diabetic pregnancy.

METHODS

PubMed, Medline, Web of Science, and CNKI databases (1981-2021) were searched.

RESULTS

Maternal and cord serum IGF-I levels are suggested to be positively associated with weight and length of neonates born to mothers with type 1 DM. The results concerning IGF-II and IGFBPs in type 1 DM or any of the IGF axis components in type 2 DM remain controversial. The alterations of maternal serum IGFs concentrations throughout diabetic and non-diabetic pregnancy do not appear to be the same. Maternal 1st trimester IGF-I level is positively associated with fetal birth weight in DM.

CONCLUSIONS

Research on the IGF axis should take gestational age of sampling, presence of DM, and insulin administration into account. Maternal 1st trimester IGF-I level might become a predictor for macrosomia development in diabetic pregnancy.

Gestational Diabetes Mellitus and Energy-Dense Diet: What Is the Role of the Insulin/IGF Axis?

Gestational diabetes mellitus (GDM), is one of the most important pregnancy complications affecting approximately 15% of pregnant women. It is related to several gestational adverse outcomes in the fetus, e.g., macrosomia, shoulder dystocia, stillbirth, neonatal hypoglycemia, and respiratory distress. Women with GDM have a high risk of developing type 2 diabetes in the future. The pathogenesis of GDM is not completely understood; nevertheless, two factors could contribute to its development: β-cell dysfunction and failure in insulin secretion in response to insulin resistance induced by gestation. Both processes, together with the physiological activities of the insulin-like growth factors (IGFs), play a crucial role in glucose transport to the fetus and hence, fetal growth and development. IGFs (both IGF-1 and IGF-2) and their binding proteins (IGFBPs) regulate glucose metabolism and insulin sensitivity. Maternal nutritional status determines the health of the newborn, as it has substantial effects on fetal growth and development. Maternal obesity and an energy-dense diet can cause an increase in insulin and IGF-1 serum levels, producing metabolic disorders, such as insulin resistance, GDM, and high birth weight (> 4,000 g) due to a higher level of body fat. In this way, in GDM pregnancies there is an increase in IGF-1 and IGF-2 serum levels, and a decrease in IGFBP-1 and 4 serum levels, suggesting the crucial role of the insulin/IGF system in this gestational outcome. Here, the present review tries to elucidate the role that energy-dense diets and the insulin/IGF-1 signaling pathway perform in GDM pregnancies.

The Impacts of Fish Oil and/or Probiotic Intervention on Low-Grade Inflammation, IGFBP-1 and MMP-8 in Pregnancy: A Randomized, Placebo-Controlled, Double-Blind Clinical Trial

Background: We investigated the impact of fish oil and/or probiotics on serum and vaginal inflammatory and metabolic proteins and their relation to the onset of gestational diabetes mellitus (GDM). Methods: Overweight/obese pregnant women received fish oil + placebo, probiotics + placebo, fish oil + probiotics or placebo + placebo from early pregnancy until six months postpartum (fish oil: 1.9 g docosahexaenoic acid and 0.22 g eicosapentaenoic acid; probiotics: Lactobacillus rhamnosus HN001 and Bifidobacterium animalis ssp. lactis 420, 10¹⁰ colony-forming units each). Serum high sensitivity C-reactive protein (hsCRP) and serum/vaginal (s/v) phosphorylated insulin-like growth factor binding-protein-1 (phIGFBP-1), IGFBP-1 and matrix metalloproteinase 8 (MMP-8) were analyzed. GDM was diagnosed according to 2 h 75 g OGTT. Results: The intervention had no impact on the change in proteins during pregnancy. Nevertheless, s-MMP-8 decreased and s-IGFBP-1 increased more in obese than in overweight women in the fish oil + probiotics group, while a decrease in s-MMP-8 was seen in obese women and an increase was seen in overweight women in the probiotics + placebo group. The late pregnancy s-phIGFBP-1 was higher in women who developed GDM in fish oil + probiotics-group compared to fish oil + placebo-group. The concentrations of s-phIGFBP-1 (635.9 ± 315.3 ng/mL vs. 753.2 ± 335.1 ng/mL, p = 0.005) and s-IGFBP-1 (3.78 ± 0.72 ng/mL vs. 3.96 ± 0.69 ng/mL, p = 0.042) were lower in early pregnancy in women who developed GDM than in women remaining healthy. Conclusions: The intervention per se had no impact on the proteins, but obesity and GDM may modify the effect. IGFBPs may affect the development of GDM.

Metformin and insulin treatment of gestational diabetes: effects on inflammatory markers and IGF-binding protein-1 - secondary analysis of a randomized controlled trial

Background

Gestational diabetes mellitus (GDM) is characterized by disturbed glucose metabolism and activation of low-grade inflammation. We studied whether metformin treatment has favorable or unfavorable effects on inflammatory markers and insulin-like growth factor-binding protein 1 (IGFBP-1) in GDM patients compared with insulin, and whether these markers associate with major maternal or fetal clinical outcomes.

Methods

This is a secondary analysis of a previous randomized controlled trial comparing metformin (n = 110) and insulin (n = 107) treatment of GDM. Fasting serum samples were collected at the time of diagnosis (baseline, mean 30 gestational weeks [gw]) and at 36 gw. Inflammatory markers serum high-sensitivity CRP (hsCRP), interleukin-6 (IL-6), matrix metalloproteinase-8 (MMP-8) and glycoprotein acetylation (GlycA) as well as three IGFBP-1 phosphoisoform concentrations were determined.

Results

In the metformin and insulin groups combined, hsCRP decreased (p = 0.01), whereas IL-6 (p = 0.002), GlycA (p < 0.0001) and all IGFBP-1 phosphoisoforms (p < 0.0001) increased from baseline to 36 gw. GlycA (p = 0.02) and non-phosphorylated IGFBP-1 (p = 0.008) increased more in patients treated with metformin than those treated with insulin. Inflammatory markers did not clearly associate with pregnancy outcomes but non-phosphorylated IGFBP-1 was inversely associated with gestational weight gain.

Conclusions

Metformin had beneficial effects on maternal serum IGFBP-1 concentrations compared to insulin, as increased IGFBP-1 related to lower total and late pregnancy maternal weight gain. GlycA increased more during metformin treatment compared to insulin. The significance of this observation needs to be more profoundly examined in further studies. There were no evident clinically relevant relations between inflammatory markers and pregnancy outcome measures.

Trial registration

The trial comparing metformin and insulin treatment was registered in ClinicalTrials.gov (NCT01240785) November 3, 2010. Retrospectively registered.

IUGR Is Associated With Marked Hyperphosphorylation of Decidual and Maternal Plasma IGFBP-1

CONTEXT

The mechanisms underpinning intrauterine growth restriction (IUGR), as a result of placental insufficiency, remain poorly understood, no specific treatment is available, and clinically useful biomarkers for early detection are lacking.

OBJECTIVE

We hypothesized that human IUGR is associated with inhibition of mechanistic target of rapamycin (mTOR) and activation of amino acid response (AAR) signaling, increased protein kinase casein kinase-2 (CK2) activity, and increased insulin-like growth factor-binding protein 1 (IGFBP-1) expression and phosphorylation in decidua and that maternal plasma IGFBP-1 hyperphosphorylation in the first trimester predicts later development of IUGR.

DESIGN, SETTING, AND PARTICIPANTS

Decidua [n = 16 appropriate-for-gestational age (AGA); n = 16 IUGR] and maternal plasma (n = 13 AGA; n = 13 IUGR) were collected at delivery from two different cohorts. In addition, maternal plasma was obtained in the late first trimester from a third cohort of women (n = 7) who later delivered an AGA or IUGR infant.

MAIN OUTCOME MEASURES

Total IGFBP-1 expression and phosphorylation (Ser101/Ser119/Ser169), mTOR, AAR, and CK2 activity in decidua and IGFBP-1 concentration and phosphorylation in maternal plasma.

RESULTS

We show that decidual IGFBP-1 expression and phosphorylation are increased, mTOR is markedly inhibited, and AAR and CK2 are activated in IUGR. Moreover, IGFBP-1 hyperphosphorylation in first-trimester maternal plasma is associated with the development of IUGR.

CONCLUSIONS

These data are consistent with the possibility that the decidua functions as a nutrient sensor linking limited oxygen and nutrient availability to increased IGFBP-1 phosphorylation, possibly mediated by mTOR and AAR signaling. IGFBP-1 hyperphosphorylation in first-trimester maternal plasma may serve as a predictive IUGR biomarker, allowing early intervention.

The application of post-translational modification oriented serum proteomics to assess experimental diabetes with complications

Proteome analysis of serum from type 2 diabetics with complications may lead to the discovery of diagnostic or prognostic biomarkers. To circumvent the principal barrier of serum proteomics, our investigation aimed to evaluate whether a study of post-translational modification enriched serum proteins could be valuable for the discovery of biomarkers or metabolic pathways related to type 2 diabetes pathogenesis. Type 2 diabetes was induced from high-fat diet fed Sprague Dawley rats with streptozotocin injection. Once diabetic status was confirmed, serum samples from either fasted healthy or diabetic rats were pooled and profiled by two-dimensional difference gel electrophoresis or comparative 2D electrophoresis after protein enrichments using immobilized metal ion, concanavalin A, and lentil affinity chromatography, respectively. Differential expressed proteins were identified and the associated networks were established by an Ingenuity Pathway Analysis. As a result, induced rats became severe diabetic and accompanied by hyperlipidemia, fatty liver, and glomerular hypertrophy. There were 3 total, 14 phosphorylated and 23 glycosylated protein targets differentially expressed. Proteins could be linked to HNF4A, HNF1A, and NF_κB transcriptional factors and antigen presentation, humoral immune response, and inflammatory response pathways. Predicted organ toxicity in kidney, heart, and liver matched with our histopathological results. In conclusion, post-translational modification based serum protein enrichment could be a valuable approach to enhance the resolution of serum proteomics without depleting potentially valuable abundant proteins. Our results also indicated the potential association of the hepatic secretome and hepatocyte nuclear factors in the pathogenesis of type 2 diabetes and its complications.

The role and regulation of IGFBP-1 phosphorylation in fetal growth restriction

Fetal growth restriction (FGR) increases the risk of perinatal complications and predisposes the infant to developing metabolic, cardiovascular, and neurological diseases in childhood and adulthood. The pathophysiology underlying FGR remains poorly understood and there is no specific treatment available. Biomarkers for early detection are also lacking. The insulin-like growth factor (IGF) system is an important regulator of fetal growth. IGF-I is the primary regulator of fetal growth, and fetal circulating levels of IGF-I are decreased in FGR. IGF-I activity is influenced by a family of IGF binding proteins (IGFBPs), which bind to IGF-I and decrease its bioavailability. During fetal development the predominant IGF-I binding protein in fetal circulation is IGFBP-1, which is primarily secreted by the fetal liver. IGFBP-1 binds IGF-I and thereby inhibits its bioactivity. Fetal circulating levels of IGF-I are decreased and concentrations of IGFBP-1 are increased in FGR. Phosphorylation of human IGFBP-1 at specific sites markedly increases its binding affinity for IGF-I, further limiting IGF-I bioactivity. Recent experimental evidence suggests that IGFBP-1 phosphorylation is markedly increased in the circulation of FGR fetuses suggesting an important role of IGFBP-1 phosphorylation in the regulation of fetal growth. Understanding of the significance of site-specific IGFBP-1 phosphorylation and how it is regulated to contribute to fetal growth will be an important step in designing strategies for preventing, managing, and/or treating FGR. Furthermore, IGFBP-1 hyperphosphorylation at unique sites may serve as a valuable biomarker for FGR.

Size at birth and insulin-like growth factor-I and its binding protein-1 among infants of diabetic mothers

OBJECTIVE

to estimate the association between intrauterine fetal growth, evaluated by anthropometric measurements, and biochemical growth factors; IGF-I and IGBP-1 among IDMs.

METHODS

Cross-sectional study carried out on 69 full term IDMs who was admitted to neonatal intensive care units, Ain Shams University Hospitals. Clinical examination including anthropometric measurements; birth weight, length, head circumference, mid-arm circumference, skinfold thickness at triceps and subscapular areas and placental weight. Laboratory investigations included maternal HbA(1c) and cord blood IGF-I and IGBP-1. They were classified into three groups: 20 small for gestational age (SGA), 25 appropriate for gestational age (AGA) and 24 large for gestational age (LGA).

RESULTS

Most of SGA neonates were born to mothers with type I diabetes, while most of AGA and LGA were born to mothers with gestational diabetes. According to maternal HbA(1c), SGA and LGA neonates were born to metabolically uncontrolled mothers while AGA neonates were born to well-controlled diabetic mothers. Anthropometric measurements had significant positive correlations with IGF-I and negative correlations with IGFBP-1.

CONCLUSIONS

Good control of diabetes during pregnancy is essential to improve fetal growth. There is an opposing effect of cord blood IGF-I and IGFBP-1 on anthropometric measurements.

Infants of diabetic mothers: echocardiographic measurements and cord blood IGF-I and IGFBP-1

BACKGROUND

Cardiac malformations in infants of diabetic mothers (IDMs) are five times higher than in normal pregnancies. Insulin-like growth factor-I (IGF-I) is the most important growth factor in utero and is predominantly bound by IGF binding protein-1 (IGFBP-1).

OBJECTIVE

To examine the echocardiographic findings of neonates of diabetic mothers and the relationship with cord blood IGF-I and IGBP-1.

SUBJECTS AND METHODS

This study was conducted on 69 neonates born to diabetic mothers who were admitted to the neonatal intensive care unit, Ain Shams University Hospitals between August 2007 and February 2008. They were classified into three groups: 20 small for gestational age, 25 appropriate for gestational age, and 24 large for gestational age. Neonates were subjected to thorough clinical examination and echocardiographic evaluation. Maternal hemoglobin A1c (HbA1c) and cord blood IGF-I and IGBP-1 were assessed.

RESULTS

Thirty neonates (43.5%) had hypertrophic cardiomyopathy (HCM); all of them were infants of suboptimally controlled diabetic mothers (HbA1c ≥ 7) with positive correlation between HbA1c and interventricular septal (IVS) thickness. Impaired left ventricular contractility was recorded in 52 IDMs (75.4%). The echocardiographic and laboratory measurements showed significant difference between the three studied groups. Cardiac morphological data were negatively correlated to IGFBP-1 and positively correlated to IGF-I and birth weight.

CONCLUSIONS

The opposing relationships between cord blood IGF-I and IGFBP-1 on the cardiac morphological measurements supporting their putative opposing roles in HCM seen in IDMs. Birth weight is the best predictor of hypertrophied IVS especially in infants born to suboptimally controlled diabetic mothers.

Fetal exposure to altered amniotic fluid glucose, insulin, and insulin-like growth factor-binding protein 1 occurs before screening for gestational diabetes mellitus

OBJECTIVE

We explored the possibility that perturbations in amniotic fluid glucose, insulin, and insulin-like growth factor-binding protein 1(IGFBP1) and/or metabolic acids exist before routine screening for GDM.

RESEARCH DESIGN AND METHODS

We selected consenting mother-infant pairs (n = 408) who met our inclusion criteria (singleton pregnancy, no genetic abnormalities, and no preexisting diabetes) and for whom sufficient amniotic fluid and appropriate medical information were available. We compared birth outcomes and second trimester amniotic fluid glucose, insulin, IGFBP1 concentrations, and amniotic fluid lactic, β-hydroxybutyric, and uric acids of mothers with gestational diabetes mellitus (GDM) (n = 52) with those of mothers with no diagnosis of GDM at >24 weeks (n = 356).

RESULTS

Higher amniotic fluid glucose, lactic acid, uric acid, and insulin and lower IGFBP1 concentrations were present by 15.1 ± 0.1 weeks in mothers in whom GDM was subsequently diagnosed. However, logistic regression showed that second trimester amniotic fluid glucose, but not insulin, IGFBP1, or metabolic acids was associated with an increased odds ratio (1.2 [95% CI 1.052-1.338]) for diagnosis of GDM at 24-28 weeks. In addition, probability contour maps that accounted for nonlinear relationships among the dynamically changing amniotic fluid constituents showed an increased risk for GDM with elevated second trimester amniotic fluid glucose in combination with either elevated amniotic fluid insulin or low amniotic fluid IGFBP1

CONCLUSIONS

Fetuses are exposed to increased amniotic fluid glucose before 15 weeks of gestation, suggesting that metabolic perturbations are underway before diagnosis and that earlier screening and intervention may be warranted.

Site-specific IGFBP-1 hyper-phosphorylation in fetal growth restriction: clinical and functional relevance

Phosphorylation enhances IGFBP-1 binding to IGF-I, thereby limiting the bioavailability of IGF-I that may be important in fetal growth. Our goal in this study was to determine whether changes in site-specific IGFBP-1 phosphorylation were unique to fetal growth restriction. To establish a link, we compared IGFBP-1 phosphorylation (sites and degree) in amniotic fluid from FGR (N = 10) and controls (N = 12). The concentration of serine phosphorylated IGFBP-1 showed a negative correlation with birth weight in FGR (P = 0.049). LC-MS/MS analysis revealed all four previously identified phosphorylation sites (Ser98, Ser101, Ser119, and Ser169) to be common to FGR and control groups. Relative phosphopeptide intensities (LC-MS) between FGR and controls demonstrated 4-fold higher intensity for Ser101 (P = 0.026), 7-fold for Ser98/Ser101 (P = 0.02), and 23-fold for Ser169 (P = 0.002) in the FGR group. Preliminary BIAcore data revealed 4-fold higher association and 1.7-fold lower dissociation constants for IGFBP-1/IGF-I in FGR. A structural model of IGFBP-1 bound to IGF-I indicates that all the phosphorylation sites are on relatively mobile regions of the IGFBP-1 sequence. Residues Ser98, Ser101, and Ser169 are close to structured regions that are involved in IGF-I binding and, therefore, could potentially make direct contact with IGF-I. On the other hand, residue Ser119 is in the middle of the unstructured linker that connects the N- and C-terminal domains of IGFBP-1. The model is consistent with the assumption that residues Ser98, Ser101, and Ser169 could directly interact with IGF-I, and therefore phosphorylation at these sites could change IGF-I interactions. We suggest that site-specific increase in IGFBP-1 phosphorylation limits IGF-I bioavailability, which directly contributes to the development of FGR. This study delineates the potential role of higher phosphorylation of IGFBP-1 in FGR and provides the basis to substantiate these findings with larger sample size.

Site specific phosphorylation of insulin-like growth factor binding protein-1 (IGFBP-1) for evaluating clinical relevancy in fetal growth restriction

Fetal growth restriction (FGR) is a leading cause of fetal and neonatal morbidity and mortality. Insulin-like growth factor binding protein-1 (IGFBP-1) is one of the major insulin-like growth factor (IGF) binding proteins involved in fetal growth and development. Our recent data shows that phosphorylation of IGFBP-1 carries both functional and biological relevance in FGR. Considering that IGFBP-1 phosphorylation can be valuable in diagnostics, we examined strategies to enrich IGFBP-1 so that its phosphorylation sites could be assessed by mass spectrometry (MS). Using <1 mL of human amniotic fluid, widely employed immunoprecipitation with IGFBP-1 monoclonal antibody (Mab 6303) coenriched IgGs that interfered with MS. Covalent coupling of Mab 6303 with Seize immunoprecipitation resin (Pierce) mitigated this drawback. However, LC-MS/MS analysis with the titanium dioxide (TiO(2)) enriched IGFBP-1 phosphopeptides in the immunoprecipitated samples revealed pSer101 and pSer119, but not pSer169 nor pSer98 of the previously identified phosphorylation sites. The alternative, ZOOM isoelectric focusing (IEF) (Invitrogen) rendered low-IGFBP-1 recovery with overlapping albumin. Subsequently, depletion of albumin using Affi-GelBlue gel (Bio-Rad) maximized IGFBP-1 yield. ELISA estimation showed approximately 8.5% residual albumin (3.73 x 10(5) +/- 2.35 x 10(5) ng/mL), whereas up to approximately 68% IGFBP-1 was recovered (1.36 x 10(3) +/- 0.174 x 10(3) microg/L, IEMA). LC-MS/MS analysis with the albumin depleted samples detected all four expected phosphorylation sites. Additionally, LC-MS analysis semiquantitatively indicated much reduced phosphopeptide peak intensities, approximately 20-fold with pSer169 and approximately 10-fold lower with pSer98 sites as compared to pSer101. With the use of our depletion strategy, this study offers a novel simple proteomic approach to enrich IGFBP-1 for identification of site-specific changes in IGFBP-1 phosphorylation. This strategy will be vital in performing differential IGFBP-1 phosphorylation profiling clinically, to help establish its link with FGR and develop diagnostic assays, as well as elucidating novel mechanisms potentially involved in regulation of fetal growth.

Identification of the amniotic fluid insulin-like growth factor binding protein-1 phosphorylation sites and propensity to proteolysis of the isoforms

Insulin-like growth factor binding protein-1 (IGFBP-1) is the major secreted protein of human decidual cells during gestation and, as a modulator of insulin-like growth factors or by independent mechanisms, regulates embryonic implantation and growth. The protein is phosphorylated and this post-translational modification is regulated in pregnancy and represents an important determinant of its biological activity. We have isolated, from human normal amniotic fluid collected in the weeks 16-18, the intact nonphosphorylated IGFBP-1 and five electrophoretically distinct phosphoisoforms and have determined their in vivo phosphorylation state. The unmodified protein was the most abundant component and mono-, bi-, tri- and tetraphosphorylated forms were present in decreasing amounts. The phosphorylation sites of IGFBP-1 were identified by liquid chromatography-tandem mass spectrometry analysis of the peptides generated with trypsin, chymotrypsin and Staphylococcus aureus V8 protease. Five serines were found to be phosphorylated and, of these, four are localized in the central, weakly conserved, region, at positions 95, 98, 101 and 119, whereas one, Ser169, is in the C-terminal domain. The post-translational modification predominantly involves the hydrophilic stretch of amino acids representing a potential PEST sequence (proline, glutamic acid, serine, threonine) and our results show that the phosphorylation state influences the propensity of IGFBP-1 to proteolysis.

Separation of the molecular forms of the insulin-like growth factor (IGF)-Binding proteins by affinity chromatography

Association of IGFBP-1, IGFBP-2 and IGFBP-3 with other proteins in human serum and placental cell membranes was investigated using affinity chromatography matrix with immobilized antibodies. Circulating IGFBP-1 was found to be predominantly bound to alpha(2)-macroglobulin and not in the binary complex with its ligand, IGFBP-2 complexes and/or polymers were detected, which was not acknowledged before, and IGFBP-3 molecular forms were differentiated into those that form binary/ternary complexes and those that form stable associations with other serum proteins. As for placental membranes, both IGFBP-1 dimers and high molecular mass IGFBP-1 associations, most probably with alpha(2)-macroglobulin, were recognized and resolved.

Functional and complementary phosphorylation state attributes of human insulin-like growth factor-binding protein-1 (IGFBP-1) isoforms resolved by free flow electrophoresis

Fetal growth restriction (FGR) is a common disorder in which a fetus is unable to achieve its genetically determined potential size. High concentrations of insulin-like growth factor-binding protein-1 (IGFBP-1) have been associated with FGR. Phosphorylation of IGFBP-1 is a mechanism by which insulin-like growth factor-I (IGF-I) bioavailability can be modulated in FGR. In this study a novel strategy was designed to determine a link between IGF-I affinity and the concomitant phosphorylation state characteristics of IGFBP-1 phosphoisoforms. Using free flow electrophoresis (FFE), multiple IGFBP-1 phosphoisoforms in amniotic fluid were resolved within pH 4.43-5.09. The binding of IGFBP-1 for IGF-I in each FFE fraction was determined with BIAcore biosensor analysis. The IGF-I affinity (K(D)) for different IGFBP-1 isoforms ranged between 1.12e-08 and 4.59e-07. LC-MS/MS characterization revealed four phosphorylation sites, Ser(P)(98), Ser(P)(101), Ser(P)(119), and Ser(P)(169), of which Ser(P)(98) was new. Although the IGF-I binding affinity for IGFBP-1 phosphoisoforms across the FFE fractions did not correlate with phosphopeptide intensities for Ser(P)(101), Ser(P)(98), and Ser(P)(169) sites, a clear association was recorded with Ser(P)(119). Our data demonstrate that phosphorylation at Ser(119) plays a significant role in modulating affinity of IGFBP-1 for IGF-I. In addition, an altered profile of IGFBP-1 phosphoisoforms was revealed between FGR and healthy pregnancies that may result from potential site-specific phosphorylation. This study provides a strong basis for use of this novel approach in establishing the linkage between phosphorylation of IGFBP-1 and FGR. This overall strategy will also be broadly applicable to other phosphoproteins with clinical and functional significance.

Hypoxia and leucine deprivation induce human insulin-like growth factor binding protein-1 hyperphosphorylation and increase its biological activity

Fetal growth restriction is often caused by uteroplacental insufficiency that leads to fetal hypoxia and nutrient deprivation. Elevated IGF binding protein (IGFBP)-1 expression associated with fetal growth restriction has been documented. In this study we tested the hypothesis that hypoxia and nutrient deprivation induce IGFBP-1 phosphorylation and increase its biological potency in inhibiting IGF actions. HepG2 cells were subjected to hypoxia and leucine deprivation to mimic the deprivation of metabolic substrates. The total IGFBP-1 levels measured by ELISA were approximately 2- to 2.5-fold higher in hypoxia and leucine deprivation-treated cells compared with the controls. Two-dimensional immunoblotting showed that whereas the nonphosphorylated isoform is the predominant IGFBP-1 in the controls, the highly phosphorylated isoforms were dominant in hypoxia and leucine deprivation-treated cells. Liquid chromatography-tandem mass spectrometry analysis revealed four serine phosphorylation sites: three known sites (pSer 101, pSer 119, and pSer 169); and a novel site (pSer 98). Liquid chromatography-mass spectrometry was used to estimate the changes of phosphorylation upon treatment. Biacore analysis indicated that the highly phosphorylated IGFBP-1 isoforms found in hypoxia and leucine deprivation-treated cells had greater affinity for IGF-I [dissociation constant 5.83E (times 10 to the power)--0 m and 6.40E-09 m] relative to the IGFBP-1 from the controls (dissociation constant approximately 1.54E-07 m). Furthermore, the highly phosphorylated IGFBP-1 had a stronger effect in inhibiting IGF-I-stimulated cell proliferation. These findings suggest that IGFBP-1 phosphorylation may be a novel mechanism of fetal adaptive response to hypoxia and nutrient restriction.

Inverse changes in fetal insulin-like growth factor (IGF)-1 and IGF binding protein-1 in association with higher birth weight in maternal diabetes

OBJECTIVE

The insulin like growth factor (IGF) system plays a key role in regulating fetal growth, is metabolically regulated, and may influence development of increased birth weight in offspring of mothers with diabetes. We examined IGF-1 and IGF binding protein-1 (IGFBP-1) concentrations in cord blood samples from offspring of mothers with gestational and type 2 diabetes.

DESIGN AND PATIENTS

Case-control study of Maori and Pacific Island mothers recruited prospectively at Middlemore Hospital, South Auckland, New Zealand.

MEASUREMENTS

Cord blood (for insulin, IGF-1 and IGFBP-1) was taken from umbilical vein at birth from singleton babies born after 32 weeks of gestation from138 mothers with gestational diabetes (GDM), 39 mothers with type 2 diabetes (T2DM) and 95 control mothers.

RESULTS

Babies born to mothers with both GDM and T2DM had significantly increased birth weight (Z-score birth weight mean +/- SD: GDM 0.94 +/- 1.31, T2DM 0.53 +/- 1.1) compared to controls (Z-score birth weight -0.08 +/- 1.10). IGFBP-1 was significantly reduced in both diabetic groups (median interquartile range: GDM 67(31-137) ng/ml, T2DM 59(29-105) ng/ml, control 114(56-249) ng/ml). Cord IGF-1 was significantly increased in cord blood of infants of mothers with GDM (42.2 +/- 16.3 ng/ml vs. control 34.7 +/- 18.5 ng/ml) but not T2DM (38.7 +/- 17.4 ng/ml). In all offspring, IGF-1 and IGFBP-1 were positively and negatively correlated with birth weight, respectively.

CONCLUSIONS

Maternal diabetes results in inverse changes of circulating fetal IGF-1 and IGFBP-1 at birth. A decrease in circulating IGFBP-1 and to a lesser extent an increase in circulating IGF-1 may present an important mechanism that contributes to increased birth weight in diabetic pregnancies.

Immunoassay of serine-phosphorylated isoform of insulin-like growth factor (IGF) binding protein (IGFBP)-1

OBJECTIVES

Development of an ELISA for phosphorylated isoform of IGFBP-1. Serine phosphorylation is an important regulator of IGFBP-1 bioactivity, but specific immunoassays for its measurement are currently lacking.

DESIGN AND METHODS

Assay design was based on a novel approach of first capturing the phosphorylated and non-phosphorylated IGFBP-1 by an anti-IGFBP-1 antibody and then selectively detecting the phosphorylated form by an anti-phosphoserine antibody. Method development involved pair-wise evaluation of the candidate antibodies and determinations of analytical performance and specificity. Specificity was monitored by reactivity with dephosphorylated IGFBP-1, with antibodies against other phosphorylated residues that are not expressed, and by comparative analysis of sample containing different IGFBP-1 phosphorylation profile.

RESULTS

Analytical evaluation demonstrated acceptable performance; detection limit 0.3 microg/L, dynamic range 1.56-100 microg/L; intra- and inter-assay CVs 2.1-8.6%; mean recovery (+/-SD) 97.8+/-9.2%, and mean recovery of sample dilution 93.4+/-6.0%. The phosphorylated and total IGFBP-1 medians in non-pregnant adult serum, which mostly contain the highly phosphorylated isoform, were 11.9 and 18.6 microg/L, respectively, and the sample values were tightly correlated (r=0.99). As expected, the corresponding medians in 1st trimester (17.4 and 63.0 microg/L) and 2nd trimester (30.9 and 75.8) samples with altered IGFBP-1 phosphorylation were significantly different (p<0.001). Similarly, a fraction (1.29%) of total IGFBP-1 (13.3 mg/L) in amniotic fluids was found to be phosphorylated (0.172 mg/L). There was no reactivity with dephosphorylated IGFBP-1.

CONCLUSIONS

The present ELISA is highly specific for the phosphorylated isoform of IGFBP-1 and its availability should help expedite further investigations of IGFBP-1 phosphorylation.