Altered placental insulin and insulin-like growth factor-I receptors in diabetes

Human placental GLUT1 glucose transporter expression and the fetal insulin-like growth factor axis in pregnancies complicated by diabetes

We have previously described regulation of syncytial GLUT1 glucose transporters by IGF-I. Despite this, it is not clear what signal regulates transplacental glucose transport. In this report we asked whether changes in GLUT1 expression and glucose transport activity in diabetic pregnancies were associated with alterations in the fetal IGF axis. Cord blood samples and paired syncytial microvillous and basal membranes were isolated from normal term pregnancies and pregnancies characterized by gestational diabetes type A2 (GDM A2) and pre-existing insulin-dependent diabetes mellitus (IDDM). Circulating IGF-I, basal membrane GLUT1 expression and glucose transporter activity were correlated with birth weight, but only in control, not diabetic groups. Basal membrane GLUT1 and transporter activity were correlated with IGF-I concentrations in control, but not diabetic groups. IGF binding protein (IGFBP) binding capacity showed a ≥50% reduction in the diabetic groups compared to control; both showed a higher level of free IGF-I. The absence of a correlation between birth weight and factors such as fetal IGF-I or GLUT1 expression in the diabetic groups suggests that IGF-I-stimulated effects may have reached a limiting threshold, such that further increases in IGF-I (or GLUT1) are without effect. These data support that fetal IGF-I acts as a fetal nutritional signal, modulating placental GLUT1 expression and birth weight via altered levels of fetal circulating IGFBPs. Diabetes appears to exert its effects on fetal and placental factors prior to the third trimester and, despite good glycemic control immediately prior to, and in the third trimester, these effects persist to term.

Human placenta-derived mesenchymal stem cells and islet-like cell clusters generated from these cells as a novel source for stem cell therapy in diabetes

Placental tissue holds great promise as a source of cells for regenerative medicine due to its plasticity, and easy availability. Human placenta-derived mesenchymal stem cells (hPDMSCs) have the potential to differentiate into insulin-producing cells. Upon transplantation, they can reverse experimental diabetes in mice. However, it is not known whether culture-expanded undifferentiated hPDMSCs are capable of restoring normoglycemia upon transplantation in streptozotocin (STZ)-induced diabetic mice. Hence we prepared long-term cultures of hPDMSCs from the chorionic villi of full-term human placenta. Flow cytometry analyses and immunocytochemistry study revealed bonafide mesenchymal nature of the isolated hPDMSCs. These cultures could differentiate into adipogenic, oesteogenic, chondrogenic, and neuronal lineages on exposure to lineage-specific cocktails. Furthermore, we showed that hPDMSCs can form islet-like cell clusters (ILCs) on stepwise exposure to serum-free defined media containing specific growth factors and differentiating agents. qRT-PCR showed the expression of insulin, glucagon, and somatostatin in undifferentiated hPDMSCs and in ILCs. Differentiated ILCs were found to express human insulin, glucagon, and somatostatin by immunocytochemistry. Additionally, ILCs also showed abundance of pancreatic transcription factors ngn3 and isl1. Both undifferentiated hPDMSCs and ILCs exihibited insulin secretion in response to glucose. Transplantation of hPDMSCs or ILCs derived from hPDMSCs in STZ-induced diabetic mice led to restoration of normoglycemia. Our results demonstrate, for the first time, reversal of hyperglycemia by undifferentiated hPDMSCs and ILCs derived from hPDMSCs. These results suggest human placenta-derived MSCs as an alternative source for cell replacement therapy in diabetes.

Growth factor concentrations and their placental mRNA expression are modulated in gestational diabetes mellitus: possible interactions with macrosomia

Background

Gestational diabetes mellitus (GDM) is a form of diabetes that occurs during pregnancy. GDM is a well known risk factor for foetal overgrowth, termed macrosomia which is influenced by maternal hypergycemia and endocrine status through placental circulation. The study was undertaken to investigate the implication of growth factors and their receptors in GDM and macrosomia, and to discuss the role of the materno-foeto-placental axis in the in-utero regulation of foetal growth.

Methods

30 women with GDM and their 30 macrosomic babies (4.75 ± 0.15 kg), and 30 healthy age-matched pregnant women and their 30 newborns (3.50 ± 0.10 kg) were recruited in the present study. Serum concentrations of GH and growth factors, i.e., IGF-I, IGF-BP3, FGF-2, EGF and PDGF-B were determined by ELISA. The expression of mRNA encoding for GH, IGF-I, IGF-BP3, FGF-2, PDGF-B and EGF, and their receptors, i.e., GHR, IGF-IR, FGF-2R, EGFR and PDGFR-β were quantified by using RT-qPCR.

Results

The serum concentrations of IGF-I, IGF-BP3, EGF, FGF-2 and PDGF-B were higher in GDM women and their macrosomic babies as compared to their respective controls. The placental mRNA expression of the growth factors was either upregulated (FGF-2 or PDGF-B) or remained unaltered (IGF-I and EGF) in the placenta of GDM women. The mRNA expression of three growth factor receptors, i.e., IGF-IR, EGFR and PDGFR-β, was upregulated in the placenta of GDM women. Interestingly, serum concentrations of GH were downregulated in the GDM women and their macrosomic offspring. Besides, the expression of mRNAs encoding for GHR was higher, but that encoding for GH was lower, in the placenta of GDM women than control women.

Conclusions

Our results demonstrate that growth factors might be implicated in GDM and, in part, in the pathology of macrosomia via materno-foeto-placental axis.

Enhancement and inhibition of mitogenic action of insulin-like growth factor I by high glucose in cultured bovine retinal pericytes

To explore the possible relationship between insulin-like growth factor I(IGF-I) and diabetic retinopathy, we examined the effects of glucose on IGF-I stimulated thymidine incorporation into DNA and IGF-I binding in cultured bovine retinal pericytes. IGF-I significantly increased thymidine incorporation, and its effect was completely inhibited by IGF-I receptor antibody. The exposure to high glucose for 8 h significantly enhanced the IGF-I induced increase in thymidine incorporation as compared with those to normal glucose and to high osmolarity. In contrast, the incubation with high glucose for 24 h decreased thymidine incorporation in response to IGF-I. Specific binding of IGF-I to pericytes was increased by the incubation with high glucose for both 8 and 24 h. These results suggest that glucose may play an important role in the regulation of mitogenic action of IGF-I in retinal pericytes.

Insulin-like growth factor-1 stimulates amino acid uptake by the cultured human placental trophoblast

Amino acid uptake by the human placenta is known to occur via several transport mechanisms. However, regulation by extracellular factors has received relatively little attention. A recent report by this laboratory characterized the uptake of alpha-aminoisobutyric acid (AIB) stimulated by insulin in the cultured human placental trophoblast. The current study evaluated the effect of insulin-like growth factor-1 (IGF-1) on AIB uptake in cultured human placental trophoblasts. Na(+)-dependent AIB uptake was significantly stimulated by IGF-I in a time-dependent manner, as early as 30 min after hormone exposure. The maximum effect was at 2-4 hr of continuous exposure to IGF-I and the stimulation was dependent upon IGF-1 concentration approaching maximal stimulation at 50 ng.ml-1. AIB uptake was inhibited by increasing concentrations of alpha-(methylamino)isobutyric acid (MeAIB). Approximately 75% of basal (unstimulated) Na(+)-dependent AIB uptake was inhibited by MeAIB. The IGF-1-stimulated increment above basal AIB uptake was completely inhibited by MeAIB. IGF-1 increased the maximum uptake velocity but not Km. Using equimolar concentrations, stimulation was greater with IGF-1 than with IGF-2. Stimulation by IGF-1, but not insulin, was inhibited by anti-IGF-1 receptor antibody, indicating mediation via the IGF-1 receptor. H7, a nonspecific inhibitor of serine-threonine kinase, inhibited IGF-1-dependent stimulation of AIB uptake. In addition, calphostin C (a specific inhibitor of protein kinase C), but not H89 (a specific inhibitor of protein kinase A), inhibited the IGF-1 action. This study further characterizes regulated amino acid uptake by the human placental trophoblasts and demonstrates that the Na(+)-dependent component of AIB uptake is stimulated by physiologic concentrations of IGF-1.

Vanadate enhances insulin-receptor binding in gestational diabetic human placenta

Although vanadium is found abundantly in animal and plant kingdoms its biological effects are not clear. Vanadate compounds have been shown to normalize blood glucose levels in streptozotocin treated rats, enhance glucose oxidation and improve the sensitivity to insulin by enhanced receptor binding in rat adipocytes. The aim of the present study was to investigate the effect of vanadate, at high (0-8 mmol l-1) and low (0-1.0 mmol l-1) physiological concentrations, on [125I]-insulin binding in the placenta of three groups of patients, namely from normal (N) controls, gestational diabetics (GDM) and women with risk factors in their medical history for developing diabetes mellitus (RF). Vanadate at low concentrations (0.2-0.6 mmol l-1) enhanced the maximal binding 2-fold in GDM placenta but only increased (up to 1.2-fold) the binding slightly at high concentrations (5 mmol l-1). However with placenta from normal or women at risk, vanadate increased the [125I]-insulin binding up to 1.2-fold both at low and high concentrations. Thus it appears that vanadate augments insulin binding in the placenta from women with gestational diabetes mellitus.

Insulin receptor binding to erythrocytes in the first half of pregnancy is increased in healthy pregnant women as compared with non-pregnant or gestational diabetic women

Insulin binding to erythrocytes was measured longitudinally by a competitive radioreceptor assay in 21 healthy pregnant (HP) and 20 well-controlled gestational diabetic women (GD) in 4-week intervals throughout pregnancy and at day 4 post-partum. Maximum insulin binding (maxbdg) at weeks 8-14 was increased (P < 0.001) in HP (median: 6.0%) but not in GD (median: 2.7%) as compared with non-pregnant control subjects (C) (median: 3.6%; previously reported: Clin. Chim. Acta 1992;207:57-71) due to an increased number of high-affinity insulin receptors. Throughout gestation the binding decreased continuously, to reach at term the levels found in C. In GD maxbdg remained close to the level of C throughout pregnancy. Binding differences between HP and GD were independent of the body mass index. Maxbdg did not differ between diet- and insulin-treated patients. It was higher in women whose offspring had low umbilical cord insulin levels (< 10 mu units/ml). The findings suggest that (a) higher insulin binding in HP could contribute to the improved glucose tolerance in early pregnancy and (b) the lack of increase in insulin binding during early pregnancy in gestational diabetes might be one factor leading to the manifestation of the disease in late pregnancy. However, it must be kept in mind that insulin receptors on erythrocytes do not necessarily resemble those on the major target tissues of insulin.

Features of insulin receptor interaction in placenta from normal, overt and poorly controlled gestational diabetic patients

Features of insulin binding to trophoblast plasma membranes were studied in six normal pregnant women (NP), six overt diabetes (ODP) and six poorly controlled glycemic gestational patients (PCDP) i.e. women who did not strictly follow the management of diabetes mellitus during pregnancy. A decreased maximum specific insulin receptor binding per 0.1 mg membrane protein in placenta from PCDP (12%) was found comparing with that from ODP or NP (17.5% and 36.2%, respectively, P < 0.01), The insulin binding in PCDP declined at a faster rate until it reached minimum when studied at a higher temperature (25-37 degrees C). The binding equilibrium was likewise attained faster at this temperature than that at lower temperature of 4 degrees C for all studied groups. The insulin receptor binding in all studied groups was pH dependent. The maximum binding in ODP and PCDP groups was attained at pH 7.8 while for NP maximum binding was at pH 7.4. The competitive binding assay was carried out with 14 concentrations of unlabelled insulin and the half maximal displacement of 125I-insulin was at 8 x 10(-9) M, 6 x 10(-9) M and 4 x 10(-9) M for NP, ODP and PCDP, respectively (P < 0.05) suggesting the differences in the effect of glycemic control on the insulin binding. Furthermore the binding yielded curvilinear Scatchard plots with the apparent affinity of the receptors being affected in the ODP and PCDP groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional alterations of type I insulin-like growth factor receptor in placenta of diabetic rats

The presence of type I insulin-like growth factor (IGF-I) receptors on placental membranes led to the hypothesis that these receptors might play a critical role in the rapid growth of this organ. Diabetes induces feto-placental overgrowth, but it is not known whether it modifies IGF-I receptor activity in fetal and/or placental tissues. To answer this question, we have partially purified and characterized placental receptors from normal and streptozotocin-induced diabetic rats. In normal rats, binding of 125I-IGF-I to a 140 kDa protein corresponding to the alpha subunit of the receptor was observed in cross-linking experiments performed under reducing conditions. Stimulation by IGF-I induces the autophosphorylation of a 105 kDa phosphoprotein representing the beta subunit of the receptor. In rats made hyperglycaemic and insulinopenic by streptozotocin injection on day 1 of pregnancy, placental IGF-I receptor-binding parameters were not different from controls on day 20 of pregnancy. In contrast, the autophosphorylation and kinase activity of IGF-I receptors of diabetic rats were increased 2-3-fold in the basal state and after IGF-I stimulation. The present study indicates that the rat placental IGF-I receptor possesses structural characteristics similar to that reported for fetal-rat muscle, and suggests that the high-molecular-mass beta subunit could represent a type of receptor specifically expressed during prenatal development. In addition, it clearly demonstrates that diabetes induces functional alterations in IGF-I receptor kinase activity that may play a major role in the placental overgrowth in diabetic pregnancy.

Insulin binding to trophoblast plasma membranes and placental glycogen content in well-controlled gestational diabetic women treated with diet or insulin, in well-controlled overt diabetic patients and in healthy control subjects

Insulin binding to trophoblast plasma membranes and the placental glycogen content were measured in twelve healthy women, in eleven well-controlled gestational diabetic women who were treated either with diet alone (n = 4) or with insulin (n = 7) and in 18 women with well-controlled overt diabetes mellitus (six White B; four White C; eight White D). The competitive binding assay was carried out with 22 concentrations of unlabelled insulin. Binding data were analysed by a non-linear direct model fitting procedure assuming one non-cooperative binding site. Maximum specific binding was unchanged in the total collective of gestational diabetic women, but was decreased by 30% in those treated with diet (6.2 +/- 2.2%) and increased by 90% in insulin-treated women (16.4 +/- 10.2%) as compared to the control subjects (8.7 +/- 2.5%). The diet-treated women had only 40% as many and those treated with insulin had more than twice as many receptors compared to control subjects on a per mg protein basis and if expressed per total placenta. In patients with overt diabetes mellitus maximum specific binding (18.5 +/- 10.6%) was higher (p less than 0.05) due to more receptors compared to control subjects but was similar to the insulin-treated gestational diabetic patients. Maximum specific binding and receptor concentrations did not correlate linearly with maternal plasma insulin levels. Receptor affinities were virtually similar in all groups (1.8 x 10(9) l/mol). The placental glycogen content was reduced (p less than 0.05) to about 80% of that of control subjects in the diet-treated collective, whereas it was unchanged compared to control subjects in the insulin-treated gestational diabetic women despite a 40% increase (p less than 0.001) of the maternal-to-cord serum glucose ratio. In overt diabetic patients the maternal-to-cord serum glucose ratio and the placental glycogen content were higher (p less than 0.05) than in the control subjects. We conclude that trophoblast plasma membranes from gestational diabetic women treated with diet alone express less and those from women treated with insulin express more insulin receptors than those from a healthy control group in vitro. These differences could not have been disclosed without consideration of the mode of treatment. Trophoblast plasma membranes from overt diabetic women have more insulin receptors than those from healthy control subjects.

Increased autophosphorylation of insulin-like growth factor-I and insulin receptors in placentas of diabetic women

Autophosphorylation of insulin and insulin-like growth factor (IGF)-I receptors were measured in lectin purified receptor preparations from placentas of normal and diabetic patients. The basal and insulin or IGF-I stimulated phosphorylation of the approximately 94 kD protein, corresponding to beta-subunit of the insulin and IGF-I receptors, were approximately 2 times greater (p less than 0.05) in placentas from diabetic patients with poor glycemic control (as judged by their serum HbA1c level) compared to the normals. The magnitude of IGF-I or insulin stimulation of the phosphorylation of the 94 kD protein was comparable in placentas from both diabetic and normal patients. Immunoprecipitation and immunodepletion of IGF-I receptor by alpha-IR3, a monoclonal antibody to IGF-I receptor, revealed the increased basal phosphorylation of the approximately 94 kD protein in placentas of diabetic patients to be associated with IGF-I and insulin receptors. The magnitude of IGF-I and insulin stimulated phosphorylation of the immunoprecipitated and immunodepleted IGF-I receptor, respectively, was the same in both normal and diabetic patients. These results suggested that the increased basal phosphorylation of the 94 kD protein in placentas from diabetic patients may be intrinsic to IGF-I and insulin receptor, however, the regulatory mechanisms effecting the increase may not be dependent on IGF-I or insulin.