Type 2 diabetes TCF7L2 risk genotypes alter birth weight: a study of 24,053 individuals

The role of genes in normal birth-weight variation is poorly understood, and it has been suggested that the genetic component of fetal growth is small. Type 2 diabetes genes may influence birth weight through maternal genotype, by increasing maternal glycemia in pregnancy, or through fetal genotype, by altering fetal insulin secretion. We aimed to assess the role of the recently described type 2 diabetes gene TCF7L2 in birth weight. We genotyped the polymorphism rs7903146 in 15,709 individuals whose birth weight was available from six studies and in 8,344 mothers from three studies. Each fetal copy of the predisposing allele was associated with an 18-g (95% confidence interval [CI] 7-29 g) increase in birth weight (P=.001) and each maternal copy with a 30-g (95% CI 15-45 g) increase in offspring birth weight (P=2.8x10-5). Stratification by fetal genotype suggested that the association was driven by maternal genotype (31-g [95% CI 9-48 g] increase per allele; corrected P=.003). Analysis of diabetes-related traits in 10,314 nondiabetic individuals suggested the most likely mechanism is that the risk allele reduces maternal insulin secretion (disposition index reduced by ~0.15 standard deviation; P=1x10-4), which results in increased maternal glycemia in pregnancy and hence increased offspring birth weight. We combined information with the other common variant known to alter fetal growth, the -30G-->A polymorphism of glucokinase (rs1799884). The 4% of offspring born to mothers carrying three or four risk alleles were 119 g (95% CI 62-172 g) heavier than were the 32% born to mothers with none (for overall trend, P=2x10-7), comparable to the impact of maternal smoking during pregnancy. In conclusion, we have identified the first type 2 diabetes-susceptibility allele to be reproducibly associated with birth weight. Common gene variants can substantially influence normal birth-weight variation.     

Biochemical Characterization of Individual Human Glycosylated pro-Insulin-like Growth Factor (IGF)-II and big-IGF-II Isoforms Associated with Cancer

Insulin-like growth factor II (IGF-II) is a major embryonic growth factor belonging to the insulin-like growth factor family, which includes insulin and IGF-I. Its expression in humans is tightly controlled by maternal imprinting, a genetic restraint that is lost in many cancers, resulting in up-regulation of both mature IGF-II mRNA and protein expression. Additionally, increased expression of several longer isoforms of IGF-II, termed “pro” and “big” IGF-II, has been observed. To date, it is ambiguous as to what role these IGF-II isoforms have in initiating and sustaining tumorigenesis and whether they are bioavailable. We have expressed each individual IGF-II isoform in their proper O-glycosylated format and established that all bind to the IGF-I receptor and both insulin receptors A and B, resulting in their activation and subsequent stimulation of fibroblast proliferation. We also confirmed that all isoforms are able to be sequestered into binary complexes with several IGF-binding proteins (IGFBP-2, IGFBP-3, and IGFBP-5). In contrast to this, ternary complex formation with IGFBP-3 or IGFBP-5 and the auxillary protein, acid labile subunit, was severely diminished. Furthermore, big-IGF-II isoforms bound much more weakly to purified ectodomain of the natural IGF-II scavenging receptor, IGF-IIR. IGF-II isoforms thus possess unique biological properties that may enable them to escape normal sequestration avenues and remain bioavailable in vivo to sustain oncogenic signaling.     

Repeated betamethasone treatment of pregnant sheep programs persistent reductions in circulating IGF-I and IGF-binding proteins in progeny

Exposure to synthetic glucocorticoids in utero markedly improves survival after preterm birth, but repeated exposures impair fetal and postnatal growth and are associated with evidence of insulin resistance in later life. The insulin-like growth factor (IGF) axis is an important regulator of growth and metabolism before and after birth. We have therefore investigated the effects of repeated maternal betamethasone injections on plasma IGF-I, IGF-II, and IGF-binding proteins (IGFBP) in fetal and postnatal progeny in the sheep. Pregnant sheep carrying male fetuses were injected with saline or betamethasone at 104, 111, and 118 days of gestation (dG, term approximately 150 dG). Plasma samples were collected postmortem from fetuses before (75, 84, 101 dG) or after one (109 dG), two (116 dG), or three (121-122, 132-133, 145-147 dG) doses of saline or betamethasone and from progeny at 42 and 84 days of age. Fetal weight was reduced after two or more maternal betamethasone injections, and this effect persisted to term. Repeated betamethasone exposures reduced plasma IGF-I and total IGFBP in fetuses at 133 dG and progeny at 84 days, and reduced plasma IGFBP-3 at 84 days. Fetal plasma IGF-II tended to increase transiently at 109 dG following the first betamethasone injection. Fetal, placental, and/or postnatal weights correlated positively with concomitant plasma IGF-I, IGF-II, and total IGFBP. We conclude that repeated exposure to synthetic glucocorticoids in utero programs the IGF axis before and after birth, which may contribute to the adverse effects of betamethasone exposure on growth and metabolism.     

Receptors for insulin-like growth factors and insulin on murine fetal cortical brain cells

Fetal murine neuronal cells bear somatomedin receptors which can be classified according to their affinities for IGF-I, IGF-II and insulin. Binding of 125I-IGF-I is half-maximally displaced by 7 ng/ml IGF-I while 15- and 700-fold higher concentrations are required for, respectively, IGF-II and insulin. Linear Scatchard plots of competitive-binding data with IGF-I suggest one single class of type I IGF receptors (Ka = 2.6 X 10(9) M-1; Ro = 4500 sites per cell). The occurrence of IGF-II receptors appears from the specific binding of 125I-IGF-II and competition by unlabeled IGF-II; the IGF-II binding sites display a low affinity for IGF-II and no affinity for insulin. IGF-II also interacts with insulin receptors although 50- to 100-fold less potent than insulin in competing for 125I-insulin binding. The presence of distinct receptors for IGF-I, IGF-II and insulin on fetal neuronal cells is consistent with a role of these peptides in neuronal development, although our data also indicate that IGF-I receptors could mediate the growth promoting effects of insulin.     

Hybrid receptors formed by insulin receptor (IR) and insulin-like growth factor I receptor (IGF-IR) have low insulin and high IGF-1 affinity irrespective of the IR splice variant

Insulin receptor (IR) and insulin-like growth factor I receptor (IGF-IR) are both from the same subgroup of receptor tyrosine kinases that exist as covalently bound receptor dimers at the cell surface. For both IR and IGF-IR, the most described forms are homodimer receptors. However, hybrid receptors consisting of one-half IR and one-half IGF-IR are also present at the cell surface. Two splice variants of IR are expressed that enable formation of two isoforms of the IGF-IR/IR hybrid receptor. In this study, these two splice variants of hybrid receptors were studied with respect to binding affinities of insulin, insulin-like growth factor I (IGF-I), and insulin-like growth factor II (IGF-II). Unlike previously published data, in which semipurified receptors have been studied, we found that the two hybrid receptor splice variants had similar binding characteristics with respect to insulin, IGF-I, and IGF-II binding. We studied both semipurified and purified hybrid receptors. In all cases we found that IGF-I had at least 50-fold higher affinity than insulin, irrespective of the splice variant. The binding characteristics of insulin and IGF-I to both splice variants of the hybrid receptors were similar to classical homodimer IGF-IR.     

Mitogenic activity of glia maturation factor: Interaction with insulin and insulin-like growth factor-II

The mitogenic activity of glia maturation factor (GMF) was tested on sparse-cultured cells. GMF stimulates the growth rate of normal astroblasts and fibroblasts grown in the presence of fetal calf serum (FCS), and raises the saturation density of the cells over what is imposed by the corresponding serum concentrations. GMF has no mitogenic effect in the complete absence of serum. The mitogenicity of GMF is also demonstrable in defined media where certain serum components are present. In particular, GMF in combination with the defined medium N2 partially mimics the proliferative effect of serum alone. Insulin, an ingredient of N2, can substitute for the complete N2 formula. Insulin-like growth factor-II (IGF-II), in turn, can substitute for insulin. The interaction of GMF with insulin or IGF-II can be demonstrated in a sequential manner, suggesting that GMF is a competence factor. Since insulin is required at a concentration well above the physiologic serum level, and must be used at a dose 1000 times higher than IGF-II, we suspected that insulin acts on IGF-II receptors. This was substantiated by the demonstration of IGF-II receptors and the absence of detectable insulin receptors on the astroblasts. The combined effect of IGF-II and GMF mimics the combined effect of 10% FCS and GMF, in both growth rate and saturation density.     

Maternal Obesity and Tobacco Use Modify the Impact of Genetic Variants on the Occurrence of Conotruncal Heart Defects

Conotruncal heart defects (CTDs) are among the most severe birth defects worldwide. Studies of CTDs indicate both lifestyle behaviors and genetic variation contribute to the risk of CTDs. Based on a hybrid design using data from 616 case-parental and 1645 control-parental triads recruited for the National Birth Defects Prevention Study between 1997 and 2008, we investigated whether the occurrence of CTDs is associated with interactions between 921 maternal and/or fetal single nucleotide polymorphisms (SNPs) and maternal obesity and tobacco use. The maternal genotypes of the variants in the glutamate-cysteine ligase, catalytic subunit (GCLC) gene and the fetal genotypes of the variants in the glutathione S-transferase alpha 3 (GSTA3) gene were associated with an elevated risk of CTDs among obese mothers. The risk of delivering infants with CTDs among obese mothers carrying AC genotype for a variant in the GCLC gene (rs6458939) was 2.00 times the risk among those carrying CC genotype (95% confidence interval: 1.41, 2.38). The maternal genotypes of several variants in the glutathione-S-transferase (GST) family of genes and the fetal genotypes of the variants in the GCLC gene interacted with tobacco exposures to increase the risk of CTDs. Our study suggests that the genetic basis underlying susceptibility of the developing heart to the adverse effects of maternal obesity and tobacco use involve both maternal and embryonic genetic variants. These results may provide insights into the underlying pathophysiology of CTDs, and ultimately lead to novel prevention strategies.     

The effects of maternal undernutrition on maternal and fetal serum insulin-like growth factors, thyroid hormones and cortisol in the guinea pig.

The insulin-like growth factors (IGF-I and -II) are potential mediators of the effects of maternal undernutrition on fetal growth and muscle development. The effects of a 40% reduction in maternal feed intake on serum levels of the IGFs, the thyroid hormones and cortisol, were investigated for the last two trimesters (day 25 to birth). This level of undernutrition is known to cause a 35% reduction in fetal and placental weights, and a 20-25% reduction in muscle fibre number. Maternal IGF-I level was greater than non-pregnant levels on day 25 gestation, in both control and restricted dams, and declined with gestational age. The increase in IGF-I level in the 40% restricted group was approximately two-thirds that of control animals. Fetal serum IGF-I was also reduced in undernourished fetuses throughout gestation. Maternal IGF-II did not change with gestational age and was unaffected by undernutrition. Fetal IGF-II reached a peak at day 55 of gestation, this peak was greatly diminished by maternal feed restriction. Both IGF-I and IGF-II tended to be related to fetal, placental and muscle weights at day 65 of gestation. Thyroid hormone concentration declined in maternal serum and increased in fetal serum with increasing gestational age. Levels were not significantly affected by undernutrition. Both triiodothyronine (T3) and thyroxine (T4) were correlated with IGF-I in maternal serum (P < 0.05), but not in fetal serum. Cortisol levels were elevated by undernutrition in both maternal and fetal serum, and increased with gestational age. Cortisol was inversely correlated with serum IGF-I in both maternal and fetal serum. Maternal serum IGF-I may mediate the effects of undernutrition on fetal growth by affecting the growth and establishment of the feto-placental unit in mid-gestation. Fetal IGF-I may mediate the effects on muscle growth, whereas IGF-II seems to be related to hepatic glycogen deposition. Cortisol may play a role via its effect on the IGFs, but the thyroid hormones are unlikely to be important until the late gestation/early postnatal period.     

Insulin receptor isoform A, a newly recognized, high-affinity insulin-like growth factor II receptor in fetal and cancer cells

Insulin-like growth factor II (IGF-II) is a peptide growth factor that is homologous to both insulin-like growth factor I (IGF-I) and insulin and plays an important role in embryonic development and carcinogenesis. IGF-II is believed to mediate its cellular signaling via the transmembrane tyrosine kinase type 1 insulin-like growth factor receptor (IGF-I-R), which is also the receptor for IGF-I. Earlier studies with both cultured cells and transgenic mice, however, have suggested that in the embryo the insulin receptor (IR) may also be a receptor for IGF-II. In most cells and tissues, IR binds IGF-II with relatively low affinity. The IR is expressed in two isoforms (IR-A and IR-B) differing by 12 amino acids due to the alternative splicing of exon 11. In the present study we found that IR-A but not IR-B bound IGF-II with an affinity close to that of insulin. Moreover, IGF-II bound to IR-A with an affinity equal to that of IGF-II binding to the IGF-I-R. Activation of IR-A by insulin led primarily to metabolic effects, whereas activation of IR-A by IGF-II led primarily to mitogenic effects. These differences in the biological effects of IR-A when activated by either IGF-II or insulin were associated with differential recruitment and activation of intracellular substrates. IR-A was preferentially expressed in fetal cells such as fetal fibroblasts, muscle, liver and kidney and had a relatively increased proportion of isoform A. IR-A expression was also increased in several tumors including those of the breast and colon. These data indicate, therefore, that there are two receptors for IGF-II, both IGF-I-R and IR-A. Further, they suggest that interaction of IGF-II with IR-A may play a role both in fetal growth and cancer biology.     

Disentangling fetal and maternal susceptibility for pre-eclampsia: a British multicenter candidate-gene study

The Genetics of Pre-Eclampsia (GOPEC) collaboration aims to identify genetic factors in U.K. families affected by pre-eclampsia. A number of genetic studies have reported associations with pre-eclampsia, but attempts to replicate these findings have yielded inconsistent results. We describe the results of extensive genotyping of seven candidate genes previously reported as conferring susceptibility to pre-eclampsia. Six hundred fifty-seven women affected by pre-eclampsia and their families were genotyped at 28 single-nucleotide polymorphisms in the genes encoding angiotensinogen, the angiotensin receptors, factor V Leiden variant, methylene tetrahydrofolate reductase, nitric oxide synthase, and TNFα. Genotypes were analyzed by the transmission/disequilibrium test. Genotype risk ratios (GRRs) associated with maternal genotypes had a range of 0.70–1.16; GRRs associated with fetal genotypes had a range of 0.72–1.11. No GRR achieved the prespecified criteria for statistical significance (posterior probability >.05). We conclude that none of the genetic variants tested in this large study of strictly defined pre-eclamptic pregnancies confers a high risk of disease. The results emphasize the importance of conducting rigorously designed studies of adequate size to provide precise genetic risks with narrow confidence intervals, if overreporting of false-positive results is to be avoided.     

Associations of Maternal Retinal Vasculature with Subsequent Fetal Growth and Birth Size

Objective

We aimed to study the maternal retinal microvasculature at mid-trimester and its relationship with subsequent fetal growth and birth size.

Methods

We recruited 732 pregnant women aged 18-46 years in the first trimester with singleton pregnancies. All had retinal photography and fetal scan performed at 26-28 weeks gestation, and subsequent fetal scan at 32-34 weeks gestation. Infant anthropometric measurements were done at birth. Retinal microvasculature was measured using computer software from the retinal photographs.

Results

In multiple linear regression models, each 10 μm narrowing in maternal retinal arteriolar caliber was associated with decreases of 1.36 mm in fetal head circumference at 32-34 weeks gestation, as well as decreases of 1.50 mm and 2.30 mm in infant head circumference and birth length at delivery, respectively. Each standard deviation decrease in maternal retinal arteriolar fractal dimension was associated with decreases of 1.55 mm in fetal head circumference at 32-34 weeks gestation, as well as decreases of 1.08 mm and 46.42 g in infant head circumference and birth weight at delivery, respectively.

Conclusions

Narrower retinal arteriolar caliber and a sparser retinal vascular network in mothers, reflecting a suboptimal uteroplacental microvasculature during mid-pregnancy, were associated with poorer fetal growth and birth size.     

Insulin-like growth factor II (IGF-II). Its role among regulatory peptides of the insulin superfamily

The review presents data on the insulin-like growth factor-II (IGF-II), a regulatory peptide included in the insulin superfamily, as its structure and function are the closest to those of insulin and IGF-I. The last decade investigations revealed the biological properties of IGF-II which distinguish it from related peptides. The primary sequence of the IGF-II structure has peculiar differences from those of insulin but insignificant ones from IGF-I. The tertiary structure of IGF-II is similar to that of the related peptide molecules, but a peculiar receptor-binding domain in the IGF-II molecule provides for its unique capability of interacting with receptors. IGF-II interacts with three types of receptors: receptors of IGF-I, IGF-2, and insulin. IGF-II has the highest affinity to IGF-2 receptors but its mitogenic effects are mediated by IGF-I receptors (i.e., the phenomenon of divergence of binding and biological activities). The arguments obtainedin vitro andin vivo are presented, which confirm propagation of mitogenic effects by IGF-I receptors but deny participation of IGF-2 receptors. The structural and functional bivalency of the M6P/IGF-2 receptor (a peculiar form of the M6P receptor in mammals) is considered in detail. The results of interactions of IGF-II and the M6P/IGF-2 receptors are not yet known. The primary function of the M6P/IGF-2 receptor (sorting and transport of the lysosomal enzymes) is likely to be due to the peptides inactivation and does not imply its participation in the IGF-II signaling. However, several data do not permit ruling out participation of the IGF-2 receptor in the IGF-II effects different from mitogenic ones. The organization of related peptide gene in the lancelet allows us to suggest the appearance of the IGF-II gene at the initial steps of the vertebrate evolution and to trace all stages of formation of two separate IGF genes up to the mammalian IGF-II and IGF-I genes with different structural organizations. The IGF-II expression by embryonic tissues is revealed earlier than that of other related peptides and reaches the highest level at the embryonal period. The general regularities of the IGF-II regulatory activity in embryogenesis and of the growth hormone effect on the IGF-II expression in embryonal tissues are considered.     

Sex-specific effects of placental restriction on components of the metabolic syndrome in young adult sheep

Prenatal and early postnatal life experiences, reflected by size at birth and postnatal catch-up growth, contribute to the risk of developing the metabolic syndrome in adulthood, but their relative importance is unclear. Therefore, we determined the effects of restricted placental and fetal growth on components of the metabolic syndrome in young adult sheep and the relationships of the latter to size at birth and early postnatal growth. Fasting plasma metabolites, glucose tolerance (by intravenous glucose tolerance test, IVGTT), insulin secretion and sensitivity, and resting blood pressure were measured in 22 control and 20 placentally restricted (PR) 1-yr-old sheep. In male sheep, PR increased the initial rise in glucose during an IVGTT and reduced diastolic blood pressure, and small size at birth independently predicted reduced adult size, glucose tolerance, and fasting plasma insulin and insulin disposition of glucose metabolism but increased insulin disposition of circulating FFAs. Also in males, high fractional growth rates in early postnatal life independently predicted impaired early glucose clearance during an IVGTT. In female animals, PR increased insulin sensitivity of glucose metabolism and reduced fasting plasma FFAs, and thinness at birth predicted increased adult size, fasting blood glucose, and pulse pressure. In conclusion, PR and small size at birth are associated with more components of the metabolic syndrome in adult male than in adult female sheep, with few independent effects of early postnatal growth. These sex differences in the onset and extent of adverse metabolic consequences after prenatal restraint in the sheep are consistent with observations in humans.     

Size at birth, postnatal growth and risk of obesity

Epidemiological studies over the last 15 years have shown that size at birth, early postnatal catch-up growth and excess childhood weight gain are associated with an increased risk of adult cardiovascular disease and type 2 diabetes. At the same time, rising rates of obesity and overweight in children, even at pre-school ages, have shifted efforts towards the identification of very early factors that predict risk of subsequent obesity, which may allow early targeted interventions. Overall, higher birth weight is positively associated with subsequent greater body mass index in childhood and later life; however, the relationship is complex. Higher birth weight is associated with greater subsequent lean mass, rather than fat mass. In contrast, lower birth weight is associated with a subsequent higher ratio of fat mass to lean mass, and greater central fat and insulin resistance. This paradoxical effect of lower birth weight is at least partly explained by the observation that infants who have been growth restrained in utero tend to gain weight more rapidly, or 'catch up', during the early postnatal period, which leads to increased central fat deposition. There is still debate as to whether there are critical early periods for obesity: does excess weight gain during infancy, childhood or even very early neonatal life have a greater impact on long-term fat deposition and insulin resistance? Early identification of childhood obesity risk will be aided by identification of maternal and fetal genes that regulate fetal nutrition and growth, and postnatal genes that regulate appetite, energy expenditure and the partitioning of energy intake into fat or lean tissue growth.     

Presence of insulinlike growth factor receptors and lack of insulin receptors on fetal bovine smooth muscle cells

Summary Previous investigations have demonstrated specific receptors and associated mitogenic actions for insulin and insulinlike growth factors I and II (IGF-I and II) in postnatal bovine aortic smooth muscle. Using fetal tissue we have observed different patterns of binding and action for these peptides. Smooth muscle cells isolated from near-term fetal bovine aortae were studied in early passage. Specific receptors for both IGF-I and IGF-II were identified. Specific binding averaged 5.7%/2.5×10⁵ cells for IGF-I, and 16.2% for IGF-II, and 0.3% for insulin. High affinity K _d for both IGF receptors were nanomolar. IGF-II was fivefold less potent than IGF-I in displacing IGF-I binding. IGF-I showed no affinity for the IGF-II receptor. Insulin, at physiologic concentrations, was incapable of displacing either IGF-I or IGF-II binding. Cellular incorporation of [methyl-³H]thymidine was stimulated at the lowest dose of IGF-I tested, 0.5 ng/ml. IGF-II showed no effect up to 100 ng/ml, after which a sharp increase in incorporation was noted. Insulin had a similar effect only at concentrations &gt;0.5 μg/ml, with a maximal response noted at 5 to 10 μg/ml. Our results indicate that fetal bovine aortic smooth muscle cells have an abundance of IGF receptors but lack specific insulin receptors. In addition, IGF-II binding levels are three times higher than for IGF-I. These results are consistent with observations in other species, in which a predominance of IGF over insulin receptors has been demonstrated in fetal tissue, and provide further evidence for a role for the IGFs in embryonic cellular metabolism. This project was supported by grants AM22190 (R. L. H.), AM28229 (R. G. R.) from the National Institutes of Health, Bethesda, MD, and Research Career Development Award AM01275 from the NIH (R. G. R.). Dr. Lee was the recipient of a fellowship award from the Juvenile Diabetes Foundation International and is currently supported by funds from the American Diabetes Association. Dr. Benitz is the recipient of a Clinician-Scientist Award from the American Heart Association, with funds contributed in part by the California Affiliate.     

Effects of Prenatal Multiple Micronutrient Supplementation on Fetal Growth Factors: A Cluster-Randomized,Controlled Trial in Rural Bangladesh

Prenatal multiple micronutrient (MM) supplementation improves birth weight through increased fetal growth and gestational age, but whether maternal or fetal growth factors are involved is unclear. Our objective was to examine the effect of prenatal MM supplementation on intrauterine growth factors and the associations between growth factors and birth outcomes in a rural setting in Bangladesh. In a double-blind, cluster-randomized, controlled trial of MM vs. iron and folic acid (IFA) supplementation, we measured placental growth hormone (PGH) at 10 weeks and PGH and human placental lactogen (hPL) at 32 weeks gestation in maternal plasma (n = 396) and insulin, insulin-like growth factor-1 (IGF-1), and IGF binding protein-1 (IGFBP-1) in cord plasma (n = 325). Birth size and gestational age were also assessed. Early pregnancy mean (SD) BMI was 19.5 (2.4) kg/m² and birth weight was 2.68 (0.41) kg. There was no effect of MM on concentrations of maternal hPL or PGH, or cord insulin, IGF-1, or IGFBP-1. However, among pregnancies of female offspring, hPL concentration was higher by 1.1 mg/L in the third trimester (95% CI: 0.2, 2.0 mg/L; p = 0.09 for interaction); and among women with height <145 cm, insulin was higher by 59% (95% CI: 3, 115%; p = 0.05 for interaction) in the MM vs. IFA group. Maternal hPL and cord blood insulin and IGF-1 were positively, and IGFBP-1 was negatively, associated with birth weight z score and other measures of birth size (all p<0.05). IGF-1 was inversely associated with gestational age (p<0.05), but other growth factors were not associated with gestational age or preterm birth. Prenatal MM supplementation had no overall impact on intrauterine growth factors. MM supplementation altered some growth factors differentially by maternal early pregnancy nutritional status and sex of the offspring, but this should be examined in other studies.

Trial Registration

ClinicalTrials.gov NCT00860470