Synthesis of somatomedin C/insulin-like growth factor I by human placenta

Maternal psychosocial stress during pregnancy and placenta weight: evidence from a national cohort study

Background

To study in a large-scale cohort with prospective data the associations between psychosocial stress during pregnancy and placenta weight at birth. Animal data suggest that the placenta is involved in stress-related fetal programming.

Methodology/Principal Findings

We defined a priori two types of psychosocial stress during pregnancy, life stress (perceived burdens in major areas of life) and emotional symptoms (e.g. anxiety). We estimated the associations of maternal stress during pregnancy with placenta weight at birth, controlled for length of gestation, by predicting gestational age- and sex-specific z-scores of placenta weight through multiple regression analysis, adjusted for potential confounders (N = 78017 singleton pregnancies). Life stress (per increase in stress score by 1, range: 0–18) during pregnancy was associated with increased placenta weight at birth (z-score, reported in 10⁻³; B, 14.33; CI, 10.12–18.54). In contrast, emotional symptoms during pregnancy were not associated with placenta weight at birth.

Conclusions/Significance

Maternal life stress but not emotional symptoms during pregnancy was associated with increased placenta weight at birth; yet, the association-estimate was rather small. Our results may contribute to a better understanding of the role of the placenta in the regulation of intrauterine processes in response to maternal stress.

Interleukin-6 and insulin-like growth factor system relationships and differences in the human placenta and fetus from the 35th week of gestation

The integrity of the insulin-like growth factor (IGF) system is essential for normal fetal growth. Cytokine and IGF-IGFBP relationships have been shown in specific tissues, but it is unknown whether these occur in the placenta. We aimed to assess possible differences in the IGF system depending on gestational age (GA) from week 35 to 40, and to study relationships of IL-6 with components of the IGF system in the placenta and newborn infant. We followed 32 normal births and collected whole villous tissue and cord serum. Total RNA was extracted from the placenta samples, reverse transcribed and then real-time quantitative (TaqMan) RT-PCR was performed to quantify cDNA for IGF-I, IGF-II, IGFBP-1, IGFBP-2 and IL-6. The corresponding proteins were assayed in placenta lysates and cord serum using specific commercial kits. Two groups of subjects (Group 1, 35-37 weeks GA, N=12 and Group 2, 38-40 weeks GA, N=20) were studied. In placenta, IGF-I mRNA was more abundant than IGF-II mRNA at all times and together with IGFBP-1mRNA were less expressed at term. IGFBP-2 and IL-6 mRNAs were higher after week 37 GA. IL-6 and IGFBP-2 gene expression were closely related. The corresponding proteins showed similar differences to the genes but IGF-I was undetectable in the lysates, whereas IGF-II was abundant. IGFBP-2 concentrations were very high and greater than those of IGFBP-1. In the newborn, no difference was seen in any cord serum protein after week 35 GA. IGFBP-1 was negatively correlated with parameters of neonatal size. In conclusion, this study reports new insights into IL-6, IGF-IGFBP relationships within the human placenta and shows the importance of comparing subjects with the same GA.

Expression of the insulin-like growth factors and their receptors in term placentas: a comparison between normal and IUGR births

Intrauterine growth retardation (IUGR) is defined as growth retarded to be below the tenth centile. The insulin-like growth factors and their receptors are implicated in pre- and postnatal growth and development, and it is believed that alteration in their activity may contribute to IUGR. In this study nine normal and nine intrauterine growth retarded births were followed and term placentas examined for expression of the insulin-like growth factors and their receptors. It was found that the expression of insulin-like growth factor 1 (IGF1), insulin-like growth factor 2 (IGF2), and the insulin, IGF1 and IGF2 receptor transcripts (IGF1R and IGF2R, respectively) was present in all term placentas examined. Expression of insulin was not detected. Quantitative polymerase chain reaction (PCR) was used to compare transcription levels in term placentas from normal with IUGR births. There was no significant difference in the levels of transcripts for IGF1, insulin receptor, or IGF2R between normal and IUGR term placentas. However, the IUGR term placentas had significantly higher levels of IGF2 and IGF1R expression compared with the normal term placentas. The increase in the transcription of IGF2 and IGF1R in IUGR term placentas may represent a counter regulatory mechanism in response to the growth retardation.

Phosphorylated insulin-like growth factor (IGF)-binding protein-1 (IGFBP-1) inhibits while non-phosphorylated IGFBP-1 stimulates IGF-I-induced amino acid uptake by cultured trophoblast cells

The effects of phosphorylated insulin-like growth factor-binding protein (pIGFBP-1) and non-phosphorylated (npIGFBP-1) IGFBP-1 on amino acid uptake induced by IGF-I were studied using cultured trophoblast cells. Trophoblast cells obtained from term pregnancy were incubated with indicated concentrations of pIGFBP-1 or npIGFBP-1 for 24 h and further incubated with 10 nM IGF-I for 3 h. Cells were then incubated with 3H-alpha-amino isobutyric acid (3H-AIB) for 30 min. Both pIGFBP-1 and npIGFBP-1 alone had no effect on 3H-AIB uptake; however, pIGFBP-1 inhibited IGF-I-stimulated 3H-AIB uptake with an ED50 of 0.26 nM while npIGFBP-1 potentiated 3H-AIB uptake with an ED50 of 0.27 nM. Maternal IGF-I promotes fetal growth by stimulating nutrient transport in the placenta. As shown in this study, pIGFBP-1 inhibits while npIGFBP-1 stimulates this IGF-I action in the placenta. Thus, it is suggested that IGFBP-1 phosphoisoforms are also involved in fetal growth by modulating IGF-I action in the placenta.

Effect of ethanol on plasma and hepatic insulin-like growth factor regulation in pregnant rats

Alcohol consumption during pregnancy has been shown to have profound developmental and behavioral effects on the fetus; however, the specific cause of these abnormalities remains unknown. These studies examined the consequences of chronic ethanol exposure during pregnancy on the regulation of maternal plasma and hepatic insulin-like growth factors (IGFs), and their associated plasma binding proteins (IGF-BPs). Ad libitum, pair, and ethanol-fed rats were fed a commercial liquid diet containing either ethanol or isocaloric maltose-dextrin from day 2 of pregnancy through parturition and killed 6 hr postpartum. Maternal plasma IGF-1 concentrations were reduced 51% in ethanol, compared with pair-fed mothers, with a corresponding 20% reduction in hepatic IGF-1 mRNA levels. In contrast, plasma IGF-2 concentrations were increased approximately 100% in ethanol-fed mothers. Whereas the smaller forms of the IGF-binding protein subunits (24 kDa and 32-29 kDa) were not affected by ethanol treatment, a significant reduction was observed in the binding subunit of IGF-BP3 (45-40 kDa) in ethanol-exposed mothers. These results suggest that alterations in plasma and hepatic IGF regulation may contribute to changes in maternal and placental metabolism and hormone regulation during pregnancy, which may in turn contribute to the intrauterine and postnatal growth retardation observed in prenatally ethanol-exposed offspring.

Regulation of the aromatase activity of human placental cytotrophoblasts by insulin, insulin-like growth factor-I, and -II

Studies to be reviewed were stimulated by the clinical observation, albeit controversial, that diabetic pregnancy may be associated with lower serum oestrogen levels than nondiabetic pregnancy. Pregnant diabetic women are usually intensively treated with insulin to maintain euglycemia, frequently resulting in peripheral hyperinsulinemia. The placenta, which is the primary source of oestrogens during pregnancy, would be exposed to this elevation in circulating insulin levels. Similarly, insulin-like growth factors (IGFs), which are synthesized and secreted by placental tissues and could influence placental function in an autocrine or paracrine fashion, may be elevated in diabetic pregnancy. We will review studies, which show that (i) insulin, insulin-like growth factor-I (IGF-I), and -II inhibit the aromatase activity of human cytotrophoblasts, (ii) these peptides can inhibit aromatase by activation of their respective receptors, and (iii) the potency of IGF-II in suppressing aromatase greatly exceeds that of either insulin or IGF-I. Finally, evidence will be reviewed, which suggests that inositol-glycan mediators ('second messengers') serve as the signal transduction system for insulin's inhibition of aromatase activity. Hence, placental exposure to increased concentrations of insulin and/or IGFs in the pregnant diabetic woman may result in inhibition of aromatase activity and decreased serum oestrogen levels.

Evidence for the expression of growth hormone receptors in human placenta

Since human placenta produces a growth hormone variant, it seemed important to search for evidence of GH receptors in that organ. Evidence for the expression of the GH receptor (GHR) gene was obtained by northern blot analysis. In addition, GHR poly A+ RNA was detected in RNA from cultured trophoblastic cells, but not from placenta fibroblasts. There was a low but significant specific binding of pituitary GH-N and placental GH-V to placenta plasma membranes. Both variants apparently bound to the same receptor, which is present in the first trimester as well as in the term placenta. These results suggest that placental GH may have paracrine or autocrine functions in the placenta.

Autocrine/paracrine regulation of prolactin release from human decidual cells

Studies from this laboratory indicate that the synthesis and release of prolactin from human decidual cells are regulated by factors released by the placenta, decidua and fetal membranes. A 23.5 kD protein (decidual prolactin-releasing factor, PRL-RF) has been purified to homogeneity from human placental tissue and placental conditioned medium. The releasing factor stimulates an acute release of prolactin that occurs within the first few minutes of exposure and a prolonged release, secondary to new hormone synthesis, that begins about 6-8 hours later. In addition, the synthesis and release of decidual prolactin are stimulated by IGF-I, insulin and relaxin, each acting through distinct plasma membrane receptors. In contrast, the synthesis and release of decidual prolactin are inhibited by arachidonic acid, lipocortin I and a 35-45 kD decidual protein (prolactin-releasing inhibitory factor) that has been partially purified from decidual conditioned medium. Studies of the second messengers involved in the regulation of decidual prolactin release strongly suggest that decidual prolactin release may be mediated, at least in part, by activation of phosphoinositide metabolism and stimulation of adenylate cyclase. The demonstration that the synthesis and release of decidual prolactin are regulated by PRL-RF, IGF-I, insulin, relaxin, arachidonic acid, PRL-IF and lipocortin I strongly suggests that there is novel autocrine/paracrine feedback regulation between the placenta, fetal membranes, and decidua in the regulation of decidual prolactin.

IGF-I production by mouse osteoblasts

Mouse osteoblasts contain and secrete insulinlike growth factor I (IGF-I), which can be measured by radioimmunoassay after separation from endogenous IGF-I binding activity. Our studies indicate that IGF-I is produced by all bone cell populations prepared by sequential digestion of mouse calvaria with collagenase and protease. Furthermore, relatively small amounts of IGF-I are cell associated, and IGF-I is recovered primarily in the cell medium after 24 h of culture. Basal IGF-I secretion is also density dependent, and secretion per cell is approximately 20-fold higher when cultures are inoculated at 0.125 versus 1.0 x 10(5) cells per cm2. Growth hormone increased the secretion of IGF-I only in cells released in the earlier stages of digestion. These growth hormone-responsive populations were previously shown to differ from late released cells in that they show a lower expression of the osteoblastic phenotype, harbor more EGF receptors per cell, and have a higher proliferative response to low doses of exogenous IGF-I and EGF. These data reaffirm the presence of different subclasses of bone cells in populations obtained by sequential digestion of bone and suggest that growth hormone stimulates IGF-I secretion by immature osteoblasts.

The interleukin 2 gene is expressed in the syncytiotrophoblast of the human placenta

The lymphokine interleukin 2 is an important immune system regulatory glycopolypeptide. It is produced by antigen- or mitogen-stimulated T lymphocytes and is required for the proliferation or clonal expansion of activated T lymphocytes. In this report, it is demonstrated by RNA transfer blot hybridization that the poly(A)+ RNA population of the human placenta contains a 0.85-kilobase RNA transcript that specifically hybridizes to a human interleukin 2 cDNA probe. By using hybridization histochemistry in situ, it is further shown that interleukin 2 RNA transcripts are localized, primarily, to the syncytial (syncytiotrophoblast) layer of the human placenta. Possible roles for syncytiotrophoblast-produced interleukin 2 are suggested and discussed.