D. Michael Nelson

Intrauterine growth restriction, human placental development and trophoblast cell death.

Intrauterine growth restriction (IUGR) is a failure to achieve the growth potential of a fetus that is promised by the genetic constitution and environmental influences endogenous to the pregnancy. Optimal placental development and the ability of the placenta to compensate for stimulus‐induced injury are central in promotion of normal fetal growth. In this review, we will overview placental development with a focus on how villous structure relates to function. We will also describe the differentiation and turnover of villous trophoblast while highlighting selected features of microscopic placental injury. Histopathological studies of the placenta in IUGR indicate that abnormalities of the maternal spiral arterioles, dysregulated villous vasculogenesis, and abundant fibrin deposition are characteristic of the injuries associated with this condition. We identify selected insults, including oxidative stress and complement activation, and key pathways that regulate apoptosis in villous trophoblast, including increased p53 activity, altered translation of AKT and mTOR proteins, and the stress response of the endoplasmic reticulum. We surmise that trophoblast dysregulation at a subcellular level and loss of functional mass of villous trophoblast via cell death pathways are key contributors to the suboptimal placental performance that yields IUGR. We predict that a better understanding of placental dysfunction in IUGR will lead to targeted therapeutic options for this important clinical condition.

Identification of intracellular bacteria in the basal plate of the human placenta in term and preterm gestations

OBJECTIVE Bacteria have been identified in different regions of the placenta. Here, we tested the hypothesis that the maternal basal plate of the placenta harbors microbes that may be associated with adverse pregnancy outcomes. STUDY DESIGN We performed a cross-sectional study of pregnancies from a single tertiary care hospital. Maternal medical and obstetric characteristics were obtained and pregnancies followed up prospectively for outcomes and placental collection. After delivery, systematic random sampling of the placental basal plate was performed. Paraffin sections of basal plates were stained with 4 histologic stains and scored for morphological evidence of bacteria. RESULTS Of 195 total patients in the study, Gram-positive and -negative intracellular bacteria of diverse morphologies were documented in the basal plates of 27% of all placentas. Of the patients, 35% delivered preterm. No difference was noted between placental basal plates from preterm or term gestations. Intracellular bacteria were found in the placental basal plates of 54% spontaneous preterm deliveries <28 weeks, and in 26% of term spontaneous deliveries (P = .02). Intracellular bacteria were also documented in placentas without clinical or pathologic chorioamnionitis. CONCLUSION A total of 27% of placentas demonstrated intracellular bacteria in the placental basal plate using morphological techniques. Thus, the maternal basal plate is a possible source of intrauterine colonization and placental pathological examination could include examination for bacteria in this important maternal-fetal interface.

Maternal Undernutrition Influences Placental-Fetal Development

Maternal nutrition during pregnancy has a pivotal role in the regulation of placental-fetal development and thereby affects the lifelong health and productivity of offspring. Suboptimal maternal nutrition yields low birth weight, with substantial effect on the short-term morbidity of the newborn. The placenta is the organ through which gases, nutrients, and wastes are exchanged between the maternal-fetal circulations. The size, morphology, and nutrient transfer capacity of the placenta determine the prenatal growth trajectory of the fetus to influence birth weight. Transplacental exchange depends on uterine, placental, and umbilical blood flow. Most important, maternal nutrition influences factors associated not only with placental homeostasis but also with optimal fetal development. This review associates fetal growth with maternal nutrition during pregnancy, placental growth and vascular development, and placental nutrient transport.

Characterization of a microvillous membrane preparation from human placental syncytiotrophoblast: A morphologic, biochemical, and physiologic study

The syncytiotrophoblast microvillous membrane must play a vital role in many essential functions of the placenta. In order to better understand the functional characteristics of this membrane, we have investigated an isolated membrane preparation by a variety of techniques. Electron microscopic observations showed membranous structures similar to microvilli of intact placental villi in size, shape, and microfilamentous content. Similarities in colloidal iron staining and transferrin localization were also shown. The preparation was enriched in enzymes characteristic of surface membranes and diminished in enzymes characteristic of intracellular organelles. Sialic acid content was also increased. SDS gel electrophoresis revealed the presence of a 45,000 molecular weight band, which may be actin. The preparation transported serine, glycine, and alpha-aminoisobutyric acid by a temperature-dependent, saturable process.

Hypoxia limits differentiation and up-regulates expression and activity of prostaglandin H synthase 2 in cultured trophoblast from term human placenta ☆ ☆☆ ★

OBJECTIVE We determined the effect of hypoxic conditions on cellular differentiation and prostaglandin H synthase expression in cultured human term trophoblast. STUDY DESIGN Cytotrophoblasts isolated from term placentas were cultured for 24-72 hours in a standard (20% oxygen) or hypoxic (1% to 2% oxygen) atmosphere. Trophoblast biochemical differentiation was determined by release of human chorionic gonadotropin. Morphologic differentiation was evaluated by epifluorescent and confocal microscopic examination of cultures after dual cytochemical staining for surface membrane desmosomes and intracytoplasmic nuclei. Prostaglandin H synthase 2 expression was determined by Western blot analysis and correlated with enzyme activity by immunoassay of 2 prostaglandin H synthase 2 products, prostaglandin E2 and thromboxane. RESULTS Human chorionic gonadotropin levels in media and syncytiotrophoblast formation were markedly diminished in trophoblast cultured in hypoxia, compared with trophoblast in control cultures, whereas viability was unchanged. Hypoxia up-regulated expression of trophoblast prostaglandin H synthase 2 but not of prostaglandin H synthase 1 and increased prostaglandin E2 and thromboxane release. CONCLUSIONS Hypoxia limits differentiation and enhances prostaglandin H synthase 2 expression in cultured villous trophoblast. These responses may account for the cytotrophoblast prominence characteristic of placentas exposed to attenuated oxygen delivery.

N-Myc Down-regulated Gene 1 Modulates the Response of Term Human Trophoblasts to Hypoxic Injury

The placenta is susceptible to diverse insults during human pregnancy. The expression of the protein N-myc down-regulated gene 1 (NDRG1) is regulated during cell proliferation, differentiation, and in response to stress. Nevertheless, the function of this protein in humans remains unknown. We tested the hypothesis that NDRG1 is up-regulated in hypoxic primary human trophoblasts and that NDRG1 modulates trophoblast response to hypoxia. We initially demonstrated that the expression of NDRG1 is enhanced in primary human trophoblasts exposed to hypoxia. Importantly, we found a similar increase in NDRG1 expression in placental samples derived from either singleton gestations complicated by intrauterine growth restriction or from dizygotic twin gestation where one twin exhibited growth restriction. Having established efficient lentivirus-mediated transfection of primary human trophoblasts, we overexpressed NDRG1 in trophoblasts, which resulted in enhanced trophoblast differentiation. In contrast, lentivirus-driven short interfering RNA-mediated silencing of NDRG1 diminished trophoblast viability and differentiation. Consistent with these results, NDRG1 reduced the expression level of p53 in trophoblasts cultured in standard or hypoxic conditions. Furthermore, NDRG1 expression was regulated by the activity of SIRT1 (Sir2-like protein 1), which promotes cell survival. Together, our data indicate that NDRG1 interacts with SIRT1/p53 signaling to attenuate hypoxic injury in human trophoblasts.

MiR-205 silences MED1 in hypoxic primary human trophoblasts

Acting through degradation of target mRNA or inhibition of translation, microRNAs (miRNAs) regulate development, differentiation, and cellular response to diverse cues. We analyzed changes in miRNA expression in human placental trophoblasts exposed to hypoxia, which may result from hypoperfusion and placental injury. Using an miRNA microarray screen, confirmed by Northern blot analysis, we defined a set of seven miRNAs (miR‐93, miR‐205, miR‐224, miR‐335, miR‐424, miR‐451, and miR‐491) that are differentially regulated in primary trophoblasts exposed to hypoxia. We combined in silico prediction of miRNA targets with gene expression profiling data to identify a series of potential targets for the miRNAs, which were further analyzed using luciferase reporter assays. Among experimentally confirmed targets, we found that the transcriptional coactivator MED1, which plays an important role in placental development, is a target for miR‐205. Using gain‐ and loss‐of‐function assays, we confirmed that miR‐205 interacts with a specific target in the 3′‐UTR sequence of MED1 and silences MED1 expression in human trophoblasts exposed to hypoxia, suggesting that miR‐205 plays a role in trophoblast injury.—Mouillet, J.‐F., Chu, T., Nelson, D. M., Mishima, T., Sadovsky, Y. MiR‐205 silences MED1 in hypoxic primary human trophoblasts. FASEB J. 24, 2030–2039 (2010). www.fasebj.org

Negligible Role of Antibodies and C5 in Pregnancy Loss Associated Exclusively with C3-Dependent Mechanisms through Complement Alternative Pathway

Factors involved in pregnancy failure due to abnormal fetomaternal tolerance are poorly understood. Here we describe distinct defects in placenta formation and subsequent pregnancy loss solely dependent on the activation of the complement alternative pathway and the effector mechanisms provided by the maternal C3. Surprisingly, this effect is independent of other complement activation pathways and of the effector mechanisms provided by other complement components. These findings provide significant insight into the role of the innate immune system in human pregnancy failure, a frequent clinical outcome.

Fatty Acid Binding Protein 4 Regulates Intracellular Lipid Accumulation in Human Trophoblasts

CONTEXT Maternal obesity, gestational diabetes (GDM), or type 2 diabetes (T2DM) is associated with altered lipid metabolism and fetal overgrowth. OBJECTIVE The objective of the study was to test the hypothesis that hyperlipidemia and hyperinsulinemia regulate lipid content and expression of lipid-trafficking proteins in human placental trophoblasts. STUDY DESIGN Pregnant women were prospectively enrolled for clinical specimens collection, and cultured human trophoblasts were used for experiments. SETTING This was a translational study conducted at an academic biomedical research center. PATIENTS OR OTHER PARTICIPANTS Normal weight, obese, or obese with gestational diabetes or type 2 diabetes pregnant women (n = 10 in each group) undergoing scheduled cesarean delivery at term were enrolled. INTERVENTIONS Cultured primary human trophoblasts, exposed to insulin (10 nM) and/or fatty acids mix (1200 μM) in the absence or presence of an fatty acid binding protein 4 (FABP4) inhibitor or after small interfering RNA-mediated knockdown of FABP4. MAIN OUTCOME MEASURES Serum lipid levels were analyzed in the maternal venous and fetal cord blood. Placental biopsies and cultured trophoblasts were analyzed for FABP expression and lipid accumulation. RESULTS Obese diabetic women and their fetuses had elevated serum triglyceride levels. Nonesterified fatty acids were elevated and triglycerides were reduced in placental villi from obese diabetic women, and this was accompanied by a 2.6-fold increase in FABP4 expression (P < 0.05). In primary human trophoblasts, fatty acids markedly increased the expression of FABP4 (20- to 40-fold, P < 0.05) and cellular triglyceride content (4-fold, P < 0.05), and this effect was attenuated by small interfering RNA-mediated knockdown of FABP4 or the selective FABP4 inhibitor BMS309403. CONCLUSIONS Hyperlipidemia alters lipid content and increases the expression of FABP4 in trophoblasts. The reduced triglyceride content after FABP4 inhibition suggests that FABP4 is essential for trophoblast lipid accumulation.

Placental dysfunction and fetal programming: the importance of placental size, shape, histopathology, and molecular composition.

Normal function of the placenta is pivotal for optimal fetal growth and development. Fetal programming commonly is associated with placental dysfunction that predisposes to obstetric complications and suboptimal fetal outcomes. We consider several clinical phenotypes for placental dysfunction that likely predispose to fetal programming. Some of these reflect abnormal development of the chorioallantoic placenta in size, shape, or histopathology. Others result when exogenous stressors in the maternal environment combine with maladaptation of the placental response to yield small placentas with limited reserve, as typical of early-onset intrauterine growth restriction and preeclampsia. Still others reflect epigenetic changes, including altered expression of imprinted genes, altered enzymatic activity, or altered efficiencies in nutrient transport. Although the human placenta is a transient organ that persists only 9 months, the effects of this organ on the offspring remain for a lifetime.