Influence of speed of sample processing on placental energetics and signalling pathways: implications for tissue collection

No evidence for a placental microbiome in human pregnancies at term

BACKGROUND

The placenta plays an important role in the modulation of pregnancy immunity; however, there is no consensus regarding the existence of a placental microbiome in healthy full-term pregnancies.

OBJECTIVE

This study aimed to investigate the existence and origin of a placental microbiome.

STUDY DESIGN

A cross-sectional study comparing samples (3 layers of placental tissue, amniotic fluid, vernix caseosa, and saliva, vaginal, and rectal samples) from 2 groups of full-term births: 50 women not in labor with elective cesarean deliveries and 26 with vaginal deliveries. The comparisons were performed using polymerase chain reaction amplification and DNA sequencing techniques and bacterial culture experiments.

RESULTS

There were no significant differences regarding background characteristics between women who delivered by elective cesarean and those who delivered vaginally. Quantitative measurements of bacterial content in all 3 placental layers (quantitative polymerase chain reaction of the 16S ribosomal RNA gene) did not show any significant difference among any of the sample types and the negative controls. Here, 16S ribosomal RNA gene sequencing of the maternal side of the placenta could not differentiate between bacteria in the placental tissue and contamination of the laboratory reagents with bacterial DNA. Probe-specific quantitative polymerase chain reaction for bacterial taxa suspected to be present in the placenta could not detect any statistically significant difference between the 2 groups. In bacterial cultures, substantially more bacteria were observed in the placenta layers from vaginal deliveries than those from cesarean deliveries. In addition, 16S ribosomal RNA gene sequencing of bacterial colonies revealed that most of the bacteria that grew on the plates were genera typically found in human skin; moreover, it revealed that placentas delivered vaginally contained a high prevalence of common vaginal bacteria. Bacterial growth inhibition experiments indicated that placental tissue may facilitate the inhibition of bacterial growth.

CONCLUSION

We found no evidence to support the existence of a placental microbiome in our study of 76 term pregnancies, which used polymerase chain reaction amplification and sequencing techniques and bacterial culture experiments. Incidental findings of bacterial species could be due to contamination or to low-grade bacterial presence in some locations; such bacteria do not represent a placental microbiome per se.

High altitude regulates the expression of AMPK pathways in human placenta

INTRODUCTION

High-altitude (>2500 m) residence augments the risk of intrauterine growth restriction (IUGR) and preeclampsia likely due, in part, to uteroplacental hypoperfusion. Previous genomic and transcriptomic studies in humans and functional studies in mice and humans suggest a role for AMP-activated protein kinase (AMPK) pathway in protecting against hypoxia-associated IUGR. AMPK is a metabolic sensor activated by hypoxia that is ubiquitously expressed in vascular beds and placenta.

METHODS

We measured gene expression and protein levels of AMPK and its upstream regulators and downstream targets in human placentas from high (>2500 m) vs. moderate (~1700 m) and low (~100 m) altitude.

RESULTS

We found that phosphorylated AMPK protein levels and its downstream target TSC2 were increased in placentas from high and moderate vs. low altitude, whereas the phosphorylated form of the downstream target translation repressor protein 4E-BP1 was increased in high compared to moderate as well as low altitude placentas. Mean birth weights progressively fell with increasing altitude but no infants, by study design, were clinically growth-restricted. Gene expression analysis showed moderate increases in PRKAG2, encoding the AMPK γ2 subunit, and mechanistic target of rapamycin, MTOR, expression.

DISCUSSION

These results highlight a differential regulation of placental AMPK pathway activation in women residing at low, moderate or high altitude during pregnancy, suggesting AMPK may be serving as a metabolic regulator for integrating hypoxic stimuli with placental function.

Effect of high altitude on human placental amino acid transport

Women residing at high altitudes deliver infants of lower birth weight than at sea level. Birth weight correlates with placental system A-mediated amino acid transport capacity, and severe environmental hypoxia reduces system A activity in isolated trophoblast and the mouse placenta. However, the effect of high altitude on human placental amino acid transport remains unknown. We hypothesized that microvillous membrane (MVM) system A and system L amino acid transporter activity is lower in placentas of women living at high altitude compared with low-altitude controls. Placentas were collected at term from healthy pregnant women residing at high altitude (HA; >2,500 m; n = 14) or low altitude (LA; <1,700 m; n = 14) following planned, unlabored cesarean section. Birth weight, but not placenta weight, was 13% lower in HA pregnancies (2.88 ± 0.11 kg) compared with LA (3.30 ± 0.07 kg, P < 0.01). MVM erythropoietin receptor abundance, determined by immunoblot, was greater in HA than in LA placentas, consistent with lower placental oxygen levels at HA. However, there was no effect of altitude on MVM system A or L activity, determined by Na⁺-dependent [¹⁴C]methylaminoisobutyric acid uptake and [³H]leucine uptake, respectively. MVM abundance of glucose transporters (GLUTs) 1 and 4 and basal membrane GLUT4 were also similar in LA and HA placentas. Low birth weights in the neonates of women residing at high altitude are not a consequence of reduced placental amino acid transport capacity. These observations are in general agreement with studies of IUGR babies at low altitude, in which MVM system A activity is downregulated only in growth-restricted babies with significant compromise.NEW & NOTEWORTHY Babies born at high altitude are smaller than at sea level. Birth weight is dependent on growth in utero and, in turn, placental nutrient transport. We determined amino acid transport capacity in placentas collected from women resident at low and high altitude. Altitude did not affect system A amino acid transport across the syncytiotrophoblast microvillous membrane, suggesting that impaired placental amino acid transport does not contribute to reduced birth weight in this high-altitude population.

Glycogen synthase kinase (GSK) 3 in pregnancy and parturition: a systematic review of literature

Introduction: Multiple factors and pathways have been reported as critical machineries for cell differentiation and survival during pregnancy; a number of them involve glycogen synthase kinase (GSK) 3a/β. Several reports on GSK3's functional role exist; however, the specific role of GSK3 in reproductive tissues and its contribution to normal or abnormal parturition are still unclear. To fill this knowledge gap, a systematic review of literature was conducted to better understand the functional role of GSK3 in various intrauterine tissues during implantation, pregnancy, and parturition.Methods: We conducted a systematic review of literature on GSK3's expression and function reported between 1980 and 2017 in reproductive tissues during pregnancy using three electronic databases (Web of Science, Medline, and ClinicalTrials.gov). Study selection, data extraction, quality assessment and analyses were performed in duplicate by two independent reviewers.Results: A total of 738 citations were identified; 80 were selected for full text evaluation and 25 were included for final review. GSK3's regulation and function were mostly studied in tissues and cells from placentas (12), fetuses (8), uteruses (6), and ovaries (2). GSK3 is primarily reported as a downstream responder of protein kinase B (AKT)-, Wnt-, and reactive oxygen species (ROS)-related pathways where it plays a critical role in cell survival and growth in reproductive tissues.Conclusions: Though GSK3 has been functionally linked to a number of biological processes in reproductive tissues, it has primarily been studied as a secondary signaler of various conserved cell signaling pathways. Lack of scientific rigor in studying GSK3's role in reproductive tissues makes this molecule's function still obscure. No studies have reported GSK3 in the cervix, and very few reports exist in myometrium and decidua. This systematic review suggests more functional and mechanistic studies focusing on GSK3 need to be conducted in reproductive biology.

Placental Adaptation to Early-Onset Hypoxic Pregnancy and Mitochondria-Targeted Antioxidant Therapy in a Rodent Model

The placenta responds to adverse environmental conditions by adapting its capacity for substrate transfer to maintain fetal growth and development. Early-onset hypoxia effects on placental morphology and activation of the unfolded protein response (UPR) were determined using an established rat model in which fetal growth restriction is minimized. We further established whether maternal treatment with a mitochondria-targeted antioxidant (MitoQ) confers protection during hypoxic pregnancy. Wistar dams were exposed to normoxia (21% O2) or hypoxia (13% to 14% O2) from days 6 to 20 of pregnancy with and without MitoQ treatment (500 μmol/L in drinking water). On day 20, animals were euthanized and weighed, and the placentas from male fetuses were processed for stereology to assess morphology. UPR activation in additional cohorts of frozen placentas was determined with Western blot analysis. Neither hypoxic pregnancy nor MitoQ treatment affected fetal growth. Hypoxia increased placental volume and the fetal capillary surface area and induced mitochondrial stress as well as the UPR, as evidenced by glucose-regulated protein 78 and activating transcription factor (ATF) 4 protein up-regulation. MitoQ treatment in hypoxic pregnancy increased placental maternal blood space surface area and volume and prevented the activation of mitochondrial stress and the ATF4 pathway. The data suggest that mitochondria-targeted antioxidants may be beneficial in complicated pregnancy via mechanisms protecting against placental stress and enhancing placental perfusion.

Transposable elements, placental development, and oocyte activation: Cellular stress and AMPK links jumping genes with the creation of human life

Transposable elements (TEs), also known as "jumping genes", are DNA sequences first described by Nobel laureate Barbara McClintock that comprise nearly half of the human genome and are able to transpose or move from one genomic location to another. As McClintock also noted that a genome "shock" or stress may induce TE activation and transposition, accumulating evidence suggests that cellular stress (e.g. mediated by increases in intracellular reactive oxygen species [ROS] and calcium [Ca2+], etc.) induces TE mobilization in several model organisms and L1s (a member of the retrotransposon class of TEs) are active and capable of retrotransposition in human oocytes, human sperm, and in human neural progenitor cells. Cellular stress also plays a critical role in human placental development, with cytotrophoblast (CTB) differentiation leading to the formation of the syncytiotrophoblast (STB), a cellular layer that facilitates nutrient and gas exchange between the mother and the fetus. Syncytin-1, a protein that promotes fusion of CTB cells and is necessary for STB formation, and its receptor is found in human sperm and human oocytes, respectively, and increases in ROS and Ca2+ promote trophoblast differentiation and syncytin-1 expression. Cellular stress is also essential in promoting human oocyte maturation and activation which, similar to TE mobilization, can be induced by compounds that increase intracellular Ca2+ and ROS levels. AMPK is a master metabolic regulator activated by increases in ROS, Ca2+, and/or an AMP(ADP)/ATP ratio increase, etc. as well as compounds that induce L1 mobilization in human cells. AMPK knockdown inhibits trophoblast differentiation and AMPK-activating compounds that promote L1 mobility also enhance trophoblast differentiation. Cellular stressors that induce TE mobilization (e.g. heat shock) also promote oocyte maturation in an AMPK-dependent manner and the antibiotic ionomycin activates AMPK, promotes TE activation, and induces human oocyte activation, producing normal, healthy children. Metformin promotes AMPK-dependent telomerase activation (critical for telomere maintenance) and induces activation of the endonuclease RAG1 (promotes DNA cleavage and transposition) via AMPK. Both RAG1 and telomerase are derived from TEs. It is our hypothesis that cellular stress and AMPK links TE activation and transposition with placental development and oocyte activation, facilitating both human genome evolution and the creation of all human life. We also propose the novel observation that various cellular stress-inducing compounds (e.g. metformin, resveratrol, etc.) may facilitate beneficial TE activation and transposition and enhance fertilization and embryological development through a common mechanism of AMPK activation.

Changes in mitochondrial respiration in the human placenta over gestation

INTRODUCTION

Placental mitochondria are subjected to micro-environmental changes throughout gestation, in particular large variations in oxygen. How placental mitochondrial respiration adapts to changing oxygen concentrations remains unexplored. Additionally, placental tissue is often studied in culture; however, the effect of culture on placental mitochondria is unclear.

MATERIAL AND METHODS

Placental tissue was obtained from first trimester and term (laboured and non-laboured) pregnancies, and selectively permeabilized to access mitochondria. Respirometry was used to compare respiration states and substrate use in mitochondria. Additionally, explants of placental tissue were cultured for four, 12, 24, 48, or 96 h and respiration measured.

RESULTS

Mitochondrial respiration decreased at 11 weeks compared to earlier gestations (p = 0.05-0.001), and mitochondrial content increased at 12-13 weeks compared to 7-10 weeks (p = 0.042). In term placentae, oxidative phosphorylation (OXPHOS) through mitochondrial complex IV (p < 0.001), the relative proportion of OXPHOS CI (p < 0.001), the total capacity of the respiratory system (p = 0.003), and mitochondrial content (p < 0.001) were higher compared to first trimester. Respiration was increased (p ≤ 0.006-0.001) in laboured compared to non-laboured placenta. After four hours of culture, respiration was depressed compared to fresh tissue from the same placenta and continued to decline with time in culture. Markers of apoptosis were increased, while markers of autophagy, mitochondrial biogenesis, and mitochondrial membrane potential were decreased after four hours of culture.

DISCUSSION

Respiration and mitochondrial content alter over gestation/with labour. Decreased respiration at 11 weeks and increased mitochondrial content at 12-13 weeks may relate to onset of maternal blood flow, and increased respiration as a result of labour may be an adaptation to ischaemia-reperfusion. At term, mitochondria were more susceptible to changes in respiratory function relative to first trimester when cultured in vitro, perhaps reflecting changes in metabolic demands as gestation progresses. Metabolic plasticity of placental mitochondria has relevance to placenta-mediated diseases.

Mitogen-Activated Protein Kinases Are Activated in Placental Injury in Rat Model of Acute Pancreatitis in Pregnancy

OBJECTIVES

To establish a rat model of acute pancreatitis in pregnancy (APIP) and evaluate its general presentations, assess placental injury, and discuss possible mechanisms.

METHODS

The APIP rat model was induced by sodium taurocholate in Sprague-Dawley rats of later gestation. Normal and sham-operated (SO) rats in later gestation were set as controls, 3 time points were set in SO and APIP groups to determine optimal modeling time. Histological changes of pancreas and placenta were assessed. Placental injury was determined by immunohistochemistry stain of caspase-3. Serum levels of amylase, lipase, and Ca; proinflammatory cytokines as tumor necrosis factor-α, interleukin-1β (IL-1β), IL-6, and anti-inflammatory cytokine IL-10 by enzyme-linked immunosorbent assay; mitogen-activated protein kinases and their phosphorylated forms by Western blotting.

RESULTS

Pancreatic necrotizing and placental injury occurred in time-dependent patterns. Serum levels of amylase and lipase significantly increased but Ca decreased; tumor necrosis factor-α, IL-1β, IL-6, and IL-10 were all increased in the APIP group; c-Jun N-terminal kinase, p38, and ERK1/2 were activated but with different distributing patterns in the placenta.

CONCLUSIONS

Placental injury is involved in the rat model of APIP, and a modeling time of 6 hours is optimal and conducive to further studies; c-Jun N-terminal kinase and p38 may play important roles in placental injury during APIP.

Hypoxia, AMPK activation and uterine artery vasoreactivity

Genes near adenosine monophosphate-activated protein kinase-α1 (PRKAA1) have been implicated in the greater uterine artery (UtA) blood flow and relative protection from fetal growth restriction seen in altitude-adapted Andean populations. Adenosine monophosphate-activated protein kinase (AMPK) activation vasodilates multiple vessels but whether AMPK is present in UtA or placental tissue and influences UtA vasoreactivity during normal or hypoxic pregnancy remains unknown. We studied isolated UtA and placenta from near-term C57BL/6J mice housed in normoxia (n = 8) or hypoxia (10% oxygen, n = 7-9) from day 14 to day 19, and placentas from non-labouring sea level (n = 3) or 3100 m (n = 3) women. Hypoxia increased AMPK immunostaining in near-term murine UtA and placental tissue. RT-PCR products for AMPK-α1 and -α2 isoforms and liver kinase B1 (LKB1; the upstream kinase activating AMPK) were present in murine and human placenta, and hypoxia increased LKB1 and AMPK-α1 and -α2 expression in the high- compared with low-altitude human placentas. Pharmacological AMPK activation by A769662 caused phenylephrine pre-constricted UtA from normoxic or hypoxic pregnant mice to dilate and this dilatation was partially reversed by the NOS inhibitor l-NAME. Hypoxic pregnancy sufficient to restrict fetal growth markedly augmented the UtA vasodilator effect of AMPK activation in opposition to PE constriction as the result of both NO-dependent and NO-independent mechanisms. We conclude that AMPK is activated during hypoxic pregnancy and that AMPK activation vasodilates the UtA, especially in hypoxic pregnancy. AMPK activation may be playing an adaptive role by limiting cellular energy depletion and helping to maintain utero-placental blood flow in hypoxic pregnancy.

Glucose and Fatty Acid Metabolism in Placental Explants From Pregnancies Complicated With Gestational Diabetes Mellitus

Placental metabolism is an important mechanism for the regulation of fetal growth and long-term health of the newborns. In this study, we investigated the effects of maternal metabolic environment on human placental fatty acid and glucose metabolism. We used placental explants from uncomplicated pregnancies or pregnancies complicated with gestational diabetes mellitus (GDM), undergoing vaginal delivery (VD) or cesarean section (CS). Fatty acid oxidation (FAO) and glucose uptake (2-DOG) were similar in both modes of delivery in normal and GDM pregnancies. However, placental explants from GDM exhibited 40% to 50% reduced FAO capacity compared to control placentas in women undergoing VD or CS. In contrast, 2-DOG uptake was 2- to 3-fold higher in placental explants from GDM compared to control placentas in women undergoing VD or CS, respectively. In conclusion, ex vivo placental fuel selection is influenced by maternal GDM, but placental metabolic characteristics are not altered by the mode of delivery.

Labor inhibits placental mechanistic target of rapamycin complex 1 signaling

INTRODUCTION

Labor induces a myriad of changes in placental gene expression. These changes may represent a physiological adaptation inhibiting placental cellular processes associated with a high demand for oxygen and energy (e.g., protein synthesis and active transport) thereby promoting oxygen and glucose transfer to the fetus. We hypothesized that mechanistic target of rapamycin complex 1 (mTORC1) signaling, a positive regulator of trophoblast protein synthesis and amino acid transport, is inhibited by labor.

METHODS

Placental tissue was collected from healthy, term pregnancies (n = 15 no-labor; n = 12 labor). Activation of Caspase-1, IRS1/Akt, STAT, mTOR, and inflammatory signaling pathways was determined by Western blot. NFĸB p65 and PPARγ DNA binding activity was measured in isolated nuclei.

RESULTS

Labor increased Caspase-1 activation and mTOR complex 2 signaling, as measured by phosphorylation of Akt (S473). However, mTORC1 signaling was inhibited in response to labor as evidenced by decreased phosphorylation of mTOR (S2448) and 4EBP1 (T37/46 and T70). Labor also decreased NFĸB and PPARγ DNA binding activity, while having no effect on IRS1 or STAT signaling pathway.

DISCUSSION AND CONCLUSION

Several placental signaling pathways are affected by labor, which has implications for experimental design in studies of placental signaling. Inhibition of placental mTORC1 signaling in response to labor may serve to down-regulate protein synthesis and amino acid transport, processes that account for a large share of placental oxygen and glucose consumption. We speculate that this response preserves glucose and oxygen for transfer to the fetus during the stressful events of labor.

Differential activation of placental unfolded protein response pathways implies heterogeneity in causation of early- and late-onset pre-eclampsia

Based on gestational age at diagnosis and/or delivery, pre-eclampsia (PE) is commonly divided into early-onset (<34 weeks) and late-onset (≥34 weeks) forms. Recently, the distinction between ‘placental’ and ‘maternal’ causation has been proposed, with ‘placental’ cases being more frequently associated with early-onset and intrauterine growth restriction. To test whether molecular placental pathology varies according to clinical presentation, we investigated stress-signalling pathways, including unfolded protein response (UPR) pathways, MAPK stress pathways, heat-shock proteins and AMPKα in placentae delivered by caesarean section for clinical indications at different gestational ages. Controls included second-trimester, pre-term and normal-term placentae. BeWo cells were used to investigate how these pathways react to different severities of hypoxia–reoxygenation (H/R) and pro-inflammatory cytokines. Activation of placental UPR and stress-response pathways, including P-IRE1α, ATF6, XBP-1, GRP78 and GRP94, P-p38/p38 and HSP70, was higher in early-onset PE than in both late-onset PE and normotensive controls (NTCs), with a clear inflection around 34 weeks. Placentae from ≥ 34 weeks PE and NTC were indistinguishable. Levels of UPR signalling were similar between second-trimester and term controls, but were significantly higher in pre-term ‘controls’ delivered vaginally for chorioamnionitis and other conditions. Severe H/R (1/20% O₂) induced equivalent activation of UPR pathways, including P-eIF2α, ATF6, P-IRE1α, GRP78 and GRP94, in BeWo cells. By contrast, the pro-inflammatory cytokines TNFα and IL-1β induced only mild activation of P-eIF2α and GRP78. AKT, a central regulator of cell proliferation, was reduced in the < 34 weeks PE placentae and severe H/R-treated cells, but not in other conditions. These findings provide the first molecular evidence that placental stress may contribute to the pathophysiology of early-onset pre-eclampsia, whereas that is unlikely to be the case in the late-onset form of the syndrome. © 2014 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.