Differential expression and regional distribution of aquaporins in amnion of normal and gestational diabetic pregnancies

Adipokines in pregnancy

Reproductive success consists of a sequential events chronology, starting with the ovum fertilization, implantation of the embryo, placentation, and cellular processes like proliferation, apoptosis, angiogenesis, endocrinology, or metabolic changes, which taken together finally conduct the birth of healthy offspring. Currently, many factors are known that affect the regulation and proper maintenance of pregnancy in humans, domestic animals, or rodents. Among the determinants of reproductive success should be distinguished: the maternal microenvironment, genes, and proteins as well as numerous pregnancy hormones that regulate the most important processes and ensure organism homeostasis. It is well known that white adipose tissue, as the largest endocrine gland in our body, participates in the synthesis and secretion of numerous hormones belonging to the adipokine family, which also may regulate the course of pregnancy. Unfortunately, overweight and obesity lead to the expansion of adipose tissue in the body, and its excess in both women and animals contributes to changes in the synthesis and release of adipokines, which in turn translates into dramatic changes during pregnancy, including those taking place in the organ that is crucial for the proper progress of pregnancy, i.e. the placenta. In this chapter, we are summarizing the current knowledge about levels of adipokines and their role in the placenta, taking into account the physiological and pathological conditions of pregnancy, e.g. gestational diabetes mellitus, preeclampsia, or intrauterine growth restriction in humans, domestic animals, and rodents.

Tanshinone IIA changed the amniotic fluid volume and regulated expression of AQP1 and AQP3 in amniotic epithelium cells: a promising drug treating abnormal amniotic fluid volume

BACKGROUND

Many studies have confirmed the association of aquaporins (AQPs) with abnormal amniotic fluid volume (AFV). In our previous experiments, we found that Tanshinone IIA was able to regulate the expression of AQP1 and AQP3. However, the exact mechanism by which Tanshinone IIA regulates AQPs protein expression and its effect on AFV remains unclear. The purpose of this study was to investigate the effects of Tanshinone IIA on AFV and the possible molecular mechanism of regulation of AQP1 and AQP3.

METHODS

The expression of AQPs protein in the amniotic membranes was compared between pregnant women with normal pregnancy and those with isolated oligohydramnios. The AQP1 knockout (AQP1-KO) mice and wild-type (WT) mice were treated with saline or Tanshinone IIA (10 mg/kg) at 13.5GD and 16.5GD. Human amniotic epithelium cells (hAECs) from pregnant women with normal AFV and isolated oligohydramnios were incubated with 35 μmmol/L Tanshinone IIA or 25 mmol/L LiCl [inhibitor of glycogen synthetic kinase 3β (GSK-3β)]. The protein expressions of AQPs, GSK-3β, phospho-GSK-3β (Ser9) in fetal membranes of mice and human amniotic epithelium cells were detected by western blotting.

RESULTS

The expression of AQP1 protein in the amniotic membrane of isolated oligohydramnios was increased compared with normal pregnancy. The AFV in AQP1-KO mice is higher than that in WT mice. In wild-type mice, AFV in Tanshinone IIA group was significantly higher than that in control group, and AQP1 protein expression was significantly lower than that in control group, but in AQP1 knockout mice, Tanshinone IIA reduced amniotic fluid volume and AQP3 protein expression at 16.5GD. Tanshinone IIA reduced AQP1, AQP3 and p-GSK-3β (Ser9) protein expression in normal hAECs, and this effect was inhibited by LiCl. In hAECs with oligohydramnios, the down-regulation of AQP1 and up-regulation of AQP3 by Tanshinone IIA was independent of GSK-3β signaling pathway.

CONCLUSIONS

Tanshinone IIA may increase AFV in normal pregnancy by downregulating AQP1 protein expression in the fetal membranes, which may be associated with p-GSK-3β signaling pathway. But a larger AFV in AQP1-KO mice was significantly attenuated by Tanshinone IIA, which may be related to AQP3. Tanshinone IIA is a promising drug for the treatment of amniotic fluid abnormality.

Aquaporins in Fetal Development

Water homeostasis is essential for fetal growth, and it depends on the successful development of the placenta. Many aquaporins (AQPs) were identified from blastocyst stages to term placenta. In the last years, cytokines, hormones, second messengers, intracellular pH, and membrane proteins were found to regulate their expression and function in the human placenta and fetal membranes. Accumulated data suggest that these proteins may be involved not only in the maintenance of the amniotic fluid volume homeostasis but also in the development of the placenta and fetal organs. In this sense, dysregulation of placental AQPs is associated with gestational disorders. Thus, current evidence shows that AQPs may collaborate in cellular events including trophoblast migration and apoptosis. In addition, aquaglyceroporins are involved in energy metabolism as well as urea elimination across the placenta. In the last year, the presence of AQP9 in trophoblast mitochondria opened new hypotheses about its role in pregnancy. However, much further work is needed to understand the importance of these proteins in human pregnancies.

Differential modulation of lung aquaporins among other pathophysiological markers in acute (Cl2 gas) and chronic (carbon nanoparticles, cigarette smoke) respiratory toxicity mouse models

Inhaled toxic chemicals and particulates are known to disrupt lung homeostasis causing pulmonary toxicity and tissue injury. However, biomarkers of such exposures and their underlying mechanisms are poorly understood, especially for emerging toxicants such as engineered nanoparticles and chemical threat agents such as chlorine gas (Cl₂). Aquaporins (AQPs), commonly referred to as water channels, are known to play roles in lung homeostasis and pathophysiology. However, little is known on their regulation in toxicant-induced lung injuries. Here, we compared four lung toxicity models namely, acute chemical exposure (Cl₂)-, chronic particulate exposure (carbon nanotubes/CNT)-, chronic chemical exposure (cigarette smoke extract/CSE)-, and a chronic co-exposure (CNT + CSE)- model, for modulation of lung aquaporins (AQPs 1, 3, 4, and 5) in relation to other pathophysiological endpoints. These included markers of compromised state of lung mucosal lining [mucin 5b (MUC5B) and surfactant protein A (SP-A)] and lung-blood barrier [protein content in bronchoalveolar lavage (BAL) fluid and, cell tight junction proteins occludin and zona-occludens]. The results showed toxicity model-specific regulation of AQPs measured in terms of mRNA abundance. A differential upregulation was observed for AQP1 in acute Cl₂ exposure model (14.71-fold; p = 0.002) and AQP3 in chronic CNT exposure model (3.83-fold; p = 0.044). In contrast, AQP4 was downregulated in chronic CSE model whereas AQP5 showed no significant change in any of the models. SP-A and MUC5B expression showed a decreasing pattern across all toxicity models except the acute Cl₂ toxicity model, which showed a highly significant upregulation of MUC5B (25.95-fold; p = 0.003). This was consistent with other significant pathophysiological changes observed in this acute model, particularly a compromised lung epithelial-endothelial barrier indicated by significantly increased protein infiltration and expression of tight junction proteins, and more severe histopathological (structural and immunological) changes. To our knowledge, this is the first report on lung AQPs as molecular targets of the study toxicants. The differentially regulated AQPs, AQP1 in acute Cl₂ exposure versus AQP3 in chronic CNT nanoparticle exposure, in conjunction with the corresponding differentially impacted pathophysiological endpoints (particularly MUC5B) could potentially serve as predictive markers of toxicant type-specific pulmonary injury and as candidates for future investigation for clinical intervention.

Amniotic Aaquaporins (AQP) in Normal and Pathological Pregnancies: Interest in Polyhydramnios

Polyhydramnios is a common feature diagnosed by ultrasound in the second half of pregnancy. Biochemical analysis of amniotic fluid can be useful when suspecting Bartter syndrome or digestive atresia but in most of cases, no etiology of polyhydramnios is found because of the complex regulation of amniotic fluid. Aquaporins (AQP) are transmembrane channel proteins contributing to water transfers. Some of them are expressed in fetal membranes and placenta. Their expression has been shown to be disrupted in some pathological conditions such as maternal diabetes, often associated with polyhydramnios. AQP-1, 3 and 8 levels in amniotic fluid were retrospectively measured in patients suffering from polyhydramnios (n=21) from 23 weeks of gestation (WG). They were compared to the levels observed in control subjects (n=96) and their relationship with maternal factors and neonatal issues was analyzed. AQP-1, 3, 8 levels were physiologically fluctuating, AQP-1 levels always being the lowest and AQP-3 the highest, with a significant decrease at the end of pregnancy. AQPs/AFP ratios increased about 8 folds during pregnancy, their kinetic profiles reflecting physiological dynamic evolution of amniotic fluid volume. In polyhydramnios, AQP-3 level tended to be decreased whereas AQP-8 level was decreased from mid-gestation whatever the etiology of polyhydramnios. No significant relationship was found between AQPs levels and either the fetal prematurity degree or macrosomia. No specific pattern was observed in idiopathic polyhydramnios, limiting the interest of AQPs dosage in amniotic fluid in the management of those complicated pregnancies.

Sub-Regional Differences of the Human Amniotic Membrane and Their Potential Impact on Tissue Regeneration Application

For more than 100 years, the human amniotic membrane (hAM) has been used in multiple tissue regeneration applications. The hAM consists of cells with stem cell characteristics and a rich layer of extracellular matrix. Undoubtedly, the hAM with viable cells has remarkable properties such as the differentiation potential into all three germ layers, immuno-modulatory, and anti-fibrotic properties. At first sight, the hAM seems to be one structural entity. However, by integrating its anatomical location, the hAM can be divided into placental, reflected, and umbilical amniotic membrane. Recent studies show that cells of these amniotic sub-regions differ considerably in their properties such as morphology, structure, and content/release of certain bioactive factors. The aim of this review is to summarize these findings and discuss the relevance of these different properties for tissue regeneration. In summary, reflected amnion seems to be more immuno-modulatory and could have a higher reprogramming efficiency, whereas placental amnion seems to be pro-inflammatory, pro-angiogenic, with higher proliferation and differentiation capacity (e.g., chondrogenic and osteogenic), and could be more suitable for certain graft constructions. Therefore, we suggest that the respective hAM sub-region should be selected in consideration of its desired outcome. This will help to optimize and fine-tune the clinical application of the hAM.

Expression and Regulation of Aquaporins in Pregnancy Complications and Reproductive Dysfunctions

Aquaporins (AQPs), small hydrophobic integral membrane proteins, mediate rapid transport of water and small solutes. The abnormal expressions of AQPs are associated with pregnancy complications and reproductive dysfunctions, including preeclampsia, gestational diabetes mellitus, tubal ectopic pregnancy, intrahepatic cholestasis of pregnancy, preterm birth, chorioamnionitis, polyhydramnios, and oligohydramnios, thus resulting in adverse pregnancy outcomes. This review explains the alterations of AQPs in pregnancy complications and reproductive dysfunctions and summarizes the molecular mechanisms involved in the regulations of AQPs by drugs such as oxytocin, polychlorinated biphenyls, all-trans-retinoic acid, salvia miltiorrhiza, and insulin, or other factors such as oxygen and osmotic pressure. All the research provides evidence that AQPs could be the new therapeutic targets of pregnancy-related diseases.

Altered Expressions of AQP3 and ADP Are Closely Related with the Risk of Preeclampsia Occurrence

To investigate the expression of aquaporin 3 (AQP3) in placenta and fetal membranes and the level of adiponectin (ADP) in the umbilical cord blood of severe preeclampsia and to analyze the relationship between the 2 proteins and severe preeclampsia, 60 pregnant women with severe preeclampsia were recruited as the case group and another group of 60 normal pregnant women in the same gestation period were selected as the control. After parturition, the transcriptional levels of AQP3 mRNA in placenta and fetal membranes were evaluated with RT-PCR. The expressions of AQP3 protein in the placenta and fetal membranes were determined by immunohistochemistry and Western blot. Meanwhile, the expression of ADP in umbilical artery blood was detected by ELISA. The content of triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), and LDL-C/high-density lipoprotein cholesterol in the case group was significantly higher than that in the control group. Multivariate logistic regression analysis showed that the level of TG was related to the onset of severe preeclampsia (OR 2.589). The relative expression of AQP3 mRNA and expression of AQP3 protein in placenta tissue of the case group were significantly lower than those of the control group, whereas in fetal membranes, they were significantly higher. The results of ELISA showed that the level of ADP in umbilical cord blood of neonates in the case group increased remarkably compared with that of the control group.

Aquaporins during pregnancy

Aquaporins (AQPs) are water channels proteins that facilitate water flux across cell membranes in response to osmotic gradients. Despite of the differences in the mammalian placentas, the conserved combination of AQPs expressed in placental and fetal membranes throughout gestation suggests that these proteins may be important in the regulation of fetal water homeostasis. Thus, AQPs may regulate the amniotic fluid volume and participate in the trans-placental transfer of water. Apart from their classical roles, recent studies have revealed that placental AQPs may also cooperate in cellular processes such as the migration and the apoptosis of the trophoblasts. Aquaglyceroporins can also participate in the energy metabolism and in the urea elimination across the placenta. Many factors including oxygen, hormones, acid-basis homeostasis, maternal dietary status, interaction with other transport proteins and osmotic stress are proposed to regulate their expression and function during gestation and alterations result in pathological pregnancies.

Effects of maternal western-style diet on amniotic fluid volume and amnion VEGF profiles in a nonhuman primate model

During pregnancy, high fat diet (HFD) induces maternal obesity, insulin resistance, and placental inflammatory responses that compromise placental and fetal development. Whether maternal HFD would adversely affect amniotic fluid volume (AFV) has not been explored. Vascular endothelial growth factor (VEGF) is expressed in the amnion and has been proposed as a regulator of AFV. Our aim was to investigate the effects of HFD on AFV and the associated changes in VEGF and soluble VEGF receptor 1 (sFlt-1) expression profiles in three amnion regions of a nonhuman primate model. Further, we examined the relationships between VEGF expression and HFD-induced changes in maternal metabolic status. Japanese macaques were maintained on control or HFD and amniotic fluid index (AFI) was measured as an ultrasonic estimate of AFV. Amniotic fluid VEGF concentrations were determined by ELISA and amnion VEGF and sFlt-1 mRNA levels by real-time RT-qPCR. HFD increased maternal plasma triglyceride while glucose levels were unchanged. Maternal weight gain was found in diet-sensitive animals whereas amniotic fluid VEGF concentration was reduced in diet-resistant animals. HFD did not alter AFI and there was no correlation between AFI and maternal weight or amniotic fluid VEGF concentrations. VEGF mRNA levels were lowest in secondary placental amnion while sFlt-1 mRNA were lowest in the primary placental amnion. HFD did not affect amnion VEGF or sFlt-1 mRNA expression. These findings suggest that although maternal HFD increased maternal weight in diet-sensitive and reduced amniotic fluid VEGF concentrations in diet-resistant phenotype, AFV as indicated by the AFI, was not significantly affected.

High-fat diet effects on amniotic fluid volume and amnion aquaporin expression in non-human primates

Western style, high-fat diet (HFD) and associated high lipid levels have deleterious effects on fetal and placental development independent of maternal obesity and/or diabetes. Our objectives were to determine whether HFD without development of obesity would alter amniotic fluid volume (AFV) and amnion aquaporin (AQP) expression in a non-human primate model. Japanese macaques were fed either a control diet or HFD before and during pregnancy. The four quadrant amniotic fluid index (AFI) was used as an ultrasonic estimate of AFV at 120 days gestation. Amnion samples were collected at 130 days gestation by cesarean section and AQP mRNA levels were determined by quantitative RT-PCR. Similar to that in human, AQP1, AQP3, AQP8, AQP9, and AQP11 were expressed in the macaque amnion with significant differences in levels among AQPs. In macaque, neither individual AQPs nor expression profiles of the five AQPs differed between control and non-obese HFD animals. There were regional differences in AQP expression in that, AQP1 mRNA levels were highest and AQP8 lowest in reflected amnion while AQP3, AQP9, and AQP11 were not different among amnion regions. When subdivided into control and HFD groups, AQP1 mRNA levels remain highest in the reflected amnion of both groups. The HFD did not significantly affect the AFI, but AFI was positively correlated with AQP11 mRNA levels independent of diet. Collectively, these data suggest that HFD in pregnant non-obese individuals may have at most modest effects on AFV as the AFI and amnion AQP expression are not substantially altered.

Retinoic Acid Pathway Regulation of Vascular Endothelial Growth Factor in Ovine Amnion

Vascular endothelial growth factor (VEGF) has been proposed as an important regulator of amniotic fluid absorption across the amnion into the fetal vasculature on the surface of the placenta. However, the activators of VEGF expression and action in the amnion have not been identified. Using the pregnant sheep model, we aimed to investigate the presence of the retinoic acid (RA) pathway in ovine amnion and to determine its effect on VEGF expression. Further, we explored relationships between RA receptors and VEGF and tested the hypothesis that RA modulates intramembranous absorption (IMA) through induction of amnion VEGF in sheep fetuses subjected to altered IMA rates. Our study showed that RA receptor isoforms were expressed in sheep amnion, and RA response elements (RAREs) were identified in ovine RARβ and VEGF gene promoters. In ovine amnion cells, RA treatment upregulated RARβ messenger RNA (mRNA) and increased VEGF transcript levels. In sheep fetuses, increases in IMA rate was associated with elevated VEGF mRNA levels in the amnion but not in the chorion. Further, RARβ mRNA was positively correlated with VEGF mRNA levels in the amnion and not chorion. We conclude that an RA pathway is present in ovine fetal membranes and that RA is capable of inducing VEGF. The finding of a positive relationship between amnion VEGF and RARβ during altered IMA rate suggests that the retinoid pathway may play a role through VEGF in regulating intramembranous transport across the amnion.

Leptin action in normal and pathological pregnancies

Leptin is now considered an important signalling molecule of the reproductive system, as it regulates the production of gonadotrophins, the blastocyst formation and implantation, the normal placentation, as well as the foeto-placental communication. Leptin is a peptide hormone secreted mainly by adipose tissue, and the placenta is the second leptin-producing tissue in humans. Placental leptin is an important cytokine which regulates placental functions in an autocrine or paracrine manner. Leptin seems to play a crucial role during the first stages of pregnancy as it modulates critical processes such as proliferation, protein synthesis, invasion and apoptosis in placental cells. Furthermore, deregulation of leptin levels has been correlated with the pathogenesis of various disorders associated with reproduction and gestation, including polycystic ovary syndrome, recurrent miscarriage, gestational diabetes mellitus, pre-eclampsia and intrauterine growth restriction. Due to the relevant incidence of the mentioned diseases and the importance of leptin, we decided to review the latest information available about leptin action in normal and pathological pregnancies to support the idea of leptin as an important factor and/or predictor of diverse disorders associated with reproduction and pregnancy.

Aquaporins in ovine amnion: responses to altered amniotic fluid volumes and intramembranous absorption rates

Aquaporins (AQPs) are transmembrane channel proteins that facilitate rapid water movement across cell membranes. In amniotic membrane, the AQP‐facilitated transfer of water across amnion cells has been proposed as a mechanism for amniotic fluid volume (AFV) regulation. To investigate whether AQPs modulate AFV by altering intramembranous absorption (IMA) rate, we tested the hypothesis that AQP gene expression in the amnion is positively correlated with IMA rate during experimental conditions when IMA rate and AFV are modified over a wide range. The relative abundances of AQP1, AQP3, AQP8, AQP9, and AQP11 mRNA and protein were determined in the amnion of 16 late‐gestation ovine fetuses subjected to 2 days of control conditions, urine drainage, urine replacement, or intraamniotic fluid infusion. AQP mRNA levels were determined by RT‐qPCR and proteins by western immunoblot. Under control conditions, mRNA levels among the five AQPs differed more than 20‐fold. During experimental treatments, mean IMA rate in the experimental groups ranged from 100 ± 120 mL/day to 1370 ± 270 mL/day. The mRNA levels of the five AQPs did not change from control and were not correlated with IMA rates. The protein levels of AQP1 were positively correlated with IMA rates (r² = 38%, P = 0.01) while the remaining four AQPs were not. These findings demonstrate that five AQPs are differentially expressed in ovine amnion. Our study supports the hypothesis that AQP1 may play a positive role in regulating the rate of fluid transfer across the amnion, thereby participating in the dynamic regulation of AFV.

Aquaporins and Fetal Membranes From Diabetic Parturient Women: Expression Abnormalities and Regulation by Insulin

CONTEXT

During pregnancy, aquaporins (AQPs) expressed in fetal membranes are essential for controlling the homeostasis of the amniotic volume, but their regulation by insulin was never explored in diabetic women.

OBJECTIVE

The aim of our study was to investigate the involvement of AQPs 1, 3, 8, and 9 expressed in fetal membranes in diabetic parturient women and the control of their expression by insulin.

DESIGN AND PARTICIPANTS

From 129 fetal membranes in four populations (controls, type 1, type 2 [T2D], and gestational diabetes [GD]), we established an expression AQP profile. In a second step, the amnion was used to study the control of the expression and functions of AQPs 3 and 9 by insulin.

MAIN OUTCOMES AND MEASURES

The expression of transcripts and proteins of AQPs was studied by quantitative RT-PCR and ELISA. We analyzed the regulation by insulin of the expression of AQPs 3 and 9 in the amnion. A tritiated glycerol test enabled us to measure the impact of insulin on the functional characteristics. Using an inhibitor of phosphatidylinositol 3-kinase, we analyzed the insulin intracellular signaling pathway.

RESULTS

The expression of AQP3 protein was significantly weaker in groups T2D and GD. In nondiabetic fetal membranes, we showed for the amnion (but not for the chorion) a significant repression by insulin of the transcriptional expression of AQPs 3 and 9, which was blocked by a phosphatidylinositol 3-kinase inhibitor.

CONCLUSION

In fetal membranes, the repression of AQP3 protein expression and functions observed in vivo is allowed by the hyperinsulinism described in pregnant women with T2D or GD.