Parallel mechanisms of Ca++ transfer across the perfused human placental cotyledon

Preeclampsia Correlates with an Increase in Cannabinoid Receptor 1 Levels Leading to Macromolecular Alterations in Chorionic Villi of Term Placenta

Preeclampsia is a human pregnancy-specific disease characterized by abnormal placentation that usually presents with maternal hypertension and proteinuria. The main hallmark of preeclampsia, impaired trophoblast migration, and the subsequent disruption of uterine arteries remodeling lead to several molecular alterations in the placental compartments with those occurring in the chorionic villi being of the utmost importance. Given the essential role of the endocannabinoid system during preimplantation and trophoblast migration, we have combined the histological and hyperspectral imaging analyses to shed light on the involvement of two cannabinoid receptors in the macromolecular alterations related to preeclampsia. The results obtained by immunohistochemistry showed a significant increase in the protein levels of cannabinoid receptor 1 (CB1) in the preeclamptic chorionic villi. However, no changes were reported regarding transient receptor potential vanilloid 1 (TRPV-1) levels either in the bulk placental samples or chorionic villi when comparing control and preeclamptic patients. Histological analysis and Fourier-transform infrared spectroscopy (FTIRI) showed an increase in collagen deposition together with higher levels of lipid peroxidation and phosphorylated compounds in the pathological villi. Since CB1 enhancement has been described as promoting fibrosis and oxidative stress in several tissues, we proposed that the higher receptor abundance in preeclampsia could be triggering similar molecular effects in preeclamptic term placentas.

Expression and regulation of sodium/calcium exchangers, NCX and NCKX, in reproductive tissues: do they play a critical role in calcium transport for reproduction and development?

Plasma membrane sodium/calcium (Na(+)/Ca(2+)) exchangers are an important component of intracellular calcium [Ca(2+)](i) homeostasis and electrical conduction. Na(+)/Ca(2+) exchangers, NCX and NCKX, play a critical role in the transport of one [Ca(2+)](i) and potassium ion across the cell membrane in exchange for four extracellular sodium ions [Na(+)](e). Mammalian plasma membrane Na(+)/Ca(2+) exchange proteins are divided into two families: one in which Ca(2+) flux is dependent only on sodium (NCX1-3) and another in which Ca(2+) flux is also dependent on potassium (NCKX1-4). Both molecules are capable of forward- and reverse-mode exchange. In cells and tissues, Na(+)/Ca(2+) (and K(+)) gradients localize to the cell membrane; thus, the exchangers transport ions across a membrane potential. Uterine NCKX3 has been shown to be involved in the regulation of endometrial receptivity by [Ca(2+)](i). In the uterus and placenta, NCKX3 expression is regulated by the sex steroid hormone estrogen (E2) and hypoxia stress, respectively. In this chapter, we described the expression and regulation of these proteins for reproductive functions in various tissues including uterus, placenta, and kidney of humans and rodents. Evidence to date suggests that NCKX3 and NCX1 may be regulated in a tissue-specific manner. In addition, we focused on the molecular mechanism involved in the regulation of NCKX3 and NCX1 in mammals, based upon our recent results and those of others.

Alteration of calcium homeostasis in primary preeclamptic syncytiotrophoblasts: effect on calcium exchange in placenta

Preeclampsia (PE) is characterized by maternal hypertension, proteinuria, oedema and, in 30% of cases, by intrauterine growth retardation. Causes are still unknown; however, epidemiological and clinical studies have suggested alterations in maternal calcium metabolism. We suggested that in PE, calcium transport by the syncytiotrophoblast (ST) is disturbed. From total placental tissues, we studied the expression of: calcium channels (TRPV5, TRPV6 [transient receptor potential vanilloid]), calcium binding proteins (CaBP-9K, CaBP-28K), plasma membrane calcium ATPase (PMCA)1,2,3,4 pumps, ATP synthase, genes implicated in Ca²⁺ release [inositol-1,4,5-triphosphate receptor (IP3R)1,2,3; Ryanodine receptor (RyR)1,2,3] and replenishment (SERCA1,2,3 [sarcoendoplasmic reticulum Ca²⁺ ATPases]) from endoplasmic reticulum, channels implicated in mitochondrial Ca²⁺ accumulation (VDAC1,2,3 [voltage-dependent anion channels]) and a marker of oxidative stress (hOGG1 [Human 8-oxoguanine-DNA glycosylase 1]), as well as the influence of these variations on calcium transport in primary ST cultures. The mRNA and protein levels were thereby examined by real-time PCR and Western blot analysis, respectively, in two different groups of pregnant women with similar gestational age: a normal group (n= 16) and a PE group (n= 8), diagnosed by a clinician. Our study showed a significant decrease in calcium transport by the ST cultured from preeclamptic placentas. We found a significant (P < 0.05) decrease in mRNA levels of TRPV5, TRPV6, CaBP-9K, CaBP-28K, PMCA1, PMCA4, ATP synthase, IP3R1, IP3R2, RyR1, RyR2 and RyR3 in PE group compared to normal one. We also noted a significant decrease in protein levels of TRPV5, TRPV6, CaBP-9K, CaBP-28K and PMCA1/4 in PE group. In contrast, SERCA1, SERCA2, SERCA3, VDAC3 and hOGG1 mRNA expressions were significantly increased in PE placentas. Calcium homeostasis and transport through placenta is compromised in preeclamptic pregnancies and it appears to be affected by a lack of ATP and an excess of oxidative stress.

Molecular mapping deep within a living human organ: analysis of microvessel function on the timescale of seconds and with sub-micrometre spatial resolution

Visualising vascular endothelial cell function in individual blood microvessels allows elucidation of molecular interactions at the vascular wall, the first barrier between blood-borne therapeutic agent and its target. Functional analysis in situ requires sub-micrometer spatial resolution and tagged molecules generating contrast in living blood vessels. Light microscopy fulfills these requirements, particularly if fluorescent tags deliver the contrast. However, vascular arborisations in living organs defy morpho-functional analysis, filling tissues with closely meshed three-dimensional networks which are inaccessible to optical imaging. We protocol here successful morpho-functional analysis of microvascular processing in a living organ, the human placental cotyledon. Fluorescence-tagged tracer was positionally fixed by snap-freezing, frozen sections were cut, freeze-dried and heat-fixed. A brief histochemical procedure then labelled all vascular elements in the sections, providing fluorescence contrast in two colour channels. Mosaic monochromatic images acquired in both channels delivered high-resolution maps of centimeter-wide tissue areas. Quantitative analysis of the images' greyscale histograms defined objectifiable, reproducible thresholds, used to reduce the images to colour-coded wide-area functional maps tracking placental vascular processing of the tagged molecules. Rapid positional fixing of tracer with reduction of images to maps was combined with ultrastructural tracking to elucidate vascular processing at scales of nanometres and seconds.

Increased maternofetal calcium flux in parathyroid hormone-related protein-null mice

The role of parathyroid hormone-related protein (PTHrP) in fetal calcium homeostasis and placental calcium transport was examined in mice homozygous for the deletion of the PTHrP gene (PTHrP^−/− null; NL) compared to PTHrP^+/+ (wild-type; WT) and PTHrP^+/− (heterozygous; HZ) littermates. Fetal blood ionized calcium was significantly reduced in NL fetuses compared to WT and HZ groups at 18 days of pregnancy (dp) with abolition of the fetomaternal calcium gradient. In situ placental perfusion of the umbilical circulation at 18 dp was used to measure unidirectional clearance of ⁴⁵Ca across the placenta in maternofetal (^CaK_mf) and fetoplacental (^CaK_fp) directions; ^CaK_fp was < 5% of ^CaK_mf for all genotypes. At 18 dp, ^CaK_mf across perfused placenta and intact placenta (^CaK_mf(intact)) were similar and concordant with net calcium accretion rates in vivo. ^CaK_mf was significantly raised in NL fetuses compared to WT and HZ littermates. Calcium accretion was significantly elevated in NL fetuses by 19 dp. Placental calbindin-D_9K expression in NL fetuses was marginally enhanced (P < 0.07) but expression of TRPV6/ECaC2 and plasma membrane Ca²⁺-ATPase (PMCA) isoforms 1 and 4 were unaltered. We conclude that PTHrP is an important regulator of fetal calcium homeostasis with its predominant effect being on unidirectional maternofetal transfer, probably mediated by modifying placental calbindin-D_9K expression. In situ perfusion of mouse placenta is a robust methodology for allowing detailed dissection of placental transfer mechanisms in genetically modified mice.

Calcium Homeostasis in Human Placenta: Role of Calcium‐Handling Proteins

The human placenta is a transitory organ, representing during pregnancy the unique connection between the mother and her fetus. The syncytiotrophoblast represents the specialized unit in the placenta that is directly involved in fetal nutrition, mainly involving essential nutrients, such as lipids, amino acids, and calcium. This ion is of particular interest since it is actively transported by the placenta throughout pregnancy and is associated with many roles during intrauterine life. At term, the human fetus has accumulated about 25-30 g of calcium. This transfer allows adequate fetal growth and development, since calcium is vital for fetal skeleton mineralization and many cellular functions, such as signal transduction, neurotransmitter release, and cellular growth. Thus, there are many proteins involved in calcium homeostasis in the human placenta.

Calcium channels activated by endothelin-1 in human trophoblast

Ca2+ transfer across the syncytiotrophoblast (ST) of the human placenta is essential for normal fetal development. However, the nature of Ca2+ conductance in the ST and the mechanisms by which it is regulated are poorly understood. With the major signal transduction pathway of endothelin-1 (ET1) acting via phospholipase C (PLC) and Ca2+, we used ET1 to analyse the nature of Ca2+ channels on cultured trophoblastic cells by means of cytofluorimetric analysis using the ratiometric Ca2+ indicator Indo-1. Results indicate that ET1 (10(-7) M) stimulates a biphasic (transient and sustained) increase in [Ca2+]i in trophoblastic cells. This response is mediated by the endothelin receptor B (ETB) coupled to PLC, since treatment with BQ788 (10(-6) M) or U73122 (2 microM) totally abolished the response. Persistence of the rapid transient rise in [Ca2+]i in Ca2+-free extracellular medium confirms the release of Ca2+ from intracellular stores in response to ET1 stimulation. Furthermore, abolition of the sustained increase in [Ca2+]i in Ca2+-free extracellular medium argues in favour of the entry of Ca2+ during the plateau phase. Abolition of this plateau phase by Ni2+ (1 mM) in the presence of extracellular Ca2+ confirmed the existence of an ET1-induced Ca2+ entry. No evidence for the presence of voltage-operated channels was demonstrated during ET1 action since nifedipine (10(-6) M) did not reduce the Ca2+ response and depolarization with a hyper-potassium solution had no effect. Pharmacological studies using the imidazole derivatives SK&F96365 (30 microM) and LOE 908 (10 microM) partially inhibited the ET1-evoked Ca2+ response, thus providing evidence for the presence of both store-operated Ca2+ channels and non-selective cationic channels in the human ST.

The effect of oscillating low intensity magnetic field on the Na+, K+, Ca++, and Mg++ concentrations in the maternal and fetal circulation of the dually perfused human placental cotyledon

Dual-sided perfusions of the human placental cotyledon in vitro were used to study effects of low intensity magnetic fields (MFs) of 2 mT, 50 Hz (E1, 10 perfusions) and 5 mT, 50 Hz (E2, 10 perfusions). In the control group C (10 experiments) no field was used. Perfusions lasted 180 min each. Increased release of calcium ions from the placental cotyledon was found in the fetal circulation during perfusion when the 2 mT, 50 Hz MF was used. No changes in the release of sodium and magnesium ions were observed compared to the control group. The 5 mT, 50 Hz oscillating MF intensified the release of sodium ions from the perfused cotyledon both to the fetal and maternal circulation up to the 150th min of the experiment. Increased release of magnesium ions was observed only to the fetal circulation between 120 and 180 min and of calcium ions to the fetal circulation between 60 and 180 min. No significant differences in K concentrations were found between the control and MF exposed cotyledons under conditions of these experiments.

Activity and expression of the Na(+)/H(+) exchanger in the microvillous plasma membrane of the syncytiotrophoblast in relation to gestation and small for gestational age birth

The effect of gestational age, low birth weight, and umbilical plasma pH on the activity and expression of the Na(+)/H(+) exchanger in the microvillous plasma membrane (MVM) of the placental syncytiotrophoblast was investigated. MVM were isolated from placentas of fetuses delivered in the first and second trimesters and from appropriately grown for gestational age (AGA) and small for gestational age (SGA) babies born at term. Na(+)/H(+) exchange activity (amiloride-sensitive Na(+) uptake) was higher (p<0.05) in second trimester and term AGA MVM versus first trimester MVM (median [range]: 1.80 [1.01-3.03], 1.72 [1.16-3.15] versus 1.48 [0.92-1.66] nmol/mg protein/30s, respectively, n = 6, 12, and 9). As regards exchanger isoforms, Western blotting showed that NHE1 expression did not change across gestation, but NHE2 and NHE3 expression were lower (p<0.01) in the first and second trimesters than in term AGA MVM. There were no differences in Na(+)/H(+) exchanger activity or in NHE1-3 expression in term AGA MVM versus SGA (n = 11) MVM. There was no correlation between exchanger activity and umbilical artery or vein plasma pH, although with a relatively small number of samples (n = 12 and 15, respectively). We conclude that there is differential regulation of the activity and expression of Na(+)/H(+) exchanger isoforms in the MVM over the course of gestation in normal pregnancy; this is not affected in pregnancies resulting in SGA babies at term.

Techniques to study human placental transport

Pregnancy in the 20th century involves women of many age groups from early teens to the fourth or fifth decade. Modern medicine and in vitro fertilization techniques have increased options for pregnancy and childbirth. Pregnancy is a dynamic state, and medical concerns may involve disorders of the fetus and mother requiring medications and special nutrients. Therefore, different techniques have been developed to evaluate the placental transfer of drugs and nutrients using tissues and cells derived from human placenta. These include (a) isolated tissues and cells to study placental transport, (b) primary and malignant trophoblast cell cultures and (c) biophysical methods for studying placental transport. Also, convenient study models have been developed to evaluate placental transfer of safe drugs in pregnant women. Some of the drugs studied by these techniques and models include (a) anesthetics and pain medications used during delivery, (b) antibiotics and anti-bacterials used to cure infections, (c) drugs abused by pregnant women and (d) nutrients required for proper fetal growth. Placental transfer and exchange mechanisms are complicated processes, and in vitro models reflect only partially the equilibria that exist among mother, placenta and fetus. The perfused cotyledon model is elegant and simple but gives only restricted information. Isolated placental tissues give useful information about the pharmacological effects of drugs. Metabolic studies using human placental models provide information on the metabolism of a drug during placental transfer and accumulation of the drug or its metabolite in the placenta or fetal circulation. Several studies on the transplacental passage of drugs exist but many questions regarding the transfer of drugs between the maternal and fetal circulations and clearance of drugs from fetal circulation have yet to be answered. This article reviews in vitro and in vivo methods for evaluation of transplacental transport of drugs and their current effectiveness to obtain clinically useful data.

Activity and expression of Na(+)-K(+)-ATPase in human placental cytotrophoblast cells in culture

1. To determine whether there is a change during differentiation, the activity and expression of Na(+)-K(+)-ATPase were studied in mononucleate cytotrophoblast cells (18 h culture) and syncytiotrophoblast-like cells (66 h culture). A choriocarcinoma-derived cell line (JAr) which, unlike the cytotrophoblast cells, divides in culture, was also studied for comparison. 2. Na(+)-K(+)-ATPase activity was assessed by measurement of ouabain-sensitive 86Rb+ uptake. Na(+)-K(+)-ATPase expression was determined by (i) measurement of [3H]ouabain binding and (ii) Northern hybridization to measure expression of alpha-1 and beta 1-subunit mRNA. 3. There was no significant difference in either activity or expression of Na(+)-K(+)-ATPase during differentiation of cytotrophoblast cells. However, expression of alpha 1- and beta 1-subunit mRNA was significantly lower in 66 vs. 18 h cultured cytotrophoblast cells. 4. Both Na(+)-K(+)-ATPase activity and [3H]ouabain binding was significantly greater in JAr cells than either cytotrophoblast cell groups, although expression of alpha 1- and beta 1-subunit mRNA was the same as cytotrophoblast cells cultured for 18 h. 5. It is concluded that N(+)-K(+)-ATPase activity and protein expression does not change during differentiation of cytotrophoblast cells but that there are changes in expression at the transcriptional or post-transcriptional level.