ATP-dependent Ca2+ transport is up-regulated during third trimester in human syncytiotrophoblast basal membranes

Phosphate, calcium, and vitamin D signaling, transport, and metabolism in the endometria of cyclic ewes

BACKGROUND

Recent evidence suggests important roles for progesterone (P4) and interferon tau in the regulation of calcium, phosphate, and vitamin D signaling in the uteri of pregnant sheep. However, the effects of P4 and estradiol (E2), with respect to the expression of their receptors PGR and ESR1, respectively, in uterine epithelia on mineral signaling during the estrous cycle has not been investigated. Estrous cycles of mature Suffolk ewes were synchronized, prostaglandin F2α was administered, and ewes were observed for estrus (designated as Day 0) in the presence of vasectomized rams. On Days 1, 9, or 14 of the estrous cycle, hysterectomies were performed.

RESULTS

25-hydroxyvitamin D was more abundant in plasma from ewes on Day 14 than Day 1 (P < 0.05). Expression of fibroblast growth factor receptor 2 (FGFR2), a disintegrin and metalloprotease 17 (ADAM17), and parathyroid hormone-related protein (PTHrP) mRNAs was greater in endometria on Day 9 compared to Days 1 and 14 (P < 0.01). Similarly, expression of transient receptor potential cation channel subfamily V member 6 (TRPV6) mRNA was greater in endometria on Day 9 than Day 1 (P < 0.05). ATPase plasma membrane Ca²⁺ transporting 4 (ATP2B4) and S100 calcium binding protein G (S100G) mRNA expression was greater in endometria on Day 14 than on Days 1 and 9 (P < 0.01). In contrast, endometrial expression of vitamin D receptor (VDR) mRNA was lower on Days 9 and 14 than Day 1 (P < 0.01). Expression of klotho (KL) (P < 0.05) and cytochrome P450 family 24 subfamily A member 1 (CYP24) (P < 0.01) mRNAs was lower on Day 14 than Days 1 and 9. ADAM17, FGF23, CYP2R1, CYP27B1, KL, and VDR proteins immunolocalized to the uterine myometrium, blood vessels, and uterine luminal (LE), superficial glandular (sGE), and glandular (GE) epithelia. S100A9 protein was weakly expressed in the uterine myometrium, LE, sGE, and GE. Immunoreactivity of CYP2R1 and KL proteins in uterine LE and sGE was less on Day 1 than on Days 9 and 14. In contrast, S100G protein was expressed exclusively by GE, and immunoreactive S100G protein was less on Day 9. S100A12 protein localized to stromal cells of the uterine stratum spongiosum and blood vessels, but not by uterine epithelial cells.

CONCLUSION

Collectively, these results implicate E2, P4, and PGR in the regulation of phosphate, calcium, and vitamin D signaling in cyclic ewes.

Effects of exogenous progesterone on expression of mineral regulatory molecules by ovine endometrium and placentomes

This study aimed to determine whether the acceleration of conceptus development induced by administration of exogenous progesterone (P4) during the pre-implantation period of pregnancy alters calcium, phosphate, and vitamin D signaling at the maternal-conceptus interface. Suffolk ewes (n = 48) were mated to fertile rams and received daily intramuscular injections of either corn oil vehicle (CO) or 25 mg progesterone in CO (P4) for the first 8 days of pregnancy and hysterectomized on either Day 9 (CO n = 5; P4 n = 6), 12 (CO n = 9; P4 n = 4) or 125 (CO n = 14; P4 n = 10) of gestation. Expression of S100A12 (P < 0.05) and FGFR2 (P < 0.01) mRNAs was lower in endometria from P4-treated ewes on Day 12. Expression of ADAM10 (P < 0.05) mRNA was greater in endometria from P4-treated ewes on Day 125. Expression of ADAM10 (P < 0.01), FGFR2 (P < 0.05), SLC20A1 (P < 0.05), TRPV5 (P < 0.05), and TRPV6 (P < 0.01) mRNAs was greater, but KL mRNA expression was lower (P < 0.05) in placentomes from P4-treated ewes at Day 125. There was lower endometrial and greater placentomal expression of mRNAs involved in mineral metabolism and transport in twin compared to singleton pregnancies. Further, expression of mRNAs involved in mineral metabolism and transport was greater in P4-treated twin placentomes. KL, FGF23, VDR, S100A9, S100A12, S100G, and CYP27B1 proteins were immunolocalized in endometria and placentomes. Exogenous P4 in early pregnancy altered expression of regulators of calcium, phosphate, and vitamin D on Day 125 of pregnancy indicating a novel effect of P4 on mineral transport at the maternal-conceptus interface.

Phosphate, Calcium, and Vitamin D: Key Regulators of Fetal and Placental Development in Mammals

Normal calcium and bone homeostasis in the adult is virtually fully explained by the interactions of several key regulatory hormones, including parathyroid hormone, 1,25 dihydroxy vitamin D3, fibroblast growth factor-23, calcitonin, and sex steroids (estradiol and testosterone). In utero, bone and mineral metabolism is regulated differently from the adult. During development, it is the placenta and not the fetal kidneys, intestines, or skeleton that is the primary source of minerals for the fetus. The placenta is able to meet the almost inexhaustible needs of the fetus for minerals by actively driving the transport of calcium and phosphorus from the maternal circulation to the growing fetus. These fundamentally important minerals are maintained in the fetal circulation at higher concentrations than those in maternal blood. Maintenance of these inordinately higher fetal levels is necessary for the developing skeleton to accrue sufficient minerals by term. Importantly, in livestock species, prenatal mineralization of the skeleton is crucial for the high levels of offspring activity soon after birth. Calcium is required for mineralization, as well as a plethora of other physiological functions. Placental calcium and phosphate transport are regulated by several mechanisms that are discussed in this review. It is clear that phosphate and calcium metabolism is intimately interrelated and, therefore, placental transport of these minerals cannot be considered in isolation.

Genes and Pathways Affecting Sheep Productivity Traits: Genetic Parameters, Genome-Wide Association Mapping, and Pathway Enrichment Analysis

Ewe productivity is a composite and maternal trait that is considered the most important economic trait in sheep meat production. The objective of this study was the application of alternative genome-wide association study (GWAS) approaches followed by gene set enrichment analysis (GSEA) on the ewes’ genome to identify genes affecting pregnancy outcomes and lamb growth after parturition in Iranian Baluchi sheep. Three maternal composite traits at birth and weaning were considered. The traits were progeny birth weight, litter mean weight at birth, total litter weight at birth, progeny weaning weight, litter mean weight at weaning, and total litter weight at weaning. GWASs were performed on original phenotypes as well as on estimated breeding values. The significant SNPs associated with composite traits at birth were located within or near genes RDX, FDX1, ARHGAP20, ZC3H12C, THBS1, and EPG5. Identified genes and pathways have functions related to pregnancy, such as autophagy in the placenta, progesterone production by the placenta, placental formation, calcium ion transport, and maternal immune response. For composite traits at weaning, genes (NR2C1, VEZT, HSD17B4, RSU1, CUBN, VIM, PRLR, and FTH1) and pathways affecting feed intake and food conservation, development of mammary glands cytoskeleton structure, and production of milk components like fatty acids, proteins, and vitamin B-12, were identified. The results show that calcium ion transport during pregnancy and feeding lambs by milk after parturition can have the greatest impact on weight gain as compared to other effects of maternal origin.

Developmental origins of metabolic diseases

Almost 2 billion adults in the world are overweight, and more than half of them are classified as obese, while nearly one-third of children globally experience poor growth and development. Given the vast amount of knowledge that has been gleaned from decades of research on growth and development, a number of questions remain as to why the world is now in the midst of a global epidemic of obesity accompanied by the "double burden of malnutrition," where overweight coexists with underweight and micronutrient deficiencies. This challenge to the human condition can be attributed to nutritional and environmental exposures during pregnancy that may program a fetus to have a higher risk of chronic diseases in adulthood. To explore this concept, frequently called the developmental origins of health and disease (DOHaD), this review considers a host of factors and physiological mechanisms that drive a fetus or child toward a higher risk of obesity, fatty liver disease, hypertension, and/or type 2 diabetes (T2D). To that end, this review explores the epidemiology of DOHaD with discussions focused on adaptations to human energetics, placental development, dysmetabolism, and key environmental exposures that act to promote chronic diseases in adulthood. These areas are complementary and additive in understanding how providing the best conditions for optimal growth can create the best possible conditions for lifelong health. Moreover, understanding both physiological as well as epigenetic and molecular mechanisms for DOHaD is vital to most fully address the global issues of obesity and other chronic diseases.

Changes in calcium channel proteins according to magnesium sulfate administration in placentas from pregnancies with pre-eclampsia or fetal growth restriction

We aimed to evaluate the changes in plasma membrane Ca²⁺-ATPase (PMCA) and sarcoendoplasmic reticulum CA²⁺-ATPase (SERCA-2) according to the antepartal magnesium sulfate (MgSO₄) administration in the placentas from pregnancies with pre-eclampsia (PE) or fetal growth restriction (FGR). Pregnant women were classified as follows: (group 1) pregnancies without PE or FGR (n=16), (group 2) pregnancies with PE or FGR but without MgSO₄ administration (n=14), and (group 3) pregnancies with PE or FGR and with MgSO₄ administration (n=28). We observed the localization of PMCA and SERCA-2 in placentas and compared its expression among 3 groups. And we observed its expression in BeWo cells following treatment with MgSO₄ and CoCl₂. PMCA staining was more observed in the basal membrane, whereas SERCA-2 staining was observed predominantly under the microvillous membrane. SERCA-2 expression was significantly increased in group 3 compared with that in group 1. Considering the gestational age at delivery, PMCA expression was increased in group 2 and group 3 compared with that in group 1 after 36 weeks of gestation. SERCA-2 was increased in group 3, but not in group 2 compared with that in group 1 after 36 weeks of gestation. In BeWo cells, MgSO₄ treatment increased PMCA and SERCA-2 expression. PMCA expression was influenced by gestational age at delivery, and SERCA-2 expression was increased in the presence of PE and antepartal MgSO₄ administration. This indicates that antepartal MgSO₄ administration has a greater influence on SERCA-2 than PMCA.

Mechanisms Underpinning Adaptations in Placental Calcium Transport in Normal Mice and Those With Fetal Growth Restriction

Fetal delivery of calcium, via the placenta, is crucial for appropriate skeletal mineralization. We have previously demonstrated that maternofetal calcium transport, per gram placenta, is increased in the placental specific insulin-like growth factor 2 knockout mouse (P0) model of fetal growth restriction (FGR) compared to wild type littermates (WTL). This effect was mirrored in wild-type (WT) mice comparing lightest vs. heaviest (LvH) placentas in a litter. In both models increased placental calcium transport was associated with normalization of fetal calcium content. Despite this adaptation being observed in small normal (WT), and small dysfunctional (P0) placentas, mechanisms underpinning these changes remain unknown. Parathyroid hormone-related protein (PTHrP), elevated in cord blood in FGR and known to stimulate plasma membrane calcium ATPase, might be important. We hypothesized that PTHrP expression would be increased in LvH WT placentas, and in P0 vs. WTL. We used calcium pathway-focused PCR arrays to assess whether mechanisms underpinning these adaptations in LvH WT placentas, and in P0 vs. WTL, were similar. PTHrP protein expression was not different between LvH WT placentas at E18.5 but trended toward increased expression (139%; P = 0.06) in P0 vs. WTL. PCR arrays demonstrated that four genes were differentially expressed in LvH WT placentas including increased expression of the calcium-binding protein calmodulin 1 (1.6-fold; P < 0.05). Twenty-four genes were differentially expressed in placentas of P0 vs. WTL; significant reductions were observed in expression of S100 calcium binding protein G (2-fold; P < 0.01), parathyroid hormone 1 receptor (1.7-fold; P < 0.01) and PTHrP (2-fold; P < 0.05), whilst serum/glucocorticoid-regulated kinase 1 (SGK1), a regulator of nutrient transporters, was increased (1.4 fold; P < 0.05). Tartrate resistant acid phosphatase 5 (TRAP5 encoded by Acp5) was reduced in placentas of both LvH WT and P0 vs. WTL (1.6- and 1.7-fold, respectively; P < 0.05). Signaling events underpinning adaptations in calcium transport are distinct between LvH placentas of WT mice and those in P0 vs. WTL. Calcium binding proteins appear important in functional adaptations in the former whilst PTHrP and SGK1 are also implicated in the latter. These data facilitate understanding of mechanisms underpinning placental calcium transport adaptation in normal and growth restricted fetuses.

Adaptations in Maternofetal Calcium Transport in Relation to Placental Size and Fetal Sex in Mice

Appropriate placental transport of calcium is essential for normal fetal skeletal mineralization. In fetal growth restriction (FGR), the failure of a fetus to achieve its growth potential, a number of placental nutrient transport systems show reduced activity but, in the case of calcium, placental transport is increased. In a genetic mouse model of FGR this increase, or adaptation, maintains appropriate fetal calcium content, relative to the size of the fetus, despite a small, dysfunctional placenta. It is unknown whether such an adaptation is also apparent in small, but normally functioning placentas. We tested the hypothesis that calcium transfer would be up-regulated in the lightest vs. heaviest placentas in the same C57Bl/6J wild-type (WT) mouse litter. Since lightest placentas are often from females, we also assessed whether fetal sex influenced placental calcium transfer. Placentas and fetuses were collected at embryonic day (E)16.5 and 18.5; the lightest and heaviest placentas, and female and male fetuses, were identified. Unidirectional maternofetal calcium clearance (^CaK_mf) was assessed following ⁴⁵Ca administration to the dam and subsequent radiolabel counts within the fetuses. Placental expression of calcium pathway components was measured by Western blot. Data (median) are lightest placenta expressed as percentage of the heaviest within a litter and analyzed by Wilcoxon signed-rank test. In WT mice having normally grown fetuses, ^CaK_mf, per gram placenta near term, in the lightest placentas was increased (126%; P < 0.05) in association with reduced fetal calcium accretion earlier in gestation (92%; P < 0.05), that was subsequently normalized near term. Increased placental expression of calbindin-D_9K, an important calcium binding protein, was observed in the lightest placentas near term (122%; P < 0.01). There was no difference in fetal calcium accretion between male and female littermates but a trend toward higher ^CaK_mf in females (P = 0.055). These data suggest a small, normal placenta adapts calcium transfer according to its size, as previously demonstrated in a mouse model of FGR. Fetal sex had limited influence on this adaptive increase. These adaptations are potentially driven by fetal nutrient demand, as evidenced by the normalization of fetal calcium content. Understanding the regulatory mechanisms involved may provide novel avenues for treating placental dysfunction.

The Plasma Membrane Calcium ATPases and Their Role as Major New Players in Human Disease

The Ca²⁺ extrusion function of the four mammalian isoforms of the plasma membrane calcium ATPases (PMCAs) is well established. There is also ever-increasing detail known of their roles in global and local Ca²⁺ homeostasis and intracellular Ca²⁺ signaling in a wide variety of cell types and tissues. It is becoming clear that the spatiotemporal patterns of expression of the PMCAs and the fact that their abundances and relative expression levels vary from cell type to cell type both reflect and impact on their specific functions in these cells. Over recent years it has become increasingly apparent that these genes have potentially significant roles in human health and disease, with PMCAs1-4 being associated with cardiovascular diseases, deafness, autism, ataxia, adenoma, and malarial resistance. This review will bring together evidence of the variety of tissue-specific functions of PMCAs and will highlight the roles these genes play in regulating normal physiological functions and the considerable impact the genes have on human disease.

Bone development and mineral homeostasis in the fetus and neonate: roles of the calciotropic and phosphotropic hormones

Mineral and bone metabolism are regulated differently in utero compared with the adult. The fetal kidneys, intestines, and skeleton are not dominant sources of mineral supply for the fetus. Instead, the placenta meets the fetal need for mineral by actively transporting calcium, phosphorus, and magnesium from the maternal circulation. These minerals are maintained in the fetal circulation at higher concentrations than in the mother and normal adult, and such high levels appear necessary for the developing skeleton to accrete a normal amount of mineral by term. Parathyroid hormone (PTH) and calcitriol circulate at low concentrations in the fetal circulation. Fetal bone development and the regulation of serum minerals are critically dependent on PTH and PTH-related protein, but not vitamin D/calcitriol, fibroblast growth factor-23, calcitonin, or the sex steroids. After birth, the serum calcium falls and phosphorus rises before gradually reaching adult values over the subsequent 24-48 h. The intestines are the main source of mineral for the neonate, while the kidneys reabsorb mineral, and bone turnover contributes mineral to the circulation. This switch in the regulation of mineral homeostasis is triggered by loss of the placenta and a postnatal fall in serum calcium, and is followed in sequence by a rise in PTH and then an increase in calcitriol. Intestinal calcium absorption is initially a passive process facilitated by lactose, but later becomes active and calcitriol-dependent. However, calcitriol's role can be bypassed by increasing the calcium content of the diet, or by parenteral administration of calcium.

UNDERSTANDING THE PLACENTAL AETIOLOGY OF FETAL GROWTH RESTRICTION; COULD THIS LEAD TO PERSONALIZED MANAGEMENT STRATEGIES?

Fetal growth restriction (FGR) is defined as the failure of a fetus to attain its full genetic growth potential. It is a leading cause of stillbirth, prematurity, cerebral palsy and perinatal mortality. Small size at birth increases surviving infants’ lifelong risk of adverse health outcomes associated with the metabolic syndrome. The pathophysiology of abnormal fetal growth is extremely complex and incompletely understood, with a plethora of genetic, signalling and metabolic candidates under investigation, many of which may result in abnormal structure and function of the placenta. In contrast to, or maybe because of, the underlying complexities of FGR, the strategies clinicians have for identifying and managing this outcome are conspicuously limited. Current clinical practice is restricted to identifying pregnancies at risk of FGR, and when FGR is detected, using intensive monitoring to guide the timing of delivery to optimise fetal outcomes. Abnormal Doppler indices in the umbilical artery are strongly associated with poor perinatal outcomes and are currently the “gold standard” for clinical surveillance of the growth-restricted fetus.

Plasma membrane Ca(2+) ATPase Atp2b1a regulates bone mineralization in zebrafish

The zebrafish transgenic lines provide a possibility to observe the development of tissues and organs in real time. Using the reporter line for the zebrafish plasma membrane Ca(2+) ATPase (SqET4), we detected its expression in the epithelium of pharyngeal teeth and analyzed its role in their calcification and that of cranial bones. atp2b1a's expression in the pharyngeal epithelium is faithfully recapitulated in the SqET4 transgenics by GFP expression. We showed by morpholino knockdown of Atp2b1a translations as well as chemical inhibition of Atp2b1a pump activity using carboxyeosin, that its activity is required to facilitate calcification of the developing pharyngeal teeth by the dental epithelium. Atp2b1a could be required during calcification of endochondral bones, where it acts at two levels: 1) by exporting Ca(2+) from ameloblasts, it provides raw material for calcifying the pharyngeal teeth by adjacent odontoblasts; and 2) by regulating terminal differentiation of pharyngeal epithelial cells, including ameloblasts required for tissue hyper-mineralization. atp2b1a's expression in the pharyngeal epithelium is regulated by the homeodomain transcription factor dlx2b.

Regulation of nutrient transport across the placenta

Abnormal fetal growth, both growth restriction and overgrowth, is associated with perinatal complications and an increased risk of metabolic and cardiovascular disease later in life. Fetal growth is dependent on nutrient availability, which in turn is related to the capacity of the placenta to transport these nutrients. The activity of a range of nutrient transporters has been reported to be decreased in placentas of growth restricted fetuses, whereas at least some studies indicate that placental nutrient transport is upregulated in fetal overgrowth. These findings suggest that changes in placental nutrient transport may directly contribute to the development of abnormal fetal growth. Detailed information on the mechanisms by which placental nutrient transporters are regulated will therefore help us to better understand how important pregnancy complications develop and may provide a foundation for designing novel intervention strategies. In this paper we will focus on recent studies of regulatory mechanisms that modulate placental transport of amino acids, fatty acids, and glucose.

Placental adaptations to the maternal-fetal environment: implications for fetal growth and developmental programming

The placenta is a transient organ found in eutherian mammals that evolved primarily to provide nutrients for the developing fetus. The placenta exchanges a wide array of nutrients, endocrine signals, cytokines and growth factors with the mother and the fetus, thereby regulating intrauterine development. Recent studies show that the placenta is not just a passive organ mediating maternal-fetal exchange. It can adapt its capacity to supply nutrients in response to intrinsic and extrinsic variations in the maternal-fetal environment. These dynamic adaptations are thought to occur to maximize fetal growth and viability at birth in the prevailing conditions in utero. However, some of these adaptations may also affect the development of individual fetal tissues, with patho-physiological consequences long after birth. Here, this review summarizes current knowledge on the causes, possible mechanisms and consequences of placental adaptive responses, with a focus on the regulation of transporter-mediated processes for nutrients. This review also highlights the emerging roles that imprinted genes and epigenetic mechanisms of gene regulation may play in placental adaptations to the maternal-fetal environment.

ATP-mediated mineralization of MC3T3-E1 osteoblast cultures

While bone is hypomineralized in hypophosphatemia patients and in tissue-nonspecific alkaline phosphatase (Tnsalp)-deficient mice, the extensive mineralization that nevertheless occurs suggests involvement of other phosphatases in providing phosphate ions for mineral deposition. Although the source of phosphate liberated by these phosphatases is unknown, pyrophosphate, ATP, pyridoxal-5'-phosphate (PLP) and phoshoethanolamine (PEA) are likely candidates. In this study, we have induced mineralization of MC3T3-E1 osteoblast cultures using ATP, and have investigated potential phosphatases involved in this mineralization process. MC3T3-E1 osteoblasts were cultured for 12 days and treated either with beta-glycerophosphate (betaGP) or ATP. Matrix and mineral deposition was examined by biochemical, cytochemical, ultrastructural and X-ray microanalytical methods. ATP added at levels of 4-5 mM resulted in mineral deposition similar to that following conventional treatment with betaGP. Collagen levels were similarly normal in ATP-mineralized cultures and transmission electron microscopy and X-ray microanalysis confirmed hydroxyapatite mineral deposition along the collagen fibrils in the ECM. Phosphate release from 4 mM ATP into the medium was rapid and resulted in approximately twice the phosphate levels than after release from 10 mM betaGP. ATP treatment did not affect mineralization by altering the expression of mineral-regulating genes such as Enpp1, Ank, and Mgp, nor phosphatase genes indicating that ATP induces mineralization by serving as a phosphate source for mineral deposition. Levamisole, an inhibitor of TNSALP, completely blocked mineralization in betaGP-treated cultures, but had minor effects on ATP-mediated mineralization, indicating that other phosphatases such as plasma membrane Ca2+ transport ATPase 1 (PMCA1) and transglutaminase 2 (TG2) are contributing to ATP hydrolysis. To examine their involvement in ATP-mediated mineralization, the inhibitors cystamine (TG2 inhibitor) and ortho-vanadate (PMCA inhibitor) were added to the cultures - both inhibitors significantly reduced mineralization whereas suppression of the phosphate release by ortho-vanadate was minor comparing to other two inhibitors. The contribution of PMCA1 to mineralization may occur through pumping of calcium towards calcification sites and TG2 can likely act as an ATPase in the ECM. Unlike the GTPase activity of TG2, its ATPase function was resistant to calcium, demonstrating the potential for participation in ATP hydrolysis and mineral deposition within the ECM at elevated calcium concentrations.

Placental calcium transporter (PMCA3) gene expression predicts intrauterine bone mineral accrual

Evidence is accruing that environmental exposures during critical periods of early development induce persisting changes in skeletal growth, and alter fracture risk in later life. We have previously demonstrated that placental calcium transport, partly determined by maternal 25-(OH) vitamin D status, may underlie this phenomenon. However, the precise relationship between expression of calcium transport proteins in the human placenta, and neonatal bone mineral accrual in the offspring, remains unknown. Tissue samples from 70 human placentae were fast frozen in liquid nitrogen and stored at -70 degrees C. A quantitative real time reverse transcriptase polymerase chain reaction was used to measure the mRNA expression of PMCA isoforms 1-4, using beta-actin as a control gene. Neonatal whole body bone area, mineral content and areal density (BA, BMC, BMD) were measured within 2 weeks of birth using DXA. PMCA3 mRNA expression predicted BA (r=0.28, p=0.02), BMC (r=0.25, p=0.04), placental weight (r=0.26, p=0.04) and birth weight (r=0.33, p=0.006) of the neonate. In a multivariate model, the relationship between placental PMCA3 expression and neonatal BMC was independent of maternal height, pre-pregnant fat stores, parity, physical activity, smoking, and calcium intake (p<0.05). Expression of the placental calcium transporter PMCA3 mRNA predicts neonatal whole body bone mineral content. This association may explain, in part, the mechanism whereby a mother's 25(OH)-vitamin D stores influence her offspring's bone mass.

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.

A developmental profile of the levels of calcium pumps in chick cerebellum

The functional expression and distribution of intracellular ATPase (sarco(endo)plasmic reticulum Ca(2+)-ATPase: SERCA) and plasma membrane Ca(2+)-ATPase (PMCA) was analyzed in the developing chick cerebellum. The activity and Ca(2+) uptake increase with development for both ATPases. However, the protein content increases with the stage of development only for SERCA, remaining constant for PMCA. Immunohistochemical assays showed that the ontogenesis of these ATPases goes along with definite stages of cerebellum histogenesis, and is complete at hatching. The SERCA is mainly distributed in Purkinje neurons, whereas the PMCA seems to be expressed initially in climbing fibers, shifting to soma and spiny branchlets of Purkinje cells at late embryonic stages. Granule cells express both ATPases according to their degree of maturity, whereas only PMCA is present in cerebellar glomeruli. These pumps are present in deep nuclei and the choroid plexus, although in this latter tissue their expression declines with development. The spatio-temporal distribution of SERCA and PMCA must be closely related to their association with the development of specific cells and processes of the chick cerebellum.

Activity and expression of Na+/H+ exchanger isoforms in the syncytiotrophoblast of the human placenta

The purpose of this study was to compare Na+/H+ exchanger (NHE) activity in the microvillous (MVM) and basal (BM) plasma membrane of the human placental syncytiotrophoblast and to determine the relative contribution of various NHE isoforms to this activity. Uptake of 22Na into isolated MVM vesicles in the presence of a H+ gradient, at initial rate, was four- to fivefold higher than that by BM vesicles (214+/-28 vs. 49+/-9 pmol/mg protein per 30 s, respectively, means+/-SEM, n=8, 6, P<0.001). The 22Na uptake by MVM, but not by BM, was reduced in the absence of a H+ gradient and in the presence of 500 microM amiloride. To determine the contribution of NHE1, NHE2 and NHE3 isoforms to NHE activity in MVM, we investigated the effect of amiloride analogues which show isoform selectivity. HOE 694, an analogue selective for NHE1 at low concentrations, inhibited 22Na uptake with an EC50 of 0.13+/-0.05 microM (n=6), whereas S3226, an analogue selective for NHE3 at low concentrations had an EC50 of 3.01+/-0.85 microM (n=5). To investigate this further, we measured recovery of syncytiotrophoblast intracellular pH (pHi) from an acid load using a H+-selective, fluorescent dye (BCECF) loaded into isolated intact placental fragments. This recovery was blocked in the absence of Na+ and the presence of amiloride (500 microM) and concentrations of HOE 694 and S3226 were comparable to those used in vesicle experiments. Overall these data show that under the conditions used NHE activity in the term placental syncytiotrophoblast is absent from BM. NHE activity in the MVM is attributable predominantly to NHE1.

Calcium channels, transporters and exchangers in placenta: a review

Calcium (Ca2+) entry in cells is crucial for development and physiology of virtually all cell types. It acts as an intracellular (second) messenger to regulate a diverse array of cellular functions, from cell division and differentiation to cell death. Among candidates for Ca2+ entry in cells are-voltage-dependant Ca2+ channels (VDCCs), transient receptor potential (TRP)-related Ca2+ channels and store-operated Ca2+ (SOC) channels. Plasma membrane Ca2+-ATPases (PMCA) and Na+/Ca2+ exchanger (NCX) are mainly responsible for Ca2+ extrusion. These different Ca2+channels/transporters and exchangers exhibit specific distribution and physiological properties. During pregnancy, the syncytiotrophoblast layer of the human placenta transfers as much as 30 g of Ca2+ from the mother to the fetus, especially in late gestation where Ca2+ transport through different channels must increase in response to the demands of accelerating bone mineralization of the fetus. The identification and characterization of the different Ca2+ channels/transporters and exchangers on the brush-border membrane (BBM) facing the maternal circulation, and the basal plasma membrane (BPM) facing the fetal circulation; placental membrane of the syncytiotrophoblasts have been the focus of numerous studies. This review discusses current views in this field regarding localization and functions during transcellular Ca2+ entry and extrusion from cells particularly in the placenta.

Site-specific localization of two distinct phosphatases along the osteoblast plasma membrane: tissue non-specific alkaline phosphatase and plasma membrane calcium ATPase

In osteoblasts, alkaline phosphatase has been reported to be restricted to the basolateral domains. In recent studies, we have demonstrated phosphatase activities different from those of tissue non-specific alkaline phosphatase (TNSALP) along the osteoidal aspect of osteoblast membrane at alkaline and neutral pH on undecalcified freshly frozen sections of rat bones. In the present study, we sought to further characterize and define the nature of membrane-associated phosphatases along the osteoidal aspect of osteoblasts. Histochemical properties of the enzymes and their localization in vivo were examined in long bones of normal Wistar rats and TNSALP null mutant mice and their wild type littermates. Molecular profiles of the enzymes in the osteoblast extracts were also examined. The enzymatic activity of the phosphatase along the osteoidal surface of osteoblasts proved to be activated by both Mg2+ and Ca2+. Unlike TNSALP, the activity was inhibited by vanadate but resistant to levamisole, implicating a similarity between this enzyme and plasma membrane Ca2+ transport ATPase (PMCA). Immunohistochemistry showed that PMCA immunoreactions were restricted to the osteoidal domain of the plasma membrane. Native-PAGE analysis of osteoblast extracts suggested the presence of two phosphatases corresponding, respectively, to TNSALP and PMCA. Western blot analysis after SDS-PAGE of osteoblast extracts confirmed the existence of PMCA (140 kDa) and TNSALP (80 kDa). Gel-chemical analysis of the osteoblast extract from TNSALP null mutant mice depicted phosphatase activity, which was resistant to levamisole. These data suggest the presence of a phosphatase different from TNSALP, most plausibly PMCA, on the osteoidal surface of osteoblasts.

Expression and role of calcium-ATPase pump and sodium-calcium exchanger in differentiated trophoblasts from human term placenta

Although placental transfer of maternal calcium (Ca(2+)) is a crucial process for fetal development, the biochemical mechanisms are not completely elucidated. Especially, mechanisms of syncytiotrophoblast Ca(2+) extrusion into fetal circulation remain to be established. In the current study we have investigated the characteristics of Ca(2+) efflux in syncytiotrophoblast-like structure originating from the differentiation of cultured trophoblasts isolated from human term placenta. Time-courses of Ca(2+) uptake by differentiated human trophoblasts displayed rapid initial entry (initial velocity (V(i)) of 8.82 +/- 0.86 nmol/mg protein/min) and subsequent establishment of a plateau. Ca(2+) efflux studies with (45)Ca(2+)-loaded cells also showed rapid decline of cell-associated (45)Ca(2+) with a V(i) of efflux (V(ie)) of 8.90 +/- 0.96 nmol/mg protein/min. Expression of membrane systems responsible for intracellular Ca(2+) extrusion from differentiated human trophoblast were investigated by RT-PCR. Messenger RNAs of four known isoforms of PMCA (PMCA 1-4) were detected. Messenger RNAs of two cloned human NCX isoforms (NCX1 and NCX3) were also revealed. More specifically, both splice variants NCX1.3 and NCX1.4 were amplified by PCR with total RNA of differentiated human trophoblast cells. Ca(2+) flux studies in Na-free incubation medium indicated that NCX played a minimal role in the cell Ca(2+) fluxes. However, erythrosine B (inhibitor of PMCA) time- and dose-dependently increased cell associated (45)Ca(2+) suggesting a principal role of plasma membrane Ca(2+)-ATPase (PMCA) in the intracellular Ca(2+) extrusion of syncytiotrophoblast-like structure originating from the differentiation of cultured trophoblast cells isolated from human term placenta.

ATP dependent Ca2+ transport across basal membrane of human syncytiotrophoblast in pregnancies complicated by intrauterine growth restriction or diabetes

Neonates born after pregnancies complicated by diabetes or intrauterine growth restriction (IUGR) have increased incidence of hypocalcaemia. Furthermore, IUGR is associated with reduced bone mineralization in infancy and osteoporosis in adult life. We tested the hypothesis that placental calcium transport is altered in these pregnancy complications. Transport of calcium into syncytiotrophoblast basal plasma membrane (BM) vesicles was studied by rapid filtration and protein expression of Ca(2+) ATPase by Western blot. In IUGR Ca(2+) ATPase activity was increased by 48 per cent (n=13; P< 0.05) whereas protein expression was 15 per cent lower (n=13; P< 0.05) than in controls (n=16). Basal membrane ATP dependent calcium transport was unaltered in gestational diabetes (GDM) but increased by 54 per cent in insulin dependent diabetes (IDDM) compared to controls (P< 0.05; n =14). Diabetes did not affect Ca(2+) ATPase expression in BM. We have previously shown that the mid-molecular fragment of parathyroid hormone related peptide (PTHrP midmolecule) stimulates BM Ca(2+) ATPase in vitro. PTHrP midmolecule concentrations in umbilical cord plasma were measured using radioimmunoassay. The concentrations in umbilical cord plasma were increased in IUGR, but unaltered in diabetes. In conclusion, placental calcium pump is activated in IUGR and IDDM, which may be secondary to increased foetal calcium demand. We speculate that PTHrP midmolecule may be one mechanism for activating BM Ca(2+) ATPase in IUGR.

Localization of alkaline phosphatase and Ca2+-ATPase in the cat placenta

We localized alkaline phosphatase and plasma membrane calcium-ATPase (PMCA) in the cat placental syncytiotrophoblast to address their polarized distribution and their potential as markers for specific plasma membrane purification. We used enzyme- (alkaline phosphatase) and immuno- (PMCA) histochemistry and, for alkaline phosphatase, compared data to observations on the human placenta. Alkaline phosphatase activity in the cat was localized to the decidual cell membranes, to within the associated interstitial space and on the subjacent apical (maternal facing) plasma membrane of the syncytiotrophoblast. Occasional maternal capillaries were positive on their basal surface and there was focal staining within the syncytiotrophoblast. This widespread distribution is less specific than in the human placenta where alkaline phosphatase was restricted to the apical and basal plasma syncytiotrophoblast membranes, with much greater density on the apical membrane. Expression of PMCA in the cat was restricted to the basal membrane of the syncytiotrophoblast only. This specific localization of PMCA is identical to the human placenta and all other species in which its placental localization has been studied. We conclude that the plasma membranes of the cat syncytiotrophoblast show a broadly similar functional polarization to the human and that PMCA would prove a useful marker in isolation of the cat syncytiotrophoblast basal plasma membrane.

Calcium fluxes in human trophoblast (BeWo) cells: calcium channels, calcium-ATPase, and sodium-calcium exchanger expression

Although placental transfer of maternal calcium (Ca(2+)) is a crucial process for fetal development, the biochemical mechanisms are poorly understood. In the current study, we have investigated the characteristics of Ca(2+) fluxes in relation with cell Ca(2+) homeostasis in the human placental trophoblast cell line BeWo. Time-courses of Ca(2+) uptake by BeWo cells displayed rapid initial entry (initial velocity (V(i)) of 3.42 +/- 0.35 nmol/mg protein/min) and subsequent establishment of a plateau. Ca(2+) efflux studies with (45)Ca(2+)-loaded cells also showed rapid declined of cell-associated (45)Ca(2+) with a V(i) of efflux (Ve(i)) of 3.30 +/- 0.08 nmol/mg protein/min. Further identification of membrane gates for Ca(2+) entry in BeWo cells was carried out. Expression of Ca(2+) transporter/channel CaT1 and L-type alpha(1S) subunit was showed by RT-PCR. However, mRNA for CaT2 channel and L-type alpha(1C) and alpha(1D) subunits were not revealed. Membrane systems responsible for intracellular Ca(2+) extrusion from BeWo cells were also investigated. Plasma membrane Ca(2+)-ATPases (PMCA) and Na/Ca exchangers (NCX) were detected by Western blot in BeWo cells. Expression of specific isoforms of PMCA and NCX was further investigated by RT-PCR. Messenger RNAs of four isoforms of PMCA (PMCA 1-4) were detected. The presence of messenger RNAs of two NCX isoforms (NCX1 and NCX3) was observed. Ca(2+) flux studies in Na-free incubation medium indicated that NCX played a minimal role in the cell Ca(2+) fluxes. Inorganic ions such as cadmium and manganese did not modify the Ca(2+) fluxes, however, barium increased cell-associated (45)Ca(2+) by, in part, by reducing radiolabel exit.

Regulation of placental transfer: the Na(+)/H(+) exchanger--a review

This review article considers the purposes and mechanisms of regulation of placental transfer in general terms and then illustrates some key points with reference to the Na(+)/H(+) exchanger (NHE), a transport protein found in the syncytiotrophoblast. NHE probably has a role in the homeostasis of syncytiotrophoblast intracellular pH and may also be involved in syncytiotrophoblast cell volume regulation as well as H(+) loss from and Na(+) transfer to the fetus. The activity and expression of NHE in the microvillous plasma membrane of the syncytiotrophoblast is reduced in placentas from preterm, growth restricted babies as compared to their gestationally matched normally grown counterparts. There are differential effects of gestation in normal pregnancy on NHE mRNA, NHE protein and NHE activity. There is also evidence of acute modulation of NHE activity. Regulation of NHE in syncytiotrophoblast is therefore complex with control at transcription, post transcription and post translational loci.

L-type Ca2+ channels in fetal and adult ovine cerebral arteries

Recently, we reported that, whereas in cerebral arteries of the adult a majority of norepinephrine (NE)-induced increase in intracellular Ca2+ concentration ([Ca2+]i) comes from release of the sarcoplasmic reticulum (SR) Ca2+ stores, in the fetus the SR Ca2+ stores are relatively small, and NE-induced increase in [Ca2+]i results mainly from activation of plasma membrane L-type Ca2+ channels (20). In an effort to establish further the role of L-type Ca2+ channels in the developing cerebral arteries, we tested the hypothesis that, in the fetus, increased reliance on plasmalemmal L-type Ca2+ channels is mediated, in part, by increased L-type Ca2+ channel density. We used 3H-labeled (+)isopropyl-4-(2,1,3-benzoxadiazol-4-y1)-1,4-dihydro-(2,6-dimethyl-5-methoxycarbonyl)pyridine-3-carboxylate (PN200-110, isradipine) to measure L-type Ca2+ channel density (Bmax) in the cerebral arteries, common carotid artery (CCA), and descending aortae of fetal (approximately 140 gestation days), newborn (7-10 days), and adult sheep. In the cerebral and common carotid arteries, B(max) values (fmol/mg protein) of fetuses and newborns were significantly greater than those of adults. Western immunoblotting assay also revealed that the density of L-type Ca2+ channel protein in the cerebral arteries and CCA was about twofold greater in the fetus than the adult. Finally, compared with the adult, fetal cerebral arteries demonstrated a significantly greater maximum tension and [Ca2+]i in response to stimulation with the L-type Ca2+ channel agonist Bay K 8644. In addition, Bay K 8644-stimulated fetal vessels demonstrated a maximal tension and [Ca2+]i similar to that observed in response to stimulation with 10(-4) NE. These results support the idea that fetal cerebrovascular smooth muscle relies more on extracellular Ca2+ and L-type Ca2+ channels for contraction than does the adult and that this increased reliance is mediated, in part, by greater L-type Ca2+ channel density. This may have important implications in the regulation of cerebral blood flow in the developing organism.