Distinct Lipid Rafts in Subdomains from Human Placental Apical Syncytiotrophoblast Membranes

Sphingolipids and acylcarnitines are altered in placentas from women with gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is the most common medical complication of pregnancy and a severe threat to pregnant people and offspring health. The molecular origins of GDM, and in particular the placental responses, are not fully known. The present study aimed to perform a comprehensive characterisation of the lipid species in placentas from pregnancies complicated with GDM using high-resolution MS lipidomics, with a particular focus on sphingolipids and acylcarnitines in a semi-targeted approach. The results indicated that despite no major disruption in lipid metabolism, placentas from GDM pregnancies showed significant alterations in sphingolipids, mostly lower abundance of total ceramides. Additionally, very long-chain ceramides and sphingomyelins with twenty-four carbons were lower, and glucosylceramides with sixteen carbons were higher in placentas from GDM pregnancies. Semi-targeted lipidomics revealed the strong impact of GDM on the placental acylcarnitine profile, particularly lower contents of medium and long-chain fatty-acyl carnitine species. The lower contents of sphingolipids may affect the secretory function of the placenta, and lower contents of long-chain fatty acylcarnitines is suggestive of mitochondrial dysfunction. These alterations in placental lipid metabolism may have consequences for fetal growth and development.

Rafting on the Evidence for Lipid Raft-like Domains as Hubs Triggering Environmental Toxicants' Cellular Effects

The plasma membrane lipid rafts are cholesterol- and sphingolipid-enriched domains that allow regularly distributed, sub-micro-sized structures englobing proteins to compartmentalize cellular processes. These membrane domains can be highly heterogeneous and dynamic, functioning as signal transduction platforms that amplify the local concentrations and signaling of individual components. Moreover, they participate in cell signaling routes that are known to be important targets of environmental toxicants affecting cell redox status and calcium homeostasis, immune regulation, and hormonal functions. In this work, the evidence that plasma membrane raft-like domains operate as hubs for toxicants' cellular actions is discussed, and suggestions for future research are provided. Several studies address the insertion of pesticides and other organic pollutants into membranes, their accumulation in lipid rafts, or lipid rafts' disruption by polychlorinated biphenyls (PCBs), benzo[a]pyrene (B[a]P), and even metals/metalloids. In hepatocytes, macrophages, or neurons, B[a]P, airborne particulate matter, and other toxicants caused rafts' protein and lipid remodeling, oxidative changes, or amyloidogenesis. Different studies investigated the role of the invaginated lipid rafts present in endothelial cells in mediating the vascular inflammatory effects of PCBs. Furthermore, in vitro and in vivo data strongly implicate raft-localized NADPH oxidases, the aryl hydrocarbon receptor, caveolin-1, and protein kinases in the toxic mechanisms of occupational and environmental chemicals.

Antidepressants and Antipsychotics in Human Pregnancy: Transfer Across the Placenta and Opportunities for Modeling Studies

There is limited information about the transfer of antidepressants and antipsychotics across the human placenta. The objective of the current review was to systematically screen the scientific literature using relevant keywords to collect quantitative data on placental transfer of these drugs in humans and to give an overview of current modeling approaches used in this context. The collected data encompassed clinically measured fetal:maternal (F:M) concentration ratios (ie, the ratio between drug concentrations measured in the umbilical cord and drug concentrations measured in the mother) and transfer data obtained from ex vivo cotyledon perfusion experiments. These data were found for 18 antidepressants and some of their pharmacologically active metabolites, and for 10 antipsychotics and the metabolites thereof. Based on the collected data, similar maternal and fetal exposure could be observed for only a few compounds (eg, norfluoxetine and desvenlafaxine), whereas for most drugs (eg, paroxetine, sertraline, and quetiapine), fetal exposure appeared to be on average lower than maternal exposure. Venlafaxine appeared to be an exception in that the data indicated equivalent or higher concentrations in the umbilical cord than in the mother. Physiologically based pharmacokinetic (PBPK) models were sporadically used to investigate maternal pharmacokinetics of antidepressants or antipsychotics (eg, for sertraline, aripiprazole, and olanzapine), although without explicitly addressing fetal drug exposure. It is recommended that PBPK modeling is applied more frequently to these drugs. Although no substitute for clinical studies, these tools can help to better understand pregnancy-induced pharmacokinetic changes and ultimately contribute to a more evidence-based pharmacotherapy of depression and psychosis in pregnant subjects.

Effects of Gangliosides on Spermatozoa, Oocytes, and Preimplantation Embryos

Gangliosides are sialic acid-containing glycosphingolipids, which are the most abundant family of glycolipids in eukaryotes. Gangliosides have been suggested to be important lipid molecules required for the control of cellular procedures, such as cell differentiation, proliferation, and signaling. GD1a is expressed in interstitial cells during ovarian maturation in mice and exogenous GD1a is important to oocyte maturation, monospermic fertilization, and embryonic development. In this context, GM1 is known to influence signaling pathways in cells and is important in sperm-oocyte interactions and sperm maturation processes, such as capacitation. GM3 is expressed in the vertebrate oocyte cytoplasm, and exogenously added GM3 induces apoptosis and DNA injury during in vitro oocyte maturation and embryogenesis. As a consequence of this, ganglioside GT1b and GM1 decrease DNA fragmentation and act as H2O2 inhibitors on germ cells and preimplantation embryos. This review describes the functional roles of gangliosides in spermatozoa, oocytes, and early embryonic development.

A Single Sphingomyelin Species Promotes Exosomal Release of Endoglin into the Maternal Circulation in Preeclampsia

Preeclampsia (PE), an hypertensive disorder of pregnancy, exhibits increased circulating levels of a short form of the auxillary TGF-beta (TGFB) receptor endoglin (sENG). Until now, its release and functionality in PE remains poorly understood. Here we show that ENG selectively interacts with sphingomyelin(SM)-18:0 which promotes its clustering with metalloproteinase 14 (MMP14) in SM-18:0 enriched lipid rafts of the apical syncytial membranes from PE placenta where ENG is cleaved by MMP14 into sENG. The SM-18:0 enriched lipid rafts also contain type 1 and 2 TGFB receptors (TGFBR1 and TGFBR2), but not soluble fms-like tyrosine kinase 1 (sFLT1), another protein secreted in excess in the circulation of women with PE. The truncated ENG is then released into the maternal circulation via SM-18:0 enriched exosomes together with TGFBR1 and 2. Such an exosomal TGFB receptor complex could be functionally active and block the vascular effects of TGFB in the circulation of PE women.

Changes of placental syndecan-1 expression in preeclampsia and HELLP syndrome

Preeclampsia is characterized by maternal systemic anti-angiogenic and pro-inflammatory states. Syndecan-1 is a cell surface proteoglycan expressed by the syncytiotrophoblast, which plays an important role in angiogenesis and resolution of inflammation. Our aim was to examine placental syndecan-1 expression in preeclampsia with or without hemolysis, elevated liver enzymes, and low platelet count (HELLP) syndrome. Placentas were obtained from women in the following groups: (1) late-onset preeclampsia (n = 8); (2) early-onset preeclampsia without (n = 7) and (3) with HELLP syndrome (n = 8); (4) preterm controls (n = 5); and (5) term controls (n = 9). Tissue microarrays (TMAs) were constructed from paraffin-embedded placentas. TMA slides were immunostained for syndecan-1 and evaluated using microscopy, virtual microscopy, and semi-automated image analysis. Maternal sera from patients with preeclampsia (n = 49) and controls (n = 32) were immunoassayed for syndecan-1. BeWo cells were treated with Forskolin or Latrunculin B or kept in ischemic conditions. SDC1 expression and syndecan-1 production were investigated with qRT-PCR, confocal microscopy, and immunoassays. Syndecan-1 was localized to the syncytiotrophoblast apical membrane in normal placentas. Syndecan-1 immunoscores were higher in late-onset preeclampsia (p = 0.0001) and early-onset preeclampsia with or without HELLP syndrome (p = 0.02 for both) than in controls. Maternal serum syndecan-1 concentration was lower in preeclampsia (median, 673 ng/ml; interquartile range, 459-1,161 ng/ml) than in controls (1,158 ng/ml; 622-1,480 ng/ml). SDC1 expression and syndecan-1 immunostainings in BeWo cells and syndecan-1 concentrations in supernatants increased during cell differentiation. Disruption of the actin cytoskeleton with Latrunculin B decreased syndecan-1 release, while ischemic conditions increased it. Syncytiotrophoblastic syndecan-1 expression depends on the differentiation of villous trophoblasts, and trophoblastic syndecan-1 release is decreased in preeclampsia and HELLP syndrome. This phenomenon may be related to the disturbed syncytiotrophoblastic cortical actin cytoskeleton and associated with maternal anti-angiogenic and pro-inflammatory states in these syndromes.

Lipid raft- and SRC family kinase-dependent entry of coxsackievirus B into human placental trophoblasts

Maternal-fetal transmission of group B coxsackieviruses (CVB) during pregnancy has been associated with a number of diverse pathological outcomes, including hydrops fetalis, fetal myocarditis, meningoencephalitis, neurodevelopmental delays, congenital skin lesions, miscarriage, and/or stillbirth. Throughout pregnancy, the placenta forms a critical antimicrobial protective barrier at the maternal-fetal interface. Despite the severity of diseases accompanying fetal CVB infections, little is known regarding the strategies used by CVB to gain entry into placental trophoblasts. Here we used both a trophoblast cell line and primary human trophoblasts to demonstrate the mechanism by which CVB gains entry into polarized placental trophoblasts. Our studies revealed that the kinetics of CVB entry into placental trophoblasts are similar to those previously described for polarized intestinal epithelial cells. Likewise, CVB entry into placental trophoblasts requires decay-accelerating factor (DAF) binding and involves relocalization of the virus from the apical surface to intercellular tight junctions. In contrast, we have identified a divergent mechanism for CVB entry into polarized trophoblasts that is clathrin, caveolin-1, and dynamin II independent but requires intact lipid rafts. In addition, we found that members of the Src family of tyrosine kinases were required for CVB entry. Our studies highlight the complexity of viral entry into human placental trophoblasts and may serve as a model for mechanisms used by diverse pathogens to penetrate the placental barrier.

Annexins as organizers of cholesterol- and sphingomyelin-enriched membrane microdomains in Niemann-Pick type C disease

Growing evidence suggests that membrane microdomains enriched in cholesterol and sphingomyelin are sites for numerous cellular processes, including signaling, vesicular transport, interaction with pathogens, and viral infection, etc. Recently some members of the annexin family of conserved calcium and membrane-binding proteins have been recognized as cholesterol-interacting molecules and suggested to play a role in the formation, stabilization, and dynamics of membrane microdomains to affect membrane lateral organization and to attract other proteins and signaling molecules onto their territory. Furthermore, annexins were implicated in the interactions between cytosolic and membrane molecules, in the turnover and storage of cholesterol and in various signaling pathways. In this review, we focus on the mechanisms of interaction of annexins with lipid microdomains and the role of annexins in membrane microdomains dynamics including possible participation of the domain-associated forms of annexins in the etiology of human lysosomal storage disease called Niemann-Pick type C disease, related to the abnormal storage of cholesterol in the lysosome-like intracellular compartment. The involvement of annexins and cholesterol/sphingomyelin-enriched membrane microdomains in other pathologies including cardiac dysfunctions, neurodegenerative diseases, obesity, diabetes mellitus, and cancer is likely, but is not supported by substantial experimental observations, and therefore awaits further clarification.

Differential expression of potassium channels in placentas from normal and pathological pregnancies: targeting of the K(ir) 2.1 channel to lipid rafts

Potassium channels play important physiological roles in human syncytiotrophoblasts (hSTBs) from placenta, an epithelium responsible for maternal-fetal exchange. Basal and apical plasma membranes differ in their lipid and protein composition, and the latter contains cholesterol-enriched microdomains. In placental tissue, the specific localization of potassium channels is unknown. Previously, we described two isolated subdomains from the apical membrane (MVM and LMVM) and their respective microdomains (lipid rafts). Here, we report on the distribution of K(ir)2.1, K(v)2.1, TASK-1, and TREK-1 in hSTB membranes and the lipid rafts that segregate them. Immunoblotting experiments showed that these channels are present mainly in the apical membrane from healthy hSTBs. Apical expression versus basal membrane was 84 and 16% for K(ir)2.1 and K(v)2.1, 60 and 30% for TREK-1, and 74 and 26% for TASK-1. Interestingly, K(v)2.1 showed differences between apical membrane subdomains: 26 ± 8% was located in the LMVM and 59 ± 9% in MVM. In pathological placentas, the expression distribution changed in the basal membrane: preeclampsia shifted to 50% and intrauterine growth restriction to 42% for TASK-1 and both pathologies increased to 25% for K(ir)2.1 and K(v)2.1, K(ir)2.1 appeared to be associated with rafts that were sensitive to cholesterol depletion in healthy, but not in pathological, placentas. K(v)2.1 and TREK-1 emerged in the nonraft fractions. The precise membrane localization of ion channels in hSTB membranes is necessary to understand the physiological events.

Expression and distribution of nucleoside transporter proteins in the human syncytiotrophoblast

The plasma membrane distribution and related biological activity of nucleoside transporter proteins (NTs) were investigated in human syncytiotrophoblast from term placenta using a variety of approaches, including nucleoside uptake measurements into vesicles from selected plasma membrane domains, NT immunohistochemistry, and subcellular localization (basal, heavy, and light apical membranes as well as raft-enriched membranes from the apical domain). In contrast with other epithelia, in this epithelium, we have identified the high-affinity pyrimidine-preferring human concentrative nucleoside transporter (hCNT) 1 as the only hCNT-type protein expressed at both the basal and apical membranes. hCNT1 localization in lipid rafts is also dependent on its subcellular localization in the apical plasma membrane, suggesting a complex cellular and regional expression. Overall, this result favors the view that the placenta is a pyrimidine-preferring nucleoside sink from both maternal and fetal sides, and hCNT1 plays a major role in promoting pyrimidine salvage and placental growth. This finding may be of pharmacological relevance, because hCNT1 is known to interact with anticancer nucleoside-derived drugs and other molecules, such as nicotine and caffeine, for which a great variety of harmful effects on placental and fetal development, including intrauterine growth retardation, have been reported.

Placental protein 13 (PP13/galectin-13) undergoes lipid raft-associated subcellular redistribution in the syncytiotrophoblast in preterm preeclampsia and HELLP syndrome

OBJECTIVE

To investigate placental protein 13 (PP13) localization in relation to cytoskeleton and lipid rafts in preeclampsia and HELLP syndrome.

STUDY DESIGN

Placental cryosections from patients with preeclampsia and HELLP, and controls were stained for PP13, actin, PLAP (lipid raft marker), and CD71 (nonraft marker). BeWo cells exposed to stress conditions were stained for PP13 and actin. Protein localizations were investigated by confocal microscopy, PP13 concentrations by ELISA.

RESULTS

PP13-actin colocalization was increased in syncytiotrophoblast juxtamembrane regions in term/preterm preeclampsia and HELLP. PP13-CD71 colocalization was decreased and PP13-PLAP proximity was increased in preterm but not term preeclampsia and HELLP. PP13-release from BeWo cells was inhibited by cytoskeleton disruption, and augmented by Ca2+-influx and ischemic stress.

CONCLUSION

The actin cytoskeleton, probably in connection with lipid rafts, controls trophoblastic "nonclassical" PP13 export. PP13 is released from the syncytiotrophoblast in preterm preeclampsia and HELLP, mimicked in BeWo cells by ischemic stress, suggesting PP13 is a placental alarmin.

Lipid rafts and cytoskeletal proteins in placental microvilli membranes from preeclamptic and IUGR pregnancies

Intrauterine growth restriction (IUGR) and preeclampsia (PE) are leading causes of perinatal and maternal morbidity and mortality. Previously we reported the expression of lipid rafts in classical microvillous membrane (MVM) and light microvillous membrane (LMVM), two subdomains in apical membrane from the human placental syncytiotrophoblast (hSTB), which constitute the epithelium responsible for maternal-fetal transport. Here the aim was to study the raft and cytoskeletal proteins from PE and IUGR. Microdomains from MVM and LMVM were tested with raft markers (placental alkaline phosphatase, lipid ganglioside, and annexin 2) and a nonraft marker (hTf-R). No changes were detected with those markers in whole purified apical membranes in normal, PE, and IUGR pregnancies; however, their patterns of distribution in lipid rafts were different in PE and IUGR. Cholesterol depletion modified their segregation, confirming their presence in lipid rafts, although unlike normal placenta, in these pathologies there is only one type of microdomain. Additionally, the cytoskeleton proteins actin, ezrin, and cytokeratin-7 showed clear differences between normal and pathological membranes. Cytokeratin-7 expression decreased to 50% in PE, and the distribution between LMVM and MVM (~43 and 57%, respectively) changed in both PE and IUGR, in contrast with the asymmetrical enrichment obtained in normal LMVM (~62%). In conclusion, lipid rafts from IUGR and PE have different features compared to rafts from normal placentae, and this is associated with alterations in the expression and distribution of cytoskeletal proteins.

Review: Placental syncytiotrophoblast membranes--domains, subdomains and microdomains

Human placental syncytiotrophoblast (STB) is an epithelium responsible for materno-fetal exchange. Ions play multiple roles in STB, as in other transport epithelia. We have been interested in the character and functional expression of ion channels in STB membrane fractions. Characterization of ion channels and their relationship with different domains, subdomains and microdomains of STB membranes is important to explain the intracellular mechanisms operating in the placental barrier. The aim of this paper is to summarize our work on this subject. We isolated and purified basal membrane (BM) and two fractions from the apical membrane, a classical fraction (MVM) and a light fraction (LMVM). They were used either for reconstitution into giant liposomes or for transplantation into Xenopus oocyte membranes followed by electrophysiological recordings to characterize chloride and cationic channels in STB from term human placenta. In addition, Western blot analysis, using ion channel antibodies, was performed on purified apical and basal membrane fractions. We also reported the presence of two functional microdomains (lipid rafts) in LMVM and MVM, using detergent resistant membranes (DRMs) and cholesterol-sensitive depletion. Moreover we found evidence of cytoskeletal participation in lipid rafts of different composition. Our results contribute to knowledge of the ion channels present in STB membranes and their participation in the physiology of this epithelium in normal and pathological pregnancies.

Placental chloride channels: a review

The human placental syncytiotrophoblast (hSTB) is a polarized epithelial structure, that forms the main barrier to materno-fetal exchange. The chloride (Cl(-)) channels in other epithelial tissues contribute to several functions, such as maintenance of the membrane potential, volume regulation, absorption and secretion. Additionally, the contributions of Cl(-) channels to these functions are demonstrated by certain diseases and knock-out animal models. There are multiple lines of evidence for the presence of Cl(-) channels in the hSTB, which could contribute to different placental functions. However, both the mechanism by which these channels are involved in the physiology of the placenta, and their molecular identities are still unclear. Furthermore, a correlation between altered Cl(-) channels functions and pathological pregnancies is beginning to emerge. This review summarizes recent developments on conductive placental chloride transport, and discusses its potential implications for placental physiology.