help button home button Endocrine Society JCEM
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Submit a related Letter to the Editor
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Copyright Permission
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Bourgeois, C.
Right arrow Articles by Ferré, F.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Bourgeois, C.
Right arrow Articles by Ferré, F.
The Journal of Clinical Endocrinology & Metabolism Vol. 82, No. 9 3116-3123
Copyright © 1997 by The Endocrine Society


Original Studies

Endothelin-1 and ETA Receptor Expression in Vascular Smooth Muscle Cells from Human Placenta: A New ETA Receptor Messenger Ribonucleic Acid Is Generated by Alternative Splicing of Exon 31

Christelle Bourgeois, Brigitte Robert, Régis Rebourcet, Françoise Mondon, Thérese-Marie Mignot, Paulette Duc-Goiran and Françoise Ferré

INSERM U-361, Université René-Descartes, Maternité Baudelocque, 75014 Paris, France

Address all correspondence and requests for reprints to: Dr. C. Bourgeois, INSERM U-361, Maternité Baudelocque, 123 boulevard de Port-Royal, 75014 Paris, France. E-mail: u361{at}cochin.inserm.fr


    Abstract
 Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Endothelin-1 (ET-1) is a potent vasoactive peptide in stem villi vessels, which are considered to be the major sites of placental vascular resistance. To investigate the influence of pregnancy-specific hormonal environment on ET and ET receptor (ET-R) expression, we first developed and characterized a culture of vascular smooth muscle cells from stem villi vessels. Secondly, we investigated whether the muscular layer of stem villi vessels could be a site of the ET expression described in the placenta, and we examined this expression in placental vascular smooth muscle cells (PVSMCs). Prepro-ET-1 and prepro-ET-3 messenger ribonucleic acid (mRNA) were identified in stem villi vessels, whereas only prepro-ET-1 mRNA was observed in PVSMCs. Third, with the goal of using PVSMCs as ET target cells, we characterized the ET-R expressed by these cells in comparison with the muscular layer of stem villi vessels. Whereas both ETA-R and ETB-R are present in stem villi vessels, we found that PVSMCs express exclusively ETA-R. In addition to the previously reported ETA-R spliced transcripts, we described a new ETA-R transcript, ETA-R{Delta}3, generated by exclusion of exon 3 in stem villi vessels and PVSMCs. Alternative splicing mechanisms of ETA-R mRNA could constitute a control of the abundance of active ETA-R in terms of contractility. PVSMCs will be a useful model to study the environmental stimuli involved in the regulation of ET and ET-R expression in the muscular layer of feto-placental vasculature.


    Introduction
 Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 
DURING pregnancy, a progressive decrease in the feto-placental vascular resistance normally occurs, leading to an increase in the blood flow necessary for healthy growth of the feto-placental unit. However, the mechanisms by which the changes in vascular resistance take place are poorly understood. As the human placenta lacks autonomous innervation, its vascular tone is under the control of circulating or locally released vasoactive substances such as endothelins (ET) (for review, see 1 . The human placenta appears to largely contribute to the release of immunoreactive ET (2, 3, 4, 5). Moreover, it has been shown that ET-1 is a potent vasoconstrictor of the human feto-placental vasculature and has the potential to influence placental blood flow either directly or in concert with other vasoactive agents (6, 7, 8). The presence of ET-1 high affinity binding sites in the vasculature of human placenta (9, 10) together with the establishment of ET vasoactive and growth properties led to the postulation that ETs might be involved in regulation of the development of feto-placental vascularization throughout pregnancy and in modulation of its tone in an autocrine/paracrine way.

ETs are a family of peptides (ET-1, ET-2, and ET-3) (for review, see 11 . Each of them is encoded by distinct genes from which peptidic precursors, the prepro-ETs (prepro-ET), are raised and subsequently cleaved to give the biologically active forms of ETs. Their receptors, ETA-R and ETB-R, belong to the superfamily of G protein-coupled receptors. The ETA subtype is selective for ET-1 and ET-2 compared to ET-3, whereas the ETB subtype is unable to distinguish among these three peptides.

In placental stem villi vessels, which are the major sites of placental vascular resistance, ET-1 exerts a direct vasoconstrictive effect on the smooth muscle layer of this vessels (8). To later investigate the influence of pregnancy-specific hormonal environment on the phenotype of the smooth muscle cells from these vessels and particularly on the regulation of ET and ET-R expression, we needed a model of isolated smooth muscle cells from stem villi vessels. In the present study, we aimed first to establish and characterize a culture of placental vascular smooth muscle cells (PVSMCs). Secondly, we investigated whether the muscular layer of stem villi vessels could itself be a site of ET production and examined this expression in PVSMCs. Finally, with the goal of using PVSMCs as ET target cells, we characterized the ET-R expressed by these cells compared with the tissue of origin, the smooth muscle layer of stem villi vessels from human term placenta.


    Materials and Methods
 Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Placenta

Human placentas were obtained aseptically, immediately after elective cesarean section, from healthy mothers in the 39th week of pregnancy. The cesarean sections, carried out before the onset of labor, were performed because of earlier diagnosed cephalopelvic disproportion.

Cell culture

Vascular smooth muscle cells were obtained by the explant method with minor modifications of the technique described by Libby and O’Brien (12). Briefly, immediately after elective cesarean section, placental tissue (1–2 cm3) was swiftly removed from between the decidual and chorionic plates and immersed in sterile ice-cold Kreb’s solution (120 mmol/L NaCl, 5.7 mmol/L KCl, 2.5 mmol/L CaCl2, 1.2 mmol/L NaH2PO4, 1.2 mmol/L MgCl2, 15.5 mmol/L NaHCO3, and 11.5 mmol/L glucose, pH 7.4). Branches of stem villi vessels (~200–300 µm of mean internal diameter) were dissected by fine scratching so that the surrounding trophoblast, stroma, adventitia, and endothelial cells were removed. They were then cut in pieces and thoroughly washed under gentle magnetic agitation in 20 mmol/L Tris-HCl, pH 7.4, containing 5 mmol/L L-leucine methyl ester (a lysosomotropic compound that causes human monocyte death) (13) and used for ribonucleic acid (RNA) extraction or for culture. Before placement in culture, vessels were rinsed in DMEM supplemented with 10% (vol/vol) FCS and 0.1% penicillin/streptomycin (Life Technologies, Cergy-Ponroise, France). Finely cut pieces of placental vascular smooth muscle (1–2 mm3) were then placed in 6-cm petri dishes (Costar, D. Dutscher, France) and covered with one drop each of FCS. The dishes were kept at 37 C in a humidified atmosphere of 5% CO2-95% air. The following day, one drop of DMEM containing 10% FCS was added to each explant. At 5 and 15 days of culture, 2 mL DMEM containing 10% FCS were added to each dish. After 25–30 days, the dishes contained homogeneous layers of cells, which were then subcultured. Cells were harvested with trypsin-ethylenediaminotetraacetic acid, plated at 106 cells/75-cm2 flask, and grown to confluence in DMEM supplemented with 10% FCS. Cells were studied from the second to the sixth passage.

Cell cultures were tested by reverse transcription-PCR (RT-PCR) for the expression of CD45 antigen messenger RNA (mRNA), a marker of lympho-monocyte strain cells, and also for the expression of the von Willebrand factor mRNA, a marker of endothelial cells (see Table 1Go for oligonucleotide sequence of primers).


View this table:
[in this window]
[in a new window]
 
Table 1. Oligonucleotide sequences of primers and probes

 
Immunocytochemistry

Cells grown to confluence in 24-well plates were rinsed twice with phosphate-buffered saline (PBS) and fixed with 50% ethanol-acetone (vol/vol) solution at -20 C for 3 min. After rehydration in PBS for 20 min and blocking of nonspecific antigenic sites by PBS containing 1.5% horse serum for 20 min, cells were incubated overnight with a monoclonal antibody against smooth muscle {alpha}-actin, diluted at 1:20 in PBS containing 1.5% horse serum (Novocastra, Newcastle, UK). Immunoreactions were detected using a second biotinylated antibody and the biotin/avidin-peroxidase/diaminobenzidine-Ni system (Elite ABC and Vectastain kits, Vector, Biosys, France) according to the manufacturer’s instructions.

RNA preparation and RT

Total RNA was extracted from vascular smooth muscle cells and stem villi vessels using a Quick II kit (Bioprobe, Montreuil, France). Total RNA from placental villi and trophoblast was obtained according to the method of Chomczynski and Sacchi (14). Human fibroblast (FS-4) RNA was prepared as previously described (15), and human lung RNA was obtained from Clontech (Ozyme, France). RT was performed as previously described (4) with 2 or 5 µg total RNA, using random hexanucleotides as primers and 200 U Moloney murine leukemia virus reverse transcriptase (Life Technologies) in a final volume of 25 µL at 37 C for 60 min.

PCR

The PCR reaction was performed as previously described (4). Briefly, 5 or 10 µL of the RT reaction were subjected to amplification in the presence of forward and reverse external oligonucleotide primers (0.4 µmol/L each), deoxynucleotides (0.4 µmol/L each), and 1 U Taq polymerase (Life Technologies) for typically 32 cycles in a DNA thermal cycler (PHC-3 Dri-Black Cycler, Techné, Cambridge, UK). Forward and reverse external oligonucleotides were designed to localize in separate exons and in the least homologous regions (Table 1Go). The specificity of each amplification product was checked by Southern blot analysis as previously described (4), except for the hybridization, which was performed with an internal oligonucleotide labeled with fluorescein-11-deoxy-UTP using an ECL 3' oligolabeling and detection system kit (Amersham, France) according to the manufacturer’s instructions.

Sequencing

After electrophoresis of the PCR product and ethidium bromide staining, the resulting DNA band was excised from the gel, treated with phenol-chloroform, and ethanol precipitated. The sequencing of the DNA template was performed in Genethon Laboratory (Evry, France) using the PRISM Ready Reaction Dye Deoxy Terminator Cycle Sequencing Kit (Perkin-Elmer, Norwalk, CT).

Binding assay

Cell plasma membrane preparations and binding studies were performed as previously described (16). Briefly, aliquots of membranes (10 µg protein) were incubated for 60 min at 30 C in the presence of 5–300 pmol/L [125I]ET-1 (Amersham) for saturation analysis or in the presence of 50 pmol/L for competition studies. Specific binding of [125I]ET-1 was defined as total binding minus binding not displaced by 1 µmol/L unlabeled ET-1. At ligand concentrations near the dissociation constant (Kd), nonspecific binding was less than 30% of total binding for [125I]ET-1.

Competition experiments were carried out using a fixed concentration of [125I]ET-1 (50 pmol/L) with increasing concentrations of competing agents (Neosystem, Strasbourg, France).

All binding assays were performed at protein concentrations within the linear range. The inhibition constant (Ki) was calculated by the equation of Cheng and Prusoff (17), and Kd was determined by Scatchard analysis. Radioligand binding data were analyzed using the Inplot Computer program (GraphPad Software, San Diego, CA). The protein concentration was determined by the method of Lowry, using BSA as standard.


    Results
 Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Culture of placental vascular smooth muscle cells

Morphology. About 10 days after the explants of placental stem villi vessels attached to the plate, PVSMCs began to migrate away from the explants (Fig. 1AGo). PVSMCs formed a continuous circular sheet around the explants after 3–4 weeks of culture. Then, these cells were treated with trypsin and subcultured in the presence of 10% FCS. They became confluent in 8–9 days. At confluence, they were spindle shaped and exhibited a "hills and valleys" appearance (Fig. 1BGo).



View larger version (146K):
[in this window]
[in a new window]
 
Figure 1. Morphology and characterization of PVSMCs in culture. A, PVSMCs migrating away from the explant 10 days after the explants have attached to the plate (phase contrast; magnification, x100). B, Confluent subculture of PVSMCs showing the hills and valleys pattern characteristic of smooth muscle cells (magnification, x10). C, PVSMCs at confluence, labeled with an antibody against smooth muscle {alpha}-actin used at a 1:20 dilution. Antigen-antibody complexes were revealed using a biotinylated antibody and the biotin/avidin-peroxidase/diamino benzidine-Ni system (magnification, x10). D, Negative control of the immunoreaction. No staining was observed in absence of antismooth muscle {alpha}-actin antibody (magnification, x10).

 
Smooth muscle contractile proteins. PVSMCs were characterized for the expression of smooth muscle {alpha}-actin and smooth muscle myosin heavy chains (MHCs).

Smooth muscle {alpha}-actin: Immunocytochemical studies using an antibody against smooth muscle {alpha}-actin resulted in the staining of long longitudinal filaments throughout the cytoplasm of confluent PVSMCs (Fig. 1CGo). No staining was obtained when the same cells were incubated with the secondary antibody alone, thus assessing the specificity of the labeling (Fig. 1DGo).

MHCs: Smooth muscle MHC isoforms (SM1 and SM2) arise by alternative RNA splicing from a single gene, SM-MHC. Inclusion of a 39-nucleotide stretch generates SM2, and its exclusion produces SM1 (27). The expression of smooth muscle MHC isoform mRNAs was investigated in confluent PVSMCs and placental stem villi vessels by RT-PCR, using external oligonucleotides specific for SM1 and SM2 mRNA sequences. When the resulting complementary DNA (cDNA) fragments were analyzed by electrophoresis and ethidium bromide staining of the agarose gel, two products of the predicted size (426 bp for SM2 and 387 bp for SM1) were obtained in placental stem villi vessels (Fig. 2Go, lane 3), whereas only the 387-bp fragment could be detected in PVSMCs (Fig. 2Go, lane 1). No amplification product was observed when reverse transcriptase was omitted (Fig. 2Go, lane 2). However, after Southern blotting of RT-PCR products and hybridization with an SM2-specific internal oligonucleotide, a cDNA fragment (426 bp) corresponding to SM2 was labeled in PVSMCs (Fig. 2Go, lane 4) as well as in placental stem villi vessels (Fig. 2Go, lane 5). No amplification product was observed in human fibroblasts (Fig. 2Go, lane 6). In PVSMCs, we also checked the absence of von Willebrand factor and CD45 antigen expression, which are markers of endothelial and lympho-monocyte strain cells, respectively (data not shown).



View larger version (50K):
[in this window]
[in a new window]
 
Figure 2. Expression of smooth muscle MHC isoforms (SM1 and SM2) analyzed by RT-PCR in PVSMCs, stem villi vessels, and human fibroblasts. The RT products were amplified for 34 cycles (1 cycle: 1 min at 94 C, 1 min at 56.9 C, and 2 min at 72 C). Lanes 1–3, Ethidium bromide-stained gel. Reverse transcriptase was added (lanes 1 and 3) or omitted (lane 2). Lanes 4–6, Southern blot analysis of RT-PCR products, probed with fluorescein-labeled forward internal SM2 oligonucleotide.

 
mRNA expression of prepro-ETs

Prepro-ET-1. The expression of the ET-1 gene was investigated in total RNA prepared from confluent PVSMCs, stem villi vessels, and human lung, used as a positive control. After RT-PCR amplification using external oligonucleotides specific for the prepro-ET-1 sequence, a product of the predicted size (442 bp) was obtained in the positive control human lung (Fig. 3AGo, lane 1), in stem villi vessels (Fig. 3AGo, lane 2), and in PVSMCs (Fig. 3AGo, lane 4), as revealed by ethidium bromide staining after agarose gel electrophoresis. No amplification product was observed when reverse transcriptase was omitted (Fig. 3AGo, lane 3). After Southern blotting and hybridization with an internal prepro-ET-1-specific oligonucleotide, the 442-bp amplification products from human lung (Fig. 3AGo, lane 5), stem villi vessels (Fig. 3AGo, lane 6), and PVSMCs (Fig. 3AGo, lane 7) were labeled.



View larger version (35K):
[in this window]
[in a new window]
 
Figure 3. Expression of prepro-ET isoform mRNA analyzed by RT-PCR in PVSMCs, stem villi vessels, and positive controls, human lung and trophoblast. A, Prepro-ET-1 mRNA expression. The RT products were amplified for 30 cycles (1 cycle: 2 min at 92 C, 1 min at 51.7 C, and 2 min at 72 C). Lanes 1–4, Ethidium bromide-stained gel. Reverse transcriptase was added (lanes 1, 2, and 4) or omitted (lane 3). Lanes 5–7, Southern blot analysis of the RT-PCR products probed with a fluorescein-labeled reverse internal prepro-ET-1 oligonucleotide. B, Prepro-ET-2 mRNA expression. The RT products were amplified for 32 cycles (1 cycle: 2 min at 92 C, 1 min at 62 C, and 1 min at 72 C). Lanes 1–3, Southern blot analysis of the RT-PCR products probed with a fluorescein-labeled reverse internal prepro-ET-2 oligonucleotide. C, Prepro-ET-3 mRNA expression. The RT products were amplified for 36 cycles (1 cycle: 1 min at 94 C, 1 min at 59 C, and 1 min 30 s at 72 C). Lanes 1–4, Southern blot analysis of the RT-PCR products probed with a fluorescein-labeled reverse internal oligonucleotide specific for prepro-ET-3. Reverse transcriptase was added (lanes 1–3) or omitted (lane 4).

 
Prepro-ET-2. The same PVSMC cDNAs were amplified with the prepro-ET-2 oligonucleotide primers. RNA from human lung was used as a positive control. To identify the RT-PCR product, Southern blotting and hybridization with an internal prepro-ET-2-specific oligonucleotide were performed. A labeled amplification product of the predicted size (232 bp) was obtained in human lung mRNA (Fig. 3BGo, lane 3), whereas no amplification product could be detected in PVSMCs (Fig. 3BGo, lane 1) or stem villi vessel mRNAs (Fig. 3BGo, lane 2).

Prepro-ET-3. The expression of prepro-ET-3 mRNA was investigated in the same stem villi vessels and PVSMC cDNAs. After Southern blotting of RT-PCR products and hybridization with an internal prepro-ET-3-specific oligonucleotide, an amplification product of the predicted size (479 bp) was labeled in the human trophoblast used as a positive control (Fig. 3CGo, lane 1) and in stem villi vessels (Fig. 3CGo, lane 3). In contrast, no amplification could be detected in PVSMCs (Fig. 3CGo, lane 2). When reverse transcriptase was omitted, no amplification product was observed (Fig. 3CGo, lane 4).

mRNA expression of ET-R

In humans, two distinct genes encoding for ETA-R and ETB-R have been described to date. The expression of ETA-R and ETB-R subtype mRNAs was investigated by RT-PCR in confluent PVSMCs and in stem villi vessels.

ETA-R. Using external ETA-specific oligonucleotides (Fig. 4AGo, PCR 1), an amplification product of the predicted size (626 bp) and two shorter fragments (498 and 299 bp) were obtained in human placental villi, which was used as a positive control (Fig. 4BGo, lane 1), in PVSMCs (Fig. 4BGo, lane 2), and in stem villi vessels (Fig. 4BGo, lane 4) as revealed after ethidium bromide staining of agarose gel. No amplification product was observed when reverse transcriptase was omitted (Fig. 4BGo, lanes 3 and 5). After Southern blotting and hybridization with an internal oligonucleotide (208–227) specific for the sequence of ETA-R gene exon 2, the 626-bp fragment as well as the 498- and 299-bp fragments were labeled in the three samples (Fig. 4BGo, lanes 6–8). In addition, a band corresponding to a 427-bp product was labeled using ETA exon-2 probe in human placental villi (Fig. 4BGo, lane 6) and stem villi vessels (Fig. 4BGo, lane 8), whereas it was not observed in PVSMCs (Fig. 4BGo, lane 7). The 427- and 299-bp PCR products correspond respectively to ETA-R{Delta}4 and ETA-R{Delta}3,4 mRNAs, two transcripts previously described in the human placenta (27). In contrast, the 498-bp fragment did not correspond to any previously described ETA-R mRNA-spliced fragment. The difference in size between the 626-bp product of the full-length ETA-R transcript and the newly described 498-bp fragment (Fig. 4BGo) is consistent with exclusion of exon 3 alone. To verify this hypothesis, we performed another amplification using the same forward external oligonucleotide but with an exon 4-specific primer as the reverse external oligonucleotide (Fig. 4AGo, PCR 2). After hybridization with exon 2-specific probe, two amplification products of the expected sizes (556 and 428 bp, respectively) were labeled in PVSMCs (Fig. 4CGo, lane 1) and stem villi vessels (Fig. 4CGo, lane 3) as well as in human placental villi (data not shown). No amplification product was observed when reverse transcriptase was omitted (Fig. 4CGo, lanes 2 and 4).



View larger version (41K):
[in this window]
[in a new window]
 
Figure 4. Expression of ETA-R mRNA analyzed by RT-PCR in PVSMCs, placental stem villi vessels, and positive control, placental villi. A, Schematic representation of the full-length hETA-R cDNA (33) and the amplification primer sets used to detect ETA mRNA splice variants. Exons are represented by open boxes and are numbered. In PCR amplification 1, the region of exons 2–5 was amplified using the primers 149–166 and 757–774. In PCR amplification 2, the region of exons 2–4 was amplified using the primers 149–166 and 685–704. B, PCR amplification 1. The RT products were amplified for 34 cycles (1 cycle: 2 min at 92 C, 1 min at 51.7 C, and 1 min at 72 C). Lanes 1–5, Ethidium bromide-stained gel. Reverse transcriptase was added (lanes 1, 2, and 4) or omitted (lanes 3 and 5). Lanes 6–8, Southern blot analysis of the RT-PCR products probed with a fluorescein-labeled oligonucleotide specific for the exon 2 sequence of the ETA-R gene. C, PCR amplification 2. The RT products were amplified for 36 cycles (PVSMCs) or 34 cycles (stem villi vessels; 1 cycle: 2 min at 92 C, 1 min at 52.3 C, and 1 min at 72 C). Lanes 1–4, Southern blot analysis of the RT-PCR products probed with a fluorescein-labeled oligonucleotide specific for the exon-2 sequence of the ETA-R gene. Reverse transcriptase was added (lanes 1 and 3) or omitted (lanes 2 and 4).

 
After direct sequencing of the 428-bp PCR product, the sequence obtained was compared to the known exon 2–4 region sequence of the human (h) ETA-R gene (21). The 428-bp fragment lacks a 128-nucleotide stretch corresponding exactly to the sequence of hETA-R exon 3 as shown in Fig. 5AGo. The splicing pattern (Fig. 5BGo) will result in a shift in the open reading frame of the ribonucleic sequence position and in the reading of a stop codon at the 22 amino acid position in exon 4 (Fig. 5AGo).



View larger version (43K):
[in this window]
[in a new window]
 
Figure 5. Nucleotide and deduced amino acid sequence of the amplification fragment of hETA-R{Delta}3 in the region of exons 2–4. A, Alignments of the nucleotide and the deduced amino acid sequences of hETA-R and hETA-R{Delta}3 in the region of exons 2–4. The region of exons 2–4 was amplified using primers of PCR amplification 2 (see Fig. 4AGo). After electrophoresis and ethidium bromide staining, the 428-bp PCR product excised from the gel was treated with phenol-chloroform and ethanol precipitated before being submitted to direct sequencing. Numbers to the right refer to the hETA-R nucleotide sequence described by Hosoda et al. (22). The deduced amino acid sequence is shown above the nucleotide sequence. Amino acids are numbered sequentially from the translation initiation site. The positions of the putative membrane-spanning domains (II–IV) are indicated, as previously described (22). The asterisk indicates a new stop codon. B, Exon-intron organization of ETA-R{Delta}3. Exons sequences are boxed and represented in uppercase letters, and intron sequences are given in lowercase letters. The splicing pattern identified in ETA-R{Delta}3 is shown, and the deduced amino acid sequences are indicated above the boxes.

 
ETB-R. ETB-R mRNA expression was investigated in PVSMCs and stem villi vessels by RT-PCR, using external ETB-specific oligonucleotides. After Southern blotting and hybridization with an internal ETB-specific oligonucleotide, the predicted 654-bp product was labeled in stem villi vessels (Fig. 6Go, lane 2), whereas no labeling was observed in PVSMC (Fig. 6Go, lane 4). No amplification product was observed when reverse transcriptase was omitted (Fig. 6Go, lanes 1 and 3).



View larger version (27K):
[in this window]
[in a new window]
 
Figure 6. Expression of ETB-R mRNA analyzed by RT-PCR in PVSMCs and stem villi vessels. The RT products were amplified for 36 cycles (1 cycle: 2 min at 92 C, 1 min at 51.7 C, and 1 min at 72 C). After Southern blotting, the RT products were hybridized with a fluorescein-labeled reverse internal oligonucleotide specific for ETB-R sequence. Reverse transcriptase was added (lanes 2 and 4) or omitted (lanes 1 and 3).

 
[125I]ET-1-binding studies

In PVSMCs, the addition of increasing concentrations (5–300 pmol/L) of [125I]ET-1 resulted in specific and saturable binding (Fig. 7AGo, inset). Scatchard analysis of the saturation curve indicated the presence of a single class of high affinity binding sites with an apparent dissociation constant (Kd) of 52 ± 6 pmol/L and a maximal capacity of 54.5 ± 6.5 fmol/mg protein (n = 4; Fig. 7AGo). The calculated number of receptors was 6426 ± 599 sites/cell. As shown in Fig. 7BGo, the binding of [125I]ET-1 was competitively inhibited by ET-1 with a Ki value of 1.7 ± 0.5 nmol/L, whereas a selective ETB-R agonist, sarafotoxin 6c (S6c), was inactive up to 1 µmol/L. A selective ETA-R antagonist, BQ-123, caused total displacement in an apparent monophasic fashion with a Ki value of 2.2 ± 0.3 nmol/L. In contrast, the ETB antagonist IRL 1038 failed to displace [125I]ET-1 binding (Fig. 7CGo).



View larger version (21K):
[in this window]
[in a new window]
 
Figure 7. Binding of [125I]ET-1 to PVSMCs. A, Scatchard analysis. PVSMC plasma membrane preparations were incubated with increasing concentrations of [125I]ET-1 (5–300 pmol/L) for 60 min at 30 C. Nonspecific binding was assessed in the presence of 1 µmol/L ET-1. Results shown are representative of four independent experiments performed in duplicate on distinct PVSMC cultures. Inset, Saturation binding of [125I]ET-1 to PVSMC plasma membranes. B and C, Competition inhibition curves for [125I]ET-1 binding to PVSMCs. PVSMC plasma membrane preparation was incubated with [125I]ET-1 (50 pmol/L) and increasing concentrations of unlabeled ligands. Binding is expressed as the percentage of specific binding in absence of competitors. Results are representative of at least three to five similar experiments performed in duplicate with distinct PVSMC cultures.

 

    Discussion
 Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 
In the present study, we provide the first description of cultured smooth muscle cells from the human feto-placental vasculature and show their ability to synthesize prepro-ET-1 mRNA and express ETA-R compared with the tissue of origin, the muscular layer of stem villi vessels from human term placenta. In addition, we described in these vessels and in PVSMCs, a new ETA-R mRNA, ETA-R{Delta}3, generated by exclusion of exon 3 alone.

Due to extensive modulation of their phenotype between the contractile and the proliferative states, cultured smooth muscle cells (for review, see 29 are notoriously difficult to characterize. A number of structural and regulatory proteins associated with smooth muscle cells allow their discrimination from fibroblasts, macrophages, and endothelial cells. PVSMCs obtained from explants of the stem villi vessel muscular layer collected from human term placenta exhibit the characteristics of explant-derived vascular smooth muscle cells: they grow to confluence with a hills and valleys pattern and express smooth muscle {alpha}-actin, a contractile protein that appears to be the earliest marker of differentiated smooth muscle. We also sought the expression of smooth muscle myosin heavy chain isoforms, SM1 and SM2, which are considered to be the most rigorous known markers for identification of differentiated smooth muscle cells. Although SM1 and SM2 protein expression was previously reported in stem villi vessels (30), these proteins were barely detectable in PVSMCs when using immunological tools. However, by RT-PCR we demonstrated the presence of SM1 and SM2 transcripts in PVSMCs, whereas these transcripts were not detected in fibroblasts. According to these morphological (hills and valleys pattern) and biochemical (contractile proteins) criteria, we concluded that PVSMCs were of smooth muscle lineage. As these cells were intended to be used to study the expression of ET and their receptors by RT-PCR, a very sensitive method, we also checked by this method the absence of contaminating cells able to synthesize ET such as endothelial and lympho-monocyte strain cells. Only the PVSMC RNA preparations found to be negative for the expression of these contaminating cell markers were selected to perform the following studies.

We showed the expression of prepro-ET-1 and prepro-ET-3 transcripts in the muscular layer of placental stem villi vessels, whereas we identified only prepro-ET-1 mRNAs in cultured PVSMCs (second to sixth passage). In contrast, prepro-ET-2 mRNAs were not expressed in placental stem villi vessels or in PVSMCs. In the conditioned medium of subcultured PVSMCs (second to third passage), preliminary results indicate a weak production of immunoreactive ET-1 (order of magnitude, 12 fmol/106 cells·24 h) (Bourgeois, C., et al., unpublished data). Our present results suggest that in the feto-placental vasculature, the smooth muscle cell itself is involved in the production of a vasoactive substance that can modulate its contractile activity in an autocrine/paracrine way.

With the aim of using PVSMCs as ET target cells, we characterized the ET-R expressed by these cells compared with the smooth muscle layer of stem villi vessels from human term placenta. In stem villi vessels, we showed the expression of ETA-R and ETB-R subtype mRNAs. These results are in agreement with our previous report describing the presence of ETA and ETB binding sites coupled to the phospholipase C/Ca2+ signaling pathway (31). In contrast, in PVSMCs only the ETA-R mRNAs were identified. Using agonists and antagonists selective for the ET-R subtypes, we confirmed the exclusive presence of ET-binding sites of the ETA subtype on PVSMCs. Their Kd value (52 ± 6 pmol/L) is consistent with Kd values previously reported in stem villi vessels (26 ± 4 pmol/L) (9).

Compared to their tissue counterparts, prepro-ET-3 and ETB-R expression were not found in PVSMCs. This alteration of gene expression pattern could occur in response to placement in culture. Subculturing has also been associated with the disappearance of ETB-R expression in tracheal smooth muscle cells (32) and in myometrial cells (16). This is not surprising given the plasticity of smooth muscle cells and the fact that it is nearly impossible to perfectly mimic in culture the in vivo conditions. Alternatively, the prepro-ET-3 and ETB-R expression observed in the smooth muscle wall of stem villi vessels could be due to the presence of contaminating cells and, consequently, would not be observed in isolated PVSMCs.

In addition to the full size ETA-R mRNA, we found that the ETA-R gene gives rise to alternatively spliced ETA-R transcripts in stem villi vessels as well as in PVSMCs. Two of them, respectively called ETA-R{Delta}4 and ETA-R{Delta}3,4, were recently described in placenta and other human tissues (28). In addition, we report in stem villi vessels and PVSMCs, the expression of a third ETA-R mRNA, ETA-R{Delta}3, in which exon 3 alone is excluded. ET-R belong to the group of G protein-coupled receptors that are characterized by their seven-membrane-spanning domain structure (for review, see 33 . In the ETA-R{Delta}3 transcript, exclusion of exon 3 results in the reading of a stop codon at the beginning of exon 4. Consequently, translation of ETA-R{Delta}3 transcripts should generate a very short ETA-R form with only membrane-spanning domains I and II according to their putative location (21). Similarly, translation of ETA-R{Delta}3,4 and ETA-R{Delta}4 mRNAs should generate very truncated ETA-R proteins with only five and three membrane-spanning domains, respectively (28). Interestingly, a similar splicing mechanism leading to truncated transcripts has been described for another G protein-coupled receptor, the dopamine receptor D3 (34).

Despite the presence of several ETA-R mRNAs, we identified a single class of ETA-binding sites on PVSMCs. This could be due to the fact that pharmacological studies produce rather global results that do not always allow one to distinguish between subtypes. However, given the truncated structure of ETA-R{Delta}3 and {Delta}4, it is unlikely that these proteins function as receptors. In the case of ETA-R{Delta}3,4, for which five membrane-spanning domains would be conserved, Miyamoto et al. (28) reported that COS-7 cells transiently transfected with ETA-R{Delta}3,4 cDNA did not exhibit any specific binding affinity for [125I]ET-1 on their plasma membrane. These data are consistent with chimera ET-R results, which suggest that all of the membrane-spanning domains were involved in ligand binding to ETA-R (35). The splicing mechanism of ETA-R mRNA may constitute a posttranscriptional control of the abundance of active ETA-R. In stem villi vessels, ETA-R activation is involved in the constrictive effect of ET-1. Therefore, at the end of pregnancy characterized by a low placental vascular resistance, the generation of truncated ETA-R transcripts in stem villi vessels may constitute a mechanism controlling the amount of functional ETA-R involved in contraction and possibly in proliferation/differentiation processes.

In conclusion, we developed a cell culture model of smooth muscle cells from placental stem villi vessels in which we report the expression of ET-1 mRNA and the presence of ETA-R. The splicing mechanism by which multiple ETA-R transcripts arise in stem villi vessels is maintained in PVSMCs. Throughout pregnancy, the placenta has to provide for fetal nutritional needs, especially near term, when the needs drastically increase. In response to this demand, placental vascularization undergoes modifications of tone and probably structural features. Little is known of the mechanisms responsible for the physiological adaptation of the feto-placental vasculature during pregnancy. PVSMCs in culture will constitute a useful cell model to study the impact of pregnancy-specific stimuli, such as steroid hormones, on the regulation of ETs and ET-R expression in the smooth muscle layer of feto-placental vasculature.


    Acknowledgments
 
We thank C. Cruaud (Genethon Laboratory, Evry, France) for sequencing the PCR products of the ETA-R gene, A. S. Ribba (INSERM U-143, Paris, France) for kindly providing us with von Willebrand primer sequences, Summer Allman for carefully reading this paper, and M. Verger for secretarial assistance.


    Footnotes
 
1 This work was supported by INSERM and in part by MGEN. The nucleotide sequence of the new ETA {Delta}3-R cDNA reported in this paper has been submitted to the GenBank/EMB Data Bank with accession number: AF014826. Back

Received September 10, 1997.

Revised March 17, 1997.

Accepted May 28, 1997.


    References
 Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Poston L, McCarthy AL, Ritter JM. 1995 Control of vascular resistance in the maternal and feto-placental arterial beds. Pharmacol Ther. 65:215–239.[CrossRef][Medline]
  2. Ferré F, Mondon F, Mignot TM, et al. 1993 Endothelin-1 binding sites and immunoreactivity in the cultured human placental trophoblast: evidence for an autocrine and paracrine role for endothelin-1. J Cardiov Pharmacol. 22:S214–S218.
  3. Malassiné A, Cronier L, Mondon F, Mignot TM, Ferré F. 1993 Localization and production of immunoreactive endothelin-1 in the trophoblast of human placenta. Cell Tissue Res. 271:491–497.[CrossRef][Medline]
  4. Robert B, Malassiné A, Bourgeois C, et al. 1996 Expression of endothelin precursor genes in human trophoblast in culture. Eur J Endocrinol. 134:490–496.[Abstract/Free Full Text]
  5. Clozel M, Fischli W. 1989 Human cultured endothelial cells do secrete endothelin-1. J Cardiovasc Pharmacol. 13:S229–S231.
  6. MacLean MR, Templeton AGB, McGrath JC. 1992 The influence of endothelin-1 on human feto-placental blood vessels: a comparison with 5-hydroxytryptamine. Br J Pharmacol. 106:937–941.[Medline]
  7. Myatt L, Bewer AS, Brockman DE. 1992 The comparative effects of big endothelin-1, endothelin-1, and endothelin-3 in the human placental circulation. Am J Obstet Gynecol. 167:1651–1656.[Medline]
  8. Sabry S, Mondon F, Levy M, Ferré F, Dinh-Xuan AT. 1995 Endothelial modulation of vasoconstrictor responses to endothelin-1 in human placental stem villi small arteries. Br J Pharmacol. 115:1038–1042.[Medline]
  9. Robaut C, Mondon F, Bandet J, Ferré F, Cavero I. 1991 Regional distribution and pharmacological characterization of [125I]endothelin-1 binding sites in human fetal placental vessels. Placenta. 12:55–67.[Medline]
  10. Wilkes BM, Macica CM, Mento PF. 1994 Endothelin-1 conversion and receptor characterization in human placental arteries. Am J Physiol. 267:E242–E249.
  11. Rubanyi GM, Polokoff MA. 1994 Endothelins: molecular biology, biochemistry, pharmacology, physiology, and pathophysiology. Pharmacol Rev. 46:325–415.[Medline]
  12. Libby P, O’Brien KV. 1983 Culture of quiescent arterial smooth muscle cells in a defined serum-free medium. J Cell Physiol. 115:217–223.[CrossRef][Medline]
  13. Thiele DL, Kurasaka M, Lipsky PE. 1983 Phenotype of the accessory cell necessary for mitogen-stimulated T and B cell responses in human peripheral blood: delineation by its sensitivity the lysosomotropic agent, L-leucine methyl ester. J Immunol. 131:2282–2289.[Abstract]
  14. Chomczynski P, Sacchi N. 1987 Single-step method of RNA isolation by acid guanidinium thiocyanate-phenol-chloroform extraction. Anal Biochem. 162:156–159.[Medline]
  15. Duc-Goiran P, Chany C, Doly J. 1989 Unusually large interferon-{alpha}-like mRNAs and high expression of interleukin-6 in human fetal annexes. J Biol Chem. 264:16507–16511.[Abstract/Free Full Text]
  16. Héluy V, Breuiller-Fouché M, Cavaillé F, Fournier T, Ferré F. 1995 Characterization of type A endothelin receptors in cultured human myometrial cells. Am J Physiol. 268:E825–E831.
  17. Cheng Y, Prusoff WH. 1973 Relationship between the inhibition constant (Ki) and the concentration inhibitor which causes 50 percent inhibition (IC50) of an enzymatic reaction. Biochem Pharmacol. 22:3059–3108.
  18. Lowe T, Sharefkin J, Yang SQ, Dieffenbach CW. 1990 A computer program for selection of oligonucelotide primers for polymerase chain reactions. Nucleic Acids Res. 18:1757–1761.[Abstract/Free Full Text]
  19. Bloch KD, Hong CC, Eddy RL, Shows TB, Quertermous T. 1991 cDNA cloning and chromosomal assignment of the endothelin-2 gene: vasoactive intestinal contractor peptide is rat endothelin-2. Genomics. 10:236–242.[CrossRef][Medline]
  20. Onda H, Ohkubo S, Ogi K, et al. 1990 One of the endothelin gene family, endothelin-3 gene, is expressed in the placenta. FEBS Lett. 261:327–330.[CrossRef][Medline]
  21. Hosoda K, Nakao K, Tamura N, et al. 1992 Organization, structure, chromosomal assignment, and expression of the gene encoding the human endothelin-A receptor. J Biol Chem. 267:18797–18804.[Abstract/Free Full Text]
  22. Elshourbagy NA, Korman DR, Wu HL, et al. 1993 Molecular characterization and regulation of the human endothelin receptors. J Biol Chem. 268:3873–3879.[Abstract/Free Full Text]
  23. Aikawa M, Sivam PN, Kuro-o M, et al. 1993 Human smooth muscle myosin heavy chain isoforms as molecular markers for vascular development and atherosclerosis. Circ Res. 73:1000–1012.[Abstract/Free Full Text]
  24. Ralph SJ, Thomas ML, Morton CC, Trowbridge IS. 1987 Structural variants of human T200 glycoprotein (leukocyte-common antigen). EMBO J. 6:1251–1257.[Medline]
  25. Mancuso DJ, Tuley EA, Westfield LA, et al. 1989 Structure of the gene for human von Willebrand factor. J Biol Chem. 264:19514–19527.[Abstract/Free Full Text]
  26. Lowry OH, Rosebrough NJ, Farr AL, Randall RJ. 1951 Protein measurement with the Folin phenol reagent. J Biol Chem. 193:265–275.
  27. Babij P, Periasamy M. 1989 Myosin heavy chain isoform diversity in smooth muscle is produced by differential RNA processing. J Mol Biol. 210:673–679.[CrossRef][Medline]
  28. Miyamoto Y, Yoshimasa T, Arai H, et al. 1996 Alternative RNA splicing of the human endothelin-A receptor generates multiple transcripts. Biochem J. 313:795–801.
  29. Owens GK. 1995 Regulation of differentition of vascular smooth muscle cells. Physiol Rev. 75:487–517.[Abstract/Free Full Text]
  30. Cavaillé F, Kacémi A, Mondon F, Fournier T, Ferré F. 1995 Contractile proteins in human fetoplacental vessels. Am J Obstet Gynecol. 173:1793–1799.[CrossRef][Medline]
  31. Mondon F, Doualla-Bell Kotto Maka F, Sabry S, Ferré F. 1995 Endothelin-induced phosphoinositide hydrolysis in the muscular layer of stem villi vessels of human term placenta. Eur J Endocrinol. 133:606–612.[Abstract/Free Full Text]
  32. Inui T, James AF, Fujitani Y, et al. 1994 ETA and ETB receptors on single smooth muscle cells cooperate in mediating guinea pig tracheal contraction. Am J Physiol. 266:L113–L124.
  33. Gudermann T, Nürnberg B, Schultz G. 1995 Receptors and G proteins as primary components of transmembrane signal transduction. I. G-Protein-coupled receptors: stucture and function. J Mol Med. 73:51–63.[CrossRef][Medline]
  34. Giros B, Martres MP, Pilon C, Sokoloff P, Schwartz JC. 1991 Shorter variants of the D3 dopamine receptor produced through various patterns of alternative splicing. Biochem Biophys Res Commun. 176:1584–1592.[CrossRef][Medline]
  35. Sakamoto A, Yanagisawa M, Sawamura T, et al.. 1993 Distinct subdomains of human endothelin receptors determine their selectivity to endothelinA-selective antagonist and endothelinB-selective agonists. J Biol Chem. 268:8547–8553.[Abstract/Free Full Text]



This article has been cited by other articles:


Home page
Reproductive SciencesHome page
M. G. Neerhof, T. Jilling, S. Synowiec, S. Khan, and L. G. Thaete
Altered Endothelin Receptor Binding in Response to Nitric Oxide Synthase Inhibition in the Pregnant Rat
Reproductive Sciences, April 1, 2008; 15(4): 366 - 373.
[Abstract] [PDF]


Home page
Biol. Reprod.Home page
L. G Thaete, T. Jilling, S. Synowiec, S. Khan, and M. G Neerhof
Expression of Endothelin 1 and Its Receptors in the Hypoxic Pregnant Rat
Biol Reprod, September 1, 2007; 77(3): 526 - 532.
[Abstract] [Full Text] [PDF]


Home page
Mol. Endocrinol.Home page
N. Hatae, N. Aksentijevich, H. W. Zemkova, K. Kretschmannova, M. Tomic, and S. S. Stojilkovic
Cloning and Functional Identification of Novel Endothelin Receptor Type A Isoforms in Pituitary
Mol. Endocrinol., May 1, 2007; 21(5): 1192 - 1204.
[Abstract] [Full Text] [PDF]


Home page
EndocrinologyHome page
M. Breuiller-Fouche, C. Moriniere, E. Dallot, S. Oger, R. Rebourcet, D. Cabrol, and M.-J. Leroy
Regulation of the Endothelin/Endothelin Receptor System by Interleukin-1{beta} in Human Myometrial Cells
Endocrinology, November 1, 2005; 146(11): 4878 - 4886.
[Abstract] [Full Text] [PDF]


Home page
Reproductive SciencesHome page
L. G. Thaete, E. R. Dewey, and M. G. Neerhof
Endothelin and the Regulation of Uterine and Placental Perfusion in Hypoxia-Induced Fetal Growth Restriction
Reproductive Sciences, January 1, 2004; 11(1): 16 - 21.
[Abstract] [PDF]


Home page
Pharmacol. Rev.Home page
A. P. Davenport
International Union of Pharmacology. XXIX. Update on Endothelin Receptor Nomenclature
Pharmacol. Rev., June 1, 2002; 54(2): 219 - 226.
[Abstract] [Full Text] [PDF]


Home page
J. Clin. Endocrinol. Metab.Home page
M. Napolitano, F. Miceli, A. Calce, A. Vacca, A. Gulino, R. Apa, and A. Lanzone
Expression and Relationship between Endothelin-1 Messenger Ribonucleic Acid (mRNA) and Inducible/Endothelial Nitric Oxide Synthase mRNA Isoforms from Normal and Preeclamptic Placentas
J. Clin. Endocrinol. Metab., June 1, 2000; 85(6): 2318 - 2323.
[Abstract] [Full Text]


Home page
Biol. Reprod.Home page
C. Cudeville, F. Mondon, B. Robert, R. Rebourcet, T.-M. Mignot, C. Benassayag, and F. Ferré
Evidence for Progesterone Receptors in the Human Fetoplacental Vascular Tree
Biol Reprod, March 1, 2000; 62(3): 759 - 765.
[Abstract] [Full Text]


Home page
Biol. Reprod.Home page
P. Duc-Goiran, C. Bourgeois, T.M. Mignot, B. Robert, G. Tanguy, and F. Ferré
Identification and Expression of Go1 and Go2 {alpha}-Subunit Transcripts in Human Myometrium in Relation to Pregnancy
Biol Reprod, June 1, 1999; 60(6): 1528 - 1535.
[Abstract] [Full Text]


This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Submit a related Letter to the Editor
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Copyright Permission
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Bourgeois, C.
Right arrow Articles by Ferré, F.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Bourgeois, C.
Right arrow Articles by Ferré, F.


HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Endocrinology Endocrine Reviews J. Clin. End. & Metab.
Molecular Endocrinology Recent Prog. Horm. Res. All Endocrine Journals