Co-expression of vascular endothelial growth factor and neuropilin-1 in ovine feto-placental artery endothelial cells

Morphological evaluation of the feline placenta correlates with gene expression of vascular growth factors and receptors†

Placental angiogenesis is critical for normal development. Angiogenic factors and their receptors are key regulators of this process. Dysregulated placental vascular development is associated with pregnancy complications. Despite their importance, vascular growth factor expression has not been thoroughly correlated with placental morphologic development across gestation in cats. We postulate that changes in placental vessel morphology can be appreciated as consequences of dynamic expression of angiogenic signaling agents. Here, we characterized changes in placental morphology alongside expression analysis of angiogenic factor splice variants and receptors throughout pregnancy in domestic shorthair cats. We observed increased vascular and lamellar density in the lamellar zone during mid-pregnancy. Immunohistochemical analysis localized the vascular endothelial growth factor A (VEGF-A) receptor KDR to endothelial cells of the maternal and fetal microvasculatures. PlGF and its principal receptor Flt-1 were localized to the trophoblasts and fetal vasculature. VEGF-A was found in trophoblast cells and associated with endothelial cells. We detected expression of two Plgf splice variants and four Vegf-a variants. Quantitative real-time polymerase chain reaction analysis showed upregulation of mRNAs encoding pan Vegf-a and all Vegf-a splice forms at gestational days 30-35. Vegf-A showed a marked relative increase in expression during mid-pregnancy, consistent with the pro-angiogenic changes seen in the lamellar zone at days 30-35. Flt-1 was upregulated during late pregnancy. Plgf variants showed stable expression during the first two-thirds of pregnancy, followed by a marked increase toward term. These findings revealed specific spatiotemporal expression patterns of VEGF-A family members consistent with pivotal roles during normal placental development.

Effect of Different Concentrations of Leukemia Inhibitory Factor on Gene Expression of Vascular Endothelial Growth Factor-A in Trophoblast Tumor Cell Line

Background

Several studies have shown that leukemia inhibitory factor (LIF) is one of the most important cytokines participating in the process of embryo implantation and pregnancy, while, the role of this factor on vascular endothelial factor-A (VEGF-A), as one of the most important angiogenic factor, has not been fully investigated yet. The aim of this study was to evaluate the effect of LIF on gene expression of VEGF in the choriocarcinoma cells (JEG-3).

Materials and Methods

In this experimental study, JEG-3 choriocarcinoma cells were treated with different concentrations of LIF (1, 10, and 50 ng) for 6, 12, 24, 48 and 72 hours. Expression of VEGF was analyzed by real-time PCR. Delta CTs were subjected to one-way analysis of variance (ANOVA) and a post hoc Tukey's test by SPSS version 25.0 software for data analyzing.

Results

In the stimulated cells, different concentrations of LIF caused significant decrease of VEGF gene expression (P<0.05) at 12, 24 and 48 hours. In contrast, it was increased after 72 hours (P<0.001). Analysis of data after 6 hours also showed that level of VEGF gene expression was significantly decreased by increasing LIF concentration (P<0.001).

Conclusion

Expression level of VEGF gene was decreased in trophoblast cells (except after 72 hours) under the effect of different concentrations of LIF in a time-dependent manner. So, this study showed that further studies are needed to determine the effect of LIF on other angiogenic factors in trophoblast cells.

Impacts of Maternal Nutrition on Vascularity of Nutrient Transferring Tissues during Gestation and Lactation

As the demand for food increases with exponential growth in the world population, it is imperative that we understand how to make livestock production as efficient as possible in the face of decreasing available natural resources. Moreover, it is important that livestock are able to meet their metabolic demands and supply adequate nutrition to developing offspring both during pregnancy and lactation. Specific nutrient supplementation programs that are designed to offset deficiencies, enhance efficiency, and improve nutrient supply during pregnancy can alter tissue vascular responses, fetal growth, and postnatal offspring outcomes. This review outlines how vascularity in nutrient transferring tissues, namely the maternal gastrointestinal tract, the utero-placental tissue, and the mammary gland, respond to differing nutritional planes and other specific nutrient supplementation regimes.

Galectins in angiogenesis: consequences for gestation

Members of the galectin family have been shown to exert several roles in the context of reproduction. They contribute to placentation, maternal immune regulation and facilitate angiogenesis encompassing decidualisation and placenta formation during pregnancy. In the context of neo-vascularisation, galectins have been shown to augment signalling pathways that lead to endothelial cell activation, cell proliferation, migration and tube formation in vitro in addition to angiogenesis in vivo. Angiogenesis during gestation ensures not only proper foetal growth and development, but also maternal health. Consequently, restriction of placental blood flow has major consequences for both foetus and mother, leading to pregnancy diseases. In this review we summarise both the established and the emerging roles of galectin in angiogenesis and discuss the possible implications during healthy and pathological gestation.

Regulation of placental angiogenesis

Ample interest has been evoked in using placental angiogenesis as a target for the development of diagnosis tools and potential therapeutics for pregnancy complications based on the knowledge of placental angiogenesis in normal and aberrant pregnancies. Although these goals are still far from reach, one would expect that two complementary processes should be balanced for therapeutic angiogenesis to be successful in restoring a mature and functional vascular network in the placenta in any pregnancy complication: (i) pro-angiogenic stimulation of new vessel growth and (ii) anti-angiogenic inhibition of vessel overgrowth. As the best model of physiological angiogenesis, investigations of placental angiogenesis provide critical insights not only for better understanding of normal placental endothelial biology but also for the development of diagnosis tools for pregnancy complications. Such investigations will potentially identify novel pro-angiogenic factors for therapeutic intervention for tissue damage in various obstetric complications or heart failure or anti-angiogenic factors to target on cancer or vision loss in which circulation needs to be constrained. This review summarizes the genetic and molecular aspects of normal placental angiogenesis as well as the signaling mechanisms by which the dominant angiogenic factor vascular endothelial growth factor regulates placental angiogenesis with a focus on placental endothelial cells.

The renin-angiotensin system from conception to old age: the good, the bad and the ugly

The renin-angiotensin system (RAS) plays a critical role in placentation and nephrogenesis. Failure to thrive during intrauterine life, possibly related to placental dysfunction and impaired expression of the renal RAS, as well as prematurity, results in smaller kidneys at birth and reduced nephron number. The remaining nephrons are therefore hyperfiltering from birth. Hyperfiltration, infections and Type 2 diabetes cause glomerular and tubular fibrosis, leading to further reductions in nephron number. The intrarenal RAS plays a key role in promoting tubulointerstitial fibrosis. Low birth weight and a high incidence of preterm birth program Indigenous children for early onset renal disease in adult life. Indigenous Australians have 404 000 fewer nephrons than non-Indigenous Australians. This, coupled with the high incidence of infectious diseases (particularly acute post-streptococcal glomerulonephritis) and the increasing prevalence of Type 2 diabetes, explains why end-stage renal disease is of epidemic proportions in Indigenous Australians. The existence of RAS gene polymorphisms and inflammatory cytokines may further potentiate susceptibility to renal disease in Indigenous Australians.

Nitric oxide induces vascular endothelial growth factor expression in the rat placenta in vivo and in vitro

We investigated the role of nitric oxide (NO) in vascular endothelial growth factor (VEGF) expression in the rat placenta. A nitric oxide synthase (NOS) inhibitor, N(G)-nitro-L-arginine-methyl ester (L-NAME), was constantly infused into pregnant rats 6-24 h before sacrifice on gestational day (GD) 15.5. NO production declined to about 15% of the control level as monitored by NO trapping and electron paramagnetic resonance spectroscopy. VEGF mRNA expression was temporally decreased by L-NAME, but recovered to normal levels after 24 h of treatment, whereas hypoxia inducible factor (HIF)-1α and induced NOS (iNOS) expression increased. VEGF expression decreased significantly in placental explants after 6 h of co-treatment with L-NAME and lipopolysaccharide, an iNOS inducer. Our data indicate that NO induce VEGF expression in vivo and in vitro in the rat placenta, suggesting that peaked NO production was maintained by a reciprocal relationship between NO and VEGF via HIF-1α.

Pattern of expression of vascular endothelial growth factor and its receptors in the ovine choroid plexus during long and short photoperiods

Vascular endothelial growth factor (VEGF-A) plays an important role in maintaining cerebrospinal fluid (CSF) homeostasis and the function of the choroid plexuses (CPs). The objective of the study was to determine the expression of vascular endothelial growth factor (VEGF-A), tyrosine kinase receptors Flt-1 and KDR and KDR co-receptor neuropilin 1 (NRP-1) in ovine CPs during different photoperiods. CPs were collected from the lateral brain ventricles from ovariectomized, estradiol-treated ewes during long day (LD; 16L:8D, n = 5) and short day (SD; 8L:16D, n = 5) photoperiods. We analyzed mRNA expression levels of two VEGF-A isoforms, VEGF-A₁₂₀ and VEGF-A₁₆₄ and our results indicate that VEGF-A₁₆₄ was the predominant isoform. Expression levels of VEGF-A and Flt-1 were similar during the SD and LD photoperiods. There were significant increases in KDR mRNA and protein expression (p < 0.05) and NRP-1 mRNA expression (p < 0.05) during SD. These data show that expression of KDR and its co-receptor NRP-1 are up-regulated by short photoperiod and that this effect is not dependent on ovarian steroids. Our results suggest that the VEGF-A-system may be involved in photoperiodic plasticity of CP capillaries and may therefore be responsible for photoperiodic changes in the CSF turnover rate in ewes.

Contributions of VEGF to age-dependent transmural gradients in contractile protein expression in ovine carotid arteries

The present study explores the hypothesis that arterial smooth muscle cells are organized into layers with similar phenotypic characteristics that vary with the relative position between the lumen and the adventitia due to transmural gradients in vasotrophic factors. A corollary hypothesis is that vascular endothelial growth factor (VEGF) is a factor that helps establish transmural variations in smooth muscle phenotype. Organ culture of endothelium-denuded ovine carotid arteries with 3 ng/ml VEGF-A(165) for 24 h differentially and significantly influenced potassium-induced (55% increase) and stretch-induced (36% decrease) stress-strain relations in adult (n = 18) but not term fetal (n = 21) arteries, suggesting that smooth muscle reactivity to VEGF is acquired during postnatal maturation. Because inclusion of fetal bovine serum significantly inhibited all contractile effects of VEGF (adult: n = 11; fetus: n = 11), it was excluded in all cultures. When assessed in relation to the distance between the lumen and the adventitia in immunohistochemically stained coronal artery sections, expression of smooth muscle α-actin (SMαA), myosin light chain kinase (MLCK), and 20-kDa regulatory myosin light chain exhibited distinct protein-dependent and age-dependent gradients across the artery wall. VEGF depressed regional SMαA abundance up to 15% in adult (n = 6) but not in fetal (n = 6) arteries, increased regional MLCK abundance up to 140% in fetal (n = 8) but not in adult (n = 10) arteries, and increased regional MLC(20) abundance up to 28% in fetal arteries (n = 7) but decreased it by 17% in adult arteries (n = 9). Measurements of mRNA levels verified that VEGF receptor transcripts for both Flt-1 and kinase insert domain receptor (KDR) were expressed in both fetal and adult arteries. Overall, the present data support the unique hypothesis that smooth muscle cells are organized into lamina of similar phenotype with characteristics that depend on the relative position between the lumen and the adventitia and involve the direct effects of growth factors such as VEGF, which acts independently of the vascular endothelium in an age-dependent manner.

Compartmentalizing VEGF-induced ERK2/1 signaling in placental artery endothelial cell caveolae: a paradoxical role of caveolin-1 in placental angiogenesis in vitro

On vascular endothelial growth factor (VEGF) stimulation, both VEGF R1 and R2 receptors were phosphorylated in ovine fetoplacental artery endothelial (oFPAE) cells. Treatment with VEGF stimulated both time- and dose-dependent activation of ERK2/1 in oFPAE cells. VEGF-induced ERK2/1 activation was mediated by VEGFR2, but not VEGFR1, and was linked to intracellular calcium, protein kinase C, and Raf-1. VEGF stimulated oFPAE cell proliferation, migration, and tube formation in vitro. Blockade of ERK2/1 pathway attenuated VEGF-induced cell proliferation and tube formation but failed to inhibit migration in oFPAE cells. Disruption of caveolae by cholesterol depletion with methyl-beta-cyclodextrin or by down-regulation of its structural protein caveolin-1 blunted VEGF-induced ERK2/1 activation, proliferation, and tube formation in oFPAE cells, indicating an essential role of integral caveolae in these VEGF-induced responses. Adenoviral overexpression of caveolin-1 and addition of a caveolin scaffolding domain peptide also inhibited VEGF-stimulated ERK2/1 activation, cell proliferation, and tube formation in oFPAE cells. Furthermore, molecules comprising the ERK2/1 signaling module, including VEGFR2, protein kinase Calpha, Raf-1, MAPK kinase 1/2, and ERK2/1, resided with caveolin-1 in caveolae. VEGF transiently stimulated ERK2/1 activation in the caveolae similarly as in intact cells. Caveolae disruption greatly diminished ERK2/1 activation by VEGF in oFPAE cell caveolae. We conclude that caveolae function as a platform for compartmentalizing the VEGF-induced ERK2/1 signaling module. Caveolin-1 and caveolae play a paradoxical role in regulating VEGF-induced ERK2/1 activation and in vitro angiogenesis as evidenced by the similar inhibitory effects of down-regulation and overexpression of caveolin-1 and disruption of caveolae in oFPAE cells.

Vascular endothelial growth factor acts through novel, pregnancy-enhanced receptor signalling pathways to stimulate endothelial nitric oxide synthase activity in uterine artery endothelial cells

During pregnancy, VEGF (vascular endothelial growth factor) regulates in part endothelial angiogenesis and vasodilation. In the present study we examine the relative roles of VEGFRs (VEGF receptors) and associated signalling pathways mediating the effects of VEGF(165) on eNOS (endothelial nitric oxide synthase) activation. Despite equal expression levels of VEGFR-1 and VEGFR-2 in UAECs (uterine artery endothelial cells) from NP (non-pregnant) and P (pregnant) sheep, VEGF(165) activates eNOS at a greater level in P- compared with NP-UAEC, independently of Akt activation. The selective VEGFR-1 agonist PlGF (placental growth factor)-1 elicits only a modest activation of eNOS in P-UAECs compared with VEGF(165), whereas the VEGFR-2 kinase inhibitor blocks VEGF(165)-stimulated eNOS activation, suggesting VEGF(165) predominantly activates eNOS via VEGFR-2. Although VEGF(165) also activates ERK (extracellular-signal-regulated kinase)-1/2, this is not necessary for eNOS activation since U0126 blocks ERK-1/2 phosphorylation, but not eNOS activation, and the VEGFR-2 kinase inhibitor inhibits eNOS activation, but not ERK-1/2 phosphorylation. Furthermore, the inability of PlGF to activate ERK-1/2 and the ability of the VEGFR-2 selective agonist VEGF-E to activate ERK-1/2 and eNOS suggests again that both eNOS and ERK-1/2 activation occur predominantly via VEGFR-2. The lack of VEGF(165)-stimulated Akt phosphorylation is consistent with a lack of robust phosphorylation of Ser(1179)-eNOS. Although VEGF(165)-stimulated eNOS phosphorylation is observed at Ser(617) and Ser(635), pregnancy does not significantly alter this response. Our finding that VEGF(165) activation of eNOS is completely inhibited by wortmannin but not LY294002 implies a downstream kinase, possibly a wortmannin-selective PI3K (phosphoinositide 3-kinase), is acting between the VEGFR-2 and eNOS independently of Akt.

Hypoxia modulation of caveolin-1 and vascular endothelial growth factor in ovine fetal membranes

During normal pregnancy, amniotic fluid is absorbed from the amniotic compartment into fetal blood through the intramembranous blood vessels in the fetal membranes. It has been hypothesized that this transport process is mediated by transcytosis of caveolae-like vesicles. Because fetal hypoxia increases intramembranous absorption, the authors explore the effects of hypoxia on the gene expression of caveolin-1, a structural protein of caveolae, in ovine fetal membranes and cultured amnion cells. Near-term ovine fetuses were rendered hypoxic for 4 days. Caveolin-1 mRNA and protein levels were significantly reduced in the amnion and chorion but not in the placenta. In cultured ovine amnion cells incubated in 2% oxygen for 24 hours, hypoxia did not significantly alter caveolin-1 mRNA or protein expression. Vascular endothelial growth factor mRNA levels were increased in response to hypoxia in the fetal membranes as well as in cultured amnion cells. The results indicate that hypoxia does not augment but instead down-regulates or has no effect on caveolin-1 gene expression in the amnion and chorion, suggesting that caveolin-1 may play a role as a negative regulator of amnion transport function under hypoxic conditions.

Exogenous Nitric Oxide Stimulates Cell Proliferation via Activation of a Mitogen-Activated Protein Kinase Pathway in Ovine Fetoplacental Artery Endothelial Cells1

Sodium nitroprusside (SNP), a nitric oxide (NO) donor and a nitrovasodilator drug used for patients with hypertensive crisis, has been shown to promote angiogenesis. However, direct evidence showing the involvement of NO in the SNP-induced angiogenesis is not available. Accordingly, we assessed whether NO generated from SNP-stimulated ovine fetoplacental artery endothelial (OFPAE) cell proliferation via activation of mitogen-activated protein kinase 3/1 (MAPK3/1, also termed ERK1/2). We observed that SNP dose dependently stimulated (P < 0.05) cell proliferation with a maximal effect at 1 microM and that SNP rapidly (<or=15 min) phosphorylated (P < 0.05) MAPK3/1 but not v-akt murine thymoma viral oncogene homolog 1 (AKT1). Treatment of cells with SNP caused a rapid increase in NO levels in media. These increased NO levels were inhibited (P < 0.05) by 2-phenyl-4,4,5,5 tetramethylimidazoline-1-oxyl 3-oxide (PTIO), a NO scavenger. The SNP-induced cell proliferation and MAPK3/1 phosphorylation were attenuated (P < 0.05) by both PTIO and PD98059, a specific mitogen-activated protein kinase kinase 1 and 2 (MAP2K1/2, also termed MEK1/2) inhibitor. Using a semiquantitative RT-PCR analysis, we also showed that up to 12 h of treatment, SNP and N(G)-monomethyl-L-arginine (L-NMMA, a NOS inhibitor) did not alter mRNA expression of VEGF, FGF2, and their major receptors in OFPAE cells. The SNP's stimulatory effects on OFPAE cell proliferation and MAPK3/1 activation were confirmed in a human placental artery endothelial (HPAE) cell line. These data indicate that exogenous NO generated from SNP is able to stimulate fetoplacental artery endothelial cell proliferation at least partly via activation of the MAP2K1/2/MAPK3/1 cascade. These data also suggest that SNP could potentially be used to modulate placental angiogenesis.

Molecular cloning of ovine endothelial nitric oxide synthase and expression in COS-7 cells

While studies of human and bovine endothelial nitric oxide synthase (eNOS) demonstrate activation by Ca(2+)/calmodulin, recent progress demonstrates that eNOS phosphorylation can alter sensitivity to intracellular free calcium ([Ca(2+)](i)). The sheep, however, is widely used as a model for cardiovascular adaptation to pregnancy and ovine uterine artery endothelial cell (UAEC) eNOS undergoes pregnancy-specific (P) enhancement of activity associated with increased Ca(2+) and protein kinase signaling in response to a number of agonists, including adenosine triphosphate (ATP). The degree of homology between the ovine and human full-length cDNAs was not previously known and yet is necessary to determine the validity in using an ovine model to study human physiology. The objectives of this study were to isolate and validate the clone of ovine eNOS cDNA and investigate ovine eNOS activation when expressed in COS-7 cells. The ovine eNOS cDNA has high homology to published human and bovine sequences and shares identity with the bovine amino acid sequence. When ovine eNOS was transiently expressed in COS-7 cells (COS-7/oeNOS), A23187 increased specific catalytic activity in a dose- and time-dependent manner. A23187-stimulated activation of eNOS was, however, also accompanied by phosphorylation of eNOS S1179 and dephosphorylation of T497, demonstrating that an increase in [Ca(2+)](i) may not be the sole mechanism of activation. The physiologic relevance of this was further underscored by the finding that ATP dose-dependently increased peak [Ca(2+)](i) and eNOS activity in COS-7/oeNOS, but also increased eNOS p-S1179 and decreased p-T497. This finding was similar to those in ovine P-UAEC treated with the Ca(2+)-mobilizing agonist ATP, wherein activation of eNOS was again concomitant with a rise p-S1179 as well as a slight decrease in p-T497. In conclusion, we describe the full-length ovine eNOS cDNA sequence and show that both physiologic and nonphysiologic calcium-mobilizing agents, which activate ovine eNOS in COS-7 and P-UAEC, do so in association with changes in eNOS phosphorylation. Given this information we can now begin to dissect the relationship between Ca(2+) elevation and specific phosphorylation events in eNOS activation in the ovine model, and thereby gain insight into the possible basis for pregnancy-related dysfunction.

Circulating levels of nitric oxide and vascular endothelial growth factor throughout ovine pregnancy

Nitric oxide (NO) production has been shown to increase uterine blood flow and be elevated in ewes carrying multiple fetuses during late gestation. Vascular endothelial growth factor (VEGF) has been reported to increase eNOS expression and NO production in endothelial cell cultures. As angiogenesis and vasodilatation of the uterine and placental vascular beds are important at all stages of pregnancy, it is important to understand how VEGF and NO change throughout gestation in circulation. Therefore the objectives of the current study were to evaluate the systemic levels of VEGF and NO metabolite (NOx) throughout ovine gestation and to determine if there was an effect of sheep carrying singletons versus multiple fetuses. NOx and VEGF concentrations were analysed in systemic blood from pregnant ewes starting on day 27 of pregnancy and at multiple intermittent intervals throughout pregnancy until term. Blood samples from non-pregnant and postpartum ewes were also analysed. NOx concentrations in maternal blood expressed a biphasic pattern with NOx concentrations increasing (P < 0.05) over non-pregnant values on days 40-69 of gestation, returning to non-pregnant concentrations from days 70-100, and again increasing (P < 0.05) until term. Postpartum NOx concentrations were similar to non-pregnant values. While ewes carrying multiple fetuses had increased (P < 0.05) concentrations of NOx on days 60-69, there were no differences in NOx concentrations in ewes carrying singletons or multiples from day 70-99 of gestation. Starting on day 100 and continuing throughout the duration of pregnancy, ewes carrying multiple fetuses had increased (P < 0.05) concentrations of NOx compared to ewes carrying singletons. Concentrations of VEGF showed a different pattern from NOx with VEGF decreasing (P < 0.05) from day 20-69 of pregnancy compared to non-pregnant ewes. Concentrations of VEGF returned to non-pregnant levels by day 70 and remained constant throughout the duration of pregnancy. On days 20-39, ewes carrying singleton fetuses had an increased VEGF concentration (P < 0.05), whereas ewes carrying multiple fetuses demonstrated elevated VEGF concentrations from day 90-109 of gestation. Concentrations from non-pregnant and postpartum ewes did not differ (P > 0.1). While there was no effect of fetal number on circulating VEGF concentrations, circulating levels of NOx were substantially increased (P < 0.05) in ewes carrying multiple fetuses, compared to ewes carrying singletons. The pattern of the rise in NOx in circulating plasma was not directly associated with changes in VEGF regardless of the number of fetuses present. However, circulating concentrations of NOx and VEGF appear to, respectively, follow patterns of uterine blood flow and angiogenesis of the uterus. An understanding of these circulatory patterns may have important implications for fetal size, birth weight and fetal/developmental origins of adult disease.

Angiotensin II regulation of ovine fetoplacental artery endothelial functions: interactions with nitric oxide

During normal pregnancy, elevated angiotensin II (Ang II) concentrations in the maternal and fetal circulations are associated with dramatic increases in placental angiogenesis and blood flow. Much is known about a local renin-angiotensin system within the uteroplacental vasculature. However, the roles of Ang II in regulating fetoplacental vascular functions are less well defined. In the fetal placenta, the overall in vivo vasoconstrictor responses of the blood vessels to Ang II infusion is thought to be less than that in its maternal counterpart, even though infused Ang II induces vasoconstriction. Recent data from our laboratories suggest that Ang II stimulates cell proliferation and increases endothelial nitric oxide synthase (eNOS) and production of nitric oxide (NO) in ovine fetoplacental artery endothelial cells. These data imply that elevations of the known vasoconstrictor Ang II in the fetal circulation may indeed play a role in the marked increases in fetoplacental angiogenesis and that Ang II-elevated endothelial NO production may partly attenuate Ang II-induced vasoconstriction on vascular smooth muscle. Together with both of these processes, the high levels of Ang II in the fetal circulation may serve to modulate overall fetoplacental vascular resistance. In this article, we review currently available data on the expression of Ang II receptors in the ovine fetal placenta with particular emphasis on the effects of Ang II on ovine fetoplacental endothelium. The potential cellular mechanisms underlying the regulation of Ang II on endothelial growth and vasodilator production are discussed.

Differential expression of vascular endothelial growth factor (VEGF), endocrine gland derived-VEGF, and VEGF receptors in human placentas from normal and preeclamptic pregnancies

Vascular endothelial growth factor (VEGF) is a potent regulator of placental vascular function. Endothelial dysfunction is a key factor associated with preeclampsia. In this study, we examined expression of VEGF, endocrine gland-derived VEGF (EG-VEGF), VEGF receptors 1 and 2 (VEGFR-1 and VEGFR-2), and neuropilin-1 and -2 (NP-1 and NP-2) in human placentas from women with normal and preeclamptic (PE) pregnancies using quantitative or semiquantitative PCR. We found that total VEGF mRNA expression was increased 2.8-fold (P < 0.05), along with increases in mRNA expression of VEGF121, 165, and 189 (P < 0.05; 1.7-, 1.9-, and 1.8-fold, respectively) in PE vs. normal placentas. Expression of VEGFR-1 mRNA, but not EG-VEGF and the other three VEGF receptors studied, was elevated (P < 0.05) 2.7-fold in PE vs. normal placentas. Protein expression of VEGF and its four receptors was determined using Western blot analysis. For VEGF, two major isoforms (VEGF165 and 189) were detected. For VEGFR-1, VEGFR-2, NP-1, and NP-2, one major band was observed at 180, 235, 130, and 130 kDa, respectively. All of these bands were corresponding to their positive controls. Of these five proteins studied, only VEGFR-1 levels were increased (P < 0.05; 1.7-fold) in PE placentas. The expression of VEGF and the four VEGF receptors was confirmed using immunohistochemistry. They were primarily present in syncytiotrophoblasts and endothelial cells of villous capillaries and large vessels. Thus, together with previous reports that VEGFR-1 mediates trophoblast function and inhibits VEGF-induced angiogenesis and endothelium-dependent vasodilation, these data suggest that the increased VEGFR-1 expression may alter VEGF- mediated function on trophoblast and endothelial cells in PE placentas.

The relationship between transplacental O2 diffusion and placental expression of PlGF, VEGF and their receptors in a placental insufficiency model of fetal growth restriction

Placental growth factor (PlGF) and vascular endothelial growth factor (VEGF) are involved in placental angiogenesis through interactions with the VEGFR-1 and VEGFR-2 receptors. The placenta of pregnancies whose outcome is fetal growth restriction (FGR) are characterized by abnormal angiogenic development, classically associated with hypoxia. The present study evaluated the near-term expression of this growth factor family in an ovine model of placental insufficiency-FGR, in relationship to uteroplacental oxygenation. Compared to controls, FGR pregnancies demonstrated a 37% increase in uterine blood flow (FGR vs. control, 610.86+/-48.48 vs. 443.17+/-37.39 ml min(-1) (kg fetus)(-1); P<0.04), which was associated with an increased maternal uterine venous PO2 (58.13+/-1.00 vs. 52.89+/-1.26 mmHg; P<0.02), increased umbilical artery systolic/diastolic ratio (3.90+/-0.33 vs. 2.12+/-0.26, P<0.05), and fetal hypoxia (arterial PO2; 12.79+/-0.97 vs. 18.65+/-1.6 mmHg, P<0.005). Maternal caruncle PlGF mRNA was increased in FGR (P<0.02), while fetal cotyledon VEGF mRNA was reduced (P<0.02). VEGFR-1 mRNA was also reduced in FGR fetal cotyledon (P<0.001) but was not altered in caruncle tissue. Immunoblot analysis of PlGF and VEGF demonstrated single bands at 19,000 and 18,600 Mr, respectively. Caruncle PlGF concentration was increased (P<0.04), while cotyledon VEGF was decreased (P<0.05) in FGR placentae. The data establish that uterine blood flow is not reduced in relationship to metabolic demands in this FGR model and that the transplacental PO2 gradient is increased, maintaining umbilical oxygen uptake per unit of tissue. Furthermore, these data suggest that an increased transplacental gradient of oxygen generates changes in angiogenic growth factors, which may underline the pathophysiology of the post-placental hypoxic FGR.