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

Transcriptomics analysis of the bovine endometrium during the perioestrus period

During the oestrous cycle, the bovine endometrium undergoes morphological and functional changes, which are regulated by alterations in the levels of oestrogen and progesterone and consequent changes in gene expression. To clarify these changes before and after oestrus, RNA-seq was used to profile the transcriptome of oestrus-synchronized beef heifers. Endometrial samples were collected from 29 animals, which were slaughtered in six groups beginning 12 h after the withdrawal of intravaginal progesterone releasing devices until seven days post-oestrus onset (luteal phase). The groups represented proestrus, early oestrus, metoestrus and early dioestrus (luteal phase). Changes in gene expression were estimated relative to gene expression at oestrus. Ingenuity Pathway Analysis (IPA) was used to identify canonical pathways and functional processes of biological importance. A total of 5,845 differentially expressed genes (DEGs) were identified. The lowest number of DEGs was observed at the 12 h post-oestrus time point, whereas the greatest number was observed at Day 7 post-oestrus onset (luteal phase). A total of 2,748 DEGs at this time point did not overlap with any other time points. Prior to oestrus, Neurological disease and Organismal injury and abnormalities appeared among the top IPA diseases and functions categories, with upregulation of genes involved in neurogenesis. Lipid metabolism was upregulated before oestrus and downregulated at 48h post-oestrus, at which point an upregulation of immune-related pathways was observed. In contrast, in the luteal phase the Lipid metabolism and Small molecule biochemistry pathways were upregulated.

Regulation of vascular angiotensin II type 1 and type 2 receptor and angiotensin-(1-7)/MasR signaling in normal and hypertensive pregnancy

Normal pregnancy (Norm-Preg) is associated with a slight reduction in blood pressure (BP) and decreased BP response to vasoconstrictor stimuli such as angiotensin II (Ang II), although the renin-angiotensin-aldosterone system (RAAS) is upregulated. Preeclampsia (PE) is a complication of pregnancy manifested as hypertension-in-pregnancy (HTN-Preg), and dysregulation of angiotensin biosynthesis and signaling have been implicated. Ang II activates vascular Ang II type-1 receptor (AT1R) and Ang II type-2 receptor (AT2R), while angiotensin-(1-7) promotes Ang-(1-7)/MasR signaling. The role of AT1R in vasoconstriction and the activated cellular mechanisms are well-characterized. The sensitivity of vascular AT1R to Ang II and consequent activation of vasoconstrictor mechanisms decrease during Norm-Preg, but dramatically increase in HTN-Preg. Placental ischemia in late pregnancy could also initiate the release of AT1R agonistic autoantibodies (AT1AA) with significant impact on endothelial dysfunction and activation of contraction pathways in vascular smooth muscle including [Ca2+]c and protein kinase C. On the other hand, the role of AT2R and Ang-(1-7)/MasR in vascular relaxation, particularly during Norm-Preg and PE, is less clear. During Norm-Preg, increases in the expression/activity of vascular AT2R and Ang-(1-7)/MasR promote the production of endothelium-derived relaxing factors such as nitric oxide (NO), prostacyclin and endothelium-derived hyperpolarizing factor leading to generalized vasodilation. Aortic segments of Preg rats show prominent endothelial AT2R staining and increased relaxation and NO production in response to AT2R agonist CGP42112A, and treatment with AT2R antagonist PD123319 enhances phenylephrine-induced contraction. Decreased vascular AT2R and Ang-(1-7)/MasR expression and receptor-mediated mechanisms of vascular relaxation have been suggested in HTN-Preg animal models, but their role in human PE needs further testing. Changes in angiotensin-converting enzyme-2 (ACE2) have been observed in COVID-19 patients, and whether ACE2 influences the course of COVID-19 viral infection/immunity in Norm-Preg and PE is an intriguing area for research.

Association of angiotensin II and receptors in peri-implantation endometrium with microvessel density and pregnancy outcomes of women with recurrent implantation failure after embryo transfer

Purpose

Investigate whether local angiotensin II (AngII) and its AngII type 1 and 2 receptors (AT1R, AT2R) in the endometrium are different and correlate with microvessel density in women with reproductive failure and pregnancy outcomes.

Methods

Endometrium during the window of implantation from 40 women with recurrent miscarriage (RM) and 40 with recurrent implantation failure (RIF) were compared with 27 fertile women. Peri-implantation endometrium from 54 women prior to euploid embryo transfer were collected and compared in women with successful pregnancy and unsuccessful pregnancy.

Results

Compared with fertile women, expression of AT2R was significantly lower, while AT1R/AT2R expression ratio was significantly higher in the stroma of the RIF group. Endometrium arteriole MVD was significantly lower and negatively correlated with the AT1R/AT2R expression ratio in the stroma of the RIF group. No significant differences and correlations were found in the RM group. Compared with the pregnancy group, expression of AT1R and AT2R were significantly lower in all compartments, but only AT1R/AT2R ratio was significantly higher in the stroma of the non-pregnancy group. Similarly, endometrium arteriole MVD was also significantly lower and negatively correlated with the AT1R/AT2R ratio in the stroma of the non-pregnancy group.

Conclusion

Local renin-angiotensin system is dysregulated in peri-implantation endometrium and associated with abnormal angiogenesis in RIF and poor implantation outcome after embryo transfer.

An Exploratory Data Analysis from Ovine and Bovine RNA-Seq Identifies Pathways and Key Genes Related to Cervical Dilatation

The present study developed a review and exploration of data in public and already validated repositories. The main objective was to identify the pathways involved in ruminants' cervical dilatation, which are conserved between cattle and sheep in the follicular and luteal phases of the reproductive cycle. In cattle, 1961 genes were more differentially expressed in the follicular phase and 1560 in the luteal phase. An amount of 24 genes were considered exclusively expressed from these. A total of 18 genes were in the follicular phase and 6 genes were in the luteal phase. In sheep, 2126 genes were more differentially expressed in the follicular phase and 2469 genes were more differentially expressed in the luteal phase. Hoxb genes were identified in both species and are correlated with the PI3K/Akt pathway. PI3K/Akt was also found in both cattle and sheep, appearing prominently in the follicular and luteal phases of both species. Our analyses have pointed out that the PI3K/Akt pathway and the Hoxb genes appear in prominence in modulating mechanisms that involve estrus alterations in the cervix. PI3K/Akt appears to be an important pathway in the cervical relaxation process.

Estrogen Receptors and Estrogen-Induced Uterine Vasodilation in Pregnancy

Normal pregnancy is associated with dramatic increases in uterine blood flow to facilitate the bidirectional maternal–fetal exchanges of respiratory gases and to provide sole nutrient support for fetal growth and survival. The mechanism(s) underlying pregnancy-associated uterine vasodilation remain incompletely understood, but this is associated with elevated estrogens, which stimulate specific estrogen receptor (ER)-dependent vasodilator production in the uterine artery (UA). The classical ERs (ERα and ERβ) and the plasma-bound G protein-coupled ER (GPR30/GPER) are expressed in UA endothelial cells and smooth muscle cells, mediating the vasodilatory effects of estrogens through genomic and/or nongenomic pathways that are likely epigenetically modified. The activation of these three ERs by estrogens enhances the endothelial production of nitric oxide (NO), which has been shown to play a key role in uterine vasodilation during pregnancy. However, the local blockade of NO biosynthesis only partially attenuates estrogen-induced and pregnancy-associated uterine vasodilation, suggesting that mechanisms other than NO exist to mediate uterine vasodilation. In this review, we summarize the literature on the role of NO in ER-mediated mechanisms controlling estrogen-induced and pregnancy-associated uterine vasodilation and our recent work on a “new” UA vasodilator hydrogen sulfide (H₂S) that has dramatically changed our view of how estrogens regulate uterine vasodilation in pregnancy.

Dysregulated flow-mediated vasodilatation in the human placenta in fetal growth restriction

Increased vascular resistance and reduced fetoplacental blood flow are putative aetiologies in the pathogenesis of fetal growth restriction (FGR); however, the regulating sites and mechanisms remain unclear. We hypothesised that placental vessels dictate fetoplacental resistance and in FGR exhibit endothelial dysfunction and reduced flow-mediated vasodilatation (FMVD). Resistance was measured in normal pregnancies (n = 10) and FGR (n = 10) both in vivo by umbilical artery Doppler velocimetry and ex vivo by dual placental perfusion. Ex vivo FMVD is the reduction in fetal-side inflow hydrostatic pressure (FIHP) following increased flow rate. Results demonstrated a significant correlation between vascular resistance measured in vivo and ex vivo in normal pregnancy, but not in FGR. In perfused FGR placentas, vascular resistance was significantly elevated compared to normal placentas (58 ± 7.7 mmHg and 36.8 ± 4.5 mmHg, respectively; 8 ml min⁻¹; means ± SEM; P < 0.0001) and FMVD was severely reduced (3.9 ± 1.3% and 9.1 ± 1.2%, respectively). In normal pregnancies only, the highest level of ex vivo FMVD was associated with the lowest in vivo resistance. Inhibition of NO synthesis during perfusion (100 μm l-NNA) moderately elevated FIHP in the normal group, but substantially in the FGR group. Human placenta artery endothelial cells from FGR groups exhibited increased shear stress-induced NO generation, iNOS expression and eNOS expression compared with normal groups. In conclusion, fetoplacental resistance is determined by placental vessels, and is increased in FGR. The latter also exhibit reduced FMVD, but with a partial compensatory increased NO generation capacity. The data support our hypothesis, which highlights the importance of FMVD regulation in normal and dysfunctional placentation.

Vasotrophic regulation of age-dependent hypoxic cerebrovascular remodeling

Hypoxia can induce functional and structural vascular remodeling by changing the expression of trophic factors to promote homeostasis. While most experimental approaches have been focused on functional remodeling, structural remodeling can reflect changes in the abundance and organization of vascular proteins that determine functional remodeling. Better understanding of age-dependent hypoxic macrovascular remodeling processes of the cerebral vasculature and its clinical implications require knowledge of the vasotrophic factors that influence arterial structure and function. Hypoxia can affect the expression of transcription factors, classical receptor tyrosine kinase factors, non-classical G-protein coupled factors, catecholamines, and purines. Hypoxia's remodeling effects can be mediated by Hypoxia Inducible Factor (HIF) upregulation in most vascular beds, but alterations in the expression of growth factors can also be independent of HIF. PPARγ is another transcription factor involved in hypoxic remodeling. Expression of classical receptor tyrosine kinase ligands, including vascular endothelial growth factor, platelet derived growth factor, fibroblast growth factor and angiopoietins, can be altered by hypoxia which can act simultaneously to affect remodeling. Tyrosine kinase-independent factors, such as transforming growth factor, nitric oxide, endothelin, angiotensin II, catecholamines, and purines also participate in the remodeling process. This adaptation to hypoxic stress can fundamentally change with age, resulting in different responses between fetuses and adults. Overall, these mechanisms integrate to assure that blood flow and metabolic demand are closely matched in all vascular beds and emphasize the view that the vascular wall is a highly dynamic and heterogeneous tissue with multiple cell types undergoing regular phenotypic transformation.

Pathogenesis and promising non-invasive markers for preeclampsia

Preeclampsia is one of the leading causes of maternal mortality/morbidity and preterm delivery in the world, affecting 3% to 5% of pregnant women. The pathophysiology of preeclampsia likely involves both maternal and fetal/placental factors. Abnormalities in the development of placental vessels early in pregnancy may result in placental hypoperfusion, hypoxia, or ischemia. Hypoperfusion, hypoxia, and ischemia are critical components in the pathogenesis of preeclampsia because the hypoperfused placenta transfers many factors into maternal vessels that alter maternal endothelial cell function and lead to the systemic symptoms of preeclampsia. There are several hypotheses to explain the pathogenesis of preeclampsia, including altered angiogenic balance, circulating angiogenic factors (such as marinobufagenin, a bufadienolide trigger), and activation of the renin-angiotensin system. Epigenetically-modified cell-free nucleic acids that circulate in plasma and serum might be novel markers with promising non-invasive clinical applications in the diagnosis of preeclampsia.

New frontiers in heart hypertrophy during pregnancy

During Pregnancy, heart develops physiological left ventricular hypertrophy as a result of the natural volume overload. Previously we have characterized the molecular and functional signature of heart hypertrophy during pregnancy. Cardiac hypertrophy during pregnancy is a complex process that involves many changes including in the signalling pathways, composition of extracellular matrix as well as the levels of sex hormones. This review summarises the recent advances and the new frontiers in the context of heart hypertrophy during pregnancy. In particular we focus on structural and extracellular matrix remodelling as well as signalling pathways in pregnancy-induced physiological heart hypertrophy. Emerging evidence shows that various microRNAs modulate key components of hypertrophy, therefore the role of microRNAs in the regulation of gene expression in pregnancy induced hypertrophy is also discussed. We also review the role of ubiquitin proteasome system, the major machinery for the degradation of damaged and misfolded proteins, in heart hypertrophy. The role of sex hormones in particular estrogen in cardiac remodeling during pregnancy is also discussed. We also review pregnancy-induced cardiovascular complications such as peripartum cardiomyopathy and pre-eclampsia and how the knowledge from the animal studies may help us to develop new therapeutic strategies for better treatment of cardiovascular diseases during pregnancy. Special emphasis has to be given to the guidelines on disease management in pregnancy.

Signaling regulation of fetoplacental angiogenesis

During normal pregnancy, dramatically increased placental blood flow is critical for fetal growth and survival as well as neonatal birth weights and survivability. This increased blood flow results from angiogenesis, vasodilatation, and vascular remodeling. Locally produced growth factors including fibroblast growth factor 2 (FGF2) and vascular endothelial growth factor A (VEGFA) are key regulators of placental endothelial functions including cell proliferation, migration, and vasodilatation. However, the precise signaling mechanisms underlying such regulation in fetoplacental endothelium are less well defined, specifically with regard to the interactions amongst protein kinases (PKs), protein phosphatase, and nitric oxide (NO). Recently, we and other researchers have obtained solid evidence showing that different signaling mechanisms participate in FGF2- and VEGFA-regulated fetoplacental endothelial cell proliferation and migration as well as NO production. This review will briefly summarize currently available data on signaling mediating fetoplacental angiogenesis with a specific emphasis on PKs, ERK1/2, AKT1, and p38 MAPK and protein phosphatases, PPP2 and PPP3.

Molecular mechanisms of preeclampsia

Preeclampsia is one of the leading causes of maternal morbidity/mortality. The pathogenesis of preeclampsia is still under investigation. The aim of this paper is to present the molecular mechanisms implicating in the pathway leading to preeclampsia.

Disrupted balance of angiogenic and antiangiogenic signalings in preeclampsia

The placenta plays a central role in governing local circulatory system that mediates maternal condition and fetal growth. In early gestational phases, the placenta exerts properties of invasion and neovascularization for successful placentation. Extravillous invasive trophoblasts replace uterine endometrial vasculature and establish local blood pathway to obtain oxygen and nutrients from the mother. In later phases, the placenta promotes villous angiogenesis and vascular maturation that are finely controlled by angiogenic and antiangiogenic molecules. Among various molecules involved in placental neovascularization, vascular endothelial growth factor receptors (VEGFRs) and angiotensin II receptor type 1 (AT1) mediate important signaling pathways for maternal circulatory system and fetal growth. VEGFR1 and VEGFR2 are functional receptors for placental growth factor (PlGF) and VEGF, respectively, and PlGF-VEGFR1 and VEGF-VEGFR2 interactions are disturbed in many preeclamptic patients by excess amount of soluble form of VEGFR1 (also named sFlt1), a natural PlGF/VEGF antagonist. Recent studies have disclosed that excessive sFlt1 production in the placenta and aberrant AT1 signaling in the mother are closely associated with the pathology of preeclampsia and intrauterine growth restriction (IUGR). In this paper, neovascularization of the placenta and pathological events associated with disrupted balance between angiogenic and antiangiogenic signaling in preeclampsia are discussed.

New evidence for the fetal insulin hypothesis: fetal angiotensinogen M235T polymorphism is associated with birth weight and elevated fetal total glycated hemoglobin at birth

BACKGROUND

Low birth weight is associated with an increased risk of cardiovascular events in later life. Insulin resistance is a key finding in adult patients with cardiovascular diseases. The neonatal phenotype of an individual with insulin resistance might be low birth weight, as insulin influences fetal growth. The renin-angiotensin-aldosterone system has been associated with cardiovascular disease and insulin resistance. We analyzed whether fetal polymorphisms of the angiotensinogen (AGT) and angiotensin-converting enzyme genes influence birth weight and/or fetal total glycated hemoglobin (fTGH), a surrogate parameter of fetal insulin resistance at birth.

METHOD

In 1132 white women delivering singletons, neonatal umbilical blood samples and clinical data of the mothers and newborns were obtained. Newborns were genotyped with respect to the AGT M235T and angiotensin-converting enzyme insertion/deletion polymorphism.

RESULTS

The AGT M235T TT polymorphism is associated with reduced birth weight (TT: 3288 g versus TM + MM: 3435 g, P < 0.05). Furthermore, newborns with a high percentage of fTGH (>6.5%) are more likely to have the TT genotype than those with normal fTGH (<or=6.5%, P < 0.05). With higher cutoffs for fTGH, the significance increases to P less than 0.005. No association was seen between these parameters and the fetal angiotensin-converting enzyme insertion/deletion phenotype.

CONCLUSION

The fetal AGT M235T polymorphism is associated with low birth weight and elevated fetal fTGH at birth. Previous findings show that elevated fetal fTGH correlates with low birth weight and that higher activity of the renin-angiotensin-aldosterone system is an independent risk factor for the development of diabetes mellitus and coronary artery disease. Therefore, our data are supportive of the fetal insulin hypothesis.

Physiological changes in maternal cortisol do not alter expression of growth-related genes in the ovine placenta

OBJECTIVES

The aim of this study was to investigate the effect of cortisol on growth-related genes in the ovine placenta.

STUDY DESIGN

Ewes carrying singleton pregnancies were operated on between 112 and 116 days of gestation (115 ± 0.4, term = 147 days) and randomly assigned into three groups: six control animals, five ewes that were administered cortisol by continuous intravenous infusion (1 mg/kg/day, high cortisol), and five ewes that were adrenalectomized and replaced with 0.5-0.6 mg cortisol/kg/day and 3 μg aldosterone/kg/day to produce cortisol concentrations equivalent to pre-pregnancy values (low cortisol). At necropsy (130 ± 0.2 days of gestation), placental tissue was frozen and stored at -80 °C for mRNA analysis.

MAIN OUTCOME MEASURES

To assess potential molecular mechanisms by which cortisol alters placental structure and function and fetal growth.

RESULTS

Cortisol levels did not significantly affect 11β-hydroxysteroid dehydrogenase 1 and 2 enzymes, glucocorticoid receptor, mineralocorticoid receptor and angiotensin II receptor, type 1 (AT1R) expression levels. Gene expression levels of AT2R were increased in the high cortisol group for type B placentomes. There was little effect of cortisol on the insulin-like growth factor (IGF) axis. There was significantly more IGF-I mRNA in B versus A type and more IGFBP-2 mRNA in B and C type versus A type placentomes regardless of treatment (p < 0.05).

CONCLUSIONS

These data suggest that cortisol increases placental AT2R expression at high concentrations whereas it has little effect on the placental IGF axis.

Activation of AP-1 transcription factors differentiates FGF2 and vascular endothelial growth factor regulation of endothelial nitric-oxide synthase expression in placental artery endothelial cells

FGF2 (fibroblast growth factor 2), but not vascular endothelial growth factor (VEGF), stimulates sustained activation of ERK2/1 for endothelial NOS3 (nitric-oxide synthase 3) protein expression in ovine fetoplacental artery endothelial cells (oFPAEC). We deciphered herein the downstream signaling of ERK2/1 responsible for NOS3 expression by FGF2 in oFPAEC. FGF2, but not VEGF, increased NOS3 mRNA levels without altering its degradation. FGF2, but not VEGF, trans-activated sheep NOS3 promoter, and this was dependent on ERK2/1 activation. FGF2 did not trans-activate NOS3 promoters with deletions upstream of the consensus AP-1 site (TGAGTC A, -678 to -685). Trans-activation of wild-type NOS3 promoter by FGF2 was significantly inhibited when either the AP-1 or the cAMP-response element (CRE)-like sequence (TGCGTCA, -752 to -758) was mutated and was completely blocked when both were mutated. EMSA analyses showed that FGF2, but not VEGF, stimulated AP-1 and CRE DNA-protein complexes primarily composed of JunB and Fra1. Chromatin immunoprecipitation assays confirmed JunB/Fra1 binding to NOS3 promoter AP-1 and CRE elements in intact cells. FGF2, but not VEGF, stimulated JunB and Fra1 expressions; all preceded NOS3 up-regulation and were inhibited by PD98059. Down-regulation of JunB or Fra-1, but not c-Jun, blocked FGF2 stimulation of NOS3 expression and NO production. AP-1 inhibition suppressed FGF2 stimulation of NOS3 expression in human umbilical vein EC and uterine artery endothelial cells. Thus, FGF2 induction of NOS3 expression is mainly mediated by AP-1-dependent transcription involving JunB and Fra1 up-regulation via sustained ERK2/1 activation in endothelial cells.

Peptide hormone regulation of angiogenesis

It is now apparent that regulation of blood vessel growth contributes to the classical actions of hormones on development, growth, and reproduction. Endothelial cells are ideally positioned to respond to hormones, which act in concert with locally produced chemical mediators to regulate their growth, motility, function, and survival. Hormones affect angiogenesis either directly through actions on endothelial cells or indirectly by regulating proangiogenic factors like vascular endothelial growth factor. Importantly, the local microenvironment of endothelial cells can determine the outcome of hormone action on angiogenesis. Members of the growth hormone/prolactin/placental lactogen, the renin-angiotensin, and the kallikrein-kinin systems that exert stimulatory effects on angiogenesis can acquire antiangiogenic properties after undergoing proteolytic cleavage. In view of the opposing effects of hormonal fragments and precursor molecules, the regulation of the proteases responsible for specific protein cleavage represents an efficient mechanism for balancing angiogenesis. This review presents an overview of the actions on angiogenesis of the above-mentioned peptide hormonal families and addresses how specific proteolysis alters the final outcome of these actions in the context of health and disease.

Hypoxia enhances FGF2- and VEGF-stimulated human placental artery endothelial cell proliferation: roles of MEK1/2/ERK1/2 and PI3K/AKT1 pathways

Placental development occurs under a low oxygen (2-8% O(2)) environment, which is critical for placental development and angiogenesis. In this study, we examined if hypoxia affected fibroblast growth factor-2 (FGF2)- and vascular endothelial growth factor (VEGF)-stimulated cell proliferation via the mitogen-activated protein kinase kinase 1/2 (MEK1/2)/extracellular signal-regulated kinases 1/2 (ERK1/2) and phosphatidylinositol-3 kinase (PI3K)/v-akt murine thymomaviral oncogene homologue (AKT1) pathways in human placental artery endothelial (HPAE) cells. We observed that under normoxia (approximately 20% O(2)), FGF2 and VEGF dose-dependently stimulated cell proliferation. Hypoxia (3% O(2)) significantly promoted FGF2- and VEGF-stimulated cell proliferation as compared to normoxia. Under both normoxia and hypoxia, FGF2 rapidly induced ERK1/2 and AKT1 phosphorylation, while VEGF-induced ERK1/2, but not AKT1 phosphorylation. However, hypoxia did not significantly alter FGF2- and VEGF-induced ERK1/2 and AKT1 phosphorylation as compared to normoxia. PD98059 (a MEK1/2 inhibitor) at 20microM and LY294002 (a PI3K inhibitor) at 5microM attenuated FGF2- and VEGF-induced phosphorylation of ERK1/2 and AKT1, respectively. PD98059, even at doses that drastically inhibited FGF2-induced ERK1/2 phosphorylation (20microM) and caused cell loss (40microM), did not affect FGF2-stimulated cell proliferation, which was confirmed by U0126 (another potent MEK1/2 inhibitor). PD98059, however, dose-dependently inhibited VEGF-stimulated cell proliferation. Conversely, LY294002 dose-dependently inhibited FGF2-, but not VEGF-stimulated cell proliferation. These data suggest that in the MEK1/2/ERK1/2 and PI3K/AKT1 pathways differentially mediate FGF2- and VEGF-stimulated HPAE cell proliferation. These results also indicate that hypoxia promotes FGF2- and VEGF-stimulated cell proliferation without further activation of the PI3K/AKT1 and MEK1/2/ERK1/2, respectively.

Suppression of protein phosphatase 2 differentially modulates VEGF- and FGF2-induced signaling in ovine fetoplacental artery endothelial cells

Vascular endothelial growth factor (VEGF) and fibroblast growth factor 2 (FGF2) elicit cellular responses via activation of protein kinases and phosphatases. We have reported that the MEK1/2/ERK1/2 and PI3K/AKT1 pathways are critical for VEGF- and FGF2-stimulated ovine fetoplacental artery endothelial (OFPAE) cell proliferation. We have also shown that protein phosphatase 3 (PPP3) differentially modulates VEGF- and FGF2-stimulated cell proliferation and activation of ERK1/2 and AKT1 in OFPAE cells. Herein, we investigated if protein phosphatase 2 (PPP2) modulated VEGF- and FGF2-induced ERK1/2, AKT1, and p38 MAPK activation and VEGF- and FGF2-stimulated cell proliferation in OFPAE cells. Small interfering RNA (siRNA) specifically targeting human PPP2CA catalytic subunit alpha (PPP2CA) was used to suppress PPP2CA expression in OFPAE cells. When compared with scrambled siRNA, PPP2CA siRNA decreased (p<0.05) PPP2CA protein levels (approximately 70%) and activity (approximately 50%) without altering protein levels of PPP3 catalytic subunit alpha (PPP3CA), nitric oxide synthase 3 (NOS3), ERK1/2, AKT1, and p38 MAPK. FGF2, but not VEGF rapidly (< or =5 min) induced p38 MAPK phosphorylation. Suppression of PPP2CA enhanced (p<0.05) VEGF-induced AKT1, but not ERK1/2 phosphorylation, whereas inhibited (p<0.05) FGF2-induced ERK1/2 and p38 MAPK and slightly attenuated FGF2-induced AKT1 phosphorylation. Suppression of PPP2CA did not significantly affect VEGF- and FGF2-stimulated OFPAE cell proliferation. Thus, suppression of PPP2CA alone differentially modulated VEGF- and FGF2-induced ERK1/2, AKT1, and p38 MAPK activation, without altering VEGF- and FGF2-stimulated cell proliferation in OFPAE cells. These data also suggest that signaling molecules other than ERK1/2, AKT1, and p38 MAPK are important mediators for VEGF- and FGF2-stimulated OFPAE cell proliferation after PPP2CA suppression.

Vasodilator factors in the systemic and local adaptations to pregnancy

We postulate that an orchestrated network composed of various vasodilatory systems participates in the systemic and local hemodynamic adaptations in pregnancy. The temporal patterns of increase in the circulating and urinary levels of five vasodilator factors/systems, prostacyclin, nitric oxide, kallikrein, angiotensin-(1-7) and VEGF, in normal pregnant women and animals, as well as the changes observed in preeclamptic pregnancies support their functional role in maintaining normotension by opposing the vasoconstrictor systems. In addition, the expression of these vasodilators in the different trophoblastic subtypes in various species supports their role in the transformation of the uterine arteries. Moreover, their expression in the fetal endothelium and in the syncytiotrophoblast in humans, rats and guinea-pigs, favour their participation in maintaining the uteroplacental circulation. The findings that sustain the functional associations of the various vasodilators, and their participation by endocrine, paracrine and autocrine regulation of the systemic and local vasoactive changes of pregnancy are abundant and compelling. However, further elucidation of the role of the various players is hampered by methodological problems. Among these difficulties is the complexity of the interactions between the different factors, the likelihood that experimental alterations induced in one system may be compensated by the other players of the network, and the possibility that data obtained by manipulating single factors in vitro or in animal studies may be difficult to translate to the human. In addition, the impossibility of sampling the uteroplacental interface along normal pregnancy precludes obtaining longitudinal profiles of the various players. Nevertheless, the possibility of improving maternal blood pressure regulation, trophoblast invasion and uteroplacental flow by enhancing vasodilation (e.g. L-arginine, NO donors, VEGF transfection) deserves unravelling the intricate association of vasoactive factors and the systemic and local adaptations to pregnancy.

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.

Pathophysiology of placentation abnormalities in pregnancy-induced hypertension

During embryogenesis and development, the fetus obtains oxygen and nutrients from the mother through placental microcirculation. The placenta is a distinctive organ that develops and differentiates per se, and that organizes fetal growth and maternal condition in the entire course of gestation. Several life-threatening diseases during pregnancy, such as pregnancy-induced hypertension (PIH) and eclampsia, are closely associated with placental dysfunction. Genetic susceptibilities and poor placentation have been investigated intensively to understand the pathophysiology of PIH. It is currently thought that “poor placentation hypothesis”, in which extravillous trophoblasts fail to invade sufficiently the placental bed, explains in part maternal predisposition to this disease. Cumulative studies have suggested that hypoxic micromilieu of fetoplacental site, shear stress of uteroplacental blood flow, and aberrantly secreted proinflammatory substances into maternal circulation synergistically contribute to the progression of PIH. For example, soluble form of vascular endothelial growth factor receptor-1 (sVEGFR-1) and soluble form of CD105 are elevated in circulation of PIH mothers. However, it remains to be poorly understood the pathological events in the placenta during the last half of gestation as maternal systemic disorders get worse. For better understanding and effective therapeutic approaches to PIH, it is important to clarify pathological course of PIH-associated changes in the placenta. In this review, current understanding of placental development and the pathophysiology of PIH placenta are summarized. In addition, recent findings of vasoactive signalings in PIH and rodent PIH models are discussed.

Dynamic changes in messenger RNA profiles of bovine endometrium during the oestrous cycle

During the oestrous cycle, the bovine endometrium exhibits characteristic morphological and functional changes, which are mainly induced by progesterone (P(4)), oestrogens and oxytocin. We studied the response of the endometrium to this changing hormonal environment at the transcriptome level using a custom-made cDNA microarray. Endometrium samples were recovered from Simmental heifers on days 0 (oestrus), 3.5 (metoestrus), 12 (dioestrus) and 18. The latter group was divided into animals with high (late dioestrus) and low P(4) levels (preoestrus). Significance analysis of microarrays revealed 269 genes exhibiting significant changes in their transcript levels during the oestrous cycle in distinct temporal patterns. Two major types of expression profiles were observed, which showed the highest mRNA levels during the oestrus phase or the highest levels during the luteal phase respectively. A minor group of genes exhibited the highest mRNA levels on day 3.5. Gene ontology (GO) analyses revealed GO categories related to extracellular matrix remodelling, transport, and cell growth and morphogenesis enriched at oestrus, whereas immune response and particular metabolic pathways were overrepresented at dioestrus. Generation of gene interaction networks uncovered the genes possibly involved in endometrial remodelling (e.g. collagen genes, TNC, SPARC, MMP2, MEP1B, TIMP1, TIMP2, HTRA1), regulation of angiogenesis (e.g. ANGPTL2, TEK, NPY, AGT, EPAS1, KLF5 ), regulation of invasive growth (e.g. PCSK5, tight junction proteins, GRP, LGALS1, ANXA2, NOV, PLAT, MET, TDGF1, CST6, ITGB4), cell adhesion (e.g. MUC16, LGALS3BP) and embryo feeding (e.g. SLC1A1, SLC11A2, SLC16A1, SEPP1, ENPP1). Localisation of mRNA expression in the endometrium was analysed for CLDN4, CLDN10, TJP1, PCSK5, MAGED1, and LGALS1.

Angiotensin II promotes NO production, inhibits apoptosis and enhances adhesion potential of bone marrow-derived endothelial progenitor cells

Endothelial progenitor cells (EPCs) participate in the processes of postnatal neovascularization and re-endothelialization in response to tissue ischemia and endothelial injury. The level of EPCs present has been found to be directly associated with the outcome of cardiovascular diseases, and could be regulated by stimulatory or inhibitory factors. Given the close relationship between angiotensin II (AngII) and the cardiovascular system, we investigated the effect of AngII on the activities of bone marrow (BM)-derived EPCs. Cells were isolated from BM of rats by density gradient centrifugation. Administration of AngII significantly promoted nitric oxide (NO) release, inhibited EPC apoptosis and enhanced EPC adhesion potential. All of these AngII-mediated effects on EPCs were attenuated by pretreatment with valsartan or L-NAME. Moreover, both LY294002 and wortmannin abolished the anti-apoptotic effect of AngII. Western blot analyses indicated that endothelial NO synthase (eNOS) protein and phosphorylated Akt increased with the treatment of AngII in EPCs. Thus, AngII improved several activities of EPCs through AngII type 1 receptor (AT1R), which may represent a possible mechanism linking AngII and AT1R with angiogenesis. Additionally, AngII-induced NO synthesis through eNOS in EPCs regulates apoptosis and adhesion, and the PI3-kinase/Akt pathway has an essential role in AngII-induced antiapoptosis signaling.

Protein phosphatase 3 differentially modulates vascular endothelial growth factor- and fibroblast growth factor 2-stimulated cell proliferation and signaling in ovine fetoplacental artery endothelial cells

A critical process for vascular endothelial growth factor (VEGF)- and fibroblast growth factor 2 (FGF2)-regulated cellular function is reversible protein phosphorylation, which is tightly controlled by a balance of protein kinases and phosphatases. We have reported that in ovine fetoplacental artery endothelial (OFPAE) cells, VEGF and FGF2 stimulate cell proliferation in part via activation of mitogen-activated protein kinase kinase 1/2 (MAP2K1/2)/mitogen-activated protein kinase 3/1 (MAPK3/1) and phosphoinositide 3-kinase (PI3K)/v-akt murine thymoma viral oncogene homolog 1 (AKT1) pathways. In the present study, we examined if protein phosphatase 3 (PPP3) mediated VEGF- and FGF2-stimulated OFPAE cell proliferation via modulating activation of MAPK3/1 and AKT1. Small interfering RNA (siRNA) targeting human PPP3 catalytic subunit alpha (PPP3CA) was used to suppress PPP3CA protein expression in OFPAE cells. Compared with the scrambled siRNA, PPP3CA siRNA decreased PPP3CA protein levels by approximately 97% without altering protein levels of protein phosphatase 2 catalytic subunit alpha, total MAPK3/1, total AKT1, or glyceraldehyde-3-phosphate dehydrogenase. Knockdown of PPP3CA protein expression enhanced VEGF-stimulated, but not FGF2-stimulated, cell proliferation. Knockdown of PPP3CA protein expression did not significantly affect VEGF-induced MAPK3/1 and AKT1 phosphorylation but attenuated FGF2-induced MAPK3/1 and AKT1 phosphorylation. Thus, to our knowledge, the present study is the first to demonstrate successful knockdown of PPP3CA protein expression in any cell model using a single pair of double-strained siRNA. Moreover, specific knockdown of PPP3CA protein expression enhances VEGF-stimulated, but not FGF2-stimulated, OFPAE cell proliferation and attenuates FGF2-induced, but not VEGF-induced, MAPK3/1 and AKT1 activation. Thus, PPP3CA differentially modulates the VEGF- and FGF2-stimulated cell proliferation and signaling cascades in OFPAE cells. These data also suggest that signaling molecules other than MAPK3/1 and AKT1 play an important role in VEGF- and FGF2-stimulated cell proliferation after knockdown of PPP3CA in OFPAE cells.

Impaired placental neovascularization in mice with pregnancy-associated hypertension

Preeclampsia is a serious disorder that may result in severe morbidity and mortality for mother and fetus, and it is thought that the placental dysfunction is important in the pathogenesis of preeclampsia. As the model of preeclampsia, we previously generated a transgenic mouse model that developed pregnancy-associated hypertension (PAH) by mating females expressing human angiotensinogen with males expressing human renin. In PAH mice, maternal blood pressure started to rise from days 12 to 13 of gestation (E12-13) to term (E19-20), which is accompanied by the fetal intrauterine growth retardation and systemic maternal disorders including proteinuria and convulsion. To understand the pathology of the complications in PAH mice that overlap with those in human preeclampsia, we analyzed the PAH placenta sequentially from the onset of hypertension to the term of delivery. In PAH placenta, histological analysis revealed that the microvessel densities of fetal vasculature at term were significantly lower than those of normal placenta, and the majority of terminal vessels of PAH placenta were lacking for pericytes and basement membrane. The interaction between fetal vasculature and maternal blood canal at labyrinth of PAH placenta was morphologically distorted, and the expression patterns of key molecules in neovascularization of PAH placenta were distinct from those of normal placenta during pregnancy. In addition, maternal plasma level of soluble form of vascular endothelial growth factor receptor-1 (sVEGFR-1) was significantly increased in PAH at E19. Furthermore, in uteroplacental site, in situ proteolytic activity of PAH mice was suppressed from E16 to term compared to that of normal pregnancy, and the expression of matrix metalloproteinase-2 mRNA was strikingly downregulated at E16 in PAH mice. Collective data suggest that the impairments of fetoplacental neovascularization and uteroplacental remodeling contribute to the development of complications in PAH.

Angiotensin II (Ang II) evoked secretion of the human placental lactogen (HPL) in intrauterine growth retardation: examination of the relationship with Ang II receptor type 1 (AT1) expression

Angiotensin II (Ang II) and its hemodynamic effects on placental vasculature mediated via Ang II receptor type 1 (AT1) may play significant role in intrauterine growth retardation (IUGR). Placental lactogen (HPL) production directly reflects placental function. We compared influence of Ang II on HPL production in normal and IUGR-complicated pregnancies and correlated this phenomenon with AT1 expression. Basal and Ang II-evoked HPL secretion was examined in perfused placental lobules using ELISA. After immunostaining of placental sections, AT1 expression was estimated using quantitative morphometry. Ang II increased HPL secretion. Ang II-evoked increase in HPL concentration in the perfusion fluid was 27.36+/-6.4 (%, +/-SEM) lower in IUGR (p<0.05) compared to normal-course pregnancies. AT1 expression was significantly decreased in IUGR and was 78.12+/-8.2 (%, +/-SEM) of the mean value of controls. Demonstrating that Ang II-evoked secretion of HPL in preeclampsia-free IUGR is decreased and correlates with down-regulated expression of AT1, we present a new approach to the pathophysiology of IUGR.

Activation of multiple signaling pathways is critical for fibroblast growth factor 2- and vascular endothelial growth factor-stimulated ovine fetoplacental endothelial cell proliferation

Fibroblast growth factor-2 (FGF2) and vascular endothelial growth factor (VEGF) are two key regulators of placental angiogenesis. The potent vasodilator nitric oxide (NO) could also act as a key mediator of FGF2- and VEGF-induced angiogenesis. However, the postreceptor signaling pathways governing these FGF2- and VEGF-induced placental angiogenic responses are poorly understood. In this study, we assessed the role of endogenous NO, mitogen-activated protein kinase 3/1 (MAPK3/1), and v-akt murine thymoma viral oncogene homolog 1 (AKT1) in FGF2- and VEGF-stimulated proliferation of ovine fetoplacental endothelial (OFPAE) cells. Both FGF2 and VEGF time-dependently stimulated (P < 0.05) NO production and activated AKT1. Both FGF2- and VEGF-stimulated cell proliferation was dose-dependently inhibited (P < 0.05) by N(G)-monomethyl-L-arginine (L-NMMA; an NO synthase inhibitor), PD98059 (a selective MAPK3/1 kinase 1 and 2 [MAP2K1/2] inhibitor), or LY294002 (a selective phosphatidylinositol 3 kinase [PI3K] inhibitor) but not by phenyl-4,4,5,5 tetramethylimidazoline-1-oxyl 3-oxide (PTIO, a potent extracellular NO scavenger). At the maximal inhibitory dose without cytotoxicity, PD98059 and LY294002 completely inhibited VEGF-induced cell proliferation but only partially attenuated (P < 0.05) FGF2-induced cell proliferation. PD98059 and LY294002 also inhibited (P < 0.05) FGF2- and VEGF-induced phosphorylation of MAPK3/1 and AKT1, respectively. L-NMMA did not significantly affect FGF2- and VEGF-induced phosphorylation of either MAPK3/1 or AKT1. Thus, in OFPAE cells, both FGF2- and VEGF-stimulated cell proliferation is partly mediated via NO as an intracellular and downstream signal of MAPK3/1 and AKT1 activation. Moreover, activation of both MAP2K1/2/MAPK3/1 and PI3K/AKT1 pathways is critical for FGF2-stimulated cell proliferation, whereas activation of either one pathway is sufficient for mediating the VEGF-induced maximal cell proliferation, indicating that these two kinase pathways differentially mediate the FGF2- and VEGF-stimulated OFPAE cell proliferation.

Interaction of Endothelial Nitric Oxide and Angiotensin in the Circulation

Discovery of the unexpected intercellular messenger and transmitter nitric oxide (NO) was the highlight of highly competitive investigations to identify the nature of endothelium-derived relaxing factor. This labile, gaseous molecule plays obligatory roles as one of the most promising physiological regulators in cardiovascular function. Its biological effects include vasodilatation, increased regional blood perfusion, lowering of systemic blood pressure, and antithrombosis and anti-atherosclerosis effects, which counteract the vascular actions of endogenous angiotensin (ANG) II. Interactions of these vasodilator and vasoconstrictor substances in the circulation have been a topic that has drawn the special interest of both cardiovascular researchers and clinicians. Therapeutic agents that inhibit the synthesis and action of ANG II are widely accepted to be essential in treating circulatory and metabolic dysfunctions, including hypertension and diabetes mellitus, and increased availability of NO is one of the most important pharmacological mechanisms underlying their beneficial actions. ANG II provokes vascular actions through various receptor subtypes (AT1, AT2, and AT4), which are differently involved in NO synthesis and actions. ANG II and its derivatives, ANG III, ANG IV, and ANG-(1-7), alter vascular contractility with different mechanisms of action in relation to NO. This review article summarizes information concerning advances in research on interactions between NO and ANG in reference to ANG receptor subtypes, radical oxygen species, particularly superoxide anions, ANG-converting enzyme inhibitors, and ANG receptor blockers in patients with cardiovascular disease, healthy individuals, and experimental animals. Interactions of ANG and endothelium-derived relaxing factor other than NO, such as prostaglandin I2 and endothelium-derived hyperpolarizing factor, are also described.

ANG II-stimulated DNA synthesis is mediated by ANG II receptor-dependent Ca2+/PKC as well as EGF receptor-dependent PI3K/Akt/mTOR/p70S6K1 signal pathways in mouse embryonic stem cells

Effect of angiotensin II (ANG II) on mouse embryonic stem (ES) cell proliferation was examined. ANG II increased [(3)H] thymidine incorporation in a time- (>4 h) and dose- (>10(-9) M) dependent manner. The ANG II-induced increase in [(3)H] thymidine incorporation was blocked by inhibition of ANG II type 1 (AT(1)) receptor but not by ANG II type 2 (AT(2)) receptor, and AT(1) receptor was expressed. ANG II increased inositol phosphates formation and [Ca(2+)](i), and translocated PKC alpha, delta, and zeta to the membrane fraction. Consequently, the inhibition of PLC/PKC suppressed ANG II-induced increase in [(3)H] thymidine incorporation. The inhibition of EGF receptor kinase or tyrosine kinase prevented ANG II-induced increase in [(3)H] thymidine incorporation. ANG II phosphorylated EGF receptor and increased Akt, mTOR, and p70S6K1 phosphorylation blocked by AG 1478 (EGF receptor kinase blocker). ANG II-induced increase in [(3)H] thymidine incorporation was blocked by the inhibition of p44/42 MAPKs but not by p38 MAPK inhibition. Indeed, ANG II phosphorylated p44/42 MAPKs, which was prevented by the inhibition of the PKC and AT(1) receptor. ANG II increased c-fos, c-jun, and c-myc levels. ANG II also increased the protein levels of cyclin D1, cyclin E, cyclin-dependent kinase (CDK) 2, and CDK4 but decreased the p21(cip1/waf1) and p27(kip1), CDK inhibitory proteins. These proteins were blocked by the inhibition of AT(1) receptor, PLC/PKC, p44/42 MAPKs, EGF receptor, or tyrosine kinase. In conclusion, ANG II-stimulated DNA synthesis is mediated by ANG II receptor-dependent Ca(2+)/PKC and EGF receptor-dependent PI3K/Akt/mTOR/p70S6K1 signal pathways in mouse ES cells.

Establishment of a functional ovine fetoplacental artery endothelial cell line with a prolonged life span

To study mechanisms governing fetoplacental vascular function, we have established a primary ovine fetoplacental artery endothelial (OFPAE) cell line. These OFPAE cells produce nitric oxide (NO), proliferate, and migrate in response to fibroblast growth factor 2 (FGF2) and vascular endothelial growth factor (VEGF). To overcome the senescence crisis that this primary OFPAE cell line will eventually enter, we attempted to establish a functional OFPAE cell line with a prolonged life span by transfecting cells with plasmids containing a neomycin resistance gene and a simian virus 40 gene (SV40) expressing large T (T) and small t (t) antigens. The OFPAE cells at passage 8 were transfected. After neomycin selection, the surviving OFPAE (designated SV40 OFPAE) cells were expanded up to passage 80. Up to passage 30, these SV40 OFPAE cells maintained a morphology similar to untransfected OFPAE cells. Expression of T and t antigens in SV40 OFPAE cells was confirmed by immunocytochemistry. These SV40 OFPAE cells exhibited positive uptake of acetylated low-density lipoprotein (Ac-LDL) and positive staining for NO synthase 3 (NOS3) and formed capillary-like tube structures on Matrigel. Up to passages 20-23, these SV40 OFPAE cells proliferated (P < 0.05) and produced (P < 0.05) NO in response to both FGF2 and VEGF. Moreover, this cell proliferation stimulated by FGF2 and VEGF was dose-dependently inhibited (P < 0.05) by PD98059 (a selective mitogen-activated protein kinase 1 and 2 [MAP2K1/2, also termed MEK1/2] inhibitor) or by LY294002 (a selective phosphoinositide 3-kinase [PI3K] inhibitor). These data indicate that SV40 OFPAE cells, at least at passage 23, retain endothelial phenotypes and functions similar to their parental, untransfected OFPAE cells. Thus, a functional OFPAE cell line with an extended life span has been successfully established, potentially providing a valuable cell model for studying fetoplacental endothelial function.

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.