Deferential Regulation of Placenta Growth Factor (PlGF)-Mediated Signal Transduction in Human Primary Term Trophoblast and Endothelial Cells

Increasing evidence supports that many common obstetrical complications may involve the disruption of normal placental and/or uterine vascular function. Placenta growth factor (PlGF) is an angiogenic factor that is abundantly expressed in the placenta, with primary site of synthesis being trophoblast. Receptors for PlGF include products of the fms-like tyrosine kinase (flt-1) gene which is expressed in several cell types including endothelial cells and trophoblast. PlGF activation of flt-1 in trophoblast induces the stress activated protein kinase (SAPK) signal transduction pathways, JNK (c-Jun-N-Terminal Kinase) and p38, with little induction of the extracellular signal-regulated protein kinase (ERK)-1/2 pathways. In contrast, PlGF induces strong ERK-1/2 activation, but little JNK or p38 responses in human umbilical vein endothelial cells (HUVEC). To better understand the biochemical functions of PlGF in trophoblast, we studied upstream signal regulatory molecules to determine those that are responsible for directing the divergent PlGF signal transduction responses in these cell types. PlGF induced similar activation of Nck and PLC-gamma in trophoblast and HUVEC. In marked contrast, SHP-2 and Gab2 were strongly activated by PlGF in endothelial cells but not trophoblast. These results suggest a general role for Nck and PLC-gamma in mediating PlGF signal transduction responses independent of the different downstream MAPK pathways activated. However, SHP-2 and Gab2 are regulatory molecules involved in the PlGF induction of different terminal pathways in HUVEC and trophoblast.

Functional analyses of placental protein 13/galectin-13

Placental protein 13 (PP13) was cloned from human term placenta. As sequence analyses, alignments and computational modelling showed its conserved structural and functional homology to members of the galectin family, the protein was designated galectin-13. Similar to human eosinophil Charcot-Leyden crystal protein/galectin-10 but not other galectins, its weak lysophospholipase activity was confirmed by 31P-NMR. In this study, recombinant PP13/galectin-13 was expressed and specific monoclonal antibody to PP13 was developed. Endogenous lysophospholipase activity of both the purified and also the recombinant protein was verified. Sugar binding assays revealed that N-acetyl-lactosamine, mannose and N-acetyl-glucosamine residues widely expressed in human placenta had the strongest binding affinity to both the purified and recombinant PP13/galectin-13, which also effectively agglutinated erythrocytes. The protein was found to be a homodimer of 16 kDa subunits linked together by disulphide bonds, a phenomenon differing from the noncovalent dimerization of previously known prototype galectins. Furthermore, reducing agents were shown to decrease its sugar binding activity and abolish its haemagglutination. Phosphorylation sites were computed on PP13/galectin-13, and phosphorylation of the purified protein was confirmed. Using affinity chromatography, PAGE, MALDI-TOF MS and post source decay, annexin II and beta/gamma actin were identified as proteins specifically bound to PP13/galectin-13 in placenta and fetal hepatic cells. Perinuclear staining of the syncytiotrophoblasts showed its expression in these cells, while strong labelling of the syncytiotrophoblasts' brush border membrane confirmed its galectin-like externalization to the cell surface. Knowing its colocalization and specific binding to annexin II, PP13/galectin-13 was assumed to be secreted to the outer cell surface by ectocytosis, in microvesicles containing actin and annexin II. With regard to our functional and immunomorphological results, PP13/galectin-13 may have special haemostatic and immunobiological functions at the lining of the common feto-maternal blood-spaces or developmental role in the placenta.

Blocking of the placental immune-modulatory ferritin activates Th1 type cytokines and affects placenta development, fetal growth and the pregnancy outcome

BACKGROUND

Placenta immunomodulatory ferritin (PLIF) cDNA was recently cloned from the human placenta, where it is expressed in syncytiotrophoblast and decidual mononuclear cells. PLIF and its subcloned bioactive domain (C48), expressed in Escherichia coli, are immunosuppressive proteins and induce pronounced IL-10 production in vitro and in vivo.

METHODS AND RESULTS

PLIF serum level, measured by enzyme-linked immunosorbent assay, was elevated in pregnant mice throughout gestation and declined towards delivery. Blocking of PLIF activity by vaccination of mice with C48 prior to mating inhibited pregnancy development. Passive transfer of anti-C48 immunoglobulin (Ig) starting at 3.5-12.5 days post coitum (dpc) resulted in high rate of embryo resorption. Furthermore, treatment with anti-C48 Ig resulted in placental and embryonal growth restriction. At gestation day 13.5, growth retardation was especially notable in the placentae, while at 16.5 dpc it was pronounced in the embryos. Histopathological examination revealed that experimental placentae were globally hypoplastic and the labyrinth was strikingly pale and contained less maternal blood compared with control. Immune-activated spleen cells harvested at 13.5 dpc from anti-C48 Ig-treated pregnant mice secreted in vitro increased level of Th1 cytokines (IL-2, TNF-alpha, IL-12) and decreased level of Th2 cytokines (IL-10, IL-4, IL-5, IL-6) as compared with the level of the respective cytokines secreted by spleen cells from control pregnant mice.

CONCLUSION

This study provides the first in vivo evidence that PLIF plays a major role in placentation and embryonic growth.

Placenta growth factor is not required for exercise-induced angiogenesis

Angiogenesis is a tightly regulated process, both during development and adult life. Animal models with mutations in the genes coding for placental growth factor (PlGF), a member of vascular endothelial growth factor (VEGF) family, or the tyrosine kinase domain of the PlGF receptor (Flt-1) have revealed differences between normal physiological angiogenesis and pathological angiogenesis associated with conditions such as tumor growth, arthritis and atherosclerosis. In the present paper, we investigated the potential role of PlGF in regulating physiological angiogenesis by analyzing vascular changes in heart and skeletal muscles of wild-type and Plgf-/- mice following prolonged and sustained physical training. Sedentary Plgf-/- mice showed a reduced capillary density in both heart and skeletal muscles as compared to wild-type mice (P < 0.05). However, after a 6-week training period, heart/body weight ratio, citrate synthase activity, vessel density and capillary/myocyte ratio were significantly increased in both wild-type and Plgf-/- mice (all P < 0.05). At the same time intercapillary distance was significantly reduced. Finally, acute exercise was not associated with any change in PlGF protein level in the skeletal muscle. Our results demonstrate that PlGF is not necessary for exercise-training-induced angiogenesis. We thus suggest that the role of PlGF is confined to the selective regulation of angiogenesis only under pathological conditions.

Identification of genes in the ovine endometrium regulated by interferon tau independent of signal transducer and activator of transcription 1

Interferon tau (IFNtau), a type I IFN produced by the conceptus trophectoderm, increases many type I IFN-stimulated genes (ISGs) in the ovine uterine endometrial stroma and glandular epithelium (GE) using signal transducer and activator of transcription 1 (STAT1)-dependent pathways. Most ISGs are not induced or increased by IFNtau in the STAT1-negative endometrial luminal epithelium (LE). The objective was to identify genes regulated by IFNtau in a STAT1-independent manner using DNA microarray and human cell lines. The RNA from human 2fTGH and U3A (STAT1 null 2fTGH) cell lines, stimulated for 24 h with nothing or recombinant ovine IFNtau, was profiled using an Affymetrix human genome U95Av2 microarray. In 2fTGH cells, IFNtau increased the expression of 101 genes at least 2-fold, including IFN-inducible 56-kDa protein (IFI56), ISG12 or p27, and guanylate binding protein isoform I (GBP-2). In U3A cells, IFNtau increased expression of 66 genes at least 2-fold, including Wnt7a. Steady-state levels of IFI56, ISG12, GBP-2, and Wnt7a mRNAs increased in the ovine uterine endometrium between d 10 and 16 of pregnancy but not during the estrous cycle. GBP-2 and IFI56 mRNAs were expressed only in endometrial stroma, ISG12 in both LE and GE, and Wnt7a only in LE of the ovine uterus. Intrauterine infusion of ovine IFNtau increased expression of all four genes in the endometrium of cyclic ewes. Therefore, IFNtau does regulate genes independent of STAT1 in the endometrial LE and U3A cells and dependent on STAT1 in the endometrial stroma and 2fTGH cells. These IFNtau -stimulated genes may be important in establishment of uterine receptivity to the embryo and conceptus implantation given their stage-specificity in endometrium across diverse species.

Overexpression of placenta growth factor contributes to the pathogenesis of pulmonary emphysema

To examine the role of placenta growth factor (PlGF) in the pathogenesis of pulmonary emphysema, we generated PlGF-transgenic (TG) mice using a phosphoglycerate kinase promoter. This resulted in constitutive overexpression of PlGF. In these TG mice, pulmonary emphysema, with enlarged air spaces and enhanced pulmonary compliance, first appeared at 6 months of age and became prominent at 12 months. Increased alveolar septal cell apoptosis was noted in their lungs. Fluorescence-activated cell sorter analysis suggests that these apoptotic septal cells are type II pneumocytes. At the same time, the messenger RNA of vascular endothelial growth factor and platelet-endothelial cell adhesion molecule-1, an endothelial cell marker, were downregulated indicating a reduced number of endothelial cells and its survival factor VEGF. In vitro, exogenous PlGF can inhibit the proliferation and promote the cell death of mouse type II pneumocytes. In normal newborn mice, abundant expression of PlGF messenger RNA was detected in the lungs during saccular division but was rapidly downregulated after alveolarization was complete. Thus, a persistently elevated PlGF was detrimental to the developed lung and causes the emphysematous change seen in our TG mice. Our study suggests that PlGF plays an important role in the pathogenesis of pulmonary emphysema via its action on type II pneumocytes.

Human cytotrophoblasts promote endothelial survival and vascular remodeling through secretion of Ang2, PlGF, and VEGF-C

Cytotrophoblasts are specialized epithelial cells of the human placenta that differentiate to acquire tumor-like properties that allow them to invade the uterus. Concurrently, they develop endothelial-like characteristics. This transformation allows cytotrophoblasts to replace the maternal cells that line uterine vessels, thereby diverting maternal blood to the placenta. Previously, we showed that invading cytotrophoblasts secrete VEGF-C and PlGF, factors that regulate their acquisition of an endothelial-like phenotype. Here, we examined the cells' expression of angiopoietin ligands and their Tie receptors. The data show that cytotrophoblasts predominantly expressed Ang2. We also studied the paracrine functions of Ang2 and the VEGFs by culturing uterine microvascular endothelial cells in cytotrophoblast-conditioned medium, which supported their growth. Removal of VEGF-C, PlGF, and/or Ang2 from the medium caused a marked reduction in cell number due to massive apoptosis. We also assayed the angiogenic potential of cytotrophoblast-derived factors in the chick chorioallantoic membrane assay. The results showed that they stimulated angiogenesis to a level comparable to that of basic FGF. These data suggest that invasive human cytotrophoblasts use an unusual repertoire of factors to influence the angiogenic state of maternal blood vessels and that this cross talk plays an important part in the endovascular component of uterine invasion.

Role of vascular endothelial growth factor and placental growth factor in basal adhesion formation and in carbon dioxide pneumoperitoneum-enhanced adhesion formation after laparoscopic surgery in transgenic mice

OBJECTIVE

To evaluate the role of vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) in adhesion formation after laparoscopic surgery.

DESIGN

Prospective, randomized study.

SETTING

Academic research center.

ANIMAL(S)

Female wild-type mice and transgenic mice (n = 110), expressing exclusively VEGF-A(164) (VEGF-A(164/164)) or deficient for VEGF-B (VEGF-B(-/-)) or for PlGF (PlGF(-/-)).

INTERVENTION(S)

Adhesions were induced during laparoscopy. To evaluate "basal adhesions" and "CO(2) pneumoperitoneum-enhanced adhesions," the pneumoperitoneum was maintained for a minimum (10 minutes) or prolonged (60 minutes) period. The role of PlGF was also evaluated by administration of antibodies.

MAIN OUTCOME MEASURE(S)

Adhesions were blindly scored after 7 days.

RESULT(S)

In all wild-type mice, CO(2) pneumoperitoneum enhanced adhesion formation. In comparison with wild-type mice, basal adhesions were higher in VEGF-A(164/164) mice and similar in VEGF-B(-/-) and PlGF(-/-) mice. Pneumoperitoneum did not enhance adhesions in any of these transgenic mice. The effects observed in PlGF(-/-) mice were confirmed in PlGF antibody-treated mice.

CONCLUSION(S)

The data demonstrate that the VEGF family plays a role in adhesion formation and confirm that CO(2) pneumoperitoneum enhances adhesions. VEGF-A(164) has a direct role in basal adhesions. Absence of pneumoperitoneum-enhanced adhesions in VEGF-A(164/164), VEGF-B(-/-), and PlGF(-/-) mice indicates up-regulation of VEGF-A(164), VEGF-B, and PlGF by CO(2) pneumoperitoneum as a mechanism for pneumoperitoneum-enhanced adhesion formation.

Differences in glycosylation and sperm-egg binding inhibition of pregnancy-related glycodelin

Glycodelin is a glycoprotein produced in many glands, particularly those of reproductive tissues. It appears as different glycoforms in amniotic fluid (glycodelin-A) and seminal plasma (glycodelin-S), but only glycodelin-A inhibits gamete adhesion. In the present study, glycodelin from secretory-phase endometrium, first-trimester pregnancy decidua, and midtrimester amniotic fluid was studied with respect to physicochemical properties, including glycosylation patterns and inhibitory activity of sperm-egg binding. Purified glycodelins from all these sources were similar in isoelectric focusing and in lectin immunoassays using lectins from Wisteria floribunda and Sambucus nigra. Likewise, the glycodelins inhibited sperm-egg binding in a dose-dependent manner, as measured by hemizona-binding assay. However, subtle quantitative physicochemical and biological differences were found between glycodelins from different sources as well as within the same tissue/fluid between different individuals. Differences were most pronounced between endometrial glycodelins from nonpregnancy and first-trimester pregnancy. The glycan structures studied by fast-atom bombardment mass spectrometry of individual amniotic fluid glycodelin-A samples also showed interindividual quantitative differences. In conclusion, glycodelins from different female reproductive tract tissues and amniotic fluid share substantial similarity, allowing all of them to be called glycodelin-A. However, these glycodelins exhibit quantitative physicochemical and functional differences between different sources and individuals.

Glycodelin in ovarian serous carcinoma: association with differentiation and survival

Ovarian cancer consists of many subtypes, serous carcinoma being the most common of them. In addition to the histopathological subtype, grading, clinical staging, and the amount of residual tumor, a great number of putative prognostic markers have been introduced. This study addresses in ovarian serous carcinoma the role of glycodelin, the major progesterone-regulated lipocalin protein of the reproductive axis with diverse actions in cell recognition and differentiation. Glycodelin expression was determined by immunohistochemistry of tissue microarrays in ovarian serous carcinomas from 460 patients, and the results were analyzed with respect to progesterone receptor subtype A (PRA) and progesterone receptor subtype B (PRB), clinical parameters, and survival. Glycodelin was localized to the cytoplasm of tumor cells, whereas vascular endothelium in tumor tissue was glycodelin-negative. Glycodelin expression was more frequent in well-differentiated (grade I, 79%) than in poorly differentiated carcinomas (grade III, 51%; P < 0.0001), and it was also more frequent in early-stage compared with advanced-stage carcinomas (P = 0.002). Nuclear PRA and PRB were often coexpressed with cytoplasmic glycodelin. Although this was not consistent in all tumors, there was a positive correlation between the presence of glycodelin and PRs in the tumor (P < 0.02), but not between the presence of, or the absence of, glycodelin in tumor and the CA-125 serum concentration. Although in multivariate analysis glycodelin was not an independent variable, the patients with glycodelin-expressing tumors showed a higher 5-year overall survival compared with those with glycodelin-negative tumors (55 versus 39%; P < 0.0001; hazard ratio in univariate analysis, 0.57; confidence interval, 0.44-0.74). This difference was notable in patients with grade I tumors and stage III disease. In the latter group, the 10-year survival probability of patients with glycodelin-positive tumors was more than twice as high as that in women with glycodelin-negative tumors. This was also found within well-defined clinical categories, e.g., stage III/grade II and stage III/grade III carcinomas, in which patients with glycodelin-positive tumors carried significantly better 10-year overall survival compared with those with glycodelin-negative tumors. It is concluded that, in ovarian serous carcinoma, glycodelin expression portends better prognosis, probably because of its differentiation-related disposition.

Assessment of requirements for IL-15 and IFN regulatory factors in uterine NK cell differentiation and function during pregnancy

In mouse and human, precursors of NK cell lineage home to decidualizing uteri. To assess the requirement for IL-15, an essential cytokine for NK differentiation in lymphoid tissue, on uterine NK (uNK) cell differentiation, implantation sites from IL-15(-/-) mice were analyzed histologically. IL-15(-/-) implantation sites had no uNK cells, no spiral-artery modification, and lacked the decidual integrity found in normal mice. IL-15(-/-) recipients of C57BL/6 marrow displayed similar pathology. However, implantation sites from recombination-activating gene-2(-/-)gamma(c)(-/-) (alymphoid) recipients of IL-15(-/-) marrow showed normal uNK cells, modified spiral arteries, and well-developed decidua basalis. Deletion of the IFN-regulatory factor (IRF)-1, but not IRF-2 (factors important in peripheral NK cell differentiation) limited but did not prevent uNK cell development. In situ hybridization localized IRF-1 largely to placental trophoblast cells. IRF-1(-/-) marrow transplanted into recombination-activating gene-2(-/-)gamma(c)(-/-) displayed competence for full uNK cell differentiation. IL-15 mRNA expression at implantation sites of IRF-1(-/-) and C57BL/6 was similar, suggesting that, unlike in bone marrow and spleen, IRF-1 does not regulate IL-15 in the pregnant uterus. Terminal differentiation of uNK cells was not promoted in pregnant IRF-1(-/-) mice by 5-day infusion of murine rIL-15, suggesting that IRF-1 deficiency rather than IL-15 deficiency limits uNK cell differentiation in these mice. Further, IRF-1 regulates placental growth, birth weight, and postnatal growth of offspring. These studies indicate that uNK cell development and maturation share some aspects with NK cell development in other tissues, but also display distinctive tissue-specific regulation.

Polyunsaturated fatty acids and bovine interferon-tau modify phorbol ester-induced secretion of prostaglandin F2 alpha and expression of prostaglandin endoperoxide synthase-2 and phospholipase-A2 in bovine endometrial cells

Embryonic mortality in cattle may occur because of inadequate inhibition of uterine secretion of prostaglandin (PG) F2alpha mediated by bovine interferon-tau (bIFN-tau). The objectives of the present study were to determine whether polyunsaturated fatty acids inhibit secretion of PGF2alpha from bovine endometrial cells induced by stimulating protein kinase C with phorbol 12,13 dibutyrate (PDBu) and to investigate possible mechanisms of action. Confluent cells were exposed for 24 h to 100 microM of linoleic, arachidonic (AA; C20:4, n-6), linolenic (LNA; C18:3, n-3), eicosapentaenoic (EPA; C20:5, n-3), or docosahexaenoic (DHA; C22:6, n-3) acid. After incubation, cells were washed and stimulated with PDBu. The EPA, DHA, and LNA attenuated secretion of PGF2alpha in response to PDBu. The EPA and DHA were more potent inhibitors than LNA. The EPA inhibited secretion of PGF2alpha at 6.25 microM. Secretion of PGF2alpha in response to PDBu decreased with increasing incubation time with EPA. Both bIFN-tau and EPA inhibited secretion of PGF2alpha, and their inhibitory effects were additive. The bIFN-tau, but not EPA, reduced the abundance of PG endoperoxide synthase-2 (PGHS-2) mRNA. Incubation with 100 microM EPA, DHA, or AA for 24 h followed by treatment with PDBu did not affect concentrations of PGHS-2 and phospholipase A2 proteins. The EPA and DHA inhibit secretion of PGF2alpha through a mechanism different from that of bIFN-tau. The effect of EPA on PGF2alpha secretion may be caused by competition with AA for PGHS-2 activity or reduction of PGHS-2 activity. The use of EPA and DHA to inhibit uterine secretion of PGF2alpha and to improve embryonic survival in cattle warrants further investigation.

Effects of the estrous cycle, pregnancy and interferon tau on expression of cyclooxygenase two (COX-2) in ovine endometrium

In sheep, the uterus produces luteolytic pulses of prostaglandin F2alpha (PGF) on Days 15 to 16 of estrous cycle to regress the corpus luteum (CL). These PGF pulses are produced by the endometrial lumenal epithelium (LE) and superficial ductal glandular epithelium (sGE) in response to binding of pituitary and/or luteal oxytocin to oxytocin receptors (OTR) and liberation of arachidonic acid, the precursor of PGF. Cyclooxygenase-one (COX-1) and COX-2 are rate-limiting enzymes in PGF synthesis, and COX-2 is the major form expressed in ovine endometrium. During pregnancy recognition, interferon tau (IFNtau), produced by the conceptus trophectoderm, acts in a paracrine manner to suppress development of the endometrial epithelial luteolytic mechanism by inhibiting transcription of estrogen receptor alpha (ERalpha) (directly) and OTR (indirectly) genes. Conflicting studies indicate that IFNtau increases, decreases or has no effect on COX-2 expression in bovine and ovine endometrial cells. In Study One, COX-2 mRNA and protein were detected solely in endometrial LE and sGE of both cyclic and pregnant ewes. During the estrous cycle, COX-2 expression increased from Days 10 to 12 and then decreased to Day 16. During early pregnancy, COX-2 expression increased from Days 10 to 12 and remained higher than in cyclic ewes. In Study Two, intrauterine infusion of recombinant ovine IFNtau in cyclic ewes from Days 11 to 16 post-estrus did not affect COX-2 expression in the endometrial epithelium. These results clearly indicate that IFNtau has no effect on expression of the COX-2 gene in the ovine endometrium. Therefore, antiluteolytic effects of IFNtau are to inhibit ERalpha and OTR gene transcription, thereby preventing endometrial production of luteolytic pulses of PGF. Indeed, expression of COX-2 in the endometrial epithelia as well as conceptus is likely to have a beneficial regulatory role in implantation and development of the conceptus.

Placenta growth factor activates monocytes and correlates with sickle cell disease severity

Sickle cell disease (SCD) results in chronic hypoxia and secondarily increased erythropoietin concentrations. Leukocytosis and activated monocytes are also observed in SCD in absence of infection or vaso-occlusion (steady state), the reasons for which are unknown. We found that erythroid cells produced placenta growth factor (PlGF), an angiogenic growth factor belonging to the vascular endothelial growth factor (VEGF) family, and its expression was induced in bone marrow CD34+ progenitor cells in the presence of erythropoietin. Furthermore, the steady state circulating PlGF levels in subjects with severe SCD (at least 3 vaso-occlusive crises [VOCs] per year) were 18.5 +/- 1.2 pg/mL (n = 9) compared with 15.5 +/- 1.2 pg/mL (n = 13) in those with mild SCD (fewer than 3 VOCs per year) and 11.3 +/- 0.7 pg/mL (n = 9) in healthy controls (P <.05), suggesting a correlation between PlGF levels and SCD severity. In addition, PlGF significantly increased mRNA levels of the proinflammatory cytochemokines interleukin-1beta, interleukin-8, monocyte chemoattractant protein-1, and VEGF in peripheral blood mononuclear cells (MNCs) of healthy subjects (n = 4; P <.05). Expression of these same cytochemokines was significantly increased in MNCs from subjects with SCD at steady state (n = 14), compared with healthy controls. Of the leukocyte subfractions, PlGF stimulated monocyte chemotaxis (P <.05, n = 3). Taken together, these data show for the first time that erythroid cells intrinsically release a factor that can directly activate monocytes to increase inflammation. The baseline inflammation seen in SCD has always been attributed to sequelae secondary to the sickling phenomenon. We show that PlGF contributes to the inflammation observed in SCD and increases the incidence of vaso-occlusive events.

VEGF-A(164/165) and PlGF: roles in angiogenesis and arteriogenesis

Angiogenic cytokines such as vascular endothelial growth factor-A(164/165) (VEGF-A(164/165)) and placenta growth factor (PlGF) are being considered for therapeutic relief of coronary heart disease and other forms of tissue ischemia caused by atherosclerosis. Before proceeding further with clinical testing, it is important to determine what types of new blood vessels these cytokines actually induce and whether they could provide a useful new blood supply to ischemic tissues. In mice, VEGF-A(164/165) induced a transient angiogenic response (mother vessels, glomeruloid bodies, daughter capillaries), and stable arteriovenous malformations, arteriogenesis, and lymphangiogenesis; whereas PlGF only induced the formation of large, stable blood vessels. The large, long-lasting blood vessels induced by VEGF-A(164/165) and PlGF could provide an improved blood supply if positioned proximal to ischemic tissue, but VEGF-A(164/165)'s angiogenic response--which is short lived and accompanied by vascular hyperpermeability, edema, and fibrosis--would seem to offer little therapeutic benefit.

Placental growth factor and its receptor, vascular endothelial growth factor receptor-1: novel targets for stimulation of ischemic tissue revascularization and inhibition of angiogenic and inflammatory disorders

In contrast to VEGF and its receptor VEGFR-2, PlGF and its receptor VEGFR-1 have been largely neglected and therefore their potential for therapy has not been previously explored. In this review, we describe the molecular properties of PlGF and VEGFR-1 and how this translates into an important role for PlGF in the angiogenic switch in pathological angiogenesis, by interacting with VEGFR-1 and synergizing with VEGF. PlGF was effective in the growth of new and stable vessels in cardiac and limb ischemia, through its action on different cell types (i.e. endothelial, smooth muscle and inflammatory cells and their precursors) that play a cardinal role in blood vessel formation. Accordingly, blocking its receptor VEGFR-1 with monoclonal antibodies (anti-VEGFR-1 mAb), expressed on al these cell types, successfully attenuated blood vessel formation during cancer, ischemic retinopathy and rheumatoid arthritis. In addition, while blocking this receptor was effective in reducing inflammatory disorders like atherosclerosis and rheumatoid arthritis, blocking the anti-angiogenic receptor VEGFR-2 was without effect. This indicates that in the latter diseases the beneficial effects of anti-VEGFR1 mAb were mainly due to its effect on inflammatory cells. Importantly, VEGFR-1 was also present on hematopoietic stem/progenitor cells, the precursors of inflammatory cells. Thus, these preclinical studies show proof-of-principle that PlGF and VEGFR-1 are promising therapeutic targets to treat angiogenesis and inflammation related disorders. Clinical trials will reveal whether this is also true for patients.

Hypoxia alters expression and function of syncytin and its receptor during trophoblast cell fusion of human placental BeWo cells: implications for impaired trophoblast syncytialisation in pre-eclampsia

The fundamental process of placental trophoblast cell fusion (syncytiotrophoblast formation or syncytialisation) which is a characteristic of this tissue is poorly understood. Pre-eclampsia is associated with placental hypoxia and suppressed syncytiotrophoblast formation. We therefore have studied the effect of low-oxygen tensions on the rate of cell fusion, relative abundance of mRNAs encoding syncytin and its receptor, amino acid transport system B(0), which are thought to be involved in trophoblast cell fusion (as well as the activity of amino acid transport through this system) in a cell model of syncytialisation (BeWo cells following forskolin treatment). Forskolin-induced cell fusion (determined by a quantitative flow cytometry assay) was reversibly suppressed in 2% oxygen compared to 20% oxygen. This was associated with suppressed secretion of human chorionic gonadotropin. Forskolin stimulated relatively less syncytin mRNA (determined by reverse transcription-polymerase chain reaction) in 2% than in 20% oxygen and there was no stimulation after 48 h in 2% oxygen. There was a spontaneous, time-dependent increase of amino acid transporter B(0) mRNA in vehicle, which was suppressed by 2% oxygen and by forskolin treatment in 20% oxygen. Forskolin-induced changes in amino acid transport system B(0) function were not seen in cells cultured for 48 h in 2% oxygen. These observations suggest that under conditions of low ambient oxygen, dysregulation of expression of syncytin and of its receptor may suppress the normal process of cell fusion necessary for syncytiotrophoblast formation and contributes to syncytiotrophoblast abnormalities characteristic of pre-eclampsia.

Expression and function of placenta growth factor: implications for abnormal placentation

OBJECTIVE

Essential requirements for successful gestation include the coordinated growth and differentiation of the placenta and the development of a functional placental vasculature. However, relatively little is known about factors that are responsible for regulating these functions. One angiogenic growth factor that might be involved in regulating both vascular endothelial cell and trophoblast function is placental growth factor (PGF).

METHODS

Current published reports were surveyed and our own work was reviewed to highlight the expression, function, and potential significance of PGF at the human maternal-fetal interface.

RESULTS

PGF is highly expressed in trophoblasts during normal pregnancy, and its expression is significantly decreased in preeclampsia, an obstetric complication presumed to be associated with placental bed hypoxia and ischemia. In agreement with this, in vitro trophoblast expression of PGF can be down-regulated by low oxygen tension. The cognate receptor for PGF, fms-like tyrosine kinase receptor, is expressed on trophoblasts as well as vascular endothelial cells, suggesting that it has autocrine and paracrine functions. Accordingly, PGF can regulate proliferation in first trimester trophoblasts, apoptosis in term trophoblasts, and it can directly or indirectly regulate vascular growth, maturation, and permeability.

CONCLUSIONS

Many obstetric complications, most notably preeclampsia, are associated with aberrant trophoblast function and inadequate or dysfunctional vasculature within the developing placenta. The ability of PGF to influence trophoblast and vascular endothelial cells provides clear impetus for further studies to investigate the biological and clinical significance of PGF in normal and abnormal human pregnancies.

Pregnancy and interferon tau regulate major histocompatibility complex class I and beta2-microglobulin expression in the ovine uterus

Major histocompatibility complex (MHC) class I molecules, consisting of an alpha chain and beta2-microglobulin (beta2MG), play an important role in immune rejection responses by discriminating self and nonself and are increased by type I interferons during antiviral responses. Interferon tau (IFNtau), the pregnancy-recognition signal in ruminants, is a type I interferon produced by the ovine conceptus between Days 11 and 21 of gestation. In study 1, expression of MHC class I alpha chain and beta2MG mRNA and protein was detected primarily in endometrial luminal epithelium (LE) and glandular epithelium (GE) on Days 10 and 12 of the estrous cycle and pregnancy. On Days 14-20 of pregnancy, MHC class I and beta2MG expression increased only in endometrial stroma and GE and, concurrently, was absent in LE and superficial ductal GE (sGE). Although neither MHC class I nor beta2MG proteins were detected in Day 20 trophectoderm, beta2MG mRNA was detected in conceptus trophectoderm. In study 2, cyclic ewes were ovariectomized on Day 5, treated daily with progesterone to Day 16, received intrauterine infusions between Days 11 and 16 of either control serum proteins or recombinant ovine IFNtau, and were hysterectomized on Day 17. The IFNtau increased MHC class I and beta2MG expression only in endometrial stroma and GE. During pregnancy, MHC class I and beta2MG gene expression is inhibited in endometrial LE and sGE but, paradoxically, is stimulated by IFNtau in the stroma and GE. The silencing of MHC class I alpha chain and beta2MG genes in the endometrial LE and sGE during pregnancy recognition and establishment may be a critical mechanism preventing immune rejection of the conceptus allograft.

Vascular endothelial growth factor is a chemoattractant for trophoblast cells

A role for angiogenic growth factors in trophoblast invasion has been postulated. Directional motility (chemotaxis) is an important function of trophoblast cells. We have previously shown that vascular endothelial growth factor (VEGF) increases the random movement of trophoblast cells although placental growth factor (PlGF) has no effect. Heparin inhibited this effect of VEGF. Motility of trophoblast cells has been proposed to be mediated by a nitric oxide (NO) pathway. We hypothesized that VEGF but not PlGF would be chemotactic for trophoblast cells. Chemotaxis of a first trimester extravillous trophoblast cell line, SGHPL-4, and primary isolates of first trimester and term trophoblast cells was measured using a Boyden chamber. Initial experiments to optimize the time of the experiment and identify a positive control were performed. Subsequent experiments ran for 20 h, used 0.5 per cent FBS or 10 ng/ml PDGF as negative and positive controls and were performed in triplicate. VEGF (1, 10 and 100 ng/ml+/-1 microg/ml heparin or +/-100 microM L-NAME) and PlGF (1, 10, 100 ng/ml) were tested. The chamber was placed in a 5 per cent CO(2) in air, 37 degrees C incubator. The number of cells in the lower chamber were counted. There was a dose dependent increase in chemotactic motility of the SGHPL-4 cell line and term trophoblast cells in response to VEGF. PlGF had no effect on the movement of the first trimester trophoblast cell line but did increase the motility of the term trophoblast cells in a dose dependent manner. Heparin increased the cellular motility of both cell types alone. It also further enhanced the chemoactivity of VEGF on the term trophoblast cells but not the cell line. L-NAME did not affect the VEGF-stimulated motility of the first trimester cell line. However, in the term trophoblast cells L-NAME increased the directional cellular motility in the absence of, or in the presence of low concentrations of VEGF. In conclusion, the first trimester and term trophoblast cells appeared to respond differently to the various factors tested in the present study that may reflect differential cellular function as gestation progresses.

Effect of luteinizing hormone (LH), pregnancy specific protein B (PSPB), or arachidonic acid (AA) on ovine endometrium of the estrous cycle or placental secretion of prostaglandins E2 (PGE2) and F2alpha (PGF2alpha) and progesterone in vitro

The objective of this experiment was to determine the effect of AA, LH, or PSPB on secretion of PGE2, PGF2alpha, or progesterone by ovine caruncular endometrium of the estrous cycle or placental tissue of pregnancy in vitro. Ovine caruncular endometrium of the estrous cycle (days 8, 11, 13, and 15) or caruncular/placental tissue on days 8, 11, 13, 15, 20, 30, 40, 50, 60, and 90 postbreeding were incubated in vitro with vehicle, AA, LH, or PSPB in M-199 for 4 and 8 h. Secretion of PGF2alpha by caruncular endometrium of non-bred ewes on days 13 and 15 and by caruncular/placental tissue of bred ewes on days 13, 15, 20, 30, and 40 was increased (P < or = 0.05) when incubated with vehicle and declined (P < or = 0.05) after day-40 in bred ewes. Secretion of PGF2alpha by day-15 caruncular endometrium of non-bred ewes and bred ewes was increased (P < or = 0.05) by AA on days 13 and 15 and by LH on day-15. Secretion of PGF2alpha by caruncular/placental tissue from bred ewes was (P < or = 0.05) by AA on days 13, 15, 20, 30, and 40 and by LH on days 15, 20, 30, and 40, after which the response decreased (P < or = 0.05). Secretion of PGF2alpha by caruncular endometrium of non-bred ewes during the estrous cycle or by caruncular/placental tissue of bred ewes during the first trimester was not affected by PSPB (P > or = 0.05). Secretion of PGE2 by caruncular endometrium of non-bred ewes did not change (P > or = 0.05) and was increased (P < or = 0.05) by caruncular/placental tissue on days 13-90 from bred ewes when incubated with vehicle. Secretion of PGE2 by endometrium from non-bred ewes was not affected (P > or = 0.05) by AA, LH, or PSPB, but was increased (P < or = 0.05) by AA or LH on days 13-50 and by PSPB on days 60 and 90 when incubated with caruncular/placental tissue from bred ewes. Secretion of progesterone by placental tissue of bred ewes increased (P < or = 0.05) on day-50 and continued to increase through day-90. In summary, uterine/placental tissue secretion of PGF2alpha is not reduced until the end of the first trimester of pregnancy in ewes. In addition, LH appears to play a role in luteolysis of non-bred ewes by stimulating caruncular endometrial secretion of PGF2alpha and on day-5 postbreeding to prevent luteolysis during early pregnancy by stimulating caruncular/placental secretion of PGE2 throughout the first trimester of pregnancy in sheep. Secretion of PGE2 by caruncular/placental tissue after day-50 of pregnancy appears to be regulated by PSPB, not LH.

Placental protein 14 regulates selective B cell responses

Placental protein 14 (PP14) is a glycoprotein of the lipocalin family that acts as a negative regulator in T cell receptor-mediated activation. In this study, we investigated PP14s potential role in regulating B cell activation. While PP14-inhibited B cell proliferation, IgM secretion and the surface expression of MHC class II, the expression of other surface molecules, such as CD69 and CD86, were unaffected. These observed effects were independent of the anti-IgM concentration used for stimulation, regardless of the presence of either T cells or IL-4, and persisted when B cells were stimulated by stimuli, which circumvent early events during B cell Ag receptor (BCR) activation, namely, protein kinase C activators in combination with Ca(2+) ionophore. Interestingly, we demonstrated that PP14s inhibitory characteristics are reminiscence of that achieved by independent ligation of CD19 using anti-CD19 mAb. Together with our previously reported effects on T cells, these findings identify PP14 as a soluble regulatory factor capable of interacting with both T and B cells in a carbohydrate-dependent manner and as a result it can affect both cellular and humoral immune responses.

Ovine placental lactogen specifically binds to endometrial glands of the ovine uterus

A hormonal servomechanism has been proposed to regulate differentiation and function of the endometrial glandular epithelium (GE) in the ovine uterus during pregnancy. This mechanism involves sequential actions of estrogen, progesterone, ovine interferon tau (IFNtau), placental lactogen (oPL), and placental growth hormone (oGH). The biological actions of oPL in vitro are mediated by homodimerization of the prolactin receptor (oPRLR) and heterodimerization of the oPRLR and oGH receptor. The objectives of the study were to determine the effects of intrauterine oPL, oGH, and their combination on endometrial histoarchitecture and gene expression and to localize and characterize binding sites for oPL in the ovine uterus in vivo using an in situ ligand binding assay. Intrauterine infusion of oPL and/or oGH following IFNtau into ovariectomized ewes treated with progesterone daily differentially affected endometrial gland number and expression of uterine milk proteins and osteopontin. However, neither hormone affected PRLR, insulin-like growth factor (IGF)-I, or IGF-II mRNA levels in the endometrium. A chimeric protein of placental secretory alkaline phosphatase (SEAP) and oPL was used to identify and characterize binding sites for oPL in frozen sections of interplacentomal endometrium from pregnant ewes. Specific binding of SEAP-oPL was detected in the endometrial GE on Days 30, 60, 90, and 120 of pregnancy. In Day 90 endometrium, SEAP-oPL binding to the endometrial GE was displaced completely by oPL and prolactin (oPRL) but only partially by oGH. Binding experiments using the extracellular domain of the oPRLR also showed that iodinated oPL binding sites could be competed for by oPRL and oPL but not by oGH. Collectively, results indicate that oPL binds to receptors in the endometrial glands and that oPRL is more effective than oGH in competing for these binding sites. Thus, effects of oPL on the endometrial glands may be mediated by receptors for oPRL and oGH.