Signal transduction and biological function of placenta growth factor in primary human trophoblast

Human cytomegalovirus-caused damage to placental trophoblasts mediated by immediate-early gene-induced tumor necrosis factor-alpha

Infection of the fetal epithelium (trophoblast) lining the villous placenta by human cytomegalovirus (HCMV) accompanies placental inflammations and fetal intrauterine growth restriction. However, the consequences of infection on the villous trophoblast have not been explored. We show that HCMV infection of primary immature (cytotrophoblast-like) or mature (syncytiotrophoblast-like) cultures results in loss of half of the cells within 24 hours of virus challenge. Two-color immunofluorescence of HCMV immediate early (IE) gene expression and apoptosis (terminal dUTP nick-end labeling) revealed apoptosis only in uninfected cells. Antibody to tumor necrosis factor (TNF)-alpha completely inhibited infection-induced trophoblast apoptosis and cell loss, as did co-incubation with epidermal growth factor, known to inhibit trophoblast apoptosis. Transfection with HCMV immediate early- (IE)1-72 and IE2-86, but not IE2-55, expression plasmids induced paracrine trophoblast apoptosis inhibitable by epidermal growth factor or antibody to TNF-alpha. These results show that HCMV infection of villous trophoblasts leads to rapid loss of neighboring cells mediated by viral IE protein-induced TNF-alpha secretion. We propose that HCMV infection damages the placental trophoblast barrier by accelerating trophoblast turnover and decreasing its capacity for renewal.

p38 MAP kinase negatively regulates endothelial cell survival, proliferation, and differentiation in FGF-2-stimulated angiogenesis

The p38 mitogen-activated protein kinase (p38) is activated in response to environmental stress and inflammatory cytokines. Although several growth factors, including fibroblast growth factor (FGF)-2, mediate activation of p38, the consequences for growth factor-dependent cellular functions have not been well defined. We investigated the role of p38 activation in FGF-2-induced angiogenesis. In collagen gel cultures, bovine capillary endothelial cells formed tubular growth-arrested structures in response to FGF-2. In these collagen gel cultures, p38 activation was induced more potently by FGF-2 treatment compared with that in proliferating cultures. Treatment with the p38 inhibitor SB202190 enhanced FGF-2-induced tubular morphogenesis by decreasing apoptosis, increasing DNA synthesis and cell proliferation, and enhancing the kinetics of cell differentiation including increased expression of the Notch ligand Jagged1. Overexpression of dominant negative mutants of the p38-activating kinases MKK3 and MKK6 also supported FGF-2-induced tubular morphogenesis. Sustained activation of p38 by FGF-2 was identified in vascular endothelial cells in vivo in the chick chorioallantoic membrane (CAM). SB202190 treatment enhanced FGF-2-induced neovascularization in the CAM, but the vessels displayed abnormal features indicative of hyperplasia of endothelial cells. These results implicate p38 in organization of new vessels and suggest that p38 is an essential regulator of FGF-2-driven angiogenesis.

Human herpesvirus 8 (HHV-8)-encoded cytokines induce expression of and autocrine signaling by vascular endothelial growth factor (VEGF) in HHV-8-infected primary-effusion lymphoma cell lines and mediate VEGF-independent antiapoptotic effects

The potential roles of human herpesvirus 8 (HHV-8) cytokines in HHV-8 pathogenesis were investigated by determining the expression of the HHV-8 chemokines viral macrophage inflammatory protein 1A (vMIP-1A) and vMIP-1B in primary effusion lymphoma (PEL)-derived cell lines and examining the signaling activities of these chemokines and HHV-8-encoded vIL-6 in these cells. Secreted vMIP-1A and vMIP-1B were detected in biologically significant concentrations following tetradecanoyl phorbol acetate treatment, which induces productive replication. vIL-6 and vMIP-1A, added exogenously to cultures of four different PEL cell lines, induced the expression of vascular endothelial growth factor type B (VEGF-B) and VEGF-A, respectively. These cells were found to express VEGF receptor 1 (Flt-1) protein, and signaling by recombinant VEGF-A(165) was demonstrated for two of the PEL cell lines, indicating the potential for autocrine, as well as paracrine, effects of viral cytokine-induced VEGF. In addition, vMIP-1A and vMIP-1B, but not VEGF-A(165), were found to inhibit chemically induced apoptosis in PEL cells. Our data suggest that vIL-6 and vMIP-1A may influence PEL through VEGF autocrine and paracrine signaling that promotes PEL cell growth and extravascular effusion and that vMIP-1A and vMIP-1B can act independently of VEGF as antiapoptotic factors.

Low maternal serum levels of placenta growth factor as an antecedent of clinical preeclampsia

OBJECTIVE

Maternal serum placenta growth factor levels have been shown to be significantly reduced in women with established preeclampsia. However, the temporal change in serum placenta growth factor levels before the clinical onset of preeclampsia is not known.

STUDY DESIGN

Serum samples were collected from patients at the first prenatal (5-15 weeks' gestation), second-trimester (16-20 weeks' gestation), and third-trimester (26-30 weeks' gestation) visits. Serum placenta growth factor levels were determined and analyzed according to pregnancy outcome.

RESULTS

Maternal placenta growth factor levels during normal gestation increased dramatically from the first to the third trimester. At the same gestational time points, in contrast, significantly lower serum placenta growth factor levels were found in patients in whom mild or severe preeclampsia eventually developed (P <.01). Low maternal serum placenta growth factor levels during early gestation were associated with a significant odds ratio for development of preeclampsia (P <.005).

CONCLUSION

Relatively decreased levels of serum placenta growth factor occur before the onset of clinical preeclampsia, which suggests that placenta growth factor measurement could be used to discriminate those pregnancies predisposed to development of preeclampsia.

Essential role for p38alpha mitogen-activated protein kinase in placental angiogenesis

The p38 family of mitogen-activated protein kinases (MAPKs) mediates signaling in response to environmental stresses and inflammatory cytokines, but the requirements for the p38 MAPK pathway in normal mammalian development have not been elucidated. Here, we show that targeted disruption of the p38alpha MAPK gene results in homozygous embryonic lethality because of severe defects in placental development. Although chorioallantoic placentation is initiated appropriately in p38alpha null homozygotes, placental defects are manifest at 10.5 days postcoitum as nearly complete loss of the labyrinth layer and significant reduction of the spongiotrophoblast. In particular, p38alpha mutant placentas display lack of vascularization of the labyrinth layer as well as increased rates of apoptosis, consistent with a defect in placental angiogenesis. Furthermore, p38alpha mutants display abnormal angiogenesis in the embryo proper as well as in the visceral yolk sac. Thus, our results indicate a requirement for p38alpha MAPK in diploid trophoblast development and placental vascularization and suggest a more general role for p38 MAPK signaling in embryonic angiogenesis.

Molecular basis of angiogenesis. Role of VEGF and VE-cadherin

The formation of new blood vessels (angiogenesis) is essential for embryonic development and contributes to the pathogenesis of numerous disorders. In contrast, insufficient angiogenesis may lead to tissue ischemia and failure. The recent discovery of novel angiogenic molecules has initiated efforts to improve tissue perfusion via therapeutic angiogenesis. However, rational design of such treatment strategies mandates a better understanding of the molecular mechanisms of angiogenesis. In this brief review, the role of a prime angiogenic candidate, namely vascular endothelial growth factor (VEGF) and its homologues, in physiological and pathological angiogenesis will be discussed with particular attention to myocardial ischemia and heart failure. In addition, a novel interaction between the junctional protein vascular endothelial-cadherin (VE-cadherin) and VEGF, essential for the endothelial survival function of VEGF, will be reviewed.

Growth factor signaling pathways in vascular development

Recent research on the formation and maintenance of the vasculature in the embryo and in the adult has provided a greater understanding of the cellular signals involved in these processes. With this understanding comes the potential means of controlling vascularization in pathological situations such as tumorigenesis and wounding. For the purpose of this review, we will discuss the key receptor tyrosine kinases involved in vascular function and the molecules which relay signals downstream of receptor activation. The receptor tyrosine kinases discussed include the vascular endothelial cell growth factor receptors, Eph receptors, Tie1, and Tie2, all of which are expressed on vascular endothelial cells. We also discuss the roles of the platelet derived growth factor receptors which are expressed on vascular smooth muscle cells. While all of these receptor tyrosine kinases activate many similar effector molecules, some of the signals initiated appear to be distinct. This may explain, at least in part, how different receptor tyrosine kinases expressed in overlapping patterns on the developing vasculature, direct unique biological functions.