Soluble Fms-like Tyrosine Kinase Receptor-1 Research Articles

Blood pressure augmentation and maternal circulating concentrations of angiogenic factors at delivery in preeclamptic and uncomplicated pregnancies

The objective of the study was to determine whether blood pressure increases are associated with maternal angiogenic factors in uncomplicated and preeclamptic pregnancies. Associations of blood pressure increases from mid- to late pregnancy with maternal serum concentrations of soluble fms-like tyrosine kinase receptor (sFlt1), soluble endoglin (sEng), and placental growth factor (PlGF) at delivery were analyzed in 43 uncomplicated and 44 preeclamptic pregnancies. In uncomplicated pregnancies, increases in diastolic and mean arterial pressure were inversely associated with PlGF at delivery and positively associated with sEng and sFlt1/PlGF ratio. There were no significant associations between blood pressure increases and angiogenic factor concentrations in preeclampsia. These data suggest that angiogenic factors are involved in blood pressure modulation in normotensive pregnancy and are consistent with the hypothesis that angiogenic balance plays a role in maternal breast cancer risk reduction associated with mid- to late blood pressure increases in uncomplicated pregnancies.

Placental Productions and Expressions of Soluble Endoglin, Soluble fms-Like Tyrosine Kinase Receptor-1, and Placental Growth Factor in Normal and Preeclamptic Pregnancies

Increased production of antiangiogenic factors soluble endoglin (sEng) and soluble fms-like tyrosine kinase receptor-1 (sFlt-1) by the placenta contributes to the pathophysiology in preeclampsia (PE). Our objective was to determine the differences in endoglin (Eng), fms-like tyrosine kinase receptor-1 (Flt-1), and placental growth factor (PlGF) expressions between normal and PE placentas and sEng, sFlt-1, and PlGF production by trophoblast cells (TC) cultured under lowered oxygen conditions. TCs isolated from normal and PE placentas were cultured under regular (5% CO2/air) and lowered (2% O2/5% CO2/93% N2) oxygen conditions. sEng, sFlt-1, and PlGF productions were determined by ELISA. Protein expressions for Eng, Flt-1, and PlGF in the placental tissues were accessed by immunohistochemical staining and Western blot analysis. Deglycosylated Eng, Flt-1, and PlGF protein expressions in placental tissues were also examined. PE TCs produced significantly more sEng, sFlt-1, and PlGF compared with those from normal TCs (P < 0.05). Under lowered oxygen conditions, PE TCs, but not normal TCs, released more sEng and sFlt-1. In contrast, both normal and PE TCs released less PlGF (P < 0.05). Enhanced expressions of Eng and Flt-1, as well as glycosylated Eng and Flt-1, were observed in PE placentas. Immunoblot also revealed that TCs released glycosylated sFlt-1, but not sEng, in culture. PE TCs produce more sEng, sFlt-1, and PlGF than normal TCs. Lowered oxygen conditions promote sEng and sFlt-1, but reduce PlGF, productions by PE TCs. More glycosylated sEng and sFlt-1 are present in PE placentas. Trophoblasts release glycosylated sFlt-1, but unglycosylated sEng, in culture.

A novel renal perspective of preeclampsia: a look from the podocyte

Sir, Preeclampsia (PE) is the most severe hypertensive complication of pregnancy. Onset of proteinuria is the main criterion for diagnosis of PE. Examination of renal biopsies of women with PE shows a pathognomonic lesion known as glomerular endotheliosis (GEN); nonetheless, GEN, from a low to a severe degree, has also been observed in women with gestational hypertension without proteinuria and in healthy pregnant women. Hence, alterations of renal function in women with PE can be attributed to a component of the glomerular filtration barrier (GFB) different from the glomerular endothelium. We propose that proteinuria in women with PE is due to direct injury of podocytes. The GFB possesses three components: the glomerular endothelium, the glomerular basement membrane and epithelial cells known as podocytes. Podocytes assemble forming the slit diaphragm (SD). The SD is located between the foot processes of the podocytes and is composed of a protein complex including Nephrin, NEPH1, NEPH2, FAT1, P-cadherin, Podocin and CD2AP. These proteins interact with each other by way of the foot processes of other podocytes, forming a critical pathway of the GFB. Hence, down-regulation of one of these proteins could be involved in the appearance and development of proteinuria in women with PE. The function of the podocyte and the SD depends on the physiological concentrations of circulating factors, such as vascular endothelial growth factor (VEGF) and its antagonist, the soluble receptor fms-like tyrosine kinase 1 (sFlt-1). Based on findings stating that, (i) GEN is present in women with PE and also in pregnant women without proteinuria, [1] (ii) physiological concentrations of VEGF are important for podocyte homeostasis and survival, [2] (iii) VEGF is important in maintaining of the SD by regulating nephrin expression, [3] (iv) sFlt-1 is a circulating antiangiogenic factor that antagonizes VEGF by binding to it and inactivating it, therefore inhibiting the action of VEGF on the SD, (v) there is an elevated concentration of sFlt-1 in the serum of women with PE as opposed to normotensive pregnant women, [4] (vi) elevated concentrations of sFlt-1 down-regulate the expression of proteins of the SD such as nephrin, [3] and (vii) down-regulation of nephrin expression leads to proteinuria, [5] we propose that proteinuria in patients with PE is mediated not only by endothelium alterations described classically, but also by disturbances of podocyte biology including impaired survival, enhanced apoptosis and down-regulation of nephrin and/or other key proteins of the SD.

Angiogenesefaktoren in der Schwangerschaft: Indikatoren für die Präeklampsie

Preeclampsia is a major cause of maternal, fetal and neonatal mortality worldwide. The etiology of preeclampsia is still unclear. Currently, the inadequate transformation of the smooth muscle cells of spiral arteries in the placental bed caused by an insufficient endovascular invasion of the trophoblast is considered to be the major reason for the development of preeclampsia. This insufficient invasion seems to lead to altered placental angiogenesis which thus has causal importance for the development of preeclampsia. Vascular endothelial growth factor (VEGF) and placental growth factor (PLGF) are the most important angiogenic factors with regulatory functions for placental vessel development. In preeclamptic pregnancies the expression of VEGF and PLGF was decreased. However, the expression of the corresponding receptor, the soluble fms-like tyrosine kinase receptor, which is considered to have anti-angiogenic properties, was elevated in preeclamptic pregnancies. CYR61 and NOV which belong to a group of proteins, the CCN-family, play also an important role in the regulation of placental angiogenesis. Recently, a decreased expression of both proteins in the placentae of preeclamptic women was detected. This review summarizes our current understanding of the role of angiogenic factors in the pathogenesis of preeclampsia.

Soluble endoglin (sEng) joins the soluble fms-like tyrosine kinase (sFlt) receptor as a pre-eclampsia molecule

Pre-eclampsia is a devastating disease of late (after week 20) pregnancy. The condition features hypertension, proteinuria, premature labor, haemolysis, liver abnormalities, thrombocytopenia (HELLP syndrome), seizures (eclampsia) and death [1]. Both mothers and children, if they survive delivery, can expect subsequent increased cardiovascular risk in the future. Preeclampsia affects about 5% of the pregnancies in affluent societies; in the rest of the world, the incidence is higher. Suffice it to say, pre-eclampsia is a major world health problem. The group led by Anand Karumanchi et al. [2] has made major contributions in terms of our understanding pre-eclampsia. They showed that preeclampsia is associated with a circulating aberrant splice variant of the vascular endothelial growth factor (VEGF) receptor fms-like tyrosine kinase (Flt). This receptor is also an important target for placental growth factor (PLGF). The soluble fms-like tryrosine kinase (sFlt) receptor is a splice variant of the VEGF receptor Flt. The Karumanchi group showed that patients with pre-eclampsia have increased circulating levels of sFlt that putatively catches VEGF and PLGF before these mediators can interact with their ligands (Figure 1, panel A). As a result, endothelial and, particularly, placental (trophoblast) growth could be stunted, causing pre-eclamspia. The hypothesis was underscored by in vitro and in vivo experiments. Serum from preeclampstic patients inhibited tube formation by endothelial cells in culture. Giving sFlt to rats caused hypertension, proteinuria and glomerular endotheliosis. Subsequently, the group collaborated with clinical investigators who had performed a randomized trial of calcium supplementation in women at risk for preeclampsia. The calcium story was negative; however, the women developing pre-eclampsia in these studies had increased circulating sFlt levels and decreased PLGF and VEGF concentrations [3]. The data appeared convincing [4].

Relationship of Smoking and Fibrosis in Patients With Chronic Hepatitis C

Preliminary studies have suggested that in patients with chronic hepatitis C (CHC), cigarette smoking increases the risk for developing liver fibrosis. Hypoxia caused by smoking may induce expression of the cytokines' vascular endothelial growth factor (VEGF) and VEGF-D and their corresponding soluble tyrosine kinase receptors fms-like tyrosine kinase receptor (s-Flt) and kinase insert domain receptor (s-KDR). These cytokine levels are increased in animals with cirrhosis and in human beings with CHC. We studied whether the concentrations of VEGF, VEGF-D, s-Flt, and s-KDR were increased in CHC smokers with and without hepatic fibrosis. A total of 170 CHC patients were identified retrospectively from a single center's database. In 59 patients, serum levels of VEGF, VEGF-D, s-Flt, and s-KDR were measured using an enzyme-linked immunosorbent assay. All 170 patients were hepatitis C virus RNA positive, 117 (69%) were men, 43 (25%) were smokers, and their mean (+/-SD) age was 47 (+/-6) years. Overall, 21% of smokers had Metavir fibrosis scores of 3 and 4 compared with 14% of nonsmokers (P < .01). In an age-weighted multivariate model using step-wise logistic regression, smoking, infection with hepatitis C virus genotype 1, male sex, and increased VEGF-D concentration all were significant independent predictors of more severe liver fibrosis (P < .05 for all observations). These data suggest that CHC patients who smoke may have more hepatic fibrosis. The data also suggest that increased VEGF and VEGF-D concentrations are associated with smoking and may be involved in the molecular mechanisms of fibrogenesis.

Antiangiogenic cancer gene therapy by adeno-associated virus 2-mediated stable expression of the soluble FMS-like tyrosine kinase-1 receptor.

Antiangiogenic gene transfer has the potential to be more efficacious than protein-based therapies or pharmacotherapies for the control of solid tumor growth, invasion and metastasis. For a sustained antiangiogenic effect, a vector capable of long-term expression without vector-associated immunity or toxicity is advantageous. The present study evaluated the potential of a recombinant adeno-associated virus-2 (rAAV) encoding the human soluble FMS-like tyrosine kinase receptor 1 (sFlt-1), which functions by both sequestering vascular endothelial growth factor (VEGF) and forming inactive heterodimers with other membrane-spanning VEGF receptors, in vitro and in vivo. Results indicated significant growth inhibitory activity of the transgenic factor in a human umbilical vein endothelial cell proliferation assay in vitro and protection against the growth of an angiogenesis-dependent human ovarian cancer cell line, SKOV3.ip1, xenograft in vivo with increased disease-free survival. Stable expression of the secretory factor and transgene persistence were confirmed by immunohistochemistry and in situ hybridization analyses, respectively. Increased therapeutic effects on both the growth index of the implanted tumor cells and tumor-free survival also correlated with an increasing dose of the vector used. These studies indicate that rAAV-mediated sFlt-1 gene therapy may be a feasible approach for inhibiting tumor angiogenesis, particularly as an adjuvant/therapy.

Inhibition of vascular endothelial cell growth factor activity by an endogenously encoded soluble receptor.

Vascular endothelial cell growth factor, a mitogen selective for vascular endothelial cells in vitro that promotes angiogenesis in vivo, functions through distinct membrane-spanning tyrosine kinase receptors. The cDNA encoding a soluble truncated form of one such receptor, fms-like tyrosine kinase receptor, has been cloned from a human vascular endothelial cell library. The mRNA coding region distinctive to this cDNA has been confirmed to be present in vascular endothelial cells. Soluble fms-like tyrosine kinase receptor mRNA, generated by alternative splicing of the same pre-mRNA used to produce the full-length membrane-spanning receptor, encodes the six N-terminal immunoglobulin-like extracellular ligand-binding domains but does not encode the last such domain, transmembrane-spanning region, and intracellular tyrosine kinase domains. The recombinant soluble human receptor binds vascular endothelial cell growth factor with high affinity and inhibits its mitogenic activity for vascular endothelial cells; thus this soluble receptor could act as an efficient specific antagonist of vascular endothelial cell growth factor in vivo.