Histochemical evaluation of placental angiotensinase A in pre-eclampsia: enzyme activity in villous trophoblast indicates an enhanced likelihood of gestational proteinuric hypertension

Distribution of sugar residues in human placentas from pregnancies complicated by hypertensive disorders

The aim of the study was to investigate the content and distribution of sugar residues in placentas from pregnancies complicated by hypertensive disorders. Placentas from women with uncomplicated pregnancies (group 1), pregnancies complicated by gestational hypertension (group 2), pregnancies complicated by pre-eclampsia (group 3), pregnancies complicated by pre-eclampsia with HELLP syndrome (hemolysis, elevated liver enzymes and low platelets) (group 4) were collected. Lectins: ConA, WGA, PNA, SBA, DBA, UEA I, GNA, DSA, MAA, SNA, in combination with chemical and enzymatic treatments, were used. Data showed a decrease and/or lack of α-d-mannose, α-d-glucose and d-galactose-(β1-4)-N-acetyl-d-glucosamine in placentas from pre-eclampsia and pre-eclampsia with HELLP syndrome compared with control and hypertension cases. N-acetyl-d-galactosamine appeared and/or increased in placentas from hypertensive disorders. A different distribution of various types of sialic acid was observed in placentas from hypertensive disorders compared with the controls. In particular, placentas from pre-eclampsia, with and without HELLP syndrome, lacked the acetylated sialic acid side-chain. These findings demonstrate various alterations of the carbohydrate metabolism in the placentas from pregnancies complicated by different types of hypertensive disorders. This indicates correlation with the placental morpho-functional changes characteristic of these complications and with the degree of clinical severity.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

Involvement of placental peptidases associated with renin-angiotensin systems in preeclampsia

Preeclampsia is characterized by pregnancy-induced hypertension accompanied with protein urea and generalized edema. Preeclampsia develops during the second half of pregnancy and resolves postpartum promptly, implicating the placenta as a primary cause in the disorder. Normal pregnancy is associated with reductions in arterial pressure and attenuated pressor response to exogenous infused angiotensin II (ANG II). In contrast, women with preeclampsia show the similar sensitivity to the pressor effect of ANG II as do non-pregnant women. To elucidate the involvement of placental peptidases associated with renin-angiotensin systems, we determined the localization of angiotensin-converting enzyme (ACE) and aminopeptidase A (AP-A), ANG II degrading enzyme, in the placenta and compared the expression of mRNA and protein in uncomplicated and preeclamptic placenta. In addition, AP-A expression in trophoblastic cells treated with ANG II and ACE expression in HUVECs under hypoxic condition were analyzed, respectively. The expression of both peptidases in the preeclamptic placenta was significantly higher than those from uncomplicated. ACE was primarily localized to venous endothelial cells of stem villous whereas AP-A expression was recognized in the trophoblast and pericytes of fetal arterioles and venules within stem villous. Hypoxia induced ACE expression in HUVECs while both hypoxia and ANG II evoked AP-A expression in trophoblast. These results suggested that hypoxic condition in preeclampsia induces ACE activation in feto-placental unit to maintain the fetal hemodynamics and placental AP-A plays a role as a component of the barrier of ANG II between mother and fetus.

Ultrastructural localization of aminopeptidase A/angiotensinase and placental leucine aminopeptidase/oxytocinase in chorionic villi of human placenta

AIMS

Membrane-bound aminopeptidases in human placenta are thought to be involved in maintaining homeostasis during pregnancy by metabolizing bioactive peptides such as oxytocin and angiotensin at the interface between the fetus and mother. Because determining the precise localization of these enzymes is required to support this notion, we investigated the ultrastructural localization of two principal enzymes, aminopeptidase A (APA; EC 3.4.11.7)/angiotensinase and placental leucine aminopeptidase (P-LAP; EC 3.4.11.3)/oxytocinase in human first trimester and full-term placenta.

METHODS

Immunohistochemical analysis using anti-P-LAP and anti-APA antibodies was performed on ultrathin frozen sections of fixed human placental villi.

RESULTS

Transmission immunoelectron microscopy revealed that both enzymes were expressed on the surface of apical microvilli of syncytiotrophoblast cells and, to a lesser extent, on the basal infoldings. The location of the two enzymes did not vary between the first trimester and full-term placenta sections, while the staining intensities were slightly enhanced in full-term villi.

CONCLUSIONS

Our observation that P-LAP and APA are present on the microvilli, which is a site of interaction between the mother and fetus, suggests possible involvement of these enzymes in cleaving peptide hormones from the fetus and mother in order to regulate bioactivity.

Differential distribution of placental leucine aminopeptidase/oxytocinase and aminopeptidase A in human trophoblasts of normal placenta and complete hydatidiform mole

Placental leucine aminopeptidase (P-LAP)/oxytocinase (OTase) degrades several small peptides such as oxytocin (OT), arginine vasopressin (AVP) and angiotensin III (ANGIII), and aminopeptidase A (AP-A) converts angiotensin II (ANGII) to ANGIII. These proteases play an important role in foetal growth and the maintenance of human homeostasis during pregnancy. In this study, we confirmed the distribution of P-LAP and AP-A proteins and messenger RNAs in human trophoblasts in normal placenta and complete hydatidiform mole by immunohistochemical and in-situ hybridization techniques. Immunoreactivity of P-LAP was mainly noted in the apical membrane of syncytiotrophoblasts, and the expression of messenger RNA (mRNA) for P-LAP was predominantly noted in the cytoplasm of syncytiotrophoblastic cells. However, immunoreactivity of AP-A was mainly noted in the apical membrane of cytotrophoblasts and in the basal zone of the syncytiotrophoblasts, and the expression of mRNA for AP-A was predominantly noted in cytoplasm of cytotrophoblastic cells and a little in cytoplasm of syncytiotrophoblastic cells. Thereby, the two proteases were differentially distributed both in normal placenta and hydatidiform mole throughout the gestational age. These results are useful for the further understanding of not only the pathophysiology of pregnancy, but also the pathogenesis of trophoblastic diseases.

Progesterone stimulates the expression of aminopeptidase A/angiotensinase in human choriocarcinoma cells

In human placenta aminopeptidase A (APA), a principal enzyme that converts angiotensin II to angiotensin III, seems to be involved in angiotensin II metabolism during pregnancy. In this study, we investigated the possible effects of progesterone and estrogen on APA mRNA and protein levels in choriocarcinoma cells as a model for placenta. By RNase protection assay, progesterone induced higher APA mRNA levels than estrogen at the same concentration. Progesterone exhibited dose-dependent stimulation of APA mRNA, 1.8-fold increase at 10(-6) m for 24 h treatment. Progesterone at 10(-6) m increased APA mRNA levels within 12 h and in time-dependent fashion up to 24 h. Fluorescence-activated cell sorting analysis and measurements of APA activities revealed the induction of APA protein by progesterone. Expression of progesterone receptors (PR) and glucocorticoid receptors (GR) were determined in these cells by RT-PCR, which suggested that the progesterone's actions might be displayed through PR and/or GR. These findings may serve as a useful model to study the effects of progesterone on angiotensin II metabolism in placenta, although the physiological validity of these studies remains to be clarified.

Placental aminopeptidase A as a possible barrier of angiotensin II between mother and fetus

Aminopeptidase A (AP-A EC 3.4.11.7), which is a membrane-bound zinc metalloprotease, is present in the placenta. AP-A selectively hydrolyzes N-terminal glutamyl and aspartyl residues and cleaves angiotensin II to form angiotensin III. To determine the role of placental aminopeptidase A under physiological and pathological conditions, we evaluated its immunolocalization and enzymatic activities in the placenta. AP-A was localized in the basal zone of the syncytiotrophoblast, in the membranes of the cytotrophoblast, and in fetal arterioles and venules within the stem villi. AP-A activity in the microsomal fraction of placental villi seemed to be remained essentially constant throughout gestation. The renin-angiotensin system is considered to be accelerated in pre-eclampsia. This AP-A activity was higher in pre-eclampsia (2.86+/-0.30 nmol beta NA/mg protein/h) than in uncomplicated pregnancy from 28 to 41 weeks of gestation (2.08+/-0.18 nmol beta NA/mg protein/h). Angiotensin II evoked AP-A activity in first trimester trophoblast, and Losartan and PD 123177 in combination significantly inhibited this induction of AP-A activity. The results of immunohistochemical evaluation and enzymatic activity suggested that placental aminopeptidase A may play a role as a component of the barrier of angiotensin II between mother and fetus.

Current topic: the uteroplacental renin-angiotensin system

The components of the renin-angiotensin system (RAS) are expressed in the uteroplacental unit. The expression varies between species, probably due to the marked species differences in placental architecture. The conditions for angiotensin (Ang) II formation exist and Ang II receptors are present throughout the human uteroplacental unit, indicating the presence of a functional local RAS. The uteroplacental RAS interacts with other regulatory systems and in this way modulates various aspects of tissue function. It is suggested that the uteroplacental RAS is important for the regeneration of the endometrium after shedding, and for decidualization, implantation and placentation. The RAS participates in the regulation of the uteroplacental blood flow, prostaglandin synthesis and oestradiol secretion. Disturbances of the uteroplacental RAS may lead to dysfunctional bleeding and to reduced uteroplacental blood flow in pregnancies complicated by pre-eclampsia and intrauterine growth retardation.

Structure of the human oxytocinase/insulin-regulated aminopeptidase gene and localization to chromosome 5q21

The human oxytocinase/insulin-regulated aminopeptidase (OTase/IRAP) is a 1024 amino acid type II integral membrane protein that is expressed mainly in fat, muscle and placenta tissues. It has been thought to be involved mainly in the control of onset of labour but recently rat OTase/IRAP was shown to participate in the regulation of glucose transporter isoform 4 vesicle trafficking in adipocytes as well. To approach an understanding of OTase/IRAP gene regulation the organization of the human gene was determined. Accordingly, three overlapping genomic clones were isolated and characterized. The human OTase/IRAP gene (OTASE) was found to span approximately 75 kb containing 18 exons and 17 introns. The gluzincin aminopeptidase motif: GAMEN-(31 amino acids)-HELAH-(18 amino acids)-E associated with Zn2+-binding, substrate binding and catalysis is encoded by exons 6 and 7. A major and a minor transcriptional initiation site in OTASE were identified by primer extension 514 bp and 551 bp, respectively, upstream of the translation start codon. Chloroamphenicol acetyltransferase-reporter assays revealed a functional CpG-rich promoter/enhancer region located between nucleotide -621 and the major transcriptional initiation site. Human OTASE was assigned to chromosome 5 by hybridization to genomic DNA from characterized somatic cell hybrids. Finally, the OTASE and the human aminopeptidase A gene were subchromosomally localized to 5q21 and 4q25, respectively, by in situ hybridization.

Expression of aminopeptidase A in human gestational choriocarcinoma cell lines and tissues

Aminopeptidase A (AP-A), a cell-surface metallopeptidase hydrolyzing peptide with N-terminal acidic residues, has been proved to be identical to the B cell differentiation antigen BP-1 and to the kidney differentiation antigen gp160, suggesting recognition of AP-A as a differentiation-related marker on certain normal and transformed cells. AP-A has also been purified from human placenta and been shown to be localized in the trophoblasts. In the present study, we examined the expression and enzymatic activity of AP-A in human gestational choriocarcinoma, a neoplastic transformant from trophoblasts which comprises a heterogenous population of trophoblastic cells in different stages of differentiation. Flow cytometry and immunoblot analysis demonstrated that AP-A was expressed in five choriocarcinoma cell lines which were secreting low or moderate levels of human chorionic gonadotropin (hCG), while two high hCG-secreting cell lines lacked AP-A expression. The AP-A enzymatic activity correlated with cell-surface levels of AP-A and was abrogated by amastatin, an inhibitor of AP-A. Immunohistochemical analysis revealed that AP-A was present in seven of eight choriocarcinoma tissues and was localized on the cell membrane of cytotrophoblastic choriocarcinoma cells, but not on cells with syncytiotrophoblast-like features. These results demonstrate that AP-A is expressed on most choriocarcinomas and its expression is restricted to low hCG-secreting, cytotrophoblastic cells and down-regulated as a function of cell differentiation, suggesting an involvement of AP-A in the differentiation/maturation process of neoplastic trophoblasts.

Detection of protease activities using specific aminoacyl or peptidyl p-nitroanilides after sodium dodecyl sulfate - polyacrylamide gel electrophoresis and its applications

A general method for detecting protease activities on acrylamide or agarose gels after sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE) using specific aminoacyl p-nitroanilide (NA) or peptidyl NA as substrate is described. This method is extended from the spectrophotometric assay of p-nitroaniline, which is a chromogenic product liberated by protease action on aminoacyl NA or peptidyl NA. The acrylamide gel containing protein bands was dipped directly into a solution which contained specific synthetic aminoacyl NA or peptidyl NA as a substrate or had been overlaid with an agarose gel containing the same substrate. The p-nitroaniline released on the acrylamide or agarose gel by the specific protease was diazotized with sodium nitrite and then coupled to N-(1-naphthyl)-ethylenediamine to produce distinct activity band(s). The substrates used for protease activity staining on gels were identical to those used for spectrophotometric assays. Some applications are described.

Histochemical evaluation of placental dipeptidyl peptidase IV (CD26) in pre-eclampsia: enzyme activity in villous trophoblast indicates an enhanced likelihood of gestational hypertensive disorders

PROBLEM

To determine whether differences in placental dipeptidyl peptidase IV (DPP IV, CD26) activities occurred in hypertensive complicated pregnancies as compared with uncomplicated pregnancies.

METHOD

DPP IV activity was detected with H-Gly-Pro-4M2NA as the substrate in placental cryostat sections from 65 patients with gestational hypertension and 67 patients with uncomplicated pregnancies. The graduated intensities of the reaction product in the villous trophoblast were scored semiquantitatively by light microscopy and were related to the relative frequencies of hypertensive disorders (proportional odds model). After detection of enzyme activity, the same tissue samples were homogenized and used for kinetic fluorometric measurements.

RESULTS

Enhanced villous trophoblastic DPP IV activity was significantly associated with an increased frequency of proteinuric hypertension in pregnant women (cumulative odds ratio theta1 = 1.6; P < 0.01).

CONCLUSION

This study demonstrates for the first time that increased villous trophoblastic DPP IV activity indicates an increased likelihood of the presence and of the severity of hypertensive disorders in pregnancy.