Renin-like immunoreactivity in uterus and placenta from normotensive and hypertensive pregnancies

Intracrine angiotensin II functions originate from noncanonical pathways in the human heart

Although it is well-known that excess renin angiotensin system (RAS) activity contributes to the pathophysiology of cardiac and vascular disease, tissue-based expression of RAS genes has given rise to the possibility that intracellularly produced angiotensin II (Ang II) may be a critical contributor to disease processes. An extended form of angiotensin I (Ang I), the dodecapeptide angiotensin-(1-12) [Ang-(1-12)], that generates Ang II directly from chymase, particularly in the human heart, reinforces the possibility that an alternative noncanonical renin independent pathway for Ang II formation may be important in explaining the mechanisms by which the hormone contributes to adverse cardiac and vascular remodeling. This review summarizes the work that has been done in evaluating the functional significance of Ang-(1-12) and how this substrate generated from angiotensinogen by a yet to be identified enzyme enhances knowledge about Ang II pathological actions.

Acute Atherosis of the Uterine Spiral Arteries: Clinicopathologic Implications

Acute atherosis is unique vascular changes of the placenta associated with poor placentation. It is characterized by subendothelial lipid-filled foam cells, fibrinoid necrosis of the arterial wall, perivascular lymphocytic infiltration, and it is histologically similar to early-stage atherosclerosis. Acute atherosis is rare in normal pregnancies, but is frequently observed in non- transformed spiral arteries in abnormal pregnancies, such as preeclampsia, small for gestational age (SGA), fetal death, spontaneous preterm labor and preterm premature rupture of membranes. In preeclampsia, spiral arteries fail to develop physiologic transformation and retain thick walls and a narrow lumen. Failure of physiologic transformation of spiral arteries is believed to be the main cause of uteroplacental ischemia, which can lead to the production of anti-angiogenic factors and induce endothelial dysfunction and eventually predispose the pregnancy to preeclampsia. Acute atherosis is more frequently observed in the spiral arteries of the decidua of the placenta (parietalis or basalis) than in the decidual or myometrial segments of the placental bed. The presence and deeper location of acute atherosis is associated with poorer pregnancy outcomes, more severe disease, earlier onset of preeclampsia, and a greater frequency of SGA neonates in patients with preeclampsia. Moreover, the idea that the presence of acute atherosis in the placenta may increase the risk of future cardiovascular disease in women with a history of preeclampsia is of growing concern. Therefore, placental examination is crucial for retrospective investigation of pregnancy complications and outcomes, and accurate placental pathology based on universal diagnostic criteria in patients with abnormal pregnancies is essential for clinicopathologic correlation.

A potential pathophysiological role for galectins and the renin-angiotensin system in preeclampsia

This review discusses a potential role of galectins and the renin-angiotensin system (RAS) in the pathophysiology of preeclampsia (PE). Preeclampsia affects between 3 and 5 % of all pregnancies and is a heterogeneous disease, which may be caused by multiple factors. The only cure is the delivery of the placenta, which may result in a premature delivery and baby. Probably due to its heterogeneity, PE studies in human have hitherto only led to the identification of a limited number of factors involved in the pathogenesis of the disease. Animal models, particularly in mice and rats, have been used to gain further insight into the molecular pathology behind PE. In this review, we discuss the picture emerging from human and animal studies pointing to galectins and the RAS being associated with the PE syndrome and affecting a broad range of cellular signaling components. Moreover, we review the epidemiological evidence for PE increasing the risk of future cardiovascular disease later in life.

Review: Preeclampsia, acute atherosis of the spiral arteries and future cardiovascular disease: two new hypotheses

Preeclampsia is a serious complication of pregnancy, potentially lethal for women and offspring. Affected women have an augmented risk of later cardiovascular disease and premature death and may have risk factors in common with older persons developing cardiovascular disease. In some cases of preeclampsia, lipid-filled foam cells accumulate in the walls of the spiral arteries of the uteroplacental circulation (acute atherosis). These lesions resemble the early stages of atherosclerosis and are thought to regress after delivery. The mechanisms that contribute to acute atherosis are largely unknown, but are related to defective vascular remodeling of the spiral arteries in the first half of pregnancy. Spiral artery lipid deposition may also occur in normal pregnancies, which suggests that it may not be confined exclusively to maladapted spiral arteries or caused by hypertension. Our first hypothesis is that there are several pathways to the development of acute atherosis, which converge at the point of excessive decidual inflammation in the final common pathway. Our second hypothesis is that acute atherosis, evolving during the short time of pregnancy, identifies a subset of women at augmented risk for atherosclerosis and later chronic arterial disease better than the diagnosis of preeclampsia itself. If confirmed, this may enable better preventive management for the affected women.

The placenta in preeclampsia

The root cause of preeclampsia is the placenta. Preeclampsia begins to abate with the delivery of the placenta and can occur in the absence of a fetus but with the presence of trophoblast tissue with hydatidiform moles. In view of this, study of the placenta should provide insight into the pathophysiology of preeclampsia. In this presentation we examine placental pathological and pathophysiological changes with preeclampsia and fetal growth restriction (FGR). It would seem that this comparison should be illuminating as both conditions are associated with similarly abnormal placentation yet only in preeclampsia is there a maternal pathophysiological syndrome. Similar insights about early and late onset preeclampsia should also be provided by such information.We report that the placental abnormalities in preeclampsia are what would be predicted in a setting of reduced perfusion and oxidative stress. However, the differences from FGR are inconsistent. The most striking differences between the two conditions are found in areas that have been the least studied. There are differences between the placental findings in early and late onset preeclampsia but whether these are qualitative, indicating different diseases, or simply quantitative differences within the same disease is difficult to determine.We attempt to decipher the true differences, seek an explanation for the disparate results and provide recommendations that we hope may help resolve these issues in future studies.

The "Great Obstetrical Syndromes" are associated with disorders of deep placentation

Defective deep placentation has been associated with a spectrum of complications of pregnancy including preeclampsia, intrauterine growth restriction, preterm labor, preterm premature rupture of membranes, late spontaneous abortion, and abruptio placentae. The disease of the placental vascular bed that underpins these complications is commonly investigated with targeted biopsies. In this review, we critically evaluate the biopsy technique to summarize the salient types of defective deep placentation, and propose criteria for the classification of defective deep placentation into 3 types based on the degree of restriction of remodeling and the presence of obstructive lesions in the myometrial segment of the spiral arteries.

Endovascular trophoblast and preeclampsia: A reassessment

Since the earliest report on impaired spiral artery remodelling in preeclamptic human pregnancies, numerous studies have been devoted to possible mechanisms of impaired trophoblast invasion. A better knowledge of early uteroplacental blood flow has provided a physiological context for the processes of spiral artery invasion and associated remodelling, revealing a closely timed relationship between increasing flow and early steps in vascular remodelling. Concerning the impaired trophoblast invasion in preeclampsia, it has also to be considered that impaired invasion not only concerns invasion depth per se, but also the extension of this deep invasion from the central towards the more lateral spiral arteries of the placental bed. Since also in preeclampsia the very central spiral arteries may be normally invaded, the existence of such spatial gradient provides a further dimension to the problem. A practical consequence is that frequently used rodent models, which show invasion of two or three spiral arteries only, may be less useful for studying this particular aspect of the disease. Amongst non-human primates, baboons and rhesus monkeys are 'shallow invaders', and only in some of the great apes deep trophoblast invasion and associated spiral artery remodelling occurs. A better knowledge of the evolutionary history of deep invasion and its possible selective benefit might ultimately improve our understanding of failed deep invasion and impaired spiral artery remodelling in preeclampsia.

Molecular evidence of a (pro)renin/ (pro)renin receptor system in human intrauterine tissues in pregnancy and its association with PGHS-2

Prorenin stimulates decidual prostaglandin (PG) production in vitro, the (pro)renin receptor ((P)RR) may mediate this action. The role of prorenin in amnion PG synthesis has not been examined, despite this being the key site of PG synthesis. To determine if (P)RR, prorenin and PGHS-2 are co-localized in gestational tissues and if expression is altered by labour, term amnion, chorion, decidua and placenta were collected during elective caesarean section or after spontaneous labour. Prorenin, (P)RR and PGHS-2 mRNA abundance was determined by real-time RT-PCR. (P)RR protein was examined by immunohistochemistry. The effect of recombinant human (rh) prorenin on PGHS-2 mRNA abundance in amnion explants was determined. Prorenin and (P)RR mRNA were highest in decidua and placenta, respectively. Decidual prorenin, (P)RR and placental (P)RR mRNA abundance decreased with labour. (P)RR protein was present in all gestational tissues. After labour, decidual prorenin was positively correlated with amnion PGHS-2 mRNA and rh-prorenin significantly increased PGHS-2 mRNA abundance in amnion explants. We conclude that the decidua is the principal source of prorenin and is downregulated with labour. All gestational tissues are targets for prorenin. Decidual prorenin may be involved in the labour-associated increase in amnion PGHS-2 abundance via the (P)RR.

The two stage model of preeclampsia: variations on the theme

The Two Stage Model of preeclampsia proposes that a poorly perfused placenta (Stage 1) produces factor(s) leading to the clinical manifestations of preeclampsia (Stage 2). Stage 1 is not sufficient to cause the maternal syndrome but interacts with maternal constitutional factors (genetic, behavioral or environmental) to result in Stage 2. Recent information indicates the necessity for modifications of this model. It is apparent that changes relevant to preeclampsia and other implantation disorders can be detected in the first trimester, long before the failed vascular remodeling necessary to reduce placental perfusion is completed. In addition, although the factor(s) released from the placenta has usually been considered a toxin, we suggest that what is released may also be an appropriate signal from the fetal/placental unit to overcome reduced nutrient availability that cannot be tolerated by some women who develop preeclampsia. Further, it is evident that linkage is not likely to be one factor but several, different for different women. Also although the initial model limited the role of maternal constitutional factors to the genesis of Stage 2, this does not appear to be the case. It is evident that the factors increasing risk for preeclampsia are also associated with abnormal implantation. These several modifications have important implications. An earlier origin for Stage 1, which appears to be recognizable by altered concentrations of placental products, could allow earlier intervention. The possibility of a fetal placental factor increasing nutrient availability could provide novel therapeutic options. Different linkages and preeclampsia subtypes could direct specific preventive treatments for different women while the role of maternal constitutional factors to affect placentation provides targets for prepregnancy therapy. The modified Two Stage Model provides a useful guide towards investigating pathophysiology and guiding therapy.

Acute atherosis in decidual tissue: not associated with systemic oxidative stress in preeclampsia

The aim of this study was to explore a possible association between the presence of decidual acute atherosis, maternal hyperlipidaemia and oxidative stress in the maternal circulation in preeclamptic and uneventful pregnancies. Decidual tissue was harvested by a vacuum suction technique following delivery of the baby and placenta in 102 caesarean deliveries. Maternal plasma lipid profile and concentration of 8-isoprostane, a marker of oxidative stress, was analysed. Acute atherosis was present in 42% of the preeclamptic patients with identified spiral arteries. CD68 positive foam cells were found in the spiral artery walls in 14% of the normal pregnancies. We have previously demonstrated an elevated plasma level of 8-isoprostane in the preeclampsia group, as compared to the uneventful pregnancy group (218 vs. 354 pg/mL, p=0.02). Presence of acute atherosis was, however, not associated with an elevated level of oxidative stress in the maternal circulation, measured as 8-isoprostane. In conclusion, the presence of decidual vascular changes in the form of acute atherosis is not necessarily paralleled by hyperlipidaemia or augmented oxidative stress in the maternal systemic circulation. This study adds to the notion of preeclampsia being a multifactorial disease with a variety of clinical forms.

The Uterine Spiral Arteries In Human Pregnancy: Facts and Controversies

Uterine spiral arteries play a vital role in supplying nutrients to the placenta and fetus, and for this purpose they are remodelled into highly dilated vessels by the action of invading trophoblast (physiological change). Knowledge of the mechanisms of these changes is relevant for a better understanding of pre-eclampsia and other pregnancy complications which show incomplete spiral artery remodelling. Controversies still abound concerning different steps in these physiological changes, and several of these disagreements are highlighted in this review, thereby suggesting directions for further research. First, a better definition of the degree of decidua- versus trophoblast-associated remodelling may help to devise a more adequate terminology. Other contestable issues are the vascular plugging and its relation with oxygen, trophoblast invasion from the outside or the inside of the vessels (intravasation versus extravasation), the impact of haemodynamics on endovascular migration, the replacement of arterial components by trophoblast, maternal tissue repair mechanisms and the role of uterine natural killer (NK) cells. Several of these features may be disturbed in complicated pregnancies, including the early decidua-associated vascular remodelling, vascular plugging and haemodynamics. The hyperinflammatory condition of pre-eclampsia may be responsible for vasculopathies such as acute atherosis, although the overall impact of such lesions on placental function is far from clear. Several features of the human placental bed are mirrored by processes in other species with haemochorial placentation, and studying such models may help to illuminate poorly understood aspects of human placentation.

Plasma cathepsin D isoforms and their active metabolites increase after myocardial infarction and contribute to plasma renin activity

Plasma renin activity (PRA) is often found to increase after myocardial infarction (MI). Elevated PRA may contribute to increased myocardial angiotensin II that is responsible for maladaptive remodeling of the myocardium after MI. We hypothesized that MI would also result in cardiac release of cathepsin D, a ubiquitous lysosomal enzyme with high renin sequence homology. Cathepsin D release from damaged myocardial tissue could contribute to angiotensin formation by acting as an enzymatic alternate to renin. We assessed circulating renin and cathepsin D from both control and MI patient plasma (7-20 hours after MI) using shallow gradient focusing that allowed for independent measurement of both enzymes. Cathepsin D was increased significantly in the plasma after MI (P < 0.001). Furthermore, circulating active cathepsin D metabolites were also significantly elevated after MI (P < 0.04), and contained the majority of cathepsin D activity in plasma. Spiking control plasma with cathepsin D resulted in a variable but significant (P = 0.005) increase in PRA using a clinical assay. We conclude that 7-20 hours after MI, plasma cathepsin D is significantly elevated and most of the active enzymatic activity is circulating as plasma metabolites. Circulating cathepsin D can falsely increase clinical PRA determinations, and may also provide an alternative angiotensin formation pathway after MI.

Implantation and immunology: maternal inflammatory and immune cellular responses to implantation and trophoblast invasion

Implantation and placentation present an immune challenge because of the semi-allogeneic nature of the conceptus. In this review, histological evidence for maternal immune cellular responses at the implantation site is summarized. Decidualization of the endometrium itself has features in common with an inflammatory response. During decidualization, infiltration by uterine natural killer (NK) cells occurs, and these interact with the non-polymorphic human leukocyte antigen (HLA) class I antigens expressed by invading extravillous trophoblasts. In humans, extension of trophoblast invasion beyond the decidual layer into the myometrium presents an additional challenge, which might be relevant for pregnancy complications such as pre-eclampsia. How far maternal cellular responses to invading trophoblasts seen at later stages of pregnancy can be traced back to the implantation period is an open question.

The myometrial junctional zone spiral arteries in normal and abnormal pregnancies: a review of the literature

Deep placentation in the human requires physiologic transformation of the spiral arteries into uteroplacental vessels. This process involves the inner myometrial segment (junctional zone) of the spiral arteries and is effected by trophoblast invasion of the vessel wall, resulting in complete loss of the arterial structure and deposition of fibrinoid and fibrous tissues. Absent or inadequate physiologic changes in the junctional zone spiral arteries limits placental blood flow in pregnancies complicated by preeclampsia and fetal growth restriction. The cause of defective deep placentation is still unknown, although it is often attributed to impaired trophoblast function and migration. However, trophoblast invasion is preceded by decidual remodeling of maternal tissues, a process that is initiated in the endometrium but extends into the junctional zone. This review examines the mechanisms that control decidualization and subsequent trophoblast invasion in normal and abnormal pregnancies. The possibility that disruption of the decidual process in the secretory phase of the menstrual cycle triggers a cascade of events resulting in failed deep placentation is explored.

Severely reduced presence of tissue macrophages in the basal plate of pre-eclamptic placentae

Pre-eclampsia is a disorder of unknown aetiology peculiar to human pregnancy. A well-described pathological feature being shallow trophoblast invasion into the spiral arteries during placenta development. Epidemiological studies have revealed an increased risk in pregnancies of primipaternity, and an association with the maternal-fetal HLA-DR relationship, both suggesting the involvement of an immunological component. We were therefore interested in the distribution of HLA-DR expressing myeloid cells in the decidua of healthy and pre-eclamptic placentae. We have studied the monocytes in maternal and fetal peripheral blood as well as in the placenta and identified the cluster of differentiation (CD) 14(+)myeloid cells in the basal plate as mannose receptor (ManR) positive tissue macrophages. In a comparison between peripheral blood monocytes from healthy pregnant and pre-eclamptic women we found no significant difference in the subpopulation size of CD14(+)/CD16(+)monocytes. The number and location of macrophages in the placental villi was similar. However, while the basal plate of the normal decidua contained numerous CD14(+), HLA-DR(bright), ManR(+)tissue macrophages, this compartment was virtually void of these phagocytic cells in the pre-eclamptic placenta. This novel finding suggests that in pre-eclampsia not only the migration of endovascular cytotrophoblasts is disturbed, but that also maternal macrophage migration is affected.