Hypertension induced in pregnant mice by placental renin and maternal angiotensinogen

The detrimental role of angiotensin receptor agonistic autoantibodies in intrauterine growth restriction seen in preeclampsia

Growth-restricted fetuses are at risk for a variety of lifelong medical conditions. Preeclampsia, a life-threatening hypertensive disorder of pregnancy, is associated with fetuses who suffer from intrauterine growth restriction (IUGR). Recently, emerging evidence indicates that preeclamptic women harbor AT₁ receptor agonistic autoantibodies (AT₁-AAs) that contribute to the disease features. However, the exact role of AT₁-AAs in IUGR and the underlying mechanisms have not been identified. We report that these autoantibodies are present in the cord blood of women with preeclampsia and retain the ability to activate AT₁ receptors. Using an autoantibody-induced animal model of preeclampsia, we show that AT₁-AAs cross the mouse placenta, enter fetal circulation, and lead to small fetuses with organ growth retardation. AT₁-AAs also induce apoptosis in the placentas of pregnant mice, human villous explants, and human trophoblast cells. Finally, autoantibody-induced IUGR and placental apoptosis are diminished by either losartan or an autoantibody-neutralizing peptide. Thus, these studies identify AT₁-AA as a novel causative factor of preeclampsia-associated IUGR and offer two possible underlying mechanisms: a direct detrimental effect on fetal development by crossing the placenta and entering fetal circulation, and indirectly through AT₁-AA–induced placental damage. Our findings highlight AT₁-AAs as important therapeutic targets.

Fetal sex determines the impact of maternal PROGINS progesterone receptor polymorphism on maternal physiology during pregnancy

BACKGROUND

Recent evidence from very rare human diseases suggests that variation in the fetal genome can modify maternal physiology during pregnancy. Here, we tested the hypothesis that fetal sex as a major genetic variant of the fetal genome may affect maternal physiology during pregnancy in genetically susceptible pregnant women.

METHODS

We analyzed the impact of fetal sex on maternal physiology during pregnancy in relationship with the maternal PROGINS progesterone receptor gene polymorphism. Two thousand and eighty-nine (2089) Caucasian women without preexisting diabetes and preexisting hypertension with singleton pregnancies delivering consecutively at the Charité obstetrics department participated in this study.

RESULTS

The maternal PROGINS progesterone receptor polymorphism on its own had no effect on blood pressure, new onset of proteinuria, and total glycated hemoglobin at delivery. However, by considering the offspring's sex, the AA variant of the PROGINS progesterone receptor polymorphism was associated with profound cardiovascular/metabolic effects; mothers carrying both A alleles (AA genotype) delivering a boy had significantly lower systolic blood pressure during the first trimester of pregnancy versus AA mothers delivering girls (107.9+/-10.2 vs. 116.6+/-15.1 mmHg, P = 0.044). Diastolic blood pressure was similarly lower during the first trimester of pregnant AA women delivering boys in comparison with AA women delivering girls (63.4+/-5.7 vs. 68.2+/-10.9 mmHg, P = 0.032). Total glycated hemoglobin at delivery was significantly (P = 0.002) higher in AA mothers delivering boys (6.6+/-0.7%) versus AA mothers delivering girls (5.9+/-0.6%).

CONCLUSION

Our study indicates that fetal sex may substantially affect maternal blood pressure as well as glycemic control during pregnancy in genetically susceptible mothers.

Gestation-induced uterine vascular remodeling

Uterine blood supply is a critical issue for fetal well-being, since it carries all the nutrients, including O2, required for fetal growth and gets rid of several fetal waste products. During pregnancy, uterine blood flow increases by almost 20 times and this is permitted by marked remodeling of the vessel wall. In the rat, uterine arterial remodeling takes place in the last 7-8 days of gestation (over 22) and is reversible in the postpartum period upon a similar time frame. It was also described as both hypertrophy and hyperplasia of all the constituents of the vascular wall. Several hypotheses have been proposed to explain such a phenomenon, including the driving role not only of sexual steroid hormones, progesterone and estrogens, but also of trophic factors of fetal origin. We have shown that alterations of the renin-angiotensin-aldosterone system, by manipulating sodium intake in the rats, reduced the pregnancy-induced remodeling of uterine arteries. These maneuvres resulted in the birth of pups that had characteristics of intrauterine growth restriction or in the development in the mother of "experimental" gestational hypertension, depending on, respectively, restriction or increased of sodium intake.

Angiogenesis inhibition causes hypertension and placental dysfunction in a rat model of preeclampsia

BACKGROUND

Preeclampsia is a serious pregnancy complication, accompanied by increased maternal and fetal morbidity. Different models have been used to study preeclampsia, but none of these display all the key features of the disease.

METHOD

We investigated the effects on maternal blood pressure and fetal outcome exerted by the angiogenesis inhibitor Suramin (100 mg/kg i.p.) during early placentation. Blood pressure and heart rate were measured continuously with telemetry in Sprague-Dawley rats of four experimental groups: nonpregnant controls, Suramin-treated nonpregnant rats, pregnant controls and pregnant Suramin-treated rats. Blood samples were collected before pregnancy and at gestational day 20 for analysis of renin and sFlt-1. The fetal and placental morphology were evaluated after caesarian section on gestational day 20.

RESULTS

The blood pressure of the pregnant Suramin-treated rats successively increased during pregnancy and differed by 17 mmHg at gestational day 20 compared with the pregnant control rats. In the pregnant Suramin-treated rats group, the renin levels increased (+122%) and the sFlt-1 levels decreased (-58%) during pregnancy. The pregnant Suramin-treated fetuses and placentae were smaller (2.8 g and 0.51 g) than the pregnant controls rats' fetuses and placentae (3.5 g and 0.56 g). Resorptions tended to be higher in the pregnant Suramin-treated rat litters compared with the pregnant control rat litters (P = 0.08). The area of the maternal blood vessels in the mesometrial triangle was smaller in the pregnant Suramin-treated rats group than in the pregnant control rats group.

CONCLUSION

The inhibition of uterine angiogenesis increases maternal blood pressure and compromises fetal and placental development. Placental hypoxia and subsequent activation of the renin-angiotensin system may play an important role for the hypertension.

Intrauterine Growth Restriction in Spontaneously Hypertensive Rats

We examined the test profile of changes in systolic blood pressure (SBP), urinary volume, urinary sodium, and protein excretion in normotensive (Sprague Dawley) and spontaneously hypertensive rats (SHR) up to the 18th day of pregnancy. On days 6, 11, and 18 of pregnancy, the number of implantation sites, number of embryos, litter size, placenta, and litter weight were determined. In SHR, SBP (mmHg) increased significantly from the start of the test and remained high throughout the experiment. There was also a significant increase in urine volume (mL per 24 hrs) and urinary sodium excretion (mEq per 24 hrs) but no significant changes in protein excretion rate. The number of implantation sites on day 6 of pregnancy and the number of embryos on day 11 were similar in both groups. Uterus weight in SHR on days 6 and 11 of pregnancy was significantly lower than in normotensive rats. On day 18 of pregnancy in SHR, a substantial decrease in litter weight (7.10 +/- 0.40 vs. 12.00 +/- 0.92 g; p < 0.001) and weight of placenta (2.35 +/- 0.07 vs. 4.74 +/- 0.21 g; p < 0.001) was observed, with no modification in litter size. The hypertension associated with pregnancy in SHR increased urine volume and urinary sodium excretion and decreased weight of uterus, litter, and placenta relative to control rats.

Vasodilator factors in the systemic and local adaptations to pregnancy

We postulate that an orchestrated network composed of various vasodilatory systems participates in the systemic and local hemodynamic adaptations in pregnancy. The temporal patterns of increase in the circulating and urinary levels of five vasodilator factors/systems, prostacyclin, nitric oxide, kallikrein, angiotensin-(1-7) and VEGF, in normal pregnant women and animals, as well as the changes observed in preeclamptic pregnancies support their functional role in maintaining normotension by opposing the vasoconstrictor systems. In addition, the expression of these vasodilators in the different trophoblastic subtypes in various species supports their role in the transformation of the uterine arteries. Moreover, their expression in the fetal endothelium and in the syncytiotrophoblast in humans, rats and guinea-pigs, favour their participation in maintaining the uteroplacental circulation. The findings that sustain the functional associations of the various vasodilators, and their participation by endocrine, paracrine and autocrine regulation of the systemic and local vasoactive changes of pregnancy are abundant and compelling. However, further elucidation of the role of the various players is hampered by methodological problems. Among these difficulties is the complexity of the interactions between the different factors, the likelihood that experimental alterations induced in one system may be compensated by the other players of the network, and the possibility that data obtained by manipulating single factors in vitro or in animal studies may be difficult to translate to the human. In addition, the impossibility of sampling the uteroplacental interface along normal pregnancy precludes obtaining longitudinal profiles of the various players. Nevertheless, the possibility of improving maternal blood pressure regulation, trophoblast invasion and uteroplacental flow by enhancing vasodilation (e.g. L-arginine, NO donors, VEGF transfection) deserves unravelling the intricate association of vasoactive factors and the systemic and local adaptations to pregnancy.

Ontogeny of placental structural development and expression of the renin-angiotensin system and 11beta-HSD2 genes in the rabbit

Common pregnancy complications are associated with impaired placental development. This study aimed to characterise the ontogeny of structural correlates of rabbit placental function, its expression of genes encoding components of the renin-angiotensin system (RAS), as well as 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) mRNA since these are known to be expressed by the placenta and are associated with pregnancy complications, including preeclampsia and intrauterine programming. Placentae were collected at gestational age (GA) 14, 21 and 28 (term=32 days). Gene expression was analysed using real time PCR and placental structures were quantified via image analyses. The volume densities and volumes of trophoblast, fetal capillaries, maternal blood space, surface density and surface area of trophoblast all progressively increased, while the arithmetic mean barrier thickness of trophoblast decreased across gestation. Maternal plasma renin activity (PRA) was positively correlated with volumes of trophoblast and maternal blood space, surface density and surface area of trophoblast. Placental renin mRNA declined ( downward arrow62%; P<0.01) across gestation and was negatively correlated with maternal PRA (GA0), fetal and placental weights, placental angiotensin type 1 and 2 receptors (AT(1)R and AT(2)R) mRNA and volume of trophoblast. AT(1)R mRNA expression was increased by 92% (P<0.001) across gestation. AT2R mRNA expression was approximately 81% (P<0.01) greater at GA14 compared to GA21. Placental 11beta-HSD2 mRNA expression was approximately 74% greater (P<0.01) at GA21 than GA14, but by GA28 was similar to that at GA14. These data show that changes in placental gene expression are associated with key events in placental and fetal development, indicating that the rabbit provides a good model for investigations of pregnancy perturbations that alter the RAS or programme the fetus.

Pathophysiology of placentation abnormalities in pregnancy-induced hypertension

During embryogenesis and development, the fetus obtains oxygen and nutrients from the mother through placental microcirculation. The placenta is a distinctive organ that develops and differentiates per se, and that organizes fetal growth and maternal condition in the entire course of gestation. Several life-threatening diseases during pregnancy, such as pregnancy-induced hypertension (PIH) and eclampsia, are closely associated with placental dysfunction. Genetic susceptibilities and poor placentation have been investigated intensively to understand the pathophysiology of PIH. It is currently thought that “poor placentation hypothesis”, in which extravillous trophoblasts fail to invade sufficiently the placental bed, explains in part maternal predisposition to this disease. Cumulative studies have suggested that hypoxic micromilieu of fetoplacental site, shear stress of uteroplacental blood flow, and aberrantly secreted proinflammatory substances into maternal circulation synergistically contribute to the progression of PIH. For example, soluble form of vascular endothelial growth factor receptor-1 (sVEGFR-1) and soluble form of CD105 are elevated in circulation of PIH mothers. However, it remains to be poorly understood the pathological events in the placenta during the last half of gestation as maternal systemic disorders get worse. For better understanding and effective therapeutic approaches to PIH, it is important to clarify pathological course of PIH-associated changes in the placenta. In this review, current understanding of placental development and the pathophysiology of PIH placenta are summarized. In addition, recent findings of vasoactive signalings in PIH and rodent PIH models are discussed.

Hyperhomocysteinemia is not sufficient to cause preeclampsia in an animal model: the importance of folate intake

OBJECTIVE

The objective of our study was to determine whether methylenetetrahydrofolate reductase (Mthfr)-deficient mice develop preeclampsia (PE).

STUDY DESIGN

Mice were placed on a normal or low-folate/high-methionine (LF/HM) diet to assess the impact of mild and severe homocysteinemia. Blood pressure and proteinuria were measured throughout gestation in Mthfr-deficient and control mice on both diets, by radiotelemetry and by determining the urinary albumin/creatinine ratio by enzyme-linked immunosorbent assay, respectively.

RESULTS

Although Mthfr-deficient mice have endothelial dysfunction, they do not develop hypertension or proteinuria during gestation. The LF/HM diet induced proteinuria, growth restriction, and a decrease in the number of pups per litter in all mice without any effect on the placenta.

CONCLUSION

Our study clearly demonstrates that hyperhomocysteinemia is not sufficient to cause PE in this animal model. Furthermore, it confirms the importance of folate intake on pregnancy outcomes.

Angiotensin II type 1 receptor has impact on murine placentation

Impaired placentation is a key step in the pathogenesis of important pregnancy disorders such as preeclampsia and fetal growth restriction. A role of angiotensin II in placental development can be assumed from the expression of angiotensin receptors on trophoblast from the earliest stages of pregnancy. To understand the role of angiotensin II type 1 (AT1) receptors in placental development, we investigated placentae of AT1a-deficient mice early in pregnancy (day 13 postconception). The number of alive newborns was significantly reduced in AT1a-deficient mice caused by placental malformations in 30% of all utero-placental units. Importantly, no embryonic structure was observable within the uterine segments harboring the malformed placentae. Immunohistochemistry with an antibody against murine betahCG-equivalent stained homogeneously in almost all cells in the altered placentae indicating still an endocrine-active trophoblast. However, the typical structure of the murine wild-type placenta in spongiotrophoblast, giant cells, and labyrinth was abolished in malformed placental tissue deficient in the AT1a receptor. Recent epidemiological studies revealed the detrimental effect of an AT1 blockade for fetal outcome due to renal malformations and a reduced birth weight. For the latter, our findings provide an early mechanistic explanation. The lack in AT1 stimulation causes an impaired trophoblast maturation leading to impaired placental function.

The functional role of the renin-angiotensin system in pregnancy and preeclampsia

During normal pregnancy, the renin-angiotensin system (RAS) plays a vitally important role in salt balance and subsequent well-being of mother and fetus. In this balance, one must consider not only the classical renal RAS but also that of the uteroplacental unit, where both maternal and fetal tissues contribute to the signaling cascade. Many studies have shown that in normal pregnancy there is an increase in almost all of the components of the RAS. In derangements of pregnancy this delicate equilibrium can become unbalanced. Preeclampsia is one such case. It is a disorder of pregnancy characterized by hypertension, proteinuria and placental abnormalities associated with shallow trophoblast invasion and impaired spiral artery remodeling. Despite being a leading cause of maternal death and a major contributor to maternal and perinatal morbidity, the mechanisms responsible for the pathogenesis of preeclampsia are poorly understood. Immunological mechanisms and the RAS have been long considered to be involved in the development of preeclampsia. Numerous recent studies demonstrate the presence of the angiotensin II type I receptor agonistic autoantibody (AT1-AA). This autoantibody can induce many key features of the disorder and upregulate molecules involved in the pathogenesis of preeclampsia. Here we review the functional role of the RAS during pregnancy and the impact of AT1-AA on preeclampsia.

Angiotensin receptor agonistic autoantibodies induce pre-eclampsia in pregnant mice

Pre-eclampsia affects approximately 5% of pregnancies and remains a leading cause of maternal and neonatal mortality and morbidity in the United States and the world. The clinical hallmarks of this maternal disorder include hypertension, proteinuria, endothelial dysfunction and placental defects. Advanced-stage clinical symptoms include cerebral hemorrhage, renal failure and the HELLP (hemolysis, elevated liver enzymes and low platelets) syndrome. An effective treatment of pre-eclampsia is unavailable owing to the poor understanding of the pathogenesis of the disease. Numerous recent studies have shown that women with pre-eclampsia possess autoantibodies, termed AT(1)-AAs, that bind and activate the angiotensin II receptor type 1a (AT(1) receptor). We show here that key features of pre-eclampsia, including hypertension, proteinuria, glomerular endotheliosis (a classical renal lesion of pre-eclampsia), placental abnormalities and small fetus size appeared in pregnant mice after injection with either total IgG or affinity-purified AT(1)-AAs from women with pre-eclampsia. These features were prevented by co-injection with losartan, an AT(1) receptor antagonist, or by an antibody neutralizing seven-amino-acid epitope peptide. Thus, our studies indicate that pre-eclampsia may be a pregnancy-induced autoimmune disease in which key features of the disease result from autoantibody-induced angiotensin receptor activation. This hypothesis has obvious implications regarding pre-eclampsia screening, diagnosis and therapy.

Impaired placental neovascularization in mice with pregnancy-associated hypertension

Preeclampsia is a serious disorder that may result in severe morbidity and mortality for mother and fetus, and it is thought that the placental dysfunction is important in the pathogenesis of preeclampsia. As the model of preeclampsia, we previously generated a transgenic mouse model that developed pregnancy-associated hypertension (PAH) by mating females expressing human angiotensinogen with males expressing human renin. In PAH mice, maternal blood pressure started to rise from days 12 to 13 of gestation (E12-13) to term (E19-20), which is accompanied by the fetal intrauterine growth retardation and systemic maternal disorders including proteinuria and convulsion. To understand the pathology of the complications in PAH mice that overlap with those in human preeclampsia, we analyzed the PAH placenta sequentially from the onset of hypertension to the term of delivery. In PAH placenta, histological analysis revealed that the microvessel densities of fetal vasculature at term were significantly lower than those of normal placenta, and the majority of terminal vessels of PAH placenta were lacking for pericytes and basement membrane. The interaction between fetal vasculature and maternal blood canal at labyrinth of PAH placenta was morphologically distorted, and the expression patterns of key molecules in neovascularization of PAH placenta were distinct from those of normal placenta during pregnancy. In addition, maternal plasma level of soluble form of vascular endothelial growth factor receptor-1 (sVEGFR-1) was significantly increased in PAH at E19. Furthermore, in uteroplacental site, in situ proteolytic activity of PAH mice was suppressed from E16 to term compared to that of normal pregnancy, and the expression of matrix metalloproteinase-2 mRNA was strikingly downregulated at E16 in PAH mice. Collective data suggest that the impairments of fetoplacental neovascularization and uteroplacental remodeling contribute to the development of complications in PAH.

Does the fetal genotype affect maternal physiology during pregnancy?

Conventional wisdom states that associations between fetal growth and diseases in pregnancy, such as pregnancy-induced hypertension (PIH) and gestational diabetes (GDM), result from effects of the mother's genotype or environment acting on her physiology which subsequently affect the fetus. However, recent evidence from human mothers carrying macrosomic offspring with Beckwith Wiedemann syndrome and pregnant mice carrying p57(kip2)-null offspring suggest that variation in the fetal genome can modify maternal physiology to increase fetal nutrient delivery and optimise growth. These are some of the first documented examples of such effects, whereby the genome of one individual directly affects the physiology of another related individual from the same species. We propose that this mechanism is involved in the aetiology of PIH and GDM.

Paternal race is a risk factor for preterm birth

OBJECTIVE

The purpose of this study was to test the hypothesis that paternal race influences the risk for preterm birth.

STUDY DESIGN

We conducted a population-based cohort study to examine the association of paternal race with preterm birth using the Missouri Department of Health's birth registry from 1989-1997. Birth outcomes were analyzed in 4 categories: white mother/white father, white mother/black father, black mother/white father, and black mother/ black father.

RESULTS

We evaluated 527,845 birth records. The risk of preterm birth at <35 weeks of gestation increased when either parent was black (white mother/black father: adjusted odds ratio, 1.28 [95% CI, 1.13, 1.46], black mother/white father: adjusted odds ratio, 2.10 [95% CI, 1.68, 2.62], and black mother/black father: adjusted odds ratio, 2.28 [95% CI, 2.18, 2.39]) and was even higher for extreme preterm birth (<28 weeks of gestation) in pregnancies with a nonwhite parent.

CONCLUSION

Paternal black race is associated with an increased risk of preterm birth in white mothers, which suggests a paternal contribution to fetal genotype that ultimately influences the risk for preterm delivery.

Preeclampsia: new insights

PURPOSE OF REVIEW

Preeclampsia is a disorder of gestation characterized by hypertension and proteinuria and can be complicated by eclamptic seizures. This review describes recent advances in the role of the renin-angiotensin system and angiogenic and anti-angiogenic factors of placental origin in its pathogenesis.

RECENT FINDINGS

Deficient uteroplacental perfusion has been recognized to be a feature in all preeclampsia syndromes. Increased renin expression observed in humans and animal models supports the concept that activation of the decidual renin-angiotensin system may mediate the pathogenesis of preeclampsia. Novel angiotensin II-related biomolecular mechanisms, angiotensin II type 1-B2 receptor heterodimerization and autoantibody against angiotensin II type 1 have recently been described in preeclampsia. New evidence suggests that vascular endothelial growth factor and its receptors, antagonists, and reduced placental growth factor may play a role in the development of proteinuria and other renal injury-mediated manifestations in preeclampsia.

SUMMARY

Vascular maladaptation, with increased vasomotor tone, endothelial dysfunction, increased sensitivity to angiotensin II and norepinephrine, and multiorgan dysfunction seen in preeclampsia, may be explained by angiotensin II-mediated mechanisms. Future investigations need to define the mechanism of activation of the decidual renin-angiotensin system and the release of placental factors in the pathogenesis of preeclampsia.

The effect of over-expression of sFlt-1 on blood pressure and the occurrence of other manifestations of preeclampsia in unrestrained conscious pregnant mice

OBJECTIVE

It has been shown that the level of soluble fms-like tyrosine kinase-1 (sFlt-1) is elevated in pregnant women who are destined to have preeclampsia, and a role for sFlt-1 in its pathogenesis has been suggested. Our objective was to determine the effect of the over-expression of sFlt-1 on blood pressure and the occurrence of other manifestations of preeclampsia in pregnant mice.

STUDY DESIGN

At day 8 of gestation CD-1 mice were allocated randomly to an injection of an adenovirus carrying sFlt-1 (10(9) plaque-forming units; sFlt-1 group), adenovirus carrying the murine immunoglobulin G2alpha Fc fragment (10(9) plaque-forming units; mFc group used as a control for the virus) or saline solution (100 microL; saline group). At day 10 of gestation, blood pressure catheters were inserted through the left carotid artery into the aortic arch and tunneled to a telemetric transmitter. Blood pressure was monitored continuously in the conscious unrestrained animals until day 18. Blood was collected from the pregnant mice at different gestational times, and plasma sFlt-1 was measured by enzyme-linked immunosorbent assay. Pups and placentae were weighed, and maternal platelet counts were determined at death on day 18.

RESULTS

Plasma levels of sFlt-1 increased significantly in the sFlt-1 mice and were significantly higher than the 2 control groups. The mean blood pressure in the sFlt-1 mice was significantly higher on days 17 and 18 of gestation, compared with the mFc and saline solution groups. The time-course of blood pressure rise mirrored that of the sFlt-1 levels. The average pup weight, placental weight, and maternal platelet counts were significantly lower in the sFlt-1 group, compared with the controls.

CONCLUSION

SFlt-1 induces hypertension and fetal growth restriction in pregnant mice, which supports its hypothesized role in the pathogenesis of preeclampsia. This animal model minimizes the need for manipulation or the administration of various compounds to induce the condition.

Genome-wide expression profiling of placentas in the p57Kip2 model of pre-eclampsia

Pre-eclampsia affects 6-10% of pregnancies and is one of the primary causes of premature birth. It is widely accepted that inappropriate placental development, combined with environmental factors, plays a major role in disease pathogenesis. The p57(Kip2) mouse is the only mouse model of pre-eclampsia that recapitulates the full spectrum of symptoms of the human disease, including placental abnormalities, hypertension, proteinuria and premature labour. In addition, pregnant females expressing wild-type levels of p57(Kip2) develop pre-eclampsia when carrying fetuses that lack p57(Kip2) expression. This demonstrates that either the fetus or the placenta causes the disease. Here, taking advantage of the unique genetics of the p57(Kip2) mouse, we have used full genome expression profiling to define the placental aspect of the p57(Kip2) phenotype at a molecular level and to conduct an unbiased search for factors involved in pre-eclampsia pathogenesis. During this analysis, we found that although mutant embryos demonstrate altered placental architecture and have histological changes indicative of reduced utero-placental blood flow, the p57(Kip2) pregnant females do not demonstrate hypertension or renal pathology. This suggests a model in which placental abnormalities cause pre-eclampsia only given other environmental variables. On the basis of this model, we expect that misregulation of molecular factors, while not able to cause a full spectrum of disease symptoms in this context, still occurs in these p57(Kip2) mutant mice. Our studies suggest a role for environmental factors in the p57(Kip2) pre-eclampsia phenotype and have identified several candidates for pre-eclampsia predisposition in this model, including known regulators of blood pressure, inflammation and apoptosis.

Placental abruption is more frequent in women with the angiotensinogen Thr235 mutation

OBJECTIVE

Obstetrical complications such as preeclampsia, fetal growth restriction, and placental abruption are associated with inadequate placental perfusion. Previous studies have shown that the angiotensinogen (AGT) Thr235 mutation is associated with abnormal remodeling of the uterine spiral arteries and occurs at higher frequencies in preeclampsia. This study was done to evaluate whether the AGT Thr235 mutation increases the risk of placental abruption.

MATERIALS AND METHODS

We compared 62 placentas from women who had placental abruption with 240 control patients of similar age and ethnicity. DNA was extracted from paraffin blocks from placentas. AGT Met235Thr mutation status was determined by single fluoresceine labeled probe real-time PCR using a LightCycler system.

RESULT

AGT genotypes were divided into three groups: MM (homozygous wild), TT (homozygous mutant), and MT (heterozygous). The constituent ratio of AGT genotype in abrupted placentas (MM 14.5%, MT 43.5%, TT 41.9%) was significantly different from in control group (MM42.5%, MT 39.6%, TT 17.9%) (p<0.001). AGT mutant allele frequency in placental abruption (0.637) was significantly higher than in the control group (0.377) (p<0.001).

CONCLUSION

The AGT Thr235 mutation was observed more frequently in placental abruption. AGT Thr235 mutation may be considered a risk factor for placental abruption.

The role of RAS in the pathogenesis of preeclampsia

Preeclampsia is a hypertensive disorder that is unique to pregnancy, with consistent involvement of the kidney. The renin-angiotensin system (RAS) has been implicated in the pathogenesis of preeclampsia. In the gravid state, in addition to the RAS in the kidney, there is a tissue-based RAS in the uteroplacental unit. Increased renin expression in human preeclampsia and in transgenic mouse models with a human preeclampsia-like syndrome shows that activation of the uteroplacental RAS, with angiotensin II entering the systemic circulation, may mediate the pathogenesis of preeclampsia. Vascular maladaptation in preeclampsia with increased vasomotor tone, endothelial dysfunction, and increased sensitivity to angiotensin II and norepinephrine in manifest preeclampsia may be explained on the basis of angiotensin II-mediated mechanisms through angiotensin receptor type I (AT1) activation. Recently, novel angiotensin II-related biomolecular mechanisms have been described in preeclampsia. These include AT1 and bradykinin B2 receptor heterodimerization and the production of autoantibody against AT1. Various organ systems with predilection for involvement in preeclampsia are sites of tissue-based RAS. Angiotensin II-mediated mechanisms may explain the primary clinicopathologic features of preeclampsia. In this review, these various aspects are critically examined and an integrated concept on the role of RAS in preeclampsia is presented.

Angiotensin II decreases system A amino acid transporter activity in human placental villous fragments through AT1 receptor activation

Reduced transport of amino acids from mother to fetus can lead to fetal intrauterine growth restriction (IUGR). The activities of several amino acid transport systems, including system A, are decreased in placental syncytiotrophoblast of IUGR pregnancies. Na(+)-K(+)-ATPase activity provides an essential driving force for Na(+)-coupled system A transport, is decreased in the placenta of IUGR pregnancies, and is decreased by angiotensin II in several tissues. Several reports have shown activation of the fetoplacental renin-angiotensin system (RAS) in IUGR. We investigated the effect of angiotensin II on placental system A transport and Na(+)-K(+)-ATPase activity in placental villi. Placental system A activity in single primary villous fragments was measured as the Na(+)-dependent uptake of alpha-(methylamino)isobutyric acid, and Na(+)/K(+) ATPase activity was measured as ouabain-sensitive uptake of (86)rubidium. Angiotensin II decreased system A activity in a concentration-dependent fashion (10-500 nmol/l). Angiotensin II type 1 receptor (AT1-R) antagonists losartan and AT1-R anti-peptide blocked the angiotensin II effect, but the angiotensin II type 2 receptor antagonist PD-123319 was without effect. System A activity was not altered by preincubation with AT1-R-independent vasoconstrictors, and antioxidants did not prevent the decrease in activity mediated by angiotensin II. Angiotensin II decreased Na(+)-K(+)-ATPase activity by an AT1-R dependent mechanism, and inhibition of Na(+)-K(+)-ATPase activity decreased system A activity in a dose-response fashion. These data suggest that angiotensin II, via AT1-R signaling, decreases system A activity by suppressing Na(+)-K(+)-ATPase in human placental villi, consistent with possible adverse effects of enhanced placental RAS on fetal growth.

Searching for genetic clues to the causes of pre-eclampsia

Pre-eclampsia and its related syndromes are significant causes of maternal and fetal death, but much remains unclear about the underlying disease mechanisms. Epidemiological research has consistently demonstrated a familial predisposition to pre-eclampsia, which has encouraged genetic research in this area. The goal is the discovery of susceptibility genes which will inform understanding of the pathophysiology of pre-eclampsia, and may prove to be targets for therapeutic or preventative strategies. This review examines the application of molecular technologies to the search for genetic clues in pre-eclampsia and emphasizes the importance of integrative approaches. The results of recent genome-wide linkage studies have been particularly encouraging, identifying a number of loci which merit closer examination. Candidate gene studies have proved less fruitful, generating conflicting and inconclusive results. Possible explanations and remedies for this deficiency are discussed with a view to stimulating closer collaboration between researchers in this field.

Adverse Perinatal Outcomes Among Interracial Couples in the United States

OBJECTIVE

We examined the association between parental race and stillbirth and adverse perinatal and infant outcomes.

METHODS

We conducted a retrospective cohort analysis using the 1995-2001 linked birth and infant death files that are composed of live births and fetal and infant deaths in the United States. The study included singleton births delivered at 20 or more weeks of gestation with a fetus weighing 500 g or more (N = 21,005,786). Parental race was categorized as mother white-father white, mother white-father black, mother black-father white, and mother black-father black. Multivariable logistic regression analysis was performed to examine the association between parental race and risks of stillbirth (at > or = 20 weeks), small for gestational age (defined as birth weight < 5th and < 10th percentile for gestational age), and early neonatal (< 7 days), late neonatal (7-27 days), and postneonatal (28-364 days) mortality. All analyses were adjusted for the confounding effects of maternal age, education, trimester at which prenatal care began, parity, marital status, and smoking during pregnancy.

RESULTS

Although risks varied across parental race categories, stillbirth was associated with a higher-than-expected risk for interracial couples: mother white-father black, relative risk (RR) 1.17 (95% confidence interval [CI] 1.10-1.26) and mother black-father white, RR 1.37 (95% CI 1.21-1.54) compared with mother white-father white parents. The RR for stillbirth was even higher among mother black-father black parents (RR 1.67, 95% CI 1.62-1.72). The overall patterns of association for small for gestational age births (< 5th and < 10th percentile) and early neonatal mortality were similar to those seen for stillbirth.

CONCLUSION

There is an increased risk of adverse perinatal outcomes for interracial couples, including stillbirth, small for gestational age infants, and neonatal mortality.

LEVEL OF EVIDENCE

II-2.

Role of the renin-angiotensin system in the pathogenesis of preeclampsia

Preeclampsia is a hypertensive disorder unique to pregnancy with consistent involvement of the kidney. The renin-angiotensin system (RAS) has been implicated in the pathogenesis of preeclampsia. In the gravid state, in addition to the RAS in the kidney, there is a tissue-based RAS in the uteroplacental unit. Increased renin expression observed both in human preeclampsia and in a transgenic mouse model with a human preeclampsia-like syndrome supports the concept that activation of the uteroplacental RAS, with angiotensin II entering the systemic circulation, may mediate the pathogenesis of preeclampsia. A novel disease paradigm of the two-kidney one-clip (2K-1C) Goldblatt model is presented for preeclampsia, wherein the gravid uterus is the clipped “kidney” and the two maternal kidneys represent the unclipped kidney. Validation of the 2K-1C Goldblatt model analogy requires evidence of elevated angiotensin II in the peripheral circulation before vascular maladaptation in preeclampsia. Convincing evidence of the elevation of angiotensin II in preeclampsia does not exist despite the fact that much of vascular pathogenesis appears to be due to angiotensin type I (AT1) receptor activation. Vascular maladaptation with increased vasomotor tone, endothelial dysfunction, and increased sensitivity to angiotensin II and norepinephrine in manifest preeclampsia may be explained on the basis of angiotensin II-mediated mechanisms. Recently, novel angiotensin II-related biomolecular mechanisms have been described in preeclampsia. These include AT1and bradykinin B2receptor heterodimerization and the production of an autoantibody against AT1. Various organ systems with a predilection for involvement in preeclampsia are each a site of a tissue-based RAS. How angiotensin II-mediated mechanisms may explain the primary clinical-pathological features of preeclampsia is described. Future investigations are proposed to more precisely define the role of activation of the uteroplacental RAS in the mechanisms underlying preeclampsia.

Maternal and fetal genetic factors account for most of familial aggregation of preeclampsia: a population-based Swedish cohort study

There is accumulated evidence for genetic influences on preeclampsia. However, no study has been able to separate the effects of maternal and fetal genetic factors from environmental factors, and there are still uncertainties about the origin and magnitude of the genetic effects. We used the population-based Swedish Birth and Multi-Generation Registries to identify a cohort of women who gave birth from 1987 through 1997. In order to separate the genetic and environmental contributions to preeclampsia, we analyzed pregnancy outcomes from families joined by full siblings. We included information from 244,564 sibling pairs (62,236 sister pairs, 63,288 brother pairs, and 119,040 sister-brother pairs), who had 701,488 pregnancies. We found that 35% of the variance in liability of preeclampsia was attributable to maternal genetic effects, 20% to fetal genetic effects (with similar contribution of maternal and paternal genetic effects), 13% to the couple effect, less than 1% to shared sibling environment, and 32% to unmeasured factors. Among women and men without a history of preeclampsia, partner change reduced the risk of preeclampsia (odds ratio, 0.6; 95 percent confidence interval, 0.4-0.9). Genetic factors account for more than half of the liability of preeclampsia, and maternal genes contribute more than fetal genes. We suggest that the couple effect is due to a genetic interaction between mother and father.

Agonistic autoantibodies to the AT1 receptor in a transgenic rat model of preeclampsia

We used rats transgenic for the human angiotensinogen (hAogen) gene and the human renin (hRen) gene and crossed the strains to produce a model of preeclampsia in the dams. The female (n=9) hAogen x male hRen cross had severe (telemetry-measured) hypertension and albuminuria, which developed during the last trimester of pregnancy and subsided after delivery. The converse cross (n=9) and control (n=9) SD rats did not. We demonstrated that the female hAogen x male hRen cross had agonistic antibodies capable of activating the angiotensin (Ang) II AT1 receptor (AT1R-AA) and defined the epitope on the receptor's second extracellular loop. The phenomenon also occurs in humans with preeclampsia. The rats displayed renal histology reminiscent of preeclampsia, including fibrin deposition confined to the glomeruli. The complement system was activated in glomeruli and IgG deposits were present that may represent AT1R-AA. Finally, we observed an atherosis-like lesion in the spiral arteries of the placental bed, which we called placental-bed arteriolosclerosis. Our model may be relevant to preeclampsia in humans.

Differential roles of renin and angiotensinogen in the feto-maternal interface in the development of complications of pregnancy

We previously identified a transgenic mouse model that developed pregnancy-associated hypertension (PAH) and intrauterine growth restriction (IUGR) by mating females expressing human angiotensinogen (hANG) with males expressing human renin (hRN). These phenotypic defects were not observed in the opposite type of mating combination, despite the feto-placental overexpression of hRN and hANG detected in both types of crossbreeding. Detailed analysis of transgene localization in the labyrinth and its permeability to the maternal circulation revealed that hRN produced in trophoblast giant cells was secreted into the maternal circulation, whereas hANG, produced in chorionic trophoblasts and trophoblastic epithelium, was undetectable in the maternal plasma, probably due to their distinct spatial and temporal expression in labyrinth. These results demonstrated that PAH and IUGR could be mediated by feto-placental hRN through its permeability to the maternal circulation, not by feto-placental hANG production. Furthermore, overexpression of maternally derived hANG in decidua and spiral arteries of pregnant females with PAH and IUGR raises the possibility of local activation of the renin-angiotensin system and its pathophysiological effects on placental hypoperfusion in complications of pregnancy. This study provides in vivo evidence that the cell-specific expression of RN and ANG in the feto-maternal interface impacts their differential roles in pregnancy.

Animal models of preeclampsia

There have been many attempts to produce animal models that mimic the hypertensive disorders of pregnancy, especially preeclampsia, but most are incomplete when compared to the full spectrum of the human disease. This review assesses a number of these models, organized according to the investigators attempt to focus on a specific pathogenic mechanism believed to play a role in the human disease. These mechanisms include uterine ischemia, impairments in the nitric oxide system, insulin resistance, overactivity of the autonomic nervous and/or renin-angiotensin systems, activation of a systemic inflammatory response, and most recently, activation of circulating proteins that interfere with angiogenesis. In addition a model of renal disease that mimics superimposed preeclampsia is discussed. Defining these animal models should help in our quest to understand the cause, as well as to test preventative and therapeutic strategies in the management of these hypertensive disorders of pregnancy.

Vasoconstrictively acting AT1R A1166C and NOS3 4/5 polymorphisms in recurrent spontaneous abortions (RSA)

PROBLEM

Inadequate uteroplacental perfusion is one of the main reasons for recurrent spontaneous abortions (RSA). Coagulation, fibrinolysis, and vasoconstriction affect tissue perfusion. These systems are regulated by different gene products. Polymorphisms can modulate the expression levels of the respective genes and can thereby affect perfusion. Vasoconstriction is influenced by the expression of endothelial nitric oxide synthase (eNOS) and of the angiotensinogen II type 1 receptor (AT1R).

METHOD

The aim of our study was to investigate, whether two polymorphisms in the AT1R and NOS3 genes shown to result in maternal vasoconstriction are associated with an increased risk for RSA.

RESULTS

Our data indicate that the vasoconstrictively acting genotypes AT1R C/C and NOS3 4/4 are of similar prevalence in RSA patients and in controls.

CONCLUSION

Results do not show any influence of the polymorphisms studied on early pregnancy development. This is in concordance with the concept of an independent regulation of placental perfusion.

The endothelin receptor antagonist ameliorates the hypertensive phenotypes of transgenic hypertensive mice with renin-angiotensin genes and discloses roles of organ specific activation of endothelin system in transgenic mice

Endothelin (ET)-1 and ET-2 are potent vasoconstrictor peptides with mitogenic activity. In this study, we investigated roles of ET system in renin-angiotensin system (RAS)-mediated hypertension, using transgenic hypertensive mice (THM) with over-expression of both human renin and angiotensinogen genes. In the first step, it was revealed that expression of ET system was locally enhanced, i.e. increases in cardiac preproET-1 mRNA and renal preproET-2 mRNA in THM, compared with the control (wild type) mice. In the next step, we studied the chronic effects of an ET antagonist (SB209670) on THM. Blood pressure (BP) in THM was significantly higher than that in the normal mice during the investigation. However, in the later phase of the study, from 12 to 20 weeks of treatment, THM receiving SB 209670 showed significantly lower BP than that in THM receiving saline. SB 209670 treatment for 20 weeks significantly attenuated phenotypes of cardiac hypertrophy, vascular wall thickening and hypertensive nephropathy observed in THM, suggesting that the ETA/B receptor antagonist is also effective even in the extraordinarily activated RAS condition. These findings suggest that organ specifically activated ET system in THM develops the phenotypes, hypertension, cardiac hypertrophy, and hypertensive nephropathy.

An essential role for angiotensin II type 1a receptor in pregnancy-associated hypertension with intrauterine growth retardation

Little is known about an in vivo significance of angiotensin II Type-1 receptor (AT1) for pregnancy-associated diseases, including hypertension and intrauterine growth retardation (IUGR). We previously demonstrated that female mice carrying the human angiotensinogen gene (hAG+/+), when mated with human renin transgenic (hRN+/+) male mice, displayed hypertension in late pregnancy due to secretion of human renin from the fetal side into the maternal circulation. In the present study, to investigate a role for AT1 in pregnancy-associated hypertension, we generated a new strain of hAG+/+/mAT1a-/- mice by genetically deleting the AT1a gene from hAG+/+ mice. When mated with hRN+/+ male mice, excessive increases in human renin, angiotensin, and plasma renin activity were detected in the plasma of pregnant hAG+/+/mAT1a-/- mice as found in that of pregnant hAG+/+ mice. Surprisingly, however, blood pressure of hAG+/+/mAT1a-/- mice was not elevated in late pregnancy despite the presence of AT1b, a subtype of AT1. The maternal and fetal defects, such as cardiac and placental abnormalities, and IUGR observed in pregnant hypertensive hAG+/+ mice were not recognized in pregnant hAG+/+/mAT1a-/- mice. The limited term administration of AT1 antagonists to hypertensive hAG+/+ mice in late pregnancy dramatically improved hypertension and IUGR, showing the clinical importance of AT1a.

Effects of static magnetic fields on plasma levels of angiotensin II and aldosterone associated with arterial blood pressure in genetically hypertensive rats

Effects of static magnetic fields (SMFs) on development of hypertension were investigated using young male, stroke resistant, spontaneously hypertensive rats (SHRs) beginning at 7 weeks of age. SHRs were randomly assigned to two different exposure groups or an unexposed group. The SHRs in the exposure groups were constantly exposed to two different types of external SMFs of 3.0-10.0 mT or 8.0-25.0 mT for 12 weeks. The SMFs were generated from permanent magnetic plates attached to the rat cage. The blood pressure (BP) of each rat was determined at weekly intervals using indirect tail-cuff method. The SMFs suppressed and retarded the development of hypertension in both exposed groups to a statistically significant extent for several weeks, as compared with an unexposed group. The antipressor effects were related to the extent of reduction in plasma levels of angiotensin II and aldosterone in the SHRs. These results suggest that the SMFs of mT intensities with spatial gradients could be attributable to suppression of early BP elevation via hormonal regulatory system.

The genetics of pre-eclampsia: a feto-placental or maternal problem?

Pre-eclampsia is a potentially life-threatening disease of women during pregnancy leading to hypertension and proteinuria. It affects 1 in 15 pregnancies but, despite intense research efforts, the cause of the disease remains mysterious. Because pre-eclampsia only occurs during pregnancy and its symptoms resolve after delivery, factors from the placenta are thought to be involved. The role of the placenta could be production of 'abnormal' factors that initiate widespread inflammation and vaso-constriction. Alternatively, because the placenta normally contributes to maternal cardiovascular adaptations of pregnancy, it may be that normal placental functions fail in pre-eclampsia or that susceptibilities in the mother to hypertensive, vascular and/or renal disease prevent the appropriate normal responses to them. The potential contributions of both maternal and fetal genes to the onset of the disease have complicated the genetic analysis of the disease in humans. Recent studies have identified strains of transgenic and mutant mice that develop the hallmark features of pre-eclampsia-like disease - gestational hypertension, proteinuria and kidney lesions (glomerulosclerosis). Comparison of three different mouse models suggests that pre-eclampsia can be initiated by at least three independent mechanisms: pre-existing borderline maternal hypertension that is exacerbated by pregnancy (BPH/5 strain of mice), elevated levels of the vasoconstrictor angiotensin II in the maternal circulation by placental over-production of renin (renin/angiotensinogen transgenic mice), and placental pathology (p57Kip2 mutant mice). These findings imply that the pathogenesis of pre-eclampsia cannot be explained by a single mechanism. Therefore, segregation of the human disease into different subtypes may be a key first step in identifying genetic risk factors.

Pregnancy-induced alterations of vascular function in mouse mesenteric and uterine arteries

Normal pregnancy involves dramatic changes to maternal vascular function, while abnormal vascular adaptations may contribute to pregnancy-associated diseases such as preeclampsia. Many genetic mouse models have recently emerged to study vascular pathologies of pregnancy. However, vascular adaptations to pregnancy in normal mice are not fully understood. Thus, we studied changes in vascular reactivity during normal mouse pregnancy. We hypothesized that pregnant mice will have enhanced endothelial-dependent vasodilation compared with nonpregnant mice, via an enhancement of the nitric oxide synthase (NOS) prostaglandin H synthase (PGHS), and other endothelial-derived hyperpolarizing pathways. Late pregnant (Day 17-18) C57BL/6J mice (n = 10) were compared with nonpregnant mice (n = 7). Uterine and mesenteric arteries were mounted on a wire myograph system and assessed for endothelium-dependent (methacholine) and -independent (sodium nitroprusside; SNP) relaxation responses. Endothelial-dependent relaxation was enhanced in pregnant uterine and mesenteric arteries, which was blunted after the addition of inhibitors of the PGHS or NOS pathways. In nonpregnant mice, these pathways had no effect in modulating relaxation in uterine arteries, whereas vasodilation in mesenteric arteries was reduced only by NOS inhibition. Both uterine and mesenteric vessels had nonnitric oxide- and nonprostaglandin-mediated relaxation, but this relaxation was not enhanced during pregnancy. Endothelial-independent relaxation was also enhanced in pregnant uterine but not mesenteric arteries. Our data indicate that uterine and mesenteric arteries from pregnant mice have enhanced vasodilation. Understanding vascular adaptations to normal mouse pregnancy is crucial for interpreting changes that may occur in genetic mouse models.

Role of AT2 receptor in the brain in regulation of blood pressure and water intake

The effects of intracerebroventricular (ICV) injection of angiotensin II (ANG II) on blood pressure and water intake were examined with the use of ANG II receptor-deficient mice. ICV injection of ANG II increased systolic blood pressure in a dose-dependent manner in wild-type (WT) mice and ANG type 2 AT(2) receptor null (knockout) (AT(2)KO) mice; however, this increase was significantly greater in AT(2)KO mice than in WT mice. The pressor response to a central injection of ANG II in WT mice was inhibited by ICV preinjection of the selective AT(1) receptor blocker valsartan but exaggerated by the AT(2) receptor blocker PD-123319. ICV injection of ANG II also increased water intake. It was partly but significantly suppressed both in AT(2)KO and AT(1)aKO mice. Water intake in AT(2)/AT(1)aKO mice did not respond to ICV injection of ANG II. Both valsartan and PD-123319 partly inhibited water intake in WT mice. These results indicate an antagonistic action between central AT(1)a and AT(2) receptors in the regulation of blood pressure, but they act synergistically in the regulation of water intake induced by ANG II.

Searching for preeclampsia genes: the current position

Although there is substantial evidence that preeclampsia has a genetic background, the complexity of the processes involved and the fact that preeclampsia is a maternal-fetal phenomenon does not make the search for the molecular basis of preeclampsia genes easy. It is possible that the single phenotype 'preeclampsia' in fact should be divided into different sub-groups on genetic or biochemical level. In the present review, the preeclampsia phenotype and its pathophysiologic features are discussed. Family studies and postulated inheritance models are summarized. A systematic overview is given on the numerous candidate gene studies and gene-expression studies performed so far and on the currently available genome-wide scan data. Despite extensive research the molecular genetic basis of preeclampsia remains unclear. Future studies will hopefully enhance our insights in the molecular pathogenesis of preeclampsia.

[Pregnancy-related hypertension]

PURPOSE

Hypertension occurs in 10 to 15 p cent of pregnancies. Among them, 10 to 20% also have proteinuria. This situation defines preeclampsia, and involves a serious threat on fetal and even maternal prognosis. Presence of the hepatic (HELLP) syndrome still severely worsens the prognosis.

CURRENT KNOWLEDGE AND KEY POINTS

Pathophysiology of preeclampsia is based on a very early abnormality of placentation, leading to insufficient blood supply to the feto-placental unit. At the maternal level, the main consequence of placental ischemia is generalized endothelial dysfunction, responsible for systemic vasoconstriction and clotting abnormalities. In such a context, lowering blood pressure with drugs is quite inefficient, or even harmful. The prognosis of this disease is mainly related to the pertinence of obstetrical management.

FUTURE PROSPECTS AND PROJECTS

An early preventive strategy is the most logical approach of preeclampsia, its modalities remain under discussion.

Resistance to neointimal hyperplasia and fatty streak formation in mice with adrenomedullin overexpression

OBJECTIVE

Several in vitro studies have implicated that adrenomedullin (AM) plays an important role in the pathogenesis of vascular injury and fatty streak formation. To test this possibility in vivo, we evaluated 2 experimental models using transgenic mice overexpressing AM in a vessel-selective manner (AMTg mice).

METHODS AND RESULTS

Placement of a periarterial cuff on femoral arteries resulted in neointimal formation at 2 to 4 weeks to a lesser extent in AMTg mice than in their wild-type littermates (at 28 days, intima/media area ratio 0.45+/-0.14 versus 1.31+/-0.41, respectively; P<0.001). This vasculoprotective effect observed in AMTg mice was inhibited by N(omega)-nitro-L-arginine methyl ester. We further examined the effect of AM on hypercholesterolemia-induced fatty streak formation by crossing AMTg mice with apolipoprotein E knockout mice (ApoEKO mice). The extent of the formation of fatty streak lesions was significantly less in ApoEKO/AMTg mice than in ApoEKO mice (percent lesion area 12.0+/-3.9% versus 15.8+/-2.8%, respectively; P<0.05). Moreover, endothelium-dependent vasodilatation as indicative of NO production was superior in AMTg/ApoEKO mice compared with ApoEKO mice.

CONCLUSIONS

Taken together, our data demonstrated that AM possesses a vasculoprotective effect in vivo, which is at least partially mediated by NO.

Angiotensin mutant mice: a focus on the brain renin-angiotensin system

With advances in genetic manipulation and molecular biological and physiological techniques, the mouse has become the animal model of choice for studying the genetic basis of human diseases. The two most commonly used methods for analyzing the function of a gene in vivo, overexpression (transgenic mouse) and deletion (knockout mouse), have been extremely useful in establishing the importance of genes in genetic disorders. The renin-angiotensin system (RAS) is one of the most widely studied systems controlling blood pressure. Although the primary site of Ang-II production is the plasma, all the components of the RAS cascade are expressed in many tissues, including the brain. This review briefly summarizes systemic and tissue-specific transgenic and knockout mouse models of the RAS for determining the role of this system in the regulation of blood pressure and in the pathogenesis of hypertension, with a focus on the RAS in the brain.

Discovery of a spontaneous genetic mouse model of preeclampsia

Preeclampsia remains a leading cause of maternal and fetal morbidity and mortality but has an unknown etiology. Women with elevated baseline blood pressure have an increased risk of this disorder. We hypothesized that BPH/5 mice, an inbred mouse strain with mildly elevated blood pressure, would develop a pregnancy-induced hypertensive syndrome. Nonpregnant female BPH/5 and C57BL/6 mice underwent thoracic aortic implantation of telemeters. After 7 days of recovery and 5 days of baseline mean arterial blood pressure (MAP) recording, strain-matched timed matings were carried out. MAP was recorded continuously during pregnancy and for 1 week after birth. In separate mice in metabolic cages, urinary protein was tracked, followed by renal histological analysis. Before pregnancy, the BPH/5 strain had elevated baseline MAP compared with the C57BL/6 strain, but both strains had similar total urinary protein levels and renal histology. MAP remained stable in both groups during the first 2 weeks of pregnancy. However, at the start of the last trimester, MAP began to rise further in the BPH/5 mice; it rose to peak levels just before delivery and returned to prepregnancy levels by 2 days after delivery. This was accompanied by late-gestational proteinuria and progressive glomerulosclerosis. No changes were observed in the C57BL/6 group except for a small decrease in MAP at mid gestation. The BPH/5 group delivered significantly smaller litters despite normal numbers of fetuses early in gestation, and longitudinal ultrasound studies documented fetal demise before the onset of hypertension and renal disease. This is the first report of an animal model that spontaneously develops a syndrome that bears close resemblance to preeclampsia, and it should have an impact on our understanding of the pathophysiology of this disorder.

Pregnancy-induced changes in renin gene expression in mice

A puzzling feature of the renin-angiotensin system during pregnancy is the appearance in the maternal circulation of a large increase in the concentration of prorenin and renin. The physiologic role of these changes is not understood. We determined that high levels of renin protein occur in the circulation of pregnant mice, thereby establishing the mouse as a valuable model for understanding gestation-induced changes in the renin-angiotensin system. We used the murine model to show that high levels of renin gene expression occur at the mother-fetus interface, first in maternal decidua and subsequently in placentas. These results were obtained using ICR mice that have 2 related renin genes, Ren1 and Ren2. We also examined renin gene expression in C57Bl/6 mice that have only the Ren1 gene. In these mice, very little renin gene expression was observed in placentas but instead was upregulated in kidneys during pregnancy. In both ICR and C57Bl/6 mice, there is an increase in renin protein in the maternal circulation during pregnancy. However, these mice differ with regard to gestation-induced sites of increased renin gene expression. These studies suggest that mice are a convenient and valuable model for studying renin gene expression during pregnancy.

Perinatal implications of maternal hypertension

Hypertensive disorders of pregnancy are prototypical of maternal conditions associated with reduced uteroplacental blood flow. Hypertensive disorders in pregnancy include chronic hypertension, preeclampsia-eclampsia, superimposed preeclampsia, and gestational hypertension. Pathophysiology of these disorders include deficient uterine vascular modeling in the process of placentation and aberrations of vasomotor regulation. Aberrations of uterine renin-angiotensin system may play a proximate role in the pathogenesis of preeclampsia syndrome. Clinical manifestations are explained in this review based on resultant vasoconstriction and ischemia in systemic and regional circulations. Perinatal implications of hypertensive disorders both in terms of early neonatal outcome and long-term neurodevelopmental effects are described. Methods of antenatal assessment of the fetus and, briefly, principles of clinical management are described.

Influence of the angiotensinogen gene on the ovulatory capacity of mice

OBJECTIVE

The tissue-bound ovarian renin-angiotensin system (OVRAS) is critically involved in ovulation in humans and rodents. Mice with disruption and overexpression of the angiotensinogen gene (Agt) have been previously generated. We investigated the influence of varying Agt gene expression on the ovulatory capacity and early embryonic development in mice.

DESIGN

Observational study of genetically altered mice and their response to a superovulation protocol.

SETTING

Academic research institution.

ANIMAL(S)

Mice with varying copy numbers of Agt (one copy: n = 48; two copies: n = 51; three copies: n = 20; four copies: n = 24).

INTERVENTION(S)

Superovulation protocol, oocyte culture.

MAIN OUTCOME MEASURE(S)

Number of oocytes harvested, early embryonic development of zygotes, evaluation of ovarian histology, serum estradiol measurements.

RESULT(S)

The mean number of oocytes harvested was greatest in wild-type mice (two copies of Agt, 39.9 +/- 14) with a reduction of ovulatory capacity in mice overexpressing Agt (three copies [34.8 +/- 11.7] and four copies [31.2 +/- 12.4], P =.026). Mice with one copy of Agt showed a slight decrease of ovulatory capacity compared to wild-type mice (35.8 +/- 15.2, P =.29). Ovarian histology, serum estradiol levels, and early embryonic development were independent of the Agt genotype.

CONCLUSION(S)

Overexpression of Agt was associated with reduced ovulatory capacity, but with none of the other parameters that were evaluated. These findings support an important role of the ovarian renin-angiotensin system in the process of follicular rupture.

Paternal and maternal components of the predisposition to preeclampsia

BACKGROUND

There is an inherited maternal predisposition to preeclampsia. Whether there is a paternal component, however, is not known.

METHODS

We used records of the Utah Population Database to identify 298 men and 237 women born in Utah between 1947 and 1957 whose mothers had had preeclampsia during their pregnancy. For each man and woman in the study group, we identified two matched, unrelated control subjects who were not the products of pregnancies complicated by preeclampsia. We then identified 947 children of the 298 male study subjects and 830 children of the 237 female study subjects who had been born between 1970 and 1992. These children were matched to offspring of the control subjects (1950 offspring of the male control group and 1658 offspring of the female control group). Factors associated with preeclampsia were identified, and odds ratios were calculated with the use of stepwise logistic-regression analysis.

RESULTS

In the group whose mothers had had preeclampsia (the male study group), 2.7 percent of the offspring (26 of 947) were born of pregnancies complicated by preeclampsia, as compared with 1.3 percent of the offspring (26 of 1973) in the male control group. In the female study group, 4.7 percent of the pregnancies (39 of 830) were complicated by preeclampsia, as compared with 1.9 percent (32 of 1658) in the female control group. After adjustment for the offspring's year of birth, maternal parity, and the offspring's gestational age at delivery, the odds ratio for an adult whose mother had had preeclampsia having a child who was the product of a pregnancy complicated by preeclampsia was 2.1 (95 percent confidence interval, 1.0 to 4.3; P=0.04) in the male study group and 3.3 (95 percent confidence interval, 1.5 to 7.5; P=0.004) in the female study group.

CONCLUSIONS

Both men and women who were the product of a pregnancy complicated by preeclampsia were significantly more likely than control men and women to have a child who was the product of a pregnancy complicated by preeclampsia.

Long-term telemetric measurement of cardiovascular parameters in awake mice: a physiological genomics tool

The recent miniaturization of implantable radiotelemetric devices offers the possibility of an accurate, reliable, and simple phenotyping tool for long-term, hands-off measurement of blood pressure in unrestrained, untethered mice; however, use has been limited because of high morbidity and mortality in all but larger-than-average mice. Also, because the device was developed for abdominal aorta implantation at the renal artery level, its use has not been feasible in studies where infrarenal blood flow is critical, i.e., in pregnant mice. We provide details of a very successful alternative approach for implanting radiotelemeters in mice, whereby thoracic aortic implantation of the pressure-sensing catheter is combined with subcutaneous placement of the transmitter body along the right flank. We used female C57/BL6 (C57) or BPH/5 mice, a strain derived from the cross of inbred hypertensive and hypotensive mouse strains. We show that this is a reliable procedure for providing high-fidelity mean arterial pressure (MAP) and heart rate (HR) recordings for 50-60 days in mice weighing 22 g on average but as small as 17 g. No morbidity or mortality was observed in either strain using this procedure. Importantly, neither strain fully recovered from anesthesia and surgery, as indicated by a return of normal circadian rhythms, until 5-7 days postsurgery. This was also reflected in significantly elevated baseline MAP and HR levels in both strains during this recovery period. Moreover, strain-related differences in relative increases in MAP during the first 5 days of recovery masked the significant elevation in BPH/5 baseline MAP (vs. C57) observed in fully recovered mice. This suggests that methods must allow at least 5-7 days recovery from surgery to provide accurate cardiovascular (CV) phenotyping in mice. Finally, we show that CV parameters can be monitored continuously before, during, and after pregnancy in mice using this alternative implantation approach. The device did not interfere with conception, gestation, delivery, or postnatal care of pups. These results demonstrate the feasibility of stress-free, long-term monitoring of CV parameters in pregnant or nonpregnant mice of typical size and offer exciting possibilities for application in CV functional genomic research.