Stéphanie Falcao

Post-ischemic cardioprotection by A2A adenosine receptors: dependent of phosphatidylinositol 3-kinase pathway.

Activation of myocardial A2A adenosine receptors during reperfusion has been shown to be cardioprotective. The intracellular mechanisms underlying this protection remain unknown. To understand the beneficial effects of activated A2A adenosine receptors in such a state, we investigated whether the enzymes phosphatidylinositol 3-kinase (PI3K) and caspase-3 can account for this post-ischemic cardioprotective effect in an anesthetized rabbit model of myocardial infarction (30 minutes ischemia; 5 hours reperfusion). Administration of the A2A agonist CGS21680 (0.2 &mgr;g/kg/min) 5 minutes before reperfusion began (Early) reduced infarct size expressed as a percentage of the area at risk (25.7 ± 5.3% versus 46.5 ± 5.3% for the control group; * P < 0.05). Treatment with the A2A agonist 5 minutes after the onset of reperfusion (Late) had no effect on infarct size (38.2 ± 6.2%). In the presence of a selective inhibitor of PI3K (LY294002), the beneficial effects of CGS21680 on infarct size was no longer observed (43.9 ± 7.9%). After 5 hours of reperfusion, higher PI3K activity in the ischemic region was observed in the Early group compared with the other experimental groups. Caspase-3 activity was not observed in these different groups. In another set of experiments, PI3K activity was significantly higher during the first 15 minutes of reperfusion in the Early group as compared with the Control group. Caspase-3 activity increased rapidly during the first 15 minutes of reperfusion in the Control group and remained stable in the Early group. These results indicated that post-ischemic cardioprotection afforded by A2A adenosine receptor activation is PI3K-dependent and modulate rapidly other signaling pathways such as caspase-3.

Impact of Exercise Training on Preeclampsia: Potential Preventive Mechanisms

Preeclampsia is characterized by hypertension and de novo proteinuria after 20 weeks of pregnancy. It is the leading cause of perinatal morbidity and mortality in the developed world, and to date, the only means of treating the disease is by inducing delivery. Many studies have shown the benefits of exercise training on normal pregnancy. Conversely, because the impact of exercise on reducing the risk of preeclampsia has long been debated, the American College of Obstetricians and Gynecologists has yet to support the prescription of exercise training to women at risk of developing the disease. There is, however, a significant body of evidence in support of the protective role of exercise training against preeclampsia. A recent animal study demonstrated that many preeclampsia features can be eliminated with prenatal followed by gestational exercise training. Hence, the present article reviews the literature on the impact of exercise training on preeclampsia risk, as well as the mechanisms that may be involved.

Mice Overexpressing Both Human Angiotensinogen and Human Renin as a Model of Superimposed Preeclampsia on Chronic Hypertension

Preeclampsia is the major cause of maternal and fetal mortality/morbidity. Because hypertension is an important risk factor for preeclampsia, we investigated whether hypertensive mice that overexpress human renin and angiotensinogen develop superimposed preeclampsia. Given that the mechanisms underlying this disease are still poorly understood, animal models are of great use for elucidatation. Blood pressure and proteinuria were measured by telemetry and ELISA, respectively. Heart function was evaluated by echocardiography, whereas pathological cardiac hypertrophy–related genes were assessed by real-time PCR. Soluble fms-like tyrosine kinase 1 plasma concentrations were quantitated by ELISA and placental expression by real-time PCR. Transgenic mice develop de novo proteinuria during gestation and marked blood pressure elevation, which are hallmarks of superimposed preeclampsia on chronic hypertension. Abnormal placentation present in these mothers produced a significant decrease in pup and placental weight and was associated with an increased placental expression of soluble fms-like tyrosine kinase 1. We also found heightened circulating levels of this receptor, when adjusted for placental mass, as has been observed in women who suffer from preeclampsia. Cardiac hypertrophy could be observed in the transgenic mice and was exacerbated by gestation. As a result, heart function was significantly decreased, and markers of pathological hypertrophy were increased. Our data, thus, confirm the characterization of a new model of superimposed preeclampsia on chronic hypertension. Because chronically hypertensive women are at risk of developing the pathology, our model reflects a clinical reality and is, thus, an excellent tool to elucidate the molecular mechanisms triggering this disease.

Novel Role of the Renin–Angiotensin System in Preeclampsia Superimposed on Chronic Hypertension and the Effects of Exercise in a Mouse Model

Gestational hypertensive disorders, such as preeclampsia, affect 6% to 8% of all pregnancies in North America, and they are the leading cause of maternal mortality in industrialized countries, accounting for 16% of deaths. Women with hypertension have an increased risk (15% to 25%) of developing preeclampsia. Our aim was to investigate the mechanisms implicated in preeclampsia superimposed on chronic hypertension and in the protective effects of exercise in a mouse model. Female mice overexpressing human angiotensinogen and human renin were used as a model of preeclampsia superimposed on chronic hypertension. In the trained group, mothers were placed in cages with access to a wheel before mating, and they remained within these throughout gestation. Blood pressure was measured by telemetry. We found that angiotensin II type I receptor was increased, whereas the Mas receptor was decreased in the placenta and the aorta of pregnant sedentary transgenic mice. This would produce a decrease in angiotensin-(1–7) effects in favor of angiotensin II. Supporting the functional contribution of this modulation, we found that the prevention of most pathological features in trained transgenic mice was associated with a normalization of placental angiotensin II type 1 and Mas receptors and an increase in aortic Mas receptor. We also found reduced circulating and placental soluble Fms-like tyrosine kinase-1 in trained transgenic mice compared with sedentary mice. This study demonstrates that modulation of the renin–angiotensin system is a key mechanism in the development of preeclampsia superimposed on chronic hypertension, which can be altered by exercise training to prevent disease features in an animal model.

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.

Impact of diet and stress on the development of preeclampsia-like symptoms in p57kip2 mice

The cyclin-dependent kinase inhibitor p57(kip2) regulates the cell cycle of trophoblastic cells. It has been established by a Japanese group that the heterozygous p57(kip2) knockout (p57(-/+)) mice are a good model of preeclampsia as they develop hypertension, proteinuria, and placental pathology. However, apart from the placental pathology, we could not observe these symptoms in our laboratory. Hence, we investigated the impact of diet and stress on this model. To do so, we compared the effects of the Japanese diet to that of the North American diet used by our animal facility. Furthermore, the impact of stress was determined by placing the mice in a restraining device before and at the end of gestation. Although the Japanese diet did not have any impact on blood pressure or proteinuria, the mice did develop endothelial dysfunction, left ventricular hypertrophy, as well as increased placental pathology. Also, all mice had smaller litters when fed the Japanese diet. However, stress response of these mice was not increased during gestation; in fact, a decrease was observed in the p57(-/+) mice, suggesting that this was probably not a player in the development of the pathology. Taken together, these results suggest that other environmental factors may have been implicated in the development of preeclampsia-like symptoms in this animal model. Moreover, we demonstrated that placental pathology and genetic factors are not sufficient to trigger preeclampsia-like symptoms in this model and that the diet might play an important part in the development of this multifactorial disease.

OS060. Exercise training promotes placental growth and development in an animal model of preeclampsia superimposed on chronic hypertension

INTRODUCTION Chronic hypertension is an important risk factor for preeclampsia, increasing the prevalence of the disease to 15-25% in pregnant women. Unfortunately there are no known treatments for this disease aside from inducing delivery of the fetus. Nonetheless, several studies have found exercise training to have a protective effect on the risk of developing preeclampsia. OBJECTIVES To determine the mechanisms implicated in the preventive effect of exercise training on preeclampsia, by focusing on the placenta. METHODS Double transgenic mice, overexpressing both human renin and angiotensinogen (R(+)/A(+)), were used to investigate the effect of exercise training on an animal model of preeclampsia superimposed on chronic hypertension. Mice were placed in cages with free access to an exercise wheel 4 weeks prior to and during pregnancy. At gestational day 18, mice were sacrificed and their organs were collected. Real time PCR and Western Blot were performed to evaluate placental genes and proteins, respectively. Circulating sFlt-1(soluble Fms-like tyrosine kinase-1) levels were investigated by ELISA. Placental alterations were assessed by histology and immunohistochemistry, while blood pressure was measured by radiotelemetry. RESULTS Sedentary R(+)/A(+) mice presented with significantly greater placental pathology, which was normalized with exercise training. This was characterized by a normalization of cytokeratin and histone H3 protein expression, thereby restoring placental development, specifically looking at trophoblasts and trophoblast giant cells, respectively. This exercise training effect appears to normalize placental growth primarily by promoting angiogenesis and development. Indeed, a pro-angiogenic shift could be detected which was characterized by an increase in placental growth factor gene expression, along with a decrease in sFlt-1 gene expression, which produced a decrease in circulating sFlt-1. Sedentary R(+)/A(+) mice also presented with a significant increase in VEGF protein, which was significantly decreased with exercise. Of interest, since it has been observed to be decreased with preeclampsia, insulin regulated aminopeptidase (IRAP) gene expression was significantly increased in the trained transgenic mice. Finally, exercise training prevented the increase in blood pressure normally observed at the end of gestation in sedentary R(+)A(+) mice. CONCLUSION Exercise training both before and during gestation appears to promote placental growth and development by producing a pro-angiogenic placental environment. Put together, along with the lack in blood pressure increase, these factors may be responsible for preventing the development of preeclampsia in our animal model of preeclampsia superimposed on chronic hypertension. Identifying the mechanisms implicated in exercise-induced preeclampsia risk reduction will be critical to improve preeclampsia prophylaxis.