The ameliorative effect of angiotensin 1-7 on experimentally induced-preeclampsia in rats: Targeting the role of peroxisome proliferator-activated receptors gamma expression & asymmetric dimethylarginine

Reduced uterine perfusion pressure as a model for preeclampsia and fetal growth restriction in murine: a systematic review and meta-analysis

The reduced uterine perfusion pressure (RUPP) model is frequently used to study preeclampsia and fetal growth restriction. An improved understanding of influential factors might improve reproducibility and reduce animal use considering the variability in RUPP phenotype. We performed a systematic review and meta-analysis by searching Medline and Embase (until 28 March, 2023) for RUPP studies in murine. Primary outcomes included maternal blood pressure (BP) or proteinuria, fetal weight or crown-rump length, fetal reabsorptions, or antiangiogenic factors. We aimed to identify influential factors by meta-regression analysis. We included 155 studies. Our meta-analysis showed that the RUPP procedure results in significantly higher BP (MD = 24.1 mmHg; [22.6; 25.7]; n = 148), proteinuria (SMD = 2.3; [0.9; 3.8]; n = 28), fetal reabsorptions (MD = 50.4%; [45.5; 55.2]; n = 42), circulating soluble FMS-like tyrosine kinase-1 (sFlt-1) (SMD = 2.6; [1.7; 3.4]; n = 34), and lower fetal weight (MD = -0.4 g; [-0.47; -0.34]; n = 113. The heterogeneity (variability between studies) in primary outcomes appeared ≥90%. Our meta-regression identified influential factors in the method and time point of BP measurement, randomization in fetal weight, and type of control group in sFlt-1. The RUPP is a robust model considering the evident differences in maternal and fetal outcomes. The high heterogeneity reflects the observed variability in phenotype. Because of underreporting, we observed reporting bias and a high risk of bias. We recommend standardizing study design by optimal time point and method chosen for readout measures to limit the variability. This contributes to improved reproducibility and thereby eventually improves the translational value of the RUPP model.

Understanding PPARγ and Its Agonists on Trophoblast Differentiation and Invasion: Potential Therapeutic Targets for Gestational Diabetes Mellitus and Preeclampsia

The increasing incidence of pregnancy complications, particularly gestational diabetes mellitus (GDM) and preeclampsia (PE), is a cause for concern, as they can result in serious health consequences for both mothers and infants. The pathogenesis of these complications is still not fully understood, although it is known that the pathologic placenta plays a crucial role. Studies have shown that PPARγ, a transcription factor involved in glucose and lipid metabolism, may have a critical role in the etiology of these complications. While PPARγ agonists are FDA-approved drugs for Type 2 Diabetes Mellitus, their safety during pregnancy is not yet established. Nevertheless, there is growing evidence for the therapeutic potential of PPARγ in the treatment of PE using mouse models and in cell cultures. This review aims to summarize the current understanding of the mechanism of PPARγ in placental pathophysiology and to explore the possibility of using PPARγ ligands as a treatment option for pregnancy complications. Overall, this topic is of great significance for improving maternal and fetal health outcomes and warrants further investigation.

The Role of Peroxisome Proliferator-Activated Receptors in Preeclampsia

Preeclampsia is a common pregnancy-related hypertensive disorder. Often presenting as preexisting or new-onset hypertension complicated by proteinuria and/or end-organ dysfunction, preeclampsia significantly correlates with maternal and perinatal morbidity and mortality. Peroxisome proliferator-activated receptors (PPARs) are nuclear receptor proteins that regulate gene expression. In order to investigate the role of PPARs in the pathophysiology of preeclampsia, we conducted a literature review using the MEDLINE and LIVIVO databases. The search terms "peroxisome proliferator-activated receptor", "PPAR", and "preeclampsia" were employed and we were able to identify 35 relevant studies published between 2002 and 2022. Different study groups reached contradictory conclusions in terms of PPAR expression in preeclamptic placentae. Interestingly, PPARγ agonists alone, or in combination with well-established pharmaceutical agents, were determined to represent novel, potent anti-preeclamptic treatment alternatives. In conclusion, PPARs seem to play a significant role in preeclampsia.

The renin-angiotensin system modulates endotoxic postconditioning of exacerbated renal vasoconstriction in preeclamptic offspring

We recently reported exacerbated endotoxic signs of neuroinflammation and autonomic defects in offspring of preeclamptic (PE) dams. Here, we investigated whether PE programming similarly modifies hemodynamic and renal vasoconstrictor responsiveness to endotoxemia in PE offspring and whether this interaction is modulated by gestational angiotensin 1-7 (Ang1-7). Preeclampsia was induced by gestational treatment with L-NAME. Adult offspring was challenged with lipopolysaccharides (LPS, 5 mg/kg) and systolic blood pressure (SBP) and renal vasoconstrictions were assessed 4 h later. Male, but not female, offspring of PE rats exhibited SBP elevations that were blunted by LPS. Renal vasoconstrictions induced by angiotensin II (Ang II), but not phenylephrine, were intensified in perfused kidneys of either sex. LPS blunted the heightened Ang II responses in male, but not female, kidneys. While renal expressions of AT1-receptors and angiotensin converting enzyme (ACE) were increased in PE offspring of both sexes, ACE2 was upregulated in female offspring only. These molecular effects were diminished by LPS in male offspring. Gestational Ang1-7 caused sex-unrelated attenuation of phenylephrine vasoconstrictions and preferentially downregulated Ang II responses and AT1-receptor and nuclear factor-kB (NFkB) expressions in females. Together, endotoxemia and Ang1-7 offset in sexually-related manners imbalances in renal vasoconstriction and AT1/ACE/ACE2 signaling in PE offspring.

ACE2: a key modulator of the renin-angiotensin system and pregnancy

Angiotensin-converting enzyme 2 (ACE2) is a membrane-bound protein containing 805 amino acids. ACE2 shows approximately 42% sequence similarity to somatic ACE but has different biochemical activities. The key role of ACE2 is to catalyze the vasoconstrictor peptide angiotensin (ANG) II to Ang-(1–7), thus regulating the two major counterbalancing pathways of the renin-angiotensin system (RAS). In this way, ACE2 plays a protective role in end-organ damage by protecting tissues from the proinflammatory actions of ANG II. The circulating RAS is activated in normal pregnancy and is essential for maintaining fluid and electrolyte homeostasis and blood pressure. Renin-angiotensin systems are also found in the conceptus. In this review, we summarize the current knowledge on the regulation and function of circulating and uteroplacental ACE2 in uncomplicated and complicated pregnancies, including those affected by preeclampsia and fetal growth restriction. Since ACE2 is the receptor for SARS-CoV-2, and COVID-19 in pregnancy is associated with more severe disease and increased risk of abnormal pregnancy outcomes, we also discuss the role of ACE2 in mediating some of these adverse consequences. We propose that dysregulation of ACE2 plays a critical role in the development of preeclampsia, fetal growth restriction, and COVID-19-associated pregnancy pathologies and suggest that human recombinant soluble ACE2 could be a novel therapeutic to treat and/or prevent these pregnancy complications.

Placental Ischemia Says "NO" to Proper NOS-Mediated Control of Vascular Tone and Blood Pressure in Preeclampsia

In this review, we first provide a brief overview of the nitric oxide synthase (NOS) isoforms and biochemistry. This is followed by describing what is known about NOS-mediated blood pressure control during normal pregnancy. Circulating nitric oxide (NO) bioavailability has been assessed by measuring its metabolites, nitrite (NO₂) and/or nitrate (NO₃), and shown to rise throughout normal pregnancy in humans and rats and decline postpartum. In contrast, placental malperfusion/ischemia leads to systemic reductions in NO bioavailability leading to maternal endothelial and vascular dysfunction with subsequent development of hypertension in PE. We end this article by describing emergent risk factors for placental malperfusion and ischemic disease and discussing strategies to target the NOS system therapeutically to increase NO bioavailability in preeclamptic patients. Throughout this discussion, we highlight the critical importance that experimental animal studies have played in our current understanding of NOS biology in normal pregnancy and their use in finding novel ways to preserve this signaling pathway to prevent the development, treat symptoms, or reduce the severity of PE.

Lycium barbarum polysaccharides attenuate cardiovascular oxidative stress injury by enhancing the Keap1/Nrf2 signaling pathway in exhaustive exercise rats

Moderate exercise is beneficial to physical and mental health. When the amount of exercise and exercise intensity exceeds a certain limit and reaches the state of exhaustion, oxidative stress levels in the body increase, which can lead to oxidative stress‑associated damage. Lycium barbarum polysaccharide (LBP) is one of the primary active ingredients extracted from wolfberry. Following exhausting exercise in rats, LBP supplements decrease damage to the myocardium and blood vessels, indicating that LBP exerts a protective effect on the cardiovascular system. The Kelch‑like ECH‑associated protein 1 (Keap1)/NF‑E2‑related factor 2 (Nrf2) anti‑oxidative stress signaling pathway improves total oxidizing ability; anti‑apoptosis and other aspects serve a vital role. In the present study, LBP intervention was performed in vivo and in vitro to observe its effect on the Keap1/Nrf2 pathway and oxidative stress‑associated indicators in order to clarify its protective mechanism. For the in vivo experiments, 60 male Sprague‑Dawley rats were randomly divided into normal control and aerobic, exhaustive and exhaustive exercise + LBP (200 mg/kg/day) groups. For the in vitro experiments, a rat thoracic aortic endothelial cell (RTAEC) oxidative stress model was established using angiotensin II (AngII) and divided into blank control, LBP (3,200 µg/ml), AngII (1x10^‑4 mol/l) and AngII + LBP groups. For in vitro experiments, small interfering (si)RNA (50 nmol) was used to transfect RTAEC and induce gene silencing of Nrf2. ELISA, hematoxylin and eosin staining, TUNEL, immunofluorescence, western blotting, immunohistochemistry and reverse transcription‑quantitative PCR were used to evaluate and verify the effect of LBP on oxidative stress indicators and the expression of Keap1/Nrf2 antioxidative stress signaling pathway. The in vivo experiments showed that LBP decreased the expression of serum malondialdehyde (MDA) and AngII, as well as apoptosis of blood vessels and cardiomyocytes and expression of TNF‑α in rats following exhaustive exercise. Meanwhile, LBP enhanced expression of the Keap1/Nrf2 signaling pathway and downstream associated protein glutamyl‑cysteine synthetase catalytic subunit (GCLC), quinone oxidoreductase 1 (NQO1) and glutamate‑cysteine ligase modified subunit (GCLM) in the thoracic aorta and myocardium of rats following exhaustive exercise. In RTAEC in vitro, LBP decreased the expression of MDA and TNF‑α in the supernatant, promoted the nuclear translocation of Nrf2 and increased expression levels of GCLC, NQO1 and GCLM. Following siNrf2 transfection into endothelial cells, the anti‑inflammatory and antioxidant stress effects of LBP were decreased. LBP was found to enhance the expression of the Keap1/Nrf2 antioxidant stress signaling pathway in endothelial cells, decreasing oxidative stress and the inflammatory response. Moreover, LBP improved the antioxidant stress ability of endothelial cells and alleviated injury of myocardial vascular tissue, thereby protecting the cardiovascular system.

Placental hypoxia: What have we learnt from small animal models?

Intrauterine hypoxia is a feature of pregnancy complications, both at high altitude and sea level. To understand the placental response to reduced oxygen availability, small animal models of maternal inhalation hypoxia (MIH) or reduced uterine perfusion pressure (RUPP) may be utilised. The aim of this review was to compare the findings of those studies to identify the role of oxygen availability in adapting placental structural and functional phenotypes in relation to fetal outcome. It also sought to explore the evidence for the involvement of particular genes and protein signalling pathways in the placenta in mediating hypoxia driven alterations. The data available demonstrate that both MIH and RUPP can induce placental hypoxia, which affects placental structure and vascularity, as well as glucose, amino acid, calcium and possibly lipid transport capacity. In addition, changes have been observed in HIF, VEGF, insulin/IGF2, AMPK, mTOR, PI3K and PPARγ signalling, which may be key in linking together observed phenotypes under conditions of placental hypoxia. Many different manipulations have been examined, with varied outcomes depending on the intensity, timing and duration of the insult. Some manipulations have detrimental effects on placental phenotype, viability and fetal growth, whereas in others, the placenta appears to adapt to uphold fetal growth despite the challenge of low oxygen. Together these data suggest a complex response of the placenta to reduced oxygen availability, which links to changes in fetal outcomes. However, further work is required to explore the role of fetal sex, altered maternal physiology and placental molecular mechanisms to fully understand placental responses to hypoxia and their relevance for pregnancy outcome.

Angiotensin-converting enzyme 2 (ACE2), angiotensin-(1-7) and Mas receptor in gonadal and reproductive functions

Angiotensin (Ang)-(1-7) is an active peptide formed from Ang I or Ang-(1-9) by multiple proteolytic steps involving angiotensin-converting enzyme (ACE) 1 and other peptidases, or by a single cleavage of Ang II catalyzed chiefly by ACE2. The effects of Ang-(1-7) are mediated by the G protein-coupled receptor Mas (or Mas1), encoded by the protooncogene MAS. The reproductive system expresses ACE2 quite abundantly and therefore is able to generate Ang-(1-7) using precursor peptides produced locally or taken from circulation. In several mammalian species, Ang-(1-7) stimulates ovarian follicle growth, oocyte maturation and ovulation. The peptide is found in human endometrium, mostly during the secretory phase of menstrual cycle when the uterus is receptive to embryo implantation. Rat models and human observational studies suggest that Ang-(1-7) is part of the maternal adaptive response to pregnancy and its deficiency is associated with poor circulation in the placental bed. Knockout mice revealed a relevant participation of Mas-mediated stimulus to the maintenance of normal spermatogenesis, even though the animal can still reproduce without it. In addition, the vasorelaxant effect of Ang-(1-7) participates in the physiological mechanism of corpus cavernosum blood influx and penile erection. We conclude that preclinical evidence encourages the pursuit of treatments for female and male reproductive dysfunctions based on Mas agonists, starting with its natural ligand Ang-(1-7).

Pathogenesis of Preeclampsia and Therapeutic Approaches Targeting the Placenta

Preeclampsia (PE) is a serious pregnancy complication, affecting about 5–7% of pregnancies worldwide and is characterized by hypertension and damage to multiple maternal organs, primarily the liver and kidneys. PE usually begins after 20 weeks’ gestation and, if left untreated, can lead to serious complications and lifelong disabilities—even death—in both the mother and the infant. As delivery is the only cure for the disease, treatment is primarily focused on the management of blood pressure and other clinical symptoms. The pathogenesis of PE is still not clear. Abnormal spiral artery remodeling, placental ischemia and a resulting increase in the circulating levels of vascular endothelial growth factor receptor-1 (VEGFR-1), also called soluble fms-like tyrosine kinase-1 (sFlt-1), are believed to be among the primary pathologies associated with PE. sFlt-1 is produced mainly in the placenta during pregnancy and acts as a decoy receptor, binding to free VEGF (VEGF-A) and placental growth factor (PlGF), resulting in the decreased bioavailability of each to target cells. Despite the pathogenic effects of increased sFlt-1 on the maternal vasculature, recent studies from our laboratory and others have strongly indicated that the increase in sFlt-1 in PE may fulfill critical protective functions in preeclamptic pregnancies. Thus, further studies on the roles of sFlt-1 in normal and preeclamptic pregnancies are warranted for the development of therapeutic strategies targeting VEGF signaling for the treatment of PE. Another impediment to the treatment of PE is the lack of suitable methods for delivery of cargo to placental cells, as PE is believed to be of placental origin and most available therapies for PE adversely impact both the mother and the fetus. The present review discusses the pathogenesis of PE, the complex role of sFlt-1 in maternal disease and fetal protection, and the recently developed placenta-targeted drug delivery system for the potential treatment of PE with candidate therapeutic agents.

Animal Models of Preeclampsia: Causes, Consequences, and Interventions

Preeclampsia is a common pregnancy complication, affecting 2% to 8% of pregnancies worldwide, and is an important cause of both maternal and fetal morbidity and mortality. Importantly, although aspirin and calcium are able to prevent preeclampsia in some women, there is no cure apart from delivery of the placenta and fetus, often necessitating iatrogenic preterm birth. Preclinical models of preeclampsia are widely used to investigate the causes and consequences of preeclampsia and to evaluate safety and efficacy of potential preventative and therapeutic interventions. In this review, we provide a summary of the published preclinical models of preeclampsia that meet human diagnostic criteria, including the development of maternal hypertension, together with new-onset proteinuria, maternal organ dysfunction, and uteroplacental dysfunction. We then discuss evidence from preclinical models for multiple causal factors of preeclampsia, including those implicated in early-onset and late-onset preeclampsia. Next, we discuss the impact of exposure to a preeclampsia-like environment for later maternal and progeny health. The presence of long-term impairment, particularly cardiovascular outcomes, in mothers and progeny after an experimentally induced preeclampsia-like pregnancy, implies that later onset or reduced severity of preeclampsia will improve later maternal and progeny health. Finally, we summarize published intervention studies in preclinical models and identify gaps in knowledge that we consider should be targets for future research.