In Vitro Human Placental Studies to Support Adenovirus-Mediated VEGF-DΔNΔC Maternal Gene Therapy for the Treatment of Severe Early-Onset Fetal Growth Restriction

Maternal Uterine Artery Adenoviral Vascular Endothelial Growth Factor (Ad.VEGF-A165) Gene Therapy Normalises Fetal Brain Growth and Microglial Activation in Nutrient Restricted Pregnant Guinea Pigs

Fetal growth restriction (FGR) is associated with uteroplacental insufficiency, and neurodevelopmental and structural brain deficits in the infant. It is currently untreatable. We hypothesised that treating the maternal uterine artery with vascular endothelial growth factor adenoviral gene therapy (Ad.VEGF-A165) normalises offspring brain weight and prevents brain injury in a guinea pig model of FGR. Pregnant guinea pigs were fed a restricted diet before and after conception and received Ad.VEGF-A165 (1 × 1010 viral particles, n = 18) or vehicle (n = 18), delivered to the external surface of the uterine arteries, in mid-pregnancy. Pregnant, ad libitum-fed controls received vehicle only (n = 10). Offspring brain weight and histological indices of brain injury were assessed at term and 5-months postnatally. At term, maternal nutrient restriction reduced fetal brain weight and increased microglial ramification in all brain regions but did not alter indices of cell death, astrogliosis or myelination. Ad.VEGF-A165 increased brain weight and reduced microglial ramification in fetuses of nutrient restricted dams. In adult offspring, maternal nutrient restriction did not alter brain weight or markers of brain injury, whilst Ad.VEGF-A165 increased microglial ramification and astrogliosis in the hippocampus and thalamus, respectively. Ad.VEGF-A165 did not affect cell death or myelination in the fetal or offspring brain. Ad.VEGF-A165 normalises brain growth and markers of brain injury in guinea pig fetuses exposed to maternal nutrient restriction and may be a potential intervention to improve childhood neurodevelopmental outcomes in pregnancies complicated by FGR.

Exploring maternal-fetal interface with in vitro placental and trophoblastic models

The placenta, being a temporary organ, plays a crucial role in facilitating the exchange of nutrients and gases between the mother and the fetus during pregnancy. Any abnormalities in the development of this vital organ not only lead to various pregnancy-related disorders that can result in fetal injury or death, but also have long-term effects on maternal health. In vitro models have been employed to study the physiological features and molecular regulatory mechanisms of placental development, aiming to gain a detailed understanding of the pathogenesis of pregnancy-related diseases. Among these models, trophoblast stem cell culture and organoids show great promise. In this review, we provide a comprehensive overview of the current mature trophoblast stem cell models and emerging organoid models, while also discussing other models in a systematic manner. We believe that this knowledge will be valuable in guiding further exploration of the complex maternal-fetal interface.

Comparison of Efficiency and Function of Vascular Endothelial Growth Factor Adenovirus Vectors in Endothelial Cells for Gene Therapy of Placental Insufficiency

Severe fetal growth restriction (FGR) affects 1:500 pregnancies, is untreatable and causes serious neonatal morbidity and death. Reduced uterine blood flow (UBF) and lack of bioavailable VEGF due to placental insufficiency is a major cause. Transduction of uterine arteries in normal or FGR sheep and guinea pigs using an adenovirus (Ad) encoding VEGF isoforms A (Ad.VEGF-A₁₆₅) and a FLAG-tagged pre-processed short form D (D^ΔNΔC, Ad.VEGF-D^ΔNΔC-FLAG) increases endothelial nitric oxide expression, enhances relaxation and reduces constriction of the uterine arteries and their branches. UBF and angiogenesis are increased long term, improving fetal growth in utero. For clinical trial development we compared Ad.VEGF vector transduction efficiency and function in endothelial cells (ECs) derived from different species. We aimed to compare the transduction efficiency and function of the pre-clinical study Ad. constructs (Ad.VEGF-A₁₆₅, Ad.VEGF-D^ΔNΔC-FLAG) with the intended clinical trial construct (Ad.VEGF-D^ΔNΔC) where the FLAG tag is removed. We infected ECs from human umbilical vein, pregnant sheep uterine artery, pregnant guinea pig aorta and non-pregnant rabbit aorta, with increasing multiplicity of infection (MOI) for 24 or 48 hours of three Ad.VEGF vectors, compared to control Ad. containing the LacZ gene (Ad.LacZ). VEGF supernatant expression was analysed by ELISA. Functional assessment used tube formation assay and Erk-Akt phosphorylation by ELISA. VEGF expression was higher after Ad.VEGF-D^ΔNΔC-FLAG and Ad.VEGF-D^ΔNΔC transduction compared to Ad.VEGF-A₁₆₅ in all EC types (*p < 0.001). Tube formation was higher in ECs transduced with Ad.VEGF-D^ΔNΔC in all species compared to other constructs (***p < 0.001, *p < 0.05 with rabbit aortic ECs). Phospho-Erk and phospho-Akt assays displayed no differences between the three vector constructs, whose effect was, as in other experiments, higher than Ad.LacZ (***p < 0.001). In conclusion, we observed high transduction efficiency and functional effects of Ad.VEGF-D^ΔNΔC vector with comparability in major pathway activation to constructs used in pre-clinical studies, supporting its use in a clinical trial.

Ethical and Regulatory Considerations of Placental Therapeutics

PURPOSE

Placental therapeutics aim to treat placental disease; however, ethical and regulatory issues should be considered if the drug also potentially affects the fetus. Drugs that might transfer or edit genes carry a specific challenge because currently fetal gene editing and fetal gene therapy are considered unethical.

METHODS

This article reviews the literature on ethical and regulatory considerations for placental therapeutics.

FINDINGS

Proposals for maternal gene therapy, directed to the maternal side of the placenta, have been discussed with patients and stakeholders. No absolute ethical, legal, or regulatory barriers to this potential treatment were identified. Patients who have experienced placental disease, such as fetal growth restriction, are interested in these therapies; some would participate in first-in-human trials. Such trials need careful regulatory considerations, such as the steps required to indicate tolerability and efficacy in preclinical models and the optimal animals for reproductive toxicology studies. Ex vivo dual human placenta perfusion experiments and villous explant in vitro studies allow drugs to be tested in normal and diseased human placenta, providing short-term tolerability and toxicologic assessment. Testing drugs in nonhuman primates is an option but carries ethical and feasibility considerations. Selection of inclusion and exclusion criteria for clinical trial participants is important to ensure that the most suitable patients are exposed to a first-in-human drug. These patients will almost certainly be pregnant women with a high risk of perinatal loss and/or perinatal and maternal morbidity. Criteria should identify sufficient numbers of patients to make a trial feasible as well as a phenotype that will respond to the mechanism of action. How to dose escalate and to capture information on adverse events are also key to optimal clinical trial design.

IMPLICATIONS

Developing placental therapeutics requires input from scientists, practitioners, and regulators and close liaison with patients to ensure that new drugs are tested as carefully as possible.

Adaptations of the human placenta to hypoxia: opportunities for interventions in fetal growth restriction

BACKGROUND

The placenta is the functional interface between the mother and the fetus during pregnancy, and a critical determinant of fetal growth and life-long health. In the first trimester, it develops under a low-oxygen environment, which is essential for the conceptus who has little defense against reactive oxygen species produced during oxidative metabolism. However, failure of invasive trophoblasts to sufficiently remodel uterine arteries toward dilated vessels by the end of the first trimester can lead to reduced/intermittent blood flow, persistent hypoxia and oxidative stress in the placenta with consequences for fetal growth. Fetal growth restriction (FGR) is observed in ∼10% of pregnancies and is frequently seen in association with other pregnancy complications, such as preeclampsia (PE). FGR is one of the main challenges for obstetricians and pediatricians, as smaller fetuses have greater perinatal risks of morbidity and mortality and postnatal risks of neurodevelopmental and cardio-metabolic disorders.

OBJECTIVE AND RATIONALE

The aim of this review was to examine the importance of placental responses to changing oxygen environments during abnormal pregnancy in terms of cellular, molecular and functional changes in order to highlight new therapeutic pathways, and to pinpoint approaches aimed at enhancing oxygen supply and/or mitigating oxidative stress in the placenta as a mean of optimizing fetal growth.

SEARCH METHODS

An extensive online search of peer-reviewed articles using PubMed was performed with combinations of search terms including pregnancy, placenta, trophoblast, oxygen, hypoxia, high altitude, FGR and PE (last updated in May 2020).

OUTCOMES

Trophoblast differentiation and placental establishment are governed by oxygen availability/hypoxia in early pregnancy. The placental response to late gestational hypoxia includes changes in syncytialization, mitochondrial functions, endoplasmic reticulum stress, hormone production, nutrient handling and angiogenic factor secretion. The nature of these changes depends on the extent of hypoxia, with some responses appearing adaptive and others appearing detrimental to the placental support of fetal growth. Emerging approaches that aim to increase placental oxygen supply and/or reduce the impacts of excessive oxidative stress are promising for their potential to prevent/treat FGR.

WIDER IMPLICATIONS

There are many risks and challenges of intervening during pregnancy that must be considered. The establishment of human trophoblast stem cell lines and organoids will allow further mechanistic studies of the effects of hypoxia and may lead to advanced screening of drugs for use in pregnancies complicated by placental insufficiency/hypoxia. Since no treatments are currently available, a better understanding of placental adaptations to hypoxia would help to develop therapies or repurpose drugs to optimize placental function and fetal growth, with life-long benefits to human health.

Placental perfusion and mathematical modelling

The isolated perfused placental cotyledon technique has led to numerous advances in placental biology. Combining placental perfusion with mathematical modelling provides an additional level of insight into placental function. Mathematical modelling of perfusion data provides a quantitative framework to test the understanding of the underlying biology and to explore how different processes work together within the placenta as part of an integrated system. The perfusion technique provides a high degree of control over the experimental conditions as well as regular measurements of functional parameters such as pressure, solute concentrations and pH over time. This level of control is ideal for modelling as it allows placental function to be studied across a wide range of different conditions which permits robust testing of mathematical models. By placing quantitative values on different processes (e.g. transport, metabolism, blood flow), their relative contribution to the system can be estimated and those most likely to become rate-limiting identified. Using a combined placental perfusion and modelling approach, placental metabolism was shown to be a more important determinant of amino acid and fatty acid transfer. In contrast, metabolism was a less important determinant of placental cortisol transfer than initially thought. Identifying the rate-limiting factors in the system allows future work to be focused on the factors that are most likely to underlie placental dysfunction. A combined experimental and modelling approach using placental perfusions promotes an integrated view of placental physiology that can more effectively identify the processes leading to placental pathologies.

Adenoviral mediated expression of anti-inflammatory progranulin by placental explants modulates endothelial cell activation by decrease of ICAM-1 expression

INTRODUCTION

Functional disorders of the villous trophoblast may result in preeclampsia through the release of endothelial activating substances. Progranulin is an anti-inflammatory, pro-angiogenic cytokine with TNF-α antagonizing activity. The trophoblastic expression of progranulin is increased during preeclampsia. The aim of the study was to investigate the impact of placental progranulin synthesis on endothelial cell activation.

METHODS

Placental progranulin expression was modified by transduction of an adenoviral vector. Primary isolated human umbilical venous endothelial cells (HUVECs) were incubated with conditioned medium of first trimester placental explants. Functional studies on HUVECs included assays for proliferation, viability, cytotoxicity and analyzes of Intercellular adhesion molecule-1 (ICAM-1) and E-selectin expression.

RESULTS

Placental progranulin expression was more than 10-fold higher by using an adenoviral-mediated overexpression system (Ad.PGRN) compared to control vector (Ad.CTRL) and untreated controls. Incubation of HUVECs with conditioned placental medium revealed a dose-dependent increase of cytotoxicity, reduced cell proliferation and viability and resulted in an increase of ICAM-1 and E-selectin expression. Overexpression of progranulin (Ad.PGRN) antagonized the ICAM-1 expression induced by conditioned medium. However progranulin did not influence the effects on cell proliferation, viability, cytotoxicity and E-selectin expression in HUVECs.

DISCUSSION

Regulation of gene expression in human placental explants is possible by usage of an adenoviral vector system. The increase of endothelial ICAM-1 expression following the incubation with placental conditioned medium was partly reversed by overexpression of placental progranulin. It is suggested that up-regulation of the placental progranulin expression is an endogenous anti-inflammatory mechanism that partially antagonizes the endothelial cell activation during preeclampsia.

Placental Origins of Preeclampsia: Potential Therapeutic Targets

Preeclampsia (PE) remains a leading cause of maternal and perinatal morbidity and mortality in obstetrics worldwide. No effective treatments to reduce its incidence and severity in clinical practice are currently available. A variety of hypotheses have been generated aiming to explain the origins of PE, notably being the genetic predispositions and placental dysfunction. As regard to placental dysfunction, much progress has been made in basic research and several potential therapeutic targets have been identified. This review will discuss in detail the potential therapeutic targets in PE models including uteroplacental blood flow, oxidative stress, vasoactive factors and inflammation/immune response, and introduce the evolving technologies for placental research nowadays.

Beyond endothelial cells: Vascular endothelial growth factors in heart, vascular anomalies and placenta

Vascular endothelial growth factors regulate vascular and lymphatic growth. Dysregulation of VEGF signaling is connected to many pathological states, including hemangiomas, arteriovenous malformations and placental abnormalities. In heart, VEGF gene transfer induces myocardial angiogenesis. Besides vascular and lymphatic endothelial cells, VEGFs affect multiple other cell types. Understanding VEGF biology and its paracrine signaling properties will offer new targets for novel treatments of several diseases.

Human placental oxygenation in late gestation: experimental and theoretical approaches

The placenta is crucial for life. It is an ephemeral but complex organ acting as the barrier interface between maternal and fetal circulations, providing exchange of gases, nutrients, hormones, waste products and immunoglobulins. Many gaps exist in our understanding of the detailed placental structure and function, particularly in relation to oxygen handling and transfer in healthy and pathological states in utero. Measurements to understand oxygen transfer in vivo in the human are limited, with no general agreement on the most appropriate methods. An invasive method for measuring partial pressure of oxygen in the intervillous space through needle electrode insertion at the time of Caesarean sections has been reported. This allows for direct measurements in vivo whilst maintaining near normal placental conditions; however, there are practical and ethical implications in using this method for determination of placental oxygenation. Furthermore, oxygen levels are likely to be highly heterogeneous within the placenta. Emerging non-invasive techniques, such as MRI, and ex vivo research are capable of enhancing and improving current imaging methodology for placental villous structure and increase the precision of oxygen measurement within placental compartments. These techniques, in combination with mathematical modelling, have stimulated novel cross-disciplinary approaches that could advance our understanding of placental oxygenation and its metabolism in normal and pathological pregnancies, improving clinical treatment options and ultimately outcomes for the patient.