The intrauterine environment and human early placental development; a new paradigm for the pathophysiology of complications of pregnancy

Adverse outcomes of pregnancy, such as growth restriction, stillbirth, pre-eclampsia and prematurity, place considerable economic and emotional burdens on society. They cause significant morbidity and mortality; in the UK 10-12% of pregnancies miscarry and there are approximately 4,000 stillbirths each year. A further 10-12% suffer growth restriction, which predisposes to an increased risk of cardiovascular and other diseases in adult life. The causes of these complications are complex, and despite much research their incidence has not changed substantially over the last 50 years; indeed, the incidence of low birth weight is increasing in the USA. This research programme takes a fresh and innovative approach to understanding their cause by focusing on a key unifying feature, impaired early development of the placenta. The placenta nourishes and protects the embryo, and so needs to develop rapidly after fertilisation. The overall aim is to investigate how that early development is stimulated, and how perturbations in the uterine environment lead to aberrant placentation. A more complete understanding of these critical events will ultimately facilitate interventions being devised that prevent complications being initiated, rather than attempting to treat them once established.
Our previous research supported by the MRC, transformed our understanding of the environment inside the uterus in early pregnancy. For many years it had been assumed that placental development was a continuum across gestation, but we demonstrated that it occurs in two very distinct phases. During the first 10-12 weeks, the placenta receives nutritional support from the glands lining the uterus, rather than from the maternal circulation as it does later. The glands provide essential nutrients, but also secrete proteins that can act as powerful stimulants to growth. Indeed, in some species, such as the sheep, the placenta sends signals to the glands to produce more of these proteins, and so enhances its own growth. The uterus therefore plays a much more dynamic role in supporting the first third of pregnancy than previously anticipated, creating a unique highly stimulatory microenvironment.

Our goal is to fully characterise that environment in the human, understand how it is regulated and investigate its impact on proliferation and differentiation of placental cells. The first aim is to identify the range of proteins secreted by the uterus using the latest sequencing techniques to analyse gene expression in samples of the lining of the uterus. We have recently applied the same technique to progenitor cells isolated from the early placenta, and so will able to identify potential growth factor/receptor interactions. The impact of these interactions on progenitor cell behaviour will then be tested in vitro. The second aim is to explore the signals coming from the placenta that might increase or alter the secretions. The third aim is to investigate using genetically modified mice whether metabolic stress alters secretions and impairs fetal growth. We will also determine whether stresses in humans such as obesity and diabetes, that are associated with adverse obstetric outcomes, reduce the effectiveness of these mechanisms and impair placental development. Finally, we will determine whether development of the uterus is compromised in offspring who are born growth restricted, resulting in intergenerational effects on birth weight.
It is anticipated that the results will have major implications for reproductive and public health medicine. Understanding the fetal-maternal dialogue during early pregnancy will help to develop novel interventions to optimise placental development. Equally, an appreciation of the impact of metabolic and other stresses on uterine function during early pregnancy may lead to improved peri-conceptional care. In the longer term, having healthier normal birth weight babies will help to reduce the burden of chronic disease in adulthood.

This programme investigates the initiation of the pathophysiology of common complications of pregnancy that have profound effects on neonatal and long-term health. There is strong evidence that poor placental development is a unifying feature, but virtually nothing is known regarding how early placental growth is regulated. Our previous research showed that contrary to textbook accounts, the maternal blood supply to the placenta is not established until 10-12 weeks gestation, and that until then the conceptus is supported by secretions from the endometrial glands. Extending data from domestic species, we hypothesise the conceptus signals to the glands to up-regulate secretion of nutrients and mitogenic growth factors that stimulate proliferation of the placental tissues through a feed-forward mechanism. To test this, we will first identify the transcriptional networks that maintain stemness within a proliferative trophoblast progenitor niche we have identified. Secondly, we will use RNA-Seq to generate a comprehensive catalogue of the potential gland secretome in early pregnancy. The importance of specific growth factor-receptor pairings will be tested in vitro using co-cultures and in vivo using temporally regulated tissue-specific knock-out mice. Clinical correlates will be sought by assessing gland function in pre-conception endometrial biopsies from a high-risk population and linking to pregnancy outcome. Having identified the relevant pathways, we will test susceptibility to perturbation by metabolic stresses known to increase risk of the complications. This will be achieved by a combination of cell cultures in vitro, mouse models in vivo, and human clinical correlates. Finally, we will test whether uterine architecture is affected by developmental programming, leading to intergenerational effects. By elucidating these regulatory pathways, we aim to identify new approaches for the development of therapeutic interventions to optimise early placental development.

Who will benefit from this research?
Scientists and clinicians investigating complications of pregnancy will benefit directly through new knowledge arising from this research. The first trimester is a crucial but under-researched period of pregnancy during which the placenta is established. This period corresponds to the phases of embryogenesis and organogenesis. Hence, perturbations may have a profound impact on both pregnancy outcome and life-long health. Remarkably, we still do not know how early placental proliferation and differentiation is regulated, and whether there is a dialogue between the placenta and the endometrial glands that stimulates placental development.
Health services are likely to also benefit through a reduction in complications of pregnancy; in the UK around 10% of the 800,000 annual pregnancies miscarry and there are approximately 4,000 stillbirths each year, while worldwide approximately 14 million infants are born growth restricted and 50,000 women die from pre-eclampsia. Preventing even a small proportion of these complications would therefore have major societal and economic benefits. Good obstetric care means that many pregnancies complicated by poor placental development end in live births. However, babies whose intrauterine life was compromised are at risk for long-term chronic diseases, such as cardiovascular disease and diabetes. Hence the economic and societal impact of a poor intrauterine environment is considerable.
Public health policy makers may benefit through the identification of critical pre-or peri-conceptional windows when supplementation with micronutrients or other interventions may improve endometrial function and hence placental development.
Finally, pharma companies may benefit if novel therapeutic targets to improve endometrial function in early pregnancy are identified.

How will they benefit from this research?
For researchers, a detailed knowledge of the transcriptional networks maintaining trophoblast stem cells and stimulating differentiation will add greatly to our knowledge of early placental development, and provide new information on an as yet unexplored stem cell niche. Isolation of a genuine trophoblast stem/progenitor cell would be a major advance in the field, replacing choriocarcinoma cell lines as model systems and preventing the need to continually isolate non-replicating primary cells form termination material.
For clinicians and health services, understanding the two-way signalling dialogue between the placenta and endometrium in early pregnancy may open avenues for novel therapeutic interventions to prevent complications of pregnancy, the incidence of which has not changed substantially for over 50 years. If the stimuli causing the glands to synthesise and release growth factors critical for placental proliferation can be identified, then the opportunity exists to target these pathways therapeutically in women at high risk of pregnancy complications. Since the glands are continuous with the uterine epithelium, they are easily accessible with minimally invasive delivery techniques.
For public health policy makers, a detailed knowledge of the role of the endometrium during early pregnancy could justify public health programmes aimed at ensuring maximal endometrial function either pre- or peri-conceptionally. This may involve treatment of low-grade infections or inflammation, or dietary supplements to improve gland activity and secretions.
Finally, for pharma companies, knowledge of the key factors and signalling pathways involved in the regulation of early placental development could open new avenues for therapeutic intervention. Any IP with commercial potential will be protected first and then exploited through Cambridge Enterprise, a wholly owned company established by the University to promote translation of basic research.