Organoid systems to identify endometrial origins of pre-eclampsia

Abstract
Diseases of pregnancy can have serious affects on both mother and baby's health, and even in mild cases can overshadow what is supposed to be one of life's most joyous events. Pre-eclampsia (PE) is a common disease occurring in up to 5% of all pregnancies and it can have both severe and more mild forms. PE is most serious when it manifests before 34 weeks of pregnancy, and although this early-onset type of the disease is the most well studied we still do not understand what the root cause is. We do know that it is the placenta not functioning properly that causes the dangerous high blood pressure and kidney symptoms characteristic of PE, but the only way we know how to stop progression of the disease is to deliver the baby, often before it is ready. If we understand why the placenta malfunctions in PE then we may be able to design better treatments and even recognise those at risk of disease before it develops.

This project aims to reconstruct the formation of key parts of the placenta and ask the question whether it is the mother's womb that initiates a chain of events leading to placental malfunction in PE. The placenta develops alongside the baby during pregnancy, acting as the go-between for nutrient and waste handling to allow baby to grow. It begins to form right as the fertilised egg implants into the womb and builds structures called placental villi that invade deep into the womb lining to access arterial blood as the nutrient source for baby's growth. It is this placental interface with maternal arteries that doesn't form properly in early-onset PE, leading to poor growth for the baby and imbalances in the mother's cardiovascular system that can eventually lead to life-threatening symptoms. A series of independent studies over the last decade detected subtle abnormalities in the womb tissue of mothers with PE or those that have had it recurrently. These mostly observational studies suggest that in early-onset PE the womb doesn't properly prepare for pregnancy prior to and after fertilisation; a process called decidualisation. Recent advances in our understanding of how cells work together to form tissues and organs has led us to be able to grow whole pieces of womb and placental tissue in the lab. Investigating how these placental and womb 'organoids' develop together will help us identify for the first time how the womb triggers malformation of the placenta in early-onset PE.

At our clinical research centre in Manchester, sufferers of recurrent early-onset PE have graciously consented to womb biopsies outside of pregnancy. Womb cells and organoids can be developed from these biopsies and re-combined to configure a 'decidual niche' in a petri dish. Placental organoids formed from standardised cells can then be developed within this PE decidual niche and compared to organoids developed in a decidual niche made with biopsies from women who have had healthy pregnancies. This comparison will take the form of extremely high resolution analysis of the organoids using a technique called single cell transcriptomics; essentially characterising each cell in the organoid based on the genes they express and so defining different cell types and their relationships with one another. Placental organoids contain the cell types that invade and access womb arteries and so the effects of the PE decidual niche on these crucial cells will be detected by single cell transcriptomics.

Validation of the effects of PE decidua relative to actual PE disease state can be made through comparison to transcriptomes from of more than 150 PE placentas. Moreover, the single cell transcriptome approach combined with computational modelling will allow the identification of the exact signals from PE decidua that drive placental malformation. Understanding this will inform future drug targeting for treatment and may lead to detection of those at risk of developing PE before pregnancy.

Technical Summary
Placental dysfunction is the root cause of most obstetric diseases, including pre-eclampsia (PE) which affects up to 5% of pregnancies and can cause both maternal and fetal morbidities and mortality. Early onset PE is associated with shallow placental trophoblast invasion into the uterine endometrium, limited endometrial arterial remodelling and associated maternal vascular malperfusion, altogether compromising fetal growth and maternal cardiovascular systems. These abnormal placental bed features suggest severe early onset PE (sPE) is caused by placental maldevelopment in early pregnancy.
Recent analyses have associated early onset PE with aberrant decidual transformation of the endometrium in preparation for pregnancy, but there has been no experimental assessment of the effects of such an aberrant decidual environment on placental development. Here I will directly test how trophoblast development is affected by an in vitro decidual niche derived from recurrent sPE patients. Endometrial fibroblasts and novel outwardly-secreting endometrial gland-like organoids together provide this niche in which development of the key early placental structures can be tracked using trophoblast organoids; villi, cell columns and invasive extra-villous trophoblasts.
I hypothesise that in sPE aberrant signals from decidual fibroblasts and glands directly drive malformation of placental tissue that ultimately leads to a dysfunctional placental bed. Single cell transcriptome analysis combined with higher-order interaction network analysis will identify decidual signals driving trophoblast maldevelopment in organoids formed in the sPE decidual niche. The transcriptomic signatures of trophoblast maldevelopment will be aligned with signatures from an array of clinically annotated PE placentas to determine how such maldevelopment later manifests as disease. Targeting decidual signals that cause sPE offers novel testing and therapeutic options for a common disease lacking treatments.