Anti-angiogenic factors and pre-eclampsia: Understanding disease pathophysiology for diagnostic and therapeutic translation

Abstract

Pre-eclampsia is a condition that complicates 3-8% of all pregnancies, inflicting significant maternal and neonatal morbidity and mortality worldwide, causing over 63,000 maternal deaths annually. In the 21st century these statistics continue unabated due to a lack of progress in clinical developments to improve pre-eclampsia diagnosis and treatment. Excitingly, scientific knowledge of the pathophysiological processes underlying pre-eclamptic development has advanced significantly in recent years. We now understand pre-eclampsia to arise from a two-stage process; beginning with abnormal placental development leading to persisting placental hypoxia, with subsequent placental release of anti-angiogenic factors causing widespread endothelial dysfunction. This endothelial dysfunction produces the clinical features of disease, namely hypertension and proteinuria. Importantly, the discovery of the anti-angiogenic proteins, soluble fms-like tyrosine kinase-1 (sFlt-1) and soluble endoglin (sEng), has presented new targets against which to develop potential therapeutic strategies to treat pre-eclampsia. The goal of such therapies would be to stabilise the maternal disease state to enable the pregnancy to progress to a gestation where delivery could occur with minimal risk to the infant. To address this goal, two aims provided the focus for the studies undertaken. Aim one sought to identify the molecular mechanisms underlying the development of pre-eclampsia with the goal of identifying new therapeutic targets, while aim two involved the development of antibodies targeting sFlt-1 and the exploration of their translational potential. This thesis details the studies performed to address these aims and their resulting findings in two parts, with each part addressing each of the aims respectively. In part one the final mechanisms of production of sFlt-1 and sEng from the placenta have been characterised for the first time. The identification that matrix metalloproteinase-14 cleaves membrane-bound endoglin on the placental surface, thereby releasing sEng into the maternal circulation, has identified a potentially new therapeutic target to prevent placental sEng release. Jumonji domain containing protein-6 has also been identified as regulating sFlt-1 production from placenta, significantly advancing our understanding of this pathway. Excitingly, jumonji domain containing protein-6 expression was also significantly reduced in pre-eclamptic placenta, being the first human condition linked to altered expression of this protein. Part two of this thesis saw the successful development of both polyclonal and monoclonal antibodies that target a placental specific sFlt-1 variant (sFlt-1 e15a) found predominately in humans. This variant could be the principle factor associated with pre-eclampsia. While exciting mRNA data exists in the literature, minimal work outlining the role of the protein exists. The development of these specific antibodies and their use in the creation of an enzyme linked immunosorbent assay has enabled for the first time the characterisation of this sFlt-1 variant in the maternal circulation of both normal and pre-eclamptic pregnancies. The translational potential for such antibodies as both diagnostic and therapeutic tools has been explored with encouraging preliminary findings. The significant findings resulting from this work not only advance pre-eclamptic scientific knowledge, but have also provided several new avenues for ongoing research. Improving outcomes for women and their babies afflicted with pre-eclampsia is now hopefully one step closer.