Redefining pregnancy outcome by angiogenic marker status: what can be learnt about the underlying placental pathophysiology and potential for personalised therapeutics?

Abstract

Placental dysfunction is the predominant cause of pregnancy complications preeclampsia (PE) and/or fetal growth restriction (FGR). Frequently, a relative imbalance of maternal circulating angiogenic factors placental growth factor (PlGF) and soluble fms-like tyrosine kinase-1 (sFlt-1) is observed in pregnancies complicated by placental dysfunction. PlGF-based testing is now recommended by NICE as a 'rule-in' and 'rule-out' test for PE diagnosis, with current clinical parameters. However, little is known regarding the relationship between circulating angiogenic biomarkers and placental function. This project tested the hypothesis that the (relative) deficiency of free PlGF in the maternal circulation indicates the presence of one of several subtypes of placental dysfunction. The principal aims were to 1) investigate the cause of a low circulating PlGF, 2) explore subtypes of placental dysfunction that exist within pregnancies with low circulating PlGF concentrations. Matched placental and maternal blood samples were collected from uncomplicated pregnancies and those complicated by one or a combination of PE, FGR or chronic hypertension (CHT). For aim 1, heat-dissociation was applied to plasma samples aiming to dissociate PlGF:sFlt-1 complexes, measuring 'total' PlGF. PlGF (mRNA and protein) was measured in placental tissue. Aim 2 investigated placental morphology (immunohistochemical assessment of villous vascularity and trophoblast turnover), placental amino acid transporter activity (radiolabelled amino acid uptake) and mitochondrial function (high resolution respirometry of isolated mitochondria). Sample data were grouped according to gestation-dependent PlGF (Quidel Triage) centile; =5th (normal) centile. To investigate potential subtypes of placental disease associated with a low circulating free PlGF centile, multi-'omic (transcriptomic and metabolomic) datasets were obtained from villous samples and subjected to unsupervised clustering analysis. The percentage increase in circulating PlGF concentrations following heat-dissociation was significantly greater in PE cases with and without FGR (559% [280-1063] and 772% [314-1091]; p=0.1261). Data suggested increased placental system A activity in the low PlGF sample group (105 [50-152] vs. 66 [25-112] pg/mg protein, p=0.013) but comparable total placental system A activity (27706 [10704-69880] vs. 35354 [13191-63754] pg/mg protein*trimmed weight, p=0.053). No differences were noted in mitochondrial respiration (p>=0.0892). Multi-'omic analysis suggested the existence of two molecular (but clinically indistinct) subtypes of placental disease within the low circulating PlGF sample group. Data supported excessive sFlt-1 binding contributing towards a low circulating PlGF. However, as some samples demonstrated a low PlGF with a relatively low sFlt-1 concentration, other mechanisms such as impaired production/release should be considered. Despite the lack of difference in placental morphology and amino acid transport/mitochondrial respirometry function, differences may exist between potential placental disease subtypes. This research may facilitate the development of future personalised therapeutics for pregnancies complicated by placental dysfunction.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Michelle Desforges (Supervisor), Jenny Myers (Supervisor), Alexander Heazell (Supervisor), Lucy Higgins (Supervisor) & Elizabeth Cottrell (Supervisor)