Author: Demi Georgiou
Georgiou, Demi, 2025 Functional characterisation of pregnancy zone protein and its relationship with maternal characteristics and pregnancy outcomes, Flinders University, College of Medicine and Public Health
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Pregnancy imposes unique physiological challenges, requiring the maternal body to undergo substantial immunological, hormonal, and metabolic adaptations. While these changes are essential to support a successful pregnancy, their underlying molecular mechanisms remain incompletely understood. Pregnancy zone protein (PZP) is a large plasma glycoprotein whose concentration markedly increases during pregnancy, yet its biological importance remains largely undefined. Although PZP is closely related to well-characterised alpha-2-macroglobulin (α2M), emerging evidence suggests that differences in their quaternary structures and bait region underlie distinct functional roles. Unlike α2M, PZP has been largely overlooked in the literature. However, a small body of research suggests that PZP may contribute to pregnancy-associated maternal adaptations, including processes that are dysfunctional in preeclampsia (PE), a leading cause of maternal and neonatal morbidity and mortality. A consensus on the relationship between circulating PZP levels and PE risk remains elusive.
This thesis aimed to characterise the putative functions of PZP in pregnancy by performing in vitro analyses of PZP-protease interactions and their functional consequences (Chapter 2). Additionally, maternal plasma PZP concentration was assessed in relation to maternal and neonatal characteristics, including pregnancy outcome, across multiple independent cohorts of pregnant women (Chapters 3 & 4). PZP was first purified from human pregnancy plasma – a technically challenging and time-intensive process. Subsequent in vitro analyses demonstrated, for the first time, that PZP forms a stable complex with chymase and that their interaction does not inhibit the ability of chymase to cleave its endogenous substrate, angiotensin I (Ang I), to generate angiotensin II (Ang II), a peptide implicated in the pathogenesis of hypertension. Flow cytometry analysis showed that co-incubation of PZP with chymase promoted the binding of putative PZP-chymase complexes to lipoprotein receptors on BeWo and SH-SY5Y cells, suggesting that receptor-mediated endocytosis is important for PZP’s ability to modulate chymase activity. Comparative analysis with α2M highlighted mechanistic differences in their effects on chymase, consistent with their divergent quaternary structures and ability to sterically hinder protease access.
To explore the biological importance of PZP in a physiological setting, maternal plasma PZP concentrations were quantified in three independent late pregnancy cohorts (Chapter 3). The novel finding that parity significantly affects PZP concentration prompted further analysis in two large, independent nulliparous cohorts (Chapter 4). Among nulliparous women, plasma PZP concentration was associated several maternal characteristics, including age, ethnicity, gestational age, smoking status, and BMI. Notably, higher circulating maternal PZP concentration was associated with hypertensive disorders of pregnancy, particularly in women with a BMI <25 kg/m2.
Collectively, the findings presented in this thesis support a distinct, context-dependent role for PZP in modulating protease activity during pregnancy. The functional divergence between PZP and α2M underscores the need to recognise PZP as a distinct biological entity, rather than a redundant analogue. By providing new knowledge regarding this enigmatic protein, this thesis offers new insight into the molecular systems that underpin maternal adaptation to pregnancy.
Keywords: Pregnancy zone protein, PZP, macroglobulin, preeclampsia, pregnancy, chymase, angiotensin II, protein misfolding, chaperone, a2M, alpha-2-macroglobulin
Subject: Medicine thesis
Thesis type: Doctor of Philosophy
Completed: 2025
School: College of Medicine and Public Health
Supervisor: Dr. Amy Wyatt