Christian Wadsack

BACKGROUND The placenta is a unique and pivotal organ in reproduction, controlling crucial growth and cell differentiation processes that ensure a successful pregnancy. Placental development is a tightly regulated and dynamic process, in which the transforming growth factor beta (TGFβ) superfamily plays a central role. This family of pleiotropic growth factors is heavily involved in regulating various aspects of reproductive biology, particularly in trophoblast differentiation during the first trimester of pregnancy. TGFβ signalling precisely regulates trophoblast invasion and the cell transition from cytotrophoblasts to extravillous trophoblasts, which is an epithelial-to-mesenchymal transition-like process. Later in pregnancy, TGFβ signalling ensures proper vascularization and angiogenesis in placental endothelial cells. Beyond its role in trophoblasts and endothelial cells, TGFβ signalling contributes to the polarization and function of placental and decidual macrophages by promoting maternal tolerance of the semi-allogeneic foetus. Disturbances in early placental development have been associated with several pregnancy complications, including preeclampsia (PE) which is one of the severe complications. Emerging evidence suggests that TGFβ is involved in the pathogenesis of PE, thereby offering a potential target for intervention in the human placenta. OBJECTIVE AND RATIONALE This comprehensive review aims to explore and elucidate the roles of the major members of the TGFβ superfamily, including TGFβs, bone morphogenetic proteins (BMPs), activins, inhibins, nodals, and growth differentiation factors (GDFs), in the context of placental development and function. The review focusses on their interactions within the major cell types of the placenta, namely trophoblasts, endothelial cells, and immune cells, in both normal pregnancies and pregnancies complicated by PE throughout pregnancy. SEARCH METHODS A literature search was carried out using PubMed and Google Scholar, searching terms: ‘TGF signalling preeclampsia’, ‘pregnancy TGF signalling’, ‘preeclampsia tgfβ’, ‘preeclampsia bmp’, ‘preeclampsia gdf’, ‘preeclampsia activin’, ‘endoglin preeclampsia’, ‘endoglin pregnancy’, ‘tgfβ signalling pregnancy’, ‘bmp signalling pregnancy’, ‘gdf signalling pregnancy’, ‘activin signalling pregnancy’, ‘Hofbauer cell tgfβ signalling’, ‘placental macrophages tgfβ’, ‘endothelial cells tgfβ’, ‘endothelium tgfβ signalling’, ‘trophoblast invasion tgfβ signalling’, ‘trophoblast invasion Smad’, ‘trophoblast invasion bmp’, ‘trophoblast invasion tgfβ’, ‘tgfβ preeclampsia’, ‘tgfβ placental development’, ‘TGFβ placental function’, ‘endothelial dysfunction preeclampsia tgfβ signalling’, ‘vascular remodelling placenta TGFβ’, ‘inflammation pregnancy tgfβ’, ‘immune response pregnancy tgfβ’, ‘immune tolerance pregnancy tgfβ’, ‘TGFβ pregnancy NK cells’, ‘bmp pregnancy NK cells’, ‘bmp pregnancy tregs’, ‘tgfβ pregnancy tregs’, ‘TGFβ placenta NK cells’, ‘TGFβ placenta tregs’, ‘NK cells preeclampsia’, ‘Tregs preeclampsia’. Only articles published in English until 2023 were used. OUTCOMES A comprehensive understanding of TGFβ signalling and its role in regulating interconnected cell functions of the main placental cell types provides valuable insights into the processes essential for successful placental development and growth of the foetus during pregnancy. By orchestrating trophoblast invasion, vascularization, immune tolerance, and tissue remodellin

Hydroxychloroquine (HCQ), an anti-malarial drug, is suggested as a promising candidate for the treatment of pregnancy-related disorders associated with endothelial activation, among which there is preeclampsia (PE). Arterial feto-placental endothelial cells (fpECAs) were isolated from control (CTR) and early-onset preeclamptic (EO-PE) placentas. The aim of this study was to test potential protective effects of HCQ in an in vitro model of endothelial activation as well as in cells isolated from EO-PE placentas. To mimic PE conditions, CTR fpECAs were exposed to a pro-inflammatory environment consisting of tumor necrosis factor α (TNF-α), interleukin (IL)-6 and IL-1β (furtherly referred as MIX) with or without varying concentrations of HCQ (1 µg/mL and 10 µg/mL). Their effect on wound healing and endothelial barrier integrity was analyzed. Variations in the expression of IL-8 and leukocyte adhesion molecules (LAM) on both mRNA and protein levels were determined between CTR and PE fpECAs in the presence or absence of HCQ. MIX decreased wound healing and stability of the endothelial barrier, but HCQ did not affect it. Significant differences between CTR and EO-PE fpECAs were observed in IL-8 mRNA, protein secretion, and vascular cell adhesion protein 1 (VCAM-1) mRNA expression levels. After challenging CTR fpECAs with MIX, upregulation of both mRNA and protein levels was observed in all molecules. Combined treatment of HCQ and MIX slightly lowered VCAM-1 total protein amount. In CTR fpECAs, treatment with low concentrations of HCQ alone (1 µg/mL) reduced basal levels of IL-8 and VCAM-1 mRNA and secretion of IL-8, while in EO-PE fpECAs, a higher (10µg/mL) HCQ concentration slightly reduced the gene expression of IL-8. Conclusion: These results provide additional support for the safety of HCQ, as it did not adversely affect endothelial functionality in control fpECAs at the tested concentration. Furthermore, the observed limited effects on IL-8 secretion in EO-PE fpECAs warrant further investigation, highlighting the need for clinical trials to assess the potential therapeutic effects of HCQ in preeclampsia. Conducting clinical trials would offer a more comprehensive understanding of HCQ’s efficacy and safety, allowing us to explore its potential benefits and limitations in a real-world clinical setting.