The mystery of the life tree: the placenta

Mitochondrial quality control alterations and placenta-related disorders

Mitochondria are ubiquitous in eukaryotic cells. Normal maintenance of function is the premise and basis for various physiological activities. Mitochondrial dysfunction is commonly observed in a wide range of pathological conditions, such as neurodegenerative, metabolic, cardiovascular, and various diseases related to foetal growth and development. The placenta is a highly energy-dependent organ that acts as an intermediary between the mother and foetus and functions to maintain foetal growth and development. Recent studies have demonstrated that mitochondrial dysfunction is associated with placental disorders. Defects in mitochondrial quality control mechanisms may lead to preeclampsia and foetal growth restriction. In this review, we address the quality control mechanisms of mitochondria and the relevant pathologies of mitochondrial dysfunction in placenta-related diseases, such as preeclampsia and foetal growth restriction. This review also investigates the relation between mitochondrial dysfunction and placental disorders.

Single-cell insights into development of the bovine placenta†

A central determinant of pregnancy success is proper development of the conceptus (embryo/fetus and associated extraembryonic membranes including the placenta). Although the gross morphology and histology of the bovine placenta have been well studied, the cellular and molecular mechanisms regulating placenta development and trophoblast differentiation and function remain essentially undefined. Here, single-cell transcriptome (scRNA-seq) analysis was performed on the day 17 bovine conceptus and chorion of day 24, 30, and 50 conceptuses (n = 3-4 samples per day) using the 10X Genomics platform. Bioinformatic analyses identified cell types and their ontogeny including trophoblast, mesenchyme, and immune cells. Loss of interferon tau-expressing trophoblast uninucleate cells occurred between days 17 and 30, whereas binucleate cells, identified based on expression of placental lactogen (CSH2) and specific pregnancy-associated glycoprotein genes (PAGs), first appeared on day 24. Several different types of uninucleate cells were present in day 24, 30, and 50 samples, but only one (day 24) or two types of binucleate cells (days 30 and 50). Cell trajectory analyses provided a conceptual framework for uninucleate cell development and binucleate cell differentiation, and bioinformatic analyses identified candidate transcription factors governing differentiation and function of the trophoblasts. The digital atlas of cell types in the developing bovine conceptus reported here serves as a resource to discover key genes and biological pathways regulating its development during the critical periods of implantation and placentation.

Orchestrated feedback regulation between melatonin and sex hormones involving GPER1-PKA-CREB signaling in the placenta

Maintaining placental endocrine homeostasis is crucial for a successful pregnancy. Pre-eclampsia (PE), a gestational complication, is a leading cause of maternal and perinatal morbidity and mortality. Aberrant elevation of testosterone (T0 ) synthesis, reduced estradiol (E2 ), and melatonin productions have been identified in preeclamptic placentas. However, the precise contribution of disrupted homeostasis among these hormones to the occurrence of PE remains unknown. In this study, we established a strong correlation between suppressed melatonin production and decreased E2 as well as elevated T0 synthesis in PE placentas. Administration of the T0 analog testosterone propionate (TP; 2 mg/kg/day) to pregnant mice from E7.5 onwards resulted in PE-like symptoms, along with elevated T0 production and reduced E2 and melatonin production. Notably, supplementation with melatonin (10 mg/kg/day) in TP-treated mice had detrimental effects on fetal and placental development and compromised hormone synthesis. Importantly, E2 , but not T0 , actively enhanced melatonin synthetase AANAT expression and melatonin production in primary human trophoblast (PHT) cells through GPER1-PKA-CREB signaling pathway. On the other hand, melatonin suppressed the level of estrogen synthetase aromatase while promoting the expressions of androgen synthetic enzymes including 17β-HSD3 and 3β-HSD1 in PHT cells. These findings reveal an orchestrated feedback mechanism that maintains homeostasis of placental sex hormones and melatonin. It is implied that abnormal elevation of T0 synthesis likely serves as the primary cause of placental endocrine disturbances associated with PE. The suppression of melatonin may represent an adaptive strategy to correct the imbalance in sex hormone levels within preeclamptic placentas. The findings of this study offer novel evidence that identifies potential targets for the development of innovative therapeutic strategies for PE.

Exploring maternal-fetal interface with in vitro placental and trophoblastic models

The placenta, being a temporary organ, plays a crucial role in facilitating the exchange of nutrients and gases between the mother and the fetus during pregnancy. Any abnormalities in the development of this vital organ not only lead to various pregnancy-related disorders that can result in fetal injury or death, but also have long-term effects on maternal health. In vitro models have been employed to study the physiological features and molecular regulatory mechanisms of placental development, aiming to gain a detailed understanding of the pathogenesis of pregnancy-related diseases. Among these models, trophoblast stem cell culture and organoids show great promise. In this review, we provide a comprehensive overview of the current mature trophoblast stem cell models and emerging organoid models, while also discussing other models in a systematic manner. We believe that this knowledge will be valuable in guiding further exploration of the complex maternal-fetal interface.

Aquaporin-8 overexpression is involved in vascular structure and function changes in placentas of gestational diabetes mellitus patients

To study the role and mechanism of aquaporin-8 (AQP8) in placental vascular development in gestational diabetes mellitus (GDM), hematoxylin–eosin staining and immunohistochemistry were utilized to analyze the histopathological changes in placentas in GDM patients. Transwell, CCK-8, and tube formation assays were performed to examine cell migration, proliferation, and tube formation. AQP8, vascular cell adhesion molecule 1 (VCAM-1), tumor necrosis factor alpha (TNF)-α, and vascular endothelial growth factor (VEGF)-A expression levels were investigated. Relative to the control group, the placentas in the GDM group showed morphological changes, the number of microvessels in the placental villi arterioles was significantly higher, and the area of microvessels in the arterioles of placental villi was significantly lower. The expression levels of VCAM-1, TNF-α, VEGF-A, and AQP8 in the GDM placentas and human umbilical vein endothelial cells (HUVECs) stimulated by high glucose were significantly higher than those in the control group, and AQP8 was located in placental endothelial cells. Overexpression of glucose and AQP8 inhibited tube formation, migration, and proliferation in HUVECs. High glucose levels can induce dysfunction in vascular endothelial cells and lead to pathological changes in the placental vascular structure in GDM. AQP8 overexpression in placental GDM can inhibit endothelial cell behavior, cause endothelial cell dysfunction, and further participate in the occurrence and development of GDM placental vascular lesions.