The placenta is the first embryonic organ, representing the connection between the embryo and the mother, and is therefore necessary for the embryo’s growth and survival. To meet the ever-growing need for nutrient and gas exchange, the maternal spiral arteries undergo extensive remodeling, thus increasing the uteroplacental blood flow by 16-fold. However, the insufficient remodeling of the spiral arteries can lead to severe pregnancy-associated disorders, including but not limited to pre-eclampsia. Insufficient endovascular trophoblast invasion plays a key role in the manifestation of pre-eclampsia; however, the underlying processes are complex and still unknown. Classical histopathology is based on two-dimensional section microscopy, which lacks a volumetric representation of the vascular remodeling process. To further characterize the uteroplacental vascularization, a detailed, non-destructive, and subcellular visualization is beneficial. In this study, we use light sheet microscopy for optical sectioning, thus establishing a method to obtain a three-dimensional visualization of the vascular system in the placenta. By introducing a volumetric visualization method of the placenta, we could establish a powerful tool to deeply investigate the heterogeneity of the spiral arteries during the remodeling process, evaluate the state-of-the-art treatment options, effects on vascularization, and, ultimately, reveal new insights into the underlying pathology of pre-eclampsia.

Preeclampsia (PE) is characterized by maternal hypertension and placental dysfunction, often leading to fetal growth restriction (FGR). It is associated with an overexpression of the anti-angiogenic sFLT1 protein, which originates from the placenta and serves as a clinical biomarker to predict PE. To analyze the impact of sFLT1 on placental function and fetal growth, we generated transgenic mice with placenta-specific human sFLT1 (hsFLT1) overexpression. Immunohistochemical, morphometrical, and molecular analyses of the placentas on 14.5 dpc and 18.5 dpc were performed with a focus on angiogenesis, nutrient transport, and inflammation. Additionally, fetal development upon placental hsFLT1 overexpression was investigated. Dams exhibited a mild increase in serum hsFLT1 levels upon placental hsFLT1 expression and revealed growth restriction of the fetuses in a sex-specific manner. Male FGR fetuses expressed higher amounts of placental hsFLT1 mRNA compared to females. FGR placentas displayed an altered morphology, hallmarked by an increase in the spongiotrophoblast layer and changes in labyrinthine vascularization. Further, FGR placentas showed a significant reduction in placental glycogen storage and nutrient transporter expression. Moreover, signs of hypoxia and inflammation were observed in FGR placentas. The transgenic spongiotrophoblast-specific hsFLT1 mouse line demonstrates that low hsFLT1 serum levels are sufficient to induce significant alterations in fetal and placental development in a sex-specific manner.

Fetal adaptations to harmful intrauterine environments due to pregnancy disorders such as preeclampsia (PE) can negatively program the offspring’s metabolism, resulting in long-term metabolic changes. PE is characterized by increased circulating levels of sFLT1, placental dysfunction and fetal growth restriction (FGR). Here we examine the consequences of systemic human sFLT1 overexpression in transgenic PE/FGR mice on the offspring’s metabolic phenotype. Histological and molecular analyses of fetal and offspring livers as well as examinations of offspring serum hormones were performed. At 18.5 dpc, sFLT1 overexpression resulted in growth-restricted fetuses with a reduced liver weight, combined with reduced hepatic glycogen storage and histological signs of hemorrhages and hepatocyte apoptosis. This was further associated with altered gene expression of the molecules involved in fatty acid and glucose/glycogen metabolism. In most analyzed features males were more affected than females. The postnatal follow-up revealed an increased weight gain of male PE offspring, and increased serum levels of Insulin and Leptin. This was associated with changes in hepatic gene expression regulating fatty acid and glucose metabolism in male PE offspring. To conclude, our results indicate that sFLT1-related PE/FGR in mice leads to altered fetal liver development, which might result in an adverse metabolic pre-programming of the offspring, specifically targeting males. This could be linked to the known sex differences seen in PE pregnancies in human.

The pregnancy disorder preeclampsia (PE) is characterized by maternal hypertension and reduced spiral artery (SpA) remodeling which is aggravated by increased levels of anti-angiogenic soluble fms-related tyrosine kinase 1 (sFLT1). One process contributing to physiological SpA remodeling in early pregnancy is the expression of lymphatic receptors on endothelial cells of SpAs, which is called lymphatic mimicry. Adverse lymphatic mimicry of SpAs is theorized to play a role in the pathophysiology of PE, but was not analyzed under preeclamptic conditions. Using the transgenic PE/FGR mouse model with ubiquitous overexpression of human sFLT1 (hsFLT1), we focused on lymphatic marker expression in early pregnancy at 12.5 dpc and 14.5 dpc and evaluated the reduction of SpA remodeling as well as mRNA expression of lymphatic markers like Lyve1, Pdpn, or Prox1 in the mesometrial triangle (MT) of murine placentas. Additionally, uterine NK cell distribution was analyzed via electron microscopy and immunohistochemistry in placentas of PE animals. We could prove significantly reduced levels of Pdpn and Nrp1 mRNA in MT of PE placentas. Additionally, the mRNA expression of chemokines like Ccl21 were reduced at from 12.5 dpc until 14.5 dpc which could inhibit infiltration of uterine NK cell populations in these compartments in later pregnancy. With this study we could show that increased levels of human sFLT1 interfere with early spiral artery (SpA) remodeling processes and could inhibit lymphatic mimicry of SpA. Immune cell infiltration until 14.5 dpc could be decreased by downregulation of the chemotactic chemokine Ccl21.

Problem The formation of uterine scars is a main reason for maternal disorders related to caesarean deliveries. Here, we aimed to investigate the poorly understood postpartal uterine regeneration, particularly with regards to apoptotic and proliferative processes and angiogenis of the lymphatic and blood system in mice. Materials and methods Uterine tissue samples were collected from virgin and day 4 postpartum C57/BL6 mice. Histological sections were stained by Masson-Goldner trichrome or by immunohistochemical detection of CD31, LYVE-1, PCNA and TUNEL. The analysis focalized in the endometrium, differentiated from the myometrium by α-SMA negativity. Results Compared to virgin uterus, in postpartum the former implantation site presented an expanded mesometrial area, spheroid in shape and surrounded peripherally by collagen. Whilst CD31+LYVE-1- blood vessels were ubiquitous in virgin and postpartum endometrium, vessels of large lumen and clusters of capillaries gathered exclusively at the former implantation site. The endometrium was largely devoid of lymphatic vessels. In contrast, the myometrium presented lymphatic vessels, particularly at the mesometrial side and of higher diameter in postpartum. TUNEL+ apoptotic cells scattered especially in the mesometrial area of postpartal endometrium, whereas their number in virgins was sparse. Proliferating PCNA+ cells located in both virgin and postpartal endometrial stroma, glands and epithelium. Conclusions Postpartal regeneration of the former implantation site is associated to cell death and increased endometrial angiogenesis and myometrial lymphatic vascularization. The cascade of events leading to complete regeneration of the postpartal uterus and how it is modulated e.g. by uterine resident immune cells requires still further elucidation. Article published online: 11 October 2022 © 2022. Thieme. All rights reserved. Georg Thieme Verlag Rüdigerstraße 14, 70469 Stuttgart, Germany