Aims/hypothesis. Increased angiogenesis of fetoplacental vessels is a feature of pregnancies complicated by Type 1 diabetes mellitus, but the underlying molecular mechanisms are unknown. This investigation tests whether the diabetic maternal environment alters the phenotypic expression of placental vascular endothelial cadherin and β-catenin, which have been implicated as key molecules in barrier formation and angiogenesis in the endothelium. Methods. Term placental microvessels from normal pregnancies (n=8) and from those complicated by Type 1 diabetes (n=8) were perfused with 76-M r dextran tracers (1 mg/ml) and subjected to immunocytochemistry, immunoblotting and microscopy. Junctional integrity, localisation and phosphorylation were investigated along with total protein levels of vascular endothelial cadherin, β-catenin and vascular endothelial growth factor. Stereological sampling and estimation tools were used to quantify aspects of angiogenesis and endothelial proliferation. Results. In the Type 1 diabetic placentae, junctional localisations of vascular endothelial cadherin and β-catenin altered significantly, with more than 50% of microvessels showing complete loss of immunoreactivity and with no overall loss of total protein. Tracer leakage was associated with these vessels. There was a two-to three-fold increase in vessels showing junctional phospho-tyrosine immunoreactivity and hyperphosphorylated β-catenin. Vascular endothelial growth factor levels were higher in these placentae. A fourfold increase in endothelial proliferation was observed, along with an increase in total length of capillaries without any change in luminal diameter. Conclusions/interpretation. Molecular perturbations of vascular endothelial cadherin and β-catenin occur in fetoplacental vessels of pregnancies complicated by Type 1 diabetes. Phosphorylation and loss of these molecules from the adherens junctional domains may be influenced in part by the elevated levels of vascular endothelial growth factor in the placenta. Perturbations of the junctional proteins may explain the observed breach in barrier integrity and may contribute to the mechanisms that drive proliferation and increases in capillary length.
Vasculogenesis and angiogenesis are regulated by the capacity of endothelial cells to adhere to each other and form new tubes. The presence and role of junctional adhesion molecules during physiological vasculogenesis is unknown. Using ultrastructural and immunocytochemical approaches, we compared the junctional phenotype of developing vessels of the first-trimester human placenta with vessels in the last trimester; the latter include newly formed terminal capillaries and the quiescent vascular bed. First-trimester placental vessels contained the adherens junctional molecules, vascular endothelial cadherin and α- and β-catenin but lacked plakoglobin, the component of fully differentiated adherens junctions. Furthermore, these vessels did not contain the transmembrane tight junctional molecules occludin and claudin-1 and -2. This profile reflects the phenotype of terminal capillaries but differs from large vessels of the full-term placenta. Electron microscopic studies revealed that endothelial tight junctions are present in the first-trimester placenta. Thus, occludin and claudin-1 appear to play no part in the formation of endothelial tight junctions, but are a later requirement. In the early placenta, the predominant growth factor appears to be vascular endothelial growth factor (VEGF), whilst at term, angiopoietin-1 was present in large vessels, with intense angiopoietin-2 immunofluorescence (and VEGF) located in terminal villous capillaries. Thus, endothelial junctions in the human placenta possess two distinct molecular phenotypes, i.e. stable or dynamic, dependent on maturity and plasticity. These distinct phenotypes may be influenced by the angiopoietins/VEGF present in the placenta.
The human placenta is a highly vascularised organ whose major functions are to allow materno-fetal exchange of solutes and oxygen. Formation of the placental fetal vessels (vasculogenesis) occurs in the first 4 weeks of pregnancy and elaboration of the microvascular beds (angiogenesis) occurs in the last trimester of pregnancy. The structure and permeability of these vessels, at term, resemble those of skeletal muscle capillaries [1,2]. Both vascular remodelling and effective barrier formation are key endothelial functions, which influence fetal well-being and perinatal outcome. One of the major complications in pregnancies is diabetes mellitus. In pregnancies in women with pre-existing diabetes, both vasculogenesis and angiogenesis, in theory, can be affected. Ges- Diabetologia (2000) Abstract Aims/hypothesis. The aim of this study was to investigate whether gestational diabetes mellitus, which occurs in the microvascular remodelling phase of placental development, causes alterations in surface expression of tight and adherens junctional molecules involved in endothelial barrier function and angiogenesis.Methods. Term placenta, delivered by elective Caesarian section, from normal pregnancy (n = 5) and those complicated by gestational diabetes (n = 5) were perfusion-fixed and analysed by indirect immunofluorescence and confocal scanning microscopy. Using systematic random sampling, the surface expression of endothelial junctional proteins and the relative incidences of immunostained vessels were compared between the two study groups. Total vessel lengths were measured by stereological techniques.Results. The adherens junctional molecules, vascularendothelial cadherin and b-catenin, and the tight junctional molecules, occludin and zonula occludens-1 were localised to paracellular clefts in both study groups. The diabetic placentae showed pronounced reductions in the intensity of immunofluorescence and in the number of immuno-positive vessels. A corresponding statistically significant increase (from 19 % to 56 %) in the percentage of vessels showing junctional anti-phosphotyrosine immunoreactivity was found. The differences observed represented real changes in the absolute lengths of immunostained regions along the vessels. The stereological measurements failed to detect any statistically significant change in the combined length of fetal vessels in gestational diabetic placenta. Conclusion/interpretation. Our results suggest that even short duration diabetic insult, alters the surface expression of placental junctional proteins. This alteration could be mediated by the tyrosine-phosphorylation pathway. The changes suggest impaired barrier function rather than accelerated vascular growth.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations –citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.