Abstract
Building on a large body of existing blood vascular research, advances in lymphatic research have helped kindle broader investigations into vascular diversity and endothelial plasticity. While the endothelium of blood and lymphatic vessels can be distinguished by a variety of molecular markers, the endothelia of uniquely diverse vascular beds can possess distinctly heterogeneous or hybrid expression patterns. These expression patterns can then provide further insight on the development of these vessels and how they perform their specialized function. In this review we examine five highly specialized hybrid vessel beds that adopt partial lymphatic programing for their specialized vascular functions: the high endothelial venules of secondary lymphoid organs, the liver sinusoid, the Schlemm’s canal of the eye, the renal ascending vasa recta, and the remodeled placental spiral artery. We summarize the morphology and endothelial expression pattern of these vessels, compare them to each other, and interrogate their specialized functions within the broader blood and lymphatic vascular systems.
Highlights
The discovery of new lymphatic markers has been a boon for lymphatic research helping to improve our understanding of the development and maintenance of lymphatics, as well as the identification of new lymphatic vessels
Three different vessels, Lymphatic Programing in Hybrid Vessels termed hybrid vessels, have been found to possess a combination of blood and lymphatics markers, presumably necessary for their highly specialized function: the Schlemm’s canal (SC) of the eye, the ascending vasa recta (AVR) of the renal medulla, and the remodeled spiral arteries of the placental decidua (Aspelund et al, 2014; Park et al, 2014; Truong et al, 2014; Kenig-Kozlovsky et al, 2018; Pawlak et al, 2019). These vessels are in addition to an existing small catalog of highly specialized non-lymphatic vessels with distinct expression patterns, including the liver sinusoid and high endothelial venules (HEV) of secondary lymphoid organs
The receptor tyrosine kinase EphB4 is a venous marker, while its cognate membrane-bound ligand ephrin B2 marks arterial endothelium, though both are Lymphatic vessels are responsible for maintaining fluid homeostasis, fat absorption, and immune cell trafficking
Summary
While the endothelium of blood and lymphatic vessels can be distinguished by a variety of molecular markers, the endothelia of uniquely diverse vascular beds can possess distinctly heterogeneous or hybrid expression patterns. These expression patterns can provide further insight on the development of these vessels and how they perform their specialized function. In this review we examine five highly specialized hybrid vessel beds that adopt partial lymphatic programing for their specialized vascular functions: the high endothelial venules of secondary lymphoid organs, the liver sinusoid, the Schlemm’s canal of the eye, the renal ascending vasa recta, and the remodeled placental spiral artery.
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