Novel function for blood platelets and podoplanin in developmental separation of blood and lymphatic circulation

Abstract

During embryonic development, lymph sacs form from the cardinal vein, and sprout centrifugally to form mature lymphatic networks. Separation of the lymphatic from the blood circulation by a hitherto unknown mechanism is essential for the homeostatic function of the lymphatic system. O-glycans on the lymphatic endothelium have recently been suggested to be required for establishment and maintenance of distinct blood and lymphatic systems, primarily by mediating proper function of podoplanin. Here, we show that this separation process critically involves platelet activation by podoplanin. We found that platelet aggregates build up in wild-type embryos at the separation zone of podoplanin ؉ lymph sacs and cardinal veins, but not in podoplanin ؊/؊ embryos. Thus, podoplanin ؊/؊ mice develop a "nonseparation" phenotype, characterized by a bloodfilled lymphatic network after approximately embryonic day 13.5, which, however, partially resolves in postnatal mice. The same embryonic phenotype is also induced by treatment of pregnant mice with acetyl salicylic acid, podoplaninblocking antibodies, or by inactivation of the kindlin-3 gene required for platelet aggregation. Therefore, interaction of endothelial podoplanin of the developing lymph sac with circulating platelets from the cardinal vein is critical for separating the lymphatic from the blood vascular system. (Blood. 2010;115(19):3997-4005)

Apolipoprotein A‐I Modulates Atherosclerosis Through Lymphatic Vessel‐Dependent Mechanisms in Mice

“…However, many other different transcription factors regulate lymphatic development. Interestingly, it has been shown that during embryogenesis, lymphatic system separation from blood vessels requires platelet activity 7. Indeed, platelets regulate the blood/lymphatic vessel separation by inhibiting the proliferation, migration, and tube formation of LECs, upon the interaction of C‐type lectin‐like receptor 2 (CLEC‐2) with podoplanin 8.…”

The New Era of the Lymphatic System: No Longer Secondary to the Blood Vascular System

“…Notably, podoplanin-deficient mice fail to develop a functional lymphatic system with a severe lymphedema in the extremities . A series of recent findings has shown that podoplanin activates a novel platelet receptor, C-type lectinlike receptor (CLEC)-2 of platelet, and has an essential role in blood -lymphatic separation during lymphatic development (see more information below) (Fu et al 2008;Kato et al 2008;Bertozzi et al 2010a,b;Suzuki-Inoue et al 2007Uhrin et al 2010;SuzukiInoue 2011). Moreover, some lymphatic vessels were found to express a high level of podoplanin (LEC podo-high ) and the others a low level of podoplanin (LEC podo-low ), and these two subpopulations differentially recruit CCR10-positive T lymphocytes during the inflammation response (Kriehuber et al 2001;Wick et al 2008).…”

“…These pioneering findings were followed by a series of molecular and genetic studies confirming the role of podoplanin/CLEC-2 interaction in lymphatic development. Notably, endothelial cell O-glycan deficiency caused blood/lymphatic misconnection in mouse (Fu et al 2008), and podoplanin or CLEC-2 knockout mice showed the blood -lymphatic mixing phenotype of mice lacking SYK, SLP-76, or PLCg-2 (Bertozzi et al 2010a,b;Suzuki-Inoue et al 2010;Uhrin et al 2010). Together, these studies show that the platelets mediate blood and lymphatic separation by activation of the CLEC-2 receptor following interaction with the podoplanin ligand found on the surface of LECs.…”

Mutation of Threonine 34 in Mouse Podoplanin-Fc Reduces CLEC-2 Binding and Toxicity in Vivo While Retaining Anti-lymphangiogenic Activity

“…Binding of the snake venom rhodocytin or Pdpn to CLEC-2 on platelets triggers intracellular signaling via Syk-SLP76 that leads to platelet activation (15). The molecular interaction between Pdpn and CLEC-2 has been shown to be important in the development of the lymphatic system, as it is involved in the physical separation of the lymph sacs from the blood-filled cardinal vein (16,17). Also, CLEC-2-positive dendritic cells interact with Pdpn-positive LEC and follicular reticular cells for their migration from the periphery to and through the lymph node where they present antigens to T-cells (18).…”