Abstract 20331: Microparticles Inhibit Angiogenic Activities of Microvascular Endothelial Cells via a CD36 Dependent Signaling Pathway Involving Reactive Oxygen Species
CD36 interactions with thrombospondin-1 and related proteins inhibit angiogenic signaling in microvascular endothelial cells (MVEC). Phosphatidylserine (PS) exposed on microparticles (MP) shed from vascular cells by activation or apoptosis, is also a ligand for CD36 so we hypothesized that CD36-MP interactions would inhibit angiogenesis. MP prepared in vitro from THP1 monocytes, erythrocytes, MVEC, or human umbilical vein endothelial cells (HUVEC) were exposed to MVEC to assess their effect on tube formation and migration. MP derived from all of these cell types inhibited tube formation by >50% (p<0.05) and THP1 MP inhibited migration by 80% (p<0.001) showing that the antiangiogenic effect of MP is independent of their cell of origin. Blocking surface exposed anionic phospholipids with annexin V reduced the inhibitory effect of MP on MVEC suggesting that PS was required (35%; p<0.001). To show a role for CD36, we found that MP induced inhibition of migration was greater in high CD36 expressing early passage MVEC compared to late passage MVEC with low or no CD36 expression (80% vs 33%; p<0.001). Similarly, CD36 negative HUVEC showed low inhibitory response to MP, but responses were restored when these cells were transfected with CD36 cDNA (82% inhibition vs 44%;p<0.001). MP isolated from plasma of 4 patients with the chronic inflammatory condition Wegener’s granulomatosis also inhibit MVEC migration >80% (p<0.001) suggesting that conditions that increase MP production in vivo can inhibit angiogenic processes. ROS generation has been implicated in macrophage and platelet CD36 mediated signaling. We found that MP exposure induced MVEC ROS by 2 fold at 1hr (p<0.05) and that the NADPH oxidase inhibitor apocynin blocked MP induced ROS (>95%) and partially (33%) reversed inhibition of migration (p<0.001). THP1 MP activated Fyn kinase in MVEC in a time dependent manner, and PP2, a Src family kinase inhibitor, blocked MP induced ROS induction by >95% and partially (25%) reversed inhibition of migration (p<0.001). These studies identify a novel mechanistic pathway through which PS exposed on MP inhibit MVEC angiogenic activities via activation of a CD36-mediated signaling pathway involving NADPH oxidase-mediated ROS generation.
Author Disclosures: D. Ramakrishnan: None. R. Hajj-Ali: None. R. Silverstein: None.
- © 2014 by American Heart Association, Inc.