ANGI-10: GLIOMA-ASSOCIATED MACROPHAGES PROMOTE ENDOTHELIAL CELL DYSFUNCTION

One of the most prominent features of glioblastoma (GBM) is hyper-vascularization, characterized by abnormal hyper-dilated, distorted, leaky vessels and increased thrombosis. Bone marrow-derived microglia/macrophages are an important host cell population that are actively recruited to the tumour, associate closely with blood vessels, and are thought to provide a supportive role in tumour neo-vascularization. The aim of this study was to investigate the unknown molecular mechanisms of how glioma-associated microglia/macrophages affect endothelial cells to promote neovascularization. Here we examined the effect of conditioned-medium (CM) from M1 (classically activated), M2 (alternatively activated), or glioma neurosphere-associated macrophages (co-cultured) on the expression of angiogenesis genes in human umbilical vein endothelial cells (HUVECs). Strikingly, CM from glioma-associated macrophages produced a substantial upregulation of genes involved in endothelial activation including VCAM-1, ICAM-1, CXCL5, CXCL10, HGF, VEGFC, and SERPINE1 (some up to several thousand-fold increase in expression) in comparison to CM from M1 or M2-polarized macrophages. Gene ontology analysis indicated the possibility of regulation by TNF-α and we therefore examined and confirmed that glioma-associated macrophages show increased secretion of this cytokine. Interestingly, CM from glioma-associated macrophages also led to a downregulation of NOS3 in HUVEC cells, which is known to promote endothelial dysfunction in activated endothelial cells. These findings suggest that glioma-associated macrophages secrete TNF-α, which acts on nearby endothelial cells to promote endothelial activation/ dysfunction. We propose that the pro-inflammatory state of dysfunctional glioma-associated endothelial cells may further increase the recruitment of macrophages through upregulation of adhesion molecules, and promote pro-thrombic properties and vascular leakage that characterize and promote GBM neo-vascularization.