A Proteome Comparison Between Physiological Angiogenesis and Angiogenesis in Glioblastoma

Abstract

The molecular pathways involved in neovascularization of regenerating tissues and tumor angiogenesis resemble each other. However, the regulatory mechanisms of neovascularization under neoplastic circumstances are unbalanced leading to abnormal protein expression patterns resulting in the formation of defective and often abortive tumor vessels. Because gliomas are among the most vascularized tumors, we compared the protein expression profiles of proliferating vessels in glioblastoma with those in tissues in which physiological angiogenesis takes place. By using a combination of laser microdissection and LTQ Orbitrap mass spectrometry comparisons of protein profiles were made. The approach yielded 29 and 12 differentially expressed proteins for glioblastoma and endometrium blood vessels, respectively. The aberrant expression of five proteins, i.e. periostin, tenascin-C, TGFbeta induced protein, integrin alpha-V, and laminin subunit beta-2 were validated by immunohistochemistry. In addition, pathway analysis of the differentially expressed proteins was performed and significant differences in the usage of angiogenic pathways were found. We conclude that there are essential differences in protein expression profiles between tumor and normal physiological angiogenesis. Molecular & Cellular Proteomics 11: 10.1074/mcp.M111.008466, 1-9, 2012.Neovascularization is a complex process taking place under physiological and pathological circumstances. There is large overlap in the cellular components, regulatory factors, and signaling mechanisms acting in the angiogenic process of regeneration, embryonic development, and tumor vascularization (1). In both physiological and pathological neovascularization signaling mechanisms, growth factors and their receptors, cell adhesion molecules and their specific extracellular matrix ligands take part (2). Angiocrine molecules like basic fibroblast growth factor and vascular endothelial growth factor and their receptors have been identified in the context of physiological and tumor angiogenesis (3). It is believed that the angiogenic switch is always triggered by hypoxia, starting with the up-regulation of vascular endothelial growth factor. The process of neovascularization consists not only of sprouting angiogenesis, but also of activation of endothelial precursor cells with the capacity to form de novo blood vessels (vasculogenesis). Vasculogenesis is also part of tumor vascularization but there is dispute about its relative importance (4, 5). Despite the similarities there are obvious differences between physiological vascularization and angiogenesis in tumors. Under physiological conditions, the regulatory mechanisms are well-coordinated and balanced and endothelial cell functions are tightly orchestrated by both pro-and anti-angiogenic factors. In tumor angiogenesis however, there is an excess of pro-angiogenic factors leading to uncoordinated proliferation and tubulogenesis of endothelial cells and migration of mural cells like pericytes (6). It is likely that the molecular diff...

Role of tenascins in the ECM of gliomas

“…Within one tumor different phenotypes like incipient proliferation of endothelial cells or sarcomatous structures are found. 77 Especially the alternatively spliced domains TNfnC 78,79 and TNfnA2 38 could be found highly up-regulated in glioma blood vessels, but also the EGF-type repeats as well as the fibrinogen globe are supposed to play a role in the formation of tumor blood vessels. 80 The TN-C-induced generation of tumor blood vessels could be related to the binding to endothelial cells 81 and its stimulating effect on this cell type.…”

“…86 Additionally to the high expression of TN-C in glioma blood vessels the known receptor for TN-C, integrin a v, is found in elevated levels in glioma tissue, as well as the protein periostin. 77 Periostin was detected as a promoter of TN-C incorporation into the ECM and to organize the architecture of the ECM. 87 For murine pancreatic neuroendocrine tumorigenesis it could be recently shown that the composition of upregulated matrisomal genes in pericytes could be correlated to genes overexpressed also in glioma.…”

The glioblastoma vasculature as a target for cancer therapy

“…IGFBP7 is induced in endothelial cells in response to tumourderived TGFβ and enhances tube formation, suggesting that IGFBP7 may contribute to glioblastoma angiogenesis [55]. Mustafa et al [56] compared protein expression in isolated glioblastoma vessels with expression in angiogenic endometrial vessels through LTQ Orbitrap MS and found 29 genes to be specifically expressed in the glioblastoma vessels including tenascin C, Nid1, Nid2 and integrin α5. These genes were also identified as glioblastoma vessel markers in a recent study in my laboratory [23].…”

Release of endothelial cell associated VEGFR2 during TGF-β modulated angiogenesis in vitro

“…TGF-β plays a dual role in angiogenesis by orchestrating a switch from vascular inhibition to pro-angiogenic activity [5–7]. In particular, there is evidence that TGF-β1 induced angiogenesis acts with VEGF to mediate apoptosis of excessive vascular sprouts and may even be required for initial sprouting from an existing vascular network [8, 9].…”