Background: Endothelial cells proliferate during brain development, are quiescent in normal adult brain but proliferate again under pathologic conditions such as glioma growth. The vascular phenotype of low grade glioma is comparable to normal brain, however high grade gliomas are focally highly vascularized and there is associated prominent endothelial cell proliferation. The mechanisms of this change in vascular phenotype are unknown but there is evidence that growth factors play an important role in this process as well as in normal angiogenesis and vascular differentiation.
Experimental design: To investigate whether endothelial cells become activated during tumorigenesis and progression of human gliomas by a platelet-derived growth factor (PDGF) dependent pathway, we analyzed platelet-derived growth factor receptor-beta (PDGFR-beta) expression by in situ hybridization and immunocytochemistry in normal human brain, astrocytoma (grade II), anaplastic oligo-astrocytoma (grade III), and glioblastoma multiforme (grade IV).
Results: PDGFR-beta mRNA was not detectable in the vessels of normal human brain, but was expressed in the vasculature of low and high grade gliomas, particularly in endothelial cell proliferations in glioblastomas. The expression of the receptor in the tumor microvessels, was confirmed by double immunofluorescence in which the staining appeared to be in the endothelial cells. Primary cultures of endothelial cells derived from glioblastoma multiforme maintained receptor expression for 2 days in vitro, whereas it was not detectable in vitro in endothelial cells derived from normal brain. Tumor cells in all grades of glioma expressed very little PDGFR-beta mRNA in situ.
Conclusions: Our results indicate that the malignant phenotype in human glial tumors is associated with an upregulation of the PDGFR-beta on endothelial cells of vessels which vascularize the tumor. These findings may contribute to our understanding of the mechanisms that regulate vessel growth and differentiation in normal and pathologic states.