Associations Between DLL4-notch Signaling And Tumor Angiogenesis In Primary Glioblastoma

Background and Purpose: Delta-like ligand-4(DLL4)-Notch signaling is known to play a pivotal role in the regulation of tumor angiogenesis. We had previously found that DLL4 was overexpressed, while Notch1 receptor, which binds to DLL4 during angiogenesis, was absent in the majority of human primary glioblastomas. Thus, DLL4-Notch signaling pathway in the regulation of tumor angiogenesis in primary glioblastoma remains unknown. In the present study, we systematically investigated the expression of the major components of DLL4-Notch signaling pathway and analyzed their effects on tumor angiogenesis. Methods: Tumor tissues from 70 patients with primary glioblastoma were analyzed by immunohistochemistry for expression of major components of DLL4-Notch signaling [DLL4, Notch1-4, HES1(hairy/enhancer of split-1; a target gene of Notch signaling)], vascular endothelial growth factor(VEGF), and microvessel density(MVD), the grade of tumor enhancement were also analysed through the preoperative MRI image. The Univariate analysis and Binary logistic regression analysis were used to analyse the relationship between the expression of major components of DLL4-Notch signaling(DLL4, Notch1-4, HES1), VEGF, and MVD, the grade of tumor enhancement. Results: Positive immunohistochemical staining was brown or yellow(VEGF, DLL4, Notch1–4 in cytoplasm and/or cytomembrane, HES1 in nucleus). In the histological distribution, the positive staining of DLL4 and Notch4 was primarily distributed in tumor vascular endothelial cells but rarely detected in tumor cells. However, VEGF, hairy/enhancer of split-1(HES1; a target gene of Notch signaling), and Notch2–3 expression was seen in both tumor vascular endothelial cells and tumor cells. Univariate analysis showed that the expression levels of VEGF and DLL4, HES1, and Notch4 in tumor endothelial cells were significantly associated with MVD and the grade of tumor enhancement in primary glioblastoma(P<0.001). Binary logistic regression analysis showed that high expression levels of DLL4, HES1, and Notch4 in tumor endothelial cells were associated with a decrease of MVD in primary glioblastoma, while MVD increased with elevated VEGF expression in contrast. In addition, Spearman rank correlation analysis showed there were positive correlation in the grade of tumor enhancement and VEGF, MVD. And negative correlation were found in the grade of tumor enhancement and DLL4, HES1, and Notch4 in tumor endothelial cells, in contrary(P<0.05). Conclusion: The VEGF signaling and vascular DLL4-Notch4 signaling complementing each other plays an important role in the progression of tumor angiogenesis in primary glioblastoma.