Overexpression of Roundabout4 predicts poor prognosis of primary glioma patients via correlating with microvessel density.

Roundabout4 (Robo4), a new member of Robo proteins family, is specifically expressed in endothelial cells. Recent studies have indicated that Robo4 could regulate tumor angiogenesis and vascular permeability. However, the role and function of Robo4 are not well understood. This study was performed to investigate the expression of Robo4 in primary glioma patients, and thus to determine the association of Robo4 expression with microvessel density and survival of glioma patients. In this study, real-time PCR and immunohistochemistry were performed to examine the mRNA level and protein expression of Robo4 in both 43 cases of glioma samples and 10 cases of normal brain tissue samples. The results demonstrated that Robo4 was significantly up-regulated in glioma tissues compared with normal brain tissues. In addition, double immunofluorescent staining revealed that Robo4 expression co-localized with CD34 expression in the vessel of glioma tissues. The expression of Robo4 positively correlated with patients' age (P = 0.0139) and glioma grade (P < 0.0001). A linear correlation was observed between the relative mRNA expression of Robo4 values and corresponding microvessel density values (r = 0.9735, P < 0.0001). Kaplan-Meier analysis and log-rank test result showed that the overall survival of patients with Robo4 high expression was significantly shorter than that of patients with Robo4 low expression (P < 0.001). The results of present study verify that overexpression of Robo4 is related to poor prognosis of primary gliomas patients through correlating with microvessel density.