gms | German Medical Science

Objective: Hemangioblastoma (HB) is a rare benign tumor (WHO grade I), located mainly in the brain and the spinal cord. This tumor is classified as either sporadic HB (70-75%) or von Hippel-Lindau disease (VHL)-associated HB. VHL disease is an autosomal dominant disorder caused by germline mutations of the VHL gene. Missense mutations of the VHL gene are also present in sporadic HB and in renal cell carcinoma. The tumor is composed of 2 major components including neoplastic stromal cells and abundant microvessels. Thus, hyper-vascularization is the hallmark of this tumor. Despite the identification of germline and/or epigenetic mutations of VHL gene as an important pathogenic mechanism of HB, little is known about the molecular signaling involved in this highly vascularized tumor. The present study was aimed to further explore angiogenic signaling in sporadic and hereditary HB.

Methods: We investigated the key players of multiple angiogenic signaling pathways including VEGF/VEGFR2 (Vascular endothelial growth factor/ - receptor 2), EphB4/EphrinB2 (Ephrin receptor B4/ ligand EphrinB2), SDF1α/CXCR4 (Stromal derived factor-1 α/ receptor CXC-motif chemokine receptor4) and Notch/Dll4 pathways in surgical specimens of 22 HB. Nineteen patients suffered from sporadic HB and three cases had a VHL-associated tumor. The expression of key angiogenic factors was detected by RT²-PCR and Western blot. Immunofluorescent staining was performed to illustrate the cellular localization of these proteins.

Results: We demonstrated a massive upregulation of mRNA level of VEGF and VEGFR2, CXCR4 and SDF1α, EphB4 and EphrinB2 as well as the main components of Dll4-Notch signaling in HB. There was no significant difference in the expression of these genes between sporadic HB and VHL-associated HB, except for HIF1α. The “fold of change” for HIF1α mRNA was 5-fold higher in VHL-associated HB than in sporadic HB. An increase in the protein expression of VEGF, CXCR4 and the core-components of Dll4-Notch signaling was associated with an activation of Akt and Erk1/2 and accompanied by an elevated expression of PCNA. Immunofluorescent staining revealed the expression of VEGF and CXCR4 in endothelial cells as well as in tumor cells. Dll4 protein was predominantly found in tumor cells, whereas EphB4 immunoreactivity was exclusively detected in endothelial cells.

Conclusion: We conclude that multiple key angiogenic pathways were activated in HB, which may synergistically contribute to the abound vascularization in this tumor. Identification of these aberrant pathways provides potential targets for a possible future application of anti-angiogenic therapy for this tumor, particularly when a total surgical resection becomes difficult due to the localization or multiplicity of the tumor. To further enlighten the molecular differences between sporadic and hereditary HB, a higher number of hereditary cases is necessary.