Object: Mammalian heparanase has been shown to function in tumor progression, invasion, and angiogenesis. However, heparanase expression in gliomas has not been well analyzed. To clarify its expression in gliomas, human glioma tissues and glioma animal models were investigated.
Methods: The expression of heparanase mRNA was determined in 33 resected human glioma tissues by semiquantitative real-time polymerase chain reaction. Heparanase expression was verified with a Western blot assay and immunohistochemistry (IHC) staining. Primary neurospheres from human glioblastoma multiforme (GBM) were developed in vitro. Heparanase expression in murine astrocytoma and human primary neurosphere animal models was examined using IHC.
Results: The authors found that heparanase mRNA is greatly increased in gliomas including oligodendroglioma (9 samples), anaplastic astrocytoma (11 samples), and GBM (13 samples) as compared with healthy brain mRNA (3 samples). Note, however, that no significant difference was observed among the 3 tumor groups. Increased heparanase expression was also found in tumor tissues on Western blotting. Immunohistochemistry staining demonstrated that heparanase was expressed by neovessel endothelial cells, infiltrated neutrophils, and in some cases, by neoplastic cells. Heparanase-expressing cells, including GBM tumor cells and neovessel endothelial cells, exhibited decreased expression of CD44, a cell adhesion molecule on the cell membrane that is important for regulating tumor invasion. In addition, heparanase-expressing tumor cells showed an elevated density of the cell proliferation marker Ki 67, as compared with its density in non-heparanase-expressing tumor cells, suggesting that heparanase expression is correlated with enhanced tumor proliferation. Two animal glioma models were tested for heparanase expression. Both murine astrocytoma cells (Ast11.9-2) and cultured primary human GBM neurospheres expressed heparanase when grown in animal brain tissue.
Conclusions: Glioma tissues contain increased levels of heparanase. Multiple cell types contribute to the expression of heparanase, including neovessel endothelial cells, tumor cells, and infiltrated neutrophils. Heparanase plays an important role in the control of cell proliferation and invasion. Animal models using Ast11.9-2 and primary neurospheres are suitable for antitumor studies targeting heparanase.