Regulation and function of aquaporin-1 in glioma cells

Glioblastoma multiformes ( GBMs) express increased aquaporin ( AQP) 1 compared to normal brain. AQPs may contribute to edema, cell motility, and shuttling of H2O and H+ from intracellular to extracellular space. We sought to gain insight into AQP1 function in GBM. In cultured 9L gliosarcoma cells, AQP1 expression was induced by dexamethasone, platelet-derived growth factor, NaCl, hypoxia, D-glucose ( but not L-glucose), and fructose. Induction of AQP1 expression correlated with the level of glycolysis, maximized by increasing medium D-glucose or fructose and decreasing O-2, and was quantified by measuring lactate dehydrogenase ( LDH) activity and medium lactate concentration. Upregulation of the protease cathepsin B was also observed in 9L cells cultured under glycolytic conditions. Immunohistochemical staining of human GBM specimens revealed increased coincident expression of AQP1, LDH, and cathepsin B in glioma cells associated with blood vessels at the tumor periphery. GBMs are known to exhibit aerobic glycolysis. Increased glucose metabolism at the tumor periphery may provide a scenario by which upregulation of AQP1, LDH, and cathepsin B contributes to acidification of the extracellular milieu and to invasive potential of glioma cells in perivascular space. The specific upregulation and metabolic consequences of increased AQP1 in gliomas may provide a therapeutic target, both as a cell surface marker and as a functional intervention.