gms | German Medical Science

Objective: Malignant gliomas show high rates of glycolysis caused by hypoxia and specific gene alterations. This leads to high glucose utilization rates combined with increased levels of lactic acid. We hypothesized that hypoxia-inducible carbonic anhydrase (CA) IX is involved in the extrusion of hydrogen ions into the extracellular space. This may cause the activation of cathepsin B due to lowered extracellular pH, which would ultimately lead to increased invasion of glioblastoma cells under glycolytic conditions. Therefore we induced glycolysis in glioblastoma cells and observed their invasive potential in the presence of a specific carbonic anhydrase inhibitor. To correlate the invasive potential with cathepsin B activation, we analyzed cathepsin B expression, its subcellular distribution and the secretion of cathepsin B into the supernatant.

Methods: U251 glioblastoma cells were cultured in a Biocoat Matrigel invasion chamber. A matrigel - coated polycarbonate filter was situated between upper and the lower well plates. The chambers were incubated in a humidified 5% CO₂ atmosphere with either 21% oxygen and 25 mM glucose in the culture medium (ctrl.), or 0% oxygen plus 125 mM glucose (glycolysis). CA activity was inhibited by 40 mM acetazolamide. Invasion was quantified by counting the cells which invaded into the lower culture compartment. Cathepsin B expression was investigated by Western Blot, its subcellular distribution was analyzed by immunofluorescent staining, and cathepsin B secretion into the supernatant was measured using a cathepsin B activity assay.

Results: In vitro glycolysis caused a significant increase of cathepsin B secretion combined with massive invasion of glioblastoma cells. Acetazolamide both reduced the cathepsin B secretion and the invasive potential. In addition, the subcellular re-distribution of cathepsin B caused by glycolysis was attenuated by acetazolamide.

Conclusions: Our data demonstrate that glycolysis leads to enhanced invasion of glioblastoma cells which is mediated by increased cathepsin B secretion. Inhibition of CA reduces the invasive potential by reducing the cathepsin B secretion. This indicates a link between glycolytic metabolism, pericellular acidification moderated by CA’s, cathepsin B activity and the invasive potential of glioblastoma cells.