Abstract
INTRODUCTION: Cathepsin K, a cysteine protease expressed in osteoclasts, involved in bone resorption is expressed in other cells including brain cells. Reports suggest that cathepsin K may be involved in cancers associated with bone metastasis. Little is known about its expression in brain tumours. There is evidence of a potential interaction of cathepsin K with stromal cell derived factor 1 (SDF-1) in haemapoietic stem cell motility. Because of the importance of SDF-1 in brain tumour angiogenesis and recruitment of glioma like stem cells to vascular niches, we investigated cathepsin K in an in vitro model of angiogenesis. METHOD: Brain endothelial cells (hCMEC) and glioma cell lines (SNB-19 and UP-007) cultured under normoxic and hypoxic conditions were analysed using flow cytometry and western blotting. Angiogenesis was assessed using an in vitro model of brain endothelial cell tube formation. Brain endothelial tube length, number of tube projections and number of branch points were measured. RESULTS: Under hypoxic conditions, there is a significant decrease in cathepsin K expression in brain endothelial cells when compared to normoxic conditions (P ≤ 0.05). Addition of Odanacatib, a cathepsin K inhibitor, to the angiogenesis assay revealed that inhibition of cathepsin K resulted in a significant increase in endothelial tube length in normoxic conditions (p < 0.05). CONCLUSION: The decrease in cathepsin K expression in endothelial cells under hypoxia, coupled with the increase in tube length following inhibition of cathepsin K, suggests an involvement of cathepsin K with angiogenesis. These data provide rationale and basis for further study into the function of cathepsin K and its relationship with SDF-1 in gliomas.
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