CTSK and glioma: Moreover, those GSCs express not only a SDF-1/CXCR4 axis but also osteopontin (OPN) and cathepsin K (CTSK), showing how the niche that surrounds arterioles resembles bone marrow hematopoietic stem cell (HSC) niche proteins and recruits glioma stem cells by promotion of migration via CD44 and CXCR4 [91,92,100].