Periostin Secreted by Glioblastoma Stem Cells Recruits M2 Tumor-associated Macrophages and Promotes Malignant Growth

Tumor-associated macrophages (TAMs) are enriched in glioblastoma (GBM) that contains glioma stem cells (GSCs) at the apex of its cellular hierarchy. The correlation between TAM density and glioma grade suggests a supportive role of TAMs in tumor progression. Here we interrogated the molecular link between GSCs and TAM recruitment in GBMs and demonstrated that GSCs secrete Periostin (POSTN) to recruit TAMs. TAM density correlates with POSTN levels in human GBMs. Silencing POSTN in GSCs markedly reduced TAM density, inhibited tumor growth, and increased survival of mice bearing GSC-derived xenografts. We found that TAMs in GBMs are not brain-resident microglia, but mainly monocyte-derived macrophages from peripheral blood. Disrupting POSTN specifically attenuated the tumor supportive M2 type of TAMs in xenografts. POSTN recruits TAMs through integrin α(v)β(3) as blocking this signaling by an RGD peptide inhibited TAM recruitment. Our findings highlight the possibility of improving GBM treatment by targeting POSTN-mediated TAM recruitment.