Glioblastoma-associated microglia-derived exosomal circKIF18A promotes angiogenesis by targeting FOXC2.

Glioblastoma multiforme (GBM) is the most lethal primary tumor with active neovascularization in the central nervous system. Studying the novel molecular mechanisms of GBM angiogenesis is very important. The glioblastoma-associated microglia (GAM) M2 polarization was constructed, and microglia-derived exosomes (MDEs) were isolated to co-culture with human brain microvessel endothelial cells (hBMECs). CircRNA sequence and molecular biological experiments were used to detect the expression levels and regulation functions among circKIF18A, FOXC2, ITGB3, CXCR4, DLL4 and the PI3K/AKT signaling. The functional effects of silencing or overexpression of these molecules were evaluated in hBMECs viability, invasion, and tube formation in vitro and tumorigenicity in vivo. M2 microglia polarization is positively correlated with microvessels' density in GBM patients. M2 GAM can promote the angiogenesis of GBM via transporting exosomal circKIF18A into hBMECs. Mechanistically, circKIF18A can bind to, maintain the stability and nuclear translocation of FOXC2 in hBMECs. Furtherly, as a transcription factor, FOXC2 can directly bind to the promoter of ITGB3, CXCR4, and DLL4 and upregulate their expressions. Besides, FOXC2 can also activate the PI3K/AKT signaling and promote the angiogenesis of GBM. Our study identified a novel molecular mechanism for M2 GAM-derived exosomal circKIF18A participating in GBM angiogenesis via targeting FOXC2. This may provide a novel treatment target to improve the outcomes for anti-angiogenic therapies in GBM.