Overexpression of miR-504 in glioma stem cells inhibits the oncogenic potential and the crosstalk of these cells with microglia via exosomal delivery
Rand D, Cazacu S, Hong X, Xiang C, She R, Datta I, Poisson L, and Brodie C. Overexpression of miR-504 in glioma stem cells inhibits the oncogenic potential and the crosstalk of these cells with microglia via exosomal delivery. J Extracell Vesicles 2018; 7:113.
J Extracell Vesicles
Background: Glioblastoma (GBM) is a highly aggressive tumour that exhibits resistance to therapy and poor prognosis. A small subpopulation of glioma stem cells (GSCs) has been implicated in radio-resistance and tumour recurrence. Mesenchymal transformation of GBM and GSCs is associated with aggressive phenotypes, radiation resistance and positive regulatory interaction with microglia. Methods: Here, we analysed miRNAs associated with the stemness and mesenchymal transformation of GSCs using miRNA microarray analysis of these cells compared with human neural stem cells (NSCs) and mesenchymal stromal cells (MSCs). Self-renewal, stemness microglia activation and exosomal delivery were studied. Data were analysed using ANOVA or a Student's t-test with correction for data sets with unequal variances. Results: We identified gene clusters associated with glioma cell invasiveness, axonal guidance and TGF-beta signaling. miR-504 was significantly downregulated in GSCs; its expression was decreased in GBM compared with normal brain specimens and was further lower in the mesenchymal subtype. The effects of miR-504 on the stemness, mesenchymal transformation of GSCs and their interaction with microglial cells were studied. Overexpression of miR-504 inhibited the self-renewal, migration and the expression of mesenchymal markers in GSCs. The inhibitory effect of miR-504 was partly mediated by upregulating the tumour suppressor miR-145. In addition, miR-504 targeted Grb10 and EGFR2, which act as oncogenes in GSCs and GBM. Using novel reporters and imaging methods we demonstrated that overexpression of miR-504 in GSCs resulted in its delivery by GSC-secreted exosomes to microglia and in the abrogation of the GSC-induced polarization of microglia to M2 phenotype. Finally, miR-504 overexpression inhibited xenograft growth and prolonged the survival of mice harbouring GSC-derived xenografts. miR-504 was detected in high levels in circulating serum exosomes of xenografted mice. Summary/Conclusion: We identified the miR-504/miR145/CTGF and miR-504/Grb10/Egr1 pathways as important regulators of the mesenchymal transformation of GBM. Overexpression of miR-504 exerts antitumour effects in GSCs as well as bystander effects on the polarization of microglia, and possibly also on peripheral immune responses, via exosomal delivery.