29 Radiation promotes transdifferentiation of glioblastoma stem cells into vascular cell types

Abstract

Introduction Glioblastoma (GBM) is a lethal, highly vascularized tumour that displays radio- and chemotherapeutic resistance. A subset of tumour cells with robust self-renewing potential, and developmental plasticity, glioblastoma stem cells (GSC) are implicated in tumour recurrence and resistance. Prior studies indicate that the transdifferentiation capacity of GSCs into endothelial cells (EC) and pericytes (PC), the key cellular components of the vasculature is a major determinant of tumour recurrence. This capacity for transdifferentiation into vascular cells is also exhibited by normal astrocytes and neural stem cells (NSCs). Recent work has demonstrated that GSC-derived ECs are predominantly found in recurrent tumours relative to matched primary tumours implying that therapy may promote GSC plasticity. This notion is supported by earlier studies that showed ionising radiation promotes dedifferentiation of non-GSCs into GSCs. Based on these findings, we hypothesised that radiotherapy induces GSC transdifferentiation into ECs and PCs to promote tumour growth and recurrence. Material and methods We used NSCs and patient-derived GBM primary and recurrent tumour lines from different molecular subtypes to test the effects of clinically relevant doses of radiation on GSC conversion to vascular cell types. Quantitative RT-PCR, immunostaining and flow cytometry was used to verify for EC and PC marker expression in radiated and non-radiated cells. Matrigel tube formation and low-density lipoprotein uptake assay were performed to determine if radiated GSCs produce functional vascular cells. Patient tumour lines were transplanted into NOD-SCID mice to generate GBM tumours in vivo . Non-radiated and radiated tumours were immunostained for GSC and vascular markers. Results and discussions Radiation increased both EC and PC marker expression in GSCs irrespective of their molecular subtype and mutation spectrum. Radiated GSCs exhibited tubular network formation on matrigel and uptake of labelled low-density lipoprotein akin to normal ECs indicating that GSCs produce functional endothelial-like cells. Radiation also enhanced GSC conversion to vascular cells in in vivo mouse GBM tumour xenografts. Conclusion Based on these findings, we conclude that radiation-therapy promotes GSC plasticity and transdifferentiation into vascular cells. Ongoing experiments are aimed at determining the functional relevance of radiaiton-induced GSC-derived vascular cells in blood vessel formation and tumour recurrence in vivo .