Abstract
BackgroundLittle is known about the role of glial host cells in brain tumours. However, supporting stromal cells have been shown to foster tumour growth in other cancers.MethodsWe isolated stromal cells from patient-derived glioblastoma (GBM) xenografts established in GFP-NOD/scid mice. With simultaneous removal of CD11b+ immune and CD31+ endothelial cells by fluorescence activated cell sorting (FACS), we obtained a population of tumour-associated glial cells, TAGs, expressing markers of terminally differentiaed glial cell types or glial progenitors. This cell population was subsequently characterised using gene expression analyses and immunocytochemistry. Furthermore, sphere formation was assessed in vitro and their glioma growth-promoting ability was examined in vivo. Finally, the expression of TAG related markers was validated in human GBMs.ResultsTAGs were highly enriched for the expression of glial cell proteins including GFAP and myelin basic protein (MBP), and immature markers such as Nestin and O4. A fraction of TAGs displayed sphere formation in stem cell medium. Moreover, TAGs promoted brain tumour growth in vivo when co-implanted with glioma cells, compared to implanting only glioma cells, or glioma cells and unconditioned glial cells from mice without tumours. Genome-wide microarray analysis of TAGs showed an expression profile distinct from glial cells from healthy mice brains. Notably, TAGs upregulated genes associated with immature cell types and self-renewal, including Pou3f2 and Sox2. In addition, TAGs from highly angiogenic tumours showed upregulation of angiogenic factors, including Vegf and Angiopoietin 2. Immunohistochemistry of three GBMs, two patient biopsies and one GBM xenograft, confirmed that the expression of these genes was mainly confined to TAGs in the tumour bed. Furthermore, their expression profiles displayed a significant overlap with gene clusters defining prognostic subclasses of human GBMs.ConclusionsOur data demonstrate that glial host cells in brain tumours are functionally distinct from glial cells of healthy mice brains. Furthermore, TAGs display a gene expression profile with enrichment for genes related to stem cells, immature cell types and developmental processes. Future studies are needed to delineate the biological mechanisms regulating the brain tumour-host interplay.
Highlights
Little is known about the role of glial host cells in brain tumours
flow cytometry (FCM) analysis of 3 GBM xenografts using antibodies against a panel of glial markers confirmed that 96% of these cells expressed Glial fibrillary acidic protein (GFAP) and 90% expressed myelin basic protein (MBP) consistent with co-expression of several glial markers, whereas Nestin and O4 were expressed at somewhat lower rates (Additional file 1: Figure S1f)
Green fluorescent protein (GFP)+CD11b−CD31− cells were defined as tumour-associated glial cells (TAGs)
Summary
Little is known about the role of glial host cells in brain tumours. supporting stromal cells have been shown to foster tumour growth in other cancers. Glioblastomas (GBMs) are aggressive brain tumours, characterised by angiogenesis and infiltrative growth [1]. Astrocytes can adapt a spectrum of altered phenotypes [6] in health and disease, in response to changing external cues They may regulate normal brain function by modulating transmission in glial and neuronal cell signalling networks [6]. Numerous studies show that fibroblasts in the tumour microenvironment undergo activation to promote cancer growth [8,9,10]. This activated state is characterised by cell proliferation, release of growth factors and matrix metalloproteinases [11]. Fewer studies have so far addressed whether glial cells and fibroblasts have similar roles in tumour progression
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