The Role of miRNAs in Glioma Stem Cell and Glioma Biology

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MicroRNAs that are over expressed in tumors might diminish the level of expression of targeted tumor suppressor genes whereas microRNAs down regulated might repress oncogenic genes contributing to the neoplasic process (oncomirs). Also, miRNAs are frequently located in regions of loss of heterozygosity, regions of amplification, or common breakpoint regions and they have been identified to regulate the expression of tumor-associated genes in several tumors including GBM. Several studies have been published to date analyzing miRNA expression profiles in normal brain and brain tumors using different detection methods. Analysis of murine and human brain miRNA indicated distinctive expression of miR-9,-101,-124 and -132 among others. miRNAs -10b and -21 have been found upregulated in astrocytic tumors appearing the former to work as an oncogene decreasing apoptosis in the malignant cells, whereas miRNA-124 and -137 were down regulated and involved in promotion of neuronal differentiation of brain tumor initiating cells (BTIC) and GBM cell cycle arrest. However, little is know about the expression levels and involvement by target genes regulation of miRNAs in astrocytic brain tumors or BTIC. To better understand the role of miRNAs in the regulation of GBM, we have started generating and comparing the global profile of expression of 365 miRNAs using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) based assays in primary GBM and BTIC derived from them, as well as neuronal stem cells and established glioma cell lines in proliferating and differentiating conditions, to identify specific miRNAs alterations. This analysis is revealing statistically significant downregulation miRNAs in tumors as well as in BTIC vs. non-tumor samples. Furthermore, this expression profile is corroborating BTIC as better models at miRNA level for the study of astrocytic brain tumors than established glioma cell lines, as we have previously described based on their genomic/gene expression profiles. We are also determining the correlation between expression of the miRNAs included in our study and the particular CNA or copy number alterations (deleted/amplified regions) of our tumor/ BTISC samples. miRNAs with non concordant CNA/expression level indicate a possible epigenetic regulation, that could point them as interesting therapeutics targets. This preliminary profile is being used in two ways. On one hand, miRNA analysis will be extended to GMDI collection of brain tumors adding highly valuable information to our already extensive data from them. On the other hand, biological validation of the involvement in gliomagenesis, cell proliferation or invasion of particular miRNAs and their specific targeted genes is being performed in our BTIC in vitro model as well as in vivo mouse models.