Abstract 2958: Transcriptome analysis of astrocytoma versus non-neoplastic human microglia
Authors: Galatro Thais Fernanda , Lerario Antonio M. , Oba-Shinjo Sueli M. , Eggen Bart J. , Marie Suely K. 
Published: July 2017

Abstract
Diffuse gliomas are primary brain tumors characterized by infiltrative growth and high heterogeneity, rendering the disease mostly incurable. Advances in genetic analysis revealed that molecular alterations predict patients’ overall survival and clinical outcome. However, glioma tumorigenicity is not exclusively caused by its genetic alterations. The crosstalk between tumor cells and the surrounding microenvironment plays a crucial role in modulating glioma growth and aggressiveness. The most abundant non-neoplastic cells in this microenvironment belong to the myeloid lineage, comprising CNS-resident microglia and infiltrating monocytes/macrophages (iTAMs). Understanding the dynamics between tumor and myeloid cells and the changes leading to pro-tumorigenic activation of innate immunity cells would elucidate potential treatment alternatives.
Microglia were isolated from the parietal cortex of 16 autopsy samples of cognitively intact humans (non-neoplastic, NN) and from 6 glioma samples (three GBMs, one anaplastic astrocytoma and two low grade astrocytoma, TU-glia), and their mRNA expression profile was determined by deep sequencing. The comparison of these transcriptome datasets provided an incomparable landscape of the crosstalk between immune and tumor cells.
Our preliminary analysis shows that differences between NN microglia and TU-uglia go beyond inflammation specific genes. While there is overexpression of anti-inflammatory markers (CD163, IL2RA, CXCL2 and TGFB1), implying pro-tumorigenic characteristics, there is also high expression of genes indicative of an acute, pro-inflammatory response, such as IL1B, CCL5, CCR7 and TNFA. Further analysis showed that TU-uglia expressed high levels of genes related to extracellular matrix (ECM) remodeling, such as fibronectin (FN1) and tenascin-C (TNC), as well as their ligands (ITGA4 and ITGB1), indicating that microglia, and not tumor cells, might be the main source for those proteins in the tumor microenvironment. We were also able to collect one sample of iTAMs from a GBM case. Despite not providing a significant number for statistical analysis, we can already see major differences in gene expression between this sample and our TU-uglia cohort. We identified surface receptors differentially expressed between both cell types (i.e.: ROBO1 and PDGFRA for TU-uglia, MARCO and MET for iTAMs), as well as transcription factors associated with stemness and proliferation, such as KLF4, SOX2 and OCT4 (the last two exclusive for TU-uglia). These results demonstrate that different activation signaling pathways occur within the same tumor sample. Microglia and iTAMs are subject to a number of signals from different clones of tumor cells, driving different responses along the progression of the disease, increasing its tumorigenicity. Better knowledge of this dynamics will help improve our understanding of gliomas and alternative treatment options.
Citation Format: Thais Fernanda Galatro, Antonio M. Lerario, Sueli M. Oba-Shinjo, Bart J. Eggen, Suely K. Marie. Transcriptome analysis of astrocytoma versus non-neoplastic human microglia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2958. doi:10.1158/1538-7445.AM2017-2958