ME-07 * INFLUENCE OF REGIONAL MICROENVIROMENT AND ASTROCYTE HETEROGENEITY ON ASTROCYTOMA DEVELOPMENT

Abstract

The role of the local microenvironment during early astrocytoma development remains elusive. We previously showed that Rb and Pten inactivation and Kras activation (TRP) transforms Gfap+ astrocytes and induces low-grade astrocytoma tumorigenesis throughout the adult brain. To confirm that astrocytes are the cell of origin, we targeted them using an alternative astrocyte-specific promoter, Glast. In the absence of oncogenic mutations, genetic lineage tracing with Glast-CreER; floxed TdTomato mice produced recombination in 8-38% of Gfap/Blbp+ astrocytes in the cortex, diencephalon, brainstem, and olfactory bulb. EdU labeling showed 0.05). Both CreER driver and brain region significantly affected astrocyte growth rate (ANOVA P < 0.0003). In both models, transformed astrocytes maintained Gfap/Blbp expression, gained expression of the stem cell marker Nestin, and formed increasingly dense perineuronal satellites over time. Ki-67 labeling showed clonal expansion, as hypercellular foci with 11-fold higher proliferation relative to less-cellular areas of tumor developed by 16 weeks. Glast-, but not hGFAP-driven tumors contained dividing, but untransformed (TdTomato;T121−) BLBP+ astrocytes, IBA1+ microglia, and PDGFRα+ oligodendrocyte progenitors (OPC). Proliferating microglia (6-0%) and OPC (18-5%) decreased over time, while dividing, untransformed astrocytes increased (57-85%). These findings support the notion that regional microenvironment and astrocyte heterogeneity contribute to astrocytoma development. The Glast-TRP model may be useful in dissecting the role of regional microenvironment during astrocytoma tumorigenesis.