PATH-29. COMPARATIVE ANALYSIS OF DNA METHYLATION PROFILES ASSOCIATED WITH IDH-WILDTYPE GLIOMA AND GLIONEURONAL TUMOR SUBTYPES
Abstract DNA Methylation profiles are highly robust and reproducible as a classification tool. Less is understood regarding the methylation differences that exist among gliomas and glioneuronal tumors. To address this, we analyzed differentially methylated probes (DMPs) of gliomas and glioneuronal tumors compared to normal brain white matter controls. After filtering (Δbeta >0.3, logFC >±1) of significant probes we observed that low grade glioma/glioneuronal tumors (LGGs) had significantly fewer DMPs (Hyper/Hypo) as compared to GBMs. For example, posterior fossa pilocytic astrocytomas (PA’s) showed 2861 DMPs (1916 hypo/945 hyper) versus 9653 for GBM-RTKI ((6563/3090) respectively, while tumors such as PXA and anaplastic PA showed intermediate changes between LGG’s and GBMs. Hypomethylated and hypermethylated probes were analyzed for gene ontology and KEGG pathway enrichment, with LGG subtypes showing hypomethylated probes/genes associated with cell adhesion, blood vessel development and viral infection (P-value = 10-7). In contrast, hypomethylated probes in GBM subtypes were enriched for plasma membrane and cell periphery gene ontologies (P-value = 10-52). With respect to hypermethylated probes, LGG subtypes showed enrichment for myelination, glial cell differentiation and sphingolipid metabolism (P-value = 10-5) while DNA-binding transcription factor activity was seen in GBM subtypes (P-value=10-35). Examples of the most significantly hypermethylated genes in GBM included the transcription factors, GATA3 and PAX9. Intermediate-grade gliomas such as anaplastic PA and PXA showed enrichment of hypermethylated genes similar to GBM, but of lower significance (P-values = 10-6 and 10-4). Overall, understanding of cancer-associated DNA methylation changes in glioma subtypes suggests a hierarchy of biological changes that may underlie the pathogenesis of these tumors and interestingly, highlight tumor types such as PXA and anaplastic PA as having intermediate methylation changes, between benign LGG and GBM. Hypermethylation of transcription-factor genes will be investigated in GBM and compared with changes in gene expression to understand possible roles in the pathogenesis.