Dottorato in MEDICINA MOLECOLARE

Titolo della tesi: “MicroRNAs expression profile In Meningioma 1 (MN1) gene altered astroblastoma”

Astroblastoma is an uncommon glial brain tumour arising more frequently in young patients (median age 15 years), with a female predominance and unclear clinical behaviour and outcome. Histological aspects are common to other brain tumours, but the diagnostic molecular alteration is the rearrangement of meningioma 1 (MN1) gene. We collected a cohort of 14 tumour samples histologically defined as astroblastoma. The DNA methylation analysis of this group showed that only 8 cases harboured the MN1 rearrangement characteristic of astroblastoma. The 6 remaining samples were 1 ependymoma RELA fusion positive, 1 glioblastoma mesenchymal subtype, 1 diffuse midline glioma H3 K27M mutant, 1 pleomorphic xanthoastrocytoma / advanced stage ganglioglioma, 1 CNS high grade neuroepithelial tumour with BCOR alteration, 1 glioblastoma RTK II subtype. Considering the importance of microRNAs (miRNAs) as regulators of gene expression and their implication in several biological processes, the expression pattern of miRNAs in the class of MN1-altered astroblastoma was determined employing Nanostring technology. The results identified 39 deregulated miRNAs in our cohort respect to normal brain tissue. In order to understand whether epigenetic factors are responsible for the aberrant expression of miRNAs, the methylation status of the promoters of 32/39 deregulated miRNAs was analysed. An epigenetic regulation on 14/32 miRNAs was observed. Concerning the hypothesis of a genomic alteration as a reason for the abnormal expression of the remaining 18/32 deregulated miRNAs, the Copy Number Variation (CNV) of tumour samples was analysed. No alteration was found on chromosome locus where miRNAs were mapped. Finally validated targets of the 32 deregulated miRNAs were identified using R open-source software. Gene Ontology (GO) enrichment analysis for the Biological Processes (BPs) category and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathways provided a correlation between miRNA target genes and MN1-altered astroblastomas. A relationship between pathways of deregulated miRNAs and clinical and pathological characteristics of MN1-altered astroblastomas was hypothesized. Notably, these findings might offer therapeutic targets and prognostic indications for patient survival.