Glioblastoma (GBM) is the most aggressive primary brain tumor in adults, marked by rapid proliferation, diffuse infiltration, and therapeutic resistance. Increasing evidence suggests that neural stem cells (NSCs) residing in the subventricular zone (SVZ) may act as cells of origin for glioblastoma, due to their self-renewal capacity and long-term proliferative potential. Recent studies show that human SVZ NSCs can carry low-frequency driver mutations identical to those in the tumor, contributing to initiation through clonal expansion and migration. In this context, microRNAs (miRNAs), key post-transcriptional regulators of gene expression, play essential roles in NSC biology and gliomagenesis, influencing proliferation, differentiation, migration, and apoptosis. While many individual miRNAs are known to be deregulated in GBM, the broader consequences of disrupting the entire miRNA pathway remain unclear.
The aim of my PhD project was to explore the impact of miRNA pathway inactivation during GBM development in vivo. I used a genetically engineered mouse model developed in our lab, enabling postnatal induction of GBM from SVZ NSCs combined with conditional inactivation of Dicer, the enzyme essential for miRNA biogenesis. Whole-brain clearing and 3D imaging revealed impaired tumor growth upon Dicer loss. Spatial analysis further identified two compartments: a dense tumor core and distal elements, small invasive cell clusters detached from the bulk. Dicer-deficient tumors displayed reduced core volume and an increased proportion of distal elements, indicating altered growth dynamics and tumor architecture. In addition, they showed enhanced invasiveness, with tumor cells diffusely dispersing beyond the main mass and aligning along blood vessels. To better characterize these features, I performed immunofluorescence on brain sections. This confirmed reduced tumor cell proliferation and widespread dispersion beyond the tumor bulk, with perivascular localization significantly enriched in Dicer deficient tumors. Phenotypic analysis revealed that tumor cells largely expressed stem/progenitor markers. To complement the in vivo data, I established primary cultures from tumor tissue. In vitro assays suggested increased migratory behavior in Dicer-deficient cells, consistent with their invasive profile. Ongoing transcriptomic analyses aim to uncover the molecular programs altered by miRNA loss and their link to tumor architecture and invasion.
In conclusion, this study provides a novel in vivo framework to investigate the impact of global miRNA pathway disruption on gliomagenesis, offering new insights into the regulation of GBM development and invasive behavior.