Dissertations, Theses, and Capstone Projects

Date of Degree

6-2025

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy

Program

Biology

Advisor

Patrizia Casaccia

Advisor

Konstantino Krampis

Committee Members

Peter Canoll

Weigang Qiu

Carmen Melendez-Vasquez

Subject Categories

Cancer Biology | Computational Biology | Molecular and Cellular Neuroscience

Keywords

Cancer biology, Glioma, Proneural Glioma, single nuclei RNA-seq, histone proteomics

Abstract

Gliomas are the most devastating adult brain tumors characterized by poor survival rate and limited options for treatment. Previous studies have shown that they are very heterogeneous and can be further sub-classified based on their transcriptional signature and the presence of specific mutations. One such subtype, is the “proneural glioma”, which is characterized by the enrichment in oligodendrocyte progenitor cell (OPC) transcripts and mutations in genes encoding for the tumor suppressor P53 (Trp53) and for Platelet Derived Grow Factor (PDGF) signaling. Since OPCs are the most abundant proliferative population in the adult brain, in this thesis we asked how these genetic mutations change the properties of normal cells and render them prone to the generation of proneural gliomas. First, we noted that OPCs carrying only the Trp53 gene deletion (p53n OPC) do not form tumors when injected in recipient mice, while OPCs with both Trp53 deletion and PDGF-BB overexpression (BB-p53n) result in tumors histologically resembling the appearance of human gliomas. We then used a reductionist approach and discovered that the BB-p53n OPCs display growth properties such as clonogenic capacity and loss of contact-inhibition, which more closely resembled the growth of glioma cells than p53n OPCs. Unbiased histone proteomics and transcriptomic analysis further revealed higher levels of specific histone post-translational modifications (e.g. H3K27me3) and higher transcript levels of genes related to proliferation and cell adhesion in the BB-p53n cells compared to p53n. Pharmacological inhibition of H3K27 trimethylation partially reverted the transcriptome and growth characteristics of BB-p53n OPCs to those of the p53n cells, suggesting that the deposition of the histone H3K27me3 mark in p53 null OPCs favors the early stages of their transformation. To further understand how the BB-p53n OPCs generate large tumors when injected into the brain of recipient mice, we then performed single nuclei RNA sequencing on nuclei isolated at early and late-stages of tumor formation. We found that late-stage tumors were characterized by the presence of an “OPC-like” and a “stemness” transcriptional signature compared to early-stage tumors, thereby suggesting that the double mutant OPCs may de-differentiate into more pluripotent cells after interacting with the local environment in the brain. This evolving state expands a population of slow-cycling, invasive glioma stem cells forming in late-stage tumors. Additionally, the late tumors were characterized by transcriptional evidence of increased glutamatergic synapse formation, suggesting a role of neuronal synaptic connections in favoring the progression of early to late-stage gliomas.

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