Abstract
Glioblastoma (GBM) is the most common and aggressive primary brain tumor in adults, with a median
life expectancy of only 15 months and a recurrence rate approaching 100%. Tumors in contact with the lateral
ventricles (LVs) account for over 50% of GBM cases and result in worse patient prognosis and increased distal
recurrence. Despite worse prognosis for patients, there are no significant changes in gene or protein
expression signatures in the bulk tumor signature when stratifying samples based on LV contact. Therefore,
patient outcome may be due in part to the interaction of GBM with the subventricular zone (SVZ)
microenvironment. The SVZ is located along the lateral walls of the LVs and contains dynamic neural stem
cells (NSCs) that contribute to brain repair and homeostasis throughout life. Through my preliminary
experiments, I have developed a novel rodent model reproducing the increased proliferation and decreased
survival of patients with LV-proximal tumors. I have observed that culturing patient GBM cells with human
NSCs increases the levels of proliferation and malignant protein expression. Additionally, I have observed
decreased levels of NSC proliferation and increased stem gene expression when stimulated with GBM cells.
I hypothesize that GBM alters the native NSC proteome and secretome, ultimately resulting in
increased tumor malignancy. My long-term goal is to determine whether SVZ factors are responsible for the
worse prognosis of LV-associated GBM and to target this interaction therapeutically. To evaluate this
hypothesis, I propose the two specific aims. In specific aim 1, I will characterize changes in the NSC-specific
proteome and secreted proteins in response to LV-proximal GBM. This will be done using the L274G mutant
methionyl-tRNA synthetase (MetRS*) protein labeling system in vitro and in vivo. For in vitro studies, human
NSCs will be transduced to express MetRS* and co-cultured with patient-derived GBM cells. In vivo, the
mutant MetRS* will be expressed under the Nestin promoter upon induction with tamoxifen, leading to specific
proteomic labeling in NSCs. For both approaches, lysate proteins and secreted factors will be isolated and
analyzed by tandem mass spectrometry, and identified targets will be confirmed using western blot, ELISA,
and immunohistochemistry. In specific aim 2, I will determine the effect of NSC-secreted components on GBM
malignancy. I will co-culture GBM cells with their NSC counterparts and measure GBM malignancy through
changes in proliferation, migration, and stemness. I will also co-inject GBM cells with NSC secreted factors into
a mouse model and analyze brains for tumor size, proliferation, cell invasiveness, and survival outcome.
Through the identification of novel, NSC-derived proteomic targets that promote GBM, this work will contribute
to my long-term goal of determining whether SVZ-derived factors are responsible for the worse prognosis of
LV-proximal GBM and to target this interaction therapeutically.