Thursday, April 3, 2025
4/3/2025
Regulation of Angpt1 and DIPG blood-brain barrier integrity by H3K27M mutations - Malignant gliomas encompass a diverse set of diseases, including pediatric and adult high-grade gliomas. Recent genomic profiling techniques have advanced our understanding of these tumors by identifying molecular subtypes and recurrent mutations, yet treatment options remain limited. The blood-brain barrier (BBB) is commonly cited as a major factor in treatment resistance since the majority of drugs and small molecules display limited BBB penetration. Advancing our understanding of the cellular and molecular mechanisms that regulate brain tumor BBB function will be crucial to improve treatment strategies and outcomes for patients. Our recent work demonstrated that BBB integrity can be dictated by brain tumor subtype specific mutations. In preliminary studies using diffuse intrinsic pontine glioma (DIPG) and cortical high-grade glioma (HGG) mouse models we have created by in utero electroporation (IUE), we identified differences in Angiopoietin1 (Angpt1) expression, a high affinity agonist of the endothelial Tie2 receptor. The Angpt1-Tie2 signaling axis plays a key role in vascular response to injury, but its endogenous expression and function in brain tumors not been thoroughly evaluated. Preliminary data in human tumors and mouse models reveal Angpt1 expression is elevated in glial brain tumors, and displays differences within glioma subtypes. These differences mirror Angpt1 expression patterns we have found in normal brain development, suggesting expression in gliomas may be linked in part to cell state programs or upstream signaling pathways that promote particular cell states. Initial experiments in IUE DIPG mouse models have shown that overexpression of the Tie2 antagonist Angpt2, or knockout of Angpt1, result in vascular alterations. These findings form the basis of our hypothesis that Angpt1 is differentially expressed in gliomas, and that its endogenous expression participates in regulating high-grade glioma blood-brain barrier integrity. To test our hypothesis, we propose the following aims: (1) Define the expression and function of Angpt1 in high- grade glioma blood-brain barrier integrity. In this aim we will (1A) determine the cellular expression pattern of Angpt1 within gliomas, (1B,C) perform a detailed analysis of BBB, vascular phenotype and transcriptional signatures to determine the role of endogenous Angpt1 in glioma BBB integrity, and (1D) assess how differences in endogenous Angpt1 expression between glioma subtypes impacts current therapeutic strategies that target this signaling axis. Aim 2 will determine the mechanisms that regulate Angpt1 expression. We will examine the influence of cell lineage states and upstream signaling determinants, along with applying unbiased genome level screens to define regulators of Angpt1. The proposed set of experiments will significantly improve our understanding of how brain tumors regulate BBB integrity, and the dynamic interactions that occur between brain tumor cells and their microenvironment. Taken together, the results and tools generated will yield new insights into the expression and function of Angpt1, with broader implications relevant to other brain cancers and neurological disorders that involve vascular alterations and BBB dysfunction.
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