Deciphering the role of pH regulator Slc4a4 in glioma progression - PROJECT SUMMARY. Malignant glioma is a devastating brain cancer with no improvements in prognosis over decades. One key mechanism for glioma progression is the dynamic metabolic communication between the tumor cells and the tumor microenvironment (TME). Although extracellular acidosis is a pathological hallmark of TME, the precise pH-dependent mechanisms underlying glioma metabolic reprogramming remain poorly defined. This proposal’s overarching goal is to discover the genes and pathways regulating glioma metabolism and glioma-vascular crosstalk. This proposal focuses on Slc4a4, a glial-enriched sodium-bicarbonate cotransporter that was previously identified as an intracellular and extracellular pH regulator. Slc4a4-mediated pH regulation is important for glial-vascular interaction after injury, but its role in glioma progression is undefined. To begin addressing this gap in knowledge, I analyzed The Cancer Genome Atlas (TCGA) database and found that high Slc4a4 expression correlates with prolonged survival in glioma patients. Corroboratively, my preliminary data showed that Slc4a4 gain of function (GOF) drastically decreases tumor growth and angiogenesis in patient- derived xenograft and CRISPR-mediated de novo mouse glioma models, which is further complemented by loss- of-function (LOF) studies using glial-specific Slc4a4 knockout mice. These data suggest an inhibitory role of Slc4a4 in glioma and associated aberrant vascular remodeling. Multi-omic profiling of Slc4a4 GOF/LOF mouse glioma found that Slc4a4 negatively regulates the expression of a key lipid binding protein, fatty acid binding protein 5 (FABP5), which is coupled with dysregulated lipid metabolism. Further analysis of the TCGA database showed an inverse expression and survival correlation between Slc4a4 and FABP5 in glioma patients. In an immunocompetent mouse glioma model, FABP5 overexpression reverses Slc4a4’s inhibitory effects on glioma growth, suggesting an antagonistic Slc4a4-FABP5 axis in glioma. Finally, comprehensive transcriptomic profiling of Slc4a4 GOF/LOF glioma revealed dysregulated gene signatures involved in acidic pH response, lipid metabolism, and endothelial function. Based on these preliminary data, my central hypothesis is that Slc4a4 suppresses glioma progression, in part by regulating lipid metabolism and glioma-vascular interaction. To test this hypothesis, I will first define Slc4a4’s role in glioma progression (Aim 1). Next, I will determine how Slc4a4 inhibits gliomagenesis via reprogramming intrinsic glioma lipid metabolism (Aim 2). Upon completion of Aims 1 and 2 in the K99 phase, I will establish Slc4a4’s role in glioma progression and associated lipid dysregulation. In the R00 phase, I will determine how Slc4a4 mediates glioma-vascular interaction with a focus on endothelial metabolism (Aim 3). The proposed studies will define the pH-dependent mechanisms by which glioma hijacks brain vasculature to progress, ultimately establishing an independent research program bridging cancer, glial, and vascular biology to decipher how glioma progresses with potential therapeutic implications.
