D-Serine facilitates aggressive migration and stemness of recurrent glioblastoma cells by interacting with host endothelial cells

Abstract

Glioblastoma (GBM) is the most aggressive primary brain tumor in adults, with recurrence driven by therapy-resistant, stem-like tumor cell populations and maladaptive interactions with the tumor microenvironment. Despite aggressive multimodal treatment, recurrent GBM (rGBM) remains consistently lethal. While glutamatergic signaling has been implicated in GBM through excitotoxic effects on neural cells, its role in tumor/endothelial communication is not fully understood. Here, we identify a previously unrecognized tumor/vascular signaling axis in which rGBM-derived D-serine, along with glutamate, activates endothelial NMDA receptors (eNMDARs) to promote tumor aggressiveness. Using patient-derived rGBM models, endothelial co-culture systems, and intracranial xenografts, we show that rGBM cells upregulate serine racemase (SRR) and secrete D-serine into the tumor microenvironment. Endothelial interaction reprograms rGBM transcriptional states toward angiogenic, inflammatory, and pro-survival states while suppressing differentiation-associated pathways. Functional assays demonstrate that extracellular D-serine is required for endothelial-mediated enhancement of rGBM migration, invasion, and self-renewal, as enzymatic depletion of D-serine reverses these phenotypes and reduces expression of mesenchymal and stemness markers. Pharmacologic inhibition or genetic deletion of SRR impairs tumor growth, reduces vascular density, and prolongs survival in vivo. Spatial transcriptomic analysis further reveals that loss of SRR disrupts angiogenic, hypoxic, migratory, and proliferative gene programs within tumor regions. Importantly, endothelial-specific deletion of the NMDAR subunit GluN1, which binds D-serine, attenuates rGBM/endothelial crosstalk. These findings define SRR-driven D-serine signaling as a key driver of the rGBM vascular niche and identify endothelial glutamatergic signaling as a therapeutic vulnerability. Targeting this signaling axis pathway offers a novel strategy to disrupt tumor/vascular crosstalk in recurrent glioblastoma.