The Dynamic UPR Rheostat Orchestrates Single-Cell Plasticity in Glioblastoma.

Glioblastoma (GBM) adapts to microenvironmental stress through the unfolded protein response (UPR), yet whether the three canonical arms IRE1/XBP1, ATF6, and PERK operate as a graded control system at single-cell resolution remains unclear. We reanalyzed publicly available scRNA-seq datasets spanning discovery (n = 871 cells) and validation cohorts (n = 11,877 cells) to quantify arm-specific activities and their coordination across tumor cell states and pseudotime. We introduce arm-resolved metrics, including a Rheostat Index (per-cell dispersion of arm scores) and balance (normalized Shannon entropy), and map dynamic dominance switching (early ATF6 → late IRE1; rare PERK dominance) along lineage trajectories. IRE1 and ATF6 consistently exhibit tight coupling, whereas PERK remains semi-independent, indicating an adaptive division of labor. Rheostat tuning is associated with hypoxia and glycolytic programs and reorganizes across platforms (SMART-seq, 10x) and datasets. To minimize artificial correlations, we employ non-overlapping target sets and validate results using transcription factor activity inference. Statistical analyses prioritize patient-level inference via pseudobulk summaries and random-effects models to mitigate pseudoreplication. Overall, our results support a graded, arm-resolved UPR rheostat that governs GBM cellular plasticity and stress tolerance. These findings motivate therapeutic strategies that rebalance the rheostat attenuating IRE1/ATF6 survival signaling while permitting PERK-mediated death programs rather than globally suppressing the UPR. Our transcriptomic analyses infer arm-resolved coordination; functional validation will require perturbation studies and protein-level readouts.