Abstract
Abstract
BACKGROUND
Hotspot mutations in the IDH genes serve as tumor-initiating events that define a subset of adult diffuse glioma that can further be divided into either oligodendroglioma or astrocytoma subtypes. Despite standard treatment, IDH-mutant gliomas inevitably recur. Previous studies suggest that therapeutic resistance may result from a combination of intratumoral cellular heterogeneity, epigenetic evolution, and acquired genetic alterations. However, how these multilayered molecular features interact to influence the evolutionary paths of IDH-mutant gliomas remains incompletely understood.
MATERIAL AND METHODS
To chart this evolution, 75 glioma samples were longitudinally collected from 35 patients (n = 13 oligodendroglioma, n = 22 astrocytoma) and profiled using single nucleus RNA sequencing, ATAC sequencing, and bulk DNA sequencing.
RESULTS
Analysis of 331,016 nuclei (snRNA) revealed eight tumor microenvironment cell types and five pan-IDH-mutant malignant cellular states. The malignant states were distributed along a cellular hierarchy of stem-like populations (neural progenitor cell-like, oligodendrocyte progenitor cell-like, and undifferentiated) and more differentiated populations (mesenchymal-like and astrocyte-like) with cycling cells enriched in the stem-like populations. Joint open chromatin accessibility data (snATAC) was available for a subset of malignant cells (71,088 nuclei) and state-specific differentially accessible peaks supported that these states are epigenetically encoded. Across both subtypes, higher tumor grade was associated with reduced malignant cell differentiation and increased cycling populations. Between the two time points, we identified that there was a longitudinal increase in the cycling, undifferentiated, and mesenchymal-like populations with a corresponding decrease in the astrocyte-like population. Longitudinal genetic analysis revealed that 19 of 35 tumors acquired at least one of the following genetic alterations: treatment-associated hypermutation, cell cycle alteration, or large changes in copy number alterations. Importantly, tumors that acquired these key genetic alterations demonstrated significant shifts towards reduced differentiation and increased cycling populations while those tumors that did not had more stable malignant profiles.
CONCLUSION
Collectively, our results suggest a common cellular hierarchy across IDH-mutant gliomas with a shift towards reduced differentiation, increased cycling populations during disease progression that is driven by acquired genetic alterations.