Altered lipid metabolism marks glioblastoma stem and non-stem cells in separate tumor niches

Abstract

BackgroundGlioblastoma (GBM) is marked by cellular heterogeneity, including metabolic heterogeneity, that varies among cellular microenvironments in the same tumor. Altered cellular metabolism in cancer is well-established, but how lipid metabolism is altered to suit different microenvironmental conditions and cellular states within a tumor remains unexplored.MethodsWe assessed GBM organoid models that mimic the transition zone between nutrient-rich and nutrient-poor pseudopalisading/perinecrotic tumor zones and performed spatial RNA-sequencing of cells to interrogate lipid metabolism. Using targeted lipidomic analysis, we assessed differences in acutely enriched cancer stem cells (CSCs) and non-CSCs from multiple patient-derived models to explore the link between the stem cell state and lipid metabolism.ResultsSpatial analysis revealed a striking difference in lipid content between microenvironments, with lipid enrichment in the hypoxic organoid cores and the perinecrotic and pseudopalisading regions of primary patient tumors. This was accompanied by regionally restricted upregulation of hypoxia-inducible lipid droplet-associated (HILPDA) gene expression in organoid cores and in clinical GBM specimens, but not lower-grade brain tumors, that was specifically localized to pseudopalisading regions of patient tumors. CSCs have low lipid droplet accumulation compared to non-CSCs in organoid models and xenograft tumors, and prospectively sorted lipid-low GBM cells are functionally enriched for stem cell activity. Targeted lipidomic analysis revealed that CSCs had decreased levels of major classes of neutral lipids compared to non-CSCs but had significantly increased polyunsaturated fatty acid production due to high fatty acid desaturase (FADS1/2) expression.ConclusionsOur data demonstrate that lipid metabolism is differentially altered across GBM microenvironments and cellular hierarchies, providing guidance for targeting of these altered lipid metabolic pathways.Key pointsGBM cells in nutrient-poor tumor regions have increased accumulation of lipid droplets.CSCs have reduced lipid content compared to non-CSCs.GBM CSCs and non-CSCs have disparate lipid metabolisms that may be uniquely targetable.Importance of the StudyMetabolic targeting has long been advocated as a therapy against many tumors including GBM, and it remains an outstanding question whether cancer stem cells (CSCs) have altered lipid metabolism. We demonstrated striking differences in lipid metabolism between diverse cell populations from the same patient. These spatially and phenotypically distinct lipid phenotypes occur clinically in the majority of patients and can be recapitulated in laboratory models. Lipidomic analysis of multiple patient-derived models shows a significant shift in lipid metabolism between GBM CSCs and non-CSCs, suggesting that lipid levels may not be simply a product of the microenvironment but also may be a reflection of cellular state. Our results suggest that therapeutic targeting of GBM lipid metabolism must consider multiple separate tumor cell populations to be effective, and we provide a methodologic framework for studying these metabolically diverse cellular populations.

An update on the molecular biology of glioblastoma, with clinical implications and progress in its treatment

“…Aspartate initiates nucleotide biosynthesis, while glutamate provides the C‐skeleton of non‐essential amino acids. Hence, α‐KG DNA repair and demethylating activities become highly inhibited by the overproduction of 2‐HG ( sensitizing IDH‐mutant cells to PARP‐1 inhibition and NAD + deficiency), which also affects the transamination of this compound into keto acids and glutamate [88]. The marginal extensions of astrocyte‐like glioma cells contain high levels of cytosolic citrate, especially in the pseudopodia, where limited access to glucose leads to the uptake of acetate and oxidation, mediated by the ACSS2 enzyme [89].…”

“…Lipid metabolism is also altered in GBM. The marked metabolic heterogeneity of GBMs allows the use of this altered lipid metabolism to mark GBM stem and non‐stem cells in separate tumor niches [88]. GBMs can use ketone bodies and fatty acids to maintain growth, thus allowing their progression during ketogenic diet therapy [90].…”

Modeling nervous system tumors with human stem cells and organoids

“…In contrast, glioma stem cell (GSC) lines appear to select for a subpopulation of tumor cells with more homogeneous transcriptional pro les. Shakya et al used spatial-capture RNA-sequencing to show that GBM organoids not only retain cells at distinct transcriptional states, but also mimics the transition between nutrient-rich (organoid rim) and nutrient-poor pseudopalisading/perinecrotic tumor zones (organoid core) (Shakya et al, 2021). These studies demonstrate that tumor organoids can faithfully mimic the genetics, transcriptional states, and possibly necrotic tumor niche of the parental tumors.…”

WDR5 represents a therapeutically exploitable target for cancer stem cells in glioblastoma

“…Day 0 controls were also collected, stored frozen, and processed in parallel for comparison. At the end of the screen, organoids were regionally labeled with CellTracker CMAC (Molecular Probes) for 2 hours as previously described (Shakya et al, 2021), and single organoids from each screen cohort were spot-checked by confocal microscopy in a compatible dish (MatTek 35 mm glass bottom dish P35G-1.5-10-C) to ensure proper CMAC labeling. Labeled organoids were dissociated and separated by FACS sorting, marked by positivity for constitutive mVenus expression and doxycycline-induced dsRed expression, and sorted into regional populations based upon retention of CMAC regional blue dye.…”