Disrupting the TGF-β-regulated epithelial-mesenchymal transition, apoptotic and autophagic phenotypes of 3D glioblastoma spheroids via glycolytic inhibition

Abstract

Aim: Glioblastoma (GBM), a rare, highly aggressive and chemoresistant brain cancer, exhibits profound metabolic plasticity that relies, in part, on aberrant transforming growth factor-β (TGF-β) signaling. Such plasticity was recently associated with TGF-β-regulated apoptosis and autophagy. Here, we questioned whether TGF-β-regulated apoptotic/autophagic phenotypes are recapitulated in a preclinical in vitro 3D spheroid culture model of human U87 GBM-derived cells, and how metabolic alterations affect such phenotypes.

Methods: 3D U87 spheroids were cultured using the hanging drop method. Western blotting was used to assess protein expression, while RT-qPCR was used to assess gene expression levels.

Results: 3D spheroids exhibited decreased AKT phosphorylation, and increased TGF-β, fibronectin, and Smad2 phosphorylation, indicative of both cell death signaling and epithelial-mesenchymal transition molecular signatures. 2-Deoxy-D-glucose (2DG), a glycolytic inhibitor, depleted ATP dose-dependently (30–300 μM) and prevented those increases both at the protein and transcriptional levels. This was also observed in 3D spheroids upon TGF-β transient siRNA-mediated silencing or when TGF-βR1 kinase activity was inhibited by galunisertib. Transcriptomic profiling revealed shared upregulation of apoptosis-related BCL2, CASP7, FAS, FASLG, GADD45A) and autophagy-related ATG7, ATG16L1, IRGM, PIK3C3, ULK1) genes in response to TGF-β or upon 3D spheroid formation. 2DG, transient silencing of TGF-β, or galunisertib treatment prevented these increases.

Conclusions: 3D spheroids require ATP and a TGF-β/TGF-βR1 autocrine signaling axis to recapitulate the apoptosis/autophagy phenotypes. Combining glycolysis inhibition with TGF-β signaling inhibition could offer a promising therapeutic strategy for this rare and lethal brain cancer.

Keywords

glioblastoma / TGF-β / epithelial-to-mesenchymal transition / 2-deoxy-D-glucose / glycolytic inhibition / apoptosis / autophagy

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