Hypoxia-Induced Reactivity of Tumor-Associated Astrocytes Affects Glioma Cell Properties

Abstract

Glioblastoma is characterized by extensive necrotic areas with surrounding hypoxia. The cancer cell response to hypoxia in these areas is well-described; it involves a metabolic shift and an increase in stem cell-like characteristics. Less is known about the hypoxic response of tumor-associated astrocytes, a major component of the glioma tumor microenvironment. Here, we used primary human astrocytes and a genetically engineered glioma mouse model to investigate the response of this stromal cell type to hypoxia. We found that astrocytes became reactive in response to intermediate and severe hypoxia, similarly to irradiated and temozolomide-treated astrocytes. Hypoxic astrocytes displayed a potent hypoxia response that appeared to be driven primarily by hypoxia-inducible factor 2-alpha (HIF-2α). This response involved the activation of classical HIF target genes and the increased production of hypoxia-associated cytokines such as TGF-β1, IL-3, angiogenin, VEGF-A, and IL-1 alpha. In vivo, astrocytes were present in proximity to perinecrotic areas surrounding HIF-2α expressing cells, suggesting that hypoxic astrocytes contribute to the glioma microenvironment. Extracellular matrix derived from hypoxic astrocytes increased the proliferation and drug efflux capability of glioma cells. Together, our findings suggest that hypoxic astrocytes are implicated in tumor growth and potentially stemness maintenance by remodeling the tumor microenvironment.

The Effect of the Classical TSPO Ligand PK 11195 on In Vitro Cobalt Chloride Model of Hypoxia-like Condition in Lung and Brain Cell Lines

“…In our present study, using ROS generation as an indicator of oxidation, PK 11195 exhibited a potent inhibitory effect on CoCl 2 -induced cardiolipin peroxidation. These findings further strengthen the previously published data on U118MG cells as a model for glioma [ 16 ].…”

“…In this study, necrosis/apoptosis assay was used to assess the harmful effects of CoCl 2 on cell viability (apoptotic or necrotic cell death). Following exposure to CoCl 2, H1299 cells showed significant elevation in apoptosis levels, but not necrosis, as was reported previously [ 16 , 19 , 21 ]. Notably, another study performed by our group using cigarette smoke as a hypoxia-causing agent leading damage to cellular hypoxia, also resulted in apoptotic cell death, rather than necrotic cell death [ 19 , 21 ].…”

“…We used an established in vitro model of pulmonary hypoxia-like condition by exposing the H1299 lung cancer cell line to cobalt chloride and investigated the protective effects of TSPO ligands in this cellular model [ 16 , 17 ]. According to our data, lung derived cells exposed to various concentrations of CoCl 2 , ranging from 0.1 mM to 1 mM, for 24 h led to a dose-dependent reduction in cell viability with maximal toxicity at 1 mM as compared to a control group.…”

“…CoCl 2 (Sigma-Aldrich, Rehovot, Israel) was prepared at the concentrations required for each specific experiment and applied to the CoCl 2 -treated groups for 24 h [ 16 , 17 ].…”

“…TSPO knockdown using siRNA, or its blockade using the TSPO antagonist PK11195, significantly counteracted the CoCl 2 -induced effects [ 9 ]. Several studies investigated CoCl 2 -induced hypoxia using different cellular models [ 16 , 17 , 18 ]. Our research group evaluated the effects of TSPO ligands on CoCl 2 -induced cytotoxicity, on the human H1299 lung cancer, and glial cell line.…”