Hypoxic and Reoxygenated Microenvironment: Stemness and Differentiation State in Glioblastoma

Abstract

Glioblastoma (GBM) is the most common and aggressive primary malignant brain tumor in adults. Hypoxia is a distinct feature in GBM and plays a significant role in tumor progression, resistance to treatment, and poor outcome. However, there is lack of studies relating type of cell death, status of Akt phosphorylation on Ser473, mitochondrial membrane potential, and morphological changes of tumor cells after hypoxia and reoxygenation. The rat glioma C6 cell line was exposed to oxygen deprivation (OD) in 5 % fetal bovine serum (FBS) or serum-free media followed by reoxygenation (RO). OD induced apoptosis on both 5 % FBS and serum-free groups. Overall, cells on serum-free media showed more profound morphological changes than cells on 5 % FBS. Moreover, our results suggest that OD combined with absence of serum provided a favorable environment for glioblastoma dedifferentiation to cancer stem cells, since nestin, and CD133 levels increased. Reoxygenation is present in hypoxic tumors through microvessel formation and cell migration to oxygenated areas. However, few studies approach these phenomena when analyzing hypoxia. We show that RO caused morphological alterations characteristic of cells undergoing a differentiation process due to increased GFAP. In the present study, we characterized an in vitro hypoxic microenvironment associated with GBM tumors, therefore contributing with new insights for the development of therapeutics for resistant glioblastoma.

FAT1 modulates EMT and stemness genes expression in hypoxic glioblastoma

“…Our lab has previously demonstrated FAT1 to positively regulate the function and activity of HIF‐1α in hypoxic GBM cells . HIF‐1α is known to modulate EMT and stemness genes in GBM . To confirm whether the regulatory effect of FAT1 on the expression of EMT and stemness genes is via HIF‐1α or independent of it, we did siRNA mediated individual/dual knockdown of FAT1 and HIF‐1α in U87MG cells under severe hypoxia.…”

“…We also showed that FAT1 upregulates HIF‐1α expression and functions under hypoxic conditions, thus affecting their metabolic status and invasive properties . Studies have demonstrated that the hypoxic microenvironment with increased HIF‐1α promotes stemness and invasiveness, which favors tumor growth and therapeutic resistance . Here, for the first time, we have demonstrated the role of FAT1 in regulating EMT and stemness properties in GBM under hypoxia, highlighting the importance of FAT1 signaling in aggressive GBM.…”

“…We have earlier reported the role of FAT1 in modulating HIF‐1α expression and function in hypoxic‐glioma cells, where FAT1 knockdown under severe‐hypoxia led to decreased expression and function of HIF‐1α along with decreased migration/invasion of GBM cells . HIF‐1α is known to alter the expression of EMT and stemness genes in GBM . HIF‐1α knockdown led to reduced expression of all EMT markers (Snail/LOX/N‐cad/Vimentin) and the stemness markers (OCT4 and REST) similar to that observed on FAT1 knockdown.…”

“…Glioblastoma is the most aggressive of all brain tumors 1,2 and its resistance to therapy is attributed to the presence of glioma stem cells (GSCs). 1,3,4 The hallmark of GBM is the presence of hypoxic regions around the necrotic core of the tumor with aberrant vascular supply. 3 Hypoxia drives the sustenance and expansion of GSCs in the tumor microenvironment.…”

Colon cancer therapy by focusing on colon cancer stem cells and their tumor microenvironment

“…Inhibition of HIF-2α decreases tumorigenicity in most cancers (Semenza, 2016). Gaelzer et al (2017) showed that hypoxic TME induced glioblastoma dedifferentiation to CD133+ CSCs. Furthermore, hypoxia, as a stress factor in TME, potentially induces and enhances the development of CSCs (Csermely et al, 2015;Kim, Lin, Glazer, & Yun, 2018).…”