HIF-1α and HIF-2α: synergistic regulation of glioblastoma malignant progression during hypoxia and apparent chemosensitization in response to hyperbaric oxygen.

Glioblastoma multiforme (GBM), the most malignant type of brain tumour, is regulated mainly by a hypoxic microenvironment. Previous studies have focused mainly on the effects of hypoxia inducible factor-1α (HIF-1α) or hypoxia inducible factor-2α (HIF-2α) alone on GBM, and the results have shown that each factor regulates the malignant progression of GBM, but the single knockout of either gene does not markedly influence this regulation. This study was performed to determine whether HIF-1α and HIF-2α synergistically regulate the malignant progression of GBM. Therefore, HIF-1α and HIF-2α were knocked out in GBM cells. Compared with single HIF-1α- or HIF-2α-knockout and control cells, cells with simultaneous knockout of HIF-1α- and HIF-2α presented significantly greater changes, including differential gene expression and changes in biological process, cellular component, and molecular function GO terms, and enriched KEGG pathways. In addition, dual-knockout cells were induced to transition to G₂/M + S phase, exhibiting the greatest growth rate but the lowest degree of stemness and invasion; after temozolomide (TMZ) treatment, the dual-knockout cells exhibited the greatest rate of apoptosis and lactate dehydrogenase (LDH) release and the lowest growth rate and tumour size and weight, resulting in the longest survival time. Hyperbaric oxygen (HBO) is an effective method for alleviating GBM-related hypoxia; we investigated phenotypic changes in HBO-treated cells and observed increased growth rates but decreased HIF-1α and HIF-2α expression and a decreased degree of stemness. After TMZ exposure, HBO-treated cells presented increased apoptosis rates and LDH release and decreased tumour size and weight, resulting in increased survival. These results suggest that HIF-1α and HIF-2α together exhibit synergistic regulation and play major regulatory roles in GBM. Simultaneous targeting of both HIF-1α and HIF-2α with TMZ is an important method for treating GBM patients and improving patients' prognosis. Therefore, HBO can be used in GBM treatment because of its ability to sensitize cells to chemotherapy via the significant inhibition of both HIF-1α and HIF-2α expression.