Abstract
Background: Glioblastoma multiforme (GBM) is a highly invasive brain tumour, characterized by its ability to secrete factors promoting its virulence. Brain endothelial cells (BECs) in the GBM environment are physiologically modulated. The present study investigated the modulatory effects of normoxically and hypoxically induced glioblastoma U-87 cell secretions on BECs. Methods: Conditioned media (CM) were derived by cultivating U-87 cells under hypoxic incubation (5% O2) and normoxic incubation (21% O2). Treated bEnd.3 cells were evaluated for mitochondrial dehydrogenase activity, mitochondrial membrane potential (ΔΨm), ATP production, transendothelial electrical resistance (TEER), and endothelial tight-junction (ETJ) gene expression over 96 h. Results: The coculture of bEnd.3 cells with U-87 cells, or exposure to either hypoxic or normoxic U-87CM, was associated with low cellular viability. The ΔΨm in bEnd.3 cells was hyperpolarized after hypoxic U-87CM treatment (p < 0.0001). However, normoxic U-87CM did not affect the state of ΔΨm. BEC ATP levels were reduced after being cocultured with U-87 cells, or with hypoxic and normoxic CM (p < 0.05). Suppressed mitochondrial activity in bEnd.3 cells was associated with increased transendothelial permeability, while bEnd.3 cells significantly increased the gene expression levels of ETJs (p < 0.05) when treated with U-87CM. Conclusions: Hypoxic and normoxic glioblastoma paracrine factors differentially suppressed mitochondrial activity in BECs, increasing the BECs’ barrier permeability.
Highlights
Brain endothelial cells (BECs) are the main functional and regulatory components of the blood-brain barrier (BBB)
Using a brain endothelial cell line, which is well described in the literature [27], the current study investigated the effects of coculturing glioblastoma cells (U-87 cells), and treatment with selected concentrations of their supernatant-derived conditioned media on bEnd.3 cells’ mitochondrial activity, and on the permeability across confluent monolayers of bEnd.3 cells (transendothelial electrical resistance (TEER))
At 24 h of exposure to hypoxic U-87 cells or their conditioned media (U-87CM), a significant reduction was observed in bEnd.3 cell viability (p < 0.05) (Figure 2C)
Summary
Brain endothelial cells (BECs) are the main functional and regulatory components of the blood-brain barrier (BBB). They are characterized by the presence of continuous apicolateral zones of structural proteins called tight junctions (TJs) which link the BECs together, significantly limiting the paracellular flux of solutes and the movement of blood-borne cells into the brain. The BBB was reported to be structurally and functionally disrupted by the fast-growing and aggressive brain tumour called glioblastoma multiforme (GBM), referred to as a grade IV astrocytoma [3,4].
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