The ATP-binding cassette transporters ABCB1 and ABCC1 are not regulated by hypoxia in immortalised human brain microvascular endothelial cells
Background: ATP-binding cassette transporters at the blood-brain barrier are actively regulated upon ischemic stroke in a way that impedes the access of pharmacological compounds to the brain tissue. The luminal endothelial transporter ABCB1 was recently shown to be increased, whereas the abluminal transporter ABCC1 was decreased on ischemic brain capillaries. In vitro studies using epithelial cells suggested that ABCB1 is regulated during hypoxia in a hypoxia-inducible factor (HIF)-1a-dependent way. Methods: In order to investigate whether hypoxia might be responsible for the expression changes of ABCB1 and ABCC1 in the ischemic brain, the immortalised human brain microvascular endothelial cell line hCMEC/D3 was exposed to hypoxia (1%) or anoxia (0%). Cell lysates were analysed by Western blot to detect the protein expression of ABCB1, ABCC1, HIF-1a and HIF-2a. Results: During hypoxia, an accumulation of HIF-1a and HIF-2a was noticed in hCMEC/D3 cells that followed different time kinetics. Both HIF-1a and HIF-2a abundance increased within 4 h of hypoxia. HIF-1a levels decreased to below detection levels within 16 h of hypoxia, whereas HIF-2a remained elevated even after 48 h. No changes of ABCB1 and ABCC1 expression were detected, neither on the mRNA nor protein level. Conclusion: Our data suggests that other factors than hypoxia may be responsible for the expression changes of ATP-binding cassette transporters in the ischemic brain.
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