The blood-brain barrier (BBB) constitutes a critical barrier for the maintenance of central nervous system homeostasis. Brain microvascular endothelial cells line the vessel walls and express tight junction (TJ) complexes that restrict paracellular passage across the BBB, thereby fulfilling a crucial role in ensuring brain function. Hypoxia, an impaired O2 delivery, is known to cause BBB dysfunction but the mechanisms that drive this disruption remain unclear. This study discloses the relevance of the master regulator of the hypoxic response, hypoxia-inducible factor-1 (HIF-1), in hypoxia-induced barrier disruption using the rat brain endothelial cell line RBE4. Hypoxic exposure rapidly induced stabilization of the HIF-1 oxygen-dependent alpha subunit (HIF-1α) concomitantly with BBB impairment and TJ disruption mainly through delocalization and increased tyrosine phosphorylation of TJ proteins. Similar observations were obtained by normoxic stabilization of HIF-1α using CoCl2 , deferoxamine, and dimethyloxalylglycine underlining the involvement of HIF-1 in barrier dysfunction particularly via TJ alterations. In agreement inhibition of HIF-1 stabilization by 2-methoxyestradiol and YC-1 improved barrier function in hypoxic cells. Overall our data suggests that activation of HIF-1-mediated signaling disrupts TJ resulting in increased BBB permeability. J. Cell. Physiol. © 2013 Wiley Periodicals, Inc.