Involvement of HIF-1α in MLCK-dependent endothelial barrier dysfunction in hypoxia

The mechanisms of endothelial barrier dysfunction induced by hypoxia are incompletely understood. Hypoxia-inducible factor-1 alpha (HIF-1α) is a key transcription factor partially responsible for hypoxia-related responses, but its role in regulation of hypoxia-induced endothelial barrier dysfunction is unclear. The aim of this study was to determine the molecular mechanism by which HIF-1α regulates endothelial barrier function during hypoxia. Endothelial cell monolayers exposed to normoxia or hypoxia were used for physiological, morphological, and biochemical analyses. The results showed that hypoxia disrupts endothelial barrier function by upregulating protein expression of myosin light chain (MLC) kinase (MLCK) and MLC phosphorylation. Hypoxia also induces HIF-1 activation by increasing HIF-1α expression, nuclear accumulation, DNA binding activity and target gene expression of HIF-1 in endothelial cells. Knockdown of HIF-1α attenuates endothelial barrier dysfunction and the increased MLCK protein expression induced by hypoxia. Inhibiting the transcription activity of HIF-1 by overexpressing factor inhibiting HIF-1(FIH) prevents the increased MLC phosphorylation and also attenuates endothelial barrier dysfunction in hypoxia. The results suggest that HIF-1α is involved in the MLCK-dependent endothelial barrier dysfunction induced by hypoxia.