Prolonged Hypoxic Exposure Impairs Endothelial Functions: Possible Mechanism of HIF-1α Signaling

PURPOSE: Hypoxic training enhances oxygen availability by elevating hemoglobin, red blood cells, and capillaries. hypoxia-inducible factor (HIF) stabilization under hypoxic conditions triggers glycolysis, erythropoiesis, and angiogenesis. However, prolonged hypoxic exposure causes endothelial cell dysfunction, contributing to cardiovascular diseases. Furthermore, endothelial mitochondria play a crucial role in maintaining endothelial cell homeostasis through the processes of biogenesis, signaling cellular response, mitochondrial dynamics, and calcium homeostasis. However, the molecular response of endothelial mitochondria has not been fully elucidated. Therefore, this study aimed to investigate the endothelial mitochondria functions and morphological change in response to hypoxia. METHODS: Cobalt chloride and 2% hypoxic condition were applied to HUVECs. The endothelial cell functions were assessed using BrdU-based proliferation assay and scratch wound healing assays. Mitochondrial functions were evaluated using Mitosox and Mito-Tracker staining for mitochondrial reactive oxygen species (mtROS) and mitochondrial morphology analysis, respectively. RESULTS: The hypoxic condition (2% of O₂) significantly decreased endothelial proliferation/migration and mitochondrial function. Furthermore, CoCl₂ treatment increased the mtROS levels and mitochondrial fragmentation in HUVECs. Additionally, hypoxic conditions were found to regulate the phosphorylation of eNOS, mitochondrial biogenesis, mitophagy, and cell cycle-related protein expression. CONCLUSIONS: These results suggest that the HIF-α pathway leads to endothelial dysfunction via mitochondrial dysfunction. Further mechanistic studies will be needed to elucidate the cellular and molecular mechanisms by which hypoxic-response pathways influence the health and homeostasis of endothelial cells. The findings reported herein underscore the importance of strategies for hypoxic training to prevent cardiovascular diseases.