Different levels of hypoxia regulate telomere length and telomerase activity

This study was designed to identify changes in telomere length and telomerase activity in human umbilical vein endothelial cells (HUVECs) exposed to various levels of hypoxia. Mild hypoxia (10%, 15% oxygen) increased telomere length, which did not appear to change under severe hypoxia (1% oxygen). Telomerase activity in HUVECs correlated inversely with oxygen concentration. Endothelial cell telomere elongation with telomerase activation in conditions of mild hypoxia was demonstrated in this study. High telomerase activity may contribute to hypoxia- related telomere elongation. The best cell growth and longest telomere length were observed at 10%O₂, and this percentage may therefore be the optimal level for maintaining vascular endothelial cells. In addition, elevated telomerase activity maintains telomere length within normal range in conditions of severe hypoxia (1%O₂). The telomere length distribution in HUVECs under hypoxia seems to be regulated by a balance between telomere attrition by hypoxia and telomere elongation by enhanced telomerase activity acting on telomeres, perhaps in a telomere-length dependent manner.