Hypoxia damages endothelial cell angiogenic function by reducing the Ca2+ restoring ability of the endoplasmic reticulum

The angiogenic function of endothelial cells (ECs) is very important to tissues and organs that suffer from hypoxic injury. Exploring the role of endoplasmic reticulum (ER) Ca²⁺ homeostasis in angiogenesis under hypoxic conditions may provide new insight into the development of novel therapeutic approaches. Our research project evaluated the damaging effect of hypoxia on ER Ca²⁺ homeostasis in ECs during angiogenesis. Human umbilical vein endothelial cells (HUVECs) were isolated from the umbilical cord. We applied cobalt (II) chloride (CoCl₂) to mimic hypoxic conditions. Changes in the angiogenic function of HUVECs under hypoxic conditions were evaluated. Dynamic changes in ER and cytosolic (Cyto) Ca²⁺ and reactive oxygen species (ROS) signalling were detected. In addition, Western blotting (WB) was performed to evaluate the expression levels of related proteins under different conditions. Treatment of HUVECs with 100 μM CoCl₂ for 4 h successfully mimicked hypoxia and induced the generation of ROS signals. Processes related to HUVEC angiogenic function, including cell viability, tube formation, and migration, were significantly inhibited under hypoxic conditions. During these processes, Ca²⁺ was released from the ER of HUVECs and extracellular Ca²⁺ entered the cells, which resulted in Cyto Ca²⁺ overloading. The WB results showed that mimicking hypoxia increased AMPK-pAMPK activity. Hypoxic conditions also reduced the Ca²⁺ restoration ability of the ER by decreasing sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2a (SERCA2a) expression and PLN phosphorylation. HUVEC angiogenic function can be disrupted under hypoxic conditions by decreasing Ca²⁺ restoration by the ER. This may provide new insight for the future development of novel therapies. However, the detailed mechanism requires further research.