Abstract
Unresolved endoplasmic reticulum (ER) stress, with the subsequent persistent activation of the unfolded protein response (UPR) is a well-recognized mechanism of endothelial cell apoptosis with a major impact on the integrity of the endothelium during the course of cardiovascular diseases. As in other cell types, Ca(2+) influx into endothelial cells can promote ER stress and/or contribute to mechanisms associated with it. In previous work we showed that in human coronary artery endothelial cells (HCAECs) the Ca(2+)-permeable non-selective cation channel Transient Receptor Potential Canonical 3 (TRPC3) mediates constitutive Ca(2+) influx which is critical for operation of inflammatory signaling in these cells, through a mechanism that entails coupling of TRPC3 constitutive function to activation of Ca(2+)/calmodulin-dependent protein kinase II (CAMKII). TRPC3 has been linked to UPR signaling and apoptosis in cells other than endothelial, and CAMKII is a mediator of ER stress-induced apoptosis in various cell types, including endothelial cells. In the present work we used a pharmacological approach to examine whether in HCAECs TRPC3 and CAMKII also contribute to mechanisms of ER stress-induced apoptosis. The findings show for the first time that in HCAECs activation of the UPR and the subsequent ER stress-induced apoptosis exhibit a strong requirement for constitutive Ca(2+) influx and that TRPC3 contributes to this process. In addition, we obtained evidence indicating that, similar to its roles in non-endothelial cells, CAMKII participates in ER stress-induced apoptosis in HCAECs.