Endothelial calreticulin deletion impairs endothelial function in aged mice.

Discrete calcium signals within the vascular endothelium decrease with age and contribute to impaired endothelial-dependent vasodilation. Calreticulin (Calr), a multifunctional calcium binding protein and endoplasmic reticulum (ER) chaperone, can mediate calcium signals and vascular function within the endothelial cells (ECs) of small resistance arteries. We found Calr protein expression significantly decreases with age in mesenteric arteries and examined the functional role of EC Calr in vasodilation and calcium mobilization in the context of aging. Third-order mesenteric arteries from mice with or without EC Calr knockdown were examined for calcium signals and constriction to phenylephrine (PE) or vasodilation to carbachol (CCh) after 75 wk of age. PE constriction in aged mice with or without EC Calr was unchanged. However, calcium signals and vasodilation to endothelial-dependent agonist carbachol were significantly impaired in aged EC Calr knockdown mice. Ex vivo incubation of arteries with the ER stress inhibitor tauroursodeoxycholic acid (TUDCA) significantly improved vasodilation in mice lacking EC Calr. Our data suggests diminished vascular Calr expression with age can contribute to the detrimental effects of aging on endothelial calcium regulation and vasodilation. Calreticulin (Calr) is responsible for key physiological processes in endoplasmic reticulum, especially in aging tissue. In particular, endothelial Calr is crucial to vascular function. In this study, we deleted Calr from the endothelium and aged the mice up to 75 wk to examine changes in vascular function. We found two key differences: ) calcium events in endothelium were severely diminished after muscarinic stimulation, which ) corresponded with a dramatic decrease in muscarinic vasodilation. Remarkably, we were able to rescue the effect of Calr deletion on endothelial-dependent vasodilatory function using tauroursodeoxycholic acid (TUDCA), an inhibitor of endoplasmic reticulum stress that is currently in clinical trials.