Loss of cell‐surface sialic acids activates calcium entry in pulmonary endothelial cells

Abstract

The endothelial glycocalyx is a complex mixture of glycoproteins, glycolipids and proteoglycans which coats the cell surface. Sialic acid is a carbohydrate residue that is typically found at the glycan chain terminus in a α‐2,3‐Gal‐ or a α‐2,6‐Gal/GalNAc‐linked configuration. We have previously demonstrated that pulmonary microvascular endothelial cells (PMVECs) express principally α‐2,3‐linked sialic acids whilst pulmonary artery endothelial cells (PAECs) express both α‐2,3‐ and α‐2,6‐linked sialic acids. Further, treatment with neuraminidase, to cleave cell‐surface sialic acids, leads to endothelial barrier disruption as evidenced by loss of cell‐cell and/or cell‐matrix adhesions. Calcium entry through store‐operated calcium entry channels is a critical event that results in endothelial barrier disruption. However it is unknown whether selective cleavage of cell surface sialic acids leads to calcium entry. Confluent monolayers of PAECs and PMVECs were treated with neuraminidase from Clostridium perfringens and cytosolic calcium levels measured by the ratiometric dye Fura2/AM. Cytosolic calcium increased following addition of neuraminidase in both PAECs and PMVECs. EDTA addition to the extracellular solution reversed this increase. Collectively our data reveal that loss of cell‐surface sialic acids triggers calcium entry in pulmonary endothelial cells. Supported by 5R00HL089361.