Differential Effects of Vascular Endothelial Growth Factor on Glycocalyx of Endothelial and Tumor Cells Uncovered by Super‐resolution Optical Microscopy and Potential Targets for Tumor Metastasis

Abstract

On the surface of every mammalian cell, there is a matrix‐like glycocalyx (GCX) consisting of proteoglycans and glycosaminoglycans (GAGs). Disruption of endothelial cell (EC) GCX by vascular endothelial growth factor (VEGF, VEGF‐A165), a tumor secretion, was found to be an early event in tumor cell (TC) metastasis across vascular barriers. But how the TC secretion VEGF affects its own GCX is unknown although bulkier GCX of tumor cells was found to enhance its metastasis. To investigate the VEGF effect on TC GCX and to elucidate the ultrastructural organization of EC and TC GCX and their alteration by VEGF, we employed super‐resolution stochastic optical reconstruction microscopy (STORM) to observe the spatio‐chemical organizations of the heparan sulfate (HS) and hyaluronic acid (HA), two representative GAGs of GCX, on human cerebral microvascular endothelial cells (hCMEC) and malignant breast cancer cells MDA‐MB‐231 (MB231). We found that HS and HA have distinct organizations on hCMEC and MB231. Only HS of hCMEC is perpendicular to the cell surface, while HA of hCMEC, as well as HS and HA of MB231 all lie in the same plane as the cell surface where they appear to weave into a 2D network covering the cell. We also found that VEGF significantly reduces the length and coverage of HS on hCMEC but does not change the thickness and coverage of HA on hCMEC. On the contrary, VEGF significantly enhances the coverage of HS and HA on MB231 although it does not alter the thickness. The differential effects of VEGF on the GCX of TC and that of EC may favor TC adhesion and transmigration across EC barriers for their metastasis.