The Roles of HS and Its Glypican-1 Core Protein in Flow-Induced Endothelial NOS Activation and Cell Remodeling

Endothelial cell (EC) glycocalyx (GCX) is an endovascular protective coat that is degraded in disease. GCX heparan sulfate (HS) proteoglycan is essential for flow-induced nitric oxide (NO) release and cell remodeling, but the HS core proteins involved in these mechanotransduction events are unknown. We hypothesize that the glypican-1 (GPC1) HS core protein mediates flow-induced EC NO synthase (eNOS) activation and is less important for flow-induced cell remodeling, because GPC1 is located in the caveolae where eNOS resides but, to our knowledge, GPC1 has no direct association with the cytoskeleton. We tested our hypotheses by exposing monolayers of bovine aortic EC (BAEC) with intact GCX, heparinase III (HepIII) enzymatically degraded HS, and RNA-silenced GPC1 to 12–15 dyne/cm² average shear stress for 3 and 24 hours. HS removal by HepIII and GPC1 inhibition by shRNA equally blocked shear-induced eNOS activation that occurs in shear-conditioned BAEC with fully intact GCX. EC remodeling in response to flow was attenuated by HS degradation, but preserved with GPC1 knockdown. These results suggest that while HS is involved in both centralized and decentralized GCX-mediated mechanotransduction mechanisms, GPC1 plays a role in only centralized GCX-mediated mechanotransduction.