The Substructure of the Endothelial Glycocalyx in Rat Aorta and Its Interaction with the Low-Density Lipoproteins

The influx and retention of the low-density lipoproteins (LDLs) in the subendothelial space are one of the early events of atherosclerosis. Initially, LDLs must traverse the endothelial glycocalyx, which is increasingly recognized for its critical role in preventing LDL penetration. However, the precise substructure of the glycocalyx and its working mechanism are still unknown. Herein, a well-preserved porous mesh-like glycocalyx at the luminal surface of rat aortas, demonstrated by high-pressure freezing/freeze substitution transmission electron microscopy, shows three subtypes. Mathematical modeling suggests the dense lower glycocalyx (0.2 to 2.9 μm) shows similar arrangement to that reported in microvessels, with the partition coefficient of LDL equaling 0. The other sparse higher one (0.8 to 17.3 μm) contributes to mechanotransduction. LDL affinity column chromatography combined with proteomic analysis, colocalization analysis, and cell transport experiments verifies, for the first time, that the glycocalyx does bind LDLs both in vitro and in vivo, but does not retain LDLs. Two-photon laser scanning microscopic imaging of mouse ear arterioles suggests that the electrostatic repulsion between LDL and glycocalyx is dominant relative to binding. These findings reveal the arrangement of dense lower glycocalyx together with its electrostatic repulsion toward LDLs works in preventing LDL penetration.