Shear stress enhances the endothelial glycocalyx layer

Abstract

Many studies over the past 30 years have conclusively demonstrated that the arterial lining of mammalian arteries becomes compromised and prone to atherosclerotic plaque in specific regions of the circulation where the blood flow exhibits low fluid shear stress and flow separation. One of the key attributes of these athero-prone regions is the fact that the thin glycocalyx layer on the apical surface of the endothelial cells in these areas is very thin. Heparin sulfate is a primary constituent of the glycocalyx and in our work we assume that the thickness of the glycocalyx is directly proportional to the local concentration of heparin sulfate as revealed by monoclonal antibody staining. In this study, we examined the effect of fluid shear stress on the amount of heparin sulfate on a cultured bovine aortic endothelial layer both in static culture and after applying a shear stress of 15 dynes/cm2 for up to 48 hours. We reported previously that the glycocalyx is in a continual state of turnover such that the layer in static medium is replaced approximately every 6-10 hours. This is consistent with shedding measurements by others4. We find that under shear stress the turnover rate of the glycocalyx is reduced and the total amount of glycocalyx rapidly rises to a new steady-state value that is approximately twice that of the layer under static conditions. Thus, shear stress recruits glycocalyx to the encothelial cell glycocalyx surface layer, an observation that suggests that the glycocalyx itself may participate in the athero-protective effects associated with fluid shear stress.