The glycocalyx: a central regulator of vascular function

Abstract

The endothelial glycocalyx is a specialized extracellular matrix that covers the apical side of vascular endothelial cells, projecting into the lumen of blood vessels. The composition of the glycocalyx has been studied in great detail, and it is known to be composed of a mixture of proteoglycans, glycosaminoglycans, and glycoproteins. Although this structure was once believed to be a passive physical barrier, it is now recognized as a multifunctional and dynamic structure that participates in many vascular processes, including but not limited to vascular permeability, inflammation, thrombosis, mechanotransduction, and cytokine signaling. Because of its participation in many physiological and pathophysiological states, comprehensive knowledge of the glycocalyx will aid future vascular biologists in their research. With that in mind, this review discusses the biochemical structure of the glycocalyx and its function in many vascular physiological processes. We also briefly review a more recent discovery in glycocalyx biology, the placental glycocalyx.

Keywords: extracellular matrix; glycocalyx; vascular.

Figure 1.

A cartoon of the glycocalyx of a cross-sectioned blood vessel divided into a “normal state” side and an “activated state” side. Normal state: under normal conditions, the glycocalyx protrudes into the lumen of blood vessels and obscures adhesion molecules like intercellular adhesion molecule 1 (ICAM-1). Other adhesion molecules like P-selectin are stored in Weibel–Palade bodies. Its proteoglycans and glycosaminoglycans actively inhibit lymphocytes’ and platelets’ interactions with the underlying endothelial cells. Activated state: activated endothelium and lymphocytes degrade the glycocalyx, exposing underlying adhesion molecules. Other adhesion molecules such as vascular cell adhesion molecule 1 (VCAM-1) are upregulated in activated endothelium and Weibel–Palade bodies are mobilized to the surface of endothelial cells with their contents. GAGs, glycosaminoglycans; GPI, glycosylphosphatidylinositol.