In vivo Imaging of the Cerebral Endothelial Glycocalyx in Mice

Endothelial glycocalyx refers to the proteoglycan or glycoprotein layer of vessel walls and has critical physiological functions. Cerebral glycocalyx may have additional functions considering the blood-brain barrier and other features. However, the assessment of it has only been performed ex vivo, which includes processes presumably damaging the glycocalyx layer. Here we visualize and characterize the cerebral endothelial glycocalyx in vivo.We visualized and quantified the cerebral endothelial glycocalyx in vivo under a 2-photon microscope by tagging glycocalyx and vessel lumen with wheat germ agglutinin lectin and dextran, respectively. The radial intensity was analyzed to measure the thickness of the cerebral endothelial glycocalyx in each vessel type.Cerebral arteries and capillaries have an intact endothelial glycocalyx, but veins and venules do not. The thickness of the glycocalyx layer in pial arteries, penetrating arteries, and capillaries was different; however, it was not correlated with the vessel diameter within each vessel type.We characterized the distribution of the cerebral endothelial glycocalyx in vivo. Compared to the results from ex vivo studies, the layer is thicker, indicating that the layer may be damaged in ex vivo systems. We also observed an inhomogeneous cerebral endothelial glycocalyx distribution that might reflect the functional heterogeneity of the vessel type.