The endothelial glycocalyx in syndecan-1 deficient mice.

The existence of a hydrodynamically relevant endothelial glycocalyx has been established in capillaries, venules, and arterioles in vivo. The glycocalyx is thought to consist primarily of membrane-bound proteoglycans with glycosaminoglycan side-chains, membrane-bound glypicans, and adsorbed plasma proteins. The proteoglycans found on the luminal surface of endothelial cells are syndecans-1, -2, and -4, and glypican-1. The extent to which any of these proteins might serve to anchor the glycocalyx to the endothelium has not yet been determined. To test whether syndecan-1, in particular, is an essential anchoring protein, we performed experiments to determine the hydrodynamically relevant glycocalyx thickness in syndecan-1 deficient (Sdc1−/−) mice. Micro-particle image velocimetry data were collected using a previously described method. Microviscometric analysis of these data consistently revealed the existence of a hydrodynamically relevant endothelial glycocalyx in Sdc1−/− mice in vivo. The mean glycocalyx thickness found in Sdc1−/− mice was 0.45±0.10μm (N =15), as compared with 0.54±0.12μm (N =11) in wild-type (WT) mice (p =0.03). The slightly thinner glycocalyx observed in Sdc1−/− mice relative to WT mice may be due to the absence of syndecan-1. These findings show that healthy Sdc1−/− mice are able to synthesize and maintain a hydrodynamically relevant glycocalyx, which indicates that syndecan-1 is not an essential anchoring protein for the glycocalyx in Sdc1−/− mice. This may also be the case for WT mice; however, Sdc1−/− mice might adapt to the lack of syndecan-1 by increasing the expression of other proteoglycans. In any case, syndecan-1 does not appear to be a prerequisite for the existence of an endothelial glycocalyx. [ABSTRACT FROM AUTHOR]