Glycome Atlas
protein
Also known as SDC1, CD138, syndecan
Plain-language answer
Syndecan-1 is a protein that sits in the surface of endothelial cells and other cells, with long sugar chains attached to the part that faces outward into the bloodstream. It acts like an anchor post for the gel-like glycocalyx coating, holding the sugar chains in place on the vessel wall.12
When the glycocalyx is damaged, enzymes cut syndecan-1 loose and its outer piece washes into the blood, where a lab test can detect it. Because of this, a rising level of syndecan-1 in blood is used as a signal that the protective vessel lining is shedding, which happens in sepsis, critical illness, and other conditions that injure blood vessels.1
Technical detail
Syndecan-1 (SDC1) is a type I transmembrane heparan sulfate proteoglycan whose ectodomain bears heparan sulfate and chondroitin sulfate chains, contributing to the endothelial glycocalyx scaffold, and whose proteolytically shed ectodomain circulates as a widely used plasma marker of glycocalyx degradation.12
Syndecans are a family of single-pass transmembrane proteoglycans whose extracellular protein core is substituted with glycosaminoglycan chains, predominantly heparan sulfate and in some positions chondroitin sulfate. In the vessel wall syndecan-1 is one of the core proteins that tethers these sulfated chains to the endothelial membrane, anchoring the negatively charged mesh of the glycocalyx to the cell surface.21
Through its heparan sulfate chains the syndecan-1 core participates in binding plasma proteins and soluble mediators at the endothelial surface, integrating the membrane-bound scaffold with the wider endothelial surface layer.12
Inflammatory mediators and enzymes such as heparanase and matrix metalloproteinases promote cleavage of the syndecan-1 ectodomain from the endothelial surface. The released fragment enters plasma, and elevated circulating syndecan-1 is reported in sepsis, ischemia-reperfusion, and other states of endothelial injury, where it is interpreted as an index of glycocalyx breakdown.1
Human relevance
Elevated plasma syndecan-1 tracks with glycocalyx shedding and vascular permeability in sepsis and critical illness, and is used in research as a marker of endothelial injury.1
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