SummarySyndecans are important cell surface proteoglycans with many functions; yet, they have not been studied to a very large extent in primary human endothelial cells. The purpose of this study was to investigate syndecan-4 expression in cultured human umbilical vein endothelial cells (HUVECs) and assess its role in inflammatory reactions and experimental wound healing. qRT-PCR analysis revealed that syndecan-3 and syndecan-4 were highly expressed in HUVECs, whereas the expression of syndecan-1 and -2 was low. HUVECs were cultured with the inflammatory mediators lipopolysaccharide (LPS) and interleukin 1β (IL-1β). As a result, syndecan-4 expression showed a rapid and strong increase. Syndecan-1 and -2 expressions decreased, whereas syndecan-3 was unaffected. Knockdown of syndecan-4 using siRNA resulted in changes in cellular morphology and focal adhesion sites, delayed wound healing and tube formation, and increased secretion of the pro-inflammatory and angiogenic chemokine, CXCL8. These data suggest functions for syndecan-4 in inflammatory reactions, wound healing and angiogenesis in primary human endothelial cells. (J Histochem Cytochem 63:280-292, 2015)

Proteoglycan (PG) expression was studied in primary human umbilical vein endothelial cells (HUVEC). RT-PCR analysesshowed that the expression of the PG serglycin core protein was much higher than that of the extracellular matrix PG decorin and the cell surface PG syndecan-1. PG biosynthesis was further studied by biosynthetic [ 35 S]sulfate labeling of polarized HUVEC. Interestingly, a major part of 35 S-PGs was secreted to the apical medium. A large portion of these PGs was trypsin-resistant, a typical feature of serglycin. The trypsin-resistant PGs were mainly of the chondroitin/dermatan sulfate type but also contained a minor heparan sulfate component. Secreted serglycin was identified by immunoprecipitation as a PG with a core protein of ϳ30 kDa. Serglycin was furthermore shown to be present in perinuclear regions and in two distinct types of vesicles throughout the cytoplasm using immunocytochemistry. To search for possible serglycin partner molecules, HUVEC were stained for the chemokine growth-related oncogene ␣ (GRO␣/CXCL1). Co-localization with serglycin could be demonstrated, although not in all vesicles. Serglycin did not show overt co-localization with tissue-type plasminogen activator-positive vesicles. When PG biosynthesis was abrogated using benzyl-␤-D-xyloside, serglycin secretion was decreased, and the number of vesicles with co-localized serglycin and GRO␣ was reduced. The level of GRO␣ in the apical medium was also reduced after xyloside treatment. Together, these findings indicate that serglycin is a major PG in human endothelial cells, mainly secreted to the apical medium and implicated in chemokine secretion.

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