Serglycin secreted by leukocytes is efficiently eliminated from the circulation by sinusoidal scavenger endothelial cells in the liver

This study was undertaken to determine the fate of the circulating chondroi tin sulfate proteoglycan serglycin, The human monocytic cell line THP-1 way cultured under serum-free conditions in the presence of [S-35]sulfate. The conditioned medium was harvested and S-35-macromolecules were purified by Q-Sepharose anion-exchange chromatography and Superose 6 gel chromatography . After labeling with I-125, the purified material was treated with chondro itinase ARC and subjected to sodium dodecyl sulfate polyacrylamide gel elec trophoresis. A major band with m(r) of approximately 14 kDa appeared, consi stent with the core protein of serglycin. The identity of the proteoglycan was confirmed by amino-terminal amino acid sequencing. Purified serglycin, labeled either with [S-35]sulfate or I-125 and fluorescein isothiocyanate, was injected intravenously into rats, The blood content of ratliolabeled se rglycin fell by 50% from 1 to 2.4 min after injection, indicating an initia l tilt of 1.4 min or shorter. Approximately 90% of the recovered radioactiv ity was localized ill the liver, 5% in the blood, and 5% altogether in urin e, kidneys, and spleen about 30 min after injection, Isolation of liver cel ls at the same time point showed that 70% of the radioactivity was taken up by the sinusoidal scavenger endothelial cells, and 23 and 7% by the hepato cytes and Kupffer cells, respectively. When excess amounts of unlabeled hya luronan was co-injected with radiolabeled serglycin, the elimination of ser glycin was significantly inhibited, indicating that the hyaluronan receptor on the sinusoidal scavenger endothelial cells is responsible for the elimi nation of serglycin.