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 chondroitin 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 chondroitinase ARC and subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis. A major band with m(r) of approximately 14 kDa appeared, consistent 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 serglycin fell by 50% from 1 to 2.4 min after injection, indicating an initial tilt of 1.4 min or shorter. Approximately 90% of the recovered radioactivity was localized ill the liver, 5% in the blood, and 5% altogether in urine, kidneys, and spleen about 30 min after injection, Isolation of liver cells 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 hepatocytes and Kupffer cells, respectively. When excess amounts of unlabeled hyaluronan was co-injected with radiolabeled serglycin, the elimination of serglycin was significantly inhibited, indicating that the hyaluronan receptor on the sinusoidal scavenger endothelial cells is responsible for the elimination of serglycin.