Characterization of a novel heparan sulfate proteoglycan found in the extracellular matrix of liver sinusoids and basement membranes

A novel heparan sulfate proteoglycan (HSPG) present in the extracellular matrix of rat liver has been partially characterized. Proteoglycans were purified from a high salt extract of total microsomes from rat liver and found to consist predominantly (approximately 90%) of HSPG. A polyclonal antiserum raised against this fraction specifically recognized HSPG by immunoprecipitation and immunoblotting. The intact, fully glycosylated HSPG migrated as a broad smear (150-300 kD) by SDS-PAGE, but after deglycosylation with trifluoromethanesulfonic acid only a single approximately 40-kD band was seen. By immunocytochemistry this HSPG was localized in the perisinusoidal space of Disse associated with irregular clumps of basement membrane-like extracellular matrix material, some of which was closely associated with the hepatocyte sinusoidal cell surface. It was also localized in biosynthetic compartments (rough ER and Golgi cisternae) of hepatocytes, suggesting that this HSPG is synthesized and deposited in the space of Disse by the hepatocyte. The anti-liver HSPG IgG also stained basement membranes of hepatic blood vessels and bile ducts as well as those of kidney and several other organs (heart, pancreas, and intestine). An antibody that recognizes the basement membrane HSPG found in the rat glomerular basement membrane did not precipitate the 150-300-kD rat liver HSPG. We conclude that the liver sinusoidal space of Disse contains a novel population of HSPG that differs in its overall size, its distribution and in the size of its core protein from other HSPG (i.e., membrane-intercalated HSPG) previously described in rat liver. It also differs in its core protein size from HSPG purified from other extracellular matrix sources. This population of HSPG appears to be a member of the basement membrane HSPG family.