Immunolocalization of laminin in normal rat liver and biosynthesis of laminin by hepatic lipocytes in primary culture.

Laminin, a glycoprotein with a molecular weight of approximately 850,000 daltons, is a major constituent of most epithelial basement membranes. Its presence in the extracellular matrix of normal liver, however, is debated. Using two affinity-purified antibodies directed against laminin, we have localized the glycoprotein within normal rat liver and identified its cellular source. Immunofluorescent staining of rat liver sections revealed laminin in a continuous distribution around hepatic sinusoids, adjacent to hepatocytes and sinusoidal lining cells. To determine the cellular origin of laminin, three perisinusoidal cell populations (hepatocytes, sinusoidal endothelial cells, and lipocytes) were purified from enzymatically dispersed rat liver and were established in primary culture. By immunofluorescence, laminin was associated almost exclusively with lipocytes. Synthesis of laminin was demonstrated by immunoprecipitation of the protein from lipocyte culture medium pulse-labeled with radioactive methionine. These results show that in adult liver, laminin is present in the perisinusoidal matrix and is produced by hepatic lipocytes. Lipocytes, which have the capacity to produce collagen as well as laminin, may be the principal source of extracellular matrix proteins in the perisinusoidal space, and may contribute to subendothelial fibrosis resulting from liver injury.