Dystroglycan Expression in Hepatic Stellate Cells: Role in Liver Fibrosis

Abstract

Dystroglycan is a membrane component of the dystrophin-glycoprotein transmembrane complex. Its expression is required for the spatial organization of laminin on the cell surface and for basement membrane assembly. In view of the constitution of a perisinusoidal basement membrane during liver fibrosis, we studied dystroglycan expression in liver fibrosis. Dystroglycan mRNA and protein expression were investigated by immunofluorescence, Western blot, and quantitative RT-PCR (TaqMan) in normal human and rat liver and in isolated rat hepatic stellate cells. On Western blot, a 43-kd band corresponding to β-dystroglycan was observed in protein extracted from normal and fibrotic human and rat livers. The specific 43-kd protein was also detected in lysates from rat hepatic stellate cells but not from hepatocytes. By immunofluorescence, patchy deposits of β-dystroglycan were detected on membrane of hepatic stellate cells in culture. On Western blot and quantitative RT-PCR, an up-regulation of β-dystroglycan was shown during spontaneous activation of hepatic stellate cells in culture. Direct evidence for the role of dystroglycan in laminin-hepatic stellate cell interaction was shown because specific antibody directed against α-dystroglycan inhibited partially hepatic stellate cell adhesion on laminin-coated plates. This mechanism was calcium dependent because EDTA inhibited cell/laminin adhesion, an effect reversed by addition of Ca2+. This study shows that dystroglycan is expressed on the membrane of hepatic stellate cells and is up-regulated during liver fibrosis. Dystroglycan interaction with laminin should be implicated in the concentration of pericellular laminin and in the constitution of a perisinusoidal basement membrane during liver fibrosis.