Acquisition of blood-tissue barrier-supporting features by hepatic stellate cells and astrocytes of myofibroblastic phenotype. Inverse dynamics of metallothionein and glial fibrillary acidic protein expression

A number of similarities between astrocytes and hepatic stellate cells (HSC ) rose the question whether or not the protective barrier features of blood -tissue interface may be provided by HSC as well. To test this hypothesis, we investigated the presence of metallothionein (MT), a functional marker o f blood-brain barrier, in HSC in situ and in cell culture and compared the results with those obtained with astrocytes. The dynamics of MT expression in cultured astrocytes and HSC was investigated by simultaneous labelling o f the cells with a monoclonal antibody (MAb MT) against a lysine-containing epitope of the cadmium-induced monomer of MT-I from rat liver and antiseru m against glial fibrillary acidic protein (GFAP). Cell activation was estim ated by the presence of smooth muscle alpha-actin (SMAA). In immunoblotting , MAb MT recognized monomeric MT protein and proteins in the 30-kDa range; both bands were pronounced in brain and barely visible in liver homogenates . In situ, MAb MT reacted with very few perivascular cells situated in the parenchyma of the liver. Double immunolabelling of brain slices with MAb MT and antiserum against GFAP showed large areas of brain containing cells ex pressing both MT and GFAP. However, there were also regions in the brain wh ere the cells produced solely GFAP or MT. In liver cell culture, MT was abs ent from HSC and hepatocytes in early periods of cultivation, during which the cells maintained their original features; however, MT was expressed str ongly in HSC during their activation under prolonged culture conditions. In versely, in astrocytes MT was expressed during early culturing and disappea red from the cells together with SMAA in late culture when GFAP was upregul ated. These results suggest that the acquisition of myofibroblastic feature s by perivascular cells empowers them to establish a protective blood-tissu e permeability barrier. In addition, this study shows that, at least in cel l culture, an enrichment of perivascular cells in GFAP results in the disap pearance of protective functions. (C) 2001 Elsevier Science Ltd. All rights reserved.