The motility of hepatic Ito cells can be acquired by their myofibroblastic transformation

Abstract

We investigated the relationship between the motility of hepatic Ito cells and their myofibroblastic transformation in cultures. Ito cells were freshly isolated from rat liver and cultured in a 10% FBS-supplemented medium. On day 2 after beginning the culture, transmission electron microscopy and oil red O staining showed that Ito cells possessed numerous lipid droplets but not actin filaments in the cytoplasm. On day 8, actin filaments were abundantly found in the cytoplasm, whereas lipid droplets dramatically decreased in number. Western blot analysis also demonstrated that protein levels of α-smooth muscle actin in the cell markedly increased with time, but no obvious change was detected in those of desmin and tubulinβ. In Boyden's chamber assay, the migration of Ito cells, which was induced by platelet-derived growth factor-BB (PDGF-BB), was activated in a time-dependent manner. This migration of transformed Ito cells was independent of the degree of their adhesion to various substances of the extracellular matrix. Among these molecules, laminin showed the highest effect upon the migratory activity. The migration of transformed Ito cells on laminin was completely inhibited by cytochalasin D, colchicine, or taxol. Furthermore, their adhesion to the matrix was also decreased by cytochalasin D or colchicine, but not by taxol. These findings indicate that the motility of Ito cells is acquired in conjunction with their myofibroblastic transformation, which is accompanied by morphological changes with a new organization of actin filaments. The results also suggest that microtubules as well as the extracellular matrix are deeply associated with the motility of Ito cells.