The plasticity of p19 ARF null hepatic stellate cells and the dynamics of activation

In the healthy adult liver, quiescent hepatic stellate cells (HSCs) present the major site for vitamin A storage in cytoplasmic lipid droplets. During liver injury due to viral infection or alcohol intoxication, HSCs get activated and produce high amounts of extracellular matrix components for tissue repair and fibrogenesis. Employing p19 ARF deficiency, we established a non-transformed murine HSC model to investigate their plasticity and the dynamics of HSC activation. Primary HSCs isolated from livers of adult p19 ARF null mice underwent spontaneous activation through long-term passaging without an obvious replicative limit. The immortalized cell line, referred to as M1-4HSC, showed stellate cell characteristics including the expression of desmin, glial fibrillary acidic protein, alpha-smooth muscle actin and pro-collagen I. Treatment of these non-tumorigenic M1-4HSC with pro-fibrogenic TGF-beta1 provoked a morphological transition to a myofibroblastoid cell type which was accompanied by enhanced cellular turnover and impaired migration. In addition, M1-4HSCs expressed constituents of cell adhesion complexes such as p120(ctn) and beta-catenin at cell borders, which dislocalized in the cytoplasm during stimulation to myofibroblasts, pointing to the epitheloid characteristics of HSCs. By virtue of its non-transformed phenotype and unlimited availability of cells, the p19(ARF) deficient model of activated HSCs and corresponding myofibroblasts render this system a highly valuable tool for studying the cellular and molecular basis of hepatic fibrogenesis.