Recovery from hepatic fibrosis is facilitated by apoptosis of activated hepatic stellate cells

Although liver cirrhosis is considered to be irreversible, examples of spon taneous resolution of advanced fibrosis and cirrhosis have been described f or those conditions in which effective treatment of the causative insult is available. Fibrotic injury is characterised by proliferation and activatio n of hepatic stellate cells (HSCs), which become the major source of the fi brillar matrix that characterises fibrosis. Thus a prerequisite of resoluti on is that a net loss of activated HSCs must occur. We have studied a model of spontaneous resolution of liver fibrosis to determine whether apoptosis mediates the loss of HSCs. Livers were harvested from rats during 0, 3, 7, 14 and 28 days of recovery from liver fibrosis induced by CCl4 intra perit oneal (IP) injections for 4 weeks. Histological analysis demonstrated remod elling of the fibrotic septae during the 28 day period of recovery in assoc iation with which, the numbers of HSCs determined by alpha-Smooth Muscle Ac tin (alpha-SMA) staining diminished 12 fold. By standard Haematoxylin and E osin (H&E) histological staining and after TUNEL staining of representative sections of experimental liver, the first 7 days of recovery were associat ed with clear evidence of HSC apoptosis. HSCs were isolated from normal rat liver and activated by culture on plastic and serial passage. Cells with a n apoptotic morphology were demonstrated on the surface of the monolayer af ter staining with Acridine Orange, Giemsa and Propidium Iodide. Culture of activated HSCs in serum free media resulted in an increase in the rate of H SC apoptosis. This data confirms that apoptosis is the major mechanism resulting in HSC c learance during recovery from fibrosis. Furthermore they provide evidence t hat growth factors may increase HSCs numbers during injury by inhibiting ap optosis in addition to promoting proliferation.