Growth inhibition and apoptosis in liver myofibroblasts promoted by hepatocyte growth factor leads to resolution from liver cirrhosis

Liver cirrhosis is characterized by hepatic dysfunction with extensive accumulation of fibrous tissue in the liver. In response to chronic hepatic injury, hepatic portal myofibroblasts and activated hepatic stellate cells (HSCs) play a role in liver fibrosis. Although administration or gene expression of hepatocyte growth factor (HGF) leads to improvement in hepatic fibrosis/cirrhosis, the related mechanisms are not fully understood. We investigated mechanisms involved in resolution from liver cirrhosis by HGF, focusing on growth regulation and apoptosis in portal myofibroblasts. Cultured rat HSCs could not proliferate, were withdrawn after passage, and were replaced by proliferating portal myofibroblasts during the passages. In quiescent HSCs, c-Met receptor expression was undetected whereas c-Met receptor expression was detected in activated HSCs and liver myofibroblasts expressing alpha-smooth muscle actin (alpha-SMA), suggesting that activated HSCs and portal myofibroblasts are targets of HGF. For cultured rat portal myofibroblasts, HGF counteracted phosphorylation of extracellular signal-regulated kinase (Erk) 1/2 and mitogenic stimulus induced by platelet-derived growth factor, induced c-jun N-terminal kinase (JNK) 1 phosphorylation, and promoted apoptotic cell death. In the dimethylnitrosamine rat model of liver cirrhosis, administration of HGF suppressed proliferation while promoting apoptosis of alpha-SMA-positive cells in the liver, events that were associated with reduced hepatic expressions of alpha alpha-SMA and histological resolution from liver cirrhosis. Growth inhibition and enhanced apoptosis in portal myofibroblasts by HGF are newly identified mechanisms aiding resolution from liver fibrosis/cirrhosis by HGF.