siRNA transfection according to the manufacturer's instructions. DNA transfections: 5x104 cells seeded per well of 24 wplate. 24h later cells were transfected with two different plasmid using 0.5 µg of total DNA. Medium changed 6h later and results were analyzed 48h after transfection.

Hepatic progenitor cells (HPCs) are activated in the chronic liver injury and are found to participate in the progression of liver fibrosis, while the precise role of HPCs in liver fibrosis remains largely elusive. In this study, by immunostaining of human liver sections, we confirmed that HPCs were activated in the cirrhotic liver and secreted transforming growth factor beta (TGF-beta) and connective tissue growth factor (CTGF), both of which were important inducers of liver fibrosis. Besides, we used HPC cell lines LE/6 and WB-F344 as in vitro models and found that TGF-beta induced secretion of CTGF in HPCs. Moreover, TGF-beta signaling was intracrine activated and contributed to autonomous secretion of CTGF in HPCs. Furthermore, we found that TGF-beta induced expression of CTGF was not mediated by TGF-beta activated Smad signaling but mediated by TGF-beta activated Erk, JNK and p38 MAPK signaling. Taken together, our results provide evidence for the role of HPCs in liver fibrosis and suggest that the production of CTGF by TGF-beta activated MAPK signaling in HPCs may be a therapeutic target of liver fibrosis.