Search

The liver regenerates by replication of differentiated hepatocytes after damage or removal of part of the liver. Although several growth factors and signaling pathways are activated during regeneration, it is unclear as to which of these are essential for hepatocyte replication. We show here that low- (1 mg/kg) and high- (10 mg/kg) dose hepatocyte growth factor (HGF) induced replication of 2.1% and 11.1% of hepatocytes in rats, respectively. Lipopolysaccharide (LPS), an inducer of the acute phase response, augmented hepatocyte replication in response to low- and high-dose HGF by 4- and 2-fold, respectively. HGF alone induced moderate levels of c-Jun-N-terminal kinase (JNK) and p44/p42 mitogen-activated protein kinase (MAPK), resulting in moderate levels of AP-1-DNA binding activity. The combination of LPS + HGF increased JNK and AP-1-DNA binding activity more than levels seen with LPS or HGF alone. The activation of Stat3 that was observed after administration of LPS + HGF, but not HGF alone, could contribute to increased transcription of AP-1 components. Because phosphorylation of the c-Jun component of AP-1 by JNK increases its ability to activate transcription, the AP-1 in hepatocytes from animals treated with LPS + HGF may be more active than in rats treated with LPS or HGF alone. LPS may contribute to hepatocyte replication by potentiating the effect of HGF on the activation of both AP-1-DNA binding and transcriptional activity.

Retroviral vectors can result in therapeutic and stable levels of expression of proteins from the liver. However, m ost retroviral vectors transduce only dividing cells, and hepatocytes are normally quiescent. The goal of this study was to determ ine if an adenoviral vector could transiently express hepatocyte growth factor (HG F) in order to induce hepatocyte replication and facilitate retroviral vector transduction of the liver. Intram uscular injection of an adenoviral vector that expressed human HGF from the cytomegalovirus promoter (Ad.C M V.HGF) resulted in m oderate levels of H GF in blood and liver, and replication of 3 to 12% of hepatocytes. No cytopathic effect was observed in the liver, and a control adenoviral vector induced no or lower levels of replication. W hen a retroviral vector expressing b -galactosidase cDNA was injected into a peripheral vein during the peak period of hepatocyte replication induced by intramuscularly adm inistered Ad.C M V.HG F, 8% of hepatocytes were transduced. W e conclude that intram uscular injection of Ad.C M V.HG F is a safe and effective way to induce transient systemic expression of HG F and hepatocyte replication, and to facilitate transduction of hepatocytes with a retroviral vector.