Effects of exogenous human heparin-binding epidermal growth factor-like growth factor on DNA synthesis of hepatocytes in normal mouse liver

Heparin-binding epidermal growth factor-like growth factor and hepatocyte growth factor inhibit cholestatic liver injury in mice through different mechanisms

In contrast to hepatocyte growth factor (HGF), the therapeutic potential and pathophysiologic roles of heparin-binding epidermal growth factor-like growth factor (HB-EGF) in liver diseases remain relatively unknown. To address the lack of effective pharmacologic treatments for cholestatic liver injuries, as well as to clarify the biologic features of these growth factors, we explored the effects of HB-EGF and HGF in mice with cholestatic liver injury induced by bile duct ligation (BDL). The mice were assessed 3, 5 and/or 14 days after BDL (acute, subacute and/or chronic phases, respectively) and intravenous injection of adenoviral vector expressing LacZ (control), HB-EGF, HGF, or HB-EGF and HGF. HB-EGF, HGF, or a combination of the growth factors exerted potent antioncotic (antinecrotic), antiapoptotic, anticholestatic, and regenerative effects on hepatocytes in vivo, whereas no robust antiapoptotic or regenerative effects were detected in interlobular bile ducts. Based on serum transaminase levels, the acute protective effects of HB-EGF on hepatocytes were greater than those of HGF. On the other hand, liver fibrosis and cholestasis during the chronic phase were more potently inhibited by HGF compared with HB-EGF. Compared with either growth factor alone, combining HB-EGF and HGF produced greater anticholestatic and regenerative effects during the chronic phase. Taken together, these findings suggest that HB-EGF and HGF inhibited BDL-induced cholestatic liver injury, predominantly by exerting acute cytoprotective and chronic antifibrotic effects, respectively; combining the growth factors enhanced the anticholestatic effects and liver regeneration during the chronic phase. Our results contribute to a better understanding of the pathophysiologic roles of HB-EGF and HGF, as well as to the development of novel effective therapies for cholestatic liver injuries.

Conditional loss of heparin-binding EGF-like growth factor results in enhanced liver fibrosis after bile duct ligation in mice

Our aims were to evaluate the involvement of heparin-binding EGF-like growth factor (HB-EGF) in liver fibrogenesis of humans and mice and to elucidate the effect of HB-EGF deficiency on cholestatic liver fibrosis using conditional HB-EGF knockout (KO) mice. We first demonstrated that gene expression of HB-EGF had a positive significant correlation with that of collagen in human fibrotic livers, and was increased in bile duct ligation (BDL)-induced fibrotic livers in mouse. We then generated conditional HB-EGF knockout (KO) mice using the interferon inducible Mx-1 promoter driven Cre recombinase transgene and wild type (WT) and KO mice were subjected to BDL. After BDL, KO mice exhibited enhanced liver fibrosis with increased expression of collagen, compared with WT mice. Finally, we used mouse hepatic stellate cells (HSCs) to examine the role of HB-EGF in the activation of these cells and showed that HB-EGF antagonized TGF-β-induced gene expression of collagen in mouse primary HSCs. Interestingly, HB-EGF did not prevent the TGF-β-induced nuclear accumulation of Smad3, but did lead to stabilization of the Smad transcriptional co-repressor TG-interacting factor. In conclusion, our data suggest a possible protective role of HB-EGF in cholestatic liver fibrosis.

Conditional knockout of heparin-binding epidermal growth factor-like growth factor in the liver accelerates carbon tetrachloride-induced liver injury in mice

AIM

  We previously demonstrated that heparin-binding epidermal growth factor-like growth factor (HB-EGF) is induced in response to several liver injuries. Because the HB-EGF knockout (KO) mice die in utero or immediately after birth due to cardiac defects, the loss of function study in vivo is limited. Here, we generated liver-specific HB-EGF conditional knockout mice using the interferon-inducible Mx-1 promoter driven cre recombinase transgene and investigated its role during acute liver injury.

METHODS

  We induced acute liver injury by a single i.p. injection of carbon tetrachloride (CCl4 ) in HB-EGF KO mice and wild-type mice and liver damage was assessed by biochemical and immunohistochemical analysis. We also used AML12 mouse hepatocyte cell lines to examine the molecular mechanism of HB-EGF-dependent anti-apoptosis and wound-healing process of the liver in vitro.

RESULTS

  HB-EGF KO mice exhibited a significant increase of alanine aminotransferase level and also showed a significant increase in the number of apoptotic hepatocytes assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling staining at 24 h after CCl4 injection. We also demonstrated that HB-EGF treatment inhibited tumor necrosis factor-α-induced apoptosis of AML12 mouse hepatocytes and promoted the wound-healing response of these cells.

CONCLUSION

  This study showed that HB-EGF plays a protective role during acute liver injury.

In vivo hepatic HB-EGF gene transduction inhibits Fas-induced liver injury and induces liver regeneration in mice: a comparative study to HGF

BACKGROUND/AIMS

It is unknown whether heparin-binding EGF-like growth factor (HB-EGF) can be a therapeutic agent, although previous studies suggested that HB-EGF might be a hepatotrophic factor. This study explores the potential of hepatic HB-EGF gene therapy in comparison with HGF.

METHODS

Mice received an intraperitoneal injection of the agonistic anti-Fas antibody 72 h after an intravenous injection of either adenoviral vector (1x10(11) particles) expressing human HB-EGF (Ad.HB-EGF), human HGF (Ad.HGF) or no gene (Ad.dE1.3), and were sacrificed 24 or 36 h later to assess liver injury and regeneration.

RESULTS

Exogenous HB-EGF was predominantly localized on the membrane, suggesting the initial synthesis of proHB-EGF in hepatocytes. The control Ad.dE1.3-treated mice represented remarkable increases in serum ALT and AST levels and histopathologically severe liver injuries with numerous apoptosis, but a limited number of mitogenic hepatocytes. In contrast, the liver injuries and apoptotic changes were significantly inhibited, but the mitogenic hepatocytes remarkably increased, in both the Ad.HB-EGF- and Ad.HGF-treated mice. More mitogenic hepatocytes and milder injuries were observed in the Ad.HB-EGF-treated mice.

CONCLUSIONS

HB-EGF has more potent protective and mitogenic effects for hepatocytes than HGF, at least for the present conditions. In vivo hepatic HB-EGF gene transduction is therapeutic for Fas-induced liver injury.

Liver regeneration in heparin-binding EGF-like growth factor transgenic mice after partial hepatectomy

BACKGROUND & AIMS

Heparin-binding epidermal growth factor-like growth factor (HB-EGF), a member of the EGF family, is synthesized in the form of a membrane-anchored precursor (proHB-EGF), which subsequently is processed proteolytically to mature HB-EGF. This study describes the effects of HB-EGF on liver regeneration after 70% partial hepatectomy in proHB-EGF transgenic mice with liver-specific expression.

METHODS & RESULTS

No significant differences in liver/body weight ratios and in bromodeoxyuridine (BrdU)-labeling index (the ratios of BrdU-positive hepatocyte nuclei) were found between adult transgenic and wild-type mice. However, in regenerating liver after partial hepatectomy, transgenic mice had higher liver/body weight ratios than wild-type mice and at 120 hours reached a level equal to that before partial hepatectomy. The BrdU-labeling index was about 5 times higher in the livers of transgenic mice compared with the wild type (51.5% vs. 10.2%, respectively; P < 0.01) at 48 hours after partial hepatectomy. Activation of microtubule-associated protein kinase after partial hepatectomy was higher and earlier in the transgenic mice as compared with the wild-type mice. Soluble HB-EGF was increased in the liver (at 8 min) after partial hepatectomy, indicating that the shedding of proHB-EGF occurred after partial hepatectomy.

CONCLUSIONS

The transgenic expression of HB-EGF accelerates the proliferation of hepatocytes after partial hepatectomy, suggesting that HB-EGF functions as a hepatotrophic factor in vivo.

NF-kappaB activation in non-parenchymal liver cells after partial hepatectomy in rats: possible involvement in expression of heparin-binding epidermal growth factor-like growth factor

BACKGROUND/AIMS

Nuclear factor (NF) B activation plays a critical role in the initiation of liver growth after partial hepatectomy (PH). However, the issue of where specifically NF-B is activated is unclear. We previously reported that heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a hepatotrophic factor. The aims of this study were to identify NF-B-activated cells and to clarify their involvement in HB-EGF expression after PH.

METHODS

Using rats, a two-thirds PH was performed, after which NF-B-activated cells and HB-EGF-positive cells were identified by Southwestern histochemistry or immunohistochemistry. NF-B binding activity and HB-EGF gene expression were analyzed in rat hepatocytes and non-parenchymal cells (NPC) in primary culture.

RESULTS

NF-B was activated in Kupffer cells and sinusoidal endothelial cells prior to activation in hepatocytes. HB-EGF immunoreactivity was detected after NF-B activation in the sinusoidal cells from those localized in the periportal zones of hepatic lobules. HB-EGF gene expression by tumor necrosis factor was accompanied by an increase in NF-B binding activity in NPC but not in hepatocytes in primary culture, which was abolished by pyrrolidine dithiocarbamate, an inhibitor of NF-B activation. CONCLUSIONS; NF-B was activated in NPC prior to activation in hepatocytes. NF-B activation may be involved in HB-EGF expression in NPC after PH.