Gene transfer of IGF1 attenuates hepatocellular apoptosis after bile duct ligation

Gene Therapy for Acquired and Genetic Cholestasis

Cholestatic diseases can be caused by the dysfunction of transporters involved in hepatobiliary circulation. Although pharmacological treatments constitute the current standard of care for these diseases, none are curative, with liver transplantation being the only long-term solution for severe cholestasis, albeit with many disadvantages. Liver-directed gene therapy has shown promising results in clinical trials for genetic diseases, and it could constitute a potential new therapeutic approach for cholestatic diseases. Many preclinical gene therapy studies have shown positive results in animal models of both acquired and genetic cholestasis. The delivery of genes that reduce apoptosis or fibrosis or improve bile flow has shown therapeutic effects in rodents in which cholestasis was induced by drugs or bile duct ligation. Most studies targeting inherited cholestasis, such as progressive familial intrahepatic cholestasis (PFIC), have focused on supplementing a correct version of a mutated gene to the liver using viral or non-viral vectors in order to achieve expression of the therapeutic protein. These strategies have generated promising results in treating PFIC3 in mouse models of the disease. However, important challenges remain in translating this therapy to the clinic, as well as in developing gene therapy strategies for other types of acquired and genetic cholestasis.

Growth Hormone Mediates Its Protective Effect in Hepatic Apoptosis through Hnf6

BACKGROUND AND AIMS

Growth hormone (GH) not only supports hepatic metabolism but also protects against hepatocyte cell death. Hnf6 (or Oc1) belonging to the Onecut family of hepatocyte transcription factors known to regulate differentiated hepatic function, is a GH-responsive gene. We evaluate if GH mediates Hnf6 activity to attenuate hepatic apoptotic injury.

METHODS

We used an animal model of hepatic apoptosis by bile duct ligation (BDL) with Hnf6 -/- (KO) mice in which hepatic Hnf6 was conditionally inactivated. GH was administered to adult wild type WT and KO mice for the 7 days of BDL to enhance Hnf6 expression. In vitro, primary hepatocytes derived from KO and WT liver were treated with LPS and hepatocyte apoptosis was assessed with and without GH treatment.

RESULTS

In WT mice, GH treatment enhanced Hnf6 expression during BDL, inhibited Caspase -3, -8 and -9 responses and diminished hepatic apoptotic and fibrotic injury. GH-mediated upregulation of Hnf6 expression and parallel suppression of apoptosis and fibrosis in WT BDL liver were abrogated in KO mice. LPS activated apoptosis and suppressed Hnf6 expression in primary hepatocytes. GH/LPS co-treatment enhanced Hnf6 expression with corresponding attenuation of apoptosis in WT-derived hepatocytes, but not in KO hepatocytes. ChiP-on-ChiP and electromobility shift assays of KO and WT liver nuclear extracts identified Ciap1 (or Birc2) as an Hnf6-bound target gene. Ciap1 expression patterns closely follow Hnf6 expression in the liver and in hepatocytes.

CONCLUSION

GH broad protective actions on hepatocytes during liver injury are effected through Hnf6, with Hnf6 transcriptional activation of Ciap1 as an underlying molecular mediator.

β-Arrestin 2 Promotes Hepatocyte Apoptosis by Inhibiting Akt Protein

Recent studies reveal that multifunctional protein β-arrestin 2 (Arrb2) modulates cell apoptosis. Survival and various aspects of liver injury were investigated in WT and Arrb2 KO mice after bile duct ligation (BDL). We found that deficiency of Arrb2 enhances survival and attenuates hepatic injury and fibrosis. Following BDL, Arrb2-deficient mice as compared with WT controls displayed a significant reduction of hepatocyte apoptosis as demonstrated by the TUNEL assay. Following BDL, the levels of phospho-Akt and phospho-glycogen synthase kinase 3β (GSK3β) in the livers were significantly increased in Arrb2 KO compared with WT mice, although p-p38 increased in WT but not in Arrb2-deficient mice. Inhibition of GSK3β following BDL decreases hepatic apoptosis and decreased p-p38 in WT mice but not in Arrb2 KO mice. Activation of Fas receptor with Jo2 reduces phospho-Akt and increases apoptosis in WT cells and WT mice but not in Arrb2-deficient cells and Arrb2-deficient mice. Consistent with direct interaction of Arrb2 with and regulating Akt phosphorylation, the expression of a full-length or N terminus but not the C terminus of Arrb2 reduces Akt phosphorylation and coimmunoprecipates with Akt. These results reveal that the protective effect of deficiency of Arrb2 is due to loss of negative regulation of Akt due to BDL and decreased downstream GSK3β and p38 MAPK signaling pathways.

Mechanistic and biological significance of DNA methyltransferase 1 upregulated by growth factors in human hepatocellular carcinoma

Dysregulation of growth factor signaling plays a pivotal role in controlling the malignancy phenotype and progression of hepatocellular carcinoma (HCC). However, the precise oncogenic mechanisms underlying transcription regulation of certain tumor suppressor genes (TSGs) by growth factors are poorly understood. In the present study, we report a novel insulin-like growth factor 1 (IGF1) pathway that mediates de novo DNA methylation and TSG (such as DLC1 and CHD5) silencing by upregulation of the DNA methyltransferase 1 (DNMT1) via an AKT/β-transducin repeat-containing protein (βTrCP)-mediated ubiquitin-proteasome pathway in HCC. Analysis of DNA methylation in CpG islands of target genes revealed high co-localization of DNMT1 and DNMT3B on the promoters of TSGs associated with enhanced CpG hypermethylation. Our results point to a novel epigenetic mechanism for growth factor-mediated repression of TSG transcription that involves DNA methylation.

Exploiting the unique regenerative capacity of the liver to underpin cell and gene therapy strategies for genetic and acquired liver disease

The number of genetic or acquired diseases of the liver treatable by organ transplantation is ever-increasing as transplantation techniques improve placing additional demands on an already limited organ supply. While cell and gene therapies are distinctly different modalities, they offer a synergistic alternative to organ transplant due to distinct architectural and physiological properties of the liver. The hepatic blood supply and fenestrated endothelial system affords relatively facile accessibility for cell and/or gene delivery. More importantly, however, the remarkable capacity of hepatocytes to proliferate and repopulate the liver creates opportunities for new treatments based on emerging technologies. This review will summarise current understanding of liver regeneration, describe clinical and experimental cell and gene therapeutic modalities and discuss critical challenges to translate these new technologies to wider clinical utility. This article is part of a Directed Issue entitled: "Regenerative Medicine: the challenge of translation".

Interleukin-10 suppresses hepatic TGF-β1 expression and attenuates hepatocyte apoptosis in biliary-obstructed rats

AIM: To explore the effect of interleukin-10 (IL-10) on hepatocyte apoptosis in biliary-obstructed rats.

METHODS: Male Wistar rats were divided randomly into sham operation (SO) group, obstructive jaundice (OJ) group and IL-10 group. Rats of the OJ and IL-10 groups underwent ligation and severing of the common bile duct, while mobilization of the common bile duct was performed in the SO group. The IL-10 group was intraperitoneally injected with IL-10 (4 μg/kg) daily after operation. The mRNA and protein expression of transforming growth factor-β1 (TGF-β1) in liver tissue was detected by fluorescence real-time quantitative PCR and immunohistochemical staining, respectively. Blood samples were taken to measure serum total bilirubin (TBIL), direct bilirubin (DBIL), alanine aminotransferase (ALT), and aspartate aminotransferase (AST) levels, while hepatic cell apoptosis was evaluated by TUNEL method.

RESULTS: Compared to the SO group, the levels of serum ALT and AST, hepatic TGF-β1 mRNA and protein expression, and hepatic cell apoptosis index significantly increased in the OJ group 3 days after operation (ALT: 91.83 U/L ± 21.47 U/L vs 47.67 U/L ± 12.79 U/L; AST: 208.67 U/L ± 32.36 U/L vs 75.17 U/L ± 11.96 U/L; TGF-β1 mRNA: 7.48 ± 1.51 vs 1.21 ± 0.79; TGF-β1 protein: 6.11% ± 1.11% vs 1.26% ± 0.64%; apoptosis: 15.06% ± 1.17% vs 3.94% ± 0.46%; all P < 0.05), and further increased 7 d after operation (ALT: 178.83 U/L ± 46.25 U/L vs 44.50 U/L ± 9.97 U/L; AST: 461.17 U/L ± 88.48 U/L vs 76.50 U/L ± 12.39 U/L; TGF-β1 mRNA: 11.98 ± 3.05 vs 1.01 ± 0.52; TGF-β1 protein: 9.97% ± 2.84% vs 1.68% ± 0.71%; apoptosis: 23.49% ± 3.35% vs 4.31% ± 0.67%; all P < 0.05). Treatment with IL-10 significantly decreased hepatic function, hepatic TGF-β1 expression, and hepatic cell apoptosis compared to the OJ group 7 d after operation (ALT: 94.17 U/L ± 20.02 U/L vs 178.83 U/L ± 46.25 U/L; AST: 257.83 U/L ± 56.53 U/L vs 461.17 U/L ± 88.48 U/L; TGF-β1 mRNA: 7.05 ± 1.15 vs 11.98 ± 3.05; TGF-β1 protein: 7.06% ± 1.32% vs 9.97% ± 2.84%; apoptosis: 15.08% ± 1.69% vs 23.49% ± 3.35%; all P < 0.05).

CONCLUSION: IL-10 could attenuate hepatocyte apoptosis by suppressing hepatic TGF-β1 expression in biliary-obstructed rats.