Zinc finger protein A20 promotes regeneration of small-for-size liver allograft and suppresses rejection and results in a longer survival in recipient rats

Emerging role of zinc finger protein A20 as a suppressor of hepatocellular carcinoma

Hepatocellular carcinoma (HCC), the third leading cause of cancer-associated mortality worldwide, is a major public health problem. Zinc finger protein A20 (A20), an acute phase response gene, is a potent inhibitor of NF-κB signaling. A20 serves a critical role in liver protection, including limiting inflammation following hepatic injury, stimulating hepatocyte growth, and preventing hepatic ischemia-reperfusion injury. A20 is also involved in different processes, including tumorigenesis, progression, and metastasis through multiple mechanisms. Accumulated studies have reported the clinical implications and biological relevance of A20 in the development and progression of HCC. The underlying mechanisms of A20 in HCC include inhibition of epithelial-mesenchymal transition, protein tyrosine kinase 2 activation and Rac family GTPase 1 activity. Combining liver protection with tumor inhibition is a unique advantage of A20, which has the potential to be a novel treatment for promoting liver regeneration following liver resection in patients with HCC with liver cirrhosis. This review discusses the hepato-protective effect of A20 on hepatocytes and its potential role in cancer development, particularly its suppressor effect on HCC.

A20 suppresses vascular inflammation by recruiting proinflammatory signaling molecules to intracellular aggresomes

A20 protects against pathologic vascular remodeling by inhibiting the inflammatory transcription factor NF-κB. A20's function has been attributed to ubiquitin editing of receptor-interacting protein 1 (RIP1) to influence activity/stability. The validity of this mechanism was tested using a murine model of transplant vasculopathy and human cells. Mouse C57BL/6 aortae transduced with adenoviruses containing A20 (or β-galactosidase as a control) were allografted into major histocompatibility complex-mismatched BALB/c mice. Primary endothelial cells, smooth muscle cells, or transformed epithelial cells (all human) were transfected with wild-type A20 or with catalytically inactive mutants as a control. NF-κB activity and intracellular localization of RIP1 was monitored by reporter gene assay, immunofluorescent staining, and Western blotting. Native and catalytically inactive versions of A20 had similar inhibitory effects on NF-κB activity (-70% vs. -76%; P > 0.05). A20 promoted localization of RIP1 to insoluble aggresomes in murine vascular allografts and in human cells (53% vs. 0%) without altering RIP1 expression, and this process was increased by the assembly of polyubiquitin chains (87% vs. 28%; P < 0.05). A20 captures polyubiquitinated signaling intermediaries in insoluble aggresomes, thus reducing their bioavailability for downstream NF-κB signaling. This novel mechanism contributes to protection from vasculopathy in transplanted organs treated with exogenous A20.

Emerging therapies targeting intra-organ inflammation in transplantation

Over the past several years, the field of transplantation has witnessed significant progress on several fronts; in particular, achievements have been made in devising novel immunosuppressive strategies. An under-explored area that may hold great potential to improve transplantation outcomes is the design of novel strategies to apply specifically to organs to reduce intra-graft inflammation. A growing body of evidence indicates a key role of intra-graft inflammatory cascade in potently instigating the alloimmune response. Indeed, controlling the activation of innate immunity/inflammatory responses has been shown to be a promising strategy to increase the graft acceptance and survival. In this minireview, we provide an overview of emerging targeted strategies, which can be directly applied to grafts to down-regulate intra-graft inflammation prior to transplantation.

Zinc finger protein A20 inhibits maturation of dendritic cells resident in rat liver allograft

BACKGROUND

In organ transplant field, although viewed traditionally as instigators of organ allograft rejection, donor-derived interstitial dendritic cells (DCs), including those resident in liver, or host DCs have also been implicated in transplant tolerance in experimental models. This functional dichotomy of DC is governed by various factors, the most important of which appears to be their stage of maturation. This study was designed to examine the effect of zinc finger protein A20 on maturation of DCs resident in rat liver allograft.

MATERIALS AND METHODS

Allogeneic (Dark Agouti [DA] rat to Lewis rat) liver transplantation was performed. Adenovirus carrying the full length of A20 was introduced into liver allografts by ex vivo perfusion via the portal vein during preservation (group A20), physiological saline (group PS), and empty Ad vector rAdEasy (group rAdEasy) that served as controls. Acute liver allograft rejection was assessed, and DCs resident in liver allografts were isolated on day 7 after transplantation. Nuclear factor kappa B (NF-κB)-binding activities, surface expression of costimulatory molecules (CD40, CD80, and CD86), expression of interleukin (IL) 12 messenger RNA (mRNA), and allocostimulatory capacity of DCs were measured with electrophoretic mobility shift assay, flow cytometry, reverse transcription-polymerase chain reaction, and mixed lymphocyte reaction (MLR), respectively.

RESULTS

Ex vivo transfer of A20 adenovirus by portal vein infusion resulted in overexpression of A20 protein in liver allograft after transplantation. On day 7 after transplantation, histologic examination revealed a mild rejection in group A20 but a more severe rejection in group PS and group rAdEasy. DCs from group A20 liver allografts exhibited features of immature DC with detectable but very low level of NF-κB activity, IL-12 mRNA expression, and surface expression of costimulatory molecules (CD40, CD80, and CD86), whereas DCs from group rAdEasy and group PS liver allograft displayed features of mature DC with high level of NF-κB activity, IL-12 mRNA expression, and surface expression of costimulatory molecules (CD40, CD80, and CD86). DCs from group PS and group rAdEasy liver allograft were potent inducers of DNA synthesis and interferon γ production in MLR, and DCs from group A20 liver allografts induced only minimal levels of cell proliferation and interferon γ production in MLR.

CONCLUSIONS

These data suggest that A20 overexpression could effectively inhibit maturation of DCs resident in liver allograft and consequently suppress acute liver allograft rejection.

Zinc finger protein A20 protects rats against chronic liver allograft dysfunction

AIM: To investigate the effect of zinc finger protein A20 on chronic liver allograft dysfunction in rats.

METHODS: Allogeneic liver transplantation from DA rats to Lewis rats was performed. Chronic liver allograft dysfunction was induced in the rats by administering low-dose tacrolimus at postoperative day (POD) 5. Hepatic overexpression of A20 was achieved by recombinant adenovirus (rAd.)-mediated gene transfer administered intravenously every 10 d starting from POD 10. The recipient rats were injected with physiological saline, rAdEasy-A20 (1 × 10⁹ pfu/30 g weight) or rAdEasy (1 × 10⁹ pfu/30 g weight) every 10 d through the tail vein for 3 mo starting from POD 10. Liver tissue samples were harvested on POD 30 and POD 60.

RESULTS: Liver-transplanted rats treated with only tacrolimus showed chronic allograft dysfunction with severe hepatic fibrosis. A20 overexpression ameliorated the effects on liver function, attenuated liver allograft fibrosis and prolonged the survival of the recipient rats. Treatment with A20 suppressed hepatic protein production of tumor growth factor (TGF)-β1, interleukin-1β, caspase-8, CD40, CD40L, intercellular adhesion molecule-1, vascular cell adhesion molecule-1 and E-selectin. A20 treatment suppressed liver cell apoptosis and inhibited nuclear factor-κB activation of Kupffer cells (KCs), liver sinusoidal endothelial cells (LSECs) and hepatic stellate cells (HSCs), and it subsequently decreased cytokine mRNA expression in KCs and LSECs and reduced the production of TGF-β1 in HSCs.

CONCLUSION: A20 might prevent chronic liver allograft dysfunction by re-establishing functional homeostasis of KCs, LSECs and HSCs.

Placenta extract promote liver regeneration in CCl4-injured liver rat model

The human placenta is an organ for fetus development and abundant reservoir of various bioactive molecules. Interest to human placenta extract (hPE) is growing, and application with trial of hPE is widening in oriental medicine including in liver diseases. However, underlying mechanisms for therapeutic effects are still unclear. Here, we investigated therapeutic effects of hPE in carbon tetrachloride (CCl(4))-injured rat liver model in vivo and in damaged rat hepatic cells exposed to CCl(4) in vitro. In addition, regulation of inflammatory responses by treatment of hPE was investigated. Serum levels of GOT/AST and GPT/ALT were significantly reduced (P<0.05), and uptake/excretion of indocyanine green in serum was significantly induced at 3 weeks after intravenous hPE administration in CCl(4)-injured rat model (P<0.05). Expression of type I collagen (Col I) and α-smooth muscle actin (α-SMA) was decreased, whereas that of matrix metalloproteinase-9 (MMP-9) was increased resulting in improvement of score for fibrotic grade in hPE group. Also, albumin, proliferation activities and molecules associated with liver regeneration (e.g. interleukin-6, gp130, ATP binding cassette transporters, cyclin A) were more increased in hPE administration group than Non-hPE group. hPE administration suppressed activated T-cell proliferation via increasing anti-inflammatory cytokines and decreasing pro-inflammatory cytokines. These results suggest that hPE could be effective for liver disease through reduction of fibrosis, induction of liver regeneration, and regulation of inflammatory responses. These findings are important for understanding the roles of hPE and provide evidences for therapeutic effects of hPE in hepatic diseases which could lead to potential clinical applications.

Anti-inflammatory treatment strategies for ischemia/reperfusion injury in transplantation

Inflammatory reactions in the graft have a pivotal influence on acute as well as long-term graft function. The main reasons for an inflammatory reaction of the graft tissue are rejection episodes, infections as well as ischemia/reperfusion (I/R) injury. The latter is of particular interest as it affects every solid organ during the process of transplantation. I/R injury impairs acute as well as long-term graft function and is associated with an increased number of acute rejection episodes that again affect long-term graft outcome.

I/R injury is the result of ATP depletion during prolonged hypoxia. Further tissue damage results from the reperfusion of the tissue after the ischemic insult. Adaptive cellular responses activate the innate immune system with its Toll-like receptors and the complement system as well as the adaptive immune system. This results in a profound inflammatory tissue reaction with immune cells infiltrating the tissue. The damage is mediated by various cytokines, chemokines, adhesion molecules, and compounds of the extracellular matrix. The expression of these factors is regulated by specific transcription factors with NF-κB being one of the key modulators of inflammation.

Strategies to prevent or treat I/R injury include blockade of cytokines/chemokines, adhesion molecules, NF-κB, specific MAP kinases, metalloproteinases, induction of protective genes, and modulation of the innate immune system. Furthermore, preconditioning of the donor is an area of intense research. Here pharmacological treatment as well as new additives to conventional cold storage solutions have been analyzed together with new techniques for the perfusion of grafts, or methods of normothermic storage that would avoid the problem of cold damage and graft ischemia.

However, the number of clinical trials in the field of I/R injury is limited as compared to the large body of experimental knowledge that accumulated during recent years in the field of I/R injury. Future activities in the treatment of I/R injury should focus on the translation of experimental protocols into clinical trials in order to reduce I/R injury and, thus, improve short- as well as long-term graft outcome.