Impaired liver regeneration and increased oval cell numbers following T cell-mediated hepatitis

Interleukin-22 promotes proliferation and reverses LPS-induced apoptosis and steroidogenesis attenuation in human ovarian granulosa cells: implications for polycystic ovary syndrome pathogenesis

OBJECTIVE

Interleukin 22 (IL-22) plays a role in inflammatory diseases. However, whether IL-22 affects the function of ovarian granulosa cells (GCs) and its relationship with Polycystic Ovary Syndrome (PCOS)remains unclear.

METHODS

We investigated the level of IL-22 in human follicular fluid using ELISA. The expression and localization of the IL-22 receptor 1 (IL-22R1) in GCs were investigated by RT-PCR and immunofluorescence staining, respectively. The proliferation of KGN cells (human GCs line) was assessed by CCK-8 assay and EdU assay after treatment with recombinant human IL-22 (rhIL-22) and lipopolysaccharide (LPS). Apoptosis was assessed using flow cytometry. Apoptotic proteins and steroidogenic genes were detected by western blotting.

RESULTS

ELISA's results showed that compared with the control group, PCOS patients showed lower expression of IL-22 in follicular fluid. Immunofluorescence showed that IL-22R1 is expressed and localized in human granulosa cell membranes. IL-22 promoted cell proliferation and reversed LPS-induced inhibition of cell proliferation. IL-22 alone did not affect apoptotic or steroidogenic protein expression, however, it reversed LPS-induced apoptosis via downregulation of Bcl-2, upregulation of Bax and cleaved caspase-3, and restoration of LPS-downregulated StAR, CYP11A1, and CYP19A1 expression. Western blotting confirmed that IL-22 activated the JAK2/STAT3 signaling.

CONCLUSION

IL-22 promotes cell proliferation, inhibits apoptosis, and regulates KGN cell steroidogenesis confronted with LPS, and decreased IL-22 may be involved in the development of PCOS.

The Role of Immune Cells in Liver Regeneration

The liver is the only organ that can regenerate and regain its original tissue-to-body weight ratio within a short period of time after tissue loss. Insufficient liver regeneration in patients after partial hepatectomy or liver transplantation with partial liver grafts often leads to post-hepatectomy liver failure or small-for-size syndrome, respectively. Enhancing liver regeneration after liver injury might improve outcomes and increase patient survival. Liver regeneration comprises hepatocyte proliferation, and hepatic progenitor cell expansion and differentiation into hepatocytes. The immune system is intensively involved in liver regeneration. The current review provides a comprehensive overview of the diverse roles played by immune cells in liver regeneration. Macrophages, neutrophils, eosinophils, basophils, mast cells, platelets, dendritic cells, type 1 innate lymphoid cells, B cells, and T cells are implicated in promoting liver regeneration, while natural killer cells and overactivated natural killer T cells are supposed to inhibit hepatocyte proliferation. We also highlight the predominant underlying mechanisms mediated by immune cells, which may contribute to the development of novel strategies for promoting liver regeneration in patients with liver diseases.

Interleukin-22 facilitates the interferon-λ-mediated production of tripartite motif protein 25 to inhibit replication of duck viral hepatitis A virus type 1

The innate immune system provides a defense against invading pathogens by inducing various interferon (IFN)-stimulated genes (ISGs). We recently reported that tripartite motif protein 25 (TRIM25), an important ISG, was highly upregulated in duck embryo hepatocyte cells (DEFs) after infection with duck viral hepatitis A virus type 1 (DHAV-1). However, the mechanism of upregulation of TRIM25 remains unknown. Here we reported that interleukin-22 (IL-22), whose expression was highly facilitated in DEFs and various organs of 1-day-old ducklings after DHAV-1 infection, highly enhanced the IFN-λ-induced production of TRIM25. The treatment with IL-22 neutralizing antibody or the overexpression of IL-22 highly suppressed or facilitated TRIM25 expression, respectively. The phosphorylation of signal transducer and activator of transcription 3 (STAT3) was crucial for the process of IL-22 enhancing IFN-λ-induced TRIM25 production, which was suppressed by WP1066, a novel inhibitor of STAT3 phosphorylation. The overexpression of TRIM25 in DEFs resulted in a high production of IFNs and reduced DHAV-1 replication, whereas the attenuated expression of IFNs and facilitated replication of DHAV-1 were observed in the RNAi group, implying that TRIM25 defended the organism against DHAV-1 propagation by inducing the production of IFNs. In summary, we reported that IL-22 activated the phosphorylation of STAT3 to enhance the IFN-λ-mediated TRIM25 expression and provide a defense against DHAV-1 by inducing IFN production.

Risk factors of primary liver cancer initiation associated with tumour initiating cell emergence: novel targets for promising preventive therapies

Primary liver cancers ranked as the sixth most commonly diagnosed cancers and the third-leading cause of cancer-related death in 2020. Despite encouraging findings on diagnosis and treatments, liver cancer remains a life-threatening disease with a still increasing incidence. Therefore, it is of interest to better characterise and understand the mechanistic process occurring at early steps of carcinogenesis. Inflammatory responses in liver diseases participate in the activation of liver progenitor cells (LPCs) facultative compartment but also to their transformation into cancer stem cells (CSCs) and give rise to primary liver cancer including hepatocellular carcinoma and cholangiocarcinoma. Higher intratumoural heterogeneity has been associated with poorer prognosis and linked to tumour escape from the immune surveillance and to resistance to chemotherapy. A better understanding of the malignant transformation of LPC as tumour initiating cells (ie, CSC) should also provide a potential new therapeutic target for anticancer therapy. In this review, we summarise the recent reports identifying underlying mechanisms by which chronic liver inflammatory responses could trigger the early steps in liver carcinogenesis, notably through the transformation of LPCs into tumour initiating cells.

Fk506 Inhibit liver regeneration in HOC model Rat

BACKGROUND

Studies have shown that lymphocytes support hepatic oval cell (HOC)-dependent liver regeneration and FK506（Tacrolimus） is known as an immunosuppressor. Therefore, we studied the role of FK506 in HOC activation and/or proliferation to guide the clinical use of FK506.

METHODS

Thirty male Lewis rats were randomly divided into 4 groups: (A) intervene in activation (n = 8), (B) intervene in proliferation (n = 8), (C) control HOC model (n = 8), and (D) pure partial hepatectomy (PH) (n = 6). The HOC model was established by 2AAF(2-acetylaminofluorene)/PH in groups A to C. FK506 (at a dose of 1 mg/kg/d) was given subcutaneously in group A except on operation day, and not until day 8 post-operation (PO) in group B. Half of the animals were euthanized on days 10 and 14 PO, respectively. The remnant liver was weighed and stained by hematoxylin and eosin and immunohistochemical staining of proliferating cell nuclear antigen and epithelial cell adhesion molecule enabled HOC proliferation analysis.

RESULTS

FK506 intervention exacerbated liver damage and hindered the recovery of the HOC model rat. Weight gain was severely retarded or even negative. Liver weight and the liver body weight ratio were lower than control group. HE and immunohistochemistry showed pooer proliferation of hepatocytes and fewer HOC numbers in group A.

CONCLUSION

FK506 inhibited HOC activation by affecting T and NK cells, ultimately blocking liver regeneration. Poor liver regeneration after auxiliary liver transplantation might be associated with the inhibition of HOC activation and proliferation caused by FK506 treatment.

Trans-activation of eotaxin-1 by Brg1 contributes to liver regeneration

Infiltration of eosinophils is associated with and contributes to liver regeneration. Chemotaxis of eosinophils is orchestrated by the eotaxin family of chemoattractants. We report here that expression of eotaxin-1 (referred to as eotaxin hereafter), but not that of either eotaxin-2 or eotaxin-3, were elevated, as measured by quantitative PCR and ELISA, in the proliferating murine livers compared to the quiescent livers. Similarly, exposure of primary murine hepatocytes to hepatocyte growth factor (HGF) stimulated eotaxin expression. Liver specific deletion of Brahma-related gene 1 (Brg1), a chromatin remodeling protein, attenuated eosinophil infiltration and down-regulated eotaxin expression in mice. Brg1 deficiency also blocked HGF-induced eotaxin expression in cultured hepatocytes. Further analysis revealed that Brg1 could directly bind to the proximal eotaxin promoter to activate its transcription. Mechanistically, Brg1 interacted with nuclear factor kappa B (NF-κB)/RelA to activate eotaxin transcription. NF-κB knockdown or pharmaceutical inhibition disrupted Brg1 recruitment to the eotaxin promoter and blocked eotaxin induction in hepatocytes. Adenoviral mediated over-expression of eotaxin overcame Brg1 deficiency caused delay in liver regeneration in mice. On the contrary, eotaxin depletion with RNAi or neutralizing antibodies retarded liver regeneration in mice. More important, Brg1 expression was detected to be correlated with eotaxin expression and eosinophil infiltration in human liver specimens. In conclusion, our data unveil a novel role of Brg1 as a regulator of eosinophil trafficking by activating eotaxin transcription.

GITR/GITRL reverse signalling modulates the proliferation of hepatic progenitor cells by recruiting ANXA2 to phosphorylate ERK1/2 and Akt

Hepatic stem/progenitor cells are the major cell compartment for tissue repair when hepatocyte proliferation is compromised in chronic liver diseases, but the expansion of these cells increases the risk of carcinogenesis. Therefore, it is essential to explore the pathways restricting their expansion and abnormal transformation. The ligand of glucocorticoid-induced tumour necrosis factor receptor (GITRL) showed the most highly increased expression in hepatic progenitor cells treated with transforming growth factor (TGF)-β1. If overexpressed by hepatic progenitor cells, GITRL stimulated cell proliferation by activating the epithelial–mesenchymal transition pathway and enhancing ERK1/2 and Akt phosphorylation via GITRL binding to ANXA2. However, GITR, the specific GITRL receptor, suppressed the epithelial–mesenchymal transition pathway of GITRL-expressing cells and decreased their growth by dissociating ANXA2 from GITRL and reducing downstream ERK1/2 and Akt phosphorylation. This study identifies GITR/GITRL reverse signalling as a cross-interaction pathway between immune cells and hepatic stem/progenitor cells that restricts the expansion of hepatic stem/progenitor cells and reduces the possibility of carcinogenesis.

A narrative review of liver regeneration-from models to molecular basis

Objective

To elucidate the characteristics of different liver regeneration animal models, understand the activation signals and mechanisms related to liver regeneration, and obtain a more comprehensive conception of the entire liver regeneration process.

Background

Liver regeneration is one of the most enigmatic and fascinating phenomena of the human organism. Despite suffering significant injuries, the liver still can continue to perform its complex functions through the regeneration system. Although advanced topics on liver regeneration have been proposed; unfortunately, complete regeneration of the liver has not been achieved until now. Therefore, increasing understanding of the liver regenerative process can help improve our treatment of liver failure. It will provide a new sight for the treatment of patients with liver injury in the clinic.

Methods

Literatures on liver regeneration animal models and involved basic research on molecular mechanisms were retrieved to analyze the characteristics of different models and those related to molecular basis.

Conclusions

The process of liver regeneration is complex and intricate, consisting of various and interactive pathways. There is sufficient evidence to demonstrate that liver regeneration is similar between humans and rodents. At the same time, many of the same cytokines, growth factors, and signaling pathways are relevant. There are many gaps in our current knowledge. Understanding of this knowledge will provide more supportive clinical treatment strategies, including small-scale liver transplantation and high-quality regenerative process after surgical resection, and offer possible targets to treat the dysregulation of regeneration that occurs in chronic hepatic diseases and tumors. Current research work, such as the use of animal models as in vivo vectors for high-quality human hepatocytes, represents a unique and significant cutting edge in the field of liver regeneration.

Smad3 gene C-terminal phosphorylation site mutation aggravates CCl4 -induced inflammation in mice

The expression of C‐terminal phosphorylated Smad3 (pSmad3C) is down‐regulated with the progression of liver disease. Thus, we hypothesized that pSmad3C expression may be negatively related to liver disease. To develop novel therapeutic strategies, a suitable animal model is required that will allow researchers to study the effect of Smad3 domain‐specific phosphorylation on liver disease progression. The current study aimed to construct a new mouse model with the Smad3 C‐terminal phosphorylation site mutation and to explore the effects of this mutation on CCl₄‐induced inflammation. Smad3 C‐terminal phosphorylation site mutant mice were generated using TetraOne™ gene fixed‐point knock‐in technology and embryonic stem cell microinjection. Resulting mice were identified by genotyping, and the effects on inflammation were explored in the presence or absence of CCl₄. No homozygous mice were born, indicating that the mutation is embryonic lethal. There was no significant difference in liver phenotype and growth between the wild‐type (WT) and heterozygous (HT) mice in the absence of reagent stimulation. After CCl₄‐induced acute and chronic liver damage, liver pathology, serum transaminase (ALT/AST) expression and levels of inflammatory factors (IL‐6/TNF‐α) were more severely altered in HT mice than in WT mice. Furthermore, pSmad3C protein levels were lower in liver tissue from HT mice. These results suggest that Smad3 C‐terminal phosphorylation may have a protective effect during the early stages of liver injury. In summary, we have generated a new animal model that will be a novel tool for future research on the effects of Smad3 domain‐specific phosphorylation on liver disease progression.

Redox Control of the Immune Response in the Hepatic Progenitor Cell Niche

The liver commonly self-regenerates by a proliferation of mature cell types. Nevertheless, in case of severe or protracted damage, the organ renewal is mediated by the hepatic progenitor cells (HPCs), adult progenitors capable of differentiating toward the biliary and the hepatocyte lineages. This regeneration process is determined by the formation of a stereotypical niche surrounding the emerging progenitors. The organization of the HPC niche microenvironment is crucial to drive biliary or hepatocyte regeneration. Furthermore, this is the site of a complex immunological activity mediated by several immune and non-immune cells. Indeed, several cytokines produced by monocytes, macrophages and T-lymphocytes may promote the activation of HPCs in the niche. On the other side, HPCs may produce pro-inflammatory cytokines induced by liver inflammation. The inflamed liver is characterized by high generation of reactive oxygen and nitrogen species, which in turn lead to the oxidation of macromolecules and the alteration of signaling pathways. Reactive species and redox signaling are involved in both the immunological and the adult stem cell regeneration processes. It is then conceivable that redox balance may finely regulate the immune response in the HPC niche, modulating the regeneration process and the immune activity of HPCs. In this perspective article, we summarize the current knowledge on the role of reactive species in the regulation of hepatic immunity, suggesting future research directions for the study of redox signaling on the immunomodulatory properties of HPCs.

Maresin 1 mitigates concanavalin A-induced acute liver injury in mice by inhibiting ROS-mediated activation of NF-κB signaling

The liver is the most important metabolic and detoxifying organ in the human body, and liver damage can seriously affect bodily function and potentially be life threatening. Accumulating evidence suggests that maresin 1 (MaR1) exhibits protective and anti-inflammatory effects in some diseases, such as pneumonia and colitis; however, its role in acute hepatitis remains unclear. Here, we established a concanavalin A (ConA)-induced acute liver-injury mouse model to determine whether MaR1 administration can attenuate liver damage. Our results indicate that MaR1 confers protective effects against ConA-induced acute liver injury, improves liver function and survival, and reduces histopathological damage. Additionally, MaR1 attenuated the inflammatory response and reduced hepatocyte apoptosis while increasing mouse macrophage apoptosis and markedly decreasing levels of reactive oxygen species (ROS) in macrophages. We also found that MaR1 significantly inhibited ConA-induced activation of the nuclear factor-kappaB (NF-κB) pathway. This work will contribute to a better understanding of acute liver injury (ALI) and advancement towards its treatment.

IL-22 suppresses HSV-2 replication in human cervical epithelial cells

Interleukin (IL)-22, a member of the IL-10 family, plays a role in antiviral immune responses to a number of viral infections. However, it is unclear whether IL-22 is involved in the mucosal immunity against herpes simplex virus 2 (HSV-2) infection in the female reproductive tract (FRT). In this study, we studied whether IL-22 could inhibit HSV-2 infection of human cervical epithelial cells (End1/E6E7 cells). We showed that End1/E6E7 cells express the functional IL-22 receptor complex (IL-22R1 and IL-10R2). When treated with IL-22, End1/E6E7 cells expressed the higher levels of IFN-stimulated genes (ISGs: ISG15, ISG56, OAS-1, OAS-2, and Mx2) than untreated cells. In addition, IL-22-treated cells produced higher levels of the tight junction proteins (ZO-1 and Occludin) than untreated cells. Mechanistically, IL-22 could activate the JAK/STAT signaling pathway by inducing the phosphorylation of STAT1 and STAT3. These observations indicate the potential of IL-22 as an anti-HSV-2 agent in the FRT mucosal innate immunity against HSV-2 infection.

Understanding the marvels behind liver regeneration

Tissue regeneration is a process by which the remaining cells of an injured organ regrow to offset the missed cells. This field is relatively a new discipline that has been a focus of intense research by clinicians, surgeons, and scientists for decades. It constitutes the cornerstone of tissue engineering, creation of artificial organs, and generation and utilization of therapeutic stem cells to undergo transformation to different types of mature cells. Many medical experts, scientists, biologists, and bioengineers have dedicated their efforts to deeply comprehend the process of liver regeneration, striving for harnessing it to invent new therapies for liver failure. Liver regeneration after partial hepatectomy in rodents has been extensively studied by researchers for many years. It is divided into three important distinctive phases including (a) Initiation or priming phase which includes an overexpression of specific genes to prepare the liver cells for replication, (b) Proliferation phase in which the liver cells undergo a series of cycles of cell division and expansion and finally, (c) termination phase which acts as brake to stop the regenerative process and prevent the liver tissue overgrowth. These events are well controlled by cytokines, growth factors, and signaling pathways. In this review, we describe the function, embryology, and anatomy of human liver, discuss the molecular basis of liver regeneration, elucidate the hepatocyte and cholangiocyte lineages mediating this process, explain the role of hepatic progenitor cells and elaborate the developmental signaling pathways and regulatory molecules required to procure a complete restoration of hepatic lobule. This article is categorized under: Adult Stem Cells, Tissue Renewal, and Regeneration > Regeneration Signaling Pathways > Global Signaling Mechanisms Gene Expression and Transcriptional Hierarchies > Cellular Differentiation.

Rapid Recapitulation of Nonalcoholic Steatohepatitis upon Loss of Host Cell Factor 1 Function in Mouse Hepatocytes

Host cell factor 1 (HCF-1), encoded by the ubiquitously expressed X-linked gene Hcfc1, is an epigenetic coregulator important for mouse development and cell proliferation, including during liver regeneration. We used a hepatocyte-specific inducible Hcfc1 knockout allele (called Hcfc1^hepKO) to induce HCF-1 loss in hepatocytes of hemizygous Hcfc1^hepKO/Y males by 4 days.

Host cell factor 1 (HCF-1), encoded by the ubiquitously expressed X-linked gene Hcfc1, is an epigenetic coregulator important for mouse development and cell proliferation, including during liver regeneration. We used a hepatocyte-specific inducible Hcfc1 knockout allele (called Hcfc1^hepKO) to induce HCF-1 loss in hepatocytes of hemizygous Hcfc1^hepKO/Y males by 4 days. In heterozygous Hcfc1^hepKO/+ females, owing to random X-chromosome inactivation, upon Hcfc1^hepKO allele induction, a 50/50 mix of HCF-1-positive and -negative hepatocyte clusters is engineered. The livers with Hcfc1^hepKO/Y hepatocytes displayed a 21- to 24-day terminal nonalcoholic fatty liver (NAFL), followed by nonalcoholic steatohepatitis (NASH) disease progression typical of severe NAFL disease (NAFLD). In contrast, in livers with heterozygous Hcfc1^hepKO/+ hepatocytes, HCF-1-positive hepatocytes replaced HCF-1-negative hepatocytes and revealed only mild NAFL development. Loss of HCF-1 led to loss of PGC1α protein, probably owing to its destabilization, and deregulation of gene expression, particularly of genes involved in mitochondrial structure and function, likely explaining the severe Hcfc1^hepKO/Y liver pathology. Thus, HCF-1 is essential for hepatocyte function, likely playing both transcriptional and nontranscriptional roles. These genetically engineered loss-of-HCF-1 mice can be used to study NASH as well as NAFLD resolution.

Impaired T cell-mediated hepatitis in peroxisome proliferator activated receptor alpha (PPARα)-deficient mice

BACKGROUND

Peroxisome proliferator activated receptor alpha (PPARα), a regulator of enzymes involved in β oxidation, has been reported to influence lymphocyte activation. The purpose of this study was to determine whether PPARα plays a role in T cell-mediated hepatitis induced by Concanavalin A (ConA).

METHODS

Wild type (wt) or PPARα-deficient (PPARα-/-) mice were treated with ConA (15 mg/kg) by intravenous injection 0, 10 or 24 h prior to sacrifice and serum and tissue collection for analysis of tissue injury, cytokine response, T cell activation and characterization.

RESULTS

Ten and 24 h following ConA administration, wt mice had significant liver injury as demonstrated by serum transaminase levels, inflammatory cell infiltrate, hepatocyte apoptosis, and expression of several cytokines including interleukin 4 (IL4) and interferon gamma (IFNγ). In contrast, PPARα-/- mice were protected from ConA-induced liver injury with significant reductions in serum enzyme release, greatly reduced inflammatory cell infiltrate, hepatocellular apoptosis, and IFNγ expression, despite having similar levels of hepatic T cell activation and IL4 expression. This resistance to liver injury was correlated with reduced numbers of hepatic natural killer T (NKT) cells and their in vivo responsiveness to alpha-galactosylceramide. Interestingly, adoptive transfer of either wt or PPARα-/- splenocytes reconstituted ConA liver injury and cytokine production in lymphocyte-deficient, severe combined immunodeficient mice implicating PPARα within the liver, possibly through support of IL15 expression and/or suppression of IL12 production and not the lymphocyte as the key regulator of T cell activity and ConA-induced liver injury.

CONCLUSION

Taken together, these data suggest that PPARα within the liver plays an important role in ConA-mediated liver injury through regulation of NKT cell recruitment and/or survival.

Interleukins-17 and 27 promote liver regeneration by sequentially inducing progenitor cell expansion and differentiation

Liver progenitor cells (LPCs)/ductular reactions (DRs) are associated with inflammation and implicated in the pathogenesis of chronic liver diseases. However, how inflammation regulates LPCs/DRs remains largely unknown. Identification of inflammatory processes that involve LPC activation and expansion represent a key step in understanding the pathogenesis of liver diseases. In the current study, we found that diverse types of chronic liver diseases are associated with elevation of infiltrated interleukin (IL)-17-positive (+) cells and cytokeratin 19 (CK19)⁺ LPCs, and both cell types colocalized and their numbers positively correlated with each other. The role of IL-17 in the induction of LPCs was examined in a mouse model fed a choline-deficient and ethionine-supplemented (CDE) diet. Feeding of wild-type mice with the CDE diet markedly elevated CK19⁺Ki67⁺ proliferating LPCs and hepatic inflammation. Disruption of the IL-17 gene or IL-27 receptor, alpha subunit (WSX-1) gene abolished CDE diet-induced LPC expansion and inflammation. In vitro treatment with IL-17 promoted proliferation of bipotential murine oval liver cells (a liver progenitor cell line) and markedly up-regulated IL-27 expression in macrophages. Treatment with IL-27 favored the differentiation of bipotential murine oval liver cells and freshly isolated LPCs into hepatocytes. Conclusion: The current data provide evidence for a collaborative role between IL-17 and IL-27 in promoting LPC expansion and differentiation, respectively, thereby contributing to liver regeneration. (Hepatology Communications 2018;2:329-343).

Resveratrol Pretreatment Attenuates Concanavalin A-induced Hepatitis through Reverse of Aberration in the Immune Response and Regenerative Capacity in Aged Mice

Loss of regenerative capacity plays a critical role in age-related autoimmune hepatitis. Evidence implicates SIRT1 and p66^shc in cell senescence, apoptosis, oxidative stress, and proliferation. This study investigated the effect of resveratrol on concanavalin A (Con A)-induced hepatitis in aged mice and the roles of SIRT1 and p66^shc. Aged mice were administrated resveratrol (30 mg/kg orally) seven times at an interval of 12 h before a single intravenous injection of Con A (20 mg/kg). Results showed that the cytokines, TNF-α, IL-6, IFN-γ, and MCP-1, as well as infiltration of macrophages, neutrophils, and T lymphocytes in liver were dramatically enhanced in the mice given only Con A. The aged mouse livers showed markedly raised oxidative stress and cell apoptosis. This oxidative stress further aggravated regenerative dysfunction as indicated by the decreased levels of Ki67, PCNA, Cyclin D1, and Cdk2. Conversely, these phenomena were attenuated by pretreatment with resveratrol. Moreover, resveratrol suppressed the elevation of p66^shc in the liver by reversing Con-A-mediated downregulation of SIRT1. The findings suggest that resveratrol protected against Con A-induced hepatitis in aged mice by attenuating an aberration of immune response and liver regeneration, partially via the mechanism of SIRT1-mediated repression of p66^shc expression.

Proliferation‑inhibiting pathways in liver regeneration (Review)

Liver regeneration, an orchestrated process, is the primary compensatory mechanism following liver injury caused by various factors. The process of liver regeneration consists of three stages: Initiation, proliferation and termination. Proliferation‑promoting factors, which stimulate the recovery of mitosis in quiescent hepatocytes, are essential in the initiation and proliferation steps of liver regeneration. Proliferation‑promoting factors act as the 'motor' of liver regeneration, whereas proliferation inhibitors arrest cell proliferation when the remnant liver reaches a suitable size. Certain proliferation inhibitors are also expressed and activated in the first two steps of liver regeneration. Anti‑proliferation factors, acting as a 'brake', control the speed of proliferation and determine the terminal point of liver regeneration. Furthermore, anti‑proliferation factors function as a 'steering‑wheel', ensuring that the regeneration process proceeds in the right direction by preventing proliferation in the wrong direction, as occurs in oncogenesis. Therefore, proliferation inhibitors to ensure safe and stable liver regeneration are as important as proliferation‑promoting factors. Cytokines, including transforming growth factor‑β and interleukin‑1, and tumor suppressor genes, including p53 and p21, are important members of the proliferation inhibitor family in liver regeneration. Certain anti‑proliferation factors are involved in the process of gene expression and protein modification. The suppression of liver regeneration led by metabolism, hormone activity and pathological performance have been reviewed previously. However, less is known regarding the proliferation inhibitors of liver regeneration and further investigations are required. Detailed information regarding the majority of known anti‑proliferation signaling pathways also remains fragmented. The present review aimed to understand the signalling pathways that inhbit proliferation in the process of liver regeneration.

Impaired liver regeneration is associated with reduced cyclin B1 in natural killer T cell-deficient mice

Background

It has been shown that the proportion of natural killer T cells is markedly elevated during liver regeneration and their activation under different conditions can modulate this process. As natural killer T cells and liver injury are central in liver regeneration, elucidating their role is important.

Methods

The aim of the current study is to explore the role of natural killer T cells in impaired liver regeneration. Concanvalin A was injected 4 days before partial hepatectomy to natural killer T cells- deficient mice or to anti CD1d1-treated mice. Ki-67 and proliferating cell nuclear antigen were used to measure hepatocytes proliferation. Expression of hepatic cyclin B1 and proliferating cell nuclear antigen were evaluated by Western Blot and liver injury was assessed by ALT and histology.

Results

Natural killer T cells- deficient or mice injected with anti CD1d antibodies exhibited reduced liver regeneration. These mice were considerably resistant to ConA-induced liver injury. In the absence of NKT cells hepatic proliferating cell nuclear antigen and cyclin B1 decreased in mice injected with Concanvalin A before partial hepatectomy. This was accompanied with reduced serum interleukin-6 levels.

Conclusions

Natural killer T cells play an important role in liver regeneration, which is associated with cyclin B1 and interleukin-6.

Systems Analysis of the Complement-Induced Priming Phase of Liver Regeneration

Liver regeneration is a well-orchestrated process in the liver that allows mature hepatocytes to reenter the cell cycle to proliferate and replace lost or damaged cells. This process is often impaired in fatty or diseased livers, leading to cirrhosis and other deleterious phenotypes. Prior research has established the role of the complement system and its effector proteins in the progression of liver regeneration; however, a detailed mechanistic understanding of the involvement of complement in regeneration is yet to be established. In this study, we have examined the role of the complement system during the priming phase of liver regeneration through a systems level analysis using a combination of transcriptomic and metabolomic measurements. More specifically, we have performed partial hepatectomy on mice with genetic deficiency in C3, the major component of the complement cascade, and collected their livers at various time points. Based on our analysis, we show that the C3 cascade activates c-fos and promotes the TNF-α signaling pathway, which then activates acute-phase genes such as serum amyloid proteins and orosomucoids. The complement activation also regulates the efflux and the metabolism of cholesterol, an important metabolite for cell cycle and proliferation. Based on our systems level analysis, we provide an integrated model for the complement-induced priming phase of liver regeneration.

The concanavalin A model of acute hepatitis in mice

The intravenous injection of the plant lectin concanavalin A (ConA) is a widely used model for acute immune-mediated hepatitis in mice. In contrast to several other models for acute hepatic damage, ConA-induced injury is primarily driven by the activation and recruitment of T cells to the liver. Hence, the ConA model has unique features with respect to its pathogenesis and important similarities to immune-mediated hepatitis in humans, such as autoimmune hepatitis, acute viral hepatitis or distinct entities of drug toxicity leading to immune activation. However, the ConA model has considerable variability, depending on the preparation of the compound, genetic background of the mice, sex, age and microbial environment of the animal facility barrier. This standard operating procedure (SOP) comprises a detailed protocol for the ConA application, including preparation of ConA working solution, handling of the animals, choice of the appropriate conditions and endpoints, as well as efficient dose-finding.

Mesenchymal stem cell therapy for cirrhosis: Present and future perspectives

Cirrhosis occurs as a result of various chronic liver injuries, which may be caused by viral infections, alcohol abuse and the administration of drugs and chemicals. Recently, bone marrow cells (BMCs), hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs) have been used for developing treatments for cirrhosis. Clinical trials have investigated the therapeutic potential of BMCs, HSCs and MSCs for the treatment of cirrhosis based on their potential to differentiate into hepatocytes. Although the therapeutic mechanisms of BMC, HSC and MSC treatments are still not fully characterized, the evidence thus far has indicated that the potential therapeutic mechanisms of MSCs are clearer than those of BMCs or HSCs with respect to liver regenerative medicine. MSCs suppress inflammatory responses, reduce hepatocyte apoptosis, increase hepatocyte regeneration, reverse liver fibrosis and enhance liver functionality. This paper summarizes the clinical studies that have used BMCs, HSCs and MSCs in patients with liver failure or cirrhosis. We also present the potential therapeutic mechanisms of BMCs, HSCs and MSCs for the improvement of liver function.

Hepatic oval cells and liver diseases

In recent years, hepatic oval cells (HOC) have gradually become a research hotspot, and their participation in the reconstruction of liver structure and function has been preliminarily confirmed. This provides a new direction for the study of the pathogenesis and treatment of liver injury, hepatitis, liver fibrosis, cirrhosis, liver neoplasms and other liver diseases. This paper will discuss the relationship between hepatic oval cells and liver diseases.

A role of microRNA-370 in hepatic ischaemia-reperfusion injury by targeting transforming growth factor-β receptor II

BACKGROUND & AIMS

MicroRNAs (miRNAs) are a group of small non-coding RNAs with modulator activity of gene expression. The role of miRNAs in hepatic ischaemia-reperfusion (IR) injury is currently largely unknown. The aim of this study was to investigate the potential role of miR-370 in hepatic IR injury.

METHODS

The expression levels of hepatic miR-370 in male C57BL/6 mice subjected to hepatic IR injury or ischaemia preconditioning were assessed by quantitative real-time PCR. The effect of miR-370 on hepatic IR injury was investigated by serum enzyme analysis and histological examination of liver following treatment of mice with antagomir-370 or control. The levels of proinflammatory cytokines and apoptosis- and proliferation-related genes were also determined by quantitative real-time PCR. Furthermore, the potential targets of miR-370 in this injury were studied by bioinformatics analysis, luciferase assays, quantitative real-time PCR and Western blot.

RESULTS

The results showed that miR-370 expression was significantly upregulated in the mice subjected to hepatic IR injury as compared with the sham-operated mice. Inhibition of miR-370 led to the downregulation of serum aminotransferase and proinflammatory cytokines, as well as the improvement of hepatic histological damage. Reporter assays confirmed that miR-370 directly targeted the 3' untranslated region of transforming growth factor-β receptor II (TβRII). Inhibition of miR-370 was sufficient to reinstate the expression of TβRII and its downstream target phosphorylated Smad3.

CONCLUSION

Our data suggest that miR-370 acting via TβRII might play a potential role in hepatic IR injury, and inhibition of miR-370 efficiently attenuated the damage to the liver.

The protective role of myeloid-derived suppressor cells in concanavalin A-induced hepatic injury

The mechanism underlying T cell-mediated fulminant hepatitis is not fully understood. In this study, we investigated whether myeloid derived suppressor cells (MDSCs) could prevent the concanavalin A (ConA)-induced hepatitis through suppressing T cell proliferation. We observed an increase in the frequencies of MDSCs in mouse spleen and liver at early stage of ConA treatment, implicating that the MDSCs might be involved in the initial resistance of mice against ConA-mediated inflammation. Subpopulation analysis showed that the MDSCs in liver of ConA-induced mice were mainly granulocytic MDSCs. Adoptive transfer of the bone marrow-derived MDSCs into ConA-treated mice showed that the MDSCs migrated into the liver and spleen where they suppressed T cell proliferation through ROS pathway. In addition, the frequencies of MDSCs in mice were also significantly increased by the treatment with immune suppressor glucocorticoids. Transfer of MDSCs into the regulatory T cell (Treg)-depleted mice showed that the protective effect of MDSCs on ConA-induced hepatitis is Treg-independent. In conclusion, our results demonstrate that MDSCs possess a direct protective role in T cell-mediated hepatitis, and increasing the frequency of MDSCs by either adoptive transfer or glucocorticoid treatment represents a potential cell-based therapeutic strategy for the acute inflammatory disease.

Smad3 signaling in the regenerating liver: implications for the regulation of IL-6 expression

Liver regeneration is vital for graft survival and adequate organ function. Smad activation regulates hepatocyte proliferation and macrophage function. The aim of the current study was to evaluate the impact of Smad3 signaling during liver regeneration in the mouse. Male C57Bl/6 wild-type (wt) mice or mice deficient in Smad3 (Smad3(-/-) ) were subjected to a 70% partial hepatectomy (pHx) or sham surgery and sacrificed 24, 42, or 48 h later. Tissue was analyzed for TGF-β signaling, the mitogenic cytokine response [i.e., tumor necrosis factor alpha, TNF-α; interleukin (IL)-6], and liver regeneration. Partial hepatectomy stimulated a strong regenerative response measured by proliferating cell nuclear antigen-positive hepatocytes 42 and 48 h post-pHx in conjunction with an increased expression of IL-6, TNF-α, and Smad2/3 phosphorylation 24 h post-pHx in both hepatocytes and nonparenchymal cells. Surprisingly, Smad3 deficiency led to reduced hepatocyte proliferation 42 h post-pHx which recovered by 48 h, a process that correlated with and was preceded by significant reductions in IL-6 expression and signal transducer and activator of transcription 3 phosphorylation, and cyclin D1 induction 24 h post-pHx. Loss of Smad3 signaling suppresses the expression of key mitogenic cytokines and delays hepatocellular regeneration. Therapies directed at finely regulating Smad3 activation early within the regenerating liver may prove useful in promoting liver cell proliferation and restoration of liver mass.

Terminally differentiated CD8⁺ T cells negatively affect bone regeneration in humans

There is growing evidence that adaptive immunity contributes to endogenous regeneration processes: For example, endogenous bone fracture repair is modulated by T cells even in the absence of infection. Because delayed or incomplete fracture healing is associated with poor long-term outcomes and high socioeconomic costs, we investigated the relationship between an individual's immune reactivity and healing outcome. Our study revealed that delayed fracture healing significantly correlated with enhanced levels of terminally differentiated CD8(+) effector memory T (TEMRA) cells (CD3(+)CD8(+)CD11a(++)CD28(-)CD57(+) T cells) in peripheral blood. This difference was long lasting, reflecting rather the individual's immune profile in response to lifelong antigen exposure than a post-fracture reaction. Moreover, CD8(+) TEMRA cells were enriched in fracture hematoma; these cells were the major producers of interferon-γ/tumor necrosis factor-α, which inhibit osteogenic differentiation and survival of human mesenchymal stromal cells. Accordingly, depletion of CD8(+) T cells in a mouse osteotomy model resulted in enhanced endogenous fracture regeneration, whereas a transfer of CD8(+) T cells impaired the healing process. Our data demonstrate the high impact of the individual adaptive immune profile on endogenous bone regeneration. Quantification of CD8(+) TEMRA cells represents a potential marker for the prognosis of the healing outcome and opens new opportunities for early and targeted intervention strategies.

Routine induction therapy in living donor liver transplantation prevents rejection but may promote recurrence of hepatitis C

BACKGROUND

Routine induction therapy in living donor liver transplantation (LDLT) has not been well described.

METHODS

We reviewed outcomes of induction therapy with rabbit antithymocyte globulin (rATG) or basiliximab within 1 year of LDLT.

RESULTS

Between 2002 and 2007, 184 adults underwent LDLT and received induction therapy in addition to standard immunosuppression. Acute cellular rejection (ACR) developed in 17 of 130 patients (13.1%) who received rATG and 13 of 54 patients (24.1%) who received basiliximab (P = .066). The interval between transplantation and rejection as well as rejection severity was similar in patients who received rATG and those who received basiliximab. Hepatitis C (HCV) recurrence requiring initiation of antiviral therapy was more common in patients who received rATG compared with basiliximab (34.5% vs 8.7%; P = .021), and in those who received induction combined with tacrolimus as opposed to cyclosporine (38.5% vs 3.9%; P = .001). rATG and basiliximab were associated with excellent patient and graft survivals well as low rates of opportunistic infections and malignancies.

CONCLUSION

Induction with rATG or basiliximab was well tolerated and highly effective at preventing ACR within 1 year of LDLT, but may be associated with a higher risk of clinically significant HCV recurrence in some patients.

The influence of donor age on liver regeneration and hepatic progenitor cell populations

BACKGROUND

Recent reports suggest that donor age might have a major impact on recipient outcome in adult living donor liver transplantation (LDLT), but the reasons underlying this effect remain unclear. The aims of this study were to compare liver regeneration between young and aged living donors and to evaluate the number of Thy-1+ cells, which have been reported to be human hepatic progenitor cells.

METHODS

LDLT donors were divided into 2 groups (Group O, donor age ≥ 50 years, n = 6 and Group Y, donor age ≤ 30 years, n = 9). The remnant liver regeneration rates were calculated on the basis of computed tomography volumetry on postoperative days 7 and 30. Liver tissue samples were obtained from donors undergoing routine liver biopsy or patients undergoing partial hepatectomy for metastatic liver tumors. Thy-1+ cells were isolated and counted using immunomagnetic activated cell sorting (MACS) technique.

RESULTS

Donor liver regeneration rates were significantly higher in young donors compared to old donors (P = .042) on postoperative day 7. Regeneration rates were significantly higher after right lobe resection compared to rates after left lobe resection. The MACS findings showed that the number of Thy-1+ cells in the human liver consistently tended to decline with age.

CONCLUSION

Our study revealed that liver regeneration is impaired with age after donor hepatectomy, especially after right lobe resection. The declining hepatic progenitor cell population might be one of the reasons for impaired liver regeneration in aged donors.

Elevated interferon gamma signaling contributes to impaired regeneration in the aged liver

Our previous study on immune-related changes in the aged liver described immune cell infiltration and elevation of inflammation with age. Levels of interferon (IFN)-γ, a known cell cycle inhibitor, were elevated in the aging liver. Here, we determine the role played by IFN-γ in the delayed regenerative response observed in the aged livers. We observed elevated IFN signaling in both aged hepatocytes and regenerating livers post-partial hepatectomy. In vivo deletion of the major IFN-γ producers-the macrophages and the natural killer cells, leads to a reduction in the IFN-γ levels accompanied with the restoration of the DNA synthesis kinetics in the aged livers. Eighteen-month-old IFN-γ-/- mice livers, upon resection, exhibited an earlier entry into the cell cycle compared with age-matched controls. Thus, our study strongly suggests that an age-related elevation in inflammatory conditions in the liver often dubbed as "inflammaging" has a detrimental effect on the regenerative response.

Cytokeratin expression as an aid to diagnosis in medical liver biopsies

The study of cytokeratin expression has provided a valuable insight into the biliary microanatomy of the liver in health and disease. The canals of Hering are a putative site of origin for progenitor cells, which may repopulate the liver after cellular damage and loss. Normal bile ducts and the bile ductular reaction that occurs in many chronic liver diseases - especially chronic biliary tract disease - express cytokeratin (CK) 7 and CK19. Therefore, both ductopenia and the process of bile ductular reaction can be highlighted with immunohistochemistry for these cytokeratins. Furthermore, CK7 is usually expressed in an increasingly widespread manner by hepatocytes as chronic cholestatic liver disease progresses. For these reasons, CK immunohistochemistry is a very useful adjunct to morphological assessment and histochemical stains for copper retention when a diagnosis of chronic biliary disease is being considered. This review describes the anatomical theory behind the use of CK immunohistochemistry for the assessment of bile duct number and distribution in the liver and provides practical advice for the application of this technique in the diagnostic setting of common medical liver diseases.

Recent advances in liver stem cell therapy

PURPOSE OF REVIEW

Patients with liver cirrhosis often require liver transplantation, which remains the only effective treatment of the end-stage cirrhosis. Here we briefly summarize the current concepts in treatment of liver diseases based on the transplantation of intrahepatic liver cells, capable of repopulating the injured liver. These cells include hepatocytes, oval cells (bipotential intrahepatic progenitor cells), bone marrow hematopoietic and mesenchymal stem cells, and induced pluripotent stem (iPS) cells.

RECENT FINDINGS

Although liver transplantation remains the only conventional treatment, liver cell transplantation is an experimental procedure which has been successfully used in clinical trials in patients with acute liver failure, chronic liver disease with end-stage cirrhosis. Extraordinary progress has been made in the field of hepatic progenitors and iPS. Liver precursor cells (oval cells) are recognized as bipotential precursor cells in the damaged liver. They can rapidly proliferate, change their cellular composition, and differentiate into hepatocytes and cholangiocytes to compensate for the cellular loss and maintain liver homeostasis in animal models of liver injury. Similarly, iPS are somatic cells obtained from patients and differentiated into hepatocytes in vitro. Future studies of iPS are designed to develop of specific conditions to expand and in vitro differentiate somatic cells into functionally mature liver cells.

SUMMARY

The current review defines and discusses different populations of hepatic cells which can be potentially used for liver cell transplantation to advance the therapy of hepatic cirrhosis.

Hepatic progenitors for liver disease: current position

Liver regeneration restores the original functionality of hepatocytes and cholangiocytes in response to injury. It is regulated on several levels, with different cellular populations contributing to this process, eg, hepatocytes, liver precursor cells, intrahepatic stem cells. In response to injury, mature hepatocytes have the capability to proliferate and give rise to new hepatocytes and cholangiocytes. Meanwhile, liver precursor cells (oval cells) have become the most recognized bipotential precursor cells in the damaged liver. They rapidly proliferate, change their cellular composition, and differentiate into hepatocytes and cholangiocytes to compensate for the cellular loss and maintain liver homeostasis. There is a growing body of evidence that oval cells originate from the intrahepatic stem cell(s), which in turn give(s) rise to epithelial, including oval cells, and/or other hepatic cells of nonepithelial origin. Since there is a close relationship between the liver and hematopoiesis, bone marrow derived cells can also contribute to liver regeneration by the fusion of myeloid cells with damaged hepatocytes, or differentiation of mesenchymal stem cells into hepatocyte-like cells. The current review discusses the contribution of different cells to liver regeneration and their characteristics.

Regenerative capacity of normal and irradiated liver following partial hepatectomy in rats

PURPOSE

To investigate the regenerative capacity and proliferation related to cell cycle modulators in irradiated livers after partial hepatectomy (PH) in rats.

METHODS AND MATERIALS

Two experimental groups were given a single dose of either 4-Gy or 8-Gy photon radiation to the whole liver following PH. The control group underwent only PH, without irradiation. The liver specimens were analysed for apoptosis, proliferation and cell cycle related genes between 0.5 and 12 days.

RESULTS

Mean change in weight of the remnant liver in the 8-Gy group was significantly lower than in the control and 4-Gy groups. The apex of proliferating cell nuclear antigen labelling and bromodeoxyuridine incorporation index in two irradiated groups were also apparently lower than that in control group. After PH, transforming growth factor beta-1 (TGFbeta1), and the type II receptor of TGFbeta (TGFbetaR-II), anti-tumour protein 53(p53) and anti-tumour protein21(p21) protein expression in the irradiated livers was higher than in unirradiated ones. Significant apoptosis was noted in 8-Gy group. However, the maximal value of hepatocyte growth factor (HGF) mRNA and protein expression in the irradiated group was suppressed and restoration of liver function was delayed.

CONCLUSION

Whole liver lower dose irradiation can attenuate regenerative capacity following partial hepatectomy in rats.

Signal molecule-mediated hepatic cell communication during liver regeneration

Liver regeneration is a complex and well-orchestrated process, during which hepatic cells are activated to produce large signal molecules in response to liver injury or mass reduction. These signal molecules, in turn, set up the connections and cross-talk among liver cells to promote hepatic recovery. In this review, we endeavor to summarize the network of signal molecules that mediates hepatic cell communication in the regulation of liver regeneration.

Liver natural killer and natural killer T cells: immunobiology and emerging roles in liver diseases

Hepatic lymphocytes are enriched in NK and NKT cells that play important roles in antiviral and antitumor defenses and in the pathogenesis of chronic liver disease. In this review, we discuss the differential distribution of NK and NKT cells in mouse, rat, and human livers, the ultrastructural similarities and differences between liver NK and NKT cells, and the regulation of liver NK and NKT cells in a variety of murine liver injury models. We also summarize recent findings about the role of NK and NKT cells in liver injury, fibrosis, and repair. In general, NK and NKT cells accelerate liver injury by producing proinflammatory cytokines and killing hepatocytes. NK cells inhibit liver fibrosis via killing early-activated and senescent-activated stellate cells and producing IFN-gamma. In regulating liver fibrosis, NKT cells appear to be less important than NK cells as a result of hepatic NKT cell tolerance. NK cells inhibit liver regeneration by producing IFN-gamma and killing hepatocytes; however, the role of NK cells on the proliferation of liver progenitor cells and the role of NKT cells in liver regeneration have been controversial. The emerging roles of NK/NKT cells in chronic human liver disease will also be discussed.Understanding the role of NK and NKT cells in the pathogenesis of chronic liver disease may help us design better therapies to treat patients with this disease.

Focal liver necrosis appears early after partial hepatectomy and is dependent on T cells and antigen delivery from the gut

INTRODUCTION

Progressive liver failure may develop following removal of a large part of the liver or transplantation of a small for size liver graft. The pathophysiology of this clinical syndrome is only partially understood.

METHODS

We assessed liver damage and hepatocyte 5-bromo-2'-deoxyuridine (BrdU) incorporation following partial hepatectomy (PH) in C57BL/6, BALB/C and immune-deficient mice. Hepatic lymphocyte subpopulations were characterized. Lipopolysaccharide (LPS) treatment and bowel decontamination determined the role of gut antigens.

RESULTS

Discrete, round necrotic lesions were observed as early as 2 h following 70%, but not 30% PH. In immune competent mice the extent of hepatocyte necrosis inversely correlated with BrdU incorporation. T, natural killer and natural killer T cells were recruited to the liver early after PH; however, only T-cell depletion abrogated hepatic necrosis. Hepatic injury was significantly reduced in non-obese diabetic/severe combined immunodeficient mice undergoing PH, while BrdU incorporation was not affected. Liver injury was augmented by LPS injection and reduced by gut decontamination.

CONCLUSIONS

A distinct pattern of early focal hepatic necrosis is observed following extensive PH in mice. T cells infiltrating the liver immediately after PH and gut-derived antigens are indispensable for the observed liver necrosis and may thus provide therapeutic targets to ameliorate liver damage following PH.

Activation of innate immunity (NK/IFN-gamma) in rat allogeneic liver transplantation: contribution to liver injury and suppression of hepatocyte proliferation

Liver transplantation is presently the only curative treatment for patients with end-stage liver disease. However, the mechanisms underlying liver injury and hepatocyte proliferation posttransplantation remain obscure. In this investigation, liver injury and hepatocyte proliferation in syngeneic and allogeneic animal models were compared. Male Lewis and Dark Agouti (DA) rats were subjected to orthotopic liver transplantation (OLT). Rat OLT was performed in syngeneic (Lewis-Lewis) and allogeneic (Lewis-DA or DA-Lewis) animal models. Allogeneic liver grafts exhibited greater injury and cellular apoptosis than syngeneic grafts but less hepatocyte proliferation after OLT. Expression of IFN-gamma mRNA and activation of the downstream signal transducer and activator of transcription 1 (STAT1) and genes (interferon regulatory factor-1 and cyclin-dependent kinase inhibitor p21(CDKN1A)) were also greater in the allogeneic grafts compared with the syngeneic grafts. In contrast, STAT3 activation was lower in the allogeneic grafts. Furthermore, in the allogeneic grafts, depletion of natural killer (NK) cells decreased IFN-gamma/STAT1 activation but enhanced hepatocyte proliferation. These findings suggest that, compared with syngeneic transplantation, innate immunity (NK/IFN-gamma) is activated after allogeneic transplantation, which likely contributes to liver injury and inhibits hepatocyte proliferation.

Innate immunity and alcoholic liver fibrosis

The hepatic innate immune system consists of predominant innate immunity, which plays an important role in innate defense against infection and tumor transformation. Emerging evidence suggests that innate immunity also contributes to liver injury, repair, and fibrosis. The present review summarizes the recent findings on the role of innate immunity in liver fibrosis. In general, Kupffer cells stimulate liver fibrosis via production of reactive oxygen species and pro-inflammatory cytokines, whereas natural killer (NK) cells inhibit liver fibrosis by directly killing activated hepatic stellate cells and production of gamma-interferon (IFN-gamma). Complement components, interferons, and Toll-like receptors have also been shown to regulate liver fibrosis. Recent evidence also suggests that modulation of innate immunity by alcohol plays an important role in the pathogenesis of alcoholic liver fibrosis. These include alcohol amplification of the profibrotic effects of Kupffer cells and suppression of the antifibrotic effects of NK/IFN-gamma.

Liver: An organ with predominant innate immunity

Blood circulating from the intestines to the liver is rich in bacterial products, environmental toxins, and food antigens. To effectively and quickly defend against potentially toxic agents without launching harmful immune responses, the liver relies on its strong innate immune system. This comprises enrichment of innate immune cells (such as macrophages, natural killer, natural killer T, and gammadelta T cells) and removal of waste molecules and immunologic elimination of microorganisms by liver endothelial cells and Kupffer cells. In addition, the liver also plays an important role in controlling systemic innate immunity through the biosynthesis of numerous soluble pathogen-recognition receptors and complement components.

CONCLUSION

The liver is an organ with predominant innate immunity, playing an important role not only in host defenses against invading microorganisms and tumor transformation but also in liver injury and repair. Recent evidence suggests that innate immunity is also involved in the pathogenesis of liver fibrosis, providing novel therapeutic targets to treat such a liver disorder.

Pivotal role of Smad3 in a mouse model of T cell-mediated hepatitis

Transforming growth factor beta (TGFbeta) promotes hepatocellular apoptosis and suppresses hepatic lymphocyte responses in part through activation of Smad3. The purpose of the current study was to determine the importance of Smad3 signaling in an experimental model of autoimmune hepatitis induced by concanavalin A (ConA), a process involving T cell activation and hepatocellular apoptosis. C57Bl/6 wild-type (Wt) or Smad3-deficient (Smad3(-/-)) mice were injected intravenously with 15 mg/kg ConA or vehicle. Nine hours post ConA injection, Wt mice presented with severe hepatitis as assessed by increased liver transferases. This injury was associated with eosinophil accumulation and preceded at 3 hours post-injection by significant increases in hepatic T helper 1 (interferon gamma) and T helper 2 (interleukin-4) cytokine production. Absence of Smad3 significantly blunted hepatocellular injury 9 hours post ConA injection, which was associated with reduced early T helper 1 and T helper 2 cytokine production and eosinophil accumulation. Smad3(-/-) livers also showed significant reductions in hepatocellular apoptosis as assessed by terminal UTP nick-end labeling when compared to ConA-treated Wt mice in conjunction with reduced caspase 3 cleavage, which was likely mediated by a Smad3-dependent inhibition of the survival factor extracellular signal-regulated kinase 1/2. In vitro, Smad3(-/-) hepatocytes were resistant to TGFbeta-induced apoptosis, and this protection was dependent on extracellular signal-regulated kinase activation.

CONCLUSION

Together, these results show, for the first time, the significance of Smad3 signaling in autoimmune hepatitis, underlining the control of Smad3-dependent TGFbeta signaling on proinflammatory cytokine production, eosinophil recruitment, and hepatocellular apoptosis. Interruption of this pathway could be beneficial clinically to limit acute fulminant liver pathologies.

What fires prometheus? The link between inflammation and regeneration following chronic liver injury

Liver progenitor cells (LPCs) play a major role in the regeneration process after chronic liver damage, giving rise to hepatocytes and cholangiocytes. Thus, they provide a cell-based therapeutic alternative to organ transplant, the current treatment of choice for end-stage liver disease. In recent years, much attention has focused on unravelling the cytokines and growth factors that underlie this response. Liver regeneration following acute damage is achieved by proliferation of mature hepatocytes; yet similar cytokines, most related to the inflammatory process, are implicated in both acute and chronic liver regeneration. Thus, many recent studies represent attempts to identify LPC-specific factors. This review summarises our current understanding of LPC biology with a particular focus on the liver inflammatory response being associated with the induction of LPCs in the liver. We will describe: (i) the pathways of liver regeneration following acute and chronic damage; (ii) the similarities and differences between the two pathways; (iii) the liver inflammatory environment; (iv) the unique features of liver immunology as well as (v) the interactions between liver immune cells and LPCs. Combining data from studies on the LPC-driven regeneration process with the knowledge in the field of liver immunology will improve our understanding of the LPC response and allow us to regulate these cells in vivo and in vitro for future therapeutic strategies to treat chronic liver disease.

Cytogenetic effects of grape extracts (Vitis vinifera) and polyphenols on mitomycin C-induced sister chromatid exchanges (SCEs) in human blood lymphocytes

In the present study, the effects of extracts and polyphenol-rich fractions as well as monomer polyphenols identified in them, from both red and white grapes, on mitomycin C (MMC) induced sister chromatid exchanges (SCEs) in human peripheral blood lymphocytes were investigated. The grape extracts and two of the three polyphenol-rich fractions promoted MMC-induced SCEs at concentrations from 75 to 300 microg/mL. However, none of the extracts or fractions alone induced SCEs. Thus, these results suggest caution especially with regard to the use of grape extracts as dietary supplements. On the other hand, the fact that these extracts were not genotoxic alone may indicate a selective activity against genetically damaged cells. This is the first study regarding the clastogenic effects of grape extracts in human cells. Moreover, from the tested polyphenols, caffeic acid, gallic acid, and rutin hydrate enhanced MMC-induced clastogenicity, whereas ferulic acid, protocatechuic acid, (+)-catechin, (-)-epicatechin, and trans-resveratrol had no effect at concentrations between 5 and 100 microM. The differences in the chemical structures of the tested polyphenols may account for their differential effects on MMC clastogenicity.