NF-kappaB activation in Kupffer cells after partial hepatectomy

Molecular mechanisms in liver repair and regeneration: from physiology to therapeutics

Liver repair and regeneration are crucial physiological responses to hepatic injury and are orchestrated through intricate cellular and molecular networks. This review systematically delineates advancements in the field, emphasizing the essential roles played by diverse liver cell types. Their coordinated actions, supported by complex crosstalk within the liver microenvironment, are pivotal to enhancing regenerative outcomes. Recent molecular investigations have elucidated key signaling pathways involved in liver injury and regeneration. Viewed through the lens of metabolic reprogramming, these pathways highlight how shifts in glucose, lipid, and amino acid metabolism support the cellular functions essential for liver repair and regeneration. An analysis of regenerative variability across pathological states reveals how disease conditions influence these dynamics, guiding the development of novel therapeutic strategies and advanced techniques to enhance liver repair and regeneration. Bridging laboratory findings with practical applications, recent clinical trials highlight the potential of optimizing liver regeneration strategies. These trials offer valuable insights into the effectiveness of novel therapies and underscore significant progress in translational research. In conclusion, this review intricately links molecular insights to therapeutic frontiers, systematically charting the trajectory from fundamental physiological mechanisms to innovative clinical applications in liver repair and regeneration.

Therapeutic strategies to improve liver regeneration after hepatectomy

Chronic liver disease is one of the most common diseases worldwide, and its prevalence is particularly high among adults aged 40-60 years; it takes a toll on productivity and causes significant economic burden. However, there are still no effective treatments that can fundamentally treat chronic liver disease. Although liver transplantation is considered the only effective treatment for chronic liver disease, it has limitations in that the pool of available donors is vastly insufficient for the number of potential recipients. Even if a patient undergoes liver transplantation, side effects such as immune rejection or bile duct complications could occur. In addition, impaired liver regeneration due to various causes, such as aging and metabolic disorders, may cause liver failure after liver resection, even leading to death. Therefore, further research on the liver regeneration process and therapeutic strategies to improve liver regeneration are needed. In this review, we describe the process of liver regeneration after hepatectomy, focusing on various cytokines and signaling pathways. In addition, we review treatment strategies that have been studied to date to improve liver regeneration, such as promotion of hepatocyte proliferation and metabolism and transplantation of mesenchymal stem cells. This review helps to understand the physiological processes involved in liver regeneration and provides basic knowledge for developing treatments for successful liver regeneration.

Lipocalin-2 Secreted by the Liver Regulates Neuronal Cell Function Through AKT-Dependent Signaling in Hepatic Encephalopathy Mouse Model

Hepatic encephalopathy (HE) associated with liver failure is accompanied by hyperammonemia, severe inflammation, depression, anxiety, and memory deficits as well as liver injury. Recent studies have focused on the liver-brain-inflammation axis to identify a therapeutic solution for patients with HE. Lipocalin-2 is an inflammation-related glycoprotein that is secreted by various organs and is involved in cellular mechanisms including iron homeostasis, glucose metabolism, cell death, neurite outgrowth, and neurogenesis. In this study, we investigated that the roles of lipocalin-2 both in the brain cortex of mice with HE and in Neuro-2a (N2A) cells. We detected elevated levels of lipocalin-2 both in the plasma and liver in a bile duct ligation mouse model of HE. We confirmed changes in cytokine expression, such as interleukin-1β, cyclooxygenase 2 expression, and iron metabolism related to gene expression through AKT-mediated signaling both in the brain cortex of mice with HE and N2A cells. Our data showed negative effects of hepatic lipocalin-2 on cell survival, iron homeostasis, and neurite outgrowth in N2A cells. Thus, we suggest that regulation of lipocalin-2 in the brain in HE may be a critical therapeutic approach to alleviate neuropathological problems focused on the liver-brain axis.

Glia Maturation Factor-β Supports Liver Regeneration by Remodeling Actin Network to Enhance STAT3 Proliferative Signals

BACKGROUND & AIMS

Glia maturation factor-β (GMFB) is a bona fide member of the actin depolymerizing factor homology family. Recently, emerging evidence suggested its implication in liver diseases, but data on its role in liver remain limited.

METHODS

Assessment of GMFB in liver histology, impact on liver regeneration and hepatocyte proliferation, and the underlying molecular pathways were conducted using mouse models with acute liver injury.

RESULTS

GMFB is widely distributed in normal liver. Its expression increases within 24 hours after partial hepatectomy (PHx). Adult Gmfb knockout mice and wild-type littermates are similar in gross appearance, body weight, liver function, and histology. However, compared with wild-type control, Gmfb knockout mice post-PHx develop more serious liver damage and steatosis and have delayed liver regeneration; the dominant change in liver transcriptome at 24 hours after PHx is the significantly suppressed acute inflammation pathways; the top down-regulated gene sets relate to interleukin (IL)6/Janus kinase/signal transducer and activator of transcription 3 (STAT3) signaling. Another mouse model intoxicated with carbon tetrachloride replicated these findings. Furthermore, Gmfb knockout and wild-type groups have the similar numbers of Kupffer cells, but Gmfb knockout Kupffer cells once stimulated produce less IL6, tumor necrosis factor, and IL1β. In hepatocytes treated with IL6, GMFB associates positively with cell proliferation and STAT3/cyclin D1 activation, but without any direct interaction with STAT3. In Gmfb knockout hepatocytes, cytoskeleton-related gene expression was changed significantly, with an abnormal-appearing morphology of actin networks. In hepatocyte modeling, actin-filament turnover, STAT3 activation, and metabolite excretion show a strong reliance on the status of actin-filament organization.

CONCLUSIONS

GMFB plays a significant role in liver regeneration by promoting acute inflammatory response in Kupffer cells and by intracellularly coordinating the responsive hepatocyte proliferation.

Protective effects of three flavonoids from Dendrobium huoshanense flowers on alcohol-induced hepatocyte injury via activating Nrf2 and inhibiting NF-κB pathways

Dendrobium huoshanense flowers have been widely used for liver protection in China. This work was aimed to discover the natural products with activity of mitigating alcoholic hepatocyte injury from Dendrobium huoshanense flowers via bioactivity-guided isolation, and to clarify the underlying mechanisms of these natural products. As a result, three flavonoids, 3'-O-methylquercetin-3-O- β -D-galactopyranoside ( 1 ), 3'-O-methylquercetin-3-O- β -D-glucopyranoside ( 2 ) and quercetin-3-O- β -D-glucopyranoside ( 3 ), were firstly isolated from D. huoshanense flowers. Results exhibited that flavonoids 1-3 could enhance the cell viability, decrease the expression of ALT and AST, inhibit the cell apoptosis, alleviate the oxidative stress, and mitigate the inflammatory response of alcohol-induced L02 cells. Mechanism study exhibited that flavonoids 1 - 3 could increase the expression of Nrf2 as well as its downstream antioxidation genes of alcohol-induced L02 cells, while ML-385 (Nrf2 inhibitor) could abolish the inhibitory effects of 1 - 3 on alcohol-induced hepatocyte injury. Flavonoids 1 - 3 could also reduce the phosphorylation levels of I κ B α and NF- κ B p65 of alcohol-induced L02 cells, while SC75741 (NF- κ B inhibitor) could not enhance the inhibitory effects of 1 - 3 on alcohol-induced L02 cells injury. The data above indicated that flavonoids 1 - 3 could inhibit alcohol-induced hepatocyte injury, which might be attributed to alleviating oxidative stress and mitigating inflammatory response by activating Nrf2 and inhibiting NF- κ B pathways.

Thorny ground, rocky soil: Tissue-specific mechanisms of tumor dormancy and relapse

Disseminated tumor cells (DTCs) spread systemically yet distinct patterns of metastasis indicate a range of tissue susceptibility to metastatic colonization. Distinctions between permissive and suppressive tissues are still being elucidated at cellular and molecular levels. Although there is a growing appreciation for the role of the microenvironment in regulating metastatic success, we have a limited understanding of how diverse tissues regulate DTC dormancy, the state of reversible quiescence and subsequent awakening thought to contribute to delayed relapse. Several themes of microenvironmental regulation of dormancy are beginning to emerge, including vascular association, co-option of pre-existing niches, metabolic adaptation, and immune evasion, with tissue-specific nuances. Conversely, DTC awakening is often associated with injury or inflammation-induced activation of the stroma, promoting a proliferative environment with DTCs following suit. We review what is known about tissue-specific regulation of tumor dormancy on a tissue-by-tissue basis, profiling major metastatic organs including the bone, lung, brain, liver, and lymph node. An aerial view of the barriers to metastatic growth may reveal common targets and dependencies to inform the therapeutic prevention of relapse.

Autophagy and Hepatic Tumor Microenvironment Associated Dormancy

The goal of successful cancer treatment is targeting the eradication of cancer cells. Although surgical removal of the primary tumors and several rounds of chemo- and radiotherapy reduce the disease burden, in some cases, asymptomatic dormant cancer cells may still exist in the body. Dormant cells arise from the disseminated tumor cells (DTCs) from the primary lesion. DTCs escape from immune system and cancer therapy and reside at the secondary organ without showing no sign of proliferation. However, under some conditions. dormant cells can be re-activated and enter a proliferative state even after decades. As a stress response mechanism, autophagy may help the adaptation of DTCs at this futile foreign microenvironment and may control the survival and re-activation of dormant cells. Studies indicate that hepatic microenvironment serves a favorable condition for cancer cell dormancy. Although, no direct study was pointing out the role of autophagy in liver-assisted dormancy, involvement of autophagy in both liver microenvironment, health, and disease conditions has been indicated. Therefore, in this review article, we will summarize cancer dormancy and discuss the role and importance of autophagy and hepatic microenvironment in this context.

Organ and brain crosstalk: The liver-brain axis in gastrointestinal, liver, and pancreatic diseases

The liver is the largest organ in the human body and is responsible for the metabolism and storage of the three principal nutrients: carbohydrates, fats, and proteins. In addition, the liver contributes to the breakdown and excretion of alcohol, medicinal agents, and toxic substances and the production and secretion of bile. In addition to its role as a metabolic centre, the liver has recently attracted attention for its function in the liver-brain axis, which interacts closely with the central nervous system via the autonomic nervous system, including the vagus nerve. The liver-brain axis influences the control of eating behaviour in the central nervous system through stimuli from the liver. Conversely, neural signals from the central nervous system influence glucose, lipid, and protein metabolism in the liver. The liver also receives a constant influx of nutrients and hormones from the intestinal tract and compounds of bacterial origin via the portal system. As a result, the intestinal tract and liver are involved in various immunological interactions. A good example is the co-occurrence of primary sclerosing cholangitis and ulcerative colitis. These heterogeneous roles of the liver-brain axis are mediated via the vagus nerve in an asymmetrical manner. In this review, we provide an overview of these interactions, mainly with the liver but also with the brain and gut.

Effects of genetically modified human skin fibroblasts, stably overexpressing hepatocyte growth factor, on hepatic functions of cocultured C3A cells

Diseases leading to terminal hepatic failure are among the most common causes of death worldwide. Transplant of the whole organ is the only effective method to cure liver failure. Unfortunately, this treatment option is not available universally due to the serious shortage of donors. Thus, alternative methods have been developed that are aimed at prolonging the life of patients, including hepatic cells transplantation and bridging therapy based on hybrid bioartificial liver devices. Parenchymal liver cells are highly differentiated and perform many complex functions, such as detoxification and protein synthesis. Unfortunately, isolated hepatocytes display a rapid decline in viability and liver-specific functions. A number of methods have been developed to maintain hepatocytes in their highly differentiated state in vitro, amongst them the most promising being 3D growth scaffolds and decellularized tissues or coculture with other cell types required for the heterotypic cell-cell interactions. Here we present a novel approach to the hepatic cells culture based on the feeder layer cells genetically modified using lentiviral vector to stably produce additional amounts of hepatocyte growth factor and show the positive influence of these coculture conditions on the preservation of the hepatic functions of the liver parenchymal cells' model-C3A cells.

Markers of liver regeneration-the role of growth factors and cytokines: a systematic review

BACKGROUND

Post-hepatectomy liver failure contributes significantly to postoperative mortality after liver resection. The prediction of the individual risk for liver failure is challenging. This review aimed to provide an overview of cytokine and growth factor triggered signaling pathways involved in liver regeneration after resection.

METHODS

MEDLINE and Cochrane databases were searched without language restrictions for articles from the time of inception of the databases till March 2019. All studies with comparative data on the effect of cytokines and growth factors on liver regeneration in animals and humans were included.

RESULTS

Overall 3.353 articles comprising 40 studies involving 1.498 patients and 101 animal studies were identified and met the inclusion criteria. All included trials on humans were retrospective cohort/observational studies. There was substantial heterogeneity across all included studies with respect to the analyzed cytokines and growth factors and the described endpoints.

CONCLUSION

High-level evidence on serial measurements of growth factors and cytokines in blood samples used to predict liver regeneration after resection is still lacking. To address the heterogeneity of patients and potential markers, high throughput serial analyses may offer a method to predict an individual's regenerative potential in the future.

Pyridoxamine improves metabolic and microcirculatory complications associated with nonalcoholic fatty liver disease

OBJECTIVE

We investigated the protective effects of pyridoxamine against metabolic and microcirculatory complications in nonalcoholic fatty liver disease.

METHODS

Nonalcoholic fatty liver disease was established by a high-fat diet administration over 28 weeks. Pyridoxamine was administered between weeks 20 and 28. The recruitment of leukocytes and the number of vitamin A-positive hepatic stellate cells were examined by in vivo microscopy. Laser speckle contrast imaging was used to evaluate microcirculatory hepatic perfusion. Thiobarbituric acid reactive substances measurement and RT-PCR were used for oxidative stress and inflammatory parameters. advanced glycation end products were evaluated by fluorescence spectroscopy.

RESULTS

The increase in body, liver, and fat weights, together with steatosis and impairment in glucose metabolism observed in the nonalcoholic fatty liver disease group were attenuated by pyridoxamine treatment. Regarding the hepatic microcirculatory parameters, rats with high-fat diet-induced nonalcoholic fatty liver disease showed increased rolling and adhesion of leukocytes, increased hepatic stellate cells activation, and decreased tissue perfusion, which were reverted by pyridoxamine. Pyridoxamine protected against the increased hepatic lipid peroxidation observed in the nonalcoholic fatty liver disease group. Pyridoxamine treatment was associated with increased levels of tumor necrosis factor alpha (TNF-α) mRNA transcripts in the liver.

CONCLUSION

Pyridoxamine modulates oxidative stress, advanced glycation end products, TNF-α transcripts levels, and metabolic disturbances, being a potential treatment for nonalcoholic fatty liver disease-associated microcirculatory and metabolic complications.

Autonomic nervous system network and liver regeneration

To date, various signal transducers, cytokines, growth factors, and hormones have been reported to play an important role in homeostasis of various organs. Various cells and organs are involved in the hepatic regeneration process, which proceeds as a result of the coordination of many factors. While these factors are well known to be involved in the liver regeneration after the liver injury, however, as the details of such mechanisms have not been sufficiently elucidated, the practical applicability of hepatic regeneration based on the action of these and cytokines growth factors is still unclear. In terms of the involvement of the autonomic nervous system in hepatic regeneration, cell proliferation resulting from direct signal transduction to the liver has also been reported and recent studies focusing on the inter-organ communication via neural network opened a novel aspect of this field for therapeutic applicability. Therefore, the appropriate understanding of the relationship between autonomic neural network and liver regeneration through various organs including brain, afferent nerve, efferent nerve, etc. is essential. This mini-review explains the principle of neural system involved in the inter-organ communication and its contribution on the liver regeneration upon the liver injury reviewing recent progress in this field.

Effect of a neural relay on liver regeneration in mice: activation of serotonin release from the gastrointestinal tract

The development of therapeutic options to promote hepatic regeneration following severe liver injury is essential. While humoral factors have been reported as mechanisms of liver regeneration, the contributions of interorgan communication to liver regeneration have not been reported. In this study, we examined the effect of a neural relay on liver regeneration via activation of serotonin release from the gastrointestinal (GI) tract. Our results demonstrated that the afferent visceral nerve from the liver activates the efferent vagus nerve from the brain, leading to activation of serotonin release from the GI tract and contributing to liver regeneration. While it is difficult to apply these results directly to human health, we believe that this study may represent a step toward developing essential therapeutics to promote liver regeneration.

Current Understanding of Stem Cell and Secretome Therapies in Liver Diseases

Liver failure is one of the main risks of death worldwide, and it originates from repetitive injuries and inflammations of liver tissues, which finally leads to the liver cirrhosis or cancer. Currently, liver transplantation is the only effective treatment for the liver diseases although it has a limitation due to donor scarcity. Alternatively, cell therapy to regenerate and reconstruct the damaged liver has been suggested to overcome the current limitation of liver disease cures. Several transplantable cell types could be utilized for recovering liver functions in injured liver, including bone marrow cells, mesenchymal stem cells, hematopoietic stem cells, macrophages, and stem cell-derived hepatocytes. Furthermore, paracrine effects of transplanted cells have been suggested as a new paradigm for liver disease cures, and this application would be a new strategy to cure liver failures. Therefore, here we reviewed the current status and challenges of therapy using stem cells for liver disease treatments.

The Inhibition of Indoleamine 2,3-Dioxygenase Accelerates Early Liver Regeneration in Mice After Partial Hepatectomy

BACKGROUND AND AIM

The inflammatory response accelerates early liver regeneration after liver injury and resection. Recent studies have demonstrated that indoleamine 2,3-dioxygenase-1 (IDO1) suppresses the activation of inflammatory cells and induces immune tolerance. In this study, we examined the role of IDO1 in liver regeneration after partial hepatectomy (PHx).

METHODS

WT or IDO1-knockout (IDO1-KO) mice received 70% PHx. The liver-body weight ratio after PHx was measured and hepatocyte growth was assessed by immunostaining. The expression of cell cycle genes and pro-inflammatory cytokines in the liver was analyzed by quantitative RT-PCR. In addition, 1-methyl-DL-tryptophan (1-MT), which is an IDO1 inhibitory agent, was given to WT mice and the liver-body weight ratio was measured after PHx.

RESULTS

The liver-body weight ratio was significantly increased in IDO1-KO mice compared with that in WT mice after PHx. More Ki-67-positive cells were present in IDO1-KO mice than in WT mice after PHx. The expression of cell cycle genes (cyclin D1, cyclin E) and pro-inflammatory cytokines (IL-1β, TNF-α and IL-6) was up-regulated in the remnant liver of IDO1-KO mice compared with WT mice. Moreover, treatment with 1-MT promoted liver regeneration.

CONCLUSION

IDO1 deficiency promoted early liver regeneration after PHx, indicating that IDO1 suppresses the production of inflammatory cytokines and subsequently inhibits hepatocyte proliferation during liver regeneration.

Hepatoprotective activities of Antrodia camphorata and its triterpenoid compounds against CCl4-induced liver injury in mice

ETHNOPHARMACOLOGY RELEVANCE

Antrodia camphorata (AC) is a rare and precious fungus indigenous to Taiwan used as a traditional medicine for the treatment of liver injury. Triterpenoids are the major bioactive constituents of A. camphorata and have been reported to possess hepatoprotective activities. To meet the increasing demand, artificial cultivation techniques have been developed.

AIM OF THE STUDY

This study aims to evaluate the hepatoprotective activities of AC samples derived from different cultivation techniques and to dissect the main active triterpenoid compounds.

MATERIALS AND METHODS

The ethanol extracts of five batches of AC samples, including wild growing fruiting bodies, cutting wood culture fruiting bodies, dish cultures, cutting wood culture mycelia, and submerged fermentation mycelia were orally administered (50mg/kg or 200mg/kg) to ICR mice for 7 days. On the last day, CCl₄ (0.2%, 7mL/kg, i.p.) was used to induce liver injury, and the activities of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were determined 24h after the injection. Moreover, a HepG2 cell model treated with CCl₄ (0.35%) was used to screen the protective activities of 29 AC triterpenoids. After incubation for 6h, viabilities of the cells were tested using MTS assay. The in vivo hepatoprotective activities of antcin B and antcin K were further studied on the mice model by ALT and AST tests and histopathologic examinations. To elucidate the mechanisms, the mRNA levels of iNOS, COX2, TNF-α and IL-1β, and the protein levels of NF-κB (p65/p-p65), iNOS and COX2 in liver tissues were determined.

RESULTS

The wild growing or cutting wood culture fruiting bodies, and the dish cultures of AC showed more potent activities than the mycelia (P<0.001). At 20μM, 16 of 29 triterpenoids showed significant protective activities, increasing HepG2 cell viability from 46% of the CCl₄ group to >90%. Antcin B and antcin K could dose-dependently (10 or 50mg/kg, 7 days, i.g.) decrease the serum levels of ALT and AST, and decrease the incidence of liver necrosis. The effects of 50mg/kg of antcin K or antcin B were almost identical to those of 100mg/kg silymarin. Furthermore, qRT-PCR and Western blotting analyses revealed they could down-regulate IL-1β, TNF-α, iNOS, COX-2 and NF-κB in liver tissues at both transcriptional and translational levels.

CONCLUSION

The results indicate that cultivation techniques remarkably affect the hepatoprotective activities of AC. Antcin K and antcin B are the major hepatoprotective compounds of A. camphorata, and the mechanism is related with anti-inflammation. Given its high natural abundance and good oral absorption, antcin K could be a promising drug candidate for liver injury.

Role and Regulation of p65/β-Catenin Association During Liver Injury and Regeneration: A "Complex" Relationship

An important role for β-catenin in regulating p65 (a subunit of NF-κB) during acute liver injury has recently been elucidated through use of conditional β-catenin knockout mice, which show protection from apoptosis through increased activation of p65. Thus, we hypothesized that the p65/β-catenin complex may play a role in regulating processes such as cell proliferation during liver regeneration. We show through in vitro and in vivo studies that the p65/β-catenin complex is regulated through the TNF-α pathway and not through Wnt signaling. However, this complex is unchanged after partial hepatectomy (PH), despite increased p65 and β-catenin nuclear translocation as well as cyclin D1 activation. We demonstrate through both in vitro silencing experiments and chromatin immunoprecipitation after PH that β-catenin, and not p65, regulates cyclin D1 expression. Conversely, using reporter mice we show p65 is activated exclusively in the nonparenchymal (NPC) compartment during liver regeneration. Furthermore, stimulation of macrophages by TNF-α induces activation of NF-κB and subsequent secretion of Wnts essential for β-catenin activation in hepatocytes. Thus, we show that β-catenin and p65 are activated in separate cellular compartments during liver regeneration, with p65 activity in NPCs contributing to the activation of hepatocyte β-catenin, cyclin D1 expression, and subsequent proliferation.

Nuclear factor-kappa B influences early phase of compensatory lung growth after pneumonectomy in mice

Background

Compensatory lung growth (CLG) is a well-established lung regeneration model. However, the sequential mechanisms, including unknown molecular triggers or regulators, remain unclear. Nuclear factor- kappa B (NF-κB) is known to be essential for inflammation and tissue regeneration; therefore, we investigated the role of NF-κB in CLG.

Methods

C57BL/6 J mice underwent either a left pneumonectomy or a thoracotomy (n = 77). Gene microarray analysis was performed to detect genes that were upregulated at 12 h after pneumonectomy. NF-κB protein expression was examined by immunohistochemistry and Western blot. To investigate the influence of NF-κB on CLG, either an NF-κB inhibitor SN50 or saline was administered following pneumonectomy and the degree of CLG was evaluated in each group by measuring the lung dry weight index (LDWI) and the mean linear intercept.

Results

Gene microarray analysis identified 11 genes that were significantly but transiently increased at 12 h after pneumonectomy. Among the 11 genes, NF-κB was selected based on its reported functions. Western blot analysis showed that NF-κB protein expression after pneumonectomy was significantly higher at 12 h compared to 48 h. Additionally, NF-κB protein expression at 12 h after pneumonectomy was significantly higher than at both 12 and 48 h after thoracotomy (p < 0.029 for all). NF-κB protein expression, evaluated through immunohistochemistry, was expressed mainly in type 2 alveolar epithelial cells and was significant increased 12 h after pneumonectomy compared to 48 h after pneumonectomy and both 12 and 48 h after thoracotomy (p < 0.001 for all). SN50 administration following pneumonectomy induced a significant decrease in NF-κB expression (p = 0.004) and LDWI compared to the vehicle administration (p = 0.009).

Conclusions

This is the first report demonstrating that NF-κB signaling may play a key role in CLG. Given its pathway is crucial in tissue regeneration of various organs, NF-κB may shed light on identification of molecular triggers or clinically usable key regulators of CLG.

Pien Tze Huang Gan Bao ameliorates carbon tetrachloride-induced hepatic injury, oxidative stress and inflammation in rats

Liver damage results from a variety of insults, including hepatitis and chemical toxicity from alcohol, drugs and other toxins. The present study evaluated the hepatoprotective effects and potential mechanisms of action of the Traditional Chinese Medicine Pien Tze Huang Gan Bao (GB) in a rat model of carbon tetrachloride (CCl₄)-induced liver injury. Sixty male Sprague-Dawley rats were randomly divided into six different groups: i) Control, ii) CCl₄ injury model and groups treated with iii) silymarin as a positive drug control, iv) 150 mg/kg GB, v) 300 mg/kg GB and vi) 600 mg/kg GB. Control rats received no treatment, while the remaining ones were intraperitoneally injected with CCl₄ (2 ml/kg) to induce acute liver disease. Silymarin or GB was orally administered prior to CCl₄ treatment in various treatment groups for 7 days. Animals were sacrificed 24 h post-CCl₄ injection. It was revealed that GB significantly reduced serum aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, gamma glutamyl transpeptidase and total bilirubin levels in the serum induced by CCl₄. BG also prevented CCl₄-induced changes in liver tissues, as revealed by histopathological analysis. CCl₄-induced reductions in endogenous liver antioxidant enzyme activities of superoxide dismutase, glutathione and glutathione peroxidase as well as increases in malondialdehyde and thiobarbituric acid reactive substances were inhibited by GB treatment. Activated NF-κB in liver tissues was also significantly increased by CCl₄, which was attenuated by GB as indicated by immunohistochemical and PCR analysis. Furthermore, CCl₄-mediated increases in the inflammatory factors tumor necrosis factor-alpha and interleukin-1β secretion into the serum and their expression in liver tissues were reversed following GB treatment, as revealed by ELISA and PCR, respectively. These findings suggested that GB protects against CCl₄-induced hepatic injury, inflammation and oxidative damage in rats and may be useful in future clinical application of liver injury and disease.

A novel comparative pattern count analysis reveals a chronic ethanol-induced dynamic shift in immediate early NF-κB genome-wide promoter binding during liver regeneration

Liver regeneration after partial hepatectomy is a clinically important process that is impaired by adaptation to chronic alcohol intake. We focused on the initial time points following partial hepatectomy (PHx) to analyze the genome-wide binding activity of NF-κB, a key immediate early regulator. We investigated the effect of chronic alcohol intake on immediate early NF-κB genome-wide localization, in the adapted state as well as in response to partial hepatectomy, using chromatin immunoprecipitation followed by promoter microarray analysis. We found many ethanol-specific NF-κB binding target promoters in the ethanol-adapted state, corresponding to the regulation of biosynthetic processes, oxidation-reduction and apoptosis. Partial hepatectomy induced a diet-independent shift in NF-κB binding loci relative to the transcription start sites. We employed a novel pattern count analysis to exhaustively enumerate and compare the number of promoters corresponding to the temporal binding patterns in ethanol and pair-fed control groups. The highest pattern count corresponded to promoters with NF-κB binding exclusively in the ethanol group at 1 h post PHx. This set was associated with the regulation of cell death, response to oxidative stress, histone modification, mitochondrial function, and metabolic processes. Integration with the global gene expression profiles to identify putative transcriptional consequences of NF-κB binding patterns revealed that several of ethanol-specific 1 h binding targets showed ethanol-specific differential expression through 6 h post PHx. Motif analysis yielded co-incident binding loci for STAT3, AP-1, CREB, C/EBP-β, PPAR-γ and C/EBP-α, likely participating in co-regulatory modules with NF-κB in shaping the immediate early response to PHx. We conclude that adaptation to chronic ethanol intake disrupts the NF-κB promoter binding landscape with consequences for the immediate early gene regulatory response to the acute challenge of PHx.

In Vivo Zonal Variation and Liver Cell-Type Specific NF-κB Localization after Chronic Adaptation to Ethanol and following Partial Hepatectomy

NF-κB is a major inflammatory response mediator in the liver, playing a key role in the pathogenesis of alcoholic liver injury. We investigated zonal as well as liver cell type-specific distribution of NF-κB activation across the liver acinus following adaptation to chronic ethanol intake and 70% partial hepatectomy (PHx). We employed immunofluorescence staining, digital image analysis and statistical distributional analysis to quantify subcellular localization of NF-κB in hepatocytes and hepatic stellate cells (HSCs). We detected significant spatial heterogeneity of NF-κB expression and cellular localization between cytoplasm and nucleus across liver tissue. Our main aims involved investigating the zonal bias in NF-κB localization and determining to what extent chronic ethanol intake affects this zonal bias with in hepatocytes at baseline and post-PHx. Hepatocytes in the periportal area showed higher NF-κB expression than in the pericentral region in the carbohydrate-fed controls, but not in the ethanol group. However, the distribution of NF-κB nuclear localization in hepatocytes was shifted towards higher levels in pericentral region than in periportal area, across all treatment conditions. Chronic ethanol intake shifted the NF-κB distribution towards higher nuclear fraction in hepatocytes as compared to the pair-fed control group. Ethanol also stimulated higher NF-κB expression in a subpopulation of HSCs. In the control group, PHx elicited a shift towards higher NF-κB nuclear fraction in hepatocytes. However, this distribution remained unchanged in the ethanol group post-PHx. HSCs showed a lower NF-κB expression following PHx in both ethanol and control groups. We conclude that adaptation to chronic ethanol intake attenuates the liver zonal variation in NF-κB expression and limits the PHx-induced NF-κB activation in hepatocytes, but does not alter the NF-κB expression changes in HSCs in response to PHx. Our findings provide new insights as to how ethanol treatment may affect cell-type specific processes regulated by NF-κB activation in liver cells.

A novel, dynamic pattern-based analysis of NF-κB binding during the priming phase of liver regeneration reveals switch-like functional regulation of target genes

Following partial hepatectomy, a coordinated series of molecular events occurs to regulate hepatocyte entry into the cell cycle to recover lost mass. In rats during the first 6 h following resection, hepatocytes are primed by a tightly controlled cytokine response to prepare hepatocytes to begin replication. Although it appears to be a critical element driving regeneration, the cytokine response to resection has not yet been fully characterized. Specifically, the role of one of the key response elements to cytokine signaling (NF-κB) remains incompletely characterized. In this study, we present a novel, genome-wide, pattern-based analysis characterizing NF-κB binding during the priming phase of liver regeneration. We interrogated the dynamic regulation of priming by NF-κB through categorizing NF-κB binding in different temporal profiles: immediate sustained response, early transient response, and delayed response to partial hepatectomy. We then identified functional regulation of NF-κB binding by relating the temporal response profile to differential gene expression. We found that NF-κB bound genes govern negative regulation of cell growth and inflammatory response immediately following hepatectomy. NF-κB also transiently regulates genes responsible for lipid biosynthesis and transport as well as induction of apoptosis following hepatectomy. By the end of the priming phase, NF-κB regulation of genes involved in inflammatory response, negative regulation of cell death, and extracellular structure organization became prominent. These results suggest that NF-κB regulates target genes through binding and unbinding in immediate, transient, and delayed patterns. Such dynamic switch-like patterns of NF-κB binding may govern different functional transitions that drive the onset of regeneration.

Salvia miltiorrhiza compounds protect the liver from acute injury by regulation of p38 and NFκB signaling in Kupffer cells

CONTEXT

Salvia miltiorrhiza Bunge is a traditional Asian medicine used to treat cerebral and cardiac ischemia. However, the effects of the active compounds of S. miltiorrhiza on liver damage are unclear.

OBJECTIVE

In this study, we tested the effects on acute liver injury of crude S. miltiorrhiza extracts from roots as well as neotanshinone B, dehydromiltirone, tanshinol A, tanshinone I, dihydrotanshinono I, neotanshinone A, cryptanshinono, tanshinone II A, and salvianolie acid B from purified S. miltiorrhiza extracts.

MATERIALS AND METHODS

Various compounds or ethanol extract of S. miltiorrhiza (50, 100, and 200 mg/kg, p.o.) were administered to rats for five consecutive days. After acute carbon tetrachloride (CCl4)-induced liver injury by treatment of rats with a single dose of CCl4 (0.75 mL/kg, p.o), rat liver function was tested by measuring serum biochemical parameters. Serum cytokine concentrations were assessed by enzyme-linked immunosorbent assay (ELISA). Expression of p38 and NFκB was evaluated by western blot.

RESULTS

All S. miltiorrhiza components showed their effects on liver function from the dose from 50 to 200 mg/kg. At the dose of 200 mg/kg, they reduced serum levels of alkaline phosphatase (ALP) by 34-77%, alanine aminotransferase (ALT) by 30-57%, aspartate aminotransferase (AST) by 43-72%, creatine total bilirubin (BIL-T) by 33-81%, albumin (ALB) by 37-67%, indicating that S. miltiorrhiza extracts protected liver from CCl4-induced damage. Moreover, S. miltiorrhiza extracts at 200 mg/kg reduced the increase in the proinflammatory cytokines tumor necrosis factor-α (TNF-α) by 25-82%, interleukin-1 (IL-1) by 42-74% and interleukin-6 (IL-6) by 67-83%, indicating an effect on alleviating liver inflammation. Furthermore, in vitro, S. miltiorrhiza extracts inhibited p38 and NFκB signaling in Kupffer cells. This effect could be a main mechanism by which S. miltiorrhiza protects against acute liver toxicity.

DISCUSSION AND CONCLUSION

Active compounds of S. miltiorrhiza protected the liver from CCl4-induced injury. Protection might have been due to inhibition of p38 and NFκB signaling in Kupffer cells, which subsequently reduced inflammation in the liver.

Activation of NF-κB after chronic ethanol intake and haemorrhagic shock/resuscitation in mice

BACKGROUND AND PURPOSE

Chronic ethanol abuse and haemorrhagic shock are major causes of global mortality and, separately, induce profound hepato- and immune-toxic effects via activation of NF-κB. Here, we assessed the effects of chronic ethanol intake upon the pathophysiological derangements after haemorrhagic shock with subsequent resuscitation (H/R), with particular attention to the contribution of NF-κB.

EXPERIMENTAL APPROACH

Transgenic NF-κB(EGFP) mice, expressing the enhanced green fluorescent protein (EGFP) under the transcriptional control of NF-κB cis-elements were fed a Lieber-DeCarli diet containing ethanol (EtOH-diet) or an isocaloric control diet for 4 weeks and were then pairwise subjected to H/R. Liver tissues and peripheral blood were sampled at 2 or 24 h after H/R. Cytokines in blood and tissue and leukocyte activation (as CD11b expression) were measured, along with EGFP as a marker of NF-κB activation.

KEY RESULTS

The EtOH-diet increased mortality at 24 h after H/R and elevated liver injury, associated with an up-regulation of NF-κB-dependent genes and IL-6 release; it also increased production of NF-κB-driven intercellular adhesion molecule 1 (ICAM-1) and EGFP in liver tissue. At 2h after the H/R procedure in ethanol-fed mice we observed the highest proportion of NF-κB activated non-parenchymal cells and an NF-κB-dependent increase in polymorphonuclear leukocyte CD11b expression.

CONCLUSIONS AND IMPLICATIONS

The EtOH-diet exacerbated liver injury after H/R, accompanying an overwhelming hepatic and systemic immune response. Our findings contribute to evidence implicating NF-κB as a key player in the orchestration of the immune response in haemorrhagic shock patients with a history of chronic ethanol abuse.

Cellular and molecular basis of liver development

Liver is a prime organ responsible for synthesis, metabolism, and detoxification. The organ is endodermal in origin and its development is regulated by temporal, complex, and finely balanced cellular and molecular interactions that dictate its origin, growth, and maturation. We discuss the relevance of endoderm patterning, which truly is the first step toward mapping of domains that will give rise to specific organs. Once foregut patterning is completed, certain cells within the foregut endoderm gain competence in the form of expression of certain transcription factors that allow them to respond to certain inductive signals. Hepatic specification is then a result of such inductive signals, which often emanate from the surrounding mesenchyme. During hepatic specification bipotential hepatic stem cells or hepatoblasts become apparent and undergo expansion, which results in a visible liver primordium during the stage of hepatic morphogenesis. Hepatoblasts next differentiate into either hepatocytes or cholangiocytes. The expansion and differentiation is regulated by cellular and molecular interactions between hepatoblasts and mesenchymal cells including sinusoidal endothelial cells, stellate cells, and also innate hematopoietic elements. Further maturation of hepatocytes and cholangiocytes continues during late hepatic development as a function of various growth factors. At this time, liver gains architectural novelty in the form of zonality and at cellular level acquires polarity. A comprehensive elucidation of such finely tuned developmental cues have been the basis of transdifferentiation of various types of stem cells to hepatocyte-like cells for purposes of understanding health and disease and for therapeutic applications.

The NF-κB subunit RelA/p65 is dispensable for successful liver regeneration after partial hepatectomy in mice

BACKGROUND

The transcription factor NF-κB consisting of the subunits RelA/p65 and p50 is known to be quickly activated after partial hepatectomy (PH), the functional relevance of which is still a matter of debate. Current concepts suggest that activation of NF-κB is especially critical in non-parenchymal cells to produce cytokines (TNF, IL-6) to adequately prime hepatocytes to proliferate after PH, while NF-κB within hepatocytes mainly bears cytoprotective functions.

METHODS

To study the role of the NF-κB pathway in different liver cell compartments, we generated conditional knockout mice in which the transactivating NF-κB subunit RelA/p65 can be inactivated specifically in hepatocytes (Rela(F/F)AlbCre) or both in hepatocytes plus non-parenchymal cells including Kupffer cells (Rela(F/F)MxCre). 2/3 and 80% PH were performed in controls (Rela(F/F)) and conditional knockout mice (Rela(F/F)AlbCre and Rela(F/F)MxCre) and analyzed for regeneration.

RESULTS

Hepatocyte-specific deletion of RelA/p65 in Rela(F/F)AlbCre mice resulted in an accelerated cell cycle progression without altering liver mass regeneration after 2/3 PH. Surprisingly, hepatocyte apoptosis or liver damage were not enhanced in Rela(F/F)AlbCre mice, even when performing 80% PH. The additional inactivation of RelA/p65 in non-parenchymal cells in Rela(F/F)MxCre mice reversed the small proliferative advantage observed after hepatocyte-specific deletion of RelA/p65 so that Rela(F/F)MxCre mice displayed normal cell cycle progression, DNA-synthesis and liver mass regeneration.

CONCLUSION

The NF-κB subunit RelA/p65 fulfills opposite functions in different liver cell compartments in liver regeneration after PH. However, the effects observed after conditional deletion of RelA/p65 are small and do not alter liver mass regeneration after PH. We therefore do not consider RelA/p65-containing canonical NF-κB signalling to be essential for successful liver regeneration after PH.

A critical appraisal of the hemodynamic signal driving liver regeneration

BACKGROUND

Many aspects of the signaling mechanisms involved in the initiation of hepatic regeneration are under current investigation. Nevertheless, the actual mechanisms switching liver regeneration on and off are still unknown. Hemodynamic changes in the liver following partial hepatectomy have been suggested to be a primary stimulus in triggering liver regeneration. Most of the new knowledge about the impact of hemodynamic changes on liver regeneration is both conceptually important and directly relevant to clinical problems.

PURPOSE

The purpose of this review is therefore to exclusively address the hemodynamic signal driving the liver regeneration process.

NADPH oxidase and reactive oxygen species contribute to alcohol-induced microglial activation and neurodegeneration

Background

Activation of microglia causes the production of proinflammatory factors and upregulation of NADPH oxidase (NOX) that form reactive oxygen species (ROS) that lead to neurodegeneration. Previously, we reported that 10 daily doses of ethanol treatment induced innate immune genes in brain. In the present study, we investigate the effects of chronic ethanol on activation of NOX and release of ROS, and their contribution to ethanol neurotoxicity.

Methods

Male C57BL/6 and NF-κB enhanced GFP mice were treated intragastrically with water or ethanol (5 g/kg, i.g., 25% ethanol w/v) daily for 10 days. The effects of chronic ethanol on cell death markers (activated caspase-3 and Fluoro-Jade B), microglial morphology, NOX, ROS and NF-κB were examined using real-time PCR, immunohistochemistry and hydroethidine histochemistry. Also, Fluoro-Jade B staining and NOX gp91^phox immunohistochemistry were performed in the orbitofrontal cortex (OFC) of human postmortem alcoholic brain and human moderate drinking control brain.

Results

Ethanol treatment of C57BL/6 mice showed increased markers of neuronal death: activated caspase-3 and Fluoro-Jade B positive staining with Neu-N (a neuronal marker) labeling in cortex and dentate gyrus. The OFC of human post-mortem alcoholic brain also showed significantly more Fluoro-Jade B positive cells colocalized with Neu-N, a neuronal marker, compared to the OFC of human moderate drinking control brain, suggesting increased neuronal death in the OFC of human alcoholic brain. Iba1 and GFAP immunohistochemistry showed activated morphology of microglia and astrocytes in ethanol-treated mouse brain. Ethanol treatment increased NF-κB transcription and increased NOX gp91^phox at 24 hr after the last ethanol treatment that remained elevated at 1 week. The OFC of human postmortem alcoholic brain also had significant increases in the number of gp91^phox + immunoreactive (IR) cells that are colocalized with neuronal, microglial and astrocyte markers. In mouse brain ethanol increased gp91^phox expression coincided with increased production of O₂^- and O₂^- - derived oxidants. Diphenyleneiodonium (DPI), a NOX inhibitor, reduced markers of neurodegeneration, ROS and microglial activation.

Conclusions

Ethanol activation of microglia and astrocytes, induction of NOX and production of ROS contribute to chronic ethanol-induced neurotoxicity. NOX-ROS and NF-κB signaling pathways play important roles in chronic ethanol-induced neuroinflammation and neurodegeneration.

Regulation of signal transduction and role of platelets in liver regeneration

Among all organs, the liver has a unique regeneration capability after sustaining injury or the loss of tissue that occurs mainly due to mitosis in the hepatocytes that are quiescent under normal conditions. Liver regeneration is induced through a cascade of various cytokines and growth factors, such as, tumor necrosis factor alpha, interleukin-6, hepatocyte growth factor, and insulin-like growth factor, which activate nuclear factor κB, signal transducer and activator of transcription 3, and phosphatidyl inositol 3-kinase signaling pathways. We previously reported that platelets can play important roles in liver regeneration through a direct effect on hepatocytes and collaborative effects with the nonparenchymal cells of the liver, including Kupffer cells and liver sinusoidal endothelial cells, which participate in liver regeneration through the production of various growth factors and cytokines. In this paper, the roles of platelets and nonparenchymal cells in liver regeneration, including the associated cytokines, growth factors, and signaling pathways, are described.

Toll-like receptor signaling in liver regeneration, fibrosis and carcinogenesis

Toll-like receptors (TLR) are the germline-coded pattern recognition receptors that sense microbial products. This signaling orchestrates complex signaling pathways that induce expression of inflammatory genes for host defense against invading microorganisms. Recent studies illustrate the role of TLR on non-infectious inflammatory diseases. The liver has a unique anatomy bridging with the intestine by portal vein and bile ducts. This allows delivery of products from intestinal microflora directly into the liver. Subsequently, microbial products cause acute and chronic inflammation through TLR signaling in the liver. Not only exogenous products, but endogenous denatured products released from dying cells also facilitate inflammation even in sterile conditions. Consequently, these responses elicit tissue repairing including liver regeneration and fibrogenesis. An aberrant regenerative response may lead to hepatic carcinogenesis. In this review, we highlight the recently accumulated knowledge about TLR signaling in liver regeneration, fibrosis and carcinogenesis.

Regulation of liver regeneration by growth factors and cytokines

The capability of the liver to fully regenerate after injury is a unique phenomenon essential for the maintenance of its important functions in the control of metabolism and xenobiotic detoxification. The regeneration process is histologically well described, but the genes that orchestrate liver regeneration have been only partially characterized. Of particular interest are cytokines and growth factors, which control different phases of liver regeneration. Historically, their potential functions in this process were addressed by analyzing their expression in the regenerating liver of rodents. Some of the predicted roles were confirmed using functional studies, including systemic delivery of recombinant growth factors, neutralizing antibodies or siRNAs prior to liver injury or during liver regeneration. In particular, the availability of genetically modified mice and their use in liver regeneration studies has unraveled novel and often unexpected functions of growth factors, cytokines and their downstream signalling targets in liver regeneration. This review summarizes the results obtained by functional studies that have addressed the roles and mechanisms of action of growth factors and cytokines in liver regeneration after acute injury to this organ.

TLRs, NF-κB, JNK, and Liver Regeneration

While hepatocytes rarely undergo proliferation in normal livers, they quickly induce proliferation in response to loss of liver mass by toxin or inflammation-induced hepatocyte injury, trauma, or surgical resection, leading to a restoration of liver mass to its original size. Recent studies suggest that Toll-like receptor (TLR) signaling participates in this regenerative response. Myeloid differentiation factor (MyD88), a common adaptor molecule in the TLR, IL-1 and IL-18 receptor signaling, plays a key role, at least, in the early phase of liver regeneration. Currently, definite ligands which bind to TLRs and initiate this process are still unclear. TLRs stimulated by their corresponding ligands, as well as tumor necrosis factor (TNF) receptors (TNFRs), can activate downstream signal molecules, including transcription factor nuclear factor (NF)-κB and c-Jun N-terminal kinase (JNK). Previous studies have revealed the important role of TNF receptor signaling, NF-κB, and JNK in liver regeneration by using hepatocyte-specific gene-modified animals. This review will summarize the current knowledge of TLR signaling and their related molecules in liver regeneration. We will also discuss whether modulating these factors may become new therapeutic strategies to promote liver regeneration in various clinical situations.

Role of nuclear factor kappaB in liver health and disease

NF-kappaB (nuclear factor kappaB) is a heterodimeric transcription factor that is constitutively expressed in all cell types and has a central role as a transcriptional regulator in response to cellular stress. In the present review, we discuss the role of NF-kappaB signalling in the maintenance of liver homoeostasis as well as in the pathogenesis of a wide variety of conditions affecting the liver, including viral hepatitis, steatohepatitis, cirrhosis and hepatocellular carcinoma. Much of the current knowledge of NF-kappaB signalling in the liver relates to the canonical pathway, the IKK [IkappaB (inhibitor of kappaB) kinase] complex and the RelA subunit. We explore the weaknesses of the experimental approaches to date and suggest that further work is needed to investigate in detail the discreet functions of each of the Rel subunits in liver physiology and disease.

Increased susceptibility to exacerbated liver injury in hypercholesterolemic ApoE-deficient mice: potential involvement of oxysterols

The contribution of metabolic factors to the severity of liver disease is not completely understood. In this study, apolipoprotein E-deficient (ApoE-/-) mice were evaluated to define potential effects of hypercholesterolemia on the severity of carbon tetrachloride (CCl4)-induced liver injury. Under baseline conditions, hypercholesterolemic ApoE-/- mice showed increased hepatic oxidative stress (SOD activity/4-hydroxy-2-nonenal immunostaining) and higher hepatic TGF-beta1, MCP-1, and TIMP-1 expression than wild-type control mice. After CCl4 challenge, ApoE-/- mice exhibited exacerbated steatosis (Oil Red O staining), necroinflammation (hematoxylin-eosin staining), macrophage infiltration (F4/80 immunohistochemistry), and fibrosis (Sirius red staining and alpha-smooth muscle actin immunohistochemistry) and more severe liver injury [alanine aminotransferase (ALT) and aspartate aminotransferase] than wild-type controls. Direct correlations were identified between serum cholesterol and hepatic steatosis, fibrosis, and ALT levels. These changes did not reflect the usual progression of the disease in ApoE-/- mice, since exacerbated liver injury was not present in untreated age-paired ApoE-/- mice. Moreover, hepatic cytochrome P-450 expression was unchanged in ApoE-/- mice. To explore potential mechanisms, cell types relevant to liver pathophysiology were exposed to selected cholesterol-oxidized products. Incubation of hepatocytes with a mixture of oxysterols representative of those detected by GC-MS in livers from ApoE-/- mice resulted in a concentration-dependent increase in total lipoperoxides and SOD activity. In hepatic stellate cells, oxysterols increased IL-8 secretion through a NF-kappaB-independent mechanism and upregulated TIMP-1 expression. In macrophages, oxysterols increased TGF-beta1 secretion and MCP-1 expression in a concentration-dependent manner. Oxysterols did not compromise cell viability. Taken together, these findings demonstrate that hypercholesterolemic mice are sensitized to liver injury and that cholesterol-derived products (i.e., oxysterols) are able to induce proinflammatory and profibrogenic mechanisms in liver cells.

Reduced liver injury in the interleukin-6 knockout mice by chronic carbon tetrachloride administration

BACKGROUND

Interleukin-6 has been involved in restoration of liver function after partial hepatectomy and toxic liver injury. However, normal liver regeneration in interleukin-6 knockout mice has also been reported. The aim of this work was to investigate the effect of interleukin-6 deficiency on liver injury and its regeneration in a model of long term carbon tetrachloride (CCl4) administration.

DESIGN

Serum and whole livers from wild type and interleukin-6 knockout mice treated with carbon tetrachloride (0.25 mL kg(-1)) twice a week were obtained after 4, 6 and 8 weeks (n = 4-6). Sections were assessed for liver regeneration, liver injury and hepatocyte apoptosis whereas sera were assayed for aminotransferase levels. Nuclear extracts and total liver lysates were assayed for transcription factor activation and apoptosis related proteins, respectively.

RESULTS

When compared to wild type, interleukin-6 knockout mice showed reduced liver damage scores, lower aminotransferase levels and diminished apoptosis, as well as reduced nuclear factor kappa B activation. Although the level of active protein was lower, activation of signal transducer and activator of transcription 3 still takes place in knockout mice. Furthermore, liver regeneration measured by bromodeoxyuridine incorporation showed no differences between wild type and knockout animals after 6 and 8 weeks of treatment.

CONCLUSIONS

Compared to the wild type mice liver regeneration after chronic treatment with carbon tetrachloride proceeds at a slower rate in interleukin-6 deficient mice. However, this low recovery rate is accompanied by a reduction not only in hepatocyte apoptosis, but also in activation of nuclear factor kappa B and liver injury.

Hepatic accumulation of Hedgehog-reactive progenitors increases with severity of fatty liver damage in mice

Progenitors regenerate fatty livers but the mechanisms involved are uncertain. The Hedgehog pathway regulates mesendodermal progenitors and modulates mesenchymal-epithelial interactions during tissue remodeling. To determine if Hedgehog signaling increases in liver progenitors during fatty liver injury, we compared expression of Hedgehog ligands and target genes across a spectrum of injury. Leptin-deficient ob/ob mice with fatty livers and their healthy lean littermates were studied before and after exposure to the hepatotoxin, ethionine. At baseline, ob/ob mice had greater liver damage than controls. Ethionine induced liver injury in both ob/ob and lean mice, with greater injury occurring in ob/ob mice. After ethionine, the ob/ob mice developed liver atrophy and fibrosis. Liver injury increased hepatic accumulation of progenitors, including ductular cells that produced and responded to Hedgehog ligands. A dose-response relationship was demonstrated between liver injury and expansion of Hedgehog-responsive progenitors. In severely damaged, atrophic livers, nuclei in mature-appearing hepatocytes accumulated the Hedgehog-regulated mesenchymal transcription factor, Gli2 and lost expression of the liver epithelial transcription factor, hepatocyte nuclear factor 6 (HNF-6). Hepatic levels of collagen mRNA and pericellular collagen fibrils increased concomitantly. Hence, fatty liver injury increases Hedgehog activity in liver progenitors, and this might promote epithelial-mesenchymal transitions that result in liver fibrosis.

Endoplasmic reticulum stress, hepatocyte CD1d and NKT cell abnormalities in murine fatty livers

The liver regulates lipid homeostasis and is enriched with natural killer T (NKT) cells that respond to lipid antigens. Optimal maturation and activation of NKT cells requires their interaction with lipid antigens that are presented by cluster of differentiation-1 (CD-1) molecules on antigen-presenting cells. Hepatocytes express CD1d and present lipid antigens to NKT cells. Depletion and dysregulation of hepatic NKT cells occurs in mice with fatty livers. Herein, we assess whether reduced CD1d content on steatotic hepatocytes contributes to fatty liver-associated NKT cell abnormalities. We show that despite expressing normal levels of CD1d mRNA, fatty hepatocytes from ob/ob mice have significantly less CD1d on their plasma membranes than normal hepatocytes. This has functional significance because ob/ob hepatocytes are less able to activate CD1d-restricted T-cell responses in vitro, and CD1d-reactive NKT cells are reduced in ob/ob livers. Events in the endoplasmic reticulum (ER) normally regulate CD1d trafficking to plasma membranes. Hepatic steatosis has been associated with ER stress. To determine if ER stress reduces CD-1 accumulation on hepatocytes, we evaluated hepatic ER stress in ob/ob mice and treated cultured hepatocytes and lean mice with tunicamycin to induce ER stress. Lipid accumulation and ER stress occurred in the livers of both ob/ob and tunicamycin-treated mice. Tunicamycin caused dose-dependent decreases in hepatocyte CD1d, inhibited hepatocyte activation of CD1d-restricted T-cell responses, depleted liver populations of CD1d-reactive NKT cells and promoted Th-1 polarization of hepatic cytokine production. In conclusion, ER stress-related decreases in hepatocyte CD1d contribute to NKT cell dysregulation in fatty livers.

Loss of NF-kappaB activation in Kupffer cell-depleted mice impairs liver regeneration after partial hepatectomy

Kupffer cells (KCs) are located in the liver sinusoids adjacent to hepatocytes and are capable of producing important growth-regulating mediators that exert both stimulatory and inhibitory influences on hepatocyte proliferation by paracrine mechanisms. To elucidate the overall effect of KC depletion on liver regeneration, mice were selectively and long-standing depleted of KCs by liposome-encapsulated dichloromethylene diphosphonate. Using in vivo fluorescence microscopy, immunohistochemistry, Western blot analysis, and NF-kappaB transcription factor DNA binding activity and cytokine assays, we analyzed livers of KC-depleted and KC-competent mice at days 3, 5, and 8 after partial (i.e., 68%) hepatectomy (PH). Selective KC elimination delayed cell proliferation, as indicated by significantly reduced PCNA and cyclin B1 protein expression in liver tissue at day 3 after PH. This was associated with a lower liver weight at day 8 upon PH. Resection-associated activation of NF-kappaB with translocation into parenchymal and nonparenchymal cell nuclei was diminished in livers of KC-depleted mice, primarily at day 3 after PH. KC-depleted mice further lacked the resection-induced rise in TNF-alpha and IL-6 serum concentrations. These findings imply that KCs play a stimulatory role in liver regeneration, mainly by activating NF-kappaB with influence on the cell cycle and by enhancing expression of the proliferative cytokines TNF-alpha and IL-6.

Hepatic tumor necrosis factor signaling and nuclear factor-kappaB: effects on liver homeostasis and beyond

The proinflammatory cytokine TNF has a pivotal role in liver pathophysiology because it holds the capacity to induce both hepatocyte cell death and hepatocyte proliferation. This dual effect of TNF on hepatocytes reflects its ability to induce both nuclear factor kappaB (NF-kappaB)-dependent gene expression and cell death. Multiple studies have demonstrated the crucial role of the transcription factor NF-kappaB in the decision between life and death of a hepatocyte. Massive hepatocyte apoptosis preceding embryonic lethality in NF-kappaB-deficient mice constituted the first indication of an essential antiapoptotic function of NF-kappaB in the liver. Although many studies confirmed this crucial cytoprotective role of NF-kappaB in adult liver, a number of genetic studies recently obtained conflicting results on the exact role of NF-kappaB in different mouse models of TNF hepatotoxicity, demonstrating that caution should be taken when interpreting studies using different NF-kappaB-deficient mice in distinct models of liver injury. Recent reports showing a role for hepatic NF-kappaB activation in the proliferation of malignant cells during hepatocarcinogenesis, and in the progression of fatty liver diseases to insulin resistance and type 2 diabetes mellitus demonstrate that NF-kappaB can also have more detrimental effects in the liver. Moreover, its role in the development of the metabolic syndrome emphasizes that hepatic NF-kappaB activation might also have adverse effects on the endocrine system. Therefore, understanding the regulation of hepatic TNF signaling and NF-kappaB activation is of critical therapeutic importance. In this review, we summarize how studies on the role of NF-kappaB in different mouse models of liver pathologies have contributed to this understanding.

Expression patterns and action analysis of genes associated with hepatitis virus infection during rat liver regeneration

AIM: To study the action of hepatitis virus infection-associated genes at transcription level during liver regeneration (LR).

METHODS: Hepatitis virus infection-associated genes were obtained by collecting the data from databases and retrieving the correlated articles, and their expression changes in the regenerating rat liver were detected with the rat genome 230 2.0 array.

RESULTS: Eighty-eight genes were found to be associated with liver regeneration. The number of genes initially and totally expressed during initial LR [0.5-4 h after partial hepatectomy (PH)], transition from G0 to G1 (4-6 h after PH), cell proliferation (6-66 h after PH), cell differentiation and reorganization of structure-function (66-168 h after PH) was 37, 8, 48, 3 and 37, 26, 80, 57, respectively, indicating that the genes were mainly triggered at the early stage of LR (0.5-4 h after PH), and worked at different phases. These genes were classified into 5 types according to their expression similarity, namely 37 up-regulated, 9 predominantly up-regulated, 34 down-regulated, 6 predominantly down-regulated and 2 up/down-regulated genes. Their total up- and down-regulation frequencies were 359 and 149 during LR, indicating that the expression of most genes was enhanced, while the expression of a small number of genes was attenuated during LR. According to time relevance, they were classified into 12 groups (0.5 and 1 h, 2 and 4 h, 6 h, 8 and 12 h, 16 and 96 h, 18 and 24 h, 30 and 42 h, 36 and 48 h, 54 and 60 h, 66 and 72 h, 120 and 144 h, 168 h), demonstrating that the cellular physiological and biochemical activities during LR were fluctuated. According to expression changes of the genes, their expression patterns were classified into 23 types, suggesting that the cellular physiological and biochemical activities during LR were diverse and complicated.

CONCLUSION: The anti-virus infection capacity of regenerating liver can be enhanced and 88 genes play an important role in LR.

Increased DNA binding activity of NF-kB, STAT-3, SMAD3 and AP-1 in acutely damaged liver

AIM: To investigate the role of genes and kinetics of specific transcription factors in liver regeneration, and to analyze the gene expression and the activity of some molecules crucially involved in hepatic regeneration.

METHODS: USING gel-shift assay and RT-PCR, transcription factors, such as NF-κB, STAT-3, SMAD3 and AP-1, and gene expression of inducible nitric oxide synthase (iNOS), hepatocyte growth factor (HGF) and c-met were analyzed in an animal model of chemically induced hepatectomy.

RESULTS: Gene expression of HGF and its receptor c-met peaked at 3 h and 24 h after acute CCl₄ intoxi-cation. iNOS expression was only observed from 6 to 48 h. Transcriptional factor NF-κB had an early activation at 30 min after acute liver damage. STAT-3 peaked 3 h post-intoxication, while AP-1 displayed a peak of activation at 48 h. SMAD3 showed a high activity at all analyzed times.

CONCLUSION: TNF-α and IL-6 play a central role in hepatic regeneration. These two molecules are responsible for triggering the cascade of events and switch-on of genes involved in cell proliferation, such as growth factors, kinases and cyclins which are direct participants of cell proliferation.

Prometheus' challenge: molecular, cellular and systemic aspects of liver regeneration

The fascinating aspect of the liver is the capacity to regenerate after injury or resection. A variety of genes, cytokines, growth factors, and cells are involved in liver regeneration. The exact mechanism of regeneration and the interaction between cells and cytokines are not fully understood. There seems to exist a sequence of stages that result in liver regeneration, while at the same time inhibitors control the size of the regenerated liver. It has been proven that hepatocyte growth factor, transforming growth factor, epidermal growth factor, tumor necrosis factor-alpha, interleukins -1 and -6 are the main growth and promoter factors secreted after hepatic injury, partial hepatectomy and after a sequence of different and complex reactions to activate transcription factors, mainly nuclear factor kappaB and signal transduction and activator of transcription-3, affects specific genes to promote liver regeneration. Unraveling the complex processes of liver regeneration may provide novel strategies in the management of patients with end-stage liver disease. In particular, inducing liver regeneration should reduce morbidity for the donor and increase faster recovery for the liver transplantation recipient.