Models Of Chronic Liver Injury Research Articles

Loss of Cyclin E1 attenuates hepatitis and hepatocarcinogenesis in a mouse model of chronic liver injury.

Chronic liver injury triggers liver fibrosis and hepatocellular carcinoma (HCC), the third leading cause of cancer-related mortality. Cyclin E1 (CcnE1, formerly designated Cyclin E) is a regulatory subunit of the Cyclin-dependent kinase 2 (CDK2). It is overexpressed in approximately 70% of human HCCs correlating with poor prognosis, while the relevance of its orthologue Cyclin E2 (CcnE2) is unclear. Hepatocyte-specific deletion of NF-kappa-B essential modulator (NEMOΔhepa) leads to chronic hepatitis, liver fibrosis, and HCC as well as CcnE upregulation. To this end, we generated NEMOΔhepa/CcnE1-/- and NEMOΔhepa/CcnE2-/- double knockout mice and investigated age-dependent liver disease progression in these animals. Deletion of CcnE1 in NEMOΔhepa mice decreased basal liver damage and reduced spontaneous liver inflammation in young mice. In contrast, loss of CcnE2 did not affect liver injury in NEMOΔhepa livers pointing to a unique, non-redundant function of CcnE1 in chronic hepatitis. Accordingly, basal compensatory hepatocyte proliferation in NEMOΔhepa mice was reduced by concomitant ablation of CcnE1, but not after loss of CcnE2. In aged NEMOΔhepa mice, loss of CcnE1 resulted in significant reduction of liver tumorigenesis, while deletion of CcnE2 had no effect on HCC formation. CcnE1, but not its orthologue CcnE2, substantially contributes to hepatic inflammatory response, liver disease progression, and hepatocarcinogenesis in NEMOΔhepa mice.

Non-parenchymal TREM-2 protects the liver from immune-mediated hepatocellular damage

ObjectiveLiver injury impacts hepatic inflammation in part via Toll-like receptor (TLR) signalling. Triggering receptor expressed on myeloid cells 2 (TREM-2) modulates TLR4-mediated inflammation in bone marrow (BM)-derived macrophages but its...

Stage-specific expression of the oncofetal marker Neighbor of Punc E11 in Mdr2-/- mice as a model of chronic cholestatic liver injury

Stage-specific expression of the oncofetal marker Neighbor of Punc E11 in Mdr2-/- mice as a model of chronic cholestatic liver injury

Human Umbilical Cord MSC-Derived Exosomes Suppress the Development of CCl4-Induced Liver Injury through Antioxidant Effect.

Mesenchymal stem cells (MSCs) have been increasingly applied into clinical therapy. Exosomes are small (30–100 nm in diameter) membrane vesicles released by different cell types and possess the similar functions with their derived cells. Human umbilical cord MSC-derived exosomes (hucMSC-Ex) play important roles in liver repair. However, the effects and mechanisms of hucMSC-Ex on liver injury development remain elusive. Mouse models of acute and chronic liver injury and liver tumor were induced by carbon tetrachloride (CCl4) injection, followed by administration of hucMSC-Ex via the tail vein. Alleviation of liver injury by hucMSC-Ex was determined. We further explored the production of oxidative stress and apoptosis in the development of liver injury and compared the antioxidant effects of hucMSC-Ex with frequently used hepatic protectant, bifendate (DDB) in liver injury. hucMSC-Ex alleviated CCl4-induced acute liver injury and liver fibrosis and restrained the growth of liver tumors. Decreased oxidative stress and apoptosis were found in hucMSC-Ex-treated mouse models and liver cells. Compared to bifendate (DDB) treatment, hucMSC-Ex presented more distinct antioxidant and hepatoprotective effects. hucMSC-Ex may suppress CCl4-induced liver injury development via antioxidant potentials and could be a more effective antioxidant than DDB in CCl4-induced liver tumor development.

Amelioration of Single Clove Black Garlic Aqueous Extract on Dyslipidemia and Hepatitis in Chronic Carbon Tetrachloride Intoxicated Swiss Albino Mice.

Single clove garlic is the product of atypical bulbing process of garlic under specific conditions. Therefore, the number of researches on single clove garlic bioactivity is limited. Recently, the hepatoprotective effect of single clove garlic has been demonstrated. In this study, we investigated amelioration of single clove black garlic aqueous extract, a processed product from single clove garlic, on dyslipidemia and hepatitis induced by chronic administration of CCl4. Mice were randomly divided into four groups: control, extract control, CCl4 intoxication, and coadministrated CCl4 and extract group. Mice were orally given a dose of 1 ml/kg body weight of CCl4 for 28 days twice a week to establish chronic liver injury model. To evaluate the hepatoprotective effect of single clove black garlic, mice were cotreated with CCl4 and single clove black garlic extract (200 mg/kg body weight) via gastric gauge for 30 days. Cotreatment with CCl4 and extract could improve the changes of body weight, liver weight, and relative liver weight as compared to CCl4 intoxicated mice. Single clove black garlic ameliorated dyslipidemia and the elevation of ALT and AST levels induced by chronic CCl4 intoxication. Histological studies revealed that single clove black garlic could prevent mononuclear cells infiltration and hepatocyte necrosis.

Microbiota transplantation reveals beneficial impact of berberine on hepatotoxicity by improving gut homeostasis.

Berberine has been shown to reduce acute liver injury although the underlying mechanism is not fully understood. Because of the anatomic connection, the liver is constantly exposed to gut-derived bacterial products and metabolites. In this study, we showed that berberine has beneficial effects on both hepatotoxicity and intestinal damage in a rat model of chronic or acute liver injury. Microbiota transplantation from the rats with chronic hepatotoxicity could aggravate acute hepatotoxicity in mice treated with diethylnitrosamine (DEN). In rat models with gut homeostasis disruption induced by penicillin or dextran sulfate sodium (DSS), their fecal microbiota could also cause an enhanced hepatotoxicity of recipient mice. When treated with berberine, the DSS-induced enteric dysbacteriosis could be mitigated and their fecal bacteria were able to reduce acute hepatotoxicity in recipient mice. This study indicates that berberine could improve intestinal dysbacteriosis, which reduces the hepatotoxicity caused by pathological or pharmacological intervention. Fecal microbiota transplantation might be a useful method to directly explore homeostatic alteration in gut microbiota.

Fate tracing of hepatocytes in mouse liver

Hepatocytes perform most of the functions of the liver and are considered terminally differentiated cells. Recently, it has been suggested that hepatocytes might have the potential to transdifferentiate or dedifferentiate under physiological or pathological conditions in vivo. Epithelial-mesenchymal transition of hepatocytes in liver fibrosis has also been proposed. However, these findings have not been fully confirmed. In this study, hepatocytes were genetically labelled for cell fate tracing using lacZ via the tamoxifen-induced CreERT/loxP system. After induction with tamoxifen, alb + cells were permanently marked by lacZ expression, and all progeny lacZ + cells were derived from a single source with no interference. We did not observe transdifferentiation or dedifferentiation of hepatocytes into cholangiocytes or hepatic progenitor cells under conditions of liver homeostasis or following a 2/3 partial hepatectomy. Meanwhile, lacZ/OPN-positive cells were observed in livers of 3,5-diethoxycarbonyl-1,4-dihydrocollidine-fed mice, and lacZ/alpha-smooth muscle actin-positive cells were detected in carbon tetrachloride-induced chronic liver injury models. These results suggested that some existing differentiated alb + cells might have the potential of transdifferentiation/dedifferentiation or epithelial-to-mesenchymal transition in vivo in some liver injury models, but the proportion of these alb + cells in liver was very low, and their significance and actual function during the pathological process remains to be elucidated.

Platelet-Derived Growth Factor Receptor α Contributes to Human Hepatic Stellate Cell Proliferation and Migration

Platelet-derived growth factor receptor α (PDGFRα), a tyrosine kinase receptor, is up-regulated in hepatic stellate cells (HSCs) during chronic liver injury. HSCs mediate hepatic fibrosis through their activation from a quiescent state partially in response to profibrotic growth factors. HSC activation entails enhanced expression of profibrotic genes, increase in proliferation, and increase in motility, which facilitates migration within the hepatic lobule. We show colocalization of PDGFRα in murine carbon tetrachloride, bile duct ligation, and 0.1% 3,5-diethoxycarbonyl-1,4-dihydrocollidine models of chronic liver injury, and investigate the role of PDGFRα on proliferation, profibrotic gene expression, and migration in primary human HSCs (HHSteCs) using the PDGFRα-specific inhibitory monoclonal antibody olaratumab. Although lacking any effects on HHSteC transdifferentiation assessed by gene expression of ACTA2, TGFB1, COL1A1, SYP1, and FN1, olaratumab specifically reduced HHSteC proliferation (AlamarBlue assay) and cell migration (transwell migration assays). Using phospho-specific antibodies, we show that olaratumab attenuates PDGFRα activation in response to PDGF-BB, and reduced phosphorylation of extracellular signal-regulated kinase 1 and 2, Elk-1, p38, Akt, focal adhesion kinase, mechanistic target of rapamycin, C10 regulator of kinase II, and C10 regulator of kinase-like, suggesting that PDGFRα contributes to mitogenesis and actin reorganization through diverse downstream effectors. Our findings support a distinct contribution of PDGFRα signaling to HSC proliferation and migration and provide evidence that inhibition of PDGFRα signaling could alter the pathogenesis ofhepatic fibrosis.

No significant impact of Foxf1 siRNA treatment in acute and chronic CCl4 liver injury.

Chronic liver injury of any etiology is the main trigger of fibrogenic responses and thought to be mediated by hepatic stellate cells. Herein, activating transcription factors like forkhead box f1 are described to stimulate pro-fibrogenic genes in hepatic stellate cells. By using a liver-specific siRNA delivery system (DBTC), we evaluated whether forkhead box f1 siRNA treatment exhibit beneficial effects in murine models of acute and chronic CCl4-induced liver injury. Systemic administration of DBTC-forkhead box f1 siRNA in mice was only sufficient to silence forkhead box f1 in acute CCl4 model, but was not able to attenuate liver injury as measured by liver enzymes and necrotic liver cell area. Therapeutic treatment of mice with DBTC-forkhead box f1 siRNA upon chronic CCl4 exposition failed to inhibit forkhead box f1 expression and hence lacked to diminish hepatic stellate cells activation or fibrosis development. As a conclusion, DBTC-forkhead box f1 siRNA reduced forkhead box f1 expression in a model of acute but not chronic toxic liver injury and showed no positive effects in either of these mice models. Impact statement As liver fibrosis is a worldwide health problem, antifibrotic therapeutic strategies are urgently needed. Therefore, further developments of new technologies including validation in different experimental models of liver disease are essential. Since activation of hepatic stellate cells is a key event upon liver injury, the activating transcription factor forkhead box f1 (Foxf1) represents a potential target gene. Previously, we evaluated Foxf1 silencing by a liver-specific siRNA delivery system (DBTC), exerting beneficial effects in cholestasis. The present study was designed to confirm the therapeutic potential of Foxf1 siRNA in models of acute and chronic CCl4-induced liver injury. DBTC-Foxf1 siRNA was only sufficient to silence Foxf1 in acute CCl4 model and did not ameliorate liver injury or fibrogenesis. This underlines the significance of the experimental model used. Each model displays specific characteristics in the pathogenic nature, time course and severity of fibrosis and the optimal time point for starting a therapy.

BMP-9 interferes with liver regeneration and promotes liver fibrosis.

Bone morphogenetic protein (BMP)-9, a member of the transforming growth factor-β family of cytokines, is constitutively produced in the liver. Systemic levels act on many organs and tissues including bone and endothelium, but little is known about its hepatic functions in health and disease. Levels of BMP-9 and its receptors were analysed in primary liver cells. Direct effects of BMP-9 on hepatic stellate cells (HSCs) and hepatocytes were studied in vitro, and the role of BMP-9 was examined in acute and chronic liver injury models in mice. Quiescent and activated HSCs were identified as major BMP-9 producing liver cell type. BMP-9 stimulation of cultured hepatocytes inhibited proliferation, epithelial to mesenchymal transition and preserved expression of important metabolic enzymes such as cytochrome P450. Acute liver injury caused by partial hepatectomy or single injections of carbon tetrachloride (CCl4) or lipopolysaccharide (LPS) into mice resulted in transient downregulation of hepatic BMP-9 mRNA expression. Correspondingly, LPS stimulation led to downregulation of BMP-9 expression in cultured HSCs. Application of BMP-9 after partial hepatectomy significantly enhanced liver damage and disturbed the proliferative response. Chronic liver damage in BMP-9-deficient mice or in mice adenovirally overexpressing the selective BMP-9 antagonist activin-like kinase 1-Fc resulted in reduced deposition of collagen and subsequent fibrosis. Constitutive expression of low levels of BMP-9 stabilises hepatocyte function in the healthy liver. Upon HSC activation, endogenous BMP-9 levels increase in vitro and in vivo and high levels of BMP-9 cause enhanced damage upon acute or chronic injury.

A morphological method for ammonia detection in liver.

Hyperammonemia is a metabolic condition characterized by elevated levels of ammonia and a common event in acute liver injury/failure and chronic liver disease. Even though hepatic ammonia levels are potential predictive factors of patient outcome, easy and inexpensive methods aiming at the detection of liver ammonia accumulation in the clinical setting remain unavailable. Thus, herein we have developed a morphological method, based on the utilization of Nessler´s reagent, to accurately and precisely detect the accumulation of ammonia in biological tissue. We have validated our method against a commercially available kit in mouse tissue samples and, by using this modified method, we have confirmed the hepatic accumulation of ammonia in clinical and animal models of acute and chronic advanced liver injury as well as in the progression of fatty liver disease. Overall, we propose a morphological method for ammonia detection in liver that correlates well with the degree of liver disease severity and therefore can be potentially used to predict patient outcome.

β-Caryophyllene protects against alcoholic steatohepatitis by attenuating inflammation and metabolic dysregulation in mice.

β-Caryophyllene (BCP) is a plant-derived FDA approved food additive with anti-inflammatory properties. Some of its beneficial effects in vivo are reported to involve activation of cannabinoid CB2 receptors that are predominantly expressed in immune cells. Here, we evaluated the translational potential of BCP using a well-established model of chronic and binge alcohol-induced liver injury. In this study, we investigated the effects of BCP on liver injury induced by chronic plus binge alcohol feeding in mice in vivo by using biochemical assays, real-time PCR and histology analyses. Serum and hepatic BCP levels were also determined by GC/MS. Chronic treatment with BCP alleviated the chronic and binge alcohol-induced liver injury and inflammation by attenuating the pro-inflammatory phenotypic `M1` switch of Kupffer cells and by decreasing the expression of vascular adhesion molecules intercellular adhesion molecule 1, E-Selectin and P-Selectin, as well as the neutrophil infiltration. It also beneficially influenced hepatic metabolic dysregulation (steatosis, protein hyperacetylation and PPAR-α signalling). These protective effects of BCP against alcohol-induced liver injury were attenuated in CB2 receptor knockout mice, indicating that the beneficial effects of this natural product in liver injury involve activation of these receptors. Following acute or chronic administration, BCP was detectable both in the serum and liver tissue homogenates but not in the brain. Given the safety of BCP in humans, this food additive has a high translational potential in treating or preventing hepatic injury associated with oxidative stress, inflammation and steatosis. This article is part of a themed section on Inventing New Therapies Without Reinventing the Wheel: The Power of Drug Repurposing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.2/issuetoc.

Role of stabilin-1 in chronic liver tissue injury and repair

BackgroundOrgan fibrosis is a major cause of global mortality. Few medical therapies are available to treat this condition. We have previously demonstrated increased expression of stabilin-1 at sites of chronic liver disease. Using models of chronic liver injury, we aimed to elucidate the role of stabilin-1 during fibrosis and repair. MethodsWe used full knockout and cell specific knockouts of stabilin-1 in murine models of chronic liver injury including carbon tetrachloride treatment and a methionine and choline deficient diet. A resolution phase after carbon tetrachloride treatment was used to study tissue repair. Tissue was analysed for fibrosis by confocal microscopy, collagen quantification, and immune cell infiltrate analysis. RNA sequencing and cell transfer experiments were done to elucidate underlying mechanisms. Human tissue was also analysed for stabilin-1 expression in chronic liver injury. FindingsWe detected a subset of stabilin-1 macrophages that were induced at sites of cellular injury close to the hepatic scar in mouse models of liver fibrosis and in human liver disease. Stabilin-1 deficiency abrogated malondialdehyde-LDL uptake by hepatic macrophages and was associated with excess collagen III deposition. Mechanistically, the lack of stabilin-1 led to elevated intrahepatic levels of the profibrogenic chemokine CCL3 and an increase in GFAP+ fibrogenic cells. Stabilin-1 knockout macrophages demonstrated a proinflammatory phenotype during liver injury and this led to delayed wound healing. InterpretationWe have demonstrated a pathway in which the evolutionarily conserved receptor stabilin-1 on tissue-infiltrating macrophages promotes the uptake of products of lipid peroxidation and thus prevents excess scarring. We propose that macrophage stabilin-1 is a crucial defence against oxidative tissue damage and thereby maintains tissue homoeostasis. FundingWellcome Trust.

Icariin-treated human umbilical cord mesenchymal stem cells decrease chronic liver injury in mice.

Human umbilical cord mesenchymal stem cells (hUMSCs) have been shown to have multiple differentiation potentials. However, a key problem is that only a small number of hUMSCs can migrate to damaged tissue after transplantation. According to "The Theory of Kidney Essence" in Traditional Chinese Medicine, some traditional Chinese medicines used for tonifying the kidneys can be applied in promoting the differentiation and migration of stem cells in vivo. Our previous study demonstrated that icariin (ICA) could up-regulate the pluripotent genes of hUMSCs in vitro and induce cell migration in mice in an acute kidney injury model in vivo. The aim of this study was to investigate the effects of ICA-induced hUMSCs in chronic liver injury (CLI) caused by carbon tetrachloride (CCl4). CLI was induced by intraperitoneal injection of CCl4. ICA-treated hUMSCs were transplanted via intra-venous injection. The animals were followed for survival, biochemistry analysis and pathology. The results show that ICA-treated hUMSCs accelerate the recovery of liver function in mice with CLI. In addition, ICA-treated hUMSCs increase the anti-oxidant activities in liver and prevent the progression to hepatic fibrosis. Moreover, ICA induces the migration of hUMSCs to the injured liver tissue. In conclusion, these data demonstrate that ICA-treated hUMSCs exhibit recovery and protective properties in the mice model of CCl4-induced CLI.

The chronic hepatotoxicity assessment of the herbal formula Zishen Yutai pill

Zishen Yutai pill (ZYP) is an oriental herbal formula, while hepatotoxicity assessment of ZYP was rarely evaluated. Therefore, our aim is to re-evaluate its hepatotoxicity in both normal and carbon tetrachloride (CCl4) induced chronic liver injury rats. In the normal model, two doses of ZYP (1.575 and 9.450 g kg−1 d−1; i.e. 1 × , 6 × clinical doses) were given orally to rats for 24 weeks. In the chronic liver injury model, 10% CCl4 was administered to rats abdominally twice a week at a dose of 5 mL kg−1 for 12 consecutive weeks. Administration time started from 4 weeks after the beginning of CCl4 treatment. Toxicological parameters included mortality, body weight, food consumption, clinical signs, biochemical parameters, gross observation, organ weight, necropsy findings and histopathology were monitored. In the normal model, we found no any mortality or abnormality in clinical signs, relative liver weight, biochemical parameters and histopathology in ZYP treatment groups. In the chronic liver injury model, liver damage related parameter such as ALT was elevated at the high dose of ZYP treatment in contrast to the CCl4-treated group (P < 0.01). In histopathological assessment, there were no significant difference between ZYP treatment groups and CCl4-treated group. No observed adverse effect on livers were established for 9.450 g kg−1 d−1 ZYP in the normal rats and 9.450 g kg−1 d−1 ZYP in the injury rats.

Plumbagin protects liver against fulminant hepatic failure and chronic liver fibrosis via inhibiting inflammation and collagen production.

Plumbagin is a quinonoid constituent extracted from Plumbago genus, and it exhibits diverse pharmacological effects. This study thoroughly investigated the effects of plumbagin on thioacetamide-induced acute and chronic liver injury. Results shown that plumbagin increased survival rate, reduced liver congestion and inflammation, and decreased macrophages and neutrophils in the fulminant hepatic failure model, and remarkably diminished liver fibrosis and inflammation in the chronic liver injury model. Furthermore, plumbagin significantly suppress the HSCs/myofibroblasts activation by reduced expression of markers α-SMA and COL-1/3, and reduced macrophage in liver. In the in vitro study, plumbagin induced apoptosis and suppressed the proliferation of LX-2 cells (human HSCs). Plumbagin treatment increased AMPK phosphorylation and attenuated NF-κB, STAT3, and Akt/mTOR signals in LX-2 cells, while SMAD2 phosphorylation was not changed. Noticeably, plumbagin promoted AMPK binding to p300 which is a cofactor of SMAD complex, this may further competitively decreases the p300/SMAD complex initiated transcription of COL-1/3 and α-SMA. Additionally, plumbagin hampered inflammation related NF-κB signal in RAW 264.7 cells. In conclusion, these findings indicate that plumbagin may be a powerful drug candidate to protect the liver from acute and chronic damage by inhibiting inflammation and collagen production.

Basic Science Liver.

Basic Science Liver.

Bone Marrow Cells Repair and Regenerate Acute and Chronic Injured Liver without Primary Evidence of Neoplastic Changes

Therapeutic potential of bone marrow (BM)-derived cells in acute and chronic liver injury model has been investigated. Apart from pathological improvement of the liver, we also studied liver regeneration and genetic alteration in donor cells towards neoplasia. Acetaminophen-induced acute and CCl4-induced chronic liver injured male mice were transplanted with BM-derived uncommitted and CD45+ cells, respectively from female mice. Transplantation of CD45 cells resulted in enhanced recovery of fibrotic liver during initial pro-fibrogenic condition as compared with sham control. Significant recovery from apoptotic death of hepatocytes was also observed. After 3 months of transplantation, donor-derived hepatocytes in acute and chronic liver injury models were found to be about 5% and 17%, respectively.

Divergent Inflammatory, Fibrogenic, and Liver Progenitor Cell Dynamics in Two Common Mouse Models of Chronic Liver Injury

Complications of end-stage chronic liver disease signify a major cause of mortality worldwide. Irrespective of the underlying cause, most chronic liver diseases are characterized by hepatocellular necrosis, inflammation, fibrosis, and proliferation of liver progenitor cells or ductular reactions. Vast differences exist between experimental models that mimic these processes, and their identification is fundamental for translational research. We compared two common murine models of chronic liver disease: the choline-deficient, ethionine-supplemented (CDE) diet versus thioacetamide (TAA) supplementation. Markers of liver injury, including serum alanine transaminase levels, apoptosis, hepatic fat loading, and oxidative stress, as well as inflammatory, fibrogenic and liver progenitor cell responses, were assessed at days 3, 7, 14, 21, and 42. This study revealed remarkable differences between the models. It identified periportal injury and fibrosis with an early peak and slow normalization of all parameters in the CDE regimen, whereas TAA-treated mice had pericentral patterns of progressive injury and fibrosis, resulting in a more severe hepatic injury phenotype. This study is the first to resolve two different patterns of injury and fibrosis in the CDE and TAA model and to indisputably identify the fibrosis pattern in the TAA model as driven from the pericentral vein region. Our data provide a valuable foundation for future work using the CDE and TAA regimens to model a variety of human chronic liverdiseases.

P21 in chronic and acute liver injury.

p21 historically has been considered a tumor suppressor since first studies showed that p21−/− mice display spontaneous tumor formation after 16 months and additionally these mice are more sensitive to chemically induced carcinogenesis [1,2]. On the contrary, recently a potential function as an oncogene has been described for p21. For instance mice deficient for p53 spontaneously develop multiple tumors and an additional deletion of p21 lead to a significant reduction of thymic lymphomas [3]. This argues that the complete spectrum of p21 function during tumorigenesis is not clearly identified. The role of p21 has been further studied in the NEMOΔhepa mice model. The NF-κB pathway regulator NEMO (also known as IKKγ) has been shown to control chronic inflammation and hepatocarcinogenesis in mice. The hepatocyte specific deletion of NEMO (NEMOΔhepa), is of clinical interest as these animals develop a cascade of events which resemble the spectrum of human chronic liver disease, which leads from chronic hepatitis to liver cirrhosis and growth of hepatocellular carcinomas (HCC). Additionally, a recent study using human HCC tissue found a downregulation of NEMO in tumor tissue, further supporting the translational relevance of the NEMOΔhepa mice model [4]. The deletion of NEMO in hepatocytes triggers increased p21 expression [5,6]. In order to study the relevance of p21 overexpression for disease progression of NEMOΔhepa livers, double knockout (NEMOΔhepa/p21−/−) mice carrying a hepatocyte specific deletion for NEMO and an additional constitutional deletion for p21 were generated. Although p21 is a cell cycle inhibitor its deletion had no impact on cell proliferation in 8 week-old NEMOΔhepa/p21−/− livers compared to NEMOΔhepa livers. This result was unexpected since p21 binds to CcnE/cdk2 and CcnA/cdk2 complexes thereby preventing progression from G1- to S-phase. Very likely the loss of p21 expression is compensated by other cell cycle inhibitors such as p-p27 and p18. Despite the unchanged cell cycle activity in p21 deficient NEMOΔhepa livers, the cell cycle regulator CcnA2 and CcnE2 were overexpressed. However, recent studies discovered that ectopic overexpression of CcnA or CcnE in mouse embryonic fibroblast (MEFs) lead to an increase in DNA double strand breakage [7]. Therefore the enhanced liver injury caused by exacerbation of DNA damage in p21-deficient NEMOΔhepa mice could be explained by elevated CcnA2 and CcnE2 expression. The DNA double strand breakage was quantified by pH2AX Immunofluorescence staining. p21 is not only protective against DNA damage in the chronic liver injury model as challenging double mutant NEMOΔhepa/p21−/− mice with Lipopolysaccharide (LPS) enhanced DNA damage massively compared to NEMOΔhepa mice. After LPS administration NEMOΔhepa mice suffer from severe liver injury which is reflected in the increased alanine aminotransferase (ALT) and aspartataminotransferase (AST) serum values and apoptotic cells in the liver of these mice. However, in NEMOΔhepa/p21−/− mice transaminases and cell death were significantly enhanced. Finally, this enhanced liver injury in the double knockout animals resulted in a higher lethality of this mice after LPS administration. The observed hypersensitivity against LPS due to the lack of p21 is mediated via the Tumor Necrosis Factor (TNF), since NEMOΔhepa/p21−/− mice which carry in addition a deletion for the TNF receptor 1 (NEMOΔhepa/p21−/−/TNF-R1−/−), showed a strong attenuation of the DNA damage and cell death. The protective role of p21 in carcinogenesis was the first time visible in 26 week old knockout animals. Here, the double knockout mice (NEMOΔhepa/p21−/−) showed enhanced hepatocyte proliferation as revealed by Ki67 staining. This resulted consequently into a higher liver weight/body weight ratio but more interestingly p21- deficient NEMOΔhepa livers showed more frequently small tumors in comparison to NEMOΔhepa livers. Finally, a significantly increased number of HCCs were found in 52 week-old NEMOΔhepa/p21−/− animals, meaning that the loss of p21 expression caused exacerbation of hepatocarcinogenesis. Analysing the livers of these mice revealed that only the number of nodules was increased, whereas the sizes of the tumors were not significantly enlarged. This suggests that the loss of p21 overexpression in NEMOΔhepa animals has more impact on tumor initiation than on tumor progression. Beside hepatocarcinogenesis p21 had an additional protective role in cholestasis. Livers of 52 week old NEMOΔhepa/p21−/− animals display yellow inclusions and serum values for alkaline phosphatase, direct and total bilirubin confirmed the cholestatic phenotype. These cholestatic serum markers were significantly lower in NEMOΔhepa mice. Taken together, the enhanced p21 expression in NEMOΔhepa animals has a protective function in this model, as p21 protects against DNA damage, acceleration of hepatocarcinogenesis and cholestasis. Since liver disease progression is reduced in the presence of p21 expression, p21 has been shown to act as a tumor suppressor in the NEMOΔhepa model.