Silke Marhenke

Nuclear factor-eythroid 2-related factor 2 prevents alcohol-induced fulminant liver injury

BACKGROUND & AIMS The transcription factor nuclear factor-eythroid 2-related factor 2 (Nrf2(-/-)) is essential for protecting cells against xenobiotic and oxidative stress. Increased oxidative stress has been implicated in the pathophysiology of many diseases including ethanol-induced liver disease. Therefore, the role of Nrf2(-/-) in ethanol-induced liver injury was investigated. METHODS Wild-type and Nrf2(-/-) mice were fed with the ethanol diet, followed by examination of liver pathology, mortality, and ethanol metabolism. RESULTS Nrf2(-/-) mice displayed a dramatically increased mortality associated with liver failure when fed doses of ethanol that were tolerated by WT mice. Nrf2(-/-) mice showed a significantly reduced ability to detoxify acetaldehyde, leading to an accumulation of the toxic metabolite. Loss of Nrf2(-/-) caused a marked steatosis in livers of ethanol-fed mice, and Srebp1 was identified as a candidate transcription factor responsible for lipogenic enzyme induction. Furthermore, ethanol consumption led to a progressive depletion of total and mitochondrial reduced glutathione, which was associated with more pronounced structural and functional changes to mitochondria of Nrf2(-/-) mice. In addition, ethanol feeding elicited an aggravated inflammatory response mediated by Kupffer cells in Nrf2(-/-) mice as shown by an increased tumor necrosis factor-alpha secretion and activation of the interleukin-6/Stat-3 pathway. Together these changes lead to a vicious cycle of accumulating hepatocellular damage, ultimately leading to liver failure and death of Nrf2(-/-) mice. CONCLUSIONS Our data establish a central role for Nrf2(-/-) in the protection against ethanol-induced liver injury.

Receptor for advanced glycation endproducts (RAGE) is a key regulator of oval cell activation and inflammation‐associated liver carcinogenesis in mice

The receptor for advanced glycation endproducts (RAGE) is a multiligand receptor and member of the immunoglobulin superfamily. RAGE is mainly involved in tissue damage and chronic inflammatory disorders, sustaining the inflammatory response upon engagement with damage‐associated molecular pattern molecules (DAMPs) such as S100 proteins and high‐mobility group box 1 (HMGB1). Enhanced expression of RAGE and its ligands has been demonstrated in distinct tumors and several studies support its crucial role in tumor progression and metastasis by still unknown mechanisms. Here we show that RAGE supports hepatocellular carcinoma (HCC) formation in the Mdr2−/− mouse model, a prototype model of inflammation‐driven HCC formation, which mimics the human pathology. Mdr2−/− Rage−/− (dKO) mice developed smaller and fewer HCCs than Mdr2−/− mice. Interestingly, although in preneoplastic Mdr2−/− livers RAGE ablation did not affect the onset of inflammation, premalignant dKO livers showed reduced liver damage and fibrosis, in association with decreased oval cell activation. Oval cells expressed high RAGE levels and displayed reduced proliferation upon RAGE silencing. Moreover, stimulation of oval cells with HMGB1 promoted an ERK1/2‐Cyclin D1‐dependent oval cell proliferation in vitro. Finally, genetic and pharmacologic blockade of RAGE signaling impaired oval cell activation in an independent mouse model of oval cell activation, the choline deficient ethionine‐supplemented dietary regime. Conclusion: Our data identified a novel function of RAGE in regulating oval cell activation and tumor development in inflammation‐associated liver carcinogenesis. (Hepatology 2013)

The degree of liver injury determines the role of p21 in liver regeneration and hepatocarcinogenesis in mice

Hepatocellular carcinoma (HCC) frequently arises in the context of chronic injury that promotes DNA damage and chromosomal aberrations. The cyclin‐dependent kinase inhibitor p21 is an important transcriptional target of several tumor suppressors, which promotes cell cycle arrest in response to many stimuli. The aim of this study was to further delineate the role of p21 in the liver during moderate and severe injury and to specify its role in the initiation and progression of HCC. Deletion of p21 led to continuous hepatocyte proliferation in mice with severe injury allowing animal survival but also facilitated rapid tumor development, suggesting that control of compensatory proliferation by high levels of p21 is critical to the prevention of tumor development. Unexpectedly, however, liver regeneration and hepatocarcinogenesis was impaired in p21‐deficient mice with moderate injury. Mechanistically, loss of p21 was compensated by activation of Sestrin2, which impaired mitogenic mammalian target of rapamycin (mTOR) signaling and activated cytoprotective Nrf2 signaling. Conclusion: The degree of liver injury and the strength of p21 activation determine its effects on liver regeneration and tumor development in the liver. Moreover, our data uncover a molecular link in the complex mTOR, Nrf2, and p53/p21‐signaling network through activation of Sestrin2, which regulates hepatocyte proliferation and tumor development in mice with liver injury. (Hepatology 2013;53:1143–1152)

Rapamycin delays tumor development in murine livers by inhibiting proliferation of hepatocytes with DNA damage

In this study, everolimus (RAD001) was used to determine the role of mammalian target of rapamycin (mTOR) in hepatocarcinogenesis. We show that RAD001 effectively inhibits proliferation of hepatocytes during chronic liver injury. Remarkably, the ability of RAD001 to impair cell cycle progression requires activation of the DNA damage response; loss of p53 significantly attenuates the antiproliferative effects of mTOR inhibition. RAD001 modulates the expression of specific cell cycle–related proteins and the assembly of cyclin–cyclin‐dependent kinase complexes to prevent cell cycle progression. Furthermore, RAD001 sustains the apoptosis sensitivity of hepatocytes during chronic liver injury by inhibiting p53‐induced p21 expression. Long‐term treatment with RAD001 markedly delays DNA damage–induced liver tumor development. Conclusion: We provide evidence that mTOR inhibition has a substantial effect on sequential carcinogenesis and may offer an effective strategy to delay liver tumor development in patients at risk. (HEPATOLOGY 2009;50:500–509.)

Activity of the mTOR inhibitor RAD001, the dual mTOR and PI3‐kinase inhibitor BEZ235 and the PI3‐kinase inhibitor BKM120 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most deadly cancers worldwide with only few therapeutic options for patients with advanced disease. There is growing evidence indicating that activation of the PI3K/Akt/mTOR pathway plays an important role in HCC and therefore represents a promising target for novel therapeutic approaches. The aim of this study was to evaluate and compare the antitumour activity of the mTOR inhibitor RAD001, the dual mTOR and PI3‐kinase inhibitor BEZ235 and the PI3‐kinase inhibitor BKM120 in vitro and in vivo.

p21 promotes sustained liver regeneration and hepatocarcinogenesis in chronic cholestatic liver injury

Background and aims The cyclin-dependent kinase inhibitor p21 has been implicated as a tumour suppressor. Moreover, recent genetic studies suggest that p21 might be a potential therapeutic target to improve regeneration in chronic diseases. The aim of this study was to delineate the role of p21 in chronic liver injury and to specify its role in hepatocarcinogenesis in a mouse model of chronic cholestatic liver injury. Methods The degree of liver injury, regeneration and tumour formation was assessed in Mdr2−/− mice and compared with Mdr2/ p21−/− mice. Moreover, the role of p21 was evaluated in hepatoma cells in vitro and in human hepatocellular carcinoma (HCC). Results Mdr2−/− mice developed HCCs as a consequence of chronic inflammatory liver injury. In contrast, tumour development was profoundly delayed in Mdr2/ p21−/− mice. Delayed tumour development was accompanied by markedly impaired liver regeneration in Mdr2/ p21−/− mice. Moreover, the regenerative capacity of the Mdr2/ p21−/− livers in response to partial hepatectomy declined with age in these mice. Hepatocyte transplantation experiments revealed that impaired liver regeneration was due to intrinsic factors within the cells and changes in the Mdr2/ p21−/− microenvironment. In human HCCs, a subset of tumours expressed p21, which was associated with a significant shorter patient survival. Conclusions We provide experimental evidence that p21 is required for sustained liver regeneration and tumour development in chronic liver injury indicating that p21 needs to be tightly regulated in order to balance liver regeneration and cancer risk. Moreover, we identify p21 as a negative prognostic marker in human HCC.

Activation of Nuclear Factor E2-Related Factor 2 in Hereditary Tyrosinemia Type 1 and Its Role in Survival and Tumor Development

In tyrosinemia type 1 (HT1), accumulation of toxic metabolites results in oxidative stress and DNA damage, leading to a high incidence of hepatocellular carcinomas. Nuclear factor erythroid‐2 related factor 2 (Nrf2) is a key transcription factor important for cellular protection against oxidative stress and chemical induced liver damage. To specifically address the role of Nrf2 in HT1, fumarylacetoacetate hydrolase (Fah)/Nrf2−/− mice were generated. In acute HT1, loss of Nrf2 elicited a strong inflammatory response and dramatically increased the mortality of mice. Following low grade injury, Fah/Nrf2−/− mice develop a more severe hepatitis and liver fibrosis. The glutathione and cellular detoxification system was significantly impaired in Fah/Nrf2−/− mice, resulting in increased oxidative stress and DNA damage. Consequently, tumor development was significantly accelerated by loss of Nrf2. Potent pharmacological inducers of Nrf2 such as the triterpenoid analogs 1[2‐cyano‐3,12‐dioxooleana‐1,9(11)‐dien‐28‐oyl]imidazole have been developed as cancer chemoprevention agents. Pretreatment with 1[2‐cyano‐3,12‐dioxooleana‐1,9(11)‐dien‐28‐oyl]imidazole dramatically protected Fah−/− mice against fumarylacetoacetate (Faa)‐induced toxicity. Our data establish a central role for Nrf2 in the protection against Faa‐induced liver injury; the Nrf2 regulated cellular defense not only prevents acute Faa‐induced liver failure but also delays hepatocarcinogenesis in HT1. (HEPATOLOGY 2008;48:487–496.)

Hepatocyte-specific S100a8 and S100a9 transgene expression in mice causes Cxcl1 induction and systemic neutrophil enrichment

BackgroundCalprotectin consists of the Ca2+-binding proteins S100a8 and S100a9 that are induced in epithelial cells in response to tissue damage and infection. Both proteins are also secreted by activated innate immune cells and numerous studies demonstrate their crucial role in pathological conditions of acute and chronic inflammation.ResultsHere, we established a conditional mouse model with simultaneous S100a8 and S100a9 transgene expression in hepatocytes (TgS100a8a9hep) under the control of doxycycline to unravel the role of epithelial-derived Calprotectin on tissue homeostasis and inflammation. TgS100a8a9hep mice displayed a significant enrichment of neutrophils in peripheral blood and tissues with high blood content. Interestingly, Cxcl1 transcription was significantly induced in the liver of TgS100a8a9hep mice and primary hepatocytes derived thereof as compared to Control mice, accompanied by an increase of Cxcl1 serum levels. However, expression of other chemokines with a known function in neutrophil mobilization from the bone marrow, e.g. Csf3 and Cxcl2, was not altered. Doxycycline treatment of TgS100a8a9hep mice reduced Cxcl1 expression in the liver and resulted in normal numbers of neutrophils.ConclusionIn summary, our data demonstrate for the first time that hepatocyte-specific S100a8 and S100a9 expression induces a systemic mobilization of neutrophils by a specific activation of Cxcl1 transcription in the liver.

Smad7 regulates compensatory hepatocyte proliferation in damaged mouse liver and positively relates to better clinical outcome in human hepatocellular carcinoma.

Transforming growth factor β (TGF-β) is cytostatic towards damage-induced compensatory hepatocyte proliferation. This function is frequently lost during hepatocarcinogenesis, thereby switching the TGF-β role from tumour suppressor to tumour promoter. In the present study, we investigate Smad7 overexpression as a pathophysiological mechanism for cytostatic TGF-β inhibition in liver damage and hepatocellular carcinoma (HCC). Transgenic hepatocyte-specific Smad7 overexpression in damaged liver of fumarylacetoacetate hydrolase (FAH)-deficient mice increased compensatory proliferation of hepatocytes. Similarly, modulation of Smad7 expression changed the sensitivity of Huh7, FLC-4, HLE and HLF HCC cell lines for cytostatic TGF-β effects. In our cohort of 140 HCC patients, Smad7 transcripts were elevated in 41.4% of HCC samples as compared with adjacent tissue, with significant positive correlation to tumour size, whereas low Smad7 expression levels were significantly associated with worse clinical outcome. Univariate and multivariate analyses indicate Smad7 levels as an independent predictor for overall (P<0.001) and disease-free survival (P=0.0123). Delineating a mechanism for Smad7 transcriptional regulation in HCC, we identified cold-shock Y-box protein-1 (YB-1), a multifunctional transcription factor. YB-1 RNAi reduced TGF-β-induced and endogenous Smad7 expression in Huh7 and FLC-4 cells respectively. YB-1 and Smad7 mRNA expression levels correlated positively (P<0.0001). Furthermore, nuclear co-localization of Smad7 and YB-1 proteins was present in cancer cells of those patients. In summary, the present study provides a YB-1/Smad7-mediated mechanism that interferes with anti-proliferative/tumour-suppressive TGF-β actions in a subgroup of HCC cells that may facilitate aspects of tumour progression.

Chronic liver inflammation and hepatocellular carcinogenesis are independent of S100A9

The S100A8/A9 heterodimer (calprotectin) acts as a danger signal when secreted into the extracellular space during inflammation and tissue damage. It promotes proinflammatory responses and drives tumor development in different models of inflammation‐driven carcinogenesis. S100A8/A9 is strongly expressed in several human tumors, including hepatocellular carcinoma (HCC). Apart from this evidence, the role of calprotectin in hepatocyte transformation and tumor microenvironment is still unknown. The aim of this study was to define the function of S100A8/A9 in inflammation‐driven HCC. Mice lacking S100a9 were crossed with the Mdr2−/− model, a prototype of inflammation‐induced HCC formation. S100a9−/− Mdr2−/− (dKO) mice displayed no significant differences in tumor incidence or multiplicity compared to Mdr2−/− animals. Chronic liver inflammation, fibrosis and oval cell activation were not affected upon S100a9 deletion. Our data demonstrate that, although highly upregulated, calprotectin is dispensable in the onset and development of HCC, and in the maintenance of liver inflammation.