Trim21 deficiency in mice increases HCC carcinogenesis in a NASH context and is associated with immune checkpoint upregulation.

The global pandemic of metabolic diseases has increased the incidence of hepatocellular carcinoma (HCC) in the context of non-alcoholic steatohepatitis (NASH). The downregulation of the E3 ubiquitin ligase TRIM21 has been linked to poor prognosis in different cancers including HCC. In order to investigate the role of TRIM21 in liver cancer progression on NASH, Trim21+/+ and Trim21-/- male mice were injected with streptozotocin at the neonatal stage. The hypoinsulinemic mice were then fed with a high-fat high-cholesterol diet (HFHCD) for 4, 8 or 12 weeks. All mice developed NASH which systematically resulted in HCC progression. Interestingly, compared to the Trim21+/+ control mice, liver damage was worsened in Trim21-/- mice, with more HCC nodules found after 12 weeks on HFHCD. Immune population analysis in the spleen and liver revealed a higher proportion of CD4+PD-1+ and CD8+PD-1+ T cells in Trim21-/- mice. The liver and HCC tumors of Trim21-/- mice also exhibited an increase in the number of PD-L1+ and CD68+ PD-L1+ cells. Thus, TRIM21 limits the emergence of HCC nodules in mice with NASH by potentially restricting the expression of PD-1 in lymphocytes and PD-L1 in tumors.

Correction: The Naturally Processed CD95L Elicits a c-Yes/Calcium/PI3K-Driven Cell Migration Pathway.

[This corrects the article DOI: 10.1371/journal.pbio.1001090.].

RIPK1 in Liver Parenchymal Cells Limits Murine Hepatitis during Acute CCl4-Induced Liver Injury.

Some life-threatening acute hepatitis originates from drug-induced liver injury (DILI). Carbon tetrachloride (CCl4)-induced acute liver injury in mice is the widely used model of choice to study acute DILI, which pathogenesis involves a complex interplay of oxidative stress, necrosis, and apoptosis. Since the receptor interacting protein kinase-1 (RIPK1) is able to direct cell fate towards survival or death, it may potentially affect the pathological process of xenobiotic-induced liver damage. Two different mouse lines, either deficient for Ripk1 specifically in liver parenchymal cells (Ripk1LPC-KO) or for the kinase activity of RIPK1 (Ripk1K45A, kinase dead), plus their respective wild-type littermates (Ripk1fl/fl, Ripk1wt/wt), were exposed to single toxic doses of CCl4. This exposure led in similar injury in Ripk1K45A mice and their littermate controls. However, Ripk1LPC-KO mice developed more severe symptoms with massive hepatocyte apoptosis as compared to their littermate controls. A pretreatment with a TNF-α receptor decoy exacerbated liver apoptosis in both Ripk1fl/fl and Ripk1LPC-KO mice. Besides, a FasL antagonist promoted hepatocyte apoptosis in Ripk1fl/fl mice but reduced it in Ripk1LPC-KO mice. Thus, the scaffolding properties of RIPK1 protect hepatocytes from apoptosis during CCl4 intoxication. TNF-α and FasL emerged as factors promoting hepatocyte survival. These protective effects appeared to be independent of RIPK1, at least in part, for TNF-α, but dependent on RIPK1 for FasL. These new data complete the deciphering of the molecular mechanisms involved in DILI in the context of research on their prevention or cure.

RIPK1 protects hepatocytes from Kupffer cells-mediated TNF-induced apoptosis in mouse models of PAMP-induced hepatitis.

BACKGROUND & AIMS: The severity of liver diseases is exacerbated by the death of hepatocytes, which can be induced by the sensing of pathogen associated molecular patterns (PAMPs) derived from the gut microbiota. The molecular mechanisms regulating these cell death pathways are poorly documented. In this study, we investigated the role of the receptor interacting protein kinase 1 (RIPK1), a protein known to regulate cell fate decisions, in the death of hepatocytes using two in vivo models of PAMP-induced hepatitis. METHODS: Hepatitis was induced in mice by independent injections of two different bacterial PAMPs: lipopolysaccharide (LPS) and unmethylated CpG oligodeoxynucleotide (CpG-DNA) motifs. The role of RIPK1 was evaluated by using mice specifically lacking RIPK1 in liver parenchymal cells (Ripk1LPC-KO). Administration of liposome-encapsulated clodronate served to investigate the role of Kupffer cells in the establishment of the disease. Etanercept, a tumor necrosis factor (TNF)-decoy receptor, was used to study the contribution of TNF-α during LPS-mediated liver injury. RESULTS: Whereas RIPK1 deficiency in liver parenchymal cells did not trigger basal hepatolysis, it greatly sensitized hepatocytes to apoptosis and liver damage following a single injection of LPS or CpG-DNA. Importantly, hepatocyte death was prevented by previous macrophage depletion or by TNF inhibition. CONCLUSIONS: Our data highlight the pivotal function of RIPK1 in maintaining liver homeostasis in conditions of macrophage-induced TNF burst in response to PAMPs sensing. LAY SUMMARY: Excessive death of hepatocytes is a characteristic of liver injury. A new programmed cell death pathway has been described involving upstream death ligands such as TNF and downstream kinases such as RIPK1. Here, we show that in the presence of LPS liver induced hepatic injury was due to secretion of TNF by liver macrophages, and that RIPK1 acts as a powerful protector of hepatocyte death. This newly identified pathway in the liver may be helpful in the management of patients to predict their risk of developing acute liver failure.

Endogenous IL-33 Deficiency Exacerbates Liver Injury and Increases Hepatic Influx of Neutrophils in Acute Murine Viral Hepatitis.

The alarmin IL-33 has been described to be upregulated in human and murine viral hepatitis. However, the role of endogenous IL-33 in viral hepatitis remains obscure. We aimed to decipher its function by infecting IL-33-deficient mice (IL-33 KO) and their wild-type (WT) littermates with pathogenic mouse hepatitis virus (L2-MHV3). The IL-33 KO mice were more sensitive to L2-MHV3 infection exhibiting higher levels of AST/ALT, higher tissue damage, significant weight loss, and earlier death. An increased depletion of B and T lymphocytes, NKT cells, dendritic cells, and macrophages was observed 48 h postinfection (PI) in IL-33 KO mice than that in WT mice. In contrast, a massive influx of neutrophils was observed in IL-33 KO mice at 48 h PI. A transcriptomic study of inflammatory and cell-signaling genes revealed the overexpression of IL-6, TNFα, and several chemokines involved in recruitment/activation of neutrophils (CXCL2, CXCL5, CCL2, and CCL6) at 72 h PI in IL-33 KO mice. However, the IFNγ was strongly induced in WT mice with less profound expression in IL-33 KO mice demonstrating that endogenous IL-33 regulated IFNγ expression during L2-MHV3 hepatitis. In conclusion, we demonstrated that endogenous IL-33 had multifaceted immunoregulatory effect during viral hepatitis via induction of IFNγ, survival effect on immune cells, and infiltration of neutrophils in the liver.

Human hepatic stellate cells are not permissive for hepatitis C virus entry and replication.

BACKGROUND: Chronic HCV infection is associated with the development of hepatic fibrosis. The direct role of HCV in the fibrogenic process is unknown. Specifically, whether HCV is able to infect hepatic stellate cells (HSCs) is debated. OBJECTIVE: To assess whether human HSCs are susceptible to HCV infection. DESIGN: We combined a set of original HCV models, including the infectious genotype 2a JFH1 model (HCVcc), retroviral pseudoparticles expressing the folded HCV genotype 1b envelope glycoproteins (HCVpp) and a subgenomic genotype 1b HCV replicon, and two relevant cellular models, primary human HSCs from different patients and the LX-2 cell line, to assess whether HCV can infect/replicate in HSCs. RESULTS: In contrast with the hepatocyte cell line Huh-7, neither infectious HCVcc nor HCVpp infected primary human HSCs or LX-2 cells. The cellular expression of host cellular factors required for HCV entry was high in Huh-7 cells but low in HSCs and LX-2 cells, with the exception of CD81. Finally, replication of a genotype 2a full-length RNA genome and a genotype 1b subgenomic replicon was impaired in primary human HSCs and LX-2 cells, which expressed low levels of cellular factors known to play a key role in the HCV life-cycle, suggesting that human HSCs are not permissive for HCV replication. CONCLUSIONS: Human HSCs are refractory to HCV infection. Both HCV entry and replication are deficient in these cells, regardless of the HCV genotype and origin of the cells. Thus, HCV infection of HSCs does not play a role in liver fibrosis. These results do not rule out a direct role of HCV infection of hepatocytes in the fibrogenic process.

Oncostatin M induces IL-33 expression in liver endothelial cells in mice and expands ST2+CD4+ lymphocytes.

Interleukin (IL)-33 is crucially involved in liver pathology and drives hepatoprotective functions. However, the regulation of IL-33 by cytokines of the IL-6 family, including oncostatin M (OSM) and IL-6, is not well studied. The aim of the present study was to determine whether OSM mediates regulation of IL-33 expression in liver cells. Intramuscular administration in mice of an adenovirus encoding OSM (AdOSM) leads to increase in expression of OSM in muscles, liver, and serum of AdOSM-infected mice compared with control mice. The increase of circulating OSM markedly regulated mRNA of genes associated with blood vessel biology, chemotaxis, cellular death, induction of cell adhesion molecules, and the alarmin cytokine IL-33 in liver. Steady-state IL-33 mRNA was upregulated by OSM at an early phase (8 h) following AdOSM infection. At the protein level, the expression of IL-33 was significantly induced in liver endothelial cells [liver sinusoidal endothelial cells (LSEC) and vascular endothelial cells] with a peak at 8 days post-AdOSM infection in mice. In addition, we found OSM-stimulated human microvascular endothelial HMEC-1 cells and human LSEC/TRP3 cells showed a significant increase in expression of IL-33 mRNA in a dose-dependent manner in cell culture. The OSM-mediated overexpression of IL-33 was associated with the activation/enrichment of CD4(+)ST2(+) cells in liver of AdOSM-infected mice compared with adenovirus encoding green fluorescent protein-treated control mice. In summary, these data suggest that the cytokine OSM regulates the IL-33 expression in liver endothelial cells in vivo and in HMEC-1/TRP3 cells in vitro and may specifically expand the target CD4(+)ST2(+) cells in liver.

Overexpression of phosphatidylinositol 4-kinase type IIIα is associated with undifferentiated status and poor prognosis of human hepatocellular carcinoma.

BACKGROUND: Hepatocellular carcinoma (HCC) is a particularly severe disease characterized by a high rate of recurrence and death even after surgical resection. Molecular characterization of HCC helps refine prognosis and may facilitate the development of improved therapy. Phosphatidylinositol 4-kinases have recently been identified as cellular factors associated with cancer. Also, phosphatidylinositol 4-kinase type IIIα (PI4KA) is necessary for the propagation of the hepatitis C virus, a major etiological factor for HCC. METHODS: Reverse transcription, quantitative real-time PCR was used to assay PI4KA mRNA. The expression levels were investigated both in a collection of molecularly and clinically characterized hepatic tissues from 344 patients with diverse liver diseases and in human hepatocyte cell lines whose proliferative and differentiation status was controlled by specific culture conditions. Analytical microarray data for 60 HCC and six normal liver tissue samples were exploited to study correlations between PI4KA mRNA levels and cell proliferation markers in vivo. Postoperative disease-specific survival and time to recurrence in a set of 214 patients with HCC were studied by univariate and multivariate analyses. RESULTS: PI4KA mRNA was more abundant in HCC than normal healthy tissues. This upregulation correlated significantly with both poor differentiation and the active proliferation rate in HCC. These associations were confirmed with in vitro models. Moreover, patients with HCC who had been treated by surgical resection and had higher PI4KA mRNA concentrations in their tumor tissue exhibited a higher risk of tumor recurrence (median time: 20 months versus 49 months, P = 0.0012) and shorter disease-specific survival (first quartile time: 16 months versus 48 months, P = 0.0004). Finally, the abundance of PI4KA mRNA proved to be an independent prognostic marker of survival for cases of HCC (hazard ratio = 2.36, P = 0.0064). CONCLUSIONS: PI4KA mRNA could be used as a new molecular marker to improve established prognostic models for HCC. These findings also indicate possible new lines of research for the development of innovative therapeutic approaches targeting PI4KA.

The naturally processed CD95L elicits a c-yes/calcium/PI3K-driven cell migration pathway.

Patients affected by chronic inflammatory disorders display high amounts of soluble CD95L. This homotrimeric ligand arises from the cleavage by metalloproteases of its membrane-bound counterpart, a strong apoptotic inducer. In contrast, the naturally processed CD95L is viewed as an apoptotic antagonist competing with its membrane counterpart for binding to CD95. Recent reports pinpointed that activation of CD95 may attract myeloid and tumoral cells, which display resistance to the CD95-mediated apoptotic signal. However, all these studies were performed using chimeric CD95Ls (oligomerized forms), which behave as the membrane-bound ligand and not as the naturally processed CD95L. Herein, we examine the biological effects of the metalloprotease-cleaved CD95L on CD95-sensitive activated T-lymphocytes. We demonstrate that cleaved CD95L (cl-CD95L), found increased in sera of systemic lupus erythematosus (SLE) patients as compared to that of healthy individuals, promotes the formation of migrating pseudopods at the leading edge of which the death receptor CD95 is capped (confocal microscopy). Using different migration assays (wound healing/Boyden Chamber/endothelial transmigration), we uncover that cl-CD95L promotes cell migration through a c-yes/Ca²âº/PI3K-driven signaling pathway, which relies on the formation of a CD95-containing complex designated the MISC for Motility-Inducing Signaling Complex. These findings revisit the role of the metalloprotease-cleaved CD95L and emphasize that the increase in cl-CD95L observed in patients affected by chronic inflammatory disorders may fuel the local or systemic tissue damage by promoting tissue-filtration of immune cells.

The complexity of ERK1 and ERK2 MAPKs in multiple hepatocyte fate responses.

Recent reports suggest that extracellular signal-regulated kinase (ERK1) and ERK2 mitogen-activated protein kinases (MAPK) may direct specific biological functions under certain contexts. In this study, we investigated the role of early and sustained epidermal growth factor (EGF) stimulation on long-term hepatocyte differentiation and the possible role of ERK1 and ERK2 in this process. We demonstrate a long-term survival and an elevated level of differentiation up to 3 weeks. The differentiation state of hepatocytes is supported by sustained expression of aldolase B, albumin, and the detoxifying enzymes CYP1A2, 2B2, and 3A23. Similarly to freshly isolated cells, cultured hepatocytes also retain the ability to respond to 3-methylcholanthrene (3MC) and phenobarbital (PB), two known CYP inducers. In addition, we show evidence that continuous MAPK/ERK kinase (MEK) inhibition enhances the level of differentiation. Using RNA interference approaches against ERK1 and ERK2, we demonstrate that this effect requires both ERK1 and ERK2 activity, whereas the specific ERK1 knockdown promotes cell survival and the specific ERK2 knockdown regulates cell proliferation. In conclusion, we demonstrate that early and sustained EGF stimulation greatly extends long-term hepatocyte survival and differentiation, and that inhibition of the ERK1/2 MAPK pathway potentiates these pro-survival/pro-differentiation phenotypes. We clearly attest that specific ERK1 and ERK2 MAPKs determine hepatocyte survival and proliferation, respectively, whereas dual inhibition is required to stabilize a highly differentiated state.

Switching to Regular Diet Partially Resolves Liver Fibrosis Induced by High-Fat, High-Cholesterol Diet in Mice.

The globally prevalent disease, non-alcoholic steatohepatitis (NASH), is characterized by a steatotic and inflammatory liver. In NASH patients, tissue repair mechanisms, activated by the presence of chronic liver damage, lead to the progressive onset of hepatic fibrosis. This scar symptom is a key prognostic risk factor for liver-related morbidity and mortality. Conflicting reports discuss the efficiency of dietary interventions on the reversibility of advanced fibrosis established during NASH. In the present study, the effect of dietary interventions was investigated in the outcome of the fibrosis settled in livers of C57BL/6J mice on a high-fat, high-cholesterol diet (HFHCD) for 5 or 12 consecutive weeks. Various clinico-pathological investigations, including a histological analysis of the liver, measurement of plasma transaminases, steatosis and fibrosis, were performed. To assess the effectiveness of the dietary intervention on established symptoms, diseased mice were returned to a standard diet (SD) for 4 or 12 weeks. This food management resulted in a drastic reduction in steatosis, liver injuries, inflammatory markers, hepatomegaly and oxidative stress and a gradual improvement in the fibrotic state of the liver tissue. In conclusion, our results demonstrated that dietary intervention can partially reverse liver fibrosis induced by HFHCD feeding.

Receptor-interacting protein kinase-1 ablation in liver parenchymal cells promotes liver fibrosis in murine NASH without affecting other symptoms.

Non-alcoholic steatohepatitis (NASH), a chronic liver disease that emerged in industrialized countries, can further progress into liver fibrosis, cirrhosis, and hepatocellular carcinoma. In the next decade, NASH is predicted to become the leading cause of liver transplantation, the only current interventional therapeutic option. Hepatocyte death, triggered by different death ligands, plays key role in its progression. Previously, we showed that the receptor-interacting protein kinase-1 (RIPK1) in hepatocytes exhibits a protective role in ligand-induced death. Now, to decipher the role of RIPK1 in NASH, Ripk1LPC-KO mice, deficient for RIPK1 only in liver parenchymal cells, and their wild-type littermates (Ripk1fl/fl) were fed for 3, 5, or 12 weeks with high-fat high-cholesterol diet (HFHCD). The main clinical signs of NASH were analyzed to compare the pathophysiological state established in mice. Most of the symptoms evolved similarly whatever the genotype, whether it was the increase in liver to body weight ratio, the steatosis grade or the worsening of liver damage revealed by serum transaminase levels. In parallel, inflammation markers followed the same kinetics with significant equivalent inductions of cytokines (hepatic mRNA levels and blood cytokine concentrations) and a main peak of hepatic infiltration of immune cells at 3 weeks of HFHCD. Despite this identical inflammatory response, more hepatic fibrosis was significantly evidenced at week 12 in Ripk1LPC-KO mice. This coincided with over-induced rates of transcripts of genes implied in fibrosis development (Tgfb1, Tgfbi, Timp1, and Timp2) in Ripk1LPC-KO animals. In conclusion, our results show that RIPK1 in hepatocyte limits the progression of liver fibrosis during NASH.

TRIM21, a New Component of the TRAIL-Induced Endogenous Necrosome Complex.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a well-known apoptosis inducer and a potential anticancer agent. When caspases and inhibitors of apoptosis proteins (IAPs) are inhibited, TRAIL induces necroptosis. Molecular mechanisms of necroptosis rely on kinase activation, and on the formation of a necrosome complex, bringing together the receptor-interacting protein kinases 1 and 3 (RIPK1, RIPK3), and the mixed lineage kinase domain-like protein (MLKL). In this study, mass spectrometry approach allowed to identify the tripartite motif containing 21 (TRIM21), an E3 ubiquitin-protein ligase as a new partner of the endogenous TRAIL-induced necrosome. Alteration of TRIM21 expression level, obtained by transient transfection of HT29 or HaCat cells with TRIM21-targeted siRNAs or cDNA plasmids coding for TRIM21 demonstrated that TRIM21 is a positive regulator of TRAIL-induced necroptosis. Furthermore, the invalidation of TRIM21 expression in HT29 cells by CRISPR-Cas9 technology also decreased cell sensitivity to TRAIL-induced necroptosis, a shortcoming associated with a reduction in MLKL phosphorylation, the necroptosis executioner. Thus, TRIM21 emerged as a new partner of the TRAIL-induced necrosome that positively regulates the necroptosis process.

The first transmembrane domain of the hepatitis B virus large envelope protein is crucial for infectivity.

The early steps of the hepatitis B virus (HBV) life cycle are still poorly understood. Indeed, neither the virus receptor at the cell surface nor the mechanism by which nucleocapsids are delivered to the cytosol of infected cells has been identified. Extensive mutagenesis studies in pre-S1, pre-S2, and most of the S domain of envelope proteins revealed the presence of two regions essential for HBV infectivity: the 77 first residues of the pre-S1 domain and a conformational motif in the antigenic loop of the S domain. In addition, at the N-terminal extremity of the S domain, a putative fusion peptide, partially overlapping the first transmembrane (TM1) domain and preceded by a PEST sequence likely containing several proteolytic cleavage sites, was identified. Since no mutational analysis of these two motifs potentially implicated in the fusion process was performed, we decided to investigate the ability of viruses bearing contiguous deletions or substitutions in the putative fusion peptide and PEST sequence to infect HepaRG cells. By introducing the mutations either in the L and M proteins or in the S protein, we demonstrated the following: (i) that in the TM1 domain of the L protein, three hydrophobic clusters of four residues were necessary for infectivity; (ii) that the same clusters were critical for S protein expression; and, finally, (iii) that the PEST sequence was dispensable for both assembly and infection processes.

Multiple division cycles and long-term survival of hepatocytes are distinctly regulated by extracellular signal-regulated kinases ERK1 and ERK2.

UNLABELLED: We investigated the specific role of the mitogen-activated protein kinase (MAPK) extracellular signal-regulated kinase 1 (ERK1)/ERK2 pathway in the regulation of multiple cell cycles and long-term survival of normal hepatocytes. An early and sustained epidermal growth factor (EGF)-dependent MAPK activation greatly improved the potential of cell proliferation. In this condition, almost 100% of the hepatocytes proliferated, and targeting ERK1 or ERK2 via RNA interference revealed the specific involvement of ERK2 in this regulation. However, once their first cell cycle was performed, hepatocytes failed to undergo a second round of replication and stayed blocked in G1 phase. We demonstrated that sustained EGF-dependent activation of the MAPK/ERK kinase (MEK)/ERK pathway was involved in this blockage as specific transient inhibition of the cascade repotentiated hepatocytes to perform a new wave of replication and multiple cell cycles. We identified this mechanism by showing that this blockage was in part supported by ERK2-dependent p21 expression. Moreover, continuous MEK inhibition was associated with a lower apoptotic engagement, leading to an improvement of survival up to 3 weeks. Using RNA interference and ERK1 knockout mice, we extended these results by showing that this improved survival was due to the specific inhibition of ERK1 expression/phosphorylation and did not involve ERK2. CONCLUSION: Our results emphasize that transient MAPK inhibition allows multiple cell cycles in primary cultures of hepatocytes and that ERK2 has a key role in the regulation of S phase entry. Moreover, we revealed a major and distinct role of ERK1 in the regulation of hepatocyte survival. Taken together, our results represent an important advance in understanding long-term survival and cell cycle regulation of hepatocytes.

Kinases required in hepatitis C virus entry and replication highlighted by small interference RNA screening.

The entry pathway of the hepatitis C virus (HCV), a major human pathogen, into the cell is incompletely defined. To better characterize this viral life cycle stage, we screened a small interfering RNA library dedicated to the membrane trafficking and remodeling with the infection model of Huh-7.5.1 cells by HCV pseudoparticles (HCVpp). Results showed that the down-regulation of different factors implied in clathrin-mediated endocytosis (CME) inhibits HCVpp cell infection. In addition, knockdown of the phosphatidylinositol 4-kinase type III-alpha (PI4KIIIalpha) prevented infection by HCVpp or by cell-culture grown JFH-1-based HCV. Moreover, the replication activity of an HCV replicon was also affected by the PI4KIIIalpha knockdown. Additional investigations on the different members of the PI4K family revealed that the presence of PI4KIIIbeta in the host cells influenced their susceptibility to HCVpp infection and their capacity to sustain the HCV replication. The PI4KIII involvement during the HCV life cycle seemed to occur by other ways than the control of the CME or of the membranous expression of HCV receptors. Finally, our library screening completed data on the CME-dependant entry route of HCV and identified 2 kinases, PI4KIIIalpha and beta, as relevant potential therapeutic targets.

Hepatocellular Carcinoma Emergence in Diabetic Mice with Non-Alcoholic Steatohepatitis Depends on Diet and Is Delayed in Liver Exhibiting an Active Immune Response.

The increase of the sedentary lifestyle and high-calorie diet have modified the etiological landscape of hepatocellular carcinoma (HCC), with a recrudescence of non-alcoholic fatty liver disease (NAFLD), especially in Western countries. The purpose of our study was to evaluate the impact of high-fat diet feeding on non-alcoholic steatohepatitis (NASH) establishment and HCC development. Streptozotocin-induced diabetic male mice were fed with high-fat-high-cholesterol diet (HFHCD) or high-fat-high-sugar diet (HFHSD) from 1 to 16 weeks. Even if liver tumors appear regardless of the high-fat diet, two distinct physiopathological patterns were evidenced, with much more severe NASH hallmarks (liver injury, inflammation and fibrosis) in diabetic mice fed with HFHCD. The mild hepatic injury, weak inflammation and fibrosis observed in HFHSD were interestingly associated with earlier emergence of more numerous liver tumors. When activated helper and cytotoxic T cells, detected by flow cytometry, infiltrated the liver of HFHCD-fed diabetic mice, a delay in the appearance of tumor nodules and a limitation of their numbers were observed, suggesting that the immune activities partly controlled tumor emergence. These data highlighted two different mouse models of HCC progression in diabetic mice depending on diet, which could be useful to evaluate new therapeutic approaches for HCC by targeting the immune response.

Antiviral effect of ribonuclease conjugated oligodeoxynucleotides targeting the IRES RNA of the hepatitis C virus.

Hepatitis C virus (HCV) translation initiation is mediated by a highly structured and conserved RNA, termed the Internal Ribosome Entry Site (IRES), located at the 5'-end of its single stranded RNA genome. It is a key target for the development of new antiviral compounds. Here we made use of the recently developed HCV cell culture system to test the antiviral activity of artificial ribonucleases consisting of imidazole(s) linked to antisense oligodeoxynucleotides targeting the HCV IRES. Results from the cell culture model indicate that the naked antisense oligodeoxynucleotide displayed an efficient antiviral activity. Despite the increased activity observed with the addition of imidazole moieties when tested with the cell-free system, it appears that these improvements were not reproduced in the cellular model.

Depletion of RIPK1 in hepatocytes exacerbates liver damage in fulminant viral hepatitis.

The protein kinase RIPK1 plays a crucial role at the crossroad of stress-induced signaling pathways that affects cell's decision to live or die. The present study aimed to define the role of RIPK1 in hepatocytes during fulminant viral hepatitis, a worldwide syndrome mainly observed in hepatitis B virus (HBV) infected patients. Mice deficient for RIPK1, specifically in liver parenchymal cells (Ripk1LPC-KO) and their wild-type littermates (Ripk1fl/fl), were challenged by either the murine hepatitis virus type 3 (MHV3) or poly I:C, a synthetic analog of double-stranded RNA mimicking viral pathogen-associated molecular pattern. Ripk1LPC-KO mice developed more severe symptoms at early stage of the MHV3-induced fulminant hepatitis. Similarly, administration of poly I:C only triggered increase of systemic transaminases in Ripk1LPC-KO mice, reflecting liver damage through induced apoptosis as illustrated by cleaved-caspase 3 labeling of liver tissue sections. Neutralization of TNF-α or prior depletion of macrophages were able to prevent the appearance of apoptosis of hepatocytes in poly I:C-challenged Ripk1LPC-KO mice. Moreover, poly I:C never induced direct hepatocyte death in primary culture whatever the murine genotype, while it always stimulated an anti-viral response. Our investigations demonstrated that RIPK1 protects hepatocytes from TNF-α secreted from macrophages during viral induced fulminant hepatitis. These data emphasize the potential worsening risks of an HBV infection in people with polymorphism or homozygous amorphic mutations already described for the RIPK1 gene.