EDI3 knockdown in ER-HER2+ breast cancer cells reduces tumor burden and improves survival in two mouse models of experimental metastasis.

BACKGROUND: Despite progress understanding the mechanisms underlying tumor spread, metastasis remains a clinical challenge. We identified the choline-producing glycerophosphodiesterase, EDI3 and reported its association with metastasis-free survival in endometrial cancer. We also observed that silencing EDI3 slowed cell migration and other cancer-relevant phenotypes in vitro. Recent work demonstrated high EDI3 expression in ER-HER2+ breast cancer compared to the other molecular subtypes. Silencing EDI3 in ER-HER2+ cells significantly reduced cell survival in vitro and decreased tumor growth in vivo. However, a role for EDI3 in tumor metastasis in this breast cancer subtype was not explored. Therefore, in the present work we investigate whether silencing EDI3 in ER-HER2+ breast cancer cell lines alters phenotypes linked to metastasis in vitro, and metastasis formation in vivo using mouse models of experimental metastasis. METHODS: To inducibly silence EDI3, luciferase-expressing HCC1954 cells were transduced with lentiviral particles containing shRNA oligos targeting EDI3 under the control of doxycycline. The effect on cell migration, adhesion, colony formation and anoikis was determined in vitro, and significant findings were confirmed in a second ER-HER2+ cell line, SUM190PT. Doxycycline-induced HCC1954-luc shEDI3 cells were injected into the tail vein or peritoneum of immunodeficient mice to generate lung and peritoneal metastases, respectively and monitored using non-invasive bioluminescence imaging. Metabolite levels in cells and tumor tissue were analyzed using targeted mass spectrometry and MALDI mass spectrometry imaging (MALDI-MSI), respectively. RESULTS: Inducibly silencing EDI3 reduced cell adhesion and colony formation, as well as increased susceptibility to anoikis in HCC1954-luc cells, which was confirmed in SUM190PT cells. No influence on cell migration was observed. Reduced luminescence was seen in lungs and peritoneum of mice injected with cells expressing less EDI3 after tail vein and intraperitoneal injection, respectively, indicative of reduced metastasis. Importantly, mice injected with EDI3-silenced cells survived longer. Closer analysis of the peritoneal organs revealed that silencing EDI3 had no effect on metastatic organotropism but instead reduced metastatic burden. Finally, metabolic analyses revealed significant changes in choline and glycerophospholipid metabolites in cells and in pancreatic metastases in vivo. CONCLUSIONS: Reduced metastasis upon silencing supports EDI3's potential as a treatment target in metastasizing ER-HER2+ breast cancer.

Acetaminophen overdose causes a breach of the blood-bile barrier in mice but not in rats.

Acetaminophen (APAP) is known to cause a breach of the blood-bile barrier in mice that, via a mechanism called futile bile acid (BA) cycling, increases BA concentrations in hepatocytes above cytotoxic thresholds. Here, we compared this mechanism in mice and rats, because both species differ massively in their susceptibility to APAP and compared the results to available human data. Dose and time-dependent APAP experiments were performed in male C57BL6/N mice and Wistar rats. The time course of BA concentrations in liver tissue and in blood was analyzed by MALDI-MSI and LC-MS/MS. APAP and its derivatives were measured in the blood by LC-MS. APAP-induced liver damage was analyzed by histopathology, immunohistochemistry, and by clinical chemistry. In mice, a transient increase of BA in blood and in peri-central hepatocytes preceded hepatocyte death. The BA increase coincided with oxidative stress in liver tissue and a compromised morphology of bile canaliculi and immunohistochemically visualized tight junction proteins. Rats showed a reduced metabolic activation of APAP compared to mice. However, even at very high doses that caused cell death of hepatocytes, no increase of BA concentrations was observed neither in liver tissue nor in the blood. Correspondingly, no oxidative stress was detectable, and the morphology of bile canaliculi and tight junction proteins remained unaltered. In conclusion, different mechanisms cause cell death in rats and mice, whereby oxidative stress and a breach of the blood-bile barrier are seen only in mice. Since transient cholestasis also occurs in human patients with APAP overdose, mice are a clinically relevant species to study APAP hepatotoxicity but not rats.

Inhibition of the renal apical sodium dependent bile acid transporter prevents cholemic nephropathy in mice with obstructive cholestasis.

BACKGROUND & AIMS: Cholemic nephropathy (CN) is a severe complication of cholestatic liver diseases for which there is no specific treatment. We revisited its pathophysiology with the aim of identifying novel therapeutic strategies. METHODS: Cholestasis was induced by bile duct ligation (BDL) in mice. Bile flux in kidneys and livers was visualized by intravital imaging, supported by MALDI mass spectrometry imaging and liquid chromatography-tandem mass spectrometry. The effect of AS0369, a systemically bioavailable apical sodium-dependent bile acid transporter (ASBT) inhibitor, was evaluated by intravital imaging, RNA-sequencing, histological, blood, and urine analyses. Translational relevance was assessed in kidney biopsies from patients with CN, mice with a humanized bile acid (BA) spectrum, and via analysis of serum BAs and KIM-1 (kidney injury molecule 1) in patients with liver disease and hyperbilirubinemia. RESULTS: Proximal tubular epithelial cells (TECs) reabsorbed and enriched BAs, leading to oxidative stress and death of proximal TECs, casts in distal tubules and collecting ducts, peritubular capillary leakiness, and glomerular cysts. Renal ASBT inhibition by AS0369 blocked BA uptake into TECs and prevented kidney injury up to 6 weeks after BDL. Similar results were obtained in mice with humanized BA composition. In patients with advanced liver disease, serum BAs were the main determinant of KIM-1 levels. ASBT expression in TECs was preserved in biopsies from patients with CN, further highlighting the translational potential of targeting ASBT to treat CN. CONCLUSIONS: BA enrichment in proximal TECs followed by oxidative stress and cell death is a key early event in CN. Inhibiting renal ASBT and consequently BA enrichment in TECs prevents CN and systemically decreases BA concentrations. IMPACT AND IMPLICATIONS: Cholemic nephropathy (CN) is a severe complication of cholestasis and an unmet clinical need. We demonstrate that CN is triggered by the renal accumulation of bile acids (BAs) that are considerably increased in the systemic blood. Specifically, the proximal tubular epithelial cells of the kidney take up BAs via the apical sodium-dependent bile acid transporter (ASBT). We developed a therapeutic compound that blocks ASBT in the kidneys, prevents BA overload in tubular epithelial cells, and almost completely abolished all disease hallmarks in a CN mouse model. Renal ASBT inhibition represents a potential therapeutic strategy for patients with CN.

Colitis ameliorates cholestatic liver disease via suppression of bile acid synthesis.

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease characterized by chronic inflammation and progressive fibrosis of the biliary tree. The majority of PSC patients suffer from concomitant inflammatory bowel disease (IBD), which has been suggested to promote disease development and progression. However, the molecular mechanisms by which intestinal inflammation may aggravate cholestatic liver disease remain incompletely understood. Here, we employ an IBD-PSC mouse model to investigate the impact of colitis on bile acid metabolism and cholestatic liver injury. Unexpectedly, intestinal inflammation and barrier impairment improve acute cholestatic liver injury and result in reduced liver fibrosis in a chronic colitis model. This phenotype is independent of colitis-induced alterations of microbial bile acid metabolism but mediated via hepatocellular NF-κB activation by lipopolysaccharide (LPS), which suppresses bile acid metabolism in-vitro and in-vivo. This study identifies a colitis-triggered protective circuit suppressing cholestatic liver disease and encourages multi-organ treatment strategies for PSC.

Digital twin demonstrates significance of biomechanical growth control in liver regeneration after partial hepatectomy.

Partial liver removal is an important therapy option for liver cancer. In most patients within a few weeks, the liver is able to fully regenerate. In some patients, however, regeneration fails with often severe consequences. To better understand the control mechanisms of liver regeneration, experiments in mice were performed, guiding the creation of a spatiotemporal 3D model of the regenerating liver. The model represents cells and blood vessels within an entire liver lobe, a macroscopic liver subunit. The model could reproduce the experimental data only if a biomechanical growth control (BGC)-mechanism, inhibiting cell cycle entrance at high compression, was taken into account and predicted that BGC may act as a short-range growth inhibitor minimizing the number of proliferating neighbor cells of a proliferating cell, generating a checkerboard-like proliferation pattern. Model-predicted cell proliferation patterns in pigs and mice were found experimentally. The results underpin the importance of biomechanical aspects in liver growth control.

Automated Detection of Portal Fields and Central Veins in Whole-Slide Images of Liver Tissue.

Many physiological processes and pathological phenomena in the liver tissue are spatially heterogeneous. At a local scale, biomarkers can be quantified along the axis of the blood flow, from portal fields (PFs) to central veins (CVs), i.e., in zonated form. This requires detecting PFs and CVs. However, manually annotating these structures in multiple whole-slide images is a tedious task. We describe and evaluate a fully automated method, based on a convolutional neural network, for simultaneously detecting PFs and CVs in a single stained section. Trained on scans of hematoxylin and eosin-stained liver tissue, the detector performed well with an F1 score of 0.81 compared to annotation by a human expert. It does, however, not generalize well to previously unseen scans of steatotic liver tissue with an F1 score of 0.59. Automated PF and CV detection eliminates the bottleneck of manual annotation for subsequent automated analyses, as illustrated by two proof-of-concept applications: We computed lobulus sizes based on the detected PF and CV positions, where results agreed with published lobulus sizes. Moreover, we demonstrate the feasibility of zonated quantification of biomarkers detected in different stainings based on lobuli and zones obtained from the detected PF and CV positions. A negative control (hematoxylin and eosin) showed the expected homogeneity, a positive control (glutamine synthetase) was quantified to be strictly pericentral, and a plausible zonation for a heterogeneous F4/80 staining was obtained. Automated detection of PFs and CVs is one building block for automatically quantifying physiologically relevant heterogeneity of liver tissue biomarkers. Perspectively, a more robust and automated assessment of zonation from whole-slide images will be valuable for parameterizing spatially resolved models of liver metabolism and to provide diagnostic information.

Interruption of bile acid uptake by hepatocytes after acetaminophen overdose ameliorates hepatotoxicity.

BACKGROUND & AIMS: Acetaminophen (APAP) overdose remains a frequent cause of acute liver failure, which is generally accompanied by increased levels of serum bile acids (BAs). However, the pathophysiological role of BAs remains elusive. Herein, we investigated the role of BAs in APAP-induced hepatotoxicity. METHODS: We performed intravital imaging to investigate BA transport in mice, quantified endogenous BA concentrations in the serum of mice and patients with APAP overdose, analyzed liver tissue and bile by mass spectrometry and MALDI-mass spectrometry imaging, assessed the integrity of the blood-bile barrier and the role of oxidative stress by immunostaining of tight junction proteins and intravital imaging of fluorescent markers, identified the intracellular cytotoxic concentrations of BAs, and performed interventions to block BA uptake from blood into hepatocytes. RESULTS: Prior to the onset of cell death, APAP overdose causes massive oxidative stress in the pericentral lobular zone, which coincided with a breach of the blood-bile barrier. Consequently, BAs leak from the bile canaliculi into the sinusoidal blood, which is then followed by their uptake into hepatocytes via the basolateral membrane, their secretion into canaliculi and repeated cycling. This, what we termed 'futile cycling' of BAs, led to increased intracellular BA concentrations that were high enough to cause hepatocyte death. Importantly, however, the interruption of BA re-uptake by pharmacological NTCP blockage using Myrcludex B and Oatp knockout strongly reduced APAP-induced hepatotoxicity. CONCLUSIONS: APAP overdose induces a breach of the blood-bile barrier which leads to futile BA cycling that causes hepatocyte death. Prevention of BA cycling may represent a therapeutic option after APAP intoxication. LAY SUMMARY: Only one drug, N-acetylcysteine, is approved for the treatment of acetaminophen overdose and it is only effective when given within ∼8 hours after ingestion. We identified a mechanism by which acetaminophen overdose causes an increase in bile acid concentrations (to above toxic thresholds) in hepatocytes. Blocking this mechanism prevented acetaminophen-induced hepatotoxicity in mice and evidence from patients suggests that this therapy may be effective for longer periods after ingestion compared to N-acetylcysteine.

Transcriptomic Cross-Species Analysis of Chronic Liver Disease Reveals Consistent Regulation Between Humans and Mice.

Mouse models are frequently used to study chronic liver diseases (CLDs). To assess their translational relevance, we quantified the similarity of commonly used mouse models to human CLDs based on transcriptome data. Gene-expression data from 372 patients were compared with data from acute and chronic mouse models consisting of 227 mice, and additionally to nine published gene sets of chronic mouse models. Genes consistently altered in humans and mice were mapped to liver cell types based on single-cell RNA-sequencing data and validated by immunostaining. Considering the top differentially expressed genes, the similarity between humans and mice varied among the mouse models and depended on the period of damage induction. The highest recall (0.4) and precision (0.33) were observed for the model with 12-months damage induction by CCl4 and by a Western diet, respectively. Genes consistently up-regulated between the chronic CCl4 model and human CLDs were enriched in inflammatory and developmental processes, and mostly mapped to cholangiocytes, macrophages, and endothelial and mesenchymal cells. Down-regulated genes were enriched in metabolic processes and mapped to hepatocytes. Immunostaining confirmed the regulation of selected genes and their cell type specificity. Genes that were up-regulated in both acute and chronic models showed higher recall and precision with respect to human CLDs than exclusively acute or chronic genes. Conclusion: Similarly regulated genes in human and mouse CLDs were identified. Despite major interspecies differences, mouse models detected 40% of the genes significantly altered in human CLD. The translational relevance of individual genes can be assessed at https://saezlab.shinyapps.io/liverdiseaseatlas/.

Spatio-Temporal Multiscale Analysis of Western Diet-Fed Mice Reveals a Translationally Relevant Sequence of Events during NAFLD Progression.

Mouse models of non-alcoholic fatty liver disease (NAFLD) are required to define therapeutic targets, but detailed time-resolved studies to establish a sequence of events are lacking. Here, we fed male C57Bl/6N mice a Western or standard diet over 48 weeks. Multiscale time-resolved characterization was performed using RNA-seq, histopathology, immunohistochemistry, intravital imaging, and blood chemistry; the results were compared to human disease. Acetaminophen toxicity and ammonia metabolism were additionally analyzed as functional readouts. We identified a sequence of eight key events: formation of lipid droplets; inflammatory foci; lipogranulomas; zonal reorganization; cell death and replacement proliferation; ductular reaction; fibrogenesis; and hepatocellular cancer. Functional changes included resistance to acetaminophen and altered nitrogen metabolism. The transcriptomic landscape was characterized by two large clusters of monotonously increasing or decreasing genes, and a smaller number of 'rest-and-jump genes' that initially remained unaltered but became differentially expressed only at week 12 or later. Approximately 30% of the genes altered in human NAFLD are also altered in the present mouse model and an increasing overlap with genes altered in human HCC occurred at weeks 30-48. In conclusion, the observed sequence of events recapitulates many features of human disease and offers a basis for the identification of therapeutic targets.

Intravital Dynamic and Correlative Imaging of Mouse Livers Reveals Diffusion-Dominated Canalicular and Flow-Augmented Ductular Bile Flux.

BACKGROUND AND AIMS: Small-molecule flux in tissue microdomains is essential for organ function, but knowledge of this process is scant due to the lack of suitable methods. We developed two independent techniques that allow the quantification of advection (flow) and diffusion in individual bile canaliculi and in interlobular bile ducts of intact livers in living mice, namely fluorescence loss after photoactivation and intravital arbitrary region image correlation spectroscopy. APPROACH AND RESULTS: The results challenge the prevailing "mechano-osmotic" theory of canalicular bile flow. After active transport across hepatocyte membranes, bile acids are transported in the canaliculi primarily by diffusion. Only in the interlobular ducts is diffusion augmented by regulatable advection. Photoactivation of fluorescein bis-(5-carboxymethoxy-2-nitrobenzyl)-ether in entire lobules demonstrated the establishment of diffusive gradients in the bile canalicular network and the sink function of interlobular ducts. In contrast to the bile canalicular network, vectorial transport was detected and quantified in the mesh of interlobular bile ducts. CONCLUSIONS: The liver consists of a diffusion-dominated canalicular domain, where hepatocytes secrete small molecules and generate a concentration gradient and a flow-augmented ductular domain, where regulated water influx creates unidirectional advection that augments the diffusive flux.

Pipe-3D: A Pipeline Based on Immunofluorescence, 3D Confocal Imaging, Reconstructions, and Morphometry for Biliary Network Analysis in Cholestasis.

Cholestasis, the impairment of bile flux out of the liver, is a common complication of many pathological liver disorders, such as cholangiopathies, primary biliary sclerosis, and primary biliary cirrhosis. Besides accumulation of bile acids in the liver and blood, it leads to a proliferative response of the biliary tree termed as a ductular reaction. The ductular reaction is characterized by enhanced proliferation of cholangiocytes, which form the epithelial lining of bile ducts. This strong reaction of the biliary tree has been reported to generate a source of progenitor cells that can differentiate to hepatocytes or cholangiocytes during regeneration. On the other hand, it can cause periportal fibrosis eventually progressing to cirrhosis and death. In 2D histology, this leads to the appearance of an increased number of duct lumina per area of tissue. Yet, the biliary tree is a 3D vstructure and the appearance of lumina in thin slices may be explained by the appearance of novel ducts or by ramification or convolution of existing ducts in 3D. In many such aspects, traditional 2D histology on thin slices limits our understanding of the response of the biliary tree. A comprehensive understanding of architecture remodeling of the biliary network in cholestasis depends on robust 3D sample preparation and analysis methods. To that end, we describe pipe-3D, a processing and analysis pipeline visualization based on immunofluorescence, confocal imaging, surface reconstructions, and automated morphometry of the biliary network in 3D at subcellular resolution. This pipeline has been used to discover extensive remodeling of interlobular bile ducts in cholestasis, wherein elongation, branching, and looping create a dense ductular mesh around the portal vein branch. Surface reconstructions generated by Pipe-3D from confocal data also show an approximately fivefold enhancement of the luminal duct surface through corrugation of the epithelial lamina, which may increase bile reabsorption and alleviate cholestasis. The response of interlobular ducts in cholestasis was shown to be in sharp contrast to that of large bile ducts, de novo duct formation during embryogenesis. It is also distinct from ductular response in other models of hepatic injury such as choline-deficient, ethionine-supplemented diet, where parenchymal tissue invasion by ducts and their branches is observed. Pipe-3D is applicable to any model of liver injury, and optionally integrates tissue clearing techniques for 3D analysis of thick (>500 µm) tissue sections.

Bile canalicular dynamics in hepatocyte sandwich cultures.

Many substances are hepatotoxic due to their ability to cause intrahepatic cholestasis. Therefore, there is a high demand for in vitro systems for the identification of cholestatic properties of new compounds. Primary hepatocytes cultivated in collagen sandwich cultures are known to establish bile canaliculi which enclose secreted biliary components. Cholestatic compounds are mainly known to inhibit bile excretion dynamics, but may also alter canalicular volume, or hepatocellular morphology. So far, techniques to assess time-resolved morphological changes of bile canaliculi in sandwich cultures are not available. In this study, we developed an automated system that quantifies dynamics of bile canaliculi recorded in conventional time-lapse image sequences. We validated the hepatocyte sandwich culture system as an appropriate model to study bile canaliculi in vitro by showing structural similarity measured as bile canaliculi length per hepatocyte to that observed in vivo. Moreover, bile canalicular excretion kinetics of CMFDA (5-chloromethylfluorescein diacetate) in sandwich cultures resembled closely the kinetics observed in vivo. The developed quantification technique enabled the quantification of dynamic changes in individual bile canaliculi. With this technique, we were able to clearly distinguish between sandwich cultures supplemented with dexamethasone and insulin from control cultures. In conclusion, the automated quantification system offers the possibility to systematically study the causal relationship between disturbed bile canalicular dynamics and cholestasis.

Protocols for staining of bile canalicular and sinusoidal networks of human, mouse and pig livers, three-dimensional reconstruction and quantification of tissue microarchitecture by image processing and analysis.

Histological alterations often constitute a fingerprint of toxicity and diseases. The extent to which these alterations are cause or consequence of compromised organ function, and the underlying mechanisms involved is a matter of intensive research. In particular, liver disease is often associated with altered tissue microarchitecture, which in turn may compromise perfusion and functionality. Research in this field requires the development and orchestration of new techniques into standardized processing pipelines that can be used to reproducibly quantify tissue architecture. Major bottlenecks include the lack of robust staining, and adequate reconstruction and quantification techniques. To bridge this gap, we established protocols employing specific antibody combinations for immunostaining, confocal imaging, three-dimensional reconstruction of approximately 100-µm-thick tissue blocks and quantification of key architectural features. We describe a standard procedure termed 'liver architectural staining' for the simultaneous visualization of bile canaliculi, sinusoidal endothelial cells, glutamine synthetase (GS) for the identification of central veins, and DAPI as a nuclear marker. Additionally, we present a second standard procedure entitled 'S-phase staining', where S-phase-positive and S-phase-negative nuclei (stained with BrdU and DAPI, respectively), sinusoidal endothelial cells and GS are stained. The techniques include three-dimensional reconstruction of the sinusoidal and bile canalicular networks from the same tissue block, and robust capture of position, size and shape of individual hepatocytes, as well as entire lobules from the same tissue specimen. In addition to the protocols, we have also established image analysis software that allows relational and hierarchical quantifications of different liver substructures (e.g. cells and vascular branches) and events (e.g. cell proliferation and death). Typical results acquired for routinely quantified parameters in adult mice (C57Bl6/N) include the hepatocyte volume (5,128.3 ± 837.8 µm(3)) and the fraction of the hepatocyte surface in contact with the neighbouring hepatocytes (67.4 ± 6.7 %), sinusoids (22.1 ± 4.8 %) and bile canaliculi (9.9 ± 3.8 %). Parameters of the sinusoidal network that we also routinely quantify include the radius of the sinusoids (4.8 ± 2.25 µm), the branching angle (32.5 ± 11.2°), the length of intersection branches (23.93 ± 5.9 µm), the number of intersection nodes per mm(3) (120.3 × 103 ± 42.1 × 10(3)), the average length of sinusoidal vessel per mm(3) (5.4 × 10(3) ± 1.4 × 10(3)mm) and the percentage of vessel volume in relation to the whole liver volume (15.3 ± 3.9) (mean ± standard deviation). Moreover, the provided parameters of the bile canalicular network are: length of the first-order branches (7.5 ± 0.6 µm), length of the second-order branches (10.9 ± 1.8 µm), length of the dead-end branches (5.9 ± 0.7 µm), the number of intersection nodes per mm(3) (819.1 × 10(3) ± 180.7 × 10(3)), the number of dead-end branches per mm(3) (409.9 × 10(3) ± 95.6 × 10(3)), the length of the bile canalicular network per mm(3) (9.4 × 10(3) ± 0.7 × 10(3) mm) and the percentage of the bile canalicular volume with respect to the total liver volume (3.4 ± 0.005). A particular strength of our technique is that quantitative parameters of hepatocytes and bile canalicular as well as sinusoidal networks can be extracted from the same tissue block. Reconstructions and quantifications performed as described in the current protocols can be used for quantitative mathematical modelling of the underlying mechanisms. Furthermore, protocols are presented for both human and pig livers. The technique is also applicable for both vibratome blocks and conventional paraffin slices.

The transcription factor CHOP, a central component of the transcriptional regulatory network induced upon CCl4 intoxication in mouse liver, is not a critical mediator of hepatotoxicity.

Since xenobiotics enter the organism via the liver, hepatocytes must cope with numerous perturbations, including modifications of proteins leading to endoplasmic reticulum stress (ER-stress). This triggers a signaling pathway termed unfolded protein response (UPR) that aims to restore homeostasis or to eliminate disturbed hepatocytes by apoptosis. In the present study, we used the well-established CCl4 hepatotoxicity model in mice to address the questions whether CCl4 induces ER-stress and, if so, whether the well-known ER-stress effector CHOP is responsible for CCl4-induced apoptosis. For this purpose, we treated mice with a high dose of CCl4 injected i.p. and followed gene expression profile over time using Affymetrix gene array analysis. This time resolved gene expression analysis allowed the identification of gene clusters with overrepresented binding sites for the three most important ER-stress induced transcription factors, CHOP, XBP1 and ATF4. Such result was confirmed by the demonstration of CCl4-induced XBP1 splicing, upregulation of CHOP at mRNA and protein levels, and translocation of CHOP to the nucleus. Two observations indicated that CHOP may be responsible for CCl4-induced cell death: (1) Nuclear translocation of CHOP was exclusively observed in the pericentral fraction of hepatocytes that deteriorate in response to CCl4 and (2) CHOP-regulated genes with previously reported pro-apoptotic function such as GADD34, TRB3 and ERO1L were induced in the pericentral zone as well. Therefore, we compared CCl4 induced hepatotoxicity in CHOP knockout versus wild-type mice. Surprisingly, genetic depletion of CHOP did not afford protection against CCl4-induced damage as evidenced by serum GOT and GPT as well as quantification of dead tissue areas. The negative result was obtained at several time points (8, 24 and 72 h) and different CCl4 doses (1.6 and 0.132 g/kg). Overall, our results demonstrate that all branches of the UPR are activated in mouse liver upon CCl4 treatment. However, CHOP does not play a critical role in CCl4-induced cell death and cannot be considered as a biomarker strictly linked to hepatotoxicity. The role of alternative UPR effectors such as XBP1 remains to be investigated.