A humanized mouse model of liver fibrosis following expansion of transplanted hepatic stellate cells

The 3Rs in Experimental Liver Disease

Patients with cirrhosis present multiple physiological and immunological alterations that play a very important role in the development of clinically relevant secondary complications to the disease. Experimentation in animal models is essential to understand the pathogenesis of human diseases and, considering the high prevalence of liver disease worldwide, to understand the pathophysiology of disease progression and the molecular pathways involved, due to the complexity of the liver as an organ and its relationship with the rest of the organism. However, today there is a growing awareness about the sensitivity and suffering of animals, causing opposition to animal research among a minority in society and some scientists, but also about the attention to the welfare of laboratory animals since this has been built into regulations in most nations that conduct animal research. In 1959, Russell and Burch published the book "The Principles of Humane Experimental Technique", proposing that in those experiments where animals were necessary, everything possible should be done to try to replace them with non-sentient alternatives, to reduce to a minimum their number, and to refine experiments that are essential so that they caused the least amount of pain and distress. In this review, a comprehensive summary of the most widely used techniques to replace, reduce, and refine in experimental liver research is offered, to assess the advantages and weaknesses of available experimental liver disease models for researchers who are planning to perform animal studies in the near future.

Modeling drug-induced liver injury and screening for anti-hepatofibrotic compounds using human PSC-derived organoids

Preclinical models that can accurately predict the toxicity and efficacy of candidate drugs to human liver tissue are in urgent need. Human liver organoid (HLO) derived from human pluripotent stem cells offers a possible solution. Herein, we generated HLOs, and demonstrated the utility of these HLOs in modeling a diversity of phenotypes associated with drug-induced liver injury (DILI), including steatosis, fibrosis, and immune responses. Phenotypic changes in HLOs after treatment with tool compounds such as acetaminophen, fialuridine, methotrexate, or TAK-875 showed high concordance with human clinical data in drug safety testings. Moreover, HLOs were able to model liver fibrogenesis induced by TGFβ or LPS treatment. We further devised a high-content analysis system, and established a high-throughput anti-fibrosis drug screening system using HLOs. SD208 and Imatinib were identified that can significantly suppress fibrogenesis induced by TGFβ, LPS, or methotrexate. Taken together, our studies demonstrated the potential applications of HLOs in drug safety testing and anti-fibrotic drug screening.

Computational simulation of liver fibrosis dynamics

Liver fibrosis is a result of homeostasis breakdown caused by repetitive injury. The accumulation of collagens disrupts liver structure and function, which causes serious consequences such as cirrhosis. Various mathematical simulation models have been developed to understand these complex processes. We employed the agent-based modelling (ABM) approach and implemented inflammatory processes in central venous regions. Collagens were individually modelled and visualised depending on their origin: myofibroblast and portal fibroblast. Our simulation showed that the administration of toxic compounds induced accumulation of myofibroblast-derived collagens in central venous regions and portal fibroblast-derived collagens in portal areas. Subsequently, these collagens were bridged between central-central areas and spread all over areas. We confirmed the consistent dynamic behaviour of collagen formulation in our simulation and from histological sections obtained via in vivo experiments. Sensitivity analyses identified dead hepatocytes caused by inflammation and the ratio of residential liver cells functioned as a cornerstone for the initiation and progression of liver fibrosis. The validated mathematical model demonstrated here shows virtual experiments that are complementary to biological experiments, which contribute to understanding a new mechanism of liver fibrosis.

Transplanted hepatocytes rescue mice in acetaminophen-induced acute liver failure through paracrine signals for hepatic ATM and STAT3 pathways

Acute liver failure constitutes a devastating condition that needs novel cell and molecular therapies. To elicit synergisms in cell types of therapeutic interest, we studied hepatocytes and liver sinusoidal endothelial in mice with acetaminophen-induced acute liver failure. The context of regenerative signals was examined by transplants in peritoneal cavity because it possesses considerable capacity and allows soluble signals to enter the systemic circulation. Whereas transplanted hepatocytes and liver sinusoidal endothelial cells engrafted in peritoneal cavity, only the former could rescue mice in liver failure by improving injury outcomes, activating hepatic DNA damage repair, and inducing liver regeneration. The cytokines secreted by donor hepatocytes or liver sinusoidal endothelial cells differed and in hepatocytes from mice undergoing acetaminophen toxicity major cytokines were even rendered deficient (eg, G-CSF, VEGF, and others). Significantly, recapitulating hepatotoxicity-related DNA damage response in cultured cells identified impairments in ATM and JAK/STAT3 intersections since replacing cytokines produced less from injured hepatocytes restored these pathways to avoid acetaminophen hepatotoxicity. Similarly, hepatocyte transplantation in acute liver failure restored ATM and JAK/STAT3 pathways to advance DNA damage/repair and liver regeneration. The unexpected identification of novel hepatic G-CSF receptor expression following injury allowed paradigmatic studies of G-CSF supplementation to confirm the centrality of this paracrine ATM and STAT3 intersection. Remarkably, DNA damage/repair and hepatic regeneration directed by G-CSF concerned rebalancing of regulatory gene networks overseeing inflammation, metabolism, and cell viability. We conclude that healthy donor hepatocytes offer templates for generating specialized cell types to replace metabolic functions and regenerative factors in liver failure.

BIR repeat-containing ubiquitin conjugating enzyme (BRUCE) regulation of β-catenin signaling in the progression of drug-induced hepatic fibrosis and carcinogenesis

BACKGROUND

BIR repeat-containing ubiquitin conjugating enzyme (BRUCE) is a liver tumor suppressor, which is downregulated in a large number of patients with liver diseases. BRUCE facilitates DNA damage repair to protect the mouse liver against the hepatocarcinogen diethylnitrosamine (DEN)-dependent acute liver injury and carcinogenesis. While there exists an established pathologic connection between fibrosis and hepatocellular carcinoma (HCC), DEN exposure alone does not induce robust hepatic fibrosis. Further studies are warranted to identify new suppressive mechanisms contributing to DEN-induced fibrosis and HCC.

AIM

To investigate the suppressive mechanisms of BRUCE in hepatic fibrosis and HCC development.

METHODS

Male C57/BL6/J control mice [loxp/Loxp; albumin-cre (Alb-cre)^-] and BRUCE Alb-Cre KO mice (loxp/Loxp; Alb-Cre⁺) were injected with a single dose of DEN at postnatal day 15 and sacrificed at different time points to examine liver disease progression.

RESULTS

By using a liver-specific BRUCE knockout (LKO) mouse model, we found that BRUCE deficiency, in conjunction with DEN exposure, induced hepatic fibrosis in both premalignant as well as malignant stages, thus recapitulating the chronic fibrosis background often observed in HCC patients. Activated in fibrosis and HCC, β-catenin activity depends on its stabilization and subsequent translocation to the nucleus. Interestingly, we observed that livers from BRUCE KO mice demonstrated an increased nuclear accumulation and elevated activity of β-catenin in the three stages of carcinogenesis: Pre-malignancy, tumor initiation, and HCC. This suggests that BRUCE negatively regulates β-catenin activity during liver disease progression. β-catenin can be activated by phosphorylation by protein kinases, such as protein kinase A (PKA), which phosphorylates it at Ser-675 (pSer-675-β-catenin). Mechanistically, BRUCE and PKA were colocalized in the cytoplasm of hepatocytes where PKA activity is maintained at the basal level. However, in BRUCE deficient mouse livers or a human liver cancer cell line, both PKA activity and pSer-675-β-catenin levels were observed to be elevated.

CONCLUSION

Our data support a “BRUCE-PKA-β-catenin” signaling axis in the mouse liver. The BRUCE interaction with PKA in hepatocytes suppresses PKA-dependent phosphorylation and activation of β-catenin. This study implicates BRUCE as a novel negative regulator of both PKA and β-catenin in chronic liver disease progression. Furthermore, BRUCE-liver specific KO mice serve as a promising model for understanding hepatic fibrosis and HCC in patients with aberrant activation of PKA and β-catenin.

Novel patient-derived preclinical models of liver cancer

Preclinical models of cancer based on the use of human cancer cell lines and mouse models have enabled discoveries that have been successfully translated into patients. And yet the majority of clinical trials fail, emphasising the urgent need to improve preclinical research to better interrogate the potential efficacy of each therapy and the patient population most likely to benefit. This is particularly important for liver malignancies, which lack highly efficient treatments and account for hundreds of thousands of deaths around the globe. Given the intricate network of genetic and environmental factors that contribute to liver cancer development and progression, the identification of new druggable targets will mainly depend on establishing preclinical models that mirror the complexity of features observed in patients. The development of new 3D cell culture systems, originating from cells/tissues isolated from patients, might create new opportunities for the generation of more specific and personalised therapies. However, these systems are unable to recapitulate the tumour microenvironment and interactions with the immune system, both proven to be critical influences on therapeutic outcomes. Patient-derived xenografts, in particular with humanised mouse models, more faithfully mimic the physiology of human liver cancer but are costly and time-consuming, which can be prohibitive for personalising therapies in the setting of an aggressive malignancy. In this review, we discuss the latest advances in the development of more accurate preclinical models to better understand liver cancer biology and identify paradigm-changing therapies, stressing the importance of a bi-directional communicative flow between clinicians and researchers to establish reliable model systems and determine how best to apply them to expanding our current knowledge.

Cellular cytokine receptor signaling and ATM pathway intersections affect hepatic DNA repair

Pathways involving ataxia telangiectasia mutated (ATM) gene and its downstream partners and effectors are critical for the DNA damage response. Cell survival, proliferation and tissue homeostasis are dependent upon preservation of DNA integrity but additional intracellular mechanisms contribute in these processes. As receptor-mediated signaling with beneficial intersections in ATM pathways could have therapeutic significance, we interrogated such intersections with assays using HuH-7 cells (hepatocytes). These cells were subjected to acetaminophen toxicity, which is a leading cause of hepatic injury and acute liver failure in people. The ATM pathway was examined in HuH-7-ATM-Prom-tdT cells containing fluorescent td-Tomato transgene reporter for ATM promoter activity. Titrated doses of specific growth factors were used as ligands for receptor-mediated signaling. The contribution of JAK/STAT3 signaling was defined by the loss-of-function approach with the JAK antagonist, ruxolitinib. In these assays, impairment in ATM-related DNA damage response following acetaminophen toxicity was ameliorated by selected growth factors, including fibroblast growth factors, granulocyte colony stimulating factor and vascular endothelial growth factor. The JAK/STAT3 signaling was exclusive to granulocyte colony stimulating factor but concerned additional pathways in cases of other growth factors. Antagonism of JAK/STAT3 by ruxolitinib abrogated benefits in ATM pathway-mediated DNA repair; and identification of the ruxolitinib-sensitive component of cytoprotection allowed separations of these pathway intersections. Therefore, this subtractive approach for ATM and other regulators in pathways will be informative for DNA damage response. These mechanisms will benefit therapeutic development for ATM-related tissue and organ injuries.

The prognostic and clinicopathological significance of PD-L1 expression in patients with diffuse large B-cell lymphoma: a meta-analysis

BACKGROUND

Programmed cell death receptor 1 ligand 1 (PD-L1) expression in various tumors, including hematologic malignancies, has recently become a research topic of great interest. We performed a meta-analysis to evaluate the prognostic and clinicopathological value of PD-L1 expressed in tumor cells of patients with diffuse large B-cell lymphoma (DLBCL).

METHODS

Relevant studies were identified from PubMed, EMBASE, Web of Science and the Cochrane Library. The hazard ratio (HR) and 95% confidence interval (95% CI) were used for analyzing survival outcomes, and the odds ratio (OR) was used for analyzing clinicopathological parameters.

RESULTS

Pooled results showed that tumor cell PD-L1 expression is associated with poor overall survival (OS) (HR = 2.128, 95% CI: 1.341-3.378, P = 0.001), the non-germinal center B-cell-like subtype (OR = 2.891, 95% CI: 2.087-4.003, P < 0.000), high international prognostic index score (3-5) (OR = 1.552, 95% CI: 1.111-2.169, P = 0.010), B symptoms (OR = 1.495, 95% Cl: 1.109-2.015, P = 0.008), positive MUM1 expression (OR = 3.365, 95% Cl: 1.578-7.175, P = 0.002) and negative BCL6 expression (OR = 0.414, 95% Cl: 0.217-0.792, P = 0.008). Sensitivity analysis showed that there was no publication bias among these studies.

CONCLUSIONS

Our meta-analysis supported the idea that tumor cell PD-L1 expression may represent a promising biomarker for predicting poor prognosis and is associated with adverse clinicopathologic features in DLBCL patients.

Efficient Reconstitution of Hepatic Microvasculature by Endothelin Receptor Antagonism in Liver Sinusoidal Endothelial Cells

Reconstitution of healthy endothelial cells in vascular beds offers opportunities for mechanisms in tissue homeostasis, organ regeneration, and correction of deficient functions. Liver sinusoidal endothelial cells express unique functions, and their transplantation is relevant for disease models and for cell therapy. As molecular targets for improving transplanted cell engraftment and proliferation will be highly significant, this study determined whether ET_A/B receptor antagonism by the drug bosentan could overcome cell losses due to cell transplantation-induced cytotoxicity. Cell engraftment and proliferation assays were performed with healthy wild-type liver sinusoidal endothelial cells transplanted into the liver of dipeptidylpeptidase IV knockout mice. Transplanted cells were identified in tissues by enzyme histochemistry. Cells with prospective ET_A/B antagonism engrafted significantly better in hepatic sinusoids. Moreover, these cells underwent multiple rounds of division under liver repopulation conditions. The gains of ET_A/B antagonism resulted from benefits in cell viability and membrane integrity. Also, in bosentan-treated cells, mitochondrial homeostasis was better maintained with less oxidative stress and DNA damage after injuries. Intracellular effects of ET_A/B antagonism were transduced by conservation of ataxia telangiectasia mutated protein, which directs DNA damage response. Therefore, ET_A/B antagonism in donor cells will advance vascular reconstitution. Extensive experience with ET_A/B antagonists will facilitate translation in people.

In Atp7b-/- Mice Modeling Wilson's Disease Liver Repopulation With Bone Marrow-Derived Myofibroblasts or Inflammatory Cells and Not Hepatocytes Is Deleterious

In Wilson's disease, Atp7b mutations impair copper excretion with liver or brain damage. Healthy transplanted hepatocytes repopulate the liver, excrete copper, and reverse hepatic damage in animal models of Wilson's disease. In Fah^-/- mice with tyrosinemia and α-1 antitrypsin mutant mice, liver disease is resolved by expansions of healthy hepatocytes derived from transplanted healthy bone marrow stem cells. This potential of stem cells has not been defined for Wilson's disease. In diseased Atp7b^-/- mice, we reconstituted bone marrow with donor cells expressing green fluorescent protein reporter from healthy transgenic mice. Mature hepatocytes originating from donor bone marrow were identified by immunostaining for green fluorescence protein and bile canalicular marker, dipeptidylpeptidase-4. Mesenchymal and inflammatory cell markers were used for other cells from donor bone marrow cells. Gene expression, liver tests, and tissues were analyzed for outcomes in Atp7b^-/- mice. After bone marrow transplantation in Atp7b^-/- mice, donor-derived hepatocytes containing bile canaliculi appeared within weeks. Despite this maturity, donor-derived hepatocytes neither divided nor expanded. The liver of Atp7b^-/- mice was not repopulated by donor-derived hepatocytes: Atp7b mRNA remained undetectable; liver tests, copper content, and fibrosis actually worsened. Restriction of proliferation in hepatocytes accompanied oxidative DNA damage. By contrast, donor-derived mesenchymal and inflammatory cells extensively proliferated. These contributed to fibrogenesis through greater expression of inflammatory cytokines. In Wilson's disease, donor bone marrow-derived cells underwent different fates: hepatocytes failed to proliferate; inflammatory cells proliferated to worsen disease outcomes. This will help guide stem cell therapies for conditions with proinflammatory or profibrogenic microenvironments.

Decellularized bovine placentome for portacavally-interposed heterotopic liver transplantation in rats

Scaffolds from healthy placentae offer advantages for tissue engineering with undamaged matrix, associated cytoprotective molecules, and embedded vessels for revascularization. As size disparities in human placenta and small recipients hamper preclinical studies, we studied alternative of bovine placentomes in smaller size ranges. Multiple cow placentomes were decellularized and anatomical integrity was analyzed. Tissue engineering used inbred donor rat livers. Placentomes were hepatized and immediately transplanted in rats with perfusion from portal vein and drainage into inferior vena cava. Cows yielded 99 ± 16 placentomes each. Of these, approximately 25% had 3 to 9 cm diameter and 7 to 63 ml volume, which was suitable for transplantation. After decellularization, angiography and casts documented 100% of vessels and vascular networks were well-perfused without disruptions or leaks. The residual matrix also remained intact for transplantation of placentomes. Perfusion in transplanted placentomes was maintained over up to 30 days. Liver tissue reassembled with restoration of hepatic acinar and sinusoidal structure. Transplanted tissue was intact without apoptosis, or necrosis. Hepatic functions were maintained. Preservation of hepatic homeostasis was verified by cytofluorimetric analysis of hepatocyte ploidy. The prevalence in healthy and transplanted liver of diploid, tetraploid and higher ploidy classes was similar with 57%, 41% and 2% versus 51%, 46.5% and 2.6%, respectively, p = 0.77, ANOVA. CONCLUSIONS: Cow placentomes will allow therapeutic development with disease models in small animals. This will also advance drug or toxicology studies. Portasystemic interposition of engineered liver will be particularly suitable for treating hepatic insufficiencies (metabolic, secretory or detoxification needs), including for children or smaller adults.

c-Met Signaling Protects from Nonalcoholic Steatohepatitis- (NASH-) Induced Fibrosis in Different Liver Cell Types

Nonalcoholic steatohepatitis (NASH) is the most common chronic, progressive liver disease in Western countries. The significance of cellular interactions of the HGF/c-Met axis in different liver cell subtypes and its relation to the oxidative stress response remains unclear so far. Hence, the present study is aimed at investigating the role of c-Met and the interaction with the oxidative stress response during NASH development in mice and humans. Conditional c-Met knockout (KO) lines (LysCre for Kupffer cells/macrophages, GFAPCre for α-SMA⁺ and CK19⁺ cells and MxCre for bone marrow-derived immune cells) were fed chow and either methionine-choline-deficient diet (MCD) for 4 weeks or high-fat diet (HFD) for 24 weeks. Mice lacking c-Met either in Kupffer cells, α-SMA⁺ and CK19⁺ cells, or bone marrow-derived immune cells displayed earlier and faster progressing steatohepatitis during dietary treatments. Severe fatty liver degeneration and histomorphological changes were accompanied by an increased infiltration of immune cells and a significant upregulation of inflammatory cytokine expression reflecting an earlier initiation of steatohepatitis development. In addition, animals with a cell-type-specific deletion of c-Met exhibited a strong generation of reactive oxygen species (ROS) by dihydroethidium (hydroethidine) (DHE) staining showing a significant increase in the oxidative stress response especially in LysCre/c-Met^mut and MxCre/c-Met^mut animals. All these changes finally lead to earlier and stronger fibrosis progression with strong accumulation of collagen within liver tissue of mice deficient for c-Met in different liver cell types. The HGF/c-Met signaling pathway prevents from steatosis development and has a protective function in the progression to steatohepatitis and fibrosis. It conveys an antifibrotic role independent on which cell type c-Met is missing (Kupffer cells/macrophages, α-SMA⁺ and CK19⁺ cells, or bone marrow-derived immune cells). These results highlight a global protective capacity of c-Met in NASH development and progression.