Non-canonical BIM-regulated energy metabolism determines drug-induced liver necrosis

Paracetamol (acetaminophen, APAP) overdose severely damages mitochondria and triggers several apoptotic processes in hepatocytes, but the final outcome is fulminant necrotic cell death, resulting in acute liver failure and mortality. Here, we studied this switch of cell death modes and demonstrate a non-canonical role of the apoptosis-regulating BCL-2 homolog BIM/Bcl2l11 in promoting necrosis by regulating cellular bioenergetics. BIM deficiency enhanced total ATP production and shifted the bioenergetic profile towards glycolysis, resulting in persistent protection from APAP-induced liver injury. Modulation of glucose levels and deletion of Mitofusins confirmed that severe APAP toxicity occurs only in cells dependent on oxidative phosphorylation. Glycolytic hepatocytes maintained elevated ATP levels and reduced ROS, which enabled lysosomal recycling of damaged mitochondria by mitophagy. The present study highlights how metabolism and bioenergetics affect drug-induced liver toxicity, and identifies BIM as important regulator of glycolysis, mitochondrial respiration, and oxidative stress signaling.

Stimulatory MAIT cell antigens reach the circulation and are efficiently metabolised and presented by human liver cells

OBJECTIVE

Mucosal-associated invariant T (MAIT) cells are the most abundant T cells in human liver. They respond to bacterial metabolites presented by major histocompatibility complex-like molecule MR1. MAIT cells exert regulatory and antimicrobial functions and are implicated in liver fibrogenesis. It is not well understood which liver cells function as antigen (Ag)-presenting cells for MAIT cells, and under which conditions stimulatory Ags reach the circulation.

DESIGN

We used different types of primary human liver cells in Ag-presentation assays to blood-derived and liver-derived MAIT cells. We assessed MAIT cell stimulatory potential of serum from healthy subjects and patients with portal hypertension undergoing transjugular intrahepatic portosystemic shunt stent, and patients with inflammatory bowel disease (IBD).

RESULTS

MAIT cells were dispersed throughout healthy human liver and all tested liver cell types stimulated MAIT cells, hepatocytes being most efficient. MAIT cell activation by liver cells occurred in response to bacterial lysate and pure Ag, and was prevented by non-activating MR1 ligands. Serum derived from peripheral and portal blood, and from patients with IBD stimulated MAIT cells in MR1-dependent manner.

CONCLUSION

Our findings reveal previously unrecognised roles of liver cells in Ag metabolism and activation of MAIT cells, repression of which creates an opportunity to design antifibrotic therapies. The presence of MAIT cell stimulatory Ags in serum rationalises the observed activated MAIT cell phenotype in liver. Increased serum levels of gut-derived MAIT cell stimulatory ligands in patients with impaired intestinal barrier function indicate that intrahepatic Ag-presentation may represent an important step in the development of liver disease.

Intracellular Proprotein convertase subtilisin/kexin type 9: Recruitment and regulatory role in mitochondrial architecture and bioenergetic

Objective

Circulating Proprotein convertase subtilisin/kexin type 9 (PCSK9) captured the scientific community's attention as powerful target to fight against high serum cholesterol and its associated adverse consequences. Despite the well-described role of PCSK9 in impairing the recycling of low-density lipoprotein receptor (LDLR) on hepatocytes, its intracellular importance in metabolism modulations remain largely unexplored. Here, we describe a novel intracellular function of PCSK9 in hepatocyte metabolism and in liver regeneration.

Methods

A surgical model of partial hepatectomy (PH) was used to induce liver cell proliferation and serological and histological lipo- and glyco-metabolic perturbations were investigated in PCSK9 knockout and wild-type mice before and after PH. Mitochondrial bioenergetic level, compartmental architecture as well as intracellular localization and function of PCSK9 were further analyzed in vitro on murine primary isolated hepatocytes and PCSK9 lentiviral knockdown human liver cancer cell lines.

Results

Loss of PCSK9 expression led to a basal higher mitochondrial bioenergetic status in hepatocytes, characterized by a profound remodeling of mitochondrial architecture. Livers from PCSK9 knockout mice displayed a diffuse oxidative stress and a significant upregulation of cellular detoxification and superoxide radicals removal genes induced by the activation of c-Jun N-terminal kinase (JNK) pathway before PH. PCSK9 deficient mice showed a primed compensatory hepatic hyperplasia after PH, accompanied by an earlier transient regeneration-associated steatosis due to a higher LDLR expression and cholesterol uptake, with an increased β-oxidation, gluconeogenesis and glycolysis rate. Tetramethylrhodamine ethyl ester staining of isolated hepatocytes and liver cancer PCSK9 knockdown clones revealed a significantly reduced mitochondrial membrane potential when compared to controls. Confocal live-cell imaging and proteins immunoprecipitation showed respectively a mitochondrial recruitment of PCSK9 in proliferating cells and its interaction with mitochondrial membrane carriers and chaperons.

Conclusion

Despite the role played by circulating PCSK9 in regulating systemic cholesterol levels, our data shed light on its intracellular impact on mitochondrial architecture, membrane polarization and related metabolic perturbations in compartmental bioenergetics.

Primary infection by E. multilocularis induces distinct patterns of hepatic crosstalk between natural killer T and regulatory T cells in mice

Objective

The larval stage of the helminthic cestode Echinococcus multilocularis can inflict tumor-like hepatic lesions that cause the parasitic disease alveolar echinococcosis (AE) in humans. Recently, opportunistic properties of the disease have been proposed based on the increased incidence in immunocompromised patients as well as on mouse models, indicating that an appropriate adaptive immune response is required for the control of the disease. However, little is known about how the local hepatic immune responses modulate the infection with E. multilocularis.

Methods

In a mouse model of oral infection that mimics the normal infection route in human patients, the adaptive immune response in the liver was assessed using single cell RNA sequencing of isolated hepatic CD3+ T cells at different infection stages.

Results

Single-cell RNA sequencing revealed specific temporal changes of natural killer T (NKT) cells and regulatory T (Treg) cells, indicating that these two cell types expand in the early phase and are subsequently inhibited in the late phase of infection. Receptor-ligand complex analysis via CellPhoneDB, consistently revealed high number of interactions between Tregs and NKT mainly at day 10 post infection. Relevant interactions between NKT and Treg cells at early phases include regulation of cell adhesion molecules such as integrins and selectins and TNF-dependent signalling. Immune suppressing interactions that include the checkpoint inhibitors (PD-1 and PD-L1), purinergic (ENTPD1, ADORA2A) and TGF-beta signalling are down regulated at early time points. String analysis supported these findings.

Conclusion

The data indicate that early interactions between NKT and Tregs potentially promote the formation of hepatic lesions and later also contribute to immunological suppression of the resolution of parasite-induced pathology. The obtained data provide a fresh insight on the adaptive immune responses and local regulatory pathways at different infection stages of E. multilocularis in mice.

Regular testing of asymptomatic healthcare workers identifies cost-efficient SARS-CoV-2 preventive measures

Protecting healthcare professionals is crucial in maintaining a functioning healthcare system. The risk of infection and optimal preventive strategies for healthcare workers during the COVID-19 pandemic remain poorly understood. Here we report the results of a cohort study that included pre- and asymptomatic healthcare workers. A weekly testing regime has been performed in this cohort since the beginning of the COVID-19 pandemic to identify infected healthcare workers. Based on these observations we have developed a mathematical model of SARS-CoV-2 transmission that integrates the sources of infection from inside and outside the hospital. The data were used to study how regular testing and a desynchronisation protocol are effective in preventing transmission of COVID-19 infection at work, and compared both strategies in terms of workforce availability and cost-effectiveness. We showed that case incidence among healthcare workers is higher than would be explained solely by community infection. Furthermore, while testing and desynchronisation protocols are both effective in preventing nosocomial transmission, regular testing maintains work productivity with implementation costs.

A systematic review of mother-daughter interventions targeting physical activity

Background

Growing gender disparities in levels of physical inactivity put women and female youths at a greater risk of associated health problems. Mother-daughter interventions have been proposed as means to promote physical activity in this at-risk cohort. However, there is a lack of clarity as to if and why these types of interventions might be effective.

Methods

This systematic review examined the intervention characteristics, and behaviour change theory and techniques used in these interventions to promote physical activity for daughters and their mothers. PubMed, EMBASE, PsycINFO, CINAHL and Cochrane Library (Wiley) databases were searched for English language studies from inception to 13th May 2020. Interventions of any design that targeted daughters and mothers' physical activity were included in the review. Data was extracted using the Template for Intervention Description and Replication checklist, and the Behaviour Change Technique Taxonomy v1.

Results

4962 articles were screened and 11 unique studies met the inclusion criteria. Risk of bias was generally high. Narrative summary highlighted that many studies used social cognitive theory as a theoretical foundation, were based in the community and less than three months in duration with multiple sessions per week. Thirty-seven behaviour change techniques were identified across studies. Some techniques were deemed potentially effective including credible source, information on the health consequences of the behaviour and the self-regulatory related techniques of goal-setting, self-monitoring and problem-solving.

Conclusions

Future research should consider using checklists, frameworks and formative work with mothers and daughters to ensure interventions are rigorously designed, implemented, and evaluated, which can inform public policy to combat physical inactivity in this at-risk cohort.

Key messages

This is the first review to assess the intervention characteristics, and behaviour change theory and techniques of mother-daughter interventions targeting physical activity. This review advances the evidence base for future intervention development and more broadly can inform public policy to tackle physical inactivity in this at-risk cohort.

Impact of left heart disease risk factors on risk stratification and treatment response in pulmonary arterial hypertension

Background

Contemporary registries have documented a change in the epidemiology of PAH patients displaying increasing co-morbidities associated with left heart disease (LHD). These patients are often excluded from randomized clinical trials. It is unclear whether the presence of LHD comorbidities may adversely impact the accuracy of risk stratification and response to PAH therapy.

Method

Data was extracted from the Pulmonary Hypertension Society of Australia and New Zealand registry for incident patients with a diagnosis with idiopathic/heritable/toxin-induced (I/H/D)-PAH and connective tissue disease (CTD) associated PAH from 2011 - 2020. Patients without available medication and follow up data were excluded. We used the AMBITION trial exclusion criteria to define the subpopulation with LHD risk factors and haemodynamic phenotype (PAH-rLHD).

Results

489 patients (I/H/D-PAH=251, CTD-PAH=238) were included in our analysis, with 103 (21.0%) fulfilling the definition of PAH-rLHD (34 had ≥3 risk factors for left heart disease (rLHD-hypertension, diabetes, obesity or ischaemic heart disease) and 76 had borderline haemodynamics (mean capillary wedge pressure 13–15 with pulmonary vascular resistance <500 dynes sec/cm5) including 7 who met both criteria). Compared to classical PAH, patients with PAH-rLHD were older at diagnosis (66±13 vs 58±19, p<0.001), had lower pulmonary vascular resistance (PVR: 393±266 vs 708±391, p=0.031) but worse exercise capacity (6MWD: 286±130m vs 327±136m, p=0.005). PAH-rLHD were more likely to be started on initial monotherapy, compared with “classical” PAH (73% vs 56%, p=0.002). In the monotherapy groups, endothelin receptor antagonists (ERA) were used in 73% PAH-rLHD, compared with 66% in classical PAH group. Both groups exhibited similar response to both mono- and combination therapy with commensurate improvements in WHO functional class (mean change 0.3±0.6 vs 0.3±0.8, p=0.443) and 6-minute walk distance (mean change 44±82 vs 48±101, p=0.723). There was no difference in survival between classical PAH and PAH-rLHD (log rank, p=0.29). The REVEAL 2.0 risk score effectively discriminated risk in both populations at baseline and first follow up (classical PAH: baseline C statistic 0.750, follow up 0.774 and PAH-rLHD: baseline C statistic 0.756, follow up 0.791).

Conclusion

Despite lower PVR at diagnosis, PAH-rLHD patients and “classical” PAH demonstrate similar response to first-line therapy with similar long term survival. The REVEAL 2.0 risk score can be effectively applied to the subpopulation of PAH-rLHD in real life clinical practice.

Funding Acknowledgement

Type of funding sources: None.

Single-cell and bulk transcriptomics of the liver reveals potential targets of NASH with fibrosis

Fibrosis is characterized by the excessive production of collagen and other extracellular matrix (ECM) components and represents a leading cause of morbidity and mortality worldwide. Previous studies of nonalcoholic steatohepatitis (NASH) with fibrosis were largely restricted to bulk transcriptome profiles. Thus, our understanding of this disease is limited by an incomplete characterization of liver cell types in general and hepatic stellate cells (HSCs) in particular, given that activated HSCs are the major hepatic fibrogenic cell population. To help fill this gap, we profiled 17,810 non-parenchymal cells derived from six healthy human livers. In conjunction with public single-cell data of fibrotic/cirrhotic human livers, these profiles enable the identification of potential intercellular signaling axes (e.g., ITGAV-LAMC1, TNFRSF11B-VWF and NOTCH2-DLL4) and master regulators (e.g., RUNX1 and CREB3L1) responsible for the activation of HSCs during fibrogenesis. Bulk RNA-seq data of NASH patient livers and rodent models for liver fibrosis of diverse etiologies allowed us to evaluate the translatability of candidate therapeutic targets for NASH-related fibrosis. We identified 61 liver fibrosis-associated genes (e.g., AEBP1, PRRX1 and LARP6) that may serve as a repertoire of translatable drug target candidates. Consistent with the above regulon results, gene regulatory network analysis allowed the identification of CREB3L1 as a master regulator of many of the 61 genes. Together, this study highlights potential cell-cell interactions and master regulators that underlie HSC activation and reveals genes that may represent prospective hallmark signatures for liver fibrosis.

Optimal liver metabolism and proliferation require the tight junction protein claudin-3

Objective

The expression of hepatic tight junction proteins and their contribution to homeostasis and regeneration remained largely unexplored. Here, we determine the cell type specific expression of tight junction genes in murine livers. We further explore the regulation and functional importance of the transmembrane protein CLDN3 in normal and regenerating livers.

Methods

Murine livers were used for tissue- and single cell RNA-seq. CLDN3 localization was determined by immunofluorescence. CLDN3+/+ or CLDN3-/- livers were analysed by electron microscopy, fluorescence-activated cell sorting and liquid chromatography mass spectrometry. Lipid content was quantified with oil-red. Mice were subjected to 2/3 partial hepatectomy. Proliferation was quantified with Ki67 and pHH3 stainings. Cell cycle gene expression was determined by RT-qPCR. Barrier impairments were assessed with total bile acid measurements. Differential gene expression was analysed by tissue RNAseq with DESeq2.

Results

We determined the profile of tight junction gene expression the main liver cell types, showing that tight junction transcripts can be found in hepatocytes and cholangiocytes but also on non-parenchymal cell populations. CLDN3 was among the highly expressed- and regulated genes in native and regenerating livers. CLDN3 had a zonated expression pattern. CLDN3-/- mice had microscopically intact tight junctions, but showed significantly downregulated hepatic energy metabolism and suboptimal cell proliferation in the regeneration model.

Conclusion

Our data suggests a functional role of CLDN3 for maintenance of energy homeostasis and optimal regeneration, proving that the function of hepatic tight junction proteins extends beyond basic membrane sealing.

Loss of Claudin-3 Impairs Hepatic Metabolism, Biliary Barrier Function, and Cell Proliferation in the Murine Liver

BACKGROUND & AIMS

Tight junctions in the liver are essential to maintain the blood-biliary barrier, however, the functional contribution of individual tight junction proteins to barrier and metabolic homeostasis remains largely unexplored. Here, we describe the cell type-specific expression of tight junction genes in the murine liver, and explore the regulation and functional importance of the transmembrane protein claudin-3 in liver metabolism, barrier function, and cell proliferation.

METHODS

The cell type-specific expression of hepatic tight junction genes is described using our mouse liver single-cell sequencing data set. Differential gene expression in Cldn3-/- and Cldn3+/+ livers was assessed in young and aged mice by RNA sequencing (RNA-seq), and hepatic tissue was analyzed for lipid content and bile acid composition. A surgical model of partial hepatectomy was used to induce liver cell proliferation.

RESULTS

Claudin-3 is a highly expressed tight junction protein found in the liver and is expressed predominantly in hepatocytes and cholangiocytes. The histology of Cldn3-/- livers showed no overt phenotype, and the canalicular tight junctions appeared intact. Nevertheless, by RNA-seq we detected a down-regulation of metabolic pathways in the livers of Cldn3-/- young and aged mice, as well as a decrease in lipid content and a weakened biliary barrier for primary bile acids, such as taurocholic acid, taurochenodeoxycholic acid, and taurine-conjugated muricholic acid. Coinciding with defects in the biliary barrier and lower lipid metabolism, there was a diminished hepatocyte proliferative response in Cldn3-/- mice after partial hepatectomy.

CONCLUSIONS

Our data show that, in the liver, claudin-3 is necessary to maintain metabolic homeostasis, retention of bile acids, and optimal hepatocyte proliferation during liver regeneration. The RNA-seq data set can be accessed at: https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE159914.

Synergistic effect of the TLR5 agonist CBLB502 and its downstream effector IL-22 against liver injury

The toll-like receptor 5 (TLR5) agonist, CBLB502/Entolimod, is a peptide derived from bacterial flagellin and has been shown to protect against radiation-induced tissue damage in animal models. Here we investigated the protective mechanism of CBLB502 in the liver using models of ischemia-reperfusion injury and concanavalin A (ConA) induced immuno-hepatitis. We report that pretreatment of mice with CBLB502 provoked a concomitant activation of NF-κB and STAT3 signaling in the liver and reduced hepatic damage in both models. To understand the underlying mechanism, we screened for cytokines in the serum of CBLB502 treated animals and detected high levels of IL-22. There was no transcriptional upregulation of IL-22 in the liver, rather it was found in extrahepatic tissues, mainly the colon, mesenteric lymph nodes (MLN), and spleen. RNA-seq analysis on isolated hepatocytes demonstrated that the concomitant activation of NF-κB signaling by CBLB502 and STAT3 signaling by IL-22 produced a synergistic cytoprotective transcriptional signature. In IL-22 knockout mice, the loss of IL-22 resulted in a decrease of hepatic STAT3 activation, a reduction in the cytoprotective signature, and a loss of hepatoprotection following ischemia-reperfusion-induced liver injury. Taken together, these findings suggest that CBLB502 protects the liver by increasing hepatocyte resistance to acute liver injury through the cooperation of TLR5-NF-κB and IL-22-STAT3 signaling pathways.

Bayesian correlation is a robust gene similarity measure for single-cell RNA-seq data

Assessing similarity is highly important for bioinformatics algorithms to determine correlations between biological information. A common problem is that similarity can appear by chance, particularly for low expressed entities. This is especially relevant in single-cell RNA-seq (scRNA-seq) data because read counts are much lower compared to bulk RNA-seq. Recently, a Bayesian correlation scheme that assigns low similarity to genes that have low confidence expression estimates has been proposed to assess similarity for bulk RNA-seq. Our goal is to extend the properties of the Bayesian correlation in scRNA-seq data by considering three ways to compute similarity. First, we compute the similarity of pairs of genes over all cells. Second, we identify specific cell populations and compute the correlation in those populations. Third, we compute the similarity of pairs of genes over all clusters, by considering the total mRNA expression. We demonstrate that Bayesian correlations are more reproducible than Pearson correlations. Compared to Pearson correlations, Bayesian correlations have a smaller dependence on the number of input cells. We show that the Bayesian correlation algorithm assigns high similarity values to genes with a biological relevance in a specific population. We conclude that Bayesian correlation is a robust similarity measure in scRNA-seq data.

P4698Survival outcomes in patients with Eisenmenger syndrome after heart-lung or bilateral sequential lung transplantation

Background

Eisenmenger syndrome (ES) is defined as pulmonary hypertension secondary to a right to left intracardiac shunt, commonly an atrial septal defect (ASD) or ventricular septal defect (VSD). Heart-lung (HLTx) or bilateral sequential lung transplantation (BSLT) are both treatment options for some candidates. The choice between these two procedures has varied historically and according to transplant centre preference and donor availability. We completed a retrospective study to determine if BSLT with cardiac repair was associated with better outcomes compared to HLTx.

Aim

This study compared post-transplant survival in patients with ES undergoing HLTx or BSLT.

Method

Using the International Society Heart and Lung Transplantation Registry data, we identified all patients with ES between October 1, 1987 and March 31, 2018.

Results

A total of 177 patients underwent HLTx for ES ASD and 101 who underwent BSLT with cardiac repair. Median follow up was 890 days (range 0–9888 days) for the entire post-transplant cohort. 126 HLTx and 66 BSLT patients died in the follow up period.

A total of 173 ES VSD patients underwent HLTx in the database, and 52 underwent BSLT with cardiac repair. Median follow up was 460 days (range 0–8406 days) for the entire post-transplant cohort. 116 HLTx and 36 BSLT patients died during the follow up period.

Figure 1 demonstratres the comparative Kaplan-Meier survival curves following BSLT or HLTx for Eisenmenger's ASD and VSD patients. No statistically significant difference in Eisenmenger survival between combined heart-lung transplantation or bilateral sequential lung transplantation group (ASD log rank test p value = 0.99, VSD log rank test p value = 0.1 performed for the first 6 year).

Figure 1

Conclusions

Our analysis determined that patients with ES and either VSD or ASD had similar long-term survival comparing HLTx with BSLT and cardiac repair.

4974Waitlist outcomes for Eisenmengers patients listed for bilateral sequential lung transplant or heart-lung transplant

Background

Eisenmenger's syndrome (ES) is the end-stage of a longstanding intracardiac shunt, commonly an atrial septal defect (ASD) or ventricular septal defect (VSD). Transplantation is the final option to address the pulmonary hypertension and right heart failure that results. Both combined heart-lung (HLTx) and bilateral sequential lung transplantation (BSLT) have been performed for ES. Overall, BSLT are performed more commonly than HLTx because of donor organ availability. We postulated that ES patients would have higher waitlist mortality and longer time to transplant compared to patients listed for other indications, and BSLT patients would have reduced waitlist mortality and reduced time to transplant compared to HLTx based on availability.

Aim

This study compared waitlist outcomes between ES ASD, ES VSD and all patients listed for BSLT or HLTx.

Methods

We analysed the Organ Procurement and Transplant Network (OPTN) database for all patients listed for BSLT or HLTx between October 1, 1987 and March 31, 2018. Mood's median test was used for all tests of significance.

Results

Table 1 summarises the results of the analysis. A total of 56,698 patients were on the waitlist for BSLT for all aetiologies, which included 176 ES ASD patients and 156 ES VSD patients. A total of 3231 patients were on the waitlist for HLTx for all aetiologies, which included 89 ES ASD and 176 ES VSD patients. Median time to transplant was significantly longer for all ES patients on the waitlist for BSLT or HLTx compare to patients listed for other indications. Comparing time to transplant for BSLT to HLTx for either ES ASD or VSD did not reach statistical significance. Waitlist mortality was substantially higher for all ES patients regardless whether they were listed for BSLT or HLTx compared to patients listed for other indications.

Table 1 ES ASD ES VSD All patients BSLT HLTx BSLT HLTx BSLT HLTx Total number of patients listed 176 89 156 176 56698 3231 Transplanted 58 (33.0%) 38 (42.7%) 41 (25.8%) 78 (44.3%) 36441 (64.3%) 1229 (38.0%) Median time to transplant in days 330 (24 to 2723)* 431 (11 to 4527)$ 517 (10 to 2345)# 292 (16 to 2399)& 99 (0 to 6592) 174 (0 to 3606) p=0.54 p=0.08 *p≤0.001, #p=≤0.0001 $p=0.000, &p=0.003 Wait list mortality 27 (15.3%) 25 (28.1%) 23 (14.5%) 46 (26.1%) 2366 (4.2%) 371 (11.5%)

Conclusion

Our analysis identified longer waitlist time and higher mortality for all ES patients listed for BSLT or HLTx in the United States. These findings indicate current listing methods and prognostication place the ES population at disadvantage for thoracic transplantation.

Evaluation of the Function of Primary Human Hepatocytes Co-Cultured with the Human Hepatic Stellate Cell (HSC) Line LI90

Most bioartificial liver devices utilise primary hepatocytes alone although some have considered the use of non parenchymal cells in addition. However the effects of co-culture of human hepatocytes with different sinusoidal cell types has not been fully investigated. In this study we have examined the influence of co-culturing primary human hepatocytes with the human hepatic stellate cell (HSC) line, LI90. Cultures were monitored by light microscopy and on days 4, 8 and 14 urea synthesis and cytochrome P450 activity were measured. Morphologically LI90 cells proliferated to fill spaces between and into adjacent islands of hepatocytes. On day 14 cytochrome P450 activity in co-culture was significantly improved compared to hepatocytes cultured alone. By contrast, urea synthesis in hepatocytes was unaffected by single or co-culture. Therefore it can be concluded that a combination of primary human hepatocytes with LI90 cells is beneficial for growth and some stability of hepatocytes and may therefore be appropriate for seeding bioartificial liver devices.

Impaired liver regeneration in aged mice can be rescued by silencing Hippo core kinases MST1 and MST2

The liver has an intrinsic capacity to regenerate in response to injury or surgical resection. Nevertheless, circumstances in which hepatocytes are unresponsive to proliferative signals result in impaired regeneration and hepatic failure. As the Hippo pathway has a canonical role in the maintenance of liver size, we investigated whether it could serve as a therapeutic target to support regeneration. Using a standard two‐thirds partial hepatectomy (PH) model in young and aged mice, we demonstrate that the Hippo pathway is modulated across the phases of liver regeneration. The activity of the core kinases MST1 and LATS1 increased during the early hypertrophic phase and returned to steady state levels in the proliferative phase, coinciding with activation of YAP1 target genes and hepatocyte proliferation. Moreover, following PH in aged mice, we demonstrate that Hippo signaling is anomalous in non‐regenerating livers. We provide pre‐clinical evidence that silencing the Hippo core kinases MST1 and MST2 with siRNA provokes hepatocyte proliferation in quiescent livers and rescues liver regeneration in aged mice following PH. Our data suggest that targeting the Hippo core kinases MST1/2 has therapeutic potential to improve regeneration in non‐regenerative disorders.

The Sydney Heart Bank: improving translational research while eliminating or reducing the use of animal models of human heart disease

The Sydney Heart Bank (SHB) is one of the largest human heart tissue banks in existence. Its mission is to provide high-quality human heart tissue for research into the molecular basis of human heart failure by working collaboratively with experts in this field. We argue that, by comparing tissues from failing human hearts with age-matched non-failing healthy donor hearts, the results will be more relevant than research using animal models, particularly if their physiology is very different from humans. Tissue from heart surgery must generally be used soon after collection or it significantly deteriorates. Freezing is an option but it raises concerns that freezing causes substantial damage at the cellular and molecular level. The SHB contains failing samples from heart transplant patients and others who provided informed consent for the use of their tissue for research. All samples are cryopreserved in liquid nitrogen within 40 min of their removal from the patient, and in less than 5-10 min in the case of coronary arteries and left ventricle samples. To date, the SHB has collected tissue from about 450 failing hearts (>15,000 samples) from patients with a wide range of etiologies as well as increasing numbers of cardiomyectomy samples from patients with hypertrophic cardiomyopathy. The Bank also has hearts from over 120 healthy organ donors whose hearts, for a variety of reasons (mainly tissue-type incompatibility with waiting heart transplant recipients), could not be used for transplantation. Donor hearts were collected by the St Vincent's Hospital Heart and Lung transplantation team from local hospitals or within a 4-h jet flight from Sydney. They were flushed with chilled cardioplegic solution and transported to Sydney where they were quickly cryopreserved in small samples. Failing and/or donor samples have been used by more than 60 research teams around the world, and have resulted in more than 100 research papers. The tissues most commonly requested are from donor left ventricles, but right ventricles, atria, interventricular system, and coronary arteries vessels have also been reported. All tissues are stored for long-term use in liquid N or vapor (170-180 °C), and are shipped under nitrogen vapor to avoid degradation of sensitive molecules such as RNAs and giant proteins. We present evidence that the availability of these human heart samples has contributed to a reduction in the use of animal models of human heart failure.

Could Connexin 43 dependent ATP release represent a new therapeutic target for sepsis?

During sepsis, ATP is released into the extracellular space where it modulates immune response via specific receptors and ectonucleotidases present on various immune cells. ATP can be released by hemichannel Connexin 43 (Cx43). Here, we examine the importance of Cx43 mediated ATP release in macrophages and the role of this pathway in modulating innate immune responses in the context of sepsis.

For murine sepsis model, caecal ligation and puncture (CLP) was used. Mice were treated with Gap27, a Cx43 inhibitor. Liver, lung, spleen, bone marrow, peritoneal fluid and blood cells expressing Cx43 were characterized (IHC, FACS). Macrophages were isolated from peritoneum and liver of wild-type mice and stimulated with PAMPs. ATP was quantified using luciferin-luciferase assay. Cytokine levels (ELISA), gene expression (qPCR) and protein expression (immunoblot) were assessed.

Blocking of Cx43 during CLP prolonged survival up to 48 hours in comparison with 24 hours for controls. In addition, it decreased systemic levels of inflammatory cytokines (TNFa, IL1b and IL6) and chemokines (CCL2) and lowered bacterial load (CFU/ml) in the blood and peritoneal fluid. Cx43 was not constitutively expressed in the liver, but was induced following CLP. Cells expressing Cx43 in septic livers were identified as infiltrating M1 macrophages and neutrophils. Ex vivo, Cx43 expression was upregulated in primary macrophages upon stimulation with LPS. Macrophages were actively releasing ATP in response to TLR 4 and 2 agonists, and Cx43 inhibition reduced extracellular ATP levels.

We observed improved survival to sepsis by blocking Cx43. By mediating release of ATP, and potentially other DAMP, Cx43 might overactivate macrophages and exacerbate the immune response.

P2X1-regulated IL-22 secretion by innate lymphoid cells is required for efficient liver regeneration

Paracrine signalling mediated by cytokine secretion is essential for liver regeneration after hepatic resection, yet the mechanisms of cellular crosstalk between immune and parenchymal cells are still elusive. Interleukin-22 (IL-22) is released by immune cells and mediates strong hepatoprotective functions. However, it remains unclear whether IL-22 is critical for the crosstalk between liver lymphocytes and parenchymal cells during liver regeneration after partial hepatectomy (PH). Here, we found that plasma levels of IL-22 and its upstream cytokine, IL-23, are highly elevated in patients after major liver resection. In a mouse model of PH, deletion of IL-22 was associated with significantly delayed hepatocellular proliferation and an increase of hepatocellular injury and endoplasmic reticulum stress. Using Rag1(-/-) and Rag2(-/-) γc(-/) (-) mice, we show that the main producers of IL-22 post-PH are conventional natural killer cells and innate lymphoid cells type 1. Extracellular adenosine triphosphate (ATP), a potent danger molecule, is elevated in patients immediately after major liver resection. Antagonism of the P2-type nucleotide receptors, P2X1 and P2Y6, significantly decreased IL-22 secretion ex vivo. In vivo, specific inhibition of P2X1 was associated with decreased IL-22 secretion, elevated liver injury, and impaired liver regeneration.

CONCLUSION

This study shows that innate immune cell-derived IL-22 is required for efficient liver regeneration and that secretion of IL-22 in the regenerating liver is modulated by the ATP receptor, P2X1. (Hepatology 2016;63:2004-2017).

Frequency and Pathophysiology of Acute Liver Failure in Ornithine Transcarbamylase Deficiency (OTCD)

Background

Acute liver failure (ALF) has been reported in ornithine transcarbamylase deficiency (OTCD) and other urea cycle disorders (UCD). The frequency of ALF in OTCD is not well-defined and the pathogenesis is not known.

Aim

To evaluate the prevalence of ALF in OTCD, we analyzed the Swiss patient cohort. Laboratory data from 37 individuals, 27 females and 10 males, diagnosed between 12/1991 and 03/2015, were reviewed for evidence of ALF. In parallel, we performed cell culture studies using human primary hepatocytes from a single patient treated with ammonium chloride in order to investigate the inhibitory potential of ammonia on hepatic protein synthesis.

Results

More than 50% of Swiss patients with OTCD had liver involvement with ALF at least once in the course of disease. Elevated levels of ammonia often correlated with (laboratory) coagulopathy as reflected by increased values for international normalized ratio (INR) and low levels of hepatic coagulation factors which did not respond to vitamin K. In contrast, liver transaminases remained normal in several cases despite massive hyperammonemia and liver involvement as assessed by pathological INR values. In our in vitro studies, treatment of human primary hepatocytes with ammonium chloride for 48 hours resulted in a reduction of albumin synthesis and secretion by approximately 40%.

Conclusion

In conclusion, ALF is a common complication of OTCD, which may not always lead to severe symptoms and may therefore be underdiagnosed. Cell culture experiments suggest an ammonia-induced inhibition of hepatic protein synthesis, thus providing a possible pathophysiological explanation for hyperammonemia-associated ALF.