A Western diet with alcohol in drinking water recapitulates features of alcohol-associated liver disease in mice

Emerging concepts in alcohol, infection & immunity: A summary of the 2023 alcohol and immunology research interest group (AIRIG) meeting

On December 8th 2023, the annual Alcohol and Immunology Research Interest Group (AIRIG) meeting was held at the University of Colorado Anschutz Medical Campus in Aurora, Colorado. The 2023 meeting focused broadly on how acute and chronic alcohol exposure leads to immune dysregulation, and how this contributes to damage in multiple tissues and organs. These include impaired lung immunity, intestinal dysfunction, autoimmunity, the gut-Central Nervous System (CNS) axis, and end-organ damage. In addition, diverse areas of alcohol research covered multiple pathways behind alcohol-induced cellular dysfunction, including inflammasome activation, changes in miRNA expression, mitochondrial metabolism, gene regulation, and transcriptomics. Finally, the work presented at this meeting highlighted novel biomarkers and therapeutic interventions for patients suffering from alcohol-induced organ damage.

Protective role of 17β-estradiol in alcohol-associated liver fibrosis is mediated by suppression of integrin signaling

BACKGROUND

Alcohol-associated liver disease is a complex disease regulated by genetic and environmental factors such as diet and sex. The combination of high-fat diet and alcohol consumption has synergistic effects on liver disease progression. Female sex hormones are known to protect females from liver disease induced by high-fat diet. In contrast, they promote alcohol-mediated liver injury. We aimed to define the role of female sex hormones on liver disease induced by a combination of high-fat diet and alcohol.

METHODS

Wild-type and protein arginine methyltransferase (Prmt)6 knockout female mice were subjected to gonadectomy (ovariectomy, OVX) or sham surgeries and then fed western diet and alcohol in the drinking water.

RESULTS

We found that female sex hormones protected mice from western diet/alcohol-induced weight gain, liver steatosis, injury, and fibrosis. Our data suggest that these changes are, in part, mediated by estrogen-mediated induction of arginine methyltransferase PRMT6. Liver proteome changes induced by OVX strongly correlated with changes induced by Prmt6 knockout. Using Prmt6 knockout mice, we confirmed that OVX-mediated weight gain, steatosis, and injury are PRMT6 dependent, while OVX-induced liver fibrosis is PRMT6 independent. Proteomic and gene expression analyses revealed that estrogen signaling suppressed the expression of several components of the integrin pathway, thus reducing integrin-mediated proinflammatory (Tnf, Il6) and profibrotic (Tgfb1, Col1a1) gene expression independent of PRMT6 levels. Integrin signaling inhibition using Arg-Gly-Asp peptides reduced proinflammatory and profibrotic gene expression in mice, suggesting that integrin suppression by estrogen is protective against fibrosis development.

CONCLUSIONS

Taken together, estrogen signaling protects mice from liver disease induced by a combination of alcohol and high-fat diet through upregulation of Prmt6 and suppression of integrin signaling.

Kupffer cell diversity maintains liver function in alcohol-associated liver disease

BACKGROUND AND AIMS

Liver macrophages are heterogeneous and play an important role in alcohol-associated liver disease (ALD) but there is limited understanding of the functions of specific macrophage subsets in the disease. We used a Western diet alcohol (WDA) mouse model of ALD to examine the hepatic myeloid cell compartment by single cell RNAseq and targeted KC ablation to understand the diversity and function of liver macrophages in ALD.

APPROACH AND RESULTS

In the WDA liver, KCs and infiltrating monocytes/macrophages each represented about 50% of the myeloid pool. Five major KC clusters all expressed genes associated with receptor-mediated endocytosis and lipid metabolism, but most were predicted to be noninflammatory and antifibrotic with 1 minor KC cluster having a proinflammatory and extracellular matrix degradation gene signature. Infiltrating monocyte/macrophage clusters, in contrast, were predicted to be proinflammatory and profibrotic. In vivo, diphtheria toxin-based selective KC ablation during alcohol exposure resulted in a liver failure phenotype with increases in PT/INR and bilirubin, loss of differentiated hepatocyte gene expression, and an increase in expression of hepatocyte progenitor markers such as EpCAM, CK7, and Igf2bp3. Gene set enrichment analysis of whole-liver RNAseq from the KC-ablated WDA mice showed a similar pattern as seen in human alcoholic hepatitis.

CONCLUSIONS

In this ALD model, KCs are anti-inflammatory and are critical for the maintenance of hepatocyte differentiation. Infiltrating monocytes/macrophages are largely proinflammatory and contribute more to liver fibrosis. Future targeting of specific macrophage subsets may provide new approaches to the treatment of liver failure and fibrosis in ALD.

Alcohol-associated liver disease

Alcohol-associated liver disease (ALD) is a major cause of chronic liver disease worldwide, and comprises a spectrum of several different disorders, including simple steatosis, steatohepatitis, cirrhosis, and superimposed hepatocellular carcinoma. Although tremendous progress has been made in the field of ALD over the last 20 years, the pathogenesis of ALD remains obscure, and there are currently no FDA-approved drugs for the treatment of ALD. In this Review, we discuss new insights into the pathogenesis and therapeutic targets of ALD, utilizing the study of multiomics and other cutting-edge approaches. The potential translation of these studies into clinical practice and therapy is deliberated. We also discuss preclinical models of ALD, interplay of ALD and metabolic dysfunction, alcohol-associated liver cancer, the heterogeneity of ALD, and some potential translational research prospects for ALD.

Alcohol-induced epigenetic changes prevent fibrosis resolution after alcohol cessation in miceresolution

BACKGROUND AND AIMS

Alcohol-associated liver disease is a major cause of alcohol-associated mortality. Recently, we identified hepatic demethylases lysine demethylase (KDM)5B and KDM5C as important epigenetic regulators of alcohol response in the liver. In this study, we aimed to investigate the role of KDM5 demethylases in alcohol-associated liver disease resolution.

APPROACH AND RESULTS

We showed that alcohol-induced liver steatosis rapidly resolved after alcohol cessation. In contrast, fibrosis persisted in the liver for up to 8 weeks after the end of alcohol exposure. Defects in fibrosis resolution were in part due to alcohol-induced KDM5B and KDM5C-dependent epigenetic changes in hepatocytes. Using cell-type-specific knockout mice, we found that adeno-associated virus-mediated knockout of KDM5B and KDM5C demethylases in hepatocytes at the time of alcohol withdrawal promoted fibrosis resolution. Single-cell ATAC sequencing analysis showed that during alcohol-associated liver disease resolution epigenetic cell states largely reverted to control conditions. In addition, we found unique epigenetic cell states distinct from both control and alcohol states and identified associated transcriptional regulators, including liver X receptor (LXR) alpha (α). In vitro and in vivo analysis confirmed that knockout of KDM5B and KDM5C demethylases promoted LXRα activity, likely through regulation of oxysterol biosynthesis, and this activity was critical for the fibrosis resolution process. Reduced LXR activity by small molecule inhibitors prevented fibrosis resolution in KDM5-deficient mice.

CONCLUSIONS

In summary, KDM5B and KDM5C demethylases prevent liver fibrosis resolution after alcohol cessation in part through suppression of LXR activity.

Glabridin ameliorates intracellular events caused by palmitic acid and alcohol in mouse hepatocytes and fast food diet and alcohol -induced steatohepatitis and fibrosis in C57BL/6J mice model

Steatohepatitis is a significant risk factor for end-stage liver disease. In this study, the therapeutic potential of Glabridin (GBD), an isoflavan derived from Glycyrrhiza glabra, is investigated in in-vitro and in-vivo models against palmitic acid (PA) or fast food (FF) diet + alcohol (EtOH). Mouse hepatocytes (AML-12 cells) were treated with PA; 250 μM + EtOH; 250 μM ± GBD (10 μM and 25 μM) for 24 h. C57BL/6J mice fed with standard chow (SC) diet, fast food (FF) diet + intermittent oral ingestion of EtOH (10-50%v/v) ± GBD (20 mg/kg and 40 mg/kg) for eight (8) weeks, were analyzed for histological features of steatohepatitis and fibrosis, biochemical indexes, and protein and gene expression studies related to oxidative stress, inflammation, lipogenesis, fibrosis, and apoptosis. GBD therapy considerably reduced intracellular events in AML-12 cells exposed to PA + EtOH. GBD treatments significantly improved body metrics, biochemical indexes, and histological features in C57BL/6J mice compared to FF + EtOH. Moreover, protein and gene expression investigations revealed a strong therapeutic effects on oxidative stress, inflammation, steatosis, fibrosis, and apoptosis -related molecular signaling cascades. In conclusion, these findings suggest that GBD has a strong therapeutic potential to be developed as anti-steatohepatitis/fibrosis medicine.

New murine model of alcoholic hepatitis in obesity-induced metabolic-associated fatty liver disease

Metabolic-associated fatty liver disease (MAFLD) and alcoholic hepatitis (AH) are among the most prevalent liver diseases worldwide, and their coexistence is common in clinical practice. However, currently established models of MAFLD-AH coexistence do not fully replicate their pathological characteristics and require sophisticated experimental techniques. Therefore, we aimed to develop an easily replicable model that mimics obesity-induced MAFLD-AH in patients. Our goal was to establish a murine model that replicates MAFLD and AH coexistence, resulting in significant liver injury and inflammation. To this end, we administered a single ethanol gavage dose to ob/ob mice on a chow diet. The administration of a single dose of ethanol led to elevated serum transaminase levels, increased liver steatosis, and apoptosis in ob/ob mice. Furthermore, ethanol binge caused a significant increase in oxidative stress in ob/ob mice, as measured via 4-hydroxynonenal. Importantly, the single dose of ethanol also markedly exacerbated liver neutrophil infiltration and upregulated the hepatic mRNA expression of several chemokines and neutrophil-related proteins, including Cxcl1, Cxcl2, and Lcn2. Whole-liver transcriptomic analysis revealed that ethanol-induced changes in gene expression profile shared similar features with AH and MAFLD. In ob/ob mice, a single dose of ethanol binge caused significant liver injury and neutrophil infiltration. This easy-to-replicate murine model successfully mimics the pathological and clinical features of patients with coexisting MAFLD and AH and closely resembles the transcriptional regulation seen in human disease.

Single ethanol binge causes severe liver injury in mice fed Western diet

BACKGROUND AND AIMS

Alcohol-associated liver disease (ALD) and NAFLD often coexist in Western societies that consume energy-rich and cholesterol-containing Western diets. Increased rates of ALD mortality in young people in these societies are likely attributable to binge drinking. It is largely unknown how alcohol binge causes liver damage in the setting of Western diets.

APPROACH AND RESULTS

In this study, we showed that a single ethanol binge (5 g/kg body weight) induced severe liver injury as shown by marked increases in serum activities of the 2 aminotransferases AST and ALT in C57BL/6J mice that have been fed a Western diet for 3 weeks. The Western diet plus binge ethanol-fed mice also displayed severe lipid droplet deposition and high contents of triglycerides and cholesterol in the liver, which were associated with increased lipogenic and reduced fatty acid oxidative gene expression. These animals had the highest Cxcl1 mRNA expression and myeloperoxidase (MPO)-positive neutrophils in the liver. Their hepatic ROS and lipid peroxidation were the highest, but their hepatic levels of mitochondrial oxidative phosphorylation proteins remained largely unaltered. Hepatic levels of several ER stress markers, including mRNAs for CHOP, ERO1A, ERO1B, BIM, and BIP, as well as Xbp1 splicing and proteins for BIP/GRP78 and IRE-α were also the highest in these animals. Interestingly, Western diet feeding for 3 weeks or ethanol binge dramatically increased hepatic caspase 3 cleavage, and the combination of the 2 did not further increase it. Thus, we successfully established a murine model of acute liver injury by mimicking human diets and binge drinking.

CONCLUSIONS

This simple Western diet plus single ethanol binge model recapitulates major hepatic phenotypes of ALD, including steatosis and steatohepatitis characterized by neutrophil infiltration, oxidative stress, and ER stress.

A small animal model of NASH with progressive steatohepatitis -induced by fast food diet and alcohol in C57BL/6J mouse with high human pathophysiological proximity

Non-alcoholic steatohepatitis (NASH) and alcoholic steatohepatitis (ASH) both can progress to end-stage liver disease (ESLD). No relevant animal models are available for studying the toxic consequences of concurrent fast food diet- and alcohol usage in fibrosing NASH. As a result, dependable and short-term In-vivo models capable of recapitulating human disease pathophysiology are required for deciphering mechanistic insights and preclinical drug discovery programs. The current study aims to develop a mouse model for progressive steatohepatitis employing a fast food (FF) diet with intermittent oral alcohol (EtOH) administration. For eight (8) weeks, C57BL/6 J mice were fed standard chow (SC) diet ± EtOH or FF ± EtOH. EtOH uses enhanced the histological characteristics of FF-induced steatohepatitis and fibrosis. A dysregulated molecular signaling cascade related to oxidative stress, steatosis, fibrosis, DNA damage, and apoptosis was evident at protein and gene expression levels in the FF + EtOH. The results from the in-vivo model were replicated in mouse hepatocyte cultures (AML-12) subjected to palmitic acid (PA) ± EtOH exposures. The results of the present study indicate that the clinical hallmarks of human progressive steatohepatitis and fibrosis were achieved in our mice model, showing its suitability for preclinical research.

Hepatocyte-Specific Triggering of Hepatic Stellate Cell Profibrotic Activation by Apoptotic Bodies: The Role of Hepatoma-Derived Growth Factor, HIV, and Ethanol

Liver disease is one of the leading comorbidities in HIV infection. The risk of liver fibrosis development is potentiated by alcohol abuse. In our previous studies, we reported that hepatocytes exposed to HIV and acetaldehyde undergo significant apoptosis, and the engulfment of apoptotic bodies (ABs) by hepatic stellate cells (HSC) potentiates their pro-fibrotic activation. However, in addition to hepatocytes, under the same conditions, ABs can be generated from liver-infiltrating immune cells. The goal of this study is to explore whether lymphocyte-derived ABs trigger HSC profibrotic activation as strongly as hepatocyte-derived ABs. ABs were generated from Huh7.5-CYP2E1 (RLW) cells and Jurkat cells treated with HIV+acetaldehyde and co-culture with HSC to induce their pro-fibrotic activation. ABs cargo was analyzed by proteomics. ABs generated from RLW, but not from Jurkat cells activated fibrogenic genes in HSC. This was driven by the expression of hepatocyte-specific proteins in ABs cargo. One of these proteins is Hepatocyte-Derived Growth Factor, for which suppression attenuates pro-fibrotic activation of HSC. In mice humanized with only immune cells but not human hepatocytes, infected with HIV and fed ethanol, liver fibrosis was not observed. We conclude that HIV+ABs of hepatocyte origin promote HSC activation, which potentially may lead to liver fibrosis progression.

A Pathogenic Role of Non-Parenchymal Liver Cells in Alcohol-Associated Liver Disease of Infectious and Non-Infectious Origin

Now, much is known regarding the impact of chronic and heavy alcohol consumption on the disruption of physiological liver functions and the induction of structural distortions in the hepatic tissues in alcohol-associated liver disease (ALD). This review deliberates the effects of alcohol on the activity and properties of liver non-parenchymal cells (NPCs), which are either residential or infiltrated into the liver from the general circulation. NPCs play a pivotal role in the regulation of organ inflammation and fibrosis, both in the context of hepatotropic infections and in non-infectious settings. Here, we overview how NPC functions in ALD are regulated by second hits, such as gender and the exposure to bacterial or viral infections. As an example of the virus-mediated trigger of liver injury, we focused on HIV infections potentiated by alcohol exposure, since this combination was only limitedly studied in relation to the role of hepatic stellate cells (HSCs) in the development of liver fibrosis. The review specifically focusses on liver macrophages, HSC, and T-lymphocytes and their regulation of ALD pathogenesis and outcomes. It also illustrates the activation of NPCs by the engulfment of apoptotic bodies, a frequent event observed when hepatocytes are exposed to ethanol metabolites and infections. As an example of such a double-hit-induced apoptotic hepatocyte death, we deliberate on the hepatotoxic accumulation of HIV proteins, which in combination with ethanol metabolites, causes intensive hepatic cell death and pro-fibrotic activation of HSCs engulfing these HIV- and malondialdehyde-expressing apoptotic hepatocytes.

Arginine Methylation of Integrin Alpha-4 Prevents Fibrosis Development in Alcohol-Associated Liver Disease

BACKGROUND & AIMS

Alcohol-associated liver disease (ALD) comprises a spectrum of disorders including steatosis, steatohepatitis, fibrosis, and cirrhosis. We aimed to study the role of protein arginine methyltransferase 6 (PRMT6), a new regulator of liver function, in ALD progression.

METHODS

Prmt6-deficient mice and wild-type littermates were fed Western diet with alcohol in the drinking water for 16 weeks. Mice fed standard chow diet or Western diet alone were used as a control.

RESULTS

We found that PRMT6 expression in the liver is down-regulated in 2 models of ALD and negatively correlates with disease severity in mice and human liver specimens. Prmt6-deficient mice spontaneously developed liver fibrosis after 1 year and more advanced fibrosis after high-fat diet feeding or thioacetamide treatment. In the presence of alcohol Prmt6 deficiency resulted in a dramatic increase in fibrosis development but did not affect lipid accumulation or liver injury. In the liver PRMT6 is primarily expressed in macrophages and endothelial cells. Transient replacement of knockout macrophages with wild-type macrophages in Prmt6 knockout mice reduced profibrotic signaling and prevented fibrosis progression. We found that PRMT6 decreases profibrotic signaling in liver macrophages via methylation of integrin α-4 at R464 residue. Integrin α-4 is predominantly expressed in infiltrating monocyte derived macrophages. Blocking monocyte infiltration into the liver with CCR2 inhibitor reduced fibrosis development in knockout mice and abolished differences between genotypes.

CONCLUSIONS

Taken together, our data suggest that alcohol-mediated loss of Prmt6 contributes to alcohol-associated fibrosis development through reduced integrin methylation and increased profibrotic signaling in macrophages.

Alcohol-associated fibrosis in females is mediated by female-specific activation of lysine demethylases KDM5B and KDM5C

Alcohol-associated liver disease is a major cause of alcohol-related mortality. However, the mechanisms underlying disease progression are not fully understood. Recently we found that liver molecular pathways are altered by alcohol consumption differently in males and females. We were able to associate these sex-specific pathways with two upstream regulators: H3K4-specific demethylase enzymes KDM5B and KDM5C. Mice were fed the Lieber-DeCarli alcohol liquid diet for 3 weeks or a combination of a high-fat diet with alcohol in water for 16 weeks (western diet alcohol model [WDA] model). To assess the role of histone demethylases, mice were treated with AAV-shControl, AAV-shKdm5b, and/or AAV-shKdm5c and/or AAV-shAhR vectors. Gene expression and epigenetic changes after Kdm5b/5c knockdown were assessed by RNA-sequencing and H3K4me3 chromatin immunoprecipitation analysis. We found that less than 5% of genes affected by Kdm5b/Kdm5c knockdown were common between males and females. In females, Kdm5b/Kdm5c knockdown prevented fibrosis development in mice fed the WDA alcohol diet for 16 weeks and decreased fibrosis-associated gene expression in mice fed the Lieber-DeCarli alcohol liquid diet. In contrast, fibrosis was not affected by Kdm5b/Kdm5c knockdown in males. We found that KDM5B and KDM5C promote fibrosis in females through down-regulation of the aryl hydrocarbon receptor (AhR) pathway components in hepatic stellate cells. Kdm5b/Kdm5c knockdown resulted in an up-regulation of Ahr, Arnt, and Aip in female but not in male mice, thus preventing fibrosis development. Ahr knockdown in combination with Kdm5b/Kdm5c knockdown restored profibrotic gene expression. Conclusion: KDM5 demethylases contribute to differences between males and females in the alcohol response in the liver. The KDM5/AhR axis is a female-specific mechanism of fibrosis development in alcohol-fed mice.

Male-Specific Activation of Lysine Demethylases 5B and 5C Mediates Alcohol-Induced Liver Injury and Hepatocyte Dedifferentiation

Alcohol-associated liver disease (ALD) is a major cause of alcohol-related mortality. Sex differences in sensitivity to ALD are well described, but these are often disregarded in studies of ALD development. We aimed to define sex-specific pathways in liver exposed to alcohol. Mice were fed the Lieber-DeCarli alcohol liquid diet or a combination of a high-fat diet with alcohol in water. Single-cell RNA sequencing (scRNA-Seq) was performed on liver cells from male and female mice. Mice were treated with adeno-associated virus (AAV)-short hairpin (sh)Control or AAV-sh lysine demethylase 5b (shKdm5b) and/or AAV-shKdm5c vectors. Changes after Kdm5b/5c knockdown were assessed by RNA-Seq and histone H3 lysine K4 (H3K4)me3 chromatin immunoprecipitation-Seq analysis. Using scRNA-Seq analysis, we found several sex-specific pathways induced by alcohol, including pathways related to lipid metabolism and hepatocyte differentiation. Bioinformatic analysis suggested that two epigenetic regulators, H3K4-specific lysine demethylases KDM5B and KDM5C, contribute to sex differences in alcohol effects. We found that in alcohol-fed male mice, KDM5B and KDM5C are involved in hepatocyte nuclear factor 4 alpha (Hnf4a) down-regulation, hepatocyte dedifferentiation, and an increase in fatty acid synthesis. This effect is mediated by alcohol-induced KDM5B and KDM5C recruitment to Hnf4a and other gene promoters in male but not in female mice. Kdm5b and Kdm5c knockdown or KDM5-inhibitor treatment prevented alcohol-induced lipid accumulation and restored levels of Hnf4a and other hepatocyte differentiation genes in male mice. In addition, Kdm5b knockdown prevented hepatocellular carcinoma development in male mice by up-regulating Hnf4a and decreasing tumor cell proliferation. Conclusion: Alcohol specifically activates KDM5 demethylases in male mice to promote alcohol-induced hepatocyte dedifferentiation and tumor development.

High-Fat Diet Augments the Effect of Alcohol on Skeletal Muscle Mitochondrial Dysfunction in Mice

Previous studies have shown that chronic heavy alcohol consumption and consumption of a high-fat (HF) diet can independently contribute to skeletal muscle oxidative stress and mitochondrial dysfunction, yet the concurrent effect of these risk factors remains unclear. We aimed to assess the effect of alcohol and different dietary compositions on mitochondrial activity and oxidative stress markers. Male and female mice were randomized to an alcohol (EtOH)-free HF diet, a HF + EtOH diet, or a low-Fat (LF) + EtOH diet for 6 weeks. At the end of the study, electron transport chain complex activity and expression as well as antioxidant activity and expression, were measured in skeletal muscles. Complex I and III activity were diminished in muscles of mice fed a HF + EtOH diet relative to the EtOH-free HF diet. Lipid peroxidation was elevated, and antioxidant activity was diminished, in muscles of mice fed a HF + EtOH diet as well. Consumption of a HF diet may exacerbate the negative effects of alcohol on skeletal muscle mitochondrial health and oxidative stress.