Inhibition of hepatocyte autophagy increases tumor necrosis factor-dependent liver injury by promoting caspase-8 activation. Cell Death Differ. 2013;20:878-887. [PMID: 23519075 DOI: 10.1038/cdd.2013.21]

Mefunidone ameliorates acute liver failure in mice by inhibiting MKK4-JNK pathway

Acute liver failure (ALF) is a critical condition that can lead to substantial liver dysfunction. It is characterized by complex clinical manifestations and rapid progression, presenting significant challenges in diagnosis and treatment. We investigated the protective effect of mefunidone (MFD), a novel antifibrosis pyridone agent, on ALF in mice, and explored its potential mechanism of action. MFD pretreatment can alleviate lipopolysaccharide (LPS) and d-galactosamine (D-GalN)-induced ALF, reduce hepatocyte apoptosis, and reduce inflammation and oxidative stress. Additionally, MFD alleviated LPS/D-GalN-stimulated reactive oxygen species (ROS) production and cell death in AML12 cells. RNA sequencing enrichment analysis showed that MFD significantly affected the Mitogen-Activated Protein Kinase (MAPK) pathway. In vivo and in vitro experiments showed that MFD inhibited MKK4 and JNK phosphorylation. JNK activation caused by MKK4 and JNK activators could eliminate the therapeutic effect of MFD on AML12. In addition, MFD pretreatment alleviated ConA-induced ALF, reduced inflammation and oxidative stress in mice, and reduced mouse mortality. These results suggest that MFD can potentially protect against ALF, partially by inhibiting the MKK4-JNK pathway, and is a promising new therapeutic drug for ALF.

Paraoxonase-2 agonist vutiglabridin promotes autophagy activation and mitochondrial function to alleviate non-alcoholic steatohepatitis

BACKGROUND AND PURPOSE

Only limited therapeutic agents have been developed for non-alcoholic steatohepatitis (NASH). Glabridin, a promising anti-obesity candidate, has only limited druggability due to its low in vivo chemical stability and bioavailability. Therefore, we developed vutiglabridin (VUTI), which is based on a glabridin backbone, and investigated its mechanism of action in treating NASH in animal models.

EXPERIMENTAL APPROACH

Anti-NASH effects of VUTI were determined in in vitro fatty liver models, spheroids of primary human hepatocytes and L02 normal liver cell lines. To identify VUTI possible cellular target/s, biotin-labelled VUTI was synthesized and underwent chemical proteomic analysis. Further, the evaluation of VUTI therapeutic efficacy was carried out using an amylin-NASH and high-fat (HF) diet-induced obese (DIO) mouse models. This was carried out using transcriptomic, lipidomic and proteomic analyses of the livers from the amylin-NASH mouse model.

KEY RESULTS

VUTI treatment markedly reduces hepatic steatosis, fibrosis and inflammation by promoting lipid catabolism, activating autophagy and improving mitochondrial dysfunction, all of which are hallmarks of effective NASH treatment. The cellular target of VUTI was identified as paraoxonase 2 (PON2), a newly proposed protein target for the treatment of NASH, VUTI enhanced PON2 activity. The results using PON2 knockdown cells demonstrated that PON2 is important for VUTI- activation of autophagy, promoting mitochondrial function, decreasing oxidative stress and alleviating lipid accumulation under lipotoxic condition.

CONCLUSION AND IMPLICATIONS

Our data demonstrated that VUTI is a promising therapeutic for NASH. Targeting PON2 may be important for improving liver function in various immune-metabolic diseases including NASH.

Targeting autophagy overcomes cancer-intrinsic resistance to CAR-T immunotherapy in B-cell malignancies

BACKGROUND

Chimeric antigen receptor T (CAR-T) therapy has substantially revolutionized the clinical outcomes of patients with hematologic malignancies, but the cancer-intrinsic mechanisms underlying resistance to CAR-T cells remain yet to be fully understood. This study aims to explore the molecular determinants of cancer cell sensitivity to CAR-T cell-mediated killing and to provide a better understanding of the underlying mechanisms and potential modulation to improve clinical efficacy.

METHODS

The human whole-genome CRISPR/Cas9-based knockout screening was conducted to identify key genes that enable cancer cells to evade CD19 CAR-T-cell-mediated killing. The in vitro cytotoxicity assays and evaluation of tumor tissue and bone marrow specimens were further conducted to confirm the role of the key genes in cancer cell susceptibility to CAR-T cells. In addition, the specific mechanisms influencing CAR-T cell-mediated cancer clearance were elucidated in mouse and cellular models.

RESULTS

The CRISPR/Cas9-based knockout screening showed that the enrichment of autophagy-related genes (ATG3, BECN1, and RB1CC1) provided protection of cancer cells from CD19 CAR-T cell-mediated cytotoxicity. These findings were further validated by in vitro cytotoxicity assays in cells with genetic and pharmacological inhibition of autophagy. Notably, higher expression of the three autophagy-related proteins in tumor samples was correlated with poorer responsiveness and worse survival in patients with relapsed/refractory B-cell lymphoma after CD19 CAR-T therapy. Bulk RNA sequencing analysis of bone marrow samples from B-cell leukemia patients also suggested the clinical relevance of autophagy to the therapeutic response and relapse after CD19 CAR-T cell therapy. Pharmacological inhibition of autophagy and knockout of RB1CC1 could dramatically sensitize tumor cells to CD19 CAR-T cell-mediated killing in mouse models of both B-cell leukemia and lymphoma. Moreover, our study revealed that cancer-intrinsic autophagy mediates evasion of CAR-T cells via the TNF-α-TNFR1 axis-mediated apoptosis and STAT1/IRF1-induced chemokine signaling activation.

CONCLUSIONS

These findings confirm that autophagy signaling in B-cell malignancies is essential for the effective cytotoxic function of CAR-T cells and thereby pave the way for the development of autophagy-targeting strategies to improve the clinical efficacy of CAR-T cell immunotherapy.

Linarin Protects Against CCl4-Induced Acute Liver Injury via Activating Autophagy and Inhibiting the Inflammatory Response: Involving the TLR4/MAPK/Nrf2 Pathway

Background

Linarin has been implicated in the inhibition of inflammatory responses and hepatoprotective effects. However, the precise mechanism by which Linarin integrates injury-induced signaling from inflammatory responses and oxidative stress remains unclear.

Methods

We evaluated the role of Linarin in a mouse model of carbon tetrachloride (CCl4)-induced acute liver injury. Mice were orally pretreated with Linarin or vehicle for seven consecutive days, followed by intraperitoneal injection with 0.2% (v/v) CCl4. To investigate the mechanism of action on oxidative stress, CCl4-stimulated HepG2 cells were utilized.

Results

Our results revealed Linarin remarkably attenuated the loss of hepatic architecture, inflammatory cell infiltration, serum transaminases, and pro-inflammatory cytokines induced by CCl4. Linarin attenuated CCl4-induced oxidative stress by increasing the expression of cytosolic Nrf2 (nuclear factor erythroid 2-related factor 2), inducing nuclear localization of Nrf2, and increasing stress-induced protein heme oxygenase-1 (HO-1). Additionally, Linarin decreased the expression of toll-like receptors (TLR)-4, and its downstream proteins, MyD88, IRAK1, and TRAF6. Furthermore, Linarin reversed CCl4-induced phosphorylation of ERK, p38, and JNK. Importantly, Linarin increased the expression of both LC3II and Beclin 1, which are hallmarks of autophagic flux. Autophagy-mediated hepatoprotective effects in Linarin-treated HepG2 cells were mitigated by the autophagy inhibitor 3-MA. However, combined treatment of Linarin with 3-MA failed to significantly reverse cell apoptosis and the production of transaminases and pro-inflammatory cytokines.

Conclusion

Linarin prevents acute liver injury, possibly by alleviating ROS-induced oxidative stress, inhibiting TLR4/MyD88 and JNK/p38/ERK-mediated inflammatory responses, and promoting Beclin 1/LC3II-mediated autophagic flux.

Hepatic stellate cells activate and avoid death under necroptosis stimuli: Hepatic fibrosis during necroptosis

BACKGROUND AND AIM

Necroptosis is an emerging cell death pathway that allows cells to undergo "cellular suicide" in a caspase-independent manner. We investigated the fate of hepatic stellate cells (HSCs) under necroptotic stimuli.

METHODS AND RESULTS

The RNA level of mixed lineage kinase domain-like protein (MLKL) is higher in patients with non-alcoholic fatty liver disease than in healthy controls. Hepatic fibrosis was significantly lower in MLKL-KO bile duct ligation (KO-BDL) mice than in wild-type-BDL mice. Necroptotic stimuli caused the death of HT-29 and U937 cells. However, necroptotic stimuli activate HSCs instead of inducing cell death. MLKL inhibitors attenuated fibrogenic changes in HSCs during necroptosis. Unlike HT-29 and U937 cells, MLKL phosphorylation and oligomerization were not observed during necroptosis in HSCs. RNA sequencing showed that NF-κB signaling-related genes were upregulated in HSCs following necroptotic stimulation. Necroptotic stimuli in HSCs increased the nuclear expression of NF-κB, which decreased after MLKL inhibitor treatment. Induction of necroptosis in HSCs led to autophagosome activation and formation, which were attenuated by MLKL inhibitor treatment.

CONCLUSION

HSCs avoid necroptosis due to the absence of MLKL phosphorylation and oligomerization and are activated through autophagosome and NF-κB pathways.

Distinct Types of Cell Death and Implications in Liver Diseases: An Overview of Mechanisms and Application

Cell death is associated with a variety of liver diseases, and hepatocyte death is a core factor in the occurrence and progression of liver diseases. In recent years, new cell death modes have been identified, and certain biomarkers have been detected in the circulation during various cell death modes that mediate liver injury. In this review, cell death modes associated with liver diseases are summarized, including some cell death modes that have emerged in recent years. We described the mechanisms associated with liver diseases and summarized recent applications of targeting cell death in liver diseases. It provides new ideas for the diagnosis and treatment of liver diseases. In addition, multiple cell death modes can contribute to the same liver disease. Different cell death modes are not isolated, and they interact with each other in liver diseases. Future studies may focus on exploring the regulation between various cell death response pathways in liver diseases.

Negative regulation of pro-apoptotic AMPK/JNK pathway by itaconate in mice with fulminant liver injury

Accumulating evidence indicates that metabolic responses are deeply integrated into signal transduction, which provides novel opportunities for the metabolic control of various disorders. Recent studies suggest that itaconate, a highly concerned bioactive metabolite catalyzed by immune responsive gene 1 (IRG1), is profoundly involved in the regulation of apoptosis, but the underlying mechanisms have not been fully understood. In the present study, the molecular mechanisms responsible for the apoptosis-modulatory activities of IRG1/itaconate have been investigated in mice with lipopolysaccharide (LPS)/D-galactosamine (D-Gal)-induced apoptotic liver injury. The results indicated that LPS/D-Gal exposure upregulated the level of IRG1 and itaconate. Deletion of IRG1 resulted in exacerbated hepatocytes apoptosis and liver injury. The phospho-antibody microarray analysis and immunoblot analysis indicated that IRG1 deletion enhanced the activation of AMP-activated protein kinase (AMPK)/c-jun-N-terminal kinase (JNK) pathway in LPS/D-Gal exposed mice. Mechanistically, IRG1 deficiency impaired the anti-oxidative nuclear factor erythroid-2 related factor 2 (Nrf2) signaling and then enhanced the activation of the redox-sensitive AMPK/JNK pathway that promotes hepatocytes apoptosis. Importantly, post-insult supplementation with 4-octyl itaconate (4-OI), a cell-permeable derivate of itaconate, resulted in beneficial outcomes in fulminant liver injury. Therefore, IRG1/itaconate might function as a negative regulator that controls AMPK-induced hepatocyte apoptosis in LPS/D-Gal-induced fulminant liver injury.

Interleukin-1 family cytokines in liver cell death: a new therapeutic target for liver diseases

INTRODUCTION

Liver cell death represents a basic biological process regulating the progression of liver diseases via distinct mechanisms. Accumulating evidence has uncovered participation of interleukin (IL)-1 family cytokines in liver cell death. Upon activation of cell death induced by hepatotoxic stimuli, IL1 family cytokines released by hepatic dead cells stimulate recruitment of immune cells, which in turn influence inflammation and subsequent liver injury, thus highlighting their potential as therapeutic targets in liver diseases. Enhancing our comprehension of mechanisms underlying IL1 family cytokine signaling in cell death responses could pave the way for novel therapeutic interventions aimed at addressing liver cell death-related liver pathologies.

AREAS COVERED

This review summarizes the recent findings reported in preclinical and clinical studies on mechanisms of liver cell death, alongside participation of IL1 family members consisting of IL1α, ILβ, IL18, and IL33 in liver cell death and their significant implications in liver diseases.

EXPERT OPINION

Discovery of new and innovative therapeutic approaches for liver diseases will need close cooperation between fundamental and clinical scientists to better understand the multi-step processes behind IL1 family cytokines' contributions to liver cell death.

The effect of lipopolysaccharide on liver homeostasis and diseases based on the mutual interaction of macrophages, autophagy, and damage-associated molecular patterns in male F344/DuCrlCrlj rats

Lipopolysaccharide (LPS) has dose-dependent biphasic functions (cell protective versus cell toxic). To clarify the different effects of LPS on liver homeostasis or liver diseases, comparisons were made between low and high doses of LPS, in terms of the mutual relation of hepatic macrophages, autophagy, and damage-associated molecular patterns (DAMPs) in male F344/DuCrlCrlj rats. Rats injected with low dose (0.1 mg/kg) or high dose (2.0 mg/kg) of LPS were examined at 6, 10, and 24 hours following single injections. Histologically, focal hepatocellular necrosis was occasionally present in high-dose animals, whereas there were no significant changes in low-dose animals. In low-dose animals, Kupffer cells reacting to CD163 and CD204 were hypertrophic and regarded as M2 macrophages, which promote resolution of inflammation and tissue repair, whereas in high-dose animals, infiltration of M1 macrophages expressing CD68 and major histocompatibility complex class II, which enhance cell injury, was seen. Hepatocytes with high-mobility-group box-1 (HMGB1) (one of DAMPs)-positive cytoplasmic granules appeared more frequently in high-dose animals than in low-dose animals, indicating the translocation of nuclear HMGB1 into the cytoplasm. However, although light-chain 3 beta-positive autophagosomes in hepatocytes increased in both doses, abnormally vacuolated autophagosomes were only seen in injured hepatocytes in the high-dose group, indicating possible extracellular release of HMGB1, which might result in cell injury and inflammation. These findings suggested that low-dose LPS induced a favorable mutual relationship among hepatic macrophages, autophagy, and DAMPs leading to cytoprotection of hepatocytes, whereas failures of the relationship in high-dose LPS caused hepatocyte injury.

Peroxisome proliferator-activated receptor γ activation ameliorates liver fibrosis-differential action of transcription factor EB and autophagy on hepatocytes and stellate cells

BACKGROUND

Peroxisome proliferator-activated receptor γ (PPARγ) activation suppresses HSC activation and liver fibrosis. Moreover, autophagy is implicated in hepatic lipid metabolism. Here, we determined whether PPARγ activation ameliorates HSC activation by downregulating transcription factor EB (TFEB)-mediated autophagy.

METHODS AND RESULTS

Atg7 or Tfeb knockdown in human HSC line LX-2 cells downregulated the expression of fibrogenic markers including α smooth muscle actin, glial fibrillary acidic protein, and collagen type 1. Conversely, Atg7 or Tfeb overexpression upregulated fibrogenic marker expression. Rosiglitazone (RGZ)-mediated PPARγ activation and/or overexpression in LX-2 cells and primary HSCs decreased autophagy, as indicated by LC3B conversion, total and nuclear-TFEB contents, mRFP-LC3 and BODIPY 493/503 colocalization, and GFP-LC3 and LysoTracker colocalization. RGZ treatment decreased liver fat content, liver enzyme levels, and fibrogenic marker expression in high-fat high-cholesterol diet-fed mice. Electron microscopy showed that RGZ treatment restored the high-fat high-cholesterol diet-mediated lipid droplet decrease and autophagic vesicle induction in primary HSCs and liver tissues. However, TFEB overexpression in LX-2 cells offset the aforementioned effects of RGZ on autophagic flux, lipid droplets, and fibrogenic marker expression.

CONCLUSIONS

Activation of PPARγ with RGZ ameliorated liver fibrosis and downregulation of TFEB and autophagy in HSCs may be important for the antifibrotic effects of PPARγ activation.

Myeloid autophagy genes protect mice against fatal TNF- and LPS-induced cytokine storm syndromes

ABBREVIATIONS

ATG5: autophagy related 5; ATG7: autophagy related 7; ATG14: autophagy related 14; ATG16L1: autophagy related 16-like 1 (S. cerevisiae); BECN1: beclin 1, autophagy related; CASP1: caspase 1; CASP4/CASP11: caspase 4, apoptosis-related cysteine peptidase; CIM: conditionally immortalized macrophage; CLP: cecal ligation and puncture; CSS: cytokine storm syndrome; DC: dendritic cell; IFNG/IFNγ: interferon gamma; IFNGR1: interferon gamma receptor 1; ip: intraperitoneal; iv: intravenous; IL12/p70: interleukin 12, p70 heterodimer; IL18: Interleukin 18; ITGAX/CD11c: integrin alpha X; LAP: LC3-associated phagocytosis; LPS: lipopolysaccharide; LYZ2/LYSM: lysozyme 2; MAP1LC3A/LC3: microtubule-associated protein 1 light chain 3 alpha; RB1CC1/FIP200: RB1-inducible coiled-coil 1; S100A8/MRP8: S100 calcium binding protein A8 (calgranulin A); TICAM1/TRIF: TIR domain containing adaptor molecule 1; TLR4: toll-like receptor 4; TNF: tumor necrosis factor.

Chronic steatosis aggravates cold-storage induced acute ischemic injury in rat donor livers through the perturbation of lipophagy

In this study, we explored the effects of cold ischemia on chronic steatosis and lipid signaling in vivo. Sprague Dawley (SD) rat models of chronic steatosis were established. Pathological observations and liver indices were assessed through hematoxylin-eosin (HE)- and Oil Red O staining. Autophagy and metabolism in adipose tissue were analyzed under post-ischemia and hypoxic conditions via western blotting and immunofluorescent analysis. We found that cold ischemia treatment exacerbated hepatic steatosis and reduced lipid phagocytosis. This manifested as a loss of Microtubule-associated protein 1A/1B-light chain 3 (LC3) and Perilipin 2 (PLIN2), and lower levels of autophagy. Cold ischemia also inhibited lipophagy in transplanted rat livers, most notably in moderate-to-severe steatosis models. Ischemia and hypoxia inhibited lipid phagocytosis and increased lipid accumulation. Collectively, these data show that chronic steatosis aggravates cold storage induced acute ischemic injury in rat donor livers through the inhibition of lipophagy. Moderate-to-severe steatosis therefore influences the postoperative recovery of liver transplant recipients, which should be immediately transplanted to reduce the risk of cold ischemia.

Innovative challenge for the inhibition of hepatocellular carcinoma progression by combined targeting of HSP90 and STAT3/HIF-1α signaling

Hepatocellular carcinoma (HCC) is the third foremost cause of cancer-related deaths. HCC has a very bad prognosis because it is asymptomatic in the early stages, resulting in a late diagnosis, and it is highly resistant to conventional chemotherapy. Such chemotherapies have been proven disappointing because they provide extremely low survival benefits. This study discloses that the STAT3/HIF-1α is an auspicious therapeutic attack site for conceivable repression of HCC development. A site that can be targeted by simultaneous administration of a STAT3 inhibitor in the context of HSP90 inhibition. 17-DMAG binds to HSP90 and constrains its function, resulting in the degradation of HSP90 client proteins HIF-1α and STAT3. Hypoxia recruits STAT3/HIF-1α complex within the VEGF promoter. Additionally, it was acknowledged that STAT3 is an essential mediator of VEGF transcription by direct binding to its promoter. Furthermore, it induces HIF-1α stability and enhances its transcriptional activity. Herein, we revealed that the combination therapy using 17-DMAG and nifuroxazide, a STAT3 inhibitor, repressed the diethylnitrosamine-induced alterations in the structure of the liver. This effect was mediated via decreasing the levels of the HSP90 client proteins HIF-1α and pSTAT3 resulting in the suppression of the STAT3/HIF-1α complex transcriptional activity. To conclude, 17-DMAG/NFXZD combination therapy-induced disruption in the STAT3/HIF-1α loop led to a potential antiangiogenic activity and showed apoptotic potential by inhibiting autophagy and inducing ROS/apoptosis signaling. Additionally, this combination therapy exhibited promising survival prolongation in mice with HCC. Consequently, the use of 17-DMAG/NFXZD renders an inspirational perspective in managing HCC. However, further investigations are compulsory.

Hepatocytes: A key role in liver inflammation

Hepatocytes, the major parenchymal cells in the liver, are responsible for a variety of cellular functions including carbohydrate, lipid and protein metabolism, detoxification and immune cell activation to maintain liver homeotasis. Recent studies show hepatocytes play a pivotal role in liver inflammation. After receiving liver insults and inflammatory signals, hepatocytes may undergo organelle damage, and further respond by releasing mediators and expressing molecules that can act in the microenvironment as well as initiate a robust inflammatory response. In this review, we summarize how the hepatic organelle damage link to liver inflammation and introduce numerous hepatocyte-derived pro-inflammatory factors in response to chronic liver injury.

Acteoside and ursolic acid synergistically protects H2O2-induced neurotrosis by regulation of AKT/mTOR signalling: from network pharmacology to experimental validation

CONTEXT

Ursolic acid (UA) and acteoside (ATS) are important active components that have been used to treat Alzheimer's disease (AD) because of their neuroprotective effects, but the exact mechanism is still unclear.

OBJECTIVE

Network pharmacology was used to explore the mechanism of UA + ATS in treating AD, and cell experiments were used to verify the mechanism.

MATERIALS AND METHODS

UA + ATS targets and AD-related genes were retrieved from TCMSP, STITCH, SwissTargetPrediction, GeneCards, DisGeNET and GEO. Key targets were obtained by constructing protein interaction network through STRING. The neuroprotective effects of UA + ATS were verified in H₂O₂-treated PC12 cells. The subsequent experiments were divided into Normal, Model (H₂O₂ pre-treatment for 4 h), Control (H₂O₂+ solvent pre-treatment), UA (5 μM), ATS (40 μM), UA (5 μM) + ATS (40 μM). Then apoptosis, mitochondrial membrane potential, caspase-3 activity, ATG5, Beclin-1 protein expression and Akt, mTOR phosphorylation levels were detected.

RESULTS

The key targets of UA + ATS-AD network were mainly enriched in Akt/mTOR pathway. Cell experiments showed that UA (ED₅₀: 5 μM) + ATS (ED₅₀: 40 μM) could protect H₂O₂-induced (IC₅₀: 250 μM) nerve damage by enhancing cells viability, combating apoptosis, restoring MMP, reducing the activation of caspase-3, lessening the phosphorylation of Akt and mTOR, and increasing the expression of ATG5 and Beclin-1.

CONCLUSIONS

ATS and UA regulates multiple targets, bioprocesses and signal pathways against AD pathogenesis. ATS and UA synergistically protects H₂O₂-induced neurotrosis by regulation of AKT/mTOR signalling.

6,6′-((Methylazanedyl)bis(methylene))bis(2,4-dimethylphenol) Induces Autophagic Associated Cell Death through mTOR-Mediated Autophagy in Lung Cancer

Autophagy is the multistep mechanism for the elimination of damaged organelles and misfolded proteins. This mechanism is preceded and may induce other program cell deaths such as apoptosis. This study unraveled the potential pharmacological effect of 24MD in inducing the autophagy of lung cancer cells. Results showed that 24MD was concomitant with autophagy induction, indicating by autophagosome staining and the induction of ATG5, ATG7 and ubiquitinated protein, p62 expression after 12-h treatment. LC3-I was strongly conversed to LC3-II, and p62 was downregulated after 24-h treatment. The apoptosis-inducing activity was found after 48-h treatment as indicated by annexin V-FITC/propidium iodide staining and the activation of caspase-3. From a mechanistic perspective, 24-h treatment of 24MD at 60 μM substantially downregulated p-mTOR. Meanwhile, p-PI3K and p-Akt were also suppressed by 24MD at concentrations of 80 and 100 μM, respectively. We further confirmed m-TOR-mediated autophagic activity by comparing the effect of 24MD with rapamycin, a potent standard mTOR1 inhibitor through Western blot and immunofluorescence assays. Although 24MD could not suppress p-mTOR as much as rapamycin, the combination of rapamycin and 24MD could increase the mTOR suppressive activity and LC3 activation. Changing the substituent groups (R groups) from dimethylphenol to ethylphenol in EMD or changing methylazanedyl to cyclohexylazanedyl in 24CD could only induce apoptosis activity but not autophagic inducing activity. We identified 24MD as a novel compound targeting autophagic cell death by affecting mTOR-mediated autophagy.

Rare ATG7 genetic variants predispose patients to severe fatty liver disease

BACKGROUND & AIMS

Non-alcoholic fatty liver disease (NAFLD) is the leading cause of liver disorders and has a strong heritable component. The aim of this study was to identify new loci that contribute to severe NAFLD by examining rare variants.

METHODS

We performed whole-exome sequencing in individuals with NAFLD and advanced fibrosis or hepatocellular carcinoma (n = 301) and examined the enrichment of likely pathogenic rare variants vs. the general population. This was followed by validation at the gene level.

RESULTS

In patients with severe NAFLD, we observed an enrichment of the p.P426L variant (rs143545741 C>T; odds ratio [OR] 5.26, 95% CI 2.1-12.6; p = 0.003) of autophagy-related 7 (ATG7), which we characterized as a loss-of-function, vs. the general population, and an enrichment in rare variants affecting the catalytic domain (OR 13.9; 95% CI 1.9-612; p = 0.002). In the UK Biobank cohort, loss-of-function ATG7 variants increased the risk of cirrhosis and hepatocellular carcinoma (OR 3.30; 95% CI 1.1-7.5 and OR 12.30, 95% CI 2.6-36, respectively; p <0.001 for both). The low-frequency loss-of-function p.V471A variant (rs36117895 T>C) was also associated with severe NAFLD in the clinical cohort (OR 1.7; 95% CI 1.2-2.5; p = 0.003), predisposed to hepatocellular ballooning (p = 0.007) evolving to fibrosis in the Liver biopsy cohort (n = 2,268), and was associated with liver injury in the UK Biobank (aspartate aminotransferase levels, p <0.001), with a larger effect in severely obese individuals in whom it was linked to hepatocellular carcinoma (p = 0.009). ATG7 protein localized to periportal hepatocytes, particularly in the presence of ballooning. In the Liver Transcriptomic cohort (n = 125), ATG7 expression correlated with suppression of the TNFα pathway, which was conversely upregulated in p.V471A carriers.

CONCLUSIONS

We identified rare and low-frequency ATG7 loss-of-function variants that promote NAFLD progression by impairing autophagy and facilitating ballooning and inflammation.

LAY SUMMARY

We found that rare mutations in a gene called autophagy-related 7 (ATG7) increase the risk of developing severe liver disease in individuals with dysmetabolism. These mutations cause an alteration in protein function and impairment of self-renewal of cellular content, leading to liver damage and inflammation.

Zanthoxylum armatum DC. extract induces liver injury via autophagy suppression and oxidative damage by activation of mTOR/ULK1 pathway

Zanthoxylum armatum DC. (ZADC) has anti-inflammatory, antioxidative, and antibacterial effects. The cytotoxicity of methanol extract of Zanthoxylum armatum DC. (MZADC) has been reported for BRL 3 A cell lines. However, whether MZADC can induce liver damage in vivo remains unclear. Therefore, it is essential to explore whether ZADC causes liver injury and, if the results confirm hepatotoxicity, to further study the potential mechanisms for the in-vitro cytotoxicity of the BRL 3 A cell lines. In vivo, different doses (0.346, 0.519, and 1.038 g/kg/day) of MZADC treatment were given by intragastric administration among male Sprague Dawley rats for 28 days. Levels of serum alanine transaminase (ALT), aspartate transaminase (AST), and alkaline phosphatase (ALP) in the high dose group increased. Steatosis and focal necrosis were found in liver cells in rats in the high dose group. In vitro, BRL 3 A cells were cultivated with MZADC at different concentrations (30, 50, and 70 μg/mL) for 24 h. The cell viability, the number of autophagosomes, and the expression levels of LC3 and Beclin-1 were on a decreasing trend. Besides, proportions of p-mTOR/mTOR and p-ULK1/ULK1 increased. Meanwhile, reactive oxygen species (ROS) accumulation and the content of malondialdehyde (MDA) were on the rise while the activity of superoxide dismutase (SOD) and the content of glutathione (GSH) was on the decline. This research suggests that MZADC may cause rats liver injury and inhibit autophagy in BRL 3 A cells by the mTOR/ULK1 pathway, and further induce intracellular oxidative damage.

Salvianolic acid B inhibits autophagy and activation of hepatic stellate cells induced by TGF-β1 by downregulating the MAPK pathway

In liver fibrosis, transforming growth factor-β1 (TGF-β1) can stimulate autophagy and activation of hepatic stellate cells (HSCs). Autophagy, playing a crucial role in HSCs activation, is related to liver fibrosis. Increasing evidence have suggested that antifibrosis effects of salvianolic acid B (Sal B) and their mechanisms of action, however, remain unclear. The aim of the article is to understand the role of Sal B in HSCs autophagy in liver fibrosis. Herein, we demonstrated that inducing TGF-β1 led to dramatic increase in autophagosome formation and autophagic flux in JS1 and LX2, which was mediated through the ERK, JNK, and p38 MAPK cascades. TGF-β1 significantly increased the protein of autophagy and liver fibrosis, including LC3BⅡ, ATG5, α-SMA, and Col.I; Sal B inhibits JS1 autophagy and activation by inhibiting the formation of autophagosomes and autophagic flux. Sal B significantly decreased the LC3BⅡ, ATG5, α-SMA, and Col.I protein expressions; pretreatment with autophagy inhibitors, chloroquine (CQ) and 3-methyladenine (3-MA) or silencing ATG7 further increase these reductions. However, pretreatment with autophagy agonist, rapamycin (Rapa), or overexpressed ATG5 attenuated this decrease. To further assess the importance of this mechanism, the antibody chip was used to detect the change of phosphorylation protein expression of the MAPK signaling pathway after treating JS1 with Sal B. Eleven differentially expressed proteins were verified. Sal B inhibits activation and autophagy of JS1 induced by TGF-β1 through downregulating the ERK, p38, and JNK signaling pathways, as demonstrated by downregulating p-ERK, p-JNK, and p-p38 MAPK protein expressions. In conclusion, Sal B inhibits autophagy and activation induced by TGF-β1 of HSCs possibly by downregulating the MAPK pathway.

Escaping Death: How Cancer Cells and Infected Cells Resist Cell-Mediated Cytotoxicity

Cytotoxic lymphocytes are critical in our immune defence against cancer and infection. Cytotoxic T lymphocytes and Natural Killer cells can directly lyse malignant or infected cells in at least two ways: granule-mediated cytotoxicity, involving perforin and granzyme B, or death receptor-mediated cytotoxicity, involving the death receptor ligands, tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) and Fas ligand (FasL). In either case, a multi-step pathway is triggered to facilitate lysis, relying on active pro-death processes and signalling within the target cell. Because of this reliance on an active response from the target cell, each mechanism of cell-mediated killing can be manipulated by malignant and infected cells to evade cytolytic death. Here, we review the mechanisms of cell-mediated cytotoxicity and examine how cells may evade these cytolytic processes. This includes resistance to perforin through degradation or reduced pore formation, resistance to granzyme B through inhibition or autophagy, and resistance to death receptors through inhibition of downstream signalling or changes in protein expression. We also consider the importance of tumour necrosis factor (TNF)-induced cytotoxicity and resistance mechanisms against this pathway. Altogether, it is clear that target cells are not passive bystanders to cell-mediated cytotoxicity and resistance mechanisms can significantly constrain immune cell-mediated killing. Understanding these processes of immune evasion may lead to novel ideas for medical intervention.

The dynamics of cell death patterns and regeneration during acute liver injury in mice

Acute liver injury is a serious clinical syndrome with multiple causes and unclear pathological process. Here, CCl₄‐ and D‐galactosamine/lipopolysaccharide (D‐gal/LPS)‐induced acute liver injury was established to explore the cell death patterns and determine whether or not liver regeneration occurred. In CCl₄‐induced hepatic injury, three phases, including the early, progressive, and recovery phase, were considered based on alterations of serum transaminases and liver morphology. Moreover, in this model, cytokines exhibited double‐peak fluctuations; apoptosis and pyroptosis persisted throughout all phases; autophagy occurred in the early and the progressive phases; and sufficient and timely hepatocyte regeneration was observed only during the recovery phase. All of these phenomena contribute to mild liver injury and subsequent regeneration. Strikingly, only the early and progressive phases were observed in the D‐gal/LPS model. Slight pyroptosis occurred in the early phase but diminished in the progressive phase, while apoptosis, reduced autophagy, and slight but subsequently diminished regeneration occurred only during the progressive phase, accompanied by a strong cytokine storm, resulting in severe liver injury with high mortality. Taken together, our work reveals variable modes and dynamics of cell death and regeneration, which lead to different consequences for mild and severe acute liver injury, providing a helpful reference for clinical therapy and prognosis.

ULK1 Signaling in the Liver: Autophagy Dependent and Independent Actions

Liver is the primary organ for energy metabolism and detoxification in the human body. Not surprisingly, a derangement in liver function leads to several metabolic diseases. Autophagy is a cellular process, which primarily deals with providing molecules for energy production, and maintains cellular health. Autophagy in the liver has been implicated in several hepatic metabolic processes, such as, lipolysis, glycogenolysis, and gluconeogenesis. Autophagy also provides protection against drugs and pathogens. Deregulation of autophagy is associated with the development of non-alcoholic fatty liver disease (NAFLD) acute-liver injury, and cancer. The process of autophagy is synchronized by the action of autophagy family genes or autophagy (Atg) genes that perform key functions at different steps. The uncoordinated-51-like kinases 1 (ULK1) is a proximal kinase member of the Atg family that plays a crucial role in autophagy. Interestingly, ULK1 actions on hepatic cells may also involve some autophagy-independent signaling. In this review, we provide a comprehensive update of ULK1 mediated hepatic action involving lipotoxicity, acute liver injury, cholesterol synthesis, and hepatocellular carcinoma, including both its autophagic and non-autophagic functions.

The complex interplay between autophagy and cell death pathways

Autophagy is a universal cellular homeostatic process, required for the clearance of dysfunctional macromolecules or organelles. This self-digestion mechanism modulates cell survival, either directly by targeting cell death players, or indirectly by maintaining cellular balance and bioenergetics. Nevertheless, under acute or accumulated stress, autophagy can also contribute to promote different modes of cell death, either through highly regulated signalling events, or in a more uncontrolled inflammatory manner. Conversely, apoptotic or necroptotic factors have also been implicated in the regulation of autophagy, while specific factors regulate both processes. Here, we survey both earlier and recent findings, highlighting the intricate interaction of autophagic and cell death pathways. We, Furthermore, discuss paradigms, where this cross-talk is disrupted, in the context of disease.

Cell Survival and Cell Death at the Intersection of Autophagy and Apoptosis: Implications for Current and Future Cancer Therapeutics

Autophagy and apoptosis are functionally distinct mechanisms for cytoplasmic and cellular turnover. While these two pathways are distinct, they can also regulate each other, and central components of the apoptosis or autophagy pathway regulate both processes directly. Furthermore, several upstream stress-inducing signaling pathways can influence both autophagy and apoptosis. The crosstalk between autophagy and apoptosis has an integral role in pathological processes, including those related to cancer, homeostasis, and aging. Apoptosis is a form of programmed cell death, tightly regulated by various cellular and biochemical mechanisms, some of which have been the focus of drug discovery efforts targeting cancer therapeutics. Autophagy is a cellular degradation pathway whereby cells recycle macromolecules and organelles to generate energy when subjected to stress. Autophagy can act as either a prodeath or a prosurvival process and is both tissue and microenvironment specific. In this review we describe five groups of proteins that are integral to the apoptosis pathway and discuss their role in regulating autophagy. We highlight several apoptosis-inducing small molecules and biologics that have been developed and advanced into the clinic and discuss their effects on autophagy. For the most part, these apoptosis-inducing compounds appear to elevate autophagy activity. Under certain circumstances autophagy demonstrates cytoprotective functions and is overactivated in response to chemo- or radiotherapy which can lead to drug resistance, representing a clinical obstacle for successful cancer treatment. Thus, targeting the autophagy pathway in combination with apoptosis-inducing compounds may be a promising strategy for cancer therapy.

Autophagy and apoptosis cascade: which is more prominent in neuronal death?

Autophagy and apoptosis are two crucial self-destructive processes that maintain cellular homeostasis, which are characterized by their morphology and regulated through signal transduction mechanisms. These pathways determine the fate of cellular organelle and protein involved in human health and disease such as neurodegeneration, cancer, and cardiovascular disease. Cell death pathways share common molecular mechanisms, such as mitochondrial dysfunction, oxidative stress, calcium ion concentration, reactive oxygen species, and endoplasmic reticulum stress. Some key signaling molecules such as p53 and VEGF mediated angiogenic pathway exhibit cellular and molecular responses resulting in the triggering of apoptotic and autophagic pathways. Herein, based on previous studies, we describe the intricate relation between cell death pathways through their common genes and the role of various stress-causing agents. Further, extensive research on autophagy and apoptotic machinery excavates the implementation of selective biomarkers, for instance, mTOR, Bcl-2, BH3 family members, caspases, AMPK, PI3K/Akt/GSK3β, and p38/JNK/MAPK, in the pathogenesis and progression of neurodegenerative diseases. This molecular phenomenon will lead to the discovery of possible therapeutic biomolecules as a pharmacological intervention that are involved in the modulation of apoptosis and autophagy pathways. Moreover, we describe the potential role of micro-RNAs, long non-coding RNAs, and biomolecules as therapeutic agents that regulate cell death machinery to treat neurodegenerative diseases. Mounting evidence demonstrated that under stress conditions, such as calcium efflux, endoplasmic reticulum stress, the ubiquitin-proteasome system, and oxidative stress intermediate molecules, namely p53 and VEGF, activate and cause cell death. Further, activation of p53 and VEGF cause alteration in gene expression and dysregulated signaling pathways through the involvement of signaling molecules, namely mTOR, Bcl-2, BH3, AMPK, MAPK, JNK, and PI3K/Akt, and caspases. Alteration in gene expression and signaling cascades cause neurotoxicity and misfolded protein aggregates, which are characteristics features of neurodegenerative diseases. Excessive neurotoxicity and misfolded protein aggregates lead to neuronal cell death by activating death pathways like autophagy and apoptosis. However, autophagy has a dual role in the apoptosis pathways, i.e., activation and inhibition of the apoptosis signaling. Further, micro-RNAs and LncRNAs act as pharmacological regulators of autophagy and apoptosis cascade, whereas, natural compounds and chemical compounds act as pharmacological inhibitors that rescue neuronal cell death through inhibition of apoptosis and autophagic cell death.

A Decade of Mighty Lipophagy: What We Know and What Facts We Need to Know?

Lipids are integral cellular components that act as substrates for energy provision, signaling molecules, and essential constituents of biological membranes along with a variety of other biological functions. Despite their significance, lipid accumulation may result in lipotoxicity, impair autophagy, and lysosomal function that may lead to certain diseases and metabolic syndromes like obesity and even cell death. Therefore, these lipids are continuously recycled and redistributed by the process of selective autophagy specifically termed as lipophagy. This selective form of autophagy employs lysosomes for the maintenance of cellular lipid homeostasis. In this review, we have reviewed the current literature about how lipid droplets (LDs) are recruited towards lysosomes, cross-talk between a variety of autophagy receptors present on LD surface and lysosomes, and lipid hydrolysis by lysosomal enzymes. In addition to it, we have tried to answer most of the possible questions related to lipophagy regulation at different levels. Moreover, in the last part of this review, we have discussed some of the pathological states due to the accumulation of these LDs and their possible treatments under the light of currently available findings.

Sex-Specific Regulation of Interferon-γ Cytotoxicity in Mouse Liver by Autophagy

BACKGROUND AND AIMS

Interferon-γ (IFNγ) is a central activator of immune responses in the liver and other organs. IFNγ triggers tissue injury and inflammation in immune diseases, which occur predominantly in females for unknown reasons. Recent findings that autophagy regulates hepatotoxicity from proinflammatory cytokines led to an examination of whether defective hepatocyte autophagy underlies sex-specific liver injury and inflammation induced by IFNγ.

APPROACH AND RESULTS

A lentiviral autophagy-related 5 (Atg5) knockdown was performed to decrease autophagy-sensitized alpha mouse liver (AML 12) hepatocytes to death from IFNγ in combination with IL-1β or TNF. Death was necrosis attributable to impaired energy homeostasis and adenosine triphosphate depletion. Male mice with decreased autophagy from a tamoxifen-inducible, hepatocyte-specific Atg5 knockout were resistant to IFNγ hepatotoxicity whereas female knockout mice developed liver injury and inflammation. Female mice had increased IFNγ-induced signal transducer and activator of transcription 1 (STAT1) levels compared to males. Blocking STAT1, but not interferon regulatory factor 1, signaling prevented IFNγ-induced hepatocyte death in autophagy-deficient AML12 cells and female mice. The mechanism of death is STAT1-induced overexpression of nitric oxide synthase 2 (NOS2) as in vitro hepatocyte death and in vivo liver injury were blocked by NOS2 inhibition.

CONCLUSIONS

Decreased hepatocyte autophagy sensitizes mice to IFNγ-induced liver injury and inflammation through overactivation of STAT1 signaling that causes NOS2 overexpression. Hepatotoxicity is restricted to female mice, suggesting that sex-specific effects of defective autophagy may underlie the increased susceptibility of females to IFNγ-mediated immune diseases.

Octanoic acid-rich enteral nutrition prevented lipopolysaccharide-induced acute liver injury through c-Jun N-terminal kinase-dependent autophagy

BACKGROUND

Acute liver injury (ALI) is an essential component of sepsis associated with poor outcomes. Octanoic acid (OA), a medium-chain fatty acid, has a protective effect on sepsis-induced organ damage, and autophagy is an adaptive response to sepsis. However, the underlying mechanism by which OA prevents ALI remains unknown. Therefore, we investigated whether OA-rich enteral nutrition (EN) prevented lipopolysaccharide (LPS)-induced ALI through the c-Jun N-terminal kinase (JNK)-dependent autophagy.

METHODS

Firstly, Sprague Dawley rats were randomly divided into four groups (sham, LPS, LPS + EN, and LPS + EN + OA) to detect the effect of OA-rich EN on LPS-induced ALI. Then, rats were randomly divided into five groups (sham, LPS, LPS + EN + OA, LPS + EN + OA + anisomycin (AN), and LPS + SP600125) to explore the mechanism by which OA-rich EN prevented ALI. EN and OA-rich EN were conducted through gastric tubes for 3 days. The liver protective effects were measured by liver histopathological changes, enzymes, inflammatory cytokines of serum and liver, the levels of autophagy, and JNK activity.

RESULTS

OA-rich EN inhibited JNK activity, up-regulated autophagy and prevented LPS-induced ALI. Inhibition of JNK activity conferred by SP promoted autophagy and prevented LPS-induced ALI. Moreover, the protective effect of autophagy and inhibition of JNK activity conferred by OA-rich EN on ALI was counteracted by AN.

CONCLUSION

OA-rich EN prevented LPS-induced ALI through JNK-dependent autophagy. This result suggested that OA-rich EN may be a therapeutic potential for ALI in patients with sepsis.

Saikosaponin-d alleviates hepatic fibrosis through regulating GPER1/autophagy signaling

BACKGROUND

Hepatic fibrosis is the final pathway of chronic liver disease characterized by excessive accumulation of extracellular matrix (ECM), which eventually develop into cirrhosis and liver cancer. Emerging studies demonstrated that Saikosaponin-d (SSd) exhibits a protective role in liver fibrosis. However, the mechanism underlying anti-liver fibrosis of SSd in vivo and in vitro remains unclear.

METHODS AND RESULTS

Transforming growth factor (TGF)-β and carbon tetrachloride (CCl₄) were used for creating liver fibrosis model in vitro and in vivo, respectively. The role of SSd in regulating liver fibrosis was assessed through Sirius red and Masson staining, and IHC assay. We found that SSd attenuated remarkably CCl₄-induced liver fibrosis as evidenced by decreased collagen level, and decreased expression of fibrotic markers Col 1 and α-SMA. Meanwhile, SSd repressed autophagy activation as suggested by decreased BECN1 expression and increased p62 expression. Compared with HSCs from CCl₄-treated group, the primary HSCs from SSd-treated mice exhibited a marked inactivation of autophagy. Mechanistically, SSd treatment enhanced the expression of GPER1 in primary HSCs and in TGF-β-treated LX-2 cells. GPER1 agonist G1 repressed autophagy activation, whereas GPER1 antagonist G15 activated autophagy and G15 also damaged the function of SSd on suppressing autophagy, leading to subsequent increased levels of fibrotic marker level in LX-2 cells.

CONCLUSIONS

Our findings highlight that SSd alleviates hepatic fibrosis by regulating GPER1/autophagy pathway.

Autophagy plays a double-edged sword role in liver diseases

As a highly evolutionarily conserved process, autophagy can be found in all types of eukaryotic cells. Such a constitutive process maintains cellular homeostasis in a wide variety of cell types through the encapsulation of damaged proteins or organelles into double-membrane vesicles. Autophagy not only simply eliminates materials but also serves as a dynamic recycling system that produces new building blocks and energy for cellular renovation and homeostasis. Previous studies have primarily recognized the role of autophagy in the degradation of dysfunctional proteins and unwanted organelles. However, there are findings of autophagy in physiological and pathological processes. In hepatocytes, autophagy is not only essential for homeostatic functions but also implicated in some diseases, such as viral hepatitis, alcoholic hepatitis, and hepatic failure. In the present review, we summarized the molecular mechanisms of autophagy and its role in several liver diseases and put forward several new strategies for the treatment of liver disease.

The (re)discovery of tumor-intrinsic determinants of immune sensitivity by functional genetic screens

Functional genetic screens by CRISPR-Cas9 allow for the unbiased discovery of proteins causally involved in complex biological processes. In recent years, this approach has been used by multiple laboratories to uncover a range of tumor cell regulators determining immune sensitivity. In this review, we provide an overview of genetic screens carried out both in vitro and in vivo. By comparative analysis we highlight commonly identified proteins and pathways that are key in establishing tumor-intrinsic immune susceptibility. Together, these screens demonstrated the importance of the antigen presentation, interferon-γ, tumor necrosis factor and autophagy pathways in governing sensitivity of tumor cells to immune attack. Moreover, they underline the complex interplay between tumor cells and their microenvironment, providing both fundamental and clinically relevant insights into the mechanisms of tumor immune resistance.

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CRISPR-Cas9 screens shed light on tumor-intrinsic mechanisms of immune sensitivity.

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Different screen settings highlight tumor-intrinsic and environmental influences.

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Effects of IFN-γ and antigen presentation pathways depend on environmental contexts.

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Cellular context impacts how TNF and autophagy pathways affect immune sensitivity.

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Potential therapeutic targets identified in the TNF, autophagy and IFN-γ pathways.

Liver injury mediated by the UII and its receptor (UT) system is possibly associated with the activation of autophagy-related and apoptosis-resisted pathways of Kupffer cells in acute liver failure

The system of urotensin II (UII) and its receptor (UT) (or: UII/UT system) mediates hepatic immune inflamed injury in acute liver failure (ALF) with autophagy inhibition. However, it is unknown whether the system has an effect on liver autophagy in ALF. In this study, we attempted to explore hepatic autophagy response in ALF through blocking the UII/UT signal. Autophagy-related genes were examined in the liver tissues of lipopolysaccharide (LPS)/d-galactosamine (D-GalN)-induced ALF after pretreatment of UT receptor specific antagonist urantide. And then, the levels of autophagy- and apoptosis-related genes were assayed in LPS-stimulated KCs via urantide pretreatment. We found that the expressions of hepatic autophagy related genes, including Beclin-1, Atg5, Atg7, LC3 and p62 mRNA, and LC3 II and p62 protein, were significantly downregulated in LPS/D-GalN-induced ALF mice; but they were not affected by pretreatment of urantide, a special UT receptor antagonist. To probe inflammatory mechanisms of the UII/UT system, we further investigated the effect of the system on Kupffer cells (KCs), the innate immune cells in liver. We found that urantide pretreatment significantly inhibited production of inflammatory injury molecules including TRAF6 and ROS in LPS-stimulated KCs. LPS stimulation induced LC3 and p62 mRNA and LC3 II and p62 protein expression in KCs. After urantide pretreatment, LC3 and p62 mRNA and LC3 II protein were downregulated, while p62 protein was upregulated in LPS-stimulated KCs. In addition, antiapoptotic protein Bcl-2 inhibition and proapoptotic protein cleaved caspase-3 increase were observed in LPS-stimulated KCs, and the effects were enhanced after urantide pretreatment in the study. We conclude that liver injury mediated by the UII/UT system is possibly associated with the activation of autophagy-related and apoptosis-resisted pathways of KCs in ALF.

Understanding the implication of autophagy in the activation of hepatic stellate cells in liver fibrosis: are we there yet?

Liver fibrosis (LF) occurs as a result of persistent liver injury and can be defined as a pathologic, chronic, wound-healing process in which functional parenchyma is progressively replaced by fibrotic tissue. As a phenomenon involved in the majority of chronic liver diseases, and therefore prevalent, it exerts a significant impact on public health. This impact becomes even more patent given the lack of a specific pharmacological therapy, with LF only being ameliorated or prevented through the use of agents that alleviate the underlying causes. Hepatic stellate cells (HSCs) are fundamental mediators of LF, which, activated in response to pro-fibrotic stimuli, transdifferentiate from a quiescent phenotype into myofibroblasts that deposit large amounts of fibrotic tissue and mediate pro-inflammatory effects. In recent years, much effort has been devoted to understanding the mechanisms through which HSCs are activated or inactivated. Using cell culture and/or different animal models, numerous studies have shown that autophagy is enhanced during the fibrogenic process and have provided specific evidence to pinpoint the fundamental role of autophagy in HSC activation. This effect involves - though may not be limited to - the autophagic degradation of lipid droplets. Several hepatoprotective agents have been shown to reverse the autophagic alteration present in LF, but clinical confirmation of these effects is pending. On the other hand, there is evidence that implicates autophagy in several anti-fibrotic mechanisms in HSCs that stimulate HSC cell cycle arrest and cell death or prevent the generation of pro-fibrotic mediators, including excess collagen accumulation. The objective of this review is to offer a comprehensive analysis of published evidence of the role of autophagy in HSC activation and to provide hints for possible therapeutic targets for the treatment and/or prevention of LF related to autophagy. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

TNFα enhances trovafloxacin-induced in vitro hepatotoxicity by inhibiting protective autophagy

Trovafloxacin (TVX) is associated with idiosyncratic drug-induced liver injury (iDILI) and inflammation-mediated hepatotoxicity. However, the inflammatory stress-regulated mechanisms in iDILI remain unclear. Herein, we elucidated the novel role of tumor-necrosis factor alpha (TNFα), an inflammatory stress factor, in TVX-induced in vitro hepatotoxicity and synergistic toxicity. TVX specifically induced synergistic toxicity in HepG2 cells with TNFα, which inhibits autophagy. TVX-treated HepG2 cells induced protective autophagy by inhibiting the expression of mTOR signaling proteins, while ATG5 knockdown in HepG2 cells, responsible for the impairment of autophagy, enhanced TVX-induced toxicity due to the increase in cytochrome C release and JNK pathway activation. Interestingly, the expression of mTOR signal proteins, which were suppressed by TVX, disrupted the negative feedback of the PI3K/AKT pathway and TNFα rebounded p70S6K phosphorylation. Co-treatment with TVX and TNFα inhibited protective autophagy by maintaining p70S6K activity, which enhanced TVX-induced cytotoxicity. Phosphorylation of p70S6K was inhibited by siRNA knockdown and rapamycin to restore TNFα-inhibited autophagy, which prevented the synergistic effect on TVX-induced cytotoxicity. These results indicate that TVX activates protective autophagy in HepG2 cells exposed to toxicity and an imbalance in negative feedback regulation of autophagy by TNFα synergistically enhanced the toxicity. The finding from this study may contribute to a better understanding of the mechanisms underlying iDILI associated with inflammatory stress.

Withaferin A alleviates fulminant hepatitis by targeting macrophage and NLRP3

Fulminant hepatitis (FH) is an incurable clinical syndrome where novel therapeutics are warranted. Withaferin A (WA), isolated from herb Withania Somnifera, is a hepatoprotective agent. Whether and how WA improves D-galactosamine (GalN)/lipopolysaccharide (LPS)-induced FH is unknown. This study was to evaluate the hepatoprotective role and mechanism of WA in GalN/LPS-induced FH. To determine the preventive and therapeutic effects of WA, wild-type mice were dosed with WA 0.5 h before or 2 h after GalN treatment, followed by LPS 30 min later, and then killed 6 h after LPS treatment. To explore the mechanism of the protective effect, the macrophage scavenger clodronate, autophagy inhibitor 3-methyladenine, or gene knockout mouse lines NLR family pyrin domain containing 3 (Nlrp3)-null, nuclear factor-erythroid 2-related factor 2 (Nrf2)-null, liver-specific AMP-activated protein kinase (Ampk)a1 knockout (Ampka1ΔHep) and liver-specific inhibitor of KB kinase β (Ikkb) knockout (IkkbΔHep) mice were subjected to GalN/LPS-induced FH. In wild-type mice, WA potently prevented GalN/LPS-induced FH and inhibited hepatic NLRP3 inflammasome activation, and upregulated NRF2 and autophagy signaling. Studies with Nrf2-null, Ampka1ΔHep, and IkkbΔHep mice demonstrated that the hepatoprotective effect was independent of NRF2, hepatic AMPKα1, and IκκB. Similarly, 3-methyladenine cotreatment failed to abolish the hepatoprotective effect of WA. The hepatoprotective effect of WA against GalN/LPS-induced FH was abolished after macrophage depletion, and partially reduced in Nlrp3-null mice. Consistently, WA alleviated LPS-induced inflammation partially dependent on the presence of NLRP3 in primary macrophage in vitro. Notably, WA potently and therapeutically attenuated GalN/LPS-induced hepatotoxicity. In conclusion, WA improves GalN/LPS-induced hepatotoxicity by targeting macrophage partially dependent on NLRP3 antagonism, while largely independent of NRF2 signaling, autophagy induction, and hepatic AMPKα1 and IκκB. These results support the concept of treating FH by pharmacologically targeting macrophage and suggest that WA has the potential to be repurposed for clinically treating FH as an immunoregulator.

Autophagy in liver diseases

Autophagy is the liver cell energy recycling system regulating a variety of homeostatic mechanisms. Damaged organelles, lipids and proteins are degraded in the lysosomes and their elements are re-used by the cell. Investigations on autophagy have led to the award of two Nobel Prizes and a health of important reports. In this review we describe the fundamental functions of autophagy in the liver including new data on the regulation of autophagy. Moreover we emphasize the fact that autophagy acts like a two edge sword in many occasions with the most prominent paradigm being its involvement in the initiation and progress of hepatocellular carcinoma. We also focused to the implication of autophagy and its specialized forms of lipophagy and mitophagy in the pathogenesis of various liver diseases. We analyzed autophagy not only in well studied diseases, like alcoholic and nonalcoholic fatty liver and liver fibrosis but also in viral hepatitis, biliary diseases, autoimmune hepatitis and rare diseases including inherited metabolic diseases and also acetaminophene hepatotoxicity. We also stressed the different consequences that activation or impairment of autophagy may have in hepatocytes as opposed to Kupffer cells, sinusoidal endothelial cells or hepatic stellate cells. Finally, we analyzed the limited clinical data compared to the extensive experimental evidence and the possible future therapeutic interventions based on autophagy manipulation.

Dengue Nonstructural Protein 1 Maintains Autophagy through Retarding Caspase-Mediated Cleavage of Beclin-1

Dengue virus (DENV) infection is a significant public health threat in tropical and subtropical regions; however, there is no specific antiviral drug. Accumulated studies have revealed that DENV infection induces several cellular responses, including autophagy and apoptosis. The crosstalk between autophagy and apoptosis is associated with the interactions among components of these two pathways, such as apoptotic caspase-mediated cleavage of autophagy-related proteins. Here, we show that DENV-induced autophagy inhibits early cell apoptosis and hence enhances DENV replication. Later, the apoptotic activities are elevated to suppress autophagy through cleavage of Beclin-1, an essential autophagy-related protein. Inhibition of cleavage of Beclin-1 by a pan-caspase inhibitor, Z-VAD, increases both autophagy and viral replication. Regarding the mechanism, we further found that DENV nonstructural protein 1 (NS1) is able to interact with Beclin-1 during DENV infection. The interaction between Beclin-1 and NS1 attenuates Beclin-1 cleavage and facilitates autophagy to prevent cell apoptosis. Our study suggests a novel mechanism whereby NS1 preserves Beclin-1 for maintaining autophagy to antagonize early cell apoptosis; however, elevated caspases trigger apoptosis by degrading Beclin-1 in the late stage of infection. These findings suggest implications for anti-DENV drug design.

Autophagy protects tumors from T cell–mediated cytotoxicity via inhibition of TNFα-induced apoptosis

Although T cell checkpoint inhibitors have transformed the treatment of cancer, the molecular determinants of tumor cell sensitivity to T cell–mediated killing need further elucidation. Here, we describe a mouse genome–scale CRISPR knockout screen that identifies tumor cell TNFα signaling as an important component of T cell–induced apoptosis, with NF-κB signaling and autophagy as major protective mechanisms. Knockout of individual autophagy genes sensitized tumor cells to killing by T cells that were activated via specific TCR or by a CD3 bispecific antibody. Conversely, inhibition of mTOR signaling, which results in increased autophagic activity, protected tumor cells from T cell killing. Autophagy functions at a relatively early step in the TNFα signaling pathway, limiting FADD-dependent caspase-8 activation. Genetic inactivation of tumor cell autophagy enhanced the efficacy of immune checkpoint blockade in mouse tumor models. Thus, targeting the protective autophagy pathway might sensitize tumors to T cell–engaging immunotherapies in the clinic.

Crosstalk between oxidative stress, autophagy and apoptosis in hemoporfin photodynamic therapy treated human umbilical vein endothelial cells

BACKGROUND

Photodynamic therapy (PDT) provides a treatment for port-wine stain (PWS) using hemoporfin (hematoporphyrin monomethyl ether, HMME), a novel photosensitizer, reporting better efficacy and lower recurrence rate. This study investigated the effects of HMME-PDT on human umbilical vein endothelial cells (HUVECs) as well as underlying mechanisms.

METHODS

Cell proliferation ability was measured by CCK8 assay and cell apoptosis was determined by TUNEL assay and Western blot analysis. Confocal fluorescence microscopy monitoring RFP-GFP-LC3 transfected HUVECs and Western blot analysis were used to evaluate autophagy. 3-Methyladenine (3-MA), Z-VAD-FMK, N-acetylcysteine (NAC) were used for inhibitor studies.

RESULTS

HMME-PDT decreased cell proliferation ability in an HMME concentration and light dose-dependent manner. Oxidative stress played an important role in HMME-PDT induced cell apoptosis and autophagy in HUVECs. Pretreatment with Z-VAD-FMK, the inhibitor of apoptosis, enhanced HMME-PDT induced autophagy. 3-MA, the suppressor of autophagy, significantly increased HMME-PDT induced apoptosis rates.

CONCLUSIONS

Our study demonstrated that HMME-PDT induced both apoptosis and autophagy in HUVECs via oxidative stress. Our data suggested that HMME-PDT- induced autophagy was able to prevent apoptotic cell death of HUVECs and rendered them more resistant to HMME-PDT induced toxicity.

Decreased Hepatocyte Autophagy Leads to Synergistic IL-1β and TNF Mouse Liver Injury and Inflammation

BACKGROUND AND AIMS

The proinflammatory cytokine IL-1β has been implicated in the pathophysiology of nonalcoholic and alcoholic steatohepatitis. How IL-1β promotes liver injury in these diseases is unclear, as no IL-1β receptor-linked death pathway has been identified. Autophagy functions in hepatocyte resistance to injury and death, and findings of decreased hepatic autophagy in many liver diseases suggest a role for impaired autophagy in disease pathogenesis. Recent findings that autophagy blocks mouse liver injury from lipopolysaccharide led to an examination of autophagy's function in hepatotoxicity from proinflammatory cytokines.

APPROACH AND RESULTS

AML12 cells with decreased autophagy from a lentiviral autophagy-related 5 (Atg5) knockdown were resistant to toxicity from TNF, but sensitized to death from IL-1β, which was markedly amplified by TNF co-treatment. IL-1β/TNF death was necrosis by trypan blue and propidium iodide positivity, absence of mitochondrial death pathway and caspase activation, and failure of a caspase inhibitor or necrostatin-1s to prevent death. IL-1β/TNF depleted autophagy-deficient cells of ATP, and ATP depletion and cell death were prevented by supplementation with the energy substrate pyruvate or oleate. Pharmacological inhibitors and genetic knockdown studies demonstrated that IL-1β/TNF-induced necrosis resulted from lysosomal permeabilization and release of cathepsins B and L in autophagy-deficient cells. Mice with a tamoxifen-inducible, hepatocyte-specific Atg5 knockout were similarly sensitized to cathepsin-dependent hepatocellular injury and death from IL-1β/TNF in combination, but neither IL-1β nor TNF alone. Knockout mice had increased hepatic inflammation, and IL-1β/TNF-treated, autophagy-deficient AML12 cells secreted exosomes with proinflammatory damage-associated molecular patterns.

CONCLUSIONS

The findings delineate mechanisms by which decreased hepatocyte autophagy promotes IL-1β/TNF-induced necrosis from impaired energy homeostasis and lysosomal permeabilization and inflammation through the secretion of exosomal damage-associated molecular patterns.

Ultra-structural study of the indomethacin-induced apoptosis and autophagy in rat gastric parietal cells

BACKGROUND AND AIM OF THE WORK

Indomethacin (IND), a non-steroidal anti-inflammatory drug, can induce gastric mucosal ulcerations. To date, the ultra-structural changes in the parietal cells (PCs) of the gastric mucosa following the intake of IND are mostly unknown. We carried out the current investigation to get insights into this issue.

MATERIALS AND METHODS

We established an animal model consisting of 35 adult male Sprague Dawley rats. The animals were divided into three groups, including; control (normal feeding), fasting, and indomethacin-treated groups. After treatment of 18-h fasting rats with IND, they were sacrificed at 3, 6, and 12-h intervals. The morphological features, including the apoptotic, and autophagic changes in the gastric mucosa PCs were examined using transmission electron microscopy.

RESULTS

In normal feeding animals (control group), the gastric PCs were present in various stages of activity. Fasting was associated with the predominance of the inactive parietal cells with features of up-regulated autophagy. In the IND -treated animals (at 3-h interval), PCs showed prominent autophagic changes, and subtle apoptotic cell death. In the IND -treated animals (at 6-12-h interval), PCs showed prominent apoptotic changes, and subtle autophagic features.

CONCLUSIONS

Our study indicates that IND treatment could induce gastropathy through time-dependent alterations in the autophagic and apoptotic machinery of PCs. Further studies are needed to examine the underlying molecular mechanisms.

Autophagy alleviates amiodarone-induced hepatotoxicity

Amiodarone is a widely used antiarrhythmic drug that can cause the development of steatohepatitis as well as liver fibrosis and cirrhosis. The molecular mechanisms of amiodarone-mediated liver injury remain largely unknown. We therefore analyzed amiodarone-mediated hepatocellular injury in patients with chronic heart failure, in primary hepatocytes and HepG2 cells. We found that amiodarone-treated patients with chronic heart failure revealed significantly higher serum levels of caspase-cleaved keratin-18, an apoptosis biomarker, compared to healthy individuals or patients not receiving amiodarone. Furthermore, amiodarone treatment of hepatocytes resulted in apoptosis associated with lipid accumulation and ER-stress induction. Liver cell steatosis was accompanied by enhanced de novo lipogenesis which, after reaching peak levels, declined together with decreased activation of ER stress. The decline of amiodarone-mediated lipotoxicity was associated with protective autophagy induction. In contrast, in hepatocytes treated with the autophagy inhibitor chloroquine as well as in autophagy gene (ATG5 or ATG7)-deficient hepatocytes, amiodarone-triggered toxicity was increased. In conclusion, we demonstrate that amiodarone induces lipid accumulation associated with ER stress and apoptosis in hepatocytes, which is mirrored by increased keratin-18 fragment serum levels in amiodarone-treated patients. Autophagy reduces amiodarone-mediated lipotoxicity and could provide a therapeutic strategy for protection from drug-induced liver injury.

Asiatic acid ameliorates acute hepatic injury by reducing endoplasmic reticulum stress and triggering hepatocyte autophagy

Endoplasmic reticulum stress (ERS), mutual crosstalk between autophagy and apoptosis-related signaling pathway, plays an important role in the process of acute liver injury (ALI). The present study was to investigate the effects and underlying mechanisms of Asiatic acid from Potentilla chinensis (AAPC) on ALI. The model of ALI in mice was induced by administration with Lipopolysaccharide/D-Galactosamine (LPS/D-GalN). The effects of AAPC on hepatic pathology and hepatocyte apoptosis were observed by hematoxylin-eosin (H&E) staining and TUNEL staining. Serum transaminases activities were measured using an automated biochemical analyzer. Moreover, ERS and autophagy were induced in LO2 cells, respectively. Cell cycle and apoptosis were analyzed using flow cytometry. In addition, ERS and autophagy-related pathways were detected in vivo and in vitro. The results showed that AAPC significantly ameliorated LPS/D-GalN-induced ALI in mice, as evidenced by the improvement of liver pathology and the decrease in serum alanine aminotransferase (ALT) and aspartate transaminase (AST) activities. Moreover, AAPC pre-treatment markedly inhibited thapsigargin-induced cell apoptosis, accompanied by cell cycle arrest at S/G1 phase in LO2 cells. AAPC notably inhibited the activation of the PERK/ATF6 and IRE1 pathway, alleviating the extent of ERS. Additionally, AAPC significantly promoted autophagy, as evidenced by the increase in the formation of autophagic vacuoles and the number of autophagosomes as well as the increased expressions of LC3II/I, Beclin-1, Atg5 and Atg7. In summary, our results indicate that AAPC significantly ameliorates ALI by inhibiting the ERS pathway and promoting hepatocyte autophagy.

Platycodin D alleviates liver fibrosis and activation of hepatic stellate cells by regulating JNK/c-JUN signal pathway

Liver fibrosis is involved in the progression of most chronic liver diseases. Even though we have made a huge progress in order to understand the pathogenesis of liver fibrosis, however, there is still a lack of productive treatments. Being a traditional Chinese medicine, Platycodin D (PD), an oleanane kind of triterpenoid saponin has been put to extensive use for treating different kinds of illnesses that include not just anti-nociceptive, but also antiviral, anti-inflammatory, and anti-cancer for thousands of years. Nonetheless, there has been no clarification made for its effects on the progression of liver fibrosis. In this manner, we carried out in vitro studies for the purpose of investigating the anti-fibrosis impact of PD. Activation of hepatic stellate cells was evaluated by means of the detection of the proliferation of HSCs and the expression of specific proteins. We discovered the fact that PD had the potential of activating HSCs. Thereafter, we detected the apoptosis and autophagy of the HSCs; as the results suggested, PD induced apoptosis and autophagy of the HSCs. It augmented the expression level of apoptotic proteins that included Bax, Cytochrome C (cyto-c), cleaved caspase3 and cleaved caspase9, in addition to the autophagy relevant proteins, for instance, LC3II, beclin1, Atg5 and Atg9. Further research was carried out for the investigation of the underlying molecular mechanism, and discovered that PD promoted the phosphorylation of JNK and c-Jun. Treating the JNK inhibitor P600125 inhibited the effect of PD, confirming the impact of PD on the regulation of JNK/c-Jun pathway. Thus, we speculated that PD alleviates liver fibrosis and activation of hepatic stellate via promoting phosphorylation of JNK and c-Jun and further altering the autophagy along with apoptosis of HSCs.

Metalloprotease Adam10 inhibition mitigates acute liver injury via repression of intrahepatic inflammation

BACKGROUND

Acute liver injury (ALI) is associated with the occurrence and progress of intrahepatic inflammation. Recent studies have shown that Adam10, a significant member of metalloproteinase family, has modulated the inflammation level in various neurologic diseases. However, it is elusive whether Adam10 regulation exert a hepatic protective effect on ALI by the suppression of inflammation level. The study aimed to explore the regulated function of Adam10 on acute liver injury.

METHODS

C57BL/6J mice (eight-week-old, male) were carried out intraperitoneal injection of tetrachloromethane (CTC) to provoke ALI. Adam 10 loaded in Adeno-associated viral vectors (AAV-Adam 10) or short hairpin RNA loaded in lentivirus aimed at murine Adam 10 mRNA (sh-RNA-Adam 10) were respectively delivered to mice via tail intravenous injection to achieve overexpression or silence of Adam 10. Western blotting, reverse transcription-polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA), immumohistochemical (IHC) and hematoxylin and eosin (HE) staining were conducted to measure Adam 10 alteration, inflammation level, histology and liver function.

RESULTS

We show that the expression of Adam 10 markedly increases in CTC-induced injured liver tissues. Moreover, we demonstrate that the knockdown of Adam 10 attenuates the intrahepatic inflammation and protects hepatic histology and function in ALI mice, however the overexpression of Adam10 aggravates inflammation and liver lesion.

CONCLUSIONS

The above suggested that the inhibition of Adam 10 ameliorates ALI through inhibiting inflammation. Our research provides novel view on the Adam 10 modulation of process of ALI by the inflammation aspect and verify a potential target for the therapy of ALI in the future.

The improvement effect of gastrodin on LPS/GalN-induced fulminant hepatitis via inhibiting inflammation and apoptosis and restoring autophagy

Fulminant hepatitis (FH), characterized by overwhelmed inflammation and massive hepatocyte apoptosis, is a life-threatening and high mortality rate. Gastrodin (GTD), a phenolic glucoside extracted from Gastrodiaelata Blume, exerts anti-apoptosis, and anti-inflammatory activities. In the present study, we aimed to evaluate whether GTD treatment could alleviate lipopolysaccharide and d-galactosamine (LPS/GalN)-induced FH in mice and its potential mechanisms. These data suggested that GTD treatment remarkably protected against LPS/GalN-induced FH by enhancing the survival rate of mice, reducing ALT and AST levels, attenuating histopathological changes, and suppressing interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α secretion. In addition, GTD treatment relieved hepatic apoptosis by the regulation of peroxisome proliferator-activated receptors (PPARs), P53 and caspase-3/9. Furthermore, GTD treatment could significantly inhibit inflammation-related signaling pathways activated by LPS/GalN, including the suppression of nucleotide-binding domain (NOD)-like receptor protein 3 (NLRP3) and nuclear factor-kappa B (NF-κB) activation. Importantly, GTD treatment effectively restored but not induced LPS/GalN-reduced the expression of AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) phosphorylation, as well as the level of pro-autophagy proteins. Taken together, our investigation indicated that GTD played an essential role in liver protection by relieving hepatocyte apoptosis and inflammation reaction, which may be closely involved in the inhibition of NLRP3 inflammasome and NF-κB activation, regulation of apoptosis-related proteins expression, and the recovery of AMPK/ACC/autophagy.