The ER stress sensor inositol-requiring enzyme 1α in Kupffer cells promotes hepatic ischemia-reperfusion injury.

Hepatic ischemia/reperfusion (I/R) injury is an inflammation-mediated process arising from ischemia/reperfusion-elicited stress in multiple cell types, causing liver damage during surgical procedures and often resulting in liver failure. Endoplasmic reticulum (ER) stress triggers the activation of the unfolded protein response (UPR) and is implicated in tissue injuries, including hepatic I/R injury. However, the cellular mechanism that links the UPR signaling to local inflammatory responses during hepatic I/R injury remains largely obscure. Here, we report that IRE1α, a critical ER-resident transmembrane signal transducer of the UPR, plays an important role in promoting Kupffer-cell-mediated liver inflammation and hepatic I/R injury. Utilizing a mouse model in which IRE1α is specifically ablated in myeloid cells, we found that abrogation of IRE1α markedly attenuated necrosis and cell death in the liver, accompanied by reduced neutrophil infiltration and liver inflammation following hepatic I/R injury. Mechanistic investigations in mice as well as in primary Kupffer cells revealed that loss of IRE1α in Kupffer cells not only blunted the activation of the NLRP3 inflammasome and IL-1ß production, but also suppressed the expression of the inducible nitric oxide synthase (iNos) and proinflammatory cytokines. Moreover, pharmacological inhibition of IRE1α's RNase activity was able to attenuate inflammasome activation and iNos expression in Kupffer cells, leading to alleviation of hepatic I/R injury. Collectively, these results demonstrate that Kupffer cell IRE1α mediates local inflammatory damage during hepatic I/R injury. Our findings suggest that IRE1α RNase activity may serve as a promising target for therapeutic treatment of ischemia/reperfusion-associated liver inflammation and dysfunction.

ALK1 signaling is required for the homeostasis of Kupffer cells and prevention of bacterial infection.

Macrophages are highly heterogeneous immune cells that fulfill tissue-specific functions. Tissue-derived signals play a critical role in determining macrophage heterogeneity. However, these signals remain largely unknown. The BMP receptor activin receptor-like kinase 1 (ALK1) is well known for its role in blood vessel formation; however, its role within the immune system has never been revealed to our knowledge. Here, we found that BMP9/BMP10/ALK1 signaling controlled the identity and self-renewal of Kupffer cells (KCs) through a Smad4-dependent pathway. In contrast, ALK1 was dispensable for the maintenance of macrophages located in the lung, kidney, spleen, and brain. Following ALK1 deletion, KCs were lost over time and were replaced by monocyte-derived macrophages. These hepatic macrophages showed significantly reduced expression of the complement receptor VSIG4 and alterations in immune zonation and morphology, which is important for the tissue-specialized function of KCs. Furthermore, we found that this signaling pathway was important for KC-mediated Listeria monocytogenes capture, as the loss of ALK1 and Smad4 led to a failure of bacterial capture and overwhelming disseminated infections. Thus, ALK1 signaling instructs a tissue-specific phenotype that allows KCs to protect the host from systemic bacterial dissemination.

Adenosine deaminase 2 produced by infiltrative monocytes promotes liver fibrosis in nonalcoholic fatty liver disease.

Elevated circulating activity of adenosine deaminase 2 (ADA2) is associated with liver fibrosis in nonalcoholic fatty liver disease (NAFLD). In the liver of NAFLD patients, ADA2-positive portal macrophages are significantly associated with the degree of liver fibrosis. These liver macrophages are CD14- and CD16-positive and co-express chemokine receptors CCR2, CCR5, and CXCR3, indicating infiltrative monocyte origin. Human circulatory monocytes release ADA2 upon macrophage differentiation in vitro. When stimulated by recombinant human ADA2 (rhADA2), human monocyte-derived macrophages demonstrate upregulation of pro-inflammatory and pro-fibrotic genes, including PDGF-B, a key pro-fibrotic cytokine. This PDGF-B upregulation is reproduced by inosine, the enzymatic product of ADA2, but not adenosine, and is abolished by E359N, a loss-of-function mutation in ADA2. Finally, rhADA2 also stimulates PDGF-B production from Kupffer cells in primary human liver spheroids. Together, these data suggest that infiltrative monocytes promote fibrogenesis in NAFLD via ADA2-mediated autocrine/paracrine signaling culminating in enhanced PDGF-B production.

Leaky Gut Driven by Dysbiosis Augments Activation and Accumulation of Liver Macrophages via RIP3 Signaling Pathway in Autoimmune Hepatitis.

The gut-liver axis has been increasingly recognized as a major autoimmunity modulator. However, the implications of intestinal barrier in the pathogenesis of autoimmune hepatitis (AIH) remain elusive. Here, we investigated the functional role of gut barrier and intestinal microbiota for hepatic innate immune response in AIH patients and murine models. In this study, we found that AIH patients displayed increased intestinal permeability and pronounced RIP3 activation of liver macrophages. In mice models, intestinal barrier dysfunction increased intestinal bacterial translocation, thus amplifying the hepatic RIP3-mediated innate immune response. Furthermore, GSK872 dampened RIP3 activation and ameliorated the activation and accumulation of liver macrophages in vitro and in vivo experiments. Strikingly, broad-spectrum antibiotic ablation significantly alleviated RIP3 activation and liver injury, highlighting the causal role of intestinal microbiota for disease progression. Our results provided a potentially novel mechanism of immune tolerance breakage in the liver via the gut-liver axis. In addition, we also explored the therapeutic and research potentials of regulating the intestinal microbiota for the therapy of AIH.

Genome-wide association study of serum liver enzymes implicates diverse metabolic and liver pathology.

Serum liver enzyme concentrations are the most frequently-used laboratory markers of liver disease, a major cause of mortality. We conduct a meta-analysis of genome-wide association studies of liver enzymes from UK BioBank and BioBank Japan. We identified 160 previously-unreported independent alanine aminotransferase, 190 aspartate aminotransferase, and 199 alkaline phosphatase genome-wide significant associations, with some affecting multiple different enzymes. Associated variants implicate genes that demonstrate diverse liver cell type expression and promote a range of metabolic and liver diseases. These findings provide insight into the pathophysiology of liver and other metabolic diseases that are associated with serum liver enzyme concentrations.

Lipopolysaccharide reduces USP13 stability through c-Jun N-terminal kinase activation in Kupffer cells.

Protein ubiquitination regulates protein stability, cellular localization, and enzyme activity. Deubiquitinases catalyze the removal of ubiquitin from target proteins and reverse ubiquitination. USP13, a deubiquitinase, has been shown to regulate a variety of cellular responses including inflammation; however, the molecular regulation of USP13 has not been demonstrated. In this study, we revealed that USP13 is degraded in response to lipopolysaccharide (LPS) in Kupffer cells. USP13 levels are significantly decreased in inflamed organs, including liver tissues from septic mice. LPS reduces USP13 protein stability, not transcription, in Kupffer cells. Furthermore, LPS increases USP13 polyubiquitination. Inhibition of proteasome, but not lysosome or immunoproteasome, attenuates LPS-induced USP13 degradation, suggesting USP13 degradation is mediated by the ubiquitin-proteasome system. A catalytically inactive form of USP13 exhibits similar degree of degradation compared with USP13 wild-type, suggesting that USP13 degradation is not dependent on its activity. Furthermore, USP13 degradation is dependent on new protein synthesis. Inhibition of c-Jun N-terminal kinase (JNK) attenuates USP13 degradation, indicating that JNK-dependent new protein synthesis is necessary for USP13 degradation. This study reveals a molecular mechanism of regulation of USP13 degradation in Kupffer cells in response to bacterial endotoxin.

Role of spleen tyrosine kinase in liver diseases.

Spleen tyrosine kinase (SYK) is a non-receptor tyrosine kinase expressed in most hematopoietic cells and non-hematopoietic cells and play a crucial role in both immune and non-immune biological responses. SYK mediate diverse cellular responses via an immune-receptor tyrosine-based activation motifs (ITAMs)-dependent signalling pathways, ITAMs-independent and ITAMs-semi-dependent signalling pathways. In liver, SYK expression has been observed in parenchymal (hepatocytes) and non-parenchymal cells (hepatic stellate cells and Kupffer cells), and found to be positively correlated with the disease severity. The implication of SYK pathway has been reported in different liver diseases including liver fibrosis, viral hepatitis, alcoholic liver disease, non-alcoholic steatohepatitis and hepatocellular carcinoma. Antagonism of SYK pathway using kinase inhibitors have shown to attenuate the progression of liver diseases thereby suggesting SYK as a highly promising therapeutic target. This review summarizes the current understanding of SYK and its therapeutic implication in liver diseases.

GDF­15 prevents LPS and D­galactosamine­induced inflammation and acute liver injury in mice.

Growth differentiation factor­15 (GDF­15) is a transforming growth factor (TGF)­ß superfamily member with a poorly characterized biological activity, speculated to be implicated in several diseases. The present study aimed to determine whether GDF­15 participates in sepsis­induced acute liver injury in mice. Lipopolysaccharide (LPS) and D­galactosamine (D­GalN) were administered to mice to induce acute liver injury. Survival of mice, histological changes in liver tissue, and levels of inflammatory biomarkers in serum and liver tissue were evaluated following treatment with GDF­15. The underlying mechanism was investigated by western blotting, ELISA, flow cytometry, and reverse transcription­quantitative polymerase chain reaction using Kupffer cells. The results demonstrated that GDF­15 prevented LPS/D­GalN­induced death, increase in inflammatory cell infiltration and serum alanine aminotransferase and aspartate aminotransferase activities. In addition, GDF­15 treatment reduced the production of hepatic malondialdehyde and myeloperoxidase, and attenuated the increase of interleukin (IL)­6, tumor necrosis factor (TNF)­α, and IL­1ß expression in serum and liver tissue, accompanied by inducible nitric oxide synthase (iNOS) inactivation in the liver. Similar changes in the expression of inflammatory cytokines, IL­6, TNF­α and IL­1ß, and iNOS activation were observed in the Kupffer cells. Further mechanistic experiments revealed that GDF­15 effectively protected against LPS­induced nuclear factor (NF)­κB pathway activation by regulating TGFß­activated kinase 1 (TAK1) phosphorylation in Kupffer cells. In conclusion, GDF­15 reduced the activation of pro­inflammatory factors, and prevented LPS­induced liver injury, most likely by disrupting TAK1 phosphorylation, and consequently inhibiting the activation of the NF­κB pathway in the liver.

SIRT1 upregulation protects against liver injury induced by a HFD through inhibiting CD36 and the NF­κB pathway in mouse kupffer cells.

Sirtuin 1 (SIRT1) is an NAD(+)­dependent deacetylase, and a critical regulator in various metabolic processes, such as non­alcoholic fatty liver disease (NAFLD). The present study aimed to investigate whether activating SIRT1 could modulate the CD36 and nuclear factor (NF)­κB pathways to protect against liver injury induced by a high­fat diet (HFD) in mice. A mouse NAFLD model was established by administration of a HFD for 8 weeks. During the last 4 weeks, SRT1720, a specific SIRT1 activator, was added daily to the HFD feed. The hepatic morphological structure was observed using hematoxylin and eosin staining, and the ultrastructures in the liver tissue were observed using transmission electron microscopy. Protein expression of SIRT1, CD36 and P65 in liver tissues was detected by immunohistochemistry. Kupffer cells (KCs) from the livers of the mouse models were isolated to determine the mRNA and protein expression of SIRT1, CD36 and P65. SIRT1 activation attenuated the HFD­induced liver injury and significantly reduced the body weight and the levels of alanine transaminase, aspartate aminotransferase, triglyceride, tumor necrosis factor­α and interleukin­6. We observed an increased expression of SIRT1 in the liver tissues from the HFD+SRT1720 group compared with the HFD group. Simultaneously, the expression of CD36 and P65 in the liver tissues was downregulated in the HFD+SRT1720 group. The mRNA and protein expression of SIRT1 was elevated in the HFD+SRT1720 group, whereas the mRNA and protein expression of CD36 and P65 in KCs was significantly decreased in the HFD+SRT1720 group. The present study demonstrated that SIRT1 activation attenuated HFD­induced liver steatosis and inflammation by inhibiting CD36 expression and the NF­κB signaling pathway.

Oxidative and ER stress-dependent ASK1 activation in steatotic hepatocytes and Kupffer cells sensitizes mice fatty liver to ischemia/reperfusion injury.

Steatosis intensifies hepatic ischemia/reperfusion (I/R) injury increasing hepatocyte damage and hepatic inflammation. This study evaluates if this process is associated to a differential response of steatotic hepatocytes (HP) and Kupffer cells (KC) to I/R injury and investigates the molecular mechanisms involved. Control or steatotic (treated with 50 µmol palmitic acid, PA) mouse HP or KC were exposed to hypoxia/reoxygenation (H/R). C57BL/6 mice fed 9 week with control or High Fat diet underwent to partial hepatic IR. PA increased H/R damage of HP and further activated the ASK1-JNK axis stimulated by ER stress during H/R. PA also induced the production of oxidant species (OS), and OS prevention nullified the capacity of PA to increase H/R damage and ASK1/JNK stimulation. ASK1 inhibition prevented JNK activation and entirely protected HP damage. In KC, PA directly activated ER stress, ASK1 and p38 MAPK and increased H/R damage. However, in contrast to HP, ASK1 inhibition further increased H/R damage by preventing p38 MAPK activation. In mice liver, steatosis induced the expression of activated ASK1 in only KC, whereas I/R exposure of steatotic liver activated ASK1 expression also in HP. "In vivo", ASK1 inhibition prevented ASK1, JNK and p38 MAPK activation and protected I/R damage and expression of inflammatory markers. CONCLUSIONS: Lipids-induced ASK1 stimulation differentially affects HP and KC by promoting cytotoxic or protective signals. ASK1 increases H/R damage of HP by stimulating JNK and protects KC activating p38MAPK. These data support the potentiality of the therapeutic employment of ASK1 inhibitors that can antagonize the damaging effects of I/R upon fatty liver surgery by the contextual reduction of HP death and of KC-mediated reactions.

Evaluation of Cytotoxicity and Hypoxic Effect of Nitroimidazole Embedded Nanoparticles.

Adenylate cyclase is a key intracellular enzyme involved in energy imbalance leading to tumor hypoxia and cytotoxicity. In this study, adenylate cyclase activities in isolated hepatocytes and Kupffer cells were compared in the presence of several metabolic stimulators. In cultured hepatocyte cells, adenylate cyclase was stimulated by guanylyl imidotriphosphate (GITP), guanosine triphosphate (GTP), progesterone and nitroimidazole embedded nanoparticle (NNP) effectors, while prostaglandin E2 and F2α were used as effectors in cultured Kupffer cells. The results showed that NNPs decreased adenylate cyclase specific activity in a dose-dependent manner after preincubation of hepatocytes with NNPs. The NNPs stimulated adenylate cyclase activities in hepatocytes were evaluated based on measurement of cyclic adenosine monophosphate (cAMP). The stimulatory effects of NNPs on adenylate cyclase were independent of the presence of GTP and may have been due to a direct effect on the catalytic subunit of adenylate cyclase. In addition, basal cAMP generation in hepatocyte cells was efficiently suppressed by the NNPs. In conclusion, NNPs exerted direct effects on the catalytic subunit of the adenylate cyclase system, and adenylate cyclase was hormone sensitive in liver cells.

Comparative study of CYP2B1/2 induction and the transport of bilirubin and taurocholate in rat hepatocyte-mono- and hepatocyte-Kupffer cell co-cultures.

INTRODUCTION: Hepatocyte-Kupffer cell (KC) co-cultures represent a promising approach for in vitro modeling of complex interactions between parenchymal and non-parenchymal cells in the liver, responsible for drug-induced liver injury (DILI). In this study we aimed to compare hepatocyte monocultures with hepatocyte-KC co-cultures regarding some basic liver functions associated with the chemical defense system. These pathways involve transporters and enzymes the function of which is highly sensitive towards hepatotoxic events. METHODS: CYP2B1/2 induction and the biliary and sinusoidal elimination of bilirubin (B) and taurocholate (TC) were studied in rat hepatocyte sandwich cultures compared with rat hepatocyte-KC sandwich co-cultures of 1:0, 6:1, 2:1 and 1:1 cell combinations representing the physiologic and pathologic conditions of the liver. RESULTS: KCs decreased phenobarbital inducibility of CYP2B1/2 in a cell ratio dependent manner and activation of KCs by lipopolisacharide (LPS) amplified this effect. Similarly, KCs decreased the transport of B and its glucuronides (BG) in both sinusoidal and canalicular directions resulting in its intracellular accumulation. In contrast, the uptake and the efflux of TC were greater in the co-cultures than in the hepatocyte monocultures. Immuno-labelling of sodium-dependent taurocholate transporter (Ntcp) revealed increased expression of the transporter in the presence of KCs. DISCUSSION: Here we presented that KCs have a direct impact on some hepatocyte functions suggesting that the co-culture model may be more suitable for drug related hepatotoxicity studies than hepatocyte monocultures.

Novel strategy to decrease reperfusion injuries and improve function of cold-preserved livers using normothermic ex vivo liver perfusion machine.

Normothermic extracorporeal liver perfusion (NELP) can decrease ischemia/reperfusion injury to the greatest degree when cold ischemia time is minimized. Warm perfusion of cold-stored livers results in hepatocellular damage, sinusoidal endothelial cell (SEC) dysfunction, and Kupffer cell activation. However, the logistics of organ procurement mandates a period of cold preservation before NELP. The aim of this study was to determine the beneficial effects of gradual rewarming of cold-stored livers by placement on NELP. Three female porcine livers were used for each group. In the immediate NELP group, procured livers were immediately placed on NELP for 8 hours. In the cold NELP group, livers were cold-stored for 4 hours followed by NELP for 4 hours. In rewarming groups, livers were cold-stored for 4 hours, then gradually rewarmed in different durations to 38°C and kept on NELP for an additional 4 hours. For comparison purposes, the last 4 hours of NELP runs were considered to be the evaluation phase. Immediate NELP livers had significantly lower concentrations of liver transaminases, hyaluronic acid, and ß-galactosidase and had higher bile production compared to the other groups. Rewarming livers had significantly lower concentrations of hyaluronic acid and ß-galactosidase compared to the cold NELP livers. In addition, there was a significant decline in international normalized ratio values, improved bile production, reduced biliary epithelial cell damage, and improved cholangiocyte function. Thus, if a NELP machine is not available at the procurement site and livers will need to undergo a period of cold preservation, a gradual rewarming protocol before NELP may greatly reduce damages that are associated with reperfusion. In conclusion, gradual rewarming of cold-preserved livers upon NELP can minimize the hepatocellular damage, Kupffer cell activation, and SEC dysfunction.

Immunophenotypical characterization and influence on liver homeostasis of depleting and repopulating hepatic macrophages in rats injected with clodronate.

Hepatic macrophages (including Kupffer cells) play a crucial role in the homeostasis and act as mediators of inflammatory response in the liver. Hepatic macrophages were depleted in male F344 rats by a single intravenous injection of liposomal clodronate (CLD; 50mg/kg body weight), and immunophenotypical characteristics of depleting and repopulating macrophages were analyzed by different antibodies specific for macrophages. CD163(+) Kupffer cells were almost completely depleted on post-injection (PI) days 1-12. Macrophages reacting to CD68, Iba-1, and Gal-3 were drastically reduced in number on PI day 1 and then recovered gradually until PI day 12. MHC class II(+) and CD204(+) macrophages were moderately decreased during the observation period. Although hepatic macrophages detectable by different antibodies were reduced in varying degrees, Kupffer cells were the most susceptible to CLD. Liver situation influenced by depleted hepatic macrophages was also investigated. No marked histological changes were seen in the liver, but the proliferating activity of hepatocytes was significantly increased, supported by changes of gene profiles relating to cell proliferation on microarray analysis on PI day 1; the values of AST and ALT were significantly elevated; macrophage induction/activation factors (such as MCP-1, CSF-1, IL-6 and IL-4) were increased exclusively on PI day 1, whereas anti-inflammatory factors such as IL-10 and TGF-ß1 remained significantly decreased after macrophage depletion. The present study confirmed importance of hepatic macrophages in liver homeostasis. The condition of hepatic macrophages should be taken into consideration when chemicals capable of inhibiting macrophage functions are evaluated.

Estudo do papel das células de kupffer na modulação dos citocromos P450 hepáticos por estímulos inflamatórios

É conhecido que processos inflamatórios podem modular a expressão e atividade deenzimas CYPs. Não é claro, entretanto, o modo pelo qual estímulos inflamatórios regulam aexpressão dessas enzimas. Neste trabalho investigamos a hipótese de que as células deKupffer do fígado exerceriam um papel na modulação dos CYPs hepáticos em resposta àinflamação exacerbada ou sepse. O cloreto de gadolínio, é um inibidor seletivo das células deKupffer, conhecido por atenuar o quadro de inflamação exacerbada, quandoadministradopreviamente ao estímulo inflamatório, em diferentes modelos animais. Algunsautores sugeriram que as células de Kupffer atuariam como intermediários na modulação daatividade de CYPs hepáticos desencadeada por estímulos inflamatórios. Há estudos quesugerem que a diminuição da população das células de Kupfferatenua ou elimina a regulaçãodas CYPs hepáticas por estímulos inflamatórios.Além disso, estudos em culturas dehepatócitos in vitro, na ausência de células de Kupffer, tem constatado a regulação negativa daexpressão de CYPs hepáticas após estimulação com LPS. Nessa linha, o objetivo destepresente trabalho é investigar o papel das células de Kupffer na regulação da atividade deenzimas hepáticas de biotransformação de xenobióticos (CYPs) após estimulação inflamatóriacom LPS. Para isso, os níveis séricos de transaminases, e a histopatologia foram empregadospara avaliar o efeito do tratamento com diferentes doses de GdCl3sobre o tecido hepático.Noexperimento principal para investigar o papel das células de Kupffer, os ratos foram alocadosao acaso em quatro grupos. Foram quantificadosmarcadores bioquímicos no soro dos animaispara evidenciar danos ao tecido hepático causados pelos tratamentos e realizado o examehistopatológico...

It is known that inflammatory processes may modulate the expression and activity ofCYP enzymes. The mode by which inflammatory stimuli regulate CYP expression andactivity, however, remains unclear. Kupffer cells are resident macrophages in the liver andthus play an important role in a systemic inflammatory process or in sepsis. Gadoliniumchloride (GdCl3) has been reported to selectively kill an/or inhibit the activity of Kupffercells. Along this line, it has also been described that Gd decreases exacerbated inflammatoryresponses when it is administered prior to inflammatory stimuli in various animal models.Therole of Kupffer cells in the modulation of CYPs activity triggered by inflammatory stimuli,however, is not entirely clear in the literature. There are studies suggesting that a reduction inthe population of Kupffer cells attenuates the down-regulation of hepatic CYPs induced byinflammatory stimuli. However, GdCl3 was also described to decrease liver CYP activityirrespective of whether it depletes or not Kupffer cells. Moreover, in vitro studies showed thatLPS down-regulates the expression of CYP forms in hepatocyte cell lines in culture (in theabsence of Kupffer cells). To investigate whether Kupffer cells play a role in the regulation ofthe activity of liver xenobiotic biotransformation enzymes (CYPs) by inflammatorystimulation with LPS. The activity of transaminases in the blood serum (a marker for liverinjury) was determined and liver histopathology was evaluated in female Wistar rats. In a setof preliminary tests, rats were treated with different doses of GdCl3 or with LPS for selectingdoses and euthanasia time in the main experiment. In the main study experimental groups.Treatment associated liver injury was evaluated by levels of transaminases and alkalinephosphatase in the blood serum and by liver histopathology examination...

Inhibition of sphingosine kinase 1 ameliorates acute liver failure by reducing high-mobility group box 1 cytoplasmic translocation in liver cells.

AIM: To determine the therapeutic potential of sphingosine kinase 1 (Sphk1) inhibition and its underlying mechanism in a well-characterized mouse model of D-galactosamine (D-GalN)/lipopolysaccharide (LPS)-induced acute liver failure (ALF). METHODS: Balb/c mice were randomly assigned to different groups, with ALF induced by intraperitoneal injection of D-GaIN (600 mg/kg) and LPS (10 µg/kg). The Kaplan-Meier method was used for survival analysis. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels at different time points within one week were determined using a multi-parametric analyzer. Serum high-mobility group box 1 (HMGB1), tumor necrosis factor-α (TNF-α), interleukin (IL)-1ß, IL-6, IL-10, and sphingosine-1-phosphate were detected by enzyme-linked immunosorbent assay. Hepatic morphological changes at 36 h after acute liver injury induction were assessed by hematoxylin and eosin staining. HMGB1 expression in hepatocytes and cytoplasmic translocation were detected by immunohistochemistry. Expression of Sphk1 in liver tissue and peripheral blood mononuclear cells (PBMCs) was analyzed by Western blot. RESULTS: The expression of Sphk1 in liver tissue and PBMCs was upregulated in GalN/LPS-induced ALF. Upregulated Sphk1 expression in liver tissue was mainly caused by Kupffer cells, the resident macrophages of the liver. The survival rates of mice in the N,N-dimethylsphingosine (DMS, a specific inhibitor of SphK1) treatment group were significantly higher than that of the control group (P < 0.001). DMS treatment significantly decreased the levels of serum ALT and AST at 6, 12, and 24 h compared with that of the control group (P < 0.01 for all). Serum HMGB1 levels at 6, 12, and 24 h, as well as serum TNF-α, IL-6, and IL-1ß levels at 12 h, were significantly lower in the DMS treatment group than in the control group (P < 0.01 for all). Furthermore, hepatic inflammation, necrosis, and HMGB1 cytoplasm translocation in liver cells were significantly decreased in the DMS treatment group compared to the control group (43.72% ± 5.51% vs 3.57% ± 0.83%, χ(2) = 12.81, P < 0.01). CONCLUSION: Inhibition of SphK1 ameliorates ALF by reducing HMGB1 cytoplasmic translocation in liver cells, and so might be a potential therapeutic strategy for this disease.

Interferon α2b increases MMP-13 and IL-10 expression in Kupffer cells through MAPK signaling pathways.

BACKGROUND/AIMS: Kupffer cells play critical roles in both progression and resolution of liver fibrosis. Interferon α2b is an important immunoregulator which has anti-fibrotic effect in addition to its antiviral effect. It remained unclear whether the anti-fibrotic effect of interferon α2b is mediated by regulating functions of Kupffer cells. METHODOLOGY: Primary isolated Kupffer cells were cultured with interferon α2b and the expression of matrix metalloproteinase-13, interleukin-10, transforming growth factor -ß1 and tumor necrosis factor-α were measured. To investigate the role of mitogen-activated protein kinase pathways in regulating cytokines production by interferon α2b-stimulated Kupffer cells, inhibitors were given before cells were treated with interferon a2b. RESULTS: Cell purity was more than 98%. Stimulating Kupffer cells with interferon α2b led to a dramatic increase in matrix metalloproteinase-13 and interleukin-10 expression. In contrast, the values of tumor necrosis factor-α and transforming growth factor -ß1 remained unchanged throughout the 24-hour observation period. Inhibited ERK1/2 pathway prevented interferon α2b-triggered matrix metalloproteinase-13 production, while inhibited p38MAPK, ERK1/2 or JNK signaling pathways all blocked interleukin-10 expression. CONCLUSIONS: Interferon α2b may exert anti-fibrotic effect by elevating the level of matrix metalloproteinase-13 and interleukin-10 in Kupffer cells, in a mitogen-activated protein kinase signaling pathways-dependent manner.

Hexokinase II binding to mitochondria is necessary for Kupffer cell activation and is potentiated by ethanol exposure.

Ethanol exposure promotes the development of steatohepatitis, which can progress to end stage liver disease. Kupffer cells have been documented to play a key role in the genesis and progression of alcoholic liver disease with ethanol exposure enhancing Kupffer cell activation. In the present study, we identified the binding of hexokinase II to the mitochondria as a requirement for LPS-induced activation of Kupffer cells and its potentiation by ethanol. LPS and ethanol exposure induced a reduction in sirtuin-3 activity. In turn, the decline of sirtuin-3 activity led to the activation of cyclophilin-D, which mediated an increased binding of hexokinase II to the mitochondria. Suppression of cyclophilin-D expression or enforced detachment of hexokinase II from the mitochondria abrogated the LPS- and ethanol-induced stimulation of Kupffer cells, preventing NADPH oxidase and inflammasome activation. Moreover, activation of AMP-activated protein kinase restored sirtuin-3 activity, thereby preventing LPS and ethanol from stimulating the binding of hexokinase II to the mitochondria and precluding NADPH oxidase and inflammasome activation.

Ron receptor-dependent gene regulation of Kupffer cells during endotoxemia.

BACKGROUND: Ron receptor tyrosine kinase signaling in macrophages, including Kupffer cells and alveolar macrophages, suppresses endotoxin-induced proinflammatory cytokine/chemokine production. Further, we have also identified genes from Ron replete and Ron deplete livers that were differentially expressed during the progression of liver inflammation associated with acute liver failure in mice by microarray analyses. While important genes and signaling pathways have been identified downstream of Ron signaling during progression of inflammation by this approach, the precise role that Ron receptor plays in regulating the transcriptional landscape in macrophages, and particular in isolated Kupffer cells, has still not been investigated. METHODS: Kupffer cells were isolated from wild-type (TK+/+) and Ron tyrosine kinase deficient (TK-/-) mice. Ex vivo, the cells were treated with lipopolysaccharide (LPS) in the presence or absence of the Ron ligand, hepatocyte growth factor-like protein (HGFL). Microarray and qRT-PCR analyses were utilized to identify alterations in gene expression between genotypes. RESULTS: Microarray analyses identified genes expressed differentially in TK+/+ and TK-/- Kupffer cells basally as well as after HGFL and LPS treatment. Interestingly, our studies identified Mefv, a gene that codes for the anti-inflammatory protein pyrin, as an HGFL-stimulated Ron-dependent gene. Moreover, lipocalin 2, a proinflammatory gene, which is induced by LPS, was significantly suppressed by HGFL treatment. Microarray results were validated by qRT-PCR studies on Kupffer cells treated with LPS and HGFL. CONCLUSION: The studies herein suggest a novel mechanism whereby HGFL-induced Ron receptor activation promotes the expression of anti-inflammatory genes while inhibiting genes involved in inflammation with a net effect of diminished inflammation in macrophages.

Aldehyde dehydrogenase 2 deficiency ameliorates alcoholic fatty liver but worsens liver inflammation and fibrosis in mice.

UNLABELLED: Aldehyde dehydrogenase 2 (ALDH2) is the major enzyme that metabolizes acetaldehyde produced from alcohol metabolism. Approximately 40-50% of East Asians carry an inactive ALDH2 gene and exhibit acetaldehyde accumulation after alcohol consumption. However, the role of ALDH2 deficiency in the pathogenesis of alcoholic liver injury remains obscure. In the present study, wild-type and ALDH2(-/-) mice were subjected to ethanol feeding and/or carbon tetrachloride (CCl4 ) treatment, and liver injury was assessed. Compared with wild-type mice, ethanol-fed ALDH2(-/-) mice had higher levels of malondialdehyde-acetaldehyde (MAA) adduct and greater hepatic inflammation, with higher hepatic interleukin (IL)-6 expression but surprisingly lower levels of steatosis and serum alanine aminotransferase (ALT). Higher IL-6 levels were also detected in ethanol-treated precision-cut liver slices from ALDH2(-/-) mice and in Kupffer cells isolated from ethanol-fed ALDH2(-/-) mice than those levels in wild-type mice. In vitro incubation with MAA enhanced the lipopolysaccharide (LPS)-mediated stimulation of IL-6 production in Kupffer cells. In agreement with these findings, hepatic activation of the major IL-6 downstream signaling molecule signal transducer and activator of transcription 3 (STAT3) was higher in ethanol-fed ALDH2(-/-) mice than in wild-type mice. An additional deletion of hepatic STAT3 increased steatosis and hepatocellular damage in ALDH2(-/-) mice. Finally, ethanol-fed ALDH2(-/-) mice were more prone to CCl4 -induced liver inflammation and fibrosis than ethanol-fed wild-type mice. CONCLUSION: ALDH2(-/-) mice are resistant to ethanol-induced steatosis but prone to inflammation and fibrosis by way of MAA-mediated paracrine activation of IL-6 in Kupffer cells. These findings suggest that alcohol, by way of acetaldehyde and its associated adducts, stimulates hepatic inflammation and fibrosis independent from causing hepatocyte death, and that ALDH2-deficient individuals may be resistant to steatosis and blood ALT elevation, but are prone to liver inflammation and fibrosis following alcohol consumption.