Pretreatment with lipopolysaccharide attenuates diethylnitrosamine-caused liver injury in mice via TLR4-dependent induction of Kupffer cell M2 polarization

An Eye on Kupffer Cells: Development, Phenotype and the Macrophage Niche

Macrophages are key participants in the maintenance of tissue homeostasis under normal and pathological conditions, and implement a rich diversity of functions. The largest population of resident tissue macrophages is found in the liver. Hepatic macrophages, termed Kupffer cells, are involved in the regulation of multiple liver functionalities. Specific differentiation profiles and functional activities of tissue macrophages have been attributed to the shaping role of the so-called tissue niche microenvironments. The fundamental macrophage niche concept was lately shaken by a flood of new data, leading to a revision and substantial update of the concept, which constitutes the main focus of this review. The macrophage community discusses contemporary evidence on the developmental origins of resident macrophages, notably Kupffer cells and the issues of heterogeneity of the hepatic macrophage populations, as well as the roles of proliferation, cell death and migration processes in the maintenance of macrophage populations of the liver. Special consideration is given to interactions of Kupffer cells with other local cell lineages, including Ito cells, sinusoidal endothelium and hepatocytes, which participate in the maintenance of their phenotypical and functional identity.

The Role of Myeloid Cells in Hepatotoxicity Related to Cancer Immunotherapy

Drug-related hepatotoxicity is an emerging clinical challenge with the widening use of immunotherapeutic agents in the field of oncology. This is an important complication to consider as more immune oncological targets are being identified to show promising results in clinical trials. The application of these therapeutics may be complicated by the development of immune-related adverse events (irAEs), a serious limitation often requiring high-dose immunosuppression and discontinuation of cancer therapy. Hepatoxicity presents one of the most frequently encountered irAEs and a better understanding of the underlying mechanism is crucial for the development of alternative therapeutic interventions. As a novel drug side effect, the immunopathogenesis of the condition is not completely understood. In the liver, myeloid cells play a central role in the maintenance of homeostasis and promotion of inflammation. Recent research has identified myeloid cells to be associated with hepatic adverse events of various immune modulatory monoclonal antibodies. In this review article, we provide an overview of the role of myeloid cells in the immune pathogenesis during hepatoxicity related to cancer immunotherapies and highlight potential treatment options.

Lipopolysaccharide from biofilm-forming Pseudomonas aeruginosa PAO1 induces macrophage hyperinflammatory responses

Introduction. Macrophages polarization is essential in infection control. Llipopolysaccharide (LPS) plays an essential role in host innate immune system-pathogen interaction. The LPS structure of Pseudomonas aeruginosa modifies in the adaptation of this pathogen to biofilm-related chronic infection.Gap statement. There have been several studies on LPS induced polarization of human and mouse macrophages with different results. And it was reported that the lipid A structure of the LPS derived from biofilm-forming Pseudomonas aeruginosa strain PAO1 was modified.Aim. This study aimed to investigate the effect and the involved pathway of LPS from biofilm-forming PAO1 on human and murine macrophage polarization.Methodology. LPS was isolated from biofilm-forming and planktonic PAO1 and quantified. Then the LPS was added to PMA-differentiated human macrophage THP-1 cells and Raw264.7 murine macrophage cells. The expression of iNOS, Arg-1, IL4, TNF-α, CCL3, and CCL22 was analysed in the different cell lines. The expression of TICAM-1 and MyD88 in human THP-1 macrophages was quantified by Western blot. PAO1 infected macrophages at different polarization states, and the intracellular bacterial growth in macrophages was evaluated.Results. LPS from biofilm-forming PAO1 induced more marked hyperinflammatory responses in THP-1 and Raw264.7 macrophages than LPS derived from planktonic PAO1, and these responses were related to the up-regulation of MyD88. Intracellular growth of PAO1 was significantly increased in THP-1 macrophages polarized by LPS from biofilm-forming PAO1, but decreased both in THP-1 and Raw264.7 macrophages polarized by LPS from planktonic PAO1.Conclusion. The presented in vitro study indicates that LPS derived from biofilm-forming PAO1 induces enhanced M1 polarization in human and murine macrophage cell lines than LPS from planktonic PAO1.

Flightless-I is a potential biomarker for the early detection of alcoholic liver disease

Alcoholic liver disease (ALD) is closely linked to oxidative stress induction. Antioxidant enzymes balance oxidative stress and function as intermediary signaling regulators. Nucleoredoxin (NXN), an antioxidant enzyme, regulates physiological processes through redox-sensitive interactions. NXN interacts with myeloid differentiation primary response gene-88 (MYD88) and flightless-I (FLII) to regulate toll-like receptor 4 (TLR4)/MYD88 pathway activation, but FLII also regulates key cell processes and is secreted into the bloodstream. However, the effects of chronic ethanol consumption recapitulated by either ethanol alone or in combination with lipopolysaccharides (LPS), as a two-hit ALD model, on FLII/NXN/MYD88 complex and FLII secretion have not been explored yet. In this study, we have demonstrated that ethanol feeding increased FLII protein levels, its nuclear translocation and plasma secretion, and modified its tissue distribution both in vivo and in vitro ALD models. Ethanol increased MYD88/FLII interaction ratio, and decreased NXN/MYD88 interaction ratio but this was partially reverted by two-hit model. While ethanol and two-hit model increased MYD88/TLR4 interaction ratio, two-hit model significantly decreased FLII nuclear translocation and its plasma secretion. Ethanol and LPS provoked similar effects in vitro; however, NXN overexpression partially reverted these alterations, and ethanol alone increased FLII secretion into culture medium. In summary, by analyzing the response of FLII/NXN/MYD88 complex during ALD early progression both in vivo and in vitro, we have discovered that the effects of chronic ethanol consumption disrupt this complex and identified FLII as a candidate non-invasive plasma biomarker for the early detection of ALD.

STAT5a induces endotoxin tolerance by alleviating pyroptosis in kupffer cells

Pyroptosis, a newly discovered type of programmed cell death, affects endotoxin tolerance in macrophages. However, the factors acting on the nod-like receptor 3 (Nlrp3) inflammasome and caspase1 activation to impede pyroptosis and resulting in tolerance and survival in sepsis were needed to discovered. Here, we found that signal transducer and activator of transcription 5A (STAT5a) restrains pyroptosis in Kupffer cells (KCs) and induces endotoxin tolerance (ET) in a sepsis model. The lentiviral knockdown of STAT5a led to enhanced pyroptosis in KCs, increased IL-1β production and decreased IL-10 production via intricate NF-κb signaling regulation. Thus, our findings reveal a novel mechanism of STAT5a-midiated endotoxin tolerance in KCs.

FcRγ deficiency improves survival in experimental sepsis by down-regulating TLR4 signaling pathway

Fc receptor common γ signaling chain (FcRγ), a common subunit shared by Fc receptors (FcγRI, III, IV, FcαRI, and FcεRI), is an important immune regulator both in innate and adaptive immunity. Previous studies have shown that FcRγ was a potential target of inflammatory diseases, whereas the role of FcRγ in sepsis has been poorly understood. In this study, we found that deficiency of FcRγ resulted in increased survival in lipopolysaccharide (LPS)/D-galactosamine and E. coli-induced sepsis in mice. This protective effect was characterized by decreased TNF-α, IL-6, and IL-10. Further experiments in bone marrow-derived macrophages (BMDMs) in vitro also showed that FcRγ deficiency resulted in decreased production of TNF-α, IL-6, and IL-10 upon LPS stimulation. The mechanism study showed that FcRγ was physiologically associated with toll-like receptor 4 (TLR4), and tyrosine phosphorylation of FcRγ mediated TLR4 signaling pathway, followed by increased ERK phosphorylation upon LPS stimulation. Our results suggest that FcRγ might be a potential therapeutic target of sepsis.

Baishouwu Extract Suppresses the Development of Hepatocellular Carcinoma via TLR4/MyD88/NF-κB Pathway

Purpose: The root of Cynanchum auriculatum Royle ex Wight, known as Baishouwu, has been widely used for a tonic supplement since ancient times. The current study was performed to explore the effect of Baishouwu extract on the development of experimental hepatocellular carcinoma (HCC) and the potential mechanism involved.

Methods: Rats were injected diethylnitrosamine (DEN) to initiate the multistep hepatocarcinogenesis. Animals were treated concurrently with Baishouwu extract given daily by oral gavage for 20 weeks to evaluate its protective effects. Time series sera and organ samples from each group were collected to evaluate the effect of Baishouwu extract on hepatic carcinogenesis.

Results: It was found that Baishouwu extract pretreatment successfully attenuated liver injury induced by DEN, as shown by decreased levels of serum biochemical indicators (AST, ALT, ALP, TP, and T-BIL). Administration of Baishouwu extract inhibited the fibrosis-related index in serum and live tissue, respectively from inflammation stage to HCC stage after DEN treatment. It significantly reduced the incidence and multiplicity of DEN-induced HCC development in a dose-dependent manner. Macroscopic and microscopic features suggested that pretreatment with Baishouwu extract for 20 weeks was effective in inhibiting DEN-induced inflammation, liver fibrosis, and HCC. Furthermore, TLR4 overexpression induced by DEN was decreased by Baishouwu extract, leading to the markedly down-regulated levels of MyD88, TRAF6, NF-κB p65, TGF-β1 and α-SMA in hepatitis, cirrhosis, and hepatocarcinoma.

Conclusion: In conclusion, Baishouwu extract exhibited potent effect on the development of HCC by altering TLR4/MyD88/ NF-κB signaling pathway in the sequence of hepatic inflammation-fibrosis-cancer, which provided novel insights into the mechanism of Baishouwu extract as a candidate for the pretreatment of HCC in the future.

A literature review for the mechanisms of stress-induced liver injury

INTRODUCTION

Experimental studies and clinical observations have shown that stress can damage hepatic tissue both directly and indirectly. Many studies have partially revealed the contributors of stress-induced liver injury; however, the whole process has not yet been uncovered. This review aims to summarize the mechanisms that have been proposed to be involved.

METHODS

A literature search was conducted using PubMed (http://www.ncbi.nlm.nih.gov/pubmed) in its entirety up to March 2018, and analyzed the animal-derived mechanistic studies on stress-induced liver injury.

RESULTS

The liver is the organ that meets and filters a mass of alien material, and then maintains immune tolerance under physiological conditions. Under stress conditions, however, immune tolerance is interrupted, which results in the induction of inflammation in the liver. Contributors to this process can be categorized as follows: hypoxia-reoxygenation, over-activation of Kupffer cells and oxidative stress, influx of gut-derived lipopolysaccharide and norepinephrine, and over-production of stress hormones and activation of the sympathetic nerve.

CONCLUSIONS

Psychological stress is associated with a variety of pathological conditions resulting in liver injury through multiple systems, including the sympathetic nervous and adrenocortical system. Mechanistic understanding of this phenomenon is important for the clinical practice of managing patients with hepatic disorders and should be explored further in the future.

USP25 promotes endotoxin tolerance via suppressing K48-linked ubiquitination and degradation of TRAF3 in Kupffer cells

The inhibition of tumor necrosis factor receptor-associated factor 3 (TRAF3) degradation induces endotoxin tolerance (ET) in macrophages. However, the mechanisms leading to TRAF3 inhibition by ET are largely unknown. Here, we found that ubiquitin-specific peptidase 25 (USP25), a deubiquitinating enzyme (DUB), interacted with TRAF3 and stabilized ET in Kupffer cells (KCs). Lentiviral knockdown of USP25 activated K48-linked ubiquitination of TRAF3 and the cytoplasmic translocation of the Myd88-associated multiprotein complex in tolerized KCs. This outcome led to a subsequent activation of Myd88-dependent c-Jun N-terminal kinase (JNK) and p38-mediated downregulation of inflammatory cytokines. The overexpression of TRAF3 attenuated the proinflammatory effects of USP25 knockdown in tolerized KCs. Thus, our findings reveal a novel mechanism of endotoxin-mediated TRAF3 degradation in KCs.

Aflatoxin B1 Promotes Influenza Replication and Increases Virus Related Lung Damage via Activation of TLR4 Signaling

Aflatoxin B₁ (AFB₁), which alters immune responses to mammals, is one of the most common mycotoxins in feeds and food. Swine influenza virus (SIV) is a major pathogen of both animals and humans. However, there have been few studies about the relationship between AFB₁ exposure and SIV replication. Here, for the first time, we investigated the involvement of AFB₁ in SIV replication in vitro and in vivo and explored the underlying mechanism using multiple cell lines and mouse models. In vitro studies demonstrated that low concentrations of AFB₁ (0.01–0.25 μg/ml) markedly promoted SIV replication as revealed by increased viral titers and matrix protein (M) mRNA and nucleoprotein (NP) levels in MDCK cells, A549 cells and PAMs. In vivo studies showed that 10–40 μg/kg of AFB₁ exacerbated SIV infection in mice as illustrated by significantly higher lung virus titers, viral M mRNA levels, NP levels, lung indexes and more severe lung damage. Further study showed that AFB₁ upregulated TLR4, but not other TLRs, in SIV-infected PAMs. Moreover, AFB₁ activated TLR4 signaling as demonstrated by the increases of phosphorylated NFκB p65 and TNF-α release in PAMs and mice. In contrast, TLR4 knockdown or the use of BAY 11-7082, a specific inhibitor of NFκB, blocked the AFB₁-promoted SIV replication and inflammatory responses in PAMs. Furthermore, a TLR4-specific antagonist, TAK242, and TLR4 knockout both attenuated the AFB₁-promoted SIV replication, inflammation and lung damage in mice. We therefore conclude that AFB₁ exposure aggravates SIV replication, inflammation and lung damage by activating TLR4-NFκB signaling.

Ethanol targets nucleoredoxin/dishevelled interactions and stimulates phosphatidylinositol 4-phosphate production in vivo and in vitro

Nucleoredoxin (NXN) is a redox-regulating protein potentially targeted by reactive oxygen species (ROS). It regulates molecular pathways that participate in several key cellular processes. However, the role of NXN in the alcohol liver disease (ALD) redox regulation has not been fully understood. Here, we investigated the effects of ethanol and ethanol plus lipopolysaccharide, a two-hit liver injury model (Ethanol/LPS), on NXN/dishevelled (DVL) interaction and on DVL-dependent phosphoinositides production both in mouse liver and in a co-culture system consisting of human hepatic stellate cells (HSC) and ethanol metabolizing-VL17A human hepatocyte cells. Ethanol and two-hit model increased Nxn protein and mRNA expression, and 4-hydroxynonenal adducts. Two-hit model promoted Nxn nuclear translocation and Dvl/Phosphatidylinositol 4-kinase type-IIα (Pi4k2a) interaction ratio but surprisingly decreased Dvl protein and mRNA levels and reverted ethanol-induced Nxn/Dvl and Dvl/frizzled (Fzd) interaction ratios. Ethanol resulted in a significant increase of Dvl protein and mRNA expression, and decreased Nxn/Dvl interaction ratio but promoted the interaction of Dvl with Fzd and Pi4k2a; formation of this complex induced phosphatidylinositol 4-phosphate [PI(4)P] production. Ethanol and LPS treatments provoked similar alterations on NXN/DVL interaction and its downstream effect in HSC/VL17A co-culture system. Interestingly, ROS and glutathione levels as well as most of ethanol-induced alterations were modified by NXN overexpression in the co-culture system. In conclusion, two-hit model of ethanol exposure disrupts NXN/DVL homeostatic status to allow DVL/FZD/PI4K2A complex formation and stimulates PI(4)P production. These results provide a new mechanism showing that NXN also participates in the regulation of phosphoinositides production that is altered by ethanol during alcoholic liver disease progression.

Shikonin protects against D-Galactosamine and lipopolysaccharide-induced acute hepatic injury by inhibiting TLR4 signaling pathway

Shikonin, a naphthoquinone isolated from the root of medical herb Lithospermum erythrorhizon, has been reported to have anti-inflammatory effect. However, there is no related research for the treatment of shikonin on hepaic injury. The purpose of this study was to investigate the effects of shikonin on D-Galactosamine and Lipopolysaccharide-induced hepatic injury in mice. Male BALB/c mice were pretreated with shikonin 1 h before LPS/D-GalN treatment. The pathological changes of hepatic injury were detected by H&E staining. The levels of TNF-α and IL-1β in hepatic tissues were detected by ELISA. The levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were also measured in this study. In addition, the expression of TLR4 and NF-κB were determined by western blot analysis. These results suggest that shikonin effectively prevents LPS/D-GalN-induced liver injury by inhibiting AST and ALT levels, as well as inflammatory cytokines TNF-α and IL-1β production. The expression of TLR4 and NF-κB activation induced by LPS/D-GalN were also inhibited by treatment of shikonin. In vitro, shikonin significantly inhibited LPS-induced TNF-α and IL-1β production, as well as TLR4 expression and NF-κB activation. In conclusion, the results of the present study suggest that shikonin attenuates LPS/D-GalN-induced hepatic injury by inhibiting TLR4 signaling pathway.

Modulation of liver tolerance by conventional and nonconventional antigen-presenting cells and regulatory immune cells

The liver is a tolerogenic organ with exquisite mechanisms of immune regulation that ensure upkeep of local and systemic immune tolerance to self and foreign antigens, but that is also able to mount effective immune responses against pathogens. The immune privilege of liver allografts was recognized first in pigs in spite of major histo-compatibility complex mismatch, and termed the "liver tolerance effect". Furthermore, liver transplants are spontaneously accepted with only low-dose immunosuppression, and induce tolerance for non-hepatic co-transplanted allografts of the same donor. Although this immunotolerogenic environment is favorable in the setting of organ transplantation, it is detrimental in chronic infectious liver diseases like hepatitis B or C, malaria, schistosomiasis or tumorigenesis, leading to pathogen persistence and weak anti-tumor effects. The liver is a primary site of T-cell activation, but it elicits poor or incomplete activation of T cells, leading to their abortive activation, exhaustion, suppression of their effector function and early death. This is exploited by pathogens and can impair pathogen control and clearance or allow tumor growth. Hepatic priming of T cells is mediated by a number of local conventional and nonconventional antigen-presenting cells (APCs), which promote tolerance by immune deviation, induction of T-cell anergy or apoptosis, and generating and expanding regulatory T cells. This review will focus on the communication between classical and nonclassical APCs and lymphocytes in the liver in tolerance induction and will discuss recent insights into the role of innate lymphocytes in this process.