Macrophage Phenotype in Liver Injury and Repair

miR-21-regulated M2 polarization of macrophage is involved in arsenicosis-induced hepatic fibrosis through the activation of hepatic stellate cells

Arsenicosis induced by chronic exposure to arsenic is recognized as one of the main damaging effects on public health. Exposure to arsenic can cause hepatic fibrosis, but the molecular mechanisms by which this occurs are complex and elusive. It is not known if miRNAs are involved in arsenic-induced liver fibrosis. We found that in the livers of mice exposed to arsenite, there were elevated levels of microRNA-21 (miR-21), phosphorylated mammalian target of rapamycin (p-mTOR), and arginase 1 (Arg1); low levels of phosphatase and tensin homolog (PTEN); and more extensive liver fibrosis. For cultured cells, arsenite-induced miR-21, p-mTOR, and Arg1; decreased PTEN; and promoted M2 polarization of macrophages derived from THP-1 monocytes (THP-M), which caused secretion of fibrogenic cytokines, including transforming growth factor-β1. Coculture of arsenite-treated, THP-M with LX-2 cells induced α-SMA and collagen I in the LX-2 cells and resulted in the activation of these cells. Downregulation of miR-21 in THP-M inhibited arsenite-induced M2 polarization and activation of LX-2 cells, but cotransfection with PTEN siRNA or a miR-21 inhibitor reversed this inhibition. Moreover, knockout of miR-21 in mice attenuated liver fibrosis and M2 polarization compared with WT mice exposed to arsenite. Additionally, LN, PCIII, and HA levels were higher in patients with higher hair arsenic levels, and levels of miR-21 were higher than controls and positively correlated with PCIII, LN, and HA levels. Thus, arsenite induces the M2 polarization of macrophages via miR-21 regulation of PTEN, which is involved in the activation of hepatic stellate cells and hepatic fibrosis. The results establish a previously unknown mechanism for arsenicosis-induced fibrosis.

IOX1 protects from TGF-β induced fibrosis in LX-2 cells via the regulation of extracellular matrix protein expression

The aim of the present study was to investigate the effect of the histone H3K9 demethylase inhibitor, IOX1, on the mechanism of hepatic fibrosis in TGF-β-induced human hepatic stellate LX-2 cells. Cellular proliferation, apoptosis, histone H3K9 dimethylation (H3K9me2), protein expression of extracellular matrix (ECM)-related proteins α-smooth muscle actin (SMA), type I collagen (Col I), MMP-1 and TIMP-1 were measured. H3K9me2 levels in the promoter region of ECM-related genes were detected by real-time cell analysis (RTCA), flow cytometry, western blotting and chromatin immunoprecipitation (ChIP) in LX-2 cells. IOX1 significantly inhibited cell proliferation and the IC₅₀ of IOX1 was 100 µM in cells treated with IOX1 for 48 h. IOX1 significantly induced apoptosis in LX-2 cells in a concentration-dependent manner. In addition, different concentration of IOX1 increased the level of H3K9me2 and downregulated the expression of α-SMA, Col I, MMP-1 and TIMP-1 in TGF-β-induced LX-2 cells. ChIP measurements indicated that H3K9me2 levels in the promotor region of the corresponding genes were increased in TGF-β-induced LX-2 cells. IOX1 may elevate H3K9me2 in the promotor region of Col I, MMP-1, and TIMP-1 genes to regulate α-SMA, Col I, MMP-1 and TIMP-1 protein expression to induce cell apoptosis, inhibit LX-2 cell proliferation and oppose hepatic fibrotic activity.

Role of Neutrophils in the Pathogenesis of Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) includes a spectrum of liver disorders, from fatty liver to nonalcoholic steatohepatitis (NASH), cirrhosis, and hepatocellular carcinoma. Compared with fatty liver, NASH is characterized by increased liver injury and inflammation, in which liver-infiltrating immune cells, with neutrophil infiltration as a hallmark of NASH, play a critical role in promoting the progression of fatty liver to NASH. Neutrophils are the first responders to injury and infection in various tissues, establishing the first line of defense through multiple mechanisms such as phagocytosis, cytokine secretion, reactive oxygen species production, and neutrophil extracellular trap formation; however, their roles in the pathogenesis of NASH remain obscure. The current review summarizes the roles of neutrophils that facilitate the progression of fatty liver to NASH and their involvement in inflammation resolution during NASH pathogenesis. The notion that neutrophils are potential therapeutic targets for the treatment of NASH is also discussed.

Macrophage Polarization and Liver Ischemia-Reperfusion Injury

Ischemia-reperfusion injury refers to organ damage caused by the previous insufficient supply of oxygen and nutrients and the involvement of metabolic by-products after blood flow is restored. Liver ischemia-reperfusion injury (IRI) has become a hot research in recent years, because it occurs in many clinical scenarios. After the introduction of liver transplantation and vascular control techniques in liver surgery, liver ischemia-reperfusion injury is considered to be an important factor affecting postoperative mortality and morbidity. As the largest immune organ in the human body, liver contain a lot of immune cells such as resident macrophages (Kupffer cells), dendritic cells, natural killer cells, and natural killer T cells which play a key role in ischemia-reperfusion injury. Among those, macrophage-mediated excessive inflammatory response is considered to be an important factor in liver ischemia-reperfusion injury. The prominent feature of liver injury is an increase in the number of macrophages in liver due to the infiltration of blood monocytes and differentiation into monocyte-derived macrophages. Liver macrophages can be divided into M1 macrophages which can promote inflammation progress and M2 macrophages that inhibit inflammation progress according to their different phenotypes and functions. Both of them can regulate liver aseptic inflammation, and play an important role in triggering, maintaining, and improving liver ischemia-reperfusion injury. This review summarizes studies of macrophage polarization on liver ischemia-reperfusion injury in recent years, to provide potential ideas for translation application in future clinical management.

Molecular Pathways Modulated by Mesenchymal Stromal Cells and Their Extracellular Vesicles in Experimental Models of Liver Fibrosis

End-stage liver fibrosis is common to all chronic liver diseases. Since liver transplantation has several limitations, including lack of donors, immunological rejection, and high medical costs, therapeutic alternatives are needed. The administration of mesenchymal stromal cells (MSCs) has been proven effective in tissue regeneration after damage. However, the risk of uncontrolled side effects, such as cellular rejection and tumorigenesis, should be taken into consideration. A safer alternative to MSC transplantation is represented by the MSC secretome, which retains the same beneficial effect of the cell of origin, without showing any considerable side effect. The paracrine effect of MSCs is mainly carried out by secreted particles in the nanometer range, known as extracellular vesicles (EVs) that play a fundamental role in intercellular communication. In this review, we discuss the current literature on MSCs and MSC-EVs, focusing on their potential therapeutic action in liver fibrosis and on their molecular content (proteins and RNA), which contributes in reverting fibrosis and prompting tissue regeneration.

Baicalein attenuates acute liver injury by blocking NLRP3 inflammasome

Infection and/or drug-mediated acute liver injury, the leading cause of lethal liver failure, is a critical health problem worldwide and lacks effective treatment. Here, we used Lipopolysaccharides (LPS)/D-galactosamine (D-gal)-treated primary hepatocytes to screen a natural library that contains 1130 chemicals. Baicalein in the library showed highest inhibitory effects against LPS/D-Gal-induced liver injury. In-vivo study similarly validated the protection of baicalein against dampened liver function and increased lethality after a challenge of LPS/D-Gal. Using a cytometric bead array, we found that IL-1α and IL-1β, the downstream of NLRP3, had highest reduction among the plasma inflammatory cytokines in LPS/D-Gal-challenged mice after a treatment of baicalein. To determine the target of baicalein and the underlying mechanism, Nlrp3^-/-, Gsdmd^-/- or WT mice were treated with or without baicalein, IL-1R antibody or recombinant mouse IL-1β (rmIL-1β) prior to a challenge of LPS/D-Gal. Deficiency of Nlrp3 or Gsdmd significantly restored LPS/D-Gal-induced acute liver injury and lethality, and further administration of baicalein did not have additive effects. In addition, the inhibition of the downstream by IL-1R antibody phenocopied the knockout of Nlrp3 or Gsdmd. Moreover, a challenge of rmIL-1β reversed the improvement in Nlrp3^-/- mice or the mice treated with baicalein. Taken together, NLRP3 functions as a pivotal promoter in acute liver injury and baicalein attenuates acute liver injury by inhibiting NLRP3 inflammasome.

A dopamine-precursor-based nanoprodrug for in-situ drug release and treatment of acute liver failure by inhibiting NLRP3 inflammasome and facilitating liver regeneration

Acute liver failure (ALF) is a severe liver disease with high mortality rate. Inflammasome is a newly-found and promising target for effective treatment of immunity-associated diseases including liver disease, and dopamine has recently been proved as an inhibitor for NLRP3 inflammasome. This work demonstrates a diselenide-based nanodrug for ALF treatment through inhibiting NLRP3 inflammasome activation and enhancing liver regeneration. A diselenide-containing molecule (DSeSeD) has been synthesized via covalently linking two l-Dopa molecules to a diselenide linker, and the resultant molecules form stable nanoparticles in aqueous media and encapsulate SW033291 (an inhibitor of prostaglandin-degrading enzyme that hampers liver regeneration) to produce the nanodrug (SW@DSeSeD). As a nanoscale prodrug, SW@DSeSeD protects its payloads from decomposition in bloodstream upon administration, accumulates in liver of ALF mice, then responds to the overexpressed ROS and thereby releases SW033291 as well as a stable dopamine precursor that can transform into dopamine in hepatic cells, thus achieving significant therapeutic efficacy against ALF through inhibiting NLRP3 inflammasome activation and enhancing hepatic regeneration. Moreover, multiple contrast agents have been loaded onto the nanodrug to achieve fluorescence, optoacoustic and magnetic resonance imaging for nanodrug location and disease evaluation.

Intrahepatic T helper 17 cells recruited by hepatitis B virus X antigen-activated hepatic stellate cells exacerbate the progression of chronic hepatitis B virus infection

Immunopathological injury induced by persistent hepatitis B virus (HBV) infection contributes to the progression from chronic hepatitis B (CHB) to hepatic cirrhosis and hepatocellular carcinoma (HCC). Regulatory T cells (Tregs), CD4⁺ T helper (Th) cells, and hepatic stellate cells (HSCs) are considered to be the pivotal factors during this progression. In this study, our aim was to investigate the molecular mechanisms of liver immunopathological injury associated with Tregs, CD4⁺ Th cells, and HSCs. Liver tissues were collected to assay the cytokines and distribution and frequencies of CD4⁺ Th cells and Tregs. The chemotaxis of Th17 cells towards the liver and the interactions between IL-22, IL-17A, and HSCs were explored. The data showed the frequencies of Th17 cells, and their effector molecules IL-22 and IL-17A were increased along with the severity of chronic liver diseases. However, the frequencies of Tregs were decreased in HBV-associated cirrhotic tissues compared with those in CHB tissues and HCC tissues. hepatitis B virus X antigen (HBxAg)-activated HSCs recruited more Th17 cells into the liver and conduced to the secretion of IL-17A and IL-22 that could in turn stimulate the proliferation and fibrotic marker secretion of the HSCs. Therefore, we suggest that the interactions between Th17 cells, IL-17A, IL-22, and HSCs form a positive feedback loop that aggravated the progression of chronic liver disease with HBV infection through the phosphoinositide-3-kinase/protein kinase B (PI3K/AKT) signalling pathway. Our findings indicated the IL-17A/IL-22 pathway might become a new treatment target for liver cirrhosis and HCC.

Sodium tanshinone IIA sulfonate restrains fibrogenesis through induction of senescence in mice with induced deep endometriosis

RESEARCH QUESTION

Does sodium tanshinone IIA sulfonate (STS) induce cellular senescence in endometriotic lesions and thus restrict lesional development and fibrogenesis in a recently established mouse model of deep endometriosis?

DESIGN

Prospective randomized animal experiment in which deep endometriosis was induced in female Balb/C mice, which were then randomly divided into three groups (low-dose STS, high-dose STS and inert vehicle control) and received treatment for 2 weeks. All mice were then sacrificed and their lesions excised and harvested. Lesion weight was quantified and all lesion samples were subjected to histochemical analysis of the extent of lesional fibrosis by Masson trichrome staining, and of cellular senescence by senescence-associated β-galactosidase (SA-β-gal), along with immunohistochemistry analyses of p53, CCN1, activate Salvador 1 (Sav1), hyaluronan synthase 2 (HAS2), survivin, granulocyte-macrophage colony-stimulating factor (GM-CSF) and CD163-positive M2 macrophages. Plasma P-selectin and hyaluronic acid levels were also quantified. Hotplate testing was also administered before the induction, then before and after treatment.

RESULTS

STS treatment resulted in significantly reduced lesion weight, stalled lesional fibrogenesis and improved hyperalgesia, seemingly through the induction of cellular senescence by activating p53, Sav1 and CCN1 while suppressing HAS2, survivin and GM-CSF, resulting in increased apoptosis and reduced lesional infiltration of alternatively activated macrophages. In addition, STS treatment significantly reduced the plasma concentration of P-selectin and hyaluronic acid, possibly leading to reduced lesional platelet aggregation.

CONCLUSIONS

STS appears to be a promising compound for treating endometriosis. The results suggest that senescence may restrict lesional progression and fibrogenesis, and targeting the senescence pathway may have desirable therapeutic potential.

Cholesterol Induces Nrf-2- and HIF-1α-Dependent Hepatocyte Proliferation and Liver Regeneration to Ameliorate Bile Acid Toxicity in Mouse Models of NASH and Fibrosis

Nonalcoholic steatohepatitis (NASH) is currently one of the most common liver diseases worldwide. The toxic effects of lipids and bile acids contribute to NASH. The regenerative pathway in response to damage to the liver includes activation of the inflammatory process and priming of hepatocytes to proliferate to restore tissue homeostasis. However, the effects of cholesterol on bile acid toxicity, inflammation, and fibrosis remain unknown. We have used two mouse models of bile acid toxicity to induce liver inflammation and fibrosis. A three-week study was conducted using wild-type mice receiving an atherogenic diet (1% (w/w) cholesterol and 0.5% (w/w) cholic acid) and its separate constituents. Mdr2-/- mice were fed a high-cholesterol-enriched diet or standard AIN-93 diet for 6 weeks. We measured serum transaminase levels to assess liver tissue necrosis and fibrosis; iNOS, SAA1, SAA2, and F4/80 levels to determine liver inflammation; PCNA and HGF levels to evaluate proliferative response; and Nrf-2, HIF-1α, and downstream gene expression to establish protective responses. In both studies, high bile acid levels increased serum transaminases and liver fibrosis, whereas cholesterol supplementation attenuated these effects. Cholesterol supplementation activated survival and the robustness of HIF-1α and Nrf-2 gene expression in hepatocytes, induced liver inflammation and hepatocyte proliferation, and inhibited stellate cell hyperplasia and fibrosis. In conclusion, our data show for the first time that cholesterol intake protects against bile acid liver toxicity. The balance between hepatic cholesterol and bile acid levels may be of prognostic value in liver disease progression and trajectory.

All Roads Lead to the Liver: Metal Nanoparticles and Their Implications for Liver Health

Metal nanoparticles (NPs) are frequently encountered in daily life, and concerns have been raised about their toxicity and safety. Among which, they naturally accumulate in the liver after introduction into the body, independent of the route of administration. Some NPs exhibit intrinsic pharmaceutical effects that are related to their physical parameters, and their inadvertent accumulation in the liver can exert strong effects on liver function and structure. Even as such physiological consequences are often categorically dismissed as toxic and deleterious, there are cell type-specific and NP-specific biological responses that elicit distinctive pharmacological consequences that can be harnessed for good. By limiting the scope of discussion to metallic NPs, this work attempts to provide a balanced perspective on their safety in the liver, and discusses both possible therapeutic benefits and potential accidental liver damage arising from their interaction with specific parenchymal and nonparenchymal cell types in the liver.

Fibrotic liver has prompt recovery after ischemia-reperfusion injury

Hepatic ischemia-reperfusion (I/R) is a major complication of liver resection, trauma, and liver transplantation; however, liver repair after I/R in diseased liver has not been studied. The present study sought to determine the manner in which the fibrotic liver repairs itself after I/R. Liver fibrosis was established in mice by CCl4 administration for 6 wk, and then liver I/R was performed to investigate liver injury and subsequent liver repair in fibrotic and control livers. After I/R, fibrotic liver had more injury compared with nonfibrotic, control liver; however, fibrotic liver showed rapid resolution of liver necrosis and reconstruction of liver parenchyma. Marked accumulation of hepatic stellate cells and macrophages were observed specifically in the fibrotic septa in early reparative phase. Fibrotic liver had higher numbers of hepatic stellate cells, macrophages, and hepatic progenitor cells during liver recovery after I/R than did control liver, but hepatocyte proliferation was unchanged. Fibrotic liver also had significantly greater number of phagocytic macrophages than control liver. Clodronate liposome injection into fibrotic mice after I/R caused decreased macrophage accumulation and delay of liver recovery. Conversely, CSF1-Fc injection into normal mice after I/R resulted in increased macrophage accumulation and concomitant decrease in necrotic tissue during liver recovery. In conclusion, fibrotic liver clears necrotic areas and restores normal parenchyma faster than normal liver after I/R. This beneficial response appears to be directly related to the increased numbers of nonparenchymal cells, particularly phagocytic macrophages, in the fibrotic liver.NEW & NOTEWORTHY This study is the first to reveal how diseased liver recovers after ischemia-reperfusion (I/R) injury. Although it was not completely unexpected that fibrotic liver had increased hepatic injury after I/R, a novel finding was that fibrotic liver had accelerated recovery and repair compared with normal liver. Enhanced repair after I/R in fibrotic liver was associated with increased expansion of phagocytic macrophages, hepatic stellate cells, and progenitor cells.

Tanshinol A Ameliorates Triton-1339W-Induced Hyperlipidemia and Liver Injury in C57BL/6J Mice by Regulating mRNA Expression of Lipemic-Oxidative Injury Genes

Tanshinol A, which is derived from a traditional Chinese herbal Radix Salviae Miltiorrhizae is indicative of a hypolipidemic candidate. Therefore, we aim to validate its hypolipidemic activity of tanshinol A and explore its mechanism in triton-1339W-induced hyperlipidemic mice model, which possess multiply pathogenesis for endogenous lipid metabolism disorder. Experimental hyperlipidemia mice are treated with or without tanshinol A (i.g. 40, 20, 10 mg/kg), and blood and liver tissue were collected for validating its hypolipidemic and hepatic protective effect, and hepatic mRNA expression profile, which was associated with lipid metabolism dysfunction and liver injury, was detected by RT-qPCR. As results show, triton-1339W-induced abnormal of serum TC, TAG, HDL-C, LDL-C, SOD, MDA, GOT, and GPT is remarkably attenuated by tanshinol A. In pathological experiment, triton-1339W-induced hepatocellular ballooning degeneration, irregular central vein congestion, and inflammation infiltration are alleviated by tanshinol A. Correspondingly, hepatic mRNA expression of Atf4, Fgf21, Vldlr, Nqo1, Pdk4, and Angptl4, which are genes regulating lipemic-oxidative injury, are significantly increased by tanshinol A by 2~6 fold. Abcg5, Cd36, and Apob, which are responsible for cholesterol metabolism, are mildly upregulated. Noticeably, triton-1339W-suppressed expressions of Ptgs2/Il10, which are genes responsible for acute inflammation resolution in liver injury, are remarkably increased by tanshinol A. Conclusively, tanshinol A exerted hypolipidemic effect and hepatoprotective effect through restoring triton-1339W-suppressed mRNA expression, which may be involved in Atf4/Fgf21/Vldlr and Ptgs2/Il-10 signaling pathways.

Type 3 cytokines in liver fibrosis and liver cancer

The type 3 cytokines IL-17 and IL-22 play a crucial, well synchronized physiological role in wound healing and repairing tissue damage due to infections or injury at barrier surfaces. These cytokines act on epithelial cells to induce secretion of early immune mediators, recruitment of inflammatory cells to the site of injury, and to trigger tissue repair mechanisms. However, if the damage persists or if these cytokines are dysregulated, then they contribute to a number of inflammatory pathologies, autoimmune conditions and cancer. The liver is a multifunctional organ that plays an essential role in metabolism, detoxification, and immune surveillance. It is also exposed to a variety of pathogens, toxins and injuries. Over the past decade, IL-17 and IL-22 have been implicated in various aspects of liver inflammation. IL-17 is upregulated in chronic liver injury and associated with liver disease progression. In contrast, IL-22 was shown to be hepatoprotective during acute liver injury but exhibited inflammatory effects in other models. Furthermore, IL-22 and IL-17 are both associated with poor prognosis in liver cancer. Finally, the regulatory mechanisms governing the physiological versus the pathological role of these two cytokines during acute and chronic liver injury remain poorly understood. In this review, we will summarize the current state of knowledge about IL-17 and IL-22 in wound healing during acute and chronic liver injury, their contribution to pathogenesis, their regulation, and their role in the transition from advanced liver disease to liver cancer.

Research Status of Mesenchymal Stem Cells in Liver Transplantation

Liver transplantation has been deemed the best choice for end-stage liver disease patients but immune rejection after surgery is still a serious problem. Patients have to take immunosuppressive drugs for a long time after liver transplantation, and this often leads to many side effects. Mesenchymal stem cells (MSCs) gradually became of interest to researchers because of their powerful immunomodulatory effects. In the past, a large number of in vitro and in vivo studies have demonstrated the great potential of MSCs for participation in posttransplant immunomodulation. In addition, MSCs also have properties that may potentially benefit patients undergoing liver transplantation. This article aims to provide an overview of the current understanding of the immunomodulation achieved by the application of MSCs in liver transplantation, to discuss the problems that may be encountered when using MSCs in clinical practice, and to describe some of the underlying capabilities of MSCs in liver transplantation. Cell–cell contact, soluble molecules, and exosomes have been suggested to be critical approaches to MSCs’ immunoregulation in vitro; however, the exact mechanism, especially in vivo, is still unclear. In recent years, the clinical safety of MSCs has been proven by a series of clinical trials. The obstacles to the clinical application of MSCs are decreasing, but large sample clinical trials involving MSCs are still needed to further study their clinical effects.

Macrophage Activation Marker Soluble CD163 Associated with Fatal and Severe Ebola Virus Disease in Humans1

Ebola virus disease (EVD) is associated with elevated cytokine levels, and hypercytokinemia is more pronounced in fatal cases. This type of hyperinflammatory state is reminiscent of 2 rheumatologic disorders known as macrophage activation syndrome and hemophagocytic lymphohistiocytosis, which are characterized by macrophage and T-cell activation. An evaluation of 2 cohorts of patients with EVD revealed that a marker of macrophage activation (sCD163) but not T-cell activation (sCD25) was associated with severe and fatal EVD. Furthermore, substantial immunoreactivity of host tissues to a CD163-specific antibody, predominantly in areas of extensive immunostaining for Ebola virus antigens, was observed in fatal cases. These data suggest that host macrophage activation contributes to EVD pathogenesis and that directed antiinflammatory therapies could be beneficial in the treatment of EVD.

Circulating Peroxiredoxin-1 is a novel damage-associated molecular pattern and aggravates acute liver injury via promoting inflammation

Sterile inflammation is initiated by damage-associated molecular patterns (DAMPs) and a key contributor to acute liver injury (ALI). However, the current knowledge on those DAMPs that activate hepatic inflammation under ALI remains incomplete. We report here that circulating peroxiredoxin-1 (Prdx1) is a novel DAMP for ALI. Intraperitoneal injection of acetaminophen (APAP) elicited a progressive course of ALI in mice, which was developed from 12 to 24 h post injection along with liver inflammation evident by macrophage infiltration and upregulations of cytokines (IL-1β, IL-6 and TNF-α); these alterations were concurrently occurred with a robust and progressive production of serum Prdx1. Similar observations were also obtained in carbon tetrachloride (CCl₄)-induced ALI in mice. Removal of the source of serum Prdx1 protected mice deficient in Prdx1 from APAP and CCl₄-induced liver injury, and decreased macrophage infiltration, IL-1β, IL-6 and TNF-α production. As a result, Prdx1^-/- mice were strongly protected from APAP-induced death that was likely progressed from ALI. Additionally, intravenous re-introduction of recombinant Prdx1 (rPrdx1) in Prdx1^-/- mice reversed or reduced all the above events, demonstrating an important contribution of circulating Prdx1 to ALI. rPrdx1 potently induced in primary macrophages the expression of pro-IL-1β, IL-6, TNF-α, and IL-1β through the NF-κB signaling as well as the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome signaling, evident by caspase-1 activation. Furthermore, a significant elevation of serum Prdx1 was demonstrated in patients (n = 15) with ALI; the elevation is associated with ALI severity. Collectively, we provide the first demonstration for serum Prdx1 contributing to ALI.

AM-1241 CB2 Receptor Agonist Attenuates Inflammation, Apoptosis and Stimulate Progenitor Cells in Bile Duct Ligated Rats

BACKGROUND:

The cannabinoid receptor 2 (CB2) plays a pleiotropic role in the innate immunity and is considered a crucial mediator of liver disease. Cannabinoid CB2 receptor activation has been reported to attenuate liver fibrosis in CCl4 exposed mice and also plays a potential role in liver regeneration in a mouse model of I/R and protection against alcohol-induced liver injury.

AIM:

In this study, we investigated the impact of CB2 receptors on the antifibrotic and regenerative process associated with cholestatic liver injury.

METHODS:

Twenty-six rats had bile duct ligation co-treated with silymarin and AM1241 for 3 consecutive weeks. Serum hepatotoxicity markers were determined, and histopathological evaluation was performed.

RESULTS:

Following bile duct ligation (BDL) for 3 weeks, there was increased aminotransferase levels, marked inflammatory infiltration and hepatocyte apoptosis with induced oxidative stress, as reflected by increased lipid peroxidation. Conversely, following treatment with the CB2 agonist, AM-1241, BDL rats displayed a reduction in liver injury and attenuation of fibrosis as reflected by expression of hydroxyproline and α-smooth muscle actin. AM1241 treatment also significantly attenuated lipid peroxidation end-products, p53-dependent apoptosis and also attenuated inflammatory process by stimulating IL-10 production. Moreover, AM1241 treated rats were associated with significant expression of hepatic progenitor/oval cell markers.

CONCLUSION:

In conclusion, this study points out that CB2 receptors reduce liver injury and promote liver regeneration via distinct mechanisms including IL-10 dependent inhibition of inflammation, reduction of p53-reliant apoptosis and through stimulation of oval/progenitor cells. These results suggest that CB2 agonists display potent hepatoregenrative properties, in addition to their antifibrogenic effects.

Phenotypic switch of human and mouse macrophages and resultant effects on apoptosis resistance in hepatocytes

Acute-on-chronic liver failure (ACLF) carries a significant burden on critical care services and health care resources. However, the exact pathogenesis of ACLF remains to be elucidated, and novel treatments are desperately required. In our previous work, we utilized mice subjected to acute insult in the context of hepatic fibrosis to simulate the development of ACLF and documented the favorable hepatoprotection conferred by M2-like macrophages in vivo and in vitro. In the present study, we focused on the phenotypic switch of human and mouse macrophages and assessed the effects of this switch on apoptosis resistance in hepatocytes. For this purpose, human and mouse macrophages were isolated and polarized into M0, M(IFN-γ), M(IFN-γ→IL-4), M(IL-4) or M(IL-4→IFN-γ) subsets. Conditioned media (CM) from these subsets were applied to human and mouse hepatocytes followed by apoptosis induction. Cell apoptosis was evaluated by immunostaining for cleaved caspase-3. As a result, M(IFN-γ) or M(IL-4) macrophages switched their phenotype into M(IFN-γ→IL-4) or M(IL-4→IFN-γ) through reprogramming with IL-4 or IFN-γ, respectively. Importantly, hepatocytes pre-treated with M(IFN-γ→IL-4) CMs exhibited much weaker expression of cleaved caspase-3, compared to those pre-treated with M(IFN-γ) CM, and vice versa. Together, phenotypic switch of macrophages toward M(IL-4) phenotype confers hepatocytes enhanced resistance to apoptosis.

A new perspective on acute-on-chronic liver failure: Liver fibrosis and injury resistance

Acute-on-chronic liver failure (ACLF) is an increasingly recognized entity encompassing an acute deterioration of liver function in patients with pre-existing chronic liver diseases, which is usually associated with a precipitating event. Compared to acute liver failure, ACLF patients exhibit relatively slow disease progression and prolonged survival. Recent studies show that patients without previous decompensation have higher short-term mortality than those with prior hepatic decompensation. These interesting and important facts motivate clinicians and researchers to dissect the underlying mechanisms of ACLF from a new perspective, namely, the correlation between chronic liver diseases and injury resistance. In this review, we will make a comment on the phenomena as well as cellular and molecular mechanisms behind injury resistance in the setting of hepatic fibrosis (simulating the development of ACLF), in hopes of providing novel insights into the pathogenesis and therapy of ACLF.

Splenectomy Promotes Macrophage Polarization in a Mouse Model of Concanavalin A- (ConA-) Induced Liver Fibrosis

Background

Splenectomy can improve liver function and survival in patients with autoimmune hepatitis (AIH) and liver cirrhosis. We investigated the underlying mechanism in a mouse model of concanavalin A- (ConA-) induced liver fibrosis.

Methods

We used ConA to induce immune liver fibrosis in BALB/c mice. Splenectomy was performed alone or with the administration of dexamethasone (DEX). Changes in blood and liver tissues were evaluated.

Results

Mice treated with ConA for 7 weeks developed advanced liver fibrosis, while splenectomy suppressed liver fibrosis. Although the populations of macrophages/monocytes and M1 macrophages decreased after splenectomy, the inflammatory factors associated with M2 macrophages increased after splenectomy. Furthermore, the population of circulating CD11b⁺Ly6C^high myeloid-derived suppressor cells (MDSCs) increased after splenectomy. After ConA treatment, elevated levels of activated and total NF-kBp65/p50 combined with DNA were observed in hepatic tissues. In contrast, the levels of NF-κB p65/p50 decreased after splenectomy.

Conclusions

Splenectomy may promote the polarization of CD11b⁺Ly6C^high MDSCs and the differentiation of M2 macrophages while restricting the level of NF-κB p65-p50 heterodimers. These factors may suppress the progression of liver fibrosis.

The role of hepatic macrophages in nonalcoholic fatty liver disease and nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is becoming common chronic liver disease because of the increasing global prevalence of obesity and consequently Nonalcoholic fatty liver disease (NAFLD). However, the mechanism for progression of NAFLD to NASH and then cirrhosis is not completely understood, yet. The triggering of these hepatic diseases is thought from hepatocyte injury caused by over-accumulated lipid toxicity. Injured hepatocytes release damage-associated molecular patterns (DAMPs), which can stimulate the Kupffer cells (KCs), liver-resident macrophages, to release pro-inflammatory cytokines and chemokines, and recruit monocyte-derived macrophages (MDMs). The increased activation of KCs and recruitment of MDMs accelerate the progression of NAFLD to NASH and cirrhosis. Therefore, characterization for activation of hepatic macrophages, both KCs and MDMs, is a baseline to figure out the progression of hepatic diseases. The purpose of this review is to discuss the current understanding of mechanisms of NAFLD and NASH, mainly focusing on characterization and function of hepatic macrophages and suggests the regulators of hepatic macrophages as the therapeutic target in hepatic diseases.

Origin and Consequences of Necroinflammation

When cells undergo necrotic cell death in either physiological or pathophysiological settings in vivo, they release highly immunogenic intracellular molecules and organelles into the interstitium and thereby represent the strongest known trigger of the immune system. With our increasing understanding of necrosis as a regulated and genetically determined process (RN, regulated necrosis), necrosis and necroinflammation can be pharmacologically prevented. This review discusses our current knowledge about signaling pathways of necrotic cell death as the origin of necroinflammation. Multiple pathways of RN such as necroptosis, ferroptosis, and pyroptosis have been evolutionary conserved most likely because of their differences in immunogenicity. As the consequence of necrosis, however, all necrotic cells release damage associated molecular patterns (DAMPs) that have been extensively investigated over the last two decades. Analysis of necroinflammation allows characterizing specific signatures for each particular pathway of cell death. While all RN-pathways share the release of DAMPs in general, most of them actively regulate the immune system by the additional expression and/or maturation of either pro- or anti-inflammatory cytokines/chemokines. In addition, DAMPs have been demonstrated to modulate the process of regeneration. For the purpose of better understanding of necroinflammation, we introduce a novel classification of DAMPs in this review to help detect the relative contribution of each RN-pathway to certain physiological and pathophysiological conditions.

Myeloid HO-1 modulates macrophage polarization and protects against ischemia-reperfusion injury

Macrophages polarize into heterogeneous proinflammatory M1 and antiinflammatory M2 subtypes. Heme oxygenase 1 (HO-1) protects against inflammatory processes such as ischemia-reperfusion injury (IRI), organ transplantation, and atherosclerosis. To test our hypothesis that HO-1 regulates macrophage polarization and protects against IRI, we generated myeloid-specific HO-1-knockout (mHO-1-KO) and -transgenic (mHO-1-Tg) mice, with deletion or overexpression of HO-1, in various macrophage populations. Bone marrow-derived macrophages (BMDMs) from mHO-1-KO mice, treated with M1-inducing LPS or M2-inducing IL-4, exhibited increased mRNA expression of M1 (CXCL10, IL-1β, MCP1) and decreased expression of M2 (Arg1 and CD163) markers as compared with controls, while BMDMs from mHO-1-Tg mice displayed the opposite. A similar pattern was observed in the hepatic M1/M2 expression profile in a mouse model of liver IRI. mHO-1-KO mice displayed increased hepatocellular damage, serum AST/ALT levels, Suzuki's histological score of liver IRI, and neutrophil and macrophage infiltration, while mHO-1-Tg mice exhibited the opposite. In human liver transplant biopsies, subjects with higher HO-1 levels showed lower expression of M1 markers together with decreased hepatocellular damage and improved outcomes. In conclusion, myeloid HO-1 expression modulates macrophage polarization, and protects against liver IRI, at least in part by favoring an M2 phenotype.

Ursolic acid ameliorates CCl4-induced liver fibrosis through the NOXs/ROS pathway

Liver fibrosis is a reversible wound-healing response that occurs after liver injury. NADPH oxidases (NOXs) and reactive oxygen species (ROS) which are expressed in hepatocytes (HCs), hepatic stellate cells (HSCs), and Kupffer cells (KCs) play an important role in the development of hepatic fibrosis. In in vitro studies, we had shown that ursolic acid (UA) could reverse liver fibrosis by inhibiting the activation of NOX-mediated fibrotic signaling networks in HSCs. In this study, we verified that UA could alleviate CCl4-induced liver fibrosis by reducing the expression of NOXs/ROS in HCs, HSCs, KCs. Meanwhile, the phagocytic index α and clearance index K which represent phagocytosis of KCs were unchanged. Together, all our data demonstrated that UA induced the proliferation of HCs, promoted apoptosis in HSCs, and prevented activation of KCs in vivo by reducing the expression of NOXs/ROS in HCs, HSCs, KCs. Besides, UA had no effect on the host defense function.

Cold shock proteins: from cellular mechanisms to pathophysiology and disease

Cold shock proteins are multifunctional RNA/DNA binding proteins, characterized by the presence of one or more cold shock domains. In humans, the best characterized members of this family are denoted Y-box binding proteins, such as Y-box binding protein-1 (YB-1). Biological activities range from the regulation of transcription, splicing and translation, to the orchestration of exosomal RNA content. Indeed, the secretion of YB-1 from cells via exosomes has opened the door to further potent activities. Evidence links a skewed cold shock protein expression pattern with cancer and inflammatory diseases. In this review the evidence for a causative involvement of cold shock proteins in disease development and progression is summarized. Furthermore, the potential application of cold shock proteins for diagnostics and as targets for therapy is elucidated.

Transforming Growth Factor-β-Induced Cell Plasticity in Liver Fibrosis and Hepatocarcinogenesis

The Transforming Growth Factor-beta (TGF-β) family plays relevant roles in the regulation of different cellular processes that are essential for tissue and organ homeostasis. In the case of the liver, TGF-β signaling participates in different stages of disease progression, from initial liver injury toward fibrosis, cirrhosis and cancer. When a chronic injury takes place, mobilization of lymphocytes and other inflammatory cells occur, thus setting the stage for persistence of an inflammatory response. Macrophages produce profibrotic mediators, among them, TGF-β, which is responsible for activation -transdifferentiation- of quiescent hepatic stellate cells (HSC) to a myofibroblast (MFB) phenotype. MFBs are the principal source of extracellular matrix protein (ECM) accumulation and prominent mediators of fibrogenesis. TGF-β also mediates an epithelial-mesenchymal transition (EMT) process in hepatocytes that may contribute, directly or indirectly, to increase the MFB population. In hepatocarcinogenesis, TGF-β plays a dual role, behaving as a suppressor factor at early stages, but contributing to later tumor progression, once cells escape from its cytostatic effects. As part of its potential pro-tumorigenic actions, TGF-β induces EMT in liver tumor cells, which increases its pro-migratory and invasive potential. In parallel, TGF-β also induces changes in tumor cell plasticity, conferring properties of a migratory tumor initiating cell (TIC). The main aim of this review is to shed light about the pleiotropic actions of TGF-β that explain its effects on the different liver cell populations. The cross-talk with other signaling pathways that contribute to TGF-β effects, in particular the Epidermal Growth Factor Receptor (EGFR), will be presented. Finally, we will discuss the rationale for targeting the TGF-β pathway in liver pathologies.

Cellular Mechanisms of Hepatoprotection Mediated by M2-Like Macrophages

Background

Acute liver injury in the setting of hepatic fibrosis is an intriguing and still unsettled issue. We previously have demonstrated the protective effects conferred by M2-like macrophages in the fibrotic liver. In the present work, we further decipher the cellular mechanisms governing this hepatoprotection.

Material/Methods

Macrophages were isolated from control mice (M0 macrophages), then polarized into M1 or M2 phenotype using IFN-γ or IL-4, respectively. Conditioned media (CM) from M0, M1, and M2 macrophages were harvested and applied to M1 macrophages. Cell apoptosis was evaluated by immunostaining and real-time PCR. Similarly, human monocyte-derived macrophages were isolated and polarized, then M0, M1, and M2 CM were applied to HL-7702 or HepG2 cells followed by apoptosis induction. Cell apoptosis was assessed by flow cytometry.

Results

For the mouse conditioned medium experiment, stronger expression of cleaved caspase 3 and higher Bax/Bcl-2 mRNA ratio were found in M1 macrophages pretreated with M2 CM compared to those in M1 macrophages pretreated with M0 or M1 CM. Similarly, exposure of HL-7702 and HepG2 cells to either M0 or M1 CM had no significant effect on cell apoptosis. Nevertheless, the frequency of hepatocyte apoptosis was substantially reduced in HL-7702 (from 32.23±2.99 to 15.37±0.69 for Annexin V+/PI+ staining, p<0.01) and HepG2 cells (from 36.1±7.26 to 15.2±1.2 for Annexin V+/PI+ staining, p<0.01) with M2 CM pretreatment.

Conclusions

M2-like macrophages exert their hepatoprotective effect by promoting M1-like macrophage apoptosis but protecting against hepatocyte apoptosis.

Selective targeting of tumor associated macrophages in different tumor models

Tumor progression largely depends on the presence of alternatively polarized (M2) tumor-associated macrophages (TAMs), whereas the classical M1-polarized macrophages can promote anti-tumorigenic immune responses. Thus, selective inhibition of M2-TAMs is a desirable anti-cancer approach in highly resistant tumor entities such as hepatocellular carcinoma (HCC) or breast cancer. We here examined whether a peptide that selectively binds to and is internalized by in vitro-differentiated murine M2 macrophages as compared to M1 macrophages, termed M2pep, could be used to selectively target TAMs in HCC and breast carcinoma. We confirmed selectivity of M2pep for in vitro M2 polarized macrophages. Upon incubation of suspended mixed 4T1 tumor cells with M2pep, high amounts of the TAMs were found to be associated with M2pep, whereas in mixed tumor cell suspensions from two HCC mouse models, M2pep showed only low-degree binding to TAMs. M2pep also showed low-degree targeting of liver macrophages. This indicates that the TAMs in different tumor entities show different targeting of M2pep and that M2pep is a very promising approach to develop selective M2-TAM-targeting in tumor entities containing M2-TAMs with significant amounts of the so far elusive M2pep receptor(s).

S-allyl-glutathione improves experimental liver fibrosis by regulating Kupffer cell activation in rats

S-allyl-glutathione (SAG) is one of the metabolites of diallyl sulfide (DAS), a component of garlic. DAS has shown preventative effects on carcinogenesis in animal models. However, whether synthetic SAG can improve liver fibrosis has not been investigated. We examined the potential preventive effects of SAG on acute and chronic models of liver fibrosis by chronic carbon tetrachloride (CCl₄) administration. SAG inhibited liver fibrogenesis induced by CCl₄ in a dose-dependent manner and reduced heat shock protein-47 (HSP47), a collagen-specific chaperone, and other fibrosis markers. In fibrosis regression models, after administration of either CCl₄ for 9 wk or dimethyl nitrosamine (DMN) for 6 wk, SAG markedly accelerated fibrolysis in both models. In the regression stage of DMN-treated liver, SAG normalized the ratio of M2 phenotype (expression of mannose receptor) in Kupffer cells (KCs). Consistent with these results, the culture supernatants of SAG-treated M2-phenotype KCs inhibited collagen-_α1(I) chain (COL1A1) mRNA expression in primary culture-activated rat hepatic stellate cells (HSCs). However, SAG did not directly inhibit HSC activation. In an acute model of CCl₄ single injection, SAG inhibited hepatic injury dose dependently consistent with the inhibited the elevation of the bilirubin and ALT levels. These findings suggest that SAG could improve the fibrogenic and fibrolysis cascade via the regulation of excess activated and polarized KCs. SAG may also serve as a preventive and therapeutic agent in fibrosis of other organs for which current clinical therapy is unavailable. NEW & NOTEWORTHY S-allyl-glutathione (SAG) is a metabolite of diallyl sulfide, a component of garlic. SAG increased hepatic glutathione levels and GSH-to-GSSG ratio in normal rats. SAG treatment before or after liver fibrosis from chronic CCl₄ administration improved liver fibrosis and regression. SAG decreased heat shock protein-47 (HSP47), a collagen-specific chaperone, and other fibrosis markers in CCl₄-treated livers. SAG-treated Kupffer cell conditioned medium also inhibited collagen-_α1(I) chain (COL1A1) mRNA expression and other markers in primary culture hepatic stellate cells.

Hyperglycemia Aggravates Hepatic Ischemia and Reperfusion Injury by Inhibiting Liver-Resident Macrophage M2 Polarization via C/EBP Homologous Protein-Mediated Endoplasmic Reticulum Stress

Aggravated liver ischemia and reperfusion (IR) injury has been observed in hyperglycemic hosts, but its underlying mechanism remains undefined. Liver-resident macrophages (Kupffer cells, KCs) and endoplasmic reticulum (ER) stress play crucial roles in the pathogenesis of liver IR injury. In this study, we evaluated the role of ER stress in regulating KC activation and liver IR injury in a streptozotocin-induced hyperglycemic/diabetic mouse model. Compared to the control group (CON group), hyperglycemic mice exhibited a significant increase in liver injury and intrahepatic inflammation following IR. KCs obtained from hyperglycemic mice secreted higher levels of the pro-inflammatory factors TNF-α and IL-6, while they secreted significantly lower levels of the anti-inflammatory factor IL-10. Furthermore, enhanced ER stress was revealed by increased C/EBP homologous protein (CHOP) activation in both IR-stressed livers and KCs from hyperglycemic mice. Specific CHOP knockdown in KCs by siRNA resulted in a slight decrease in TNF-α and IL-6 secretion but dramatically enhanced anti-inflammatory IL-10 secretion in the hyperglycemic group, while no significant changes in cytokine production were observed in the CON group. We also analyzed the role of hyperglycemia in macrophage M1/M2 polarization. Interestingly, we found that hyperglycemia inhibited IL-10-secreting M2-like macrophage polarization, as revealed by decreased Arg1 and Mrc1 gene induction accompanied by a decrease in STAT3 and STAT6 signaling pathway activation. CHOP knockdown restored Arg1 and Mrc1 gene induction, STAT3 and STAT6 activation, and most importantly, IL-10 secretion in hyperglycemic KCs. Finally, in vivo CHOP knockdown in KCs enhanced intrahepatic anti-inflammatory IL-10 gene induction and protected the liver against IR injury in hyperglycemic mice but had no significant effects in control mice. Our results demonstrate that hyperglycemia induces hyper-inflammatory activation of KCs during liver IR injury. Thus, hyperglycemia-induced CHOP over-activation inhibits IL-10-secreting M2-like macrophage polarization by liver-resident macrophages, thereby leading to excessive inflammation and the exacerbation of liver IR injury in diabetic/hyperglycemic hosts. This study provides novel mechanistic insight into macrophage inflammatory activation under hyperglycemic conditions during liver IR.

M2-like macrophages in the fibrotic liver protect mice against lethal insults through conferring apoptosis resistance to hepatocytes

Acute injury in the setting of liver fibrosis is an interesting and still unsettled issue. Most recently, several prominent studies have indicated the favourable effects of liver fibrosis against acute insults. Nevertheless, the underlying mechanisms governing this hepatoprotection remain obscure. In the present study, we hypothesized that macrophages and their M1/M2 activation critically involve in the hepatoprotection conferred by liver fibrosis. Our findings demonstrated that liver fibrosis manifested a beneficial role for host survival and apoptosis resistance. Hepatoprotection in the fibrotic liver was tightly related to innate immune tolerance. Macrophages undertook crucial but divergent roles in homeostasis and fibrosis: depleting macrophages in control mice protected from acute insult; conversely, depleting macrophages in fibrotic liver weakened the hepatoprotection and gave rise to exacerbated liver injury upon insult. The contradictory effects of macrophages can be ascribed, to a great extent, to the heterogeneity in macrophage activation. Macrophages in fibrotic mice exhibited M2-preponderant activation, which was not the case in acutely injured liver. Adoptive transfer of M2-like macrophages conferred control mice conspicuous protection against insult. In vitro, M2-polarized macrophages protected hepatocytes against apoptosis. Together, M2-like macrophages in fibrotic liver exert the protective effects against lethal insults through conferring apoptosis resistance to hepatocytes.

Identification of pro-inflammatory CD205+ macrophages in livers of hepatitis B virus transgenic mice and patients with chronic hepatitis B

Hepatic macrophages play a central role in disease pathogenesis during hepatitis B virus (HBV) infection. Our previous study found that CD205⁺ macrophages in the liver of hepatitis B surface antigen transgenic (HBs-Tg) mice increased significantly compared with those in wild-type mice, and these increased CD205⁺ macrophages were involved in CpG-oligodeoxynucleotide-induced liver injury in HBs-Tg mice. Here, we analysed the phenotype and function of CD205⁺ macrophages derived from the liver of HBs-Tg mice and patients with chronic hepatitis B (CHB). We found that HBs-Tg mice-derived hepatic macrophages produced larger amounts of pro-inflammatory cytokines, including IL-6, IL-12, TNF-α, and of the anti-inflammatory cytokine IL-10 after stimulation with CpG-oligodeoxynucleotides or commensal bacteria DNA than B6 mice-derived hepatic macrophages. Furthermore, hepatic CD205⁺ macrophages from HBs-Tg mice showed an activated phenotype and expressed higher levels of inflammatory cytokine genes, chemokine genes, and phagocytosis-related genes than hepatic CD205⁻ macrophages. In addition, CD205⁺ macrophages displayed an inflammatory phenotype and were increased in the liver of patients with CHB compared with those in healthy controls. Our data suggest that hepatic CD205⁺ macrophages are a unique pro-inflammatory subset observed during HBV infection. Thus, development of intervention targeting these cells is warranted for immunotherapy of HBV-induced liver diseases.