Liver Macrophages: Old Dogmas and New Insights

Macrophage malfunction in Triptolide-induced indirect hepatotoxicity

Background and Objective: Indirect hepatotoxicity is a new type of drug-induced hepatotoxicity in which the character of a drug that may induce its occurrence and the underlying mechanism remains elusive. Previously, we proved that Triptolide (TP) induced indirect hepatotoxicity upon LPS stimulation resulting from the deficiency of cytoprotective protein of hepatocyte. However, whether immune cells participated in TP-induced indirect hepatotoxicity and the way immune cells change the liver hypersensitivity to LPS still need to be deeply investigated. In this study, we tried to explore whether and how macrophages are involved in TP-induced indirect hepatotoxicity.

Method: Firstly, TP (500 μg/kg) and LPS (0.1 mg/kg) were administrated into female C57BL/6 mice as previously reported. Serum biochemical indicators, morphological changes, hepatic macrophage markers, as well as macrophage M1/M2 markers were detected. Secondly, macrophage scavenger clodronate liposomes were injected to prove whether macrophages participated in TP-induced indirect hepatotoxicity. Also, the ability of macrophages to secrete inflammatory factors and macrophage phagocytosis were detected. Lastly, reverse docking was used to find the target of TP on macrophage and the possible target was verified in vivo and in RAW264.7 cells.

Results: TP pretreatment increased the liver hypersensitization to LPS accompanied by the recruitment of macrophages to the liver and promoted the transformation of macrophages to M1 type. Depletion of hepatic macrophages almost completely alleviated the liver injury induced by TP/LPS. TP pretreatment increased the secretion of pro-inflammatory factors and weakened the phagocytic function of macrophages upon LPS exposure. Reverse docking results revealed that MerTK might be the real target of TP.

Conclusion: TP disrupts inflammatory cytokines profile and phagocytic function of hepatic macrophages, resulting in the production of massive inflammatory factors and the accumulation of endotoxin in the liver, ultimately leading to the indirect hepatotoxicity of TP. MerTK might be the target of TP on the macrophage, while the binding of TP to MerTK should be investigated in vivo and in vitro.

Applications of machine learning in tumor-associated macrophages

Evaluation of tumor-host interaction and intratumoral heterogeneity in the tumor microenvironment (TME) is gaining increasing attention in modern cancer therapies because it can reveal unique information about the tumor status. As tumor-associated macrophages (TAMs) are the major immune cells infiltrating in TME, a better understanding of TAMs could help us further elucidate the cellular and molecular mechanisms responsible for cancer development. However, the high-dimensional and heterogeneous data in biology limit the extensive integrative analysis of cancer research. Machine learning algorithms are particularly suitable for oncology data analysis due to their flexibility and scalability to analyze diverse data types and strong computation power to learn underlying patterns from massive data sets. With the application of machine learning in analyzing TME, especially TAM’s traceable status, we could better understand the role of TAMs in tumor biology. Furthermore, we envision that the promotion of machine learning in this field could revolutionize tumor diagnosis, treatment stratification, and survival predictions in cancer research. In this article, we described key terms and concepts of machine learning, reviewed the applications of common methods in TAMs, and highlighted the challenges and future direction for TAMs in machine learning.

Changes of macrophage and CD4+ T cell in inflammatory response in type 1 diabetic mice

Immune cells play an important role in the development of inflammation in type 1 diabetes mellitus, so we want to explore the changes of CD4+ T cells and macrophages in vivo, which can provide an experimental basis for immunotherapy based on CD4+ T cells and macrophages. The intraperitoneal injection of streptozocin was used to induce a type 1 diabetes mellitus mouse model; the blood glucose, body weight, and the expression of inflammatory factors in the kidney were measured. Immunohistochemistry was applied to determine and analyze the infiltration of CD4+ T cells and macrophages in the spleen, pancreas, and kidney. The subtypes of macrophages in the kidney and CD4+ T cells in the spleen were analyzed by flow cytometry. Our study suggests that CD4+ T cells and macrophages increase, while the inflammatory immune response system is activated in the development of T1DM. CD4+ T cells positively correlated with macrophages in the pancreas and kidney of T1DM. CD4+ T cells turn to pro-inflammatory subtypes in the spleen of T1DM, while macrophages turn to pro-inflammatory subtypes in the kidney of T1DM. Therefore, regulation of CD4+ T cells and macrophages may be a potential target for T1DM and kidney complications.

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 versatility of macrophage heterogeneity in liver fibrosis

Liver fibrosis is a highly conserved wound healing response to liver injury, characterized by excessive deposition of extracellular matrix (ECM) in the liver which might lead to loss of normal functions. In most cases, many types of insult could damage hepatic parenchymal cells like hepatocytes and/or cholangiocytes, and persistent injury might lead to initiation of fibrosis. This process is accompanied by amplified inflammatory responses, with immune cells especially macrophages recruited to the site of injury and activated, in order to orchestrate the process of wound healing and tissue repair. In the liver, both resident macrophages and recruited macrophages could activate interstitial cells which are responsible for ECM synthesis by producing a variety of cytokines and chemokines, modulate local microenvironment, and participate in the regulation of fibrosis. In this review, we will focus on the main pathological characteristics of liver fibrosis, as well as the heterogeneity on origin, polarization and functions of hepatic macrophages in the setting of liver fibrosis and their underlying mechanisms, which opens new perspectives for the treatment of liver fibrosis.

Single-cell transcriptomes identifies characteristic features of mouse macrophages in liver Mallory-Denk bodies formation

Mallory-Denk bodies (MDBs) consist of intracellular aggregates of misfolded proteins in ballooned hepatocytes and serve as important markers of progression in certain liver diseases. Resident hepatic macrophage-mediated inflammation influences the development of chronic liver diseases and cancer. Here, the first systematic study of macrophages heterogeneity in mice was conducted to illustrate the pathogenesis of MDB formation using single-nucleus RNA sequencing (snRNA-seq). Furthermore, we provided transcriptional profiles of macrophages obtained from the fractionation of mouse liver tissues following chronic injury. We equally identified seven discrete macrophage subpopulations, each involved in specific cellular activated pathways such as basal metabolism, immune regulation, angiogenesis, and cell cycle regulation. Among these, a specific macrophage cluster (Cluster4), a subpopulation specifically expressing genes that regulate cell division and the cell cycle, was identified. Interestingly, we found that CCR2 was significantly induced in Cluster2, thereby inducing monocytes to migrate to macrophages to promote MDB pathogenesis. Thus, our study is the first to demonstrate the heterogeneity of macrophages associated with liver MDB formation in mice through single-cell resolution. This serves as the basis for further insights into the pathogenesis of liver MDB formation and molecular mechanisms of chronic liver disease progression.

Glycyrrhetinic acid regulates impaired macrophage autophagic flux in the treatment of non-alcoholic fatty liver disease

Macrophages are involved in hepatocyte steatosis and necroinflammation and play an important role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Impaired autophagy function (decreased autophagy or blocked autophagic flow) leads to cell damage and death and promotes NAFLD progression. The experimental and clinical research of glycyrrhetinic acid (GA) in the treatment of NAFLD has gradually attracted attention with clear pharmacological activities such as immune regulation, antiviral, antitumor, antioxidant, liver protection, and anti-inflammatory. However, the effects of GA on the STAT3-HIF-1α pathway and autophagy in macrophages are still unclear, and its mechanism of action in the treatment of NAFLD remains to be further elucidated. We constructed a NAFLD mouse model through a high-fat and high-sugar diet to investigate the therapeutic effects of GA. The results showed that GA reduced weight, improved the pathological changes and hepatic lipid deposition of liver, and abnormally elevated the levels of serum biochemical (AST, ALT, TG, T-CHO, LDL-C, and HDL-C) and inflammatory indexes (IL-1β, IL-4, IL-6, MCP-1, and TNF-α) in NAFLD mice. Further examination revealed that GA ameliorates excessive hepatic macrophage infiltration and hepatocyte apoptosis. The results of the cell experiments further elaborated that GA modulated the PA-induced macrophage STAT3-HIF-1α pathway and ameliorated impaired autophagic flux (blockade of autophagosome–lysosome fusion) and overactivation of inflammation. Excessive hepatocyte apoptosis caused by the uncontrolled release of inflammatory cytokines was also suppressed by GA.

Conclusion

This study demonstrated that GA could regulate the STAT3-HIF-1α pathway of macrophages, ameliorate the impaired autophagy flux, and reduce the excessive production of inflammatory cytokines to improve the excessive apoptosis of liver cells, thus playing a therapeutic role on NAFLD.

Macrophages, Low-Grade Inflammation, Insulin Resistance and Hyperinsulinemia: A Mutual Ambiguous Relationship in the Development of Metabolic Diseases

Metabolic derangement with poor glycemic control accompanying overweight and obesity is associated with chronic low-grade inflammation and hyperinsulinemia. Macrophages, which present a very heterogeneous population of cells, play a key role in the maintenance of normal tissue homeostasis, but functional alterations in the resident macrophage pool as well as newly recruited monocyte-derived macrophages are important drivers in the development of low-grade inflammation. While metabolic dysfunction, insulin resistance and tissue damage may trigger or advance pro-inflammatory responses in macrophages, the inflammation itself contributes to the development of insulin resistance and the resulting hyperinsulinemia. Macrophages express insulin receptors whose downstream signaling networks share a number of knots with the signaling pathways of pattern recognition and cytokine receptors, which shape macrophage polarity. The shared knots allow insulin to enhance or attenuate both pro-inflammatory and anti-inflammatory macrophage responses. This supposedly physiological function may be impaired by hyperinsulinemia or insulin resistance in macrophages. This review discusses the mutual ambiguous relationship of low-grade inflammation, insulin resistance, hyperinsulinemia and the insulin-dependent modulation of macrophage activity with a focus on adipose tissue and liver.

Plasticity of monocytes and macrophages in cirrhosis of the liver

Cirrhosis of the liver is a systemic condition with raising prevalence worldwide. Patients with cirrhosis are highly susceptible to develop bacterial infections leading to acute decompensation and acute-on-chronic liver failure both associated with a high morbidity and mortality and sparse therapeutic options other than transplantation. Mononuclear phagocytes play a central role in innate immune responses and represent a first line of defence against pathogens. Their function includes phagocytosis, killing of bacteria, antigen presentation, cytokine production as well as recruitment and activation of immune effector cells. Liver injury and development of cirrhosis induces activation of liver resident Kupffer cells and recruitment of monocytes to the liver. Damage- and pathogen-associated molecular patterns promote systemic inflammation which involves multiple compartments besides the liver, such as the circulation, gut, peritoneal cavity and others. The function of circulating monocytes and tissue macrophages is severely impaired and worsens along with cirrhosis progression. The underlying mechanisms are complex and incompletely understood. Recent 'omics' technologies help to transform our understanding of cellular diversity and function in health and disease. In this review we point out the current state of knowledge on phenotypical and functional changes of monocytes and macrophages during cirrhosis evolution in different compartments and their role in disease progression. We also discuss the value of potential prognostic markers for cirrhosis-associated immuneparesis, and future immunotherapeutic strategies that may reduce the need for transplantation and death.

The Dual Role of Innate Immune Response in Acetaminophen-Induced Liver Injury

Acetyl-para-aminophenol (APAP), a commonly used antipyretic analgesic, is becoming increasingly toxic to the liver, resulting in a high rate of acute hepatic failure in Europe and the United States. Excessive APAP metabolism in the liver develops an APAP-protein adduct, which causes oxidative stress, MPTP opening, and hepatic necrosis. HMGB-1, HSP, nDNA, mtDNA, uric acid, and ATP are DMAPs released during hepatic necrosis. DMAPs attach to TLR4-expressing immune cells such KCs, macrophages, and NK cells, activating them and causing them to secrete cytokines. Immune cells and their secreted cytokines have been demonstrated to have a dual function in acetaminophen-induced liver injury (AILI), with a role in either proinflammation or pro-regeneration, resulting in contradicting findings and some research confusion. Neutrophils, KCs, MoMFs, NK/NKT cells, γδT cells, DCs, and inflammasomes have pivotal roles in AILI. In this review, we summarize the dual role of innate immune cells involved in AILI and illustrate how these cells initiate innate immune responses that lead to persistent inflammation and liver damage. We also discuss the contradictory findings in the literature and possible protocols for better understanding the molecular regulatory mechanisms of AILI.

The performance of soluble CD163 as a non-invasive biomarker of liver damage in chronically HCV and HCV/HIV infected subjects

Macrophage activation plays a key role in liver disease progression. Soluble CD163 (sCD163) is a specific macrophage activation biomarker useful for clinical estimating damage severity and predicting outcome in different liver conditions. sCD163 performance as a non-invasive marker of liver damage was evaluated in plasma samples at time of biopsy in 120 patients with different hepatic conditions (56 HCV, 20 HCV/HIV, 10 HBV and 34 MAFLD). sCD163 values were compared with those of healthy donors and analyzed related to histological damage. sCD163 together with other clinical parameters were used to create a logistical regression model to predict significant fibrosis. Only patients with viral hepatitis showed higher sCD163 values compared to the control group (HCV p<0.0001; HCV/HIV p<0.0001; HBV p = 0.0003), but no significant differences regarding fibrosis stages were observed. The proposed model predicts fibrosis severity using the logarithm sCD163 concentration, platelet count and age, it demonstrated to be a good marker for the HCV monoinfected group (AUROC 0.834) and an excellent one for the HCV/HIV co-infected group (AUROC 0.997). Moreover, the model displayed a diagnostic performance similar to FIB-4 in HCV cases and FIB-4 and APRI in HCV/HIV coinfected cases, and it even managed to correctly classify some cases that had been misclassified. The proposed model is able to determine, in a non-invasive way, the liver fibrosis stage of HCV and HCV/HIV patients, so after validation, it could be used in a complementary way in the clinical practice whenever APRI and FIB-4 failed to determine damage severity in HCV and HCV/HIV cases.

Loss of TRIM67 Attenuates the Progress of Obesity-Induced Non-Alcoholic Fatty Liver Disease

Obesity is considered as a major cause for the development and progress of non-alcoholic fatty liver disease (NAFLD), which is one of the most prevalent chronic liver diseases worldwide. However, molecular mechanisms that implicate in obesity-driven pathophysiology of NAFLD are not well defined. Here, we report a tripartite motif (TRIM) protein family member—TRIM67—that is hardly expressed in liver but is inducible on obese conditions. Enhanced expression of TRIM67 activates hepatic inflammation to disturb lipid metabolic homeostasis and promote the progress of NAFLD induced by obesity, while the deficiency in TRIM67 is protective against these pathophysiological processes. Finally, we show that the important transcription coactivator PGC-1α implicates in the response of hepatic TRIM67 to obesity.

The Role of Macrophages in Liver Fibrosis: New Therapeutic Opportunities

Chronic inflammation is the hallmark of fibrotic disorders and is characterized by the activation of immune cells in the damaged tissues. Macrophages have emerged as central players in the fibrotic process since they initiate, sustain and amplify the inflammatory reaction. As regards the liver, distinct populations of phagocytic cells, like Kupffer cells and monocyte-derived macrophages, are indisputably key cells implicated in the pathogenesis of several chronic liver diseases. In this review, we summarize the current knowledge on the origin, role and functions of macrophages in fibrotic conditions, with a specific focus on liver fibrosis; then, we discuss some innovative therapeutic strategies targeting macrophages in fibrotic liver diseases.

Familial hemophagocytic lymphohistiocytosis hepatitis is mediated by IFN-γ in a predominantly hepatic-intrinsic manner

Interferon gamma (IFN-γ) is the main cytokine driving organ dysfunction in Familial Hemophagocytic Lymphohistiocytosis (FHL). Blockade of IFN-γ pathway ameliorates FHL hepatitis, both in animal models and in humans with FHL. Hepatocytes are known to express IFN-γ receptor (IFN-γ-R). However, whether IFN-γ induced hepatitis in FHL is a lymphocyte or liver intrinsic response to the cytokine has yet to be elucidated. Using a IFNgR-/- bone marrow chimeric model, this study showed that non-hematopoietic IFN-γ response is critical for development of FHL hepatitis in LCMV-infected Prf1-/- mice. Lack of hepatic IFN-γ responsiveness results in reduced hepatitis as measured by hepatomegaly, alanine aminotransferase (ALT) levels and abrogated histologic endothelial inflammation. In addition, IFN-γ non-hematopoietic response was critical in activation of lymphocytes by soluble interleukin 2 receptor (sIL-2r) and recruitment of CD8+ effector T lymphocytes (CD8+ CD44hi CD62Llo) (Teff) and inflammatory monocytes. Lastly, non-hematopoietic IFN-γ response results in increased hepatic transcription of type 1 immune response and oxidative stress response pathways, while decreasing transcription of genes involved in extracellular matrix (ECM) production. In summary, these findings demonstrate that there is a hepatic transcriptional response to IFN-γ, likely critical in the pathogenesis of FHL hepatitis and hepatic specific responses could be a therapeutic target in this disorder.

Novel immunotherapy combinations in clinical trials for hepatocellular carcinoma: will they shape the future treatment landscape?

INTRODUCTION

Underlying liver disease and the intrinsic chemoresistance have historically hampered the development of efficacious treatments in HCC. However, in the last few years, immunotherapy-based combinations have emerged as efficacious therapeutic strategy in this setting. This paper critically summarizes the recent therapeutic progress in the systemic treatment of HCC.

AREA COVERED

This paper examines the preclinical rationale of the following combinations in HCC: dual checkpoint inhibitors, immune checkpoint inhibitors plus anti-angiogenic agents, and immune checkpoint inhibitors plus tyrosine kinase inhibitors. Results of recent clinical studies are presented, along with a brief overview of ongoing and future trials.

EXPERT OPINION

The approval of atezolizumab plus bevacizumab and the positive results of the HIMALAYA trial have broadened the therapeutic scenario for advanced HCC, opening, at the same time, new challenges. First of all, predictive biomarkers to allocate patients to the best treatment are eagerly required; second, specific studies are urgently needed to define the use of new combinations in patients usually excluded from clinical trials, e.g. those with deranged liver function and HIV or transplant recipients. Finally, with new combinations being translated into earlier stages, profound changes are soon expected in the adjuvant and neoadjuvant setting.

Roles of heterogenous hepatic macrophages in the progression of liver diseases

Hepatic macrophages are key immune cells associated with the broad ranges of liver diseases including steatosis, inflammation and fibrosis. Hepatic macrophages interact with other immune cells and orchestrate hepatic immune circumstances. Recently, the heterogenous populations of hepatic macrophages have been discovered termed residential Kupffer cells and monocyte-derived macrophages, and identified their distinct population dynamics during the progression of various liver diseases. Liver injury lead to Kupffer cells activation with induction of inflammatory cytokines and chemokines, which triggers recruitment of inflammatory monocyte-derived macrophages. To understand liver pathology, the functions of different subtypes of liver macrophages should be regarded with different perspectives. In this review, we summarize recent advances in the roles of hepatic macrophages under liver damages and suggest hepatic macrophages as promising therapeutic targets for treating liver diseases.

Liver ischaemia-reperfusion injury: a new understanding of the role of innate immunity

Liver ischaemia-reperfusion injury (LIRI), a local sterile inflammatory response driven by innate immunity, is one of the primary causes of early organ dysfunction and failure after liver transplantation. Cellular damage resulting from LIRI is an important risk factor not only for graft dysfunction but also for acute and even chronic rejection and exacerbates the shortage of donor organs for life-saving liver transplantation. Hepatocytes, liver sinusoidal endothelial cells and Kupffer cells, along with extrahepatic monocyte-derived macrophages, neutrophils and platelets, are all involved in LIRI. However, the mechanisms underlying the responses of these cells in the acute phase of LIRI and how these responses are orchestrated to control and resolve inflammation and achieve homeostatic tissue repair are not well understood. Technological advances allow the tracking of cells to better appreciate the role of hepatic macrophages and platelets (such as their origin and immunomodulatory and tissue-remodelling functions) and hepatic neutrophils (such as their selective recruitment, anti-inflammatory and tissue-repairing functions, and formation of extracellular traps and reverse migration) in LIRI. In this Review, we summarize the role of macrophages, platelets and neutrophils in LIRI, highlight unanswered questions, and discuss prospects for innovative therapeutic regimens against LIRI in transplant recipients.

Roles of heterogenous hepatic macrophages in the progression of liver diseases

Hepatic macrophages are key immune cells associated with the broad ranges of liver diseases including steatosis, inflammation and fibrosis. Hepatic macrophages interact with other immune cells and orchestrate hepatic immune circumstances. Recently, the heterogenous populations of hepatic macrophages have been discovered termed residential Kupffer cells and monocyte-derived macrophages, and identified their distinct population dynamics during the progression of various liver diseases. Liver injury lead to Kupffer cells activation with induction of inflammatory cytokines and chemokines, which triggers recruitment of inflammatory monocyte-derived macrophages. To understand liver pathology, the functions of different subtypes of liver macrophages should be regarded with different perspectives. In this review, we summarize recent advances in the roles of hepatic macrophages under liver damages and suggest hepatic macrophages as promising therapeutic targets for treating liver diseases. [BMB Reports 2022; 55(4): 166-174].

Macrophages in cholangiopathies

PURPOSE OF REVIEW

Cholangiopathies are a heterogeneous class of liver diseases where cholangiocytes are the main targets of liver injury. Although available and emerging therapies mainly target bile acids (ursodeoxycholic acid/UDCA, 24-Norursodeoxycholic acid/norUDCA) and related signaling pathways (obeticholic acid, fibrates, FXR, and PPAR agonists), the mechanisms underlying inflammation, ductular reaction and fibrosis in cholestatic liver diseases remain poorly understood.

RECENT FINDINGS

Data from patients with cholestatic diseases, such as primary biliary cholangitis (PBC) or primary sclerosing cholangitis (PSC) as well as mouse models of biliary injury emphasize the role of immune cells in the pathogenesis of cholestatic disorders and indicate diverse functions of hepatic macrophages. Their versatile polarization phenotypes and their capacity to interact with other cell types (e.g. cholangiocytes, other immune cells) make macrophages central actors in the progression of cholangiopathies.

SUMMARY

In this review, we summarize recent findings on the response of hepatic macrophages to cholestasis and biliary injury and their involvement in the progression of cholangiopathies. Furthermore, we discuss how recent discoveries may foster the development of innovative therapies to treat patients suffering from cholestatic liver diseases, in particular, treatments targeting macrophages to limit hepatic inflammation.

Nuclear Receptors Linking Metabolism, Inflammation, and Fibrosis in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) and its progressive form nonalcoholic steatohepatitis (NASH) comprise a spectrum of chronic liver diseases in the global population that can lead to end-stage liver disease and hepatocellular carcinoma (HCC). NAFLD is closely linked to the metabolic syndrome, and comorbidities such as type 2 diabetes, obesity and insulin resistance aggravate liver disease, while NAFLD promotes cardiovascular risk in affected patients. The pathomechanisms of NAFLD are multifaceted, combining hepatic factors including lipotoxicity, mechanisms of cell death and liver inflammation with extrahepatic factors including metabolic disturbance and dysbiosis. Nuclear receptors (NRs) are a family of ligand-controlled transcription factors that regulate glucose, fat and cholesterol homeostasis and modulate innate immune cell functions, including liver macrophages. In parallel with metabolic derangement in NAFLD, altered NR signaling is frequently observed and might be involved in the pathogenesis. Therapeutically, clinical data indicate that single drug targets thus far have been insufficient for reaching patient-relevant endpoints. Therefore, combinatorial treatment strategies with multiple drug targets or drugs with multiple mechanisms of actions could possibly bring advantages, by providing a more holistic therapeutic approach. In this context, peroxisome proliferator-activated receptors (PPARs) and other NRs are of great interest as they are involved in wide-ranging and multi-organ activities associated with NASH progression or regression. In this review, we summarize recent advances in understanding the pathogenesis of NAFLD, focusing on mechanisms of cell death, immunometabolism and the role of NRs. We outline novel therapeutic strategies and discuss remaining challenges.

Evaluation of Liposome-Loaded Microbubbles as a Theranostic Tool in a Murine Collagen-Induced Arthritis Model

Rheumatoid arthritis (RA) is an autoimmune disease characterized by severe inflammation of the synovial tissue. Here, we assess the feasibility of liposome-loaded microbubbles as theranostic agents in a murine arthritis model. First, contrast-enhanced ultrasound (CEUS) was used to quantify neovascularization in this model since CEUS is well-established for RA diagnosis in humans. Next, the potential of liposome-loaded microbubbles and ultrasound (US) to selectively enhance liposome delivery to the synovium was evaluated with in vivo fluorescence imaging. This procedure is made very challenging by the presence of hard joints and by the limited lifetime of the microbubbles. The inflamed knee joints were exposed to therapeutic US after intravenous injection of liposome-loaded microbubbles. Loaded microbubbles were found to be quickly captured by the liver. This resulted in fast clearance of attached liposomes while free and long-circulating liposomes were able to accumulate over time in the inflamed joints. Our observations show that murine arthritis models are not well-suited for evaluating the potential of microbubble-mediated drug delivery in joints given: (i) restricted microbubble passage in murine synovial vasculature and (ii) limited control over the exact ultrasound conditions in situ given the much shorter length scale of the murine joints as compared to the therapeutic wavelength.

DNMT3a-mediated methylation of PSTPIP2 enhances inflammation in alcohol-induced liver injury via regulating STAT1 and NF-κB pathway

Alcohol-induced liver injury (ALI) is associated with inflammatory responses regulated by macrophages. Activation of macrophages plays a crucial role in ALI while DNA methylation-regulated gene silencing is associated with inflammation processes in macrophages. Proline-Serine-Threonine Phosphatase Interacting Protein 2 (PSTPIP2), which belongs to the Fes/CIP4 homology-Bin/Amphiphysin/Rvs domain family of proteins and plays a role in macrophages. Previous studies have shown that Pstpip2 can be methylated. Herein, its expression was found to be significantly downregulated in primary liver macrophages isolated from EtOH-fed mice and EtOH-induced RAW264.7 cells. Overexpression of PSTPIP2 using liver-specific recombinant AAV serotype 9 (rAAV9)-PSTPIP2 in EtOH-fed mice dramatically alleviated liver injury and inflammatory responses. In addition, silencing of PSTPIP2 aggravated the alcohol-induced inflammatory response in vitro. Mechanistically, PSTPIP2 might affect macrophage-induced inflammatory responses by regulating the STAT1 and NF-κB signaling pathways. The downregulation of PSTPIP2 in ALI may be associated with DNA methylation. Methylation-specific PCR and western blotting analyses showed that EtOH induced abnormal DNA methylation patterns and increased the protein expression levels of DNMT1, DNMT3a, and DNMT3b. The chromatin immunoprecipitation assay showed that DNMT3a could directly bind to the Pstpip2 promoter and act as a principal regulator of PSTPIP2 expression. Moreover, silencing of DNMT3a significantly restored the EtOH-induced low expression of PSTPIP2 and inhibited EtOH-induced inflammation. Overall, these findings provide a detailed understanding of the possible functions and mechanisms of PSTPIP2 in ALI, thus providing new substantive research to elucidate the pathogenesis of ALI and investigate potential targeted treatment strategies.

Scavenger Receptors: Novel Roles in the Pathogenesis of Liver Inflammation and Cancer

The scavenger receptor superfamily represents a highly diverse collection of evolutionarily-conserved receptors which are known to play key roles in host homeostasis, the most prominent of which is the clearance of unwanted endogenous macromolecules, such as oxidized low-density lipoproteins, from the systemic circulation. Members of this family have also been well characterized in their binding and internalization of a vast range of exogenous antigens and, consequently, are generally considered to be pattern recognition receptors, thus contributing to innate immunity. Several studies have implicated scavenger receptors in the pathophysiology of several inflammatory diseases, such as Alzheimer's and atherosclerosis. Hepatic resident cellular populations express a diverse complement of scavenger receptors in keeping with the liver's homeostatic functions, but there is gathering interest in the contribution of these receptors to hepatic inflammation and its complications. Here, we review the expression of scavenger receptors in the liver, their functionality in liver homeostasis, and their role in inflammatory liver disease and cancer.

Macrophage MerTK promotes profibrogenic cross-talk with hepatic stellate cells via soluble mediators

Background & Aims

Activation of Kupffer cells and recruitment of monocytes are key events in fibrogenesis. These cells release soluble mediators which induce the activation of hepatic stellate cells (HSCs), the main fibrogenic cell type within the liver. Mer tyrosine kinase (MerTK) signaling regulates multiple processes in macrophages and has been implicated in the pathogenesis of non-alcoholic steatohepatitis-related fibrosis. In this study, we explored if MerTK activation in macrophages influences the profibrogenic phenotype of HSCs.

Methods

Macrophages were derived from THP-1 cells or differentiated from peripheral blood monocytes towards MerTK⁺/CD206⁺/CD163⁺/CD209^- macrophages. The role of MerTK was assessed by pharmacologic and genetic inhibition. HSC migration was determined in Boyden chambers, viability was measured by the MTT assay, and proliferation was evaluated by the BrdU incorporation assay.

Results

Gas-6 induced MerTK phosphorylation and Akt activation in macrophages, and these effects were inhibited by UNC569. During polarization, MerTK⁺/CD206⁺/CD163⁺/CD209^- macrophages exhibited activation of STAT3, ERK1/2, p38 and increased expression of VEGF-A. Activation of MerTK in THP-1 macrophages induced a secretome which promoted a significant increase in migration, proliferation, viability and expression of profibrogenic factors in HSCs. Similarly, conditioned medium from MerTK⁺ macrophages induced a significant increase in cell migration, proliferation, STAT3 and p38 phosphorylation and upregulation of IL-8 expression in HSCs. Moreover, conditioned medium from Gas-6-stimulated Kupffer cells induced a significant increase in HSC proliferation. These effects were specifically related to MerTK expression and activity in macrophages, as indicated by pharmacologic inhibition and knockdown experiments.

Conclusions

MerTK activation in macrophages modifies the secretome to promote profibrogenic features in HSCs, implicating this receptor in the pathogenesis of hepatic fibrosis.

Lay summary

Fibrosis represents the process of scarring occurring in patients with chronic liver diseases. This process depends on production of scar tissue components by a specific cell type, named hepatic stellate cells, and is regulated by interaction with other cells. Herein, we show that activation of MerTK, a receptor present in a population of macrophages, causes the production of factors that act on hepatic stellate cells, increasing their ability to produce scar tissue.

•

MerTK, a member of the TAM family of proteins, is highly expressed in MerTK⁺/CD206⁺/CD163⁺/CD209^- macrophages.

•

In these macrophages, activation of MerTK induces phosphorylation of Akt, STAT3, ERK1/2, p38 and increased expression of VEGF-A.

•

MerTK activation in macrophages modulates the secretome to promote the profibrogenic phenotype of human HSCs.

•

Profibrogenic effects of macrophages expressing high levels of MerTK were blocked by knockdown or inhibition of MerTK.

Elucidating Spatially-Resolved Changes in Host Signaling During Plasmodium Liver-Stage Infection

Upon transmission to the human host, Plasmodium sporozoites exit the skin, are taken up by the blood stream, and then travel to the liver where they infect and significantly modify a single hepatocyte. Low infection rates within the liver have made proteomic studies of infected hepatocytes challenging, particularly in vivo, and existing studies have been largely unable to consider how protein and phosphoprotein differences are altered at different spatial locations within the heterogeneous liver. Using digital spatial profiling, we characterized changes in host signaling during Plasmodium yoelii infection in vivo without disrupting the liver tissue. Moreover, we measured alterations in protein expression around infected hepatocytes and identified a subset of CD163⁺ Kupffer cells that migrate towards infected cells during infection. These data offer the first insight into the heterogeneous microenvironment that surrounds the infected hepatocyte and provide insights into how the parasite may alter its milieu to influence its survival and modulate immunity.

Tumor-Associated Macrophages in Hepatocellular Carcinoma Pathogenesis, Prognosis and Therapy

Simple Summary

Hepatocellular carcinoma (HCC) constitutes a major health burden, accounting for >80% of primary liver cancers globally. Inflammation has come into the spotlight as a hallmark of cancer, and it is evident that tumor-associated inflammation drives the involvement of monocytes in tumor growth and metastasis. Tumor-associated macrophages (TAMs) actively participate in tumor-related inflammation, representing the main type of inflammatory cells in the tumor microenvironment, setting the crosstalk between tumor and stromal cells. Infiltrating TAMs exert either anti-tumorigenic (M1) or pro-tumorigenic (M2) functions. In most solid human tumors, increased TAM infiltration has been associated with enhanced tumor growth and metastasis, while other studies showcase that under certain conditions, TAMs exhibit cytotoxic and tumoricidal activity, inhibiting the progression of cancer. In this review, we summarize the current evidence on the role of macrophages in the pathogenesis and progression of HCC and we highlight their potential utilization in HCC prognosis and therapy.

Abstract

Hepatocellular carcinoma (HCC) constitutes a major health burden globally, and it is caused by intrinsic genetic mutations acting in concert with a multitude of epigenetic and extrinsic risk factors. Cancer induces myelopoiesis in the bone marrow, as well as the mobilization of hematopoietic stem and progenitor cells, which reside in the spleen. Monocytes produced in the bone marrow and the spleen further infiltrate tumors, where they differentiate into tumor-associated macrophages (TAMs). The relationship between chronic inflammation and hepatocarcinogenesis has been thoroughly investigated over the past decade; however, several aspects of the role of TAMs in HCC development are yet to be determined. In response to certain stimuli and signaling, monocytes differentiate into macrophages with antitumor properties, which are classified as M1-like. On the other hand, under different stimuli and signaling, the polarization of macrophages shifts towards an M2-like phenotype with a tumor promoting capacity. M2-like macrophages drive tumor growth both directly and indirectly, via the suppression of cytotoxic cell populations, including CD8+ T cells and NK cells. The tumor microenvironment affects the response to immunotherapies. Therefore, an enhanced understanding of its immunobiology is essential for the development of next-generation immunotherapies. The utilization of various monocyte-centered anticancer treatment modalities has been under clinical investigation, selectively targeting and modulating the processes of monocyte recruitment, activation and migration. This review summarizes the current evidence on the role of TAMs in HCC pathogenesis and progression, as well as in their potential involvement in tumor therapy, shedding light on emerging anticancer treatment methods targeting monocytes.

CCL5/CCR5 axis in human diseases and related treatments

To defense harmful stimuli or maintain the immune homeostasis, the body produces and recruits a superfamily of cytokines such as interleukins, interferons, chemokines etc. Among them, chemokines act as crucial regulators in defense systems. CCL5/CCR5 combination is known for facilitating inflammatory responses, as well as inducing the adhesion and migration of different T cell subsets in immune responses. In addition, recent studies have shown that the interaction between CCL5 and CCR5 is involved in various pathological processes including inflammation, chronic diseases, cancers as well as the infection of COVID-19. This review focuses on how CCL5/CCR5 axis participates in the pathological processes of different diseases and their relevant signaling pathways for the regulation of the axis. Moreover, we highlighted the gene therapy and chemotherapy studies for treating CCR5-related diseases, including the ongoing clinical trials. The barriers and perspectives for future application and translational research were also summarized.

Macrophage Polarization and Its Role in Liver Disease

Macrophages are important immune cells in innate immunity, and have remarkable heterogeneity and polarization. Under pathological conditions, in addition to the resident macrophages, other macrophages are also recruited to the diseased tissues, and polarize to various phenotypes (mainly M1 and M2) under the stimulation of various factors in the microenvironment, thus playing different roles and functions. Liver diseases are hepatic pathological changes caused by a variety of pathogenic factors (viruses, alcohol, drugs, etc.), including acute liver injury, viral hepatitis, alcoholic liver disease, metabolic-associated fatty liver disease, liver fibrosis, and hepatocellular carcinoma. Recent studies have shown that macrophage polarization plays an important role in the initiation and development of liver diseases. However, because both macrophage polarization and the pathogenesis of liver diseases are complex, the role and mechanism of macrophage polarization in liver diseases need to be further clarified. Therefore, the origin of hepatic macrophages, and the phenotypes and mechanisms of macrophage polarization are reviewed first in this paper. It is found that macrophage polarization involves several molecular mechanisms, mainly including TLR4/NF-κB, JAK/STATs, TGF-β/Smads, PPARγ, Notch, and miRNA signaling pathways. In addition, this paper also expounds the role and mechanism of macrophage polarization in various liver diseases, which aims to provide references for further research of macrophage polarization in liver diseases, contributing to the therapeutic strategy of ameliorating liver diseases by modulating macrophage polarization.

Liver regeneration biology: Implications for liver tumour therapies

The liver has remarkable regenerative potential, with the capacity to regenerate after 75% hepatectomy in humans and up to 90% hepatectomy in some rodent models, enabling it to meet the challenge of diverse injury types, including physical trauma, infection, inflammatory processes, direct toxicity, and immunological insults. Current understanding of liver regeneration is based largely on animal research, historically in large animals, and more recently in rodents and zebrafish, which provide powerful genetic manipulation experimental tools. Whilst immensely valuable, these models have limitations in extrapolation to the human situation. In vitro models have evolved from 2-dimensional culture to complex 3 dimensional organoids, but also have shortcomings in replicating the complex hepatic micro-anatomical and physiological milieu. The process of liver regeneration is only partially understood and characterized by layers of complexity. Liver regeneration is triggered and controlled by a multitude of mitogens acting in autocrine, paracrine, and endocrine ways, with much redundancy and cross-talk between biochemical pathways. The regenerative response is variable, involving both hypertrophy and true proliferative hyperplasia, which is itself variable, including both cellular phenotypic fidelity and cellular trans-differentiation, according to the type of injury. Complex interactions occur between parenchymal and non-parenchymal cells, and regeneration is affected by the status of the liver parenchyma, with differences between healthy and diseased liver. Finally, the process of termination of liver regeneration is even less well understood than its triggers. The complexity of liver regeneration biology combined with limited understanding has restricted specific clinical interventions to enhance liver regeneration. Moreover, manipulating the fundamental biochemical pathways involved would require cautious assessment, for fear of unintended consequences. Nevertheless, current knowledge provides guiding principles for strategies to optimise liver regeneration potential.

ROCK2 inhibition attenuates profibrogenic immune cell function to reverse thioacetamide-induced liver fibrosis

Background & Aims

Fibrosis, the primary cause of morbidity in chronic liver disease, is induced by pro-inflammatory cytokines, immune cell infiltrates, and tissue resident cells that drive excessive myofibroblast activation, collagen production, and tissue scarring. Rho-associated kinase 2 (ROCK2) regulates key pro-fibrotic pathways involved in both inflammatory reactions and altered extracellular matrix remodelling, implicating this pathway as a potential therapeutic target.

Methods

We used the thioacetamide-induced liver fibrosis model to examine the efficacy of administration of the selective ROCK2 inhibitor KD025 to prevent or treat liver fibrosis and its impact on immune composition and function.

Results

Prophylactic and therapeutic administration of KD025 effectively attenuated thioacetamide-induced liver fibrosis and promoted fibrotic regression. KD025 treatment inhibited liver macrophage tumour necrosis factor production and disrupted the macrophage niche within fibrotic septae. ROCK2 targeting in vitro directly regulated macrophage function through disruption of signal transducer and activator of transcription 3 (STAT3)/cofilin signalling pathways leading to the inhibition of pro-inflammatory cytokine production and macrophage migration. In vivo, KDO25 administration significantly reduced STAT3 phosphorylation and cofilin levels in the liver. Additionally, livers exhibited robust downregulation of immune cell infiltrates and diminished levels of retinoic acid receptor-related orphan receptor gamma (RORγt) and B-cell lymphoma 6 (Bcl6) transcription factors that correlated with a significant reduction in liver IL-17, splenic germinal centre numbers and serum IgG.

Conclusions

As IL-17 and IgG–Fc binding promote pathogenic macrophage differentiation, together our data demonstrate that ROCK2 inhibition prevents and reverses liver fibrosis through direct and indirect effects on macrophage function and highlight the therapeutic potential of ROCK2 inhibition in liver fibrosis.

Lay summary

By using a clinic-ready small-molecule inhibitor, we demonstrate that selective ROCK2 inhibition prevents and reverses hepatic fibrosis through its pleiotropic effects on pro-inflammatory immune cell function. We show that ROCK2 mediates increased IL-17 production, antibody production, and macrophage dysregulation, which together drive fibrogenesis in a model of chemical-induced liver fibrosis. Therefore, in this study, we not only highlight the therapeutic potential of ROCK2 targeting in chronic liver disease but also provide previously undocumented insights into our understanding of cellular and molecular pathways driving the liver fibrosis pathology.

•

ROCK2 inhibition with the small-molecule inhibitor KD025 prevents and reverses hepatoxin-induced liver fibrosis.

•

ROCK2 inhibition attenuates profibrogenic immune function.

•

KD025 exerts direct effects on liver macrophages resulting in decreased TNF secretion and impeded migration.

•

KD025 administration attenuates T cell IL-17 production and B-cell IgG production, which indirectly contributes to downregulation of profibrogenic macrophage function.

Therapeutic HNF4A mRNA attenuates liver fibrosis in a preclinical model

BACKGROUND & AIMS

Therapeutic targeting of injuries that require transient restoration of proteins by mRNA delivery is an attractive approach that, until recently, has remained poorly explored. In this study, we examined the therapeutic utility of mRNA delivery for liver fibrosis and cirrhosis. Specifically, we aimed to demonstrate the therapeutic efficacy of human hepatocyte nuclear factor alpha (HNF4A) mRNA in mouse models of fibrosis and cirrhosis.

METHODS

We investigated restoration of hepatocyte functions by HNF4A mRNA transfection in vitro, and analyzed the attenuation of liver fibrosis and cirrhosis in multiple mouse models, by delivering hepatocyte-targeted biodegradable lipid nanoparticles (LNPs) encapsulating HNF4A mRNA. To identify potential mechanisms of action, we performed microarray-based gene expression profiling, single-cell RNA sequencing, and chromatin immunoprecipitation. We used primary liver cells and human liver buds for additional functional validation.

RESULTS

Expression of HNF4A mRNA led to restoration of the metabolic activity of fibrotic primary murine and human hepatocytes in vitro. Repeated in vivo delivery of LNP-encapsulated HNF4A mRNA induced a robust inhibition of fibrogenesis in 4 independent mouse models of hepatotoxin- and cholestasis-induced liver fibrosis. Mechanistically, we discovered that paraoxonase 1 is a direct target of HNF4A and it contributes to HNF4A-mediated attenuation of liver fibrosis via modulation of liver macrophages and hepatic stellate cells.

CONCLUSION

Collectively, our findings provide the first direct preclinical evidence of the applicability of HNF4A mRNA therapeutics for the treatment of fibrosis in the liver.

LAY SUMMARY

Liver fibrosis and cirrhosis remain unmet medical needs and contribute to high mortality worldwide. Herein, we take advantage of a promising therapeutic approach to treat liver fibrosis and cirrhosis. We demonstrate that restoration of a key gene, HNF4A, via mRNA encapsulated in lipid nanoparticles decreased injury in multiple mouse models of fibrosis and cirrhosis. Our study provides proof-of-concept that mRNA therapy is a promising strategy for reversing liver fibrosis and cirrhosis.

Pediatric liver failure with massive sinusoidal infiltration of histiocytes

Histiocytic neoplasms, such as Langerhans cell histiocytosis (LCH) and disseminated juvenile xanthogranuloma (JXG), can involve the liver and sometimes cause liver failure. We aimed to classify non-LCH histiocytic proliferating disorders that do not exhibit typical disseminated JXG histology. We examined four pediatric patients who presented with liver failure and splenomegaly. Two patients with liver cirrhosis without cholestasis underwent liver transplantation (LT). The other two patients presented with giant cell hepatitis causing neonatal/infantile acute liver failure (ALF). The infantile ALF patient also underwent LT. Liver dysfunction developed after LT in all three transplant cases and the grafts exhibited massive sinusoidal infiltration of histiocytes with hemophagocytosis, similar to the native liver. The neonatal ALF patient was treated with an LCH-type chemotherapy regimen, and is alive and well at 18 months. Infiltrating histiocytes were positive for CD68 and CD163, and negative for CD1a, CD207, and S-100 protein. The BRAF V600E mutation was not present. Liver histological findings were not consistent with conventional disseminated JXG or LCH, although the histological findings in other organs overlapped those of well-known histiocytic neoplasms. The histological and immunohistochemical findings of infiltrating histiocytes suggest that these four cases constituted a disseminated JXG-like systemic disease.

Single-cell RNA transcriptome landscape of hepatocytes and non-parenchymal cells in healthy and NAFLD mouse liver

Nonalcoholic fatty liver disease (NAFLD) is a global health-care problem with limited therapeutic options. To obtain a cellular resolution of pathogenesis, 82,168 single-cell transcriptomes (scRNA-seq) across different NAFLD stages were profiled, identifying hepatocytes and 12 other non-parenchymal cell (NPC) types. scRNA-seq revealed insights into the cellular and molecular mechanisms of the disease. We discovered a dual role for hepatic stellate cells in gene expression regulation and in the potential to trans-differentiate into myofibroblasts. We uncovered distinct expression profiles of Kupffer cells versus monocyte-derived macrophages during NAFLD progression. Kupffer cells showed stronger immune responses, while monocyte-derived macrophages demonstrated a capability for differentiation. Three chimeric NPCs were identified including endothelial-chimeric stellate cells, hepatocyte-chimeric endothelial cells, and endothelial-chimeric Kupffer cells. Our work identified unanticipated aspects of mouse with NAFLD at the single-cell level and advanced the understanding of cellular heterogeneity in NAFLD livers.

Kupffer cell receptor CLEC4F is important for the destruction of desialylated platelets in mice

The liver has recently been identified as a major organ for destruction of desialylated platelets. However, the underlying mechanism remains unclear. Kupffer cells, which are professional phagocytic cells in the liver, comprise the largest population of resident tissue macrophages in the body. Kupffer cells express a C-type lectin receptor, CLEC4F, that recognizes desialylated glycans with an unclear in vivo role in mediating platelet destruction. In this study, we generated a CLEC4F-deficient mouse model (Clec4f^-/-) and found that CLEC4F was specifically expressed by Kupffer cells. Using the Clec4f^-/- mice and a newly generated platelet-specific reporter mouse line, we revealed a critical role for CLEC4F on Kupffer cells in mediating destruction of desialylated platelets in the liver in vivo. Platelet clearance experiments and ultrastructural analysis revealed that desialylated platelets were phagocytized predominantly by Kupffer cells in a CLEC4F-dependent manner in mice. Collectively, these findings identify CLEC4F as a Kupffer cell receptor important for the destruction of desialylated platelets induced by bacteria-derived neuraminidases, which provide new insights into the pathogenesis of thrombocytopenia in disease conditions such as sepsis.

TLR-4 Agonist Induces IFN-γ Production Selectively in Proinflammatory Human M1 Macrophages through the PI3K-mTOR- and JNK-MAPK-Activated p70S6K Pathway

IFN-γ, a proinflammatory cytokine produced primarily by T cells and NK cells, activates macrophages and engages mechanisms to control pathogens. Although there is evidence of IFN-γ production by murine macrophages, IFN-γ production by normal human macrophages and their subsets remains unknown. Herein, we show that human M1 macrophages generated by IFN-γ and IL-12- and IL-18-stimulated monocyte-derived macrophages (M0) produce significant levels of IFN-γ. Further stimulation of IL-12/IL-18-primed macrophages or M1 macrophages with agonists for TLR-2, TLR-3, or TLR-4 significantly enhanced IFN-γ production in contrast to the similarly stimulated M0, M2a, M2b, and M2c macrophages. Similarly, M1 macrophages generated from COVID-19-infected patients' macrophages produced IFN-γ that was enhanced following LPS stimulation. The inhibition of M1 differentiation by Jak inhibitors reversed LPS-induced IFN-γ production, suggesting that differentiation with IFN-γ plays a key role in IFN-γ induction. We subsequently investigated the signaling pathway(s) responsible for TLR-4-induced IFN-γ production in M1 macrophages. Our results show that TLR-4-induced IFN-γ production is regulated by the ribosomal protein S6 kinase (p70S6K) through the activation of PI3K, the mammalian target of rapamycin complex 1/2 (mTORC1/2), and the JNK MAPK pathways. These results suggest that M1-derived IFN-γ may play a key role in inflammation that may be augmented following bacterial/viral infections. Moreover, blocking the mTORC1/2, PI3K, and JNK MAPKs in macrophages may be of potential translational significance in preventing macrophage-mediated inflammatory diseases.

The Gut-Liver Axis in Chronic Liver Disease: A Macrophage Perspective

Chronic liver disease (CLD) is a growing health concern which accounts for two million deaths per year. Obesity, alcohol overconsumption, and progressive cholestasis are commonly characterized by persistent low-grade inflammation and advancing fibrosis, which form the basis for development of end-stage liver disease complications, including hepatocellular carcinoma. CLD pathophysiology extends to the intestinal tract and is characterized by intestinal dysbiosis, bile acid dysregulation, and gut barrier disruption. In addition, macrophages are key players in CLD progression and intestinal barrier breakdown. Emerging studies are unveiling macrophage heterogeneity and driving factors of their plasticity in health and disease. To date, in-depth investigation of how gut-liver axis disruption impacts the hepatic and intestinal macrophage pool in CLD pathogenesis is scarce. In this review, we give an overview of the role of intestinal and hepatic macrophages in homeostasis and gut-liver axis disruption in progressive stages of CLD.

SREBP-1c and lipogenesis in the liver: an update1

Sterol Regulatory Element Binding Protein-1c is a transcription factor that controls the synthesis of lipids from glucose in the liver, a process which is of utmost importance for the storage of energy. Discovered in the early nineties by B. Spiegelman and by M. Brown and J. Goldstein, it has generated more than 5000 studies in order to elucidate its mechanism of activation and its role in physiology and pathology. Synthetized as a precursor found in the membranes of the endoplasmic reticulum, it has to be exported to the Golgi and cleaved by a mechanism called regulated intramembrane proteolysis. We reviewed in 2002 its main characteristics, its activation process and its role in the regulation of hepatic glycolytic and lipogenic genes. We particularly emphasized that Sterol Regulatory Element Binding Protein-1c is the mediator of insulin effects on these genes. In the present review, we would like to update these informations and focus on the response to insulin and to another actor in Sterol Regulatory Element Binding Protein-1c activation, the endoplasmic reticulum stress.

Molecular and Cellular Mediators of the Gut-Liver Axis in the Progression of Liver Diseases

The gut-liver axis covers the bidirectional communication between the gut and the liver, and thus includes signals from liver-to-gut (e.g., bile acids, immunoglobulins) and from gut-to-liver (e.g., nutrients, microbiota-derived products, and recirculating bile acids). In a healthy individual, liver homeostasis is tightly controlled by the mostly tolerogenic liver resident macrophages, the Kupffer cells, capturing the gut-derived antigens from the blood circulation. However, disturbances of the gut-liver axis have been associated to the progression of varying chronic liver diseases, such as non-alcoholic fatty liver disease, non-alcoholic steatohepatitis, and primary sclerosing cholangitis. Notably, changes of the gut microbiome, or intestinal dysbiosis, combined with increased intestinal permeability, leads to the translocation of gut-derived bacteria or their metabolites into the portal vein. In the context of concomitant or subsequent liver inflammation, the liver is then infiltrated by responsive immune cells (e.g., monocytes, neutrophils, lymphoid, or dendritic cells), and microbiota-derived products may provoke or exacerbate innate immune responses, hence perpetuating liver inflammation and fibrosis, and potentiating the risks of developing cirrhosis. Similarly, food derived antigens, bile acids, danger-, and pathogen-associated molecular patterns are able to reshape the liver immune microenvironment. Immune cell intracellular signaling components, such as inflammasome activation, toll-like receptor or nucleotide-binding oligomerization domain-like receptors signaling, are potent targets of interest for the modulation of the immune response. This review describes the current understanding of the cellular landscape and molecular pathways involved in the gut-liver axis and implicated in chronic liver disease progression. We also provide an overview of innovative therapeutic approaches and current clinical trials aiming at targeting the gut-liver axis for the treatment of patients with chronic liver and/or intestinal diseases.

β-Catenin-NF-κB-CFTR interactions in cholangiocytes regulate inflammation and fibrosis during ductular reaction

Expansion of biliary epithelial cells (BECs) during ductular reaction (DR) is observed in liver diseases including cystic fibrosis (CF), and associated with inflammation and fibrosis, albeit without complete understanding of underlying mechanism. Using two different genetic mouse knockouts of β-catenin, one with β-catenin loss is hepatocytes and BECs (KO1), and another with loss in only hepatocytes (KO2), we demonstrate disparate long-term repair after an initial injury by 2-week choline-deficient ethionine-supplemented diet. KO2 show gradual liver repopulation with BEC-derived β-catenin-positive hepatocytes and resolution of injury. KO1 showed persistent loss of β-catenin, NF-κB activation in BECs, progressive DR and fibrosis, reminiscent of CF histology. We identify interactions of β-catenin, NFκB, and CF transmembranous conductance regulator (CFTR) in BECs. Loss of CFTR or β-catenin led to NF-κB activation, DR, and inflammation. Thus, we report a novel β-catenin-NFκB-CFTR interactome in BECs, and its disruption may contribute to hepatic pathology of CF.

The liver has an incredible capacity to repair itself or ‘regenerate’ – that is, it has the ability to replace damaged tissue with new tissue. In order to do this, the organ relies on hepatocytes (the cells that form the liver) and bile duct cells (the cells that form the biliary ducts) dividing and transforming into each other to repair and replace damaged tissue, in case the insult is dire.

During long-lasting or chronic liver injury, bile duct cells undergo a process called ‘ductular reaction’, which causes the cells to multiply and produce proteins that stimulate inflammation, and can lead to liver scarring (fibrosis). Ductular reaction is a hallmark of severe liver disease, and different diseases exhibit ductular reactions with distinct features. For example, in cystic fibrosis, a unique type of ductular reaction occurs at late stages, accompanied by both inflammation and fibrosis. Despite the role that ductular reaction plays in liver disease, it is not well understood how it works at the molecular level.

Hu et al. set out to investigate how a protein called β-catenin – which can cause many types of cells to proliferate – is involved in ductular reaction. They used three types of mice for their experiments: wild-type mice, which were not genetically modified; and two strains of genetically modified mice. One of these mutant mice did not produce β-catenin in biliary duct cells, while the other lacked β-catenin both in biliary duct cells and in hepatocytes.

After a short liver injury – which Hu et al. caused by feeding the mice a specific diet – the wild-type mice were able to regenerate and repair the liver without exhibiting any ductular reaction. The mutant mice that lacked β-catenin in hepatocytes showed a temporary ductular reaction, and ultimately repaired their livers by turning bile duct cells into hepatocytes. On the other hand, the mutant mice lacking β-catenin in both hepatocytes and bile duct cells displayed sustained ductular reactions, inflammation and fibrosis, which looked like that seen in patients with liver disease associated to cystic fibrosis. Further probing showed that β-catenin interacts with a protein called CTFR, which is involved in cystic fibrosis. When bile duct cells lack either of these proteins, another protein called NF-B gets activated, which causes the ductular reaction, leading to inflammation and fibrosis.

The findings of Hu et al. shed light on the role of β-catenin in ductular reaction. Further, the results show a previously unknown interaction between β-catenin, CTFR and NF-B, which could lead to better treatments for cystic fibrosis in the future.

Hepatic macrophages: Key players in the development and progression of liver fibrosis

Hepatic fibrosis is a common pathological process involving persistent liver injury with various etiologies and subsequent inflammatory responses that occur in chronic liver diseases. If left untreated, liver fibrosis can progress to liver cirrhosis, hepatocellular carcinoma and eventually, liver failure. Unfortunately, to date, there is no effective treatment for liver fibrosis, with the exception of liver transplantation. Although the pathophysiology of liver fibrosis is multifactorial and includes the activation of hepatic stellate cells, which are known to drive liver fibrogenesis, hepatic macrophages have emerged as central players in the development of liver fibrosis and regression. Hepatic macrophages, which consist of resident macrophages (Kupffer cells) and monocyte-derived macrophages, have been shown to play an intricate role in the initiation of inflammatory responses to liver injury, progression of fibrosis, and promotion of fibrosis resolution. These features have made hepatic macrophages uniquely attractive therapeutic targets in the fight against hepatic fibrosis. In this review, we synthesised the literature to highlight the functions and regulation of heterogeneity in hepatic macrophages. Furthermore, using the existing findings, we attempt to offer insights into the molecular mechanisms underlying the phenotypic switch from fibrogenic macrophages to restorative macrophages, the regulation of heterogeneity, and modes of action for hepatic macrophages. A better understanding of these mechanisms may guide the development of novel anti-fibrotic therapies (eg macrophage subset-targeted treatments) to combat liver fibrosis in the future.

Cell-Based Regeneration and Treatment of Liver Diseases

The liver, in combination with a functional biliary system, is responsible for maintaining a great number of vital body functions. However, acute and chronic liver diseases may lead to irreversible liver damage and, ultimately, liver failure. At the moment, the best curative option for patients suffering from end-stage liver disease is liver transplantation. However, the number of donor livers required by far surpasses the supply, leading to a significant organ shortage. Cellular therapies play an increasing role in the restoration of organ function and can be integrated into organ transplantation protocols. Different types and sources of stem cells are considered for this purpose, but highly specific immune cells are also the focus of attention when developing individualized therapies. In-depth knowledge of the underlying mechanisms governing cell differentiation and engraftment is crucial for clinical implementation. Additionally, novel technologies such as ex vivo machine perfusion and recent developments in tissue engineering may hold promising potential for the implementation of cell-based therapies to restore proper organ function.

Hepatic Radiofrequency Ablation: Monitoring of Ablation-Induced Macrophage Recruitment in the Periablational Rim Using SPION-Enhanced Macrophage-Specific Magnetic Resonance Imaging

OBJECTIVES

Macrophages accumulating in the periablational rim play a pivotal role in initiating and sustaining the perifocal inflammatory reaction, which has been shown to be at least 1 of the mechanisms responsible for the systemic pro-oncogenic effects of focal hepatic radiofrequency ablation (RFA). Herein, we tested the hypothesis to use superparamagnetic iron oxide nanoparticle (SPION)-enhanced magnetic resonance imaging (MRI) for noninvasive quantification of iron-loaded macrophages in the periablational rim of VX2 tumor-bearing rabbits.

MATERIALS AND METHODS

Twelve VX2 tumor-bearing rabbits underwent MRI immediately after and up to 3 weeks after focal hepatic RFA. For noninvasive quantification of macrophage accumulation in the periablational rim, animals were scanned before and 24 hours after SPION injection. T2*-weighted images were analyzed and correlated with histopathological and immunohistochemical findings. Furthermore, correlations with quantitative measurements (ICP-MS [inductively coupled plasma-mass spectrometry] and LA-ICP-MS [laser ablation-ICP-MS]) were performed.

RESULTS

SPION-enhanced T2*-weighted MRI scans displayed a progressive increase in the areas of signal intensity (SI) loss within the periablational rim peaking 3 weeks after RFA. Accordingly, quantitative analysis of SI changes demonstrated a significant decline in the relative SI ratio reflecting a growing accumulation of iron-loaded macrophages in the rim. Histological analyses confirmed a progressive accumulation of iron-loaded macrophages in the periablational rim. The ICP-MS and LA-ICP-MS confirmed a progressive increase of iron concentration in the periablational rim.

CONCLUSIONS

SPION-enhanced MRI enables noninvasive monitoring and quantification of ablation-induced macrophage recruitment in the periablational rim. Given the close interplay between ablation-induced perifocal inflammation and potential unwanted tumorigenic effects of RFA, SPION-enhanced MRI may serve as a valuable tool to guide and modulate adjuvant therapies after hepatic RFA.

Immunological Determinants of Liver Transplant Outcomes Uncovered by the Rat Model

For many individuals with end-stage liver disease, the only treatment option is liver transplantation. However, liver transplant rejection is observed in 24%-80% of transplant patients and lifelong drug regimens that follow the transplant procedure lead to serious side effects. Furthermore, the pool of donor livers available for transplantation is far less than the demand. Well-characterized and physiologically relevant models of liver transplantation are crucial to a deeper understanding of the cellular processes governing the outcomes of liver transplantation and serve as a platform for testing new therapeutic strategies to enhance graft acceptance. Such a model has been found in the rat transplant model, which has an advantageous size for surgical procedures, similar postoperative immunological progression, and high genome match to the human liver. From rat liver transplant studies published in the last 5 years, it is clear that the rat model serves as a strong platform to elucidate transplant immunological mechanisms. Using the model, we have begun to uncover potential players and possible therapeutic targets to restore liver tolerance and preserve host immunocompetence. Here, we present an overview of recent literature for rat liver transplant models, with an aim to highlight the value of the models and to provide future perspectives on how these models could be further characterized to enhance the overall value of rat models to the field of liver transplantation.

Identification of infiltrating immune cell subsets and heterogeneous macrophages in the lesion microenvironment of hepatic cystic echinococcosis patients with different cyst viability

Human cystic echinococcosis (CE) is characterized by lesion microenvironment formation through gathering various immune cells, including macrophages. However, immune cell subsets and heterogeneous macrophages in CE lesion microenvironment are poorly defined. Massive infiltrating immune cells formed lesion microenvironment, among which CD4⁺T cells and CD19⁺B cells were predominant and CD68⁺ macrophages were more evident in patients with active cysts. Different degrees of liver fibrosis was observed in Peri-Lesion (PL) liver samples, which was more evident in patients with active cysts. Expression of both M1 and M2 macrophage markers was significantly increased in PL liver samples. Importantly, elevation of M1 macrophage markers was more obvious in patients with inactive cysts, whereas M2 macrophage markers represented dominant macrophage phenotype in patients with active cysts. Additionally, macrophage-derived MIF, TGF-β1 and ECM1 were also expressed at higher level in CE lesion microenvironment of patients with active cysts. Moreover, MIF was evidently enhanced in the serum of hepatic CE patients, which was also predominant in patients with active cysts. Correlation analysis demonstrated positive correlation between expression of macrophage-derived cytokines and liver fibrosis degree. Heterogeneous macrophages may play significant roles in liver fibrosis of CE lesion microenvironment through producing pro-fibrogenic cytokines.

Identification of miRNA-target gene regulatory networks in liver fibrosis based on bioinformatics analysis

Background

Liver cirrhosis is one of the leading causes of death worldwide. MicroRNAs (miRNAs) can regulate liver fibrosis, but the underlying mechanisms are not fully understood, and the interactions between miRNAs and mRNAs are not clearly elucidated.

Methods

miRNA and mRNA expression arrays of cirrhotic samples and control samples were acquired from the Gene Expression Omnibus database. miRNA-mRNA integrated analysis, functional enrichment analysis and protein-protein interaction (PPI) network construction were performed to identify differentially expressed miRNAs (DEMs) and mRNAs (DEGs), miRNA-mRNA interaction networks, enriched pathways and hub genes. Finally, the results were validated with in vitro cell models.

Results

By bioinformatics analysis, we identified 13 DEMs between cirrhotic samples and control samples. Among these DEMs, six upregulated (hsa-miR-146b-5p, hsa-miR-150-5p, hsa-miR-224-3p, hsa-miR-3135b, hsa-miR-3195, and hsa-miR-4725-3p) and seven downregulated (hsa-miR-1234-3p, hsa-miR-30b-3p, hsa-miR-3162-3p, hsa-miR-548aj-3p, hsa-miR-548x-3p, hsa-miR-548z, and hsa-miR-890) miRNAs were further validated in activated LX2 cells. miRNA-mRNA interaction networks revealed a total of 361 miRNA-mRNA pairs between 13 miRNAs and 245 corresponding target genes. Moreover, PPI network analysis revealed the top 20 hub genes, including COL1A1, FBN1 and TIMP3, which were involved in extracellular matrix (ECM) organization; CCL5, CXCL9, CXCL12, LCK and CD24, which participated in the immune response; and CDH1, PECAM1, SELL and CAV1, which regulated cell adhesion. Functional enrichment analysis of all DEGs as well as hub genes showed similar results, as ECM-associated pathways, cell surface interaction and adhesion, and immune response were significantly enriched in both analyses.

Conclusions

We identified 13 differentially expressed miRNAs as potential biomarkers of liver cirrhosis. Moreover, we identified 361 regulatory pairs of miRNA-mRNA and 20 hub genes in liver cirrhosis, most of which were involved in collagen and ECM components, immune response, and cell adhesion. These results would provide novel mechanistic insights into the pathogenesis of liver cirrhosis and identify candidate targets for its treatment.

Crosstalk between hepatic stellate cells and surrounding cells in hepatic fibrosis

Hepatic fibrosis represents as a dynamic pathological process characterized by the net accumulation of extracellular matrix in the progression of various chronic liver diseases, including viral hepatitis, alcoholic liver disease, and metabolic associated fatty liver disease (MAFLD). Activation of hepatic stellate cells (HSCs) is well-defined to play a central role in the initiation and progression of hepatic fibrosis. However, the activation of HSCs is affected by the complicated microenvironments in liver, which largely attributes to the communication between hepatocytes and multiple tissue-resident cells, including sinusoidal endothelial cells, bile duct epithelial cells, platelets, T cells, B cells, macrophages, natural killer cells, neutrophils, dendritic cells, in the direct or indirect mechanisms. Cellular crosstalk between HSCs and surrounding cells contributes to the activation of HSCs and the progression of hepatic fibrosis. Currently, accumulating evidence have proven the complexity and plasticity of HSCs activation, and further clarification of cellular communication between HSCs and surrounding cells will provide sufficient clue to the development of novel diagnostic methods and therapeutic strategies for hepatic fibrosis.

The Role of Innate Immune Cells in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a very common hepatic pathology featuring steatosis and is linked to obesity and related conditions, such as the metabolic syndrome. When hepatic steatosis is accompanied by inflammation, the disorder is defined as nonalcoholic steatohepatitis (NASH), which in turn can progress toward fibrosis development that can ultimately result in cirrhosis. Cells of innate immunity, such as neutrophils or macrophages, are central regulators of NASH-related inflammation. Recent studies utilizing new experimental technologies, such as single-cell RNA sequencing, have revealed substantial heterogeneity within the macrophage populations of the liver, suggesting distinct functions of liver-resident Kupffer cells and recruited monocyte-derived macrophages with regards to regulation of liver inflammation and progression of NASH pathogenesis. Herein, we discuss recent developments concerning the function of innate immune cell subsets in NAFLD and NASH.

Ongoing Exposure to Peritoneal Dialysis Fluid Alters Resident Peritoneal Macrophage Phenotype and Activation Propensity

Peritoneal dialysis (PD) is a more continuous alternative to haemodialysis, for patients with chronic kidney disease, with considerable initial benefits for survival, patient independence and healthcare costs. However, long-term PD is associated with significant pathology, negating the positive effects over haemodialysis. Importantly, peritonitis and activation of macrophages is closely associated with disease progression and treatment failure. However, recent advances in macrophage biology suggest opposite functions for macrophages of different cellular origins. While monocyte-derived macrophages promote disease progression in some models of fibrosis, tissue resident macrophages have rather been associated with protective roles. Thus, we aimed to identify the relative contribution of tissue resident macrophages to PD induced inflammation in mice. Unexpectedly, we found an incremental loss of homeostatic characteristics, anti-inflammatory and efferocytic functionality in peritoneal resident macrophages, accompanied by enhanced inflammatory responses to external stimuli. Moreover, presence of glucose degradation products within the dialysis fluid led to markedly enhanced inflammation and almost complete disappearance of tissue resident cells. Thus, alterations in tissue resident macrophages may render long-term PD patients sensitive to developing peritonitis and consequently fibrosis/sclerosis.

The Evolving Roles of Cardiac Macrophages in Homeostasis, Regeneration, and Repair

Macrophages were first described as phagocytic immune cells responsible for maintaining tissue homeostasis by the removal of pathogens that disturb normal function. Historically, macrophages have been viewed as terminally differentiated monocyte-derived cells that originated through hematopoiesis and infiltrated multiple tissues in the presence of inflammation or during turnover in normal homeostasis. However, improved cell detection and fate-mapping strategies have elucidated the various lineages of tissue-resident macrophages, which can derive from embryonic origins independent of hematopoiesis and monocyte infiltration. The role of resident macrophages in organs such as the skin, liver, and the lungs have been well characterized, revealing functions well beyond a pure phagocytic and immunological role. In the heart, recent research has begun to decipher the functional roles of various tissue-resident macrophage populations through fate mapping and genetic depletion studies. Several of these studies have elucidated the novel and unexpected roles of cardiac-resident macrophages in homeostasis, including maintaining mitochondrial function, facilitating cardiac conduction, coronary development, and lymphangiogenesis, among others. Additionally, following cardiac injury, cardiac-resident macrophages adopt diverse functions such as the clearance of necrotic and apoptotic cells and debris, a reduction in the inflammatory monocyte infiltration, promotion of angiogenesis, amelioration of inflammation, and hypertrophy in the remaining myocardium, overall limiting damage extension. The present review discusses the origin, development, characterization, and function of cardiac macrophages in homeostasis, cardiac regeneration, and after cardiac injury or stress.