Characterization of two F4/80-positive Kupffer cell subsets by their function and phenotype in mice

FGF1 Signaling Modulates Biliary Injury and Liver Fibrosis in the Mdr2-/- Mouse Model of Primary Sclerosing Cholangitis

Fibroblast growth factor 1 (FGF1) belongs to a family of growth factors involved in cellular growth and division. MicroRNA 16 (miR-16) is a regulator of gene expression, which is dysregulated during liver injury and insult. However, the role of FGF1 in the progression of biliary proliferation, senescence, fibrosis, inflammation, angiogenesis, and its potential interaction with miR-16, are unknown. In vivo studies were performed in male bile duct-ligated (BDL, 12-week-old) mice, multidrug resistance 2 knockout (Mdr2-/-) mice (10-week-old), and their corresponding controls, treated with recombinant human FGF1 (rhFGF1), fibroblast growth factor receptor (FGFR) antagonist (AZD4547), or anti-FGF1 monoclonal antibody (mAb). In vitro, the human cholangiocyte cell line (H69) and human hepatic stellate cells (HSCs) were used to determine the expression of proliferation, fibrosis, angiogenesis, and inflammatory genes following rhFGF1 treatment. PSC patient and control livers were used to evaluate FGF1 and miR-16 expression. Intrahepatic bile duct mass (IBDM), along with hepatic fibrosis and inflammation, increased in BDL mice treated with rhFGF1, with a corresponding decrease in miR-16, while treatment with AZD4547 or anti-FGF1 mAb decreased hepatic fibrosis, IBDM, and inflammation in BDL and Mdr2-/- mice. In vitro, H69 and HSCs treated with rhFGF1 had increased expression of proliferation, fibrosis, and inflammatory markers. PSC samples also showed increased FGF1 and FGFRs with corresponding decreases in miR-16 compared with healthy controls. Conclusion: Our study demonstrates that suppression of FGF1 and miR-16 signaling decreases the presence of hepatic fibrosis, biliary proliferation, inflammation, senescence, and angiogenesis. Targeting the FGF1 and miR-16 axis may provide therapeutic options in treating cholangiopathies such as PSC.

The Functional Roles of Immune Cells in Primary Liver Cancer

Primary liver cancer includes hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA). Incidence of liver cancer has been increasing in recent years, and the 5-year survival is <20%. HCC and CCA are often accompanied with a dense stroma coupled with infiltrated immune cells, which is referred to as the tumor microenvironment. Populations of specific immune cells, such as high density of CD163+ macrophages and low density of CD8+ T cells, are associated with prognosis and survival rates in both HCC and CCA. Immune cells in the tumor microenvironment can be a therapeutic target for liver cancer treatments. Previous studies have introduced immunotherapy using immune checkpoint inhibitors, pulsed dendritic cells, or transduced T cells, to enhance cytotoxicity of immune cells and inhibit tumor growth. This review summarizes current understanding of the roles of immune cells in primary liver cancer covering HCC and CCA.

Prognostic role of myeloid-derived tumor-associated macrophages at the tumor invasive margin in gastric cancer with liver metastasis (GCLM): a single-center retrospective study

BACKGROUND

Liver metastasis is one of the important factors leading to poor prognosis of gastric cancer. According to the classic "seed soil theory", it is speculated that the liver microenvironment at the invasion margin of gastric cancer liver metastases (GCLM) may have a crucial impact on tumor progression. However, few studies had stated the correlation between the patients' prognosis and the densities of stromal cells infiltrating into the invasive margin, where our retrospective study designed to identify the role of infiltrating macrophages on the prognosis of GCLM as a reliable supplement of predictive tumor markers.

METHODS

The material consisted of a group of 72 gastric cancer (GC) patients with liver metastasis diagnosed from February 2015 and December 2020. The CD68+, CD206+, and Clec4f+ macrophages in their specimens were counted by immunohistochemistry (IHC), and the analysis area was the invasive margin of metastatic lesions. Clinical data were collected retrospectively. Overall survival (OS) was calculated from the date of initial diagnosis to the date of last follow-up or death. Survival analyses were performed using the Kaplan-Meier method and log-rank test. Multivariate Cox regression was performed to asses impact of macrophages on OS.

RESULTS

The expression of CD206 could indicate the prognosis of patients with GCLM, and patients with high expression of CD206 had worse prognoses (P=0.0002). Univariate and multivariate analyses showed that CD206 was an independent risk factor for prognosis (HR 5.276, 95% CI: 1.730-16.089, P=0.003).

CONCLUSIONS

The CD206+ myeloid-derived tumor associated macrophages (TAMs) may predict whether patients could benefit from R1 resection of liver-metastatic lesions, which has important theoretical significance and practical value for accurately evaluating the clinical prognosis of patients with GCLM and guiding clinical treatment.

Why nanoparticles prefer liver macrophage cell uptake in vivo

Effective delivery of therapeutic and diagnostic nanoparticles is dependent on their ability to accumulate in diseased tissues. However, most nanoparticles end up in liver macrophages regardless of nanoparticle design after administration. In this review, we describe the interactions of liver macrophages with nanoparticles. Liver macrophages have significant advantages in interacting with circulating nanoparticles over most target cells and tissues in the body. We describe these advantages in this article. Understanding these advantages will enable the development of strategies to overcome liver macrophages and deliver nanoparticles to targeted diseased tissues effectively. Ultimately, these approaches will increase the therapeutic efficacy and diagnostic signal of nanoparticles.

Activation of LXR Nuclear Receptors Impairs the Anti-Inflammatory Gene and Functional Profile of M-CSF-Dependent Human Monocyte-Derived Macrophages

Liver X Receptors (LXR) control cholesterol metabolism and exert anti-inflammatory actions but their contribution to human macrophage polarization remains unclear. The LXR pathway is enriched in pro-inflammatory macrophages from rheumatoid arthritis as well as in tumors-associated macrophages from human tumors. We now report that LXR activation inhibits the anti-inflammatory gene and functional profile of M-CSF-dependent human macrophages, and prompts the acquisition of a pro-inflammatory gene signature, with both effects being blocked by an LXR inverse agonist. Mechanistically, the LXR-stimulated macrophage polarization shift correlates with diminished expression of MAFB and MAF, which govern the macrophage anti-inflammatory profile, and with enhanced release of activin A. Indeed, LXR activation impaired macrophage polarization in response to tumor-derived ascitic fluids, as well as the expression of MAF- and MAFB-dependent genes. Our results demonstrate that LXR activation limits the anti-inflammatory human macrophage polarization and prompts the acquisition of an inflammatory transcriptional and functional profile.

Hepatoprotective effect of diallyl trisulfide against lipopolysaccharide and D-galactosamine induced acute liver failure in mice via suppressing inflammation and apoptosis

Acute liver failure (ALF), characterized by the quick occurrence of disorder in liver, is a serious liver injury with extremely high mortality. Therefore, we investigated whether diallyl trisulfide (DATS), a natural product from garlic, protected against ALF in mice and studied underlying mechanisms. In the present study, lipopolysaccharide (LPS) (10 μg·kg^-1)/D-galactosamine (D-gal) (500 mg·kg^-1) was intraperitoneally injected to ICR mice to induce ALF. The mice were orally administered 20-, 40-, or 80-mg·kg^-1 DATS) 1 h before LPS/D-gal exposure. Serum biochemical analyses and pathological study found that DATS pretreatment effectively prevented the ALF in LPS/D-gal-treated mice. Mechanistically, pretreatment of DATS inhibited the increase of the numbers of CD11b⁺ Kupffer cells and other macrophages in the liver, the release of tumor necrosis factor-α into the blood, and Caspase-1 activation induced by LPS/D-gal treatment in mice. Furthermore, DATS inhibited the activation of Caspase-3, downregulation of Bcl-2/Bax ratio, and increase of TUNEL positive staining. Altogether, our findings suggest that DATS exhibits hepatoprotective effects against ALF elicited by LPS/D-gal challenge, which probably associated with anti-inflammation and anti-apoptosis.

Hepatic Macrophages Express Melanoma Differentiation-Associated Gene 5 in Nonalcoholic Steatohepatitis

The activation of innate immune system is essential for the pathogenesis of nonalcoholic steatohepatitis (NASH). Among pattern recognition receptors, it is well-characterized that toll-like receptors (TLRs) are deeply involved in the development of NASH to reflect exposure of the liver to gut-driven endotoxins. In contrast, it has not been elucidated whether retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) are similarly implicated in the disease progression. In the present study, we examined the expression of melanoma differentiation-associated antigen 5 (MDA5), known to be a member of RLRs, in a diet-induced murine model of NASH. The liver tissues were collected from C57BL/6 J mice at 1, 3, and 6 weeks after choline-deficient L-amino acid-defined high-fat diet (CDAHFD), and the expression of MDA5 was analyzed by western blotting, immunofluorescence (IF), and real-time quantitative PCR (qPCR). The results of western blotting showed that hepatic expression of MDA5 was increased at 3 and 6 weeks. In IF, MDA5-positive cells co-expressed F4/80 and CD11b, indicating they were activated macrophages, and these cells began to appear at 1 week after CDAHFD. The mRNA expression of MDA5 was significantly upregulated at 1 week. Additionally, we performed IF using liver biopsy specimens collected from 11 patients with nonalcoholic fatty liver diseases (NAFLD), and found that MDA5-positive macrophages were detected in eight out of eleven patients. In an in vitro study, MDA5 was induced upon stimulation with lipopolysaccharide in murine bone marrow-derived macrophages and THP-1 cells. Our findings suggest that MDA5 may be involved in the inflammation of NASH.

MicroRNA-15a/16-1 Prevents Hepatocellular Carcinoma by Disrupting the Communication Between Kupffer Cells and Regulatory T Cells

BACKGROUND & AIMS

Hepatocellular carcinoma (HCC) is characterized by intratumoral accumulation of regulatory T cells (Tregs), which suppresses antitumor immunity. This study was designed to investigate how microRNAs regulate immunosuppression in HCC.

METHODS

FVB/NJ mice were hydrodynamically injected with AKT/Ras or c-Myc and Sleeping Beauty transposon to induce HCC. The Sleeping Beauty system was used to deliver microRNA-15a/16-1 into livers of mice. Flow cytometry and immunostaining were used to determine changes in the immune system.

RESULTS

Hydrodynamic injection of AKT/Ras or c-Myc into mice resulted in hepatic enrichment of Tregs and reduced cytotoxic T cells (CTLs) and HCC development. HCC impaired microRNA-15a/16-1 biogenesis in Kupffer cells (KCs) of AKT/Ras and c-Myc mice. Hydrodynamic injection of microRNA-15a/16-1 fully prevented HCC in AKT/Ras and c-Myc mice, while 100% of control mice died of HCC. Therapeutically, microRNA-15a/16-1 promoted a regression of HCC in both mouse models, impaired hepatic enrichment of Tregs, and increased hepatic CTLs. Mechanistically, a significant increase was observed in serum C-C motif chemokine 22 (CCL22) and transcription of Ccl22 in KCs of AKT/Ras and c-Myc mice. MicroRNA-15a/16-1 prevented KCs from overproducing CCL22 by inhibiting nuclear factor-κB that activates transcription of Ccl22. By reducing CCL22 binding to C-C chemokine receptor type 4 on Tregs, microRNA-15a/16-1 impaired Treg chemotaxis. Disrupting the interaction between microRNA-15a/16-1 and nuclear factor-κB impaired the ability of microRNA-15a/16-1 to prevent hepatic Treg accumulation and HCC. Depletion of cluster of differentiation 8⁺ T cells and additional treatment of CCL22 recovered growth of HCC that was fully prevented by microRNA-15a/16.

CONCLUSIONS

MicroRNA-15a/16-1 attenuates immunosuppression by disrupting CCL22-mediated communication between KCs and Tregs. MicroRNA-15a/16-1 represents a potential immunotherapy against HCC.

Infections, Reactions of Natural Killer T Cells and Natural Killer Cells, and Kidney Injury

Natural killer T (NKT) cells and NK cells are representative innate immune cells that perform antitumor and antimicrobial functions. The involvement of these cells in various renal diseases, including acute kidney injury (AKI), has recently become evident. Murine NKT cells are activated and cause AKI in response to various stimuli, such as their specific ligand, cytokines, and bacterial components. Both renal vascular endothelial cell injury (via the perforin-mediated pathway) and tubular epithelial cell injury (via the tumor necrosis factor-alpha/Fas ligand pathway) are independently involved in the pathogenesis of AKI. NK cells complement the functions of NKT cells, thereby contributing to the development of infection-associated AKI. Human CD56⁺ T cells, which are a functional counterpart of murine NKT cells, as well as a subpopulation of CD56⁺ NK cells, strongly damage intrinsic renal cells in vitro upon their activation, possibly through mechanisms similar to those in mice. These cells are also thought to be involved in the acute exacerbation of pre-existing glomerulonephritis triggered by infection in humans, and their roles in sepsis-associated AKI are currently under investigation. In this review, we will provide an overview of the recent advances in the understanding of the association among infections, NKT and NK cells, and kidney injury, which is much more profound than previously considered. The important role of liver macrophages in the activation of NKT cells will also be introduced.

A Novel Function of Mitochondrial Phosphoenolpyruvate Carboxykinase as a Regulator of Inflammatory Response in Kupffer Cells

Background: There has been a recent appreciation that some metabolic enzymes can profoundly influence the nature of the immune response produced in macrophages. However, the role of mitochondrial phosphoenolpyruvate carboxykinase (PCK2) in immune response remains unknown. This study aims to investigate the role of PCK2 in lipopolysaccharides (LPS)-induced activation in Kupffer cells. Methods: Inflammatory cytokines were determined by real-time quantitative reverse transcription-polymerase chain action (qRT-PCR) and flow cytometric analysis using a cytometric bead array. Western blotting and immunofluorescence staining were used to determine PCK2 expression and subcellular distribution under confocal laser microscopy. qRT-PCR, flow cytometry, and high-performance liquid chromatography (HPLC) were used to determine mitochondrial function. Pharmacological inhibition, knockdown, and overexpression of PCK2 were used to confirm its function. Co-immunoprecipitation (Co-IP) was performed to determine MAPK/NF-κB phosphorylation. Results: Inflammatory response was significantly increased in LPS-treated mice and Kupffer cells. During the inflammatory process, the protein level of PCK2 was significantly upregulated in Kupffer cells. Interestingly, the localization of PCK2 was mainly in cytosol rather than mitochondria after LPS stimulation. Gain-of-function and loss-of-function analyses found that PCK2 overexpression significantly upregulated the levels of inflammation markers, whereas PCK2 knockdown or inhibition significantly mitigated LPS-induced inflammatory response in Kupffer cells. Furthermore, PCK2 promoted protein phosphorylation of NF-κB and AKT/MAPK, the major signaling pathways, controlling inflammatory cascade activation. Conclusion: We identified a novel function of PCK2 in mediating LPS-induced inflammation and provided mechanistic insights into the regulation of inflammatory response in Kupffer cells. Therefore, PCK2 may serve as a novel therapeutic target for the regulation of Kupffer cells-mediated inflammatory responses.

A preliminary study of the innate immune memory of Kupffer cells induced by PEGylated nanoemulsions

The accelerated blood clearance (ABC) phenomenon describes a dilemma of polyethylene glycol (PEG) applied in drug delivery system (DDS) caused by its immunogenicity, that results in the enhanced blood clearance rate and increased hepatic and splenic accumulation after secondary injection of PEGylated nanocarriers. However, the ABC index, as the judgement of ABC phenomenon, only describes the accelerated blood clearance rate, but ignores the enhanced hepatic and splenic accumulation. Therefore, we proposed the hepatic accumulation (HA) index and the splenic accumulation (SA) index as supplements for assessing the ABC phenomenon, to emphasize the contribution of liver and spleen, especially the liver, possessing the most population of tissue resident macrophages. By altering the first injection site from the tail vein to the liver portal vein, there was no impact on anti-PEG IgM production, and the secondary hepatic accumulation of PEGylated nanoemulsions (PE) was observed to be proportionate to the first PE stimulation strength on the liver. We also determined that Kupffer cells (KCs) were the main contributor to this enhancement. On this basis, we revealed a definite phenomenon that PE could induce innate immune memory in KCs, by enhancing the phagocytosis of KCs toward PE during the secondary stimulation. The PE-stimulated KCs could carry this memory to the naïve rats through adoptive transfer, resulting in increased hepatic accumulation in the recipient rats without antibody production. Studies examining the phagocytosis of KCs in vivo, ex vivo and in vitro revealed that the memory of KCs against PE triggered by first-stimulated PE could be maintained independently of other cells or components until 21 days after the first stimulation, and possessing specificity to PEG, which was invalid to long-circulating GE (GM1 modified nanoemulsions). The discovery of immune memory in KCs induced by PE highlights the importance of focusing on the relationship between the innate immune system and PEGylated nanocarriers during the development of DDS to improve medication safety in the clinic.

CD169-positive macrophages enhance abscopal effect of radiofrequency ablation therapy in liver cancer

Radiofrequency ablation (RFA) is a widely used and effective treatment for primary or metastatic liver cancer with small-size lesions. However, the therapeutic effectiveness of RFA in controlling metastatic lesion or recurrence is still limited. As the major cell population in tumor microenvironment (TME), macrophages have been reported to be recruited to RFA-treated lesion, but their roles are still unclear. Herein, we successfully established the mouse model mimicking RFA-induced abscopal effect, in which RFA eliminated the local orthotopic liver tumor but failed to control growth of distant tumor. Correspondently, RFA suppressed protumoral activation of local tumor-associated macrophages (TAMs), but failed to reprogram TAMs in distance. Importantly, although RFA led to reduced proportion of hepatic CD169⁺ macrophages in local and decreased expression of immune inhibitory molecules Tim-3 and PD-L1, these alterations were not observed for CD169⁺ macrophages in distant TME. Further RNA-seq and flow cytometry analysis showed that hepatic CD169⁺ macrophages contributed to reprograming TME through recruiting CD8⁺ T/NK cells and suppressing accumulation of MDSCs/Tregs. Consistently, depletion of CD169⁺ macrophages in CD169-DTR mouse greatly promoted liver tumor progression and largely dampened RFA-induced tumor suppression. Notably, transfer of CD169⁺ macrophages synergistically enhanced RFA-induced inhibition of distant tumor. To our knowledge, this is the first study which demonstrates hepatic CD169⁺ macrophages as a key factor responsible for RFA-induced abscopal effect. Our data suggest RFA with transfer of CD169⁺ macrophages as a promising combination therapy to lessen metastasis or recurrence of liver cancer in patients.

Effects of a CCR2 antagonist on macrophages and Toll-like receptor 9 expression in a mouse model of diabetic nephropathy

The pathogenesis of diabetic nephropathy (DN) is related to macrophage (Mφ) recruitment to the kidneys, tumor necrosis factor-α (TNF-α) production, and oxidative stress. Toll-like receptor 9 (TLR9) activation is reportedly involved in systemic inflammation, and it exacerbates this condition in metabolic syndrome. Therefore, we hypothesized that TLR9 plays a role in the pathogenesis of DN. Two subsets of kidney Mφs in DN model (db/db) mice were analyzed using flow cytometry to evaluate their distribution and TLR9 expression and function. Mice were administered the CCR2 antagonist INCB3344 for 8 wk; changes in Mφ distribution and function and its therapeutic effects on DN pathology were examined. Bone marrow-derived CD11bhigh (BM-Mφ) and tissue-resident CD11blow Mφs (Res-Mφ) were identified in the mouse kidneys. As DN progressed, the BM-Mφ number, TLR9 expression, and TNF-α production increased significantly. In Res-Mφs, reactive oxygen species (ROS) production and phagocytic activity were enhanced. INCB3344 decreased albuminuria, serum creatinine level, BM-Mφ abundance, TLR9 expression, and TNF-α production by BM-Mφs and ROS production by Res-Mφs. Both increased activation of BM-Mφ via TLR9 and TNF-α production and increased ROS production by Res-Mφs were involved in DN progression. Thus, inactivating Mφs and their TLR9 expression by INCB3344 is a potential therapeutic strategy for DN.NEW & NOTEWORTHY We classified kidney macrophages (Mφs) into bone marrow-derived Mφs (BM-Mφs) expressing high CD11b and tissue-specific resident Mφ (Res-Mφs) expressing low CD11b. In diabetic nephropathy (DN) model mice, Toll-like receptor 9 (TLR9) expression and TNF-α production via TLR9 activation in BM-Mφs and ROS production in Res-Mφs were enhanced. Furthermore, CCR2 antagonist suppressed the kidney infiltration of BM-Mφs and their function and the ROS production by Res-Mφs, with concomitant TLR9 suppression. Our study presents a new therapeutic strategy for DN.

Nitric oxide facilitates the targeting Kupffer cells of a nano-antioxidant for the treatment of NASH

Kupffer cells are a key source of reactive oxygen species (ROS) and are implicated in the development of steatohepatitis and fibrosis in nonalcoholic steatohepatitis (NASH). We recently developed a polythiolated and mannosylated human serum albumin (SH-Man-HSA), a nano-antioxidant that targets Kupffer cells, in which the mannosyl units on albumin allows their specific uptake by Kupffer cells via the mannose receptor C type 1 (MRC1), and in which the polythiolation confers antioxidant activity. The aim of this study was to investigate the therapeutic potential of SH-Man-HSA in NASH model mice. In livers from mice and/or patients with NASH, we observed a reduced blood flow in the liver lobes and the down-regulation in MRC1 expression in Kupffer cells, and SH-Man-HSA alone failed to improve the pathological phenotype in NASH. However, the administration of a nitric oxide (NO) donor restored hepatic blood flow and increased the expression of the mannose receptor C type 2 (MRC2) instead of MRC1. Consequently, treatment with a combination of SH-Man-HSA and an NO donor improved oxidative stress-associated pathology. Finally, we developed a hybrid type of nano-antioxidant (SNO-Man-HSA) via the S-nitrosation of SH-Man-HSA. This nanomedicine efficiently delivered both NO and thiol groups to the liver, with a hepatoprotective effect that was comparable to the combination therapy of SH-Man-HSA and an NO donor. These findings suggest that SNO-Man-HSA has the potential for functioning as a novel nano-therapy for the treatment of NASH.

A novel HSF1 activator ameliorates nonalcoholic steatohepatitis by stimulating mitochondrial adaptive oxidation

BACKGROUND AND PURPOSE

Nonalcoholic steatohepatitis (NASH) is the more severe form of metabolic associated fatty liver disease (MAFLD), and no pharmacologic treatment approved as yet. Identification of novel therapeutic targets and their agents are critical to overcome the current inadequacy of drug treatment for NASH.

EXPERIMENTAL APPROACH

The correlation between heat shock factor 1 (HSF1) levels and the development of NASH and the target genes of HSF1 in hepatocyte were revealed by chromatin-immunoprecipitation sequencing. The effects and mechanisms of SYSU-3d in alleviating NASH were examined in relevant cell models and mouse models (the Ob/Ob mice, high-fat and high-cholesterol diet, the methionine-choline deficient diet fed mice). The drug-like properties of SYSU-3d in vivo were evaluated.

KEY RESULTS

HSF1 is progressively reduced with mitochondrial dysfunction in NASH pathogenesis and activation of this transcription factor by its newly-identified activator SYSU-3d efficiently ameliorated all manifestations of NASH in mice. When activated, the phosphorylated HSF1 (Ser326) translocated to nucleus and bound to the promoter of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) to induce mitochondrial biogenesis, thus increasing mitochondrial adaptive oxidation and inhibiting oxidative stress. The deletion of HSF1 and PGC-1α or recovery of HSF1 in HSF1-deficiency cells revealed the HSF1/PGC-1α metabolic axis mainly responsible for the anti-NASH effects of SYSU-3d independent of adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK).

CONCLUSION AND IMPLICATIONS

Activation of HSF1 is a practicable therapeutic approach for NASH treatment via the HSF1/PGC-1α/mitochondrial axis, and SYSU-3d would take into consideration as a potential candidate for the treatment of NASH.

The immune niche of the liver

The liver is an essential organ that is critical for the removal of toxins, the production of proteins, and the maintenance of metabolic homeostasis. Behind each liver functional unit, termed lobules, hides a heterogeneous, complex, and well-orchestrated system. Despite parenchymal cells being most commonly associated with the liver's primary functionality, it has become clear that it is the immune niche of the liver that plays a central role in maintaining both local and systemic homeostasis by propagating hepatic inflammation and orchestrating its resolution. As such, the immunological processes that are at play in healthy and diseased livers are being investigated thoroughly in order to understand the underpinnings of inflammation and the potential avenues for restoring homeostasis. This review highlights recent advances in our understanding of the immune niche of the liver and provides perspectives for how the implementation of new transcriptomic, multimodal, and spatial technologies can uncover the heterogeneity, plasticity, and location of hepatic immune populations. Findings from these technologies will further our understanding of liver biology and create a new framework for the identification of therapeutic targets.

Lipopolysaccharide Preconditioning Augments Phagocytosis of Malaria-Parasitized Red Blood Cells by Bone Marrow-Derived Macrophages in the Liver, Thereby Increasing the Murine Survival after Plasmodium yoelii Infection

Malaria remains a grave concern for humans, as effective medical countermeasures for Plasmodium infection have yet to be developed. Phagocytic clearance of parasitized red blood cells (pRBCs) by macrophages is an important front-line innate host defense against Plasmodium infection. We previously showed that repeated injections of low-dose lipopolysaccharide (LPS) prior to bacterial infection, called LPS preconditioning, strongly augmented phagocytic/bactericidal activity in murine macrophages. However, whether LPS preconditioning prevents murine Plasmodium infection is unclear. We investigated the protective effects of LPS preconditioning against lethal murine Plasmodium infection, focusing on CD11b^high F4/80^low liver macrophages, which are increased by LPS preconditioning. Mice were subjected to LPS preconditioning by intraperitoneal injections of low-dose LPS for 3 consecutive days, and 24 h later, they were intravenously infected with pRBCs of Plasmodium yoelii 17XL. LPS preconditioning markedly increased the murine survival and reduced parasitemia, while it did not reduce tumor necrosis factor (TNF) secretions, only delaying the peak of plasma gamma interferon (IFN-γ) after Plasmodium infection in mice. An in vitro phagocytic clearance assay of pRBCs showed that the CD11b^high F4/80^low liver macrophages, but not spleen macrophages, in the LPS-preconditioned mice had significantly augmented phagocytic activity against pRBCs. The adoptive transfer of CD11b^high F4/80^low liver macrophages from LPS-preconditioned mice to control mice significantly improved survival after Plasmodium infection. We conclude that LPS preconditioning stimulated CD11b^high F4/80^low liver macrophages to augment the phagocytic clearance of pRBCs, which may play a central role in resistance against Plasmodium infection.

The Liver and the Hepatic Immune Response in Trypanosoma cruzi Infection, a Historical and Updated View

Chagas disease was described more than a century ago and, despite great efforts to understand the underlying mechanisms that lead to cardiac and digestive manifestations in chronic patients, much remains to be clarified. The disease is found beyond Latin America, including Japan, the USA, France, Spain, and Australia, and is caused by the protozoan Trypanosoma cruzi. Dr. Carlos Chagas described Chagas disease in 1909 in Brazil, and hepatomegaly was among the clinical signs observed. Currently, hepatomegaly is cited in most papers published which either study acutely infected patients or experimental models, and we know that the parasite can infect multiple cell types in the liver, especially Kupffer cells and dendritic cells. Moreover, liver damage is more pronounced in cases of oral infection, which is mainly found in the Amazon region. However, the importance of liver involvement, including the hepatic immune response, in disease progression does not receive much attention. In this review, we present the very first paper published approaching the liver's participation in the infection, as well as subsequent papers published in the last century, up to and including our recently published results. We propose that, after infection, activated peripheral T lymphocytes reach the liver and induce a shift to a pro-inflammatory ambient environment. Thus, there is an immunological integration and cooperation between peripheral and hepatic immunity, contributing to disease control.

Hepatic Clearance of Cell-Free DNA: Possible Impact on Early Metastasis Diagnosis

Circulating DNA in the bloodstream has been studied since the 1940s, leading to its identification as a possible early marker for the presence of a primary tumor. Recently, it has been more successfully employed in liquid biopsies to determine the early presence of a metastatic tumor arising after chemotherapy, radiotherapy, and surgery. The appearance of such circulating tumor DNA permits the identification of the metastatic tumor before it is detected by either palpation or radiological analysis. Nevertheless, the liquid biopsy may possibly be affected by the removal of circulating tumor DNA via the kidneys and spleen as it is released. Furthermore, the liver removal of cell-free DNA has not yet been considered to be involved in this process. Here, we review the literature on the removal of free single- and double-stranded DNA and nucleosomal, vesicular, and exosomal DNA via the liver and examine its possible impact on circulating DNA levels. The removal of all forms of DNA by the liver, together with that removed by the kidneys and spleen, may delay the timing of positive results from liquid biopsies.

A conserved pathway of transdifferentiation in murine Kupffer cells

Abundant long-lived liver-resident macrophages, termed Kupffer cells, are activated during chronic liver injury. They secrete both pro-inflammatory and pro-fibrotic cytokines, which act on hepatic stellate cells causing their transdifferentiation into myofibroblasts that deposit collagen. In other tissues, wound-associated macrophages go further, and transdifferentiate into fibrocytes, secreting collagen themselves. We tested Kupffer cells for this property in two experimental models: mixed non-parenchymal cell culture, and precision-cut liver slice culture. Using the Emr1-Cre transgene as a driver and the RiboTag transgene as a reporter, we found that Kupffer cells undergo transdifferentiation under these circumstances. Over time, they lose the expression of both Kupffer cell-specific and macrophage-specific genes and the transcription factors that control their expression, and they begin to express multiple genes and proteins characteristic of either myofibroblasts or tissue fibroblasts. These effects were strongly conserved between non-parenchymal cell culture and liver tissue slice culture, arguing that such transdifferentiation is a conserved function of Kupffer cells. We conclude that in addition to supporting fibrosis through an action on stellate cells, Kupffer cells also participate in liver fibrosis through transdifferentiation into fibrocytes.

CD40 agonist-induced IL-12p40 potentiates hepatotoxicity

Background

CD40 is a compelling target for cancer immunotherapy, however, attempts to successfully target this pathway have consistently been hampered by dose-limiting toxicity issues in the clinic that prevents the administration of efficacious doses.

Methods

Here, using cytokine and cytokine receptor depletion strategies in conjunction with a potent CD40 agonist, we investigated mechanisms underlying the two primary sources of CD40 agonist-associated toxicity, hepatotoxicity and cytokine release syndrome (CRS).

Results

We demonstrate that CD40 agonist -induced hepatotoxicity and CRS are mechanistically independent. Historical data have supported a role for interleukin-6 (IL-6) in CRS-associated wasting, however, our findings instead show that an inflammatory cytokine network involving TNF, IL-12p40, and IFNγ underlie this process. Deficiency of TNF or IFNγ did not influence CD40-induced hepatitis however loss of IL-12p40 significantly decreased circulating concentrations of liver enzymes and reduced the frequency of activated CD14⁺MHCII⁺ myeloid cells in the liver, indicating a role for IL-12p40 in liver pathology.

Conclusions

As clinical research programs aim to circumnavigate toxicity concerns while maintaining antitumor efficacy it will be essential to understand which features of CD40 biology mediate antitumor function to develop both safe and efficacious agonists.

Contrasting functional responses of resident Kupffer cells and recruited liver macrophages to irradiation and liver X receptor stimulation

In the murine liver, there are two major macrophage populations, namely resident Kupffer cells (resKCs) with phagocytic activity and recruited macrophages (recMφs) with cytokine-producing capacity. This study was performed to clarify the functional differences between these two populations, focusing on their susceptibility to radiation and response to stimulation via liver X receptors (LXRs), which are implicated in cholesterol metabolism and immune regulation. Liver mononuclear cells (MNCs) were obtained from C57BL/6 (WT) mice with or without 2 Gy irradiation, and the phagocytic activity against Escherichia coli (E. coli) as well as TNF-α production were compared between the two macrophage populations. To assess LXR functions, phagocytosis, TNF-α production, and endocytosis of acetylated low-density lipoprotein (LDL) were compared after synthetic LXR ligand stimulation. Furthermore, LXRα/β knockout (KO) mice and LXRα KO mice were compared with WT mice. Irradiation decreased intracellular TNF-α production by recMφs but did not affect the phagocytic activity of resKCs. In vitro LXR stimulation enhanced E. coli phagocytosis by resKCs but decreased E. coli-stimulated TNF-α production by recMφs. Phagocytic activity and acetylated LDL endocytosis were decreased in both LXRα/β KO mice and LXRα KO mice, with serum TNF-α levels after E. coli injection in the former being higher than those in WT mice. In conclusion, resKCs and recMφs exhibited different functional features in response to radiation and LXR stimulation, highlighting their distinct roles liver immunity and lipid metabolism.

Lipopolysaccharide preconditioning reduces liver metastasis of Colon26 cells by enhancing antitumor activity of natural killer cells and natural killer T cells in murine liver

BACKGROUND AND AIM

Lipopolysaccharide (LPS) preconditioning drastically augments bactericidal activity but reduces the host inflammatory response. Therefore, it may be beneficial to prevent postoperative infectious complications and mitigate host damage by surgical stress. Considering its clinical application, how LPS preconditioning influences the antitumor effect in the liver is an important issue. We then investigated the effect of LPS preconditioning on antitumor activity against Colon26 tumor cells in mice.

METHODS

Lipopolysaccharide preconditioning was induced in mice by the intraperitoneal injection of 5 μg/kg LPS for three consecutive days. Intraportal inoculation of Colon26 cells, which express luminescent protein called Nano-lantern, was performed to evaluate the effect of LPS preconditioning on tumor liver metastasis. The antitumor activities of cytotoxic liver lymphocytes, especially natural killer (NK) cells and natural killer T (NKT) cells, against Colon26 cells were also examined in LPS preconditioned mice.

RESULTS

Lipopolysaccharide preconditioning remarkably prevented liver metastasis of Colon26 cells, as observed by IVIS imaging system, and prolonged survival after tumor inoculation. LPS preconditioning increased the proportions and number of liver NK cells and NKT cells and augmented their intracellular perforin and granzyme B expression, while reducing their intracellular expression of IFN-γ. An in vitro antitumor cytotoxicity assay revealed that LPS preconditioning significantly augmented antitumor cytotoxicities of the liver NK cells and NKT cells, especially NKT cells, against Colon26 cells.

CONCLUSIONS

Lipopolysaccharide preconditioning potently augmented antitumor cytotoxicity of liver NK cells and NKT cells, thereby improving mouse survival after intraportal inoculation of Colon26 tumor cells. It may be useful for perioperative care in oncological patients.

Macro- and microtranscriptomic evidence of the monocyte recruitment to regenerating liver after partial hepatectomy in mouse model

Macrophages are important regulators of liver repair. Participation of migratory monocytes/macrophages in regeneration of hepatic tissues after resection remains disputable. In mouse the resection promotes migration of Ly6C+CD11b+ monocytes/macrophages to the remnant liver accompanied by a reduction in its CD206 + macrophage content. Macrophage proliferation within the liver reaches maximum on day 3 after the surgery. Corresponding macro- and microtranscriptomic profiles of macrophages in regeneration liver cannot be unambiguously defined as pro- or anti-inflammatory. Their typical features include elevated expression of leukocyte chemoattractant factors, and many of the differentially expressed sequences are related to the control of cell growth and metabolic processes in the liver. These findings revealed essential roles of immigration of monocytes/macrophages and macrophages proliferation in maintenance of macrophage populations in the mouse liver during its recovery from a massive resection.

Enhancement of the Tolerogenic Phenotype in the Liver by ImmTOR Nanoparticles

ImmTOR biodegradable nanoparticles encapsulating rapamycin have been shown to induce a durable tolerogenic immune response to co-administered biologics and gene therapy vectors. Prior mechanism of action studies have demonstrated selective biodistribution of ImmTOR to the spleen and liver following intravenous (IV) administration. In the spleen, ImmTOR has been shown to induce tolerogenic dendritic cells and antigen-specific regulatory T cells and inhibit antigen-specific B cell activation. Splenectomy of mice resulted in partial but incomplete abrogation of the tolerogenic immune response induced by ImmTOR. Here we investigated the ability of ImmTOR to enhance the tolerogenic environment in the liver. All the major resident populations of liver cells, including liver sinusoidal endothelial cells (LSECs), Kupffer cells (KC), stellate cells (SC), and hepatocytes, actively took up fluorescent-labeled ImmTOR particles, which resulted in downregulation of MHC class II and co-stimulatory molecules and upregulation of the PD-L1 checkpoint molecule. The LSEC, known to play an important role in hepatic tolerance induction, emerged as a key target cell for ImmTOR. LSEC isolated from ImmTOR treated mice inhibited antigen-specific activation of ovalbumin-specific OT-II T cells. The tolerogenic environment led to a multi-pronged modulation of hepatic T cell populations, resulting in an increase in T cells with a regulatory phenotype, upregulation of PD-1 on CD4⁺ and CD8⁺ T cells, and the emergence of a large population of CD4^–CD8^– (double negative) T cells. ImmTOR treatment protected mice in a concanavalin A-induced model of acute hepatitis, as evidenced by reduced production of inflammatory cytokines, infiltrate of activated leukocytes, and tissue necrosis. Modulation of T cell phenotype was seen to a lesser extent after administration by empty nanoparticles, but not free rapamycin. The upregulation of PD-1, but not the appearance of double negative T cells, was inhibited by antibodies against PD-L1 or CTLA-4. These results suggest that the liver may contribute to the tolerogenic properties of ImmTOR treatment.

Prevention of non-alcoholic steatohepatitis by long-term exercise via the induction of phenotypic changes in Kupffer cells of hyperphagic obese mice

Exercise ameliorates nonalcoholic fatty liver disease (NAFLD) by inducing phenotypic changes in Kupffer cells (KCs). p62/Sqstm1-knockout (p62-KO) mice develop NAFLD alongside hyperphagia-induced obesity. We evaluated (1) the effects of long-term exercise on the foreign-body phagocytic capacity of KCs, their surface marker expression, and the production of steroid hormones in p62-KO mice; and (2) whether long-term exercise prevented the development of non-alcoholic steatohepatitis (NASH) in p62-KO mice fed a high-fat diet (HFD). In experiment 1, 30-week-old male p62-KO mice were allocated to resting (p62-KO-Rest) or exercise (p62-KO-Ex) groups, and the latter performed long-term exercise over 4 weeks. Then, the phenotype of their KCs was compared to that of p62-KO-Rest and wild-type (WT) mice. In experiment 2, 5-week-old male p62-KO mice that were fed a HFD performed long-term exercise over 12 weeks. In experiment 1, the phagocytic capacity of KCs and the proportion of CD68-positive cells were lower in the p62-KO-Rest group than in the WT group, but they increased with long-term exercise. The percentage of CD11b-positive KCs was higher in the p62-KO-Rest group than in the WT group, but lower in the p62-KO-Ex group. The circulating dehydroepiandrosterone (DHEA) concentration was higher in p62-KO-Ex mice than in p62-KO-Rest mice. In experiment 2, the body mass and composition of the p62-KO-Rest and p62-KO-Ex groups were similar, but the hepatomegaly, hepatic inflammation, and fibrosis were less marked in p62-KO-Ex mice. The DHEA concentration was higher in p62-KO-Ex mice than in WT or p62-KO-Rest mice. Thus, long-term exercise restores the impaired phagocytic capacity of KCs in NAFLD obese mice, potentially through greater DHEA production, and prevents the development of NASH by ameliorating hepatic inflammation and fibrogenesis. These results suggest a molecular mechanism for the beneficial effect of exercise in the management of patients with NAFLD.

The Efficacy of Posttreatment with Synthetic C-Reactive Protein in Murine Bacterial Peritonitis via Activation of FcγRI-Expressing Kupffer Cells

Pretreatment with synthetic C-reactive protein (CRP), a functional CRP peptide, has the potential to augment macrophage phagocytosis by bacterial challenge. However, the posttreatment is clinically ideal. We investigated the efficacy of posttreatment with synthetic CRP on murine cecal ligation and puncture (CLP), focusing on liver macrophages. Mice received CLP, and 1 h later, synthetic CRP or saline was intraperitoneally administered. Posttreatment with synthetic CRP increased the murine survival after CLP. It reduced viable bacterial counts in the liver 24 h after CLP with an increase in the number of Kupffer cells but not monocyte-derived liver macrophages. Posttreatment with synthetic CRP increased the phagolytic activity of Kupffer cells against Escherichia coli (E. coli) as well as capsulated Klebsiella pneumoniae at 3 h after CLP. Synthetic CRP therapy augmented TNF production by E. coli-phagocytosing Kupffer cells, resulting in an increase in tissue TNF levels in the liver at 24 h. Kupffer cells substantially expressed FcγRI, which is a ligand of CRP, and their FcγRI expression was further increased after CLP. In contrast, synthetic CRP therapy affected neither the phagocytic function of monocyte-derived liver macrophages (showing a weak FcγRI expression) nor their TNF production. Depletion of Kupffer cells in mice inhibited these beneficial effects of synthetic CRP in CLP mice. Conclusion: Posttreatment with synthetic CRP effectively improves murine bacterial peritonitis via the activation of phagocytosis of FcγRI-expressing Kupffer cells.

Hepatic F4/80+ CD11b+ CD68- cells influence the antibacterial response in irradiated mice with sepsis by Enterococcus faecalis

Gut-associated sepsis is a major problem in patients undergoing abdominal radiation therapy; the majority of pathogens causing this type of sepsis are translocated from the gut microbiota. While treating sepsis, bacterial clearance must be achieved to ensure patient survival, and the hepatic immune response is responsible for this process. In particular, Kupffer cells play a crucial role in the hepatic immune response against infectious agents. Recently, two populations of Kupffer cells have been described: liver-resident macrophages (Mϕ) (F4/80+ CD11b- CD68+ cells) and hepatic Mϕ derived from circulating monocytes (F4/80+ CD11b+ CD68- cells). We examined the properties of both types of hepatic Mϕ obtained from irradiated and normal mice and their role in sepsis. Hepatic F4/80+ CD11b- CD68+ cells from both normal and irradiated mice did not show any antibacterial activity. However, F4/80+ CD11b+ CD68- cells from normal mice behaved as effector cells against sepsis by Enterococcus faecalis, although those from irradiated mice lost this ability. Moreover, hepatic F4/80+ CD11b+ CD68- cells from normal infected mice were shown to be IL-12+ IL-10- CD206- CCL1- (considered M1Mϕ), and hepatic F4/80+ CD11b- CD68+ cells from the same mice were shown to be IL-12- IL-10+ CD206+ CCL1- (considered M2aMϕ). When normal mice were exposed to radiation, hepatic F4/80+ CD11b+ CD68- cells altered their phenotype to IL-12- IL-10+ CD206- CCL1+ (considered M2bMϕ), independent of infection, but hepatic F4/80+ CD11b- CD68+ cells remained IL-12- IL-10+ CD206+ CCL1- (M2aMϕ). In addition, hepatic F4/80+ CD11b+ CD68- cells from irradiated mice acquired antibacterial activity upon treatment with CCL1 antisense oligodeoxynucleotides. Therefore, the characteristics of hepatic F4/80+ CD11b+ CD68- cells play a key role in the antibacterial response against gut-associated sepsis.

F4/80+ Kupffer Cell-Derived Oncostatin M Sustains the Progression Phase of Liver Regeneration through Inhibition of TGF-β2 Pathway

The role of Kupffer cells (KCs) in liver regeneration is complicated and controversial. To investigate the distinct role of F4/80⁺ KCs at the different stages of the regeneration process, two-thirds partial hepatectomy (PHx) was performed in mice to induce physiological liver regeneration. In pre- or post-PHx, the clearance of KCs by intraperitoneal injection of the anti-F4/80 antibody (α-F4/80) was performed to study the distinct role of F4/80⁺ KCs during the regenerative process. In RNA sequencing of isolated F4/80⁺ KCs, the initiation phase was compared with the progression phase. Immunohistochemistry and immunofluorescence staining of Ki67, HNF-4α, CD-31, and F4/80 and Western blot of the TGF-β2 pathway were performed. Depletion of F4/80⁺ KCs in pre-PHx delayed the peak of hepatocyte proliferation from 48 h to 120 h, whereas depletion in post-PHx unexpectedly led to persistent inhibition of hepatocyte proliferation, indicating the distinct role of F4/80⁺ KCs in the initiation and progression phases of liver regeneration. F4/80⁺ KC depletion in post-PHx could significantly increase TGF-β2 serum levels, while TGF-βRI partially rescued the impaired proliferation of hepatocytes. Additionally, F4/80⁺ KC depletion in post-PHx significantly lowered the expression of oncostatin M (OSM), a key downstream mediator of interleukin-6, which is required for hepatocyte proliferation during liver regeneration. In vivo, recombinant OSM (r-OSM) treatment alleviated the inhibitory effect of α-F4/80 on the regenerative progression. Collectively, F4/80⁺ KCs release OSM to inhibit TGF-β2 activation, sustaining hepatocyte proliferation by releasing a proliferative brake.

Inhibition of androgen/AR signaling inhibits diethylnitrosamine (DEN) induced tumour initiation and remodels liver immune cell networks

A promotional role for androgen receptor (AR) signaling in hepatocellular carcinogenesis is emerging. In pre-clinical models, including diethylnitrosamine- (DEN-) induced hepatocellular carcinoma (HCC), anti-androgen therapies delay hepatocarcinogenesis. However, pharmacologic anti-androgen therapy in advanced HCC patients fails, suggesting that AR plays a role in HCC onset. This study aims to characterize AR expression and function throughout DEN-induced liver inflammation and carcinogenesis and evaluate the efficacy of prophylactic AR antagonism to prevent hepatocarcinogenesis. We demonstrate that pharmacologic AR antagonism with enzalutamide inhibits hepatocellular carcinogenesis. With enzalutamide treatment, we observe decreased CYP2E1 expression, reducing DEN-induced hepatocyte death and DNA ethyl-adducts. AR protein expression analyses show that DEN causes an initial upregulation of AR in portal fibroblasts and leukocytes, but not hepatocytes, suggesting that hepatocyte-autonomous AR signaling is not essential for DEN-induced carcinogenesis. Ablating androgen signaling by surgical castration reduced pre-carcinogen Kupffer cell populations but did not alter DEN-mediated immune cell recruitment nor AR expression. In this study, we identified that anti-androgen interventions modulate mutagenic DNA adducts, tumour initiation, and immune cell composition. Additionally, we find that AR expression in hepatocytes is not present during nor required for early DEN-mediated carcinogenesis.

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

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

Current perspectives on the pathophysiology of metabolic associated fatty liver disease: are macrophages a viable target for therapy?

INTRODUCTION

Metabolic associated fatty liver disease (MAFLD) is a new nomenclature for fatty liver replacing nonalcoholic fatty liver disease (NAFLD). MAFLD has emerged as the leading cause of liver-related morbidity and mortality with increasing incidence due to its close association with the global epidemic of obesity and type 2 diabetes mellitus. Macrophages play a key role in MAFLD development and progression of steatohepatitis and fibrosis. Therefore, targeting macrophages may be a new therapeutic approach for MAFLD and MAFLD with steatohepatitis.

AREAS COVERED

We provide a comprehensive review of the significant role of macrophages in MAFLD. Further, we evaluate the current status of lifestyle interventions and pharmacological treatments with a focus on effects mediated through direct or indirect targeting of macrophages.

EXPERT OPINION

Targeting macrophages holds promise as a treatment option for the management of MAFLD and steatohepatitis. Improved stratification of patients according to MAFLD phenotype would contribute to more adequate design enhancing the yield of clinical trials ultimately leading to personalized medicine for patients with MAFLD. Furthermore, reflecting the multifactorial pathogenesis of MAFLD, combination therapies based on the various pathophysiological driver events including as pertinent to this review, macrophage recruitment, polarization and action, present an intriguing target for future investigation.

Comparative Analysis of the Transcriptome, Proteome, and miRNA Profile of Kupffer Cells and Monocytes

Macrophage populations in most mammalian organs consist of cells of different origin. Resident macrophages originate from erythromyeloid precursors of the yolk sac wall; maintenance of the numbers of such macrophages in postnatal ontogenesis is practically independent of bone marrow haematopoiesis. The largest populations of the resident macrophages of embryonic origin are found in the central nervous system (microglia) and liver (Kupffer cells). In contrast, skin dermis and mucous membranes become predominantly colonized by bone marrow-derived monocytes that show pronounced functional and phenotypic plasticity. In the present study, we compared Kupffer cells and monocytes using the immunophenotype, gene expression profile, proteome, and pool of microRNA. The observed differences did not consider the resident liver macrophages as purely M2 macrophages or state that monocytes have purely M1 features. Monocytes show signs of high plasticity and sensitivity to pathogen-associated molecular patterns (e.g., high levels of transcription for Tlr 2, 4, 7, and 8). In contrast, the resident liver macrophages were clearly involved in the regulation of specific organ functions (nitrogen metabolism, complement system protein synthesis).

Characterizing disease progression of nonalcoholic steatohepatitis in Leptin-deficient rats by integrated transcriptome analysis

Nonalcoholic steatohepatitis (NASH) is an aggressive liver disease threatening human health, yet no medicine is developed to treat this disease. In this study, we first discovered that Leptin mutant rats (Lep^ΔI14/ΔI14) exhibit characteristic NASH phenotypes including steatosis, lymphocyte infiltration, and ballooning after postnatal week 16. We then examined NASH progression by performing an integrated analysis of hepatic transcriptome in Leptin-deficient rats from postnatal 4 to 48 weeks. Initially, simple steatosis in Lep^ΔI14/ΔI14 rats were observed with increased expression of the genes encoding for rate-limiting enzymes in lipid metabolism such as acetyl-CoA carboxylase and fatty acid synthase. When NASH phenotypes became well developed at postnatal week 16, we found gene expression changes in insulin resistance, inflammation, reactive oxygen species and endoplasmic reticulum stress. As NASH phenotypes further progressed with age, we observed elevated expression of cytokines and chemokines including C-C motif chemokine ligand 2, tumor necrosis factor ɑ, interleukin-6, and interleukin-1β together with activation of the c-Jun N-terminal kinase and nuclear factor-κB pathways. Histologically, livers in Lep^ΔI14/ΔI14 rats exhibited increased cell infiltration of MPO⁺ neutrophils, CD8⁺ T cells, CD68⁺ hepatic macrophages, and CCR2⁺ inflammatory monocyte-derived macrophages associated with macrophage polarization from M2 to M1. Subsequent cross-species comparison of transcriptomes in human, rat, and mouse NASH models indicated that Leptin-deficient rats bear more similarities to human NASH patients than previously established mouse NASH models. Taken together, our study suggests that Lep^ΔI14/ΔI14 rats are a valuable pre-clinical rodent model to evaluate NASH drug safety and efficacy.

Characterization of hepatic macrophages and evaluation of inflammatory response in heme oxygenase-1 deficient mice exposed to scAAV9 vectors

Adeno-associated viral (AAV) vectors are characterised by low immunogenicity, although humoral and cellular responses may be triggered upon infection. Following systemic administration high levels of vector particles accumulate within the liver. Kupffer cells (KCs) are liver resident macrophages and an important part of the liver innate immune system. Decreased functional activity of KCs can contribute to exaggerated inflammatory response upon antigen exposure. Heme oxygenase-1 (HO-1) deficiency is associated with considerably reduced numbers of KCs. In this study we aimed to investigate the inflammatory responses in liver and to characterise two populations of hepatic macrophages in adult wild type (WT) and HO-1 knockout (KO) mice following systemic administration of one or two doses (separated by 3 months) of self-complementary (sc)AAV9 vectors. At steady state, the livers of HO-1 KO mice contained significantly higher numbers of monocyte-derived macrophages (MDMs), but significantly less KCs than their WT littermates. Three days after re-administration of scAAV9 we observed increased mRNA level of monocyte chemoattractant protein-1 (Mcp-1) in the livers of both WT and HO-1 KO mice, but the protein level and the macrophage infiltration were not affected. Three days after the 1^st and 3 days after the 2^nd vector dose the numbers of AAV genomes in the liver were comparable between both genotypes indicating similar transduction efficiency, but the percentage of transgene-expressing MDMs and KCs was higher in WT than in HO-1 KO mice. In the primary culture, KCs were able to internalize AAV9 particles without induction of TLR9-mediated immune responses, but no transgene expression was observed. In conclusion, in vivo and in vitro cultured KCs have different susceptibility to scAAV9 vectors. Regardless of the presence or absence of HO-1 and initial numbers of KCs in the liver, scAAV9 exhibits a low potential to stimulate inflammatory response at the analysed time points.

Live Imaging of Innate and Adaptive Immune Responses in the Liver

Immune response in the liver is determined by the spatial organization and cellular dynamics of hepatic immune cells. The liver vasculature accommodates abundant tissue-resident innate immune cells, such as Kupffer cells, natural killer cells, and natural killer T cells, to ensure efficient intravascular immunosurveillance. The fenestrated sinusoids also allow direct contact between circulating T cells and non-canonical antigen-presenting cells, such as hepatocytes, to instruct adaptive immune responses. Distinct cellular behaviors are exploited by liver immune cells to exert proper functions. Intravital imaging enables real-time visualization of individual immune cell in living animals, representing a powerful tool in dissecting the spatiotemporal features of intrahepatic immune cells during steady state and liver diseases. This review summarizes current advances in liver immunology prompted by in vivo imaging, with a particular focus on liver-resident innate immune cells and hepatic T cells.

In utero inflammatory challenge induces an early activation of the hepatic innate immune response in late gestation fetal sheep

Chorioamnionitis is associated with inflammatory end-organ damage in the fetus. Tissues in direct contact with amniotic fluid drive a pro-inflammatory response and contribute to this injury. However, due to a lack of direct contact with the amniotic fluid, the liver contribution to this response has not been fully characterized. Given its role as an immunologic organ, we hypothesized that the fetal liver would demonstrate an early innate immune response to an in utero inflammatory challenge. Fetal sheep (131 ± 1 d gestation) demonstrated metabolic acidosis and high cortisol and norepinephrine values within 5 h of exposure to intra-amniotic LPS. Likewise, expression of pro-inflammatory cytokines increased significantly at 1 and 5 h of exposure. This was associated with NF-κB activation, by inhibitory protein IκBα degradation, and nuclear translocation of NF-κB subunits (p65/p50). Corroborating these findings, LPS exposure significantly increased pro-inflammatory innate immune gene expression in fetal sheep hepatic macrophages in vitro. Thus, an in utero inflammatory challenge induces an early hepatic innate immune response with systemic metabolic and stress responses. Within the fetal liver, hepatic macrophages respond robustly to LPS exposure. Our results demonstrate that the fetal hepatic innate immune response must be considered when developing therapeutic approaches to attenuate end-organ injury associated with in utero inflammation.

Hepatic Stellate Cell-Specific Platelet-Derived Growth Factor Receptor-α Loss Reduces Fibrosis and Promotes Repair after Hepatocellular Injury

Platelet-derived growth factor receptor (PDGFR)-α plays roles in cell survival, proliferation, and differentiation; however, its function in chronic liver injury sequelae, such as fibrosis, is unknown. Hepatic stellate cells (HSCs), the primary mediators of fibrosis, undergo activation, which entails differentiation to myofibroblasts, proliferation, migration, and collagen deposition, partially in response to PDGFs. To examine the role of PDGFR-α in HSCs, Lrat-Cre recombinase and Pdgfra-floxed mice were bred to generate Lrat-CrePdgfra-/- (knockout) animals, which were subjected to chronic liver injury through carbon tetrachloride treatment, bile duct ligation, and 0.1% 3,5-diethoxycarbonyl-1,4-dihydrocollidine. Although no major difference was observed after other types of liver injury, PDGFR-α loss in HSCs led to a significant albeit transient reduction in fibrosis after carbon tetrachloride injury, associated with increased HSC death and reduced migration. There was continued alleviation of hepatocellular injury in knockout mice despite ongoing carbon tetrachloride insult, associated with increased numbers of CD68 and F480 macrophages and increased clearance of damaged hepatocytes. Altogether our findings support a profibrotic role of PDGFR-α in HSCs during chronic liver injury in vivo via regulation of HSC survival and migration and affect the immune microenvironment, especially macrophages in clearing dying hepatocytes. Thus, our study provides a preclinical foundation for the future testing of therapeutic PDGFR-α inhibition in hepatic fibrosis, especially in combination with other therapies.

Human Liver Macrophage Subsets Defined by CD32

Human liver myeloid cells are imperfectly defined, but it is broadly agreed that cells of stellate appearance in situ, expressing the markers CD11b and CD68, are the liver's resident macrophages, classically termed Kupffer cells. Recent investigations using single cell RNA sequencing and unsupervised clustering algorithms suggest there are two populations of cells with the characteristics of tissue macrophages in human liver. We therefore analyzed dissociated human liver tissue using the markers CD11b and CD68 to define macrophage-like cells and found within this population two subsets that differ in their expression of multiple surface markers. These subsets were FACS-sorted based on CD32 expression, and gene expression analysis identified them with human liver myeloid cell subsets that were previously defined by two independent single cell RNA sequencing studies. Using qRT-PCR we found that the two subsets differed in the expression of genes associated with T cell activation and immunosuppression, suggesting distinct roles in T cell tolerance. In addition, one subset expressed two markers, CD1C and CD11c, more often seen on classical dendritic cells. Criteria used to distinguish macrophages from dendritic cells in other tissues may need to be revised in the human liver.

Role of Mesencephalic Astrocyte-Derived Neurotrophic Factor in Alcohol-Induced Liver Injury

Consumption of alcohol in immoderate quantity induces endoplasmic reticulum (ER) stress response (alcohol-induced ER stress). Mesencephalic astrocyte-derived neurotrophic factor (MANF), an ER stress-inducible protein, works as an evolutionarily conserved regulator of systemic and liver metabolic homeostasis. In this study, the effects of MANF on alcohol-induced liver injury were explored by using hepatocyte-specific MANF-knockout mice (MANF ^ΔHep) in a chronic-plus-binge alcohol feeding model. We found that alcohol feeding upregulated MANF expression and MANF ^ΔHep mice exhibited more severe liver injury with extra activated ER stress after alcohol feeding. In addition, we found that MANF deficiency activated iNOS and p65 and increased the production of NO and anti-inflammatory cytokines, which was further enhanced after alcohol treatment. Meanwhile, MANF deletion upregulated the levels of CYP2E1, 4-HNE, and MDA and downregulated the levels of GSH and SOD. These results indicate that MANF has potential protection on alcohol-induced liver injury, and the underlying mechanisms may be associated with meliorating the overactivated ER stress triggered by inflammation and oxidative stress via inhibiting and reducing NO/NF-κB and CYP2E1/ROS, respectively. Therefore, MANF might be a negative regulator in alcohol-induced ER stress and participate in the crosstalk between the NF-κB pathway and oxidative stress in the liver. Conclusions. This study identifies a specific role of MANF in alcohol-induced liver injury, which may provide a new approach for the treatment of ALI.

High Glucose-Aggravated Hepatic Insulin Resistance: Role of the NLRP3 Inflammasome in Kupffer Cells

OBJECTIVE

This study aimed to investigate whether the NLRP3 inflammasome in Kupffer cells (KCs) can be activated in response to high glucose (HG) and to evaluate its influence on hepatic insulin sensitivity.

METHODS

Primary KCs and hepatocytes were isolated from mice, and lipid accumulation, glucose output, and insulin sensitivity of hepatocytes were investigated after culturing either alone or with KCs exposed to HG. The influence of HG-induced NLRP3 inflammasome activation in KCs on insulin sensitivity of hepatocytes was examined. Treatment with gadolinium trichloride caused KC depletion, and, subsequently, a streptozotocin-induced hyperglycemic mouse model was used to confirm the influence of KCs on hepatic insulin sensitivity.

RESULTS

Hepatocytes cocultured with KCs showed enhanced lipid accumulation, glucose output, and impaired insulin sensitivity when exposed to HG. Enhanced NLRP3 inflammasome activation was also evident in both hepatocytes and KCs. Moreover, KCs that were pretreated with caspase-1 inhibitor, NLRP3 inhibitor, and NLRP3 small interfering RNA corrected coculture-induced aberrances in insulin action and NLRP3 inflammasome activation in hepatocytes. KC coculture also increased interleukin-1β (IL-1β)-mediated nuclear factor-κB (NF-κB) activation in hepatocytes. In hyperglycemic mice, KC depletion inhibited NLRP3 inflammasome activation and improved hepatic insulin sensitivity.

CONCLUSIONS

NLRP3 inflammasome activation impaired insulin sensitivity through KC-derived IL-1β-mediated NF-κB activation in hepatocytes exposed to HG.

Liver, Tumor and Viral Hepatitis: Key Players in the Complex Balance Between Tolerance and Immune Activation

Liver cancer is the third most common cause of cancer related death in the World. From an epidemiological point of view the risk factors associated to primary liver cancer are mainly viral hepatitis infection and alcohol consumption. Even though there is a clear correlation between liver inflammation, cirrhosis and cancer, other emerging liver diseases (like fatty liver) could also lead to liver cancer. Moreover, the liver is the major site of metastasis from colon, breast, ovarian and other cancers. In this review we will address the peculiar status of the liver as organ that has to balance between tolerance and immune activation. We will focus on macrophages and other key cellular components of the liver microenvironment that play a central role during tumor progression. We will also discuss how current and future therapies may affect the balance toward immune activation.

Role of Kupffer cells in liver injury induced by CpG oligodeoxynucleotide and flucloxacillin in mice

CpG oligodeoxynucleotide (CpG-ODN) is a Toll-like receptor 9 (TLR9) agonist that can induce innate immune responses. In a previous study, flucloxacillin (FLUX; 100 mg/kg, gavage)-induced liver injury in mice was enhanced by co-administration of CpG-ODN (40 μg/mouse, intraperitoneally). In this study, the mechanism of CpG-ODN sensitization to FLUX-induced liver injury was further investigated in mice inhibited of Kupffer cells (KCs) function by gadolinium chloride (GdCl3; 10 mg/kg, intravenously). GdCl3-treated mice administrated with CpG-ODN and FLUX showed lower liver injury than wild-type (WT) mice treated with CpG-ODN and FLUX. Upregulation of Fas and FasL by CpG-ODN was also inhibited in GdCl3-treated mice and mitochondrial swelling in response to FLUX failed to occur regardless of pre-treatment with CpG-ODN. When FasL-mutant gld/gld mice were treated with CpG-ODN, mitochondrial swelling in response to FLUX was also inhibited. These results suggest that KCs play an essential role in liver injury induced by CpG-ODN and FLUX. CpG-ODN may activate KCs, resulting in induction of Fas/FasL-mediated apoptosis of hepatocytes. The Fas/FasL pathway may also be an upstream regulator of CpG-ODN- and FLUX-induced changes in mitochondrial permeability transition. These results enhance our understanding of the mechanism of the adjuvant effect of CpG-ODN in this mouse model of liver injury.

Caveolin-1 dictates ferroptosis in the execution of acute immune-mediated hepatic damage by attenuating nitrogen stress

Ferroptosis is a new regulated cells death manner defined as results of iron-dependent accumulation of lipid peroxidation. However, the specific mechanisms of regulating ferroptosis remain unclear. In our present study, we demonstrated that Caveolin-1 (Cav-1) played a central role in protecting hepatocytes against ferroptosis in autoimmunity-mediated hepatitis (AIH). The down-regulated Cav-1 in liver tissues, accompanied by ferroptotic events and RNS production, were contributed to the outcome of ConA-induced hepatic damage, which were rescued by ferrostatin-1 (an inhibitor of ferroptosis) in vivo and in vitro. Additionally, Cav-1 deficiency aggravated ConA-induced hepatocellular death and ferroptosis associated with excessive nitrogen stress response. Short hairpin RNA of Cav-1 in hepatocytes promoted ferroptosis and nitrative stress in response to erastin in vitro, which was ameliorated by Cav-1 over-expression. Meanwhile, administration of the iNOS inhibitor (1400W) or ONOO^- scavenger (Fe-TMPyP), diminished reactive nitrogen species (RNS), remarkably reduced hepatocytes ferroptosis and attenuated ConA-induced liver damage. Furthermore, immune inhibition by gadolinium chloride (GdCl₃), a well-known Kupffer cell depletor, elevated hepatic Cav-1 but inhibited ferroptosis and nitrative stress under ConA exposure. In conclusion, these data revealed a novel molecular mechanism of ferroptosis with the Cav-1 regulation was essential for pathogenesis of ConA-induced hepatitis. Downstream of Cav-1, RNS-mediated ferroptosis was a pivotal step that drives the execution of acute immune-mediated hepatic damage.

A time-resolved multi-omic atlas of the developing mouse liver

Liver organogenesis and development are composed of a series of complex, well-orchestrated events. Identifying key factors and pathways governing liver development will help elucidate the physiological and pathological processes including those of cancer. We conducted multidimensional omics measurements including protein, mRNA, and transcription factor (TF) DNA-binding activity for mouse liver tissues collected from embryonic day 12.5 (E12.5) to postnatal week 8 (W8), encompassing major developmental stages. These data sets reveal dynamic changes of core liver functions and canonical signaling pathways governing development at both mRNA and protein levels. The TF DNA-binding activity data set highlights the importance of TF activity in early embryonic development. A comparison between mouse liver development and human hepatocellular carcinoma (HCC) proteomic profiles reveal that more aggressive tumors are characterized with the activation of early embryonic development pathways, whereas less aggressive ones maintain liver function-related pathways that are elevated in the mature liver. This work offers a panoramic view of mouse liver development and provides a rich resource to explore in-depth functional characterization.

M2 macrophages predict worse long-term outcomes in human acute tubular necrosis

Although macrophages are important players in the injury/repair processes in animal models of acute kidney injury (AKI), their roles in human AKI remains uncertain owing to a paucity of human biopsy studies. We investigated the role of macrophages in 72 cases of biopsy-proven acute tubular necrosis (ATN) and six cases of healthy kidney. Macrophages were identified by CD68 and CD163 immunohistochemistry and analyzed for their effect on renal outcomes. CD163+ M2 macrophages outnumbered CD68+ cells in the healthy kidneys, suggesting that CD163+ macrophages are resident macrophages. The infiltration of both subtypes of macrophages increased significantly in ATN. The density of the CD68+ macrophages was significantly higher in advanced-stage AKI, whereas CD163+ M2 macrophages was not. Eighty percent of patients exhibited renal functional recovery during follow-up. Older age and a higher density of CD163+ macrophages predicted non-recovery, whereas the AKI stage, tubular injury score, and density of CD68+ cells did not. The density of CD163+ M2 macrophages was an independent predictor of low eGFR at 3 months in advanced-stage AKI. This is the first human study demonstrating the possible role of macrophages in the injury and repair phases of AKI.

Inflammation and Ectopic Fat Deposition in the Aging Murine Liver Is Influenced by CCR2

Aging is associated with inflammation and metabolic syndrome, which manifests in the liver as nonalcoholic fatty liver disease (NAFLD). NAFLD can range in severity from steatosis to fibrotic steatohepatitis and is a major cause of hepatic morbidity. However, the pathogenesis of NAFLD in naturally aged animals is unclear. Herein, we performed a comprehensive study of lipid content and inflammatory signature of livers in 19-month-old aged female mice. These animals exhibited increased body and liver weight, hepatic triglycerides, and inflammatory gene expression compared with 3-month-old young controls. The aged mice also had a significant increase in F4/80+ hepatic macrophages, which coexpressed CD11b, suggesting a circulating monocyte origin. A global knockout of the receptor for monocyte chemoattractant protein (CCR2) prevented excess steatosis and inflammation in aging livers but did not reduce the number of CD11b+ macrophages, suggesting changes in macrophage accumulation precede or are independent from chemokine (C-C motif) ligand-CCR2 signaling in the development of age-related NAFLD. RNA sequencing further elucidated complex changes in inflammatory and metabolic gene expression in the aging liver. In conclusion, we report a previously unknown accumulation of CD11b+ macrophages in aged livers with robust inflammatory and metabolic transcriptomic changes. A better understanding of the hallmarks of aging in the liver will be crucial in the development of preventive measures and treatments for end-stage liver disease in elderly patients.

Plant seed protease inhibitors differentially affect innate immunity in a tumor microenvironment to control hepatocarcinoma

Identifying tolerance responses to ingested foodstuff over life is essential for understanding dysfunction in metabolic diseases. This study presents a comparative structural and functional analysis of serine-type protease inhibitors (STPIs) from Chenopodium quinoa, Salvia hispanica L., Avena sativa and Triticum durum. It also evaluates their influence on an in vivo hepatocarcinoma (HCC) model. STPIs are found in all samples with significant differences in protease inhibitory capacity: C. quinoa = S. hispanica < A. sativa = T. durum. STPIs in C. quinoa and S. hispanica appear as heterologous complexes, while those in A. sativa are present as homologous complexes. T. durum provides different subunits with STPI capacity. HPLC-RP-ESI analyses revealed homology between STPIs in the different samples and the partial resistance of those to simulated gastrointestinal digestion. In vivo, STPIs from S. hispanica showed the most positive effects, increasing F4/80+ cells normalizing the expression (mRNA) of CD36 and the innate immune 'Toll-like' receptor (TLR)-4. Only STPIs from C. quinoa and S. hispanica did not impair the production of inflammatory mediators (granulocyte-monocyte colony stimulating factor, stem cell factor and TNFα), contributing to maintaining the polarization of the antitumoral M1 macrophage phenotype. These structural and functional features of STPIs from C. quinoa and S. hispanica can be used to control HCC aggressiveness.