Role of NK, NKT cells and macrophages in liver transplantation

Dynamic immune cell profiling identified natural killer cell shift as the key event in early allograft dysfunction after liver transplantation

Early allograft dysfunction (EAD) is a life-threatening and fast-developing complication after liver transplantation. The underlying mechanism needs to be better understood, and there has yet to be an efficient therapeutic target. This study retrospectively reviewed 109 patients undergoing liver transplantation, with dynamic profiling of CD3/4/8/16/19/45/56 on the peripheral immune cells (before transplant and 2-4 days after). Altogether, 35 out of the 109 patients developed EAD after liver transplantation. We observed a significant decrease in the natural killer cell proportion (NK cell shift, p = 0.008). The NK cell shift was linearly correlated with cold ischemic time (p = 0.016) and was potentially related to the recipients' outcomes. In mouse models, ischemic/reperfusion (I/R) treatments induced the recruitment of NK cells from peripheral blood into liver tissues. NK cell depletion blocked a series of immune cascades (including CD8+ CD127+ T cells) and inhibited hepatocyte injury effectively in I/R and liver transplantation models. We further found that I/R treatment increased hepatic expression of the ligands for natural killer group 2 member D (NKG2D), a primary activating cell surface receptor in NK cells. Blockade of NKG2D showed a similar protective effect against I/R injury, indicating its role in NK cell activation and the subsequent immunological injury. Our findings built a bridge for the translation from innate immune response to EAD at the bedside. Peripheral NK cell shift is associated with the incidence of EAD after liver transplantation. NKG2D-mediated NK cell activation is a potential therapeutic target.

The role of natural killer T cells in liver transplantation

Natural killer T cells (NKTs) are innate-like lymphocytes that are abundant in the liver and participate in liver immunity. NKT cells express both NK cell and T cell markers, modulate innate and adaptive immune responses. Type I and Type II NKT cells are classified according to the TCR usage, while they recognize lipid antigen in a non-classical major histocompatibility (MHC) molecule CD1d-restricted manner. Once activated, NKT cells can quickly produce cytokines and chemokines to negatively or positively regulate the immune responses, depending on the different NKT subsets. In liver transplantation (LTx), the immune reactions in a series of processes determine the recipients' long-term survival, including ischemia-reperfusion injury, alloresponse, and post-transplant infection. This review provides insight into the research on NKT cells subpopulations in LTx immunity during different processes, and discusses the shortcomings of the current research on NKT cells. Additionally, the CD56-expressing T cells are recognized as a NK-like T cell population, they were also discussed during these processes.

Interorgan communication with the liver: novel mechanisms and therapeutic targets

The liver is a multifunctional organ that plays crucial roles in numerous physiological processes, such as production of bile and proteins for blood plasma, regulation of blood levels of amino acids, processing of hemoglobin, clearance of metabolic waste, maintenance of glucose, etc. Therefore, the liver is essential for the homeostasis of organisms. With the development of research on the liver, there is growing concern about its effect on immune cells of innate and adaptive immunity. For example, the liver regulates the proliferation, differentiation, and effector functions of immune cells through various secreted proteins (also known as "hepatokines"). As a result, the liver is identified as an important regulator of the immune system. Furthermore, many diseases resulting from immune disorders are thought to be related to the dysfunction of the liver, including systemic lupus erythematosus, multiple sclerosis, and heart failure. Thus, the liver plays a role in remote immune regulation and is intricately linked with systemic immunity. This review provides a comprehensive overview of the liver remote regulation of the body's innate and adaptive immunity regarding to main areas: immune-related molecules secreted by the liver and the liver-resident cells. Additionally, we assessed the influence of the liver on various facets of systemic immune-related diseases, offering insights into the clinical application of target therapies for liver immune regulation, as well as future developmental trends.

Functional integration of natural killer cells in a microfluidically perfused liver on-a-chip model

OBJECTIVE

The liver acts as an innate immunity-dominant organ and natural killer (NK) cells, are the main lymphocyte population in the human liver. NK cells are in close interaction with other immune cells, acting as the first line of defense against pathogens, infections, and injury. A previously developed, three-dimensional, perfused liver-on-a-chip comprised of human cells was used to integrate NK cells, representing pivotal immune cells during liver injury and regeneration. The objective of this study was to integrate functional NK cells in an in vitro model of the human liver and assess utilization of the model for NK cell-dependent studies of liver inflammation.

RESULTS

NK cells from human blood and liver specimen were isolated by Percoll separation with subsequent magnetic cell separation (MACS), yielding highly purified blood and liver derived NK cells. After stimulation with toll-like-receptor (TLR) agonists (lipopolysaccharides, Pam3CSK4), isolated NK cells showed increased interferon (IFN)-gamma secretion. To study the role of NK cells in a complex hepatic environment, these cells were integrated in the vascular compartment of a microfluidically supported liver-on-a-chip model in close interaction with endothelial and resident macrophages. Successful, functional integration of NK cells was verified by immunofluorescence staining (NKp46), flow cytometry analysis and TLR agonist-dependent secretion of interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha. Lastly, we observed that inflammatory activation of NK cells in the liver-on-a-chip led to a loss of vascular barrier integrity. Overall, our data shows the first successful, functional integration of NK cells in a liver-on-a-chip model that can be utilized to investigate NK cell-dependent effects on liver inflammation in vitro.

Innate Immune Cells during Machine Perfusion of Liver Grafts-The Janus Face of Hepatic Macrophages

Machine perfusion is an emerging technology in the field of liver transplantation. While machine perfusion has now been implemented in clinical routine throughout transplant centers around the world, a debate has arisen regarding its concurrent effect on the complex hepatic immune system during perfusion. Currently, our understanding of the perfusion-elicited processes involving innate immune cells remains incomplete. Hepatic macrophages (Kupffer cells) represent a special subset of hepatic immune cells with a dual pro-inflammatory, as well as a pro-resolving and anti-inflammatory, role in the sequence of ischemia-reperfusion injury. The purpose of this review is to provide an overview of the current data regarding the immunomodulatory role of machine perfusion and to emphasize the importance of macrophages for hepatic ischemia-reperfusion injury.

Immune response associated with ischemia and reperfusion injury during organ transplantation

Background

Ischemia and reperfusion injury (IRI) is an ineluctable immune-related pathophysiological process during organ transplantation, which not only causes a shortage of donor organs, but also has long-term and short-term negative consequences on patients. Severe IRI-induced cell death leads to the release of endogenous substances, which bind specifically to receptors on immune cells to initiate an immune response. Although innate and adaptive immunity have been discovered to play essential roles in IRI in the context of organ transplantation, the pathway and precise involvement of the immune response at various stages has not yet to be elucidated.

Methods

We combined “IRI” and “organ transplantation” with keywords, respectively such as immune cells, danger signal molecules, macrophages, neutrophils, natural killer cells, complement cascade, T cells or B cells in PubMed and the Web of Science to search for relevant literatures.

Conclusion

Comprehension of the immune mechanisms involved in organ transplantation is promising for the treatment of IRI, this review summarizes the similarities and differences in both innate and adaptive immunity and advancements in the immune response associated with IRI during diverse organ transplantation.

The liver-resident immune cell repertoire - A boon or a bane during machine perfusion?

The liver has been proposed as an important “immune organ” of the body, as it is critically involved in a variety of specific and unique immune tasks. It contains a huge resident immune cell repertoire, which determines the balance between tolerance and inflammation in the hepatic microenvironment. Liver-resident immune cells, populating the sinusoids and the space of Disse, include professional antigen-presenting cells, myeloid cells, as well as innate and adaptive lymphoid cell populations. Machine perfusion (MP) has emerged as an innovative technology to preserve organs ex vivo while testing for organ quality and function prior to transplantation. As for the liver, hypothermic and normothermic MP techniques have successfully been implemented in clinically routine, especially for the use of marginal donor livers. Although there is evidence that ischemia reperfusion injury-associated inflammation is reduced in machine-perfused livers, little is known whether MP impacts the quantity, activation state and function of the hepatic immune-cell repertoire, and how this affects the inflammatory milieu during MP. At this point, it remains even speculative if liver-resident immune cells primarily exert a pro-inflammatory and hence destructive effect on machine-perfused organs, or in part may be essential to induce liver regeneration and counteract liver damage. This review discusses the role of hepatic immune cell subtypes during inflammatory conditions and ischemia reperfusion injury in the context of liver transplantation. We further highlight the possible impact of MP on the modification of the immune cell repertoire and its potential for future applications and immune modulation of the liver.

Liraglutide Attenuates Hepatic Ischemia-Reperfusion Injury by Modulating Macrophage Polarization

Ischemia-reperfusion injury (IRI) is a common complication associated with liver surgery, and macrophages play an important role in hepatic IRI. Liraglutide, a glucagon-like peptide-1 (GLP-1) analog primarily used to treat type 2 diabetes and obesity, regulates intracellular calcium homeostasis and protects the cardiomyocytes from injury; however, its role in hepatic IRI is not yet fully understood. This study aimed to investigate whether liraglutide can protect the liver from IRI and determine the possible underlying mechanisms. Our results showed that liraglutide pretreatment significantly alleviated the liver damage caused by ischemia-reperfusion (I/R), as evidenced by H&E staining, serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels, and TUNEL staining. Furthermore, the levels of inflammatory cytokines elicited by I/R were distinctly suppressed by liraglutide pretreatment, accompanied by significant reduction in TNF-α, IL-1β, and IL-6 levels. Furthermore, pretreatment with liraglutide markedly inhibited macrophage type I (M1) polarization during hepatic IRI, as revealed by the significant reduction in CD68⁺ levels in Kupffer cells (KCs) detected via flow cytometry. However, the protective effects of liraglutide on hepatic IRI were partly diminished in GLP-1 receptor-knockout (GLP-1R^-/-) mice. Furthermore, in an in vitro study, we assessed the role of liraglutide in macrophage polarization by examining the expression profiles of M1 in bone marrow-derived macrophages (BMDMs) from GLP-1R^-/- and C57BL/6J mice. Consistent with the results of the in vivo study, liraglutide treatment attenuated the LPS-induced M1 polarization and reduced the expression of M1 markers. However, the inhibitory effect of liraglutide on LPS-induced M1 polarization was largely abolished in BMDMs from GLP-1R^-/- mice. Collectively, our study indicates that liraglutide can ameliorate hepatic IRI by inhibiting macrophage polarization towards an inflammatory phenotype via GLP-1R. Its protective effect against liver IRI suggests that liraglutide may serve as a potential drug for the clinical treatment of liver IRI.

Natural Killer Cells in Hepatic Ischemia-Reperfusion Injury

Ischemia-reperfusion injury can be divided into two phases, including insufficient supply of oxygen and nutrients in the first stage and then organ injury caused by immune inflammation after blood flow recovery. Hepatic ischemia-reperfusion is an important cause of liver injury post-surgery, consisting of partial hepatectomy and liver transplantation, and a central driver of graft dysfunction, which greatly leads to complications and mortality after liver transplantation. Natural killer (NK) cells are the lymphocyte population mainly involved in innate immune response in the human liver. In addition to their well-known role in anti-virus and anti-tumor defense, NK cells are also considered to regulate the pathogenesis of liver ischemia-reperfusion injury under the support of more and more evidence recently. The infiltration of NK cells into the liver exacerbates the hepatic ischemia-reperfusion injury, which could be significantly alleviated after depletion of NK cells. Interestingly, NK cells may contribute to both liver graft rejection and tolerance according to their origins. In this article, we discussed the development of liver NK cells, their role in ischemia-reperfusion injury, and strategies of inhibiting NK cell activation in order to provide potential possibilities for translation application in future clinical practice.

Navigating immune cell immunometabolism after liver transplantation

Liver transplantation (LT) is the most effective treatment for end-stage liver diseases. The immunometabolism microenvironment undergoes massive changes at the interface of immune functionalities and metabolic regulations after LT. These changes considerably modify post-transplant complications, and immune cells play an influential role in the hepatic immunometabolism microenvironment after LT. Therefore, adequate studies on the complex pathobiology of immune cells are critical to prevent post-transplant complications, and the interplay between cellular metabolism and immune function is evident. Furthermore, immune cells perform their specified functions, such as activation or differentiation, accompanied by alterations in metabolic pathways, such as metabolic reprogramming. This transformation remarkably affects post-transplant complications like rejection. By targeting different metabolic pathways, regulations of metabolism are employed to shape immune responses. These differences of metabolic pathways allow for selective regulation of immune responses to further develop effective therapies that prevent graft loss after LT. This review examines immune cells in the hepatic immunometabolism microenvironment after LT, summarizes possible mechanisms and potential prevention on rejection to acquire immune tolerance, and offers some insight into references for scientific research along with clinical treatment.

Understanding, predicting and achieving liver transplant tolerance: from bench to bedside

In the past 40 years, liver transplantation has evolved from a high-risk procedure to one that offers high success rates for reversal of liver dysfunction and excellent patient and graft survival. The liver is the most tolerogenic of transplanted organs; indeed, immunosuppressive therapy can be completely withdrawn without rejection of the graft in carefully selected, stable long-term liver recipients. However, in other recipients, chronic allograft injury, late graft failure and the adverse effects of anti-rejection therapy remain important obstacles to improved success. The liver has a unique composition of parenchymal and immune cells that regulate innate and adaptive immunity and that can promote antigen-specific tolerance. Although the mechanisms underlying liver transplant tolerance are not well understood, important insights have been gained into how the local microenvironment, hepatic immune cells and specific molecular pathways can promote donor-specific tolerance. These insights provide a basis for the identification of potential clinical biomarkers that might correlate with tolerance or rejection and for the development of novel therapeutic targets. Innovative approaches aimed at promoting immunosuppressive drug minimization or withdrawal include the adoptive transfer of donor-derived or recipient-derived regulatory immune cells to promote liver transplant tolerance. In this Review, we summarize and discuss these developments and their implications for liver transplantation.

Organ Restoration With Normothermic Machine Perfusion and Immune Reaction

Liver transplantation is the only recognized effective treatment for end-stage liver disease. However, organ shortages have become the main challenge for patients and physicians within the transplant community. Waiting list mortality remains an issue with around 10% of patients dying whilst waiting for an available organ. The post-transplantation period is also associated with an adverse complication rate for these specific cohorts of high-risk patients, particularly regarding patient and graft survival. Ischaemia reperfusion injury (IRI) has been highlighted as the mechanism of injury that increases parenchymal damage, which eventually lead to significant graft dysfunction and other poor outcome indicators. The consequences of IRI in clinical practice such as reperfusion syndrome, primary non-function of graft, allograft dysfunction, ischaemic biliary damage and early biliary complications can be life-threatening. IRI dictates the development of a significant inflammatory response that drives the pathway to eventual cell death. The main mechanisms of IRI are mitochondrial damage due to low oxygen tension within the hepatic micro-environment and severe adenosine triphosphate (ATP) depletion during the ischaemic period. After the restoration of normal blood flow, this damage is further enhanced by reoxygenation as the mitochondria respond to reperfusion by releasing reactive oxygen species (ROS), which in turn activate Kupffer cells within the hepatic micro-environment, leading to a pro-inflammatory response and eventual parenchymal cell apoptosis and associated tissue degradation. Machine perfusion (MP) is one emergent strategy considered to be one of the most important advances in organ preservation, restoration and transplantation. Indeed, MP has the potential to rescue frequently discarded organs and has been shown to limit the extent of IRI, leading to suppression of the deleterious pro-inflammatory response. This immunomodulation reduces the prevalence of allograft rejection, the use of immunosuppression therapy and minimizes post-transplant complications. This review aims to update the current knowledge of MP with a focus on normothermic machine liver perfusion (NMLP) and its potential role in immune response pathways.

Transplant Tolerance Induction: Insights From the Liver

A comparison of pre-clinical transplant models and of solid organs transplanted in routine clinical practice demonstrates that the liver is most amenable to the development of immunological tolerance. This phenomenon arises in the absence of stringent conditioning regimens that accompany published tolerizing protocols for other organs, particularly the kidney. The unique immunologic properties of the liver have assisted our understanding of the alloimmune response and how it can be manipulated to improve graft function and survival. This review will address important findings following liver transplantation in both animals and humans, and how these have driven the understanding and development of therapeutic immunosuppressive options. We will discuss the liver's unique system of immune and non-immune cells that regulate immunity, yet maintain effective responses to pathogens, as well as mechanisms of liver transplant tolerance in pre-clinical models and humans, including current immunosuppressive drug withdrawal trials and biomarkers of tolerance. In addition, we will address innovative therapeutic strategies, including mesenchymal stem cell, regulatory T cell, and regulatory dendritic cell therapy to promote liver allograft tolerance or minimization of immunosuppression in the clinic.

Identification of HO-1 as a novel biomarker for graft acute cellular rejection and prognosis prediction after liver transplantation

Background

Liver transplantation (LT) is the most effective treatment for patients with end-stage liver diseases, but acute rejection is still a major concern. However, the mechanisms underlying rejection remain unclear. Biomarkers are lacking for predicting rejection and long-term survival after LT.

Methods

Isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomics was performed between acute cellular rejection (ACR) and non-rejection recipients. The molecular signature differences and potential biomarkers were identified by comprehensive bioinformatics. Heme oxygenase-1 (HO-1) expression and its association with clinical outcomes were investigated by tissue microarrays consisted of liver specimens from recipients with (n=80) and without ACR (n=57).

Results

A total of 287 differentially expressed proteins (DEPs) were identified. Pathway analysis revealed that T/B cell activation, integrin/inflammation signaling pathway, etc. were significantly correlated with ACR. Through comprehensive bioinformatics, HO-1 was identified as a candidate potential biomarker for ACR. In tissue microarray (TMA) analysis, HO-1 expression was significantly higher in ACR group than in non-rejection group (P<0.01). Preoperative Child-Pugh and Meld scores were significantly higher in recipients with high HO-1 expression (P<0.01). In a mean 5-year follow-up, recipients with high HO-1 expression were associated with a shorter overall survival (P<0.05). Further multivariate analyses indicated that HO-1 could be an independent adverse prognostic factor for post-transplant survival (P=0.005).

Conclusions

A total of 287 DEPs were identified, providing a set of targets for further research. Recipients with high preoperative HO-1 expression were associated with ACR. HO-1 may be used as a potential biomarker for predicting the development of post-transplant allograft ACR and recipient's survival.

Observation and characterisation of macrophages in zebrafish liver

Kupffer cells are liver-resident macrophages that play an important role in mediating immune-related functions in mammals and humans. They are well-known for their capacity to phagocytose large amounts of waste complexes, cell debris, microbial particles and even malignant cells. Location, appearance and functional aspects are important features used to identify these characteristic cells of the liver sinusoid. To-date, there is limited information on the occurrence of macrophages in zebrafish liver. Therefore, we aimed to characterise the ultrastructural and functional aspects of liver-associated macrophages in the zebrafish model by taking advantage of the latest advances in zebrafish genetics and multimodal correlative imaging. Herein, we report on the occurrence of macrophages within the zebrafish liver exhibiting conventional ultrastructural features (e.g. presence of pseudopodia, extensive lysosomal apparatus, a phagolysosome and making up ∼3% of the liver volume). Intriguingly, these cells were not located within the sinusoidal vascular bed of hepatic tissue but instead resided between hepatocytes and lacked phagocytic function. While our results demonstrated the presence and structural similarities with liver macrophages from other experimental models, their functional characteristics were distinctly different from Kupffer cells that have been described in rodents and humans. These findings illustrate that the innate immune system of the zebrafish liver has some distinctly different characteristics compared to other animal experimental models. This conclusion underpins our call for future studies in order to have a better understanding of the physiological role of macrophages residing between the parenchymal cells of the zebrafish liver.

Research Status of Mesenchymal Stem Cells in Liver Transplantation

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

The killer cell lectin-like receptor B1 (KLRB1) 503T>C polymorphism (rs1135816) and acute rejection after liver transplantation

The killer cell lectin-like receptor B1 (KLRB1) gene encodes for CD161 expressed by different subsets of leukocytes involved in the development of acute liver transplant rejection. The single nucleotide polymorphism (SNP) 503T>C (rs1135816) in the KLRB1 gene represents a missense mutation modifying functional properties of CD161. The aim of our study is to determine whether the SNP 503T>C is associated with acute liver transplant rejection. We genotyped the SNP for 163 liver recipients without acute rejection, 125 recipients with a single acute rejection, and 53 recipients with multiple acute rejections. The genotype frequencies within the groups did not show any significant difference. Our data suggest that the SNP 503T>C has no impact on the susceptibility of acute liver transplant rejection.

Clinical use of an immune monitoring panel in liver transplant recipients: A prospective, observational study

Immunosuppressive therapy greatly contributed to making liver transplantation the standard treatment for end-stage liver diseases. However, it remains difficult to predict and measure the efficacy of pharmacological immunosuppression. Therefore, we used a panel of standardized, commonly available, biomarkers with the aim to describe their changes in the first 3 weeks after the transplant procedure and assess if they may help therapeutic drug monitoring in better tailoring the dose of the immunosuppressive drugs. We prospectively studied 72 consecutive patients from the day of liver transplant (post-operative day #0) until the post-operative day #21. Leukocytes, neutrophils, lymphocytes (CD4+, CD8+), natural killer cells, monocytes, immunoglobulins and tacrolimus serum levels were measured on peripheral blood (at day 0, 3, 7, 14, 21 after surgery). Patients who developed infections showed significantly higher CD64+ monocytes on post operative day #7. IgG levels were lower on post operative day #3 among patients who later developed infections. We also found that a sharp decrease in IgA from post operative day #0 to 3 (-226 mg/dL in the ROC curve analysis) strongly correlates with the onset of infections among HCV- patients. No specific markers of rejection emerged from the tested panel of markers. Our results show that some early changes in peripheral blood white cells and immunoglobulins may predict the onset of infections and may be useful in modulating the immunosuppressive therapy. However, a panel of commonly available, standardized biomarkers do not support in improving therapeutic drug monitoring ability to individualize immunosuppressive drugs dosing.

Induction of antiinflammatory purinergic signaling in activated human iNKT cells

Invariant natural killer T (iNKT) cells are activated at sites of local tissue injury, or globally during vaso-occlusive episodes of sickle cell disease (SCD). Tissue damage stimulates production of CD1d-restricted lipid antigens that activate iNKT cells to produce Th1- and Th2-type cytokines. Here, we show that circulating iNKT cells in SCD patients express elevated levels of the ectonucleoside triphosphate diphosphosphohydrolase, CD39, as well the adenosine A2A receptor (A2AR). We also investigated the effects of stimulating cultured human iNKT cells on the expression of genes involved in the regulation of purinergic signaling. iNKT cell stimulation caused induction of ADORA2A, P2RX7, CD38, CD39, ENPP1, CD73, PANX1, and ENT1. Transcription of ADA, which degrades adenosine, was reduced. Induction of CD39 mRNA was associated with increased ecto-ATPase activity on iNKT cells that was blocked by POM1. Exposure of iNKT cells to A2AR agonists during stimulation reduced production of IFN-γ and enhanced production of IL-13 and CD39. Based on these findings, we define "purinergic Th2-type cytokine bias" as an antiinflammatory purinergic response to iNKT cell stimulation resulting from changes in the transcription of several genes involved in purine release, extracellular metabolism, and signaling.

Immune Responses in the Liver

The liver is a key, frontline immune tissue. Ideally positioned to detect pathogens entering the body via the gut, the liver appears designed to detect, capture, and clear bacteria, viruses, and macromolecules. Containing the largest collection of phagocytic cells in the body, this organ is an important barrier between us and the outside world. Importantly, as portal blood also transports a large number of foreign but harmless molecules (e.g., food antigens), the liver's default immune status is anti-inflammatory or immunotolerant; however, under appropriate conditions, the liver is able to mount a rapid and robust immune response. This balance between immunity and tolerance is essential to liver function. Excessive inflammation in the absence of infection leads to sterile liver injury, tissue damage, and remodeling; insufficient immunity allows for chronic infection and cancer. Dynamic interactions between the numerous populations of immune cells in the liver are key to maintaining this balance and overall tissue health.

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

Steatosis intensifies hepatic ischemia/reperfusion (I/R) injury increasing hepatocyte damage and hepatic inflammation. This study evaluates if this process is associated to a differential response of steatotic hepatocytes (HP) and Kupffer cells (KC) to I/R injury and investigates the molecular mechanisms involved. Control or steatotic (treated with 50 μmol palmitic acid, PA) mouse HP or KC were exposed to hypoxia/reoxygenation (H/R). C57BL/6 mice fed 9 week with control or High Fat diet underwent to partial hepatic IR. PA increased H/R damage of HP and further activated the ASK1-JNK axis stimulated by ER stress during H/R. PA also induced the production of oxidant species (OS), and OS prevention nullified the capacity of PA to increase H/R damage and ASK1/JNK stimulation. ASK1 inhibition prevented JNK activation and entirely protected HP damage. In KC, PA directly activated ER stress, ASK1 and p38 MAPK and increased H/R damage. However, in contrast to HP, ASK1 inhibition further increased H/R damage by preventing p38 MAPK activation. In mice liver, steatosis induced the expression of activated ASK1 in only KC, whereas I/R exposure of steatotic liver activated ASK1 expression also in HP. "In vivo", ASK1 inhibition prevented ASK1, JNK and p38 MAPK activation and protected I/R damage and expression of inflammatory markers.

CONCLUSIONS

Lipids-induced ASK1 stimulation differentially affects HP and KC by promoting cytotoxic or protective signals. ASK1 increases H/R damage of HP by stimulating JNK and protects KC activating p38MAPK. These data support the potentiality of the therapeutic employment of ASK1 inhibitors that can antagonize the damaging effects of I/R upon fatty liver surgery by the contextual reduction of HP death and of KC-mediated reactions.

Engineering in vitro models of hepatofibrogenesis

Chronic liver disease is a major cause of morbidity and mortality worldwide marked by chronic inflammation and fibrosis/scarring, resulting in end-stage liver disease and its complications. Hepatic stellate cells (HSCs) are a dominant contributor to liver fibrosis by producing excessive extracellular matrix (ECM), irrespective of the underlying disease aetiologies, and for many decades research has focused on the development of a number of anti-fibrotic strategies targeting this cell. Despite major improvements in two-dimensional systems (2D) by using a variety of cell culture models of different complexity, an efficient anti-fibrogenic therapy has yet to be developed. The development of well-defined three-dimensional (3D) in vitro models, which mimic ECM structures as found in vivo, have demonstrated the importance of cell-matrix bio-mechanics, the complex interactions between HSCs and hepatocytes and other non-parenchymal cells, and this to improve and promote liver cell-specific functions. Henceforth, refinement of these 3D in vitro models, which reproduce the liver microenvironment, will lead to new objectives and to a possible new era in the search for antifibrogenic compounds.

C-C Chemokine Ligand-5 is critical for facilitating macrophage infiltration in the early phase of liver ischemia/reperfusion injury

CCL5/RANTES, a chemoattractant for myeloid cells, is induced by hepatic ischemia/reperfusion injury (IRI). The roles of CCL5 in hepatic IRI were carried out by means of CCL5 immunodepletion, antagonistic competition by Met-CCL5, and treatment with recombinant murine CCL5 (rmCCL5). Depletion or inhibition of CCL5 reduced severity of hepatic IRI, whereas rmCCL5 treatment aggravated liver IRI as manifested in elevated serum alanine aminotransferase (ALT) and tissue myeloperoxidase (MPO) levels. Moreover, IRI severity was reduced in CCL5-knockout (CCL5-KO) mice versus wildtype (WT) mice, with drops in serum ALT level, intrahepatic MPO activity, and histological pathology. Bone marrow transplantion (BMT) studies show that myeloid cells and tissue cells are both required for CCL5-aggravated hepatic IRI. The profile of liver-infiltrating leukocyte subsets after hepatic reperfusion identified CD11b+ cells as the only compartment significantly reduced in CCL5-KO mice versus WT controls at early reperfusion phase. The role of CCL5 recruiting CD11b+ cells in early reperfusion was validated by in vitro transwell migration assay of murine primary macrophages (broadly characterized by their CD11b expression) in response to liver lysates after early reperfusion. Taken together, our results demonstrate a sequence of early events elicited by CCL5 chemoattracting macrophage that result in inflammatory aggravation of hepatic IRI.