Glycine blunts transplantative liver ischemia-reperfusion injury by downregulating interleukin 1 receptor associated kinase-4

IL-1 receptor-associated kinase family proteins: An overview of their role in liver disease

The interleukin-1 receptor-associated kinase (IRAK) family is a group of serine-threonine kinases that regulates various cellular processes via toll-like receptor (TLR)/interleukin-1 receptor (IL1R)-mediated signaling. The IRAK family comprises four members, including IRAK1, IRAK2, IRAK3, and IRAK4, which play an important role in the expression of various inflammatory genes, thereby contributing to the inflammatory response. IRAKs are key proteins in chronic and acute liver diseases, and recent evidence has implicated IRAK family proteins (IRAK1, IRAK3, and IRAK4) in the progression of liver-related disorders, including alcoholic liver disease, non-alcoholic steatohepatitis, hepatitis virus infection, acute liver failure, liver ischemia-reperfusion injury, and hepatocellular carcinoma. In this article, we provide a comprehensive review of the role of IRAK family proteins and their associated inflammatory signaling pathways in the pathogenesis of liver diseases. The purpose of this study is to explore whether IRAK family proteins can serve as the main target for the treatment of liver related diseases.

Combating Ischemia-Reperfusion Injury with Micronutrients and Natural Compounds during Solid Organ Transplantation: Data of Clinical Trials and Lessons of Preclinical Findings

Although extended donor criteria grafts bear a higher risk of complications such as graft dysfunction, the exceeding demand requires to extent the pool of potential donors. The risk of complications is highly associated with ischemia-reperfusion injury, a condition characterized by high loads of oxidative stress exceeding antioxidative defense mechanisms. The antioxidative properties, along with other beneficial effects like anti-inflammatory, antiapoptotic or antiarrhythmic effects of several micronutrients and natural compounds, have recently emerged increasing research interest resulting in various preclinical and clinical studies. Preclinical studies reported about ameliorated oxidative stress and inflammatory status, resulting in improved graft survival. Although the majority of clinical studies confirmed these results, reporting about improved recovery and superior organ function, others failed to do so. Yet, only a limited number of micronutrients and natural compounds have been investigated in a (large) clinical trial. Despite some ambiguous clinical results and modest clinical data availability, the vast majority of convincing animal and in vitro data, along with low cost and easy availability, encourage the conductance of future clinical trials. These should implement insights gained from animal data.

Resolving the graft ischemia-reperfusion injury during liver transplantation at the single cell resolution

Ischemia–reperfusion injury (IRI) remains the major reason for impaired donor graft function and increased mortality post-liver transplantation. The mechanism of IRI involves multiple pathophysiological processes and numerous types of cells. However, a systematic and comprehensive single-cell transcriptional profile of intrahepatic cells during liver transplantation is still unclear. We performed a single-cell transcriptome analysis of 14,313 cells from liver tissues collected from pre-procurement, at the end of preservation and 2 h post-reperfusion. We made detailed annotations of mononuclear phagocyte, endothelial cell, NK/T, B and plasma cell clusters, and we described the dynamic changes of the transcriptome of these clusters during IRI and the interaction between mononuclear phagocyte clusters and other cell clusters. In addition, we found that TNFAIP3 interacting protein 3 (TNIP3), specifically and highly expressed in Kupffer cell clusters post-reperfusion, may have a protective effect on IRI. In summary, our study provides the first dynamic transcriptome map of intrahepatic cell clusters during liver transplantation at single-cell resolution.

Therapeutics administered during ex vivo liver machine perfusion: An overview

Although the use of extended criteria donors has increased the pool of available livers for transplant, it has also introduced the need to develop improved methods of protection against ischemia-reperfusion injury (IRI), as these "marginal" organs are particularly vulnerable to IRI during the process of procurement, preservation, surgery, and post-transplantation. In this review, we explore the current basic science research investigating therapeutics administered during ex vivo liver machine perfusion aimed at mitigating the effects of IRI in the liver transplantation process. These various categories of therapeutics are utilized during the perfusion process and include invoking the RNA interference pathway, utilizing defatting cocktails, and administering classes of agents such as vasodilators, anti-inflammatory drugs, human liver stem cell-derived extracellular vesicles, and δ-opioid agonists in order to reduce the damage of IRI. Ex vivo machine perfusion is an attractive alternative to static cold storage due to its ability to continuously perfuse the organ, effectively deliver substrates and oxygen required for cellular metabolism, therapeutically administer pharmacological or cytoprotective agents, and continuously monitor organ viability during perfusion. The use of administered therapeutics during machine liver perfusion has demonstrated promising results in basic science studies. While novel therapeutic approaches to combat IRI are being developed through basic science research, their use in clinical medicine and treatment in patients for liver transplantation has yet to be explored.

Inflammasome activation involved in early inflammation reaction after liver transplantation

Liver transplantation has emerged as a vital therapy for end-stage liver diseases. Acute -phase inflammation play an important role in liver graft injury.Recent studies have revealed that inflammasome are responsible for initiating inflammation in early stage of acute organ rejection in liver transplantation, however the underlying mechanism remains unclear. Here we explored to block inflammasome activation to see whether it can alleviate early inflammation reaction during rejection of allgrafts in a rat model and gain further insights into the mechanism of inhibiting inflammation in allografts. By using Ac-YVAD-CMK, a highly selective caspase-1 inhibitor, to inhibit inflammation reaction involved in allograft rejection in a rat model. Our results showed that the rejection activity index (RAI) of Ac-YVAD-CMK-treated allografts is significantly diminished in similar magnitude to that of isografts. Compared with isografts, the expression of apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) and IL-1β in allograft group increased significantly with the development of rejection, exhibiting apparent correlation. Expression of IFN-γ mRNA in untreated allografts was maximal on day 3 while in Ac-YVAD-CMK-treated allografts and isografts, IFN-γ mRNA levels remained low over the duration of the time course. ELISA results revealed serum elevation of IL-1β by day 7 after othotopic liver transplantation (OLT) in comparison with isografts. There were no statistically significant differences between isografts and Ac-YVAD-CMK-treated allografts. For the first time, our data reveal that inhibition of the inflammasome activation pathway attenuates inflammation reaction of hepatic transplant rejection.

IRAK-4-shRNA Prevents Ischemia/Reperfusion Injury Via Different Perfusion Periods Through the Portal Vein After Liver Transplantation in Rat

BACKGROUND

This study analyzed the effects of short hairpin RNA targeting interleukin-1 receptor-associated kinase-4 (IRAK-4-shRNA) via portal vein perfusion during different periods on ischemia/reperfusion injury after liver transplantation.

METHODS

Rats were randomly divided into 3 groups: the cold ischemia transfection group (CIT group, n = 18), in which graft livers were perfused with the plasmid of pSIIRAK-4 expressing IRAK-4-shRNA for 4 minutes (0.5 mL/min) via the portal vein during the cold ischemia period; the in vivo transfection group (IVT group, n = 18), in which equivalent volumes (2 mL) of IRAK-4-ShRNA plasmid (pSIIRAK-4) were injected during the operation; and the control group (n = 18), in which the rats received equivalent volumes of blank plasmid. At 0, 60, and 180 minutes after portal vein reperfusion, blood and liver tissues were collected for examination. IRAK-4 expression, nuclear factor kB (NF-kB) activity, tumor necrosis factor α, interleukin (IL)-1β, and IL-6 serum levels, as well as histologic changes, were detected.

RESULTS

At 0 minutes after reperfusion, IRAK-4 expression, NF-κB activity, and serum levels of tumor necrosis factor α, IL-1β, and IL-6 showed no significant differences among the 3 groups (P > .05). At 60 and 180 minutes after reperfusion, all indices of the IVT and control groups were significantly higher than those of the CIT group (P < .01). Meanwhile, all indices of the CIT group showed no significant differences at various time points (P > .05). Liver function and histologic changes exhibited less liver injury in the CIT group than in the other groups.

CONCLUSIONS

IRAK-4 activity was suppressed by IRAK-4-shRNA through portal vein perfusion during the cold ischemia period, and IRAK-4-shRNA effectively prevented ischemia/reperfusion injury after liver transplantation.

The role of Kupffer cells in hepatic diseases

Kupffer cells (KCs) constitute 80-90% of the tissue macrophages present in the body. Essential to innate and adaptive immunity, KCs are responsible for the swift containment and clearance of exogenous particulates and immunoreactive materials which are perceived as foreign and harmful to the body. Similar to other macrophages, KCs also sense endogenous molecular signals that may result from perturbed homeostasis of the host. KCs have been implicated in host defense and the pathogenesis of various hepatic diseases, including endotoxin tolerance, liver transplantation, nonalcoholic fatty liver disease, and alcoholic liver disease. In this review, we summarized some novel findings associated with the role of KCs in hepatic diseases, such as the origin and mechanisms KCs polarization, molecular basis for caspase-1 activation called "non-canonical inflammasome pathway" involving the cleavage of Gsdmd by caspase-11, the important role of microRNA in liver transplantation, and so on. A better understanding of KCs biological characteristics and immunologic function in liver homeostasis and pathology may pave the way to investigate new diagnostic and therapeutic approaches for hepatic diseases.

Down-Regulated Receptor Interacting Protein 140 Is Involved in Lipopolysaccharide-Preconditioning-Induced Inactivation of Kupffer Cells and Attenuation of Hepatic Ischemia Reperfusion Injury

Background

Lipopolysaccharide (LPS) preconditioning is known to attenuate hepatic ischemia/reperfusion injury (I/RI); however, the precise mechanism remains unclear. This study investigated the role of receptor-interacting protein 140 (RIP140) on the protective effect of LPS preconditioning in hepatic I/RI involving Kupffer cells (KCs).

Methods

Sprague—Dawley rats underwent 70% hepatic ischemia for 90 minutes. LPS (100 μg/kg) was injected intraperitoneally 24 hours before ischemia. Hepatic injury was observed using serum and liver samples. The LPS/NF-κB (nuclear factor-κB) pathway and hepatic RIP140 expression in isolated KCs were investigated.

Results

LPS preconditioning significantly inhibited hepatic RIP140 expression, NF-κB activation, and serum proinflammatory cytokine expression after I/RI, with an observation of remarkably reduced serum enzyme levels and histopathologic scores. Our experiments showed that protection effects could be effectively induced in KCs by LPS preconditioning, but couldn’t when RIP140 was overexpressed in KCs. Conversely, even without LPS preconditioning, protective effects were found in KCs if RIP140 expression was suppressed with siRNA.

Conclusions

Down-regulated RIP140 is involved in LPS-induced inactivation of KCs and hepatic I/RI attenuation.

Mesenchymal stromal cell-dependent reprogramming of Kupffer cells is mediated by TNF-α and PGE2 and is crucial for liver transplant tolerance

The role of mesenchymal stromal cells (MSCs) in the modulation of liver transplant tolerance has attracted significant interest. However, the interaction between MSCs and Kupffer cells (KCs) has received little attention, and the effect of this interaction on liver transplant tolerance remains unclear. KCs were cultured in the presence and absence of MSCs. After 24 h, cells were treated with lipopolysaccharide (LPS), after which the production of cytokines and the expression of surface antigens were measured for cell function identification. Moreover, the effects of the KCs and the prostaglandin E2 (PGE2) levels produced by the MSCs were determined using an experimental rat liver transplantation model. Blood and liver samples were collected at three time points after transplantation for further analysis. After LPS treatment, when compared with the KC single cultures, the expression of pro-inflammatory cytokines (IL-1β, IL-6, MHC-II, CD40, CD80, and CD86) in the coculture system was down-regulated, whereas the expression of anti-inflammatory cytokines (TGF-β, IL-4, PGE2, and IL-10) was markedly increased. These data indicate that MSCs can reprogram the phenotype of KCs. However, KCs treated with miR/TNF-α (tumor necrosis factor) plasmid prior to coculture to inhibit the production of TNF-α resulted in an inhibition of the reprogramming effect of MSCs. Moreover, overexpression of PGE2 in MSCs increased the effect of MSCs on KC reprogramming. After rat liver transplantation, allograft recipients that received MSCs showed better allograft tolerance when compared with rats in which KC function was inhibited. Furthermore, rats treated with MSCs overexpressing PGE2 demonstrated the best liver tolerance of all of the groups tested. MSCs reprogram the phenotype of KCs through TNF-α and PGE2, and this process is crucial for the immunomodulatory function of MSCs in liver transplantation.

A systematic review of pharmacological treatment options used to reduce ischemia reperfusion injury in rat liver transplantation

BACKGROUND

Although animal studies models are frequently used for the purpose of attenuating ischemia reperfusion injury (IRI) in liver transplantation (LT), many of pharmacological agents have not become part of clinical routine.

METHODS

A search was performed using the PubMed database to identify agents, from which 58 articles containing 2700 rat LT procedures were selected. The identified pharmacological agents were categorized as follows: I - adenosine agonists, nitric oxide agonists, endothelin antagonists, and prostaglandins, II - Kupffer cell inactivator, III - complement inhibiter, IV - antioxidant, V - neutrophil inactivator, VI -anti-apoptosis agent, VII - heat shock protein and nuclear factor kappa B inducer, VIII - metabolic agent, IX - traditional Chinese medicine, and X - others. Meta-analysis using 7-day-survival rate was also performed with Mantel-Haenszel's Random effects model.

RESULTS

The categorization revealed that the rate of donor-treated experiments in each group was highest for agents from Group II (70%) and VII (71%), whereas it was higher for agents from Group V (83%) in the recipient-treated experiments. Furthermore, 90% of the experiments with agents in Group II provided 7-day-survival benefits. The Risk Ratio (RR) of the meta-analysis was 2.43 [95% CI: 1.88-3.14] with moderate heterogeneity. However, the RR of each of the studies was too model-dependent to be used in the search for the most promising pharmacological agent.

CONCLUSION

With regard to hepatic IRI pathology, the categorization of agents of interest would be a first step in designing suitable multifactorial and pleiotropic approaches to develop pharmacological strategies.

Augmenter of liver regeneration promotes hepatic regeneration depending on the integrity of Kupffer cell in rat small-for-size liver transplantation

BACKGROUND

Augmenter of liver regeneration (ALR) can promote hepatocyte proliferation and thereby augment liver mass restoration. This study was performed to further explore the mechanism of ALR on liver regeneration in small-for-size liver transplanted rats.

METHODS

Donor Sprague-Dawley rats were divided into a Kupffer cell (KC)-depleted group (pretreated with GdCl3) and KC-competent group and then further divided into two subgroups: the ALR subgroup (infused with 100 μg/kg ALR through the portal vein) and non-ALR subgroup. Only the median lobe was retained to establish the small-for-size liver transplantation model. Ten rats from each subgroup were used for the 7 d survival study. In addition, the nuclear factor κB activity, reperfusion injury, regeneration of the remnant liver, and tumor necrosis factor α and interleukin 6 expression levels were evaluated.

RESULTS

ALR could accelerate graft regeneration by increasing nuclear factor κB activity to induce tumor necrosis factor α and interleukin 6 expression in the KC-competent rats, which resulted in a higher 7 d survival rate.

CONCLUSIONS

ALR could enhance the hepatocellular proliferation of small-for-size liver grafts, and these effects appeared to deeply depend on the integrity of KCs.

Glycogen synthase kinase 3 inhibitor attenuates endotoxin-induced liver injury

BACKGROUND/AIMS

Endotoxin (lipopolysaccharide, LPS)-induced acute liver injury was attenuated by endotoxin tolerance (ET), which is characterized by phosphatidylinositol 3-kinase pathway/Akt signaling. Glycogen synthase kinase 3 (GSK-3) acts downstream of phosphatidylinositol 3-kinase pathway/Akt and GSK-3 inhibitor protects against organic injury. This study evaluates the hypothesis that ET attenuated LPS-induced liver injury through inhibiting GSK-3 functional activity and downstream signaling.

METHODS

Sprague-Dawley rats with or without low-dose LPS pretreatment were challenged with or without large dose of LPS and subsequently received studies. Serum tumor necrosis factor-alpha, interleukin-10, alanine aminotransferase, lactate dehydrogenase, and total bilirubin levels were analyzed, morphology of liver tissue was performed, glycogen content, myeloperoxidase content, phagocytosis activity of Kupffer cells, and the expression and inhibitory phosphorylation as well as kinase activity of GSK-3 were examined. Survival after LPS administration was also determined.

RESULTS

LPS induced significant increases of serum TNF-α, alanine aminotransferase, lactate dehydrogenase, and total bilirubin (P < 0.05), which were companied by obvious alterations in liver: the injury of liver tissue, the decrease of glycogen, the infiltration of neutrophils, and the enhancement of phagocytosis of Kupffer cells (P < 0.05). LPS pretreatment significantly attenuated these alterations, promoted the inhibitory phosphorylation of GSK-3 and inhibited its kinase activity, and improved the survival rate (P < 0.05).

CONCLUSIONS

ET attenuated LPS-induced acute liver injury through inhibiting GSK-3 functional activity and its downstream signaling.

Glycine, a simple physiological compound protecting by yet puzzling mechanism(s) against ischaemia-reperfusion injury: current knowledge

Ischaemia is amongst the leading causes of death. Despite this importance, there are only a few therapeutic approaches to protect from ischaemia-reperfusion injury (IRI). In experimental studies, the amino acid glycine effectively protected from IRI. In the prevention of IRI by glycine in cells and isolated perfused or cold-stored organs (tissues), direct cytoprotection plays a crucial role, most likely by prevention of the formation of pathological plasma membrane pores. Under in vivo conditions, the mechanism of protection by glycine is less clear, partly due to the physiological presence of the amino acid. Here, inhibition of the inflammatory response in the injured tissue is considered to contribute decisively to the glycine-induced reduction of IRI. However, attenuation of IRI recently achieved in experimental animals by low-dose glycine treatment regimens suggests additional/other (unknown) protective mechanisms. Despite the convincing experimental evidence and the large therapeutic width of glycine, there are only a few clinical trials on the protection from IRI by glycine with ambivalent results. Thus, both the mechanism(s) behind the protection of glycine against IRI in vivo and its true clinical potential remain to be addressed in future experimental studies/clinical trials.

Effect of taurine on IRAK4 and NF-kappa B in Kupffer cells from rat liver grafts after ischemia-reperfusion injury

BACKGROUND

The aim of this study was to explore the protective mechanisms of taurine pretreatment against hepatic ischemia/reperfusion injury after liver transplantation.

METHODS

A Sprague-Dawley-to-Sprague-Dawley rat liver transplantation model was used in this study. At 0, 60, and 180 minutes after reperfusion, expression of interleukin-1 receptor-associated kinase-4 (IRAK-4) messenger ribonucleic acid and protein in Kupffer cells was determined by real-time polymerase chain reaction and Western blotting. The activity of nuclear factor κB in Kupffer cells was determined by electrophoretic mobility shift assay. The serum tumor necrosis factor-α level was detected by enzyme-linked immunosorbent assay. Serum transaminases, liver histology, and animal survival were also investigated.

RESULTS

At 60 and 180 minutes after reperfusion, levels of IRAK-4 messenger ribonucleic acid and protein, activities of nuclear factor κB, and levels of serum transaminases and tumor necrosis factor-α were all obviously elevated. However, changes in these parameters in rats treated with taurine were remarkably attenuated at the indicated time points.

CONCLUSIONS

These data suggest that taurine could protect against hepatic ischemia/reperfusion injury after liver transplantation, and the protective effects may be through downregulation of IRAK-4 and downstream nuclear factor κB and tumor necrosis factor-α expression in Kupffer cells.

Endotoxin tolerance attenuates liver ischemia/reperfusion injury by down-regulation of interleukin-1 receptor-associated kinase 4 in kupffer cells

AIM

The aim of this study was to study the role of interleukin-1 receptor-associated kinase 4 (IRAK-4) in the formation of endotoxin tolerance (ET) in liver ischemia/reperfusion (I/R) injury.

METHODS

Animals were randomly divided into 3 groups: control group, I/R group, and ET group. Liver morphological changes were observed using optical microscopy with hematoxylin eosin (HE) staining. Alanine aminotransferase (ALT) was quantified to measure liver functional injury. The messenger RNA (mRNA) and protein expressions of IRAK-4 in Kupffer cells (KCs) isolated from recipients were detected using real-time polymerase chain reaction (PCR) and Western blot, respectively. The activities of NF-κB and the supernatant levels of tumor necrosis factor-alpha (TNF-α), IL-10 were assayed using enzyme-linked immunosorbent assay (ELISA).

RESULTS

Endotoxin preconditioning improved hepatic tissue injury as indicated by morphological analysis, whereas serum ALT levels were significantly decreased at various times (P < .05); concurrently, the expression of IRAK-4 and TNF-α in KCs was down-regulated (P < .05) and the secretion of IL-10 was enhanced (P < .05); NF-κB DNA-binding activity of KCs was also significantly inhibited by endotoxin preconditioning (P < .05).

CONCLUSION

Endotoxin preconditioning attenuated the liver I/R injury caused by transplantation. The expression of IRAK-4 in KCs may play an important role in the formation of ET.

Antioxidant effects of xanthohumol and functional impact on hepatic ischemia-reperfusion injury

Therapeutic effects of dietary flavonoids have been attributed mainly to their antioxidant capacity. Xanthohumol (1), a prominent flavonoid of the hop plant, Humulus lupulus, was investigated for its antioxidant potential and for its effect on NF-kappaB activation. To examine the biological relevance of 1, a hepatic ischemia/reperfusion model was chosen as a widely accepted model of oxidative stress generation. The impact of 1 on endogenous antioxidant systems, on the NF-kappaB signal transduction pathway as well as on apoptotic parameters, and on hepatic tissue damage was evaluated. Compound 1 markedly decreased the level of reactive oxygen species in vitro. Furthermore, levels of enzymatic and nonenzymatic antioxidants were restored after pretreatment in postischemic hepatic tissue, and lipid peroxidation was attenuated. NF-kappaB activity was reduced in vitro as well as in hepatic tissue after ischemia/reperfusion upon pretreatment with 1. In addition, the phosphorylation of Akt was markedly inhibited. Surprisingly, 1 decreased the expression of the antiapoptotic protein Bcl-X and increased caspase-3 like-activity, a proapoptotic parameter. Moreover, hepatic tissue damage as well as TNF-alpha levels increased in xanthohumol-pretreated liver tissue after ischemia/reperfusion. In summary, xanthohumol did not protect against ischemia/reperfusion injury in rat liver, despite its antioxidant and NF-kappaB inhibitory properties.

Triggering receptor in myeloid cells (TREM-1) specific expression in peripheral blood mononuclear cells of sepsis patients with acute cholangitis

To determine its relationship with acute cholangitis (AC), we sought to quantify expression of triggering receptor expressed on myeloid cells (TREM-1) in peripheral blood mononuclear cells (PBMC) of sepsis patients with AC. Peripheral blood samples of 42 AC patients and 48 patients with AC of severe type (ACST) were collected from January to September, 2008 and tested for TREM-1 mRNA by RT-PCR and protein expression by immunocytochemistry and Western blotting. ELISA and immunoturbidimetry were employed to detect the changes of TNF-alpha or C-reactive protein in the serum respectively. TREM-1 expression was higher in ACST group than in AC group (P < 0.01). TREM-1 was positive in mononuclear cells by immunochemistry in both groups before operative therapy, but the positive expression rate decreased at 48 h postoperatively. Compared with healthy controls, TREM-1 protein expression levels were up-regulated in sepsis patients with AC. TREM-1 expression has highly sensitivity and specificity in sepsis patients with AC or ACST. TREM-1 is up-regulated in PBMC of AC patients, and has higher sensitivity and specificity than other clinical inflammation markers, suggesting its importance in AC-induced sepsis.

Advances in the relationship between Kupffer cells and liver ischemia reperfusion injury

Kupffer cells, residing within the lumen of liver sinusoids, constitute 80%-90% of tissue macrophages present in the body. Upon activation Kupffer cells release various products, including cytokines, prostanoides, nitric oxide and reactive oxygen species. These factors regulate the phenotype of Kupffer cells themselves, and the phenotypes of neighboring cells, such as hepatocytes, stellate cells, endothelial cells and other immune cells that traffic through the liver. Therefore, Kupffer cells are intimately involved in the liver's response to warm or cold ischemia reperfusion injury (IRI). This review summarizes the role of Kupffer cells in the pathogenesis of liver IRI to explore the reasonable therapeutic target.

The effects of SOCS-1 on liver endotoxin tolerance development induced by a low dose of lipopolysaccharide are related to dampen NF-kappaB-mediated pathway

BACKGROUND

Endotoxin tolerance is an important mechanism to maintain the homeostasis of liver. It was reported that suppressors of cytokine signalling-1 was a negative regulator of lipopolysaccharide-induced macrophages activation, however, the mechanism underlying endotoxin tolerance and suppressors of cytokine signalling-1 has not been fully elucidated.

AIM

Our aim here is to clarify whether suppressors of cytokine signalling-1 was involved in the mechanisms of endotoxin tolerance in liver through dampening nuclear factor-kappaB-mediated pathway.

METHODS

Endotoxin tolerance models of C57BL/6J mice and isolated Kupffer cells were established by pretreating them with a low dose of lipopolysaccharide to observe the changes of suppressors of cytokine signalling-1 expression during endotoxin tolerance inducement. Moreover, a vector-based short hairpin RNA expression system was used to specifically inhibit suppressors of cytokine signalling-1 expression in RAW264.7 macrophage cells to further explore the role of suppressors of cytokine signalling-1 in endotoxin tolerance inducement. The expression of suppressors of cytokine signalling-1 was analysed by immunohistochemistry, reverse transcription-polymerase chain reaction and Western blotting, respectively. The responses to lipopolysaccharide were assessed by the activation of nuclear factor-kappaB and the production of tumour necrosis factor-alpha, which were analysed by ELISA.

RESULTS

The histopathologic changes in the liver of the non-endotoxin tolerance group were more serious than those of the endotoxin tolerance group. The phagocytic activity of Kupffer cells were depressed and suppressors of cytokine signalling-1 expression in the endotoxin tolerance group obviously increased. Endotoxin tolerance also led to a hyporesponse of Kupffer cells to lipopolysaccharide with less activation of nuclear factor-kappaB, less production of tumour necrosis factor-alpha and more expression of suppressors of cytokine signalling-1 than those of non-endotoxin tolerance group. Moreover, the inhibitive effect was partly refracted in pSOCS-1-short hairpin RNA transfected RAW264.7 cells.

CONCLUSIONS

Endotoxin tolerance induced by lipopolysaccharide pretreatment was accompanied with upregulation of suppressors of cytokine signalling-1 and the silence of suppressors of cytokine signalling-1 by RNA interference obviously attenuated this inhibitive effect, indicating that the absence of suppressors of cytokine signalling-1 caused abnormal enhancement of inflammatory cytokine production and suppressors of cytokine signalling-1 was involved in endotoxin tolerance inducement through dampening nuclear factor-kappaB-mediated pathway. Therefore, suppressors of cytokine signalling-1 may be a new target for the clinical treatment of sepsis.

Up-regulation of IRAK-M is essential for endotoxin tolerance induced by a low dose of lipopolysaccharide in Kupffer cells

BACKGROUND

Endotoxin tolerance (ET) is an important mechanism to maintain the homeostasis of Kupffer cells (KCs), because KCs are continually exposed to various pathogen-associated molecular patterns including lipopolysaccharide (LPS). ET involves multiple changes in cell signal transduction pathways; however, not all signaling pathways are down-regulated and some proteins are up-regulated. The latter proteins may be counter regulatory, including interleukin-1 receptor-associated kinase M (IRAK-M) expression. The aim of this study is to clarify weather or not IRAK-M is involved in the mechanisms of ET in KCs through dampening nuclear factor-kappa B (NF-kappaB) mediated pathway.

MATERIALS AND METHODS

KCs isolated from male C57BL/6J mice were seeded in 24-well plates at 1 x 10(6) cells/well and cultured overnight prior to transfection, were randomly divided into two groups: the pIRAK-M-short hairpin RNA (shRNA) group (transfected with IRAK-M shRNA) and the control group (transfected with control vector); 24 h after transfection, the two groups were further randomly divided into two subgroups: non-endotoxin pretreatment group (incubation in Dulbecco's modified Eagle's medium [Invitrogen, Carlsbad, CA] with 10% fetal bovine serum) and endotoxin pretreatment group (incubation in the same medium containing 10 ng/mL LPS), named pIRAK-M-EP, pIRAK-M-NEP, pCV-EP, and pCV-NEP, respectively. Each subgroup contained 6 wells; 24 h later, fresh media containing LPS (100 ng/mL) was added to each subgroup and incubated for an additional 3 h. The expression of IRAK-M gene and protein level were determined by reverse transcription-polymerase chain reaction and Western blot, the activities of NF-kappaB were estimated by electrophoretic mobility shift assay and enzyme-linked immunosorbent assay, and the supernatant tumor necrosis factor-alpha levels were analyzed by enzyme-linked immunosorbent assay.

RESULTS

The recombinant plasmid of pIRAK-M-shRNA specifically inhibited IRAK-M expression after it was transfected into KCs. At 3 h after 100 ng/mL LPS was added to the medium, IRAK-M expression was significantly induced in pCV-EP than that in pCV-NEP; however, there was no difference between pIRAK-M-NEP and pIRAK-M-EP, accompanied with lowest level of NF-kappaB activation and tumor necrosis factor-alpha levels in pCV-EP, and a dramatic enhancement in the other three groups (P < 0.01).

CONCLUSIONS

Although a primary low dose of LPS stimulation obviously attenuated KCs response to the second LPS stimulation, the inhibitive influences were partly refracted in pIRAK-M-EP than in pCV-EP, indicating that the absence of IRAK-M caused abnormal enhancement of inflammatory effects. IRAK-M negatively regulates toll-like receptors signaling and involves in the mechanisms of ET in KCs through dampening NF-kappaB mediated pathway; therefore it may be a key component of this important control system, and a new target for the clinical treatment of sepsis.