Peizhi Li

An efficient method to isolate and culture mouse Kupffer cells.

Kupffer cells (KCs) play an essential role in the physiological and pathological functions of the liver. Although the isolation methods of KCs have been well-described, most of them are sophisticated and time-consuming. In addition, these methods are mainly used for isolating the KCs of the human and rat. In this study, a three-step procedure was applied to isolate KCs in sufficient number and purity from mouse liver, including the techniques of enzymatic tissue treatment, gradient centrifugation, and selective adherence. F4/80 immunofluorescence and flow cytometry were used for cell identification. The combination method resulted in a satisfactorily high yield of 5-6×10(6) KCs per liver, over 92.0% positive for F4/80 and 98.5% viable cells. After 24h of culturing, the KCs showed typical macrophage morphologic features such as irregular shape, transparent cytoplasm and kidney-like nucleus. The phagocytic assay showed that the isolated cells exhibited strong phagocytosis activity. The KCs we isolated were functionally intact and exhibited a concentration dependent TNF-α production induced by LPS. The method we described is an effective method to isolate mouse KCs in high purity and yield, which consuming fewer collagenase and time without altering the functional capacity of the KCs.

The role of Kupffer cells in hepatic diseases.

&NA; 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. HighlightsCytoplasmic LPS can activate macrophage via TLR4‐independent pathway that results in activation of the enzyme caspase‐11.The negative regulators associated with endotoxin tolerance in KCs include IRAK‐M, SHIP1, and SCOS1 and Twist‐2.KCs are responsible for the initiation of the pro‐inflammatory response in IRI.KCs are involved in liver immune tolerance through inducing apoptosis of T cells.KCs release IL‐1&bgr; that promotes development of NAFLD by activating TLR4, TLR9 and NLRP3 inflammasome pathways.

NLRP3 Deletion Inhibits the Non-alcoholic Steatohepatitis Development and Inflammation in Kupffer Cells Induced by Palmitic Acid

The cleavage and secretion of pro-inflammatory cytokines IL-1β and IL-18 is regulated by NLRP3 (NACHT, LRR, and PYD domain-containing protein 3) inflammasome activation. Kupffer cells (KCs) are implicated in the pathogenesis of various liver diseases, such as non-alcoholic fatty liver disease (NAFLD), alcoholic liver disease, and liver fibrosis. However, the role of NLRP3 played in the non-alcoholic steatohepatitis (NASH) has yet to be evaluated. In the present study, methionine–choline-deficient (MCD) diet was used to establish the mice NASH model. The expression levels of F4/80 and NLRP3 in liver tissues were evaluated, and the IL-1β and IL-18 in serum were also evaluated. KCs were isolated from wild-type (WT) mice and NLRP3 knockout (NLRP3−/−) mice and then randomly divided into two groups: the control and palmitic acid (PA) groups. The expression levels of NLRP3, ASC, and caspase-1 in KCs were determined by RT-PCR, western blotting, and immunofluorescence. The levels of IL-1β and IL-18 in the supernatant (SN) of KCs were evaluated by enzyme-linked immunosorbent assay (ELISA). We found that KCs and NLRP3 play pro-inflammatory roles in the progression of NASH, probably through secretions of IL-1β and IL-18 by KCs induced by PA. PA could act as a kind of damage-associated molecular patterns to elevate the messenger RNA and protein expression levels of NLRP3, ASC, and caspase-1 in KCs from WT mice. In the contrast, NLRP3 deletion could inhibit the NLRP3 inflammasome upregulation and activation in KCs induced by PA. Furthermore, the levels of pro-inflammatory cytokines IL-1β and IL-18 in the SN of KCs from WT mice were all elevated with the stimulation of PA, and the increase of these cytokines in the SN was blocked by NLRP3 deletion. In conclusion, our novel findings demonstrate that NLRP3 plays a pivotal role in NASH development and pro-inflammatory cytokines IL-1β and IL-18 secretion induced by PA stimulation, and NLRP3 might be an effective potential target for the treatment of liver inflammatory diseases associated with NLRP3 inflammasome activation.

Association Between Gene Polymorphisms of IRAK-M and the Susceptibility of Sepsis

The aim of this study was to explore the association between the single-nucleotide polymorphisms of interleukin-1 receptor-associated kinase-M (IRAK-M) gene and the susceptibility of sepsis. The allele frequency and genotype distribution of IRAK-M gene polymorphisms were assessed in 118 controls and 82 sepsis patients by semiquantitative polymerase chain reaction and restriction fragment length polymorphism (RFLP) analysis. The plasma levels of tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) were detected by enzyme-linked immunosorbent assay. Associations between IRAK-M polymorphisms and the susceptibility of sepsis were analyzed by Cox regression. Data were analyzed by the χ2 test and the Student’s t test, whenever appropriate. Statistical calculations were performed by using statistical package SPSS version 18.0. The genotype distribution of IRAK-M+22148 polymorphism significantly differed between the sepsis and control groups (P < 0.0001). The frequency of the G allele was remarkably more common in the sepsis group than that of the control group (P < 0.0001). However, the frequency of the A allele was significantly less common in the sepsis group than that of control group (P < 0.0001). Moreover, the plasma levels (in picograms per milliliter) of TNF-α and IL-6 in patients with G/G genotype were greatly higher than those with A/A genotype after lipopolysaccharide stimulation (P < 0.05). The genetic polymorphism of IRAK-M+22148 G>A is associated with the susceptibility of sepsis. The G/G genotype of IRAK-M increases the risk of developing sepsis, and the A/A genotype may play a protective role in the process of developing sepsis.

Endotoxin Tolerance Inhibits Degradation of Tumor Necrosis Factor Receptor–Associated Factor 3 by Suppressing Pellino 1 Expression and the K48 Ubiquitin Ligase Activity of Cellular Inhibitor of Apoptosis Protein 2

Pellino 1 positively regulates Toll-like receptor 4 signaling by regulating tumor necrosis factor receptor-associated factor 3 (TRAF3) degradation and is suppressed with the induction of endotoxin tolerance. However, the role of TRAF3 in endotoxin tolerance is largely unknown. In this study, we found that lipopolysaccharide (LPS) stimulation decreased TARF3 protein expression in mouse Kupffer cells (KCs) and liver tissues, whereas endotoxin tolerization abrogated this effect. Degradative TRAF3 K48-linked ubiquitination and the cytoplasmic translocation of the MYD88-associated multiprotein complex were significantly inhibited in tolerized KCs, which led to markedly impaired activation of MYD88-dependent JNK and p38 and downregulation of inflammatory cytokines. TRAF3 ablation failed to induce a fully endotoxin-tolerant state in RAW264.7 cells. Pellino 1 knockdown in Raw264.7 cells did not impair induction of cIAP2 in response to LPS but inhibited the K63-linked ubiquitination of cellular inhibitor of apoptosis protein 2 (cIAP2) and K48-linked ubiquitination of TRAF3 protein. We also found upregulation of Pellino 1 and downregulation of TRAF3 in liver tissues of patients with cholangitis. Our findings reveal a novel mechanism that endotoxin tolerance reprograms mitogen-activated protein kinase signaling by suppressing Pellino 1-mediated K63-linked ubiquitination of cIAP2, K48-linked ubiquitination, and degradation of TRAF3.

Inhibition of NLRP3 inflammasome by thioredoxin-interacting protein in mouse Kupffer cells as a regulatory mechanism for non-alcoholic fatty liver disease development

NOD-like receptor (NLR) NLRP3 inflammasome activation has been implicated in the progression of non-alcoholic fatty liver disease (NAFLD) from non-alcoholic fatty liver (NAFL) to non-alcoholic steatohepatitis (NASH). It has been also shown that palmitic acid (PA) activates NLRP3 inflammasome and promotes interleukin-1β (IL-1β) secretion in Kupffer cells (KCs). However, the specific mechanism of the NLRP3 inflammasome activation is unclear. We studies the molecular mechanisms by investigating the roles of Thioredoxin-interacting protein (TXNIP) and NLRP3 on NAFLD development in patients, high-fat diet (HFD)-induced NAFL and methionine choline deficient (MCD) diet-induced NASH in wild type (WT), TXNIP−/− (thioredoxin-interacting protein) and NLRP3−/− mice, and isolated KCs. We found that the expressions of NLRP3 and TXNIP in human liver tissues were higher in NASH group than in NAFL group. Furthermore, co-immunoprecipitation analyses show that activation of the TXNIP-NLRP3 inflammasome protein complex occurred in KCs of NASH WT mice rather than NAFL WT mice, thus suggesting that the formation and activation of this protein complex is mainly involved in the development of NASH. NLRP3−/− mice exhibited less severe NASH than WT mice in MCD diet model, whereas TXNIP deficiency enhanced NLRP3 inflammasome activation and exacerbated liver injury. PA triggered the activation and co-localization of the NLRP3 inflammasome protein complex in KCs isolated from WT and TXNIP−/− but not NLRP3−/− mice, and most of the complex co-localized with mitochondria of KCs following PA stimulation. Taken together, our novel findings indicate that TXNIP plays a protective and anti-inflammatory role in the development of NAFLD through binding and suppressing NLRP3.

Investigation for role of tissue factor and blood coagulation system in severe acute pancreatitis and associated liver injury

This study aims to investigate the molecular mechanisms underlying the pathogenesis of severe acute pancreatitis (SAP) and SAP-associated liver injury, we performed an association analysis of the functions of tissue factor (TF) and blood coagulation system in both SAP patients and mouse SAP model. Our results showed that serum TF and tissue factor-microparticle (TF-MP) levels were highly up-regulated in both SAP patients and SAP mouse model, which was accompanied by the dysfunction of blood coagulation system. Besides, TF expression was also highly up-regulated in the Kupffer cells (KCs) of SAP mouse model. After inhibiting KCs in SAP mouse model, the amelioration of blood coagulation system functions was associated with the decrease in serum TF and TF-MPs levels, and the reduction of SAP-associated liver injury was associated with the decrease of TF expression in KCs. In conclusion, the dis-regulated TF expression and associated dysfunction of blood coagulation system are critical factors for the pathogenesis of SAP and SAP-associated liver injury. TF may serve as a potential and effective target for treating SAP and SAP-associated liver injury.

Bone marrow stromal cells attenuate LPS-induced mouse acute liver injury via the prostaglandin E 2-dependent repression of the NLRP3 inflammasome in Kupffer cells

The nucleotide-binding and oligomerization domain-like receptor 3 (NLRP3) inflammasome participates in the pathogenesis of acute liver injury during sepsis. Bone marrow mesenchymal stem cells (BMSCs) attenuate sepsis through prostaglandin E 2 (PGE2) by increasing the interleukin-10 (IL-10) production of macrophages; moreover, NLRP3 inflammasome assembly is effectively regulated by IL-10 during infection. Whether BMSCs have an effect on the activation of the NLRP3 inflammasome and its underlying mechanism is unclear. Administering of BMSCs to mice or KCs after LPS stimulating have improved liver function and reduced activation of NLRP3 inflammasome in KCs. The beneficial effect of BMSCs was enhanced by over-expression of PGE2 and eliminated by silence of PGE2. Additionally, The IL-10 levels in the serum and supernatant were increased by given BMSCs and further increase by PGE2 over-expressed BMSCs, but decreased markedly by PGE2 silenced BMSCs. Furthermore, extracellular signal-regulated kinase 1 (ERK1) inhibitor reduced IL-10 production in KCs and blocked the inhibitory effect of PGE2 on the activation of the NLRP3 inflammasome. Our data reveal a novel mechanism of BMSC-mediated suppression of the activation of KCs through the secretion of PGE2 by BMSCs, which promotes KCs to secrete IL-10, leading to the inhibition of the NLRP3 inflammasome in KCs.

The Effects of Twist-2 on Liver Endotoxin Tolerance Induced by a Low Dose of Lipopolysaccharide

Endotoxin tolerance is an important mechanism for preventing uncontrolled inflammatory cytokine production in bacterial sepsis. However, its molecular mechanisms remain largely unknown. It was reported that Twist-2 protein was a negative regulator for cytokine signaling by repressing the nuclear factor (NF)–κB-dependent cytokine pathway. However, the relationship between Twist-2 and endotoxin tolerance is unclear. Endotoxin tolerance models of BABL/c mice and isolated Kupffer cells (KCs) were established to observe the changes of Twist-2 during endotoxin tolerance. Then, Twist-2 shRNA was used to specifically inhibit Twist-2 gene in KCs to further explore the role of Twist-2 in endotoxin tolerance. The expression of Twist-2 was analyzed by immunohistochemistry, reverse transcription polymerase chain reaction, and Western blotting, respectively. The responses to lipopolysaccharide were assessed by the activation of nuclear factor–κB and the production of tumor necrosis factor-α. The histopathologic changes in the liver of the non-endotoxin tolerance group were more serious than those of the endotoxin tolerance group. Endotoxin tolerance also led to less activation of nuclear factor–κB, lower expression levels of tumor necrosis factor-α mRNA, and more expression of Twist-2 than those of non-endotoxin tolerance group in liver and KCs. Moreover, the inhibitive effects partly weaken in KCs transfected with Twist-2 shRNA. Twist-2 was involved in endotoxin tolerance through inhibiting NF–κB trans-activation and cytokines transcriptional activities. It may be a new target for the clinical treatment of sepsis and other inflammatory diseases.

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.