Depletion Of Kupffer Cells Research Articles

Kupffer cells facilitate the acute effects of leptin on hepatic lipid metabolism.

Leptin has potent effects on lipid metabolism in a number of peripheral tissues. In liver, an acute leptin infusion (~120 min) stimulates hepatic fatty acid oxidation (~30%) and reduces triglycerides (TG, ~40%), effects that are dependent on phosphoinositol-3-kinase (PI3K) activity. In the current study we addressed the hypothesis that leptin actions on liver-resident immune cells are required for these metabolic effects. Myeloid cell-specific deletion of the leptin receptor (ObR) in mice or depletion of liver Kupffer cells (KC) in rats in vivo prevented the acute effects of leptin on liver lipid metabolism, while the metabolic effects of leptin were maintained in mice lacking ObR in hepatocytes. Notably, liver TG were elevated in both lean and obese myeloid cell ObR, but the degree of obesity and insulin resistance induced by a high-fat diet was similar to control mice. In isolated primary hepatocytes (HEP), leptin had no effects on HEP lipid metabolism and only weakly stimulated PI3K. However, the coculture of KC with HEP restored leptin action on HEP fatty acid metabolism and stimulation of HEP PI3K. Notably, leptin stimulated the release from KC of a number of cytokines. However, the exposure of HEP to these cytokines individually [granulocyte macrophage colony-stimulating factor, IL-1α, IL-1β, IL-6, IL-10, and IL-18] or in combination had no effects on HEP lipid metabolism. Together, these data demonstrate a role for liver mononuclear cells in the regulation of liver lipid metabolism by leptin.

Kupffer cells induce Notch-mediated hepatocyte conversion in a common mouse model of intrahepatic cholangiocarcinoma.

Intrahepatic cholangiocarcinoma (ICC) is a malignant epithelial neoplasm composed of cells resembling cholangiocytes that line the intrahepatic bile ducts in portal areas of the hepatic lobule. Although ICC has been defined as a tumor arising from cholangiocyte transformation, recent evidence from genetic lineage-tracing experiments has indicated that hepatocytes can be a cellular origin of ICC by directly changing their fate to that of biliary lineage cells. Notch signaling has been identified as an essential factor for hepatocyte conversion into biliary lineage cells at the onset of ICC. However, the mechanisms underlying Notch signal activation in hepatocytes remain unclear. Here, using a mouse model of ICC, we found that hepatic macrophages called Kupffer cells transiently congregate around the central veins in the liver and express the Notch ligand Jagged-1 coincident with Notch activation in pericentral hepatocytes. Depletion of Kupffer cells prevents the Notch-mediated cell-fate conversion of hepatocytes to biliary lineage cells, inducing hepatocyte apoptosis and increasing mortality in mice. These findings will be useful for uncovering the pathogenic mechanism of ICC and developing prevenient and therapeutic strategies for this refractory disease.

Kupffer Cell p38 Mitogen-Activated Protein Kinase Signaling Drives Postburn Hepatic Damage and Pulmonary Inflammation When Alcohol Intoxication Precedes Burn Injury.

Clinical and animal studies demonstrate that alcohol intoxication at the time of injury worsens postburn outcome. The purpose of this study was to determine the role and mechanism of Kupffer cell derangement in exacerbating postburn end organ damage in alcohol-exposed mice. Interventional study. Research Institute. Male C57BL/6 mice. Alcohol administered 30 minutes before a 15% scald burn injury. Antecedent Kupffer cell depletion with clodronate liposomes (0.5 mg/kg). p38 mitogen-activated protein kinase inhibition via SB203580 (10 mg/kg). Kupffer cells were isolated 24 hours after injury and analyzed for p38 activity and interleukin-6 production. Intoxicated burned mice demonstrated a two-fold (p < 0.05) elevation of Kupffer cell p38 activation relative to either insult alone, and this corresponded to a 43% (p < 0.05) increase in interleukin-6 production. Depletion of Kupffer cells attenuated hepatic damage as seen by decreases of 53% (p < 0.05) in serum alanine aminotransferase and 74% (p < 0.05) in hepatic triglycerides, as well as a 77% reduction (p < 0.05) in serum interleukin-6 levels compared to matched controls. This mitigation of hepatic damage was associated with a 54% decrease (p < 0.05) in pulmonary neutrophil infiltration and reduced alveolar wall thickening by 45% (p < 0.05). In vivo p38 inhibition conferred nearly identical hepatic and pulmonary protection after the combined injury as mice depleted of Kupffer cells. Intoxication exacerbates postburn hepatic damage through p38-dependent interleukin-6 production in Kupffer cells.

FcγRIIB on liver sinusoidal endothelial cells is essential for antibody-induced GPVI ectodomain shedding in mice

AbstractThe activating platelet collagen receptor glycoprotein VI (GPVI) is a promising antithrombotic target because of its central role in arterial thrombosis and its minor relevance for normal hemostasis. The receptor can be specifically targeted by antibodies and irreversibly downregulated in circulating platelets in vivo, resulting in long-term antithrombotic protection in mice. This GPVI immunodepletion predominantly occurs through ectodomain shedding, which is accompanied by a transient drop in peripheral platelet counts. Mechanistic studies on this targeted GPVI loss have been hampered because it cannot be reproduced in isolated platelets in vitro. Here we show that both the transient thrombocytopenia and GPVI ectodomain shedding depend on the Fc portion of the anti-GPVI antibody and its interaction with the inhibitory Fcγ receptor (FcγR)IIB. In wild-type, but not Fcgr2b−/− mice, anti–GPVI-opsonized platelets became transiently trapped in the liver followed by the appearance of the soluble GPVI ectodomain in the plasma. Depletion of Kupffer cells neither affected anti–GPVI-induced platelet accumulation nor GPVI shedding, demonstrating that the other major FcγRIIB-expressing cell type, liver sinusoidal endothelial cells, is required for both processes to occur. These results reveal a novel and unexpected function of hepatic FcγRIIB in the targeted downregulation of GPVI in vivo.

Resolvin D1 protects the liver from ischemia/reperfusion injury by enhancing M2 macrophage polarization and efferocytosis

Resolution of inflammation is an active process involving a novel category of lipid factors known as specialized pro-resolving lipid mediators, which includes Resolvin D1 (RvD1). While accumulating evidence suggests that RvD1 counteracts proinflammatory signaling and promotes resolution, the specific cellular targets and mechanisms of action of RvD1 remain largely unknown. In the present study, we investigated the role and molecular mechanisms of RvD1 in ischemia/reperfusion (IR)-induced sterile liver inflammation. Male C57BL/6 mice underwent 70% hepatic ischemia for 60min, followed by reperfusion. RvD1 (5, 10, and 15μg/kg, i.p.) was administered to the mice 1h before ischemia and then immediately prior to reperfusion. RvD1 attenuated IR-induced hepatocellular damage and the proinflammatory response. In purified Kupffer cells (KCs) from mice exposed to IR, the levels of M1 marker genes (Nos2a and Cd40) increased, while those of M2 marker genes (Arg1, Cd206, and Mst1r) decreased, demonstrating a proinflammatory shift. RvD1 markedly attenuated these changes. Depletion of KCs by liposome clodronate abrogated the effects of RvD1 on proinflammatory mediators and macrophage polarization. In addition, RvD1 attenuated increases in myeloperoxidase activity and Cxcl1 and Cxcl2 mRNA expression. RvD1 markedly augmented the efferocytic activity of KCs, as indicated by increases in F4/80+Gr-1+ cells in the liver. However, antagonist pretreatment or gene silencing of the RvD1 receptor, ALX/FPR2, abrogated the anti-inflammatory and pro-resolving actions of RvD1. These data indicate that RvD1 ameliorates IR-induced liver injury, and this protection is associated with enhancement of M2 polarization and efferocytosis via ALX/FPR2 activation.

CD205-TLR9-IL-12 axis contributes to CpG-induced oversensitive liver injury in HBsAg transgenic mice by promoting the interaction of NKT cells with Kupffer cells

Gut-derived bacterial products contribute to liver inflammation and injury during chronic hepatitis B virus infection; however, the underlying mechanisms remain obscure. In this study, hepatitis B surface antigen transgenic (HBs-Tg) mice and their wild-type (WT) control C57BL/6 mice were injected with CpG-oligodeoxynucleotides (ODNs) to mimic the translocation of gut microbial products into the systemic circulation. We found that, compared with the WT mice, the HBs-Tg mice were oversensitive to CpG-ODN-induced liver injury, which was dependent on natural killer T (NKT) cells. CpG-ODN injection enhanced the expression of Fas ligand (FasL) on NKT cells. In addition, hepatocytes from the HBs-Tg mice expressed higher levels of Fas than did those from the WT mice, which was further augmented by CpG-ODN. Interaction of Fas and FasL was involved in the cytotoxicity of NKT cells against hepatocytes in the HBs-Tg mice. Moreover, Kupffer cells in the HBs-Tg mice expressed higher levels of CD205 and produced greater amounts of interleukin (IL)-12 than did those in the WT mice. Finally, the depletion of Kupffer cells, neutralization of IL-12 or specific silencing of CD205 on Kupffer cells significantly inhibited CpG-ODN-induced liver injury and NKT activation in the HBs-Tg mice. Our data suggest that CD205-expressing Kupffer cells respond to CpG-ODNs and subsequently release IL-12 to promote NKT cell activation. Activated NKT cells induce liver damage through the Fas signaling pathway in HBs-Tg mice.

Endoplasmic reticulum stress of Kupffer cells involved in the conversion of natural regulatory T cells to Th17 cells in liver ischemia-reperfusion injury.

Our previous studies have shown that regulatory T cells (Tregs) are reduced and Th17 cells are elevated in liver insults. Recent studies have indicated the critical role of endoplasmic reticulum (ER) stress of Kupffer cells (KCs) in evoking liver inflammation following reperfusion. The objective of this study was to investigate the role of ER stress of KCs in the conversion of Tregs to Th17 cells and the effect on liver ischemia-reperfusion injury. The partial warm liver ischemia-reperfusion injury mouse model was adopted. ER stress of KCs and the frequency of Tregs and Th17 cells following reperfusion were analyzed. Apart from depletion and adoptive transfer of KCs, KCs were isolated from ischemic lobes and co-cultured with Tregs to study the effect of KCs on Tregs and Th17 cells. It was found that KCs induced ER stress, decreased natural Tregs (nTregs), and increased Th17 cells after reperfusion. Depletion of KCs modulated the reduction of nTregs and elevation of Th17 cells. Co-culture with stressed KCs led to the reduction in nTregs and elevation of Th17 cells. This effect was suppressed by anti-interleukin-6. Adoptive transfer of these stressed KCs resulted in the reduction in nTregs and elevation of Th17 cells and caused liver injury. Endoplasmic reticulum stress of KCs contributed to the conversion of nTregs to Th17 cells due to interleukin-6, resulting in the worsening of liver insult.

Cellular distribution of injected PLGA-nanoparticles in the liver

The cellular fate of nanoparticles in the liver is not fully understood. Because the effectiveness and safety of nanoparticles in liver therapy depends on targeting nanoparticles to the right cell populations, this study aimed to determine a relative distribution of PLGA-nanoparticles (sizes 271±1.4 nm) among liver cells in vivo. We found that Kupffer cells were the major cells that took up nanoparticles, followed by liver sinusoidal endothelial cells and hepatic stellate cells. Nanoparticles were found in only 7% of hepatocytes. Depletion of Kupffer cells by clodronate liposomes increased nanoparticle retention in liver sinusoidal endothelial cells and hepatic stellate cells, but not in hepatocytes. It is importantly suggested that studies of drug-loaded nanoparticle delivery to the liver have to demonstrate not only uptake of nanoparticles by the target cell type but also non-uptake by other cell types to assess their effect as well as ensure their safety.

Bone marrow-derived monocytes give rise to self-renewing and fully differentiated Kupffer cells.

Self-renewing tissue-resident macrophages are thought to be exclusively derived from embryonic progenitors. However, whether circulating monocytes can also give rise to such macrophages has not been formally investigated. Here we use a new model of diphtheria toxin-mediated depletion of liver-resident Kupffer cells to generate niche availability and show that circulating monocytes engraft in the liver, gradually adopt the transcriptional profile of their depleted counterparts and become long-lived self-renewing cells. Underlining the physiological relevance of our findings, circulating monocytes also contribute to the expanding pool of macrophages in the liver shortly after birth, when macrophage niches become available during normal organ growth. Thus, like embryonic precursors, monocytes can and do give rise to self-renewing tissue-resident macrophages if the niche is available to them.

Persistence of cirrhosis is maintained by intrahepatic regulatory T cells that inhibit fibrosis resolution by regulating the balance of tissue inhibitors of metalloproteinases and matrix metalloproteinases.

Fibrosis is the result of the abnormal accumulation of the extracellular matrix and ineffective clearance of fibroplasia. CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) are immunosuppressive lymphocytes that are highly expressed in the fibrotic tissues and peripheral blood of patients with cirrhosis or hepatocellular carcinoma. The role of Tregs in the progression of liver fibrosis is not well understood. Our experiments reveal that abundant of Tregs was scattered around sites of fibroplasia. Conversely, the depletion of Tregs promoted the resolution of liver fibrosis. As a consequence of Tregs depletion, the expression of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) was altered; mmp9 and timp1 were reduced, whereas mmp2 and mmp14 were enhanced. The mmp9/timp1, mmp13/timp1, and mmp14/timp2 ratios were significantly increased in association with fibrosis resolution. Kupffer cells (KCs) are the main source of MMP. We observed that when KCs were cocultured with Tregs, the Tregs were able to inhibit MMP expression of KCs even at a low ratio; and anti-transforming growth factor-β (TGF-β) significantly reversed the inhibition of Tregs on MMP. Meanwhile, we also found that after Tregs depletion, TGF-β levels decreased in the mice liver, unlike in fibrosis. Furthermore, double depletion of both KCs and Tregs did not cause fiber resolution in mice. Thus, our results demonstrate that the persistence of liver cirrhosis is maintained by increased Tregs in the sites of fibroplasia and the subsequent regulation of the MMP/TIMP balance and that the suppression of KC-mediated MMP expression contributed to the regulatory process.

Kupffer cells modulate hepatic fatty acid oxidation during infection with PR8 influenza

In response to infection, patients with inborn errors of metabolism may develop a functional deterioration termed metabolic decompensation. The biochemical hallmarks of this disruption of metabolic homeostasis are disease specific and may include acidosis, hyperammonemia or hypoglycemia. In a model system previously published by our group, we noted that during influenza infection, mice displayed a depression in hepatic mitochondrial enzymes involved in nitrogen metabolism. Based on these findings, we hypothesized that this normal adaptation may extend to other metabolic pathways, and as such, may impact various inborn errors of metabolism. Since the liver is a critical organ in inborn errors of metabolism, we carried out untargeted metabolomic profiling of livers using mass spectrometry in C57Bl/6 mice infected with influenza to characterize metabolic adaptation. Pathway analysis of metabolomic data revealed reductions in CoA synthesis, and long chain fatty acyl CoA and carnitine species. These metabolic adaptations coincided with a depression in hepatic long chain β-oxidation mRNA and protein. To our surprise, the metabolic changes observed occurred in conjunction with a hepatic innate immune response, as demonstrated by transcriptional profiling and flow cytometry. By employing an immunomodulation strategy to deplete Kupffer cells, we were able to improve the expression of multiple genes involved in β-oxidation. Based on these findings, we are the first to suggest that the role of the liver as an immunologic organ is central in the pathophysiology of hepatic metabolic decompensation in inborn errors of metabolism due to respiratory viral infection.

Abstract 698: Increases Reticulated Platelets due to Enhanced Proliferation and Expansion of Bone Marrow Megakaryocyte Progenitors Accelerates Atherosclerosis in Diabetes

Diabetes (type 1 &amp; 2) is a major risk factor for cardiovascular disease which represents the major cause of mortality in this group. Patients with diabetes present with reticulated thrombocytosis (increased immature platelets), which lower the efficacy of current anti-platelet therapies. We hypothesized that the reticulated thrombocytosis observed in people with diabetes plays an important role in atherogenesis. Thus, we investigated the mechanisms contributing to increased reticulated platelets in diabetes. Streptozotocin induced diabetic mice had significantly higher level (2-fold) of reticulated platelets. This was paralleled by an increase in the population of megakaryocyte progenitors (MkPs) and megakaryocytes in the bone marrow (BM). Diabetes caused an increase in circulating thrombopoietin (TPO) without altering the expression of the TPO receptor (c-MPL) on any of the BM progenitor cells or circulating platelets. TPO expression is generally upregulated by Kupffer cell derived interleukin-6 (IL-6). We found more Kupffer cells in the liver of diabetic mice which expressed higher levels of cell surface RAGE (Receptor for Advanced Glycated End-products) and produced more IL-6. Depletion of Kupffer cells using clodronate liposomes normalized the levels of total and reticulated platelets along with MkPs in the BM. Rage-/- BM transplantation (BMT) into mice that were then made diabetic were protected from diabetes-induced thrombocytosis and MkP expansion. Kupffer cells from diabetic Rage-/- BMT mice failed to express IL-6 and plasma TPO levels remained similar to the non-diabetic mice. IL-6-/- BMT mice were also protected from diabetes-induced thrombocytosis. Together, we identified a role for RAGE in the liver Kupffer cells of diabetic mice that triggers IL-6 expression, which in-turn promotes TPO production. TPO then enhances proliferation and expansion of MkPs in the BM, resulting in an increase in the abundance of reticulated platelets. Using BM from a genetic model (Bcl-xPlt20) of low platelets transplanted into Ldlr+/- mice we found that lower circulating platelets resulted in smaller atherosclerotic lesions. Our data suggests that increased platelet production contributes to accelerated atherogenesis in diabetes.

TLR2 and TLR9 contribute to alcohol-mediated liver injury through induction of CXCL1 and neutrophil infiltration.

Although previous studies reported the involvement of the TLR4-TRIF pathway in alcohol-induced liver injury, the role of TLR2 and TLR9 signaling in alcohol-mediated neutrophil infiltration and liver injury has not been elucidated. Since alcohol binge drinking is recognized to induce more severe form of alcohol liver disease, we used a chronic-binge ethanol-feeding model as a mouse model for early stage of alcoholic hepatitis. Whereas a chronic-binge ethanol feeding induced alcohol-mediated liver injury in wild-type mice, TLR2- and TLR9-deficient mice showed reduced liver injury. Induction of neutrophil-recruiting chemokines, including Cxcl1, Cxcl2, and Cxcl5, and hepatic neutrophil infiltration were increased in wild-type mice, but not in TLR2- and TLR9-deficient mice. In vivo depletion of Kupffer cells (KCs) by liposomal clodronate reduced liver injury and the expression of Il1b, but not Cxcl1, Cxcl2, and Cxcl5, suggesting that KCs are partly associated with liver injury, but not neutrophil recruitment, in a chronic-binge ethanol-feeding model. Notably, hepatocytes and hepatic stellate cells (HSCs) produce high amounts of CXCL1 in ethanol-treated mice. The treatment with TLR2 and TLR9 ligands synergistically upregulated CXCL1 expression in hepatocytes. Moreover, the inhibitors for CXCR2, a receptor for CXCL1, and MyD88 suppressed neutrophil infiltration and liver injury induced by chronic-binge ethanol treatment. Consistent with the above findings, hepatic CXCL1 expression was highly upregulated in patients with alcoholic hepatitis. In a chronic-binge ethanol-feeding model, the TLR2 and TLR9-dependent MyD88-dependent pathway mediates CXCL1 production in hepatocytes and HSCs; the CXCL1 then promotes neutrophil infiltration into the liver via CXCR2, resulting in the development of alcohol-mediated liver injury.

Kupffer Cell p38 MAPK Drives Hepatic Damage and Pulmonary Inflammation after Intoxication and Burn Injury

Alcohol intoxication precedes half of adult burn injuries and leads to worsened clinical outcomes. We recently reported intoxication before burn alters the gut‐liver axis which drives pulmonary inflammation through interleukin‐6 (IL‐6) and we now seek to determine the mechanisms of this aberrant response. C57/BL6 mice were given ethanol (1.2 g/kg) by oral gavage 30 min prior to a 15% scald burn. Depletion of Kupffer cells (KCs) was achieved with clodronate liposomes (0.5 mg/kg). KCs were isolated and analyzed for p38 MAPK ± LPS stimulation (100 ng/ml) and p38 inhibition (SB203580, 20 μM). In vivo p38 inhibition was achieved via intraperitoneal injection of SB203580 (100 mg/kg) 30 min after injury. The absence of KCs attenuated hepatic damage as seen by decreases of 53% (p&lt;0.05) in serum ALT, 37% (p&lt;0.05) in hepatic triglycerides, as well as a 77% reduction (p&lt;0.05) in serum IL‐6 levels compared to intoxicated burned mice receiving empty liposomes. This mitigation of hepatic damage was associated with a 34% decrease (p&lt;0.05) in pulmonary neutrophil infiltration and attenuated alveolar wall thickening. KC's isolated from intoxicated burned mice had a 2‐fold (p&lt;0.05) and 3‐fold (p&lt;0.05) elevation of baseline and LPS‐stimulated p38 activation, respectively. This corresponded to a 2‐fold (p&lt;0.05) increase in IL‐6 which was decreased by 80% (p&lt;0.05) when p38 was inhibited. In vivo p38 inhibition after injury conferred nearly identical hepatic and pulmonary protection after the combined injury as mice depleted of KCs suggesting p38 signaling in KCs may serve as a therapeutic target in this common clinical scenario. This work was supported by NIH R01AA012034 (EJK), F30AA022856 (MMC), T32AA013527 (EJK) and the Falk Foundation.

Effects of Kupffer cell inactivation on graft survival and liver regeneration after partial liver transplantation in rats

Gadolinium chloride (GdCl3) selectively inactivates Kupffer cells and protects against ischemia/reperfusion and endotoxin injury. However, the effect of Kupffer cell inactivation on liver regeneration after partial liver transplantation (PLTx) is not clear. This study was to investigate the role of GdCl3 pretreatment in graft function after PLTx, and to explore the potential mechanism involved in this process. PLTx (30% partial liver transplantation) was performed using Kamada's cuff technique, without hepatic artery reconstruction. Rats were randomly divided into the control low-dose (5 mg/kg) and high-dose (10 mg/kg) GdCl3 groups. Liver injury was determined by the plasma levels of alanine aminotransferase and aspartate aminotransferase, liver regeneration by PCNA staining and BrdU uptake, apoptosis by TUNEL assay. IL-6 and p-STAT3 levels were measured by ELISA and Western blotting. GdCl3 depleted Kupffer cells and decreased animal survival rates, but did not significantly affect alanine aminotransferase and aspartate aminotransferase (P>0.05). GdCl3 pretreatment induced apoptosis and inhibited IL-6 overexpression and STAT3 phosphorylation after PLTx in graft tissues. Kupffer cells may contribute to the liver regeneration after PLTx through inhibition of apoptosis and activation of the IL-6/p-STAT3 signal pathway.

Invariant NKT cells promote alcohol-induced steatohepatitis through interleukin-1β in mice

It was reported that alcohol consumption activated the NLRP3 inflammasome in Kupffer cells, leading to mature interleukin (IL)-1β release in alcoholic liver injury; however, how IL-1β promotes liver injury remains unclear. We investigated the role of IL-1β in alcoholic steatohepatitis by using a chronic plus single-binge ethanol consumption mouse model. Here, liver steatosis was accompanied by notably increased invariant natural killer T (iNKT) cell numbers and activation, and iNKT-deficient Jα18(-/-) mice developed less alcohol-induced steatosis, with reduced liver inflammation and neutrophil infiltration. Kupffer cells and IL-1β were required for the hepatic iNKT accumulation, as either blocking IL-1β signaling with a recombinant IL-1 receptor antagonist (IL-1Ra), depleting Kupffer cells by clodronate liposomes, or specifically silencing IL-1β in Kupffer cells by nanoparticle-encapsulated siRNA, resulted in inhibited hepatic iNKT cell accumulation and activation, as well as amelioration of alcoholic fatty liver. In addition, IL-1β overexpression in hepatocytes was sufficient to compensate for Kupffer cell depletion. Increased gene and protein expression of mature IL-1β correlated with elevated expression of the NLRP3 inflammasome components NLRP3, ASC, and cleaved caspase-1 in Kupffer cells from ethanol-exposed wild-type mice. NLRP3 deficiency led to the attenuation of alcoholic steatosis, similarly as Kupffer cell depletion, almost without hepatic NKT cells. After alcohol-exposure Kupffer cell-derived IL-1β triggered by NLRP3 activation, recruits and activates hepatic iNKT cells, subsequently promoting liver inflammation and neutrophil infiltration, and inducing alcoholic liver injury.

Depletion of Kupffer cells attenuates systemic insulin resistance, inflammation and improves liver autophagy in high-fat diet fed mice

The objective of this study was to reveal the exact role of Kupffer cells in the diet-induced insulin resistance, inflammation and liver autophagy. C57BL/6j male mice were fed with either chow diet or high-fat diet (HFD) for 12 weeks. Meanwhile, HFD feeding mice received an intraperitoneal injection of either 0.2% GdCl3 solution (20mg/kg) twice a week to deplete Kupffer cells or natural saline (5mL/kg) as control. The mRNA expressions of Kupffer cells markers (CD68 and F4/80), insulin sensitivity, TNF-α concentration and NF-κB activation and parameters of autophagy were assessed. Results demonstrated that CD68 and F4/80 mRNA expressions in the liver were up-regulated in HFD fed animals, while significantly reduced after GdCl3 administration. HFD feeding led to insulin resistance and TNF-α level and activation of NF-κB in insulin-sensitive tissues (liver, adipose tissue and skeletal muscle) were significantly elevated. Interestingly, alterations above were reversed by varying degrees but significantly after Kupffer cells depletion. Furthermore, western blot showed hepatic LC3-II as well as phosphorylation of AMPK in liver and skeletal muscle were significantly lower in mice fed HFD, and these changes dramatically ameliorated by GdCl3 treating. In conclusion, selective depletion of Kupffer cells significantly attenuated diet-induced insulin resistance, inflammation and promoted liver autophagy. Strategies targeting Kupffer cells function or autophagic processes could be a promising approach to counteract diet induced obesity and related metabolic disorders.

Activation of NLRP3 and AIM2 inflammasomes in Kupffer cells in hepatic ischemia/reperfusion.

Inflammasome activation by danger signals in ischemia/reperfusion (I/R) injury is responsible for the sterile inflammatory response. Signals triggering formation and activation of the inflammasome involve the generation of oxidative stress. The aim of this study was to examine the molecular mechanisms of inflammasome activation and the involvement of reactive oxygen species in hepatic I/R. I/R induced the formation of nucleotide-binding domain leucine-rich repeat containing family pyrin domain containing 3 (NLRP3) and absent in melanoma 2 (AIM2) inflammasomes and the subsequent serum release of interleukin 1β. Pannexin-1 inhibitor and anti-cathepsin B antibody attenuated I/R-induced inflammasome activation and hepatic injury. The expression of the thioredoxin-interacting protein gene and the interaction between NLRP3 and the thioredoxin-interacting protein increased after I/R. Treatment with the antioxidant N-acetylcysteine significantly attenuated protein conversion of interleukin 1β after hepatic I/R. Moreover, pannexin-1 protein expression and cathepsin B release were strongly attenuated by N-acetylcysteine. The depletion of Kupffer cells with gadolinium chloride markedly decreased NLRP3 and AIM2 inflammasome expression and activation of their signaling pathways, and also reduced the level of caspase-1 protein in F4/80-positive cells. Our findings suggest that reactive-oxygen-species-mediated activation of NLRP3 and AIM2 inflammasomes leads to I/R-induced inflammatory responses in which Kupffer cells play a crucial role.

Role of Preferential Cyclooxygenase-2 Inhibition by Meloxicam in Ischemia/Reperfusion Injury of the Rat Liver

Background: Ischemia/reperfusion injury (IRI) is one of the major clinical problems in liver and transplant surgery. Livers subjected to warm ischemia in vivo often show a severe dysfunction and the release of numerous inflammatory cytokines and arachidonic acid metabolites. Cyclooxygenase (COX)-2 is the inducible isoform of an intracellular enzyme that converts arachidonic acid into prostaglandins. The aim of the study was to evaluate the effect of COX-2 inhibition and the role of Kupffer cells in IRI of the liver. Methods: Male Wistar rats [250- 280 g body weight (BW)] were anesthetized and subjected to 30-min warm ischemia of the liver (Pringle's maneuver) and 60-min reperfusion after median laparotomy. The I/R group received no additional treatment. In the COX-2 inhibitor (COX-2I) group, the animals received 1 mg/kg BW meloxicam prior to operation. Gadolinium chloride (GdCl₃) (10 mg/kg BW) was given 24 h prior to operation in the GdCl₃ and GdCl₃ + COX-2I groups for the selective depletion of Kupffer cells. The GdCl₃ + COX-2I group received both GdCl₃ and meloxicam treatment prior to operation. Blood and liver samples were obtained at the end of the experiments for further investigations. Results: After 30 min of warm ischemia in vivo, severe hepatocellular damage was observed in the I/R group. These impairments could be significantly prevented by the selective COX-2 inhibition and the depletion of Kupffer cells. Alanine aminotransferase was significantly reduced upon meloxicam and GdCl₃ treatment compared to the I/R group: I/R, 3,240 ± 1,262 U/l versus COX-2I, 973 ± 649 U/l, p < 0.001; I/R versus GdCl₃, 1,611 ± 600 U/l, p < 0.05, and I/R versus GdCl₃ + COX-2I, 1,511 ± 575 U/l, p < 0.01. Plasma levels of tumor necrosis factor alpha (TNF-α) were significantly reduced in the COX-2I treatment group compared to I/R (3.5 ± 1.5 vs. 16.3 ± 11.7 pg/ml, respectively; p < 0.05). Similarly, the amount of TxB₂, a marker for COX-2 metabolism, was significantly reduced in the meloxicam treatment groups compared to the I/R group: I/R, 22,500 ± 5,210 pg/ml versus COX-2I, 1,822 ± 938 pg/ml, p < 0.001, and I/R versus GdCl₃ + COX-2I, 1,530 ± 907 pg/ml, p < 0.001. All values are given as mean ± SD (n = 6). Conclusion: These results suggest that the inhibition of COX-2 suppressed the initiation of an inflammatory cascade by attenuating the release of TNF-α, which is an initiator of the inflammatory reaction in hepatic IRI. Therefore, we conclude that preferential inhibition of COX-2 is a possible therapeutic approach against warm IRI of the liver.

Fatty Acid Elongation in Non-Alcoholic Steatohepatitis and Hepatocellular Carcinoma

Non-alcoholic steatohepatitis (NASH) represents a risk factor for the development of hepatocellular carcinoma (HCC) and is characterized by quantitative and qualitative changes in hepatic lipids. Since elongation of fatty acids from C16 to C18 has recently been reported to promote both hepatic lipid accumulation and inflammation we aimed to investigate whether a frequently used mouse NASH model reflects this clinically relevant feature and whether C16 to C18 elongation can be observed in HCC development. Feeding mice a methionine and choline deficient diet to model NASH not only increased total hepatic fatty acids and cholesterol, but also distinctly elevated the C18/C16 ratio, which was not changed in a model of simple steatosis (ob/ob mice). Depletion of Kupffer cells abrogated both quantitative and qualitative methionine-and-choline deficient (MCD)-induced alterations in hepatic lipids. Interestingly, mimicking inflammatory events in early hepatocarcinogenesis by diethylnitrosamine-induced carcinogenesis (48 h) increased hepatic lipids and the C18/C16 ratio. Analyses of human liver samples from patients with NASH or NASH-related HCC showed an elevated expression of the elongase ELOVL6, which is responsible for the elongation of C16 fatty acids. Taken together, our findings suggest a detrimental role of an altered fatty acid pattern in the progression of NASH-related liver disease.