Murine Kupffer cells are protective in total hepatic ischemia/reperfusion injury with bowel congestion through IL-10

Hepatic stellate cells undermine the allostimulatory function of liver myeloid dendritic cells via STAT3-dependent induction of IDO

Hepatic stellate cells (HSCs) are critical for hepatic wound repair and tissue remodeling. They also produce cytokines and chemokines that may contribute to the maintenance of hepatic immune homeostasis and the inherent tolerogenicity of the liver. The functional relationship between HSCs and the professional migratory APCs in the liver, that is, dendritic cells (DCs), has not been evaluated. In this article, we report that murine liver DCs colocalize with HSCs in vivo under normal, steady-state conditions, and cluster with HSCs in vitro. In vitro, HSCs secrete high levels of DC chemoattractants, such as MΙP-1α and MCP-1, as well as cytokines that modulate DC activation, including TNF-α, IL-6, and IL-1β. Culture of HSCs with conventional liver myeloid (m) DCs resulted in increased IL-6 and IL-10 secretion compared with that of either cell population alone. Coculture also resulted in enhanced expression of costimulatory (CD80, CD86) and coinhibitory (B7-H1) molecules on mDCs. HSC-induced mDC maturation required cell-cell contact and could be blocked, in part, by neutralizing MΙP-1α or MCP-1. HSC-induced mDC maturation was dependent on activation of STAT3 in mDCs and, in part, on HSC-secreted IL-6. Despite upregulation of costimulatory molecules, mDCs conditioned by HSCs demonstrated impaired ability to induce allogeneic T cell proliferation, which was independent of B7-H1, but dependent upon HSC-induced STAT3 activation and subsequent upregulation of IDO. In conclusion, by promoting IDO expression, HSCs may act as potent regulators of liver mDCs and function to maintain hepatic homeostasis and tolerogenicity.

Matrix metalloprotease 9 promotes liver recovery from ischemia and reperfusion injury

BACKGROUND

Matrix metalloprotease (MMP) 9 has been always considered as a destructor of extracellular matrix, promoting liver injury and metastasis of carcinoma. In this study, we investigated the role of MMP-9 in liver wound healing from ischemia and reperfusion injury (IRI).

METHODS

MMP9-/- mice were used to establish partial hepatic IRI model. Serum alanine aminotransferase and hepatic cytokines (tumor necrosis factor alpha, interleukin [IL]-1β, IL-10, and transforming growth factor beta [TGF-β]) levels were analyzed after IRI. Hepatic stellate cells were isolated from wild-type mice to determine the effect of MMP-9 on TGF-β activation. In addition, the effect of TGF-β on liver wound healing from IRI was determined.

RESULTS

Liver recovery from IRI was impaired in MMP9-/- mice, which was described as elevated serum alanine aminotransferase, hepatic tumor necrosis factor alpha, and IL-1β levels. Meanwhile, TGF-β-active protein level was decreased in the liver of MMP9-/- mice. In vitro test, the activation of TGF-β was suppressed in the presence of anti-MMP-9 monoclonal antibody. TGF-β treatment promoted liver recovery from IRI in MMP9-/- mice.

CONCLUSIONS

MMP-9 promoted liver recovery from IRI by activating TGF-β. Thus, MMP-9 plays dual roles (bad and good) in liver IRI, depending on the timing.

Nilotinib protects the murine liver from ischemia/reperfusion injury

BACKGROUND & AIMS

The mitogen-activated protein kinases (MAPKs), c-Jun N-terminal kinase (JNK), and p38, mediate liver ischemia/reperfusion (I/R) injury via cell death and inflammatory cytokine expression, respectively. Nilotinib is an orally available receptor tyrosine kinase inhibitor used for chronic myelogenous leukemia that also has in vitro activity against JNK and p38. In this study, we examine its therapeutic potential against hepatic I/R injury.

METHODS

The effects of nilotinib on liver I/R injury were tested using a murine model of warm, segmental liver I/R. Serum ALT was measured and livers were analyzed by histology, RT-PCR, Western blot, and flow cytometry. The in vitro effects of nilotinib on hepatocyte and non-parenchymal cell (NPC) MAPK activation and cytokine production were also tested.

RESULTS

Mice receiving nilotinib had markedly lower serum ALT levels and less histologic injury and apoptosis following liver I/R. Nilotinib did not inhibit its known receptor tyrosine kinases. Nilotinib lowered intrahepatic expression of IL-1β, IL-6, MCP-1, and MIP-2 and systemic levels of IL-6, MCP-1, and TNF. Nilotinib reduced NPC activation of p38 MAPK signaling and decreased the recruitment of inflammatory monocytes and their production of TNF. Nilotinib attenuated JNK phosphorylation and hepatocellular apoptosis. In vitro, nilotinib demonstrated direct inhibition of JNK activation in isolated hepatocytes cultured under hypoxic conditions, and blocked activation of p38 MAPK and cytokine production by stimulated NPCs.

CONCLUSIONS

Nilotinib lowers both liver JNK activation and NPC p38 MAPK activation and may be useful for ameliorating liver I/R injury in humans.

Kupffer cells ameliorate hepatic insulin resistance induced by high-fat diet rich in monounsaturated fatty acids: the evidence for the involvement of alternatively activated macrophages

BACKGROUND

Resident macrophages (Kupffer cells, KCs) in the liver can undergo both pro- or anti-inflammatory activation pathway and exert either beneficiary or detrimental effects on liver metabolism. Until now, their role in the metabolically dysfunctional state of steatosis remains enigmatic. Aim of our study was to characterize the role of KCs in relation to the onset of hepatic insulin resistance induced by a high-fat (HF) diet rich in monounsaturated fatty acids.

METHODS

Male Wistar rats were fed either standard (SD) or high-fat (HF) diet for 4 weeks. Half of the animals were subjected to the acute GdCl3 treatment 24 and 72 hrs prior to the end of the experiment in order to induce the reduction of KCs population. We determined the effect of HF diet on activation status of liver macrophages and on the changes in hepatic insulin sensitivity and triacylglycerol metabolism imposed by acute KCs depletion by GdCl3.

RESULTS

We found that a HF diet rich in MUFA itself triggers an alternative but not the classical activation program in KCs. In a steatotic, but not in normal liver, a reduction of the KCs population was associated with a decrease of alternative activation and with a shift towards the expression of pro-inflammatory activation markers, with the increased autophagy, elevated lysosomal lipolysis, increased formation of DAG, PKCε activation and marked exacerbation of HF diet-induced hepatic insulin resistance.

CONCLUSIONS

We propose that in the presence of a high MUFA content the population of alternatively activated resident liver macrophages may mediate beneficial effects on liver insulin sensitivity and alleviate the metabolic disturbances imposed by HF diet feeding and steatosis. Our data indicate that macrophage polarization towards an alternative state might be a useful strategy for treating type 2 diabetes.

Synthetic Toll like receptor-4 (TLR-4) agonist peptides as a novel class of adjuvants

Background

Adjuvants serve as catalysts of the innate immune response by initiating a localized site of inflammation that is mitigated by the interactions between antigens and toll like receptor (TLR) proteins. Currently, the majority of vaccines are formulated with aluminum based adjuvants, which are associated with various side effects. In an effort to develop a new class of adjuvants, agonists of TLR proteins, such as bacterial products, would be natural candidates. Lipopolysaccharide (LPS), a major structural component of gram negative bacteria cell walls, induces the systemic inflammation observed in septic shock by interacting with TLR-4. The use of synthetic peptides of LPS or TLR-4 agonists, which mimic the interaction between TLR-4 and LPS, can potentially regulate cellular signal transduction pathways such that a localized inflammatory response is achieved similar to that generated by adjuvants.

Methodology/Principal Findings

We report the identification and activity of several peptides isolated using phage display combinatorial peptide technology, which functionally mimicked LPS. The activity of the LPS-TLR-4 interaction was assessed by NF-κB nuclear translocation analyses in HEK-BLUE™-4 cells, a cell culture model that expresses only TLR-4, and the murine macrophage cell line, RAW264.7. Furthermore, the LPS peptide mimics were capable of inducing inflammatory cytokine secretion from RAW264.7 cells. Lastly, ELISA analysis of serum from vaccinated BALB/c mice revealed that the LPS peptide mimics act as a functional adjuvant.

Conclusions/Significance

Our data demonstrate the identification of synthetic peptides that mimic LPS by interacting with TLR-4. This LPS mimotope-TLR-4 interaction will allow for the development and use of these peptides as a new class of adjuvants, namely TLR-4 agonists.

Cell biology of ischemia/reperfusion injury

Disorders characterized by ischemia/reperfusion (I/R), such as myocardial infarction, stroke, and peripheral vascular disease, continue to be among the most frequent causes of debilitating disease and death. Tissue injury and/or death occur as a result of the initial ischemic insult, which is determined primarily by the magnitude and duration of the interruption in the blood supply, and then subsequent damage induced by reperfusion. During prolonged ischemia, ATP levels and intracellular pH decrease as a result of anaerobic metabolism and lactate accumulation. As a consequence, ATPase-dependent ion transport mechanisms become dysfunctional, contributing to increased intracellular and mitochondrial calcium levels (calcium overload), cell swelling and rupture, and cell death by necrotic, necroptotic, apoptotic, and autophagic mechanisms. Although oxygen levels are restored upon reperfusion, a surge in the generation of reactive oxygen species occurs and proinflammatory neutrophils infiltrate ischemic tissues to exacerbate ischemic injury. The pathologic events induced by I/R orchestrate the opening of the mitochondrial permeability transition pore, which appears to represent a common end-effector of the pathologic events initiated by I/R. The aim of this treatise is to provide a comprehensive review of the mechanisms underlying the development of I/R injury, from which it should be apparent that a combination of molecular and cellular approaches targeting multiple pathologic processes to limit the extent of I/R injury must be adopted to enhance resistance to cell death and increase regenerative capacity in order to effect long-lasting repair of ischemic tissues.

Ex vivo induced regulatory T cells regulate inflammatory response of Kupffer cells by TGF-beta and attenuate liver ischemia reperfusion injury

In the presence of TGF-β, CD4+CD62L+T cells can be induced to CD4+CD25+FoxP3+ regulatory T cells (iTregs). In our previous work, we have shown that adoptive transfer of iTregs promoted liver recovery from ischemia reperfusion injury (IRI). In this study, we examined the molecular mechanism underlying the liver IRI attenuation by iTregs in a mouse partial hepatic IRI model. We found that the population of hepatic Tregs decreased significantly at 24 h after reperfusion. Adoptive transfer of iTregs before IRI markedly increased the numbers of hepatic Tregs and attenuated liver IRI as indicated by reduced serum aminotransferases and proinflammatory cytokines, such as interleukin-1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α). Ex vivo study indicated that iTregs suppressed IL-1β and TNF-α expression, promoted transcription of interleukin-10 (IL-10), and elevated phosphorylation of SMAD3 in Kupffer cells (KCs). Furthermore, inhibition of TGF-β signaling by anti-TGF-β abolished the effects on KCs. Treatment with TGF-β suppressed matrix metalloprotease (MMP9) production in KCs and protected liver from IRI. In conclusion, our results suggest that iTregs play a critical role in hepatic IRI by regulating pro-inflammatory and anti-inflammatory function of KCs through TGF-β.

New insights into the role of macrophages in adipose tissue inflammation and Fatty liver disease: modulation by endogenous omega-3 Fatty Acid-derived lipid mediators

Obesity is causally linked to a chronic state of “low-grade” inflammation in adipose tissue. Prolonged, unremitting inflammation in this tissue has a direct impact on insulin-sensitive tissues (i.e., liver) and its timely resolution is a critical step toward reducing the prevalence of related co-morbidities such as insulin resistance and non-alcoholic fatty liver disease. This article describes the current state-of-the-art knowledge and novel insights into the role of macrophages in adipose tissue inflammation, with special emphasis on the progressive changes in macrophage polarization observed over the course of obesity. In addition, this article extends the discussion to the contribution of Kupffer cells, the liver resident macrophages, to metabolic liver disease. Special attention is given to the modulation of macrophage responses by omega-3-PUFAs, and more importantly by resolvins, which are potent anti-inflammatory and pro-resolving autacoids generated from docosahexaenoic and eicosapentaenoic acids. In fact, resolvins have been shown to work as endogenous “stop signals” in inflamed adipose tissue and to return this tissue to homeostasis by inducing a phenotypic switch in macrophage polarization toward a pro-resolving phenotype. Collectively, this article offers new views on the role of macrophages in metabolic disease and their modulation by endogenously generated omega-3-PUFA-derived lipid mediators.

Toll-like receptor 4 knockout mice are protected from endothelial overactivation in the absence of Kupffer cells after total hepatic ischemia/reperfusion

Kupffer cells (KCs) have been shown to be critical mediators of ischemia/reperfusion (I/R) injury in the murine liver. Using liposomal clodronate (LC), we found that KCs were protective in models of total hepatic ischemia with bowel congestion. We investigated the role of toll-like receptor 4 (TLR4) in the damage that occurs after I/R in KC-depleted livers. We injected 8-week-old C57BL/10J mice and C57BL/10ScN [toll-like receptor 4 knockout (TLR4KO)] mice with LC 48 hours before 35 minutes of warm hepatic ischemia with bowel congestion, which was followed by either 6 or 24 hours of reperfusion. The KC-depleted animals had increased mortality as well as a 10-fold increase in their aminotransferase levels that correlated with increases in centrilobular necrosis. These changes were absent in the TLR4KO animals. Lipopolysaccharide was bound extensively to endothelial cells after I/R, and this binding was diminished in the TLR4KO animals. In conjunction with this, there was an up-regulation of endothelial cell adhesion molecules in the LC-treated animals that was absent in the TLR4KO animals. Finally, there was a dramatic increase in the proinflammatory cytokine levels of the LC-treated animals, and the TLR4KO animals were protected against this increase. In conclusion, TLR4 promotes endothelial overactivation after I/R in the absence of KCs.

Liver ischemia and reperfusion injury: new insights into mechanisms of innate-adaptive immune-mediated tissue inflammation

Ischemia and reperfusion injury (IRI) is a dynamic process that involves two distinctive yet interrelated phases of ischemic organ damage and inflammation-mediated reperfusion injury. Although multiple cellular and molecular pathways contribute and regulate tissue/organ damage, integration of different players into a unified mechanism is warranted. The crosstalk between innate and adaptive immune systems plays a significant role in the pathogenesis of liver IRI. In this review, we focus on recent progress in the mechanism of liver innate immune activation by IR. Kupffer cells (KC), DCs, NK, as well as T cells initiate local inflammation response, the hallmark of IRI, by utilizing distinctive immune receptors to recognize and/or trigger various molecules, both endogenous and exogenous. The interlocked molecular signaling pathways in the context of multiple liver cell types, the IRI kinetics and positive versus negative regulatory loops in the innate immune activation process are discussed. Better appreciation of molecular interactions that mediate these intricate cascades, should allow for the development of novel therapeutic approached against IRI in liver transplant recipients.

Antigen-presenting cell function in the tolerogenic liver environment

The demands that are imposed on the liver as a result of its function as a metabolic organ that extracts nutrients and clears gut-derived microbial products from the blood are met by a unique microanatomical and immunological environment. The inherent tolerogenicity of the liver and its role in the regulation of innate and adaptive immunity are mediated by parenchymal and non-parenchymal antigen-presenting cells (APCs), cell-autonomous molecular pathways and locally produced factors. Here, we review the central role of liver APCs in the regulation of hepatic immune function and also consider how recent insights may be applied in strategies to target liver tolerance for disease therapy.