Neil C. Henderson

Galectin-3 expression and secretion links macrophages to the promotion of renal fibrosis.

Macrophages have been proposed as a key cell type in the pathogenesis of renal fibrosis; however, the mechanism by which macrophages drive fibrosis is still unclear. We show that expression of galectin-3, a beta-galactoside-binding lectin, is up-regulated in a mouse model of progressive renal fibrosis (unilateral ureteric obstruction, UUO), and absence of galectin-3 protects against renal myofibroblast accumulation/activation and fibrosis. Furthermore, specific depletion of macrophages using CD11b-DTR mice reduces fibrosis severity after UUO demonstrating that macrophages are key cells in the pathogenesis of renal fibrosis. Disruption of the galectin-3 gene does not affect macrophage recruitment after UUO, or macrophage proinflammatory cytokine profiles in response to interferon-gamma/lipopolysaccharide. In addition, absence of galectin-3 does not affect transforming growth factor-beta expression or Smad 2/3 phosphorylation in obstructed kidneys. Adoptive transfer of wild-type but not galectin-3(-/-) macrophages did, however, restore the fibrotic phenotype in galectin-3(-/-) mice. Cross-over experiments using wild-type and galectin-3(-/-) macrophage supernatants and renal fibroblasts confirmed that secretion of galectin-3 by macrophages is critical in the activation of renal fibroblasts to a profibrotic phenotype. Therefore, we demonstrate for the first time that galectin-3 expression and secretion by macrophages is a major mechanism linking macrophages to the promotion of renal fibrosis.

Regulation of Alternative Macrophage Activation by Galectin-3

Alternative macrophage activation is implicated in diverse disease pathologies such as asthma, organ fibrosis, and granulomatous diseases, but the mechanisms underlying macrophage programming are not fully understood. Galectin-3 is a carbohydrate-binding lectin present on macrophages. We show that disruption of the galectin-3 gene in 129sv mice specifically restrains IL-4/IL-13-induced alternative macrophage activation in bone marrow-derived macrophages in vitro and in resident lung and recruited peritoneal macrophages in vivo without affecting IFN-γ/LPS-induced classical activation or IL-10-induced deactivation. IL-4-mediated alternative macrophage activation is inhibited by siRNA-targeted deletion of galectin-3 or its membrane receptor CD98 and by inhibition of PI3K. Increased galectin-3 expression and secretion is a feature of alternative macrophage activation. IL-4 stimulates galectin-3 expression and release in parallel with other phenotypic markers of alternative macrophage activation. By contrast, classical macrophage activation with LPS inhibits galectin-3 expression and release. Galectin-3 binds to CD98, and exogenous galectin-3 or cross-linking CD98 with the mAb 4F2 stimulates PI3K activation and alternative activation. IL-4-induced alternative activation is blocked by bis-(3-deoxy-3-(3-methoxybenzamido)-β-D-galactopyranosyl) sulfane, a specific inhibitor of extracellular galectin-3 carbohydrate binding. These results demonstrate that a galectin-3 feedback loop drives alternative macrophage activation. Pharmacological modulation of galectin-3 function represents a novel therapeutic strategy in pathologies associated with alternatively activated macrophages.

The regulation of inflammation by galectin-3.

Summary:  Galectin‐3 is a β‐galactoside‐binding animal lectin of appro‐ ximately 30 kDa and is evolutionarily highly conserved. Galectin‐3 is promiscuous, its localization within the tissue micro‐environment may be extracellular, cytoplasmic, or nuclear, and it has a concentration‐dependent ability to be monomeric or form oligomers. These properties impart great flexibility on galectin‐3 as a specific regulator of many biological systems including inflammation. For example, in acute tissue damage galectin‐3 is a key component in the host defense against microbes such as Streptococcus pneumoniae. However, if tissue injury becomes repetitive galectin‐3 also appears to be intimately involved in the transition to chronic inflammation, facilitating the walling off of tissue injury with fibrogenesis and organ scarring. Therefore galectin‐3 can be viewed as a regulatory molecule acting at various stages along the continuum from acute inflammation to chronic inflammation and tissue fibrogenesis. In this review, we examine the role of galectin‐3 in inflammation, and discuss the manipulation of galectin‐3 expression as a potentially novel therapeutic strategy in the treatment of a broad range of inflammatory diseases.

Liver fibrosis: cellular mechanisms of progression and resolution

Liver fibrosis represents a major worldwide health care burden. The last 15 years have seen a rapid growth in our understanding of the pathogenesis of this clinically relevant model of inflammation and repair. This work is likely to inform the design of effective antifibrotic therapies in the near future. In this review, we examine how the innate and adaptive immune response interacts with other key cell types in the liver, such as the myofibroblast, regulating the process of hepatic fibrosis and, where relevant, resolution of fibrosis with remodelling. Emphasis is placed on the increasing knowledge that has been generated by the use of transgenic animals and animals in which specific cell lines have been deleted. Additionally, we review the increasing evidence that, although significant numbers of wound-healing myofibroblasts are derived from the hepatic stellate cell, significant contributions may occur from other cell lineages, including those from distant sites such as bone marrow stem cells.

Modeling liver fibrosis in rodents

Animal models of hepatic fibrosis provide a means to study the cell and molecular mediators of fibrosis in a serial manner during both progression and recovery. Several approaches to induction of fibrosis have been described. Of these, CCl(4) intoxication in rats and mice is probably the most widely studied. In addition, the CCl(4) model is the best characterized with respect to histological, biochemical, cell, and molecular changes associated with the development of fibrosis. CCl(4) can be given intraperitoneally or by oral gavage; it induces zone III necrosis and hepatocyte apoptosis with associated hepatic stellate cell activation and tissue fibrosis. With repetitive dosing CCl(4) can be used to induce bridging hepatic fibrosis (4 wk of twice-weekly dosing), cirrhosis (8 wk of twice-weekly dosing) and advanced micronodular cirrhosis (12 wk of twice-weekly dosing). In addition, for each of these models spontaneous recovery from fibrosis can be studied after cessation of dosing. Mechanistic studies using gene knockout and transgenic animals can also be established using CCl(4). Together these models have provided unparalleled insights into the mechanisms underlying hepatic fibrosis.

Critical role of c-jun (NH2) terminal kinase in paracetamol- induced acute liver failure

Background: Acute hepatic failure secondary to paracetamol poisoning is associated with high mortality. C-jun (NH2) terminal kinase (JNK) is a member of the mitogen-activated protein kinase family and is a key intracellular signalling molecule involved in controlling the fate of cells. Aim: To examine the role of JNK in paracetamol-induced acute liver failure (ALF). Methods: A previously developed mouse model of paracetamol poisoning was used to examine the role of JNK in paracetamol-induced ALF. Results: Paracetamol-induced hepatic JNK activation both in human and murine paracetamol hepatotoxicity and in our murine model preceded the onset of hepatocyte death. JNK inhibition in vivo (using two JNK inhibitors with different mechanisms of action) markedly reduced mortality in murine paracetamol hepatotoxicity, with a significant reduction in hepatic necrosis and apoptosis. In addition, delayed administration of the JNK inhibitor was more effective than N-acetylcysteine after paracetamol poisoning in mice. JNK inhibition was not protective in acute carbon tetrachloride-mediated or anti-Fas antibody-mediated hepatic injury, suggesting specificity for the role of JNK in paracetamol hepatotoxicity. Furthermore, disruption of the JNK1 or JNK2 genes did not protect against paracetamol-induced hepatic damage. Pharmacological JNK inhibition had no effect on paracetamol metabolism, but markedly inhibited hepatic tumour necrosis foctor α (TNF α) production after paracetamol poisoning. Conclusions: These data demonstrated a central role for JNK in the pathogenesis of paracetamol-induced liver failure, thereby identifying JNK as an important therapeutic target in the treatment of paracetamol hepatotoxicity.

Gut Homing Receptors on CD8 T Cells Are Retinoic Acid Dependent and Not Maintained by Liver Dendritic or Stellate Cells

BACKGROUND & AIMS Lymphocytes primed by intestinal dendritic cells (DC) express the gut-homing receptors CCR9 and alpha4beta7, which recognize CCL25 and mucosal addressin cell-adhesion molecule-1 in the intestine promoting the development of regional immunity. In mice, imprinting of CCR9 and alpha4beta7 is dependent on retinoic acid during T-cell activation. Tissue specificity is lost in primary sclerosing cholangitis (PSC), an extraintestinal manifestation of inflammatory bowel disease, when ectopic expression of mucosal addressin cell-adhesion molecule-1 and CCL25 in the liver promotes recruitment of CCR9+alpha4beta7+ T cells to the liver. We investigated the processes that control enterohepatic T-cell migration and whether the ability to imprint CCR9 and alpha4beta7 is restricted to intestinal DCs or can under some circumstances be acquired by hepatic DCs in diseases such as PSC. METHODS Human and murine DCs from gut, liver, or portal lymph nodes and hepatic stellate cells were used to activate CD8 T cells. Imprinting of CCR9 and alpha4beta7 and functional migration responses were determined. Crossover activation protocols assessed plasticity of gut homing. RESULTS Activation by gut DCs imprinted high levels of functional CCR9 and alpha4beta7 on naïve CD8 T cells, whereas hepatic DCs and stellate cells proved inferior. Imprinting was RA dependent and demonstrated plasticity. CONCLUSIONS Imprinting and plasticity of gut-homing human CD8 T cells requires primary activation or reactivation by gut DCs and is retinoic acid dependent. The inability of liver DCs to imprint gut tropism implies that alpha4beta7+CCR9+ T cell that infiltrate the liver in PSC are primed in the gut.

Extracellular matrix degradation in liver fibrosis: Biochemistry and regulation

Fibrosis is a highly conserved wound healing response and represents the final common pathway of virtually all chronic inflammatory injuries. Over the past 3 decades detailed analysis of hepatic extracellular matrix synthesis and degradation using approaches incorporating human disease, experimental animal models and cell culture have highlighted the extraordinarily dynamic nature of tissue repair and remodelling in this solid organ. Furthermore emerging studies of fibrosis in other organs demonstrate that basic common mechanisms exist, suggesting that bidirectionality of the fibrotic process may not solely be the preserve of the liver. In this review we will examine the cellular and molecular mechanisms that govern extracellular matrix degradation and fibrosis resolution, and highlight how manipulation of these processes may result in the development of effective anti-fibrotic therapies. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Galectin-3 reduces the severity of pneumococcal pneumonia by augmenting neutrophil function

The Gram-positive Streptococcus pneumoniae is the leading cause of community-acquired pneumonia worldwide, resulting in high mortality. Our in vivo studies show that galectin-3(-/-) mice develop more severe pneumonia after infection with S. pneumoniae, as demonstrated by increased bacteremia and lung damage compared to wild-type mice and that galectin-3 reduces the severity of pneumococcal pneumonia in part by augmenting neutrophil function. Specifically, we show that 1) galectin-3 directly acts as a neutrophil-activating agent and potentiates the effect of fMLP, 2) exogenous galectin-3 augments neutrophil phagocytosis of bacteria and delays neutrophil apoptosis, 3) phagocytosis of apoptotic neutrophils by galectin-3(-/-) macrophages is less efficient compared to wild type, and 4) galectin-3 demonstrates bacteriostatic properties against S. pneumoniae in vitro. Furthermore, ad-back of recombinant galectin-3 in vivo protects galectin-3-deficient mice from developing severe pneumonia. Together, these results demonstrate that galectin-3 is a key molecule in the host defense against pneumococcal infection. Therapeutic strategies designed to augment galectin-3 activity may both enhance inflammatory cell function (by directly affecting neutrophil responsiveness and prolonging neutrophil longevity) and have direct bacteriostatic activity, improving clinical outcomes after severe pneumococcal infection.

The utilization of liver transplantation in the management of acute liver failure: Comparison between acetaminophen and non-acetaminophen etiologies†

Liver transplantation (LT) may be life‐saving in severe acute liver failure (ALF). The aim of this study was to compare the utilization of LT in acetaminophen and non‐acetaminophen ALF. Between 1992 and 2006, 469 patients with ALF were admitted, and 104 underwent LT. Acetaminophen was the most common etiology, but LT proceeded more frequently in the non‐acetaminophen cohort (acetaminophen: 45/326 patients received LT, 13.8%; non‐acetaminophen: 59/143 patients received LT, 41.3%; P < 0.01). A retrospective analysis of the individual steps in the management of patients revealed more ALF patients in the non‐acetaminophen cohort fulfilled the Kings College Hospital poor prognostic criteria (non‐acetaminophen: 91/143, 63.6%; acetaminophen: 165/326, 50.6%; P < 0.01), more patients had contraindications to LT in the acetaminophen cohort (acetaminophen: 99/165, 60%; non‐acetaminophen: 21/91, 23.1%; P < 0.01), and survival on the LT waiting list was reduced in the acetaminophen cohort (acetaminophen: 45/66, 68.2%; non‐acetaminophen: 59/70, 84.3%; P < 0.05). Post‐LT survival was similar in the 2 groups. An analysis of cohorts admitted in 1993‐1996 and 2002‐2005 revealed that LT proceeded less commonly in acetaminophen ALF in the later cohort (1993‐1996: 16/99 LT, 16.2%; 2002‐2005: 4/81 LT, 5%; P < 0.01) in comparison with the non‐acetaminophen cohort, in which transplantation proceeded more commonly in the later cohort (1993‐1996: 11/34 LT, 32.4%; 2002‐2005: 24/49 patients, 49.0%; P < 0.01). This was due to an increase in the number of patients with psychiatric contraindications to transplantation (predominantly resistant and severe alcohol dependence). In conclusion, at all decision steps between admission and emergency LT, LT is favored in non‐acetaminophen patients, and nonoperative management is favored in acetaminophen ALF patients. Liver Transpl 15:600–609, 2009.