Regulation of secretion and surface expression of Mac-2, a galactoside-binding protein of macrophages

Emerging role of galectin 3 in neuroinflammation and neurodegeneration

Neuroinflammation and neurodegeneration are key processes that mediate the development and progression of neurological diseases. However, the mechanisms modulating these processes in different diseases remain incompletely understood. Advances in single cell based multi-omic analyses have helped to identify distinct molecular signatures such as Lgals3 that is associated with neuroinflammation and neurodegeneration in the central nervous system (CNS). Lgals3 encodes galectin-3 (Gal3), a β-galactoside and glycan binding glycoprotein that is frequently upregulated by reactive microglia/macrophages in the CNS during various neurological diseases. While Gal3 has previously been associated with non-CNS inflammatory and fibrotic diseases, recent studies highlight Gal3 as a prominent regulator of inflammation and neuroaxonal damage in the CNS during diseases such as multiple sclerosis, Alzheimer's disease, and Parkinson's disease. In this review, we summarize the pleiotropic functions of Gal3 and discuss evidence that demonstrates its detrimental role in neuroinflammation and neurodegeneration during different neurological diseases. We also consider the challenges of translating preclinical observations into targeting Gal3 in the human CNS.

Spinal muscular atrophy-like phenotype in a mouse model of acid ceramidase deficiency

Mutations in ASAH1 have been linked to two allegedly distinct disorders: Farber disease (FD) and spinal muscular atrophy with progressive myoclonic epilepsy (SMA-PME). We have previously reported FD-like phenotypes in mice harboring a single amino acid substitution in acid ceramidase (ACDase), P361R, known to be pathogenic in humans (P361R-Farber). Here we describe a mouse model with an SMA-PME-like phenotype (P361R-SMA). P361R-SMA mice live 2-3-times longer than P361R-Farber mice and have different phenotypes including progressive ataxia and bladder dysfunction, which suggests neurological dysfunction. We found profound demyelination, loss of axons, and altered sphingolipid levels in P361R-SMA spinal cords; severe pathology was restricted to the white matter. Our model can serve as a tool to study the pathological effects of ACDase deficiency on the central nervous system and to evaluate potential therapies for SMA-PME.

Melatonin ameliorates bleomycin-induced pulmonary fibrosis via activating NRF2 and inhibiting galectin-3 expression

Pulmonary fibrosis (PF) is a chronic interstitial lung disease with no effective therapies. Galectin-3 (Gal-3), a marker of oxidative stress, plays a key role in the pathogenesis of PF. Fibroblast-myofibroblast differentiation (FMD) is an important source of fibrotic cells in PF. Previous studies showed that melatonin (MT) exerted anti-fibrotic effect in many diseases including PF through its antioxidant activity. In the present study we investigated the relationships among Gal-3, NRF2, ROS in FMD and their regulation by MT. We established an in vitro model of FMD in TGF-β1-treated human fetal lung fibroblast1 (HFL1) cells and a PF mouse model via bleomycin (BLM) intratracheal instillation. We found that Gal-3 expression was significantly increased both in vitro and in vivo. Knockdown of Gal-3 in HFL1 cells markedly attenuated TGF-β1-induced FMD process and ROS accumulation. In TGF-β1-treated HFL1 cells, pretreatment with NRF2-specific inhibitor ML385 (5 μM) significantly increased the levels of Gal-3, α-SMA and ROS, suggesting that the expression of Gal-3 was regulated by NRF2. Treatment with NRF2-activator MT (250 μM) blocked α-SMA and ROS accumulation accompanied by reduced Gal-3 expression. In BLM-induced PF model, administration of MT (5 mg·kg⁻¹·d⁻¹, ip for 14 or 28 days) significantly attenuated the progression of lung fibrosis through up-regulating NRF2 and down-regulating Gal-3 expression in lung tissues. These results suggest that Gal-3 regulates TGF-β1-induced pro-fibrogenic responses and ROS production in FMD, and MT activates NRF2 to block FMD process by down-regulating Gal-3 expression. This study provides a useful clue for a clinical strategy to prevent PF.

Identification of macrophages in normal and injured mouse tissues using reporter lines and antibodies

Reliable tools for macrophage identification in mouse tissues are critical for studies investigating inflammatory and reparative responses. Transgenic reporter mice and anti-macrophage antibodies have been used as “specific pan-macrophage” markers in many studies; however, organ-specific patterns of expression and non-specific labeling of other cell types, such as fibroblasts, may limit their usefulness. Our study provides a systematic comparison of macrophage labeling patterns in normal and injured mouse tissues, using the CX3CR1 and CSF1R macrophage reporter lines and anti-macrophage antibodies. Moreover, we tested the specificity of macrophage antibodies using the fibroblast-specific PDGFR\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm{\alpha }$$\end{document}α reporter line. Mouse macrophages exhibit organ-specific differences in expression of macrophage markers. Hepatic macrophages are labeled for CSF1R, Mac2 and F4/80, but lack CX3CR1 expression, whereas in the lung, the CSF1R+/Mac2+/Mac3+ macrophage population is not labeled with F4/80. In the splenic red pulp, subpopulations of CSF1R+/F4/80+/Mac3+cells were labeled with Mac2, CX3CR1 and lysozyme M. In the kidney, Mac2, Mac3 and lysozyme M labeled a fraction of the CSF1R+ and CX3CR1+ macrophages, but also stained tubular epithelial cells. In normal hearts, the majority of CSF1R+ and CX3CR1+ cells were not detected with anti-macrophage antibodies. Myocardial infarction was associated with marked expansion of the CSF1R+ and CX3CR1+ populations that peaked during the proliferative phase of cardiac repair, and also expressed Mac2, Mac3 and lysozyme M. In normal mouse tissues, a small fraction of cells labeled with anti-macrophage antibodies were identified as PDGFR\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm{\alpha }$$\end{document}α+ fibroblasts, using a reporter system. The population of PDGFR\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm{\alpha }$$\end{document}α+ cells expressing macrophage markers expanded following injury, likely reflecting emergence of cellular phenotypes with both fibroblast and macrophage characteristics. In conclusion, mouse macrophages exhibit remarkable heterogeneity. Selection of the most appropriate markers for identification of macrophages in mouse tissues is dependent on the organ and the pathologic condition studied.

The Role of Serum Galectin-3 Levels in Patients with Sarcoidosis

INTRODUCTION

Galectin-3 is a multifunctional protein, the levels of which increase in the presence of diseases that progress with pulmonary fibrosis. This study investigated the role of galectin-3 levels in the staging and assessing of the severity of sarcoidosis.

METHODS AND SUBJECTS

Seventy-three subjects were studied; 25 were healthy individuals and 48 patients had pathologically confirmed diagnosis of sarcoidosis in which other potential causes had been ruled out. Galectin-3 levels were measured and compared in terms of such parameters as hemogram, biochemistry, age, body mass index, and smoking status.

RESULTS

The mean galectin-3 levels of the sarcoidosis patients (14.87 ± 5.57) were significantly higher than those in the healthy subjects (11.81 ± 2.67), and the mean galectin-3 levels differed significantly among different stages of the disease (p < 0.05). The serum galectin-3 level in patients with stage 2, 3, and 4 sarcoidosis was found to be higher than in patients with stage 0 and 1 sarcoidosis and the control group. In addition, serum galectin-3 levels in the sarcoidosis patients had significant positive correlations with blood urea nitrogen, alkaline phosphatase, white blood cells, red blood cell, hemoglobin, and neutrophil levels (34.9% [p < 0.05]; 40.1% [p < 0.05]; 41.2% [p < 0.01]; 43.3% [p < 0.01]; 34.7% [p < 0.05]; and 40.6% [p < 0.01], respectively) and a significant negative correlation with the platelet distribution width levels (p < 0.05).

CONCLUSION

Serum galectin-3 levels are significantly elevated in sarcoidosis patients with parenchymal involvement at stage 2 or higher, suggesting that serum galectin-3 levels can be used to estimate disease severity in sarcoidosis.

Physical Activity Attenuates the Obesity-Induced Dysregulated Expression of Brown Adipokines in Murine Interscapular Brown Adipose Tissue

In recent years, brown adipose tissue (BAT), which has a high heat-producing capacity, has been confirmed to exist even in adults, and it has become a focal point for the prevention and the improvement of obesity and lifestyle-related diseases. However, the influences of obesity and physical activity (PA) on the fluid factors secreted from BAT (brown adipokines) are not well understood. In this study, therefore, we focused on brown adipokines and investigated the effects of obesity and PA. The abnormal expressions of gene fluid factors such as galectin-3 (Lgals3) and Lgals3 binding protein (Lgals3bp), whose proteins are secreted from HB2 brown adipocytes, were observed in the interscapular BAT of obese mice fed a high-fat diet for 4 months. PA attenuated the abnormalities in the expressions of these genes. Furthermore, although the gene expressions of factors related to brown adipocyte differentiation such as peroxisome proliferator-activated receptor gamma coactivator 1-α were also down-regulated in the BAT of the obese mice, PA suppressed the down-regulation of these factors. On the other hand, lipogenesis was increased more in HB2 cells overexpressing Lgals3 compared with that in control cells, and the overexpression of Lgals3bp decreased the mitochondrial mass. These results indicate that PA attenuates the obesity-induced dysregulated expression of brown adipokines and suggests that Lgals3 and Lgals3bp are involved in brown adipocyte differentiation.

Secretory Galectin-3 promotes hepatic steatosis via regulation of the PPARγ/CD36 signaling pathway

Galectin-3 (Gal3) is an essential regulator of a number of metabolic disorders. Previous studies have established that Gal3 is a positive regulator of inflammation, fibrosis, and insulin resistance. However, its function in the early pathogenesis of hepatic lipid accumulation in non-alcoholic fatty liver disease (NAFLD) remains unresolved. Here, we demonstrate the presence of significantly upregulated extracellular concentrations of Gal3 in the fatty livers of high-fat diet (HFD)-induced mice. Systemic inhibition of Gal3 by injection of TD139 reduced the accumulation of lipid in the livers of HFD-fed mice, accompanied by the decreased expression of CD36 and peroxisome proliferator-activated receptor-gamma (PPARγ). Treatment with Gal3 protein elicited the opposite response in palmitic acid (PA)-induced HepG2 hepatocytes. It was additionally discovered that Gal3 positively regulates CD36 transcription by increased activation of PPARγ, thereby increasing fatty acid uptake, resulting in hepatic steatosis. In conclusion, the present study confirmed the roles of Gal3 in hepatic lipid metabolism in both in vitro and in vivo studies and revealed that Gal3 is a secretory protein that promotes hepatic steatosis through the PPARγ-CD36-dependent pathway, suggesting that targeting Gal3 may represent a potential therapeutic approach for the treatment of NAFLD and related metabolic disorders.

Galectin-3 N-terminal tail prolines modulate cell activity and glycan-mediated oligomerization/phase separation

Galectin-3 (Gal-3) has a long, aperiodic, and dynamic proline-rich N-terminal tail (NT). The functional role of the NT with its numerous prolines has remained enigmatic since its discovery. To provide some resolution to this puzzle, we individually mutated all 14 NT prolines over the first 68 residues and assessed their effects on various Gal-3-mediated functions. Our findings show that mutation of any single proline (especially P37A, P55A, P60A, P64A/H, and P67A) dramatically and differentially inhibits Gal-3-mediated cellular activities (i.e., cell migration, activation, endocytosis, and hemagglutination). For mechanistic insight, we investigated the role of prolines in mediating Gal-3 oligomerization, a fundamental process required for these cell activities. We showed that Gal-3 oligomerization triggered by binding to glycoproteins is a dynamic process analogous to liquid-liquid phase separation (LLPS). The composition of these heterooligomers is dependent on the concentration of Gal-3 as well as on the concentration and type of glycoprotein. LLPS-like Gal-3 oligomerization/condensation was also observed on the plasma membrane and disrupted endomembranes. Molecular- and cell-based assays indicate that glycan binding-triggered Gal-3 LLPS (or LLPS-like) is driven mainly by dynamic intermolecular interactions between the Gal-3 NT and the carbohydrate recognition domain (CRD) F-face, although NT-NT interactions appear to contribute to a lesser extent. Mutation of each proline within the NT differentially controls NT-CRD interactions, consequently affecting glycan binding, LLPS, and cellular activities. Our results unveil the role of proline polymorphisms (e.g., at P64) associated with many diseases and suggest that the function of glycosylated cell surface receptors is dynamically regulated by Gal-3.

Galectin-3 in Cardiovascular Diseases

Galectin-3 (Gal-3) is a β-galactoside-binding protein belonging to the lectin family with pleiotropic regulatory activities and several physiological cellular functions, such as cellular growth, proliferation, apoptosis, differentiation, cellular adhesion, and tissue repair. Inflammation, tissue fibrosis and angiogenesis are the main processes in which Gal-3 is involved. It is implicated in the pathogenesis of several diseases, including organ fibrosis, chronic inflammation, cancer, atherosclerosis and other cardiovascular diseases (CVDs). This review aims to explore the connections of Gal-3 with cardiovascular diseases since they represent a major cause of morbidity and mortality. We herein discuss the evidence on the pro-inflammatory role of Gal-3 in the atherogenic process as well as the association with plaque features linked to lesion stability. We report the biological role and molecular mechanisms of Gal-3 in other CVDs, highlighting its involvement in the development of cardiac fibrosis and impaired myocardium remodelling, resulting in heart failure and atrial fibrillation. The role of Gal-3 as a prognostic marker of heart failure is described together with possible diagnostic applications to other CVDs. Finally, we report the tentative use of Gal-3 inhibition as a therapeutic approach to prevent cardiac inflammation and fibrosis.

Galectin-3 enhances neutrophil motility and extravasation into the airways during Aspergillus fumigatus infection

Aspergillus fumigatus is an opportunistic mold that infects patients who are immunocompromised or have chronic lung disease, causing significant morbidity and mortality in these populations. While the factors governing the host response to A. fumigatus remain poorly defined, neutrophil recruitment to the site of infection is critical to clear the fungus. Galectin-3 is a mammalian β-galactose-binding lectin with both antimicrobial and immunomodulatory activities, however the role of galectin-3 in the defense against molds has not been studied. Here we show that galectin-3 expression is markedly up-regulated in mice and humans with pulmonary aspergillosis. Galectin-3 deficient mice displayed increased fungal burden and higher mortality during pulmonary infection. In contrast to previous reports with pathogenic yeast, galectin-3 exhibited no antifungal activity against A. fumigatus in vitro. Galectin-3 deficient mice exhibited fewer neutrophils in their airways during infection, despite normal numbers of total lung neutrophils. Intravital imaging studies confirmed that galectin-3 was required for normal neutrophil migration to the airspaces during fungal infection. Adoptive transfer experiments demonstrated that stromal rather than neutrophil-intrinsic galectin-3 was necessary for normal neutrophil entry into the airspaces. Live cell imaging studies revealed that extracellular galectin-3 directly increases neutrophil motility. Taken together, these data demonstrate that extracellular galectin-3 facilitates recruitment of neutrophils to the site of A. fumigatus infection, and reveals a novel role for galectin-3 in host defense against fungal infections.

The environmental mold Aspergillus fumigatus commonly causes lung infections in people with impaired immunity or those suffering from a chronic lung disease. While neutrophils are a key cell type necessary for the eradication of this infection, the precise mechanism of their recruitment to the site of infection remains incompletely understood. Here we show that the secreted mammalian protein galectin-3 plays an important role in helping neutrophils reaching the fungus within the airways. We found that both mice and humans produce galectin-3 when infected with A. fumigatus, and mice lacking galectin-3 were more susceptible to infection than normal mice. Galectin-3-deficient mice had impaired neutrophil recruitment to the site of infection. In the absence of galectin-3, neutrophils exhibited reduced motility in mouse lungs and in tissue culture. Our study offers insights into the mechanisms underlying the recruitment of neutrophils to the airways during A. fumigatus infection and reveals a new role for galectin-3 in increasing neutrophil motility.

Dermatological Implications of Galectin-3 in Circulation: An Evaluation From the Perspective of Patients With Differential Manifestations of Post-Kala-Azar Dermal Leishmaniasis

Galectin-3, a β-galactoside-binding lectin, has been implicated in vast repertoire of inflammatory and immunomodulatory processes including skin diseases. However, galectin-3 has not been comprehensively studied in infectious diseases. This study emphasizes on fascinating aspects of galectin-3 expression in dermal infection by studying post-kala-azar dermal leishmaniasis (PKDL), an intracellular infection caused by Leishmania donovani. Indian PKDL is a well-recognized parasitic dermatosis, with a high risk of anthroponotic transmission of L. donovani in causing leishmaniasis. This study aims to investigate the levels of galectin-3 and galectin-3-binding site expression in circulation of different forms of Indian patients with PKDL. Thirty-seven confirmed untreated PKDL patients, comprising 20 polymorphic and 17 macular PKDL manifestations, were evaluated for the levels of sera galectin-3 with respect to 28 age- and sex-matched healthy controls from endemic areas. Result shows a significant increment (P < 0.001) in circulatory galectin-3 levels in PKDL variants as compared to healthy controls. In addition, there were heightened levels of galectin-3 and galectin-3-binding sites on cellular infiltrates on lesional sites. Furthermore, there was a positive correlation between frequencies of mononuclear cells and galectin-3 during microcirculation in lesions. Data were well corroborated with positive correlation of IL-10 and IFN-γ with sera galectin-3 levels. Moreover, flow cytometry demonstrated the enhanced expression levels of the galectin-3-binding site in circulation in patients with PKDL as compared to healthy controls. Taken together, elevated levels of galectin-3 reflect its involvement in PKDL pathogenesis.

Galectins in the Pathogenesis of Cerebrovascular Accidents: An Overview

Due to limitations of neuroimaging, such as the isodense appearance of blood to neuronal tissue in subacute hemorrhagic stroke, a body of studies have been performed to evaluate candidate biomarkers which may aid in accurate determination of cerebrovascular accident type. Beyond aiding in the delineation of stroke cause, biomarkers could also confer useful prognostic information to help clinicians plan use of resources. One of the candidate biomarkers studied for detection of cerebrovascular accident (CVA) includes a class of proteins called galectins. Galectins bind β-galactoside through a highly conserved carbohydrate recognition domain, endowing an ability to interact with carbohydrate moieties on glycoproteins, some of which are relevant to CVA response. Furthermore, galectins-1, -2, -3, -9, and -12 are expressed in tissues relevant to CVA, and some exhibit characteristics (eg, extracellular secretion) that could render feasible their detection in serum. Galectins-1 and -3 appear to have the largest amounts of preclinical evidence, consistently demonstrating increased activity and expression levels during CVA. However, a lack of standardization of biochemical assays across cohort studies limits further translation of these basic science studies. This review aims to increase awareness of the biochemical roles of galectins in CVA, while also highlighting challenges and remaining questions preventing the translation of basic science observations into a clinically useful test.

Delayed Galectin-3-Mediated Reprogramming of Microglia After Stroke is Protective

Galectin-3 (Gal-3), a β-galactoside-binding lectin, has recently emerged as a molecule with immunoregulatory functions. We investigated the effects of Gal-3 on microglia morphology, migration, and secretory profile under physiological conditions and in the context of ischemic injury. We show that in the control conditions, exposure to recombinant Gal-3 increases microglial ramification and motility in vitro and in vivo via an IL-4-dependent mechanism. Importantly, after stroke, Gal-3 exerted marked immune-modulatory properties. Delivery of Gal-3 at 24 h after middle cerebral artery occlusion (MCAO) was associated with an increase in Ym1-positive microglia and decrease in iNOS. Analysis of cytokine profiles at the protein level revealed downregulation of pro-inflammatory cytokines and a marked upregulation of the anti-inflammatory cytokine, IL-4, 24 h after i.c.v. injection of Gal-3. Importantly, the observed shift in cytokines in microglia was associated with a significant decrease in the infarct size. Taken together, our results suggest that when delivered well after ischemic injury, Gal-3 might fine tune innate immunity and induce a therapeutic shift in microglia polarization.

Distinct Effects of Carrageenan and High-Fat Consumption on the Mechanisms of Insulin Resistance in Nonobese and Obese Models of Type 2 Diabetes

Exposure to low concentration of the common food additive carrageenan (10 mg/L) for only six days led to glucose intolerance and insulin resistance in the C57BL/6J mouse. Longer exposure produced fasting hyperglycemia but with no increase in weight, in contrast to the HFD. Glucose intolerance was attributable to carrageenan-induced inflammation and to increased expression of GRB10. Both HFD and carrageenan increased p(Ser32)-IκBα and p(Ser307)-IRS1, and the increases were greater following the combined exposure. The effects of carrageenan were inhibited by the combination of the free radical inhibitor Tempol and BCL10 siRNA, which had no impact on the HFD-mediated increase. In contrast, the PKC inhibitor sotrastaurin blocked the HFD-induced increases, without an effect on the carrageenan-mediated effects. HFD had no impact on the expression of GRB10. Both carrageenan and high fat increased hepatic infiltration by F4/80-positive macrophages. Serum galectin-3 and galectin-3 binding to the insulin receptor increased by carrageenan and by HFD. Tyrosine phosphorylation of the insulin receptor declined following either exposure and was further reduced by their combination. Carrageenan reduced the activity of the enzyme N-acetylgalactosamine-4-sulfatase (ARSB; arylsulfatase B), which was unchanged following HFD. Dietary exposure to both high fat and carrageenan can impair insulin signaling through both similar and distinct mechanisms.

Galectin-3 and N-acetylglucosamine promote myogenesis and improve skeletal muscle function in the mdx model of Duchenne muscular dystrophy

The muscle membrane, sarcolemma, must be firmly attached to the basal lamina. The failure of proper attachment results in muscle injury, which is the underlying cause of Duchenne muscular dystrophy (DMD), in which mutations in the dystrophin gene disrupts the firm adhesion. In patients with DMD, even moderate contraction causes damage, leading to progressive muscle degeneration. The damaged muscles are repaired through myogenesis. Consequently, myogenesis is highly active in patients with DMD, and the repeated activation of myogenesis leads to the exhaustion of the myogenic stem cells. Therefore, approaches to reducing the risk of the exhaustion are to develop a treatment that strengthens the interaction between the sarcolemma and the basal lamina and increases the efficiency of the myogenesis. Galectin-3 is an oligosaccharide-binding protein and is known to be involved in cell-cell interactions and cell-matrix interactions. Galectin-3 is expressed in myoblasts and skeletal muscle, although its function in muscle remains elusive. In this study, we found evidence that galectin-3 and the monosaccharide N-acetylglucosamine, which increases the synthesis of binding partners (oligosaccharides) of galectin-3, promote myogenesis in vitro. Moreover, in the mdx mouse model of DMD, treatment with N-acetylglucosamine increased muscle-force production. The results suggest that treatment with N-acetylglucosamine might mitigate the burden of DMD.-Rancourt, A., Dufresne, S. S., St-Pierre, G., Lévesque, J.-C., Nakamura, H., Kikuchi, Y., Satoh, M. S., Frenette, J., Sato, S. Galectin-3 and N-acetylglucosamine promote myogenesis and improve skeletal muscle function in the mdx model of Duchenne muscular dystrophy.

Histochemical characteristics of regressing vessels in the hyaloid vascular system of neonatal mice: Novel implication for vascular atrophy

The hyaloid vasculature constitutes a transitory system nourishing the internal structures of the developing eye, but the mechanism of vascular regression and its cell biological characteristics are not fully understood. The present study aimed to reveal the specificity of the hyaloid vessels by a systematic immunohistochemical approach for marker substances of myeloid cells and the extracellular matrix (ECM) in neonatal mice. Macrophages immunoreactive for F4/80, cathepsin D, and LYVE-1 gathered around the vasa hyaloidea propria (VHP), while small round cells in vascular lumen of VHP were selectively immunoreactive for galectin-3; their segmented nuclei and immunoreactivities for Ly-6G, CD11b, and myeloperoxidase indicated their neutrophilic origin. VHP possessed thick ECM and a dense pericyte envelope as demonstrated by immunostaining for laminin, type IV collagen, integrin β1, and NG2. The galectin-3⁺ cells loosely aggregated with numerous erythrocytes in the lumen of hyaloid vessels in a manner reminiscent of vascular congestion. Galectin-3 is known to polymerize and form a complex with ECM and NG2 as well as recruit leukocytes on the endothelium. Observation of galectin-3 KO mice implicated the involvement of galectin-3 in the regression of hyaloid vasculature. Since macrophages may play central roles including blocking of the blood flow and the induction of apoptosis in the regression, galectin-3⁺ neutrophils may play a supportive role in the macrophage-mediated involution of the hyaloid vascular system.

Galectin-3: One Molecule for an Alphabet of Diseases, from A to Z

Galectin-3 (Gal-3) regulates basic cellular functions such as cell-cell and cell-matrix interactions, growth, proliferation, differentiation, and inflammation. It is not surprising, therefore, that this protein is involved in the pathogenesis of many relevant human diseases, including cancer, fibrosis, chronic inflammation and scarring affecting many different tissues. The papers published in the literature have progressively increased in number during the last decades, testifying the great interest given to this protein by numerous researchers involved in many different clinical contexts. Considering the crucial role exerted by Gal-3 in many different clinical conditions, Gal-3 is emerging as a new diagnostic, prognostic biomarker and as a new promising therapeutic target. The current review aims to extensively examine the studies published so far on the role of Gal-3 in all the clinical conditions and diseases, listed in alphabetical order, where it was analyzed.

The balancing act of the liver: tissue regeneration versus fibrosis

Epithelial cell loss alters a tissue's optimal function and awakens evolutionarily adapted healing mechanisms to reestablish homeostasis. Although adult mammalian organs have a limited regeneration potential, the liver stands out as one remarkable exception. Following injury, the liver mounts a dynamic multicellular response wherein stromal cells are activated in situ and/or recruited from the bloodstream, the extracellular matrix (ECM) is remodeled, and epithelial cells expand to replenish their lost numbers. Chronic damage makes this response persistent instead of transient, tipping the system into an abnormal steady state known as fibrosis, in which ECM accumulates excessively and tissue function degenerates. Here we explore the cellular and molecular switches that balance hepatic regeneration and fibrosis, with a focus on uncovering avenues of disease modeling and therapeutic intervention.

Galectin-3: mediator of microglia responses in injured brain

Galectin-3 is a pleiotropic protein involved in cell activation, proliferation and migration and plays a pivotal part as an inflammatory mediator in neurodegeneration. Galectin-3 is associated with microglial activation and proliferation after ischemia. Given its putative role as a dynamic fine-tuner of microglia, activation of Galectin-3 provides molecular cues in design of new immunomodulatory strategies for stroke management. This review summarizes recent evidence on the role of Galectin-3 as a mediator of immune responses in damaged brain and mechanisms employed by Galectin-3 to affect microglial function.

Mesenchymal Stromal Cells from the Maternal Segment of Human Umbilical Cord is Ideal for Bone Regeneration in Allogenic Setting

Umbilical cord (UC) is a discarded product from the operating theatre and a ready source of mesenchymal stromal cells (MSCs). MSCs from UC express both embryonic and adult mesenchymal stem cell markers and are known to be hypoimmunogenic and non-tumorigenic and thus suitable for allogeneic cell transplantation. Our study aimed to determine the degree of immunotolerance and bone-forming capacity of osteodifferentiated human Wharton's jelly-derived mesenchymal stromal cells (hWJ-MSCs) from different segments of UC in an allogenic setting. UCs were obtained from healthy donors delivering a full-term infant by elective Caesarean section. hWJ-MSCs were isolated from 3 cm length segment from the maternal and foetal ends of UCs. Three-dimensional fibrin constructs were formed and implanted intramuscularly into immunocompetent mice. The mice were implanted with 1) fibrin construct with maternal hWJ-MSCs, 2) fibrin construct with foetal hWJ-MSCs, or 3) fibrin without cells; the control group received sham surgery. After 1 month, the lymphoid organs were analysed to determine the degree of immune rejection and bone constructs were analysed to determine the amount of bone formed. A pronounced immune reaction was noted in the fibrin group. The maternal segment constructs demonstrated greater osteogenesis than the foetal segment constructs. Both maternal and foetal segment constructs caused minimal immune reaction and thus appear to be safe for allogeneic bone transplant. The suppression of inflammation may be a result of increased anti-inflammatory cytokine production mediated by the hWJ-MSC. In summary, this study demonstrates the feasibility of using bone constructs derived from hWJ-MSCs in an allogenic setting.

Hematopoietic-Derived Galectin-3 Causes Cellular and Systemic Insulin Resistance

In obesity, macrophages and other immune cells accumulate in insulin target tissues, promoting a chronic inflammatory state and insulin resistance. Galectin-3 (Gal3), a lectin mainly secreted by macrophages, is elevated in both obese subjects and mice. Administration of Gal3 to mice causes insulin resistance and glucose intolerance, whereas inhibition of Gal3, through either genetic or pharmacologic loss of function, improved insulin sensitivity in obese mice. In vitro treatment with Gal3 directly enhanced macrophage chemotaxis, reduced insulin-stimulated glucose uptake in myocytes and 3T3-L1 adipocytes and impaired insulin-mediated suppression of glucose output in primary mouse hepatocytes. Importantly, we found that Gal3 can bind directly to the insulin receptor (IR) and inhibit downstream IR signaling. These observations elucidate a novel role for Gal3 in hepatocyte, adipocyte, and myocyte insulin resistance, suggesting that Gal3 can link inflammation to decreased insulin sensitivity. Inhibition of Gal3 could be a new approach to treat insulin resistance.

Lack of galectin-3 increases Jagged1/Notch activation in bone marrow-derived dendritic cells and promotes dysregulation of T helper cell polarization

Galectin-3, an endogenous glycan-binding protein, is abundantly expressed at sites of inflammation and immune cell activation. Although this lectin has been implicated in the control of T helper (Th) polarization, the mechanisms underlying this effect are not well understood. Here, we investigated the role of endogenous galectin-3 during the course of experimental Leishmania major infection using galectin-3-deficient (Lgals3(-/-)) mice in a BALB/c background and the involvement of Notch signaling pathway in this process. Lgals3(-/-) mice displayed an augmented, although mixed Th1/Th2 responses compared with wild-type (WT) mice. Concomitantly, lymph node and footpad lesion cells from infected Lgals3(-/-) mice showed enhanced levels of Notch signaling components (Notch-1, Jagged1, Jagged2 and Notch target gene Hes-1). Bone marrow-derived dendritic cells (BMDCs) from uninfected Lgals3(-/-) mice also displayed increased expression of the Notch ligands Delta-like-4 and Jagged1 and pro-inflammatory cytokines. In addition, activation of Notch signaling in BMDCs upon stimulation with Jagged1 was more pronounced in Lgals3(-/-) BMDCs compared to WT BMDCs; this condition resulted in increased production of IL-6 by Lgals3(-/-) BMDCs. Finally, addition of exogenous galectin-3 to Lgals3(-/-) BMDCs partially reverted the increased sensitivity to Jagged1 stimulation. Our results suggest that endogenous galectin-3 regulates Notch signaling activation in BMDCs and influences polarization of T helper responses, thus increasing susceptibility to L. major infection.

Low or No Inhibitory Potency of the Canonical Galectin Carbohydrate-binding Site by Pectins and Galactomannans

Some complex plant-derived polysaccharides, such as modified citrus pectins and galactomannans, have been shown to have promising anti-inflammatory and anti-cancer effects. Most reports propose or claim that these effects are due to interaction of the polysaccharides with galectins because the polysaccharides contain galactose-containing side chains that might bind this class of lectin. However, their direct binding to and/or inhibition of the evolutionarily conserved galactoside-binding site of galectins has not been demonstrated. Using a well established fluorescence anisotropy assay, we tested the direct interaction of several such polysaccharides with physiological concentrations of a panel of galectins. The bioactive pectic samples tested were very poor inhibitors of the canonical galactoside-binding site for the tested galectins, with IC₅₀ values >10 mg/ml for a few or in most cases no inhibitory activity at all. The galactomannan Davanat® was more active, albeit not a strong inhibitor (IC₅₀ values ranging from 3 to 20 mg/ml depending on the galectin). Pure synthetic oligosaccharide fragments found in the side chains and backbone of pectins and galactomannans were additionally tested. The most commonly found galactan configuration in pectins had no inhibition of the galectins tested. Galactosylated tri- and pentamannosides, representing the structure of Davanat®, had an inhibitory effect of galectins comparable with that of free galactose. Further evaluation using cell-based assays, indirectly linked to galectin-3 inhibition, showed no inhibition of galectin-3 by the polysaccharides. These data suggest that the physiological effects of these plant polysaccharides are not due to inhibition of the canonical galectin carbohydrate-binding site.

Myocardial Galectin-3 Expression Is Associated with Remodeling of the Pressure-Overloaded Heart and May Delay the Hypertrophic Response without Affecting Survival, Dysfunction, and Cardiac Fibrosis

The β-galactoside-binding animal lectin galectin-3 is predominantly expressed by activated macrophages and is a promising biomarker for patients with heart failure. Galectin-3 regulates inflammatory and fibrotic responses; however, its role in cardiac remodeling remains unclear. We hypothesized that galectin-3 may be up-regulated in the pressure-overloaded myocardium and regulate hypertrophy and fibrosis. In normal mouse myocardium, galectin-3 was constitutively expressed in macrophages and was localized in atrial but not ventricular cardiomyocytes. In a mouse model of transverse aortic constriction, galectin-3 expression was markedly up-regulated in the pressure-overloaded myocardium. Early up-regulation of galectin-3 was localized in subpopulations of macrophages and myofibroblasts; however, after 7 to 28 days of transverse aortic constriction, a subset of cardiomyocytes in fibrotic areas contained large amounts of galectin-3. In vitro, cytokine stimulation suppressed galectin-3 synthesis by macrophages and cardiac fibroblasts. Correlation studies revealed that cardiomyocyte- but not macrophage-specific galectin-3 localization was associated with adverse remodeling and dysfunction. Galectin-3 knockout mice exhibited accelerated cardiac hypertrophy after 7 days of pressure overload, whereas female galectin-3 knockouts had delayed dilation after 28 days of transverse aortic constriction. However, galectin-3 loss did not affect survival, systolic and diastolic dysfunction, cardiac fibrosis, and cardiomyocyte hypertrophy in the pressure-overloaded heart. Despite its potential role as a prognostic biomarker, galectin-3 is not a critical modulator of cardiac fibrosis but may delay the hypertrophic response.

Trichomonas vaginalis Lipophosphoglycan Exploits Binding to Galectin-1 and -3 to Modulate Epithelial Immunity

Trichomoniasis is the most common non-viral sexually transmitted infection caused by the vaginotropic extracellular protozoan parasite Trichomonas vaginalis. The infection is recurrent, with no lasting immunity, often asymptomatic, and linked to pregnancy complications and risk of viral infection. The molecular mechanisms of immune evasion by the parasite are poorly understood. We demonstrate that galectin-1 and -3 are expressed by the human cervical and vaginal epithelial cells and act as pathogen-recognition receptors for the ceramide phosphoinositol glycan core (CPI-GC) of the dominant surface protozoan lipophosphoglycan (LPG). We used an in vitro model with siRNA galectin knockdown epithelial clones, recombinant galectins, clinical Trichomonas isolates, and mutant protozoan derivatives to dissect the function of galectin-1 and -3 in the context of Trichomonas infection. Galectin-1 suppressed chemokines that facilitate recruitment of phagocytes, which can eliminate extracellular protozoa (IL-8) or bridge innate to adaptive immunity (MIP-3α and RANTES (regulated on activation normal T cell expressed and secreted)). Silencing galectin-1 increased and adding exogenous galectin-1 suppressed chemokine responses to Trichomonas or CPI-GC/LPG. In contrast, silencing galectin-3 reduced IL-8 response to LPG. Live Trichomonas depleted the extracellular levels of galectin-3. Clinical isolates and mutant Trichomonas CPI-GC that had reduced affinity to galectin-3 but maintained affinity to galectin-1 suppressed chemokine expression. Thus via CPI-GC binding, Trichomonas is capable of regulating galectin bioavailability and function to the benefit of its parasitic survival. These findings suggest novel approaches to control trichomoniasis and warrant further studies of galectin-binding diversity among clinical isolates as a possible source for symptom disparity in parasitic infections.

Endogenous galectin-3 expression levels modulate immune responses in galectin-3 transgenic mice

Galectin-3 (Gal-3), a β-galactoside-binding mammalian lectin, is involved in cancer progression and metastasis. However, there is an unmet need to identify the underlying mechanisms of cancer metastasis mediated by endogenous host galectin-3. Galectin-3 is also known to be an important regulator of immune responses. The present study was aimed at analysing how expression of endogenous galectin-3 regulates host immunity and lung metastasis in B16F10 murine melanoma model. Transgenic Gal-3(+/-) (hemizygous) and Gal-3(-/-) (null) mice exhibited decreased levels of Natural Killer (NK) cells and lower NK mediated cytotoxicity against YAC-1 tumor targets, compared to Gal-3(+/+) (wild-type) mice. On stimulation, Gal-3(+/-) and Gal-3(-/-) mice splenocytes showed increased T cell proliferation than Gal-3(+/+) mice. Intracellular calcium flux was found to be lower in activated T cells of Gal-3(-/-) mice as compared to T cells from Gal-3(+/+) and Gal-3(+/-) mice. In Gal-3(-/-) mice, serum Th1, Th2 and Th17 cytokine levels were found to be lowest, exhibiting dysregulation of pro-inflammatory and anti-inflammatory cytokines balance. Marked decrease in serum IFN-γ levels and splenic IFN-γR1 (IFN-γ Receptor 1) expressing T and NK cell percentages were observed in Gal-3(-/-) mice. On recombinant IFN-γ treatment of splenocytes in vitro, Suppressor of Cytokine Signaling (SOCS) 1 and SOCS3 protein expression was higher in Gal-3(-/-) mice compared to that in Gal-3(+/+) and Gal-3(+/-) mice; suggesting possible attenuation of Signal Transducer and Activator of Transcription (STAT) 1 mediated IFN-γ signaling in Gal-3(-/-) mice. The ability of B16F10 melanoma cells to form metastatic colonies in the lungs of Gal-3(+/+) and Gal-3(-/-) mice remained comparable, whereas it was found to be reduced in Gal-3(+/-) mice. Our data indicates that complete absence of endogenous host galectin-3 facilitates lung metastasis of B16F10 cells in mice, which may be contributed by dysregulated immune responses resulting from decreased NK cytotoxicity, disturbed serum Th1, Th2, Th17 cytokine milieu, reduced serum IFN-γ levels and attenuation of splenic STAT1 mediated IFN-γ signalling in Gal-3(-/-) mice.

Re-wiring regulatory cell networks in immunity by galectin-glycan interactions

Programs that control immune cell homeostasis are orchestrated through the coordinated action of a number of regulatory cell populations, including regulatory T cells, regulatory B cells, myeloid-derived suppressor cells, alternatively-activated macrophages and tolerogenic dendritic cells. These regulatory cell populations can prevent harmful inflammation following completion of protective responses and thwart the development of autoimmune pathology. However, they also have a detrimental role in cancer by favoring escape from immune surveillance. One of the hallmarks of regulatory cells is their remarkable plasticity as they can be positively or negatively modulated by a plethora of cytokines, growth factors and co-stimulatory signals that tailor their differentiation, stability and survival. Here we focus on the emerging roles of galectins, a family of highly conserved glycan-binding proteins in regulating the fate and function of regulatory immune cell populations, both of lymphoid and myeloid origins. Given the broad distribution of circulating and tissue-specific galectins, understanding the relevance of lectin-glycan interactions in shaping regulatory cell compartments will contribute to the design of novel therapeutic strategies aimed at modulating their function in a broad range of immunological disorders.

Binding of Galectin-3, a β-Galactoside-binding Lectin, to MUC1 Protein Enhances Phosphorylation of Extracellular Signal-regulated Kinase 1/2 (ERK1/2) and Akt, Promoting Tumor Cell Malignancy

Both mucin 1 (MUC1) and galectin-3 are known to be overexpressed in various malignant tumors and associated with a poor prognosis. It has been extensively reported that MUC1 is involved in potentiation of growth factor-dependent signal transduction. Because some carbohydrate moieties carried on MUC1 change to preferable ones for binding of galectin-3 in cancer cells, we speculated that MUC1-mediated signaling may occur through direct binding of galectin-3. Immunochemical studies showed that the distribution of galectin-3 coincided with that of MUC1 in various human tumor tissues but not in human nonmalignant tissues, and the level of galectin-3 retained on the surface of various cancer cells paralleled that of MUC1. Treatment of MUC1-expressing cells with galectin-3 induced phosphorylation of ERK1/2 and Akt following enhanced phosphorylation of MUC1 C-terminal domain, consistently promoting tumor cell malignancy. It is also noted that this enhanced phosphorylation occurred independently of EGF receptor-mediated signaling in both EGF receptor- and MUC1-expressing cells, and multivalency of galectin-3 was important for initiation of MUC1-mediated signaling. Expectedly, both silencing of endogenous galectin-3 and treatment with galectin-3 antagonists down-regulated cell proliferation of MUC1-expressing cells. These results suggest that the binding of galectin-3 to MUC1 plays a key role in MUC1-mediated signaling. Thus, constitutive activation of MUC1-mediated signaling in an autocrine/paracrine manner caused by ligation of galectin-3 promotes uncontrolled tumor cell malignancy. This signaling may be another MUC1-mediated pathway and function in parallel with a growth factor-dependent MUC1-mediated signaling pathway.

Structural, functional, and evolutionary aspects of galectins in aquatic mollusks: From a sweet tooth to the Trojan horse

Galectins constitute a conserved and widely distributed lectin family characterized by their binding affinity for β-galactosides and a unique binding site sequence motif in the carbohydrate recognition domain (CRD). In spite of their structural conservation, galectins display a remarkable functional diversity, by participating in developmental processes, cell adhesion and motility, regulation of immune homeostasis, and recognition of glycans on the surface of viruses, bacteria and protozoan parasites. In contrast with mammals, and other vertebrate and invertebrate taxa, the identification and characterization of bona fide galectins in aquatic mollusks has been relatively recent. Most of the studies have focused on the identification and domain organization of galectin-like transcripts or proteins in diverse tissues and cell types, including hemocytes, and their expression upon environmental or infectious challenge. Lectins from the eastern oyster Crassostrea virginica, however, have been characterized in their molecular, structural and functional aspects and some notable features have become apparent in the galectin repertoire of aquatic mollusks. These including less diversified galectin repertoires and different domain organizations relative to those observed in vertebrates, carbohydrate specificity for blood group oligosaccharides, and up regulation of galectin expression by infectious challenge, a feature that supports their proposed role(s) in innate immune responses. Although galectins from some aquatic mollusks have been shown to recognize microbial pathogens and parasites and promote their phagocytosis, they can also selectively bind to phytoplankton components, suggesting that they also participate in uptake and intracellular digestion of microalgae. In addition, the experimental evidence suggests that the protozoan parasite Perkinsus marinus has co-evolved with the oyster host to be selectively recognized by the oyster hemocyte galectins over algal food or bacterial pathogens, thereby subverting the oyster's innate immune/feeding recognition mechanisms to gain entry into the host cells.

CD13 mediates phagocytosis in human monocytic cells

The myelomonocytic marker aminopeptidase N/CD13 is a novel phagocytic receptor in monocytes and macrophages.

CD13 is a membrane‐bound ectopeptidase, highly expressed on monocytes, macrophages, and dendritic cells. CD13 is involved in diverse functions, including degradation of peptide mediators, cellular adhesion, migration, viral endocytosis, signaling, and positive modulation of phagocytosis mediated by FcγRs and other phagocytic receptors. In this work, we explored whether besides acting as an accessory receptor, CD13 by itself is a primary phagocytic receptor. We found that hCD13 mediates efficient phagocytosis of large particles (erythrocytes) modified so as to interact with the cell only through CD13 in human macrophages and THP‐1 monocytic cells. The extent of this phagocytosis is comparable with the phagocytosis mediated through the canonical phagocytic receptor FcγRI. Furthermore, we demonstrated that hCD13 expression in the nonphagocytic cell line HEK293 is sufficient to enable these cells to internalize particles bound through hCD13. CD13‐mediated phagocytosis is independent of other phagocytic receptors, as it occurs in the absence of FcγRs, CR3, and most phagocytic receptors. Phagocytosis through CD13 is independent of its enzymatic activity but is dependent on actin rearrangement and activation of PI3K and is partially dependent on Syk activation. Moreover, the cross‐linking of CD13 with antibodies rapidly induced pSyk in human macrophages. Finally, we observed that antibody‐mediated cross‐linking of hCD13, expressed in the murine macrophage‐like J774 cell line, induces production of ROS. These results demonstrate that CD13 is a fully competent phagocytic receptor capable of mediating internalization of large particles.

Value of pentraxin-3 and galectin-3 in acute coronary syndrome: a short-term prospective cohort study

BACKGROUND

Acute coronary syndrome (ACS) continues to be a leading cause of morbidity and mortality worldwide. Galectin-3 and pentraxin-3 are two prognostic biomarkers that have been studied in heart failure (HF). However, there are limited data on these biomarkers in the ACS population. The objective of the study was to determine the variables that are most affected by high concentrations of pentraxin-3 and galectin-3, and the influence they have on outcomes of all-cause mortality in patients with ACS.

METHODS

We included a total of 160 patients [ST elevation myocardial infarction (STEMI),n = 64; non STEMI/unstable angina (NSTEMI/UA), n = 38; and control subjects with chronic stable angina (CSA)/microvascular angina (MVA) n = 58]. Plasma pentraxin-3 and galectin-3 levels were assessed from these patients at the time of hospital admission. Major adverse cardiovascular events including all-cause mortality, rehospitalizations and coronary artery bypass graft surgery (CABG) were assessed at 6 months.

RESULTS

The median concentration of pentraxin-3 and galectin-3 were significantly higher in STEMI than in NSTEMI patients (p < 0.005) or controls (p < 0.005). Greater numbers of deaths (4 versus 0) were observed in STEMI patients with higher levels of these biomarkers. In addition, ACS patients with high levels of pentraxin-3 and galectin-3 had lower left ventricular ejection fraction (LVEF) (p < 0.005), and a moderate correlation was observed between LVEF and pentraxin-3 levels (r = -0.45, p < 0.005). Patients with higher galectin-3 levels were also observed to have a lower estimated glomerular fraction rate (eGFR), and a moderate correlation was observed between them (r = -0.34, p < 0.005).

CONCLUSION

Pentraxin-3 and galectin-3 hold much promise in the ACS population as prognostic biomarkers.

Evolving mechanistic insights into galectin functions

Galectins are an evolutionarily ancient family of glycan-binding proteins (GBPs) and are found in all animals. Although they were discovered over 30 years ago, ideas about their biological functions continue to evolve. Current evidence indicates that galectins, which are the only known GBPs that occur free in the cytoplasm and extracellularly, are involved in a variety of intracellular and extracellular pathways contributing to homeostasis, cellular turnover, cell adhesion, and immunity. Here we review evolving insights into galectin biology from a historical perspective and explore current evidence regarding biological roles of galectins.

Tumor-released Galectin-3, a soluble inhibitory ligand of human NKp30, plays an important role in tumor escape from NK cell attack

Human Galectin-3 (Gal-3), a β-galactoside-binding protein expressed by tumor cells, has been reported to act as an immune regulator in antitumor T cells. However, its effect on natural killer (NK) cells is elusive. Using a recombinant human NK cell-activating receptor, NKp30 fusion protein (NKp30-Fc), we found that soluble NKp30-Fc could immunoprecipitate Galectin-3. The direct interaction between NKp30 and Galectin-3 was further confirmed using surface plasmon resonance experiments. Because Galectin-3 was mainly released from tumor cells in a soluble form in our study, the binding assay was performed to show that soluble Galectin-3 specifically bound to NK cells and NKp30 on the surface of the NK cells. Functionally, when soluble Galectin-3 was added to the NK-tumor cell coculture system, the NKp30-mediated, but not NKG2D-mediated, cytolysis and CD107a expression in the NK cells were inhibited, and these phenotypes could be restored by preincubation of soluble Galectin-3 with NKp30-Fc fusion protein or the addition of anti-Gal-3 antibody alone. Moreover, genetic down-regulation of Galectin-3 (shGal-3) resulted in tumor cells being more sensitive to NK cell lysis, and, reversely, Galectin-3-overexpressing HeLa cells (exGal-3) became less sensitive to NK cell killing. The results of these in vitro experiments were supported by studies in shGal-3-HeLa or exGal-3-HeLa xenograft non-obese diabetic/severe combined immunodeficiency mice after NK cell adoptive immunotherapy, indicating that Galectin-3 strongly antagonizes human NK cell attack against tumors in vivo. These findings indicate that Galectin-3 may function as an immune regulator to inhibit NK cell function against tumors, therefore providing a new therapeutic target for tumor treatment.

Fracture healing via periosteal callus formation requires macrophages for both initiation and progression of early endochondral ossification

The distribution, phenotype, and requirement of macrophages for fracture-associated inflammation and/or early anabolic progression during endochondral callus formation were investigated. A murine femoral fracture model [internally fixed using a flexible plate (MouseFix)] was used to facilitate reproducible fracture reduction. IHC demonstrated that inflammatory macrophages (F4/80(+)Mac-2(+)) were localized with initiating chondrification centers and persisted within granulation tissue at the expanding soft callus front. They were also associated with key events during soft-to-hard callus transition. Resident macrophages (F4/80(+)Mac-2(neg)), including osteal macrophages, predominated in the maturing hard callus. Macrophage Fas-induced apoptosis transgenic mice were used to induce macrophage depletion in vivo in the femoral fracture model. Callus formation was completely abolished when macrophage depletion was initiated at the time of surgery and was significantly reduced when depletion was delayed to coincide with initiation of early anabolic phase. Treatment initiating 5 days after fracture with the pro-macrophage cytokine colony stimulating factor-1 significantly enhanced soft callus formation. The data support that inflammatory macrophages were required for initiation of fracture repair, whereas both inflammatory and resident macrophages promoted anabolic mechanisms during endochondral callus formation. Overall, macrophages make substantive and prolonged contributions to fracture healing and can be targeted as a therapeutic approach for enhancing repair mechanisms. Thus, macrophages represent a viable target for the development of pro-anabolic fracture treatments with a potentially broad therapeutic window.

Functions of galectin-3 and its role in fibrotic diseases

Fibrotic diseases occur in a variety of organs and lead to continuous organ injury, function decline, and even failure. Currently effective treatment options are limited. Galectin-3 (Gal-3) is a pleiotropic lectin that plays an important role in cell proliferation, adhesion, differentiation, angiogenesis, and apoptosis. Accumulating evidence indicates that Gal-3 activates a variety of profibrotic factors, promotes fibroblast proliferation and transformation, and mediates collagen production. Recent studies have defined key roles for Gal-3 in fibrogenesis in diverse organ systems, including liver, kidney, lung, and myocardial. To help set the stage for future research, we review recent advances about the role played by Gal-3 in fibrotic diseases. Herein we discuss the potential profibrotic role of Gal-3, inhibition of which may represent a promising therapeutic strategy against tissue fibrosis.

Endothelial dysfunction in adipose triglyceride lipase deficiency

Systemic knockout of adipose triglyceride lipase (ATGL), the pivotal enzyme of triglyceride lipolysis, results in a murine phenotype that is characterized by progredient cardiac steatosis and severe heart failure. Since cardiac and vascular dysfunction have been closely related in numerous studies we investigated endothelium-dependent and -independent vessel function of ATGL knockout mice. Aortic relaxation studies and Langendorff perfusion experiments of isolated hearts showed that ATGL knockout mice suffer from pronounced micro- and macrovascular endothelial dysfunction. Experiments with agonists directly targeting vascular smooth muscle cells revealed the functional integrity of the smooth muscle cell layer. Loss of vascular reactivity was restored ~50% upon treatment of ATGL knockout mice with the PPARα agonist Wy14,643, indicating that this phenomenon is partly a consequence of impaired cardiac contractility. Biochemical analysis revealed that aortic endothelial NO synthase expression and activity were significantly reduced in ATGL deficiency. Enzyme activity was fully restored in ATGL mice treated with the PPARα agonist. Biochemical analysis of perivascular adipose tissue demonstrated that ATGL knockout mice suffer from perivascular inflammatory oxidative stress which occurs independent of cardiac dysfunction and might contribute to vascular defects. Our results reveal a hitherto unrecognized link between disturbed lipid metabolism, obesity and cardiovascular disease.

Differential effects of high-fish oil and high-lard diets on cells and cytokines involved in the inflammatory process in rat insulin-sensitive tissues

Dietary fat sources may differentially affect the development of inflammation in insulin-sensitive tissues during chronic overfeeding. Considering the anti-inflammatory properties of ω-3 fatty acids, this study aimed to compare the effects of chronic high-fish oil and high-lard diets on obesity-related inflammation by evaluating serum and tissue adipokine levels and histological features in insulin-sensitive tissues (white adipose tissue, skeletal muscle and liver). As expected, a high-lard diet induced systemic and peripheral inflammation and insulin resistance. Conversely, compared with a high-lard diet, a high-fish oil diet resulted in a lower degree of systemic inflammation and insulin resistance that were associated with a lower adipocyte diameter as well as lower immunoreactivity for transforming growth factor β 1 (TGFβ1) in white adipose tissue. A high-fish oil diet also resulted in a lower ectopic lipid depot, inflammation degree and insulin resistance in the skeletal muscle and liver. Moreover, a high-fish oil diet attenuated hepatic stellate cell activation and fibrogenesis in the liver, as indicated by the smooth muscle α-actin (α-SMA) and TGFβ1 levels. The replacement of lard (saturated fatty acids) with fish oil (ω-3 fatty acids) in chronic high-fat feeding attenuated the development of systemic and tissue inflammation.

Galectin-3 binds to MUC1-N-terminal domain and triggers recruitment of β-catenin in MUC1-expressing mouse 3T3 cells

BACKGROUND

Galectin-3 is expressed in a variety of tumors and its expression level is related with tumor progression. Aberrant expression of MUC1 in various tumors is also associated with a poor prognosis. It has been reported that MUC1 is a natural ligand of galectin-3.

METHODS

A stable MUC1 transfectant was produced by introducing MUC1 cDNA into mouse 3T3 fibroblasts (MUC1/3T3 cells). MUC1 was prepared from MUC1/3T3 cells; MUC1-N-terminal domain (MUC1-ND) and -C-terminal domain (MUC1-CD) were separated by CsCl ultracentrifugation, and then the galectin-3-binding domain was determined by co-immuniprecipitation assay. After ligation of galectin-3 to 3T3/MUC1 cells, MUC1-CD was immunoprecipitated from the cell lysate. The immunoprecipitate was subjected to SDS-PAGE and Western blotting, followed by detection of co-immunoprecipitated β-catenin.

RESULTS

Galectin-3 binds to the N-terminal domain of MUC1 but not to the C-terminal one. Galectin-3 present on the cell surface increased with the expression of MUC1 and is colocalized with MUC1. It should be noted that β-catenin was detected in the immunoprecipitate with anti-MUC1-CD Ab from a lysate of galectin-3-treated 3T3/MUC1 cells.

CONCLUSIONS

Galectin-3 binds to MUC1-ND and triggers MUC1-mediated signaling in 3T3/MUC1 cells, leading to recruitment of β-catenin to MUC1-CD.

GENERAL SIGNIFICANCE

This signaling may be another MUC1-mediated pathway and function in parallel with a growth factor-dependent MUC1-mediated pathway.

DTU I isolates of Trypanosoma cruzi induce upregulation of Galectin-3 in murine myocarditis and fibrosis

Chagas heart disease is a major public concern since 30% of infected patients develop cardiac alterations. The relationship between Trypanosoma cruzi discrete typing units (DTUs) and the biological properties exhibited by the parasite population has yet to be elucidated. In this study, we analysed the expression of α-smooth muscle actin (α-SMA) and galectin-3 (Gal-3) associated with cardiac extracellular matrix (ECM) remodelling a murine chronic cardiomyopathy induced by Tc I genotypes. We found the induction of myocarditis was associated with the upregulation of Col I, α-SMA, Gal-3, IFN-γ and IL-13, as analysed by q-PCR. In myocardial areas of fibrosis, the intensity of myocarditis and significant ECM remodelling correlated with the presence of Col I-, Gal-3- and α-SMA-positive cells. These results are promising for the further efforts to evaluate the relevance of Gal-3 in Chagas heart disease, since this galectin was proposed as a prognosis marker in heart failure patients.

Cadmium-free sugar-chain-immobilized fluorescent nanoparticles containing low-toxicity ZnS-AgInS2 cores for probing lectin and cells

Sugar chains play a significant role in various biological processes through sugar chain-protein and sugar chain-sugar chain interactions. To date, various tools for analyzing sugar chains biofunctions have been developed. Fluorescent nanoparticles (FNPs) functionalized with carbohydrate, such as quantum dots (QDs), are an attractive imaging tool for analyzing carbohydrate biofunctions in vitro and in vivo. Most FNPs, however, consist of highly toxic elements such as cadmium, tellurium, selenium, and so on, causing problems in long-term bioimaging because of their cytotoxicity. In this study, we developed cadmium-free sugar-chain-immobilized fluorescent nanoparticles (SFNPs) using ZnS-AgInS2 (ZAIS) solid solution nanoparticles (NPs) of low or negligible toxicity as core components, and investigated their bioavailability and cytotoxicity. SFNPs were prepared by mixing our originally developed sugar-chain-ligand conjugates with ZAIS/ZnS core/shell NPs. In binding experiments with lectin, the obtained ZAIS/ZnS SFNPs interacted with an appropriate lectin to give specific aggregates, and their binding interaction was visually and/or spectroscopically detected. In addition, these SFNPs were successfully utilized for cytometry analysis and cellular imaging in which the cell was found to possess different sugar-binding properties. The results of the cytotoxicity assay indicated that SFNPs containing ZAIS/ZnS have much lower toxicity than those containing cadmium. These data strongly suggest that our designed SFNPs can be widely utilized in various biosensing applications involved in carbohydrates.

Cardiac oxidative stress in a mouse model of neutral lipid storage disease

Cardiac oxidative stress has been implicated in the pathogenesis of hypertrophy, cardiomyopathy and heart failure. Systemic deletion of the gene encoding adipose triglyceride lipase (ATGL), the enzyme that catalyzes the rate-limiting step of triglyceride lipolysis, results in a phenotype characterized by severe steatotic cardiac dysfunction. The objective of the present study was to investigate a potential role of oxidative stress in cardiac ATGL deficiency. Hearts of mice with global ATGL knockout were compared to those of mice with cardiomyocyte-restricted overexpression of ATGL and to those of wildtype littermates. Our results demonstrate that oxidative stress, measured as lucigenin chemiluminescence, was increased ~ 6-fold in ATGL-deficient hearts. In parallel, cytosolic NADPH oxidase subunits p67phox and p47phox were upregulated 4–5-fold at the protein level. Moreover, a prominent upregulation of different inflammatory markers (tumor necrosis factor α, monocyte chemotactant protein-1, interleukin 6, and galectin-3) was observed in those hearts. Both the oxidative and inflammatory responses were abolished upon cardiomyocyte-restricted overexpression of ATGL. Investigating the effect of oxidative and inflammatory stress on nitric oxide/cGMP signal transduction we observed a ~ 2.5-fold upregulation of soluble guanylate cyclase activity and a ~ 2-fold increase in cardiac tetrahydrobiopterin levels. Systemic treatment of ATGL-deficient mice with the superoxide dismutase mimetic Mn(III)tetrakis (4-benzoic acid) porphyrin did not ameliorate but rather aggravated cardiac oxidative stress. Our data suggest that oxidative and inflammatory stress seems involved in lipotoxic heart disease. Upregulation of soluble guanylate cyclase and cardiac tetrahydrobiopterin might be regarded as counterregulatory mechanisms in cardiac ATGL deficiency.

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ATGL(−/−) mice suffer from severe cardiac oxidative stress originating from upregulation of NOX2-dependent NADPH oxidase.

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Inflammation markers TNFα, MCP-1, IL-6, and Mac-2 are increased in cardiac ATGL deficiency.

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Activity of sGC and cardiac BH4 levels are elevated in ATGL(−/−) hearts.

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Systemic treatment of ATGL(−/−) mice with the SOD mimetic MnTBAP did not ameliorate oxidative stress.

Galectin-3 plays an important role in protection against disseminated candidiasis

Recent in vitro studies have implicated galectin-3 as an important receptor in host recognition and response to specific Candida species; however, its role in protection against disseminated candidiasis in vivo has not been evaluated. This study investigated the importance of galectin-3 in host defense against systemic infection with the highly virulent species Candida albicans, and the less virulent species, C. parapsilosis. Mice deficient in galectin-3 (gal3-/-) were more susceptible to infection than wild-type (WT) mice. When infected with C. albicans, gal3-/- mice died significantly faster and exhibited a trend towards increased fungal burden and increased abscess formation in infected brains compared to WT mice. When infected with C. parapsilosis, gal3-/- mice had significantly higher renal fungal burdens and abscess formation compared to WT mice. To evaluate whether galectin-3 may contribute to susceptibility to candidiasis in human infants, galectin-3 levels in sera of newborn infants, a patient population uniquely susceptible to infections with both C. albicans and C. parapsilosis, were compared to serum galectin-3 levels of adults. Galectin-3 levels were significantly lower in newborn infant sera compared to adult sera. These data indicate that galectin-3 plays an important role in a murine model of disseminated candidiasis and suggest a potential mechanism of neonatal susceptibility to these infections.

Expressions of Iba1 and galectin-3 (Gal-3) in thioacetamide (TAA)-induced acute rat liver lesions

Ionized calcium binding adaptor molecule 1 (Iba1) is associated with membrane ruffling and motility of cells. Galectin-3 (Gal-3) is a β-galactoside binding animal lectin, and regulates fibrogenesis probably through transforming growth factor-β1. To evaluate macrophage properties, expressions of Iba1 and Gal-3 were investigated, in relation to macrophages expressing CD68 (ED1; reflecting increased phagocytosis) and CD163 (ED2; implying proinflammatory factor productions) in centrilobular lesions induced in rat livers with thioacetamide (TAA; 300 mg/kg body weight, once intraperitoneally). In agreement with expression patterns of CD68(+) and CD163(+) macrophages, cells reacting to Iba1 and Gal-3 were increased in numbers on post-injection (PI) days 1-5, peaking on day 2; thereafter, the positive cells gradually decreased to control levels until PI days 7 and 10. The increased expressions of Iba1 and Gal-3 were confirmed at mRNA levels by the RT-PCR. Double immunofluorescence staining on PI days 2 and 3 demonstrated Iba1 expression in 15-46% of CD68(+) and CD163(+) macrophages, and Gal-3 expression in 65-82% of CD68(+) and CD163(+) macrophages; Gal-3 expression was observed in 84-93% of Iba1(+) cells. Interestingly, Gal-3 was also expressed in a small number of α-smooth muscle actin-positive myofibroblasts in fibrotic lesions developed in injured centrilobular areas. These findings indicate that macrophages with various functions can participate in development of liver lesions and resultant fibrosis. Besides CD68 and CD163, Iba1 and Gal-3 immunohistochemistry for macrophages would be useful to analyze the pathogenesis behind developing hepatotoxicity.