Regulation of cellular adhesion to extracellular matrix proteins by galectin-3

Fibroblasts' secretome from calcified and non-calcified dermis in Pseudoxanthoma elasticum differently contributes to elastin calcification

Pseudoxanthoma elasticum (PXE) is a rare disease characterized by ectopic calcification, however, despite the widely spread effect of pro/anti-calcifying systemic factors associated with this genetic metabolic condition, it is not known why elastic fibers in the same patient are mainly fragmented or highly mineralized in clinically unaffected (CUS) and affected (CAS) skin, respectively. Cellular morphology and secretome are investigated in vitro in CUS and CAS fibroblasts. Here we show that, compared to CUS, CAS fibroblasts exhibit: a) differently distributed and organized focal adhesions and stress fibers; b) modified cell-matrix interactions (i.e., collagen gel retraction); c) imbalance between matrix metalloproteinases and tissue inhibitor of metalloproteinases; d) differentially expressed pro- and anti-calcifying proteoglycans and elastic-fibers associated glycoproteins. These data emphasize that in the development of pathologic mineral deposition fibroblasts play an active role altering the stability of elastic fibers and of the extracellular matrix milieu creating a local microenvironment guiding the level of matrix remodeling at an extent that may lead to degradation (in CUS) or to degradation and calcification (in CAS) of the elastic component. In conclusion, this study contributes to a better understanding of the mechanisms of the mineral deposition that can be also associated with several inherited or age-related diseases (e.g., diabetes, atherosclerosis, chronic kidney diseases).

Soluble galectin-3 as a microenvironment-relevant immunoregulator with prognostic and predictive value in lung adenocarcinoma

Despite the success of therapies in lung cancer, more studies of new biomarkers for patient selection are urgently needed. The present study aims to analyze the role of galectin-3 (GAL-3) in the lung tumor microenvironment (TME) using tumorspheres as a model and explore its potential role as a predictive and prognostic biomarker in non-small cell lung cancer patients. For in vitro studies, lung adenocarcinoma (LUAD) and lung squamous carcinoma (LUSC) primary cultures from early-stage patients and commercial cell lines were cultured, using tumorsphere-forming assays and adherent conditions for the control counterparts. We analyzed the pattern of secretion and expression of GAL-3 using reverse transcription-quantitative real-time PCR (RTqPCR), immunoblot, immunofluorescence, flow cytometry, and immunoassay analysis. Our results using three-dimensional (3D) models of lung tumor cells revealed that soluble GAL-3 (sGAL-3) is highly expressed and secreted. To more accurately mimic the TME, a co-culture of tumorspheres and fibroblasts was used, revealing that GAL-3 could be important as an immunomodulatory molecule expressed and secreted in the TME, modulating immunosuppression through regulatory T cells (TREGS ). In the translational phase, we confirmed that patients with high expression levels of GAL-3 had more TREGS , which suggests that tumors may be recruiting this population through GAL-3. Next, we evaluated levels of sGAL-3 before surgery in LUAD and LUSC patients, hypothesizing that sGAL-3 could be used as an independent prognostic biomarker for overall survival and relapse-free survival in early-stage LUAD patients. Additionally, levels of sGAL-3 at pretreatment and first response assessment from plasma to predict clinical outcomes in advanced LUAD and LUSC patients treated with first-line pembrolizumab were evaluated, further supporting that sGAL-3 has a high efficiency in predicting durable clinical response to pembrolizumab with an area under curve of 0.801 (P = 0.011). Moreover, high levels might predict decreased progression-free survival and OS to anti-PD-1 therapy, with sGAL-3 being a prognosis-independent biomarker for advanced LUAD.

Development of glycan-targeted nanoparticles as a novel therapeutic opportunity for gastric cancer treatment

Chemotherapy resistance remains a major cause of therapeutic failure in gastric cancer. The combination of genetic material such as interference RNAs (iRNAs) to silence cancer-associated genes with chemotherapeutics has become a novel approach for cancer treatment. However, finding the right target genes and developing non-toxic, highly selective nanocarrier systems remains a challenge. Here we developed a novel sialyl-Tn-targeted polylactic acid—didodecyldimethylammonium bromide nanoparticle (PLA-DDAB) nanoparticles (NPs) loaded with dsRNA targeting ST6GalNac-I and/or galectin-3 genes. Using single photon emission computed tomography (SPECT), we have demonstrated that 99mtechnetium radiolabeled sialyl-Tn-targeted nanoparticles can reach the tumor site and downregulate ST6GalNAc-I and galectin-3 RNA expression levels when injected intravenously. Furthermore, using an in vivo gastric tumor model, these nanoparticles increased the effectiveness of 5-FU in reducing tumor growth. Our findings indicate that cancer-associated glycan-targeted NPs loaded with dsRNA targeting ST6GalNAc-I and/or galectin-3 in combination with standard chemotherapy, have the potential to become a novel therapeutic tool for gastric cancer.

The Role of Galectin-3 in Heart Failure-The Diagnostic, Prognostic and Therapeutic Potential-Where Do We Stand?

Heart failure (HF) is a clinical syndrome with high morbidity and mortality, and its prevalence is rapidly increasing. Galectin-3 (Gal-3) is an important factor in the pathophysiology of HF, mainly due to its role in cardiac fibrosis, inflammation, and ventricular remodeling. Fibrosis is a hallmark of cardiac remodeling, HF, and atrial fibrillation development. This review aims to explore the involvement of Gal-3 in HF and its role in the pathogenesis and clinical diagnostic and prognostic significance. We report data on Gal-3 structure and molecular mechanisms of biological function crucial for HF development. Over the last decade, numerous studies have shown an association between echocardiographic and CMR biomarkers in HF and Gal-3 serum concentration. We discuss facts and concerns about Gal-3's utility in acute and chronic HF with preserved and reduced ejection fraction for diagnosis, prognosis, and risk stratification. Finally, we present attempts to use Gal-3 as a therapeutic target in HF.

Galectin-3: therapeutic targeting in liver disease

INTRODUCTION

The rising incidence of liver diseases is a worldwide healthcare concern. However, the therapeutic options to manage chronic inflammation and fibrosis, the processes at the basis of morbidity and mortality of liver diseases, are very limited. Galectin 3 (Gal-3) is a protein implicated in fibrosis in multiple organs. Several Gal-3 inhibitors are currently in clinical development.

AREAS COVERED

This review describes our current understanding of the role of Gal-3 in chronic liver diseases, with special emphasis on fibrosis. Also, we review therapeutic advances based on Gal-3 inhibition, describing drug properties and their current status in clinical research.

EXPERT OPINION

Currently, the known effects of Gal-3 point to a direct activation of the NLRP3 inflammasome leading to its activation in liver macrophages and activated macrophages play a key role in tissue fibrogenesis. However, more research is needed to elucidate the role of Gal-3 in the different activation pathways, dissecting the intracellular and extracellular mechanisms of Gal-3, and its role in pathogenesis. Gal-3 could be a target for early therapy of numerous hepatic diseases and, given the lack of therapeutic options for liver fibrosis, there is a strong pharmacologic potential for Gal-3-based therapies.

Galectin-3 Plays an Important Role in BMP7-Induced Cementoblastic Differentiation of Human Periodontal Ligament Cells by Interacting with Extracellular Components

Human periodontal ligament stem cells (hPDLSCs) contain multipotent postnatal stem cells that differentiate into PDL progenitors, osteoblasts, and cementoblasts. Previously, we obtained cementoblast-like cells from hPDLSCs using bone morphogenetic protein 7 (BMP7) treatment. Differentiation into appropriate progenitor cells requires interactions and changes between stem or progenitor cells and their so-called environment niches, and cell surface markers play an important role. However, cementoblast-specific cell surface markers have not yet been fully studied. Through decoy immunization with intact cementoblasts, we developed a series of monoclonal antibodies against cementoblast-specific membrane/extracellular matrix (ECM) molecules. One of these antibodies, the anti-CM3 antibody, recognized an approximate 30 kDa protein in a mouse cementoblast cell line, and the CM3 antigenic molecule accumulated in the cementum region of human tooth roots. Using mass spectrometric analysis, we found that the antigenic molecules recognized by the anti-CM3 antibody were galectin-3. As cementoblastic differentiation progressed, the expression of galectin-3 increased, and it localized at the cell surface. Inhibition of galectin-3 via siRNA and a specific inhibitor showed the complete blockage of cementoblastic differentiation and mineralization. In contrast, ectopic expression of galectin-3 induced cementoblastic differentiation. Galectin-3 interacted with laminin α2 and BMP7, and these interactions were diminished by galectin-3 inhibitors. These results suggested that galectin-3 participates in binding to the ECM component and trapping BMP7 to induce, in a sustained fashion, the upregulation of cementoblastic differentiation. Finally, galectin-3 could be a potential cementoblast-specific cell surface marker, with functional importance in cell-to-ECM interactions.

Short report galectins use N-glycans of FGFs to capture growth factors at the cell surface and fine-tune their signaling

Fibroblast growth factors (FGFs) and their receptors (FGFRs) constitute complex signaling hubs that are crucial for the development and homeostasis of the human body. Most of FGFs are released by cells using the conventional secretory pathway and are N-glycosylated, yet the role of FGFs glycosylation is largely unknown. Here, we identify N-glycans of FGFs as binding sites for a specific set of extracellular lectins, galectins - 1, -3, -7 and - 8. We demonstrate that galectins attract N-glycosylated FGF4 to the cell surface, forming a reservoir of the growth factor in the extracellular matrix. Furthermore, we show that distinct galectins differentially modulate FGF4 signaling and FGF4-dependent cellular processes. Using engineered variants of galectins with altered valency we demonstrate that multivalency of galectins is critical for the adjustment of FGF4 activity. Summarizing, our data reveal a novel regulatory module within FGF signaling, in which the glyco-code in FGFs provides previously unanticipated information differentially deciphered by multivalent galectins, affecting signal transduction and cell physiology. Video Abstract.

Development of Galectin-3 Targeting Drugs for Therapeutic Applications in Various Diseases

Galectin-3 (Gal3) is one of the most studied members of the galectin family that mediate various biological processes such as growth regulation, immune function, cancer metastasis, and apoptosis. Since Gal3 is pro-inflammatory, it is involved in many diseases that are associated with chronic inflammation such as cancer, organ fibrosis, and type 2 diabetes. As a multifunctional protein involved in multiple pathways of many diseases, Gal3 has generated significant interest in pharmaceutical industries. As a result, several Gal3-targeting therapeutic drugs are being developed to address unmet medical needs. Based on the PubMed search of Gal3 to date (1987-2023), here, we briefly describe its structure, carbohydrate-binding properties, endogenous ligands, and roles in various diseases. We also discuss its potential antagonists that are currently being investigated clinically or pre-clinically by the public and private companies. The updated knowledge on Gal3 function in various diseases could initiate new clinical or pre-clinical investigations to test therapeutic strategies, and some of these strategies could be successful and recognized as novel therapeutics for unmet medical needs.

Spatial regulation of the glycocalyx component podocalyxin is a switch for prometastatic function

The glycocalyx component and sialomucin podocalyxin (PODXL) is required for normal tissue development by promoting apical membranes to form between cells, triggering lumen formation. Elevated PODXL expression is also associated with metastasis and poor clinical outcome in multiple tumor types. How PODXL presents this duality in effect remains unknown. We identify an unexpected function of PODXL as a decoy receptor for galectin-3 (GAL3), whereby the PODXL-GAL3 interaction releases GAL3 repression of integrin-based invasion. Differential cortical targeting of PODXL, regulated by ubiquitination, is the molecular mechanism controlling alternate fates. Both PODXL high and low surface levels occur in parallel subpopulations within cancer cells. Orthotopic intraprostatic xenograft of PODXL-manipulated cells or those with different surface levels of PODXL define that this axis controls metastasis in vivo. Clinically, interplay between PODXL-GAL3 stratifies prostate cancer patients with poor outcome. Our studies define the molecular mechanisms and context in which PODXL promotes invasion and metastasis.

Characterization of Galectin Fusion Proteins with Glycoprotein Affinity Columns and Binding Assays

Galectins are β-galactosyl-binding proteins that fulfill essential physiological functions. In the biotechnological field, galectins are versatile tools, such as in the development of biomaterial coatings or the early-stage diagnosis of cancer diseases. Recently, we introduced galectin-1 (Gal-1) and galectin-3 (Gal-3) as fusion proteins of a His₆-tag, a SNAP-tag, and a fluorescent protein. We characterized their binding in ELISA-type assays and their application in cell-surface binding. In the present study, we have constructed further fusion proteins of galectins with fluorescent protein color code. The fusion proteins of Gal-1, Gal-3, and Gal-8 were purified by affinity chromatography. For this, we have prepared glycoprotein affinity resins based on asialofetuin (ASF) and fetuin and combined this in a two-step purification with Immobilized Metal Affinity chromatography (IMAC) to get pure and active galectins. Purified galectin fractions were analyzed by size-exclusion chromatography. The binding characteristics to ASF of solely His₆-tagged galectins and galectin fusion proteins were compared. As an example, we demonstrate a 1.6-3-fold increase in binding efficiency for HSYGal-3 (His₆-SNAP-yellow fluorescent protein-Gal-3) compared to the HGal-3 (His₆-Gal-3). Our results reveal an apparent higher binding efficiency for galectin SNAP-tag fusion proteins compared to His₆-tagged galectins, which are independent of the purification mode. This is also demonstrated by the binding of galectin fusion proteins to extracellular glycoconjugates laminin, fibronectin, and collagen IV. Our results indicate the probable involvement of the SNAP-tag in apparently higher binding signals, which we discuss in this study.

Chimeric galectin-3 and collagens: Biomarkers and potential therapeutic targets in fibroproliferative diseases

Fibrosis, stiffening and scarring of an organ/tissue due to genetic abnormalities, environmental factors, infection, and/or injury, is responsible for > 40% of all deaths in the industrialized world, and to date, there is no cure for it despite extensive research and numerous clinical trials. Several biomarkers have been identified, but no effective therapeutic targets are available. Human galectin-3 is a chimeric gene product formed by the fusion of the internal domain of the collagen alpha gene [N-terminal domain (ND)] at the 5'-end of galectin-1 [C-terminal domain (CRD)] that appeared during evolution together with vertebrates. Due to the overlapping structural similarities between collagen and galectin-3 and their shared susceptibility to cleavage by matrix metalloproteases to generate circulating collagen-like peptides, this review will discuss present knowledge on the role of collagen and galectin-3 as biomarkers of fibrosis. We will also highlight the need for transformative approaches targeting both the ND and CRD domains of galectin-3, since glycoconjugate binding by the CRD is triggered by ND-mediated oligomerization and the therapies targeted only at the CRD have so far achieved limited success.

Early Doxorubicin Myocardial Injury: Inflammatory, Oxidative Stress, and Apoptotic Role of Galectin-3

Doxorubicin (DOXO) is an effective drug that is used in the treatment of a large number of cancers. Regardless of its important chemotherapeutic characteristics, its usage is restricted because of its serious side effects; the most obvious is cardiotoxicity, which can manifest acutely or years after completion of treatment, leading to left ventricular dysfunction, dilated cardiomyopathy, and heart failure. Galectin 3 (Gal-3) is a beta galactoside binding lectin that has different roles in normal and pathophysiological conditions. Gal-3 was found to be upregulated in animal models, correlating with heart failure, atherosclerosis, and myocardial infarction. Male C57B6/J and B6.Cg-Lgals3 <tm 1 Poi>/J Gal-3 knockout (KO) mice were used for a mouse model of acute DOXO-induced cardiotoxicity. Mice were given DOXO or vehicle (normal saline), after which the mice again had free access to food and water. Heart and plasma samples were collected 5 days after DOXO administration and were used for tissue processing, staining, electron microscopy, and enzyme-linked immunosorbent assay (ELISA). There was a significant increase in the heart concentration of Gal-3 in Gal-3 wild type DOXO-treated mice when compared with the sham control. There were significantly higher concentrations of heart cleaved caspase-3, plasma troponin I, plasma lactate dehydrogenase, and plasma creatine kinase in Gal-3 KO DOXO-treated mice than in Gal-3 wild type DOXO-treated mice. Moreover, there were significantly higher heart antioxidant proteins and lower oxidative stress in Gal-3 wild type DOXO-treated mice than in Gal-3 KO DOXO-treated mice. In conclusion, Gal-3 can affect the redox pathways and regulate cell survival and death of the myocardium following acute DOXO injury.

Experimental and Computational Models of Transport of Galectin-3 Through Glycosylated Matrix

Altered extracellular matrix (ECM) production is a hallmark of many fibroproliferative diseases, including certain cancers. The high incidence of glycan-rich components within altered ECM makes the use of glycan-binding proteins such as Galectin-3 (G3) a promising therapeutic strategy. The complexity of ECM as a rich 3D network of proteins with varied glycosylation states makes it challenging to determine the retention of glycan-binding proteins in altered ECM environments. Computational models capable of predicting the transport of glycan-binding proteins in altered ECM can benefit the design and testing of such proteins and associated novel therapeutic strategies. However, such computational models require many kinetic parameters that cannot be estimated from traditional 2D pharmacokinetic assays. To validate transport properties of G3 in 3D ECM constructs, we developed a species transport model that includes diffusion and matrix-binding components to predict retention of G3 fusion proteins in glycan-rich ECM. By iteratively comparing our computational model to experimental results, we are able to determine a reasonable range of parameters for a robust computational model of G3 transport. We anticipate this overall approach to building a data-driven model is translatable to other ECM-targeting therapeutic strategies.

Structure and function of glycosphingolipids on small extracellular vesicles

Extracellular vesicles (EVs) are membrane-delineated particles secreted by most types of cells under both normal and pathophysiological conditions. EVs are believed to mediate intercellular communication by serving as carriers of different bioactive ingredients, including proteins, nucleic acids and lipids. Glycoconjugates are complex molecules consisting of covalently linked carbohydrate with proteins or lipids. These glycoconjugates play essential roles in the sorting of vesicular protein and the uptake of small extracellular vesicles (30–100 nm, sEVs) into recipient cells. Glycosphingolipids (GSLs), one subtype of glycolipids, which are ubiquitous membrane components in almost all living organisms, are also commonly distributed on sEVs. However, the study of functional roles of GSLs on sEVs are far behind than other functional cargos. The purpose of this review is to highlight the importance of GSLs on sEVs. Initially, we described classification and structure of GSLs. Then, we briefly introduced the essential functions of GSLs, which are able to interact with functional membrane proteins, such as growth factor receptors, integrins and tetraspanins, to modulate cell growth, adhesion and cell motility. In addition, we discussed analytical methods for studying GSLs on sEVs. Finally, we focused on the function of GSLs on sEVs, including regulating the aggregation of extracellular α-synuclein (α-syn) or extracellular amyloid-β (Aβ) and influencing tumor cell malignancy.

Analysis of the Association between Galectin-3 Concentration in Tears and the Severity of Dry Eye Disease: A Case-Control Study

This study aimed to investigate the relationship between the severity of dry eye disease (DED) and galectin-3 concentration (gal-3) and its cleavage (gal-3C) in tear fluid. Twenty-eight DED patients and 14 controls were recruited at Keio University Hospital. The lissamine green conjunctival staining (LG) score, fluorescein corneal staining (FL) score, tear film break-up time (TBUT), Schirmer’s test, and ocular symptoms questionnaire score (dry eye questionnaire score, DEQS) were evaluated. Furthermore, the correlation between these parameters and the concentrations of gal-3 in tears (ng/µg) and the detection rate of gal-3C (%) were analyzed. Gal-3 concentration in tears was positively correlated with the LG score (R = 0.60, p < 0.01), FL score (R = 0.49, p < 0.01), and DEQS (R = 0.45, p < 0.01), and negatively correlated with the TBUT score (R = −0.40, p < 0.01) and Schirmer’s I value (R = −0.36, p < 0.01). The detection rate of gal-3C in tears was significantly associated with the severity of DED, especially with the LG (p < 0.01) and FL (p < 0.01) scores. Therefore, the concentration of gal-3 and the detection rate of gal-3C in tears had a significant relationship with the severity of ocular surface barrier disruption.

Novel Galectin-3 Roles in Neurogenesis, Inflammation and Neurological Diseases

Galectin-3 (Gal-3) is an evolutionarily conserved and multifunctional protein that drives inflammation in disease. Gal-3's role in the central nervous system has been less studied than in the immune system. However, recent studies show it exacerbates Alzheimer's disease and is upregulated in a large variety of brain injuries, while loss of Gal-3 function can diminish symptoms of neurodegenerative diseases such as Alzheimer's. Several novel molecular pathways for Gal-3 were recently uncovered. It is a natural ligand for TREM2 (triggering receptor expressed on myeloid cells), TLR4 (Toll-like receptor 4), and IR (insulin receptor). Gal-3 regulates a number of pathways including stimulation of bone morphogenetic protein (BMP) signaling and modulating Wnt signalling in a context-dependent manner. Gal-3 typically acts in pathology but is now known to affect subventricular zone (SVZ) neurogenesis and gliogenesis in the healthy brain. Despite its myriad interactors, Gal-3 has surprisingly specific and important functions in regulating SVZ neurogenesis in disease. Gal-1, a similar lectin often co-expressed with Gal-3, also has profound effects on brain pathology and adult neurogenesis. Remarkably, Gal-3's carbohydrate recognition domain bears structural similarity to the SARS-CoV-2 virus spike protein necessary for cell entry. Gal-3 can be targeted pharmacologically and is a valid target for several diseases involving brain inflammation. The wealth of molecular pathways now known further suggest its modulation could be therapeutically useful.

Galectin-3 as a modifier of anti-microbial immunity: Unraveling the unknowns

Galectins play diverse roles in pathophysiology of infectious diseases and cancers. Galectin-3 is one of the most studied family member and the only chimeric type lectin. Many aspects of its biogenesis, range of activities, and the disease-modifying potential particularly during microbial infections are yet to be known. We review our current understanding of these issues and also highlight gaps in better defining the immune modulatory potential of galectin-3 during different stages of host responsiveness when an infection sets in. Additionally, we discuss commonly used strategies to disrupt galectin-3 functions both extracellulalry and intracellularly. Existing and improved novel strategies could help fine-tune immune responses to achieve better prognosis of infectious diseases.

Immunoprotective neo-glycoproteins: Chemoenzymatic synthesis of multivalent glycomimetics for inhibition of cancer-related galectin-3

Galectin-3 plays a crucial role in cancerogenesis; its targeting is a prospective pathway in cancer diagnostics and therapy. Multivalent presentation of glycans was shown to strongly increase the affinity of glycoconjugates to galectin-3. Further strengthening of interaction with galectin-3 may be accomplished using artificial glycomimetics with apt aryl substitutions. We established a new, as yet undescribed chemoenzymatic method to produce selective C-3-substituted N,N'-diacetyllactosamine glycomimetics and coupled them to human serum albumin. From a library of enzymes, only β-N-acetylhexosaminidase from Talaromyces flavus was able to efficiently synthesize the C-3-propargylated disaccharide. Various aryl residues were attached to the functionalized N,N'-diacetyllactosamine via click chemistry to assess the impact of the aromatic substitution. In ELISA-type assays with galectin-3, free glycomimetics exhibited up to 43-fold stronger inhibitory potency to Gal-3 than the lactose standard. Coupling to human serum albumin afforded multivalent neo-glycoproteins with up to 4209-fold increased inhibitory potency per glycan compared to the monovalent lactose standard. Surface plasmon resonance brought further information on the kinetics of galectin-3 inhibition. The potential of prepared neo-glycoproteins to target galectin-3 was demonstrated on colorectal adenocarcinoma DLD-1 cells. We investigated the uptake of neo-glycoproteins into cells and observed limited non-specific transport into the cytoplasm. Therefore, neo-glycoproteins primarily act as efficient scavengers of exogenous galectin-3 of cancer cells, inhibiting its interaction with the cell surface, and protecting T-lymphocytes against galectin-3-induced apoptosis. The present neo-glycoproteins combine the advantage of a straightforward synthesis, selectivity, non-toxicity, and high efficiency for targeting exogenous galectin-3, with possible application in the immunomodulatory treatment of galectin-3-overexpressing cancers.

Cancer Extracellular Matrix Proteins Regulate Tumour Immunity

The extracellular matrix (ECM) plays an increasingly recognised role in the development and progression of cancer. Whilst significant progress has been made in targeting aspects of the tumour microenvironment such as tumour immunity and angiogenesis, there are no therapies that address the cancer ECM. Importantly, immune function relies heavily on the structure, physics and composition of the ECM, indicating that cancer ECM and immunity are mechanistically inseparable. In this review we highlight mechanisms by which the ECM shapes tumour immunity, identifying potential therapeutic targets within the ECM. These data indicate that to fully realise the potential of cancer immunotherapy, the cancer ECM requires simultaneous consideration.

The therapeutic potential of galectin-3 inhibition in fibrotic disease

Galectin-3 is a beta-galactoside-binding mammalian lectin and part of the 15 member galectin family that are evolutionarily highly conserved. It is the only chimeric protein with a C-terminal carbohydrate recognition domain (CRD) linked to a proline, glycine, and tyrosine rich additional N-terminal domain. Galectin-3 binds several cell surface glycoproteins via its CRD domain as well as undergoing oligomerization, via binding at the N-terminal or the CRD, resulting in the formation of a galectin-3 lattice on the cell surface. The galectin-3 lattice has been regarded as being a crucial mechanism whereby extracellular galectin-3 modulates cellular signalling by prolonging retention time or retarding lateral movement of cell surface receptors in the plasma membrane. As such galectin-3 can regulate various cellular functions such as diffusion, compartmentalization and endocytosis of plasma membrane glycoproteins and glycolipids and the functionality of membrane receptors. In multiple models of organ fibrosis, it has been demonstrated that galectin-3 is potently pro-fibrotic and modulates the activity of fibroblasts and macrophages in chronically inflamed organs. Increased galectin-3 expression also activates myofibroblasts resulting in scar formation and may therefore impact common fibrotic pathways leading to fibrosis in multiple organs. Over the last decade there has been a marked increase in the scientific literature investigating galectin-3 in a range of fibrotic diseases as well as the clinical development of new galectin-3 inhibitors. In this review we will examine the role of galectin-3 in fibrosis, the therapeutic strategies for inhibiting galectin-3 in fibrotic disease and the clinical landscape to date.

Galectin-3 Released by Pancreatic Ductal Adenocarcinoma Suppresses γδ T Cell Proliferation but Not Their Cytotoxicity

Pancreatic ductal adenocarcinoma (PDAC) is characterized by an immunosuppressive tumor microenvironment with a dense desmoplastic stroma. The expression of β-galactoside-binding protein galectin-3 is regarded as an intrinsic tumor escape mechanism for inhibition of tumor-infiltrating T cell function. In this study, we demonstrated that galectin-3 is expressed by PDAC and by γδ or αβ T cells but is only released in small amounts by either cell population. Interestingly, large amounts of galectin-3 were released during the co-culture of allogeneic in vitro expanded or allogeneic or autologous resting T cells with PDAC cells. By focusing on the co-culture of tumor cells and γδ T cells, we observed that knockdown of galectin-3 in tumor cells identified these cells as the source of secreted galectin-3. Galectin-3 released by tumor cells or addition of physiological concentrations of recombinant galectin-3 did neither further inhibit the impaired γδ T cell cytotoxicity against PDAC cells nor did it induce cell death of in vitro expanded γδ T cells. Initial proliferation of resting peripheral blood and tumor-infiltrating Vδ2-expressing γδ T cells was impaired by galectin-3 in a cell-cell-contact dependent manner. The interaction of galectin-3 with α3β1 integrin expressed by Vδ2 γδ T cells was involved in the inhibition of γδ T cell proliferation. The addition of bispecific antibodies targeting γδ T cells to PDAC cells enhanced their cytotoxic activity independent of the galectin-3 release. These results are of high relevance in the context of an in vivo application of bispecific antibodies which can enhance cytotoxic activity of γδ T cells against tumor cells but probably not their proliferation when galectin-3 is present. In contrast, adoptive transfer of in vitro expanded γδ T cells together with bispecific antibodies will enhance γδ T cell cytotoxicity and overcomes the immunosuppressive function of galectin-3.

Role of galectin-glycan circuits in reproduction: from healthy pregnancy to preterm birth (PTB)

Growing evidence suggests that galectins, an evolutionarily conserved family of glycan-binding proteins, fulfill key roles in pregnancy including blastocyst implantation, maternal-fetal immune tolerance, placental development, and maternal vascular expansion, thereby establishing a healthy environment for the growing fetus. In this review, we comprehensively present the function of galectins in shaping cellular circuits that characterize a healthy pregnancy. We describe the current understanding of galectins in term and preterm labor and discuss how the galectin-glycan circuits contribute to key immunological pathways sustaining maternal tolerance and preventing microbial infections. A deeper understanding of the glycoimmune pathways regulating early events in preterm birth could offer the broader translational potential for the treatment of this devastating syndrome.

Galectin-3 as a Next-Generation Biomarker for Detecting Early Stage of Various Diseases

Galectin-3 is a β-galactoside-binding lectin which is important in numerous biological activities in various organs, including cell proliferation, apoptotic regulation, inflammation, fibrosis, and host defense. Galectin-3 is predominantly located in the cytoplasm and expressed on the cell surface, and then often secreted into biological fluids, like serum and urine. It is also released from injured cells and inflammatory cells under various pathological conditions. Many studies have revealed that galectin-3 plays an important role as a diagnostic or prognostic biomarker for certain types of heart disease, kidney disease, viral infection, autoimmune disease, neurodegenerative disorders, and tumor formation. In particular, it has been recognized that galectin-3 is extremely useful for detecting many of these diseases in their early stages. The purpose of this article is to review and summarize the recent literature focusing on the biomarker characteristics and long-term outcome predictions of galectin-3, in not only patients with various types of diseases, but associated animal models.

Trypanosoma cruzi cleaves galectin-3 N-terminal domain to suppress its innate microbicidal activity

Galectin-3 is the best-characterized member of galectins, an evolutionary conserved family of galactoside-binding proteins that play central roles in infection and immunity, regulating inflammation, cell migration and cell apoptosis. Differentially expressed by cells and tissues with immune privilege, they bind not only to host ligands, but also to glycans expressed by pathogens. In this regard, we have previously shown that human galectin-3 recognizes several genetic lineages of the protozoan parasite Trypanosoma cruzi, the causal agent of Chagas' disease or American trypanosomiasis. Herein we describe a molecular mechanism developed by T. cruzi to proteolytically process galectin-3 that generates a truncated form of the protein lacking its N-terminal domain - required for protein oligomerization - but still conserves a functional carbohydrate recognition domain (CRD). Such processing relies on specific T. cruzi proteases, including Zn-metalloproteases and collagenases, and ultimately conveys profound changes in galectin-3-dependent effects, as chemical inhibition of parasite proteases allows galectin-3 to induce parasite death in vitro. Thus, T. cruzi might have established distinct mechanisms to counteract galectin-3-mediated immunity and microbicide properties. Interestingly, non-pathogenic T. rangeli lacked the ability to cleave galectin-3, suggesting that during evolution two genetically similar organisms have developed different molecular mechanisms that, in the case of T. cruzi, favoured its pathogenicity, highlighting the importance of T. cruzi proteases to avoid immune mechanisms triggered by galectin-3 upon infection. This study provides the first evidence of a novel strategy developed by T. cruzi to abrogate signalling mechanisms associated with galectin-3-dependent innate immunity.

Pectasol-C Modified Citrus Pectin targets Galectin-3-induced STAT3 activation and synergize paclitaxel cytotoxic effect on ovarian cancer spheroids

Here we sought to determine the relationship between STAT3 activity and Galectin‐3 (Gal‐3) and to investigate the cytotoxic effect of PectaSol‐C Modified Citrus Pectin (Pect‐MCP) as a specific competitive inhibitor of Galectin‐3 (Gal‐3) in combination with Paclitaxel (PTX) to kill the ovarian cancer cell SKOV‐3 multicellular tumor spheroid (MCTS). To this order, SKOV‐3 cells in 2D and 3D cultures were treated with exogenous Gal‐3 for the assessment of STAT3 activity. Two‐way ANOVA main effect and IC₅₀ of each drug Paclitaxel (PTX) and Pect‐MCP or in combination were obtained from MTT assay results. The phosphorylated STAT3 levels, migration, invasion, integrin mRNA and p‐AKTser⁴⁷³ levels were assessed in the absence or presence of each drug alone or in combination. Gal‐3 expression levels were assessed in human serous ovarian cancer (SOC) specimens and its correlation with different integrin mRNA levels was further assessed. Our results showed that Gal‐3 expression level was significantly increased in MCTS compared to monolayer SKOV‐3 cells which triggered STAT3 phosphorylation. Moreover, Pect‐MCP synergized with PTX to kill SKOV3 MCTS through abrogation of STAT3 activity and reduced expression of its downstream target HIF‐1α, reduced integrin mRNA levels, and subsequently decreased AKT activity. There were higher expression levels of Gal‐3 in human high‐grade SOC specimens compared to the normal ovary and borderline SOC which positively and significantly correlated with α5, β2 and β6 integrin mRNA levels. Together, these results revealed for the first time that Pect‐MCP could be considered as a potential drug to enhance the PTX effect on ovarian cancer cells MCTS through inhibition of STAT3 activity.

Protein Glycosylation and Tumor Microenvironment Alterations Driving Cancer Hallmarks

Decades of research have disclosed a plethora of alterations in protein glycosylation that decisively impact in all stages of disease and ultimately contribute to more aggressive cell phenotypes. The biosynthesis of cancer-associated glycans and its reflection in the glycoproteome is driven by microenvironmental cues and these events act synergistically toward disease evolution. Such intricate crosstalk provides the molecular foundations for the activation of relevant oncogenic pathways and leads to functional alterations driving invasion and disease dissemination. However, it also provides an important source of relevant glyco(neo)epitopes holding tremendous potential for clinical intervention. Therefore, we highlight the transversal nature of glycans throughout the currently accepted cancer hallmarks, with emphasis on the crosstalk between glycans and the tumor microenvironment stromal components. Focus is also set on the pressing need to include glycans and glycoconjugates in comprehensive panomics models envisaging molecular-based precision medicine capable of improving patient care. We foresee that this may provide the necessary rationale for more comprehensive studies and molecular-based intervention.

Effects of linker and liposome anchoring on lactose-functionalized glycomacromolecules as multivalent ligands for binding galectin-3

We combine multivalent presentation of glycan ligands on sequence-defined oligo(amidoamines) and liposomes to achieve high avidity ligands targeting galectin-3.

Histological investigation of human glaucomatous eyes: Extracellular fibrotic changes and galectin 3 expression in the trabecular meshwork and optic nerve head

Glaucoma is a leading cause of irreversible vision loss and is associated with fibrotic changes in two ocular tissues-the optic nerve head (ONH) and trabecular meshwork (TM). We investigated the differences in extracellular matrix components (ECM) including collagen, elastin, transforming growth factor beta-2, type-II receptor (TGFβRII) and Galectin3 (Gal3) in the glaucomatous human eyes to quantify fibrotic changes in ONH and TM. Glaucomatous and control human donor eyes were prepared for chemical and immunological staining to quantify ECM protein expression in the TM and ONH. Chemical staining included: Trichrome (collagen), Vernhoeff-Van Giesen (elastin) and Sirius Red (collagen). Immunohistochemistry was used to determine levels of Gal3 and TGFβ2RII. Quantitative analyses were performed using Image J software. Student's t-test was used to compare groups and Pearson's test was used to determine correlations P-values of 0.05 (or less) were considered statistically significant. Deposition of ECM proteins was elevated in glaucomatous tissues. There was increased collagen (P = 0.0469), Gal3 (P < 0.0001) and TGFβ2RII (P = 0.0005) in the TM of glaucomatous eyes. Likewise, collagen (P = 0.0517) and Galectin3 (P = 0.041) were increased in the ONH glaucomatous eyes. There was a correlation of TGFβRII with Gal3 in the TM (P < 0.0001) and optic nerve (P = 0.0003). The TM and ONH of glaucomatous eyes showed increased expression of ECM proteins supporting a fibrotic pathology. Galectin3 and TGFβ-2R II showed a positive correlation in TM and optic nerve supporting co-localization and suggesting their potential role in the glaucoma fibrotic process. Clin. Anat. 31:1031-1049, 2018. © 2018 The Authors. Clinical Anatomy published by Wiley Periodicals, Inc. on behalf of American Association of Clinical Anatomists.

Xanthohumol and 8-prenylnaringenin reduce type 2 diabetes-associated oxidative stress by downregulating galectin-3

Background

Galectin-3 (Gal3) expression is associated with accumulation of Advanced Glycation End products (AGE), a common feature in diabetes mellitus (DM). The role of Gal3 in oxidative stress is, however, controversial, being considered in the literature to play either a protective role or exacerbating disease.

Methods

Herein, we examined the interplay between Gal3 and oxidative stress in a high-fat diet -induced type 2 DMC57Bl/6 mice model. Because natural polyphenols are known to play antioxidant and anti-inflammatory roles and to modulate metabolic activity, we further evaluated the effect of xanthohumol and 8-prenylnaringenin polyphenols in this crosstalk.

Results

Gal3 expression was accompanied by 3-nitrotyrosine and AGE production in liver and kidney of diabetic mice compared to healthy animals (fed with standard diet). Oral supplementation with polyphenols decreased the levels of these oxidative biomarkers as evaluated by immunohistochemistry and western blotting. Interestingly, blocking Gal3 by incubating human microvascular endothelial cells with modified citrus pectin increased 3-nitrotyrosine protein expression.

Conclusions

These findings imply that Gal3 overexpression is probably controlling oxidative stress in endothelial cells. In conclusion, our results indicate that supplementation with 8-prenylnaringenin or xanthohumol reverses diabetes-associated oxidation in liver and kidney, and consequently decreases this diabetic biomarker that predispose to cardiovascular complications.

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.

Galectin-3 Activation and Inhibition in Heart Failure and Cardiovascular Disease: An Update

Galectin-3 is a versatile protein orchestrating several physiological and pathophysiological processes in the human body. In the last decade, considerable interest in galectin-3 has emerged because of its potential role as a biotarget. Galectin-3 is differentially expressed depending on the tissue type, however its expression can be induced under conditions of tissue injury or stress. Galectin-3 overexpression and secretion is associated with several diseases and is extensively studied in the context of fibrosis, heart failure, atherosclerosis and diabetes mellitus. Monomeric (extracellular) galectin-3 usually undergoes further "activation" which significantly broadens the spectrum of biological activity mainly by modifying its carbohydrate-binding properties. Self-interactions of this protein appear to play a crucial role in regulating the extracellular activities of this protein, however there is limited and controversial data on the mechanisms involved. We therefore summarize (recent) literature in this area and describe galectin-3 from a binding perspective providing novel insights into mechanisms by which galectin-3 is known to be "activated" and how such activation may be regulated in pathophysiological scenarios.

Role of Galectin-3 in Bone Cell Differentiation, Bone Pathophysiology and Vascular Osteogenesis

Galectin-3 is expressed in various tissues, including the bone, where it is considered a marker of chondrogenic and osteogenic cell lineages. Galectin-3 protein was found to be increased in the differentiated chondrocytes of the metaphyseal plate cartilage, where it favors chondrocyte survival and cartilage matrix mineralization. It was also shown to be highly expressed in differentiating osteoblasts and osteoclasts, in concomitance with expression of osteogenic markers and Runt-related transcription factor 2 and with the appearance of a mature phenotype. Galectin-3 is expressed also by osteocytes, though its function in these cells has not been fully elucidated. The effects of galectin-3 on bone cells were also investigated in galectin-3 null mice, further supporting its role in all stages of bone biology, from development to remodeling. Galectin-3 was also shown to act as a receptor for advanced glycation endproducts, which have been implicated in age-dependent and diabetes-associated bone fragility. Moreover, its regulatory role in inflammatory bone and joint disorders entitles galectin-3 as a possible therapeutic target. Finally, galectin-3 capacity to commit mesenchymal stem cells to the osteoblastic lineage and to favor transdifferentiation of vascular smooth muscle cells into an osteoblast-like phenotype open a new area of interest in bone and vascular pathologies.

Quantitative proteomics reveal the anti-tumour mechanism of the carbohydrate recognition domain of Galectin-3 in Hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a serious threat to human health. The carbohydrate recognition domain of Galectin-3 (Gal3C) has been reported to be an anti-tumour molecule. In this study, we aim to explore effects of Gal3C in HCC and its possible molecular mechanism with quantitative proteomics approach. We found that rGal3C stimulation could inhibit cell viability, migration and invasion of HepG2. After rGal3C stimulating, 190 proteins were differentially expressed. Eighty up-regulated proteins located mainly in extracellular exosome and involved in cell adhesion and metabolism, and 110 down-regulated proteins located in mitochondria and extracellular exosome, and related to processes of metabolism and oxidation-reduction. Of the differentially expressed proteins, CLU, NDRG1, CD166, S100A11 and Galectin-1 were carcinoma-related proteins affected by rGal3C. Potential receptors of rGal3C were explored by an UV cross-linking capture strategy. We showed that rGal3C could induce dephosphorylating of FAK/SRC. Blocking of the FAK/SRC pathway resulted in down-regulation of NDRG1. Immunofluorescence suggested that rGal3C could disrupt integrin clustering. Our study provides valuable insight into the anti-tumour mechanism of rGal3C in HCC on a proteomics level and is the first to reveal the possible mechanism involving integrin/FAK/SRC pathway and NDRG1. These results provide useful guidance of developing new therapies for HCC.

Proteome-wide Identification of Glycosylation-dependent Interactors of Galectin-1 and Galectin-3 on Mesenchymal Retinal Pigment Epithelial (RPE) Cells

Identification of interactors is a major goal in cell biology. Not only protein-protein but also protein-carbohydrate interactions are of high relevance for signal transduction in biological systems. Here, we aim to identify novel interacting binding partners for the β-galactoside-binding proteins galectin-1 (Gal-1) and galectin-3 (Gal-3) relevant in the context of the eye disease proliferative vitreoretinopathy (PVR). PVR is one of the most common failures after retinal detachment surgeries and is characterized by the migration, adhesion, and epithelial-to-mesenchymal transition of retinal pigment epithelial cells (RPE) and the subsequent formation of sub- and epiretinal fibrocellular membranes. Gal-1 and Gal-3 bind in a dose- and carbohydrate-dependent manner to mesenchymal RPE cells and inhibit cellular processes like attachment and spreading. Yet knowledge about glycan-dependent interactors of Gal-1 and Gal-3 on RPE cells is very limited, although this is a prerequisite for unraveling the influence of galectins on distinct cellular processes in RPE cells. We identify here 131 Gal-3 and 15 Gal-1 interactors by galectin pulldown experiments combined with quantitative proteomics. They mainly play a role in multiple binding processes and are mostly membrane proteins. We focused on two novel identified interactors of Gal-1 and Gal-3 in the context of PVR: the low-density lipoprotein receptor LRP1 and the platelet-derived growth factor receptor β PDGFRB. Addition of exogenous Gal-1 and Gal-3 induced cross-linking with LRP1/PDGFRB and integrin-β1 (ITGB1) on the cell surface of human RPE cells and induced ERK/MAPK and Akt signaling. Treatment with kifunensine, an inhibitor of complex-type N-glycosylation, weakened the binding of Gal-1 and Gal-3 to these interactors and prevented lattice formation. In conclusion, the identified specific glycoprotein ligands shed light into the highly specific binding of galectins to dedifferentiated RPE cells and the resulting prevention of PVR-associated cellular events.

Potent pro-inflammatory and pro-fibrotic molecules, osteopontin and galectin-3, are not major disease modulators of laminin α2 chain-deficient muscular dystrophy

A large number of human diseases are caused by chronic tissue injury with fibrosis potentially leading to organ failure. There is a need for more effective anti-fibrotic therapies. Congenital muscular dystrophy type 1A (MDC1A) is a devastating form of muscular dystrophy caused by laminin α2 chain-deficiency. It is characterized with early inflammation and build-up of fibrotic lesions, both in patients and MDC1A mouse models (e.g. dy^3K/dy^3K). Despite the enormous impact of inflammation on tissue remodelling in disease, the inflammatory response in MDC1A has been poorly described. Consequently, a comprehensive understanding of secondary mechanisms (impaired regeneration, enhanced fibrosis) leading to deterioration of muscle phenotype in MDC1A is missing. We have monitored inflammatory processes in dy^3K/dy^3K muscle and created mice deficient in laminin α2 chain and osteopontin or galectin-3, two pro-inflammatory and pro-fibrotic molecules drastically increased in dystrophic muscle. Surprisingly, deletion of osteopontin worsened the phenotype of dy^3K/dy^3K mice and loss of galectin-3 did not reduce muscle pathology. Our results indicate that osteopontin could even be a beneficial immunomodulator in MDC1A. This knowledge is essential for the design of future therapeutic interventions for muscular dystrophies that aim at targeting inflammation, especially that osteopontin inhibition has been suggested for Duchenne muscular dystrophy therapy.

O-glycan sialylation alters galectin-3 subcellular localization and decreases chemotherapy sensitivity in gastric cancer

ST6GalNAc-I, the sialyltransferase responsible for sialyl-Tn (sTn) synthesis, has been previously reported to be positively associated with cancer aggressiveness. Here we describe a novel sTn-dependent mechanism for chemotherapeutic resistance. We show that sTn protects cancer cells against chemotherapeutic-induced cell death by decreasing the interaction of cell surface glycan receptors with galectin-3 and increasing its intracellular accumulation. Moreover, exogenously added galectin-3 potentiated the chemotherapeutics-induced cytotoxicity in sTn non-expressing cells, while sTn overexpressing cells were protected. We also found that the expression of sTn was associated with a reduction in galectin-3-binding sites in human gastric samples tumors. ST6GalNAc-I knockdown restored galectin-3-binding sites on the cell surface and chemotherapeutics sensibility. Our results clearly demonstrate that an interruption of O-glycans extension caused by ST6GalNAc-I enzymatic activity leads to tumor cells resistance to chemotherapeutic drugs, highlighting the need for the development of novel strategies to target galectin-3 and/or ST6GalNAc-I.

Glycolipids and Lectins in Endocytic Uptake Processes

A host of endocytic processes has been described at the plasma membrane of eukaryotic cells. Their categorization has most commonly referenced cytosolic machinery, of which the clathrin coat has occupied a preponderant position. In what concerns intra-membrane constituents, the focus of interest has been on phosphatidylinositol lipids and their capacity to orchestrate endocytic events on the cytosolic leaflet of the membrane. The contribution of extracellular determinants to the construction of endocytic pits has received much less attention, depite the fact that (glyco)sphingolipids are exoplasmic leaflet fabric of membrane domains, termed rafts, whose contributions to predominantly clathrin-independent internalization processes is well recognized. Furthermore, sugar modifications on extracellular domains of proteins, and sugar-binding proteins, termed lectins, have also been linked to the uptake of endocytic cargoes at the plasma membrane. In this review, we first summarize these contributions by extracellular determinants to the endocytic process. We thus propose a molecular hypothesis - termed the GL-Lect hypothesis - on how GlycoLipids and Lectins drive the formation of compositional nanoenvrionments from which the endocytic uptake of glycosylated cargo proteins is operated via clathrin-independent carriers. Finally, we position this hypothesis within the global context of endocytic pathway proposals that have emerged in recent years.

The Two Faces of Galectin-3: Roles in Various Pathological Conditions

Galectin-3, a unique chimaera-type member of the lectin family, displays a wide range of activities. This versatile molecule is involved in fundamental biological processes, including cell proliferation, cell-cell adhesion, apoptosis and immune responses.

This review is aimed at providing a general overview of the biological actions and diverse effects of Galectin-3 in many pathological conditions, with a specific focus on autoimmunity, inflammation and tumour progression. We report herein that Galectin-3 exerts deleterious functions determined by promotion of tumour progression and liver inflammation or aggravation of T cell-mediated autoimmune diseases. On the other hand, Galectin-3 exhibits a protective role in metabolic abnormalities and primary biliary cirrhosis.

The paradoxical “yin and yang” functions of Galectin-3 depend not only on its tissue and cellular localization but also on its availability, glycosylation status and the expression level of its ligands.

Current biomarkers of invasive sporadic pituitary adenomas

Though pituitary adenomas (PA) are considered benign, some of them exhibit invasive behaviors such as recurrence and low rate of total surgical resection. Reliable prognostic biomarkers for invasive PA are highly desired; however they remain to be identified. In this review, we summarize the current controversial findings of biomarkers for invasive sporadic PA, and we discuss the possible reasons for the controversies.

Identification of galectin-3 as a possible antibody target for secondary progressive multiple sclerosis

Background:

Recent studies have revealed that the disruption of the blood–brain barrier (BBB) might contribute to the induction of neurodegeneration in the progressive stage of multiple sclerosis (MS).

Objective:

We investigated a potential target for the serum auto-antibodies responsible for the BBB impairment in patients with secondary progressive MS (SPMS).

Methods:

We identified undetermined target antigens in human brain microvascular endothelial cells (BMECs) that reacted with auto-antibodies in sera from SPMS patients using a proteomic approach. In addition, we examined how the identified auto-antibodies compromise the BBB integrity.

Results:

We found that 10 of 11 SPMS sera had auto-antibodies against galectin-3, although the patients with other neurological diseases did not have these antibodies. Downregulation of galectin-3 led to elevated intercellular adhesion molecule-1 (ICAM-1) and phospho-nuclear factor-kappa (NFκ) B p65 expression in the BMECs. Exposure to SPMS patients’ sera also increased the protein levels of ICAM-1 and phospho-NFκB p65 in BMECs, but these effects induced by anti-galectin-3 immunoreactivity were canceled by the downregulation of galectin-3.

Conclusion:

Galectin-3 is a possible immunological target molecule of the pathogenic auto-antibodies and contributes to the persistent BBB breakdown in patients with SPMS. These antibodies may also serve as a novel biomarker for SPMS.

TGFβ regulates Galectin-3 expression through canonical Smad3 signaling pathway in nucleus pulposus cells: implications in intervertebral disc degeneration

Galectin-3 is highly expressed in notochordal nucleus pulposus (NP) and thought to play important physiological roles; however, regulation of its expression remains largely unexplored. The aim of the study was to investigate if TGFβ regulates Galectin-3 expression in NP cells. TGFβ treatment resulted in decreased Galectin-3 expression. Bioinformatic analysis using JASPAR and MatInspector databases cross-referenced with published ChIP-Seq data showed nine locations of highly probable Smad3 binding in the LGALS3 proximal promoter. In NP cells, TGFβ treatment resulted in decreased activity of reporters harboring several 5' deletions of the proximal Galectin-3 promoter. While transfection of NP cells with constitutively active (CA)-ALK5 resulted in decreased promoter activity, DN-ALK5 blocked the suppressive effect of TGFβ on the promoter. The suppressive effect of Smad3 on the Galectin-3 promoter was confirmed using gain- and loss-of-function studies. Transfection with DN-Smad3 or Smad7 blocked TGFβ mediated suppression of promoter activity. We also measured Galectin-3 promoter activity in Smad3 null and wild type cells. Noteworthy, promoter activity was suppressed by TGFβ only in wild type cells. Likewise, stable silencing of Smad3 in NP cells using sh-Smad3 significantly blocked TGFβ-dependent decrease in Galectin-3 expression. Treatment of human NP cells isolated from tissues with different grades of degeneration showed that Galectin-3 expression was responsive to TGF-β-mediated suppression. Importantly, Galectin-3 synergized effects of TNF-α on inflammatory gene expression by NP cells. Together these studies suggest that TGFβ, through Smad3 controls Galectin-3 expression in NP cells and may have implications in the intervertebral disc degeneration.

Galectin-3 as a Potential Target to Prevent Cancer Metastasis

Interactions between two cells or between cell and extracellular matrix mediated by protein–carbohydrate interactions play pivotal roles in modulating various biological processes such as growth regulation, immune function, cancer metastasis, and apoptosis. Galectin-3, a member of the β-galactoside-binding lectin family, is involved in fibrosis as well as cancer progression and metastasis, but the detailed mechanisms of its functions remain elusive. This review discusses its structure, carbohydrate-binding properties, and involvement in various aspects of tumorigenesis and some potential carbohydrate ligands that are currently investigated to block galectin-3 activity.

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.

Galectin-3 enhances extracellular matrix associations and wound healing in monkey corneal epithelium

Poor healing of epithelial wounds in cornea is a major clinical problem, leading to persistent epithelial defects and ulceration. The primary cause is poor cell migration over the wound. Carbohydrate-binding protein galectin-3 binds to extracellular matrixes (ECMs) and promotes lamellipodia formation by cross-linking to α3 integrin. Recombinant galectin-3 also facilitates wound healing in the rodent cornea. The purposes of the present experiments were to: (1) establish epithelial wound healing models in monkey corneal explant culture, the models more relevant to human, (2) evaluate the healing effect of galectin-3 in our models, and (3) determine if galectin-3 enhances cell adhesion by interacting with ECMs on corneal surface and their ligand integrins. Monkey corneas with central wounds produced by sodium hydroxide (NaOH) or n-heptanol were incubated with or without recombinant galectin-3. The defected area was stained with sodium fluorescein. Primary isolated corneal epithelial cells from monkey were cultured with or without galectin-3 on plates coated with ECMs or integrins, and the number of adhering cells was counted. Galectin-3 expression in various eye tissues was visualized by immunoblotting. NaOH caused loss of epithelial cells and basement membrane. n-Heptanol removed epithelial cells, but the basement membrane was retained. These corneal defects spontaneously became smaller in a time-dependent manner. Exogenous galectin-3 enhanced wound healing in both NaOH and n-heptanol models. Galectin-3 also enhanced cell adhesion onto the major ECMs found in the basement and Bowman's membranes and onto integrins. Relatively high levels of galectin-3 were detected in corneal and conjunctival epithelium, but tear fluid contained negligible galactin-3. These results suggested that the enhanced binding of epithelial cells to ECMs and integrins caused by galectin-3 might promote cell migration over wounded corneal surfaces. Since tear fluid contained relatively low levels of galectin-3, exogenous galectin-3 may be a beneficial drug to enhance re-epithelialization in human corneal diseases.

Serum galectin-3 as a potential marker for gastric cancer

Background

The identification of cancer biomarkers can advance the possibility for early detection and better monitoring of tumor progression. The aim of this study was to assess the diagnostic and prognostic value of serum galectin-3(Gal-3) in patients with gastric cancer (GC).

Material/Methods

We measured serum Gal-3 levels using ELISA method in 87 patients with GC, 53 patients with benign gastric lesions, and 51 healthy controls.

Results

Serum levels of Gal-3 in patients with GC were significantly higher than those in benign disease patients and healthy controls (P<0.001), but no difference was found between benign disease patients and healthy controls (P=0.635). Additionally, serum Gal-3 level was associated with lymph node metastasis (P=0.001) and distant metastasis (P<0.001), whereas it was not related to gender (P=0.204), age (P=0.269), tumor size (P=0.399), location (P=0.715), TNM stage (P=0.385), differentiation (P=0.135), or invasion depth (P=0.273). The Kaplan-Meier survival analysis revealed that overall survival rates in patients with high Gal-3 levels were not significantly different that those with low Gal-3 levels (P=0.099).

Conclusions

Results of the current study suggests that serum Gal-3 represents a potential diagnostic marker for patients with GC, and may be an adjunct to determine the individual prognosis of these patients.

Galectin-3 regulates hepatic progenitor cell expansion during liver injury

OBJECTIVE

Following chronic liver injury or when hepatocyte proliferation is impaired, ductular reactions containing hepatic progenitor cells (HPCs) appear in the periportal regions and can regenerate the liver parenchyma. HPCs exist in a niche composed of myofibroblasts, macrophages and laminin matrix. Galectin-3 (Gal-3) is a β-galactoside-binding lectin that binds to laminin and is expressed in injured liver in mice and humans.

DESIGN

We examined the role of Gal-3 in HPC activation. HPC activation was studied following dietary induced hepatocellular (choline-deficient ethionine-supplemented diet) and biliary (3,5-diethoxycarbonyl-1,4-dihydrocollidine supplemented diet) injury in wild type and Gal-3(-/-) mice.

RESULTS

HPC proliferation was significantly reduced in Gal-3(-/-) mice. Gal-3(-/-) mice failed to form a HPC niche, with reduced laminin formation. HPCs isolated from wild type mice secrete Gal-3 which enhanced adhesion and proliferation of HPCs on laminin in an undifferentiated form. These effects were attenuated in Gal3(-/-) HPCs and in wild type HPCs treated with the Gal-3 inhibitor lactose. Gal-3(-/-) HPCs in vitro showed increased hepatocyte function and prematurely upregulated both biliary and hepatocyte differentiation markers and regulated cell cycle genes leading to arrest in G0/G1.

CONCLUSIONS

We conclude that Gal-3 is required for the undifferentiated expansion of HPCs in their niche in injured liver.