Soluble Lectin Research Articles

Functions and Inhibition of Galectin-7, an Emerging Target in Cellular Pathophysiology.

Galectin-7 is a soluble unglycosylated lectin that is able to bind specifically to β-galactosides. It has been described to be involved in apoptosis, proliferation and differentiation, but also in cell adhesion and migration. Several disorders and diseases are discussed by covering the aforementioned biological processes. Structural features of galectin-7 are discussed as well as targeting the protein intracellularly or extracellularly. The exact molecular mechanisms that lie behind many biological processes involving galectin-7 are not known. It is therefore useful to come up with chemical probes or tools in order to obtain knowledge of the physiological processes. The objective of this review is to summarize the roles and functions of galectin-7 in the human body, providing reasons why it is necessary to design inhibitors for galectin-7, to give the reader structural insights and describe its current inhibitors.

Glycocalyx crowding with mucin mimetics strengthens binding of soluble and virus-associated lectins to host cell glycan receptors

Membrane-associated mucins protect epithelial cell surfaces against pathogenic threats by serving as nonproductive decoys that capture infectious agents and clear them from the cell surface and by erecting a physical barrier that restricts their access to target receptors on host cells. However, the mechanisms through which mucins function are still poorly defined because of a limited repertoire of tools available for tailoring their structure and composition in living cells with molecular precision. Using synthetic glycopolymer mimetics of mucins, we modeled the mucosal glycocalyx on red blood cells (RBCs) and evaluated its influence on lectin (SNA) and virus (H1N1) adhesion to endogenous sialic acid receptors. The glycocalyx inhibited the rate of SNA and H1N1 adhesion in a size- and density-dependent manner, consistent with the current view of mucins as providing a protective shield against pathogens. Counterintuitively, increasing the density of the mucin mimetics enhanced the retention of bound lectins and viruses. Careful characterization of SNA behavior at the RBC surface using a range of biophysical and imaging techniques revealed lectin-induced crowding and reorganization of the glycocalyx with concomitant enhancement in lectin clustering, presumably through the formation of a more extensive glycan receptor patch at the cell membrane. Our findings indicate that glycan-targeting pathogens may exploit the biophysical and biomechanical properties of mucins to overcome the mucosal glycocalyx barrier.

SARS-CoV-2 S glycoprotein binding to multiple host receptors enables cell entry and infection.

The severe acute respiratory syndrome-related coronavirus-2 (SARS-CoV-2) infection displays a wide array of clinical manifestations. Although some risk factors for coronavirus disease 2019 (COVID-19) severity and outcomes have been identified the underlying biologic mechanisms are still not well understood. The surface SARS-CoV-2 proteins are heavily glycosylated enabling host cell interaction and viral entry. Angiotensin-converting enzyme 2 (ACE2) has been identified to be the main host cell receptor enabling SARS-CoV-2 cell entry after interaction with its S glycoprotein. However, recent studies report SARS-CoV-2 S glycoprotein interaction with other cell receptors, mainly C-type lectins which recognize specific glycan epitopes facilitating SARS-CoV-2 entry to susceptible cells. Here, we are summarizing the main findings on SARS-CoV-2 interactions with ACE2 and other cell membrane surface receptors and soluble lectins involved in the viral cell entry modulating its infectivity and potentially playing a role in subsequent clinical manifestations of COVID-19.Graphical abstract

Recombinant lectins as pioneering anti-viral agents against COVID-19

The primary target for vaccine design and anti-viral therapeutics for the deadly severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causing coronavirus disease 2019 (COVID-19) is the coronavirus surface spike (S) glycoprotein. Like other enveloped viruses, S glycoproteins are masked by a dense sugar “coat” of host-derived glycans that mediate immune evasion by molecular mimicry through shielding the immunogenic surface proteins from host immune responses. Paradoxically, this same protective glycan shield can make these sugar-coated viruses vulnerable to immune attack by soluble lectins of the innate immune system that are still able to recognise these glycans as pathogen-associated molecular patterns (PAMPs) leading to complement activation. In reality, recombinant lectins that target virus-associated glycans have the potential to be used as anti-viral agents; and therefore, binding of recombinant lectins to viruses could represent a paradigm shift for viral infection therapy. Likewise, SARS-CoV-2- associated glycans can offer novel targets for recombinant lectins as innovative anti-SARSCoV-2 agents. Unfortunately, pharmacological hurdles currently constrain the entry of recombinant lectins into clinical trials but more vigorous research into potentially useful modifications of these agents can truly develop a new landscape of anti-viral lectin-based therapeutics.

The Relationship between Inflammation Markers (CRP, IL-6, sCD40L) and Colorectal Cancer Stage, Grade, Size and Location.

The aim of the study was the evaluation whether in primary colorectal cancer (CRC) patients (n = 55): age, sex, TNM classification results, WHO grade, tumor location (proximal colon, distal colon, rectum), tumor size, platelet count (PLT), mean platelet volume (MPV), mean platelet component (MCP), levels of carcinoembryonic antigen (CEA), cancer antigen (CA 19-9), as well as soluble lectin adhesion molecules (L-, E-, and P-selectins) may influence circulating inflammatory biomarkers: IL-6, CRP, and sCD40L. We found that CRP concentration evaluation in routine clinical practice may have an advantage as a prognostic biomarker in CRC patients, as this protein the most comprehensively reflects clinicopathological features of the tumor. Univariate linear regression analysis revealed that in CRC patients: (1) with an increase in PLT by 10 × 103/μL, the mean concentration of CRP increases by 3.4%; (2) with an increase in CA 19-9 of 1 U/mL, the mean concentration of CRP increases by 0.7%; (3) with the WHO 2 grade, the mean CRP concentration increases 3.631 times relative to the WHO 1 grade group; (4) with the WHO 3 grade, the mean CRP concentration increases by 4.916 times relative to the WHO 1 grade group; (5) with metastases (T1-4N+M+) the mean CRP concentration increases 4.183 times compared to non-metastatic patients (T1-4N0M0); (6) with a tumor located in the proximal colon, the mean concentration of CRP increases 2.175 times compared to a tumor located in the distal colon; (7) in patients with tumor size > 3 cm, the CRP concentration is about 2 times higher than in patients with tumor size ≤ 3 cm. In the multivariate linear regression model, the variables that influence the mean CRP value in CRC patients included: WHO grade and tumor localization. R2 for the created model equals 0.50, which indicates that this model explains 50% of the variance in the dependent variable. In CRC subjects: (1) with the WHO 2 grade, the mean CRP concentration rises 3.924 times relative to the WHO 1 grade; (2) with the WHO 3 grade, the mean CRP concentration increases 4.721 times in relation to the WHO 1 grade; (3) with a tumor located in the rectum, the mean CRP concentration rises 2.139 times compared to a tumor located in the distal colon; (4) with a tumor located in the proximal colon, the mean concentration of CRP increases 1.998 times compared to the tumor located in the distal colon; if other model parameters are fixed.

Structural insights in galectin-1-glycan recognition: Relevance of the glycosidic linkage and the N-acetylation pattern of sugar moieties

Galectins, soluble lectins widely expressed intra- and extracellularly in different cell types, play major roles in deciphering the cellular glycocode. Galectin-1 (Gal-1), a prototype member of this family, presents a carbohydrate recognition domain (CRD) with specific affinity for β-galactosides such as N-acetyllactosamine (β-d-Galp-(1 → 4)-d-GlcpNAc), and mediate numerous physiological and pathological processes.In this work, Gal-1 binding affinity for β-(1 → 6) galactosides, including β-d-Galp-(1 → 6)-β-d-GlcpNAc-(1 → 4)-d-GlcpNAc was evaluated, and their performance was compared to that of β-(1 → 4) and β-(1 → 3) galactosides. To this end, the trisaccharide β-d-Galp-(1 → 6)-β-d-GlcpNAc-(1 → 4)-d-GlcpNAc was enzymatically synthesized, purified and structurally characterized.To evaluate the affinity of Gal-1 for the galactosides, competitive solid phase assays (SPA) and isothermal titration calorimetry (ITC) studies were carried out. The experimental dissociation constants and binding energies obtained were compared to those calculated by molecular docking. These analyses evidenced the critical role of the glycosidic linkage between the terminal galactopyranoside residue and the adjacent monosaccharide, as galactosides bearing β-(1 → 6) glycosidic linkages showed dissociation constants six- and seven-fold higher than those involving β-(1 → 4) and β-(1 → 3) linkages, respectively. Moreover, docking experiments revealed the presence of hydrogen bond interactions between the N-acetyl group of the glucosaminopyranose moiety of the evaluated galactosides and specific amino acid residues of Gal-1, relevant for galectin-glycan affinity. Noticeably, the binding free energies (ΔGbindcalc) derived from the molecular docking were in good agreement with experimental values determined by ITC measurements (ΔGbindexp), evidencing a good correlation between theoretical and experimental approaches, which validates the in silico simulations and constitutes an important tool for the rational design of future optimized ligands.

Protective Role of Collectin 11 in a Mouse Model of Rheumatoid Arthritis.

Collectin 11 (CL-11) is a soluble C-type lectin, a mediator of innate immunity. Its role in autoimmune disorders is unknown. We undertook this study to determine the role of CL-11 in a mouse model of rheumatoid arthritis (RA). A murine collagen-induced arthritis (CIA) model was used and combined two approaches, including gene deletion of Colec11 and treatment with recombinant CL-11 (rCL-11). Joint inflammation and tissue destruction, circulating levels of inflammatory cytokines, and adaptive immune responses were assessed in mice with CIA. Splenic CD11c+ cells were used to examine the influence of CL-11 on antigen-presenting cell (APC) function. Serum CL-11 levels in RA patients were also examined. Colec11-/- mice developed more severe arthritis than wild-type mice, as determined by disease incidence, clinical arthritis scores, and histopathology (P < 0.05). Disease severity was associated with significantly enhanced APC activation, Th1/Th17 responses, pathogenic IgG2a production and joint inflammation, as well as elevated circulating levels of inflammatory cytokines. In vitro analysis of CD11c+ cells revealed that CL-11 is critical for suppression of APC activation and function. Pharmacologic treatment of mice with rCL-11 reduced the severity of CIA in mice. Analysis of human blood samples revealed that serum CL-11 levels were lower in RA patients (n = 51) compared to healthy controls (n = 53). Reduction in serum CL-11 was inversely associated with the Disease Activity Score in 28 joints, erythrocyte sedimentation rate, and C-reactive protein level (P < 0.05). Our findings demonstrate a novel role of CL-11 in protection against RA, suggesting that the underlying mechanism involves suppression of APC activation and subsequent T cell responses.

BIOCHEMICAL CHARACTERISTIC OF SOLUBLE LECTINS IN CORN UNDER THE IMPACT OF WATER DEFICIT AND HYPERTHERMIA

Introduction. Drought and high temperature are two of the key factors of the environment limiting crop capacity of grains. Response of the plants to drought and high temperature is very complex and includes interaction between various molecular, physiological and biochemical processes. Synthesis of a number of proteins present under normal conditions, including lectins, increases along with synthesis of stress proteins under adverse conditions.Aim. The goal of our study is to identify the changes in the activity and biochemical characteristics of soluble lectins in maize seedlings with different drought tolerance under water and heat stress in order to create new biochemical methods for assessing drought tolerance.Methods. Three-day young sprouts of corn lines (Zea mays L.) with different levels of drought tolerance were used in the research: drought-tolerant lines Od 329, IK107 zM, non-drought tolerant lines GK 26, IK107VS3 / 66. Lectin activity was defined on the basis of their ability to agglutinate trypsinized erythrocytes of white rats. Electrophoresis was performed in 10 % PAGE following the Laemmli method.Results. The study enabled us to identify increase in soluble lectin activity (244-281 % of the reference value) under the given stress factors in drought-tolerant lines, and decrease in soluble lectin activity (39 - 79 % of reference value) under the given stress factors in non-drought-tolerant lines. Soluble lectins were isolated and purifid using salting out with ammonium sulfate, dialysis and affiity chromatography. The molecular weight of the isolated soluble lectins is in the range of 50-60 kDa. The isolated lectins had a high affiity for N-acetylglucosamine and D-fructose-6-phosphate.Conclusion. Therefore, it has been established that corn lines with positively different levels of drought tolerance are characterized by varying activity of soluble lectins.

Modulation of the carbohydrate-binding specificity of two Xenopus proto-type galectins by site-directed mutagenesis

The galectin family is a representative soluble lectin group, which is responsible for the modulation of various cell functions. Although the carbohydrate-binding specificity of galectins has been well-studied, the relationship between protein structure and specificity remains to be elucidated. We previously reported the characteristics of a Xenopus laevis skin galectin, xgalectin-Va, which had diverged from galectin-1. The carbohydrate selectivity of xgalectin-Va was different from that of human galectin-1 and xgalectin-Ib (a Xenopus laevis galectin-1 homolog). In this study, we clarified the key residues for this selectivity by site-directed mutagenesis. Substitution of two amino acids of xgalectin-Va, Val56Gly/Lys76Arg, greatly enhanced the binding ability to N-acetyllactosamine and conferred significant T-cell growth inhibition activity, although the wild type had no activity. These two residues, Gly54 and Arg74 in galectin-1, would cooperatively contribute to the N-acetyllactosamine recognition. The loop region between the S4 and S5 β-strands was involved in the binding to the TF-antigen disaccharide. The loop substitution successfully changed the carbohydrate selectivity of xgalectin-Va and xgalectin-Ib.

Recalibrating Immunity in Cancer and Autoimmune Inflammation by Galectin-1-Driven Regulatory Circuits

Endogenous lectins play key roles in cell homeostasis by decoding the information encrypted in glycans present on the cell surface or extracellular matrix. Galectins, a family of soluble lectins, have emerged as central regulators of innate and adaptive immune responses. In this article, we review seminal work demonstrating the immunoregulatory roles of Galectin-1 (Gal-1), a proto-type member of the galectin family, and highlight central mechanisms that control its functions in cancer and autoimmune inflammation. Understanding the cellular pathways that control Gal-1 expression and function in tumor and inflammatory microenvironments will set the bases for the design of rational therapies based on positive or negative modulation of this endogenous lectin in cancer and autoimmune diseases.

Role of Plasma Soluble Lectin Like Oxidized Low-Density Lipoprotein Receptor-1 in Severity of CAD Patients and Relationship with Microrna-98

Coronary artery diseases are the most important cause of premature death and it is predominantly related to atherosclerosis. Soluble lectin like oxidized low-density lipoprotein receptor-1 (sLOX-1) and microRNAs are closely associated with atherosclerotic coronary heart diseases. The current study investigated the relationship of plasma slOX-1and the severity of coronary artery disease patients (CAD) and association with microRNA-98. Case control study. Angiographically documented 38 single coronary lesions, 75 double coronary artery disease, 62 multi-vessel coronary artery disease patients, 62 healthy control subjects, and 24h hypoxic (1% O2) HUVEC cells were included in this study. Circulating sLOX-1concentrations were determined through enzyme-linked immunosorbent assays and microRNA-98 expressions were measured by the quantitative real- time polymerase chain reaction. The expressions of plasma sLOX-1 levels were progressively and significantly higher in single, double, and multi-vessel CAD patients than healthy control subjects (p<0.001). Circulating sLOX-1 concentrations in multi-vessel, double vessel and single vessel CAD female subjects had evidently elevated than male subjects (p<0.001). Plasma sLOX-1 values were remarkably increased in female different age groups CAD patients as compared with the same male age subjects (p<0.001). Single vessel diseased (AUC 0.879), double vessel diseased (AUC 0.928) and multi-vessel diseased (AUC 0.943) CAD patients have been clearly differentiated from healthy participants with high sensitivity and specificity. The expression of microRNA-98 noticeably down-regulated in single, double and multi-vessel occluded CAD patients and hypoxic exposed HUVEC than controls (p<0.001). Significantly elevated LOX-1 and caspase-3 activity and remarkably decreased cellular viability in hypoxic injured HUVEC. On the contrary, mimic of microRNA-98 markedly reduced caspase-3 and LOX-1 levels and highly increased cellular viability. Elevated circulating plasma sLOX-1 levels have a potential impact to identify the severity of coronary artery disease and a strong correlation with aging as well as the female gender. Reduced plasma miR-98 level possible considers a risk factor for CAD, and agomiR-98 prevents atherosclerosis and cellular injury through targeting LOX-1.

Increased Galectin-9 expression, a prognostic biomarker of aGVHD, regulates the immune response through the Galectin-9 induced MDSC pathway after allogeneic hematopoietic stem cell transplantation

Galectin-9 (Gal-9) is a β-galactoside-binding soluble lectin family member that exerts its primary biological functions via specific glycoconjugate interactions. Gal-9 expression is closely related to tumor occurrence, development, metastasis and prognosis. In transplant immunology, a high level of Gal-9 expression has been shown to markedly reduce the severity of acute graft rejection and effectively prolong survival time in organ and bone marrow transplantation (BMT) models. The main mechanism of Gal-9-mediated immunoregulation involves the Tim-3/Gal-9 axis in T cells. However, myeloid-derived suppressor cell (MDSC) accumulation in transgenic mice with persistently high Gal-9 expression was observed in a model of lung inflammation, indicating that a potential immunosuppressive mechanism distinct from the Gal-9/Tim-3 axis might exist. In the present study, increased Gal-9 expression and MDSC frequencies before acute graft-versus-host disease (aGVHD) onset were observed in patients who developed aGVHD. Patients with higher Gal-9 expression (≥14.8417 ng/ml) exhibited reduced overall survival and increased cumulative incidences of GVHD at +100 day. We considered the elevated Gal-9 expression before aGVHD onset a secondary inflammatory response. This increase might be part of a negative feedback pathway corresponding to aGVHD pathogenesis. Additionally, a high Gal-9 concentration induced MDSC proliferation in vivo and in vitro. Gal-9-induced MDSCs (G9-MDSCs) suppressed T cell proliferation and activation. An infusion of G9-MDSCs into a graft contributed to the successful control of severe aGVHD and long-term survival in an allogeneic (allo)-BMT mouse model. Thus, we speculated that increased Gal-9 expression after allo-hematopoietic stem cell transplantation is a potential prognostic biomarker of aGVHD. The Gal-9-associated immunosuppressive effects on aGVHD development might occurr through G9-MDSCs and were independent of the Gal-9/Tim-3 axis.

Protective role of Galectin-7 for skin barrier impairment in atopic dermatitis.

BackgroundAtopic dermatitis (AD) patients have a barrier disorder in association with Th2 dominant skin inflammation. Galectin‐7 (Gal‐7), a soluble unglycosylated lectin, is highly expressed in the stratum corneum of AD patients. However, the biological significance of increased Gal‐7 expression in AD skin lesions remains unclear.ObjectiveWe aimed to investigate the production mechanism and functional role of Gal‐7 in AD patients and IL‐4/IL‐13–stimulated epidermal keratinocytes.MethodsWe assessed the Gal‐7 expression levels in skin lesions and sera from AD patients. Gal‐7 levels were also measured in monolayered normal human epidermal keratinocytes (NHEKs) and 3‐dimensional (3D)–reconstructed epidermis in the presence or absence of IL‐4/IL‐13 with or without Stat3, Stat6 or Gal‐7 gene silencing.ResultsGal‐7 was highly expressed in the stratum corneum or intercellular space of AD lesional epidermis as assessed by the stratum corneum proteome analysis and immunohistochemistry. A positive correlation was noted between serum Gal‐7 level and transepidermal water loss in patients with AD. These clinical findings were corroborated by our in vitro data, which showed that IL‐4/IL‐13 facilitated the extracellular release of endogenous Gal‐7 in both monolayered NHEKs and 3D‐reconstructed epidermis. This machinery was caused by IL‐4/IL‐13–induced cell damage and inhibited by knockdown of Stat6 but not Stat3 in NHEKs. Moreover, we performed Gal‐7 knockdown experiment on 3D‐reconstructed epidermis and the result suggested that endogenous Gal‐7 serves as a protector from IL‐4/IL‐13–induced disruption of cell‐to‐cell adhesion and/or cell‐to‐extracellular matrix adhesion.Conclusion and Clinical RelevanceOur study unveils the characteristic of Gal‐7 and its possible role as an alarmin that reflects the IL‐4/IL‐13–induced skin barrier impairment in AD.

Lectins as probes of the human intestinal microbiome

The human microbiota is intimately linked to health and disease. However, identifying community members that contribute to a healthy or dysbiotic state remains a challenge. Host factors regulate microbiome composition by promoting colonization or clearance of microbes. One such factor, soluble lectins, can detect microbes at strain‐level resolution by specific recognition of glycans. Several human lectins expressed at mucosal surfaces can bind microbes, but lectin specificity for microbes is under‐characterized. To this end, we have generated and characterized a suite of fluorescently labeled human soluble lectins to elucidate their microbe‐specificity. Using these probes, we analyzed recognition of bacteria from the human intestinal microbiota, and found that different lectins bind distinct populations. These data support the use of lectins as specific probes of microbial glycosylation. Further, analysis of fecal samples using lectins implicated in clearance of pathogens or promotion of colonization could provide a facile method of profiling the microbiota in health and disease.

Biochemical Characterization of Oyster and Clam Galectins: Selective Recognition of Carbohydrate Ligands on Host Hemocytes and Perkinsus Parasites.

Both vertebrates and invertebrates display active innate immune mechanisms for defense against microbial infection, including diversified repertoires of soluble and cell-associated lectins that can effect recognition and binding to potential pathogens, and trigger downstream effector pathways that clear them from the host internal milieu. Galectins are widely distributed and highly conserved lectins that have key regulatory effects on both innate and adaptive immune responses. In addition, galectins can bind to exogenous (“non-self”) carbohydrates on the surface of bacteria, enveloped viruses, parasites, and fungi, and function as recognition receptors and effector factors in innate immunity. Like most invertebrates, eastern oysters (Crassostrea virginica) and softshell clams (Mya arenaria) can effectively respond to most immune challenges through soluble and hemocyte-associated lectins. The protozoan parasite Perkinsus marinus, however, can infect eastern oysters and cause “Dermo” disease, which is highly detrimental to both natural and farmed oyster populations. The sympatric Perkinsus chesapeaki, initially isolated from infected M. arenaria clams, can also be present in oysters, and there is little evidence of pathogenicity in either clams or oysters. In this review, we discuss selected observations from our studies on the mechanisms of Perkinsus recognition that are mediated by galectin-carbohydrate interactions. We identified in the oyster two galectins that we designated CvGal1 and CvGal2, which strongly recognize P. marinus trophozoites. In the clam we also identified galectin sequences, and focused on one (that we named MaGal1) that also recognizes Perkinsus species. Here we describe the biochemical characterization of CvGal1, CvGal2, and MaGal1 with focus on the detailed study of the carbohydrate specificity, and the glycosylated moieties on the surfaces of the oyster hemocytes and the two Perkinsus species (P. marinus and P. chesapeaki). Our goal is to gain further understanding of the biochemical basis for the interactions that lead to recognition and opsonization of the Perkinsus trophozoites by the bivalve hemocytes. These basic studies on the biology of host-parasite interactions may contribute to the development of novel intervention strategies for parasitic diseases of biomedical interest.

Stereoelectronic Effects Impact Glycan Recognition.

Recognition of distinct glycans is central to biology, and lectins mediate this function. Lectin glycan preferences are usually centered on specific monosaccharides. In contrast, human intelectin-1 (hItln-1, also known as Omentin-1) is a soluble lectin that binds a range of microbial sugars, including β-d-galactofuranose (β-Galf), d-glycerol 1-phosphate, d-glycero-d-talo-oct-2-ulosonic acid (KO), and 3-deoxy-d-manno-oct-2-ulosonic acid (KDO). Though these saccharides differ dramatically in structure, they share a common feature-an exocyclic vicinal diol. How and whether such a small fragment is sufficient for recognition was unclear. We tested several glycans with this epitope and found that l-glycero-α-d-manno-heptose and d-glycero-α-d-manno-heptose possess the critical diol motif yet bind weakly. To better understand hItln-1 recognition, we determined the structure of the hItln-1·KO complex using X-ray crystallography, and our 1.59 Å resolution structure enabled unambiguous assignment of the bound KO conformation. This carbohydrate conformation was present in >97% of the KDO/KO structures in the Protein Data Bank. Bioinformatic analysis revealed that KO and KDO adopt a common conformation, while heptoses prefer different conformers. The preferred conformers of KO and KDO favor hItln-1 engagement, but those of the heptoses do not. Natural bond orbital (NBO) calculations suggest these observed conformations, including the side chain orientations, are stabilized by not only steric but also stereoelectronic effects. Thus, our data highlight a role for stereoelectronic effects in dictating the specificity of glycan recognition by proteins. Finally, our finding that hItln-1 avoids binding prevalent glycans with a terminal 1,2-diol (e.g., N-acetyl-neuraminic acid and l-glycero-α-d-manno-heptose) suggests the lectin has evolved to recognize distinct bacterial species.

LecA (PA-IL): A Galactose-Binding Lectin from Pseudomonas aeruginosa.

LecA/PA-IL (Pfam PF07828) is a soluble galactose-binding lectin from bacterium Pseudomonas aeruginosa. The lectin is specific for α-galactose present on glycosphingolipids of the globoside family and has therefore been proposed to play a role in cell adhesion and in internalization of bacteria in epithelial cells. The lectin has also direct toxic activity. Search for high-affinity inhibitors can be performed on the recombinant lectin, with use of surface plasmon resonance assays and structural studies.

Mannan-Binding Lectin Regulates Inflammatory Cytokine Production, Proliferation, and Cytotoxicity of Human Peripheral Natural Killer Cells.

Natural killer (NK) cells represent the founding members of innate lymphoid cells (ILC) and play critical roles in inflammation and the immune response. NK cell effector functions are regulated and fine-tuned by various immune modulators. Mannan (or mannose)-binding lectin (MBL), a soluble C-type lectin, is traditionally recognized as an initiator of the complement pathway. Recently, it is also considered as an immunomodulator by its interaction with kinds of immune cells. However, the effect of MBL on NK cell function remains unexplored. In this study, we found that human plasma MBL could interact directly with peripheral NK cells partially via its collagen-like region (CLR). This MBL binding markedly suppressed the interleukin-2- (IL-2-) induced inflammatory cytokine tumor necrosis factor-alpha (TNF-α) and interferon-gamma (IFN-γ) production but increased the IL-10 production in NK cells. In addition, the expression of activation surface markers such as CD25 and CD69 declined after MBL treatment. Also, MBL impaired the proliferation and lymphokine-activated killing (LAK) of NK cells. Moreover, we demonstrated that MBL inhibited IL-2-induced signal transducers and activators of transcription 5 (STAT5) activation in NK cells. In conclusion, we have uncovered a far unknown regulatory role of MBL on NK cells, a new clue that could be important in the immunomodulatory networks of immune responses.

Galectin-1 interacts with the human endogenous retroviral envelope protein syncytin-2 and potentiates trophoblast fusion in humans.

Syncytin (Syn)-2 is an important fusogenic protein that contributes to the formation of the placental syncytiotrophoblast. Galectin (Gal)-1, a soluble lectin, is also involved in trophoblast cell fusion and modulates the interaction of certain retroviral envelopes with their cellular receptor. This study aimed to investigate the association between Syn-2 and Gal-1 during human trophoblast cell fusion. This association was evaluated in vitro on primary villous cytotrophoblasts (vCTBs) and cell lines using recombinant Gal-1 and Syn-2-pseudotyped viruses. Using lactose, a Gal antagonist, and Gal-1-specific small interfering RNA (siRNA) transfections, we confirmed the implication of Gal-1 in vCTBs and BeWo cell fusion, although RT-PCR and ELISA analyses suggested that Gal-1 alone did not induce syncytialization. Infection assays showed a specific and significant effect of Gal-1 on the infectivity of Syn-2-pseudotyped viruses that depended on the expression of major facilitator superfamily domain-containing 2A (MFSD2a). Moreover, Gal-3, another placental Gal, did not modulate the infectivity of Syn-2-positive viruses, strengthening the specific association between Gal-1 and Syn-2. Interestingly, Gal-1 significantly reduced the infectivity of Syn-1-pseudotyped viruses, suggesting the opposite effects of Gal-1 on Syn-1 and -2. Finally, coimmunoprecipitation experiments showed a glycan-dependent interaction between Syn-2-bearing virions and Gal-1. We conclude that Gal-1 specifically interacts with Syn-2 and possibly regulates Syn-2/MFSD2a interaction during syncytialization of trophoblastic cells.-Toudic, C., Vargas, A., Xiao, Y., St-Pierre, G., Bannert, N., Lafond, J., Rassart, É., Sato, S., Barbeau, B. Galectin-1 interacts with the human endogenous retroviral envelope protein syncytin-2 and potentiates trophoblast fusion in humans.

Dual function of galectin-1 in microglial activation of the brain

Abstract Galectins-1, one of the β-galactosides-binding soluble lectin family, exert various roles in immune responses, and have been reported to be closely linked with several inflammation-associated diseases including cancer. However, their roles and underlying mechanisms remain largely unknown in the brain inflammation. In this study, we provide that galectin-1 could act as a regulatory molecule in the brain pathological conditions. Galectin-1 expression is markedly induced in IFN-g-treated microglial cells. In intracranial brain tumor model, we show that expression level of galectin-1 is significantly higher in B35 brain tumor cells and tumor neighboring microglial cells. Treatment of exogenous galectin-1 changes morphology of microglia, and induces expression of ICAM-1, adhesion molecule. In addition, galectin-1 triggers production of both pro-inflammatory mediators and anti-inflammatory mediators. Galectin-1-treated microglial cells activate lymphocytes. These findings indicate that galectin-1 involved in regulation of M1 and M2 phenotype of microglial cells. Therefore, we strongly suggest that galectin-1 may be dual roles in microglial activation of the brain pathophysiological environment.