Lack of galectin-3 modifies differentially Notch ligands in bone marrow and spleen stromal cells interfering with B cell differentiation

Identification of immune subsets with distinct lectin binding signatures using multi-parameter flow cytometry: correlations with disease activity in systemic lupus erythematosus

Objectives

Cell surface glycosylation can influence protein-protein interactions with particular relevance to changes in core fucosylation and terminal sialylation. Glycans are ligands for immune regulatory lectin families like galectins (Gals) or sialic acid immunoglobulin-like lectins (Siglecs). This study delves into the glycan alterations within immune subsets of systemic lupus erythematosus (SLE).

Methods

Evaluation of binding affinities of Galectin-1, Galectin-3, Siglec-1, Aleuria aurantia lectin (AAL, recognizing core fucosylation), and Sambucus nigra agglutinin (SNA, specific for α-2,6-sialylation) was conducted on various immune subsets in peripheral blood mononuclear cells (PBMCs) from control and SLE subjects. Lectin binding was measured by multi-parameter flow cytometry in 18 manually gated subsets of T-cells, NK-cells, NKT-cells, B-cells, and monocytes in unstimulated resting state and also after 3-day activation. Stimulated pre-gated populations were subsequently clustered by FlowSOM algorithm based on lectin binding and activation markers, CD25 or HLA-DR.

Results

Elevated AAL, SNA and CD25+/CD25- SNA binding ratio in certain stimulated SLE T-cell subsets correlated with SLE Disease Activity Index 2000 (SLEDAI-2K) scores. The significantly increased frequencies of activated AALlow Siglec-1low NK metaclusters in SLE also correlated with SLEDAI-2K indices. In SLE, activated double negative NKTs displayed significantly lower core fucosylation and CD25+/CD25- Siglec-1 binding ratio, negatively correlating with disease activity. The significantly enhanced AAL binding in resting SLE plasmablasts positively correlated with SLEDAI-2K scores.

Conclusion

Alterations in the glycosylation of immune cells in SLE correlate with disease severity, which might represent potential implications in the pathogenesis of SLE.

Membrane organization by tetraspanins and galectins shapes lymphocyte function

Immune receptors are not randomly distributed at the plasma membrane of lymphocytes but are segregated into specialized domains that function as platforms to initiate signalling, as exemplified by the B cell or T cell receptor complex and the immunological synapse. 'Membrane-organizing proteins' and, in particular, tetraspanins and galectins, are crucial for controlling the spatiotemporal organization of immune receptors and other signalling proteins. Deficiencies in specific tetraspanins and galectins result in impaired immune synapse formation, lymphocyte proliferation, antibody production and migration, which can lead to impaired immunity, tumour development and autoimmunity. In contrast to conventional ligand-receptor interactions, membrane organizers interact in cis (on the same cell) and modulate receptor clustering, receptor dynamics and intracellular signalling. New findings have uncovered their complex and dynamic nature, revealing shared binding partners and collaborative activity in determining the composition of membrane domains. Therefore, immune receptors should not be envisaged as independent entities and instead should be studied in the context of their spatial organization in the lymphocyte membrane. We advocate for a novel approach to study lymphocyte function by globally analysing the role of membrane organizers in the assembly of different membrane complexes and discuss opportunities to develop therapeutic approaches that act via the modulation of membrane organization.

The role of N-glycosylation in B-cell biology and IgG activity. The aspects of autoimmunity and anti-inflammatory therapy

The immune system is strictly regulated by glycosylation through the addition of highly diverse and dynamically changing sugar structures (glycans) to the majority of immune cell receptors. Although knowledge in the field of glycoimmunology is still limited, numerous studies point to the key role of glycosylation in maintaining homeostasis, but also in reflecting its disruption. Changes in oligosaccharide patterns can lead to impairment of both innate and acquired immune responses, with important implications in the pathogenesis of diseases, including autoimmunity. B cells appear to be unique within the immune system, since they exhibit both innate and adaptive immune activity. B cell surface is rich in glycosylated proteins and lectins which recognise glycosylated ligands on other cells. Glycans are important in the development, selection, and maturation of B cells. Changes in sialylation and fucosylation of cell surface proteins affect B cell signal transduction through BCRs, CD22 inhibitory coreceptor and Siglec-G. Plasmocytes, as the final stage of B cell differentiation, produce and secrete immunoglobulins (Igs), of which IgGs are the most abundant N-glycosylated proteins in human serum with the conserved N-glycosylation site at Asn297. N-oligosaccharide composition of the IgG Fc region affects its secretion, structure, half-life and effector functions (ADCC, CDC). IgG N-glycosylation undergoes little change during homeostasis, and may gradually be modified with age and during ongoing inflammatory processes. Hyperactivated B lymphocytes secrete autoreactive antibodies responsible for the development of autoimmunity. The altered profile of IgG N-glycans contributes to disease progression and remission and is sensitive to the application of therapeutic substances and immunosuppressive agents. In this review, we focus on the role of N-glycans in B-cell biology and IgG activity, the rearrangement of IgG oligosaccharides in aging, autoimmunity and immunosuppressive therapy.

Glycome dynamics in T and B cell development: basic immunological mechanisms and clinical applications

Glycans cover the surfaces of all mammalian cells through a process called glycosylation. Nearly all proteins and receptors that integrate the intricate series of co-stimulatory/inhibitory pathways of the immune system are glycosylated. Growing evidence indicates that the development of the immune system at the origins of T and B cell development is tightly regulated by glycosylation. In this opinion, we hypothesize that the glycome composition of developing T and B cells is developmentally regulated. We discuss how glycans play fundamental roles in lymphocyte development and how glycans early define T and B cell functionality in multiple aspects of adaptive immunity. These advances can provide opportunities for the discovery of novel disease factors and more effective candidate treatments for various conditions.

Notch1 and Galectin-3 Modulate Cortical Reactive Astrocyte Response After Brain Injury

After a brain lesion, highly specialized cortical astrocytes react, supporting the closure or replacement of the damaged tissue, but fail to regulate neural plasticity. Growing evidence indicates that repair response leads astrocytes to reprogram, acquiring a partially restricted regenerative phenotype in vivo and neural stem cells (NSC) hallmarks in vitro. However, the molecular factors involved in astrocyte reactivity, the reparative response, and their relation to adult neurogenesis are poorly understood and remain an area of intense investigation in regenerative medicine. In this context, we addressed the role of Notch1 signaling and the effect of Galectin-3 (Gal3) as underlying molecular candidates involved in cortical astrocyte response to injury. Notch signaling is part of a specific neurogenic microenvironment that maintains NSC and neural progenitors, and Gal3 has a preferential spatial distribution across the cortex and has a central role in the proliferative capacity of reactive astrocytes. We report that in vitro scratch-reactivated cortical astrocytes from C57Bl/6J neonatal mice present nuclear Notch1 intracellular domain (NICD1), indicating Notch1 activation. Colocalization analysis revealed a subpopulation of reactive astrocytes at the lesion border with colocalized NICD1/Jagged1 complexes compared with astrocytes located far from the border. Moreover, we found that Gal3 increased intracellularly, in contrast to its extracellular localization in non-reactive astrocytes, and NICD1/Gal3 pattern distribution shifted from diffuse to vesicular upon astrocyte reactivation. In vitro, Gal3^–/– reactive astrocytes showed abolished Notch1 signaling at the lesion core. Notch1 receptor, its ligands (Jagged1 and Delta-like1), and Hes5 target gene were upregulated in C57Bl/6J reactive astrocytes, but not in Gal3^–/– reactive astrocytes. Finally, we report that Gal3^–/– mice submitted to a traumatic brain injury model in the somatosensory cortex presented a disrupted response characterized by the reduced number of GFAP reactive astrocytes, with smaller cell body perimeter and decreased NICD1 presence at the lesion core. These results suggest that Gal3 might be essential to the proper activation of Notch signaling, facilitating the cleavage of Notch1 and nuclear translocation of NICD1 into the nucleus of reactive cortical astrocytes. Additionally, we hypothesize that reactive astrocyte response could be dependent on Notch1/Jagged1-Hes5 signaling activation following brain injury.

Allergen-Specific Treg Cells Upregulated by Lung-Stage S. japonicum Infection Alleviates Allergic Airway Inflammation

Schistosoma japonicum infection showed protective effects against allergic airway inflammation (AAI). However, controversial findings exist especially regarding the timing of the helminth infection and the underlying mechanisms. Most previous studies focused on understanding the preventive effect of S. japonicum infection on asthma (infection before allergen sensitization), whereas the protective effects of S. japonicum infection (allergen sensitization before infection) on asthma were rarely investigated. In this study, we investigated the protective effects of S. japonicum infection on AAI using a mouse model of OVA-induced asthma. To explore how the timing of S. japonicum infection influences its protective effect, the mice were percutaneously infected with cercaria of S. japonicum at either 1 day (infection at lung-stage during AAI) or 14 days before ovalbumin (OVA) challenge (infection at post–lung-stage during AAI). We found that lung-stage S. japonicum infection significantly ameliorated OVA-induced AAI, whereas post–lung-stage infection did not. Mechanistically, lung-stage S. japonicum infection significantly upregulated the frequency of regulatory T cells (Treg cells), especially OVA-specific Treg cells, in lung tissue, which negatively correlated with the level of OVA-specific immunoglobulin E (IgE). Depletion of Treg cells in vivo partially counteracted the protective effect of lung-stage S. japonicum infection on asthma. Furthermore, transcriptomic analysis of lung tissue showed that lung-stage S. japonicum infection during AAI shaped the microenvironment to favor Treg induction. In conclusion, our data showed that lung-stage S. japonicum infection could relieve OVA-induced asthma in a mouse model. The protective effect was mediated by the upregulated OVA-specific Treg cells, which suppressed IgE production. Our results may facilitate the discovery of a novel therapy for AAI.

Emerging role of galectin family in inflammatory autoimmune diseases

Galectin family is a group of glycan-binding proteins. Members in this family are expressed in different tissues, immune or non-immune cells. These molecules are important regulators in innate and adaptive immune response, performing significantly in a broad range of cellular and pathophysiological functions, such as cell proliferation, adhesion, migration, and invasion. Findings have shown that expression of galectins is abnormal in many inflammatory autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, osteoarthritis, sjögren's syndrome, systemic sclerosis. Galectins also function as intracellular and extracellular disease regulators mainly through the binding of their carbohydrate recognition domain to glycoconjugates. Here, we review the state-of-the-art of the role that different galectin family members play in immune cells, contributing to the complex inflammatory diseases. Hopefully collection of the information will provide a preliminary theoretical basis for the exploration of new targets for treatment of the disorders.

Notch signaling induces a transcriptionally permissive state at the Complement C3d Receptor 2 (CR2) promoter in a pre-B cell model

During mammalian lymphoid development, Notch signaling is necessary at multiple stages of T lymphopoiesis, including lineage commitment, and later stages of T cell effector differentiation. In contrast, outside of a defined role in the development of splenic marginal zone B cells, there is conflicting evidence regarding whether Notch signaling plays functional roles in other B cell sub-populations. Complement receptor 2 (CR2) modulates BCR-signaling and is tightly regulated throughout differentiation. During B lymphopoiesis, CR2 is detected on immature and mature B cells with high surface expression on marginal zone B cells. Here, we have explored the possibility that Notch regulates human CR2 transcriptional activity using in vitro models including a co-culture system, co-transfection gene reporters and chromatin accessibility assays. We provide evidence that Notch signaling regulates CR2 promoter activity in a mature B cell line, as well as the induction of endogenous CR2 mRNA in a non-expressing pre-B cell line. The dynamics of endogenous gene activation suggests additional unidentified factors are required to mediate surface CR2 expression on immature and mature B lineage cells.

The oligomeric assembly of galectin-11 is critical for anti-parasitic activity in sheep (Ovis aries)

Galectins are a family of glycan-binding molecules with a characteristic affinity for ß-D-glycosides that mediate a variety of important cellular functions, including immune and inflammatory responses. Galectin-11 (LGALS-11) has been recently identified as a mediator induced specifically in animals against gastrointestinal nematodes and can interfere with parasite growth and development. Here, we report that at least two natural genetic variants of LGALS-11 exist in sheep, and demonstrate fundamental differences in anti-parasitic activity, correlated with their ability to dimerise. This study improves our understanding of the role of galectins in the host immune and inflammatory responses against parasitic nematodes and provides a basis for genetic studies toward selective breeding of animals for resistance to parasites.

The Emerging Role of Galectins and O-GlcNAc Homeostasis in Processes of Cellular Differentiation

Galectins are a family of soluble β-galactoside-binding proteins with diverse glycan-dependent and glycan-independent functions outside and inside the cell. Human cells express twelve out of sixteen recognized mammalian galectin genes and their expression profiles are very different between cell types and tissues. In this review, we summarize the current knowledge on the changes in the expression of individual galectins at mRNA and protein levels in different types of differentiating cells and the effects of recombinant galectins on cellular differentiation. A new model of galectin regulation is proposed considering the change in O-GlcNAc homeostasis between progenitor/stem cells and mature differentiated cells. The recognition of galectins as regulatory factors controlling cell differentiation and self-renewal is essential for developmental and cancer biology to develop innovative strategies for prevention and targeted treatment of proliferative diseases, tissue regeneration, and stem-cell therapy.

N-Glycan Branching Is Required for Development of Mature B Cells

Galectins have been implicated in inhibiting BCR signaling in mature B cells but promoting pre-BCR signaling during early development. Galectins bind to branched N-glycans attached to cell surface glycoproteins to control the distribution, clustering, endocytosis, and signaling of surface glycoproteins. During T cell development, N-glycan branching is required for positive selection of thymocytes, inhibiting both death by neglect and negative selection via enhanced surface retention of the CD4/CD8 coreceptors and limiting TCR clustering/signaling, respectively. The role of N-glycan branching in B cell development is unknown. In this study, we report that N-glycan branching is absolutely required for development of mature B cells in mice. Elimination of branched N-glycans in developing B cells via targeted deletion of N-acetylglucosaminyl transferase I (Mgat1) markedly reduced cellularity in the bone marrow and/or spleen and inhibited maturation of pre-, immature, and transitional stage 2 B cells. Branching deficiency markedly reduced surface expression of the pre-BCR/BCR coreceptor CD19 and promoted spontaneous death of pre-B cells and immature B cells in vitro. Death was rescued by low-dose pre-BCR/BCR stimulation but exacerbated by high-dose pre-BCR/BCR stimulation as well as antiapoptotic Bcl_xL overexpression in pre-B cells. Branching deficiency also enhanced Nur77 induction, a marker of negative selection. Together, these data suggest that, as in T cells, N-glycan branching promotes positive selection of B cells by augmenting pre-BCR/BCR signaling via CD19 surface retention, whereas limiting negative selection from excessive BCR engagement.

Galectin-3 orchestrates the histology of mesentery and protects liver during lupus-like syndrome induced by pristane

Galectin-3 (Gal-3) controls intercellular and cell-extracellular matrix interactions during immunological responses. In chronic inflammation, Gal-3 is associated with fibrotic events, regulates B cell differentiation and delays lupus progression. Gal-3 deficient mice (Lgals3^−/−) have intense germinal center formation and atypical plasma cell generation correlated to high levels IgG, IgE, and IgA. Here, we used pristane (2,6,10,14-tetramethylpentadecane) to induce lupus-like syndrome in Lgals3^−/− and Lgals3^+/+ BALB/c mice. Mesentery and peritoneal cells were monitored because promptly react to pristane injected in the peritoneal cavity. For the first time, mesenteric tissues have been associated to the pathogenesis of experimental lupus-like syndrome. In Lgals3^+/+ pristane-induced mice, mesentery was hallmarked by intense fibrogranulomatous reaction restricted to submesothelial regions and organized niches containing macrophages and B lymphocytes and plasma cells. In contrast, Lgals3^−/− pristane-treated mice had diffuse mesenteric fibrosis affecting submesothelium and peripheral tissues, atypical M1/M2 macrophage polarization and significant DLL1⁺ cells expansion, suggesting possible involvement of Notch/Delta pathways in the disease. Early inflammatory reaction to pristane was characterized by significant disturbances on monocyte recruitment, macrophage differentiation and dendritic cell (DC) responses in the peritoneal cavity of pristane-induced Lgals3^−/− mice. A correlative analysis showed that mesenteric damages in the absence of Gal-3 were directly associated with severe portal inflammation and hepatitis. In conclusion, it has suggested that Gal-3 orchestrates histological organization in the mesentery and prevents lupoid hepatitis in experimental lupus-like syndrome by controlling macrophage polarization, Notch signaling pathways and DC differentiation in mesenteric structures.

Galectin-Glycan Interactions as Regulators of B Cell Immunity

Cell surface glycans and their glycan-binding partners (lectins) have generally been recognized as adhesive assemblies with neighbor cells or matrix scaffolds in organs and the blood stream. However, our understanding of the roles for glycan-lectin interactions in immunity has expanded substantially to include regulation of nearly every stage of an immune response, from pathogen sensing to immune contraction. In this Mini-Review, we discuss the role of the ß-galactoside-binding lectins known as galectins specifically in the regulation of B-lymphocyte (B cell) development, activation, and differentiation. In particular, we highlight several recent studies revealing new roles for galectin (Gal)-9 in the modulation of B cell receptor-mediated signaling and activation in mouse and man. The roles for cell surface glycosylation, especially I-branching of N-glycans synthesized by the glycosyltransferase GCNT2, in the regulation of Gal-9 binding activity are also detailed. Finally, we consider how dysregulation of these factors may contribute to aberrant immune activation and autoimmune disease.

HH1-1, a novel Galectin-3 inhibitor, exerts anti-pancreatic cancer activity by blocking Galectin-3/EGFR/AKT/FOXO3 signaling pathway

Pancreatic ductal adenocarcinoma is a highly malignant gastrointestinal tumor. Molecular targeting therapy for pancreatic cancer is still limited. High expressed Galectin-3 in pancreatic cancer is positively correlated with disease progression, indicating that Galectin-3 can be employed as a predictor of poor prognosis. From safflower, we isolated and purified a homogeneous polysaccharide, HH1-1, which could bind to and inhibit Galectin-3. HH1-1 could block the interaction between Galectin-3 and EGFR. Following HH1-1 treatment, the binding ability between EGFR and Galectin-3 was reduced by 245.28 folds. HH1-1 could suppress pancreatic cancer cell proliferation, arrest the cell cycle in S phase, induce cell apoptosis, inhibit angiogenesis and impede tumor cell migration and invasion. Moreover, HH1-1 affected the Galectin-3/EGFR/AKT/FOXO3 signaling pathway and possessed anti-pancreatic cancer activity in vitro and in vivo, especially in patient-derived xenografts. Further study suggested that HH1-1 had almost no toxicity both in vitro and in vivo. This adds new evidence to suggest that HH1-1 could be a promising therapeutic agent and support the pursuit of the Galectin-3 as a target in pancreatic cancer treatment.

Galectins as regulators of cell survival in the leukemia niche

The microenvironment within the bone marrow (BM) contains support cells that promote leukemia cell survival and suppress host anti-tumor defenses. Galectins are a family of beta-galactoside binding proteins that are critical components in the tumor microenvironment. Galectin 1 (LGALS1) and Galectin 3 (LGALS3) as regulators of RAS signaling intracellularly and as inhibitors of immune cells extracellularly are perhaps the best studied members for their role in leukemia biology. Interest in Galectin 9 (LGALS9) is growing as this galectin has been identified as an immune checkpoint molecule. LGALS9 also supports leukemia stem cells (LSCs) though a mechanism of action is not clear. LGALS1 and LGALS3 each participate in a diverse number of survival pathways that promote drug resistance by supporting pro-tumor molecules such BCL2, MCL-1, and MYC and blocking tumor suppressors like p53. Acute myeloid leukemia (AML) BM mesenchymal stromal cells (MSC) have protein signatures that differ from healthy donor MSC. Elevated LGALS3 protein in AML MSC is associated with refractory disease/relapse demonstrating that MSC derived galectin impacts patient survival. LGALS3 is a critical determining factor whether MSC differentiate into adipocytes or osteoblasts so the galectin influences the cellular composition of the leukemia niche. Both LGALS3 and LGALS1 when secreted can suppress immune function. Both galectins can induce apoptosis of T cells. LGALS3 also modulates T cell receptor endocytosis and impairs interferon mediated chemokine production by binding glycosylated interferon. LGALS3 as a TIM3 binding partner acts to suppress T cell function. Galectins also impact leukemia cell mobilization and may participate in homing mechanisms. LGALS3 participates in transport mechanism of integrins, receptors, and other molecules that control cell adhesion and cell:cell interactions. The diversity of these various functions demonstrate the importance of these galectins in the leukemia niche. This review will cover the role of LGALS1, LGALS3, and LGALS9 in the various processes that are critical for maintaining leukemia cells in the tumor microenvironment.

Lack of Galectin-3 Disrupts Thymus Homeostasis in Association to Increase of Local and Systemic Glucocorticoid Levels and Steroidogenic Machinery

Maintenance of thymus homeostasis is a delicate interplay involving hormones, neurotransmitters and local microenvironmental proteins, as well as saccharides, acting on both thymocytes and stromal cells. Disturbances in these interactions may lead to alterations on thymocyte development. We previously showed that galectin-3, a β-galactoside-binding protein, is constitutively expressed in the thymus, interacting with extracellular matrix glycoproteins and acting as a de-adhesion molecule, thus modulating thymocyte-stromal cell interactions. In this work, we aimed to investigate the participation of galectin-3 in the maintenance of thymus homeostasis, including hormonal-mediated circuits. For that, we used genetically engineered galectin-3-deficient mice. We observed that the thymus of galectin-3-deficient mice was reduced in mass and cellularity compared to wild-type controls; however, the proportions of different thymocyte subpopulations defined by CD4/CD8 expression were not changed. Considering the CD4^-CD8^- double-negative (DN) subpopulation, an accumulation of the most immature (DN1) stage was observed. Additionally, the proliferative capacity of thymocytes was decreased in all thymocyte subsets, whereas the percentage of apoptosis was increased, especially in the CD4⁺CD8⁺ double-positive thymocytes. As glucocorticoid hormones are known to be involved in thymus homeostasis, we evaluated serum and intrathymic corticosterone levels by radioimmunoassay, and the expression of steroidogenic machinery using real-time PCR. We detected a significant increase in corticosterone levels in both serum and thymus samples of galectin-3-deficient mice, as compared to age-matched controls. This was paralleled by an increase of gene transcription of the steroidogenic enzymes, steroidogenic acute regulatory protein (Star) and Cyp11b1 in thymus, 11β-Hydroxysteroid Dehydrogenase (Hsd11b1) in the adrenal, and Cyp11a1 in both glands. In conclusion, our findings show that the absence of galectin-3 subverts mouse thymus homeostasis by a mechanism likely associated to intrathymic and systemic stress-related endocrine circuitries, affecting thymocyte number, proliferation and apoptosis.