The universe of galectin-binding partners and their functions in health and disease

Argatroban and Menadione exert protective effects in ultraviolet-irradiated skin inflammation: A transcriptomic analysis based on identification of iron overload related biomarkers

Ultraviolet light (UV) can cause serious damage to human skin. The inflammatory reaction arising from repeated UV exposure leads to severe skin lesions and even promotes photo-carcinogenesis. Iron overload is featured by excessive iron intake and deposition and will promote inflammatory response inside cells. However, the core molecules involved in UV radiation induced iron overload and related anti-inflammatory strategies remain unclear. Signature genes involved in UV-irradiated skin were filtered through integrated datasets from the Gene Expression Omnibus (GEO) database. Subsequently, immune cell infiltration analysis was carried out to examine the relationship between signature gene expression and immune cell abundance. Single cell RNA-seq matrix data implicated in UV-irradiated skin was then applied to assess the expression level of signature genes in different cell clusters and to find out the core cell type and the key signaling pathway involved in UV radiation. Finally, cytological and animal experiments were conducted to investigate the potential of signature genes as therapeutic targets. SAT1 and RBMS1 were screened and validated as signature genes of UV irradiation. Immune cell infiltration analysis demonstrated that SAT1 and RBMS1 expression were associated closely with immune cell abundance, and skin fibroblasts were identified as the central cell type to communicate with other cell clusters in UV-irradiated skin. Disturbance of SAT1 exerted observably more suppressive effects on the release of inflammatory cytokines than overexpression of RBMS1. Two small molecule drugs targeting SAT1, namely Argatroban and Menadione, were predicted. Moreover, their therapeutic potentials in the treatment of UV-irradiated skin injury were confirmed experimentally.

Galectin-8 drives ERK-dependent mitochondrial fragmentation, perinuclear relocation and mitophagy, with metabolic adaptations for cell proliferation

Mitochondria adapt to the cell proliferative demands induced by growth factors through dynamic changes in morphology, distribution, and metabolic activity. Galectin-8 (Gal-8), a carbohydrate-binding protein that promotes cell proliferation by transactivating the EGFR-ERK signaling pathway, is overexpressed in several cancers. However, its impact on mitochondrial dynamics during cell proliferation remains unknown. Using MDCK and RPTEC kidney epithelial cells, we demonstrate that Gal-8 induces mitochondrial fragmentation and perinuclear redistribution. Additionally, mitochondria adopt donut-shaped morphologies, and live-cell imaging with two Keima-based reporters demonstrates Gal-8-induced mitophagy. ERK signaling inhibition abrogates all these Gal-8-induced mitochondrial changes and cell proliferation. Studies with established mutant versions of Gal-8 and CHO cells reveal that mitochondrial changes and proliferative response require interactions between the N-terminal carbohydrate recognition domain of Gal-8 and α-2,3-sialylated N-glycans at the cell surface. DRP1, a key regulator of mitochondrial fission, becomes phosphorylated in MDCK cells or overexpressed in RPTEC cells in an ERK-dependent manner, mediating mitochondrial fragmentation and perinuclear redistribution. Bafilomycin A abrogates Gal-8-induced cell proliferation, suggesting that mitophagy serves as an adaptation to cell proliferation demands. Functional analysis under Gal-8 stimulation shows that mitochondria maintain an active electron transport chain, partially uncoupled from ATP synthesis, and an increased membrane potential, indicative of healthy mitochondria. Meanwhile, the cells exhibit increased extracellular acidification rate and lactate production via aerobic glycolysis, a hallmark of an active proliferative state. Our findings integrate mitochondrial dynamics with metabolic adaptations during Gal-8-induced cell proliferation, with potential implications for physiology, disease, and therapeutic strategies.

The sweet and the bitter sides of galectin-1 in immunity: its role in immune cell functions, apoptosis, and immunotherapies for cancer with a focus on T cells

Galectin-1 (Gal-1), a member of the β-galactoside-binding soluble lectin family, is a double-edged sword in immunity. On one hand, it plays a crucial role in regulating diverse immune cell functions, including the apoptosis of activated T cells. These processes are key in resolving inflammation and preventing autoimmune diseases. On the other hand, Gal-1 has significant implications in cancer, where tumor cells and the tumor microenvironment (TME) (e.g., tumor-associated fibroblasts, myeloid-derived suppressor cells) secrete Gal-1 to evade immune surveillance and promote cancer cell growth. Within the TME, Gal-1 enhances the differentiation of tolerogenic dendritic cells, induces the apoptosis of effector T cells, and enhances the proliferation of regulatory T cells, collectively facilitating tumor immune escape. Therefore, targeting Gal-1 holds the potential to boost anti-tumor immunity and improve the efficacy of cancer immunotherapy. This review provides insights into the intricate role of Gal-1 in immune cell regulation, with an emphasis on T cells, and elucidates how tumors exploit Gal-1 for immune evasion and growth. Furthermore, we discuss the potential of Gal-1 as a therapeutic target to augment current immunotherapies across various cancer types.

Uptake of small extracellular vesicles by recipient cells is facilitated by paracrine adhesion signaling

Small extracellular vesicles (sEVs) play crucial roles in intercellular communication. However, the internalization of individual sEVs by recipient cells has not been directly observed. Here, we examined these mechanisms using state-of-the-art imaging techniques. Single-molecule imaging shows that tumor-derived sEVs can be classified into several subtypes. Simultaneous single-sEV particle tracking and observation of super-resolution movies of membrane invaginations in living cells reveal that all sEV subtypes are internalized via clathrin-independent endocytosis mediated by galectin-3 and lysosome-associated membrane protein-2C, while some subtypes that recruited raft markers are internalized through caveolae. Integrin β1 and talin-1 accumulate in recipient cell plasma membranes beneath all sEV subtypes. Paracrine, but not autocrine, sEV binding triggers Ca2+ mobilization induced by the activation of Src family kinases and phospholipase Cγ. Subsequent Ca2+-induced activation of calcineurin-dynamin promotes sEV internalization, leading to the recycling pathway. Thus, we clarified the detailed mechanisms of sEV internalization driven by paracrine adhesion signaling.

Color-coded galectin fusion proteins as novel tools in biomaterial science

The inherent carbohydrate-binding specificities of human galectins can serve as recognition elements in both biotechnological and biomedical applications. The combination of the carbohydrate-recognition domain (CRD) of galectins fused to peptides or proteins for purification, immobilization, and imaging enables multifunctional utilization within a single protein. We present here a library of color-coded galectin fusion proteins that incorporate a His6-tag, a fluorescent protein, and a SpyCatcher or SpyTag unit to enable immobilization procedures. These galectin fusion proteins exhibit similar binding properties to the non-fused galectins with micromolar apparent binding affinities. N- and C-terminal fusion partners do not interfere with the SpyCatcher/SpyTag immobilization. By applying SpyCatcher/SpyTag-mediated SC-ST-Gal-3 conjugates, we show the stepwise formation of a three-layer ECM-like structure in vitro. Additionally, we demonstrate the SpyCatcher/SpyTag-mediated immobilization of galectins in microgels, which can serve as a transport platform for localized targeting applications. The proof of concept is provided by the galectin-mediated binding of microgels to colorectal cancer cells.

New perspectives on galectin in major depressive disorder treatment

Galectins, a family of carbohydrate-binding proteins, regulate immune responses, neuroinflammation, and neurogenesis within the central nervous system (CNS). Among the 15 known galectins, galectins-1, -3, -4, -8, and -9 play significant roles in neuroinflammation and have been investigated in the context of CNS pathologies. This review synthesizes recent advancements in understanding galectins' involvement in the neurobiology of brain disorders, focusing on their interplay with signaling pathways underlying major depressive disorder (MDD). It explores their impact on neuroinflammation, neurogenesis, and brain signaling, highlighting the therapeutic potential of targeting galectins while addressing challenges in translating these findings into clinical practice. Comprehensive studies are essential to unravel the complex mechanisms of galectin-mediated pathways and unlock their full potential for managing neuropsychiatric conditions.

Decoding the multifaceted roles of galectins in self-defense

In this review, we aim to explore the multifaceted roles of galectins in host defense from a broader perspective, particularly regarding their functions when host integrity is compromised. Numerous comprehensive reviews on galectin functions in immunity have already been published. For researchers new to the field, this wealth of information may create an impression of galectins as proteins involved in a wide array of biological processes. Furthermore, due to the heterogeneity of galectin ligands, glycans, there is a risk of perceiving galectin-specific functions as ambiguous, potentially obscuring their core biological significance. To address this, we revisit foundational aspects, focusing on the significance of the recognition of galactose, a "late-comer" monosaccharide in evolutionary terms, provide an overview of galectin glycan binding specificity, with emphasis on the potential biological importance of each carbohydrate-recognition domain. We also discuss the biological implications of the galectin location paradox wherein these cytosolic lectins function in host defense despite their glycan ligands being synthesized in the secretory pathway. Additionally, we examine the role of galectins in liquid-liquid phase separation on membranes, which may facilitate their diverse functions in cellular responses. Through this approach, we aim to re-evaluate the complex and diverse biological roles of galectins in host defense.

Synthetic and plant-derived multivalent galactans as modulators of cancer-associated galectins-3 and -9

Galectins are β-galactoside-binding proteins with numerous functions. Some of them are involved in proliferation and metastasis of cancer, making them promising therapeutic targets. As different plant glycans have been shown to bind to galectins, plant saccharides might be potential galectin inhibitors. To produce plant galactans rich in galactose and smaller in size, we degraded arabinogalactan-proteins from Echinacea purpurea and Zostera marina as well as arabinogalactan from larch. As galectin (Gal)-3 and -9 both have been described to be involved in cancer development, we quantified the binding capacities of the different galactans to both galectins by biolayer-interferometry. Our results revealed that all plant-derived galactans and Yariv reagents with terminal galactose and lactose residues bind to Gal-3 in micromolar ranges. Surprisingly, only the higher charged galactans from Zostera marina showed affinity to Gal-9. Investigations of two different pancreatic cancer cell lines (Panc1 and Panc89) and different cell variants thereof revealed that Gal-3 was expressed by both cell lines with a significantly higher Gal-3 level in Panc1 cells compared to Panc89 cells. Conversely, Gal-9 was only detected in Panc89 cells. The findings revealed that galactans are promising sources to develop galectin antagonists and plant galactans from different species express specificities for distinct galectins.

Exploring Glycan-Lectin Interactions in Natural-Like Environments: A View Using NMR Experiments Inside Cell and on Cell Surface

Glycan-mediated molecular recognition events are essential for life. NMR is widely used to monitor glycan binding to lectins in solution using isolated glycans and lectins. In this context, we herein explore diverse NMR methodologies, from both the receptor and ligand perspectives, to monitor glycan-lectin interactions under experimental conditions mimicking the native milieu inside cells and on cell surface. For the NMR experiments inside cells, galectin-7 is employed as model, since most galectins are soluble and carry out their functions in the cellular micro-environment. Using Danio Rerio oocytes, the 1H-15N HMQC NMR spectrum of a folded galectin has been observed inside cell for the first time, using a glycomimetic ligand (TDG) to overcoming the natural tendency of galectins to bind to numerous galactose-containing receptors within cells. Alternatively, most lectins, other than galectins, are displayed on the cell surface, providing a multivalent presentation to bind their glycan partners in cis (at the same cell) or in trans (on other cells). In this case, ligand-based STD-NMR experiments have been successfully applied to account for the interactions of natural glycans and glycomimetics with Siglec-10. These methodologies provide the proof-of-concept to open the door to the NMR analysis of the recognition of glycans in native-like settings.

Analysis of chicken LGALSL (galectin-related protein) gene's proximal promoter and its control by Krüppel-like factors 3 and 7

The Galectin-Related Protein (GRP), encoded by the LGALSL gene, assigned to the protein family of β-galactoside-binding Galectins, has lost carbohydrate-binding abilities. Its chicken homolog (C-GRP) occurs in the bursa of Fabricius' epithelial and B cells. Our study investigates the unknown regulatory mechanisms controlling its expression by analyzing the promoter region of the chicken (C-)LGALSL gene in chicken cells. We aimed to identify the sequence elements of the C-LGALSL gene promoter responsible for maximum activity and transcription factors (TFs) that can modulate this activity. Using luciferase reporter assays, we investigated deletion variants of the 5' region (-2480 bp to +26 bp). Through in silico analyses and site-directed mutagenesis, we explored potential transcription factor binding sites, identified crucial transcription factors through transient overexpression and tested its direct binding by ChIP. Our findings highlight that the region from -274 to -75 bp, conserved among bird species, is crucial for promoter regulation. Among other tested factors, only the chicken (ch) Krüppel-like factors, chKLF3 and chKLF7, modulate the promoter's activity. The TFs chKLF3 acts as a repressor, and chKLF7 as an activator, although direct binding could not be confirmed. In conclusion, chKLF3 and chKLF7 contribute, in contrast to other factors with binding sites in the region from -274 to -75 bp, to C-LGALSL gene promoter regulation with a balanced impact on activity.

Galectin-1 and galectin-3 in male reproduction - impact in health and disease

The formation and differentiation of mature, motile male germ cells, which can fertilize the egg and ensure successful implantation and development of a healthy embryo, are essential functions of the testis and epididymis. Spermatogenesis is a complex, multistep process that results in the formation of motile haploid gametes, requiring an immunoregulatory environment to maintain tolerance to developing neo-antigens. Different cell types (Sertoli cells, macrophages), immunoregulatory factors and tolerance mechanisms are involved. In this context, possible effects of galectins on the immunoregulatory functions and fertilization ability of male germ cells are postulated. Galectins are pleiotropic lectins involved in the homeostasis, modulation of immune responses and pathological processes. Despite the well-recognized role of galectins in female reproduction, the functions of galectins in the male reproductive organs, particularly the testis and epididymis, remain largely unexplored. Among the galectins, galectin-1 and galectin-3 are the best-studied in these organs. This review summarizes the current knowledge of the cellular expression and the roles of galectin-1 and galectin-3 in testis and epididymis and discusses their functions in spermatogenesis, steroidogenesis, epididymal maturation of spermatozoa and inflammatory response.

Isolation and Characterization of Antibodies Against Vascular Cell Adhesion Molecule-1 Reveals Putative Role for Ig-like Domains 2 and 3 in Cell-to-Cell Interaction

The vascular cell adhesion molecule-1 (VCAM-1) plays an important role in inflammation, where it facilitates the recruitment of leukocytes to the inflamed area via leukocytes' VLA-4 and endothelial cells' VCAM-1 interaction. VCAM-1 expression is also upregulated in certain cancers. VCAM-1 has seven Ig-like domains, with domains 1 and 4 shown to be critical for VLA-4 binding. However, the specific functions of individual VCAM-1 Ig-like domains remain poorly understood. In this study, we identified single-chain variable fragment (scFv) antibodies targeting domains 2, 3, and 5 of VCAM-1, and investigated the ability of these antibodies to block VCAM-1-mediated cell adhesion to macrophages. We show that scFv antibodies against Ig-like domains 2 and 3 interfere with the ability of macrophages to bind endothelial cells, suggesting that these domains also play a role in facilitating this interaction. These results emphasize the need to more carefully study the role of each domain on VCAM-1 function and highlight the potential of targeting these VCAM-1 domains for more tailored therapeutic interventions in inflammatory diseases and cancer.

Galectin Plasmatic Levels Reveal a Cluster Associated with Disease Aggressiveness and Kidney Damage in Multiple Myeloma Patients

Multiple myeloma (MM) is a malignant disease characterized by the proliferation of plasma cells, primarily in the bone marrow. It accounts for approximately 1% of all cancers and 10% of hematologic malignancies. Clinical manifestations include hypercalcemia, anemia, renal failure, and bone lesions. The pathogenesis of MM involves complex interactions between myeloma cells and their microenvironment. Galectins, a family of β-galactoside-binding proteins, particularly galectin-1, -3, -4, -7, and -9, have been implicated in MM development. This study aimed to assess the plasma levels of these galectins in newly diagnosed MM patients and explore their correlation with clinical parameters. Peripheral blood samples were collected from patients at the Oncohematology Service of the Hospital de Câncer de Pernambuco, and galectin levels were measured using ELISA. Plasma levels of galectins-3, -7, and -9 were significantly higher in MM patients compared to the control group. Three clusters of MM patients were identified based on galectin plasma levels, with cluster 3, characterized by high levels of galectin-1, -4, and -7, being associated with a worse prognosis. A strong positive correlation was found between galectin-1, -4, and -7 levels and markers of kidney function (urea, creatinine, and β2-microglobulin), while negative correlations were observed with hematocrit and hemoglobin. Additionally, galectin-9 showed high accuracy in distinguishing MM patients from healthy controls (AUC = 0.931). Elevated galectin levels were indicative of disease aggressiveness and renal impairment in MM patients. Overall, our findings suggest that galectins-1, -4, -7, and -9 could serve as potential biomarkers for MM progression and severity, warranting further investigation into their utility in MM diagnosis and treatment.

Sulfonamide-derivatized galactosides selectively target an unexplored binding site in the galectin-9N-terminal domain

Four directional and positional variants of sulfonamide-derivatized galactopyranosides were synthesized and evaluated against human galectin-1, -3, -4C (C-terminal), -7, -8N (N-terminal), -8C (C-terminal), -9N (N-terminal), and -9C (C-terminal), which revealed that one of the sulfonamide positions and directionalities (methyl 3-{4-[2-(phenylsulfonylamino)-phenyl]-triazolyl}-3-deoxy-α-d-galactopyranosides) bound with 6-15 fold higher affinity than the corresponding phenyltriazole (lacking the phenylsulfonamide moiety) for galectin-9N. Molecular dynamic simulations suggested that inhibitor adopted a conformation that is complementary to the galectin-9N binding site and where the sulfonamide moiety protrudes into an unexplored and non-conserved binding site perpendicular to and below the A-B subsite to interact with a His61 NH proton. This resulted in the discovery of galectin-9N inhibitors with unprecedented selectivity over other galectins, thus constituting valuable tools for studies of the biological functions of galectin-9.

Central role of Galectin-3 at the cross-roads of cardiac inflammation and fibrosis: Implications for heart failure and transplantation

Cardiac inflammation and fibrosis are central pathogenic mechanisms leading to heart failure. Transplantation is still the treatment of choice for many patients undergoing end-stage heart failure who remain symptomatic despite optimal medical therapy. In spite of considerable progress, the molecular mechanisms linking inflammation, fibrosis and heart failure remain poorly understood. Galectin-3 (GAL3), a chimera-type member of the galectin family, has emerged as a critical mediator implicated in cardiac inflammatory, vascular and fibrotic processes through modulation of different cellular compartments including monocytes and macrophages, fibroblasts, endothelial cells and vascular smooth muscle cells via glycan-dependent or independent mechanisms. GAL3-driven circuits may hierarchically amplify cytokine production and function, immune cell activation and fibrosis cascades, influencing a wide range of cardiovascular disorders. Thus, GAL3 emerges as a potential therapeutic target to counteract aberrant inflammation and fibrosis during heart failure and a potential biomarker of heart failure and clinical outcome of heart transplantation.

The tissue glycome as regulator of immune activation and tolerance mediated by C-type lectins and Siglecs

The immune system is a complex network of highly specialized microenvironments, denominated niches, which arise from dynamic interactions between immune and parenchymal cells as well as acellular components such as structural elements and local molecular signals. A critical, yet underexplored, layer shaping these niches is the glycome, the complete repertoire of glycans and glycoconjugates produced by cells. The glycome is prevalent in the outer membrane of cells and their secreted components, and can be sensed by glycan binding receptors on immune cells. These receptors detect changes in glycosylation and consequently modulate immune cell activity, trafficking, and signalling, altering homeostasis. Tissues like the brain and the placenta are prone to accommodate tolerance, while the gut and the thymus are sensitive to inflammation. We provide here an overview of current literature that shows the impact of altered glycosylation of tissues on host immune cells and how interference in this process may lead to new diagnostics and immune therapeutics, aiming to restore the immune balance in autoimmunity and cancer.

Insights Into Glycobiology and the Protein-Glycan Interactome Using Glycan Microarray Technologies

Glycans linked to proteins and lipids and also occurring in free forms have many functions, and these are partly elicited through specific interactions with glycan-binding proteins (GBPs). These include lectins, adhesins, toxins, hemagglutinins, growth factors, and enzymes, but antibodies can also bind glycans. While humans and other animals generate a vast repertoire of GBPs and different glycans in their glycomes, other organisms, including phage, microbes, protozoans, fungi, and plants also express glycans and GBPs, and these can also interact with their host glycans. This can be termed the protein-glycan interactome, and in nature is likely to be vast, but is so far very poorly described. Understanding the breadth of the protein-glycan interactome is also a key to unlocking our understanding of infectious diseases involving glycans, and immunology associated with antibodies binding to glycans. A key technological advance in this area has been the development of glycan microarrays. This is a display technology in which minute quantities of glycans are attached to the surfaces of slides or beads. This allows the arrayed glycans to be interrogated by GBPs and antibodies in a relatively high throughput approach, in which a protein may bind to one or more distinct glycans. Such binding can lead to novel insights and hypotheses regarding both the function of the GBP, the specificity of an antibody and the function of the glycan within the context of the protein-glycan interactome. This article focuses on the types of glycan microarray technologies currently available to study animal glycobiology and examples of breakthroughs aided by these technologies.

Gal-3 blocks the binding between PD-1 and pembrolizumab

INTRODUCTION

Immune checkpoint inhibitors (ICI) have revolutionized the treatment of metastatic malignant melanoma (MM) and improved long-term survival. Despite the impressive results, some patients still have progressive disease, and the search for biomarkers predicting response to ICI treatment is ongoing. In this search, galectin-3 (Gal-3) has been suggested as a molecule of interest, both as a marker of treatment response and as a treatment target to potentiate ICI therapy. We have previously demonstrated the binding between programmed cell death 1 (PD-1) and Gal-3, and here, we investigated the interaction between PD-1, pembrolizumab, and Gal-3 in metastatic MM patients.

METHODS

The binding between PD-1, pembrolizumab and Gal-3 was investigated by surface plasmon resonance (SPR) and cryogenic electron microscopy (cryo-EM). The function was studied in in vitro cultures and soluble levels of both PD-1 and Gal-3 were measured in metastatic MM patients, treated with pembrolizumab.

RESULTS

By SPR, we demonstrated that Gal-3 can block the binding between PD-1 and pembrolizumab, and further visualized a steric inhibition using cryo-EM. T cells cultured with Gal-3 had reduced pro-inflammatory cytokine production, which could not be rescued by pembrolizumab. In patients with metastatic MM, high levels of Gal-3 in plasma were found in patients with a longer progression-free survival in the study period, whereas high Gal-3 expression in the tumor was seen in patients with disease progression. Soluble PD-1 levels in plasma increased after treatment with pembrolizumab and correlated with disease progression.

CONCLUSION

We demonstrate that the interaction between PD-1 and Gal-3 interferes with the binding of pembrolizumab, supporting that an immune suppression induced by Gal-3 in the tumor microenvironment cannot be rescued by pembrolizumab.

Modulation of galectin-9 mediated responses in monocytes and T-cells by pregnancy-specific glycoprotein 1

Successful pregnancy relies on a coordinated interplay between endocrine, immune, and metabolic processes to sustain fetal growth and development. The orchestration of these processes involves multiple signaling pathways driving cell proliferation, differentiation, angiogenesis, and immune regulation necessary for a healthy pregnancy. Among the molecules supporting placental development and maternal tolerance, the families of pregnancy-specific glycoproteins and galectins are of great interest in reproductive biology. We previously found that PSG1 can bind to galectin-1 (GAL-1). Herein, we characterized the interaction between PSG1 and other members of the galectin family expressed during pregnancy, including galectin-3, -7, -9, and -13 (GAL-3, GAL-7, GAL-9, and GAL-13). We observed that PSG1 binds to GAL-1, -3, and -9, with the highest apparent affinity seen for GAL-9, and that the interaction of PSG1 with GAL-9 is carbohydrate-dependent. We further investigated the ability of PSG1 to regulate GAL-9 responses in human monocytes, a murine macrophage cell line, and T-cells, and determined whether PSG1 binds to both carbohydrate recognition domains of GAL-9. Additionally, we compared the apparent affinity of GAL-9 binding to PSG1 with other known GAL-9 ligands in these cells, Tim-3 and CD44. Lastly, we explored functional conservation between murine and human PSGs by determining that Psg23, a highly expressed member of the murine Psg family, can bind some murine galectins despite differences in amino acid composition and domain structure.

CUREs for high-level Galectin-3 expression

Galectins are a large and diverse protein family defined by the presence of a carbohydrate recognition domain (CRD) that binds β-galactosides. They play important roles in early development, tissue regeneration, immune homeostasis, pathogen recognition, and cancer. In many cases, studies that examine galectin biology and the effect of manipulating galectins are aided by, or require the ability to express and purify, specific members of the galectin family. In many cases, E. coli is employed as a heterologous expression system, and galectin expression is induced with isopropyl β-galactoside (IPTG). Here, we show that galectin-3 recognizes IPTG with micromolar affinity and that as IPTG induces expression, newly synthesized galectin can bind and sequester cytosolic IPTG, potentially repressing further expression. To circumvent this putative inhibitory feedback loop, we utilized an autoinduction protocol that lacks IPTG, leading to significantly increased yields of galectin-3. Much of this work was done within the context of a course-based undergraduate research experience, indicating the ease and reproducibility of the resulting expression and purification protocols.

Galectin-2 Agglutinates Helicobacter pylori via Lipopolysaccharide Containing H Type I Under Weakly Acidic Conditions

Galectins are β-galactoside-binding animal lectins involved in various biological functions, such as host defense. Galectin-2 and -3 are members of the galectin family that are expressed in the stomach, including the gastric mucosa and surface mucous cells. Galectin-3 exhibits aggregation and bactericidal activity against Helicobacter pylori in a β-galactoside-dependent manner. We previously reported that galectin-2 has the same activity under neutral pH conditions. In this study, the H. pylori aggregation activity of galectin-2 was examined under weakly acidic conditions, in which H. pylori survived. Galectin-2 agglutinated H. pylori even at pH 6.0, but not at pH 5.0, correlating with its structural stability, as determined using circular dichroism. Additionally, galectin-2 binding to the lipopolysaccharide (LPS) of H. pylori cultured under weakly acidic conditions was investigated using affinity chromatography and Western blotting. Galectin-2 could bind to H. pylori LPS containing H type I, a Lewis antigen, in a β-galactoside-dependent manner. In contrast, galectin-3 was structurally more stable than galectin-2 under acidic conditions and bound to H. pylori LPS containing H type I and Lewis X. In conclusion, galectin-2 and -3 might function cooperatively in the defense against H. pylori in the stomach under different pH conditions.

Exploring galectin interactions with human milk oligosaccharides and blood group antigens identifies BGA6 as a functional galectin-4 ligand

Galectins (Gals), a family of multifunctional glycan-binding proteins, have been traditionally defined as β-galactoside binding lectins. However, certain members of this family have shown selective affinity toward specific glycan structures including human milk oligosaccharides (HMOs) and blood group antigens. In this work, we explored the affinity of human galectins (particularly Gal-1, -3, -4, -7, and -12) toward a panel of oligosaccharides including HMOs and blood group antigens using a complementary approach based on both experimental and computational techniques. While prototype Gal-1 and Gal-7 exhibited differential affinity for type I versus type II Lac/LacNAc residues and recognized fucosylated neutral glycans, chimera-type Gal-3 showed high binding affinity toward poly-LacNAc structures including LNnH and LNnO. Notably, the tandem-repeat human Gal-12 showed preferential recognition of 3-fucosylated glycans, a unique feature among members of the galectin family. Finally, Gal-4 presented a distinctive glycan-binding activity characterized by preferential recognition of specific blood group antigens, also validated by saturation transfer difference nuclear magnetic resonance experiments. Particularly, we identified oligosaccharide blood group A antigen tetraose 6 (BGA6) as a biologically relevant Gal-4 ligand, which specifically inhibited interleukin-6 secretion induced by this lectin on human peripheral blood mononuclear cells. These findings highlight unique determinants underlying specific recognition of HMOs and blood group antigens by human galectins, emphasizing the biological relevance of Gal-4-BGA6 interactions, with critical implications in the development and regulation of inflammatory responses.

Insights into the recognition of hypermucoviscous Klebsiella pneumoniae clinical isolates by innate immune lectins of the Siglec and galectin families

Klebsiella pneumoniae is an opportunistic bacterium that frequently colonizes the nasopharynx and gastrointestinal tract and can also cause severe infections when invading other tissues, particularly in immunocompromised individuals. Moreover, K. pneumoniae variants exhibiting a hypermucoviscous (HMV) phenotype are usually associated with hypervirulent strains that can produce invasive infections even in immunocompetent individuals. Major carbohydrate structures displayed on the K. pneumoniae surface are the polysaccharide capsule and the lipopolysaccharide, which presents an O-polysaccharide chain in its outermost part. Various capsular and O-chain structures have been described. Of note, production of a thick capsule is frequently observed in HMV variants. Here we examined the surface sugar epitopes of a collection of HMV and non-HMV K. pneumoniae clinical isolates and their recognition by several Siglecs and galectins, two lectin families of the innate immune system, using bacteria microarrays as main tool. No significant differences among isolates in sialic acid content or recognition by Siglecs were observed. In contrast, analysis of the binding of model lectins with diverse carbohydrate-binding specificities revealed striking differences in the recognition by galactose- and mannose-specific lectins, which correlated with the binding or lack of binding of galectins and pointed to the O-chain as the plausible ligand. Fluorescence microscopy and microarray analyses of galectin-9 binding to entire cells and outer membranes of two representative HMV isolates supported the bacteria microarray results. In addition, Western blot analysis of the binding of galectin-9 to outer membranes unveiled protein bands recognized by this galectin, and fingerprint analysis of these bands identified several proteins containing potential O-glycosylation sites, thus broadening the spectrum of possible galectin ligands on the K. pneumoniae surface. Moreover, Siglecs and galectins apparently target different structures on K. pneumoniae surfaces, thereby behaving as non-redundant complementary tools of the innate immune system.

Different roles of the heterodimer architecture of galectin-4 in selective recognition of oligosaccharides and lipopolysaccharides having ABH antigens

The dimeric architecture of tandem-repeat type galectins, such as galectin-4 (Gal-4), modulates their biological activities, although the underlying molecular mechanisms have remained elusive. Emerging evidence show that tandem-repeat galectins play an important role in innate immunity by recognizing carbohydrate antigens present on the surface of certain pathogens, which very often mimic the structures of the human self-glycan antigens. Herein, we have analyzed the binding preferences of the C-domain of Gal-4 (Gal-4C) toward the ABH-carbohydrate histo-blood antigens with different core presentations and their recognition features have been rationalized by using a combined experimental approach including NMR, solid-phase and hemagglutination assays, and molecular modeling. The data show that Gal-4C prefers A over B antigens (two-fold in affinity), contrary to the N-domain (Gal-4N), although both domains share the same preference for the type-6 presentations. The behavior of the full-length Gal-4 (Gal-4FL) tandem-repeat form has been additionally scrutinized. Isothermal titration calorimetry and NMR data demonstrate that both domains within full-length Gal-4 bind to the histo-blood antigens independently of each other, with no communication between them. In this context, the heterodimeric architecture does not play any major role, apart from the complementary A and B antigen binding preferences. However, upon binding to a bacterial lipopolysaccharide containing a multivalent version of an H-antigen mimetic as O-antigen, the significance of the galectin architecture was revealed. Indeed, our data point to the linker peptide domain and the F-face of the C-domain as key elements that provide Gal-4 with the ability to cross-link multivalent ligands, beyond the glycan binding capacity of the dimer.

The galectin-3 inhibitor selvigaltin reduces liver inflammation and fibrosis in a high fat diet rabbit model of metabolic-associated steatohepatitis

Introduction

Galectin-3 is a pro-fibrotic β-galactoside binding lectin highly expressed in fibrotic liver and implicated in hepatic fibrosis. Selvigaltin (previously known as GB1211) is a novel orally active galectin-3 small molecule inhibitor that has high affinity for galectin-3 (human KD = 25 nM; rabbit KD = 12 nM) and high oral bioavailability in rabbits and man. In this study the efficacy of selvigaltin was investigated in a high fat diet (HFD) rabbit model of metabolic-associated steatohepatitis (MASH).

Methods

Male New Zealand White rabbits were individually caged under standard conditions in a temperature and humidity-controlled room on a 12 h light/darkness cycle. After 1 week of regular diet (RD), rabbits were randomly assigned for 8 or 12 weeks to different groups: RD/vehicle, RD/selvigaltin, HFD (8 weeks), HFD/vehicle and HFD/selvigaltin (0.3, 1.0, 5.0 or 30 mg/kg selvigaltin with vehicle/selvigaltin p.o. dosed therapeutically q.d. 5 days per week from week 9 or 12). Liver inflammation, steatosis, ballooning, and fibrosis was measured via blood metabolic markers, histomorphological evaluation [Oil Red O, Giemsa, Masson's trichome, picrosirius red (PSR) and second harmonic generation (SHG)], and mRNA and protein expression.

Results

Steatosis, inflammation, ballooning, and fibrosis were all increased from RD to HFD/vehicle groups. Selvigaltin demonstrated target engagement by significantly decreasing galectin-3 levels in the liver as measured via immunohistochemistry and mRNA analysis. Selvigaltin dose-dependently reduced biomarkers of liver function (AST, ALT, bilirubin), inflammation (cells foci), and fibrosis (PSR, SHG), as well as decreasing the mRNA and protein expression of several key inflammation and fibrosis biomarkers (e.g., IL6, TGFβ3, SNAI2, collagen). Doses of 1.0 or 5.0 mg/kg demonstrated consistent efficacy across most biological endpoints supporting the current clinical doses of selvigaltin being investigated in liver disease.

Discussion

Selvigaltin significantly reduced hepatic inflammation and fibrosis in an HFD rabbit model of MASH following therapeutic dosing for 4 weeks in a dose-dependent manner. These data support the human selvigaltin dose of 100 mg b.i.d. that has been shown to reduce key liver biomarkers during a clinical study in liver cirrhosis.

The role of galectins in the regulation of autophagy and inflammasome in host immunity

Galectins, a family of glycan-binding proteins have been shown to bind a wide range of glycans. In the cytoplasm, these glycans can be endogenous (or "self"), originating from damaged endocytic vesicles, or exogenous (or "non-self"), found on the surface of invading microbial pathogens. Galectins can detect these unusual cytosolic exposures to glycans and serve as critical regulators in orchestrating immune responses in innate and adaptive immunity. This review provides an overview of how galectins modulate host cellular responses, such as autophagy, xenophagy, and inflammasome-dependent cell death program, to infection.

ABO blood groups and galectins: Implications in transfusion medicine and innate immunity

ABO blood group antigens, which are complex carbohydrate moieties, and the first human polymorphisms identified, are critical in transfusion medicine and transplantation. Despite their discovery over a century ago, significant questions remain about the development of anti-ABO antibodies and the structural features of ABO antigens that cause hemolytic transfusion reactions. Anti-ABO antibodies develop naturally during the first few months of life, in contrast to other red blood cell (RBC) alloantibodies which form after allogeneic RBC exposure. Anti-ABO antibodies are the most common immune barrier to transfusion and transplantation, but the factors driving their formation are incompletely understood. Some studies suggest that microbes that express glycans similar in structure to the blood group antigens could play a role in anti-blood group antibody formation. While the role of these microbes in clinically relevant anti-blood group antibody formation remains to be defined, the presence of these microbes raises questions about how blood group-positive individuals protect themselves against blood group molecular mimicry. Recent studies suggest that galectins can bind and kill microbes that mimic blood group antigens, suggesting a unique host defense mechanism against microbial molecular mimicry. However, new models are needed to fully define the impact of microbes, galectins, or other factors on the development of clinically relevant naturally occurring anti-blood group antibodies.

Shaping hematopoietic cell ecosystems through galectin-glycan interactions

Hematopoiesis- the formation of blood cell components- continually replenishes the blood system during embryonic development and postnatal lifespans. This coordinated process requires the synchronized action of a broad range of cell surface associated proteins and soluble mediators, including growth factors, cytokines and lectins. Collectively, these mediators control cellular communication, signalling, commitment, proliferation, survival and differentiation. Here we discuss the role of galectins - an evolutionarily conserved family of glycan-binding proteins - in the establishment and dynamic remodelling of hematopoietic niches. We focus on the contribution of galectins to B and T lymphocyte development and selection, as well as studies highlighting the role of these proteins in myelopoiesis, with particular emphasis on erythropoiesis and megakaryopoiesis. Finally, we also highlight recent findings suggesting the role of galectin-1, a prototype member of this protein family, as a key pathogenic factor and therapeutic target in myelofibrosis. Through extracellular or intracellular mechanisms, galectins can influence the fate and function of distinct hematopoietic progenitors and fine-tune the final repertoire of blood cells, with critical implications in a wide range of physiologically vital processes including innate and adaptive immunity, immune tolerance programs, tissue repair, regeneration, angiogenesis, inflammation, coagulation and oxygen delivery. Additionally, positive or negative regulation of galectin-driven circuits may contribute to a broad range of blood cell disorders.

A Quantitative Human Red Blood Cell Agglutination Assay for Characterisation of Galectin Inhibitors

Galectins are a family of beta-galactoside-binding proteins that are characterised by their carbohydrate recognition domain (CRD) and include galectin-1 and galectin-3. These galectins have been implicated in numerous diseases due to their pleiotropic nature, including cancer and fibrosis, with therapeutic inhibitors being clinically developed to block the CRD. One of the early methods developed to characterise these galectins was the hemagglutination of red blood cells. Although it is insightful, this approach has been hampered by a lack of sensitivity and accurate quantification of the agglutination observed. In this study, we aimed to validate a more precise and quantitative method to enable the further investigation of differences between galectins in respect to agglutination induction in different blood groups, as well as the characterisation of small molecule inhibitors. Quantification of hemagglutination was shown to be optimal using U-bottom plates imaged and analysed with FIJI ImageJ rather than flat-bottom plates read for absorbance on an optical density plate reader. Galectin-3-induced red blood cell agglutination efficacy increased significantly from blood group O to A to B. However, for both the galectin-1 monomer and concatemer, a more comparable effect was observed between blood group B and O, but with more potent effects than in blood group A. Inhibition assays for both galectin-3 and galectin-1 induced-hemagglutination were able to demonstrate clear concentration responses and expected selectivity profiles for a set of small-molecule glycomimetics, confirming the historical profiles obtained in biochemical binding and functional cellular assays.

Determining the Affinity and Kinetics of Small Molecule Inhibitors of Galectin-1 Using Surface Plasmon Resonance

The beta-galactoside-binding mammalian lectin galectin-1 can bind, via its carbohydrate recognition domain (CRD), to various cell surface glycoproteins and has been implicated in a range of cancers. As a consequence of binding to sugar residues on cell surface receptors, it has been shown to have a pleiotropic effect across many cell types and mechanisms, resulting in immune system modulation and cancer progression. As a result, it has started to become a therapeutic target for both small and large molecules. In previous studies, we used fluorescence polarization (FP) assays to determine KD values to screen and triage small molecule glycomimetics that bind to the galectin-1 CRD. In this study, surface plasmon resonance (SPR) was used to compare human and mouse galectin-1 affinity measures with FP, as SPR has not been applied for compound screening against this galectin. Binding affinities for a selection of mono- and di-saccharides covering a 1000-fold range correlated well between FP and SPR assay formats for both human and mouse galectin-1. It was shown that slower dissociation drove the increased affinity at human galectin-1, whilst faster association was responsible for the effects in mouse galectin-1. This study demonstrates that SPR is a sound alternative to FP for early drug discovery screening and determining affinity estimates. Consequently, it also allows association and dissociation constants to be measured in a high-throughput manner for small molecule galectin-1 inhibitors.

Bioactive Properties of Venoms Isolated from Whiptail Stingrays and the Search for Molecular Mechanisms and Targets

The venom-containing barb attached to their 'whip-like' tail provides stingrays a defensive mechanism for evading predators such as sharks. From human encounters, dermal stingray envenomation is characterized by intense pain often followed by tissue necrosis occurring over several days to weeks. The bioactive components in stingray venoms (SRVs) and their molecular targets and mechanisms that mediate these complex responses are not well understood. Given the utility of venom-derived proteins from other venomous species for biomedical and pharmaceutical applications, we set out to characterize the bioactivity of SRV extracts from three local species that belong to the Dasyatoidea 'whiptail' superfamily. Multiple cell-based assays were used to quantify and compare the in vitro effects of these SRVs on different cell lines. All three SRVs demonstrated concentration-dependent growth-inhibitory effects on three different human cell lines tested. In contrast, a mouse fibrosarcoma cell line was markedly resistant to all three SRVs, indicating the molecular target(s) for mediating the SRV effects are not expressed on these cells. The multifunctional SRV responses were characterized by an acute disruption of cell adhesion leading to apoptosis. These findings aim to guide future investigations of individual SRV proteins and their molecular targets for potential use in biomedical applications.

Galectins in epithelial-mesenchymal transition: roles and mechanisms contributing to tissue repair, fibrosis and cancer metastasis

Galectins are soluble glycan-binding proteins that interact with a wide range of glycoproteins and glycolipids and modulate a broad spectrum of physiological and pathological processes. The expression and subcellular localization of different galectins vary among tissues and cell types and change during processes of tissue repair, fibrosis and cancer where epithelial cells loss differentiation while acquiring migratory mesenchymal phenotypes. The epithelial-mesenchymal transition (EMT) that occurs in the context of these processes can include modifications of glycosylation patterns of glycolipids and glycoproteins affecting their interactions with galectins. Moreover, overexpression of certain galectins has been involved in the development and different outcomes of EMT. This review focuses on the roles and mechanisms of Galectin-1 (Gal-1), Gal-3, Gal-4, Gal-7 and Gal-8, which have been involved in physiologic and pathogenic EMT contexts.

Interplay in galectin expression predicts patient outcomes in a spatially restricted manner in PDAC

BACKGROUND

Galectins (Gal's) are a family of carbohydrate-binding proteins that are known to support the tumour microenvironment through their immunosuppressive activity and ability to promote metastasis. As such they are attractive therapeutic targets, but little is known about the cellular expression pattern of galectins within the tumour and its neighbouring stromal microenvironment. Here we investigated the cellular expression pattern of Gals within pancreatic ductal adenocarcinoma (PDAC).

METHODS

Galectin gene and protein expression were analysed by scRNAseq (n=4) and immunofluorescence imaging (n=19) in fibroblasts and epithelial cells of pancreatic biopsies from PDAC patients. Galectin surface expression was also assessed on tumour adjacent normal fibroblasts and cancer associated primary fibroblasts from PDAC biopsies using flow cytometry.

RESULTS

scRNAseq revealed higher Gal-1 expression in fibroblasts and higher Gal-3 and -4 expression in epithelial cells. Both podoplanin (PDPN+, stromal/fibroblast) cells and EpCAM+ epithelial cells expressed Gal-1 protein, with highest expression seen in the stromal compartment. By contrast, significantly more Gal-3 and -4 protein was expressed in ductal cells expressing either EpCAM or PDPN, when compared to the stroma. Ductal Gal-4 cellular expression negatively correlated with ductal Gal-1, but not Gal-3 expression. Higher ductal cellular expression of Gal-1 correlated with smaller tumour size and better patient survival.

CONCLUSIONS

In summary, the intricate interplay and cell-specific expression patterns of galectins within the PDAC tissue, particularly the inverse correlation between Gal-1 and Gal-4 in ducts and its significant association with patient survival, highlights the complex molecular landscape underlying PDAC and provides valuable insights for future therapeutic interventions.