A Novel Function for Galectin-1 at the Crossroad of Innate and Adaptive Immunity: Galectin-1 Regulates Monocyte/Macrophage Physiology through a Nonapoptotic ERK-Dependent Pathway

Glycosylation-driven programs coordinate immunoregulatory and pro-angiogenic functions of myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) promote tumor progression by suppressing antitumor immunity and inducing angiogenesis; however, the mechanisms linking these processes remain uncertain. Here, we identified a glycosylation-dependent program driven by galectin-1 (GAL1) that imparted both immunoregulatory and pro-angiogenic functions to MDSCs through shared receptor signaling pathways. GAL1 expression was associated with enhanced MDSC phenotypes and poor prognosis in diverse human cancers. Analysis of monocytic and polymorphonuclear MDSCs from tumor-bearing mice revealed niche-specific glycan signatures that selectively regulated GAL1 binding. Through glycosylation-dependent interactions with the CD18-CD11b-CD177 receptor complex and STAT3 signaling, GAL1 simultaneously orchestrated immunosuppressive and pro-angiogenic programs in MDSCs, driving tumor growth in vivo. Myeloid-specific deletion of β-galactoside α(2,6)-sialyltransferase 1, which prevented α(2,6)-linked sialic acid incorporation, enhanced GAL1-driven regulatory circuits and accelerated tumor progression, effects that were mitigated by GAL1-neutralizing antibodies. Thus, targeting GAL1-glycan interactions may offer opportunities to reprogram MDSCs and enhance the efficacy of immunotherapeutic and anti-angiogenic strategies.

Galectins as Drivers of Host-Pathogen Dynamics in Mycobacterium tuberculosis Infection

Galectins form a protein family with a conserved carbohydrate-binding domain that specifically interacts with β-galactoside-containing glycoconjugates, which are found abundantly on mammalian cell surfaces. These proteins play crucial roles in various physiological and pathological processes including immune responses, cell adhesion, inflammation, and apoptosis. During tuberculosis infection, galectins exert diverse impacts on pathogenesis. The interaction between host and pathogen during TB involves intricate mechanisms influencing disease outcomes, where the pathogen exploits host glycosylation patterns to evade immune detection, underscoring the significant role of galectins in regulating these crucial host-pathogen interactions. Galectins facilitate pathogen recognition, enhance the phagocytosis of mycobacteria, support the formation of granuloma, and carefully balance the protective immunity against potential tissue damage. Additionally, galectins have an impact on the cytokine milieu by regulating the levels of pro-inflammatory cytokines and chemokines, essential for orchestrating granuloma formation and maintaining tuberculosis-associated homeostasis. This review delves into the intricate connection between galectins and tuberculosis; uncovering essential molecular mechanisms that deepen our understanding of how these proteins contribute to combating this pervasive infectious disease. Here we discuss the multifaceted roles that galectins play to uniquely and critically influence the core dynamics of host-pathogen interactions in tuberculosis.

GFP Transfection Alters Protein Expression Patterns in Prostate Cancer Cells: A Proteomic Study

PURPOSE

Green Fluorescent Protein is widely used as a cellular marker tool, but its potential influence on cells has been questioned. Although the potential off-target effects of GFP on tumor cells have been studied to some extent, the findings at the molecular level are insufficient to explain the effect of GFP expression on the tumorigenic capacity of cancer cells. Here, we aimed to investigate the effect of GFP expression on the tumorigenicity of PC3 prostate cancer cells.

METHODS

Using GFP-expressing and wild-type PC-3 cells, xenograft models were generated in athymic BALB/C mice. To identify differentially expressed proteins, the change in cells proteome was investigated by label-free quantification with nano-high performance liquid chromatography to tandem mass spectrometry (nHPLC-MS/MS). Proteins that showed significantly altered expression levels were evaluated using the bioinformatics tools.

RESULTS

Unlike the wild-type PC-3 cells, GFP-expressing cells failed to develop tumor. Comparative proteome analysis of GFP-expressing cells with WT PC-3 cells revealed a total of 216 differentially regulated proteins, of which 98 were upregulated and 117 were downregulated.

CONCLUSION

Upon GFP expression, differential changes in several pathways including the immune system, translational machinery, energy metabolism, elements of cytoskeletal and VEGF signaling pathway were observed. Therefore, care should be taken into account to prevent reporting deceitful mechanisms generated from studies utilizing GFP.

Multifaceted roles of Galectins: from carbohydrate binding to targeted cancer therapy

Galectins play pivotal roles in cellular recognition and signaling processes by interacting with glycoconjugates. Extensive research has highlighted the significance of Galectins in the context of cancer, aiding in the identification of biomarkers for early detection, personalized therapy, and predicting treatment responses. This review offers a comprehensive overview of the structural characteristics, ligand-binding properties, and interacting proteins of Galectins. We delve into their biological functions and examine their roles across various cancer types. Galectins, characterized by a conserved carbohydrate recognition domain (CRD), are divided into prototype, tandem-repeat, and chimera types based on their structural configurations. Prototype Galectins contain a single CRD, tandem-repeat Galectins contain two distinct CRDs linked by a peptide, and the chimera-type Galectin-3 features a unique structural arrangement. The capacity of Galectins to engage in multivalent interactions allows them to regulate a variety of signaling pathways, thereby affecting cell fate and function. In cancer, Galectins contribute to tumor cell transformation, angiogenesis, immune evasion, and metastasis, making them critical targets for therapeutic intervention. This review discusses the multifaceted roles of Galectins in cancer progression and explores current advancements in the development of Galectin-targeted therapies. We also address the challenges and future directions for integrating Galectin research into clinical practice to enhance cancer treatment outcomes. In brief, understanding the complex functions of Galectins in cancer biology opens new avenues for therapeutic strategies. Continued research on Galectin interactions and their pathological roles is essential for developing effective carbohydrate-based treatments and improving clinical interventions for cancer patients.

Matricellular proteins: From cardiac homeostasis to immune regulation

Tissue repair after myocardial injury is a complex process involving changes in all aspects of the myocardial tissue, including the extracellular matrix (ECM). The ECM is composed of large structural proteins such as collagen and elastin and smaller proteins with major regulatory properties called matricellular proteins. Matricellular cell proteins exert their functions and elicit cellular responses by binding to structural proteins not limited to interactions with cell surface receptors, cytokines, or proteases. At the same time, matricellular proteins act as the "bridge" of information exchange between cells and ECM, maintaining the integrity of the cardiac structure and regulating the immune environment, which is a key factor in determining cardiac homeostasis. In this review, we present an overview of the identified matricellular proteins and summarize the current knowledge regarding their roles in maintaining cardiac homeostasis and regulating the immune system.

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.

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.

Galectin-1 correlates with inflammatory markers and T regulatory cells in children with type 1 diabetes and/or celiac disease

Type 1 diabetes (T1D) and celiac disease (CeD) are common autoimmune diseases in children where the pathophysiology is not fully characterized. The autoimmune process involves a complex scenario of both inflammatory and regulatory features. Galectin-1 (GAL-1) has a wide range of biological activities e.g. interaction with immune cells. We examined the relationship between GAL-1 and soluble immune markers and T-cell subsets in a cohort of children with T1D and/or CeD relative to healthy children. GAL-1, together with several soluble immune markers [e.g. interleukins (IL)], tumor necrosis factor (TNF), acute phase proteins, and matrix metalloproteinases (MMP) were measured in sera from children with T1D and/or CeD by fluorochrome (Luminex) technique using children without these diseases as a reference. Subgroups of T cells, including T-regulatory (Treg) cells, were analysed by flow cytometry. Association between GAL-1, pro-inflammatory markers, and Treg cells differed depending on which illness combination was present. In children with both T1D and CeD, GAL-1 correlated positively with pro-inflammatory markers (IL-1β, IL-6, and TNF-α). Composite scores increased the strength of correlation between GAL-1 and pro-inflammatory markers, Th1-associated interferon (IFN)-γ, and T1D-associated visfatin. Contrary, in children diagnosed with exclusively T1D, GAL-1 was positively correlated to CD25hi and CD25hiCD101+ Treg cells. For children with only CeD, no association between GAL-1 and other immune markers was observed. In conclusion, the association observed between GAL-1, soluble immune markers, and Treg cells may indicate a role for GAL-1 in the pathophysiology of T1D and, to some extent, also in CeD.

Sex-dependent expression of galectin-1, a cardioprotective β-galactoside-binding lectin, in human calcific aortic stenosis

We aimed to analyze sex-related differences in galectin-1 (Gal-1), a β-galactoside-binding lectin, in aortic stenosis (AS) and its association with the inflammatory and fibrocalcific progression of AS. Gal-1 was determined in serum and aortic valves (AVs) from control and AS donors by western blot and immunohistochemistry. Differences were validated by ELISA and qPCR in AS samples. In vitro experiments were conducted in primary cultured valve interstitial cells (VICs). Serum Gal-1 was not different neither between control and AS nor between men and women. There was no association between circulating and valvular Gal-1 levels. The expression of Gal-1 in stenotic AVs was higher in men than women, even after adjusting for confounding factors, and was associated with inflammation, oxidative stress, extracellular matrix remodeling, fibrosis, and osteogenesis. Gal-1 (LGALS1) mRNA was enhanced within fibrocalcific areas of stenotic AVs, especially in men. Secretion of Gal-1 was up-regulated over a time course of 2, 4, and 8 days in men's calcifying VICs, only peaking at day 4 in women's VICs. In vitro, Gal-1 was associated with similar mechanisms to those in our clinical cohort. β-estradiol significantly up-regulated the activity of an LGALS1 promoter vector and the secretion of Gal-1, only in women's VICs. Supplementation with rGal-1 prevented the effects elicited by calcific challenge including the metabolic shift to glycolysis. In conclusion, Gal-1 is up-regulated in stenotic AVs and VICs from men in association with inflammation, oxidative stress, matrix remodeling, and osteogenesis. Estrogens can regulate Gal-1 expression with potential implications in post-menopause women. Exogenous rGal-1 can diminish calcific phenotypes in both women and men.

Selective modifications of lactose and N-acetyllactosamine with sulfate and aromatic bulky groups unveil unique structural insights in galectin-1-ligand recognition

Galectins, a family of endogenous glycan-binding proteins, play crucial roles in a broad range of physiological and pathological processes. Galectin-1 (Gal-1), a proto-type member of this family, is overexpressed in several cancers and plays critical roles in tumor-immune escape, angiogenesis and metastasis. Thus, generation of high-affinity Gal-1 inhibitors emerges as an attractive therapeutic approach for a wide range of neoplastic conditions. Small-molecule carbohydrate inhibitors based on lactose (Lac) and N-acetyllactosamine (LacNAc) structures have been tested showing different results. In this study, we evaluated Lac- and LacNAc-based compounds with specific chemical modifications at key positions as Gal-1 ligands by competitive solid-phase assays (SPA) and isothermal titration calorimetry (ITC). Both assays showed excellent correlation, highlighting that lactosides bearing bulky aromatic groups at the anomeric carbon and sulfate groups at the O3' position exhibited the highest binding affinities. To dissect the atomistic determinants for preferential affinity of the different tested Gal-1 ligands, molecular docking simulations were conducted and PRODIGY-LIG structure-based method was employed to predict binding affinity in protein-ligand complexes. Notably, calculated binding free energies derived from the molecular docking were in accordance with experimental values determined by SPA and ITC, showing excellent correlation between theoretical and experimental approaches. Moreover, this analysis showed that 3'-O-sulfate groups interact with residues of the Gal-1 subsite B, mainly with Asn33, while the ester groups of the aromatic anomeric group interact with Gly69 and Thr70 at Gal-1 subsite E, extending deeper into the pocket, which could account for the enhanced binding affinity. This study contributes to the rational design of highly optimized Gal-1 inhibitors to be further studied in cancer models and other pathologic conditions.

Galectin-1 induces a tumor-associated macrophage phenotype and upregulates indoleamine 2,3-dioxygenase-1

Galectins are a group of carbohydrate-binding proteins with a presumed immunomodulatory role and an elusive function on antigen-presenting cells. Here we analyzed the expression of galectin-1 and found upregulation of galectin-1 in the extracellular matrix across multiple tumors. Performing an in-depth and dynamic proteomic and phosphoproteomic analysis of human macrophages stimulated with galectin-1, we show that galectin-1 induces a tumor-associated macrophage phenotype with increased expression of key immune checkpoint protein programmed cell death 1 ligand 1 (PD-L1/CD274) and immunomodulator indoleamine 2,3-dioxygenase-1 (IDO1). Galectin-1 induced IDO1 and its active metabolite kynurenine in a dose-dependent manner through JAK/STAT signaling. In a 3D organotypic tissue model system equipped with genetically engineered tumorigenic epithelial cells, we analyzed the cellular source of galectin-1 in the extracellular matrix and found that galectin-1 is derived from epithelial and stromal cells. Our results highlight the potential of targeting galectin-1 in immunotherapeutic treatment of human cancers.

Hypothyroidism-associated immunosuppression involves induction of galectin-1-producing regulatory T cells

Hypothyroidism exerts deleterious effects on immunity, but the precise role of the hypothalamic-pituitary-thyroid (HPT) axis in immunoregulatory and tolerogenic programs is barely understood. Here, we investigated the mechanisms underlying hypothyroid-related immunosuppression by examining the regulatory role of components of the HPT axis. We first analyzed lymphocyte activity in mice overexpressing the TRH gene (Tg-Trh). T cells from Tg-Trh showed increased proliferation than wild-type (WT) euthyroid mice in response to polyclonal activation. The release of Th1 pro-inflammatory cytokines was also increased in Tg-Trh and TSH levels correlated with T-cell proliferation. To gain further mechanistic insights into hypothyroidism-related immunosuppression, we evaluated T-cell subpopulations in lymphoid tissues of hypothyroid and control mice. No differences were observed in CD3/CD19 or CD4/CD8 ratios between these strains. However, the frequency of regulatory T cells (Tregs) was significantly increased in hypothyroid mice, and not in Tg-Trh mice. Accordingly, in vitro Tregs differentiation was more pronounced in naïve T cells isolated from hypothyroid mice. Since Tregs overexpress galectin-1 (Gal-1) and mice lacking this lectin (Lgals1^-/- ) show reduced Treg function, we investigated the involvement of this immunoregulatory lectin in the control of Tregs in settings of hypothyroidism. Increased T lymphocyte reactivity and reduced frequency of Tregs were found in hypothyroid Lgals1^-/- mice when compared to hypothyroid WT animals. This effect was rescued by the addition of recombinant Gal-1. Finally, increased expression of Gal-1 was found in Tregs purified from hypothyroid WT mice compared with their euthyroid counterpart. Thus, a substantial increase in the frequency and activity of Gal-1-expressing Tregs underlies immunosuppression associated with hypothyroid conditions, with critical implications in immunopathology, metabolic disorders, and cancer.

Galectin-1: A Traditionally Immunosuppressive Protein Displays Context-Dependent Capacities

Galectin–Carbohydrate interactions are indispensable to pathogen recognition and immune response. Galectin-1, a ubiquitously expressed 14-kDa protein with an evolutionarily conserved β-galactoside binding site, translates glycoconjugate recognition into function. That galectin-1 is demonstrated to induce T cell apoptosis has led to substantial attention to the immunosuppressive properties of this protein, such as inducing naive immune cells to suppressive phenotypes, promoting recruitment of immunosuppressing cells as well as impairing functions of cytotoxic leukocytes. However, only in recent years have studies shown that galectin-1 appears to perform a pro-inflammatory role in certain diseases. In this review, we describe the anti-inflammatory function of galectin-1 and its possible mechanisms and summarize the existing therapies and preclinical efficacy relating to these agents. In the meantime, we also discuss the potential causal factors by which galectin-1 promotes the progression of inflammation.

Gal-1 Expression Analysis in the GLIOCAT Multicenter Study: Role as a Prognostic Factor and an Immune-Suppressive Biomarker

Glioblastoma (GBM) is the most frequent primary malignant brain tumor and has a dismal prognosis. Unfortunately, despite the recent revolution of immune checkpoint inhibitors in many solid tumors, these have not shown a benefit in overall survival in GBM patients. Therefore, new potential treatment targets as well as diagnostic, prognostic, and/or predictive biomarkers are needed to improve outcomes in this population. The β-galactoside binding protein Galectin-1 (Gal-1) is a protein with a wide range of pro-tumor functions such as proliferation, invasion, angiogenesis, and immune suppression. Here, we evaluated Gal-1 expression by immunohistochemistry in a homogenously treated cohort of GBM (the GLIOCAT project) and correlated its expression with clinical and molecular data. We observed that Gal-1 is a negative prognostic factor in GBM. Interestingly, we observed higher levels of Gal-1 expression in the mesenchymal/classical subtypes compared to the less aggressive proneural subtype. We also observed a Gal-1 expression correlation with immune suppressive signatures of CD4 T-cells and macrophages, as well as with several GBM established biomarkers, including SHC1, PD-L1, PAX2, MEOX2, YKL-40, TCIRG1, YWHAG, OLIG2, SOX2, Ki-67, and SOX11. Moreover, Gal-1 levels were significantly lower in grade 4 IDH-1 mutant astrocytomas, which have a better prognosis. Our results confirm the role of Gal-1 as a prognostic factor and also suggest its value as an immune-suppressive biomarker in GBM.

Molecular Cloning and Functional Characterization of Galectin-1 in Yellow Drum (Nibea albiflora)

Galectins are proteins that are involved in the innate immune response against pathogenic microorganisms. In the present study, the gene expression pattern of galectin-1 (named as NaGal-1) and its function in mediating the defense response to bacterial attack were investigated. The tertiary structure of NaGal-1 protein consists of homodimers and each subunit has one carbohydrate recognition domain. Quantitative RT-PCR analysis indicated that NaGal-1 was ubiquitously distributed in all the detected tissues and highly expressed in the swim-bladder of Nibea albiflora, and its expression could be upregulated by the pathogenic Vibrio harveyi attack in the brain. Expression of NaGal-1 protein in HEK 293T cells was distributed in the cytoplasm as well as in the nucleus. The recombinant NaGal-1 protein by prokaryotic expression could agglutinate red blood cells from rabbit, Larimichthys crocea, and N. albiflora. The agglutination of N. albiflora red blood cells by the recombinant NaGal-1 protein was inhibited by peptidoglycan, lactose, D-galactose, and lipopolysaccharide in certain concentrations. In addition, the recombinant NaGal-1 protein agglutinated and killed some gram-negative bacteria including Edwardsiella tarda, Escherichia coli, Photobacterium phosphoreum, Aeromonas hydrophila, Pseudomonas aeruginosa, and Aeromonas veronii. These results set the stage for further studies of NaGal-1 protein in the innate immunity of N. albiflora.

The sweet side of wound healing: galectins as promising therapeutic targets in hemostasis, inflammation, proliferation, and maturation/remodeling

INTRODUCTION

Understanding the molecular and cellular processes involved in skin wound healing may pave the way for the development of innovative approaches to transforming the identified natural effectors into therapeutic tools. Based on the extensive involvement of the ga(lactoside-binding)lectin family in (patho)physiological processes, it has been well established that galectins are involved in a wide range of cell-cell and cell-matrix interactions.

AREAS COVERED

In the present paper, we provide an overview of the biological role of galectins in repair and regeneration, focusing on four main phases (hemostasis, inflammation, proliferation, and maturation/remodeling) of skin repair using basic wound models (open excision vs. sutured incision).

EXPERT OPINION

The reported data make a strong case for directing further efforts to treat excisional and incisional wounds differently. Functions of galectins essentially result from their modular presentation. In fact, Gal-1 seems to play a role in the early phases of healing (anti-inflammatory) and wound contraction, Gal-3 accelerates re-epithelization and increases tensile strength (scar inductor). Galectins have also become subject of redesigning by engineering to optimize the activity. Clinically relevant, these new tools derived from the carbohydrate recognition domain platform may also prove helpful for other purposes, such as potent antibacterial agglutinins and opsonins.

Placental galectins regulate innate and adaptive immune responses in pregnancy

Introduction

Galectins are master regulators of maternal immune responses and placentation in pregnancy. Galectin-13 (gal-13) and galectin-14 (gal-14) are expressed solely by the placenta and contribute to maternal-fetal immune tolerance by inducing the apoptosis of activated T lymphocytes and the polarization of neutrophils toward an immune-regulatory phenotype.Furthermore, their decreased placental expression is associated with pregnancy complications, such as preeclampsia and miscarriage. Yet, our knowledge of the immunoregulatory role of placental galectins is incomplete.

Methods

This study aimed to investigate the effects of recombinant gal-13 and gal-14 on cell viability, apoptosis, and cytokine production of peripheral blood mononuclear cells (PBMCs) and the signaling pathways involved.

Results

Herein, we show that gal-13 and gal-14 bind to the surface of non-activated PBMCs (monocytes, natural killer cells, B cells, and T cells) and increase their viability while decreasing the rate of their apoptosis without promoting cell proliferation. We also demonstrate that gal-13 and gal-14 induce the production of interleukin (IL)-8, IL-10, and interferon-gamma cytokines in a concentration-dependent manner in PBMCs. The parallel activation of Erk1/2, p38, and NF-ĸB signaling evidenced by kinase phosphorylation in PBMCs suggests the involvement of these pathways in the regulation of the galectin-affected immune cell functions.

Discussion

These findings provide further evidence on how placenta-specific galectins assist in the establishment and maintenance of a proper immune environment during a healthy pregnancy.

A roadmap for translational cancer glycoimmunology at single cell resolution

Cancer cells can evade immune responses by exploiting inhibitory immune checkpoints. Immune checkpoint inhibitor (ICI) therapies based on anti-CTLA-4 and anti-PD-1/PD-L1 antibodies have been extensively explored over the recent years to unleash otherwise compromised anti-cancer immune responses. However, it is also well established that immune suppression is a multifactorial process involving an intricate crosstalk between cancer cells and the immune systems. The cancer glycome is emerging as a relevant source of immune checkpoints governing immunosuppressive behaviour in immune cells, paving an avenue for novel immunotherapeutic options. This review addresses the current state-of-the-art concerning the role played by glycans controlling innate and adaptive immune responses, while shedding light on available experimental models for glycoimmunology. We also emphasize the tremendous progress observed in the development of humanized models for immunology, the paramount contribution of advances in high-throughput single-cell analysis in this context, and the importance of including predictive machine learning algorithms in translational research. This may constitute an important roadmap for glycoimmunology, supporting careful adoption of models foreseeing clinical translation of fundamental glycobiology knowledge towards next generation immunotherapies.

The interplay of galectins-1, -3, and -9 in the immune-inflammatory response underlying cardiovascular and metabolic disease

Galectins are β-galactoside-binding proteins that bind and crosslink molecules via their sugar moieties, forming signaling and adhesion networks involved in cellular communication, differentiation, migration, and survival. Galectins are expressed ubiquitously across immune cells, and their function varies with their tissue-specific and subcellular location. Particularly galectin-1, -3, and -9 are highly expressed by inflammatory cells and are involved in the modulation of several innate and adaptive immune responses. Modulation in the expression of these proteins accompany major processes in cardiovascular diseases and metabolic disorders, such as atherosclerosis, thrombosis, obesity, and diabetes, making them attractive therapeutic targets. In this review we consider the broad cellular activities ascribed to galectin-1, -3, and -9, highlighting those linked to the progression of different inflammatory driven pathologies in the context of cardiovascular and metabolic disease, to better understand their mechanism of action and provide new insights into the design of novel therapeutic strategies.

Possible important roles of galectins in the healing of human fetal membranes

The fetal membranes healing is a complex and dynamic process of replacing devitalized and missing cellular structures and tissue layers. Multiple cells and extracellular matrices, and cell differentiation, migration and proliferation may participate in restoring the integrity of damaged tissue, however this process still remains unclear. Therefore, there is a need to identify and integrate new ideas and methods to design a more effective dressing to accelerate fetal membrane healing. This review explores the function and role of galectins in the inflammatory, epithelial mesenchymal transition, proliferative migration, and remodeling phases of fetal membrane healing. In conclusion, the preliminary findings are promising. Research on amnion regeneration is expected to provide insight into potential treatment strategies for premature rupture of membranes.

The kidney protects against sepsis by producing systemic uromodulin

Sepsis is a significant cause of mortality in hospitalized patients. Concomitant development of acute kidney injury (AKI) increases sepsis mortality through unclear mechanisms. Although electrolyte disturbances and toxic metabolite buildup during AKI could be important, it is possible that the kidney produces a protective molecule lost during sepsis with AKI. We have previously demonstrated that systemic Tamm-Horsfall protein (THP; uromodulin), a kidney-derived protein with immunomodulatory properties, falls in AKI. Using a mouse sepsis model without severe kidney injury, we showed that the kidney increases circulating THP by enhancing the basolateral release of THP from medullary thick ascending limb cells. In patients with sepsis, changes in circulating THP were positively associated with a critical illness. THP was also found de novo in injured lungs. Genetic ablation of THP in mice led to increased mortality and bacterial burden during sepsis. Consistent with the increased bacterial burden, the presence of THP in vitro and in vivo led macrophages and monocytes to upregulate a transcriptional program promoting cell migration, phagocytosis, and chemotaxis, and treatment of macrophages with purified THP increases phagocytosis. Rescue of septic THP-/- mice with exogenous systemic THP improved survival. Together, these findings suggest that through releasing THP, the kidney modulates the immune response in sepsis by enhancing mononuclear phagocyte function, and systemic THP has therapeutic potential in sepsis.NEW & NOTEWORTHY Specific therapies to improve outcomes in sepsis with kidney injury have been limited by an unclear understanding of how kidney injury increases sepsis mortality. Here, we identified Tamm-Horsfall protein, known to protect in ischemic acute kidney injury, as protective in preclinical sepsis models. Tamm-Horsfall protein also increased in clinical sepsis without severe kidney injury and concentrated in injured organs. Further study could lead to novel sepsis therapeutics.

Galectin-1 prevents pathological vascular remodeling in atherosclerosis and abdominal aortic aneurysm

Pathological vascular remodeling is the underlying cause of atherosclerosis and abdominal aortic aneurysm (AAA). Here, we analyzed the role of galectin-1 (Gal-1), a β-galactoside-binding protein, as a therapeutic target for atherosclerosis and AAA. Mice lacking Gal-1 (Lgals1^-/-) developed severe atherosclerosis induced by pAAV/D377Y-mPCSK9 adenovirus and displayed higher lipid levels and lower expression of contractile markers of vascular smooth muscle cells (VSMCs) in plaques than wild-type mice. Proteomic analysis of Lgals1^-/- aortas showed changes in markers of VSMC phenotypic switch and altered composition of mitochondrial proteins. Mechanistically, Gal-1 silencing resulted in increased foam cell formation and mitochondrial dysfunction in VSMCs, while treatment with recombinant Gal-1 (rGal-1) prevented these effects. Furthermore, rGal-1 treatment attenuated atherosclerosis and elastase-induced AAA, leading to higher contractile VSMCs in aortic tissues. Gal-1 expression decreased in human atheroma and AAA compared to control tissue. Thus, Gal-1-driven circuits emerge as potential therapeutic strategies in atherosclerosis and AAA.

Galectins as Emerging Glyco-Checkpoints and Therapeutic Targets in Glioblastoma

Despite recent advances in diagnosis and treatment, glioblastoma (GBM) represents the most common and aggressive brain tumor in the adult population, urging identification of new rational therapeutic targets. Galectins, a family of glycan-binding proteins, are highly expressed in the tumor microenvironment (TME) and delineate prognosis and clinical outcome in patients with GBM. These endogenous lectins play key roles in different hallmarks of cancer by modulating tumor cell proliferation, oncogenic signaling, migration, vascularization and immunity. Additionally, they have emerged as mediators of resistance to different anticancer treatments, including chemotherapy, radiotherapy, immunotherapy, and antiangiogenic therapy. Particularly in GBM, galectins control tumor cell transformation and proliferation, reprogram tumor cell migration and invasion, promote vascularization, modulate cell death pathways, and shape the tumor-immune landscape by targeting myeloid, natural killer (NK), and CD8⁺ T cell compartments. Here, we discuss the role of galectins, particularly galectin-1, -3, -8, and -9, as emerging glyco-checkpoints that control different mechanisms associated with GBM progression, and discuss possible therapeutic opportunities based on inhibition of galectin-driven circuits, either alone or in combination with other treatment modalities.

Enhanced Susceptibility of Galectin-1 Deficient Mice to Experimental Colitis

Galectin-1 is a β-galactoside-binding lectin, ubiquitously expressed in stromal, epithelial, and different subsets of immune cells. Galectin-1 is the prototype member of the galectin family which shares specificity with β-galactoside containing proteins and lipids. Immunomodulatory functions have been ascribed to endogenous galectin-1 due to its induction of T cell apoptosis, inhibitory effects of neutrophils and T cell trafficking. Several studies have demonstrated that administration of recombinant galectin-1 suppressed experimental colitis by modulating adaptive immune responses altering the fate and phenotype of T cells. However, the role of endogenous galectin-1 in intestinal inflammation is poorly defined. In the present study, the well-characterized acute dextran sulfate sodium (DSS)-induced model of ulcerative colitis was used to study the function of endogenous galectin-1 during the development of intestinal inflammation. We found that galectin-1 deficient mice (Lgals1-/- mice) displayed a more severe intestinal inflammation, characterized by significantly elevated clinical scores, than their wild type counterparts. The mechanisms underlying the enhanced inflammatory response in colitic Lgals1-/- mice involved an altered Th17/Th1 profile of effector CD4+ T cells. Furthermore, increased frequencies of Foxp3+CD4+ regulatory T cells in colon lamina propria in Lgals1-/- mice were found. Strikingly, the exacerbated intestinal inflammatory response observed in Lgals1-/- mice was alleviated by adoptive transfer of wild type Foxp3+CD4+ regulatory T cells at induction of colitis. Altogether, these data highlight the importance of endogenous galectin-1 as a novel determinant in regulating T cell reactivity during the development of intestinal inflammation.

Control of intestinal inflammation by glycosylation-dependent lectin-driven immunoregulatory circuits

Diverse immunoregulatory circuits operate to preserve intestinal homeostasis and prevent inflammation. Galectin-1 (Gal1), a β-galactoside-binding protein, promotes homeostasis by reprogramming innate and adaptive immunity. Here, we identify a glycosylation-dependent "on-off" circuit driven by Gal1 and its glycosylated ligands that controls intestinal immunopathology by targeting activated CD8⁺ T cells and shaping the cytokine profile. In patients with inflammatory bowel disease (IBD), augmented Gal1 was associated with dysregulated expression of core 2 β6-N-acetylglucosaminyltransferase 1 (C2GNT1) and α(2,6)-sialyltransferase 1 (ST6GAL1), glycosyltransferases responsible for creating or masking Gal1 ligands. Mice lacking Gal1 exhibited exacerbated colitis and augmented mucosal CD8⁺ T cell activation in response to 2,4,6-trinitrobenzenesulfonic acid; this phenotype was partially ameliorated by treatment with recombinant Gal1. While C2gnt1^-/- mice exhibited aggravated colitis, St6gal1^-/- mice showed attenuated inflammation. These effects were associated with intrinsic T cell glycosylation. Thus, Gal1 and its glycosylated ligands act to preserve intestinal homeostasis by recalibrating T cell immunity.

Galectin-3: A factotum in carcinogenesis bestowing an archery for prevention

Cancer metastasis and therapy resistance are the foremost hurdles in oncology at the moment. This review aims to pinpoint the functional aspects of a unique multifaceted glycosylated molecule in both intracellular and extracellular compartments of a cell namely galectin-3 along with its metastatic potential in different types of cancer. All materials reviewed here were collected through the search engines PubMed, Scopus, and Google scholar. Among the 15 galectins identified, the chimeric gal-3 plays an indispensable role in the differentiation, transformation, and multi-step process of tumor metastasis. It has been implicated in the molecular mechanisms that allow the cancer cells to survive in the intravascular milieu and promote tumor cell extravasation, ultimately leading to metastasis. Gal-3 has also been found to have a pivotal role in immune surveillance and pro-angiogenesis and several studies have pointed out the importance of gal-3 in establishing a resistant phenotype, particularly through the epithelial-mesenchymal transition process. Additionally, some recent findings suggest the use of gal-3 inhibitors in overcoming therapeutic resistance. All these reports suggest that the deregulation of these specific lectins at the cellular level could inhibit cancer progression and metastasis. A more systematic study of glycosylation in clinical samples along with the development of selective gal-3 antagonists inhibiting the activity of these molecules at the cellular level offers an innovative strategy for primary cancer prevention.

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.

Resident and elicited murine macrophages differ in expression of their glycomes and glycan-binding proteins

The pleiotropic functions of macrophages in immune defense, tissue repair, and maintenance of tissue homeostasis are supported by the heterogeneity in macrophage sub-populations that differ both in ontogeny and polarization. Although glycans and glycan-binding proteins (GBPs) are integral to macrophage function and may contribute to macrophage diversity, little is known about the factors governing their expression. Here, we provide a resource for characterizing the N-/O-glycomes of various murine peritoneal macrophage sub-populations, demonstrating that glycosylation primarily reflects developmental origin and, to a lesser degree, cellular polarization. Furthermore, comparative analysis of GBP-coding genes in resident and elicited macrophages indicated that GBP expression is consistent with specialized macrophage functions and correlates with specific types of displayed glycans. An integrated, semi-quantitative approach was used to confirm distinct expression patterns of glycans and their binding proteins across different macrophages. The data suggest that regulation of glycan-protein complexes may be central to macrophage residence and recruitment.

Myeloma-Secreted Galectin-1 Potently Interacts with CD304 on Monocytic Myeloid-Derived Suppressor Cells

Progression of multiple myeloma is regulated by factors intrinsic to the clonal plasma cells (PC) and by the immune effector cells in the tumor microenvironment. In this study, we investigated the interaction between CD304 expression on myeloid-derived suppressor cells (MDSC) and galectin-1 from malignant PCs in the context of autologous stem cell transplantation (ASCT) for multiple myeloma. Using high-throughput screening, CD304 expression on circulating monocytic MDSCs (M-MDSC; CD14⁺HLA-DR^low/-) was compared before and after ASCT. There was a significantly higher M-MDSC expression of CD304 before ASCT and a clear correlation between circulating pre-ASCT M-MDSC frequency and serum galectin-1 concentration. Treatment of pre-ASCT M-MDSCs, but not post-ASCT M-MDSCs, with galectin-1 in vitro expanded the M-MDSC population and increased expression of CD304. High galectin-1 expression by malignant PCs was associated with poor clinical outcomes. M-MDSC development and expression of CD304 were differentially induced when healthy donor peripheral blood mononuclear cells were cultured with the human multiple myeloma cell lines RPMI-8226 and JJN3, which express high and low galectin-1, respectively. Inhibition of galectin-1 reduced M-MDSC proliferation induced by RPMI-8226 cells but not by JJN3 cells, and blockade of CD304 reduced M-MDSC migration induced by RPMI-8226 cells but not by JJN3 cells. In addition, blockade of CD304 reversed suppression of the in vitro cytotoxic effect of melphalan by pre-ASCT M-MDSCs. Our data demonstrate that multiple myeloma-derived galectin-1 could mediate the tumor-promoting effect of M-MDSCs through its interaction with CD304 on M-MDSCs and contribute to multiple myeloma progression after ASCT.See related Spotlight on p. 488.

Tissue-specific control of galectin-1-driven circuits during inflammatory responses

The relevance of glycan-binding protein in immune tolerance and inflammation has been well established, mainly by studies of C-type lectins, siglecs and galectins both in experimental models and patient samples. Galectins, a family of evolutionarily conserved lectins, are characterized by sequence homology in the carbohydrate-recognition domain (CRD), atypical secretion via an ER-Golgi-independent pathway and the ability to recognize β-galactoside-containing saccharides. Galectin-1 (Gal-1), a prototype member of this family displays mainly anti-inflammatory and immunosuppressive activities, although, similar to many cytokines and growth factors, it may also trigger paradoxical pro-inflammatory effects under certain circumstances. These dual effects could be associated to tissue-, time- or context-dependent regulation of galectin expression and function, including particular pathophysiologic settings and/or environmental conditions influencing the structure of this lectin, as well as the availability of glycosylated ligands in immune cells during the course of inflammatory responses. Here, we discuss the tissue-specific role of Gal-1 as a master regulator of inflammatory responses across different pathophysiologic settings, highlighting its potential role as a therapeutic target. Further studies designed at analyzing the intrinsic and extrinsic pathways that control Gal-1 expression and function in different tissue microenvironments may contribute to design tailored therapeutic strategies aimed at positively or negatively modulate this glycan-binding protein in pathologic inflammatory conditions.

Sweetening the hallmarks of cancer: Galectins as multifunctional mediators of tumor progression

Hanahan and Weinberg have proposed 10 organizing principles that enable growth and metastatic dissemination of cancer cells. These distinctive and complementary capabilities, defined as the "hallmarks of cancer," include the ability of tumor cells and their microenvironment to sustain proliferative signaling, evade growth suppressors, resist cell death, promote replicative immortality, induce angiogenesis, support invasion and metastasis, reprogram energy metabolism, induce genomic instability and inflammation, and trigger evasion of immune responses. These common features are hierarchically regulated through different mechanisms, including those involving glycosylation-dependent programs that influence the biological and clinical impact of each hallmark. Galectins, an evolutionarily conserved family of glycan-binding proteins, have broad influence in tumor progression by rewiring intracellular and extracellular circuits either in cancer or stromal cells, including immune cells, endothelial cells, and fibroblasts. In this review, we dissect the role of galectins in shaping cellular circuitries governing each hallmark of tumors, illustrating relevant examples and highlighting novel opportunities for treating human cancer.

Trichinella spiralis co-infection exacerbates Plasmodium berghei malaria-induced hepatopathy

Background

Although Plasmodium parasites and intestinal helminths share common endemic areas, the mechanisms of these co-infections on the host immune response remain not fully understood. Liver involvement in severe Plasmodium falciparum infections is a significant cause of morbidity and mortality. However, the effect of pre-existing Trichinella spiralis infection on the immune response and liver immune-pathogenesis in P. berghei ANKA (PbANKA)-infected mice needs to be elucidated.

Methods

Outbred Kunming mice were infected with T. spiralis and 9 days later were challenged with P. berghei ANKA (PbANKA), and the investigation occurred at 13 days after co-infection.

Results

Compared with PbANKA-mono-infected mice, T. spiralis + PbANKA-co-infected mice had similar survival rate but lower PbANKA parasitaemia; however, there were more severe hepatosplenomegaly, increased liver and spleen indexes, and increased liver pathology observed by hematoxylin and eosin staining; higher expression levels of galectin (Gal)-1, Gal-3, CD68⁺ macrophages, and elastase-positive neutrophils measured by immunohistochemical staining; upregulated mRNA expression levels of Gal-1, Gal-3, cytokines (interferon-gamma (IFNγ) and interleukin (IL)-6), and M1 macrophage polarization marker (inducible nitric oxide synthase (iNOS)) in the liver, and increased expression levels of Gal-1, IFNγ, IL-6, eosinophil cationic protein, eosinophil protein X, and M1 (IL-1β and iNOS) and M2 (Ym1) macrophage polarization markers in the spleen of co-infected mice detected by using quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR). In vitro study showed that compared with PbANKA-mono-infected mice, there were significantly increased expression levels of Gal-1, Gal-3, IL-6, IL-1β, and iNOS in the peritoneal macrophage isolated from co-infected mice detected by using qRT-PCR. Correlation analysis revealed significant positive correlations between Gal-3 and IL-1β in the peritoneal macrophages isolated from PbANKA-mono-infected mice, between Gal-3 and IFNγ in the spleen of co-infected mice, and between Gal-1 and Ym1 in the peritoneal macrophages isolated from co-infected mice.

Conclusions

Our data indicate that pre-existing infection of T. spiralis may suppress P. berghei parasitaemia and aggravate malaria-induced liver pathology through stimulating Gal-1 and Gal-3 expression, activating macrophages, neutrophils, and eosinophils, and promoting mediator release and cytokine production.

Galectins as Checkpoints of the Immune System in Cancers, Their Clinical Relevance, and Implication in Clinical Trials

Galectins are small proteins with pleiotropic functions, which depend on both their lectin (glycan recognition) and non-lectin (recognition of other biomolecules besides glycans) interactions. Currently, 15 members of this family have been described in mammals, each with its structural and ligand recognition particularities. The galectin/ligand interaction translates into a plethora of biological functions that are particular for each cell/tissue type. In this sense, the cells of the immune system are highly sensitive to the action of these small and essential proteins. While galectins play central roles in tumor progression, they are also excellent negative regulators (checkpoints) of the immune cell functions, participating in the creation of a microenvironment that promotes tumor escape. This review aims to give an updated view on how galectins control the tumor’s immune attack depending on the tumor microenvironment, because determining which galectins are essential and the role they play will help to develop future clinical trials and benefit patients with incurable cancer.

A Pro-resolving Role for Galectin-1 in Acute Inflammation

Galectin-1 (Gal-1) exerts immune-regulatory and anti-inflammatory actions in animal models of acute and chronic inflammation. Its release into the extracellular milieu often correlates with the peak of inflammation suggesting that it may serve a pro-resolving function. Gal-1 is reported to inhibit neutrophil recruitment and induce surface exposure of phosphatidylserine (PS), an "eat me" signal on the surface of neutrophils, yet its role in resolution remains to be fully elucidated. We hypothesized that the anti-inflammatory and pro-resolving properties of Gal-1 are mediated through its ability to inhibit neutrophil recruitment and potentiate neutrophil clearance. To investigate this, a murine model of self-resolving inflammation was utilized to uncover the role of both the endogenous and exogenous protein using Gal-1 null mice and recombinant protein, respectively. We found that peritoneal macrophages express increased Gal-1 during the resolution phase and enhanced neutrophil recruitment occurs in the early phases of zymosan peritonitis in Gal-1 null mice compared to their wild-type (WT) counterparts. Administration of recombinant Gal-1 following the peak of inflammation led to reduced neutrophil numbers at 24 and 48 h, shortening the resolution interval from 39 to 14 h. Gal-1 treatment also enhanced neutrophil apoptosis, indicating a pro-resolving action. Together these results indicate an important role for Gal-1 in the timely resolution of acute inflammation.

Suppression of age-related salivary gland autoimmunity by glycosylation-dependent galectin-1-driven immune inhibitory circuits

Aging elicits quantitative and qualitative changes in different immune components, leading to disruption of tolerogenic circuits and development of autoimmune disorders. Galectin-1 (Gal1), an endogenous glycan-binding protein, has emerged as a regulator of immune cell homeostasis by shaping the fate of myeloid and lymphoid cells. Here, we demonstrate that aged Gal1-null mutant (Lgals1 ^-/- ) mice develop a spontaneous inflammatory process in salivary glands that resembles Sjögren's syndrome. This spontaneous autoimmune phenotype was recapitulated in mice lacking β1,6N-acetylglucosaminyltransferase V (Mgat5), an enzyme responsible for generating β1,6-branched complex N-glycans, which serve as a major ligand for this lectin. Lack of Gal1 resulted in CD11c⁺ dendritic cells (DCs) with higher immunogenic potential, lower frequency of Foxp3⁺ regulatory T cells (Tregs), and increased number of CD8⁺ T cells with greater effector capacity. Supporting its tolerogenic activity, Gal1 expression decreased with age in autoimmunity-prone nonobese diabetic (NOD) mice. Treatment with recombinant Gal1 restored tolerogenic mechanisms and reduced salivary gland inflammation. Accordingly, labial biopsies from primary Sjögren's syndrome patients showed reduced Gal1 expression concomitant with higher number of infiltrating CD8⁺ T cells. Thus, endogenous Gal1 serves as a homeostatic rheostat that safeguards immune tolerance and prevents age-dependent development of spontaneous autoimmunity.

Role of Human Galectins in Inflammation and Cancers Associated with Endometriosis

Galectins are a family of β-galactoside-binding proteins that contribute to multiple cellular functions, including immune surveillance and apoptosis. Human galectins are also important regulators of inflammation, making them a research target for various inflammatory diseases and tumorigenesis associated with pro-inflammatory conditions. This review focuses on the involvement of human galectins in modulation of inflammation and in the pathophysiology of endometriosis and endometriosis-associated neoplasms. Endometriosis is a chronic inflammatory disease with unknown etiology. Galectins-1, -3 and -9 were found to be overexpressed in ectopic and eutopic endometrium of females with endometriosis compared to those without endometriosis. These findings suggest galectins’ role in the progression on endometriotic lesions and their potential use as diagnostic biomarkers and/or targets for therapeutic approaches. Galectins-1, -3, and -9 have also been implicated in the development of endometriosis-associated neoplasms. Furthermore, galectin-3 has been shown to interact with KRAS protein and contribute to cellular growth, proliferation, inflammation, and the uptake of nutrients in endometriotic lesions and may be involved in the maintenance and propagation of endometriosis. These galectins have been shown to be upregulated in certain forms of cervical, ovarian, endometrial, and colon cancer associated with endometriosis and have become a potential target for anti-cancer therapies.

Sweetening the hallmarks of cancer: Galectins as multifunctional mediators of tumor progression

Hanahan and Weinberg have proposed 10 organizing principles that enable growth and metastatic dissemination of cancer cells. These distinctive and complementary capabilities, defined as the "hallmarks of cancer," include the ability of tumor cells and their microenvironment to sustain proliferative signaling, evade growth suppressors, resist cell death, promote replicative immortality, induce angiogenesis, support invasion and metastasis, reprogram energy metabolism, induce genomic instability and inflammation, and trigger evasion of immune responses. These common features are hierarchically regulated through different mechanisms, including those involving glycosylation-dependent programs that influence the biological and clinical impact of each hallmark. Galectins, an evolutionarily conserved family of glycan-binding proteins, have broad influence in tumor progression by rewiring intracellular and extracellular circuits either in cancer or stromal cells, including immune cells, endothelial cells, and fibroblasts. In this review, we dissect the role of galectins in shaping cellular circuitries governing each hallmark of tumors, illustrating relevant examples and highlighting novel opportunities for treating human cancer.

Intracellular Galectin-9 Controls Dendritic Cell Function by Maintaining Plasma Membrane Rigidity

Endogenous extracellular Galectins constitute a novel mechanism of membrane protein organization at the cell surface. Although Galectins are also highly expressed intracellularly, their cytosolic functions are poorly understood. Here, we investigated the role of Galectin-9 in dendritic cell (DC) surface organization and function. By combining functional, super-resolution and atomic force microscopy experiments to analyze membrane stiffness, we identified intracellular Galectin-9 to be indispensable for plasma membrane integrity and structure in DCs. Galectin-9 knockdown studies revealed intracellular Galectin-9 to directly control cortical membrane structure by modulating Rac1 activity, providing the underlying mechanism of Galectin-9-dependent actin cytoskeleton organization. Consequent to its role in maintaining plasma membrane structure, phagocytosis studies revealed that Galectin-9 was essential for C-type-lectin receptor-mediated pathogen uptake by DCs. This was confirmed by the impaired phagocytic capacity of Galectin-9-null murine DCs. Together, this study demonstrates a novel role for intracellular Galectin-9 in modulating DC function, which may be evolutionarily conserved.

A chimeric, multivalent assembly of galectin-1 and galectin-3 with enhanced extracellular activity

Galectins are attractive therapeutic candidates to control aberrant immune system activation because they can alter the phenotype and function of various innate and adaptive immune cells. However, use of exogenous galectin-1 ("G1") and galectin-3 ("G3") as immunomodulators is challenged by their high dosing requirements and dynamic quaternary structures. Here we report a chimeric assembly of G1 and G3 with enhanced extracellular activity ("G1/G3 Zipper"), which was created by recombinant fusion of G1 and G3 via a peptide linker that forms a two-stranded α-helical coiled-coil. G1/G3 Zipper had higher apparent binding affinity for immobilized lactose and a lower concentration threshold for inducing soluble glycoprotein crosslinking than G1, a recombinant fusion of G1 and G3 with a flexible peptide linker ("G1/G3"), or a recently reported stable G1 dimer crosslinked by poly(ethylene glycol) diacrylate ("G1-PEG-G1"). As a result, G1/G3 Zipper was more effective at inducing Jurkat T cell apoptosis in media containing serum, and was the only variant that could induce apoptosis at low concentrations under serum-free conditions. The monomeric G1/G3 fusion protein lacked extracellular activity under all conditions tested, suggesting that the enhanced activity of G1/G3 Zipper was due to its quaternary structure and increased carbohydrate-recognition domain valency. Thus, combining G1 and G3 into a non-native chimeric assembly provides a new candidate therapeutic with greater immunomodulatory potency than the wild-type proteins and previously reported engineered variants.

Differential Cellular Expression of Galectin-1 and Galectin-3 After Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is a devastating sub-type of stroke with no proven treatment. Given the emerging role of Galectin-1 and Galectin-3 in neuroimmune responses, the objective of the current manuscript is to elucidate hemorrhagic-injury induced modulation and cellular expression of Galectin-1 and Galectin-3 in the brain in a pre-clinical model of ICH. To address this, ICH was induced in male CD1 mice by collagenase injection method. Western blotting as well as Immunofluorescence staining was performed to characterize the temporal expression pattern as well as cellular localization of Galectin-1 and Galectin-3 after ICH. Further, genetic studies were conducted to assess the functional role of Galectin-1 and Galectin-3 in inflammatory response employing a murine macrophage cell line, RAW 264.7. Galectin-1 and Galectin-3 exhibited very profound and increased expression from day 3 to day 7-post-injury, in the perihematomal brain region after ICH in comparison to Sham. Further, Galectin-1 expression was mostly observed in GFAP-positive astrocytes whereas Galectin-3 expression was observed mostly in Iba1-positive microglia/macrophages as well as CD16/32 (M1 microglial/macrophage marker)-positive cells. Moreover, genetic studies revealed a negative regulatory role of both Galectin-1 and Galectin-3 in the release of a proinflammatory cytokine, IL-6 from RAW 264.7 cells depending on the stimulus. Altogether, the present manuscript demonstrates for the first time, increased expression as well as cellular localization of Galectin-1 and Galectin-3 in the perihematomal brain regions after ICH. In addition, the manuscript raises the potential of Galectin-1 and Galectin-3 in modulating glial responses and thereby brain injury after ICH, warranting further investigation.

Neuroinflammation induced by the peptide amyloid-β (25-35) increase the presence of galectin-3 in astrocytes and microglia and impairs spatial memory

Galectins are animal lectins that bind to β-galactosides, such as lactose and N-acetyllactosamine, contained in glycoproteins or glycolipids. Galectin-1 (Gal-1) and Galectin-3 (Gal-3) are involved in pathologies associated with the inflammatory process, cell proliferation, adhesion, migration, and apoptosis. Recent evidence has shown that the administration of Amyloid-β 25-35 (Aβ_25-35) into the hippocampus of rats increases the inflammatory response that is associated with memory impairment and neurodegeneration. Galectins could participate in the modulation of the neuroinflammation induced by the Aβ_25-35. The aim of this study was to evaluate the presence of Gal-1 and Gal-3 in the neuroinflammation induced by administration of Aβ_25-35 into the hippocampus and to examine spatial memory in the Morris water maze. After the administration of Aβ_25-35, animals were tested for learning and spatial memory in the Morris water maze. Behavioral performance showed that Aβ_25-35 didn't affect spatial learning but did impair memory, with animals taking longer to find the platform. On the day 32, hippocampus was examined for astrocytes (GFAP), microglia (Iba1), Gal-1 and Gal-3 via immunohistochemical analysis, and the cytokines IL-1β, TNF-α, IFN-γ by ELISA. This study's results showed a significant increase in the expression of Gal-3 in the microglia and astrocytes, while Gal-1 didn't increase in the dorsal hippocampus. The expression of galectins is associated with increased cytokines in the hippocampal formation of Aβ_25-35 treated rats. These findings suggest that Gal-3 could participate in the inflammation induced by administration of Aβ_25-35 and could be involved in the neurodegeneration progress and memory impairment.

Expression of C-type lectin receptor mRNA in otitis media with effusion and chronic otitis media with and without cholesteatoma

BACKGROUND & OBJECTIVES

C-type lectin receptors (CLRs) are a family of pattern recognition receptors (PRPs). The expression of CLRs has been analyzed in other diseases but has not yet been compared in patients with otitis media with effusion (OME), chronic otitis media (COM) and COM with cholesteatoma (Chole OM). This study therefore evaluated the levels of expression of mRNAs encoding Dectin-1, MR1, MR2, DC-SIGN, Syk, Card-9, Bcl-10, Malt-1, Src, DEC-205, Tim-3, Trem-1, and DAP-12 in patients with OME, COM, and Chole OM.

METHODS

CLR mRNA levels in patients with OME, COM, and Chole OM were assessed by real-time polymerase chain reaction. The level of expression of each mRNA was compared in patients with and without bacteria, and in patients with conductive hearing loss (CHL) and sensorineural hearing loss (SNHL).

RESULTS

The patterns of expression of CLRs differed in patients with OME, COM, and Chole OM. Galectin-1 mRNA level was significantly higher in the COM than in the Chole OM group (p<0.05), and MR1 and Galectin-1 mRNA levels among patients with CHL were significantly higher in those with COM than with Chole OM (p<0.05). Galectin-1 mRNA level among patients with SNHL was also significantly higher in the COM than in the Chole OM group (p<0.05).

CONCLUSIONS

The levels of expression of mRNAs encoding the CLRs Dectin-1, MR1, MR2, DC-SIGN, Syk, Card-9, Bcl-10, Malt-1, Src, DEC-205, Tim-3, Trem-1 and DAP-12 differ among patients with OME, COM, and Chole OM.

Identification of a novel galectin in Sinonovacula constricta and its role in recognition of Gram-negative bacteria

Galectins are soluble lectins that perform a pattern recognition function in invertebrate immunity and specifically recognise β-galactoside residues via conserved carbohydrate recognition domains. However, their function in bivalve molluscs has received little attention. Herein, a galectin (ScGal2) in razor clam (Sinonovacula constricta) consisting of a 507 bp open reading frame encoding a protein of 168 amino acids was identified and characterised. The protein includes a carbohydrate recognition domain (CRD), and several residues involved in dimerisation were found. ScGal2 mRNAs were mainly detected in hemolymph and liver, and expression was upregulated significantly following challenge with Vibrio anguillarum. Recombinant rScGal2 protein displayed strong agglutination activity toward Gram-negative bacteria, and flow cytometry revealed that ScGal2 strongly promoted phagocytosis in hemocytes. These results suggest that ScGal2 plays an indispensable role in innate immunity in razor clam, and likely participates in immune recognition and clearance processes.

Glycosylation-dependent galectin-receptor interactions promote Chlamydia trachomatis infection

Chlamydia trachomatis (Ct) constitutes the most prevalent sexually transmitted bacterium worldwide. Chlamydial infections can lead to severe clinical sequelae including pelvic inflammatory disease, ectopic pregnancy, and tubal infertility. As an obligate intracellular pathogen, Ct has evolved multiple strategies to promote adhesion and invasion of host cells, including those involving both bacterial and host glycans. Here, we show that galectin-1 (Gal1), an endogenous lectin widely expressed in female and male genital tracts, promotes Ct infection. Through glycosylation-dependent mechanisms involving recognition of bacterial glycoproteins and N-glycosylated host cell receptors, Gal1 enhanced Ct attachment to cervical epithelial cells. Exposure to Gal1, mainly in its dimeric form, facilitated bacterial entry and increased the number of infected cells by favoring Ct-Ct and Ct-host cell interactions. These effects were substantiated in vivo in mice lacking Gal1 or complex β1-6-branched N-glycans. Thus, disrupting Gal1-N-glycan interactions may limit the severity of chlamydial infection by inhibiting bacterial invasion of host cells.

Galectins: Multitask signaling molecules linking fibroblast, endothelial and immune cell programs in the tumor microenvironment

Tumor cells corrupt surrounding normal cells instructing them to support proliferative, pro-angiogenic and immunosuppressive networks that favor tumorigenesis and metastasis. This dynamic cross-talk is sustained by a range of intracellular signals and extracellular mediators produced by both tumoral and non-tumoral cells. Galectins -whether secreted or intracellularly expressed- play central roles in the tumorigenic process by delivering regulatory signals that contribute to reprogram fibroblasts, endothelial and immune cell programs. Through glycosylation-dependent or independent mechanisms, these endogenous lectins control a variety of cellular events leading to tumor cell proliferation, survival, migration, inflammation, angiogenesis and immune escape. Here we discuss the role of galectin-driven pathways, particularly those activated in non-tumoral stromal cells, in modulating tumor progression.

Galectins in Intestinal Inflammation: Galectin-1 Expression Delineates Response to Treatment in Celiac Disease Patients

Galectins, a family of animal lectins characterized by their affinity for N-acetyllactosamine-enriched glycoconjugates, modulate several immune cell processes shaping the course of innate and adaptive immune responses. Through interaction with a wide range of glycosylated receptors bearing complex branched N-glycans and core 2-O-glycans, these endogenous lectins trigger distinct signaling programs thereby controling immune cell activation, differentiation, recruitment and survival. Given the unique features of mucosal inflammation and the differential expression of galectins throughout the gastrointestinal tract, we discuss here key findings on the role of galectins in intestinal inflammation, particularly Crohn’s disease, ulcerative colitis, and celiac disease (CeD) patients, as well as in murine models resembling these inflammatory conditions. In addition, we present new data highlighting the regulated expression of galectin-1 (Gal-1), a proto-type member of the galectin family, during intestinal inflammation in untreated and treated CeD patients. Our results unveil a substantial upregulation of Gal-1 accompanying the anti-inflammatory and tolerogenic response associated with gluten-free diet in CeD patients, suggesting a major role of this lectin in favoring resolution of inflammation and restoration of mucosal homeostasis. Thus, a coordinated network of galectins and their glycosylated ligands, exerting either anti-inflammatory or proinflammatory responses, may influence the interplay between intestinal epithelial cells and the highly specialized gut immune system in physiologic and pathologic settings.