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 ß-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 ß6-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.

Spatiotemporal regulation of galectin-1-induced T-cell death in lamina propria from Crohn's disease and ulcerative colitis patients.

Inflammatory bowel disease (IBD), including Crohn's disease (CD) and ulcerative colitis (UC), is characterized by chronic, relapsing intestinal inflammation. Galectin-1 (Gal-1) is an endogenous lectin with key pro-resolving roles, including induction of T-cell apoptosis and secretion of immunosuppressive cytokines. Despite considerable progress, the relevance of Gal-1-induced T-cell death in inflamed tissue from human IBD patients has not been ascertained. Intestinal biopsies and surgical specimens from control patients (n = 52) and patients with active or inactive IBD (n = 97) were studied. Gal-1 expression was studied by RT-qPCR, immunoblotting, ELISA and immunohistochemistry. Gal-1-specific ligands and Gal-1-induced apoptosis of lamina propria (LP) T-cells were determined by TUNEL and flow cytometry. We found a transient expression of asialo core 1-O-glycans in LP T-cells from inflamed areas (p < 0.05) as revealed by flow cytometry using peanut agglutinin (PNA) binding and assessing dysregulation of the core-2 ß 1-6-N-acetylglucosaminyltransferase 1 (C2GNT1), an enzyme responsible for elongation of core 2 O-glycans. Consequently, Gal-1 binding was attenuated in CD3+CD4+ and CD3+CD8+ LP T-cells isolated from inflamed sites (p < 0.05). Incubation with recombinant Gal-1 induced apoptosis of LP CD3+ T-cells isolated from control subjects and non-inflamed areas of IBD patients (p < 0.05), but not from inflamed areas. In conclusion, our findings showed that transient regulation of the O-glycan profile during inflammation modulates Gal-1 binding and LP T-cell survival in IBD patients.

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.

Clinical Relevance of Galectin-1 and Galectin-3 in Rheumatoid Arthritis Patients: Differential Regulation and Correlation With Disease Activity.

Galectins, a family of animal lectins, play central roles in immune system regulation, shaping both innate and adaptive responses in physiological and pathological processes. These include rheumatoid arthritis (RA), a chronic multifactorial autoimmune disease characterized by inflammatory responses that affects both articular and extra-articular tissues. Galectins have been reported to play central roles in RA and its experimental animal models. In this perspective article we present new data highlighting the regulated expression of galectin-1 (Gal-1) and galectin-3 (Gal-3) in sera from RA patients under disease-modifying anti-rheumatic drugs (DMARDs) and/or corticoid treatment in the context of a more comprehensive discussion that summarizes the roles of galectins in joint inflammation. We found that Gal-1 levels markedly increase in sera from RA patients and positively correlate with erythrocyte sedimentation rate (ERS) and disease activity score 28 (DAS-28) parameters. On the other hand, Gal-3 is downregulated in RA patients, but positively correlates with health assessment questionnaire parameter (HAQ). Finally, by generating receiver-operator characteristic (ROC) curves, we found that Gal-1 and Gal-3 serum levels constitute good parameters to discriminate patients with RA from healthy individuals. Our findings uncover a differential regulation of Gal-1 and Gal-3 which might contribute to the anti-inflammatory effects elicited by DMARDs and corticoid treatment in RA patients.

Galectin-1: A Jack-of-All-Trades in the Resolution of Acute and Chronic Inflammation.

Regulatory signals provide negative input to immunological networks promoting resolution of acute and chronic inflammation. Galectin-1 (Gal-1), a member of a family of evolutionarily conserved glycan-binding proteins, displays broad anti-inflammatory and proresolving activities by targeting multiple immune cell types. Within the innate immune compartment, Gal-1 acts as a resolution-associated molecular pattern by counteracting the synthesis of proinflammatory cytokines, inhibiting neutrophil trafficking, targeting eosinophil migration and survival, and suppressing mast cell degranulation. Likewise, this lectin controls T cell and B cell compartments by modulating receptor clustering and signaling, thus serving as a negative-regulatory checkpoint that reprograms cellular activation, differentiation, and survival. In this review, we discuss the central role of Gal-1 in regulatory programs operating during acute inflammation, autoimmune diseases, allergic inflammation, pregnancy, cancer, and infection. Therapeutic strategies aimed at targeting Gal-1-glycan interactions will contribute to overcome cancer immunosuppression and reinforce antimicrobial immunity, whereas stimulation of Gal-1-driven immunoregulatory circuits will help to mitigate exuberant inflammation.

Glycosylation-dependent binding of galectin-8 to activated leukocyte cell adhesion molecule (ALCAM/CD166) promotes its surface segregation on breast cancer cells.

BACKGROUND: We previously demonstrated that the activated leukocyte cell adhesion molecule (ALCAM/CD166) can interact with galectin-8 (Gal-8) in endothelial cells. ALCAM is a member of the immunoglobulin superfamily that promotes homophilic and heterophilic cell-cell interactions. Gal-8 is a "tandem-repeat"-type galectin, known as a matricellular protein involved in cell adhesion. Here, we analyzed the physical interaction between both molecules in breast cancer cells and the functional relevance of this phenomenon. METHODS: We performed binding assays by surface plasmon resonance to study the interaction between Gal-8 and the recombinant glycosylated ALCAM ectodomain or endogenous ALCAM from MDA-MB-231 breast cancer cells. We also analyzed the binding of ALCAM-silenced or control breast cancer cells to immobilized Gal-8 by SPR. In internalization assays, we evaluated the influence of Gal-8 on ALCAM surface localization. RESULTS: We showed that recombinant glycosylated ALCAM and endogenous ALCAM from breast carcinoma cells physically interacted with Gal-8 in a glycosylation-dependent fashion displaying a differential behavior compared to non-glycosylated ALCAM. Moreover, ALCAM-silenced breast cancer cells exhibited reduced binding to Gal-8 relative to control cells. Importantly, exogenously added Gal-8 provoked ALCAM segregation, probably trapping this adhesion molecule at the surface of breast cancer cells. CONCLUSIONS: Our data indicate that Gal-8 interacts with ALCAM at the surface of breast cancer cells through glycosylation-dependent mechanisms. GENERAL SIGNIFICANCE: A novel heterophilic interaction between ALCAM and Gal-8 is demonstrated here, suggesting its physiologic relevance in the biology of breast cancer cells.

Regulatory role of glycans in the control of hypoxia-driven angiogenesis and sensitivity to anti-angiogenic treatment.

Abnormal glycosylation is a typical hallmark of the transition from healthy to neoplastic tissues. Although the importance of glycans and glycan-binding proteins in cancer-related processes such as tumor cell adhesion, migration, metastasis and immune escape has been largely appreciated, our awareness of the impact of lectin-glycan recognition in tumor vascularization is relatively new. Regulated glycosylation can influence vascular biology by controlling trafficking, endocytosis and signaling of endothelial cell (EC) receptors including vascular endothelial growth factor receptors, platelet EC adhesion molecule, Notch and integrins. In addition, glycans may control angiogenesis by regulating migration of endothelial tip cells and influencing EC survival and vascular permeability. Recent evidence indicated that changes in the EC surface glycome may also serve "on-and-off" switches that control galectin binding to signaling receptors by displaying or masking-specific glycan epitopes. These glycosylation-dependent lectin-receptor interactions can link tumor hypoxia to EC signaling and control tumor sensitivity to anti-angiogenic treatment.