Galectin-8 binds specific β1 integrins and induces polarized spreading highlighted by asymmetric lamellipodia in Jurkat T cells

Galectin-8 counteracts folic acid-induced acute kidney injury and prevents its transition to fibrosis

Acute kidney injury (AKI), characterized by a sudden decline in kidney function involving tubular damage and epithelial cell death, can lead to progressive tissue fibrosis and chronic kidney disease due to interstitial fibroblast activation and tissue repair failures that lack direct treatments. After an AKI episode, surviving renal tubular cells undergo cycles of dedifferentiation, proliferation and redifferentiation while fibroblast activity increases and then declines to avoid an exaggerated extracellular matrix deposition. Appropriate tissue recovery versus pathogenic fibrotic progression depends on fine-tuning all these processes. Identifying endogenous factors able to affect any of them may offer new therapeutic opportunities to improve AKI outcomes. Galectin-8 (Gal-8) is an endogenous carbohydrate-binding protein that is secreted through an unconventional mechanism, binds to glycosylated proteins at the cell surface and modifies various cellular activities, including cell proliferation and survival against stress conditions. Here, using a mouse model of AKI induced by folic acid, we show that pre-treatment with Gal-8 protects against cell death, promotes epithelial cell redifferentiation and improves renal function. In addition, Gal-8 decreases fibroblast activation, resulting in less expression of fibrotic genes. Gal-8 added after AKI induction is also effective in maintaining renal function against damage, improving epithelial cell survival. The ability to protect kidneys from injury during both pre- and post-treatments, coupled with its anti-fibrotic effect, highlights Gal-8 as an endogenous factor to be considered in therapeutic strategies aimed at improving renal function and mitigating chronic pathogenic progression.

Vascular galectins in tumor angiogenesis and cancer immunity

Sustained tumor angiogenesis, i.e., the induction and maintenance of blood vessel growth by tumor cells, is one of the hallmarks of cancer. The vascularization of malignant tissues not only facilitates tumor growth and metastasis, but also contributes to immune evasion. Important players in all these processes are the endothelial cells which line the luminal side of blood vessel. In the tumor vasculature, these cells are actively involved in angiogenesis as well in the hampered recruitment of immune cells. This is the result of the abnormal tumor microenvironment which triggers both angiostimulatory and immune inhibitory gene expression profiles in endothelial cells. In recent years, it has become evident that galectins constitute a protein family that is expressed in the tumor endothelium. Moreover, several members of this glycan-binding protein family have been found to facilitate tumor angiogenesis and stimulate immune suppression. All this has identified galectins as potential therapeutic targets to simultaneously hamper tumor angiogenesis and alleviate immune suppression. The current review provides a brief introduction in the human galectin protein family. The current knowledge regarding the expression and regulation of galectins in endothelial cells is summarized. Furthermore, an overview of the role that endothelial galectins play in tumor angiogenesis and tumor immunomodulation is provided. Finally, some outstanding questions are discussed that should be addressed by future research efforts. This will help to fully understand the contribution of endothelial galectins to tumor progression and to exploit endothelial galectins for cancer therapy.

The role of galectins in mediating the adhesion of circulating cells to vascular endothelium

Vascular cell adhesion is a complex orchestration of events that commonly feature lectin-ligand interactions between circulating cells, such as immune, stem, and tumor cells, and endothelial cells (ECs) lining post-capillary venules. Characteristically, circulating cell adherence to the vasculature endothelium is initiated through interactions between surface sialo-fucosylated glycoprotein ligands and lectins, specifically platelet (P)- or endothelial (E)-selectin on ECs or between leukocyte (L)-selectin on circulating leukocytes and L-selectin ligands on ECs, culminating in circulating cell extravasation. This lectin-ligand interplay enables the migration of immune cells into specific tissue sites to help maintain effective immunosurveillance and inflammation control, the homing of stem cells to bone marrow or tissues in need of repair, and, unfortunately, in some cases, the dissemination of circulating tumor cells (CTCs) to distant metastatic sites. Interestingly, there is a growing body of evidence showing that the family of β-galactoside-binding lectins, known as galectins, can also play pivotal roles in the adhesion of circulating cells to the vascular endothelium. In this review, we present contemporary knowledge on the significant roles of host- and/or tumor-derived galectin (Gal)-3, -8, and -9 in facilitating the adhesion of circulating cells to the vascular endothelium either directly by acting as bridging molecules or indirectly by triggering signaling pathways to express adhesion molecules on ECs. We also explore strategies for interfering with galectin-mediated adhesion to attenuate inflammation or hinder the metastatic seeding of CTCs, which are often rich in galectins and/or their glycan ligands.

Galectin-8 modulates human osteoclast activity partly through isoform-specific interactions

In overactive human osteoclasts, we previously identified an alternative splicing event in LGALS8, encoding galectin-8, resulting in decreased expression of the long isoform. Galectin-8, which modulates cell-matrix interactions and functions intracellularly as a danger recognition receptor, has never been associated with osteoclast biology. In human osteoclasts, inhibition of galectin-8 expression revealed its roles in bone resorption, osteoclast nuclearity, and mTORC1 signaling regulation. Galectin-8 isoform-specific inhibition asserted a predominant role for the short isoform in bone resorption. Moreover, a liquid chromatography with tandem mass spectrometry (LC-MS/MS) proteomic analysis of galectin-8 isoforms performed in HEK293T cells identified 22 proteins shared by both isoforms. Meanwhile, nine interacting partners were specific for the short isoform, and none were unique to the long isoform. Interactors specific for the galectin-8 short isoform included cell adhesion proteins and lysosomal proteins. We confirmed the interactions of galectin-8 with CLCN3, CLCN7, LAMP1, and LAMP2, all known to localize to secretory vesicles, in human osteoclasts. Altogether, our study reveals direct roles of galectin-8 in osteoclast activity, mostly attributable to the short isoform.

Membrane organization by tetraspanins and galectins shapes lymphocyte function

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

Endocytic Roles of Glycans on Proteins and Lipids

Most cell surface proteins are decorated by glycans, and the plasma membrane is rich in glycosylated lipids. The mechanisms by which the enormous complexity of these glycan structures on proteins and lipids is exploited to control glycoprotein activity by setting their cell surface residence time and the ways by which they are taken up into cells are still under active investigation. Here, two mechanisms are presented, termed galectin lattices and glycolipid-lectin (GL-Lect)-driven endocytosis, which are among the most prominent to establish a link between glycan information and endocytosis. Types of glycans on glycoproteins and glycolipids are reviewed from the angle of their interaction with glycan-binding proteins that are at the heart of galectin lattices and GL-Lect-driven endocytosis. Examples are given to show how these mechanisms affect cellular functions ranging from cell migration and signaling to vascularization and immune modulation. Finally, outstanding challenges on the link between glycosylation and endocytosis are discussed.

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

Galectins, a family of evolutionarily conserved glycan-binding proteins, play key roles in diverse biological processes including tissue repair, adipogenesis, immune cell homeostasis, angiogenesis, and pathogen recognition. Dysregulation of galectins and their ligands has been observed in a wide range of pathologic conditions including cancer, autoimmune inflammation, infection, fibrosis, and metabolic disorders. Through protein-glycan or protein-protein interactions, these endogenous lectins can shape the initiation, perpetuation, and resolution of these processes, suggesting their potential roles in disease monitoring and treatment. However, despite considerable progress, a full understanding of the biology and therapeutic potential of galectins has not been reached due to their diversity, multiplicity of cell targets, and receptor promiscuity. In this article, we discuss the multiple galectin-binding partners present in different cell types, focusing on their contributions to selected physiologic and pathologic settings. Understanding the molecular bases of galectin-ligand interactions, particularly their glycan-dependency, the biochemical nature of selected receptors, and underlying signaling events, might contribute to designing rational therapeutic strategies to control a broad range of pathologic conditions.

The interrelation of galectins and autophagy

Autophagy is a vital physiological process that maintains intracellular homeostasis by removing damaged organelles and senescent or misfolded molecules. However, excessive autophagy results in cell death and apoptosis, which will lead to a variety of diseases. Galectins are a type of animal lectin that binds to β-galactosides and can bind to the cell surface or extracellular matrix glycans, affecting a variety of immune processes in vivo and being linked to the development of many diseases. In many cases, galectins and autophagy both play important regulatory roles in the cellular life course, yet our understanding of the relationship between them is still incomplete. Galectins and autophagy may share common etiological cofactors for some diseases. Hence, we summarize the relationship between galectins and autophagy, aiming to draw attention to the existence of multiple associations between galectins and autophagy in a variety of physiological and pathological processes, which provide new ideas for etiological diagnosis, drug development, and therapeutic targets for related diseases.

Investigation of anti-galectin-8 levels in patients with multiple sclerosis: A consort-clinical study

BACKGROUND

Galectins are a family of endogenous mammalian lectins involved in pathogen recognition, killing, and facilitating the entry of microbial pathogens and parasites into the host. They are the intermediators that decipher glycan-containing information about the host immune cells and microbial structures to modulate signaling events that cause cellular proliferation, chemotaxis, cytokine secretion, and cell-to-cell communication. They have subgroups that take place in different roles in the immune system. The effect of galectin-8 on multiple sclerosis disease (MS) has been studied in the literature, but the results seemed unclear. In this study, we aimed to determine anti-galectin-8 (anti-Gal-8) levels in MS and their potential use as biomarkers.

METHODS

In this experimental study, 45 MS patients diagnosed according to McDonald criteria were included in the patient group. The healthy control group contained 45 people without MS diagnosis and any risk factors. Demographic data, height, weight, body mass index, blood glucose, thyroid-stimulating hormone, alanine transaminase, aspartate transaminase, creatinine, low-density lipoprotein, anti-Gal-8 levels, the prevalence of hypertension, diabetes mellitus and coronary artery disease were recorded. In addition, the expanded disability status scale and disease duration were evaluated in the patient group. Data were presented as mean ± standard deviations.

RESULTS

The mean blood anti-galectin-8 value of the patient group was 4.84 ± 4.53 ng/mL, while it was 4.67 ± 3.40 ng/mL in the control group, and the difference in these values was found statistically insignificant (P > .05). Moreover, body mass index, glucose, alanine transaminase, aspartate transaminase, thyroid-stimulating hormone, and low-density lipoprotein levels were also statistically insignificant (P > .05).

CONCLUSION

This study examined anti-Gal-8 levels in MS patients. The relationship between MS and galectin-8 and anti-Gal-8 levels in patients needs further clarification. As a result, the study's results could help elucidate the pathogenesis of MS and give more evidence for diagnosis.

Galectin functions in cancer-associated inflammation and thrombosis

Galectins are carbohydrate-binding proteins that regulate many cellular functions including proliferation, adhesion, migration, and phagocytosis. Increasing experimental and clinical evidence indicates that galectins influence many steps of cancer development by inducing the recruitment of immune cells to the inflammatory sites and modulating the effector function of neutrophils, monocytes, and lymphocytes. Recent studies described that different isoforms of galectins can induce platelet adhesion, aggregation, and granule release through the interaction with platelet-specific glycoproteins and integrins. Patients with cancer and/or deep-venous thrombosis have increased levels of galectins in the vasculature, suggesting that these proteins could be important contributors to cancer-associated inflammation and thrombosis. In this review, we summarize the pathological role of galectins in inflammatory and thrombotic events, influencing tumor progression and metastasis. We also discuss the potential of anti-cancer therapies targeting galectins in the pathological context of cancer-associated inflammation and thrombosis.

Galectins in Esophageal Cancer: Current Knowledge and Future Perspectives

Esophageal cancer is a disease with poor overall survival. Despite advancements in therapeutic options, the treatment outcome of esophageal cancer patients remains dismal with an overall 5-year survival rate of approximately 20 percent. To improve treatment efficacy and patient survival, efforts are being made to identify the factors that underlie disease progression and that contribute to poor therapeutic responses. It has become clear that some of these factors reside in the tumor micro-environment. In particular, the tumor vasculature and the tumor immune micro-environment have been implicated in esophageal cancer progression and treatment response. Interestingly, galectins represent a family of glycan-binding proteins that has been linked to both tumor angiogenesis and tumor immunosuppression. Indeed, in several cancer types, galectins have been identified as diagnostic and/or prognostic markers. However, the role of galectins in esophageal cancer is still poorly understood. Here, we summarize the current literature with regard to the expression and potential functions of galectins in esophageal cancer. In addition, we highlight the gaps in the current knowledge and we propose directions for future research in order to reveal whether galectins contribute to esophageal cancer progression and provide opportunities to improve the treatment and survival of esophageal cancer patients.

Galectin-8, cytokines, and the storm

Galectin-8 (Gal-8) belongs to a family of animal lectins that modulate cell adhesion, cell proliferation, apoptosis, and immune responses. Recent studies have shown that mammalian Gal-8 induces in an autocrine and paracrine manner, the expression and secretion of cytokines and chemokines such as RANKL, IL-6, IL-1β, SDF-1, and MCP-1. This involves Gal-8 binding to receptor complexes that include MRC2/uPAR/LRP1, integrins, and CD44. Receptors ligation triggers FAK, ERK, Akt, and the JNK signaling pathways, leading to induction of NF-κB that promotes cytokine expression. Indeed, immune-competent Gal-8 knockout (KO) mice express systemic lower levels of cytokines and chemokines while the opposite is true for Gal-8 transgenic animals. Cytokine and chemokine secretion, induced by Gal-8, promotes the migration of cancer cells toward cells expressing this lectin. Accordingly, Gal-8 KO mice experience reduced tumor size and smaller and fewer metastatic lesions when injected with cancer cells. These observations suggest the existence of a ‘vicious cycle’ whereby Gal-8 expression and secretion promotes the secretion of cytokines and chemokines that further promote Gal-8 expression. This ‘vicious cycle’ could enhance the development of a ‘cytokine storm’ which is a key contributor to the poor prognosis of COVID-19 patients.

Galectins in Glioma: Current Roles in Cancer Progression and Future Directions for Improving Treatment

Simple Summary

Glioblastomas are among the most common and aggressive brain tumors. The high rate of recurrence and mortality associated with this cancer underscores the need for the development of new therapeutical targets. Galectins are among the new targets that have attracted the attention of many scientists working in the field of cancer. They form a group of small proteins found in many tissues where they accomplish various physiological roles, including regulation of immune response and resistance to cell death. In many types of cancer, however, production of abnormally high levels of galectins by cancer cells can be detrimental to patients. Elevated levels of galectins can, for example, suppress the ability of the host’s immune system to kill cancer cells. They can also provide cancer cells with resistance to drugs-induced cell death. Here, we review the recent progress that has contributed to a better understanding of the mechanisms of actions of galectins in glioblastoma. We also discuss recent development of anti-galectin drugs and the challenges associated with their use in clinical settings, with particular attention to their role in reducing the efficacy of immunotherapy, a promising treatment that exploits the capacity of the immune system to recognize and kill cancer cells.

Abstract

Traditional wisdom suggests that galectins play pivotal roles at different steps in cancer progression. Galectins are particularly well known for their ability to increase the invasiveness of cancer cells and their resistance to drug-induced cell death. They also contribute to the development of local and systemic immunosuppression, allowing cancer cells to escape the host’s immunological defense. This is particularly true in glioma, the most common primary intracranial tumor. Abnormally high production of extracellular galectins in glioma contributes to the establishment of a strong immunosuppressive environment that favors immune escape and tumor progression. Considering the recent development and success of immunotherapy in halting cancer progression, it is logical to foresee that galectin-specific drugs may help to improve the success rate of immunotherapy for glioma. This provides a new perspective to target galectins, whose intracellular roles in cancer progression have already been investigated thoroughly. In this review, we discuss the mechanisms of action of galectins at different steps of glioma progression and the potential of galectin-specific drugs for the treatment of glioma.

Transcriptomic Data Analysis Reveals a Down-Expression of Galectin-8 in Schizophrenia Hippocampus

Schizophrenia (SCZ) is a severe psychiatric disorder with several clinical manifestations that include cognitive dysfunction, decline in motivation, and psychosis. Current standards of care treatment with antipsychotic agents are often ineffective in controlling the disease, as only one-third of SCZ patients respond to medications. The mechanisms underlying the pathogenesis of SCZ remain elusive. It is believed that inflammatory processes may play a role as contributing factors to the etiology of SCZ. Galectins are a family of β-galactoside-binding lectins that contribute to the regulation of immune and inflammatory responses, and previous reports have shown their role in the maintenance of central nervous system (CNS) homeostasis and neuroinflammation. In the current study, we evaluated the expression levels of the galectin gene family in post-mortem samples of the hippocampus, associative striatum, and dorsolateral prefrontal cortex from SCZ patients. We found a significant downregulation of LGALS8 (Galectin-8) in the hippocampus of SCZ patients as compared to otherwise healthy donors. Interestingly, the reduction of LGALS8 was disease-specific, as no modulation was observed in the hippocampus from bipolar nor major depressive disorder (MDD) patients. Prediction analysis identified TBL1XR1, BRF2, and TAF7 as potential transcription factors controlling LGALS8 expression. In addition, MIR3681HG and MIR4296 were negatively correlated with LGALS8 expression, suggesting a role for epigenetics in the regulation of LGALS8 levels. On the other hand, no differences in the methylation levels of LGALS8 were observed between SCZ and matched control hippocampus. Finally, ontology analysis of the genes negatively correlated with LGALS8 expression identified an enrichment of the NGF-stimulated transcription pathway and of the oligodendrocyte differentiation pathway. Our study identified LGALS8 as a disease-specific gene, characterizing SCZ patients, that may in the future be exploited as a potential therapeutic target.

Leukaemia: a model metastatic disease

In contrast to solid cancers, which often require genetic modifications and complex cellular reprogramming for effective metastatic dissemination, leukaemic cells uniquely possess the innate ability for migration and invasion. Dedifferentiated, malignant leukocytes retain the benign leukocytes' capacity for cell motility and survival in the circulation, while acquiring the potential for rapid and uncontrolled cell division. For these reasons, leukaemias, although not traditionally considered as metastatic diseases, are in fact models of highly efficient metastatic spread. Accordingly, they are often aggressive and challenging diseases to treat. In this Perspective, we discuss the key molecular processes that facilitate metastasis in a variety of leukaemic subtypes, the clinical significance of leukaemic invasion into specific tissues and the current pipeline of treatments targeting leukaemia metastasis.

Differential cellular responses to adhesive interactions with galectin-8- and fibronectin-coated substrates

The mechanisms underlying the cellular response to extracellular matrices (ECMs) that consist of multiple adhesive ligands are still poorly understood. Here, we address this topic by monitoring specific cellular responses to two different extracellular adhesion molecules - the main integrin ligand fibronectin and galectin-8, a lectin that binds β-galactoside residues  - as well as to mixtures of the two proteins. Compared with cell spreading on fibronectin, cell spreading on galectin-8-coated substrates resulted in increased projected cell area, more-pronounced extension of filopodia and, yet, the inability to form focal adhesions and stress fibers. These differences can be partially reversed by experimental manipulations of small G-proteins of the Rho family and their downstream targets, such as formins, the Arp2/3 complex and Rho kinase. We also show that the physical adhesion of cells to galectin-8 was stronger than adhesion to fibronectin. Notably, galectin-8 and fibronectin differently regulate cell spreading and focal adhesion formation, yet act synergistically to upregulate the number and length of filopodia. The physiological significance of the coherent cellular response to a molecularly complex matrix is discussed. This article has an associated First Person interview with the first author of the paper.

Glycosylation and raft endocytosis in cancer

Changes in glycosylation on proteins or lipids are one of the hallmarks of tumorigenesis. In many cases, it is still not understood how glycan information is translated into biological function. In this review, we discuss at the example of specific cancer-related glycoproteins how their endocytic uptake into eukaryotic cells is tuned by carbohydrate modifications. For this, we not only focus on overall uptake rates, but also illustrate how different uptake processes-dependent or not on the conventional clathrin machinery-are used under given glycosylation conditions. Furthermore, we discuss the role of certain sugar-binding proteins, termed galectins, to tune glycoprotein uptake by inducing their crosslinking into lattices, or by co-clustering them with glycolipids into raft-type membrane nanodomains from which the so-called clathrin-independent carriers (CLICs) are formed for glycoprotein internalization into cells. The latter process has been termed glycolipid-lectin (GL-Lect) hypothesis, which operates in a complementary manner to the clathrin pathway and galectin lattices.

Plump endothelial cells integrated into pre-existing venules contribute to the formation of 'mother' and 'daughter' vessels in pyogenic granuloma: possible role of galectin-1, -3 and -8

INTRODUCTION

Pyogenic granuloma (PG) is a reactive inflammatory vascular lesion of the skin and mucous membranes, characterised by the presence of enlarged venules and seamed and seamless capillaries with plump endothelial cells (EC), and numerous macrophages. EC activation upregulates the synthesis of galectins and induces their translocation to the EC surface promoting angiogenesis and lymphangiogenesis, particularly galectin-1 (Gal-1), Gal-3 and Gal-8. However, the presence and distribution of Gal-1, -3 and -8, as well as their implications in the pathogenesis of PG, has not been considered.

MATERIALS AND METHODS

Eight biopsies from patients diagnosed with PG were selected. The presence of PECAM-1/CD31, IL-1β, VEGF-C, VEGFR-2, VEGFR-3, integrin β1, CD44, fibronectin and Gal-1, -3 and -8 was assessed by immunofluorescence staining using confocal laser scanning microscopy.

RESULTS AND DISCUSSION

Immunostaining revealed that these molecules were present in the enlarged venules with plump ECs, in some macrophages and other immune cells. We propose that macrophages release VEGF-A and VEGF-C inducing VEGFR-2/VEGFR-3 expression and activation, leading macrophages to transdifferentiate into plump ECs that might integrate into pre-existing venules, contributing to the formation of enlarged venules with transluminal bridges and capillaries. EC activation, induced by certain cytokines, has been shown to stimulate galectin expression and changes in the cellular localisation through association and activation of specific EC surface glycoproteins. Therefore, it is plausible that Gal-1, -3 and -8, acting in a concerted manner, could be mediating the transdifferentiation of macrophages into plump ECs and facilitating their migration and incorporation into the new vessels.

LAY SUMMARY

In this study, immunostaining of pyogenic granuloma (PG) tissue sections showed immunoreactivity for PECAM-1/CD31, IL-1β, VEGF-C, VEGFR-2 and VEGFR-3, and galectin-1, -3 and -8 in enlarged venules with plump endothelial cells (EC), as well as in some macrophages and other immune cells. Interestingly, enlarged and thin-walled transient vessels lined by PECAM-1/CD31 and VEGFR-2 immunopositive ECs that form from pre-existing normal venules in response to VEGF-A (called 'mother' vessels [MV]) and that undergo intraluminal bridging evolving into various types of capillaries (called 'daughter' vessels [DV]) have been observed in benign and malignant tumours, in physiological and pathological angiogenesis as well as in vascular malformations, suggesting an important role for VEGF-A and VEGFR-2 in such a process. However, it is not only the mechanisms by which the MVs evolve in different types of DVs that remains to be elucidated, but also whether the cells that form intraluminal bridges proceed from locally activated ECs or whether they are derived from bone marrow precursors or from resident macrophages.Given that the formation of homodimers by Gal-1 and Gal-8 and pentamers by Gal-3 to generate gal-glycan lattices at the cell surface and in the extracellular space has been shown, it is possible that in PG tissue Gal-1, -3 and -8, through their binding partners, form a supramolecular structure at the surface of ECs and plump ECs, macrophages and in the extracellular space that might be mediating the transdifferentiation of macrophages into plump ECs and facilitating the migration and incorporation of these cells into the pre-existing venules, thus contributing to the formation of MVs and DVs.

Characterization of Rhesus Macaque Liver-Resident CD49a+ NK Cells During Retrovirus Infections

CD49a⁺ tissue resident NK cells have been implicated in memory-like NK cell responses, but while this population is well-characterized in mice and in humans, they are poorly described in non-human primates (NHP) which are particularly critical for modeling human viral infections. Others and we have shown that memory-like NK cells are enriched in the liver and because of the importance of NHP in modeling HIV infection, understanding the immunobiology of CD49a⁺ NK cells in SIV-infected rhesus macaques is critical to explore the role of this cell type in retroviral infections. In this study mononuclear cells isolated from livers, spleens, and peripheral whole blood were analyzed in acutely and chronically lentivirus-infected and experimentally-naïve Indian rhesus macaques (RM). NK cells were then identified as CD45⁺CD14⁻CD20⁻CD3⁻NKG2A/C⁺ cells and characterized using multiparametric flow-cytometry. Our data show that in RM, CD49a⁺ NK cells increase in the liver following retroviral infections [median = 5.2% (naïve) vs. median = 9.48% (SIV+) or median = 16.8% (SHIV+)]. In contrast, there is little change in CD49a⁺ NK frequencies in whole blood or spleens of matched animals. In agreement with human and murine data we also observed that CD49a⁺ NK cells were predominantly Eomes^low T-bet^low, though these frequencies are elevated in infected animal cohorts. Functionally, our data suggests that infection alters TNF-α, IFN-γ, and CD107a expression in stimulated CD49a⁺ NK cells. Specifically, our analyses found a decrease in CD49a⁺ CD107a⁺ TNFα⁺ IFNγ⁻ NK cells, with a simultaneous increase in CD49a⁺ CD107a⁺ TNFα⁻ IFNγ⁺ NK cells and the non-responsive CD49a⁺ CD107a⁻ TNFα⁻ IFNγ⁻ NK cell population following infection, suggesting both pathogenic and inflammatory changes in the NK cell functional profile. Our data also identified significant global differences in polyfunctionality between CD49a⁺ NK cells in the naïve and chronic (SHIV+) cohorts. Our work provides the first characterization of CD49a⁺ NK cells in tissues from RM. The significant similarities between CD49a⁺ NK cells from RM and what is reported from human samples justifies the importance of studying CD49a⁺ NK cells in this species to support preclinical animal model research.

Galectin-8 Enhances T cell Response by Promotion of Antigen Internalization and Processing

Galectin-8 (Gal-8) is a mammalian lectin endowed with immunostimulatory ability. In the present work, we demonstrate that Gal-8-glycan interactions on the surface of antigen-presenting cells (APCs) promote antigen binding and internalization, independently from antigen nature. Both Gal-8 and antigen were together internalized and localized in early endosomes. Interestingly, antigen processing by APCs was also accelerated in the presence of Gal-8 as a separate mechanism, distinct from the increased antigen internalization. Moreover, APCs pulsed together with antigen and Gal-8 were able to activate cognate CD4+ T cells more efficiently than those pulsed with antigen alone. This enhanced antigen presentation was still evident in the absence of costimulatory signals and APCs-derived soluble mediators. Therefore, our results provide evidence for as yet unrecognized mechanism by which Gal-8 stimulates the elicitation of the immune response in a lectin-dependent manner, by inducing antigen uptake and processing upon lattice formation at APCs surface.

Galectin-8 mediates fibrogenesis induced by cyclosporine in human gingival fibroblasts

BACKGROUND AND OBJECTIVE

During cyclosporine-induced gingival overgrowth, the homeostatic balance of gingival connective tissue is disrupted leading to fibrosis. Galectins are glycan-binding proteins that can modulate a variety of cellular processes including fibrosis in several organs. Here, we study the role of galectin-8 (Gal-8) in the response of gingival connective tissue cells to cyclosporine.

METHODS

We used human gingival fibroblasts and mouse NIH3T3 cells treated with recombinant Gal-8 and/or cyclosporine for analyzing specific mRNA and protein levels through immunoblot, real-time polymerase chain reaction, ELISA and immunofluorescence, pull-down with Gal-8-Sepharose for Gal-8-to-cell surface glycoprotein interactions, short hairpin RNA for Gal-8 silencing and Student's t test and ANOVA for statistical analysis.

RESULTS

Galectin-8 stimulated type I collagen and fibronectin protein levels and potentiated CTGF protein levels in TGF-β1-stimulated human gingival fibroblasts. Gal-8 interacted with α5β1-integrin and type II TGF-β receptor. Gal-8 stimulated fibronectin protein and mRNA levels, and this response was dependent on FAK activity but not Smad2/3 signaling. Cyclosporine and tumor necrosis factor alpha (TNF-α) increased Gal-8 protein levels. Finally, silencing of galectin-8 in NIH3T3 cells abolished cyclosporine-induced fibronectin protein levels.

CONCLUSION

Taken together, these results reveal for the first time Gal-8 as a fibrogenic stimulus exerted through β1-integrin/FAK pathways in human gingival fibroblasts, which can be triggered by cyclosporine. Further studies should explore the involvement of Gal-8 in human gingival tissues and its role in drug-induced gingival overgrowth.

Galectin-8 induces endothelial hyperpermeability through the eNOS pathway involving S-nitrosylation-mediated adherens junction disassembly

The permeability of endothelial cells is regulated by the stability of the adherens junctions, which is highly sensitive to kinase-mediated phosphorylation and endothelial nitric oxide synthase (eNOS)-mediated S-nitrosylation of its protein components. Solid tumors can produce a variety of factors that stimulate these signaling pathways leading to endothelial cell hyperpermeability. This generates stromal conditions that facilitate tumoral growth and dissemination. Galectin-8 (Gal-8) is overexpressed in several carcinomas and has a variety of cellular effects that can contribute to tumor pathogenicity, including angiogenesis. Here we explored whether Gal-8 has also a role in endothelial permeability. We show that recombinant Gal-8 activates eNOS, induces S-nitrosylation of p120-catenin (p120) and dissociation of adherens junction, leading to hyperpermeability of the human endothelial cell line EAhy926. This pathway involves focal-adhesion kinase (FAK) activation downstream of eNOS as a requirement for eNOS-mediated p120 S-nitrosylation. This suggests a reciprocal, yet little understood, regulation of phosphorylation and S-nitrosylation events acting upon adherens junction permeability. In addition, glutathione S-transferase (GST)-Gal-8 pull-down experiments and function-blocking β1-integrin antibodies point to β1-integrins as cell surface components involved in Gal-8-induced hyperpermeability. Endogenous Gal-8 secreted from the breast cancer cell line MCF-7 has similar hyperpermeability and signaling effects. Furthermore, the mouse cremaster model system showed that Gal-8 also activates eNOS, induces S-nitrosylation of adherens junction components and is an effective hyperpermeability agent in vivo. These results add endothelial permeability regulation by S-nitrosylation as a new function of Gal-8 that can potentially contribute to the pathogenicity of tumors overexpressing this lectin.

Galectin-8 Favors the Presentation of Surface-Tethered Antigens by Stabilizing the B Cell Immune Synapse

Complete activation of B cells relies on their capacity to extract tethered antigens from immune synapses by either exerting mechanical forces or promoting their proteolytic degradation through lysosome secretion. Whether antigen extraction can also be tuned by local cues originating from the lymphoid microenvironment has not been investigated. We here show that the expression of Galectin-8-a glycan-binding protein found in the extracellular milieu, which regulates interactions between cells and matrix proteins-is increased within lymph nodes under inflammatory conditions where it enhances B cell arrest phases upon antigen recognition in vivo and promotes synapse formation during BCR recognition of immobilized antigens. Galectin-8 triggers a faster recruitment and secretion of lysosomes toward the B cell-antigen contact site, resulting in efficient extraction of immobilized antigens through a proteolytic mechanism. Thus, extracellular cues can determine how B cells sense and extract tethered antigens and thereby tune B cell responses in vivo.

Galectin-8 in the onset of the immune response and inflammation

Galectins (Gals), a family of mammalian lectins, have emerged as key regulators of the immune response, being implicated in several physiologic and pathologic conditions. Lately, there is increasing data regarding the participation of Galectin-8 (Gal-8) in both the adaptive and innate immune responses, as well as its high expression in inflammatory disorders. Here, we focus on the pro- and anti-inflammatory properties of Gal-8 and discuss the potential use of this lectin in order to shape the immune response, according to the context.

GALECTIN-8 Is a Neuroprotective Factor in the Brain that Can Be Neutralized by Human Autoantibodies

Galectin-8 (Gal-8) is a glycan-binding protein that modulates a variety of cellular processes interacting with cell surface glycoproteins. Neutralizing anti-Gal-8 antibodies that block Gal-8 functions have been described in autoimmune and inflammatory disorders, likely playing pathogenic roles. In the brain, Gal-8 is highly expressed in the choroid plexus and accordingly has been detected in human cerebrospinal fluid. It protects against central nervous system autoimmune damage through its immune-suppressive potential. Whether Gal-8 plays a direct role upon neurons remains unknown. Here, we show that Gal-8 protects hippocampal neurons in primary culture against damaging conditions such as nutrient deprivation, glutamate-induced excitotoxicity, hydrogen peroxide (H₂O₂)-induced oxidative stress, and β-amyloid oligomers (Aβo). This protective action is manifested even after 2 h of exposure to the harmful condition. Pull-down assays demonstrate binding of Gal-8 to selected β1-integrins, including α3 and α5β1. Furthermore, Gal-8 activates β1-integrins, ERK1/2, and PI3K/AKT signaling pathways that mediate neuroprotection. Hippocampal neurons in primary culture produce and secrete Gal-8, and their survival decreases upon incubation with human function-blocking Gal-8 autoantibodies obtained from lupus patients. Despite the low levels of Gal-8 expression detected by real-time PCR in hippocampus, compared with other brain regions, the complete lack of Gal-8 in Gal-8 KO mice determines higher levels of apoptosis upon H₂O₂ stereotaxic injection in this region. Therefore, endogenous Gal-8 likely contributes to generate a neuroprotective environment in the brain, which might be eventually counteracted by human function-blocking autoantibodies.

Dual knockdown of Galectin-8 and its glycosylated ligand, the activated leukocyte cell adhesion molecule (ALCAM/CD166), synergistically delays in vivo breast cancer growth

Galectin-8 (Gal-8), a 'tandem-repeat'-type galectin, has been described as a modulator of cellular functions including adhesion, spreading, growth arrest, apoptosis, pathogen recognition, autophagy, and immunomodulation. We have previously shown that activated leukocyte cell adhesion molecule (ALCAM), also known as CD166, serves as a receptor for endogenous Gal-8. ALCAM is a member of the immunoglobulin superfamily involved in cell-cell adhesion through homophilic (ALCAM-ALCAM) and heterophilic (i.e. ALCAM-CD6) interactions in different tissues. Here we investigated the physiologic relevance of ALCAM-Gal-8 association and glycosylation-dependent mechanisms governing these interactions. We found that silencing of ALCAM in MDA-MB-231 triple negative breast cancer cells decreases cell adhesion and migration onto Gal-8-coated surfaces in a glycan-dependent fashion. Remarkably, either Gal-8 or ALCAM silencing also disrupted cell-cell adhesion, and led to reduced tumor growth in a murine model of triple negative breast cancer. Moreover, structural characterization of endogenous ALCAM N-glycosylation showed abundant permissive structures for Gal-8 binding. Importantly, we also found that cell sialylation controls Gal-8-mediated cell adhesion. Altogether, these findings demonstrate a central role of either ALCAM or Gal-8 (or both) in controlling triple negative breast cancer.

Galectin-8 induces partial epithelial-mesenchymal transition with invasive tumorigenic capabilities involving a FAK/EGFR/proteasome pathway in Madin-Darby canine kidney cells

Epithelial cells can acquire invasive and tumorigenic capabilities through epithelial–mesenchymal-transition (EMT). The glycan-binding protein galectin-8 (Gal-8) activates selective β1-integrins involved in EMT and is overexpressed by certain carcinomas. Here we show that Gal-8 overexpression or exogenous addition promotes proliferation, migration, and invasion in nontumoral Madin–Darby canine kidney (MDCK) cells, involving focal-adhesion kinase (FAK)-mediated transactivation of the epidermal growth factor receptor (EGFR), likely triggered by α5β1integrin binding. Under subconfluent conditions, Gal-8–overexpressing MDCK cells (MDCK-Gal-8^H) display hallmarks of EMT, including decreased E-cadherin and up-regulated expression of vimentin, fibronectin, and Snail, as well as increased β-catenin activity. Changes related to migration/invasion included higher expression of α5β1 integrin, extracellular matrix-degrading MMP13 and urokinase plasminogen activator/urokinase plasminogen activator receptor (uPA/uPAR) protease systems. Gal-8–stimulated FAK/EGFR pathway leads to proteasome overactivity characteristic of cancer cells. Yet MDCK-Gal-8^H cells still develop apical/basolateral polarity reverting EMT markers and proteasome activity under confluence. This is due to the opposite segregation of Gal-8 secretion (apical) and β1-integrins distribution (basolateral). Strikingly, MDCK-Gal-8^H cells acquired tumorigenic potential, as reflected in anchorage-independent growth in soft agar and tumor generation in immunodeficient NSG mice. Therefore, Gal-8 can promote oncogenic-like transformation of epithelial cells through partial and reversible EMT, accompanied by higher proliferation, migration/invasion, and tumorigenic properties.

Galectin-8 as an immunosuppressor in experimental autoimmune encephalomyelitis and a target of human early prognostic antibodies in multiple sclerosis

Galectin-8 (Gal-8) is a member of a glycan-binding protein family that regulates the immune system, among other functions, and is a target of antibodies in autoimmune disorders. However, its role in multiple sclerosis (MS), an autoimmune inflammatory disease of the central nervous system (CNS), remains unknown. We study the consequences of Gal-8 silencing on lymphocyte subpopulations and the development of experimental autoimmune encephalitis (EAE), to then assess the presence and clinical meaning of anti-Gal-8 antibodies in MS patients. Lgals8/Lac-Z knock-in mice lacking Gal-8 expression have higher polarization toward Th17 cells accompanied with decreased CCR6⁺ and higher CXCR3⁺ regulatory T cells (Tregs) frequency. These conditions result in exacerbated MOG_35-55 peptide-induced EAE. Gal-8 eliminates activated Th17 but not Th1 cells by apoptosis and ameliorates EAE in C57BL/6 wild-type mice. β-gal histochemistry reflecting the activity of the Gal-8 promoter revealed Gal-8 expression in a wide range of CNS regions, including high expression in the choroid-plexus. Accordingly, we detected Gal-8 in human cerebrospinal fluid, suggesting a role in the CNS immune-surveillance circuit. In addition, we show that MS patients generate function-blocking anti-Gal-8 antibodies with pathogenic potential. Such antibodies block cell adhesion and Gal-8-induced Th17 apoptosis. Furthermore, circulating anti-Gal-8 antibodies associate with relapsing-remitting MS (RRMS), and not with progressive MS phenotypes, predicting clinical disability at diagnosis within the first year of follow-up. Our results reveal that Gal-8 has an immunosuppressive protective role against autoimmune CNS inflammation, modulating the balance of Th17 and Th1 polarization and their respective Tregs. Such a role can be counteracted during RRMS by anti-Gal-8 antibodies, worsening disease prognosis. Even though anti-Gal-8 antibodies are not specific for MS, our results suggest that they could be a potential early severity biomarker in RRMS.

On the trail of the glycan codes stored in cancer-related cell adhesion proteins

Changes in the profile of protein glycosylation are a hallmark of ongoing neoplastic transformation. A unique set of tumor-associated carbohydrate antigens expressed on the surface of malignant cells may serve as powerful diagnostic and therapeutic targets. Cell-surface proteins with altered glycosylation affect the growth, proliferation and survival of those cells, and contribute to their acquisition of the ability to migrate and invade. They may also facilitate tumor-induced immunosuppression and the formation of distant metastases. Deciphering the information encoded in these particular glycan portions of glycoconjugates may shed light on the mechanisms of cancer progression and metastasis. A majority of the related review papers have focused on overall changes in the patterns of cell-surface glycans in various cancers, without pinpointing the molecular carriers of these glycan structures. The present review highlights the ways in which particular tumor-associated glycan(s) coupled with a given membrane-bound protein influence neoplastic cell behavior during the development and progression of cancer. We focus on altered glycosylated cell-adhesion molecules belonging to the cadherin, integrin and immunoglobulin-like superfamilies, examined in the context of molecular interactions.

Galectin-8 promotes migration and proliferation and prevents apoptosis in U87 glioblastoma cells

Background

Glioblastoma is one of the most aggressive cancers of the brain. Malignant traits of glioblastoma cells include elevated migration, proliferation and survival capabilities. Galectins are unconventionally secreted glycan-binding proteins that modulate processes of cell adhesion, migration, proliferation and apoptosis by interacting with beta-galactosides of cell surface glycoproteins and the extracellular matrix. Galectin-8 is one of the galectins highly expressed in glioblastoma cells. It has a unique selectivity for terminally sialylated glycans recently found enhanced in these highly malignant cells. A previous study in glioblastoma cell lines reported that Gal-8 coating a plastic surface stimulates two-dimensional motility. Because in other cells Gal-8 arrests proliferation and induces apoptosis, here we extend its study by analyzing all of these processes in a U87 glioblastoma cell model.

Methods

We used immunoblot and RT-PCR for Gal-8 expression analysis, recombinant Gal-8 produced in a bacteria system for Gal-8 treatment of the cells, and shRNA in lentivirus transduction for Gal-8 silencing. Cell migration as assessed in transwell filters. Cell proliferation, cell cycle and apoptosis were analyzed by FACS.

Results

Gal-8 as a soluble stimulus triggered chemotactic migration of U87 cells across the polycarbonate filter of transwell chambers, almost as intensively as fetal bovine serum. Unexpectedly, Gal-8 also enhanced U87 cell growth. Co-incubation of Gal-8 with lactose, which blocks galectin–glycan interactions, abrogated both effects. Immunoblot showed Gal-8 in conditioned media reflecting its secretion. U87 cells transduced with silencing shRNA in a lentiviral vector expressed and secreted 30–40 % of their normal Gal-8 levels. These cells maintained their migratory capabilities, but decreased their proliferation rate and underwent higher levels of apoptosis, as revealed by flow cytometry analysis of cell cycle, CFSE and activated caspase-3 staining. Proliferation seemed to be more sensitive than migration to Gal-8 expression levels.

Conclusions

Gal-8, either secreted or exogenously enriched in the media, and acting through extracellular glycan interactions, constitutes a strong stimulus of directional migration in glioblastoma U87 cells and for the first time emerges as a factor that promotes proliferation and prevents apoptosis in cancerous cells. These properties could potentially contribute to the exaggerated malignancy of glioblastoma cells.

Galectin-8 enhances adhesion of multiple myeloma cells to vascular endothelium and is an adverse prognostic factor

Multiple myeloma is characterized by abnormal infiltration of malignant plasma cells into bone marrow. Testing the hypothesis that bivalent galectin-8 (Gal-8) may influence homing of myeloma cells to vascular endothelium as a key prerequisite for infiltration, we analyzed the two Gal-8 splice variants (Gal-8S, Gal-8L). They differ in the length of their linker peptide connecting the two lectin domains. Both Gal-8 isoforms bind to cells of the myeloma lines Gal-8⁺ MOLP-8 and Gal-8^- LP-1 in a glycan-inhibitable manner. Both Gal-8 isoforms led to enhanced adhesion of myeloma cells to vascular endothelium under dynamic shear stress conditions, Gal-8L (by more than 40-fold) even stronger than Gal-8S. Additional treatment of endothelial cells with tumour necrosis factor prior to the dynamic shear stress assay entailed an almost 100-fold enhanced adhesion of myeloma cells without addition of Gal-8 variants and a further 1.5-1.7-fold enhancement by addition of Gal-8 variants. We also found that elevated expression of Gal-8 in native multiple myeloma cells is an adverse prognostic factor for overall and event-free survival using patients' gene expression profile data of the total therapy 2 and 3 myeloma studies. Also, elevated concentrations of Gal-8 were detected (45%, 19/42 patients) in sera of multiple myeloma patients compared to those of healthy, age-matched donors. Both experimental and clinical data strongly point to the significance of Gal-8 for multiple myeloma development.

The mammalian lectin galectin-8 induces RANKL expression, osteoclastogenesis, and bone mass reduction in mice

Skeletal integrity is maintained by the co-ordinated activity of osteoblasts, the bone-forming cells, and osteoclasts, the bone-resorbing cells. In this study, we show that mice overexpressing galectin-8, a secreted mammalian lectin of the galectins family, exhibit accelerated osteoclasts activity and bone turnover, which culminates in reduced bone mass, similar to cases of postmenopausal osteoporosis and cancerous osteolysis. This phenotype can be attributed to a direct action of galectin-8 on primary cultures of osteoblasts that secrete the osteoclastogenic factor RANKL upon binding of galectin-8. This results in enhanced differentiation into osteoclasts of the bone marrow cells co-cultured with galectin-8-treated osteoblasts. Secretion of RANKL by galectin-8-treated osteoblasts can be attributed to binding of galectin-8 to receptor complexes that positively (uPAR and MRC2) and negatively (LRP1) regulate galectin-8 function. Our findings identify galectins as new players in osteoclastogenesis and bone remodeling, and highlight a potential regulation of bone mass by animal lectins.

DOI:http://dx.doi.org/10.7554/eLife.05914.001

The forces applied to the body during daily activities cause bones to be constantly remodeled, which is essential for keeping them healthy. In most adult organisms, new bone is created at the same rate at which old bone is destroyed. This means that overall bone mass remains the same. But, in diseases such as osteoporosis or bone cancer, bone is destroyed more rapidly than at which new bone is made. This leads to brittle bones that are more likely to fracture. Understanding how to increase the rate of bone renewal might therefore help scientists develop new treatments for bone diseases.

Bone is created by cells called osteoblasts and destroyed by other cells called osteoclasts. Both of these types of cells develop from stem cells in the bone marrow. The activity of these cells is controlled by a number of factors, including the matrix of proteins that holds bone together. A group of proteins called galectins are known to act as a bridge between some of the matrix proteins and molecules on the surface of the cells.

Vinik et al. took osteoblasts from a mouse skull, grew them in the laboratory, and then exposed them to a galectin protein called galectin-8. This made the osteoblasts release a protein called RANKL, which is known to boost osteoclast activity. When osteoblasts that had been exposed to galectin-8 were grown alongside bone marrow stem cells, more of the stem cells developed into the bone-destroying osteoclasts.

Mice that were genetically engineered to produce more galectin-8 than normal mice develop brittle bones, despite also creating new bone at a higher rate than do normal mice. This is because osteoclast activity increases at a greater rate, resulting in an overall loss of bone in these animals. This is similar to what occurs in some individuals with osteoporosis. These experiments therefore suggest that galectin-8 plays an important role in bone remodeling and that it may be a potential target for drugs that treat diseases that weaken bones.

DOI:http://dx.doi.org/10.7554/eLife.05914.002

Role of galectins in re-epithelialization of wounds

Re-epithelialization is a critical contributing process in wound healing in the human body. When this process is compromised, impaired or delayed, serious disorders of wound healing may result that are painful, difficult to treat, and affect a variety of human tissues. Recent studies have demonstrated that members of the galectin class of β-galactoside-binding proteins modulate re-epithelialization of wounds by novel carbohydrate-based recognition systems. Galectins constitute a family of widely distributed carbohydrate-binding proteins with the affinity for the β-galactoside-containing glycans found on many cell surface and extracellular matrix (ECM) glycoproteins. There are 15 members of the mammalian galectin family that so far have been identified. Studies of the role of galectins in wound healing have revealed that galectin-3 promotes re-epithelialization of corneal, intestinal and skin wounds; galectin-7 promotes re-epithelialization of corneal, skin, kidney and uterine wounds; and galectins-2 and -4 promote re-epithelialization of intestinal wounds. Promising prospects for developing novel therapeutic strategies for the treatment of problematic, slow- or non-healing wounds are implicit in the findings that galectins stimulate the re-epithelialization of wounds of the cornea, skin, intestinal tract and kidney. Molecular mechanisms by which galectins modulate the process of wound healing are beginning to emerge and are described in this review.

Alternative splicing in osteoclasts and Paget's disease of bone

Background

Mutations in the SQSTM1/p62 gene have been reported in Paget’s disease of bone (PDB), but they are not sufficient to induce the pagetic osteoclast (OC) phenotype. We hypothesized that specific RNA isoforms of OC-related genes may contribute to the overactivity of pagetic OCs, along with other genetic predisposing factors.

Methods

Alternative splicing (AS) events were studied using a PCR-based screening strategy in OC cultures from 29 patients with PDB and 26 healthy donors (HD), all genotyped for the p62^P392L mutation. Primer pairs targeting 5223 characterized AS events were used to analyze relative isoform ratios on pooled cDNA from samples of the four groups (PDB, PDB^P392L, HD, HD^P392L). Of the 1056 active AS events detected in the screening analysis, 192 were re-analyzed on non-amplified cDNA from each subject of the whole cohort.

Results

This analysis led to the identification of six AS events significantly associated with PDB, but none with p62^P392L. The corresponding genes included LGALS8, RHOT1, CASC4, USP4, TBC1D25, and PIDD. In addition, RHOT1 and LGALS8 genes were upregulated in pagetic OCs, as were CASC4 and RHOT1 genes in the presence of p62^P392L. Finally, we showed that the proteins encoded by LGALS8, RHOT1, USP4, TBC1D25, and PIDD were expressed in human OCs.

Conclusion

This study allowed the identification of hitherto unknown players in OC biology, and our findings of a differential AS in pagetic OCs may generate new concepts in the pathogenesis of PDB.

Integrin α1β1

Integrin α1β1 is widely expressed in mesenchyme and the immune system, as well as a minority of epithelial tissues. Signaling through α1 contributes to the regulation of extracellular matrix composition, in addition to supplying in some tissues a proliferative and survival signal that appears to be unique among the collagen binding integrins. α1 provides a tissue retention function for cells of the immune system including monocytes and T cells, where it also contributes to their long-term survival, providing for peripheral T cell memory, and contributing to diseases of autoimmunity. The viability of α1 null mice, as well as the generation of therapeutic monoclonal antibodies against this molecule, have enabled studies of the role of α1 in a wide range of pathophysiological circumstances. The immune functions of α1 make it a rational therapeutic target.

Schwann cell-derived exosomes enhance axonal regeneration in the peripheral nervous system

Axonal regeneration in the peripheral nervous system is greatly supported by Schwann cells (SCs). After nerve injury, SCs dedifferentiate to a progenitor-like state and efficiently guide axons to their original target tissues. Contact and soluble factors participate in the crosstalk between SCs and axons during axonal regeneration. Here we show that dedifferentiated SCs secrete nano-vesicles known as exosomes which are specifically internalized by axons. Surprisingly, SC-derived exosomes markedly increase axonal regeneration in vitro and enhance regeneration after sciatic nerve injury in vivo. Exosomes shift the growth cone morphology to a pro-regenerating phenotype and decrease the activity of the GTPase RhoA, involved in growth cone collapse and axon retraction. Altogether, our work identifies a novel mechanism by which SCs communicate with neighboring axons during regenerative processes. We propose that SC exosomes represent an important mechanism by which these cells locally support axonal maintenance and regeneration after nerve damage.

Galectin-8 promotes cytoskeletal rearrangement in trabecular meshwork cells through activation of Rho signaling

Purpose

The trabecular meshwork (TM) cell-matrix interactions and factors that influence Rho signaling in TM cells are thought to play a pivotal role in the regulation of aqueous outflow. The current study was designed to evaluate the role of a carbohydrate-binding protein, galectin-8 (Gal8), in TM cell adhesion and Rho signaling.

Methods

Normal human TM cells were assayed for Gal8 expression by immunohistochemistry and Western blot analysis. To assess the role of Gal8 in TM cell adhesion and Rho signaling, the cell adhesion and spreading assays were performed on Gal8-coated culture plates in the presence and the absence of anti-β₁ integrin antibody and Rho and Rho-kinase inhibitors. In addition, the effect of Gal8-mediated cell-matrix interactions on TM cell cytoskeleton arrangement and myosin light chain 2 (MLC2) phosphorylation was examined.

Principal Findings

We demonstrate here that Gal8 is expressed in the TM and a function-blocking anti-β₁ integrin antibody inhibits the adhesion and spreading of TM cells to Gal8-coated wells. Cell spreading on Gal8 substratum was associated with the accumulation of phosphorylated myosin light chain and the formation of stress fibers that was inhibited by the Rho inhibitor, C3 transferase, as well as by the Rho-kinase inhibitor, Y27632.

Conclusions/Significance

The above findings present a novel function for Gal8 in activating Rho signaling in TM cells. This function may allow Gal8 to participate in the regulation of aqueous outflow.

The effect of galectins on leukocyte trafficking in inflammation: sweet or sour?

The trafficking of leukocytes from the blood stream to the surrounding tissue is a fundamental feature of an inflammatory response. Although many of the adhesion molecules and chemokines that direct leukocyte trafficking have been identified, there is still much to be discovered, particularly with regard to the persistence of leukocyte infiltrates in chronic inflammation. Elucidating the molecular mechanisms involved in this process is critical to understanding and treating inflammatory pathologies. Recent studies have identified members of the galectin family as immunoregulatory proteins. Included among the actions of galectins are modulatory effects, both positive and negative, on leukocyte recruitment. The focus of this review is to summarize current knowledge on the role of galectins in leukocyte trafficking during inflammation. A better understanding of the function of this family of endogenous lectins will open new avenues for innovative drug discovery.

Glycoproteomic identification of galectin-3 and -8 ligands in bronchoalveolar lavage of mild asthmatics and healthy subjects

BACKGROUND

Galectins, a family of small carbohydrate binding proteins, have been implicated in regulation of inflammatory reactions, including asthma and fibrosis in the lungs. Galectins are found in cells of the airways and in airway secretions, but their glycoprotein ligands there have only been studied to a very limited extent.

METHODS

Bronchoalveolar lavage (BAL) fluid from mild asthmatics and healthy volunteers were fractionated by affinity chromatography on the immobilized galectins. Total (10-30 μg) and galectin bound (~1-10 μg) protein fractions were identified, quantified and compared using shot-gun proteomics and spectral counts.

RESULTS

About 175 proteins were identified in unfractionated BAL-fluid, and about 100 bound galectin-3 and 60 bound galectin-8. These included plasma glycoproteins, and typical airway proteins such as SP-A2, PIGR and SP-B. The concentration of galectin-binding proteins was 100-300 times higher than the concentration of galectins in BAL.

CONCLUSION

The low relative concentration of galectins in BAL makes it likely that functional interactions with glycoproteins occur at sites rich in galectin, such as cells of the airways, rather than the extracellular fluid itself. The profile of galectin bound proteins differed between samples from asthma patients and healthy subjects and correlated with the presence of fibroblasts or eosinophils. This included appearance of a specific galectin-8-binding glycoform of haptoglobin, previously shown to be increased in serum in other inflammatory conditions.

GENERAL SIGNIFICANCE

It is technically feasible to identify galectin-binding glycoproteins in low concentration patient samples such as BAL-fluid, to generate biomedically interesting results. This article is part of a Special Issue entitled Glycoproteomics.

Galectin-8 in IgA nephritis: decreased binding of IgA by galectin-8 affinity chromatography and associated increased binding in non-IgA serum glycoproteins

Background

Immunoglobulin A nephritis (IgAN) is the most common primary glomerulonephritis worldwide. It is caused by accumulation of IgA1-containing immune complexes in the kidney resulting in renal failure, which is thought to be due to altered glycosylation of IgA with a decrease of 2–3-sialylated galactosides (NeuAcα2-3Gal).

Purpose

The purpose of this study was to analyze whether altered glycosylation of IgA would lead to an altered binding to galectin-8, an endogenous lectin with strong affinity for 2–3-sialylated galactosides. Galectins are a family of β-galactoside-binding proteins; by binding various glycoproteins, they play important roles in the regulation of cellular functions in inflammation and immunity. Hence, an altered binding of IgA to galectin-8 could lead to pathologic immune functions, such as glomerulonephritis.

Methods

Affinity chromatography of serum glycoproteins on the human sialogalactoside-binding lectin galectin-8N permitted quantitation of bound and unbound fractions, including IgA.

Results

Analysis of ∼100 IgA nephritis sera showed that the galectin-8N unbound fraction of IgA increased compared to ∼100 controls, consistent with the known loss of galactosylation. A subgroup of ∼15% of the IgAN patients had a ratio of galectin-8 bound/unbound IgA <0.09, not found for any of the controls. Unexpectedly, the galectin-8N-binding fraction of serum glycoproteins other than IgA increased in the sera of IgAN patients but not in controls, suggesting a previously unrecognized change in this disease.

Conclusion

This is the first study that relates a galectin, an endogenous lectin family, to IgA nephritis and thus should stimulate new avenues of research into the pathophysiology of the disease.

Electronic supplementary material

The online version of this article (doi:10.1007/s10875-011-9618-3) contains supplementary material, which is available to authorized users.

Glycosylation, galectins and cellular signaling

Glycosylation is a common posttranslational modification of proteins and lipids of the secretory pathway that generates binding sites for galactose-specific lectins or galectins. Branching of Asn-linked (N-)glycans by the N-acetylglucosaminyltransferases (Mgat genes) increases affinity for galectins. Both tissue-specific expression of the enzymes and the metabolic supply of sugar-nucleotides to the ER and Golgi regulate glycan distribution while protein sequences specify NXS/T site multiplicity, providing metabolic and genetic contributions to galectin-glycoprotein interactions. Galectins cross-link glycoproteins forming dynamic microdomains or lattices that regulate various mediators of cell adhesion, migration, proliferation, survival and differentiation. There are a similar number of galactose-specific galectins in C. elegans and humans, but expression of higher-affinity branched N-glycans are a more recent feature of vertebrate evolution. Galectins might be considered a reading code for repetition of the minimal units of binding [Gal(NAc)β1-3/4GlcNAc] and NXS/T site multiplicity in proteins. The rapidly evolving and structurally complex Golgi modifications to surface receptors are interpreted through affinity for the lattice, which regulates receptor levels as a function of the cellular environment, and thereby the probability of various cell fates. Many important questions remain concerning the regulation of the galectins, the glycan ligands and lattice interaction with other membrane domains and endocytic pathways.

Galectin-8-N-domain recognition mechanism for sialylated and sulfated glycans

Galectin-8 has much higher affinity for 3'-O-sulfated or 3'-O-sialylated glycoconjugates and a Lewis X-containing glycan than for oligosaccharides terminating in Galβ1→3/4GlcNAc, and this specificity is mainly attributed to the N-terminal carbohydrate recognition domain (N-domain, CRD) (Ideo, H., Seko, A., Ishizuka, I., and Yamashita, K. (2003) Glycobiology 13, 713-723). In this study, we elucidated the crystal structures of the human galectin-8-N-domain (-8N) in the absence or presence of 4 ligands. The apo molecule forms a dimer, which is different from the canonical 2-fold symmetric dimer observed for galectin-1 and -2. In a galectin-8N-lactose complex, the lactose-recognizing amino acids are highly conserved among the galectins. However, Arg(45), Gln(47), Arg(59), and the long loop region between the S3 and S4 β-strands are unique to galectin-8N. These amino acids directly or indirectly interact with the sulfate or sialic acid moieties of 3'-sialyl- and 3'-sulfolactose complexed with galectin-8N. Furthermore, in the LNF-III-galectin-8N complex, van der Waals interactions occur between the α1-3-branched fucose and galactose and between galactose and Tyr(141), and these interactions increase the affinity toward galectin-8N. Based on the findings of these x-ray crystallographic analyses, a mutagenesis study using surface plasmon resonance showed that Arg(45), Gln(47), and Arg(59) of galectin-8N are indispensable and coordinately contribute to the strong binding of galectins-8N to sialylated and sulfated oligosaccharides. Arg(59) is the most critical amino acid for binding in the S3-S4 loop region.

Galectin-8 tandem-repeat structure is essential for T-cell proliferation but not for co-stimulation

Gal (galectin)-8 is a tandem-repeat Gal containing N-CRDs (Nterminal carbohydrate-recognition domains) and C-CRDs (C-terminal carbohydrate-recognition domains) with differential glycan-binding specificity fused by a linker peptide. Gal-8 has two distinct effects on CD4 T-cells: at high concentrations it induces antigen-independent proliferation, whereas at low concentrations it co-stimulates antigen-specific responses. Associated Gal-8 structural requirements were dissected in the present study. Recombinant homodimers N–N (two N-terminal CRD chimaera) and C–C (two C-terminal CRD chimaera), but not single C-CRDs or N-CRDs, induced proliferation; however, single domains induced co-stimulation. These results indicate that the tandem-repeat structure was essential only for the proliferative effect, suggesting the involvement of lattice formation, whereas co-stimulation could be mediated by agonistic interactions. In both cases, C–C chimaeras displayed higher activity than Gal-8, indicating that the C-CRD was mainly involved, as was further supported by the strong inhibition of proliferation and co-stimulation in the presence of blood group B antigen, specifically recognized by this domain. Classic Gal inhibitors (lactose and thiodigalactoside) prevented proliferation but not co-stimulatory activity, which was inhibited by 3-O-β-D-galactopyranosyl-D-arabinose. Interestingly, Gal-8 induced proliferation of naïve human CD4 T-cells, varying from non- to high-responder individuals, whereas it promoted cell death of phytohaemagglutinin or CD3/CD28 pre-activated cells. The findings of the present study delineate the differential molecular requirements for Gal-8 activities on T-cells, and suggest a dual activity relying on activation state.

Human platelets express and are activated by galectin-8

Gals (galectins) are proteins with glycan affinity that are emerging as mediators of atherosclerosis. Despite the similarities in structure and sequence, different Gals exert distinct effects on their target cells. We have shown that Gal-1 triggers platelet activation, suggesting a role for Gals in thrombus formation. Since Gal-8 is expressed upon endothelial activation and also contributes to inflammation, to understand further the role of these lectins in haemostasis, we evaluated the effect of Gal-8 on human platelets. Gal-8 bound specific glycans in the platelet membrane and triggered spreading, calcium mobilization and fibrinogen binding. It also promoted aggregation, thromboxane generation, P-selectin expression and granule secretion. GP (glycoprotein) αIIb and Ib-V were identified as putative Gal-8 counter-receptors by MS. Studies performed using platelets from Glanzmann's thromboasthenia and Bernard-Soulier syndrome patients confirmed that GPIb is essential for transducing Gal-8 signalling. Accordingly, Src, PLC2γ (phospholipase C2γ), ERK (extracellular-signal-regulated kinase) and PI3K (phosphoinositide 3-kinase)/Akt downstream molecules were involved in the Gal-8 signalling pathway. Gal-8 fragments containing either the N- or C-terminal carbohydrate-recognition domains showed that activation is exerted through the N-terminus. Western blotting and cytometry showed that platelets not only contain Gal-8, but also expose Gal-8 after thrombin activation. These findings reveal Gal-8 as a potent platelet activator, supporting a role for this lectin in thrombosis and inflammation.

Galectin-3 promotes lamellipodia formation in epithelial cells by interacting with complex N-glycans on alpha3beta1 integrin

Recent studies have shown that galectin-3 (Gal-3; also known as LGALS3), a beta-galactoside-binding lectin, promotes cell migration during re-epithelialization of corneal wounds. The goal of this study was to characterize the molecular mechanism by which Gal-3 stimulates cell migration. We demonstrate here that exogenous Gal-3, but not Gal-1 or Gal-8, promotes cell scattering and formation of lamellipodia in human corneal epithelial cells in a beta-lactose-inhibitable manner. alpha3beta1 integrin was identified as the major Gal-3-binding protein in corneal epithelial cells by affinity chromatography of cell lysates on a Gal-3-Sepharose column. Preincubation of cells with anti-alpha3 integrin function-blocking antibody significantly inhibited the induction of lamellipodia by Gal-3. Furthermore, exogenous Gal-3 activated both focal adhesion kinase, a key regulator of integrin-dependent intracellular signaling, and Rac1 GTPase, a member of the family of Rho GTPases, well known for its role in the reorganization of the actin cytoskeleton and formation of lamellipodial extensions. Experiments involving knockdown of beta-1,6-N-acetylglucosaminytransferase V, an enzyme that synthesizes high-affinity glycan ligands for Gal-3, revealed that carbohydrate-mediated interaction between Gal-3 and complex N-glycans on alpha3beta1 integrin plays a key role in Gal-3-induced lamellipodia formation. We propose that Gal-3 promotes epithelial cell migration by cross-linking MGAT5-modified complex N-glycans on alpha3beta1 integrin and subsequently activating alpha3beta1-integrin-Rac1 signaling to promote lamellipodia formation.