Integration of lectin–glycan recognition systems and immune cell networks in CNS inflammation

Single-cell transcriptional profiling reveals aberrant gene expression patterns and cell states in autoimmune diseases

Multiple sclerosis(MS), primary Sjögren syndrome (pSS), and systemic lupus erythematosus (SLE) share numerous clinical symptoms and serological characteristics. We analyzed 153550 cells of scRNA-seq data of 17 treatment-naive patients (5 MS, 5 pSS, and 7 SLE) and 10 healthy controls, and we examined the enrichment of biological processes, differentially expressed genes (DEGs), immune cell types, and their subpopulations, and cell-cell communication in peripheral blood mononuclear cells (PBMCs). The percentage of B cells, megakaryocytes, monocytes, and proliferating T cells presented significant changes in autoimmune diseases. The enrichment of cell types based on gene expression revealed an elevated monocyte. MIF, MK, and GALECTIN signaling networks were obvious differences in autoimmune diseases. Taken together, our analysis provides a comprehensive map of the cell types and states of ADs patients at the single-cell level to understand better the pathogenesis and treatment of these ADs.

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.

An insight into new glycotherapeutics in glial inflammation: Understanding the role of glycosylation in mitochondrial function and acute to the chronic phases of inflammation

INTRODUCTION

Glycosylation plays a critical role during inflammation and glial scar formation upon spinal cord injury (SCI) disease progression. Astrocytes and microglia are involved in this cascade to modulate the inflammation and tissue remodeling from acute to chronic phases. Therefore, understating the glycan changes in these glial cells is paramount.

METHOD AND RESULTS

A lectin microarray was undertaken using a cytokine-driven inflammatory mixed glial culture model, revealing considerable differential glycosylation from the acute to the chronic phase in a cytokine-combination generated inflamed MGC model. It was found that several N- and O-linked glycans associated with glia during SCI were differentially regulated. Pearson's correlation hierarchical clustering showed that groups were separated into several clusters, illustrating the heterogenicity among the control, cytokine combination, and LPS treated groups and the day on which treatment was given. Control and LPS treatments were observed to be in dense clusters. This was further confirmed with lectin immunostaining in which GalNAc, GlcNAc, mannose, fucose and sialic acid-binding residues were detected in astrocytes and microglia. However, the sialyltransferase inhibitor inhibited this modification (upregulation of the sialic acid expression), which indeed modulates the mitochondrial functions.

CONCLUSIONS

The present study is the first functional investigation of glycosylation modulation in a mixed glial culture model, which elucidates the role of the glycome in neuroinflammation in progression and identified potential therapeutic targets for future glyco therapeutics in neuroinflammation.

Role and therapeutic implications of protein glycosylation in neuroinflammation

The importance of glycosylation (post-translational attachment of glycan residues to proteins) in the context of neuroinflammation is only now beginning to be understood. Although the glycome is challenging to investigate due to its complexity, this field is gaining interest because of the emergence of novel analytical methods. These investigations offer the possibility of further understanding the molecular signature of disorders with underlying neuroinflammatory cascades. In this review, we portray the clinically relevant trends in glyconeurobiology and suggest glyco-related paths that could be targeted therapeutically to decrease neuroinflammation. A combinatorial insight from glycobiology and neurology can be harnessed to better understand neuroinflammatory-related conditions to identify relevant molecular targets.

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.

Mass Spectrometry-Based Methods for Immunoglobulin G N-Glycosylation Analysis

Mass spectrometry and its hyphenated techniques enabled by the improvements in liquid chromatography, capillary electrophoresis, novel ionization, and fragmentation modes are truly a cornerstone of robust and reliable protein glycosylation analysis. Boost in immunoglobulin G (IgG) glycan and glycopeptide profiling demands for both applied biomedical and research applications has brought many new advances in the field in terms of technical innovations, sample preparation, improved throughput, and confidence in glycan structural characterization. This chapter summarizes mass spectrometry basics, focusing on IgG and monoclonal antibody N-glycosylation analysis on several complexity levels. Different approaches, including antibody enrichment, glycan release, labeling, and glycopeptide preparation and purification, are covered and illustrated with recent breakthroughs and examples from the literature omitting excessive theoretical frameworks. Finally, selected highly popular methodologies in IgG glycoanalytics such as liquid chromatography-mass spectrometry and matrix-assisted laser desorption ionization are discussed more thoroughly yet in simple terms making this text a practical starting point either for the beginner in the field or an experienced clinician trying to make sense out of the IgG glycomic or glycoproteomic dataset.

A Peptide Targeting Inflammatory CNS Lesions in the EAE Rat Model of Multiple Sclerosis

Multiple sclerosis is characterized by inflammatory lesions dispersed throughout the central nervous system (CNS) leading to severe neurological handicap. Demyelination, axonal damage, and blood brain barrier alterations are hallmarks of this pathology, whose precise processes are not fully understood. In the experimental autoimmune encephalomyelitis (EAE) rat model that mimics many features of human multiple sclerosis, the phage display strategy was applied to select peptide ligands targeting inflammatory sites in CNS. Due to the large diversity of sequences after phage display selection, a bioinformatics procedure called "PepTeam" designed to identify peptides mimicking naturally occurring proteins was used, with the goal to predict peptides that were not background noise. We identified a circular peptide CLSTASNSC called "Ph48" as an efficient binder of inflammatory regions of EAE CNS sections including small inflammatory lesions of both white and gray matter. Tested on human brain endothelial cells hCMEC/D3, Ph48 was able to bind efficiently when these cells were activated with IL1β to mimic inflammatory conditions. The peptide is therefore a candidate for further analyses of the molecular alterations in inflammatory lesions.

A potential impact of Helicobacter pylori-related galectin-3 in neurodegeneration

Neurodegeneration represents a component of the central nervous system (CNS) diseases pathogenesis, either as a disability primary source in the frame of prototype neurodegenerative disorders, or as a secondary effect, following inflammation, hypoxia or neurotoxicity. Galectins are members of the lectin superfamily, a group of endogenous glycan-binding proteins, able to interact with glycosylated receptors expressed by several immune cell types. Glycan-lectin interactions play critical roles in the living systems by involving and mediating a variety of biologically important normal and pathological processes, including cell-cell signaling shaping cell communication, proliferation and migration, immune responses and fertilization, host-pathogen interactions and diseases such as neurodegenerative disorders and tumors. This review focuses in the role of Galectin-3 in shaping responses of the immune system against microbial agents, and concretely, Helicobacter pylori (Hp), thereby potentiating effect of the microbe in areas distant from the ordinary site of colonization, like the CNS. We hereby postulate that gastrointestinal Hp alterations in terms of immune cell functional phenotype, cytokine and chemokine secretion, may trigger systemic responses, thereby conferring implications for remote processes susceptible in immunity disequilibrium, namely, the CNS inflammation and/or neurodegeneration.

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.

Building a PGC-LC-MS N-glycan retention library and elution mapping resource

Porous graphitised carbon-liquid chromatography (PGC-LC) has been proven to be a powerful technique for the analysis and characterisation of complex mixtures of isomeric and isobaric glycan structures. Here we evaluate the elution behaviour of N-glycans on PGC-LC and thereby provide the potential of using chromatographic separation properties, together with mass spectrometry (MS) fragmentation, to determine glycan structure assignments more easily. We used previously reported N-glycan structures released from the purified glycoproteins Immunoglobulin G (IgG), Immunoglobulin A (IgA), lactoferrin, α1-acid glycoprotein, Ribonuclease B (RNase B), fetuin and ovalbumin to profile their behaviour on capillary PGC-LC-MS. Over 100 glycan structures were determined by MS/MS, and together with targeted exoglycosidase digestions, created a N-glycan PGC retention library covering a full spectrum of biologically significant N-glycans from pauci mannose to sialylated tetra-antennary classes. The resultant PGC retention library ( http://www.glycostore.org/showPgc ) incorporates retention times and supporting fragmentation spectra including exoglycosidase digestion products, and provides detailed knowledge on the elution properties of N-glycans by PGC-LC. Consequently, this platform should serve as a valuable resource for facilitating the detailed analysis of the glycosylation of both purified recombinant, and complex mixtures of, glycoproteins using established workflows.

Resolution of Cochlear Inflammation: Novel Target for Preventing or Ameliorating Drug-, Noise- and Age-related Hearing Loss

A significant number of studies support the idea that inflammatory responses are intimately associated with drug-, noise- and age-related hearing loss (DRHL, NRHL and ARHL). Consequently, several clinical strategies aimed at reducing auditory dysfunction by preventing inflammation are currently under intense scrutiny. Inflammation, however, is a normal adaptive response aimed at restoring tissue functionality and homeostasis after infection, tissue injury and even stress under sterile conditions, and suppressing it could have unintended negative consequences. Therefore, an appropriate approach to prevent or ameliorate DRHL, NRHL and ARHL should involve improving the resolution of the inflammatory process in the cochlea rather than inhibiting this phenomenon. The resolution of inflammation is not a passive response but rather an active, highly controlled and coordinated process. Inflammation by itself produces specialized pro-resolving mediators with critical functions, including essential fatty acid derivatives (lipoxins, resolvins, protectins and maresins), proteins and peptides such as annexin A1 and galectins, purines (adenosine), gaseous mediators (NO, H₂S and CO), as well as neuromodulators like acetylcholine and netrin-1. In this review article, we describe recent advances in the understanding of the resolution phase of inflammation and highlight therapeutic strategies that might be useful in preventing inflammation-induced cochlear damage. In particular, we emphasize beneficial approaches that have been tested in pre-clinical models of inflammatory responses induced by recognized ototoxic drugs such as cisplatin and aminoglycoside antibiotics. Since these studies suggest that improving the resolution process could be useful for the prevention of inflammation-associated diseases in humans, we discuss the potential application of similar strategies to prevent or mitigate DRHL, NRHL and ARHL.

Galectin-1 circumvents lysolecithin-induced demyelination through the modulation of microglial polarization/phagocytosis and oligodendroglial differentiation

Galectin-1 (Gal-1), a member of a highly conserved family of animal lectins, binds to the common disaccharide [Galβ(1-4)-GlcNAc] on both N- and O-glycans decorating cell surface glycoconjugates. Current evidence supports a role for Gal-1 in the pathophysiology of multiple sclerosis (MS), one of the most prevalent chronic inflammatory diseases. Previous studies showed that Gal-1 exerts neuroprotective effects by promoting microglial deactivation in a model of autoimmune neuroinflammation and induces axonal regeneration in spinal cord injury. Seeking a model that could link demyelination, oligodendrocyte (OLG) responses and microglial activation, here we used a lysolecithin (LPC)-induced demyelination model to evaluate the ability of Gal-1 to preserve myelin without taking part in T-cell modulation. Gal-1 treatment after LPC-induced demyelination promoted a significant decrease in the demyelinated area and fostered more efficient remyelination, concomitantly with an attenuated oligodendroglial progenitor response reflecting less severe myelination damage. These results were accompanied by a decrease in the area of microglial activation with a shift toward an M2-polarized microglial phenotype and diminished astroglial activation. In vitro studies further showed that, mechanistically, Gal-1 targets activated microglia, promoting an increase in their myelin phagocytic capacity and their shift toward an M2 phenotype, and leads to oligodendroglial differentiation. Therefore, this study supports the use of Gal-1 as a potential treatment for demyelinating diseases such as MS.

Ligand-mediated Galectin-1 endocytosis prevents intraneural H2O2 production promoting F-actin dynamics reactivation and axonal re-growth

Axonal growth cone collapse following spinal cord injury (SCI) is promoted by semaphorin3A (Sema3A) signaling via PlexinA4 surface receptor. This interaction triggers intracellular signaling events leading to increased hydrogen peroxide levels which in turn promote filamentous actin (F-actin) destabilization and subsequent inhibition of axonal re-growth. In the current study, we demonstrated that treatment with galectin-1 (Gal-1), in its dimeric form, promotes a decrease in hydrogen peroxide (H2O2) levels and F-actin repolimerization in the growth cone and in the filopodium of neuron surfaces. This effect was dependent on the carbohydrate recognition activity of Gal-1, as it was prevented using a Gal-1 mutant lacking carbohydrate-binding activity. Furthermore, Gal-1 promoted its own active ligand-mediated endocytosis together with the PlexinA4 receptor, through mechanisms involving complex branched N-glycans. In summary, our results suggest that Gal-1, mainly in its dimeric form, promotes re-activation of actin cytoskeleton dynamics via internalization of the PlexinA4/Gal-1 complex. This mechanism could explain, at least in part, critical events in axonal regeneration including the full axonal re-growth process, de novo formation of synapse clustering, axonal re-myelination and functional recovery of coordinated locomotor activities in an in vivo acute and chronic SCI model.

SIGNIFICANCE STATEMENT

Axonal regeneration is a response of injured nerve cells critical for nerve repair in human spinal cord injury. Understanding the molecular mechanisms controlling nerve repair by Galectin-1, may be critical for therapeutic intervention. Our results show that Galectin-1; in its dimeric form, interferes with hydrogen peroxide production triggered by Semaphorin3A. The high levels of this reactive oxygen species (ROS) seem to be the main factor preventing axonal regeneration due to promotion of actin depolymerization at the axonal growth cone. Thus, Galectin-1 administration emerges as a novel therapeutic modality for promoting nerve repair and preventing axonal loss.

Re-wiring regulatory cell networks in immunity by galectin-glycan interactions

Programs that control immune cell homeostasis are orchestrated through the coordinated action of a number of regulatory cell populations, including regulatory T cells, regulatory B cells, myeloid-derived suppressor cells, alternatively-activated macrophages and tolerogenic dendritic cells. These regulatory cell populations can prevent harmful inflammation following completion of protective responses and thwart the development of autoimmune pathology. However, they also have a detrimental role in cancer by favoring escape from immune surveillance. One of the hallmarks of regulatory cells is their remarkable plasticity as they can be positively or negatively modulated by a plethora of cytokines, growth factors and co-stimulatory signals that tailor their differentiation, stability and survival. Here we focus on the emerging roles of galectins, a family of highly conserved glycan-binding proteins in regulating the fate and function of regulatory immune cell populations, both of lymphoid and myeloid origins. Given the broad distribution of circulating and tissue-specific galectins, understanding the relevance of lectin-glycan interactions in shaping regulatory cell compartments will contribute to the design of novel therapeutic strategies aimed at modulating their function in a broad range of immunological disorders.

Sugar recognition: designing artificial receptors for applications in biological diagnostics and imaging

At the cellular level, numerous processes ranging from protein folding to disease development are mediated by a sugar-based molecular information system that is much less well known than its DNA- or protein-based counterparts. The subtle structural diversity of such sugar tags nevertheless offers an excellent, if challenging, opportunity to design receptors for the selective recognition of biorelevant sugars. Over the past 40 years, growing interest in the field of sugar recognition has led to the development of several promising artificial receptors, which could soon find widespread use in medical diagnostics and cell imaging.