Macrophage Galactose-type Lectin Research Articles

Targeted and Self-Adjuvated Nanoglycovaccine Candidate for Cancer Immunotherapy.

Advanced-stage solid primary tumors and metastases often express mucin 16 (MUC16), carrying immature glycans such as the Tn antigen, resulting in specific glycoproteoforms not found in healthy human tissues. This presents a valuable approach for designing targeted therapeutics, including cancer glycovaccines, which could potentially promote antigen recognition and foster the immune response to control disease spread and prevent relapse. In this study, we describe an adjuvant-free poly(lactic-co-glycolic acid) (PLGA)-based nanoglycoantigen delivery approach that outperforms conventional methods by eliminating the need for protein carriers while exhibiting targeted and adjuvant properties. To achieve this, we synthesized a library of MUC16-Tn glycoepitopes through single-pot enzymatic glycosylation, which were then stably engrafted onto the surface of PLGA nanoparticles, generating multivalent constructs that better represent cancer molecular heterogeneity. These glycoconstructs demonstrated affinity for Macrophage Galactose-type Lectin (MGL) receptor, known to be highly expressed by immature antigen-presenting cells, enabling precise targeting of immune cells. Moreover, the glycopeptide-grafted nanovaccine candidate displayed minimal cytotoxicity and induced the activation of dendritic cells in vitro, even in the absence of an adjuvant. In vivo, the formulated nanovaccine candidate was also nontoxic and elicited the production of IgG specifically targeting MUC16 and MUC16-Tn glycoproteoforms in cancer cells and tumors, offering potential for precise cancer targeting, including targeted immunotherapies.

Abstract 5361: Aberrant glycosylation in mPDAC is associated with increased epithelial-mesenchymal transition and recruitment of immunosuppressive cells

Abstract The tumor-associated glycan Tn antigen (GalNAc-α-O-Ser/Thr) is associated with poor prognosis in various solid tumors. However, the mechanisms that Tn antigen promotes tumorigenesis are incompletely understood. Here, we generated Tn antigen-expressing murine pancreatic ductal adenocarcinoma (mPDAC) tumor cell lines through CRISPR/Cas9-mediated knockout of the C1galt1c1 gene. Tn antigen expressing mPDAC cell lines exhibited increased in vitro proliferation and migration compared to parental controls. RNA sequencing revealed that loss of C1galt1c1 in mPDAC cells correlated with increased expression of genes associated with epithelial-mesenchymal transition, myeloid recruitment, and extracellular matrix deposition. Consequently, knock-down of elevated genes using CRISPR interference dampened in vitro cell proliferation of C1galt1c1 knockout mPDAC cells to the growth rate of parental controls. Additionally, C1galt1c1 knockout mPDAC cells implanted into mice led to accelerated tumor growth and increased tumor infiltration of myeloid-derived suppressor cells and neutrophils as determined by flow cytometry and scRNAseq. Interestingly, surface expression of a binding partner of Tn antigen, macrophage galactose-type lectin 2 (Mgl2), was altered in the immune infiltrate of C1galt1c1 knockout tumors suggesting a role for the Mgl2-Tn interaction in tumor progression. Mgl2-deficient mice exhibit increased T effector cells in the draining lymph nodes of tumors highlighting a potential mechanism for promoting the influx of immune cells in ordinarily cold tumors. Together, our data indicate that truncated O-glycans expressed commonly on tumor cells promotes tumorigenesis through creating an immunosuppressive microenvironment in mPDAC. Citation Format: Shawna Brookens, David Degaramo, Kiesha Wilson, Wilder Condori Obregon, Prakash Nagarkatti, Mitzi Nagarkatti, Avery Posey Jr.. Aberrant glycosylation in mPDAC is associated with increased epithelial-mesenchymal transition and recruitment of immunosuppressive cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5361.

The unique 3D arrangement of macrophage galactose lectin enables Escherichia coli lipopolysaccharide recognition through two distinct interfaces.

Lipopolysaccharides are a hallmark of gram-negative bacteria, and their presence at the cell surface is key for bacterial integrity. As surface-exposed components, they are recognized by immunity C-type lectin receptors present on antigen-presenting cells. Human macrophage galactose lectin binds Escherichia coli surface that presents a specific glycan motif. Nevertheless, this high-affinity interaction occurs regardless of the integrity of its canonical calcium-dependent glycan-binding site. NMR of macrophage galactose-type lectin (MGL) carbohydrate recognition domain and complete extracellular domain revealed a glycan-binding site opposite to the canonical site. A model of trimeric macrophage galactose lectin was determined based on a combination of small-angle X-ray scattering and AlphaFold. A disulfide bond positions the carbohydrate recognition domain perpendicular to the coiled-coil domain. This unique configuration for a C-type lectin orients the six glycan sites of MGL in an ideal position to bind lipopolysaccharides at the bacterial surface with high avidity.

The direct and gut microbiota-mediated effects of dietary bile acids on the improvement of gut barriers in largemouth bass (Micropterus salmoides).

Fish gut barrier damage under intensive culture model is a significant concern for aquaculture industry. This study aimed to investigate the effects of bile acids (BAs) on gut barriers in Micropterus salmoides. A germ-free (GF) zebrafish model was employed to elucidate the effects of the direct stimulation of BAs and the indirect regulations mediated by the gut microbiota on gut barrier functions. Four diets were formulated with BAs supplemented at 0, 150, 300 and 450mg/kg, and these 4 diets were defined as control, BA150, BA300 and BA450, respectively. After 5 weeks of feeding experiment, the survival rate of fish fed with BA300 diet was increased (P<0.05). Histological analysis revealed an improvement of gut structural integrity in the BA150 and BA300 groups. Compared with the control group, the expression of genes related to chemical barrier (mucin, lysozyme and complement 1) and physical barrier (occludin and claudin-4) was increased in the BA150 and BA300 groups (P<0.05), and the expression of genes related to immunological barrier (interleukin [IL]-6, tumor growth factor β, IL-10, macrophage galactose-type lectin and immunoglobulin M [IgM]) was significantly increased in the BA300 group (P<0.05), but the expression of genes related to chemical barrier (hepcidin) and immunological barrier (IL-1β, tumor necrosis factor-α, IL-6 and arginase) was significantly decreased in the BA450 group (P<0.05). Gut microbiota composition analysis revealed that the abundance of Firmicutes was augmented prominently in the BA150 and BA300 groups (P<0.05), while that of Actinobacteriota and Proteobacteria showed a downward trend in the BA150 and BA300 groups (P>0.05). The results of the gut microbiota transferring experiment demonstrated an upregulation of gut barrier-related genes, including immunoglobulin Z/T (IgZ/T), IL-6, IL-1β and IL-10, by the gut microbiota transferred from the BA300 group compared with the control (P<0.05). Feeding the BA300 diet directly to GF zebrafish resulted in enhanced expression of IgM, IgZ/T, lysozyme, occludin-2, IL-6 and IL-10 (P<0.05). In conclusion, BAs can improve the gut barriers of fish through both direct and indirect effects mediated by the gut microbiota.

C1GalT1 expression reciprocally controls tumour cell-cell and tumour-macrophage interactions mediated by galectin-3 and MGL with double impact on cancer development and progression

Although most cell membrane proteins are modified by glycosylation, our understanding of the role and actions of protein glycosylation is still very limited. β1,3galactosyltransferase (C1GalT1) is a key glycosyltransferase that controls the biosynthesis of the Core 1 structure of O-linked mucin type glycans and is overexpressed by many common types of epithelial cancers. This study reports that suppression of C1GalT1 expression in human colon cancer cells caused substantial changes of protein glycosylation of cell membrane proteins, many of which were ligands of the galactoside-binding galectin-3 and the macrophage galactose-type lectin (MGL). This led to significant reduction of cancer cell proliferation, adhesion, migration and the ability of tumour cells to form colonies. Crucially, C1GalT1 suppression significantly reduced galectin-3-mediated tumour cell-cell interaction and galectin-3-promoted tumour cell activities. In the meantime, C1GalT1 suppression substantially increased MGL-mediated macrophage-tumour cell interaction and macrophage-tumour cell phagocytosis and cytokine secretion. C1GalT1-expressing cancer cells implanted in chick embryos resulted in the formation of significantly bigger tumours than C1GalT1-suppressed cells and the presence of galectin-3 increased tumour growth of C1GalT1-expressing but not C1GalT1-suppressed cells. More MGL-expressing macrophages and dendritic cells were seen to be attracted to the tumour microenvironment in ME C1galt1-/-/Erb mice than in C1galt1f/f /Erb mice. These results indicate that expression of C1GalT1 by tumour cells reciprocally controls tumour cell-cell and tumour-macrophage interactions mediated by galectin-3 and MGL with double impact on cancer development and progression. C1GalT1 overexpression in epithelial cancers therefore may represent a fundamental mechanism in cancer promotion and in reduction of immune response/surveillance in cancer progression.

MUC1 Glycopeptide Vaccine Modified with a GalNAc Glycocluster Targets the Macrophage Galactose C-type Lectin on Dendritic Cells to Elicit an Improved Humoral Response.

Mucin expression and glycosylation patterns on cancer cells differ markedly from healthy cells. Mucin 1 (MUC1) is overexpressed in several solid tumors and presents high levels of aberrant, truncated O-glycans (e.g., Tn antigen). Dendritic cells (DCs) express lectins that bind to these tumor-associated carbohydrate antigens (TACAs) to modulate immune responses. Selectively targeting these receptors with synthetic TACAs is a promising strategy to develop anticancer vaccines and to overcome TACA tolerance. In this work, we prepared, via a solid phase peptide synthesis approach, a modular tripartite vaccine candidate, incorporating a high-affinity glycocluster based on a tetraphenylethylene scaffold, to target the macrophage galactose-type lectin (MGL) on antigen presenting cells. MGL is a C-type lectin receptor that binds Tn antigens and can route them to human leukocyte antigen class II or I, making it an attractive target for anticancer vaccines. Conjugation of the glycocluster to a library of MUC1 glycopeptides bearing the Tn antigen is shown to promote uptake and recognition of the TACA by DCs via MGL. In vivo testing revealed that immunization with the newly designed vaccine construct bearing the GalNAc glycocluster induced a higher titer of anti-Tn-MUC1 antibodies compared to the TACAs alone. Additionally, the antibodies obtained bind a library of tumor-associated saccharide structures on MUC1 and MUC1-positive breast cancer cells. Conjugation of a high-affinity ligand for MGL to tumor-associated MUC1 glycopeptide antigens has a synergistic impact on antibody production.

Macrophage plasticity and activation states drive differential expression of murine macrophage galactose-type lectin (MGL) orthologs

Abstract Macrophage plasticity and functional activation are critical to the broad array of macrophage-mediated functions that help determine disease outcomes. Macrophage galactose-type lectin (MGL), a type-2 C-type lectin receptor (CLR) primarily expressed on myeloid cells, has been shown to play an anti-inflammatory role in the innate response to some infectious agents. Our lab recently demonstrated that MGL-1 contributes an antimicrobial and anti-inflammatory role in a murine model of experimental tuberculosis. We further observe that MGL-1 and MGL-2 expression by RAW 264.7 macrophages are similarly activated by whole mycobacteria, but differentially regulated by signaling through toll-like receptors (TLR) as well as cytokine and glucocorticoid receptors. We find that synthetic agonists and microbial ligands of TLR2, TLR4, and TLR7 positively regulate MGL-2 expression, suggesting responsiveness to a broad repertoire of antigens compared to MGL-1. Additionally, activation of MGL-2 expression differs between ligands of multiple bacterial species, both pathogenic and non-pathogenic. Pathway inhibition experiments show that MGL-2 upregulation by microbial stimuli occurs through MyD88-dependent Toll-like receptor (TLR) signaling. Although both MGL-1 and MGL-2 are classically associated with alternatively activated macrophages, we show that MGL-2 expression is associated with both M1 and M2 polarized macrophages, while MGL-1 expression is restricted to M2. These results demonstrate a strong relationship between macrophage activation states and the differential activation of MGL signaling and indicate non-redundant roles of MGL-1 and MGL-2 in innate immunity of murine models of disease. Supported by grants from NIH, NIAID (R61 AI138328, R33 AI138328)

C-type lectin receptor dysregulation in HIV and Mycobacterium tuberculosisco-infection

Abstract Infection with Mycobacterium tuberculosis (Mtb) is a serious and potentially life-threatening condition, especially in people with HIV (PWH). According to the WHO, there were 10.6 million new tuberculosis (TB) cases in 2021, and 700,000 of those cases were among PWH. Macrophages are a host cell for both pathogens and play an important innate immune role in determining the outcome of disease. C-type lectin receptors (CLR) are pattern recognition receptors (PRR) abundantly expressed on the macrophage surface that orchestrate the innate immune response to microbial insults. We previously identified a role for the macrophage galactose-type lectin receptor (MGL) CLR in protection against TB. In subsequent studies, we observed suppression of MGL in tissues of HIV-infected decedents and in human macrophages following in vitro infection with HIV. In human THP-1 cells and a humanized mouse model, we observe that HIV infection markedly impairs activation of MGL by mycobacteria in comparison to other CLRs with defined roles in antimycobacterial immunity including DC-SIGN and Dectin 1. We further determine roles for TLR2/6 heterodimer, TLR4, and TGF-β signaling pathways for transcriptional regulation of MGL. Importantly, these pathways have roles in innate immunity and pathogenesis following Mtb or HIV infections. These findings advance our understanding of MGL regulation as part of the CLR repertoire, as well as its role in the response to Mtb and to Mtb/HIV co-infection. NIH R31AI138328, R61AI138328

Enantioselective Degrader for Elimination of Extracellular Aggregation-Prone Proteins hIAPP Associated with Type 2 Diabetes.

Targeted protein degradation has demonstrated the power to modulate protein homeostasis. For overcoming the limitation to intracellular protein degradation, lysosome targeting chimeras have been recently developed and successfully utilized to degrade a range of disease-relevant extracellular and membrane proteins. Inspired by this strategy, here we describe our proof-of-concept studies using metallohelix-based degraders to deliver the extracellular human islet amyloid polypeptide (hIAPP) into the lysosomes for degradation. Our designed metallohelix can bind and inhibit hIAPP aggregation, and the conjugated tri-GalNAc motif can target macrophage galactose-type lectin 1 (MGL1), yielding chimeric molecules that can both inhibit hIAPP aggregation and direct the bound hIAPP for lysosomal degradation in macrophages. Further studies demonstrate that the enhanced hIAPP clearance has been through the endolysosomal system and depends on MGL1-mediated endocytosis. Intriguingly, Λ enantiomers show even better efficiency in preventing hIAPP aggregation and promoting internalization and degradation of hIAPP than Δ enantiomers. Moreover, metallohelix-based degraders also faciltate the clearance of hIAPP through asialoglycoprotein receptor in liver cells. Overall, our studies demonstrate that chiral metallohelix can be employed for targeted degradation of extracellular misfolded proteins and possess enantioselectivity.

Life stage-specific glycosylation of extracellular vesicles from Schistosoma mansoni schistosomula and adult worms drives differential interaction with C-type lectin receptors DC-SIGN and MGL.

Schistosomes can survive in mammalian hosts for many years, and this is facilitated by released parasite products that modulate the host's immune system. Many of these products are glycosylated and interact with host cells via C-type lectin receptors (CLRs). We previously reported on specific fucose-containing glycans present on extracellular vesicles (EVs) released by schistosomula, the early juvenile life stage of the schistosome, and the interaction of these EVs with the C-type lectin receptor Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin (DC-SIGN or CD209). EVs are membrane vesicles with a size range between 30-1,000nm that play a role in intercellular and interspecies communication. Here, we studied the glycosylation of EVs released by the adult schistosome worms. Mass spectrometric analysis showed that GalNAcβ1-4GlcNAc (LacDiNAc or LDN) containing N-glycans were the dominant glycan type present on adult worm EVs. Using glycan-specific antibodies, we confirmed that EVs from adult worms were predominantly associated with LDN, while schistosomula EVs displayed a highly fucosylated glycan profile. In contrast to schistosomula EV that bind to DC-SIGN, adult worm EVs are recognized by macrophage galactose-type lectin (MGL or CD301), and not by DC-SIGN, on CLR expressing cell lines. The different glycosylation profiles of adult worm- and schistosomula-derived EVs match with the characteristic glycan profiles of the corresponding life stages and support their distinct roles in schistosome life-stage specific interactions with the host.

Defects in macrophage galactose-type lectin (MGL) signaling and pathogenesis of Mycobacterium tuberculosis and Human Immunodeficiency virus co-infection

Abstract Mycobacterium tuberculosis (Mtb) and Human Immunodeficiency virus (HIV) are important causes of death in infected patients worldwide, and act synergistically to worsen disease in those with co-infection. C-type lectin receptors (CLRs) are an important component of innate immunity that can recognize and respond to pathogen-associated signals. The macrophage galactose-type lectin (MGL, CLEC10) has been described as an immunomodulatory CLR associated with M2 macrophages and regulation of inflammation following infection. Our lab previously identified an important antibacterial role of murine MGL-1 in host immunity to Mtb. More recently we observed that human peripheral blood mononuclear cell-derived macrophages, and THP-1 cells, upregulated MGL following in vitro exposure to Mtb, Mycobacterium bovis BCG, and TLR2 agonists. Silencing of MGL in primary human macrophages permitted greater intracellular Mtb replication. Interestingly, we observed that MGL is suppressed by HIV in differential transcriptome analysis of lung from HIV-infected humanized mice, in lung and spleen of autopsy specimens from HIV-infected decedents, and upon in vitro infection of human macrophages. Using a recombinant human MGL/Fc chimeric molecule we observed that Mtb, and not HIV, directly bound MGL. MGL surface expression was reduced in lung of mice with chronic HIV infection compared to those with Mtb, and variable in co-infected animals. These results indicate that human MGL is an important CLR for pathogen recognition and initiation of protective immunity by host macrophages to Mtb. The suppression of MGL due to HIV may increase susceptibility to Mtb in people with HIV or exacerbate disease progression in those with co-infection. Supported by grants from NIH (R33 AI138328, R61 AI138328, U24 MH100930)

C-type lectin receptor MGL-1 in SARS-CoV-2 disease pathogenesis

Abstract Pattern recognition receptors, such as the C-type lectin receptor (CLR) family, play an important role in the generation of the innate immune response against a variety of pathogens. The CLR Macrophage galactose-type lectin (MGL), also known as CLEC10, is one member of this family which we and others found can bind SARS-CoV-2. MGL is known to increase in expression during SARS-CoV-2 infection and, in concert with other CLRs, is associated with elevated proinflammatory immune responses. Dexamethasone, a clinical treatment commonly used to mitigate the hyperinflammatory response in individuals with COVID-19, is also a positive stimulus for MGL expression. We therefore sought to investigate the role of MGL in disease pathogenesis using MGL-1 receptor deficient mice. Mice were intranasally infected with mouse adapted SARS-CoV-2 strain CMA3p20 and euthanized 3- or 7-days post infection. Following acute infection at 3 days, MGL-1 deficiency did not affect the viral burden in the lungs of mice. This was supported by multiplex cytokine and chemokine data which revealed similar acute inflammatory responses in the lung of infected WT and MGL-1 knockout (KO) mice. Interestingly, MGL-1 KO mice did display a significant increase in the lung viral burden when compared to WT mice 7 days post-infection. These results suggest a role for MGL-1 in resolution of SARS-CoV-2 at later stages of infection. Further investigations to determine differences in cellular recruitment and lung pathology in the absence of MGL-1 are warranted. In addition, assessment of a role for the MGL-2 orthologue expressed by murine myeloid cells may identify roles for MGL pathways in SARS-CoV-2 disease severity and pathogenesis. Supported by UTMB Institute for Human Infection and Immunity COVID-19 Pilot Grant

Differential regulation of macrophage galactose-type lectin (MGL) orthologs by mycobacterial ligands

Abstract Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is responsible for approximately 10 million new infections and 1.5 million deaths each year. Pattern recognition receptors (PRRs) expressed on the surface of macrophages play an important role in orchestrating the immune response to pathogens. Amongst these, the C-type lectin receptors (CLRs) are an important PRR system that is increasingly understood to mediate innate immunity to mycobacteria. We recently described a new anti-bacterial and anti-inflammatory role for the macrophage galactose-type lectin-1 (MGL-1) in a murine model of experimental TB. MGL is a type II CLR that is known to recognize galactose and N-acetylgalactosamine monosaccharides. We observed that exposure to Mtb activated expression of both murine MGL orthologues, MGL-1 and MGL-2. The specific pathogen-associated molecular patterns that activate MGL orthologue transcription, however, have yet to be determined. Here we demonstrate that expression of MGL-1 and MGL-2 are differentially regulated by cytokines, TLR agonists, and mycobacterial ligands. MGL-1 expression is activated by dexamethasone, IL-4, IL-10, and the mycobacterial cell wall glycolipid Trehalose 6,6′-dimycolate. In contrast, MGL-2 expression is activated by TLR2/6 and TLR2/1 agonists and total lipid extracts of mycobacteria. Use of a MyD88 inhibitor further showed that molecular regulation of MGL-1 and MGL-2 transcription, following exposure of macrophages to mycobacteria, is TLR pathway-dependent. These results identify overlapping and unique host immune pathways that differentially activate MGL orthologues following exposure to Mtb and could be targeted through immune modulation.

The Tn antigen promotes lung tumor growth by fostering immunosuppression and angiogenesis via interaction with Macrophage Galactose-type lectin 2 (MGL2).

Tn is a tumor-associated carbohydrate antigen that constitutes both a diagnostic tool and an immunotherapeutic target. It originates from interruption of the mucin O-glycosylation pathway through defects involving, at least in part, alterations in core-1 synthase activity, which is highly dependent on Cosmc, a folding chaperone. Tn antigen is recognized by the Macrophage Galactose-type Lectin (MGL), a C-type lectin receptor present on dendritic cells and macrophages. Specific interactions between Tn and MGL shape anti-tumoral immune responses by regulating several innate and adaptive immune cell programs. In this work, we generated and characterized a variant of the lung cancer murine cell line LL/2 that expresses Tn by mutation of the Cosmc chaperone gene (Tn+ LL/2). We confirmed Tn expression by lectin glycophenotyping and specific anti-Tn antibodies, verified abrogation of T-synthase activity in these cells, and confirmed its recognition by the murine MGL2 receptor. Interestingly, Tn+ LL/2cells were more aggressive in vivo, resulting in larger and highly vascularized tumors than those generated from wild type Tn- LL/2cells. In addition, Tn+ tumors exhibited an increase in CD11c+ F4/80+ cells with high expression of MGL2, together with an augmented expression of IL-10 in infiltrating CD4+ and CD8+ T cells. Importantly, this immunosuppressive microenvironment was dependent on the presence of MGL2+ cells, since depletion of these cells abrogated tumor growth, vascularization and recruitment of IL-10+ T cells. Altogether, our results suggest that expression of Tn in tumor cells and its interaction with MGL2-expressing CD11c+F4/80+ cells promote immunosuppression and angiogenesis, thus favoring tumor progression.

Novel Role for Macrophage Galactose-Type Lectin-1 to Regulate Innate Immunity againstMycobacterium tuberculosis

Tuberculosis (TB) caused by infection with Mycobacterium tuberculosis is characterized by inflammatory pathology and poorly understood mechanisms of innate immunity. Pattern recognition receptors, expressed on the surface of macrophages, determine the balance of inflammatory and antimicrobial functions that influence disease outcome. Carbohydrate moieties displayed by mycobacteria can serve as pattern recognition receptor ligands for some members of the C-type lectin receptor (CLR) family, interactions that mediate a variety of incompletely understood immune outcomes. This work identifies a novel role for the CLR macrophage galactose-type lectin (MGL)-1 in a mouse model (C57BL/6 and MGL-1-/-) of experimental TB. Murine macrophages upregulated MGL-1 following in vitro exposure to M. tuberculosis, whereas MGL+ cells accumulated at sites of mycobacteria-driven inflammation in the lung. Pulmonary macrophages from MGL-1-deficient mice displayed increased production of proinflammatory cytokines (IL-1β, IL-6, and IFN-γ) that were associated with greater lipid accumulation, following M. tuberculosis infection. Surprisingly, for a CLR, we also observed MGL-1-dependent antimycobacterial activity as evidenced by greater M. tuberculosis proliferation in bone marrow-derived macrophages, and the lung, of MGL-1-deficient mice. Differential transcriptome analysis further revealed that loss of MGL-1 perturbs the activation of various genes involved in the regulation of inflammation and lipid metabolism in the setting of M. tuberculosis infection. These results identify MGL-1 signaling as an important mechanism that regulates innate immunity against M. tuberculosis and indicates the potential for the MGL pathway as a novel therapeutic target for anti-TB immunity.

Calorimetric Analysis of the Interplay between Synthetic Tn Antigen-Presenting MUC1 Glycopeptides and Human Macrophage Galactose-Type Lectin.

Human macrophage galactose-type lectin (hMGL, HML, CD301, CLEC10A), a C-type lectin expressed by dendritic cells and macrophages, is a receptor for N-acetylgalactosamine α-linked to serine/threonine residues (Tn antigen, CD175) and its α2,6-sialylated derivative (sTn, CD175s). Because these two epitopes are among malignant cell glycan displays, particularly when presented by mucin-1 (MUC1), assessing the influence of the site and frequency of glycosylation on lectin recognition will identify determinants governing this interplay. Thus, chemical synthesis of the tandem-repeat O-glycan acceptor region of MUC1 and site-specific threonine glycosylation in all permutations were carried out. Isothermal titration calorimetry (ITC) analysis of the binding of hMGL to this library of MUC1 glycopeptides revealed an enthalpy-driven process and an affinity enhancement of an order of magnitude with an increasing glycan count from 6–8 μM for monoglycosylated peptides to 0.6 μM for triglycosylated peptide. ITC measurements performed in D2O permitted further exploration of the solvation dynamics during binding. A shift in enthalpy–entropy compensation and contact position-specific effects with the likely involvement of the peptide surroundings were detected. KinITC analysis revealed a prolonged lifetime of the lectin–glycan complex with increasing glycan valency and with a change in the solvent to D2O.

Fluorinated Carbohydrates as Lectin Ligands: Simultaneous Screening of a Monosaccharide Library and Chemical Mapping by 19F NMR Spectroscopy.

Molecular recognition of carbohydrates is a key step in essential biological processes. Carbohydrate receptors can distinguish monosaccharides even if they only differ in a single aspect of the orientation of the hydroxyl groups or harbor subtle chemical modifications. Hydroxyl-by-fluorine substitution has proven its merits for chemically mapping the importance of hydroxyl groups in carbohydrate–receptor interactions. 19F NMR spectroscopy could thus be adapted to allow contact mapping together with screening in compound mixtures. Using a library of fluorinated glucose (Glc), mannose (Man), and galactose (Gal) derived by systematically exchanging every hydroxyl group by a fluorine atom, we developed a strategy combining chemical mapping and 19F NMR T2 filtering-based screening. By testing this strategy on the proof-of-principle level with a library of 13 fluorinated monosaccharides to a set of three carbohydrate receptors of diverse origin, i.e. the human macrophage galactose-type lectin, a plant lectin, Pisum sativum agglutinin, and the bacterial Gal-/Glc-binding protein from Escherichia coli, it became possible to simultaneously define their monosaccharide selectivity and identify the essential hydroxyls for interaction.

ASGR1 and Its Enigmatic Relative, CLEC10A.

The large family of C-type lectin (CLEC) receptors comprises carbohydrate-binding proteins that require Ca2+ to bind a ligand. The prototypic receptor is the asialoglycoprotein receptor-1 (ASGR1, CLEC4H1) that is expressed primarily by hepatocytes. The early work on ASGR1, which is highly specific for N-acetylgalactosamine (GalNAc), established the foundation for understanding the overall function of CLEC receptors. Cells of the immune system generally express more than one CLEC receptor that serve diverse functions such as pathogen-recognition, initiation of cellular signaling, cellular adhesion, glycoprotein turnover, inflammation and immune responses. The receptor CLEC10A (C-type lectin domain family 10 member A, CD301; also called the macrophage galactose-type lectin, MGL) contains a carbohydrate-recognition domain (CRD) that is homologous to the CRD of ASGR1, and thus, is also specific for GalNAc. CLEC10A is most highly expressed on immature DCs, monocyte-derived DCs, and alternatively activated macrophages (subtype M2a) as well as oocytes and progenitor cells at several stages of embryonic development. This receptor is involved in initiation of TH1, TH2, and TH17 immune responses and induction of tolerance in naïve T cells. Ligand-mediated endocytosis of CLEC receptors initiates a Ca2+ signal that interestingly has different outcomes depending on ligand properties, concentration, and frequency of administration. This review summarizes studies that have been carried out on these receptors.

Differential O- and Glycosphingolipid Glycosylation in Human Pancreatic Adenocarcinoma Cells With Opposite Morphology and Metastatic Behavior.

Changes in the glycosylation profile of cancer cells have been strongly associated with cancer progression. To increase our insights into the role of glycosylation in human pancreatic ductal adenocarcinoma (PDAC), we performed a study on O-glycans and glycosphingolipid (GSL) glycans of the PDAC cell lines Pa-Tu-8988T (PaTu-T) and Pa-Tu-8988S (PaTu-S). These cell lines are derived from the same patient, but show an almost opposite phenotype, morphology and capacity to metastasize, and may thus provide an attractive model to study the role of glycosylation in progression of PDAC. Gene-array analysis revealed that 24% of the glycosylation-related genes showed a ≥ 1.5-fold difference in expression level between the two cell lines. Subsequent validation of the data by porous graphitized carbon nano-liquid chromatography coupled to a tandem ion trap mass spectrometry and flow cytometry established major differences in O-glycans and GSL-glycans between the cell lines, including lower levels of T and sialylated Tn (sTn) antigens, neoexpression of globosides (Gb3 and Gb4), and higher levels of gangliosides in the mesenchymal-like PaTu-T cells compared to the epithelial-like PaTu-S. In addition, PaTu-S cells demonstrated a significantly higher binding of the immune-lectins macrophage galactose-type lectin and galectin-4 compared to PaTu-T. In summary, our data provide a comprehensive and differential glycan profile of two PDAC cell lines with disparate phenotypes and metastatic behavior. This will allow approaches to modulate and monitor the glycosylation of these PDAC cell lines, which opens up avenues to study the biology and metastatic behavior of PDAC.

Defects in the Macrophage Galactose-type Lectin Pathway due to HIV Infection

Abstract In the era of highly active antiretroviral therapy, HIV infection still produces 800,000 deaths and 1.2 million new infections per year. People living with HIV (PLWH) are vulnerable to several co-morbidities and co-infections, due to depletion of CD4+T cells and other incompletely characterized immune disturbances. To address the mechanisms involved, lung mRNAs from humanized mice co-infected with HIV and Mycobacterium tuberculosis (Mtb) were screened. Macrophage Galactose-type Lectin (MGL) was differentially regulated in co-infected animals. When MGL protein was quantified in biobanked frozen human lung specimens from 47 HIV-infected decedents, it was lower in the lung specimens with actively replicating HIV-1, as compared to those lacking detectable viral load. Lung MGL levels were negatively correlated with HIV RNA copies in the lung, and in the spleen, which is a key lymphoid organ that influences systemic immunity. Peripheral blood leukocytes from HIV infected patients showed that MGL activation was abnormal in those cells; comparable results were obtained in cultured HIV-infected macrophages. Molecular silencing of MGL in human monocyte-derived macrophages in vitro produced increased growth of Mtb, suggesting that lower MGL expression in PLWH could compromise their innate immunity to opportunistic pathogens such as Mtb. Macrophage MGL is a novel target to elucidate how HIV infection disrupts innate immunity and increases vulnerability to tuberculosis.