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Schmidt EN, Guo XY, Bui DT, Jung J, Klassen JS, Macauley MS. Dissecting the abilities of murine Siglecs to interact with gangliosides. J Biol Chem 2024; 300:107482. [PMID: 38897567 PMCID: PMC11294694 DOI: 10.1016/j.jbc.2024.107482] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2024] [Revised: 05/21/2024] [Accepted: 06/10/2024] [Indexed: 06/21/2024] Open
Abstract
Siglecs are cell surface receptors whose functions are tied to the binding of their sialoglycan ligands. Recently, we developed an optimized liposome formulation and used it to investigate the binding of human Siglecs (hSiglec) against a panel of gangliosides. Animal models, more specifically murine models, are used to understand human biology; however, species-specific differences can complicate the interpretation of the results. Herein, we used our optimized liposome formulation to dissect the interactions between murine Siglecs (mSiglecs) and gangliosides to assess the appropriateness of mSiglecs as a proxy to better understand the biological roles of hSiglec-ganglioside interactions. Using our optimized liposome formulation, we found that ganglioside binding is generally conserved between mice and humans with mSiglec-1, -E, -F, and -15 binding multiple gangliosides like their human counterparts. However, in contrast to the hSiglecs, we observed little to no binding between the mSiglecs and ganglioside GM1a. Detailed analysis of mSiglec-1 interacting with GM1a and its structural isomer, GM1b, suggests that mSiglec-1 preferentially binds α2-3-linked sialic acids presented from the terminal galactose residue. The ability of mSiglecs to interact or not interact with gangliosides, particularly GM1a, has implications for using mice to study neurodegenerative diseases, infections, and cancer, where interactions between Siglecs and glycolipids have been proposed to modulate these human diseases.
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Affiliation(s)
- Edward N Schmidt
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Xue Yan Guo
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Duong T Bui
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Jaesoo Jung
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada
| | - John S Klassen
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Matthew S Macauley
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada; Neuroscience and Mental Health Institute, University of Alberta, Edmonton, Alberta, Canada; Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada.
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2
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Wißfeld J, Abou Assale T, Cuevas-Rios G, Liao H, Neumann H. Therapeutic potential to target sialylation and SIGLECs in neurodegenerative and psychiatric diseases. Front Neurol 2024; 15:1330874. [PMID: 38529039 PMCID: PMC10961342 DOI: 10.3389/fneur.2024.1330874] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Accepted: 02/21/2024] [Indexed: 03/27/2024] Open
Abstract
Sialic acids, commonly found as the terminal carbohydrate on the glycocalyx of mammalian cells, are pivotal checkpoint inhibitors of the innate immune system, particularly within the central nervous system (CNS). Sialic acid-binding immunoglobulin-like lectins (SIGLECs) expressed on microglia are key players in maintaining microglial homeostasis by recognizing intact sialylation. The finely balanced sialic acid-SIGLEC system ensures the prevention of excessive and detrimental immune responses in the CNS. However, loss of sialylation and SIGLEC receptor dysfunctions contribute to several chronic CNS diseases. Genetic variants of SIGLEC3/CD33, SIGLEC11, and SIGLEC14 have been associated with neurodegenerative diseases such as Alzheimer's disease, while sialyltransferase ST8SIA2 and SIGLEC4/MAG have been linked to psychiatric diseases such as schizophrenia, bipolar disorders, and autism spectrum disorders. Consequently, immune-modulatory functions of polysialic acids and SIGLEC binding antibodies have been exploited experimentally in animal models of Alzheimer's disease and inflammation-induced CNS tissue damage, including retinal damage. While the potential of these therapeutic approaches is evident, only a few therapies to target either sialylation or SIGLEC receptors have been tested in patient clinical trials. Here, we provide an overview of the critical role played by the sialic acid-SIGLEC axis in shaping microglial activation and function within the context of neurodegeneration and synaptopathies and discuss the current landscape of therapies that target sialylation or SIGLECs.
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Affiliation(s)
- Jannis Wißfeld
- Institute of Reconstructive Neurobiology, Medical Faculty and University Hospital Bonn, University of Bonn, Bonn, Germany
| | - Tawfik Abou Assale
- Institute of Reconstructive Neurobiology, Medical Faculty and University Hospital Bonn, University of Bonn, Bonn, Germany
| | - German Cuevas-Rios
- Institute of Reconstructive Neurobiology, Medical Faculty and University Hospital Bonn, University of Bonn, Bonn, Germany
| | - Huan Liao
- Florey Institute of Neuroscience and Mental Health, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Parkville, VIC, Australia
| | - Harald Neumann
- Institute of Reconstructive Neurobiology, Medical Faculty and University Hospital Bonn, University of Bonn, Bonn, Germany
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3
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McCord K, Wang C, Anhalt M, Poon WW, Gavin AL, Wu P, Macauley MS. Dissecting the Ability of Siglecs To Antagonize Fcγ Receptors. ACS CENTRAL SCIENCE 2024; 10:315-330. [PMID: 38435516 PMCID: PMC10906256 DOI: 10.1021/acscentsci.3c00969] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/01/2023] [Revised: 12/19/2023] [Accepted: 12/21/2023] [Indexed: 03/05/2024]
Abstract
Fcγ receptors (FcγRs) play key roles in the effector function of IgG, but their inappropriate activation plays a role in several disease etiologies. Therefore, it is critical to better understand how FcγRs are regulated. Numerous studies suggest that sialic acid-binding immunoglobulin-type lectins (Siglecs), a family of immunomodulatory receptors, modulate FcγR activity; however, it is unclear of the circumstances in which Siglecs can antagonize FcγRs and which Siglecs have this ability. Using liposomes displaying selective ligands to coengage FcγRs with a specific Siglec, we explore the ability of Siglec-3, Siglec-5, Siglec-7, and Siglec-9 to antagonize signaling downstream of FcγRs. We demonstrate that Siglec-3 and Siglec-9 can fully inhibit FcγR activation in U937 cells when coengaged with FcγRs. Cells expressing Siglec mutants reveal differential roles for the immunomodulatory tyrosine-based inhibitory motif (ITIM) and immunomodulatory tyrosine-based switch motif (ITSM) in this inhibition. Imaging flow cytometry enabled visualization of SHP-1 recruitment to Siglec-3 in an ITIM-dependent manner, while SHP-2 recruitment is more ITSM-dependent. Conversely, both cytosolic motifs of Siglec-9 contribute to SHP-1/2 recruitment. Siglec-7 poorly antagonizes FcγR activation for two reasons: masking by cis ligands and differences in its ITIM and ITSM. A chimera of the Siglec-3 extracellular domains and Siglec-5 cytosolic tail strongly inhibits FcγR when coengaged, providing evidence that Siglec-5 is more like Siglec-3 and Siglec-9 in its ability to antagonize FcγRs. Additionally, Siglec-3 and Siglec-9 inhibited FcγRs when coengaged by cells displaying ligands for both the Siglec and FcγRs. These results suggest a role for Siglecs in mediating FcγR inhibition in the context of an immunological synapse, which has important relevance to the effectiveness of immunotherapies.
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Affiliation(s)
- Kelli
A. McCord
- Department
of Chemistry, University of Alberta, 11227 Saskatchewan Drive, Edmonton, Alberta T6G 2G2, Canada
| | - Chao Wang
- Department
of Molecular Medicine, Scripps Research
Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - Mirjam Anhalt
- Department
of Chemistry, University of Alberta, 11227 Saskatchewan Drive, Edmonton, Alberta T6G 2G2, Canada
| | - Wayne W. Poon
- Institute
for Memory Impairments and Neurological Disorders, University of California, Irvine, California 92617, United States
| | - Amanda L. Gavin
- Department
of Immunology and Microbiology, Scripps
Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - Peng Wu
- Department
of Molecular Medicine, Scripps Research
Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - Matthew S. Macauley
- Department
of Chemistry, University of Alberta, 11227 Saskatchewan Drive, Edmonton, Alberta T6G 2G2, Canada
- Department
of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
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4
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O'Sullivan JA, Youngblood BA, Schleimer RP, Bochner BS. Siglecs as potential targets of therapy in human mast cell- and/or eosinophil-associated diseases. Semin Immunol 2023; 69:101799. [PMID: 37413923 PMCID: PMC10528103 DOI: 10.1016/j.smim.2023.101799] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 07/08/2023]
Abstract
Siglecs (sialic acid-binding immunoglobulin-like lectins) are a family of vertebrate glycan-binding cell-surface proteins. The majority mediate cellular inhibitory activity once engaged by specific ligands or ligand-mimicking molecules. As a result, Siglec engagement is now of interest as a strategy to therapeutically dampen unwanted cellular responses. When considering allergic inflammation, human eosinophils and mast cells express overlapping but distinct patterns of Siglecs. For example, Siglec-6 is selectively and prominently expressed on mast cells while Siglec-8 is highly specific for both eosinophils and mast cells. This review will focus on a subset of Siglecs and their various endogenous or synthetic sialoside ligands that regulate eosinophil and mast cell function and survival. It will also summarize how certain Siglecs have become the focus of novel therapies for allergic and other eosinophil- and mast cell-related diseases.
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Affiliation(s)
- Jeremy A O'Sullivan
- Division of Allergy and Immunology, Department of Medicine, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
| | | | - Robert P Schleimer
- Division of Allergy and Immunology, Department of Medicine, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
| | - Bruce S Bochner
- Division of Allergy and Immunology, Department of Medicine, Northwestern University Feinberg School of Medicine, Chicago, IL, USA.
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Bochner BS, O'Sullivan JA, Chang AT, Youngblood BA. Siglecs in allergy and asthma. Mol Aspects Med 2023; 90:101104. [PMID: 35835621 PMCID: PMC10757266 DOI: 10.1016/j.mam.2022.101104] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2022] [Revised: 06/28/2022] [Accepted: 07/03/2022] [Indexed: 01/21/2023]
Abstract
The term "allergic diseases" encompasses several common, IgE-mediated conditions that range from being annoying to those that are life-threatening. Available treatments include active avoidance of the instigating allergen and the use of a variety of oral, inhaled, intranasal, intraocular and injected agents. While most individuals with allergies do well with existing therapies, there are still unmet therapeutic needs. Siglecs (sialic acid-binding, immunoglobulin-like lectins) are a family of single-pass transmembrane I-type lectins found on various subsets of cells, especially those of the immune system. All Siglecs have extracellular domains recognizing sialoside ligands, and most contain cytoplasmic domains with inhibitory signaling activity. This review focuses on Siglecs that likely play a role in regulating allergic and asthmatic responses, and how specific Siglecs, expressed on cells such as eosinophils and mast cells, are being targeted for therapeutic benefit.
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Affiliation(s)
- Bruce S Bochner
- Division of Allergy and Immunology, Department of Medicine, Northwestern University Feinberg School of Medicine, Chicago, IL, USA.
| | - Jeremy A O'Sullivan
- Division of Allergy and Immunology, Department of Medicine, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
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CD33 isoforms in microglia and Alzheimer's disease: Friend and foe. Mol Aspects Med 2023; 90:101111. [PMID: 35940942 DOI: 10.1016/j.mam.2022.101111] [Citation(s) in RCA: 20] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Revised: 07/18/2022] [Accepted: 07/27/2022] [Indexed: 02/08/2023]
Abstract
Alzheimer's disease (AD) is the most common form of neurodegenerative disease and is considered the main cause of dementia worldwide. Genome-wide association studies combined with integrated analysis of functional datasets support a critical role for microglia in AD pathogenesis, identifying them as important potential therapeutic targets. The ability of immunomodulatory receptors on microglia to control the response to pathogenic amyloid-β aggregates has gained significant interest. Siglec-3, also known as CD33, is one of these immunomodulatory receptors expressed on microglia that has been identified as an AD susceptibility factor. Here, we review recent advances made in understanding the multifaceted roles that CD33 plays in microglia with emphasis on two human-specific CD33 isoforms that differentially correlate with AD susceptibility. We also describe several different therapeutic approaches for targeting CD33 that have been advanced for the purpose of skewing microglial cell responses.
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Gonzalez-Gil A, Li TA, Kim J, Schnaar RL. Human sialoglycan ligands for immune inhibitory Siglecs. Mol Aspects Med 2023; 90:101110. [PMID: 35965135 DOI: 10.1016/j.mam.2022.101110] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2022] [Revised: 07/26/2022] [Accepted: 07/27/2022] [Indexed: 02/08/2023]
Abstract
Most human Siglecs (sialic acid binding immunoglobulin-like lectins) are expressed on the surfaces of overlapping subsets of immune cells, and most carry immunoreceptor tyrosine-based inhibitory domains on their intracellular motifs. When immune inhibitory Siglecs bind to complementary sialoglycans in their local milieu, engagement results in down-regulation of the immune response. Siglecs have come under scrutiny as potential targets of drugs to modify the course of inflammation (and other immune system responses) and as immune checkpoints in cancer. Human Siglecs bind to endogenous human sialoglycans. The identities of these endogenous human sialoglycan immune regulators are beginning to emerge, along with some general principles that may inform future investigations in this area. Among these principles is the finding that a cell type or tissue may express a ligand for a particular Siglec on a single or a very few of its sialoglycoproteins. The selected protein carrier for a particular Siglec may be unique in a certain tissue, but vary tissue-to-tissue. The binding affinity of endogenous Siglec ligands may surpass that of its binding to synthetic sialoglycan determinants by several orders of magnitude. Since most human Siglecs have evolved rapidly and are distinct from those in most other mammals, this review describes endogenous human Siglec ligands for several human immune inhibitory Siglecs. As the identities of these immune regulatory sialoglycan ligands are defined, additional opportunities to target Siglecs therapeutically may emerge.
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Affiliation(s)
- Anabel Gonzalez-Gil
- Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA.
| | - T August Li
- Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA.
| | - Jean Kim
- Department Medicine, Division of Allergy and Clinical Immunology, Johns Hopkins University School of Medicine, Baltimore, MD, 21287, USA; Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, MD, 21287, USA.
| | - Ronald L Schnaar
- Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA; Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA.
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8
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Stanczak MA, Läubli H. Siglec receptors as new immune checkpoints in cancer. Mol Aspects Med 2023; 90:101112. [PMID: 35948467 DOI: 10.1016/j.mam.2022.101112] [Citation(s) in RCA: 33] [Impact Index Per Article: 33.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Revised: 07/26/2022] [Accepted: 07/28/2022] [Indexed: 02/08/2023]
Abstract
Cancer immunotherapy in the form of immune checkpoint inhibitors and cellular therapies has improved the treatment and prognosis of many patients. Nevertheless, most cancers are still resistant to currently approved cancer immunotherapies. New approaches and rational combinations are needed to overcome these resistances. There is emerging evidence that Siglec receptors could be regarded as new immune checkpoints and targets for cancer immunotherapy. In this review, we summarize the experimental evidence supporting Siglec receptors as new immune checkpoints in cancer and discuss their mechanisms of action, as well as current efforts to target Siglec receptors and their interactions with sialoglycan Siglec-ligands.
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Affiliation(s)
- Michal A Stanczak
- The Bloomberg-Kimmel Institute for Cancer Immunotherapy at Johns Hopkins, Baltimore, MD, 21287, USA
| | - Heinz Läubli
- Laboratory for Cancer Immunotherapy, Department of Biomedicine, University of Basel, Division of Oncology, University Hospital Basel, Switzerland.
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