SIGLEC1 Protein <table class="infobox infobox-protein">
SIGLEC1 (Sialic Acid Binding Ig Like Lectin 1), also known as CD169 or Sialoadhesin, is a cell surface receptor expressed primarily on myeloid cells. It belongs to the Siglec family of sialic acid-binding lectins and plays important roles in immune regulation and neuroinflammation.
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Overview ...
SIGLEC1 Protein <table class="infobox infobox-protein">
SIGLEC1 (Sialic Acid Binding Ig Like Lectin 1), also known as CD169 or Sialoadhesin, is a cell surface receptor expressed primarily on myeloid cells. It belongs to the Siglec family of sialic acid-binding lectins and plays important roles in immune regulation and neuroinflammation.
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Overview
Introduction SIGLEC1 (also known as CD169 or Sialoadhesin) is a member of the Siglec family of sialic acid-binding immunoglobulin-type lectins[@crocker2007]. It is predominantly expressed on macrophages and activated [microglia](/cell-types/microglia-neuroinflammation), where it functions as a phagocytic receptor for sialylated targets. In the central nervous system, SIGLEC1 is a well-established marker of disease-associated microglia (DAM) and plays complex roles in neuroinflammation and neurodegeneration.
Structure SIGLEC1 has distinctive structural features:
Extracellular Domain : 17 Ig-like domains, making it one of the largest SiglecsSialic Acid Binding Domain : N-terminal V-type Ig domain specifically recognizes sialylated glycansTransmembrane Region : Single pass membrane protein with a transmembrane helixIntracellular Tail : Contains signaling motifs but lacks obvious activation motifsThe extensive extracellular domain (~1600 aa) enables multivalent interactions with sialylated ligands, enhancing binding avidity[@may2010].
Normal Function
Sialic Acid Recognition SIGLEC1 binds specifically to sialylated glycans:
Ligand Specificity : Prefers α2,3-linked sialic acids over other linkagesCarbohydrate Recognition Domain (CRD) : N-terminal V-type Ig domain mediates bindingCalcium-dependent : Lectin activity requires calcium ionsSialylated ligands :包括糖蛋白、糖脂和其他细胞表面分子Immune Functions In the immune system, SIGLEC1 mediates several functions:
Macrophage Activation : Modulates inflammatory responses to stimuliPhagocytosis : Mediates binding and phagocytosis of sialylated targetsCell Adhesion : Facilitates cell-cell interactions in immune tissuesT Cell Interactions : Modulates T cell activation and cytokine productionImmune Complex Clearance : Binds to sialylated antibodies in immune complexesCNS Functions In the central nervous system:
Microglial Marker : Activated microglia express SIGLEC1 in response to injury or diseaseMyelin Phagocytosis : Clears myelin debris through recognition of sialylated targetsNeuroinflammation : Mediates inflammatory responses to pathological stimuliAntigen Presentation : May participate in CNS immune surveillanceRole in Neurodegenerative Diseases
Alzheimer's Disease (AD) SIGLEC1 is significantly upregulated in AD brain:
Expression Pattern : Strong expression on microglia surrounding amyloid plaquesAmyloid Clearance : May help clear [Aβ](/proteins/amyloid-beta) through phagocytosisNeuroinflammation : Can promote pro-inflammatory cytokine productionDual Role : Both protective (phagocytosis) and pathogenic (inflammation) effectsResearch has shown increased SIGLEC1+ microglia in AD brain tissue, particularly in regions with high plaque burden[@perry2010].
Multiple Sclerosis (MS) SIGLEC1 plays a complex role in MS:
Immune Cell Trafficking : Mediates inflammatory cell entry into CNSDemyelination : Regulates immune-mediated myelin damageBiomarker : SIGLEC1 expression correlates with disease activityTherapeutic Target : Potential for immunomodulatory therapiesParkinson's Disease
Microglial Activation : SIGLEC1+ microglia in substantia nigra[α-synuclein](/proteins/alpha-synuclein) Clearance : May participate in clearing α-synuclein aggregatesNeuroinflammation : Contributes to dopaminergic neuron lossAmyotrophic Lateral Sclerosis (ALS)
Motor [Cortex](/brain-regions/cortex) [Microglia](/entities/microglia) : SIGLEC1+ microglia in affected regionsDisease Progression : Correlates with motor neuron degenerationImmune Dysregulation : Altered phagocytic functionOther Neurological Conditions
Traumatic Brain Injury : Upregulated in activated microgliaViral Encephalitis : Mediates antiviral immune responsesNeuropathic Pain : Contributes to glial activationTherapeutic Targeting SIGLEC1 represents a therapeutic target for several conditions:
Therapeutic Strategies
Monoclonal Antibodies : Anti-CD169 antibodies for immunomodulationSmall Molecule Inhibitors : Block sialic acid binding domainSiglec-Fc Fusion Proteins : Decoy receptors to sequester ligandsAntibody-Drug Conjugates : Target macrophages for drug delivery
Clinical Applications
Neuroinflammation : Modulating microglial activation statesAutoimmune Diseases : Regulating aberrant immune responsesDrug Delivery : Targeting therapeutic agents to macrophagesBiomarker Potential SIGLEC1 has biomarker potential:
Disease State : Elevated SIGLEC1 indicates activated microgliaTherapeutic Response : Changes in expression may track treatment effectsPrognosis : High SIGLEC1 may correlate with disease severityInteractions
Protein Interactions SIGLEC1 interacts with several molecules:
Sialylated Ligands : Primary binding partnersSiglec Family Members : May form heterodimersCytosolic Proteins : Signaling adaptors (limited data)Signaling Pathways
Src Family Kinases : Involved in downstream signalingPhosphoinositide 3-kinase (PI3K) : Associated with phagocytosisMAPK Pathways : Regulate inflammatory responsesRelated Pages
[SIGLEC1 Gene](/genes/SIGLEC1)
[Alzheimer's Disease](/diseases/alzheimers-disease)
[Multiple Sclerosis](/diseases/multiple-sclerosis)
[Parkinson's Disease](/diseases/parkinsons-disease-disease)
[Microglia](/cell-types/microglia)
[Neuroinflammation](/mechanisms/neuroinflammation)
[Disease-Associated Microglia (DAM)](/mechanisms/disease-associated-microglia)
External Links
UniProt : [Q9PMN3](https://www.uniprot.org/uniprot/Q9PMN3)PDB : [1QFO](https://www.rcsb.org/structure/1QFO), [2H9L](https://www.rcsb.org/structure/2H9L)NCBI Gene : [SIGLEC1](https://www.ncbi.nlm.nih.gov/gene/11027)Allen Brain Atlas : [SIGLEC1 expression](https://human.brain-map.org/microarray/search/show?search_term=SIGLEC1)GeneCards : [SIGLEC1](https://www.genecards.org/cgi-bin/carddisp.pl?gene=SIGLEC1)Background The study of Siglec1 Protein has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
See Also
[Alzheimer's Disease](/diseases/alzheimers-disease)
[Amyloid Hypothesis](/mechanisms/amyloid-hypothesis)
[Tau Pathology](/mechanisms/tau-pathology)
[Parkinson's Disease](/diseases/parkinsons-disease)
[Alpha-Synuclein](/mechanisms/alpha-synuclein)
References
[Crocker PR, et al, (2007) (2007)](https://doi.org/10.1038/nri2056)
[May AP, et al, (2010) (2010)](https://doi.org/10.1038/35000642)
[Perry VH, et al, (2010) (2010)](https://doi.org/10.1002/glia.21024)
[Griciuc A, et al, (2019) (2019)](https://doi.org/10.1016/j.neuron.2019.09.016)
[Wang Y, et al, (2020) (2020)](https://doi.org/10.1038/s41582-020-0370-0)
[Jiang L, et al, (2021) (2021)](https://doi.org/10.1038/s41593-021-00800-4)
[Hammond TR, et al, (2019) (2019)](https://doi.org/10.1016/j.cell.2019.08.036)
[Mathys H, et al, (2019) (2019)](https://doi.org/10.1038/s41586-019-1197-0) Show full description