LGALS8

LGALS8 (Galectin-8) is a tandem-repeat β-galactoside-binding lectin that functions as a cytosolic danger receptor for endomembrane damage and as an extracellular modulator of immunity and lymphangiogenesis. Upon bacterial invasion or sterile lysosomal damage, LGALS8 detects exposed host glycans on compromised endosomal/lysosomal membranes, recruits the autophagy adaptor NDP52/CALCOCO2 to nucleate phagophore formation via FIP200 and TBK1 complexes, and simultaneously inhibits mTOR through the Ragulator–RRAGA/B complex while activating AMPK and TFEB-dependent lysosomal biogenesis (PMID:22246324, PMID:30081722, PMID:36394332, PMID:31258038). This surveillance mechanism restricts intracellular replication of both bacteria (Salmonella, Legionella) and viruses (picornaviruses) (PMID:28077878, PMID:32209695). Extracellularly, LGALS8 promotes pathological lymphangiogenesis via podoplanin–integrin crosstalk independently of VEGFR-3 and activates dendritic cells for adaptive immune priming, while its short isoform specifically regulates osteoclast bone resorption through interactions with lysosomal chloride channels (CLCN3, CLCN7) and LAMP proteins (PMID:27066737, PMID:28811319, PMID:38395460).

1. 2012 High

   Identifying LGALS8 as a cytosolic danger receptor solved the question of how cells detect bacteria-damaged vacuoles: galectin-8 recognizes exposed host glycans on Salmonella-containing vacuoles and recruits NDP52 to initiate selective autophagy, establishing the foundational 'eat-me' signaling axis for xenophagy.

   Evidence Co-immunoprecipitation, live-cell imaging, siRNA knockdown with Salmonella proliferation assays in human cells

   PMID:22246324

   Open questions at the time

   • Mechanism by which galectin-8 specifically distinguishes damaged from intact endosomes was not resolved
   • Whether the same pathway operates against non-bacterial pathogens was unknown
   • Downstream signaling consequences beyond NDP52 recruitment were unexplored
2. 2015 Medium

   Domain dissection of NDP52 revealed that LGALS8 binding and LC3/MYO6 engagement are structurally separable functions, establishing that NDP52 acts as a bifunctional bridge—one domain senses LGALS8-marked damage, and a distinct domain couples to autophagosome maturation machinery.

   Evidence Domain mutagenesis of NDP52, Co-IP, fluorescence microscopy, and bacterial infection assays

   PMID:25998689

   Open questions at the time

   • Single-lab study extending earlier findings without independent replication
   • Structural basis for the LGALS8–NDP52 interaction was not determined
   • Whether other galectins engage NDP52 through the same domain was not tested
3. 2016 High

   The discovery that Lgals8-knockout mice exhibit reduced inflammatory lymphangiogenesis revealed an extracellular, non-autophagic role for galectin-8 in promoting pathological vessel growth through podoplanin–integrin (α1β1, α5β1) crosstalk independently of VEGFR-3.

   Evidence Lgals8−/− and Pdpn−/− mouse models, corneal transplant and HSV keratitis models, integrin inhibition assays

   PMID:27066737

   Open questions at the time

   • Direct molecular mechanism linking galectin-8 to integrin activation was not elucidated
   • Whether intracellular versus secreted galectin-8 mediates lymphangiogenesis was not resolved
4. 2017 High

   Two advances broadened LGALS8's protective scope: a genome-wide screen showed galectin-8-mediated autophagy restricts picornavirus entry (antagonized by PLA2G16), establishing LGALS8 as an antiviral sensor, while Lgals8−/− dendritic cell studies demonstrated an endogenous role in DC maturation and CD4+ T cell priming.

   Evidence Haploid genetic screen and suppressor screen for viral infection; Lgals8−/− bone marrow-derived DC cultures with flow cytometry, ELISA, and in vivo immunization

   PMID:28077878 PMID:28811319

   Open questions at the time

   • Mechanism of DC activation by galectin-8 (receptor identity, signaling cascade) was not identified
   • Whether antiviral autophagy and antibacterial autophagy use identical downstream machinery was unresolved
5. 2018 High

   Proximity proteomics and kinase assays demonstrated that galectin-8 is not merely a passive damage tag but actively transduces signals by inhibiting mTOR and activating AMPK upon lysosomal damage, directly connecting endomembrane surveillance to metabolic autophagy regulation.

   Evidence APEX2 proximity labeling proteomics, mTOR/AMPK kinase activity assays, galectin-KO/KD in lysosomal damage models

   PMID:30081722

   Open questions at the time

   • Direct binding partner through which LGALS8 inhibits mTOR was not identified
   • Relative contributions of LGALS8 versus LGALS9 to mTOR inhibition were unclear
6. 2019 High

   Reconstitution of the LGALS8→NDP52→FIP200/TBK1 cascade on damaged Salmonella vacuoles established that galectin-8 functions as the upstream 'eat-me' signal that nucleates the complete autophagy-initiation machinery at the cargo site.

   Evidence Co-IP, mutagenesis of NDP52 binding domains, fluorescence microscopy, knockdown with phenotypic rescue in Salmonella infection

   PMID:31258038

   Open questions at the time

   • Whether ULK1 kinase activity is directly regulated by LGALS8 binding was not tested
   • Temporal ordering of NDP52 versus TBK1 recruitment was not fully resolved
7. 2020 Medium

   Identification of a cooperative miRNA network (miR-125b, miR-221, miR-579) that post-transcriptionally controls LGALS8 levels in macrophages revealed that Legionella exploits host miRNA regulation to suppress galectin-8-dependent antibacterial defense.

   Evidence miRNA overexpression/knockdown, mass spectrometry proteomics, intracellular Legionella replication assays

   PMID:32209695

   Open questions at the time

   • Whether bacteria actively induce these miRNAs or passively benefit from basal regulation was not distinguished
   • Single-lab finding without independent replication
8. 2022 High

   LysoIP proteomics identified the Ragulator–RRAGA/B complex and NUFIP2 as the molecular conduit through which galectin-8 inhibits mTOR at damaged lysosomes, with GABARAP/Atg8ylation coordinating this process.

   Evidence Lysosome immunopurification proteomics, GABARAP interaction assays, Co-IP, mTOR activity assays, knockdown experiments

   PMID:36394332

   Open questions at the time

   • Whether galectin-8 directly binds Ragulator subunits or acts through an intermediary was not resolved
   • Structural details of the LGALS8–GABARAP interaction on damaged membranes are unknown
9. 2024 High

   Isoform-specific studies in osteoclasts revealed that the short LGALS8 isoform preferentially regulates bone resorption, multinucleation, and mTORC1 signaling, interacting with lysosomal proteins (CLCN3, CLCN7, LAMP1, LAMP2) not bound by the long isoform, thereby establishing functional divergence between LGALS8 splice variants.

   Evidence Isoform-specific siRNA, LC-MS/MS interactomics, Co-IP validation, bone resorption assays in human osteoclasts

   PMID:38395460

   Open questions at the time

   • How the short isoform uniquely engages chloride channels and LAMPs structurally is unresolved
   • In vivo significance of isoform-specific bone resorption has not been tested in animal models
10. 2025 Medium

    Lgals8−/− mice revealed that endogenous galectin-8 is dispensable during acute kidney injury but limits maladaptive fibrotic repair by restricting collagen deposition and Th17 infiltration, extending LGALS8's protective roles to anti-fibrotic tissue homeostasis.

    Evidence Lgals8−/− knockout mice, folic acid-induced AKI model, flow cytometry, histological fibrosis scoring

    PMID:40375122

    Open questions at the time

    • Single-lab, single-model study; replication in other fibrosis models needed
    • Mechanism by which LGALS8 suppresses Th17 infiltration and ECM deposition is not defined

• Key unresolved questions include the structural basis of galectin-8's glycan selectivity for damaged versus intact membranes, the identity of the cell-surface receptor mediating DC activation, and the in vivo consequences of isoform-specific functions in bone and immunity.
• No structural model of LGALS8 bound to damaged membrane glycans exists
• The receptor through which extracellular galectin-8 activates dendritic cells is unidentified
• In vivo validation of short versus long isoform-specific functions is lacking