title: Galectin-9 protein is up-regulated in astrocytes by tumor necrosis factor and promotes encephalitogenic T-cell apoptosis.
abstract: Demyelination and axonal damage in multiple sclerosis (MS) are thought to be a consequence of inflammatory processes that are perpetuated by activated glia and infiltrating leukocytes. Galectin-9 is a β-galactoside binding lectin capable of modulating immune responses and appears to be up-regulated in MS. However, its role in the pathogenesis of MS has yet to be determined. Here, we report that proinflammatory cytokines induce galectin-9 (Gal-9) expression in primary astrocytes and the mechanism by which TNF up-regulates Gal-9. Astrocytes did not express Gal-9 under basal conditions nor did IL-6, IL-10, or IL-13 trigger Gal-9 expression. In contrast, IL-1β, IFN-γ, and particularly TNF up-regulated Gal-9 in astrocytes. TNF-induced Gal-9 expression was dependent on TNF receptor 1 (TNFR1) as TNF failed to induce Gal-9 in TNFR1(-/-) astrocytes. Blockade of the JNK MAP kinase pathway with the JNK inhibitor SP600125 abrogated TNF-induced Gal-9, whereas p38 and MEK inhibitors had minimal effects. Furthermore, specific knockdown of c-Jun via siRNA in astrocytes before TNF treatment greatly suppressed Gal-9 transcription, suggesting that TNF induces astroglial Gal-9 through the TNF/TNFR1/JNK/cJun signaling pathway. Finally, utilizing astrocytes from Lgals9 mutant (Gal-9(-/-)) mice as well as a myelin basic protein-specific Tim-3(+) encephalitogenic T-cell clone (LCN-8), we found that conditioned medium from TNF-stimulated Gal-9(+/+) but not Gal-9(-/-) astrocytes increased the percentage of apoptotic encephalitogenic T-cells. Together, our results suggest that Gal-9 is induced in astrocytes by TNF via the JNK/c-Jun pathway and that astrocyte-derived Gal-9 may function as an immunoregulatory protein in response to ongoing neuroinflammation.
authors.affiliation: Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas 77843, USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Steelman
authors.forename: Roger
authors.initials: R
authors.lastname: Smith
authors.forename: C Jane
authors.initials: CJ
authors.lastname: Welsh
authors.forename: Jianrong
authors.initials: J
authors.lastname: Li
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D002478:Cells, Cultured; D004660:Encephalitis / Q000473:pathology*; D004789:Enzyme Activation / Q000187:drug effects; D037161:Galectins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D018836:Inflammation Mediators / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000235:genetics; D051379:Mice; D051381:Rats; D017207:Rats, Sprague-Dawley; D018124:Receptors, Tumor Necrosis Factor / Q000172:deficiency / Q000378:metabolism; D034421:Sus scrofa; D013601:T-Lymphocytes / Q000187:drug effects / Q000473:pathology*; D014158:Transcription, Genetic / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects* / Q000235:genetics
chemical_list: D037161:Galectins; D018836:Inflammation Mediators; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha; C508186:galectin 9, mouse; C513912:galectin 9, rat; D048031:JNK Mitogen-Activated Protein Kinases
keywords: Astrocytes; Galectin; Galectin-9; Jun N-terminal Kinase (JNK); Multiple Sclerosis; Neuroinflammation; Tumor Necrosis Factor (TNF)