title: Astrocyte galectin-9 potentiates microglial TNF secretion.
abstract: BACKGROUND
  Aberrant neuroinflammation is suspected to contribute to the pathogenesis of myriad neurological diseases. As such, determining the pathways that promote or inhibit glial activation is of interest. Activation of the surface glycoprotein T-cell immunoglobulin and mucin-domain containing protein 3 (Tim-3) by the lectin galectin-9 has been implicated in promoting innate immune cell activation by potentiating or synergizing toll-like receptor (TLR) signaling. In the present study we examined the role of the Tim-3/galectin-9 pathway in glial activation in vitro.
  
  
  METHODS
  Primary monocultures of microglia or astrocytes, co-cultures containing microglia and astrocytes, and mixed glial cultures consisting of microglia, astrocytes and oligodendrocytes were stimulated with poly(I:C) or LPS, and galectin-9 up-regulation was determined. The effect of endogenous galectin-9 production on microglial activation was examined using cultures from wild-type and Lgals9 null mice. The ability for recombinant galectin-9 to promote microglia activation was also assessed. Tim-3 expression on microglia and BV2 cells was examined by qPCR and flow cytometry and its necessity in transducing the galectin-9 signal was determined using a Tim-3 specific neutralizing antibody or recombinant soluble Tim-3.
  
  
  RESULTS
  Astrocytes potentiated TNF production from microglia following TLR stimulation. Poly(I:C) stimulation increased galectin-9 expression in microglia and microglial-derived factors promoted galectin-9 up-regulation in astrocytes. Astrocyte-derived galectin-9 in turn enhanced microglial TNF production. Similarly, recombinant galectin-9 enhanced poly(I:C)-induced microglial TNF and IL-6 production. Inhibition of Tim-3 did not alter TNF production in mixed glial cultures stimulated with poly(I:C).
  
  
  CONCLUSIONS
  Galectin-9 functions as an astrocyte-microglia communication signal and promotes cytokine production from microglia in a Tim-3 independent manner. Activation of CNS galectin-9 likely modulates neuroinflammatory processes in which TNF and IL-6 contribute to either pathology or reparation.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Steelman
authors.affiliation: Department of Veterinary Integrative Biosciences and Institute for Neuroscience, Texas A&M University, Mail Stop 4458, College Station 77843, TX, USA. jrli@cvm.tamu.edu.
authors.forename: Jianrong
authors.initials: J
authors.lastname: Li
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002478:Cells, Cultured; D018920:Coculture Techniques; D016207:Cytokines / Q000378:metabolism; D037161:Galectins / Q000235:genetics / Q000378:metabolism*; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008840:Microfilament Proteins / Q000378:metabolism; D017628:Microglia / Q000187:drug effects / Q000378:metabolism*; D011089:Polydeoxyribonucleotides / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology; D013997:Time Factors; D051197:Toll-Like Receptor 4 / Q000172:deficiency; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D002135:Calcium-Binding Proteins; D016207:Cytokines; D037161:Galectins; D005904:Glial Fibrillary Acidic Protein; D008840:Microfilament Proteins; D011089:Polydeoxyribonucleotides; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; C491049:Aif1 protein, mouse; C569429:Havcr2 protein, rat; C493487:Tlr4 protein, mouse; C508186:galectin 9, mouse; C031156:poly d(I-C)