Astrocyte TLR4 activation induces a proinflammatory environment through the interplay between MyD88-dependent NFκB signaling, MAPK, and Jak1/Stat1 pathways.
There is increasing evidence that astrocytes play important roles in immune regulation in the brain. Astrocytes express toll-like receptors (TLR) and build up responses to innate immune triggers by releasing proinflammatory molecules. We investigate signaling pathways and released molecules after astrocyte TLR4 activation. Purified rodent brain astrocyte cultures were treated with the TLR4 activator bacterial lipopolysaccharide (LPS). Tools used to interfere with this system include small interference RNA, inhibitory drugs, and MyD88 or Stat1 deficient mice. LPS induced early activation of the transcription factor NFκB, through the MyD88 adaptor, and expression of TNF-α, VCAM-1, IL-15, and IL-27. LPS also induced delayed Jak1/Stat1 activation, which was MyD88-independent but was not mediated by IFN-β. Jak1/Stat1 activation induced the expression of negative cytokine regulator SOCS-1 and CXCL10 chemokine (IP-10). Mitogen-activated protein kinases (MAPK) were also involved in TLR4 signaling in a MyD88-independent fashion. p38 exerted a strong influence on LPS-induced gene expression by regulating the phosphorylation of Stat1 and the transcriptional activity of NFκB, while JNK regulated the Jak1/Stat1 pathway, and ERK1/2 controlled the expression of Egr-1 and influenced MyD88-dependent MMP-9 expression. Interplay between these signals was evidenced by the increased induction of MMP-9 in Stat1-deficient cells challenged with LPS, suggesting that Stat1 negatively regulates the expression of MMP-9 induced by LPS. Therefore, astrocytes are responsive to TLR4 activation by inducing a complex set of cell-dependent molecular reactions mediated by NFκB, MAPK and Jak1/Stat1 signaling pathways. Here we identified cross-talking signals generating a proinflammatory environment that will modulate the response of surrounding cells.
Department of Brain Ischemia and Neurodegeneration, Institut d'Investigacions Biomèdiques de Barcelona (IIBB)-Consejo Superior de Investigaciones Científicas (CSIC), Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain.
Roser
R
Gorina
Miriam
M
Font-Nieves
Leonardo
L
Márquez-Kisinousky
Tomàs
T
Santalucia
Anna M
AM
Planas
D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D002540:Cerebral Cortex / Q000166:cytology; D004347:Drug Interactions; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D005434:Flow Cytometry / Q000379:methods; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000235:genetics; D051548:Histone Acetyltransferases / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000187:drug effects; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D053594:Myeloid Differentiation Factor 88 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D050794:STAT1 Transcription Factor / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D013997:Time Factors; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism
D004791:Enzyme Inhibitors; D008070:Lipopolysaccharides; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D050794:STAT1 Transcription Factor; C494080:Stat1 protein, mouse; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D014443:Tyrosine; D051548:Histone Acetyltransferases; D020928:Mitogen-Activated Protein Kinases