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Regulation of Toll‐like receptor 4 expression and its signaling by hypoxia in cultured microglia
Author(s) -
Ock Jiyeon,
Jeong Jaeyoon,
Choi Wan Sung,
Lee WonHa,
Kim SangHyun,
Kim In Kyeom,
Suk Kyoungho
Publication year - 2007
Publication title -
journal of neuroscience research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.72
H-Index - 160
eISSN - 1097-4547
pISSN - 0360-4012
DOI - 10.1002/jnr.21322
Subject(s) - microglia , hypoxia (environmental) , toll like receptor , receptor , microbiology and biotechnology , toll , signal transduction , neuroscience , chemistry , biology , immunology , inflammation , innate immune system , biochemistry , organic chemistry , oxygen
Hypoxia is an important biological signal that regulates a wide variety of physiological responses. At the same time, hypoxia is involved in multiple pathological situations. In particular, hypoxia is closely associated with neural injury in the brain. Hypoxia has been recently proposed as a neuroinflammatogen, as it can induce the inflammatory activation of microglia, a major cellular source of inflammatory mediators in the brain. In this article, we present evidence that hypoxia enhances Toll‐like receptor 4 (TLR4) expression in cultured microglia and differentially regulates the downstream signaling pathways of TLR4. Hypoxia up‐regulated TLR4 expression at the mRNA and protein levels in a microglia cell line, as well as in primary microglia cultures. Hypoxia, however, differentially regulated MyD88‐dependent and ‐independent pathways of TLR4 signaling: Hypoxia enhanced lipopolysaccharide (LPS)–induced interferon regulatory factor–3 (IRF‐3) activation and the subsequent expression of IFNβ (MyD88‐independent pathway), whereas it suppressed LPS‐induced NF‐κB activation (MyD88‐dependent pathway). Hypoxia did not affect IFNγ signaling, which was represented by signal transducer and activator of transcription–1 (STAT1) activation and interferon‐regulatory factor‐1 (IRF‐1) induction. Taken together, although hypoxia up‐regulates TLR4 expression, its downstream signaling pathways appear to be differentially modulated by hypoxia. © 2007 Wiley‐Liss, Inc.