Hypoxic stress up-regulates the expression of Toll-like receptor 4 in macrophages via hypoxia-inducible factor
Hypoxic stress up-regulates the expression of Toll-like receptor 4 in macrophages via hypoxia-inducible factor
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DOI：
10.1111/j.1365-2567.2009.03203.x
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发表时间：
2010-04-01
期刊：
影响因子：
6.4
通讯作者：
Lee, Joo Young
中科院分区：
文献类型：
--
作者：
Kim, So Young;Choi, Yong Jun;Lee, Joo Young
Toll样受体（TLR）是生殖细胞编码的先天免疫受体，识别入侵的微生物并诱导免疫和炎症反应。已知TLR的失调与各种免疫病症和炎性疾病密切相关。炎症部位的细胞暴露于缺氧应激，这进一步加剧了炎症过程。我们已经研究了低氧应激是否调节巨噬细胞的TLR活性。低氧和CoCl 2（低氧模拟物）可增加巨噬细胞（RAW264.7细胞）TLR 4 mRNA和蛋白的表达，而其它TLRs mRNA的表达则无明显增加。为了确定潜在的机制，我们研究了缺氧诱导因子1（HIF-1）在调节TLR 4表达中的作用。通过小干扰RNA敲低HIF-1 α表达抑制了低氧诱导和CoCl 2诱导的巨噬细胞中TLR 4的表达，而HIF-1 α的过度表达增强了TLR 4的表达。染色质免疫沉淀分析显示，缺氧条件下HIF-1 α结合TLR 4启动子区。此外，TLR 4启动子中假定的HIF-1结合基序的缺失或突变极大地减弱了HIF-1 α诱导的TLR 4启动子报告基因表达。低氧应激上调TLR 4表达增强了巨噬细胞对脂多糖的反应，导致环氧合酶-2、白细胞介素-6和干扰素诱导蛋白-10的表达增加。这些结果表明，TLR 4在巨噬细胞中的表达通过HIF-1响应于缺氧应激而上调，表明炎症部位的缺氧应激通过上调TLR 4增强了对后续感染和炎症信号的易感性。
P>Toll-like receptors (TLRs) are germline-encoded innate immune receptors that recognize invading micro-organisms and induce immune and inflammatory responses. Deregulation of TLRs is known to be closely linked to various immune disorders and inflammatory diseases. Cells at sites of inflammation are exposed to hypoxic stress, which further aggravates inflammatory processes. We have examined if hypoxic stress modulates the TLR activity of macrophages. Hypoxia and CoCl2 (a hypoxia mimetic) enhanced the expression of TLR4 messenger RNA and protein in macrophages (RAW264.7 cells), whereas the messenger RNA of other TLRs was not increased. To determine the underlying mechanism, we investigated the role of hypoxia-inducible factor 1 (HIF-1) in the regulation of TLR4 expression. Knockdown of HIF-1 alpha expression by small interfering RNA inhibited hypoxia-induced and CoCl2-induced TLR4 expression in macrophages, while over-expression of HIF-1 alpha potentiated TLR4 expression. Chromatin immunoprecipitation assays revealed that HIF-1 alpha binds to the TLR4 promoter region under hypoxic conditions. In addition, deletion or mutation of a putative HIF-1-binding motif in the TLR4 promoter greatly attenuated HIF-1 alpha-induced TLR4 promoter reporter expression. Up-regulation of TLR4 expression by hypoxic stress enhanced the response of macrophages to lipopolysaccharide, resulting in increased expression of cyclooxygenase-2, interleukin-6, regulated on activation normal T cell expressed and secreted, and interferon-inducible protein-10. These results demonstrate that TLR4 expression in macrophages is up-regulated via HIF-1 in response to hypoxic stress, suggesting that hypoxic stress at sites of inflammation enhances susceptibility to subsequent infection and inflammatory signals by up-regulating TLR4.