PDF(Pubmed)
Abstract：
Macrophages undergo different cellular states upon activation that can be hyporesponsive (tolerated) or hyperresponsive (primed or trained) to subsequent stimuli. Epigenetic modifications are known to play key roles in determining these cellular states. However, little is known about the role of signaling pathways that lead to these epigenetic modifications. Here, we examined the effects of various inhibitors targeting key signaling pathways induced by lipopolysaccharide (LPS) on tolerance and priming in murine macrophages. We found that a prolonged inhibition (>18 h) of the mitogen-activated protein kinase (MEK)1/2-extracellular signal-regulated kinase (ERK)1/2 signaling axis reversed tolerance and primed cells in expressing interleukin (IL)-1β and other inflammatory cytokines such as IL-6, tumor necrosis factor (TNF)α, and CXCL10. The ectopic expression of catalytically active and inactive MEK1 mutants suppressed and enhanced IL-1β expression, respectively. A transcriptomic analysis showed that cells primed by the MEK1/2 inhibitor U0126 expressed higher levels of gene sets associated with immune responses and cytokine/chemokine production, but expressed lower levels of genes with cell cycle progression, chromosome organization, and heterochromatin formation than non-primed cells. Of interest, the mRNA expressions of the histone 3 lysine 9 (H3K9) methyltransferase Suv39h1 and the H3K9 methylation reader Cbx5 were substantially suppressed, whereas the H3K9 demethylase Kdm7a was enhanced, suggesting a role of the MEK1/2-ERK signaling axis in H3K9 demethylation. The H3K9 trimethylation levels in the genomic regions of IL-1β, TNFα, and CXCL10 were decreased by U0126. Also, the H3K9 methyltransferase inhibitor BIX01294 mimicked the U0126 training effects and the overexpression of chromobox homolog (CBX)5 prevented the U0126 training effects in both RAW264.7 cells and bone-marrow-derived macrophages. Collectively, these data suggest that the prolonged inhibition of the MEK1/2-ERK signaling axis reverses tolerance and primed macrophages likely through decreasing the H3K9 methylation levels.
摘要：
巨噬细胞在激活时经历不同的细胞状态,其可以对随后的刺激是低反应的(耐受的)或高反应的(引发的或训练的)。已知表观遗传修饰在确定这些细胞状态中起关键作用。然而,对导致这些表观遗传修饰的信号通路的作用知之甚少。这里,我们研究了针对脂多糖(LPS)诱导的关键信号通路的各种抑制剂对小鼠巨噬细胞耐受和启动的影响.我们发现，丝裂原活化蛋白激酶（MEK）1/2-细胞外信号调节激酶（ERK）1/2信号轴的长时间抑制（>18h）逆转了表达白细胞介素（IL）-1β和其他炎性细胞因子，如IL-6，肿瘤坏死因子（TNF）α，和CXCL10。催化活性和非活性MEK1突变体的异位表达抑制和增强了IL-1β的表达，分别。转录组学分析表明，由MEK1/2抑制剂U0126引发的细胞表达了更高水平的与免疫反应和细胞因子/趋化因子产生相关的基因集，但是随着细胞周期的进展，基因的表达水平较低，染色体组织，和异染色质形成比未引发的细胞。感兴趣的，组蛋白3赖氨酸9（H3K9）甲基转移酶Suv39h1和H3K9甲基化读数器Cbx5的mRNA表达被显著抑制，而H3K9脱甲基酶Kdm7a增强，提示MEK1/2-ERK信号轴在H3K9去甲基化中的作用。IL-1β基因组区域的H3K9三甲基化水平,TNFα,CXCL10降低了U0126。此外，H3K9甲基转移酶抑制剂BIX01294模拟了U0126的训练效应,而染色体盒同源物(CBX)5的过表达阻止了U0126在RAW264.7细胞和骨髓源性巨噬细胞中的训练效应.总的来说，这些数据表明,MEK1/2-ERK信号轴的长期抑制逆转了耐受,并可能通过降低H3K9甲基化水平引发巨噬细胞.
