A Novel Mechanism Underlying the Basic Defensive Response of Macrophages against Mycobacterium Infection
A Novel Mechanism Underlying the Basic Defensive Response of Macrophages against Mycobacterium Infection
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DOI：
10.4049/jimmunol.1301526
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发表时间：
2014-05-01
影响因子：
4.4
通讯作者：
Fukai, Fumio
中科院分区：
文献类型：
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作者：
Iyoda, Takuya;Takada, Muneaki;Fukai, Fumio
在吸入结核分枝杆菌，包括卡介苗(BCG)后，病原体通过吞噬机制进入并在巨噬细胞内生长。巨噬细胞常常不能清除细胞内的结核分枝杆菌，导致宿主巨噬细胞死亡。尽管有越来越多的证据，但结核分枝杆菌感染诱导细胞死亡的分子机制仍然存在争议。在这项研究中，我们展示了由TLR2和β(2)整合素触发的两条不同的通路参与了卡介苗感染诱导的巨噬细胞凋亡。首先，卡介苗感染诱导ERK1/2激活，进而导致小鼠巨噬细胞样Raw 264.7细胞中促凋亡蛋白Bim的磷酸化/激活。用MEK/ERK抑制剂U0126处理BCG感染的Raw细胞后，Bim的磷酸化受到抑制，同时存活的巨噬细胞数量显著增加。小干扰RNA介导的Bim基因敲除可使巨噬细胞免于卡介苗感染所致的细胞死亡。TLR2激动剂Pam3CSK可诱导巨噬细胞凋亡，并伴随MEK/ERK和Bim的磷酸化/活化增加。提示TLR2/MEK/ERK/Bim通路在卡介苗感染诱导巨噬细胞凋亡中起重要作用。其次，我们使用b2整合素激动剂C3bi和纤维连接蛋白来证明b2整合素衍生信号参与了卡介苗感染诱导的细胞凋亡，而不依赖于MEK/ERK的激活。有趣的是，包被Pam3CSK和C3bi的乳胶珠能够诱导巨噬细胞凋亡，其程度和特异性与卡介苗相同。总之，两种不同的模式识别膜受体TLR2和b2整合素在卡介苗感染诱导巨噬细胞凋亡中起触发作用，其中MEK/ERK激活在TLR2参与其中起关键作用。
Following inhalation of Mycobacterium tuberculosis, including bacillus Calmette-Guerin (BCG), pathogens enter and grow inside macrophages by taking advantage of their phagocytic mechanisms. Macrophages often fail to eliminate intracellular M. tuberculosis, leading to the induction of host macrophage death. Despite accumulating evidence, the molecular mechanisms underlying M. tuberculosis infection-induced cell death remain controversial. In this study, we show the involvement of two distinct pathways triggered by TLR2 and beta(2) integrin in BCG infection-induced macrophage apoptosis. First, BCG infection induced activation of ERK1/2, which in turn caused phosphorylation/activation of the proapoptotic protein Bim in mouse macrophage-like Raw 264.7 cells. BCG-infected Raw cells treated with U0126, an MEK/ERK inhibitor, led to the suppression of Bim phosphorylation alongside a remarkable increase in the number of viable macrophages. Small interfering RNA-mediated knockdown of Bim rescued the macrophages from the apoptotic cell death induced by BCG infection. Stimulation with Pam3CSK, a TLR2 agonist, induced macrophage apoptosis with a concomitant increase in the phosphorylation/activation of MEK/ERK and Bim. These observations indicate the important role of the TLR2/MEK/ERK/Bim pathway in BCG infection-induced macrophage apoptosis. Second, we used the b2 integrin agonists C3bi and fibronectin to show that the b2 integrin-derived signal was involved in BCG infection-induced apoptosis, independent of MEK/ERK activation. Interestingly, latex beads coated with Pam3CSK and C3bi were able to induce apoptosis in macrophages to the same extent and specificity as that induced by BCG. Taken together, two distinct pattern-recognition membrane receptors, TLR2 and b2 integrin, acted as triggers in BCG infection-induced macrophage apoptosis, in which MEK/ERK activation played a crucial role following the engagement of TLR2.