Kabara Edward, Coussens Paul M
Department of Biochemistry, Center for Animal Functional Genomics, Michigan State University East Lansing, MI, USA.
Front Microbiol. 2012 Jul 20;3:215. doi: 10.3389/fmicb.2012.00215. eCollection 2012.
Mycobacterium avium subspecies paratuberculosis (MAP) is able to survive intracellularly in macrophages by preventing normal phagosome maturation processes utilized to destroy bacteria. Infected macrophages often undergo apoptotic cell death to efficiently present bacterial antigens to the host adaptive immune system in a process known as efferocytosis. Recent studies with Mycobacterium tuberculosis (MTB) showed that macrophages infected with MTB are less likely to undergo apoptosis than control, uninfected cells. It is proposed that regulation of macrophage apoptosis is an important immune evasion tactic for MTB. Based on the similarity of MAP and MTB, we hypothesized that MAP-infected macrophages would be resistant to apoptosis compared to uninfected cells within the same culture and to cells from uninfected cultures. Our results demonstrate that, indeed, populations of MAP-infected macrophages contain fewer apoptotic cells than similar populations of control cells, and that MAP infection reduces the sensitivity of infected macrophages to induction of apoptosis by H(2)O(2). We further demonstrate that MAP-infected cells contain reduced caspase activity for caspases 3/7, 8, and 9. Reduced caspase activity in MAP-infected macrophages is also maintained after H(2)O(2) induction. This reduction in caspase activity is accompanied by a pronounced reduction in transcription of caspase genes encoding caspases 3, 7, and 8, but not for caspase 9, when compared to control, uninfected cells. Furthermore, MAP infection drastically effects the expression of several host cell proteins important for regulation of apoptosis. Studies using mutant MAP strains demonstrate the importance of bacterial specific factors in the control of host macrophage apoptosis. Together these data demonstrate that MAP specific factors may prevent caspase activity and caspase gene transcription as well as apoptosis signaling protein expression, resulting in decreased spontaneous host cell apoptosis and decreased sensitivity to apoptosis inducing agents.
副结核分枝杆菌鸟型亚种（MAP）能够通过阻止用于破坏细菌的正常吞噬体成熟过程在巨噬细胞内生存。受感染的巨噬细胞通常会经历凋亡性细胞死亡，以便在一个称为胞葬作用的过程中有效地将细菌抗原呈递给宿主适应性免疫系统。最近关于结核分枝杆菌（MTB）的研究表明，与未感染的对照细胞相比，感染MTB的巨噬细胞发生凋亡的可能性较小。有人提出，调节巨噬细胞凋亡是MTB重要的免疫逃避策略。基于MAP和MTB的相似性，我们假设与同一培养物中的未感染细胞以及未感染培养物中的细胞相比，感染MAP的巨噬细胞对凋亡具有抗性。我们的结果表明，实际上，感染MAP的巨噬细胞群体中凋亡细胞比类似的对照细胞群体少，并且MAP感染降低了受感染巨噬细胞对H₂O₂诱导凋亡的敏感性。我们进一步证明，感染MAP的细胞中半胱天冬酶3/7、8和9的活性降低。在H₂O₂诱导后，感染MAP的巨噬细胞中降低的半胱天冬酶活性也得以维持。与未感染的对照细胞相比，这种半胱天冬酶活性的降低伴随着编码半胱天冬酶3、7和8的半胱天冬酶基因转录的显著降低，但半胱天冬酶9的转录没有降低。此外，MAP感染极大地影响了几种对凋亡调节重要的宿主细胞蛋白的表达。使用MAP突变株的研究证明了细菌特异性因子在控制宿主巨噬细胞凋亡中的重要性。这些数据共同表明，MAP特异性因子可能会阻止半胱天冬酶活性、半胱天冬酶基因转录以及凋亡信号蛋白表达，从而导致宿主细胞自发凋亡减少以及对凋亡诱导剂的敏感性降低。
