Insufficient Acidification of Autophagosomes Facilitates Group A Streptococcus Survival and Growth in Endothelial Cells.
Insufficient Acidification of Autophagosomes Facilitates Group A Streptococcus Survival and Growth in Endothelial Cells.
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DOI：
10.1128/mbio.01435-15
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发表时间：
2015-09-29
期刊：
影响因子：
6.4
通讯作者：
Lin YS
中科院分区：
文献类型：
--
作者：
Lu SL;Kuo CF;Chen HW;Yang YS;Liu CC;Anderson R;Wu JJ;Lin YS
A组链球菌（GAS）是一种重要的人类病原体，其通过血管的入侵在严重事件如菌血症或多器官衰竭中至关重要。虽然GAS被鉴定为细胞外细菌，但GAS内化到非吞噬细胞中可能提供了逃避免疫监视和抗生素杀伤的策略。然而，GAS也被报道诱导自噬，并且在上皮细胞中的溶酶体融合的自噬体内被有效地杀死。在这项研究中，我们表明，GAS可以在内皮细胞中复制，链球菌溶血素O是GAS生长所必需的。细菌复制可以通过在内化到内皮细胞之前改变GAS基因在酸性介质中的表达来抑制。对GAS复制的抑制作用可以通过用液泡型H+-ATP酶的特异性抑制剂巴弗洛霉素A1处理来逆转。与酸化导致自噬介导的GAS清除的上皮细胞相比，内皮细胞中含GAS囊泡的酸化存在缺陷。因此，内皮细胞不能在含GAS的自噬体中维持低pH，从而允许GAS在LAMP-1和LC 3阳性囊泡内复制。此外，用巴弗洛霉素A1处理上皮细胞导致自噬引起GAS清除缺陷，随后细菌在细胞内生长。因此，低pH是自噬介导的抑制上皮细胞内GAS生长的关键因素，而含GAS囊泡的缺陷性酸化导致内皮细胞中的细菌生长。先前的报道表明，GAS可以诱导自噬，并在上皮细胞中的溶酶体融合的自噬体内被有效地杀死。相反，在内皮细胞中，诱导自噬不足以杀死GAS。在这项研究中，我们提供了第一个证据表明，低pH值是必要的，以防止细胞内生长的GAS在上皮细胞，这种机制是有缺陷的内皮细胞。用低pH值处理GAS改变了GAS的生长速率和毒力因子的基因表达，并导致GAS对细胞内溶酶体杀伤的敏感性增强。我们的研究结果揭示了上皮细胞和内皮细胞之间存在不同的宿主防御GAS侵袭的机制。
Group A streptococcus (GAS) is an important human pathogen, and its invasion via blood vessels is critically important in serious events such as bacteremia or multiorgan failure. Although GAS was identified as an extracellular bacterium, the internalization of GAS into nonphagocytic cells may provide a strategy to escape from immune surveillance and antibiotic killing. However, GAS has also been reported to induce autophagy and is efficiently killed within lysosome-fused autophagosomes in epithelial cells. In this study, we show that GAS can replicate in endothelial cells and that streptolysin O is required for GAS growth. Bacterial replication can be suppressed by altering GAS gene expression in an acidic medium before internalization into endothelial cells. The inhibitory effect on GAS replication can be reversed by treatment with bafilomycin A1, a specific inhibitor of vacuolar-type H+-ATPase. Compared with epithelial cells in which acidification causes autophagy-mediated clearance of GAS, there was a defect in acidification of GAS-containing vesicles in endothelial cells. Consequently, endothelial cells fail to maintain low pH in GAS-containing autophagosomes, thereby permitting GAS replication inside LAMP-1- and LC3-positive vesicles. Furthermore, treatment of epithelial cells with bafilomycin A1 resulted in defective GAS clearance by autophagy, with subsequent bacterial growth intracellularly. Therefore, low pH is a key factor for autophagy-mediated suppression of GAS growth inside epithelial cells, while defective acidification of GAS-containing vesicles results in bacterial growth in endothelial cells. Previous reports showed that GAS can induce autophagy and is efficiently killed within lysosome-fused autophagosomes in epithelial cells. In endothelial cells, in contrast, induction of autophagy is not sufficient for GAS killing. In this study, we provide the first evidence that low pH is required to prevent intracellular growth of GAS in epithelial cells and that this mechanism is defective in endothelial cells. Treatment of GAS with low pH altered GAS growth rate and gene expression of virulence factors and resulted in enhanced susceptibility of GAS to intracellular lysosomal killing. Our findings reveal the existence of different mechanisms of host defense against GAS invasion between epithelial and endothelial cells.