ABSTRACT

The intracellular pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium) exploits host macrophage as a crucial survival and replicative niche. To minimize host immune response stimulated by flagellin, the expression of flagellar genes is downregulated during S. Typhimurium growth within host macrophages. However, the underlying mechanisms are largely unknown. In this study, we show that STM14_1285 (named AsiR), a putative RpiR-family transcriptional regulator, which is downregulated within macrophages as previously reported and also confirmed here, positively regulates the expression of flagellar genes by directly binding to the promoter of flhDC. By generating an asiR mutant strain and a strain that persistently expresses asiR gene within macrophages, we confirmed that the downregulation of asiR contributes positively to S. Typhimurium replication in macrophages and systemic infection in mice, which could be attributed to decreased flagellar gene expression and therefore reduced flagellin-stimulated secretion of pro-inflammatory cytokines IL-1β and TNF-α. Furthermore, the acidic pH in macrophages is identified as a signal for the downregulation of asiR and therefore flagellar genes. Collectively, our results reveal a novel acidic pH signal-mediated regulatory pathway that is utilized by S. Typhimurium to promote intracellular replication and systemic pathogenesis by repressing flagellar gene expression.

摘要

细胞内病原体肠炎沙门氏菌血清型鼠伤寒沙门氏菌 ( S. Typhimurium) 利用宿主巨噬细胞作为关键的生存和复制生态位。为了最大限度地减少由鞭毛蛋白刺激的宿主免疫反应，鞭毛基因的表达在S期间下调。宿主巨噬细胞内的鼠伤寒杆菌生长。然而，潜在的机制在很大程度上是未知的。在这项研究中，我们展示了 STM14_1285（命名为 AsiR），一种推定的 RpiR 家族转录调节因子，如先前报道的那样在巨噬细胞内下调，并在此处得到证实，通过直接结合flhDC的启动子正向调节鞭毛基因的表达。通过生成asiR突变菌株和在巨噬细胞内持续表达asiR基因的菌株，我们证实asiR的下调对S . 鼠伤寒杆菌在巨噬细胞中的复制和小鼠的全身感染，这可能是由于鞭毛基因表达降低，从而减少鞭毛蛋白刺激的促炎细胞因子 IL-1β 和 TNF-α 的分泌。此外，巨噬细胞中的酸性 pH 值被确定为下调asiR和鞭毛基因的信号。总的来说，我们的结果揭示了一种新的酸性 pH 信号介导的调节途径，该途径被S. Typhimurium 通过抑制鞭毛基因表达促进细胞内复制和全身发病机制。