Bacteria‑host transcriptional response during intestinal epithelial cells infection by Klebsiella pneumoniae

Klebsiella pneumoniae (K. pneumoniae) is an opportunistic pathogen responsible for severe hospital and community infections. Despite intestinal infections caused by K. pneumoniae are relatively rare, most systemic infections originate from its initial colonization of the gastrointestinal tract. However, the understanding of how K. pneumoniae interacts with human hosts is limited. In this study, we employed dual RNA-seq to characterize the interactions between K. pneumoniae and human intestinal epithelial cell (Caco-2). Differential gene expression analysis highlighted 331 altered genes in K. pneumoniae and 173 in infected Caco-2 cells. KEGG analysis revealed enrichment of these host genes in the HIF-1 and PI3K-Akt signaling pathways. Notably, the host genes encoding REDD1, BHLHE40, ANKRD37 and NLRP3 exhibited significant upregulation upon infection. REDD1 expression was progressively induced during infection, both at the mRNA and protein levels (significantly at 2h and 4h infection). In addition, functional study showed that siRNA-mediated knock-down of REDD1 did not affect intestinal epithelial tight junction integrity. However, REDD1 was critical for facilitating the intracellular invasion of K. pneumoniae. Finally, we found that molybdenum cofactor biosynthesis protein of K. pneumoniae encoded by mogA may promote bacterial invasion through host REDD1. This study for the first time demonstrated the potential interaction between K. pneumoniae and human intestinal epithelium.

肺炎克雷伯菌（Klebsiella pneumoniae, K. pneumoniae）是一种机会致病菌，可引发严重的医院获得性及社区获得性感染。尽管该菌引发的肠道感染相对罕见，但绝大多数全身性感染均源于其在胃肠道的初始定植。然而，目前学界对肺炎克雷伯菌与人类宿主的互作机制认知仍较为有限。本研究采用双转录组测序（dual RNA-seq）技术，解析肺炎克雷伯菌与人类肠道上皮细胞（Caco-2）之间的互作过程。差异基因表达分析显示，肺炎克雷伯菌中有331个基因表达发生显著改变，受感染的Caco-2细胞中则有173个基因表达异常。KEGG富集分析结果表明，这些宿主基因显著富集于HIF-1信号通路与PI3K-Akt信号通路中。值得注意的是，编码REDD1、BHLHE40、ANKRD37及NLRP3的宿主基因在感染后均呈现显著上调表达。在感染过程中，REDD1的mRNA与蛋白水平均呈渐进式诱导表达，在感染后2小时及4小时时上调差异尤为显著。此外，功能实验结果显示，通过小干扰RNA（small interfering RNA, siRNA）敲低REDD1的表达，并不会影响肠道上皮细胞的紧密连接完整性，但REDD1对于促进肺炎克雷伯菌的细胞内侵袭过程至关重要。最后，本研究发现，由mogA基因编码的肺炎克雷伯菌钼辅因子生物合成蛋白，可能通过靶向宿主REDD1蛋白促进细菌侵袭。本研究首次揭示了肺炎克雷伯菌与人类肠道上皮之间的潜在互作机制。