AUTHOR=Zhang Wang , Zhou Hua , Jiang Yan , He Jintao , Yao Yue , Wang Jianfeng , Liu Xiaochen , Leptihn Sebastian , Hua Xiaoting , Yu Yunsong 

TITLE=Acinetobacter baumannii Outer Membrane Protein A Induces Pulmonary Epithelial Barrier Dysfunction and Bacterial Translocation Through The TLR2/IQGAP1 Axis

JOURNAL=Frontiers in Immunology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2022.927955

DOI=10.3389/fimmu.2022.927955

ISSN=1664-3224

ABSTRACT=<p>Pulmonary epithelial barrier dysfunction is a critical pathophysiological process in pneumonia and associated invasive infections, such as those caused by <italic>Acinetobacter baumannii</italic>. However, the mechanisms underlying <italic>A. baumannii</italic>-induced pulmonary epithelial barrier dysfunction and bacterial translocation remain unclear. In this study, lungs of mice and A549 human epithelial cell monolayers were challenged with the <italic>A. baumannii</italic> wild-type strain and an outer membrane protein A (<italic>ompA</italic>) deletion strain. In addition, epithelial cells in culture were treated with purified OmpA protein or transfected with a eukaryotic expression vector encoding <italic>ompA</italic> (pCMV-<italic>ompA</italic>). Bacterial translocation across cell monolayers and intrapulmonary burden were measured, barrier function was evaluated <italic>in vivo</italic> and <italic>in vitro</italic>; cell migration ability was determined. The specific inhibitors C29 and JSH-23 were used to suppress the activity of Toll-like receptor 2 (TLR2) and of NF-κB, respectively. IQ-GTPase-activating protein 1 (IQGAP1) small interfering RNA was used to knock down endogenous IQGAP1 expression. In this work, we show that OmpA from <italic>A. baumannii</italic> increased the production of pro-inflammatory cytokines, remodeled the cytoskeleton, and internalized intercellular adherens junctions (AJs); these changes eventually induced pulmonary epithelial barrier dysfunction to promote bacterial translocation. IQGAP1-targeting small interfering RNA and chemical inhibition of TLR2 or NF-κB prevented high permeability of the pulmonary epithelial barrier. TLR2/NF-κB signaling was involved in OmpA-induced inflammation, IQGAP1-mediated OmpA-induced opening of the pulmonary epithelial barrier <italic>via</italic> cytoskeleton dynamic remodeling, and cellular redistribution of the major AJ protein, E-cadherin. These observations indicate that <italic>A. baumannii</italic> uses OmpA to overcome epithelial defences and cross the pulmonary epithelial barrier.</p>