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

Abstract

Pulmonary epithelial barrier dysfunction is a critical pathophysiological process in pneumonia and associated invasive infections, such as those caused by Acinetobacter baumannii. However, the mechanisms underlying A. baumannii-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 A. baumannii wild-type strain and an outer membrane protein A (ompA) deletion strain. In addition, epithelial cells in culture were treated with purified OmpA protein or transfected with a eukaryotic expression vector encoding ompA (pCMV-ompA). Bacterial translocation across cell monolayers and intrapulmonary burden were measured, barrier function was evaluated in vivo and in vitro; 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 A. baumannii 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 via cytoskeleton dynamic remodeling, and cellular redistribution of the major AJ protein, E-cadherin. These observations indicate that A. baumannii uses OmpA to overcome epithelial defences and cross the pulmonary epithelial barrier.

Interactions between host epithelial cells and Acinetobacter baumannii promote the emergence of highly antibiotic resistant and highly mucoid strains

“…sepsis), particularly in immunosuppressed patients or those on mechanical ventilation, leading to a high mortality rate [ 7 ]. Virulence factors such as OmpA, lipopolysaccharides, and capsule [ 8 , 9 ] mediate host colonization and damage. Especially, capsular exopolysaccharide and associated mucoid phenotype have emerged as a universal virulence factor owing to several observations [ 10 ].…”

Exposure of Aspergillus fumigatus to Klebsiella pneumoniae Culture Filtrate Inhibits Growth and Stimulates Gliotoxin Production

“…Analysis of the K. pneumoniae culture filtrate identified 160 high-confidence proteins ( Table S1 ), of which 35 were identified to have possible effects on fungal development ( Table 1 ) and three of which (putative lipoprotein, outer membrane protein A and chaperone protein DnaK) were also bound to the fungal mycelia. Outer membrane protein A is essential for A. baumannii cell attachment to Candida albicans filaments and A549 human alveolar epithelial cells [ 23 ] and has been demonstrated to induce leaky barriers in murine lungs and human A549 cells without affecting cell viability [ 24 ]. Elongation factor Tu was identified in the K. pneumoniae culture filtrate is involved in bacterial virulence and is associated with adhesion to host extracellular matrix components.…”

“…Proteomic analysis revealed that five proteins involved in the biosynthesis of gliotoxin were increased in abundance; glutathione S-transferase (+6.17 fold), non-ribosomal peptide synthase (+3.67 fold), O-methyltransferase (+3.5 fold), gamma-glutamyl acyltransferase (+2.89 fold) and thioredoxin reductase (+2.33 fold). The increase in gliotoxin production may be attributed to the physical binding of outer membrane protein A, due to its ability to induce leakage in epithelial cells [ 24 ] in a similar manner to fungistatic concentrations of amphotericin B which increases A. fumigatus permeability and stimulates de novo gliotoxin biosynthesis [ 36 ].…”

Deciphering the virulence factors, regulation, and immune response to Acinetobacter baumannii infection

“…Outer membrane proteins (OMPs) such as OmpA help in attachment and internalization into host epithelial cells. In addition to this, OmpA induces secretion of apoptotic factors inside the host cell that initiates the apoptosis process leading to cell death (Choi et al, 2008a;Choi et al, 2008;Moon et al, 2012;Zhang et al, 2022). Capsular exopolysaccharides in A. baumannii protect the pathogen from environmental and host-mediated stresses, and the composition determines the degree of virulence (Tipton and Rather, 2017;Singh et al, 2019;Talyansky et al, 2021).…”

“…It causes downregulation and internalization of Ecadherin, an important adhesion junction protein, thereby increasing lung epithelial permeability. It also causes actin reorganization in lung epithelial cells (Zhang et al, 2022).…”