N-3-Hydroxy Dodecanoyl-DL-homoserine Lactone (OH-dDHL) Triggers Apoptosis of Bone Marrow-Derived Macrophages through the ER- and Mitochondria-Mediated Pathways.

Kyungho Woo,Dong Ho Kim,Man Hwan Oh,Ho Sung Park,Chul Hee Choi

doi:10.3390/ijms22147565

Abstract

Quorum sensing of Acinetobacter nosocomialis for cell-to-cell communication produces N-3-hydroxy dodecanoyl-DL-homoserine lactone (OH-dDHL) by an AnoR/I two-component system. However, OH-dDHL-driven apoptotic mechanisms in hosts have not been clearly defined. Here, we investigated the induction of apoptosis signaling pathways in bone marrow-derived macrophages treated with synthetic OH-dDHL. Moreover, the quorum-sensing system for virulence regulation was evaluated in vivo using wild-type and anoI-deletion mutant strains. OH-dDHL decreased the viability of macrophage and epithelial cells in dose- and time-dependent manners. OH-dDHL induced Ca2+ efflux and caspase-12 activation by ER stress transmembrane protein (IRE1 and ATF6a p50) aggregation and induced mitochondrial dysfunction through reactive oxygen species (ROS) production, which caused cytochrome c to leak. Pretreatment with a pan-caspase inhibitor reduced caspase-3, -8, and -9, which were activated by OH-dDHL. Pro-inflammatory cytokine and paraoxonase-2 (PON2) gene expression were increased by OH-dDHL. We showed that the anoI-deletion mutant strains have less intracellular invasion compared to the wild-type strain, and their virulence, such as colonization and dissemination, was decreased in vivo. Consequently, these findings revealed that OH-dDHL, as a virulence factor, contributes to bacterial infection and survival as well as the modification of host responses in the early stages of infection.

Highlights

Several Acinetobacter species, such as A. baumannii, A. nosocomialis, and A. pitti, have emerged as clinically significant in nosocomial infections and antibiotic resistance [1,2]
In Acinetobacter species, AbaI synthesizes Nacyl-homoserine lactone as autoinducer synthases and AbaR regulates the AHL synthesis of AbaI through an AbaR-AHL complex formation that binds to specific promoter sequences as autoinducer receptors [5,8]
We investigated the induction of an endoplasmic reticulum (ER)-mediated apoptosis pathway with caspase-12 and Ca2+ release and a mitochondrial-mediated pathway by OH-dDHL in macrophages

Summary

Introduction

Several Acinetobacter species, such as A. baumannii, A. nosocomialis, and A. pitti, have emerged as clinically significant in nosocomial infections and antibiotic resistance [1,2]. Quorum sensing (QS) is a communication mechanism that bacteria use to monitor their cell density in order to regulate biofilm formation, virulence factor expression, and survival under stress conditions in different environments [5]. The QS of Gram-negative bacteria is regulated by the LuxI/LuxR regulatory system, which produces N-acyl-homoserine lactone (AHL) [6,7]. In Acinetobacter species, AbaI synthesizes Nacyl-homoserine lactone as autoinducer synthases and AbaR regulates the AHL synthesis of AbaI through an AbaR-AHL complex formation that binds to specific promoter sequences as autoinducer receptors (lux-box) [5,8]. Acinetobacter species generate various acyl chain lengths of QS signal molecules, A. baumannii and A. nosocomialis generate prime N-(3-hydroxy dodecanoyl)-L-homoserine lactone (OH-dDHL) [8,9,10]. Studies have reported that AHL of the lengths C14 and C16 has been detected in Acinetobacter clinical strains; production differences may occur depending on the growth conditions in the laboratory [8,11]

Methods

Results

Conclusion