Abstract
Neisseria gonorrhoeae causes the sexually transmitted disease gonorrhoea by evading innate immunity. Colonizing the mucosa of the reproductive tract depends on the bacterial outer membrane porin, PorB, which is essential for ion and nutrient uptake. PorB is also targeted to host mitochondria and regulates apoptosis pathways to promote infections. How PorB traffics from the outer membrane of N. gonorrhoeae to mitochondria and whether it modulates innate immune cells, such as macrophages, remains unclear. Here, we show that N. gonorrhoeae secretes PorB via outer membrane vesicles (OMVs). Purified OMVs contained primarily outer membrane proteins including oligomeric PorB. The porin was targeted to mitochondria of macrophages after exposure to purified OMVs and wild type N. gonorrhoeae. This was associated with loss of mitochondrial membrane potential, release of cytochrome c, activation of apoptotic caspases and cell death in a time-dependent manner. Consistent with this, OMV-induced macrophage death was prevented with the pan-caspase inhibitor, Q-VD-PH. This shows that N. gonorrhoeae utilizes OMVs to target PorB to mitochondria and to induce apoptosis in macrophages, thus affecting innate immunity.
Highlights
Neisseria gonorrhoeae causes the sexually transmitted disease gonorrhoea
In the absence of effective vaccines and the rise of antibiotic resistance, understanding the molecular interactions between innate immune cells and N. gonorrhoeae may lead to new strategies to combat bacterial growth and the symptoms of gonorrhoea
To study the role of N. gonorrhoeae secreted outer membrane vesicles (OMVs), we first established methods for the purification of OMVs under optimal growth conditions to minimize bacterial autolysis and contamination with membranous and cytosolic materials, all of which are affected by culture conditions [30]
Summary
With more than 100 million cases reported every year, gonorrhoea is the second most commonly reported sexually transmitted bacterial infection. N. gonorrhoeae replicates primarily extracellularly within the mucosa of reproductive organs, resulting in localized inflammation and pelvic inflammatory diseases due to bacterial dissemination. Mucosal resident macrophages and the recruited neutrophils and monocytes fail to control N. gonorrhoeae replication [3]. It is thought that N. gonorrhoeae modulates the antimicrobial activities of neutrophils and macrophages, including apoptosis pathways, to promote bacterial survival [4]. The major porin protein, PorB, has been identified to modulate apoptotic pathways in N. gonorrhoeae infections [4,5,6,7,8,9,10,11]
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