Legionella pneumophila-Derived Outer Membrane Vesicles Promote Bacterial Replication in Macrophages

Abstract

The formation and release of outer membrane vesicles (OMVs) is a phenomenon of Gram-negative bacteria. This includes Legionella pneumophila (L. pneumophila), a causative agent of severe pneumonia. Upon its transmission into the lung, L. pneumophila primarily infects and replicates within macrophages. Here, we analyzed the influence of L. pneumophila OMVs on macrophages. To this end, differentiated THP-1 cells were incubated with increasing doses of Legionella OMVs, leading to a TLR2-dependent classical activation of macrophages with the release of pro-inflammatory cytokines. Inhibition of TLR2 and NF-κB signaling reduced the induction of pro-inflammatory cytokines. Furthermore, treatment of THP-1 cells with OMVs prior to infection reduced replication of L. pneumophila in THP-1 cells. Blocking of TLR2 activation or heat denaturation of OMVs restored bacterial replication in the first 24 h of infection. With prolonged infection-time, OMV pre-treated macrophages became more permissive for bacterial replication than untreated cells and showed increased numbers of Legionella-containing vacuoles and reduced pro-inflammatory cytokine induction. Additionally, miRNA-146a was found to be transcriptionally induced by OMVs and to facilitate bacterial replication. Accordingly, IRAK-1, one of miRNA-146a’s targets, showed prolonged activation-dependent degradation, which rendered THP-1 cells more permissive for Legionella replication. In conclusion, L. pneumophila OMVs are initially potent pro-inflammatory stimulators of macrophages, acting via TLR2, IRAK-1, and NF-κB, while at later time points, OMVs facilitate L. pneumophila replication by miR-146a-dependent IRAK-1 suppression. OMVs might thereby promote spreading of L. pneumophila in the host.

A MicroRNA Network Controls Legionella pneumophila Replication in Human Macrophages via LGALS8 and MX1

“…Exemplarily, the miRNAs miR-146a, miR-155, miR-27a, and miR-125a were upregulated in a time-dependent manner, whereas miR-221, miR-222, miR-125b, miR-26a, and miR-29b were downregulated in response to L. pneumophila infection. We have shown before that miR-146a can facilitate Legionella replication inside the host cell via degradation of IRAK1 mRNA (42). In the present study, miR-125b, miR-221, and miR-579 were of particular interest.…”

“…L. pneumophila strain Corby wild type or a gfp-expressing strain (kindly provided by K. Heuner, RKI, Berlin, Germany) was routinely grown on buffered charcoal-yeast extract (BCYE) agar plates at 37°C for 3 days. Infection was carried out as described before (42).…”

Methylomic Changes of Autophagy-Related Genes by Legionella Effector Lpg2936 in Infected Macrophages

“…Legionella infection of macrophages induces a variety of proinflammatory cytokines during bacterial replication (McHugh et al, 2000;Jung et al, 2016). To determine whether RNAi of Legionella effector Lpg2936 affects cytokine secretion, the concentration of IL-1α, IL-1β, IL-6, and TNF-α was monitored in culture media of infected macrophages using ELISA.…”

Non-coding RNAs in pneumonia diagnosis

“…Выживаемость инфицированных макрофагов повышалась, несмотря на внутриклеточный рост бактерии, кроме этого, происходила активация транскрипции противовоспалительной miRNA-146а и снижение уровня белка ее гена-мишени -связанной с IL-1 киназы IRAK-1. Предполагается, что бактерии L. pneumophila с помощью своих мембранных везикул облегчают собственную репликацию внутри макрофагов путем зависимой от miRNA-146а супрессии IRAK-1 [35].…”