Staphylococcus aureussecretes immunomodulatory RNA and DNA via membrane vesicles

Abstract

Bacterial-derived RNA and DNA can function as ligands for intracellular receptor activation and induce downstream signaling to modulate the host response to bacterial infection. The mechanisms underlying the secretion of immunomodulatory RNA and DNA by pathogens such as Staphylococcus aureus and their delivery to intracellular host cell receptors are not well understood. Recently, extracellular membrane vesicle (MV) production has been proposed as a general secretion mechanism that could facilitate the delivery of functional bacterial nucleic acids into host cells. S. aureus produce membrane-bound, spherical, nano-sized, MVs packaged with a select array of bioactive macromolecules and they have been shown to play important roles in bacterial virulence and in immune modulation through the transmission of biologic signals to host cells. Here we show that S. aureus secretes RNA and DNA molecules that are mostly protected from degradation by their association with MVs. Importantly, we demonstrate that MVs can be delivered into cultured macrophage cells and subsequently stimulate a potent IFN-β response in recipient cells via activation of endosomal Toll-like receptors. These findings advance our understanding of the mechanisms by which bacterial nucleic acids traffic extracellularly to trigger the modulation of host immune responses.

Environmental Plasticity of the RNA Content of Staphylococcus aureus Extracellular Vesicles

“…The low RNA coverage in the HG003 EVs might perhaps reflect the absence of transcription within EVs and, thus, the progressive degradation of a substantial fraction of the EVs-associated RNAs after their formation and/or during their purification. These findings are consistent with a recent report showing that the predominant RNA type in EVs from S. aureus Newman is <300-nucleotide long (Rodriguez and Kuehn, 2020). The presence of numerous processed or degraded RNAs could be a common feature of the bacterial EVs, as Gram-negative S. Typhimurium OMV-associated RNAs are also processed or degraded (Malabirade et al, 2018).…”

“…Transfer of functional RNAs to bacterial cells that do not encode the corresponding genes in their genome could also be part of a transient horizontal phenotype acquisition, which could be of use during infection to disseminate specific virulence-associated factors through the bacterial community. Finally, beside interactions between bacterial cells, S. aureus EV associated RNAs, notably sRNAs, may be involved in the host-pathogen interactions (Eberle et al, 2009;Li and Chen, 2012;Furuse et al, 2014;Sha et al, 2014;Koeppen et al, 2016;Westermann et al, 2016;Choi et al, 2017;Frantz et al, 2019;Han et al, 2019;Lee, 2019;Rodriguez and Kuehn, 2020). The 28 potential annotated sRNA detected within HG003 EVs are potential candidates for further functional characterization, especially during S. aureus-host cell interactions.…”

“…The 28 potential annotated sRNA detected within HG003 EVs are potential candidates for further functional characterization, especially during S. aureus-host cell interactions. S. aureus secreted EVs elicit immune responses that mimic those of the EV-producing cells (Gurung et al, 2011;Hong et al, 2011Hong et al, , 2014Kim et al, 2012Kim et al, , 2019Thay et al, 2013;Choi et al, 2015;Jeon et al, 2016;Jun et al, 2017;Askarian et al, 2018;Tartaglia et al, 2018;Wang et al, 2018Wang et al, , 2020Rodriguez and Kuehn, 2020). Strikingly, within their RNA cargo, several mRNAs encode immunomodulatory proteins, as Sbi, Spa and PSMβ1, and may participate into the immune response triggered by the protein cargo if they are ultimately translated.…”

“…Likewise, transfection of OMV-associated sRNAs from the periodontal pathogens Aggregatibacter actinomycetemcomitans, Phorphyromonas gingivalis, and Trepanema denticola into human cells reduced host interleukine release (Choi et al, 2017). The presence of RNAs within Gram-positive EVs has been reported for fewer species (Resch et al, 2016;Dauros Singorenko et al, 2017;Frantz et al, 2019;Rodriguez and Kuehn, 2020). Interestingly, Frantz et al (2019) recently reported that the EV-associated rli32 sRNA of Listeria monocytogenes can trigger the induction of a type I IFN response in host cells.…”

“…Data about RNA cargo in EVs released by S. aureus are scarce, with only two recent reports. While the first provided a partial RNA profile of S. aureus MSSA476 EVs without functional analyses (Joshi et al, 2021), the second showed that the uncharacterized RNA content of S. aureus Newman EVs likely stimulate the potent IFN-β response observed in cultured macrophage cells (Rodriguez and Kuehn, 2020).…”