Staphylococcus aureus secretes 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.

Membrane Microvesicles as Potential Vaccine Candidates

“…In short, MVs serve as messengers between the host and the pathogen and are also used for defense. It is very important that pathogen-derived MVs carrying pathogen particles could elicit a host immune response by activating immune cells including monocytes, macrophages, T cells and NK cells [ 184 , 185 , 186 ]. Thus, MVs could be considered as a potential vaccine candidate against infectious diseases.…”

Extracellular Vesicles and Their Role in Staphylococcus aureus Resistance and Virulence

“…Regarding nucleic acids, in the study by Andreoni et al, quantification with PicoGreen dsDNA kit revealed the association of DNA molecules to S. aureus EVs [68]. Finally, Rodriguez and Kuehn recently demonstrated that S. aureus Newman strain secrets EVs containing DNAs of ~500 base-pair long and RNAs with sizes of <300 nucleotides in length [70]. However, further investigations are necessary to better characterize the nucleic acid content of S. aureus EVs.…”

“…A recent study conducted by Rodriguez et al demonstrated that nucleic acid associated with S. aureus EVs is immunomodulatory [70]. They identified DNA and RNA populations associated with EVs derived from Newman strain and provided evidence that these nucleic acids are delivered into host endosomal compartments [70]. In vitro experiments showed that murine macrophages exposed to EVs presented a strong IFN-β mRNA expression after 3 hours of stimulation [70].…”

“…They identified DNA and RNA populations associated with EVs derived from Newman strain and provided evidence that these nucleic acids are delivered into host endosomal compartments [70]. In vitro experiments showed that murine macrophages exposed to EVs presented a strong IFN-β mRNA expression after 3 hours of stimulation [70]. Pretreatment of macrophages with inhibitors of endosomal acidification strongly reduced IFN-ß mRNA expression after EV stimulation, suggesting that EVs' processing depends on the acidic endosomal environment to release their immunomodulatory cargo and promote TLR signaling [70].…”

“…In vitro experiments showed that murine macrophages exposed to EVs presented a strong IFN-β mRNA expression after 3 hours of stimulation [70]. Pretreatment of macrophages with inhibitors of endosomal acidification strongly reduced IFN-ß mRNA expression after EV stimulation, suggesting that EVs' processing depends on the acidic endosomal environment to release their immunomodulatory cargo and promote TLR signaling [70]. These results were corroborated when the exposition of TLR3−/−, TLR7−/−, and TLR9−/− mouse macrophages to EVs reflected in a substantial decrease in IFN-ß mRNA expression [70].…”