Outer Membrane Vesicles From Probiotic and Commensal Escherichia coli Activate NOD1-Mediated Immune Responses in Intestinal Epithelial Cells

Abstract

Gut microbiota plays a critical role in maintaining human intestinal homeostasis and host health. Bacterial extracellular vesicles are key players in bacteria–host communication, as they allow delivery of effector molecules into the host cells. Outer membrane vesicles (OMVs) released by Gram-negative bacteria carry many ligands of pattern recognition receptors that are key components of innate immunity. NOD1 and NOD2 cytosolic receptors specifically recognize peptidoglycans present within the bacterial cell wall. These intracellular immune receptors are essential in host defense against bacterial infections and in the regulation of inflammatory responses. Recent contributions show that NODs are also fundamental to maintain intestinal homeostasis and microbiota balance. Peptidoglycan from non-invasive pathogens is delivered to cytosolic NODs through OMVs, which are internalized via endocytosis. Whether this pathway could be used by microbiota to activate NOD receptors remains unexplored. Here, we report that OMVs isolated from the probiotic Escherichia coli Nissle 1917 and the commensal ECOR12 activate NOD1 signaling pathways in intestinal epithelial cells. NOD1 silencing and RIP2 inhibition significantly abolished OMV-mediated activation of NF-κB and subsequent IL-6 and IL-8 expression. Confocal fluorescence microscopy analysis confirmed that endocytosed OMVs colocalize with NOD1, trigger the formation of NOD1 aggregates, and promote NOD1 association with early endosomes. This study shows for the first time the activation of NOD1-signaling pathways by extracellular vesicles released by gut microbiota.

Interplay between Peptidoglycan Biology and Virulence in Gram-Negative Pathogens

“…The biologically active PGN fragments reviewed in this section, derived from active degradation during bacterial growth, are qualitatively and quantitatively different from those released from lysed bacteria, which, however, can also stimulate the innate immune system through our PGN-specific receptors (85). Therefore, this classic concept In this sense, it has to be noted that some works have recently shown in E. coli but also in other more niche-specific species, such as some periodontal pathogens (Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia), the association between their released OMVs and the activation of NOD1 and/or NOD2 in the host, which strongly suggests that the presence of PGN fragments within the cited vesicles potentially contributes to the inflammatory response in the infected tissues (152)(153)(154). In fact, in recent years OMVs have been recognized to be effective virulence factor delivery systems, and hence, the presence of certain PGN fragments within OMVs could contribute to this role (155)(156)(157).…”

Extracellular Vesicles Derived From Mesenchymal Stem Cells (MSC) in Regenerative Medicine: Applications in Skin Wound Healing

“…Their functionality has been observed not only between cells of the same organism, but also among cells from different organisms of the same or different species, even involving prokaryotes and eukaryotes (Kim et al, 2015;Gho and Lee, 2017). For instance, inter-kingdom communications have been found between the microbiota and the epithelial cells of the large intestine, contributing to maintain the intestinal homeostasis (Cañas et al, 2018).…”

Outer Membrane Vesicles Mediated Horizontal Transfer of an Aerobic Denitrification Gene betweenEscherichia coli

“…Vesicles in the environment transfer DNA into the recipient cell by fusing with the outer membrane (23), or entire vesicles are absorbed into receptor cells by dynamin-dependent endocytosis (26, 42). These pathways are equally applicable to the transport of virulence factors between bacteria and vesicles.…”