Sustained exposure to outer membrane vesicles from Escherichia coli develop mitochondrial oxidative stress and induce autophagy of macrophage.

Escherichia coli constitutively release nano-sized outer membrane vesicles (OMVs) containing numerous virulence factors and immunomodulatory proteins. In this research, we demonstrate that OMVs isolated from the E. coli readily entered Raw 264.7 macrophages and were randomly dispersed within the cytoplasm, and therefore able to deliver their molecular cargos to host cells. With electron microscopy, it can also be observed that OMVs attached to the cell surface or existed in the membrane vesicles of the cell. E. coli-OMVs proved to be non-toxic and had no obvious negative impact on the viability of macrophage cells when the concentration ranged from 1 to 10 µg/mL. The OMVs were targeted to mitochondria of Raw 264.7 macrophage, which was accompanied by elevated intracellular reactive oxygen species levels, activated autophagy, and a marked reduction in intracellular ATP levels-a hallmark of mitochondrial dysfunction. Consistent with this, E. coli-OMVs induced massive and dose-dependent proinflammatory responses in macrophage cells. Altogether, these results indicated that E. coli exploits OMVs to target virulence factors and immunomodulatory proteins to host cells, triggering mitochondrial dysfunction, autophagy, and proinflammatory responses, thus consequently affecting host-pathogen interactions in course of infection.