Data showing levels of interleukin-1β and nitric oxide in the plasma of uropathogenic E. coli infected UTI patients

Outer membrane vesicles from Escherichia coli are efficiently internalized by macrophage cells and alter their inflammatory response

The release of extracellular vesicles (EV) by pathogenic microbes is considered an alternative cell-to-cell transport of macromolecules transport mechanism. In Gram-negative bacteria, EVs may be formed by outer membrane budding, so-called outer membrane vesicles (OMVs). Previous studies have revealed E. coli constitutively release nano-sized OMVs, which can be potent activators of cellular functions without live bacteria. But the immunomodulatory activity of E. coli OMVs is still relatively poorly understood. Here we investigated the morphological characterization and composition of E.Coli OMVs, kinetics of internalization by Raw 264.7 macrophage cells, and their immunomodulatory activity on cells. By transmission electron microscopy and dynamic light scattering, E.Coli OMVs were identified as typical cup-shaped, bilayered membranous structures, mainly distributed between 72.5 and 212.5 nm. We also demonstrated by confocal fluorescence microscopy that exposure of Raw 264.7 cells to E.Coli OMVs resulted in internalization of these nanoparticles and decreased mitochondrial membrane potential. In addition, E. Coli OMVs treatment induced the production of ROS, iNOS, IL-1β, IL-6, IL-10 and up-regulation of CD86 and CD206. Taken together, our results indicated that E.Coli OMVs are immunobiologically active, can directly interact with macrophage and participate in immune responses.

Involvement of NLRP3 and NLRC4 Inflammasome in Uropathogenic E. coli Mediated Urinary Tract Infections

Background

Inflammatory response during urinary tract infection (UTI) is mediated by innate immune defense. Nod like receptors (NLRs) have been proposed to work simultaneously beside TLR pathways to mediate pro-inflammatory response and maintain tissue homeostasis. Some in vitro reports have showed the involvement of NLRP3 inflammasome during uropathogenic Escherichia coli (UPEC) mediated UTI. So we have sought to determine the status of various inflammasomes and their components in UPEC mediated UTI.

Methods

A total of 186 females experiencing the first episode of UTI were recruited for the study and forty were found to be positive for UPEC (≥10⁵ CFU/ml) in their urine (N = 40). Further, we analyzed the expression of NLRP3, NLRC4, NAIP, AIM2, ASC, CASPASE-4, and CASPASE-1 gene at mRNA and protein level in the blood of UPEC confirmed study subjects through real time qPCR and immunoblotting. Healthy females (N = 40) visiting the OPD for health checkups, family planning advice and subjects undergoing routine medical examinations, were recruited as healthy control subjects. Pro-inflammatory cytokines (IL-6, IL-8, IFN-γ, TNF-α and MCP-1) were measured in the plasma of patients and controls through ELISA. For investigation of the involvement of NLRC4 and NLRP3 inflammasome, in vitro studies were performed using co-immunoprecipitation and confocal microscopy.

Results

Most of the inflammatory regulators studied (i.e., NLRP3, NAIP, NLRC4, ASC, and CASPASE-1) were found to be up-regulated at both mRNA and protein levels in the UPEC infected UTI patients. Also, pro-inflammatory cytokines (IL-6, IL-8, IFN-γ, TNF-α, and MCP-1) were found to be up-regulated in the patients group. However, no significant difference was observed in the expression of AIM2 and CASPASE-4 genes at both mRNA and protein levels. Further, in vitro studies have shown the involvement of NLRC4 inflammasome in UPEC infected THP1 derived macrophages.

Conclusion

Involvement of NLRP3 and NLRC4 inflammasomes in UPEC infected UTI is evident from our findings. This is the first report showing levels of inflammasome and its components in UTI patients suggesting a possible role during UPEC mediated UTI. We have also reported the involvement of NLRC4 inflammasome for the first time during UTI infection.