TLR4 Participates in the Inflammatory Response Induced by the AAF/II Fimbriae From Enteroaggregative Escherichia coli on Intestinal Epithelial Cells.

Alejandra Alvestegui,Mauricio J Farfan,James P Nataro,Mauricio Olivares-Morales,Rachel Smith,Ernesto Muñoz,Fernando Ruiz-Perez

doi:10.3389/fcimb.2019.00143

Abstract

Enteroaggregative Escherichia coli (EAEC) infections are one of the most frequent causes of persistent diarrhea in children, immunocompromised patients and travelers worldwide. The most prominent colonization factors of EAEC are aggregative adherence fimbriae (AAF). EAEC prototypical strain 042 harbors the AAF/II fimbriae variant, which mediates adhesion to intestinal epithelial cells and participates in the induction of an inflammatory response against this pathogen. However, the mechanism and the cell receptors implicated in eliciting this response have not been fully characterized. Since previous reports have shown that TLR4 recognize fimbriae from different pathogens, we evaluated the role of this receptor in the response elicited against EAEC by intestinal cells. Using a mutual antagonist against TLR2 and TLR4 (OxPAPC), we observed that blocking of these receptors significantly reduces the secretion of the inflammatory marker IL-8 in response to EAEC and AAF/II fimbrial extract in HT-29 cells. Using a TLR4-specific antagonist (TAK-242), we observed that the secretion of this cytokine was significantly reduced in HT-29 cells infected with EAEC or incubated with AAF/II fimbrial extract. We evaluated the participation of AAF/II fimbriae in the TLR4-mediated secretion of 38 cytokines, chemokines, and growth factors involved in inflammation. A reduction in the secretion of IL-8, GRO, and IL-4 was observed. Our results suggest that TLR4 participates in the secretion of several inflammation biomarkers in response to AAF/II fimbriae.

Highlights

Enteroaggregative Escherichia coli (EAEC) strains form a heterogeneous group of enteric pathogens that has been associated with both acute and persistent diarrhea in children, immunocompromised patients, and travelers worldwide (Huang et al, 2006; Hebbelstrup et al, 2014).The infective cycle of EAEC begins with bacterial adhesion to the intestinal epithelium, followed by enterotoxin and cytotoxin secretion and the induction of an inflammatory responseTLR4 and EAEC-Induced Inflammation (Estrada-Garcia and Navarro-Garcia, 2012)
aggregative adherence fimbriae (AAF)/II fimbriae have been shown to contribute to the inflammatory response elicited by EAEC in colonic epithelial cells (Harrington et al, 2005; Boll et al, 2012) and the migration of neutrophils across the epithelium mediated by MUC1 mucin (Boll et al, 2017)
In order to study the participation of TLR4 in IL-8 secretion as a response to EAEC, we determined an adequate intestinal epithelial cell line as our study model

Summary

Introduction

Enteroaggregative Escherichia coli (EAEC) strains form a heterogeneous group of enteric pathogens that has been associated with both acute and persistent diarrhea in children, immunocompromised patients, and travelers worldwide (Huang et al, 2006; Hebbelstrup et al, 2014).The infective cycle of EAEC begins with bacterial adhesion to the intestinal epithelium, followed by enterotoxin and cytotoxin secretion and the induction of an inflammatory responseTLR4 and EAEC-Induced Inflammation (Estrada-Garcia and Navarro-Garcia, 2012). EAEC strains can be divided into typical and atypical strains depending on the presence or absence of the plasmid-encoded virulence regulator AggR. This master regulator controls the expression of several chromosome- and plasmid-encoded genes, including aggregative adherence fimbriae (AAFs), a key colonization factor in EAEC pathogenesis (Harrington et al, 2006; Morin et al, 2013). AAF/II fimbriae have been shown to contribute to the inflammatory response elicited by EAEC in colonic epithelial cells (Harrington et al, 2005; Boll et al, 2012) and the migration of neutrophils across the epithelium mediated by MUC1 mucin (Boll et al, 2017). The molecular mechanism involved in the inflammatory response to these fimbriae and the receptors associated with this process are unknown

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