Formyl peptide receptor 2 orchestrates mucosal protection against<i>Citrobacter rodentium</i>infection

Abstract

<i>Citrobacter rodentium</i> is an attaching and effacing intestinal murine pathogen which shares similar virulence strategies with the human pathogens enteropathogenic- and enterohemorrhagic <i>Escherichia coli</i> to infect their host. <i>C. rodentium</i> is spontaneously cleared by healthy wild-type (WT) mice whereas mice lacking Muc2 or specific immune regulatory genes demonstrate an impaired ability to combat the pathogen. Here we demonstrate that apical formyl peptide receptor 2 (Fpr2) expression increases in colonic epithelial cells during <i>C. rodentium</i> infection. Using a conventional inoculum dose of <i>C. rodentium</i>, both WT and Fpr2^-/- mice were infected and displayed similar signs of disease, although Fpr2^-/- mice recovered more slowly than WT mice. However, Fpr2^-/- mice exhibited increased susceptibility to <i>C. rodentium</i> colonization in response to low dose infection: 100% of the Fpr2^-/- and 30% of the WT mice became colonized and Fpr2^-/- mice developed more severe colitis and more <i>C. rodentium</i> were in contact with the colonic epithelial cells. In line with the larger amount of <i>C. rodentium</i> detected in the spleen in Fpr2^-/- mice, more <i>C. rodentium</i> and enteropathogenic <i>Escherichia coli</i> translocated across an <i>in vitro</i> mucosal surface to the basolateral compartment following FPR2 inhibitor treatment. Fpr2^-/- mice also lacked the striated inner mucus layer that was present in WT mice. Fpr2^-/- mice had decreased mucus production and different mucin <i>O-</i>glycosylation in the colon compared to WT mice, which may contribute to their defect inner mucus layer. Thus, Fpr2 contributes to protection against infection and influence mucus production, secretion and organization.