Atg16l1 is required for autophagy in intestinal epithelial cells and protection of mice from Salmonella infection

Abstract

Background & aims: Intestinal epithelial cells aid in mucosal defense by providing a physical barrier against entry of pathogenic bacteria and secreting antimicrobial peptides (AMPs). Autophagy is an important component of immune homeostasis. However, little is known about its role in specific cell types during bacterial infection in vivo. We investigated the role of autophagy in the response of intestinal epithelial and antigen-presenting cells to Salmonella infection in mice.

Methods: We generated mice deficient in Atg16l1 in epithelial cells (Atg16l1(f/f) × Villin-cre) or CD11c(+) cells (Atg16l1(f/f) × CD11c-cre); these mice were used to assess cell type-specific antibacterial autophagy. All responses were compared with Atg16l1(f/f) mice (controls). Mice were infected with Salmonella enterica serovar typhimurium; cecum and small-intestine tissues were collected for immunofluorescence, histology, and quantitative reverse-transcription polymerase chain reaction analyses of cytokines and AMPs. Modulators of autophagy were screened to evaluate their effects on antibacterial responses in human epithelial cells.

Results: Autophagy was induced in small intestine and cecum after infection with S typhimurium, and required Atg16l1. S typhimurium colocalized with microtubule-associated protein 1 light chain 3β (Map1lc3b or LC3) in the intestinal epithelium of control mice but not in Atg16l1(f/f) × Villin-cre mice. Atg16l1(f/f) × Villin-cre mice also had fewer Paneth cells and abnormal granule morphology, leading to reduced expression of AMPs. Consistent with these defective immune responses, Atg16l1(f/f) × Villin-cre mice had increased inflammation and systemic translocation of bacteria compared with control mice. In contrast, we observed few differences between Atg16l1(f/f) × CD11c-cre and control mice. Trifluoperazine promoted autophagy and bacterial clearance in HeLa cells; these effects were reduced upon knockdown of ATG16L1.

Conclusions: Atg16l1 regulates autophagy in intestinal epithelial cells and is required for bacterial clearance. It also is required to prevent systemic infection of mice with enteric bacteria.

Keywords: AMP; ATG; Autophagy; Discosoma sp. red fluorescent protein; EGFP; FAE; GFP; IL; Intestinal Barrier; LC3; MEF; MLN; Map1lc3b; Mouse Model; Mucosa; SCV; Salmonella-containing vacuole; TFP; antimicrobial peptide; autophagy-related gene; dsRed; enhanced green fluorescent protein; follicle-associated epithelium; green fluorescent protein; interleukin; light chain 3; mRNA; mesenteric lymph nodes; messenger RNA; microtubule-associated protein 1 light chain 3b; mouse embryonic fibroblast; trifluoperazine.