Autophagy Protects against Colitis by the Maintenance of Normal Gut Microflora and Secretion of Mucus

Koichiro Tsuboi,Mayo Nishitani,Atsushi Takakura,Yasuyuki Imai,Masaaki Komatsu,Hiroto Kawashima

doi:10.1074/jbc.m114.632257

Koichiro Tsuboi, Mayo Nishitani + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m114.632257

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Abstract

Genome-wide association studies of inflammatory bowel diseases identified susceptible loci containing an autophagy-related gene. However, the role of autophagy in the colon, a major affected area in inflammatory bowel diseases, is not clear. Here, we show that colonic epithelial cell-specific autophagy-related gene 7 (Atg7) conditional knock-out (cKO) mice showed exacerbation of experimental colitis with more abundant bacterial invasion into the colonic epithelium. Quantitative PCR analysis revealed that cKO mice had abnormal microflora with an increase of some genera. Consistently, expression of antimicrobial or antiparasitic peptides such as angiogenin-4, Relmβ, intelectin-1, and intelectin-2 as well as that of their inducer cytokines was significantly reduced in the cKO mice. Furthermore, secretion of colonic mucins that function as a mucosal barrier against bacterial invasion was also significantly diminished in cKO mice. Taken together, our results indicate that autophagy in colonic epithelial cells protects against colitis by the maintenance of normal gut microflora and secretion of mucus.

Highlights

The role of autophagy in colonic homeostasis is not clear
Generation of Colonic Epithelial Cell-specific autophagy-related gene 7 (Atg7) Conditional Knock-out Mice—To generate conditional knock-out (cKO) mice, we first examined the expression of Chst4 and Villin1, whose regulatory elements were used to drive Cre expression in GlcNAc6ST-2-Cre transgenic mice [26] and in Villin-Cre transgenic mice, respectively
The reduction of Atg7 mRNA expression and accumulation of autophagy substrate p62 and ubiquitinated proteins in the colon in cKO mice were confirmed by quantitative RT-PCR and Western blot analyses (Fig. 1)

Summary

Background

Results: Colonic epithelial cell-specific and autophagy-deficient mice showed exacerbation of colitis and abnormal gut microflora with less abundant antimicrobial peptide production and secretion of mucus. It is unlikely that previous studies using these mutant mice could have clarified the role of autophagy in the colon, which is a major affected area in IBDs. In this study, we took advantage of the specific Cre recombinase expression in colonic epithelial cells in a GlcNAc6ST-2-Cre transgenic mouse model [26] to delete Atg in a colonic epithelial cell-specific manner. We took advantage of the specific Cre recombinase expression in colonic epithelial cells in a GlcNAc6ST-2-Cre transgenic mouse model [26] to delete Atg in a colonic epithelial cell-specific manner By using these mutant mice, we analyzed the function of autophagy in the maintenance of gut commensal microflora and protection against UC-like colitis

Experimental Procedures

Results

Discussion