A common role for Atg16L1, Atg5 and Atg7 in small intestinal Paneth cells and Crohn disease

Abstract

Recently identified genetic determinants for enhanced susceptibility to Crohn disease (CD) included polymorphisms in the ATG16L1 and IRGM1 loci suggesting that the autophagy pathway plays a role in the pathogenesis of this disease. We have generated and analyzed three mouse models with diminished expression of autophagy proteins and show how the loss of function of various autophagy components contributes to CD pathogenesis. In the mouse small intestine, one common cellular target of Atg16L1, Atg5 and Atg7 is the Paneth cell, a specialized epithelial cell whose main function is the delivery of antimicrobial factors into the intestinal lumen by production and secretion of its characteristic cytoplasmic granules. Autophagy-deficient Paneth cells exhibited a striking loss of function in this granule exocytosis pathway. Transcriptional analysis revealed a gain of function whereby the gene expression associated with inflammatory responses was increased in autophagy-deficient Paneth cells. Importantly, we validated these findings by analyzing intestinal tissues from CD patients. Similar Paneth cell abnormalities were observed in CD patients homozygous for the ATG16L1 risk allele. Thus, one role for the autophagy pathway in CD pathogenesis is through selective effects on the biology and specialized properties of Paneth cells.

Figure 1

Loss of Atg7 in the intestinal epithelium leads to Paneth cell abnormalities similar to those associated with loss of function for both Atg16L1 and Atg5. Atg7^flox/flox mice were bred with mice expressing the Cre recombinase from the villin promoter (villin-Cre) to generate mice with conditional deletion of Atg7 in the intestinal epithelium (Atg7^flox/floxvillin-Cre). (A–D) Histological examination of the distal (ileal) small intestine reveals morphologically aberrant Paneth granules in mice with loss of Atg7. Ileal sections from Atg7^flox/flox control (A,C,E) or Atg7^flox/floxvillin-Cre mice (B,D,F) were stained with hematoxylin and eosin (A,B), PAS/alcian blue (C,D), or goat-anti lysozyme antisera and Alexaflour 488-labled donkey anti-goat Ig (E,F). Mice with loss of Atg7 in the intestinal epithelium contain Paneth cell granules that are abnormal in size, morphology, and number. Instead of labeling granules as in Atg7^flox/flox control Paneth cells, lysozyme staining displayed abnormal diffuse cytoplasmic distribution in Atg7^flox/floxvillin-Cre samples. Green represents lysozyme, blue represents nuclei, and the dashed line denotes the crypt unit. Bars=10 µm.