Chronic smoke exposure is associated with autophagy in murine Peyer's patches

INTRODUCTION: Cigarette smoke causes oxidative stress, leading to smoke-induced autophagy in several organs. Autophagy is a homeostatic process regulating the turnover of proteins and cytoplasmatic organelles. However, recently it has also been associated with many autoimmune and inflammatory disorders, among which Crohn’s disease. The purpose of the present study was to investigate whether cigarette smoke exposure is associated with increased autophagy in Peyer’s patches and its epithelium. AIMS & METHODS: C57BL/6 mice were exposed to cigarette smoke or air. After 24 weeks, the animals were sacrificied and Peyer’s patches were collected. m RNA expression of autophagy-related genes was determined by RT-PCR. Transmission electron microscopy (TEM) was used to evaluate the presence of autophagic vesicles in the follicleassociated epithelium of Peyer’s patches. RESULTS: Expression of Beclin-1, a protein involved in the nucleation of autophagosomes, and of Atg5 and Atg7, which both play a role in the autophagosome vesicle elongation and completion, increased after chronic smoke exposure. Furthermore, electron microscopy of the follicle-associated epithelium demonstrated that the mean area of autophagic vesicles per epithelial cell increased considerably from 1.1 μm2 ± 0.4 μm2 in the air group to 2.4 μm2 ± 0.4 μm2 in the smoke group (p < 0.05). Epithelial cells had a significantly higher number of autophagic vesicles after smoke exposure (1.1 ± 0.1 after smoke exposure versus 0.5 ± 0.1 vesicles per cell after air exposure, p < 0.05), but the size of the vesicles did not differ between both groups. CONCLUSION: Here we provide the first evidence that chronic exposure to cigarette smoke is associated with autophagy in murine Peyer’s patches, and more in particular in the follicle-associated epithelium covering Peyer’s patches. Our findings can help to understand the role of smoking in the pathogenesis of inflammatory bowel disease, such as Crohn’s disease