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P694. Chronic cigarette smoke exposure alters the murine gut microbiome

L. Allais1, F.-M. Kerckhof2, S. Verschuere1, K. Bracke3, R. De Smet1, D. Laukens4, M. Devos4, N. Boon2, G. Brusselle3, T. Van de Wiele2, C. Cuvelier1, 1Ghent University, Pathology, Faculty of Medicine & Health Sciences, Ghent, Belgium, 2Ghent University, Laboratory of Microbial Ecology and Technology, Faculty of Bioscience Engineering, Ghent, Belgium, 3Ghent University, Laboratory for Translational Research in Obstructive Pulmonary diseases, Department of Respiratory Medicine, Faculty of Medicine & Health Sciences, Ghent, Belgium, 4Ghent University, Department of Gastroenterology, Faculty of Medicine & Health Sciences, Ghent, Belgium

Background

The microbiome plays a crucial role in maintaining intestinal homeostasis. Disruption of this homeostatic environment leads to destabilisation of the gut immune system and aberrant immune responses against harmless microbiota, which may be involved in the development of Crohn's disease (CD). The most prominent environmental risk factor for CD is smoking. Therefore, the present study aims to investigate the influence of cigarette smoke on the microbiome, in particular the mucosa-adherent microbiota, and how this is linked to changes in mucin production.

Methods

C57BL/6 mice were exposed to cigarette smoke (n = 6) or air (n = 6) according to a well-established protocol. After 24 weeks, the animals were sacrificed and multiple parts of the gut (ileum, proximal and distal colon) were collected. The microbial composition was analysed using denaturing gradient gel electrophoresis (DGGE) and 454 pyrosequencing. Furthermore, the expression of mucins was determined at both the mRNA level (real-time PCR) and the protein level (Alcian Blue (AB)/Periodic Acid Schiff (PAS), High Iron Diamine (HID)/AB staining).

Results

Analysis of the microbiome in smoke- and air-exposed mice revealed that the diversity of the bacterial population changed significantly after smoke exposure in all parts of the gut. In addition, the abundance of specific species, in particular Bifidobacterium sp. and Clostridium sp., tended to decrease in response to cigarette smoke in both colonic and ileal samples. A general analysis of mucin expression, using AB/PAS and HID/AB, could not demonstrate an altered expression of acidic and neutral mucins, nor changes in sulphated and sialylated mucins after cigarette smoke exposure. However, in the ileum, mRNA expression of MUC2 and MUC3 significantly increased after cigarette smoke exposure (p = 0.04 and p = 0.03 respectively). In contrast, colonic expression of MUC2 and MUC3 was unaltered, but an increased expression of MUC4 was observed (p = 0.04).

Conclusion

Comparative microbial analysis in mice showed a general shift in the mucosa-adherent bacterial population, as well as specific changes in Bifidobacterium sp. and Clostridium sp., in response to cigarette smoke. In addition, smoking alters intestinal mucins, which play an important role in the gut barrier, but also in the colonization efficiency of specific gut microbiota. These findings may point to a role for altered interactions between the microbiome and intestinal mucosa contributing to the effect of smoking on intestinal homeostasis.