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DOP015. Gut microbiota can induce autophagy in intestinal epithelial cells, a concern for Crohn's disease

M.-L. Tran-Minh1, E. Quévrain1, L. Brot1, G. Thomas1, J.-P. Grill1, G. Trugnan1, P. Seksik1,2, 1INSERM, Université Paris 6, ERL U1057/UMR 7203, Paris, France, 2Hopital Saint Antoine, Gastro Enterologie, Paris, France

Background

Autophagy, a physiologic self-degradation process of intracellular components is involved in Crohn's disease (CD) pathogeny. CD associated dysbiosis is characterized by a decrease of the Firmicutes phylum, especially of the species Faecali-bacterium prausnitzii. Animal studies suggest a link between autophagy and gut microbiota. In order to explore whether dysbiosis could impact autophagy, we searched to determine if gut commensal bacteria are able to modulate autophagic process in intestinal epithelial cells.

Methods

Modulation of autophagy by supernatants of ten major commensal bacteria of gut microbiota has been evaluated by quantifying LC3 lipidation (LC3-II) in MDCK GFP-LC3 transfected cells and in human intestinal Caco-2 cells. LC3-II protein level was monitored by fluorescence microscopy, immunofluorescence (IF) and western blotting (WB) with and without chloroquine (50 µM) in order to discriminate induction in the autophagic flux from an impaired downstream protein degradation. For one of these bacteria, F. prausnitzii, a butyrate-producing strain, we compared activity of its supernatant to butyrate 10 nM. Moreover, in order to explore which signaling pathway was involved, we studied two proteins of autophagy initiation, mTOR and Beclin-1, by WB and a siRNA approach.

Results

Most of the bacterial supernatants showed increase in LC3-II protein in epithelial cells (WB quantification). This effect was higher for Bacteroides fragilis, Clostridium leptum and Faecali-bacterium prausnitzii with 3.5 to 4 times increase compared to control (p < 0.05). F. prausnitzii supernatant related effect was due to an induction in the autophagic flux as shown by a significant increase of LC3-II positive IF dots/cells (260 vs 160 in control cells) after chloroquine treatment. The same effect was observed with butyrate 10 nM. mTOR inhibition by F. prausnitzii supernatant and butyrate confirmed the autophagic flux induction in this process. Finally, using Beclin-1 siRNA, we observed a decrease in LC3-II.

Conclusion

We have shown that some gut microbiota bacteria were able to modulate the autophagic process in intestinal epithelial cells by diffusible molecules from bacterial supernatants. F. prausnitzii, which is under-represented in CD, can induce autophagic flux by the canonical Beclin-1 dependent pathway and this pro-autophagic activity may be related to butyrate. Our results suggest that dysbiosis could impact autophagic process in epithelial cells and that gut microbiota modulation might enhance autophagic flux in the intestinal barrier during CD.