Interdisciplinary approach uncovers new clues to triggers of gut inflammation

[Andy]

New details about what happens when a key cellular process is impaired in cells that are vital for a healthy gut have been uncovered by a wide-ranging analysis.

Paneth cells are found at the bottom of crypts in the lining of the gut. They help defend against pathogenic microbes, as well as protecting the integrity of the lining of the gut. Carrying out these functions relies on them being able to secrete antimicrobial factors and other molecules that ensure a balanced gut microbiome and functioning stem cells that regenerate the gut lining. Given their vital role, it’s not surprising that abnormalities in Paneth cells are associated with gut conditions such as Crohn’s disease.

Similar symptoms are seen when a cellular process called autophagy is dysfunctional. Cells use autophagy to remove defective and potentially harmful proteins within themselves by surrounding the offending object in a membrane “bag” that is then tagged for destruction. Paneth cells also use this mechanism to bag up antimicrobial molecules for export from the cell in response to attack by pathogenic microbes.

This new study aimed to fill a gap in our understanding of the effects of autophagy impairment on Paneth cells, and was led by Dr Tamás Korcsmáros, a research fellow at the Earlham Institute and the Quadram Institute, which are strategically funded by the Biotechnology and Biological Sciences Research Council.

http://www.earlham.ac.uk/newsroom/i...-uncovers-new-clues-triggers-gut-inflammation

Paper is open access at http://dmm.biologists.org/content/early/2019/02/26/dmm.037069

Abstract
Paneth cells are key epithelial cells providing an antimicrobial barrier and maintaining integrity of the small intestinal stem cell niche. Paneth cell abnormalities are unfortunately detrimental to gut health and often associated with digestive pathologies such as Crohn's disease or infections. Similar alterations are observed in individuals with impaired autophagy, a process which recycles cellular components. The direct effect of autophagy-impairment on Paneth cells has not been analysed. To investigate this, we generated a mouse model lacking Atg16l1 specifically in intestinal epithelial cells making these cells impaired in autophagy. Using 3D intestinal organoids enriched for Paneth cells, we compared the proteomic profiles of wild-type (WT) and autophagy-impaired organoids.

We used an integrated computational approach combining protein-protein interaction networks, autophagy targeted proteins and functional information to identify the mechanistic link between autophagy-impairment and disrupted pathways. Of the 284 altered proteins, 198 (70%) were more abundant in autophagy-impaired organoids, suggesting reduced protein degradation. Interestingly, these differentially abundant proteins comprised 116 proteins (41%), predicted targets of the selective autophagy proteins p62, LC3 and ATG16L1. Our integrative analysis revealed autophagy-mediated mechanisms degrading proteins key to Paneth cell functions, such as exocytosis, apoptosis and DNA damage repair. Transcriptomic profiling of additional organoids confirmed that 90% of the observed changes upon autophagy alteration affect protein level and not gene expression. We performed further validation experiments showing differential lysozyme secretion, confirming our computationally inferred down-regulation of exocytosis. Our observations could explain how protein level alterations affect Paneth cell homeostatic functions upon autophagy impairment.