Ulcerative colitis: functional analysis of the in-depth proteome.

Background: Ulcerative colitis (UC) is one major form of inflammatory bowel disease. The cause and the pathophysiology of the disease are not fully understood and we therefor aim in this study to identify important pathophysiological features in UC from proteomics data.

Methods: Colon mucosa biopsies from inflamed tissue of untreated UC patients at diagnosis and from healthy controls were obtained during colonoscopy. Quantitative protein data was acquired by bottom-up proteomics and furthermore processed with MaxQuant. The quantitative proteome data was analyzed with Perseus and enrichment data was analyzed by ClueGO for Cytoscape.

Results: The generated proteome dataset is to-date the deepest from colon mucosa biopsies with 8562 identified proteins whereof 6818 were quantified in > 70% of the samples. We report abundance differences between UC and healthy controls and the respective p values for all quantified proteins in the supporting information. From this data set enrichment analysis revealed decreased protein abundances in UC for metallothioneins, PPAR-inducible proteins, fibrillar collagens and proteins involved in bile acid transport as well as metabolic functions of nutrients, energy, steroids, xenobiotics and carbonate. On the other hand increased abundances were enriched in immune response and protein processing in the endoplasmic reticulum, e.g. unfolded protein response and signal peptidase complex proteins.

Conclusions: This explorative study describes the most affected functions in UC tissue. Our results complemented previous findings substantially. Decreased abundances of signal peptidase complex proteins in UC are a new discovery.