Elevated fecal peptidase D at onset of colitis in Galphai2-/- mice, a mouse model of IBD

Abstract

BackgroundThe identification of novel fecal biomarkers in inflammatory bowel disease (IBD) is hampered by the complexity of the human fecal proteome. On the other hand, in experimental mouse models there is probably less variation. We investigated the fecal protein content in mice to identify possible biomarkers and pathogenic mechanisms.MethodsFecal samples were collected at onset of inflammation in Galphai2-/- mice, a well-described spontaneous model of chronic colitis, and from healthy littermates. The fecal proteome was analyzed by two-dimensional electrophoresis and quantitative mass spectrometry and results were then validated in a new cohort of mice.ResultsAs a potential top marker of disease, peptidase D was found at a higher ratio in Galphai2-/- mouse feces relative to controls (fold change 27; p = 0.019). Other proteins found to be enriched in Gαi2-/- mice were mainly pancreatic proteases, and proteins from plasma and blood cells. A tendency of increased calprotectin, subunit S100-A8, was also observed (fold change 21; p = 0.058). Proteases are potential activators of inflammation in the gastrointestinal tract through their interaction with the proteinase-activated receptor 2 (PAR2). Accordingly, the level of PAR2 was found to be elevated in both the colon and the pancreas of Galphai2-/- mice at different stages of disease.ConclusionsThese findings identify peptidase D, an ubiquitously expressed intracellular peptidase, as a potential novel marker of colitis. The elevated levels of fecal proteases may be involved in the pathogenesis of colitis and contribute to the clinical phenotype, possibly by activation of intestinal PAR2.

Protease‐activated receptor signaling in intestinal permeability regulation

“…In this context, PAR1‐induced apoptosis contributes to the epithelial barrier function in a caspase‐3 dependent manner both in vitro and in vivo . On the other hand, PAR‐2 was found overexpressed in biopsies from IBD patients, thus hinting towards a pathophysiological role in the etiology of colonic inflammation , as well as in a mouse model of spontaneous chronic colitis . Indeed, luminal activation of PAR‐2 by trypsin, bacterial proteases or infusion of a PAR‐2 agonist in mice is known to increase intestinal paracellular permeability by contraction of the cytoskeleton .…”