OP003. Circadian clock function maintains mucosal architecture and protects against intestinal inflammation in mice
R. Pagel, F. Bär, T. Schröder, J. Büning, K. Fellermann, C. Sina, University Hospital Schleswig-Holstein, Campus Lübeck, Medical Department I, Gastroenterology, Lübeck, Germany
In the last years, the interest of circadian rhythms as regulators of intestinal inflammation has increased substantially. Consisting of a range of clock genes including Per1 and Per2, the molecular clock machinery is thought to be engaged in modulating intestinal barrier function and gut homeostasis, features which are highly disturbed in inflammatory bowel disease (IBD). Elucidating the precise role of clock genes in the intestine may therefore highlight new pathophysiological mechanisms and new therapeutic approaches.
Here, we used Per1/Per2 mutant mice and wildtype controls to investigate the functional consequence of circadian disruption on gastrointestinal tract morphology and intestinal inflammation. Small and large intestines were evaluated histologically at basal conditions. Experimental chronic colitis was induced by cyclic administration of 2% dextran sulphate sodium (DSS) in the drinking water, and colitis severity was determined by mouse endoscopy and clinical scores (murine endoscopic index of colitis severity, disease activity index). Biopsies were taken and further investigated via RT-PCR, western blotting and immunofluorescence staining.
At baseline, Per1/2 mice displayed mucosal alterations in the small and large intestines, characterized by a diminished crypt length-to-width ratio and reduced numbers of goblet and Paneth cells. Strikingly, mutant mice exhibited severely increased clinical symptoms of colitis (e.g. body weight loss, rectal bleeding, and diarrhea) and gross lethality in response to DSS. BrdU labeling revealed increased numbers of proliferative intestinal epithelial cells (IEC) in Per1/2 mice, but a restricted migratory capacity along the crypt axis. Analyzing the fate of individual IEC, we detected elevated protein level of RIP3, a marker of necroptotic cell death, in IEC at the crypt base, indicating that aberrant cell death in the proliferative region of intestinal crypts is responsible for the observed morphological changes in Per1/2 mice. Together, these data suggest that Per1/Per2 deficiency modulates cell death events, and thus influences intestinal homeostasis.
Our data render intact circadian rhythm crucially important for intestinal barrier function and maintenance. Thus, therapeutic interventions stabilizing circadian rhythm may be promising options for the treatment of IBD.