A266 TISSUE-SPECIFIC FUNCTION OF THE CIRCADIAN GENE, BMAL1, DURING COLITIS RECOVERY

TL;DR

This study shows that the circadian gene BMAL1 is important for recovery from colitis, especially in intestinal epithelial cells.

Contribution

The novel finding is that Bmal1 in intestinal epithelial cells, but not stromal cells, is critical for post-colitis regeneration.

Findings

Bmal1 disruption in intestinal epithelial cells leads to delayed recovery and increased inflammation after colitis.

Bmal1 is essential for efficient repair of the intestinal epithelium following DSS-induced colitis.

Conditional knockout of Bmal1 in stromal cells does not affect survival or disease severity in early stages.

Abstract

The circadian clock is a self-sustained molecular oscillator which drives 24-hour physiological rhythms in nearly every cell of the body. It consists of the genes Bmal1 and Clock that positively regulate Cry and Per, their negative regulators, resulting in a 24-hour transcription/translation feedback cycle. Shift work, which causes disruptions to 24-hour physiological rhythms, has been linked with an increased incidence of inflammatory bowel disease (IBD).

We have previously established that mice lacking the non-redundant circadian regulator, Bmal1, exhibit more severe colitis compared to controls. The loss of Bmal1 also negatively impacts post-colitis regeneration and recovery. However, the role of Bmal1 in specific cell types remains unknown in regard to regenerative capacity following colitis. The intestinal stem cell niche includes stromal cells that provide signaling factors to regulate the proliferation of epithelial cells in the colonic crypt.

To test the role of the circadian clock in these cell types, we conditionally disrupted Bmal1 in intestinal epithelial versus stromal cells using VilCre/+;Bmal1flox/flox and PdgfraCre/+;Bmal1flox/flox mice, respectively. Dextran Sulfate Sodium (DSS) was applied to induce acute colitis, disease progression was evaluated, and regeneration at different stages of recovery was analyzed. We hypothesize that the cell-specific disruption of Bmal1 in both intestinal epithelial and stromal cells negatively impacts the regenerative capacity following colitis, leading to delayed recovery and increased inflammation.

No differences in survival and colitis disease activity were observed between Vil+/+;Bmal1flox/flox control and VilCre/+;Bmal1flox/flox but increases in lesion number, inflammation, and disrupted recovery are evident in VilCre/+;Bmal1flox/flox colons histologically. Whereas control animals are able to recover two weeks following DSS treatment, regenerative proliferation is still present in conditional knockouts. Thus, Bmal1 is required in intestinal epithelial cells for efficient repair. Preliminary results in the PdgfraCre/+;Bmal1flox/flox conditional stromal mutanats do not show differences in survival or disease severity, and we are currently evaluating effects on regeneration.

Our results support a critical role for Bmal1 in intestinal epithelial cells during post-colitis regeneration and recovery.

CCC, CIHR