260-OR: The L-Cell Clock Is Required for Circadian GLP-1 Secretion and Maintenance of Intestinal Homeostasis

Abstract

Glucagon-like peptide-1 (GLP-1) is an incretin hormone released by the intestinal L cell in response to nutrient intake. Recent studies identified a circadian rhythm in GLP-1 secretion that is disrupted in whole-body Bmal1 KO mice. However, the extent to which the L cell clock regulates circadian GLP-1 secretion and overall diurnal metabolic and intestinal homeostasis is unknown. Gcg-creERT2/+;Bmal1flox/flox KO mice with a disrupted clock in L cells, alpha cells and some CNS cells were thus generated. M/F- and age-matched KO mice had normal body weight and 24hr food intake patterns vs. all genetic and chemical controls. Upon oral glucose gavage at the known peak and trough timepoints of GLP-1 release, KO animals lost the rhythmic GLP-1 secretory pattern in association with impaired secretion (p<0.001) at the peak timepoint. Interestingly, the reduced GLP-1 secretion did not translate to decreased insulin or hyperglycemia, perhaps due to decreased glucagon levels (p<0.05). However, L cell Bmal1 KO caused increases in colonic weight and interleukin-6 (p<0.05) and interferon gamma (p<0.05) expression, suggesting a pro-inflammatory state. In line with findings that altered intestinal epithelial cell function decreases the frequency of intraepithelial CD4+ T cells, KO animals had reduced proportions of these immune cells (p<0.05). Furthermore, 16S rRNA gene analysis revealed increased actinobacteria in the colon, consistent with data from GLP-1 receptor KO mice. KO mice also had decreased levels of cecal bile acids (p<0.05-0.001) and short-chain fatty acids (p<0.05) suggestive of a functional impairment in the KO microbiome. Finally, siRNA-mediated knockdown of Bmal1 in the murine GLUTag L cell line also resulted in impaired rhythmic GLP-1 secretion (p<0.001). Together, these data establish the L cell clock as an essential regulator of circadian GLP-1 secretion which is, then, critical to the maintenance of overall intestinal homeostasis. Disclosure S. E. Martchenko: None. A. Martchenko: None. A. Biancolin: None. P. L. Brubaker: None. Funding Canadian Institutes of Health Research (PJT-15308)