L-cell Arntl is required for rhythmic glucagon-like peptide-1 secretion and maintenance of intestinal homeostasis.

OBJECTIVES: Recent studies using whole-body clock-disrupted animals identified a disruption in the circadian rhythm of the intestinal L-cell incretin hormone, glucagon-like peptide-1 (GLP-1). Although GLP-1 plays an essential role in metabolism, through enhancement of both glucose-stimulated insulin secretion and satiety, recent evidenced has also demonstrated its importance in regulating intestinal and microbial homeostasis. Therefore, using in vivo and in vitro models, this study assessed the requirement for the core circadian clock gene Arntl in the regulation of GLP-1 secretion and its impact on the intestinal environment.

METHODS: Oral glucose tolerance tests were conducted at zeitgeber 2 and 14 in control and inducible Gcg-Arntl knockout (KO) mice. Colonic intraepithelial lymphocytes were isolated, mucosal gene expression analysis was conducted, and 16S rRNA gene sequencing of colonic feces as well as analysis of microbial metabolites were performed. Time-dependent GLP-1 secretion and transcriptomic analysis were conducted in murine (m) GLUTag L-cells following siRNA-mediated knockdown of Arntl.

RESULTS: Gcg-Arntl KO mice displayed disrupted rhythmic release of GLP-1 associated with reduced secretion at the established peak time point. Analysis of the intestinal environment in KO mice revealed a decreased proportion of CD4+ intraepithelial lymphocytes in association with increased proinflammatory cytokine gene expression and increased colonic weight. Moreover, increased Actinobacteria within the colonic microbiome was found following L-cell Arntl disruption, in association with reductions in the microbial products, short chain fatty acids and bile acids. Finally, siRNA-mediated knockdown of Arntl in mGLUTag L-cells resulted in impaired time-dependent GLP-1 secretion, as well as disruption of pathways related to key cellular processes.

CONCLUSIONS: These data establish, for the first time, the essential role of Arntl in the intestinal L-cell for the regulation of time-dependent GLP-1 secretion. Furthermore, this study revealed an integral role for L-cell Arntl in mediating the intestinal environment which may, ultimately, provide novel insight into the development of therapeutics for the treatment intestinal and metabolic disorders.