Intestinal nutrient sensing and transport are gaining increasing attention in the field of obesity research. To date, in vitro studies in this area have largely used two dimensional (2D) cell culture models. However, 2D cell cultures are limited by a lack of cellular heterogeneity, behaviour, and communication observed in vivo. There has consequently been growing interest for the application of three-dimensional (3D) cell culture systems. Recently, a 3D model system cultured from mouse intestinal crypts has been developed, known as mini-gut or organoid culture. Supplemented with the appropriate medium and growth factor cocktail and cultured in an extracellular matrix, stem cells derived from isolated mouse crypts are able to proliferate and differentiate into all cell types present in the in vivo intestinal epithelium. Crypts can be isolated from the different intestinal sections (duodenum, jejunum, ileum and colon) and grown up into organoids characteristic of the specific intestinal segment, enabling comparison studies between regions. These organoids functionally recapitulate intestine physiology, and are therefore a powerful model to investigate nutrient sensing and transport and subsequent incretin hormone secretion including intracellular signalling processes.
We have used intestinal organoids to investigate the role of specific nutrient sensing systems on gut hormone release. For example, hormone secretion assays in mouse ileum organoids have revealed significantly higher release of the anorectic gut hormone glucagon-like peptide-1 (GLP-1) after 24 hours of treatment with the amino acid L-Phenylalanine. This effect was significantly attenuated with the addition of a calcium-sensing receptor (CaSR) antagonist. This suggests that L-Phenylalanine stimulates GLP-1 release, and that the CaSR, a promiscuous amino acid sensor, may mediate satiety in the gastrointestinal tract via detection of amino acid products from protein digestion. This effect was recapitulated in vivo, suggesting that intestinal organoids are a useful tool for understanding physiological gut sensing mechanisms.