Classically enteroendocrine cells are classified based on the hormone they contain. I-cells are a subset of enteroendocrine cells that are concentrated in the duodenum and that express cholecystokinin (CCK). The aim of the current study was to determine the hormone repertoire of CCK-containing I-cells.

Duodenum was removed from CCK-eGFP transgenic mice, cells were dissociated and sorted by fluorescence activated cell sorting (FACS) into eGFP+ and eGFP-. RNA was isolated from sorted cells and subject to targeted transcriptomic analysis using semi-quantitative RT-PCR. Duodenal sections were subject to immunostaining with antibodies against CCK and other gut hormones.

More than 90% of duodenal eGFP+ cells co-stained with anti-CCK antibody, confirming the fidelity of CCK-eGFP transgene expression. RT-PCR revealed that I-cells were enriched in mRNA transcripts of CCK and importantly other hormones including neurotensin, GIP (Gastric Inhibitory Polypeptide), secretin and PYY (Peptide YY). Immunofluorescence staining confirmed the presence of multiple hormones in eGFP expressing I-cells.

In conclusion, duodenal I-cells express multiple hormones. These data challenge the "one cell-one hormone" traditional enteroendocrine cells classification and suggest that duodenal CCK-containing cells secrete multiple hormones in response to nutrient signals.