Enteroendocrine Cells Sense Sucrose and Alter Enteric Neuron Excitability via Insulin Signaling

Neurosensory circuits of the gastrointestinal tract sense microbial and nutrient changes in the gut; however, studying these circuits in vivo is hindered by invasive techniques and ethical concerns. Here, an in vitro model of enteroendocrine cells (EECs) and calcium reporting enteric neurons (ENs) is established and validated for functional signaling. Both mechanical and sucrose stimulation of co-cultures increased the percentage of neurons undergoing a calcium flux, indicating an action potential. Neuronal activation is blocked with either a piezo or insulin receptor blocker. At baseline, a flow only stimulus elicited 51.9% of neurons to activate in co-culture, which is decreased to 15.1% with a piezo blocker. Piezo blocked and sucrose stimulated EECs increased neuronal activation to 43.9%, and an insulin blocker reduced response to 12.4%. Since a cell line is used to model the EEC in the previous experiments, primary rat duodenal epithelium enriched for EECs are also stimulated and found to produced measurable insulin. This work shows the ability of EECs to produce insulin and for ENs to sense insulin. These results inspire further work on how insulin production outside the pancreas effects diabetes, insulin as a neurotransmitter, and exploration of additional nutritional and microbiotic stimuli on enteroendocrine-to-neuronal signaling.