Gut microbiota regulates the nutrient sensing enteroendocrine cell maturation and mitochondrial function.

Enteroendocrine cells (EECs) are crucial for sensing ingested nutrients and regulating feeding behavior. How gut microbiota regulates the nutrient-sensing EEC activity is unclear. Our transcriptomic analysis demonstrates that commensal microbiota colonization significantly increases the expression of many genes associated with mitochondrial function. Using new methods to image EECs' cytoplasmic and mitochondrial Ca2+ activity in live zebrafish, our data revealed that EECs' cytoplasmic and mitochondrial Ca2+ is dynamically regulated during EECs' development process. Mature EECs display an increased mitochondrial-to-cytoplasmic Ca2+ ratio. Mitochondria are evenly distributed in the cytoplasm of immature EECs. As EECs mature, their mitochondria are highly localized at the basal membrane where EEC vesicle secretion occurs. CV EECs, but not GF EECs, exhibit spontaneous low-amplitude Ca2+ fluctuation. The mitochondrial-to-cytoplasmic Ca2+ ratio is significantly higher in CV EECs. Nutrient stimulants like fatty acid increase cytoplasmic Ca2+ in a subset of EECs and promote a sustained mitochondrial Ca2+ and ATP increase. However, the nutrient induced EEC mitochondrial activation is nearly abolished in GF zebrafish. Together, our study reveals that commensal microbiota are critical in supporting EEC mitochondrial function and maturation.