SignificanceThe gut microbiota affects several physiological processes, including gut motility. Here we observed that germ-free mice have an immature enteric nervous system (ENS) that is normalized upon colonization with a normal microbiota. We identified the mechanism of communication between the microbiota and enteric neurons as the initiation of serotonin release and subsequent activation of the 5-HT4 receptor. This demonstrates a strong interaction between the microbiota and the ENS and indicates potential mechanisms linking microbial dysbiosis to gastrointestinal disorders. The ability to modulate the microbiota, e.g., by diet, will open new perspectives of research in neurogastroenterology.
Human colonic carcinoma Caco-2 cells grown in vitro undergo epithelial differentiation. Electrical measurements showed that they form resistant monolayers of polarized cells. On millipore filters, transepithelial electrical resistance (154 +/- 6.5 omega X cm2) was accompanied by a small potential difference (0.29 +/- 0.02 mV, serosal side positive) and by short-circuit current (1.9 +/- 0.14 microA X cm-2), both of which were ouabain sensitive. Micropuncture of domes formed on plastic supports under standard culture conditions revealed electrical polarity similar to that of filter-grown cells (0.8 +/- 0.2 mV, serosal side positive) combined with a highly negative cytoplasm (-57 +/- 1 mV) and very marked cell asymmetry (76% of total electrical cell resistance was located in the mucosal membrane). These parameters were not affected by the diuretic amiloride nor the hormone aldosterone, suggesting that sodium conductance is very limited in the mucosal membrane. Addition to the mucosal side of the ionophore nystatin or amphotericin B unmasked the possibility of high electrical transport activity. Electrical measurements made it possible to define the epithelial properties of Caco-2 cells, which may resemble those of colonic crypt or fetal cells. These measurements also confirmed that functional differentiation is homogeneous in Caco-2 cells. It is suggested that dome cell micropuncture may be useful in investigating the functional properties of other dome-forming cell lines.
Glucagon-like peptide-1 (GLP-1)-based therapies control glycemia in type 2 diabetic (T2D) patients. However, in some patients the treatment must be discontinued, defining a state of GLP-1 resistance. In animal models we identified a specific set of ileum bacteria impairing the GLP-1-activated gut-brain axis for the control of insulin secretion and gastric emptying. Using prediction algorithms, we identified bacterial pathways related to amino acid metabolism and transport system modules associated to GLP-1 resistance. The conventionalization of germ-free mice demonstrated their role in enteric neuron biology and the gut-brain-periphery axis. Altogether, insulin secretion and gastric emptying require functional GLP-1 receptor and neuronal nitric oxide synthase in the enteric nervous system within a eubiotic gut microbiota environment. Our data open a novel route to improve GLP-1-based therapies.
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