An Integrated microbiota-gut-brain axis model for Hypertension Signaling - Abstract A growing number of conditions have been characterized by changes in abundance and composition of the gut microbiota, commonly termed the gut dysbiosis. However, the complexities of the host-microbiota interactions present us with difficulties in elucidating mechanistic pathways for development of new therapeutics. In our rodent model of gut dysbiosis-induced hypertension, reduced abundance of Akkermansia muciniphila (A.muciniphila) was associated with reduced colonic serotonin (5HT) and diminished expression of serotonergic 5HT3a receptors (5HT3aRs) on gut vagal afferents. Using an intersectional viral approach in transgenic 5HT3aR Cre rats, we show that the colon-projecting 5HT3aR-expressing gut vagal afferents are necessary for maintenance of blood pressure homeostasis, and that administration of A.muciniphila can reduce blood pressure in hypertensive rodents. However, whether the blood pressure-lowering effects of A. muciniphila are mediated via the gut epithelial 5HT and vagal afferent 5-HT3aR signaling is unknown. Thus, a reductionist approach that mimics the in vivo gut microbiota microenvironment, in which the conditions of each compartment can be independently manipulated and functionally investigated, may be beneficial for initial mechanistic and functional screening of gut bacterial effects on the host neuronal signaling that is mediated via the gut epithelium. We developed a microfluidic tri-culture model that allows side-by-side co-culturing of anaerobic gut bacteria, colonic epithelial cells, and vagal sensory neurons in a microfluidics device in vitro. This will allow semi-high throughput screening of select bacterial effects on colonic 5HT and vagal 5HT3aR-dependent signaling by live imaging of calcium-dependent neuronal activity in tri-culture. This is an innovative approach that expands on the capabilities of the currently available dual compartment microfluidics devices and organs on chip by adding the third manipulable microbiota anaerobic compartment, but further developments of the device are necessary for full realization of its potential. To aid with this, the in vitro investigations will be functionally validated in vivo in a rodent model of gut dysbiosis-associated hypertension in which the activity of the gut-projecting vagal 5HT3aR afferents can be manipulated using an intersectional Cre-FLPo recombinase strategy. This will allow investigation of a direct causative and mechanistic link between A. muciniphila, serotonergic gut vagal signaling, and blood pressure. Findings will further our understanding of host-microbiota interactions and support early phase of research that will yield new models and methodologies which are expected to transition into future grant funding and potential new therapeutics to restore gut homeostasis and alleviate conditions associated with dysfunctional gut-brain axis.
