Serotonin promotes epithelial restitution through goblet cell mediated secretion of Muc2 and TFF3
Authors: Engevik Melinda Anne , Chang‐Graham Alexandra , Hyser Joseph M. , Versalovic James 
Published: June 2021

BackgroundSerotonin is best characterized in the central nervous system. However, recent studies are beginning to shed light on the critical role for serotonin in intestinal epithelial homeostasis. Serotonin is primarily produced and secreted by intestinal enterochromaffin cells. Once released serotonin can activate receptors located in various cell types including goblet cells. To date, few studies have explored the link between serotonin and goblet cells. We hypothesize that a commensal bacterium, Bifidobacterium dentium, is able to stimulate serotonin production by enterochromaffin cells and that serotonin activates serotonin receptor 4 (5‐HTR4) on goblet cells to promote Muc2 and Trefoil factor 3 (TFF3) release. We speculate that TFF3 will activate its receptor CXCR4 to promote actin cytoskeleton rearrangement and restitution.Methods & ResultsHuman Intestinal enteroids (also known as organoids) derived from jejunum were lentivirus transduced with the calcium sensor GCaMP6s to identify intracellular calcium mobilization and the actin sensor LifeAct to monitor the actin cytoskeleton. In separate studies, human intestinal enteroids were lentivirus transduced to stably engineer doxycycline‐inducible expression of neurogenin‐3 (NGN3), a transcription factor that drives enterochromaffin cell differentiation. Addition of B. dentium secreted products to human intestinal enteroid monolayers and NGN3‐transduced enteroid monolayers resulted in serotonin release by 30 min in a dose‐dependent manner. The presence of 5‐HTR4 in human enteroids was confirmed by qPCR and treatment of Ca2+‐sensor transduced enteroids with serotonin or B. dentium products stimulated increased intracellular Ca2+ and Muc2 release. Addition of the 5‐HTR4 antagonist SB 204070 or chelation of Ca2+ using BAPTA‐AM prevented Muc2 release in the presence of serotonin. Consistent with Muc2 secretion, we also observed release of TFF3 in response to serotonin. Since TFF3 is known to be involved in wound healing, we tested if serotonin could promote TFF3‐mediated epithelial repair. Scratch assays of human enteroid monolayers revealed that addition of B. dentium metabolites or serotonin increased repair rates compared to that of media controls. Complete healing was observed by 12 hrs in serotonin and B. dentium treated monolayers. Inhibition of the TFF3 receptor CXCR4 in presence of both B. dentium metabolites and serotonin delayed repair, indicating the requirement of TFF3 in epithelial repair.ConclusionsCollectively this work indicates that microbe‐induced serotonin activates 5‐HTR4 on goblet cells to stimulate Muc2 and TFF3 release. In turn, TFF3 mediates epithelial repair. This work points to commensal microbes and serotonin as potential modulators of TFF3 and has broad implications for developing novel therapeutic strategies for treating wounds.Support or Funding InformationDK056338This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.