Serotonin attenuates tumor-necrosis-factor-alpha-induced intestinal inflammation by interacting with human mucosal tissue

The intestine houses the largest reservoir of immune cells and is serviced by the largest and most complex peripheral nervous system in the human body. The gut-brain axis orchestrates bidirectional communication between the central and enteric nervous systems, playing a pivotal role in regulating overall body function and intestinal homeostasis. Using a human 3D in vitro model, we investigated the effect of serotonin, a neuromodulator produced in the gut, on immune cell and intestinal tissue interactions. Our findings revealed that serotonin attenuates the tumor-necrosis-factor-alpha-induced pro-inflammatory response, mostly by affecting the expression of chemokines. Serotonin was found to impact tissue-migrating monocytes phenotype and distribution, without direct contact with the cells, by remodeling the intestinal tissue. Collectively, using fully human 3D model of intestine, our results show for the first time that serotonin has a crucial role in communication among gut-brain axis components and regulates monocyte migration and plasticity, thereby contributing to gut homeostasis and the progression of intestinal inflammation. In vivo studies focused on role of neuromodulators in gut homeostasis and inflammation have shown controversial results, highlighting importance of development of human experimental models. Moreover, our results emphasize importance of human health research in human-cell-based models and suggests serotonin signaling pathway as new potential therapeutic target for inflammatory bowel disease patients.