We decide to take two pathways to explore solutions for curing depression based on the 5-HT theory. On the one hand, we intend to construct in vitro RIN14B cells, which function similarly to EC cells responsible for the secretion of 95% of 5-HT in the human body. Electrophysiological experiments will be carried out on RIN14 cells to screen out compounds that could effectively stimulate RIN14B cells for the preparation of anti-depression drugs in the future. On the other hand, we also plan to recombine the Escherichia coli system, which could secret TPH and TDC enzyme to further exogenously synthesize 5-HT with tryptophan as the transformation substrate. This work is aiming to prepare engineered probiotics to ease depression. We hope to help patients who suffer from different levels of depression through this project.