PTGS2 and major depressive disorder: Clinically, some common COX-2 inhibitors can have side effects such as cardiovascular and gastrointestinal diseases after long-term use, thus, it is important to fully understand the role of COX-2 and its related pathways in the development of depression, and to use COX-2 inhibitors as lead compounds to synthesize compounds with high bioavailability, good stability performance, safety, and significant biological activity.