PDE4D and major depressive disorder: After applying degree (DC > 16) and betweenness centrality (BC) filters between 0.039 and 0.157, we obtained the 10 most important genes of the arketamine, depression, and suicide network, as illustrated in Figure 4B. Most of these genes coded for signaling pathway-related proteins (CREB1, CREBBP, and COPS5), enzyme-related genes (PDE4B, PDE4D, NOS2, and HMOX1), genes related to immune responses (MIF and CD74), and cytoskeleton (ACTN4).