Dendrobine and Erianin alleviate inflammation-induced depressive-like behaviors by targeting phosphodiesterase 4B in adolescent mice

Adolescent depression is highly prevalent due to current adverse circumstances such as academic struggles and substance abuse. Early-life inflammation is able to evoke adolescent depression. Dendrobine (DEN) and Erianin (ERI), two active compounds from Dendrobium officinale, a traditional Chinese medicine, are known to help regulate immune responses and gastrointestinal functions under the theory of Yin and Yang balance. However, their roles in inflammation-related adolescent depression remain unclear. This study aims to investigate the roles and mechanisms of DEN and ERI on adolescent depression. An inflammation-induced depression model was performed by intraperitoneal injections of lipopolysaccharide (LPS) and various behaviors were assessed in adolescent mice. Neuronal survival and synaptic structure were evaluated using Golgi staining, Nissl staining and transmission electron microscope. Neuroinflammation and microglial activation were analyzed using Elisa, immunofluorescence and Sholl analysis. Network pharmacology and molecular docking were applied to identify and select target proteins. RNA sequencing, cellular thermal shift assay (CETSA) and lentivirus were used to elucidate the interaction between DEN, ERI and phosphodiesterase 4B (PDE4B) along with the underlying mechanisms. Network pharmacology analysis showed that DEN and ERI were closely associated with depressive disorders, sharing 385 intersecting proteins. Administration of 10 mg/kg dose of DEN and ERI showed the most effective antidepressant effect in LPS-treated depressive mice, reducing immobilization time by approximately 45% and 38% in the forced swim test (FST) and tail suspension test (TST), while increasing the sucrose preference rate by 26% and 25%, respectively. Interestingly, compared with fluoxetine, DEN treatment exhibited better antidepressant effect. In addition, there was no significant difference between DEN and ERI combination therapy and DEN monotherapy. DEN and ERI treatment also alleviated neuronal damage, inhibited microglial activation, and reduced release of pro-inflammatory cytokines and oxidative stress in the hippocampus (HIP) and prefrontal cortex (PFC) of adolescent mice. Importantly, RNA sequencing data identified 886 and 788 differentially expressed genes (DEGs) following DEN and ERI treatment compared to LPS-treated group. KEGG pathway enrichment analyses, quantitative PCR and western blot results confirmed that DEN and ERI prevented inhibition of TLR4 expression and activation of PI3K/AKT/NF-κB pathway. Molecular docking model showed that the minimum binding energy of DEN and ERI with PDE4B were below -5 kcal/mol, and CETSA results further proved that PDE4B was a crucial target protein for DEN and ERI. Overexpression of PDE4B counteracted the effects of DEN and ERI on the TLR4//NF-κB pathway and the production of pro-inflammatory cytokines in LPS-treated microglial cells. Our data revealed that both DEN and ERI have antidepressant effects in LPS-treated mice. Mechanically, DEN and ERI alleviated LPS-induced microglial activation and neuroinflammation by binding to PDE4B and preventing TLR4/NF-κB signaling pathway. Together, the protective effects of DEN and ERI against inflammation-induced depressive disorders highlight DEN and ERI-mediated PDE4B/TLR4/NF-κB pathway as a potential therapeutic target for adolescent patients.